Knocking Sensor Insulation Using PPS Resin at High Temperatures
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Solution Overview
Problem
Conventional knocking sensors with polyimide resin molded bodies experience decreased insulation resistance and altered sensor capacitance at high temperatures, affecting their accuracy in detecting knocking phenomena in internal combustion engines, especially when operating above 150°C.
Innovation Solution
The knocking sensor employs a polyphenylene sulfide (PPS) resin molded body and insulating plates without ester bonds, which maintain their dielectric constants and thickness, combined with high surface resistivity, to ensure stable insulation and detection accuracy even at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polyimide resin molded body is used in the knocking sensor, then the sensor can be manufactured with good moldability and structural integrity, but the insulation resistance decreases and sensor capacitance changes at high temperatures (150°C or higher)
Solution Approach 1:
The patent changes the chemical composition parameter of the resin from polyimide (containing amide bonds) to polyester resin (containing ester bonds), which fundamentally alters the thermal stability characteristics. This material substitution resolves the contradiction by selecting a resin whose molecular structure inherently maintains insulation properties at high temperatures while still providing good moldability for manufacturing.
Solution Approach 2:
The patent employs a composite structure where the resin molded body is made of polyester resin combined with specific insulating plates (flange portion-side insulating plate and weight-side insulating plate) that are also made of polyester resin. This composite material approach ensures consistent thermal expansion characteristics and maintains insulation resistance across all components even at elevated temperatures, while the polyester resin provides both moldability and high-temperature stability.
2Stability of the object's composition
If a polyimide resin molded body is used in the knocking sensor, then the sensor structure can be maintained, but the sensor capacitance varies at high temperatures, affecting detection accuracy
Solution Approach 1:
The patent changes the material composition from polyimide resin to polyester resin, which has different dielectric properties and thermal expansion characteristics. This parameter change ensures that the capacitance of the insulating plates remains stable at high temperatures, thereby maintaining measurement precision for knocking detection while preserving the overall structural integrity of the sensor.
Solution Approach 2:
The patent uses polyester resin for both the molded body and the insulating plates, creating a homogeneous material system throughout the sensor structure. This homogeneity ensures uniform thermal expansion and consistent dielectric properties across all components, preventing capacitance variation that would otherwise occur due to differential expansion between dissimilar materials, thus maintaining detection accuracy at high temperatures.
3Ease of manufacture
If conventional resins are used for insulating plates, then the sensor can be manufactured easily, but the insulation characteristics deteriorate at temperatures of 150°C or higher
Solution Approach 1:
The patent changes the material parameter of the insulating plates from conventional resins (such as polyimide or other high-temperature resistant materials) to polyester resin. This parameter change is specifically selected because polyester resin maintains its insulation characteristics at high temperatures while still being easily manufacturable using conventional molding processes, thus resolving the contradiction between ease of manufacture and high-temperature reliability.
Solution Approach 2:
The patent creates a composite structure where the insulating plates are made of polyester resin that matches the molded body material. This composite material approach ensures that all resin components have identical thermal and electrical properties, maintaining consistent insulation characteristics across the entire sensor assembly at high temperatures, while the polyester resin itself provides good manufacturability through standard molding techniques.
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 maintains satisfactory insulation characteristics and enhances knocking detection accuracy at temperatures up to 150°C or higher, reducing the risk of insulation failure and capacitance variation.
Implementation Method 1
a piezoelectric element 14 which is sandwiched between the flange portion 11B and the weight 17
Data Source
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AI summary
A knocking sensor is provided which, even at an operating temperature of 150°C or higher, exhibits satisfactory insulation characteristics and excellent knocking detecting characteristics. The knocking sensor includes: a sensor body 10 including: a metal shell 11 including, a tubular portion 11A and a flange portion 11B, a piezoelectric element 14, a weight 17 which is placed so as to sandwich the piezoelectric element 14 with the flange portion 11A, a flange portion-side electrode plate 13 which is placed between the piezoelectric element 14 and the flange portion 11B, a weight-side electrode plate 15 which is placed between the piezoelectric element 14 and the weight 17, a flange portion-side insulating plate 12 which is placed between the flange portion 11B and the flange portion-side electrode plate 13, and a weight-side insulating plate 17 which is placed between the weight 17 and the weight-side electrode plate 15; and a resin molded body 30 which covers the sensor body 10. The resin molded body 30 is made of PPS. The flange portion-side insulating plate 12 and the weight-side insulating plate 16 are made of a resin that does not contain ester bond. A change of sensor capacitance depending on the temperature is suppressed, and decrease in accuracy of detection of knocking is suppressed.