Internal-combustion engines – Poppet valve operating mechanism – Tappet
Reexamination Certificate
2002-04-10
2004-05-04
Moulis, Thomas N. (Department: 3757)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
C123S090510, C123S495000
Reexamination Certificate
active
06729286
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Related Art
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.
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
.
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.
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
.
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
.
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.
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.
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 (&mgr;m) 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
.
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
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.
The fuel supply apparatus for supplying a fuel to an engine according to the present invention includes a cylin
Onishi Yoshihiko
Tsugami Hiromichi
Uryu Takuya
Mitsubishi Denki & Kabushiki Kaisha
Moulis Thomas N.
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