JP5540475B2 - Fuel injection valve using high pressure injection parts - Google Patents

Description

The present invention relates to a fuel injection valve using a high-pressure jetting unit products having excellent erosion resistance.

  An outline of a common rail fuel injection system is shown in FIG. As shown in the figure, in this system, the fuel in the fuel tank 21 is supplied to the high-pressure pump 24 via the filter 22 and the feed pump 23, and is increased to a high pressure (several tens to several hundred MPa) by the high-pressure pump 24. After the pressure is increased, the pressure is supplied to a pressure accumulating container called a common rail 26 through a passage 25. The fuel in the common rail 26 is supplied to each fuel injection valve (injector) 28 through a fuel supply passage 27.

  As shown in FIG. 20, a part of the high-pressure fuel supplied to each fuel injection valve 28 is supplied to the pressure control chamber 30 via the passage 29, and the rest is the tip of the needle valve 32 via the passage 31. Is supplied to the fuel reservoir 33 on the side. The fuel pressure in the pressure control chamber 30 is held and released by the relief valve 34. The relief valve 34 is normally pressed by the spring 35 to close the relief hole 36, holds the fuel pressure in the pressure control chamber 30, and is lifted against the spring 35 when the electromagnetic solenoid 37 is energized to open the relief hole 36. The fuel pressure in the pressure control chamber 30 is released. The needle valve 32 is always urged downward by a spring 38.

  In the fuel injection valve 28, when the electromagnetic solenoid 37 is turned off, the relief hole 36 is closed by the relief valve 34 pushed down by the spring 35, and the fuel pressure in the pressure control chamber 30 is maintained. The lowering force of the needle valve 32 by 38 becomes larger than the raising force of the needle valve 32 due to the fuel pressure of the pressure receiving portion 39 on the tip side (fuel reservoir 33) of the needle valve 32, and the needle valve 32 is lowered. Therefore, the conical portion 40 at the tip of the needle valve 32 is seated on the seat portion 41, the injection hole 42 of the fuel injection valve 28 is closed, and fuel is not injected.

  When the electromagnetic solenoid 37 is energized, the relief valve 34 is pulled up against the spring 35, the relief hole 36 is opened, and the fuel pressure in the pressure control chamber 30 is released (relief). The ascending force of the needle valve 32 due to the fuel pressure of the pressure receiving portion 39 on the front end side (the fuel reservoir 33) becomes larger than the descending force of the needle valve 32 due to the spring 38, and the needle valve 32 rises. Therefore, the conical portion 40 of the needle valve 32 is separated from the seat portion 41, and high-pressure fuel is injected from the injection hole 42 of the fuel injection valve 28. The fuel that has flowed out of the pressure control chamber 30 returns to the fuel tank 21 through the fuel recovery passage 43 (see FIG. 19).

  Such a pressure balance type fuel injection valve is also described in Patent Document 1 and the like.

JP 2000-320419 A

  By the way, in the fuel injection valve 28 described above, when used at an injection pressure of 200 MPa or more, the seat surface of the valve seat portion 44 (see FIG. 20) in which the relief hole 36 is formed is radially broken (erosion) from the inner peripheral side. It progresses and the amount of static leak increases. When radial erosion reaches the outer periphery of the seat surface of the valve seat portion 44, the sum of the pump discharge amount and the leak amount and the injection amount exceeds, and the fuel injection valve 28 becomes unusable. The cause is cavitation.

  A negative pressure is generated at a portion where the flow is separated, thereby causing boiling under reduced pressure to form bubbles (fuel vapor). Next, when the bubbles enter the downstream high pressure region, they rapidly disappear, and a shock wave is generated at this time. When this shock wave is repeatedly generated, fatigue failure (erosion) occurs on the metal surface.

  Here, the cavitation coefficient is expressed by the following formula (1), and is generally used as an index indicating that cavitation is likely to occur as the coefficient decreases.

In equation (1), K is a cavitation coefficient, P _∞ is a pressure in a uniform flow, P _ν is a saturated vapor pressure, ρ is a density, and V is a velocity in a uniform flow.

In the case of the fuel injection valve 28 of the pressure balance type, it is necessary to release the fuel pressure in the pressure control chamber 30 to the low pressure side when fuel is injected. The flow rate within is determined. Therefore, when the injection pressure is increased, an increase in the dynamic pressure term (the denominator of Equation (1)) is unavoidable, and cavitation tends to occur. The area of the seat surface of the valve seat portion 44 (an orifice seat diameter) is also limited by the thrust of the actuator for driving the relief valve 3 4 (electromagnetic solenoid 37), enlargement of the consideration of the actuator mounting property It is a difficult situation. Therefore, in order to suppress the load relief valve 3 4 is subjected by receiving the injection pressure even when high pressure in the present level, the relief hole 36 should be downsized. As a result, the flow velocity in the relief hole 36 tends to further increase.

