Fuel injection valve

Abstract

A fuel injection valve realizing improved circumferential uniformity of swirling fuel is provided. The fuel injection valve includes a swirling chamber having an inner peripheral wall whose curvature is gradually larger from upstream to downstream, a path for swirling which, having a fuel flow-in region formed along a valve axis direction, guides fuel to the swirling chamber, and a fuel injection orifice open into the swirling chamber. In the fuel injection valve, the path for swirling is inclined toward the fuel injection orifice formed on a downstream side of the swirling chamber.

Claims

1. A fuel injection valve, comprising: a slidably installed valve element; a nozzle body having a valve seat surface formed thereon where the valve element is seated when the valve is closed and an opening formed on a downstream side of a fuel flow; a path for swirling communicated with the opening of the nozzle body and formed, relative to the nozzle body, on a downstream side of the fuel flow; a swirling chamber formed, relative to the path for swirling, on a downstream side of the fuel flow, the swirling chamber having a cylindrical inner surface and swirling fuel therein thereby providing the fuel with a swirling force; and a fuel injection orifice cylindrically formed at a bottom of the swirling chamber to outwardly spray fuel, wherein the swirling chamber is provided inclinedly toward the fuel injection orifice, so that a longitudinal axis of the path for swirling intersects a line that passes through a center of the opening and a center of the fuel injection orifice, wherein the path for swirling has walls that are straight, the straight walls of the path for swirling defining a projection, the fuel injection orifice has walls that are straight, the straight walls of the fuel injection orifice defining another projection; the entire another projection of the fuel injection orifice does not intersect the projection defined by the path for swirling along both a width direction of the fuel injection valve and a longitudinal direction of the fuel injection valve.

2. The fuel injection valve according to claim 1, wherein a thickness forming part is provided between the swirling chamber and the path for swirling.

3. The fuel injection valve according to claim 1, wherein the swirling chamber directly overlaps the fuel injection orifice, and the path for swirling is offset from the fuel injection orifice, so that the path for swirling does not directly overlap the fuel injection orifice along the width direction of the fuel injection valve, and along the length direction of the fuel injection valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a longitudinal sectional view taken along the valve axis of a fuel injection valve according to an embodiment of the present invention and represents an overall structure of the fuel injection valve;

(2) FIG. 2 is a vertical sectional view of a nozzle body and its vicinity in the fuel injection valve according to the embodiment of the present invention;

(3) FIG. 3 is a plan view of an orifice plate disposed in a lower end portion of the nozzle body included in the fuel injection valve according to the embodiment of the present invention;

(4) FIG. 4 is an enlarged partial view showing an inclined structure of a path for swirling included in the fuel injection valve according to the embodiment of the present invention;

(5) FIG. 5 is a sectional view in the direction of arrows D in FIG. 4;

(6) FIG. 6 is a sectional view in the direction of arrows C in FIG. 4;

(7) FIG. 7 is an enlarged partial plan view for describing the flow of fuel in a path for swirling and a swirling chamber included in an existing orifice plate;

(8) FIG. 8 is a sectional view in the direction of arrows F in FIG. 7;

(9) FIG. 9 is a sectional view in the direction of arrows E in FIG. 7;

(10) FIG. 10 is a sectional view in the direction of arrows G in FIG. 7;

(11) FIG. 11 is a sectional view in the direction of arrows G in FIG. 7;

(12) FIG. 12 is an enlarged partial plan view showing a projecting part formed on a bottom portion of a path for swirling included in the fuel injection valve according to the embodiment of the present invention;

(13) FIG. 13 is a sectional view in the direction of arrows B in FIG. 12;

(14) FIG. 14 is an enlarged partial plan view for describing the flow of fuel in a path for swirling and a swirling chamber included in the orifice plate included in the fuel injection valve according to the embodiment of the present invention; and

(15) FIG. 15 is a sectional view in the direction of arrows G in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(16) An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. FIG. 1 is a longitudinal sectional view taken along the valve axis of a fuel injection valve 1 according to an embodiment of the present invention and represents an overall structure of the valve.

(17) Referring to FIG. 1, in the fuel injection valve 1, a thin-walled, stainless-steel pipe 13 accommodates a nozzle body 2 and a valve element 6, and the valve element 6 is reciprocally moved (for opening/closing operation) by an electromagnetic coil 11 disposed outside the valve element 6. In the following, the structure of the fuel injection valve 1 will be described in detail.

