JP2004225583A

JP2004225583A - Common-rail and method for manufacturing the same

Info

Publication number: JP2004225583A
Application number: JP2003012588A
Authority: JP
Inventors: Masateru Kishi; 正輝貴志
Original assignee: Otics Corp
Current assignee: Otics Corp
Priority date: 2003-01-21
Filing date: 2003-01-21
Publication date: 2004-08-12
Anticipated expiration: 2023-01-21
Also published as: JP3842222B2

Abstract

PROBLEM TO BE SOLVED: To provide a common-rail in which stress concentration can not take place easily even if an orifice is provided therein and which is easy to manufacture. SOLUTION: A main pipe hole 3 is formed inside of a rail main body 2 of the common-rail 1 along a longitudinal direction thereof. A plurality of cylindrical branch parts 4 formed on the rail main body 2 projectingly to a radially outside are provided on the rail main body 2 in the longitudinal direction. Branch holes 5 from the main pipe hole 3 to upper surface side of the branch parts 4 are formed through an axial center parts of the branch parts 4. The branch hole 5 is provided with an orifice 5C. A large diameter part 5A larger than the orifice 5C is put between the orifice 5C and the main pipe hole 3. Consequently, there is a part where stress tends to concentrate in a joint part of the main pipe hole 3 and the brunch hole 5 when fuel is injected or high pressure fuel is accumulated in the rail main body 2, conventionally. But, sudden change of hole diameter in this part is avoided and stress concentration at the joint part can be reduced in this common rail. COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、エンジンのコモンレール式燃料噴射装置におけるコモンレールに関する。
【０００２】
【従来の技術】
コモンレール式燃料噴射装置では、加圧燃料を複数のインジェクタに分配する手段として、筒状のレール本体の外周に複数の分岐部を突出形成してなるコモンレールを用いている。コモンレールは各分岐部の突出端にインジェクタの燃料配管を接続する構造がとられており、レール本体内の主管孔に供給された加圧燃料が、各分岐部内の分岐孔と燃料配管を通して各インジェクタに分配されるようになっている。
この種のコモンレールでは、インジェクタの開閉に伴う脈動を抑制して燃料の安定供給を図るため、分岐部内の分岐孔に径の小さいオリフィスを設ける構造が知られている（特許文献１）。
【０００３】
