Vehicle acoustics
The vehicle acoustics deals with the noise of land vehicles, mostly viewed automobiles and motorcycles, to a lesser extent also track-bound vehicles.
development
Until the 1950s, the noise generated by road vehicles received little attention. In the course of time, however, the comfort requirements of vehicle operators and the proportion of the population annoyed by road noise increased. In Germany today, road traffic is the source of noise that affects the largest proportion of the population. It ranks well ahead of air traffic and rail traffic (see also road noise ). Therefore, vehicle acoustics are an important part of vehicle development.
At the beginning of the activities in the field of vehicle acoustics, the acoustic engineers used simple aids such as sound level meters . The first high-performance frequency analyzers were used in the 1970s . They made it possible to determine and document the frequency content of a sound signal in a few seconds . After the advent of digital technology, acoustic engineers now have a range of tools that allow a comprehensive analysis of the mechanisms of sound generation. This enables a targeted reduction in the noise level at the source.
The main activities initially focused on the noise of the internal combustion engine. In the 1970s and 1980s, tire-road contact also became the focus of interest. The intensive research and development work in the field of flow noise did not begin until 1990 and resulted in the construction of a number of aeroacoustic wind tunnels .
The construction of other special acoustic test stands was also pushed ahead:
- Vehicle acoustic test stands (mostly drum test stands)
- anechoic engine test stands ("anechoic rooms")
- Transmission test stands for testing vehicle segments
- Reverberation rooms for engines and vehicles
- servohydraulic vehicle test stands (partly air-conditioned)
The measurement technology was also further developed. So z. B. used for sound source localization concave mirror microphones and microphone arrays . The sound intensity measurement technology offers a tool for determining the sound power of a source, even in the case of background noise . In addition, laser measurement techniques (e.g. laser Doppler vibrometry ) are used to determine surface vibrations.
Artificial heads enable binaural noise measurement, which can also be used for psychoacoustic analyzes.
The possibilities of numerical acoustics are also becoming ever more extensive. The finite element method (FEM) and the boundary element method (BEM) , but also the statistical energy analysis (SEA) and numerical aeroacoustics (CAA), should be mentioned here.
Noise sources on the vehicle
Road vehicle noise has three main components: engine noise , tire-road noise or rolling noise, and aerodynamic noise . The drive noise dominates at high engine torques and low speeds, e.g. B. when approaching a traffic light. At constant speed on country roads, but also in city traffic, the tire-road noise is the loudest component. On motorways, the flow around the vehicle becomes the main source of noise above approx. 130 km / h.
Not least because of the regulations for type testing , which stipulate an accelerated drive past as a measurement condition, the drive noises, and here especially the intake and exhaust noises, have been significantly reduced in the past decades. Since the tire-road noise could not be reduced to the same extent, these now dominate most areas of operation of a car. In modern vehicles, they make up about half of the total noise even when accelerating. At constant speed, the tire-road noise predominates in all gear stages, except in first gear. According to a more recent study, 90% of the sound energy in city traffic can be attributed to the tire-road noise. Noise reductions during tire-road contact therefore have a significant effect on the noise emissions that are effective for the population .
Investigations by the Research Institute for Automotive Engineering and Vehicle Engines Stuttgart ( FKFS ) show that at speeds above approx. 130 km / h, for both exterior and interior noise, the noise around the airflow generates the highest noise levels with acoustically favorable tire-road combinations. This speed limit can be much lower for small vans.
literature
- Heinemann Gahlau: Vehicle acoustics: Development and use of systems for noise reduction . Landsberg: Verlag Moderne Industrie, 1998; ISBN 3-478-93184-3 .