  As shown in FIG. 18, the cavitation coefficient increases (the cavitation is less likely to occur) as the injection pressure is reduced. Generally, erosion does not occur at a low pressure of about 160 MPa. Even if a hard coating such as CrN or DLC (diamond-like coating) is formed on the seat surface of the valve seat 44 in order to improve durability at a high pressure, radial destruction occurs in about 2 hours at an injection pressure of 300 MPa. It reaches the outer periphery of the seat surface of the valve seat portion 44.

An object of the present invention is to provide a suitable fuel injection valve to the high pressure injection.

In order to achieve the above object, the present invention lifts a valve body, which is pushed down by receiving the fuel pressure of a high-pressure fuel in a pressure control chamber provided in a nozzle body, by relieving the fuel pressure through a relief passage. A fuel injection valve, comprising: a high pressure injection component comprising a valve seat portion having a relief hole for releasing the fuel pressure in the pressure control chamber and a seat surface formed around an outlet of the relief hole; The injection component includes a pillar, and an inner diameter of the relief hole formed along the axial direction is smaller than an inner diameter of the relief passage, and an upper surface is formed around an outlet of the relief hole, and the high pressure The injection component is mounted on the nozzle body so that the relief hole forms an outlet of the relief passage and the upper surface forms the seat surface, Corner between the upper and outer surfaces for the propensity are chamfered, the parts for high pressure injection, each alumina and yttria sintering aid to the silicon nitride powder to silicon nitride powder 10 mass% It is made of silicon nitride ceramics obtained by adding the following to form a molded body, and heating and sintering the molded body at 1750 to 1850 ° C. in a nitrogen atmosphere of 5 to 10 MPa, and the silicon nitride ceramic has four-point bending strength. Is 980 MPa or more.

Here, the silicon nitride ceramics may have an aspect ratio of sintered silicon nitride particles of 1.8 or more and a particle volume of 0.1 μm ³ or less.

  Here, the high-pressure injection component may be press-fitted into the nozzle body.

According to the present invention, an excellent effect of being able to obtain a suitable fuel injection valve to the high pressure injection.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  The high-pressure injection component according to the present embodiment has a passage through which high-pressure fluid flows, and a silicon nitride particle is added with a sintering aid to form a molded body, and the nitride obtained by sintering the molded body It consists of silicon ceramics, and the silicon nitride ceramics has a four-point bending strength of 980 MPa or more.

Here, the silicon nitride ceramics preferably has a sintered silicon nitride particle having an aspect ratio of 1.8 or more and a particle volume of 0.1 μm ³ or less.

  By using this silicon nitride ceramics, it is possible to obtain a high-pressure injection part having excellent erosion resistance and wear resistance.

In order to set the aspect ratio of the sintered silicon nitride particles to 1.8 or more and the particle volume to 0.1 μm ³ or less, the silicon nitride powder used for molding has an average particle size of 1.0 μm or less. Preferably use particles of 0.5 μm or less.

  Here, the particle volume after sintering is obtained by observing the sintered body with a scanning electron microscope (SEM), extracting the silicon nitride particles from the photographed image using image software, and obtaining the size of the minor axis and the major axis. To determine the particle volume and aspect ratio.

That is, since the silicon nitride particles are hexagonal columnar crystals, this is regarded as a cylinder, the short diameter is the diameter, the long diameter is the height,
Particle volume = (square of minor axis) ÷ 4 × π × major axis, and the aspect ratio is
The aspect ratio is determined by the major axis / minor axis.

Silicon nitride (Si ₃ N ₄ ) is obtained by using metal silicon powder as a raw material and heating it to 1450 ° C. for a long time in a nitrogen atmosphere, and by reacting a metal silicon compact with nitrogen. It can be obtained by pulverizing the molded body.

  In general, low-grade particles are distributed with a particle size of around 50 μm, and the maximum particle size is coarse particles of 100 μm. However, high-quality silicon nitride has a particle distribution of 0.5% or less with a purity of 99% or more. A relatively complete ultrafine powder is commercially available.

To this silicon nitride (Si ₃ N ₄ ) powder, a sintering aid such as alumina or yttria is added to the silicon nitride powder in an amount of 10 mass% or less to form a granulated powder, which is filled into a rubber mold, A silicon nitride ceramic is obtained by forming a molded body having a desired shape by hot isostatic pressing and then heating and sintering at 1750 ° C. to 1900 ° C. in a nitrogen atmosphere of 1 to 10 MPa.

