| An engine crankshaft is subjected to periodic dynamic loads, generating TorsionalVibration (TV) due to the flexibility of crankshaft. With the accumulation of fatigue,alternating stress produced by TV will result in sudden fracture of the crankshaft. And the TVfrequency of crankshaft is low, which can easily be excited to resonance under the enginenormal speed. The resonance may incur more noise, increase the wear of other parts, and evenmake the crankshaft broken and other serious engine damage accident. An effective way forreducing the TV of a crankshaft is to install a Torsional Vibration Damper (TVD) in the frontend of a crankshaft. Thus, the study on analysis of crankshaft TV and selection of TVD is ofgreat significance.Taking a prototypical engine crankshaft system as an example, a Lumped Parameter (LP)model of TV in crankshaft system is established. A detailed procedure for determining theinertias, torsional stiffness and damping coefficients of the LP model is presented, and themechanism of excitation torque is analyzed. The proposed model is then used to calculate thenatural frequencies of crankshaft and the TV of crank nose with cylinder loads.A mathematical model of crankshaft system including TVD is presented for design ofTVD. Taking the design parameters of TVD as variables, the effects of these parameters tocrankshaft TV are discussed. The multi Degree of Freedom (DOF) LP model of crankshaft isthen simplified as one DOF model with dynamic model of TVD attached to it. Based on themodel, the design parameters of TVD are optimized. The calculated results show that thepresented damper can control the TV of engine crankshaft effectively.Tests are carried out respectively to obtain the TV of an engine crankshaft with differentTVDs and without TVD. And the experiment data is compared with the calculated results.The comparison shows that the calculated natural frequencies of crankshaft and TV amplitudeof crank nose agree well with the measured values, which validated the proposed model andthe method for determining parameters of the LP model. The torsional displacements of crank nose with different TVDs attaching to crankshaft are also compared and the damping effectsare showed out. According to the results of test data analysis, a reasonable natural frequencyrange of TVD is determined.The TVD described above includes only one inertial mass, which is usually nominated asSingle Mode TVD (SMTVD). The damping ratio provided by rubber materials for arubber-damped SMTVD is not large enough to meet the optimized value. Recently, in somepassenger vehicles, Multi-Mode TVD (MMTVD) including more than one inertial mass isused to reducing TV of crankshaft. A model for describing MMTVD is presented. The modelis then combined with the preceding one DOF model of crankshaft, which is used toinvestigate the design method of MMTVD. The formula for depicting response of crankshaftTV is obtained, and the effectiveness of MMTVD in controlling TV of crankshaft is discussed.The results show that MMTVD can reduce crankshaft TV greatly although the damping ofMMTVD is still provided by rubber materials. |
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