How ‘noise chambers’ help Perkins build quieter engines.

While all three are serious concerns for engine builders, noise, in particular, has become increasingly important. This is largely a result of the trend toward physically smaller machines powered by compact, power dense diesel engines.

High noise levels can increase operator fatigue, and a smaller machine typically places the operator closer to the engine. Smaller machines also tend to be used more often in populated urban environments where neighbourhood perceptions have to be considered.

Chris Hill knows a lot about noise and how to reduce it. His team operates three large ‘noise chambers’ in which Perkins engines are tested and tuned to be as quiet as possible. The ‘noise chambers’, technically known as anechoic cells, are completely lined with specially shaped blocks of sound-absorbing foam.

“Once the doors are closed there are virtually no echoes and no reflected sounds”, Chris explained, “so the only sounds present are those produced by the engine under test. The silence can be a bit eerie at first, but you quickly get used to it.”

These chambers are large enough to test virtually any Perkins engine. They can handle anything from the smallest, 3-cylinder destined for a compact excavator to the huge diesels generating electric power for a small city. They also can accommodate entire diesel powered machines on occasion to evaluate noise produced by customer equipment such as hydraulic or HVAC systems.

The ‘noise chambers’ are equipped with sensitive microphones that are strategically placed around the engine being tested to capture the sounds it produces. Those recordings, together with data captured by cameras and other instruments, are then analysed to pinpoint the exact source of each of the sounds that create the engine’s noise signature.

“The best option is to design noise reduction features into the engine right from the start,” Chris said. “Based on data we’ve developed in nearly a century of engine design, we can incorporate things like extra ribbing or thicker material in strategic locations to reduce noise.

“And, today, we can control things like fuelling on common rail engines, injection timing, rail pressures and fuel quantities. They all affect noise and small changes can have big effects.

“Of course, we still have to meet emissions goals. But, once we do there are a lot of options we can evaluate and test to make the engine quieter.”

Sometimes, the solution to a noise issue can be something as simple as changing how a component is mounted. A large, flat surface like the side of an engine block can actually amplify the sound of something attached to it. Adding a piece of rubber or other resilient material to the mount can uncouple the two components and switch off the ‘amplifier’.

“Everything from the cooling fan to the gears under the timing case cover and even the oil pan have been identified as the culprits in different noise issues on different engines,” Chris noted. “We apply those lessons in every new engine design and they are often 5dB(A) or more quieter than the preceding generation of the same engine as a result.

“Oddly enough,” Chris observed, “there are no regulations I am aware of covering engine noise until it’s installed in a machine which then is subject to various legislative requirements. However, the engine is typically the largest potential source of noise on most machines, so it makes good sense for us to make it as quiet as possible.

“A quieter engine makes it easier for our OEM customers to meet legislated noise levels. It makes Perkins engines more competitive, and it helps us and our customers meet our social responsibility goals.

”Quietly, of course.”

Chris recently caught up with industry journalist Peter Haddock for his Discovering the Power of Perkins video series. Check out the video below.