Study On Electro-hydraulic Shift Quality And Fault Diagnosis Of Power Shift Transmission Of Heavy Duty Tractor Based On CAN Bus

At present,China's agricultural tractors are developing to be heavy-duty and intelligent.In order to avoid the interruption of power when the tractor shifts gears,reduce shift shocks,and reduce the problems of electro-hydraulic control systems caused by frequent shifts,power shift transmission(PST)technology was gradually adopted by heavy-duty tractors.And the lightweight handling and automation of power shift transmissions is an important part of its technology development.This paper takes the full power shift transmission of a self-developed tractor as the research object.Research on shifting quality of heavy-duty tractor PST and faults in transmission electro-hydraulic system.According to the ISO11783 standardization protocol,the CAN communication network of the tractor is designed to meet the communication requirements between the modules of the whole vehicle;then the hardware circuit connecting the PST node and the CAN bus is designed to realize the function of the PST system;and the power shift application layer data frame is designed to improve the working efficiency of the PST node in the CAN communication network.The tractor kinematics model,the power shift transmission torque transfer model and the shift wet clutch model were established,and the simplified PST mechanical model,vehicle body model and electro-hydraulic control model were established in AMESim.The flow and pressure characteristic curves of the electro-hydraulic proportional valve,the shifting clutch displacement and torque curve are simulated,and the reliability of the system simulation model is verified.The torque transmission characteristics of the clutch power coupling process are analyzed.It is concluded that the key to the smooth control of the wet clutch is the pressure control of the clutch cylinder.The shifting overlap time and the clutch cylinder engagement pressure are taken as the entry points to study the influence of different pressure control strategies on the shifting quality.The simulation shows that when the shifting overlap time is 0.3s,the shift hydraulic shock is the smallest,the sliding friction and the torque loss are the least,and the optimal shifting quality is obtained.The output torque is the same when the engagement pressure in the range of 0.40-0.63 MPa(speed difference 455-560 r/min),and the sliding friction work and the shift hydraulic shock have a minimum value when the shift hydraulic shock is 0.40 MPa.The common faults of the electro-hydraulic control system of the power shift transmissionare analyzed.According to the characteristics of the previous recorded fault data,some feature vectors are selected.The multi-class classification method of support vector machine is adopted.The fault pattern recognition is realized in Matlab by LibSVM toolkit.The correct rate is between 90% and 95%,which meets the actual engineering needs.This method can realize online identification of fault mode based on CAN communication.