SWITCH AS-ROCKER 2364615 - Caterpillar

Illustration 1 g03799009
Typical hydrostatic piston pump
(1) Servo piston
(2) Pump control valve
(3) Piston
(4) Housing
(5) Input Shaft
(6) Swashplate
(7) Barrel
(8) Port plate
(9) Head
(10) Spring The piston pump is a variable displacement pump. The pump is driven from the engine flywheel by a coupling that is fastened to the splines of the pump input shaft. The pump provides flow in order to drive a bidirectional motor. The actuator piston controls the angle of the pump swashplate. The charge pump provides the source for signal pressure in order to control the pump . The signal pressure is controlled electronically in order to vary proportionally to the engine speed. This relationship is handled electronically. As the engine speed becomes higher, the signal pressure will become higher.When the engine is running, shaft (5) and barrel (7) are rotating. The pistons (3) are in the barrel assembly. The port plate (8) and swashplate (6) are fastened to housing (4). The port plate and swashplate (6) do not rotate. The spring (10) keeps a force on the barrel in order to make a high-pressure seal between the barrel and port plate (8). When the barrel is rotating, each piston follows the angle of the swashplate. If the swashplate angle is at zero, the pistons do not move in and out of the barrel and there is no oil flow.Charge oil from the charge pump maintains oil pressure in the pump in order to keep the barrel full of oil. Charge oil from the charge pump lubricates the pump components. Charge oil from the charge pump makes up for the normal, internal loss of oil that is due to leakage.The position of swashplate (6) is controlled by pump control valve (2) and servo piston (1). A pulse width modulation signal is sent to the solenoid on the control valve. The pump control valve directs oil to one side of the servo piston. The servo piston then changes the angle of the swashplate.Oil flows from the pump to the piston motor and back to the pump through main loop . The position of swashplate (6) determines the direction of flow in the two passages of the main loop.As pistons (3) follow the swashplate, the pistons move in and out of the barrel (7). As pistons move out of the cylinder, oil from the main loop of the motor fills the cylinder behind each piston. This oil is supplied under pressure from the charge circuit through a passage.Oil that is pushed out of the cylinders ahead of the pistons goes through the outlet passages of port plate (8). The oil leaves the pump through the passage for the loop line. Inlet oil is sealed from the outlet oil by a seal that is metal to metal. The seal is between the spherical faces of port plate (8) and barrel (7).The spring (10) seats against a ring on shaft (5). The ring on the barrel (7) holds the spring compressed against the shaft ring. The compression of the spring is the force