Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-10-26
2001-04-03
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S511000, C123S458000
Reexamination Certificate
active
06209525
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fuel supply equipment used in a variable fuel pressure system and, particularly, to fuel supply equipment for a direct injection gasoline engine, which comprises a single-cylinder high-pressure fuel pump and directly injects high-pressure fuel into the cylinders of an engine.
BACKGROUND OF THE INVENTION
Diesel engine technology is widely known as an example of an engine technology where the fuel is injected into its cylinders, which is so called “in-cylinder injection engine” or “direct injection engine”. For spark ignition (gasoline) engine also, in-cylinder injection type has recently been proposed. For such in-cylinder injection engines, it is required that the fuel pressure pulsation should be small enough to achieve stable injection as well as the fuel injection pressure should be sufficiently high.
Therefore, a single-cylinder high-pressure fuel pump which is simple in structure, produced at a low cost and compact is already known.
Since the single-cylinder high-pressure fuel pump has only one plunger, it generates a larger pulsation width in the fuel pressure than a multi-cylinder high-pressure fuel pump does. Therefore, a metal bellows type or metal diaphragm type pulsation absorber is provided in a fuel supply system to absorb the pulsation.
FIG. 8
is a diagram showing the configuration of a fuel supply system for a direct injection gasoline engine disclosed by Japanese Laid-open Patent Application No. 9-310661, for example. In this fuel supply system for a direct injection gasoline engine, the pressure of fuel (gasoline) stored in a fuel tank
70
is increased to a low level by a low-pressure fuel pump
71
and then the fuel is supplied to a high-pressure fuel pump
73
by a low-pressure pipe
72
. The high-pressure fuel pump
73
further increases the pressure of the fuel to a high level by the reciprocating motion of a plunger
75
driven by the cam shaft
74
of an unshown engine and discharges the fuel from an outlet port
76
. This outlet port
76
is connected to a common rail
79
through a high-pressure check valve
77
and a high-pressure pipe
78
. High-pressure fuel stored in the common rail
79
is supplied to injectors
81
attached to the respective cylinders
80
of the engine through branch passages
82
.
This common rail
79
is connected to a metal bellows type pulsation absorber
85
. This metal bellows type pulsation absorber
85
is constituted such that a barrel portion is composed of metal bellows
85
a,
an opening at one end of the metal bellows
85
a
is closed by an end plate
85
b,
a peripheral portion at the other end of the metal bellows
85
a
is connected to the end surface
85
c
of the absorber by welding or the like, a closed space is formed inside the metal bellows
85
a,
and gas such as nitrogen or argon is charged into this closed space. The pressure pulsation of high-pressure fuel to be applied to the end plate
85
b
is absorbed by the expansion and contraction of the metal bellows
85
a
so that the pressure pulsation of the high-pressure fuel supplied into the common rail
79
is absorbed.
FIG. 9
is a sectional view showing the configuration of a high-pressure fuel supply system
10
D equipped with a metal diaphragm type pulsation absorber. The high-pressure fuel supply system
10
D comprises a high-pressure fuel pump
11
, a low-pressure damper
14
provided in an inlet passage
12
connected to an inlet port side of the high-pressure fuel pump
11
and equipped with metal bellows
14
a,
a high-pressure damper
90
provided in an outlet passage
15
connected to an outlet port side of the high-pressure fuel pump
11
and equipped with a metal diaphragm
90
m,
and a high-pressure check valve
17
arranged on a downstream side of the high-pressure damper
90
, all of which are integrally arranged in a casing
100
.
The high-pressure pump
11
pressurizes the low pressure fuel supplied from the unshown fuel inlet port through the inlet passage to a high pressure level and discharges it to the outlet passage
15
by utilizing the plunger
112
which is arranged in a cylinder
111
in such a manner it can reciprocate and is driven by a cam
19
whose rotational speed is a half of an unshown engine's crank speed.
The metal diaphragm type pulsation absorber
90
is provided to suppress the pressure pulsation of this discharged high-pressure fuel. As shown in FIG.
9
and
FIG. 10
, the metal diaphragm type pulsation absorber
90
comprises a case
91
constituting one part of a high-pressure container, a plate
92
constituting the other part of the high-pressure container, and a flexible thin metal disk-like diaphragm
90
m
forming a first high-pressure chamber
93
with the above case
91
and a second high-pressure chamber
94
with the above plate
92
. The above second high pressure chamber
94
is connected via multiple through holes
96
with a recess
95
which constitutes a path between the first passage
15
P to an outlet of the high-pressure fuel pump located in the casing
100
and the second passage
15
Q to a check valve
17
. The above first high-pressure chamber
93
is filled with unshown gas from a gas filling port
97
formed in the case
91
at a predetermined pressure. This predetermined pressure is required to absorb the pulsation of the high-pressure fuel running through the second passage portion
15
Q from the first passage portion
15
P through the recessed portion
95
.
When pulsation occurs in the above fuel while the first high-pressure chamber
93
is filled with gas and the second high-pressure chamber
94
is filled with fuel, the diaphragm
90
m
absorbs the pressure pulsation by bending towards the case
91
and towards the plate
92
from the balance point (for example, a position having no deflection shown by a bold line in
FIG. 10
) where the total of the gas pressure in the first high-pressure chamber
93
and the spring force of the diaphragm
90
m
itself becomes equivalent to the average pressure of the fuel.
However, in the metal diaphragm type pulsation absorber
90
, since the metal diaphragm which is an expansion member expands and contracts repeatedly by an amount equivalent to the pressure pulsation of fuel with the balance point at an average fuel pressure as a center, when this fuel supply system for a direct injection gasoline engine is used in a fuel pressure variable system, the balance point changes, whereby average stress generated in the diaphragm alters, thereby causing a problem with durability.
For instance, when the variable range of fuel supply pressure of the fuel supply system is 5 to 10 MPa and the balance point of the metal diaphragm
90
m
is set to P
0
=7.5 MPa which is the center of the above variable range, as shown in
FIG. 10
, if P
0
=10 MPa, the metal diaphragm
90
m
vibrates with the balance point greatly displaced to the first high-pressure chamber
93
side and if P
0
=5 MPa, the metal diaphragm
90
m
vibrates with the balance point greatly displaced to the second high-pressure chamber
94
side. Since average stress applied to the metal diaphragm
90
m
becomes larger as the balance point displaces more from the center of the variable range, the durability of the metal diaphragm
90
m
deteriorates.
To prevent deterioration in the durability of the metal diaphragm, it is conceivable, for example, to reduce the volume of the first high-pressure chamber
93
so as to lessen the amount of charged gas. In this case, pulsation absorption capability becomes less. It is also possible to improve the durability of the metal diaphragm by reducing average stress to be applied to the metal diaphragm by increasing the diameter. However, in this case, the pulsation absorber becomes large in size.
Even when a metal bellows type pulsation absorber is used as a high-pressure damper, if fuel supply pressure is made variable, the gas charging pressure must be reduced to achieve the minimum fuel pressure and the number of pleats of the metal bellows must be increased to obtain the larg
Fujita Masahiko
Konishi Keiichi
Miyaji Wakaki
Mitsubishi Denki & Kabushiki Kaisha
Moulis Thomas N.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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