Abstract
Brake squeal is an elusive problem which has been intensively investigated in recent decades. The brake pads of passenger cars usually consist of organic materials. Brake pads consisting of sintered materials are used for high-speed trains, race cars and motorcycles due to the higher friction coefficient, which makes the brakes more powerful. However, brake squeal is more frequent among sintered materials compared to organic pads. The presented project deals with prototype brake pads which consist of sintered material for a powerful sports car brake system. Thereby these prototype pads have been compared among others with the original brake pads. The different pads have been tested on a special equipped test rig.
For the test runs, the guide pins of the brake calliper are modified in shape enabling installation of strain gauges. Thus it is possible to measure the forces acting on the guide pins. During squeal a superposed vibration can be detected. Using Fast Fourier Transformation, the amplitude and the frequency spectra of the strain gauges are compared with those of a microphone. The dominant vibration frequency of the force correlates well with the dominant frequency of the microphone.
Next, four different kinds of brake pads are investigated using the standardised SAE J2521 test, which consists of approximately 1500 different modes of braking. The four types are the series-production organic brake pads, replacement organic brake pads and two different sintered brake pads, which vary in their additives. As already mentioned, only the materials of the brake pads are changed, the geometric shapes are almost the same.
The series-production brake pads squeal at about 0.5 percent of all brake manoeuvres of the SAE J2521 test. These pads are already optimized by the manufacturer to the tested brake system. The tests of the sintered brake pads result in a clearly higher percentage of squeals. The squeal noise is also higher, but the squeal frequency is the same as for the organic pads. Thus the use of sintered material influences the excitation and the squeal triggering mechanism, but not the squeal frequency.
Further research using an innovative measuring system, modelling and simulation including analytical models as well as finite element analysis will provide tools for brake development. Thereby the acoustical behaviour of the sintered brake pads will be investigated.
Keywords: Brake Squeal, Brake Pad Material, Experimental Research, Vibration Measurement, Frictioninduced Vibration