PLATE AS 8X3444 - Caterpillar

Illustration 3 g03714977
Propel Pump Cross Section
(1) Right propel pump
(2) Left propel pump
(7) Charge relief valve
(8) Forward solenoid
(9) Reverse solenoid
(12) Reverse multifunction valve
(16) Forward multifunction valve
(21) Electric displacement control
(22) Displacement control spool
(23) Plunger
(24) Line to pump case
(25) Servo cylinder
(26) Servo piston
(27) Swashplate feedback linkage
(28) Line to pump case
(29) Line to case drain
(30) Rotating group
(31) Input shaft
(32) Swashplate
(33) Servo relief valves
(34) High-pressure side of loop
(35) Charge pump
(36) Return pressure line
(37) Combined suction and return filter Pump input shaft (31) turns rotating group (30) and charge pump (35) when the engine is running. The rotating group contains the piston assemblies and cylinder barrel. The charge pump receives supply oil from combined suction and return filter (37). Charge oil flows through internal passages to charge relief valve (7), to reverse multifunction valve (12), forward multifunction valve (16), and to EDC (21).Forward solenoid (8) and reverse solenoid (9) are proportional solenoids. The transmission ECM uses a pulse-width modulated signal to energize the EDC solenoids. When the EDC solenoid is energized, plunger (23) moves. The distance that the EDC plunger moves is proportional to the signal from the transmission ECM. Metered charge oil from displacement control spool (22) acts against one side of servo piston (26). The opposite side of the servo piston is vented to case drain (29). The pressure of the metered charge oil against the servo piston causes the piston to move. This movement tilts swashplate (32) and causes piston displacement in rotating group (30). As the swashplate tilts, the rotation of the pump generates oil flow. Pump supply oil flows through the propel motor. The oil which flows through the motor causes the output shaft to rotate. As the load on the propel system increases, increased pressure in the system tends to move swashplate (32) toward the neutral position. This movement causes feedback linkage (27) to reposition displacement control spool (22) in order to send additional charge oil to servo piston (26). The increased pressure in the servo piston prevents the swashplate from moving back toward the neutral position. The feedback linkage prevents the servo from tilting the swashplate too far. Pump supply oil acts against forward multifunction valve (16). In the high-pressure side of loop (34), the multifunction valve acts as a pressure limiter and a pressure relief valve. When the pump supply oil pressure reaches the pressure-limiter setting, the pressure limiter opens. At this time, pump supply oil is metered to end of servo piston (26) that is open to the case drain. This action causes the pump to destroke in order to relieve the excessive load on the propel system. Note: The pressure-limiter function is used because no heat is generated, as is normal with relief valves. However, a sequenced pressure-relief function limits the momentary pressure surges that normally occur with machine acceleration. These pressure surges are purged into the charge circuit. The relief-pressure setting is greater than the pressure-limiter setting.When leakage and flushing occur in the propel circuit, the pressure in return pressure line (36) becomes lower