Experimental Investigation of Low-Frequency Vibration Patterns in Automotive Disk Brake Systems: Utilization Study for Modal Simulation Methods

Increasing demands on automotive comfort as well as diminishing vehicle noise levels draw new attention towards low-frequency vibration and noise issues of disk brake systems such as creep groan and moan. In view of this problem, the experimental investigation of relevant phenomena is within the scope of this article. The related experiments concerning two different setups have been performed at a drum driven suspension and brake test rig. Both assemblies consisted of a front axle corner including all parts of the integrated brake system. In order to gain understanding of characteristic triggering mechanisms and fundamental subsystem interactions, and moreover, to verify the suitability of modal methods for simulative evaluations of creep groan or moan, specifically elaborated Operating Deflection Shape (ODS) techniques have been applied. Via analyses of four different creep groan emergences, global stick-slip cycles between disk and pads are revealed. For two dissimilar vibrations in the typical frequency range of moan, mechanisms rather associated with dynamic instabilities are identified. Based on measurement results and further theoretical considerations, the suitability of a disk brake Complex Eigenvalue Analysis (CEA), which is a linear modal simulation method designated to efficiently evaluate disk brake squeal noise, is verified with respect to the relevant friction-induced low-frequency phenomena. Even though the disk brake CEA is inappropriate to estimate a highly non-linear behavior such as involved in all four creep groan signatures, its application for accompanying damped natural oscillations as well as for both observed moan appearances is plausible. By investigation of characteristic pad vibration patterns and speeds belonging to the disk rotation, generic parameter spaces for the utilization of modal methods on harmonic low-frequency phenomena are deduced.