Study Of Crankshaft Free End Structure Of YC6105ZLQ Diesel Engine

YC6105ZLQ series diesel engine was developed by Guangxi Yuchai Machinery Co. Ltd. Specially for trucks and buses applications. To meet the varied operation requirement of different buses, especially for the rear engine mounting which ask for much stiffer crankshaft free end, structure optimization and strength increasing has been carried out in development phase. Main investigation and study work of the project group show as following: 1. Torsional vibration calculation of YC6105ZLQ crankshaft system has been carried out. Rubber damper has been upgrades to viscous damper to make sure that the vibration amplitude and torsional stress of free end cause by main syntonic harmonics are lower than permission limit. 2. FE analysis has been carried out for free end structure to make sure designation modification come out with better structure strength. 3. Torsional vibration test has been carried out on engine test bench, in which sympathetic vibration speed and amplitude have been measured and compared with calculation results. Fatigue test has been done to predict the life of the free end structure; and noise measurement (especially front end of engine) has been record to compare different contribution of modified free end structure. Torsional vibration calculation of YC6105ZLQ crankshaft system was proceed by build up equivalent torsional vibration model which describe moment of inertia of integrate mass and stiffness of varies shaft to calculate free vibration frequencies and amplitude. Calculation results are transfer to designation of vibration damper carried out by Unigraphics. Basing on experience, viscous damper should be applied to the YC6105ZLQ engine. And because free end space of the crankshaft is limit, viscous damper and belt pulley should be integrated skillfully together. Torsional vibration calculation result show that, with viscous damper, sympathetic vibration amplitude cause by 6th harmonic (2037rpm) is ±0.11°, and its maximum sympathetic torsional stress on crankshaft (±44(kgf/cm2)) is located between 6th cylinder and the flywheel which is lower the permission stress of the carbon steel ([τ]= ±300(kgf/cm2)). It means that the viscous damper meet the operation requirement. Besides using viscous damper to control the vibration amplitude of free end, free end structure has been modified according to installation and strength requirement. New designation use 6 high strength M10 bolts to mount the pulley which is very convenient for assembly and disassembly. To evaluate the strength of new and old designation, FEM analysis has proceed separately to compare the free end strength which is a key and an innovation. In the modified structure, the belt pulley was mounted on the the back end using 6 high strength M10 bolts, the 6 bolts have enough strength to transfer the torsional torque, so the fatigue strength is sufficient. The newly modified structure of the back end have obviously higher anti torsional strength than the old structure. The analysis results: for the old structure before modification, while the back end was twisted in the maximum vibration amplitude mode its maximum of unit equivalent stress is 31.73Mpa, it occurred on the journal groove in which the back end connect the the viscous damper; and for the newly modified back end of crankshaft, while theback end was twisted in the maximum vibration amplitude mode its maximum of unit equivalent stress is 13.27Mpa, it have been transferred to the journal of NO.1 connecting rod. The modified structure of crankshaft back end have obviously higher anti torsional strength than the old structure, the gained results are meet the expectation of modified design. As prototype accomplished, project team carried out vibration test on crank train on test bench. Vibration test use special equipment and software: NITM developed by H&W Co.Ltd.. Test results accord with calculation nicely, in which sympathetic vibration amplitude cause by 6th harmonic (2050rpm) is ±0.12°. And permission sympathetic vibration amplitude is ±0.20°means that the designation is acceptable. Traditional test method of fatigue strength of crankshaft free end is engine test on test bench which means long test period and big samples. To speed up the validation test, a simulation fatigue test program has been work out. Con-rod fatigue strength test machine is use for the test program. Cyclic load has be act on the crankshaft free end by the machine and 3 original pieces and 3 modified samples have been test. Test Result show that strength increased dramatically. Finally, we made the noise test on the bench test, and contrast the different contributions of newly modified structure of crankshaft front end with the old structure for the engine noise especially the noise from the front end of engine. For the modified structure, the noise was reduced obviously in the measuring point of engine front end, reach 3 dB(A). It is highly advantage for us to apply the engine in the bus. After calculating analysis and test validation in this article, it prove that for the modified optimization of crankshaft front end structure of YC6105ZLQ diesel engine use the investigation method, we gain the satisfied results, it can be applied widely.