ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V001T00A001. doi:10.1115/FPMC2017-NS.

This online compilation of papers from the ASME/BATH 2017 Symposium on Fluid Power and Motion Control (FPMC2017) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Symposium on Fluid Power and Motion Control

2017;():V001T01A001. doi:10.1115/FPMC2017-4202.

It is not uncommon for simulation models for the dynamics of hydraulic systems to contain fluid lines with turbulent flow. This paper demonstrates applications of an analytical model for pressure transients in lines with turbulent flow for lines with boundary conditions defined by hydraulic components such as pumps, valves, actuators, and restrictions; the model can be simplified for cases of laminar flow. The equations for conducting simulations with time varying inputs and for calculating eigenvalues of systems in which fluid lines are internal components are formulated. For an example demonstrating application of the equations, the model is used to simulate and optimize the performance of a hydraulic fracking system which involves the pumping of large volumes of water with additives through pipes under turbulent flow conditions into rock fissures. Specifically, the model is used to generate the frequency response of the flow transients in the pipe resulting from pump flow pulsations. This frequency response is then used to compute the eigenvalues of the system. The model is then used to conduct time domain simulations to determine the potential flow amplifications into rock fissures associated with pulsing the flow from the pump at the resonant frequency of the pressure transients in the pipe. The results reveal flow amplifications into the fissures of up to 22 times depending on the pulse shape of the input flow, the Reynolds number of the mean flow, the fluid properties of the slurry, and the length and diameter of the pipe.

Commentary by Dr. Valentin Fuster
2017;():V001T01A002. doi:10.1115/FPMC2017-4206.

As one of the micro motions of slipper in axial piston pumps, the slipper spinning motion has a significant effect on the lubrication characteristics of slipper/swash plate interface. However, no experimental investigations on the slipper spin were available in previous studies. The aim of this work is to design a novel test rig to measure the slipper spinning speed. A detailed description of this test rig will be given followed by a sample result of the slipper spinning motion. Also, a simulation model considering the slipper spin will be developed to investigate the effects of the spinning motion on the slipper performance. It can be concluded that the slipper spinning motion does exist during pump operation, which is helpful to prevent the slipper from further tilting motion.

Commentary by Dr. Valentin Fuster
2017;():V001T01A003. doi:10.1115/FPMC2017-4207.

This paper proposes a novel approach to control the velocity of a piston using dilatant fluid. Commonly, a pressure compensated flow control valve is used for this purpose. It produces excellent results but is mechanically complex. A setup is proposed that makes use of the unique properties of dilatant (i.e. shear thickening) non-Newtonian fluids. A simple tube section filled with dilatant material can be used to achieve very low sensitivity of flow rate vs. pressure difference. A numerical study shows how the power law which relates the fluid shear rate to its viscosity results in this low sensitivity of flow to pressure difference. An experimental setup was build to validate the findings using a cheap and commercially available shear thickening fluid. It was found that the dilatant material used does not have a highly pronounced dilatant property and therefore the sensitivity of flow vs. pressure difference was not as low as desired. Nevertheless, the results support the practical applicability of this novel type of velocity control.

Commentary by Dr. Valentin Fuster
2017;():V001T01A004. doi:10.1115/FPMC2017-4219.

In this paper, the cavitation phenomenon in hydraulic oil is investigated, and a new gaseous cavitation model based on the dynamic stimulation is examined. Before modeling, to confirm the characteristics of cavitation occurrence in hydraulic oil flow, the comparison of our previous experiment with the pressure distribution by CFD has been conducted. It is clarified that the region where the cavitation bubbles appear do not agree with the low pressure region, which indicates they are not in the case of vaporous cavitation. This comparison indicates that the gaseous cavitation has been occurred predominantly in the previous experiment. In modeling, the dynamic stimulation of unsteady flow field is assumed to play a major role in the liberation of dissolved air. The dynamic stimulation is transferred into the dimension of pressure and applied to the threshold pressure of liberation. Several models considering dynamic stimulation are proposed and comparison of the effect of those models has conducted to estimate the most appropriate modeling.

Commentary by Dr. Valentin Fuster
2017;():V001T01A005. doi:10.1115/FPMC2017-4220.

Even though the majority of currently published exoskeletons prototypes employ electrical drives, great opportunities are seen for hydraulic drives. Their main advantages are the unrivalled force and power density, facilitating the low additional masses at the peripheral limb joints, and the simple realization of locking, damping, and recuperation functions. The latter function is feasible with some hydraulic control concepts, like primary or secondary motion control. In this paper a digital cylinder drive is studied for getting up from a crouch. This motion is a sound benchmark to test the ability of the drive for exoskeleton knee joint actuation. Digital cylinders can realize output torques only in steps and the transition between different steps can create jerky motions. In this study the motion quality and the losses are evaluated for a binary stepped digital cylinder with four different chambers.

Commentary by Dr. Valentin Fuster
2017;():V001T01A006. doi:10.1115/FPMC2017-4221.

Compared with traditional valve control systems, the independent metering valve control system (IMVCS) broke down the mechanical connection of the meter-in and meter-out orifices so that it increased the control degrees of freedom. More importantly, it achieved a more energy-efficient control mode for hydraulic system. This paper studied the dynamic characteristics of IMVCS based on fuzzy PID control algorithm. A controller included power amplifier module, voice coil motor (VCM) drive module, data acquisition module and CAN communication module was designed. A SYS/BIOS based embedded operating system was adopted in this controller for fast response. A host computer program based on CAN bus was developed to monitor status of the IMVCS. A series of experiments of displacement control and pressure control have been carried out, and results showed a good dynamic performance and huge potential of energy-efficient control.

Topics: Control systems
Commentary by Dr. Valentin Fuster
2017;():V001T01A007. doi:10.1115/FPMC2017-4222.

Proper functioning of the pitch system is essential to both normal operation and safety critical shut down of modern multi megawatt wind turbines. Several studies on field failure rates for such turbines show that pitch systems are a major contributor to failures which entails an increased risk. Thus, more reliable and safe concepts are needed. A review of patents and patent applications covering fluid power pitch concepts, reveals that many propose closed-type hydraulic systems. This paper proposes a closed-type concept with a bootstrap reservoir. In contrary to a conventional system where a common supply delivers to cylinder drives mounted at each blade, the concept using bootstraps are fully contained in the rotating hub and act as standalone actuators. Clear advantages of such systems are a reduction of high pressure leakage paths, but in turn more components are used for each supply circuit. To allow for comparison, this paper deals with a risk-based analysis of these two types of pitch concepts. The risk-based analysis is conducted according to a qualitative failure analysis method which is verified against recent field failure data for hydraulic pitch systems. The method combines Fault Tree Analysis and Failure Mode and Effect Criticality Analysis in a systematic framework that lowers the bias issues normally encountered for qualitative studies. Under the assumption of similar components, the results indicate an equal risk of the two concepts. A decreased reliability is seen for the bootstrap concept due to additional components in the supply circuit compared to the conventional system. It is noted that careful selection of high reliable pumps and relief valves may significantly reduce risk and increase reliability of the bootstrap concept.

Topics: Fluids , Risk
Commentary by Dr. Valentin Fuster
2017;():V001T01A008. doi:10.1115/FPMC2017-4223.

Positive displacement pumps produce flow and pressure ripple due to their pumping mechanism. Two ISO standard methods for measuring pump ripple were compared in terms of accuracy, sensitivity, reliability and practical difficulty. These were the “secondary source” (SS) method (ISO 10767-1: 1996) and the “2 pressures / 2 systems” (2P2S) method (ISO 10767-1: 2015). The 2P2S method has recently replaced the secondary source as the ISO standard for precision testing although the UK has retained the SS method for its BS ISO standard.

The methods produced similar source impedance and flow ripple results. The SS method enabled a wider range of operating conditions to be tested due to the more flexible circuit arrangement but the impedance results were affected by interference between the test pump and secondary source at the pumping harmonic frequencies. It was found that the simpler 2P2S circuit allowed measurements to be taken faster, but measurements were only valid at the pumping harmonic frequencies. Both methods were found to produce repeatable results provided there was no trapped air in the circuit.

Overall, the SS method was considered the stronger technique in terms of repeatability, accuracy, sensitivity and practicality, but it had a more complex data processing and experimental set up. It had more flexibility, which enabled the pump to be tested over the widest range of operating conditions, and the fluid borne noise characteristics of the test pump could be evaluated completely. The authors consider that the 2P2S method could be improved by the inclusion of a third transducer, and that it would be beneficial to retain the SS method as an alternative Standard.

Commentary by Dr. Valentin Fuster
2017;():V001T01A009. doi:10.1115/FPMC2017-4225.

This paper presents a modified integral sliding surface, sliding mode control law for pneumatic artificial muscles. The cutoff frequency tuning parameter λ is squared to increase the gradient from absement (integral of position) to position and higher derivatives to reflect the more dominant terms in the actuator dynamics. The sliding mode controller is coupled with proportional and integral action compensation. The control system is sufficiently robust so that use of an observer and input-output feedback linearization are not required. Closed-loop control experiments are compared with traditional sliding mode controller designs presented in the literature for pneumatic artificial muscles. Experiments include the tracking of sinusoidal waves at 0.5 and 1 Hz, tracking of square-like waves with seventh-order trajectory transitions at a rate of 0.2 Hz without and with a steady-state period of 10 seconds, as well as a step input response. These experiments indicate that the control law provides similar bandwidth, tracking, and steady-state performance as approaches requiring nonlinear feedback and model observation for pneumatic artificial muscles. Experiments demonstrate an accuracy of 50 μm at steady-state with no overshoot and maximum tracking errors less than 0.4 mm for smooth square-like trajectories.

Commentary by Dr. Valentin Fuster
2017;():V001T01A010. doi:10.1115/FPMC2017-4226.

Standard Computational Fluid Dynamic (CFD) techniques are widely used in the design of hydraulic valves for optimising the valve performance and reducing the production effort. They calculate the turbulent flow and predict cavitation. Unfortunately, the currently used models are often inadequate and out of date to catch the complexity of these phenomena such as the transient interaction between cavitation and turbulence. Advanced computational methods have been developed and applied to other engineering branches. Despite this fact, they face many difficulties to be employed in hydraulics. In this paper, a first step is taken towards the usage of these cutting edge CFD methods for hydraulic valves. At first, the different challenges for a CFD code to simulate valve flows are highlighted. A novel computational approach is then presented. It combines a Large Eddy Simulation (LES) model for the turbulence modelling as well as a Full Cavitation Model (FCM). The LES technique explicitly resolves the large turbulence scales while the smaller ones are modelled. The FCM not only predicts vapour but also gas cavitation, which plays a vital role in hydraulic fluids. This method is tested to simulate the flow in a pilot stage of a jet-pipe servo-valve. The test case is presented and the different boundary conditions used for the simulations are given. The results of the simulation are compared with experimental results showing a good agreement. A comparison between the LES model and the standard two-equation turbulence model shows the advantages of the LES approach. Finally, the transient features of the flow are highlighted in terms of velocity oscillation.

