Experimental Analysis of Electro-Hydraulic Hybrid Actuator System for Off-Highway Working Vehicles

Abstract

Electro-hydraulic hybrid power transmission system can save energy and thus reduce the pollution while maintaining the same performance in comparison to the conventional fluid power system in off-highway working vehicles. This paper introduces experimental analysis of an electro-hydraulic hybrid actuator system specially developed for the recuperation of the potential and kinetic energy in off-highway working vehicles. In this compact assembly all the components are located near each other to save space. Proposed hybrid actuator system can be controlled directly by an electrical frequency converter which allows the replacement of long lossy fluid power transmission lines with electrical cables. Integrated electro-hydraulic energy converter (IEHEC) is the principal component of the proposed hybrid actuator system. The energy converter consists of a fixed-displacement hydraulic pump-motor and an integrated electrical permanent magnet synchronous motor-generator. IEHEC unit can be driven in four quadrants to produce the mechanical power required for the hydraulic actuator, or to recover the energy released by the actuator mechanism and supply it back to electrical circuit. Suitable places for this application are all actuators that carry out work cycle in which the kinetic and potential energy is available for recovery, e.g. lifting cylinders in cranes, fork lift trucks, etc. The test rig allows the experimental analysis of behavior of real power transmission system in two modes while using simulated loads. The first mode is the work cycle mode using IEHEC as motor connected to the hydraulic pump. The other mode is the energy recovery mode while direction of operation is reversed. The real-time simulated loads, which are carried out by simulating typical work cycle of a mechanism, enable the loading in the work cycle and provide the recoverable energy in the recovery mode. The forces acting in actuator connection point are implemented in the test rig by a hydraulic cylinder which is controlled by bandwidth proportional cartridge valves and a dSpace Real-time Control system. The electro-hydraulic hybrid actuator system was simulated in a certain loading case using virtual simulation and also hardware-in-the-loop (HIL) simulation in the test rig. The responses were compared. Experimental analysis of the dynamic behaviour of a real electro-hydraulic hybrid actuator system has been carried out by using HIL simulation.