Update on EU and UN-ECE Noise Emission Limit Values
EU Directive 70/157/EEC and UN-ECE Regulation No. 51 specify the sound level that is allowed for road vehicles. Since the old test method was considered to no longer reflect real-world driving, a new draft test method was made available to automotive manufacturers and authorities in 2007. The old test method underestimated the effect of tire rolling noise. The new test method rectifies this situation. For a period of three years, the new test method was monitored alongside the old test method and recommendations were then made concerning what test method should be used and what the noise emission limit values should be.
The old test method was developed under worst case urban conditions, meaning full throttle in urban areas. For passenger cars, the old test method is completed on a test track that is 20 m long and one that had a very smooth and quiet road surface. Halfway along the test track, on either side, a microphone is placed at a distance of 7.5 m from the centerline of the track and 1.2 m above the ground. The vehicle is required to enter the test area at 50 kph and then accelerate at wide open throttle, usually in 2nd or 3rd gear. The minimum required tire thread depth is 1.6 mm. The pass-by noise level is then measured. For other types of vehicles the test is similar, but the test speed and gear selection may vary.
The new test method was developed to be “design independent” and was developed to improve its representation of urban driving conditions. To achieve this improvement, the new method includes a constant speed section as well as a more complicated wide open throttle acceleration test section. During the new test method for passenger cars, the vehicle must enter the test track so that a speed of 50 kph is reached where the microphones are placed (halfway along the test track as in the old test method). The minimum required tire thread depth is at least 80% of the full depth. The pass-by noise of the acceleration section of the test is measured, and if necessary a weighted average sound level is calculated based on each gear that is used during the runs. For the constant speed section of the test, the vehicle is operated at a constant speed of 50 kph along the test track in the same gear that was needed for the acceleration section of the test. The pass-by noise for the constant speed section is then recorded as the maximum level measured by each of the microphones. The total urban sound level is finally calculated as the weighted summation of the sound levels from the acceleration and constant speed tests. A weighting factor is used. For other types of vehicles, the test procedure is less complex and does not include the constant speed section of the test.
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