GB2422885A - Double cardan joint with coincident crosses - Google Patents

Abstract

A constant velocity joint has two yokes 32, 40 and two coincident intermediate members 34, 37 (also known as crosses, cruciforms or spiders) which are pivotally connected to each other on axis B. Each of the intermediate members 34, 37 is pivotally connected to respective yoke, and these two pivotal axes A, C are both perpendicular to pivot axis B. There is also a stabilising member 44 extending between the two yokes and contacting at least one of the intermediate members 34, which ensures that the angles between the yokes and the two intermediate members are divided equally, and the transmission between first and second yokes is homokinetic with no cyclic speed variation. As the two yokes are coincident, the coupling requires minimal space. One of the yokes 40 may be generally ball shaped, to further reduce the size of the coupling. Alternatively the intermediate members may be provided by a flexible disc (63, figure 6) with appropriate cut-outs to allow movement equivalent to the pivoting between conventional intermediate members.

Description

CONSTANT VELOCITY UNIVERSAL JOINT

The present invention relates to a constant velocity (CV) joint. More particularly but not exclusively, it relates to a constant velocity joint which has advantages of simplicity of construction, cost of manufacture and small size, compared to currently available constant velocity universal joints.

A Hooke's joint (also known as a Cardan or universal joint) is widely used to connect two rotating shafts having rotational axes extending at an angle, each to the other. A Hooke's joint comprises two yokes, each mounted to a respective one of the rotating shafts and pivotably connected to a common linking element, generally referred to as a "cruciform".

The two yokes are pivotable about two transversely extending axes; these are usually perpendicular, one to another, and intersect at a centre of the linking element. The term cruciform is thus derived from the form of these crossed axes, and the cruciform itself need not actually be physically cross-shaped (examples are shown in Figures 1, 4a and 4b below) .

A drawback of such joints is that for a constant rotational speed of a first (driving) shaft, the second (driven) shaft rotates at a variable speed, the magnitude of this variation depending on the angle between the axes of the shafts.

This problem has been addressed by linking the first and second shafts to opposite ends of an intermediate shaft, by means of two Hooke's joints. This double Hookes CV joint arrangement results in a constant rotational speed of the first shaft producing a variable rotational speed of the intermediate shaft, which is converted back to a constant rotational speed of the second shaft. However, this will only work filly when the angles between the first shaft and the intermediate shaft, and between the intermediate shaft and the second shaft, are identical. If they are not, some of the variation in rotational speed will not be compensated for or will be overcompensated, depending on which angle is the greater (see Figures 1 and 2 and the associated description, below). The intermediate shaft also adds to the bulk of the joint.

This is a particular problem for motor vehicles with front-wheel drive or four-wheel drive, in which the front wheels must be powered while being steered at a variable angle.

Considerable development has therefore been carried out on "constant velocity" (CV) joints, which permit delivery of a constant rotational speed across a variably angled joint in a vehicle's drive train. Common varieties of these include the "Birfield", "Lobro" "Rzeppa", "Bendix-Weiss" and "tripode" CV joints. These all involve complex arrangements of ball races and the like, requiring precise machining and close tolerances, and being expensive to manufacture and replace.

Although not limiting in any way, an example applicable is in the field of model motor vehicles, where very high performances can now be achieved. For example, radio- controllable 1:10 scale model sports cars can now reach actual (not scale) speeds of around mph (approximately l3Okph). It is necessary to drive their front wheels at very high rotational speeds while steering accurately and controllably. Unfortunately, conventional CV joints as used in full-scale motor vehicles cannot be used, mainly due to size constraints. A diameter of no more than 12 millimetres is typically required, and conventional CV joints cannot be scaled down to such dimensions while retaining the necessary tolerances, at an acceptable price. Variations of the Hookes joint are presently used, and have provided acceptable results at relatively low speeds and small steering angles, but there is a need, in modem high-performance model vehicles, for a joint giving far more stable transmission of rotational motion over a wide range of steering angles, capable of being made sufficiently compact to fit in a model vehicle without requiring extremely precise and costly production methods.

