PUMP MODE PREDICTION FOR FOUR-QUADRANT VELOCITY CONTROL OF VALUELESS HYDRAULIC ACTUATORS

Abstract

Displacement-controlled actuation offers energy savings by eliminating the metering losses associated with hydraulic valves and allowing energy recovery. In a closed-circuit configuration, four-quadrant pump operation can be achieved. This paper considers displacement-controlled boom lift cylinders on a skid-steer loader. Undesirable pump mode oscillation is observed while rapidly lowering small loads. Avoiding this oscillation requires actuator pressure control, which cannot be directly achieved due to insufficient pump dynamic response. The authors propose a predictive observer to provide sufficient lead time for feedforward control of actuator pressure. Design and analysis are presented for a discrete time linear observer which predicts future system states by delaying the input signal. Successful state prediction is demonstrated through simulation and experiment.