Piezoelectric Element Resin Buffer Suppresses Bonding Cracks
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Solution Overview
Problem
Multi-layer piezoelectric elements face cracking issues in the electrically conductive bonding material, leading to detachment of external electrode plates and impaired electrical conduction, which affects the durability and long-term stability of the elements, especially in applications like injection devices and fuel-injection systems.
Innovation Solution
Incorporating a resin layer between the stacked body and external electrode plates, with a gap and specific dimensions to reduce stress on the conductive bonding material, and using a separate resin layer with different thermal expansion coefficients to mitigate cracking and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrically conductive bonding material is used to mount external electrode plates on the stacked body, then electrical conduction is achieved, but cracking occurs in the bonding material leading to detachment and reduced durability
Solution Approach 1:
An insulating resin layer is introduced as an intermediary between the stacked body and the external electrode plate. This resin layer acts as a stress-absorbing buffer that prevents direct stress transmission to the electrically conductive bonding material, thereby suppressing crack formation and improving the durability of the electrical connection.
Solution Approach 2:
The insulating resin layer is positioned beforehand between the stacked body and external electrode plate to provide cushioning against thermal expansion stresses and mechanical shocks before they can reach the bonding material. This pre-cushioning effect prevents crack initiation in the bonding material under operating conditions.
2Reliability
If external electrode plates are mounted directly on the stacked body, then electrical connection is established, but thermal expansion stress causes bonding material failure over time
Solution Approach 1:
The insulating resin layer serves as a stress-isolating intermediary that has different thermal expansion properties from both the stacked body and the external electrode plate. This intermediary layer absorbs and distributes thermal expansion stresses, preventing concentrated stress on the electrically conductive bonding material during temperature cycles.
3Reliability
If the bonding material covers the entire side surface from active to inactive sections, then electrical conduction is ensured, but stress concentration increases leading to cracking
Solution Approach 1:
The electrically conductive bonding material is applied selectively only to the active section of the side surface where electrical conduction is required, rather than covering the entire side surface including inactive sections. This localized application reduces the total area subjected to stress, minimizing crack propagation risk while maintaining necessary electrical connectivity.
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 solution effectively suppresses cracking in the conductive bonding material, ensuring improved durability and stable operation of multi-layer piezoelectric elements over extended periods, even under continuous driving conditions.
Implementation Method 1
a stacked body 10 in which piezoelectric layers 11 and internal electrode layers 12 are laminated
Data Source
Figure 1A~2
Figure 3~5
Figure 6~7
AI summary
[Object] To provide a multi-layer piezoelectric element for which cracks in an electrically conductive bonding material are suppressed and durability is improved, and an injection device and fuel-injection system provided with the piezoelectric element. [Solution] This multi-layer piezoelectric element (1) includes the following: a stacked body (10) including piezoelectric layers (11) and internal electrode layers (12) laminated together; an external electrode plate (2) connected to the side surface of the stacked body (10) and electrically connected to the internal electrode layers (12); and an electrically conductive bonding material (3) disposed between the side surface of the stacked body (10) and one main surface of the external electrode plate (2). A resin layer (4) is disposed on at least one end of a space between the side surface of the stacked body (10) and the one main surface of the external electrode plate (2) in the width direction in a cross-sectional view perpendicular to the side surface of the stacked body (10).