Development of a laboratory brake for a flywheel mass test rig for variable pad sizes and shapes with a force distribution unit for ideal contact pressure and a topography measurement system for in-situ recording of surface changes and wear.

Pin-on-disc tribometers are used to determine the frictional behaviour and boundary layer dynamics of material pairings. Material pairings are examined under defined conditions in order to make statements about the friction behaviour and wear. Pairings for real brake systems with larger pad sizes can be tested on flywheel mass test benches in order to provide proof of suitability. This is mainly due to a lack of knowledge about the scaling behaviour of friction linings. The Department of Machinery System Design at TU Berlin has combined the classic approach of a pin-on-disc tribometer with a flywheel mass test rig (up to 12.78 kgm²) and thus set up a laboratory brake on which material pairings with different pad shapes and sizes (up to 48 cm²) can be examined. The flywheel mass test stand consists of an adjustable DC-motor that drives a shaft on which variable flywheel masses and brake disks can be installed. The variability allows for different kinetic energies at different friction speeds. The test stand also has a linear table on which the pad sample holder sits. The specified braking force is generated by a hydraulic cylinder. The normal force is applied to the friction lining sample by means of a force expansion and distribution unit. This expansion ensures a uniform contact force over the entire pad surface, which has been designed with fem simulations and proven with pressure measurement film. Different force expansions are possible for different pad geometries. During the tests, the torque, the forces in the normal and tangential directions, the temperature of the brake disk and lining sample as well as the speed are recorded using NI measuring cards and corresponding sensors. Furthermore, the lining sample can be moved with the linear table to a topography measuring unit including a camera system. By using the linear table and a laser distance sensor mounted on a linear motor, the topography of the lining sample is recorded and images can also be taken. This flexible setup allows the topography to be recorded between individual braking operations without the need for long changeover times. The laboratory brake can be used to investigate the influence of brake force distribution on the friction process. Topographical changes can be observed in situ in between braking operations. The test rig has already been used in an initial series of tests and the first results of a running-in process of a material pairing consisting of a gray cast iron disc and an organic friction lining for truck brakes are shown.