Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Title of Invention: COUPLING
[0001] The present invention relates to a coupling.
[0002] Mechanical couplings are well known. Examples include couplings for
coupling
angularly misaligned shafts, universal joints, constant velocity joints,
couplings for
coupling a drive shaft to a driven shaft; couplings for connecting a torque
shaft to a
structural element of for example a suspension system.
[0003] According to the present invention a coupling has an inner member
and an outer
annular member and comprises:
= one or more pairs of members, which may or may not include one or both
the
inner and outer members, each pair being a first member and a second annular
member with a common axis and having a common first centre on the axis;
= the first member having an outer convex spherical periphery;
= the second annular member having an inner spherical concave periphery in
which the outer convex periphery of the first annular member is received;
= the outer convex periphery and the inner concave peripheries being
concentric
about the first centre and complementary to one another and co-acting with
one another to transmit axial loads acting along the torsional axis between
them;
= one or a diametrically opposed pair of axles disposed radially of the
common
centre of the pair of members coupling the first and second members for
transmitting torsional load from one of the members to the other; the first
and
second annular members being constrained by the axle(s) to be rotatable one
relative to the other about the axle(s).
[0004] For most practical applications the said members, other than the
outer member,
comprise spherical segments including a common centre. A spherical segment is
a
portion of a sphere between with a pair of parallel planes. However, it is
possible to
consider, in some circumstances, situations in which a segment of a sphere is
used in
which the planes are not parallel but non-intersecting or which is cut by
cones whose
apexes are on the common axis - such alternatives would have disadvantages
both in
manufacture, assembly and use and seem less likely to be adopted.
[0005] The inner member and the outer annular member may comprise a pair of
members
coupled by the at least one axle, or there may be one or more intermediate
members
disposed between the inner and outer members, each pair of adjacent members
comprising a pair of members coupled together by axles.
[0006] The axle(s) carries torque and the spherical surfaces of the first
and second members
carry axial and radial loads. Most of any axial load is carried by the
spherical surfaces.
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The axle(s) may also carry some of the axial load. Thus radial and axial loads
are
separated from torsional loads. In an embodiment, the axle(s) are configured
to not
transmit radial loads between the members coupled thereby so that radial loads
are not
carried by the axles. Thus radial loads are carried mostly or wholly by the
spherical
surfaces.
[0007] Other features of the invention are set out in the claims and,
without limitation in the
examples below.
[0008] Couplings according to various embodiments the present invention
described may be
used for coupling any two structural elements that must be coupled with at
least one
rotational degree of freedom. Some examples are useful as 'structural static
couplings'
coupling an element to a fixed structure. Other examples are useful as
rotational
'flexible couplings' coupling two rotational elements. Couplings according to
the
invention, for example, may be used to couple angularly misaligned shafts, or
as
universal joints, constant velocity joints, couplings for coupling a drive
shaft to a
driven shaft, and as couplings for connecting steered hub to a fixed
structural element
such as a suspension arm in a suspension system.
