Research On Powershift Control Of Combined Transmission For High-powered Tractor

The powershift transmission has the characteristics of uninterrupted power flow and self-adapting fluctuation of working load during shifting process.It has remarkable advantages in improving agricultural production efficiency than traditional manual mechanical transmission,so it has considerable application prospects.In-depth research on power shift technology will provide theoretical basis for independent research and development of powershift transmission in China,and it is a realistic need to promote the transformation and upgrading of domestic tractor transmission industry.In this paper,the powershift control process,control objectives,control methods and working characteristics of control elements of combined transmission for high-powered tractor are studied in depth.The research contents are as follows:Firstly,the structural characteristics of series transmission of three-piece transmission mechanism of combined transmission and powershift working process are analyzed.The hydraulic circuit of the electro-hydraulic control system matched with the combined transmission is designed.The simulation model of the tractor transmission system is established.Secondly,phase-splitting dynamics analysis of powershift is carried out.The powershift process is divided into three phases: low gear torque phase,sliding phase and high gear torque phase.The formulas for calculating the jerk,friction work and output torque of each phase are derived.The three-factor evaluation system of powershifting quality is constructed.Thirdly,based on the analysis of the key factors affecting the powershifting quality,the pattern search algorithm is proposed to optimize the powershifting quality.The multi-objective optimization function of shifting quality is constructed by the expression of the oil pressure linear variation law of the clutch and the calculation formulas of the evaluation index of shifting quality of each phase.The weighted coefficient method is used to pretreat the multi-objective function.The clutch oil pressure variation law is optimized accurately and the powershifting quality is improved effectively.Fourthly,in order to reduce the axial dynamic load produced at the moment of clutch engagement,the target variation law of displacement of clutch piston in empty stroke stage is designed.The tracking control of clutch displacement is realized.An optimization method to reduce the clutch displacement tracking error is proposed,which improves the clutch displacement tracking accuracy.Finally,aiming at the fatigue failure of reset spring of traditional on-off valve,a new type of on-off valve driven by micro-motor is designed.The dynamic model of the new type of on-off valve is established and its dynamic and static characteristics are studied.The new type of on-off valve keeps the spool position constant through the self-locking screw and has stable on-off performance.