Emission control - Td5 (EGR systems): Description and operation

EGR systems

There are two types of exhaust gas recirculation system used with the Td5 engine dependent on legislation and market requirements, these are type 1 and type 2.

Type 1 EGR system is fitted to all Td5's built up to the introduction of 2002 MY, except for Japanese specification vehicles.

Type 2 EGR system is fitted to all Japanese specification vehicles and was introduced into European markets for 2002 MY to meet EU3 emission requirements. An additional feature introduced at 2002 MY is the EGR cooler, which is bolted to the front of the cylinder head.

EGR system - type 1

This EGR system features a single modulator which is electrically controlled to modulate a vacuum source to the EGR valve. The controlled vacuum opens and closes the valve by the amount required to ensure the optimal proportion of exhaust gas is allowed through to the inlet manifold to be combined with the fresh air intake. Control feedback is achieved by monitoring the mass of fresh air flowing through the mass air flow sensor.

The modulator operation is controlled by a signal from the ECM which determines the required amount of EGR needed in response to inputs relating to air flow and engine operating and ambient conditions. The ECM is low-side driven, sinking current returned from the vacuum modulator for switching operating condition.

The exhaust gases are routed from the exhaust manifold through a shaped metal pipe which connects to the underside of the EGR valve. The pipe is held securely in position to the front of the cylinder head using a clamp bracket. The EGR pipe is attached to a mating port at the front end of the exhaust manifold using two Allen screws and at the EGR valve assembly by a metal band clamp. The two Allen screws fixing the EGR pipe to the exhaust manifold should be replaced every time the EGR pipe is removed. Extreme care should be exercised when removing and refitting the EGR pipe to avoid damage.

When a vacuum is applied to the EGR suction port, it causes a spindle with sealing disc (EGR valve) to be raised, thus opening the port at the EGR pipe to allow the recirculated exhaust gas to pass through into the inlet manifold. The valve is spring loaded so that when the vacuum is removed from the suction port the valve returns to its rest position to tightly close the exhaust gas port.

By controlling the quantity of recirculated exhaust gas available in the inlet manifold, the optimum mix for the prevailing engine operating conditions can be maintained, which ensures the intake gas to the combustion chambers will have burning rate properties which will reduce the NO_x emissions to an acceptable level. Normally, full recirculation is only applicable when the NO_x emissions are most prevalent.

EGR system - type 2

This system features twin modulators mounted one above the other on a metal plate located on the inner wing at the RH side of the engine. The modulators are electrically controlled by the engine management system and are used to modulate a vacuum source to the EGR valve and a supplementary Inlet Throttle (ILT) valve; the two valves are controlled to operate in tandem. The ILT valve vacuum pot is mounted adjacent to the EGR valve housing and has a linkage which connects to a butterfly valve mounted in front of the EGR valve at the air intake manifold.

The modulator operations are electrically controlled by signals from the engine management system which determines the required volume of exhaust gas needed in response to inputs relating to air flow, engine operating conditions and ambient parameters such as temperature and altitude. The engine management ECM switches on the circuit by completing the path to ground, operating the vacuum modulators.

Pre EU3 models: The exhaust gases are routed from the exhaust manifold through a shaped metal pipe which connects to the underside of the EGR valve. The pipe is held securely in position to the front of the engine cylinder head using a metal clamp bracket. The EGR pipe is attached to a mating port at the front end of the exhaust manifold using two Allen screws and at the EGR valve assembly by a metal band clamp. The two Allen screws fixing the EGR pipe to the exhaust manifold should be replaced every time the EGR pipe is removed. Extreme care should be exercised when removing and refitting the EGR pipe to avoid damage.