Abstract:
A flexible coupling capable of transmitting moments and comprising a first member having a longitudinal axis ( 30 ) connected by at least three joints ( 27 ) to a second member ( 41 ) having a longitudinal axis substantially aligned with the longitudinal axis of the first member, the joints being circumferentially spaced apart about said axis, each joint comprising a first part ( 27 ) on one of the members and a second part ( 31 ) on the other member, the parts of each joint interfitting so that moments can be transmitted between said members by the joints and so that relative sliding and rotational movement can take place between the parts of teach joint, the joint parts on at least one of the members being flexibly arranged ( 41 ) so that the members may articulate relative to one another.

Description:
TECHNICAL FIELD 
     This invention relates to a flexible coupling. The invention is particularly applicable to flexible couplings which include parts made of plastic material, e.g. fiber reinforced epoxy, polyamide or other resin. 
     BACKGROUND ART 
     Numerous types of flexible couplings are known for connecting two shafts in driving engagement. In one type, there is a thin flexible disc to which each shaft is joined by three, circumferentially-spaced, bolted or other rigid connections. Such connections impose strains on the disc in addition to those required for torque transmission and articulation. These strains are associated with additional stresses which reduce the torsional strength and fatigue life of the coupling. 
     The present invention provides a coupling in which shafts, for example, may be joined to a flexible element by connections with additional degrees of freedom so that the stresses and strains on the flexible element are reduced as compared with the above type of coupling and the life of the coupling thereby increased. 
     The present invention also increases, with respect to prior art couplings, the maximum articulation angle of the coupling as well as its maximum continuous running angle. Further, the invention provides a coupling in which the stresses are reduced so that the coupling may include a flexible element made from a relatively low cost plastic material, such as fiber-reinforced epoxy, polyamide or other resin, and which may be manufactured easily, for example by injection molding. 
     The coupling of the invention may also be used as a static coupling for connecting two non-rotating parts so that moments may be transmitted across the coupling. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention we provide a flexible coupling capable of transmitting moments and comprising a first member having a longitudinal axis connected by at least three joints to a second member having a longitudinal axis substantially aligned with the longitudinal axis of the first member, the joints being circumferentially spaced apart about said axes, each joint comprising a first part on one of the members and a second part on the other member, the parts of each joint interfitting so that moments can be transmitted between said members by the joints and so that relative sliding and rotational movement can take place between the parts of each joint, the joint parts on at least one of the members being flexibly arranged so that the members may articulate relative to one another. 
     According to a second aspect of the invention we provide a flexible coupling capable of transmitting torque and comprising a first member having a rotary axis connected by at least three joints to a second member having a rotary axis, the joints being circumferentially spaced apart about said axes, each joint comprising a first part on one of the members and a second part on the other member, the parts of each joint interfitting so that torque can be transmitted between said members by the joint and so that relative sliding and rotational movement can take place between the parts of each joint, the joint parts on at least one of the members being flexibly arranged so that the members may articulate relative to one another. 
     According to a third aspect of the invention we provide a flexible coupling capable of transmitting torque from a first member having a rotary axis via a second member to a third member having a rotary axis, the first member being connected to the second member and the second member being connected to the third member by joints, there being at least three joints between the first and second members and between the second and third members respectively, the joints being circumferentially spaced about said axes, each joint comprising a first part on one of the members which is connected by the joint and a second part on the other connected member, the parts of each joint interfitting so that torque can be transmitted between said members by the joint and so that relative sliding and rotational movement can take place between the parts of each joint, the joint parts on at least one of the members being flexibly arranged so that the first and third members may articulate relative to one another. 
     Each joint may comprise a pin carried by one of the members and a socket carried by the other member, the pin fitting into the socket so that torque can be transmitted by the joint and so that relative sliding and rotational movement can take place between each pin and the socket which receives it. 
     The joint parts may be mounted flexibly on only one member or may be mounted flexibly on more than one member. 
     The pins or sockets may be mounted on a ring and interconnected by flexible elements or the pins and/or sockets may be mounted on a rigid member to which they are connected by flexible elements. 
