Exhaust flap (on specific models)

The exhaust flap installed in exhaust systems on vehicles with a single rear silencer varies according to specific model. The exhaust flap is controlled by the electric exhaust flap changeover valve.

Depending on the motorization an electrical exhaust flap can also be used (see CORRESPONDING BRIEF COMPONENT DESCRIPTION ).

Fig 1: Identifying Electric Changeover Valve Exhaust Flap

Courtesy of BMW OF NORTH AMERICA, INC.

The exhaust flap is integrated within the rear silencer. The exhaust flap reduces the noise level when the engine is idle and when the engine speed is close to idle. The exhaust flap provides active noise control on the order of 8 dB.

The DME digital engine electronics system controls the electric changeover valve for the exhaust flap. The partial vacuum applied opens the exhaust flap. When air impacts against the diaphragm in the aneroid capsule (vacuum system depressurized) a spring closes the exhaust flap.

An aneroid capsule is mounted on the rear silencer's endpipe. The diaphragm box is linked to the exhaust flap via an adjustment mechanism. A vacuum hose leads from the exhaust flap's electric changeover valve to the aneroid capsule. When the engine is off no power is supplied to the exhaust flap and the exhaust flap is closed. Both conditions, open and closed, occur during normal vehicle operation.

Control of the exhaust flap is governed by:

• Load
• Gear engaged
• Engine speed.