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Technical Publications Catalog
April 2011

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27April 2011 Publications Catalog

10FTM12. Flank Load Carrying Capacity and Power
Loss Reduction by Minimized Lubrication
Authors: B.--R. Höhn, K. Michaelis and H.--P. Otto

The lubrication of gears has two major functions:
Reducing friction and wear as well as dissipating heat.
The power losses, especially the no--load losses,
decrease with decreasing immersion depth using dip
lubrication. The load--dependent gear power losses
are nearly unaffected by minimized lubrication.
However, the gear bulk temperatures rise dramatically
by using minimized lubrication due to a lack of heat
dissipation.

With minimized lubrication the scuffing load
carrying capacity decreased by up to more
than60%compared to rich lubrication conditions. The
dominating influence of the bulk temperature is
therefore very clear. Starved lubrication leads to more
frequent metal -- to contact and the generation of high
local flash temperatures must be considered. An
additional factor for the scuffing load carrying capacity
calculation in case of minimized lubrication conditions
is proposed.

Concerning pitting damage test runs showed that
by lowering the oil level the load cycles without pitting
damage decreased by approximately 50% up to 75%
for minimized lubrication compared to the results with
rich lubrication conditions. The allowable contact
stress is clearly reduced (up to 30%) by minimized
lubrication. A reduced oil film thickness as a
consequence of increased bulk temperatures results
in more frequent metal--to--metal contacts causing a
higher surface shear stress. In combination with a
decreased material strength due to a possible
tempering effect at high bulk temperatures the failure
risk of pitting damage is clearly increased. The
common pitting load carrying capacity calculation
algorithms according to DIN/ISO are only valid for
moderate oil temperatures and rich lubrication
conditions. For increased thermal conditions, the
reduction of the pitting endurance level at increased
gear bulk temperatures can be approximated with the
method of Knauer (FZG TU München, 1988). An
advanced calculation algorithm for pitting load carrying
capacity calculation at high gear bulk temperatures
(valid for high oil temperatures as well as forminimized
lubrication) is proposed.

The micropitting risk was increased by low oil
levels, especially at high loads and during the
endurance test. Themicropitting damage is causedby
poor lubrication conditions which are characterized by
a too low relative oil film thickness due to high bulk
temperatures. Again, the actual bulk temperatures are
of major significance for calculation of the micropitting
load carrying capacity.

The wear rate of the gears is almost unaffected by
the oil level. Only a slight increase of wear could be
observed with minimized lubrication. This increase
can be explained by the higher bulk temperature of the
gears running under minimized lubrication conditions.
The investigations showed that there exists a natural
limitation for lowering the oil quantity in transmissions
without detrimental influence on the load carrying

capacity. Knowing these limitations enables the user to
determine the possible potential benefits of reduced oil
lubrication. The correct prediction of the actual gear
bulk temperatures is of major importance in this
context. A method for the estimation of the gear bulk
temperature at reduced immersion depth respectively
poor lubrication conditions is proposed.
ISBN: 978--1--55589--987--5 Pages: 15

10FTM13. Gear Design for Wind Turbine Gearboxes
to Avoid Tonal Noise According to ISO/IEC 61400--11
Author: J. Litzba

Present wind turbine gearbox design usually
includes one or two planetary gear stages and at least
one high speed helical gear stage, which play an
important role regarding noise and vibration behavior.
Next to the overall noise of the gearbox and the
structure--born noise on the gearbox housing also
tonal noise is becoming a much more important issue
in recent years. Since tonal noise is problematic due to
the human perception as “uncomfortable”, avoidance
is important. Conventional theories regarding low
noise gear design are not developed in view of tonal
noise. This leads to the question: How to deal with
tonal noise in the design stage and which gear
parameters can be used for an optimization regarding
good tonal noise behavior?

Within a research project measurements have
been performed on different gearboxes using different
gear designs. These measurements have been
evaluated according to ISO/IEC 61400--11 and the
results have been analyzed in view of the influence of
different gear parameters. It was also investigated if it
is possible to rank gearboxes in wind turbines
according to their tonal noise behavior as observed on
the test rig.

The paper will give an introduction into the
definition of tonal noise according to ISO/IEC
61400--11 and give insight in measurement results
from test rigs and from gearboxes in the field, where
noise behavior is also evaluated according to ISO/IEC
61400--11. Furthermore, the paper will show and
discuss the link between measurement results and
different gear parameters, which are affecting tonal
noise behavior. In addition simulation results will be
presented, showing how tonal noise can be estimated
within the design stage using state--of--the–art
calculation software.