Commentary by Dr. Valentin Fuster
2017;():V001T01A011. doi:10.1115/FPMC2017-4228.

The increase of system dynamic within the area of pneumatics requires sophisticated numerical methods to determine the systems’ performance. Cycle durations in the range of just a few milliseconds and below violate the assumption of a stationary process. State of the art pneumatic calculations are built upon this assumption and, therefore, gas dynamic solvers have to be used to predict the systems’ behavior accurately.

In general it is possible to calculate several flow parameters for transient gaseous flows using computational fluid dynamics (CFD) software, but despite increasing processing power of modern computers, solving particular problems is yet time-consuming. A simulation of a few milliseconds results in a computational time of several hours which makes the design of a highly dynamic pneumatic system lengthy.

This paper presents a one dimensional transient numerical model which is capable of computing a transient pneumatic system’s performance time-efficiently yet retaining the accuracy of a CFD simulation. It allows to determine flow parameters, e.g., density, pressure and velocity, within transient gaseous flows including discontinuities.

In particular the proposed model depicts an approach to calculate transient flows with discontinuous flow curvature. Such jumps naturally occur in pneumatic systems within hose connectors or valves. Numerical results are compared to a CFD parameter study to verify the one dimensional simulation.

Commentary by Dr. Valentin Fuster
2017;():V001T01A012. doi:10.1115/FPMC2017-4229.

Cavitation erosion is a serious problem in the hydraulic system of construction machinery. In particular, the erosion which occurs even when cavitation bubbles only pass through oil passages, occurs at a connecting portion between the hydraulic components and piping, and the erosion causes oil leakage, which is a serious problem for hydraulic systems. However, it is difficult to predict the eroded area and to prevent the erosion because of a lack of research findings. The present study investigated erosion in the portion through which cavitation bubbles passes using a basic experimental apparatus that simulates an oil passage of hydraulic components, and by conducting a computational fluid dynamics simulation. The following results were obtained. Erosion occurs near the outlet of the oil passage, cavitation bubbles frequently disappear rapidly near the area of erosion, and the cause of bubble disappearance is the pressure distribution and amplification of the pressure wave of cavitation jets at the outlet of the oil passage. These results help explain the erosion generation mechanism and the characteristics of erosion in oil passages of hydraulic components, and can be used to design methods of reducing erosion.

Commentary by Dr. Valentin Fuster
2017;():V001T01A013. doi:10.1115/FPMC2017-4230.

This paper comprises a detailed study of the forces acting on a Fast Switching Valve (FSV) plunger. The objective is to investigate to what extend different models are valid to be used for design purposes. These models depend on the geometry of the moving plunger and the properties of the surrounding medium. A few analytic expressions have been suggested in the literature and these have been supported by CFD simulations, yielding accurate coherence for a large part of the fluid domain. However, when a moving body approaches a stationary body, squeeze film effects will occur if the plunger velocity is non-zero. This is the case in FSVs, where it results in an additional dampening effect, which is of relevance when analyzing contact-impact. Experimental data from different tests cases of a FSV has been gathered, with the plunger moving through a medium of either oil or air. This data is used to compare and validate different models, where an effort is directed towards capturing the fluid squeeze effect just before material on material contact. The test data is compared with simulation data relying solely on analytic formulations. The general dynamics of the plunger is validated for the established models, but an additional investigation of the dampening force is necessary. Therefore, numerical analyses are introduced to enhance the knowledge of the hydrodynamic end dampening. This has a visible effect on the velocity profile at the end-stop. This profile represents the measurements more accurately, but it is not possible to verify the velocity profile at the valve seat end-stop due to measurement uncertainties.

Commentary by Dr. Valentin Fuster
2017;():V001T01A014. doi:10.1115/FPMC2017-4231.

The cluster of excellence „Tailor-Made Fuels from Biomass“ at RWTH Aachen University develops and investigates new biofuel candidates, to reduce global emissions and create an alternative and sustainable diesel fuel. Biofuels pose a new challenge to existing common-rail injection pumps. Since fuels are used as lubricants for tribological contacts in these pumps, the deviating hydrodynamic properties in comparison to diesel can cause high leakage, wear, and a low overall-efficiency.

In order to ensure a reliable pump performance, especially for low-viscosity fuels or fuels with worse lubricity than diesel, an optimization of the tribological contacts is necessary. The most critical contact is the piston-cylinder contact. One possibility to reduce the leakage in this contact is the use of a hollow piston design. This design can reduce the gap between piston and cylinder by minor pressure-dependent elastic deformations of the piston.

In this paper, a first simulative look is taken at the compression behavior of the new piston design. The focus lies on the delayed pressure build-up due to the additional capacity caused by the shape of the piston. Based on the results, a new design approach is proposed subsequently in order to ensure a sufficient pressure build-up.

The manufactured contour of the new design is investigated in order to ensure the geometric properties and first measurement results are discussed. For the measurement, a low-viscosity fluid is used to compare leakage rates of the standard and the new hollow piston design. Based on the results, a conclusion is made, deriving further usage of the hollow piston.

Commentary by Dr. Valentin Fuster
2017;():V001T01A015. doi:10.1115/FPMC2017-4232.

Most test benches for hydraulic pumps and motors are designed for operating speeds of 500 rpm or higher. Worldwide, there are only a few test benches which allow measurements at near zero operating speeds or startup conditions.

Low-speed testing is, however, of great importance for hydraulic motors, since the torque losses increase exponential at these conditions due to mixed lubrication and stick-slip effects. Low-speed operation is also important for hydraulic pumps which are used in electro-hydraulic actuators, in which the flow rate is controlled by the operating speed of the electric motors. Finally, measurements at low operating speeds can give detailed information about the pump or motor issues, since it is possible to measure the operation at many rotational positions of the rotating group, giving the ability to measure the losses of individual displacement volumes.

This paper describes the design and operation of a new test bench for testing hydraulic pumps and motors at extremely low operating speeds, below 1 rpm.

Commentary by Dr. Valentin Fuster
2017;():V001T01A016. doi:10.1115/FPMC2017-4235.

A gerotor gear generation algorithm has been developed that evaluates key performance objective functions to be minimized or maximized, and then an optimization algorithm is applied to determine the best design. Because of their popularity, circular-toothed gerotors are the focus of this study, and future work can extend this procedure to other gear forms. Parametric equations defining the circular-toothed gear set have been derived and implemented. Two objective functions were used in this kinematic optimization: maximize the ratio of displacement to pump radius, which is a measure of compactness, and minimize the kinematic flow ripple, which can have a negative effect on system dynamics and could be a major source of noise. Designs were constrained to ensure drivability, so the need for additional synchronization gearing is eliminated. The NSGA-II genetic algorithm was then applied to the gear generation algorithm in modeFRONTIER, a commercial software that integrates multi-objective optimization with third-party engineering software. A clear Pareto front was identified, and a multi-criteria decision-making genetic algorithm was used to select three optimal designs with varying priorities of compactness vs low flow variation. In addition, three pumps used in industry were scaled and evaluated with the gear generation algorithm for comparison. The scaled industry pumps were all close to the Pareto curve, but the optimized designs offer a slight kinematic advantage, which demonstrates the usefulness of the proposed gerotor design method.

Commentary by Dr. Valentin Fuster
2017;():V001T01A017. doi:10.1115/FPMC2017-4236.

Reciprocating rod seals play an important role in the aviation hydraulic system. As a new type of the aerospace reciprocating seal, VL seal is gradually used in crucial and complicated working conditions. When the seal is installed in the groove, there is large deformation in the circumferential direction, which would cause the deviation while the traditional axisymmetric 2D model is used for analyzing its performance. Therefore the new 3D finite element model is developed in this paper to obtain more accurate results of the contact pressure and the stress of the VL seal. Furthermore a mixed lubrication model combined with the 3D model is implemented to obtain the friction and leakage characteristics of the VL seal, which is composed of the fluid lubrication model, the micro contact model and the deformation model. The performance of the seal in the outstroke and instroke is studied respectively and the effects of different working velocities on the seal are also discussed. The analysis results show that the 3D model can demonstrates more comprehensive performance than the traditional axisymmetric model when there is a tangential strain in the VL seal.

Commentary by Dr. Valentin Fuster
2017;():V001T01A018. doi:10.1115/FPMC2017-4238.

Steerable thrusters are used to maneuver a vessel in open sea environment. The harsh environment of arctic seas introduces certain challenges with propellers hitting ice and decreasing lifetime of the system, as the loads generated by ice impacts are significantly higher than nominal loads. Damping of an ice impact load is a difficult task since the impacts have high torsional loads and they occur only in a fraction of the lifetime of the system. Commercial dampers are hard to find since they do not generally have the capacity for damping such high loads. The proposed active hydraulic damper reduces ice impact loads by accelerating and decelerating the shaft line. The lack of space and commercial components narrow down the possibilities but simulation results with the system show some positive effects in typical ice impact scenario. The system also recuperates most of the used energy and stores it to accumulator.

Topics: Stress , Dampers , Ice
Commentary by Dr. Valentin Fuster
2017;():V001T01A019. doi:10.1115/FPMC2017-4239.

Weight reduction is an ongoing trend in multiple industries. Especially in the mobility sectors, hot forming of sheet metal parts has become an alternative production process for high strength components. New material concepts, e.g., boron-manganese steels, enable the design of lighter parts at equivalent or even higher strength. During the preliminary process development phase detailed knowledge of the thermo-mechanical material properties of these sheet metals is required at elevated temperatures and high strain rates. Since hot tensile tests can only be evaluated up to comparably low strains, new test designs are needed to supply material parameters at elevated temperatures and higher strain rates. Therefore, the hot gas bulge test has been developed, that allows for such test conditions. In this paper, first the concept of the hot gas bulge test and the developed test bench are described. Opposed to standardized bulge tests, which use hydraulic oil as forming medium, the newly designed test uses gas as medium to account for the hot stamping conditions, i.e., temperatures of up to 950°C. As the forming speed has an increasing influence on the material behaviour at increasing temperatures, a closed loop control of the forming speed was developed. Since there are no proportional pneumatic valves available for the required pressure range, a parallel valve concept was chosen. By combining different valves, the characteristics of a larger proportional valve are imitated. A control algorithm was developed, that maps the required valves conductance into a valve combination to control the mass flow into the pressure chamber. The developed control system is presented and experimental results from the material test procedure are shown. These results reveal that the developed system is capable to track the required mass flow rate for low as well as high forming speeds up to a certain deformation when the deformation of the sheet becomes uncontrollable.

Commentary by Dr. Valentin Fuster
2017;():V001T01A020. doi:10.1115/FPMC2017-4241.

