Temperature Sensor Pad Thermal Expansion Control
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Solution Overview
Problem
Conventional temperature sensors used in exhaust systems of internal combustion engines face issues with separation of output lines from pads due to thermal expansion, leading to performance deterioration at higher temperatures, as engines are downsized and temperature ranges widen.
Innovation Solution
A temperature sensitive element with a ceramic base, a metallic resistor layer, and pads made of a glass-based material with a thermal expansion coefficient smaller than the output lines, covered by a glass-based covering member, which applies compressive stress to reduce separation and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the temperature sensor is used at higher temperatures (850°C or higher) due to engine downsizing, then the temperature measurement range is improved, but the output lines separate from the pads due to thermal expansion
Solution Approach 1:
The invention changes the material parameters of the pad by forming it from a glass-based material containing specific oxides (SiO2: 40-70 wt%, B2O3: 10-30 wt%, Al2O3: 5-20 wt%) to achieve a thermal expansion coefficient that matches the output line material (Pt or Pt alloy). This parameter matching prevents separation during thermal cycling at high temperatures up to 850°C or higher.
Solution Approach 2:
The invention uses a composite glass-based material for the pad that combines multiple oxide components (silica, boron oxide, aluminum oxide) to create a material with tailored thermal expansion properties. This composite material bridges the thermal expansion mismatch between the metal output lines and the ceramic substrate, maintaining connection reliability at elevated temperatures.
2Ease of manufacture
If conventional materials are used for pads, then the manufacturing process is simple, but the thermal expansion mismatch causes separation at high temperatures
Solution Approach 1:
The invention modifies the compositional parameters of the pad material by using a glass-based system with controlled oxide ratios. This allows the thermal expansion coefficient to be tuned to match the output line material while maintaining a relatively simple manufacturing process involving screen printing or dip-coating of glass paste followed by firing.
Solution Approach 2:
The invention explicitly addresses thermal expansion mismatch by selecting a glass-based material whose thermal expansion coefficient can be matched to the output line material (Pt or Pt alloy). The glass composition is designed so that its thermal expansion behavior compensates for the mismatch between metal and ceramic components, preventing separation during thermal cycling.
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 effectively reduces the likelihood of output line separation from pads, thereby improving the durability and performance of temperature sensors at high temperatures, such as 850°C or higher, by applying compressive stress and controlling thermal expansion coefficients.
Implementation Method 1
the pad having a thermal expansion coefficient smaller than that of the output line
Data Source
AI summary
In a temperature sensitive element, a covering member containing a glass as a main component and having a thermal expansion coefficient smaller than that of output lines is provided on pads to cover at least portions of output lines located on the pads. The pads are formed of a glass-based material which contains, as main components, a metal and a glass having a thermal expansion coefficient smaller than that of a ceramic substrate, and the thermal expansion coefficient of the pads is set to be smaller than that of the output lines. Accordingly, in the case where the temperature sensitive element is exposed to a temperature change between a high temperature and ordinary temperature, compressive stress can be applied to the output lines by the covering member and the pads. Thus, the fixing force between the output lines and the pads can be increased.