PUMP GP-MAIN HYDRAULIC 3768862 - Caterpillar

Illustration 1 g00839039
(1) Gear pump (2) Charge pump (3) Piston pump ( hydrostatic) (4) Speed sensing valve (5) Creeper control (if equipped) (6) Master cylinder (7) Hydraulic oil filter (8) Piston motor ( hydrostatic) (A) Pilot pressure for the pilot valve (B) Pressure for engaging the service brakes
Illustration 2 g00839345
(8) Piston motor ( hydrostatic) (9) Rear axle (10) Hydrostatic drive box (11) Drive shaft
Illustration 3 g00847177
(12) Front axleThe 902 and 906 Compact Wheel Loaders have a hydrostatic power train. The engine drives the piston pump ( hydrostatic) (3) which then drives the piston motor ( hydrostatic) (8). The hydrostatic system is a closed loop. Oil is continuously pumped between the piston pump and the piston motor. The charge pump (2) provides oil to the speed sensing valve (4) which regulates the signal pressure and the charge pressure. The supply oil from the charge pump is filtered by the hydraulic oil filter (7) before the oil gets to the speed sensing valve. The speed sensing valve regulates the signal pressure and the charge pressure. Signal pressure controls the displacement of the piston motor. The charge system provides oil for the hydrostatic system in order to replenish the oil that is lost due to leakage in the system.The piston motor is mounted to a hydrostatic drive box (10) in order to turn the front wheels and the rear wheels. Power from the drive box is transferred to the front axle (12) through a drive shaft (11). The rear axle (9) receives power directly from the drive box. The parking brake is mounted on the drive shaft.The direction of the machine is controlled by the direction control switch that is located in the cab on the pilot valve ( joystick). The speed of the machine is controlled by the accelerator pedal. If the machine is equipped with a creeper control (5), the speed of the machine can also be controlled by the creeper control.If the parking brake lever is engaged and the direction control switch is in the FORWARD position or in the REVERSE position, the machine will shift to NEUTRAL. In order to get the machine to move, the direction control switch must be moved to the NEUTRAL and the parking brake must be disengaged. Then, the direction control switch must be moved to the desired direction.