Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2001-04-05
2002-12-24
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S469000, C123S456000
Reexamination Certificate
active
06497219
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2000-111520 filed on Apr. 13, 2000, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a common rail fuel injection system in which highly pressurized fuel accumulated in a pressure accumulation chamber of a common rail housing is supplied to injectors of an internal combustion engine, and in particular to the construction of the common rail housing.
2. Description of Related Art
A common rail fuel injection system as disclosed in JP-A-4-287866 is well known. The injection system has a common rail housing which acts as a kind of a surge tank and is provided with a pressure accumulation chamber extending in a lateral direction thereof. Highly pressurized fuel accumulated in the pressure accumulation chamber is supplied to injectors of an internal combustion engine.
In the conventional common rail system, as shown in
FIG. 6
, a common rail housing
101
is provided with a pressure accumulation chamber
102
in which highly pressurized fuel is temporally accumulated, a plurality of fuel supply ports (not shown) through which highly pressurized fuel delivered by a fuel supply pump is supplied to the pressure chamber
102
, and a plurality of fuel delivery ports
103
through which the highly pressurized fuel in the pressure accumulation chamber
102
is delivered to injectors installed in respective cylinders of the internal combustion engine.
A cylindrical pressure accumulation pipe
104
, whose outer circumference is formed in round shape, constitutes the pressure chamber
102
. A cylindrical outlet pipe
105
, which is connected to the cylindrical pressure accumulation pipe
104
, constitutes each of the fuel delivery ports
103
. The cylindrical pipe
105
is provided at an outer circumferential surface on a leading end thereof with a male thread portion
106
into which a high-pressure pipe is screwed for fastening.
In the common rail housing
101
of the conventional fuel injection system, the pressure chamber
102
is formed in complete round shape in cross section so that tensile stresses are induced at and concentrated on intersecting portions
107
where the pressure chamber
102
and the respective fuel delivery ports
103
intersect each other. As the fuel injection pressure in the system is higher, the stresses induced at and concentrated on the intersecting portions
107
are larger so that reliability in strength of the common rail housing
101
is likely to be jeopardized. Accordingly, the conventional common rail housing
101
has a drawback on realizing the fuel injection system with much higher pressure.
As a way of solving the drawback, it may be contemplated to reduce an inner diameter of the pressure chamber
102
so that the stresses induced at the intersecting portions
107
become smaller. However, as it is necessary to secure a given inner volume of the pressure chamber
102
, which is predetermined for one or more injectors, for a purpose of limiting injection fluctuation of injectors, a longitudinal length of the common rail housing
101
is obliged to be longer so that manufacturing efficiency of the common rail housing
101
and installation efficiency thereof to the internal combustion engine are adversely affected.
As another way of reducing the stresses, JP-A-10-169527 discloses, as shown in
FIGS. 7A
to
7
C, common rail housing
101
having an oval shaped pipe
114
provided with an oval shaped pressure accumulation chamber
113
and also provided with a fuel supply or delivery bore
115
connected to the pressure accumulation chamber
111
at a position where a curvature of the oval is small.
It also describes that the oval shaped pipe
114
having the oval shaped pressure accumulation chamber
113
as shown in
FIG. 7B
is shaped by plastically deforming a complete round pipe
112
having a pressure accumulation chamber
111
as shown in
FIG. 7A
with press working or roll forming. In the deformation process, residual stresses (tensile stresses) are induced in the common rail housing
101
. Accordingly, stresses (&agr;) always remain at the intersecting portion
116
where the fuel input or output bore
115
is connected to the pressure accumulation bore as shown in
FIGS. 7B and 7C
. Even if the tensile stresses at the intersecting portion, which is induced by inner pressure (P) of highly pressurized fuel in the pressure accumulation chamber
113
, is reduced, a sum of the residual stresses (&agr;) and the stresses due to the inner pressure (P) is likely to be relatively large so that strength at the intersecting portion
116
is jeopardized.
If wall thickness of the oval shaped pipe
114
is equal to or more than a diameter of the oval pressure accumulation chamber
113
in a minor axis of the oval thereof, that is, if an outer diameter (for example, 30 mm) of the oval shaped pipe
114
in a minor axis length of the oval thereof is larger by three times or more than the diameter (for example, 10 mm) of the oval pressure accumulation chamber
113
in a minor axis of the oval thereof, the strength at the intersecting portion
116
can be sufficiently assured.
However, deformation of the complete round pipe made of iron steel into the oval shaped pipe
114
having such a thick thickness wall needs a several tens or hundreds pressing load. Even if deformed by the press working or the roll forming, as shown in
FIGS. 8A and 8B
, the oval shaped pipe
114
is likely to have wrinkles or cracks so that pressure endurance of the oval shaped pipe
114
is reduced.
SUMMARY OF THE INVENTION
An object of the invention is to provide a common rail fuel injection system having a common rail housing in which stresses concentrated on given portions are remarkably reduced and, further, resisting pressure strength is distinctively improved.
It is another aspect of the invention to provide a method of manufacturing the common rail housing in which residual stresses induced therein are limited.
To achieve the above objects, the common rail housing is composed of a pressure accumulation pipe, whose outer circumference is formed in roughly complete round shape in cross section, being provided inside with a pressure accumulation chamber having given shaped cross section and extending in a longitudinal direction thereof, and a branch pipe being provided inside with a fuel conduit bore. Outer circumference of the given cross section has a first portion whose curvature is smaller than that of complete round shape having an area equal to that of the given cross section. The branch pipe is connected to the pressure accumulation pipe so that the fuel conduit bore and the pressure accumulation chamber intersect nearly perpendicularly to each other at the first portion.
It is preferable that wall thickness of the pressure accumulation pipe at the first portion is thickest. Therefore, when highly pressurized fuel is supplied to the pressure accumulation chamber, not only the stresses concentrated on the first portion are limited but also wall strength of the pressure accumulation pipe at the first portion is reinforced.
Accordingly, the common rail housing may be made of relatively low hardness material such as low carbon steel that is easily formed in the given shape on manufacturing. Further, as the wall thickness of the pressure accumulation pipe is relatively thick at the first portion and relatively thin at the portions other than the first portion around the circumference of the pressure accumulation chamber, the wall thickness of the pressure accumulation pipe of the present invention is thinner as a whole than the conventional common rail housing, resulting in saving fuel consumption.
It is preferable that the given shaped cross section of the pressure accumulation chamber is formed in roughly flat oval shape or in roughly oval shape.
To limit residual stresses to be induced on manufacturing the common rail housing mentioned above, it
Denso Corporation
Gimie Mahmoud
Nixon & Vanderhye PC
Wolfe Willis R.
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