Patent Publication Number: US-2016230868-A1

Title: Mechanical system forming a cam follower or a rocker arm, injection pump or valve actuator comprising such a mechanical system and method for manufacturing such a mechanical system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a Non-Provisional Patent Application, filed under the Paris Convention, claiming the benefit of Europe (EP) Patent Application Number 15305192.5, filed on 10 Feb. 2015 (10.02.2015), which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD OF THE INVENTION 
     The invention concerns a mechanical system, forming a cam follower or a rocker arm, and comprising a pin or a roller. The invention also concerns an injection pump or a valve actuator comprising such a mechanical system. Finally, the invention concerns a method for manufacturing such a mechanical system. 
     BACKGROUND OF THE INVENTION 
     Classically, a cam follower comprises at least a tappet, a pin and a roller. The tappet extends along a longitudinal axis, while the pin and the roller are centered on a transversal axis. The tappet delimits an intermediate gap and comprises two coaxial cylindrical bores. The roller is positioned in the intermediate gap, between both bores. The pin is fitted in the two bores, such that the roller is movable in rotation relative to the pin around its axis. 
     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 in a bore belonging to the injection pump, with the cylindrical outer surface of the tappet sliding in this bore. The roller is movable in rotation around its central axis. 
     As shown by example in EP-A-2 607 636, it is known to provide the tappet with a single piece body equipped with two flanges having holes for supporting the ends of the pin on which the roller is mounted. For assembling the cam follower, the roller is mounted between the flanges of the tappet. Then, the pin is inserted in the roller, through the holes of the flanges, the ends of the pin being supported by the flanges. The tappet is made by stamping. The tool used for the stamping is expensive and it is not able to make all the shapes of the tappet. Then, in order to create the specific geometry of the body, the tappet has to be machined, which is long and expensive. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to provide an improved mechanical system having a reduced cost. 
     To this end, the invention concerns a mechanical system forming a cam follower or a rocker arm, the mechanical system comprising: 
     a support element, 
     a pin extending between two opposite ends along a first axis and supported by the support element, and 
     a roller mounted on the pin, movable in rotation relative to the pin around the first axis and adapted to roll on a cam, 
     wherein the support element comprises a hollow cylindrical wall delimiting a cavity in which the pin and the roller are housed, the wall having two edges perpendicular to the first axis, and joined together. 
     Thanks to the invention, the shape of the tappet is simple and can be easily obtained by cutting and rolling a flat metal sheet. 
     According to further aspects of the invention which are advantageous but not compulsory, such a mechanical system may incorporate one or several of the following features: 
     The thickness of the cylindrical wall is substantially constant. 
     Each edge is equipped with assembling means for joining the edges together. 
     The assembling means are integral with the cylindrical wall. 
     The assembling means comprise tabs projecting from a first edge and recesses located on the second edge, having a hollow shape complementary to the shape of the tabs. 
     The edges are welded together. 
     The cylindrical wall includes two bores supporting the pin. 
     The mechanical system includes an insert located inside the support element and configured for receiving a shaft or a plunger for moving the mechanical system. 
     The insert is a disc having radial protrusions housed inside cut-outs made in the cylindrical wall. 
     The insert has two holding portions supporting the pin. 
     The insert is assembled to the support element by means of punched deformations protruding inside the support element. 
     Another object of the invention concerns an injection pump for a motor vehicle, comprising such a mechanical system. 
     Another object of the invention concerns a valve actuator for a motor vehicle, comprising such a mechanical system. 
     Another aspect of the invention concerns a method for manufacturing such a mechanical system, wherein: 
     a) a flat metal sheet is cut to make the contours of the support element, 
     b) the sheet is rolled to obtain the cylindrical shape of the cylindrical wall, 
     c) the edges are joined together, 
     d) the roller is mounted on the support element. 
     Preferably, the edges are joined by clamping or by welding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in correspondence with the annexed figures, as two illustrative examples, without restricting the object of the invention. In the annexed figures: 
         FIG. 1  is an exploded perspective view of a mechanical system according to a first embodiment of the invention, of the cam follower type; 
         FIG. 2  is a partial sectional view of the mechanical system of  FIG. 1  along plane II of  FIG. 1 ; 
         FIG. 3  is a perspective view of a tappet of the mechanical system of  FIG. 1 , during a manufacturing step; 
         FIG. 4  is a perspective view of a metal sheet used to make the tappet of  FIG. 3 ; 
         FIG. 5  is a perspective view of a mechanical system according to a second embodiment of the invention, of the cam follower type; and 
         FIGS. 6  is a sectional view of the mechanical system along plane VI of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF SOME EMBODIMENTS 
     The mechanical system  1  represented on  FIGS. 1 to 4  is of the cam follower type, adapted to equip an injection pump for a motor vehicle, not shown. 
     Mechanical system  1  comprises a support element or tappet  10 , an insert  20 , a pin  30  and a roller  40 , together forming a plain bearing. Pin  30  and roller  40  are shown on  FIG. 1  only. 