     The longitudinal axes of the sockets and pins may be in a single plane or the axes of some of the sockets and pins may lie in one plane and the longitudinal axes of the remaining sockets and pins lie in a second plane parallel to the first plane. 
     The sockets and/or pins may be connected by flexible elements which are bowed in shape. 
     The sockets may be formed by inserts received in bores in a ring, the bores being flexibly interconnected. The pins may have part-spherical heads received in cylindrical bores in the sockets or they may have cylindrical surfaces which are engaged with cylindrical bores in the sockets or inserts. The joints may be pin and socket joints with the pins detachably connected to the member on which they are carried. 
     The first member may comprise a wheel having internally projecting radial pins, the second member comprising a ring on which sockets are mounted, the sockets being inter-connected by flexible members, some of the sockets receiving the pins on the wheel and the third member having outwardly projecting pins which are received in the remainder of the sockets. The sockets may contain inserts in the form of bushes in which the pins are received. The inserts may be a snap-fit into the sockets. 
     The coupling may include a flexible annular disc having sockets secured thereto at positions spaced equi-angularly about the disc and two members each having a rotary axis and a plurality of outwardly projecting pins and wherein the pin&#39;s of each of the two members are received in alternate sockets on the disc. All the sockets may be arranged to project inwardly from the disc and the pins on the members project outwardly. Alternatively the sockets may project inwardly and outwardly from the disc and each of said members may have radially inwardly and outwardly directed pins which are received in the inwardly and outwardly directed sockets respectively. 
     The coupling may include sockets formed in or carried by a ring which comprises two parts which are detachably secured together, each said ring part providing a portion of each socket so that when the ring parts are secured together the socket portions are aligned to form the sockets, each ring part including flexible elements which inter-connect the socket portions on the ring part. The ring parts may be identical and may clip together. The ring parts may be prevented from becoming detached from each other by inserts received in the sockets and which receive the pins. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an exploded perspective view of a first embodiment of the invention; 
         FIG. 1B  illustrates an alternative type of trunnion. 
         FIG. 2  is an exploded perspective view of a second embodiment of the invention; 
         FIG. 3  is an exploded perspective view of a third embodiment of the invention; 
         FIG. 4  is a perspective view of a form of torque transmitting member which may be used in a coupling according to the invention; 
         FIGS. 5 and 6  are cross-sections through additional forms of torque-transmitting members; 
         FIG. 7  is an exploded perspective view of a further embodiment of the invention. 
         FIG. 8  is a partial exploded perspective view of a still further embodiment of the invention; 
         FIG. 9  is a diagram of another embodiment of the invention; 
         FIG. 10  is a diagram of another embodiment similar to  FIG. 9 ; 
         FIG. 11  is a section through a further embodiment of the invention; and 
         FIG. 12  is an exploded perspective view showing the invention applied to a wheel; 
         FIG. 13  is an end view of the wheel of  FIG. 12 ; and 
         FIG. 14  is a perspective view showing a coupling in which the ring carrying the sockets comprises two detachable parts. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1A , the coupling comprises a first member  10  having a rotary axis  10   a  and which includes an element  11  for receiving or transmitting drive from or to the first member. The member carries three cylindrical sockets  12  each of which has a cylindrical bore  13 . The sockets  12  are connected to the element  11  by flexible elements  14  and by parts  15 . Preferably the parts  11 ,  12 ,  14  and  15  are made as a single moulding of, for example, fibre-reinforced polyamide. The fibre reinforcement may be glass fibre. The member  10  may be joined to a companion flange, not shown, by bolts  16 . The longitudinal axes of the bores  13  lie in a single plane and the sockets  12  are equi-angularly spaced about the rotary axis  10   a.    
     The coupling includes a second member  17  having a rotary axis  17   a  substantially aligned with the axis  10   a  and which has a shaft  18  and a tubular part  19 . The second member can conveniently be made of metal, e.g. steel, and has three arms  20  projecting from the end thereof. Each arm carries a trunnion  21 , the trinnions being equi-angularly spaced about the axis  17   a , and each trunnion has a reduced-section neck portion  22  and a head  23  which has a cylindrical surface  24 , longitudinal axes of the surface  24  lying in a plane perpendicular to the axis  17   a.    
