Note: Descriptions are shown in the official language in which they were submitted.
~ 169669
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,
RESILIENT ROTARY COUPLING
The abstract is not to be taken as limitina the
invention of this application and in order to understand
the full nature and extent of the technical disclosure
of this application, reference must be made to the accom-
panying drawing and the following detailed description.
The invention pertains to a resilient rotary
coupling. The coupling is particularly suited for use
in a marine propeller drive, although it is not intended
that the invention be limited to such application.
The need for torsional shock and vibration
absorption between the propeller drive shaft and the
propeller has long been recognized. Many arrangements
have been proposed.
~5 Various aspects of this invention are as follows:
In a marine propeller drive having a propeller
and propeller drive shaft, the improvement of a
resilient, indexing, rotary marine drive coupling having
an axis of rotation and being for coupling the
propeller and the propeller drive shaft of the marine
drive, the coupling comprising: (a) an outer rotary
member having an axially elongated inner surface which
in section taken perpendicularly to said axis includes
at least two arcs of greater radius of curvature
symmetrically disposed about said axis connected in
alternate manner by an equal number of arcs of lesser
radius of curvature, said arcs of greater radius of
curvature being located closer to said axis than said
arcs of lesser radius of curvature, the center of 2
curvature of each of said arcs lying on or within the
boundary of the closed figure defined by said inner
surface in said section and the arcs being connected to
one another without any abrupt change of radius or
radius of curvature, (b) an inner rotary member having
~ 169~
-- 2
an axially elongated periphery opposing the inner
surface of said outer member, said periphery being of a
cross-sectional configuration generally corresponding
and complementary to that of the inner surface of said
outer member but being of lesser radial dimensions such
that the periphery of said inner member is spaced
radiallv from the inner surface of said outer member
when each is centered on said axis and no load is
imposed on the coupling, and (c) resilient elastomeric
means disposed between said outer and inner members,
said resilient means being in radial compression and
contacting completely in the circumferential direction
~ of said coupling at least a portion of each of said
inner surface and said periphery, (d) in which the
corresponding arcs of lesser radius of curva~ure of the
inner and outer members are generally aligned when
there is no load imposed on the coupling, and (e) in
which the radial distance from the axis of the arcs of
lesser radius of curvature of the inner member i8 less
than the radial distance from the axis of the arcs of
greater radius of curvature of the outer member and
thereby provides permanent rotary displacement of the
inner member relative to the outer member.
In a marine propeller drive having a propeller
and propeller drive shaft, a resilient, indexing,
rotary marine drive coupling having an axis of rotation
and being for coupling the propeller and the propeller
drive shaft of the marine drive, the coupling
comprising: (a) an outer rotary member having an
axially elongated inner surface of generally square
cross-sectional configuration comprising a series of
four chordally disposed flat areas connected by rounded
corners disposed a great radial distance from said axis
than the radial distance of bi-secting radius normal to
said flat areas, the circumferentially measured arc
length of each rounded corner being at least equal to
- 1 lB966~
the circumferentially measured dimension of each flat.
area, (b) an inner rotary member comprising a metallic
bushing adapted to be received on and matingly engage a
shaft, said inner member having an axially elongated
periphery opposing the inner surface of said outer
member, said periphery being of generally square
cross-sectional configuration generally corresponding
and complementary to that of the inner surface of said
outer member but being of lesser radial dimensions such
that the periphery of said inner member is spaced
radially inwardly from the inner surface of said outer
member when each is centered on said axis and no load
is imposed on the coupling, and (c) resilient
elastomeric means o~ vulcanized rubber disposed between
said outer and inner members and bonded to said inner
member, said resilient means being approximately
equally radially compressed throughout itQ
circumferential and axial extent between said inner
surface and said periphery and contacting compLetely in
the circumferential direction of said coupling at least
a portion of each of said inner surface and said
periphery, the amount of compression being about 35
percent upon assembly of the coupling and about 60
percent when the inner member and outer member are
angularly displaced such that the corners of the inner
member are nearest the f].at areas of the inner surface
of the outer member, (d) in which the corresponding
flat areas of the outer and inner members are generally
parallel and symmetrically disposed about said axis
when there is no load imposed on the coupling, and (e)
in which the radial distance from the axis of the
rounded corners of the inner member is less than the
radial distance of the bi-secting radius of the
outer member and thereby provides permanent rotary
displacement of the inner member relative to the
outer member.
