JP2002195125A - Common rail and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve manufacturing efficiency and to reduce cost. SOLUTION: A main pipe 11, branch tube part 12 and an external thread part 13 are formed on common rail base material 18 of high strength bolt steel, and the common rail base material 18 is quenched and tempered to manufacture a common rail 10. Since high strength bolt steel is used as common rail base material 18, surface hardness can be increased by just quenching and tempering without carburizing, inner pressure fatigue strength of inner walls of the main pipe 11 and the branch tube part 12 can be secured, and deterioration of resistance against delayed fracture of the external thread part 13 can be avoided although hardness is very high. Also, a forming process and removing process of carburized layer are unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail and a method for manufacturing the common rail in a common rail fuel injection system for an engine.

[0002]

2. Description of the Related Art As shown in FIG. 1, a common rail in a common rail type fuel injection device has a plurality of branch cylinders 12 formed on an outer periphery of a main pipe 11, and an injection pipe (see FIG. 1) is formed on the outer periphery of the branch cylinder 12. (Not shown).

[0003] In the common rail 10 having such a configuration, the internal pressure of the pressurized fuel is applied to the inner wall of the main pipe 11 and the inner wall of the branch tube portion 12, and the internal pressure fluctuates according to the running state of the vehicle. Therefore, it is necessary to secure the internal pressure fatigue strength on the inner wall of the main pipe 11 and the inner wall of the branching tube portion 12. On the other hand, in the male screw portion 13 into which the injection pipe is screwed, a static load is applied for a long period of time, so that a measure for improving delayed fracture resistance is required.

[0004] Therefore, conventionally, the common rail 10 is manufactured by using a main pipe 1 in a first step with respect to a common rail material 100 made of SCM material (chromium-molybdenum steel).
1 and a protruding portion 101 (a prototype portion serving as the branching tube portion 12) are formed by pre-processing (see FIG. 3). The carburizing layer 102 is formed on the surface and the outer peripheral surface by a carburizing slow cooling process (see FIG. 3), and in a third step, the outer periphery of the protruding portion 101 is cut to form the branching tubular portion 12 and the male screw portion 13 and The carburizing layer 102 in the male screw portion 13 is removed (see FIG. 4), and vacuum quenching and tempering are performed in a fourth step.

According to such a manufacturing method, the second step and the fourth step
The formation of the carburized layer 102 and the quenching and tempering in the process increase the surface hardness of the inner wall of the main pipe 11 and the branching tube portion 12 to 600 Hv or more, thereby ensuring the internal pressure fatigue fracture strength. Further, when the surface hardness is increased by the carburizing and quenching and tempering processes, the delayed fracture resistance is reduced. However, in the male screw portion 13, the hardness is reduced by 400% by removing the carburized layer 102 in the third step.
Since it is suppressed to about Hv, delayed fracture of the male screw portion 13 is avoided.

[0006]

However, in the above-mentioned conventional manufacturing method, there are problems that the number of processing steps is large, so that the manufacturing efficiency is low and the cost is high. The present invention has been made in view of the above circumstances, and has an object to improve manufacturing efficiency and reduce costs.

[0007]

The invention according to claim 1 is a common rail having a form in which a branch tube is formed from the outer periphery of a main pipe and a male screw portion is provided on the outer periphery of the branch tube. The main rail, the branch hole, and the male screw portion are formed in a common rail material made of high-strength bolt steel, and the common rail material is manufactured by quenching and tempering.

A second aspect of the present invention is a method for manufacturing a common rail in which a branch tube is formed from the outer periphery of a main pipe and a male thread is provided on the outer periphery of the branch tube. The main pipe, the branch tube portion, and the male screw portion are formed in a common rail material made of steel for bolts, and the common rail material is subjected to a quenching and tempering process.

[0009]

Advantages and Effects of the Invention [Inventions of Claims 1 and 2] Since high-strength bolt steel is used as the common rail material, the surface hardness can be obtained simply by quenching and tempering without carburizing. And the internal pressure fatigue strength at the inner wall of the main pipe and the branching tube is ensured. In addition, in the male screw portion, there is a concern that the hardness of the surface is increased and the delayed fracture resistance is reduced. However, since the present invention uses steel for high-strength bolts, it is excellent in delayed fracture resistance. As described above, in the present invention, since the high-strength bolt steel is used as the common rail material, the step of forming the carburized layer and the step of removing the carburized layer, which are required for the SCM material, are unnecessary.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of the present invention will be described below with reference to FIGS. The common rail 10 of the present embodiment has a configuration in which a plurality of branch cylinders 12 protrude from the outer periphery of a main pipe 11, and coaxial male screw portions 13 are formed on the outer periphery of each branch cylinder 12, respectively. is there. The main pipe 11 has a cylindrical shape, and its peripheral wall has a uniform thickness throughout. The main pipe 11 is provided at a plurality of positions on the outer periphery of the peripheral wall that are spaced apart in the length direction.
The branching cylinder 12 having a cylindrical shape smaller than the inner diameter of the main pipe 11 is integrally formed so as to protrude in a radial direction of the main pipe 11 (a direction in which an axis is orthogonal to an axis of the main pipe 11). A male screw portion 13 for connecting an injection pipe (not shown) is formed concentrically on the outer periphery of the branch tube portion 12. Branching tube 1 on the peripheral wall of main pipe 11
In the region where 2 is formed, a branch hole 14 opening on the inner peripheral surface of the peripheral wall and an inner peripheral side tapered hole 15 continuing to the outer peripheral end of the branch hole 14 are formed. This inner peripheral side tapered hole 1
Reference numeral 5 increases in diameter toward the outer peripheral side. Further, the outer peripheral end of the inner peripheral side tapered hole 15 having the maximum outer diameter is connected to the inner peripheral end of the connection hole 16 of the branching tubular portion 12. Tapered holes 17 are formed continuously. The outer peripheral side tapered hole 17 increases in diameter toward the outer peripheral side, and the outer peripheral end of the outer peripheral side tapered hole 17 is opened at the protruding end surface of the branching tubular portion 12. The branch hole 14, the inner peripheral side tapered hole 15, the connection hole 16, and the outer peripheral side tapered hole 17 are coaxially connected to each other.
It is coaxial with the branching tube 12. Further, the male screw portion 13 is formed over substantially the entire length of the branching tube portion 12 in the length direction, and a nut (not shown) for connecting an injection pipe to the male screw portion 13. They are screwed together.

