Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Title of Invention: COUPLING
Technical Field and Background
[0001] This 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.
Summary of the invention
[0003] According to the present invention a coupling having an inner member
and an outer
annular member comprises one or more pairs of members, which may or may not
include one or both the innermost and outermost 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
into
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;
= at least one elongate projection from one member of a pair of members
into an
elongate slot in the other of the pair of members, each projection and each
slot
being elongate in a plane containing or parallel to the central axis of the
pair
of members concerned, the slot and projection projecting in the direction of
the said plane, and arranged to co-act with the pair of members to transmit
torque from the innermost of the pair of members to the other member of the
pair;
= each member, other than the inner member, having a pair of diametrically
opposed loading slots extending half way across their width to enable the in-
troduction of the first member of a pair of members into the concave inner
periphery of the second of the pair of members, and to be retained axially by
the second of the pair of members.
[0004] For most practical applications the said members, other than the
outer member,
comprise spherical segments including a common centre.
[0005] A spherical segment is a portion of a sphere between with a pair of
parallel planes.
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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.
[0006] Other features of the invention are found in the claims and/or the
accompanying de-
scription.
[0007] Couplings according to the invention 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 ro-
tational elements. By way of example, various couplings according to the
invention
may be used to couple angularly misaligned shafts, such as universal joints,
constant
velocity joints, couplings for coupling a drive shaft to a driven shaft, or as
couplings
for connecting a torque shaft to a fixed structural element, as in, for
example, a
suspension system.
Brief Description of Drawings
[0008] Examples of the invention described below with reference to the to
the ac-
companying drawings, in which:
[0009] Figure 1 illustrates a reference frame of operation of couplings
according to em-
bodiments of the invention;
[0010] Figures 2A to 2D show an example of a coupling according to the
invention, of
which Figure 2A is an isometric view of a coupling with its elements un-
aligned,
Figure2B is an axial side view of a coupling in the frame of reference, Figure
2C is a
cross-sectional view along axis A2 of Figure 2B and Figure 2D is a cross-
sectional
view along the axis A3 of Figure 2B;
[0011] Figures 3A to 3E illustrate a method of assembling the coupling of
Figure 2;
[0012] Figures 4A and 4B show a hub centre steering mechanism including an
example of a
coupling in accordance with the invention;
[0013] Figures 5A and 5B are cross-sectional views of pairs of couplings
connected
together;
[0014] Figures 6A to 6C show another example of a coupling according to the
invention, of
which Figure 6A is a cross-sectional view of Figure 6B along axis A2, Figure
6B is an
axial view along axis Al of Figure 1, and Figure 6C is a perspective view in
which the
elements of the coupling are misaligned;
[0015] Figures 7A to C show a pair of the couplings connected together, in
which Figure 7A
is a cross-sectional view with the elements of the couplings aligned, Figure
7B shows
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the elements un-aligned, and Figure 7C is an isometric view in which the
elements are
unaligned;
[0016] Figure 8A to 8E show a further example of a coupling according to
the invention, of
which Figure 8A is an axial view along axis Al of Figure 1, Figure 8B is an
isometric
axial view showing the elements of the coupling un-aligned, Figure 8C is a
cros s-
sectional view along axis A3, Figure 8D is a cross-sectional view along axis
A2 and
Figure 8E is a side view of the coupling as shown in Figure 8A;
[0017] Figures 9A to 9E show bearings in examples of couplings according to
the invention,
in which Figure 9A is an axial view of an element of a coupling, Figure 9B is
a side
view of the element of Figure 9A, Figure 9 C is a top view of the element of
Figure
9A, Figure 9D is a cross sectional view of a coupling and Figure 9E is an
isometric
view of a coupling;
[0018] Figure 10 shows means for limiting relative rotation of elements of
a coupling
according to the invention;
[0019] Figure 11 is a schematic diagram of a projection and slot useful in
examples of
couplings according to the invention;
[0020] Figure 12A is a cross-sectional view of a modification of the
couplings of the
preceding drawings showing the elements un-aligned and Figure 12B is an
isometric
view of the coupling of Figure 12A;
[0021] Figures 13A to 13C show a yet further example coupling according to
the invention,
of which, Figure 13A is an axial view along axis Al of Figure 1, Figure 13B is
a per-
spective view showing elements of the coupling un-aligned, and Figure 13C is
another
isometric view showing elements of the coupling un-aligned;
[0022] Figures 14A to 14E show yet another example of a coupling according
to the
invention, of which Figure 14A is a axial view along axis Al of Figure 1 with
elements
of the coupling un-aligned, Figure 14B is an axial cross-sectional view along
plane
C-C of Figure 14D, Figure 14C is a cross-sectional view along plane A-A in
Figure
14A, Figure 14D is a side view of the coupling of Figure 14A, and Figure 14E
is an
isometric view of the coupling;
[0023] Figures 15A and 15B show another example of a coupling according to
the
invention;
[0024] Figure 16 shows an example of a coupling combining the use of
projections and slots
in part of the coupling and axles in another part, wherein Figures 16A, 16B,
16D are
rear, front and side isometric views of the coupling with the members
unaligned; and
Figure 16C is a cross sectional view of the coupling, and
[0025] Figures 17A to 17D shows another example of a coupling according to
the invention,
in which Figure 17A is an isometric front view of the coupling, Figure 17B is
an
isometric rear view of the coupling, Figure 17C is a cross-sectional view on
axis A3
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and Figure 17D is an isometric side view.
