Patent Abstract:
The invention concerns a freewheel bearing device including an outer element and inner element arranged inside the outer element, and a free wheel provided with at least a wedging element, arranged between the inner element and the outer element to allow a free rotational movement in one direction between the outer element and the inner element and for transmission of a torque in the other direction between the outer element and the inner element, the free wheel including a ring provided with a cylindrical inner surface and a cylindrical outer surface, substantially aligned on a radial plane perpendicular to the axis of rotation of the device, and a torque limiting member adapted to limit the torque transmitted by the free wheel, the torque limiting member being arranged radially between said ring and the outer element or the inner element in contact with said ring and said element.

Full Description:
PRIORITY CLAIM 
     This application is a continuation of U.S. patent application Ser. No. 10/566,669 entitled “FREEWHEEL BEARING DEVICE WITH TORQUE LIMITER” filed on Oct. 23, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of bearings comprising a unidirectional clutch or freewheel, usually interposed between an inner element and an outer element. 
     2. Description of the Relevant Art 
     The freewheel makes it possible to transmit a torque in one direction and to allow a relative rotation in the other direction. A bearing may also be interposed between the inner element and the outer element to support radial and, where necessary, axial loads. Document FR A 2 726 059 describes a device of this kind. 
     Also known is document GB-A-2 259 962 which describes a torque limiter making it possible to limit the torque to different values depending on the direction of rotation of one race relative to the other race, by means of friction balls in one direction and a spring in the other direction. However, this torque limiter is structurally and functionally different from a freewheel, because the free rotation of one race relative to the other race is not possible. 
     It would be beneficial to limit the torque transmitted by a freewheel when the freewheel is in a locked position, particularly to reduce the stresses sustained by other mobile elements, and reduce their fatigue. Document FR A 2 615 568 describes a freewheel starter drive comprising a torque limiter. Such a drive is however relatively bulky. 
     SUMMARY OF THE INVENTION 
     The freewheel bearing device described herein proposes to limit the torque transmitted by a freewheel in a simple and compact manner. 
     Described herein is a freewheel device with torque limiter that is easy to transport and handle and incorporate into a mechanical assembly. 
     The freewheel device, according to one embodiment, is of the type including an outer element, an inner element placed in the outer element, and a freewheel provided with at least one jamming element, placed between the inner element and the outer element to leave free a rotation movement in one direction between the outer element and the inner element and to transmit a torque in the other direction between the outer element and the inner element. The freewheel includes a race provided with an inner cylindrical surface and an outer cylindrical surface, substantially aligned on a radial plane perpendicular to the axis of rotation of the device, and a torque limiter member capable of limiting the torque transmitted by the freewheel, the torque limiter member being placed radially between said race and the outer element or the inner element in contact with said race and said element. 
     A slipping raceway may be formed on the inner cylindrical surface or the outer cylindrical surface, the torque limiter member being placed in contact with the outer cylindrical surface or the inner cylindrical surface respectively. The freewheel and the torque limiter member are thus linked in a manner requiring little space. 
     Any type of known freewheel with tilting cams, rollers, spring or pawl may be used. 
     In one embodiment, the torque limiter member is mounted in series with the freewheel to limit the torque transmitted by the unidirectional engagement member in the torque transmission position. 
     In one embodiment, the torque limiter member includes at least one friction element. The friction element may include a radial friction surface. The friction element may include an axial friction surface delimited by two radial planes. 
     In one embodiment, the device includes a bearing allowing the outer element to rotate relative to the inner element. The bearing may be a rolling bearing. Raceways for the rolling elements of said bearing are arranged in the inner and outer elements. Alternatively, the raceways are arranged in inner and outer races fixedly attached to the inner and outer elements. 
     In one embodiment, the torque limiter member is placed on an outer surface of the freewheel. 
     In another embodiment, the torque limiter member is placed in a bore of the freewheel. 
     In one embodiment, the torque limiter member includes an open elastic ring provided with an outer friction surface and an inner friction surface. The ring may be made of steel sheet and may have a U-channel provided with two axial flanges. 
     In one embodiment, the torque limiter member includes a plurality of elastic friction tongues. 
     In another embodiment, the torque limiter member includes an elastic ring made of synthetic material provided with an outer or inner friction surface and a respectively inner or outer attachment surface. 
     In one embodiment, the torque limiter member includes at least one friction ring and an elastic washer for placing the friction ring bearing axially on a friction surface. The torque limiter member may include two friction rings between which said elastic washer is mounted. The friction rings may have radial friction surfaces. 
