Continuous Trap Oxidizer: Description and Operation

GF14.40-P-3023OG Component Description For Nitrogen Oxides Control Unit With NOx Sensor
ENGINES 642.850 in MODEL 212.024, 224
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment





Shown on model 212.0 from the right

12 Diesel particulate filter (DPF) (with code (474) Particulate filter)
N37/7 Nitrogen oxides control unit downstream of diesel particulate filter
N37/7b1 NOx sensor downstream of diesel particulate filter

Location
The NOX sensor is screwed into the exhaust pipe downstream of the diesel particulate filter (DPF). The nitrogen oxides control unit is connected inseparably with the NOX sensor and located on the underfloor.





Shown on model 212.0 from the front

13 SCR catalytic converter (selective catalytic reduction)
N37/8b1 NOx sensor downstream of SCR catalytic converter

Location
The NOX sensor is screwed into the exhaust pipe downstream of the SCR catalytic converter. The nitrogen oxides control unit downstream of the SCR catalytic converter (N37/8) is connected inseparably with the NOX sensor and located on the underfloor.

Task
Nitrogen oxides control units are delivered 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 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
- Terminal 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 sensor NOX sensor (double chamber sensor with it 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) 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 O2 molecules to be split into double charged oxygen ions and then 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 2 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 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 CDI control unit via the drive train sensor CAN.

Schematic function diagram of the NOX sensor (double chamber sensors)

1 Diffusion slit 1
2 Diffusion slit 2
3 Solid electrolyte
Ip1 Pump current 1
Ip2 Pump current 2