Design Of The 2×2 Type HMCVT Of Large Power Tractor And Study On The Shift Quality Of HMCVT

Because of complex operating conditions of tractor that it not only at a very low working speed to carry out heavy load plough operation,but also at a higher speed in light load transport operations,the required number of blocks is much more than that of road vehicles(the maximum number of advance gears of domestic high-power tractors has exceeded 40),however,the increase of gear not only makes the gearbox structure complex,but also difficult to grasp the shift timing.The Hydro-mechanical Continuously Variable Transmission(abbreviated as HMCVT)is composite transmission device with mechanical transmission and stepless speed change.It has the advantages of large driving power,high transmission efficiency and simple operation,and is easy to realize the fuel economy of the high power output and light load operation when the tractor is in heavy load operation.This paper focus on the quality of its segment,and the HMCVT with 2×2 step of single row planet gear was designed based on the operating characteristics of high power tractor.The main research work is summarized as follows:1.The transmission scheme design of HMCVT.In this paper,the transmission scheme design of HMCVT was demonstrated in detail and identified based on the tractor operation demand.Its working process was analyzed and the interval of velocity ratio in each part was determined.According to the condition of constant velocity section and the relationship between the speed of each section and the displacement ratio of pump motor,the transmission parameters of the gearbox were determined,and the structural parameters of the transmission and the parameters of the hydraulic circuit are obtained.2.Transmission characteristic analysis of HMCVT.(1)The speed characteristics of the gearbox were analyzed,and the relationship between the displacement ratio of the pump motor and the transmission ratio of each section was drawn by Matlab.The analysis shows that through the coordinated control of the displacement of the clutch and the variable pump,the HMCVT can realize the continuous change of the speed ratio and the smooth connection between the adjacent sections in the hydraulic mechanical section,thus the stepless speed regulation of large power tractor in a large range was achieved;(2)The torque characteristic analysis of HMCVT showed that the ratio of the output torque and the motor torque of the gearbox is constant in the HM1 and HM2 sections,and the gearbox is constanttorque output in each section,and it does not change with the change of the displacement ratio;(3)though the analysis of circulating power of HMCVT,the speed ratio interval of the hydraulic circulating power of the gearbox is defined,which provides an important theoretical reference for the subsequent control strategy.3.The dynamic modeling and simulation of HMCVT.The effects of various factors on the shift quality of HMCVT are analyzed.Firstly,the dynamic model of the CVT is established,including the gearbox model,engine model,tractor rear axle model and load model based on the Simulaiton X plantform.Secondly,the standard simulation conditions are defined,and the quality evaluation indexes of five sections,such as speed drop,dynamic load coefficient,maximum sliding mode power,sliding friction work and comprehensive index,are given;Thirdly,the effect of various factors on the quality of segment was obtained by simulating and analyzing various factors.4.Study on abnormal pattern recognition of shift hydraulic system of HMCVT.(1)The oil pressure datas of the clutch obtained by tests were pre-treated;(2)The training sample set and the test sample set were generated by the method of random sampling.After the training sample set is used to train the BP neural network,the classify test of the input test sample set was carried out;(3)The attribute reduction on neural network was conducted by the neural network feature selection method,and the results comparison and analysis with the multi-value classification method were carried out.The results showed that the average recognition rate that the two value classification method for BP network on five typical modes of oil flow is over 98%.With attribute reduction,the several typical models including normal mode,piston stuck,seal ring is damaged,oil passage is blocked and seal is lax can reduction samples attribute with 3,4,3,3,and 3 respectively.There is a specific correlation between the fluctuation of the oil pressure and the failure modes during shifting(It has qualities of dividing).The current state of the system can be distinguished effectively by the BP network.This technology can be applied to the abnormal pattern recognition and fault diagnosis of the hydraulic system,and to ensure the reliability of the gearbox.The research of this topic provides a solid theoretical basis for improving the shift quality of HMCVT with single row and multi section,and it is of great theoretical significance to promote the application of HMCVT in the industrialization of high power tractors in china.