Measuring System Approach to Analyze Brake Squeal Triggering Mechanism 2011-01-2359
There are several different possibilities to analyze a squealing brake system. The present paper introduces a complex measuring system which is mounted on a complete vehicle axle at a test rig. This system was developed because the previously performed state-of-the-art tests did not allow any insights in the squeal triggering mechanisms.
First of all, a frequency analysis was performed. Thereby the main vibrating parts and the directions of the oscillation could be determined during a squeal event. The second was a modal analysis of the vehicle axle, which was necessary to get further insights into the system as well as to verify an existing Finite Element Method model. Through these tests, however, it was not possible to get any insight into the contact area, and therefore it was impossible to determine the squeal triggering mechanism. Because of this limitation, special guide pins were developed, which are able to measure the vibrating friction force. Strain gauges allow this measurement through an optimized shape of the pins. The movement of the pads is measured by using eddy current sensors, hence with a non-contact measuring method. Triaxial accelerometers were installed inside the brake disk vents, at the brake caliper, the brake pads and other parts of the wheel suspension. Finally an incremental rotary encoder measures the rotary movement of the axle. In order to get clear and repeatable results, special prototype brake pads were developed, which are very noisy.
The measurement system described above allows the detection of the main vibrating parts and to test different countermeasures as well as the effect of environmental influences, such as humidity and temperature. Thus, the measured variables are as closely as possible to the contact area of brake pad and brake disk. The aim is to develop a brake disk/pad contact model for the virtual design of less noisy brake systems.