JP4405102B2 - Common rail for diesel engines - Google Patents

Description

【００１７】
【発明の効果】
以上説明したごとく、本発明に係るディーゼルエンジン用コモンレールは、分岐孔と本管レール側流通路との交差部や分岐孔の内周縁部に析出させた硬さ、引張り強さ共に向上した加工誘起マルテンサイトと、圧縮残留応力により優れた耐内圧疲労特性を有し、さらにオートフレッテージ加工を施すことにより、分岐孔と本管レール側流通路との交差部や分岐孔の内周縁部のみならず、コモンレールの全内表面にわたり優れた耐内圧疲労特性を有するので、超高圧での耐久性を確保することができる。また、優れた耐内圧疲労特性に加え、耐振動疲労特性、耐キャビテンション性、シート面の耐疵付き性に優れ、かつ薄肉軽量化も可能であるなどの効果も奏する。
【図面の簡単な説明】
【図１】本発明の対象とするボス一体型のコモンレールの一例を示す縦断正面図である。
【図２】同じくリング状の継手金具を使用したコモンレールの一例を示す要部縦断側面図である。
【図３】同じく筒状のスリーブニップルを凹凸嵌合螺着方式にて本管レールに取着した構成のコモンレールの一例を示す縦断側面図である。
【図４】同じく筒状のスリーブニップルを溶接にて本管レールに取着した構成のコモンレールの一例を示す縦断側面図である。
【符号の説明】
１ 本管レール
１−１ 流通路
１−２ 分岐孔
１−３ 受圧座面
１−２ａ Ｒ面取部
２ 分岐枝管
２−２ 接続頭部
２−３ 押圧座面
３ 継手金具
４、６ ナット
５ スリーブワッシャー[0001]
BACKGROUND OF THE INVENTION
The present invention generally relates to a common rail such as a high-pressure fuel manifold or a block rail in a pressure accumulation fuel injection system of a diesel internal combustion engine, and more particularly to a common rail for a diesel engine having increased internal pressure fatigue strength.
[0002]
[Prior art]
Conventionally, as this type of common rail, for example, as shown in FIG. 1, a boss 3 c integrated with the main rail 1 is formed on the main rail 1 of the common rail, and the press formed by the connection head 2-2 of the branch branch pipe 2. The seat surface 2-3 is brought into contact with and engaged with the pressure-receiving seat surface 1-3 on the main rail 1 side, and a cap nut 6 that is screwed into a screw portion 3-2 provided on the outer peripheral surface of the boss 3c is fastened. 2 and a pressure receiving seat that opens outwardly at a branch hole 1-2 portion communicating with a circular cross-sectional flow passage 1-1 provided in a peripheral wall portion on the main rail 1 side as shown in FIG. A ring-shaped joint fitting 3 that surrounds the outer periphery of the main rail 1 near the pressure-receiving seat surface is formed as a surface 1-3, and the diameter of the branch connection is increased by, for example, tapered conical buckling. The pressing seat surface 2-3 formed by the connection head 2-2 on the side of the branch branch pipe 2 as a body is brought into contact with and engaged, The screw wall 3-1 projecting outward from the main rail 1 provided in the joint fitting so as to project in the radial direction of 1, and the nut 4 assembled in advance via the sleeve washer 5 on the branch branch pipe 2 side. The connection head 2-2 is tightened and connected in accordance with the press under the neck of the connection head 2-2 or is replaced with a ring-shaped joint fitting 3 as shown in FIGS. The sleeve nipples 3a and 3b are directly attached to the outer peripheral wall of the main rail 1 by an uneven fitting screwing method, welding or the like so as to protrude outward in the radial direction of the main rail 1, and The pressing seat surface 2-3 formed by the connecting head 2-2 is brought into contact with and engaged with the pressure receiving seat surface 1-3 on the main rail 1 side, and the nut 4 screwed into the sleeve nipples 3a and 3b is fastened. Are also known, such as those that connect to each other and block rail type common rails (not shown) There.
[0003]
[Problems to be solved by the invention]
However, any of the above-described conventional common rails has a shaft applied to the pressure receiving seat surface 1-3 in accordance with the internal pressure of the main rail 1 and the pressing of the connection head 2-2 of the branch connection body such as the branch branch pipe 2. Due to the force, a large stress is generated at the inner peripheral edge portion P of the lower end of the branch hole 1-2, and cracks are likely to occur from the inner peripheral edge portion P of the lower end, which may cause fuel leakage. Further, it is the inner surface of the main rail that is likely to crack next. This is because the main rail is a thick-walled cylinder but has a large inner diameter, which causes a large circumferential tensile stress on the inner surface.
