JPH109083A - Fuel injection valve for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the fuel injection valve from being erroneously operated due to the difference in thermal expansion of each member constituting the fuel injection valve. SOLUTION: The fuel injection valve is formed out of a needle valve 11 which opens/closes an injection hole 13a formed in a needle valve holder 13, a coil spring 17 energizing the needle valve 11 to the valve opening direction, a piezo-electric element 16 which is expanded from its compressed condition at the time of no operation in order to press the needle valve 11 to the valve closing direction, and of a coil spring 18 energizing the needle valve 11 to the valve closing direction by way of the piezo-electric element 16. The relation of energizing force between the coil spring 17 and the coil spring 18 is set up in such a way that the energizing force of the coil spring 18 is greater than the energizing force of the coil spring 17, and concurrently the piezo-electric element 16 is so set that it can be moved to the direction of the energizing force of the coil spring 18 when the piezo-electric element 16 is contracted from its expanded condition, and furthermore, a stopper 14a placing regulations on the moving amount of the piezo-electric element 16, is provided for the inner circumference of a casing 14.

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 as a drive unit of the injection hole opening / closing means in the fuel injection valve, the response of the fuel injection valve can be improved, and a low idling speed can be achieved for the purpose of improving fuel efficiency. There has been proposed a technique for expanding an injectable range (dynamic range) for achieving a stable supply of a small amount of fuel injection and a stable supply of a large amount of fuel injection capable of coping with high output.

As an example of such a technique, as shown in FIG. 3, a metal valve case 6 having an injection hole 6a at a tip end is provided.
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 relates to a fuel injection valve using a piezoelectric element as a drive unit of an injection hole opening / closing means, in which the ambient temperature around the fuel injection valve changes. It is another object of the present invention to provide a fuel injection valve capable of performing stable operation.

[0006]

According to the present invention, there is provided an injection hole opening / closing means for opening / closing an injection hole formed in a fuel injection valve body, and urging the injection hole opening / closing means in an opening direction. A first urging means, a piezoelectric element which expands from a contracted state when not actuated to press the nozzle opening / closing means in the closing direction, and biases the nozzle opening / closing means in the closing direction via the piezoelectric element. And a second urging means, wherein the relationship between the urging forces of the first urging means and the second urging means is determined by the second urging means. Is set to be larger than the urging force of the first urging means, and the piezoelectric element is movable in the urging force direction of the second urging means when the piezoelectric element contracts from the expanded state. And regulating means for regulating the amount of movement of the piezoelectric element in the direction.

According to a second aspect of the present invention, the injection hole opening / closing means is constituted by a needle valve. According to a third aspect of the present invention, both the first urging means and the second urging means are constituted by springs. According to a fourth aspect of the present invention, the regulating means is constituted by a mechanical stopper provided inside the fuel injection valve body.

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 body is opened and closed by means driven by the output of the piezoelectric element, the temperature of the fuel injection valve changes. Occasionally, a means for absorbing a difference in thermal expansion between members constituting the fuel injection valve is provided.

[0009]

According to the first aspect of the present invention, the second urging means for urging the nozzle opening / closing means in the closing direction is provided via the piezoelectric element for pressing the nozzle hole opening / closing means in the closing direction. For example, because the ambient temperature around the fuel injection valve rises, there is a difference between the respective linear expansion coefficients of the injection hole opening / closing means, the piezoelectric element, and the fuel injection valve body that constitute the fuel injection valve. Therefore, even if a thermal expansion difference occurs, the second biasing means absorbs the thermal expansion difference, and the nozzle opening / closing means and the piezoelectric element always come into close contact with each other, thereby causing malfunction of the fuel injection valve due to thermal expansion. The fuel injection valve can be prevented and perform stable operation. Further, since the first urging means for urging the nozzle hole opening / closing means in the opening direction is also provided, the pressing force of the nozzle hole opening / closing means is reduced, and the noise generated when the nozzle hole opening / closing means is closed is suppressed. You can also.

According to the second aspect of the present invention, since the injection hole opening / closing means is constituted by the needle valve, the structure of the fuel injection valve can be simplified and downsized. Claim 3
According to the invention described above, since the first urging means and the second urging means are both constituted by springs, it is possible to promote cost reduction by employing a general distribution member.

