基于增益模糊滑模变结构的线控液压转向控制

在分析全液压转向结构与转向偏差机理的基础上，设计了一种线控液压转向系统以实现车辆转向同步，消除转向偏差；针对现有方法确定的期望转向曲线可跟踪性差而无法实现转向同步，提出一种基于转向效率的期望转向曲线及其可行域确定方法，以最大、最小转向效率对应转向曲线为期望转向曲线可行域的上、下边界，确保期望转向曲线的可跟踪性；针对系统扰动不确定性及油液泄漏非线性，基于组合趋近律滑模控制，并引入饱和函数代替符号函数，在一定程度上抑制了控制系统的抖振；由于组合趋近律增益自适应性不足，导致车轮转角及角速度发生变化时，存在系统动态响应能力差的问题，通过分析车轮转角、角速度与趋近律增益的关系，制定了基于车轮转角及角速度的模糊规则表以自适应调整趋近律增益，实现增益模糊滑模控制，进一步提高油液补偿自适应能力和线控液压转向系统的鲁棒性；最后基于MATLAB/Simulink进行了仿真和试验验证。结果表明：提出的基于转向效率的期望转向曲线均具有良好的可跟踪性能；增益模糊滑模变结构控制具有良好的动态响应特性及控制精度，可有效地消除转向偏差，实现线控液压转向系统的同步转向。

Hydraulic Steering by Wire Control Based on Gain Fuzzy Sliding Mode Variable Structure

By analyzing the mechanism of steering deviation and the structure of full hydraulic steering, a type of line-controlled hydraulic steering system was designed for vehicle steering synchronization and steering deviation elimination. Owing to the poor traceability of the expected steering curve determined by existing methods, steering synchronization is impossible. A new method of determining the expected steering curve and its feasible region based on steering efficiency was proposed; it can be used to determine the maximum and minimum steering. The efficiency corresponding to the steering curve is the upper and lower boundary of the feasible region of the expected steering curve to ensure the traceability of the desired steering curve; to address the uncertainty of system disturbances and the nonlinearity of oil leakages, sliding mode control based on the combined approach law was adopted, and a saturation function was introduced instead of a symbol function, thereby restraining the chattering of the control system to some degree. Because of the insufficient self-adaptability of the gain of the combined approach law, the system exhibits poor dynamic responses when the wheel angle and angular speed change. By analyzing the relationship between wheel angle, angular speed, and the gain of approach law, a fuzzy rule table based on wheel angle and angular speed was developed to adjust the gain of the approach law, realize fuzzy sliding mode control of the gain, further improve the self-adaptability of oil-liquid compensation and hydraulic steering by line control, and the robustness of the system. The simulation and test verification were carried out based on MATLAB/Simulink. The simulation and test results indicate that the expected steering curve based on steering efficiency has satisfactory tracking performance. Moreover, the gain fuzzy sliding mode variable structure control has good dynamic response and high control accuracy, and it can effectively eliminate steering deviations and realize synchronous steering of line-controlled hydraulic steering systems.