System pressure compensated variable displacement hydraulic motor

In a hydraulic drive system, the combination of:

• a source of hydraulic fluid under pressure;
• a variable displacement hydraulic motor on a rotary output having a displacement controlling wobbler and adapted to be connected to a load that can alternatively be an opposing load or an aiding load, said motor having an inlet port and an outlet port;
• a double acting hydraulic actuator connected to said wobbler for setting the displacement of said motor, said actuator having two ports;
• a control valve connected to said motor for controlling the speed and direction of said output;
• and
• means defining a system pressure compensated wobbler control pilot valve interposed between one of the said actuator ports and said source and said motor for changing the pressure differential across aid motor inlet port and said motor outlet port as a function of said source fluid pressure.