JP2004027968A - Common rail and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a common rail improved in inner pressure fatigue strength of an opening peripheral part of branched holes formed on an inner wall of a rail hole. <P>SOLUTION: The hollow of the common rail 10 is used as a main tubular hole 12, recessed holes 15 are formed on a hole wall of the main tubular hole 12, and branched holes 16 are formed on hole walls of the recessed holes 15. The hole walls of the recessed holes 15 have the recessed spherical shape formed by coining to be a surface hardened part H, whereby the compressive residual stress is generated, and the tensile stress caused by the inner pressure of the pressurized fuel is reduced. Further the tensile stress caused by the inner pressure of the pressurized fuel can be reduced by the recessed spherical shape of the recessed holes 15. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a common rail in a common rail fuel injection device for an engine.
[0002]
[Prior art]
Conventionally, as a common rail in this type of common rail type fuel injection device, there is one shown in FIG. The common rail 51 has a rail main body 53 having a main pipe hole 52 extending in the rail length direction at the center thereof. The rail main body 53 has a plurality of branch holes 54 formed at intervals in the length direction. Reference numeral 54 is open to the inner wall of the main pipe hole 52. A communication hole 55 coaxially expanded in diameter communicates with the branch hole 54, and an outer peripheral end of the communication hole 55 is tapered to the outside as a connection portion 56 with an injection pipe (not shown). It is open.
[0003]
[Problems to be solved by the invention]
In the common rail 51 as described above, since the internal pressure of the pressurized fuel is applied to the inner wall of the main pipe hole 52 and the branch hole 54, a tensile stress is generated on the inner wall of both the main pipe hole 52 and the branch hole 54. Particularly, at the periphery of the opening of the branch hole 54 on the inner wall of the main pipe hole 52, the stress of both the main pipe hole 52 and the branch hole 54 is combined, so that the value of the tensile stress is larger than that of the other portions.
The internal pressure due to the pressurized fuel, which is the source of the tensile stress, varies according to the running state of the vehicle and the like, and the tensile stress also varies accordingly. However, the value of the varying tensile stress is large. At a portion, that is, around the opening of the branch hole 54 on the inner wall of the main pipe hole 52, there is a concern that metal fatigue may occur.
[0004]
The present invention has been made in view of the above circumstances, and has an object to improve the internal pressure fatigue strength around the opening of the branch hole in the inner wall of the rail hole.
[0005]
[Means for Solving the Problems]
As means for achieving the above object, the invention according to claim 1 is characterized in that the main pipe hole is formed in a rail main body having a hollow inside as a main pipe hole and a branch hole opening to the main pipe hole is formed. It is characterized in that a surface hardened portion is formed around the opening of the branch hole on the inner wall.
[0006]
According to a second aspect of the present invention, in the first aspect, the surface hardening is performed by coining, and the periphery of the opening of the branch hole on the inner wall of the main pipe hole is formed into a concave spherical shape by the coining. It has a feature in the configuration that is described.
[0007]
According to a third aspect of the present invention, there is provided a method for manufacturing a common rail, wherein a branch hole that opens to an inner wall of the main pipe hole is formed in a rail body having a main pipe hole inside the hollow. It is characterized in that a surface hardening treatment is applied to the periphery of the opening.
[0008]
Function and effect of the present invention
<Invention of claim 1>
Since the surface hardened portion is formed around the opening of the branch hole on the inner wall of the main pipe hole to form a surface hardened portion, a compressive residual stress is applied to the surface hardened portion to increase the internal pressure fatigue strength.
[0009]
<Invention of Claim 2>
Due to the coining process, the periphery of the opening of the branch hole in the inner wall of the main pipe hole is formed into a concave spherical shape, so in addition to the improvement of internal pressure fatigue strength due to the coining process itself, the internal pressure fatigue strength also from the concave spherical shape Can be improved.
[0010]
<Invention of Claim 3>
Since the surface hardening treatment is applied to the periphery of the opening of the branch hole on the inner wall of the main pipe hole, compressive residual stress is applied to the periphery of the opening to increase the internal pressure fatigue strength.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
<First embodiment>
A first embodiment of the present invention will be described with reference to FIGS. This embodiment is applied to a common rail type fuel injection device of a diesel engine, and a supply pipe (not shown) for connecting a fuel pump and an injection pipe (not shown) for connecting an injector are provided on the common rail 10. ) Are connected.
