Browse Topic: Steer-by-wire
SBW(Steer-by-wire) is a steering system that transmits the driver’s request and gives feedback to the driver through electrical signals. This system eliminates the mechanical connection of the traditional steering system, and can realize the decoupling of the steering wheel and the road wheel. In addition, this system has a perfect torque feedback system, which can accurately and delicately feedback the road surface information to the driver. However, vehicle driving deviation is one of the most common failure modes affecting vehicle performance in the automotive aftermarket, this failure mode can exacerbates tire wear, reducing their life cycle, at the same time, the driver must apply a counter torque to the steering wheel for a long time to maintain straight-line travel during driving. This increases the driver’s operational burden and poses safety hazards to the vehicle’s operation. Based on the steer-by-wire system and vehicle driving deviation characteristics, this paper proposes Pull Drift Compensation (PDC) function. This function is based on the identification of vehicle driving deviation conditions. Based on Hardware In Loop Test (HIL) platform for tuning and simulation verification.
A significant portion of the global population about 13.6% of the world's population faces challenges due to upper limb disabilities caused by accidents, genetics, health issues or aging. These people struggle with everyday mobility tasks and often need help. Hence, the research is focused on creating special vehicle control systems to help them. This study gathers knowledge from various science and technology fields to develop foot-operated steering systems letting those with upper limb differences control vehicles with their feet. The research explores various technologies like modified steering, brain-controlled vehicles, foot-operated steering, steer-by-wire and Ackermann steering. Most of these systems are custom-made for people with upper limb differences. Ensuring safety, security, malfunction prevention, precise steering, user-friendliness and affordability is a significant challenge that demands advanced technology. Furthermore, there is a requirement to develop this system to meet modern demands while sustaining cost-effectiveness. In the pursuit of addressing the mobility challenges encountered by individuals with upper limb differences the research undertook a thorough assessment of various steering mechanisms such as Disk Steering, Joystick Steering, Push Button Steering…etc. The proposal introduces a foot-operated press button system to replace hand-operated steering wheels. Drivers can steer with their feet by engaging a press button on the steering pad. It connects directly to a controller which interfaces with a motor connected to a pinion pin. This motor moves the wheels precisely responding to the driver's interaction with the foot-operated press button and it is seamlessly connecting with steer-by-wire technology ensuring precise and responsive steering. whether they are using custom made vehicles or regular vehicles equipped with our proposed mechanism.
In steer-by-wire (SbW) vehicles, understanding the steering rack force is essential to replicate a realistic steering feel, allowing conclusions to be drawn about road surface conditions by the decoupled manual actuator. Since internal friction varies with each steering system manufactured and installed, these models differ greatly in accuracy. This paper presents a concept for continuously calculating fluctuating friction based on the internal steering variables to avoid additional and complex individual measurements. An SbW system offers the right approach by adjusting the driver’s desired steering angle and the required motor control. The underlying steering clearance and the Kalman filter are used to calculate the steering rack force. The validity of the proposed concept is shown in drive tests according to ISO 13674 and ISO 7401 to gauge high and low friction values in different speed ranges.
Applications in commercial and military fields created high demands on the steering performance of multi-axle vehicle. With the characteristic of more degrees of freedom (DOF), all-wheel cooperative steering is more conducive to improve the steering performance of multi-axle vehicle. This paper studies multi-axle vehicle assembled with steer-by-wire system, and proposes a control strategy to achieve all-wheel cooperative steering to improve the low-speed steering flexibility and high-speed steering stability of multi-axle vehicle. Based on the ideal steering performance at low-speed and high-speed, the steady-state gain of multi-axle vehicles at different speeds is reshaped. Also, the corresponding vehicle reference model is constructed to provide the ideal vehicle state as a reference. The precision of the vehicle reference model is verified by an all-wheel independent steering platform. Accordingly, the state feedback control module which contains a sliding mode controller and a disturbance observer is designed to make the actual state of the vehicle track the designed idea state, which is verified under a variety of path tracking conditions in the simulation environment. Simulation results show that the control strategy proposed for multi-axle vehicle can achieve all-wheel cooperative steering, improving the low-speed steering flexibility and high-speed steering stability of multi-axle vehicle.
Lexus' first BEV arrives with innovative touches, dual-axle propulsion and less-than-spectacular range. Even while Toyota was being criticized for its electrification strategy and its pace in embracing BEVs, the company's engineers were quietly prepping the Lexus brand's first EV, the 2023 RZ 450e crossover. SAE Media recently drove the RZ and spoke with engineers about its development at an event in Provence, France. While not under-powered, with a total of 230kW (313 hp) available when both front and rear motors are at peak output, some will question the vehicle's below-average driving range.
With high integration, high efficiency and high flexibility, the front wheel independent Steer-by-Wire system (SbW) is a key link between autonomous vehicles and intelligent chassis technology, and is one of the current focused research in industry and academia. In this paper, a strategy for active control of steering geometry of the Steer-by Wire independent steering system is proposed based on the nonlinear three-step method and Ackermann geometry relationship with the control goal of improving the driving stability and handling performance of the vehicle. The control strategy takes the front wheel steering angle difference and yaw moment as the control variables, and tracks the expected side slip angle and yaw rate as the control objectives. A more accurate vehicle model, and a nonlinear tire model with a reference vehicle model, is used to design the three-step controller to improve the effectiveness of the steady-state control and reduce the system error. When designing the relationship between steering wheel angle and wheel angle, the relationship between vehicle speed and steering wheel angle was considered to improve the vehicle response. After the controller design was completed, a joint simulation of an electric four-wheel drive(4WD) vehicle under multiple operating conditions was conducted based on Simulink and Carsim platforms to verify the effectiveness of the controller. The longitudinal and lateral postures of the vehicle were coordinated and controlled using a transverse moment controller and a front wheel angle controller. The results show that the nonlinear three-step controller can effectively track the desired value of the control target, maintain the stability of the vehicle, and achieve active Ackermann steering geometry control under complex operating conditions.
In order to solve the problems of accuracy, comfort and robustness of driverless vehicles under parallel parking condition, a control method of path tracking based on model predictive control (MPC) is studied. The kinematics model of driverless vehicle under parking condition is established. The calculation method of minimum parking space size required for parking is proposed. The linear error model of vehicle kinematics is established. In order to make the vehicle track the desired path quickly and smoothly, an appropriate objective function is designed. In rolling optimization, the constraint conditions of velocity and front wheel steering angle are imposed on the objective function to achieve the solution in the control period, the control input constraint and control increment constraint are set. In order to ensure the stability of the path tracking process, constraint condition of velocity is set. Based on MATLAB environment, the effects of control method of path tracking based on MPC under typical parallel parking condition is studied. Two vehicle models are selected to verify effects of the path tracking control method, and good tracking results are achieved. The results show that compared with the pure pursuit control method, MPC method can make the vehicle reach the end of the planned path, the path tracking error is smaller, the change of front wheel angle is smoother, the vehicle stability and passenger comfort are better, and parking robustness is improved.
This paper describes a fail-operational evaluation of the controllability and comfortability for the safety architecture development of steer-by-wire (SbW) systems. According to the functional safety requirement, it is demanded that Steer-by-Wire systems shall continue to function and not misbehave after a failure by the intended fail tolerant sub-system. Most recently, developing Steer-by-Wire Systems are well advanced in fail-operational design utilizing the redundant systems, principally using Sensor voting or ECU switching functions. The system can sustainably keep the lateral motion of vehicle even though a failure is detected while driving. During such events, the controllability assessment is used to determine the fault-tolerant time interval (FTTI), including failure detection and the safe state transition time. Furthermore, typically highly automated vehicles will be controlled without the human driver's input or reaction; this study considers test assessment containing the controllability for the driver and the comfortability for the passenger. The evaluation is accomplished by the comprehensive methodological approach composed of questionnaire jury ratings, vehicle behaviors, and physiological measures. The results can be applied to determine the requirements of SbW systems.
The advent of steer-by-wire technologies has changed the driving paradigm for drivers and vehicle autonomy. Such technologies integrate electric motors to actuate the tire-road plus human-machine interfaces. Steer-by-wire vehicles can benefit from haptic concepts through the provision of tunable force feedback, coupled with nonlinear control, to introduce lane keeping and pathway following technologies that minimize and possibly eliminate driver actions. In this article, two vehicle haptic interfaces, including a robotic grip and a joystick, both of which are accompanied by nonlinear sliding mode control, have been developed and studied on a steer-by-wire platform integrated with a virtual reality driving environment. An operator-in-the-loop evaluation that included 30 human test subjects investigated these haptic steering interfaces over a prescribed series of driving maneuvers through real-time data logging and post-test questionnaires. A conventional steering wheel with the robust sliding mode controller was used for all the driving events for comparison. Subjective and objective results from the tests demonstrate that the driver’s experience can be enhanced by up to 76.3% with a robotic grip steering input when compared to the steering wheel during extreme maneuvers. The robotic grip’s superior performance in certain vehicle maneuvers indicates its potential as an alternative haptic steering adaptation for future semi-autonomous vehicles.
Vehicle dynamics is one of the most important vehicle attributes. It is classified into three domains, the longitudinal, vertical, and lateral dynamics. This paper focuses on optimizing the lateral vehicle dynamics which is driven by the straight ahead controllability and cornering controllability of the vehicle. One of the important parameters that dictates these sub-attributes is the steering ratio. Therefore, designing the right steering ratio is critical to meet the vehicle “specific” targets. Significant amount of work has been done by many researchers on variable steering ratio by implementing variable gear ratio (VGR) rack, active steering, and steer-by-wire systems. This paper discusses the methodology and considerations to optimize the steering ratio for a constant gear ratio rack by optimizing the steering column layout, viz., orientation and the phase angle in universal joints. A detailed analysis of steering system layout is done to optimize the steering ratio to enhance the vehicle dynamics performance. Full vehicle-level multibody dynamics (MBD) simulations are done in ADAMS® to compare the vehicle response behavior for different steering ratios in the open-loop objective tests. The Computer Aided Engineering (CAE) results show significant impact of the proposed design methodology on vehicle controllability. When the phase angle and the initial column angle are optimized for a quick on-center steering ratio, the response gains are higher, resulting in a sporty and agile feel. However, when the same vehicle is tuned for a slower on-center steering ratio, the gains are lower, resulting in a sluggish, lazy feel. This methodology can be implemented during the initial vehicle design phase to optimize vehicle performance.
