Abstract:
A device for frictional inter-engagement between two mutually movable parts ( 13, 14 ). A lever mechanism exerts counter-directed pressing forces towards both parts to transfers movement between them. A lever ( 25 ) has a free lever end ( 27 ) contacted by a first ( 13 ) of the parts, and opposite to the free end a part-cylindrical convex surface ( 31 ) journalled in a part-cylindrical concave bearing surface ( 33 ). In order to eliminate the risk of jamming of the lever due to excessive surface pressure, it is journalled with rolling bodies, preferably cylindrical bodies ( 34 ).

Description:
BACKGROUND OF THE INVENTION 
   The present invention concerns a frictional engagement device, particularly for use in a freewheel mechanism. 
   DESCRIPTION OF THE RELATED ART 
   Swedish Patent No. 8307120-9 by the present inventor concerns an engagement device for frictional inter-engagement between two mutually movable parts. The mutual movement may be linear or rotational. In case the mutual movement is a rotational movement, as is the case when a freewheel mechanism is concerned, a first part may be an inner circular cylindrical body, and a second part may be an outer annular body co-axially arranged about the first part. When one of the parts, e.g., the inner body, is actuated to perform a rotational movement in one rotational direction, it positively engages an engagement device which in turn is caused to frictionally engage both parts so that the rotational movement is transferred to the other part, in this case the outer body, whereas rotational movement in the opposite direction of the inner body does not trig the engagement device to transfer movement between the parts. Thus, a reciprocating rotational movement of one of the parts will be transformed into a stepwise rotation in the one direction of the other part. 
   The engagement device according to the patent mentioned is constituted by a lever mechanism including a lever operable by the inner body so as to exert counter-directed pressing forces towards portions of both parts. A free end of the lever is contacted by a contact member of the inner body, whereas the opposite end of the lever is shaped with a part-cylindrical convex surface journalled in a corresponding part-cylindrical concave bearing surface of a block-shaped body. An opposite surface of this body is part-cylindrically shaped in conformity with an inner cylindrical surface of the outer body and is slidable therealong. When the contact member contacts the free end of the lever, its part-cylindrical surface slides in a rotational movement about a pivot axis in relation to the bearing surface of the block-shaped body. A clamp body eccentrically carried by the lever then contacts and presses against the radially outer periphery of an axial flange of the outer body, whereas the part-cylindrical convex surface of the lever simultaneously exerts a corresponding pressure against the opposed concave surface of the block-shaped body. This, in turn, presses its part-cylindrical surface against the inner periphery of the outer annular body. At the time a sufficient pressure is achieved, and thereby a sufficient frictional engagement in the two contact areas, the engagement device is operative to transfer rotational movement and torque between the inner body and the outer body, or, vice versa. 
   In operation of this known mechanism, it has turned out that movement of the inner body in the opposite direction does not always sufficiently release the inter-engagement between the part-cylindrical surface of the block-shaped body and the inner periphery of the outer annular body to disengage these two bodies from one another so as to allow the freewheel function. 
   It is believed that the reason for this phenomenon is that the surface pressure in the contact area between the part-cylindrical convex surface of the lever and the part-cylindrical concave surface of the block-shaped body tends to become so high that the oil film in the contact surface is overloaded and breaks, thus resulting in metallic contact. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to find a solution to this problem, i.e., to provide bearing means for the lever that withstands extremely high contact pressures. 
   According to the present invention this is accomplished by providing—instead of a plain slide bearing—a bearing utilizing rolling bodies, preferably a needle bearing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described, reference being made to the accompanying drawings, wherein: 
       FIG. 1  is a part-sectional view of a device utilizing two freewheel mechanisms; and 
       FIG. 2  is a part-sectional view along line II-II in  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The device shown in  FIG. 1  includes two equal freewheel mechanisms  11  and  12 , mechanism  11  being shown in axial section. Each mechanism includes an inner annular body  13  and an outer annular body  14  co-axially arranged about the inner body. The outer body constitutes a housing for the device and comprises—for each mechanism—two housing parts  14   a  and  14   b , the housing parts  14   b  of the two mechanisms being joined by a common hub portion  15 . The hub portion  15  is keyed to a shaft  16  by means of, e.g., opposed woodruff keys  17  secured by screws  18 . The shaft  16  extends through the inner bodies  13  of both mechanisms and is journalled therein by means of needle bearings  19 . The axis of the shaft is denominated C 1 . 
