UN R51 — Supplement 4 to the 03 series of amendments

The sound must now be measured either indoors or outdoors by the methods of Annex 3, and the outdoor and indoor results are deemed equivalent. For each specific test condition, the manufacturer can select to test the vehicle either indoors or outdoors. The Type Approval Authority may always mandate an outdoor test for verification, for any test of this Regulation, including conformity of production testing. A new subparagraph keeps the measurement on the stationary vehicle and the rules for vehicles where an internal combustion engine cannot operate when stationary. Appendix 1 to Annex 1 has new items on testing method information, with the item “Test method selected: Outdoor/Indoor”. A new footnote reads “Delete what does not apply.”

For indoor testing, if conformance of the sound level meter cannot be stated for each array channel, a simulated pass-by run must be performed. This run is at a constant speed of 50 km/h, with a constant tone signal supplied to all channels of the arrays. The deviation of the simulated A-weighted sound level from a reference tone signal must be checked in accordance with IEC 61672-3. For indoor testing, the entire measurement system must be checked at the beginning and at the end of a series of sessions. The hardware supplier is recommended to provide a qualified calibration method (that is, electrical calibration); the measurement software must then implement it. Simulation algorithms using sound source localization detection should deactivate that feature for these tests.

Outdoor and indoor test environments that meet the specifications of this Regulation provide equivalent acoustic environments and produce results that are equally valid. New paragraph 2.1.2. on the indoor test site refers to ISO 362-3:2016 for test room dimensions, floor condition, dynamometer and vehicle fixing system. All room dimensions may be adjusted to meet the specific application for the products being tested according to Annex 8, paragraph 4. The test facility must meet the requirements of ISO 26101:2012. The qualification criteria and measurement requirements appropriate to this test method are as described in ISO 362-3:2016, paragraph 7.3. For indoor testing, background noise must take into account noise emissions from the dynamometer rollers, ventilation systems and facility exhaust gas systems.

Indoor tests must be performed according to paragraph 3.1. using the specifications of ISO 362-3:2016, variant A. Variant A is a combination of indoor testing (power train sound) and outdoor testing (tyre/road sound). For indoor application, the manufacturer must give the technical service documentation according to Annex 8, paragraph 1. When testing indoors, the control system of the dyno roller must use the test mass mt. Actual vehicle mass has no effect on results; the vehicle may be loaded as necessary to prevent slip between tyres and dyno rolls. For indoor testing, virtual lines AA', PP' and BB' mark the track start, the virtual pass-by microphone position and the track end.

Paragraph 1. lists the documentation for indoor application, including validation of the facility and the procedures to be applied for indoor testing. Documentation must include test results on a representative selection of the manufacturer’s production, to show comparable indoor and outdoor results within acceptable accuracy. The indoor pass-by test is simulated by measurement of power train sound on the dynamometer and energetical addition of the outdoor tyre/road sound. The tyre/road sound need not be measured again every time a vehicle is tested; a matching data set from a database can be used. The remaining tyre/road sound must be at least 10 dB below the maximum A-weighted sound pressure level produced by the vehicle under test. If this condition cannot be fulfilled, a correction according to ISO 362-3:2016 Annex B, paragraph B.6. must be carried out.

Paragraph 3.1.2.1.4.1., for vehicles with manual, automatic or adaptive transmissions or CVTs tested with locked gear ratios, has a new subparagraph (e). If no gear ratio gives an acceleration below 2.0 m/s², the manufacturer must, if possible, take measures to avoid awot test above 2.0 m/s². New Table 1 (Appendix to Annex 3) lists lock of a discrete gear ratio, controlled gear shift management, partial load driving and mixed solutions (modes). Partial load driving applies only to Pure Electric Vehicles (PEV) as defined in the 07 series of amendments to UN Regulation No. 83. Some Table 1 measures require an acceleration between aurban and awot,ref, not exceeding 2.0 m/s², for vehicles of category M1, N1 and M2 ≤ 3,500 kg. Any measure the manufacturer uses to control gear downshift or avoid accelerations beyond 2.0 m/s² must be documented in the test report.