EMISSION CONTROL - TD5
DESCRIPTION AND OPERATION 17-1-11
EU3 models: The exhaust gases are routed from the exhaust manifold through the EGR cooler to the underside of
the EGR valve. The EGR cooler is bolted to the front of the engine cylinder head. An EGR pipe connects the EGR
cooler to the exhaust manifold and is secured by two Allen screws. The two Allen screws fixing the EGR pipe to the
exhaust manifold should be replaced every time the EGR pipe is removed. A second pipe connects the EGR cooler
to the EGR valve; this pipe is secured to the EGR valve by a clip, and to the cooler by two Allen screws.Extreme care
should be exercised when removing and refitting the EGR pipe to avoid damage. When refitting the EGR
cooler, always tighten the pipe connections BEFORE tightening the bolts securing the cooler to the cylinder
head.
When a vacuum is applied to the EGR suction port, it causes a spindle with sealing disc (EGR valve) to be raised,
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.
A vacuum is simultaneously applied to the inlet throttle (ILT) valve suction port which causes the butterfly valve in the
inlet manifold to close by means of a spindle and lever mechanism. Closing the butterfly valve limits the supply of
fresh intercooled air entering the inlet manifold and causes a depression within the inlet manifold to create a greater
suction at the open port to the EGR delivery pipe. In this condition a greater mass of recirculated exhaust gas is drawn
into the inlet manifold for use in the combustion process. When the vacuum is released from the ILT valve suction port
a spring returns the butterfly valve to its fully open position.
By controlling the quantities of recirculated exhaust gas and fresh intake air 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.