Research On Estimation Method Of State Parameters For Critical Instability Conditions Of Electrified Chassis

With the development of integrated and intelligent electric chassis,the dynamic coupling between the main subsystems of the electric chassis has become a hot topic in the field of automotive dynamics.In the steering process of the electric chassis system,the driving state of the vehicle can be divided into stable region,unstable region and critical instability region.It is not only theoretical significance to study the coupling problem between the main subsystems of the electric chassis and establish the vehicle nonlinear dynamics model in the critical instability region,but also has a far-reaching significance to promote the development of the active safety of the electric vehicle.This paper carried out theoretical research and simulation analysis on the establishment of the nonlinear dynamics model in the critical instability region,the criterion of the critical instability boundary and the accurate estimation of the vehicle critical state parameters under the critical instability condition.The following aspects:(1)Under the condition of critical instability,consider the braking,steering and suspension subsystem of the electric chassis that involving the longitudinal,lateral and vertical dynamics of the vehicle.Simultaneously,discuss the structure and mechanism of the main subsystems and determine the direct or indirect relationship between the various systems.The nonlinear dynamic model of vehicle including longitudinal,lateral and vertical under critical fault conditions is established.(2)Exploring the causes of automobile instability,such as sidesliping,emergency steering,emergency braking and so on can lead to the instability.Analyze the boundary conditions of the vehicle driving state from the stable area to the unstable area,and define the comprehensive stability coefficient k of the vehicle to characterize the degree of vehicle stability while traveling.While k(27)0.5,the car was in a stable region;while 175.0(27)(27)k it is in a critical state of instability and k(29)1 that is in a state of instability.Verify the coefficient based on the virtual test in two road conditions that the straight line of acceleration/braking and the double line path.The results show that the stability coefficientk can effectively reflect the stability of the vehicle during the driving process.(3)Simplify the tire structure and consider the longitudinal deformation of the tread and the side deflection characteristics.Establish the improved tire brush model and discuss the boundary between the attachment zone and the slip zone in the contact area.Using the dynamics simulation software Carsim to test the vehicle handling and stability in the double lane change.The test results show that the value k is always in the range of(0,1)during the running process,which can mean that the vehicle is always in the controllable stable range during process.The reliability of the vehicle with improved tire brush model is verified in the vehicle handling and stability test.(4)In order to adapt to the nonlinear mutation phenomenon in the boundary area of critical instability,a strong tracking filter theory is introduced.Based on the classical UKF,a strong tracking unscented Kalman filter algorithm(STUKF)is proposed.Estimate real-time the key parameters such as yaw rate,lateral acceleration and slip angle of the dynamic state and verified by Carsim & Simulink's joint simulation under serpentine condition.The test results show that the estimation accuracy of the STUKF algorithm is slightly higher than the commonly used UKF algorithm,and the time spent in the Matlab is only about 80% of the UKF algorithm.At the same time,the value k is always in the stable range of [0,0.5],which proves that the value can effectively reflect the degree of stability.