ENGINE | 936 in MODEL 963, 964 |
Location
1 | Exhaust gas recirculation cooler |
2 | Charge air pipe |
B613 | Fresh air differential pressure sensor |
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The fresh air differential pressure sensor (B613) is located on the front side of the engine, where it is screwed in from the outside into the charge air pipe (2) downstream of the charge air cooler.
Task
The fresh air differential pressure sensor (B613) delivers information to the engine management (MCM) control unit (A4) to calculate the EGR rate.
Body
3 | Electrical connection |
4 | Sealing ring |
5 | Measuring probe |
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The fresh air differential pressure sensor (B613) consists of a plastic housing which it fitted inside with two chambers which are separated from a thin membrane which functions as a mechanical intermediate stage. Four strain gauge resistances (DMS) are located on the membrane in a bridge circuit. The membrane is subjected on one side to the pressure of the supercharged fresh air. To transmit signals to the engine management (MCM) control unit (A4) the fresh air differential pressure sensor (B613) is fitted with an electronic analysis system and a power supply due to the bridge circuit it contains.
Function
If the charge air pipe (2) has supercharged fresh air flowing through it there is a respective pressure applied at the part of the membrane in the fresh air differential pressure sensor (B613) exposed to the fresh air. This is therefore distorted and the strain gauge resistances (DMS) are elongated or squashed.
The strain gauge resistances (DMS) reacts to the change in length with a change in its ohmic resistance. These values are prepared by the electronic analysis system and transmitted as analog signals to the engine management (MCM) control unit (A4). Since the fresh air differential pressure sensor (B613) has a constant measuring current flowing through it there is a voltage drop due to the change in resistance over which the engine management (MCM) control unit (A4) can deduce the associated pressure value.