     In heavy duty applications such as in diesel truck engines, there is a lack of space for the implementation of a rolling bearing, thus justifying the use of a plain bearing between parts  30  and  40  Pin  30  and roller  40  are centered on a transversal axis X 1 , while tappet  10  is centered on a longitudinal axis Y 1  of mechanical system  1 . Axes X 1  and Y 1  are perpendicular. Roller  40  is adapted to roll on a cam  2 , partly shown on  FIG. 1  only, in centerline. More precisely, an external surface  41  of roller  40  can roll on the outer surface of cam  2 . When cam  2  and roller  40  are cooperating, a force F is applied on surface  41  along longitudinal axis Y 1 . 
     A cavity C is delimited inside tappet  10 . This cavity C is adapted to receive a shaft or plunger not shown, against insert  20 , for moving tappet  10  along axis Y 1 . Tappet  10  is movable back and forth along axis Y 1 , in a non-represented bore belonging to the injection pump. 
     Tappet  10  has a cylindrical wall or skirt  11  centered along longitudinal axis Y 1 , with a first end or lower end  10 . 1 , on the side of plunger, and a second end or upper end  10 . 2  on the side of pin  30  and roller  40 . An internal surface S 11  of cylindrical wall  11  delimits cavity C. Tappet  10  is made from a metallic material. The thickness of cylindrical wall  11  is substantially constant. 
     Roller  40  has an outer cylindrical surface  41  and an internal cylindrical bore  42 , both centered on transversal axis X 1 . Pin  30  comprises a cylindrical outer surface  32  extending between pin ends  35  and  36 . Roller  40  is movable in rotation relative to pin  30  around axis X 1 . Both pin  30  and roller  40  axes merge with transversal axis X 1 . 
     Optionally, a bushing  50  is located at the interface between pin  30  and roller  40 . Bushing  50  has an outer cylindrical surface  51  and an inner cylindrical bore  52  During assembly of system  1 , surface  51  of bushing  50  is adjusted with bore  42  of roller  40 , while surface  32  of pin  30  is adjusted with bore  52  of bushing  50 , such that roller  40  is movable in rotation relative to pin  30  around axis X 1 . Pin  30 , roller  40  and bushing  50  axes merge with axis X 1 . 
     Two bores  111  and  112  are arranged on the cylindrical wall  11  to receive ends  35  and  36  of pin  30 . Bores  111  and  112  are diametrically opposed with respect to longitudinal axis Y 1 . The diameter of bores  111  and  112  are identical. 
     Insert  20  is made from a metallic sheet, or by sintering. Insert  20  is shaped like a disc equipped with external and radial protrusions, for example three protrusions  21 ,  22  and  23 . In a variant, the number of protrusions is higher than three, for example four, five or six protrusions. 
     Each protrusion  21 ,  22  and  23  of insert  20  is housed into a rectangular cut-out  12 ,  13  and  14  of cylindrical wall  11 . Protrusions  21  to  23  and cut-outs  12  to  14  form assembling means for assembling insert  20  with tappet. 
     During operation, the load F applied by cam  2  on roller  40  is transferred to insert  20  and plunger via pin  30 . 
     Hereunder is described a method for manufacturing mechanical system  1 . 
     A flat metal sheet  10   a,  shown on  FIG. 4 , is used to make tappet  10 . The geometry of the edges of metal sheet  10   a  is obtained by cutting. 
     Sheet  10   a  is generally rectangular and has two longitudinal edges  15  and  16 , parallel to longitudinal axis Y 1 , and two transversal edges  10 . 1  and  10 . 2 , perpendicular to longitudinal edges  15  and  16 . 
     First edge  15  has first assembling means  151  and  152 , designed to cooperate respectively with second assembling means  161  and  162  equipping the second edge  16 , for joining edges  15  and  16 . Assembling means  151 ,  152 ,  161  and  162  are integral with sheet  10   a.  First assembling means  151  and  152  are tabs projecting from first edge  15 , shaped like an excrescence of the piece of a puzzle. Second assembling means  161  and  162  are recesses having a hollow shape complementary to the shape of tabs  151  and  152 . 
     Cut-offs  12  to  14  and bores  111  and  112  are cut in the metal sheet  10   a.    
     As shown on  FIG. 3 , sheet  10   a  is rolled to obtain a cylindrical shape, centered on longitudinal axis Y 1 . At this stage, edges  15  and  16  of tappet  10  are distant from each other, so assembling means  151 ,  152 ,  161  and  162  remain separate, allowing insert  20  to be mounted inside sheet  10   a  with protrusions  21 ,  22  and  23  partially housed inside cut-outs  12 ,  13  and  14 . Preferably, at least one protrusion  21 ,  22  or  23  is housed inside the corresponding cut-out  12 ,  13  or  14 . 
     Then, assembling means  151 ,  152 ,  161  and  162  are clamped in order to join edges  15  and  16 . Tabs  151  and  152  are inserted into recesses  161  and  162 . Simultaneously, protrusions  21 ,  22  and  23  move inside the corresponding cut-out  12 ,  13  and  14 , thanks to the deformation of the sheet  10   a.    