[0012]
The common rail 10 is entirely made of steel such as carbon steel, and has a rail main body 11 having a short cylindrical shape in the axial direction, and a main pipe hole 12 in which pressurized fuel is stored is formed in the hollow. Is formed. The rail main body 11 has a bottomed cylindrical front part 11C integrally formed with a side wall 11A surrounding the side of the main pipe hole 12 and a front wall 11B closing the front of the main pipe hole 12, and a rear part of the main pipe hole 12. The rear portion 11D is overlapped with the protruding edge of the side wall 11A so as to be aligned, and is joined to the front portion 11B by welding at the joint.
On the front surface of the front wall 11B of the rail main body 11, a branching cylindrical portion 13 having a cylindrical shape smaller in diameter than the rail main body 11 is formed so as to protrude parallel or coaxially in the axial direction. As shown in FIG. 2, the branching tube portions 13 are provided at a central position on the front surface of the front wall 11 </ b> B and at four positions in a cross direction from the central position, for a total of five positions. On the outer periphery of each branching tube portion 13, a male screw portion 14 for connecting a supply pipe or an injection pipe is formed. The supply pipe corresponds to the branching cylinder 13 at the center position on the front surface of the front wall 11B, and the injection pipe corresponds to the remaining branching cylinder 13 located in the cross direction.
[0013]
In the area of the front wall 11B of the rail main body 11 where the branching tubular portion 13 is formed, a concave hole 15 having a concave spherical shape opening on the inner wall of the main pipe hole 12 and a fixed hole opening on the peripheral surface of the concave hole 15. A branch hole 16 having an inside diameter and a connection hole 18 having a constant inside diameter connected to the other end of the branch hole 16 via a tapered hole 17 are formed so as to communicate with each other. A tapered sealing surface 19 is formed at the opening edge of the connection hole 18 so that the distal end surfaces of the injection pipe and the supply pipe come into close contact with each other. The concave hole 15, the branch hole 16, the tapered hole 17, and the connection hole 18 are concentrically connected to each other, and their axes are parallel to or coaxial with the axis of the rail main body 11. In particular, the center of curvature of the concave hole 15 having a concave spherical shape is positioned on the axis of the branch hole 16.
[0014]
Next, a method for manufacturing this common rail will be described. In the present embodiment, the concave hole 15 is formed by coining, and the following description will focus on this point.
As shown in FIG. 3, in manufacturing, first, as a pre-process, the connection hole 18 and the branch hole 16 are formed by cutting, but the rail body 11 in a state where the concave hole 16 is not formed yet. A front part 11C is prepared. In the front part 11C in this state, a branch hole 16 is opened on the inner side surface of the front wall 11B (the part which will later become the inner wall of the main pipe hole 12). Subsequently, as shown in FIG. 4, the front portion 11C is fixed to a receiving stand (not shown) from the side where the branching tube portion 13 projects, and in this state, the branch hole 16 in the inner surface of the front wall 11B is formed. The coining punch 30 is pressed against the periphery of the opening from the head 31 side. The head 31 of the coining punch 30 has a convex spherical shape, and by receiving the pressing action of the coining punch 30, the periphery of the opening of the branch hole 16 on the inner surface of the front wall 11B is crushed. After that, when the pressing by the coining punch 30 is released, a concave spherical hole 15 corresponding to the convex spherical shape of the head 31 of the coining punch 30 is formed around the opening of the branch hole 16 on the inner surface of the front wall 11B. It is formed.
Thus, the hole wall of the concave hole 15 becomes a hardened surface H by coining, and a compressive residual stress is generated in this region. After the pressing by the coining punch 30 is released, the front portion 11C is removed from the pedestal, and then the peripheral edge of the rear portion 11D is overlapped with the projecting edge of the side wall 11A in the front portion 11C in an aligned state. Welding is performed on the entire periphery of the portion to be joined to integrally join the two. By integrally joining the front portion 11C and the rear portion 11D, the entire rail main body 11 in which the main pipe hole 12 is formed in the hollow is formed.
