UEN00099-01 10 Structure, function and maintenance standard
18 PC210, 230, 240-8
2. PC valve
PA : Pump port
PA2 : Pump pressure pilot port
PDP : Drain port
PM : Mode selector pressure pilot port
PPL : Control pressure output port (to LS valve)
1. Plug
2. Servo piston assembly
3. Pin
4. Spool
5. Retainer
6. Sheet
7. Cover
8. Wiring
Function
q When the pump discharge pressure (PP1)
(self-pressure) and (PP2) (other pump pres-
sure) are high, the PC valve controls the pump
so that the volume of oil beyond the discharge
pressure-based specific flowrate may not be
conducted however you may increase the con-
trol valve stroke. Namely it is intended at con-
trolling the horse power for the pumps so that it
may not exceed the engine hose power.
q If the pump discharge pressure increases due
to increased load during operation, this valve
decreases the pump delivery.
q And if the pump delivery pressure goes low, it
increases the pump delivery.
q In this case, relation between the mean dis-
charge pressure of the front and rear pumps
[(PP1) + (PP2)]/2 and the pump delivery (Q)
will becomes as shown in the diagram if the
relation is represented as the parameter the
current value (X) to be given to PC-EPC valve
solenoid.
q The controller continues counting the actual
engine speed.
q If the engine speed is slowed down due to
increased load, the controller reduces the
pump delivery to recover the speed.
q If the engine speed goes below the specified
value because of increased load, the controller
sends a command current to PC-EPC valve
solenoid in order to reduce the slope angle in
proportion to reduction in the engine speed.
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