Component description for NOx sensor control unit - GF14.40-P-3024MMB
ENGINES 276.9 in MODEL 221.0/1 for an engine with stratified operation
Shown: the exhaust system
Location
In every exhaust gas system there is an NOx sensor located with the permanently attached nitrogen oxides control unit. The NOx sensors are screwed into the exhaust pipe. The nitrogen oxides sensors control units are located on the underfloor.
Task
The nitrogen oxides sensors control units are delivered by the company "Continental".
The NOx sensors detect the NOx and the O2 concentration in the exhaust downstream of every NOx storage catalytic converter and passes this information to the nitrogen oxides control units in the form of voltage signals. These process the information and transmit it via the drive train sensor CAN (CAN I) to the ME-SFI [ME] control unit (N3/10).
Input and output signals
The nitrogen oxides control units evaluate the following input signals and send the corresponding output signals:
- Direct input signals
- CAN input signals from the ME-SFI [ME] control unit
- CAN output signals to the ME-SFI [ME] control unit
Direct input signals
- Circuit 87
CAN input signals from the ME-SFI [ME] control unit
- Diagnosis requests
CAN output signals to the ME-SFI [ME] control unit
- NOx concentration in the exhaust
- O2 concentration in the exhaust
- Diagnostic data
Design
Every NOx sensor (double chamber sensor with evaluation circuit) is inseparably connected via an 8-pin sensor line with the NOx sensor control unit.
An integral sensor heater which is controlled by the respective nitrogen oxides control unit ensures rapid readiness to operate of the NOx sensors.
Function
The active ceramic probe bodies consist of many layers with two reaction chambers. The oxygen (O2 ) in the exhaust is detected in the first chamber, as in an oxygen sensor.
To do this, a pump voltage is applied to the electrodes in the first chamber. This causes the O2 molecules to be split into double charged oxygen ions and for them to be pumped out of or into the first contact cavity (depending on whether richer or leaner exhaust gas is present) until a 450 mV voltage difference at the electrodes is reached. The oxygen concentration is calculated from the size of the required pump current "Ip1".
The nitrogen oxide is split at the earth electrode into nitrogen and oxygen in the second chamber if present.
The oxygen is pumped out of the chamber again.
The concentration of the nitrogen oxides in the exhaust is calculated from the resulting pump current "Ip2".
The voltage signals from NOx sensors are transmitted to the respective nitrogen oxides control unit and processed there. The nitrogen oxides control unit send the NOx and the O2 concentration to the ME-SFI [ME] control unit via the drive train sensor CAN. Using this information the exhaust treatment can be monitored in shift operation (lean-burn operation) of the engine and thus the NOx storage catalytic converter purging can be controlled.
The NOx sensors also recognize damage and "sulfur poisoning" of the NOX storage catalytic converters.
A desulfuring process can be initiated as a reaction by the ME-SFI [ME] control unit by increasing the temperature of the NOx storage catalytic converters.
Schematic function diagram of the NOx sensor (double chamber sensors)
| Designation | Unit | Values | Tolerance range | Remarks | |
|---|---|---|---|---|---|
| Left NOx sensor control unit (N37/5), Right NOx sensor control unit (N37/6) | |||||
| Power supply to the control unit: | Minimum | V | 6.0 | ||
| Power supply to the sensor heater: | minimum | V | 12.0 | ||
| maximum | V | 16.5 | |||
| Power consumption | A | 2, 1 | |||
| Power consumption | W | 20 | Maximum | ||
| Measuring range for the NOx concentration | ppm | 0 - 500 | |||
| Wiring diagram for gasoline direct injection system control unit | N3/10 | Vehicle plug | PE07.08-P-2101-97SAA |