Descriptions of examples
[0026] Examples of the invention in figures 2 to 17are described in
relation to a reference
frame as shown in Figure 1.
[0027] 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 axes 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 trough the centre point C is perpendicular to the other planes.
A third
axis A3, perpendicular to axes Al and A2, lies in the third plane and passes
through
the central point C.
[0028] 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.
[0029] In some 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 re-
spectively pass through the central point C2.
[0030] In Figure 2, a coupling comprises a pair of members, 201 and 202, an
inner annular
member 201 and an outer annular member 202 each comprising spherical segments.
The inner annular member 201, around axis Al, is centred on the central point
C which
is on that axis and has an outer peripheral surface S1 which is convexly
spherical and
centred on the central point C. The inner annular member 201 has a central
aperture 40
which in this example has splines 42 for engaging a correspondingly splined
shaft.
[0031] An outer annular member 202 has an inner peripheral concave
spherical surface S21
which is complementary to the convex outer surface S1 of the inner member 201.
The
concave spherical surface S21 is centred on the same central point C. The
inner
spherical surface S21 of the outer member 202 and the outer spherical surface
S1 of
the inner member 201 are contiguous plain bearing surfaces.
[0032] Elongate projections M1 and Mll extend radially of the central point
C, and parallel
to the first axis Al, from the convex spherical surface S1 of the inner member
201. The
outer surfaces of the projections also extend parallel to the spherical
surface Sl. The
projections extend into complementary slots K1 and K1 1 in the inner concave
surface
S21 of the outer annular member 202. The projections and slots constrain the
inner and
outer annular members to be rotatable, one relative to the other, about the
second axis
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A2 of rotation through the central point and perpendicular to the first axis.
Projection
Mll and slot K1 1 are identical to, and diametrically opposite, projection M1
and slot
K1 respectively. The coupling will work without projection Mll and slot K11,
but it is
less robust against failure.
[0033] The central point C of the adjacent convex and concave spherical
surfaces Si, 521,
lies between the axial facing faces Fl and F3 of the inner member 201 and
between the
outer 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 annular member is
retained
axially in the outer annular member over the operational range of rotation of
the outer
member 202 about the second axis.
[0034] In the examples El shown in Figures 2 there are splines 42 in the
central bore of
inner member 201 for engaging a shaft. Splines (not shown) may additionally or
alter-
natively be provided on the outer periphery of the outer member 202 for
engaging
another shaft. The coupling may be allowed to slide relative to the shaft(s)
providing
an axial degree of freedom.
[0035] In the example shown the projections Ml, Mll which fit into
associated slots Kl,
K1 1 with minimal clearance between the sides of the projections and the sides
of the
slots. However in another example one of the projections projects into its
associated
slot with a predetermined substantial clearance between the sides of the
projection and
the sides of the slot to act as a back-up if the other projection, which fits
into its as-
sociated slot with minimal clearance, fails.
[0036] The inner 201 and outer 202 members are both annular in Figure 2.
Each is a section
of a sphere centred on the central point C at the intersection of the first Al
and second
A2 axes.
[0037] As shown in Figure 2A to 2D, the projection(s) project(s) from the
inner annular
member 201 into slot(s) in the outer member 202. However the projection(s) may
project from the outer member into slot(s) in the inner annular member 201.
[0038] In figure 2, the spherical surfaces bear loads acting radially of
the axis and in the
direction of the axis. The projection and slot transmit torque about the first
axis
between the inner and outer members. The inner member 201 and outer member 202
comprise spherical segments.
[0039] In one use of the coupling, rotation of the shaft about the first
axis is transmitted
from the inner member 201 by the projections M1 and Mll and slots K1 and K1
lto
the outer member 202 which also rotates. The outer member may be connected to
another shaft. In another use, one of the members, e.g. the outer member is
fixed and
static torque is transmitted from the inner member to the outer member.
