HYDRAULIC CONTROL SYSTEM FOR AUXILIARY POWER SOURCE

A hydraulic control system includes a variable displacement hydraulic pump drivably connectable to a primary power source, the pump having an inlet for receiving fluid, an outlet for discharging fluid under pressure, and a pump displacement input, a hydraulic motor having an inlet for receiving fluid under pressure and an outlet for discharging spent fluid, the motor being drivably connectable to an auxiliary power source, a fluid circuit including a supply conduit for conducting fluid discharged by the pump to the motor and a return conduit for returning fluid discharged by the motor to the pump, a pump displacement control cooperating with the pump displacement input in order to vary a displacement of the pump, a control circuit in communication with the pump displacement control for controlling the pump output such that the motor is driven at a constant rotational speed to thereby drive the auxiliary power source at a constant rotational speed despite fluctuations in rotational speed of the primary power source, and at least two valves controlling a rotational speed of the motor, wherein one of the valves provides coarser flow control resolution and another of the valves provides finer flow control resolution.