このものは、図９に示すように、内部に主管孔５１が形成されたレール本体５０の外周に分岐部５３が突出形成され、その内部には分岐部５３の先端側から主管孔５１に貫通する分岐孔５５が設けられるが、その加工手順は予め、レール本体５０に対し主管孔５１の加工を行い、その後に分岐孔５５の加工が行われる。ところが、レール本体５０は環状をなして閉じているため、主管孔５１側からの加工は困難であって、分岐孔５５の加工は分岐部５３の突出端側から行われる。従って、分岐孔５５にオリフィス５５Ａを一体的に形成する場合には、オリフィス５５Ａの加工が分岐孔５５の加工より先になるからオリフィス５５Ａは主管孔５１に繋がるように形成される。
【０００４】
【特許文献１】
特開２００１−２９５７２２公報
【０００５】
【発明が解決しようとする課題】
上記構造によると、主管孔５１とオリフィス５５Ａとのつなぎ目においては孔径が急激に細くなる。そのため、レール本体５０内に高圧燃料が蓄圧された際には、主管孔５１及びオリフィス５５Ａの孔径の拡大によりこのつなぎ目部分に応力が集中し、コモンレールが疲労する虞があった。また、つなぎ目部分への応力集中を防止する対策として、図１０に示すようにオリフィス部分を別部品７０により構成し主管孔５１とオリフィス７０Ａとの間をオリフィス７０Ａより大径の接続部７１を介して接続するものがある。しかし、このものの場合、オリフィス部分（別部品７０）の組み付けのために圧入工程が付加され（製造時の工数が多くなる）、更に圧入のために専用の設備等が必要となる。また、別部品７０の肉厚分（図１０のＧ寸法部分）だけ分岐部５３の外形が大きくなり、その分重量が重くなる。
本発明は上記のような事情に基づいて完成されたものであって、オリフィスを設けた場合であっても応力の集中が起こりにくく、また製造が容易なコモンレールを提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記の目的を達成するための手段として、請求項１の発明は、内部に軸心に沿って主管孔が形成されたレール本体の外周に径方向外向きに複数の分岐部が一体に突出形成されるとともに、その分岐部の内部にはオリフィスとこのオリフィスより大径の大径部とを備え前記主管孔から分岐する分岐孔が形成され、前記分岐部の突出端部にインジェクタの燃料配管が接続されるようになっているコモンレールであって、前記大径部はその一端側が前記主管孔に繋がり他端側が前記分岐部の軸心に沿って径方向外側に伸びるように形成されるとともに、この大径部より更に径方向外側に前記オリフィスが形成された構成であるところに特徴を有する。
【０００７】
請求項２の発明は、請求項１に記載のものにおいて、前記レール本体における前記分岐部の反対側に前記大径部を穿設するための閉止可能な開口部が設けられた構成であるところに特徴を有する。
【０００８】
請求項３の発明は内周側には軸心に沿って主管孔が、外周側には径方向外向きに複数の分岐部が一体に突出形成されたレール本体に対し、前記レール本体における前記分岐部の反対側に開口部を形成し、その後、一端側が前記主管孔に繋がり他端側が前記分岐部の軸心に沿って径方向外側に伸びる大径部を前記開口部を通じて形成するとともに、この大径部の成形と前後して、前記大径部より更に径方向外側に前記大径部より細径のオリフィスを形成し、更に前記大径部の成形をした後、前記オリフィスの成形と前後して前記開口部を塞ぐところに特徴を有する。
【０００９】
【発明の作用及び効果】
＜請求項１の発明＞
請求項１の発明によれば、主管孔からオリフィスへは大径部を経て接続されることとなる。従って、主管孔にオリフィスが直接つながれる形式のものと比較した場合に、主管孔と分岐孔（オリフィス、大径部）とのつなぎ目部分における孔径の急激な変動が避けられそこでの応力集中を緩和することが出来る。
【００１０】
＜請求項２の発明＞
請求項２の発明によれば、大径部の加工は主管孔側より行う必要があるが、その加工を開口部を通じて外側から行うことが出来る。そのため、分岐孔の加工が容易である。
【００１１】
＜請求項３の発明＞
請求項３の発明によれば、大径部の加工を開口部側より行う製造方法であるから、主管孔とオリフィス間に大径部が設定されたもの（内径が主管孔側より段階的に縮径する）であっても、容易に加工することが出来る。
【００１２】
【発明の実施の形態】
本発明の一実施形態を図１ないし図６によって説明する。コモンレール１を構成する長尺状のレール本体２はＳ４５Ｃ材、ＳＣＭ（クロム・モリブデン鋼）材または炭素鋼材等を鍛造したものであって、その内部に長手方向に延びた主管孔３が形成されている。主管孔３の左右端には、それぞれ接続部材２０が螺合される第１ねじ部２ａおよび第２ねじ部２ｂが形成される。第１ねじ部２ａに螺合される接続部材２０は圧力センサを備えた制御装置（図示せず）に、第２ねじ部２ｂに接続される接続部材２０にはリリーフバルブ（図示せず）にそれぞれ連結される。制御装置は主管孔３内の圧力を圧力センサにより検出するとともに、その圧力の調整をリリーフバルブの開閉により行う。本実施形態のコモンレール１は４気筒エンジン用であり、レール本体２には径方向外側に突出形成された円筒型の分岐部４がレール本体２の長手方向に均等な間隔で５つ設けられている。尚、以下の説明において、図１における分岐部４の突出端側を上側とし、その反対側を下側とする。
