Study On Gear Design Method And Control Strategy Of Power-shift Transmission

As the main power machinery for agricultural transportation and field operations,tractors play an important role in achieving modern precision agriculture.Intelligent heavy-duty tractors have attracted the attentions of agricultural machinery manufacturers and consumers in various countries because they can match advanced supporting equipment,carry out joint duplex operations,reduce the number of operators,reduce operating time,and improve operating efficiency.Although China has become a major agricultural machinery manufacturing country,its products are still dominated by lowend and mid-range products.It is still far behind developed countries such as Europe and the United States in terms of research & development and manufacturing capabilities of intelligent heavy-duty tractors.Its manufacturing key technologies have long been monopolized by European and American agricultural machinery giants,forming technical blockade.Therefore,it is of great significance to break through the long-term foreign monopoly in this technical field,establish an intelligent heavy tractor manufacturing method and technology system,and promote the industrialization of domestic heavy tractors.Power-shift transmission(PST)is characterized by high transmission efficiency,convenient shifting,easy expansion of the number of gears,and easy implementation of automatic control.It has become one of the core components commonly used in intelligent heavy tractors.The breakthrough of PST key design technology and intelligent control technology can promote the intelligence and industrialization of heavy tractors in China,which is an important means to achieve simple,safe,comfortable and efficient farm work.Therefore,under the support of the National Key R&D Program "Research on Intelligent Key Technology for Heavy Tractors and Development of Complete Machines(2016YFD0701100)",PST of heavy tractor is taken as the research object in this paper to carry out researches on structure design,parameter matching,gear shifting schedule and gear shifting process control.The main research contents are as follows:(1)The suitable operation contents of heavy-duty tractors are classified according to the force,power flow and working condition characteristics of the tractor-implement combination during operation.The force characteristics,operation speed,and operation goals of each type of operation are summarized and analyzed.According to the characteristics of regions and farming habits,a method for estimating the operating frequency of heavy tractors throughout the life cycle is proposed.The PST structure is designed based on the characteristics of the speed utilization rate in the whole life cycle of the heavy tractor.The transmission scheme is designed by the combination of floral shift and sequential shift.The transmission ratio parameters of each gear of the transmission are designed and matched according to the use requirements,the principle of ‘high frequency and high density’.The PST is designed which has a simple structure,low processing difficulty and low cost,and good overall performance.(2)According to the designed PST,the dynamic model of the tractor transmission system with multiple degrees of freedom is established.Taking the heavy-duty tractor under development as an example,the steady state model,dynamic mean value model and the mathematical model of gear shift actuator are established respectively.Based on the analysis of the random load characteristics of tractor operation,the load model of the whole vehicle is set up to simulate the load changes of the tractor during actual operation.Then,according to the characteristics of each type of operation,the test conditions for different types of tractors are constructed.The situation lays a foundation for the formulation of control strategies and simulation analysis.(3)According to the characteristics of the full-range speed-regulated diesel engine and the reference to the engine load rate during the operation,the PST tractor standard type shifting schedule with two parameters(engine speed and throttle opening)is formulated to meet the automatic shift requirements of PST tractor in various operation types and working conditions.In order to further improve the power or economy of PST tractors in common typical operations,targeted control strategies are formulated for typical operation modes: In traction operations without power output of Power Take-Off(PTO),The working condition factor is introduced as the shifting parameter,and the automatic shifting schedule of the tractor based on the Recursive Least-Squares Algorithm(RLS)working condition recognition is formulated;for the tractor equipped with PST,it is formulated for light-load field operations;The automatic shifting schedule of fuel economy for the tractor with PST in light load field operation is formulated,and the method of further improving fuel economy in cruise operation mode is given;A targeted automatic gear shift schedule is developed for road driving/transportation of tractors.(4)A dynamic model of the entire transmission system equipped with a PST tractor is established for PST shift process research.Taking the power-on gearshift with four clutches as an example,the implementation method of timing synchronization superposition of the main phases of shifting is proposed,and the gear shifting process with the sequences of torque phase-inertia phase-torque phase and inertia phase-torque phase-inertia phase are designed respectively.The automatic shift control strategy based on the integrated coordinated control of the engine and multi-clutch is formulated.Fast,smooth,power-on shift without interruption in power during tractor operation is achieved.Compared with the traditional segmented control strategy,the shift time is greatly saved(about 25 %),the number of speed fluctuation and engine speed regulation is reduced,and the shift efficiency is improved.(5)The PST principle prototype is designed and the PST comprehensive test bench is built.The test bench and PST test program are developed based on Matlab/Simulink and D2 P rapid prototype control platform,and the data acquisition and calibration control system is established based on ATI-VISION platform.The effectiveness and reliability of the test bench are tested,and the PST simplified prototype is preliminarily tested with the platform.The test results show that the designed test bed can adapt to PST performance test,and the principle prototype meets the design and use requirements.It provides support for the development and testing of subsequent complete prototypes.