JP2013224640A - Fuel injection valve of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further enhance combustion performance during low load by suppressing deterioration of atomization of fuel while securing the strength of a distal end wall part by reducing tension stress generated in the distal end wall part of a valve body by combustion pressure in a fuel injection valve of an engine.SOLUTION: An outer surface of a distal end wall part of a valve body constituting a fuel injection valve has a dome shape concaved into an inner side of the valve body and a precompressing generating ring applying compression force in advance is arranged at least in an outer peripheral surface of the distal end wall part of the valve body.

Description

  The present invention relates to an engine fuel injection valve, and more particularly to a fuel injection valve suitable for shortening an injection time, and belongs to the field of engine fuel supply technology.

  In recent years, gasoline engines for vehicles and the like have been proposed in which the compression ratio is set high and the temperature of the mixture is increased in the compression process so that the mixture is compressed and ignited in a low load region. According to this ignition method, the thermal efficiency in the low load region becomes high, and further improvement in fuel efficiency is expected compared to the lean burn method in which a conventional lean air-fuel mixture is spark-ignited.

  In this engine, ignition is performed by spark ignition in the high load region, but since the compression ratio is set high, the unburned mixture is self-ignited during the compression stroke, particularly in the high load low rotation region. There is a problem that ignition or knocking in which an unburned portion of the air-fuel mixture is locally self-ignited after the start of combustion is likely to occur.

  In response to this, by increasing the injection rate (injection amount per unit time) of the fuel injection valve and injecting in a short time at a timing near the compression top dead center, the time from the start of fuel injection to ignition is shortened. It is considered effective to do. In other words, premature ignition is suppressed by shortening the time from the start of injection to ignition, and it is considered that the agitation of the air-fuel mixture is promoted by the increase of the spraying speed due to the shortened injection time and knocking is suppressed. is there.

  In order to increase the injection rate of the fuel injection valve and shorten the fuel injection time, it is considered to increase the fuel injection pressure (hereinafter referred to as “fuel pressure”).

  In Patent Document 1, the cross-sectional shape of the nozzle hole plate is configured to be a convex shape from the nozzle hole plate side toward the tip side of the valve member (that is, a shape recessed toward the inner side). In the embodiment, the injection direction of the plurality of injection holes arranged in the nozzle is inclined outward with respect to the axial direction of the fuel injection valve, and the turning angle when the fuel flows into the injection hole is increased. Further, it is disclosed to promote atomization of fuel.

JP 2005-155547 A

Incidentally, as shown in FIG. 8, the fuel injection valve is generally inserted in a cylindrical shape with a valve body 112 having a tip wall portion 112a at the tip, and the inside of the valve body 112 so as to be movable in the axial direction. Needle valve 114. The inside of the valve body 112 has a tapered shape, and the cross-sectional shape of the distal end wall portion 112a has a dome shape that rises outward. A plurality of nozzle holes 116 are formed in the tip wall portion 112a. Further, the tip portion 114 a of the needle valve 114 is moved away from the valve seat 112 a ₃ on the outer peripheral portion of the inner surface of the tip wall portion 112 a of the valve body 112, so that fuel is sprayed from the nozzle 116.

  In such a structure, for the reasons described above, in order to increase the fuel pressure at the time of high load in order to shorten the fuel injection time, for example, the thickness of the tip wall portion of the valve body is increased (hereinafter referred to as “thickening of the wall”). It is necessary to be able to withstand the tensile stress caused by this fuel pressure (increase the rigidity), but the length in the thickness direction of the nozzle hole (hereinafter referred to as the “hole diameter”) Inevitably becomes longer.

  Here, generally, when the nozzle hole length becomes long, the turbulent flow that is effective for atomizing the fuel is weakened while the fuel is passing through the nozzle hole, so that the atomization of the fuel tends to deteriorate. Further, when the fuel pressure is lowered, the collision between the fuel injected from the nozzle and the air is weakened, so that the atomization of the fuel tends to be deteriorated. And when the atomization of fuel deteriorates, it becomes difficult to form a good air-fuel mixture.

  On the other hand, when the fuel injection amount is low and the load is low, the fuel consumption is significantly deteriorated due to the drive loss of the fuel pump. Therefore, there is a demand for reducing the fuel pressure when the load is low (compression ignition). In response to this demand, the fuel pump is generally driven so as to have a high fuel pressure at a high load and a low fuel pressure at a low load. Therefore, when the nozzle hole length is increased by increasing the thickness of the tip wall portion, the atomization of the fuel is most deteriorated particularly at a low load where the fuel pressure is low.