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[0040] Figures 3A to 3E illustrate how the coupling in figure 2 is
assembled. The same
method is used of all the other couplings illustrated in figures 4 to 17
below. The outer
member 202 has two, diametrically opposite loading slots Li and L2. As shown
in
Figure 3E, the slots extend halfway across the width of the outer member. The
slots are
dimensioned so that the diametrically opposite floors 6 of the slots are
spaced by the
diameter of the outer surface S lof the inner member 201. The width of each
slot is
equal to or slightly greater than the width of the inner member. The inner
member 201
is introduced sideways into the slots as shown in Figures 3A, 3B and 3C with
its
projection(s) Ml, Mll aligned with the slot(s) Kl, K1 1 and then rotated so
the
projection(s) enter(s) the slot(s).
[0041] Other couplings described below have two or more annular members
around the
inner member concentric rings. Each pair of annular members may be assembled
as
described with reference to figure 3. It will be noted that Figures 3D and 3E
show an
annular member 602 of, for example, the embodiment of Figure 6A to 6C which
has
two annular members around the inner member, intermediate annular member 602
fitting within the outermost annular member 603.
[0042] The assembly method of Figure 3 provides a robust, strong, coupling.
It enables the
individual members to be machined from solid material and minimises the risk
of
failure as a result of joining two halves of members together. The method
described
enables all the bearing surfaces described in this specification to be
continuous i.e.
avoiding any joins (and thus weak areas) at the join of a member assembled in
two
halves bolted or welded together.
[0043] One possible use of the coupling of Figure 2 is in a hub centre
steering mechanism of
a vehicle. In Figure 4 a steered wheel hub 62 is supported by a support member
64
which in this example is a suspension arm.
[0044] The coupling P1 couples the suspension arm 64 to the steered wheel
hub 62. The arm
64 is engaged by splines 42, in the central aperture 40 of the first inner
annular
member 201 of the coupling. The projection(s) Ml, Mll and slot(s) Kl, K1 1
allow the
outer member 202 to rotate about one axis (the steering axis) relative to the
first inner
annular member 201 and arm 64. The outer 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 first inner annular member and shaft 64.
[0045] In this example the projection(s) Ml, Mll and slot(s) Kl, K1 1
provide support to
allow relative rotation but do not drive the wheel hub 62.
[0046] Figure 5A shows a coupling arrangement comprising two couplings as
shown in
Figure 2 connected together by a connecting structure 66. The structure 66
rigidly
connects the two couplings. In Figure 5A it connects the outer member 202 of
the
couplings. The projections of the two couplings are orthogonal relative to
each other,
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but could be non-orthogonal. In the example of Figure 5A the connecting
structure is a
tube coupling the outer members. In a modification of Figure 6A, one of the
couplings
is fixed in the tube and the other is free to move axially within the tube.
[0047] In another example, shown in Figure 5B, the outer member 202 of one
coupling is
connected to the inner member 201 of the other by a connecting structure shown
schematically at 68.
[0048] One illustrative use of such a coupling is a crank handle. If the
projections of the two
couplings are in the same orientation. In other examples the projection(s) of
one
coupling are orthogonal to the projection(s) of the other.
[0049] In Figures 6A to 6C, a coupling comprises a first, inner annular
member 601, annular
intermediate member 602 and an annular outermost member 603. Each of the
members
601, 602, 603 comprises spherical segments about the centre C. The inner
annular
member 601 is centred on a first axis Al, the inner annular member 601 having
an
outer peripheral surface S1 which is convexly spherical centred on the point C
on the
axis Al. The first inner annular member 601 has a central bore 40 which in
this
example has splines 42 for engaging a correspondingly splined shaft.
[0050] The intermediate annular member 602 has an inner peripheral surface
S21 which is
concavely spherical complementary to the outer surface S1 of the first inner
member
601. In this example the inner spherical surface S21 of the intermediate
member 602
and the outer spherical surface S1 of the first inner member 601 are
contiguous plain
bearing surfaces.
[0051] Diametrically opposite elongate projections M1 and Mll extends
radially of, and
parallel to, the first axis Al from the convex spherical surface S1 of the
inner member
601. The radially outer surface of the projection also extends parallel to the
spherical
surface Sl. The projections extend into complementary slots K1 and K1 1 in the
inner
concave surface S21 of the intermediate member 602. The projections Ml, M1 1
and
slots K1 K1 1 constrain the first inner 601 and intermediate member 602
members to be
rotatable one relative to the other about the second axis A2 of rotation
through and per-
pendicular to the first axis Al.
