Patent Application
20060191511
The present application claims priority from Japanese application serial no. 2005-025307, filed on Feb. 1, 2005, the content of which is hereby incorporated by reference into this application.
The present invention relates to a fuel injector used in an internal-combustion engine.
With regard to fuel injectors used in internal-combustion engines, a conventional method of injecting fuel from a plurality of nozzle holes is proposed to enhance injection pattern control and atomization (as described in, for example, Patent Document 1: Japanese Application Patent Laid-open Publication No. 2003-314411 (pages 5 and 6, FIG. 1). The fuel injection nozzle described in Patent Document 1 has a nozzle front chamber, which is flat overall. So fuel flows horizontally from the outer periphery side toward the inner periphery side and isotropically collides immediately above the nozzle holes, thereby encouraging dispersion at the time of injection to enhance atomization.
A means for generating a flat spray pattern is also proposed for a fuel injector used in an internal-combustion engine (as described in, for example, Patent Document 2: Japanese Application Patent Laid-open Publication No. 2004-28078 (pages 6 and 7, FIG. 1)). The fuel injector described in Patent Document 2 has a first nozzle hole section that forms flat fuel sprays in a particular direction, and a second nozzle hole section that forms another fuel spray pattern deflected in one of the directions orthogonal to the fuel sprays formed by the first nozzle hole section. The fuel sprays is formed for injection in the cylinder that is suitable for stratified combustion and homogeneous combustion.
Another means provided for a fuel injector used in an internal-combustion engines produces a spray pattern by which a suitable air-fuel mixture can be formed around the ignition plug (as described in, for example, Patent Document 3: Japanese Application Patent Laid-open Publication No. 2003-534485 (pages 7 and 8, FIG. 1)). The fuel injector described in Patent Document 3 has at least one spacing between spray flows in an area apart from the ignition plug so as to form fuel sprays for in-cylinder injection that are suitable for stratified combustion and homogeneous combustion.
To atomize fuel through a plurality of nozzle holes, the fuel flow rate at the time of injection needs to be kept high in the nozzle holes.
In the prior arts described in Patent Documents 1 to 3, the entire nozzle front chamber is flat so that the fuel flow from the outer periphery toward the inner periphery and subsequent collisions immediately above the nozzle holes allow dispersion to be caused easily to enhance atomization; the structure is not necessarily preferable to further increase the fuel flow rate in the nozzle holes (to, for example, further increase the pressure), and better atomization performance may not be obtained.
Recently, in-cylinder direct-injection gasoline engines (referred to below as in-cylinder injection engines) aimed at achieving high output with low fuel consumption are put in practical use. These in-cylinder injection engines require a fuel spray pattern suitably formed according to the combustion method, combustion chamber shape, combustion chamber size, and other parameters.
As for the technologies disclosed in Patent Documents 2 and 3, exemplary methods of forming spray patterns critically related to the forming of an air-fuel mixture are described; fuel sprays suitable for both stratified combustion and homogeneous combustion can be injected in the cylinder, so fuel pattern collisions with the piston and intake valve can be suppressed (Patent Document 2); an air-fuel mixture that enables stable combustion without contaminating the ignition plug due to smoldering is formed in an ignition plug area so as to achieve stratified combustion operation (Patent Document 3).
The in-cylinder injection engine takes only a short time from when fuel is sprayed until an ignition occurs, so fuel must be evaporated in a short time. This requires fuel to be atomized in order to perform fast evaporation on a larger surface area for the comparable amount of fuel. Accordingly, the spray pattern and fuel atomization affect fuel economy and the amount of unburned fuel (referred to below as HC) and nitrogen oxides (referred to below as NOx) in the exhaust gas from the engine.
