Cylindrical Battery Pack Case Welding for Thin Impact-Resistant Walls
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Solution Overview
Problem
Battery packs containing cylindrical batteries face challenges in achieving sufficient strength while maintaining a compact and lightweight design, as existing structures are prone to damage from impacts and require increased thickness to ensure strength, which contradicts the need for miniaturization and increased capacity.
Innovation Solution
The battery pack design incorporates an exterior case composed of first and second cases made of thermoplastic resin, with a curved portion and integral vertical walls that include a fitting protrusion and groove for ultrasonic welding, allowing the case to be reduced in thickness while maintaining strength by guiding the protrusion into the groove and securely welding the cases together.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the exterior case is increased to achieve sufficient strength, then the strength is improved, but the size of the battery pack increases
Solution Approach 1:
The exterior case is divided into first case and second case that are separately molded and then connected together. The first case includes a first vertical wall with a fitting protrusion, and the second case includes a second vertical wall with a fitting groove. This segmentation allows each case to be thinner while the connection structure provides the necessary strength.
Solution Approach 2:
The connection between the first and second cases is achieved not by increasing thickness in one dimension, but by creating a three-dimensional connection structure with fitting protrusions and grooves that interlock. The vertical walls extend in the vertical dimension, and the fitting structures create connection in the horizontal dimension, distributing the strength requirement across multiple dimensions rather than concentrating it in case thickness.
2Reliability
If the thickness of the exterior case is increased to prevent damage from impacts, then the reliability is improved, but the weight increases
Solution Approach 1:
By dividing the exterior case into separate first and second cases that are connected through fitting protrusions and grooves, the structure can absorb impact forces through the connection interface rather than requiring uniformly thick walls throughout. The segmented structure provides impact resistance through the interlocking connection rather than through material thickness alone.
Solution Approach 2:
The exterior case is formed by connecting two separate case components (first case and second case) made of the same or different materials. This composite structure achieves enhanced reliability and impact resistance through the combination of multiple parts with fitting structures, rather than requiring a single thick-walled structure.
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
This configuration achieves sufficient strength without increasing the battery pack's size, enabling a compact and lightweight design that can accommodate increased capacity while preventing damage from impacts.
Implementation Method 1
first vertical wall 11 has fitting protrusion 15 protruding from opposed surface 11a facing second vertical wall 21. Second vertical wall 21 has fitting groove 25 that is formed in opposed surface 21a facing first vertical wall 11 and that guides fitting protrusion 15. Fitting protrusion 15 is guided into fitting groove 25
Implementation Method 2
first vertical wall 11 and second vertical wall 21 are welded together
Implementation Method 3
first case 10 has curved portion 12 that curves along an outer peripheral surface of cylindrical battery 1
Data Source
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AI summary
The battery pack includes cylindrical battery (1), a circuit board, and an exterior case including first case (10) and second case (20). First case (10) has a curved portion along an outer peripheral surface of cylindrical battery (1) and first vertical wall (11) connected to an end edge of the curved portion. Second case (20) has second vertical wall (21) connected to first vertical wall (11). First vertical wall (11) has fitting protrusion (15) protruding from opposed surface (11a) facing second vertical wall (21). Second vertical wall (21) has fitting groove (25) that is formed in opposed surface (21a) facing first vertical wall (11) and that guides fitting protrusion (15). Fitting protrusion (15) is guided into fitting groove (25), and first vertical wall (11) and second vertical wall (21) are welded together. First vertical wall (11) has inner surface (11c) in a concave shape along a surface of cylindrical battery (1), and a leading end portion with opposed surface (11a), being thicker than curved portion (12).