Energy Efficient Variable Pressure Valve-Controlled Hydraulic Actuation

Abstract

The subject of this paper is a VPVC (variable pressure valve-controlled) hydraulic actuation system, which is a hydraulic plant with variable supply pressure. The concept is similar to a load sensing system but it is implemented using an electronic controller, instead of a hydraulic one, and the flow is provided using a servo pump, instead of a variable displacement pump. The intention is to maintain a high dynamic response but substantially improve efficiency compared to a conventional system with fixed supply pressure. FPVC (fixed pressure valve-controlled) systems are unable to completely modulate the input energy due to the constant supply pressure. However, since the ability to control the energy flow is usually needed, a proportional valve for each actuator is used to dissipate the extra input energy. This leads to a simple but inefficient way to control, for example, the velocity of a piston. The idea of a VPVC system is that, instead of dissipating energy by throttling flow, it is better to generate less fluid power in the first place: this is achieved by adjusting the speed of the servo pump as well as the spool positions. In this paper, a controller for a VPVC system is presented along with numerical simulations showing a comparison with a fixed pressure system. Up to 70% energy saving is predicted.