【００１３】
図２に示すように、各分岐部４は同幅で形成された円柱状の台座部７と、台座部７上に形成された供給管接続部８とから構成されている。各分岐部４の内部には主管孔３から分岐部４の上面側に分岐部４の軸心に沿って貫通する分岐孔５が形成されるとともに、各分岐部４の上面には末広がりの配管座面６が形成されている。分岐部４のうちのいずれか１つの配管座面６には、入力用として燃料供給用の高圧ポンプが連結された燃料供給管が接続され、高圧ポンプによって燃料タンクの燃料が昇圧された後、主管孔３内に導入される。その他の４つの分岐部４の配管座面６には、図示しない各インジェクタに接続される燃料供給管のシール面が液密的に係合する。尚、各供給管接続部８の外周部には上述した燃料供給管を連結する際に、配管締付用のナットが螺合するねじ部８ａが形成されている。
【００１４】
分岐孔５はその一端側が主管孔３に繋がり他端側が前記分岐部４の軸心に沿って径方向外側（同図の上側）に伸びる大径部５Ａを設けている。この大径部５Ａより更に径方向外側には前記配管座面６に連通し前記大径部より細径のオリフィス５Ｃが形成されるとともに、オリフィス５Ｃと大径部５Ａとの間にはオリフィス５Ｃ側に向けて徐々に先細りとなるテーパ部５Ｂが形成されている。このように、オリフィス５Ｃと主管孔３との間には大径部５Ａ及びテーパ部５Ｂが介在されており、分岐孔５はその孔径が主管孔３側から突出端側に向けて段階的に縮径されてゆく。そのため、従来より主管３と分岐孔５とのつなぎ目部分（同図に示すＡ部）は燃料を噴射する際、或いはレール本体２内に高圧燃料が蓄圧された際には応力が集中しやすい場所であったが、この部位での孔径の急激な変動が避けられＡ部における応力集中を緩和することが出来る。
更に、主管孔３と分岐孔５のつなぎ目部分、或いは大径部５Ａとオリフィス５Ｃのつなぎ目部分など孔径が変化する部位をＲによって揺るやかに接続する形態としておけば、より効果的である。
【００１５】
また、レール本体２のうち主管孔３を隔てて前記分岐孔５と対峙する部分には開口部（円形の貫通孔）１０が設けられている。この開口部１０の中心と前記分岐部４の軸心とは整合しており、開口部１０と分岐部４とは同軸をなす。この開口部１０は前述した大径部５Ａを図１における下方側からドリル等によって穿設するための逃がしである。
開口部１０は内周側にねじ部１１が形成されるとともに、開口部１０の先端部分（図１における下側）には底面（シール面）１２Ａが平面加工されたシール用凹部１２が形成されている。一方、この開口部１０に対しては端部に鍔部１６を設けたシールボルト１５が螺合するようになっている。シールボルト１５の鍔部１６は外形が前記シール用凹部１２より小さく形成されるとともに、その上面には環状をなすシールリング１６Ａが突出形成されている。このシールリング１６Ａの上面側も平面加工が施されている。そのため、シールボルト１５がレール本体２にねじ込まれた時には、シールボルト１５のシールリング１６Ａがシール用凹部１２のシール面１２Ａに密着し、開口部１０がシールされる（メタルシール）。
【００１６】
また、以下に説明する２つの場合（ケース１、ケース２）について、主管孔３内に所定の大きさの圧力（高圧燃料が蓄圧された状態を想定した圧力）が加わった際に前述したつなぎ目部分（図４のＡ部）に生ずる応力についての解析をコンピュータにより行った。
ケース１はオリフィス５Ｃが主管孔３に繋がるように形成された形式のものである（従来品想定形状）。
ケース２はオリフィス５Ｃと主管孔３との間に大径部５Ａが形成された形式のものである（実施例想定形状）。
尚、ケース１、２共に主管孔３の内径（同図のＢ寸法）は６ｍｍ、オリフィス５Ｃの内径（同図のＣ寸法）は１ｍｍ、オリフィス５Ｃの全長（同図のＦ寸法）は２．２ｍｍ、大径部５Ａの内径（同図のＤ寸法）は３ｍｍ、大径部５Ａの全長（同図のＥ寸法）は１９ｍｍ、主管孔３に加える圧力は２００ＭＰＡとした。
【００１７】
上記、解析に基づき以下の結果（表１）が得られた。

【００１８】
このように、ケース１のつなぎ目部分（図４のＡ部）の応力値は８４５ＭＰＡに対し、ケース２のつなぎ目部分の応力値は６５５ＭＰＡであり、実施例想定品では従来品を想定したものに比べて応力値が２２．５％低減されている。従って、本実施例のものは、従来品に比べて金属疲労によるレール本体の強度低下が緩和される。
【００１９】
