Volvo seeks to stop the noise levels inside its commercial vehicles
Volvo is currently working on controlling and reducing the noise levels inside its commercial vehicles. This, according to the Swedish company, is not driven by legislation. Instead, Volvo is taking this initiative on its own in order to boost safety and driver comfort.
‘The legal limit for noise in the work place in Sweden is 85dB and we are already down to 70dB inside the cab. It’s a question of comfort and, even more importantly, safety. Low, monotonous sounds are known to reduce brain activity. The driver gets tired and, eventually, risks falling asleep,’ says Kaj Bodlund, a technology specialist working with product development on Volvo Trucks.
The noise made by on-board systems can also be disturbing, especially when drivers are trying to sleep or rest. Excessive noise from heaters, fans, air conditioning systems or refrigerators could prevent the driver from sleeping soundly. Drivers who are prevented from sleeping well are seldom the safest or most efficient on the road.
At Volvo Trucks’ sound lab at in Gothenburg, Sweden, noise level tests are carried out using simulations, where a computer registers and measures the decibel levels. In-cab noise is measured using an artificial head with microphones in its ears. The measurements are extremely accurate and very realistic. Real tests are then performed on prototype trucks at Volvo Trucks’ proving ground outside Gothenburg.
‘We started using simulations and artificial heads in the 1990s. Now we can carry out more tests in less time and obtain more detailed data. In addition to decibels, we can also measure frequencies and several other aspects of the noise,’ Bodlund. Of course, things have moved on quite a bit since Volvo started working on noise reduction in the 1990s. Back in the early 1990s, in-cab noise levels of 74–75dB were not uncommon, but today, they are down to a far more tolerable 70dB.
According to Volvo, a major breakthrough in noise research was made in 1993 with the introduction of the new FH range of Volvo trucks. The new, slim, aerodynamic cab was not only better from the point of view of fuel-efficiency, but also considerably reduced wind noise. The air-tight sealing of the cab also reduced noise from the engine and the road.
The next significant development for in-cab noise came in 2002. The Globetrotter cab was further improved by the addition of insulation between the sheet metal and the trim panel. This reduced condensation between the cab wall and the trim panels and improved temperature control inside the cab, as well as making a considerable difference to sound-proofing quality.
Over the years, the noise curve has progressed continuously downwards. At some point, it will begin to even out. ‘We realise that there will come a point at which we can’t reduce the general noise levels any more, but there is plenty more work to do on more specific noise sources that may also impact the overall driving experience. Squeaking, creaking or scratching sounds can be equally unpleasant for the driver,’ explains Christina Keulemans, who works at the Volvo R&D sound lab. ‘Our work is continuous and we still have a great deal left to do. Every time a design parameter is altered or a new product is developed, we have to analyse the way in which the change might affect the noise level,’ she adds.
The five factors that affect noise levels:
1. Mass: A heavy component is less noisy (but of course heavy trucks consume more fuel).
2. Insulation: The cab, the engine and many vibrating components can be insulated with sound-proofing materials in order to keep noise to a minimum.
3. Materials: Light metals such as aluminium may reinforce noise, while heavy metals or rubber tend to dampen noise.
4. Damping materials: If parts and components made of sheet metal are covered with damping materials, they generate less noise.
5. Aerodynamics: Wind noise is one of the worst noise offenders. An aerodynamically-optimised cab is both less noisy and more fuel efficient.
Source: www.indiaautomotive.net
