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For tribological investigations of automotive brakes, both full and reduced scale brake dynamometers are used. Full scale brake dynamometers test the entire brake system, including caliper, brake pad, brake disk, wheel suspension, etc. The AUT (automated universal tribotester) is a reduced scale brake dynamometer with a pin on disk test configuration. A brake pad specimen is used as the pin and a brake disk is used as the counter body. Compared to full scale brake dynamometers, the AUT encounters fewer influences from the test systems themselves. The AUT was developed at the Institute of Dynamics and Vibrations in Braunschweig. It can be used for high frequency analyses of the coefficient of friction, and investigations of the boundary layer between brake pad and disk, along with the associated NVH behaviors. A digital camera and two laser triangulation sensors are used for optical investigations of the brake pad and brake disk [1, 2]. The focus of this paper is the development of a new control feature of the AUT. The AUT employs a compactRIO from National Instruments as its measurement and control device. The velocity and position control loops are implemented in the compactRIO’s FPGA along with high frequency synchronous measurement data acquisition. Its real-time controller coordinates the measurement and the storage of measured data. The test device has three degrees of freedom: normal load, sliding speed, and temperature, all of which can be defined by the user for each brake application. New control strategies based on the friction force as a feedback parameter allow for the implementation of new features. In this paper, the realization of measurements with constant friction power throughout the friction procedure will be shown. This new degree of freedom in the friction measurements enables investigations to be carried out in which it is necessary to bring a specific energy in the friction process. In this paper, a p-controller on the real-time system calculates the required set point for the position control loop. The new feature is verified through a benchmark test [6]. Based on the control loop with the friction force as the feedback parameter, it is also possible to emulate in-stop brakes with virtual inertia. In this way, many other types of full scale brake dynamometers can be simulated. The long-term aim is the identification of the influence of test devices on the test results.

Development and Implementation of Constant Friction Power Control in a Reduced Scale Brake Dynamometer for Investigations of Automotive Brake Systems