     In one embodiment, the torque limiter member includes a body in the shape of an open ring. The race of the freewheel and the body of the torque limiter member may be a single element whose outer surface is in friction contact with the outer element in the case of angular rotation, and whose inner surface interacts with the jamming element, or whose inner surface is in friction contact with the inner element in the case of angular rotation, and whose outer surface interacts with the jamming element. 
     In one embodiment, the torque limiter member also includes an elastic element for prestressing said body. The elastic element may be a ring of the circlip type. 
     In one embodiment, the freewheel includes a spring provided with an end fixedly attached to the torque limiter member and coils in friction contact on the inner or outer element. 
     In one embodiment, the jamming elements of the freewheel are cams, rollers or pawls. 
     In one embodiment, the torque limiter member includes a friction element and an element for prestressing the friction element against said race and/or the outer element or the inner element. More particularly, the friction element may be prestressed between said race and the outer element, between said race and the inner element, between two surfaces fixedly attached to the outer element, or else between two surfaces fixedly attached to the inner element. The prestress element is advantageously a piece separate from the friction element. 
     In one embodiment, the torque limiter member is prestressed between two separate pieces in opposite directions. More particularly, the torque limiter member may be prestressed radially outward against the outer element and radially inward against said race, radially outward against said race and radially inward against the inner element, or axially against two opposite surfaces fixedly attached to the outer element or the inner element. 
     “Freewheel” as used herein refers to a device for transmitting a torque in one direction and a relative rotation in the other direction, with, where necessary, a negligible residual drag torque in normal operating conditions between an input element and an output element of the device. 
     Advantages of the freewheel bearing devices described herein include that the space requirement of the device is limited and it has the shape of a compact, preassembled cartridge relatively well protected against the outer elements. The lifetime of the moving parts upstream and downstream of the freewheel is lengthened thanks to the smoothing of the torque peaks, hence more economical running and a reduced risk of breakage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on studying the detailed description of several embodiments taken as nonlimiting examples and illustrated by the appended drawings in which: 
         FIG. 1  is a view in axial section of a freewheel device according to a first embodiment of the invention; 
         FIG. 2  is a detail view of  FIG. 1 ; 
         FIG. 3  is a view in cross section along a plane passing through the jamming elements of the device of  FIG. 1 ; 
         FIG. 4  is a detail view of  FIG. 3 ; 
         FIG. 5  is a view in axial section of a freewheel device according to a second embodiment of the invention; 
         FIG. 6  is a detail view of  FIG. 5 ; 
         FIG. 7  is a view in axial section of a freewheel device according to a third embodiment; 
         FIG. 8  is a view in axial section of a freewheel device according to a fourth embodiment of the invention; 
         FIG. 9  is a detail view of the freewheel device of  FIG. 8  taken in cross section along a plane passing through the jamming elements; 
         FIG. 10  is a detail view of  FIG. 8 ; 
         FIG. 11  is a view in axial section of a freewheel device according to a fifth embodiment of the invention; 
         FIG. 12  is a detail view of the freewheel device of  FIG. 11  taken in cross section along a plane passing through the jamming elements; 
         FIG. 13  is a detail view of  FIG. 11 ; 
         FIG. 14  is a view in section along XIV-XIV of  FIG. 15  of a freewheel device according to a sixth embodiment of the invention; 
         FIG. 15  is a view in section along XV-XV of  FIG. 14 ; and 
         FIG. 16  is a detail view of  FIG. 15 . 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawing and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As can be seen in  FIGS. 1 to 4 , the freewheel device, reference number  1  in its entirety, includes a tubular sleeve  2  with its axis  3 , a rolling bearing  4  mounted on the sleeve  2 , an outer element  5  mounted on the rolling bearing  4 , a freewheel  6  mounted on the sleeve  2  and a friction element  7  mounted between the outer element  5  and the freewheel  6 . 
     The sleeve  2  includes a bore  2   a , a transverse radial surface  2   b , an outer cylindrical surface  2   c  extending over the major part of its length from the end radial surface  2   b , a radial surface  2   d  extending toward the outside from the end of the outer cylindrical surface  2   c , a short axial surface  2   e  extending from the free end of the radial portion  2   d , axially opposite the end radial surface  2   b , and an end radial surface  2   f  opposite the end radial surface  2   b.    
