Page 193 - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 177

Figure 2.194 Exhaust system

It also has to match the engine gas fl ow, resist internal corrosion from the
exhaust gas, and resist external corrosion from water and road salt.
The exhaust system consists of the exhaust manifold, silencers, muffl ers,
expansion boxes and resonators ( Fig. 2.194 ). It also has down or front pipes,
intermediate and tail pipes, heat shields and mountings. Also included are one or
more catalytic converters, one or two lambda sensors and a connection for the
EGR system.
The exhaust gases are at a very high temperature when they leave the combustion
chambers and pass through the exhaust ports. The exhaust manifold is made
Safety fi rst
from cast iron to cope with the high temperatures. The remainder of the exhaust
system is made from steel, which is alloyed and treated to resist corrosion. The The exhaust gases are at a very
downpipe, or front pipe, is attached to the manifold with a fl at, or ball, fl ange. high temperature when they leave
the combustion chambers and pass
This joint is subject to bending stresses with the movement of the engine in the through the exhaust ports.

vehicle. To accommodate the movement and reduce stress fractures, some
fl ange connections have a fl exible coupling made from a ball fl ange joint and
compression springs on the mounting studs.
Another system to accommodate movement is a fl exible pipe constructed from
interlocking stainless-steel coils or rings. Where a fl exible joint is not required,
the front pipe may be supported by a bracket welded to the pipe, which is bolted
to a convenient position on the engine or gearbox. Where a catalytic converter
is used, it is fi tted to the front pipe so that the exhaust heat is used to aid the
chemical reactions taking place within the catalytic converter. The pipe continues
and then connects to an expansion box or silencer (muffl er). The exhaust gases
are allowed to expand into this box and begin to cool. They contract on cooling
and slow down.
Silencers or muffl ers are constructed as single- or twin-skin boxes, and there
are two main types: the absorption type, which uses glass fi bre or steel wool
to absorb the sound, and the baffl e type, which uses a series of baffl es to
create chambers ( Figs 2.195 and 2.196 ). In the baffl e type, the exhaust gases
are transferred from a perforated inlet pipe to a similarly perforated outlet pipe.
These silencers have a large external surface area so that heat is radiated to the
atmosphere. Additional pipes and silencers carry the exhaust gas to the rear.
Pipes are joined together by a fl ange, or clamp, fi tting. Flange connections have
a heat-resistant gasket and through-bolts to hold the fl ange together ( Fig. 2.197 ).