Research On All-wheel Steering System With Electronically Controlled Hydraulic Method Applied For Heavy-duty Vehicle

With the development of heavy vehicle specialization,the mobility and maneuverability of heavy vehicles have become the focus of research due to the contradiction between the construction site conditions and the excessive length of the body and the need for certain needs to be in place in a hurry.This paper is based on the transversal project "A heavy engineering vehicle special chassis system development",with a full load of twenty-one tons of two-axle heavy vehicles as the research object.This vehicle adopts the traditional mechanical hydraulic steering system for front wheel steering and electro-hydraulic proportional steering system for rear wheel steering.The front wheel steering hydraulic system and the rear wheel steering hydraulic system are connected by hydrostatic transmission to realize the real time following of the rear axle wheels with the front axle wheels.In this paper,the working characteristics,control algorithm,all-wheel steering mode control strategy and all-wheel steering vehicle stability control algorithm of the all-wheel steering actuation system are studied,and the verification of the actuation system execution state and the validity of the upper and lower control algorithms are carried out based on the joint software simulation platform.The feasibility of the designed all-wheel electro-hydraulic steering system is verified by the test feedback.The contents of the paper mainly include.(1)Two-degree-of-freedom operation and stability dynamics model is based on the allwheel steering vehicle,followed by the analysis of the effects of longitudinal vehicle speed and rear axle corner gain on the lateral stability of the vehicle for the steady-state steering conditions,and the Trucksim presents a dynamics model for the verification of steering mode control strategies.(2)The detailed design of the all-wheel electro-hydraulic steering system based on the hydrostatic transmission principle is carried out,and the design of the potential table of Solenoid valve is completed for the all-wheel steering mode.Finally,the selection of hydraulic actuating cylinder,hydraulic pump,steering gear,electro-hydraulic proportional valve and accumulator was finished.(3)The actuation system modeling was carried out with the help of AMESim platform,and the main factors affecting the rear wheel corner following were proposed and their relationship with the response characteristics of the rear axle was derived.Then,the basic functional verification of the system was completed.Finally,the logic threshold control of the accumulator replenishment control subsystem was carried out for the hydrostatic transmission line,and the equivalent sliding mode variable structure control of the electro-hydraulic proportional system was carried out for the rear wheel corner response to optimize the robust and steady-state characteristics of all-wheel steering.(4)The low-speed maneuverability control is carried out for the all-wheel steering system with the same and inverse phase steering modes,and the all-wheel steering stability control mode is given for the medium-speed and high-speed steering conditions.In the all-wheel inverse-phase mode,the rear axle corner gain is controlled based on the Ackermann steering principle to reduce the turning radius and tire wear,and in the all-wheel in-phase mode,the rear axle corner gain is controlled to 1 to ensure the vehicle to side shift parallelly based on the effect of vehicle speed and rear wheel corner gain on the steady-state yaw velocity and steady-state side slip angle.The vehicle is restored to stability from the unstable state by controlling the front and rear wheel angle ratios in the all-wheel steering stability control mode.The speed range of the all-wheel inverse-phase steering mode is derived by limiting the maximum lateral acceleration of the vehicle,and the speed range of the all-wheel in-phase steering mode is derived by limiting the maximum lateral speed of the vehicle,and the allwheel steering stability control mode is used as the high-speed mode of the all-wheel inversephase steering mode and the destabilization correction mode of the front-wheel steering mode and the all-wheel inverse-phase steering mode.Finally,the switching conditions of each steering mode were calibrated based on the sensor output signals.(5)The steering wheel angle step steering test of all-wheel steering modes on a dry concrete road was carried out by the constructed real vehicle system,and the test results showed that the actual rear wheel angle and the actual yaw velocity of the vehicle could match the simulation values well in both all-wheel steering modes,which further illustrated that the rear wheel steering drive by hydrostatic transmission could optimize the angle lag following of the rear wheel steering and The All-wheel steering system with electronically controlled hydraulic method designed in this paper is feasible in the realization of all-wheel steering mode.