Automatic generation of the non-holonomic equations of motion for vehicle stability analysis

The mathematical analysis of vehicle stability has been utilised as an important tool in the design, development, and evaluation of vehicle architectures and stability controls. This paper presents a novel method for automatic generation of the linearised equations of motion for mechanical systems that is well suited to vehicle stability analysis. Unlike conventional methods for generating linearised equations of motion in standard linear second order form, the proposed method allows for the analysis of systems with non-holonomic constraints. In the proposed method, the algebraic constraint equations are eliminated after linearisation and reduction to first order. The described method has been successfully applied to an assortment of classic dynamic problems of varying complexity including the classic rolling coin, the planar truck–trailer, and the bicycle, as well as in more recent problems such as a rotor–stator and a benchmark road vehicle with suspension. This method has also been applied in the design and analysis of a novel three-wheeled narrow tilting vehicle with zero roll-stiffness. An application for determining passively stable configurations using the proposed method together with a genetic search algorithm is detailed. The proposed method and software implementation has been shown to be robust and provides invaluable conceptual insight into the stability of vehicles and mechanical systems.     

Loss of stability of a railway wheel-set,subcritical or supercritical

Most researches on railway vehicle stability analysis are focused on the codimension 1 (for short, codim 1) bifurcations like subcritical and supercritical Hopf bifurcation. The analysis of codim 1 bifurcation can be completed based on one bifurcation parameter. However, two bifurcation parameters should be considered to give a general view of the motion of the system when it undergoes a degenerate Hopf bifurcation. This kind of bifurcation named the generalised Hopf bifurcation belongs to the codimension 2 (for short, codim 2) bifurcations where two bifurcation parameters need to be taken into consideration. In this paper, we give a numerical analysis of the codim 2 bifurcations of a nonlinear railway wheel-set with the QR algorithm to calculate the eigenvalues of the linearised system incorporating the Golden Cut method and the shooting method to calculate the limit cycles around the Hopf bifurcation points. Here, we found the existence of a generalised Hopf bifurcation where a subcritical Hopf bifurcation turns into a supercritical one with the increase of the bifurcation parameters, which belong to the codim 2 bifurcations, in a nonlinear railway wheel-set model. Only the nonlinear wheel/rail interactive relationship has been taken into consideration in the lateral model that is formulated in this paper. The motion of the wheel-set has been investigated when the bifurcation parameters are perturbed in the neighbourhood of their critical parameters, and the influences of different parameters on critical values of the bifurcation parameters are also given. From the results, it can be seen that the bifurcation types of the wheel-set will change with a variation of the bifurcation parameters in the neighbourhood of their critical values.     

Driving segment simulation for determination of the most effective driving features for HEV intelligent control

This paper presents a methodological approach for determination of the most effective driving features for hybrid electric vehicle intelligent control, using the driving segment simulation. In this approach, driving data gathering is first performed in real traffic conditions using Advanced Vehicle Locator systems. The vehicle's speed time series are then divided into small segments. Subsequently, 19 driving features are defined for each driving segment, and the influence of the driving features on the vehicle's fuel consumption (FC) and exhaust emissions is investigated, using driving the driving segment simulation. The simulation approach is also verified by experimental test. Finally, the driving features are ranked by a new approach based on the definition of an effectiveness index and a correlation analysis. The results demonstrate that the velocity-dependent driving features such as ‘energy’, ‘mean of velocity’, ‘displacement’ and ‘maximum velocity’ are more effective on vehicle's FC and exhaust emissions. However, because of high dependency between these features, this study suggests independent driving features among the most effective driving features.     

Design of safety-oriented control allocation strategies for overactuated electric vehicles

The new vehicle platforms for electric vehicles (EVs) that are becoming available are characterised by actuator redundancy, which makes it possible to jointly optimise different aspects of the vehicle motion. To do this, high-level control objectives are first specified and solved with appropriate control strategies. Then, the resulting virtual control action must be translated into actual actuator commands by a control allocation layer that takes care of computing the forces to be applied at the wheels. This step, in general, is quite demanding as far as computational complexity is considered. In this work, a safety-oriented approach to this problem is proposed. Specifically, a four-wheel steer EV with four in-wheel motors is considered, and the high-level motion controller is designed within a sliding mode framework with conditional integrators. For distributing the forces among the tyres, two control allocation approaches are investigated. The first, based on the extension of the cascading generalised inverse method, is computationally efficient but shows some limitations in dealing with unfeasible force values. To solve the problem, a second allocation algorithm is proposed, which relies on the linearisation of the tyre–road friction constraints. Extensive tests, carried out in the CarSim simulation environment, demonstrate the effectiveness of the proposed approach.     

