WO2009015425A1

WO2009015425A1 - Improvements in constant velocity couplings

Info

Publication number: WO2009015425A1
Application number: PCT/AU2008/001093
Authority: WO
Inventors: Joseph Scalzo
Original assignee: Scalzo Automotive Research Pty Ltd
Priority date: 2007-07-30
Filing date: 2008-07-29
Publication date: 2009-02-05

Abstract

A double Cardan type of coupling, to achieve equal angular velocities, has first and second members rigidly connectable to an end of respective first and second shafts rotatable on first and second axes. The first member is pivotally coupled to a hub member, and a yoke with which the second member is pivotally coupled is disposed around and pivotally coupled to the hub. The first and second members are respectively pivotable relative to the hub and the yoke on mutually perpendicular third and fourth axes. The four axes intersect at a geometric centre for the coupling, with the third and fourth axes disposed in a first plane perpendicular to a second plane containing the first and second axes. A control linkage mechanism between the first and second members controls relative pivoting on the third and fourth axes to maintain the first plane as a bisector of an obtuse angle of inclination between the first and second axes, with variation of the obtuse angle of inclination.

Description

Improvements in Constant Velocity Couplings

Field of the Invention

This invention relates to improvements in couplings of the double Carden type, able to transmit a constant velocity between two angled shafts.

Background to the Invention

The end to end transmission of motion between two shafts, to allow for their mutual inclination, is used extensively in industry and in the automotive industry. The simple, single Cardan (or Hooke) joint is said to have been invented by the ancient Greeks in about 300 B.C. and re-invented by the Italian mathematician and physician Gerolamo Cardano in the 16^th Century as a gimbel for a ship's compass. In the 17^th Century, the English mathematician Robert Hooke re-developed the joint for the purpose of transmitting torque. The single Cardan joint is simple in design, robust, efficient and compact. However, as the angle between the input and output shafts increases the speed and torque characteristics of the Cardan joint are compromised.

The single Cardan joint transmits a constant average velocity. The velocity fluctuates semisoidally to give four phases of motion in each revolution. With increase in the. mutual inclination of the shafts (ie with an increase in the working angle by which one shaft departs from axial alignment with the other), the velocity fluctuations increase in amplitude and frequency. The characteristics can be cancelled out by coupling the shafts by two Cardan joints spaced by an intermediate shaft, to form a double Cardan joint. This results in homokinetic rotation of the coupled shafts, but heterokinetic rotation of the intermediate shaft. The intermediate shaft thus has a dynamic effect in that it produces torsional pulsations which are proportional to the square of the product of the working angle and the speed of rotation.

For uniform constant velocities between the coupled shafts, rather than merely constant average velocity, a symmetrical condition must be maintained between the coupled shafts. Thus, the coupled shafts must be parallel to each other and inclined at a common acute angle to the intermediate shaft, or the coupled shafts must be mutually inclined, but again at an acute common angle to the intermediate shaft. However, a symmetrical condition is not always met or sufficiently maintained in dynamic drive systems, such as in motor vehicles, giving rise to additional complications. At high speeds, and with large connected masses, resulting unbalanced inertia forces and torque is transferred to bearings supporting the coupled shafts. This leads to premature and rapid wear of the bearings and the coupled shafts. Even with coupled shafts at small working angles, the high speeds common in modern machines and vehicles cause unacceptable levels of vibrations and noise.

The intermediate shaft can be made very short in order to minimise or eliminate undesirable conditions produced in or by the intermediate shaft. However, this necessitates use of a centering device which constrains the two joints to maintain a common angle between each of the coupled shafts and a transverse plane through the centering device. The centering device usually is a ball joint connection between two internal shafts. The device must be able to withstand considerable loads in maintaining symmetry, and typically necessitates a heavy and bulky coupling.

The solution to problems inherent in a closely coupled double Cardan joint is to eliminate the intermediate shaft. This necessitates bringing the two joints, together to intersect at the intersection of axes of the coupled shafts. However, an assembly of such a double Cardan joint without an intermediate shaft creates an encircling outer yoke on which one of the coupled shafts is to be mounted. Without a control device to restrain the yoke the joint would fail. A suitable control device must maintain the yoke in the homokinetic or bisecting plane if uniform constant velocity is to be achievable. This is a plane which passes through the axes of the coupled shafts and which is perpendicular to a plane containing those axes. The control device usually is mounted on the yoke at 90° to the one of the coupled shafts mounted on the yoke. The angular position of the control yoke must be at the bisecting angle between the axis of one shaft and the extended axis of the other shaft, Many attempts have been made in the past to find a simple and practical control device enabling uniform constant velocity transmission between coupled shafts. However, these generally have been impractical, difficult to implement and/or assemble, or they weaken the torque carrying capacity of the joint, are difficult to lubricate, or too large and bulky to be practical.

