Patent Publication Number: US-9850785-B2

Title: Cam follower and method for manufacturing such a cam follower

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a Non-Provisional Patent Application, filed under the Paris Convention, claiming the benefit of European Patent (EP) Patent Application Number 15305170.1, filed on 5 Feb. 2015 (05.02.2015), which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD OF THE INVENTION 
     The invention concerns a cam follower. The invention also concerns an injection pump or a valve actuator comprising such a mechanical system. The invention also concerns a method for manufacturing such a cam follower. 
     BACKGROUND OF THE INVENTION 
     EP-A-2 607 636 discloses an example of cam follower, comprising a tappet, a pin and a roller. The tappet extends along a longitudinal axis, while the pin and the roller are centered on a transverse axis. The tappet is formed with two lateral flanges, delimiting an intermediate gap between them and each comprising a cylindrical bore. The roller is positioned in the intermediate gap, between both flanges and bores. The pin is fitted in the two bores, such that the roller is movable in rotation relative to the pin around its axis. The pin is then caulked, in other words plastically deformed, on both opposite ends to create a mechanical connection by press-fit in the tappet bores. 
     When the cam follower is in service, the roller collaborates with a cam synchronized with the internal combustion engine camshaft. The rotation of the camshaft leads to a periodic displacement of a piston of the pump that rests against the tappet, to allow fuel to be delivered. The tappet is movable back and forth along the longitudinal axis, while the roller is movable in rotation around its central axis. 
     In EP-A-2 607 636, the caulking operation allows to retain the pin along the transverse axis. The roller is positioned in the tappet, then the pin is inserted through the bores and the roller. Finally, the pin ends are caulked by press-fit in the bores. Thus, the pin is secured relative to the tappet, both in rotation and in translation. 
     Alternatively, it is known to implement caulking on the tappet, such that the pin is partly movable relative to this tappet. The pin can rotate around the transverse axis. Besides, the pin can move on a small distance along the transverse axis, but cannot be removed from the tappet. 
     However, caulking processes are difficult to control and require powerful machines. 
     JP-A-2013/029027 discloses another example of cam follower. The tappet comprises two flanges including holes for receiving the end of the pin. However, due to their particular shapes, the flanges are difficult to mold. Moreover, due to limited access for the tool, the holes are difficult to shape by machining. Moreover, the flanges must be deformed in order to insert the pin into the holes. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to provide a cam follower overcoming the disadvantages mentioned here-above. 
     To this end, the invention concerns a cam follower, comprising: a tappet which includes two flanges provided with opposite holes centered on a transverse axis; a pin extending along the transverse axis between two opposite ends received in the opposite holes; and a roller movable in rotation relative to the pin around the transverse axis and adapted to roll on a cam. 
     According to the invention, each of the opposite holes is provided with: an open portion for mounting the pin by translation in a first direction perpendicular to the transverse axis, a cylindrical portion for supporting the pin along the first direction and a plane portion for retaining the pin along the transverse axis during transport and mounting of the cam follower. 
     Thanks to the invention, the sub-assembly including the pin and the roller is easier to mount into the tappet. Given that the flanges are machined but do not need to be deformed, specific treatments can be performed on the tappet, by example cementation then heat treatment. 
     According to further aspects of the invention which are advantageous but not compulsory, such a cam follower may incorporate one or several of the following features:
         The flanges are provided with secondary holes each open, on the one hand, along the transverse axis between the plane portion and an outer side of the tappet and, on the other hand, perpendicular to the transverse axis in a second direction opposite the first direction, the secondary holes allowing passage of a tool shank for machining the opposite holes in the tappet.   The flanges are provided with deformed portions to prevent dismounting of the pin by translation in a second direction opposite the first direction.   The pin is secured to the tappet in the opposite holes, the flanges having deformed portions in contact with the ends of the pin.   The pin is partly movable in the opposite holes, the flanges having deformed portions devoid of contact with the ends of the pin.   The pin is movable in rotation around the transverse axis in the opposite holes.   The pin is partly movable in translation and is retained by the plane portions along the transverse axis in the opposite holes.   The flanges have deformed portions formed on both sides of the secondary holes.       