The mechanism for the coupler and draft gear and its influence on safety during a train collision

A mechanical model of the coupler and draft gear was established to study the mechanism during an intercity train collision. The model includes four rigid bodies, one spherical joint, two nonlinear torsion spring units and two nonlinear hysteresis units. Simulation and test results show that the axial characteristics of the model are reasonable and the model can reasonably simulate the pitching movement of the coupler. The influence of the coupler and draft gear on the collision behaviour of the train is analysed considering a four-section intercity train. The results show that during the collision process, the amount of compression of the middle coupler is an important factor influencing the pitching deflection angle. The pitching motion posture of the coupler changes with the initial pitching deflection angle, but the initial pitching deflection angle has little effect on its yawing deflection angle. When the pitching angle of the middle coupler is elevated, as the elevation angle increases, the derailment risk of the ‘A’ end bogie of the previous vehicle increases, whereas the risk of derailment of the ‘B’ end bogie of the subsequent vehicle decreases. When the pitching angle of the middle coupler is depressed, the derailment trends for the front and rear bogies exhibit the opposite trend from that of the elevation angle. As the train collision speed increases, the pitching motion of the middle coupler is limited to forcing a yawing motion, causing the yawing deflection angle to increase sharply, which causes the wheel–rail lateral force to increase rapidly. From this, the derailment risk of the bogie increases, which further causes large displacement lateral buckling of the train. An anti-lateral buckling device can limit the yawing deflection angle of the middle coupler, preventing lateral buckling from large displacement and decreasing the risk of derailment.     

Dynamic emulation of road/tyre longitudinal interaction for developing electric vehicle control systems

Current research on electric vehicles (EVs) is focusing on the environment and energy aspects. However, electric motors also have much better control performance than conventional internal combustion engines. EVs could not only be ‘cleaner’ and ‘more energy efficient’, but also become ‘safer’ with ‘better driving performance’. In this paper, a discrete elasto-plastic friction model is proposed for a dynamic emulation of road/tyre friction in order to validate the control design of EV control systems in laboratory facilities. Experimental results show the dynamic emulation is able to capture the transient behaviour of the road/tyre friction force during braking and acceleration, therefore enabling a more reliable validation of various EV control methods. And the computation of inverse dynamics, which usually needs to be considered in conventional emulation approaches, can be avoided using the proposed dynamic friction model.     

Optimization of the Lateral Stability of Rail Vehicles

Summary The lateral stability of a rail vehicle is optimized using a combination of multibody dynamics, sequential quadratic programming, and a genetic algorithm. Several steps are taken to validate this integrated approach and to show its effectiveness. First, a hand-derived solution to a 17 degree of freedom linear rail vehicle model is compared to the simulation results from the A'GEM multibody dynamics software. Second, the calculation of the ‘critical speed’ (above which a rail vehicle response becomes unstable) using sequential quadratic programming is validated for a specific example. In the process, the existence of sharply-discontinuous ‘cliffs’ in the plots of critical speed versus suspension stiffnesses are identified. These cliffs, which are due to switching of the least-damped mode in the system, greatly hinder the application of gradient-based optimization methods. Two methods that do not require gradient information, a genetic algorithm and the Nelder-Mead's Simplex algorithm, are used to optimize the critical speed. The two algorithms and their results are compared. In recognition of the cliff phenomenon, the definition of critical speed is generalized to make it a more practical measure of lateral stability.     