[0052] The intermediate member 602 has an outer periphery S22 which is
convexly
spherical. The outermost annular member 603 has an inner peripheral surface
S31
which is concavely spherical complementary to the outer surface S22 of the in-
termediate member 602. In this example the inner spherical surface S31 of the
outermost member and the outer spherical surface S22 of the intermediate
member 602
are contiguous plain bearing surfaces.
[0053] Second elongate projections M2 and M22 extend radially of, and
parallel to, the first
axis from the convex spherical surface S22 of the intermediate member 602. The
radially outer surface of the second projections M2and M22 also extends
parallel to the
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spherical surface.
[0054] The projections M2and M21 extend into complementary, second, slots
K2 and K21
in the inner concave surface of the outermost member 603. The second
projection M2
and M21 and second slots K2 and K21 are perpendicular to the first projections
Ml,
M11, and first slots Kl, K11. They constrain the intermediate 602 and
outermost 603
members to be rotatable one relative to the other about the third axis A3 of
rotation
(see Figure 1) through the centre point C, and perpendicular to both the first
axis
Aland second axis A2.
[0055] The inner member 601 is retained in the intermediate member 602, and
the in-
termediate member 602 is retained in the outermost member 603.
[0056] In this example the second projections M2 and M21 and corresponding
slots K2 and
K21 could be omitted but with less security in the event of failure.
[0057] One use of the couplings of Figure 6 is as a universal joint as it
allows angular mis-
alignment of the shafts by virtue of the relative rotation of the inner and
outermost
members about the second axis.
[0058] The coupling of Figure 6 has a flange 44, fixed to or integral with
the third annular
member for connecting the third annular member to a structural element, for
example a
shaft. The flange 44 may be replaced by splines or some other connecting
means.
[0059] The projections Ml, Mll and M2 M21 may be in intermediate member 602
and
outermost member 603 respectively projecting into slots Kl, K11, K2, K21 in
inner
member 601 and intermediate member 602.
[0060] The pairs of members 601 and 602, and 602 and 603 each comprise a
pair of
members within the meaning the claims below.
[0061] Figure 7 shows a coupling arrangement comprising two couplings E2 of
the kind
shown in Figure 6 (without the flange 44) connected together by a connecting
structure
66. The structure rigidly connects the two couplings. In Figure 7 it connects
the
outermost members 603 of the couplings. In the example of Figure 7 the
connecting
structure is a tube coupling the outer members. In another example, instead of
the tube,
the outermost member of one coupling is connected to the inner member of the
other.
One illustrative use of the coupling of Figure 7 is as an approximation to a
double
Cardin shaft arrangement, if the projection or projections of one of the
couplings are
non-orthogonal to those of the other. One of the couplings E2 may be free to
move
axially in the tube 66.
[0062] The projections Ml, M11, M2, and M21 of one coupling may be
orthogonal to those
of the other or preferably parallel to those of the other in further examples
depending
on the application.
[0063] In Figures 8A to 8E the coupling comprises an inner, annular member
801 centred on
the central point C on the first axis Al, first, second and third intermediate
annular
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members 802, 803, and 804, and outer annular member 805. The members 801 and
802 and their spherical bearing surfaces are concentric about central point C.
The
members 804 and 805 and their spherical bearing surfaces are concentric about
a
central point C2 offset along axis Alas described in the reference frame of
figure 1
The second intermediate member 803 has its inner spherical surface centred on
C and
its outer spherical surface centred on C2.
[0064] The inner annular member 801 has an outer peripheral surface S1
which is convexly
spherical centred on the central point C on the first axis Al. The inner
annular member
801 has a central aperture which has splines for engaging a correspondingly
splined
shaft.
[0065] A first intermediate member 802 has an inner peripheral surface S21
which is
concavely spherical complementary to the outer surface S1 of the first annular
member
801. In this example the inner spherical surface S21 of the annular member 802
and the
outer spherical surface S1 of the first annular member 801 are contiguous
plain bearing
surfaces.
[0066] Diametrically opposed elongate projections M1 and Mll extend
radially of, and
parallel to, the first axis Al from the convex spherical surface S1 of the
inner ring 801.
The radially outer surface of the projections Ml and Mll also extends parallel
to the
spherical surface Sl. The projections extend into complementary first slots K1
and
K1 1 in the inner concave surface S21 of the first intermediate annular member
802.
The first projections and first slots constrain the pair of members comprising
the inner
member 801 and first intermediate annular member 802 to be rotatable one
relative to
the other about second axis A2 perpendicular to the first axis Al.
