Page 735 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 2 2. 1 Exterior noise: Assessment and control

22.1.3 Air intake systems and 22.1.3.2 Intake noise – objectives
exhaust systems: Performance
Some intake noise is desirable and can help create an
and noise effects impression of speed or power. Other noise is undesirable
and can contribute to excessive interior noise levels or
22.1.3.1 Introduction failure of the legislative drive-pass test.
Unwanted intake noise may be classified into two
Intake and exhaust noise must feature prominently in categories:
this chapter as they both can be significant sources of 1. Exterior noise which contributes to the overall noise
exterior vehicle noise. Arguably, for the first sixty years of level during the type approval drive-pass test (see
the motor car the exhaust tailpipe was the most Section 22.1.1).
significant cause of vehicle noise (even brief exposure
to an unsilenced light aircraft provides a clear reminder 2. Interior noise which reduces the comfort of the
of that). With the rise in popularity of front-wheel driver or passengers, or interferes with speech com-
drive passenger cars, permitting the adoption of large- munication (see Chapter 21.1).
volume exhaust silencers (driven of course by the arrival
of noise control legislation), the levels of exhaust tailpipe
noise reduced considerably from around 1960. This un- 22.1.3.3 The issues involved in intake
covered hitherto unheard intake noise. system design
For some twenty years (from around 1980) the intake
system was commonly the dominant noise source in It is important to understand the constraints on design
family sedans operating at full load. It has only been which include:
much more recently that improvements in plastic wave action tuning of the intake system to improve
moulding technologies (and the adoption of port fuel engine performance;
injection removing the need for a metallic intake mani- intake acoustic design;
fold) have freed intake designers to add several silencing intake system static pressure loss;
elements to even low-cost intake systems. As a result, the
levels of intake noise now match those of the exhaust intake system mounting;
system and so both engine and tyre noise now commonly packaging space (under-hood);
dominate the noise emissions from most family sedans. turbo or super-charging;
This chapter is more heavily biased towards intake cost;
system design rather than exhaust system design. There controlling vibration in the system;
are two reasons for this: intake snorkel positioning;
1. The careful design of the intake system for a natu- intake water inhalation;
rally aspirated (NA) engine can raise volumetric manufacturing process;
efficiency by more than 10%, whereas the intake filter durability/servicing;
corresponding improvement caused by detailed
exhaust system design is seldom more than 3–4%. 22.1.3.4 Intake systems
Therefore, the intake designer must consider both
engine performance and noise control, whereas
(within back pressure limits) the exhaust designer is Intake systems fulfil a number of roles in an overall
vehicle design which are:
free to concentrate more on noise control.
channel air to the engine;
2. The skills and techniques used for exhaust system
design are only slightly modified versions of those filter particulates;
acquired for intake system design. enhance engine performance through wave action
tuning;
This rather extended section will commence with an reduce noise.
overview of intake system requirements and then move
on to a detailed assessment of intake design for engine
performance followed by intake design for noise control. 22.1.3.5 The intake system designer
Only a brief discussion of exhaust system design is of-
fered as this concentrates on the main differences in The intake system designer is in a unique position within
approach for exhaust system design as compared with a vehicle development programme, falling within the
intake system design. interest areas of several design groups. His or her design

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