For example, fuel may adhere to the inner wall of the cylinder and piston crown surface depending on some spray pattern or fuel drip coarseness, and adhering fuel that remains unevaporated is exhausted without being burned, which decreases the fuel economy and increases the amount of HC. In operation in which injection is performed in an intake process, interference may occur between the intake valve in the open state and the spray. Part of the fuel adhering to the intake valve does not flow into the combustion chamber, which may impede accurate control for the air-to-fuel ratio in the combustion chamber. If the air-to-fuel ratio control is not performed accurately as described above, a too large amount of injection to be supplied to the fuel injector is commanded by feedback control based on an oxygen concentration sensor or the like provided in the exhaust system. Consequently, the amount of HC exhausted may be increased.
When the fuel injector is disposed at the center of the combustion chamber, the positional relation between the spray and ignition plug as well as fuel atomization are important. If liquid fuel or coarse fuel drips directly collide against the ignition plug, the ignition plug may smolder.
To increase the fuel economy and exhaustion performance of an in-cylinder injection engine, it is important to improve the atomization property and perform optimum spray pattern control.
It is an object of the present invention to improve atomization performance of a fuel injector and to provide a fuel injector that enables adjustment of a spray pattern to obtain sprays preferable for an engine.
A fuel injector of the present invention is comprised of: a plunger for opening/closing a fuel path to control the amount of fuel to be injected; a seat portion for the plunger; a plurality of nozzle holes for injecting fuel passed through between the plunger and the seat portion, and the fuel injector further is comprising of:
a nozzle plate provided with the seat portion, and a taper-fuel inlet hole whose diameter is gradually reduced from the seat toward its outlet; and
a orifice plate arranged downstream the taper-fuel inlet hole, and provided with a concave portion opposite to the nozzle plate, and a plurality of nozzle holes being formed concentrically at a bottom of the concave,
wherein the plurality of nozzle holes are formed so that each nozzle hole has an inclined angle in the direction of the plate thickness within the concave area.
Specifically, a fuel inlet hole having a tapered diameter is formed in the fuel path extending from the seat portion of the fuel injector to the plurality of nozzle holes, an orifice plate in a concave shape is provided downstream of the fuel inlet hole, and a plurality of nozzle holes are formed concentrically at the concave bottom of the orifice plate toward the outside. After the fuel flow toward the nozzle holes collides against the central part of the concave bottom, the fuel flows radially and reaches the respective nozzle holes. Since the radial paths are tapered, the fuel flow rates at the outer periphery do not decrease significantly. Accordingly, high-speed fuel flows are achieved, enhancing atomization. The nozzle holes formed concentrically make the fuel flow rates homogeneous, resulting in superior atomization in each hole. Since the orifice plate has a concave shape which enables the mechanical strength to be increased, the injection fuel is highly pressurized. This further increases the fuel flow rate, thereby further enhancing atomization.
Each of the plurality of nozzle holes formed concentrically at the concave bottom of the orifice plate toward the outside has a desired inclined angle inside the concave bottom surface and in the direction of the plate thickness, which enables adjustment of a spray pattern. Particularly, interaction of the spray flows from the individual nozzle holes can be used; when, for example, the nozzle holes are formed close to one another, the surrounding air is suppressed from being introduced and the distance by which the spray travels can be controlled. Conversely, when the nozzle holes are spaced apart from one another, the sprays can be oriented in desired directions by avoiding their interference so as to create substantially flat sprays. This enables injection even in a flat combustion chamber.
A fuel injector according to the present invention forms sprays preferable for an engine by improving atomization performance of the fuel injector and enabling adjustment of a spray pattern.
Embodiments of a fuel injector according to the present invention will be now described.
In
In the nozzle body 13, a guide plate 15 is fixed inside the one end side (upper side in
A ring-shaped damper plate 10 is fixed inside the movable core 7, and its outer periphery edge is supported longitudinally by the top surface of the junction member 8.