[0067] The first intermediate annular member 802 has an outer periphery S22
which is
convexly spherical. A second intermediate annular member 803 has an inner
peripheral
surface S31 which is concavely spherical complementary to the outer surface
S22 of
the first intermediate annular member 802. In this example the inner spherical
surface
S31 of the second intermediate member 803 and the outer spherical surface S22
of the
first intermediate annular member 802 are contiguous, plain, bearing surfaces.
[0068] Second elongate projections M2 and M21 extends radially of, and
parallel to, the first
axis Al from the convex spherical surface S22 of the first intermediate member
802.
The radially outer surface of the second projections M2 and M21 also extend
parallel
to the spherical surface S22. The projections extends into a complementary,
second,
slots K2 and K21 in the inner concave surface S31 of the second intermediate
member
803. The second projections M2 and M21 and second slots K2 and K21 are per-
pendicular to the first projections Ml, Mll and first slots K1 and K11. They
constrain
the pair of members comprising the first intermediate annular member 802 and
the
second intermediate annular member 803 to be rotatable one relative to the
other about
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third axis A3 through the central point C, and perpendicular to the first and
axes Al
and A2.
[0069] The second intermediate annular member 803 has an outer periphery
S32 which is
convexly spherical. A third intermediate annular member 804 has an inner
peripheral
surface S41 which is concavely spherical complementary to the outer surface
S32 of
the second intermediate annular member 803. In this example the inner
spherical
surface S41 of the third intermediate annular member 804 and the outer
spherical
surface S32 of the second intermediate annular member 803 are contiguous,
plain,
bearing surfaces.
[0070] Third elongate projections M3 and M31 extends radially of, and
parallel to, the first
axis Al from the convex spherical surface S32 of the second intermediate
annular
member 803. The radially outer surface of the projections M3 and M31 also
extends
parallel to the spherical surface S32. The projections M3 and M31 extends into
a com-
plementary, third, slots K3 and K31 in the inner concave surface of the third
in-
termediate annular member 804. The third projections M3 and M31 and third
slots K3
are K31 are in the same plane as projections M2 and M21, and slots K2 and K21
of and
thus constrain the pair of members comprising the second intermediate member
803
and third intermediate member 804 o be rotatable one relative to the other
about axis
A31parallel to axis A3 . The it will be seen that the second intermediate
annular
member 803 differs from the other annular members in that its internal slots
K2 and
K21co-operating with projections M2 and M21 of the first intermediate annular
member 802 is in the same plane as its projections M3 and M31.
[0071] The third intermediate annular member 804 has an outer periphery S42
which is
convexly spherical. A concavely spherical complementary to the outer surface
S42 of
the third annular member 804. In this example the inner spherical surface S51
of an
outermost annular member 805 and the outer spherical surface S42 of the third
in-
termediate annular 804 are contiguous, plain, bearing surfaces. Fourth
elongate pro-
jections M4 and M41 extend radially of, and parallel to, the first axis Al
from the
convex spherical surface S42 of the third annular member 804.
[0072] The radially outer surface of the fourth projections M4 and M41 also
extend parallel
to the spherical surface. The projections extends into a complementary,
fourth, slots
K4 and K41 in the inner concave surface S51 of the outermost member 805. The
fourth
projections M4 and M41 and fourth slots K4 and K41 are perpendicular to the
third
projections M3, M31, and third slots K3, K31. They constrain the pair of
members
comprising the third intermediate annular member 804 and the outermost member
805
to be rotatable one relative to the other about axis A21 parallel to axis A2
as shown in
Figure 8D. The further axis A21 is through and perpendicular to the first axis
because
the fourth projection M4, M4land fourth slots K4, K41 are parallel to the
first pro-
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jections Ml, Mll and first slots K1 and K11.
[0073] The members are assembled and retained in the coupling in the same
way as
described with reference to Figure 3.
[0074] As in previous examples projections M11, M21, M31 and M41 and
corresponding
slots K11, K21. K31 and K41 could be omitted but with less security in the
event of
failure.
[0075] In the examples of figure 8, it has been found that the third
intermediate member and
outermost members should be offset relative to the first and second members
along the
axis Al. This may be achieved by offsetting the outer spherical surface S32 of
the
second intermediate member 803 axially of the inner spherical surface S31 of
the
second intermediate member 803 as shown in Figure 8D.