次に、本実施形態によるコモンレール１の製造方法について説明する。図５に示すように、最初に、円柱状の本体部ＭＢの上に等間隔に５つの円柱形のボス部ＢＳが形成された素材ＷＭに、ガンドリル等によって本体部ＭＢの長手方向に主管孔３を形成する（主管孔形成ステップ）。必要であれば、ガンドリルによる切削の後、リーマー等によって主管孔３の表面仕上げを行ってもよい。その後、主管孔３の両端部にねじ切り用の下穴を開けた後、図１に示した第１ねじ部２ａおよび第２ねじ部２ｂを形成する。第１ねじ部２ａおよび第２ねじ部２ｂは、主管孔３が形成された後であれば、いつ形成されてもよく、分岐孔５が形成された後に形成されてもよい。
【００２０】
次に、図６の（ａ）に示すように、本体部ＭＢに対し開口部１０を構成するシール用凹部１２の加工を行う。それには、まず、開口部１０の中心がボス部ＢＳの軸心上に位置するように位置決めを行い、その後、本体部ＭＢを旋盤等により切削加工する。続いて、ねじ部１１の下孔をドリルあるいはエンドミル等によってシール用凹部１２側から加工し、その後、ねじ部１１の加工を行う（シール用凹部形成ステップ）。
続いて、同図の（ｂ）に示すように、再びドリルあるいはエンドミル等を開口部１０内に進入させ、同図の下側からボス部ＢＳの軸心に沿って大径部５Ａを形成する（大径部形成ステップ）。尚、大径部５Ａはその先端がボス部ＢＳの中心を越えた所定の深さに至ると加工が完了するが、このとき先端部分にドリルの外形に倣った形状、すなわちテーパ部５Ｂが形成される。
続いて、ドリル或いはポンチによってボス部ＢＳの上面の中心部分から大径部５Ａに向けてオリフィス５Ｃが形成される（オリフィス孔形成ステップ）。その後、ボス部ＢＳの上面側に配管座面６を、外周部にねじ部８ａをそれぞれ形成し、これにてレール本体２の加工が完了する。
【００２１】
レール本体２の加工に続いて、シールボルト１５を開口部１０に対しねじ込んでゆき、シール用凹部１２にシールリング１６Ａを密着させる。最後に、流体研磨ノズル（図示せず）の先端を分岐部４の配管座面６に液密的に係合させて、流体研磨ノズルの流体通路を介して分岐孔５に流体を注入する。流体研磨ノズルからは砥粒または研磨剤を含んだ流体が吐出され、通路内に流通することによって通路壁面（主管孔３の孔壁及び分岐孔５の孔壁）が滑らかとなる。
【００２２】
このように、本実施形態によるコモンレール１の製造方法によれば、分岐孔５の加工を分岐部４の上面側と開口部１０側の双方から行うものであるから、オリフィス５Ｃと主管孔３との間に大径部５Ａを設ける形式のものであっても複雑な加工工程を必要とせず容易に製造出来る。
尚、コモンレール１の製造工程は、必ずしも上述した順序でなければならないわけではなく、種々の変更が可能である。例えば、オリフィス孔形成ステップは大径部形成ステップと前後して行えばよく、また、シールボルト１５の組み付けは大径部５Ａを成形した後であれば、オリフィス５Ｃの形成ステップと前後して行ってもよい。
【００２３】
＜他の実施形態＞
本発明は上記記述及び図面によって説明した実施形態に限定されるものではなく、例えば次のような実施形態も本発明の技術的範囲に含まれ、さらに、下記以外にも要旨を逸脱しない範囲内で種々変更して実施することができる。
【００２４】
（１）本実施形態ではレール本体２は環状をなし閉じた形式のものであったが、例えば、図７や図８に示すように、レール本体２が分割構成されたものであれば、分岐孔５を２方向から加工することが可能で、本実施形態と同様の効果が得られる。
【００２５】
（２）本実施形態のコモンレール１は４気筒エンジン以外の多気筒エンジンにも適用され、分岐部４及び分岐孔５についてそれぞれ７個または４個、あるいはそれ以外の数を有してもよい。
【図面の簡単な説明】
【図１】本発明の一実施形態に係るコモンレールの縦断面図である。
【図２】分岐部の縦断面図である。
【図３】シールナットの取り付け状況を表すレール本体の下面図である。
【図４】コンピュータによる解析に使用した分岐部の断面図である。
【図５】レール孔の形成ステップを示す図である。
【図６】分岐孔の製造ステップを示す図である。
【図７】他の実施形態におけるコモンレールの縦断面図である。
【図８】同じく他の実施形態におけるコモンレールの縦断面図である。
【図９】従来例の断面図
【図１０】従来例の断面図
【符号の説明】
１…コモンレール
２…レール本体
３…主管孔
４…分岐部
５…分岐孔
５Ａ…大径部
５Ｃ…オリフィス
１０…開口部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a common rail in a common rail fuel injection device for an engine.
