JP2002299709A - Actuator and injection device - Google Patents

Abstract

(57) Abstract: An actuator and an ejection device that can be driven for a long period of time with a constant preload applied in a stacking direction of a multilayer piezoelectric element. A displacement-generating laminated piezoelectric element (1) in which piezoelectric bodies and internal electrodes are alternately laminated, a base member (3) to which one end in the laminating direction of the displacement-generating laminated piezoelectric element (1) is fixed,
One end is fixed to the base member 3 and the preload applying case 5 in which the displacement generating multilayer piezoelectric element 1 is accommodated, and the inner surface of the preload applying case 5 and the stacking direction of the displacement generating multilayer piezoelectric element 1 An actuator comprising a preload applying unit 9 provided between the other end and a spring member 13 provided at the other end in the stacking direction of the displacement-generating piezoelectric element 1. And the spring member 13 and the preload applying case 5
Multilayer piezoelectric element 1 for applying a preload provided between inner layer and inner surface
And 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator and an injection device, for example, an actuator and an injection device used for a precision positioning device such as a fuel injection valve for an automobile, an optical device, and a driving element for preventing vibration. Things.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric body has an inverse piezoelectric effect that expands and contracts when a voltage is applied. However, since the amount of expansion and contraction of each piezoelectric body is very small, a laminated piezoelectric element formed by laminating a plurality of piezoelectric bodies has been manufactured. In the laminated piezoelectric element, a voltage is applied to the piezoelectric body to extend the piezoelectric body by several to several tens of μm, and is used as a driving force source of the actuator.

[0003] Conventionally, an actuator is constructed by accommodating a laminated piezoelectric element in a metal case in order to shut off the outside air, improve moisture resistance and prevent intrusion of foreign matters such as oil and fuel. In addition, the displacement of the laminated piezoelectric element is transmitted to a metal case, and the metal case itself is displaced.

[0004] As such an actuator, one disclosed in Japanese Patent Application Laid-Open No. 6-283778 is known. In the actuator disclosed in this publication,
By enclosing the laminated piezoelectric element in a metal case, the air is blocked from the outside air, the moisture resistance is improved, and the intrusion of oil, fuel, and the like is prevented.

FIG. 4 shows an actuator disclosed in this publication, in which one end of a laminated piezoelectric element 51 is fixed to a base member 52, and an opening of a bellows (diaphragm) 53 is formed in the base member 52. As a result, a preload is applied to the laminated piezoelectric element 51 in the direction opposite to the displacement direction. That is, the bellows (diaphragm) 53 applies a preload to the multilayer piezoelectric element 51 and transmits a displacement amount.

[0006]

However, in the actuator disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-283778, if the actuator is continuously driven for a long time under a high electric field and a high pressure, self-heating and fluctuation of the external atmosphere may occur. When the actuator is exposed to a high temperature, a difference in thermal expansion occurs between the laminated piezoelectric element 51 and the bellows (diaphragm) 53, causing a problem that the preload fluctuates and a predetermined displacement cannot be obtained.
That is, when the multi-layer piezoelectric element is driven, heat is generated, and the temperature around the multi-layer piezoelectric element also increases. With this, the multi-layer piezoelectric element shrinks and the metal case expands. Therefore, there is a problem that the displacement fluctuates.
In addition, the load differs due to the deformation of the bellows before and after the multi-layer piezoelectric element is fully extended.
The preload applied to the multi-layer piezoelectric element fluctuates in one cycle, and when an attempt is made to expand, a sudden load is applied to the multi-layer piezoelectric element. By acting, there is a problem that the piezoelectric body constituting the laminated piezoelectric element is deteriorated and is damaged accordingly.

An object of the present invention is to provide an actuator and an injection device which can be driven for a long period of time while a constant preload is applied in the stacking direction of a stacked piezoelectric element.

[0008]

According to the present invention, there is provided an actuator according to the present invention, wherein a displacement-generating laminated piezoelectric element in which piezoelectric bodies and internal electrodes are alternately laminated, and one end of the displacement-generating laminated piezoelectric element in the expansion / contraction direction is provided. A fixed base member, a preload application case having one end fixed to the base member and containing the displacement-generating multilayer piezoelectric element, an inner surface of the preload application case, and the displacement-generating multilayer piezoelectric device. An actuator provided with a preload applying section provided between the other end of the element in the expansion and contraction direction, wherein the preload applying section is provided at the other end of the displacement generating laminated piezoelectric element in the expansion and contraction direction. It is characterized by including a spring member, and a preload applying laminated piezoelectric element provided between the spring member and the inner surface of the preload applying case.

