The effects of wheelset driving system suspension parameters on the re-adhesion performance of locomotives

In this study, in order to examine the effects of a wheelset driving system suspension parameters on the re-adhesion performance of locomotives, the stick–slip vibration was analysed according to theoretical and simulation analysis. The decrease of the slip rate vibration amplitude improved the stability of the stick–slip vibration and the re-adhesion performance of locomotives. Increasing the longitudinal guide stiffness of the wheelset and the motor suspension stiffness were proposed as effective measures to improve the re-adhesion performance of locomotives. These results showed that the dynamic slip rate was inversely proportional to the series result of the square root of the longitudinal guide and motor suspension stiffness. The larger the motor suspension stiffness was, the smaller the required longitudinal guidance stiffness was at the same re-adhesion time once the wheel slip occurred, and vice versa. The simulation results proved that the re-adhesion time of the locomotive was approximately proportional to amplitude of the dynamic slip rate. When the stick–slip vibration occurred, the rotary and the longitudinal vibrations of the wheelset were coupled, which was confirmed by train's field tests.     

Experimental investigation into the mechanism of the polygonal wear of electric locomotive wheels

Experiments were conducted at field sites to investigate the mechanism of the polygonal wear of electric locomotive wheels. The polygonal wear rule of electric locomotive wheels was obtained. Moreover, two on-track tests have been carried out to investigate the vibration characteristics of the electric locomotive's key components. The measurement results of wheels out-of-round show that most electric locomotive wheels exhibit polygonal wear. The main centre wavelength in the 1/3 octave bands is 200?mm and/or 160?mm. The test results of vibration characteristics indicate that the dominating frequency of the vertical acceleration measured on the axle box is approximately equal to the passing frequency of a polygonal wheel, and does not vary with the locomotive speed during the acceleration course. The wheelset modal analysis using the finite element method (FEM) indicates that the first bending resonant frequency of the wheelset is quite close to the main vibration frequency of the axle box. The FEM results are verified by the experimental modal analysis of the wheelset. Moreover, different plans were designed to verify whether the braking system and the locomotive's adhesion control have significant influence on the wheel polygon or not. The test results indicate that they are not responsible for the initiation of the wheel polygon. The first bending resonance of the wheelset is easy to be excited in the locomotive operation and it is the root cause of wheel polygon with centre wavelength of 200?mm in the 1/3 octave bands.     

空间缆索自锚式悬索桥动力特性及刚度影响规律

空间缆索自锚式悬索桥的主缆直接锚固在加劲梁上,同时由于主缆的空间特性,与地锚式悬索桥及传统平面索相比,其动力性能存在很大的差异.针对青岛海湾大桥大沽河航道桥建立非线性空间有限元模型,对其动力特性及结构刚度影响规律进行了分析.结果表明,该桥振型基本合理,具有密布的频谱;作为自锚式悬索桥其整体刚度较低,固有周期较长;单柱式桥塔的横向刚度较弱,横向振动出现较早;另外,由于缆索横向间距较小,刚度较小,前10阶振型中有5阶索振.各振型受结构刚度的影响不同,主缆刚度主要影响悬索桥的1阶竖弯及扭转,加劲梁竖向刚度对加劲梁1阶竖弯及加劲梁扭转振型影响较大,横向刚度主要影响悬索桥的加劲梁横向振型,扭转刚度主要影响悬索桥的1阶扭转振型;主塔纵向刚度主要影响悬索桥的纵飘振型;横向刚度主要影响索塔的1阶横向振型.     

Research into the problem of wheel tread spalling caused by wheelset longitudinal vibration

This study mainly focuses on the mechanism of wheel tread spalling through wheelset longitudinal vibration that has been often neglected. Analysis of two actual cases of the wheel tread spalling problem leads to the conclusion that the wheel tread spalling is closely related to the wheelset longitudinal vibration in some locomotives, and many of these problems can be reasonably explained if the wheelset longitudinal vibration is considered. For better understanding of some abnormal wheel spalling problems, the formations of the wheelset longitudinal vibration and the wheel/rail contact parameters were analysed in the initial wheel tread spalling. With the preliminary analytical results, the wheelset longitudinal dynamic behaviour, the characteristics of wheel/rail contact and the mechanics in the condition of the wheelset longitudinal vibration were further studied quantitatively. The results showed that the wheelset longitudinal vibration changed not only the limit of these parameters and the position of principal stress, but also the direction of the principal stress on the surface of wheel/rail contact patch. It is likely that the significant stress changes provoke too much stress on the surface of wheel/rail contact patch, cause fatigue in wheel/rail contact patch and eventually lead to wheel tread spalling. The results of these studies suggest that the suppression of the wheelset longitudinal vibration extends wheel/rail life and the addition of a vertical damper with an ahead angle provides a possible solution to the wheel spalling problem.     

