Glowplug Lead Terminal Bonding via Conductive Agent
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Solution Overview
Problem
Ceramic heaters used in combustion vehicle heating systems and glow plugs face reliability issues due to thermal expansion of metal caps caused by inrush currents, leading to potential disconnection of lead terminals from the metal cap.
Innovation Solution
A heater design featuring a silicon nitride ceramic body with a molybdenum or tungsten heating resistor, a metal cap with a through hole and a lead terminal bonded within a gap to reduce thermal stress, and a conductive bonding agent to enhance bonding and absorb external forces, ensuring strong connections and reduced risk of terminal disconnection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lead terminal is bonded to a metal cap in a conventional ceramic heater, then electrical connection is achieved, but the lead terminal may be pulled out due to thermal expansion of the metal cap during heat cycles
Solution Approach 1:
The patent introduces a conductive bonding agent as an intermediary substance between the lead terminal and the metal cap. This bonding agent serves dual functions: it provides electrical conductivity to maintain circuit continuity while also creating a stronger mechanical bond that resists thermal expansion forces during heat cycles, preventing lead terminal pull-out
Solution Approach 2:
The patent changes the bonding parameters by transitioning from direct metal-to-metal bonding to bonding through a conductive bonding agent. This parameter change allows the system to accommodate thermal expansion differences between the lead terminal and metal cap, maintaining both electrical connectivity and mechanical strength under thermal stress
2Power
If electricity is supplied through the lead terminal, then heating function is activated, but inrush current heats the lead terminal to high temperature
Solution Approach 1:
The conductive bonding agent acts as a thermal intermediary with higher heat capacity and thermal conductivity than the metal cap alone. It absorbs and distributes the thermal energy from inrush current more effectively, preventing excessive temperature concentration at the lead terminal-metal cap interface
3Temperature
If the metal cap is heated by transmitted heat, then thermal expansion occurs, but this causes lead terminal disconnection
Solution Approach 1:
The patent changes the thermal and mechanical parameters of the bonding interface by introducing a conductive bonding agent. This agent has thermal expansion properties that are intermediate between the metal cap and lead terminal, creating a gradient that reduces thermal stress concentration and maintains connection reliability under temperature variations
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 long-term reliability of ceramic heaters by minimizing thermal stress and enhancing durability, preventing lead terminal disconnection and maintaining performance across heat cycles.
Implementation Method 1
when electricity is supplied to the heating resistor through the lead terminal
Implementation Method 2
the lead terminal will be pulled out of the metal cap due to thermal expansion of the metal cap
Data Source
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AI summary
A heater includes a ceramic body having a rod shape; a heating resistor embedded in the ceramic body; a conductor layer on at least one end surface of the ceramic body, electrically connected to the heating resistor; a metal cap attached to an end portion of the ceramic body at a site near the end surface, the metal cap covering at least a portion of the conductor layer and the end surface with a gap therebetween and including a through hole; and a lead terminal inserted in the through hole and electrically connected to the conductor layer. An end portion of the lead terminal disposed in the gap includes a portion that is outside the through hole when viewed in a penetrating direction of the through hole.