Abstract:
An over-running clutch is provided having an outer race and an inner race defining a varying gap therebetween. A plurality of rolling elements are positioned between the inner and outer races and are interconnected by a retainer. A rotor is secured to the outer race by a non-magnetic sleeve. An armature is rotationally locked to the retainer. Mounted onto the rotor and adapted to produce an electromagnetic flux to attract the armature into contact with the rotor is an electromagnetic coil; wherein rotation of the outer race is frictionally transferred to the armature and the retainer, thereby moving the rollers such that the rollers engage and wedge between the inner and outer races to lock the clutch.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     This invention is related to a two way over-running clutch, preferably for use in automotive differential or transfer case applications. More specifically, the present invention relates to a two-way over-running clutch assembly of a roller/ramp variety which includes a rotor that is supported by a non-magnetic sleeve.  
       BACKGROUND OF THE INVENTION  
       [0002]     Referring to  FIG. 1 , an example of previous over-running clutches of this type is shown generally at  100 . The clutch  100  includes an inner race  120 , and outer race  112 , a plurality of rolling elements  126  positioned therebetween, and an electromagnetic coil  144  adapted to generate a flux that causes the rolling elements  126  to lock the inner race  120  and outer race  112  to one another, thereby locking the clutch  100 . A portion  102  of the outer race  112  extends axially to provide support for a rotor  136  that envelopes and the electromagnetic coil  144  that is mounted on a housing.  
         [0003]     Due to the large forces that the inner and outer races  120 ,  112  experience, the outer race  112  is typically made from steel. The portion  102  of the outer race  112  that extends axially to provide support for the rotor  136  adds more steel to the clutch  100 , thereby making the clutch  100  heavier. Further, steel is generally magnetically conductive. Using the portion  102  of the steel outer race  112  to support the rotor  136  creates the possibility that the flux generated by the electromagnetic coil  144  will leak or short-circuit through the outer race  112 , thereby degrading or impeding the performance of the clutch  100 .  
         [0004]     Therefore, there is a need for an electromagnetic clutch assembly that supports the rotor and electromagnetic coil while allowing the clutch assembly to be lighter and reducing the chance that the electromagnetic flux will leak or short-circuit through the outer race.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In accordance with an aspect of the present invention, an over-running clutch assembly comprises an outer race having a cylindrical inner surface and being rotatable about an axis, an inner race having an outer surface coaxial with the cylindrical inner surface and defining a gap therebetween.  
         [0006]     The inner race is also rotatable about the axis, with rotational movement relative to the outer race also being possible. A plurality of ramp surfaces are formed at spaced apart locations on the outer surface of the inner race. Positioned between the outer race and the inner race are a plurality of rollers with one of the rollers being located centrally within each of the ramped surfaces and with each of the rollers having a diameter less than the gap between the center of the ramp surfaces on the inner race and the cylindrical inner surface of the outer race.  
         [0007]     A retainer interconnects all of the rollers and causes the rollers to circumferentially move in unison with one another. The retainer is rotatable about the axis, with limited relative rotation being possible with respect to the inner race. Additionally, a first biasing element is supported on the retainer to circumferentially bias the retainer into a position relative to the inner race such that each of the rollers is held in the center of the ramped surfaces on the inner race.  
         [0008]     A rotor is rotationally secured to the outer race such that the rotor rotates along with the outer race. Disposed between the retainer and the rotor, an armature includes a plurality of openings formed therein and located radially thereabout. Retainer tabs of the retainer extend axially to engage the openings such that the armature is rotationally locked to the retainer while allowing limited axial movement of the armature relative to the retainer.  
         [0009]     An electromagnetic coil is mounted to the stationary housing and adjacent to the rotor and is adapted to produce an electromagnetic flux that will magnetically attract the armature into contact with the rotor. Upon contact, rotation of the outer race is frictionally transferred to the armature and the retainer, thereby moving the rollers along the ramp surfaces to a position where the rollers engage and wedge between the inner and outer races and prevent relative rotation between the inner and outer races. To reduce the size and weight of the outer race and to reduce the possibility that the magnetic flux will short circuit through the outer race, a non-magnetic sleeve is positioned between and interconnects the rotor and the outer race.  
