Torque vectoring based drive assistance system for turning an electric narrow tilting vehicle

The increasing number of cars leads to traffic congestion and limits parking issue in urban area. The narrow tilting vehicles therefore can potentially become the next generation of city cars due to its narrow width. However, due to the difficulty in leaning a narrow tilting vehicle, a drive assistance strategy is required to maintain its roll stability during a turn. This article presents an effective approach using torque vectoring method to assist the rider in balancing the narrow tilting vehicles, thus reducing the counter-steering requirements. The proposed approach is designed as the combination of two torque controllers: steer angle–based torque vectoring controller and tilting compensator–based torque vectoring controller. The steer angle–based torque vectoring controller reduces the counter-steering process via adjusting the vectoring torque based on the steering angle from the rider. Meanwhile, the tilting compensator–based torque vectoring controller develops the steer angle–based torque vectoring with an additional tilting compensator to help balancing the leaning behaviour of narrow tilting vehicles. Numerical simulations with a number of case studies have been carried out to verify the performance of designed controllers. The results imply that the counter-steering process can be eliminated and the roll stability performance can be improved with the usage of the presented approach

고성능 한계 핸들링을 위한 인휠모터 토크벡터링 제어

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계항공공학부, 2021.8. 이경수.지난 10년 동안 차량 자세 제어시스템(ESC)은 치명적인 충돌을 방지하기 위해 많은 상용 차량에서 비약적으로 발전되고 개발되고 있다. 특히, 차량 자세 제어 시스템은 악천후로 인한 미끄러운 도로와 같은 위험한 도로에서 불안정한 차량 주행 조건에서 사고를 피하는데 큰 역할을 한다. 그러나, 최근의 경우, 고성능 차량 또는 스포츠카 등의 경우 제동제어의 빈번한 개입은 운전의 즐거움을 감소시키는 불만도 존재한다. 최근 차량의 전동화와 함께, 자량 자세 제어시스템의 작동 영역인 한계 주행 핸들링 조건에서 각 휠의 독립적인 구동을 적용 할 수 있는 시스템 중 하나인 인휠 모터 시스템을 사용하여 차량의 종, 횡방향 특성을 제어 가능하게 하는 토크 벡터링 제어기술에 대한 연구가 활발하다. 따라서, 본 연구에서는 차량의 선회 한계 핸들링 조건에서 안정성과 주행 다이나믹 성능을 향상시킬 수 있는 토크 벡터링 제어기를 제안하고자 한다. 먼저, 차량의 비선형 주행 구간인 한계 핸들링 조건에 대한 자동 드리프트 제어 알고리즘을 제안한다. 이 알고리즘을 이용하여 토크벡터링제어에 차량의 다이나믹한 주행모드에 대한 통찰력을 제공하고 미끄러운 도로에서 차량의 높은 슬립 각도의 안정성 제어를 제공 할 수 있다. 또한, 인휠 모터 시스템을 차량의 전륜에 2개 모터로 사용하여 차량 고유의 특성인 차량 언더스티어 구배를 직접적 제어를 수행하여, 차량의 핸들링 성능을 향상시켰다. 제어기의 채터링 효과를 줄이고 빠른 응답을 얻기 위해 새로운 과도 매개 변수가 이용하여 수식화하여 구성하였으며, 차량의 정상 상태 및 과도 특성 향상을 검증하기 위하여 ISO 기반 시뮬레이션 및 차량 실험을 수행하였다. 마지막으로 요 제어기와 횡 슬립 각도 제어기로 구성된 MASMC (Multiple Adaptive Sliding Mode Control) 접근 방식을 사용하는 4륜 모터 시스템을 사용한 동적 토크벡터링 제어를 수행하였다. 높은 비선형 특성을 가진 차량의 전후륜 타이어의 코너링 강성은 적응제어기법을 이용하여 예측하였다. 따라서, 안전모드와 다이나믹 모드를 구성하여, 운전자로 하여금 원하는 주행의 조건에 맞게 선택할 수 있는 알고리즘을 구현하였다. 이 MASMC 알고리즘은 향후 전동화 차량에 주행안정성 향상과 다이나믹한 주행의 즐거움을 주는 기술로써, 전차량 시뮬레이션을 이용하여 검증하였다.In the last ten decades, vehicle stability control systems have been dramatically developed and adapted in many commercial vehicles to avoid fatal crashes. Significantly, ESC (Electric Stability Control) system can help escape the accident from unstable driving conditions with dangerous roads such as slippery roads due to inclement weather conditions. However, for the high performed vehicle, frequent intervention from ESC reduces the pleasure