JPH04175594A - High pressure fuel injection pipe and its manufacture - Google Patents

Abstract

PURPOSE:To improve mechanical property and stress distribution against fatigue through eliminating stress concentration in the vicinity of a under head portion by forming a straight pipe portion having an enlarged diameter in the vicinity of the under head portion of a connecting head portion, a tapered wall portion whose diameter decreases from the straight pipe portion gradually, and, in addition, by press fitting a washer member on the enlarged diameter straight pipe portion so that compression stress may remain in the enlarged diameter straight pipe portion. CONSTITUTION:At an end portion of a thick wall small diameter metal pipe 1, a trapezoidal cone-shaped connecting head portion 2, whose external peripheral surface toward the connecting direction is a pressing seat surface 2' to be brought into contact with a seat of a mated injection nozzle, a straight pipe portion 3, whose diameter is enlarged slightly in the vicinity of the under head portion of the head portion, and a backward tapered wall 4 connected to the straight pipe portion 3 are formed. Then, a washer member 5 is located by press fitting at the straight pipe portion 3. Next, a tightening nut 6 is brought into contact with a rear end peripheral surface of the washer member 5 and is connected to a mated part by tightening the screw. As the result, it is possible to reduce and prevent crack and fracture greatly, and to keep stable connection and useful life for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a pipe with a diameter of 4.5 m/m to 20 m/m, which is often used as a fuel supply path in a diesel internal combustion engine near the engine. The present invention relates to a high-pressure twisted fl injection tube made of a relatively thick-walled and small-diameter metal tube with an inner diameter of about 1.0 m/m to 5.0 m/m, and a method for manufacturing the same.

(Prior Art) Conventionally, this type of high-pressure fuel injection pipe and its manufacturing method include, for example, as shown in FIG. A truncated cone-shaped connecting head (12) with a diameter of 12") is provided, and then a ring-shaped washer member is attached to the N-diameter portion (13) of the metal tube (11) formed at the lower part of the neck of the head. (14) is loosely attached, and in this state, the back of the connecting head (12) is assembled via the washer member (14) and tightened by the nut (15) on the inner bottom. It engaged with a wall surface and was connected by being pressed against the seat surface of the mating holder as it was screwed and tightened.

(Problem to be Solved by the Invention) However, in such conventional technology, the structure of the pipe diameter portion (13) of the metal pipe (11) that is just N in the vicinity of the neck portion of the connection head (12) is , and the loose fitting structure of the washer member (14) at the pipe diameter section, the connection head (1
2) Due to buckling fatigue at the lower part of the neck that occurs during molding, when the product is bent forcibly when the shape is defective, mechanical vibrations due to stress concentration in the lower part of the neck of the connecting head, combined with engine vibration, may occur. This resulted in a problem of deterioration of strength, local fatigue, and the tendency for cracks and breakage to occur.

The present invention has been made in view of the above-mentioned problems of the prior art, and can be manufactured easily, and can significantly reduce cracking and breakage by improving the mechanical strength near the lower part of the neck and by dispersing the stress. It is an object of the present invention to provide a high-pressure fuel injection pipe and a method for manufacturing the same, which can reduce and prevent the above problems.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an end portion of a thick-walled, small-diameter metal tube with an outer circumferential surface in the connection direction that serves as a pressing seat surface against the seat surface of a mating nozzle holder. It has a truncated cone-shaped or arc-shaped connecting head integrally, and has a straight pipe portion with a slightly enlarged diameter near the lower part of the neck of the head, and a rearwardly tapered wall connected to the straight pipe portion. In addition, a high-pressure fuel injection pipe formed by press-fitting a short cylindrical washer member located in the straight pipe portion, and an end portion of a thick-walled small-diameter metal pipe cut to a specified product length,
A short cylindrical washer member is assembled in advance by leaving a machining allowance for the connection head on the tip side, and then the tip is pressed from the outside in the axial direction with a pressing die while the vicinity of the end is held between a pair of left and right chuck dies. A truncated cone-shaped or arc-shaped connecting head is formed at the end, and a rearwardly tapered wall that connects to a straight pipe portion with a slightly enlarged diameter near the lower part of the neck of the head. At the same time, along with the formation, the washer member is press-fitted to the straight pipe portion, or the end of a thick-walled, small-diameter metal pipe cut to a specified product length,
Leaving a machining allowance for the connecting head on the tip side in advance, the vicinity of the end is clamped between a pair of left and right chuck dies, and the tip is pressed from the outside in the axial direction by a pressing die to form a buckle, and the end is cut. A conical or arcuate connection head and a tapered wall connected to a straight pipe portion with a slightly enlarged diameter are formed near the bottom of the neck of the head, and then a separate short pipe is placed on the straight pipe portion. The gist of each of these is a manufacturing method in which a washer member of a shape is press-fitted.

