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A four valve controller and electronic control circuits were developed to control the displacement of hydrostatic pump/motors (P/M's) utilized in an automobile with a hydrostatic transmission and hydropneumatic accumulator energy storage. Performance of the control system was evaluated. The controller uses four high-speed, two-way, single-stage poppet valves, functioning in the same manner as a 4-way, 3-position spool valve. Two such systems were used to control the displacement of two P/Ms, each system driving a front wheel of the vehicle. The valves were controlled electronically by a distributed-control dead-band circuit and valve driver boards. Testing showed that the control system's time response satisified driving demand needs, but that the control system's error was slightly larger than desired. This may lead to complications in some of the vehicle's operating modes.

An internal combustion engine/hydropneumatic accumulator energy storage automobile can provide for regenerative braking and more efficient engine operation. A configuration is considered which requires only a single hydrostatic pump-motor (P/M) unit. The engine drives through a gearbox to a final reduction unit at the drive axle. The variable-displacement P/M unit is geared to the gearbox input shaft and controlled to alternately put energy into or take energy out of the accumulator. Computer simulations covering a wide range of parameter variations show that, with a proper control strategy, the concept has the potential of providing significant fuel savings.