Abstract
KEYWORDS – friction force measurement, NVH, brake noise, stick-slip, simulation
ABSTRACT - Noise, Vibration and Harshness (NVH) is an important issue in the development process of brake systems. This is because brake noises such as squeal, moan/honk and creep groan are not only seen as unpleasant but partly also as a quality defect. For a better understanding of these friction-induced vibrations it is crucial to investigate the acting forces and the friction coefficient in the contact area between brake pad and disc.
Today the friction coefficient is usually calculated, or rather estimated, by the approximated effective friction radius, the brake torque and the brake pressure measured on test rigs. In addition simplifications are made, e.g. the friction coefficient is averaged over many different brake applications. This can be very useful to compare different brake pad materials. Yet to understand the underlying mechanisms of the operating system it is necessary to investigate the instantaneous value of the resulting friction forces more in detail. This way the time dependent friction characteristic of the contact area can be analysed.
This paper deals with an improved method for measuring the friction force in fixed monobloc brake systems. Thus a high resolution measurement in time and magnitude of the dynamic friction force and the superposed vibrations during the brake application is possible. As the sensors are located close to the friction surface, it is possible to identify not only the magnitude of the force but also the point of load incidence. At the same time the system properties of the brake pad guiding, e.g. the mass and stiffness distributions, are hardly changed.
Besides the advantage of getting a deeper insight into the underlying excitation mechanisms of different brake noise phenomena it is also possible to implement these directly measured excitation signals into simulation models. Therefore the system response of different brake pad materials can be described. The results of this approach will be presented and discussed in a case study.