Locomotive dynamic performance under traction/braking conditions considering effect of gear transmissions

Traction or braking operations are usually applied to trains or locomotives for acceleration, speed adjustment, and stopping. During these operations, gear transmission equipment plays a very significant role in the delivery of traction or electrical braking power. Failures of the gear transmissions are likely to cause power loses and even threaten the operation safety of the train. Its dynamic performance is closely related to the normal operation and service safety of the entire train, especially under some emergency braking conditions. In this paper, a locomotive–track coupled vertical–longitudinal dynamics model is employed with considering the dynamic action from the gear transmissions. This dynamics model enables the detailed analysis and more practical simulation on the characteristics of power transmission path, namely motor–gear transmission–wheelset–longitudinal motion of locomotive, especially for traction or braking conditions. Multi-excitation sources, such as time-varying mesh stiffness and nonlinear wheel–rail contact excitations, are considered in this study. This dynamics model is then validated by comparing the simulated results with the experimental test results under braking conditions. The calculated results indicate that involvement of gear transmission could reveal the load reduction of the wheelset due to transmitted forces. Vibrations of the wheelset and the motor are dominated by variation of the gear dynamic mesh forces in the low speed range and by rail geometric irregularity in the higher speed range. Rail vertical geometric irregularity could also cause wheelset longitudinal vibrations, and do modulations to the gear dynamic mesh forces. Besides, the hauling weight has little effect on the locomotive vibrations and the dynamic mesh forces of the gear transmissions for both traction and braking conditions under the same running speed.     

车用发动机曲轴扭振与整车传动系的相互关系

为了使曲轴系统扭转振动计算能准确地反映出发动机装入载货车后扭振情况，应正建立曲轴系统扭转振动计算数学模型和力学模型，对ＣＡ１１５０ＰＫ２Ｌ２Ｔ型载货车伟动系统扭转振动进行当量系统的转化和计算，利用汽车传动系统扭振计算程度对ＣＡ１１５０ＰＫ２１２Ｔ型载货汽车传动系进行了扭转振动计算。     

Analytical extension of the effective axle characteristics concept for the development of a structured chassis design process

The lateral vehicle dynamics is defined by the effects of side forces at the front and rear axle. These forces are caused by the slip and camber angle at the individual tyres, which are results of the kinematics and compliances of the chassis. This paper extends the approach of the effective axle characteristics by Paceyka to the analytical expression of the axle cornering stiffness and the axle relaxation behaviour with the aim of the development of a chassis design process as it applies in the early design stage. The obtained expression is integrated into a single track model and validated against a full nonlinear two-track model. By this means of these analytical expressions for the axle cornering stiffness and the axle relaxation behaviour it is possible to directly calculate and analyse the effective slip angles for linear quasi-static and dynamic driving manoeuvres.     

板簧变形与制动振跳分析

操纵稳定性是汽车重要性能,车桥摆振严重恶化汽车操纵稳定性,制动振跳是车桥摆振的表现形式之一。文章通过理论与试验相结合的方式探索制动振跳的诱发因素,对可能影响制动振跳的悬架布置形式、铜板弹簧刚度、前后轴制动力及其分配、前后轮抱死时间差、前桥下沉量、悬架系统阻尼等因素进行全面分析,简述了其对制动振跳的影响。然后根据装配工艺性、行驶平顺性等约束条件进行综合考虑,得出解决问题的方案。     

Effect of vehicle vibration environment of high-speed train on dynamic performance of axle box bearing

In this study, we developed a comprehensive three-dimensional vehicle–track coupled dynamics model considering the traction drive system and axle box bearing. In this model, dynamic interactions between the axle box bearing and other components, such as the wheelset and bogie frame, are considered based on a detailed analysis of the structural properties and working mechanism of the axle box bearing. A few complicated dynamic excitations, such as the time-varying mesh stiffness of gears, time-varying stiffness of bearing, bearing gaps and track irregularities, are considered. Then, the dynamic responses of the vehicle–track system are demonstrated via numerical simulations based on the established dynamics model. The results indicate that the traction drive system and track irregularities can significantly influence the dynamic interactions of the axle box bearing. The necessity of considering the excitation caused by gear meshing and track irregularities when assessing the dynamic performance of the axle box bearing is demonstrated.     