[0002]
[Prior art]
In the common rail type fuel injection device, as a means for distributing pressurized fuel to a plurality of injectors, a common rail having a plurality of branch portions protrudingly formed on the outer periphery of a cylindrical rail body is used. The common rail has a structure in which the fuel pipe of the injector is connected to the protruding end of each branch, and the pressurized fuel supplied to the main pipe hole in the rail body is supplied to each injector through the branch hole and the fuel pipe in each branch. Is to be distributed.
In this type of common rail, there is known a structure in which a small diameter orifice is provided in a branch hole in a branch portion in order to suppress pulsation caused by opening and closing of an injector and to stably supply fuel (Patent Document 1).
[0003]
As shown in FIG. 9, a branch portion 53 projects from the outer periphery of a rail body 50 having a main pipe hole 51 formed therein, and penetrates into the main pipe hole 51 from the distal end side of the branch portion 53 as shown in FIG. A branch hole 55 is provided. In the processing procedure, the main pipe hole 51 is formed in the rail main body 50 in advance, and then the branch hole 55 is formed. However, since the rail main body 50 is closed in an annular shape, it is difficult to work from the main pipe hole 51 side, and the processing of the branch hole 55 is performed from the protruding end side of the branch portion 53. Accordingly, when the orifice 55A is formed integrally with the branch hole 55, the orifice 55A is formed so as to be connected to the main pipe hole 51 because the processing of the orifice 55A is performed before the processing of the branch hole 55.
[0004]
[Patent Document 1]
JP 2001-295722 A
[Problems to be solved by the invention]
According to the above structure, the diameter of the hole at the joint between the main pipe hole 51 and the orifice 55A is sharply reduced. Therefore, when high-pressure fuel is accumulated in the rail main body 50, stress is concentrated at the joint due to the increase in the diameter of the main pipe hole 51 and the orifice 55A, and the common rail may be fatigued. As a countermeasure for preventing stress concentration at the joint portion, as shown in FIG. 10, the orifice portion is formed of a separate component 70, and the connection between the main pipe hole 51 and the orifice 70A is made via a connecting portion 71 having a larger diameter than the orifice 70A. There is something to connect. However, in this case, a press-fitting step is added for assembling the orifice portion (separate component 70) (manufacturing steps are increased), and special equipment for press-fitting is required. Further, the outer shape of the branch portion 53 is increased by the thickness of the separate component 70 (the G dimension portion in FIG. 10), and the weight is increased accordingly.
The present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a common rail in which stress is less likely to be concentrated even when an orifice is provided, and which is easy to manufacture.
[0006]
[Means for Solving the Problems]
As a means for achieving the above object, the invention of claim 1 is characterized in that a plurality of branch portions are integrally formed radially outward on an outer periphery of a rail main body in which a main pipe hole is formed along an axis. A branch hole is formed inside the branch portion and has an orifice and a large-diameter portion having a larger diameter than the orifice. A branch hole branching from the main pipe hole is formed, and a fuel pipe of an injector is provided at a protruding end of the branch portion. A common rail adapted to be connected, wherein the large-diameter portion is formed so that one end thereof is connected to the main pipe hole and the other end extends radially outward along the axis of the branch portion. It is characterized in that the orifice is formed further radially outside of the large diameter portion.
[0007]
The invention according to claim 2 is the device according to claim 1, wherein a closeable opening for drilling the large-diameter portion is provided on a side of the rail main body opposite to the branch portion. It has features.
[0008]
The invention according to claim 3 is characterized in that a main pipe hole is formed along an axial center on an inner peripheral side, and a plurality of branch portions are integrally formed to protrude radially outward on an outer peripheral side. An opening is formed on the opposite side of the branch portion, and then a large-diameter portion is formed through the opening, one end of which is connected to the main pipe hole and the other end extends radially outward along the axis of the branch. Before or after the molding of the large diameter portion, an orifice having a smaller diameter than the large diameter portion is formed further radially outside the large diameter portion, and after the large diameter portion is further molded, the orifice is formed. It is characterized in that the opening is closed before and after.
