JPH1144277A - Manufacture of high pressure fuel injection pipe and the pipe produced thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain an easy and simple production by forming a double metal pipe of an outer pipe and an inner pipe which is inserted into the outer pipe and which pipes are press fitted by pipe elongation work, and forming a connection head by chucking with a work margin satisfying a specified formula in forming thread at a connection end of the double metal pipe. SOLUTION: In manufacturing a high pressure fuel injection pipe to be used for a diesel internal combustion engine, firstly, an inner pipe 3 made of a thin wall steel pipe having the hardness of 400-550 is inserted into an outer pipe 1 formed of a thick wall steel pipe, and both the pipes 1, 3 are press fitted by pipe elongation work, thereby forming a double metal pipe. Secondly, a connection head 2 is formed at a connection end of this double metal pipe. At this time, the head 2 is formed by chucking with a work margin satisfying a relation represented by 11 <=1.3D+12 , where D is an outer diameter of the inner pipe 3, I is an axial length of the head 2. Accordingly, buckling of the inner pipe 3 in the head 2 is prevented, whereby a sufficient cavitation resistant characteristic is obtained even when high pressure fuel is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel internal combustion engine, and has a relatively small diameter of about 20 mm or less, which is connected to a nozzle holder on each of a cylinder head side and a fuel pump side as a fuel supply path. And a high-pressure fuel injection pipe obtained by the method.

[0002]

2. Description of the Related Art Heretofore, as a high pressure fuel injection pipe for a diesel internal combustion engine of this type, Japanese Patent Publication No.
No. 46712 is known. The high-pressure fuel injection tubing described in this publication forms a double metal pipe by press-fitting a thin-walled inner pipe made of a stainless steel pipe having a flow passage formed inside to an outer pipe made of a thick-walled steel pipe. The thickness of the pipe is 1.2 to 8.5% of the outer diameter of the entire double metal pipe.

[0003] The high-pressure fuel injection pipe described in this publication has an injection time of 1 to 1 as a measure against NOx reduction and black smoke.
2 msec, flow rate up to 50 m / sec, internal pressure 600 ~
Even when operated and tested under conditions corresponding to the recent increase in fuel injection pressure of 1000 bar (peak pressure), not only can cavitation, erosion, and corrosion (hereinafter, cavitation) occur on the inner peripheral surface, but also it can be prevented. The durability against repeated high-pressure fatigue was almost satisfactory.

[0004]

Under actual conditions of use, in order to arrange the fuel supply passages connected to the nozzle holders on the cylinder head side and the fuel pump side, respectively, the pipe of the high-pressure fuel injection tube described above is required. It is necessary to form a frusto-conical, arc-shaped or abacus spherical connecting head at the end by press working or the like.

[0005] However, when the connection head is formed on the high-pressure fuel injection tube described in the above-mentioned publication by press working or the like, buckling occurs as shown in FIG. 6 in the inner pipe located on the inner peripheral surface of the connection head. was there. The reason for this is not clear, but it is presumed that the inner pipe is extremely harder than the outer pipe, and the shape of the connection head formed by press working is special.

The present applicant has proposed a method of forming a connection head as disclosed in Japanese Patent Publication No. 60-44547 in order to prevent such buckling of the inner tube. According to this publication, a high-pressure fuel injection pipe made of a double metal pipe is formed by providing an inner pipe at a position that is depressed by an appropriate length from an end face of a thick outer pipe, and a connection end of the pipe thus formed is formed. When the connecting head is formed, deformation such as buckling of an inner tube provided on the inner peripheral surface of the connecting head is prevented.

Although the method described in this publication effectively prevented the buckling of the inner tube at the connecting head, the method of providing the inner tube at a position that is a suitable length below the end surface of the outer tube requires the inner tube to be immersed. It is necessary to accurately and surely press-fit the tube at the position, or to once press-fit the end surface of the outer tube to the end surface of the inner tube, and then remove the inner tube by a certain length. Under mass production systems such as those in the industry, practical use has been shunned because it is too laborious and requires complicated processes, and improvements have been desired.

