Development And Implementation Of Fault Diagnosis System For CVT Based On UDS

The vehicle of automatic transmission is favored by more and more consumers because of its simple operation,comfort and safety.Metal belt type CVT(Continuously Variable Transmission)is the ideal automatic transmission whose fuel economy is good and power output is smooth.CVT is composed of hydraulic torque converter,hydraulic control system,shift mechanism,electronic control system and other devices generally.CVT is a complex system of machine,electricity and liquid,so it is difficult to identify and diagnose faults once the failure occurs.With more and more attention to the safety of automobiles,how to avoid accidents causing by the failure of functions and reduce the possibility of risks have become the goal of automotive electronic safety design.Therefore,the fault diagnosis system,which protects the components of CVT from further damaging when the fault occurs and helps the assistant maintenance personnel confirm the faulty parts quickly,is an important part of CVT control system and the guarantee of the CVT safe operation.This thesis,based on the industrialization demand of a domestic automobile CVT,develops a CVT fault diagnosis system based on the UDS(Unified Diagnostic Services)protocol to ensure the safety and reliable operation of CVT in the market.The fault diagnosis,fault protection,diagnosis communication and diagnostic service of CVT are designed.The diagnosis strategies of CVT and the communication of UDS diagnosis are tested and validated in detail.In this thesis,the key technologies of CVT fault diagnosis system are studied as follows:(1)Using FMEA(Failure Mode and Effects Analysis)analysis method,the potential failure modes of CVT electronic control system are analyzed,the hardware of CVT control system is designed according with the ISO26262 function safety standard,and the basic software acquisition method of sensor signal is optimized;(2)The fault diagnosis mechanism of CVT based on the diagnostic criteria of UDS is studied,the process of fault diagnosis and fault protection for CVT are designed.The signal amplitude detection method,analytic redundancy method,and time series redundancy method are used to diagnose CVT electrical fault and performance fault.The fault diagnosis and protection strategy of the sensors,actuators,and CAN(Controller Area Network)communications in CVT electronic control system are designed;(3)The rationality and reliability of fault diagnosis and fault protection strategies are verified using multiple test methods.In the early stage of development,the hardware in the loop test system is used to diagnose the fault,the signal disconnection box and the diagnostic tester are used for real vehicle test in the late stage of development,then the data are collected by INCA in real time and analyzed by MATLAB;(4)CVT diagnostic specification is developed based on CAN communication according to the ISO14229 international standard.UDS diagnosis database is set up using VECTOR tool software,the UDS diagnosis communication and diagnostic service function of CVT software are tested comprehensively.After a lot of tests and market verification,the CVT fault diagnosis system designed in this thesis enhances the stability of CVT and the safety of the vehicle,and improves the fault diagnosis rate and maintenance efficiency of CVT.