[0009] Some examples of the invention are described below with reference to
the ac-
companying drawings, in which:
[0010] Figure 1 illustrates a reference frame of operation of couplings
according to em-
bodiments of the invention;
[0011] Figures 2A to 2C show an example of a coupling according to the
invention, of
which Figure 2A is an axial view with the elements of the coupling un-aligned,
Figure
2B is a cross-sectional view of Figure 2A along axis A3 and Figure 2C is a
cross-
sectional view of Figure 2A along axis A2;
[0012] Figures 3A and 3B show a hub centre steering mechanism including an
example of a
coupling according to Figure 2, of which Figure 3A is an isometric view and
Figure 3B
is a cross-sectional view.;
[0013] Figures 4A to 4F show another example of a coupling according to the
invention, of
which Figure 4A is an axial view along axis Al of Figure 1, Figure 4B is a
cross-
sectional view along plane A-A in Figure 4A, Figure 4C is a cross-sectional
view
along plane B-B in Figure 4A, Figure 4D is an axial view showing the elements
of the
coupling un-aligned, Figure 4E is an axial cross-sectional view of the
coupling of in
Figure 4A and Figure 4F is a cross sectional view along plane A-A of Figure
4D;
[0014] Figures 5A and 5B are cross-sectional views of a pair of the
couplings of Figure 4
connected together;
[0015] Figures 6A to 6F show a further example of a coupling according to
the invention, of
which Figure 6A is an axial view along axis Al of Figure 1, Figure 6B is a
cross-
sectional view along plane A-A in Figure 6A, and Figure 6C is a cross-
sectional view
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on plane B-B of Figure 6A, Figure 6D is a side view; Figure 6E is a cross-
sectional
view along plane C-C of Figure 6D; and Figure 6F is a side cross-sectional
view of the
coupling along plane D-D of Figure 6D;
[0016] Figures 7A, 7B and 7C show bearings on one representative member of
a coupling
according to the invention, in which Figure 7A is an isometric view of the
coupling,
and Figure 7B is a cross sectional axial view, and Figure 7C is an exploded
view;
[0017] Figure 8 shows means for limiting relative rotation of elements of a
coupling
according to the invention;
[0018] Figure 9 is a cross-sectional view of a modification which may be
applied to
couplings in accordance with the invention;
[0019] Figure 10 is across-sectional view of a representative coupling in
accordance with the
invention within a bearing; and
[0020] Figures 11A and 11B illustrate a way of assembling the coupling
described in the
previous examples.
[0021] The examples of the invention in the drawings are described in
relation to a reference
frame as shown in Figure 1.
[0022] The reference frame has a first axis Al defining an axial direction.
A second axis A2
is perpendicular to the first axis Al. At the intersection of the first and
second axes is a
central point C of concentric spherical surfaces of concentric members of the
couplings. The first and second axis and the central point lie in first plane
P1 and the
first axis and central point lie in a second plane P2 perpendicular to the
first plane. A
third plane P3 through the centre point C is perpendicular to the other
planes. A third
axis A3 defines is perpendicular to axes Al and A2, lies in the third plane
and passes
through the central point C.
[0023] The first axis Al is a torsional axis on which, for example, a drive
shaft or driven
shaft is connected to the coupling and the second A2 and third A3 axes are
axes of
relative rotation of members of the couplings.
[0024] In further examples, couplings have some members centred on the
central point C
and other members centred on a further central point C2 offset from C along
the first
axis Al when the members are aligned. The offset of C2 from C may be slight,
for
example a fraction of a millimetre. Further axes A21 and A31, parallel to axes
A2 and
A3 respectively pass through the central point C2.
[0025] In Figure 2, a coupling comprises an inner annular member 201 around
the first axis
Al. The inner member 201 comprises a spherical segment about central point C
and
has an outer peripheral surface S1 which is convexly spherical centred on the
central
point C on the first axis. The inner member 201 has a central cylindrical bore
40 which
in this example has splines 42 for engaging a correspondingly splined shaft.
[0026] An outer annular member 202 has an inner peripheral surface S21
which is convexly
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spherical complementary to the outer surface Si of the inner member 201. The
concave spherical surface S21 is centred on the same central point C on the
axis as the
spherical surface of the inner ring. In this example the inner spherical
surface S21 of
the outer ring and the outer spherical surface Si of the inner member 201 are
contiguous plain bearing surfaces.
[0027] The inner and outer annular members 201, 202 are coupled by an axle
arrangement
comprising a diametrically opposed pair of axles X1 and X11 which are on a
common
axis through the central point C, in this case on axis A3. The pair of axles
constrains
the inner and outer rings to be rotatable, one relative to the other, about
axis A3.
[0028] Each of the axles X1 and X11 comprises an axle shaft XS fixed in a
bore B2 in the
outer annular member 202 and extending into a bore B1 in the inner member 201
in
which it is free to rotate. The shafts are arranged so that they do not
transmit radial
loads between the inner and outer rings. That is done by providing radial
clearance
between the ends of the axles and the radially adjacent spherical surfaces and
by
allowing some radial freedom of movement in the bore B1 between the shaft XS
and
the inner member 201: these arrangements isolate the axles from both radial
and axial
loads.
