The present invention relates to a fuel injection valve.
As a conventional fuel injection valve making direct injection into a cylinder, there has been proposed a fuel injection valve that is capable of making injection with respect to any target position, without being affected by air flow in the cylinder, and further that includes a plurality of nozzle holes each having a small diameter. In such a fuel injection valve, to make smooth injection with respect to respectively different target positions, the configuration of a cavity, which is situated from a seal portion of a valve to numerous nozzle holes, and the direction of nozzle holes are varied.
However, in such a case, depending on layout of respective nozzle holes and direction of respective nozzle holes, there are different flows of fuel flow from the cavity to the nozzle holes. Consequently, to obtain stable spray characteristics (particle size, directivity, divergence angle of spray, and penetration force) at respective nozzle holes, it is necessary to repeat test or the like, thus a large number of time is required.
For example, there has been conventionally proposed a fuel injection valve, which comprises a valve body including a hole and a cavity that are formed in a valve seat, a plate that is joined to the cavity by welding, as well as includes a plurality of nozzle holes, and a valve element that moves up and down along the central axis of the valve body to open and close the hole, and in which the atomization of spray is achieved by designing the structures of the nozzle hole plate and the cavity (refer to Patent Document 1).
In such a fuel injection valve, when setting the configuration of nozzle holes and the angle of the nozzle holes individually at respective nozzle holes, the flows of fuel from the cavity to the nozzle holes will be changed at each of the nozzle holes respectively. Hence a problem exists in that the nozzle holes have respectively different spray characteristics (particle size, directivity, divergence angle of spray, and penetration force).
Furthermore, there has been proposed another fuel injection nozzle in which whirling means is located at the end portion of a needle (refer to Patent Document 2).
In this case, even if a whirling force is generated in fuel, since the nozzle holes are positioned in the center of a cavity, it is difficult to construct the nozzle holes for making injection with respect to different positions. Furthermore, the strength of a whirling force is largely affected by a centrifugal force, so that the whirling force comes to be smaller in the central portion of the cavity. Moreover, the diameter of nozzle holes is apparently smaller as compared with the diameter of a cavity, and thus a whirling force having been generated in the cavity is largely decreased when fuel flows into the nozzle holes. Consequently, a problem exists in that effective whirling force cannot be obtained.
Moreover, there has been provided a fuel injection valve in which a plurality of nozzle holes are formed in a measuring plate, as well as a whirl flow-generating groove is formed on the top of the measuring plate (refer to Patent Document 3).
Providing only such a whirl flow-generating groove raises the possibility that there is some fuel not passing through the whirl flow-generating groove, but flowing directly into nozzle holes. Furthermore, in the case where there is provided any whirl flow-generating groove in order to generate the whirl flow upstream of respective nozzle holes, when a nozzle hole pitch is made small, flows of fuel toward the adjacent nozzle holes are interfered with each other. Thus, a problem exists in the occurrence of fluctuation in characteristics.
Further, it becomes necessary that the whirling groove and nozzle holes be formed in the same measuring plate, thus arising a dimensional problem that the nozzle hole pate comes to be larger. Then, in case of a large nozzle hole plate, the area presented to pressure is increased when it is used under high fuel pressure. Consequently, a further problem exists in lower reliability.
Patent Document 1: the Japanese Patent No. 3655905
Patent Document 2: the Japanese Patent Publication (unexamined) No. 158989/1996
Patent Document 3: the Japanese Patent Publication (unexamined) No. 340121/2004
The problem to be solved is that stable spray characteristics (particle size, directivity, and penetration force) cannot be obtained at respective nozzle holes, and flows of fuel toward respective nozzle holes are interfered with each other. Moreover, a further problem exits in that spray characteristics cannot be arbitrarily changed at respective nozzle holes.
In the present invention, there is provided a member giving a whirling force to fuel, the whirl flow is formed in a cavity downstream of a seal portion of a valve, and all nozzle holes are disposed at positions of substantially the same diameter on the outer circumferential portion of the cavity where velocity of the flow is high. As a result of such a construction, it becomes possible to cause fuel of high flow velocity having an inflow angle to flow into openings of the nozzle holes.
In this construction, the inflow area of fuel when flowing into the openings of the nozzle holes comes to be smaller, and further the flow velocity thereof at the time of flowing into the nozzle holes becomes higher. Furthermore, in the vicinity of the openings of the nozzle holes, fuel having higher flow velocity flows only in one side with respect to the cross section of the nozzle holes, so that a contraction flow is generated in the nozzle holes, and further atomization is achieved as well. This phenomenon occurs only in the openings of the nozzle holes. Even if the direction of nozzle holes is changed, the same effect can be obtained.
Thus, in the case of relatively low pressure of fuel, even when nozzle hole directions are set with respect to predetermined respectively different targets, it is possible for respective nozzle holes to easily obtain stable spray characteristics (particle size, directivity, and penetration force).
