运动副间隙及受力状态对空间转向机构转向误差的影响

Influence of Clearances and Force State of Joints on Steering Error of Spatial Steering Mechanism

根据车辆转向梯形机构中转向节主销上下端受力方向不同和转向横拉杆的二力平衡状态,用主销的销、孔倾斜模型和转向横拉杆的变长杆模型描述机构中的运动副间隙,并用螺旋理论分析地面对轮胎反力传递作用在转向节的情况和转向节参考点绕含间隙主销回转副的运动,求出主销约束反力和左右车轮转向角,提出附加转向误差和敏感度指标用于评价参数对转向误差的影响程度和对间隙的敏感性。通过样例分析转向误差的变化趋势及12个参数对间隙的敏感度,结果表明,与无间隙情形产生的原理性误差相比,车辆朝装有摇臂机构侧大转向角转弯时,有运动副间隙时的转向误差反而有所减小;小转向角转弯时两处副间隙都会引起比较大的转向误差;主销后倾角、车速对间隙显著敏感;与纵向力和法向力对主销取矩相关的因素则相对不敏感。结果可为合理设计对运动副间隙敏感的参数值及合适的间隙制造公差和其许用大小提供指导。

According to the different force directions of the upper and lower ends of the steering knuckles and the balance state of the two forces on the tie rod in a steering trapezoid mechanism of a vehicle, the tilted axis model, which assumes that the axes of the two pairing elements of revolute kingpin are not coincident but inclined each other, and the variable length rod model of the tie rod are firstly addressed to describe the joint clearances in the steering trapezium. The screw theory is used to analyze the force situation acting on the steering knuckle from the reactions of the ground to the tires and the exponential product formula of an interesting point on the steering knuckle around the revolute pair with clearance. The constraint reactions of the kingpin and the steering angles of left and right wheels are calculated, and the additional steering error and the sensitivity index are proposed to evaluate the influence of parameters on the steering error and sensitivity to the joint clearances. The variations of steering errors and the sensitivity of 12parameters to the joint clearances are analyzed by an example. The results show that when vehicle steering to the driving side at a larger angle, the steering error analyzed by the case of the mechanism with the joint clearance is relatively smaller than that calculated by the clearance-free case;the kingpin caster angle, vehicle speed and other factors related to the lateral force acting on tires are significantly sensitive to the clearance;the longitudinal and the normal forces acting on tires and the factors related to their moments about kingpin are relatively small insensitive. The results can provide guidance for reasonable design of the parameter values sensitive to the joint clearances, appropriate manufacturing tolerances and allowable sizes of the clearances.