According to the fourth aspect of the present invention, since the restricting means is a mechanical stopper, a rigid structure is obtained, and the reliability can be improved. According to the fifth aspect of the invention, even if the temperature of the fuel injection valve changes, the means for absorbing the difference in thermal expansion of each member constituting the fuel injection valve is provided, so that the fuel injection valve due to thermal expansion is provided. Erroneous operation can be prevented, and a fuel injection valve that performs stable operation can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the attached drawings. FIG. 1 shows a configuration of an embodiment of a fuel injection valve according to the present invention. Casing 1 that constitutes a part of a fuel injection valve (hereinafter abbreviated as “injection valve”) body
At one end of a needle valve holder 1, a posture holding portion 11 a of a needle valve 11 (injection hole opening / closing means) is slidably fitted.
The outer diameter portions 3 are fitted together and joined by welding or the like at the end (A portion) of the casing 14. On the other hand, the other end of the casing 14 is open for inserting a member constituting the injection valve, and after inserting such a member into the casing 14, the casing end member 15 is moved to the end (B
Part) and joined by welding or the like.

At the tip of the needle valve holder 13,
An injection hole 13a for injecting fuel and a seat surface 13b for sealing the fuel by pressing the spherical tip 12 of the needle valve 11 are formed. A poppet valve is constituted by the seat surface 13b and the spherical tip portion 12, and the fuel is injected and non-injected according to the operation of the needle valve 11. Further, a fuel passage 19a and a fuel passage 19b communicating with the fuel passage 19a at a substantially right angle are formed in the casing 14, and fuel supplied from outside is introduced into the injection valve. This fuel passage 19
“b” has one end closed by a blind plug 20 after drilling, and the other end is open to a fuel chamber 26 between a posture holding portion 11a of the needle valve 11 and a needle rear end portion 11b described later. The blind plug 20 can also be used as an air vent inside the injection valve. Further, the casing end member 15 has a fuel inlet 21 having a tapered thread shape used for connecting a fuel pipe and a fuel passage 19 communicating therewith.
The fuel passage 19c of the casing end member 15 and the fuel passage 19a of the casing 14 communicate with each other. Here, on the joint surface between the casing 14 and the casing end member 15, for the purpose of preventing fuel leakage from the communicating portion between the fuel passages 19c and 19a,
An O-ring 25 is provided. Reference numeral 19d, which has not been described above, is a hole for taking out a wiring 28 of the piezoelectric element 16 described later.

Next, the needle valve holder 1 described above
3, constituent members of the injection valve disposed inside the casing 14 and the casing end member 15 will be described. First, as described above, the posture holding portion 11a of the needle valve 11
Is slidably fitted to the inner periphery of the needle valve holder 13 joined to one end of the casing 14. The posture holding portion 11a has a fuel chamber 26 and a fuel chamber 27 in the needle valve holder 13. One or more communication holes 22 are opened in the axial direction of the needle valve 11 in order to communicate with each other. On the other hand, a needle rear end 11b of the needle valve 11 opposite to the spherical front end 12 is slidably fitted on the inner periphery of the casing 14, and a peripheral groove is formed on the outer peripheral surface of the needle rear end 11b. A O-ring 24 is provided for the purpose of sealing the fuel.

A piezoelectric element (for example, a piezo element) 16 for sliding the needle valve 11 to perform the operation of the injection valve is slidably fitted to the rear end 11b of the needle and the inner periphery of the casing 14. A coil spring 18 (second biasing means) sandwiched between the spring seat 23 and the spring seat 23 and the casing end member 15;
It is held by the urging force of a coil spring 17 (first urging means) provided between the end of the needle valve holder 13 and the rear end 11b of the needle.

Further, a stopper 14a (regulating means) is formed on the inner peripheral surface of the casing 14 so that the clearance between the end surface of the spring seat 23 and the end surface of the spring seat 23 in the initial state (predetermined state) is C (details will be described later). ing. In the present embodiment, the stopper 14a is formed integrally with the casing 14. However, the stopper 14a is not limited to such a configuration. For example, a snap ring (restriction means) may be provided in a recess formed on the inner peripheral surface of the casing 14. You may make it fit.

Here, within the operating temperature range of the injection valve, the clearance C is set at the normal temperature (predetermined temperature within the operating temperature range) when the piezoelectric element 16 is in the maximum expansion state. Thermal expansion (elongation) of the casing 14)-(thermal expansion (elongation) of the needle valve 11 at the maximum ambient temperature)-(thermal expansion (extension) of the piezoelectric element 16 at the maximum ambient temperature) And C ≧ (thermal expansion (shrinkage) of needle valve 11 at minimum ambient temperature) + (thermal expansion (shrinkage) of piezoelectric element 16 at minimum ambient temperature) − (casing 14 at minimum ambient temperature) C = (maximum contraction from the maximum expansion state of the piezoelectric element 16)
-(The lift amount of the required needle valve 11 from the viewpoint of engine performance) (that is, C <the maximum contraction amount of the piezoelectric element 16 from the maximum expansion state) is set.

As shown in FIGS. 2A and 2B, the relationship between the urging force F1 by the coil spring 17 and the urging force F2 by the coil spring 18 is as follows. The area where the end 11b receives the fuel pressure is A1, the combustion pressure of the engine is P2, and the area of the injection hole 13a is A2.
Is set as follows. F2> F1 + P1 × A1 + P2 × A2 (1) Next, the operation of the fuel injection valve having such a configuration will be described with reference to FIGS.

When the engine is stopped, since P1 = 0 and P2 = 0 and F2> F1 in the relational expression (1), the needle valve 1 is turned on by the urging force F2 of the coil spring 18.
One spherical tip 12 is a seating surface 13 of a needle valve holder 13.
As a result, the fuel is sealed and the injection stop state is maintained. When the engine is started, fuel adjusted to a predetermined pressure P1 by a high-pressure fuel pump and a pressure regulator (not shown) flows in from a fuel inlet 21 and is guided to a fuel chamber 26 through fuel passages 19c, 19a and 19b. The needle 11 is guided to the fuel chamber 27 in the needle valve holder 13 through the communication hole 22 formed in the posture holding part 11a. In this state, when a high voltage (for example, 500 V) is applied to the piezoelectric element 16 by an injection valve control drive circuit (not shown), the piezoelectric element 16 is moved from its contracted state when not operated to its entire length in the axial direction of the piezoelectric element 16. It grows in proportion (about 0.1
%), Together with the urging force F2 of the coil spring 18, the spherical tip portion 12 of the needle valve 11 is pressed against the seating surface 13b of the needle valve holder 13, the fuel is sealed, and the fuel injection stop state is maintained. Preparation is completed. This state is the initial state.

In this state, the voltage applied to the piezoelectric element 16 is reduced to 0 at the same time when the engine is rotated by the starter.
V, the piezoelectric element 16 is contracted, that is, returned to the contracted state when not in operation (see FIG. 2A). Here, the coil spring 17
The relationship between the urging force F1 of the coil spring 18 and the urging force F2 of the coil spring 18 is as follows, assuming that the fuel pressure is P1 and the area of the needle rear end 11b that receives the fuel pressure is A1.
Is: F2> F1 + P1 × A1 (P2
= 0), and under the condition of clearance C> 0, the piezoelectric element 16 is moved by the urging force F2 of the coil spring 18 as shown in FIG.
(a) It moves to the middle left direction, and the needle valve 11 remains closed. When the clearance C becomes zero due to the leftward movement of the piezoelectric element 16, the urging force F by the coil spring 18 is applied.
2 is supported by the stopper 14a.
6 stops moving to the left, and this time the piezoelectric element 1
6, the urging force F1 by the coil spring 17 and the fuel pressure P1
Due to the resultant force (F1 + P1 × A1) of the force P1 × A1 due to the above, a rightward force in the figure acts as shown in FIG. 2 (b).
As described above, since C <the maximum contraction amount from the maximum expansion state of the piezoelectric element 16, even after the clearance C = 0, the piezoelectric element 16 contracts until it reaches the maximum contraction amount, and the needle valve 11 Is the resultant force (F1 +) through the needle rear end 11b.
(P1 × A1), because it is in close contact with the piezoelectric element 16,
The needle valve 11 moves (opens) rightward in the figure, and fuel is injected.

Here, from the above-mentioned formula of the clearance C, (the amount of lift of the needle valve) = (the amount of contraction from the maximum expansion state of the piezoelectric element) -C. Further, when the valve is closed, when a high voltage is applied again to the piezoelectric element 16, the needle element 11 is closed due to the expansion of the piezoelectric element 16, and then the clearance C> 0, and the initial state is established.

In the above basic operation, a case is considered in which the entire injection valve is heated by the combustion heat of the engine or the like. The linear expansion coefficient of each member that affects the needle valve lift is about 1 for the needle valve 11 and the casing 14 made of a metal material.
To 1 × is the 10 ^-6 [1 / ° C.], the piezoelectric element made of ceramic material 16 is about 1/5 to about 2 × 10 ^-6 [1 / ° C.]. Therefore, when the temperature of the entire injection valve rises, the amount of extension of the piezoelectric element 16 is reduced by the needle valve 11 and the casing 1.
4 is smaller than the elongation. Here, the elongation amount (L) of the needle valve 11 and the casing 14 having the same linear expansion coefficient
(1) is considered to be substantially the same (actually, the length is different), and the difference between the extension L1 and the extension L2 of the piezoelectric element 16 is represented by L
3, the dimension D in FIG.
Becomes D + L3, and absorbs the difference in thermal expansion. Thereafter, the same operation as the above-described basic operation is performed.

Here, D → D + L3 and the coil spring 1
Assuming that the spring constant of the urging force F2 of FIG. 8 is k, F2 → F2-
L3 × k, and the above-mentioned relational expression (1) is expressed by the following equation: F2−L3 × k> F1 + P1 × A1 + P2 × A2 By setting the injection valve nozzle area to A2), no problem occurs.

Further, as described above, C ≧ (thermal expansion (extension) of the casing 14 at the maximum ambient temperature) − (thermal expansion (extension) of the needle valve 11 at the maximum ambient temperature) − ( Since the amount of thermal expansion (the amount of expansion) of the piezoelectric element 16 at the maximum ambient temperature is used, malfunction of the needle valve due to thermal expansion can be prevented.

Further, as an additional effect, the valve closing force is reduced by the coil spring 17 for urging the needle valve 11 in the valve opening direction, and the wear of the seating surface 13b is suppressed.
It is also possible to suppress the sitting hammering sound. As described above, (the lift amount of the needle valve) = (the maximum contraction amount from the piezoelectric element in the maximum expansion state) −C, and the thermal expansion difference L3 gives C → CL−3, and the lift amount is L3 at room temperature. Change. This means
When the ambient temperature around the injector changes due to the environment and operating conditions, it means that the lift amount changes. If the influence on the engine performance is large, for example, sensing (detecting) the injector temperature is performed. It is possible to cope with this by estimating a lift change amount corresponding to that and controlling the injection time.

When the temperature is lower than room temperature, the effect is the same as that described above, except that the elongation is reduced.

[Brief description of the drawings]

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

FIGS. 2A and 2B are explanatory diagrams of the operation of the fuel injection valve, in which FIG. 2A shows the start of valve opening and FIG. 2B shows the end of valve opening.

FIG. 3 is an explanatory view of a fuel injection valve using a conventional piezoelectric element.

[Explanation of symbols]

 Reference Signs List 11 needle valve 13 needle valve holder 13a injection hole 14 casing 14a stopper 16 piezoelectric element 17 coil spring 18 coil spring

Claims (5)

[Claims] An injection hole opening / closing means for opening / closing an injection hole formed in a fuel injection valve body; a first urging means for urging the injection hole opening / closing means in an opening direction; and closing the injection hole opening / closing means. A piezoelectric element that expands from a contracted state when not actuated in order to press the nozzle in the opening direction;
And a biasing means, comprising: a fuel injection valve for an internal combustion engine configured to include: a biasing force relationship between the first biasing means and the second biasing means;
The urging force of the second urging means is set to be larger than the urging force of the first urging means, and when the piezoelectric element contracts from the expanded state, the direction of the urging force of the second urging means is reduced. A fuel injection valve for an internal combustion engine, characterized in that the fuel injection valve is set so as to be movable in a predetermined direction and is provided with a regulating means for regulating a moving amount of the piezoelectric element in the direction. 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 said first urging means and said second urging means are both constituted by springs. 4. The internal combustion engine according to claim 1, wherein said regulating means is constituted by a mechanical stopper provided inside said fuel injection valve body. Fuel injection valve. 5. A fuel injection valve for opening and closing an injection hole formed in a fuel injection valve body by means driven by an output of a piezoelectric element, wherein the fuel injection is performed when the temperature of the fuel injection valve changes. A fuel injection valve for an internal combustion engine, wherein a means for absorbing a difference in thermal expansion between members constituting the valve is provided.