[0008] The present invention can be manufactured simply and easily without the troublesome manufacturing process and complicated steps, which are problematic in the above-mentioned publication, and has a sufficient inner peripheral surface even when high-pressure fuel is used. It is an object of the present invention to provide a method for manufacturing a high-pressure fuel injection pipe capable of exhibiting anti-cavitation performance and a high-pressure fuel injection pipe obtained by the method.

[0009]

SUMMARY OF THE INVENTION The present inventors have determined the axial dimension of each portion of the connection end, that is, the axial length of the formed connection head, the shrinkage allowance due to the connection head molding, The machining allowance between the chuck end face before forming the connection head and the end face of the tip of the injection pipe material, which is the sum of these, and the outer diameter of the inner pipe are the seat of the inner pipe at the time of forming the connection head. It is closely related to the occurrence of buckling, and it has been found that buckling of the inner tube can be effectively prevented by forming the connection head in consideration of this relationship, and completed the present invention.

That is, in order to achieve the above object, a first embodiment of the present invention is to insert an inner pipe made of a thin steel pipe having a hardness (Hv) of 400 to 550 into an outer pipe made of a thick steel pipe. The two pipes are press-fitted by drawing to form a double metal pipe, and then a frusto-conical, arc-shaped or abacus-shaped connection head is formed at the connection end of the double metal pipe. A machining allowance (l ₁ ) that satisfies the formula l ₁ ≦ 1.3D + l ₂ [where (D) is the outer diameter of the inner tube, and (l ₂ ) is the length of the formed connection head in the axial direction]. ), And a method for manufacturing a high-pressure fuel injection pipe in which the connection head is formed by chucking.

A second embodiment of the present invention relates to a double metal pipe formed by press-fitting an inner pipe made of a thin steel pipe having a hardness (Hv) of 400 to 550 to an outer pipe made of a thick steel pipe. A truncated cone-shaped, arc-shaped or abacus-shaped connection head is formed at the connection end of the head by molding, and the length (l ₂ ) of the connection head is set to l ₂ ≧ l ₁ -1.3D [ However, (D) is the outer diameter of the inner pipe, and (l ₁ ) is the processing allowance for forming the connection head].

As described above, according to the present invention, the inner pipe made of a thin steel pipe having a hardness (Hv) of 400 to 550 is gently inserted into the outer pipe made of a thick steel pipe, and both pipes are drawn. To form a double metal pipe, and then the vicinity of the connection end of the double metal pipe is chucked with a split type chuck and pressed by a punch member to form a frusto-conical, arc-shaped or abacus-shaped connection head. When the part is formed, the following formula l ₁ ≦ 1.3D + l _{2 is} satisfied (where (D) is the outer diameter of the inner tube, and (l ₂ ) is the length of the formed connection head in the axial direction). The connecting head is formed by chucking with a processing margin (l ₁ ) that does not require a complicated process and not only can be manufactured easily and easily. the length of _{(l 2)} a _{l 2} ≧ l 1 -1.3D [however (D) the outer diameter of the inner tube, the (l ₁₎ is thereby formed in a machining margin for the connection head molding, the 400 to 550 which are press fit on the inner peripheral surface hardness (Hv) By using the inner pipe having the same, it is possible to provide a high-pressure fuel injection pipe that does not buckle the inner pipe at the connection head and can exhibit sufficient cavitation resistance even when high-pressure fuel is used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. FIG. 1 is a view showing a high-pressure fuel injection pipe of the present invention, (a) is a longitudinal sectional side view of one embodiment, (b) ) Is a side view of another embodiment with a partial cutout, FIG. 2 is an explanatory view showing a cross-section before forming a connection head, showing one step of the manufacturing method of the present invention,
FIG. 3 is an explanatory view of a cross section after the connection head is formed, and FIG. 4 is a photograph of a metal structure obtained by observing a high-pressure injection fuel pipe manufactured according to the first embodiment of the present invention with a microscope. , (B) is a photograph of 50 times magnification, FIG. 5 is a photograph of a metallographic structure obtained by observing a high pressure injection fuel pipe manufactured according to Example 2 of the present invention with a microscope, (a) is a photograph of 12 times magnification, (b) Is 5
It is a photograph of 0 times, and 1 is a steel pipe for high-pressure piping having a relatively thick wall having a diameter of 20 mm or less and an inner diameter of a small diameter, for example, an outer pipe formed of a single layer or a multi-layer pipe formed of carbon steel. It has a hardness (Hv) of, for example, 220 to 240.

