Research On Gearshift Control For Automatic Transmission Based On Off-road Vehicle

Resistance and attachment characteristic of roads have a significant limitation on the vehicle driveline due to the complex road conditions of off-road vehicles.Therefore,off-road vehicles are generally equipped with hydraulic mechanical automatic transmissions.At the same time,shift quality control and reasonable gear selection are adopted to improve the ability to pass through complex roads,improve ground mobility and ride comfort of vehicles.This paper takes the off-road vehicle power transmission system consisting of an electronically controlled diesel engine and an automatic transmission as the research object,which is supported by "Off-Road Vehicle Integrated Control Technology-AT Control Technology Research" project which is studied by Jilin University and China FAW Group Corporation R&D Center.This paper establishes a dynamic model for off-road vehicle powertrain and analyzes the clutch-to-clutch shifting process for four basic gear-shift types(Power-on upshift,Power-on downshift,Power-off upshift and Power-off downshift).This research is mainly focusing on the shift quality improvement methods for the various stages of the Power-on upshift and the shift schedules that are suitable for road resistance conditions and attachment conditions.The specific research work is as follows:According to the structural characteristics and working mechanism of the hydraulic mechanical automatic transmission,a power transmission system model is established.The N-division method is used to establish the transmission power input model for the matching work between the electronically controlled diesel engine and the torque converter;the planetary gear transmission mechanism model is established using the Lagrange dynamics modeling method;the improved Woods model is established to build the wet clutch torque transmission,the above two models jointly construct a power transmission mechanism model;a complete vehicle dynamics model as the transmission output section and an electro-hydraulic control system model are built.Considering the complexity of the planetary gear transmission system,a simplified clutch-to-clutch shifting process equivalent gear shift model was developed,and then the basic shift pattern is analyzed.The state parameters of the shift process are reduced and a 2-gear gear-shift process model including power input,transmission mechanism,power output and coupling torque is constructed based on the Lagrange dynamic model.Combining this model,from the perspective of the master-slave end-to-end angular velocity control,the different types of shift processes are analyzed and corresponding shift process control strategies are formulated.The research of shift quality control in each phase of Power-on gear-shift process is as follows.The torque fluctuations of the output shaft during each stage and the moment of stage switching during the Power-on gear-shift-process are analyzed.A feed forward-feedback control strategy is adopted for the control of the clutch-to-be-engaged clutch during the initial stage of shifting.The model-based adaptive control method based on the torque exchange characteristics of the torque-to-be-engaged clutch and the to-be-detached clutch is used,and the external phase is easily disturbed by the inertial phase shift.With the characteristics of system characteristics changes,an auto-disturbance rejection control strategy based on clutch equivalent speed difference was proposed.In view of the characteristics of off-road vehicles' driving roads,the shifting schedule adapted to road resistance conditions and attachment conditions is studied.A vehicle longitudinal dynamic model under complex conditions is established,and a joint identification model of the generalized resistance coefficient of the road and the equipment quality of the entire vehicle is established.Based on the double-hidden hidden Markov model for the average resistance and fluctuation of the road section,the resistance conditions of the current scope of road are identified.Based on the power shifting schedule,the fixed shifting schedule of the off-road vehicle is established according to the resistance condition,and the shift type for the off-road vehicle is determined.According to the relationship between the output shaft speed and the vehicle speed,the vehicle's sliding state under the driving conditions is determined,and the transmission gear is properly intervened to avoid unreasonable gear selection.The simulation analysis of the control strategy for the off-road vehicle powertrain system and the HIL test verification platform are constructed based on the dSPACE rapid prototyping control system.Through the vehicle road test,the designed control strategy is verified,and the shift quality and dynamic performance of the vehicle are analyzed.The improvement effects of its shift quality,dynamics and economy are analyzed.