Prof. Dr.-Ing. Georg-Peter Ostermeyer, TU Braunschweig, GERMANY

Mr. Chengyuan Fang, Institute of Dynamics and Vibration of TU Braunschweig, GERMANY

Mr. Guido Lehne-Wandrey, Institute of Dynamics and Vibration of TU Braunschweig, GERMANY

Mr. Malte Sandgaard, Institute of Dynamics and Vibration of TU Braunschweig, GERMANY

Mr. Alexander Vogel, Institute of Dynamics and Vibration of TU Braunschweig, GERMANY

Mr. Jacek Kijanski, Institute of Dynamics and Vibration of TU Braunschweig, GERMANY

Mr. Thomas Hillner, wenglor sensoric GmbH, GERMANY

Mr. Fabian Repetz, wenglor sensoric GmbH, GERMANY

Friction tests under controlled conditions are crucial for the understanding of the boundary layer dynamics in technical brake systems. The dynamics of the friction interface characterize the braking performance. In order to evaluate and monitor the dynamics of the friction interface, detailed insights into the friction behavior is obtained by high precision tribotesters under laboratory conditions. Especially in the low sliding speed range, specialized machines such as the Variable Velocity Tribotester (VVT) make it possible to mimic real world phenomena under controlled conditions, e.g. creep groan or COF in low temperatures.

This paper presents the wenglor sensoric 3D sensor ShapeDrive MLAS201 for measuring the pad surface between friction applications at VVT. With this device, quasi in-situ measurements with high speed and precision of the pad’s surface are attained. The 3D sensor consists of a light engine which projects several patterns onto the pad surface and a high resolution camera which can record these patterns again. The topography and intensity information of the pad surface would be stored in a point cloud file with high precision of 12 megapixels. Such information can be used to analyze the surface properties such as roughness and height. With further algorithms it is also possible to observe the change of the entire topography and in further way to determine the wear volume and analyze the contact situations.

Prof. Dr.-Ing. Georg-Peter Ostermeyer, TU Braunschweig, GERMANY

Mr. Alexander Vogel, TU Braunschweig, GERMANY

Mr. Jacek Kijanski, TU Braunschweig, GERMANY

Mr. Malte Sandgaard, TU Braunschweig, GERMANY

Mr. Guido Lehne-Wandrey, TU Braunschweig, GERMANY

Friction tests under controlled conditions are crucial for the understanding of the boundary layer dynamics in technical brake systems. The dynamics of the friction interface characterize the braking performance, which has to be evaluated and monitored in the early stages and throughout the development process of new friction materials. For this purpose, detailed insights into the friction behavior is obtained by high precision tribotesters under laboratory conditions. Especially in the low sliding speed range, specialized machines such as the Variable Velocity Tribotester (VVT) make it possible to mimic real world phenomena under controlled conditions, e.g. creep groan or COF in low temperatures.

The VVT is modularly designed with two linear stages to move the test specimen and a highly capable servor motor for the rotation of the brake disc. A rotational disk speed of up to 400 rpm is reached with a resolution of 25 bit and a 1:10 gearbox. The normal load can reach up to 300 N (approx. 45 bar brake line pressure) by utilizing a leaf spring load unit. A 3-axis piezoelectric force sensor directly at the test specimen measures the applied and resulting forces.

In addition to the friction testing, it is possible to automatically move the specimen to a high precision 3D laser scanning device with stripe light projection and to record height information and pictures of the friction surface. For measurements below room temperature, the VVT is located in an insulated chamber and equipped with two cooling aggregates.

Mr. Jacek Kijanski, TU Braunschweig, GERMANY

Prof. Dr.-Ing. Georg-Peter Ostermeyer, TU Braunschweig, GERMANY

Investigations of wear and wear dust behavior of brake systems are increasingly becoming the focus of research activities in science and industry. Environmental protection as well as health and economic aspects play a driving role in this context. In contrast to these important issues, the wear behavior of brake pads is still poorly understood. Due to the different material compositions of brake pads, it is also very difficult to gain universally valid insights, even when testing under stationary conditions.

In previous publications, it was already identified that the friction history or a dynamic load collective can lead to different wear rates despite the same idle work. This was demonstrated by means of a multitude of real driving profiles and decreasing velocity profile measurements using the Automated Universal Tribotester at the Institute of Dynamics and Vibrations. The results of the investigations accordingly raised new questions, which will be addressed here. In addition, the knowledge gained here should serve as a metrological basis for the mathematical description of wear processes in the boundary layer of brake systems in the future.

For this purpose, tests are carried out on the AUT with further load profiles on different brake pads. The results of these systematically performed measurements allow a step-by-step comparison of the wear results and friction coefficients as well as the surface topographies. This, in turn, makes it possible to establish a link between the results of the previously performed stationary wear procedures and real driving profile measurements, which leads to a better understanding of the wear behavior of brake pads and its influencing factors.