Tracking Performance of Electric Power Steering System Based on the Mixed H_2/H_∞ Strategy

The tracking performance of motor current is an important factor that affects the assistance torque of electric power steering （EPS） system. Bad tracking performance will cause assistant torque delay, and make road feeling bad, and is influenced by the input steering torque and system measuring noise. However the existing methods have some shortages on system＇s robust dynamic performance and robust stability. The mixed H2/H∞ strategy for recirculating ball-type EPS system in a pure electric bus is proposed, and vehicle dynamic model of the system is established. Due to the existence of system model uncertainty, disturbance signals, sensor noises and the demand of system dynamic performance, the indexes of robust performance and road feeling for drivers are defined as the appraisal control objectives. The H∞ method is introduced to design the H∞ controller, and the H2 method is applied to optimize the H∞ controller, thus the mixed H2/H∞ controller is designed. The response of EPS system to the motor current command with amplitude of 20 A, the road disturbance with amplitude of 500 N and the sensor random noise with the amplitude of 1 A is simulated. The simulation results show that the recirculating ball-type EPS system with the mixed H2/H∞ controller can attenuate the random noises and disturbances and track the boost curve well, so the mixed H2/H∞ controller can improve the system＇s robust performance and dynamic performance. For the purpose of verifying the performance of the designed control strategy, the motor current tracking performance ground tests are conducted with step response input of the steering wheel, double-lane steering test and lemniscate steering test, respectively. The tests show that the mixed H2/H∞ controller for the recirculating ball-type EPS system of pure electric bus is feasible. The designed controller can solve the robust performance and robust stability of the system, thus improve the tracking performance of the EPS system and provide satisfied road feeling for the drivers.

Controller Design for Electric Power Steering System Using T-S Fuzzy Model Approach

Pressure ripples in electric power steering （EPS） systems can be caused by the phase lag between the driver s steering torque and steer angle, the nonlinear frictions, and the disturbances from road and sensor noise especially during high-frequency maneuvers. This paper investigates the use of the robust fuzzy control method for actively reducing pressure ripples for EPS systems. Remarkable progress on steering maneuverability is achieved. The EPS dynamics is described with an eight-order nonlinear state-space model and approximated by a Takagi-Sugeno （T-S） fuzzy model with time-varying delays and external disturbances. A stabilization approach is then presented for nonlinear time-delay systems through fuzzy state feedback controller in parallel distributed compensation （PDC） structure. The closed-loop stability conditions of EPS system with the fuzzy controller are parameterized in terms of the linear matrix inequality （LMI） problem. Simulations and experiments using the proposed robust fuzzy controller and traditional PID controller have been carried out for EPS systems. Both the simulation and experiment results show that the proposed fuzzy controller can reduce the torque ripples and allow us to have a good steering feeling and stable driving.

Model development and parameter investigation of a column-type electric power steering system

In this paper, the performance of a column-type electric power steering （EPS） system and vehicle has been studied and a detailed mathematical model for the system has been established. Based on the mathematic model of the optimization design for steering feel, the parameters of the EPS system and vehicle on steering performance have been investigated. Moreover, the effects of the parameters on system stability have been analyzed and compared by the method of absolute sensitivity and the results are given in the end.

Integration optimization of novel electric power steering system based on quality engineering theory

The dynamic model of a novel electric power steering (EPS) system integrated with active front steering function (the novel EPS system) is built.The concepts and quantitative expressions of the steering road feel,steering sensibility,and steering operation stability are introduced.Based on quality engineering theory,the optimization algorithm is proposed by integrating the Monte Carlo descriptive sampling,elitist non-dominated sorting genetic algorithm (NSGA-Ⅱ) and 6-sigma design method.With the steering road feel and the steering portability as optimization targets,the system parameters are optimized by the proposed optimization algorithm.The simulation results show that the system optimized based on quality engineering theory can improve the steering road feel,guarantee steering stability and steering portability and thus provide a theoretical basis for the design and optimization of the novel electric power steering system.

