JPH10205406A - Fuel injection valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a driving means for fuel injection valves, securing the required driving stroke of a valve body driven by piezoelectric elements. SOLUTION: As a driving means for a needle valve 22, a bimorph 26 (or unimorph) are used. There are provided; a plurality of bimorph 26 at the both sides of the needle valve 22, each bimorph 26 being faced to the perpendicular direction (horizontal direction) against the needle valve 22 with the displacement direction thereof by the stress being set to the opening and closing direction (up and down direction) of the needle valve 22. The base end of an elastic plate 35 of each bimorph 26 is fixed to a supporting base 37 in a ring form press fitted into the upper part of the inner periphery of the valve body 12. Also the front ends of the elastic plates 35 of each bimorph 26 are connected to the needle valve by welding and the like. Further, to control the displacement by a deflection of the bimorph 26 depending on the temperature characteristics thereof, a unimorph 38 for compensating the above temperature characteristics by reversing the direction of the displacement by the stress are provided at the both sides of the needle valve in parallel to the elastic plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection valve using a piezoelectric element as driving means.

[0002]

2. Description of the Related Art A piezoelectric element is a ferroelectric ceramic which generates a strain displacement in one direction when a voltage is applied, and has a very excellent responsiveness. It has been considered that a piezoelectric element is used instead of the solenoid coil used in the above. Generally, since the amount of strain displacement of the piezoelectric element itself is very small,
In order to secure the drive stroke of the valve element, there is a type in which a large number of piezoelectric elements are stacked to use a stacked piezoelectric actuator in which the amount of strain displacement is increased. However, the displacement amount is still insufficient.
As disclosed in Japanese Patent Publication No. 274, there is an apparatus in which the strain displacement of a laminated piezoelectric actuator is enlarged by an enlargement lever mechanism to drive a valve element.

[0003]

However, in the configuration in which the laminated piezoelectric actuator and the magnifying lever mechanism are combined, the configuration becomes complicated, the number of parts increases, the assemblability decreases, and the manufacturing cost increases. In addition, there is a problem that the size of the driving means is increased and the size of the fuel injection valve is increased.

[0004] The present invention has been made in view of such circumstances, and its object is to simplify the configuration while ensuring the drive stroke of the valve element by the piezoelectric element.
An object of the present invention is to provide a fuel injection valve capable of realizing improved assemblability, lower cost, and smaller size.

[0005]

According to a first aspect of the present invention, there is provided a fuel injection valve comprising a driving means for driving a valve element, a plate-like piezoelectric element provided on one or both sides of an elastic plate. And a bending displacement type piezoelectric driver (bimorph or unimorph) is formed by joining the piezoelectric actuator and the valve. The bending displacement direction of the piezoelectric driver is adjusted to the opening / closing direction of the valve body. The valve body is driven by the front end of the piezoelectric driving body supported on the housing side. Here, the bending displacement type piezoelectric driving body used as the driving means, when a voltage is applied to a plate-shaped piezoelectric element on one side or both sides of the elastic plate,
The piezoelectric element expands / displaces in the direction of the plate surface, whereby the piezoelectric driving member is bent and bent so as to bend in a direction perpendicular to the plate surface, and the amount of the bending displacement becomes the drive stroke of the valve body. As described above, the bending displacement type piezoelectric driver can greatly increase the displacement amount by converting the extension / shrinkage displacement of the piezoelectric element into a bending displacement in a direction perpendicular to the piezoelectric element. The driving stroke of the valve element can be sufficiently ensured without using the valve. Therefore, the enlargement lever mechanism is not required, so that the configuration can be simplified and downsized, and the assemblability can be improved and the cost can be reduced.

According to the present invention, a plurality of piezoelectric driving members may be provided in order to increase the driving force.
As described above, it is preferable to dispose a plurality of piezoelectric drivers at a plurality of locations around the valve so that the driving forces around the valve are balanced. With this configuration, an unbalanced load does not act on the valve body, and uneven wear of the valve body and its sliding portion can be prevented, so that durability can be improved.

By the way, when the piezoelectric driving body is freely bent and displaced in a cantilever state, the linear distance between both ends of the piezoelectric driving body is slightly shortened accordingly. There is a possibility that the restraining force acts from the fixed end in a direction that hinders the bending displacement of the piezoelectric driver, and the bending displacement is reduced.

As a countermeasure against this, the driving force of the piezoelectric driving body is provided by setting the tip of the piezoelectric driving body as a free end and engaging the free end with a step formed on the outer periphery of the valve body. May be transmitted to the valve element. With this configuration, a change in the linear distance between both ends due to the bending displacement of the piezoelectric driving body is freely allowed, and the restraining force does not act in a direction that hinders the bending displacement of the piezoelectric driving body. It can be increased efficiently.

Further, a plurality of piezoelectric driving bodies are arranged and arranged in the axial direction of the valve body, and a connecting member for connecting the piezoelectric driving bodies is attached to the tips of the plurality of piezoelectric driving bodies. The driving force of the piezoelectric driver may be transmitted to the valve body by engaging the axial end surface of the member with a step formed on the outer periphery of the valve body. As described above, when the plurality of piezoelectric driving bodies arranged in the axial direction of the valve body are simultaneously bent and displaced in the cantilever state, the positions of their tips are aligned, so that the tips are connected by the connecting member. Even
If the connecting member is not fixed to the valve body, no restraining force is exerted on the plurality of piezoelectric drivers from the connecting member, and the bending displacement of the piezoelectric driver can be efficiently increased. In addition, by connecting a plurality of piezoelectric driving bodies with a connecting member at the time of manufacturing and assembling, these can be handled as one unit component, and assemblability can be improved.

Further, since the temperature of the fuel injector rises considerably due to the heat radiation of the engine, the piezoelectric driver may be slightly displaced due to the temperature characteristics without applying a voltage to the piezoelectric driver.

As a countermeasure, in order to suppress the bending displacement due to the temperature characteristic of the piezoelectric driving body, a piezoelectric driving body for temperature characteristic correction in which the direction of the bending displacement due to the temperature characteristic is opposite is provided. May be. With this configuration, the bending displacement due to the temperature characteristics of the piezoelectric driver can be automatically suppressed, and the temperature characteristics of the fuel injection valve can be improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment (1)] Hereinafter, an embodiment (1) of the present invention will be described with reference to FIGS. First, the configuration of the entire fuel injection valve will be described with reference to FIG. The valve housing 10 of the fuel injection valve is formed by welding a metal fuel pipe 11 and a metal valve body 12 constituting a fuel passage by welding. At an upper end of the fuel pipe 11, a fuel connector 13 connected to a fuel pipe (not shown) is formed, and an outer peripheral portion of the fuel connector 13 is made of a resin for sealing a connection with the fuel pipe. An O-ring 14 is fitted, and a filter 15 for filtering the fuel sent from the fuel pipe is mounted inside the fuel connector portion 13. The fuel that has passed through the filter 15 flows through the fuel pipe 11 and flows into the valve body 12.

The outer peripheral portion of the fuel pipe 11 is
The resin molded body 31 is molded integrally with an electric connector 32, and a connector pin 33 for applying a voltage to a bimorph 26 described later is embedded in the electric connector 32 by insert molding.

On the other hand, a valve seat 16 having a tapered hole shape is formed at the lower end of the valve body 12, and a metal injection plate 17 is hermetically fixed to the outside thereof by laser seam welding or the like. A fuel injection hole 18 (see FIG. 1) formed at 17 is located inside the opening of the valve seat 16. A resin O-ring 19 that seals a connection portion with an intake manifold (not shown) is fitted to an outer peripheral portion of the valve body 12, and a resin cap that prevents the O-ring 19 from falling off below the resin O-ring 19. 20 is press-fitted and fixed so as to cover the injection plate 17, and the cap 20 is formed with a tapered hole 21 for exposing a peripheral portion of the fuel injection hole 18.

Inside the valve body 12, a metal needle valve 22 is housed as a valve body. The needle valve 22 is formed in a hollow shape for weight reduction, and a large-diameter portion 23 formed in a lower portion thereof is slidable in a vertical direction in a sliding hole portion 24 formed in the valve body 13. Are fitted and supported. A cut surface portion 25 for forming a gap for a fuel passage in the sliding hole portion 24 is formed on the outer peripheral portion of the large diameter portion 23 of the needle valve 22.

