Study On Strength And Reliability Of Over-running Clutch Of Dual-turbine Torque Convetrer

At present, more than80%of wheel loaders are equipped with dual-turbinetorque converter. It is equivalent to a two-speed automatic transmission, which canreduce the number of gear shifts. The dual-turbine torque converter is a typical kindof internal power distribution torque converter with the advantages of large torqueratio and wide high efficient area which exports its power through over-running clutchto gearbox. The loader usually works in the low-speed&heavy-load status with theover-running clutch locked while in the high-speed&light load status with the clutchseparated. Thus the loader can adapt to the transformation between the two typicalworking conditions so as to improve the production efficiency.According to the field test, a complete work cycle of a wheel loader averagelytakes48seconds with the over-running clutch locking and separating8times.Assuming that the loader was designed to work reliably8000hours which made it anecessity for the over-running clutch to lock and separate reliably5.12million timesto meet the design requirement. But in fact， most over-running clutches loseeffectiveness after working2000hours which significantly increase the workload aswell as the cost for replacement. In this case, the main manufacturers have improvedtheir design. Under this circumstance, this article takes the field test result of workcycle of wheel loader as basis to analyze both static and dynamic strength of theover-running clutch in order to find factors that affect its fatigue. Besides, modifieddesign on its structure has been made to improve the anti-fatigue performance of theclutch which has the vital significance to improve the reliability of wheel loader.Based on the field test and the strength analyses as well as the redesign of thestructure，some conclusions can be made as follows:1. The analysis of working process of the over-running clutch and the test ofthe loader’s work cycle Two typical working situations of over-running clutch are taken intoconsideration in this article: locked when the loader is in low-speed&heavy-dutyworking status and separated when the loader is in high-speed&light-duty workingstatus.Field test of the wheel loader is taken to gain the data of a typical work cycle andbased on which working load is calculated in three steps. Firstly, speed information ofengine and output shaft of the torque converter in12conditions is gained from the testresults. Secondly, speed ratio of torque converter and the speed of turbineⅠ&Ⅱ arecalculated based on the speed information gained in step1. Thirdly, the CFD methodis applied to calculate the torque of turbineⅠ&Ⅱ in different speeds. Then the loaddata of the dynamic simulation is calculated.2. The static strength analysis of the existing over-running clutchThe model of over-running clutch is simplified to analyze its static strength usingthe finite element method resulted in the variation of stress distribution anddisplacement in the contact roller and inner&outer rings.3. The dynamic strength analysis of the existing over-running clutchThe finite element method is used to analyze the dynamic performance ofover-running clutch to obtain the instantaneous stress distribution of both inner andouter rollers of over-running clutch and get the position of the maximum stress.4. The improved design of the existing over-running clutch and contrastanalyzeBased on the analyze result, factors that caused the failure are found whichcontributes in the modification of the structure of the over-running clutch. After all,the modified structure is taken into the similar finite element analyze as mentionedbefore. Finally, the result comparison indicates that the modification is effective andthe new structure performs better than the former one.