Experimental Modal Methodologies for Quantification of Body/Chassis Response to Brake Torque Variation

Brake torque variation is a source of objectionable NVH body/chassis response. Such input commonly results from brake disk thickness variation. The NVH dynamic characteristics of a vehicle can be assessed and quantified through experimental modal testing for determination of mode resonance frequency, damping property, and shape. Standard full vehicle modal testing typically utilizes a random input excitation into the vehicle frame or underbody structure. An alternative methodology was sought to quantify and predict body/chassis sensitivity to brake torque variation. This paper presents a review of experimental modal test methodologies investigated for the reproduction of vehicle response to brake torque variation in a static laboratory environment. Brake caliper adapter random and sine sweep excitation input as well as body sine sweep excitation in tandem with an intentionally locked brake will be detailed. The associated body/chassis response of each methodology will be examined through modal parameter extraction. Results will be compared to the body/chassis response measured through standard experimental modal test input. Potential methods for quantifying and predicting body/chassis sensitivity to brake torque variation will be examined.