Glow Plug Center Rod Runout Correction
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Solution Overview
Problem
Conventional glow plugs for diesel engines face issues with ceramic heater cracking due to high bending stress caused by large circular runout in center rod members, particularly when formed from coiled materials, leading to reduced reliability.
Innovation Solution
Incorporating runout correction portions on the center rod member, such as diameter reduced or knurled sections, to improve coaxiality and reduce bending stress on the ceramic heater, thereby enhancing the reliability and reducing the likelihood of cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the center rod member is formed from a wire rod obtained by cutting a coiled material, then the manufacturing process is simplified, but the circular runout of the center rod member becomes large, causing high bending stress on the ceramic heater
Solution Approach 1:
The invention applies preliminary action by forming runout correction portions on the center rod member before final assembly. These correction portions are created through plastic deformation processes that pre-correct the circular runout of the trunk portion, ensuring that when the glow plug is assembled, the center rod member has sufficiently small runout to prevent ceramic heater cracking while maintaining the simplified wire rod manufacturing approach
2Ease of manufacture
If the trunk portion of the center rod member has a fixed diameter over the entire length, then cutting operation is unnecessary, but the rigidity is too high, preventing the trunk portion from bending to absorb stress
Solution Approach 1:
The invention applies local quality by creating runout correction portions with locally modified properties on the trunk portion of the center rod member. These portions have different cross-sectional shapes or diameters compared to the rest of the trunk, creating localized areas with different rigidity characteristics. This allows the trunk portion to bend locally at these correction portions to absorb stress from circular runout, while maintaining overall structural integrity and eliminating the need for cutting operations
Data Source
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AI summary
[Objective] To provide a glow plug whose ceramic heater is unlikely to crack and which is high in reliability and to provide a method of manufacturing such a glow plug. [Means for Solution] A glow plug 1 includes a metallic shell 10, a ceramic heater 20 held on the forward end side GS of the metallic shell 10, a center rod member 40 formed of a metal, inserted into the metallic shell 10, and extending in an axial direction HJ; and a connection member 50 connecting a heater rear end portion 25 and a center rod forward end portion 41. A center rod trunk portion 43 of the center rod member 40 located between the center rod forward end portion 41 and a center rod rear end portion 45 has a plurality of runout correction portions 43f having corrected the circular runout of a trunk forward end portion 43s in relation to a trunk rear end portion 43k serving as a reference. The runout correction portions 43f are spaced from one another in the axial direction HJ.