Abstract:
A one-way clutch comprises plural sprags to be arranged between an outer ring and an inner ring, a retainer made of wire bent in a square-U zig-zag form so that the wire alternately extends in an axial and peripheral directions of the retainer to form sprag windows for holding the sprags, and side plates arranged on opposite sides of the retainer as viewed in the axial direction of the retainer. At least one protrusion corresponding to each of the sprags is formed on an inner wall of at least one of the side plates opposite to the sprags and extending toward the corresponding sprag.

Description:
This application is a division of application Ser. No. 09/228,424, filed Jan. 12, 1999 now U.S. Pat. No. 6,044,947. 
    
    
     BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     This invention relates to a sprag-type one-way clutch, which is adapted to be mounted between a driving shaft and a driven shaft in an automotive vehicle, general industrial equipment or the like so that motive power of rotation of the driving shaft, said rotation being only in one direction, can be transmitted to the driven shaft. 
     b) Description of the Related Art 
     A sprag-type one-way clutch is mounted between a driving shaft and a driven shaft and by way of sprags arranged between an outer ring and an inner ring, transmits rotational force of one direction from the driving shaft to the driven shaft. 
     When the rotational force of the one direction is applied from the driving shaft to the sprags, the sprags are wedged between the outer ring and the inner ring so that torque is transmitted to the driven shaft. Upon application of rotational force of an opposite direction, however, the sprags remain unwedged between the outer ring and the inner ring so that no transmission of torque takes place between the driving shaft and the driven shaft. 
     Depending primarily upon the manner of holding of sprags, these sprag-type one-way clutches can be classified into three types, that is, the single cage type, the wire cage type and the double cage type. 
     A description will hereinafter be made of the constructions of one-way clutches of the respective types. 
     A conventional one-way clutch  60  of the single cage type will be described while making reference to FIGS. 1A through 1C for the sake of convenience. 
     The one-way clutch  60  comprises plural sprags  13 , which are to be wedged between an outer ring  21  and an inner ring  22 , and a retainer  15  arranged between the outer ring  21  and the inner ring  22  and holding the sprags  13  in place. 
     The retainer  15  is composed of a cylindrical part  18  and a flange  17 . Sprag windows  19  for the sprags  13  are formed in the cylindrical part  18 . The flange  17  is formed in an elliptical or oval shape having a short-diameter portion and a long-diameter portion. 
     A ring-shaped spring  16  is fitted beforehand on the cylindrical part  19  of the retainer  15 . When the sprags  13  are inserted in the sprag windows  19  of the cylindrical part  18  and the spring  16  is fitted in spring-receiving slots formed in the sprags  13 , the sprags  13  are held in the sprag windows  19  under pressing force of the spring  16 . 
     As has been described above, the conventional one-way clutch  60  has substantially the same construction as a one-way clutch  10  according to a first embodiment of the present invention except that the conventional one-way clutch  60  is different in the shape of the sprag windows formed in the retainer from the one-way clutch  10 . 
     To show this difference more clearly, a side view of the conventional one-way clutch  60  of the single cage type is illustrated in FIG.  6 . 
     If any one of the sprags  13  begins to move in an axial direction of a cylindrical part  68 , one of side faces of the sprag  13 , said one side face being on a side of the moving direction of the sprag  13 , comes into contact with the corresponding one of two edges  692 , 692  out of four edges of the associated sprag window  69  formed in the retainer  65 , said two edges  692 , 692  extending in a peripheral direction of the cylindrical part  68 , so that the sprag  13  is prevented from moving in the axial direction of the cylindrical part  68 . 
     A description will next be made of a conventional one-way clutch  70  of the wire cage type. 
     FIGS. 7A and 7B illustrate at numeral  70  the conventional one-way clutch of the wire cage type as assembled between an outer ring  21  and an inner ring  22 . FIG. 7A is a front view of the conventional one-way clutch  70  of the wire cage type, while FIG. 7B is a vertical cross-sectional view of the same conventional one-way clutch  70  taken in the direction of arrows VIIB—VIIB of FIG.  7 A. 