[0029] The shafts may be fixed in the outer annular member 202 by an
interference fit or be
otherwise fixed by for example a cold weld.
[0030] The axles may take other forms. The shaft XS may have a head in a
recess in the
outer surface of the outer member 202 so as to not protrude above the outer
surface and
be fixed in the outer member 202 by a screw-threaded engagement in the bore B2
in
the outer member.
[0031] The axles retain the inner member 201 axially within the outer
member 202. In
addition, the spherical surfaces of the inner and outer members co-act to
retain the
inner member axially within the outer member.
[0032] The central point C of the adjacent convex and concave spherical
surfaces lies
between the axial facing faces F 1 and F3 of the inner member 201 and between
the
faces F2 and F4 of the outer member 202. As a result of that, the periphery of
the inner
convex spherical surface mid-way between the axially facing faces Fl and F3 is
at a
greater radius than the periphery of the concave surface of the outer member
202 at the
axially facing faces thereof F2 and F4. Thus the inner member 201 is retained
axially
in the outer annular outer member 202 over an operational range of rotation of
the
inner annular member 201 about the second axis and/or about the first axis.
[0033] In the example in Figure 2, the inner member 201 has splines in its
central cylindrical
bore for engaging a shaft. Splines (not shown) may additionally or
alternatively be
provided on the outer periphery of the outermost member (in this case outer
annular
member 202) for engaging another shaft. The coupling may be allowed to slide
relative
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to the shaft(s) providing an axial degree of freedom.
[0034] The first and second annular members are each a section of a sphere
centred on the
central point C at the intersection of the first Al and second A2 axes.
[0035] In figure 2 as shown there are two diametrically opposite axles X1
and X11 which
share loads on the coupling. One could be omitted if a coupling is being
designed to
operate under light loads.
[0036] The example of figure 2 has static applications such as Hub Centre
Steering as shown
in Figure 3.
[0037] In Figure 3 a steered wheel hub 62 of a wheel is supported by a
support member 64
which in this example is a suspension arm. The coupling El, as described with
reference to figure 2 couples the suspension arm 64 to the steered wheel hub
62. The
arm 64 is engaged, for example by splines, in the central bore 40 of the inner
ring 201
of the coupling El. The axles(s) Xl, X11 (only X1 shown) allow the outer
annular
member 202 to rotate about one axis (the steering axis) relative to the inner
annular
member 201 and arm 64. The outer annular member 202 supports the wheel 62
which
is free to rotate on bearings 63. A steering arm 60 is fixed to the outer
annular member
202 to rotate it relative to the inner ring and arm 64.
[0038] In this example the axle(s) Xl, X11 provide support to allow
relative rotation but do
not drive the wheel hub 62.
[0039] A further example of a coupling is shown in figure 4 comprising an
inner annular
member 401 centred on a first axis, the inner annular member 401 having an
outer pe-
ripheral surface Si which is convexly spherical centred on the point C on the
axis Al.
The inner annular member 401 has a central cylindrical bore 40 has splines for
engaging a correspondingly splined shaft.
[0040] An intermediate annular member 402 has an inner peripheral surface
S21 which is
concavely spherical complementary to the outer surface S1 of the inner member
402.
In this example the inner spherical surface S21 of the second member and the
outer
spherical surface Si of the inner member 401 are contiguous plain bearing
surfaces.
[0041] A first pair of diametrically opposed axles X1 and X11 extend
radially of, the first
axis Al on the third axis A3 to couple the inner member 401to the intermediate
member 402. The first and second axles constrain the inner and intermediate
members
to rotate one relative to the other about the third axis A3. The intermediate
member
402 has an outer periphery S22 which is convexly spherical. An outer annular
member
403 has an inner peripheral surface S31 which is concavely spherical
complementary
to the outer surface S22 of the intermediate member 402. In this example the
inner
spherical surface S31 of the outer member 403 and the outer spherical surface
S22 of
the intermediate member 402 are contiguous plain bearing surfaces.
