JP2004204714A - Common rail and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a common rail preventing stress concentration on a specified portion by high pressure fuel to increase internal pressure fatigue strength of a rail main body, and its manufacturing method. <P>SOLUTION: Inside of the rail body 2 of the common rail 1, a rail hole 3 extends in a longitudinal direction thereof, a branched hole 5 is formed from an outer peripheral part of the rail body 2 toward the rail hole 3, and an orifice hole 6 is opened to a peripheral wall of the rail hole 3 to be connected with the branched hole 5. An opening end part 6a of the orifice hole 6 opened to the rail hole 3, an end part 6b of the orifice 6 connected to the branched hole 5, and a corner part 5d constituted of a straight pipe part 5b and a tapered part 5c of the branched hole 5 are smoothly chamfered all around in a rounded shape by fluid polishing method to remove edges of them. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a common rail that is used in a common rail fuel injection device and transmits high-pressure fuel generated by a fuel pump to an injector.
[0002]
[Prior art]
As a conventional technique related to the common rail, as shown in FIG. 9, a rail hole 52 extending in the longitudinal direction is formed inside the rail body 51, and a plurality of branch holes are formed from the outer periphery of the rail body 51 toward the rail hole 52. 53, and a common rail 50 having a plurality of orifice holes 54 having one end opened in the rail hole 52 and the other end connected to the branch hole 53 (see, for example, Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-213045 (page 3-4, FIG. 1)
[0004]
In the common rail 50 according to this prior art, the high-pressure fuel generated by the fuel pump is transmitted to the injector, and the valve opening / closing operation of the injector is performed by the orifice hole 54 interposed between the rail hole 52 and the branch hole 53. There was a function to suppress the accompanying fuel pulsation. Further, in the above-described common rail 50, if there is an edge portion at the opening end H (shown in FIG. 9) of the orifice hole 54 to the rail hole 52, the opening end H is large due to the high-pressure fuel in the rail hole 52. Since the stress is generated and the internal pressure fatigue strength is considered to decrease, the open end H is chamfered.
[0005]
[Problems to be solved by the invention]
In the above-described common rail 50, the chamfering of the opening end H of the orifice hole 54 to the rail hole 52 is effective in preventing stress concentration from occurring at the opening end H due to high-pressure fuel. However, since the opening end H of the orifice hole 54 is chamfered, the orifice hole 54 indicated by J in FIG. 9 is connected to the branch hole 53 by the high-pressure fuel introduced into the rail hole 52. It was found that a new stress concentration occurs at the edge formed at the end. Therefore, stress concentration on the end portion J may cause the internal pressure fatigue strength to decrease in the vicinity of the end portion J.
[0006]
The present invention has been completed based on the above circumstances, and provides a common rail capable of preventing stress concentration at a specific location due to high-pressure fuel and improving the internal pressure fatigue strength of the rail body, and a method for manufacturing the common rail. For the purpose.
[0007]
[Means for Solving the Problems]
As means for achieving the above object, in the invention of claim 1, a plurality of rail holes extending in the longitudinal direction inside the rail body and a plurality of rail holes arranged in the longitudinal direction of the rail body, each of which is an outer peripheral portion of the rail body A branch hole extending from the rail hole toward the rail hole, and each of the orifice holes has a plurality of orifice holes with one end opening in the peripheral wall of the rail hole and the other end connected to the branch hole. The common rail is characterized in that the opening end to the rail hole and the end connected to the branch hole are chamfered.
[0008]
According to a second aspect of the present invention, the common rail according to the first aspect is characterized in that a corner portion constituted by a connecting portion connected to the orifice hole of the branch hole and a side surface portion of the branch hole is chamfered. did.
[0009]
In the invention of claim 3, a rail hole forming step for forming a rail hole in the longitudinal direction inside the rail body, and a branch hole extending from the outer periphery of the rail body toward the rail hole in the longitudinal direction of the rail body. A plurality of branch hole forming steps, one end of each opening in the peripheral wall of the rail hole, and each other end forming a plurality of orifice holes connected to each of the branch holes; and The common rail manufacturing method is characterized by comprising a chamfering step of chamfering an opening end portion of the orifice hole to the rail hole and an end portion of the orifice hole connected to the branch hole.