[0015]
As described above, in the common rail 10 of the present embodiment, the residual stress is applied to the periphery of the opening of the branch hole 16 on the inner wall of the main pipe hole 12 by the coining process. The tensile stress resulting from the internal pressure of the pressurized fuel is suppressed, and the internal pressure fatigue strength is increased.
[0016]
Further, by forming the peripheral portion of the opening on the inner wall of the main pipe hole 12 into a concave spherical shape, the tensile stress in the region where the internal pressure acts rather than the internal pressure of the pressurized fuel acts on the region formed in a planar shape. Since the pressure is reduced, the internal pressure fatigue strength can be increased also by the involvement of the form having the concave spherical shape. In addition, the branch hole 16 communicating with the concave hole 15 having the concave spherical shape is formed to be parallel or coaxial with the axis of the main pipe hole 12 in the present embodiment. The arrangement is not limited to this, and can be arranged in various ways. In other words, the direction in which the branch hole 16 extends needs to match the direction in which the internal pressure of the pressurized fuel is applied. However, in the present embodiment, the surface on which the internal pressure is applied has a concave spherical shape. It can be arranged at a radial position centered on the center of curvature of the concave spherical surface in the concave hole 15, thereby increasing the range of variations in the arrangement.
[0017]
<Second embodiment>
Next, a second embodiment of the present invention will be described with reference to FIG.
In the second embodiment, unlike the first embodiment, the branch hole 16 is opened directly on the inner wall of the main pipe hole 12 without passing through the concave hole 15, but other configurations are the same as those of the first embodiment. Since the configuration is the same as that of the embodiment, the same reference numerals are given in the drawings, and duplicated description will be omitted. In the second embodiment, the induction hardening coil 35 is opposed to the inner wall of the main pipe hole 12 at a predetermined distance from the periphery of the opening of the branch hole 16, and the high-frequency current is applied to the periphery of the opening of the branch hole 16 from that state. To harden locally, thereby forming the surface hardened portion H without forming the concave hole 15. The reason why the induction hardening method is adopted in the second embodiment is that the trouble of removing or carburizing a carburized layer such as carburizing and quenching can be avoided, the common rail is a hardenable steel material, Various advantages are taken into consideration, such as being able to perform quenching, controlling surface hardness, and not requiring complicated equipment.
[0018]
<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and furthermore, besides the following, within the scope not departing from the gist. Can be implemented with various modifications.
[0019]
(1) As shown in FIG. 6, a laser beam 36 is applied to the inner wall of the main pipe hole 12 around the opening of the branch hole 16 to perform local quenching or shot peening to obtain a hardened surface. An embodiment in which H is formed may be used.
[0020]
(2) The form of the common rail is not particularly limited. For example, the common rail may include a rail body having a circular cross section and extending in the axial direction.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a first embodiment. FIG. 2 is a front view of the same. FIG. 3 is a longitudinal sectional view showing a state before a surface hardened portion is formed. FIG. FIG. 5 is a view corresponding to FIG. 4 of the second embodiment. FIG. 6 is a view corresponding to FIG. 4 of another embodiment. FIG. 7 is a vertical cross-sectional view of a conventional example.
H: Surface hardened portion 10: Common rail 11: Rail main body 12: Main pipe hole 13: Branching tube portion 15: Concave hole 16: Branch hole

Claims (3)

In a common rail formed in a rail body in which a hollow is a main pipe hole, a branch hole that opens to an inner wall of the main pipe hole,
A common rail, wherein a hardened surface is formed around an opening of the branch hole on an inner wall of the main pipe hole. 2. The common rail according to claim 1, wherein the surface hardening is performed by coining, and the periphery of the opening of the branch hole in the inner wall of the main pipe hole is formed in a concave spherical shape by the coining. 3. . In a method for manufacturing a common rail, a hollow main body is formed with a main pipe hole, and a branch hole is formed on the inner wall of the main pipe hole.
A method of manufacturing a common rail, wherein a surface hardening process is performed on an inner peripheral portion of a branch hole on an inner wall of the main pipe hole.

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