DESCRIPTION TITLE OF THE INVENTION FUEL INJECTION VALVE BACKGROUND OF THE INVENTION
[FIELD OF THE INVENTION]
[0001] The present invention relates to a fuel injection valve that is used to supply fuel to an internal combustion engine of an automobile, etc., and particularly relates to a fuel injection valve that achieves promotion of atomization in spraying characteristics, DESCRIPTION OF THE ART
[BACKGROUND ART]
[0002] In recent years, while exhaust emission regulations for internal combustion engines of automobiles, etc., have been tightened, there is demand for atomization of fuel sprays that are emitted from fuel injection valves. For example, in the conventional art described in Patent Document 1, an examination is made for achieving atomization by forming a swirl flow.
That is, in Patent Document 1, a type in which a valve closing member that cooperates with a valve seat surface is disposed within a valve casing, is configured to have the valve casing that is formed symmetrically with respect to a longitudinal direction thereof and is characterized in that a center opening is provided downstream

of the valve seat surface, at least two tangential passages extend in a radial direction from the center opening, the respective tangential passages are opened at respective swirl chambers in a tangential direction, and a constant-quantity opening for fuel leads from the center of each swirl chamber to the outside. A flow regulated and accelerated by a guide passage enters into each swirl chamber, and the fuel causes a swirl flow in the swirl chamber. Then, while the fuel is swirling within an injection hole, the fuel is jetted out from an outlet of an injection hole plate as a hollow conical spray, whereby atomization is promoted.
[CITATION LIST] PATENT DOCUMENT
[0003] Patent Document 1: Japanese Laid-Open Patent Publication No. H01-271656
SUMMARY OF THE INVENTION
[PROBLEMS TO BE SOLVED BY THE INVENTION]
[0004] In such an atomization method using a swirl flow, a liquid film peels off within the injection hole due to the swirl flow. Thus, the fuel injection flow rate per injection hole is low as compared to a method in which each injection hole is filled with fuel. Moreover, the layout property is poor due to the presence of the swirl chambers and the fuel

passages, so that it is difficult to provide many injection holes. Because of these problems, with the atomization method using a swirl flow, it is difficult to achieve a high flow rate required by an engine having a large displacement volume.
In addition, since the passages and the swirl chambers are provided at the upstream side with respect to the injection holes, a dead volume is larger than that in other atomization methods. Thus, immediately after start of injection, fuel that is insufficiently regulated in flow and insufficiently accelerated is injected, so that there is a problem that atomization of fuel spray in the initial period of injection deteriorates.
The present invention has been made to solve the above-described problems, and provides a fuel injection valve having a high injection flow rate and a small dead volume even while achieving favorable atomization by using a swirl type atomization method.
[SOLUTION TO THE PROBLEMS]
[0005] A fuel injection valve according to the present invention includes: a valve seat; a valve body for opening/closing the valve seat; an injection hole plate mounted at an opening portion of the valve seat and having injection holes, wherein, as a result of actuating the valve

body, fuel passes through a gap between the valve seat and the valve body and is injected from the injection holes of the injection hole plate, a plurality of cylindrical swirl chambers in which the injection holes are opened, and a first fuel introduction passage for introducing the fuel to the plurality of swirl chambers are formed in the injection hole plate, and when a diameter of each swirl chamber is defined as D, a width of the first fuel introduction passage is defined as W, and a distance between a center of the swirl chamber and a line obtained by linearly extending a central axis of the first fuel introduction passage at a downstream-side end portion is defined as L, a relationship of L<(D-W)/2 is satisfied.
[EFFECT OF THE INVENTION]
[0006] With the fuel injection valve of the present invention, a high injection flow rate can be achieved without decreasing the diameter of each swirl chamber. In addition, since it is not necessary to decrease the diameter of each swirl chamber, machinability of the injection holes is favorable. Furthermore, a dead volume can be reduced, so that a favorably atomized spray can be achieved from the initial period of injection.
[BRIEF DESCRIPTION OF THE DRAWINGS]

