NOx Kit: Description and Operation
GF14.40-D-3023HU Component Description For Nitrogen Oxides Control Unit With NOx Sensor
- with CODE (MG5) Engine OM 642 DE 30 LA, 140 kW (190 hp) 3800 rpm
- with CODE (MH1) Low-emission engine EPA 10/CARB
- with CODE (ZU7) National version for Canada
- with CODE (MG5) Engine OM 642 DE 30 LA, 140 kW (190 hp) 3800 rpm
- with CODE (MH1) Low-emission engine EPA 10/CARB
- with CODE (ZU8) National version for USA
1 Diesel particulate filter (DPF)
2 Exhaust pipe
3 Nitrogen oxides (NOx) sensor upstream of SCR catalytic converter
A97/1 Control unit for NOx sensor upstream of SCR catalytic converter
4 SCR catalytic converter
5 NOx sensor downstream of SCR catalytic converter
6 Heat shield
A97/2 Control unit for NOx sensor downstream of SCR catalytic converter
Location
The NOx sensor upstream of SCR catalytic converter is located on the front right crossmember. The NOx sensor upstream of SCR catalytic converter is screwed into the exhaust pipe upstream of SCR catalytic converter
The control unit for the NOx sensor downstream of SCR catalytic converter is located on the vehicle underbody behind the heat shield above the SCR catalytic converter. The NOx sensor downstream of SCR catalytic converter is screwed into the exhaust pipe downstream of SCR catalytic converter.
Task
The NOx sensors detect the NOx and the oxygen concentration in the exhaust upstream and downstream of the SCR catalytic converter and pass this information to the control unit for the NOx sensor upstream of SCR catalytic converter and to control unit for the NOx sensor downstream of SCR catalytic converter in the form of voltage signals. These process the information and transmit it via the drive train sensor CAN (CAN I) to the CDI control unit (N3/30).
Input and output signals
The following input signals are evaluated by the control unit for the NOx sensor upstream of SCR catalytic converter and to control unit for the NOx sensor downstream of SCR catalytic converter and appropriate output signals are issued:
^ Direct input signals
^ Drive train sensor CAN input signals from the CDI control unit
^ Drive train sensor CAN output signals to the CDI control unit
Direct input signals
- Circuit 87
Drive train sensor CAN input signals from the CDI control unit
- Diagnosis communication
Drive train sensor CAN output signal to CDI control unit
- NOx concentration in the exhaust
- Oxygen concentration in the exhaust
- Diagnosis communication
Design
a Sensor cable
b Electrical connection
3 NOx sensor upstream of SCR catalytic converter
5 NOx sensor downstream of SCR catalytic converter
A97/1 Control unit for NOx sensor upstream of SCR catalytic converter
A97/2 Control unit for NOx sensor downstream of SCR catalytic converter
The NOx sensor upstream of SCR catalytic converter and the NOx sensor downstream of SCR catalytic converter are double chamber sensors with an evaluation circuit. The NOx sensor upstream of SCR catalytic converter and the NOx sensor downstream of SCR catalytic converter are connected inseparably with the control unit for the NOx sensor upstream of SCR catalytic converter and the control unit for the NOx sensor downstream of SCR catalytic converter over an 8-pin sensor line.
An integrated sensor heater actuated by the control unit for the NOx sensor upstream of SCR catalytic converter and the control unit for the NOx sensor downstream of SCR catalytic converter ensures rapid readiness to operate of the respective NOx sensor.
Schematic function diagram of the NOx sensor (double chamber sensors)
21 Diffusion slit 1
22 Diffusion slit 2
23 Solid electrolyte
Ip1 Pump current 1
Ip2 Pump current 2
N2 Nitrogen
NOx Nitrogen oxides
O Oxygen ions
O2 Oxygen
Function
The active ceramic probe bodies consist of many layers with two reaction chambers. The oxygen is detected in the exhaust in the first chamber as in the case of an oxygen sensor.
To do this, a pump voltage is applied to the electrodes in the first chamber. This causes the O molecules to break down into double-charged oxygen ions, which are pumped either out or into the first chamber, depending on the exhaust gas composition (rich or lean). The pumping process takes place until the there is a voltage difference of 450 mV at the electrodes. The oxygen concentration is calculated from the size of the required pump current "Ip1".
The NOx is split at the earth electrode into nitrogen and oxygen in the second chamber if present. The oxygen is pumped out if the chamber again. The concentration of the nitrogen oxides in the exhaust is calculated from the resulting pump current "Ip2". The voltage signals of the respective NOx sensor are transmitted to the control unit for the NOx sensor upstream of SCR catalytic converter and the control unit for the NOx sensor downstream of SCR catalytic converter and processed there. The control unit for the NOx sensor upstream of SCR catalytic converter and the control unit for the NOx sensor downstream of SCR catalytic converter transmit the NOx and the oxygen concentration to the CDI control unit via the drive train sensor CAN.