JP3888217B2 - Fuel injection valve with fuel heater - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection valve for an internal combustion engine, and more particularly to a fuel injection valve provided with a fuel heater.
[0002]
[Prior art]
A fuel injection valve of an internal combustion engine generally has a fuel injection passage that opens as a nozzle hole with a narrowed tip, and a needle valve body that selectively opens and closes the nozzle hole, and fuel that is pumped through the fuel injection path When the needle valve body opens the nozzle hole, the needle valve body has a basic structure of jetting through the nozzle hole.
[0003]
Furthermore, this type of fuel injection valve has a fuel injection system that improves atomization by better atomizing the fuel injected at the cold start of the engine and at the same time suppresses the generation of harmful unburned components as much as possible. It is known to incorporate a heater that heats the fuel flowing in the injection passage. When such a heater is formed as a relatively narrow passage extending in parallel to the side of the needle valve, such a heater is disclosed in Japanese Utility Model Publication No. 59-107973. A sheath-like heater (sheath heater) is provided in a part of the fuel injection passage, or is inserted into the fuel injection passage to extend along the fuel injection passage as disclosed in Japanese Utility Model Publication No. 3-83370. It is provided as a heating wire.
[0004]
Further, in the fuel injection valve having a structure in which the fuel injection passage is formed as a relatively large-diameter cylindrical space constricted to the injection nozzle at the tip, and a needle valve that opens and closes the injection nozzle extends into the fuel injection passage. Japanese Unexamined Patent Publication No. 2000-508041 discloses that a ceramic heater extending in a cylindrical shape around a needle valve body is provided in the fuel injection passage.
[0005]
[Problems to be solved by the invention]
The heating of the injected fuel at the time of engine cold start is the same as the effect of improving the startability of the engine better, but in particular, the effect of suppressing the generation of harmful unburned components is better, It is effective that the initial fuel injection is performed so that the fuel is heated starting from the first injected fuel. For this purpose, the heater for fuel heating not only has a rapid rise as much as possible and has a high heat generation density, but can also heat the fuel present in the portion in contact with the nozzle hole. It is desirable.
[0006]
On the other hand, in this type of fuel injection valve, the needle valve is urged by a spring toward the closed position where the tip of the needle valve closes, and when the nozzle is opened, the needle valve is formed by an armature provided at the base of the needle valve. The valve lift is attracted by an electromagnet, and the valve opening lift is determined by the armature coming into contact with the core of the electromagnet. Therefore, when the needle valve is heated by the fuel heater and thermal expansion occurs, the valve lift decreases accordingly. Therefore, it is desirable for the fuel heater to have a structure capable of suppressing as much as possible the occurrence of thermal expansion in the needle valve by heating the fuel.
[0007]
The present invention is conceived of the above-described requirements regarding the fuel heater in the fuel injection valve of the internal combustion engine, and an object of the present invention is to provide a fuel injection valve including a fuel heater that can satisfy these requirements.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a fuel injection passage that opens as a nozzle with a narrowed tip of a cylindrical space, and a needle valve that extends into the fuel injection passage and selectively opens and closes the nozzle. A fuel injection valve configured to inject fuel pumped through the fuel injection passage through the injection port when the needle valve body opens the injection port. have a fuel heater consisting heating wire extending pivot around the needle valve body, septum from the injection port the density of the swirling along the fuel injection passage at the portion close to the nozzle hole of the heating wire The present invention provides a fuel injection valve characterized in that the fuel injection valve is made higher than the corresponding portion .
[0010]
[Action and effect of the invention]
As described above, a fuel injection passage that opens as a nozzle hole whose tip of the cylindrical space is constricted, and a needle valve body that extends into the fuel injection path and selectively opens and closes the nozzle hole, In a fuel injection valve configured to inject fuel pumped through the nozzle opening when the needle valve body opens the nozzle hole, a fuel heater is swung around the needle valve element in the fuel injection passage. If configured as an extended heating wire, the length of the heating wire can be increased compared to the length of the fuel injection passage, and a heater having a large heat generating surface area compared to the storage space is formed. be able to. Further, in this case, since the fuel flows across the heating wire extending while swirling, heat transfer from the heating wire to the fuel is performed with a high heat transfer coefficient. Furthermore, with such a swirl-shaped heating wire, the tip of the winding is concentrated around the nozzle hole, so that the fuel existing around the nozzle hole can be heated strongly. In addition, a powerful heating effect can be given to the first fuel injected from the time of the first fuel injection.
[0011]
Furthermore, by changing the swirl pitch appropriately, the density distribution of the heat generating surface can be set with a large degree of freedom, and the density distribution of the heat generating surface is thereby separated from the nozzle near the nozzle hole. The heating can be accelerated at an accelerated rate as the fuel flows in the fuel injection passage from the inlet portion toward the injection port. By doing so, even if the heating degree of the fuel injected from the nozzle hole is increased, the heating exerted on the needle valve accompanying the heating of the fuel can be suppressed to a limited length range close to the nozzle hole, When the entire needle valve is heated, even if the coefficient of thermal expansion is not modest, the overall thermal expansion allowance increases due to the large length, leading to an undesirable situation where the valve lift is greatly reduced. Can be avoided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 attached herewith is a schematic view showing an essential part of one embodiment of a fuel injection valve equipped with a fuel heater according to the present invention.
[0013]
In the figure, reference numeral 1 denotes a housing of a fuel injection valve, which gives the fuel injection valve a nozzle shape. In the illustrated schematic diagram, the housing 1 is shown as an integral stepped cylindrical body. However, in practice, such a housing is an arbitrary combination of several members for convenience of manufacture and installation. It may be made in the structure of The housing is provided with a cylindrical fuel injection passage 2 at the inside, particularly at the tip thereof, and the tip of the housing is squeezed to form a nozzle hole 3. In the illustrated embodiment, the fuel injection passage 2 is formed in a cylindrical shape, and the injection hole 3 opens in alignment with the center of the cylindrical fuel injection passage.
[0014]
A needle valve 4 extending along the central axis is provided in the fuel injection passage 2. The needle valve 4 is guided and supported by the holder 5 so as to slide along the guide hole 6 at the base portion, and the nozzle 3 is opened and closed at the tip formed in a conical shape. The holder 5 is further provided with a fuel hole 7 through which fuel passes and a terminal hole 8 through which an energization terminal for a heater described later is passed. Reference numeral 9 denotes a snap ring for attaching the holder 5. An armature 10 is attached to the rear end of the needle valve 4. The armature is constructed in a structure that allows fuel to pass across it, as shown diagrammatically as hole 11 in the figure.
[0015]
An electromagnetic coil 12 constitutes an electromagnet that selectively attracts the armature 10 together with a core 13 that is excited by energization thereof. A compression coil spring 15 is provided at the center of the core 13 along a cylindrical gap 14 formed in the core 13, and a root portion of the compression spring 15 is supported by a spring holder 16. The needle valve 4 is urged to a closed position where the nozzle hole 3 is closed at its tip.
[0016]
The fuel pumped from a fuel injection pump (not shown) is introduced into the housing 1 through the gap 14 from the upper side of the drawing, and travels toward the injection port 3 through the fuel injection passage 2. When the electromagnetic coil 12 is not energized, the nozzle hole 3 is closed by the needle valve 4. However, when the electromagnetic coil 12 is energized, the needle valve is a spring of the compression coil spring 15 until the armature 10 contacts the core 13. It is lifted upward in the figure against the force, and the nozzle 3 is opened. The opening lift of the needle valve in this case corresponds to the clearance L between the armature 10 and the core 13 when the valve is closed.
[0017]
In the fuel injection passage 2, there is provided a heater for heating the fuel including a heating wire 17 that turns around the needle valve 4. The upper end of the heating wire 17 in the figure is connected to a terminal 18 disposed through the terminal hole 8, and the lower end abuts around the nozzle hole 3 of the housing 1 and is grounded via the housing. .
[0018]
In this way, the heating element is a linear heating wire, and the heating wire is placed in the annular cylindrical space left between the needle valve extending along the center of the cylindrical fuel injection passage. By swiveling around the needle valve, it is possible to increase the heat transfer rate by forming a larger heat generation surface compared to a cylindrical ceramic heater, etc. A powerful heating effect can be given to the fuel injected first. Further, the density of the heating wire 17 swirling around the needle valve 4 may be made higher in the portion closer to the nozzle 3 than in the portion farther than this, as shown in the illustrated embodiment. . In the illustrated embodiment, the density adjacent to the nozzle hole 3 and the distance from the nozzle hole 3 are different in density, but the change in the density of the heating wire is not limited to such density, and any other appropriate It may be a change.
