JPH0472066B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection valve used in a fuel injection device for an internal combustion engine, and particularly relates to an improvement of a fuel injection valve using a piezoelectric element.

[Conventional technology]

Unexamined patent application published in 1973 on fuel injection valve using piezoelectric element
There is one described in No. 60630. The purpose of this conventional technology is to provide an injection valve that does not use a return spring, has a simple configuration, and is unaffected by magnetic fields and has faster opening and closing responses.
This is intended to improve responsiveness, enable high-pressure fuel supply, and also promote atomization of fuel.

Furthermore, as is well known, in internal combustion engines, various studies have been made from the viewpoint of fuel economy, such as improving the fuel system and air supply system, and making the engine smaller and lighter. In particular, in fuel injection valves used in fuel injection devices, efforts are being made to promote atomization, improve responsiveness, and reduce size for the purpose of improving combustion.

[Problem to be solved by the invention]

However, in the above-mentioned fuel injection valve, studies have been made to promote atomization by swirling the fuel, reduce magnetic resistance, make the movable parts smaller, and make the weight lighter. It is difficult to speed up both the valve opening and valve closing responses, as this is achieved through balance with force. Further, since the electromagnet has a small electromagnetic force, this type of fuel injection valve cannot supply high-pressure fuel, and there is a natural limit to the atomization of the fuel using the kinetic energy of the low-pressure fuel itself. To put it simply, the reality is that electromagnetic fuel injection valves cannot be expected to dramatically improve their performance over their current state.

Furthermore, miniaturization is an important factor for proper operation of an internal combustion engine, and the basis of this requirement lies in the mounting position to the internal combustion engine. That is, in a gasoline engine, a fuel injection valve is attached to an intake pipe, and in particular, from the viewpoint of improving fuel efficiency, it is attached close to an intake valve. In this case, the area around the intake valve is located in the intake manifold pipe section, and the parts including the valve mechanism are mixed together, so that a mounting space can be obtained. In current gasoline engines, it is approximately 14 mm from the intake hole.
The fuel injection valve is installed at the cm position. Therefore, there may be a delay in fuel transportation from the injection position to the combustion chamber, or there may be unburned fuel adhering to the intake pipe around the attachment point, which is an unfavorable situation for improving combustion efficiency. . It is preferable that the fuel injection valve be located as close to the intake hole as possible, and it is safe to assume that in the future it will be installed directly into the combustion chamber as in a diesel engine.
If it were to be installed close to the intake hole, the installation space would inevitably become even narrower than it currently is, and in either case, the importance of miniaturization is emphasized.

On the other hand, various attempts have been recently made in related fields to apply piezoelectric elements to fuel injection valves. This piezoelectric element (for example, lead zirconate titanate) has characteristics such as excellent response due to its high natural frequency, and large force generated due to expansion and contraction of the piezoelectric element itself. If a fuel injection valve can exhibit these characteristics, it will not only shorten the valve opening and closing time, but also make it possible to supply high-pressure fuel that cannot be obtained with an electromagnet by utilizing the generated force. As a result, the energy of the fuel itself is increased, and as a result, the atomization of the fuel can be promoted.

An object of the present invention is to downsize a fuel injection valve,
As mentioned above, the object of the present invention is to provide a fuel injection valve that plays an important role in improving combustion efficiency.

[Means to solve the problem]

The above object includes a valve case having an injection hole at its most distal end, and a needle valve mechanically coupled to a piezoelectric element that is displaced at high speed by application of a voltage. In a fuel injection valve that opens and closes an injection hole to intermittently inject fuel, the piezoelectric element is formed into a hollow cylindrical shape, the needle is disposed in the hollow part of the piezoelectric element, and the length of the needle is determined by the length of the hollow cylindrical piezoelectric element. This is achieved by arranging the axial length to be approximately equal to the axial length of the axial length.

[Effect]

A needle made of a movable member is disposed in the hollow part of the hollow cylindrical laminated piezoelectric member, and the needle length is configured to be equal to the axial length of the laminated piezoelectric member, so the axial length can be reduced, and the fuel The injection valve can be made smaller.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing the first embodiment of the present invention;
The figure is a sectional view showing a second embodiment of the present invention.

