Keeping it quiet: How Perkins targeted noise reduction in new engine line - Noise & Vibration - Brief Article

Diesel Progress North American Edition, Feb, 2002 by Ben Messenger, Brent Haight

In view of the intense focus on how engine manufacturers will meet imminent emission regulations, there has been comparatively little discussion of what is being done to reduce noise emissions. But oncoming environmental, health and safety legislation made reducing noise emissions a priority for Perkins Engine Co. in the development of its new 1100 series engines.

Designed from the bottom up with noise reduction in mind, the company claimed the 1100 series (see January 2002 Diesel Progress) to be some of the quietest engines ever made for the off-highway industry. Perkins said noise reductions on the four-cylinder versions of the new range add up to an impressive 3 dB(A). This is a dramatic improvement that has halved the level of perceived engine noise emitted.

Perkins said its OEM customers are now demanding quieter engines, as they strive to meet legislative targets for noise pollution with quieter machines. The company believes the 1100 series will play a key role in this, as the company claimed to have radically improved the way the new engine performs in three critical areas. The noise of the engine itself has been reduced, the engine's contribution to overall machine noise has been lowered, and through rigorous subjective evaluation, the quality of noise produced by the engine has been improved.

"The Perkins 1100 Series represents a genuine bottom-up redesign for lower noise, something our engineers have been wanting to do for years, said Malcolm Trimm, senior NVH engineer at Perkins. "You cannot cut noise levels by half with just cosmetic changes, and all the time legislation is making noise an increasingly critical issue, with OEMs also under pressure to meet their own targets, and all at the lowest possible cost.

"Right now, there are no sound regulations for the engine builder," added Trimm. "Regulations come at the customer end. As building and construction becomes more urbanized, more people are affected by loud equipment. Neighbors don't want to hear equipment. Sound is a pollution, especially at 7 a.m. when you are trying to sleep and workers have begun construction."

Perkins reported that engine noise has been assessed throughout the development process with the engine at idle, at frill load rated speed, and at high-speed under light load (the legislative benchmark). The company claims to have achieved its objective of significantly reducing engine noise throughout the operating range. Perkins said that an engine as quiet as the 1100 series can only be produced by identifying and tackling the three main causes of engine noise.

'Force' is one cause of engine noise and includes noise created by the combustion of fuel, and the mechanical movement of engine components. To combat the effects of force as a source of engine noise, Perkins has modified the design of the combustion system, as well as fitted a new quieter front gear train across the range to reduce mechanical noise. This has seen the previously fitted 28-tooth timing gear replaced by a new 40-tooth gear.

Another main cause of noise is 'transmission' noise, which Perkins describes as the noise that is carried through the engine structure. To reduce transmission noise, company engineers have stiffened block structures across the 1100 series range, and on the three- and four-cylinder models have introduced what is described as an open-top deck block. This places a layer of water between the cylinder and the block exterior, effectively acting as an insulation against the noise of combustion.

The third main cause of noise is radiation, which Perkins explained as being noise that "escapes" rather than being contained within the engine. This escaping noise has been minimized on the whole 1100 series range with sound-deadening baffle plates on the front engine covers, and isolated top covers. The three- and four-cylinder versions also benefit from integral inlet manifolds.

Perkins believes that a key benefit to an OEM in using an 1100 series engine is that it will enable the customer to meet its own targets -- without increased sound insulation, engineering effort and cost. This, Perkins points out, will let the OEM concentrate its own noise reduction efforts elsewhere on the machine. Perkins also says its engineers will be able to work in partnership with a customer's own team to identify where extra improvements can be made.

Perhaps the most innovative approach Perkins has taken in improving noise emissions is in looking not only at absolute noise, but also noise quality. During product development, a group of 30 "subjective noise panelists" regularly rated the subjective quality of the noise in order to select their preferred sound.

"It's fine to work on sound improvements isolated in a lab or test cell," said Trimm, "but if you don't work with the customer then why bother? An engine sound much different in a test cell than it does installed in a piece of equipment."

Perkins believes that while this is a subjective measure, it is important when customers have high expectations of such refinements, particularly with machines that operate in built-up areas. "By improving the subjective quality of the noise as well, Perkins can help make customers' machines more desirable, premium products," Trimm said. "Our new family of engines will make the workplace a more pleasant environment for the operator and for those in the local vicinity, while helping OEMs meet legislative targets for the whole machine in a cost effective manner."