A damper motion member 12 is slidably inserted longitudinally across an inner radius of the stationary core 11 and an inner radius of the movable core 7. One end of the damper motion member 12 is positioned so that it is brought into contact with an inner side top surface of the damper plate 10. The damper plate 10 functions as a leaf spring because its outer side potion is supported by the top surface of the joint member 8 and its inner side portion is capable of warping in the axial direction. For example, the damper plate 10 is in a ring-shape, and plural elastic pieces (not shown) formed inside the ring-shape plate protrude inwardly.
The nozzle body 13 is fixed in the nozzle housing 16. A ring 17 for adjusting the stroke of the plunger 6 is interposed between the upper end of the nozzle body 13 and a ring receiving portion of the nozzle housing 16.
A spring adjustment pin 20 is fixed inside the stationary core 11, and a spring 21 is interposed in a compressed state between the spring adjustment pin 20 and the damper motion member 12. One end of the spring 21, which is the spring pin 20-side, acts as a fixed end, and the other end thereof acts as a free end. The spring force of the spring 21 is transferred to the plunger 6 through the damper motion member 12 and damper plate 10. Accordingly, the plunger 6 is pressed against a seat 4 of the nozzle plate 1. In this state, the fuel path is closed, so fuel remains in the fuel injector 100 and the fuel is not injected from a plurality of nozzle holes 29. These nozzle holes 29 are arranged downstream from the fuel inlet hole 3.
The nozzle housing 16, movable core 7, stationary core 11, and yoke 18 form a magnetic circuit that surrounds the electromagnet 19 by one turn.
When an injection pulse as an electric signal is issued, a current flows into the electromagnet 19 and the movable core 7 is attracted toward the stationary core 11 by an electromagnetic force. The plunger 6 then moves up to a position where its upper end comes into contact with the lower end of the stationary core 11. In this state, the plunger 6 is detached from the valve seat 4, and then a circular gap is formed between the plunger 6 and seat 2. So the fuel path is opened, and fuel is injected out from the plurality of fuel nozzle holes 29.
When the injection pulse is turned off, the current to the electromagnet 19 is discontinued and the electromagnetic force is lost; the plunger 6 is returned to the closed state by the spring force of the spring 21, terminating the fuel injection.
An operation of the fuel injector 100 is to control the amount of fuel to be supplied by switching the position of the plunger 6 between the open state and closed state according to the injection pulse, as described above. Another operation of the fuel injector 100 is to form fuel sprays with small fuel particle sizes, that is, superiorly atomized fuel sprays by injecting the fuel from the plurality of nozzle holes 29.
At the tip of the nozzle body 13, the cylindrical fuel path member 14, nozzle plate 1, and orifice place 25 are inserted in that order. The outer periphery of the nozzle plate 1 is fixed by, for example, welding 23.
The nozzle plate 1 has the seat 2, which is a contact portion where the tip of the plunger 6 comes into contact with at the time of valve closing, and the fuel inlet hole 3. The fuel inlet hole 3 is configured by a taper upstream portion 3′, a middle portion 3″ and an extended downstream portion 4. The diameter of the taper upstream portion 3′ is gradually reduced from the seat 2 up to the middle portion 3″. The diameter of the extended downstream portion 4 is extended in a shallow conical-shape from the middle portion 3″ toward downstream. On the downstream side face of the nozzle plate 1, a circular groove 5 is formed around the extended downstream portion 4. A circular protrusion of the orifice plate 25 is fitted into the concave groove 5, and the outer periphery of the orifice plate 25 is fixed to the nozzle plate 1 by, for example, welding 24.
Fuel in nozzle body 13 flows from the upstream of the fuel path member 14 to the fuel inlet hole 3 in the nozzle plate 1 through the outer path of the fuel path member 14 and the bottom path of the member 14. Fuel further proceeds to the plural nozzle holes 29 formed downstream of the fuel inlet hole 3, as indicated by arrows. Then, the fuel is injected out being controlled in a desired direction.
The thickness of the orifice plate 25 and the nozzle holes therein are machined by cutting or stamping. When the outlet portion of the nozzle hole is polished after the machining, the outlet portion of the nozzle hole can have a shape edge.
In
Assuming that the pitch between the nozzle holes, which is formed concentrically in the orifice plate 25, is d2 and the thickness of a concave formed-plate for the fuel path is t, the following relation is obtained:
4<d2/t<8
As d2/t approaches 4, stress decreases and resistance to pressure increases, but too small d2/t makes it difficult to machine holes.
The amount of fuel to be injected can be checked by using the orifice plate 25 alone under low pressure or in an assembled state in which the nozzle plate 1 is combined to the orifice plate 25. It is important to reduce failure rates in subsequent processes.
The nozzle holes 29 are concentrically formed as shown in
This layout of the nozzle holes enables fuel to be equally supplied to the holes which thereby reduces variations in flow rate and assures accurate injection. As for the number of nozzle holes 29 to be preset, various investigations were made in terms of machining and injection performance, and 6 holes were selected as the optimum design value. If, for example, the number of holes is reduced, each hole diameter has to be increased to assure the same amount of flow, so atomization performance is deteriorated.
Conversely, if the number of holes is too increased, each hole-diameter can be reduced to suppress the amount of flow to the comparable value. Consequently, in this case, holes have to be formed closely to one another due to geometrical size restrictions. This causes atomized sprays to mutually interfere or recombine. The resulting sprays are not preferable in terms of both atomization and the shape. The geometrical size restrictions include, for example, the necessity to determine a size required to resist to the pressure and to minimize the spatial volume not required for injection control.
Another surface 28 on which the nozzle holes 29 are open has a surface roughness of 1 μm or less. This enables the opening end of each nozzle hole 29 to have a sharp edge. This structure is advantageous in that, for example, extra drips are not scatter, the injected fuel is directed reliably to a predetermined direction, and atomization performance is improved by a better anti-dripping property of fuel.
In addition, the nozzle holes 29 are open at desired angels on the other surface 28 as shown in
The holes 30a, 30b, and 30c in
For example, the hole 30a is inclined in the 0-degree direction with respect to the X axis in
Reference numeral 31 indicates a mark formed by, for example, marking or punching after the holes have been made. The mark clearly indicates the position at which to attach the orifice plate and the direction in which to direct fuel; the marking is useful when, for example, an engine is mounted.
In view of machinability and mechanical strength as described above, the material of the orifice plate is preferably ferrite-based stainless steel.
Embodiments of injection in a nozzle construction as described above will be described below.
Fuel flows into the fuel inlet hole 3 through the taper upstream portion 3′, and collides against the concave bottom 26 of the orifice plate 25. Thereby, after the fuel-collision to the concave bottom, the fuel flows in radial direction. As the extended downstream portion 4 prevents the fuel flow rate from being reduced, the fuel is supplied to the plurality of nozzle holes 29 that are concentrically formed while high-speed (high-pressure) energy is maintained.
As the fuel radially proceeds along the outward wall surface portion of each nozzle hole 29, a fuel spray injected from the nozzle 29 has a C-shaped flow rate distribution in cross section. The fuel spray having the C-shaped flow rate distribution exchanges its energy with the ambient atmosphere more actively than usual contraction flow-sprays. Consequently, fragmentation of fuel spray particles is encouraged and well-atomized sprays are obtained. To form the C-shaped flow rate distribution more reliably, the ratio do/d of the distance do between the centers of nozzle holes to the diameter d of the fuel inlet hole 3 is preferably preset to 2 or more.
FIGS. 5 (a), 5 (b), and 5 (c) schematically show fuel sprays 31 in three ways, according to a picture of sprays that is obtained by using strobe light or a laser beam to optically take the picture.