~ 169669
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In the drawing:
Figure 1 is a side elevation partially in section
of a portion of a marine drive according to an embodiment
of the invention;
Figure 2 is a fragmentary cross-sectional view
taken perpendicular to the axis of rotation of the coupling
along line II-II of Figure l;
Figure 3 is a fragmentary cross-sectional view
taken parallel to the axis of rotation of the coupling
along line III-III of Figure l;
Figure 4 is an end view of the inner member and
resilient means shown in Figures 2 and 3;
Figure 5 is a cross-sectional view taken along
lines V-V of Figure 4;
Figure 6 is a cross-sectional view taken perpendicular
to the axis of rotation of another embodiment of a coupling
according to the invention; and
Figure 7 is a cross-sectional view taken per-
pendicular to the axis of rotation of another embodiment
of a coupling according to the invention.
Referring to Figure 1 there is shown a portion of a
marine drive 8 including a resilient rotary coupling 10
P 169
according to an embodiment of the invention coupling
a ~haft 24 to a marine propeller 11.
Referring to Figure~ 2 and 3 there is shown an
embodiment of a resilient rotary coupling 10 according
to the invention as applied to a marine propeller drive
installation. The resilient rotary coupling 10 includes
an outer rotary member 12 shown as an example as propeller
hub 13, an inner rotary member 14 shown as an example
as bushing 15, o~ complementary configuration and
resilient means 17 disposed between the outer and inner
members.
The outer rotary member 12 includes an axially
elongated inner surface 18 of polygonal cross section.
As illustrated in Figure 2 the lnner surface 18 of the
propeller hub 13 includes four chordally di~posed flat
areas 20 with the adjacent ones of the flat areas connected
to one another by rounded corners 22. The rounded corners
22 are disposed a greater radial dlstance R from the axis
of rotation 23 of the re~ilient rotary coupling 10 than
the radial distance r of a bi-secting radius normal to
said flat areas 20. Mathematically expressed, R/r~ 1.
While the outer rotary member 12 illustrated is a
marine propeller, or more particularly, the hub 13 of a
marine propeller, it is to be understood that such outer
rotary member could be any suitable driving or driven
member in a machine arrangement.
The resilient rotary coupling 10 also includes an
inner rotary member 14 which in the examples shown is a
metallic bushing 15 having a configured bore 16 for mating
engagement with the propeller drive shaft 24. me inner
rotary member 14 includes an axially elongated periphery
26 in confronting or opposing relationship to the inner
surface 18 of the hub 13 of the propeller 11. me per-
iphery 26 of the inner member 14 i8 of polygonal cross
section generally corresponding and complementary to
that of the inner surface 18 of the outer member 12.
169669
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As shown in Figures 2 and 3, the periphery 26 of the
bushing 15 i~ of lesser radial dimensions than those of
the inner surface 18 of the propeller hub 13, In other
words the periphery 26 of the bushing 15 is spaced
radially inwardly toward the axis of rotation from the
inner surface 18 of the outer member 12 when each is
centered on the axis of rotation 23 of the coupling 10
and no load is imposed.
It is to be understood that the inner member 14
could alternately be formed so as to be an integral iart
of the drive shaft 24 or could itself be the driven
member rather than the driving member of the coupling.
The coupling 10 also includes resilient means 17
disposed between the outer member 12 and inner member 14.
The resilient means 17 is in radial compression even
when no load or torque is applied or being transmitted
through the coupling 10. The resilient means 17 is
brought into lnitial radial compression upon assembly
of the coupling 10. The resilient means 17 contacts
completely in the circumferential direction of the
coupling 10 at least a portion of ~aid axially
elongated inner surface 18 of the outer member 12 and
the axially elongated periphery 26 of the inner member 14.
When viewed in the CrosS section shown in Figure 2, the
resilient means 17 contacts all of the periphery 26 of
the bushing 15. In this cross-section, the periphery 28
of the resilient means 17 is itself contacted by all of
the inner surface 18 of the outer member 12. As shown
in Figures 2 and 3, there are no void~ between the oppo~ed
.working curfaces 26, 18 of the inner and outer members
since this space i~ occupied completely by the resilient
means 17. The resilient means 17 is prefenably contlnuous
in the circumferential direction of the coupling 10 and
bonded to one of the respective inner or outer rotary
35- members 14,12. It is most preferable that the resilient
means 17 be bonded to the inner rotary member 14 such as
.SU. 169~69
- 7
to bushing 15 illustrated in Figures 1 through 5.
