Komatsu PC20R-8 Shop Manual page 50

OPERATION
1. When control valve is at HOLD position
4
x
P
LS
LS valve
a
8
c
d
. LS pressure P is brought from the control valve
LS
outlet port to spring chamber a of the LS valve.
Pump pressure P is brought to chamber b at the
P
tip of piston (6) on the opposite side.
. The position of piston (6) is determined by the size
of pump pressure P
pressure P + force of spring (8), and the size
LS
of the differential pressure (GH - GL) on both sides
of the gear pump metering throttle.
. Before the engine is started, servo piston (4) is
pushed to the left (direction of maximum swash
plate angle) by spring (1).
. After the engine is started, if all the control valves
are at the HOLD position, no pressure oil flows to
the control valve outlet port, so LS pressure P
2
is 0 bar (0 kg/cm ).
10-32
G
P
H
P
b
6
G
L
6
e
, the combined force of LS
P
M
4
y
(Spring chamber a is connected to the drain circuit
through the control valve spool).
At the same time, pump pressure P
unload pressure of approx. 26 bar (27 kg/cm
. For this reason, piston (6) is pushed to the left (
port c and port d are interconnected, and pump
pressure P
P
brought to chamber X at the large diameter end
of servo piston (4).
. Pump pressure P
at the small diameter end of servo piston (4), but
the force applied to the large diameter end of servo
piston (4) is greater because of the difference in
area at both ends of the piston, so servo piston
(4) moves to the right (
LS
minimum swash plate angle.
Control valve
P
P
G G
H L
P
passes from port c to port d, and is
is always supplied to chamber Y
P
) in the direction of the
PC20R-8 PC27R-8
To actuator
P
LS
RKP01291
is held at the
2
).
),