In FIG. 1, 1 is a hollow cylindrical laminated piezoelectric member made by laminating a large number of piezoelectric elements, 2 is a movable member having a needle 3 disposed in the hollow part of the laminated piezoelectric member 1, and the needle 3 is at the tip. It has a sheet 3a nearby. Further, the rapidly expanding portion 4 that is continuous with the needle 3 has a recess 4a and a pressure fluid passage 4b. 5 is a space formed between the hollow part of the laminated piezoelectric member 1 and the needle 3; 6 is a valve case having an injection hole 6a at the leading edge; 7 is a valve lid screwed to the valve case; has. A fuel pipe (not shown) is coupled to the pressure fluid inlet 7a. 8 is a compression spring provided between the recess 4a of the movable member 2 and the valve cover 7, and 9 is a conductive wire for applying voltage to the laminated piezoelectric member 1. With this configuration, the seat 3a of the needle 3 is pressed by the restoring force of the compression spring 8 so as to close the injection hole 6a of the valve case 6, thereby preventing leakage of pressure fluid to the outside.

FIG. 2 is a sectional view showing a second embodiment, which has a needle 10 of a different structure. That is, the needle 10 is provided with a pressure fluid passage 10b inside and a stepped portion near the seat 10a, and a plurality of different pressure fluids communicate with the space 11 formed between the stepped portion and the hollow portion of the laminated piezoelectric member 1. It has a fluid passage 10c.

In the embodiment of the present invention, a coiled spring is used as the compression spring 8, but a plate-shaped spring may also be used.

In FIGS. 1 and 2, the same reference numerals indicate the same parts.

The operation of this configuration will be explained below. In FIG. 1, when a pulse voltage is applied to the laminated piezoelectric member 1, the laminated piezoelectric member 1 is displaced (stretched) corresponding to the ON time of the pulse. Due to the expansion of the laminated piezoelectric member 1, the movable member 2 is pushed against the spring force of the compression spring 8, and the sheet 3 provided on the needle 3 is pushed.
a is removed from the valve case 6. Valve case 6
The injection hole 6a provided in is opened. The pressure fluid passes through a conveyance device such as a pressure pump (not shown), flows from the pressure fluid inlet 7a into the recess 4a provided in the movable member 2, and reaches the pressure fluid passage 4b. Thereafter, the pressure fluid is collected in the space 5, flows through the gap between the sheets 3a toward the injection hole 6a, and is injected to the outside from the injection hole 6a without impairing the kinetic energy held by the pressure fluid. At this time, the pressure fluid takes on the shape of a spreading thin film spray and is subdivided into fine droplets.

On the other hand, when the voltage is turned off, the movable member 2
is instantly returned to its original position by the restoring force of the compression spring 8, and the seat 3a of the needle 3 closes the injection hole 6a. Then, the injection of pressure fluid to the outside is stopped. The operation in the second embodiment is almost the same as in the first embodiment, but after the pressure fluid flows into the recess 4a of the movable member 2, another pressure fluid is transferred from the pressure fluid passage 10a provided in the needle 10. Passage 10c
leading to. Thereafter, the pressure fluid is collected in the space 11 and is injected to the outside from the injection hole 6a without damaging the kinetic energy held by the pressure fluid.

As is clear from the above explanation, in this structure, the needle 3 made of the movable member 2 is arranged in the hollow part of the laminated piezoelectric member, so that the axial length of the fuel injection valve is shorter than that of the conventional fuel injection valve of this type. It will be about half. As mentioned above, it is clear that the mounting position of the fuel injector is a particularly important factor in properly operating an internal combustion engine and improving engine efficiency. This can be realized by That is, by installing the fuel at a position closer to the intake hole (combustion chamber), it is possible to shorten the fuel transportation delay time and prevent fuel from adhering to the intake pipe wall. As a result, combustion efficiency can be significantly improved and fuel can be saved.