[0042] A second pair of diametrically opposed axles X2 and X21 extend
radially of, the first
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axis Al along the second axis A2 perpendicular to the third axis A3 to couple
the in-
termediate member 402 to the outer member 403. The axles X2 and X21 constrain
the
intermediate 402 and outer 403 members to be rotatable one relative to the
other about
the second axis A2 of rotation (see Figure 1) through the centre point C, and
per-
pendicular to the first axis Al and perpendicular to the third axis A3. The
second pair
of axles allows relative rotation of the pair of members comprising
intermediate and
outer members 402 and 403 independently of the pair of members comprising
inner
and intermediate members 401 and 402.
[0043] In similar manner as described with reference to figure 2, the
spherical surfaces Si,
S21, S22 and S31 bear loads acting radially of the axis Al and in the
direction of the
axis Al. The axles transmit torque between the inner 401, intermediate 402,
and outer
403 members.
[0044] The inner member 401 is retained in the intermediate member 402, and
the in-
termediate member 402 is retained in the outer member 403 in the same way that
the
inner member 201 in figure 2 is retained in the outer member 202.
[0045] A first shaft or other structural element may be engaged in the
central bore in the first
annular member 401 and a second shaft or other structural element may be
engaged
with the outer member 403. For that purpose the outer member 403 may be fixed
to or
integral with a flange (not shown) or it may comprise other means, for example
external splines, for coupling to a structural element.
[0046] One use of couplings of Figure 4 is as a universal joint. The
coupling allows angular
misalignment of the shafts by virtue of the relative rotation of the
intermediate member
402 and outer member 403 about the third axisA3 and second axis A3
respectively.
[0047] Both the inner member 401 and the intermediate member 402 comprise
spherical
segments about the central point C.
[0048] In figures 5A and 5B coupling arrangements comprising two couplings
of the kind il-
lustrated in figure 4 are shown.
[0049] In figure 5A the comprising two couplings E2 of figure 4 connected
together by a
connecting structure 66. The structure rigidly connects the two couplings. The
connecting structure 66 is a tube coupling the outer members 403. In another
example,
instead of the tube, the outer member 403 of one coupling is connected by a
connecting
structure 67 to the first member 401 of the other as shown for example in
Figure 5B.
[0050] The coupling arrangement of Figure 5A is an approximation to a
double Cardan
joint, if the axle pairs of one of the individual couplings E2 are non-
orthogonal to cor-
responding axle pairs of the other.
[0051] If instead of using the couplings E2 of figure 4, the couplings of
figure 2 are used,
the coupling arrangement is a crank handle if the axles of the two couplings
are in the
same orientation. In other examples the axle(s) of one coupling are orthogonal
to the
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projection(s) of the other.
[0052] One of the couplings may be free to move axially in the tube 66.
[0053] The coupling of Figure 6 comprises an inner annular member 601,
first, second third
intermediate annular members 602, 603, 604 and outer annular member 605.
[0054] It has been found that the third intermediate 604 and outer member
605 must be
offset relative to the inner and first intermediate members 601 and 602 along
the axis
Al when the members are aligned (see figure 6D).The offset may be slight. This
may
be achieved by offsetting the outer spherical surface S32 of the second
intermediate
member 603 axially of the inner spherical surface S31 of the second
intermediate
member 603. Thus using the frame reference of Figure 1, the inner and first in-
termediate members 601 and 602 are centred on central point C and the second
and
third intermediate members 603 and 604 are centred on point C2.
[0055] The first annular member 601 has an outer peripheral surface Si
which is convexly
spherical centred on the central point C on the first axis Al. The first
annular member
601 has a central cylindrical bore 40 which in this example has splines 42 for
engaging
a correspondingly splined shaft.
