GB2521208A

GB2521208A - Coupling

Info

Publication number: GB2521208A
Application number: GB1322096.7A
Authority: GB
Inventors: Simon Parker
Original assignee: Punk Couplings Ltd
Current assignee: Punk Couplings Ltd
Priority date: 2013-12-13
Filing date: 2013-12-13
Publication date: 2015-06-17
Also published as: MX2016007693A; JP2016540176A; WO2015087080A3; CA2932037A1; CN106104037A; KR20160097236A; GB2522767A; GB2522767B; EP3080469A2; GB201322096D0; WO2015087080A2

Abstract

A coupling comprises an inner member 1 having an outer convex spherical periphery S1 centred about a central point C. The inner member has a torsional axis A1 extending through the central point. An outer ring 2 has an inner concave spherical periphery complementary to the outer periphery of the inner member. One of the inner member 1 and outer ring 2 has an elongate projection M1 projecting parallel to a line extending radially of the central point into a corresponding elongate slot K1 in the other. The slot and projection are elongate in a plane parallel the torsional axis A1. The projection and slot act to transmit torque about the torsional axis A1 from one to the other. The inner member and outer ring are rotatable one relative to the other about the said central point in a direction constrained by the projection and slot. The coupling may have additional members (3, 4 & 5, fig 9) and a coupling arrangement (66, 68, figs 6 & 8) may connect two couplings.

Description

Coupling

Technical Field

The present invention relates to a coupling.

Background

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

According to one aspect of the present invention, there is provided a coupling comprising a first, inner, member having an outer convex spherical periphery centred about a central point, a torsional axis extending through the central point, and a second, outer, member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the inner member and aranged to co-act vith the inner member to transmit load therebetween, one of the inner member and outer ring having a first elongate projection projecting into a corresponding first elongate slot in the other, the slot and projection being elongate in a first plane parallel to the said torsional axis, the projection and slot projecting in the direction of the said first plane, the projection and slot acting to transmit torque about the said torsional axis from one of the outer ring and inner member to the other, the inner member and outer ring being constrained by the projection and slot to be rotatable one relative to the other about an axis through the central point and perpendicular to the said first plane.

The projections and slots carry torque and the spherical surfaces of the first and second members carry axial and radial loads, Thus axial loads are separated from torsional loads. In an example there is a clearance between the facing radial faces of the projections and slots, so that radial loads are not carried by the projections and slots.

Thus radial loads are carried mostly or wholly by the spherical surfaces.

An example further incorporates an axle coupling the members, the axle being on the axis of rotation of one member relative to the other about the said central point in a direction constrained by the projection and slot. The axle is additional to the projection and slot. In one example of such a coupling the axle provides a fail-safe mechanism in the event a projection fails or vice versa.

Some embodiments of the invention combine one or more such couplings.

In an example of the coupling the second member has an outer periphery which is convexly spherical and further comprises a third member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the second member and arranged to co-act with the second member to transmit load therebetween, one of the second member and to third member having a second elongate projection projecting in a second plane parallel to the said torsional axis into a corresponding second elongate slot in the other, the second slot and second projection being elongate in the said second plane, the second projection and second slot acting to transmit torque about the said torsional axis from one of the second and third members to the other, the second member and third member being further rotatable one relative to the other about the said central point in a direction constrained by the projection and slot.

Yet another example further comprises a third member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the second member and arranged to co-act with the second member to transmit load therebetween, the second arid third members being coupled by an axle on an axis of rotation of one of the second and third members relative to the other which is perpendicular to the axis of relative rotation of the first and second members.

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings, in which:

Brief Description of the Drawings

Figure 1 illustrates a reference frame of operation of couplings according to embodiments of the invention; Figures 2Ato 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, Figure 2B 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; Figures 3Ato 3F are loading diagrams; Figures 4Ato 4E illustrate a method of assembling the coupling of Figure 2; Figures SA and SB show ahub centre steering mechanism including an example of a coupling in accordance with the invention; Figures 6A and 6B are cross-sectional views of pairs of couplings connected together; to Figures 7A to 7C show another example of a coupling according to the invention, of which Figure 7A is a cross-sectional view along Line A-A of figure 7B, Figure 7B is an axial view along axis Al of Figure 1, and Figure 7C is a perspective view in which the elements of the coupling a misaligned; Figures SA to C show a pair of the couplings connected together, in which Figure 8A is a cross-sectional view with the elements of the couplings aligned, Figure 8B shows the elements un-aligned, and Figure 8C is an isometric view in which the elements are unaligned; Figure 9A to 9E show a further example of a coupling according to the invention, of which Figure 9Ais an axial view along axis Al of Figure 1, Figure 9B is an isometric axial view showing the elements of the coupling un-aligned, Figure 9C is a cross-sectional view along plane C-C in Figure 9B, Figure 9D is a cross-sectional view along line D-D of Figure 9A and Figure 9E is a side view ofthe coupling as shown in Figure 9A; Figures IDA to E show bearings in examples of couplings according to the invention, in which Figure 1 OA is an axial view of an element of a coupling, Figure 1DB is a side view of the element of Figure bA, Figure 10 C is a top view of the element of Figure IDA, Figure IOD is a cross sectional view of a coupling and Figure IDE is an isometric view of a coupling; Figure ii shows means for limiting relative rotation of elements of a coupling according to the invention; Figure 12 is a schematic diagram of a projection and slot useful in examples of couplings according to the invention; Figure 13 is a schematic diagram of an involute projection useful in examples of couplings according to the invention; Figure 14A is a cross-sectional view of a modification of the couplings of the preceding drawings showing the elements un-aligned and Figure 14B is an isometric view of the coupling of Figure 14A; Figures ISA to NC show a yet further example coupling according to the invention, of which, Figure lSAis an axial view along axis Al of Figure 1, Figure 1SB is a perspective view showing elements of the coupling un-aligned, and Figure ISC is another isometric view showing elements of the coupling un-aligned; to Figures 16A to I6E show yet another example of a coupling according to the invention, of which Figure l6Ais a axial view along axis Al of Figure 1 with elements of the coupling un-aligned, Figure t6B is an axial cross-sectional view along plane C-C of Figure 1 6D, Figure 1 ÔC is a cross-sectional view along plane A-A in Figure 1 oA, Figure 16D is a side view of the coupling of Figure 16A, and Figure loHs an isometric view of the coupling; Figure 17 shows yet another example of a coupling according to the invention; Figures ISA to I SD shows another example of a coupling according to the invention, in which Figure ISA is an isometric view showing the elements un-aligned, Figure 1 SB is an axial view, Figure 1SC is a cross-sectional view and Figure 18D is a side view; and Figure 19 shows an example of a coupling combining the use of projections and slots in part of the coupling and axles in another part, wherein Figure 19 A is an axial view, Figure t9 B is a cross sectional view on plane B-B in Figure i9A, Figure i9C is a cross sectional view on plane C-C in Figure 19A, and Figure l9D is an isometric view of the coupling.