The upper portion of the needle valve 22 is supported by a bimorph 26, which is a flexural displacement type piezoelectric driver described later. An adjuster pipe 28 with a slot 27 is press-fitted and fixed inside the fuel pipe 11, and a spring 29 is mounted below the adjuster pipe 28. The resilient force of the spring 29 causes the needle valve 22 to close in the valve closing direction ( Downward). When not driven (when injection is stopped), the lower end of the needle valve 22 is pressed against the valve seat 16 of the valve body 12 by the elastic force of the spring 29 and the fuel injection hole 18 is kept closed.
By adjusting the press-fitting position of the adjuster pipe 28, the biasing force of the spring 29 in the valve closing direction of the needle valve 22 can be adjusted. The fuel sent into the fuel pipe 11 flows through the inner diameter of the adjuster pipe 28 and the inner diameter of the spring 29 into the valve body 12.

Next, the structure and assembling method of the bimorph 26 used as the driving means of the needle valve 22 are shown in FIG.
A description will be given based on FIG. The bimorph 26 is formed by joining plate-shaped piezoelectric elements 36 to both sides of an elastic plate 35 such as a thin leaf spring. A plurality (same number) of bimorphs 26 are arranged on both sides of the needle valve 22 in the axial direction, and each bimorph 26 is oriented in a direction perpendicular to the needle valve 22 (horizontal direction).
The direction of the bending displacement of 6 is adjusted to the opening / closing direction (vertical direction) of the needle valve 22. Elastic plate 3 of each bimorph 26
5 is fixed to a ring-shaped support base 37 fitted into the upper inner periphery of the valve body 12 by press fitting or the like, and the distal end of the elastic plate 35 of each bimorph 26 is attached to the needle valve 2.
2 are connected by welding or the like. The fuel sent from the fuel pipe 11 into the valve body 12 flows downward through the gap between the bimorph 26 and the support base 37.

The piezoelectric elements 36 on both sides of each bimorph 26
Each has an electrode surface on its surface, and each piezoelectric element 36
When a voltage is applied between the electrode surface on the surface and the elastic plate 35 (common electrode), the piezoelectric element 36 on the upper surface contracts and displaces in the plate surface direction, and the piezoelectric element 36 on the lower surface moves in the plate surface direction. The distal end of the bimorph 26 is flexed and displaced upward (toward the valve opening direction of the needle valve 22), thereby driving the needle valve 22 in the valve opening direction against the spring 29.

On both sides of the needle valve 22, in order to suppress the bending displacement due to the temperature characteristics of the bimorph 26, a piezoelectric driver for temperature characteristics correction, for example, a unimorph 38, in which the direction of the bending displacement due to the temperature characteristics is reversed. It is juxtaposed. The unimorph 38 is made of an elastic plate 3 such as a thin leaf spring.
9 is formed by joining a plate-shaped piezoelectric element 40 to one surface, and the method of assembling the unimorph 38 is the same as that of the bimorph 26. The deflection displacement force due to the temperature characteristics of the unimorph 38 is caused by the bimorph 26 generated in the opposite direction.
Are set so as to be substantially the same as the total value of the bending displacement force due to the temperature characteristics of the above. Thereby, the bending displacement due to the temperature characteristics of the bimorph 26 can be automatically suppressed,
The temperature characteristics of the fuel injection valve can be improved.

The unimorph 38 is a bimorph 2
6, the voltage is not applied to the unimorph 38 even when the voltage of the bimorph 26 is applied. However, when a voltage is applied to the bimorph 26,
A voltage is also applied to the unimorph 38 so that the unimorph 38
May be bent and displaced in the same direction as the bimorph 26. In this case, the unimorph 3 for temperature characteristic correction
8 can also be used as a driving means of the needle valve 22.

According to the embodiment (1) described above, while fuel injection is stopped, no voltage is applied to the bimorph 26, and the lower end of the needle valve 22 is moved by the resilience of the spring 29 so that the valve seat of the valve body 12 is closed. The fuel injection hole 18 is kept in a closed state by being pressed against the fuel injection hole 16. Then, at the time of fuel injection, a voltage is applied to each bimorph 26, the upper piezoelectric element 36 contracts and displaces in the plate surface direction, and the lower piezoelectric element 36 extends and displaces in the plate surface direction. The tip side of the valve member 26 is flexed and displaced upward (toward the valve opening direction of the needle valve 22), and the needle valve 22 is pulled up against the spring 29 by the flexing displacement, and the fuel injection hole 18 is opened.

