Shih-Ken Chen

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.

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.

Modelling of Tire Overturning Moment and Loaded Radius

For evaluation of vehicle handling, subjective assessment is currently almost the only criterion. For the purpose of reducing cycle time and avoiding error of subjective assessment, the close-loop objective evaluation system through computer simulations has become an inevitable choice [Gwanghun, G.I.M. and Yongchul, C.H.O.I., 2001, Role of tire modeling on the design process of a tire and vehicle system. ITEC ASIA 2001, Busan, Korea, September 18–20; Guo, K., Ding, H., Zhang, J., Lu, J. and Wang, R., 2003, Development of longitudinal and lateral driver model for autonomous vehicle control. International Journal of Vehicle Design, 36(1), 50–65]. For this reason, the more accurate models of vehicle, tire and driver are necessary. Since structure and operating conditions of tires are very complicated, many researchers have paid more attention to the modeling of tire properties and varieties of tire model have been done to describe the tire behaviour of longitudinal, lateral forces and aligning moment [Pacejka, H.B., 2002, Tyre and Vehicle Dynamics. Butterworth-Heinemann, an imprint of Elsevier Science, ISBN 0-7506-5141-5]. However, there are few studies for the tire overturning moment (TOM), especially under large slip angle and camber angle. For the simulation of vehicle rollover, the expression accuracy of TOM is rather important. In addition, the difference of the loaded radius of left and right tires yields tire roll angle and that also affects vehicle roll behavior. In this paper, the modeling of TOM and loaded radius are presented first, and then the modeling results are compared with tire test data.

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