Generally, a laminated piezoelectric element has a negative coefficient of thermal expansion. On the other hand, the spring member for applying the preload and the preload application case for housing the laminated piezoelectric element are generally made of metal and have a positive coefficient of thermal expansion. Therefore, when the actuator is exposed to a high temperature due to external factors or self-heating of the laminated piezoelectric element, the overall length of the laminated piezoelectric element is reduced,
Since the spring member and the preload application case extend, the preload acting on the laminated piezoelectric element decreases as the temperature rises.

In the present invention, the preload applying portion is provided at a spring member provided at the other end in the expansion and contraction direction of the laminated piezoelectric element for generating displacement, and a preload member provided between the spring member and the inner surface of the preload application case. Because of the presence of the load-applying multilayer piezoelectric element, for example, when a thermal expansion difference occurs between the multilayer piezoelectric element and the preload application section, the preload application case, or the preload decreases over time In this case, the preload can be kept constant by controlling the voltage applied to the preload applying multilayer piezoelectric element.

Generally, when a displacement-generating laminated piezoelectric element is driven, a spring member for applying a preload causes a change in a load applied to the piezoelectric element due to a reaction force of the spring member. This load variation is caused by the spring constant k of the spring member used.
However, when a disc spring or the like in consideration of miniaturization is used, the load variation inevitably increases due to a high spring constant k.

That is, in the actuator of the present invention, the preload-applying multilayer piezoelectric element is driven synchronously so as to contract when the displacement-generating multilayer piezoelectric element expands, thereby providing the displacement-generating multilayer piezoelectric element. The preload applied to the displacement-producing multilayer piezoelectric element hardly fluctuates during one cycle even when it is about to elongate and when it is fully extended, and it is possible to suppress load fluctuation and secure stable displacement characteristics. It is possible to provide a highly reliable actuator.

In the present invention, it is desirable that the preload applying section has a sensor for measuring the preload. By controlling the voltage applied to the preload applying multilayer piezoelectric element based on the data from the sensor, the preload can be adjusted with higher accuracy.

Further, the amount of deformation of the multilayer piezoelectric element for generating displacement due to thermal expansion of the preload applying section in the expansion and contraction direction is smaller than the amount of deformation of the multilayer piezoelectric element for generating displacement due to thermal expansion of the preload applying case. Is also desirable. Since the preload applying section is more thermally deformed than the preload applying case, the amount of deflection of the preload applying section for applying the preload is reduced, and the adjustment width of the preload applying multilayer piezoelectric element is reduced. Since the voltage applied to the preload applying multilayer piezoelectric element can be reduced, the reliability can be improved.

[0015] The injection device of the present invention comprises a storage container having an injection hole, the actuator stored in the storage container, and a valve for discharging liquid from the injection hole by driving the actuator. Things.

[0016]

FIG. 1 shows an actuator according to the present invention. In FIG. 1, reference numeral 1 denotes a quadrangular prism-like displacement generator formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes. 2 shows a laminated piezoelectric element. The displacement-generating laminated piezoelectric element 1 has inert bodies 1a and 1b that do not generate displacement at both ends.

One end of the displacement-generating multilayer piezoelectric element 1 in the expansion / contraction direction, that is, an inert body 1a, is fixed to the base member 3, and the base member 3 accommodates the displacement-generating multilayer piezoelectric element 1. One end of the preload application case 5 is fixed. The preload application case 5 is housed in a sealed case 6 whose opening is fixed to the base member 3.

A displacement transmitting member 7 and a preload applying section 9 are provided between the inner surface of the preload applying case 5 and the other end in the expansion and contraction direction of the multilayer piezoelectric element 1 for generating displacement, that is, the inert body 1b. ing. The displacement transmitting member 7 is composed of a rod 7b and an enlarged-diameter portion 7a that comes into contact with the inert body 1b. By contacting the inner surface of the case 6, the displacement of the displacement-generating multilayer piezoelectric element 1 is transmitted to the closed case 6. Although not shown, the closed case 6 is provided with an easily deformable portion formed in, for example, a bellows shape, and is easily deformed in the expansion and contraction direction of the multilayer piezoelectric element 1 for generating displacement.