[0019]
When the heating wire 17 is energized during the operation of the fuel injection valve, that is, in the state where the fuel flows in the fuel injection passage 2 toward the injection port 3, the fuel flowing along the fuel injection passage 2 is at the beginning of the heating wire. Starting from the 0 position where the is located, it is heated, and its temperature gradually increases toward the nozzle hole 3. Considering a state where a constant current is flowing through the heating wire while the fuel is flowing at a constant flow rate, the fuel is proportional to the heating wire density per unit amount sequentially along the flow direction. It receives an amount of heat and the temperature rises by a proportional temperature difference. In this case, if such a state continues for a predetermined time or more, even if the fuel continues to flow, the temperature distribution of the fuel along the fuel injection passage 2 becomes steady and enters the fuel injection passage 2 of the needle valve 4. The temperature of each part of the extending portion corresponds to the temperature distribution of the fuel along the fuel injection passage 2.
[0020]
Therefore, the degree to which the needle valve 4 is heated and expanded by the operation of the fuel heater according to the present invention and the opening lift of the needle valve is reduced is determined by the cylinder in the above-mentioned Japanese Patent Publication No. 2000-508041. This is compared with the case of a heater that generates heat at a uniform heat generation density along the fuel injection passage 2 such as a ceramic heater. If the cylindrical ceramic heater is correspondingly replaced with a heating wire, it corresponds to the heating wire being arranged in the fuel injection passage so as to turn at a uniform pitch.
[0021]
FIG. 2 is a graph in which the horizontal axis represents the distance S for each station from the heating start position of the needle valve, and the vertical axis represents the temperature T for each station. When the heat generation density of the heater along the fuel injection passage 2 is uniform, the temperature of each part of the needle valve increases uniformly as the distance from the heating start position increases, as shown by the straight line A, and the distance. Reaches a certain maximum temperature Tf corresponding to the energization amount at the tip where becomes St. Therefore, in this case, the elongation due to heating of the needle valve is an accumulation of the elongation at each local portion. If the micro length of each local portion is ΔS and the temperature is T, the total elongation of the needle valve, that is, The reduction amount of the valve opening lift is a value obtained by integrating (T−To) ΔS from S = 0 to S = St, which is an area of the area formed by the straight line A with respect to the horizontal axis (triangle 0−e−St). It is a proportional value.
[0022]
On the other hand, when the pitch of the swirl of the heating wire 17 is roughened in the first half of the fuel injection passage 2 and made nectar in the second half as in the embodiment of the present invention shown in FIG. Even when the temperature of the injected fuel is the same and the temperature at the tip of the needle valve is the same temperature Tf, the temperature of each local area leading to it is connected to the straight lines B ₁ and B ₂ , and the entire needle valve is stretched. Is a value proportional to the area formed by the straight line B ₁ -B ₂ with respect to the horizontal axis, that is, the sum of the triangle 0-m-Sm and the square Sm-m-e-St. This is smaller than the above triangle 0-e-St by an amount corresponding to the area of the triangle 0-e-m, and the amount by which the valve lift of the needle valve is reduced due to fuel heating is reduced by this amount. It means less.
[0023]
Further, since the arrangement density of the heating wires 17 may be arbitrarily set as described above, for example, the heating wire 17 is gradually increased from the start end toward the end adjacent to the injection port, and the temperature of the local portion of the needle valve is as shown in FIG. In this case, if it is changed as shown by curve C, it is possible to further reduce the decrease in valve lift caused by fuel heating even if the final heating temperature of the fuel ejected from the nozzle is higher than Tf. is there.
[0024]
While the invention has been described in detail with reference to an embodiment thereof, it will be apparent to those skilled in the art that various modifications may be made to the embodiment without departing from the scope of the invention.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an essential part of one embodiment of a fuel injection valve equipped with a fuel heater according to the present invention.
FIG. 2 is a graph showing an aspect in which thermal expansion occurs in a needle valve due to a change in heat generation density of a heater along a fuel injection passage, in comparison with the present invention and a known example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Housing 2 ... Fuel injection passage 3 ... Injection hole 4 ... Needle valve 5 ... Holder 6 ... Guide hole 7 ... Fuel hole 8 ... Terminal hole 9 ... Snap ring 10 ... Armature 11 ... Fuel passage hole 12 ... Electromagnetic coil 13 ... Core 14 ... cylindrical gap 15 ... compression coil spring 16 ... spring holder 17 ... heating wire 18 ... terminal

Claims (1)

A fuel injection passage that opens as a nozzle with a narrowed tip of a cylindrical space, and a needle valve body that extends into the fuel injection passage and selectively opens and closes the nozzle, and pumps the inside of the fuel injection passage A fuel injection valve configured to inject the generated fuel through the injection port when the needle valve body opens the injection port, and extends around the needle valve body in the fuel injection passage. the fuel heater consisting heating wire possess the density of the swirling along said fuel injection passages of the heating wire is characterized in that it is higher than the portion spaced from the nozzle hole at the portion close to the injection port Fuel injection valve.

Images