ACCUMULATOR 5446560 - Caterpillar

Pilot Oil Circuit
The pilot circuit pressure is limited by pilot relief valve (43) .The oil delivery from pilot pump (38) performs the following main functions.
Create pilot oil pressure in order to control the output flows of the main pumps.
Provide pilot oil pressure to the pilot control valves for swing and travel in order to perform machine operations.
Create pilot oil pressure in order to automatically operate the control devices.The pilot circuit is classified into the following circuits and each circuit performs one of the above functions.
Power shift pressure system
Pilot control valve circuit
Pressure switch circuits
Straight travel valve circuit
Swing brake
Swing priority
Automatic travel speed changePower Shift Pressure System
Illustration 3 g01358797
(28) Drive pump (37) Idler pump (38) Pilot pump (42) Proportional reducing valve (PS pressure) (47) Machine ECM (48) Monitor (49) Engine speed dial (50) Drive pump pressure sensor (51) Idler pump pressure sensor (52) Engine speed pickup (flywheel housing)During machine operation, machine ECM (47) receives input signals from the following components:
Monitor in the cab (48)
Engine speed dial (49)
Idler pump pressure sensor (50)
Drive pump pressure sensor (51)
Engine speed pickup (52) that is located on the flywheel housingThe machine ECM (47) continually monitors all of the input signals. The input signals are processed by the machine ECM and an output signal is sent to proportional reducing valve (42) at the pump regulator. The proportional reducing valve assists in controlling the output flow of idler pump (37) and drive pump (28) .The oil delivery from pilot pump (38) flows through the pilot filter to proportional reducing valve (42) at the pump regulator. The electrical signal that is sent from machine ECM (47) causes proportional reducing valve (42) to regulate the pilot pressure to a reduced pressure. This reduced pressure is called power shift pressure (PS). The proportional reducing valve sends the reduced pilot oil pressure through the idler pump regulator and through the drive pump regulator. The output flow of idler pump (37) and drive pump (28) is controlled in accordance with the power shift pressure. The power shift pressure is used to regulate the maximum allowable hydraulic pump output.The output signal that is sent from the machine ECM to the proportional reducing valve will change when the machine ECM detects a change in any of the input signals. The power shift pressure that is sent to the regulators at the idler pump and the drive pump will change in order to regulate the maximum allowable hydraulic pump output. The desired engine speed is maintained.A decrease in engine speed increases the power shift pressure. An increase in power shift pressure causes destroke condition of the idler pump and the drive pump. The maximum allowable hydraulic power output is decreased.An increase in engine speed decreases the power shift pressure. A decrease in power shift pressure causes an upstroke condition of the idler pump and the drive pump. The maximum allowable hydraulic power output is increased.Note: For more information concerning the operation of the machine ECM, refer to Systems Operation/Testing and Adjusting, "Machine Electronic Control System".Pilot Control Valve