TUBE ASSEM. 4J4773 - Caterpillar

Piston Pump
Illustration 1 g01340769
(1) Actuator piston
(2) Feedback lever
(3) Solenoid
(4) Passage
(5) Servo valve
(6) Port for the drive loop
(7) Input shaft
(8) Swashplate
(9) Piston
(10) Barrel
(11) Spring
(12) Port Plate
(13) Port for drive loop
(14) Charge pump
(15) Pilot inlet port "Y" The tandem pumps for the hydrostatic drive system are variable displacement piston pumps. The tandem pumps are mounted to the rear of the engine. The input shaft of the front pump engages a coupling that is mounted to the flywheel of the engine in order to drive the tandem pumps. When the engine is running, shaft (7) and barrel (10) are rotating. There are nine pistons (9) in barrel (10). Port plate (12) and swashplate (8) are stationary within the pump housing. Port plate (12) and swashplate (8) do not rotate. Spring (11) maintains a force against barrel (10) and port plate (12). When barrel (10) is rotating, each piston (9) follows the angle of swashplate (8).If the angle of swashplate (8) is zero, pistons (9) do not move in and out of barrel (10) and there is no oil flow. Charge oil from charge pump (14) maintains oil pressure in the pump in order to perform the following tasks:
Keep barrel (10) full of oil.
Lubricate the pump components.
Provide makeup oil for internal loss of oil that is due to leakage.
In addition to the above tasks, the charge pump of the rear piston pump also provides oil in order to release the parking brake. The rear charge pump also provides pilot oil to servo valve (5) of both piston pumps in order to shift actuator piston (1) and actuator piston (1) changes the angle of swashplate (8).For additional information, refer to "Charge Pump".The position of swashplate (8) is determined by actuator piston (1). The speed and direction control that is located on the left console sends signals to the electronic control module (ECM). The ECM interprets the signals and the ECM sends pulse width modulated signals to solenoids (3) on either side of servo valve (5). As servo valve (5) is shifted to either direction, signal oil from passage (4) is directed to the corresponding end of actuator piston (1).As actuator piston (1) begins to move, the angle of swashplate (8) begins to increase. As piston (9) follows swashplate (8), pistons (9) begin to move in and out of barrel (10). As piston (9) moves out of barrel (10), oil is drawn from the passage of port (6) of the drive loop through port plate (12). As piston (9) follows swashplate (8) and the piston moves into barrel (10), the oil is pushed through port plate (12) into the passage to port (13) of the drive loop.As the angle of swashplate (8) increases, the output flow of the pump also increases.Charge Pump
Illustration 2 g01341039
Charge pump
(1) Crossover relief valve
(2) Supply passage from the charge pump
(3) Passage
(4) Charge relief valve
(5) Pilot port "G"
(6) Crossover relief valve
(7) Oil filter
(8) Line
(9) Line
(10) Passage
(11) Ring gear
(12) Filter bypass passage
(13) Passage
(14) Supply passage for charge oil from the hydraulic tank
(15) Pinion gear
(A)