As described above, the bimorph 26, which is a bending displacement type piezoelectric driving body, can greatly increase the amount of displacement by converting the extension / shrinkage displacement of the piezoelectric element 36 into a flexural displacement in a direction perpendicular thereto. Also, the drive stroke of the needle valve 22 can be sufficiently ensured without using a conventional enlargement lever mechanism. Therefore, the enlargement lever mechanism is not required, so that the structure can be simplified and the driving means can be downsized, so that the assemblability can be improved and the cost can be reduced.

Since the same number of bimorphs 26 are provided on both sides of the needle valve 22, the driving forces on both sides of the needle valve 22 are the same. For this reason, an unbalanced load does not act on the needle valve 22, and uneven wear of the sliding portion (the large diameter portion 23, the sliding hole portion 24, the valve seat portion 16) of the needle valve 22 can be prevented, and the durability is reduced. Can be improved.

In the above embodiment (1), the bimorphs 26 are arranged only on both sides of the needle valve 22, but the bimorphs 26 are provided at three or more places around the needle valve 22.
May be arranged, and in this case, the needle valve 22
If the bimorph 26 is arranged so that the driving force around the needle valve 22 is balanced, an uneven load does not act on the needle valve 22 and uneven wear of the sliding portion of the needle valve 22 can be prevented, and the durability is improved. Can be.

[Embodiment (2)] When the bimorph 26 is freely bent and displaced in a cantilever state, the linear distance between both ends of the bimorph 26 is slightly shortened. When the bimorph 26 is fixed, a restraining force is exerted from the fixed end in a direction that hinders the bending displacement of the bimorph 26, and the bending displacement may be reduced.

As a countermeasure, in the embodiment (2) of the present invention shown in FIG. 4, the base end of each bimorph 26 is cantilevered by a support base 37, and the elastic plate 35 of each bimorph 26 is supported.
Of the elastic plate 35 is loosely fitted into a groove 41 (step portion) formed on the outer periphery of the needle valve 22. Therefore, the position of the distal end of the elastic plate 35 can be freely shifted and moved in the groove 41 with the bending displacement of the bimorph 26. When the bimorph 26 is flexed and displaced, the distal end of the elastic plate 35 engages the upper surface of the groove 41, so that the driving force of the bimorph 26 in the valve opening direction (upward) is transmitted to the needle valve 22. The method of assembling the unimorph 38 for temperature characteristic correction is the same as that of the bimorph 26. The base end of the unimorph 38 is cantilevered by the support base 37, and the tip of the elastic plate 39 of the unimorph 38 is the needle valve 22. It is loosely fitted into a groove 42 formed on the outer periphery.

In this configuration, a change in the linear distance between both ends due to the bending displacement of the bimorph 26 is freely allowed, and no restraining force acts in a direction that hinders the bending displacement of the bimorph 26.
The deflection displacement of the bimorph 26 can be efficiently increased, and the drive stroke of the needle valve 22 can be increased. Moreover, thermal expansion / contraction due to temperature change of the bimorph 26 is freely allowed, and the influence of temperature can be effectively reduced in combination with the presence of the unimorph 38 for temperature characteristic correction.

As means for engaging the tip of the elastic plate 35 of the bimorph 26 with the outer periphery of the needle valve 22,
Instead of the groove 41, a convex rib may be formed, and the tip of the elastic plate 35 may be engaged with the lower surface of the convex rib.

[Embodiment (3)] In the embodiment (3) of the present invention shown in FIGS. 5 and 6, a plurality of bimorphs 26 are arranged on both sides of the needle valve 22 in the axial direction (vertical direction). The base end of each bimorph 26 is supported by a support base 37.
A metal connecting member 43 for connecting the elastic plates 35 of the plurality of bimorphs 26 arranged in the axial direction is attached by welding or the like, and the axial end face of the connecting member 43 is The driving force in the valve opening direction (upward) of the bimorph 26 is transmitted to the needle valve 22 by engaging with the lower surface of a spring receiving portion 44 (step portion) formed on the outer periphery of the upper end of the needle valve 22. A slight gap is provided between the connecting member 43 and the needle valve 22. Also in this embodiment (3), a unimorph 38 for temperature characteristic correction is provided in the same manner as the bimorph 26.