The preload applying section 9 includes a spring member 13 provided between the enlarged diameter portion 7a of the displacement transmitting member 7 and a ring-shaped reaction force plate 11 through which the rod 7a is inserted. A preload application laminated piezoelectric element 15 provided between the force plate 11 and the inner surface of the preload application case 5 is provided. A through-hole is formed in the preload-applying laminated piezoelectric element 15, and the rod 7 a passes through the through-hole. The spring member 13 is formed by laminating two disc springs and facing each other. In the present invention, the spring member 13 is not limited to a disc spring, but may be a coil spring or a preload applying mechanism having a hydraulic pressure.

When a disc spring is used as the spring member 13,
The spring constant k of the disc spring itself is determined by the diameter and thickness of the disc spring and the manner of arrangement, that is, serial arrangement, parallel arrangement, and the like, and the spring constant k is preferably 100 to 1000 kg / mm. This is, for example, a load of 100 to 50.
When a higher preload of about 0 kg is applied to the displacement-generating laminated piezoelectric element 1, when the spring constant k is smaller than 100 kg / mm, more disc springs having a large diameter enough to withstand the load are connected in series. This is because it is necessary to combine them, and the actuator itself becomes large.

When the spring constant k is larger than 1000 kg / mm, the reaction force from the disc spring increases. That is, the load fluctuation becomes large, and the displacement of the displacement-generating multilayer piezoelectric element 1 is significantly reduced by the load fluctuation, so that the efficiency as an actuator is lowered. In addition, when the actuator is operated at a high speed due to a large load variation, an impact force applied to the displacement-generating laminated piezoelectric element 1 is increased, so that the piezoelectric plate is damaged or deteriorated.
This is because long-term reliability cannot be maintained.

The multilayer piezoelectric element 15 for applying a preload, like the multilayer piezoelectric element 1 for generating displacement, is configured by alternately laminating internal electrodes and piezoelectric bodies. The number of stacked piezoelectric bodies is smaller than that. The preload-applying multilayer piezoelectric element 15 is driven synchronously so that when the displacement-generating multilayer piezoelectric element 1 expands, it contracts.

In the actuator configured as described above, since the preload applying section 9 includes the spring member 13 and the preload applying multilayer piezoelectric element 15, the displacement generating multilayer piezoelectric element 1 and the preload When a difference in thermal expansion occurs between the application section 9 and the preload application case 5 or when the preload decreases over time, the voltage applied to the preload application multilayer piezoelectric element 15 is controlled. By doing so, the preload can be made constant.

Further, the laminated piezoelectric element 15 for applying a preload
Are driven synchronously so as to contract when the displacement-generating multilayer piezoelectric element 1 expands, so that when the displacement-generating multilayer piezoelectric element 1 is about to extend, and when the displacement-generating multilayer piezoelectric element 1 is fully extended, The preload applied to the piezoelectric element 1 is 1
Almost no fluctuation during the cycle
The stable displacement characteristics can be secured without b being damaged.

That is, when the displacement-generating multilayer piezoelectric element 1 is expanded by receiving a voltage from the outside, the spring member 13 of the preload applying section 9 connected to the upper part thereof is moved in the extension direction of the displacement-generating multilayer piezoelectric element 1, In other words, the load is reduced in a direction in which the load is further increased, and a change in the load generated when the load is reduced becomes a change in the load on the displacement-generating multilayer piezoelectric element 1. This load variation depends on the expansion and contraction of the spring member 13 when the preload application unit 9 and the preload application case 5 are firmly connected, but by making the deformation of the spring member 13 constant, Load fluctuation can be suppressed. Therefore, the voltage applied to the preload applying laminated piezoelectric element 15 is controlled to
By keeping the deformation constant, a stable amount of displacement can be supplied.

Further, since the preload applying case 5 can be made of a rigid body, the preload can be made more constant. Furthermore, since the easily deformable portion is formed in the closed case 6, the displacement generating lamination The displacement of the piezoelectric element 1 can be effectively transmitted to the outside via the displacement transmitting member 7.

FIG. 2 shows another example of the present invention, in which a laminated piezoelectric element 15 for applying a preload and a case 5 for applying a preload.
Between them, a ring-shaped sensor 25 for measuring a preload is provided. The sensor 25 is configured by alternately stacking piezoelectric bodies and internal electrodes, and the rod-shaped body 7a of the displacement transmitting member 7 is inserted therethrough.

In such an actuator, if the preload is constant, the voltage generated at the sensor 25 is constant. Therefore, the fluctuation of the preload can be monitored by the fluctuation of the voltage of the sensor 25. By feeding back to the piezoelectric element 15, the fluctuation of the load can be more accurately suppressed.