     A retainer  75  employed in this one-way clutch  70  has been formed by bending a wire in a square-U zig-zag endless form so that said wire alternately extends in an axial and peripheral directions of the retainer  75 . Each sprag  13  is arranged and held in place in a sprag window which is formed of two axially-extending adjacent portions of the wire and one peripherally-extending portion of the wire, said peripherally-extending portion connecting the axially-extending portions with each other at their proximal ends. 
     The one-way clutch  70  is constructed by arranging the sprags  13  in the retainer  75 , fitting a spring  16  in spring-receiving slots formed in the sprags  13 , and the arranging two side plates  72 , 74  on opposite sides of the sprags  13 . 
     Depending on which side each sprag  13  moves toward in the axial direction, one of the side faces of the sprag  13 , said one side face being on a side of the moving direction of the sprag  13 , comes into contact at substantially the entire area thereof with the opposing one of the side plates  72 , 74  (see FIG.  7 B). 
     Finally, a conventional one-way clutch  80  of the double cage type will be described while making reference to FIGS. 4A,  4 B,  5 A and  5 B for the sake of convenience. 
     The one-way clutch  80  is different in the shape of sprags and the sprag-holding structure from the above-described one-way clutch of the single cage type. 
     The one-way clutch  80  is constructed by holding sprags  43  in place by an outer retainer  87  shown in FIG. 8A, an inner retainer  88  depicted in FIG. 8B and a ribbon spring  50  illustrated in FIGS. 5A and 5B. 
     As is shown in the perspective view of FIG. 5A, the ribbon spring  50  is provided with windows formed as spaces by side bars  54 , which extend in a lengthwise direction and include plural wrinkles  540  formed at equal intervals, and also by cross bars  52  extending in a widthwise direction. A wrinkle  520  extends from a central portion of each cross bar  52  and terminates in a tab  522 . 
     FIG. 5B is a perspective view, which illustrates the sprags  43  assembled in the ribbon spring  50  shown in FIG.  5 A. 
     When each sprag  43  with a constricted portion formed in a central part thereof is assembled in one of the windows of the ribbon spring  50 , the constricted portion of the sprag  43  is brought into contact with the tab  522  of the wrinkle  520  so that the sprag  43  is urged by the wrinkle  520  via the tab  522 . 
     The sprags  43 , which are in a state assembled in the ribbon spring  50 , is held by the retainers  87 , 88  which will be described below. 
     Incidentally, the outer retainer  87  is provided with resilient pieces (note shown) at several locations on an outer peripheral portion of the outer retainer  87 . Resilient engagement of the resilient pieces with an inner peripheral portion of the outer ring produces drag torque. 
     In FIG. 4B, numerals  94 , 96  indicate a pair of end bearings. 
     FIGS. 8A and 8B are side views of the outer retainer  87  and inner retainer  88  for use in the conventional one-way clutch  80  of the double cage type. 
     The sprags  43  are held in sprag windows  870 , 880 , which are formed in the outer retainer  87  and inner retainer  88 , respectively. 
     Each of the above-described one-way clutches  60 , 70 , 80  is used by assembling it between the outer ring  21  and the inner ring  22  in such a way that the inner ring  22  is located inside the retainer or retainers and the outer ring  21  is located outside the retainer or retainers. 
     Each of the above-described one-way clutches of the single cage type, wire cage type and double cage type is designed so that an oil film of lubricating oil is formed at an area of contact between each edge of each sprag window of each retainer and its associated sprag or between each side plate and each sprag to produce frictional force by way of the oil film. This frictional force acts as resistance when a relative motion takes place between the retainer or retainers and the sprags or between the side plates and the sprags. It is therefore necessary to set the biasing force of the spring member at a high level in view of the resistance. As a result, excess drag torque is unavoidably produced during a slip of the clutch, leading to a problem in that the fuel economy of an automobile or a motorcycle is deteriorated. 