[0007] [FIG. 1] FIG. 1 is a cross-sectional view of a fuel injection valve of Embodiment 1.
[FIG. 2A] FIG. 2A shows a cross-sectional view of a tip portion of the fuel injection valve of Embodiment 1.
[FIG. 2B] FIG. 2B shows a plan view of a tip portion of the fuel injection valve of Embodiment 1.
[FIG. 3] FIG. 3 is an enlarged diagram of the plan view of the tip portion of the fuel injection valve of Embodiment 1.
[FIG. 4] FIG. 4 is a diagram showing a dimensional relationship in a plan view of the tip portion of the fuel injection valve of Embodiment 1.
[FIG. 5] FIG. 5 is a diagram showing a fuel flow at the tip portion of the fuel injection valve of Embodiment 1.
[FIG. 6] FIG. 6 is a diagram showing a dimensional relationship in a plan view of a tip portion of a conventional fuel injection valve.
[FIG. 7] FIG. 7 is a diagram showing a fuel flow at the tip portion of the conventional fuel injection valve.
[FIG. 8] FIG. 8 is a plan view of a tip portion of a fuel injection valve of Embodiment 2,
[FIG. 9] FIG. 9 is a plan view of a tip portion of a fuel injection valve of Embodiment 3,

[FIG. 10] FIG. 10 is a plan view of a tip portion of a fuel injection valve of Embodiment 4.
[FIG. 11] FIG. 11 is a plan view of a tip portion of a fuel injection valve of Embodiment 5.
DETAILED DESCRIBED OF THE PREFERRED EMBODIMENT [0008] Embodiment 1
FIG. 1 shows a cross-sectional view of a fuel injection valve of Embodiment 1. FIGS. 2A to 4 show a tip portion of the fuel injection valve of Embodiment 1, FIG. 2A and 2B show a cross-sectional view and a plan view of the tip portion, FIG. 3 shows an enlarged view of the plan view, and FIG. 4 shows a dimensional relationship in a plan view. In the drawings, reference character 1 denotes the fuel injection valve, reference character 4 denotes a solenoid device, reference character 5 denotes a housing that is a yoke portion of a magnetic circuit, reference character 6 denotes a core that is a fixed core portion of the magnetic circuit, reference character 7 denotes a coil, reference character 8 denotes an armature that is a movable core portion of the magnetic circuit, reference character 9 denotes a valve device, and the valve device 9 includes a valve body 10, a valve main body 11, and a valve seat 12. The valve main body 11 is press-fitted onto an outer diameter portion of the core 6 and then welded thereto. The armature

8 is press-fitted onto the valve body 10 and then welded thereto. An injection hole plate 13 is connected to the valve seat 12. In the injection hole plate 13, a plurality of injection holes 14 are provided so as to penetrate in a plate thickness direction thereof. In each embodiment, components designated by the same reference characters denote same or corresponding components.
[0009] Next, operation will be described. When an actuating signal is sent from a controller (not shown) of an engine to a drive circuit (not shown) of the fuel injection valve 1, an electric current is applied to the coil 7 of the fuel injection valve 1, and a magnetic flux occurs in the magnetic circuit, which is composed of the armature 8, the core 6, the housing 5, and the valve main body 11, so that the armature 8 is attracted and moved to the core 6 side, and the valve body 10, which is integrated with the armature 8, is separated from a valve seat portion 12a to form a gap therebetween. At this time, fuel flows from chamfered portions 15a of a ball 15 that is welded to a tip portion of the valve body 10, through the gap between the valve seat portion 12a and the valve body 10, and is injected through the plurality of injection holes 14 to an engine air intake passage (not shown). Next, when an operation stop signal is sent from the controller of the engine to the drive circuit of the fuel injection valve, the application of the electric