It is hence an object of the present invention to provide a constant velocity joint that can be produced more economically than existing CV joints and in smaller sizes, while reliably transmitting a constant rotational speed over a wide range ofjoint angles.

According to the present invention, there is provided a constant velocity joint comprising first and second yoke means, each mounted to a respective rotatable shaft means, and first and second cruciform means, each pivotably mounted to a respective yoke means, wherein a centre of the first cruciform means is substantially coincident with a centre of the second cruciform means.

In a preferred embodiment, the joint is provided with means to stabilise it in such a symmetrical conformation that rotational motion of a first shaft means is transmitted synchronously to the second shaft means.

Advantageously, when the rotational axes of the shaft means extend at an angle, each to the other, an angle between the rotational axis of the first shaft means and the second axis of the first cruciform means is equal to an angle between the rotational axis of the second shaft means and the second axis of the second cruciform means.

The stabilising means preferably comprises a member extending between the first and second yoke means and contacting one or each of the first and second cruciform means.

Said member may comprise an elongate rod means provided at each remote end with head means receivable in recess means of a respective yoke means.

Said head means may be freely swivellable within a respective recess means.

The rod means may tilt according to the angle of the first shaft means and impose an angle on the cruciform means connected to the second shaft means.

The stabilising means may comprise means, such as spring means, to bias it into contact with the or each cruciform means and the yoke means.

Preferably, the first and second cruciform means are directly mounted each to the other.

Advantageously, the first and second cruciform means are pivotably mounted, each to the other.

Alternatively, the first and second cruciform means are flexibly mounted, each to the other.

Preferably, each cruciform means is so connected to a respective yoke means as to be pivotable about a first axis thereof, and the cruciform means are so connected, each to the other, that each is pivotable about its second axis.

The second axes of each cruciform means are thus collinear.

The second cruciform means may be disposed generally within the first cruciform means.

Each cruciform means is preferably so connected to a respective yoke means as to be pivotable about an axis extending transversely to a rotational axis of a respective shaft means.

Advantageously, each cruciform means is pivotable about an axis extending substantially perpendicularly to said rotational axis.

Optionally, one or each of the cruciform means may be pivotably mounted to a respective yoke means by means of a flexible, optionally resilient, member, and/or the cruciform means may be pivotably mounted each to the other by means of a flexible, optionally resilient, member.

In a first embodiment, each of the yoke means and the cruciform means comprises a strong, rigid material, such as metal, a plastics material, or a ceramics material.

In an alternative embodiment, one or each cruciform means may comprise a flexible, preferably resilient, material, such as an elastomeric plastics material.

Each of the yoke means and the cruciform means may then be pivotably moveable through flexure of said flexible material.

The first and second cruciform means may then be formed as a single body having two portions, moveable each with respect to the other.

Said single body may comprise a substantially planar sheet of flexible material.

Embodiments of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side elevation of an existing double Hooker's CV joint universal shaft arrangement, correctly set up for constant velocity; Figure 2 is a side elevation of the arrangement shown in Figure 1, incorrectly set up for constant velocity; Figure 3 is a schematic perspective view of a single Hooke' s joint; Figure 4A is a perspective view of a cruciform element isolated from the Hooke's joint shown in Figure 3; Figure 4B is a perspective view of an alternative form of cruciform element to that shown in Figure 4A; Figure 5 is a perspective view in separated condition of a first double Hooke's CV joint embodying the present invention; Figure 6 is a perspective view in separated condition of a second double Hooke's CV joint embodying the present invention; and Figure 7 is perspective view in separated condition of a third double Hooke's CV joint embodying the present invention.

Referring now to the Figures, and to Figure 1 in particular, a conventional double Hooke's joint arrangement I comprises an elongate powered shaft 2, connected by a first Hooke's joint 3 to an elongate intermediate shaft 4. The intermediate shaft 4 is in turn connected by a second Hooke's joint 5 to an elongate driven shaft 6.

The powered shaft 2 is driven to rotate about its longitudinal axis 7, the intermediate shaft 4 is rotatable about its longitudinal axis 8, and the driven shaft 6 is rotatable in turn about its longitudinal axis 9. The universal shaft arrangement 1 thus turns rotatory motion of the powered shaft 2 through an angle 0 between the longitudinal axis 7 of the powered shaft 2 and the longitudinal axis 9 of the driven shaft 6.