     Further, a large area of contact between each sprag and each edge of its corresponding sprag window or a large area between each sprag and each side plate tends to develop wearing at the contact area, leading to a problem in that the durability of the clutch is reduced. 
     The above problems tend to arise especially at low temperatures where the viscosity of the oil film becomes higher. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve or lessen the above-described problems of the conventional one-way clutches and to provide a one-way clutch which does not produce excess drag torque during a slip and which has lower tendency of development of wearing at a contact area between each sprag and each edge of its corresponding sprag window or between each sprag and each side wall. 
     In one aspect of the present invention, there is thus provided a one-way clutch, which comprises plural sprags to be arranged between an outer ring and an inner ring and at least one retainer holding the sprags in place. The retainer is provided with sprag windows for the sprags. At least one indentation is formed in an edge of each of the sprag windows, said edge extending in a peripheral direction of the retainer, so that the edge is maintained at the indentation thereof out of contact with an opposing end face of the associated one of the sprags. 
     In a preferred embodiment, the one-way clutch is provided with one retainer. Each of the sprag windows in the retainer is in a quadrilateral shape, and has first opposing edges extending in the peripheral direction of the retainer and second opposing edges extending in an axial direction of the retainer. Two indentations are formed at an interval therebetween in each of the first opposing edges. 
     In another preferred embodiment, the one-way clutch is provided with two retainers. Each of the sprag windows in each of the retainers is in a quadrilateral shape, and has first opposing edges extending in the peripheral direction of the retainer and second opposing edges extending in an axial direction of the retainer. Two indentations are formed at an interval therebetween in each of the first opposing edges. 
     As the indentation or indentations are formed in each sprag window of each retainer, each end face of the corresponding sprag is maintained out of contact with the indentation or indentations so that the sprag is held in place while being allowed to come into contact with only portions of edges of the corresponding sprag window. Friction by way of an oil film between each sprag and the corresponding sprag window is therefore reduced. The one-way clutch is therefore provided with improved durability. Further, owing to the reduced friction, it is no longer necessary to set the biasing force of a spring member at such a high level as that required for conventional one-way clutches. As a result, smaller drag torque is produced during a slip of the clutch, thereby bringing about an improvement in fuel economy. 
     In another aspect of the present invention, there is also provided a one-way clutch, which comprises plural sprags to be arranged between an outer ring and an inner ring, a retainer made of a wire bent in a square-U zig-zag form so that the wire alternately extends in an axial and peripheral directions of the retainer to form sprag windows, said retainer holding the sprags in the sprag windows, respectively, and side plates arranged on opposite sides of the retainer as viewed in the axial direction of the retainer. Corresponding to each of the sprags, at least one protrusion is formed on an inner wall of at least one of the side plates, said inner wall being located opposite to the sprags, so that the protrusion extends toward the corresponding sprag. 
