Komatsu 75001, Shop Manual

Page: 83 / 1293

SEN03825-00
10-100
14
WA250, 250PZ-6
100 Engine and cooling system
Cooling fan motor
4. Flow control valve
(continuously-variable type)
Function
This valve supplies the necessary pump delivery to
the motor, and returns the excessive oil to the
hydraulic tank.
q
The motor speed increases in proportion to the
increase of the incoming oil (Q) as shown in
Fig. 1.
q
When the incoming flow rate is (Q1), motor
speed becomes (B) rpm.
q
In order to reduce noise and loss of the motor,
this valve keeps the fan speed constant inde-
pendent of the flow rate to the motor.
q
Even if the flow rate is increased from (Q0) to
(Q1), the valve maintains the motor speed con-
stant between points (A) and (C).
Operation
q
For the flow control valve, the upstream pres-
sure of the orifice is conducted to the right side
of spool (1) and the downstream pressure of
the orifice is led to its left side.
q
The differential pressure before and after ori-
fice (E) by the incoming flow rate to the motor
works on spring (2).
q
In Fig. 1, when the flow rate (Q0) is increased
beyond, the differential pressure before and
after spool (1) becomes larger than the
installed load of spring (2).
q
Spool (1) moves to the left and port (P) is con-
nected to port (T).
q
The excessive oil in (Z) portion of Fig. 1 flows
to the hydraulic tank through the flow control
valve, and the motor speed is kept constant
from (A) to (C).
q
This flow control valve is a continuously-vari-
able type.
q
As shown in Fig. 2, it is possible to change the
flow control valve continuously while maintain-
ing the motor speed constant between (A') to
( C ') by c ha n g i n g t h e c o m m an d c u r r e n t
between the motor speed (A) and (C).