The difficulty of developing a suitable control device for a double Cardan constant velocity coupling, without an intermediate shaft, has led some to depart from the Cardan joint. One line of departure commenced with US patent 1665280 to Rzeppa, and was followed by an improvement disclosed in US patent 2010899 also to Rzeppa. Large versions of the arrangement of the '899 patent have been used, but the main relevance of the arrangement is that it led through successive modifications to ball constant velocity joints, which came to achieve extensive use in motor vehicles.

The arrangement of US 1665280 includes outer and inner ball race members provided with registering, curved, ball-receiving grooves. A ball cage between the race members carries balls within the grooves to lock the race members to rotate together. A socket at an end of one of the shaft is receivable over the unit and the outer race is locked and rotatable with the socket. An end of the other shaft is receivable in and rotatable with the inner race.

US 2010899 starts with the recognition that a coupling unit as disclosed in the '280 patent has limitations. It is appreciated that the coupling unit of the '280 patent will transmit constant speed rotation between the shafts provided the balls that transmit the torque are in a plane midway between the planes of rotation of the race members when the axes of the race members are mutually inclined. However, it is found that when the shafts are adjusted angularly from a position at or near to axial alignment, there is nothing in the coupling unit of the '280 patent to compel adjustment of the ball cage to position the balls in the midway plane. As a consequence, there will be a binding action preventing the angular adjustment. To overcome the problem with the coupling unit of the '280 patent, the proposal of the '899 patent is to add a linkage between the race members which compels angular movement of the ball cage which is substantially half the relative angular movement between the race members. The linkage comprises a lever having a spherical bearing at each end engaged in a respective end recess of each of the coupled shafts and having an intermediate spherical bearing engaging a cylindrical recess in the ball cage. The cylindrical recess may be in a part-spherical ball cage of integral form, or in a part-spherical portion of the ball cage which is separable from a portion of the cage for carrying the balls. The length of the lever and the position of its intermediate bearing are such as to compel the required angular positioning of the ball cage and, hence, of the balls.

Figure 1 shows a joint proposed in the '899 patent for coupling shafts B and D. The coupling has an outer spherical member A integral with shaft B, and an inner spherical member C in which shaft D is retained in a splined connection. The inner surface of member A has what are referred to as meridian ball races F each opposed to a meridian ball race G in the outer surface of member C. A spherical cage E between members A and C holds a respective ball I in each opposed pair of races F and G.

Further features are necessary in the joint of Figure 1 in order to prevent a binding action that will resist or prevent desired angular adjustment of the relative inclination between shafts B and D. Binding is avoided if, despite change in that relative inclination, the balls I adjust so as to remain centred in a common plane through the point of intersection of the axes of shafts B and D, with the common plane both perpendicular to a plane containing the axis of the shafts and at an equal angle to the axis of each shaft. The common plane thus is perpendicular to a line which bisects the working angle by which the axis of one shaft departs from axial alignment with the axes of the other shaft. The joint of Figure 1 has a link arrangement comprising a part spherical member J and a pilot pin K for maintaining the balls I centred in a common plane. The link is such that, with relative angular movement between the shafts B and D, the cage E is compelled to move angularly by pin K and member J through substantially one-half the relative movement of spherical members A and C with the shafts, thereby adjusting the position of the balls.

In the joint of the '899 patent shown in Figure 1 the assembly procedure and the limited space at the rear of the inner and outer ball races, prevent the intermediate spherical bearing K¹ of the pin K in contact with the member J, to be held captive. This requires a spring P within a bore of the respective shaft B acting on spherical end M, to force the pin K against the semi-spherical faces K² of the member J.

The present invention seeks to provide an improved double Cardan constant velocity universal joint without an intermediate shaft.

