Exhaust gas recirculation, function - GF14.20-P-3000A

ENGINE 112.910 /911 /912 /913 /914 /916 /917 /920 /921 /922 /923 /940 /941 /942 /943 /944 /946 /947 /949 /953 /954 /955 /970 /972 /973 /975 

ENGINE 113.940 /941 /942 /943 /948 /960 /961 /963 /965 /966 /967 /968 /969 

Fig 1: Identifying Exhaust Gas Recirculation Function Diagram

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 NO 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.

Fig 2: Identifying Exhaust Gas Recirculation Valve Components