JP3349611B2 - High-pressure fuel injection tubing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high pressure fuel pipe for diesel injection (hereinafter referred to as "high pressure fuel pipe") used for a pipe between a pump and a nozzle holder in a diesel internal combustion engine, and a high pressure fuel pipe having a pressure accumulating section interposed in the pipe. (Hereinafter referred to as "injection tube"), and has a relatively small diameter and a large wall thickness of about 20 mm or less.

[0002]

2. Description of the Related Art Conventionally, a high-pressure fuel injection pipe of this type prevents cavitation, erosion, and corrosion (hereinafter simply referred to as erosion) on an inner peripheral surface which is generated due to a recent increase in injection pressure of fuel. In relation to the above, a thin inner pipe made of austenitic stainless steel is polymerized by drawing processing over the entire length of the inner peripheral surface of an outer pipe made of a thick carbon steel pipe material for a high-pressure pipe having a ferrite structure. A known high-pressure fuel injection pipe is formed by forming connection heads having outer peripheral surfaces thereof as pressing surfaces against mating seats at both end portions of the pipe material (Japanese Patent Publication No. 46712/1989). It had been.

[0003]

However, in the prior art in which the outer tube of carbon steel having such a ferrite structure is superposed on the inner tube of stainless steel having an austenitic structure, there are the following problems. That is, when the processing heat immediately after the drawing process for producing the polymerization tube is about 150 ° C., the joint between the inner tube and the outer tube of the polymerization tube is in a close contact state. However, when cooled to room temperature, a gap is formed between the inner tube and the outer tube because the inner tube having an austenite structure having a higher thermal expansion coefficient than the outer tube having a ferrite structure is formed, and such a polymerization tube is subjected to high pressure. When used as an injection pipe to which internal pressure is repeatedly applied, fretting wear occurs between the peripheral walls of the gap between the inner pipe and the outer pipe, which may cause cracking (breakage).

[0004] Further, after cooling in the strain relief annealing treatment after the drawing process, a larger gap is formed, and the tendency of the fretting wear phenomenon similar to the above becomes remarkable.

In order to prevent such a fretting wear phenomenon, it has been proposed that the inner tube be made of a standard type ferritic stainless steel so that the thermal expansion coefficient substantially matches the carbon steel material of the outer tube. When a hoop material made of a ferritic stainless steel material is pipe-formed by electric resistance welding, a new problem that crystal grains grow in a wide area near a bead portion by the electric resistance welding after pipe formation has occurred.

[0006] Since the crystal grain growth portion causes cracks such as axial cracks in precision pipe drawing such as material pipe drawing and polymerization pipe drawing, plastic processing such as pipe drawing is later performed as a high-pressure fuel injection pipe. It was not suitable as a tubing to which was added.

The present invention has been made in view of the above-mentioned problems of the prior art, and not only prevents erosion, but also prevents the inner tube from being deformed even when there is a temperature variation from high to low during plastic working or use. It is an object of the present invention to provide a high-pressure fuel injection tube material that has no gap between the outer tube and can prevent the fretting wear phenomenon, and has no growth of crystal grains near a bead portion by electric resistance welding.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a high-pressure fuel injection pipe made by press-fitting a thin stainless steel inner pipe to the inner peripheral surface of a thick ferritic carbon steel outer pipe. In the above, the inner pipe contains more than 1% by weight of Si and 3% by weight.
A high-pressure fuel injection tube, which comprises an electric resistance welded tube of a ferritic stainless steel material contained below.

[0009]

According to the present invention, as described above, a thin inner tube made of a ferritic stainless steel electric resistance welded tube having a thermal expansion coefficient substantially equal to that of the outer tube and containing more than 1% by weight and not more than 3% by weight of Si is used. , Which are press-fitted to a thick outer tube made of steel to constitute a superposed tube.

By using a ferritic stainless steel material having a thermal expansion coefficient substantially equal to that of the outer tube for the inner tube, the temperature can be reduced from high to low during heat treatment such as plastic working and strain relief annealing after drawing and during use. Even if the temperature fluctuates over time, there is no gap between the inner tube and the outer tube, so that the fretting wear phenomenon can be prevented.

