Abstract:

The electronic hydraulic steering system of a third axis aimed at reducing the wear of the rear tires of the multi-axis vehicles. The actuator of electric hydraulic steering system and the working principles of the centering and self-locking cylinder of hydraulic system were focused.An expected angle of the third axle was fitted based on the Ackerman angle theorem. A model of electronic hydraulic steering system was built. A fractional order PID controller and the algorithm of fractional order PID controller parameters were put forward．At last  the simulation  analyses, a bench test and a vehicle test were conducted. The fitting results show that the residual square between the expected values and the real values of the angles of the third axle are within 0.16 and the fitting degree is above 0.985 when the speed of vehicle is as  10m/s or 20m/s. And the simulation results show that the system controlled by fractional order PID controller has smaller overtime and shorter adjusting time than the one of integral order PID controller. The bench test results show the errors between the expect values and the real values of the third axle are within (±0.3°) when the speed of vehicle is as 10m/s or 20m/s. Vehicle experimental  results show that tire wear are reduced no matter in the case of no-loaded or full-loaded after the fractional order PID control electric hydraulic steering system is installed.

Key words: multi-axle vehicle, steering system, hydraulic actuator, expected angle, fractional order PID controller

摘要：

为了改善多轴车辆后轴轮胎的磨损,设计了一种第三轴电控液压转向系统。重点研究了该系统的液压执行机构和对中自锁油缸的工作原理,拟合出了符合阿克曼转角定理的第三轴预期转角,建立了电控液压转向系统的模型，设计了分数阶PID控制器并提出了该分数阶PID控制器参数的选取方法,最后进行了仿真分析、台架试验、实车试验。拟合结果表明,第三轴预期转角在车速为10m/s和20m/s时,期望值和实际值的残差平方都在0.16以内,拟合度都在0.985以上。仿真分析结果表明,分数阶PID控制系统比整数PID控制系统具有更小的超调量和更短的调节时间。台架试验结果表明,第三轴预期转角在车速为10m/s和20m/s时,期望值和实际值的误差都在±0.3°以内。由实车试验可以定性看出,安装该第三轴电控液压转向系统比不安装该系统在空载和满载时轮胎磨损情况都有所改善。

关键词: 多轴车辆, 转向系统, 液压执行机构, 期望转角, 分数阶PID控制器