Abstract:
A fuel supply apparatus capable of reducing the abrasion of a driving cam and a tappet without increasing the dimensions and weight of the apparatus. This fuel supply apparatus is provided with a tappet which has a pressure receiving surface contacting the driving cam of an engine. The tappet is provided at the part of a outer surface thereof which is in the vicinity of an outer circumference of the pressure receiving surface with a groove adapted to prevent the local concentration of stress on the tappet and having a V-shaped, semicircular or U-shaped cross section.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a fuel supply apparatus, and more particularly to a fuel supply apparatus for supplying a fuel under a high pressure to a fuel injection type internal combustion engine, for example, an automobile engine.  
           [0003]    2. Description of the Related Art  
           [0004]    FIGS.  8  to  14  are drawings describing a related art general fuel supply system for a fuel injection type internal combustion engine. FIG. 8 is a schematic illustration of this fuel supply system, FIG. 9 a sectional view of a principal portion of a fuel supply apparatus included in this fuel supply system, FIG. 10 a sectional view taken along the line X-X in FIG. 9, FIG. 11 a partial enlarged sectional view of what is shown in FIG. 9, taken along a plane Y-Z and illustrating the contacting condition of a driving cam and a tappet of the fuel supply apparatus, FIG. 12 a sectional view taken along a plane Y-X with respect to the plane Y-Z in FIG. 11, FIG. 13 a graph showing the condition of the deformation of a pressure receiving surface of the tappet which receives a force of the driving cam, and FIG. 14 a graph showing the condition of the distribution of Hertz stress on the pressure receiving surface.  
           [0005]    Referring to FIGS.  8  to  9 , the fuel supply system includes a fuel tank  1 , a fuel supply apparatus  6  and fuel injection valves  10  as main elements, the fuel supply apparatus  6  having a filter  11 , a low-pressure damper  12 , a suction valve  13 , an electromagnetic valve  17 , a pump  16 , and a discharge valve  14 .  
           [0006]    Fuel  2  in the fuel tank  1  is sent out by the low-pressure pump  3 , pressure regulated by a low-pressure regulator  5  via the filter  4 , and supplied to the fuel supply apparatus  6 . Only such a quantity of the fuel  2  thus supplied to the apparatus that is necessary for fuel injection is pressure-increased by the fuel supply apparatus  6 , and supplied to a common rail  9  of an internal combustion engine (not shown), the fuel being then injected as a high-pressure atomized fuel from the fuel injection valves  10  into cylinders (not shown) of the internal combustion engine. The quantity of fuel needed during this time is determined by a control unit (not shown) and controlled by the electromagnetic valve  17 , and an excess fuel is discharged from the electromagnetic valve  17  to the portion of a fuel passage which is between the low-pressure damper  12  and suction valve  13 . A reference numeral  7  in FIG. 8 denotes a filter, and  8  a high-pressure relief valve, which is opened when the pressure in the interior of the common rail becomes abnormally high, to prevent the common rail  9  and fuel injection valve  10  from being broken.  
           [0007]    Referring to FIG. 9 showing a principal portion of the fuel supply apparatus  6 , the pump  16  includes a cylinder  25  incorporated in a cylinder casing  30  and provided with a pressure chamber  24  therein which has a fuel suction port  22  and a fuel discharge port  23 ; a piston  26  moving slidingly in the axial direction thereof in the cylinder  25  to vary the volume of the pressure chamber  24 ; a columnar tappet  28  joined to the piston  26 ; and a bolt  29  fitted slidably around the tappet  28  and having a threaded portion engaged with the cylinder casing  30 . Referring to FIGS.  10  to  12 , a driving cam  41  mounted on a cam shaft  40  of the engine contacts a pressure receiving surface  28   a  at a lower end in the drawing of the tappet  28 , and a rotational force of the driving cam  41  occurring due to the rotation of the cam shaft  40  is transmitted to the tappet  28  and piston  26  via the pressure receiving surface  28   a  as a driving force. Owing to the driving force thus transmitted to the piston  26 , the piston  26  is moved vertically to vary the volume of the pressure chamber  24 .  