Detailed Description

Uses of the Couplimzs Couplings according to various embodiments the present invention described herein after may be used for coupling any two structural elements that must be coupled with at least two rotational degrees 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. By way of example, various couplings according to the invention may be used to couple angularly misaligned shafts, 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.

Examples of couplings will now be described. Each of these examples is designed to couple one shaft, for example a drive shaft to another shaft, for example a driven shat, the shafts being removably connected to the coupling. Other examples to having one or both shafts fixed to the coupling will be described hereinbelow. Other examples which connect to a static shaft will be described hereinbelow.

Reference Frame-Figure 1 Examples of the invention will be described in relation to a reference frame as showninFigurel.

The reference frame has a first axis Al defining an axial direction. A second axis A2 defining an axis of rotation 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 Pt 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 defining an axis of rotation lies in the third plane and passes through the central point C. In examples of couplings described hereinbelow, the first axis Al is a torsional axis on which, amongst other examples, 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.

First example of a coupling-Figures 2Ato 2D Referring to Figure 2, a coupling according to a first example El of the invention comprises a first, inner, member 1 in the form of a ring centred on the central point C on the first axis, The inner ring has an outer peripheral surface SI which is convexly spherical centred on the central point C on the first axis. The inner ring I has a central aperture 40 which in this example has splines 42 for engaging a correspondingly splined shaft.

A second, outer, member 2 in the form of a ring has an inner peripheral surface S 521 which is convexly spherical complementary to the outer surface Si of the inner ring 1. 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 521 of the outer ring and the outer spherical surface St of the inner ring 1 are contiguous plain bearing surfaces.

to An elongate projection Ml extends radially of the central point C, and parallel to the first axis Al, from the convex spherical surface SI of the inner ring 1. The radially outer surface of the projection also extends parallel to the spherical surface St. The projection extends into a complementary slot K] in the inner concave surface S21 of the outer ring 2. The projection and slot constrain the inner and outer rings to be rotatable, one relative to the other, about the second axis A2 of rotation through the central point and perpendicular to the first axis.

"Self Retaining" arrangement The central point C of the adjacent convex and concave spherical surfaces lies between the axial facing faces Fl and F3 of the inner member 1 and between the outer faces P2 and P4 of the outer member 2. As a result of that, the periphery of the inner convex spherical surface mid-way between the axially facing faces F] and P3 is at a greater radius than the periphery of the concave surface of the outer member 2 at the axially facing faces thereof F2 and F4. Thus the inner ring is retained axially in the outer ring over an operational range of rotation of the inner ring about the second axis and/or about the first axis.

Second Example of a Coupling Referring to Figure 2, the first example Et as described above has only one projection Ml and one associated slot Ki. Such a coupling is operable. in this second example, as shown in Figure 2 as El, the inner member t has a further projection Mit, identical to, and diametrically opposite, the first projection Nil and the outer member 2 has a complementary further slot KI identical to and diametrically opposite to the first slot KI, The first and second examples El shown in Figure 2 have splines 42 in the central bore of inner member 1 for engaging a shaft. Splines (not shown) may additionally or alternatively be provided on the outer periphery of the outer member 2 for engaging another shaft. The coupling may be allowed to slide relative to the shaft(s) providing an axial degree of freedom.

The second example has two projections MI, Ivili which fit into associated slots K], KI I with minimal clearance between the sides of the projections and the sides of to the slots. However in another example one ofthe 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 associated slot with minimal clearance, fails.

Form of inner and outer members The inner and outer members are both rings in the examples of 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.

In the examples of Figure 2, the projection(s) project(s) from the inner ring into slot(s) in the outer ring. However the projection(s) may project from the outer ring into slot(s) in the inner ring.

Loading, Figure 3 In the first and second examples, 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.

In figures 3A to 3F, load bearing paths or surfaces are shown shaded.

As shown in Figure 3 the bearing surfaces SI, S21 allow large forces to be carried. Because the contact surfaces SI, S21 are tangential to the torque axis Al, radial burst forces are avoided. The coupling efficiently separates the translational (axial and radial) and torsional T load paths. Radial forces RI, R2 (Figures 3B1 and 3B2, and Figures 3d and 3C2) and axial forces Ax (Figures 3D1 and 3D2) are carried by the spherical surfaces S and 52] as shown by the shading in those Figures. Torsional forces Ts (Figures 3A and 3El and 3E2) are carried by the projection Ml and slot Kl or by the projections Mi, Mu and slots Ki, Ku. Preferably as shown in Figure 13 or 14 there is a clearance between the radially outer surface of a projection arid the facing surface (bottom) of its associated slot.

As shown in Figure 3F2 a single projection is able to carry the torsional load in combination with the spherical bearing surfaces Si and S21. This provides redundancy in case one of two projections fails; compare Figure 3F2 having one operative projection with Figure 3F] having two operative projections.

Uses of Coupling The first and second examples have static applications such as Hub Centre Steering as will be described with reference to Figure 5.

In one use ofthe coupling, rotation of the shaft aboutthe first axis is transmitted from the inner member by the projection M and slot K to the outer member 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.

