Page 763 - Automotive Engineering Powertrain Chassis System and Vehicle Body

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

Intake filter box with simplified model of manifold and zip tube
90
500mm zip tube
900mm zip tube
80
70
60
Attenuation (dB) 40
50

30
20
10
0

–10
0 100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)

Fig. 22.1-40 Influence of zip tube length calculated using APINEX software.

Temperature gradients are very steep, particularly in into the silencer, achieving noise reduction with

the exhaust manifold (300 C drop in gas tempera- a lesser backpressure penalty. Several parallel flow
ture between the exhaust port and the outlet of the paths may be provided, each linked via perforated
catalytic converter is typical). tube (Davies et al., 1997).
Durability/corrosion resistance is often a limiting Many silencer chambers can be provided within
factor in the design of silencers. a single silencer shell by dividing the silencer using
Backpressure has a stronger influence on engine per- baffle plates. The flow path through the silencer may
formance than the wave action in the exhaust be convoluted with many reversals of flow direction.
manifold. In this way, the flow path length is commonly much
Perforate tubes are commonly used (porosity less longer than the physical length of the exhaust
than 15%) to provide gradual expansion of the gas system. This is sharp contrast to common practice

Fig. 22.1-41 An intake system where the design has been optimised using linear acoustic theory.

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