Driver's Steering Input Research Articles

Nonlinear shimmy and dynamic bifurcation in vehicle system with driver steering input

Based on the dynamic coupling analysis of the front wheel shimmy and vehicle plane motion, a three degrees of freedom (DOF) nonlinear shimmy model considering driver steering input is established. Firstly, when the driver steering input is not considered, the modal properties and dynamic stability of the system are investigated by solving the Jacobian matrix. Then, the nonlinear shimmy behavior considering the driver steering input is discussed by means of numerical calculations. The slow flow equations of the vehicle system considering the driver steering input are derived based on the complexification-averaging (CA) method. According to the nonlinear dynamics theory, the saddle node (SN) and Hopf bifurcation characteristics of the system are analyzed, the analytical solution of the front wheel shimmy angle is also obtained. Finally, with the help of the understeer gradient, the influence of the linear cornering stiffness of the front wheel on the nonlinear shimmy motion is discussed. It is summarized that the SN and Hopf bifurcation are more likely to occur in the shimmy system for an oversteered vehicle. The relevant conclusions are useful for the early anti-shimmy design of vehicles.

Design and Evaluation of Lane-Change Collision Avoidance Systems in Semi-Automated Driving

Hands on the steering wheel partial driving automation, in which the system controls the lateral and longitudinal vehicle motion while the driver holds the steering wheel, monitors the roadway, and intervenes when necessary, is an example of shared control driving. To insure mutual safety in shared control driving, the system also needs to guide the driver's interventions to avoid hazardous actions, such as risky lane changes. This study proposes three steering interventions that activate automatically when the system detects a lane change by monitoring the steering wheel angle inputted by the driver and road section and determining that the two vehicles are on a collision course. A driving simulation experiment with 80 drivers was conducted to compare four conditions: 1) no steering intervention; 2) a haptic steering intervention that increases stiffness against steering toward the lane where a collision may occur; 3) an automatic steering intervention that decouples the driver's steering input and autonomously steered the vehicle away from the hazard; and 4) multiple steering interventions that generate different degrees of haptic and automatic steering interventions based on the time headway and time-to-collision between vehicles. Analysis of driving performance and safety under conditions with and without steering interventions indicate that all participants, at some points, initiated lane changes that are likely to result in a crash during partial driving automation. However, the three interventions effectively reduced lane-change collisions compared to the baseline. While the automatic steering intervention avoided all collisions, the multiple steering interventions were determined to provide sufficient safety while being more thoroughly accepted by the drivers than the haptic and automatic interventions separately. These findings have implications for developing adaptive collision avoidance systems considering user preference and driving performance.

Data-Driven Feedforward Compensation Tuning in Torque Vectoring Control

In automotive control, torque vectoring enhances a vehicle dynamical characteristic by independently allocating wheel torques. Torque vectoring algorithms are often based on some form of closed-loop yaw rate tracking, whose reference is generated according to the driver's steering input. Thus, unless the vehicle is equipped with steer-by-wire, from the torque vectoring point of view, the driver's input simultaneously acts as a reference and as a disturbance. This paper presents a method to explicitly consider this aspect in the torque vectoring design by means of a feedforward compensation. At first, we identify the plant model highlighting the effects of the driver input steer on the system. Then, we design the compensation term with H∞ techniques based on the identified model. This solution is then refined using a Data-Driven approach based on a Bayesian optimization algorithm. Results show that the compensation term can reduce the tracking error by 40% and the control effort by 35%.

Electric vehicle powertrain and fuzzy controller optimization using a planar dynamics simulation based on a real-world driving cycle

The four-wheel independent-drive electric vehicle (FWID-EV) stands out among the electrically-propelled vehicles due to its higher efficiency. This EV configuration faces an energy management challenge, needing a controller to define the best power split among the motors, decreasing the energy consumption while keeping the EV performance. Aiming to overcome this challenge, this paper presents a fuzzy logic control (FLC) strategy to perform the power split among the electric motors to improve vehicle energy efficiency and dynamic performance under real driving conditions. The implemented controller is developed hierarchically, ensuring the speed follows a driving cycle and acting as an electronic differential to correct the vehicle trajectory along the path. Multi-objective optimization is presented using a particle swarm algorithm (MOPSO) to minimize the mass of the electrical components (motors and battery) and extend the driving range throu gh the maximization of the battery state of charge (SoC). Moreover, the optimization process also aims to enhance vehicle handling by minimizing the driver steering input during the cycle. The best trade-off solution was able to reach a 124.2 km drive range with a 235.8 kg battery (387.8 V and 91.2 Ah), presenting improved handling performance with 78.5% decrease in the driver steering action.

