Noise pollution 08 July 2013

Millbrook Proving Ground recently re-opened its noise test track, with an upgraded noise surface to meet the new ISO 10844:2011 specification. Brian Tinham talks to principal engineer Darren Carter

OEMs, tyre manufacturers and commercial vehicle engineers will almost certainly be aware of ISO 10844, the international standard governing the specification of test tracks designed to measure noise emitted by road vehicles and their tyres. But what many may not know is that, in 2014, new surface specifications will be mandated into legislative type approval requirements for ECE Regulation 51 (which governs noise from category 'M' and 'N' vehicles), under the updated ISO 10844:2011.

It's that development that has forced all test facilities in Europe that purport to measure vehicle noise to instigate a programme of upgrading their test tracks. And hence the recently re-opened upgraded noise track at Millbrook Proving Ground, in Bedfordshire, which, according to Millbrook principal engineer Darren Carter, was the result of investing "a substantial amount of money".

Backtracking a moment, ISO 10844 is the mandatory specification for test tracks used for evaluating pass-by noise to European type approval standards. Its purpose is to ensure reproducibility between test tracks, ensuring that noise transmission measurements are not unduly affected by the surface and so minimising the variability of tyre-to-surface noise generation. The 2011 version of the specification aims to more accurately achieve this objective.

So what's new? The most significant amendments from the 1994 version to the 2011 standard can be grouped into three categories: composition of the test track surface; its geometry; and the surface properties. "Surface composition relates to specifications that span surface texture, smoothness and noise," explains Carter. "The new ISO specification mandates very stringent requirements for the quality and composition of the top surface of the site, while allowing a degree of flexibility in the construction of the track's substrate."

As for geometry, the new standard covers more than the overall size and shape of the site. "Proximity of large reflecting objects, gradient and cross fall [including longitudinal and transverse slopes], and surface irregularities all matter, and have been tightened up in the new standard," says Carter.

And it's a similar story with the surface properties, which, under the new standard, are now measured in terms of mean profile depth (MPD), instead of the old mean texture depth (MTD). "The significance of this is that there are now lower and upper bounds placed on the MPD, whereas previously the standard only had a lower limit. Sound absorption now has a requirement for each one-third-octave band from 315 to 1,600Hz, and separate requirements for the drive lane and propagation area."

Beyond that, legislation on vehicle pass-by noise levels means that future noise testing will be driven equally by the need to understand the contribution from tyres and the powertrain. For Carter, that's where Millbrook now scores, with the new track enabling engineers to isolate tyre-generated noise from the overall pass-by noise of test vehicles, and so help manufacturers to understand aspects of their vehicles that are contributing to total noise.

With the new Millbrook noise facility now open and built to the 2011 standard, the proving ground is now ahead of the curve, in terms of noise legislation. So ahead that it's the only commercially available facility in the UK to offer a noise surface that is fully compliant. What's more, Carter says the new track is equally capable of running tests on vans, trucks, coaches and buses. Indeed, even the heaviest of road-legal vehicles can be tested, because Millbrook took advantage of the new standard's flexibility around track substrate in its construction.

And there's more. "Importantly, the physical changes to the effective length of Millbrook's noise site will enable engineers to extend testing capabilities, and so help manufacturers to conduct the newly introduced 'off-cycle' higher-speed testing requirements," explains Carter.

"The composition and quality of the new test track surface will mean that manufacturers benefit from the most consistent and repeatable test surface commercially available in the UK," he insists. "Millbrook's new noise testing site will provide an excellent development tool, as well as helping with the all-important type approval of vehicles."

Author
Brian Tinham

Related Downloads
52716\noise_pollution.pdf

Related Companies
Millbrook Proving Ground Ltd

This material is protected by MA Business copyright
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.