Sensor Technology; Active Sensors; Special Sensors - Mercedes-Benz M 447 hLAG Service Manual

3.2

Sensor technology

3.2.1

Active sensors

3.2.1.1 Internal control-unit sensors
A pressure sensor is used for comparative measurements of the respective atmospheric pressure (high
altitudes).
3.2.1.2 External control-unit sensors
Requirements for sensor inputs for external sensors:
Active sensors with an operating voltage of 5 volts are used. These sensors are capable of drawing a sink
current through a pull-up resistor toward their 5 volt supply. The sensors may use up to 15 mA of current
from the power supply. There are two sensor supplies. These are designed for the connection of up to
three sensors each (total current load is max. 45 mA).
The current limitation begins at currents greater than 60 mA.
Through the output voltage range (0.5 to 4.5 V) of the sensors used, the diagnosability with regard to
wiring breaks and short-circuits to earth is ensured. Active sensors are provided for the following input
variables.
Sensor data: (M447hLaG)
Measured Variable
RV in kΩ
Pressure in kPa
Voltage in V
3.2.2

Special sensors

3.2.2.1 Throttle-valve position sensors
In modern throttle devices the actuator, throttle valve and throttle valve sensor are integrated in one
housing. In the throttle device of the M 447 hLAG a potentiometer is used as a throttle valve sensor. This
is supplied by the internal electronics of the throttle device.
3.2.2.2 Lambda probe (Bosch LSU)
To control the air/fuel ratio on the inlet side, a Bosch model LSU broadband lambda probe can be
connected to the CNG control unit. Due to its constant characteristic curve in the area λ=0.7 to air, this
two-cell limit current probe with an integrated heater is suitable both for λ=1 engines and for
planar ZrO
2
lean engines. The lambda raw signal is processed with a specific evaluation IC of the probe manufacturer.
To compensate production-related sensor tolerances, a trimming resistor is integrated in the connector of
the lambda probe.
Status September 2003 (EvoBus-Service / AFT)
Boost Pressure
10
15 284 100
0.22 4.50 0.79
Electrical Description of EGM
Gas Pressure Active Oil Pressure
(Woodward) Absolute Pressure
(Bosch Combi)
10
1200 0
3.98 6
Air Mass
(not present)
Sensor
3.6
500 --
4.5 --
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