           [0008]    A surface  261 , which contacts the tappet  28 , of the piston  26  bulges slightly toward the tappet  28  as shown in FIGS. 11 and 12. The reason why the surface  261  is thus bulged resides in that, when the tappet  28  is moved slidingly in the axial direction owing to the rotation of the driving cam  41 , inclination of the tappet  28  occurs due to a clearance set between the tappet  28  and bolt  29 , which inclination reduces a lateral force transmitted from an upper surface  28   b  of the tappet  28  to the piston  26 .  
           [0009]    Referring to FIG. 11, all of arrows a, b, c represent positions from which a force from the driving cam  41  is applied to the pressure receiving surface  28   a . Out of these arrows, the arrow b represents a position from which the force is applied to the portion of the pressure receiving surface  28   a  which is close to the center thereof, while both of the arrows a, c represent positions from which the force is applied to the portions of the pressure receiving surface  28   a  which are on somewhat inner side of the outer circumference thereof. As shown in FIG. 11, the driving cam  42  is generally formed wider than the tappet  28 . In an initial stage of an operation of the driving cam  41 , the condition of the application of the force by the driving cam  41  to the receiving surface  28   a  is uniform over the whole of the same surface  28   a . Accordingly, the levels of the force applied to the force applying positions represented by the arrows a, b, c are also uniform.  
           [0010]    However, as described above, the portion of the upper surface  28   b  of the tappet  28  which is around the force applying position represented by the arrow b contacts the bulging portion of the surface  261  of the piston  26 , while the portions of this surface  28   b  which are around the force applying positions of the arrows a, c have a narrow clearance between the upper surface  28   b  and the surface  261 . Due to the existence of this clearance, the pressure receiving surface  28   a  is deformed as shown by a solid line in FIG. 13, and the distribution of Hertz stress during this time becomes as shown by a solid line in FIG. 14. FIGS. 13 and 14 show data obtained when a fuel discharge pressure is as high as 15 MPa.  
           [0011]    What are shown in FIGS. 13 and 14 will now be described. The lateral axis of each of FIGS. 13 and 14 represents a position of the tappet  28  in the direction of Z-axis, and the longitudinal axis of each of FIGS. 13 and 14 a displacement distance (μm) based on the deformation of the pressure receiving surface  28   a  and measured from an initial position thereof, and Hertz stress (MPa). Each of the solid curves in FIGS. 13 and 14 shows the distribution of Hertz stress recorded when the fuel discharge pressure is 15 MPa. The a, b, c in each of these drawings represent displacement distances (FIG. 13) and Hertz stress (FIG. 14) in the force applying positions of the arrows a, b, c. As is clear from FIG. 13, the displacement distance becomes maximal around the positions of arrows a, c, and decreases at an outer circumference. As a result, the Hertz stress becomes maximal at inflexion points of the displacement distance around the arrows a, c as is clear from FIG. 13.  
           [0012]    When the fuel discharge pressure is thus high, the abrasion of the driving cam  41  and tappet  28  increases due to the high Hertz stress occurring locally in positions around those of the arrows a, c, i.e. the positions near the outer circumference of the pressure receiving surface  28   a . In order to deal with this problem, the related techniques employed a method of reducing Hertz stress by increasing the outer diameter of the tappet  28  and the width and outer diameter of the driving cam  41 , but this method caused the dimensions and weight of the fuel supply apparatus  6  to increase.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention has been made in view of the above-mentioned circumstances, and provides a fuel supply apparatus capable of reducing the abrasion of a driving cam and a tappet without increasing the dimensions and weight of the apparatus.  
           [0014]    The fuel supply apparatus for supplying a fuel to an engine according to the present invention includes a cylinder, a piston and a tappet. The cylinder is provided with a fuel pressurization chamber having a fuel suction port and a fuel discharge port. The piston is moving slidingly in the axial direction thereof in the cylinder and thereby increasing and decreasing the volume of the fuel pressurization chamber. The tappet has a pressure receiving surface for contacting a driving cam of the engine and receiving a driving force of the driving cam, and which transmits the driving force to the piston. The tappet has a groove on its outer surface. The groove is positioned in the region which corresponds to the vicinity of an outer circumference of the pressure receiving surface for preventing the local concentration of stress thereon. Accordingly, the groove gives an easily deformable portion of a low rigidity. The easily deformable portion is positioned in the region which corresponds to the vicinity of the outer circumference of the pressure receiving surface. The easily deformable portion works to relax the Hertz stress, and, owing to this action of the easily deformable portion, an effect of reducing the abrasion of the driving cam and tappet is obtained.  