     In this construction, each end face of each sprag comes into contact with only the corresponding protrusion formed on the inner wall of the corresponding side wall, so that friction by way of an oil film between each sprag and the corresponding side wall is therefore reduced. The one-way clutch is therefore provided with improved durability. Further, owing to the reduced friction, it is no longer necessary to set the biasing force of a spring member at such a high level as that required for conventional one-way clutches. As a result, smaller drag torque is produced during a slip of the clutch, thereby bringing about an improvement in fuel economy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A through 1C illustrate a one-way clutch of the single cage type according to one embodiment of the present invention, in which FIG. 1A is a front view of the one-way clutch as assembled between an outer ring and an inner ring, FIG. 1B is a vertical cross-sectional view of the one-way clutch taken in the direction of arrows IB—IB of FIG. 1A, and FIG. 1C is a side view of the one-way clutch; 
     FIG. 2 is a front view of a one-way clutch according to a second embodiment of the present invention; 
     FIGS. 3A and 3B show a one-way clutch of the wire cage type according to a third embodiment of the present invention, in which FIG. 3A is a front view of the one-way clutch as assembled between an outer ring and an inner ring and FIG. 3B is a vertical cross-sectional view of the one-way clutch taken in the direction of arrows IIIB—IIIB of FIG. 3A; 
     FIGS. 4A through 4D depict a one-way clutch of the double cage type according to a fourth embodiment of the present invention, in which FIG. 4A is a front view of the one-way clutch as assembled between an outer ring and an inner ring, FIG. 4B is a vertical cross-sectional view of the one-way clutch taken in the direction of arrows IVB—IVB of FIG. 4A, and FIGS. 4C and 4D are side views of an outer retainer and inner retainer used in the one-way clutch, respectively; 
     FIGS. 5A and 5B show a ribbon spring and sprags used in the one-way clutch according to the fourth embodiment of the present invention, in which FIG. 5A is a perspective view of the ribbon spring and FIG. 5B is a perspective view of the ribbon spring with the sprags assembled therein; 
     FIG. 6 is a side view of a conventional one-way clutch of the single cage type; 
     FIGS. 7A and 7B illustrate a conventional one-way clutch of the wire cage type, in which FIG. 7A is a front view of the one-way clutch as assembled between an outer ring and an inner ring and FIG. 7B is a vertical cross-sectional view of the one-way clutch taken in the direction of arrows VIIB—VIIB of FIG. 7A; and 
     FIGS. 8A and 8B are side views of an outer retainer and inner retainer used in a conventional one-way clutch of the double cage type, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIGS. 1A through 1C, the one-way clutch of the single cage type according to the first embodiment of the present invention will be described. 
     This one-way clutch, which is generally indicated at numeral  10 , is similar to the conventional one-way clutch of the single cage type except for the construction of a retainer  15  which holds sprags  13  in place, so that a description of elements other than the retainer  15  is omitted herein. 
     In a cylindrical part  18  of the retainer  15 , sprag windows  19  are formed. Each sprag window  19  is defined by a pair of edges  190 , 190  extending in a peripheral direction of the cylindrical part  18  and a pair of edges  194 , 194  extending in an axial direction of the cylindrical part  18 . In each of the paired edges  190 , 190  extending in the peripheral direction of the sprag window  19 , two indentations  192 , 192  are formed to maintain the edge  190  out of contact at the indentations with an opposing end face of the associated sprag  13  (see FIG.  1 C). 
     When each sprag  13  is held in the corresponding sprag window  19 , the sprag  13  is prevented from moving in the axial direction by portions of the edges  190 , 190  other than the indentations  192 . Compared with the conventional one-way clutch of the single cage type (see FIG.  6 ), the area of contact between the edges of each sprag window  19  and the associated sprag  13  is reduced. In the illustrated embodiment, the area of contact is as small as about one third of that in the conventional one-way clutch of the single cage type. 
     Referring next to FIG. 2, the one-way clutch according to the second embodiment of the present invention will be described. 
     The one-way clutch, which is generally designated at numeral  20 , additionally includes block bearings B, as bearings between an outer ring  21  and an inner ring  22 , in the construction of the above-described one-way clutch  10  of the single cage type. 
     As elements of the one-way clutch  20  other than the block bearings B are similar to the corresponding elements in the first embodiment of the present invention, their description is omitted herein. Incidentally, a practical example of one-way clutches equipped with such block bearings is disclosed in U.S. Pat. No. 5,372,227 issued Dec. 13, 1994 and assigned to the same assignee as the present invention, which is incorporated herein by reference. 
     With reference to FIGS. 3A and 3B, a description will next be made of the one-way clutch of the wire cage type according to the third embodiment of the present invention, which is designated generally at numeral  30 . 