Here, when the aspect ratio of the sintered silicon nitride particles is 1.8 or more and the particle volume is 0.1 μm ³ or less, the four-point bending strength is 980 MPa or more, and the surface roughness after the wear resistance test is obtained. The silicon nitride ceramics having a thickness Rz of 0.5 μm or less and excellent erosion resistance and wear resistance can be obtained.

  In this embodiment, in addition to silicon nitride and a sintering aid, Mo, W, or the like may be added. To include Mo, W, the molded body is impregnated with an aqueous solution of Mo, W. This is dried and temporarily fired to support Mo and W on the molded body, and then heated and sintered at 1900 ° C. in a high-pressure nitrogen atmosphere of 190 to 200 MPa to nitride the Mo and W. Silicon ceramics can be obtained.

When molding the molded body, an alcohol-based binder is appropriately added, put into a mold, molded into a predetermined shape, removed from the mold, and then formed into a molded body by hot isostatic pressing. May be.
〔Example〕
Examples 1 to 10 and Comparative Examples 1 to 3 will be described below together with Table 1.

Examples 1-7, Comparative Examples 1-3
A granulated powder was prepared by mixing silicon nitride (Si ₃ N ₄ ) powder with alumina (Al ₂ O ₃ ) and yttria (Y ₂ O ₃ ) as a sintering aid in a weight ratio of 92: 2: 6.

  This granulated powder was filled into a rubber mold, and a molded body of φ80 mm × L40 mm was produced by isotropic pressure molding.

  The molded body was degreased at 550 ° C. in an atmospheric furnace and then sintered in 1 to 10 MPa of nitrogen. The sintering temperature was 1750 ° C. to 1900 ° C., the holding time was 4 to 8 hours, and 10 types of samples of Examples 1 to 7 and Comparative Examples 1 to 3 were produced.

Examples 8-10
A granulated powder was produced by mixing silicon nitride (Si ₃ N ₄ ) powder with alumina (Al ₂ O ₃ ) and yttria (Y ₂ O ₃ ) as sintering aids.

  This granulated powder was filled into a rubber mold, and a molded body of φ80 mm × L40 mm was produced by isotropic pressure molding. The obtained molded body was degreased at 550 ° C. in an atmospheric furnace and then calcined at 1450 ° C. in a nitrogen atmosphere of 0.9 MPa.

  Next, the calcined product was immersed in a 10 mass% aqueous solution of ammonium heptamolypdenate and a 10 mass% aqueous solution of ammonium metatungstate, dried at room temperature, and then heat treated at 230 ° C. Furthermore, sintering was performed in 196 MPa nitrogen. Three types of samples of Examples 8 to 10 were prepared with a sintering temperature of 1900 ° C. and a holding time of 4 hours.

  The 13 types of samples of Examples 1 to 10 and Comparative Examples 1 to 3 were each processed into a bending test piece and a pin-on-disk wear test test piece specified in JIS R1601.

  The strength of the test piece was measured by a four-point bending strength by a test method specified in JIS R1601, and the wear measurement of the test piece was measured by a pin-on-disk wear test shown in FIG.

  As shown in FIG. 1, in the pin-on-disk wear test, a test piece (disk) 10 having a 50 mm square and a thickness of 10 mm was rotated so that the pin 11 made of FCD400 at the tip SR18 drawn a circle with a radius of 20 mm. . At this time, the load applied to the pin 11 was 49 N, and the rotation speed was 0.5 m / s.

  Moreover, several drops of 10W-30 engine oil was replenished to the sliding surface every 2 minutes. A wear test was performed for 100 hours, and the amount of wear of each sample was measured.

  The particle diameter of each sample was measured by observing the surface of each sample with a scanning electron microscope (SEM) and calculating the particle volume and the aspect ratio using image processing software. These measurements were performed on 1000 to 1500 particles, and the average value was obtained.

  The particle volume was obtained by (square of minor axis) ÷ 4 × π × major axis, and the aspect ratio A was obtained by A = major axis / minor axis.

  FIG. 2 shows the relationship between the particle aspect ratio and the particle volume.

FIG. 2 is a plot of the aspect ratio and particle volume (μm ³ ) of the sintered bodies of Examples 1 to 7 and Comparative Examples 1 to ^{3. The} black circles are examples, and the black squares are comparative examples.

In Examples 1 to 7, the aspect ratio is 1.8 or more and the particle volume is in the range of 0.014 to 0.058 μm ³ , but in Comparative Examples 1 to 3 in which the aspect ratio is less than 1.8, The particle volume tends to increase.

