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The vehicle interior constitutes the multi-sensory environment of driver and passengers. Beside overall design and execution, materials and its surfaces are of specific interest to the customer. They are not only needed to fulfil technical functions, but are in direct focus of the customer’s perception. The perceived quality is based on all sensory data collected by the human perceptual system. Surfaces express design intent and craftsmanship by their visual appearance. Haptic features supervene when materials are touched. And even smell has an influence on the perception of ambience. Although sound is generated nearly every time when fingers slide across a surface, touch-sounds have been disregarded so far. In various cases, these contact sounds are clearly audible. As essential sound responses to haptic activity, they can degrade perceived quality. A method has been developed for a standardized generation of touch-sounds.

Material authenticity is an important factor for appearance and perceived quality of the vehicle interior. The term authenticity implies ambivalence: For the product designer, it means identification and trueness of the origin of the material. The customers, however, can only access information on the nature of the materials via their own perception of surface features. Thus, the intended authenticity of a material always needs to be conveyed by its surface. Specific cases illustrate the context: 1. The customer touches a part of known matter, but various layers prevent from directly touching the natural material: e.g. leather at the steering wheel, applications of wood. 2. Perception of a thin surface layer indicates authentic material, which is not fulfilled by the whole part: e.g. plastic parts plated with metal. 3. A part consists of authentic material, but newly composed, so that it is not easily identified, such as recycled materials, e.g. leather fiber layers for seats.

Rust accumulated on disc rotor surfaces causes brake judder and excessive grind noise. This low frequency noise phenomenon is audible especially at low vehicle speed without masking from other noise sources like wind and road noise or power train sound. This often leads to customer complaints resulting in significant warranty costs. Alternative drive systems like hybrid or full electric power trains will emphasize this problem. Most studies concentrate on optimization of the brake system to reduce low frequency brake noise. In this work, the potential for optimization on vehicle level was investigated. The most effective NVH optimization can be achieved by improving and matching the acoustic properties of the vehicle and the brake system. In a first step, the main structure borne noise transfer paths have been identified by means of Transfer Path Analysis.

Predominant brake noise evaluation and rating was developed many years ago and no longer fulfills the need of modern development work. An extended description of a noisy brake event (European expert group guideline EKB 3006) and a standardized test data exchange format, allowing the comparison of different source test results (EKB 3008) are presented. Today's noise rating systems are described and compared by selected examples. The paper proposes an open 4 level noise rating system (EKB 3007). It starts with simple occurrence statistics, noise rating based on sound levels, situational noise rating including duration and finally based on the human perception, described by psychoacoustics.

With a view on the statistic nature of most brake noises occurring under normal driving conditions, vehicle sign-off drives, under specific road conditions, have been established and are now state-of-the-art procedures within the automotive industry. In contrast to the other fields of acoustical engineering, however, assessment is often based on subjective ratings rather than on measured data. This causes uncertainties in the assessment and makes it difficult to compare results of different test routes. The relation of results gained on specific routes to normal customer driving is quite unknown and cannot be clarified by means of subjective ratings. The paper first provides an overview on psycho-acoustic findings relevant for perception and subjective assessment of brake noise. It is clarified that brake squeal must be analyzed with respect to the psycho-acoustic properties of the background noise.