When the universal shaft arrangement 1 is correctly set up for constant velocity, as in Figure I, the angle between the axis 7 of the powered shaft 2 and the axis 8 of the intermediate shaft 4 equals the angle between the axis 8 of the intermediate shaft 4 and the axis 9 of the driven shaft 6; i.e. each said angle equals 0/2.

As is well known for Hooke's joints 3, when the powered shaft 2 is rotated at a constant angular velocity, the intermediate shaft 4 does not rotate at a constant velocity, but at a velocity that varies sinusoidally, depending on the instantaneous rotational disposition of the Hooke's joint 3. The magnitude of this variation depends on the angle 0/2 between the shafts 2, 4 connected to the joint 3.

However, the second Hooke's joint 5 is aligned at the same angle as the first 3, and is disposed in phase therewith, as shown. The variation in the angular velocity of the intermediate shaft 4 is then cancelled out as its rotation is transmitted to the driven shaft 6.

The driven shaft 6 thus rotates at a constant angular velocity.

The double Hooke's CV joint arrangement 1 hence acts as a constant velocity joint for any value of 0, as long as each of the powered 2 and driven shafts 6 make an angle of 0/2 with the intermediate shaft 4.

In Figure 2, although the axes 7, 9 of the powered 2 and driven shafts 6 are aligned as in Figure 1, and still extend at an angle ofO, each to the other, the intermediate shaft 4 is no longer symmetrically aligned. The angle between the axes 7, 8 of the powered 2 and intermediate shafts 4 has fallen to (0/2 - a), while the angle between the axes 8, 9 of the intermediate 4 and driven shafts 6 has correspondingly risen to (0/2 + a). As a result, the variation in angular velocity created in the intermediate shaft 4 by the first Hooke's joint 3 is not exactly compensated for by the second Hooke's joint 5, and the driven shaft 6 does not rotate at a constant angular velocity.

A typical single Hooke's joint 10 is shown in Figure 3. A first shaft 11 has a symmetrical first yoke 12 mounted to one end thereof A cruciform element 13 in Figure 4a comprises a first 14 and a second elongate member 15, mounted together at their respective midpoints so as to extend perpendicularly each to the other. The first member 14 is pivotably mounted at each end to the first yoke 12, which is thus free to pivot about an axis A extending along the first member 14. A second shaft 16 has a second yoke 17 mounted to one end; the second member 15 of the cruciform element 13 is pivotably mounted at each end to the second yoke 17, which is thus free to pivot about an axis B extending through the second member 15. A rotational axis 18 of the first shaft 11 and a rotational axis 19 of the second shaft 16 each extend through the midpoint of the cruciform element 13, where the first and second elongate members 14, 15 (and perpendicular axes A and B) cross. Note: although in this case rotational axis 18 is perpendicular to axis A, and rotational axis 19 is perpendicular to axis B, this need not always be so.

As the first shaft 11 is turned, the first yoke 12 turns the cruciform element 13, which turns the second yoke 17 and the second shaft 16; the cruciform element 13 thus undergoes a relatively complex motion, pivoting about both of its axes A, B. In its simplest form, the cruciform element 13 appears as shown in Figure 4A. However, it can be made in other physical shapes, such as a sphere, as shown in Figure 4B. The spherical or "ball" cruciform element 20 has a first pair of diametrically opposite pivot points 21 and a second pair of diametrically opposite pivot points 22. The first pair of pivot points 21 are pivotably connected to the first yoke 12 and the second pair 22 to the second yoke 17. They thus define two perpendicular axes A and B, as for the conventional cruciform element 13.

The ball cruciform element 20 is hence functionally equivalent to the conventional cruciform element 13, although it is easier and cheaper to machine at small dimensions. (The term "cruciform element" thus refers to the two perpendicular axes A, B, rather than to the physical shape of the element 13, 20).

A first universal CV joint embodying the present invention is shown in Figure 5, in exploded form. A first input shaft 31 is terminated by a symmetrical first yoke 32 provided at each tip with an inwardly-extending first pivot pin 33. The two first pivot pins 33 lie along a common axis A. Axis A is here perpendicular to the first input shaft 31, although this need not be the case.