High power density and good controllability are the most appealing characteristics that make hydraulic systems the best choice for many applications. Current state of the art hydraulic variable displacement pumps show high efficiency at high displacement while they have poor efficiencies at low displacement. This paper proposes a novel alternating flow (AF) variable displacement hydraulic pump to 1) eliminate metering losses by acting as a high-bandwidth pump for displacement control, 2) achieve high efficiency across a wide range of operating conditions and displacements, and 3) allow multiple units to be easily common-shaft mounted for a compact multi-actuator displacement control system from a single prime-mover. A dynamic model using first principles describes the cylinder pressure, flows between pairs of cylinders, and net inlet and outlet flows as a function of the pump’s phase shift angle. The model captures hydraulic check valve dynamics, the effective bulk modulus, leakage flows, and viscous friction. Piston kinematics and dynamics are discussed and energy loss models are presented and used to guide the design for a first prototype of the AF hydraulic pump. The paper presents simulation results from the model that offer an initial evaluation of this novel pump concept and potential applications.

Commentary by Dr. Valentin Fuster
2017;():V001T01A021. doi:10.1115/FPMC2017-4243.

The large flow water hydraulic proportional cartridge valve is one of the most important components and also the technical difficulties in the high performance large-tonnage engineering machinery, such as the die casting machine. The structure and principle of the large flow water hydraulic proportional cartridge valve are presented in this paper. The valve utilizes a two-stage structure with the high performance proportional valves as the pilot stage and the cartridge poppet valve as the main stage to overcome the fundamental tradeoff between the flow capacity and dynamic characteristics. A detailed and precise nonlinear mathematical model of the cartridge valve considering both structural parameters and nonlinear factors (compressibility of water, leakage, friction, flow force, etc.) is established. And then MATLAB/Simulink software is employed to build the simulation model and the dynamic simulation is carried out. Compared with the simulation results of the valve with different design parameters, the static and dynamic characteristics of the proportional cartridge throttle valve have been analyzed. The impacts of the parameters on the performance of step-response have been studied. Finally, based on multi-objective optimization method, the optimal parameters of the cartridge valve have been obtained. The simulation results show that the performances have been significantly improved.

Commentary by Dr. Valentin Fuster
2017;():V001T01A022. doi:10.1115/FPMC2017-4246.

The pressure drop needs to be kept constant in the flow rate/input signal performance test of proportional directional control (PDC) valve. In general, the control of valve pressure drop is implemented by regulating the relief valve or flow control valve that located between port A and port B of the PDC valve. But in this study, the load of the test valve is fixed and the stable pressure drop is obtained by changing the proportional relief valve which is placed in the inlet of the PDC valve. Then the mathematical model of the test rig and several controllers are established based on this idea. To be specific, proportional-integral (P-I) controller, proportional-integral-double-integral (P-I-II) controller, and fuzzy proportional-integral-double-integral (FP-I-II) controller are all applied to stabilize the pressure drop in this study. And the FP-I-II controller with compensation (FP-I-II-WC) is proved to be the best for this work both in the simulation and the actual experiment.

Commentary by Dr. Valentin Fuster
2017;():V001T01A023. doi:10.1115/FPMC2017-4248.

High pressure oil-free miniature air compressor has an irreplaceable role in some high demand areas such as cooling, scuba diving and pneumatic catapult due to its remarkable advantages such as compacted size, lightened weight and clean output gas. As the important sealing component in the high pressure oil-free miniature air compressor, piston rings hold the properties such as tiny diameter (less than 10mm), high sealing pressure (up to 410 bar) and high surrounding temperature (up to 500K), which make them distinctive from conventional piston rings. A mathematical model was established to simulate the pressure distribution of the compressor chamber, as well as the gap between the sealing rings. Sensitive parameters were considered to investigate their effects on the sealing performance such as the number and the cut size of the piston rings, the suction and discharge pressure and the rotary speed. The mathematical model was verified by comparing to published experimental research work. These work help to reveal the severe non-uniformity of the pressure distribution of different chambers, which were suggested be the primary cause of the premature failure of the sealing rings, thus improving the sealing performance and the service life of the air compressor.

Commentary by Dr. Valentin Fuster
2017;():V001T01A024. doi:10.1115/FPMC2017-4253.

The fluid power accumulator is a high-risk component in the safety shutdown system of most modern wind turbines. Recent studies of failures in wind turbines have shown a high failure rate of such accumulators. This paper proposes an estimation method for detecting one of the most common faults for accumulators, namely gas leakage. The method utilizes an Extended Kalman Filter for joint state and parameter estimation with special attention to limiting the use of sensors to those commonly used in wind turbines. The precision of the method is investigated on an experimental setup which allows for operation of the accumulator similar to the conditions in a turbine. The results show that gas leakage is indeed detectable during start-up of the turbine and robust behavior is achieved in a multi-fault environment where both gas and external fluid leakage occur simultaneously. The estimation precision is shown to be sensitive to initial conditions for the gas temperature and volume.

Commentary by Dr. Valentin Fuster
2017;():V001T01A025. doi:10.1115/FPMC2017-4254.

Digital hydraulic control valve technology has shown its strengths in providing reliable, leak-tight and high performance valve control regardless of the pressure medium used, oil or water. This is enabled by the intelligent use of robust on/off seat valves. However, the availability of these valves for water hydraulics is limited, especially that of compact valves, which are needed for digital valve systems. Thus, with the aim to create a compact digital water hydraulic valve system, this paper presents the development process of a water hydraulic miniature valve. The starting point for the development is a previously developed miniature valve for oil hydraulics. Experimental results with the new prototype show that good performance can be achieved for the miniature valve even with using stainless steel materials. This enables high-performance digital water hydraulic control.

Topics: Hydraulics , Valves , Water
Commentary by Dr. Valentin Fuster
2017;():V001T01A026. doi:10.1115/FPMC2017-4255.

High-efficiency hydraulic machines using digital valves are presently a topic of great focus. Digital valve performance with respect to pressure loss, closing time as well as electrical power consumption, is key to obtaining high efficiency. A recent digital seat valve design developed at Aalborg University utilizing moving coil actuation, meets these performance demands but is challenged by practical issues. This paper builds upon that design by proposing a retrofit which preserves both the seat valve topology and the outer dimensions, but utilizes moving magnet actuation. Through constrained multi-objective optimization, six initial topologies and three derived topologies, including designs with one, two and four coils, are optimized with respect to overall efficiency. Apart from the actuator, the flow forces on the seat valve geometry is modeled using CFD and included in optimization. In simulation the final optimized design closes in 2.1 ms, has a pressure drop of 0.8 bar at 150 l/min and yields a digital displacement machine average chamber efficiency of 98.9%. The design is simple in construction and uses a single coil, positioned outside the pressure chamber, eliminating the need for an electrical interface to the pressurized valve chamber.

Commentary by Dr. Valentin Fuster
2017;():V001T01A027. doi:10.1115/FPMC2017-4258.

Hydraulic manipulators on mobile machines, whose hydraulic actuators are usually controlled by mobile hydraulic valves, are being considered for robotic closed-loop control. A feed-forward-based strategy combining position and velocity feedback has been found to be an effective method for the motion control of pressure-compensated mobile hydraulic valves that have a significant dead zone. The feed-forward can be manually identified. However, manually identifying the feed-forward models for each valve-actuator pair is often very time-consuming and error-prone. For this practical reason, we propose an automated feed-forward learning method based on velocity and position feedback. We present experimental results for a heavy-duty hydraulic manipulator on a forest forwarder to demonstrate the effectiveness of the proposed method. These results motivate the automated identification of velocity feed-forward models for motion control of heavy-duty hydraulic manipulators controlled by pressure-compensated mobile hydraulic valves that have a significant input dead zone.

Commentary by Dr. Valentin Fuster
2017;():V001T01A028. doi:10.1115/FPMC2017-4259.

Manufacturers of fluid power equipment have decreased the size of hydraulic fluid reservoirs in response to economic, environmental and performance requirements. Residence times as brief as 30 seconds in mobile equipment are not unusual. Shorter fluid residence times dictate use of hydraulic fluids with improved air release characteristics. In this investigation, hydraulic fluids of the same ISO viscosity grade but varying base oil and additive composition were evaluated in a dynamometer fitted with a reservoir that incorporated an aerator at the inlet, and a mass flow meter at the outlet. The effects of aeration on piston pump efficiency and air borne noise generation were evaluated. Fluids of the same ISO viscosity grade exhibited significantly different air release rates and as a result sustained different volume fractions of entrained air. Hydraulic oils that entrained a greater volume of air demonstrated lower volumetric efficiencies and higher sound levels. Aerated fluids of the identical viscosity grade differed in volumetric efficiency by as much as 8% and perceived sound level by as much as 50%. Models for the effect of aeration on pump performance are presented.

Topics: Fluids , Pumps , Pistons
Commentary by Dr. Valentin Fuster
2017;():V001T01A029. doi:10.1115/FPMC2017-4260.

The design and analysis of feedback controllers for digital displacement machines requires a control oriented model. The displacement throughput of a full stroke operated machine is altered on a stroke-by-stroke basis at fixed rotation angles. In the case of a fixed speed operation, it may be treated as a Discrete Linear Time Invariant control problem with synchronous sampling rate. To make synchronous linear control theory applicable for a variable speed digital displacement machine, a method based on event-driven control is presented. Using this method, the time domain differential equations are converted into the spatial (position) domain to obtain a constant sampling rate and thus allowing for use of classical control theory. The method is applied to a down scaled digital fluid power motor, where the motor speed is controlled at varying references under varying pressure and load torque conditions. The controller synthesis is carried out as a discrete optimal deterministic problem with full state feedback. Based on a linear analysis of the feedback control system, stability is proven in a pre-specified operation region. Simulation of a non-linear evaluation model with the controller implemented shows great performance, both with respect to tracking and disturbance rejection.

Commentary by Dr. Valentin Fuster
2017;():V001T01A030. doi:10.1115/FPMC2017-4261.

Hydraulic actuators benefit robotic systems as they can produce significant force/torque for their size and are robust. However, their dynamic behavior is highly nonlinear, making high-performance closed-loop control a challenging task. With articulated robotic systems, the associated nonlinear multibody dynamics make the control design task even more challenging.

Nonlinear model-based (NMB) control methods can be used to address the system nonlinearities. Among NMB control methods, a number of state-of-the-art control performance improvements have been demonstrated for hydraulic manipulators using the virtual decomposition control (VDC) approach. However, all studies on hydraulic systems with VDC have focused on high-inertia and heavy-duty manipulators. In hydraulic cylinder actuated low-inertia and light-weight systems, highly uncertain and hard-to-model nonlinearities, such as actuator friction, can become very dominant in the system’s dynamic behaviour.

This paper details the design of a VDC-based controller for a hydraulically actuated light-weight robotic leg. An adaptive friction compensation is incorporated in the control design. The stability of the designed controller is rigorously guaranteed. The experiments with the controller demonstrate a comparable free-space control performance in relation to the state-of-the-art controller for heavy-duty hydraulic manipulators.

Commentary by Dr. Valentin Fuster
2017;():V001T01A031. doi:10.1115/FPMC2017-4263.