Broad Summary of the Invention

According to the present invention, there is provided a double Cardan type of coupling, able to transmit torque between shafts coupled end to end by the coupling to achieve equal angular velocities, wherein the coupling has a first member rigidly connectable or connected to an end of a first one of the shafts for rotation of the first shaft on a first axis, a second member rigidly connectable or connected to an end of a second one of the shafts for rotation of the second shaft on a second axis, a hub member to which the first member is pivotally coupled, and a yoke disposed around and pivotally coupled to the hub with the second member pivotally coupled to the yoke, wherein the first member is pivotable relative to the hub on a third axis and the second member is pivotable relative to the yoke on a fourth axis perpendicular to the third axis, with the first, second, third and fourth axes all intersecting at a geometric centre for the coupling and with the third and fourth axes disposed in a first plane perpendicular to a second plane in which the first and second axes are contained; and wherein the coupling further includes a control linkage mechanism between the first and second members for controlling relative pivoting on the third and fourth axes to maintain the first plane as a bisector of an obtuse angle of inclination between the first and second axes, with variation of the obtuse angle of inclination. As will be appreciated, as end to end coupled rotatable shafts depart from end to end axial alignment, their axes intersect at an acute angle, usually not exceeding about 30°, with there simultaneously being a complementary obtuse angle between the axes. In relation to the present invention acute and obtuse are used in relation to such complementary angles.

In one form, the control linkage mechanism includes a control yoke and a control link which interact to control the relative pivoting on the third and fourth axes. In that form, the control yoke preferably is pivotally coupled on the fourth axis to the yoke disposed around the hub. Also, the control link extends through and is journalled in the control yoke and has first and second ends by which it cooperates with the first member and the second member, respectively. The control link most preferably is journalled in the control yoke by a ball and socket engagement centred on a line through the geometric centre of the coupling and perpendicular to the first plane. That is, the ball and socket engagement is centred on the bisector of an acute angle of inclination between the first and second axes.

The cooperation between an end of the control link and the respective one of the first and second members may be by engagement between the end and the member. Alternatively, the cooperation may be between the end of the control link and the shaft of, or when connected to, the respective member. In each case, the end of the link may locate in an axial bore or bearing bush of the member or shaft. The end most preferably has a spherical enlargement by which the link engages the member or shaft.

The ball and socket engagement between the control yoke and the control link preferably is provided by a spherical enlargement of the link which is retained in an annular, part spherical seat defined by the control yoke.

In a first embodiment of the invention, the hub comprises a cruciform member. In that embodiment, the cruciform member has a first pair of arms which extend oppositely on the third axis and a second pair of arms which extend oppositely on the fourth axis. The first member preferably is a yoke such as of

U-shape journalled on the first pair of arms, with the yoke disposed around the hub journalled on the second pair of arms. In that first embodiment, the control yoke may be journalled on the second pair of arms of the cruciform member, or the control yoke may be journalled on a respective extension pin engaged with each of the arms of the second pair.

The third yoke may be in the form of a ring. The form may be square, rectangular, circular or elliptical or other convenient form.

In a second embodiment, the yoke disposed around the hub is a first yoke, with the hub comprising a second yoke. The second yoke also may be in the form of a ring, such as of square, rectangular, circular or elliptical form. In the second embodiment, the first member may be in the form of a boss located within the second yoke and pivotable relative to the second yoke on pins or trunnions extending oppositely on the third axis.

The second member preferably comprises a yoke, such as of U-shape.

Detailed Description of the Drawings

In order that the invention may more readily be understood, description now is directed to the accompanying drawings, in which:

Figure 1 is a cross-sectional view of a prior art universal joint;

Figure 2 is a perspective view of the assembled constant velocity coupling according to a first embodiment of the present invention;

Figure 3 is a partially exploded perspective view of the coupling of Figure 2;

Figures 3a to 3c show respective components of the coupling of Figure 1 ; Figure 4 is a cross sectional view of the coupling of Figure 2 through one axis, but with the input and output shafts at the maximum angle;

Figure 5 is a cross sectional view of the coupling of Figure 2 rotated by 90 degrees from the view of Figure 4, with the input and output shafts at the maximum angle;

Figure 6 is a cross sectional view of the coupling of Figure 2 through the same axis of Figure 5 but with the input and output shafts in line;

Figure 7 is a side elevation of a component of the coupling of Figure 2;

Figure 8 is a graph showing the control yoke angle error against input and output shaft angle for a typical coupling;