A first cruciform element 34 comprises a generally hemispherical cage structure, having a pair of first pivot apertures 35 disposed at diametrically opposite points on a generally equatorial portion of the hemispherical cage (one said first pivot aperture 35 is not visible in this view). When the joint is assembled, each first pivot pin 33 is pivotably engaged with a respective first pivot aperture 35, surrounded by a localised flat or with a convex face of the hemispherical cage disposed towards the first yoke 32. The first pivot apertures 35 thus also lie along axis A. The first cruciform element 34 has a pair of second pivot apertures 36 disposed at diametrically opposite points on the generally equatorial portion of the hemispherical cage, equidistant between the first pivot apertures 35. The second pivot apertures lie along an axis B, substantially perpendicular to axis A and intersecting therewith at a centre of the hemispherical cage.

It is possible for the axes A and B, B and C etc to be up to 5 away from absolutely perpendicular.

A second cruciform element 37 is of more conventional form, comprising a first 38 and second 39 elongate member, mounted together at their respective midpoints so as to extend substantially perpendicularly each to the other. When the joint is assembled, each end of the first member 38 is engaged pivotably with a respective second pivot aperture 36 of the first cruciform element 34. The first member 38 thus lies along axis B, and the second cruciform element 37 is disposed within the hemispherical cage of the first cruciform element 34. The second member 39 lies along axis C, substantially perpendicular to axis B; the intersection of axes B and C thus lies at a centre of the hemispherical cage.

A second yoke 40 has a second output shaft 41 mounted thereto. It is substantially smaller than the first yoke 32, and has the form of a sphere containing an elongate slot 42 closely fitting the internal spherical diameter of cruciform 34. The second yoke 40 is provided with two diametrically opposed third pivot apertures 43, lying along axis C. When the joint is assembled, each end of the second member 39 of the second cruciform element 37 is pivotably engaged with a respective one of the third pivot apertures 43. The first member 38 of the second cruciform element 37 thus extends outwardly at each end from the slot 42, and the second yoke 40 is disposed substantially within the hemispherical cage of the first cruciform element 34.

In general terms, the second cruciform element 37 is disposed concentrically within the second yoke 40, which is in turn disposed concentrically within the first cruciform element 34, which in turn is disposed symmetrically between the arms of the first yoke 32.

The first universal joint thus acts as two concentrically nested Hooke's joints. Rotation of the input shaft 31 is transmitted through the joint to the output shaft 41 at the same constant angular velocity, as in the case of the conventional double Hooke's joint arrangement of Figure 1. However, the first universal joint of Figure 5 is far more compact, having no elongate intermediate shaft 4. No expensive ball races may be needed, merely simple pivot connections between (relatively) easily machineable or mouldable components.

A stabilising element 44 may be provided to confine the maximum angle of articulation of the cruciforms 34, 37 and axis A to be half of the angle between input shaft 31 and output shaft 41, thus ensuring constant velocity. The element 44 comprises an elongate shaft 45 with a substantially spherical head 46 at each end and a collar 47 encircling the shaft 45 adjacent one said head 46. The collar 47 is preferably substantially spherical but may take other forms, such as a transverse cylinder or the like.

A coaxial blind bore 48 extends into the first input shaft 31 from a point within the first yoke 32. A spring 49 is held within the blind bore 48. The first cruciform member 34 has an elongate slot 50 extending parallelly to or in the general direction of axis A, across a portion of the hemispherical cage disposed towards the first yoke 32 and the input shaft 31. The elongate slot 50 is sufficiently wide for a head 46 of the stabilising element 44 to pass therethrough, the collar 47 being a close fit in the slot 50. The second yoke 40 is provided with a rounded recess 51 at a point on the loop remote from the output shaft 41.

