JP4686575B2 - Fuel injection device for diesel engine, method for manufacturing the same, and valve device - Google Patents

Description

  The present invention controls the fuel injection from the nozzle hole opened in the nozzle body by moving the needle valve inside the nozzle body to which fuel is supplied, thereby opening and closing the seat surface where the nozzle body and the needle valve are in contact. The present invention relates to a fuel injection device or a valve device for a diesel engine, and particularly relates to a technique for improving durability of a seat portion.

  In general, a fuel injection device for a diesel engine has a nozzle body (nozzle body) to which fuel is supplied, and a needle valve that is slidable inside the body. At the time of fuel injection, the needle valve is moved by the pressure of the fuel supplied to the nozzle body, the seat surface where the nozzle body and the needle valve are in contact is opened inside the nozzle body, and the fuel is discharged from the nozzle hole opened in the nozzle body. Spray. When fuel is not injected, a needle valve that is biased by a load such as a spring contacts the nozzle body to close the seat surface and stops fuel injection from the nozzle.

  Thus, since the seat part of the fuel injection nozzle for diesel engines is repeatedly subjected to a high impact force when the valve is closed, wear and spalling occur. Spalling is a phenomenon in which a crack occurs at the boundary between the surface hardened layer and the base material and the surface hardened layer peels off. In particular, with the recent increase in spraying pressure, there is a problem of a decrease in life due to early wear of the seat portion or occurrence of spalling. Wear occurs in both the needle valve and the nozzle body, but the nozzle body tends to wear more. Further, spalling occurs in the nozzle body. In order to enable a stable long-time operation of the diesel engine, it is important to improve the wear resistance and spalling resistance of the seat portion.

In conventional diesel engine fuel injection nozzles, a tempered material such as SKH51 is used for the needle valve, and a carburized material such as SNCM420 or a nitride material such as SKD61 is used for the nozzle body. The SKH51 tempered material of the needle material is a high speed steel called Mo high speed and has good toughness and wear resistance. The microstructure is a high-temperature tempered martensite substrate in which relatively large angular eutectic carbides (MC, M ₆ C) and fine precipitated carbides (Cr ₂₃ C ₆ , Mo ₂ C) generated by tempering are precipitated. . The SNCM420 carburized material of the nozzle body material is a fine carbide precipitated on the low-temperature tempered martensite substrate and is affected by the tempering temperature, so it softens when used at a temperature higher than the tempering temperature. In the SKD61 nitride material, fine double carbide (M ₆ C) is dispersed in a high-temperature tempered martensite substrate, and hard nitride is dispersed in the diffusion layer.

The inventors of the present application have earnestly studied the wear and spalling generated in the seat portion of the conventional fuel injection device for diesel engines, and have obtained the following knowledge.
That is, a relatively large co-crystal (MC, M ₆ C) precipitated on the SKH 51 can be considered as a factor that affects the wear resistance of the sheet portion. The carbides deposited on the needle valve seat are angular, and are harder than the substrate, so that they float on the surface without being worn, and the nozzle body side seat can be scraped off. In particular, if the quenching temperature is too high or the holding time is too long, it will become square and coarse, so care must be taken.

  Next, with respect to the spalling of the sheet part, shear stress due to contact becomes a problem. The aforementioned carbides are considered to increase the shear stress in the vicinity of the surface due to the excavation force when seated, and easily generate spalling.

  A nitride layer such as SKD61 nitride is generally considered to be divided into an outermost compound layer and a diffusion layer therein. Since the outermost compound layer is brittle and weak to impact force, it is generally removed and used by polishing.

  However, in the seat portion of the fuel injection device for diesel engines, even when the compound layer is removed, the seating surface may be subject to fatigue failure (spalling) due to repeated impact force.

  The present invention has been made to solve the above problems, and it is an object of the present invention to make it difficult for wear and spalling to occur in the seat portion of a diesel engine fuel injection device that repeatedly receives a high impact force when the valve is closed.

  The inventors of the present application have analyzed the damaged product in order to investigate the cause of the fatigue failure of the seating surface due to repeated impact force even when the compound layer is removed in the seat portion of the diesel engine fuel injection device. As a result, the inventors have discovered a new fact that this phenomenon occurs at a specific site in the diffusion layer.

  When the surface is nitrided to increase the hardness of the alloy steel, the outermost compound layer and the diffusion layer region (the first layer) having a relatively high nitrogen content immediately below the hard nitride are the grain boundaries and Since it precipitates in the grains and is brittle, it is easily damaged by repeated high impact forces. However, according to the knowledge of the inventors of the present application, the diffusion layer region immediately below the compound layer is divided into a diffusion layer region (first layer) having a relatively high nitrogen content and a tough diffusion layer region having a low nitrogen content (first layer). The second layer), and by removing the first layer, the tough diffusion layer region (second layer) with a low nitrogen content can be used as the seat surface. It is thought that durability can be improved against fatigue accompanying impact.

  The present invention has been made on the basis of the above findings or findings by the inventors of the present invention. The nozzle body and the seat portion of the needle valve are made of nitriding alloy steel, and the compound layer is formed from the surface. Further, by removing the first layer of the diffusion layer, a fuel injection device for a diesel engine using a tough second layer with a low nitrogen content as a seat surface is provided.