  From the above, in order to improve atomization at low load, the tip wall must be thinned by reducing the tensile stress generated in the tip wall by the fuel pressure.

  Accordingly, the present invention provides a fuel injection valve for an engine while reducing the tensile stress generated in the tip wall portion of the valve body by the fuel pressure, while ensuring the strength of the tip wall portion that can withstand the high fuel pressure at the time of high load. It is an object of the present invention to suppress the deterioration of fuel atomization and further improve the combustibility at low load.

  In order to solve the above-described problems, a fuel injection valve for an engine according to the present invention is configured as follows.

First, the invention according to claim 1 of the present application is
A valve body, and a needle valve that is inserted in the valve body so as to be movable in the axial direction. The valve body has a plurality of injection holes in a tip wall portion, and the tip end portion of the needle valve is connected to the valve body. In the fuel injection valve of the engine that sprays fuel from the nozzle by moving away from the valve seat provided on the outer peripheral portion of the inner surface of the tip wall,
The tip wall portion has a dome shape whose outer surface is recessed toward the inside of the valve body,
A precompression generating ring for applying a compressive force in advance to at least the outer peripheral surface of the tip wall portion of the valve body is provided.

The invention according to claim 2 of the present application is the invention according to claim 1,
Each of the nozzle holes is disposed such that the direction in which the fuel is sprayed is inclined outward from the center line of the valve body,
The tip wall portion is characterized in that the bottom surface of the central portion of the inner surface thereof has a flat shape.

Furthermore, the invention according to claim 3 of the present application is the invention according to claim 1,
Each of the nozzle holes is disposed such that the direction in which the fuel is sprayed is inclined outward from the center line of the valve body,
The tip wall portion has a dome shape in which a bottom surface of a central portion of the inner surface of the tip wall portion rises toward the inside of the valve body.

  First, according to the first aspect of the present invention, when a high fuel pressure acts on the inner surface of the tip wall portion of the valve body, a large tensile stress acts on the tip wall portion. By forming a dome shape recessed to the side and applying a compressive force to the outer periphery of the tip wall portion with the precompression generating ring, it is possible to efficiently suppress the tensile stress generated in the vicinity of the nozzle hole. Therefore, the thickness in the vicinity of the nozzle hole is not increased excessively, the nozzle length can be shortened, and atomization of the spray can be ensured.

  According to the second aspect of the present invention, the bottom surface of the central portion of the inner surface of the tip wall portion of the valve body has a flat shape, so that high fuel pressure fuel flows between the tip portion of the needle valve and the valve body valve seat. It is possible to suppress the generation of a contracted flow when flowing into the nozzle hole from the gap, thereby suppressing variations in the fuel flow rate, and reducing stress concentration at the inner surface of the tip wall portion, particularly at the corner of the outer edge of the bottom surface of the central portion.

  Further, according to the third aspect of the present invention, since the bottom surface of the central portion of the inner surface of the tip wall portion of the valve body has a dome shape rising to the inner side of the valve body, the low fuel pressure fuel is supplied to the tip of the needle valve. Turbulent flow when flowing into the nozzle through the gap between the valve body and the valve seat can promote atomization of the sprayed fuel, and the outer surface of the tip wall, particularly near the nozzle outlet The stress concentration in can be reduced.

It is sectional drawing which shows the whole structure of the fuel injection valve (at the time of valve closing) of the engine which concerns on one Embodiment of this invention. (A) is an expanded sectional view which shows the structure of the principal part of the valve body of the fuel injection valve shown in FIG. 1, (b) is a bottom view which shows the structure of the principal part of the valve body. It is an expanded sectional view showing the structure of the principal part of the valve body concerning the modification of one embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view illustrating the flow of fuel inside the tip of the fuel injection valve (when opened) shown in FIG. 1. It is a graph which shows the relationship between fuel pressure and intensity | strength required from a fuel injection valve of this invention and a prior art. It is an expanded sectional view which shows the stress concentration part in the valve body of the fuel injection valve shown in FIG. It is an expanded sectional view which shows the tensile stress by the fuel pressure in the valve body of the fuel injection valve (at the time of valve opening) of this invention and a prior art. It is an expanded sectional view which shows the structure of the principal part of the fuel injection valve (at the time of valve opening) which concerns on a prior art.