When the joint is assembled, a respective first head 46 of the stabilising element 44 is received within the blind bore 48 of the first input shaft 31. The shaft 45 extends towards the slot 50 of the first cruciform element 34, the collar 47 being in close contact with the slot 50 of the first cruciform element 34 and urged by the spring 49 acting on the first head 46 of the stabilising element 44, the second head 46 of the element 44 extending through the slot 50 and into the recess 51 of the second yoke 40. The stabilising element 44 thus maintains contact with each yoke 32, 40 and with the first cruciform element 34, its length proportions ensuring that when the rotational axes of the input shaft 31 and the output shaft 41 are disposed at an angle, the joint remains symmetrical, with equal angles of each component Hooke's joint, in relation to its shaft, and varying from zero to half the joint angle according to shaft rotation.

A second universal CV joint embodying the present invention is shown in Figure 6. A first input shaft 61 is terminated by a first yoke 62.

A transmission element 63 comprises a planar sheet of a moderately, flexible, resilient material. It is divided into an outer portion 64 and an inner portion 65, connected solely by two diametrically opposite linking portions 66. The linking portions 66 may be twisted such that the two portions 64, 65 are no longer coplanar. They thus define an axis B, about which the two annuli 64, 65 may effectively pivot. The portions are shown as annuli but are preferably generally square.

While the transmission element 63 may be sufficiently robust for light duty applications, in a preferred embodiment a reinforcing bar 67 is mounted thereto, extending substantially diametrically across the transmission element 63 along axis B. Mounting apertures 68 are provided in both the outer 64 and inner 65 portions, on axis B, adjacent the linking portions 66 and corresponding mounting apertures 69 are provided on the reinforcing bar 67. The two portions 64, 65 may still twist about axis B, but the transmission element 63 is not depending entirely on the durability and integrity of the linking portions 66 for its operation.

A second yoke 70 is mounted to a second output shaft 71.

When the joint is assembled, the first yoke 62 is mounted to the inner portions 65 at two diametrically opposite inner mounting points 72, equidistant between the linking portions 66.

The first yoke 62 may he pivoted about an axis A extending between the inner mounting points 72, thus twisting the flexible, resilient inner portions 65.

The second yoke 70 is similarly mounted to the outer portion 64 at two diametrically opposite outer mounting points 73, equidistant between the linking portions 66. The second yoke 70 may be pivoted about an axis C extending between the outer mounting points 73, thus twisting the flexible, resilient outer portion 64.

The axes A, B and C all intersect at a centre of the transmission element 63. Axes A and B are mutually substantially perpendicular, as are axes B and C. The inner portion 65 thus has two substantially perpendicular axes, A and B, about which essentially pivotal movement may occur, and is thus functionally equivalent to a cruciform element of a conventional Hooke's joint. The outer portion 64 is similarly equivalent to a cruciform element of another Hooke's joint. These two "cruciform elements" are connected by the linking portions 66 and optionally the reinforcing bar 67. The entire joint thus acts as a constant velocity joint equivalent to the conventional universal shaft arrangement as shown in Figure 1, but with the two Hooke's joint equivalents nested concentrically and no cumbersome intermediate shaft present.

In lighter-duty applications, the resilience of the material of the transmission element 63 may be sufficient to ensure that the joint remains symmetrical when the input shaft 61 and the output shaft 71 are disposed at an angle, each to the other, such that constant velocity is achieved. However, it may be necessary to provide a stabilising element 74, analogous to that in the first universal joint shown in Figure 5. The stabilising element 74 comprises an elongate shaft 75 with a substantially spherical head 76 at each end and a collar 77 encircling the shaft 75 adjacent one said head 76. Again, the collar 77 may preferably be substantially spherical, but it may also take other forms, such as a transverse cylinder.

A coaxial blind bore 78 holding a spring 79 extends into the input shaft 61. The reinforcing bar 67 is provided with a slot 80 extending through its midpoint, flanked by two restricting walls 81. The second yoke 70 is provided with a central prong 82, extending collinearly with the output shaft 71 towards the transmission element 63, and having a recess 83 in its tip.

