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The digital-displacement pump-motor is a hybrid device, which combines reciprocating hydraulics with micro-processor control, creating a highly integrated machine capable of producing variable flow and power. It is based on the conventional hydraulic piston pump but with actively controlled poppet valves for each cylinder. This allows enabling or disabling on a stroke-by-stroke basis in any desired sequence. Time-domain modeling of the pump-motor system predicts the performance under variable-demand, variable-speed at different control-modes. The advantages of this approach over conventional techniques lie with both the response speed and the inherent energy efficiency. S0022-0434(00)00801-7
Ehsan et al. (Thu,) studied this question.