  FIGS. 3 to 6 show SEM images (5. SEM images) of the surface of ceramics in a typical particle form of the silicon nitride ceramics obtained in Examples 1 to 10 and the silicon nitride ceramics obtained in Comparative Examples 1 to 3 in FIG. 0 kV, × 10,000). The aspect ratio A, particle volume V, and four-point bending strength ST are also shown together with the SEM image.

3 to 7, black portions are silicon nitride (Si ₃ N ₄ ) particles, and white portions are grain boundary layers formed of a sintering aid or the like.

  As shown in FIGS. 3 to 6, the silicon nitride ceramics of Examples 1 to 10 have a fine structure in which silicon nitride particles having a minor axis of 0.5 μm or less and a major axis of 1 μm or more are intertwined. .

  On the other hand, in Comparative Examples 1 to 3 in FIG. 7, except that the silicon nitride particles are extremely large, the average diameter of the silicon nitride particles is 1 μm or more and the long diameter is 1.5 μm or less. Is done.

  Next, FIG. 8 shows the relationship between the four-point bending strength and the particle volume.

  FIG. 8 is a plot of the four-point bending strength and the particle volume using the sintered bodies of Examples 1 to 10 and Comparative Examples 1 to 3 as test pieces. The black circles are examples, and the black squares are comparative examples. .

8, in Examples 1 to 10, and the particle volume 0.014～0.058Myuemu ^3, and at 0.1 [mu] m ³ or less, four-point bending strength, while at least 980 MPa, compared examples 1-3, the particle volume exceeds the 0.1 [mu] m ^3, the particle volume Comparative example 1 of 2.516Myuemu ³ drops is much four-point bending strength and 738MPa.

In addition, when Example 2 and Example 3 in Table 1 are compared, the bending strength is higher when the sintering temperature is higher (Example 3) even when the particle volume is the same (0.048 μm ³ ). The higher the nitrogen pressure during sintering (Example 6), the higher the bending strength.

  FIG. 9 is a plot of the results of FIG. 8 in terms of four-point bending strength and aspect ratio, with black circles indicating examples and black squares indicating comparative examples.

  9, in Examples 1 to 10, the aspect ratio is 1.8 or more and the four-point bending strength is 980 MPa or more, while in Comparative Examples 1 and 2, the aspect ratio is 1.64, 1. Since the strength is as small as 79, the strength is as low as 738 and 803 MPa.

In Comparative Example 3, the aspect ratio is 1.79, the particle volume is 0.126 μm ³ , and the bending strength is as high as 1001 MPa, but the surface roughness Rz after a wear test described later is poor.

  10 and 11 show typical sample surface SEM images after the wear test.

  10A is a sample surface SEM image (× 5,000) of Example 1, FIG. 10B is a sample surface SEM image of Example 5 (× 1,000), and FIG. The sample surface SEM image (x5,000) of Example 10 is shown, FIG.11 (a)-FIG.11 (c) show the sample surface SEM image (x1,000) of Comparative Examples 1-3, and each SEM image In addition, the aspect ratio A, the particle volume V, the strength ST, and the surface roughness Rz are shown.

  In Examples 1, 5, and 10, no change is observed in the surface structure even after the wear test, but in Comparative Examples 1 to 3, it can be seen that the surface structure is rough.

  FIG. 12 shows the relationship between the surface roughness Rz after the abrasion test of Examples 1 to 10 and Comparative Examples 1 to 3 and the particle volume. The black circle marks are examples, and the black square marks are comparative examples.

From FIG. 12, Examples 1 to 10 have a particle volume of 0.1 μm ³ or less and a surface roughness Rz of 0.5 μm or less, but Comparative Examples 1 to 3 have a particle volume exceeding 0.1 μm ^3. , Rz was 1 μm or more, resulting in a sharp increase in the amount of wear.

From the above results, in order to obtain a high-pressure injection part made of high-strength silicon nitride ceramics with excellent erosion resistance and wear resistance, the four-point bending strength is 980 MPa or more, and more preferably, the aspect ratio Is 1.8 or more and the particle volume is 0.1 μm ³ or less.

  Next, a fuel injection valve using the above-described high pressure injection component will be described.

  FIG. 13 is a schematic view of a fuel injection valve according to an embodiment of the present invention, and FIG. 14 is a partially enlarged view of the fuel injection valve.

  The fuel injection valve 28a shown in FIGS. 13 and 14 is applied to the above-described common rail fuel injection system shown in FIG. 19, and includes a nozzle body 45 to which the fuel supply passage 27 and the fuel recovery passage 43 are connected. Have. The fuel supply passage 27 is connected to the first passage 46 and the second passage 47 in the nozzle body 45, and the fuel recovery passage 43 is connected to the third passage 48 of the nozzle body 45. The nozzle body 45 is configured such that an upper nozzle body 45a and a lower nozzle body 45b are integrated via a screw 50 with a cylindrical connecting member 49, and a needle is placed in a receiving hole 51 formed therein. The valve 52 is slidably accommodated in the axial direction.

  A pressure control chamber 53 is formed above the needle valve 52. As shown in FIG. 14, the pressure control chamber 53 includes a top surface 54 of the needle valve 52, a side surface 55 of the accommodation hole 51 formed in the upper nozzle body 45 a, and an insertion inserted into the accommodation hole 51 from above. A partition is formed from the lower end surface portion 57 of the member 56. An annular fuel storage portion 58 into which fuel from the first passage 46 flows is formed on the side portion of the insertion member 56. Inside the insertion member 56, an intermediate passage 59 that guides the fuel in the fuel reservoir 58 to the pressure control chamber 53 and a relief passage 60 that relieves the fuel pressure (fuel) in the pressure control chamber 53 upward are formed. Yes.

A central valve seat 63 is formed on the upper portion of the insertion member 56 in a convex shape. The central valve seat 63 is an outlet of the relief passage 60, and has a relief hole (orifice hole) 61 having an inner diameter smaller than the inner diameter of the relief passage 60, and a seat surface 63 a formed around the outlet of the relief hole 61. And have. Around the central valve seat portion 63, an annular peripheral valve seat portion 64 is formed on the upper portion of the insertion member 56 so as to have a height substantially equal to that of the central valve seat portion 63. A relief valve 62 formed in a disc shape is seated on and separated from the central valve seat portion 63 and the peripheral valve seat portion 64.

  The relief valve 62 is normally pressed downward by a spring 65 and is seated on the valve seats 63 and 64 to close the relief hole 61. When the electromagnetic solenoid 66 is energized, the relief valve 62 is lifted upward against the spring 65. The relief hole 61 is opened away from the seats 63 and 64. That is, the relief valve 62 also serves as an armature for the electromagnetic solenoid 66. The spring 65 and the electromagnetic solenoid 66 are respectively provided on a lid member 67 attached to the top of the upper nozzle body 45a. A relief chamber 68 is formed between the lower surface of the lid member 67 and the upper surface of the insertion member 56 to contain the fuel flowing out from the pressure control chamber 53 through the relief passage 60 and the relief hole 61 in a liquid-tight manner.

  A spacer 69 formed in a ring shape so as to surround the relief valve 62 is placed on the peripheral valve seat portion 64. The spacer 69 is formed thicker than the relief valve 62, and ensures an opening / closing stroke of the relief valve 62 between the valve seats 63, 64 and the lower surface of the lid member 67. A passage 70 is formed in the relief valve 62 through communication between the upper and lower surfaces thereof. The passage 70 causes the fuel in the relief chamber 68 to flow up and down the relief valve 62 when the relief valve 62 is raised and lowered, thereby reducing the raising and lowering resistance of the relief valve 62. The fuel in the relief chamber 68 is guided to the fuel recovery passage 43 shown in FIG. 19 via the insertion member 56 and the third passage 48 formed in the upper nozzle body 45 a and returns to the fuel tank 21.

  A second passage 47 connected to the fuel supply passage 27 is formed in the upper nozzle body 45a. The tip of the second passage 47 is connected to a fuel passage 71 formed along the axial direction on the outer periphery of the needle valve 52. The fuel passage 71 includes a groove formed on the surface of the needle valve 52 and a gap formed by forming the needle valve 52 with a smaller diameter than the accommodation hole 51. The needle valve 52 has a large-diameter portion 72 that partitions the fuel passage 71 and the pressure control chamber 53 in the upper portion, has a flange portion 74 that is pressed downward by a spring 73 in the middle portion, and is seated on the seat portion 75 in the lower portion. -It has the cone part 76 which detaches | leaves. The sheet portion 75 and the injection hole 77 are formed at the lower end of the lower nozzle body 45b.

  According to the above configuration, the high-pressure (several tens to several hundreds of MPa) fuel in the common rail 26 shown in FIG. 19 is supplied to the fuel injection valve 28a shown in FIG. 46, the fuel reservoir 58 and the intermediate passage 59 are supplied into the pressure control chamber 53, and the second passage 47 is supplied to the distal end side of the needle valve 52 so that the nozzle body 45 is filled with high-pressure fuel. It is filled.

