Coordinated Control Of Longitudinal/Lateral/Vertical Tire Forces For Distributed Electric Vehicles

Global chassis control (GCC) is able to improve vehicle dynamics performance bycoordinated control of driving, braking, steering and suspension systems. In order todeal with the shortcomings of the current GCC methods, which frequently make use ofempirical control rules and simple vertical force control allocation methods, and areinsufficient to obtain optimal vehicle dynamics performance, this paper proposes anovel hierarchical coordinated control system of longitudinal/lateral/vertical tire forcesfor a distributed electric vehicle (DEV), which is equipped with four wheeldriving/steering and active suspension systems. Key technologies includingdetermination of vehicular control objectives, longitudinal/lateral/vertical forcedistribution, actuator control for tire forces and fault tolerant control are studied.In the upper layer of the coordinated system, the strategy for determination ofvehicular control objectives is proposed. By clarifying the desired vehicular drivingstate and taking driver’s input, vehicle state parameters and raod information intoconsideration, the desired forces and moments are determined and then the controlobjectives are obtained to follow the desired vehicular driving state. In the middle layerof the coordinated system, optimal distribution of longitudinal/lateral/vertical tire forcesis emphatically studied. A universal objective function combining the tire workload andthe dynamic ratio of vertical forces is developed,14equality and inequality constraintsincluding desired driving demands, tire friction limitations and actuator characteristicsare overall considered, an optimization algorithm for multi-constrained non-convexoptimization problem is discussed, and the key problem of optimal distribution oflongitudinal/lateral/vertical tire forces is successfully solved. In the lower layer of thecoordinated system, actuator control methods are discussed. By accuarate control ofmotor driving torque, steering angles and active suspension forces, each optimal tireforce is conducted.On the basis of the proposed coordinated control system, a fault tolerant controlmethod of longitudinal/lateral/vertical tire force actuators is developed. Based ondefinition of each type of driving/steering and active force actuator failure and analysisof actuator redundancy and vehicle safety state, the actuator system failures are dividedinto compensatable or uncompensatable failure modes, and then fault tolerant control methods based on longitudinal/lateral/vertical redistribution are designed for thecompensatable failures and fault control methods based on longitudinal/lateral tire forceredistribution or emergency rules are designed for uncompensatable failures, whichcontribute to solving the fault tolerant control problem for DEVs.In order to validate the effectiveness of the proposed coordinated control systemand the fault tolerant control method, simulation using CarSim and Matlab/Simulink isconducted in several driving conditions and actuator failure modes. The simulationresults show that the coordinated control system effectively achieves better vehicleattitude and handling stability, and the fault tolerant control method improves vehicledriving safety and actuation ability of the rest normal actuators when actuator failureoccurs.Based on the simulation validation, experiments are carried out using a driversimulator. The experimental results show that the coordinated control system and thefault tolerant control method effectively control the vehicle attitude and also enhancevehicle driving safety.