According to the invention, an advantage exists in that, in spite of different target positions to be subjected to injection at respective nozzle holes, it is possible to suppress fluctuation in spray characteristics (particle size, directivity, divergence angle of spray, and penetration force) at respective nozzle holes, and to easily obtain a stable spray. Furthermore, in the conventional apparatuses, the generation of high fuel pressure (for example, 20 Mpa) is required to carry out atomization. Whereas, according to the invention, a further advantage exists in that about the same level of effect as that of the conventional apparatuses can be obtained under lower fuel pressure (for example, 12 Mpa).
A preferred embodiment according to the present invention is hereinafter described with reference to the drawings.
In the valve main body 3, there is provided a valve body 10. To this valve body 10, a whirler 11 acting to generate a whirling force in fuel, a valve seat 12 including a seat portion 12a and a cylindrical portion 12b, as well as an orifice plate 14 that includes a plurality of nozzle holes 13 and measures the quantity of flow, are fixed.
A needle valve 16, being a valve element including an armature 15 acting as a moving iron core is supported in a slidable manner in the valve body 10 and the whirler 11. By this needle valve 16 moving up and down, the valve is opened and closed. The compressive force of a spring 17, which is located in an internal part of the core 4, is adjusted by means of a rod 18. Sealing properties of the valve element 16 are determined by the compressive force provided by the spring 17 and the fluid force that is generated by the fact that the pressure of fuel is applied to the valve element 16.
In response to a valve-opening signal from a control device, not shown, due to the fact that current is carried through the coil 9, the armature 15, being a moving iron core, is attracted to the core 4, being a fixed iron core. Then, at a time point when this attraction is larger than the compressive force provided by the spring 17 and the fluid force generated by fuel pressure, the valve is open. At this time, as to an opening area of the seat portion 12a, a lift amount of the needle 16 is a distance until the needle 16 comes in contact with a stopper 19, so that the opening area of the seat portion 12a is determined by this lift amount. At the time of valve closing, current having been carried through the coil 9 is interrupted, and thus the valve comes to be closed due to the compressive force provided by the spring 17.
As for the flow of fuel herein, fuel, to which pressure has been applied to a higher pressure by means of a fuel pump, not shown (for example, a fuel pressure is 12 Mpa), is fed to the fuel injection valve 1 through a delivery pipe, not shown. At the time of valve closing, an internal part of the fuel injection valve 1 is filled with a high-pressure fuel up to the needle valve 16 and the seat portion 12a of the valve seat 12. With valve opening signal from the control device, not shown, the needle 16 is lifted to valve-open position, and first a high-pressure fuel flows into a cavity 20 that is formed of the valve seat 12 downstream of the seat portion 12a, and the orifice plate 14. After the cavity 20 has been filled with the high-pressure fuel, the fuel is injected toward respective predetermined target positions from the nozzle holes 13 respectively.
According to the invention, openings of respective nozzle holes 13 facing to the cavity 20 are formed at the outer circumferential portion on the downstream side of the cavity 20, so that fuel having a certain amount of inflow angle and the maximum velocity flows into the openings of the nozzle holes 13. That is, fuel including the main flow that is formed in the entire cavity 20 and is stable, comes to flow in each of the nozzle holes 13.
As shown in
According to the invention, flow rate is measured by means of the orifice plate 14, and pressure loss that is generated in the internal part of a fuel injection valve 1 comes to be the maximum in the nozzle holes 13. Accordingly, even if fuel flows out from the nozzle holes 13, the whirl flow in the cavity 20 is not affected. Therefore, fuel flows into respective nozzle holes 13 in a stable manner irrespective of the angle from an opening to an outlet. Thus, even if the direction of nozzle holes 13 is changed, only a direction with respect to any target position comes be changed, thus making it possible to easily set the nozzle holes 13 corresponding to individual target positions respectively without affecting fuel spray characteristics (particle size, divergence angle of spray, and penetration force). In this manner, it is possible to set various spray characteristics by arbitrarily setting angles from the opening to the outlet of respective nozzle holes 13.
Due to the fact that fuel flows in the internal part of nozzle holes 13, it becomes possible to atomize fuel with low fuel pressure as compared with the conventional apparatuses. Further, as shown in
Thus, it is possible that fuel having been pressed to the outer circumferential surface of the cavity 20 is further pressurized by the centrifugal force, and that the inflow angle of fuel is made larger with respect to the axis of respective nozzle holes 13. Consequently, it is possible to achieve further atomization of fuel.
a) and (b) are enlarged cross sectional views showing a tapered portion.
Due to the construction as described above, conventionally the fuel pressure of approximately 20 Mpa is required, while according to the invention, about the same level of effect can be obtained with the fuel pressure of approximately 12 Mpa.
