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Instability Due to Interacting Hydraulic and Mechanical Dynamics in Backhoes

[+] Author Affiliations
Donald Margolis

University of California at Davis, Davis, CA

Taehyun Shim

University of Michigan at Dearborn, Dearborn, MI

Paper No. IMECE2002-33192, pp. 81-86; 6 pages
doi:10.1115/IMECE2002-33192
From:
  • ASME 2002 International Mechanical Engineering Congress and Exposition
  • Design Engineering
  • New Orleans, Louisiana, USA, November 17–22, 2002
  • Conference Sponsors: Design Engineering Division
  • ISBN: 0-7918-3628-2 | eISBN: 0-7918-1691-5, 0-7918-1692-3, 0-7918-1693-1
  • Copyright © 2002 by ASME

abstract

A backhoe is a tractor-like vehicle that has a hydraulically actuated bucket loader at the front and a hydraulically actuated backhoe shovel at the rear. The operator sits inside a canopy or cab that is mounted to the tractor chassis, and operates the hydraulic controls. The cab is typically isolated somewhat from the chassis using cab mounts. There are instances when the bucket is raised or lowered or wrapped that an instability of the entire machine is excited. In this mode, a frequency oscillation of the vehicle occurs and the operator is unable to keep his hands on the controls. This instability is investigated here and demonstrated through simulation. The instability described here is due to an interaction between the mechanical dynamics and hydraulic dynamics of the machine. All instabilities require an energy source, and, in this case, the energy comes from the fuel. It turns out that the hydro-mechanical interaction has positive feedback components and produces an instability. In order to expose the fundamental cause of the instability, a model is needed that allows the interaction of mechanical and hydraulic components. Bond graphs are a logical choice for development of the model. Bond graphs are a concise pictorial representation of the interactive dynamics of all types of energetic systems. They allow the model to be developed in pieces and then put together into an overall computational model. This procedure is demonstrated for the system here. The end result is a reasonably low order model that exposes the fundamental cause of the instability in backhoes. It also allows assessment of cures for the problem, some requiring redesign of components, and some requiring an automatic stabilization control system.

Copyright © 2002 by ASME

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