Feasibility study of hydrostatic transmissions for automobile applications

Abstract

The feasibility of obtaining improved fuel efficiency by incorporating a hydrostatic transmission was investigated. The proposed transmission was composed of positive-displacement axial-piston hydraulic devices. The displacement of the pump and motor units could be varied to allow the prime mover to operate within its most efficient range.

A dynamic model representing a Ford Pinto was developed using bond graphs and the IBM CSMP language to simulate the performance of the proposed design. The required input to this program consists of three independent, or control variables. These are the pump and motor swashplate angles and the engine throttle angle. In present form, the output of this program includes instantaneous values of vehicle velocity, pump and motor efficiencies, engine bsfc, and fuel economy.

Observations from the simulations indicate that the test vehicle is capable of exceeding the EPA highway fuel economy estimates for the 1978 production Pinto by 11%. This increase in economy is a result of operating the engine near the minimum bsfc. Although comparisons were not made in this study, it is believed that even higher increases in economy may be realized in urban-type periods of operation.