Figure 9 is a perspective view of the assembled constant velocity coupling according to a second embodiment of the present invention;

Figure 10 is a partially exploded perspective view of the coupling of Figure 9;

Figures 10a to 10c show respective components of the coupling of Figure 9;

Figure 11 is a cross sectional view of the coupling of Figure 9 though one axis, but with the input and output shafts at the maximum angle;

Figure 12 is a cross sectional view of the coupling of Figure 9 rotated by 90 degrees from the view of Figure 11 and with the input and output shafts at the maximum angle;

Figure 13 is a cross sectional view of the coupling of Figure 9 through the same axis of Figure 11 but with the input and output shafts in line;

Figure 14 is a cross sectional view of an alternate control mechanism able to be applied to the couplings of Figures 2 and 9; and Figure 15 is a cross sectional view of the main components of the alternate control mechanism of Figure 14 in an in-line configuration.

Figures 2 to 6 illustrate a coupling 10 by which mutually inclined first and second shafts 12 and 14 are coupled end to end. The coupling 10 allows the transmission of torque between shafts 12 and 14, at a substantially constant velocity and at any angle within allowable or designed limits of the coupling. One of shafts 12 and 14 may be adjusted relative to the other from an axial in- line position through an acute or working angle of up to about 30°.

Shaft 12 is designated as an input shaft, with shaft 14 designated as an output shaft. However, coupling 10 enables this designation to be reversed, as coupling 10 can be driven from either direction.

The coupling 10 of Figures 2 to 6 has a geometric centre 16 (see Figure 4) at which the first and second axes 12" and 14' of shafts 12 and 14 intersect. Coupling 10 includes a principal supporting element comprising a hub in the form of a cruciform cross member 18. Centred on a third axis X-X, member 18 has a first oppositely extending pair of trunnions 26 and, centred on a fourth axis Y-Y, member 18 has a second oppositely extending pair of hollow trunnions 44. The axes X-X and Y-Y are in a common plane and at right angles to each other, while member 18 is retained in coupling 10 with the intersection of axes X-X and Y-Y co-incident with geometric centre 16.

The input shaft has a first member, comprising an input yoke 20, formed on or made to be integral with its end. For ease of assembly the yoke 20 and an end cap 22 are bolted together at the split line for journals 24 defined by yoke 20 and cap 22. Prior to bolting cap 22 to yoke 20, member 18 is positioned against yoke 20 with its trunnions 26 and trunnion bearings 28, such as needle roller bearings, positioned to be retained in journals 24 when cap 22 is bolted to yoke 20. In this way, yoke 20 and cap 24, as an assembly, are able to reversibly rotate on axis X-X through a sufficient angular range for part of the range of relative angular adjustment between shafts 12 and 14. The arrangement prevents movement of yoke 20 with respect to member 18 along the axes of shaft 12.

The assembly of yoke 20, cap 22 and member 18, with trunnions 26 rotatably secured in journals 24, is located within and coupled to a yoke ring 36. As shown, ring 36 has a respective journal 38 on each of opposite sides in each of which there is a bearing 40. The journals 38 and bearings 40 are axially in line and spaced so that a respective trunnion 44 of member 18 is located in each bearing 40. Thus, ring 36 is disposed around hub member 18 and is reversibly rotatable via journals 38 on trunnions 44 and, hence, on the axis Y- Y. To enable this arrangement, ring 36 has a main ring-shaped body 38 which defines one half of each journal 38, with the other half of each journal 38 defined by a respective bearing cap 46 bolted to body 38.

In the arrangement shown, ring 36 is of a somewhat square form, with each journal 38 centrally located at one of opposed sides, although other forms, such as rectangular other than square, circular or elliptical, can be used. In any event, the ring 36 includes two axially inline, outwardly extending trunnion pins 42. Each of the pins 42 may be pressed into a respective bore in the ring 36 or, alternatively, the ring may be split along a plane containing the axes of journals 38 and such bores to provide sections which are bolted together to retain pins 42. The common axis of the pins 42 is in a plane which is mid-way between journals 38 and which, with ring 36 mounted on member 18, contains the X-X axis and is perpendicular to the Y-Y axis.

The shaft 14 has a second member, comprising an output yoke 48, formed on or made to be integral with its end. The yoke 48 has laterally spaced arms each defining a respective journal 50. The yoke 48 is reversibly rotationally mounted on trunnion pins 42 via journals 50 and a respective trunnion bearing located in each journal 50. This mounting of yoke 48 secures shaft 14 against axial movement relative to shaft 12. Thus, the trunnion pins 42 enable completion of coupling between shafts 12 and 14 to form a double Cardan joint of coupling 10. In the structure of the double Cardan joint of coupling 10, the yoke ring 36 is to be constrained in its movement. This is necessary in order that there is transmission of constant velocity between shafts 12 and 14. To constrain the movement of yoke ring 36, coupling 10 includes a control mechanism 54.

Mechanism 54 includes a U-shaped control yoke 56 and an elongate control link 66. The yoke 56 defines a respective journal 60 at each of its ends by which yoke 56 is pivotally mounted on yoke ring 36 so as to be reversibly pivotable, within yoke 48, on the Y-Y axis. For this, a respective trunnion bearing 62 and respective trunnion pin 58 is located in each journal 60, with each pin 58 inserted into and forming an extension of a respective trunnion pin 44. For ease of assembly, each pin 58 may be screwed into its trunnion pin 44. At its mid-section or web, yoke 56 is increased in thickness and has a central opening 65. Within that thickness opening 65 is stepped to define in a direction away from yoke 36 a bore 76 and, from the step, to define a part- spherical journal surface 64. The surface 64 faces towards ring yoke 36 and has a centre of curvature which is at a designed distance from the geometric centre 16 of coupling 10. The opening 65 is in a plane parallel to the rotational axis of journals 60 and the Y-Y axis.

The elongate control link 66 of control mechanism 54 has three in-line spherical surfaces 68, 70 and 72, herein referred to as spheres. As shown most clearly in Figure 7, spheres 68 and 72 are at respective ends of link 66, while sphere 70 is adjacent to sphere 68. The sphere 70 has a radius substantially equal to the radius of curvature of journal surface 64. Sphere 72 is smaller than sphere 70 and able to fit through central opening 65 to seat sphere 70 against surface 64, where it is retained by part-spherical ring 74 secured in bore 76. With link 66 positioned to achieve this, it is able to cooperate through sphere 72 with shaft 14 and through sphere 68 with shaft 12. The arrangement is such that control mechanism 54 provides a connection via link 66 between control yoke 56 and each of shafts 12 and 14, to control the position of the yoke ring 36. The control of the position of ring 36 is such as to maintain ring 36 in a respective position for each working angle of shaft 14 relative to shaft 12 which enables constant velocity transmission between shafts 12 and 14.

On passing of sphere 72 through opening 65, sphere 68 is located in a bearing bush 34 fitted in a bore 32 defined in a boss 30 of end cap 22 (see Figure 3a).

The axis of bore 32 is co-incident with the axis 12' of shaft 17. Thus, sphere

68 is constrained such that its centre is on the axis 12' of shaft 12, although sphere 68 is able to swivel, rotate and move axially within bush 34. Also, the sphere 72 is retained in a bearing bush 78 which is located in a bore 80 of shaft 14, with the bore 80 co-axial with the axis 14' of shaft 14. The sphere 72 is able to swivel and rotate on, and to move along, axis 14'

Returning to Figures 4 and 7, the distance "c" between centres for spheres 68 and 70 relative to the distance "d" between centres for spheres 70 and 72 is determined to ensure there is a centre of spherical connection 84, between the part spherical surface 64 of control yoke 56 and the sphere 70, which is located on a line L bisecting the angle between the axes 12' and 14' of shafts 12 and 14. That is the line L is at the same angle β to each of axes 12' and 14'.

The control mechanism 54 can allow a small error in the angular positioning of control yoke 56 relative to a respective optimum position for each working angle of inclination of shaft 14 relative to shaft 12. This can result in an angle error which varies with the angle between axes 12' and 14', and with the distance "d" between centres for spheres 70 and 72. Figure 8 is a graph showing the maximum angular shaft error between the input shaft 12 and output shaft 14 during one revolution over an angle range of 0° to 30° of the inclination between axes 12' and 14'. It can be observed that the angle error is within ±0.025° between 0° and 25° for the inclination between axes 12' and 14', for a given value of "d". Even with an increase in that range to 30°, the angle error still does not exceed about 0.12° which is quite acceptable. The effects of such small angle error on the constant velocity characteristics of the coupling 10 are within manufacturing tolerances for industrial and automotive couplings having a considerable number of bearing elements all contributing to backlash errors. The angle error for coupling 10 can be altered and minimised even further, below the levels indicated above, if the operating or working range of angles of the indication of one shaft relative to the other is known for a specific application. This is achieved by adopting a control link 66 having a suitable, different length "d". In this way the angle error can be reduced substantially to zero.

The coupling 10 preferably is prevented by provision of mechanical stops from exceeding designed angular limits for shafts 12 and 14. In the plane illustrated in Figure 4, one of two cylindrical portions 86 of cross member 18, each between a respective trunnion pin 44 and the X-X axis, is able to come into contact with a respective angle face 88 on end cap 22 for each direction of rotation of yoke 20 about the X-X axis on pins 26. In the plane shown in Figure 5, each of two diametrically opposite sides of the conical face 90 on input yoke 20 comes into contact with a respective part of the internal face 92 of ring yoke 36 at each limit of opposite rotation of the input yoke 20 about the

Y-Y axis on trunnion pins 44 of cross member 18. These respective sets of limits prevent sphere 68 of control link 68 from moving out of bearing bush 34 fixed on end cap 22.

The coupling 10 is able to provide for ease of lubrication through channels drilled through cross member 18, along the X-X and Y-Y axes, with trunnion pins 58 communicating through a port 94 in one of the trunnion bearings 92 for all bearings on member 18. Trunnion pins 42 on ring yoke 36 are able to be lubricated via ports 96 and 98 in yoke 36. A respective grease nipple (not shown) is able to be fitted to each of ports 94, 96 and 98.

As shown in Figure 6 (but not in other Figures for ease of illustration) lubrication of the spheres 68 and 70 is provided by respective flexible membranes 100 and 104. The membrane 100 is mounted between boss 30 of end cap 22 and the internal face of control yoke 56, creating a sealed lubricant chamber 102. Membrane 104 is mounted between the outer face of yoke 56 and an inner face of output yoke 48 to create a sealed lubricant chamber 106. In coupling 10 lubricant is also retained within the space of bearing bushes 34 and 78 and the lubricant can flow to the bearing surfaces via passage 83 in control link 66. A radial hole 87 feeds lubricant to the circumferential groove 89 of sphere 70. As indicated, membranes 100 and 104, and chambers 203 and 106 have not been included in Figures 2 to 5.

Figures 9 to 13 illustrate a coupling 110 according to a second embodiment of the present invention. Many components of coupling 110 are similar to those of coupling 10 of Figures 2 to 7 and, where this is the case, the same reference numerals plus 100 are used. Also, as functioning of the coupling 110 generally will be understood from the description in relation coupling 10, the description of coupling 110 will be limited to the principal features by which it differs from coupling 10.

The coupling 110 incorporate an input shaft 112 and an output shaft 114. It is the purpose of this invention to allow the transmission of torque between the two shafts 112 and 114 at a substantially constant velocity at any angle within the allowable or designed limits of the coupling.

The geometric centre 116 of the coupling 110 refers to the point of intersection of the axes of the input and output shafts 112 and 114. The principal difference between coupling 110 and coupling 10 is the replacement of cross member 18 in coupling 10 with (as shown in Figures 10a and 10b) a ring shaped inner yoke 200 and input shaft 112 with a boss 202 with bore 204 perpendicular to, and intersecting, the axis of input shaft 112. Shaft 206 with trunnion pins 208, is rigidly mounted in bore 204 allowing input shaft 112 to pivot on the trunnion pins 208 by pins 208 being located through inner yoke journals 210 along axis X1-X1, via trunnion bearings 128, usually needle roller bearings. Boss 202 is axially located between internal faces 212 of inner yoke 200. The input shaft 112 extends further to create another cylindrical boss 130 with bore 132 concentric with the axis of the input shaft 112. A bearing bush 134 is fixed in bore 132. Trunnion pins 213 are rigidly mounted on inner yoke 200 perpendicular to journals 210 along the Y1-Y1 axis. A ring shaped outer yoke 136 has journals 138 with bearings 140 and trunnion pins 142 mutually perpendicular to one another. Journals 138 with bearings 140 are rotationally mounted and axially fixed on trunnion pins 213 of inner yoke 200 along axis Y1-Y1. To allow ease of assembly, the outer yoke 136 may be split along a plane containing the axes of the journals and trunnion pins, to provide parts of yoke 136 which are bolted together (by bolts not shown).