     The rolling bearing  4  may be of a standard type, with a low production cost and includes a solid inner race  8  provided with a bore mounted, for example by sleeve-fitting, onto the outer cylindrical surface  2   c  of the sleeve  2 , and in contact with the radial portion  2   d , a solid outer race  9 , a row of rolling elements  10 , here balls, placed between a raceway of the inner race  8  and a raceway of the outer race  9 , a cage  11  for retaining the circumferential spacing of the rolling elements  10  and seals  12  and  13  fixedly attached to the outer race  9  and rubbing on a cylindrical bearing surface of the inner race  8 , placed on one side and the other of the row of rolling elements  10  to prevent foreign elements from intruding close to the rolling elements  10  and to retain a lubricant such as grease inside the rolling bearing and close to the rolling elements  10 . The outer race  9  is provided with an outer cylindrical surface  9   a , coaxial with the outer cylindrical surface  2   c  of the sleeve  2 . 
     The outer element  5  includes a central bore  5   a  mounted, for example by sleeve-fitting, onto the outer cylindrical surface  9   a  of the outer race  9 . The rolling bearing  4  thus provides the freedom of rotation of the outer element  5  relative to the sleeve  2 , and the acceptance of the radial forces. The outer element  5  also includes a bore  5   b , with a diameter very slightly greater than the central bore  5   a , and placed at the axial end of the outer element  5  situated opposite the support  4 . The rolling bearing  4  and the outer element  5  are symmetrical relative to a radial plane passing through the center of the rolling elements  10 . An annular radial surface  5   c  is formed between the bores  5   a  and  5   b.    
     The freewheel  6 , mounted adjacent to the rolling bearing  4 , includes an outer race  14 , for example of the solid type, whose bore forms a slipping raceway  14 c, a row of jamming elements  15 , here cams, a cage  16  provided with windows in which are placed the jamming elements  15  in the form of cams and a spring  17  for the return of the jamming elements  15  keeping said jamming elements in permanent contact with the raceways. The jamming elements  15  are placed radially between the outer cylindrical surface  2   c  of the sleeve  2 , axially between the rolling bearing  4  and the end radial surface  2 b of the sleeve  2 , and the raceway  14   c  of the outer race  14 . 
     Between the periphery of the outer race  14  and the bore  5   b  of the outer element  5 , there is a radial space in which the friction element  7  is placed. More precisely, the outer race  14  includes two circular ribs  14   a ,  14   b , directed radially outward. The ribs  14   a  and  14   b  are placed axially at the ends of the outer race  14  while being aligned with the end radial surfaces of the outer race  14  and surround an outer axial surface  14   d  of the outer race  14 . The friction element  7  is placed between the ribs  14   a  and  14   b  and is thus fixedly attached axially to the outer race  14 . 
     The friction element  7  has the shape of a ring open over a small angular sector, for example of the order of a few degrees. The friction element  7  is, in axial cross section, U-shaped with two axial flanges and may be made of rolled metal sheet, In other words, the friction element  7 , in axial section, includes a small diameter axial portion  7   a , a radial portion  7   b  extending outward from one end of the axial portion  7   a , an axial portion  7   c  extending opposite the axial section  7   a  from the large diameter end of the radial portion  7   b , a radial portion  7   d  extending inward from the free end of the axial portion  7   c  and an axial portion  7   e  extending opposite the axial portion  7   a  from the small diameter end of the radial portion  7   b . The axial portions  7   a  and  7   e  have a substantially identical diameter and are in contact with the outer surface of the solid race  14 , the free end of the axial portion  7   a  being placed close to the rib  14   a  and the free end of the axial portion  7   e  being placed close to the rib  14   b . The friction element  7  is symmetrical relative to a radial plane passing through the middle of the axial portion  7   c . The axial portion  7   c  is in contact with the bore  9   b  of the outer element  5 . The friction element  7  may be provided with a local or general coating to improve its friction or anti-corrosion properties. 
     The operation of the device will be better understood with reference to  FIG. 3 . When the outer element  5  rotates in the counterclockwise direction relative to the sleeve  2 , the freewheel  6  is in the freewheeling position with the jamming elements  15  in the tilted position, rubbing on the outer cylindrical surface  2   c  of the sleeve  2  and/or on the raceway  14   c  of the outer race  14 . The sleeve  2  is only subjected to the drag torque of the rolling bearing  4  and of the freewheel  6 . The friction element  7  drives the outer race  14  at the same speed as the outer element  5 . 