The resilient means 17 is formed of an elastic
polymeric material and is preferably made of natural
rubber, or of a synthetic polyisoprene blended with
styrene butadiene rubber. When rubber is used for the
resilient means, it should be compounded to a durometer
of about 75 to 80 Shore A Hardness and be high in tear
strength and adhesion as measured on a peel-type strip
test such as ASTM D429, Method B. Compression set should
be as low as obtainable while maintain~ng the above given
properties and preferably should not exceed 25 to 30%
when measured according to ASTM D395, Method B, for 22
hours at about 158F. It is believed that other elasto-
meric materials may be satisfactory in this application,
including polyurethane. Specific formulations are not
presented herein as suitable formulations are known or
readily developed by those skilled in the art.
The undeformed configuration o~ a preferred embodl-
ment of the resilient means 17 is shown in Figures 4 and
5 in which the bushing 15 of the coupling 10 qhown in
Figures 1, 2 and 3 is illustrated including in its as-
manufactured, undeformed state the resilient mean~l7 of
vulcanized rubber of thickness T bonded to the central
portion 32 of its periphery 26. The thickness T of the
resilient means 17 as measured along a radius extending
perpendicularly from the axis of rotation 23 of the
- bushing 15 is i~ a preferred embodiment reduced about
- 35% upon installation of the bushing 15 with the
resilient means 17 bonded thereto into the outer member
12. The configuration of, the outer member 12 and the
bushing 15 are prefer~bly chosen such that the resilient
means 17 is further compressed at maximum torsional load
to about 60% of its original undeformed radial dimension.
In oth~r words, ~hen the corner~ 30 of the inner member
14 are nearest the flat areas 20 of the outer member 12,
~ 169669
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the resilient means 17 is compressed about 60% in the
radial direction at those areas.
Because the resilfent means 17 undergoes considerable
radial compression upon assembly of the coupling 10 the
resilient elastomeric means in its undeformed, as-
manufactured state is preferably of considerably greater
radial dimension and lesser axial dimension than in the
assembled coupling. In this regard compare Figure 5
with Figure 3. For this reason the resilient means 17
preferably in its undeformed state contacts and is
bonded to the central portion 32 of the periphery 26 of the
bushing 15 and is of generally unifbrm thickness T
throughout both its circumferential and axial extent in
central portion 32. The resilient means 17 preferably
has radiused corners 34-which extend about its circum-
ference at its axial extremities and fillets 35 at its
junction with the periphery 26 of bushing 15 to reduce
stresses at these locations. These stresses are particu-
larly high during assembly of the coupling 10. The
bushing 15 includes an internal bore 16 for mating en-
gagement with a drive shaft such as propeller shaft 24
shown in Figures 1, 2 and 3.
Referring now to Figure 6 there is illustrated another
embodiment according to the invention of a rotary coupling
37. The periphery 40 of the inner member 38 when viewed
from the end or in a cross section taken normal to the
- axis of rotation 41 of the inner member 38 is of generally
elliptical configuration. It is believed that the ratio
of the major axis to minor axis should be in the range
3 of 1.05 to 1.15 to obtain maximum angular displacement
of the inner member 38 and outer member 39 relative
to each other without seriously damaging the rubber of
resilient means 42 when it is subjected to maximum impact
torsional loading. This design permits a full 90 angular
displac~ment before the resilient means 42 is sub~ected
~ 169~69
to its maximum radial compression whereas in the embodiment
illustrated in Figures 1-5 the resilient means 17 is sub-
~ected to its maximum radial compression at 45 displace-
ment of the inner member 14 relative to the outer member
5 12. In the embodiment illustrated in Figure 6 the outer
rotary member 39 includes an axially elongated inner
surface 43 which in a section taken perpendicularly to
the axis of rotation 41 includes two arcs 44 of greater
radius of curvature which are diametrically opposed from
one another. These arcs 44 are connected in alternate
manner by two arcs 45 of lesser radius of curvature which
are also diametrically opposed from one another. The arcs
44 of greater radius of curvature are located closer to
the axis of rotation 41 than the arcs 45 of lesser radius
of curvature. As with the embodiments already discussed,
the periphery 40 of the inner rotary member 38 opposes
the inner surface 46 of the outer member 39. The
periphery 40 of the inner member 38 is of a configuration
generally corresponding and complementary to that of the
lnner surface 46 of the outer member 39 but is of lesser
radial dimensions such that the periphery 40 of the inner
member 38 is spaced radially fr~m the inner surface of
the outer member when each is centered on the axis of
rotation 41 and no load is imposed on the coupling.
