Piezoelectric Sensor Protection Against Shock Waves and Heat
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Solution Overview
Problem
Piezoelectric sensors in combustion chambers of internal combustion engines face damage from shock waves, pressure spikes, and heat due to their mechanical contact with the combustion medium, leading to potential defects and impaired functionality.
Innovation Solution
A protective device is designed with passages that direct shock waves away from the piezoelectric pickup, allowing them to dissipate kinetic energy before reaching the sensor, and the device is positioned to cover the membrane's radial area, minimizing heat transfer and protecting the sensor from mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the piezoelectric sensor is placed in direct contact with the combustion chamber medium via a thin diaphragm to maximize pressure detection sensitivity, then measurement precision is improved, but the sensor becomes vulnerable to damage from shock waves and pressure spikes
Solution Approach 1:
A protective device is introduced as an intermediary element between the combustion chamber medium and the piezoelectric sensor. This protective device includes a protective diaphragm with openings that allows pressure fluctuations to reach the sensor while blocking shock waves and pressure spikes, thus mediating the interaction to preserve both measurement precision and sensor reliability
Solution Approach 2:
The protective device employs a protective diaphragm made of flexible material with specific thickness and opening patterns. This thin film structure allows normal pressure transmission for measurement while providing mechanical protection against extreme pressure events, resolving the contradiction between sensitivity and durability
2Measurement precision
If the diaphragm is made thin in certain areas to maximize force transmission from the medium to the piezoelectric transducer, then measurement precision is improved, but the diaphragm becomes more susceptible to mechanical damage from heat and pressure
Solution Approach 1:
A protective diaphragm is introduced as an additional thin film layer that covers the existing measurement diaphragm. This protective film absorbs mechanical stress and heat exposure, allowing the original thin diaphragm to maintain its force transmission efficiency while the protective layer bears the mechanical damage risk from thermal and pressure exposure
Solution Approach 2:
The protective device is positioned beforehand between the combustion medium and the sensor assembly, creating a cushioning effect that absorbs extreme pressure events before they reach the thin measurement diaphragm, thus preventing mechanical damage while preserving measurement capability
3Reliability
If a protective device with numerous small openings is used to extinguish flame fronts and reduce heat exposure to the diaphragm, then reliability is improved, but the openings can become clogged with combustion residues
Solution Approach 1:
The protective device features a non-uniform opening pattern with varying sizes and distributions across different regions. This local quality variation allows larger openings in areas prone to residue accumulation while maintaining smaller openings where flame front extinction is most needed, thus balancing protection effectiveness with clogging resistance
Solution Approach 2:
The opening parameters (size, shape, distribution) of the protective device are optimized to balance multiple functions: small enough to extinguish flame fronts and filter heat, but large and strategically positioned enough to resist clogging from combustion residues, resolving the contradiction between protection and maintainability
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 reduces the impact of shock waves and heat on the piezoelectric material, enhancing the sensor's durability and accuracy by dissipating kinetic energy and minimizing mechanical stress, thus preventing damage and maintaining sensor functionality.
Implementation Method 1
A piezoelectric transducer is positioned centrally within the housing, against the diaphragm. As the pressure changes, the medium exerts a normal force on the diaphragm, which in turn acts on the piezoelectric transducer. The normal force generates electrical polarization charges on the piezoelectric sensor
Implementation Method 2
Pressure spikes occur as shock waves, in which parts of the medium move faster than the speed of sound. Shock waves exhibit a sudden pressure increase and a sudden pressure drop. This pressure increase and drop occur within a period of a few nanoseconds.
Implementation Method 3
The diaphragm is not only exposed to pressure fluctuations with high pressure peaks, but also to a heat flow with temperature peaks of 850 K and higher. Through contact with the medium, the diaphragm is mechanically stretched, and a significant amount of heat is transferred to it.
Data Source
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AI summary
The invention relates to a system (T) comprising a combustion chamber (K) of an internal combustion engine, a piezoelectric sensor (S) for detecting a pressure profile in the combustion chamber (K), and a protective device (V) for the piezoelectric sensor (S); wherein the piezoelectric sensor (S) comprises a diaphragm (2) and a piezoelectric transducer (3), wherein the piezoelectric sensor (S) is mechanically fixed in a wall (W) of the combustion chamber (K); wherein the protective device (V) largely covers a side of the diaphragm (2) facing away from the piezoelectric transducer (3); wherein the protective device (V) has passages (8) through which liquid or gaseous medium from the combustion chamber (K) passes to the diaphragm (2); and wherein the passages (8) are arranged at the greatest possible distance from the piezoelectric transducer (3).