current to the coil 7 stops, and the magnetic flux in the magnetic circuit decreases, so that the gap between the valve body 10 and the valve seat portion 12a is closed by a compression spring 16 that presses the valve body 10 in a valve-closing direction, whereby the fuel injection ends. The valve body 10 slides at an armature side surface 8a relative to a guide portion of the valve main body 11, and an armature upper surface 8b is in contact with the lower surface of the core 6 in a valve-opened state. [0010] In Embodiment 1, as shown in FIGS. 2A to 4, a plurality of swirl chambers 17, and an fuel introduction passage 18 for introducing the fuel from a valve seat opening 12b to the swirl chambers 17 are formed by recessing a part of the upstream-side end surface of the injection hole plate 13, and the injection holes 14 are opened at the centers of the swirl chambers 17. Each swirl chamber 17 is formed in a cylindrical shape having a diameter larger than the width of the fuel introduction passage 18. The fuel introduction passage 18 communicates at the upstream side thereof with the valve seat opening portion 12b, communicates at the downstream side thereof with the swirl chambers 17, and is located such that an extension of the central axis of the fuel introduction passage 18 does not intersect the center of each swirl chamber 17. The bottom surfaces of the fuel introduction passage 18 and the swirl chambers 17 are flat

surfaces having the same depth from the upstream-side end surface of the injection hole plate 13.
[0011] With the above configuration, the fuel that has flowed from the fuel introduction passage 18 into each swirl chamber 17 flows into the injection hole while causing a swirl flow. By the swirl flow being maintained also within the injection hole, a liquid film peels off, and a thin liquid film is formed on an inner wall of the injection hole and jetted out from the injection hole, whereby atomization is promoted.
Furthermore, since the plurality of the swirl chambers 17 and the plurality of injection holes 14 corresponding to the swirl chambers 17 are provided, the injection flow rate per injection hole can be reduced as compared to a configuration in which only one injection hole 14 is provided. Thus, the liquid film formed on the inner wall of each inj ection hole is further thinned, so that atomization becomes further favorable.
[0012] However, as described above, in an atomization method using a swirl flow, since a liquid film peels off within each injection hole by the swirl flow, the fuel injection flow rate per injection hole is low as compared to a method in which each injection hole is filled with fuel, and also, due to the layout property of the fuel introduction passages and the swirl chambers, it is difficult to provide

many injection holes. Thus, there is a problem that it is difficult to achieve a high flow rate required by an engine having a large displacement volume. FIG. 6 shows a fuel injection valve employing a conventional swirl method. In the case where the fuel introduction passage 18 has a linear shape and communicates with the swirl chamber 17 such that the wall surface of the fuel introduction passage 18 has a tangential relationship with the wall surface of the swirl chamber 17 as shown in FIG. 6, the distance L between the center of the swirl chamber 17 and a line 19 obtained by linearly extending the central axis of the fuel introduction passage 18, the diameter D of the swirl chamber 17, and the width W of the fuel introduction passage 18 have a relationship of L=(D-W)/2. In this case, as shown in FIG. 7, a fuel flow is formed along the inner wall of the swirl chamber 17.
[0013] A formula based on the potential theory is applicable to prediction of a flow rate of a fuel injection valve employing a general swirl method, and a flow rate q, a cross-sectional area Si of a fuel introduction passage, an injection hole diameter re, a swirl chamber diameter ri, and a ratio k of the injection hole diameter and the diameter of a hollow portion formed within the injection hole have a
relationship of q^k, Si, re/ri. Thus, examples of means for increasing an injection flow rate in order to allow the fuel

injection valve to be mounted on an engine that requires a high injection flow rate include a method for increasing the cross-sectional area Si of the fuel introduction passage, a method for decreasing the swirl chamber diameter ri, and a method for increasing the injection hole diameter re. In the case where the cross-sectional area Si of the fuel introduction passage is increased, a dead volume increases, so that fuel that is insufficiently regulated in flow and insufficiently accelerated is injected immediately after start of injection. Thus, there is a problem that atomization of fuel spray in the initial period of injection deteriorates.
In addition, in the case where the swirl chamber diameter ri is decreased, the angular velocity of a fuel flow within the injection hole decreases, so that the spread angle of spray decreases. On the other hand, in the case where the injection hole diameter re is increased, the angular velocity of a fuel flow within the injection hole increases, so that the spread angle of spray increases. Thus, in order to achieve a high injection flow rate with an appropriate spread angle of spray maintained, it is necessary to find out a combination of appropriate dimensions of the swirl chamber diameter ri and the injection hole diameter re. However, due to reasons such as displacement, shear drop, and a fracture surface that occur in machining the injection hole, when