Reference numeral 3 denotes an inner pipe made of a steel pipe having a hardness (Hv) of 400 to 550, which is press-fitted so as to be located inside the outer pipe 1 and forms a flow passage therein, and is, for example, work hardened. And / or spring tempered SUS 3
01, SUS 304 and the like. Hardness (Hv) of the inner tube 3
The reason for setting the value to 400 to 550 is that if it is less than 400, the cavitation resistance to the high-pressure fuel used for the fuel injection pipe cannot be obtained, while if it exceeds 550, the hardness is too high and the connection as shown in FIG. This is because the possibility of buckling of the inner tube on the inner peripheral surface of the end portion increases.

After the inner pipe 3 is inserted into the outer pipe 1, the inner pipe 3 is press-fitted by drawing to form an injection pipe made of a double metal pipe. The ratio of the thickness of the inner pipe 3 to the diameter is as described in the above-mentioned Japanese Patent Publication No. 1-467.
It is 1.2 to 8.5% as described in JP-A-12. As described in Japanese Patent Application No. 9-58510, an austenitic stainless steel pipe which is subjected to spring conditioning in a subsequent step can be used as the inner pipe.

Next, when forming the connection head 2 at the connection end of the injection pipe made of the double metal pipe formed as described above, in the present invention, the outer diameter D of the inner pipe and the shrinkage due to the formation of the connection head are reduced. The relationship between the margin Δl, the machining margin l ₁ , and the length l ₂ of the formed connection head in the axial direction is formed as shown in FIGS. 2 and 3.

[0017] That is, the chuck the injection pipe material by split chuck 6 so that the position at its end face from the end face 2a of the distal end portion holding the machining margin l ₁ of the connecting end portion comes as shown in FIG. 2, the injection The connection head 2 is formed by press working with a punch member 7 which projects and moves in the axial direction of the tube. At this time, the present inventors have obtained a shrinkage allowance Δl by head shaping by subtracting l ₂ which is the axial length of the connection head after shaping from the processing allowance l ₁ by various experiments, ie, Δl = l _{When 1−} l ₂ represents the outer diameter of the inner tube 3 as D,
It has been found that when the length is set in advance to be 1.3D or less, preferably 1.0D or less, the buckling of the inner tube 3 on the inner peripheral surface of the formed connection head 2 can be effectively prevented. .

In other words, based on this finding, the above equation Δl
= L ₁ −l ₂ ≦ 1.3D, various conditions,
That is, the shape and length of the connection head to be molded, the processing margin of the connection end, the material of the inner tube and the outer tube, the outer diameter and thickness of the injection tube made of a double metal tube, the stroke of the punch member, etc. are previously tested. In the actual connection head forming processing, a predetermined processing allowance l ₁ that satisfies the formula l ₁ ≦ 1.3D + l ₂
Can be formed without buckling of the inner tube 3 by chucking and pressing, and by forming the connection head 2 having a length l ₁ or less than (l ₁ -1.3D), the inner tube 3 can be seated. A stiff high-pressure fuel injection tube is obtained. Connection head 2
The reason why the shrinkage Δl must be 1.3D or less is that if it exceeds 1.3D, the possibility of buckling of the inner tube 3 as shown in FIG. It is preferable that the shrinkage allowance Δl is smaller because there is no possibility of buckling of the inner tube 3. Even if it comes into contact with the pressure-receiving seat surface of a mating member such as a holder (not shown), the necessary sealing property cannot be obtained and it does not serve as the connection head 2.

[0019] Then by pressing the punch member 7 connecting end portion of the chuck and the injection tubing by the chuck 6 has a machining margin l ₁ so that the position corresponding to the value within the above range, as shown in FIG. 3 Frusto-conical shape (Fig. 1 (a)
See), those arcuate, abacus bead-shaped (FIG. 1 (b) refer) high-pressure fuel injection pipe by molding the connecting head 2 having a length 1 ₂ in the axial direction made of is formed.

In FIG. 1, reference numeral 4 denotes a sleeve washer fitted to the lower part of the neck of the connection head 2 as required, and at the same time, a pressing seat surface 2 'of the connection head 2 is provided behind the sleeve washer. And a tightening nut 5 which is screwed into the mating member in a state of contact with the nut.