  Here, when the electromagnetic solenoid 66 is energized off, the relief hole 61 is closed by the relief valve 62 pushed down by the spring 65, and the fuel pressure in the pressure control chamber 53 is held. Accordingly, the fuel pressure in the pressure control chamber 53 and the downward force of the needle valve 52 due to the spring 73 are larger than the upward force of the needle valve 52 due to the fuel pressure of the pressure receiving portion 78 on the distal end side of the needle valve 52, and the needle valve 52 is lowered. To do. Therefore, the conical portion 76 at the tip of the needle valve 52 is seated on the seat portion 75, the injection hole 77 is closed, and fuel is not injected.

  When the electromagnetic solenoid 66 is energized, the relief valve 62 is pulled up against the spring 65, the relief hole 61 is opened, and the fuel pressure in the pressure control chamber 53 is released (relieved). Therefore, the ascending force of the needle valve 52 due to the fuel pressure of the pressure receiving portion 78 on the distal end side of the needle valve 52 becomes larger than the descending force of the needle valve 52 due to the spring 73, and the needle valve 52 rises. Therefore, the conical portion 76 of the needle valve 52 is separated from the seat portion 75, and fuel is injected from the injection hole 77 at a high pressure.

  Here, in this embodiment, the high-pressure injection part 79 (see FIG. 15) made of the above-mentioned silicon nitride ceramics (four-point bending strength is 980 MPa or more) is used for the central valve seat portion 63. The high-pressure injection part 79 is composed of a cylindrical body, a prismatic body, or the like. The passage 80 is formed along the axial direction in the inside thereof, and a high-pressure fluid (fuel) can flow therethrough, and the upper formed around the outlet of the passage 80. Surface 82. The high pressure injection component 79 is mounted on the insertion member 56 such that the passage 80 forms the relief hole 61 (see FIG. 14) and the upper surface 82 forms the seat surface 63a (see FIG. 14). . The high-pressure injection component 79 is mounted in an accommodation hole 81 formed continuously from the relief passage 60 in the upper part of the insertion member 56. As shown in FIG. 15, the high-pressure injection part 79 (central valve seat 63) is chamfered (for example, the chamfering angle θ is 64 degrees) as shown in FIG. Thus, the area of the upper surface 82 is reduced.

  The high-pressure injection component 79 is preferably fitted into the accommodation hole 81 by press-fitting (tight fit). It goes without saying that the high-pressure injection part 79 may be mounted in the accommodation hole 81 by using brazing or bonding.

  The reason why only the central valve seat 63 is made of ceramic (made of silicon nitride ceramics) is that the relief hole 61 used as the orifice hole requires precision machining, and the ceramic formed by sintering is excellent in workability, and This is because it is very strong against compressive stress. There is a cemented carbide as a high-strength material, but a cemented carbide that is inferior in workability compared with ceramics cannot be used as the material of the central valve seat portion 63.

  The insertion member 56 is made of, for example, carbon steel. This type of material is softer than ceramics, which is the material of the high-pressure injection part 79 (central valve seat 63).

  The operation of the present embodiment having the above configuration will be described.

  When the relief hole 61 is opened, the high-pressure (several tens to several hundreds of MPa) fuel in the pressure control chamber 53 flows into the relief chamber 68 through the relief passage 60 and the relief hole 61. At this time, the shock wave generated at the fuel outlet of the pressure control chamber 53 due to cavitation is generated in the high-pressure injection part 79 made of silicon nitride ceramics that is much harder than the material of the insertion member 56 itself (carbon steel or the like). Works. For this reason, the erosion of the seat surface 63a of the central valve seat portion 63, which occurs with a long-term operation due to the repeated action of the shock wave generated at the fuel outlet of the pressure control chamber 53 due to cavitation, Prevented in advance.

  That is, there is no high-pressure injection part 79 made of relatively hard silicon nitride ceramics (four-point bending strength of 980 MPa or more), and the central valve seat portion 63 in which the relief hole 61 and the seat surface 63a are formed is the insertion member 56. Since the shock wave generated at the fuel outlet of the pressure control chamber 53 directly acts on the insertion member 56 (carbon steel or the like) made of a relatively soft material, it is generated at the fuel outlet of the pressure control chamber 53. In this embodiment, the shock wave generated at the fuel outlet of the pressure control chamber 53 is nitrided much harder than the material of the insertion member 56 (carbon steel or the like). Since it acts on the high-pressure injection part 79 made of silicon ceramics (four-point bending strength of 980 MPa or more), the occurrence of such erosion is avoided.