     The coupling is assembled by inserting the heads  23  of the trunnions  21  into the bores  13  of the sockets  12 . The orientation and position of the sockets  12  is such that the relative movement of the first and second members is constrained in directions parallel to the plane containing the longitudinal axes of the bores  13 . The heads  23  of the trunnions can slide and rotate in the bores  13  and this, and the flexibility of the elements  14 , permits some articulation between the rotary axes  10   a  and  17   a  of the first and second members  10  and  17  and allows a small amount of relative axial movement between the members  10  and  17 . Each socket  12  and trunnion  21  forms a joint to transmit torque between the first and second members, the joints being pin and socket joints. The trunnions  21  may be detachably connected to the member  17  to ease assembly. 
       FIG. 1B  shows an alternative type of trunnion  21   a  having a part spherical surface  24   a . The centres of these surfaces for all the trunnions lie in a plane perpendicular to the rotary axis  17   a.    
     Turning now to  FIG. 2 , the coupling comprises three members; the first and third members are identical. The first member is indicated generally at  25  and is identical in, construction to the second member  17  shown in  FIG. 1A  and will not be described further except to say that the trunnions have heads  26  with circumferential cylindrical surfaces  27 . The third member is shown at  25   a , is identical to the first member  25  and has a rotary axis  25   b.    
     The second member  28  consists of six sockets  29  equi-angularly spaced around the rotary axis  30  and each having a cylindrical bore  31 . The longitudinal axes of the bores  31 , which are indicated at  32 , are equi-angularly spaced around the rotary axis  30  and all lie in a single plane. The coupling is assembled by inserting the heads  27  of the trunnions on the first member  25  into alternate ones of the bores  31  and inserting the heads of the trunnions of the third member  25   a  into the remaining bores  31 . 
     The heads of the trunnions can slide and rotate in the bores but the orientation and position of the bores is such that relative movement of the members to one another in the plane containing the longitudinal axis of the bores  31  is constrained. 
     The sockets  29  are interconnected by flexible elements  41  which are thinner in the middle than at the ends and which form a ring with the sockets  29  so that the second member  28  can be moulded as one piece. The flexible elements  41  are parallel to and include the plane containing the axes  32  of the bores  31 . Articulation of the first and third members is permitted by the flexibility of the elements  41  and the movement of the trunnion heads in the bores  31 . Some relative axial movement is also permitted by the flexibility of the elements  41 . As in  FIG. 1A , each socket  29  and trunnion forms a pin and socket joint connecting the first member to the second member or the second member to the third member. 
     The heads of the trunnions may be steel part-spherical elements instead of steel cylinders such as indicated. The part-spherical shape would be used where the misalignment between the rotary axes  30  and  25   b  of the first and third members is more than minimal and only a low torque has to be transmitted because there would be a high contact pressure between the spherical surface and the bores  31 . The cylindrical heads  26  would be used where there is a low angle of misalignment between said axes and high torque is to be transmitted since the contact pressures between the cylindrical surface and the bores would be less. 
     To aid assembly, the bores  31  may be fitted from the interior or exterior of the member  28  with plugs one of which is indicated at  35  having a flange  36  at one end and a tubular portion  37  at the other. The tubular portion  37  fits into the bore  31  and the head  26  of a trunnion would fit into the bore  38  of the tubular portion. The plugs  35  may be made of a wear-resistant or self-lubricating material. The trunnions could also be detachable. 
     Referring now to  FIG. 3 , this shows a coupling which is similar to  FIG. 2  except that the sockets on the second member  42  are arranged on both sides thereof. Thus there are three sockets  43  which are equi-angularly spaced on one side and three sockets  44  which are equi-angularly spaced on the other side of the member. All the sockets are equi-angularly spaced around the rotary axes of the coupling. The longitudinal axes of the bores in the sockets  43  lie in one plane perpendicular to the rotary axis of the member  42  and the longitudinal axes of the bores of the sockets  44  lie in a second and parallel plane. The sockets are inter-connected by flexible elements  45 . The member  42  is preferably molded in one piece from fiber-reinforced plastic, e.g. glass-reinforced polyamide. Such a coupling can accommodate, as well as angular misalignment, a small radial misalignment between the first and third members  25   c  and  25   d  which have substantially aligned rotary axes  25   e  and  25   f  respectively. 
       FIG. 4  shows the second member  46  for a coupling such as shown in  FIG. 2  or  FIG. 3  of somewhat different shape. The member has six sockets  47  each of which has a cylindrical bore  48 . The longitudinal axes of the bores are indicated by the lines  49  all of which lie in the same plane. The flexible elements  50 ,  51  which join the sockets  47  are in this instance curved so that they lie alternately on different sides of the plane containing the longitudinal axes of the bores  48 . Thus the flexible elements  50  lie on one side of the plane and the flexible elements  51  lie on the other side of the plane. 
     The advantage of this construction is that it has increased torsional compliance and articulation capability. Also if there is a tendency for the flexible elements  50  or  51  to buckle during operation they will not buckle in a bi-stable way, i.e. they will not move from one side of the plane containing the longitudinal axes to the other during operation of the coupling. 
     Referring now to  FIG. 5 , this is a cross-section through another form of second member of a coupling similar to that of  FIG. 2  or  FIG. 3  in which the sockets are arranged in parallel pairs. Thus there are sockets  52  which have bores  53  with parallel longitudinal axes  54 , there are sockets  55  which have bores  56  with parallel longitudinal axes  57  and there are sockets  58  which have bores  59  with parallel longitudinal axes  60 . The sockets are inter-connected by flexible elements  61  in a manner similar to  FIG. 3 . The first and third coupling members will have trunnion heads which engage in alternate sockets. Thus the trunnions  62   a  (shown in full lines) of the first member  62  engage in one each of the sockets  52 ,  55  and  58  and the trunnions  63  (shown in dotted lines) of the third member, not shown, engage in the other alternate sockets. 
       FIG. 6  shows an arrangement similar to  FIG. 5  in which there are sockets in pairs with parallel axes. Thus there are sockets  70  having bores  71  with parallel longitudinal axes  72 ; sockets  73  having bores  74  with parallel longitudinal axes  75  and sockets  76  having bores  77  with parallel longitudinal axes  78 . The bores are shown containing the heads of the trunnions of the first and second members thus the heads of the trunnions of the first member  81  are indicated in full lines at  79  and those of the third member in dotted lines at  80 . 
     Both in  FIG. 5  and in  FIG. 6  the trunnions are slidable and rotatable in the bores of the sockets but the orientations and positions of the bores constrain the first and third members in the plane containing the longitudinal axes of the sockets. All the longitudinal axes of the sockets lie in a single plane. There are flexible elements  82  interconnecting adjacent sockets as described in relation to  FIG. 3 . 
     Referring now to  FIG. 7 , this shows a three member coupling in which there is a first member  83 , a second member  84  and a third member  85 . The first and third members have substantially aligned rotary axes  83   a  and  85   a  respectively. The first member  83  is cylindrical and has three sockets formed in the circumference thereof, two of the sockets being indicated at  86  and the sockets being equi-angularly spaced around the rotary axis of the member  83 . The second member,  84 , is in the form of a one-piece molding and comprises six pins interconnected by flexible elements  87  in the form of a ring. Three of the pins  88  project inwardly from the ring and three of the pins  89  project outwardly from the ring. 
     The third member  85  is a cylindrical member similar to the first member  83  and is also provided with three sockets  90  equi-angularly spaced around the member. The sockets  86  and  90  may have inserts  91  similar to the inserts  35  described in relation to  FIG. 2 . 
     The pins  88  fit into the sockets  86  and the pins  89  fit into the sockets  90 . Thus the first member  83  is connected to the second member  84  by pin and socket joints allowing rotation and sliding between the parts of each joint and the second member  84  is connected to the third member also by similar pin and socket joints. Torque will be transmitted from the first member  83  to the third member  85  through these joints and articulation between the first and third members  83  and  85  and some axial movement will be permitted by the flexibility of the portions  87 . 
