Abstract:  To evaluate the influences of the joint clearances, including the joint radial clearances and the rack moving direction inclination to lateral direction of vehicle, on the steering errors of a rack and pinion steering mechanism, the joint radial clearances in the steering mechanisms were treated as joint clearance link or variable length link, and then the kinematic model of the spatial steering mechanisms with the joint clearances and the analytical relationship between the rotation angles of kingpin axis and steering wheel were deduced by using the screw theory. An optimization model for the steering mechanisms was established by aiming at minimizing steering errors and taking the maximum values of pressure angles and the minimum value of the maximum steering angle as the constrained conditions. The kinematic analysis of an example shows that the forward and the return steering processes of the steering mechanisms with joint clearances have different steering errors and the return steering errors are larger than that of the forward steering; the steering errors at the moment of revering operation increase sharply; the increase of the joint clearance or the inclination of the rack may increase the minimum steering radius of the vehicle. Steering accuracy of the steering mechanisms with joint clearances may be improved by the optimal design considering the joint clearances. 

Key words: steering mechanism, screw theory, kinematic accuracy analysis, steering error, optimization design, joint clearance

摘要： 为评价运动副径向间隙和齿条倾斜对齿轮齿条转向机构转向误差的影响，将不同位置的运动副径向间隙用间隙杆和变长杆来代替，利用螺旋理论推导了转向机构的空间运动模型及主销转角与转向轮转角的理论模型。以最小转向误差为目标，以转向过程中压力角的最大值和车辆的最大转角最小值为约束条件，建立了含间隙转向机构优化模型。运动分析表明：含间隙转向机构的正转及回正过程具有不同的转向误差，且回正转向误差比正转转向误差更大；换向瞬间会产生比较大的转向误差；运动副间隙或齿条倾斜程度的增大会使车辆的最小转弯半径增大。考虑运动副间隙的转向机构优化设计，可以提高转向机构的转向精度。

关键词: 转向机构, 螺旋理论, 运动精度分析, 转向误差, 优化设计, 运动副间隙