           [0015]    Preferably, in the fuel supply apparatus, the tappet includes a larger-diameter portion and a smaller-diameter portion. The larger diameter portion is engaged with a tappet stopper provided on an opened end portion of a cylinder casing. The smaller-diameter portion is capable of passing through the tappet stopper and has the pressure receiving surface. The groove is formed on the outer surface of the smaller-diameter portion.  
           [0016]    Still preferably, in the fuel supply apparatus, the tappet has a board-like portion between the pressure-receiving surface and the groove. Accordingly, the board-like portion functions as a pressure receiving portion which effectively receives the driving force from the driving cam.  
           [0017]    Still preferably, the fuel supply apparatus in which the outer diameter of the larger-diameter portion is 10 mm to 15 mm with the thickness of the board-like portion is 0.5 mm to 1.5 mm. Accordingly, the board-like portion functions as a pressure receiving portion which effectively receives the driving force from the driving cam, without being broken even when the board-like portion receives the driving force from the driving cam.  
           [0018]    Still preferably, the fuel supply apparatus in which the depth of the groove measured from the outer surface of the lager-diameter portion is 0.5 mm to 2 mm.  
           [0019]    Still preferably, the fuel supply apparatus in which the groove has a V-shaped, semicircular or U-shaped cross section. Accordingly, the easily deformable portion given by the groove maintains a low rigidity and, moreover, does not have the problem of the occurrence of the breakage thereof even when the easily deformable portion receives the driving force from the driving cam. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    Preferred embodiments of the present invention will now be described in detail with reference to the following figures, wherein:  
         [0021]    [0021]FIG. 1 is a sectional view of a first embodiment of the fuel supply apparatus according to the present invention;  
         [0022]    [0022]FIG. 2 is a partial enlarged sectional view of what is shown in FIG. 1;  
         [0023]    [0023]FIG. 3 is another partial enlarged sectional view of what is shown in FIG. 1;  
         [0024]    [0024]FIG. 4 is a graph showing the condition of the deformation of a pressure receiving surface of a tappet;  
         [0025]    [0025]FIG. 5 is a graph showing the condition of the distribution of Hertz stress on the pressure receiving surface;  
         [0026]    [0026]FIG. 6 is a sectional view of a tappet used in a second embodiment of the fuel supply apparatus according to the present invention;  
         [0027]    [0027]FIG. 7 is a sectional view of a tappet used in a third embodiment of the fuel supply apparatus according to the present invention;  
         [0028]    [0028]FIG. 8 is a schematic illustration of a related art fuel supply system;  
         [0029]    [0029]FIG. 9 is a sectional view of a related art fuel supply apparatus;  
         [0030]    [0030]FIG. 10 is a sectional view taken along the line X-X in FIG. 9;  
         [0031]    [0031]FIG. 11 is a partial enlarged sectional view of what is shown in FIG. 9;  
         [0032]    [0032]FIG. 12 is another partial enlarged sectional view of what is shown in FIG. 9;  
         [0033]    [0033]FIG. 13 is a graph showing the condition of the deformation of a pressure receiving surface of a related art tappet; and  
         [0034]    [0034]FIG. 14 is a graph showing the condition of the distribution of Hertz stress on the related art pressure receiving surface.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    In the following description, the parts identical with those of the above-described related art fuel supply apparatus and previously-described embodiments will be designated by the same reference numerals and the description thereof will be omitted in some cases.  
         [0036]    First Embodiment  
         [0037]    FIGS.  1  to  5  illustrate a first embodiment of the fuel supply apparatus according to the present invention. FIG. 1 is a sectional view of a principal portion of the fuel supply apparatus, FIG. 2 a partial enlarged sectional view taken along a plane Y-Z and illustrating the condition of the driving cam and tappet in contact with each other, FIG. 3 a sectional view taken along a plane Y-X with respect to the plane Y-Z in FIG. 2, FIG. 4 a graph showing the condition of the deformation of a pressure receiving surface of the tappet which receives a force of the driving cam, and FIG. 5 a graph showing the condition of the distribution of Hertz stress on the pressure receiving surface. What are meant by the lateral axis, longitudinal axis, and reference letters a, b, c in FIGS. 4 and 5 are the same as those in FIGS. 13 and 14. A thick curve G 1  in FIG. 4 and that G 3  in FIG. 5 represent the distribution of Hertz stress in the first embodiment which are recorded when a discharge pressure of the fuel is 15 MPa, and a thin curve G 2  in FIG. 4 and that G 4  in FIG. 5 are the reproduction of the curves shown in FIGS. 13 and 14.  
