Squeal noise phenomenon in disc brakes is a complicated dyna mic challenge which brake manufacturers have confronted for decades. Car manufacturers around the world are facing warranty issues due to the squeal noise occurrence. Automotive engineers all over the world are working to reduce squeal noise occurrence to improve the comfort of the vehicle passenger, but there exists no general solution. The most prevalent technique apprehended by the brake manufactures is to simulate the braking conditions using a noise dynamometer. This is a well-established, expensive technique which is time-consuming. The objective of this paper is to understand the phenomenon of brake squeal, modal coupling and publish an analytical approach to predict a suitable damping material and thereby to optimize the dynamometer tests and time. The objective of a noise dynamometer test is to simulate the field braking conditions and bring out all possible noises of the brake system. This is the most prevalent technique apprehended by brake manufacturers all around the globe. Among the various perquisites of dynamometer testing over vehicle testing, the most influential factor is its feasibility to support acoustic/root cause analysis in dynamic conditions. There are two fundamental brake dynamometer designs. 1) Shaft-type dynamometer that drives the brake assembly from a shaft. 2) Roller dynamometer, a driven road roller is used to drive a tire that drives the brake assembly. Experimental modal analysis is carried on every brake component to obtain its natural frequency, energy level, damping ratio and mode shape. The temperature increases the stiffness of the component, thereby the resonance frequency tends to decrease. Compressing the pad increases its stiffness and thereby its resonance frequency. Compressibility being inversely proportional to stiffness has direct influence over the frequency response function of the brake components. Shim suppliers use generic structure to obtain the damping ratio at its resonance at every other degree. The data is interpolated and is presented over temperature and frequency with a fixed Z and color scale representing the damping ratio of the specimen at that specific frequency & temperature. The damping ratio is measured only at the resonance of the generic structure which misses out the majority of the resonance frequencies of the brake pad. Three shims were taken for study. The damping ratio measured is a reflection of the system’s damping and not merely of the shim. So, pad shim assembly is ran over critical temperature obtained from the dynamometer results and the damping ratio is captured at critical frequency and plotted for various shims. Pad shim assembly is assembled in the brake dynamometer and the damping ratio is captured at the various pressures and plotted for various shims. From the plotted graphs, optimal shim can be selected. Pad shim assembly is ran over a specific temperature in oven and damping ratio is measured, identifying the exact temperature of the assembly in oven is tedious process. When damping ratio is measured at specific pressure at dynamometer, the damping may get affected due to influence of other components. The damping ratio is measured at resonance peaks of the brake pad itself which addresses the frequency band of concern directly. The damping ratio is measured with actual system itself giving more accurate and relevant damping graph data. This helps us understand how the shim behaves with our brake system and thereby choose the ideal shim for the system. Damping ratio are measured at the critical temperatures where the noise occurrence is maximum. Damping ratio are measured at critical pressures in the dynamic loaded conditions. Squeal phenomenon occurs when two or more brake components having resonance close to each other with synchronizing mode shape starts to vibrate together creating a highly unstable coupled system. Damping ratio is measured at critical temperature and critical pressure obtained from the results of dynamometer test, so the results obtained from the process is effective. Selection of shims through dynamometer test is very time-consuming process, following the above-mentioned methodology can reduce the time. Following this analytical approach will optimize the dynamometer test.
Mr. Anand Ramamoorthy, General Manager -NVH, Brakes India Private Limited; Mr. Vasanth Kannan, Engineer-NVH, Brakes India Private Limited; Mr. Venkatesh Kitchanna, Deputy Manager- NVH, Brakes India Private Limited; Mr. Rakesh Sadhasivam, Engineer-NVH, Brakes India Private Limited