Piezoelectric Sensor Signal Processing Circuit for Piston Engine Cylinder Pressure
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Solution Overview
Problem
Existing methods for processing signals from piezoelectric sensors in piston engines fail to reliably compensate for undesirable signal shifts due to pyroelectricity, particularly in internal combustion engines with abrupt amplitude and frequency variations, and require complex configurations or additional electronic circuits.
Innovation Solution
A method and circuit that detect plateaux in the signal using derivative analysis to reliably compensate for shifts, employing a closed-loop servo control with a high sampling frequency and adaptive calculation of signal variations, allowing for effective compensation without additional circuits and independent of engine frequency and amplitude variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-pass filter is added to the charge amplifier to suppress low-frequency variations, then low-frequency signal drift is reduced, but a constant reference value cannot be ensured and pyroelectric drift is not correctly compensated
Solution Approach 1:
The patent implements a closed-loop feedback system where the output signal is continuously monitored and fed back to adjust the compensation current. The servo control unit compares the output signal with a reference value and automatically adjusts the compensation current to maintain accuracy, resolving the contradiction between filtering and reference value stability.
Solution Approach 2:
The patent dynamically changes the compensation current parameter based on detected signal drift. By monitoring the output signal and adjusting the compensation current in real-time, the system adapts to pyroelectric drift and temperature variations while maintaining accurate reference values.
2Reliability
If Kalman filters are used to correct signal drift, then pyroelectricity compensation is improved, but additional distinct circuits are required and cost increases
Solution Approach 1:
The patent merges the drift compensation function directly into the existing charge amplifier circuit by adding a compensation current source that feeds into the same input node. This integration eliminates the need for separate distinct circuits while achieving effective pyroelectricity compensation.
Solution Approach 2:
The system uses its own output signal to generate the compensation current through the servo control unit. The circuit monitors its own drift and automatically corrects it without requiring external complex processing systems, achieving self-service compensation.
3Device complexity
If compensation is delayed from one cycle to the next, then simple circuit implementation is achieved, but abrupt amplitude and frequency variations cannot be compensated
Solution Approach 1:
The patent implements continuous compensation by maintaining an active servo control loop that operates throughout the signal measurement process. The compensation current is continuously adjusted based on real-time feedback, ensuring that abrupt variations are compensated immediately rather than being delayed to the next cycle.
4Measurement precision
If the sampling frequency is increased to improve compensation accuracy, then measurement precision improves, but the dynamics of the amplifier and ADC resolution must be compatible with maximum drifts
Solution Approach 1:
The patent performs preliminary drift compensation by detecting plateaux and calculating the required compensation current before the actual measurement cycle begins. This preliminary adjustment reduces the magnitude of drift that occurs during measurement, allowing the use of moderate sampling frequencies with standard amplifier and ADC specifications.
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 provides reliable and adaptive compensation for signal shifts, ensuring accurate measurement of cylinder pressure in piston engines, even at high speeds, with reduced component size and cost, and integrated within a single mechanical assembly like a glow plug.
Implementation Method 1
a piezoelectric sensor supplying a signal indicating the cylinder pressure
Implementation Method 2
the phenomenon of pyroelectricity, since a piezoelectric crystal is additionally sensitive to temperature
Data Source
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Figure 2
Figure 3~5
AI summary
The invention relates to a method and a circuit for processing a signal supplied by a piezoelectric sensor (10) indicating the cylinder pressure of a piston engine such as a heat engine. Undesirable variations in the value of the signal supplied by the sensor and corresponding to plateaux in the pressure are compensated by a closed-loop servo control which is suitable for setting an output signal to a predetermined constant reference value, independently of undesirable variations in the signal from the sensor (10). The value of the output signal is sampled, and at each sampling moment, if the absolute value of the variation in the output signal is less than a comparison value, the servo control is kept active. The invention further relates to a circuit for processing and a pressure-measuring device comprising a circuit of this kind.