         [0038]    Referring to FIGS.  1  to  3 , especially, FIG. 3, a columnar tappet  28  has an outer surface  28   c , and includes a larger-diameter portion  281  and a smaller-diameter portion  282 , the portion of the outer surface  28   c  which corresponds to the smaller-diameter portion  282  being provided with an annular groove  5  which extends around a circumference of the outer surface. A board-like portion  284  is provided between the groove  5  and pressure receiving surface  28   a , and a lower surface in the drawing of the board-like portion forms the pressure receiving surface  28   a . The board-like portion  284  substantially functions as a pressure receiving portion which receives a driving force from a driving cam  41 . Referring to FIG. 2, a reference symbol L 1  denotes the length of the larger-diameter portion  281 , L 2  the length of the smaller-diameter portion, R 1  the outer diameter of the larger-diameter portion  281 , R 2  the outer diameter of the smaller-diameter portion  282 , T 1  the thickness of the board-like portion  284 , T 2  the thickness of a thin portion  283  existing between a bottom of the groove  5  and the board-like portion  284 , D the depth of the groove  5  measured from the side surface  28   c  of the larger-diameter portion  281 , and θ the angle of inclination of an inclined surface of the portion of the groove  5  which is on the side of the board-like portion  284 , in other words, an inclined surface of the thin portion  283 .  
         [0039]    The effect of the provision of the groove  5  will now be described. Providing the groove  5  causes the thin portion  283  and board-like portion  284  to be formed on the smaller-diameter portion  282 . The outer circumferences and their near-by parts (which will hereinafter be referred to as easily deformable parts) of the thin portion  283  and board-like portion  284  are made thin and have a low rigidity. Therefore, when the pressure receiving surface  28   a  or board-like portion  284  receives the driving force from the driving cam  41 , the easily deformable parts, in other words, the force applying positions indicated by arrows a and c are deformed at the outer circumference more greatly than those indicated by arrows a, c in FIG. 2. The curve G 1  in FIG. 4 indicates the condition of this deformation. The curve G 1  does not have inflexion points in regions of arrows a, c, as compared with the curve G 2 , but clearly shows that the deformation of the pressure receiving surface occurs increasingly in a monotonous manner toward an outer circumference thereof, at which the greatest deformation occurs. Since an inflexion point representing the occurrence of such large deformation does not appear, the Hertz stress in the force applying positions of the arrows a, c is sufficiently low as compared with that in the corresponding positions shown on the curve G 4  as is clear from the curve G 3  in FIG. 5. Therefore, it is understood that the stress relaxation with respect to the above-mentioned deformed shape of the pressure receiving surface has been achieved. The achievement of this stress relaxation is an effect obtained by the provision of the groove  5 . Owing to this effect, the abrasion of the driving cam  1  and tappet  28  is reduced, and the solving of the above-mentioned object of the present invention has thus come to be attained.  
         [0040]    In order to prevent the tappet from falling from the cylinder casing  30  during the assembling of the fuel supply apparatus  6 , the tappet  28  includes the larger-diameter portion  281  having the outer diameter slightly larger than the inner diameter of a tappet stopper  31  provided in an opened portion of the cylinder casing  30 ; and the smaller-diameter portion  282  having the outer diameter slightly smaller than the mentioned inner diameter. During the assembling of the fuel supply apparatus  6 , the tappet  28  is inserted through the cylinder casing  30  from an upper side thereof in the drawing. When the tappet  28  is thus inserted through the cylinder casing  30 , the larger-diameter portion  281  alone is held in the cylinder casing  30 , and the smaller-diameter portion  282  passes through the tappet stopper  31  to be put in the condition shown in FIGS.  1  to  3 . In the first embodiment, the groove  5  is provided over substantially the whole region of the outer surface of the smaller-diameter portion  282  except the region thereof which corresponds to the board-like portion  284 , and has a V-shaped cross section.  
