Experimental validation of a soft switch for a virtually variable displacement pump

As an alternative to a variable displacement pump, a fixed displacement pump can be made to function as a virtually variable displacement unit by using a high-speed valve to pulse-width modulate the flow, creating a switch-mode circuit. A major drawback of switch-mode circuits is throttling and compressibility energy losses during valve transitions. One method of minimizing these losses is soft switching, where the flow that would normally be throttled across the high speed valve during transitions is absorbed in a small variable volume chamber. The concept for a novel soft switch mechanism that uses the pressure signal at the exit of the pump to release a lock on the soft switch chamber was previously presented. This paper describes the soft switch concept in more detail and outlines a numerical model used to predict and optimize soft switch operation. Experimental results are presented that demonstrate proper operation of the soft switch lock-release mechanism.