The characteristics of engine-hydrostatic transmission systems

• Main Author: Edge, Kevin Anthony
• Published: University of Bath 1975
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767486

This thesis examines the performance characteristics of diesel engine and hydrostatic transmission combinations. A digital computer model of an engine-hydrostatic transmission is developed and used to investigate the steady state performance of a typical system, with constant torque and constant power loads. Both load torque and speed are shown to have significant effects on efficiency. The computer model is extended to examine two types of hydromechanical transmission and engine combinations. Both transmission systems are based on a fully floating epicyclic gear train. These transmissions are shown to have substantially higher efficiencies when compared to a pure hydrostatic transmission system. A graphical method of analysing the two hydromechanical transmissions is also developed and design procedures for vehicle applications are presented. The models of the hydrostatic and hydromechanical transmissions are used to determine the conditions necessary for optimum engine-transmission system efficiency. Particular attention is given to the effect of load duty cycle on fuel consumption. Substantially reduced fuel consumption may be achieved by scheduling the engine speed and the pump and motor displacements according to the power requirements. An on-line digital computer was programmed to optimise the efficiency of an engine-hydrostatic transmission rig and an extensive series of tests were performed. The results are shown to be in close agreement with those obtained from the computer model. Work was also performed on the test rig to determine the effects of air in the transmission fluid on steady state and dynamic performance. The test results show that the effects of air release on the static and dynamic characteristics were relatively insignificant except during the first few minutes of running. Entrained air is shown to affect the motor speed but would not be a real problem unless air entrainment is continuous due to poor tank design or low oil level.