Integrated Control Of Longitudinal/Lateral/Vertical For Distributed Electric Vehicles

With the strong support of national policies,new energy vehicles are widely used,and all kinds of electric vehicles are traveling in the streets,which has become a new research hotspot for the safety of electric vehicles.In view of the fact that today's chassis electronic control systems mostly start with combine the control of longitudinal forces and lateral forces,but it is difficult to fully improve the vehicle dynamics performance by simply dividing the vertical forces or designing based on empirical rules.Therefore,this paper selects distributed electric vehicles for the controlled vehicle.Distributed electric vehicle has independent drive or brake motor,independent steering motor and active suspension.With its superior chassis structure,it can be used as an important platform to enhance active safety and even improve the stability of the vehicle.Therefore,the unique chassis structure of distributed electric vehicles to design the vehicle controller to achieve optimal vehicle dynamics performance is very necessary.This article begins with comprehensively improving the vehicle dynamics performance,and conducts research on key issues such as vehicle safety,handling stability,ride comfort,and road tracking ability.Because of the highly controllable distributed,the electric vehicle has been choose as the controlled object,a top-down hierarchical integrated controller was designed to achieve the desired control objectives.A reference model is used at the upper level of the integrated controller to formulate vehicle attitude control requirements.A linear two-degree-of-freedom monorail model is used as the vehicle's ideal steering model,and an optimal preview lateral acceleration model is added to simulate the operator's control over the vehicle operation to expect driving response;the middle layer of the integrated controller is divided into two parts,the body control layer and the optimal distribution layer of tire force,and the body control layer converts the kinematic requirements into mechanical requirements through a nonlinear sliding mode control algorithm,and the calculations are met with the upper level instructions,the desired resultant force and resultant torque of the desired body;Tire force distribution layer is designed to establish a optimize function of the tire,to improve the handling stability of the vehicle by reducing the tire load rate,and to improve the ride comfort by balancing the vertical dynamic load coefficient,and also establish the Constraints;The lower actuator control layer controls the corresponding actuators to achieve the optimal distribution of the tire force output in the middle layer.Finally,the vehicle model was choose in the Car Sim environment to verify the effectiveness of the designed chassis integrated control system.The main content of this article:1.The distributed electric vehicle have four-wheel independent wheel hub motor,fourwheel independent steering motor and active suspension system,and also equipped with a plurality of other actuators.In order to fully improve the performance of the chassis of the vehicle,it is necessary to determine the control requirements in the driving process,and optimize the allocation of tire forces in the control process,then we will clarify the executive commands of different executing agencies,and finally achieve the control goal through precise control of actuators.Therefore,this paper establishes a modelbased layered integrated control strategy to control the various execution systems of the chassis in order to achieve a comprehensive improvement of vehicle dynamic response.The upper layer introduces the reference model and the two-degree-of-freedom steering model formulates the control objectives to obtain the required kinematics requirements.The middle layer converts the kinematics requirements to the mechanical requirements of the car body based on the sliding mode control algorithm,and use the optimal solution algorithm to assign the force and moment of the body to the tire.The lower layer translates optimized tire forces into actuator control commands acting on the drive brake system,steering system and suspension system.2.The main function of the upper layer of the chassis layered integrated controller is to accept manipulation information(accelerator opening,steering wheel angle,etc.),vehicle current status information,and road information,and formulate kinematic control objectives according to the desired reference model.Such as the desired longitudinal speed,lateral vehicle speed and vehicle body vertical velocity and set ideal pitch and roll angles for vehicle attitude during smooth running.A linear two-degree-of-freedom monorail model was introduced as the steering reference model for vehicle steering and the desired yaw rate was obtained to realize the operator's steering expectation on the vehicle.In simulation stage the lateral manipulation of the operator is simulated based on the lateral preview acceleration model so that the vehicle can runs in the target trajectory.3.The main role of the middle layer of the integrated controller is to convert the upperlevel kinematic control target into a resultant force and resultant moment that satisfy the vehicle's desired driving target through a nonlinear sliding mode control algorithm.The advantage of sliding mode control is that it can effectively solve the coupling problem of non-linear vehicles in all directions.It uses a simple sliding mode to track longitudinal,lateral,and vertical body speeds.In view of the deviation caused by the yaw angle error accumulation during steering and the abnormality of the control target caused by the accumulation of pitch angle and roll angle error,the terminal sliding mold surface is used for design,and the desired resultant force and resultant torque of the vehicle body are obtained.The tire force distribution layer is designed to adjust the tire load coefficient and the vertical dynamic load coefficient objective function,to further improve the vehicle handling stability and comfort,and also determine a series of practical constraints.4.The lower level of the integrated controller converts the tire's optimal distribution force through the tire's inverse model into executable commands that can be applied to the four-wheel hub motor,steering motor,and suspension system.Finally,through Car Sim and Matlab/Simulink joint simulation experiments and traditional uncontrolled passive suspension vehicles for comparison and verification,confirmed that the chassis integrated control system has improved the road tracking ability,handling stability and ride comfort of distributed electric vehicles.