Heating Element Density Gradient for Exhaust Hot Spot Reduction
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Solution Overview
Problem
Existing heating devices for exhaust gas purification members experience reduced service life due to high electrical current density and significant temperature gradients, particularly at U-shaped cusps, leading to hot spots and uneven heating.
Innovation Solution
A heating device with a central area made of a first electrically conductive material and a peripheral edge made of a second material with higher relative density, forming an S-shaped path through the heating element, which reduces current density at elbows and minimizes hot spots by increasing the cross-sectional area of the material at these points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If slots are cut to create sinuous path for electric current, then heating element can heat exhaust gas purification member, but electrical current density becomes particularly high at U-shaped cusps causing hot spots and reduced service life
Solution Approach 1:
The patent applies local quality by making the peripheral edge material (second material) have different properties than the central area material (first material). Specifically, the second material has higher electrical conductivity and/or higher melting point, making it better suited to withstand the high current density and temperatures at the elbows and U-shaped cusps where hot spots occur.
Solution Approach 2:
The heating element is constructed as a composite structure with two different materials: a central area made of first material and a peripheral edge made of second material. This composite construction allows each material to be optimized for its specific function - the central area for overall heating and the peripheral edge for withstanding high stress and temperature at the slots and elbows.
2Reliability
If material at elbows is made with higher relative density to reduce current density, then hot spots are reduced, but manufacturing complexity increases
Solution Approach 1:
The heating element is segmented into two distinct regions: a central area and a peripheral edge, each made of different materials. This segmentation allows the peripheral edge to be specifically designed with higher relative density and better thermal properties to handle the concentrated current and heat at the elbows, while the central area maintains optimal properties for overall heating efficiency.
Solution Approach 2:
The patent changes the physical parameters of the material at the peripheral edge compared to the central area. The second material has higher relative density, higher electrical conductivity, and higher melting point, which are parameter changes that enable it to withstand the more severe operating conditions at the elbows and slot regions.
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 results in a more uniform current density distribution and reduced temperature gradients, extending the service life of the heating element by reducing the surface area of high-temperature hot spots and minimizing material degradation.
Implementation Method 1
heating device having a plate-like element made of an electrically conductive material... Two electrodes are connected to the peripheral edge of the element... Slots substantially parallel to each other are cut in the plate, so as to create a sinuous path for the electric current flowing from one electrode to the other
Data Source
AI summary
A heating device comprises a heating element having a central area and a peripheral edge. The heating element has a series of slots delimiting a series of longitudinal branches connected to one another by elbows. The central area is made of a first electrically conductive material that is permeable to exhaust gases and has a first relative density. The elbows are located in the peripheral edge and are made of a second electrically conductive material and that has a second relative density greater than the first relative density.