Next, a method of manufacturing the common rail 10 will be described. In the present embodiment, high-strength bolt steel (13T bolt material) is used as the common rail material 18. The common rail material 18 is, as shown in FIG.
It is formed into a shape having a rod-shaped portion 18A constituting the outer periphery of the main pipe 11 and a plurality of projecting portions 18B constituting the branching tubular portion 12. First, in the first step, the main pipe 11 is formed by performing a cutting process so as to pierce the rod-shaped portion 18A of the common rail material 18, and a cutting process is performed so that the outer periphery of the protruding portion 18B is cut off and pierced. Is applied to the branch cylinder 12 (branch hole 1).
4. The inner peripheral side tapered hole 15, the connection hole 16, the outer peripheral side tapered hole 17, and the male screw portion 13 are formed (see FIG. 1). That is, a completed shape is obtained as the common rail 10.
Next, in a second step, a quenching process and a tempering process are performed on the common rail material 18 on which the main pipe 11 and the branching tube portion 12 are formed. Thus, the manufacture of the common rail 10 is completed.

According to the present embodiment, the common rail material 1
Since the high-strength bolt steel is used as 8, the hardness of the entire common rail 10 is increased to approximately 400 to 450 Hv by simply performing quenching and tempering without carburizing, and the inner wall of the main pipe 11 and the branch pipe The internal pressure fatigue strength of the inner wall of the portion 12 is ensured. In addition, in order to avoid a decrease in the delayed fracture resistance of the male screw portion 13, if it is a conventional SCM material, it is necessary to suppress the hardness to less than 400 Hv. Since the hardness of the surface of the male screw part 13 is 400 to 450 Hv
Even if it is high, the delayed fracture resistance of the male screw portion 13 is excellent.

As described above, in the present embodiment, since the steel for high-strength bolts is used as the common rail material 18, the step of forming the carburized layer and the step of removing the carburized layer, which are necessary for the SCM material, become unnecessary, and the number of manufacturing steps is reduced. Done. Thereby, the manufacturing efficiency can be improved and the manufacturing cost can be reduced. [Other Embodiments] The present invention is not limited to the embodiment described above with reference to the drawings. For example, the following embodiments are also included in the technical scope of the present invention. Various changes can be made without departing from the scope of the invention.

(1) In the above embodiment, the hardness of the surface is set to 400 to 450 Hv by quenching and tempering. However, according to the present invention, the required hardness is the required internal pressure fatigue strength and the required delayed fracture resistance. It can be set appropriately according to the type of high-strength bolt steel.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a common rail according to a first embodiment.

FIG. 2 is a partial sectional view of a common rail material.

FIG. 3 is a partial sectional view showing a manufacturing process of a conventional example.

FIG. 4 is a partial sectional view showing a manufacturing process of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Common rail 11 ... Main pipe 12 ... Molecule cylinder part 13 ... Male screw part 18 ... Common rail material

Continuing from the front page (72) Inventor Takahiro Okada 10 Hamadashita, Nakahata-machi, Nishio-shi, Aichi Prefecture Inside the optics company (72) Inventor Tetsuya Niwa 10 Hamadashita, Nakahata-machi, Nishio-city, Aichi prefecture Inside the optics company (72 ) Inventor Motohide Mori 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G066 AA02 AA07 AB02 AC09 BA61 CB03 3H019 BA42 BC02 BD03

Claims (2)

[Claims] Claims: 1. A branch tubular portion is formed from an outer periphery of a main pipe,
A common rail in a form in which a male screw portion is provided on the outer periphery of the branch tube portion, wherein the main pipe, the branch tube portion, and the male screw portion are formed on a common rail material made of high-strength bolt steel, A common rail manufactured by subjecting the common rail material to quenching and tempering. 2. A branch tube portion is formed from the outer periphery of the main pipe,
A method of manufacturing a common rail in which a male screw portion is provided on an outer periphery of the branch tube portion, wherein the main pipe, the branch tube portion, and the male screw portion are formed on a common rail material made of high-strength bolt steel. Forming a common rail and subjecting the common rail material to quenching and tempering.