Effect Of Structure And Configuration Of Brake Friction Blocks Of High-speed Train On Braking Tribological Behavior

Traditional brake way of disc brake mainly relies on the friction between the brake pad and the brake disc to stop the train.The tribological behavior of the brake interface is a crucial aspect that determines the braking equality,which influences the safety,reliability and ride comfort of the high-speed train.The operation speed of the train can’t be promoted without a safe and reliable brake system.Nowadays,brake noise has become a prominent problem as the train speed is continuously increased.Therefore,it is important to obtain a deep knowledge about the tribological behavior of the brake interface,so as to find effective ways to improve the wear and friction noise properties.There is not a universal design standard for the brake pads of high-speed trains.The shape,number,and configuration of the friction blocks are diversity among different type of brake pads.These factors,however,can directly influence the tribology behavior at the brake interface.Up to now,few studies are reported to discuss the influence of the friction block structure and configuration on the tribological behavior of the brake interface.The influence mechanisms of the block structure and the block configuration on the brake interfacial tribological behavior is not clear.The friction braking of high speed train is often involved at low speed.Therefore,to provide a better design standard of the brake pad,this paper systematically studied the influence of the connection mode,structure as well as the configuration of the friction block on the tribological behavior of the brake interface at low speed using a high-speed train comprehensive performance test bench.The main innovative work and research contents as follows:(1)The interface contact characteristics,surface wear,heat distribution,vibration and noise performance were systematically studied and compared under the fixed connection mode and the floating connection mode.The results showed that the friction block connection mode can significantly affect the brake performance.Compared with the fixed connection mode,the floating connection mode results in a better contact state,as well as a better performance of the interface wear and the vibration and noise.The floating connection mode can well modify the interfacial contact state with its flexibility.With this connection mode,less high-frequency squeal is generated during the brake process,and the intensity of the friction-induced vibration is lowered.(2)By selecting unperforated friction block,one-hole block and three-hole block to conduct brake experiments,combined with finite element methods,the effect of the friction block structure on the brake interfacial wear behavior was discussed.The results show that the structure of the friction block has a great influence on the wear behavior of the brake interface,temperature distribution and the friction-induced vibration and noise.The wear debris generated in the brake process flows along the direction of friction and gravity.The hole structure on the friction block changes the flow of the wear debris on the brake interface,which can both collect and scatter the wear debris.The friction surface of the unperforated friction block was severely worn,on which lots of wear debris is observed.While less wear debris is found on the worn surfaces of the one-hole block and the three-hole block.The hole structure on the friction block can dissipate the heat generated at the brake interface,as a result,the surface temperature of the perforated block is much lower than that of the unperforated block.Since the pore structure can improve of the contact state of the interface and result in better tribological properties,thus the friction-induced vibration and noise performance is improved.(3)The tribological behavior of a brake pad composed of multiple friction blocks under different brake parameters is studied.the results suggest that the instability of the brake system and the brake squeal first increase and then decrease as the rotation speed of the brake disc increases.In addition,the brake loses its stability when the brake pressure gets larger.Unlike the case in which only one friction block is adopted,the unstable mode shape of the brake pad is very complicated.The vibration intensity,contact state and wear degree of friction blocks locating at different positions are different.The friction blocks locating on the inner ring and the outer ring bear most of the contact load due to the eccentric wear effect,which experience severe surface wear.(4)To investigate the effect of the friction block configuration on the brake squeal,three simplified brake pads with several friction blocks are designed to conduct brake test,combined with finite element analysis,the relationship between the friction-induced vibration and the contact pressure is revealed.Based on the discoveries,a full-scale finite element model of brake disc-pad-clamp on the high-speed train is established.The squeal tendency of two fullscale pad is analyzed through complex eigenvalue analysis.The results showed that the configuration of friction blocks on the brake pad has a significant impact on the stability of the brake system and the generation of the brake squeal.Modal coupling between the brake disc and the brake pad is one of the main reasons accounting for the brake squeal.The configuration of friction blocks on the brake pad affects the mass center and the structural stiffness of the brake pad,which in turn affects its natural frequency and vibration mode.Meanwhile,the configuration of friction blocks also affects the interfacial contact pressure distribution.It has been demonstrated that a uniform distribution of contact pressure contributes to stabilize a friction system.The contact properties can be improved by properly designing the block configuration.