Jinsong Zhou

Influences of car body vertical flexibility on ride quality of passenger railway vehicles

Abstract To study the influences of carbody vertical stiffness on vehicle ride quality, a vertical model of railway passenger vehicles, which includes the carbody flexible effects and all vertical rigid modes, is built. With the model and the covariance method, the requirements for the carbody bending frequency are researched. The results show that when the stiffness of a carbody decreases to certain frequencies there are significant vibrations in the carbody, although structural damping provided by a fully equipped carbody will help attenuate the vibration to some extent. A simple way to avoid resonant vibration is to increase the bending frequencies of a carbody: the higher the vehicle running speed, the higher carbody stiffness could be required. However, there are practical limitations to such an increase and the method used in this study can readily obtain the lowest bending frequency required by vehicle ride quality. Finally, the geometric filtering phenomenon and its influences on the carbody resonant flexural vibration are analysed. Results show that it is this phenomenon rather than the natural vibrations of bogie bounce that most strongly influences the resonant flexural vibration of a railway carbody.

On the resonant vibration of a flexible railway car body and its suppression with a dynamic vibration absorber

The geometric filtering phenomenon is first analyzed with a simplified vertical vehicle model. Analytical solutions obtained with this model show that geometric filtering phenomenon consists of ‘wheelbase filtering’ and ‘bogie spacing filtering’ effects. The wheelbase filtering effect occurs when there is neither car body bounce nor pitch response at certain track wavelengths, whereas the bogie spacing filtering effect occurs when there is a null in either the car body bounce or pitch response at particular track wavelengths. Then, the correlated frequency response function for railway vehicles is defined to assess the effect of geometric filtering upon the resonant frequencies of a flexible car body. It is found that if the car body’s first bending frequency coincides with the peak values of bounce acceleration transmissibility, that is, it is near the null pitch response frequencies, resonant vibration of the flexible car body will happen. Finally, to suppress the resonant vibration of the flexible car body, it is proposed to use a dynamic vibration absorber (DVA) suspended under the car body underframe. The DVA parameters are optimized according to car body bending frequency and the null pitch frequency. The optimal DVAs show very good performance and robustness in suppression of the car body resonant vibration.

Application of modal parameters on ride quality improvement of railway vehicles

In this paper, a synthesised performance analysis with modal parameters (SPAMP) method is proposed to solve vibration problems of railway vehicle. With the SPAMP method, relations between modal parameters, physical parameters and ride quality are built at first with a unified ‘track–vehicle–human’ model. Then they are used with experimentally identified modal parameters and response power spectral densities to find ways to improve ride quality. Using this method, the low-frequency vibration problem of a kind of speed-up vehicle in China is researched. It was found that low-frequency vibration of the vehicle is mainly caused by lower sway mode vibration, whose identified damping ratio is very low. So once excited, it cannot be effectively suppressed. With the help of relations built with a virtual prototype, the physical parameters of the bogie are changed, and then the low-frequency vibration problem is solved.

Vertical random vibration analysis of vehicle--track coupled system using Green's function method

A vertical vehicle–track coupled dynamic model, consisting of a high-speed train on a continuously supported rail, is established in the frequency-domain. The solution is obtained efficiently by use of the Greens function method, which can determine the vibration response over a wide range of frequency without any limitations due to modal truncation. Moreover, real track irregularity spectra can be used conveniently as input. The effect of the flexibility of both track and car body on the entire vehicle–track coupled dynamic response is investigated. A multi-body model of a vehicle with either rigid or flexible car body is defined running on three kinds of track: a rigid rail, a track stiffness model and a Timoshenko beam model. The results show that neglecting the track flexibility leads to an overestimation of both the contact force and the whole vehicle vibration response. The car body flexibility affects the ride quality of the vehicle and the coupling through the track and can be significant in certain frequency ranges. Finally, the effect of railpad and ballast stiffness on the vehicle–track coupled vibration is analysed, indicating that the stiffness of the railpad has an influence on the system in a higher frequency range than the ballast.

Influence of under-chassis-suspended equipment on high-speed EMU trains and the design of suspension parameters

A numerical method for the calculation of the frequencies of vibration of a car body on a high-speed electric multiple unit train with under-chassis-suspended equipment is proposed. In addition, the design of the parameters of the suspension system for the equipment is presented; it is based on the principles of mode matching, transmissibility matching, and consideration of the optimal vibration of both car body and equipment. It is shown that by tuning the suspension stiffness, the first vertical bending frequency of the car body displays a frequency-hopping phenomenon. The first vertical bending frequency of the car body can be enhanced by optimizing the suspension parameters, so as to suppress the vibrations of both the car body and the suspended equipment.