         [0010]     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a sectional view of a prior art over-running clutch assembly;  
         [0012]      FIG. 2  is a sectional view of a first embodiment of the over-running clutch of the present invention;  
         [0013]      FIG. 3  is a sectional view of a second embodiment of the over-running clutch of the present invention;  
         [0014]      FIG. 4  is a sectional view taken generally along line  4 - 4  of  FIG. 3 ;  
         [0015]      FIG. 5  is a sectional view of a third embodiment of the over-running clutch of the present invention;  
         [0016]      FIG. 6  is a perspective view of a portion of the outer diameter of the outer race of a fourth embodiment of the over-running clutch of the present invention; and  
         [0017]      FIG. 7  is a sectional view of a fifth embodiment of the over-running clutch of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The following description of the preferred embodiment of the invention is not intended to limit the scope of the invention to this preferred embodiment, but rather to enable any person skilled in the art to make and use the invention.  
         [0019]     Referring to  FIG. 2 , an over-running clutch of the present invention is shown generally at  10 . The over-running clutch  10  includes an outer race  12  that is rotatable about a first axis  16  and has an inner surface  14 . An inner race  20  includes an outer surface  22  coaxial with the inner surface  14  of the outer race  12 . The inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20  define a gap  24  between the inner race  20  and the outer race  12  Positioned within the gap  24  are a plurality of rolling elements  26 .  
         [0020]     Preferably, the rolling elements  26 , the inner race  20  and the outer race  12  are made from steel. Due to the high hertzian contact stresses experienced, the rolling elements  26 , the inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20 , and the rolling elements  26  are also preferably hardened and ground.  
         [0021]     The outer surface  22  of the inner race  20  is defined by a plurality of ramp surfaces adjacent, that are preferably planar and oriented perpendicular to radii drawn from the axis of rotation. Provided this way, the gap  24  has a maximum dimension at the midpoint of the ramp surface and a minimum dimension at the juncture to two adjacent surfaces. The rolling elements  26  are positioned between the outer race  12  and the inner race  20  with one rolling element  26  being located at a midpoint of each of ramp surfaces of the inner race  20 . The rolling elements  26  have a diameter which is smaller than the gap  24  between the inner surface  14  and the midpoint of the ramp surfaces of the outer surface  22 , but greater than the gap  24  between the juncture between adjacent ramp surfaces and the inner surface  14  of the outer race.  
         [0022]     A retainer  28  interconnects all of the rolling elements  26  and causes the rolling elements  26  to circumferentially move in unison with one another. The retainer  28  is rotatable about the first axis  16  with limited relative rotation with respect to the inner race  20 . The retainer  28  also includes at least one retainer tab  30  extending axially from the retainer.  
         [0023]     A first biasing element  34  is mounted onto the retainer  28  to maintain the position of the retainer  28  with respect to the inner race  20  such that the rolling elements  26  are normally held at the midpoints of the ramp surfaces.  
         [0024]     A rotor  36  is rotationally secured to the outer race  12  by a sleeve  38 . The sleeve  38  is non-magnetic and is secured to an outer surface  40  of the outer race  12 , with the rotor  36  being secured to an inner surface  42  of the non-magnetic sleeve  38 . The non-magnetic sleeve  38  is accordingly located between and interconnects the rotor  36  to the outer race  12 . Because an end portion of the outer race  12  is not required to support the rotor  36 , the non-magnetic sleeve  38  allows the outer race  12  to be designed smaller and lighter.  
         [0025]     The rotor  36  itself surrounds an electromagnetic coil  44  and coil housing  46 , the former of which is adapted to produce an electromagnetic flux. The use of the non-magnetic sleeve  38  to support the rotor  36  on the outer race  12  prevents this flux from leaking or short-circuiting through the outer race  12 . Preferably, the non-magnetic sleeve  38  is made from aluminum or other suitable non-magnetic material. A sleeve bearing  48  is positioned within an inner diameter  50  of the rotor  36  and abuts a back face  52  of the inner race  20  to axially position the rotor  36  within the over-running clutch  10 .  