[0076] One illustrative use of the coupling of Figure 8 is as an
approximation to a constant
velocity joint or double Cardan joint. In one double Cardan design the inner
annular
member 801 would be configured to move in the horizontal plane, the first in-
termediate annular member 802 would be configured to move in the vertical
plane, the
second intermediate annular member 803 would be configured to move in the
vertical
plane (but has the offset) and the third intermediate 804 would be configured
to move
in the horizontal plane. In another design, the inner annular member 801 is
configured
to move in a vertical plane, the first intermediate member 802 in a horizontal
plane and
so-on.
[0077] The projections may be in outer annular members projecting into
slots in inner
annular members in the examples of Figure 8.
[0078] The pairs of members 801 and 802, 802 and 803, 803 and 804, and 804
and 805 each
comprise a pair of members within the meaning of the claims below.
[0079] Members 801 and 802 comprise spherical segments about the centre C.
Members
803, 804 and 805 comprise spherical segments about the centre C2. However, the
central aperture of second intermediate member 803 is a spherical segment
centred on
centre C.
[0080] In the examples of Figures 2 to 8, the spherical surfaces are all
contiguous, plain,
bearing surfaces. Ball barrel roller or other rotational bearings may be
provided
between the adjacent spherical surfaces of a pair of annular members.
[0081] Rolling element bearings may be provided on the projections.
[0082] Referring to Figures 9A, B and C rolling element bearings in the
form of ball
bearings 90 held in two cages 91 are provided between the inner member 901 of
the
pair of members 901 and 902. As an alternative or in addition roller bearings
92, held
in cages G, are provided in recesses L2 in the sides of the projections M1 and
M2.
[0083] Turning to figure 10, as discussed the spherical surfaces of pairs
of adjacent members
co-operate to bear radial and axial loads. To ensure that the coupling can
bear a desired
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axial and radial load the spherical surfaces need to overlap sufficiently.
Thus means
may be provided to limit the relative rotation of pairs of adjacent members.
Such
limiting means also assists the retention of each inner annular member in its
associated
outer annular member. In Figure 10 the limiting means may comprise a fixed pin
N
projecting from an outer member 1002 of a pair of members, 1001 and 1002 into
a
groove L in an adjacent member, in this example in a projection M1 of the
inner
annular member 1 of the pair of members. Other examples of such limiting means
include a stop within the coupling and a support structure which limits
movement.
[0084] Figure 11 shows the forms of projections, Ml, M2... etc. A
projection M projects
into a slot K. As shown schematically in Figure 11, preferably the radially
outer
surface of the projection is spaced from the radial outer end of the slot to
avoid or at
least reduce radial loading on the projection.
[0085] The projections and slots of any of the examples of the invention
may have an
involute or pseudo-involute shape. The radially outer end of the projection M
may be
spaced from the radially outer face of the slot K to reduce radial loading on
the
projection and slot.
[0086] The purpose of the involute shape is to improve/reduce bearing
pressure distribution
on and stress distribution in the projection, as with involute splines.
[0087] In figure 11, the ends of the outer ends of the projections Ml, M2
... etc are shown
as being of a part cylindrical profile in cross section, they can have a flat
profile in
cross section. Normally, lengthways, they are contoured to be concentric with
the
annular member with which they are associated. However, if the projections and
as-
sociated slots are sufficiently deep and sufficient clearance allowed between
the outer
ends of the projections and the bases of the slots, the surfaces can be
spherical,
cylindrical or flat (straight through).
[0088] As shown in Figure 12, to increase the operational range of relative
rotation, the
outer one 2, or 3 of two adjacent pairs of members 1 and 2 or 2 and 3 may be
larger in
the axial direction Al than the inner one 1 or 2. Figure 12 shows three
annular
members 1, 2 and 3. The principle of Figure 12 may be applied to any of the
pairs of
annular members of the examples of the invention. In other words the angle
subtended
at the centre by the inner spherical concave periphery of the outer member 2
or 3 is
greater than the angle subtended at the centre by the outer spherical convex
periphery
of the inner member 1 or 2 as appropriate.
[0089] In all of the examples described above with reference to Figures 1
to 12, each
projection M and associated slot K defines a radial plane P2 and or P3
coincident with
the first axis Al in which the adjacent members coupled thereby are
constrained to
rotate one relative to the other about an axis A2, A3,A21, or A31. It will be
noted that
in the examples described above the projections and slots all project radially
of the
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central point C or C2 on the axis Al.
[0090] As shown in Figure 13, each single projection and associated slot in
adjacent pairs of
members (shown in figure 13 as 1 and 2) of the examples described above may be
replaced by two (or more) parallel, spaced apart, projections and slots. In
the example
shown in Figure 13 each single projection and slot is replaced by two
projections M16,
M16' and slots K16, K16', one projection and slot being each side of, and
equidistant
from, the said radial plane P of relative rotation. In the example of Figure
13 the pro-
jections and slots are each side of and equidistant from the plane P2.
