Abstract:
A one-way clutch comprising an inner race and an outer race radially spaced apart from each other and concentrically disposed for rotation relative to each other, and a spray disposed between the inner race and the outer race for transmitting torque is characterized in that the cam surface of the sprag which contacts with the outer peripheral surface of the inner race is formed with a plurality of axially extending grooves.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a one-way clutch for a torque converter used as a part for torque transmission, back stop, etc., in the driving apparatus of,-for example, an automobile, and more particularly to an improvement in a sprag. 
   2. Related Background Art 
   Generally, a one-way clutch comprises an inner race and an outer race radially spaced apart from each other and concentrically disposed for rotation relative to each, and a torque transmitting member disposed between the inner race and the outer race for transmitting torque, and the cam surface of a sprag meshes with the raceway surfaces of the inner and outer races to thereby transmit the torque. 
   In order to form an oil film, it is preferable that the cam surface of the sprag be as smooth as possible, but in order to give predetermined surface roughness to the cam surface, there is a sprag in which as described in Japanese Patent Application Laid-open No. H6-313445, minute unevenness is formed on a meshing surface to improve the forming rate of oil film on the cam surface. 
   The sprag, however, if the viscosity of lubricating oil becomes high under a very low temperature environment (e.g. −20° C. to −40° C. or lower), does not normally mesh but continuously causes slip when shift is made from idle rotation to meshing, and there may occur the inconvenience that the meshing of a sprag clutch does not function. When as in Japanese Patent Application Laid-open No. H6-313445, minute unevenness is formed on the surface, there is the possibility that lubricating oil of high viscosity collects in the unevenness and becomes oil film to thereby cause continuous slip. 
   To overcome these problems, it is conceivable to increase a ribbon spring force which applies a load in a meshing direction to the sprag, but an increase in the ribbon spring force may increase the drag during idle rotation, and may cause the aggravation of fuel consumption in a one-way clutch used in an automatic transmission. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is the object of the present invention to provide a one-way clutch which eliminates the above-noted problems and is greatly improved in meshing during a low temperature, and a sprag for use in the one-way clutch. 
   In order to achieve the above object, the one-way clutch of the present invention is a one-way clutch comprising an inner race and an outer race radially spaced apart from each other and concentrically disposed for rotation relative to each other, and a sprag disposed between the inner race and the outer race for transmitting torque, wherein the cam surface of the sprag which contacts with the inner race and the outer race is formed with a plurality of axially extending grooves. 
   Also, the sprag of the present invention is a sprag used in a one-way clutch comprising an inner race and an outer race radially spaced apart from each other and concentrically disposed for rotation relative to each other, and disposed between the inner race and the outer race for transmitting torque, wherein a cam surface contacting with the outer peripheral surface of the inner race is formed with a plurality of axially extending grooves. 
   According to the present invention, there is obtained the following effect. 
   Since the meshing surface of the sprag which is adjacent to the inner race is formed with a plurality of axially extending grooves, a sufficient meshing property can be secured even during a low temperature at which the viscosity of lubricating oil rises. This is because the grooves formed in the cam surface of the sprag eliminates oil film between the sprag and the inner race which has become high in viscosity during the low temperature, during meshing, and the sprag and the inner race achieve metal-to-metal contact and mesh with each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a sprag used in a one-way clutch according to an embodiment of the present invention. 
       FIG. 2  is a fragmentary front view of the sprag of  FIG. 1 . 
       FIG. 3  is a partly broken-away front view of the one-way clutch. 
       FIG. 4  is a front view of a one-way clutch of other type to which the present invention is applicable. 
       FIG. 5  is a front view of a sprag used in the one-way clutch as shown in  FIG. 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will hereinafter be described in detail with reference to the drawings. The embodiment hereinafter described illustrates the present invention by way of example, and of course does not restrict the present invention. Also, throughout the drawings, like portions are designated by like reference characters. 
     FIG. 1  is a perspective view of a sprag  3  used in a one-way clutch  10  ( FIG. 3 ) according to an embodiment of the present invention, and  FIG. 2  is a fragmentary front view of the sprag  3  of  FIG. 1 . While here is shown an example in which a gourd-shaped sprag  3  is used as a torque transmitting member, the present invention can also of course be applied to a one-way clutch using other form of sprag. 
