Glow Plug Insulating Powder Particle Size Gradient
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Solution Overview
Problem
Conventional glow plugs experience a deterioration in rapid temperature rising characteristic due to increased pulverization of insulating powder, leading to fewer contact points for heat conduction, which hampers the startability of internal combustion engines.
Innovation Solution
The glow plug design features a specific particle size distribution for insulating powder, where the median diameter in the maximally heat-generating region is larger than in other regions, optimizing the number of contact points for improved thermal conductivity, thereby enhancing the rapid temperature rising characteristic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the filling density of insulating powder is increased by reducing the tube diameter through drawing, then the filling density is improved, but the insulating powder is pulverized into finer particles, increasing the number of contact points, which reduces thermal conductivity from the coil to the tube
Solution Approach 1:
The patent applies local quality by creating different particle size distributions in different regions of the tube. The front region (first region) contains coarser insulating powder particles with a median diameter of 10 μm or more, while the rear region (second region) contains finer particles. This spatial differentiation of particle sizes allows the front region to maintain fewer contact points and higher thermal conductivity for rapid temperature rise, while the rear region provides adequate heat distribution.
2Quantity of substance
If the number of contact points between particles is increased through pulverization, then the filling density is improved, but heat transmission from the coil to the tube is reduced
Solution Approach 1:
The patent implements local quality by establishing distinct particle size characteristics in different axial regions. The first region surrounding the front coil contains particles with median diameter ≥10 μm, creating fewer contact points and better thermal conductivity for rapid heating. The second region contains finer particles that provide sufficient contact points for heat distribution, thus resolving the contradiction between filling density and rapid temperature rise capability.
3Temperature
If heat is transferred to the rear side of the tube, then the overall heat distribution is improved, but the rapid temperature rise at the maximally heat-generating portion is suppressed
Solution Approach 1:
The patent applies local quality by creating a gradient in particle size distribution along the axial direction. The front region has coarser particles (median diameter ≥10 μm) that facilitate rapid heat transfer to achieve quick temperature rise at the maximally heat-generating portion. The rear region has finer particles that enable heat to be transferred to the rear side of the tube, achieving uniform heat distribution without compromising the rapid temperature rise at the front.
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 design improves thermal conductivity to the maximally heat-generating portion while suppressing heat transfer to other regions, resulting in a more efficient rapid temperature rising characteristic.
Implementation Method 1
heat is conducted from a coil through the particles to the tube
Data Source
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AI summary
[Objective] To provide a glow plug (10) enabling improvement in rapid temperature rising characteristic. [Means for Solution] The glow plug includes: a tube which has a small-diameter portion (42) and a large-diameter portion (44) having an outer diameter larger than the outer diameter of the small-diameter portion; a coil disposed at least in the small-diameter portion; and insulating powder (60) sealed in the small-diameter portion and the large-diameter portion, wherein a relationship is established where a median diameter of particle diameters of the insulating powder disposed in the small-diameter portion and disposed within a first region (46) is larger than a median diameter of particle diameters of the insulating powder disposed in the large-diameter portion and disposed within a second region (47), the first region being a part in the direction of the axial line of the small-diameter portion and including a maximally heat-generating portion at which the temperature of the surface of the small-diameter portion reaches the maximum temperature, the second region being a part in the direction of the axial line of the large-diameter portion.