Page 759 - Automotive Engineering Powertrain Chassis System and Vehicle Body

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

Notional effect of the expansion in a simple intake filter box
30
25

20
Attenuation (dB) 10 5
15

0

–5

–10
0 100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)
Fig. 22.1-30 Attenuation of the expansion section of a simple intake filter box calculated using APINEX software.

constructed using sophisticated flow duct acoustic engine performance by throttling the intake flow as
modelling tools (Davies, 1988; Harrison et al., 2004). a result.
These results compare favourably with common Note: It is generally assumed that all intake snorkels,
understanding of how reactive silencers work (see tapered/conical or not have a slight flare at the intake
Fig. 22.1-21). orifice in order to improve the initial inlet flow.

22.1.3.13.1 Conical snorkels 22.1.3.13.2 Protrusions of the snorkel into
A conical snorkel can be used to reduce the depth of the the filter box
troughs in the attenuation due to the tuning effect of the Protrusions of the snorkel into the base of the filter box
snorkel length as shown in Fig. 22.1-32. The typical act like sidebranch resonators. The effect of a 120-mm
conical snorkel is tapered such that the snorkel orifice is protrusion to the snorkel along the bottom of the filter
reduced in area. Care must be taken not to seriously limit box is shown in Fig. 22.1-33.

Notional effect of the snorkel on a simple intake filter box
0

–5

Attenuation (dB) –10

–15

–20

–25
0 100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)
Fig. 22.1-31 Attenuation of the contraction section of a simple intake filter box calculated using APINEX software.

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