Next, a method of manufacturing the high-pressure fuel injection pipe according to the present invention will be described. A work hardening and / or a spring is formed inside an outer pipe 1 made of a steel pipe which has been subjected to a pretreatment for cleaning. The inner tube 3 made of a steel tube having a tempering property is gently inserted. Then, using a die fixed with the inner tube 3 gently inserted into the outer tube 1, the drawing process is performed by integrally drawing to one side using a die.
The entire pipes 1 and 3 are reduced in diameter over their entire length and press-fitted, and simultaneously stretched to form an injection pipe made of a double metal pipe having an inner pipe having a hardness (Hv) of 400 to 550.

When an austenitic stainless steel pipe is used for the inner pipe 3, an injection pipe made of a double metal pipe which has been drawn and press-fitted as described in Japanese Patent Application No. 9-58510 is then placed in a heating furnace. Charged at 375-455 ° C, 30
When the heat treatment is performed for minutes to 24 hours, the inner tube 3 made of an austenitic stainless steel tube is subjected to spring tempering and its hardness (Hv) can be improved to 400 to 550.

[0023] Upon molding the connecting head 2 to the connection end portion of the thus double metal tube formed, as described above machining margin l ₁ becomes a predetermined length by the chuck 6 as shown in FIG. 2 As shown in FIG. 3, the connection end portion of the held injection pipe made of a double metal tube is pressed by a punch member 7 to form a connection head 2 having a desired shape such as a truncated cone, an arc or an abacus. Is formed to form a high-pressure fuel injection pipe, which is usually thereafter subjected to bending for piping near the diesel internal combustion engine. It should be noted that prior to molding the connection head 2 at the connection end, the sleeve washer 4
The fitted into the connection end portion, can be molded connecting head 2 by pressing the sleeve washers allowed position at a machining margin l ₁ of the predetermined length.

[0024]

Next, examples of the present invention will be described below together with comparative examples. Example 1 Pretreatment for cleaning was performed, and the length was 3,200 m.
an outer pipe (outer diameter 11.0 mm, inner diameter 6.2 mm, wall thickness 2.4 mm) having a hardness (Hv) of 110 and a SUS 301 having a length of 3200 mm; Inner tube of stainless steel tube with hardness (Hv) of 220 (outer diameter 4.5 mm, inner diameter 3.5 m
m, wall thickness 0.5 mm), and the inner tube was gently inserted into the outer tube. Then, one-sided drawing was performed on one side by a fixed die to reduce the diameter of the entire pipe, and then the outer diameter was 7.0 m.
m, an inner diameter of 2.5 mm, a wall thickness of 2.25 mm, an inner diameter of 1.75 mm, a hardness (Hv) of 490, and a hardness (Hv) of the outer diameter of 224 and a work hardened double metal pipe. Injection tubing was obtained, and then 20 samples cut to a length of 300 mm were prepared.

The injection pipe made of 20 double metal pipes prepared as described above is chucked by a split chuck with a processing allowance of 9 mm from the pipe end, and the shrinkage allowance is about 1.0 times the outer diameter of the inner pipe. A high pressure fuel injection pipe is obtained by forming a connection head having an arc shape and having a length of 5.5 mm at the connection end of an injection pipe made of a double metal pipe by press working with a punch member. Was. The buckling state of the inner tube on the inner peripheral surface of the connection head was observed for each of the obtained samples, but no buckling was observed for all the samples as shown in FIG.

EXAMPLE 2 A steel pipe corresponding to STS 410 having a hardness (Hv) of 150 was used as an outer pipe, and a stainless steel pipe made of SUS 304 having a hardness (Hv) of 380 was used as an inner pipe. In the same manner as in Example 1, an injection tube made of a double metal tube was obtained. At this time, the thickness of the inner tube was the same as that of Example 1, but the hardness (Hv) of the inner tube was 440 and the hardness (Hv) of the outer tube was 243 due to the work hardening by the drawn tube processing. Was. Thereafter, the sample was cut into a length of 300 mm to obtain 20 samples.