     When the outer element  5  rotates in the clockwise direction relative to the sleeve  2 , the freewheel  6  is placed in the locking position, the jamming cams  15  pressing on the outer cylindrical surface  2   c  of the sleeve  2  and on the raceway  14   c  of the solid race  14 . The sleeve  2  is therefore subjected to a torque that may be high and which tends to make it rotate in the clockwise direction. However, when the torque transmitted from the outer element  5  to the friction element  7 , from the friction element  7  to the freewheel  6  and from the freewheel  6  to the sleeve  2 , exceeds a predetermined threshold, the friction element  7  begins to slip, relative to the solid race  14  and/or relative to the outer element  5 , and thus smoothes the torque peaks transmitted to the outer element  5 . The predetermined torque threshold may be chosen on assembly and depends on the features of the friction element and of the surfaces with which said friction element is in contact. 
     By analogy with an electric system, the assembly formed by the freewheel  6  and the torque limiter friction element  7  may be seen as a Zener diode which allows free passage of the electric current in one direction and prevents it in the other until a certain voltage is reached, a voltage beyond which the current may again pass freely. 
     Thus, placing the friction element  7  and the freewheel  6  in series makes it possible, on the one hand, to allow a free rotation in one direction, and to prevent rotation in the opposite direction up to the limit of a maximum torque beyond which the rotation is again allowed with, in addition, losses through friction of the friction element  7  on the outer race  14  and on the bore  5   b  of the outer element  5 . 
     The embodiment illustrated in  FIGS. 5 and 6  is similar to the foregoing embodiments, except that the relative dispositions of the freewheel  6  and the friction element  7  are inverted, the friction element  7  is placed between the outer cylindrical surface  2   c  of the sleeve  2  and the inner solid race  14  of the freewheel  6 . The jamming elements  15  are placed between the raceway  14   c  formed on the outer cylindrical surface of the solid race  14  and the bore  5   b  of the outer element  5 . The operation is similar, except that the freewheel  6 , in the jamming position, is fixedly attached to the outer element  5  and can move angularly relative to the sleeve  2  by slipping of the friction element  7 . 
     The embodiment illustrated in  FIG. 7  is comparable with that illustrated in  FIGS. 1 to 4 , except that the friction element  7  is replaced by a circumferentially continuous friction element  18  attached, for example by overmolding, to the outer race  14  of the freewheel  6  between the ribs  14   a  and  14   b  and radially protruding outward. The friction element  18  is made of synthetic material. The choice of the material and the radial prestress of the friction element  18  between the solid race  14  and the bore  5   b  of the outer element  5  determine the friction torque and therefore the maximum torque that can be transmitted between the outer element  5  and the sleeve  2 . Raceways for the rolling elements  10  are made directly on the sleeve  2  and on the outer element  5 , respectively from the surfaces  2   e  and  5   a . The axial surface  2   e  has an axial length greater than the preceding embodiments. In other words, the rolling races are of a single piece with the sleeve  2  and the outer element  5  respectively. 
     The embodiment illustrated in  FIGS. 8 to 10  is similar to that illustrated in  FIGS. 1 to 4 , except that the friction element  7  is replaced by a friction element  19  having the shape of a metal sheet ring comprising radially elastic tongues  19   a  originating from the body  19   b  of the ring. The ring may be circumferentially continuous or have the shape of a band cut to the correct length and rolled on itself with its two ends abutting. The body  19   b  of the friction element  19  is placed in contact with the solid race  14  between the ribs  14   a  and  14   b , while the tongues  19   a , protruding radially outward, are in contact with the bore  9   b  of the outer element  5 . 
     In the embodiment illustrated in  FIGS. 11 and 12 , the friction element  7  is replaced by an axial-action friction device  20 . The solid race  14  of the freewheel  6  has a reduced radial thickness to leave a greater space to the torque limiter device  20  and is provided with an axial outer surface. In addition, a groove  21  is formed in the bore  5   b  of the outer element  5  so that a circlip  22  can be housed therein, close to the free end of the bore  5   b.    
     The torque limiter device  20  which surrounds the solid race  14  includes two friction rings  23  comprising a friction portion  23   a  made of synthetic material and a support portion  23   b , for example in the shape of a flat metal washer. The friction portions  23   a  are fixedly attached to the support portion  23   b  for example by bonding or overmolding. The friction rings  23  are fixedly attached in rotation to the outer race  14  of the freewheel  6  by means such as axial splines  24  interacting with the bore of the support portions  23   b  of matching shape. The friction rings  23  may move axially relative to the solid race  14 . Between the two friction rings  23  is placed an axial-action washer  25 , of the Belleville washer type or else of the corrugated type. The torque limiter device  20  also includes a ring  27  in the shape of an L-section dish, sleeve-fitted into the bore  5   b  of the outer element  5  and axially in abutment contact against the circlip  22  placed in the groove  21 . The ring  27  includes a radial friction surface  27   a.    
