A/F Sensor Element With Bottomed Cylindrical Substrate
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Solution Overview
Problem
Conventional A/F sensor elements with a plate-like shape are prone to thermal shock damage and slow activation due to low thermal conductivity materials like zirconia, and the use of partially stabilized zirconia increases manufacturing costs.
Innovation Solution
An A/F sensor element with a bottomed cylindrical shape featuring a substrate made of insulating ceramic with higher thermal conductivity, where the solid electrolyte is embedded in the side wall, reducing the amount of expensive rare earth materials needed and allowing quicker heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire A/F sensor element is formed by zirconia, then the element can be manufactured with good electrical properties, but the thermal conductivity is low causing slow heating and long activation time
Solution Approach 1:
The sensor element uses a composite structure combining zirconia (for electrical properties) with a material having higher thermal conductivity (for rapid heating). The substrate is made of zirconia to maintain electrical functionality, while the heater contact portion is made of a material with higher thermal conductivity to enable rapid heat transmission, thus resolving the contradiction between electrical properties and activation speed.
Solution Approach 2:
Different portions of the sensor element are made of materials with different thermal conductivity properties. The heater contact portion is specifically designed with higher thermal conductivity to facilitate rapid heating, while other portions can use zirconia for electrical stability. This localized material differentiation allows the element to achieve both good electrical properties and fast activation.
2Reliability
If the entire element is made of partially stabilized zirconia, then the element achieves good electrical and chemical stability, but the manufacturing cost increases due to expensive rare earths
Solution Approach 1:
The invention extracts the expensive partially stabilized zirconia material from the entire element structure and uses it only for the electrolyte portion where its chemical stability and electrical properties are essential. The substrate and heater contact portion use more cost-effective materials with higher thermal conductivity, thus reducing overall manufacturing cost while maintaining necessary performance in critical areas.
Solution Approach 2:
The sensor element employs different materials in different locations based on functional requirements. The electrolyte portion uses partially stabilized zirconia for chemical stability and electrical conductivity, while the substrate and heater contact portions use materials optimized for thermal conductivity and cost-effectiveness. This localized material selection balances performance needs with manufacturing costs.
3Ease of manufacture
If a plate-shaped A/F sensor element is used, then the element is easy to manufacture by laminating sheets, but corners are formed at ends making the element poor at handling thermal shock and prone to damage
Solution Approach 1:
The sensor element adopts a bottomed cylindrical shape instead of a plate shape. This curved geometry eliminates sharp corners and edges that are prone to stress concentration during thermal shock. The cylindrical form with rounded surfaces distributes thermal stress more evenly, significantly improving thermal shock resistance while maintaining manufacturing feasibility through established ceramic forming techniques.
4Reliability
If a bottomed cylindrical-shaped element is used, then thermal shock is dispersed and cracks are prevented, but the element takes longer to heat when made entirely of zirconia
Solution Approach 1:
The bottomed cylindrical element combines zirconia (for chemical stability and electrical properties) with a material of higher thermal conductivity in the heater contact portion. This composite structure maintains the thermal shock resistance benefits of the cylindrical shape while the high thermal conductivity material in the heater contact area enables rapid heat transmission, thus reducing heating time.
Solution Approach 2:
The heater contact portion of the cylindrical element is made of a material with higher thermal conductivity to facilitate rapid heating, while the rest of the element can use zirconia for chemical stability and electrical performance. This localized material differentiation allows the element to achieve both thermal shock resistance and fast heating capability.
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 solution enables low-cost manufacturing, rapid activation of the A/F sensor element, and prevents damage from thermal shock and assembly-related stress, while maintaining detection sensitivity.
Implementation Method 1
the insulating ceramic is made of a material having a higher thermal conductivity than the solid electrolyte
Implementation Method 2
detects an oxygen concentration in a measurement gas (exhaust gas) using an electromotive force as limit current generated in a solid electrolyte of the A/F sensor element due to an oxygen concentration difference between a reference gas and the measurement gas
Implementation Method 3
The diffusion resistance layer can allow the measurement gas such as the exhaust gas to permeate therethrough
Data Source
AI summary
An A/F sensor element includes a substrate made of an insulating ceramic having a bottomed cylindrical shape, an electrolyte part made of a solid electrolyte, and a pair of electrode portions. The electrolyte part is embedded in at least a portion of the side wall of the substrate. The A/F sensor element is used by inserting a rod-like heater in the substrate having the bottomed cylindrical shape. The substrate is formed of the insulating ceramic at a contact position to the heater within the substrate. In a manufacturing of the substrate, a molded body having a space for a forming position of the electrolyte part is formed by using substrate-forming clay, and then the molded body is molded by filling electrolyte-forming clay into the space.