Noise, Vibration and Harshness (NVH)
This chapter aims to provide chassis engineers with knowledge of the background theory and techniques so that they can make informed judgements on NVH solution strategies at an early stage of vehicle development. The chapter commences with a review of the fundamentals of acoustic theory as this topic is often not covered in detail in Bachelor level engineering programmes. The human response to sound is then outlined followed by a description of general noise measurement and control techniques. The main sources of noise in road vehicles are then reviewed and common assessment and mitigation techniques are outlined for each type of noise. The next section introduces the sources and nature of automotive mechanical vibration as distinct from air-borne noise. There is a focus on vibration arising from the internal combustion engine since this remains the predominant motive power source for the majority of road vehicles. Principles of vibration control are then described with a focus on vibration absorbers and the isolation of engine-induced vibration. The final section of the chapter deals with the particular problems of brake noise and vibration, the latter affecting not only the brake itself but also the entire chassis due to transmission of the vibration through the suspension and steering systems.