     Referring now to  FIG. 8 , a conventional flexible disc is indicated at  100 . The disc comprises six fixing bosses, some of which are shown at  101  interconnected by flexible leaves  102 . One example of such a coupling is shown in DE-A- 41   40   311 . A three-armed spider is indicated at  103  and on the arm  104  are secured two brackets  105  having circular apertures  106 . Mounted on one of the bosses  101  is a pin  107 . The pin has a cylindrical outer surface  108  and a central slot  109 . The boss  101  is received in the slot  109 . The pin  107  is held in position on the disc  100  by a bolt  110  and a nut  111 . The bolt is received in circular bores  112  in the pin  107  which are provided on each side of the slot  109 . The bolt passes through the bores  112  and receives the nut  111 . 
     When the coupling is assembled, the pin  107  is received in the apertures  106  in the brackets  105 . Thus a pin and socket connection is provided the pin being provided by the pin  107  and the socket by the apertured brackets  105 . The pin can slide radially and rotate within the apertures  106 . Although not shown, each arm of the spider  103  would have brackets such as  105  receiving pins such as  107  and there would be a second spider which would receive similar apertured pins such as  113 . 
     In practice, the coupling would be assembled by placing the disc within the brackets  105  in each spider and then assembling the pins from the inside by moving them radially outwardly into the apertures  106  and then securing the pins to the disc by the bolts and nuts  110  and  111 . 
     Referring now to  FIG. 9 , this shows, in diagrammatic form another coupling. As in  FIG. 8 , there is a conventional flexible disc  114  having six, equi-angularly spaced bosses  115  interconnected by flexible leaves  116 . To each boss is connected a cylindrical socket such as  117 , three on one side of the disc and three on the other. Each socket has a cylindrical bore  118  and a lug  119  at its radially outer end. The lug is secured to a boss  115  in a pivotal manner by means of a bolt assembly  120 . Each of the bosses of the coupling is provided with a socket similar to the socket  117  and these are indicated at  121 ,  122 ,  123 ,  124  and  125 . The sockets  117 ,  122  and  124  are on one side of the disc and receive the arms  126 ,  127  and  128  respectively of a three-armed spider  129 . The arms  126 ,  127  and  128  are cylindrical and can slide and turn in the bores  118  of the sockets. The similar arms of a second spider  130  are received in the sockets  121 ,  123  and  125 . 
     In every case the arms of the spiders are cylindrical and can slide and turn in the sockets and the sockets are flexibly interconnected by the leaves  116  of the composite disc. 
       FIG. 10  shows an arrangement similar to  FIG. 9 . Thus there is a composite disc  131  having bosses such as  132  connected by flexible leaves  133 . Connected to each boss  132  is a socket one of which is indicated at  134 . Each socket has two oppositely-facing bores  135  and  136  and in each is received a pin  137  and  138  respectively. The pins  137  and  138  are carried by an arm of a spider, the pins  137  being looped over and connected to the pins  138 . This looping over has been omitted from  FIG. 10  for clarity. 
     There are six sockets such as  134 , three of which are connected to the arms of one spider and three of which are connected to the arms of the other. Three of the sockets are on one side of the disc and three on the other. The pins connected to the spider arms can slide and rotate in the sockets and the sockets are flexibly interconnected by the leaves  133  of the composite disc. 
     Referring now to  FIG. 11 , there is shown a ring  140  made of composite material and this has six bores  141  equi-angularly spaced around the axis of the ring. The bores are interconnected by flexible leaves  142 . Two spiders  143   a  and  143   b  complete the coupling. The spider  143   a  has, referring to  FIG. 11 , three pins  144  extending radially and equi-angularly spaced around the rotary axis  145 . Each pin is received in the bore  156  of a socket  157  having flange  158  at its closed end. The socket is received in a bore  141 . 