   Each inner body  13  is connected to an arm  20  by means of which reciprocating stepwise rotational movements may be imparted to the inner bodies in an alternating manner (arrow A in  FIG. 2 ). 
   Each inner body has two radially extending, parallel flanges  21 ,  22 , each having a plurality of annularly equally spaced bores  23 . Each pair of aligned bores receives a pin  24 . Each of a plurality of T-shaped levers  25  (only one being shown) has a web portion  26  having a free lever end  27  introduced into the free space between two adjacent pins  24 . 
   An opposed end of each lever includes two flange portions  28  extending in opposite directions from the web portion  26  ( FIG. 1 ). Each of the flange portions has a generally flat surface  29  facing a surface  30 ′ of a respective axially directed, annular flange  30  of the body  14 . Furthermore, the flange portions have a common part-cylindrical surface  31  convexly curved about an axis C 2  ( FIG. 2 ). 
   A block-shaped pressure member  32  has a part-cylindrical surface  33  concavely curved about the axis C 2 , but having a somewhat larger radius. A plurality of cylindrical bodies  34 , together forming a needle bearing, have diameters corresponding to the difference in diameters between the two concentric part-cylindrical surfaces  31  and  33  and occupy the free space between them. Apparently, a swinging motion of the lever  25  about the axis C 2  will cause the cylindrical bodies  34  of the needle bearing to roll between the part-cylindrical surfaces  31  and  33 . 
   The pressure member  32  has a part-cylindrical, convexly curved surface  35  abutting an internal cylindrical surface  36  of the outer body  14  and being slidable therealong. 
   Upon rotation of the inner annular body  13  in a clockwise direction according to  FIG. 2 , one pin  24  contacts the free end  27  of the lever  25  and moves it to the right of  FIG. 2 . Hereby, the entire lever  25  rotates about the axis C 2  causing one end of each surface  29  of the flange portions  28  to approach a respective one of the surfaces  30 ′ of the annular flanges  30 . Thereby, a pressure body  37  supported in an eccentrically located recess  38  in the respective surface  29  contacts the respective surface  30 ′ exerting a pressure thereon. Simultaneously, the convex surface  31  of the lever exerts a corresponding pressure against the bodies  34  of the needle bearing, and they in turn press on the concave surface  33  of the pressure member  32  which, in turn, presses its surface  35  against the surface  36  of the outer body  14 . 
   Typical values of the operative lever arms of lever  25  are about 20 mm from the contact area between pin  24  to the axis C 2  and from about 2 mm to about 4 mm from the axis C 2  to the contact area between the pressure body  37  and the surface  30 ′. 
   Consequently, there is a simultaneous clamping frictional engagement at two locations between the lever/pressure member combination and the outer body  14 , viz., its surfaces  30 ′ and  36 . 
   In the prior art arrangement initially referred to, the pressure body is a circular cylinder. In the embodiment of the present invention shown in  FIG. 2 , it is preferred to make the pressure body  37  with an oval cross section, thereby achieving a better pressure distribution, particularly in the contact area with the surface  30 ′. 
   Operation of a freewheel mechanism utilizing improved engagement devices as described above has revealed that there is no tendency whatsoever for the lever to become stuck in its clamping position. On the contrary, immediately upon release of the engaging rotational force, the engagement devices loosen their clamping engagement with the outer body, and the inner body  13  together with the operating arm  20  is free to move in the opposite direction. It should be pointed out here, that movements of the lever  25  are extremely small; in practice, its stroke from engagement to disengagement is invisible with the naked eye. 
   In order to avoid a possible ‘slow’ engagement of a lever  25 , and also a possible rattling noise in operation, it is preferred to resiliently urge the levers  25  in their engagement direction. This is shown here to be accomplished by a helical spring  39  having one leg  39   a  engaged in a groove  40  in a free end of a pin  24  and one leg  39   b  supported in a circumferential groove  13   a  of the inner body  13 . In this case, the pin  24  is mounted in the radial flanges  21 ,  22  in a manner allowing at least a limited rotational movement. Furthermore, it carries a radially extending arm  41 , which, due to the spring action of spring  39 , exerts a constant resilient pressure on the web portion  26  of the lever  25  such that its free end  27  is in constant contact with a pin  24  as seen in  FIG. 1 . 
   In order to prevent a possible escape of the needles  34 , the pressure member  32  is provided with a lip  42   a  preventing escape in one direction, and the flanges  28  are provided with lips  28   a  preventing escape in the other direction.