停车视距制动模型

Braking model of stopping sight distance

从运动学原理出发,对停车视距的制动模型进行了改进,用制动减速度综合考察汽车制动这一复杂过程,规避了制动摩擦系数这一难以动态测量的变化参数.新的制动模型将汽车制动过程分为3个阶段:制动反应时间阶段、制动力上升时间阶段和全制动时间阶段,推导了在制动力上升时间阶段和全制动时间阶段的制动距离,得出新的停车视距计算公式.并与现有标准和规范的取值进行了比较,研究了差值的变化规律.结果表明:随着车速的增大,修正后取值与规范计算值的差异趋于增大;当车速小于60km/h时,修正取值与规范计算值的差值较小;当车速大于80km/h时,差值明显增大.在设计条件允许时可适当减小视距取值以降低工程造价.

The braking model of stopping sight distance is revised based on kinematics theory. The vehicle braking process is expressed by deceleration, which avoids complex measure of braking friction coefficient. The braking process is divided into three successive phases： braking-reaction time step, brake force climbing time step, and full braking time step. Braking distance is deduced in the later two steps and new formula of stopping sight distance is obtained. The result is compared with guide criterion, and the variation of the difference is researched. It is shown that the difference rises with the increase of traffic speed, which is small when traffic speed is less than 60 km/h and increases remarkably when traffic speed is greater than 80 km/h. Under suitable design conditions, stopping sight distance should be reduced for saving cost.