Study On The Disc Brake Squeal Noise And The Improvement Of Noise Performance By Modifying The Characteristics Of Pad Surface

In recent years,disc brake has been widely used in braking link of many fields including transportation,industry,wind and nuclear power,oil field and so on because of its superior comprehensive performance.Especially with the rapid development of modern vehicle,such as automobile,high-speed rail and so on,the squeal noise problem is becoming more and more serious during its braking process.In addition,as the riding comfort of vehicles is continuously improved by people,brake squeal noise has become a prominent problem in vehicle NVH(noise,vibration and harshness)and got a great concern.However,due to its strong randomicity,complex mechanism,multidisciplinary and so on,brake squeal has been an unsolved problem in engineering and academia.Therefore,researching on the generating mechanism and influencing factors of brake squeal and farther exploring effective methods of suppressing brake squeal is indeed particularly urgent and significant.Experimental comparison test of friction noise was performed under different braking forces and contact states conditions to investigate their effect on brake squeal properties,wear characteristics and friction heat of surface,by using a new self-developed friction brake noise experimental set-up.The friction pair was created between the forged steel brake disc and copper-based powder metallurgy(P/M)pad.Based on the analysis results,a further exploringof the effective method to suppress the brake squeal was carried on.The contrast test was conducted after pad surface was modified by slotting and chamfering.And the finite element software ABAQUS was used to simulate the test to investigatethe influence of different surface modification on the instability of friction system.Meanwhile,analysis of unstable vibration characteristics of the chamfered pad system from the view of dynamic was carried out to investigate its mechanism of suppressing squeal noise.Accordingly,the main conclusions could be drawn as following:1.The friction system had more tendencies to generate more severe unstable vibration and a higher potential in generating higher squeal noise with the increase of braking force.Braking force had little effect on the frequency of squeal noise,but it did affect the energy of the dominant frequency.Moreover the larger braking force would induce the system to produce the multi order harmonic response,and the frequency components of squeal noise became more complicated.2.The friction system generated severe unstable vibration when the leading edge of pad was contacting the disc.The intensity and frequency of generating squeal was the highest,and the energy distribution was very uneven.The intensity and frequency of squeal noise of normal contacting was lower than that of leading edge contacting,and the energy distribution was more uniform.However,the stability of the friction system was good and almost no squeal was measured when the trailing edge of pad was contacting the disc.The stability of the system and the performance of squeal tended to be better when the contact stress region of pad surface was transferred from the leading edge to the trailing edge.3.Under the present experimental conditions and parameters,chamfering of different angles had different potential in suppressing and reducing squeal in the experimental test.Among them,the comprehensive effect of noise reduction of 15 degree chamfering modification was the best.Nevertheless,slotting modification showed no obvious effect on suppressing squeal.The chamfering modification of pad surface could change the distribution of contact stress and further affected the performance of brake squeal.4.ABAQUS was used to analyze and verify the noise reduction scheme of surface modification.The results showed that for chamfered pad,the time of generating unstable vibration and squeal was morehysteretic,and the tendency of unstable vibration became weaker.But the tendency of generating unstable vibration was stronger and the vibration might be more severe for slotted pad.5.A mathematical model of three degrees of freedom was established,based on the sliding friction state of brake pad/disc configuration,to investigate the effect of contact angleθ on system stability.The results indicated that the system generated more severe unstable vibration when the contact angle θ became larger,and further induced the generation of squeal.For chamfered pad,the contact angle θ of brake pad/disc was obviously reduced compared to the original condition and the stability of system was better,which could suppress squeal.