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Planetary gear sets are widely used in hybrid or electric vehicles. Although they have many advantages, they have been known to develop noise and vibration problems. There have been many reports dealing with the problems' characteristics for two-axis driving, but very few for three-axis driving. This paper reports three-axis driving performed on a developed driving stand, with driving torque measured by a high response torque sensor on each driving axis. Under these conditions it was found that the meshing frequency occurred at two kinds of frequency harmonics.

Some papers on gear noise indicate that for helical gears,the vibrational excitation becomes a minimum when the gears in mesh rotate at a total tooth-contact ratio,where the variation of tooth-stiffnes may be minimized (1). Based on this finding, we have designed a pair of herlical gears, of which number of teeth in contact (2,3,or4) would be fixed at any instant of time during the gear rotation. Both the face- and total-contact ratios of involute tooth-face have often been considered to be integers, and a little higher value for the gear with inaccurate tooth-face. Meanwhile, it has been confirmed by computation and experiments that the vibrational excitation of carburized production gears,paired with carburized or hard-finished ones,would decrease if their total contact ratios have been set higher. The present study reveals that the exciting force is much dependent on the total contact ratio, and is little affected by chosing a integer contact ratio.