Abstract:
Example aspects of the present invention comprise two concentric rings, the rings movable relative to each other and defining a clearance between them for receiving at least one ball. The first ring is a coupling member, the second ring is a tubular slipper with a friction surface on the far side of the clearance, and the ball contacts the coupling member to the tubular slipper. At least one ring has a first recess with side walls for receiving the least one ball, and the friction surface is configured to displace in a radial direction when the at least one ball is axially aligned with the first recess and forced to run up the side walls by rotating the rings relative to one another. In an example embodiment of the invention, the first recess is a calotte.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a bi-directional coupling, and more specifically to a bi-directional clutch with axial disengagement. 
       BACKGROUND OF THE INVENTION 
       [0002]    Couplings are commonly used to transmit torque from one rotating body to another body. Sometimes it is desirable to incorporate axial compliance in the coupling to allow the rotating bodies to move relative to one another. In this type of coupling, the two rotating bodies are rotationally fixed and axially movable. One application for this type of coupling is a driveshaft for a motor vehicle. 
         [0003]    U.S. Pat. No. 6,751,503 (Breese), hereby incorporated by reference in its entirety as if set forth fully herein, discloses a splined member for use in a slip joint for transmitting rotational force between two members, while accommodating a limited amount of relative axial movement therebetween. The slip joint includes a female splined member with a female tubular member and a plurality of elongated rods; a male member with a plurality of circumferentially spaced, longitudinally extending grooves; a plurality of balls disposed in the grooves; and a cage that retains the balls in a fixed relation to one another and limits the travel of the balls in the grooves. The balls engage the rods in a circumferential direction to transmit torque between the female member and the male member, while facilitating unencumbered telescopic displacement between the members. 
         [0004]    Breese is limited in that the members are always rotationally fixed. That is, the female member and the male member cannot be disengaged from one another. Sometimes it is desirable to have a disengageable coupling, for example to change gears in a transmission. Often a combination of synchronizer rings and dog clutches are used to engage and disengage the trans-mission gears. This combination requires a considerable amount of axial space in the transmission. 
         [0005]    U.S. Pat. No. 6,409,001 (Kerr), hereby incorporated by reference in its entirety as if set forth fully herein, discloses a multi-directional coupling including a tubular slipper, a tubular member, a race, and roller members disposed in a channel defined by the tubular slipper and the tubular member. Torque applied to the member forces the rollers to roll up the side walls of the channels, forcing the slipper to radially expand, thereby increasing the radial force exerted on the slipper against the race. As more torque is applied to the member, the slipper and the race will become rotationally locked to the member. 
         [0006]    Kerr further includes a tapered spigot and a channel extending through the slipper and member. When the spigot is partially inserted into the channel, the coupling responds as described above. When the spigot is fully inserted into the channel, the member is prevented from rotating relative to the slipper, allowing the race to freewheel. However, Kerr is limited in that once engaged, the coupling cannot be easily disengaged while torque is applied to the member. That is, in order to reduce the radial force exerted on the slipper against the race, the slipper must rotate opposite to the member and against the torque being transmitted. Furthermore, the rollers in the Kerr design do not permit axial displacement of the tubular slipper relative to the tubular slipper. 
         [0007]    Thus, there is a long-felt need for a disengageable coupling which permits axial displacement. There is also a long-felt need for a disengageable coupling that can be easily disengaged while transmitting torque. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Example aspects of the present invention comprise two concentric rings, the rings movable relative to each other and defining a clearance between them for receiving at least one ball. The first ring is a coupling member, the second ring is a tubular slipper with a friction surface on the far side of the clearance, and the ball contacts the coupling member to the tubular slipper. At least one ring has a first recess with side walls for receiving the least one ball, and the friction surface is configured to displace in a radial direction when the at least one ball is axially aligned with the first recess and forced to run up the side walls by rotating the rings relative to one another. In an example embodiment of the invention, the first recess is a calotte. 
         [0009]    In some example embodiments of the invention, at least one of the coupling member and the tubular slipper has a second recess axially disposed from the first recess, and the friction surface is configured to not displace in a radial direction when the at least one ball is axially aligned with the second recess and the coupling member and the tubular slipper are rotated relative to one another. In an example embodiment of the invention, the at least one ball is a plurality of balls forming single or multiple rows in a sheet metal ball cage. 
