137
Open valve –
full fan speed
Closed control valve –
reduced fan speed
Cooling fan
Up front the temperature-controlled cooling fan has
two temperature-sensitive bi-metal plates that regulate
fan engagement.
The bi-metal plates start to bend when the cooling air
reaches a temperature of approx. 40
°
C. The hotter the
air flowing through, the greater the bending. A control
pin (4) transfers the bi-metal washer movements to a
spring-loaded valve (5) in the fan hub.
A thermostat-controlled fan should always be in
the vertical position. Placed horizontally could
cause leakage and impair the efficiency of the fan.
The fan engagement fluid is a silicone oil of high vis-
cosity. At temperatures below approx. 40
°
C, the spring-
loaded valve (5) is fully closed. Oil can then go through
a return channel from the coupling housing (9) to the
space in the cover (2). In this mode, the fan speed is re-
duced to approx. 1/4 of the drive shaft (10) speed. This
is the lowest stage at which engagement takes place.
As the temperature increases, the valve starts to open
and the degree of engagement increases to full engage-
ment at approx. 65
°
C, at which the spring-loaded valve
is fully open.
However, because of slip caused by the silicone oil, fan
speed will never be higher than 95% of the drive shaft
speed.
When the cooling air temperature drops, the fan speed
decreases, rapidly between 60
°
C and 50
°
C, but fan
speed reduction is slower when the temperature drops
down towards 37
°
C.
Oil
Oil
1. Temperature-sensitive
bi-metal plate
2. Cover
3. Oil scraper
4. Control pin
5. Spring-loaded valve
6. Intermediate plate with
valve arm
7. Drive plate
8. Fan bearings
9. Coupling housing
10. Drive shaft hub