Ride dynamic evaluations and design optimisation of a torsio-elastic off-road vehicle suspension

The ride dynamic characteristics of a novel torsio-elastic suspension for off-road vehicle applications are investigated through field measurements and simulations. A prototype suspension was realised and integrated within the rear axle of a forestry skidder for field evaluations. Field measurements were performed on forestry terrains at a constant forward speed of 5 km/h under the loaded and unloaded conditions, and the ride responses were acquired in terms of accelerations along the vertical, lateral, roll, longitudinal and pitch axes. The measurements were also performed on a conventional skidder to investigate the relative ride performance potentials of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in magnitudes of transmitted vibration to the operator seat. Compared with the unsuspended vehicle, the prototype suspended vehicle resulted in nearly 35%, 43% and 57% reductions in the frequency-weighted rms accelerations along the x-, y- and z-axis, respectively. A 13-degree-of-freedom ride dynamic model of the vehicle with rear-axle torsio-elastic suspension was subsequently derived and validated in order to study the sensitivity of the ride responses to suspension parameters. Optimal suspension parameters were identified using the Pareto technique based on the genetic algorithm to obtain minimal un-weighted and frequency-weighted rms acceleration responses. The optimal solutions resulted in further reduction in the pitch acceleration in the order of 20%, while the reductions in roll and vertical accelerations ranged from 3.5 to 6%.     

Shape optimization of a torsion beam axle for improving vehicle handling performance

In this study, shape optimization was conducted for a vehicle’s rear suspension torsion beam to improve its dynamic handling performance. To determine the design variables affecting the vehicle roll characteristics, a sensitivity analysis was conducted using the result of a Taguchi experiment with 6 factors in 8 runs. The upper and lower-flange lengths and web thickness of the torsion beam section, as well as the vertical height difference between the inner and outer of torsion beams, were determined as design variables through sensitivity analysis of the opposite wheel travel test for optimization of the torsion beam axle. The Box–Behnken experimental design with 4 factors and 27 runs was performed using the selected design variables and by performing opposite wheel travel analysis according to the experimental design, and the response surface functions of the roll stiffness, roll steer coefficient, roll center height, and mass of the torsion beam were generated. Using these response functions, shape optimization was conducted for the torsion beam of the rear suspension system. Dynamic performance analysis was performed by applying the optimized H-shaped torsion beam to the rear suspension of the vehicle dynamics model, and it was validated that the dynamic response performance of the optimized vehicle was improved.     

Dynamic responses of a high-speed railway car due to wheel polygonalisation

The polygonal wear around the wheel circumference could pose highly adverse influences on the wheel/rail interactions and thereby the performance of the vehicle system. In this study, the effects of wheel polygonalisation on the dynamic responses of a high-speed rail vehicle are investigated through development and simulations of a comprehensive coupled vehicle/track dynamic model. The model integrates flexible slab track, wheelsets and axle boxes subsystem models so as to account for elastic deformations caused by impact loads induced by the wheel polygonalisation. A field-test programme was undertaken to acquire the polygonal wear profile and axle box acceleration response of a high-speed train, and the data are used to demonstrate the validity of the coupled vehicle/track system model. Subsequently, the effects of wheel polygonalisation are evaluated in terms of wheel/rail impact forces, axle box vertical acceleration and dynamic stress developed in the axle considering different amplitudes and harmonic orders of the polygonal wear. The results suggest that the high-order wheel polygonalisation can give rise to high-frequency impact loads at the wheel/rail interface, and excite some of the vibration modes of the wheelset and the axle box leading to high-magnitude axle box acceleration and dynamic stress in the wheelset axle.     

A rail roughness growth model for a wheelset with non-steady,non-Hertzian contact

This paper presents a model simulating rail roughness growth in which the interaction of a wheelset with the track is considered. The aim is to investigate any possible mechanism for roughness growth due to the coupling between the vertical dynamics, the torsional vibration across the axle of the wheelset and the non-steady contact mechanics. The time-domain simulations are carried out for a driven wheelset on tangent track. Both rigid and flexible are considered with parameter variations for moments of the wheelset, vehicle speeds and wavelengths of initial roughnesses. The 2D non-Hertzian and non-steady contact model used in simulations are based on influence coefficients obtained from a boundary element model. The nonlinear development of the rail roughnesses after millions of wheelset passages is also presented.     

An investigation into the mechanism of the polygonal wear of metro train wheels and its effect on the dynamic behaviour of a wheel/rail system

This paper presents a detailed investigation conducted into the mechanism of the polygonal wear of metro train wheels through extensive experiments conducted at the sites. The purpose of the experimental investigation is to determine from where the resonant frequency that causes the polygonal wear of the metro train wheels originates. The experiments include the model tests of a vehicle and its parts and the tracks, the dynamic behaviour test of the vehicle in operation and the observation test of the polygonal wear development of the wheels. The tracks tested include the viaducts and the tunnel tracks. The structure model tests show that the average passing frequency of a polygonal wheel is approximately close to the first bending resonant frequency of the wheelset that is found by the wheelset model test and verified by the finite element analysis of the wheelset. Also, the dynamic behaviour test of the vehicle in operation indicates the main frequencies of the vertical acceleration vibration of the axle boxes, which are dominant in the vertical acceleration vibration of the axle boxes and close to the passing frequency of a polygonal wheel, which shows that the first bending resonant frequency of the wheelset is very exciting in the wheelset operation. The observation test of the polygonal wear development of the wheels indicates an increase in the rate of the polygonal wear of the wheels after their re-profiling. This paper also describes the dynamic models used for the metro vehicle coupled with the ballasted track and the slab track to analyse the effect of the polygonal wear of the wheels on the wheel/rail normal forces.     

The stability and mechanical characteristics of heavy haul couplers with restoring bumpstop

To investigate the stability and mechanical characteristics of a type of heavy haul coupler with restoring bumpstop, the geometry and force states of couplers were analysed at different yaw angles and the longitudinal forces. The structural characteristics of this coupler were summarised. To aid in the investigation, a multi-body dynamics model with four heavy haul locomotives and three detailed couplers was established to simulate the process of emergency braking. In addition, the coupler yaw instability and lateral forces were tested in order to investigate the effect of relevant parameters on the locomotive's wheelset lateral forces. The results show that only when the bumpstop force exceeds half of the coupler longitudinal compression force, can the follower be rotated and the yaw angle of the coupler increase. The bumpstop preload is the most important stabilising factor. The coupler lateral force is constant when the coupler longitudinal force is smaller than the critical values of 2000, 1400 and 1150 kN at coupler free angles of 7°, 8° and 9°, respectively, for operation on straight track. The coupler free angle and the locomotive's lateral clearance of the secondary stopper are important in decreasing the wheelset lateral forces of the locomotive. It is advised that a smaller locomotive's secondary lateral suspension stiffness, a free clearance of 35 mm and an elastic clearance of 15 mm from the secondary lateral stopper be selected. If the coupler's free angle is less than the self-stabilising angle which is 5.5° for operation on straight track, the coupler is stable no matter how great the longitudinal force is. The wheelset lateral forces are allowed at the coupler longitudinal force of 2500 kN when the free angle is 6°. These studies establish meaningful improvements for the stability of couplers and match the heavy haul locomotive with its suspension parameters.     