This spacing need not be exactly equal throughout
the circumferential direction. The periphery 40 of the
inner member 38 may be mathematically specified and the
inner surface 46 of the outer member 39 constructed there-
from or mathematically specified. When both are mathematic-
ly specified as true elipses, the distance betweenthem will not be a true constant at all polnts. This
non-uniformity is believed not to adversely affect
the coupling and may provide a means for tuning the
torsional load versus angular deflection characteristics
of the coupling. Resilien~t elastomeric means 42 is dis-
posed between the inner and outer members. The resilient
~ 1~95~9
-- 10 --
means 42 is in radial compression and contacts completely
in a circumferential direction of the coupling the inner
working surface 46 of the outer member 39 and the working
periphery 40 of the inner member 38. When no load is
5 imposed on the coupling the corresponding arcs 44,47 of
lesser radius of curvature of the outer and inner members
are generally aligned. When a torsional load is imposed
on the coupling these corresponding areas 44,47 of lesser
radius of curvature are angularly displaced relative to
one another thus increasing the amount of compression of
the resilient means 42 adjacent the arcs 49 of lesser
radius curvature of the inner rotary member 38. The
resilient means 42 is compressed about 35% from its un-
deformed configuration upon assembly of the coupling 37,
15 The periphery 48 of the resilient means 42 before being
compressed is shown by dashed lines in Figure 6. The
resilient member 42 is of approximately even thickness
throughout and is approximately evenly compressed through-
out upon assembly of the coupling 37.
In Figure 7 there is shown yet another embodiment
of a coupling 50 according to the invention. The outer
rotary member 51 includes an axially elongated inner
surface 52 which in a section taken perpendicularly to the
axis of rotation 53 includes three arcs 54 of greater
25 radius of curvature symmetrically disposed about the axis
of rotation 53. The arcs 54 of greater radius o~ curvature
are connected in alternate manner by an equal number of
arcs 55 of lesser radius of curvature which are also
symmetrically disposed about the axis of rotation 53.
The arcs 54 of greater radius or curvature are located
closer to the axis of rotation 53 than the arcs 55 of lesser
radius of curvature. The center of curvature of each of
said arcs lies within the outer boundary of the section
of the inner surface 52. The arcs 54,55 are connected
35 to one another without any abrupt change of radius or
~ 169869
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of radiu~ of curvature. The configuration depicted in
Figure 7 may be called tri-oval. As in the other em-
bodlment~ ~hown the resilient means 56 is of sub~tan-
tially even thickness throughout between the inner
surface 52 of outer member 51 and the periphery 57 of
inner member 58 and is ~ub~tantially evenly compres ed
upon as~embly o~ the coupling 50. The inner and outer f
rotary members are of complementary configuration. The
arcs 59 of lesser radius of curvature of the inner
rotary member 58 are generally aligned with the arcs
55 of les~er radius of curvature of the outer rotary
member when no load is impo~ed onto the coupling and
are angularly displaced relative to one another upon
impo~ition of a torsional load, thus increasing compression
oi the resilient means 56.
A coupling according to the present invention can
be designed so as to permit permanent angular displacement
or, in other words, rotary slip, ratcheting or indexing
or the inner and outer members relative to one another.
In the embodiment ~hown in Figures 1-5 if rotary slip
at a predetermined torque is desired the radial distance
P from the axis of rotation 23 of the rounded corner~ 30
of the inner member 14 mu~t be le~s than the radial di~-
tance r of a bisecting radiu~ normal to the flat areaq 20
of the outer member 12. Expres~ed mathematically, P~ r.
