Rolling noise: fresh demands
Page 89
Page 90
If you've noticed an error in this article please click here to report it so we can fix it.
The ominous words 'Strengthening Noise Abatement Policies' mean workshops may have to measure rolling noise when preparing for MoT tests
11 One-time Ford chief engineer Harley Copp is quoted as saying about vehicle noise that "leaving it all to insulation is like wearing rubber gloves to cure a leaky pen." He was right, of course, but he ignored the fact that designing out the noise can be a very long and expensive business. Insulation, as Ford itself amply demonstrated in later years, is a quick and effective way of reducing most kinds of vehicle noise.
For the workshop, insulation has one big drawback — it gets in the way of maintenance. Acoustic hoods that lift up with the tilt cab are only a partial answer and the increasing legislative pressure for yet more noise reduction is going to increase the problem.
Now comes a demand that a rolling noise test be included in the regulations without delay. This could mean the noise test being included at the annual test, in which case workshops are going to have to be able to measure vehicle noise for themselves to prepare vehicles for test.
The demand for testing the noise that vehicles actually make in service, rather than when they were made. comes in a report from the Organisation for Economic Co-operation and Development (OECD). Called Fighting Noise and omi nously subtitled Strengthening Noise Abatement Policies, the lECD report has tough words about present policies, and it calls for much more to be done by regular inspections.
So if you are about to design a new workshop, or are currently costing out the next five year's maintenance plan, which all good workshops should do, it would be wise to take this report and its possible outcome into account. It seems very likely that a noise test may soon become mandatory in the same way that a weighbridge test can now be demanded, so someone somewhere is going to have to keep up with the in service noise performance of the fleet.
Tougher legislation
Despite a lot of work by manufacturers and a heap of laws, so far there has been very little improvement to the impact of noise on the environment. The OECD report concudes that worldwide more than 130 million people are exposed to unacceptable noise and that 300 million live in "discomfort", most of which, it says, is caused by motor vehicles. The report urges much tougher legislation, and says that compulsory inspection of noise levels and vehicle tuning is the only effective way forward.
Therein lies the heart of the problem on noise, both in its effect on people and the work that the vehicle operator has to do. For all the legislation so far has done little more than begin a long process, as anyone who has been trying to tune an engine when a motor bike roars by or next door's lawn mower starts up will know.
One of the main snags is that measuring noise is extraordinarily tricky. The necessary meters can be bought for only a few hundred pounds, but the effect of noise on those listening to it is complex, depending at least as much on the quality of the noise as its actual recorded level — such as with some small-engined motorbikes.
Most of the insulation to be found today is of the stick-on variety, which is attached to panels during manufacture to cut down the drumming that a piece of metal makes when exposed to the vibrations which stern from the cumbustion in the cylinders and the rotation of parts which are not quite in perfect balance.
Over a period of time, the glue which attaches the panels becomes less effective and the panels detach at the corners. Since they appear to a mechanic to serve no useful purpose, to look untidy and to get in the way, the rest is often ripped off.
The result is that a vehicle which met all the noise regulations when it was built, now no longer does so, and the operator will probably be quite unaware of this. So often will the driver, for the noise felt in the driving position is not at all the same as that which is radiated outside.
Deteriorating silencers
In the case of the stick-on panels, it is normally only the low-frequency noise that is affected — the sort that rattles the windows in the boss's office on the other side of the yard. The higher frequencies are generated from within the the engine itself, and particularly from moving parts that are subject to in-service wear. The amount of wear might be quite insufficient to cause the part to be replaced, but it will cause noise — extra noises that were not there on the manufacturer's acceptance tests.
Deteriorating silencers are another source of unexpected noise. At present if there is a hole in it, or if the vehicle makes an obvious "unacceptable noise," it will be rejected at an annual testing. The gradual rusting and wear of exhaust components, however, cause a change in the acoustic performance of the items, such as the simple case of baffles rattling. Not a loud noise, it is true, but one that can be extremely irritating if you live or work near a workshop where engines are often revved during tuning work.
Noise is usually measured in decibels (dB) which with the methods of measurements chosen is meant to approximate to the noise heard by the human ear. At the Transport and Road Research laboratory a lot of work went on in the later 70s and early 80s with the so called quiet, heavy vehicle. This Fodenbased machine, which made another appearance some years later in the run-up to the GLC lorry ban events, was a maintainer's nightmare, with shrouding and insulation panels all over the place. It did show clearly, however, what could be done, and how important it was to keep the hush kits in place.
During the arguments about that lorry ban, it was shown what a large effect can be achieved by driver education, and the OECD report acknowledges that as much could be done that way as by technical developments. There is, however, no way you can legislate for driver — or mechanic — behaviour.
The OECD report also points out that many lorries are now gaining approval figures that are considerably under current legislation, and that there is obviously some scope for tightening those rules without undue cost penalties. Again it insists "it is very possible that only a very few of the vehicles actually in use achieve noise levels lower than the current limits."
The workshop operator must also not forget that apart from the vehicles that pass through the doors, the workshop itself is a noise generator, and will always attract the attention of the planning authorities on that account. So think about how you will design your workshop now to minimise noise to those around you.
According to that report, you could even be happier as one of the effects of less noise is to reduce stress.
Be ready for the imposition of routine in-service noise tests — it could well be the price to pay for the next uplift in maximum gross weights. The cost of extra maintenance as a result of using more insulation has been put at one per cent of current costs per decibel gained. Make sure some of it comes your way.
by John Parsons