<div class="section abstract"><div class="htmlview paragraph">This paper proposes a dynamic obstacle avoidance system to help autonomous vehicles drive on high-speed structured roads. The system is mainly composed of trajectory planning and tracking controllers. The potential field (PF) model is introduced to establish a three-dimensional potential field for structured roads and obstacle vehicles. The trajectory planning problem that considers the vehicle’s and tires’ dynamics constraints is transformed into an optimization problem with muti-constraints by combining the model predictive control (MPC) algorithms. The trajectory tracking controller used in this paper is based on the 7 degrees of freedom (DOF) vehicle model and the UniTire tire model, which was discussed in detail in previous work [<span class="xref">25</span>, <span class="xref">26</span>]. The controller maintains good trajectory tracking performance even under extreme driving conditions, such as roads with poor adhesion conditions, where the car’s tires enter the nonlinear region easily. The innovation of this paper lies in introducing a high-fidelity vehicle model and a muti-conditions UniTire tire model with high precision obtained after parameter identification through tire test data. In addition, the nonlinear relationship between tire lateral force and slip angle is expressed as a linear function. This method updates the equivalent cornering stiffness in the linear function by solving the slope of the secant of the tire cornering characteristic curve at the current moment online, which solves the problem of high computational complexity caused by applying complex tire models in the control system. The co-simulation results of Simulink and CarSim show that the designed system has good dynamic obstacle avoidance and driving stability performance under driving conditions with high speed and poor road adhesion.</div></div>
The variation of inflation pressure has an important effect on the mechanical characteristics of tires that can affect vehicle performance, so the influence of inflation pressure should be taken into account in high-precision tire models. Much research has focused on tire mechanical characteristics under different inflation pressures and modeling methods, such as the Improved Magic Formula/Swift Tire model developed by Schmeitz et al. that takes inflation pressure into account. Based on a large number of tire testing data under different inflation pressures, an empirical model can be obtained, but numerous tire tests are expensive and cannot reveal the mechanism. In previous studies, most tire tests were based on load control, wherein the load is constant while the footprint, carcass, and belt stiffness can change with the variation of inflation pressure, making the cornering characteristics much more complicated. Herein, a method of deflection control is used and the contact patch is well maintained. The effect of tire inflation pressure is simplified to be the change of structure stiffness and averaged contact pressure. The effect of inflation pressure on cornering properties under deflection control is systematically observed under different tire deflection values. In addition, a prediction model extended from the Magic Formula model is proposed. The model of Schmeitz et al. [ 1, 2] needs test data from at least three inflation pressures; the model proposed herein requires tests at only two inflation pressures. The validation shows that this prediction method has good accuracy, almost the same as that of the model of Schmeitz et al. The error index of the lateral force is at most 2%, and the error index of the self-aligning torque is 4% at the maximum.
Based on the results of tire handling test, the cornering properties of the tire at a small range of steer angles under different temperature are obtained, and the variation law of the tire cornering characteristic parameters with the tire temperature is obtained. By establishing a tread temperature model and finite element tire model considering temperature, the mechanism of tire mechanical properties with temperature is clarified, and the expression of tread stiffness and aligning stiffness considering temperature is obtained. Then, based on the above expression and the tire brush model considering the tire temperature state, a complex brush model is established. Through the model derivation, the relationship between the temperature and the tire cornering stiffness is obtained. The relationship is used as the basic expression formula to establish the UniTire cornering model considering tire temperature. In order to verify the correctness of the model, four kinds of temperature state cornering data are used for parameter identification, and the tire cornering properties in the other two temperature states is predicted. The error between the simulation results of the prediction model and the experimental results is very small, which effectively proves the predictive ability of the UniTire cornering model considering tire temperature. This research is helpful to improve the application of UniTire model, and provide theoretical and technical support for UniTire model indoor and outdoor expansion applications
:Based on the results of tire handling test of tires, the cornering properties of the tire under different wear conditions are studied, and the variation law of the tire lateral deflection characteristic parameters with the tire wear amount is obtained. By establishing a tread wear model to clarify the mechanism of tire wear characteristics change, the expression of tread stiffness, aligning stiffness and wear amount is obtained. Then, based on the expression and the tire brush model considering the tire wear state, a complex brush model of the tire considering the tread wear is established. The relationship between the wear amount and the tire cornering stiffness is obtained by the model derivation. The relationship is used as the basic expression formula of UniTire modeling to establish the UniTire cornering model considering the tread wear. In order to verify the correctness of the model, three kinds of wear state cornering slip data are used to fit, and the UniTire cornering model considering wear is obtained, the tire cornering properties in the other two wear states is predicted. The error between the simulation results of the prediction model and the experimental results is small, which effectively proves the predictive ability of the UniTire cornering model considering wear. The UniTire tire model helps provide theoretical and technical support for the UniTire model indoor and outdoor expansion applications. Key words:tire;wear;cornering stiffness;aligning stiffness;bush tire model;UniTire tire model 0 前言 * 随着汽车工业的发展,车辆在人们日常生活中
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