  Thus, in this embodiment, since the occurrence of erosion of the seat surface 63a of the central valve seat 63, which has been a problem when the injection pressure is increased, can be avoided, the injection pressure is increased (about 300 MPa). Even if it exists, the exact seal with the relief hole 61 and the relief valve 62 can be ensured, and the leak of fuel when the relief valve 62 is seated on the central valve seat 63 can be prevented. Therefore, even when the injection pressure is increased (about 300 MPa), the raising and lowering of the needle valve 52, that is, the fuel injection from the injection hole 77 can be controlled with high accuracy. Specifically, when the relief valve 62 is seated on the central valve seat 63 (when the fuel pressure in the pressure control chamber 53 is maintained), the fuel does not leak, so the fuel pressure in the pressure control chamber 53 caused by the leak does not leak. The delay of the rise can be avoided. Therefore, even when the injection pressure is increased (about 300 MPa), the descent response of the needle valve 62 is maintained well, and the durability and reliability are improved.

  A high-pressure injection part 79 shown in FIG. 15 was incorporated in the fuel injection valve 28a, and a continuous injection test was performed at an injection pressure of 300 MPa.

  Table 2 shows the characteristics of the silicon nitride ceramic of the present embodiment.

  On the other hand, as shown in FIG. 17, comparative material 1 is a commercially available general silicon nitride ceramic (four-point bending strength of about 700 to 800 MPa), and comparative material 2 is a CrN film (chromium nitride) on a base material (metal). Comparative material 3 is a base material (metal) coated with a DLC film (diamond-like coating), and comparative material 4 is a film not formed with a film (metal) (four-point bending strength is 780 MPa). is there.

  FIG. 16 shows a typical sample surface SEM image used in the continuous injection test.

FIG. 16 (a) sample surface SEM image of the present embodiment (× 5,000), FIG. 1 6 (b) shows the specimen surface SEM images of comparative material 1 (× 5,000), together with the respective SEM images The aspect ratio A, the particle volume V, and the strength ST were shown.

  FIG. 17 shows the results of the continuous injection test at an injection pressure of 300 MPa.

  As shown in FIG. 17, in the silicon nitride ceramic of the present embodiment, no abnormality such as erosion occurs on the upper surface 82 (the seat surface 63a of the central valve seat 63) of the high-pressure injection part 79 even after 50 hours. It was.

  On the other hand, as shown in FIG. 17, the comparative material 2 is 1.5 hours, the comparative material 3 is 2 hours, and the comparative material 4 is 0.3 hours or less on the seat surface 63a of the central valve seat 63. As a result, the test could not be continued. The comparison materials 2 and 3 in which the base material was coated with the coating became unable to continue the test in a short time because the elastic modulus of the base material and the coating film was due to the impact force of the shock wave applied to the seat surface 63a of the central valve seat 63. Cracks and delamination occurred in the film due to the difference, in addition, the generation of stress due to the difference in the thermal expansion coefficient between the substrate and the film promoted the generation of cracks and delamination in the film, and the film was thin because the film was thin. It is possible that the effect did not last.

  Moreover, in the comparative material 1, before the erosion occurred on the seat surface 63a of the central valve seat 63, the central valve seat 63 could not withstand the pressure of 300 MPa, and the central valve seat 63 was cracked from the inside in several minutes, so that the test could not be continued. It has become possible. As described above, the high-pressure injection part 79 (central valve seat portion 63) is chamfered at the corners of the upper surface 82 and the outer surface to improve the sealing performance, thereby reducing the area of the upper surface 82. . For this reason, when the internal pressure of 300 MPa is applied to the passage 80 (relief hole 61) of the high-pressure injection part 79, the vicinity of the top of the high-pressure injection part 79 serving as the fuel outlet of the pressure control chamber 53 is thin. 2) The internal pressure in the vicinity of the top of the high-pressure injection part 79 is 643 MPa.

In formula (2), r ₁ is the relief hole inner diameter Ri (Φ0.38) / 2, r ₂ is the fuel outlet outer diameter (Φ0.63) / 2, and p is the internal pressure (300 MPa).

  In the comparative material 1 made of silicon nitride ceramics having a four-point bending strength of about 700 to 800 MPa, the safety factor is 1.08 (700 MPa / 643 MPa) to 1.24 (800 MPa / 643 MPa). In the comparative material 1, considering the stress concentration such as the surface roughness and notch of the relief hole 61, there is almost no margin in safety factor, so it is considered that the central valve seat 63 has cracked so that the test cannot be continued in a few minutes. It is done.

  As described above, the fuel injection valve 28a according to the present embodiment makes it possible to increase the injection pressure (about 300 MPa), and to rapidly form a lean premixed gas by improving the turbulent mixing speed. At the same time, since the injection time can be shortened, the air-fuel mixture is homogenized, so that it is difficult to form an excessively thin region, and the discharge of unburned components can be suppressed.