(Function) Since the present invention is configured in this manner, the straight pipe portion has an increased cross-sectional area by expanding the diameter near the neck portion, and the tapered wall that has a gradually reduced cross-sectional area connected to the straight pipe portion. Furthermore, by press-fitting a washer member in the straight pipe part with compressive stress remaining in the diameter-enlarged straight pipe part, stress concentration near the lower part of the neck is eliminated, and mechanical strength and fatigue stress dispersion are significantly improved. Therefore, even if the product is forcibly installed due to a defect in the bent shape of the product under vibration-like suspension, cracks and breakage can be significantly reduced and prevented, resulting in a stable connection over a long period of time. , to maintain durability.

(Embodiments) Hereinafter, embodiments of the present invention will be described based on the drawings. Fig. 1 shows a high-pressure fuel injection pipe constructed by the high-pressure fuel injection pipe of the present invention and the manufacturing method thereof. FIG. 2 is a diagram corresponding to FIG. 1 showing another embodiment, in which (1) is a thick-walled, small-diameter metal pipe as a high-pressure fuel injection pipe, and the range of the pipe diameter is It is made of carbon steel pipe material, stainless steel pipe material, or a composite pipe material of these materials for high pressure piping. Then, a short cylindrical washer member (5) is installed in the end of the straight pipe cut to the specified product length, leaving a machining allowance for the connection head on the tip side, and then the vicinity of the end is assembled. By performing buckling molding by pressing the tip from the outside in the axial direction with a press die while it is held between a pair of left and right chuck dies, the outer peripheral surface of the end in the connection direction is shaped like a mating injection nozzle (not shown). A truncated conical shape (Fig. 1) or an arc shape (
The connecting head (2) shown in Fig. 2), a straight pipe part (3) whose diameter is slightly enlarged near the lower part of the neck of the head, and a rearwardly tapered wall (4) connected to the straight pipe part. At the same time as the washer member (5) is formed, the washer member (5) is positioned on the straight pipe portion (3) and press-fitted, or the cut straight pipe is attached to the end thereof in advance on the distal end side. The connecting head (2 ), a straight pipe portion (3) and a tapered wall (4), and then a separate short cylindrical washer member (5) is press-fitted onto the straight pipe portion (3). Compressive stress remains in the straight pipe portion (3) whose diameter has been expanded by the press-fitting, further improving the stress dispersion effect.

(6) is tightened by a nut, and when attached to a partner injection nozzle, the inner bottom wall surface of the nut engages with the rear end circumference of the washer member (5) and is screwed and tightened for connection. .

The diameter-enlarged straight pipe portion (3) should be formed to have a length equal to or shorter than that of the washer member (5), and if the diameter expansion rate of the straight pipe portion (3) is less than 5%, the cross-sectional area will increase. On the other hand, if it exceeds 25%, the washer member (5
5 to 25%, preferably 10 to 25%, as there is an adverse effect on
It should be 20%.

Furthermore, if the inclination of the tapered wall (3) with respect to the central axis of the metal tube (1) is less than 5°, workability will be poor;
If the angle exceeds 5 to 15 degrees, the stress dispersion effect will not be achieved.
, preferably 8-12°.