  Hereinafter, an embodiment of a fuel injection valve according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an overall structure of a fuel injection valve of an engine according to the present embodiment, and FIG. 2 is an enlarged cross-sectional view of a main part, that is, a tip portion of a valve body constituting the fuel injection valve of FIG. And a bottom view.

  The main body of the fuel injection valve 10 has a structure in which a large-diameter cylindrical housing 11 and a small-diameter cylindrical valve body 12 extending from one end of the housing 11 and closed at the tip are connected by a coupling member 13. .

  A needle valve 14 extending from the middle portion of the housing 11 to the tip end portion of the valve body 12 along the center line thereof is inserted into the housing 11 and the valve body 12, and the tip wall portion 12a of the valve body 12 and A fuel injection portion 15 is constituted by the tip portion 14 a of the needle valve 14.

  An electromagnetic coil 20 is housed in the housing 11, and a cylindrical fixed iron core 30 is disposed inside the electromagnetic coil 20.

  Furthermore, a ring-shaped movable iron core 50 is provided with an axial gap X between the fixed iron core 30 and the spacer 40 provided on the tip side thereof.

  And the part located in the housing 11 of the needle valve 14 penetrates the movable iron core 50 and the fixed iron core 30 from the front end portion 14a side, and the needle 14 is placed on the rear end side of the needle valve 14 at the front end portion 14a. A coil spring 60 is provided to urge toward the side, that is, in the valve closing direction.

  Further, a stepped portion 14 b is provided on the side of the needle valve 14 that passes through the movable iron core 50 on the fixed iron core 30 side.

  Thereby, the movable iron core 50 is attracted to the fixed iron core 30 side by the attraction force generated by energization of the electromagnetic coil 20, and the needle valve 14 resists the urging force of the coil spring 60 through the stepped portion 14b. Thus, the stroke is made in the valve opening direction by a distance corresponding to the gap X.

On the other hand, the fuel injection portion 15 composed of the distal end wall portion 12a of the valve body 12 and the distal end portion 14a of the needle valve 14 is similar to the conical valve seat 12a ₃ provided on the outer peripheral portion of the distal end wall portion 12a. The conical tip portion 14a is configured to close and open by contacting and separating in accordance with the movement of the needle 14.

  When the valve is opened, a pipe (not shown) connected to the connector 70 at the rear end of the housing 11 is connected between the valve body 12 and the needle 14 via a fuel passage (not shown) in the housing 11. The high-pressure fuel that has been pumped up to the fuel reservoir 12c is sprayed in the form of a mist from the plurality of nozzles 16 provided in the tip wall 12a to the outside (combustion chamber). FIG. 1 shows a state when the fuel injection valve is closed.

  Note that switching between excitation and demagnetization of the electromagnetic coil 20 is controlled by a fuel control unit (not shown). The fuel control unit is provided in the engine control unit, inputs various signals indicating the operating state of the engine, and controls the fuel injection valve 10 so as to obtain an injection amount required according to the operating state indicated by these signals. A pulsed control current is output to the electromagnetic coil 20.

  Next, the structure of the valve body 12 constituting the fuel injection valve 10 will be described in detail with reference to FIG.

  FIG. 2A is an enlarged cross-sectional view showing the structure of the main portion, that is, the tip portion of the valve body 12 shown in FIG. 1, and FIG. 2B is a bottom view of the tip portion of the valve body 12 as well. . 2A is a cross-sectional view taken along line AA in FIG. 2B.

As shown in FIG. 2 (a), the inside of the cylindrical valve body 12 is generally tapered, and the tip wall portion 12a at the tip of the valve body 12 has a conical shape on the outer peripheral portion of the inner surface thereof. provided with a valve seat 12a _3, comprises a central bottom face 12a ₂ of the flat shape in its central portion, the central portion bottom surface 12a ₂ is given from the tip portion of the valve seat 12a ₃ distance of the valve body 12 It is arranged at a position recessed on the tip side. In addition, as shown in the drawing, it is desirable to add a roundness (R portion) to the corner of the outer edge of the central bottom surface 12a ₂ arranged at this recessed position. Further, front end wall portion 12a, the dome-shaped outer surface 12a ₁ is recessed into the inner side (hereinafter referred to. As "inverted dome structure") is formed on. Further, the front end wall portion 12a, so as to penetrate the central portion bottom surface 12a ₂ to the outer surface 12a _1, a plurality of nozzle holes 16 are formed.

