Brake Impedance Test Stand - Modal Testing of Brake Pads under Pressurized Condition Using 3D SLDV and a Scalable Automatic Modal Hammer

Brake squeal is an NVH issue experienced by brake systems and vehicle manufacturers for decades. This leads to customer dissatisfaction and the questioning of the quality of the brake system. Advanced testing tools, design modification, dynamometer testing, vehicle validation etc., are performed to study, analyze and eliminate this problem. But still it continues to exist nowadays. One of the most important reasons is the complexity of the brake pad having non-linear material properties. Therefore, it is imperative to understand the behavior of the brake pad in terms of its dynamic properties (eigenfrequencies, damping and mode shapes) under varying boundary conditions. Experimental Modal Analysis (EMA) is used to study the dynamic properties of any structure and is generally performed under free-free boundary conditions. An approach to study brake pads under pressure condition is a step towards reality, as brake pads squeal only during braking events. Therefore, the Brake Impedance Test machine (BIT) was developed. This work describes the development of the BIT to study brake pads under different piston compression loads, analyzing their results and proposing an approach to standardize the testing procedure. The brake pads are excited by a Scalable Automatic Modal hammer (SAM), with a precise controllable force level. The vibration response is measured contactless using a 3D Scanning Laser Doppler Vibrometer (3D SLDV). This research, under these conditions and advanced techniques, results in dynamic characteristics of brake pads closer to those in a real braking event. These results can be correlated with brake dynamometer data for further validation. The conclusions of these upcoming studies will lead to effective brake pad parameters for a robust brake design against squeal research.