Assembling a Coupling Referring to Figure 4, the outer member 2 has two, diametrically opposite loading slots LI and L2. As shown in Figure 4E, the slots extend halfway across the width of the outer member. The slots are dimensioned so that the diametrically opposite floors of the slots are spaced by the diameter of the outer surface Sthf the inner member i. The width of each slot is equal to or slightly greater than the width of the inner member, The inner member I is introduced sideways into the slots as shown in Figures 4A, 4B and 4C with its proj ection(s) Ml, M II aligned with the slot(s) K I, K] I and then rotated so the projection(s) enter(s) the slot(s).

Figure 4 shows one option for assembling a coupling. In another option the outer member 2 is formed of two halves (or three or more sections) which are assembled around the inner member 1 and then fixed together. The two halves may be fixed by bolts, welding, fusing, swaging or in any other suitable way Other couplings described hereinafter have three or more concentric rings. Each pair of outer and inner rings may be assembled as described here. It will be noted that Figures 4Dand 4E show a ring 2' of for example the embodiment of Figure 7 which has three rings, ring 2' fitting within a third ring 3.

Steering Mechanism-Figure 5 One illustrative use of the first or second example of the coupling of Figure 2 is in a steering mechanism of a vehicle. In the example of FigureS a steered hub 62 of a wheel is supported by a support member 64 which in this example is a suspension arm.

to The coupling P1 couples the suspension ann 64 to the steered hub 62.

The arm 64 is engaged, for example by splines, in the central aperture 40 of the inner ring I of the coupling. The projection(s) Mi, Mt 1 and slot(s) 1(1, 1(1 t allow the outer ring 2 to rotate about one axis (the steering axis) relative to the inner ring I and arm 64. The outer ring 2 supports the wheel 62 which is free to rotate on bearings 63.

A steering arm 60 is fixed to the outer ring 2 to rotate it relative to the inner ring and shaft 64.

In this example the projection(s)Ml, Ml] and slot(s) K], K]] provide support to allow relative rotation but do not drive the wheel 62.

Third Example of a Coupling -Figure 6, Figure 6A shows a coupling arrangement comprising two couplings El of Figure 2 connected together by a connecting structure 66. The structure 66 rigidly connects the two couplings. In Figure 6A it connects the outer members 2 of the couplings. The projections of the two couplings are orthogonal relative to each other, but could be non-orthogonal. In the example of Figure 6A 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.

In another example, shown in Figure 6B, the outer member 2 of one coupling is connected to the inner member 1 of the other by a connecting structure shown schematically at 68.

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.

Fourth Example of a Coupling -Figure 7, The coupling of Figure 7 comprises a first, inner member 1 in the form of a ring and a second member 2 similar to the members I and 2 described with reference to Figure 2. The inner member is centred on a first axis Al, the inner ring I having an outer peripheral surface S which is convexly spherical centred on the point C on the to axis Al The inner ring has a central bore 40 which in this example has splines 42 for engaging a correspondingly splined shaft.

A second, intermediate, member 2 in the form of a ring has an inner peripheral surface S2 I which is concavely spherical complementary to the outer surface SI of the inner member 1, In this example the inner spherical surface S21 of the intermediate member and the outer spherical surface Si of the inner member i are contiguous plain bearing surfaces.

A first elongate projection Ml extends radially of, and parallel to, the first axis Al from the convex spherical surface SI of the inner member 1, The radially outer surface of the proj ection also extends parallel to the spherical surface Si. The projection extends into a complementary, first, slot Ki in the inner concave surface S21 of the intermediate member 2. The first projection MI and first slot K] constrain the inner I and intermediate 2 members to be rotatable one relative to the other about the second axis A2 of rotation through and perpendicular to the first axis Al.

The intermediate member 2 has an outer periphery S22 which is convexly spherical. A third member 3 in the form of a ring has an inner peripheral surface S3 i which is concavely spherical complementary to the outer surface S22 of the intermediate member 2, In this example the inner spherical surface S31 of the third member and the outer spherical surface S22 of the intermediate member 2 are contiguous plain bearing surfaces.

A second elongate projection M2 extends radially of, and parallel to, the first axis from the convex spherical surface S22 of the intermediate member 2. The radially outer surface of the second projection M2 also extends parallel to the spherical surface.

The projection M2 extends into a complementary, second, slot K2 in the inner concave surface of the outer member 3, The second projection M2 and second slot K2 are perpendicular to the first projection Ml and first slot Kl. They constrain the intermediate 2 and outer 3 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 the first axis A land perpendicular to the second axisA2, In similar manner as described with reference to figure 3, 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 projections Ml and M2 and slots K], K2 transmit torque between the to first (inner) I, second (intermediate) 2, and third (outer) 3, members.

The inner member 1 is retained in the intermediate member 2, and the intermediate member 2 is retained in the outer member 3 in the same way that the inner member I of the first or second example is retained in the outer member 2.

Fifth Example of a CouplinQ -Figure 7 Referring to Figure 7, the inner member I may have a further projection MIt, identical to, and diameffically opposite, the first projection M] and the intermediate member may have a complementary ftirther slot KI] identical to and diametrically opposite to the first slot 1(1. Likewise the intermediate member 2 may have a yet further projection 1v12 t, identical to, and diametrically opposite, the second projection M2 and the outer member 3 may have a complementary yet further slot K21 identical to and diametrically opposite to the second slot K2.

One illustrative use of the fourth and fifth examples of the couplings of Figure 7 is as a universal joint.

The coupling of Figure 7 allows angular misalignment of the shafts by virtue of the relative rotation of the inner and outer members about the second axis.

The coupling of Figure 7 has a flange, fixed to or integral with the third ring for connecting the third ring to a structural element, for example a shaft. The flange 422 may be replaced by splines or some other connecting means.

The projections may be in outer rings projecting into slots in inner rings in the examples of Figure 7.

Sixth Example of a Coupling -FigureS Figure 8 shows a coupling arrangement comprising two couplings of Figure 7 (without the flange 422) connected together by a connecting structure 66. The structure rigidly connects the two couplings. In Figure 8 it connects the third, outer, members 3 of the couplings. in the example of Figure 8 the connecting structure is a tube coupling the outer members. Tn another example, instead of the tube, the outer member 3 of one coupling is connected to the inner member 1 of the other as shown for example in Figure 6.

