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Modelling and control of a hydrostatic transmission for a load-haul-dump underground-mining machine Gosal, Amritpal Singh

Abstract

This thesis focuses on the modelling and control of the hydrostatic transmission (HST) on an extremely-low-profile, front-end-loader configuration, load-haul-dump (LHD) machine: the 88XLP, designed and built by EJC Mining Equipment Inc. of Burlington, Ontario. The machine uses four pump-motor hydrostatic closed loops to power its four wheels. Speed regulation is required on such a machine in order to achieve the differential effect needed when the machine turns, as well as to maintain consistent wheel speeds and efficiency when travelling straight. Hydraulic pressure/flow sharing/coupling techniques are commonly employed to create the differential effect: experimental evaluation of eleven such hydraulic arrangements is presented to determine the efficacy of each, based on a calculation of a drivability-index for each arrangement. A review of techniques for feedback control of HSTs is presented, and proportional-integral (PI) control is selected to implement-speed feedback control for the variable-pump-variable-motor (PVMV) HST on the 88XLP. The results of tuning and drivability tests using the PI controller are presented. A model of the HST and controller, based on offline system-identification of the HST is implemented in Simulink, including nonlinearities, such as hysteresis and controller feedback quantization, as well as the discrete-time nature of the controller. It is found that this model does not provide close correspondence to behaviour of the actual system under feedback control. This discrepancy is attributable to the nature of the HST: its components with extremely nonlinear and time-varying characteristics, which further have a strong dependence on the operating conditions. As a result of the comparison between the various hydraulic sharing/coupling techniques and speed-feedback control, it is concluded that simple feedback control does not yield the best performance for this application, and that hydraulic system redesign is a more effective means of achieving design objectives for this application. The best performing hydraulic sharing/coupling technique is identified and suggestions are made to further improve its performance through simplifying the overall configuration of the HST.

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