Continuous Trap Oxidizer: Description and Operation
GF14.40-P-3023OGG Component Description For Nitrogen Oxides Control Unit With NOx Sensor
ENGINES 642.820 in MODEL 164.124 as of model year 2009
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment / YoM 08 model refinement package
ENGINES 642.820 in MODEL 164.125
- with CODE (494) USA version
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment
ENGINES 642.820 in MODEL 164.824 as of model year 2009
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment / YoM 08
ENGINES 642.820 in MODEL 164.825
- with CODE (494) USA version
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment
ENGINES 642.870 in MODEL 251.124 /125 as of model year 2009
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment / YoM 08
View of the vehicle from the front left on model 251.1
N37/7 NOx control unit downstream of diesel particulate filter
N37/7b1 NOx sensor downstream of diesel particulate filter
N37/8 NOx control unit downstream of SCR catalytic converter
N37/8b1 NOx sensor downstream of SCR catalytic converter
Location
The NOX sensor downstream of the diesel particulate filter is screwed into the exhaust pipe downstream of the diesel particulate filter (DPF) and the NOX sensor downstream of the SCR catalytic converter is screwed into the exhaust pipe downstream of the SCR catalytic converter. The NOX control unit downstream of the diesel particulate filter and the nitrogen oxides control unit downstream of the SCR catalytic converter are connected inseparably with the respective NOX sensor and located on the underfloor.
Task
Nitrogen oxides control units are supplied by the company "VDO Automotive AG".
The NOx sensors detect the NOX and the O2 concentration in the exhaust downstream of the DPF and the SCR catalytic converter and pass this information on to the nitrogen oxides control units in the form of voltage pulses. These control units process the information and transmit it via the drive train sensor CAN (CAN I) to the CDI control unit (N3/9).
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 CDI control unit
^ CAN output signals to the CDI control unit
Direct input signals
- Circuit 87
CAN input signals from the CDI control unit
- Diagnosis requests
CAN output signals to the CDI control unit
- NOX concentration in the exhaust
- O2 concentration in the exhaust
- Diagnostic data
Design
N37/7 Nitrogen oxides control unit downstream of diesel particulate filter
N37/7b1 NOx sensor downstream of diesel particulate filter
N37/8 Nitrogen oxides control unit downstream of SCR catalytic converter
N37/8b1 NOx sensor downstream of SCR catalytic converter
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 respective nitrogen oxides 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 2 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 units send the NOX and the O2 concentration to the CDI control unit via the drive train sensor CAN.
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