     The invention also concerns an injection pump for a motor vehicle, comprising a mechanical system as mentioned here-above. 
     The invention also concerns a valve actuator for a motor vehicle, comprising a mechanical system as mentioned here-above. 
     The invention also concerns a method for manufacturing a cam follower as mentioned here-above. The method comprises a mounting step b) consisting in mounting the pin into the opposite holes by translation in the first direction, without deforming the flanges. 
     According to further aspects of the invention which are advantageous but not compulsory, such a cam follower may incorporate one or several of the following features:
         The method comprises a machining step a) consisting in machining the opposite holes in the flanges before the mounting step b).   The method comprises a deforming step c) consisting in plastically deforming the flanges to prevent dismounting of the pin by translation in a second direction opposite the first direction after the mounting step b).   After the deforming step c), the flanges have deformed portions in contact with the ends of the pin, such that the pin is secured to the tappet in the opposite holes.   After the deforming step c), the flanges have deformed portions devoid of contact with the ends of the pin, such that the pin is partly movable in the opposite holes.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in correspondence with the annexed figures, and as an illustrative example, without restricting the object of the invention. In the annexed figures: 
         FIG. 1  is a perspective view of a cam follower according to the invention, comprising a tappet, a pin and a roller; 
         FIG. 2  is a perspective view similar to  FIG. 1 , before mounting of the pin and the roller on the tappet; 
         FIG. 3  is a side view along arrow III on  FIG. 1 ; 
         FIG. 4  is a sectional view along line IV-IV on  FIG. 3 ; 
         FIG. 5  is a sectional view along line V-V on  FIG. 4 ; 
         FIG. 6  is a view of detail VI on  FIG. 3 , at a larger scale and with a partial section, of the cam follower after localized caulking; 
         FIG. 7  is a partial perspective view, at a larger scale and from a different angle, of the cam follower of  FIG. 1  after localized caulking; and 
         FIG. 8  is a view of detail VIII on  FIG. 7 , at a larger scale. 
     
    
    