Independent Suspension, Self Steered Axle, and 4WS for Busses

The dynamic behavior of commercial vehicles fitted with differentr types of suspension mechanisms and steering devices is investigated in this paper. Six vehicle models have been constructed: 2WS-SA is a standard two wheel steering bus with solid axles; 2WS-DW is a 2WSA vehicle with independent double wishbone suspension in front and rear axles; SSA-SA is a 2WS system with solid axles, the rear one being mounted on a self steered mechanism; SSA-DW is a vehicle with independent double wishbone suspension in the front axle, and a solid self steered rear axle; 4WS-SA has four wheel steering with solid axles; and 4WS-DW is a 4WS vehicle with independent double wishbone suspension in front and rear axles. The dynamic response of these models has been assessed in terms of lateral acceleration, yaw velocity, tire forces, tire force reserves, and slip angles. The expected advantages of a 4WS system (higher acceleration rates and lower slip angles) will be corroborated but, at the same time, it will be shown that they are obtained at the cost of lower force reserves. Self steered mechanisms produce smaller body slip angles, but it will be shown that they give rise to larger yaw velocity overshootings. The particular independent suspension analyzed does not show significant improvements with respect to the solid axle counterpart.     

电子差速系统轮胎附着特性模拟仿真研究

电子差速系统相对于传统的机械式差速器可以实现转矩的精准分配,根据轮胎的纵向运动特性以及侧向运动特性,结合轮胎滑移率让内外侧车轮在过弯时拥有足够的附着力,减小整车的横摆角速度,提高过弯稳定性。采用后轮双电机的驱动方案,驱动电机采用直接转矩控制的方法,由整车控制器将指定的计算转矩信号发送给电机控制器完成动力分配,所需转矩根据驾驶员的加速踏板及方向盘转角,运用阿克曼转向模型计算得到。     

Investigation of the effects of sleeper-passing impacts on the high-speed train

The sleeper-passing impact has always been considered negligible in normal conditions, while the experimental data obtained from a High-speed train in a cold weather expressed significant sleeper-passing impacts on the axle box, bogie frame and car body. Therefore, in this study, a vertical coupled vehicle/track dynamic model was developed to investigate the sleeper-passing impacts and its effects on the dynamic performance of the high-speed train. In the model, the dynamic model of vehicle is established with 10 degrees of freedom. The track model is formulated with two rails supported on the discrete supports through the finite element method. The contact forces between the wheel and rail are estimated using the non-linear Hertz contact theory. The parametric studies are conducted to analyse effects of both the vehicle speeds and the discrete support stiffness on the sleeper-passing impacts. The results show that the sleeper-passing impacts become extremely significant with the increased support stiffness of track, especially when the frequencies of sleeper-passing impacts approach to the resonance frequencies of wheel/track system. The damping of primary suspension can effectively lower the magnitude of impacts in the resonance speed ranges, but has little effect on other speed ranges. Finally, a more comprehensively coupled vehicle/track dynamic model integrating with a flexible wheel set is developed to discuss the sleeper-passing-induced flexible vibration of wheel set.     

Steady-State Curving Performance of Railway Freight Truck with Damper-Coupled Wheelsets

SUMMARY

The focus of this paper is on the steady-state curving behaviour of a freight car system with Damper Coupled Wheelset (DCW), where the wheels of conventional shape within an axle are coupled through a damper element. A freight truck model with two DCW and pseudo-car body on curved track is developed to study the influence of wheelset coupler parameter on the curving response and performance. The response is primarily evaluated in terms of wheelset tracking error and yaw misalignment in response to track curvature and cant deficiency. The curving performance is evaluated in terms of slip and flange boundaries. The results in general, indicate that when the value of coupler parameter is reduced, the wheelset response to track curvature increases, and results in flanging and wheel slip on a less tighter curve than those corresponding to conventional rigid axled wheelsets.     

Safety of a railway wheelset – derailment simulation with increasing lateral force

The motivation for this research is to make a comparison between dynamic results of a free railway wheelset derailment and safety limits. For this purpose, a numerical simulation of a wheelset derailment submitted to increasing lateral force is used to compare with the safety limit, using different criteria. A simplified wheelset model is used to simulate derailments with different adhesion conditions. The contact force components, including the longitudinal and spin effects, are identified in a steady-state condition on the verge of a derailment. The contact force ratios are used in a three-dimensional (3D) analytical formula to calculate the safety limits. Simulation results obtained with two contact methods were compared with the published results and the safety limit was identified with the two criteria. Results confirm Nadal’s conservative aspect and show that safety 3D analytical formula presents slightly higher safety limits for lower friction coefficients and smaller limits for high friction, in comparison with the simulation results with Fastsim.