William C. Lin

INTEGRATED CHASSIS CONTROL SYSTEM TO ENHANCE VEHICLE STABILITY.

Vehicle stability enhancement system, by controlling vehicle dynamics, is the latest active safety technology introduced since Antilock Brake System (ABS) and Traction Control System (TCS). This system provides the driver with enhanced vehicle stability and handling. It is the intent of this paper to provide an understanding of the fundamentals of control of vehicle stability. The paper describes a complete stability control algorithm. Starting with a model for the vehicle yaw-plane dynamics, we derive a desired vehicle response, using both time-domain and frequency-domain approaches. Control structures include both yaw rate feedback design, and full-state feedback design. The latter approach requires the estimation of vehicle side-slip velocity. Estimations based on integration of lateral acceleration, the use of algebraic equation using vehicle kinematics, and the use of a Luenberger observer are presented. Computation of the required wheel differential velocity to achieve control objectives is described. Finally, computer simulation is used to investigate and confirm the concepts being discussed.

A Pattern-Recognition Approach for Driving Skill Characterization

Information about a drivers driving skill can be used to adapt vehicle control parameters to facilitate the specific drivers needs in terms of vehicle performance and safety. This paper presents an approach to driving skill characterization from a pattern-recognition perspective. The basic idea is to extract patterns that reflect the drivers driving skill level from the measurements of the drivers behavior and the vehicle response. The experimental results demonstrate the feasibility of using a pattern-recognition approach to characterize a drivers handling skill. This paper concludes with the discussions of the challenges and future works to bring the proposed technique to practical use.

The UniTire model: a nonlinear and non-steady-state tyre model for vehicle dynamics simulation

The UniTire model is a nonlinear and non-steady-state tyre model for vehicle dynamics simulation and control under complex wheel motion inputs involving large lateral slip, longitudinal slip, turn slip and camber. The model is now installed in the driving simulator in the Automobile Dynamic Simulation Laboratory at Jilin University for studying vehicle dynamics and their control systems. Firstly, the nonlinear semiphysical steady-state tyre model, which complies with analytical boundary conditions up to the third order of the simplified physical model, is presented. Special attention has been paid to the expression for the dynamic friction coefficient between the tyre and the road surface and to the modification of the direction of the resultant force under combined-slip conditions. Based on the analytical non-steady-state tyre model, the effective slip ratios and quasi-steady-state concept are introduced to represent the non-steady-state nonlinear dynamic tyre properties in transient and large-slip-ratio cases. Non-steady-state tyre models of first-order approximation and of high-order approximation are developed on the basis of contact stress propagation processes. The UniTire model has been verified by different pure and combined test data and its simulation covered various complex wheel motion inputs, such as large lateral slip, longitudinal slip, turn slip and camber.

Driving skill characterization: A feasibility study

Information about drivers driving skill can be used to adapt vehicle control parameters to facilitate the specific drivers needs in terms of vehicle performance and driving pleasure. This paper presents an approach to driving skill characterization from a pattern-recognition perspective. The basic idea is to extract patterns that reflect the drivers driving skill level from the measurements of the drivers behavior and the vehicle response. The preliminary experimental results demonstrate the feasibility of using pattern recognition approach to characterize drivers handling skill. This paper concludes with the discussions of the challenges and future works to bring the proposed technique to practical use.

A study on speed-dependent tyre-road friction and its effect on the force and the moment

The purpose of this paper is to investigate the effects of dynamic road friction on a tyre’s mechanical properties. Despite the fact that most existing analytical tyre models tend to ignore the speed-dependent effects on the tyre’s forces, many experiments have demonstrated that the force and moment of a tyre actually vary with the travelling speed especially when the force and moment are nearly saturated. For this reason, the speed-dependent effects of tyre–road friction need to be reviewed intensively in an attempt to enhance the accuracy and reliability of the existing tyre models. In this paper, a tyre rubber friction tester and a series of testing methods are first developed. An analytical tyre model based on dynamic friction is then established by incorporating the speed effects into the model. Finally, comparison between test data and simulation results of the analytical model and the semiphysical model are conducted and analysed prior to the conclusions.