  According to such an inverted dome structure, the tensile stress in the vicinity of the nozzle hole 16 of the tip wall portion 12a caused by the fuel pressure is relaxed, the wall thickness in the vicinity of the nozzle hole 16 is not increased excessively, and the nozzle length can be shortened. Atomization of the spray can be ensured. The effect will be described in detail later.

  Further, as shown in FIG. 2B, a total of ten nozzle holes 16 are provided, and are arranged at equal intervals on the circumference of the same radius around the center line of the valve body 12. Further, as shown in FIG. 2A, the direction in which the central axis of each nozzle 16 is directed, that is, the direction in which the fuel is sprayed is inclined so as to spread outward from the center line of the valve body 12. Has been. Further, each nozzle hole 16 is formed with a counterbore 8a on the outside.

By thus arranged inclined orientation of the nozzle hole, the low fuel pressure fuel turbulence when flowing from the gap between the valve seat 12a ₃ of the tip portion 14a and the valve body 12 of the needle valve 14 to the injection port 16 Generation can be promoted and atomization of the fuel to be sprayed can be promoted. The effect will be described in detail later.

  The number, size, and orientation of the nozzle holes 16 are determined according to the desired injection amount, spray reach distance, combustion chamber shape, fuel pump supply capacity, and the like. In general, the injection amount by the fuel injection valve is mainly determined by the size of the nozzle and the fuel pressure by the fuel pump. The larger the nozzle, the more fuel can be injected with the same fuel pressure. Conversely, if the fuel pressure is different even if the nozzle holes are the same size, the higher the fuel pressure, the more fuel can be injected. In general, the smaller the nozzle hole, the finer the fuel oil particles and the better the atomization, but the smaller the penetration force, the more likely the nozzle hole becomes clogged.

  Further, as shown in FIG. 2A, the valve body 12 includes a precompression generating ring 18 around the distal end wall portion 12a. However, the precompression generating ring 18 is not simply provided around the tip wall portion 12a of the valve body 2, but the precompression generating ring 18 always applies a compressive force to at least the outer peripheral surface of the tip wall portion 12a of the valve body 12. Provided to have a structure (hereinafter referred to as “preload ring structure”).

  In order to produce the preload ring structure as described above, a known press-fitting method such as cold press-fitting or hot press-fitting can be used. In addition, when quenching steel such as SCR430 is used as the material of the precompression generating ring 18 and the valve body 12, the press-fitting allowance is 10 μm, and the height of the press-fitting part is 2 mm, the surface pressure (compression force) by press-fitting is 100 MPa. there were.

  According to such a preload ring structure, even when the fuel pressure is increased, the tensile stress in the vicinity of the nozzle hole 16 in the tip wall portion 12a can be suppressed within a desired range by the compressive force of the precompression generation ring 18. .

According to this embodiment (when the center bottom surface 12a ₂ of the tip wall portion 12a has a flat shape), a later-described modified example (a dome shape in which the center bottom surface 12a ₂ of the tip wall portion 12a swells on the inner side). If) as compared to, high fuel pressure fuel to suppress the formation of contraction flow when flowing from the gap between the valve seat 12a ₃ of the tip portion 14a and the valve body 12 of the needle valve 14 to the injection port 16, fuel flow variation it is suppressed, the effect can be realized that can reduce the stress concentration at the center bottom surface 12a ₂ of the front end wall portion 12a. The effect will be described in detail later.

  Next, a modification of the above-described embodiment will be described with reference to FIG. FIG. 3 is an enlarged cross-sectional view showing the structure of the distal end portion of the valve body 12.

FIGS. 2 (a) and as is clear Mikurabere and 3, the variation in the previous embodiments, different shape of the central bottom face 12a ₂ of the front end wall portion 12a. Specifically, the center bottom surface 12a ₂ of the tip wall portion 12a has a flat shape in the previous embodiment, whereas the modified example of the previous embodiment has a dome raised to the inner side of the valve body 12. Both differ in the shape. The remaining structure, for example, the direction in which the fuel in each nozzle is sprayed is inclined outward from the center line of the valve body and is common to both.

  In the case of this modification, as in the previous embodiment, the tensile stress in the vicinity of the nozzle hole 16 is relieved by the dome shape, the wall thickness in the vicinity of the nozzle hole 16 is not increased unnecessarily, the nozzle length can be shortened, Atomization can be ensured.

