Abstract: The principle and the design requirements for assist characteristic of the bypass proportional valve type ECHPS were presented. A design method for parabolic ideal assist characteristic curve for a bus based on the ECHPS was proposed. Based on MATLAB/Simulink, the three degrees of freedom vehicle steering dynamic model and the ECHPS simulation model with hydraulic control module consisting of the electro-hydraulic proportional valve were established. The assist characteristic curve of ECHPS which was approximated to parabola was obtained by simulation. Eventually, the bench test of a certain bus ECHPS was carried out. The test result of the assist characteristic curve of ECHPS is well-matched with the simulation one, which validates that the proposed design method and simulation model of the ideal parabolic assist characteristic curve are right and effective; and the bypass proportional valve type ECHPS has excellent assist characteristic, which can satisfy both the low-speed steering portability and the high-speed handling stability of heavy-duty vehicles.

Key words: vehicle engineering, variable assist characteristics, electronically controlled hydraulic power steering (ECHPS), electro-hydraulic proportional valve

摘要： 介绍了采用电液比例阀控制旁通流量的电控液压助力转向系统（ECHPS）的原理和助力特性设计要求，提出了ECHPS抛物线型理想助力特性曲线设计方法。在MATLAB/Simulink中建立了基于整车三自由度动力学模型和电液比例阀控制模块的ECHPS系统仿真模型，通过仿真得到了近似于抛物线型的ECHPS助力特性曲线。最后对某大客车ECHPS系统进行台架试验，得到的ECHPS助力特性试验结果与仿真结果吻合良好，表明所提出的ECHPS助力特性曲线设计方法及其仿真模型是正确有效的；采用电液比例阀控制旁通流量的ECHPS具有良好的助力特性，可以实现重型车辆低速转向时的轻便性和高速转向时的操纵稳定性要求。

关键词: 车辆工程, 可变助力, 电控液压助力转向, 电液比例阀