One illustrative use of the coupling of Figure 8 is as an approximation to a to double Cardan joint 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 inthetube 66.

The projections of one coupling may be orthogonal to those of the other or parallel to those of the other in further examples.

Seventh Example of a Coupling-Figure 9 The coupling of Figure 9 comprises a first, inner, member I in the fomi of a ring centred on the central; point C on the first axis Al, the inner ring I having an outer peripheral surface Si which is convexly spherical centred on the central point C on the first axis. The inner ring I has a central aperture 40 which in this example has splines for engaging a correspondingly splined shaft.

A second member 2 in the form of a ring has an inner peripheral surface S21 which is concavely spherical complementary to the outer surface SI of the first ring I. In this example the inner spherical surface S21 of the second ring I and the outer spherical surface Si of the first ring I are contiguous plain bearing surfaces.

A first elongate projection Mi extends radially of and parallel to, the first axis Al from the convex spherical surface S of the inner ring 1. The radially outer surface of the projection Ml also extends parallel to the spherical surface SI. The projection extends into a complementary, first, slot Ki in the inner concave surface 521 of the second ring 2. The first projection and first slot constrain the first and second rings to be rotatable one relative to the other about the second axis A2 of rotation through and perpendicular to the first axis A], The second ring 2 has an outer periphery S22 which is convexly spherical. A third member 3 in the form of a ring has an inner peripheral surface S31 which is concavely spherical complementary to the outer surface S22 of the second member 2.

In this example the inner spherical surface S3 1 of the third member 3 and the outer spherical surface S22 of the second member 2 are contiguous, plain, bearing surfaces.

A second elongate projection M2 extends radially ot and parallel to, the first axis Al from the convex spherical surface S22 of the second member 2. The radially outer surface of the second projection J\{2 also extends parallel to the spherical surface S22. The projection extends into a complementary, second, slot K2 in the inner concave to surface S3 I of the third member 3. The second projection M2 and second slot K2 are perpendicular to the first projection Ml and first slot KI. They constrain the second 2 and third 3 members to be rotatable one relative to the other about the third axis A3 of rotation through the central point C, and perpendicular to the first axis A] and perpendicular to the second axis A2.

The third member 3 is a ring which has an outer periphery S32 which is convexly spherical. A fourth member 4 in the form of a ring has an inner peripheral surface S4] which is concavely spherical complementary to the outer surface S32 of the third member 3, In this example the inner spherical surface S41 of the fourth member 4 and the outer spherical surface S32 of the third member 3 are contiguous, plain, bearing surfaces.

A third elongate projection M3 extends radially of, and parallel to, the first axis Al from the convex spherical surface S32 of the third member 3. The radially outer surface of the projection M3 also extends parallel to the spherical surface S32. The projection M3 extends into a complementary, third, slot K3 in the inner concave surface of the fourth member. The third projection M3 and third slot K3 are parallel to the projection M2, and slot 1(2 of the second member 2, and thus constrain the third and fourth members to be rotatable one relative to the other about the third axis A3 of rotation. The third ring 3 differs from the other rings in that its internal slot K2 co-operating with projection vU of the second ring 2 is in the same plane as its projection M3.

The fourth member has an outer periphery S42 which is convexly spherical. A fifth member 5 in the form of a ring has an inner peripheral surface S5l which is concavely spherical complementary to the outer surface S42 of the fourth member 4, In this example the inner spherical surface S5l of the fifth member 5 and the outer spherical surface S42 of the fourth member 4 are contiguous, plain, bearing surfaces.

A fourth elongate projection M4 extends radially of; and parallel to, the first axis Al from the convex spherical surface S42 of the fourth member 4. The radially outer surface of the fourth projection also extends parallel to the spherical surface. The projection extends into a complementary, fourth, slot K4 in the inner concave surface S5 1 of the fifth member 5. The fourth projection M4 and fourth slot K4 are perpendicular to the third projection M3 and third slot K3. They constrain the fourth to and fifth members to be rotatable one relative to the other about a further axis A2] axis parallel to, but offset along the axis Al from, the second axis A2 of rotation as shown in Figure 1 and as shown in Figure 9D. The further axis A21 is through, and perpendicular to the first axis because the fourth projection and fourth slot are parallel to the first projection Ml and first slot ICL The members are retained in the coupling in the same way as described hereinabove with reference to Figure 2.

The members I and 2 and their spherical bearing surfaces are concentric about central point C (Cl in Figure 9D) as described with reference to Figure 2. The members 4 and 5 and their spherical bearing surfaces are concentric about a central point C2 offset from C. The third member has an inner spherical surface centred on Cl and an outer spherical surface centred on C2.

Eighth Example of a Coupling -Figure 9 Referring to Figure 9, the first member I may have a further projection Ml, identical to, and diametrically opposite, the first projection Ml and the second member may have a complementary further slot 1(1 1 identical to and diametrically opposite to the first slot K I. Likewise the second member 2 may have a yet further projection M21, identical to, and diametrically opposite, the second projection and the third member may have a complementary yet further slot 1(21 identical to and diametrically opposite to the second slot. Likewise the third and fourth rings may be coupled by two diametrically opposite projections M3, M3 I and slots K3, K3 1 and the fourth and fifth rings may be coupled by two diametrically opposite projections M4, M4l and slots K4 and K41, The third ring 3 is differs from the other rings in that its internal slots K2 and K21 co-operating with projections M2 and M2iof the second ring 2 are in the same plane as its projections M3 and M3 I Offset -Figure 9D It has been found that the fourth and fifth members should be offset relative to the first and second members along the axis Al This may be achieved by offsetting the to outer spherical surface S32 of the third member 3 axially of the inner spherical surface S31 of the third member 3 as schematically shown in Figure 9D.

