Engine Pressure Estimation via Sabathe Cycle Model
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Solution Overview
Problem
Current methods for estimating the maximum pressure inside the combustion chamber of an internal combustion engine are either complex or economically unfavorable, lacking a simplified and reliable model.
Innovation Solution
A method using a Sabathé cycle to model the combustion process, estimating maximum pressure through energy contributions during constant volume and constant pressure phases, with parameters like compression ratio, heat capacity ratio, and MFB50 combustion index, implemented in the engine's control unit to calculate pressure values without the need for dedicated pressure sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated pressure sensor is arranged on the crown of each cylinder to determine maximum pressure, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a virtual copy of the pressure measurement function through computational modeling. Instead of using physical pressure sensors in each cylinder, the system uses a pressure estimation model that calculates maximum pressure based on readily available data from other engine sensors (temperature, pressure at intake valve closing, combustion characteristics). This virtual copy achieves sufficient measurement precision without the complexity and cost of physical sensor installation.
Solution Approach 2:
The patent replaces the mechanical/physical measurement system (pressure sensors) with a computational/mathematical system. The pressure estimation model uses thermodynamic equations and combustion analysis to substitute for direct mechanical pressure measurement, thereby eliminating the need for expensive pressure sensors while maintaining adequate measurement capability for engine control applications.
2Device complexity
If existing pressure estimation methods are used, then device complexity is reduced, but reliability and accuracy deteriorate
Solution Approach 1:
The patent improves reliability by carefully selecting and utilizing specific parameters that have strong correlation with maximum pressure. The model uses pressure at intake valve closing (P_IVC), temperature at intake valve closing (T_IVC), combustion duration (MFB50), and heat capacity ratio (γ) as key input parameters. By changing and optimizing which parameters are used in the estimation, the model achieves high reliability without increasing device complexity.
Solution Approach 2:
The patent incorporates feedback mechanisms to improve estimation reliability. The model uses actual combustion data (MFB50 from crankshaft position sensor) and adjusts the estimation based on observed combustion characteristics. This feedback loop allows the system to adapt to varying engine conditions and maintain accurate pressure estimation across different operating ranges, thereby improving reliability.
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 method provides a reliable and cost-effective estimation of maximum pressure with a mean absolute percentage error of 3%, simplifying the process and eliminating the need for expensive pressure sensors.
Implementation Method 1
fuel is injected into the combustion chamber of the cylinder and in the expansion stroke or in the final part of the preceding compression stroke, the electrodes of the spark plug cause a spark that ignites the air-fuel mixture inside the cylinder giving rise to combustion, which produces an increase of temperature and pressure
Implementation Method 2
Once the charge is trapped in the cylinder, the compression stroke and the combustion that takes place inside the cylinder determine the increase of pressure inside the combustion chamber
Data Source
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AI summary
There is described a method to estimate the maximum pressure (PMAX, P3) inside the combustion chamber of a cylinder (2) of an internal combustion engine (1) which comprises estimating said maximum pressure (PMAX, P3) based on the pressure value (P2) obtained at the end of the compression stroke of the combustion cycle and on the MFB50 combustion index, which represents the engine angle at which, inside the cylinder (2) 50% of the fuel mass was burnt.