Glow Plug Heater Lead Tapering for Impedance Matching
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Solution Overview
Problem
The existing heaters for glow plugs in automobile engines suffer from microcrack generation and resistance value changes due to impedance mismatching at the seam portion between the lead and resistor, especially when high-frequency components are transmitted or large electric currents flow during rapid temperature elevation.
Innovation Solution
A heater design where the lead is joined to surround the resistor with a narrowed profile towards the heat-generating portion, and an insulating base body covers both, ensuring impedance matching by spacing the resistor from the base body through the lead, thus preventing microcrack formation and maintaining resistance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the lead and resistor are joined with a seam portion formed by laminating surfaces with different impedances, then the joining area is increased to prevent thermal expansion influence, but the high frequency component is reflected at the seam portion causing local heating and microcrack generation
Solution Approach 1:
The patent changes the geometric parameters of the lead by forming a tapered portion that gradually narrows toward the distal end. This gradual change in cross-sectional area modifies the impedance distribution along the lead, enabling smooth impedance transition at the joining portion and preventing high frequency reflection that causes local heating and microcracks
Solution Approach 2:
The patent transitions from a conventional flat laminated interface to a three-dimensional tapered structure. The lead is designed with a longitudinal gradient in cross-sectional area, creating a volumetric impedance transition zone rather than a sharp two-dimensional interface, which eliminates abrupt impedance mismatch
2Productivity
If a large electric current flows into the resistor for rapid temperature elevation, then the heating efficiency is improved, but the seam portion experiences high power inrush containing high frequency components causing microcrack generation
Solution Approach 1:
The patent incorporates a tapered portion in the lead that acts as a protective structure before the high current reaches the joining portion. The gradual narrowing of the lead cross-section beforehand creates a smooth impedance transition zone that cushions the high frequency components of the power inrush current, preventing microcrack generation at the seam portion while allowing rapid heating
3Reliability
If the lead profile is narrowed toward the distal end, then impedance matching is achieved at the joining portion, but the joining area is reduced
Solution Approach 1:
The patent resolves this contradiction by moving from a two-dimensional joining area optimization to a three-dimensional volumetric design. The tapered portion extends along the longitudinal axis, creating a gradual impedance transition through volume rather than relying solely on interface area, thus achieving both impedance matching and adequate mechanical bonding
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 secures impedance matching at the seam portion, preventing microcrack generation and ensuring stable resistance over time, enhancing the reliability and durability of the heater regardless of driving methods, whether pulse or DC.
Implementation Method 1
a lead (8) joined to an end portion of the resistor (3) to surround the end portion of the resistor (3)... the lead (8) being made to have a portion whose profile is narrowed toward a distal end on a heat-generating portion side of the lead (8)
Implementation Method 2
secures impedance matching at the seam portion... preventing microcrack generation and ensuring stable resistance
Implementation Method 3
a resistor (3) including a heat-generating portion (4)... a ceramic heater for ignition or the like
Implementation Method 4
an insulating base body (9) covering the resistor (3) and the lead (8)... embedded in the insulating base body (9)
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
There are provided a heater in which generation of microcracks or the like in a joining portion of a resistor and a lead can be suppressed even when a large electric current flows into the resistor at the time of rapid temperature elevation and the like and a glow plug provided with the heater. A heater (1) of the invention includes: a resistor (3) having a heat-generating portion (4); a lead (8) joined to an end portion of the resistor (3); and an insulating base body (9) covering the resistor (3) and the lead (8), the lead (8) being made to have a portion whose profile is narrowed toward a distal end on a heat-generating portion side of the lead (8), a joining portion of the resistor (3) and the lead (8) being a region where the resistor (3) is spaced apart from the insulating base body (9) through the lead (8) as viewed in cross section perpendicular to an axial direction of the lead (8).