         [0026]     The non-magnetic sleeve  38  is mounted onto the outer diameter  40  of the outer race  12  such that the non-magnetic sleeve  38  is rotationally and axially fixed to the outer race  12 . In a first embodiment, the outer surface  40  of the outer race  12  has dimples  54  formed therein. Portions  55  of the non-magnetic sleeve  38  correspondingly formed and received into the dimples  54  to rotationally and axially fix the non-magnetic sleeve  38  to the outer surface  40  of the outer race  12 , as shown in  FIG. 2 .  
         [0027]     Referring to  FIGS. 3 and 4 , in a second embodiment, the outer surface  40  of the outer race  12  is provided with recesses  56  that extend radially inward. The inner surface  42  of the non-magnetic sleeve  38  includes corresponding lugs  60  extend radially inward and received within the recesses  56 . The recesses  56  of the outer race  12  and the lugs  60  of the non-magnetic sleeve  38  engage one another to rotationally fix the non-magnetic sleeve  38  to the outer race  12 . The outer surface  40  of the outer race  12  further includes a radial ridge  62  extending circumferentially around the outer race  12 . Portions of the non-magnetic sleeve  38  are formed into a lip  63  defining an inner diameter that is less than the outer diameter of the ridge  62 . The lip  63  is located on an end of the sleeve  38  so as to be positioned or snap over the radial ridge  62  to axially fix the non-magnetic sleeve  38  to the outer race  12 . The lugs  60  can be replaced with separate “keys” which fit into the slots  56  in the outer surface  40  and new slots in the inner surface  42  of the non-magnetic sleeve  38 .  
         [0028]     In a third embodiment, the outer diameter  40  of the outer race  12  includes a cutting spline  64  formed therein. The cutting spline  64  engages the inner diameter  42  of the non-magnetic sleeve  38  to rotationally lock the non-magnetic sleeve  38  onto the outer race  12 , as shown in  FIG. 5 . The outer surface  40  of the outer race  12  further includes a circumferentially extending groove  66  formed therein. Portions  67  of the non-magnetic sleeve  38  are formed radially inward and received into the groove  66  to axially lock the non-magnetic sleeve  38  to the outer race  12 .  
         [0029]     Referring to  FIG. 6 , in a fourth embodiment the outer surface  40  of the outer race  12  includes a first or radial groove  68  extending circumferentially around the outer surface  40  and a plurality of axially extending second or axial grooves  70  are circumferentially spaced about the outer surface  40 . Portions of the non-magnetic sleeve  38  are formed so as to extend or are deformed to extend into the first and second grooves  68 ,  70  to both rotationally and axially lock the non-magnetic sleeve  38  onto the outer race  12 .  
         [0030]     In a fifth embodiment, the non-magnetic sleeve  38  is screwed onto the outer surface  40  of the outer race  12 . In this fifth embodiment, the outer surface  40  of the outer race  12  includes external screw threads  72  formed thereon. The inner surface  42  of the non-magnetic sleeve  38  includes internal screw threads  74  formed therein. The non-magnetic sleeve  38  is screwed onto the outer diameter  40  of the outer race  12  to both rotationally and axially lock the non-magnetic sleeve  38  to the outer race  12 . Once the non-magnetic sleeve  38  is screwed onto the outer race  12 , the material of the non-metallic sleeve  38  can be staked or otherwise deformed in such a way to prevent the non-metallic sleeve  38  from coming loose or disengaging therefrom.  
         [0031]     In all the embodiments, an armature  76  is disposed between the retainer  28  and the rotor  36 . The armature  76  includes at lease one opening  78  therein that receives the retainer tab  30  to rotationally couple the armature  76  to the retainer  28 . The opening  78  within the armature  76  is large enough to allow the retainer tab  30  to slide axially therein such that the armature  76  is rotationally linked to the retainer  28 , but the armature  76  is allowed to move axially with respect to the retainer  28 .  
         [0032]     A second biasing element  80  is disposed between the armature  76  and the rotor  36  to bias the armature  76  away from the rotor  36  and toward the retainer  28 . Preferably, the second biasing element  80  is a wave spring.  