Study on Characteristic of Electric Power Assist Steering System

A pinion-type electric power steering (EPS) equipped on a sedan is reached in this paper. A three-freedom dynamic model of this system is created. The variables affecting assist character is analyzed. The formulas of simpled steering resistance force and the relationship between assist gain and vehicle speed are presented for the first time. Assist character is found based on the parameters of a sedan at last. This assist character is fit for the control rule of the EPS system through analyzing this character. The assist character figure offers reference for system design and control. Furthermore, this research method has generality for assist character of different kinds of vehicles.

H∞ control of novel active steering integrated with electric power steering function

Based on the traditional active steering system, a novel active steering system integrated with electric power steering function was introduced, which can achieve the functions of both active steering and electric power steering. In view of the interference from road random signal and sensor noise in the novel active steering system, the H∞ control model of the novel active steering system was built. With satisfying steering feel, good robust performance and steering stability being the control objectives, the H∞ controller for the novel active front steering (AFS) system was designed. The simulation results show that the novel AFS system with H∞ control strategy can attenuate the road interference quickly, and there is no resonance peak in the bode diagram. It can make the driver obtain more useful information in the low frequency range, and attenuate the road interference better in the high frequency range, thus the driver can get more satisfying road feeling. Therefore, the designed H∞ controller can synthesize the advantages of both robust performance and robust stability, and has certain contribution to the design of novel AFS system.

Precise Compound Control of Loading Force for Electric Load Simulator of Electric Power Steering Test Bench

Electric load simulator(ELS) systems are employed for electric power steering(EPS) test benches to load rack force by precise control. Precise ELS control is strongly influenced by nonlinear factors. When the steering motor rapidly rotates, extra force is directly superimposed on the original static loading error, which becomes one of the main sources of the final error. It is key to achieve ELS precise loading control for the entire EPS test bench. Therefore, a three-part compound control algorithm is proposed to improve the loading accuracy. First, a fuzzy proportional–integral plus feedforward controller with force feedback is presented. Second, a friction compensation algorithm is established to reduce the influence of friction. Then, the relationships between each quantity and the extra force are analyzed when the steering motor rapidly rotates, and a net torque feedforward compensation algorithm is proposed to eliminate the extra force. The compound control algorithm was verified through simulations and experiments. The results show that the tracking performance of the compound control algorithm satisfies the demands of engineering practice, and the extra force in the ELS system can be suppressed by the net torque corresponding to the actuator’s acceleration.

Performance optimization of electric power steering based on multi-objective genetic algorithm

The vehicle model of the recirculating ball-type electric power steering (EPS) system for the pure electric bus was built. According to the features of constrained optimization for multi-variable function, a multi-objective genetic algorithm (GA) was designed. Based on the model of system, the quantitative formula of the road feel, sensitivity, and operation stability of the steering were induced. Considering the road feel and sensitivity of steering as optimization objectives, and the operation stability of steering as constraint, the multi-objective GA was proposed and the system parameters were optimized. The simulation results show that the system optimized by multi-objective genetic algorithm has better road feel, steering sensibility and steering stability. The energy of steering road feel after optimization is 1.44 times larger than the one before optimization, and the energy of portability after optimization is 0.4 times larger than the one before optimization. The ground test was conducted in order to verify the feasibility of simulation results, and it is shown that the pure electric bus equipped with the recirculating ball-type EPS system can provide better road feel and better steering portability for the drivers, thus the optimization methods can provide a theoretical basis for the design and optimization of the recirculating ball-type EPS system.

Control strategy of a novel electric power steering system integrated with active front steering function

A novel electric power steering system(EPS) integrated with active front steering(AFS) is developed.It has functions of both AFS system and EPS system with two actuator units:the AFS actuator unit and the EPS actuator unit.The AFS actuator unit controls the displacement transfer behavior of the steering system,and improves the handling stability under adverse road conditions by varying the steering ratio directly related to the speed and road conditions.The EPS actuator unit controls the force transfer behavior of the steering system,and improves the steering portability and road feel of the vehicle.Based on a dynamic model,the mixed H2/H∞ control strategy of the EPS actuator and the active steering intervention control strategy of the AFS actuator are designed.The simulation indicates that the novel EPS system with the designed control strategies has obvious advantages in vehicle handling stability and the driver's road feel over the traditional EPS system,and extends the vehicle's steering performance.

