11
Fan control
The control unit for radiator fan V293 regulates
the output of the radiator fan and controls the
continued coolant circulation. The induced-air
fan V7 and the forced-air fan V177 are
activated simultaneously.
Forced-air fan V177 is located upstream of the
condenser, water cooler and visco fan. It
assists the visco fan.
The electronic power control
The various fan settings are executed by an
electronic power control.
The fan motors are operated periodically, the
length of the operating cycle depending on the
fan setting selected. Fan output level is
controlled via pulse-width-modulated outputs.
Should a fan fail, the radiator fan control unit
increases the speed of the fan motor still
available.
Advantages of the power control:
•
The series resistors previously used for
power control are no longer required.
•
Lower power consumption in lower fan
settings.
•
Safety functions.
The power supply is protected by a
fuse on the 8-socket relay plate. For
the correct fuse rating, please refer
to wiring diagram.
Vehicles equipped with an air
conditioner require a higher fuse
rating than vehicles without an air
conditioner.
SSP 198/50
8-socket relay plate
SSP 198/55
Control unit for radiator fan
attached to front right
vehicle side member
Fuse, terminal 30
Fuse, terminal 61
47
SSP/198/13
Exhaust gas temperature sender
G235 and G236
To facilitate exhaust gas temperature control,
the exhaust gas temperature must be recorded
to a high degree of accuracy.
An accuracy of ± 5 °C is achieved in the
measurement range from 950 °C to 1025 °C.
The exhaust gas temperature sender is located
inside the exhaust manifold upstream of the
exhaust gas turbocharger.
It comprises a measuring sensor and
evaluation electronics.
The measuring sensor and the control unit are
permanently connected by means of a
shielded, heat-resistant wire.
The evaluation electronics convert the signal
which the measuring sensor generates into a
pulse-width-modulated signal (PWM signal).
This is a square-wave signal with a fixed
frequency and a variable pulse duty factor.
The pulse duty factor is expressed as a
percentage . The measurement range extends
from
³
10% to
£
90%.
A specific pulse duty factor is assigned to each
temperature (refer to diagram).
Substitute function and self-diagnosis:
A pulse duty factor of <1% or >99% is
recognised as a fault.
A fault is detected as of a certain enrichment
quantity.
If a sender fails, the charge pressure is reduced
to a safe level and an emergency enrichment
characteristic (engine speed-dependent) is
used.
Exhaust gas temperature sender
evaluation electronics
SSP 198/56
90%
70%
50%
30%
10%
945°C
950°C
960°C
970°C
980°C
990°C
1000°C
1010°C
1025°C
1030°C
Exhaust gas temperature
Pulse duty factor
Meas.