     Roller  40  is inserted inside tappet  10 , between bores  111  and  112 . Then, pin  30  is inserted through bores  111  and  112  of tappet  10  and through bore  42  of roller  40 . 
     A caulking operation is performed for retaining pin  30  inside tappet  10 . The plastic deformation of ends  35  and  36  of pin  30  block the translation of pin  30  and roller  40  along transverse axis X 1 , with respect to tappet  10 . 
     Mechanical system  1  is simple and fast to produce, and has a reduced cost thanks to the rolling of sheet  10   a.  No stamping operation is required. 
       FIGS. 5 and 6  show a second embodiment of a mechanical system  1001  according to the invention. Hereinafter, the parts of mechanical system  1001  similar to corresponding parts of mechanical system  1  of  FIGS. 1 to 4  bear the same references and are not described. The description focuses on differences between mechanical systems  1  and  1001 . 
     Mechanical system  1  includes a tappet  1010 , an insert  1020 , a pin  30 , a roller  40  and a bushing  50 . 
     Tappet  1010  includes a hollow cylindrical wall or skirt  1011  centered on longitudinal axis Y 1  and delimiting an internal cavity C. 
     Insert  1020  includes a first holding portion  1020 A and a second holding portion  1020 B generally parallel with longitudinal axis Y 1 , and a connecting portion  1020 C perpendicular to holding portions  1020 A and  1020 B. 
     Each holding portion  1020 A and  1020 B is designed to receive one end  35  or  36  of pin  30 , for example by means of a semi-circular recess  1021  centered on transversal axis X 1  and having a diameter roughly equal to the diameter of pin  30 . Holding portions  1020 A and  1020 B have a convex external and radial surface curved like a portion of cylinder, centered on longitudinal axis Y 1 , having a diameter roughly equal to the diameter of the internal surface S 1011  of tappet  1010 . 
     Insert  1020 , pin  30 , roller  40  and bushing  50  form a pin assembly movable in translation inside cavity C of tappet  1010 . 
     In a first direction from lower end  10 . 1  of tappet  1010  towards upper end  10 . 2 , the translation of pin assembly along longitudinal axis Y 1  is blocked by tabs  1012 A protruding from upper end  10 . 2  of tappet  10 . Tabs  1012 A are external with respect to cavity C. Each pin end  35  and  36  is blocked by a tab  1012 A. 
     In a second direction opposite the first direction, from upper end  10 . 2  of tappet  10  towards lower end  10 . 1 , the translation of pin assembly along longitudinal axis Y 1  is stopped by a second axial abutment formed by deformations  1012 ,  1013  and  1014  protruding inside cavity C. Deformations  1012  to  1014  are made by punching. 
     Upper end  10 . 2  of tappet  3010  has additional tabs  1012 B located on one side and another of each tab  1012 A. Additional tabs  1012 B prevent pin assembly  1020 ,  30 ,  40 ,  50  from rotating around longitudinal axis Y 1  with respect to tappet  1010 . 
     The manufacturing method for manufacturing system  1  is globally similar to the method described in reference to  FIGS. 1 to 4 . 
     A flat metal sheet is used to make tappet  1010 . The geometry of the edges of this metal sheet is obtained by cutting or stamping. 
     This metal sheet is generally rectangular and has two longitudinal flat edges  1015  and  1016 , parallel to longitudinal axis Y 1 , and two transversal edges  10 . 1  and  10 . 2 , perpendicular to longitudinal edges  1015  and  1016 . 
     Similarly to what is shown on  FIG. 3  for the first embodiment, the metal sheet is rolled to obtain a cylindrical shape, centered on longitudinal axis Y 1 . At this stage, edges  1015  and  1016  of tappet  1010  are distant from each other, so edges  1015  and  1016  remain separate. 
     Edges  1015  and  1016  are then welded together. In the example of  FIGS. 5 and 6 , edges  1015  and  1016  are rectilinear In a variant, they are curved. 
     Insert  1020  and sub-assembly  30 ,  40  and  50  are mounted on tappet  1010 . 
     A punching operation is performed to make deformations  1012  to  1014 . 
     In a non-depicted variant, bushing  50  is eliminated or replaced by another type of sliding element, such as needle roller bearings with plastic cage, used for injection pumps for gasoline engines. 
     Other non-show embodiments can be implemented within the scope of the invention. For example, support element  10  or  1010  may have a different configuration depending on the intended application of system  1 . 
     Moreover, the mechanical system  1  according to the invention is not limited to a cam follower. For example, system  1  may form a rocker arm, wherein the support element  10  is an arm movable in rotation along a pivot axis parallel to axis X 1 . 
     According to another non-shown embodiment, system  1  may comprise a rolling or sliding bearing, with bearing elements positioned at the interface between pin  30  and roller  40 . 
     The invention also concerns an injection pump or a valve actuator comprising such a mechanical system  1  or  1001 . 
     In addition, technical features of the different embodiments can be, in whole or part, combined with each other. Thus, mechanical systems can be adapted to the specific requirements of the application.