Articulated hydraulic manipulators are widely used for moving heavy loads. Commercial manipulators are most often equipped with a rotating load-grasping tool connected at the end of the manipulator via a pair of passive (unactuated) revolute joints. In free-space motion, these passive joints are subject to swaying motions due to the manipulator tip accelerations. Because these passive joints are not directly controllable due to their passive nature, a skilled driver is needed to compensate for the load swaying. In this paper, we extend the nonlinear model-based Virtual Decomposition Control (VDC) theory to cover anti-sway control of underactuated multiple degrees-of-freedom (DOF) hydraulic redundant manipulators. The proposed nonlinear controller performs the control design and stability analysis of the hydraulic robotic manipulator at the subsystem level. Experiments are conducted in a full-scale loader manipulator to verify that the proposed controller can efficiently damp the load swaying in a case study of redundant vertical plane motion.

Commentary by Dr. Valentin Fuster
2017;():V001T01A032. doi:10.1115/FPMC2017-4264.

In this study, a stability-guaranteed, nonlinear, finite element-based control is presented for a single-link flexible manipulator with hydraulic actuation, subject to experimental validation. The strong, inherent nonlinearities of the hydraulic cylinder and fluid dynamics, coupled with flexible link dynamics, cause remarkable challenges in controlling the system effectively. In an attempt to cope with these challenges, a controller based on the Virtual Decomposition Control (VDC) approach is introduced. The VDC approach takes advantage of subsystem-dynamics-based control, enabling the handling of the dynamics and control of the hydraulic actuator and the flexible link separately, thus keeping the controller design relatively simple. The rigorous stability theory of the VDC approach guarantees the stability of the entire system. The experiments demonstrate the VDC controller’s performance in end-point control with built-in vibration dampening.

Commentary by Dr. Valentin Fuster
2017;():V001T01A033. doi:10.1115/FPMC2017-4265.

The application of sliding mode algorithms for control of hydraulic drives has gained increasing interest in recent years due to algorithm simplicity, low number of parameters and possible excellent control performance. Both application of first- and higher order sliding mode control algorithms in hydraulic drive controls have been presented in various literature, demonstrating the possible successful application of these. However, a major drawback is the presence of e.g. valve dynamics which often necessitates the usage of continuous approximations of discontinuities in order to avoid control chattering, which on the other hand compromises the robustness properties. This may also be the case when discontinuities are only present in the control derivative. This fact suggests that sliding mode algorithms may be more appropriate for assisting the control, i.e. for state observation, disturbance observer based control etc., and several examples of such approaches have been presented in literature. The latter case appear especially interesting as a sliding mode actually takes place, but only the low-pass filtered sliding mode algorithm output is used in the actual control input. However, the successful implementation relies heavily on the low-pass filter design where the drive dynamics, sample rate etc. play a significant role. In this paper the utilization of the super twisting algorithm for disturbance compensation is considered. The fact that the discontinuity here is nested in an integral causes less restrictions on the used low-pass filter, enabling the possibility for a wide range of usage when the sampling frequency is in the range of industrial grade control hardware. The proposed control structure is designed and considered in relation to a valve driven hydraulic winch drive, and results demonstrate that excellent and high precision control may be achieved in the presence of large and highly varying external loads.

Commentary by Dr. Valentin Fuster
2017;():V001T01A034. doi:10.1115/FPMC2017-4266.

The application of valve driven hydraulic winch drives is related to substantial power losses, primarily due to throttle generated valve flows. More energy efficient solutions are also commonly applied in terms of conventional hydrostatic closed circuit drives as well as so-called secondary controls. Such solutions are typically constituted by many and rather expensive components, and are furthermore often suffering from low frequency dynamics. In this paper an alternative solution is proposed for winch drive operation, which is based on the so-called speed-variable switched differential pump, originally designed for direct drive of hydraulic differential cylinders. This concept utilizes three pumps, driven by a single electric servo drive. The concept is redesigned for usage in winch drives, driven by flow symmetric hydraulic motors and single directional loads as commonly seen in e.g. active heave compensation applications. A general drive configuration approach is presented, along with a proper control strategy and design. The resulting concept is evaluated when applied for active heave compensation. Results demonstrate control performance on level with conventional valve solutions in terms of motion tracking, however with improved efficiency, especially in the event that the electrical servo drive can realize four quadrant operation.

Topics: Pumps
Commentary by Dr. Valentin Fuster
2017;():V001T01A035. doi:10.1115/FPMC2017-4267.

The dominant physical phenomena in hydraulic drives are generally well known, why the model equations describing the dominant dynamics may be established with a high level of certainty. To some extend, this is also the case for the model parameters when these are based on data sheet information. However, parameters such as the effective bulk modulus, leakage, external disturbances etc. may be difficult to evaluate, and may furthermore be varying. In regard to control design, linear methods may be difficult to apply and stability margins difficult to evaluate, unless dynamic models are established prior to the control design. This problem may be overcome using adaptive controllers, adjusting themselves to uncertainties/variations. This often shifts the problem from adjusting the controller parameters, to adjusting the parameters of the control parameter adaption mechanism, which in many cases involves a significant number of parameters. This paper considers a novel adaptive control algorithm, theoretically applicable to systems of arbitrary orders, and potentially only with three tuning parameters. The proposed algorithm is considered in relation to the position control of a hydraulic winch drive, and results imply that excellent motion tracking performance may be achieved utilizing only state feedback.

Commentary by Dr. Valentin Fuster
2017;():V001T01A036. doi:10.1115/FPMC2017-4269.

The metering out sensing system represents the latest, and most promising, architectural concept for improving the performance of mobile multiple actuation systems through hydraulic proportional components control.

The first part of the paper introduces the novel architecture of meter-out sensing control system, properly designed to distribute the flow rate directed to actuators according to the proportional control of the metering out element only. To do this, an innovative piloting subsystem controls the pump displacement, while a set of compensated proportional control valves applied to actuators outlet work to manage the load unbalance. The inlet doesn’t have any proportional throttle element thus reducing control losses with respect to state-of-the-art systems. In this way, the architecture is able to control both resisting and overrunning loads, and its design could easily include the automatic activation of the regenerative function to limit the requested hydraulic power.

Then, the paper highlights how the proposed architecture of meter-out sensing system, which does not require complex sensor networks or complex electronic controls, could overcome the most important limitations affecting other control technologies currently adopted in mobile hydraulics.

The third part of the paper depicts the main results obtained in the evaluation of the performance figures of merit for the metering out sensing system, performed through a Virtual Test Procedure applied to a lumped and distributed parameter numerical model.

Commentary by Dr. Valentin Fuster
2017;():V001T01A037. doi:10.1115/FPMC2017-4271.

The paper focuses on the development of a predictive numerical tool for the performance assessment of air-cooled cross-flow heat exchangers for vehicle application. First, a CFD approach for the simulation of vehicles’ radiators under actual operating conditions is proposed. The numerical analysis accounts both for the thermo-fluid dynamics behavior of each section of the heat exchanger and for the flow characteristics of the adopted fan. The full-scale geometry of the fan is included in the simulation as well as the casing and the real rotational speed. The CFD results are used to correlate the flow distribution across the different radiator’s sections and the actual working conditions of both the heat exchanger and the fan operation.

Following this methodology, a generic radiator was divided in two different sub-domain types (internal/boundary), and for each one the Wall Heat Transfer Coefficient and the pressure drop 2D maps are determined on the basis of preliminary CFD simulations as functions of fluid velocity and temperature. These elements became the elementary blocks to be used by a custom-made algorithm to characterize exchangers of any size. The algorithm was extended to develop a fully featured PC software to calculate the performance of multiple sections exchangers.

Commentary by Dr. Valentin Fuster
2017;():V001T01A038. doi:10.1115/FPMC2017-4272.

Bi-stable latching valves are an energy efficient alternative to mono-stable switching valves especially in applications of process technology requiring low switching frequencies. The bi-stability of such valves may be disadvantageous. Valve’s states may not only change by controlling the coil current, but also by undesired external forces. A sensorless position determination by detecting the armature position allows condition monitoring. Additionally, an appropriate power supply for switching the valve’s state increases the energy efficiency even further and can be realized by detecting the end stop with the basics of the position estimation method.

The paper deals with simulation-based investigations of a promising sensorless position determination of a novel bi-stable valve, which is partly manufactured from injection moldable magnetic material. The constraints and potentials of the estimation method are described, especially according to condition monitoring the valve’s state. Selected simulation results are validated by measurements. Furthermore, simulations of the magnetic behavior and the mechanical motion are performed demonstrating the potential for detection of the motion’s end stop to apply only the required switching energy to the actuator.

Commentary by Dr. Valentin Fuster
2017;():V001T01A039. doi:10.1115/FPMC2017-4273.

Electrical switched-mode DC-DC converters have become ubiquitous in the last decade, primarily driven by their high energy efficiency. Although considerable academic research has been performed on the analogous hydraulic switched-inertance converters, widespread adoption has lagged. This paper presents a comparison of the two technologies, comparing theoretical and practical limits to their performance. First we develop a simple model for the efficiency and specific power capacities of buck and boost converters in the ideal case, so that critical parameters can be identified as well as their physical limitations. We then expand our analysis to include practical effects such as wave propagation, switching losses and operating limits, in an attempt to identify if there are any reasons to continue or discontinue development of the hydraulic switched-inertance converter.

Commentary by Dr. Valentin Fuster
2017;():V001T01A040. doi:10.1115/FPMC2017-4277.

In this paper an innovative design solution of a vane pump integrated with an electric motor is presented. In the proposed solution the double vane pump is embedded into the rotor of electric permanent magnets motor (BLDC). CFD simulations of the flow have been carried out to analyze the flow in the pump crossover areas and to avoid the cavitation phenomena at the inlet channel. Results of experimental investigations of the motor pump assembly prototype are presented.

Commentary by Dr. Valentin Fuster
2017;():V001T01A041. doi:10.1115/FPMC2017-4281.

Switched inertance hydraulic systems are switch mode fluid power circuit topologies that allow the load pressure to be modulated in an efficient manner. A unique feature of these circuits is a long, small diameter, inertance tube, which stores energy in the fluid kinetic domain during a switching cycle. A barrier to application of these circuits is that current models require an elevated reservoir pressure, which is difficult to implement in practice. Research has focused on analyzing inertance tube wave delay effects in the frequency domain, which necessarily excludes non-linear physical phenomena such as cavitation and pressure dependent wave speed. A circuit with an ambient reservoir pressure exposes the fluid in the inertance tube to local pressure conditions where these non-ideal behaviors may have a strong effect on system dynamics. In this paper, a method of characteristics cavitation model with unsteady friction is presented that accurately captures the incidence and severity of cavitation in a long pipeline undergoing cyclic high and low pressure boundary conditions. This model is validated experimentally by examining the pressure response in a 3.95m steel pipeline with an upstream switching valve capable of 0.5ms transition at 120Hz. Experiments are conducted over a range of switching frequencies at 60% duty. The proposed pipeline model can be used to predict conditions leading to cavitation as well as help develop cavitation avoidance strategies, such as soft switching and utilization of line resonance.

Topics: Cavitation , Circuits
Commentary by Dr. Valentin Fuster
2017;():V001T01A042. doi:10.1115/FPMC2017-4284.

