Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation, Function




89 Exhaust gas recirculation valve
B2/5 Hot film mass air flow sensor
B11/4 Coolant temperature sensor
B37 Accelerator pedal sensor
L5 Crankshaft position sensor
M16/6 Throttle valve actuator
N3/10 ME-SFI control unit
Y31/1 EGR vacuum transducer
a Vacuum supply from intake manifold
b Controlled vacuum from EGR [ARF] vacuum transducer to exhaust gas recirculation valve

The EGR valve (89) is combined with an electric EGR vacuum transducer (Y31/1).

The EGR [ARF] vacuum transducer (Y31/1) stabilizes the sharply varying intake manifold vacuum and is actuated by the ME control unit by means of a PWM signal, frequency approx. 10 HZ, on/off ratio approx. 30 - 100%.

The EGR valve is opened to a varying extent as a result of this actuation with a vacuum of approx. 80 to 200 mbar and the quantity of exhaust gases which are recirculated, is controlled in this way.

The exhaust gases are recirculated in line with the map stored in the ME control unit as soon as the following conditions are met:
- Coolant temperature between 60°C and 110°C
- Engine speed <3500 rpm
- Partial load.

The map is designed to achieve optimum fuel consumption. In this case as much exhaust gas as possible is recirculated without impairing engine running or exhaust emissions.

Low-oxygen exhaust is inducted at the EGR valve, depending on the opening cross-section. As a result, the fuel-air mixture contains less oxygen. The combustion temperature drops and the formation of NOX is reduced.
The inducted air mass is reduced by the quantity of exhaust gases which are recirculated. In line with this, the ME control unit meters less fuel.




Right
89/1 Compression spring
89/2 Vacuum reservoir
89/3 Diaphragm
89/4 Valve seat
89/5 Housing

Left
89 Exhaust gas recirculation valve
Y31/1 EGR vacuum transducer
a Vacuum supply from intake manifold
b Controlled vacuum from EGR [ARF] vacuum transducer to exhaust gas recirculation valve
c Air admission