[0010]
According to a fourth aspect of the present invention, there is provided the common rail manufacturing method according to the third aspect, wherein a fluid polishing method is used in the chamfering step.
[0011]
[Action and effect of the invention]
<Invention of Claim 1>
By chamfering the end of the orifice hole connected to the branch hole, stress concentration on the end of the orifice hole can be prevented and the internal pressure fatigue strength of the rail body can be improved.
[0012]
<Invention of Claim 2>
By chamfering the corner formed by the connecting part connected to the orifice hole of the branch hole and the side part of the branch hole, stress concentration at the corner of the branch hole is prevented and the internal pressure fatigue strength of the rail body is improved. Can be made.
[0013]
<Invention of Claim 3>
The common rail manufacturing method is composed of a rail hole forming step, a branch hole forming step, an orifice hole forming step, and a chamfering step by using many conventional methods, so that the conventional common rail manufacturing process is not significantly changed. The common rail of the invention can be manufactured.
[0014]
<Invention of Claim 4>
By using the fluid polishing method, it is possible to easily chamfer without entering a tool into the rail body. Moreover, since the surface roughness of the inner wall of the branch hole is improved by applying the fluid polishing method, stress concentration on the inner wall of the branch hole can be prevented, and the internal pressure fatigue strength can be improved.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. The long rail body 2 constituting the common rail 1 is formed of a forged product of S45C material or SCM (chromium / molybdenum steel) material, and a rail hole 3 extending in the longitudinal direction is formed therein. Yes. The left and right ends of the rail hole 3 are formed with a first screw portion 2a and a second screw portion 2b, respectively, to which a connecting member (not shown) is screwed, and a pressure sensor is connected to the connecting member screwed to the first screw portion 2a. Are concatenated. The common rail 1 is for a four-cylinder engine, and five cylindrical fuel pipe connection portions 4 are formed in the rail body 2 at equal intervals in the longitudinal direction.
[0016]
Each fuel pipe connection portion 4 protrudes from the rail body 2, and a branch hole 5 is formed in each of the fuel pipe connection portions 4. 5a is formed. A fuel supply pipe connected to a high-pressure pump for fuel supply as an input is connected to any one of the pipe seat surfaces 5a of the fuel pipe connection portion 4, and the fuel in the fuel tank is boosted by the high-pressure pump. Then, it is introduced into the rail hole 3. The seal surfaces of the fuel supply pipes connected to the respective injectors (not shown) are fluid-tightly engaged with the pipe seat surfaces 5a of the other four fuel pipe connection portions 4. Further, one end of each orifice hole 6 is opened on the inner peripheral wall of the rail hole 3, and the other end of the orifice hole 6 is connected to each branch hole 5. A threaded portion 4a into which a nut for tightening a pipe is screwed when the above-described fuel supply pipe is connected is formed on the outer peripheral portion of each fuel pipe connecting portion 4.
[0017]
As shown in FIG. 2, the branch hole 5 includes a straight pipe portion 5 b connected to the pipe seat surface 5 a shown in FIG. 1, and a tapered portion that is formed at the lower end of the straight pipe portion 5 b and tapers toward the orifice hole 6. 5c. The straight pipe part 5b and the taper part 5c correspond to the side part of the branch hole 5 of the present invention and the connecting part that connects the branch hole 5 and the orifice hole 6, respectively. The orifice hole 6 is connected to the tapered portion 5c at its upper end. In the opening end portion 6a of the orifice hole 6 to the rail hole 3, in order to eliminate the edge shape, smooth R chamfering is performed over the entire circumference. Here, the R chamfering refers to chamfering in which a curved surface having an appropriate radius is formed.
[0018]
On the other hand, the end 6b connected to the tapered portion 5c of the orifice hole 6 is also smoothly chamfered over the entire circumference in order to eliminate the edge shape. In the present embodiment, the end 6b of the orifice hole 6 is subjected to R chamfering by a curved surface portion 6b1 having a single radius, as shown in FIG. 3 showing the B portion of FIG. 2 in detail. Further, the corner 5d formed by the straight pipe portion 5b and the tapered portion 5c of the branch hole 5 is also subjected to smooth R chamfering over the entire circumference in order to eliminate the edge shape. The size of the radius of the curved surface of each R chamfer is not particularly limited as long as it has a size that can prevent stress concentration on each part.
