JPH09329068A - Fuel injection valve for internal combustion engine - Google Patents

Abstract

(57) [Problem] To prevent a malfunction of a fuel injection valve due to a difference in thermal expansion between members constituting the fuel injection valve. A needle valve (2) for opening and closing a nozzle hole (5a) formed in a nozzle (5), a coil spring (10) for biasing the needle valve (2) in a valve opening direction, and a non-operating state for pressing the needle valve (2) in a valve closing direction. Of the piezoelectric element 6 that expands from the compressed state, and the piezoelectric element 6 in the expanded state includes the piezoelectric element 6 in the expanded state and the maximum thermal expansion difference in the axial direction of the casing 1 within the operating temperature range of the fuel injection valve. The piezoelectric element 6 was incorporated by giving an initial compression displacement larger than the deviation from the maximum thermal expansion difference in the axial direction of the piezoelectric element 6 within the operating temperature range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection valve for an internal combustion engine using a piezoelectric element as a drive unit of an injection hole opening / closing means, and more particularly to a technique for improving the operation stability of the fuel injection valve.

[0002]

2. Description of the Related Art In internal combustion engines in recent years, there is an increasing need to improve engine response, fuel efficiency and output.
Fuel injectors play an important role. Therefore, by using a piezoelectric element having a high-speed response for the fuel injection valve as a drive unit for the injection hole opening / closing means, the response of the fuel injection valve is improved, and at the same time, low idle rotation and lean combustion for the purpose of improving fuel consumption are achieved. A technique has been proposed for expanding the injectable range (dynamic range) that realizes stable supply of a small amount of fuel injection that enables fuel injection and stable supply of a large amount of fuel injection that enables high output. .

To give an example of such a technique, as shown in FIG. 2, a metallic valve case 6 having an injection hole 6a at its tip is shown.
A metal needle valve 3 for opening and closing the injection hole 6a
Are slidably fitted to each other, and a coil spring 8 for urging the needle valve 3 in the valve closing direction and a hollow cylindrical piezoelectric element 1 for displacing the needle valve 3 in the valve opening direction are arranged concentrically with the needle valve 3. (Japanese Unexamined Patent Publication (Kokai) No. 2-112663).
Reference).

[0004]

However, such a conventional fuel injection valve has a configuration in which the fuel injection valve is opened and closed by a hollow cylindrical piezoelectric element 1 disposed concentrically with the needle valve 3. Therefore, when the ambient temperature around the fuel injection valve changes, there is a difference between the linear expansion coefficient of the piezoelectric element 1 and the linear expansion coefficients of the needle valve 3 and the valve case 6 (generally, the linear expansion coefficient of the piezoelectric element 1). Expansion coefficient is smaller)
For this reason, the displacement of the needle valve 3 may vary, or a gap may be generated between the needle valve 3 and the piezoelectric element 1 to hinder the opening and closing of the fuel injection valve.

In view of the above-mentioned conventional problems, the present invention is a fuel injection valve using a piezoelectric element as a drive unit for the injection hole opening / closing means, and the ambient temperature around the fuel injection valve changes. Even if it is, it aims at supplying the fuel injection valve which can perform stable operation.

[0006]

Therefore, according to the invention of claim 1, the injection hole opening / closing means for opening / closing the injection hole formed in the fuel injection valve main body, and the injection hole opening / closing means are urged in the opening direction. A fuel injection valve for an internal combustion engine, comprising: a biasing means for operating the injection hole opening / closing means and a piezoelectric element that expands from a contracted state when not operating to press the injection hole opening / closing means in a closing direction. From the deviation between the maximum thermal expansion difference in the axial direction of the fuel injection valve main body within the operating temperature range of the fuel injection valve and the maximum thermal expansion difference in the axial direction of the piezoelectric element within the operating temperature range. Was also installed by giving a large initial compression displacement.

According to a second aspect of the invention, the nozzle hole opening / closing means is constituted by a needle valve. The invention according to claim 3 is
The biasing means is composed of a spring. In the invention according to claim 4, the fuel injection valve main body is made of a metal-based material, and the piezoelectric element is made of a ceramic-based material. According to a fifth aspect of the present invention, in the fuel injection valve in which the injection hole formed in the fuel injection valve main body is opened and closed by means driven by the output of the piezoelectric element, when the temperature of the fuel injection valve changes. The initial compression displacement was applied to the piezoelectric element in order to absorb the difference in thermal expansion between the fuel injection valve body and the piezoelectric element.