of fun-to-drive. Recently, the development of traction control technologies has been taking place with that of the electrification of vehicles. The IWMs (In-Wheel Motor system), which is one of the systems that can apply independent drive of each wheel, for the limit handling characteristics, which are the operation areas of the ESC, is introduced for the control that enables the lateral characteristics of the vehicle dynamics. Firstly, the automated drift control algorithm can be proposed for the nonlinear limit handling condition of vehicles. This approach can give an insight of fun-to-drive mode to TV (Torque Vector) control scheme, but also the stability control of high sideslip angle of the vehicle on slippery roads. Secondly, using IWMs system with front two motors, understeer gradient of vehicle, which is the unique characteristics of vehicle can be used for the proposed control strategy. A new transient parameter is formulated to be acquired rapid response of controller and reducing chattering effects. Simulation and vehicle tests are conducted for validation of TV control algorithm with steady-state and transient ISO-based tests. Finally, dynamic torque vectoring control with a four-wheel motor system with Multiple Adaptive Sliding Mode Control (MASMC) approach, which is composed of a yaw rate controller and sideslip angle controller, is introduced. Highly nonlinear characteristics, cornering stiffnesses of front and rear tires are estimated by adaptation law with measuring data. Consequently, there are two types of driving modes, the safety mode and the dynamic mode. MASMC algorithm can be found and validated by simulation in torque vectoring technology to improve the handling performance of fully electric vehicles.Chapter 1 Introduction 7 1.1. Background and Motivation 7 1.2. Literature review 11 1.3. Thesis Objectives 15 1.4. Thesis Outline 15 Chapter 2 Vehicle dynamic control at limit handling 17 2.1. Vehicle Model and Analysis 17 2.1.1. Lateral dynamics of vehicle 17 2.1.2. Longitudinal dynamics of vehicle 20 2.2. Tire Model 24 2.3. Analysis of vehicle drift for fun-to-drive 28 2.4. Designing A Controller for Automated Drift 34 2.4.1. Lateral controller 35 2.4.2. Longitudinal Controller 37 2.4.3. Stability Analysis 39 2.4.4. Validation with simulation and test 40 Chapter 3 Torque Vectoring Control with Front Two Motor In-Wheel Vehicles 47 3.1. Dynamic Torque Vectoring Control 48 3.1.1. In-wheel motor system (IWMs) 48 3.1.2. Dynamic system modeling 49 3.1.3. Designing controller 53 3.2. Validation with Simulation and Experiment 59 3.2.1. Simulation 59 3.2.2. Vehicle Experiment 64 Chapter 4 Dynamic handling control for Four-wheel Drive In-Wheel platform 75 4.1. Vehicle System Modeling 76 4.2. Motion Control based on MASMC 78 4.2.1. Yaw motion controller for the inner ASMC 80 4.2.2. Sideslip angle controller for the outer ASMC 84 4.3. Optimal Torque Distribution (OTD) 88 4.3.1. Constraints of dynamics 88 4.3.2. Optimal torque distribution law 90 4.4. Validation with Simulation 91 4.4.1. Simulation setup 91 4.4.2. Simulation results 92 Chapter 5 Conclusion and Future works 104 5.1 Conclusion 104 5.2 Future works 106 Bibliography 108 Abstract in Korean 114박

극한 주행 핸들링 성능 개선을 위한 토크벡터링 제어 알고리즘

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계공학부, 2023. 2. 이경수.This dissertation comprehensively details the design of a torque vectoring control algorithm for enhanced cornering performance using two front in-wheel motors (IWMs) and electronic limited slip differential (eLSD) at the rear axle. The main scopes to be covered in this dissertation can be divided into two categories: 1) individual control of IWM for torque vectoring control at the front axle; 2) integrated control of IWM and eLSD for both front and rear axle. First, an individual control strategy of two front IWMs in a rear-wheel-drive vehicle has been designed to improve the cornering performance. The individual control of IWMs consists of steady-state and transient control input. The steady-state control input is devised to improve the steady-state cornering response with modifying the vehicle understeer gradient, and the transient control input is designed to enhance the lateral stability by increasing the yaw rate damping coefficient. The proposed algorithm has been investigated through both computer simulations and vehicle tests, in order to show that the proposed algorithm can enhance the cornering response achieving the control objectives and to show the superior control performance compared to the other cases, such as yaw rate tracking algorithm and uncontrolled case. Second, the integrated control of two front IWMs and eLSD is designed to enhance the cornering performance at high speeds considering the characteristics of each actuator. The two front IWMs are controlled to improve the cornering performance based on a feedforward control, and the eLSD is utilized for the yaw rate feedback control. The computer simulations are conducted to show the effects of each actuator on the vehicle lateral motion at aggressive cornering with longitudinal acceleration and deceleration. Additionally, vehicle test results show that the proposed controller improves the cornering performance at the limits of handling compared to the uncontrolled case. In summary, this dissertation proposes a control algorithm for an enhanced limit handling performance based on vehicle understeer gradient and yaw rate damping characteristics, addressing also integrated control of in-wheel motors and electronic limited slip differential with considering the characteristics of each actuator. The proposed IWM control law is formulated to shape the understeer characteristics during steady-state cornering and yaw rate damping characteristic during transient cornering, and the eLSD control is designed to track the reference yaw rate. Computer simulations and vehicle tests are conducted to validate the control performance of the proposed algorithm, showing significant improvements in the agility and the stability of a test vehicle without chattering issues. Additionally, the vehicle tests at a racing track confirm the enhanced limit handling performance.본 논문은 전륜 인휠모터와 후륜 전자식 차동 제한 장치를 이용하여 선회 성능 개선을 위한 토크벡터링 제어 알고리즘에 대해 포괄적으로 설명하였다. 본 논문에서 다루는 주요 연구 범위는 크게 두 가지 범주로 나뉠 수 있다. 첫 번째는 전륜 인휠모터를 이용한 개별적인 토크벡터링 제어이고, 두 번째는 전륜 인휠모터 및 후륜 전자식 차동제한장치를 모두 이용한 전후륜 통합 토크벡터링 제어이다. 첫 번째로, 후륜 구동 차량 내에서 두 개의 전륜 인휠 모터를 활용한 선회 성능 개선을 위한 제어 알고리즘이 설계되었다. 인휠 모터 독립 제어는 정상상태 제어 입력과 과도응답 상태 제어 입력으로 구성되어 있다. 정상상태 제어 입력은 차량의 언더스티어 구배를 변형하면서 정상상태 선회 반응을 개선하기 위해 고안되었고, 과도응답 상태 제어 입력은 차량의 요댐핑 계수를 증가시킴으로써 차량의 횡방향 안정성을 개선하기 위해 설계되었다. 제안된 알고리즘의 성능은 컴퓨터 시뮬레이션과 차량 실험을 통해 확인하였다. 실험 결과에서 알 수 있듯이, 제안된 알고리즘은 제어 목표를 달성하며 차량의 선회 성능을 개선할 수 있었다. 두 번째로, 각 엑츄에이터의 특성을 고려하고 고속 주행 상황에서의 선회 성능을 개선하기 위해, 두 개의 전륜 인휠 모터와 후륜의 전자식 차동 제한 장치의 통합 제어 알고리즘이 설계되었다. 두 개의 전륜 인휠 모터는 피드포워드 제어를 기반으로 선회 성능을 개선하기 위해 제어되었고, 후륜의 전자식 차동 제한 장치는 요레이트 피드백 제어를 위해 활용되었다. 컴퓨터 시뮬레이션은 감가속을 포함한 공격적인 선회 상황에서 각 엑츄에이터의 제어 효과를 보여주기 위해 수행되었다. 추가적으로, 차량 실험 결과를 통해 제안된 제어기가 제어되지 않은 경우에 비해 핸들링 한계 상황에서의 선회 성능을 개선할 수 있다는 점을 보여주었다. 요약하자면, 본 연구에서는 차량의 언더스티어 그레디언트와 요레이트 댐핑 특성에 기반한 한계 핸들링 성능 개선을 위한 제어 알고리즘을 제안하였다. 또한, 인휠모터와 전자식 차동 제한 장치의 각 엑츄에이터 특성을 고려하여 인휠모터와 전자식 차동 제한 장치의 통합 제어에 대해 다루었다. 제안된 인휠모터 제어기는 정상상태 선회에서의 언더스티어 그레디언트와 과도응답상태 선회에서의 요레이트 댐핑 특성을 변형하기 위해 고안되었고, 전자식 차동 제한 장치 제어는 목표 요레이트를 추종하기 위해 설계되었다. 제안된 제어기를 검증하기 위해, 컴퓨터 시뮬레이션과 실차 실험이 진행되었고, 차량의 선회 안정성과 민첩성이 채터링 문제없이 확연히 개선된다는 것을 보여주었다. 추가적으로, 레이싱 트랙에서의 실차 실험을 통해 개선된 한계 핸들링 성능 또한 제시되었다.Chapter 1. Introduction 1 1.1. Background and motivation 1 1.2. Previous research on considering tire characteristics 4 1.2. Previous research on vehicle controller design 8 1.3. Thesis objectives 13 1.4. Thesis outline 15 Chapter 2. Vehicle Control System 17 2.1. Vehicle chassis system 17 2.2. Vehicle tire-road interactions 22 2.3. Tire characteristics at the limits of handling 35 Chapter 3. Torque Vectoring Control with In-Wheel Motors (IWMs) 49 3.1. Upper level controller 53 3.1.1. Control strategies for steady-state response 54 3.1.2. Control strategies for transient response 57 3.1.3. Analysis on the closed-loop system with proposed controller 60 3.2. Lower level controller 65 3.2.1. Actuator characteristics of in-wheel motors 65 3.2.2. Torque inputs for yaw moment generation 66 Chapter 4. Integrated Control of Two Front In-Wheel Motors (IWMs) and Rear-Axle Electronic Limited Slip Differential (eLSD) 68 4.1. Upper level controller 71 4.1.1. Analysis on actuator characteristics and vehicle responses 71 4.1.2. Feedforward control using in-wheel motors 79 4.1.3. Feedback control using electronic limited slip differential 80 4.2. Lower level controller 82 4.2.1. Transforming the desired yaw moments to the torque command 82 4.2.2. Saturating the torque inputs considering the actuator and tire friction limit 83 4.2.3. Transferring the eLSD clutch torque in the desired direction 84 Chapter 5. Simulation Results 87 5.1. Effect of IWM control on vehicle motion 87 5.2. Effect of IWM/eLSD integrated control 98 Chapter 6. Vehicle Test Results 108 6.1. Test results for IWM control 108 6.2. Test results for integrated control of IWM and eLSD 116 Chapter 7. Conclusion 121 Appendix A. Integrated control of two front in-wheel motors and rear wheel steering 123 A.1. Prediction model for vehicle motion 124 A.2. Controller design 128 A.3. Simulation results 131 Bibliography 138 Abstract in Korean 148박