[0056] A first intermediate annular member 602 has an inner peripheral
surface S21 which is
concavely spherical complementary to the outer surface S1 of the inner member
601.
Surfaces Si and S21 are contiguous plain bearing surfaces.
[0057] A first pair of diametrically opposed axles X 1, X11 extends along
the third axis A3
radially of the first axis Al to couple the inner member 601 and first
intermediate
member 602. The first pair of axles constrains the pair of members comprising
inner
and first intermediate members 601 and 602 to be rotatable one relative to the
other
about the third axis A3 of rotation through and perpendicular to the first
axis Al.
[0058] The first intermediate member 602 has an outer periphery S22 which
is convexly
spherical. A second intermediate annular member 603 has an inner peripheral
surface
S31 which is concavely spherical complementary to the outer surface S22 of the
first
intermediate member 602. In this example the inner spherical surface S31 of
the
second intermediate member 603 and the outer spherical surface S22 of the
first in-
termediate member 602 are contiguous, plain, bearing surfaces.
[0059] A second pair of diametrically opposed axles X2, X21 extend along
the second axis
A2 radially of the first axis Al coupling the pair of members comprising the
first and
second intermediate members 602 and 603. The second axle pair constrains the
first in-
termediate member 602 and second intermediate member 603 to be rotatable one
relative to the other about the second axis A2 of rotation through the central
point C,
and perpendicular to the first axis and perpendicular to the third axis A3.
The second
pair of axles allows relative rotation of the pair of members 602 and 603
members in-
dependently of the pair of members 601 and 602.
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[0060] The second intermediate member 603 has an outer periphery S32 which
is convexly
spherical. A third intermediate annular member 604 has an inner peripheral
surface
S41 which is concavely spherical complementary to the outer surface S32 of the
second intermediate member 603. In this example the inner spherical surface
S41 of
the third intermediate member 604 and the outer spherical surface S32 of the
second
intermediate member 603 are contiguous, plain, bearing surfaces.
[0061] A third pair of diametrically opposed axles X3, X31 extend along the
second axis A2
radially of the first axis Al coupling the pair of members comprising the
second and
third intermediate members 603 and 604. The third axle pair constrains the
members
603 and 604 to be rotatable one relative to the other about the axis A21 of
rotation
through the central point C2, parallel to axis A2. They thus constrain the
pair of
members 603 and 604 to be rotatable one relative to the other about axis A21.
The
third pair of axles allows relative rotation of the second and third
intermediate
members independently of the first and second intermediate members.
[0062] The third intermediate member 604 has an outer periphery S42 which
is convexly
spherical.
[0063] An outer annular member 605 has an inner peripheral surface S51
which is
concavely spherical complementary to the outer surface S42 of the third
intermediate
member 604. In this example the inner spherical surface S51 of the outer
member 605
and the outer spherical surface S42 of the third intermediate member 604 are
contiguous, plain, bearing surfaces.
[0064] A fourth pair of diametrically opposed axles X4, X41 extends along
axis of rotation
A31 parallel to axis A3 but though centre point C2. The fourth axle pair
constrains
members 604 and 605 to be rotatable one relative to the other about A31 and
per-
pendicular to axis A21. They thus constrain the members 604 and 605 to be
rotatable
one relative to the other about axis A31. The fourth pair of axles allows
relative
rotation of the pair of members 604 and 605 independently of the pair of
members 603
and 604.
[00651 The members are retained in the coupling in the same way as
described hereinabove
with reference to Figure 2.
[0066] The axles X1 to X41 are identical to the axles X1 and X11 of Figure
2.
[0067] In figures 6A to 6F the inner and first intermediate members 601 and
602 comprises
spherical segments about the central point C, the second and third
intermediate
members 603 and 604 also comprises spherical segments but about point C2.
However,
the central aperture of second intermediate member 603 is a spherical segment
about
the central point C, the first intermediate member 602 is received into this
aperture.
