Patent ID: 7100732

Claim:
A hydraulic drive system for a vehicle, the vehicle having a pair of turning wheels for directing the vehicle, wherein the wheels having different rates of rotation when the vehicle is turning due to the turning radius of the vehicle, the drive system comprising: a pair of hydraulic drive motors, each of which includes i) a hydraulic drive mechanism operatively connected to a drive shaft for driving a respective wheel for moving the vehicle, ii) an inlet port and an outlet port for directing fluid to and from the drive mechanism, and iii) a hydraulic circuit fluidly communicating with the hydraulic drive mechanism and with the hydraulic circuit of the other motor, and responsive to a pressure differential across the motors to provide increased flow to the motor of a wheel having a greater rate of rotation than the other, wherein the drive motors are connected in series, with the inlet port of one motor fluidly connected to receive fluid from a fluid source, the outlet port of the one motor fluidly connected to the inlet port of the other motor for directing fluid from the one motor into the other motor, and the outlet port of the other motor fluidly connected to direct fluid from the other motor to a reservoir, wherein each hydraulic circuit includes a control valve responsive to the pressure differential across the motors enclosed within an end cover assembly of the respective motor.