Design of Novel Closed-Circuit Hydrostatic Transmission Without Charge Pump

Abstract This paper deals with the design of the control system for novel two-pumps one-motor (TPOM) systems for applications which require the deployment of a closed-circuit hydro-static transmission (HST). In conventional closed-circuit HST, the charge/booster pump is an integral part of the main pump used to compensate the leakages occurring in the circuit in order to maintain the lowest system pressure to avoid cavitation. The charge/booster pump in the closed-circuit HST is a source of constant power loss and increases heat load in the system. This reduces the efficiency of the transmission at part load operation. Also, the lowest system pressure in the conventional circuit is held constant by the relief valve deployed at the charge pump outlet. Hence, the stiffness of the system cannot be controlled based upon the transmission working condition. To overcome this limitation and enhancing transmission efficiency, the TPOM system is designed and evaluated without changing the basic functionality of the closed-circuit transmission. In TPOM, one of the displacement machines driven by permanent magnet synchronous motors (PMSM) works in open-circuit configuration and the other in closed-circuit configuration, without the need of a charge/booster pump. The TPOM is capable to operate in four-quadrants and capable to regenerate the energy during assistive load condition. This arrangement does not require the need of pilot pressure for varying the displacement of pump and motor, which generally is supplied by a booster/charge pump in a conventional closed-circuit transmission. However, innovative use of a hydraulic intensifier is proposed for the fulfilment of pilot pressure requirements. The feasibility in control shows the energy-saving potential of the HST without booster/charge pump.