FIG. 1 is an explanatory diagram of a pin-on-disk wear test method for measuring the wear of a silicon nitride ceramic test piece in the examples and comparative examples of the present invention. FIG. 2 is a diagram showing the relationship between the aspect ratio of the silicon nitride particles and the particle volume of the sintered body of silicon nitride ceramics in the examples and comparative examples of the present invention. FIG. 3 is a structure diagram obtained by photographing the surface texture state of the silicon nitride ceramics of Examples 1 to 3 of the present invention with an SEM image. FIG. 4 is a structure diagram obtained by photographing the surface texture state of the silicon nitride ceramics of Examples 4 and 5 of the present invention with an SEM. FIG. 5 is a structure diagram obtained by photographing the surface texture state of the silicon nitride ceramics of Examples 6 and 7 of the present invention with an SEM. FIG. 6 is a structural diagram obtained by photographing the surface texture state of the silicon nitride ceramics of Examples 8 to 10 of the present invention with an SEM. FIG. 7 is a structural diagram obtained by photographing the surface texture state of the silicon nitride ceramics of Comparative Examples 1 to 3 with an SEM. FIG. 8 is a graph showing the relationship between the four-point bending strength and particle volume of silicon nitride ceramics in the examples of the present invention and comparative examples. FIG. 9 is a diagram showing the relationship between the four-point bending strength and aspect ratio of silicon nitride ceramics in the examples of the present invention and comparative examples. FIG. 10 is a structure diagram obtained by photographing the surface texture state of the silicon nitride ceramics after the abrasion test of Examples 1, 5, and 10 of the present invention with an SEM. FIG. 11 is a structure diagram obtained by photographing the surface structure of the silicon nitride ceramics after the abrasion test of Comparative Examples 1 to 3 with an SEM. FIG. 12 is a diagram showing the relationship between the surface roughness and the particle volume after the abrasion test of Examples 8 to 10 and Comparative Examples 1 to 3 of the present invention. FIG. 13 is a schematic view of a fuel injection valve according to an embodiment of the present invention. FIG. 14 is a partially enlarged view of the fuel injection valve. FIG. 15 is a cross-sectional view of the valve seat portion. FIG. 16 is a structural diagram obtained by photographing the surface texture state of this embodiment and the comparative material 1 with an SEM. FIG. 17 is a diagram showing the results of a continuous injection test at an injection pressure of 300 MPa. FIG. 18 is a diagram showing the relationship between the injection pressure and the cavitation coefficient. FIG. 19 is a schematic diagram of a common rail fuel injection system. FIG. 20 is a schematic view of a fuel injection valve showing a conventional example.

Explanation of symbols

28a Fuel injection valve 45 Nozzle body 52 Needle valve (valve element)
53 Pressure control chamber 61 Relief hole 62 Relief valve 63 Central valve seat (valve seat)
63a Seat surface 79 High pressure injection parts 80 Passage 82 Upper surface

Claims (3)

A fuel injection valve that lifts a valve body pushed down by receiving a fuel pressure of a high-pressure fuel in a pressure control chamber provided in a nozzle body by relieving the fuel pressure through a relief passage ,
A high-pressure injection part comprising a valve seat having a relief hole for releasing the fuel pressure in the pressure control chamber and a seat surface formed around the outlet of the relief hole;
The high-pressure injection part is composed of a pillar, and the inside diameter of the relief hole formed along the axial direction is smaller than the inside diameter of the relief passage, and an upper surface is formed around the outlet of the relief hole ,
The high-pressure injection component is mounted on the nozzle body such that the relief hole constitutes an outlet of the relief passage and the upper surface constitutes the seat surface, and the upper surface and the upper surface for improving the sealing performance. The corner with the outer surface is chamfered ,
The high-pressure injection component is formed by adding 10 mass% or less of alumina and yttria sintering aids to silicon nitride powder to silicon nitride powder, respectively, and forming the molded body under a nitrogen atmosphere of 5 to 10 MPa. A fuel injection valve comprising silicon nitride ceramics obtained by heating and sintering at 1750 to 1850 ° C, wherein the silicon nitride ceramics has a four-point bending strength of 980 MPa or more . 2. The fuel injection valve according to claim 1, wherein the silicon nitride ceramic has an aspect ratio of sintered silicon nitride particles of 1.8 or more and a particle volume of 0.1 μm ³ or less. The fuel injection valve according to claim 1 or 2 , wherein the high-pressure injection component is press-fitted into the nozzle body.

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