One illustrative use of the coupling of Figure 9 is as an approximation to a constant velocity joint or double Cardan joint. To define the double Cardan operation, in one design the l inner ring I would be configured to move in the horizontal plane, the 2'" ring 2 would be configured to move in the vertical plane, the 3" ring 3 would be configured to move in the vertical plane (but has the offset) and the 4111 ring 4 would be configured to move in the horizontal plane. In another design, the string I is configured to move in a vertical plane, the 2' ring in a horizontal plane and so-on.

The projections may be in outer rings projecting into slots in inner rings in the examples of Figure 9, Bearings-Figure 10 In the examples of Figures 2 to 2, the spherical surfaces are all contiguous, plain, bearing surfaces. , Ball, barrel, roller or other rotational bearings may be provided between the adjacent spherical surfaces.

Rolling element bearings may be provided on the projections.

Referring to Figures 0A, B and C, ball bearings 100 held in two cages 101 are provided between the projections Ml and Ml I of the inner member I. Roller bearings 102, held in cages G, are provided in recesses L2 in the sides of the projections Mi and M2.

Limit to relative rotation of adiacent members, Figure II The spherical surfaces of adjacent members 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, or a support structure which limits movement. Referring to Figure 11 the limiting means may comprise a fixed pin N projecting from an outer member 2 into a groove L in an adjacent member, in this example in a projections Ml ofan inner member 1.

Form of Projections, Figures 12 and 13 A projection M projects into a slot K. As shown schematically in Figure 12, 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.

Involute -Figure 13 The projections and slots of any of the examples of the invention may have an involute or pseudo-involute shape. The radially out end of the projection Ni may be spaced from the radially outer face of the slot K to reduce radial loading on the projection and slot.

The purpose of the involute shape is to improve/reduce bearing pressure distribution on, and stress distribution in, the projection, as with involute splines, Increase range of relative rotation-Figure 14 As shown in Figure 14, to increase the operational range of relative rotation, the outer one 2, or 3 of two adjacent members t and 2 or 2 and 3 may be larger in the axial direction Al than the inner one I or 2. Figure 14 shows three rings 1, 2 and 3, The principle of Figure 14 may be applied to any of the pairs of rings of the examples of the invention.

Ninth Example of a coupling -Figure 15 In all of the examples described above with reference to Figures 1 to 14, each single projection M and associated slot K defines a radial plane P. for example plane P2, 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 or A2 1. It will be S noted that in the examples described above the projections and slots all project radially of the central point C or C2 on the axis Al As shown in Figure 15, each single projection and associated slot of the examples described above may be replaced by two (or more) parallel, spaced apart, projections and slots. In the example shown in Figure 5 each single projection and slot to is replaced by two projections M6, 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 15 the proj ections and slots are each side of and equidistant from the plane P2.

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.

This may also be applied to the examples of Figures 16 to 19.

Tenth Example of a coupling -Figure 16 As shown by way of example in Figure 16, axles X may be provided in addition to the projections M and slots K for coupling adjacent members 1, 2, 3 etc.. Figure 16 shows a modification of the coupling of Figure 7 in which axles X are provided on the axes A2 and A3, defined by the projections Ml, Ml I, M2, M2 and slots K], K] , K2, K21, of relative rotation of the adjacent members 1 and 2 and 2 and 3. 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 the two members.

In Figure 16, as best shown in Figure l6C axles Xl and XII connect the inner member I to the intermediate ring 2, and as best shown in Figure l6B axles X2 and X21 connect the intermediate ring 2 to the outer ring 3.

The axles provide redundancy in the coupling and share torque transmission with the projections and slots and can take up torque if a projection fails.

Axles may be provided in addition to the projections and slots on some but not all pairs of members I and 2, 2 and 3, etc. in examples where there are a plurality of pairs of members 1, 2, 3, etc.. In one example, the axles are provide in addition to the projections and slots on the inner most pair of members I and 2 Eleventh Example of a coupling-Figure 17 Figure 17 shows a modification of the fifth example of a coupling as shown in Figure 7, In the modification of Figure 17, the first, inner, member I has diametrically opposite radially projecting projections MI and MI projecting from the outer spherical surface into complementary slots K1 and K1 1 in the inner spherical surface of the second, intermediate, member 2. The projections constrain the first and second members to be relatively rotatable in the plane of the projections.

The second member 2 has an outer spherical surface engaged with an inner concave surface of the third, outer, member 3. In the example of Figure 17, the second member and third member are coupled by axle shalis X23 and X23' coplanar (aligned with) with the projections Ml, MI] so that the second and third members are relatively rotatable orthogonally to the relative rotation of the first and second members.

Such a coupling is useful because the torque at the second and third members is relatively lower than the torque at the first and second members.

The projections may be in outer ring 2 projecting into slots in the inner ring 1 in the example of Figure 17.

Twelfth Example -Figure 18 Referring to Figure 1 8A, any of the first, second, fourth, fifth and seventh to eleventh examples E of the couplings may be fixed within a bearing 201 which may be fixed by for example a flange 202 to a fixed structure for example a bulkhead, floor or wall, That allows the coupling to couple to any two stmctural 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.

Figure 18 shows one coupling E within a bearing. However, the third and sixth examples, which comprise two couplings joined in tandem by a tube, may be supported within a bearing around the tube 66.

Other Variants The above embodiments are to be understood as illustrative examples of the to invention. Further embodiments of the invention are envisaged, for example:-Thirteenth Example of a coupling -Figure 19 Figure 19 shows a modification of the example of Figure 9 in which the projections between the third and fourth members 3 and 4 and between the fourth and fifth members, 4 and 5 are replaced by axles X34, X341, X45 and X451. There maybe one axle shaft or, as shown, two diametrically opposite axle shafts coupling adjacent members 3, 4 and 4, 5 The third member is thicker radially than the third member of Figure 9 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 10 the third member 3 provides an axial offset between the inner group of the first, second and third members and the outer group of the third, fourth and fifth members.

Such a coupling is useful because the torque at the outer group is relatively lower than the torque applied to the inner group.) Shaft(s') fixed to couplings In an alternative embodiment a shaft is fixed to, or integral with, the first, inneost, member of a coupling. In art alternative embodiment, 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.

