Ceramic Glow Plug Sleeve Design for Shock Resistance
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Solution Overview
Problem
Conventional ceramic glow plugs face issues with shock resistance due to excessive contact pressure on the ceramic heater, which can lead to breakage under strong shocks from diesel engines.
Innovation Solution
The ceramic glow plug design features a sleeve with a small-diameter portion not press-fitted into the housing, reducing contact pressure on the ceramic heater and distributing stress more evenly, thereby enhancing shock resistance. Additionally, a gap between the sleeve and housing improves coaxiality and alignment, and a tapered portion further reduces stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the sleeve is press-fitted into the front end portion of the housing, then the ceramic heater is firmly held, but the contact pressure on the ceramic heater becomes excessively large, making it likely to break under shock
Solution Approach 1:
The sleeve is divided into two functional sections: a large-diameter portion that holds the ceramic heater with appropriate contact pressure, and a small-diameter portion that fits into the housing without transmitting excessive pressure. This segmentation allows the holding function and pressure isolation function to be separated, resolving the contradiction between firm holding and excessive contact pressure.
Solution Approach 2:
The small-diameter portion of the sleeve acts as an intermediary element between the housing and the large-diameter portion. It provides a transition zone that prevents direct transmission of high contact pressure from the housing to the ceramic heater, while still maintaining structural integrity and alignment.
2Strength
If the small-diameter portion is press-fitted into the housing, then the assembly is reinforced, but the stress from shock is superimposed on the contact pressure, causing the ceramic heater to break
Solution Approach 1:
By segmenting the sleeve into small-diameter and large-diameter portions, the patent creates a pressure isolation zone. The small-diameter portion provides mechanical reinforcement and alignment without transmitting harmful contact pressure to the ceramic heater during shock events, thus improving both assembly strength and shock resistance.
Solution Approach 2:
The small-diameter portion serves as a pre-designed cushioning element that absorbs and isolates shock stresses before they can be transmitted to the ceramic heater. This beforehand cushioning prevents the superposition of shock stress on contact pressure, protecting the ceramic heater from breakage.
3Strength
If the small-diameter portion has the same diameter as the housing bore, then press-fitting provides strong connection, but alignment and coaxiality are difficult to maintain
Solution Approach 1:
The sleeve features an asymmetric diameter profile with a small-diameter portion for housing insertion and a large-diameter portion for holding the ceramic heater. This asymmetric design allows the small-diameter portion to provide precise alignment and coaxiality during installation, while the large-diameter portion provides the necessary holding force, resolving the contradiction between connection strength and alignment precision.
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 configuration significantly improves the shock resistance of the ceramic heater, preventing breakage even under significant impacts and maintaining alignment and airtightness, as demonstrated by testing.
Implementation Method 1
the ceramic heater receives the pressure (contact pressure) which the sleeve exerts on the ceramic heater so as to hold the ceramic heater and also receives the contact pressure which the sleeve receives from the housing when the sleeve is press-fitted into the housing
Implementation Method 2
a part of the large-diameter portion and a part of the front end portion of the housing, which parts are in contact with each other, are externally welded and joined together for reinforcement
Implementation Method 3
a heater element formed of a conductive ceramic and embedded in the base
Data Source
Figure 1(a)~1(b)
Figure 2
AI summary
A ceramic glow plug includes a ceramic heater including a base formed of an insulating ceramic and a heater element formed of a conductive ceramic and embedded in the base, the ceramic heater extending in an axial direction; a tubular sleeve which holds, on the inner circumference thereof, the outer circumference of the ceramic heater with a front end portion of the ceramic heater protruding from the front end of the sleeve; and a tubular housing which surrounds a rear end portion of the ceramic heater and has a mounting portion for mounting the housing to a mounting hole of an internal combustion engine. The sleeve has a small-diameter portion which is accommodated in a front end portion of the housing and has an outer diameter smaller than the inner diameter of the front end portion of the housing, and a large-diameter portion which is connected to the small-diameter portion, disposed frontward of the front end portion of the housing, and has a diameter larger than the inner diameter of the front end portion of the housing. The front end portion of the housing is welded to the large-diameter portion.