Port plate Counter balance valve Motor unit 3) 3) HIGH PRESSURE DEPENDENT CONTROL HIGH PRESSURE DEPENDENT CONTROL The displacement is-dependent on operating pressure - automatically adjusted. Upon reaching the operating pressure set at the control valve - internally measured at A or B - the motor swivels from V gmin to V gmax until output torque = load torque. For values lower than the adjusted one the motor keeps min swivel angle. The necessary positioning energy is taken from the respective high pressure side via shuttle valve. Swivelling results in a change of the displacement. Swivel time is controlled by an orifice installed in the cover of the large positioning piston side.
4) 4) COUNTERBALANCE VALVE COUNTERBALANCE VALVE Mounted at the rear of the port plate. Incase of downhill traveling or deceleration of the machine a counterbalance valve avoids overspeeding and cavitation of hydraulic motor. 5) 5) FUNCTION AS TO CIRCUIT DIAGRAM FUNCTION AS TO CIRCUIT DIAGRAM Check valves in the inlet line A and B for by passing of the counterbalance valve. At traveling forward the return oil flow is controlled by a counterbalance spool. At drop in inlet pressure the counterbalance spool throttles the return oil flow. The motor is locked. The oil behind the spool is led to the low pressure side via an additional check valve. Same function for traveling forward and backward.
Braking means for the motor that - At reduced or zero inlet flow the counterbalance spool reaches a modulating position or a neutral position caused by spring force - The high pressure oil (at outlet side of the motor) is returned to the low pressure side(At inlet side) of the motor via crossover relief valves. As the control pressure for regulation of the HA control via the integrated shuttle valve is no longer available, the motor with HA control and counterbalance valve will swivel to its minimum displacement during deceleration. In addition, an external boost flow/pressure can be applied at port S for preventing cavitation.
Counterbalance valves do not replace the service and parking brake. 2-25