         [0033]     Preferably, the first biasing element  34  is a centering spring supported by the inner race  20  and engaging the retainer  28  to keep the retainer  28  in position and to keep the rolling elements  26  positioned at the midpoints of the ramp surfaces  23  of the inner race  20 , thereby allowing the outer race  12  and the inner race  20  to rotate freely with respect to one other. The first biasing element  34  further includes a plurality of tangs (not shown) extending radially in or out to engage notches (not shown) on the retainer  28 . The biasing force of the first biasing element  34  must be carefully calibrated for the over-running clutch  10  and must provide enough force to move the retainer  28  and rolling elements  26  to the neutral position (mid-point) easily when the over-running clutch  10  is disengaged, but not so much force that friction between the armature  76  and the rotor  36  cannot overcome it to actuate the clutch  10 .  
         [0034]     As mentioned above, the electromagnetic coil  44  is adapted to generate a magnetic flux. The rotor  36  includes a plurality of partially circumferential slots  82  extending through the rotor  36  and spaced circumferentially about the rotor  36 . When energized, the electromagnetic coil  44  produces a magnetic flux which is focused around the slots  82  and concentrated on the armature  76 . When the magnetic flux passes through the armature  76 , the armature  76  is magnetically drawn toward the rotor  36 . Once the magnetic force of the electromagnetic coil  44  overcomes the force of the second biasing element  80 , the armature  76  will start to move toward the rotor  36 .  
         [0035]     The armature  76  is free to move axially with respect to the retainer  28 , so, when the attractive force of the electromagnetic coil  44  overcomes the force of the second biasing element  80 , the armature  76  will move axially toward the rotor  36  until the armature  76  and the rotor  36  come into contact with one another. When the armature  76  and the rotor  36  are brought into contact with one another, the frictional force between the outer race  12  and the armature  76  will force the armature  76  to rotate with the rotor  36  and the outer race  12 . The armature  76  is rotationally linked to the retainer  28 ; therefore, the rotational movement of the outer race  12  will be transferred through the armature  76  to the retainer  28 .  
         [0036]     Rotational movement of the retainer  28  with respect to the inner race  20  moves the rolling elements  26  along the ramp surfaces until the rolling elements  26  are no longer positioned at the midpoints of the ramp surfaces. Since the gap  24  is not large enough to accommodate the diameter of the rolling elements  26  when the rolling elements  26  move out of the midpoints of the ramp surfaces, the rolling elements  26  become wedged between the outer surface  22  of the inner race  20  and the inner surface  14  of the outer race  12 , thereby rotationally locking the inner race  20  and outer race  12  together. The ramp surfaces and the interaction of the ramp surfaces with the rolling elements  26  are described in detail in U.S. Pat. Nos. 5,927,456 and 5,924,510, which are hereby incorporated by reference.  
         [0037]     When the electromagnetic coil  44  is de-energized, the magnetic attraction of the armature  76  to the rotor  36  dissipates. As this attraction dissipates, the second biasing element  80  quickly overcomes the magnetic attraction and forces the armature  76  back away from the rotor  36 , thereby eliminating the frictional transfer of rotation to the armature  76 .  
         [0038]     Without a rotational force to pull the retainer  28  and rolling elements  26  out of the neutral position, the first biasing element  34  will force the retainer  28  back into the neutral position and the rolling elements  26  back into the middle of the ramp surfaces, thereby allowing the outer race  12  to rotate freely with respect to the inner race  20 , and un-locking the over-running clutch  10 .  
         [0039]     Preferably, the armature  76  includes an annular step  84  extending around the inner diameter of the armature  76 . The annular step  84  faces the rotor  36 , and provides a recess into which the second biasing element  80  is piloted and can collapse when the armature  76  is drawn into contact with the rotor  36 . Preferably, the second biasing element  80  is a wave spring that fits within the annular step  84  on the armature  76  and collapses within the annular step  84  when the magnetic force of the electromagnetic coil  44  exceeds the spring force of the second biasing element  80 .  
         [0040]     The foregoing discussion discloses and describes various aspects of the invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the fair scope of the invention as defined in the following claims. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.