Power Conversion Device Thermal Stress Buffering
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Solution Overview
Problem
The difference in thermal shrinkage between the metal housing and the smoothing capacitor in power conversion devices leads to stress concentration, potentially causing fatigue fractures and screw loosening, especially when the device is exposed to rapid cooling.
Innovation Solution
The power conversion device incorporates a support case with boss portions on a heat sink and leg portions on the smoothing capacitor, where the materials and dimensions of these components are matched to ensure a total thermal expansion/contraction ratio within 0.9 to 1.1 of the support case and bus bar, preventing direct contact between the capacitor and housing and reducing stress on the leg portions and screws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the smoothing capacitor is fixed directly to the metal housing, then the device structure is simple and easy to manufacture, but stress concentration occurs due to thermal shrinkage difference causing fatigue fractures and screw loosening
Solution Approach 1:
The patent introduces a resin layer as an intermediary substance between the metal housing and the smoothing capacitor. This resin layer acts as a buffer that absorbs thermal stress and prevents direct contact between the capacitor and housing, thereby eliminating stress concentration and fatigue fractures while maintaining ease of assembly through simple coating or injection processes.
Solution Approach 2:
The patent employs a composite structure combining metal housing, resin material, and capacitor components. The resin layer with different thermal expansion properties than the metal housing creates a composite assembly that accommodates thermal shrinkage differences, preventing stress concentration and improving reliability without complicating manufacturing.
2Device complexity
If the smoothing capacitor is fixed directly to the metal housing, then the device structure is simple, but screw loosening occurs due to thermal shrinkage difference
Solution Approach 1:
The resin layer serves as a mediator between the screw, metal housing, and capacitor. It distributes the clamping force uniformly and prevents direct stress transmission to the screw, thereby preventing screw loosening while maintaining a simple mounting structure that still provides reliable fixation.
Solution Approach 2:
The patent changes the physical parameters of the mounting interface by introducing a resin layer with specific viscoelastic properties. This resin layer can deform under thermal stress, maintaining constant contact pressure and preventing screw loosening without requiring complex anti-loosening mechanisms.
3Temperature
If the smoothing capacitor is exposed to rapid cooling, then the device can operate in high-temperature environments, but thermal shrinkage difference increases causing stress concentration
Solution Approach 1:
The resin layer acts as a thermal stress buffer that decouples the thermal response between the metal housing and capacitor. During rapid cooling, the resin layer absorbs the differential thermal shrinkage through its viscoelastic deformation, preventing stress concentration while allowing the device to operate across wide temperature ranges.
Solution Approach 2:
The patent utilizes the temperature-dependent viscoelastic parameters of the resin material to dynamically accommodate thermal stress. The resin's ability to change its mechanical properties with temperature allows it to remain flexible during thermal cycling, preventing stress concentration even during rapid cooling from high-temperature 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
This configuration prevents fatigue fractures and screw loosening, maintains vibration resistance, and reduces operational noise by isolating the smoothing capacitor from direct cooling and thermal expansion differences, while allowing for weight and cost reduction in the housing design.
Implementation Method 1
a resin layer is interposed between the housing and the smoothing capacitor
Implementation Method 2
a water-cooled heat sink, a control circuit board, a step-up converter, and other such components. The water-cooled heat sink is adapted to cool a heat generating element, for example, a switching element
Data Source
AI summary
Provided is a power conversion device including: power semiconductor elements, a support case, a heat sink, in which a plurality of boss portions are formed; a smoothing capacitor including a case member having a plurality of leg portions; and a bus bar configured to connect the smoothing capacitor and the DC input terminal, wherein, in the power conversion device in which the plurality of leg portions of the case member being respectively fixed to the plurality of boss portions of the heat sink, wherein materials and dimensions of the respective boss portions, the respective leg portions, the support case, and the bus bar are determined so that a total thermal expansion/contraction amount of the respective boss portions and the respective leg portions falls within a range of 0.9 to 1.1 relative to a total thermal expansion/contraction amount of the support case and the bus bar.