ALTERNATOR 5468898 - Caterpillar

Engine Off
Illustration 2 g03717810
Main pump hydraulic schematic
(1) EPC spool
(4) Power-shift spool
(5) Main control valve
(6) Unloading valve
(7) Signal limiting valve
(8) Main relief valve
(9) Signal drain valve
(10) Main pump group
(11) Maximum angle piston
(12) Power shift piston
(13) Lever
(14) Actuator piston
(15) Minimum angle piston
(16) Port - inlet
(17) Main pump pressure sensor
(18) Load sense pressure sensor When the engine is not running, the spring in maximum angle piston (11) moves the pump swashplate to the UPSTROKED position. This action allows the pump to provide flow as the engine is started.Power shift spool (4) is held to the right and EPC spool (1) is held to the left by the respective springs when the engine is not running. The spring on the right end of power-shift piston (12) holds the power shift piston to the left.Pump Control Operation
Signal drain valve (9) is used to regulate the signal flow and to allow the signal oil to flow to the tank when implements are returned to NEUTRAL. The extra flow provides faster response when an implement is initially activated.Because minimum output is near zero, the system is in STANDBY. When the system is in standby, margin pressure is lower than the opening point of the margin valve.The force created by actuator piston (14) working on lever (13) changes with the following:
Position of maximum angle piston (11)
Value of the pump supply pressure
Value of the power shift pressureActuator piston (14) rides along lever (13) as the pump UPSTROKES and DESTROKES. As the actuator piston moves closer to the pivot pin, the mechanical advantage decreases. As the piston moves away from the pivot pin, the mechanical advantage increases. If the mechanical advantage increases to the point that the lever is able to move power-shift piston (12) to the right to overcome a given power-shift pressure, spring force will then move power-shift spool (4) to the right. This action will DESTROKE the pump.Signal limiting valve (7) limits the maximum load sensing signal pressure. The signal limiter valve regulates pressure within the load sense circuit. Load sense pressure sensor (18) will be monitored by the machine ECM in order to control EPC spool (1) to control the maximum system pressure. The signal limiter pressure will increase when the heavy lift solenoid is energized.Main relief valve (8) serves as a backup to the signal relief valve. The main relief valve set point is above the signal relief valve set point.Upstroke
Illustration 3 g03717972
Main pump hydraulic schematic - UPSTROKE
(1) EPC spool
(4) Power-shift spool
(5) Main control valve
(6) Unloading valve
(7) Signal limiting valve
(8) Main relief valve
(9) Signal drain valve
(10) Main pump group
(11) Maximum angle piston
(12) Power shift piston
(13) Lever
(14) Actuator piston
(15) Minimum angle piston
(16) Port - inlet
(17) Main pump pressure sensor
(18) Load sense pressure sensor The following are some of the conditions that cause the pump to upstroke:
Pump is being controlled by EPC spool (1) and