Next, a piece of STS 40 with an inner diameter of 1.8 mm and an outer diameter of 6.
The high-pressure fuel injection pipe according to the present invention is made of a 35m+n thick-walled, small-diameter metal pipe, which has a tapered wall with an inclination of 9° and a straight pipe part expanded to an outer diameter of 7.3mm, and into which a washer member is press-fitted. A fatigue characteristic test was conducted using a conventional high-pressure fuel injection pipe having a shape shown in FIG. 3 without a tapered wall and an enlarged diameter straight pipe portion, and the results are shown in FIG.

As shown in curve (A), the product of the present invention has a maximum of 21 kgf/
l1lfi12, whereas the conventional one is a curve (b)
As shown in , it is 17 f/mm2, resulting in 23,
A 5% improvement in mechanical strength was observed.

(Effects of the Invention) As explained above, the high-pressure fuel injection pipe and the manufacturing method thereof according to the present invention, in particular, the connecting head (2
) The straight pipe part (
3) and a tapered wall (4) with a gradually decreasing cross-sectional area connected to the straight pipe section, and a pressure wall located in the straight pipe section (3) so that compressive stress remains in the straight pipe section (3). Since it is constructed with a fitted short cylindrical washer member (5), the above-mentioned simple manufacturing eliminates stress concentration near the lower part of the neck and improves mechanical strength. Even if the product is hung forcibly due to a defect in its bending shape, cracks and breakage can be significantly reduced and prevented, and stable connections and durability can be maintained over a long period of time. , an extremely useful high-pressure fuel injection pipe and a method for manufacturing the same.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway plan view of a high-pressure fuel injection pipe constructed by a high-pressure fuel injection pipe and a manufacturing method thereof according to an embodiment of the present invention, and FIG. 2 shows another embodiment of the high-pressure fuel injection pipe. Fig. 3 is a partially cutaway plan view of a high-pressure fuel injection pipe constructed by a conventional manufacturing method, and Fig. 4 is a comparative fatigue characteristic of the product of the present invention and a conventional product in terms of breakage. It is a curve diagram. (1)...Metal tube, (2)...Connection head, (2°)
... Pressed sheet surface, (3) ... Straight pipe part, (4)
...Tapered wall, (5)...Washer member. Patent applicant Usui Kokusai Sangyo Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) At the end of the thick-walled, thin-diameter metal tube (1), press the outer peripheral surface in the connection direction against the seat surface of the mating nozzle holder (2).
') and a truncated conical or arc-shaped connecting head (2)
and a straight pipe part (3) whose diameter is slightly enlarged near the lower part of the neck of the head, and a rearwardly tapered wall (4) connected to the straight pipe part, and the straight pipe A high-pressure fuel injection pipe characterized in that a short cylindrical washer member (5) is press-fitted to the portion (3). (2) Incorporate a short cylindrical washer member into the end of a thick-walled, small-diameter metal tube that has been cut to a specified product length, leaving a machining allowance for the connection head on the tip side, and then attach the washer member near the end. is clamped between a pair of left and right chuck molds, and the tip is pressed from the outside in the axial direction by a pressing mold to form a buckling shape, and a truncated cone-shaped or arc-shaped connecting head is formed at the end, and a neck of the head is formed. A rearwardly tapered wall connected to a straight pipe portion with a slightly enlarged diameter is formed in the vicinity of the lower part, and along with the formation, the washer member is press-fitted to the straight pipe portion. A method of manufacturing a high-pressure fuel injection pipe characterized by: (3) At the end of a thick-walled, small-diameter metal tube that has been cut to a specified product length, leave a machining allowance for the connection head on the tip side in advance, and clamp the vicinity of the end between a pair of left and right chuck molds. The axial tip is buckled by pressing from the outside with a press mold, and has a truncated conical or arc-shaped connecting head at the end, and a straight pipe portion with a slightly enlarged diameter near the bottom of the neck of the head. 1. A method for manufacturing a high-pressure fuel injection pipe, which comprises forming a tapered wall connected to the straight pipe portion, and then press-fitting a separate short cylindrical washer member located on the straight pipe portion.