         [0010]    Also, in some example embodiments of the invention, the coupling member or the slipper or both include the first recess. In some example embodiments of the invention, the rings include multiple first recesses circumferentially displaced, the first recesses are radially aligned, and the side walls of the first recess have an arched shape. In some example embodiments of the invention, one of the rings has a bordered flange for limiting the axial movement of the rings. 
         [0011]    In some example embodiments of the invention, a cylindrical roller element is placed in the clearance axially next to the at least one ball. The ball is elastic and has a slightly bigger diameter than the diameter of the cylinders, so that an axial movement between the rings in unencumbered condition is carried only by the balls, and the cylindrical roller elements carry the load in the charged state. 
         [0012]    An example method of the invention comprises axially aligning a plurality of balls in a first arched recess of at least one of a coupling member and a tubular slipper, arranged concentrically; and rotating at least one of the coupling member and the tubular slipper to apply a radial force to at least one of the coupling member and the tubular slipper. Another example method of the invention further comprises axially aligning the plurality of balls in a second recess to eliminate the radial force. 
         [0013]    A better understanding of these and other aspects, features, and advantages of the invention may be had by reference to the drawings and to the accompanying description, in which example embodiments of the invention are illustrated and described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The nature and mode of operation of example aspects of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures. 
           [0015]      FIG. 1  is an exploded view of a coupling design according to an example aspect of the invention. 
           [0016]      FIG. 2  is a section view of the coupling of  FIG. 1  taken perpendicular to the rotational axis. 
           [0017]      FIG. 3  is a section view of the coupling of  FIG. 1  taken parallel to the rotational axis, wherein the coupling is shown in a first axial position. 
           [0018]      FIG. 4  is the section view of  FIG. 3 , wherein the coupling is shown in a second axial position. 
           [0019]      FIG. 5  is a perspective view of an example embodiment of the coupling including a disengagement recess according to an aspect of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural element of the invention. Furthermore, it is understood that this invention is not limited to the particular embodiments, methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
         [0021]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the following methods, devices, and materials are now described. 
         [0022]      FIG. 1  is an exploded view of a coupling design according to an example aspect of the invention, and  FIG. 2  is a section view of the coupling of  FIG. 1  taken perpendicular to the rotational axis. The following description is made with reference to  FIGS. 1 and 2 . 
         [0023]    Coupling assembly  10  includes coupling member  12 , tubular slipper  14  with friction surface  16 , balls  18 . Member  12  and slipper  14  are concentric rings with clearance between them for receiving balls  18 . Optional ball race  20  is concentrically disposed between member  12  and slipper  14 . Race  20  is a cylindrical tube with holes for positioning multiple rows of balls  18  relative to one another. Balls  18  can freely rotate within the positioning holes. Any number and arrangement of balls, i.e., a single ball or one or more rows of balls, and any suitable number of and/or circumferential distribution of balls per row are within the spirit and scope of the invention. 
         [0024]    An example embodiment (not shown) includes a cylindrical roller element (not shown) disposed axially adjacent ball  18 . The roller element (not shown) has a diameter slightly smaller than ball  18 , but ball  18  is elastic. Therefore, axial movement between rings  12  and  14  in an unencumbered (unlocked) condition is carried only by balls  18 , but in the charged (locked) state the cylindrical roller elements carry the load. 
         [0025]    Coupling member  12  includes arched recess  22  ( FIG. 2 ). Tubular slipper  14  includes arched recess  24  ( FIG. 2 ). Recesses  22  and  24  are designed to receive ball  18  therebetween. In an example embodiment, recess  22  and/or recess  24  is a calotte. Although recesses  22  and  24  are shown in member  12  and slipper  14 , respectively, in other embodiments only one such recess may be present. For example, recess  22  may not be present in coupling member  12 . Likewise, recess  24  may not be present in tubular slipper  14 . 
         [0026]    Friction surface  16  is configured to displace in a radial direction, i.e., direction  26  when balls  18  are disposed in recesses  22  and  24  and coupling member  12  and tubular slipper  14  are rotated relative to one another. For example, when member  12  is rotated in direction  28  and slipper  14  rotates in direction  30 , balls  18  are forced against walls of recesses  22  and  24 , causing balls  18  to apply radial force to slipper  14 , thereby displacing slipper  14  in direction  26 . The same discussion applies when member  12  is rotated in direction  30  and slipper  14  is rotated in direction  28 . 