Effect of Inner and Outer Wheels Driving Force Control on Small Electric Vehicle

In this study, in order to improve steering stability during turning, we devised an inner and outer wheel driving force control system that is based on the steering angle and steering angular velocity, and verified its effectiveness via running tests. In the driving force control system based on steering angle, the inner wheel driving force is weakened in proportion to the steering angle during a turn, and the difference in driving force is applied to the inner and outer wheels by strengthening the outer wheel driving force. In the driving force control (based on steering angular velocity), the value obtained by multiplying the driving force constant and the steering angular velocity, that differentiates the driver steering input during turning output as the driving force of the inner and outer wheels. By controlling the driving force of the inner and outer wheels, it reduces the maximum steering angle by 40 deg and it became possible to improve the cornering marginal performance and improve the steering stability at the J-turn. In the pylon slalom it reduces the maximum steering angle by 45 deg and it became possible to improve the responsiveness of the vehicle. Control by steering angle is effective during steady turning, while control by steering angular velocity is effective during sharp turning. The inner and outer wheel driving force control are expected to further improve steering stability.

Rear-Wheel Steering Control for Enhanced Steady-State and Transient Vehicle Handling Characteristics

This paper presents a rear-wheel steering (RWS) control algorithm to enhance the vehicle handling performance without prior knowledge of tire characteristics. A RWS system is a chassis control module that can effectively improve vehicle maneuverability and stability. Since the tire-road friction coefficient is difficult to obtain in real world application, the proposed RWS control algorithm is designed so that it can be implemented without any tire-road information. The proposed RWS control algorithm consists of steady-state and transient control inputs. The steady-state control input is proportional to the driver's steering input for achieving the desired yaw rate gain. The desired yaw rate gain is obtained through an offline optimization that is aimed to minimize the vehicle lateral velocity. The transient control input consists of feedforward and feedback control inputs. The feedforward input is designed to improve transient responses of the yaw rate. Computer simulation studies have shown that a trade-off relationship between overshoot and response time exists when the RWS control input is a sum of the steady-state and feedforward inputs. To compromise this conflict, a feedback input has been designed. The overshoot can be significantly reduced while the response time is slightly changed via the feedback input. The proposed algorithm has been investigated via computer simulations. The simulation has been conducted for step steer and sine with dwell scenarios under various road friction conditions. The performance of a RWS vehicle was evaluated using objective indices. Simulation results show that the proposed algorithm enhances vehicle handling performance.

Robust Vehicle Driver Assistance Control for Handover Scenarios Considering Driving Performances

Handover scenarios referred as the transitions between a human driver and an automated driving system are challenging because some human drivers are not adapted to the vehicle steering characteristics in a handover process and thus may exhibit deteriorative driving performances. This paper proposes a robust controller to assist human drivers in the handover scenarios. A driver-vehicle model including the driver steering input is developed to enhance the cooperation between a human driver and an automated driving controller. The driver parametric uncertainties are explicitly modeled to consider different human driving performances. Then a robust controller is designed to assist the driver considering his/her steering input and parametric uncertainties. The effectiveness of the designed controller is validated through several driver-in-the-loop tests on a driving simulator. The handover test results show that the driver steering loads and the vehicle lateral deviations can be reduced by the designed controller, thereby improving the driving safety in the handover processes.

Robust lateral control of long-combination vehicles under moments of inertia and tyre cornering stiffness uncertainties

ABSTRACTA robust steering-based controller synthesis is presented for an A-double combination vehicle with a steerable dolly. The controller ensures robust stability and performance in the face of uncertainties in the cornering stiffness of the tyres and the moments of inertia of the semitrailers, which are treated as time-varying and time-invariant parameters respectively. A descriptor-type representation of the system is employed since a standard state-space model depends rationally on the moments of inertia. The controller synthesis is formulated as an -type static output feedback, which uses information from only one articulation angle. The driver steering input is also used by including a static feed-forward. The proposed synthesis method is based on linear matrix inequality (LMI) optimisation. The controller is verified based on the simulation results obtained from both (approximate) linear and (high-fidelity) nonlinear vehicle models. The results indicate significant improvement in the high-speed lateral performance of the A-double in the presence of parametric uncertainties.

Reference Governor Strategies for Vehicle Rollover Avoidance

This paper addresses the problem of vehicle rollover avoidance using reference governors (RGs) applied to modify the driver steering input in vehicles with an active steering system. Several RG designs are presented and tested with a detailed nonlinear simulation model. The vehicle dynamics are highly nonlinear for large steering angles, including the conditions where the vehicle approaches a rollover onset, which necessitates RG design changes. Simulation results show that RG designs are effective in avoiding rollover. The results also demonstrate that the controllers are not overly conservative, adjusting the driver steering input only for very high steering angles.

