Page 736 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Exterior noise: Assessment and control C HAPTER 22.1

Runners join each intake port to the intake
plenum. These are also commonly
known as primary lengths.
Vehicle Powertrain
design design
There are many issues that need to be considered
when designing air intake systems. The following will be
discussed here:
location of the snorkel orifice;
Refinement
Intake/exhaust snorkel and filter box dimensions;
design
intake system design for improved engine
performance;
sources of intake (and exhaust) noise;
Fig. 22.1-3 The role of the intake system designer.
flow duct acoustics;
decisions will directly affect the work of other designers acoustic performance of a simple intake system;
as illustrated in Fig. 22.1-3. conical snorkels;
Changes to the system geometry or layout which are protrusion of the snorkel into the filter box;
beneficial for noise control may well not be advantageous Helmholtz resonators;
for power or pollutant emissions. sidebranch (quarter wave) resonators;
effect of flow on sidebranch resonators;
22.1.3.6 The development cycle intake system mounting.
for intake systems
22.1.3.8 Location of the snorkel orifice
The initial design and further development of a vehicle
intake system takes place in step with the design and Issues to consider are:
development cycle for the whole car. Location is often chosen for packaging reasons only.
The key activities are:
A long snorkel will give good low-frequency attenua-
Concept stage: Claim packaging volumes. tion but will also result in many dips in the attenua-
Engine prototype stages: Develop engine breathing and tion at the resonant frequencies of the snorkel.
wave action tuning through manifold design. Minimise Acoustic flow duct silencing predictions usually
system pressure loss. Develop air filtration. Bench- relate to an unflanged snorkel. Fitting the snorkel
mark orifice noise. Develop silencers and resonators. into a hole in the bodywork will act like a flange and
Vehicle prototype stages: Refine packaging. Test for alter the acoustic performance of the system.
exterior noise levels. Positioning the snorkel orifice near to reflective
Pre-production vehicles: Refine interior and exterior surfaces may increase interior or exterior noise levels.
noise levels. The intake air needs to be relatively cool to preserve
Pre-production assessment: Address any problems of intake charge density.
noise quality. Possible water ingestion must be considered.
A snorkel orifice position that is good for interior
noise may not be appropriate for the control of
22.1.3.7 Principal intake system drive-pass noise.
The snorkel orifice position should not excite acous-
components
tic cavity modes, whether in the engine bay, the inner
wing of the bodyshell or passenger cell.
Filter box housing for a paper filter element. Has
a dirty side and a clean side. 22.1.3.9 Snorkel and filter box
Snorkel dirty-side pipe feeding fresh air to the dimensions
filter box.
Zip tube clean-side tube feeding air into the Consider a snorkel position at the top of the front grille,
plenum. above the radiator. The filter box is to be mounted on the
Plenum collecting volume used to join the inner wheel arch. This effectively fixes the snorkel length
manifold runners together. to, for example, 375 mm.

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