     As elements of the one-way clutch  30  other than side plates are similar to the corresponding elements of the conventional one-way clutch of the wire cage type, their description is omitted herein. 
     Each of the side plates  32 , 34  is provided with plural protrusions  320  or  340 , which extend toward opposing side faces of the associated sprags  13 . 
     When the above-described side plates  32 , 34  are fitted on a wire cage  35  in which the plural sprags  13  have been arranged, the opposite side faces of the sprags are maintained out of contact with the side plates  32 , 34  at areas other than the corresponding protrusions  320 , 340 . 
     As is illustrated in FIG. 3B, each sprag  13  in this one-way clutch  30  comes into contact with the side plates  32 , 34  only at the corresponding protrusions  320 , 340 . Compared with the conventional one-way clutch of the wire cage type (see FIG.  7 B), the area of contact between each sprag  13  and the side plates  32 , 34  is significantly reduced. Specifically, it can be reduced to about one tenth or so. 
     Referring next to FIGS. 4A through 4C, a description will be made of the one-way clutch of the double cage type according to the fourth embodiment of the present invention, which is generally designated at numeral  40 . 
     As elements of the one-way clutch  40  other than an outer retainer  47  and an inner retainer  48  are similar to the corresponding elements of the conventional one-way clutch of the double cage type, their description is omitted herein. 
     Each of the outer retainer  47  and inner retainer  48  is provided with a cylindrical part, through which sprag windows  470  or  480  are formed. Each sprag window  470  or  480  is defined by a pair of edges  476  or  486  extending in a peripheral direction of the cylindrical part and a pair of edges  474  or  484  extending in an axial direction of the cylindrical part. 
     In each of the paired edges  476  or  486  of each sprag window, said paired edges extending in the peripheral direction of the corresponding cylindrical part, indentations  472  or  482  are formed at an angular interval therebetween. 
     When each sprag  43  is held in the associated sprag window  470  or  480  of the corresponding retainer  47  or  48 , the sprag  43  is maintained out of contact with the indentations  472 , 482  formed in the retainer  47  or  48 . Compared with the conventional one-way clutch of the double cage type, the area of contact between the sprag  43  and the edges  476  or  486  of the associated sprag window  470  or  480 , said edges extending in the peripheral direction, is reduced. In the illustrated embodiment, the area of contact is as small as about one third or so of that in the conventional one-way clutch of the double cage type. 
     In the above-described fourth embodiment of the present invention, the indentations  472 , 482  are formed in the edges  476  and  486  of the sprag windows  470 , 480  in both of the outer retainer  47  and inner retainer  48 . However, the sprag windows  470  or  480  of only one of the outer retainer  47  and inner retainer  48  may be provided with such indentations. 
     In each of the above-described one-way clutch  10  of the single cage type and one-way clutch  40  of the double cage type, the friction-reducing effect can be enhanced by forming the indentations in each of the edges of each sprag window  19 ,  470  or  480  in such a way that the resulting protrusion is located as close to a center of rocking of the associated sprag  13 , which rocks in the sprag window, as possible, in other words, is located at or adjacent to the center of rocking of the associated sprag  13 . 
     In the one-way clutch  30  of the wire cage type, it is desired to arrange each protrusion  320  or  340  on the corresponding side plate  32  or  34  so that the protrusion  320  or  340  is located as close to a center of rocking of the associated sprag  13  as possible, in other words, is located at or adjacent to the center of rocking of the associated sprag  13 . 
     Further, the retainers  15  in the first and second embodiments and the outer retainer  47  and inner retainer  48  in the fourth embodiment may be formed of metal or resin. 
     The block bearings in the second embodiment of the present invention can also be incorporated in the one-way clutch  30  of the wire cage type according to the third embodiment of the present invention. 
     This application claims the priority of Japanese Patent Application No. HEI 10-014737 filed Jan. 12, 1998, which is incorporated herein by reference.