Study Into Mechanism Of Wheel Polygonalization Of Metro Vehicle

Wheel polygonalization exists in a wide range of railway vehicles extensively. It will increase the wheel/rail interaction force, bring about noise both inside and outside the vehicle and reduce the fatigue life of structure components in the vehicle and track, which can significantly have negative impact on the ride comfort, safety and economy of railway vehicles.However, there is no consensus about the forming mechanism of wheel polygonalization and no effective and universal solution of wheel polygonalization. The key approach for studying the evolution law of wheel polygonalization is to simulate wear process, which is difficult to achieve. The studies about wear simulation of wheel polygonalization is very rare in China,and abroad.Wear model for wheel polygonalization is established in this dissertation and systematic research of eight to nine order polygonalization problem existing in some domestic metro vehicle is performed by analyzing the characteristic of vehicle structure vibration and predicting the wear law of wheel polygonalization. This dissertation proposes that wheel polygonalization problem can be tackled from three aspects: adjusting operation speed,modifying suspension stiffness and modifying the process of wheel reprofiling. A new idea has been put forward, which make it clear that the breakthough point and research focus of wheel polygonalization problem.The main work and conclusions in dissertation are listed as follows:1. Vehicle dynamics model was established to analyze abnormal vibrations of vehicle after emergence of the eight-to-nine-order wheel polygonalization. Field test was also carried out to study wheel polygonalization. Both simulation results and field tests indicate that there will be abnormal vibrations when the vehicle speed is 40km/h. And further understanding is found that the excitation frequency 40Hz, casued by of eight to nine order polygon wheel at speed of 40km/h is close to the natural frequency(41.7Hz) of linear motor vertical vibration,which will induce the resonance of motor. It could explain the increase of wave depth of eight-to-nine-order wheel polygon deformation.2. Wear model for wheel polygonalization is established to achieve the predicting of the polygonal wear. Based on Archard model, wear power and index model, calculating model of wear depth on single contact patch is built to achieve calculating wheel circumferential wear depth. Compared with tread horizontal wear model, specific curve fit problem in the iteration in the wheel polygonalization wear simulation is found and corresponding mathematical solution is given out. The effects of step length of calculation, number of Fourier series expansion and judgement of refreshing wheel profile on the calculating results are investigated,and stability and calculation tolerance of simulation are analyzed. In addition, the calculating method of wheel polygonalization wear speed is presented.3. The development law of wheel circumferential wear with initial first to fourth order wheel polygon and mass eccentricity is calculated. The results indicate that without considering the elasticity of wheel and axle and the influence of track vibration, the depth of the initial wave depth of polygon will increase and the order of polygon shows the tendency to be twice of the initial order, which is common wear case of wheel polygonalization. And the fundamental reasons leading to the change of the order is Phase Difference between wear power of wheel, wheel/rail tangent contact force and wheel radius when wheel rotates a circle.4. The linear motor metro vehicle operates under the speed of 85km/h for the longest time, and the generating frequency of wheel fourth order polygon of this speed is 40Hz,which cause the resonance of linear motor. With the effect of resonance of the motor, wheel-rail friction power and wheel-rail normal force will vary in a specific regular pattern. The wear simulation indicates that the depth of polygon will increase rapidly and order will evolve to eighth and higher order polygon, which coincide with the actual situation happening in the operation.5. There are three factors which probably lead to the polygon wear of linear motor metro vehicle, which are operation speed, natural frequency of motor and initial fourth order polygon of wheel. Adjusting the operation speed and suspension parameters of motor can avoid the resonance under the operation, which is the key to deal with the wheel polygonalization of linear motor vehicle. Adjusting operation speed, modifying suspension stiffness and modifying the process of wheel reprofiling are applicable to wheel polygonalization problem occur on other types of vehicles.6. A new opinion is proposed that the wear process of wheel polygonalization can be divided into three phases, and wheel polygonalization problem can be studied by finding out the speed under which abnormal vibration occurs and the study for mechanism of wheel polygonalization should focus on the order of the initial wheel polygonalization.