Work cycle efficiency for a hydrostatic machine

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] If the hydraulic Pump and motor are connected together through hydraulic hoses, the system is called a hydrostatic transmission or a hydrostatic drive. The hydrostatic drive used in this work is a variable displacement pump and motor. In this work, the efficiency of a hydrostatic transmission with a variable displacement motor for a Caterpillar 320D excavator has been studied for forward flow cycle and compared to the efficiency with a fixed displacement motor. The uncertainty (the error) has been studied and quantified using both additive and multiplicative uncertainty analyses to test the robustness of the hydrostatic transmission. Furthermore, the stability and performance have been checked in order to analyze the performance of the system and determine whether or not the system remains stable for all plants within the uncertainty. Likewise, a PID controller has been designed to control the motor position and the velocity of the excavator. Fixed PID controller results are compared with variable PID controller results. The word "fixed" refers to the fixed displacement motor model while "variable" refers to the variable displacement motor model. Also, the error dynamic was investigated for both fixed and variable displacement motor models. The error dynamic represents the difference between the results of PID controller and proportional controller with unity gain for both position and velocity controls. This work showed that the hydrostatic transmission with a variable displacement motor is more efficient than the one with a fixed displacement motor at the same conditions.