State Estimation and Control of Active Systems for High Performance Vehicles

In recent days, mechatronic systems are getting integrated in vehicles ever more. While stability and safety systems such as ABS, ESP have pioneered the introduction of such systems in the modern day car, the lowered cost and increased computational power of electronics along with electrification of the various components has fuelled an increase in this trend. The availability of chassis control systems onboard vehicles has been widely studied and exploited for augmenting vehicle stability. At the same time, for the context of high performance and luxury vehicles, chassis control systems offer a vast and untapped potential to improve vehicle handling and the driveability experience. As performance objectives have not been studied very well in the literature, this thesis deals with the problem of control system design for various active chassis control systems with performance as the main objective. A precursor to the control system design is having complete knowledge of the vehicle states, including those such as the vehicle sideslip angle and the vehicle mass, that cannot be measured directly. The first half of the thesis is dedicated to the development of algorithms for the estimation of these variables in a robust manner. While several estimation methods do exist in the literature, there is still some scope of research in terms of the development of estimation algorithms that have been validated on a test track with extensive experimental testing without using research grade sensors. The advantage of the presented algorithms is that they work only with CAN-BUS data coming from the standard vehicle ESP sensor cluster. The algorithms are tested rigorously under all possible conditions to guarantee robustness. The second half of the thesis deals with the design of the control objectives and controllers for the control of an active rear wheel steering system for a high performance supercar and a torque vectoring algorithm for an electric racing vehicle. With the use of an active rear wheel steering, the driver’s confidence in the vehicle improves due a reduction in the lag between the lateral acceleration and the yaw rate, which allows drivers to push the vehicle harder on a racetrack without losing confidence in it. The torque vectoring algorithm controls the motor torques to improve the tire utilisation and increases the net lateral force, which allows professional drivers to set faster lap times