Multi-objective optimization of active steering system with force and displacement coupled control

A novel active steering system with force and displacement coupled control(the novel AFS system) was introduced,which has functions of both the active steering and electric power steering.Based on the model of the novel AFS system and the vehicle three-degree of freedom system,the concept and quantitative formulas of the novel AFS system steering performance were proposed.The steering road feel and steering portability were set as the optimizing targets with the steering stability and steering portability as the constraint conditions.According to the features of constrained optimization of multi-variable function,a multi-variable genetic algorithm for the system parameter optimization was designed.The simulation results show that based on parametric optimization of the multi-objective genetic algorithm,the novel AFS system can improve the steering road feel,steering portability and steering stability,thus the optimization method can provide a theoretical basis for the design and optimization of the novel AFS system.

Electrical power assisted steering for EVs and HEVs

Electrical power assisted steering (EPAS) is one of the key components, especially for electrical vehicle. It has attracted much attention for their advantages with respect to improved fuel economy and has been widely adopted as automotive power-steering equipment in recent years. EPS (electrical power steering) controllers contain MCU (microprocessor control unit) to implement the complex control algorithms. EPS control strategy development is the core technology of the whole system. To achieve the better performance of driving, both mechanical structures and electrical structures are totally designed as a whole. Model-based development is recommended to software design. There are several trends about EPS’ future, such as high power EPS development, high voltage EPS development and steering-by-wire technology.

四轮转向干预下电动助力转向控制策略研究

四轮转向(4WS)车辆相较于前轮转向(FWS)车辆具有更高的灵活性,其后轮转向在提高车辆操稳性的同时转向阻力矩也发生变化,使得原电动助力转向系统助力策略与四轮转向车辆不匹配,对行车安全产生影响.本文以线性二自由度车辆模型为基础,对比分析了前轮转向车辆与四轮转向车辆的转向特性,提出电动助力转向修正控制策略.仿真结果表明,角阶跃工况下,有助力修正的四轮转向车辆,驾驶员操纵方向盘力矩与驾驶前轮转向车辆基本一致,既保证了四轮转向车辆低速时的操纵轻便性,也兼顾了高速时的操纵稳定性.

乘用车双电机冗余电动助力转向系统研究

为了提高电动助力转向系统的安全性以及可靠性,基于乘用车提出一种双电机冗余电动助力转向技术,采用转向执行双助力电机,可以从硬件上实现冗余,避免任意单电机发生故障时导致转向系统的失效,不仅可以满足转向系统对于轻便型、助力跟随性的要求,还可以减轻单个助力电机的负载提高电机的使用寿命。针对提出的问题,介绍了对双电机阻力转向系统整体结构及工作原理,并对其关键零部件进行分析论述。搭建双电机冗余系统仿真模型,双电机电流分配采用“一主一辅”的控制方式,并进行方向盘多种工况仿真验证。针对助力转向出现抖动问题,结合“扫频试验”,设计输出转矩超前滞后补偿方式进行相位校正补偿。通过实车试验验证了该算法的准确性和有效性。实验结果表明双冗余电动助力转向系统极大提高了转向力矩的稳定性,抑制其扰动性,有较好的助力效果,极大提高系统的可靠性和安全性。

电动助力转向系统Carsim-Simulink联合仿真控制研究

电动助力转向系统作为电动汽车的主流配置,其性能好坏对整车转向操纵稳定性能有重要影响。以某款自主品牌电动汽车EPS系统为研究对象,进行动力学分析并依次建立Simulink子系统模型。根据实车参数,设计直线型助力特性曲线并输入前述模型,最终建立Carsim/Simulink联合仿真运动学模型并开展国标操纵稳定性仿真试验。结果表明:在方向盘转向角脉冲和角阶跃试验中,较无EPS助力控制车型,有EPS助力控制车型具有良好的车辆瞬态响应度和操纵稳定性;在转向轻便性试验中,验证本款车型助力特性合理,车辆具有较好的助力效果。

基于扭矩闭环的人-车协同转向舒适性控制策略研究

为了解决传统电动助力转向系统在变路面附着系数以及载荷变化工况下方向盘力矩的变化影响驾驶员舒适性的问题,提出了一种基于修正线性三自由度动力学模型的扭矩闭环人-车协同转向舒适性控制策略。首先,通过驾驶员风格辨识建立横摆角速度与车速、方向盘力矩的非线性关系;其次,根据此非线性关系与操纵动力学稳态特性得到驾驶员期望回正力矩,再通过考虑车厢侧倾以及悬架导向装置变形的修正线性三自由度模型和轮胎模型对回正力矩进行精确计算,进而构建扭矩闭环控制器;然后,经扭矩闭环控制器计算得到的补偿助力力矩与基本助力力矩进行叠加获得最终的控制力矩。最后,通过Matlab/Simulink软件建立扭矩闭环系统仿真模型,验证了修正动力学模型的准确性,同时也验证了所提出的控制策略能有效减小方向盘力矩的波动,提升了驾驶员的舒适性。

电动助力转向系统NVH特性数据采集与性能评价

针对汽车电动助力转向系统NVH特性数据存在多点位异步采样误差较大,且选取性能评价依据单一的问题,设计一种二十四通道NVH特性数据同步采集与多角度特性分析系统;采用多个数据采集模块联结、同步动态随机存储器读写、高速串行计算机扩展总线融合的方式,实现二十四通道NVH特性数据的同步精确采集与快速传输;从机械性能与声振特性方面对电动助力转向系统NVH特性进行多角度分析与评价。结果表明,与传统测试方法相比,所提方法可实现多点位同步高精度采样与多角度信号时频域分析,每个通道数据采集速率可达200 kHz/s,时频域分析依据更丰富、更全面。

基于功能安全的汽车EPS系统安全冗余研究

电动助力转向(electric power steering,EPS)系统是车辆常用的转向执行器,其失效将严重影响驾乘人员的安全。为提高EPS系统的安全性与可靠性,基于功能安全标准建立EPS系统安全冗余机制:基于ISO26262对EPS系统进行研究,通过相关项定义、危害分析与风险评估(HARA),得到系统的功能安全目标与需求,并对其进行分配;设计EPS系统架构、容错机制,以提高系统的安全性;最后,对所设计的安全冗余机制进行台架试验。结果表明,在单侧桥驱芯片故障、单侧电机位置传感器故障、双侧电机位置传感器故障等故障注入的情况下,系统能够实现预期响应,满足功能安全目标,验证了所设计安全冗余机制的有效性。

结合转向系统电气控制的道路模拟台架试验技术研究

为解决道路模拟试验中无法验证转向电控系统的问题,基于汽车道路模拟耐久性试验技术和汽车总线通信原理,提出了一种转向系统道路模拟台架试验方案进行转向系统的精确验证。首先在道路模拟试验台架中搭建转向系统的控制电路,然后使用总线工具软件按照时间顺序输出转向系统控制器控制信号至转向系统,最后,通过转向系统应变和转向盘力矩信号进行试验方案有效性验证。结果表明,该方法可在传统台架有效启动电动助力转向(EPS)系统的转向助力功能。

大齿条力冗余R-EPS转向器开发及验证

为了满足前轴载荷较大乘用车电动助力转向产品的需要,对大齿条力冗余R-EPS转向系统进行开发,全新设计了齿条、滚珠丝杠及皮带传动等机构,制定了R-EPS电控系统冗余方案,设计了电控系统失效时的容错机制,通过转向手力调校和匹配,转向手力和转向跟随性均满足车辆使用需求,产品经台架试验和整车道路试验验证了产品性能优良、安全可靠。

汽车电动助力转向系统分析

汽车电动助力转向系统是机电一体化的典型代表,它将电机和电子设备结合在一起,完善了汽车的转向驱动系统。为了满足驾驶员控制系统的可操作性,电动转向系统显示出了很大的优越性。汽车电动助力转向系统的电子控制单元实时监测车身的运行过程,按照驻车、启动、低速、高速等状态下转向扭矩的大小计算出相应的驱动信号,驱动电机运行,为驾驶员提供助力。