A sleeve washer was fitted to the injection pipe made of 20 double metal pipes prepared as described above, and was positioned 7.4 mm from the pipe end. A connecting head having the same shape as that of the first embodiment and having a length of 4.2 mm is formed at the connecting end so that the shrinkage is about 0.9 times the outer diameter of the inner pipe. An injection tube was obtained. The buckling state of the inner tube on the inner peripheral surface of the connection head was observed for each of the obtained samples, but no buckling was observed for all the samples as shown in FIG.

Comparative Example An injection tube made of a double metal tube was obtained in the same manner as in Example 1 by using the same material as in Example 2, and then 300 mm
Twenty samples cut to length were prepared. The thickness of the inner tube was the same as in Example 1. 20 prepared in this way
Injection tubing consisting of two double metal pipes 12 mm from the pipe end
With the processing allowance, the split end chuck is chucked and the shrinkage allowance becomes approximately 1.7 times the outer diameter of the inner tube. It is made of an arc and its length is 6mm
To form a high pressure fuel injection pipe. Observation of the buckling state of the inner tube on the inner peripheral surface of the connection head of each of the obtained samples revealed that buckling occurred as shown in FIG. 6 for all 20 samples.

[0029]

As described above, according to the present invention, it is possible to not only easily and easily manufacture without the troublesome manufacturing steps and complicated steps which have been a problem in the prior art, but also to use high-pressure fuel. It is also possible to provide a method of manufacturing a high-pressure fuel injection pipe capable of exhibiting sufficient cavitation resistance on the inner peripheral surface thereof, and a high-pressure fuel injection pipe obtained by the method.

[Brief description of the drawings]

FIG. 1 is a view showing a high-pressure fuel injection pipe of the present invention, in which (a) is a longitudinal sectional side view of one embodiment, and (b) is a side view of another embodiment with a partial cutaway.

FIG. 2 is an explanatory view showing a step of a manufacturing method according to the present invention by a cross section before forming a connection head.

FIG. 3 is an explanatory diagram showing a cross-section after forming a connection head, showing one step of the manufacturing method of the present invention.

FIG. 4 is a photograph of a metallographic structure obtained by observing a high-pressure injection fuel pipe manufactured according to the first embodiment of the present invention using a microscope.
Is a partially enlarged photograph, and (b) is a further enlarged photograph of (a).

FIG. 5 is a photograph of a metallographic structure obtained by observing a high-pressure injection fuel pipe manufactured according to the second embodiment of the present invention with a microscope.
Is a partially enlarged photograph, and (b) is a further enlarged photograph of (a).

FIGS. 6A and 6B are photographs of a metallographic structure obtained by observing a high-pressure injection fuel pipe manufactured by a conventional technique using a microscope. FIG. 6A is a partially enlarged photograph, and FIG. 6B is a further enlarged photograph of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Outer pipe 2 Connection head 2 'Press seat surface 2a End face 3 Inner pipe 4 Sleeve washer 5 Tightening nut 6 Chuck 7 Punch member D Inner pipe outer diameter l ₁ Processing margin l ₂ Connection head length Δl Shrinkage margin

Claims (2)

[Claims] An outer pipe made of a thick steel pipe has a hardness (H).
v) is inserted into an inner pipe made of a thin steel pipe having a thickness of 400 to 550 to form a double metal pipe by press-fitting both pipes by drawing, and then a frusto-conical shape is formed at the connection end of the double metal pipe. When molding an arc-shaped or abacus-shaped connection head,
A machining allowance (l) that satisfies the following equation: l ₁ ≦ 1.3D + l ₂ [where (D) is the outer diameter of the inner tube and (l ₂ ) is the length of the formed connection head in the axial direction] ₁ ) A method for manufacturing a high-pressure fuel injection pipe, wherein the connection head is formed by chucking the connection head. 2. An outer pipe made of a thick steel pipe has a hardness (H
v) is formed at the connection end of a double metal pipe formed by press-fitting an inner pipe made of a thin steel pipe having a thickness of 400 to 550, and a frusto-conical, arc-shaped or abacus-shaped connection head is formed by head forming. And
Let the length (l ₂ ) of the connection head be l ₂ ≧ l ₁ -1.3D [where (D) is the outer diameter of the inner tube and (l ₁ ) is the processing allowance for forming the connection head] A high-pressure fuel injection pipe characterized by being formed in: