Acoustic Vibration Characteristics of High Contact Ratio Planetary Gears

Limited laboratory tests were conducted to determine the effects of a high contact ratio buttress (HCRB) planetary gearset on the acoustic (high frequency) vibration signature of the BLACK HAWK main transmission. Contrary to expectations, the HCRB planetary had increased vibrations at the ring gear clash frequency and its associated sidebands, however, the harmonics of the ring gear clash frequency were reduced. The primary reason for this increase is that the face widths of the HCRB planetary were reduced (providing a weight benefit) to take full advantage of the increased strength associated with HCRB gearing. Therefore, the potential vibration benefits associated with increased contact ratio were compromised. Another reason for the increase in vibration levels is that the tooth to tooth spacing errors in the HCRB gears may be too high. It is recommended that laboratory tests such as those conducted in this program be continued in an effort to demonstrate design concepts capable of simultaneously reducing weight and vibration (and by implication cabin noise). Concepts must be evaluated on the basis of their impact on total system weight (i.e. including the potential impact on cabin acoustic treatement weight). It is also highly desirable that such additional tests be conducted in an environment where the impact of a given concept on acoustic radiation as well as vibration could be measured.