[0068] One illustrative use of the coupling of Figure 6 is as a double
Cardan joint.
[0069] In the examples of Figures 2 to 6, the spherical surfaces are all
contiguous plain
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bearing surfaces. Rolling element bearings may be provided between the
adjacent
spherical surfaces. In Figure 7, ball bearings 100 held in one or more cages
101 may be
provided at the surface of a member of a coupling. In the example of Figure 7,
the balls
are held in two ball baskets, which are half spherical pieces, between the
axles X,
which may be axles X1 and X11 of the inner member 701 and outer member 702.
Thus
the spherical surfaces have rolling elements for carrying radial and axial
loads. The
radial load path is independent of the torque load being applied. This
approach is more
efficient than using balls in grooves to carry both the torsion and the radial
load. As
shown figure 7 is a two member coupling, however, the principles of figure 7
can be
extended to a bearing having one or more intermediate members as shown in
figure 4
or 6.
[0070] As an alternative or in addition rolling element bearing 102 may
also be mounted on
the axles to reduce friction.
[0071] The inner member 701 comprises a spherical segment about the central
point C. In
figure 7 the axles X1 and X11 have heads H inset into outer member 702 and
screw
threads engaging threads in the bores of outer member 702.
[0072] The spherical surfaces of adjacent members in the examples co-
operate to bear radial
and axial loads. To ensure that the coupling can bear a desired axial and
radial load the
spherical surfaces need to overlap sufficiently. Thus in embodiments of the
invention,
means may be provided to limit the relative rotation of adjacent members. Such
limiting means also assists the retention of each inner ring in its associated
outer ring.
Examples of such limiting means include a stop within the coupling. As shown
for
example in Figure 8, in one example a fixed pin N projecting from an outer
member 2
into a slot L in an inner member 1. It will be appreciated that any other
suitable means
of limiting relative may be used. In some examples the coupling is supported
by a
support structure which limits relative rotation. In others the structural
elements
coupled by the coupling limit the relative rotation.
[0073] As shown in Figure 9, to increase the operational range of relative
rotation, the outer
2 or 3 of adjacent members 1 and 2 or 2 and 3 may be larger in the axial
direction than
the inner one 1 or 2. Figure 9 shows three annular members 1, 2 and 3 as in
figure 4.
The principle of this Figure 9 may be applied to any of the pairs of annular
members of
the examples of the invention.
[0074] Referring to Figure 10, any of the examples of figures 2, 4 and 6
may be fixed within
a bearing 110 which may be fixed to a fixed structure 112 for example a
bulkhead,
floor or wall. That allows the coupling to couple to any two structural
elements, one
each side of the fixed structure 112, that must be coupled with at least two
rotational
degrees of freedom. For example the fixed structure may be a bulkhead of a
vehicle
and the coupling couples section of a steering mechanism of the vehicle.
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[0075] The bearing 110 allows the coupling E of Figure 10 to rotate within
the fixed
structure 112.
[0076] Figures 11A and 11B illustrate the assembly of a coupling. The
coupling comprises a
pair of annular members 1 and 2, an outer member 2 being outside an inner
member 1.
Member 2 has two diametrically opposite loading slots Li and L2. The loading
slots
extend halfway across the width of the outer member 2 (the loading slots can
also be
seen in figure 7C). The slots are dimensioned so that the diametrically
opposite floors
6 of the slots are spaced by the diameter of the outer surface Si (including
if provided
the cages101 as in figures 7) of inner member 1. The width of each slot is
equal to or
slightly greater than the width of the inner member. The inner member 1 is
introduced
sideways into the slots as shown in Figure 11A and then rotated into the same
plane as
the outer member 2. The axle bore (s) of the pair of members 1 and 2 are
brought into
alignment at a suitable stage in the assembly process.
[0077] This option enables each member to be machined from a solid piece of
material and
minimises the risk of failure as a result of joining to halves together. The
method
described enables all the bearing surfaces described in this specification to
be
continuous, ie avoiding any joins (and thus weak areas) at the join of a
member
assembled in two halves bolted or welded together.
