SAE International On Similarities and Differences of Measurements on Inertia Dynamometer and Scale Testing Tribometer for Friction Coefficient Evaluation 2014-01-2523

Inertia dynamometers are commonly used to determine the friction coefficient of brake assemblies. Dynamometers are a well-established platform, allow testing under controlled conditions, exhibit a good correlation to many situations encountered in real driving, and are comparatively economical and less time-consuming than full vehicle test. On the other side of the spectrum is the use of scaled tribometer. These test systems make possible a test without the entire brake corner. This separation allows the investigation of the frictional-contact only (frictional boundary layer) speedily and independently of a given brake system or vehicle configuration. As the two test systems (inertia dynamometers and tribometers) may have different users with possibly different tasks, the question remains regarding how comparable the two systems are. These issues provide incentives to better define the fields of investigations, correlation, and applicability for the two systems. In order to provide further insights and learning on this topic, this paper focuses on the measurement of the friction coefficient and the wear behavior using inertia dynamometer and scaled pin-on-disc tribometer testing. Thus, friction coefficient levels and sensitivity are investigated on both systems when using a tribometer based test sequence (test with constant speed) as well as using a standard inertia dynamometer test procedure (with dynamic braking with in-stop deceleration). Different types of lining-materials (e.g. low-met or OES, and NAO or RE) are tested and compared. One major difference between the two systems is the energy input and thus the different temperature regimes. Therefore the influence of the initial temperature is a critical item the paper focuses on. Lastly, the paper presents potential areas for integration with the objective of improving the overall correlation between the two methods and the ability to use a scale tribometer to predict full inertia dynamometer results for friction and wear evaluations during the product life-cycle.