Exhaust system temperature sensor, basic function

P49.20-2078-79

P49.20-2084-79

Overview

This document contains information on:

 General

 Function

General

Via temperature sensors in the exhaust system, the temperature of the exhaust flow is recorded in several areas of the exhaust system.

The combustion engine control unit uses the exhaust gas temperature detected by the temperature sensors to monitor the exhaust gas aftertreatment and for the cooling function of the exhaust gas recirculation cooler in the case of external exhaust gas recirculation.

For diesel engines, the exhaust gas aftertreatment control unit additionally uses the temperature values to coordinate the process of exhaust gas aftertreatment.

Function

The exhaust gas flowing by the sensor influences the measuring element on the inside depending on its temperature and leads to a change in its electric resistance. As a constant measuring current flows through the temperature sensor, the change in resistance leads to a voltage drop. As a result, the combustion engine control unit and, additionally for diesel engines, the exhaust gas aftertreatment control unit define the associated temperature value.

For digital design of the sensor, the electronics of the sensor chips generate a signal voltage, which processes the control unit and calculates the associated temperature value.

The installed PTC precision resistor changes its electrical resistance according to the exhaust temperature. The electrical resistance increases as temperature increases. The resistance change results in a change to the voltage signal. The signal for the voltage change is used by control unit to calculate the exhaust gas temperature.

 PTC stands for "Positive Temperature Coefficient", i.e. : The electrical resistance increases if the temperature increases (PTC thermistor).

For the digital design of the sensor, a Sensor Control Unit (SCU) is installed. The temperature has an effect on a piezoresistive operating sensor chip.