[0078] In figure lithe pair of members 1 and 2 are representative of each
member re-
spectively of the pairs of members 201 and 202 in figure 2, 401 and 402, 402
and 403
in figure 4, 601 and 602, 602 and 603, 603 and 604, 604 and 605 in figure 6,
701 and
702 in figure 7.
[0079] In the examples above, for plain bearing surfaces, the mating convex
and concave
spherical surfaces should match accurately. That requires appropriately
precise man-
ufacture of the couplings.
[0080] A lining material may be injected between the spherical bearing
surfaces. The convex
spherical surfaces may be accurately machined. The concave spherical surfaces
may be
roughly machined to form a rough surface which is also a piece-wise linear ap-
proximation to a curved surface also known as cathedraling, and lining
material
injected between an accurately machined convex surface and the rough concave
surface to form an accurately matched concave spherical surface. The convex
spherical
surface is coated with a release agent before the lining is injected into the
coupling.
[0081] The lining material may be of plastic. The compositions of some of
the plastics are
not publically known as the suppliers are often commercially sensitive about
their
compositions. However Delrin is one known product that could be used or PTFE
based materials could be used.
[0082] In an alternative embodiment to those shown above, a structural
element such as a
shaft is fixed to or is integral with the inner member of a coupling. In an
alternative
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embodiment, a structural element such as a shaft is fixed to or is integral
with the outer
member of a coupling. Structural elements may be fixed to or be integral with
both the
inner and outer members of a coupling.
[0083] The examples described above may have splines in the inner ring and
or on the outer
most peripheral surface of the coupling for connecting the coupling to
structural
elements to be coupled.
[0084] Alternatively any other suitable means of connecting the coupling to
structural
elements may be used. For example the outer periphery may have screw thread
for
connecting it to a correspondingly threaded structural element. Likewise the
inner
member may have a central bore which is screw threaded or employ keys to
engage a
shaft. The inner member may be integral with a shaft which is screw threaded
for
connection to another structural element. The outer member of the coupling may
be
connected to a structural element by any suitable means.
[0085] Couplings as described above may be made of any suitable material.
The examples
having plain bearing surfaces may be of metal, e.g. high performance steels,
brass,
bronze, aluminium, titanium etc. or of plastic, e.g. nylon, glass filled
nylon, acetal,
ABS, Delrin .
[0086] It should be noted that the inner and outer annular members 401 and
403 of the
coupling of Figure 4 may be connected to respective shafts or other structural
members
so the intermediate member 402 is the only part which moves relative to the
other two;
this might lead a designer to select brass or bronze for the moving middle
ring and
steel for the inner and outer rings. The same philosophy could be applied to
the other
examples of the couplings.
[0087] Metal annular members rings may be lubricated by conventional
lubricants for
example grease. Alternatively, dry lubricant surfaces may be provided such as
plastic
liners as discussed above. The choice of materials and lubricants depends on
the
intended use of the coupling.
[0088] The inner member in all the examples comprises an annular spherical
member with a
central aperture for receiving a shaft. However, it may not have a central
aperture but,
for example, be bolted to a flange on a shaft.
[0089] In the examples shown, for maximum compactness, in each member of a
pair of
members comprising spherical segments has parallel sides in common planes when
the
segments are aligned. In particular:
= in the arrangement of figure 2 each member of a pair of members comprises
spherical segments has parallel sides in common planes when aligned.
= in the arrangement of figure 4 each member comprises spherical segments
having parallel sides in common planes when aligned.
= in the arrangement of figure 6 the first pair of members (601, 602) each
CA 02932041 2016-05-30
WO 2015/087081
PCT/GB2014/053680
12
comprise spherical segments haying parallel sides in common planes when
aligned and the third pair of members (603, 604) and fourth pair of members
(604, 605) each comprise spherical segments haying parallel sides in common
planes when aligned. Although this does not apply to the second pair of
members (602, 603).
