| Powershift transmission can realize moving gearshift by means of wet friction elements.Due to the circumferential speed of meshing gears in the shifting process don't have to be synchronized, it can reduce the time and operating force required by gearshift. It has a series of advantages such as not stalled under overload, not interrupted power flow, reduce the vibration and shock caused by the sudden change of extemal load, and improve productivity,which shows a good application prospect in large power tractors and construction machinery.Takes powershift transmission of tractor as the object, the problem in the process of control system development such as transmission characteristics analysis, modeling and simulation technology, automatic gear shift rule and control strategy, gear shift quality, hardware and software design of controller and other aspects are investigated in the thesis.Based on the analysis of the structure and principle of powershift transmission of fixed shaft type, combined with the performance requirements of tractor and its drive system, the gear distribution and setting principle of tractor transmission are studied, and a kind of 40F+40R powershift transmission scheme which suitable for equipment by tractor is put forward.Through analysis of the speed and torque characteristics of powershift transmission, indicate it has a wide range of transmission ratio, and its travel speed between 0.3km/h-50km/h, which can-meet the speed requirements of various farming operating conditions. Compared with the manual mechanical transmission that currently widely used in the domestic, the power and fuel economy has been effectively improved, and the productivity of tractor to be increased.Through analysis of traction characteristics of tractor equipped with powershift transmission, it shows that the common ratio of different gears is smaller due to more gear setup of transmission, which can guarantee the speed stability when load changes. The gear that used at maximum frequency is located in the high traction power area, whose setting is more reasonable, which can meet the installation requirements of tractor and realize good matching with it.Take the research and development of control system of powershift transmission as the main purpose,the mathematical model of tractor drive system and the traction load was established based on the principle of dynamics and modular method.By fitting the experimental data of the engine,the output torque and the fuel consumption model of engine are create.According to the combination features of electro-hydraulic control and mechanical transmission of powershift drive system owned,a co-simulation system of tractor performance are build on the application of AMEsim and Simulink software.And a manual control speed changing process is simulated,which provides conditions for the control strategy establishment.Through analysis of the gear shift rule and characteristics of tractor,the power and economical shift rules and its control strategy are put forward for the purpose of energy saving and high efficiency.Based on the analysis of factors affecting the maximum productivity,confirm that the traction power and efficiency of tractor is the effective measure to obtain maximum productivity.In order to achieve this goal,the power shift rule and its control strategy are put forward,which take the engine speed and throttle opening as the control parameters.By analyzing the best economy index and its influence factors of tractor,indicate that the economical shift rule's goal is to make fuel consumption rate of tractor to be the lowest,which requires not only the operating point of the engine located at the lowest fuel consumption zone,also need the tractor traction efficiency to be higher.For this reason,the slip rate of driving wheel is introduced to constitute economical shift rule and its control strategy,which takes tractor's speed,drive wheel speed,engine speed,throttle opening and transmission gear ratio as control parameters.Through simulation,it verifies the rationality of gear shift rules and the validity of control strategy for engineering application,which provides a theoretical basis for the development of control system.On the basis of analyzing the influence factors and evaluation indexes of the shift quality of the tractor powershift transmission,the load and power characteristics of clutch under different shifting schemes are studied.The gearshift method with fixed shift overlap time is determined,which can guarantee the shift has good shift smoothness under different engine load.Through analysis the compositions of gear shift control system,it takes the output speed variation amplitude of powershift transmission as the index to optimize shift overlap time and contact oil pressure of the clutch.The gearshift parameters chosen with the optimization algorithm is less affacted by the change of tractor traction load,the transmission output speed transition smoothly.It can reduce the negative output torque generated,which avoid tractor deceleration or power transfer interruption during gearshifting,and improved the tractor's productivity.The control scheme is verified by simulation and bench test,which validate the selected parameters of control scheme are reasonable,and the shift quality is obviously improved.The functional requirements of control system of tractor powershift transmission are analyzed.The hardware of controller is designed based on DSP.Such as real time precision measurement technology for several speed signals with wide range variation,PWM control technology for several solenoid valves and the slip rate detection technology are studied in control system.The real-time operating system DSP/BIOS is applied to develop the multi-task real-time control software of transmission.The main operation control flow of tractor such as start,gear shift,brake and cruise control are analyzed.And the implementation scheme of auxiliary operation such as electronic headland turning,automatic PTO,differential lock and the automatic management system for front wheel drive are also provided.To solve the problem of data sharing between different tractor ECU devices,ISO11783 protocol is used as the network communication standard to make out the topological structure of the tractor bus,and the bus interface circuit and communication flow of transmission controller is analyzed in detail.Research results provide a foundation for the practical application of the tractor's powershift transmission. |
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