Page 730 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Exterior noise: Assessment and control C HAPTER 22.1

The results from each side of the vehicle are averaged 22.1.1.3 Track and atmospheric effects
separately. The intermediate result is the highest of
the two averages. Directive 92/97/EEC introduced a requirement for
The final reported result for the 5-speed M1 car is a standard road surface to be adopted at all test tracks
the arithmetic average of the two intermediate used for drive-pass noise homologation. 92/97/EEC is
results obtained from the tests for both gears. not completely prescriptive over the details of con-
The reported level may be reduced by 1 dBA to struction for such a standard track and so many Member
account for the natural variability of the test. States have adopted ISO 10844 as a specification.
According to Sandberg (1991), the specification in ISO
The homologation noise levels for type approval have 10844 was aimed initially at achieving three goals:
reduced significantly since their introduction in 70/157/
EEC. The level for M1 passenger cars has been reduced 1. To make the results achieved at any given track
by 8 dBA from 82 dBA to the current level of 74 dBA repeatable and reproducible at any other track.
(92/97/EEC). The reduction has been in stages as shown 2. To make the track surface highly reflective so that all
in Table 22.1-1. noise sources on the vehicle (even those hidden from
The current homologation levels correspond to the view under the vehicle) make a contribution to the
test detailed in 92/97/EEC. ISO 362:1998 is broadly overall drive-pass level and thus this would encourage
similar but not identical in all details. In particular, manufacturers to treat the whole vehicle.
92/97/EEC requires additional measurements to be 3. Minimise the noise radiated from the tyre/road

made 0.5 m (45 angle of incidence, 0.2 m above the
contact as this is a fairly unavoidable source of noise
ground) from the exhaust tailpipe of a stationary ve- and if it were to dominate, manufacturers would not
hicle in order to facilitate subsequent checks of vehicles be incentivised to treat the noise from other sources
in use. The engine is run at three-quarters speed and on the vehicle.
the maximum sound pressure level (fast, A-weighted)
is recorded. The results from three of these tests must Before the widespread adoption of ISO 10844 surfaces,
be reported as part of the vehicle certification process. Dunne and Yarnold (1993) reported that they knew of
92/97/EEC also includes a method for assessing com- 4 dBA variations in the drive-pass noise levels recorded
pressed air noise. for the same car at different test tracks around Europe.

Table 22.1-1 EC homologation noise levels for type approval

EC Directive 70/157/EEC 77/212/EEC 81/334/EEC 84/424/EEC 92/97/EEC
Enforced for new vehicles 1976 1983 1984** 1990 1996
Category of vehicle Maximum permissible noise level (dBA) at 7.5 m (acceleration test)
Cars (<9 seats) 82 80 80 77 74*

Minibus <2 tonnes 84 81 81 78 76
Minibus 2–3.5 tonnes 84 81 81 79 77
Bus 150 kW 89 82 82 80 78
Bus >150 kW 91 85 85 83 80

Light truck <2 tonnes 84 81 81 79 76
Light truck 2–3.5 tonnes 84 81 81 80 77
Truck >3.5 tonnes
75 kW 89 86 86 83 77
75–150 kW 89 86 86 85 78

>150 kW 91 88 88 86 80

*75 dBA if fitted with a DI diesel engine or if very powerful ‘supercar’.
**Imposed more stringent requirements for exhaust and intake systems.

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