[0008]

According to the invention described in claim 1, when the ambient temperature around the fuel injection valve rises due to the combustion heat of the engine, for example, as in claim 4, the fuel injection made of a metal-based material is performed. Even if the piezoelectric element relatively contracts due to the difference in the coefficient of linear expansion between the valve body and the piezoelectric element made of a ceramic material, the piezoelectric element causes an initial compression displacement larger than this contraction length. Given and built in,
It is possible to prevent malfunction of the fuel injection valve due to thermal expansion without hindering the opening and closing of the injection hole opening / closing means, and to provide a fuel injection valve that operates stably. further,
Since the urging means that urges the injection hole opening / closing means in the opening direction is provided, the pressing force of the injection hole opening / closing means is relieved and the contact surface between the injection hole opening / closing means and the fuel injection valve main body is not worn. In addition to the suppression, it is also possible to suppress the sound generated when the injection hole opening / closing means is closed.

According to the second aspect of the invention, since the injection hole opening / closing means is constituted by the needle valve, simplification and miniaturization of the structure of the fuel injection valve can be promoted. Claim 3
According to the above-mentioned invention, since the biasing means is constituted by the spring, it is possible to promote the cost reduction due to the adoption of the general circulation member. According to the invention of claim 5, even if the temperature of the fuel injection valve changes, the initial compression displacement is applied to the piezoelectric element in order to absorb the difference in thermal expansion between the fuel injection valve main body and the piezoelectric element. A malfunction of the fuel injection valve due to expansion can be prevented, and the fuel injection valve can be operated stably.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a configuration of an embodiment of a fuel injection valve according to the present invention. At the tip of a nozzle 5 that constitutes the tip of a fuel injection valve (hereinafter abbreviated as "injection valve"), a nozzle hole 5a for injecting fuel and a tip 2a of a needle valve 2 to be described later are pressed to push the fuel. Valve seat 5 for sealing
b are formed. Further, a stepped large-diameter portion 5c is formed at the rear end portion of the nozzle 5, and an O-ring groove 5d into which an O-ring 9 for sealing the fuel is fitted is formed therein.

The outer diameter portion of the nozzle 5 is fitted to one end of the casing 1 constituting the main portion of the fuel injection valve,
The thin portion 1g at the end of the casing 1 is joined by welding or the like. At this time, the O-ring 9 fitted in the large-diameter portion 5c of the nozzle 5 prevents fuel from leaking from the joint between the casing 1 and the nozzle 5. On the other hand, the other end of the casing 1 is opened to insert a member forming the injection valve, and after inserting such a member into the casing 1, the casing end 3 forming the rear end portion of the injection valve is a casing. It is joined to the end of No. 1 by welding or the like.

Further, the casing 1 is formed with a fuel passage 1a and a fuel passage 1b communicating with the fuel passage 1a at a substantially right angle, and the fuel supplied from the outside is introduced into the injection valve through the fuel passages 1a and 1b. are doing. This fuel passage 1b
After the boring process, one end is closed by the blind plug 4, and the other end is opened inside the casing 1. The blind plug 4 can also be used as an air vent hole inside the injection valve.

Further, the casing end 3 is provided with a taper screw-shaped fuel inlet 3a used for connecting a fuel pipe,
A fuel passage 3b communicating with this is formed, and the fuel passage 3b of the casing end 3 and the fuel passage 1a of the casing 1 communicate with each other. Here, at the joint surface between the casing 1 and the casing end 3, for the purpose of preventing fuel leakage from the communicating portion between the fuel passages 3b and 1a,
In the O-ring groove 1f formed on the end surface of the casing 1, O
The ring 11 is fitted.

A knock pin 8 is used for positioning the casing end 3 joined to the casing 1 in order to ensure communication between the fuel passage 1a of the casing 1 and the fuel passage 3b of the casing end 3. There is. That is, the knock pin 8 is provided on the other end surface of the casing 1.
A hole 1c for the knock pin 8 is formed on the end surface of the casing end 3, and the knock pin 8 is fitted into the hole 3c for positioning. Although only one position is shown in FIG. 1 for the knock pin 8 and the holes 1c and 3c for fitting the knock pin 8, the knock pin 8 is fitted to the end face (not shown), and positioning is performed by the two knock pins 8. Done.

