Multilayer Piezo Element Thick-Walled Metal Cover Layer
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Solution Overview
Problem
Multi-layer piezoelectric elements experience separation of the external electrode plate due to inrush current, leading to heat generation and quality degradation of the electrically-conductive joining member, causing instability and potential sparking, which affects the long-term reliability of piezoelectric actuators, injection devices, and fuel injection systems.
Innovation Solution
A multi-layer piezoelectric element design featuring a metal cover layer with a thick-walled portion at the ends and a thin-walled portion in the middle, made of materials with lower resistance, reduces heat generation and thermal expansion differences, preventing separation and sparking by distributing heat more evenly and reducing stress on the electrically-conductive joining member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform thickness metal cover layer is disposed on the external electrode plate, then the manufacturing process is simple, but heat generation during inrush current causes separation of the external electrode plate and sparking between the electrically-conductive joining member and the external electrode plate
Solution Approach 1:
The metal cover layer is designed with non-uniform thickness: a first thickness in a first area and a second thickness greater than the first thickness in a second area. This local variation in thickness allows the thicker region to dissipate heat more effectively during inrush current, preventing the quality degradation and separation issues that occur with uniform thickness designs, while still maintaining manufacturing feasibility through controlled deposition processes.
2Reliability
If the metal cover layer has uniform thickness, then the electrical conductivity is consistent, but local heat generation degrades the electrically-conductive joining member and causes separation
Solution Approach 1:
By varying the thickness of the metal cover layer locally across different areas, the design optimizes heat dissipation in regions prone to high heat generation during inrush current. The thicker second area specifically addresses thermal management needs without compromising the overall electrical conductivity consistency of the external electrode plate.
Solution Approach 2:
The invention changes the thickness parameter of the metal cover layer from a uniform value to a spatially varying profile. This parameter modification allows the structure to better manage thermal loads during operation, reducing local heat generation effects that would otherwise degrade the electrically-conductive joining member.
3Productivity
If inrush current is repeatedly applied to the external electrode plate, then the piezoelectric element can be driven, but the repeated local heat generation causes quality degradation of the electrically-conductive joining member and separation
Solution Approach 1:
The non-uniform metal cover layer thickness provides enhanced thermal management specifically in the second area where heat generation is most critical during repeated drive operations. This allows the piezoelectric element to maintain operational capability while significantly improving long-term stability by preventing the cumulative heat damage that leads to joining member degradation and separation.
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 effectively suppresses separation and sparking, enabling stable operation of multi-layer piezoelectric elements, actuators, and fuel injection systems for extended periods without fluctuations in drive performance.
Implementation Method 1
the end of the external electrode plate liberates heat, and the electrically-conductive joining member liberates heat correspondingly
Implementation Method 2
reduces heat generation and thermal expansion differences
Implementation Method 3
A multi-layer piezoelectric element includes: a stacked body composed of piezoelectric layers and internal electrode layers which are laminated
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3~4
AI summary
There are provided a multi-layer piezoelectric element which is capable of suppressing separation of an external electrode plate, as well as a piezoelectric actuator, an injection device, and a fuel injection system that are provided with the multi-layer piezoelectric element. A multi-layer piezoelectric element (1) of the invention includes a stacked body (4) composed of piezoelectric layers (2) and internal electrode layers (3) which are laminated; an external electrode plate (6) attached to a side face of the stacked body (4) via an electrically-conductive joining member (5); and a metal cover layer (7) being disposed on a surface of the external electrode plate (6), an area of the metal cover layer (7) corresponding to one end portion (4a) of the stacked body (4) in a stacking direction of the stacked body having a thick-walled portion (71) which is larger in thickness than an area of the metal cover layer corresponding to a midportion (4b) of the stacked body (4).