CONE 1183117 - Caterpillar

Illustration 3 g01428459
(10) Pump electric displacement control (EDC) (11) Pump case (12) EDC metering spool (13) Pump case (14) Pump case (15) Multifunction valve (16) Servo pressure relief valves (17) From hydraulic tank (18) Propulsion loop return pressure (19) To material feed (20) Charge pump (21) Charge relief valve (22) Propulsion loop high pressure (23) Case drain (24) Servo pressure relief valves (25) Multifunction valve (26) Case drain from propulsion motor (27) Servo cylinder (28) Propulsion pump (29) Swashplate (30) Input shaft (31) Rotating group (32) Double acting (33) Case drain (34) Servo cylinder (35) Swashplate feedback linkage (36) Spool barrel feedbackThe pump input shaft turns the rotating group and the charge pump when the engine is running. Charge oil flows through internal passages to the charge relief valve, to the multifunction valves, and to the EDC. External lines carry charge oil to the material feed pumps. The forward EDC and reverse EDC are proportional solenoids. The machine ECM uses a pulse width modulated signal to energize the solenoids for the EDC. Energizing the solenoid for the EDC causes the plunger to move. The distance that the plunger for the EDC moves is proportional to the signal that is received from the machine ECM. Note: The coils in the forward EDC and reverse EDC are not designed for 24 volt operation. The signal from the machine ECM provides an average of approximately 12 volts.When the plunger for the EDC shifts, charge oil is metered into the end of the displacement control spool. This action creates a pressure differential between the ends of the displacement control spool. The pressure differential causes the spool to move in order to send the charge oil to the appropriate servo cylinder. The swashplate in the pump then moves an amount which is proportional to the output signal from the machine ECM. Metered charge oil from the displacement control spool acts against one side of the servo piston. The opposite side of the servo piston is vented to the case drain. The pressure of the metered charge oil against the servo piston causes the piston to move. This movement tilts the swashplate which causes piston displacement in the rotating group. As the swashplate tilts, the rotation of the pump generates oil flow. Pump supply oil flows through the propulsion motor. The oil which flows through the motor causes the output shaft to rotate. As the load on the propulsion system increases, increased pressure in the system tends to move the swashplate toward the neutral position. This movement causes the feedback linkage to reposition the direction control spool in order to send additional charge oil into the servo piston. 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 the bottom multifunction valve. In the high pressure side of the loop, the multifunction valve acts as a pressure limiter and a pressure relief