[0091] In other examples each radially extending single projection and
associated slot of the
examples describe above may be replaced by a single projection and slot in a
plane
offset from and parallel to radial plane through the radially extending
projection and
slot.
[0092] Figure 14 shows an important embodiment of the invention for use in
highly safety
critical applications, such as found in the aircraft industry. In figure 14
axles X are be
provided in addition to the projections M and slots K for coupling adjacent
members.
Figure 14 shows a modification of the coupling of Figure 6 in which axles X2,
X21,
and X 1, X11 are provided on the axes A2 and A3 respectively, defined by the
pro-
jections Ml, M11, M2, M21 and slots Kl, K11, K2, K21, of relative rotation of
the
adjacent pairs of members 601 and 602 and 602 and 603. The axles joining
adjacent
members may comprise two diametrically opposed shafts fixed at one end to the
outer
of the two members and projecting into a bore in the outer surface of the
inner one of
the two members. Each such shaft acts as a plain bearing in the inner one of
the two
members. A ball roller or other rotational bearing may be provided around the
shaft in
the inner one of a pair of members.
[0093] The axles X have clearance around their bores in the inner of the
pair of annular
members. For example in Figure 14B axles X2 and X21 have clearance within
their
bores in annular member 602, nor do their bases touch the projections M1 and
M11.
Similarly axles X1 and X11 have no contact with inner annular member 601 in
figure
14C.As a result, normally torsional loads are transmitted between the members
601,
602, 603 through the projections and slots Ml, M2. .etc. Kl, K2. .etc. If a
projection
say M1 fails, projection Mll provides sufficient redundancy to enable normal
operation. However if projection Mll also fails, then axles X1 and X11 can
replace
them in transmitting torsional loads. Even then there is further redundancy as
the
coupling can continue operation even if one of the axles X1 and X11 fails.
This re-
dundancy provides sufficient continuity of safe operation to enable the
failures to be
identified in normal maintenance, and the coupling replaced.
[0094] In the preceding paragraph, the coupling is designed so that
torsional loads will
normally be transmitted by the projections and slots. By designing narrow
projections
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(or wider slots), and reducing the clearance around the axles, the position
can be
reversed with the axles normally bearing the loads and the projections and
slots acting
as back ¨up in the event of failure.
[0095] Axles may be provided in addition to the projections and slots on
some but not all
pairs of members in examples where there are a plurality of pairs of members
as in
figures 6 and 8 For example, the axles may only be provided in addition to the
pro-
jections and slots on the inner most pair of members i.e. members 601 and 602
in
figures 6 and 801 and 802 in figures 8.
[0096] Figure 15 shows another modification of the coupling shown in Figure
6. In Figure
15, the inner member 601 has diametrically opposite radially projecting
projections M1
and M1 1 projecting from the outer spherical surface into complementary slots
K1 and
K1 1 in the inner spherical surface of the intermediate member 602. The
projections
constrain the first and second members to be relatively rotatable in the plane
of the
projections.
[0097] The intermediate member 602 has an outer spherical surface engaged
with an inner
concave surface of the outermost member 603. The second member and third
member
are coupled by axle shafts X23 and X23 coplanar (aligned with) with the
projections
Ml, Mll so that the pair of members 602 and 603 are relatively rotatable
orthogonally
to the relative rotation of the pair of members 601 and 602.
[0098] Such a coupling is useful because the torque between the
intermediate and outer
members 602 and 603 is relatively lower than the torque between the inner and
first in-
termediate members 601 and 602.
[0099] The projections M1 and Mll may be in intermediate member 602
projecting into
slots in the inner member 601 in the example of Figure 15.
[0100] Figure 16 shows a modification of the example of Figure 8 in which
the projections
between the pairs of members comprising the second and third intermediate
members
803 and 804 and the third intermediate member 804 and outmost member 805 are
replaced by axles X34, X341, X45 and X451. There may be one axle shaft or, as
shown, two diametrically opposite axle shafts coupling adjacent pairs of
members 803
and 804, and 804 and 805 The third member is thicker radially than the third
member
of Figure 8 because it must accommodate both slot(s) associated with
projection(s) of
the second member and axle shaft(s) connecting it to the fourth member. As
shown in
Figure 8 the second intermediate member 803 provides an axial offset between
the
inner group of the inner member 801, first intermediate member 802 and second
in-
termediate member 803 and the outer group of the second intermediate member
803,
third intermediate member 804, and outermost member 805.