As in the embodiment (3), a plurality of bimorphs 26 arranged in the axial direction of the needle valve 22 are provided.
However, if they are simultaneously bent and displaced in a cantilever state, the positions of their tips are aligned, so that even if those tips are connected by the connecting member 43, the connecting member 43 must be fixed to the needle valve 22. For example, a plurality of bimorphs 26
Does not receive the binding force from the connecting member 43 and the bimorph 2
6 can be efficiently increased, and the driving stroke of the needle valve 22 can be increased as in the embodiment (2). Moreover, the connecting member 4
By providing a small gap between the valve 3 and the needle valve 22, thermal expansion / contraction due to a temperature change of the bimorph 26 is freely allowed, and in combination with the presence of the unimorph 38 for temperature characteristic correction, The effect can be effectively reduced. In addition, a plurality of bimorphs 26
Are connected by the connecting member 43, these can be handled as one unit component, and assemblability can be improved.

[Other Embodiments] In each of the above embodiments, the bimorph 26 is used as the bending displacement type piezoelectric driving body for driving the needle valve 22, but a unimorph may be used. Further, a unimorph 38 for temperature characteristic correction is provided.
A bimorph may be used. It should be noted that the piezoelectric driver for temperature characteristic correction is not necessarily provided, and even in this case, the intended object of the present invention can be sufficiently achieved.

In addition, the present invention can be implemented with various changes without departing from the gist of the invention, such as by appropriately changing the number of bending displacement type piezoelectric actuators for driving the needle valve 22.

[Brief description of the drawings]

FIG. 1 is an enlarged longitudinal sectional view of a main part of a fuel injection valve showing an embodiment (1) of the present invention.

FIG. 2 is a cross-sectional view taken along line AA of FIG.

FIG. 3 is a longitudinal sectional view of the entire fuel injection valve.

FIG. 4 is an enlarged vertical sectional view showing an assembling structure of a bimorph for driving a needle valve according to the embodiment (2) of the present invention.

FIG. 5 is an enlarged longitudinal sectional view of a main part of a fuel injection valve showing an embodiment (3) of the present invention.

FIG. 6 is a cross-sectional view taken along the line BB of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Valve housing, 11 ... Fuel pipe, 12 ... Valve body, 15 ... Filter, 16 ... Valve seat part, 17 ... Injection plate, 18 ... Fuel injection hole, 22 ... Needle valve (valve element), 23 ... Large diameter part , 24 ... sliding hole portion, 25 ... cut surface portion, 26 ... bimorph (flexible displacement type piezoelectric driver), 2
Reference numeral 8: adjuster pipe, 29: spring, 32: electric connector, 35: elastic plate, 36: piezoelectric element, 37: support base, 38: unimorph for temperature characteristic correction (piezoelectric driver for temperature characteristic correction), 39 ... Elastic plate, 40: piezoelectric element, 41, 42: groove (step), 43: connecting member, 4
4: Spring receiving portion (step portion).

Claims (5)

[Claims] In a valve housing constituting a fuel passage,
In a fuel injection valve provided with a valve element that opens and closes a fuel injection hole and a driving unit that drives the valve element, the driving unit may be configured by joining a plate-shaped piezoelectric element to one or both surfaces of an elastic plate. A piezoelectric actuator of a displacement type, the bending displacement direction of the piezoelectric actuator is adjusted to the opening / closing direction of the valve body, and the base end of the piezoelectric actuator is supported on the valve housing side. A fuel injection valve characterized in that the valve body is driven by a tip. 2. The fuel injection system according to claim 1, wherein the piezoelectric driving body is arranged at a plurality of positions around the valve body so that driving forces around the valve body are balanced. valve. 3. The driving force of the piezoelectric driving body is transmitted to the valve body by setting the tip of the piezoelectric driving body as a free end and engaging the free end with a step formed on the outer periphery of the valve body. The fuel injection valve according to claim 1 or 2, wherein: 4. A plurality of the piezoelectric driving bodies are arranged in the axial direction of the valve body, and a connecting member for connecting the piezoelectric driving bodies is attached to a tip of the plurality of piezoelectric driving bodies, and an axial end face of the connecting member. The fuel injection valve according to claim 1, wherein the driving force of the piezoelectric driving body is transmitted to the valve body by engaging the step with a step formed on the outer periphery of the valve body. 5. A piezoelectric driver for temperature characteristic correction in which the direction of the deflection displacement due to the temperature characteristic is suppressed in order to suppress the deflection displacement due to the temperature characteristic of the piezoelectric driver. 5. The fuel injection valve according to any one of claims 1 to 4.