         [0027]      FIG. 3  is a section view of the coupling of  FIG. 1  taken parallel to the rotational axis, wherein the coupling is shown in a first axial position.  FIG. 4  is the section view of  FIG. 3 , wherein the coupling is shown in a second axial position. The following description is made with reference to  FIGS. 1-4 . 
         [0028]      FIG. 3  depicts tubular member  12  in a first axial position indicated by arrow  32 . Retaining ring  34  prevents member  12  from sliding past distal end  36  of slipper  14  in direction  32 . Ring  34  may be a snap ring or any other style of retaining ring known in the art. Axial position of ring  34  is maintained, relative to member  12  by groove  38  and radially formed portion  40 . Therefore, axial travel of member  12  relative to slipper  14  is limited by ring  34 . 
         [0029]    Inside length  42  of slipper  14  is the sum of length  44  of race  20  and gap  46  between race  20  and inside surface  47  of distal end  36 . In order to facilitate free axial motion of member  12 , gap  46  can be at least half as long as travel distance  48 . Because locking members  18  are balls, member  12  can move axially relative to slipper  14  when coupling  10  is transmitting torque. That is, the spherical nature of balls  18  allow axial displacement of coupling member  12  relative to slipper  14 , while maintaining radial force on slipper  14  through contact of balls  18  with recesses  22  and  24 . 
         [0030]      FIG. 4  depicts tubular member  12  in a second axial position indicated by arrow  50 . In this position, ring  34  is displaced axially, in direction  50  away from distal end  36  of slipper  14 . Also, in  FIG. 4 , gap  46  is reduced because race  20  has displaced in direction  50  with balls  18 . In general, race  20  moves about half as far as member  12  when member  12  slides axially in direction  50 . Radially formed portion  52  of member  12  prevents member  12  from sliding past distal end  54  of slipper  14 . Bordered flange  52  limits the axial movement of the rings. 
         [0031]    In operation, member  12  may be engaged with a shaft (not shown) and slipper  14  may be inserted into a gear (not shown). Rotation of member  12  relative to slipper  14  results in radial displacement of friction surface  16  to engage slipper  14  with the gear (not shown). When the slipper and gear are engaged, torque from the shaft is transferred through coupling assembly  10  to the gear. To prevent engagement of the gear, a pin (not shown) may be inserted to prevent rotational motion between member  12  and slipper  14 . 
         [0032]    Axial displacement of member  12  relative to slipper  14  on balls  18  allows reduced friction motion of the gear relative to the shaft under torque loading. In a typical splined arrangement of a gear and a shaft, significant friction forces must be overcome when sliding a splined gear on a splined shaft. 
         [0033]      FIG. 5  is a perspective view of an example embodiment of the coupling including at least one disengagement recess according to an aspect of the invention. In this embodiment, coupling member  12  includes at least one recess  56  axially disposed from one or more recesses  22 . Recess  56  is deeper than recess  22  in one example, although it need not be. Although recesses  56  are shown in member  12  and the depth of recess  56  is shown as being greater than the depth of recess  22 , recess  56  may be present in slipper  14  as well, in which case the depth of recess  56  would be greater than the depth of recess  24 . In one example, recess  56  may not be present in coupling member  12 . Likewise, recess  56  may be present in both coupling member  12  and tubular slipper  14 . 
         [0034]    Here, additional depth of recess  56  prevents balls  18  from contacting slipper  14  when balls  18  are disposed in recess  56 . Therefore, in that case the friction surface  16  does not displace in direction  26  when balls  18  are disposed in recess  56  and coupling member  12  and tubular slipper  14  are rotated relative to one another. Stated another way, rotation of coupling member  12  relative to tubular slipper  14  is ineffective to displace friction surface  16  because in that case recess  56  allows balls  18  situated therein to avoid contact with edges of recess  24 . 
         [0035]    According to another example aspect of the invention, a method of operating a coupling is provided that comprises axially aligning a plurality of balls (e.g., balls  18 ) in a first arched recess (e.g., recess  22 ) and rotating a coupling member (e.g., member  12 ) relative to a tubular slipper (e.g., slipper  14 ) to apply a radial force to a friction surface (e.g., surface  16 ). In some example embodiments, the method also includes axially aligning the plurality of balls in a second recess (e.g., recess  56 ) to eliminate the radial force. 
         [0036]    Although example aspects of this invention have been described in certain specific embodiments, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that this invention may be practiced otherwise than as specifically described. Thus, the present example embodiments of the invention should be considered in all respects as illustrative and not restrictive.