According to the present invention, the amount of deformation of the multilayer piezoelectric element 1 for generating displacement due to thermal expansion of the preload applying unit 9 in the expansion and contraction direction is determined by the amount of deformation of the multilayer piezoelectric element for generating displacement due to thermal expansion of the preload applying case 5. The amount of deformation of the element 1 in the direction of expansion and contraction is made larger. This is because the preload application section 9 is used for the preload application case 5.
Due to the larger thermal deformation, the change in the amount of deflection of the preload applying unit 9 for applying the preload is reduced, and the adjustment width of the preload applying laminated piezoelectric element 15 can be reduced. Since the voltage applied to the application multilayer piezoelectric element 15 can be reduced, the reliability can be improved.

FIG. 3 shows the injection device of the present invention.
In the figure, reference numeral 31 indicates a storage container. An injection hole 33 is provided at one end of the storage container 31, and a needle valve 25 that can open and close the injection hole 33 is stored in the storage container 31.

A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate therewith. The fuel passage 37 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 37 at a constant high pressure. Therefore, when the needle valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is jetted at a constant high pressure into a fuel chamber (not shown) of the internal combustion engine.

The upper end of the needle valve 35 has a large diameter, and has a piston 41 slidable with a cylinder 39 formed in the storage container 31. The above-described actuator 43 is provided in the storage container 31.
Is stored.

In such an injection device, when the actuator 43 is extended by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. Further, when the application of the voltage is stopped, the actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 to perform the fuel injection.

[0034]

According to the actuator of the present invention, the preload applying portion is provided between the spring member provided at the other end in the expansion / contraction direction of the laminated piezoelectric element for generating displacement, and the spring member and the inner surface of the preload applying case. Since the multi-layer piezoelectric element for applying a pre-load is provided, for example, when there is a difference in thermal expansion between the multi-layer piezoelectric element and the pre-load applying section or the pre-load applying case, or when the When the load decreases, the preload can be made constant by controlling the voltage applied to the preload-applying laminated piezoelectric element.

Further, the preload applying multilayer piezoelectric element is driven synchronously so as to contract when the displacement generating multilayer piezoelectric element expands, so that the displacement generating multilayer piezoelectric element attempts to expand. In addition, even when fully extended, the preload applied to the displacement-generating laminated piezoelectric element hardly fluctuates in one cycle, and the fluctuation of the load can be suppressed.

Accordingly, when the actuator is operated continuously at a high speed with a high applied electric field at a high speed for a long period of time, a highly reliable actuator capable of securing a stable displacement characteristic even when there is a change in temperature or load due to external factors is provided. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an actuator of the present invention.

FIG. 2 is a sectional view showing another actuator of the present invention.

FIG. 3 is an explanatory view showing an injection device of the present invention.

FIG. 4 is a sectional view showing a conventional actuator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element for displacement generation 3 ... Base member 5 ... Preload application case 9 ... Preload application part 13 ... Spring member 15 ... Laminated piezoelectric element for preload application 25 sensor 31 storage container 33 injection hole 35 valve 43 actuator

Claims (5)

[Claims] 1. A laminated piezoelectric element for generating displacement by alternately laminating piezoelectric bodies and internal electrodes, a base member having one end fixed in the expansion and contraction direction of the laminated piezoelectric element for generating displacement, and the base member. One end is fixed to the preload applying case in which the displacement generating multilayer piezoelectric element is accommodated, and between the inner surface of the preload applying case and the other end of the displacement generating multilayer piezoelectric element in the expansion / contraction direction. An actuator provided with a preload applying unit, wherein the preload applying unit includes a spring member provided at the other end in the expansion and contraction direction of the displacement-generating laminated piezoelectric element; An actuator comprising: a preload-applying laminated piezoelectric element provided between the load-applying case and the inner surface of the case. 2. The actuator according to claim 1, further comprising a sensor for measuring the preload in the preload applying section. 3. The amount of deformation in the expansion / contraction direction of the displacement-generating multilayer piezoelectric element due to thermal expansion of the preload applying unit is calculated from the amount of deformation of the displacement-generating multilayer piezoelectric element in the expansion / contraction direction due to thermal expansion of the preload applying case. 3 is also large.
An actuator as described. 4. The multi-layer piezoelectric element for applying a preload according to claim 1, wherein the multi-layer piezoelectric element for generating displacement is driven synchronously so as to contract when the multi-layer piezoelectric element for generating displacement expands. Actuator. 5. A storage container having an injection hole, the actuator according to any one of claims 1 to 4 stored in the storage container, and a valve for discharging liquid from the injection hole by driving the actuator. An injection device characterized by comprising: