COVER 7N7595 - Caterpillar

Illustration 1 g06131986
(1) Pressure sensor
(2) Pressure tap
(3) Implement pump
(4) Bias spring
(5) Actuator
(6) Super charger impeller
(7) Implement ECM
(8) Control spool
(9) Coil assembly
(A) Implement supply oil
(B) Return oil
(C) Pilot supply oil
(D) Suction oil
Illustration 2 g06234540
Pump compartment
(10) Implement pump (right)
(11) Implement pump (center)Note: During normal operation, the two implement pumps (10) and (11) operates in the manner that is described below.The implement pumps are variable displacement axial piston pumps that supply hydraulic oil to the main control valves. Each pump contains a swashplate that is driven by a single actuator (5). The small end of the actuator is connected to system pressure (A) from the discharge of the implement pump (3). The small end of the actuator also has bias spring (4) that assists in up-stroking the pump during low discharge pressure. The large end of the actuator is connected to modulated pilot pressure that is controlled by control spool (8). The pilot pressure that is used to control the large end of the actuator is externally supplied. The pump displacement is controlled by a proportional current from the implement electronic control module (ECM) (7) to coil assembly (9).When higher pump displacement is desired, the current that is supplied to coil assembly (9) is increased. This shifts control spool (8) upward. This action drains a portion of the pilot pressure that is acting against the large end of actuator (5). The oil drains to the case drain of the pump. Pump discharge pressure (A) and the force of bias spring (4) are now greater than the modulated pilot pressure and spring force on the large end of the actuator. Actuator (5) shifts downward. This action increases the angle of the swashplate.When lower pump displacement is desired, the current that is supplied to coil assembly (9) is decreased. This shifts control spool (8) downward. This action increases the pilot pressure that is acting against the large end of actuator (5) by closing the path to the case drain of the pump. Pump discharge pressure (A) and the force of bias spring (4) are now less than the modulated pilot pressure and spring force on the large end of the actuator. Actuator (5) shifts upward. This action decreases the angle of the swashplate.When the implement system is in standby operation, the implement pumps are controlled in order to provide the necessary flow that lubricates the rotating group. This lubrication also cools the rotating group. Adequate response from the pump is maintained and parasitic load on the engine is minimized. Standby control is active when no command is received from the tilt control lever or the lift control lever. During standby, a proportional current is sent to coil assembly (9). This current shifts control spool (8). This action modulates the pilot pressure that is applied to the large end of actuator (5). Pump discharge pressure (A) is read by implement ECM (7) by using pressure sensor (1). Implement ECM (7) adjusts the proportional current in order to maintain a pump discharge pressure of 2500 kPa (360