Incidentally, according to this modified example, as compared with the previous embodiment, the low fuel pressure fuel when flowing from the gap between the valve seat 12a ₃ of the tip portion 14a and the valve body 12 of the needle valve 14 to the injection port 16 Generation of turbulent flow can be promoted, atomization of the sprayed fuel can be promoted, and an effect of reducing stress concentration in the outer surface 12a ₁ of the tip wall portion 12a, particularly in the vicinity of the outlet of the injection hole 16, can be realized. The effect will be described in detail later.

  In addition, although the bottom view of the said modification is not described in drawing, since the bottom view of the modification is the same as FIG.2 (b) which is a bottom view of previous embodiment, it abbreviate | omitted.

Next, referring to FIG. 4 to FIG. 7, the above-described embodiment and its modifications, that is, the case where the central bottom surface 12 a ₂ of the tip wall portion 12 a is flat and the dome that rises to the inside of the valve body 12. In the case of a shape, the common effect compared with a prior art and the individual effect which this embodiment and its modification have are demonstrated in detail below.

First, with reference to FIG. 4, individual effects relating to spray formation of the present embodiment and the modifications thereof according to the difference in the shape of the center bottom surface 12 a ₂ of the inner surface of the tip wall portion 12 a in the valve body 12 will be described. .

Although the drawings relates to a fuel flow modification is not described, as is clear Mikurabere 2 (a) and FIG. 3, than the central portion bottom 12a ₂ is flat embodiment of the front end wall portion 12a Trip modification of dome-shaped central portion bottom surface 12a ₂ is raised to the interior side, is steeper angle of bending of the jet when the fuel that has flowed along the central bottom surface 12a ₂ flows into the injection hole 16 is there.

  Here, when the angle of bending is steep, the turbulent flow inside the jet is more strongly generated at the bent portion, and the atomization tends to be promoted. However, if the angle of bending is steep, cavitation is likely to occur at the bent portion, so that the spray form (penetration, atomization, etc.) for each injection tends to vary. Note that when the direction of the nozzle hole 16 is inclined outward from the center line of the valve body 12, the angle of bending becomes steeper, and these tendencies become stronger.

Therefore, as shown in FIGS. 2A and 4, when the center bottom surface 12 a ₂ of the tip wall portion 12 a is flattened, the center bottom surface 12 a ₂ has a dome shape that rises toward the inside of the valve body 12. Compared to the case, since the angle of bending becomes more gradual, cavitation becomes weak, and variations in each injection can be suppressed.

On the contrary, as shown in FIG. 3, when the center bottom surface 12 a ₂ is formed in a dome shape that rises to the inside of the valve body 12, the angle of bending is steeper than when the center bottom surface 12 a ₂ is flattened. Therefore, strong turbulence is generated and atomization is further promoted.

From the above, whether the fuel injection valve of each embodiment by the difference in the shape of the central part bottom face 12a ₂ comprises a separate effect on the spray forming, using a fuel injection valve of any form to the engine, the fuel injection Those skilled in the art can select according to the specific characteristics and performance required for the valve.

  Next, the embodiment of the present invention and the modification thereof are different from the related art in that the shape of the outer surface of the tip wall portion is different and a precompression generating ring is provided around the tip wall portion. Common effects.

As described with reference to FIGS. 2 (a) and 3, in the embodiment of the present invention and the modifications thereof, the distal end wall portion 12 a of the valve body 12 has an outer surface 12 a ₁ recessed toward the inside of the valve body 12. This is a reverse dome structure having a dome shape and a preload ring structure provided with a precompression generating ring 18 that always applies a compressive force to the outer periphery of the tip wall portion 12a. At this time, the present invention of the reverse dome structure and the preload ring structure has a dome shape in which the cross section of the tip wall portion 112a is raised to the outside (hereinafter simply referred to as “dome structure”). With respect to the fuel pressure on the bottom surface at the center of the tip wall, the so-called arch effect significantly increases the rigidity in terms of structural mechanics. Therefore, the minimum necessary plate thickness of the tip wall having the strength to withstand the same fuel pressure is thinner in the present invention than in the prior art.