     Each pin can rotate and slide in its socket. There are three other pins  149 ,  150  and  151  carried by the other spider  143   b  which slide in sockets similar to the socket  157  which are received in the bores  141 . This arrangement makes for ease of assembly since the ring can be assembled to the two spiders and then the sockets assembled onto the pins of the spiders. The sockets  157  have projections  159  at their open ends which snap under the inner end of the sockets  141  to hold the sockets  157  in place as shown in  FIG. 11 . 
     Referring now to  FIGS. 12 and 13 , a wheel, for example a road wheel of a vehicle, is shown at  160 . The wheel has a disc  161  which has a generally triangular aperture  162 . Projecting radially inwardly from each side of the aperture is a pin, two of which are shown at  163 . A ring  164  similar to that shown in  FIG. 2  is provided with six equi-angularly spaced sockets some of which are indicated at  165 . A third member  166 , which could be a drive shaft for the wheel, is provided with a cutaway tubular portion  167  which has three equi-angularly-spaced cylindrical trunnions, two of which are indicated at  168 . 
     Three of the sockets  165  fit over the pins  163  and the other three sockets  165  receive the trunnions  168 . Inserts such as  169  are inserted from the center of the aperture  162  so as to receive the pins  163 . The inserts  169  are a snap fit in the sockets  165  as described in relation to  FIG. 11 . 
     Similarly, inserts  170  are inserted in a radially inward direction over the pins  168  which are received in the other sockets in the ring  164 , again the inserts  170  are a snap fit into the sockets. The inserts have bores such as  171  which receive the pins such as  163  or  168  and allow for rotation and sliding of the pins in the bores. 
       FIG. 14  shows a coupling which is similar to that shown in  FIG. 2  except that the second member such as  28  in  FIG. 2  is in this case made in two identical parts. Thus referring to  FIG. 14  the member  172  provides six sockets  173  equi-angularly spaced around the ring. The sockets receive the pins  174  on a member  175  as described and the sockets also receive inserts  10 ′  176  which are snap fits in the sockets  173 . The inserts  176  have bores  177  in which the pins  174  are received so as to be able to rotate and slide. A further member such as shown in  FIG. 2  at  25   a  completes the coupling. 
     The ring  172  comprises two identical parts  178  and  179 . Each part provides half of each of the sockets  173 , the halves being indicated at  180  and  181  respectively. Each socket portion  180   181  is connected to its adjacent socket portion by a flexible web  182   183  respectively. The portions  182   183  are provided with inter-fitting formations indicated generally at  185  which snap together to hold the ring parts  178   179  together. When the inserts  176  are inserted into the sockets  173  it will be seen that the ring parts cannot become disengaged. 
     It will be seen that in each of the embodiments the first and second members are connected by pin and socket joints which are equi-angularly spaced around the rotary axes of the members. Where a third member is provided as in  FIGS. 2 to 14 , the second member and the third member are also connected by pin and socket joints. The flexibility of the coupling is provided in the arrangement of  FIGS. 2 to 14  by flexibly interconnecting the sockets. In  FIG. 1A  the parts  14  provide a flexible interconnection of the sockets via the element  11 . 
     In  FIG. 1A  the flexibility of the coupling is provided by the flexible elements  14 . However the trunnions  21  could be flexibly mounted on the second member  17  in place of, or in addition to, the flexible elements  14 . 
     In  FIGS. 2 to 14  the flexibility of the coupling is provided by the flexible elements between the sockets. However trunnions such as  21  on the first member and/or on the third member of each of these couplings could be flexibly mounted on the member in place of or in addition to the provisions of the flexible elements between the sockets. 
     In  FIGS. 2 to 14  also, the sockets or pins on the second members of the coupling could, instead of being inter-connected by flexible elements, be connected by flexible elements to a rigid ring or the like. 
     To ease assembly the trunnions in each of the embodiments may be detachably secured to the members and secured to the members that carry them after these have been located relative to the flexible ring. 
     As described the trunnions may be spherical or cylindrical and in most cases the use of cylindrical trunnions is to be preferred so as to avoid twisting of the sockets during the transmission of torque. 
     It will also be understood that although the device of the present invention has been described in terms of a rotating coupling, it could be used as a static coupling for flexibly connecting two non-rotating parts in such a way as to enable moments to be transmitted therebetween.