The output yoke 148 integral with output shaft 114 (or mounting flange), is rotationally mounted but axially fixed, on trunnion pins 142 via journals 150 on output yoke 148, and trunnion bearings 152.

To achieve constant velocity between the input and output shafts 112 and 114 respectively, outer yoke 136 needs to be constrained in its movement by the control mechanism 154 through the action of control yoke 156. The control yoke 156 is pivotally mounted on the outer yoke 136 by trunnion pins 158 on inner yoke 200 along the Y1-Y1 axis via split journals 160 and trunnion bearings 162 rigidly held by bearing caps. Trunnion pins 158 are an extension of trunnion pins 213 and may be of smaller diameter.

The function of the control mechanism 154 is identical to that of control mechanism 54 in coupling 10. The elements of the control mechanism 154 include the control yoke 156 with its central part spherical journal surface 164; the control link 166 with spherical surfaces 168, 170 and 172; spherical retainer 174; bearing bush 134 in bore 132 of input shaft 112 extension 130, and bearing bush 178 in bore 180 of output shaft 114. The assembly of all of these elements is illustrated in Figures 11 , 12 and 13.

The coupling 110 is prevented from exceeding its angular limits between the input and output shafts 112 and 114 respectively by mechanical stops. In one plane as shown in Figure 11 , the cylindrical portion of input shaft 112 comes in contact with angled faces 284 on inner yoke 200 as shown in Figure 11 as the input shaft boss 202 rotates about axis X1-X1 on trunnion pins 208 of shaft 206. In the plane as shown in Figure 12, the angled faces 220 on inner yoke 200 comes in contact with the internal face 222 of outer yoke 136 as the inner yoke 200 rotates about axis Y1-Y1 on trunnion pins 213 of inner yoke 200. These stops also prevent sphere 168 of control link 166 from moving out of bearing bush 134 fixed in boss 130.

The coupling 110 provides for ease of lubrication through channels drilled in the input shaft 112; shaft 206 and control link 166 via port 224 on one side of input shaft 112. Lubrication of bearings 140 and 162 on the outer yoke 136 and control yoke 156 respectively, is via channels in trunnion pins 213 and 158 in inner yoke 200, and ports 196 and 198 on the front face of inner yoke 200. A respective grease nipple (not shown) is fitted to each of ports 224, 196 and 198.

Referring to Figure 13, the lubrication of the spherical elements of control link 166 in the control mechanism 154 is achieved by providing a flexible membrane 226 mounted between boss 130 and the internal face of control yoke 156 creating sealed chamber 228. A second flexible membrane 230 is mounted between the outer face of control yoke 156 and an inner face of output yoke 148 (or output shaft 114) to create sealed chamber 232. In coupling 110, the lubricant to the spherical elements is also fed via port 224 with drilled channels communicating with the chamber within bearing bush 134 and channel 183 within control link 166 in a similar manner to coupling 10.

The characteristics and angle error as illustrated by the graph in Figure 8 for coupling 10, also applies to coupling 110.

Figures 14 and 15 illustrate a coupling 210 which has an alternative form of control mechanism 254. Many components of Figures 14 and 15 are similar to those of coupling 110 of Figures 9 to 13 respectively, where this is the case, the same reference numerals as in Figures 9 to 13, plus 200 are used. It is to be understood that this alternate control mechanism 254 can be applied to both couplings 10 and 110 of Figures 2 and 9. The control mechanism 254 allows connection between control yoke 256 and the input and output shafts 212 and 214, respectively, to control the position of the outer yoke 236. The principal component of the control mechanism 254 is the control link 266 with two spherical surfaces 268 and 272 at its extremities.

Sphere 268 is retained in ball socket 234 axially fixed to extension 230 of input shaft 212. Sphere 268 can swivel and rotate within ball socket 234. Sphere

272 is retained in ball socket 278 in bore 280 of extension 282 of output shaft

214 and can swivel and rotate within bush 278. The ball socket 278 can also move axially in bore 280.

Spherical bush 270 mates with the semi-spherical journal 264 in control yoke 256 and is retained in the swiveling position by the semi-spherical element 274. Spherical bush 270 is slideable and rotatable on the inner shaft portion of control link 266.

To ensure that the centre of the spherical connection between the spherical journal 264 of control yoke 256 and spherical bush 270 are on a line bisecting the angle between the axes of output shaft 214 and the extension of the input shaft 212 axis (as per Figure 4), it is necessary for the position of ball socket 234 relative to the geometric centre 316 of the coupling 210, the radial distance of the centre of control yoke 256 relative to the geometric centre 316, and the distance between sphere 268 and 272 formed in control link 266, to be determined to produce the desired characteristics of the coupling. Similar characteristics of the angle error as illustrated by the graph in Figure 8 for coupling 10, also applies to coupling 210.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Claims

CLAIMS:

1. A double Cardan type of coupling, able to transmit torque between shafts coupled end to end by the coupling to achieve equal angular velocities, wherein the coupling has a first member rigidly connectable or connected to an end of a first one of the shafts for rotation of the first shaft on a first axis, a second member rigidly connectable or connected to an end of a second one of the shafts for rotation of the second shaft on a second axis, a hub member to which the first member is pivotally coupled, and a yoke disposed around and pivotally coupled to the hub with the second member pivotally coupled to the yoke, wherein the first member is pivotable relative to the hub on a third axis and the second member is pivotable relative to the yoke on a fourth axis perpendicular to the third axis, with the first, second, third and fourth axes all intersecting at a geometric centre for the coupling and with the third and fourth axes disposed in a first plane perpendicular to a second plane in which the first and second axes are contained; and wherein the coupling further includes a control linkage mechanism between the first and second members for controlling relative pivoting on the third and fourth axes to maintain the first plane as a bisector of an obtuse angle of inclination between the first and second axes, with variation of the obtuse angle of inclination.

2. The coupling of claim 1 , wherein the control linkage mechanism includes a control yoke and a control link which interact to control the relative pivoting on the third and fourth axes.

3. The coupling of claim 2, wherein the control yoke is pivotally coupled on the fourth axis to the yoke disposed around the hub, and the control link extends through and isjournalled in the control yoke and has first and second ends by which it cooperates with the first member and the second member, respectively.

4. The coupling of claim 3, wherein the control link is journalled in the control yoke by a ball and socket engagement centred on a line through the geometric centre of the coupling and perpendicular to the first plane, so that the ball and socket engagement is centred on the bisector of an acute angle of inclination between the first and second axes.

5. The coupling of claim 4, wherein cooperation between an end of the control link and the respective one of the first and second members is by engagement between the end and the member.

6. The coupling of claim 4, wherein the cooperation is between the end of the control link and the shaft of, or when connected to, the respective member.

7. The coupling of claim 5 or claim 6, wherein the end of the link locates in an axial bore or bearing bush of the member or shaft.

8. The coupling of claim 7, wherein the end has a spherical enlargement by which the link engages the member or shaft.

9. The coupling of any one of claims 4 to 8, wherein the ball and socket engagement between the control yoke and the control link is provided by a spherical enlargement of the link which is retained in an annular part spherical seat defined by the control yoke.

10. The coupling of any one of claims 1 to 9, wherein the hub comprises a cruciform member which has a first pair of arms which extend oppositely on the third axis and a second pair of arms which extend oppositely on the fourth axis.

11. The coupling of claim 10, wherein the first member is a yoke, such as of U-shape, journalled on, the first pair of arms, with the yoke disposed around the hub journalled on the second pair of arms.

12. The coupling of claim 10 or claim 11 , when appended to any one of claims 3 to 9, wherein the control yoke is journalled on the second pair of arms of the cruciform member, or on a respective extension pin engaged with each of the arms of the second pair.

13. The coupling of any one of claims 10 to 12, wherein the yoke disposed around the hub is in the form of a ring of square, rectangular, circular, elliptical or other ring form.

14. The coupling of any one of claims 1 to 9, wherein the yoke disposed around the hub is a first yoke, with the hub comprising a second yoke.

15. The coupling of claim 14, wherein the second yoke is in the form of a ring, such as of square, rectangular, circular or elliptical form.

16. The coupling of claim 14 or claim 15, wherein the first member is in the form of a boss located within the second yoke and pivotable relative to the second yoke on pins or trunnions extending oppositely on the third axis.

17. The coupling of any one of claims 1 to 16, wherein the second member comprises a yoke, such as of U-shape.