Abstract
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.
Highlights
Vehicle steering performance can be described in two general ways, that is, steering stability and portability
Advances in Mechanical Engineering static steering torque is mostly calculated by empirical formula, assuming that the tire–road contact patch is similar to a circle.[9,10]
It can be seen that the estimation results of empirical formula are larger than the experiment ones in region of small steering angles, but they become smaller in region of large steering angles. This phenomenon illustrates that the empirical formula has large error in estimating static steering torque of radial tire, whose tire patch is more similar to a rectangle
Summary
Vehicle steering performance can be described in two general ways, that is, steering stability and portability. Aiming at studying the static steering torque, tirepatch sliding torque on the basis of rectangular contact patch assumption is analyzed in this article. The movement of tire can be divided into two processes in static steering: tire elastic deformation phase and tire–road contact patch sliding phase. According to the principle of static torque generation,[15,27] the tire-patch sliding torque cannot be larger than tire–road friction torque. It is obvious from equations (10) and (11) that ex and ey remain constant as steered wheel angle varies, which means tire-patch sliding torque is constant as steered wheel angle varies.
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