Abstract
In this paper a measuring device is described, which enables measuring the clamping forces acting during a braking process in the friction area between pad and disc. Thus the amount and the effective contact point of the clamping force are determined fingerand piston-sided at the same time. State of research is the measurement of the distribution of clamping forces by means of pressure indication films. However, these are destroyed by shear stress or friction and in this way they can be only used with a stationary brake disc, that is, under no circumstances during a braking process.
An analysis of the force lines in a caliper shows that the preferred position for the measurement of the clamping and tangential forces can be found in the friction material of the brake pads, since all forces which contribute to the braking process must be supported by the brake pad. As soon as these forces are induced in the back plate of the brake pad, a correct measurement becomes almost impossible because of the multitude of contact points with the caliper.
For the measuring device four slim-line piezo quartz sensors are integrated in an original brake pad. The slim design of the sensors enables the measurement with the same thickness of the pad like the original ones.
The piezo quartz prototype was applied and tested in a standard brake on a brake test rig. The measurements show the shifting of the point of application of load related to the back plate of the brake pad during a braking process. The consideration of the point of application of load of the clamping force by a stationary brake disc causes a radial shifting to the brake disc´s outer edge (this is primarily adjudged to the expansion of the caliper). During a braking process the acting tangential force causes a shifting in tangential direction. By reason of movement of the caliper during a braking process a visual measurement method was developed, which enables recording the movement of brake pads.
The chance of measuring the amount and the contact point of the piston- and finger-sided clamping force opens a window for understanding the braking process more in detail, e.g. of the emergence and development of the wear conditions of the pads and the brake disc. Furthermore, measurements are carried out in order to analyze the influences on the clamping force in a disc brake (e.g. of the hydraulic pressure and the pressure rate, of the wheel´s speed and of the disc´s temperature).
Keywords - disc brake, piezo brake pad prototype, clamping force, effective contact point, braking process