[0004]
The present invention has been made in view of the above-mentioned problems of the prior art, and uses transformation-induced plastic-type strength steel to increase the internal pressure fatigue strength of the main rail and the branch hole, To provide a common rail for a diesel engine capable of further improving internal pressure fatigue strength by lowering the degree of concentration of stress generated at the intersection of the branch hole including the inner peripheral edge of the lower end of the pipe and the main rail side flow passage It is intended.
[0005]
[Means for Solving the Problems]
A common rail for a diesel engine according to the present invention is provided with a branch hole that communicates with the flow passage in an axial peripheral wall portion of a main rail having a flow passage in the axial center thereof, and is a joint that is integral with or separate from the main rail. In a common rail for a diesel engine configured by connecting a branch connector to the branch hole via a member, the main rail is made of transformation-induced plastic type strength steel, and the main rail is processed after heat treatment This is characterized by the fact that residual austenite is generated by the above process, and the work concentration and compressive residual stress remain on the inner surface by reducing the stress concentration at the intersection of the branch hole and the main rail side flow passage. Residual austenite is produced by heat treatment in the main rail made of plastic-type strength steel, and then the main rail is processed to accommodate the branch hole and the intersection of the main rail side flow passage. It is characterized in that the inner surface work hardening and compressive residual stress remain by applying concentration reduction processing, and after applying reduction processing of stress concentration at the intersection of the branch hole and main rail side flow passage, It is characterized by inducing induced plastic transformation on the inner surface by fretting and leaving compressive residual stress.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The transformation-induced plastic type strength steel in the present invention has been developed in recent years for the purpose of reducing the weight of undercarriage press-formed parts of passenger cars, and presses using strain-induced transformation (TRIP) of retained austenite (γ _R ). Ferritic (α _f ) + bainite (α _b ) + γ _R composite structure steel [TRIP type Dual-Phase steel, TDP steel] and bainitic ferrite (α _bf ) + γ _R steel [TRIP type bainite] Steel, TB steel].
Here, the transformation-induced plasticity is a large elongation accompanying the transformation of an austenite (γ) layer that exists in a scientifically unstable state into martensite by the addition of mechanical energy.
That is, the TRIP steel is a steel obtained by performing a specific heat treatment on a steel having a limited composition to obtain a metal structure in which retained austenite and bainite structure are mixed around the grain boundary of the α layer. The characteristics of TRIP steel having such a metal structure include high plastic deformability and high strength and hardness because it becomes a martensite structure by plastic working.
[0007]
Since the common rail for diesel engines according to the present invention is made of transformation-induced plastic-type strength steel having such characteristics, workability is good during forging and a desired shape is easily obtained. On the other hand, when specific heat treatment is not performed (when there is little retained austenite and bainite), the elongation and tensile strength are low, and cutting can be easily performed. In the case of a common rail that uses pipes, the reduction during drawing can be greatly reduced, so that the number of times of drawing can be reduced. Further, if the same reduction is performed, processing can be performed with a small drawing machine and a small die.
In addition, transformation induced plasticity strength steel has the property that the locally deformed austenite transforms into hard martensite and strengthens that portion (TRIP phenomenon). In the case of the common rail, even if the internal pressure fatigue progresses, the fatigue portion is strengthened by the above characteristics, and a resistance force that prevents the rail from being broken is generated, so that the life is long.
Furthermore, stress concentration reduction processing presses the intersection of the branch hole and the main rail side flow passage, so that compressive residual stress remains around the branch hole, and the deformed part has hardness and tensile strength due to precipitation of work-induced martensite. Since both are improved, fatigue resistance is excellent.
[0008]
In the heat treatment in the present invention, the main rail is heated to 950 ° C. and held for a predetermined time to be austenitized, and then held at a temperature between 350 ° C. and 500 ° C. for a predetermined time to perform austempering. By performing this austempering treatment, a metal structure in which a retained austenite (γ) layer and a bainite structure are mixed around the grain boundary of the α layer is obtained.
[0009]
As a method for reducing the stress concentration at the intersection of the branch hole and the main rail side flow passage in the present invention, a method of leaving compressive residual stress by a pressing method is known. The method is described in, for example, Japanese Patent Application Laid- Open No. 10-318081 proposed by the applicant of the present application. (1) A main rail flow passage opening end portion of a branch hole by applying a pressing force by an external pressure method. (2) Applying a pressing force to the inner peripheral surface of the main rail near the branch hole by the internal pressure method to compress the residual stress around the opening end of the main rail flow passage in the branch hole (3) Flow through the main rail of the branch hole by applying a pressing force to the inner peripheral surface of the main rail near the branch hole by a pipe expansion method that applies a pressing force from the inside of the main rail to the pipe radial direction. A method of generating compressive residual stress around the end of the road opening, (4) A branch hole by applying a pressing force to the inner peripheral surface of the branch hole by a diameter expansion method that applies a pressing force in the radial direction from the inside of the branch hole. There is a method of generating compressive residual stress around the opening end of the main rail flow passage.
In addition, if it is hardened too much by heat treatment (high strength, low elongation) to increase the fatigue strength as steel, cracking may occur if the pressing by the pressing method is too strong, and a tool for pressing pressure However, the transformation-induced plastic-type strength steel (TRIP steel) has not only such a high strength but also a large elongation, so there is no such problem.
[0010]
Autofrettage processing in the present invention is a method in which only the inner peripheral surface is plastically deformed by applying internal pressure, and the work is hardened by plastic deformation in the entire inner surface portion by this autofrettage processing (by precipitation of work-induced martensite, Both the hardness and the tensile strength are improved), and the compressive stress is further left on the entire inner surface portion to improve the durability of the main flow path which becomes the next weak point.
[0011]
In the present invention, as described above, the TRIP steel is subjected to heat treatment and pressing after machine processing, preferably further autofrettage processing, so that the austenite (γ) structure is hardened due to the precipitation of work-induced martensite. In addition, by improving both the tensile strength and residual compressive stress, the internal pressure fatigue resistance of the entire inner surface as well as the branch hole and the main rail side flow passage intersection is improved, and the durability of the main flow path Will be excellent.
[0012]
【Example】
Example 1
TRIP type bainitic steel (TB steel) forging round bar having the components shown in Table 1 is cut to a predetermined size, heated to hot forging temperature, and boss integrated common rail material (outer diameter of tubular part) 34mmφ) forged, and then machining the desired parts such as the inner diameter 10mmφ, boss part branch hole diameter 3mmφ, sheet surface, screw part by cutting, etc., this is austenitized at 950 ° C × 20 minutes, then held at 400 ° C × 3 minutes austempering alms, and a boss integrated common rail with mixed tissue of the residual austenite (gamma) layer or bainite structure around the grain boundaries of the α layer, thereafter, especially in the branch hole of the bosses of the rail A compressive residual stress was generated in the vicinity of the opening end portion of the main rail flow passage of the branch hole by applying a pressing force by the external pressure method described in Kaihei 10-318081. In addition, since there was little residual austenite layer and bainite structure at the time of cutting, the tensile strength was low and the elongation was small, so the processing was extremely easy. As a result of investigating the fatigue limit by applying this common rail to a repeated pressure tester, normal high strength steel (SCM435) used as a comparative material (C0.33-0.38 mass%, Si0.15-0.35 mass%, Mn0.60) ~ 0.85mass%, P0.030mass% or less, S0.030mass% or less, Cr0.90 to 1.20mass%, Mo0.15 to 0.30mass%) common rail of the same size, 180-1500Bar Whereas the common rail according to the present invention was damaged in a repeated test by hydraulic pressure at 800,000 times, the common rail according to the present invention was not damaged even at a repeated test of 10 million times at 2200 Bar, and exhibited excellent internal pressure fatigue resistance.
[0013]
Example 2
A forged round bar made of TRIP-type bainite steel (TB steel) having the components shown in Table 1 was cut into a predetermined size, and this was austenitized at 950 ° C. for 20 minutes, and then held at 350 to 475 ° C. for 3 minutes. Austempering is applied to form a mixed structure of residual austenite (γ) layer and bainite structure around the grain boundary of α layer, and this is forged into a boss-integrated common rail (outside diameter 34mmφ of tubular part) by die forging , and then the inner diameter by cutting or the like 10.6Mmfai, boss branch hole diameter 3 mm.phi, sheet surface, and processing the desired location such as a screw portion, and a boss integrated common rail, thereafter, especially in the branch hole of the bosses of the rail A compressive residual stress was generated in the vicinity of the opening end portion of the main rail flow passage of the branch hole by applying a pressing force by the external pressure method described in Kaihei 10-318081. In addition, at the time of forging, a retained austenite layer and a bainite structure are present, but forging can be performed because of high elongation although tensile strength is high. Furthermore, an auto-frettage process was performed by applying an internal pressure capable of yielding about 50% of the wall thickness of the tubular portion.
As a result of examining the fatigue limit by applying this common rail to a repetitive pressure test machine, it was not damaged even at a repetitive test of 10 million times at 2400 Bar, and showed superior internal pressure fatigue resistance durability.
[0014]
Example 3
A common rail material (outer diameter of pipe 36 mmφ, inner diameter 10 mmφ) made by cutting seamless steel pipes made of TRIP-type bainite steel (TB steel) having the components shown in Table 1 into predetermined dimensions, by cutting or the like, branch hole diameter 3 mmφ, sheet surface, screw The austenite is processed at 950 ° C. for 20 minutes, then austempered for 3 minutes at 350 ° C. to 475 ° C., and retained austenite (γ) centering on the grain boundary of the α layer. A common rail having a structure in which layers and bainite structures are mixed, and then the main rail circulation of the branch hole by applying a pressing force to the branch hole portion of this common rail by the external pressure method described in Japanese Patent Laid- Open No. 10-318081 Compressive residual stress was generated around the edge of the road opening. In addition, at the time of cutting, since the retained austenite layer and the bainite structure were small, the tensile strength was low and the elongation was small, so the processing was extremely easy.
As a result of examining the fatigue limit by applying this common rail to a repetitive pressure test machine, in this example as well, even in a repetitive test of 10 million times at 2200 Bar, it was not damaged and showed excellent internal pressure fatigue resistance durability.
[0015]
Needless to say, the same effect can be obtained with a block rail made of TRIP-type bainite steel (TB steel).
[0016]
[Table 1]

[0017]
【The invention's effect】
As described above, the diesel engine common rail according to the present invention has improved machining induction with improved hardness and tensile strength deposited at the intersection of the branch hole and the main rail side flow passage and at the inner peripheral edge of the branch hole. It has excellent internal pressure fatigue resistance due to martensite and compressive residual stress. Furthermore, by applying auto-frettage processing, if only the intersection of the branch hole and the main rail side flow passage or the inner peripheral edge of the branch hole, In addition, since it has excellent internal pressure fatigue resistance over the entire inner surface of the common rail, durability at ultra-high pressure can be ensured. Further, in addition to excellent internal pressure fatigue resistance, it has excellent effects such as vibration fatigue resistance, cavitation resistance, and scratch resistance on the sheet surface, and can be reduced in thickness and weight.
[Brief description of the drawings]
FIG. 1 is a longitudinal front view showing an example of a boss-integrated common rail targeted by the present invention.
FIG. 2 is a longitudinal sectional side view of an essential part showing an example of a common rail that similarly uses a ring-shaped joint fitting.
FIG. 3 is a longitudinal side view showing an example of a common rail having a configuration in which a cylindrical sleeve nipple is similarly attached to a main rail by an uneven fitting screwing method.
FIG. 4 is a longitudinal side view showing an example of a common rail having a configuration in which a cylindrical sleeve nipple is similarly attached to a main rail by welding.
[Explanation of symbols]
1 Main rail 1-1 Flow path 1-2 Branch hole 1-3 Pressure receiving seat surface 1-2a R chamfered portion 2 Branch branch tube 2-2 Connection head 2-3 Pressing seat surface 3 Joint fittings 4 and 6 Nut 5 Sleeve washer

Claims (2)

  A branch hole leading to the flow path is provided in the axial peripheral wall portion of the main rail having a flow path inside the axial direction, and branch connection is made to the branch hole through a joint member that is integral with or separate from the main rail. In a diesel engine common rail constructed by connecting bodies, the main rail is made of transformation-induced plastic-type strength steel. A common rail for a diesel engine that has left the work hardening and compressive residual stress of the inner surface by applying a process of reducing stress concentration at the intersection of the branch hole and the main rail side flow passage. The branch hole and was subjected to a reduction processing of the stress concentration of the main pipe rail side flow passage cross section, further claim 1 Symbol placement left compressive residual stress with causing a induced plasticity transformation on the inner surface by autofrettage processing Common rail for diesel engines.

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