Handling performance control for hybrid 8-wheel-drive vehicle and simulation verification

In order to improve handling performance of a hybrid 8-Wheel-Drive vehicle, the handling performance control strategy was proposed. For armoured vehicle, besides handling stability in high speed, the minimum steer radius in low speed is also a key tactical and technical index. Based on that, the proposed handling performance control strategy includes ‘Handling Stability’ and ‘Radius Minimization’ control modes. In ‘Handling Stability’ control mode, ‘Neutralsteer Radio’ is defined to adjust the steering characteristics to satisfy different demand in different speed range. In ‘Radius Minimization’ control mode, the independent motors are controlled to provide an additional yaw moment to decrease the minimum steer radius. In order to verify the strategy, a simulation platform was built including engine and continuously variable transmission systems, generator and battery systems, independent motors and controllers systems, vehicle dynamic and tyre mechanical systems. The simulation results show that the handling performance of the vehicle can be enhanced significantly, and the minimum steer radius can be decreased by 20% which is significant improvement compared to the common level of main battle armoured vehicle around the world.     

地铁车站与立交桥施工顺序对车站主体结构的影响研究

针对太原地铁西涧河车站和立交桥实际工程案列，为了探明二者施工顺序对车站主体结构楼板、车站框架柱的受力与变形的影响。运用大型有限元软件MIDAS/GTS建立精细化的三维模型，模拟“先桥后站”与“先站后桥”施工全过程，分析主体结构楼板及格构柱的力学特性。结果表明:底板竖向位移对站桥的施工顺序较中板和顶板更为敏感，“先桥后站”底板位移显著小于“先站后桥”施工的底板位移，两种方案施工下中板、顶板变形均表现为格构柱处隆起，柱点周围下沉；两种施工顺序下车站底板弯矩差别最大，顶板次之，中板变化最小，施工顺序对底板横向弯矩、纵向弯矩差异百分比分别为88.41%，89.73%；“先桥后站”格构柱的受力及变形均小于“先站后桥”施工工序，其中变形更加敏感，格构柱最大水平位移的差异百分比达到53.02%。     

Anti-jackknife reverse tracking control of articulated vehicles in the presence of actuator saturation

It is well known that backward motion control of an articulated vehicle is difficult because it is an open loop unstable system and such motion is also dangerous due to ‘jackknifing’. In this paper, an anti-jackknife reverse tracking control strategy for autonomous articulated vehicles is proposed based on the combined longitudinal and lateral control scheme. In the proposed lateral-longitudinal control scheme, the major task is to control the reverse heading of the trailer by automatic steering strategies that observe both the anti-jackknife condition and input limitations. The main contribution of this paper is the development of globally asymptotic anti-jackknife stabilising and tracking controls of heading angles with both state and input constraints considered a priori. The proposed control inherently has an anti-windup mechanism that prevents the hitch angle from going beyond any specified critical value to avoid jackknifing, during which time, the steering angle remains at its limit. Stability of the controller is theoretically proven via the Lyapunov argument. Effectiveness of the proposed approach is demonstrated by CarSim and Simulink joint simulations.     

多性能强耦合分析技术及应用

在车辆性能开发过程中,各个学科的交叉耦合问题越来越突出,采用多学科分析技术是提高车辆综合性能的必要手段。传统的多学科分析是一种弱耦合技术,不同学科之间只是简单的信息交互,没有求解器层面的耦合,因而难以完全表达不同学科之间的相互影响关系。此外,在车辆性能集成过程中,供应商为保护自身的核心技术,不会把子模型以“白箱”(所有结构特征均开放)的方式完全提供给主机厂,给整车性能集成带来困难。因此,需要探索一种强耦合算法,使不同学科在求解器层面进行耦合,同时每个子模型仅需提供界面上的力与运动信息,实现“分而治之”的多学科强耦合分析。     

Solving conformal contacts using multi-Hertzian techniques

Recently, publications aiming at wheel–rail contact surveys let readers think that multi-Hertzian methods present severe drawbacks with respect to ‘virtual penetration’ methods. These surveys criticise multi-Hertzian solutions mainly because presenting ‘larger contacts overlaps’ and ‘frequent secondary contacts near the border of the first contact’, both obvious geometric possibilities of which the practical occurrence and eventual inconvenience would remain purely theoretical unless established over definite methods demonstrating poor practical results. Recent surveys all quote Piotrowski–Chollet 2005 survey of wheel–rail contact models that attempted to illustrate defective multi-Hertzian techniques by concentrating on the method initiated by Sauvage in the 1990s and further developed by Pascal. The 2005 paper not only gives no evidence of practical inconveniences of Sauvage’s method but also confuses static geometric contact overlaps with the dynamical overlapping of forces. In reality it mixes Sauvage method up with a quite different technique. Thus a clarification is now necessary by reminding what the proper Sauvage technique really is and by showing some of its practical successful applications. The present paper, focusing on determination of normal contact forces in conformal situations, intends to explain clearly the advantages of the unequivocal localisation of secondary ellipses in that multi-Hertzian method which has been developed in INRETS VOCO codes in the 1990s and successfully used by SNCF and ALSTOM in the INRETS-SNCF code, VOCODYM, and later in Pascal’s online calculation of railway elastic contacts code. It proved its effectiveness for studying freight wagons derailments as well as rail wear and head-check, unrounded wheels wear, high-speed lines’ deformations or TGV comfort. While simulating American ACELA trainsets’ behaviour on the US North-East Corridor tracks, prior to actual tests, as part of the commercial contract. It has been also a major tool for bringing back together French and American Safety Standards.     

