Xuewu Ji

Nonlinear robust control of integrated vehicle dynamics

A new methodology to design the vehicle GCC (global chassis control) nonlinear controller is developed in this paper. Firstly, to handle the nonlinear coupling between sprung and unsprung masses, the vehicle is treated as a mechanical system of two-rigid-bodies which has 6 DOF (degree of freedom), including longitudinal, lateral, yaw, vertical, roll and pitch dynamics. The system equation is built in the yaw frame based on Lagranges method, and it has been proved that the derived system remains the important physical properties of the general mechanical system. Then the GCC design problem is formulated as the trajectory tracking problem for a cascade system, with a Lagranges system interconnecting with a linear system. The nonlinear robust control design problem of this cascade interconnected system is divided into two H ∞ control problems with respect to the two sub-systems. The parameter uncertainties in the system are tackled by adaptive theory, while the external uncertainties and disturbances are dealt with the H ∞ control theory. And the passivity of the mechanical system is applied to construct the solution of nonlinear H ∞ control problem. Finally, the effectiveness of the proposed controller is validated by simulation results even during the emergency manoeuvre.

Matching strategy of electric power steering assistant characters based on the vehicle inherent road feel

Matching the assistant characters of an electric power steering (EPS) system so that the vehicle achieves a high performance is one of the key technologies in EPS design. A study on the matching strategy of EPS assistant characters is conducive to obtaining a good ‘vehicle performance’ earlier in the design process. This paper describes a method for designing the assistant characters of an EPS system based on the vehicle’s inherent ‘road feel’ denoted here as the steering torque gradient at a 0g or 0.1g lateral acceleration under the condition that the steering system is not a power-assisted system. With the aim of obtaining the vehicle’s inherent road feel, the relations between the steering resistant torque and the vehicle’s travel states are analysed on the basis of a two-wheel vehicle model with a uniform normal tyre force distribution in steady state circle cornering. It is found that the vehicle’s inherent road feel decreases with increasing speed especially in the low-speed regions. The matching strategy of EPS assistant characters based on the vehicle’s inherent road feel is presented and illustrated by designing the assistant characters of a sample EPS system utilized in a passenger car. It is found that the EPS system designed by this strategy can supply a good steering feel to the driver.

Generalized Internal Model Robust Control for Active Front Steering Intervention

Because of the tire nonlinearity and vehicle’s parameters’ uncertainties, robust control methods based on the worst cases, such as H∞, µ synthesis, have been widely used in active front steering control, however, in order to guarantee the stability of active front steering system (AFS) controller, the robust control is at the cost of performance so that the robust controller is a little conservative and has low performance for AFS control. In this paper, a generalized internal model robust control (GIMC) that can overcome the contradiction between performance and stability is used in the AFS control. In GIMC, the Youla parameterization is used in an improved way. And GIMC controller includes two sections: a high performance controller designed for the nominal vehicle model and a robust controller compensating the vehicle parameters’ uncertainties and some external disturbances. Simulations of double lane change (DLC) maneuver and that of braking on split-µ road are conducted to compare the performance and stability of the GIMC control, the nominal performance PID controller and the H∞ controller. Simulation results show that the high nominal performance PID controller will be unstable under some extreme situations because of large vehicle’s parameters variations, H∞ controller is conservative so that the performance is a little low, and only the GIMC controller overcomes the contradiction between performance and robustness, which can both ensure the stability of the AFS controller and guarantee the high performance of the AFS controller. Therefore, the GIMC method proposed for AFS can overcome some disadvantages of control methods used by current AFS system, that is, can solve the instability of PID or LQP control methods and the low performance of the standard H∞ controller.

A new robust control method for active front steering considering the intention of the driver

The influence of the active front steering system on the driver’s intention and the trade-off between the robustness and the performance of the active front steering controller have not been adequately addressed by current research studies. A new robust control method based on the normalized left coprime factorization model including uncertainty and perturbations is introduced, and the robustness of this method against high speeds and variations in the cornering stiffness without changing the intention of the driver is guaranteed by the design of the feedforward controller and the feedback controller. A single-step method is adopted to solve the feedforward robust controller and the feedback robust controller. The resulting controllers obtained by the proposed robust control method have a simple structure and do not require online optimization. Furthermore, simulations of the double-lane-change manoeuvre and of braking on a split-μ road are conducted to compare the performance and the stability of the new robust control method with those of the proportional–integral–derivative controller and the standard H∞ controller. Simulation results show that, in comparison with the other two control methods, the established new robust control method can enhance the vehicle stability and handling, and the tracking rapidity is improved by the introduction of feedforward control so that the active steering intervention does not affect the driver’s intention, regardless of the external interferences or emergency evasive manoeuvres.

Method for measuring a driver’s steering efficiency using electromyography

This paper is concerned with developing a new method for measuring a driver’s steering efficiency during a steering manoeuvre, for investigating the driver’s steering performance and for evaluating the steering comfort. Electromyography was successfully used to measure the driver’s muscle activity and to reveal the function of the driver’s key muscles in the steering manoeuvre. A measurement of the driver’s steering efficiency during a dynamic steering manoeuvre with two hands is presented on the basis of a regression analysis of the electromyography and steering-force data. The proposed measurement procedure consists of two parts. First, a multiple-regression analysis of the steering-force and electromyography data is conducted, and the steering forces in the steering wheel plane are predicted using the electromyography data of the key muscles producing the steering torque. Second, by predicting the steering force, the force capacity of the driver in the steering manoeuvre is estimated, and then the steering efficiency of the driver is measured. The steering efficiency of the driver, which characterizes the inefficiency, is thought to be a significant movement control strategy employed by driver, and its application in investigating the driver’s steering strategy is the subject of further study.