In this study, we focus on “camber angle control” and “derivative steering assistance” using “steer-by-wire” as maneuverability and stability improvement techniques that are appropriate for the electric vehicle (EV) era. Movements that produce a negative camber angle generate camber thrust, and vehicle motion performance improvements extend from the fact that the tire side force is increased by the camber thrust effect. In our experimental vehicle, a proportional steering angle system was used to create negative camber angle control via an electromagnetic actuator that allowed us to confirm improvements to both the effectiveness and stability of steering control in restricted cornering areas. More specifically, we determined that it is possible to improve critical cornering performance by executing ground negative camber angle control in proportion to the steering angle. Steer-by-wire refers to an electrical steering technique that allows the steering angle of the entire vehicle to be controlled independently of the front wheel steering angle, thereby providing a high level of steering system control freedom. When derivative steering assistance control is applied, the phase of the front wheel steering angle advances faster in proportion to the steering angle velocity change than would normally occur based on the driver’s steering actions, which can improve ease of operation and maneuvering stability. In an experimental vehicle equipped with derivative steering assistance via a steer-by-wire system, the steer effectiveness was improved because the phase of the front wheel steering angle advanced due to the derivative steering assist, thereby improving the vehicle responsiveness.
Since steering-by-wire (SBW) system decouples mechanical linkages between front tires and the steering wheel, the road feeling characteristics of SBW system can be designed flexibly to improve the driving experience. In this article, a road feeling system with adjustable performance is proposed based on integrating the elements of the steering wheel module and the steering actuator module of SBW system. In this system, the road feeling torque consists of a main toque and a tuning torque, which are deduced by parametric method. The main torque is to feed back the tire dynamics and road properties to the driver intuitively, and the tuning torque is designed as a compensation of the main torque to tune the road feeling performance. The parameters in the formula of road feeling torque are selected properly and the driver can get the preferred road feeling performance by tuning these parameters in the formula. Next, to obtain the desired road feeling characteristics for different drivers, the sensitivity of formula parameters is analyzed quantitatively according to objective evaluation indices for on-center handling. Then, in the light of moderate type drivers, a set of tuning rules is proposed to determine specific values of parameters. Finally, contrast tests are conducted on the test bench to compare the road feeling performance of SBW test vehicle and electric power steering (EPS) test vehicle to verify the effectiveness of the proposed road feeling system in this article.
With the popularity of electrification and driver assistance systems on vehicle dynamics and controls, the steering performance of the vehicle put forward higher requirements. Thus, the steer-by-wire technology is becoming particularly important. Through specific control algorithm, the steer-by-wire system electronic control unit can receive signals from other sensors on the vehicle, realize the personalized vehicle dynamics control on the basis of understanding the driver’s intention, and grasp the vehicle movement state. At the same time, to make these driver assistance systems better cooperate with human drivers, reduce system frequent false warning, full consideration of mutual adaptation for the systems and the driver’s characteristics is critical. This paper focuses on the steering performance of steer-by-wire vehicle. Feature parameters are obtained from the virtual turning experiment designed on the driving simulator experimental platform. The identification model of driver steering behavior characteristics is established based on the experiment data with Back Propagation neural network as the aid of pattern recognition theory. The model is able to predict human driving behaviors and distinguish among different drivers, to classify the steering behavior. On this basis, according to different types of steering behavior, the variable steering angle ratio of steer-by-wire vehicle is designed to meet the individual needs of different driving habits. Finally, the hardware-in-the-loop simulation experiment validation shows that the proposed personalized variable steering angle ratio control strategy can meet the different steering preferences of the driver, and realize the angle ratio self-adaptive adjustment at high and low speed, improve the vehicle low-speed steering sensitivity, high-speed handling stability and active safety. This control strategy effectively enhances the steering performance and overall dynamics characteristics of steer-by-wire vehicles, achieving the human driver and vehicle coordination control.
Recently, a lot of electric vehicle (EV) has been developed to improve the energy consumption problem and electric power steering system has attracted the researchers’ concern. Steer-by-Wire (SbW) system is an electric steering system where the mechanical link between the steering wheel and front wheels is eliminated. Due to the absence of direct mechanical linkage, the most challenging issue is to ensure that the front wheels closely follow the driver’s command. A sliding mode predictive controller (SMPC) for Steer-by-Wire systems (SbW) is proposed to achieve a proper tracking performance. The sliding mode predictive controller has two parts: sliding mode control (SMC) and model predictive control (MPC). The SMC is applied to improve the robustness of MPC in the presence of model uncertainties while the MPC is applied to enhance the tracking performance of SMC. The simulation results and experimental results demonstrate the effectiveness of the proposed controller in steering angle tracking tasks.
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