Research On The Key Technologies Of Virtual Test Of Tractor Powershift Transmission

Tractor is an important agricultural power equipment with large quantity and wide area."Made in China 2025" and "Agricultural Machinery Equipment Development Action Plan(2016-2025)" both propose new requirements for tractor products innovative development with the intelligent agriculture and precision agriculture as targets,the networked,digital and intelligent technologies as core,and high-power,high-speed,low-consumption,and efficient duplex modern operation methods as new product development direction.The power shift transmission system(PST)is the key power transmission component of the tractor,which can realize automatic shift without interruption of power during the operation.PST is now widely used in high-power tractors,which significantly improves the tractor’s power,fuel economy,comfort,safety and operating efficiency.As one of the important technologies for advanced product development,test verification runs through the entire life cycle of product demand analysis,design,development and use.The virtual test combines computer simulation technology,measurement and control technology,and communication technology to provide new test technologies for product performance tests.The virtual test converts the test environment,test system,and test product into a digital model,and the modification of test parameters,optimization of control strategies,and control of the test process run on the computer.Virtual test has low consumption,short cycle and zero emission,which can provide effective a priori guidance for product innovation design.In order to improve the system scalability,model reusability,model interoperability and real-time of PST virtual test,this study designs a PST virtual test system based on architecture.Through researching the key technologies of PST virtual test,a virtual test support platform covering virtual prototype model construction,test design,test operation,test management and test result evaluation is developed,laying a foundation for the tractor PST virtual test.The key technologies of PST virtual test architecture construction are studied.According to the characteristics of PST test,the functions and performance requirements of PST virtual test are analyzed,and the construction and operation principle of PST virtual test system are studied.Based on the comparative analysis of high level architecture(HLA)and data distribution service(DDS),a PST virtual testsystem framework based on HLA-DDS is constructed,and the hardware support platform for distributed virtual test system based on Ethernet is established,which provides a framework support for improving the system scalability,model reusability,model interoperability and real-time.The key technologies of PST virtual test architecture interconnection are studied.Based on the analysis of HLA,the data interaction mechanism of DDS and the data mapping relationship between HLA and DDS,the data interaction solution of PST virtual test system based on bridge component is developed by comparing the three interconnection schemes of HLA and DDS.The bridge component metamodel and system component UML model are established based on the metamodel theory and the Rational Rose platform,and the model mapping rules are formulated.Utilizing the round-trip engineering function of Rational Rose,the UML model of the bridge component is transcoded,and the plug-in framework code is generated.The time advancement strategy of virtual test based on bridge component and the time advancement algorithm of virtual test based on lower bound time stamp(LBTS)are proposed,and the data interaction mechanism of PST virtual test system is improved.The key technologies of PST virtual test architecture modeling are studied.The architecture modeling method of model transformation is analyzed.The PST mechanical component,PST hydraulic component and PST control component based on the multi-domain simulation models,and load component based on the Access database are established.The message correspondence between components is analyzed,and HLA encapsulation is performed on the simulation component and the load component.A PST test bench component and a PST controller component are established,and the DDS data type and subject encapsulation of physical components is performed.Thus,the integration of PST simulation component,load component and physical component with PST virtual test system is realized.The key technologies of PST virtual test management and human-computer interaction are studied.The operation principle of the test management component is analyzed,the basic instruction format of the virtual test is defined,the basic instruction set library of test procedure is developed,and the standard virtual test procedure file format is defined using XML Schema language.The data characteristics of PST virtual test results and the data management principle are analyzed,the logical structure of the database is described by using the entity relational diagram(ERD),and the data management function of the test management component based on the database andversion control system(VCS)is developed.The unified modeling language(UML)is used to establish the static class diagram and dynamic activity diagram of the test management component,and the test management component with friendly humancomputer operation interface is developed.The operation principle of the test monitoring component is analyzed,and the test monitoring component is developed based on Lab VIEW software.The key technologies of PST virtual test verification are studied.The PST output shaft torque loads of the tractor-implement combination in the field experiments of tractor ploughing,rotary tilling and driving harrow are measured.The load is preprocessed using the empirical mode decomposition soft threshold noise reduction method,and the boundary local characteristic scale extension algorithm is used to suppress the end effect that occurs during the load decomposition process.The PST virtual test load environment under typical single working conditions and integrated multiple working conditions is established through extrapolation and synthesis of the load frequency.The key parameters of the PST gear shift information,working condition information,and shift point information hidden in the test data are extracted.The method of consistency check between the virtual test results and the bench test results based on gray correlation method and empirical mode decomposition method are studied.The data transmission delay and data transmission throughput performance of the bridge component are tested.The test results show that the bridge component meets the system design requirements.The virtual test is performed on the performance of the PST electronic control unit,the clutch engagement law,the starting quality and the shift quality.The virtual test results have a high consistency with the bench test results,which proves the PST virtual test system is effective.The virtual test system developed in the study has the advantages of scalability,model reuse,model interoperability and real-time,which can provide new methods and technologies for the development and verification of new tractor products.