| 摘要 |
A hydraulic drive system for a vehicle includes a pressurizing circuit and a working circuit that are interconnected by suitable valving. The pressurizing circuit incorporates a fixed displacement pump which is driven by a prime mover having a nominal horsepower rating. The prime mover is shifted between an idling speed when the pressure sensed within the pressurizing circuit is within a desired range and an optimum high RPM range when the pressure within the pressurizing circuit falls below the desired range. At least one accumulator is provided in the pressurizing circuit. The working circuit includes a plurality of motor units for driving the vehicle wheels and a plurality of motor control valves which can be placed in a de-activated position to isolate the associated motor unit from the flow of pressurized fluid and an activated position wherein the motor unit aids in driving the vehicle. The vehicle is shifted between various gear ranges by controlling the activation/de-activation of the motor control valves such that, as vehicle speed and drive resistance decreases, the number of motor units being used to propel the vehicle is reduced from a maximum number of four motor units to a single motor unit. A flow control valve is provided to alter the volume of fluid flowing to the various motor units based on desired speed/acceleration parameters as determined by the vehicle operator through a conventional accelerator pedal.
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