Analysis of Dynamic Stiffness Effect of Primary Suspension Helical Springs on Railway Vehicle Vibration

Helical springs within the primary suspension are critical components for isolating the whole vehicle system from vibration generated at the wheel/rail contact. As train speeds increase, the frequency region of excitation becomes larger, and a simplified static stiffness can no longer represent the real stiffness property in a vehicle dynamic model. Coil springs in particular exhibit strong internal resonances, which lead to high vibration amplitudes within the spring itself as well as degradation of the vibration isolation. In this paper, the dynamic stiffness matrix method is used to determine the dynamic stiffness of a helical spring from a vehicle primary suspension. Results are confirmed with a finite element analysis. Then the spring dynamic stiffness is included within a vehicle-track coupled dynamic model of a high speed train and the effect of the dynamic stiffening of the spring on the vehicle vibration is investigated. It is shown that, for frequencies above about 50 Hz, the dynamic stiffness of the helical spring changes sharply. Due to this effect, the vibration transmissibility increases considerably which results in poor vibration isolation of the primary suspension. Introducing a rubber layer in series with the coil spring can attenuate this effect.

Analysis of modal frequency optimization of railway vehicle car body

High structural modal frequencies of car body are beneficial as they ensure better vibration control and enhance ride quality of railway vehicles. Modal sensitivity optimization and elastic suspension parameters used in the design of equipment beneath the chassis of the car body are proposed in order to improve the modal frequencies of car bodies under service conditions. Modal sensitivity optimization is based on sensitivity analysis theory which considers the thickness of the body frame at various positions as variables in order to achieve optimization. Equipment suspension design analyzes the influence of suspension parameters on the modal frequencies of the car body through the use of an equipment-car body coupled model. Results indicate that both methods can effectively improve the modal parameters of the car body. Modal sensitivity optimization increases vertical bending frequency from 9.70 to 10.60 Hz, while optimization of elastic suspension parameters increases the vertical bending frequency to 10.51 Hz. The suspension design can be used without alteration to the structure of the car body while ensuring better ride quality.

Boundary conditions of active steering control of independent rotating wheelset based on hub motor and wheel rotating speed difference feedback

ABSTRACT The source of torque ripple in a permanent-magnet synchronous motor was analysed. Based on the feedback of the rotating speed difference between the left and right wheels, the error value of torque ripple in an in-wheel motor was calculated. Next, a simulation model of active steering control of an independently rotating wheel (IRW) in an in-wheel motor was developed to investigate effects of torque ripple. The relationship between the accuracy of active steering control of an IRW in an in-wheel motor and wheel/rail profile was derived, and then the boundary conditions of active steering control were obtained. Finally, a method was proposed to improve the active steering control of an IRW by optimising the tread.

Study on Vibration Reduction Design of Suspended Equipment of High Speed Railway Vehicles

The design methods of the under-chassis equipment of a high speed railway vehicle based on dynamic vibration absorber (DVA) theory and vibration isolation theory are proposed, respectively. A detailed rigid-flexible coupled dynamic model of a high speed railway vehicle which includes car body flexibility and the excitation of the suspended equipment is established. The vibrations of the car body and the suspension equipment with the proposed design methods are studied. Results show that the elastic vibration of the car body can be decreased effectively by mounting the under-chassis equipment with elastic suspension. Comparing with vibration isolation theory, the method based on DVA theory is more effective for suppressing the car body flexible vibration, but it will increase the vibration of the equipment to a certain extent. The method based on vibration isolation theory can reduce the vibration of both the car body and the equipment at the same time. Therefore, the design method should be selected appropriately according to the specific requirement.

Enhancing the Resistance to Derailment and Side-Wear for a Tramway Vehicle with Independently Rotating Wheels

Focusing on severe wheel flange-wear/rail side-wear and on a series of derailments of tramway vehicles with independently rotating wheels, an investigation has been carried out by comparing against a solid wheelset. Efforts have been made on both aspects of vehicle and track design. Significant reduction of flange-wear has been achieved. The possible causes of derailments have been proposed.