Exhaust flap-controlled emission control system function

S14.00-3002-06

Task

 Rapidly heating up the catalytic converter to its operating temperature and thus reducing the exhaust emissions

 Protecting the catalytic converter from overheating or overcooling

Design

1 Engine

2 Cooling muffler

3 Exhaust flap

4 Vacuum unit

5 Catalytic converter

6 Vacuum line

7 Vacuum line

8 Bypass line

A13 PEC control module

Y2 Exhaust flap switchover valve

Function

The exhaust flap (3) is regulated by the PEC control module (A13) which operates the exhaust flap switchover valve (Y2). The exhaust flap is controlled in line with engine speed, throttle valve position and coolant temperature.

In the warming-up phase and during the complete driving cycle at idle speed in the lower part load range, the exhaust flap switchover valve (Y2) is actuated electronically by the PEC control module (A13) and the exhaust flap (3) is closed by means of the vacuum unit (4). The exhaust flow is thus diverted along a short bypass line (8) directly into the catalytic converter (5) (bypassing the cooling muffler). This ensures that the catalytic converter (5) heats up rapidly and prevents an undercooling. The function of the catalytic converter is thus assured all the time the vehicle is driven.

In the upper engine speed range and at full load, the exhaust flap (3) is open and the exhaust flow passes through the cooling muffler (2) into the catalytic converter. This eliminates any risk of the catalytic converter overheating.

Advantages

 Reduces exhaust emissions

 Ensures longer catalytic converter life