machinability of the injection hole is taken into consideration, it is necessary to provide a gap between the circumference of the injection hole and the inner wall portion of the swirl chamber. When not only the swirl chamber diameter ri is decreased but also the injection hole diameter re is increased, the gap between the circumference of the injection hole and the inner wall portion of the swirl chamber becomes narrow, so that there is a limit on an increase in the injection flow rate.
[0014] Therefore, in Embodiment 1, when the diameter of each swirl chamber 17 is defined as D, the width of the fuel introduction passage 18 is defined as W, and the distance between the center of the swirl chamber 17 and the line 19 obtained by linearly extending the central axis of the fuel introduction passage 18 at a downstream-side end portion of the fuel introduction passage 18 is defined as L as shown in FIG. 4, a relationship of L<(D-W)/2 is satisfied. Here, the fuel introduction passage 18 is defined as a region having a uniform width W, and the downstream end portion of the fuel introduction passage 18 intersects the swirl chamber 17 and indicates a position where the uniform width W is not obtained. By causing the distance L between the line 19 and the center of the swirl chamber 17 to have a smaller relationship than in the conventional art, a fuel flow 20 entering from the fuel introduction passage 18 into the swirl

chamber 17 flows into a position near the center of the swirl chamber 17 as shown in FIG. 5, so that a swirl flow occurs in a range narrower than the region surrounded by the inner wall of the swirl chamber 17. Thus, since the swirl flow occurs in the narrow range similarly as in the case where the diameter of the swirl chamber 17 is decreased in the above-described formula based on the potential theory, a high injection flow rate can be achieved without decreasing the diameter of the swirl chamber.
In addition, as compared to the means for achieving a high flow rate by decreasing the diameter of the swirl chamber 17, it is not necessary to decrease the diameter of the swirl chamber 17, and a desired gap can be ensured between the circumference of the injection hole 14 and the inner wall portion of the swirl chamber 17, so that machinability of the injection hole 14 becomes favorable.
Furthermore, as compared to the means for achieving a high flow rate by increasing the cross-sectional area of the fuel introduction passage 18, the dead volume can be reduced, so that a favorably atomized spray can be achieved from the initial period of injection. [0015] Embodiment 2
FIG. 8 shows a tip portion of a fuel injection valve of Embodiment 2. For achieving atomization of a fuel spray, it is important to form a thin and uniform liquid film

on the inner wall of the injection hole. If a swirl flow occurring in the injection hole 14 is biased, a liquid film formed on the inner wall of the injection hole is locally thick, so that there is a possibility that atomization performance is impaired. Therefore, in Embodiment 2, a second fuel introduction passage 21 for introducing the fuel to each swirl chamber 17 from a direction different from that of the fuel introduction passage 18 is provided. In this case, the fuel introduction passage 18 and the second fuel introduction passage 21 communicate with each swirl chamber 17 such that the direction of swirl caused by the fuel flowing from the fuel introduction passage 18 into the swirl chamber 17 coincides with the direction of swirl caused by the fuel flowing from the second fuel introduction passage 21 into the swirl chamber 17. Accordingly, the fuel flows into the swirl chamber 17 from two directions, and thus the thickness of a liquid film formed on the inner wall of the injection hole 14 becomes uniform as compared to the case where the fuel flows into the swirl chamber 17 from only one direction, so that the degree of atomization of a fuel spray becomes favorable.
[0016] In addition, each injection hole 14 is opened at the center of the swirl chamber 17, and a relationship of L