Objective evaluation method of steering comfort based on movement quality evaluation of driver steering maneuver

The existing research of steering comfort mainly focuses on the subjective evaluation, aiming at designing and optimizing the steering system. In the development of steering system, especially the evaluation of steering comfort, the objective evaluation methods considered the kinematic characteristics of driver steering maneuver are not proposed, which means that the objective evaluation of steering cannot be conducted with the evaluation of kinematic characteristics of driver in steering maneuver. In order to propose the objective evaluation methods of steering comfort, the evaluation of steering movement quality of driver is developed on the basis of the study of the kinematic characteristics of steering maneuver. First, the steering motion trajectories of the driver in both comfortable and certain extreme uncomfortable operation conditions are detected using the Vicon motion capture system. The operation conditions are under the restrictions of the vertical height and horizontal distance between steering wheel center and the H-point of driver, and the steering resisting torque else. Next, the movement quality evaluation of driver steering maneuver is assessed using twelve kinds of evaluation indices based on the kinematic analyses of the steering motion trajectories to propose an objective evaluation method. Finally, an integrated discomfort index of steering maneuver is proposed on the basis of the regression analysis of subjective evaluation rating and the movement quality evaluation indices, including the Jerk, Discomfort and Joint Torque indices. The test results show that the proposed integrated discomfort index gives a good fitting with the subjective evaluation of discomfort, which means it can be used to evaluate or predict the discomfort level of steering maneuver. This paper proposes an objective evaluation method of steering comfort based on the movement quality evaluation of driver steering maneuver.

State estimation in roll dynamics for commercial vehicles

ABSTRACT Accurate lateral load transfer estimation plays an important role in improving the performance of the active rollover prevention system equipped in commercial vehicles. This estimation depends on the accurate prediction of roll angles for both the sprung and the unsprung subsystems. This paper proposes a novel computational method for roll-angle estimation in commercial vehicles employing sensors which are already used in a vehicle dynamic control system without additional expensive measurement units. The estimation strategy integrates two blocks. The first block contains a sliding-mode observer which is responsible for calculating the lateral tyre forces, while in the second block, the Kalman filter estimates the roll angles of the sprung mass and those of axles in the truck. The validation is conducted through MATLAB/TruckSim co-simulation. Based on the comparison between the estimated results and the simulation results from TruckSim, it can be concluded that the proposed estimation method has a promising tracking performance with low computational cost and high convergence speed. This approach enables a low-cost solution for the rollover prevention in commercial vehicles.

Preliminary Research on Muscle Activity in Driver’s Steering Maneuver for Driver’s Assistance System Evaluation

The quantification of the driver’s workload to complement the subjective evaluation is required in order to evaluate the driver assistant system. Preliminary investigation results of muscle behavior during steering maneuver have been described. The role and the feature of muscle activities in simulated steering conditions have been clarified. Driver tends to maneuver with “push steering” in both clockwise direction and counter-clockwise direction. Muscle alternation and co-contraction between the two muscles corresponding to the opposite one could be seen at the change of the torque directions. According to the result, the driver’s steering workload might be estimated by evaluating the simultaneous activities of pectoralis clavicular and anterior deltoid of the both arms. The result of this research can be considered to be useful for the evolution of driver assistant system. Furthermore, it would contribute to spread the system and improve its performance. It might contribute to reduce traffic accidents as well.

Analysis of vehicle static steering torque based on tire–road contact patch sliding model and variable transmission ratio:

Static steering torque at parking is an important factor for steering portability of vehicle. At present, the most commonly used estimation method is empirical formula calculation, which, however, cannot explain the phenomenon that the steering torque increases rapidly when steering angle becomes very large (over 300°). This article proposes an estimation method of static steering torque on the basis of a mathematic model of tire-patch sliding torque, taking into account the changeable torque transmission ratio from steered wheel to steering wheel. Three components of static steering torque are modeled and analyzed, including the tire-patch sliding torque, gravity aligning torque, and internal friction torque of the steering system. In order to investigate the static steering torque at steering wheel, the transmission ratio of steering torque is obtained on the basis of rack-suspension mathematical analysis. An example of static steering torque estimation is conducted with the proposed method and is compared with experimental results. The comparison shows that the estimation results given by the proposed method are in better accordance with experimental results than other approaches.

Simulated Effects of Head Movement on Contact Pressures Between Headforms and N95 Filtering Facepiece Respirators-Part 1: Headform Model and Validation

In a respirator fit test, a subject is required to perform a series of exercises that include moving the head up and down and rotating the head left and right. These head movements could affect respirator sealing properties during the fit test and consequently affect fit factors. In a model-based system, it is desirable to have similar capability to predict newly designed respirators. In our previous work, finite element modeling (FEM)-based contact simulation between a headform and a filtering facepiece respirator was carried out. However, the headform was assumed to be static or fixed. This paper presents the first part of a series study on the effect of headform movement on contact pressures-a new headform with the capability to move down (flexion), up (extension), and rotate left and right-and validation. The newly developed headforms were validated for movement by comparing the simulated cervical vertebrae rotation angles with experimental results from the literature.