EGR Cooler Bypass Valve: Description and Operation

Electric Changeover Valve, Bypass Flap, Exhaust-Gas Recirculation Cooler

Electric changeover valve, bypass flap, exhaust-gas recirculation cooler
The electric changeover valve is attached to the engine via the exhaust-gas recirculation cooler (EGR cooler). The EGR cooler has a bypass flap with which the exhaust gas can be routed past the EGR cooler. In the warm-up phase of the engine, the bypass flap is opened to get the oxidation catalytic converter to operating temperature more quickly. It also prevents dirt contamination in the EGR cooler by exhaust residues. The bypass flap is adjusted by means of a partial-vacuum canister.

Functional description
The engine control activates the electric changeover valve. This switches the partial vacuum in the system through to the partial-vacuum canister. The partial vacuum applied opens the bypass flap. The partial vacuum applied opens the bypass flap. On ventilation of the diaphragm canister (vacuum system de-pressurised), the bypass flap is closed by a spring.







Structure and inner electrical connection
Vacuum and ambient pressure are both present at the electro-pneumatic changeover valve. The Digital Diesel Electronics system determines whether to relay system vacuum to the vacuum unit. There are only two working positions, on and off.







Function principle and target values
Without a partial vacuum, the bypass flap is closed, i.e., the exhaust gas flows through the EGR cooler. If a partial vacuum is applied, the bypass flap opens the bypass and simultaneously closes the inlet to the EGR cooler. The exhaust gas is routed past the EGR cooler directly to the intake air collector. The bypass of the EGR cooling is opened during EGR operation if the coolant temperature is lower than 50 °C.







Observe the following nominal values for the electric changeover valve bypass flap:

Size Value
Voltage range 9 to 16 V
Operating pressure 0.8 to 1.5 bar
Power consumption 0.55 A
Temperature range -40 to 140 °C

Diagnosis instructions

Failure of the component
If the electric changeover valve bypass flap fails, the following Behavior is to be expected:
- Fault entry in the engine control unit
- Nominal position for bypass flap, bypass opened

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