Dynamic Analysis And Drive Control Of Four-wheel-driven Vehicle Based On Constant Pressure Network

As the national economy constantly develops, higher performance requirementsfrom multiple domestic economy spheres for vehicle are raised. To some extent, theoverall efficiency and fuel economy of vehicle adopted hydrostatic transmissiontechnology are improved which is consonant with the energy-saving andemission-reduction policy. Four wheel independent drive vehicle has no traditionaldriving axles, thus chassis drive system is simplified and transmission efficiency israised. Meanwhile, mass is reduced, flexibility of drive system is improved andadaptability to complex road condition is strengthened. This configuration which isbest suitable for special vehicle lays the foundation for realization of comprehensivevehicle dynamic control.The technological base of the four-wheel drive system of this paper is constantpressure network, namely CPN technology. By going through relative literature ofhome and abroad, the working principle and existing problems of CPN in engineeringpractice are clear. Twin pump constant pressure network is put forward aimed atsolving these problems and variable universe fuzzy PID algorithm is designed torealize constant pressure control. In order to verify the feasibility and effectiveness oftwin pump system and constant pressure control algorithm, control model is builtwith Matlab/Simulink and simulation test is carried out.7DOF nonlinear vehicle model is established to investigate four-wheel drivedynamic characteristic. All mathematical expressions of important variables are given.Nonlinear magic formula is used as tire model. Tire mechanical behavior is carefullyanalyzed with magic formula tyre model under varies kind of working conditions.Based on these expressions, simulation model is built with Matlab/Simulink andpreliminary verification is carried out under straight line running.Road condition is vital for vehicle dynamic control. Extend state observer isdesigned to estimate the utilization factor of adhesion coefficient of driving wheels inthis paper. Then peak adhesion coefficient and best slip rate are estimated byRecursive Least Squares method with utilization factor of adhesion coefficient andtemporary slip rate. On this basis slip rate controller based on logic threshold strategyis designed to prevent driving wheels from slipping and secure safety driving.Estimator and slip rate control strategy is incorporated into nonlinear dynamicvehicle model. Simulation and analysis are carried out.Electric differential is one of the problems which has to be solved for four-wheeldrive system. In this paper front-wheel steering four-wheel drive vehicle is taken asobject of research and electric differential control strategy based on multi-modetransition ideology is designed. The strategy can decide which control method to use, speed or torque control according to the temporary slip rate of corresponding drivingwheel to achieve best differential result. Then speed control system with PIDalgorithm is designed for hydraulic pump/motor. The electric differential controlstrategy is employed in nonlinear vehicle model to verify its effectiveness.