A brake with tradition

A totally different approach to analysing and tackling the problem of car brake squeal could be applied in most industrial situations. Jon Excell reports.

Whether you’re on a crowded train or sitting in a motorway traffic jam, few things are more likely to finally tip you over the edge than the banshee-like squeal of dodgy brakes.

Thankfully, a recent EU study into the causes of brake noise has armed designers with a methodical and coherent approach to the problem. And that, claimed project leader Dr. Herman Van de Auweraer, is exactly what brake designers have been missing.

Van de Auweraer, manager of research and technology development at software company LMS, said his group’s research demonstrates that identifying the cause of, and then curing, brake noise is a far more complicated problem than traditionally thought. Historically, designers have adopted something of a trial and error approach to brake noise, he said, with little understanding of how different variables influence noise generation.

At the core of the study was Holomodal – an analysis technique developed by LMS and BMW. Holomodal works by aiming a laser beam at a rotating brake disc. By measuring the light reflected by the disc, the system produces a high-resolution 3D image of the whole surface as it vibrates.

Traditionally, vibration measurement has relied on attaching sensors to a test panel. However, the problem with this is that it only measures the vibration at the sensor, and attaching too many sensors can actually change the way the panel moves, leading to inaccurate results. The Holomodal technique enables engineers to see the effect on every part of the panel’s surface at the same time.

Van De Auweraer said that extremely careful analysis on a test bench demonstrated that a huge variety of factors influence noise and vibration generation. These include braking speed and force, rotation speed and material properties.

One important conclusion, he said, is that it is not only the dynamics of the brake-disc itself which are important, but also those of the surrounding structure, such as the brake pad and suspension dynamics. He said that by changing just the brake disc fixture stiffness, important changes in the noise frequency were observed.

‘It’s important to stress that we didn’t look into finding a specific innovative design solution,’ he said. ‘The aim of the project was to develop testing, analysis and modelling tools that can be used during the brake design and design analysis phases at the manufacturer’s site.’

Van De Auweraer also stressed that the project’s findings are not solely applicable to the car industry but relevant to friction-induced vibration in practically any industrial applications containing systems with rotating or sliding parts.

LMS is now in the process of commercialising the resulting methods as software tools. ‘We are integrating the project findings in a dedicated suite of measurement and analysis tools aimed at the brake manufacturing industry,’ he said, adding that he expects wider industry to reap the benefits of the technology within the next two years.

One organisation likely to benefit from the new-found expertise is Bosch, one of LMS’ main partners in the brake noise project. Michael Fischer, a chief R&D engineer with Bosch, said that predicting the causes of brake noise was as imprecise as weather forecasting. Although he would not comment about any design developments resulting from the project, he said the findings have enabled Bosch to improve on brake design.