Referring to Figure 6, i~ rotary slip at a predetermined
torque is desired the radial distance from the axis of ro-
tation 41 of the arc 49 of les~er radius of curvature of
the inner member 38 mu~t be le3s than the radlal distance
of the arc 44 of greater radiu~ of curvature of the outer
member 39.
On the other hand, if it is desired to provide
limited angular displacement between the inner and outer
rotary members of a coupling according to the invention,
this too, can be provided by design choice o~ the relative
dimensions of the inner and outer rotary members. For
g~69
example, in the embodiment shown in Figures 1-5 the
radial distance P from the axis of rotation 23 of the
rounded corners 30 o~ the inner member 14 would be es-
tablished greater than the radial distance r of a bi-
secting radius normal to the flat areas 20 of the outermember 12. Expre~sed mathematically, P~ r. When this
relationship exists, upon ~u~fic~ent angular or rotary
deflection or displacement of the rounded corners 30 of
the inner member 14 relative to those of the outer member
12 the rounded corners 30 of the inner member 14 come
into contact with the flat areas 20 of the correspondingly
configured outer member 12 and prevent any further angular
displacement of the members 12 and 14 relative to one
another, Because the resilient means is not fluid,
lockup will occur at some value of P~ r, provided the torque
load does not càuse total failure of the re~ilient means
through exce~sive shearing. At displacements below that
at which mechanical loc~up occurs the resilient ela8tomeric
means 17 cushions any torque loadlng between the inner
member 14 and outer member 12, In similar fashion the
dimensions of the inner and outer members in the embodi-
ment shown in Figures 6 and 7 can be establi~hed such
that upon sufficient angular or rotary deflection of the
inner and outer members relative to one another the arcs
of lesser radius of curvature of the inner rotary member
will come into contact or interference with the arcs of
greater radius of curvature of the outer rotary member
to prevent further angular displacement of the inner and
outer rotary members relative to one another.
It is believed that the radial distance between
the inner surface of the outer member and the periphery
of the inner member should be established such that the
resilient means when ~ormed of rubber is compres~ed
about 35% upon assembly of the coupling. Because the
inner and outer rotary members are of generally corres-
ponding and complementary cross-sectional oonfiguration
~169669
_ 13 -
the resilient means is approximately compressed uniformly
about the circumference of the coupling. In a preferred
high t~rque capability embodiment of the coupling
similar to that shown in Figu~es 1-5 the radial distance
between the inner surface 18 of the outer member 12 and
the periphery 26 of the inner member 14 as well as the
radial distance p of the corners 30 of the inner member 14
in comparison to the radial distance r of bisectine radlus
normal to the flat areas 20 was chosen such that when
the inner member 14 and the outer member 12 are angularly
displaced relative to one another so that the corners 30
of the inner member 14 are nearest the flat area 20 of
- the inner surface 18 of the outer member 12 the resilient
means 17 is compre8sed to about 60% of its new undeformed
configuration. It is believed that when rubber is used
for the resilient means that maximum radial compression
should be restricted to about 60%. An exception to this
guideline, of course, exists when the member~ of the
coupling are dimensioned 9uch that lnterference of the
periphery of the inner member and the inner suriace of
the outer member will occur upon sufficient angular
deflection.
It ha~ already been explained that the coupling can
be designed so as to permit angular slip between its 25 inner and outer members or to be of a lock-up or non-
slipping type design. The radius of the corners 30 or
areas of smaller radius of curvature on the inner member
14 also have an effect on torque characteristics and the
life of the coupling 10 and particularly on the llfe of
the intermediate resilient means 17. If the corner~ 30
of the inner member 14 are sharper, that is, of a smaller
radius of curvature, when all other factors are equal,
it is more likely that the resilient means 17 may become
cut, torn or ruptured. It is thus preferable that the
circumferential arc length 62 of each rounded corner 30
oi the inner member or arc of lesser radius oi curvature
669
- 14 -
be at least equal to the circumferential dimension 63
of each flat area 64 or arc of greater radius of curva-
ture of the inner member 14. It i~ most preferable that
the circumferential arc length of each rounded corner 30
or arc of lesser radius of curvature of the inner member
be at least 150% of the circumferential dimension of
each flat area 20 or area of greater radius of curvature
of the respective inner member. In the embodiment shown
- in Figures 1-5, which is a preferred embodiment, the cir-
cumferential arc length of each rounded corner is equal
to or greater than the circumferential dimension of the
corresponding flat area of the respective inner member 14,
outer member 12 or resilient means 17.
