Luo Shihui

The dynamic study of locomotives under saturated adhesion

In order to study the dynamic behaviours of locomotives under saturated adhesion, the stability and characteristics of stick–slip vibration are analysed using the concepts of mean and dynamic slip rates. The longitudinal vibration phenomenon of the wheelset when stick–slip occurs is put forward and its formation mechanism is made clear innovatively. The stick–slip vibration is a dynamic process between the stick and the slip states. The decreasing of mean and dynamic slip rates is conducive to its stability, which depends on the W/R adhesion damping. The torsion vibration of the driving system and the longitudinal vibration of the wheelset are coupled through the longitudinal tangential force when the wheelset alternates between the stick and the slip states. The longitudinal oscillation frequencies of the wheelset are integral multiples of the natural frequency of torsion vibration of the driving system. A train dynamic model integrated with an electromechanical and a control system is established to simulate the stick–slip vibration phenomenon under saturated adhesion to verify the theoretical analysis. The results show that increases of the longitudinal axle guidance stiffness and the motor suspension stiffness are beneficial to the stick–slip vibration stability and the locomotives traction ability. The optimised matching of the longitudinal axle guidance stiffness and the motor suspension stiffness are helpful to avoid longitudinal resonance when the stick–slip vibration occurs.

Influence of the orientation stiffness of tumbler journal box to the stability of high speed vehicles

The structure of tumbler journal box orientation mode was widely used in the high speed EMU, as it has the excellence of the stiffness in longitudinal, lateral and vertical direction can be set respectively. The longitudinal stiffness and lateral stiffness of the journal box was supplied by the stiffness of the elasticity node of tumbler. The stability of the high speed vehicle has a big relation with the stiffness of the elasticity node of tumbler. The dynamic model of the high speed vehicle was set up based on the analysis of the structure of the tumbler journal box in detail. The linear and nonlinear stability analysis of the model in which the parameter of the real vehicle was used was carried out first, the influence of the variable of the longitudinal stiffness and the lateral stiffness of the elasticity node of tumbler to the hunting stability of the high speed vehicle was researched. The stiffness of the elasticity node of tumbler especially the longitudinal stiffness has a big influence to the hunting speed of the high speed vehicle.

An integrated draft gear model with the consideration of wagon body structural characteristics

ABSTRACT With the increase of railway wagon axle load and the growth of marshalling quantity, the problem caused by impact and vibration of vehicles is increasingly serious, which leads to the damage of vehicle structures and the components. In order to improve the reliability of longitudinal connection model for vehicle impact tests, a new railway wagon longitudinal connection model was developed to simulate and analyse vehicle impact tests. The new model is based on characteristics of longitudinal force transmission for vehicles and parts. In this model, carbodies and bogies were simplified to a particle system that can vibrate in the longitudinal direction, which corresponded to a stiffness-damping vibration system. The model consists of three sub-models, that is, coupler and draft gear sub-model, centre plate sub-model and carbody structure sub-model. Compared with conventional draft gear models, the new model was proposed with geometrical and mechanical relations of friction draft gears considered and with behaviours of sticking, sliding and impact between centre plate and centre bowl added. Besides, virtual springs between discrete carbodies were built to describe the structural deformation of carbody. A computation program for longitudinal dynamics based on vehicle impact tests was accomplished to simulate. Comparisons and analyses regarding the train dynamics outputs and vehicle impact tests were conducted. Simulation results indicate that the new wagon longitudinal connection model can provide a practical application environment for wagons, and the outputs of vehicle impact tests agree with those of field tests. The new model can also be used to study on longitudinal vibrations of different vehicles, of carbody and bogie, and of carbody itself.

Influence of the journal box positioning method to the load of tumbler node

The damage of the tumbler node was one of the common phenomena of the damage of the tumbler journal box setting. Aimed to the easy damage problem of the tumbler node of the CW-2 style bogie, two positioning method of the tumbler journal box was compared, one is the tumbler journal box of the CW-2 bogie, the other is the tumbler journal box on the high speed motor car of CRH2. The position of the journal box spring has a big influence to the load of the tumbler node. The dynamic model of the high speed vehicles with the two different tumbler journal boxes were set up through the dynamic simulation soft SIMPACK. The simulation cases of high speed on straight line, brake condition and the condition of the horizon wind were carried to research load of the tumbler node. All the results of the three different cases were coincided with the theory analysis result. The tumbler node of the model which the CRH2 tumbler journal box was adopted has a big longitudinal and lateral force; the tumbler node of the model which the CW-2 tumbler journal box was adopted not only has a big longitudinal and lateral force, but also has a bigger vertical force. The simulation results shown that the tumbler node of the CW-2 bogie has a bigger and complex force in total, this is the just reason why the tumbler node more easy damaged than other tumbler journal box.

OUT-OF-ROUND WHEELS AND THE CORRELATION PROBLEM OF METRO VEHICLES

Spalling like scales of fish will emerge on the connection area between wheel tread and flange of one metro vehicle after it running a period of time on the track. The method of polish the track has not solved the phenomena yet. When wheel is out-of-round, the vertical vibration of the car-body is very big, and the tread must be cut to eliminate the phenomena of vertical vibration big of the car-body, but this method could not solve the problem indeed. These phenomena show that the secondary suspension of the vehicles has not damp function. Both the results of linear frequency analyses and the nonlinear analyses show that the too big stiffness of the traction bar which connected the car-body and the bogie in longitudinal direction has big relation with the vertical dynamic performance of the metro vehicle. From the point of view of the wheel-set longitudinal vibration find that the wheel-set resonance speed is in the usually running speed scope of the metro vehicle and this may be the reason of wheel tread easy splling and out-of-round. The stiffness of the traction bar was depressed by change the two ends to big rubber joints, so the longitudinal force affected by the traction bar is depressed notability, and the vertical dynamic performance of the metro vehicles is then be improved.