Brazed Plated-Steel Cooling Structure for Leak-Tight Battery Units
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Solution Overview
Problem
Current cooling structures for electric vehicle battery packs face challenges in achieving high cooling efficiency, liquid tightness, and corrosion resistance, particularly with plated steel sheets, as existing methods like spot welding damage the plating and compromise corrosion resistance and liquid tightness.
Innovation Solution
A cooling structure using press-formed plated steel sheets with Al-based or Zn-based plating, where the sheets are brazed together with a joining metal to form a flow path, ensuring a partial flow path interval of 20 mm or less and a joining width of 3 mm or more, and incorporating additional joints like spot welding, projection welding, or laser welding to minimize plating damage and enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If spot welding is used to join plated steel sheets, then joining strength is improved, but plating damage occurs and corrosion resistance deteriorates
Solution Approach 1:
The joining process is segmented into two distinct stages: first, ultrasonic welding creates initial joint strength; second, brazing fills plating-damaged areas and provides final corrosion resistance. This segmentation allows each process to optimize for its specific function without compromising the other.
Solution Approach 2:
The solution employs composite joining metal comprising both welding metal and brazing metal. The welding metal provides initial bond strength while the brazing metal fills gaps and protects plating surfaces, creating a composite structure that delivers both joining strength and corrosion resistance simultaneously.
2Reliability
If brazing is used to join plated steel sheets, then liquid tightness is improved, but manufacturing complexity increases
Solution Approach 1:
Ultrasonic welding is performed as a preliminary action before brazing to create initial joint strength and positioning. This preliminary joining facilitates subsequent brazing operations by ensuring proper alignment and contact between parts, thereby simplifying the overall manufacturing process despite the two-stage approach.
Solution Approach 2:
The welding metal serves as an intermediary that facilitates the brazing process. By creating initial contact and joint strength through ultrasonic welding, the brazing metal can more effectively fill gaps and create liquid-tight seals, reducing the complexity of achieving both properties simultaneously.
3Reliability
If aluminum material is used for outer wall and cooling structure, then corrosion resistance to cooling liquid is improved, but cost increases and weight reduction becomes difficult
Solution Approach 1:
The solution uses composite materials combining steel base material with aluminum-based or zinc-based plating layers. The steel provides structural strength and weight efficiency, while the plating layer delivers corrosion resistance to cooling liquid, achieving both requirements without using pure aluminum which would be heavier and more expensive.
Solution Approach 2:
Corrosion resistance is applied locally through plating only on the surfaces requiring cooling liquid contact, rather than using aluminum throughout the entire structure. This local quality approach allows the bulk structure to remain steel for weight efficiency while specific surfaces gain the necessary corrosion protection.
4Reliability
If plating thickness is increased to improve corrosion resistance, then cooling liquid corrosion resistance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The corrosion protection function is segmented between the plating layer (providing base corrosion resistance) and the brazing metal (filling plating-damaged areas). This segmentation reduces the burden on plating uniformity, as the brazing process compensates for local plating deficiencies, allowing for more practical manufacturing precision tolerances.
Solution Approach 2:
The brazing process serves as beforehand cushioning against plating damage. By applying brazing metal that fills gaps and protects vulnerable areas, the system pre-compensates for potential plating deficiencies, reducing the need for extremely high plating uniformity while maintaining adequate corrosion resistance.
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 provides a cooling structure with high cooling efficiency, excellent liquid tightness, and enhanced corrosion resistance, preventing plating damage and exposure of the base steel sheet, thus extending the structure's lifespan and maintaining thermal conductivity.
Implementation Method 1
the joint portion is made of a joining metal which brazes the base steel sheets of the press forming member and the flow path upper lid to each other
Data Source
AI summary
A cooling structure according to an aspect of the present invention includes a press forming member including a groove part and a bank part provided around the groove part, a flow path upper lid positioned on a position covering the groove part of the press forming member, and a joint portion which joins opposing surfaces of the flow path upper lid and the bank part to form a flow path through which a cooling liquid is capable of flowing, in which the press forming member and the flow path upper lid are plated steel sheets having a base steel sheet and having an Al-based plating having a film thickness of 10.0 μm or more or a Zn-based plating having a film thickness of 5.0 μm or more, in which a sheet thickness of the plated steel sheets 0.3 mm to 1.2 mm, the joint portion is formed of a joining metal brazing the base steel sheets of the press forming member and the flow path upper lid, and a partial flow path interval is 20 mm or less and a joining width is 3 mm or more.