[0009]
Function and effect of the present invention
<Invention of claim 1>
According to the first aspect of the present invention, the main pipe hole is connected to the orifice via the large diameter portion. Therefore, when compared with the type in which the orifice is directly connected to the main pipe hole, the sudden fluctuation of the hole diameter at the joint between the main pipe hole and the branch hole (orifice, large diameter portion) is avoided, and the stress concentration there is reduced. You can do it.
[0010]
<Invention of Claim 2>
According to the second aspect of the invention, it is necessary to process the large diameter portion from the side of the main pipe hole, but the processing can be performed from the outside through the opening. Therefore, processing of the branch hole is easy.
[0011]
<Invention of Claim 3>
According to the third aspect of the present invention, since the large diameter portion is processed from the opening side, the large diameter portion is set between the main pipe hole and the orifice. (Reducing the diameter) can be easily processed.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of the present invention will be described with reference to FIGS. The elongated rail main body 2 constituting the common rail 1 is made by forging S45C material, SCM (chromium / molybdenum steel) material, carbon steel material, or the like, and has a main pipe hole 3 extending in the longitudinal direction formed therein. ing. A first screw portion 2a and a second screw portion 2b into which the connection member 20 is screwed are formed at the left and right ends of the main pipe hole 3, respectively. The connection member 20 screwed to the first screw portion 2a is connected to a control device (not shown) having a pressure sensor, and the connection member 20 connected to the second screw portion 2b is connected to a relief valve (not shown). Each is connected. The control device detects the pressure in the main pipe hole 3 with a pressure sensor, and adjusts the pressure by opening and closing a relief valve. The common rail 1 of the present embodiment is for a four-cylinder engine, and the rail main body 2 is provided with five cylindrical branches 4 projecting radially outward at equal intervals in the longitudinal direction of the rail main body 2. I have. In the following description, the projecting end side of the branch portion 4 in FIG. 1 is referred to as an upper side, and the opposite side is referred to as a lower side.
[0013]
As shown in FIG. 2, each branch portion 4 includes a column-shaped pedestal portion 7 having the same width and a supply pipe connection portion 8 formed on the pedestal portion 7. Inside each branch part 4, a branch hole 5 penetrating along the axis of the branch part 4 from the main pipe hole 3 on the upper surface side of the branch part 4 is formed, and a divergent pipe is formed on the upper surface of each branch part 4. A seat surface 6 is formed. A fuel supply pipe to which a high-pressure pump for fuel supply is connected as an input is connected to any one of the pipe seat surfaces 6 of the branch portions 4, and after the fuel in the fuel tank is pressurized by the high-pressure pump, It is introduced into the main pipe hole 3. A sealing surface of a fuel supply pipe connected to each injector (not shown) is liquid-tightly engaged with the pipe seating surfaces 6 of the other four branch portions 4. In addition, a screw portion 8a is formed on the outer peripheral portion of each supply pipe connection portion 8 to which a nut for pipe tightening is screwed when connecting the above-described fuel supply pipe.
[0014]
The branch hole 5 is provided with a large-diameter portion 5A whose one end is connected to the main pipe hole 3 and the other end is extended radially outward (upward in the drawing) along the axis of the branch portion 4. An orifice 5C communicating with the pipe seating surface 6 and having a smaller diameter than the large diameter portion is formed further radially outside of the large diameter portion 5A, and an orifice 5C is provided between the orifice 5C and the large diameter portion 5A. A tapered portion 5B that gradually tapers toward the side is formed. As described above, the large diameter portion 5A and the tapered portion 5B are interposed between the orifice 5C and the main pipe hole 3, and the diameter of the branch hole 5 is stepwise from the main pipe hole 3 side to the protruding end side. The diameter is reduced. For this reason, the joint portion between the main pipe 3 and the branch hole 5 (portion A shown in FIG. 1) is conventionally a place where stress tends to concentrate when fuel is injected or when high-pressure fuel is accumulated in the rail body 2. However, a sharp change in the hole diameter at this portion can be avoided, and the stress concentration at the portion A can be reduced.
Further, it is more effective if a portion where the hole diameter changes, such as a joint portion between the main pipe hole 3 and the branch hole 5 or a joint portion between the large diameter portion 5A and the orifice 5C, is gently connected by R.
