Pumps – Expansible chamber type – Having pumping chamber pressure responsive distributor
Reexamination Certificate
2001-08-30
2003-06-10
Walberg, Teresa (Department: 3742)
Pumps
Expansible chamber type
Having pumping chamber pressure responsive distributor
C417S569000
Reexamination Certificate
active
06575718
ABSTRACT:
REFERENCE TO RELATED APPLICATIONS
This application is based on Japanese Patent Application No. 2000-263195, filed in Japan on Aug. 31, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
This invention relates to a fuel supply apparatus. In particular, it relates to a high pressure fuel supply apparatus for supplying a fuel under high pressure to an internal combustion engine.
FIG. 8
schematically illustrates a typical fuel supply system for an automotive internal combustion engine equipped with fuel injectors. As shown in this figure, fuel
2
within a fuel tank
1
is discharged from the fuel tank
1
by a low pressure pump
3
and passes through a filter
4
, and after its pressure is adjusted by a low pressure regulator
5
, it is supplied to a high pressure fuel supply apparatus
6
. The fuel is pressurized by the fuel supply apparatus
6
and is supplied to a common rail
9
of an internal combustion engine (not shown). Excess fuel not needed by the engine is transferred by an electromagnetic valve
17
to a point between a low pressure damper
12
and an intake valve
13
. A control unit (not shown) determines the necessary amount of fuel to be supplied to the engine and controls the electromagnetic valve
17
accordingly. The high pressure fuel which is supplied in this manner is sprayed as a high pressure mist from fuel injectors
10
connected to the common rail
9
and is injected into cylinders (not shown) of the internal combustion engine. A high pressure relief valve
8
connected to the discharge side of the supply apparatus
6
through a filter
7
opens when there is an abnormal pressure within the common rail
9
and prevents damage to the common rail
9
and the fuel injectors
10
.
The high pressure fuel supply apparatus
6
includes a filter
11
which filters the supplied fuel, the above-mentioned low pressure damper
12
which absorbs pressure pulses of the low pressure fuel, and a pump
16
which pressurizes fuel which is supplied through the intake valve
13
and discharges high pressure fuel through a discharge valve
14
and a fuel pressure maintaining valve
15
.
FIG. 9
illustrates the actual structure of an example of the high pressure fuel supply apparatus
6
schematically illustrated in FIG.
8
. As shown in
FIG. 9
, the high pressure fuel supply apparatus
6
has a casing
21
containing a cylinder
25
which defines a compression chamber
24
of a high pressure pump
16
. The casing
21
also includes an intake passage
22
for fuel to be pressurized in the compression chamber
24
and a discharge passage
23
for pressurized fuel. A piston
26
in the form of a plunger is supported in the cylinder
25
for sliding movement in the axial direction thereof so as to vary the volume of the compression chamber
24
. A compression spring
27
is provided at the inner end (the upper end in
FIG. 9
) of the piston
26
, and at the outer end (the lower end in
FIG. 9
) an operating member in the form of a tappet
28
which receives a drive force from the camshaft of the unillustrated engine and transmits it to the piston
26
is supported by a bracket
30
for sliding movement in the axial direction of the piston
26
.
The high pressure fuel supply apparatus
6
comprises, as a unitary structure, the high pressure pump
16
which is a plunger pump for example, the electromagnetic valve
17
connected to the compression chamber
24
of the high pressure pump
16
, and the low pressure damper
12
. The high pressure fuel supply apparatus
6
also includes a metal bellows
29
which substantially surrounds the cylinder
25
and the piston
26
and which prevents fuel which leaks out from between the cylinder
25
and the piston
26
from leaking to the outside of the apparatus
6
.
The piston
26
is driven up and down in
FIG. 9
by a drive cam mounted on an unillustrated camshaft, and fuel is sucked into and discharged from the compression chamber
24
by the movement of the piston
26
. The electromagnetic valve
17
is opened when a prescribed amount of fuel is discharged into the common rail
9
, so that some of the high pressure fuel within the compression chamber
24
is sent (released) to the inlet side rather than being sent under pressure to the common rail
9
. By controlling the timing of opening of the electromagnetic valve
17
, the amount of fuel discharged from the fuel supply apparatus
6
can be variably controlled.
Low pressure fuel from the fuel tank
1
passes through an intake valve
13
into the compression chamber
24
, and is then discharged from the compression chamber
24
through a discharge valve
14
.
FIG. 10
is an enlarged view of region A of
FIG. 9
, showing a valve assembly including the intake valve
13
and the discharge valve
14
, and
FIGS. 11-16
show various portions of the valve assembly in detail. The valve assembly includes an upper plate
33
, a lower plate
31
, and a reed plate
33
sandwiched between the upper and lower plates
33
and
31
. As shown in plan in
FIG. 11
, the upper plate
33
is a disk-shaped member having a relief flow passage
34
which communicates with the electromagnetic valve
17
, two valve holes
35
which function as intake openings, and a cavity
36
which communicates with the discharge passage
23
and which has a size and shape so as not to interfere with the movement of a discharge valve reed
38
of the reed plate
32
. As shown in plan in
FIG. 12
, the reed plate
32
is a thin disk-shaped member having two flat intake valve reeds
37
and a flat discharge valve reed
38
. As shown in plan in
FIG. 13
, the lower plate
31
is a disk-shaped member having a cavity
39
which communicates with the compression chamber
24
and has a size and shape so as not to interfere with the movement of the intake valve reeds
37
, and a valve hole
40
which functions as a discharge opening.
FIG. 14
is an enlarged plan view of the discharge valve reed
38
of
FIG. 12
,
FIG. 15
is a cross-sectional elevation taken along line
15
—
15
of
FIG. 14
, and
FIG. 16
is an enlarged cross-sectional elevation taken along line
16
—
16
of FIG.
14
. The discharge valve reed
38
includes a flexible neck
42
and a disk-shaped head
43
which is secured to one end of the neck
42
and which can move between an open and a closed position to open and close the valve hole
40
of the lower plate
31
. In
FIG. 16
, the dashed lines show the shape of the reed
38
in an unloaded state, and the solid lines show the shape when the discharge side of the valve assembly is at a higher pressure than the compression chamber
24
and the reed
38
is pressed against and closes the valve hole
40
. The discharge valve reed
38
is strongly pressed by the high pressure P on the discharge side, so the reed
38
is deformed downwards at its center into the shape of a bowl such that the reed
38
is in sealing contact with substantially only the edge
41
of the valve hole
40
. The amount of deformation of the reed
38
in its deformed state with respect to its shape in an unloaded state is H. The seal due to contact between the reed
38
and the edge
41
of the valve hole
40
is an edge seal involving line contact between the two members. This edge seal generates a large local stress in the seal portion of the discharge valve reed
38
. Furthermore, the discharge valve reed
38
has a high stiffness at its neck
42
, so the deformed shape of the head
43
when subjected to pressure is different where the head
43
adjoins the neck
42
than in other locations, so a gap develops in this region, and the sealing performance decreases (particularly at the border
44
of the neck
42
and the head
43
). This same problem occurs with the intake valve reeds
37
.
The thickness of the reed plate
32
is usually very thin, such as on the order of 0.3 mm, in order to decrease stresses generated at the time of valve opening and pressure losses. Therefore, in the device of
FIG. 9
, when the discharge pressure is set to a value such as 12 MPa, a defective seal can easily
Ojima Kouichi
Onishi Yoshihiko
Mitsubishi Denki & Kabushiki Kaisha
Patel Vinod D.
Sughrue & Mion, PLLC
Walberg Teresa
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