[0019]
As described above, in the common rail 1 according to the present embodiment, the end portion 6b connected to the branch hole 5 of the orifice hole 6 and the corner portion 5d formed by the straight pipe portion 5b and the tapered portion 5c of the branch hole 5 are smooth. By chamfering, stress concentration on the end 6b of the orifice hole 6 and the corner 5d of the branch hole 5 can be prevented, and the internal pressure fatigue strength can be improved.
[0020]
Next, a method for manufacturing the common rail 1 according to the present embodiment will be described. As shown in FIG. 4, first, a rail hole is formed in the longitudinal direction of the main body MB by a gun drill or the like on a material WM in which five cylindrical bosses BS are formed at equal intervals on the cylindrical main body MB. 3 is formed (rail hole forming step). If necessary, the surface of the rail hole 3 may be finished with a reamer after cutting with a gun drill. Then, after making a pilot hole for threading at both ends of the rail hole 3, the first screw portion 2a and the second screw portion 2b shown in FIG. 1 are formed. The first screw portion 2a and the second screw portion 2b may be formed anytime after the rail hole 3 is formed, or may be formed after the branch hole 5 and the orifice hole 6 are formed.
[0021]
Next, as shown in FIG. 5, the branch hole 5 is formed from the upper end surface of the boss portion BS toward the rail hole 3 by a drill or an end mill (branch hole forming step). Then, as shown in FIG. 6, the orifice hole 6 is penetrated so that the branch hole 5 and the rail hole 3 may be connected (orifice hole formation step). The orifice hole 6 is formed by inserting a drill into the branch hole 5 and cutting from the bottom thereof, or by punching from the branch hole 5 side toward the rail hole 3 with a punch, or from the rail hole 3 side. A method of punching with a punch toward the branch hole 5 can be used. In addition, a threaded portion 4a is formed on the outer peripheral portion of the boss portion BS, and a tapered pipe seating surface 5a is formed in the opening of the branch hole 5 to complete the fuel pipe connecting portion 4. The threaded portion 4a and the pipe seating surface 5a may be formed either before or after the branch hole 5 and the orifice hole 6 are formed.
[0022]
Finally, as shown in FIG. 7, the tapered surface 7 a at the tip of the fluid polishing nozzle 7 is liquid-tightly engaged with the pipe seat surface 5 a of the fuel pipe connection portion 4, and the fluid polishing nozzle 7 passes through the fluid passage 7 b. Then, a fluid is injected into the branch hole 5. A fluid containing abrasive grains or an abrasive is discharged from the fluid polishing nozzle 7 and smoothly flows into the passage wall surface by flowing through the passage. The fluid containing the above-described abrasive is discharged from the fluid polishing nozzle 7 for several hundred seconds and flows into the rail hole 3 from the branch hole 5 through the orifice hole 6. As the fluid flows through the branch hole 5 and the orifice hole 6, the abrasive contained in the fluid smoothly processes the corner portion 5d of the branch hole 5, the end portion 6b of the orifice hole 6 and the open end portion 6a, respectively. Chamfering (chamfering step).
[0023]
As described above, the common rail manufacturing method according to the present embodiment is configured by a rail hole forming step, a branch hole forming step, an orifice hole forming step, and a chamfering step by using many conventional methods. The common rail 1 of the present invention can be manufactured without significantly changing the manufacturing process of the common rail. Further, by using the fluid polishing method, it is possible to easily chamfer without entering a tool or the like into the rail body 2. Further, by applying the fluid polishing method, the surface roughness of the straight pipe part 5b and the taper part 5c of the branch hole 5 is improved, so that stress concentration on the straight pipe part 5b and the taper part 5c is prevented, and internal pressure fatigue strength is reduced. Can be improved.
