In-Cylinder Pressure Sensor EGR Ratio Estimation
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Solution Overview
Problem
Existing EGR ratio estimating methods for internal combustion engines, particularly low-pressure EGR devices, face challenges in accurately estimating the EGR ratio due to the time lag of external EGR gas reaching the cylinder, leading to inaccurate calculations.
Innovation Solution
A control device for internal combustion engines that includes an in-cylinder pressure sensor, a driving condition detector, a reference crank angle setter, a reference in-cylinder pressure calculator, an EGR ratio estimator, and a controller, which calculates the EGR ratio based on the pressure difference between actual and reference in-cylinder pressures at a set reference crank angle, reflecting the temperature properties of the mixture gas under stoichiometric conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If external EGR gas is recirculated through a long passage in a low-pressure EGR device, then the EGR system can operate at lower pressures, but the EGR gas reaches the cylinder with a long time lag causing inaccurate EGR ratio estimation
Solution Approach 1:
The patent replaces the conventional mechanical/EGR-ratio-based estimation method with a thermodynamic method. Instead of relying on airflow sensors and pressure sensors to calculate EGR ratio, the system uses in-cylinder pressure measurements and polytropic process equations to determine the EGR ratio, thereby eliminating the time lag problem associated with physical EGR gas transport.
Solution Approach 2:
The patent changes the measurement parameter from direct EGR gas flow measurement to in-cylinder pressure measurement. By measuring pressure at specific crank angles and using the heat capacity ratio (which changes with EGR content), the system can accurately determine EGR ratio without being affected by the time lag in gas transport through the EGR passage.
2Device complexity
If the EGR ratio is estimated using conventional methods with airflow and pressure sensors, then the system structure remains simple, but the estimation accuracy deteriorates due to time lag in low-pressure EGR systems
Solution Approach 1:
The patent substitutes the mechanical sensor-based estimation system with a thermodynamic calculation system. The in-cylinder pressure sensor data is processed using polytropic process equations and heat capacity ratio relationships to determine EGR ratio, replacing the need for complex multi-sensor fusion algorithms while improving accuracy.
Solution Approach 2:
The patent introduces the heat capacity ratio (κ) as an intermediary parameter. The in-cylinder pressure measurements at different crank angles are used to calculate κ, which then serves as the basis for determining the EGR ratio. This intermediary approach decouples the measurement from the time lag problem by using thermodynamic properties rather than direct gas flow measurements.
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 approach enables accurate estimation of the EGR ratio, independent of the time lag of external EGR gas, allowing for precise engine control and improved combustion efficiency.
Implementation Method 1
an in-cylinder pressure sensor that detects a pressure inside the cylinder as an in-cylinder pressure
Implementation Method 2
a method disclosed in Japanese Unexamined Patent Application Publication No. 2008-231995 has been known, for example. This estimating method is based on the assumption that a state change of a mixture gas in a compression stroke of the internal combustion engine is a polytropic change
Implementation Method 3
a heat capacity ratio κ of the mixture gas is calculated from the in-cylinder pressures P1, P2 and cylinder volumes V1, V2 corresponding to the crank angles CA1, CA2 in accordance with the following formula: κ=log(P1/P2)/log(V2/V1)
Implementation Method 4
an EGR ratio estimator that estimates an EGR ratio based on a pressure difference between an actual in-cylinder pressure detected at the set reference crank angle by the in-cylinder pressure sensor, and the calculated reference in-cylinder pressure
Data Source
AI summary
A control device includes a cylinder pressure sensor, a driving condition detector, a reference crank angle setter, a reference cylinder pressure calculator, an EGR ratio estimator, and a controller. The cylinder pressure sensor detects a cylinder pressure inside a cylinder. The driving condition detector detects a driving condition in an internal combustion engine. The reference crank angle setter calculates, according to the driving condition, a reference crank angle immediately before which mixture gas starts combusting. The reference cylinder pressure calculator calculates a reference cylinder pressure at the reference crank angle based on temperature characteristics of a heat capacity ratio of the mixture gas under a condition. The EGR ratio estimator calculates an EGR ratio based on a pressure difference between the reference cylinder pressure and the cylinder pressure at the reference crank angle. The controller controls the internal combustion engine according to the EGR ratio.