A study on the role of powertrain system dynamics on vehicle driveability

Vehicle driveability describes the complex interactions between the driver and the vehicle, mainly related to longitudinal vibrations. Today, a relevant part of the driveability process optimisation is realised by means of track tests, which require a considerable effort due to the number of parameters (such as stiffness and damping components) affecting this behaviour. The drawback of this approach is that it is carried on at a stage when a design iteration becomes very expensive in terms of time and cost. The objective of this work is to propose a light and accurate tool to represent the relevant quantities involved in the driveability analysis, and to understand which are the main vehicle parameters that influence the torsional vibrations transmitted to the driver. Particular attention is devoted to the role of the tyre, the engine mount, the dual mass flywheel and their possible interactions. The presented nonlinear dynamic model has been validated in time and frequency domain and, through linearisation of its nonlinear components, allows to exploit modal and energy analysis. Objective indexes regarding the driving comfort are additionally considered in order to evaluate possible driveability improvements related to the sensitivity of powertrain parameters.     

Evaluating delivery of cycling activity and training programmes for disabled people in the UK

Globally, a 15% of the population has some form of disability [1]. While cycling is becoming a popular transport mode, it is crucial to accommodate disabled cyclists, and key for this would be appropriate cycling training for the disabled and those who are involved in the training.This study investigated the delivery of cycling activity and training sessions for disabled people in the UK. The study focused on 1) the delivery systems, in particular the methods, supporting materials, instructor training, and 2) the perceptions of participants, parents/carers, and instructors. It involved semi-structured interviews with promotors and training/activity providers, and a questionnaire survey for instructors, people with disabilities and their carers. It was found that most participants come to training/activity sessions on voluntary basis for physical exercise and socialising. As a result, sessions are often unstructured and designed as ‘activity’ rather than ‘training’.Looking forward it is recommended to, whilst continuing to accommodate the need for flexibility and inclusiveness, introduce a top-down approach designed specifically for disabled participants and initiated by policy-makers, with potential for disability-specific structured sessions in the course of time. The importance of raising awareness among disabled people and their parents and carers is instrumental, as is accessible provision of educational resources for instructors.     

Quasi-steady-state linearisation of the racing vehicle acceleration envelope: a limited slip differential example

In the motorsport environment, passive limited slip differentials are a well-established means of improving the traction limitation imposed by the open differential. Torque sensing types are highly adjustable, and can alter both the stability and agility of the vehicle in the various cornering phases of a typical manoeuvre. In this paper, an adjustable clutch plate or ‘Salisbury’ differential model is presented, which can significantly alter its torque bias characteristics through adjustments in the drive/coast ramp angle, the number of friction faces and preload. To allow robust evaluation of differential parameter changes on ultimate vehicle performance and handling balance, a unified acceleration or ‘GG’ diagram framework is then described. This builds on traditional GG diagram approaches, by using nonlinear constrained optimisation to define both the vehicle acceleration limits and a ‘feasibility’ region within the performance envelope. By linearising a seven degrees of freedom vehicle model at multiple operating points, eigenvalue and yaw rate response analysis is then used to establish contours of stability and agility throughout the GG envelope. This brings new insights into the way in which handling balance changes below and up to the vehicle's acceleration limits.     