Lateral handling improvement with dynamic curvature control for an independent rear wheel drive EV

The integrated longitudinal and lateral dynamic motion control is important for four wheel independent drive (4WID) electric vehicles. Under critical driving conditions, direct yaw moment control (DYC) has been proved as effective for vehicle handling stability and maneuverability by implementing optimized torque distribution of each wheel, especially with independent wheel drive electric vehicles. The intended vehicle path upon driver steering input is heavily depending on the instantaneous vehicle speed, body side slip and yaw rate of a vehicle, which can directly affect the steering effort of driver. In this paper, we propose a dynamic curvature controller (DCC) by applying a the dynamic curvature of the path, derived from vehicle dynamic state variables; yaw rate, side slip angle, and speed of a vehicle. The proposed controller, combined with DYC and wheel longitudinal slip control, is to utilize the dynamic curvature as a target control parameter for a feedback, avoiding estimating the vehicle side-slip angle. The effectiveness of the proposed controller, in view of stability and improved handling, has been validated with numerical simulations and a series of experiments during cornering engaging a disturbance torque driven by two rear independent in-wheel motors of a 4WD micro electric vehicle.

Preview Controller Design for Vehicle Stability With V2V Communication

This paper presents a design method of a preview controller for vehicle stability with vehicle-to-vehicle (V2V) communication. Using V2V communication technology, a driver's steering input of a preceding vehicle is obtained on a following vehicle for preview control. To cope with changes in speed and intervehicle distance in a real situation, a position-based sampling is used. With the position-based sampling data, the time-based preview data are resampled by interpolation. For the controller design, linear vehicle modes describing yaw and roll motions are used. To design a preview controller on the following vehicle with the previewed steering input, a linear optimal preview control methodology is adopted. To validate the preview control with V2V communication in terms of vehicle stability, a simulation is conducted using a vehicle simulation package.

Steering control collision avoidance system and verification through subject study

Many of vehicle crash related fatalities are caused by run-off-road crashes and failures of the drivers to avoid obstacles in front of them. This can happen in near collision encounters, where the driver should steer in order to avoid a crash. In these situations, some drivers steer too much and go off the road, and some do not steer enough and collide with the obstacle. In this study, the authors developed a steering control collision avoidance system (SCCAS) to help drivers to safely perform severe manoeuvres and avoid such crashes. This system is activated by the driver's steering input, and was implemented in a car driving simulator to study human interactions. Testing the subjects with no collision avoidance feature resulted in collision with the obstacles in 61 out of 63 encounters; whereas, using the implemented SCCAS, the subjects avoided 44 out of 60 near collision encounters in a new scenario with the same level of difficulty as the original tests. The post-experiment surveys revealed that besides the effectiveness of the system in reducing the crashes, it was acceptable to the drivers and they found the activation type intuitive.

Lateral Handling Improvement with Dynamic Curvature Control for an Independent Rear Wheel Drive EV

The integrated longitudinal and lateral dynamic motion control is important for four wheel independent drive (4WID) electric vehicles. Under critical driving conditions, direct yaw moment control (DYC) has been proved as effective for vehicle handling stability and maneuverability by implementing optimized torque distribution of each wheel, especially with independent wheel drive electric vehicles. The intended vehicle path upon driver steering input is heavily depending on the instantaneous vehicle speed, body side slip and yaw rate of a vehicle, which can directly affect the steering effort of driver. In this paper, we propose a dynamic curvature controller (DCC) by applying a newly-defined parameter, the dynamic curvature of the path, derived from vehicle dynamic state variables; yaw rate, side slip angle, and speed of a vehicle. The proposed controller, combined with DYC and wheel longitudinal slip control, is to utilize the dynamic curvature as a target control parameter for a feedback, avoiding estimating the vehicle side-slip angle. The effectiveness of the proposed controller, in view of stability and improved handling, has been validated with numerical simulations and a series of experiments during cornering engaging a disturbance torque driven by two rear independent in-wheel motors of a 4WD micro electric vehicle.

Extremum-Seeking Control of ABS Braking in Road Vehicles With Lateral Force Improvement

An ABS control algorithm based on extremum seeking is presented in this brief. The optimum slip ratio between the tire patch and the road is searched online without having to estimate road friction conditions. This is achieved by adapting the extremum-seeking algorithm as a self-optimization routine that seeks the peak point of the tire force-slip curve. As an additional novelty, the proposed algorithm incorporates driver steering input into the optimization procedure to determine the operating region of the tires on the “tire force”-“slip ratio” characteristic-curve. The algorithm operates the tires near the peak point of the force-slip curve during straight line braking. When the driver demands lateral motion in addition to braking, the operating regions of the tires are modified automatically, for improving the lateral stability of the vehicle by increasing the tire lateral forces. A validated, full vehicle model is presented and used in a simulation study to demonstrate the effectiveness of the proposed approach. Simulation results show the benefits of the proposed ABS controller.