         [0041]    When the depth D of the groove  5  and the size of the opened portion are small with the thickness of the easily deformable portion being large, the rigidity of the easily deformable portion is still large. Therefore, the degree of the above-mentioned deformation (degree of stress relaxation) becomes insufficient, so that the effect of the groove  5  becomes poor. Conversely, when the depth D of the groove  5  is excessively large with the thickness of the easily deformable portion being excessively small, the grooved portion is broken in some cases due to the force of the driving cam  41 . Therefore, it is preferable that the depth D of the groove  5  and the size of the opened portion be at levels between excessively high levels and excessively low levels. Such intermediate levels can be set generally by an analysis based on a rule of trial and error or a finite element method when the size of the tappet  28  are determined.  
         [0042]    Apart from the determining by a rule of trial and error of the depth and size mentioned above, examples of optimum values of the size of the tappet  28 , thickness T 2  of the thin portion  283  and other sizes will be shown on the basis of FIG. 2. When the length L 1  of the larger-diameter portion  281  of the tappet  28  is around 15 mm to 20 mm with R 1  around 10 mm to 15 mm, the length L 2  is around 4 mm to 5 mm, a difference between R 1  and R 2  around 0.05 mm to 0.2 mm, the thickness T 1  around 0.5 mm to 1.5 mm and preferably around 0.5 mm to 1.2 mm, an angle θ of inclination around 30 to 60 degrees, the thickness T 2  of the thin portion  283  around 1 mm to 2 mm, and D around 0.5 mm to 2 mm.  
         [0043]    According to the present invention, the groove  5  is provided basically in the portion of the outer surface  28   c  of the tappet which is close to the outer circumference of the pressure receiving surface  28   a . However, when the groove  5  is provided excessively close to the mentioned outer circumference, the thickness of the board-like portion  284  becomes excessively small, so that the board-like portion  284  is easily broken due to the force of the driving cam  41 . Therefore, it is preferable that the groove  5  be provided in a position in which the board-like portion  284  can secure the thickness of around the above-mentioned level.  
         [0044]    Second Embodiment  
         [0045]    [0045]FIG. 6 illustrates a second embodiment of the fuel supply apparatus according to the present invention, and is a sectional view of a tappet  28  only. The sectional views of a principal portion of the second embodiment of the fuel supply apparatus will be omitted since these sectional views except a sectional view of a tappet  28  are identical with FIGS.  1  to  3 .  
         [0046]    The second embodiment differs from the first embodiment only in the cross-sectional shape of a smaller-diameter portion  282  of the tappet  28 , and the construction of the remaining portions of the former is identical with that of the corresponding portions of the latter. An annular groove  5  in the second embodiment has a semicircular cross-sectional shape, and the depth D thereof is equal to that of the groove  5  of the first embodiment. Although the size of an opened portion in the second embodiment is set somewhat smaller with the thickness T 1  of a board-like portion  284  set somewhat larger to around 0.8 mm to 1.5 mm, the same operation and effect as in the first embodiment are obtained.  
         [0047]    Third Embodiment  
         [0048]    [0048]FIG. 7 illustrates a third embodiment of the fuel supply apparatus according to the present invention, and is a sectional view of a tappet  28  only. The sectional views of a principal portion of the third embodiment of the fuel supply apparatus will be omitted since these sectional views except a sectional view of the tappet  28  are identical with FIGS.  1  to  3 .  
         [0049]    The third embodiment differs from the first and second embodiments in only the cross-sectional shapes of a smaller-diameter portion  282  of the tappet  28 , and the construction of the remaining portions of the former is identical with that of the corresponding portions of the latter. An annular groove  5  in the third embodiment extends over the whole region of a smaller-diameter portion  282  except the region thereof which corresponds to the thickness of a board-like portion  284 , and has a U-shaped, especially, flat-bottomed U-shaped cross-sectional shape. The thickness of the board-like portion  284  is around 0.8 mm to 1.5 mm which is equal to that of the same portion in the second embodiment. Only an outer circumferential portion of the board-like portion  284  functions as an easily deformable portion, and the operation and effect identical with those of the first embodiment is obtained.  
         [0050]    The present invention is not limited to the above-described first, second and third embodiments but includes various modes of modifications in conformity with the spirits of the problem-solving method used in the present invention.