In
The sprays 31 in
The sprays 31 in
As described above, the fuel spray pattern of the fuel injector 100 is flat. The sprays 31 are inclined relative to the angle at which the fuel injector 100 is installed, so that the sprays travel toward the ignition plug 110. In ignition in the compression process, the energy of the sprays injected tends to be reduced because the pressure in the cylinder is high. However, the spray 31a of the sprays 31 in the present invention travels a sufficient distance toward the ignition plug 110. As a result, a fuel/air mixture, which is produced by mixing fuel drips or evaporated fuel and air, stays near the ignition plug 110 for a relative long period of time, thereby increasing the stability of combustion. The increased combustion stability provides a great degree of freedom in the setting of an ignition timing or injection timing. This improves the thermal efficiency of the engine and reduces fuel consumption. When this type of engine is mounted in an automobile, the high consumption stability enables stratified combustion to be performed over a wide range of engine loads and the number of revolutions, thereby reducing the fuel consumption.
Another advantage of the flat sprays is that collisions between the fuel and piston 103 are reduced and unburned fuel is suppressed from being exhausted. When fuel is injected in the compression process, the amount of fuel directed toward the piston 103 is preferably small because the distance between the fuel injector 100 and piston 103 is short and the piston approaches the fuel injector 100 with the time elapsed from the ignition. The travel distance is also preferably small.
As for ordinary in-cylinder injection gasoline engines, combustion stability is assured by colliding fuel to the piston to direct an air/fuel mixture to the ignition plug. When the fuel injector as shown in
In
In
Reference numeral 44 in
Sprays 43 are nearly flat as shown in FIGS. 7 (a) to 7 (c). This is because the spreads of the sprays 43 injected from the nozzle holes are almost the same and energy conversion into the ambient atmosphere is also almost the same. Such a spray form causes the sprays to travel by the almost the same distance. The fuel injector is designed so that the sprays 43 do not cause mutual interference. Well-atomized sprays are thus obtained. It is advisable to provide these sprays in the space in the combustion chamber where they become flat in the compression process. Since the sprays are in a V-shaped form, adhesion of the fuel to the intake valve can be avoided, thereby increasing the stability of combustion.
In
The sprays 60 in
When the fuel injector 300 is disposed near the center of the combustion chamber as shown in
The fuel injector 300 in this embodiment enables creation of an area 61 in which there is almost no fuel distribution. Therefore, an air-fuel mixture can be formed near the ignition plug 110 without the ignition plug 110 from being contaminated, increasing the stability of combustion.
The contamination of the ignition plug 110 occurs in an injection layout as shown in
According to the this embodiment, a fuel injector 300 that can form a suitable spray pattern can be provided even for an engine in which the fuel injector 300 is disposed near the center of the combustion chamber. As a result, the stability of combustion by the engine is increased, less fuel is consumed, and exhaustion is reduced.
FIGS. 10 (a) and 10 (b) show a fifth embodiment of the present invention in which exemplary positions of nozzle holes 63 and 64 formed in the orifice plate. That is, reference numerals 63a to 63f are one example of the nozzle holes on in the orifice plate, reference numerals 64a to 64f are another example of the nozzle holes in the orifice plate. The sprays are formed by modifying the layout and inclination of the nozzle holes of the previously mentioned embodiments.
In FIGS. 10 (a) and 10 (b), the nozzle holes 63a to 63f and 64a to 64f are concentrically formed; the nozzle holes 63a to 63f are disposed in an uneven pitch, and the nozzle holes 64a to 64f are also disposed in an uneven pitch and have uneven diameters. An advantage of the nozzle holes 63a to 63f formed concentrically in an uneven pitch is that the amount of fuel injected from each hole can be equalized and the degree of freedom in the spray pattern can be increased. As for the nozzle holes 64a to 64f that are also formed concentrically in an uneven pitch and have uneven diameters, in addition to equalizing the amount of fuel injected from each hole and increasing the degree of freedom in the spray pattern, the amount of injection at each hole position can be changed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-025307 | Feb 2005 | JP | national |
