Research On And Development Of Control System For Three-axle Electro-hydraulic Steering System

To improve the flexibility and stability of multi-axle steering, according to the sideslipphenomena that easily occur in actual working conditions, the lateral characteristics of typicalthree-axle steering in multi-axle steering vehicles are analyzed and discussed theoretically andexperimentally. The main points are in the following two parts:1）Analysis of control algorithms for three-axle electro-hydraulic active steering systemOn the basis of the mathematical models for front-wheel steering and four-wheel steering oftwo-axle vehicles, by using the momentum theorem and the moment theorem of Newton vectormechanics, a linear2-DOF lateral dynamics model for three-axle steering vehicles based on frontwheel angle was established; by the model, the mathematical model for uniform circular runningwas formulated; based on the centroidal zero sideslip angle control strategy, the relationship ofthe longitudinal displacement variation of the instantaneous turning center with velocity wasderived, and the mathematical expressions for lateral oscillation angular velocity gain, lateralacceleration gain and turning radius variation with the longitudinal displacement ofinstantaneous turning center were developed as well; the variations of the characteristicsparameters gains with velocity and the longitudinal displacement of instantaneous turning centerare further analyzed in steady-state working conditions, the effects of the longitudinaldisplacement of instantaneous turning center on the steering flexibility and lateral stability ofwhole vehicles are discussed from theoretical viewpoints; through optimization of the variationof the longitudinal displacement of turning center with velocity, the centroidal zero sideslip anglescheduling control strategy is proposed; the transient characteristics and the inherent attributes ofthree-axle steering are analyzed. The results of simulation analysis demonstrated that thecentroidal zero sideslip angle control strategy improves the steering flexibility and lateralstability of whole vehicles to a certain extent.2）Development of the control system for three-axle electro-hydraulic active steering systemTo verify the control effect of the centroidal zero sideslip angle scheduling control strategy,three-axle active steering test platform was designed and developed. The experimental study onthree-axle steering was made on the three-axle active steering test. The closed-loopelectro-hydraulic displacement based feedback steering control system was built up throughdisplacement sensors with an industrial PLC used as the central control unit for the controlsystem and flow servo valves and cylinders being the control objects. By using the CodeSys configuration software, the control algorithm was fixed in PLC, the actuators errors are adjustedthrough PID control modules, and the wheel steering angles errors and response speed areensured in the required range. The feasibility of application of the control strategy and the systemin practice was verified experimentally.