  The present invention also provides a technique for expressing the second layer of the diffusion layer of nitride alloy steel on the surface. That is, it has not been conventionally performed as a method for observing the structure of steel, and provides an etching method that has been found for the first time by trial and error experiments by the inventors of the present application. A sheet surface made of nitrided alloy steel by separating the first layer and the second layer so as to be observable, determining a polishing amount necessary for exposing the second layer to the surface, and performing polishing by this polishing amount. A method of removing only the first layer of the compound layer and the diffusion layer from the surface and exposing the second layer to the surface is provided.

That is, the fuel injection device for a diesel engine described in claim 1 of the present invention is:
Fuel injection for a diesel engine that controls the fuel injection from the nozzle hole opened in the nozzle body by opening and closing the seat portion where the nozzle body and the needle valve contact by moving the needle valve inside the nozzle body to which fuel is supplied In the device
The portion of the nozzle body and the needle valve that is the seat portion is made of a nitriding alloy steel, and is a brittle and weak impact force compound layer on the outermost surface from the surface and a lower layer of the nitriding alloy steel. The first nitride on the surface side of the diffusion layer, which is easily damaged by repeated impact forces, is likely to precipitate hard nitrides having a relatively high nitrogen content on the surface side of the site where fatigue fracture occurs in the diffusion layer. After the layer is removed , the first layer inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is the lower layer of the first layer It is characterized by having two layers.

A fuel injection device for a diesel engine according to claim 2,
Fuel injection for a diesel engine that controls the fuel injection from the nozzle hole opened in the nozzle body by opening and closing the seat portion where the nozzle body and the needle valve contact by moving the needle valve inside the nozzle body to which fuel is supplied In the device
The portion of the nozzle body and the needle valve that is the seat portion is made of a nitriding alloy steel, and the surface of the nozzle body that becomes the seat portion is the outermost brittle compound layer that is weak against impact force and A hard nitride with a relatively high nitrogen content on the surface side of the site where fatigue fracture occurs in the diffusion layer of nitriding alloy steel, which is the lower layer, is likely to precipitate at the grain boundaries and within the grains, by repeated impact forces. Relatively nitrogen content in the site where fatigue fracture occurs in the diffusion layer of the alloy steel which is the lower layer of the first layer and is nitrided after the first layer on the surface side of the easily damaged layer is removed It is characterized by being the second layer inside the diffusion layer with little toughness .

The fuel injection device for a diesel engine described in claim 3 is the fuel injection device for a diesel engine according to claim 1 or 2,
The portion to be the sheet portion of the nozzle main body is a second layer of a diffusion layer whose surface roughness is smoothed by polishing at least less than Ra 0.4.

The method for manufacturing a fuel injection device for a diesel engine according to claim 4 comprises:
Fuel injection for a diesel engine that controls the fuel injection from the nozzle hole opened in the nozzle body by opening and closing the seat portion where the nozzle body and the needle valve contact by moving the needle valve inside the nozzle body to which fuel is supplied In the device manufacturing method,
The nozzle body and the needle valve are formed of alloy steel,
Next, the entire surface of the nozzle body and the needle valve is nitrided,
Next, the surface of the nozzle body and the portion of the needle valve that becomes the seat portion is polished to cause fatigue failure in the fragile and weak impact force compound layer on the outermost surface and the nitriding-treated alloy steel diffusion layer below it. Removing the first layer on the surface side of the diffusion layer on the surface side of the site where cracking occurs, where the relatively high nitrogen content and hard nitride are likely to precipitate at the grain boundaries and within the grains and are easily damaged by repeated impact forces , Leaving a second layer inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is a lower layer of the first layer ,
Next, the nozzle body and the needle valve are assembled.

The method for manufacturing a fuel injection device for a diesel engine according to claim 5 is the method for manufacturing a fuel injection device for a diesel engine according to claim 4,
A first layer of a diffusion layer is obtained by mirror-polishing a cross section of alloy steel, which is made of the same material as the nozzle body and the needle valve and is similarly nitrided, etching the cross section with 10% or more of nitric alcohol, and observing under a microscope. And determine the amount of polishing necessary to remove the first layer of the compound layer and the diffusion layer by polishing the surfaces of the nozzle body and the portion of the needle valve that becomes the seat portion. It is characterized by including the process to perform.

The valve device according to claim 6 is:
A valve which is provided in a fuel injection device for a diesel engine, and opens and closes a seat portion where the main body and the valve body are in contact with each other by moving the valve body inside the main body to which fuel is supplied from the inlet, thereby allowing the fuel to flow out from the outlet of the main body. In the device
The main body and the portion of the valve body that is the sheet portion are made of a nitrided alloy steel, and the diffusion of the nitrided alloy steel that is brittle and weak against impact force from the surface to the outermost surface and the nitrided alloy steel. The first layer on the surface side of the diffusion layer on the surface side of the portion where fatigue fracture occurs in the layer, where hard nitrides with a relatively high nitrogen content are likely to precipitate at the grain boundaries and within the grains and are easily damaged by repeated impact forces Is removed , and the second inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is the lower layer of the first layer . It is characterized by layers.