   As shown in  FIG. 1 , the sprag  3  has a plurality of axially extending substantially parallel grooves  20  in a cam surface  21 . The grooves  20  extend from one axial edge portion  3   a  to the other edge portion  3   b  of the sprag  3 . That is, the grooves  20  extend over the entire axial width of the cam surface  21  of the sprag  3 . 
   The depth and pitch of the grooves  20  will now be described with reference to  FIG. 2 . The depth of the grooves  20  in about 0.005 mm or greater and 0.05 mm or less for the durability of the sprag, but may desirably be within the amount of elastic deformation of the surface during a maximum load, and may more preferably be about 0.015 mm or greater and about 0.03 mm or less. 
   Also, the pitch between adjacent ones of the grooves  20  can be arbitrarily set, but may desirably be about 0.5 mm or less to secure a meshing property. In  FIG. 1 , and particularly  FIG. 2 , for the convenience of illustration, the grooves  20  are depicted at a size larger than the actual size thereof. Also, when the sprag  3  is used in a one-way clutch, the cam surface  21  of the sprag  3  is opposed to the outer peripheral surface of an inner race and therefore, the grooves  20  shown in  FIGS. 1 and 2  are located in the lower portion of the sprag  3 . That is, in order to show the grooves  20 , the sprag  3  is shown as being inverted relative to a state in which it is actually used. 
   Description will now be made of the construction of a one-way clutch  10  using the sprag  3  formed with the grooves  20  in the cam surface  21 .  FIG. 3  is a partly broken-away front view of the one-way clutch  10 . 
   In  FIG. 3 , the one-way clutch  10  is provided with an outer race  1  and an inner race  2 . The outer race  1  is provided with a substantially completely round inner peripheral surface la. Also, the inner race  2  is provided with a substantially completely round outer peripheral surface  2   a.  The outer race  1  and the inner race  2  are disposed for rotation relative to each other with the inner peripheral surface la and the outer peripheral surface  2   a  thereof opposed to each other. 
   In an annular space defined by the outer race  1  and the inner race  2 , a plurality of torque transmitting members for transmitting torque between the two races, i.e., ground-shaped sprags  3 , are equally arranged in the circumferential direction of the annular space, and transmit the torque between the inner and outer races. The sprags  3  are held in substantially rectangular windows  8  provided in a pair of holders, i.e., an outer holder  5  and an inner holder  6 . 
   A ribbon spring  4  is disposed between the outer and inner holders  5  and  6 , and gives the sprags  3  a rising moment in a direction to mesh with an engagement surface. The grooves  20  shown in  FIGS. 1 and 2  are formed in the cam surface  21  by which the sprags  3  mesh with the outer peripheral surface  2   a  of the inner race  2 . 
   It is preferable in terms of cost that the grooves  20  be formed at a time when the sprags  3  are manufactured at the drawing-out step, but the grooves  20  can also be formed after the completion of the sprag  3 . Also, the grooves  20  are formed so as to extend over the entire axial width of the cam surface  21  of each sprag  3 , whereas they need not always be formed over the entire width, but can also be formed so as not to extend to the axial opposite ends of each sprag  3 . 
   Also, if a desired meshing property is obtained under a very low temperature, the number of the grooves  20  is arbitrary, and is not restricted to the shown number. 
   While the present invention has been described with respect to a one-way clutch having two holders, i.e., the outer holder and the inner holder, the present invention can also of course be applied to a one-way clutch of a type having a single holder. 
     FIGS. 4 and 5  show a case in which the present invention is applied to a one-way clutch of other type.  FIG. 4  is a front view of one-way clutch of other type to which the present invention is applicable and  FIG. 5  is a front view of a sprag used in the one-way clutch as shown in  FIG. 4 . The one-way clutch  30  comprises a sprag  33  provided between inner and outer races to transmit torque, a wire gauge  32  for retaining the sprag  33 , a garter spring  31  fitted in a circumferential groove  35  (in  FIG. 5 ) formed in the sprag  33  and a side plate  34  for supporting the sprag  33  in an axial direction. The inner and outer races are not shown. 
   As shown in  FIG. 5 , the sprag  33  is provided with a plurality of grooves  37  extending in the axial direction on a cam surface  36  which is in contact with the inner race (not shown). Pitch and depth of the grooves  37  can be designed as in the grooves  20 , and the grooves  37  have substantially the same function as the grooves  20 .