Komatsu F30791, Shop Manual

Page: 50 / 298

. LS pressure P
LS
is brought from the control valve
outlet port to spring chamber a of the LS valve.
Pump pressure P
P
is brought to chamber b at the
tip of piston (6) on the opposite side.
. The position of piston (6) is determined bythe size
of pump pressure P
P
, the combined force of LS
pressure P
LS
+ force of spring (8), and the size
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) byspring (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
LS
is 0 bar (0 kg/cm
2
).
(Spring chamber a is connected to the drain circuit
through the control valve spool).
At the same time, pump pressure P
P
is held at the
unload pressure of approx. 26 bar (27 kg/cm
2
).
. For this reason, piston (6) is pushed to the left ( ),
port c and port d are interconnected, and pump
pressure P
P
passes from port c to port d , and is
brought to chamber X at the large diameter end
of servo piston (4).
. Pump pressure P
P
is always supplied to chamber Y
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 ( ) in the direction of the
minimum swash plate angle.
OPERATION
1. When control valve is at HOLDposition
10-32
PC20R-8 PC27R-8
Control valve
To actuator
LS valve
b
d
a
RKP01291
4
P
P
M
G
H
G
L
P
LS
P
LS
c e
G
H
6
P
P
x
G
L
y
4
8
6