Research On Vibration Characteristics Of Noncircular Gear

Noncircular gears are normally used in the cases where various speed ratio is needed.Due to the variation of pitch curve,the speed ratio is not a constant.The various speed ratio and time-variant mesh stiffness can lead to significant noise and vibration.This dissertation discusses the dynamic properties of the noncircular gears by focusing on parametric instability.The main contents are as follows:(1)The geometric restriction during the rotation of noncircular gear is examined and the pitch curve radius,pressure angle and time-variant mesh stiffness are formulated.A rotational model is developed,based on which the effect of eccentricity on dynamic behaviors are investigated.(2)The eccentricity,time-variant mesh stiffness and load torque on vibration behaviors are examined by using Floquét theory and Runge-Kutta algorithm.The results show that the variation of speed ratio can cause additive combination and difference combination resonances.The response amplitude at mesh frequency is lower for noncircular gears.In addition,the load torque and rotation speed have significant effect on dynamic characteristics.(3)A model of noncircular-gear-slider-crank mechanism is developed,where the eccentricity,modification coefficient,mesh stiffness and time-variant inertia are incorporated.The results show that the slider-crank assembly(SCA)with elliptical gear(EG)and modified elliptical gear(MEG)have similar instability properties but they are different from that with circular gear(CG).Moreover,the forced vibration analysis verify that SCA with EG and MEG are performed better than that with CG.Their vibration is mainly dependent on the behavior of external torque.The research and results provide a theoretical reference for the dynamic design of noncircular gear or other mechanism alike.