Engine Management
Secondary Air TechnologyComponents of the Secondary Air System
Depending on the vehicle generation, additional components, such as electric switchover valves, cut-off and non-return valves are installed in the secondary air system.
A pneumatically actuated shut-off valve prevents air from arriving in the exhaust manifold after the cold start phase, to prevent the lambda signal from being falsified. The required setting force is achieved by a vacuum taken from the induction pipe. After the coldstart, the engine management system assumes the time-dependent setting of the shut-off valve to passage via an electric switchover valve. Right: Electric switchover valve (EUV) The non-return valve prevents pressure peaks being generated in the exhaust branch, e.g. preventing misfires in the "front" part of the secondary air system causing damage and stopping exhaust gas or condensate arriving in the secondary air pump. In the opposite direction, the non-return valve opens as a result of the pressure from the secondary air flow.
More recent types of secondary-air valves (since about 1998) are opened by the pressure from the secondary air. Consequently, the pneumatic actuation by an electric switchover valve is no longer necessary. Left: Cut-off secondary air valve |
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The shut-off valve and non-return valve are frequently combined in one component, the "cut-off secondary air valve".| Previous page | Next page |