Piezoresistive Pressure Plug for Combustion Engine
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Solution Overview
Problem
Existing pressure-measuring plugs for combustion engines have limited bandwidth due to the length of the heating rod, which restricts accurate pressure feedback and is prone to electronic failure from temperature extremes.
Innovation Solution
A pressure-measuring plug with a miniaturized sensing structure integrated within the plug body, reducing the length and mass of the rod, and using a sealing element to allow friction-free axial movement, while positioning sensor electronics closer to the engine's temperature for improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the heating rod length is increased to improve pressure transmission, then the pressure sensor bandwidth is limited to 3-4 kHz, but the measurement accuracy and response speed are degraded
Solution Approach 1:
The plug body is divided into distinct functional sections: a first section with the rod arranged displaceably for pressure transmission, and a second section with the sensing structure integrated for signal detection. This segmentation allows the rod to be optimized for pressure transmission while the sensing structure handles measurement, resolving the bandwidth-accuracy tradeoff
Solution Approach 2:
The rod acts as an intermediary element between the combustion chamber pressure and the sensing structure. By making the rod displaceable within the plug body, it mediates the pressure transmission while allowing the sensing structure to remain in a favorable position for high-bandwidth operation, achieving both accurate pressure transmission and fast response
2Temperature
If the sensing structure is positioned outside the engine in a housing, then the electronics are protected from combustion heat, but the temperature variation from 0-30°C to 200°C increases electronic failure rate
Solution Approach 1:
The sensing structure is merged with the plug body, integrating the sensor electronics directly into the combustion chamber environment. This eliminates the housing and reduces the temperature swing experienced by the electronics, improving reliability despite exposure to higher operating temperatures
Solution Approach 2:
The plug body serves multiple functions: it provides structural support, transmits pressure via the displaceable rod, and houses the sensing structure integrated within. This multi-functionality eliminates the need for a separate housing, reducing thermal stress on electronics while maintaining protection and functionality
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 design enhances bandwidth for accurate pressure measurement and reduces electronic failure rates by minimizing temperature-induced stress on the electronics.
Implementation Method 1
a piezoresistive element mounted on the sensing structure provides a resistance change when the rod is moved in axial direction
Data Source
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AI summary
A piezoresistive pressure-measuring plug (100) for a combustion engine for measuring a pressure is disclosed. The piezoresistive pressure-measuring plug (100) comprises: a plug body (106, 108, 110) for insertion into a cylinder of the combustion engine, a rod (102) that is arranged in the plug body (106, 108, 110), a sensing structure (104) comprising a piezoresistive element, that is arranged between the rod (102) and the plug body (106, 108, 110) in such a way that the sensing structure is acted upon, in use, by the pressure prevailing in the combustion chamber of the cylinder, whereby the rod (102) transmits the pressure in the combustion chamber of the cylinder to the sensing structure due to the pressure in the combustion chamber leading to an axial motion of the rod (102) relative to the plug body (106, 108, 110) so as to apply a force to the sensing structure (104) and a PWB (114) provided with sensor electronics for measuring and conditioning a resistance change. The sensing structure (104) is arranged in the plug body (106, 108, 110) and, in use is compressed in axial direction by the force applied to the sensing structure (104) and a piezoresistive element (206) mounted on the sensing structure (104) to provide a resistance change when the sensing structure (104) is compressed in axial direction. Furthermore, the PWB (114) is arranged in the plug body (106, 108, 110). In this way a pressure-measuring plug is obtained with improved bandwidth and reduced build-in height.