When the joint is assembled, a respective first head 76 of the stabilising element 74 is received within the blind bore 78 of the input shaft 61. The shaft 75 extends towards the slot of the reinforcing bar 67 of the transmission member 63, the collar 77 being closely located between the restricting walls 81 and the second head 76 extending through the slot 80 and into the recess 83 of the second yoke 70. The spring 79 acts on the first head 76 to urge the collar 77 through the reinforcing bar 67 and the second head 76 securely into the recess 83, and the stabilising element 74 thus maintains contact with each yoke 62, 70 and with the transmission element 63. The restricting walls 81 limit the movement of the reinforcing bar 67 and thus element 63 to that plane which provides a nett constant velocity, ensuring that the joint remains symmetrical and operates as a CV joint.

By its nature, the joint has a low axial stiffness and would tolerate small axial movements between the input and output shafts, thus avoiding the need for a sliding spline or similar device.

A third double Hookes constant velocity joint embodying the present invention is shown in Figure 7. A first input shaft 81 is terminated by a first yoke 82, provided at each tip with an outwardly-extending first pivot pin 83. The two first pivot pins 83 lie along a common axis A, here perpendicular to the input shaft 81 (although this is not essential).

A first "cruciform" element 84 comprises a generally octagonal frame, having a pair of first pivot apertures 85 disposed at diametrically opposite points thereon. When the joint is assembled, each first pivot pin 83 is pivotably engaged with a respective first pivot aperture 85; the first pivot apertures 85 thus also lie along axis A. The first cruciform element 84 has a pair of second pivot apertures 86, disposed at diametrically opposite points, equidistant between the first pivot apertures 85. The second pivot apertures 86 lie along an axis B, substantially perpendicular to axis A and intersecting therewith at a centre of the octagonal frame.

A second "cruciform" element 87 also comprises a generally octagonal frame, smaller than that of the first cruciform element 84. It is provided with a pair of third pivot apertures 88 disposed at diametrically opposite points, and a pair of fourth pivot apertures 89, disposed at diametrically opposite points, equidistant between the third pivot apertures 88. When the joint is assembled, an elongate axle pin 90 extends pivotably through each of the second pivot apertures 86 of the first cruciform element 84 and the third pivot apertures 88 of the second cruciform element 87. The axle pin 90 and the third pivot apertures 88 hence also lie along axis B. A second output shaft 91 has a hollow spherical body 92 mounted thereto, which acts as a second yoke. It is provided with two diametrically oppositely disposed outwardly extending second pivot pins 93. These lie along a common axis C, here perpendicular to the output shaft 91 (although this is not essential). When the joint is assembled, each second pivot pin 93 is pivotably engaged with a respective fourth pivot aperture 89 of the second cruciform element 87, such that the fourth pivot apertures 89 also lie on axis C. Axes B and C are thus mutually substantially perpendicular and intersect at a centre of the octagonal frame of the second cruciform element 87.

Clearly, the axle pin 90 must pass through the spherical yoke body 92. In a preferred embodiment, a support body 106 is provided for the axle pin 90, comprising a central ball 94 with a cylindrical member 95 passing diametrically therethrough. A cylindrical bore 96 passes coaxially through the cylindrical member 95, and is dimensioned to receive the axle pin 90 therethrough. The cylindrical member 95 and the ball 94 are disposed in an interior of the hollow spherical yoke body 92, with each end of the cylindrical member 95 protruding therefrom through circular windows 97 (one of which is concealed in this view). The windows 97 are larger in diameter than the cylindrical members 95 so that the ball 94, cylindrical member 95 and supported axle pin 90 may swivel independently of the hollow spherical yoke body 92.

In general terms, the support body 1 O6is disposed concentrically within the hollow spherical yoke body 92, which is in turn disposed concentrically within the second cruciform element 87, which is disposed concentrically within the first cruciform element 84, which is in turn disposed symmetrically on the first yoke 82.

The third universal CV joint thus also acts as two concentrically nested Hooke's joints, transmitting a constant rotational velocity of the input shaft 81 through to the output shaft 91. As for the first and second universal CV joints, above, the third

universal CV joint is far more compact, having no elongate intermediate shaft.

As for the first and second universal joints, the third may require the addition of a stabilising element 98 to ensure constant velocity. The stabilising element 98 comprises an elongate shaft 99 with a substantially spherical head 100 at each end and a collar 101 encircling the shaft 99 adjacent one said head 100. The collar 101 is preferably substantially spherical but may take other forms.

A coaxial blind bore 102 holding a spring 103 extends into the input shaft 81. The second cruciform element 87 is provided with a pair of parallel restricting walls 104, extending transversely to axis B (and so parallelly to axis A), and located adjacent and to opposing sides of a centre of the octagonal frame of the element 87. A recess 105 is provided in the spherical yoke body 92 at a point remote from the output shaft 91.

When the joint is assembled, a respective first head 100 of the stabilising element 98 is received within the blind bore 102. The shaft 99 extends towards a centre of the first 84 and second 87 cruciform elements and the spherical yoke body 92, the collar 101 being close fittingly disposed between the restricting walls 104 and the second head 100 being received in the recess 105. The spring 103 urges the stabilising element 98 to remain so disposed, in contact with each of the first yoke 82, through the second cruciform element 87 and into recess 105 of the spherical yoke body 92. The restricting walls 104 limit the movement of the cruciform 87 to that plane which provides a nett constant velocity, ensuring that the joint remains symmetrical and operates as a CV joint.

Except where stated above, the components of each of the universal joints described may comprise metal, a plastics material, a composite material, a ceramic or combinations thereof.

Claims (17)

1. I. A constant velocity joint comprising first and second yoke means, each mounted to a respective rotatable shaft means, and first and second cruciform means, each pivotably mounted to a respective one of said yoke means, wherein a centre of the first cruciform means is substantially coincident with a centre of the second cruciform means.
2. 2. A jOint as claimed in claim I, further comprising means to stabihise it in such a symmetrical conformation that rotational motion of a first shaft means is transmitted synchronously to the second shaft means.
3. 3. A joint as claimed in either claim I or in claim 2, wherein the rotational axes of the shaft means extend at an angle, each to the other, an angle between the rotational axis of the first shaft means and the second axis of the first cruciform means is equal to an angle between the rotational axis of the second shaft means and the second axis of the second cruciform means.
4. 4. A joint as claimed in either claim 2 or claim 3, wherein the stabilising means comprises a member extending between the first and second yoke means and contacting one or each of the first and second cruciform means.
5. 5. A joint as claimed ill claim 4, wherein the member comprise an elongate rod means provided at each remote end with head means receivable in recess means of a respective yoke means.
6. 6. A joint as claimed in claim 5, wherein the head means is freely swivellable within a respective recess means.
7. 7. A joint as claimed in either claim 5 or claim 6. wherein the rod means tilts according to the angle of the Iirst shall means and impose an angle on the cruciform means connected to the second shaft means.
8. 8. A joint as claimed in any one of claims 2 to 7, wherein the stabilising means comprises means to bias it into contact with the or each cruciform means and the yoke means.
9. 9. A joint as claimed in any one of the preceding claims, wherein the first and second cruciform means are directly mounted each to the other.
10. 10. A joint as claimed in claim 9, wherein the first and second cruciform means are pivotably mounted. each to the other.
11. 11. A joint as claimed in claim 9, wherein the first and second cruciform means are flexibly mounted, each to the other.
12. 12. A joint as claimed in claim 9, wherein each cruciform means is so connected to a respective yoke means as to he pivotable about a first axis thereof, and the cruciform means are SO connected, each to the other, that each is pivotable about its second axis.
13. 13. A joint as claimed in any one of the preceding claims, wherein the second cruciform means is disposed generally within the first cruciform means.
14. 14. A joint as claimed in any one of the preceding claims, wherein one or each of the cruciform means is pivotably mounted to a respective yoke means by means of a flexible, optionally resilient, member, and/or the cruciform means are pivotably mounted each to the other by means of a flexible, optionally resilient, member.
15. 15. A joint as claimed in any one of the preceding claims, wherein each of the yoke means and the cruciform means are pivotably moveable through fiexure of flexible material, and the first and second cruciform means are formed as a single body having two portions, each moveable with respect to the other.
16. 16. A joint as claimed in claim 15, wherein the single body comprises a substantially planar sheet of flexible material.
17. 17. A constant velocity joint substantially as described herein with reference to Figures 5 to 7 of the accompanying drawings.