Integration of Active Systems for a Global Chassis Control Design

Vehicle chassis control active systems (braking, suspension, steering and driveline), from the first ABS/ESC control unit to the current advanced driver assistance systems (ADAS), are progressively revolutionizing the way of thinking and designing the vehicle, improving its interaction with the surrounding world (V2V and V2X) and have led to excellent results in terms of safety and performances (dynamic behavior and drivability). They are usually referred as intelligent vehicles due to a software/hardware architecture able to assist the driver for achieving specific safety margin and/or optimal vehicle dynamic behavior. Moreover, industrial and academic communities agree that these technologies will progress till the diffusion of the so called autonomous cars which are able to drive robustly in a wide range of traffic scenarios. Different autonomous vehicles are already available in Europe, Japan and United States and several solutions have been proposed for smart cities and/or small public area like university campus. In this context, the present research activity aims at improving safety, comfort and performances through the integration of global active chassis control: the purposes are to study, design and implement control strategies to support the driver for achieving one or more final target among safety, comfort and performance. Specifically, the vehicle subsystems that are involved in the present research for active systems development are the steering system, the propulsion system, the transmission and the braking system. The thesis is divided into three sections related to different applications of active systems that, starting from a robust theoretical design procedure, are strongly supported by objective experimental results obtained fromHardware In the Loop (HIL) test rigs and/or proving ground testing sessions. The first chapter is dedicated to one of the most discussed topic about autonomous driving due to its impact from the social point of view and in terms of human error mitigation when the driver is not prompt enough. In particular, it is here analyzed the automated steering control which is already implemented for automatic parking and that could represent also a key element for conventional passenger car in emergency situation where a braking intervention is not enough for avoiding an imminent collision. The activity is focused on different steering controllers design and their implementation for an autonomous vehicle; an obstacle collision avoidance adaptation is introduced for future implementations. Three different controllers, Proportional Derivative (PD), PD+Feedforward (FF) e PD+Integral Sliding Mode (ISM), are designed for tracking a reference trajectory that can be modified in real-time for obstacle avoidance purposes. Furthermore, PD+FF and PD+ISM logic are able to improve the tracking performances of automated steering during cornering maneuvers, relevant fromthe collision avoidance point of view. Path tracking control and its obstacle avoidance enhancement is also shown during experimental tests executed in a proving ground through its implementation for an autonomous vehicle demonstrator. Even if the activity is presented for an autonomous vehicle, the active control can be developed also for a conventional vehicle equipped with an Electronic Power Steering (EPS) or Steer-by-wire architectures. The second chapter describes a Torque Vectoring (TV) control strategy, applied to a Fully Electric Vehicle (FEV) with four independent electric motor (one for each wheel), that aims to optimize the lateral vehicle behavior by a proper electric motor torque regulation. A yaw rate controller is presented and designed in order to achieve a desired steady-state lateral behaviour of the car (handling task). Furthermore, a sideslip angle controller is also integrated to preserve vehicle stability during emergency situations (safety task). LQR, LQR+FF and ISM strategies are formulated and explained for yaw rate and concurrent yaw rate/sideslip angle control techniques also comparing their advantages and weakness points. The TV strategy is implemented and calibrated on a FEV demonstrator by executing experimental maneuvers (step steer, skid pad, lane change and sequence of step steers) thus proving the efficacy of the proposed controller and the safety contribution guaranteed by the sideslip control. The TV could be also applied for internal combustion engine driven vehicles by installing specific torque vectoring differentials, able to distribute the torque generated by the engine to each wheel independently. The TV strategy evaluated in the second chapter can be influenced by the presence of a transmission between themotor (or the engine) and wheels (where the torque control is supposed to be designed): in addition to the mechanical delay introduced by transmission components, the presence of gears backlashes can provoke undesired noises and vibrations in presence of torque sign inversion. The last chapter is thus related to a new method for noises and vibration attenuation for a Dual Clutch Transmission (DCT). This is achieved in a new way by integrating the powertrain control with the braking system control, which are historically and conventionally analyzed and designed separately. It is showed that a torsional preload effect can be obtained on transmission components by increasing the wheel torque and concurrently applying a braking wheel torque. For this reason, a pressure following controller is presented and validated through a Hardware In the Loop (HIL) test rig in order to track a reference value of braking torque thus ensuring the desired preload effect and noises reduction. Experimental results demonstrates the efficacy of the controller, also opening new scenario for global chassis control design. Finally, some general conclusions are drawn and possible future activities and recommendations are proposed for further investigations or improvements with respect to the results shown in the present work

Direct yaw-moment control of an in-wheel-motored electric vehicle based on body slip angle fuzzy observer

A stabilizing observer-based control algorithm for an in-wheel-motored vehicle is proposed, which generates direct yaw moment to compensate for the state deviations. The control scheme is based on a fuzzy rule-based body slip angle (beta) observer. In the design strategy of the fuzzy observer, the vehicle dynamics is represented by Takagi-Sugeno-like fuzzy models. Initially, local equivalent vehicle models are built using the linear approximations of vehicle dynamics for low and high lateral acceleration operating regimes, respectively. The optimal beta observer is then designed for each local model using Kalman filter theory. Finally, local observers are combined to form the overall control system by using fuzzy rules. These fuzzy rules represent the qualitative relationships among the variables associated with the nonlinear and uncertain nature of vehicle dynamics, such as tire force saturation and the influence of road adherence. An adaptation mechanism for the fuzzy membership functions has been incorporated to improve the accuracy and performance of the system. The effectiveness of this design approach has been demonstrated in simulations and in a real-time experimental settin