Research And Control Of Braking Judder In A Certain Vehicle Model

With the increasing maturity of the automobile industry,people are not satisfied with the most basic function of a car as transportation.When we choose a car,in addition to the consideration of power,appearance,safety,economy and other factors,we also take comfort as an important indicator to refer to.Automobile brake jitter is a problem in many cars.It is the vibration generated by the braking system,which is transmitted to the steering wheel,seat,brake pedal and other parts through the suspension-steering system,thus causing discomfort to the driver.Vibration may also be transmitted to the door,window,ceiling,instrument panel and other parts,causing abnormal sound and car passengers upset.When a model NVH is adjusted,the braking condition will be specially evaluated in a road test.Therefore,it is very necessary for NVH practitioners to study the mechanism and control method of brake vibration.In this paper,the braking vibration problem of a certain type of vehicle encountered in practical engineering is analyzed,and the source and path of vibration are respectively explored to find a solution to the braking jitter.Firstly,the vibration model is established to calculate how the brake pressure variation(BPV)is affected by the thickness variation of the brake disc(DTV),and analyze that the brake pressure variation will cause the brake torque variation(BTV).Through the structure analysis of the brake,the following conclusions are drawn: 1.Brake pressure variation causes the vibration of the brake pedal through the brake pipe.2.The braking torque is transmitted to the floor through the suspension to cause floor vibration.3.The braking torque is transmitted to the steering wheel through the suspension--steering system,causing the steering wheel to vibrate.In this paper,the dynamic model is used to analyze how to convert the torsional vibration of the brake disc into the local resonance of the suspension and steering system.The three-dimensional model of brake disc and friction block was established according to the real vehicle,and then the model was analyzed by thermo-mechanical coupling with ABAQUS.With the occurrence of the braking process,the corresponding temperature and internal stress of the brake disc are obtained.The heat dissipation effect of brake process structure,the specific heat capacity of brake disc material,the thermal expansion coefficient of brake disc material and other factors can all affect the thermal deformation,providing a certain direction for the improvement of the brake.It is suggested that the change of the air-cooling passage form of the brake disc can reduce the thermal deformation of the brake disc.In practice,we customize the same DTV internal ventilated disc brake and external ventilated disc brake.The change of the form of the air-cooled passage was obtained through the brake caliper acceleration of the two to effectively reduce the braking excitation force.The vibration acceleration of the steering wheel also decreases,indicating that the braking jitter is effectively suppressed.LMS was used for the road test and the suspension-steering system modal test.In the road test,the order characteristics of the excitation are analyzed and the braking excitation force generated by the cold and hot braking is compared.The local resonance of the suspension,the lower triangle control arm and the wheel is obtained during the modal test of the suspension steering system.By improving the stiffness of point A bushing of the lower triangular control arm,the braking jitter can be effectively improved.