The control strategy in a hydraulic hybrid vehicle is very important for taking advantage of its full potential. In a hydraulic hybrid vehicle, the hydrostatic transmission can be controlled to optimize the entire system. A hydrostatic transmission is composed basically of a hydraulic motor and a hydraulic pump. For an electric hybrid vehicle, an electric motor is the prime mover. In this study, the control variables are the displacements of the hydraulic devices and the objective is to optimize the system efficiency. All possible combinations of displacements were tested through simulation and the most efficient combination was recorded. Compared with a fixed displacement hydrostatic transmission, around 4.5% of the energy can be saved using the most efficient configuration of the hydrostatic transmission. Fuzzy logic theory was used to simulate the driver input and it was used as a control strategy for the hydrostatic transmission.

Commentary by Dr. Valentin Fuster
2017;():V001T01A043. doi:10.1115/FPMC2017-4285.

Water as a working fluid in hydraulic systems: the benefits of this particular hydraulic fluid are both numerous and consequential, but its implementation remains nontrivial for certain key applications. One of these key applications is the axial piston machine of swashplate type, which counts among its selling points efficiency, the possibility of variable displacement, and the ability to function in high-pressure systems [1]. Water as a working fluid tends to mar that last point with its extremely low viscosity — and the high leakages and low load support that stand as effects of that fluid property in the context of tribological interfaces. However, water’s environmentally friendly, fire resistant nature is coupled with a high thermal conductivity and high heat capacity favorable for keeping hydraulic systems cool, as well as a high bulk modulus that cuts slack in the exact execution of machine motions [2]. That makes it worth implementing in hydraulic systems, even in the face of the aforementioned troubles. This paper investigates the effects of a surface shape that can be applied to the cylinder bores of axial piston machines with the goal of improving load support while keeping down leakage in the critical piston cylinder tribological interface of axial piston machines operating at high pressures with water as their hydraulic fluid.

Commentary by Dr. Valentin Fuster
2017;():V001T01A044. doi:10.1115/FPMC2017-4287.

The leakage past the tooth flanks of the gears in transition contacts in involute external toothed gear pump is analyzed in details using CFD in Fluent®. Analytical results support the experimentally visualized flow patterns [1]. Extending the approach of an earlier investigation [2] more rigorous analyses are carried out considering actual gear data of a pump and a full cycle of contact. However, the relieve groove and cavitation are not considered. The basic purpose is to establish the flow pattern analyses using CFD in Fluent-Ansys® environment. The beginning and the end of entrapment, squeezing of fluid, pressure build up, separation and generation of gap at the active contact and instantaneous flow through the gap are estimated meticulously.

Commentary by Dr. Valentin Fuster
2017;():V001T01A045. doi:10.1115/FPMC2017-4290.

In rock excavation processes, hydraulic rotary-percussive drilling is used for drilling and blasting in both surface and underground drilling operations. A hydraulic percussive drilling system is composed of percussion, rotation, feed, and flushing functions. In this paper, we detail the interaction of feed and rotation functions using a rock model. The feed actuator is a cylinder drive and a hydraulic motor actuator rotates the drill bit. The feed is force controlled and rotation is torque controlled by a feed reduction valve acting on the pressure compensator of the mobile hydraulic proportional directional control valve. In addition, in this work an individual load sensing variable displacement pump is used for both hydraulic functions. A suitable rock model is developed and verified against a measurement set. The inputs of the rock model are percussion drill flow rate, percussion pressure, feed force, and rotation torque, and the outputs are drill bit penetration rate and rotational speed. The modeling work is carried out to enable intelligent rock drilling control system development for changing rock conditions. The simulation results obtained verify that the simple rock model emulates various rock characteristics ranging from extremely hard rock like granite to softer minerals and that the changes in drilling parameters were as expected.

Commentary by Dr. Valentin Fuster
2017;():V001T01A046. doi:10.1115/FPMC2017-4292.

Pump controlled hydraulic circuit is an energy efficient alternative to valve controlled system, as they eliminate the throttling loss and require less cooling power. In all pump controlled systems, the internal and external leakages of the pump and actuator, especially the unequal flow rates of the single rod cylinder must be compensated. In presently existing solutions, an additional pump or some valves are used to compensate the unequal flow rates, leakages and to pressurize the system. However, these approaches increase the system complexity and complex control strategies are required to improve the overall system dynamic performances. Also, some of them suffer from undesired and uncontrolled pressure and velocity oscillations when the load force is small or its direction changes. This paper addresses the unequal flow rates compensation problem and stability problem of pump controlled single rod cylinder system, and proposes a novel solution for it. The system under consideration utilizes a new designed asymmetric pump which can match the unequal flow rates of the single rod cylinder basically. The feasibility of the new circuit is validated by both mathematics and multi-body simulation model. The results show that the undesired velocity oscillations can be removed up. Furthermore, the operating characteristics and energy efficiency of the arm cylinder with the new scheme based on the designed open-loop and closed-loop strategies are studied on a real excavator. The results show that there is no obvious velocity fluctuation with the asymmetric pump and the position controlled precision is satisfied. Compared with the independent metering circuit, the energy-saving ratio reaches to 57% during a working cycle.

Commentary by Dr. Valentin Fuster
2017;():V001T01A047. doi:10.1115/FPMC2017-4294.

This paper introduces the simulation of a wave-to-wire (W2W) wave energy converter (WEC) design that includes the complete system from the original wave capture device to the final generated electricity supplied to the grid. Instead of designing the sub-systems separately, this holistic approach allows the optimization of the WEC performance. The Energy Capture Device (ECD), the absorption stage, is based on heaving theory, namely a point absorber. The Power Take-Off (PTO) system, the transmission stage, is based upon a hydrostatic transmission. Lastly the WIRE side, the generation stage, is achieved by connecting a three-phase round-rotor synchronous generator driven by the hydraulic motor from the PTO system. The control strategy primarily aims to meet the criteria of the grid while extracting as much energy from the waves as possible.

Commentary by Dr. Valentin Fuster
2017;():V001T01A048. doi:10.1115/FPMC2017-4297.

This paper presents a generic method for generating joint trajectories for robotic manipulators with collision avoidance capability. The coordinate motion control system of the heavy-duty hydraulic manipulator resolves joint references so that a goal pose can be reached in real-time without any collisions. The control system checks whether any part of the manipulator is at risk of colliding with itself, with other manipulators, or with environmental obstacles. If there is a risk of collision, then the collision server searches the points where the collision is about to occur and calculates the shortest distance between the colliding objects. The collision server retains static and dynamic point clouds, and it uses point cloud data to calculate the shortest distance between the colliding objects. The point clouds on the server are kept up to date with the manipulators’ joint sensors and an external surveillance system. During coordinated motion control, the joint trajectories of the hydraulic manipulator are modified so that collisions can be avoided, while at the same time, the trajectory of the end-effector maintains its initial trajectory if possible. Results are given for a seven degrees of freedom redundant hydraulic manipulator to demonstrate the capability of this collision avoidance control system.

Commentary by Dr. Valentin Fuster
2017;():V001T01A049. doi:10.1115/FPMC2017-4299.

In powersplit systems, which are state-of-the-art in tractor transmissions, the efficiency is of much higher importance than in most other vehicles. Key for high efficiency is to transmit only some power hydrostically and a high amount mechanically (Fig. 1 and 2) because the mechanical path has higher efficiency than the hydrostatic path. The hydrostatic path is needed to get an infinitely variable transmission.

The understanding of powerloss characteristics of hydrostatic components helps to choose between swashplate and bent axis components. Best total efficiencies of 97% are key arguments for using 45° bent axis technology. This is the reason for a dominant use of 45° bent axis in powersplit transmissions.

The search for further reduction in powerloss shows the weak volumetric efficiency at small displacements and high pressure levels. The compression loss is now a dominant subject for improvement. The paper will explain a new design for reduced compression loss, which can be applied to 45° bent axis units. The powerloss reduction will be shown for a powersplit transmission with 2 and 3 modes, which are state of the art today [7].

Topics: Hydrostatics , Design
Commentary by Dr. Valentin Fuster
2017;():V001T01A050. doi:10.1115/FPMC2017-4300.

Digital hydraulics have attracted attention towards fast switching valves and the increased focus on reliable fluid power entail that the lifetime of such valves is of great concern. An inherent feature of most valves for digital hydraulics is that of a mechanical end stop. Consequently, the squeeze film damping associated with end stops of switching valves is an interesting topic. This damping effect is perceived as beneficial for high lifetime and low impact sound, as the consequence of lowering the impact velocity at the mechanical end stops. In this paper the squeeze film damping effect is reviewed with a focus on maximum surface stresses. Using the Barus relation for viscosity-pressure dependency and different film geometries, the classical lubrication theory is applied together with the equation of motion, to obtain the gap height motion equation, both for the iso-viscous and piezo-viscous case. In consequence, this enable insights concerning the influence of piezo-viscosity on this damping effect. These models are used to investigate the loads, which the approaching surfaces experiences. Based on Hertzian theory, comparisons of impact loads and the dynamic squeeze loading are performed, whereby the relation between design parameters and the relative severity of these occurrences are analyzed.

Topics: Stress , Damping
Commentary by Dr. Valentin Fuster
2017;():V001T01A051. doi:10.1115/FPMC2017-4302.

This paper presents an optimized control for independent metering hydraulic systems that integrates machine diagnostic features. The machine under study is a hydraulic crane for truck applications equipped with a post compensated Load Sensing Pressure Compensated (LSPC) independent metering valve. Control challenges of such hydraulic system pertain to the determination of the opening of the meter-out section under overrunning load conditions. In this work, the inlet actuator pressure was used as feedback for a PI control architecture. The gains of the PI regulator were defined through an Extremum Seeking (ES) optimization algorithm, which minimizes cost functions representative of energy consumption and occurrence of cavitation, to achieve optimal performance in different operating conditions. The control was tested on a simulation model of the reference machine developed in AMESim and validated against experimental results.

The paper shows that the same cost functions used to define the controller parameters can be used as additional inputs, along with conventional sensors, to monitor the health status of the machine.

Topics: Valves
Commentary by Dr. Valentin Fuster
2017;():V001T01A052. doi:10.1115/FPMC2017-4303.

Hydraulic hybrid powertrains, which can be applied to many types of vehicles including cars, have several important advantages over electric hybrids, such as lower costs, higher power density, and more regenerative energy available from braking. There have been various investigations for hydraulic hybrid architectures and there always exists room for improvement in terms of performance and efficiency. In order to achieve improved performance and efficiency, a novel hydraulic hybrid transmission architecture has recently been suggested in Maha Fluid Power Research Center, which is implemented in the platform of 1999 Range Rover. Previous studies of the Maha hydraulic hybrid vehicle (HHV) mainly focused on the optimization of system components and controller. In order to further study and optimize hydraulic hybrid architectures, the thermal behavior has to be considered as well. A few existing thermal studies on other hydraulic systems have mostly focused on steady state characteristics due to the difficulty of simulating the unsteady state conditions. In this paper, a novel approach to thermal modeling of HHV for a novel HHV architecture is presented. The results have been validated with the measured data collected while driving the vehicle. The thermal model utilizes the flow rate and pressure obtained from the hydraulic system model and calculates the system temperature at different locations. In order to capture the rapid transition of the hydraulic system in HHV, a novel simulation scheme considering the flow direction for the control volume inputs is applied in the presented study. In addition, the presented model considers compressible flow in order to improve the accuracy of the model.