     The friction portions  23   a  of the friction rings  23  have radial friction surfaces  23   c , one in contact with the ring  27 , and the other in contact with a radial surface  5   c  of the outer element  5  forming a shoulder between the bores  5   a  and  5   b . The friction rings  23  are therefore pressing elastically against the corresponding friction surfaces of the outer element  5  and of the ring  27  fixedly attached to the outer element  5 . The choice of the material of the friction rings  23  and of the axial prestress of the rings by the washer  25  determines the friction torque and the maximum transmissible torque threshold. Naturally, a variant could be provided comprising two washers  25  or else a single ring  23  and a single washer  25 . 
     The embodiment illustrated in  FIGS. 14 to 16  is close to that illustrated in  FIGS. 1 to 4 , except that the freewheel  6  includes a spring  28  provided with coils  29  in contact with the outer surface  2   c  of the sleeve  2  and with one end  30  protruding outward. The friction element  7  includes a body  31  in the shape of an open ring made of synthetic material and provided with an axial outer surface  31   a  in contact with the bore  5   b  of the outer element  5 , a radial surface  31   b  connecting to the axial surface  31   a , directed inward and in contact with the shoulder  5   c  of the outer element  5  and with a transverse radial surface of the outer race  9  of the rolling bearing  4 , an axial bore surface  31   c  adjusted on the outer surface  2   c  of the sleeve  2  and a radial surface  31   d  placed opposite the radial surface  31   b  and joining the inner axial surface  31   c  and outer axial surface  31   a . Seen in cross section, the body  31  has a generally rectangular shape. 
     However, in the inner axial surface  31   c , an annular housing  32  is made, placed substantially in the center of the body  31  in the axial direction. Also, a notch  33  occupying a small angular sector is made between the housing  32  and the radial surface  31   b  in contact with the rolling bearing  4 . The notch  33  opens onto a transverse radial surface of the inner race  8  of the rolling bearing  4 . The coils  29  of the spring  28  are housed in the annular housing  32  while the outward protruding end  30  is housed in the notch  33 . 
     Thus, one of the free ends of the spring  28  is fixedly attached in rotation to the body  31  while the coils  29  are in friction contact on the outer axial surface  2   c  of the sleeve  2 . The result is that, in one direction of relative rotation between the sleeve  2  and the body  31 , the spring tends to tighten and angularly connects said sleeve  2  and said body  31 . On the other hand, in the opposite direction of relative rotation, the coils  29  tend to loosen; The sleeve  2  and the body  31  may rotate freely relative to one another in said direction of relative rotation with a slight friction of the coils  29  on the outer axial surface  2   c  of the sleeve  2 . 
     The body  31  also includes another annular groove  34  made from the radial surface  31   d  placed opposite the rolling bearing  4  and having a bottom slightly more extended radially than the entrance of said groove  34 . A circlip  35  is placed in the bottom of the groove  34  while being temporarily radially restricted when it is mounted. The groove  34  is dimensioned so that, when the circlip  35  is in place in the bottom of the groove  34 , said circlip  35  exerts on the body  31  a radially outward force. The body  31  being radially deformable due to the material used and due to said body  31  being an open ring, the outer surface  31   a  of the body  31  is prestressed radially on the bore  5   b  of the outer element  5  which ensures that the body  31  is fixedly attached to the outer element  5  up to a certain torque which may be determined by the dimensions of the outer element  5 , the body  31  and the circlip  35  and by their component materials. 
     In other words, the body  31  forms a single element forming part of both the freewheel  6  and the friction element  7 . Specifically, the annular housing  32  and the notch  33  interact with the spring  28 , and the outer axial surface  31   a  is in contact with the bore  5   b  of the outer element  5  with the possibility of slipping angularly relative to said bore  5   b  in the event of excess torque. 
     Thus, in torque take-up operation, beyond a certain torque value, the body  31  of the friction element  7  begins to rotate relative to the outer element  5 , thus limiting the transmitted torque to the predetermined value. 
     The illustrated embodiments relate to freewheels whose jamming elements are cams or a spring. Naturally the invention could also operate with a freewheel whose jamming element or elements are one or more pawls interacting with a serrated raceway. 
     Thanks to the invention, the longevity of the freewheel and the mechanical members mounted upstream and downstream is increased by the filtering of the torque peaks by the friction member. The race of the freewheel interacts also with the friction member thus giving a particularly compact assembly that is easy to transport, handle and install in a mechanical assembly, for example between a cylindrical housing and a shaft. 
     Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description to the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. In addition, it is to be understood that features described herein independently may, in certain embodiments, be combined.

Technology Classification (CPC): 5