[0101] Such a coupling is useful because the torque at the outer group is
relatively lower
than the torque applied to the inner group.)
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[0102] Referring to Figure 17, any of the examples of a coupling shown in
figures 2, 6, 8,
14, 15 and 16 may be fixed within a bearing 1701 which may be fixed by for
example
a flange 1702 to a fixed structure 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, 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.
[0103] Figure 17 shows one coupling within a bearing. In the examples of
figures 5 and 7
the two couplings joined in tandem by a tube 66, may be supported within a
bearing
around the tube 66.
[0104] In further arrangement a shaft is fixed to, or integral with the
innermost, member of a
coupling. In another arrangement, a shaft is fixed to, or integral with, the
outermost,
member of a coupling. Shafts may be fixed to, or integral with, both the
innermost and
outermost members of a coupling.
[0105] The examples described above may have splines in the inner member
and or on the
peripheral surface of the outermost member to connecting the coupling to
structural
elements to be coupled.
[0106] 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
central
aperture as shown in Figure 2, may have a screw thread or keys to couple to a
shaft
which is screw threaded or has keys slots. Especially for those examples
having two or
more projections on a member, the projections should share loads substantially
equally. For plain bearing surfaces, the surfaces of the projections and slots
should
match accurately. Also for plain bearing surfaces, the mating convex and
concave
spherical surfaces should match accurately. That requires appropriately
precise man-
ufacture of the couplings.
[0107] In one illustrative method of making the couplings a lining material
is injected
between the projections and slots to provide a precise fit. Likewise a lining
material
may be injected between the spherical bearing surfaces. The convex spherical
surfaces
may be accurately machined. The convex spherical surfaces may be roughly
machined
to form a rough surface which is also a piece-wise linear approximation to a
curved
surface, 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.
[0108] Plastic could be injected to provide the bearing liner material; the
compositions of
some of the plastics used for a liner are not known as the suppliers are
commercially
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sensitive about their composition. However Dekin is one known product that
could
be used or PTFE based materials could be used.
[0109] Couplings as described above made be of any suitable material. The
examples having
plain bearing surfaces may be of metal, e.g. high performance steels, brass,
bronze,
aluminium, titanium etc. and machined to shape or of plastic, e.g. nylon,
glass filled
nylon, acetal, ABS, Dekin and moulded or machined to shape. In particular it
can be
seen that the use of loading slots as described with reference to figure 3
avoids the
need to manufacture the annular members in two halves and bolt, weld or swage
them
together, which will always be a source of weakness, particularly in safety
critical
situations. It should be noted that the coupling of Figure 6 may be configured
so that
the inner 601 and the outermost member 603 are connected to shafts or other
structural
elements with only the intermediate member 602 free to move relative to the
other two
members; this might lead a designer to select brass or bronze for the moving
in-
termediate member middle and steel for the inner member 601 and outermost
member
603. The same philosophy could be applied to the other couplings. The choice
of
material depends on the intended use of the coupling.
[0110] The above embodiments are illustrative examples of the invention.
Further em-
bodiments of the invention are envisaged. It is to be understood that any
feature
described in relation to any one embodiment may be used alone, or in
combination
with other features described, and may also be used in combination with one or
more
features of any other of the embodiments, or any combination of any other of
the em-
bodiments. Furthermore, equivalents and modifications not described above may
also
be employed without departing from the scope of the invention, which is
defined in the
accompanying claims.
[0111] In the specific examples in figures 2 to 17, the inner member is an
annular member
with a central aperture to fit on a shaft. In some applications the inner
member may
have no central aperture, and can be bolted to a shaft or flange on the end of
a shaft for
example. Members other than the inner member have central apertures to allow a
member within that member to nest.
[0112] In all the illustrated, the examples the members comprise spherical
segments having
parallel sides. It is feasible to construct couplings in which the sides are
not parallel,
however, in practice, such constructions are likely to be awkward to deploy.
[0113] 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.
[0114] 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:
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= 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 6 each member comprises spherical segments
having parallel sides in common planes when aligned;
= in the arrangement of figure 8 the first pair of members (801, 802) each
comprise spherical segments having parallel sides in common planes when
aligned and the third pair of members (803, 804) and fourth pair of members
(804, 805) each comprise spherical segments having parallel sides in common
planes when aligned. This does not apply to the second pair of members (802,
803).
[0115] The discussion in the preceding paragraph, obviously, does not
apply to a pairs of
members in a coupling where the outer member of the pair has an enhanced
operating
range as shown in figure 12.
