The Influence Of Friction Block Shape And Size Of High-speed Train Brakes On Brake Noise Characteristics

High-speed railway develops rapidly,and plays an increasingly important role in the world economy development and communication.As a crucial part of the high-speed train,a train brake system has attracted much attention.The mechanical brake is a main type of train brakes.During successive braking applications,the friction between the rotating brake disc and the brake pads largely determines the braking capabilities of a train.Additionally,a braking generates the vibration of brake components and unwanted noise emitted from the contact interface.These affect the comfort of railway passengers and cause noise pollution.According to previous studies,it can be speculated that the geometrical parameters(such as shape and size)of the friction block of a train brake have a considerable influence on its brake noise.Therefore,it is of great significance to systematically study the influence mechanism of the geometrical parameters of the friction block on brake noise,to provide theoretical foundation for optimizing the design of friction blocks for brake vibration and noise suppression.In this study,the common circular,triangular,hexagonal friction blocks and so on are used to carry out the brake experiments on a customized small-scale brake dynamometer.The influence of the shape,installation direction,size and chamfering modification of friction blocks on brake noise characteristics are explored.At the same time,the interface wear characteristics after brake are compared,the interface contact pressure is simulated,and the interface friction arc length is calculated.The influence mechanism of the shape,installation direction,size and chamfering modification of friction block on the brake noise characteristics is preliminarily explored.It can provide basis for the shape and size design of low-noise friction block.The main conclusions are as follows:1.The contact pressures and wear characteristics on the interfaces of friction blocks with different shapes are different.Contact pressure of the hexagonal friction block is the largest.Correspondingly,surface wear of the hexagonal friction block is the most serious.So the hexagonal friction block excites the highest brake noise.The brake noise intensity of the circular friction block is in the middle level,and that of the triangular friction block is the lowest.Friction blocks of different shapes can form different contact states with the brake disc.It can lead to the change of the coupling mode of friction system.Finally,the frequency components of brake noises are different.2.The installation direction of the triangular friction block has a certain influence on brake noise characteristics.There is less wear debris on the surface of the triangular friction block with closed angle at the bottom,the block excites low-frequency flutter.The extensive wear debris on the surfaces of the other three triangular friction blocks increase the number of micro-convex bodies in real contact,thus the high-frequency squeal is exited.Contact pressure concentration occurs at the leading point of the triangular friction block with closed angle on the top,therefore its brake noises is higher.3.The installation direction of the hexagonal friction block has a great influence on brake noise characteristics.The leading point of the hexagonal friction block with closed angle on the top is the region of pressure concentration and severe wear.And squeal with high frequency and high intensity is excited.In the brake process,the contact tightness between the hexagonal friction block with the edge on the top and the brake disc varies obviously along friction radius.It is prone to low-frequency flutter.4.Among the friction blocks with three sizes,brake noise intensity of the medium and small circular friction blocks are much higher than that of the large circular friction block.The "irregularity" factors on the surface of the medium and small circular friction blocks are more obvious.Also,the friction arc lengths of the medium and small circular friction blocks are obviously longer within a wide friction radius range.As a result,the brake noise intensities of the medium and small circular friction blocks are significantly higher.5.The contact surface of the chamfered friction block can be divided into three areas according to the wear characteristics.The accumulation of wear debris can form the secondary contact platform in central area.It makes the contact center between the brake disc and the friction block move down,then the stress concentration degree at the leading point(leading edge)decreases.Consequently,the brake noise decreases after chamfering modification.Chamfering modification can also increase the non-linearity of the friction system.