Abstract
Noise pollution is the main object of complaint of major parts of the population concerning vehicle traffic. To guarantee the acceptance of vehicle traffic further on intensive efforts have to be done to reduce emissions of traffic derived noise. Due to former advances in reducing outside-noises of automobiles, which at first concentrated on drive train and primarily on exhaust silencer and intake noise, contribution of tyre/road surface noises to total outside-noise of automobiles increased. Measures regarding the system vehicle-tyre-road surface have to be taken to achieve even in future effective reductions of noise pollution. Because of this reason a joined research program was performed in Austria with specialists for automobiles, tyres and road engineering, and companies and research departments investigating noise origins and working together on measures to reduce noise.
The Scientific Umbrella Low-noise Road of the Austrian ministry of transport proved that the extremely quiet 70dB(A) car in combination with a low noise road surface is possible. Further more the possibilities of reducing noise emission were analysed in detail. With special regard to the noise generated by the contact of running surface of the tire and the road surface, more than 40 car tires were systematically tested at different measurement methods. These methods are pass-by in rolling mode at various vehicle speeds (as mentioned in the EU pre regulation 92/23/EEC), accelerated pass-by appropriate to 92/97/EEC and at constant speeds. The last two modes are used due to the fact that the engine noise should be included in the research program. The measurement program was carried out on six different road surfaces on ISO measurement sites. Beside the influence of the surface structure the profile styling and the foundations of the tires on the pass-by noise was also determined.
The analysis of the results over the measuring distance was carried out with regard to the noise level, the spectrums and digital acoustic methods. The transient rise of the engine torque at the pass-by found also consideration as well as the slip of the powered wheels. The position of the level maximum in dependence of vehicle, tire and road surface represents also a significant characteristic quantity. Following systematic comparisons of measurements at the ISO surface and at the acoustics vehicle chassis dynamometer were carried out. The simulation of the pass-by at the in-door equipment brought deeper understanding of existing differences.
Measurements of the pass-by noise of seven series vehicles equipped with in total eighteen series tyres of different companies were performed on the six road surfaces to verify the influence of the road surfaces on the noise emissions of the vehicle fleet. Trial tyres of 37 passenger cars were used to systematically investigate the influence of single tyre parameters on the pass-by-noise on the five different low-noise research road surfaces. Reference vehicles were an A-class passenger car with petrol engine and a maximum power output of 66 kW. In the scope of this project a close to production prototype of a low-noise passenger car, was developed. Using these vehicles and selected tyres pass-by-noise measurements will be performed on the five different research road surfaces. The outside noise measurements include accelerated pass-by using the relevant speeds, pass-by at constant velocities of 80 km/h using the fourth speed and 120 km/h using he fifth speed, and the rolling noise for two velocity classes (55 +/- 5 km/h and 80 +/- 5 km/h).
In the scope of the project umbrella Low noise road systematically investigations were performed to determine the influence of different tyre/road surface combinations on the exterior noise of passenger cars and heavy duty vehicles and to consider potentials to reduce noise emissions. Level reductions of up to 6 dB(A) depending on the driving conditions were achieved in comparison to a series vehicle equipped with a series tyre on a regarding the acoustic characteristics already optimised split-mastic asphalt. Using a low-noise tyre sound pressure levels below 70 dB(A) were obtained on thin film surfaces during accelerated pass-by in the second and in the third speed.