Friction Force Measurement at Brake Discs

摘要

Experimental researches on brake squeal have been performed since many years in order to get an insight into friction-excited vibrations and squeal triggering mechanisms. There are many different possibilities to analyse brake squeal. The different operating deflection shapes can be detected using e.g. laser vibrometer systems or acceleration sensors. Piezoelectric load cells can be used for the measurement of the normal contact force of the brake pad. The presented test setup measures not only the mean value of the friction force between brake pad and disc at a certain brake pressure, but also the superposed vibration of this force, which only occurs during a squeal event. Therefore the guide pins of the brake caliper are replaced by modified ones. The brake pads are held in position by these pins and the resulting force of the brake torque, hence the friction force, acts on these pins. The shape of the pins is optimized for measuring these forces. For the measurement strain gauges are mounted on the pin. The dominant frequency of this measured vibration correlates with the microphone used in parallel. Simultaneously to the test runs a simple analytical model has been developed, which represents the tested brake system. Further research on the test rig regarding the squeal triggering mechanism and the contact between disc and pad is expected to provide new insight into the elusive problem of brake squeal. This will be used to adapt the simple analytical model. The aim is to develop an experimentally verified contact algorithm, which can be used in simplified multi-body simulations or detailed finite element analyses. Thus, it will be possible to predict the critical squeal frequencies of a new brake system and to estimate the effect of potential countermeasures.