In the embodiment illustrated in Figures 1-5, the
periphery 26 of the inner member 14, the inner surface
18 of the outer member 12, and the resilient means 17
are each of generally square cross-sectional configuration
and include four flat areas connected by rounded corners
and are of generally uniform size throughout the axial
extent of the confronting surfaces. No taper in the
direction of the axis of rotation is required in a coupling
according to the invention, although such taper may be
employed to ease a~sembly and disassembly of the coupling.
When used in a marine drive, the coupling i~ removed as
a unit from the propeller shaft. The coupling itself is
not intended to be serviced in the field due to press
fitting of the inner member into the outer member with
attendant compression of the resilient means.
The configuration of the inner and outer members
and the resilient means have been described to be poly-
gonal or polyoval. The minimum number of flat area~,
i.e., areas of greater radius of curvature is two and
this will usually by employed in a lock-up type design
having a limited angular deflection between the inner
and outer members of the coupling. All el~e belng held
~966
5 -
constant, as the number of flat areas on the inner and
outer members is increased it becomes easier to cause
the inner and outer members to slip rotationally relative
to one another. As the number of flat areas on the inner
and outer members is increa~ed the angular displacement
between the inner and outer members prior to permanent
slip or angular displacement of these members relative
to one another is lowered as is the maximum torque
transmission capability o~ the coupling for a given over-
all physical size, similar compounding for the resilientmeans, and same degree of precompression of the resilient
means upon assembly of the coupling. It is believed that
about eight flat areas on the inner and outer members are
a practical maximum number, It is to be noted that the
configuration of the inner and outer members does not
have to be that of a regular polygon having rounded
corners as illustrated but rather can be rectangular ~ith
rounded corners or elliptical, tri-oval or polyoval. A
configuration whi¢h is symmetrlcal about the axis of
rotation of the coupling however is preferred to avoid
radial displacement of the inner or outer members relative
to the axis of rotation upon application of a torque load.
In preferred embodiments, the resilient means is
formed of wlcanized rubber and is sized so as to be
subjected to substantially equal radial compression at
all points about its circumference upon assembly of the
inner and outer members to form a coupling of the
invention. Increasing the amount of radial compression
of the resilient means upon assembly of the coupling
will increa~e the torsional spring rate and maximum torque
capability of the coupling, all else being equal and vice
versa. Preferably the resilient means is adhered to the
inner member and has a relatively high adhesion, for
exàmple, about 50 pounds per inch width as measured by
; 35 cutting the resilient means and allowing the part to
g 16~6~9
-- 16
roll and thereby peeling the resilient means from the
inner member.
The resilient means is preferably molded and bonded
to the inner member. Transfer or injection molding are
preferred over compression molding since the latter is
not believed to be as accurate. It is desired that
concentricity of the inner and outer members be maintained
and therefore an accurate molding process for evenly
forming the resilient means about the inner member is
desirable.
The term "axially" and related terms as used herein
mean in the direction of or parallel to the axis of
rotation of the coupling or that of any of its constituent
elements such as the inner member, the resilient means, or
the outer member as herein described. The term "radially"
and related terms as used herein mean in a plane inter- -
secting the axis of rotation and perpendicular to the
axis of rotation as defined hereln, The term "circum-
ferentially" and related term~ as used herein mean in a
directlon around the axls of rotation as defined herein.
The term "arc" and related terms as used herein mean
a curved line or any section of a curve and are not to
be limited to a constant radius of curva~,ure but are in-
tended to include a continuously changing radius of
curvature.
The term "polyoval" as used herein refers to a closed
two dimensional figure all of whose boundary portions are
straight or curved such that the center of radius of
curvature of all points of the boundary lie on or within
the figure. An example of a polyoval is shown by the
periphery of the inner member in Figure 7, which is a
tri-oval. A coupling could, of course, be designed with
a greater number of arcs of les~er radius of curvature,
with about eight such areas believed to be the practical
maximum,
9669
- ï7-
While certain representative embodiments and details
have been shown for the purpose of illustrating the ,n-
vention it will be apparent to those skilled in the art
that various changes and modifications may be made
therein without departing ~rom the spirit or scope of
the invention.
