TUBE 0878491 - Caterpillar

Illustration 1 g03717259
Inside of Right Front Wheels (1) Front-wheel assist motor (2) Front-wheel assist motor (3) Port "B" (4) Port "L" (5) Port "A" (6) Port "F"Machines with the four-wheel drive system have a front-wheel assist motor (1) on each front steering wheel. Machines with the all-wheel drive system have additional front-wheel assist motor (2) on each rear steering wheel. The motor housing is mounted to the machine, and the spindle is bolted to the wheel.The front-wheel assist motor is a radial piston motor. The front-wheel assist manifold controls the flow of supply oil to the motors. When supply oil is directed into port "A" (5) of the motor, the output shaft rotates clockwise. When supply oil is directed into port "B" (3) of the motor, the output shaft spins counterclockwise. Charge oil from the propel system is directed into the case drain of each front-wheel assist motor though port "F" (6). Port "L" (4) of each motor is connected to port "CD" of the front-wheel assist manifold.
Illustration 2 g03745831
Front-wheel Assist Motor Cross Section (7) Cam follower (8) Piston (9) Case drain (10) Output shaft (11) Cylinder block (12) Cam ring (13) Motor operating (typical) (14) Freewheel operation (typical)The front-wheel assist motor is a radial-piston motor. Cam ring (12) is stationary. Cylinder block (11) and pistons (8) rotate. The pistons move radially in the cylinder block.During motor operation, each piston (8) in the motor goes through a four-phase cycle. The phases in the cycle correspond to the position of cam follower (7) in relation to the lobes of cam ring (12) .When cam follower (7) is at the highest point on the cam lobe, piston (8) is in the top-neutral phase. Now, the valve blocks the piston chamber from the inlet port and from the outlet port. The pistons with the cam followers which are on the downhill face of the cam lobe are in the full-power phase. During this phase, the valve connects the piston chamber to an inlet port, and pump supply oil fills the chamber. The supply oil forces the piston out of the barrel and the cam follower to move down the cam lobe. This radial movement of the pistons causes cylinder block (11) to rotate.The piston chamber remains connected to the inlet port until cam follower (7) reaches the lowest point in the valley of cam ring (12). Now, piston (8) is in the bottom-neutral phase, and the piston chamber is not connected to an inlet or outlet port. When the cam follower is on the uphill face of the cam lobe, the valve connects the piston chamber to the return line. Now, the piston is in the discharge phase. During the discharge phase, the piston moves in, toward the center of the motor. The oil in the piston chamber flows into the outlet port.When the front-wheel assist system is not operating, a check valve in the front-wheel assist manifold maintains a back pressure of 450 kPa (65 psi) in case drain (9) of each