On the other hand, the content of Si is 1% by weight as described above.
The reason for exceeding 3% by weight is that when Si is 1% by weight or less, the growth of crystal grains near the bead portion during ERW is not so much suppressed, and an axial crack occurs along the bead portion during plastic working. On the other hand, if Si exceeds 3% by weight, the elongation of the base material is lost and tearing is likely to occur during the drawing process, so that a large diameter reduction ratio cannot be obtained. In order to suppress the crystal grain growth, prevent cracks in the bead portion of the electric resistance welding, and increase the diameter reduction ratio, the content of Si is set to 1.5 to
It is preferably 2.5% by weight.

As the outer tube, various materials can be used as long as it is a carbon steel material. Preferred examples include STS and STK.
M, SPCC, etc., and a single-layer thick-walled tube is preferable. However, a thick-walled tube may be formed by polymerizing two or more single-layered tubes or double-wound tubes with each other.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a central sectional view of a high-pressure fuel injection pipe according to the present invention, and FIG. 2 is a process for manufacturing the high-pressure fuel injection pipe according to the present invention. It is explanatory drawing by the notch vertical cross section at the time of the pipe-drawing process which shows (1) The outer pipe which consists of a comparatively small diameter and a thick wall ferritic carbon steel material about 15 mm or less in diameter, Over the entire length of the inner circumference of the borehole of about 4 mm or less,
A thin inner tube (2) made of a ferritic stainless steel material having a wall thickness of about 0.3 to 1.2 mm and containing Si in an amount of more than 1% by weight and 3% by weight or less and subjected to electric resistance welding is inserted and press-fitted. It is a polymerization tube.

Such a polymerization tube has a thick wall as shown in FIG.
A state in which an inner tube (2 ') made of a stainless steel electric resistance welded tube containing more than 1% by weight and not more than 3% by weight of Si is fastened to an inner peripheral surface of an outer tube (1') made of ferritic carbon steel. After passing through a die (3) and subjecting it to at least one drawing by integral drawing, reducing the entire diameter, press-fitting and superimposing,
A connection head is formed at both ends to form a high-pressure fuel injection pipe as a product. Example 1 Material Outer tube made of ferritic carbon steel of JIS G 3455 STS 35 (outer diameter 9.5 mm, wall thickness 2.3)
(5 mm, inner diameter 4.3 mm), an inner tube made of an electric resistance welded tube made from a hoop material made of ferritic stainless steel based on SUS 405 adjusted to have a Si content of 2.0% by weight. (Outer diameter 4 mm, wall thickness 0.4 mm, inner diameter 3.2 mm) were inserted and loosened. Next, as shown in FIG. 2, with a fixed die, the drawing process was performed twice by integral drawing in the direction of the arrow to reduce the diameter of the whole over the entire length,
After that, it is straightened to an outer diameter of 6.4 mm and a wall thickness of 2.2 m.
m and a high-pressure injection tube material having an inner diameter of 2.0 mm were obtained.

Since the thermal expansion coefficients of the inner pipe and the outer pipe of the obtained pipe material are substantially equal, no gap is generated between both pipes.
Subsequent drawing work was not required, and no gap was found even when the strain relief annealing treatment was performed. Example 2 STKM 11A EC ferrite-based carbon steel outer tube (outer diameter 9.5 mm, wall thickness 2.35 mm, inner diameter 4.8)
mm), an electric resistance welded tube formed from a hoop material made of ferritic stainless steel based on SUS 405 and adjusted to have a Si content of 1.6% by weight in the same manner as in Example 1. Pipe (outer diameter 4.0mm, wall thickness 0.4m
m, an inner diameter of 3.2 mm) and the same processing as in Example 1 was performed once to obtain a polymerization tube having an outer diameter of 6.4 mm, a wall thickness of 2.2 mm, and an inner diameter of 2.0 mm.

