Continuous Trap Oxidizer: Description and Operation
GF14.40-P-3024MM Component Description For NOx Sensor Control Unit
ENGINE 276.9 in MODEL 204.0 /2 /3 /9, 207.3 /4, 212.0 /2, 218 with engine with stratified operation
Shown is exhaust system model 218
N37/5 Left NOx sensor control unit
N37/5b1 Left NOx sensor
N37/6 Right NOx sensor control unit
N37/6b1 Right NOx sensor
Location
In every exhaust gas system there is an NOX sensor located with the permanently attached NOx sensor control unit. The NOx sensors are screwed into the exhaust pipe. The NOx sensors control units are located on the underfloor.
Task
The NOx sensors control unit are supplied by the company "Continental".
The NOx sensors detect the NOx and the O2 concentration in exhaust after every NOx storage catalytic converter and passes this information to the nitrogen oxides sensors 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 NOx sensors 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
N37/5 Left NOx sensor control unit
N37/5b1 Left NOx sensor
N37/6 Right NOx sensor control unit
N37/6b1 Right NOx sensor
a Sensor cable
b Electrical connection
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 NOx sensor 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 then pumped out of or into the first chamber (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 NOx sensor control unit and processed 2 there. The NOx sensor control units 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)
1 Diffusion gap 1
2 Diffusion gap 2
3 Solid electrolyte
Ip1 Pump current 1
Ip2 Pump current 2
