Komatsu PC500LC-10R, Shop Manual, Page: 186 / 758

FUNCTION OF PC-EPC VALVE AND LS-EPC VALVE
Engine pump control (working mode)
• P,ATT mode hyperbola shows the setting to use maximum
output of engine for hydraulic system, and indicates “Pres-
sure (P) x Discharged volume (Q) = Constant = Engine
output”.
• Command current from the controller to the PC-EPC valve
and LS-EPC valve decreases the pump absorbing horse-
power and maximum pump discharged volume. The com-
mand current increases and the discharged volume de-
creases.
• When E, B or L is selected for the working mode, the set-
tings of engine speed and pump absorbing horsepower
are decreased simultaneously by the controller.
• When the command current is increased and L mode is
selected, LS-EPC valve controls to decrease the maximum
discharged volume.
• When the pressure sensor detects the high pressure close
to the max. set pressure, it is cut off by PC-EPC valve.
Travel control
• As travel speed selector switch is switched to Hi, Mi or Lo,
command current from controller changes, and the output
pressure from LS-EPC valve to LS valve changes, and
pump discharged volume change point “LS differential
pressure (PLS)” in the LS valve changes.
• The start-up time of the pump discharged volume is opti-
mized and the combined operation and fine control per-
formance are improved.
Cut-off function
• This function increases PC-EPC current to reduce the flow rate in the relief state and improve the fuel econ-
omy.
• Operating condition for turning on cut-off function
When the one-touch power maximizing function is not activated and the average of front pump and rear
pump oil pressure sensor values is 27.9 MPa {285 kg/cm
2
} or higher.
It does not operate when machine is traveling or swing lock switch is “ON”.
CLSS 10 STRUCTURE AND FUNCTION
10-92 PC500LC-10R