The Design Of Fault Diagnostic System About Automated Mechanical Transmission On Heavy Truck

This study focused on the on-board and off-board fault diagnostic parts of the project--The Design of AMT system on heavy truck, which is an 863 project.Firstly, we introduce the overall structure of AMT. AMT was a kind of automatic transmission. It used the electronic control devices instead of manual operations on the manual transmission in order to achieve automatic gear ratio changing.Secondly,we introduced the process of software and hardware designing about the on-board fault diagnostic system briefly. The hardware of the electronic control system used two TCUs, one of them is the TMS which used to calculate the control strategy of the whole vehicle, and the other one is the TCU which used to control the gear shifting motion. The fault diagnostic module shared the hardware platform with TMS, and its software function includes the sensors'fault diagnostic, open/closed loop controlling function test and fault code memory management. We used the analytical redundancy method to deal with the sensors'fault, tested and analyzed the malfunctions with math models. The errors which related to the engine are the throttle sensor error, the engine speed sensor error and the throttle executing agency error. We can check out the fault on the sensor or on the engine itself based on the relationship between the throttle position and the engine speed. The sensors of transmission are shift position sensor, input shaft speed sensor, output shaft speed sensor, etc. We can get transmission's troubles if the control signal is not similar to the gear position feedback, or the gear position signal is not the same as the transmission ratio output. The part of clutch included the action cylinder of clutch, proportional valve and clutch routing sensor. We judged the control solenoid fault by means of logic relationship, estimated the clutch routing sensor fault based on extremum method. We encoded diagnostic trouble code (DTC) according to the fault type, position, frequency and source, saved the DTCs for further application. We followed the SAE J1939 protocol to encode the DTCs for convenient to communicate to other ECUs. We used fault status array as the temporary memory between diagnostic program and DTC memory, and the contents of fault status array were fault status word which standing for both DTCs'storage location and the fault status.Finally, we introduced the design and application of the off-board diagnostic system. The main topic of the off-board diagnostic system was getting the DTCs after vehicle running with special equipment, analyzing the reason why fault occurred and putting forward mending method. The off-board diagnostic system used CAN bus to communicate with the on-board diagnostic system. After getting the DTCs, off-board diagnostic system found out the trouble type and gave an alarm.The main target of the AMT fault diagnostic system was to establish a reasonable approach to improve vehicle safety and monitor vehicle status by establishing a reasonable diagnostic method.