Abstract
To quantify the intensity of automobile brake creep groan, both experimental and analytical studies are innovatively conducted on the friction-induced vibration and noise of the disc brake in this paper. Experimentally, three factors, brake disc initial temperature, terrain, and gear position, are comprehensively contemplated to design six different test conditions, based on which a creep groan vehicle road test is conducted. Depending on the subjective evaluation and statistical analysis of the annoyance degree caused by vibration and noise in the starting and braking process under different test conditions, the influence of each factor on creep groan intensity is obtained. By processing the brake caliper and lower suspension arm acceleration and the interior sound pressure signals acquired in the test, the occurrence conditions and transient dynamic characteristics of creep groan are explored. One of the creep groan vibration modes is triggered by the rapid removal of the force exerted on the brake pedal when the vehicle starts at an extremely low speed, which presents intermittent impact and chaotic characteristics. The other vibration mode shows periodic harmonic characteristics, whose energy is concentrated on specific frequencies in the form of frequency doubling. This vibration mode occurs when continuously maintaining a low brake oil pressure or slowly releasing the force exerted on the brake pedal during the vehicle low-speed starting process, the velocity-displacement phase-plane portrait of which shows a stable limit cycle of stick-slip motion. Analytically, four vibration indexes and four noise indexes are established to evaluate the intensity of creep groan, the validity of which is verified by linear regression analysis. Finally, by combining all effective indexes, multiple linear regression analysis is performed, based on which the mapping relationship between the subjective evaluation of creep groan and effective indexes is obtained. The results demonstrate that the combination of the logarithmic vibration dose value of maximum brake caliper acceleration pulse and the loudness of interior noise can accurately describe the annoying degree caused by creep groan. The regression model can quantify and predict creep groan intensity of the test vehicle under different test conditions, which has guiding significance for engineering applications.
Highlights
NVH is a comprehensive issue that weighs the quality of automobile manufacturing and directly deteriorates the subjective impression of automobile users
Based on the experimental and theoretical analysis of automobile brake creep groan, the following conclusions can be drawn: (1) Experimentally, a vehicle road test of creep groan is conducted under six test conditions, and the influence of the initial temperature of brake discs, terrain, and gear position on creep groan severity is found
In a lower temperature range, the friction coefficient of brake discs decreases with the decrease in its temperature, which leads to poorer braking performance and severer brake friction-induced vibration and noise
Summary
NVH (noise, vibration, and harshness) is a comprehensive issue that weighs the quality of automobile manufacturing and directly deteriorates the subjective impression of automobile users. Based on different test methods and purposes, creep groan tests that study brake friction-induced vibration and noise can be divided into vehicle road test [5,6,7,8,9,10], vehicle drum test [5, 6], brake inertia dynamometer test [11,12,13], and specially designed brake bench test [14,15,16]. E annoyance degree caused by vibration and noise under different conditions is subjectively evaluated by the experimenters, and the influence of each factor on creep groan intensity is obtained by using statistical methods for data processing and comparative analysis. Multiple regression analysis is performed based on all effective indexes and subjective scores, and the regression model that describes the mapping relationship between the subjective evaluation of creep groan and effective indexes is obtained. e score calculated by the regression model quantifies the intensity of the creep groan from the perspective of drivers’ subjective feelings
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