Research On Cylindrical-roller Enveloping Hourglass Worm Drive

Cylindrical-roller enveloping hourglass worm drive is another new type of rotating the worm gear enveloping worm drive.The worm drive is characterized by: the worm gear tooth are the rollers and the roller is distributed on the tooth surface,and every roler can rotate around its own axis.The roller is a certain defection angle between the roller axis and the radial.This is another form of roller enveloping worm drive,which is different from the traditional worm drive.The worm surface of this worm drive is generated by the rollers.This paper studies the meshing performance,elastohydrodynamic lubrication characters,friction characteristics and parameters optimization.The main achievements are presented as follows:Based on the gear engagement theory and live-coordinates frame,according to the working principle of the new worm drive,the the dynamic and static coordinate system and the moving coordinate system are established.the meshing theory and the mathematical model was derivation.The tooth surface equations,meshing function,contact line equation,induced principal curvature,lubrication angle,rotation angle and relatively enttainment velocity are presented.The meshing performance was analyzed,such as orifice coefficient,roller radius,and inclined angler.The researches show that this worm gear pairs drive has good meshing performance and contact characteristics.The elastohydrodynamic lubrication(EHL)simplified model is established based on the research of meshing performance of cylindrical-roller enveloping hourglass worm drive and the theory of EHL.The elastohydrodynamic lubrication(EHL)line contact mathematical model are established.The distribution of the minimum film thickness of EHL and thermal EHL(TEHL)are analyzed.The orifice coefficient,roller radius and inclined angler,which impacted the lubrication performance of this worm drive,are analyzed.The analyzed results indicate that the cylindrical-roller enveloping hourglass worm drive has better lubrication performance,roller radius and inclined angler are the most important cause for the EHL characters,orifice coefficient influence less relative to other two factors.The roller radius and orifice coefficient should not too smaller,roller radius should not too bigger,for effectively improving the lubrication performance.In order to overcome such problems as severe wear,higher fever and easy scuffing caused by excessive friction of cylindrical-roller enveloping hourglass worm drive,based on the differential geometry and the analytic basis of space engagement,the formulas are given of helix angle and pressure angle of this worm drive.The change trend of helix angle and pressure angle are calculated and analyzed.Based on Hertz contact theory and friction theory,the friction calculation formulas caused by the elastic hysteresis and micro-glide are given of this worm drive.The numerical calculation is carried out by adopting main meshing parameters,the influence of meshing parameters on the tooth surface temeperature and the change trend are analyzed.The researches show that the helix angel and pressure angel reaches the maximum at the throat of the worm,which increases at first and then decreases.The tooth surface temeperature can be obviously decreased when the inclined angler should not too smaller,orifice coefficient and roller radius should not too bigger.The optimization model of the worm gearing is established,in which the lubrication angle and the roller rotation angle and the oil film thickness and the tooth surface temeperature are taken as optimization objectives.The optimization model of the worm gearing is presented with the better transmission efficiency and meshing strength,in which the strength and stiffness of the worm shaft and the without undercut and the tooth surface contact fatigue strength are taken as constraint conditions.Effect of design parameters on the meshing performances are compared,then the throat path coefficients,the roller radius,the roller inclination angle are taken as design variables.It makes cylindrical-roller enveloping hourglass worm drive with the best lubrication performances and carrying capacity.Based on the mathematical model of this worm gearing is complicated,to calculate lubrication angle and roller rotation angle and the oil film thickness and the tooth surface temeperature was difficult and complex.This paper used the Matlab software programming with fmincon function to solve the optimization model and to calculate reasonable design parameters.The optimization results can obviously improve the meshing performance of the cylindrical-roller enveloping hourglass worm drive,and the solid model of the cylindrical-roller enveloping hourglass worm drive was established under this optimized conditions.