Connecting a Coupling to a Structural Element 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.

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 first, inner most member 1 may have a central aperture as shown in Figure 2, which is screw threaded, The first member may be integral with a shaft which is screw threaded for connection to another structural element Making a coupling Especially for those examples having two or more projections on a ring, 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 manufacture of the couplings.

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.

Plastic could be injected to provide the bearing liner material; the composition of some of the plastics used for a liner are not known as the suppliers are commercially sensitive about their composition. However Delrin is one known product that could be used or PTFE based materials could be used.

Materials 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. or of plastic, e.g. nylon, glass filled nylon, acetal, ABS, delirium. It should be noted that the coupling of Figure 7 may be configured so that the inner member 1 and the outer member 3 are connected to shafts or other structural elements so only the middle ring 2 moves relative to the other two members, which might lead the designer to select brass or bronze for the moving middle ring and steel for the first innermost ring I and third outermost ring 3. The same philosophy could be applied to the other couplings.

to The choice of material depends on the intended use of the coupling.

The above embodiments are to be understood as illustrative examples of the invention, Further embodiments 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 embodiments. 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.

Claims

Claims 1. A coupling comprising a first, inner, member having an outer convex spherical periphery centred about a central point, a torsional axis extending through the central point, and a second, outer, member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the inner member and arranged to co-act with the inner member to transmit load therebetween, to one of the inner member and outer ring having a first elongate projection projecting into a corresponding first elongate slot in the other, the slot and projection being elongate in a first plane parallel to the said torsional axis, the projection and slot projecting in the direction of the said first plane, the projection and slot acting to transmit torque about the said torsional axis from one of the outer ring and inner member to the other, the inner member and outer ring being constrained by the projection and slot to be rotatable one relative to the other about an axis through the central point and perpendicular to the said first plane.
2. A coupling according to claim 1, wherein the said first plane is spaced from and parallel to the torsional axis.
3. A coupling according to claim 2, comprising a further elongate projection projecting from one of the inner and outer members into a further slot in the other, the further projection and frirther slot projecting in and being elongate in a further plane parallel to the said torsional axis and spaced from the first plane.
4. A coupling according to claim 3, wherein the further plane is spaced from and parallel to the torsional axis.
5. A coupling according to claim 3 or 4, comprising another projection and another slot projecting in the said first plane in the opposite direction to the first projection and first slot and a yet further projection and yet further slot projecting in the said further plane in the opposite direction to the further projection and further slot.
6. A coupling according to claim 1, the said a first elongate projection projects radially of the central point into the corresponding first elongate slot.
7. A coupling according to claim 6, comprising a further elongate projection projecting radially of the central point into a corresponding further elongate slot, the further projection and further slot being diametrically opposite the first radially to projecting projection and first radially projecting slot, the further projection and further slot being elongate in the first said plane containing the said torsional axis.
8. A coupling according to any preceding claim, wherein the first member is a ring having a cylindrical bore centred on the said torsional axis for receiving a shaft.
9. A coupling according to claim 8, wherein the bore has splines for engaging a correspondingly splined shaft.
10. A coupling according to any preceding claim, wherein a shaft extending along the said torsional axis is fixed to the first member.
IL A coupling according to any preceding claim, wherein the second member has means for coupling to a structural element.
12. A coupling according to claim 11, wherein the coupling means comprises splines.
13. A coupling according to any preceding claim, wherein radially Lacing periphery of the or each projection is spaced from the corresponding radially facing surface of the slot into which it projects.
14. A coupling according to any preceding claim, wherein the convex and concave spherical surfaces, which are co-acting bearing surfaces of the coupling, are contiguous plain bearing surfaces which bear radial loads of the coupling and which bear loads of the coupling acting along the said torsional axis.
15. A coupling according to any one of claims ito 13, further comprising a ball or roller bearing arrangement between the convex and concave spherical surfaces.
16. A coupling according to claim 15, wherein the bearing arrangement between the to convex and concave spherical surfaces comprises balls within a cage.t7. A coupling according to any preceding claim, further comprising a bearing arrangement between the elongate circumferentially facing side of the or each projection and the corresponding elongate side of its associated slot.t8. A coupling according to any preceding claim, wherein the or each slot extends over the whole width of its associated ring or member.19. A coupling arrangement according to any preceding claim, wherein the or each projection extends over the whole width of its associated ring or member.20. A coupling according to any preceding claim, wherein the second member is configured to retain the first member within the coupling.21. A coupling according to any preceding claim, wherein the said central point is on the said torsional axis between the axially facing sides of the first member and between the axially facing sides of the second member.22. A coupling according to any preceding claim, further comprising an axle coupling the first and second members, the axle being on the axis of rotation of one member relative to the other about the said central point in a direction constrained by the projection and slot.23. A coupling according to any preceding claim, wherein one of the inner member and the outer ring is fixed against rotation about the torsional axis.24. A coupling according to any one of claims 1 to 22, wherein the torsional axis is an axis of rotation and the inner member and the outer ring are free to rotate about the torsional axis.25. A coupling according to any preceding claim, wherein the second member has to an outer periphery which is convexly spherical and thither comprising a third member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the second member and arranged to co-act with the second member to transmit load therebetween, one of the second member and third member having a second elongate projection projecting in a second plane parallel to the said torsional axis into a corresponding second elongate slot in the other, the second slot and second projection being elongate in the said second plane, the second projection and second slot acting to transmit torque about the said torsional axis from one of the second and third members to the other, the second member and third member being further rotatable one relative to the other about the said central point in a direction constrained by the projection and slot.26. A coupling according to claim 25, wherein the second plane is coincident with the said torsional axis.27. A coupling according to claim 26, wherein the second and third members have a further projection and slot diametrically opposite the second projection and slot.28. A coupling according to claim 25, 26 or 27, wherein the second projection and second slot are orthogonal to the first projection and first slot.29 A coupling according to any one of claims Ito 24, further comprising a a third member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the second member and arranged to co-act with the second member to transmit load therebetween, the second and third