The valve device according to claim 7 is:
A main body in which a tapered main body sheet portion is formed at the inlet;
A valve body that is movably housed inside the main body and includes a valve body seat portion that contacts the main body seat portion and closes the inlet; and
An urging means provided inside the main body for closing the inlet by bringing the valve body sheet portion into contact with the main body sheet portion with a predetermined urging force;
Have
When the force acting on the valve body due to the fuel pressure at the inlet becomes greater than the biasing force relative to the force acting on the valve body due to the fuel pressure at the outlet, the valve body seat portion and the main body seat portion are separated from each other. The fuel moves from the inlet to the outlet,
When the force acting on the valve body due to the fuel pressure at the inlet is smaller than the sum of the force acting on the valve body due to the fuel pressure at the outlet and the biasing force, the valve body seat portion and the main body seat portion are Configured to contact and block the fuel flow path,
In a valve device provided in a fuel injection device for a diesel engine,
The main body sheet portion and the valve body sheet portion are made of nitriding alloy steel, and are fatigued in the diffusing layer of the nitriding alloy steel which is a brittle and weak impact force layer on the outermost surface and a lower layer thereof. The first layer on the surface side of the diffusion layer on the surface side of the site where the fracture occurs has a relatively high nitrogen content and hard nitrides are likely to precipitate at the grain boundaries and within the grains and are easily damaged by repeated impact forces. The second layer inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is the lower layer of the first layer. It is characterized by having.

  In the fuel injection device or valve device for a diesel engine of the present invention, the nitrided alloy steel applied to the nozzle body (or body) and the needle valve (or valve body) is the outermost compound layer and the lower layer thereof. It has the 1st layer of a diffusion layer, and also the 2nd layer provided with the toughness in the lower layer. However, the boundary between the first layer and the second layer of the diffusion layer cannot be confirmed by etching with about 3% (about 3 to 5%) nitrate alcohol, which has been used for observation of the structure of conventional steel. In the method for measuring the nitrided layer depth of steel specified in JIS G 0562, a method for measuring the nitrided layer depth by etching using about 3% nitrate alcohol by a metallographic test is specified. There are only two definitions, depth and diffusion layer depth, and there is no recognition of the presence of the second layer. Of course, this measurement method cannot separate the boundary between the first layer and the second layer of the diffusion layer.

  However, according to the method of the present invention, using a nitrate alcohol of 10% or more, for example, about 15%, the cross section of the nitrided alloy steel is etched in an ultrasonic cleaner for several tens of seconds, and then the cross section is scanned. By observing with an electron microscope, the boundary between the first layer and the second layer of the diffusion layer can be separated.

  Therefore, when analyzing a conventional damaged product, the fatigue fracture of the sheet portion occurs at a specific part of the diffusion layer, which hits the boundary between the first layer on the surface side of the diffusion layer and the second layer inside. I was able to confirm. Therefore, the seat portion of the fuel injection device or valve device for a diesel engine of the present invention measures the depth of the first layer by the above-described method, determines the polishing amount based on the measurement result, and is nitrided alloy steel. A portion corresponding to the sheet portion can be removed by polishing by a determined polishing amount, and only the tougher second layer can be exposed on the surface and used.

  Thus, according to the fuel injection device or valve device for a diesel engine of the present invention, the material of the nozzle body (or the body) and the needle valve (or valve body) is made of nitriding alloy steel, and the compound layer is further formed from the surface. Since the first layer of the diffusion layer is removed, the second layer having high toughness becomes a sheet portion, and durability can be increased against fatigue accompanied by an impact when the nozzle is closed (when the valve body is moved). . That is, wear resistance and fatigue resistance are improved, and by reducing the frictional force, the shear stress near the surface when seated can be reduced, and spalling of the seat portion of the nozzle body (or body) can be generated. Can be prevented.

  By reducing the wear and damage of the seat portion of the fuel injection device for a diesel engine or the valve device, it is possible to prevent a change in injection characteristics over time or fuel leakage due to a defective seat. Aged deterioration of injection characteristics and fuel leakage due to defective seats deteriorate engine performance (especially exhaust gas components), but according to the present invention, by improving the durability of the seat portion of the fuel injection nozzle or valve device The engine performance can be maintained for a long time. Accordingly, the replacement period of the fuel injection device or the device assembly can be extended, and the cost for replacement can be reduced.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a sectional view of a diesel engine fuel injection device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the processing steps of the nozzle body of the fuel injection device for diesel engines of the embodiment, FIG. 3 is a cross-sectional view showing the processing steps of the needle valve of the fuel injection device for diesel engines of the embodiment, FIG. FIG. 2 is an electron micrograph showing a nitrided layer form of nitrided alloy steel (SKD61), which is a material for the fuel injection device for a diesel engine of the same embodiment.
FIG. 5 is a schematic diagram showing an outline of a reciprocating wear test applied to each material of the embodiment and the comparative example, FIG. 6 is a diagram showing an outline of a seizure test in the reciprocating wear test, and FIG. It is a figure which shows the point of the sliding speed fluctuation | variation test in an abrasion test.
FIG. 8 is a diagram comparing the frictional forces of the respective materials of the embodiment and the comparative example obtained in the reciprocating wear test, and FIG. 9 is a view showing an external appearance photograph of the test piece of the comparative example after the reciprocating wear test. FIG. 10 is a view showing an appearance photograph of the test piece of the embodiment after the reciprocating wear test, FIG. 11 is a view showing an appearance photograph of the test piece of the embodiment after the reciprocating wear test, and FIG. It is a figure which shows the external appearance photograph of the test piece of the embodiment after the reciprocating wear test.
FIG. 13 is a cross-sectional view of a valve device that is another embodiment of the present invention and that is applied to a fuel injection device for a diesel engine as a check valve, a relief valve, or the like.

1. Structure of Fuel Injection Device for Diesel Engine of Embodiment (FIG. 1)
As shown in FIG. 1, the fuel injection device for a diesel engine of this example includes a nozzle body 1 (nozzle body) to which fuel is supplied and a needle valve 2 that is movable inside the nozzle body 1.

  The nozzle body 1 is a tapered substantially cylindrical block body, and a guide hole 3 for a needle valve 2 is formed at the center of the base end portion. The tip of the guide hole 3 is a fuel reservoir 4 having an enlarged diameter, and fuel is supplied from the outside into the fuel reservoir 4 through the fuel supply hole 5. Further, a tapered seat portion 6 is formed at the tip of the fuel reservoir 4. A small-diameter hole 7 communicating with the fuel reservoir 4 is formed further ahead of the seat portion 6, and a nozzle hole 8 formed in communication with the outside is provided in the wall portion of the hole 7. .

  The needle valve 2 is formed integrally with the base 10 having a round bar-like base 10 (needle diameter φD) slidably held in the guide hole 3 of the nozzle body 1 and a smaller diameter than the inner diameter of the fuel reservoir 4. The tip has a round bar-like tip portion 12 (sheet diameter φd <D) in which a tapered sheet portion 11 that contacts the sheet portion 6 of the nozzle body 1 is formed.

  The needle valve 2 is urged with a load W by an urging means such as a spring in a direction in which the seat portion 11 abuts on the seat portion 6 of the nozzle body 1, and in a state where no external force is applied, the needle valve 2 The sheet portion 11 is in contact with the sheet portion 6 of the nozzle body 1 to close the space between the sheet portions 6 and 11 and the fuel reservoir 4 and the nozzle hole 8 are blocked. At the time of fuel injection, fuel of a predetermined pressure is supplied from the fuel supply hole 5 into the fuel reservoir 4, and the needle valve 2 receives force due to the increase in internal pressure and is guided upward by the guide hole 3 to move upward. 11 is opened, and fuel is injected from the nozzle hole 8 to the outside.

2. Manufacturing process (FIGS. 2 to 4)
In the diesel engine fuel injection nozzle of this example, the nozzle body 1 and the needle valve 2 are made of a material obtained by nitriding the surface of SKD61 or similar steel under predetermined conditions. Since the nozzle body 1 is required to have high strength, impact resistance, and wear resistance at the same time, it cannot be replaced with metal materials other than steel, and alloys such as Al, Cr, Mo, V, Ti, etc., that form stable nitrides are alloyed. The steel which has as a component is preferable. After forming the nozzle body 1 and the needle valve 2 with the SKD 61, the nozzle body 1 and the needle valve 2 are nitrided, and the first layer of the compound layer and the diffusion layer is removed by polishing in each of the sheet portions 6 and 11 of the nozzle body 1 and the needle valve 2. The tough second layer is used as the sheet portions 6 and 11.

  That is, in FIGS. 2 and 3 showing the nitriding polishing step, the C and D portions are the sheet portions 6 and 11, and the first layer is removed after nitriding. In polishing the sheet portion, the surface roughness of the finished surface composed of the second layer is reduced to make the surface smoother. For example, it is preferable that the surface roughness is smoothed with less than Ra0.4 by polishing with sandpaper of about # 800. By adopting such a surface finish, it is possible to reduce the influence on the friction of carbides and the like precipitated from the material and lower the friction coefficient.

  2 and 3 showing the nitriding polishing step, the portions B, E, and F are polished because they are functionally necessary, but there is no problem if the first layer remains. Part A plays a role of a stopper when the injection valve is opened, so that a large impact is generated. Since the nitride layer is peeled off by the impact, both the first layer and the second layer are completely removed from the A portion nitride layer. The G portion is nitrided in a conical shape as shown in FIG. 3A for processing reasons, but finally the conical portion is cut and removed as shown in FIG. 3B. In addition, about A part and G part, processing changes with processing equipment and a processing method.

  In each of the sheet portions 6 and 11, the compound layer and the first layer of the diffusion layer are removed by polishing and the tough second layer is left as a sheet portion. In the polishing step, the first layer and the second layer of the diffusion layer are formed. It is necessary to clearly recognize the boundary and to determine the polishing amount (thickness to be polished). In other words, depending on the type of steel used and the nitriding conditions, the nitriding situation on the surface differs, and it is confirmed beforehand by experiments and observations how far the boundary between the first layer and the second layer of the diffusion layer is from the surface. In the manufacturing process, it is necessary to polish the second layer on the surfaces of the sheet parts 6 and 11 by polishing to that extent.

  The boundary between the first layer and the second layer in this diffusion layer cannot be confirmed by etching with the usual 5% nitric acid alcohol defined in the above-mentioned JIS or the like. According to the knowledge obtained through trial and error experiments by the present inventors, a predetermined type of steel whose surface is nitrided under predetermined conditions is cut perpendicularly to the surface to represent a cross section, which is about 10% or more, Preferably, about 15% nitrate alcohol is used and etching is performed in an ultrasonic cleaner for several tens of seconds. By observing the cross section with a scanning electron microscope, the boundary between the first layer and the second layer can be confirmed. Become.

  FIG. 4 is an electron micrograph showing the form of the nitrided layer on the surface of alloy steel (SKD61) employed as a material for the fuel injection device for a diesel engine of this example. In this figure, each white bar (micron bar) at the bottom of the photograph represents 200 μm. The compound layer is about 10 μm on the surface, and the black layer on the surface corresponds to this. By observing the surface nitrided layer in such a cross section, the polishing amount (dimension) necessary for removing the compound layer and the first layer to represent the second layer is determined.

  In this example, the purpose of nitriding the steel surface is to increase the hardness, and other special steels cannot obtain the necessary hardness in light of the purpose of this example. In addition, considering wear resistance, adhesion between steel and steel tends to occur and wear is faster, but contact between nitride and steel or nitrided steel is less likely to cause adhesion, and the coefficient of friction is lower. It is low and has the advantage of slow wear. Further, even the second layer is a nitrided layer, and therefore has a sufficient hardness as compared with other non-nitrided steels. Further, if the friction coefficient is lowered, there is an advantage that the shearing force due to the friction of the surface is reduced and the spalling resistance is improved.

  In SKD61 adopted in this example, the precipitated carbide appears on the surface, but compared to SKH51, which is a conventionally adopted material, SKD61 is a small and rounded carbide and has less damage such as wear against the counterpart material. On the other hand, the carbide of SKH51 is large and angular, and damage to the mating material is large. In this example, not only the nozzle body 1 but also the needle valve 2 side is nitrided to reduce the friction coefficient, so that the spalling and wear resistance are improved, and as described above, the surface roughness is reduced. By smoothing, the effect on friction of precipitated carbides and the like is reduced.

3. Reciprocating wear test (Figs. 5-12)
(1) Test method (FIGS. 5 to 7)
In order to confirm the effect of the fuel injection device for a diesel engine of this example manufactured as described above, a test piece made of the same material as that used for the nozzle body 1 and the needle valve 2 in this example is prepared, The test piece for comparison is subjected to a reciprocating wear test, and the results are compared.

  As shown in FIG. 5, in the reciprocating wear test, a pin test piece whose tip shape is a spherical surface having a radius of 50 mm is brought into contact with the upper surface of a plate-shaped test piece having a predetermined size (14 × 10 × 115 mm) with a predetermined load. The pin test piece is reciprocated with a stroke of 100 mm along the longitudinal direction of the plate-like test piece while lubricating oil is dripped at 9 ml / h onto the sliding area of the upper surface of the plate-like test piece.

FIG. 6 shows an outline of the seizure test in which the test is continued while increasing the load as the test time elapses until scuffing is generated by this reciprocating wear test method. The test conditions are as follows.
Test load: Step up by holding 5kgf / 5min and load up to 100kgf.
Test temperature: plate test piece heating temperature constant 150 ° C, lubricant container is at room temperature Average sliding speed: 1.5 m / s
Stroke: 100mm
Lubricating oil dripping amount: 9 ml / h
Lubricating oil: MARINE T204 manufactured by Nippon Oil Corporation

The material and surface treatment of the test piece used for the test are as follows.
Plate test piece: SKD61 nitridation polishing, SKD61 nitridation polishing and # 800 polishing finish.
Pin test piece: SKD61, SKD61 two types of polishing after nitriding.

FIG. 7 shows in more detail the sliding speed variation mode and the load step-up mode of the sliding operation of the pin test piece with respect to the plate test piece in the seizure test shown in FIG.
That is, after starting, the sliding speed is set to 0.02 m / s, and the load is set to 5 kgf and held for several cycles (a). Next, speed up to 1.5 m / s and hold for 5 minutes (b). Next, it is lowered to 0.02 m / s and held for several cycles (c). Next, the load is stepped up to 10 kgf and then held for several cycles (d). Thereafter, the load is similarly stepped up to 100 kgf (e).

(2) Test results (FIGS. 8 to 12)
FIG. 8 shows the results of a seizure test performed using two types of pin test pieces, SKD61 and SKD61 post-nitridation polishing, and using SKD61 post-nitridation polishing and adding # 800 polishing finish as plate test pieces. . This result shows that the friction force is consistently low until the load reaches 100 kgf when using a pin that has been nitrided and polished, compared to the case where the pin is not nitrided.

Appearance photographs of the pin test piece and the plate test piece after the sliding speed variation test are shown in FIGS.
As shown in FIG. 9, the combination of the pin test piece SKD61 without nitriding treatment and the plate test piece SKD61 post-nitriding polishing is worn so that the spherical surface of the pin test piece disappears completely.

  On the other hand, in the combination of the pin test piece SKD61 post-nitriding polishing and the plate test piece SKD61 post-nitridation polishing, a small wear mark is observed at the center of the spherical surface of the pin test piece as shown in FIG. Degree. This indicates that seizure is eliminated by polishing the pin specimen after nitriding.

  Further, in the case where the pin test piece SKD61 is not subjected to nitriding treatment and the plate test piece SKD61 is polished after nitriding and the surface roughness is prototyped by # 800 polishing finish, as shown in FIG. It can be seen that the seizure is reduced and the state is improved as compared with.

  Furthermore, in the combination of the pin test piece SKD61 nitridation polishing, the plate test piece SKD61 nitridation polishing and the surface roughness prototyped by # 800 polishing finish, as shown in FIG. Good results were obtained.

  Although not shown, according to the shape measurement result of the pin test piece after the test, the surface roughness was prototyped by polishing after the pin test piece SKD61 nitriding treatment, polishing after the plate test piece SKD61 nitriding, and # 800 polishing finish. The combination had the least amount of wear.

The result of measuring the size (diameter) of the wear mark of the pin test piece after the sliding speed variation test will be described.
The combination of no pin test piece SKD61 nitriding treatment and plate test piece SKD61 polishing after nitriding is galling at a load of 30 kgf, so the wear trace is 7.81 mm, which is almost the same as the outer diameter of the pin test piece. (Corresponding to FIG. 9).

  Next, in the combination of no pin test piece SKD61 nitriding treatment and polishing after plate test piece SKD61 nitriding and # 800 polishing finish, the wear mark width in the sliding mark direction is 1.51 mm and 1.58 mm in two tests. The results are almost the same (corresponding to FIG. 11).

  Next, in the combination of the pin test piece SKD61 nitriding treatment and the plate test piece SKD61 nitriding polish, the wear mark width in the sliding mark direction is 1.54 mm, and the pin test piece SKD61 is not nitrided. In comparison, the result is good (corresponding to FIG. 10).

  Further, in the combination of the pin test piece SKD61 after nitriding treatment, the plate test piece SKD61 after nitriding polishing and the surface roughness produced by # 800 polishing, the wear mark width in the sliding mark direction is 1.44 mm, and 1. 43 mm and almost the same result in the two tests, which is a better result than the pin test piece SKD61 without nitriding (corresponding to FIG. 12).

  From the above results, it was found that by nitriding and polishing both the pin test piece and the plate test piece, the frictional force can be reduced and the wear resistance can be improved. It has also been found that wear resistance is further improved by reducing the surface roughness of the test piece.

  From these results, in the fuel injection device for a diesel engine, at least each sheet portion of the nozzle body and the needle valve is nitrided, and both the nitrided sheet portions of the nozzle body and the needle valve are polished together to form the second layer of the diffusion layer. Good results are obtained if it is expressed or at least the sheet portion of the nozzle body is polished to represent the second layer of the diffusion layer.

  In addition to removing the first layer of the compound layer and the diffusion layer by polishing to prevent spalling from the nitrided surface, if the surface of the sheet representing the second layer is further polished, The influence of the precipitated carbides on the friction is reduced, the surface roughness is reduced, and the friction coefficient is lowered, so that a better result can be obtained.

4). Effect of Embodiment The wear state of the seat portion after the fuel injection device for a diesel engine of this example and the conventional product were mounted on a diesel engine and used was compared.
In the diesel engine fuel injection device of this example, the nozzle body and the seat portion of the needle valve are polished after SKD61 nitriding to remove the first layer of the compound layer and the diffusion layer.
In the conventional product, the nozzle body is SKD61 and the needle valve is SKH51 (the nozzle body is nitrided).
When used under the same conditions, the wear of the conventional product was 3 to 4 μm, whereas in this example, the wear was reduced to 2 μm.

  In the embodiment described above, after nitriding the entire surfaces of the nozzle body 1 and the needle valve 2 made of alloy steel, the compound layer and the diffusion layer are formed from the surfaces of both the sheet portions 6 and 11 of the nozzle body 1 and the needle valve 2. By removing one layer, the effects as described above were obtained. However, only the sheet parts 6 and 11 of the nozzle body 1 and the needle valve 2 are made of alloyed steel, and other parts of the nozzle body 1 and the needle valve 2 are made of other metal materials at a low cost. Good. Further, each of the sheet parts 6 and 11 of the nozzle body 1 and the needle valve 2 is made of an alloyed steel, and the first layer of the compound layer and the diffusion layer is removed from the surface of the sheet part 6 of the nozzle body 1, Even if only the compound layer is removed from the surface of the seat portion 11 of the needle valve 2, an effect of making it difficult to generate wear or spalling in the seat portion 6 of the nozzle body 1 that tends to cause a problem in durability in particular. .

5. Other embodiment (FIG. 13)
The embodiment described above relates to the nozzle portion in which fuel injection is performed in the fuel injection device for diesel engines, but the valve device of this example is provided in the fuel system of the fuel injection device for diesel engines, It can be used as a check valve (suction valve, discharge valve, isobaric valve) for a pump that pumps fuel, a relief valve (safety valve) that operates so that the pressure does not exceed a certain value.

The structure of this valve device will be described.
A main body 21 of the valve device has an inlet 23 through which fuel flows and an outlet 24 through which fuel flows out. The inlet 23 and the outlet 24 communicate with each other through an internal space 25, and the inlet 23 has a tapered shape. A main body sheet portion 26 is formed. A valve body 22 is movably accommodated in a space 25 inside the main body 21. At one end of the valve body 22 on the inlet 23 side, a tapered valve body seat portion 27 that contacts the main body seat portion 26 and closes the inlet 23 is provided. And in the space 25 of the main body 21, between the outlet 24 and the receiving part 28 provided in the other end part of the valve body 22, the valve body 22 is pressed toward the inlet 23 with a predetermined urging force. A spring 29 is provided as an urging means. When the fuel pressure on the inlet 23 side is small as will be described later, the valve body seat portion 27 is brought into contact with the main body seat portion 26 by the spring 29 and the inlet 23 is pressed. 23 is configured to be closed. In addition, in this example, although the valve body sheet | seat part 27 is made into the taper shape, shapes other than this, for example, planar shape, may be sufficient.

The relationship between the biasing force of the spring 29 and the fuel pressure is set as follows.
That is, when the force that the fuel pressure at the inlet 23 gives to the valve body 22 becomes larger than the force that the fuel pressure at the outlet 24 gives to the valve body 22 by a difference greater than the biasing force of the spring 29, the valve body 22 Regardless of the urging force of the valve, it is pushed back to the outlet 24 side (downward in the figure), the valve seat part 27 and the main body seat part 26 are separated to form a gap, and the fuel moves from the inlet 23 to the outlet 24 through the gap. To do.

  When the force that the fuel pressure at the inlet 23 gives to the valve body 22 becomes smaller than the sum of the force that the fuel pressure at the outlet 24 gives to the valve body 22 and the urging force of the spring 29, the valve body 22 moves toward the inlet 23 (upper side in the figure). ), The valve body seat portion 27 and the main body seat portion 26 come into contact with each other, and the fuel flow path is blocked. Since the valve body 22 collides with the main body 21 at this time, each seat portion is worn in the conventional structure. In this example, the following means for solving the wear are taken.

  That is, the main body sheet part 26 and the valve body sheet part 27 are made of nitriding alloy steel, and the first layer of the compound layer and the diffusion layer is removed from the surface thereof. Since the material, manufacturing method, microscopic structure, property, modification and the like of both the seat portions are the same as those of the above-described diesel engine fuel injection device, the description thereof is incorporated.

  In the conventional product, carburizing material of SCM420 was applied to the main body of the valve device, and SUJ2 or the like was applied to the valve body. Therefore, the seat portion was worn, but by configuring as in this example, the seat portion Wear can be reduced and product life can be extended.

FIG. 1 is a sectional view of a diesel engine fuel injection device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the processing steps of the nozzle body 21 of the fuel injection device for a diesel engine according to the embodiment. FIG. 3 is a cross-sectional view showing the processing steps of the needle valve of the diesel engine fuel injection device of the embodiment. FIG. 4 is an electron micrograph showing a nitrided layer form of nitrided alloy steel (SKD61) which is a material of the fuel injection device for a diesel engine of the embodiment. FIG. 5 is a schematic diagram showing an outline of a reciprocating wear test applied to each material of the embodiment and the comparative example. FIG. 6 is a diagram showing a point of a seizure test in the reciprocating wear test. FIG. 7 is a diagram showing a point of a sliding speed variation test in the reciprocating wear test. FIG. 8 is a diagram comparing the frictional forces of the respective materials of the embodiment and the comparative example obtained in the reciprocating wear test. FIG. 9 is a view showing an appearance photograph of a test piece of a comparative example after the reciprocating wear test. FIG. 10 is a view showing an appearance photograph of the test piece of the same embodiment after the reciprocating wear test. FIG. 11 is a view showing an appearance photograph of the test piece of the same embodiment after the reciprocating wear test. FIG. 12 is a view showing an appearance photograph of the test piece of the same embodiment after the reciprocating wear test. FIG. 13 is another embodiment of the present invention, and is a cross-sectional view of a valve device applied as a check valve, a relief valve or the like to a diesel engine fuel injection device.

Explanation of symbols

1 Nozzle body (nozzle body) of fuel injection system for diesel engines
2 Needle valve of fuel injection device for diesel engine 3 Guide hole 4 Fuel reservoir 5 Fuel supply hole
6 Nozzle body seat 8 Nozzle hole 10 Needle valve base 11 Needle valve seat 12 Needle valve tip 21 Valve device body 22 Valve device valve body 23 Inlet 24 Outlet 26 Main body seat portion 27 Valve body seat portion 29 Spring as biasing means

Claims (7)

Fuel injection for a diesel engine that controls the fuel injection from the nozzle hole opened in the nozzle body by opening and closing the seat portion where the nozzle body and the needle valve contact by moving the needle valve inside the nozzle body to which fuel is supplied In the device
The portion of the nozzle body and the needle valve that is the seat portion is made of a nitriding alloy steel, and is a brittle and weak impact force compound layer on the outermost surface from the surface and a lower layer of the nitriding alloy steel. The first nitride on the surface side of the diffusion layer, which is easily damaged by repeated impact forces, is likely to precipitate hard nitrides having a relatively high nitrogen content on the surface side of the site where fatigue fracture occurs in the diffusion layer. After the layer is removed , the first layer inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is the lower layer of the first layer A fuel injection device for a diesel engine, characterized in that it has two layers. Fuel injection for a diesel engine that controls the fuel injection from the nozzle hole opened in the nozzle body by opening and closing the seat portion where the nozzle body and the needle valve contact by moving the needle valve inside the nozzle body to which fuel is supplied In the device
The portion of the nozzle body and the needle valve that is the seat portion is made of a nitriding alloy steel, and the surface of the nozzle body that becomes the seat portion is the outermost brittle compound layer that is weak against impact force and A hard nitride with a relatively high nitrogen content on the surface side of the site where fatigue fracture occurs in the diffusion layer of nitriding alloy steel, which is the lower layer, is likely to precipitate at the grain boundaries and within the grains, by repeated impact forces. Relatively nitrogen content in the site where fatigue fracture occurs in the diffusion layer of the alloy steel which is the lower layer of the first layer and is nitrided after the first layer on the surface side of the easily damaged layer is removed A fuel injection device for a diesel engine, characterized by being a second layer inside a diffusion layer with little toughness . The seat portion and becomes part of the nozzle body, according to claim 1 or 2 surface roughness by polishing, characterized in that said second layer of diffusion layer being a smoothness of less than at least Ra0.4 Fuel injection system for diesel engines. Fuel injection for a diesel engine that controls the fuel injection from the nozzle hole opened in the nozzle body by opening and closing the seat portion where the nozzle body and the needle valve contact by moving the needle valve inside the nozzle body to which fuel is supplied In the device manufacturing method,
The nozzle body and the needle valve are formed of alloy steel,
Next, the entire surface of the nozzle body and the needle valve is nitrided,
Next, the surface of the nozzle body and the portion of the needle valve that becomes the seat portion is polished to cause fatigue failure in the fragile and weak impact force compound layer on the outermost surface and the nitriding-treated alloy steel diffusion layer below it. Removing the first layer on the surface side of the diffusion layer on the surface side of the site where cracking occurs, where the relatively high nitrogen content and hard nitride are likely to precipitate at the grain boundaries and within the grains and are easily damaged by repeated impact forces , Leaving a second layer inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is a lower layer of the first layer ,
Next, the method for producing a fuel injection device for a diesel engine, wherein the nozzle body and the needle valve are assembled. Said nozzle body and said needle valve as well as nitriding treated alloy steel of the cross-section of the same material was mirror-polished, the first diffusion layer was observed with a microscope after the the cross section was etched with a 10% or more of nitric acid alcohol check the boundary of the the layer second layer, required to remove the first layer of the compound layer and the diffusion layer by polishing the surface of the portion serving as the seat of the nozzle body and the needle valve 5. The method for manufacturing a fuel injection device for a diesel engine according to claim 4, further comprising a step of determining a polishing amount. A valve which is provided in a fuel injection device for a diesel engine, and opens and closes a seat portion where the main body and the valve body are in contact with each other by moving the valve body inside the main body to which fuel is supplied from the inlet, thereby allowing the fuel to flow out from the outlet of the main body. In the device
The main body and the portion of the valve body that is the sheet portion are made of a nitrided alloy steel, and the diffusion of the nitrided alloy steel that is brittle and weak against impact force from the surface to the outermost surface and the nitrided alloy steel. The first layer on the surface side of the diffusion layer on the surface side of the portion where fatigue fracture occurs in the layer, where hard nitrides with a relatively high nitrogen content are likely to precipitate at the grain boundaries and within the grains and are easily damaged by repeated impact forces Is removed , and the second inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is the lower layer of the first layer . A valve device characterized by being a layer. A main body in which a main body sheet portion is formed at the inlet;
A valve body that is movably housed inside the main body and includes a valve body seat portion that contacts the main body seat portion and closes the inlet; and
An urging means provided inside the main body for closing the inlet by bringing the valve body sheet portion into contact with the main body sheet portion with a predetermined urging force;
Have
When the force acting on the valve body due to the fuel pressure at the inlet becomes greater than the biasing force relative to the force acting on the valve body due to the fuel pressure at the outlet, the valve body seat portion and the main body seat portion are separated from each other. The fuel moves from the inlet to the outlet,
When the force acting on the valve body due to the fuel pressure at the inlet is smaller than the sum of the force acting on the valve body due to the fuel pressure at the outlet and the biasing force, the valve body seat portion and the main body seat portion are Configured to contact and block the fuel flow path,
In a valve device provided in a fuel injection device for a diesel engine,
The main body sheet portion and the valve body sheet portion are made of nitriding alloy steel, and are fatigued in the diffusing layer of the nitriding alloy steel which is a brittle and weak impact force layer on the outermost surface and a lower layer thereof. The first layer on the surface side of the diffusion layer on the surface side of the site where the fracture occurs has a relatively high nitrogen content and hard nitrides are likely to precipitate at the grain boundaries and within the grains and are easily damaged by repeated impact forces. The second layer inside the diffusion layer having a relatively low nitrogen content and toughness inside the site where fatigue fracture occurs in the diffusion layer of the alloyed steel that is the lower layer of the first layer. A valve device characterized by that.