Effect of tooth profile on lubrication performance at the conjugate meshing domain of harmonic gear

Using the double-circular-arc common-tangent tooth profile as the flexspline of harmonic drive, conjugate tooth profile equation and conjugate zone of flexspline and rigid wheel was deduced through the envelope method. Meanwhile, the least-squares method was used to fit the discrete points of rigid wheel's tooth profile to get the fitting circular radius of curvature of rigid wheel. A mixed lubrication model at conjugate meshing domain (CMD) of the double-circular-arc tooth profile and involute tooth profile of harmonic gear were established considering the normal load of meshing point, real surface roughness and tooth contact geometry. The lubrication of the tooth root meshing-in point and addendum circle meshing point of harmonic gear at CMD were calculated at different speed. The results show that the effect of tooth profile on lubrication performance is significant, and using the double-circular-arc tooth profile can obviously increase the average film thickness and decrease the maximum oil film pressure, which makes the lubrication performance better. The decrease in speed of wave generator reduces the average film thickness and film thickness ratio, and increases contact load ratio at tooth root meshing-in point and addendum circle meshing point at CMD, leading to poor lubrication.