  FIG. 5 is a graph showing the necessary plate thickness from the strength on the vertical axis and the fuel pressure on the horizontal axis. By changing the shape of the tip wall portion from the dome structure of the prior art to the reverse dome structure and the preload ring structure of the present invention, the plate thickness d of the tip wall portion 12a of the present invention required for the same fuel pressure is the prior art. It is possible to make it thinner than the thickness D of the tip wall portion 112a. In any case, the necessary wall thickness of the tip wall portion is almost proportional to the fuel pressure, so that the difference in the necessary plate thickness between the present invention and the prior art (D−d) increases as the fuel pressure increases. ) Becomes prominent.

Next, with reference to FIG. 6 and FIG. 7, individual stress concentration caused by the fuel pressure of the embodiment of the present application and the variation thereof due to the difference in the shape of the center bottom surface 12 a ₂ in the tip wall portion 12 a of the valve body 12 is described. The effect will be described.

The details of the shape of the valve body 12 of the present embodiment and its modification have already been described with reference to FIGS. 2 and 3, but the cross section changes abruptly in any valve body 12 shape. Since the stress concentrates on the part, the part where the fuel pressure acts from the inside and the stress is particularly concentrated is, as shown in FIG. 6, near the bottom edge of the spot 16a on the outer surface 12a ₁ side of the tip wall part 12a (hereinafter referred to as the following). , “A portion”), and the vicinity of the corner of the outer edge of the center bottom surface 12a ₂ of the inner surface (hereinafter referred to as “B portion”). However, since the shape of the central bottom surface 12a ₂ is different between the embodiment of the present application and the modification thereof, a relative difference is also generated in the stress concentration generated in the A part and the B part. This difference is discussed in detail below.

  The tensile stress generated by the fuel pressure will be described with reference to FIGS. 7 (a) to 7 (c). FIG. 7 (a) shows an embodiment of the present application in which the tip wall has an inverted dome structure with a flat bottom surface at the center and a precompression ring structure, and FIG. 7 (b) shows the tip wall inside. FIG. 7C shows a modified example of the embodiment of the present invention which is an inverted dome structure with a center bottom surface raised to the side and a precompression ring structure, and FIG. Show.

  As shown in FIGS. 7A to 7C, in common with the present invention and the prior art, the inner surface of the cylindrical side wall portion of the valve body and the inner surface of the tip wall portion are perpendicular to the bottom surface of the central portion. Fuel pressure acts (see white arrow).

First, in the prior art, as shown in FIG. 7 (c), the fuel pressure to the central portion bottom surface 112a ₂ of the inner surface of the front end wall portion 112a, a bending moment is generated in the front end wall portion 112a (curved arrow See). This bending moment, the outer surface 112a ₁ of the front end wall portion 112a tensile stress is generated (see black arrow). Further, tensile stress is generated in the tip wall portion 112a by the fuel pressure applied to the cylindrical side wall portion 112b. That is, the fuel pressure applied to the tip wall portion 112a and the cylindrical side wall portion 112b generates tensile stress in the tip wall portion 112a.

In contrast, in the present embodiment, as shown in FIG. 7 (a), since the outer surface 12a ₁ of the front end wall portion 12a is inverted dome structure recessed into the interior side of the valve body 12, the prior art compared to, by the fuel pressure in the central portion bottom surface 12a ₂ of the front end wall portion 12a, the bending moment relaxation occurs in the front end wall portion 12a, the tensile stress (black occurs on the outer surface 12a ₁ of the front end wall portion 12a by the bending moment (See fill arrow) is also relaxed. Further, since a compressive stress is applied to at least the outer periphery of the tip wall portion 12a by the pre-compression imparting ring 18 provided around the tip wall portion 12a, the tip wall is caused by the fuel pressure acting on the tip wall portion 112a and the cylindrical side wall portion 112b. The tensile stress generated in the portion 12a is further smaller than that in the prior art. Incidentally, than the compression stress due to precompression imparting ring 18, since a very stronger tensile stress due to the influence of the fuel pressure in the cylindrical side wall portion 12b, stress generated on the outer surface 12a ₁ of the front end wall portion 12a is compressed as a total It becomes tensile stress, not stress.

Furthermore, in the case of modification of the present embodiment, as shown in FIG. 7 (b), FIG. 7 in comparison with the embodiment of (a), the central portion bottom 12a ₂ the valve body of the inner surface of the front end wall portion 12a 12 of an inverted dome structure raised into the inner side, and is easily effectiveness called arch effect further, the bending moment generated in the front end wall portion 12a by the fuel pressure in the central portion bottom surface 12a ₂ of the front end wall portion 12a is more relaxed. Accordingly, (see black arrow) tensile stress occurring on the outer surface 12a ₁ of the front end wall portion 12a caused by the bending moment is nearest alleviated.