[0016] There was no gap between the inner pipe and the outer pipe of the obtained pipe material, so that subsequent drawing work was not required, and no gap was observed even after performing the strain relief annealing treatment. Example 3 After pretreatment, a ferrite carbon steel material of SPCC having a Cu plating layer of about 3 μm for welding at the time of pipe making on the surface was used for an outer pipe, having an outer diameter of 10.0 mm and a wall thickness of 1. 0
mm, inner diameter 8.0 mm, outer diameter 7.94 mm, wall thickness 1.
Two double-wound tubes having a diameter of 0 mm and an inner diameter of 5.94 mm were prepared, and one inner tube was made of a ferritic stainless steel material based on SUS 405 adjusted to have a Si content of 2.8% by weight. ERW pipe made from hoop material (outer diameter 5.0 mm, wall thickness 0.5 mm, inner diameter 4.0 mm)
Was prepared.

As shown in FIG. 2, the three tubes are loosened with each other, and the tube is drawn once by an integrated drawing in the direction of the arrow using a fixed die to reduce the diameter of the entire tube over its entire length. To obtain a five-fold high-pressure injection tube having an outer diameter of 6.0 mm, a wall thickness of 2.0 mm, and an inner diameter of 2.0 mm.

There is no gap between each tube of the obtained tube material,
Subsequent drawing work was not required, and no gap was found even when the strain relief annealing treatment was performed.

Comparative Example 1 An outer tube (outer diameter: 9.5 mm, wall thickness: 2.35 mm, inner diameter: 4.8 mm) made of ferritic carbon steel of STS 35 similar to that in Example 1 was put in a normal SUS405 (containing Si). Amount of 1.0% by weight or less) made of an electric resistance welded tube (outer diameter of 4.
0 mm, a thickness of 0.4 mm, and an inner diameter of 3.2 mm).
5 Hoop material was formed by roll forming and then welded by ERW. However, axial cracks occurred along the bead portion and the inner tube could not be manufactured. Could not.

Comparative Example 2 The same construction as in Example 1 was adopted except that an electric resistance welded tube made of austenitic carbon steel of standard type SUS 304 (Si content: 1.0% by weight or less) was used as the inner tube.

There was a gap of 5 μm on one side between the inner tube and the outer tube of the obtained tube material. In order to remove this gap, it was necessary to perform a drawing process of about 1% of the outer diameter. However, even if such a processing is performed, if a subsequent strain relief annealing treatment (at 500 ° C. for 15 minutes) is performed, 15 μm on one side is again obtained.
A gap of m was generated, and it was necessary to perform an additional drawing process in order to remove the gap.

[0022]

As described above, according to the present invention, an electric resistance welded tube made of ferritic stainless steel material having a thermal expansion coefficient substantially equal to that of the outer tube and containing more than 1% by weight and not more than 3% by weight of Si. The high-pressure fuel injection tube is formed as a superposed tube by press-fitting the thin inner tube to the thick outer tube made of a carbon steel material having a ferrite structure. Therefore, the erosion resistance is naturally exhibited by the stainless steel material of the inner tube. That,
Because there is no gap between the outer pipes due to heat treatment processing such as drawing pipe processing and annealing processing, even if the high pressure fuel injection pipe as a product is under any temperature conditions based on the gap, No fretting wear between outer tubes
In addition, the expansion of the inner tube due to the pressure fluctuation is eliminated and the fatigue damage of the inner tube can be prevented. Further, even if an inner tube made of an electric resistance welded pipe is used, no crystal grains grow in the bead part by the electric resistance welding and no crack is generated in the bead part during plastic working.

[Brief description of the drawings]

FIG. 1 is a central sectional view of a high-pressure fuel injection tube according to the present invention.

FIG. 2 is an explanatory view showing a step of manufacturing a high-pressure fuel injection pipe material according to the present invention by a partially cut-out vertical section at the time of pipe drawing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer pipe 1 'Outer pipe 2 Inner pipe 2' Inner pipe 3 Dice

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02M 55/02 320 F16L 9/18

Claims (1)

(57) [Claims] 1. A high-pressure fuel injection pipe material in which a thin stainless steel inner pipe is press-fitted on the inner peripheral surface of a thick ferritic carbon steel outer pipe, wherein the inner pipe exceeds 1% by weight of Si. A high-pressure fuel injection tube made of an electric resistance welded tube of ferritic stainless steel containing not more than 10% by weight.