Planetary gear trains (PGTs) are widely used in many machines and are one of the most important mechanisms in hybrid and electric vehicles. Previous research, based on empirical knowledge gained from the automobile industry, indicates that high carrier-support stiffness and low ring-gear support stiffness are required to reduce ring-gear errors. Therefore, here, we evaluate the vibration characteristics of a PGT as a function of the support stiffness, which is varied by inserting urethane rubber into the driving shaft. We conducted experiments using a 2K-HV-type tester, which contains a coaxially rotating and revolving planet gear shaft based on a universal joint. This mechanism allows the observation of the inner workings of the mechanism with the use of a transparent acrylic carrier. We were able to detect the so-called “bounce” phenomenon consisting of a swaying motion when the rotation of the ring gear is reversed, and this result was confirmed by our internal observations of the mechanism. It is evident that the index of vibration increases due to the bounce phenomenon because the reversal of the ring gear causes a larger vibration than that of the carrier because the ring gear can vibrate without restraint, unlike the planet gear that is sandwiched between the sun and ring gears. Furthermore, the influence of the radial support stiffness of the driving shaft, load torque to the output shaft, and acceleration time of the reversing gear on the “bounce” phenomenon were evaluated. We found that a larger load torque corresponds to a greater difference depending on the acceleration conditions of the sun gear. During reversal, at the moment when the rotation speed is zero and rotation recommences, the ring gear exerts the maximum force, and the larger is the load torque, the greater is the effect of the difference in acceleration.

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