Exploring paratransit service quality based on low-income women's perception: A case study in Dhaka city by structural equation model (SEM)

In developing countries paratransit plays a vital role as a public transport mode since mass transit system is inadequate. This research investigates low-income working womens satisfaction level on various service features of paratransit modes based on their experience. Structural Equation Model (SEM) was employed to capture low-income working women's perceptions of paratransit service quality (SQ) in Dhaka city, Bangladesh. Achieving the study objective, a questionnaire survey was conducted on existing paratransit routes from Kamrangichor and Jhauchor slum areas where no bus service is available. Total 410 regular paratransit users who usually use this mode getting to and from workplace participated in the survey during July 2018. To evaluate the paratransit SQ the passengers were asked to rate their perception about 22 service attributes on a likert scale of five points. A series of SEMs were developed to explore the relationship of service features for the overall paratransit SQ. Among the five models the best one is selected by different goodness-of-fit values (CFI = 0.82, TLI = 0.79, RMSEA = 0.12, SRMR = 0.059, AIC = 18,666.94). Model 5 is the best structure developed with four latent variables: ‘Service feature’, ‘System performance’, ‘Safety and security’ and ‘Reliability’ This research explores that ‘Security of goods’, ‘Security of passengers’, ‘Movement flexibility in any road’, ‘Travel expenditure compared to other transport’, and ‘Quality of driver’ are 1st, 2nd, 3rd, 4th and 5th most significant variables that impact on the SQ positively, which represents the real scenario. The outcomes of this research might assist operators and policymakers in formulating policies to enhance urban paratransit SQ.     

Modelling and model predictive control for a bicycle-rider system

This study proposes a bicycle-rider control model based on model predictive control (MPC). First, a bicycle-rider model with leaning motion of the rider’s upper body is developed. The initial simulation data of the bicycle rider are then used to identify the linear model of the system in state-space form for MPC design. Control characteristics of the proposed controller are assessed by simulating the roll-angle tracking control. In this riding task, the MPC uses steering and leaning torques as the control inputs to control the bicycle along a reference roll angle. The simulation results in different cases have demonstrated the applicability and performance of the MPC for bicycle-rider modelling.     

Snowplow Steering Guidance with Gain Stabilization

Acquisition and utilization of lateral guidance information is crucial for steering a vehicle. With practice, drivers can successfully perform the steering function using visual perception and hand-eye coordination. However, this seemingly simple task becomes difficult when the visual information loses its clarity. Driving a snowplow during whiteout conditions is one such example. In order to improve the safety and efficiency of snow removal operations, a supplemental guidance display was proposed and successfully implemented in a California Department of Transportation (Caltrans) snowplow. The guidance information was calculated based on the magnetic markers embedded in the roadway. The crucial step to this success is a transformation of the guidance display problem into a robust driver-in-the-loop control problem. This transformation considers the ‘display’ law as part of the overall driver-steering-control algorithm. Two key ‘assumptions’ for this design are (1) the ‘display’ law should be designed in such a way that drivers can use ‘proportional’ control gain alone to satisfy the performance and stability requirements of the steering tasks, and (2) the driver steering model can be described as a combination of gain and dynamic delay under the display law in (1). This paper describes the validation process for the ‘gain’ stabilization design concept as well as the associated driver steering model using the initial snowplow test data.     

“十二五”期间汽车及零部件面临4大障碍

2011年是我国"十二五"发展规划的开局之年,中国汽车产业将面对更加严峻的转型和升级考验。一系列的外部政策和竞争环境都在发生激变。面对这种从"顺境"到"逆境"的变化,中国汽车业要勇于抓住转型升级的"倒逼机遇",着力解决汽车工业生存环境艰难、结构失衡、市场竞争激烈、核心竞争力不强的障碍和顽疾,加速产业转型和升级,促进我国汽车工业又好又快发展。     

Vehicle rollover avoidance by application of gain-scheduled LQR controllers using state observers

Many researches have been conducted in the area of control applied to vehicle dynamics, aiming at reducing the possibility of the occurrence of the type of accident known as rollover. In this research, based on a common nonlinear model and its linearisation, a method for properly selecting matrices for solving the Riccati equation considering different speeds was proposed. The method showed in which ways speed really influences the choice of controller gains. By developing the dynamic equations for the yaw- and roll-coupled motions and modelling of controllers and state observers, it is possible to compare the efficacy of this control strategy using both linear and nonlinear simulations using Matlab. Significant results were obtained regarding the reduction of the rollover coefficient for a double-lane change manoeuvre at different speeds, thus indicating advantages of using this controller in practical cases.