The flow velocity and the angle of inclination of fuel in the internal part of the cavity 20, as well as the pressure of fuel above the nozzle holes 13 are affected by the configuration of the substantially cylindrical portion 12b, the taper angle C, and the pitch diameter φd of the nozzle holes 13. For example, in the case where a taper angle C is small, the fuel pressure above the nozzle holes 13 is reduced. On the contrary, in the case where the taper angle C is large, the resistance when fuel runs against the wall of the cavity 20 becomes larger, so that the flow velocity does not come to be larger.
Furthermore, the same problem as described above arises also in a ratio between the inside diameter of the substantially cylindrical portion 12b and the pitch diameter φd of the nozzle holes 13. It has been acknowledged from test results that the balance between the fuel pressure and the flow velocity is appropriately achieved in the case in which a taper angle C is 120° to 150°.
Supposing that the contact part between the valve seat 12 and the orifice plate 14, and the outermost diameter portion of the nozzle holes 13 come close, a problem exists in that the velocity of fuel is decreased due to resistance on the wall in the vicinity of the wall of the cavity 20. To cope with this, it is necessary to provide a certain difference between the contact diameter φe between the valve seat 12 and the orifice plate 14, and the pitch diameter φd1 of the outermost diameter of the nozzle holes 13.
It has been acknowledged from test results that, as the above-mentioned difference, setting a difference of about the nozzle diameter φh is required. In addition, it has been acknowledged from test results that setting a ratio between the inside diameter φf the substantially cylindrical portion 12b and the pitch diameter φd of the nozzle holes 13 to be 1.5 to 2.0 is suitable. Further, it is necessary that the pitch diameter φd2 of the innermost diameter in the opening of the nozzle holes 13 facing the cavity 20 side is formed larger than the inside diameter Of the substantially cylindrical portion 12b. Such construction is employed because of smaller effect of the centrifugal force, and lower flow velocity within the range of the inside diameter φf of the substantially cylindrical portion.
Moreover, the cavity 20 is formed on the downstream side of the seat portion 12a, so that when the capacity of the cavity 20 is made larger, it will take a long time period for the cavity 20 to be filled with high-pressure fuel. Hence, a problem exists in a longer time period until fuel injection. Furthermore, after a valve has been opened, a problem exists in that the fuel left in the cavity 20 drips in the internal part of the cylinder of an engine. It has been acknowledged that forming the inside diameter φf of the substantially cylindrical portion 12b in the cavity 20 to be in the range of 0.6 mm to 1.0 mm is suitable.
Further, when the cross section of the substantially cylindrical portion 12b comes to be small as compared with the gross sectional area of the nozzle holes 13, the whirling force of fuel will be reduced. Therefore, it is necessary that the cross section of the cylindrical portion 12b is not less than 1.5 times the gross sectional area of the nozzle holes 13.
As to the layout of nozzle holes 13, when a distance k between pitches of the adjacent nozzle holes is a small value, fuel to flow into the adjacent nozzle holes 13 will be interfered with each other, and thus fluctuation in inflow angle and flow velocity of fuel to flow into the nozzle holes 13 may take place between the nozzle holes 13. Consequently, fluctuation in spray characteristics will also arise, so that it is necessary that the distance k between pitches of the nozzle holes 13 is set to be not less than 2.5 times the nozzle hole diameter φh.
According to the invention, as is understood from the situation of flow in the internal part of the nozzle holes 13 shown in
With regard to the design of a cylinder injection engine, for example, in a center-injection system in which the fuel injection valve 1 is located in the center of an engine, a distance from the fuel injection valve 1 to an ignition plug is short (e.g., approximately 15 mm). L/D is set to be small, whereby fuel is made to spray before it is rectified in the internal part of the nozzle holes 13, thus making it possible to form a spray pattern in which penetration force is suppressed, and divergence angle of spray is large.
Meanwhile, in a side-injection system in which the fuel injection valve 1 is located on the side of an engine, a distance from the fuel injection valve 1 to an ignition plug becomes longer (for example, approximately 40 mm). L/D is set to be larger, whereby fuel is made to spray in the state of being rectified to a certain degree in the internal part of the nozzle holes 13, thus making it possible to form a spray pattern of large penetration force, and narrow spray angle. In the valve according to the invention, it is suitable that L/D is set to be about 2 to 4 in the former system, and L/D is set to be about 4 to 6 in the latter system.
Concerning the layout of the nozzle holes 13, it is possible to adjust angles of the nozzle holes 13 so that lines made by extending the center lines of respective nozzle holes 13 from the outlets are not crossed over each other. By employing such a construction, there will be no collision of fuel having been sprayed from each of the nozzle holes. Then, a single outlet corresponds to a single target position, resulting in higher efficiency.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP05/13923 | 7/29/2005 | WO | 00 | 11/16/2006 |