Laminated Piezoelectric Element Electrode Bonding
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Solution Overview
Problem
Multi-layer piezoelectric elements experience heat generation at the external electrode plate and electrically conductive bonding material, leading to deterioration and detachment, as well as cracking due to thermal expansion differences, which can halt the element's operation.
Innovation Solution
A multi-layer piezoelectric element design with an external electrode plate extending past the electrically conductive bonding material, featuring a wider region at one end to reduce electrical resistance and heat generation, and a stress mitigation region with gradually increasing piezoelectric layer thickness to minimize detachment and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the external electrode plate is connected to the stacked body via electrically conductive bonding material, then electrical connection is achieved, but heat is generated at the entrance side of the external electrode plate and in the bonding material, leading to deterioration and detachment
Solution Approach 1:
The patent extends the external electrode plate in the stacking direction beyond the bonded region, creating a three-dimensional configuration where the electrode plate protrudes from both ends of the bonded area. This dimensional extension allows the electrode plate to serve multiple functions: providing electrical connection through the bonding material while also acting as a heat sink and current distributor. The extended structure reduces current density at the entrance side by distributing rush current across a larger surface area, thereby reducing localized heat generation and improving thermal management without compromising electrical connection stability.
2Reliability
If the external electrode plate is connected via electrically conductive bonding material, then electrical conductivity is achieved, but repeated localized heat generation causes deterioration of the bonding material and decline in holding force, leading to detachment
Solution Approach 1:
The extended electrode plate structure distributes thermal and mechanical stresses across a larger volume, reducing the stress concentration at any single point in the bonding material. This dimensional extension enhances the overall structural integrity and reduces the likelihood of bonding material deterioration from repeated thermal cycling.
3Reliability
If the external electrode plate is connected via electrically conductive bonding material, then electrical connection is established, but difference in thermal expansion between bonding material and electrode plate causes cracking that progresses to halt driving
Solution Approach 1:
The extended electrode plate creates a gradient structure where the bonded region is surrounded by additional electrode material in the stacking direction. This three-dimensional configuration provides a buffer zone that accommodates differential thermal expansion between the bonding material and electrode plate. The extended structure allows for thermal expansion in multiple directions, reducing stress concentration and preventing crack initiation and propagation that would otherwise halt device operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design minimizes detachment of the external electrode plate and suppresses crack formation in the bonding material, enabling stable operation over an extended period without changes in driving amount, and ensures stable high-pressure fuel injection.
Implementation Method 1
heat is generated at an end of an entrance side of the external electrode plate when rush current enters. Also, heat is generated in the electrically conductive bonding material
Implementation Method 2
a stacked body formed by laminating piezoelectric layers and internal electrode layers together
Implementation Method 3
a stacked body formed by laminating piezoelectric layers and internal electrode layers together
Data Source
Figure 1~2B
Figure 3A~3B
Figure 4A~4B
AI summary
[Object] To provide a multi-layer piezoelectric element that minimizes detachment of an external electrode plate and crack formation in an electrically conductive bonding material. Also, to provide an injection device and a fuel-injection system containing the multi-layer piezoelectric element. [Solution] A multi-layer piezoelectric element (1) comprising the following: a stacked body (4) including an active section (4a) including piezoelectric layers (2) and internal electrode layers (3) laminated together and an inactive section (4b) located outside the active section (4a) in the stacking direction; an electrically conductive bonding material (5) disposed on a side surface of the stacked body (4) parallel to the stacking direction; and an external electrode plate (6) connected to the side surface of the stacked body (4) with the electrically conductive bonding material (5) interposed therebetween. One end of the external electrode plate (6) extends past the electrically conductive bonding material (5) in the stacking direction, and the external electrode plate (6) includes, on said end, an area connected to an external circuit. The electrically conductive bonding material (5) includes a wider region (51) with a greater width than other regions, at one end thereof closer to the one end than to the other end, both of the external electrode plate (6).