Reference numeral 1d not described above is a lead-out hole for a lead wire 12 of the piezoelectric element 6 which will be described later, and 13 is a rubber bush for easily fixing the lead-out hole 1d after the lead wire 12 is taken out. It is an adhesive. Next, the constituent members arranged inside the injection valve case constituted by the nozzle 5, the casing 1, and the casing end 3 described above will be described.

The needle valve 2 (injection hole opening / closing means) for opening and closing the injection hole 5a of the nozzle 5 has a tip portion 2a which is pressed by the valve seat 5b described above, as well as a central portion on the inner circumference of the nozzle 5. A large diameter portion 2d slidably fitted to the casing 1 at the rear end.
And a rear end portion 2b slidably fitted to the inner periphery of the. In this large-diameter portion 2d, four communication holes 2e are provided in the axial direction of the needle valve 2 in order to communicate the inside of the nozzle 5 and the inside of the casing 1 with each other and to allow the fuel to pass therethrough. (4 locations in total). Further, an O-ring groove 2c is formed on the outer peripheral surface of the rear end portion 2b into which an O-ring 7 for preventing fuel from leaking to the piezoelectric element 6 side described later is fitted. A poppet valve is formed by the tip 2a of the needle valve 2 and the valve seat 5b of the nozzle 5, and the fuel is injected or not injected depending on the operation of the needle valve 2.

The end of the rear end 2b of the needle valve 2 is
It holds one end of the piezoelectric element 6. This piezoelectric element 6 is
For example, when a voltage of 500 V is applied, the voltage of about 50 μm
It is an element with a total length of 50 mm that can obtain displacement. Of this element
Approximately 3.6kg / mm as a characteristic^TwoWhen applying the stress of about 6
The piezoelectric element has a characteristic that the length shrinks by about 0 μm.
Approximately 3.6kg / mm when 6 is activated (when voltage is applied)^TwoThe stress of
Assembled in a working state, that is, a state of contracting about 60 μm
Have been. In addition, this piezoelectric element 6 is 5 kg / mm ^TwoFor up to
It has a characteristic that the change in displacement is small with respect to stress.
Therefore, the displacement of about 0.1% of the total length is about 50 μm.
It is the amount of displacement of the element, that is, the stroke. In short, pressure
The assembled state of the electric element 6 is when it is extended. From this state
The charge is removed, that is, the voltage applied to the piezoelectric element 6 is set to 0.
When it is V, it shrinks by about 50 μm (0.05 mm).

Further, a coil spring 10 (urging means) for urging the needle valve 2 in the valve opening direction is provided with a large diameter portion 5 of the nozzle 5.
It is arranged between c and the rear end portion 2b of the needle valve 2 and has an effect of relieving the stress applied to the valve seat 5b of the nozzle 5 when the piezoelectric element 6 is expanded. In the present embodiment, as an example, the casing 1 is made of a titanium alloy (metallic material), and its linear expansion coefficient is about 8 × 10 ^−6.
[1 / ° C.], the piezoelectric element 6 is made of ceramic (ceramic-based metal), and its linear expansion coefficient is about 2 × 10.
^-6 [1 / ° C].

Next, the operation of the fuel injection valve thus constructed will be described. During engine operation, fuel adjusted to a predetermined pressure by a high-pressure fuel pump and a pressure regulator (not shown) flows in from the fuel inlet 3a, is guided into the casing 1 through the fuel passages 3b, 1a and 1b, and further, the needle valve 2 Is introduced into the nozzle 5 through a communication hole 2e formed in the large diameter portion 2b. In this state, when a voltage of 500 V is gently applied to put the piezoelectric element 6 into the initial state, the piezoelectric element 6 tries to expand by about 50 μm.
Since there is no clearance in which a is pressed against the valve seat 5b, strain (internal stress) generated inside the piezoelectric element 6
Balance and remain stationary. In this state, the stress acting on the piezoelectric element 6 is about 3 due to the resultant force of the fuel pressure acting on the rear end portion 2b of the needle valve 2 (fuel pressure × pressure receiving area) and the urging force of the coil spring 10. .6 kg
/ Mm ² , and the piezoelectric element 6 is about 60 μm when activated.
It is in a contracted state (0.06 mm).