members being coupled by an axle on an axis of rotation of one of the second and third members relative to the other which is perpendicular to the axis of relative rotation of the first and second members.30. A coupling arrangement comprising two couplings according to any preceding claim, connected by a connecting structure.31. A coupling arrangement according to claim 30, wherein the connecting structure connects the outermost said members of the couplings.32. A coupling arrangement according to claim 31, wherein one of the couplings is free t5 to move relative to the connecting structure.33. A coupling arrangement according to claim 30, wherein the connecting structure connects the outermost said member of one of the couplings to the inner most said member of the other.34, A coupling or coupling arrangement according to any preceding claim, mounted within a bearing.35. A coupling according to any one of claims 25 to 28, wherein the third member has an outer periphery which is convexly spherical about a further central point which is offset the said first mentioned central point in the direction of the torsional axis and further comprising a fourth member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the third member and arranged to co-act with the third member to transmit load therebetween, one of the third member and fourth member having a third elongate projection projecting in a third plane parallel to the said torsional axis into a corresponding third elongate slot in the other, the third slot and third projection being elongate in the third plane, the third projection and third slot acting to transmit torque about the said torsional axis from one of the third and fourth members to the other, the third member and fourth member being further rotatable one relative to the other about the said further central point in a direction constrained by the third projection and third slot, wherein the said third plane is parallel to the second plane, and to wherein the fourth member has an outer periphery which is convexly spherical about the further central point which is offset the said first mentioned central point in the direction of the torsional axis and further comprising a fifth member in the form of a ring having an inner concave spherical periphery centred about the further central point and complementary to the outer periphery of the fourth member and arranged to co-act with the fourth member to transmit load thereb etween, one of the fourth member and fifth member having a fourth elongate projection projecting in a fourth plane parallel to the said torsional axis into a corresponding fourth elongate slot in the other, the fourth slot and fourth projection being elongate in the fourth plane, the fourth projection and fourth slot acting to transmit torque about the said torsional axis from one of the fourth and fifth members to the other, the fourth member and fifth member being further rotatable one relative to the other about the said further central point in a direction constrained by the fourth projection and fourth slot, wherein the said fourth plane is parallel to the third plane.36. A coupling according to any one of claims 25 to 28, wherein the third member has an outer periphery which is convexly spherical about a further central point which is offset the said first mentioned central point in the direction of the torsional axis and further comprising a fourth member in the form of a ring having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the third member and arranged to co-act with the third member to transmit load therebetween, an axle coupling the third and fourth members, the fourth member having an outer periphery which is convexly spherical about the further central point which is offset the said first mentioned central point in the direction of the torsional axis a fifth member in the form of a ring having an inner concave spherical periphery centred about the further central point and complementary to the outer periphery of the fourth member and aranged to co-act with the fourth member to transmit load to therebetween, and a frirther axle coupling the fourth and fifth members, the further axle being perpendicular to the axle coupling the third and fourth members.37. A coupling substantially as hereinbefore described with reference to Figure 2, 4, 7, 9, 14, 15, 16, 17, 18 or 19 optionally as modified by Figure 10, 11, 12 and/or 13.38. A coupling arrangement comprising two couplings according to claim 37 connected by a connecting means.Amendments to the claims have been filed as follows Claims 1. A coupling comprising a first, inner, member having an outer convex spherical periphery centred about a central point, a torsional axis extending through the central point, and a second annular member concentric with the first member and having an inner concave spherical periphery centred about the central point and complementary to the convex spherical outer periphery of the first inner member, which convex spherical outer surface is also centred on the centre point and arranged to co-act with the first inner member to transmit load therebetween, one of the first inner member and second member having a first elongate projection projecting into a corresponding first elongate slot in the other, the slot and projection being elongate in a first plane containing or parallel to the said torsional axis, the projection and slot projecting in the direction of the said first plane, the projection and slot acting to transmit torque about the said torsional axis from one of the first inner member and second member to the other, the 0') second member having a central axis and a pair of diametrically opposed loading slots extending half way across the width of the second member to C\J enable introduction of the first inner member within the second member and (4 the engagement of convex outer surface of the first inner member within the concave inner surface of the second member, the first inner member and second member being constrained by the projection and slot to be rotatable one relative to the other about an axis through the central point and perpendicular to the said first plane, and in which the first inner member is retained axially by the second annular member.2. A coupling according to claim 1, wherein the said first plane is spaced from and parallel to the torsional axis.3. A coupling according to claim 2, comprising a further elongate projection projecting from one of the first and second members into a further slot in the other, the further projection and further slot projecting in and being elongate in a further plane parallel to the said torsional axis and spaced from the first plane.4. A coupling according to claim 3, wherein the further plane is spaced from and parallel to the torsional axis.5. A coupling according to claim 3 or 4, comprising another projection and another first slot and a yet further projection and yet further slot projecting in the said further plane in the opposite direction to the further projection and further slot.6. A coupling according to claim 1, the said a first elongate projection projects radially of the central point into the corresponding first elongate slot.7. A coupling according to claim 6, comprising a further elongate projection projecting radially of the central point into a corresponding further elongate slot, the further projection and further slot being diametrically opposite the first radially projecting projection and first radially projecting slot, the further projection and further slot being elongate in the first said plane containing the said torsional axis.8. A coupling according to any preceding claim, wherein the first member is annular and whose cylindrical bore may receive a shaft.o 9. A coupling according to claim 8, wherein the first annular member inwardly directed splines for engaging a correspondingly splined shaft.(\J 10. A coupling according to any preceding claim, wherein a shaft extending along the said torsional axis is fixed to the first member.11. A coupling according to any preceding claim, wherein the second member has means for coupling to a structural element.12. A coupling according to claim 11, wherein the coupling means comprises splines.13. A coupling according to any preceding claim, wherein radially facing periphery of the or each projection is spaced from the corresponding radially facing surface of the slot into which it projects.14. A coupling according to any preceding claim, wherein the convex and concave spherical surfaces, which are co-acting bearing surfaces of the coupling, are contiguous plain bearing surfaces which bear radial loads of the coupling and which bear loads of the coupling acting along the said torsional axis.15. A coupling according to any one of claims ito 13, further comprising a ball or roller bearing arrangement between the convex and concave spherical surfaces.16. A coupling according to claim 15, wherein the bearing arrangement between the convex and concave spherical surfaces comprises balls within a cage.
