Calibrating Cylinder Pressure Sensor Offset in Combustion Engines
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Solution Overview
Problem
Existing methods for calibrating cylinder pressure sensor signals in internal combustion engines face challenges due to variations in signal offset, which hinder the accurate estimation of combustion parameters like maximum pressure and combustion noise, especially under varying engine speeds and loads.
Innovation Solution
A method that involves acquiring and filtering the pressure signal from a cylinder pressure sensor, calculating and filtering the absolute derivative of the pressure signal, and applying a correction formula to adjust the signal offset, using a low-pass linear filter and constants A and B for calibration, either analogically or digitally.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermodynamic approach with polytropic model is used for calibration (as in prior art), then comprehensive pressure evolution modeling is achieved, but computational cost increases and numerical solution is required
Solution Approach 1:
The patent extracts only the essential calibration relationship from the complex thermodynamic model, isolating the offset correction function from the full polytropic pressure evolution model. This allows using a simplified mathematical relationship that captures the necessary calibration behavior without requiring comprehensive thermodynamic modeling, thereby reducing computational complexity while maintaining calibration accuracy.
Solution Approach 2:
The patent changes the calibration approach from solving a complex thermodynamic system with multiple parameters to using a simplified parameter-based correction formula. By focusing on offset correction as a separate parameter adjustment rather than full thermodynamic state reconstruction, the method reduces computational burden while achieving the necessary calibration precision for combustion parameter estimation.
2Loss of information
If cylinder pressure sensors are installed close to the combustion zone, then rich combustion information is obtained, but signal offset variation increases with engine speed and load
Solution Approach 1:
The patent segments the signal processing into distinct stages: raw signal acquisition, offset correction using the calibration formula, and then combustion parameter extraction. By separating the offset correction step from the combustion analysis, the method handles the signal reliability issue independently while preserving all combustion information, allowing algorithms to work with corrected signals that have stable offsets regardless of engine operating conditions.
Solution Approach 2:
The patent introduces an intermediary calibration step that processes the raw sensor signal before it reaches the combustion analysis algorithms. This intermediary offset correction function acts as a mediator that stabilizes the signal by removing variations caused by engine speed and load changes, allowing the downstream combustion parameter extraction algorithms to work with reliable, stable signals while still accessing rich combustion information.
3Measurement precision
If signal offset correction is implemented, then combustion parameter estimation becomes possible, but additional processing steps are required
Solution Approach 1:
The patent performs offset correction as a preliminary action before combustion parameter estimation. By applying the calibration formula to correct the signal offset in advance, the method enables subsequent combustion algorithms to work with already-corrected signals, making parameter estimation possible without requiring complex real-time corrections during the analysis phase. This preliminary correction simplifies the overall processing architecture.
4Reliability
If margins are defined in engine tuning to account for variations, then reliability across different engines is improved, but overall engine performance degrades
Solution Approach 1:
The patent implements a feedback-based calibration approach where the correction formula parameters (A and B) are determined based on actual sensor behavior under different operating conditions. This feedback mechanism allows each sensor to be calibrated to its specific characteristics, enabling precise combustion parameter estimation for individual engines without requiring conservative margins in tuning. The calibrated signals provide reliable data that eliminates the need for performance-degrading safety margins.
Data Source
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Figure 3a~3
AI summary
The invention relates to a method for calibrating the offset of a signal representative of a pressure (P_brut) in the combustion chamber (2) of a thermal engine, a cylinder pressure sensor (4) being provided in the combustion chamber (2) and connected to a calibration unit (7) including a means for acquiring and a means for processing the pressure signal (P_brut) and memory. The method comprises: the step of acquiring (40) and storing (400) the pressure signal (P_brut) from the cylinder pressure sensor (4); a first processing step (41) for processing the pressure signal (P_brut) into a filtered signal (P_filt) that is stored; a second processing step for processing the pressure signal (P_brut) for obtaining a filtered signal of the absolute value of the derivative of the pressure signal (I P' brutl filt) that is stored; and a third processing step (45) for obtaining a pressure signal with an offset correction (P_corr).