The laminated piezoelectric member used in this example is made by laminating a large number of piezoelectric elements, and when a DC voltage V is applied to the n piezoelectric elements laminated, the displacement δ becomes δ=
It is given by n・d ₃₃・V・t ^-1 . where d ₃₃ : Piezoelectric strain constant, t : Thickness of the element, generally the piezoelectric element is
When 100 sheets are stacked, a displacement of about 40 microns can be obtained. The applied voltage at this time was 400V DC. Furthermore, since the piezoelectric element has a high natural frequency, the displacement response is good. Usually a response of 100μsec is obtained.
Therefore, the electromagnetic fuel injection valve (opening/closing valve response time is
(approximately 100 msec). As described above, since the movable member is mechanically coupled to the laminated piezoelectric member, the high-speed operation of the laminated piezoelectric member can be effectively utilized, and the valve opening/closing operation of the injection hole 6a can be performed at high speed. That is, by improving the responsiveness, the injection amount per injection can be accurately measured and the injection amount can be controlled with high precision. Further, the laminated piezoelectric member 1 generates a force of about 70 kg when its displacement is restrained. Therefore, in this embodiment, sheet 3
It is possible to improve the pressing force of a to several tens of kilograms. That is, the spring constant of the compression spring 8 provided between the recess 4a of the movable member 2 and the valve cover 7 can be increased. As a result, even if the pressure of the supplied fuel is increased, the movable member 2 will not be pushed against the spring force of the compression spring 8, the seat 3a will open, and the fuel will not leak to the outside. According to this embodiment, the pressure of the supplied fuel is
It has been confirmed that it is possible to increase the pressure up to 5MPa.
At this time, the size of the fuel particles injected from the injection hole 6a is several tens of microns, which is about 1/5 that of an electromagnetic fuel injection valve. As a result, atomization can be sufficiently promoted. Furthermore, since the piezoelectric element can be treated as a capacitor, it consumes power only momentarily during the ON-OFF time, but during the ON time, power is only stored in the capacitor and is not consumed. This example also confirmed that when a pulse voltage of 400 V is applied to the laminated piezoelectric member 1 made of 100 layers described above, the power consumed is about 5 W, which is less than 1/3 of that of an electromagnetic fuel injector. .

〔Effect of the invention〕

As explained above, according to the fuel injection valve of the present invention, various effects can be obtained in improving the operating efficiency of an internal combustion engine, but in particular, in its configuration,
A needle made of a movable member is disposed in the hollow part of the hollow cylindrical laminated piezoelectric member, and the needle length (needle valve length)
Since it is configured to be approximately equal to the axial length of the laminated piezoelectric member, it is shorter than the conventional fuel injection valve of this type.
The axial length can be approximately halved. That is, a small fuel injection valve can be provided. As a result, the mounting position on the internal combustion engine can be placed closer to the intake hole (combustion chamber) than before, which results in shortening the fuel transport delay time and reducing the amount of fuel that adheres to the intake pipe wall. It is possible to prevent lost unburned fuel from remaining upstream of the intake hole. This has a great practical effect in that the internal combustion engine can be operated properly and fuel can be significantly saved by improving engine efficiency.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention;
FIG. 2 is a longitudinal sectional view showing a second embodiment of the present invention. 1... Laminated piezoelectric member, 3... Needle, 3a...
...Seat, 6...Valve case, 6a...Injection hole, 7
a... Pressure fluid inlet.

Claims (1)

[Claims] 1. In a fuel injection valve that changes a needle using a piezoelectric element and uses this needle to open and close an injection hole to intermittently inject fuel, the injection hole is provided on one side of a hollow valve case, and the injection hole is provided on one side of a hollow valve case. A valve lid having a fuel supply hole is provided at the other end of the valve case, a cylindrical rapidly expanding part is slidably provided in the valve case, and a needle for opening and closing the injection hole is provided on the end face of the rapidly expanding part on the side of the injection hole. A piezoelectric element is provided between the valve case and the rapidly expanding portion on the outer periphery of the needle, a spring is installed between the side of the rapidly expanding portion opposite to the needle and the valve cover, and fuel is supplied to the rapidly expanding portion. A fuel injection valve for an internal combustion engine, characterized in that a passage is provided for supplying fuel to a needle side.