Search Results

In the past years, Eberspaecher has developed active exhaust silencers for several passenger vehicles with different engines on a prototype level. In general, a substantial reduction of the exhaust noise is regularly achieved in a frequency range of 40 - 400 Hz covering the most relevant engine orders. In exhaust system development the main design conflicts are noise reduction, silencer volume/weight and backpressure. Recent progress was made in the development of the durability and industrialization of the actuator. This component could be reduced in size and weight thus allowing the integration in different design spaces of many vehicles. In some cases, the conventional dual exhaust system can even be replaced by an active single exhaust line without compromising on the acoustic or backpressure targets but saving > 50 % of space and > 30% weight. The potential impact of this technology on future vehicle designs will be discussed.

In the past, Eberspaecher has installed active exhaust mufflers on several vehicles. In all cases, a substantial reduction of the exhaust noise was achieved. Moreover, not only silencing but also the shaping of different types of sound in these vehicles was implemented. Hence, a variety of sounds are available from one and the same engine. Unlike with conventional passive exhaust systems, the active silencer can be specifically adapted (customized) to the vehicle; to the driving situation; and/or from a request of the driver. To guarantee that an “anti-noise” system can actually work in practice, various fundamental problems had to be solved. In particular, the ambient conditions prevailling in exhaust systems (enormous heat, moisture and high sound pressure levels) have previously reduced the life span of the loudspeaker that generates the “anti-noise”.

Automotive exhaust mufflers are not only attenuating noise, but can, in fact, along with other exhaust components, generate noise within the exhaust system. This type of noise is commonly called “flow generated noise” to distinguish it from the “pulsation noise” excited by the combustion engine. Flow generated noise is normally very broad band but it can also have tonal regions. This tonal flow noise can sound like a whistle. In this contribution an experimental study of the generation and prevention of such whistle tones will be presented. The study was focused on perforated pipes in mufflers with different perforation patterns, hole sizes and hole shapes. The noise spectra have been measured on a flow bench at room temperature as well as under real (hot) conditions on a vehicle. The results will be correlated in terms of frequency and Strouhal number. Concepts to avoid or suppress these tones will also be discussed.

Exhaust acoustics simulation is an important part of the exhaust system process. Especially important is the trend towards a coupled approach to performance and acoustics design. The present paper describes a new simulation tool developed for such coupled simulations. This tool is based on a one-dimensional fluid dynamics solution of the flow in the engine manifolds and exhaust and intake elements. To represent the often complex geometries of mufflers, an easy-to-use graphical pre-processor is provided, with which the user builds a model representation of mufflers using a library of basic elements. A comparison made to two engines equipped with exhaust silencers, shows that the predictions give good results.