Design of Novel Closed-Circuit Hydrostatic Transmission Without Charge Pump

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.