A New Predictive Lateral Load Transfer Ratio for Rollover Prevention Systems

In rollover prevention systems, a real-time lateral load transfer ratio (LTR) is typically computed to predict the likelihood of a vehicle to rollover and, hence, initiate rollover prevention measures. A traditional LTR largely relies on a lateral accelerometer signal to calculate rollover propensity. A new predictive LTR (PLTR) is developed in this paper, which utilizes a driver's steering input and several other sensor signals available from the vehicle's electronic stability control system. The new PLTR index can provide a time-advanced measure of rollover propensity and, therefore, offers significant benefits for closed-loop rollover prevention. Simulation results are presented using the industry-standard software CarSim to demonstrate the benefits of the new PLTR index. Experimental results of open-loop comparisons between LTR and PLTR indexes are presented, followed by experimental results on the closed-loop implementation of a PLTR-based rollover prevention system. The results in this paper document how a predictive rollover index can be developed and the advantages of such a system in rollover prevention.

The importance of unsteady aerodynamics to road vehicle dynamics

This paper investigates the influence that different unsteady aerodynamic components have on a vehicle's handling. A simulated driver and vehicle are subject to two time-dependent crosswinds, one representative of a windy day and the second an extreme crosswind gust. Initially a quasi-static response is considered and then 5 additional sources of aerodynamic unsteadiness, based on experimental results, are added to the model.From the simulated vehicle and driver, the responses are used to produce results based on lateral deviation, driver steering inputs and also to create a ‘subjective’ handling rating. These results show that the largest effects are due to the relatively low frequency, time-dependent wind inputs. The additional sources of simulated unsteadiness have much smaller effect on the overall system and would be experienced as increased wind noise and reduced refinement rather than a worsening of the vehicle's handling.

A Comparison of 25 High Speed Tire Disablements Involving Full and Partial Tread Separations

Tire tread separation events, a category of tire disablements, can be sub-categorized into two main types of separations. These include full tread separations, in which the tread around the entire circumference of the tire separates from the tire carcass, and partial tread separations, in which a portion of the tread separates and the flap remains attached to the tire for an extended period of time. In either case, the tire can remain inflated or lose air. Relatively, there have been few partial tire tread separation tests presented in the literature compared to full tread separation tests. In this study, the results of 25 full and partial tire tread separation tests, conducted with a variety of vehicles at highway speeds, are reported. Cases in which the tire remains inflated and loses air pressure are both considered. The testing was performed on a straight section of road and primarily focused on rear tire disablements. The driver steering inputs required to keep the vehicle within its travel lane and the vehicle's dynamic response during the events were documented with video and data acquisition equipment. The results from the testing are presented and compared. It was found that the steering inputs required to keep the vehicle within its lane during a partial tread separation were similar in magnitude to those in the full separation testing. These results were also similar to the results of full separation testing documented by other researchers. In all cases, the vehicle was controlled within its lane with minor corrective steering. Figure 1 depicts video documentation and vehicle speed during one of the test runs. Language: en

A Robust Steering Assistance System for Road Departure Avoidance

A driver-assistance system (DAS) that combines an automatic road departure avoidance (RDA) system with the driver's steering input is presented. The system is based on a closed-loop driver decision estimator (DDE), which establishes the risk of road departure. If a road departure is likely to occur, the RDA system intervenes by correcting the steering angle. Robustness is guaranteed by an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">inf</sub> controller designed to take into consideration the main uncertainties affecting the dynamics. Driver-in-the-loop tests evaluate the performance of the system in terms of robustness, risk of road departure, and driving experience. Experiments show that the system is effective in reducing the risk of road departure without impeding maneuverability.

Reference trajectory generation for control in single-unit heavy vehicle: focus on rollover prevention

The problem of reference trajectory generation for single unit heavy vehicle motion is investigated. The Reference Governor is integrated in the control structure with control allocation. This nonlinear block filters the driver steering inputs in order to modify the reference trajectories in such a manner that if followed by the vehicle the wheels keep contact with the road. The simulation results for a vehicle represented by an 8 DOF nonlinear model and controlled by front active steering and braking systems are performed for fishhook manoeuvre. They demonstrate the effectiveness of the proposed scheme.

Design of a Preview Controller for Vehicle Rollover Prevention

This paper presents a method for designing a preview controller for vehicle rollover prevention. It is assumed that a driver's steering input is previewable with a Global Positioning System (GPS) and an inertial measurement unit (IMU), or with an automatic steering system for collision avoidance. Based on a linear vehicle model, a linear optimal preview controller is designed. To avoid the full-state measurement of a linear quadratic regulator (LQR), linear quadratic static output feedback (LQ SOF) control is adopted. To compare with several types of controllers such as LQR or LQ SOF with respect to rollover prevention capabilities, Bode plot analysis based on a linear vehicle model is performed. To show the effectiveness of the proposed controller, simulations are performed on a vehicle simulation package CarSim.