The paper will give recommendations regarding a
gear design process that is considering tonal noise in
the design stage and will compare an, regarding tonal
noise, improved gear set with an older one.
ISBN: 978--1--55589--988--2 Pages: 19

10FTM14. Analysis and Testing of Gears with
Asymmetric Involute Tooth Form and Optimized Fillet
Form for Potential Application in Helicopter Main
Drives
Authors: F.W. Brown, S.R. Davidson, D.B. Hanes,
D.J. Weires and A. Kapelevich

Gears with an asymmetric involute gear tooth
form were analyzed to determine their bending and
contact stresses relative to symmetric involute gear

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28 April 2011Publications Catalog

tooth designs which are representative of helicopter
main drive gears. Asymmetric and baseline
(symmetric) toothed gear test specimens were
designed, fabricated and tested to experimentally
determine their single--tooth bending fatigue strength
and scuffing resistance. Also, gears with an
analytically optimized root fillet form were tested to
determine their single--tooth bending fatigue
characteristics relative to baseline specimens with a
circular root fillet form. Test results demonstrated
higher bending fatigue strength for both the
asymmetric tooth form and optimized fillet form
compared to baseline designs. Scuffing resistance
was significantly increased for the asymmetric tooth
form compared to a conventional symmetric involute
tooth design.
ISBN: 978--1--55589--989--9 Pages: 15

10FTM15. Drive Line Analysis for Tooth Contact
Optimization of High Power Spiral Bevel Gears
Authors: J. Rontu, G. Szanti and E. Mäsä

It is a common practice in high power gear design
to apply relieves to tooth flanks. They are meant to
prevent stress concentration near the tooth edges.
Gears with crownings have point contact without load.
When load is applied, instantaneous contact turns
from point into a Hertzian contact ellipse. The contact
area grows and changes location as load increases. To
prevent edge contact, gear designer has to choose
suitable relieves considering contact indentations as
well as relative displacements of gearmembers. In the
majority of spiral bevel gears spherical crownings are
used. The contact pattern is set to the center of active
tooth flank and the extent of crownings is determined
by experience. Feedback from service, as well as from
full torque bench tests of complete gear drives have
shown that this conventional design practice leads to
loaded contact patterns, which are rarely optimal in
location and extent. Too large relieves lead to small
contact area and increased stresses and noise;
whereas too small relieves result in a too sensitive
tooth contact.

Today it is possible to use calculative methods to
predict the relative displacements of gears under
operating load and conditions. Displacements and
deformations originating from shafts, bearings and
housing are considered. Shafts aremodeled based on
beam theory. Bearings are modeled as 5--DOF
supports with non--linear stiffness in all directions.
Housing deformations are determined by
FEM--analysis and taken into account as translations
and rotations of bearing outer rings. The effect of
temperature differences, bearing preload and
clearances are also incorporated.

With the help of loaded tooth contact analysis
(LTCA), it is possible to compensate for these
displacements and determine a special initial contact
position that will lead to well centered full torque
contact utilizing a reasonably large portion of the
available tooth flank area. At the same time, crownings
can be scaled to theminimumnecessary amount. This
systematic approach leads to minimum tooth

stressing, lower noise excitation as well as increased
reliability and/or power density as compared to
conventional contact design method.

During recent years ATA Gears Ltd. has gained
comprehensive know--how and experience in such
analyses and advanced contact pattern optimization.
The methodology and calculation models have been
verified in numerous customer projects and case
studies.
ISBN: 978--1--55589--990--5 Pages: 14

10FTM16. Analysis of Load Distribution in
Planet--Gear Bearings
Authors: L. Mignot, L. Bonnard and V. Abousleiman

In epicyclic gear sets aimed at aeronautical
applications, planet--gears are generally supported by
spherical roller bearings with bearing outer race being
integral to the gear hub. This paper presents a new
method to compute roller load distribution in such
bearings where the outer ring can’t be considered
rigid. Based on well known Harris method, a modified
formulation enables to account for centrifugal effects
due to planet--carrier rotation and to assess roller
loads at any position throughout the rotation cycle.
New model load distribution predictions show
discrepancies with results presented by Harris, but are
well correlated with 1D and 3D Finite Element Models.
Several results validate the use of simplified analytical
models to assess the roller load distribution instead of
more time consuming Finite element Models. The
effects of centrifugal effects due to planet--carrier
rotation on roller loads are also analyzed. Finally the
impact of the positions of rollers relative to the gear
mesh forces on the load distribution is shown.
ISBN: 978--1--55589--991--2 Pages: 11

10FTM17. Self-Locking Gears: Design and
Potential Applications
Authors: A.L. Kapelevich and E. Taye

Inmost of the gear drives, when the driving torque
is suddenly reduced as a result of power off, torsional
vibration, power outage or any mechanical failure at
the transmission input side, then gears will be rotating
either in the same direction driven by the system
inertia, or in the opposite direction driven by the
resistant output load due to gravity, spring load, etc.
The latter condition is known as backdriving. During
inertial motion or backdriving, the driven output shaft
(load) becomes the driving one and the driving input
shaft (load) becomes the driven one. There are many
gear drive applications where the output shaft driving
is less desirable. In order to prevent it, different types of
brake or clutch devices are used. However, there are
also solutions in gear transmission that prevent inertial
motion or backdriving using self--locking gears without
any additional devices. The most common one is a
worm gear with a low lead angle. In self--locking worm
gears, torque applied from the load side (worm gear) is
blocked, i.e. cannot drive the worm. However, their
application comes with some limitations: the crossed
axis shafts’ arrangement, relatively high gear ratio, low

Page 64

59April 2011 Publications Catalog

TECHNICAL PAPERS

2010 Full Set of Fall Technical Meeting Papers (17 papers on CD) $550.00. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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