Crank Angle Offset Determination Using Manifold Pressure Integration
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Solution Overview
Problem
Existing methods for determining crank angle offset in internal combustion piston engines face challenges in accuracy due to temperature fluctuations and initial instability of pressure sensors, leading to cumbersome detection of combustion parameters like indicated mean effective pressure (IMEP).
Innovation Solution
A method that determines a crank angle position offset value by calculating an integral value of indicated mean effective pressure over a range of crank angles during which the combustion chamber is closed, using a formula that integrates pressure and volume derivatives, allowing for improved accuracy in IMEP measurement and combustion control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensor is directly attached to the engine to detect cylinder pressure, then combustion parameters can be measured, but the sensor is subjected to significant temperature changes causing deterioration and initial instability
Solution Approach 1:
The patent introduces an intermediary calculation method that uses manifold pressure sensor readings and compression ratio to derive cylinder pressure, rather than directly using the temperature-prone cylinder pressure sensor. This mediator approach (calculating expected cylinder pressure through P_expected = P_manifold × CR) allows comparison with actual sensor readings to determine and compensate for offset errors, thereby maintaining measurement precision while bypassing the reliability issues of direct temperature exposure
Solution Approach 2:
The patent changes the measurement parameters by introducing offset compensation values that are calculated based on temperature-compensated reference measurements. By dynamically adjusting the pressure readings through offset correction (P_corrected = P_measured - offset), the system maintains accurate combustion parameter detection despite temperature-induced sensor drift
2Device complexity
If crank angle offset is determined based on simple pressure comparison at top dead center, then the method is simple, but accuracy is insufficient due to temperature effects and sensor instability
Solution Approach 1:
The patent implements a feedback mechanism where the crank angle offset determination is based on comparing expected cylinder pressure (calculated from manifold pressure and compression ratio) with actual measured pressure. The offset value is continuously refined through this feedback loop, allowing accurate offset detection that compensates for temperature effects and sensor instability while maintaining reasonable method complexity
Solution Approach 2:
The patent performs preliminary offset determination during engine operation by accumulating offset values over multiple measurement cycles. This preliminary action of gathering reference data and calculating average offset values before final offset application improves accuracy by averaging out temperature fluctuations and sensor instability effects
Data Source
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AI summary
Invention relates to method of determining an offset (38) relating to crank angle measurement in connection with a cylinder (12) of an internal combustion pis- ton engine (10), in which method the engine (10) is rotated and it is refrained from fuel combustion in the cylinder, a reference value for the indicated mean effective pressure is determined, an integral value of indicated mean effective pressure in the cylinder is determined over a range of crank angle during all of the gas exchange valves of the cylinder are maintained closed, and wherein a dead center position of the piston is located with the range, a crank angle position offset value is determined based on the determined integral value of indicated mean effective pressure and the reference value for the indicated mean effective pressure.