(18) The fuel injection valve 1 includes a magnetic yoke 10 surrounding the electromagnetic coil 11, a core 7 centrally positioned in the electromagnetic coil 11 with one end thereof magnetically connected to the yoke 10, a valve element 6 which can be lifted by a predetermined distance, a valve seat surface 3 which is brought into contact with the valve element 6, a fuel injection chamber 4 which allows fuel flowing between the valve element 6 and the valve seat surface 3 to pass therethrough, and an orifice plate 20 positioned downstream of the fuel injection chamber 4 with plural fuel injection orifices 23a, 23b, 23c, and 23d formed therethrough (see FIGS. 2 to 4).

(19) The core 7 is provided with a spring 8 centrally disposed therein as an elastic member to press the valve element 6 against the valve seat surface 3. The elastic force of the spring 8 is adjusted by the distance by which a spring adjustor 9 is shifted toward the valve seat surface 3.

(20) When the coil 11 is not energized, the valve element 6 and the valve seat surface 3 are kept tightly in contact with each other. In this state, the fuel path is closed, so that the fuel in the fuel injection valve 1 stays there and so that no fuel is injected through the fuel injection orifices 23a, 23b, 23c, and 23d.

(21) When the coil 11 is energized, an electromagnetic force is applied to the valve element 6 causing the valve element 6 to move until it comes into contact with an opposing lower end surface of the core 7.

(22) In this valve-open state, there is a gap between the valve element 6 and the valve seat surface 3, i.e. a fuel path is formed, allowing fuel to be injected through the fuel injection orifices 23a, 23b, 23c, and 23d.

(23) The fuel injection valve 1 includes a fuel path 12 which is provided with a filter 14 installed at an inlet portion thereof. The fuel path 12 includes a through-hole portion centrally extending through the core 7 to guide the fuel pressurized by a fuel pump, not shown, to the fuel injection orifices 23a, 23b, 23c, and 23d via the inside of the fuel injection valve 1. The exterior of the fuel injection valve 1 is covered by an electrically insulating resin mold 15.

(24) As described above, the fuel injection valve 1 controls the amount of fuel supply by reciprocating the valve element 6 between its open and closed positions. This is done by controlling energization/de-energization (using injection pulses) of the coil 11. The fuel injection valve 1, particularly, the valve element 6 used to control the amount of fuel supply is designed not to cause fuel leakage in a closed state thereof in particular.

(25) The valve element 6 used in this type of fuel injection valve includes a mirror-finished ball with high circularity (steel ball for ball bearing based on JIS) which can improve the valve element seat ability. The angle of the valve seat surface 3 with which the ball is to come into tight contact ranges from 80 to 100 degrees which are optimum to facilitate valve seat grinding to achieve high circularity. This makes it possible to maintain very high ball seat ability on the valve seat surface 3. The nozzle body 2 that includes the valve seat surface 3 has high hardness achieved by quenching and is, having undergone demagnetization treatment, free of unwanted magnetism. The valve element 6 structured as described above enables fuel injection amount control free of fuel leakage. Thus, a valve element structure with high cost performance is realized.

(26) FIG. 2 is a vertical sectional view of the nozzle body 2 and its vicinity in the fuel injection valve according to the present embodiment. As shown in FIG. 2, an upper surface 20a of the orifice plate 20 is in contact with an under surface 2a of the nozzle body 2. The outer periphery of the portion in contact with the nozzle body 2 of the orifice plate 20 is fixed by laser welding to the nozzle body 2. In FIG. 2, the orifice plate 20 is shown in a sectional view in the direction of arrows A in FIG. 3.

(27) In the description of the present embodiment, the up-down direction is based on FIG. 1. Namely, in the valve axis direction of the fuel injection valve 1, the fuel path 12 side is the upper side, and the side with the fuel injection orifices 23a, 23b, 23c, and 23d provided is the lower side.

(28) A fuel inlet hole 5 whose diameter is smaller than diameter S of a seating portion 3a of the valve seat surface 3 is provided in a lower end portion of the nozzle body 2. The valve seat surface 3 is conically shaped and the fuel inlet hole 5 is centrally formed at a downstream end of the valve seat surface 3.

(29) The valve seat surface 3 and the fuel inlet hole 5 are formed to be coaxial with the valve axis Y. With the fuel inlet hole 5 formed as described above, flow-in openings 20b communicated with the corresponding downstream fuel paths are formed where the under surface 2a of the nozzle body 2 and the upper surface 20a of the orifice plate 20 are in contact with each other.

(30) The structure of the orifice plate 20 will be described below with reference to FIG. 3. FIG. 3 is a plan view of the orifice plate 20 disposed in a lower end portion of the nozzle body 2 included in the fuel injection valve 1 according to the present embodiment.

(31) The orifice plate 20 has four paths for swirling 21a, 21b, 21c, and 21d which are radially spaced a predetermined distance from the center of the orifice plate 20 and extend radially outwardly while being circumferentially equidistantly spaced from one another (to be 90 degrees apart). The paths for swirling 21a, 21b, 21c, and 21d are concave fuel paths formed on the upper surface 20a of the orifice plate 20.

(32) The path for swirling 21a is formed to communicate, at a downstream end thereof, with a swirling chamber 22a. The path for swirling 21b is formed to communicate, at a downstream end thereof, with a swirling chamber 22b. The path for swirling 21c is formed to communicate, at a downstream end thereof, with a swirling chamber 22c. The path for swirling 21d is formed to communicate, at a downstream end thereof, with a swirling chamber 22d.

(33) The paths for swirling 21a, 21b, 21c, and 21d are for supplying fuel to the swirling chambers 22a, 22b, 22c, and 22d, respectively. In this sense, the paths for swirling 21a, 21b, 21c, and 21d may be referred to as swirling fuel supply paths 21a, 21b, 21c, and 21d.

(34) The swirling chambers 22a, 22b, 22c, and 22d are formed such that their walls are, in the upstream-to-downstream direction, gradually larger in curvature (gradually smaller in curvature radius). The curvature may continuously increase, or it may increase in stages to be constant in each of predetermined ranges.

(35) Typical examples of curves whose curvatures are gradually larger from upstream to downstream include, for example, involute curves (shapes), spiral curves (shapes), and curves formed based on a design technique for centrifugal blowers. Even though the present embodiment is described using a spiral curve as an example, the description also applies to cases where a different curve, for example, one of those mentioned above whose curvature is gradually larger from upstream to downstream is adopted.

(36) Next, with reference to FIGS. 4 to 6, how the path for swirling 21a and the swirling chamber 22a according to the present embodiment are formed and their relationships with the fuel injection orifice 23a will be described.

(37) FIG. 4 is a partial enlarged view for describing relationships between the path for swirling 21a having an inclined structure and each of the swirling chamber 22a and the fuel injection orifice 23a. FIG. 5 is a sectional view in the direction of arrows D in FIG. 4 for describing fuel flows in the path for swirling 21a. FIG. 6 is a sectional view in the direction of arrows C in FIG. 4 for describing fuel flows in the path for swirling 21a and the swirling chamber 22a. The path for swirling 21a is open to, i.e. communicated with, the swirling chamber 22a in the tangential direction of the swirling chamber 22a forming a desired angle shown in FIG. 4. The fuel injection orifice 23a is open in a central portion of swirling of the swirling chamber 22a.

(38) As described in the foregoing, according to the present embodiment, the inner peripheral wall of the swirling chamber 22a is formed to be spiral, as seen on a plane (in a planar sectional view) perpendicular to the valve center axis. The characteristic structure of the swirling chamber 22a that is formed spirally will be briefly described below.

(39) The swirling chamber 22a and the path for swirling 21a are designed such that, in a planar view, the line extended from (line tangential to) the inner wall of the swirling chamber 22a and the line extended from a side wall 21 as of the path for swirling 21a do not intersect on the swirling chamber 22 side. There is a thickness forming part 24a formed between the end of the inner wall of the swirling chamber 22a and the side wall 21 as of the path for swirling 21a. The thickness forming part 24a is required in forming the swirling chamber 22a and the path for swirling 21a.

(40) The spiral curve of the spirally formed inner wall of the swirling chamber 22a has a point of origin (it may be said to be a point of termination in the present embodiment) which coincides with the center of the fuel injection orifice 23a. Hence, the center of the swirling fuel flow along the spiral inner wall of the swirling chamber 22a coincides with the center of the fuel injection orifice 23a. Furthermore, referring to FIG. 4, the inner peripheral wall of the swirling chamber 22a is designed using the following arithmetic spiral equations (1) and (2). The center o of a reference circle X for drawing an arithmetic spiral, the center o based on which the swirling chamber 22a is formed, and the center o of the fuel injection orifice 23a mutually coincide.
R=D/2(1a)(1)
a=Wk/(D/2)/(2)(2)

(41) where R is the distance between the center o based on which the swirling chamber 22a is formed and the inner peripheral wall of the swirling chamber 22a, D is the diameter of the reference circle X for drawing an arithmetic spiral, and Wk is the distance between the ending point E and the starting point S of the swirling chamber 22a.

(42) The path for swirling 21a has a rectangular cross-section to allow fuel to flow through. Though not illustrated, the width and height of the rectangular cross-section are determined by selecting appropriate values meeting specification requirements out of various data obtained by making experiments beforehand based on the diameter of the fuel injection orifice 23a and the diameter of the reference circle used as a size reference for the swirling chamber 22a. Namely, they are selected according to the flow rate and injection angle requirements on the fuel injection valve.

(43) In the following, an inclined structure used in the present embodiment and its effects will be described. First, with reference to FIGS. 7 to 9 schematically showing characteristic portions of a path for swirling 21a having no inclined portion, the flow of fuel in such a path will be described based on the results of analysis conducted by the present inventors.

(44) FIG. 7 is an enlarged partial plan view for describing the flow of fuel in the path for swirling 21a and the swirling chamber 22a included in the orifice plate 20. FIG. 8 is a sectional view in the direction of arrows F in FIG. 7 and is for describing characteristic portions of the fuel flow as observed in the longitudinal direction of the path for swirling 21a. FIG. 9 is a sectional view in the direction of arrows E in FIG. 7 and is for describing characteristic portions of the fuel flow as observed in the height direction of the path for swirling 21a and the swirling chamber 22a.

(45) The fuel flowing in the path for swirling 21a tends to flow, on the inlet side of the swirling chamber 22a, toward the fuel injection orifice 23a. Therefore, in terms of the fuel flow distribution in the width direction of the path for swirling 21a, a fast flow 31b is formed on the side wall 21 as side of the path for swirling 21a compared with the side wall 21 at side and a slow flow 31c is formed on the side wall 21 at side compared with the side wall 21 as side.

(46) The flows 31b and 31c are generated when a flow 31a in the valve axis direction hits, after flowing in through a flow-in opening 20b, a bottom surface 21ab of the path for swirling 21a to be perpendicularly bent there. The flow-in opening 20b is an approximately semicircular gap formed between the opening of the fuel inlet hole 5 and the orifice plate 20.

(47) As shown in FIG. 8, after hitting the bottom surface 21ab of the path for swirling 21a, the flow 31a is slowed down while flowing in the longitudinal direction of the path for swirling 21a and is changed into a slowed-down flow 31e, but the fuel flowing toward the height direction of the swirling chamber 22a cannot form a flow strong enough to generate an adequate swirling effect. A flow 31f flowing toward the bottom of the path for swirling 21a is a flow induced by the flow 31e. It consequently forms a stagnant flow region 31i. Referring to FIG. 9, at the inlet portion of the swirling chamber 22a, a flow 31g formed along the bottom surface 21ab of the path 21a for swirling flows to the thickness forming part 24a side of the swirling chamber 22a. As a result, the flow 31g strongly interferes with a flow 31d (see FIG. 7) on the fuel injection orifice 23a side. This interference results in generating, in the inlet portion of the fuel injection orifice 23a, a flow 31h of a widely different speed, impairing the fuel flow symmetry (the uniformity of swirling fuel flow). This makes a spray Z from the fuel injection orifice 23a asymmetrical as shown in FIG. 10.

(48) The inclined structure of the path for swirling 21a according to the present embodiment suppresses generation of such an unwanted sharp flow and also rectifies the fuel flow in the inlet portion of the swirling chamber 22a in the height direction of the swirling chamber 22a. Reverting to FIGS. 4 to 6, the inclined structure of the path for swirling 21a and the fuel flow therein will be described.

(49) The path for swirling 21a is inclined toward the fuel injection orifice 23a by a desired angle with respect to the inlet portion of the swirling chamber 22a. Namely, referring to FIG. 4, center line D-D of the path for swirling 21a is inclined by angle with respect to line segment B-B perpendicularly crossing line segment C-C passing through the center of the fuel injection orifice 23a. The inclination angle is preferably in the range of 10 to 30. A flow 30a flowing in along the valve axis direction forms, after hitting the bottom 21ab of the path for swirling 21a, flows 30b and 30c which head for the inner peripheral wall near an inlet portion of the swirling chamber 22a. The flow 30b being closer to the fuel injection orifice 23a than the flow 30c flows faster than the flow 30c. In this manner, interference between the fast flow 30b and a flow 30d having swirled in the swirling chamber 22a can be avoided, so that the fuel flowing in the swirling chamber 22a can be adequately swirled. Also, as shown in FIG. 5, a flow 30e heading toward the inlet portion of the swirling chamber 22a is rectified toward the height direction of the path for swirling 21a. Therefore, unlike in existing cases, no large stagnant flow area like the one denoted as 31i in FIG. 8 is generated. With the fuel flow speed in the height direction recovered in the swirling chamber 22a as shown in FIG. 6, the fuel flowing in the swirling chamber 22a reaches the fuel injection orifice 23a after being adequately swirled. This improves the swirling flow symmetry in the outlet portion of the fuel injection orifice 23a.

(50) As shown in FIG. 12, a projecting part 25a is formed to extend over the entire width W of the path for swirling 21a. Length b, in the longitudinal direction of the path for swirling 21a, of the projecting part 25a does not exceed of length L of the path for swirling 21a.

(51) Referring to FIG. 13, height h, in the height direction of the path for swirling 21a, of the projecting part 25a does not exceed of height H of the path for swirling 21a. The projecting part 25a is formed on the downstream side of the path for swirling 21a (on the inlet side of the swirling chamber 22a).

(52) In the structure described above, the fuel entering the path for swirling 21a through the flow-in opening 20b flows, as shown in FIGS. 14 and 15, from the bottom 21ab of the path for swirling 21a toward the upper side of the swirling chamber 22a to be rectified toward the height direction of the swirling chamber 22a (41a and 41b). In this way, the fuel flowing in the swirling chamber 22a is adequately swirled, then reaches the fuel injection orifice 23a. This makes the swirling flow symmetric in the outlet portion of the fuel injection orifice 23a. As a result, the symmetry of the fuel spray from the fuel injection orifice 23a is improved as shown in FIG. 11.

(53) Though not illustrated, the nozzle body 2 and the orifice plate 20 are structured such that they can be positioned with ease in a simple manner using, for example, jigs. This enhances dimensional accuracy when they are assembled. The orifice plate 20 is formed by pressing (plastic forming) advantageous for mass-production. Possible alternative forming methods include electro-discharge machining, electroforming, and etching which can achieve high forming accuracy without applying much stress to the object being formed. With the nozzle body 2 and the orifice plate 20 structured as described above, their production costs are lowered and, with their workability improved, their dimensional variations are reduced. This greatly improves the robustness of the shape and volume of fuel spray generated by the fuel injection valve.

(54) As described above, the fuel injection valve according to an embodiment of the present invention has paths for swirling each inclined with respect to the associated swirling chamber. This serves to suppress interference between the fuel flowing out of each path for swirling and the fuel swirled in the associated swirling chamber and causes the fuel flow to be rectified as observed in a sectional view (in the width and height directions) of each path for swirling. Particularly, the fuel out of each path for swirling enters the inlet portion of the associated swirling chamber where its flow speed is adequately distributed in the height direction of the swirling chamber and is then fed into the swirling chamber. In the swirling chamber, the fuel flows being guided by the spirally formed inner peripheral wall of the swirling chamber, so that the fuel is adequately swirled. In the inlet portion of a fuel injection orifice positioned to be at the center of the swirling fuel, a circumferentially uniformly swirling fuel flow is formed. This promotes causing the fuel to be formed like a thin film.

(55) Furthermore, with the thickness forming parts also provided, the collision between the fuel flowing in each path for swirling and the fuel flowing in the associated swirling chamber is reduced. This further promotes forming a circumferentially uniformly swirling fuel flow and causing the fuel to be formed like a thin film.

(56) A fuel spray formed like a uniformly thin film as described above actively exchanges energy with surrounding air, so that its breakup is promoted immediately after being sprayed. This realizes a finely atomized fuel spray.