Enhanced traction stability control system

This paper is directed to an Enhanced Traction Stability Control System (ETSC) that is based on the estimate of vehicle yaw rate and does not require yaw rate or lateral accelerometer sensors information. The validity of the yaw rate estimate is determined and used to select the appropriate control methodology. We estimate the vehicle yaw rate based on the measured speeds of the un-driven wheels of the vehicle, and we utilize various other conditions to determine if the estimated yaw rate is valid for control purposes. When it is determined that the yaw rate is valid, a combined closed-loop yaw rate feedback, and an open-loop feed-forward derivative control based on the driver input is employed. Whereas in conditions under which it is determined that the estimated yaw rate is not valid, an open-loop feed-forward control with a proportional, derivative and a diminishing integrator terms, is employed. In addition, we develop a bank angle compensation algorithm using the steering angle, vehicle speed, and the estimated yaw rate to compensate for the effect of banked road. Test results indicate marked enhancement of vehicle stability with ETSC when compared with ABS and TCS. Finally, we present test results to compare the performance of ETSC system to yaw rate feedback control only Electronic Stability Control System (ESC) using yaw rate and lateral accelerometer sensors information.

EKF-Based In-Vehicle Estimation of Relative CG Height

The distance from the center of gravity (CG) of the sprung mass to the roll axis, referred to as the relative CG height, is a critical parameter in vehicle roll motion. Although the nominal value of the relative CG height can be measured, its actual value generally varies due to different vehicle loading conditions. To facilitate the control of vehicle roll motion, this paper presents a model-based in-vehicle estimation of the relative CG height. The parameter estimation utilizes information measured by common in-vehicle sensors and employs an approach for the parameter estimation in stochastic gray-boxes models. An Extended Kalman Filter (EKF) is developed based on a linear vehicle yaw/lateral/roll model and the best estimate was solved by minimizing the EKF prediction error. A simplified estimation algorithm for in-vehicle implementation is also presented; the simplified algorithm limits the parameter space to a finite number of candidate parameters and the candidate that yields the smallest EKF innovation is identified as the best estimate. The estimation results with vehicle experimental data are included to verify the effectiveness of the proposed design.© 2008 ASME

Experimental Research on Friction of Vehicle Tire Rubber

A newly developed tire rubber friction test machine is introduced. Friction test method of tire rubber is provided. Test data of tire rubber friction on concrete and icy road surfaces are obtained and analyzed. The effect of different road surface, ambient temperature, contact pressure, and slip velocity on friction coefficient is apprehended. The dynamic friction is introduced to tire semi-empirical modeling, and the accuracy of the model is improved. A way of forecasting tire property on high-rolling speed using data from low-rolling speed tire test is illustrated.

Active Front Steering Damping Control

This paper investigates the feasibility of steering-wheel damping enhancement control of an active front steer (AFS) system without the benefit of closed-loop feedback control and actuator control parameter adjustment. Through a comprehensive modeling and analysis of the AFS system, a simple, yet effective solution is reached to incorporate an additional control term to the actuator angular displacement command, which permits the fine-tuning of the steering wheel damping characteristics as a function of vehicle operation states beyond the pre-determined specification. Furthermore, the analysis also identifies a fundamental relationship between steering effort and the damping control, and thus leads to a proposed fine tuning of the Variable-Effort Steering for further development and implementation.© 2007 ASME

Vehicle Handling and Stability Enhancement With Active Steering Control Systems

This paper presents an analysis and comparison of a vehicle with active front steering and rear-wheel steering. Based on linear analysis of base vehicle characteristics under varying speed and road surfaces, desirable vehicle response characteristics are presented and a set of performance matrices for active steering systems is formulated. Using pole-placement approach, controllability issues under active front wheel steering and rear- wheel steering controls are discussed. A frequency response optimization approach is then used to design the closed-loop controllers.Copyright