Komatsu PC20R-8 Shop Manual page 49

LS VALVE
Function
. The LS valve controls the pump discharge amount
according to the amount of movement of the control
lever (that is the oil flow demanded by the actuator).
. The LS valve detects the oil flow demanded by the
actuator from the differential pressure DP
tween main pump discharge pressure P
trol valve outlet pressure P
pump discharge amount Q.
(P is called the pump pressure, P
P
LS pressure, and DP
pressure).
. In other words, the pressure loss (=LS differential
pressure DP ) generated by the flow of oil from the
LS
pump passing through opening area of the control
valve spool is detected.
By controlling pump discharge amount Q so that
this pressure loss remains constant, a pump dis-
charge amount is supplied in accordance with the
demands of the control valve by controlling pump
discharge amount Q.
. However, when carrying out fine control or in other
cases where the range does not exceed the maxi-
mum flow of the pump (the flow demanded by the
control valve is always supplied), the discharge
amount is the same as when the engine is at high
idling, even if the engine is at low idling.
To overcome this, a function has been added to
automatically lower the LS differential pressure
and reduce the discharge amount when the engine
is running at low idling.
. The engine speed is detected by pressures GH and
GL on both sides of the fixed throttle (metering
throttle) in the gear pump discharge passage.
This acts on LS valve No. 3 and No. 4 pressure re-
ceiving chambers a2 and b2, and changes the LS
setting. When the engine is running at low idling,
the gear pump discharge amount is reduced, so
pressures GH and GL on both sides of the metering
throttle become almost the same (the metering dif-
ferential pressure between GH and GL becomes
lower).
On the other hand, when the engine is run at full
throttle, the gear pump discharge amount is in-
creased and the metering differential pressure be-
comes higher.
. When the metering pressure is high (engine
speed is high) the LS setting is made higher.
. When the metering pressure is low (engine
speed is low) the LS setting is made lower.
. Pump pressure P , LS pressure P
P
sures on both sides of gear pump metering throttle
(GH and GL) are brought to the LS valve.
The relationship between pump discharge amount
Q and LS differential pressure DP
shown in the diagram on the right.
PC20R-8 PC27R-8
and con-
P
, and controls main
LS
is called the
LS
is called the LS differential
LS
, and the pres-
LS
changes as
LS
be-
LS
b2
Engine at
low idling
0
G
H
a2
G
L
Engine at
high idling
7 16
Differential pressure PLS
Valve
p ( )
bar
(kg /cm )
2
RKP01321
10-31