1. INTRODUCTION
A continuing need exists to design and develop advanced power
train systems in order to keep pace with the advancing technology
of prime movers (such as gas turbine engines) and vehicle
design requirements including helicopter, surface effects
ships, hydrofoils, etc.
For the past decade, power transfer systems have primarily
dictated improvements in the power-to-weight ratio, reliability/
maintainability, vibration/noise levels and system life.
To achieve these improvement goals, past studies indicated a
strong need to investigate advanced-concept-type mechanical
power train systems such as the Maroth Nutating Drive, Harmonic
Drive, Cyclo drive, Planocentric drive, etc. Recent Boeing
Vertol studies indicated that the Maroth Nutating transmission
had the most promise of achieving the improvement goals as
compared to other advanced concepts. This drive, referred to
as the nutating mechanical transmission (NMT), has unique
features when compared to conventional gear arrangements which
include very high profile contact ratio, high reduction ratio
in one stage, the potential for low vibration/noise levels,
high efficiency and design flexibility.
Current power train system designs utilize gear teeth as the
critical connecting links in the continuity of the drive train.
Standard gear designs have one pair of teeth carrying the major
percentage of load in a given mesh. Failure of one tooth will
result in relatively rapid loss of torque and possible system
failure. By comparison however, the NMT concept provides for
multiple load sharing between input and output by virtue of
the numerous action and reaction cams and planes coupled by a
nutating ring containing tapered pins. For this reason,
failure of one or more cams, planes or pins would only increase
load on those remaining, thereby reducing their B-10 lives.
Since the pins are actually bearings, torque and phasing will
be maintained, thereby immediate catastrophic failure would be
precluded.
In addition, since the contact is theoretically pure rolling in
the NMT (while that of gear teeth is theoretically rolling and
sliding) the heat generated should be lower and the efficiency
higher. Due to its general arrangement and number of load
sharing elements, a decrease in relative vulnerability is to
be expected.
This report presents the results of an analytical program
undertaken to define the operational characteristics and
potential load capacity of the nutating mechanical transmission
(NMT) concept. Since a fully operational NMT capable of any
substantial loading has not been constructed, the scope of this
analysis has been largely analytical. Substantial technology
has, however, been borrowed from the gear and bearing fields to
provide a sound basis for the derivation of some aspects of
the analysis.
The basic geometry of the mechanism and its general kinematic
characteristics have been thoroughly investigated. The dynamic
characteristics (unbalance) and load capacity of the NMT have
also been analyzed during this program. Utilizing this analysis,
the suitability of the mechanism for high speed/high power
systems through the use of design examples is investigated.
In order to provide a clear, concise description of the NMT and
its applications, limitations, and benefits, the main body of
this report presents derived equations as required. For the
sake of completeness, however, the full analysis including
applicable equations, figures, etc. is presented as an appendix.
In addition, in a format similar to that used in the
annual report, capsule summaries in the form of narrative
figures are utilized throughout the main body of the report to
highlight key topics.