[0024]
The manufacturing process of the common rail 1 does not necessarily have to be in the order described above, and various modifications are possible. For example, the branch hole forming step, the orifice hole forming step, the rail hole forming step, and the chamfering step may be performed in this order, or the branch hole forming step, the rail hole forming step, the orifice hole forming step, and the chamfering step may be performed in this order. Good.
[0025]
Second Embodiment
The chamfering of the end portion 6b of the orifice hole 6 does not necessarily have to be performed by R chamfering with a curved surface having a single radius, but as shown in FIG. It can also be formed by a linear portion 6b2 having a very small length and curved portions 6b3 and 6b4 connecting the tapered portion 5c and the orifice hole 6 respectively.
[0026]
<Other embodiments>
The present invention is not limited to the embodiment described with reference to the above description and drawings. For example, the following embodiment is also included in the technical scope of the present invention, and further departs from the gist other than the following description. Various modifications can be made without departing from the scope. (1) The common rail according to the present invention is also applied to a multi-cylinder engine other than a four-cylinder engine, and may have seven or four branch holes and orifice holes, respectively, or other numbers.
(2) The chamfered part is processed not only by the fluid polishing method, but also by electrolytic processing, cutting by a cutter, or chamfering that forms a chamfered part by pressing the edge part with a punch from the branch hole side or rail hole side. Is possible.
(3) The shape of the chamfered portion prevents stress concentration such as a combination of R chamfering with a plurality of curved surfaces with different radii, a combination of a plurality of straight lines with a curved surface, a gradually curved surface, etc. Any shape can be chamfered as long as it can.
(4) As a material for forming the rail body, a carbon steel pipe for machine structure (seamless steel pipe) or a steel pipe for high-pressure piping equivalent to STS480 can be used. When these materials are used, the fuel pipe connecting portion provided with the branch hole is coupled to the main body portion by welding, brazing, screw tightening or the like. Moreover, when using the above-mentioned material, the rail hole forming step can be omitted.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a common rail according to the present embodiment.
FIG. 2 is a detailed view of a part A in FIG.
FIG. 3 is a cross-sectional view showing the shape of a chamfered portion at the end of an orifice hole according to the first embodiment.
FIG. 4 is a diagram showing a rail hole forming step.
FIG. 5 is a diagram showing a branch hole forming step.
FIG. 6 is a diagram showing an orifice hole forming step.
FIG. 7 is a diagram showing a chamfering step by a fluid polishing method.
FIG. 8 is a cross-sectional view showing the shape of a chamfered portion at the end of an orifice hole according to a second embodiment.
FIG. 9 is a detailed view of a main part of a conventional common rail.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Common rail 2 ... Rail main body 3 ... Rail hole 5 ... Branch hole 5b ... Straight pipe part 5c ... Tapered part 5d ... Corner part 6 ... Orifice hole 6a ... Orifice hole opening edge part 6b ... Orifice hole edge part 6b1, 6b3, 6b4 ... curved surface portion 6b2 ... linear portion 7 ... fluid polishing nozzle

Claims (4)

Rail holes extending longitudinally inside the rail body,
A plurality of branch holes arranged in the longitudinal direction of the rail body, each extending from the outer periphery of the rail body toward the rail hole, and each having one end opened in the peripheral wall of the rail hole, and the other end A plurality of orifice holes connected to the respective branch holes;
A common rail, wherein an opening end portion of the orifice hole to the rail hole and an end portion connected to the branch hole are chamfered. The common rail according to claim 1, wherein a corner portion formed by a connecting portion connected to the orifice hole of the branch hole and a side surface portion of the branch hole is chamfered. A rail hole forming step for forming a rail hole in the longitudinal direction inside the rail body;
A branch hole forming step of forming a plurality of branch holes extending from the outer periphery of the rail body toward the rail hole in a longitudinal direction of the rail body;
An orifice hole forming step of forming a plurality of orifice holes each having one end opened on the peripheral wall of the rail hole and each other end connected to each of the branch holes, and opening the orifice hole to the rail hole A common rail manufacturing method comprising a chamfering step of chamfering an end portion and an end portion of the orifice hole connected to the branch hole. 4. The method for manufacturing a common rail according to claim 3, wherein a fluid polishing method is used in the chamfering step.

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