Forced Steering of Rail Vehicles: Stability and Curving Mechanics

SUMMARY

A forced steering rail vehicle employs linkages between.the carbody and wheelsets to force a more radial wheelset alignment. It is shown that the curve negotiation capability of forced steering trucks is significantly improved over conventional and self steering radial trucks. Parametric curves are presented showing angle-of-attack and lateral flange force as a function of steering gain parameters and truck bending stiffness. It is also shown that the forced steering concept can produce kinematic instability and severely reduced critical speeds for low conicities and creep coefficients. Analytic expressions are derived that illustrate how these kinematic instabilities can be avoided.     

载货汽车转向系统分析

阐述了载货汽午转向系统运动学特忭的计算方法和分析方法;研究了载货汽车原地转向阻力的主要组成及动力转向器的效率特性,给出了原地转向性能的计算分析方法。通过对4种动力转向系统匹配方案的分析表明,转向机构的传动比和动力转向器的效率对车辆原地转向性能具有重要影响。     

汽车转向传动与悬挂系统运动干涉优化

以某中型载货车为例,通过建立前悬挂一转向传动系统的仿真模型,应用ADAMS分析软件,对前悬挂和转向传动系统的运动学特性进行仿真分析,提出优化汽车转向传动系统与悬挂系统之间运动干涉量的方法,解决整车加载过程中方向盘偏转的问题。     

Kinematic and dynamic analysis of a heavy truck with individual front suspension

The main focus of this work is on the characteristics of a commercial vehicle with individual front suspension (IFS). Both kinematic and dynamic properties of the vehicle are investigated through simulations and analytical expressions. Moreover, employing the model of the tractor semitrailer combination, the study presents the results of comparison between the trucks with IFS and rigid front axle with respect to comfort and handling. This is done by analysing the responses of the vehicles to different road and steering inputs. The obtained results show enhanced comfort and steering feeling for the truck with IFS.     

基于ADAMS重型汽车双前桥转向系统动力学仿真

随着市场的发展,双前桥转向汽车在载货车中的比重越来越大,为了保证汽车的行驶安全性能,汽车在使用时各杆件不应过早破坏,在汽车设计时要对杆件的受力进行测试,使其在许用范围内。鉴于双转向汽车更为复杂的转向结构,并且受力也不容易测得,笔者考虑到多体动力学软件的优越性,利用ADAMS／view建立双前桥转向系动力学模型,分析了各个主要链接点空载满载状况下的受力。     

Steering and Dynamic Stability of Railway Vehicles

SUMMARY

For railway vehicles having coned wheels mounted on solid axles there is a conflict between dynamic stability and steering ability

It is shown that the stiffness and kinematic properties of all possible interwheelset connections are characterised by two properties describing the distortional characteristics of the vehicle in plan. Within this framework, the various possibilities for steered wheelsets are considered, and several past and current proposals are reviewed. Using the linear approach to dynamic stabibty and curve negotation the performance of existing and newly proposed configurations is discussed

For any symmetric, two-axle vehicle it is shown that for perfect steering on a curve there should be zero bending stiffness between the wheelsets. It is further shown that if the bending stiffness is zero, the vehicle lacks dynamic stability as the critical speed of instability, is zero. In this case, the vehicle undergoes a steering oscillation which occurs at the kinematic frequency of a single wheelset and which is a motion in which pure rolling occurs

Similar results are obtained with vehicles with three or more axles if adjacent axles are connected by shear structures. However, it is shown that it is possible to satisfy both the requirements of perfect steering and a non-zero critical speed if the vehicle has zero bending stiffness and if, in addition to adjacent wheelsets being connected in shear, at least one pair of non-adjacent axles are connected by a shear structure.     

Steering and Dynamic Stability of Railway Vehicles

For railway vehicles having coned wheels mounted on solid axles there is a conflict between dynamic stability and steering ability

It is shown that the stiffness and kinematic properties of all possible interwheelset connections are characterised by two properties describing the distortional characteristics of the vehicle in plan. Within this framework, the various possibilities for steered wheelsets are considered, and several past and current proposals are reviewed. Using the linear approach to dynamic stabibty and curve negotation the performance of existing and newly proposed configurations is discussed

For any symmetric, two-axle vehicle it is shown that for perfect steering on a curve there should be zero bending stiffness between the wheelsets. It is further shown that if the bending stiffness is zero, the vehicle lacks dynamic stability as the critical speed of instability, is zero. In this case, the vehicle undergoes a steering oscillation which occurs at the kinematic frequency of a single wheelset and which is a motion in which pure rolling occurs

Similar results are obtained with vehicles with three or more axles if adjacent axles are connected by shear structures. However, it is shown that it is possible to satisfy both the requirements of perfect steering and a non-zero critical speed if the vehicle has zero bending stiffness and if, in addition to adjacent wheelsets being connected in shear, at least one pair of non-adjacent axles are connected by a shear structure.     

High Speed Stability and Curving Performance of Longitudinally Unsymmetric Trucks with Semi-active Control

The possibility of improving both the dynamic stability and curving performance of railway trucks through the use of semi-active control is discussed. According to the direction of vehicle motion, the truck parameters are switched in a longitudinally asymmetric manner. Using a method of evaluation proposed here, the stability of trucks having the same steering ability was examined using linear models. A truck equipped with independently rotating wheels on the trailing axle and with unsymmetric primary suspension has the best performance. A realistic method of achieving this is proposed: using harder primary longitudinal stiffness on the trailing axle and using a primary yaw damper only on the leading, allows bidirectional operation by changing the damping force.     

Active Steering of a Rail Vehicle with Two-Axle Bogies Based on Wheelset Motion

Summary This paper deals with a basic study on the actively steered rail vehicle with two-axle bogie trucks, which employs a control law based on the self-steering ability of wheelset. However, this control law not only helps the steering performance, but also tends to lower the running stability. Two methods are proposed to improve the stability. The first method is to add a feedback of wheelset lateral velocity, the second one is to give some time lag to the control force, and both are proved to be affective. Here, the latter is more practical method and the delay of control due to the time lag does not deteriorate the steering performance.     

Active Steering of a Rail Vehicle with Two-Axle Bogies Based on Wheelset Motion

Summary This paper deals with a basic study on the actively steered rail vehicle with two-axle bogie trucks, which employs a control law based on the self-steering ability of wheelset. However, this control law not only helps the steering performance, but also tends to lower the running stability. Two methods are proposed to improve the stability. The first method is to add a feedback of wheelset lateral velocity, the second one is to give some time lag to the control force, and both are proved to be affective. Here, the latter is more practical method and the delay of control due to the time lag does not deteriorate the steering performance.     

Theory and experimental research on six-track steering vehicles

The structural characteristics and steering behaviour of a six-track vehicle are described in this paper. Kinematic analysis for skid steering of a six-track vehicle under steady-state conditions on firm ground is conducted, with the relationship between thrust force and speed instantaneous centre of the track–terrain interface taken into consideration. A mechanical model for steady steering of a six-track vehicle is also presented based on the kinematic analysis. In this model, the steering inaccuracy and efficiency are defined to evaluate steering performance. The steering performance of a six-track vehicle is numerically simulated to analyse the effect of the structural parameters and deflection angles on tracks. A virtual prototype model is established based on the multi-body dynamics software RecurDyn for steering simulation and the findings coincide well with theoretical results. The theory and the virtual prototype simulations presented are verified by a power test of a bucket-wheel excavator. The method for analysing the steering performance of a six-track vehicle proposed in this paper provides a basis for designing a six-track vehicle.     

矿用汽车转向机构的最优化设计

本文以矿用汽车为研究对象，对立了整体车轴和非整体车轴的转向机构的数学模型，并结合最优化理论偏制了转向机构的最优化设计软件，计算实例表明该软件具有较强的实用性。     

Advanced emergency braking under split friction conditions and the influence of a destabilising steering wheel torque

The steering system in most heavy trucks is such that it causes a destabilising steering wheel torque when braking on split friction, that is, different friction levels on the two sides of the vehicle. Moreover, advanced emergency braking systems are now mandatory in most heavy trucks, making vehicle-induced split friction braking possible. This imposes higher demands on understanding how the destabilising steering wheel torque affects the driver, which is the focus here. Firstly, an experiment has been carried out involving 24 subjects all driving a truck where automatic split friction braking was emulated. Secondly, an existing driver–vehicle model has been adapted and implemented to improve understanding of the observed outcome. A common conclusion drawn, after analysing results, is that the destabilising steering wheel torque only has a small effect on the motion of the vehicle. The underlying reason is a relatively slow ramp up of the disturbance in comparison to the observed cognitive delay amongst subjects; also the magnitude is low and initially suppressed by passive driver properties.     

Analysis of Influence of Design Parameters on Steered Wheels Shimmy of Heavy Vehicles

In choosing the steering system parameters the tendency is towards the minimization of kinematic errors that appear during turning. For that developed procedures exist that take into account also the influence of kinematic of the suspension system on kinematic parameters of vehicle turning. Besides that, maintenance tests have shown, that increased deflections of the suspension system lead to increased wear of tires of steered wheels. In this paper, a method is developed for minimization of steered wheel shimmy and its wear also during the straight-line drive of heavy vehicles. The procedure can also be used in the phase of designing the heavy vehicles.     

The Definition of the Tires Limit of Admissible Nonuniformity by Using the Vehicle Vibratory Model

Purpose of this article was to especially emphasize the contribution of tires nonuniformity radial and lateral force variation to vehicles vibrations, within developed nonlinear dynamic model of a vehicle. The tire nonuniformity force variations are introduced in simulations processes by radial and lateral dynamic forces in the area of wheels-road contact. The limits of admissible Peak - to - Peak radial and lateral force variation and Peak - to - Peak first harmonic radial and lateral force variation nonuniformity were defined by using a vehicle vibratory model. The tire nonuniformity parameters were defined from the aspect of vertical seat cushion and the steering wheel rim vibrations using the developed optimization program and the Pentium 90 MHz computer.     

Minimizing the Path Radius of Curvature for Collision Avoidance

Purpose of this article was to especially emphasize the contribution of tires nonuniformity radial and lateral force variation to vehicles vibrations, within developed nonlinear dynamic model of a vehicle. The tire nonuniformity force variations are introduced in simulations processes by radial and lateral dynamic forces in the area of wheels-road contact. The limits of admissible Peak - to - Peak radial and lateral force variation and Peak - to - Peak first harmonic radial and lateral force variation nonuniformity were defined by using a vehicle vibratory model. The tire nonuniformity parameters were defined from the aspect of vertical seat cushion and the steering wheel rim vibrations using the developed optimization program and the Pentium 90 MHz computer.     

Analysis of Influence of Design Parameters on Steered Wheels Shimmy of Heavy Vehicles

SUMMARY

In choosing the steering system parameters the tendency is towards the minimization of kinematic errors that appear during turning. For that developed procedures exist that take into account also the influence of kinematic of the suspension system on kinematic parameters of vehicle turning. Besides that, maintenance tests have shown, that increased deflections of the suspension system lead to increased wear of tires of steered wheels. In this paper, a method is developed for minimization of steered wheel shimmy and its wear also during the straight-line drive of heavy vehicles. The procedure can also be used in the phase of designing the heavy vehicles.     

A Qualitative Analysis of the Dynamics of Self-Steering Locomotive Trucks

The primary purpose of this study is to provide a qualitative analysis of the dynamics of the self-steering trucks that are commonly used for freight locomotives – namely, EMD's Radial Truck and GE's Steerable Truck – on improving curving performance and increasing adhesion in curves. Although there exists a number of anecdotal statements on the ability of steerable trucks to reduce curving forces and increase adhesion in curves, to the best of our knowledge, there exists no study that provides a qualitative or quantitative analysis of these features of steerable trucks. Two aspects of locomotive trucks are essential for their ability to deliver small curving forces and high adhesion in curves. First, the ability to allow the axles to yaw sufficiently relative to the truck frames, such that they can hold a small angle of attack with the rail. Second, providing sufficiently large longitudinal stiffness between the end axles and the axles and truck frame, to accommodate high adhesions. An equivalent stiffness analysis is used to show that the two steerable trucks that are considered for this study are far superior to conventional, three-axle, straight trucks in providing both a smaller angle of attack and a higher longitudinal stiffness for better curving and adhesion characteristics. The qualitative analysis of this study agrees with the experience the railroads have had with their self-steering trucks. The findings of this study indicate that self-steering trucks can result in lower lateral forces, accommodate tighter curves, and deliver higher adhesion in curves; without lowering the critical hunting speed of the locomotive. The results further show that the steering mechanism stiffness can have a large effect on the lateral, longitudinal, and yaw stiffness between the end axles; therefore, significantly lowering curving forces, and increasing adhesion and critical hunting speed of the truck.     

A Qualitative Analysis of the Dynamics of Self-Steering Locomotive Trucks

The primary purpose of this study is to provide a qualitative analysis of the dynamics of the self-steering trucks that are commonly used for freight locomotives - namely, EMD's Radial Truck and GE's Steerable Truck - on improving curving performance and increasing adhesion in curves. Although there exists a number of anecdotal statements on the ability of steerable trucks to reduce curving forces and increase adhesion in curves, to the best of our knowledge, there exists no study that provides a qualitative or quantitative analysis of these features of steerable trucks. Two aspects of locomotive trucks are essential for their ability to deliver small curving forces and high adhesion in curves. First, the ability to allow the axles to yaw sufficiently relative to the truck frames, such that they can hold a small angle of attack with the rail. Second, providing sufficiently large longitudinal stiffness between the end axles and the axles and truck frame, to accommodate high adhesions. An equivalent stiffness analysis is used to show that the two steerable trucks that are considered for this study are far superior to conventional, three-axle, straight trucks in providing both a smaller angle of attack and a higher longitudinal stiffness for better curving and adhesion characteristics. The qualitative analysis of this study agrees with the experience the railroads have had with their self-steering trucks. The findings of this study indicate that self-steering trucks can result in lower lateral forces, accommodate tighter curves, and deliver higher adhesion in curves; without lowering the critical hunting speed of the locomotive. The results further show that the steering mechanism stiffness can have a large effect on the lateral, longitudinal, and yaw stiffness between the end axles; therefore, significantly lowering curving forces, and increasing adhesion and critical hunting speed of the truck.