When the electric charge of the piezoelectric element 6 is removed from this state, the piezoelectric element 6 contracts by its stroke of about 50 μm, the needle valve 2 is opened by the urging force of the coil spring 10, and the fuel is injected from the injection hole 5a. It Further, when a voltage of 500 V is applied to the piezoelectric element 6 when stopping the fuel injection, the piezoelectric element 6 expands by about 50 μm. Therefore, the tip portion 2a of the needle valve 2 is opposed while opposing the biasing force of the coil spring 10. Presses (seats) the valve seat 5b, and fuel injection is stopped. At this time, since the valve closing force of the needle valve 2 is relaxed by the biasing force of the coil spring 10, wear of the valve seat 5b is suppressed and the valve closing noise is reduced.

When the engine is stopped, the piezoelectric element 6 is stopped in an operating state, and contracts along with spontaneous discharge of electric charge within a few minutes to a few tens minutes. In this case, since the fuel pressure drops shortly after the engine stops, a stress of about 10 μm displacement remains in the piezoelectric element 6, and the tip portion 2a of the needle valve 2 causes the nozzle 5 to move to the nozzle 5 due to the biasing force generated by the compressive stress. It is pressed by the valve seat 5b, the fuel is sealed, and the fuel injection stopped state is maintained.

Next, the case where the temperature of the fuel injection valve changes will be described. The operating temperature range of the injection valve, for example,
If the temperature is from -30 ° C to + 130 ° C, there is a temperature difference of about 160 ° C. In the present embodiment, as described above, the casing 1
Has a linear expansion coefficient of about 8 × 10 ⁻⁶ [1 / ° C.], the piezoelectric element 6 has a total length of 50 mm, and a linear expansion coefficient of about 2 × 10 ⁻⁶ [1 / ° C.].
Since the linear expansion coefficient difference is about 6 × 10 ⁻⁶ [1 / ° C.], when a temperature change of 160 ° C. occurs in the injection valve, 160 × 6 × 10 ⁻⁶ × 50 = 0.048 mm , A thermal expansion difference of about 48 μm will occur.

However, in the injection valve of the present invention, since the piezoelectric element 6 is installed in a state of being compressed by about 60 μm when the piezoelectric element 6 is operated, the difference in linear expansion coefficient in the operating temperature range of the injection valve (temperature difference of 160 ° C.). The initial compression absorbs the difference in linear expansion caused by the above, and the displacement of the needle valve 2 is varied, or a gap is generated between the needle valve 2 and the piezoelectric element 6, which hinders the opening and closing of the fuel injection valve. Is prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a fuel injection valve according to the present invention.

FIG. 2 is an explanatory view of a fuel injection valve using a conventional piezoelectric element.

[Explanation of symbols]

 1 Casing 2 Needle valve 5 Nozzle 5a Injection hole 6 Piezoelectric element 10 Coil spring

Claims (5)

[Claims] 1. An injection hole opening / closing means for opening / closing an injection hole formed in a fuel injection valve body, an urging means for urging the injection hole opening / closing means in an opening direction, and the injection hole opening / closing means in a closing direction. A fuel injection valve for an internal combustion engine, comprising: a piezoelectric element that expands from a contracted state when not pressed to press the piezoelectric element in an expanded state within a working temperature range of the fuel injection valve. It is characterized in that it is incorporated by giving an initial compression displacement larger than a deviation between the maximum axial expansion difference of the fuel injection valve main body and the maximum axial expansion difference of the piezoelectric element within the operating temperature range. Fuel injection valve for internal combustion engine. 2. A fuel injection valve for an internal combustion engine according to claim 1, wherein said injection hole opening / closing means is constituted by a needle valve. 3. The fuel injection valve for an internal combustion engine according to claim 1, wherein the urging means is a spring. 4. The fuel injection valve for an internal combustion engine according to claim 1, wherein the fuel injection valve body is made of a metallic material and the piezoelectric element is made of a ceramic material. . 5. A fuel injection valve in which an injection hole formed in a fuel injection valve main body is opened and closed by means driven by an output of a piezoelectric element, wherein the fuel is injected when the temperature of the fuel injection valve changes. A fuel injection valve for an internal combustion engine, wherein an initial compression displacement is applied to the piezoelectric element in order to absorb a difference in thermal expansion between the injection valve body and the piezoelectric element.