     DETAILED DESCRIPTION OF SOME EMBODIMENTS 
     The cam follower  1  represented on  FIGS. 1 to 8  is adapted to equip an injection pump or a valve actuator for a motor vehicle, not shown. 
     Cam follower  1  comprises a tappet  10 , a pin  30 , a roller  40  and a bearing  50 . Elements  30 ,  40  and  50  are centered on a transverse axis X 1  and form a roller sub-assembly  60 . Tappet  10  is centered on a longitudinal axis Y 1 . Axes X 1  and Y 1  are perpendicular. Roller  40  is adapted to roll on a cam  2 , partly shown on  FIG. 3 . 
     Tappet  10  comprises a cylindrical body  11  centered on axis Y 1  and extending between opposite ends  13  and  14 . Tappet  10  also comprises a transverse central portion  12  extending radially to axis Y 1  and delimiting two cavities  15  and  16  inside body  11 . Cavity  15  is open at end  13 , has a cylindrical shape and receives a shaft or plunger, not shown, for moving tappet  10  along axis Y 1 . Cavity  16  is open at end  14 , has a generally parallelepiped shape and partly receives sub-assembly  60 . Body  11  has a cylindrical outer surface  18  centered on axis Y 1  and extending between ends  13  and  14 . Body  11  includes several recesses  182 ,  184  and  186 , open at surface  18  and provided for lubrication or other functions that are not subjects of the present invention. 
     Tappet  10  is movable back and forth along axis Y 1 , in a non-represented bore belonging to the injection pump, with surface  18  sliding in this bore. Tappet  10  can be made of synthetic material, by example polyamide 6.6 (PA) or polyether-ether-ketone (PEEK), or made of metal, by example steel. 
     Furthermore, tappet  10  forms a support element for sub-assembly  60 . Specifically, tappet  10  comprises a bearing portion  20  formed in body  11  and delimiting cavity  16  near end  14 . Bearing portion  20  is adapted to receive pin  30 , on which roller  40  and bearing  50  are mounted. To this end, bearing portion  20  comprises two lateral flanges  21  and  22  extending perpendicular to axis X 1  and parallel to axis Y 1 , on both side of axis Y 1 . Flanges  21  and  22  are connected around axis Y 1  by portions  19  of body  11 . Each flange  21  and  22  includes an opening or hole, respectively  23  and  24 , for receiving ends  33  and  34  of pin  30 . Each flange  21  and  22  also includes a secondary opening or hole, respectively  25  and  26 , in communication with holes  23  and  24 . Each hole  25  and  26  allows the passage of a tool shank for machining corresponding hole  23  or  24 . Holes  23 ,  24 ,  25  and  26  are formed by molding tappet  10 , then holes  23  and  24  are machined to their final shape. 
     Each hole  23  and  24  is open at end  14  of tappet  10 , inside cavity  16 , and in corresponding hole  25  or  26 . Hole  23  has an open portion  231  at end  14 , so that pin  30  can be mounted in hole  23  by translation in a first direction D 1  perpendicular to axis X 1  and parallel to axis Y 1 , passing through portion  231 . Hole  23  has an open portion  232  in communication with cavity  16 , so that pin  30  positioned in hole  23  extends through cavity  16 . Hole  23  has a cylindrical portion  233  for supporting end  33  of pin  30  along direction D 1 . More precisely, portion  233  is a half-cylindrical portion centered on axis X 1  and formed opposite open portion  231  relative to axis X 1 . Hole  23  has two plane portions  234  extending parallel to each other from portion  233  up to portion  231 . Hole  23  has a plane portion  235  for retaining pin  30  along axis X 1  during transport and mounting of cam follower  1 . Portion  235  extends perpendicular to axis X 1 , facing opposite hole  24 . Similarly, hole  24  is provided with portions  241 ,  242 ,  243 ,  244  and  245 , having reference numbers increased by ten. Each hole  25  and  26  is open, on the one hand, along axis X 1  between plane portion  235  or  245  and the outer side of flange  21  or  22  and, on the other hand, perpendicular to axis X 1  in a second direction D 2  opposite direction D 1 . 
     Pin  30  comprises an inner cylindrical bore  41  and an outer cylindrical surface  42  centered on axis X 1 . Pin  30  extends along axis X 1  between two pin ends  33  and  34  mounted in holes  23  and  24 . Pin  30  is made of metal, such as steel or bronze. Roller  40  has an inner cylindrical bore  41  and an outer cylindrical surface  41  centered on axis X 1 . Surface  42  is intended to bear against the outer surface of cam  2  synchronized with the internal combustion engine camshaft. Bearing  50  is a bushing interposed between surface  32  of pin  30  and surface  41  of roller  40 . Alternately, bearing  50  may be a rolling bearing including needles or cylindrical rollers. 
     The method for manufacturing cam follower  1  is detailed here-after. 
     The method comprises a molding step consisting in molding tappet  10 . The method comprises steps of fabricating and assembling pin  30 , roller  40  and bearing  50 , to obtain roller sub-assembly  60 . 
     When tappet  10  is molded, the method comprises a machining step a) consisting in machining holes  23  and  24  in flanges  21  and  22 . Holes  25  and  26  allow passage of a tool shank. Holes  23  and  24  are machined to their final shape by a tool such as a reamer. 
     After the machining step a), the method comprises a mounting step b) consisting in mounting sub-assembly  60  into holes  23  and  24  by translation in direction D 1 , without deforming flanges  21  and  22 . Ends  33  and  34  of pin  30  pass through open portions  231  and  241  and are received in holes  23  and  24 , in contact with cylindrical portions  233  and  235 . Thus, sub-assembly  60  is retained in translation relative to tappet  10  in direction D 1 . 
     After the mounting step b), the method comprises a deforming step c) consisting in plastically deforming flanges  21  and  22  to prevent dismounting of the pin  30  by translation in a direction D 2  opposite direction D 1 . Preferably, the deforming step c) consists in caulking flanges  21  and  22 . Alternately, the deforming step c) can implement a plastic deformation process different from caulking, by example crimping or punching. As shown on the example of  FIGS. 6 to 8 , the flanges  21  and  22  are provided with caulked portions  27  and  28  formed on both sides of holes  25  and  26 , near open portions  231  and  241  of holes  23  and  24 . Preferably, ends  33  and  34  of pin  30  are provided with chamfers  37  and  38 . Portions  27  and  28  are outstretched over chamfers  37  and  38 , so that ends  33  and  34  are blocked in holes  23  and  24  and cannot be accidentally removed by translation in direction D 2 , in particular during transport of cam follower  1 . 
     According to a first embodiment of the deforming step c), caulked portions  27  and  28  expanded in contact with ends  33  and  34  of pin  30 , such that pin  30  is secured to tappet  10  in holes  23  and  24 . 
     According to a second embodiment of the deforming step c), caulked portions  27  and  28  are expanded without contact with ends  33  and  34  of pin  30 , such that pin  30  is partly movable in holes  23  and  24 . In this case, pin  30  is movable in rotation around axis X 1  and/or partly movable in translation along axis X 1 . However, pin  30  is retained in opposite holes  23  and  24  along axis X 1  by plane portions  235  and  245 . Moreover, pin  30  cannot be accidentally from removed holes  23  and  24  by translation in direction D 2 . 
     When manufacturing of cam follower  1  is complete, roller  40  is then adapted to roll, more precisely its surface  42  can roll, on an outer surface of cam  2 . The load applied on surface  42  of roller  40  is transmitted to rolling bearing  50 , then to pin  30 , then to bearing portion  20  of tappet  10 . 
     Other non-shown embodiments can be implemented within the scope of the invention. 
     According to a non-shown embodiment, body  11  is not provided with portions connecting  19  flanges  21  and  22  around axis Y 1 . Flanges  21  and  22  extend from portion  12  parallel to axis Y 1  in a bifurcated manner, on both side of axis Y 1 . 
     According to another non-shown embodiment, flanges  21  and  22 , holes  23 ,  24 ,  25  and  26 , or deformed portions  27  and  28  may have different shapes, positions and/or dimensions. 
     Whatever the embodiment, each of the opposite holes  23  and  24  is provided with an open portion  231  or  241  for mounting pin  30  by translation in direction D 1  perpendicular to axis X 1 , a cylindrical portion  233  or  243  for supporting pin  30  along direction D 1  and a plane portion  235  or  245  for retaining pin  30  along axis X 1  during transport and mounting of cam follower  1 . 
     In addition, technical features of the different embodiments can be, in whole or part, combined with each other. Thus, the cam follower  1  and its manufacturing method can be adapted to the specific requirements of the application.