Abstract
Brake disc natural modes and frequencies have a crucial influence on noise, vibration and harshness (NVH) of the entire brake assembly. Disc theoretical and experimental analyses are often conducted for a ‘free-free’ or restrained disc but there are few published data on the factors that influence modes and natural frequencies. The paper presents Finite Element (FE) disc analyses for different boundary conditions, design features and modifications, and thermal loading. The results indicate that boundary conditions greatly influence NVH – the method of disc fastening to the wheel hub –. This can be expected but brake and vehicle designers can do relatively little to change natural modes and frequencies, since the fastening method is largely defined by strength requirements. However, the brake designer can impact disc design features such as number, shape and position of vanes, disc ring/hub attachment geometry and face thickness, all of which directly influence disc natural modes and frequencies. The relationships can be complex but FE analyses can be effective in analysing and optimising brake NVH characteristics at the design stage. Furthermore, disc wear and thermal loading also have considerable influence on disc natural frequencies: these two variable ‘service conditions’ cannot be avoided but can be successfully analysed in order to predict more realistically disc behaviour throughout its life. The research shows substantial design and manufacturing possibilities in affecting disc natural frequencies through both major and subtle design modifications. These powerful tools should be used from early stages of disc design in order to improve brake NVH characteristics. Traditional disc design approach of focusing predominately on mechanical and thermal loading must be complemented by NVH considerations.
KEYWORDS – Brake, noise, FE disc analysis, design modifications, thermal effects