[0015]
An opening (a circular through-hole) 10 is provided in a portion of the rail main body 2 which faces the branch hole 5 with the main pipe hole 3 therebetween. The center of the opening 10 and the axis of the branch 4 are aligned, and the opening 10 and the branch 4 are coaxial. The opening 10 is a relief for drilling the large diameter portion 5A described above from below in FIG.
In the opening 10, a screw portion 11 is formed on the inner peripheral side, and a sealing concave portion 12 in which a bottom surface (seal surface) 12 A is flattened is formed in a tip portion (a lower side in FIG. 1) of the opening 10. ing. On the other hand, a seal bolt 15 provided with a flange 16 at the end is screwed into the opening 10. The flange 16 of the seal bolt 15 is formed to have an outer shape smaller than the sealing recess 12, and has an annular seal ring 16 A protruding from the upper surface thereof. The upper surface side of the seal ring 16A is also flattened. Therefore, when the seal bolt 15 is screwed into the rail main body 2, the seal ring 16A of the seal bolt 15 comes into close contact with the seal surface 12A of the sealing recess 12, and the opening 10 is sealed (metal seal).
[0016]
In the two cases described below (case 1 and case 2), when a predetermined pressure (pressure assuming a state in which high-pressure fuel is stored) is applied to the main pipe hole 3, the above-described joint is formed. The analysis of the stress generated in the portion (A portion in FIG. 4) was performed by a computer.
The case 1 is of a type formed such that an orifice 5C is connected to the main pipe hole 3 (conventional product assumed shape).
The case 2 is of a type in which a large diameter portion 5A is formed between the orifice 5C and the main pipe hole 3 (the assumed shape in the embodiment).
In both

cases

1 and 2, the inner diameter of the main pipe hole 3 (dimension B in the drawing) is 6 mm, the inner diameter of the orifice 5C (dimension C in the drawing) is 1 mm, and the total length of the orifice 5C (dimension F in the drawing) is 2. The inner diameter of the large diameter portion 5A (dimension D in the figure) was 3 mm, the total length of the large diameter portion 5A (dimension E in the figure) was 19 mm, and the pressure applied to the main bore 3 was 200 MPa.
[0017]
Based on the above analysis, the following results (Table 1) were obtained.

[0018]
As described above, the stress value at the joint portion of Case 1 (A portion in FIG. 4) is 845 MPa, while the stress value at the joint portion of Case 2 is 655 MPa. Thus, the stress value is reduced by 22.5%. Therefore, in the case of the present embodiment, a decrease in the strength of the rail body due to metal fatigue is alleviated as compared with the conventional product.
[0019]
Next, a method for manufacturing the common rail 1 according to the present embodiment will be described. As shown in FIG. 5, first, in a raw material WM in which five cylindrical bosses BS are formed at equal intervals on a cylindrical main body MB, a main pipe hole is formed in a longitudinal direction of the main body MB by a gun drill or the like. 3 is formed (main hole forming step). If necessary, the surface of the main pipe hole 3 may be finished with a reamer or the like after cutting with a gun drill. Then, after drilling pilot holes at both ends of the main pipe 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 any time after the main pipe hole 3 is formed, or may be formed after the branch hole 5 is formed.
[0020]
Next, as shown in FIG. 6A, the sealing recess 12 that forms the opening 10 is formed on the main body MB. For this purpose, first, the positioning is performed so that the center of the opening 10 is located on the axis of the boss BS, and then the main body MB is cut by a lathe or the like. Subsequently, the pilot hole of the screw portion 11 is machined from the sealing recess 12 side by a drill or an end mill, and thereafter, the screw portion 11 is machined (sealing recess forming step).
Subsequently, as shown in (b) of the figure, a drill or an end mill or the like is reentered into the opening 10 to form a large-diameter portion 5A from the lower side of the figure along the axis of the boss BS. (Large diameter portion forming step). Processing is completed when the tip of the large diameter portion 5A reaches a predetermined depth beyond the center of the boss portion BS. At this time, a shape following the outer shape of the drill, that is, a tapered portion 5B is formed at the tip portion. Is done.