Commentary by Dr. Valentin Fuster
2017;():V001T01A053. doi:10.1115/FPMC2017-4304.

In this paper, active vibration control concept using the existing pump control system based on the multi-frequency two-weight notch LMS (Least Mean Square) filter was investigated and tested experimentally. This research also includes the direct swash plate acceleration measurement, the case acceleration measurement, and the simultaneous multi-position microphone measurement in the semi-anechoic chamber. A 75 cc/rev swash plate type axial pump was modified to implement swash plate active vibration control combining a high speed direct drive servovalve, an electronic swash plate angle sensor, a swash plate acceleration sensor, and a high speed real-time controller with the NI Labview FPGA. Vibration measurements utilizing a tri-axial swash plate acceleration sensor and two tri-axial case acceleration sensors, and noise measurements using three microphones were conducted in the semi-anechoic chamber to investigate the influence and effectiveness of the developed system and the proposed swash plate active vibration control.

Commentary by Dr. Valentin Fuster
2017;():V001T01A054. doi:10.1115/FPMC2017-4309.

In pressure compensated external gear machines (EGMs), lateral lubricating interfaces exist between floating lateral bushings and gears. These interfaces are primarily responsible for supporting the high pressure bearing loads in these gaps and promoting good operating efficiencies of these units. A fully coupled fluid-structure-thermal interaction lateral gap model has been developed previously in the authors’ research team which considers this highly coupled physical phenomena to predict the lubrication performance of the interface under full film as well as mixed film conditions. In the current work, capabilities of the lateral gap model are utilized in studying the impact of the variations in surface finishes on the performance of a commercially available EGM chosen for this study.

Lateral plate designs of varying surface roughness are chosen for the same EGM unit, to analyze their influence on the lubricating performance of the unit. Detailed surface profile measurements were carried out on these lateral plates under study to determine precise inputs to the lateral gap model. Resulting numerical simulations from the gap model over different operating conditions are used to examine the significant performance features associated with the lateral interface which are affected by such surface variations. Furthermore, the paper compares the simulated leakages obtained directly from the lateral gap model for each of the lateral plate designs, with corresponding experimental data over a wide range of operating conditions.

Commentary by Dr. Valentin Fuster
2017;():V001T01A055. doi:10.1115/FPMC2017-4310.

This work introduces a new way to control hydraulic cylinder velocity using an inlet metering pump system to control the hydraulic flow entering the cylinder. The inlet metering system consists of a fixed displacement pump and an inlet metering valve that adjusts the hydraulic fluid flow entering the pump as required. The energy losses associated with flow metering in the system are reduced because the pressure drop across the inlet metering valve can be arbitrarily small. The fluid is supplied to the inlet metering valve at a fixed pressure using a charge pump. A velocity control system is designed using the inlet metering system as means to control the fluid flow to a hydraulic cylinder. In addition to the inlet metering system, the velocity control system designed in this work includes a four-way directional valve to set the fluid flow direction according to the desired direction of the hydraulic cylinder velocity. Open-loop and closed-loop proportional and proportional derivative (P and PD) controllers are designed. Designs with the goals of stability and performance of the system are studied so that a precise and smooth velocity control system for the hydraulic cylinder is achieved. In addition to potentially high efficiency of this system, there is potential for other benefits including low cost, fast response, and less complicated dynamics compared to other systems. The results presented in this work show that the inlet metering velocity control system can be designed so that the system is stable, there is zero overshoot and no oscillation.

Commentary by Dr. Valentin Fuster
2017;():V001T01A056. doi:10.1115/FPMC2017-4311.

Electro-hydraulic pressure-control valves are used in many applications, such as manufacturing equipment, agricultural machinery, and aircrafts to name a few. A traditional electro-hydraulic pressure-control valve regulates an output pressure for a corresponding input current by balancing solenoid force, spring force, and regulated pressure force. This results in a repeatable steady-state pressure output that is nearly proportional to the input current. This is helpful in open loop applications when one wants to achieve a consistent output pressure for a corresponding input current. The transient pressure response, however, is highly sensitive to the component tolerances and manufacturing processes as well as the fluid properties in the regulated volume, such as bulk modulus, viscosity, density, and aeration. These properties are often unknown in a system and can vary significantly from system to system and also during use in a typical application, making controllability difficult. Since there is variation in the steady-state pressure output for a given valve population, these valves are often calibrated in the end system to better achieve the desired output. This helps, but there is variation in this process, and also variation within a single valve over life. So although various attempts are made to minimize steady-state error, it will always exist and therefore closed loop control is desirable. Unfortunately, attempts at closed loop control of a traditional pressure-control valve often yield unacceptable and inconsistent performance. This is due to the sensitivity of the transient response to system characteristics, primarily fluid and mechanical properties of the regulated control port volume. The transient performance sensitivity of the valve can be reduced by de-coupling the regulated pressure dynamics from the spool dynamics. This will conversely increase the sensitivity of the steady state performance; however this can be solved through the implementation of a closed loop controller. In this paper a dynamic model is developed for a traditional pressure-control valve and different pressure-control valves without the traditional pressure balancing force. The new valve models are validated experimentally and then used to compare the performance characteristics of the valves. Linear analysis is performed on the validated models to further illustrate the impact of the system properties. The objective of this work is to develop a pressure-control valve with more consistent transient performance characteristics that are less sensitive to the system parameters so that a closed loop controller can be developed for the valve.

Commentary by Dr. Valentin Fuster
2017;():V001T01A057. doi:10.1115/FPMC2017-4313.

A key component of hydraulic fluid power systems — the standard orifice and, consequently, all equivalent components — apparently has, to this day, some mysteries yet to be unveiled. Knowledge on cavitation-induced liquid flow choking or saturation, which is a well founded topic in some areas of the wide field of hydraulics, e.g. water distribution piping systems, is practically neglected when assessing the design of typical mineral-oil-based power generation and control systems, for both mobile and industrial applications. This conclusion holds true at every level of study, from the technical reference literature adopted by designers to the more popular textbooks and journal papers. Moreover, the rare works addressing the phenomenon are focused on the underlying physical mechanics, completely missing any kind of evaluation of the functional consequences, especially the need to “revise” the standard quadratic law of turbulent flow. Prompted by one of these works, a preliminary experimental activity has been carried out, aimed at determining the actual flow characteristic of standard screw-in orifices used in fluid power pilot circuits. The results confirmed the undoubted presence of flow saturation; based on that, a suitable theoretical description was developed, and some practical applications are outlined in the paper. Finally, few open questions are listed, which need to be answered.

Commentary by Dr. Valentin Fuster
2017;():V001T01A058. doi:10.1115/FPMC2017-4314.

Pump-controlled hydraulic actuators of single rod cylinders, while efficient, often exhibit undesirable performances during pump mode of operation switching. Although the oscillatory performances have been found in both simulations and experiments, a rigorous proof of such undesirable dynamics has rarely been reported due to lack of proper theoretical tools. In many previous works, traditional stability analysis of pump-controlled single rod hydraulic actuator systems was carried out by studying eigenvalues of the linearized models in each of various regions, separately. This may lead to a conservative conclusion. In this paper, such mode switching instability is analyzed using the concept of Lyapunov exponents. More specifically, the impact of the cracking pressures of the pilot operated check valves on system dynamics of a commonly used pump-controlled circuit is investigated. The numerical results are in agreement with the experimental findings, indicating the efficacy of the proposed method. The paper thus contributes to the systematic stability analysis for non-smooth hydraulic actuator systems, which can subsequently facilitate the controller design.

Commentary by Dr. Valentin Fuster
2017;():V001T01A059. doi:10.1115/FPMC2017-4315.

The ideal variable displacement pump for a displacement control circuit is efficient across a wide operating range and readily mounted on a common shaft with multiple pumps. This paper presents a novel variable displacement pump architecture for displacement control circuits that uses the concept of alternating flow (AF) between piston pairs that share a common cylinder. The displacement is adjusted by varying the phase angle between the piston pairs. When the pistons are in phase, the pump displacement is at a maximum and when the pairs of pistons are out of phase, fluid is shuttled between the pistons and the pump produces no net flow. A prototype of the AF pump was constructed from two inline triplex pumps that were modified so that three piston pairs were created. The crankshafts of the two pumps were connected via a sprocket-and-chain transmission. The sprockets allow for accurate measurement of the phase angle, which is adjusted, in this early phase prototype, by disassembling the chain and shifting the sprockets. The prototype AF pump was then mounted to the test stand and experiments were conducted to map the AF pump efficiency and cylinder pressure dynamics across a range of operating pressure, speed, and displacement. The AF pump’s efficiency was measured for 8 diferent phase angles with an efficiency of near 90% at full flow and 65% at 36% displacement. The experimental results were compared to simulation results, presented in a companion paper at this conference.

Commentary by Dr. Valentin Fuster
2017;():V001T01A060. doi:10.1115/FPMC2017-4320.

Stirling engines are silent, high-efficiency power sources that generate work by shuttling a working fluid between hot and cold volumes while exploiting the working fluid’s change in pressure. Stirling engines are able to use multiple sources of heat to create this needed temperature difference, making them ideally suited for diverse waste heat recovery applications. A novel application of this technology would be to reuse waste heat from one industrial process to generate compressed air to power a second, pneumatic process, thus increasing a manufacturing facility’s overall energy efficiency. In this paper the authors explore the expected performance of using a modified Stirling engine, known as a Stirling thermocompressor, to intake air at standard atmospheric conditions and compress it into a storage container. Simulations were conducted with a multi-stage experimentally validated dynamic model, using input variables that match the author’s physical prototype. Models employing 5 or more thermocompressor stages predicted a 10-fold increase in compressed air pressure compared to ambient conditions. Future work will experimentally verify the paper’s conclusions.

Topics: Ejectors , Modeling
Commentary by Dr. Valentin Fuster
2017;():V001T01A061. doi:10.1115/FPMC2017-4323.

As the force output of an electromagnetic actuator is limited, achieving reliable operation of a direct-acting solenoid valve at high pressures and flow rates can be challenging. The major performance obstacle is the hydrodynamic flow force acting on the spool as it moves between energized and de-energized states. With trends in the fluid power industry requiring valves to operate at higher pressures and volumetric flow rates, while minimizing electrical power consumption, methods to reduce hydrodynamic flow forces become critical in developing functional products.

This paper presents CFD simulation and correlating experimental results in using back angles to reduce the hydrodynamic flow forces in a direct-acting, solenoid operated, cartridge-style, directional control valve. Traditional methods of calculating flow forces are discussed and a brief summary of prior research is presented. A commercially available CFD package, Fluent, was used to numerically estimate the flow forces using a realizable k-ε turbulence closure model. A parametric analysis of flow, pressure, and spool stroke showed sensitivity to the metering edge geometry. A special fixture was created to isolate and directly measure the forces acting on the spool. The addition of a +60° back-angle showed the largest flow force reduction of 36% compared to a spool with no back angle.

Commentary by Dr. Valentin Fuster
2017;():V001T01A062. doi:10.1115/FPMC2017-4324.

Due to recent advances in technologies ranging from hydraulically-assisted prostheses to human-scale robotics, there is a growing need for compact and efficient delivery of hydraulic power. Existing electric driven pumps require conversion from electric to rotational power before generating hydraulic output power. This work presents a dynamic model and experimental results of a linear pump that uses an electromagnetic force applied directly to the piston, resulting in a more direct conversion of electrical to hydraulic power in a compact package at the human power level. The model uses a quasi-steady state magnetic equivalent circuit model for the linear electromagnetic actuator coupled to a numerical time-domain piston pump model. The coupled model calculates the piston trajectory, cylinder pressures, and flowrates as a function of time. The modeled force generation and resulting mechanical dynamics match results generated from finite element analysis within 7%, with a predicted power density of 0.19 W/cc and efficiency of 73% for an unoptomized geometry. A multi-objective genetic algorithm is used to determine the geometry and operating parameters that give maximum power density and maximum efficiency, demonstrating that power densities of 0.7 W/cc and efficiencies of 85% are achievable.

Commentary by Dr. Valentin Fuster
2017;():V001T01A063. doi:10.1115/FPMC2017-4326.

The reduction of the noise emission level of hydraulic pumps has been a primary research goal in the fluid power field for decades. To pursue this goal, a significant effort has been put in identifying the sources of noise generation, and formulating proper methods to reduce them. Most common methods include the analysis of the kinematic features of the displacing action realized by the unit, and/or the pressure fluctuation at the pump ports. However, the physical complexity associated with the noise transmission into the pump structure and the surrounding environment has not permitted so far to achieve clear correlations between fluid-borne noise sources and actual emitted noise. Recently, the advancement in numerical acoustic modelling techniques has permitted to explore these features, so that in future, quieter units could be designed with the help from simulation.

This paper contributes in this topic, considering as a particular reference unit, the case of external gear pumps. An acoustic model developed by the authors’ research group permits to perform analysis of both structure- and air-borne noise, by combining a modal analysis performed in ANSYS and an acoustic simulation in LMS.Virtual.Lab. As pressure and force loading inputs, the model utilizes the results of the authors’ HYGESim tool.

To show the model’s potentials, the paper takes into considerations two alternative gear designs suitable for the same pump casing: one single flank and one dual flank (zero-backlash). The dual-flank design is commonly considered as a quieter solution for spur gear pumps. These designs are properly selected to show differences in fluid-borne noise source, and describes the features of the noise transmission as predicted by the model. By showing the simulated level of airborne noise for the two considered designs, the results of this paper confirm the advantages of the dual-flank solution, and point out how the proposed model can be used in future for virtual design purposes.

Commentary by Dr. Valentin Fuster
2017;():V001T01A064. doi:10.1115/FPMC2017-4327.

The lifetime of axial piston pumps is depending on the application and it’s overall robustness to external loads, but even in ideal conditions pumps will fail eventually. The analytics to this problem are known to pump manufacturers. Bearing and shaft calculations paired with FEM models are invaluable tools, however the main questions remain with the rotating kit – cylinder block, pistons, and slippers. If properly designed these parts should theoretically outlast the finite lifetime parts, such as roller bearings due to their hydrostatic and hydrodynamic bearings. In reality however failures still occur due to fatigue or other factors such as contamination or wear.

This paper describes an approach for the thermal analysis of the cylinder block / valve plate sealing interface. Using a state of the art test rig the temperature distribution, instantaneous gap height as well as particle wear have been analyzed across the entire operating range of an axial piston pump at the block / valve plate sealing interface. Simulations are done with cooperation of Purdue University by using their developed gap simulation model called Caspar FSTI. These simulations along with the measurements are used to locate potential lifetime reducing operating conditions and analyze them. The first results of the thermal behavior of this interface will be presented in this paper.

Topics: Pumps , Valves , Cylinders , Pistons
Commentary by Dr. Valentin Fuster
2017;():V001T01A065. doi:10.1115/FPMC2017-4328.

This paper describes an innovative design concept to enable electronic control of the flow delivered by external spur gear pumps. The basic principle used to obtain flow variation relies on a variable timing concept previously demonstrated by the author’s research team. This principle permits to vary the flow within a certain range, without introducing additional sources of power loss. Previous work proved the applicability of the proposed concept in a pressure compensated design of an external gear pump for high pressure applications. This concept took advantage of the pressure differential acting on the “slider”, which is an internal element performing the flow regulation.

In this paper, a solution that permits to achieve balance of the pressure forces acting on the slider is proposed. This solution reduces the actuation forces, thus enabling direct flow control actuation through an electronic control system. The proposed solution is cost effective, it consists of a limited number of parts, and it is suitable for pumps without pressure compensation, i.e. for low or intermediate pressures.

The paper details the aspects of the pump design, which was performed by using a multi-objective algorithm that maximizes the flow operating range and at the same time the pump. The optimum design could achieve a flow variation of about 32% in simulation and this was also demonstrated in actual experiments on a prototype realized at the author’s Research Center.

The proposed design can impact several of the current applications of external gear pumps, introducing the additional “flow on demand” capability.

Topics: Gear pumps
Commentary by Dr. Valentin Fuster
2017;():V001T01A066. doi:10.1115/FPMC2017-4330.

Hemodynamic flow loops are widely used for research on causes and cures of cardiovascular diseases. They replicate physiological blood flow pulsatility in vitro. Many different pump types exist for such flow loops. The variety of the flow loop types shows the lack of one concept that satisfies all requirements, which are ease of handling and sterilization, flexible and accurate realization of various profiles, low shear rate exerted on fluid, low amount of circulating fluid. This paper experimentally proves the concept of a new type of pulse damping/pulse generating device that can be used for flow loops that are operated with a peristaltic pump. The pulse generating device fulfills the double function of damping the undesired pulsatility of the peristaltic pump and injecting a desired pulsatility that replicates the flow profile delivered by the heart. The injection of the desired pulsatility is achieved by modulation of air pressure in a damping device. The experimental results show that it is possible to achieve the dual function in one device. An electromagnetic flow sensor provides the feedback for the air pressure control and a high-response flow control valve controls the pressure in the pulse damper/generator. The response time and accuracy of the sensor proved to be critical for achieving the objective. With the limitations of the relatively cheap components used for this functional prototype, the mean error in the flow rate signal could be kept below 10% for a simulated adult pulse rate of 60bpm.

Commentary by Dr. Valentin Fuster
2017;():V001T01A067. doi:10.1115/FPMC2017-4336.

The stability of the internal gear motor/pump is mostly determined by the stability of the ring gear. In order to get insight into the stability of the motor/pump, the Sommerfeld theory and the micro-motion of the ring gear are used to define stable and unstable operating areas of the internal gear motor/pump. A test rig was designed and built. Experimental investigations were performed to validate the theoretical analytical results. The internal gear motor/pump worked in different regimes. The minimum film thickness, trajectories of the ring gear, as well as the whirl motion phenomena have been studied experimentally. Moreover, it is interesting that both forward and backward whirling motion of the ring gear have been observed experimentally. Based on the minimum film thickness, the trajectories, forward and backward whirling motion of the ring gear allow determining the stability and instability of the internal gear motor/pump corresponding to the rotating speed and the working pressure.

Commentary by Dr. Valentin Fuster
2017;():V001T01A068. doi:10.1115/FPMC2017-4337.

This paper is focused on the study of the sloshing in the fuel tank of vehicles. As well known, fluid dynamic in an automotive fuel tank have to be studied and optimized to allow the correct fuel suction in all driving conditions, prevent undesired slosh noise and limit its influence on fuel vapor formation and management. Experimentation to predict the sloshing with a good accuracy depends on the ability to replace real working parameters and conditions like accelerations, decelerations, slope variations and rotations.

This paper shows results obtained studying the sloshing inside a reference tank with computational fluid-dynamic and experimental approaches.

The test bench for automotive fuel tank, employed in this analysis, has been designed by Moog Inc. on specification from Fiat Chrysler Automobiles and it is aimed at covering the wider possible range of dynamic conditions. It basically consists of a hexapod, which uses six independent actuators arranged in three triangles and connecting a base and a top platform, thus allowing all six DOFs. Above the top platform is mounted a tilt table with two additional actuators, to extend pitch and roll envelope, thus the name of “8-DOF bench”.

A dedicated CFD model has been built up using a CFD commercial code. The model has been integrated with the multiphase tool in order to correctly reply the real free surface.

Results, numerical and experimental, have been post-processed with Matlab® comparing percentage gaps of the free surfaces each other. The comparison has shown a good agreement.

This research is the result of a scientific collaboration between the Industrial Engineering Department of University of Naples Federico II and FCA Fiat Chrysler Automobiles.

Commentary by Dr. Valentin Fuster
2017;():V001T01A069. doi:10.1115/FPMC2017-4341.

Government regulations incentivize investigation of the potential for hybridization of non-road mobile machinery (NRMM). Many approaches to energy saving in hydraulic systems have been established. One of the methods first introduced in the aerospace industry is “decentralized” or “zonal” hydraulics. The decentralized system is realized with pump-controlled actuators, which are distributed throughout the system. In this research, decentralized hydraulics are realized with a direct-driven hydraulics (DDH) drive and implemented on a 1-ton class JCB micro excavator. The original valve-controlled system for boom, stick, and bucket is replaced with three DDH units. In a DDH unit, a double fixed displacement pump/motors with a speed-controlled electric servomotor directly controls the amount of hydraulic oil pumped into and out of the system. The hydraulic pump/motors create flows dependant on the rotating speed of the servomotor. A hydraulic accumulator is used as a conventional tank replacement. The aim of this paper is to investigate the efficiency improvement of the excavator with decentralized hydraulics compared to an electrified conventional load sensing system, from an energy consumption point of view under a typical digging cycle. In order to acquire the energy consumption distributions of the DDH and load sensing (LS) system, a model of the micro excavator which comprises mechanics, hydraulics, electronics, and control systems is developed in Matlab/Simulink. Simulation results demonstrate that the total efficiency of the excavator with LS control is 18.3%, and with DDH (decentralized hydraulics) is 71.3 % for a selected typical working cycle.

Commentary by Dr. Valentin Fuster
2017;():V001T01A070. doi:10.1115/FPMC2017-4342.

Digital hydraulics is an emerging field in fluid power, complementing conventional hydraulic and potentially improving efficiency and dynamic performance. High speed electrically controlled on/off valves are key enablers for many digital hydraulic systems, and specifically for digital pump/motors. This work investigates a 4-quadrant 3-piston digital pump/motor utilizing two electrically controlled high speed on/off valves per displacement chamber. The test unit was simulated, built, and experimentally tested. Simulation and experimental results showed the importance of valve response times on the overall performance and efficiency of the digital pump/motor, where a small error in the delay in the valve opening or closing could lead to significant energy losses.

To minimize the impact of valve variability, a real-time valve correction algorithm was developed to account for the error in valve timing. The algorithm uses the pressure readings at the low and high pressure ports to detect the time at which the pressure ripple occurred and then obtain the delay in the valve timing. It calculates the turn-on and turn-off valve delay times in all displacement chambers in a three-piston pump with two valves per chamber, detecting a total of 12 valve delay times. The code was tested for sequential flow diverting and sequential flow limiting operating modes at a wide range of displacement (25% to 100%) with pressures ranging from 25 bar to 105 bar and shaft speeds up to 700 rpm (limited by the valves speed). It was also tested for flow diverting mode and gave good results for displacements between 70% and 100%. The error in the calculated delay times was below 5% in all of the tested conditions, providing major improvements to the digital pump system, and to digital hydraulics in general.

Topics: Pressure , Algorithms , Valves
Commentary by Dr. Valentin Fuster
2017;():V001T01A071. doi:10.1115/FPMC2017-4344.

Closed-circuit hydraulic systems, like hydrostatic transmissions and Displacement Controlled (DC) architecture systems, require an integrated low-pressure system. These low-pressure systems provide several important functions to the hydraulic system. They prevent cavitation, provide cooling flow through the cooler, replenish the hydraulic system with cool oil, assist in the oil filtration process, provide pressure to the hydraulic unit control systems and, in the case of DC systems with differential cylinders, balance the unequal cylinder flow. Traditionally, the sizing of low-pressure systems is accomplished using a static sizing approach. In this approach, a constant efficiency of the hydraulic units is assumed, and the system is operating at a maximum power condition. The result is often an oversized charge pump and accumulator, if one is present. A dynamic sizing method has been developed using MATLAB/Simulink® with high fidelity empirical loss models for hydraulic displacement machines. Using realistic duty cycles for hydraulic systems and measured data, the low-pressure system can be accurately sized. Dynamically sizing low-pressure systems reduce parasitic losses on the prime mover because of smaller pump sizes, thus freeing power to be used elsewhere. Another concept presented in this work is the possibility of isolating the hydraulic unit control pressure supply and the low-pressure system. Realistic examples have been simulated to demonstrate the power savings of dynamically sizing low-pressure systems.

Topics: Pressure
Commentary by Dr. Valentin Fuster
2017;():V001T01A072. doi:10.1115/FPMC2017-4345.

Scaling three main lubricating interfaces (piston/cylinder interface, cylinder block/valve plate interface, and slipper/swash plate interface) of swash plate type axial piston machine while remaining the pump performance is a rewarding but challenging task. Instead of designing a new unit for the desired displacement, scaling a well-designed existing unit to the desired size requires much less computational and experimental cost. However, scaling all the components linearly is far from enough to remain the original sized unit’s performance due to the unscalable fluid properties and material properties. This paper proposes a novel scaling method for the piston/cylinder interface which is able to achieve the baseline performance at some of the operating conditions, and closing the gap between the scaled unit performance and the baseline performance at the rest of the operating conditions.

The authors use a special in-house developed simulation tool to study the design parameters of the piston/cylinder interface impacts on the performance in terms of leakage flow rate, and the energy dissipation. This in-house developed tool is able to model the lubricating fluid film behavior considering the complex fluid and structure interaction, the macro and micro motion of the piston, the three-dimensional fluid heat-transfer, the three-dimensional solid part heat-transfer, and the solid part deformation due to both the pressure and the thermal load.

This paper includes a brief introduction of the simulation tool, the results of the design parameters investigation, the proposed scaling method, and the simulation results comparison between the baseline unit and the scaled unit using the proposed method.

Topics: Cylinders , Pistons
Commentary by Dr. Valentin Fuster
2017;():V001T01A073. doi:10.1115/FPMC2017-4348.

Hydraulic cylinders are the most common actuators for small, passive hydraulic systems. Friction and leakage of the actuators are the most crucial factors for force and volume efficiency. Development of a frictionless and leak-free cylinder would enable implementation of a passive human body controlled device. Due to the limitation of short stroke length in commercial rolling diaphragm (RD) cylinders, a novel fabric-elastomer long-stroke rolling diaphragm (LSRD) cylinder was developed, evaluated, and compared to the commercial rolling diaphragm, O-ring, and gap seal cylinders. The LSRD cylinder has low friction, zero leakage, and can operate at up to 700 kPa (100 psi). The performance of the LSRD cylinders was evaluated using an antagonist hydraulic transmission benchtop device.

Axial motion of the LSRD cylinders was converted to a rotary motion on the input and output shafts using timing belts and pulleys. Two LSRD cylinders were engaged on each shaft and two lever arms were used to control the transmission device. A rotation of 90 degrees was achieved using LSRD cylinders with 1.5-inch stroke length.

Friction, stiffness, tracking, impulse response, and step response tests were performed at 70, 170, and 275 kPa (10, 25, and 40 psi) preload pressures to evaluate the transmission device and LSRD cylinder dynamic performance. The results demonstrated that at least 275 kPa preload pressure is needed to have a satisfactory performance.

The passive antagonist hydraulic transmission can be used in applications such as wearable robots and telepresence devices.

Commentary by Dr. Valentin Fuster
2017;():V001T01A074. doi:10.1115/FPMC2017-4352.

Gearbox is a concern in modern wind turbines, increasing the maintenance cost and therefore the cost of energy (COE). A hydrostatic transmission (HST) improves the turbine drivetrain reliability by using slightly compressible mineral oil as the working medium rather than a rigid gearbox. An HST eliminates the power converter since it is a continuous variable transmission (CVT), making the turbine simpler and more cost effective. The turbine operates below the rated wind speed for a considerable time in a year, making the variable hydraulic motor run at partial displacement for the most common configuration of a hydrostatic wind turbine, a fixed displacement pump and a variable displacement motor. This results in low drivetrain efficiency. Moreover, large variable displacement motors for megawatt turbine are commercially unavailable. A digitalized hydrostatic drive for a modern wind turbine is proposed to improve the drivetrain efficiency at low wind speeds. The digital coding method for hydrostatic wind turbine is studied. A dynamic simulation model of the digitalized hydrostatic (dHST) wind turbine has been developed in Simulink. A widely used efficiency model for the hydrostatic pump and motors is used in the simulation to make the study practical. The proposed digitalized hydrostatic solution has been compared with a conventional hydrostatic solution. Simulation results show the benefits of digitalized hydrostatic transmission over conventional hydrostatic transmission in drivetrain efficiency, system complexity and cost.

Commentary by Dr. Valentin Fuster
2017;():V001T01A075. doi:10.1115/FPMC2017-4353.

A hydraulic hybrid powertrain for passenger vehicle is studied in this paper. The hydraulic hybrid powertrain consists of a hydro-mechanical transmission and a hydraulic accumulator. The key component of this hydro-mechanical transmission is a pressure-controlled hydraulic transmission. It combines pumping and motoring function in one unit and is potentially more competitive in terms of both energy efficiency and cost effectiveness than a conventional hydrostatic transmission. By feeding the output flow of the pressure-controlled hydraulic transmission to a variable displacement motor coupled to the transmission output shaft, a more compact and simpler hydro-mechanical transmission is constituted. In this paper the systematic approach of applying the hydraulic hybrid powertrain to a passenger vehicle is studied. A dynamic simulation model is developed in Simulink and the U.S. EPA’s urban cycle is used as the test driving cycle. A rule-based energy management strategy (EMS) for the hydraulic hybrid powertrain has also been developed. The system parameter design, controller design and the energy management strategy are evaluated through simulation.

Topics: Design , Modeling , Vehicles
Commentary by Dr. Valentin Fuster
2017;():V001T01A076. doi:10.1115/FPMC2017-4355.

Sensors are playing a more important role in the modern hydraulic systems. Increasing needs for closed loop controls, high precision measurement, power control and energy monitoring, diagnosis and safety concerns, ask for both pressure and flow acquisition in both industrial and mobile applications.

Traditional pressure sensors need specific bored screw for mounting, and both pipes and components must be modified in order to apply pressure sensors. Traditional pressure sensors are related to mini-mess and to oil flow modification in the sensor area.

Sensors position in hydraulic circuits or components must be defined at design phase, in order to design the proper screw in desired circuit positions.

Most of times sensors result in a efficiency loss in the circuit.

Last but not least, the cost of traditional sensors, the need for proper connections for sensors installation and the work needed for sensor placement in machines production phase, could be avoided if sensors could be integrated in smart components.

Modern Silicon based technologies offer new solutions for a less invasive pressure measurement. Micro Electro-Mechanical Systems (MEMS) Technology is suitable to design new sensors for indirect pressure measurement. Also traditional technologies, coupled with modern electronics could offer solutions that were not enough precise 10 years ago, but presenting some tricks to be solved accurately.

The paper presents the first experimental results of the early stage of application of a MEMS strain gauge sensor application on components, where hydraulic pressure is measured through the component strain due to internal pressure force and component deformation.

New sensors called Double Ended Tuning Fork (DETF) MEMS Resonant Extensometer sensor, based on a silicon diapason made in void environment in a system on chip will be applied at components due to the sensor’s sensitivity and precision that can reach the 0,15 nε/ε.

At the same time the paper will show that pipes offer a deformation function of the mechanical characteristics and that the pressure effect is causing a deformation that can be even too high for the MEMS sensor.

The strain position sensor and component deformation are also proved by the FEM analysis in order to validate both pressure measurement and FEM analysis in respect to test bench results applied to the sensor strain acquisition.

Commentary by Dr. Valentin Fuster
2017;():V001T01A077. doi:10.1115/FPMC2017-4356.

Pneumatic positioning systems (PPS) are widely used in fields were mechatronics applications exist. In order to improve the performance and robustness, either by designing new controllers or studying other characteristics of PPSs under different load conditions, a test bench with a load simulator is required. Hydraulic load simulators (HLS) are one of the most significant applications of hydraulic force control systems. The HLS aims to control the forces according to static and dynamic requirements. Typically, a force control system interacts with the external environment such that a good performance and robustness are not easily achieved. Different approaches are being discussed in the literature consisting on increasing the system compliance. System compliance can be controlled or modified in active or passive ways. Active compliance is obtained by force-based feedback control, allowing more flexibility to perform tasks where compliance is required. On the other hand, passive compliance is typically obtained by introducing mechanical elastic components between the actuator and the environment. In this paper, the influence of PPS compliance in the force controlled tuning of HLS is discussed. Because HLS is applying a controlled force against to a very compliant system like a pneumatic system, stable force responses could be expected. However, the dynamic interaction between the HLS with the PPS effected the force responses. This paper focuses in analyzing these effects, highlighting the design of PI and QFT controllers for force control based on these characteristics. Both of Systems are analyzed mathematically via simulation.

Topics: Stress
Commentary by Dr. Valentin Fuster

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