Abstract:

The braking system is one of the key components of high-speed trains.It is also the important guarantee for the safe operation of a train.With the continuous increase of high-speed train operation speed and the increasingly complex operating environment,safety issues of the braking system have received widespread attention.During the braking process,relative friction is generated between the brake pads and brake discs,and the friction torque reduces the wheel rotational speed through the wheel-disc relative torsion,eventually generating the braking force between the wheel and the rail to achieve train braking.However,the disc-pad friction can lead to unstable vibration of the braking system,resulting in abnormal wear of brake pads,the fracture of brake clamps and the shortening of the service life of brake discs.In addition,the unstable vibration of brake discs and pads can exacerbate wheel-rail interactions,worsen wheel-rail contact relationships,and weaken the stability of train systems,then posing a threat to the safety of train services.Therefore,it is urgent to study the friction vibration mechanism and methods for suppressing unstable vibration of high-speed train braking systems.

Most of the braking system models in the existing researches only include braking devices while neglecting the adhesion relationship between the wheel and the rail when the train brakes.During train actual service,wheel-rail adhesion can lead to more complex vibration of high-speed train braking systems.Therefore,in order to more realistically reproduce the dynamic response of the braking system in the braking process,this paper establishes a three-degree-of-freedom nonlinear dynamic model of a high-speed train braking system considering Polach wheel-rail creep.The correctness of the model is also verified through train line tests.This model not only considers the wheel-disc relative torsion,but also adopts a wheel-rail creep model that can more accurately reflect the impact of wheel-rail interaction on the braking system.Based on this model,the nonlinear dynamic operation of the braking system is studied at relatively low speeds,and the difference between Polach wheel-rail creep model and the linear wheel-rail creep model is analyzed.Further,the effects of average creep rate and rail surface conditions on vibration of the braking system are explored.Finally,the interaction mechanism between the wheel-rail adhesion and the disc-block friction are revealed.

The results show that,compared with the linear wheel-rail creep model,Polach wheel-rail creep model,which is related to train running speeds,is more in line with the actual service conditions.With the increase of the average creep rate and the deterioration of the rail surface condition,the chaotic motion is more likely to occur and the vibration of the brake system is more complex.Based on the above analysis results,it can be concluded that the adhesion state of the wheel-rail is greatly influenced by the average creep rate and the rail surface condition.The average creep rate is the initial creep state during braking,which directly affects the magnitude of wheel-rail creep force.The rail surface conditions determine the upper limit of the wheel-rail adhesion coefficient,which directly affects the variation of the creep force.Then,the wheel-disc torsion is affected by the creep force,resulting in a change in the vibration form of the brake disc,ultimately affecting the nonlinear vibration of the braking system through disc-block friction.Similarly,the nonlinear friction of the disc-block interface affects the wheel-rail relative slip through wheel-disc torsion,ultimately affecting the wheel-rail adhesion state.