Patent ID: 7293841

Claim:
A hydraulic drive system for a wheeled vehicle comprising: a hydraulic motor operably connected to at least one vehicle wheel, the hydraulic motor having a fluid input and a fluid output and operable at a motor activation pressure; a hydraulic pump supplying fluid at a fluid pressure; a reservoir tank fluidly connected to the pump to supply fluid to the pump; a first hydraulic sub-circuit connecting the pump to the motor to provide a motor input pressure at the fluid input on the motor; a hydraulic brake operably engaging the motor and operable at a brake deactivation pressure; a brake sub-circuit connecting the pump to the brake; a second hydraulic sub-circuit connecting the fluid output on the motor to the tank, the second hydraulic sub-circuit further comprising a return valve connected between the fluid output on the motor and the tank, the return valve including a return valve control input; and the first hydraulic sub-circuit further comprising a high limit valve connected between the pump and the motor and a low limit valve connected fluidly parallel to the high limit valve and between the pump and the motor wherein: the low limit valve restricts fluid flow to the motor after an initial pressure is reached; the high limit valve restricts fluid flow to the motor until the brake deactivation pressure is reached; and the initial pressure is less than the brake deactivation pressure; and wherein operation of the hydraulic drive system restricts the rotation of the motor until the brake is operably disengaged from the motor.