17. A coupling according to any preceding claim, further comprising a bearing arrangement between the elongate circumferentially facing side of the or each projection and the corresponding elongate side of its associated slot.
18. A coupling according to any preceding claim, wherein the or each slot extends over the whole width of its associated member.
19. A coupling arrangement according to any preceding claim, wherein the or each projection extends over the whole width of its associated member.
20. A coupling according to any preceding claim, wherein the said central point is on the said torsional axis between the axially facing sides of the first member and between the axially facing sides of the second member.
21. A coupling according to any preceding claim, further comprising an axle coupling the first and second members, the axle being on the axis of rotation of one member relative to the other about the said central point in a (Y) direction constrained by the projection and slot.
22. A coupling according to any preceding claim, wherein the second member has an outer periphery which is convexly spherical and furthei comprising a third annular member having a central axis having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the second member and arranged to co-act with the second member to transmit load therebetween, one of the second member and third member having a second elongate projection projecting in a second plane containing or parallel to its central axis into a corresponding second elongate slot in the other, the second slot and second projection being elongate in the said second plane, the second projection and second slot acting to transmit torque about the said torsional axis from one of the second and third members to the other, the second member and third member being further rotatable one relative to the other about the said central point in a direction constrained by the projection and slot.
23. A coupling according to claim 22, wherein the second plane is coincident with the said torsional axis.
24. A coupling according to claim 23, wherein the second and third members have a further projection and slot diametrically opposite the second projection and slot.
25. A coupling according to claim 22, 23, or 24, wherein the second projection and second slot are orthogonal to the first projection and first slot.
26. A coupling according to any one of claims 1 to 20, further comprising a third annular member having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the second member and arranged to co-act with the second member to transmit load therebetween, the second and third members being coupled by an axle on an axis of rotation of one of the second and third members relative to the other which is perpendicular to the axis of relative rotation of the first and second members.
27. A coupling according to any one of claims 22 to 25, wherein the third o member has an outer periphery which is convexly spherical about a further central point which is offset the said first mentioned central point in the (\J direction of the torsional axis and further comprising a fourth annular member having a central axis and having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the third member and arranged to co-act with the third member to transmit load therebetween, one of the third member and fourth member having a third elongate projection projecting in a third plane containing or parallel to its central axis into a corresponding third elongate slot in the other, the third slot and third projection being elongate in the third plane, the third projection and third slot acting to transmit torque about the said torsional axis from one of the third and fourth members to the other, the third member and fourth member being further rotatable one relative to the other about the said further central point in a direction constrained by the third projection and third slot, wherein the said third plane is coincident with or parallel to the second plane, and wherein the fourth member has an outer periphery which is convexly spherical about the further central point which is offset the said first mentioned central point in the direction of the torsional axis and further comprising a fifth annular member having a central axis having an inner concave spherical periphery centred about the further central point and complementary to the outer periphery of the fourth member and arranged to co-act with the fourth member to transmit load therebetween, one of the fourth member and fifth member having a fourth elongate projection projecting in a fourth plane containing or parallel to its central axis into a corresponding fourth elongate slot in the other, the fourth slot and fourth projection being elongate in the fourth plane, the fourth projection and fourth slot acting to transmit torque about the said torsional axis from one of the fourth and fifth members to the other, the fourth member and fifth member being further rotatable one relative to the other about the said further central point in a direction constrained by the fourth projection and fourth slot, wherein the said fourth plane is coincident with or parallel to the third plane.
28. A coupling according to any one of claim 22 to 25, wherein the third member o has an outer periphery which is convexly spherical about a further central point which is offset from the said first mentioned central point in the (\J direction of the axis of the third member and further comprising a fourth annular member having an inner concave spherical periphery centred about the central point and complementary to the outer periphery of the third member and arranged to co-act with the third member to transmit load therebetween, an axle coupling the third and fourth members, the fourth member having an outer periphery which is convexly spherical about the further central point which is offset the said first mentioned central point in the direction of the torsional axis, a fifth annular member having an inner concave spherical periphery centred about the further central point and complementary to the outer periphery of the fourth member and arranged to co-act with the fourth member to transmit load therebetween, and a further axle coupling the fourth and fifth members, the further axle being perpendicular to the axle coupling the third and fourth members.
29. A coupling according to any one of claims 22 to 28 and in which the second, third and fourth (if present) annular members are retained axially by the third, fourth (if present) and fifth (if present) annular member.
30. A coupling according to any one of claims 22 to 29 in which the third, fourth and fifth (if present) annular members have pairs of diametrically opposed loading slots extending half way across their widths to enable introduction of the second, third and fourth annular members (if present), within the third fourth and fifth (if present) annular and the engagement of convex outer surface(s) of the second, third and fourth annular members within the concave inner surface(s) of the third, fourth and fifth annular members(s).,
31. A coupling according to any preceding claim, wherein one of the first inner annular member and the outer annular member is fixed against rotation about the torsional axis.
32. A coupling according to any preceding claim, wherein the torsional axis is an axis of rotation and the first inner member and the outermost annular 0) member are free to rotate about the torsional axis.o
33. A coupling arrangement comprising two couplings according to any preceding claim, connected by a connecting structure.(\J
34. A coupling arrangement according to claim 33, wherein the connecting structure connects the outermost annular members of the couplings.
35. A coupling arrangement according to claim 34, wherein one of the couplings is free to move relative to the connecting structure.
36. A coupling arrangement according to claim 33, wherein the connecting structure connects the outermost annular member of one of the couplings to the first inner member of the other.
37. A coupling or coupling arrangement according to any preceding claim, mounted within a bearing.
38. A coupling substantially as hereinbefore described with reference to Figure 2,4, 7,9, 14, 15, 16, 17, 18 or 19 optionally as modified by Figure 10, 11, 12 and/or 13.
39. A coupling arrangement comprising two couplings according to claim 37 connected by a connecting means.