Komatsu F30791, Shop Manual

Page: 57 / 298

OPERATION
1. When actuator load is large (pump discharge pressure P
P
is high)
. When the load on the actuator becomes high and
pump discharge pressure P
P
rises, piston (3) is
pushed to the left ( ).
. As a result, port f and chamber Y are intercon-
nected, pump pressure P
P
flows from chamber Y
to port f , and at the same time, port f and the drain
circuit are shut off.
. If the LS valve takes action to increase the pump
discharge amount, spool (6) of the LS valve is
moved to the right ( ) and port d and port e are
interconnected.
. As a result, pump pressure P
P
from port f of the
TCC valve flows from port e of the LS valve to port
d , enters chamber X at the large diameter end of
servo piston (4), and stops the movement of servo
piston (4).
. If pump discharge P
P
rises further, piston (3) moves
to the left ( ) and servo piston (4) moves to the
right ( ) in the direction of the minimum swash
plate angle because of the pressure in chamber X
at the large diameter end.
. When servo piston (4) moves to the right ( ) in
the direction of the minimum swash plate angle,
spring (1) is compressed, and piston (3) is moved
to the right ( ).
. When piston (3) is moved to the right ( ) and port
f and chamber Y are shut off, servo piston (4) stops
moving to the right.
. The position where servo piston (4) stops is higher
(closer to the minimum swash plate angle) than
when the pump discharge pressure is low.
10-39
PC20R-8 PC27R-8
Control valve
To actuator
LS valve
f
y
x
RKP01191
4
1
3
P
P
M
G
H
G
L
P
LS
P
LS
c e
d
6