Glow Plug Heat Generating Coil Local Quality Design
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Solution Overview
Problem
Existing glow plugs face a trade-off between durability and quick-temperature-increasing ability due to thermal expansion stresses on the heat generating coil, where increasing coil diameter to reduce breakage leads to increased tube volume and decreased heat capacity.
Innovation Solution
A glow plug design with a heat generating coil having a smaller wire diameter in the embedded portion compared to the coil inside the tube, along with a fused portion to prevent oxidation, and a convex portion to increase resistance and heat generation, maintains durability while reducing tube volume and enhancing quick-temperature-increasing ability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wire diameter of the heat generating coil is increased to reduce breakage against thermal expansion stress, then the durability of the heat generating coil is improved, but the volume of the front end portion of the tube increases and the quick-temperature-increasing ability decreases
Solution Approach 1:
The heat generating coil is designed with different wire diameters in different regions: a first wire diameter in the embedded portion and a second wire diameter in the internal portion. This local differentiation allows the embedded portion to have sufficient strength against thermal expansion stress while keeping the overall volume small, thus resolving the contradiction between durability and quick-temperature-increasing ability
Solution Approach 2:
The heat generating coil is segmented into multiple portions with different characteristics: an embedded portion with larger wire diameter for strength, an internal portion with smaller wire diameter for compactness, and potentially a protruding portion. This segmentation allows each region to be optimized for its specific function, balancing durability and heat capacity
2Reliability
If the wire diameter of the heat generating coil is increased to reduce breakage against thermal expansion stress, then the durability of the heat generating coil is improved, but the heat capacity of the tube increases and the quick-temperature-increasing ability decreases
Solution Approach 1:
By applying local quality differentiation to the coil wire diameter, the design achieves sufficient local strength in the embedded portion without uniformly increasing the overall material quantity. This maintains low heat capacity while ensuring durability where thermal expansion stress is most critical
3Reliability
If a fused portion is formed to prevent oxidation of the embedded portion, then the durability is improved, but the manufacturing complexity increases
Solution Approach 1:
The fused portion merges the embedded portion of the heat generating coil with the front end portion of the tube, creating a unified structure that prevents oxidation. This combining approach protects the coil while integrating the protection function into the existing structure, minimizing additional manufacturing complexity
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 design improves the durability of the heat generating coil, reduces breakage, and maintains quick-temperature-increasing ability by optimizing wire diameters and resistances within the coil and tube structure.
Implementation Method 1
a heat generating coil that is disposed inside the tube and mainly composed of tungsten
Implementation Method 2
a stress is applied to the heat generating coil due to thermal expansion of the heat generating coil and the tube
Data Source
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AI summary
[Object] To provide a glow plug that can improve the durability of a heat generating coil while maintaining quick-temperature-increasing ability. [Solving Means] A glow plug includes a metal tube that extends along an axial line, and a heat generating coil (50) that is disposed inside the tube and mainly composed of tungsten, an embedded portion in a front end portion (41) of the heat generating coil being embedded in a front end portion of the tube. The heat generating coil includes a helical portion that includes at least a part of the embedded portion and that is continuously formed from the embedded portion to an inside of the tube. In the heat generating coil that is present in a longitudinal section of the glow plug including the axial line, a first average value, which is calculated by dividing a first sum that is a sum of areas of cross sections of the helical portion in the embedded portion by the number of the cross sections of the helical portion in the embedded portion, is smaller than a second average value, which is calculated by dividing a second sum that is a sum of areas of cross sections of the helical portion inside the tube by the number of the cross sections of the helical portion inside the tube.