Multilayer piezoelectric element, injection device using same and fuel injection system

Abstract

The present invention provides a multilayer piezoelectric element having excellent durability, wherein a conductive member is not separated from an external electrode even when the element is continuously operated for a long time at high electric field and high pressure. The multilayer piezoelectric element (1) comprises a laminate (7) wherein piezoelectric layers (3) and internal electrode layers (5) are alternately laminated, and an external electrode (9) which is bonded to a lateral surface of the laminate (7) and electrically connected to the internal electrode layers (5). The surface of the external electrode (9) is provided with a plurality of open pores (2). Due to the open pores (2), the bonding strength of the external electrode (9) to a conductive member is improved, thereby preventing separation of the conductive member. In addition, since the heat dissipation characteristics of the external electrode are improved, the external electrode can be prevented from a thermal breakdown due to heat generation.

Description

technical field [0001] The present invention relates to a multilayer piezoelectric element used for, for example, a drive element (piezoelectric actuator), a sensor element, a circuit element, and the like. As the driving element, for example, a fuel injection device of a motor vehicle engine, a liquid injection device such as an inkjet head, a precision positioning device such as an optical device, and an anti-vibration device are exemplified. As the sensor element, for example, a combustion pressure sensor, a knock sensor, an acceleration sensor, a load sensor, an ultrasonic sensor, a pressure sensitive sensor, and a yaw rate sensor are exemplified. Moreover, as a circuit element, a piezoelectric gyroscope, a piezoelectric switch, a piezoelectric transformer, and a piezoelectric circuit breaker are mentioned, for example. Background technique [0002] As an external electrode in a conventional multilayer piezoelectric element, as disclosed in Patent Document 1, a conducti...

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Problems solved by technology

[0005] However, when the multilayer piezoelectric element using the external electrodes described in Patent Document 1 is used under severe conditions such as high voltage, high pressure, or long-term continuous driving, the following problems may occur: connection The conductive member fixed to the external electrode peels off, so that the voltage cannot be supplied to the external electrode and the multi-layer piezoelectric element does not displace

[0006] Furthermore, when a multi-layer piezoelectric element is driven at high speed by passing a large current to the external electrodes, there is a problem that the external electrodes generate heat and cause thermal breakdown.

[0007] Or there is a problem that a part of the external electrode may be peeled off from the side of the laminated body, and a voltage cannot be supplied to the internal electrode layer of the laminated body, so that the initial displacement of the multi-layer piezoelectric element cannot be maintained.

That is, in the multi-layer piezoelectric element, when the high voltage is continuously driven for a long time, due to the stress generated at the joint interface between the side surface of the multi-layer body and the external electrode, a part of the external electrode is removed from the side surface of the multi-layer body Therefore, a voltage cannot be supplied from the external electrode to a part of the piezoelectric layer through the internal electrode layer, resulting in a decrease in displacement characteristics.

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