Patent Application
20140251263
The present application claims priority from Japanese application serial no. 2013-046088, filed on Mar. 8, 2013, the content of which is hereby incorporated by reference into this application.
The present invention relates to a fuel injection valve for use in an internal combustion engine and, more particularly, to a fuel injection valve capable of spraying swirling fuel to improve fuel atomization performance.
An example of fuel injection valve using a known technique is disclosed in Japanese Unexamined Patent Publication No. 2003-336562. In the technique, atomization of fuel injected from plural fuel injection orifices is promoted making use of a swirling fuel flow.
The fuel injection valve has a valve seat member in which a downstream end of a valve seat cooperating with a valve element has opening formed through the front end surface of the valve seat member and an injector plate joined to the front end surface of the valve seat member. Between the valve seat member and the injector plate, lateral paths and swirling chambers are formed. The lateral paths communicate with the downstream end of the valve seat. The downstream ends of the lateral paths are communicated with the swirling chambers in the tangential directions of the swirling chambers. The injector plate has fuel injection orifices formed therethrough for injecting fuel swirled in the swirling chambers. Each of the fuel injection orifices is shifted by a predetermined distance from the center of the associated swirling chamber toward the upstream end side of the associated lateral path.
The structure described above can effectively promote atomization of fuel injected from each fuel injection orifice.
The fuel injection valve described in Japanese Translation of PCT International Application Publication No. 2000-508739 has a valve seat member including a stationary valve seat, a valve closing member which cooperates with the valve seat member and which can move along the longitudinal axis of the valve, and a circular plate which includes a hole and which is disposed downstream of the valve seat. The circular plate having a hole has at least one flow-in area and at least one flow-out opening. The upper functional plane having at least one flow-in area differs in opening geometry in a cross-sectional view from the lower functional plane having at least one flow-out opening. In the fuel injection valve, the lower end surface of the valve seat member partly and directly covers at least one flow-in area of the circular plate causing at least two flow-out openings to be covered by the valve seat member.
In the structure described above, S-shaped drifting is realized in the fuel flow for fuel atomization improvement, so that a highly-atomized fuel spray shape is obtained.
To inject, from each fuel injection orifice, swirling fuel in which the swirling intensity is substantially symmetric in the circumferential direction of swirling (highly uniform in the circumferential direction), it is necessary to make the fuel swirling in an outlet portion of each fuel injection orifice substantially symmetric (highly uniform in the circumferential direction). For this, it is necessary to properly design fuel flow path shapes including the shapes of swirling chambers and lateral fuel paths (fuel paths for swirling). Particularly, the total volume of fuel flow paths affects the accuracy of fuel injection characteristics (the accuracy deteriorates when the total volume is large). Hence, it is necessary to minimize the total volume of fuel flow paths and increase the uniformity of fuel flow in the circumferential direction in each fuel swirling chamber.
In the existing techniques described in the above patent documents, the fuel coming in along the valve axis direction reaches swirling chambers via lateral paths extending perpendicularly to the valve axis direction. In the above flow path structure, the fuel flow direction abruptly changes in the inlet portion of each lateral path, making the fuel flow uneven as observed in a cross-sectional plane of the flow path. When such an uneven flow of fuel enters each swirling chamber without being adequately rectified, part of the fuel is caused to rapidly flow toward the associated fuel injection orifice, possibly impairing the substantial symmetry (high circumferential uniformity) of the swirling fuel flow.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel injection valve which can improve the circumferential uniformity of swirling fuel.
To achieve the above object, the fuel injection valve according to the present invention includes 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. In the fuel injection valve, the path for swirling is provided inclinedly toward the fuel injection orifice.
According to the present invention, the circumferential uniformity of each swirling fuel flow is increased, forming fuel like a thin film is promoted, and the fuel is finely atomized.
An embodiment of the present invention will be described below with reference to
Referring to
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
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.
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.
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.
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.
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.
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.
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.
In the description of the present embodiment, the up-down direction is based on
A fuel inlet hole 5 whose diameter is smaller than diameter φS 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.
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.
The structure of the orifice plate 20 will be described below with reference to
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.
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.
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.
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.
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.
Next, with reference to
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.
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.
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
R=D/2×(1−a×θ) (1)
a=Wk/(D/2)/(2π) (2)
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.
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.
In the following, an inclined structure used in the present embodiment and its effects will be described. First, with reference to
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.
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.
As shown in
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
The path for swirling 21a is inclined toward the fuel injection orifice 23a by a desired angle θ with respect to the inlet portion of the swirling chamber 22a. Namely, referring to
As shown in
Referring to
In the structure described above, the fuel entering the path for swirling 21a through the flow-in opening 20b flows, as shown in
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-046088 | Mar 2013 | JP | national |