Subsequently, an orifice 5C is formed from the center portion of the upper surface of the boss portion BS toward the large-diameter portion 5A by a drill or a punch (orifice hole forming step). Thereafter, the pipe seat surface 6 is formed on the upper surface side of the boss portion BS, and the screw portion 8a is formed on the outer peripheral portion, whereby the processing of the rail main body 2 is completed.
[0021]
Subsequent to the processing of the rail body 2, the sealing bolt 15 is screwed into the opening 10, and the sealing ring 16 A is brought into close contact with the sealing recess 12. Finally, the tip of the fluid polishing nozzle (not shown) is engaged with the pipe seat surface 6 of the branch portion 4 in a liquid-tight manner, and the fluid is injected into the branch hole 5 through the fluid passage of the fluid polishing nozzle. A fluid containing abrasive grains or an abrasive is discharged from the fluid polishing nozzle, and flows through the passage, so that the passage wall surface (the hole wall of the main pipe hole 3 and the hole wall of the branch hole 5) becomes smooth.
[0022]
As described above, according to the method of manufacturing the common rail 1 according to the present embodiment, since the processing of the branch hole 5 is performed from both the upper surface side of the branch portion 4 and the opening 10 side, the orifice 5C and the main pipe hole 3 are formed. Even if a large-diameter portion 5A is provided between them, it can be easily manufactured without requiring a complicated processing step.
Note that the manufacturing process of the common rail 1 does not necessarily have to be in the order described above, and various changes can be made. For example, the orifice hole forming step may be performed before or after the large diameter portion forming step, and the assembling of the seal bolt 15 is performed before or after the orifice 5C forming step if the large diameter portion 5A is formed. You may.
[0023]
<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and furthermore, besides the following, within the scope not departing from the gist. Can be implemented with various modifications.
[0024]
(1) In the present embodiment, the rail main body 2 is of an annular and closed type. However, for example, as shown in FIGS. The hole 5 can be machined from two directions, and the same effect as in the present embodiment can be obtained.
[0025]
(2) The common rail 1 of the present embodiment is also applied to a multi-cylinder engine other than the four-cylinder engine, and the branch part 4 and the branch hole 5 may each have seven or four or other numbers.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a common rail according to an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view of a branch portion.
FIG. 3 is a bottom view of the rail main body showing a mounting state of a seal nut.
FIG. 4 is a sectional view of a branch portion used for analysis by a computer.
FIG. 5 is a diagram showing a step of forming a rail hole.
FIG. 6 is a view showing a manufacturing step of a branch hole.
FIG. 7 is a longitudinal sectional view of a common rail according to another embodiment.
FIG. 8 is a longitudinal sectional view of a common rail according to another embodiment.
FIG. 9 is a cross-sectional view of a conventional example. FIG. 10 is a cross-sectional view of a conventional example.
DESCRIPTION OF SYMBOLS 1 ... Common rail 2 ... Rail main body 3 ... Main pipe hole 4 ... Branch part 5 ... Branch hole 5A ... Large diameter part 5C ... Orifice 10 ... Opening

Claims

A plurality of branch portions are integrally formed radially outward on the outer periphery of the rail body in which a main pipe hole is formed along the axis, and an orifice and a larger diameter than the orifice are formed inside the branch portion. Having a large diameter portion, a branch hole branching from the main pipe hole is formed,
A common rail configured to connect a fuel pipe of an injector to a protruding end of the branch portion,
The large-diameter portion is formed such that one end thereof is connected to the main pipe hole and the other end extends radially outward along the axis of the branch portion, and the orifice is further radially outward from the large-diameter portion. A common rail having a formed configuration.

2. The common rail according to claim 1, wherein a closeable opening for drilling the large-diameter portion is provided on a side of the rail main body opposite to the branch portion. 3.

On the inner peripheral side, a main pipe hole is formed along the axis, and on the outer peripheral side, a plurality of branch portions are integrally formed to protrude radially outward.
Forming an opening on the opposite side of the branch portion in the rail body,
Thereafter, a large-diameter portion, one end of which is connected to the main pipe hole and the other end of which extends radially outward along the axis of the branch portion, is formed through the opening.
Before or after the molding of the large-diameter portion, an orifice with a smaller diameter than the large-diameter portion is formed further radially outside the large-diameter portion,
Further, a method of manufacturing a common rail for closing the opening before and after forming the orifice after forming the large diameter portion.