From the above, the tip of the center bottom surface 12a ₂ having the inverted dome structure (see FIG. 7B) is more distal than the center bottom surface 12a ₂ having the flat shape (see FIG. 7A). Since the tensile stress on the outer surface 12a ₁ of the wall 12a is small, the stress concentration on the vicinity of the bottom edge of the counterbore 16a on the outer surface 12a ₁ side of the tip wall 12a (part A in FIG. 6) is relatively small.

Moreover, as is clear from FIG. 2 (a) and FIG. 3, the central portion bottom 12a ₂ include the flat shape towards (see FIG. 7 (a) to) those central bottom 12a ₂ is inverted dome structure Since the change in the cross section in the vicinity of the corner of the outer edge of the central bottom surface 12a ₂ (part B in FIG. 6) is more gradual than (see FIG. 7B), the outer edge of the central bottom surface 12a ₂ The stress concentration near the corner is relatively small.

  Therefore, the fuel injection valve of each embodiment has an individual effect on stress concentration due to the difference in the shape of the bottom surface of the central portion on the inner surface of the tip wall, and which form of fuel injection valve is used for the engine. Can be selected by those skilled in the art according to the specific characteristics and performance required for the fuel injection valve.

  As mentioned above, although the present invention has been described with reference to the above-described embodiments and modifications thereof, the present invention is not limited to these embodiments.

  For example, in the above-described embodiment, the case of an electromagnetic type using an iron core and an electromagnetic coil as the driving means of the needle valve has been described. For example, a mechanical type, a hydraulic type using a cam, a fuel pressure, a piezoelectric element, etc. An electric driving means or the like may be used, and the same effect can be obtained by this. In the above-described embodiment, the cylindrical shape of the valve body has been described. However, the present invention is not limited to the cylindrical valve body. For example, the valve body has a conical shape or a prismatic shape. It may be used.

  As described above, according to the present invention, in the fuel injection valve of the engine, the tensile stress generated in the tip wall portion of the valve body constituting the fuel injection valve by the fuel pressure is reduced, whereby the strength of the tip wall portion is increased. It is possible to further suppress the deterioration of fuel atomization and further improve the combustibility at low loads while securing the fuel. For example, in a vehicle engine, particularly an engine equipped with an air-fuel mixture ignition means May be suitably used in the manufacturing industry of fuel injection valves for injecting fuel.

10 fuel injection valve 11 housing 12, 112 valve body 12a, 112a front end wall portion 12a _1, 112a ₁ outer surface 12a _2, 112a ₂ central bottom 12a _3, 112a ₃ valve seat 12b, 112b cylindrical side wall portion 12c fuel reservoir section 13 Joint member 14, 114 Needle valve 14a, 114a Tip part 14b Stepped part 15 Fuel injection part 16, 116 Injection hole 16a Counterbore 18 Precompression generating ring 20 Electromagnetic coil 30 Fixed iron core 40 Spacer 50 Movable iron core 60 Coil spring 70 Connector X Gap

Claims (3)

A valve body, and a needle valve that is inserted in the valve body so as to be movable in the axial direction. The valve body has a plurality of injection holes in a tip wall portion, and the tip end portion of the needle valve is connected to the valve body. In the fuel injection valve of the engine that sprays fuel from the nozzle by moving away from the valve seat on the outer peripheral portion of the inner surface of the tip wall,
The tip wall portion has a dome shape whose outer surface is recessed toward the inside of the valve body,
A fuel injection valve for an engine, wherein a precompression generating ring for applying a compressive force in advance to at least an outer peripheral surface of the tip wall portion of the valve body is provided. Each of the nozzle holes is disposed such that the direction in which the fuel is sprayed is inclined outward from the center line of the valve body,
The fuel injection valve for an engine according to claim 1, wherein the front end wall portion has a flat bottom surface at the center of the inner surface thereof. Each of the nozzle holes is disposed such that the direction in which the fuel is sprayed is inclined outward from the center line of the valve body,
2. The fuel injection valve for an engine according to claim 1, wherein the tip wall portion has a dome shape in which a bottom surface of a central portion of an inner surface thereof is raised toward an inner side of the valve body.

Images