True TDC Determination via Heat Loss Offset Correction
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Solution Overview
Problem
Existing methods for determining true Top Dead Center (TDC) in internal combustion engines are inaccurate due to dynamic effects like piston blow-by and heat transfer, and are not applicable individually to each cylinder of a multi-cylinder engine, leading to errors in combustion calculations.
Innovation Solution
A method that calculates the Heat Loss Offset (HLO) using engine speed, molar mass, and heat loss rate to correct the Location of Peak Pressure (LPP) and determine true TDC for each cylinder, accounting for machining errors and misalignment in the crankshaft position sensor, allowing for accurate combustion statistics and feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Location of Peak Pressure (LPP) is used to approximate TDC, then the measurement process is simple, but the measurement precision deteriorates due to heat transfer effects and piston blow-by causing LPP to occur slightly ahead of true TDC
Solution Approach 1:
The patent applies preliminary action by pre-calculating Heat Loss Offset (HLO) values and storing them in lookup tables before engine operation. These tables are generated based on engine speed and other parameters, allowing the ECU to quickly retrieve and apply the appropriate offset during combustion calculations without performing complex real-time heat transfer simulations, thus maintaining both accuracy and computational efficiency
Solution Approach 2:
The patent introduces Heat Loss Offset (HLO) as an intermediary parameter that mediates between the easily measurable LPP and the difficult-to-determine true TDC. The HLO acts as a correction factor that accounts for heat transfer effects and piston blow-by, allowing the system to derive accurate TDC information from simple LPP measurements without directly measuring the complex thermal and mechanical effects
2Adaptability or versatility
If a single TDC determination method is used for the first cylinder, then the device complexity is low, but the adaptability deteriorates because crankshaft variations cause TDC bias for other cylinders
Solution Approach 1:
The patent applies segmentation by dividing the TDC determination process into individual cylinder-specific calculations. Instead of using a single TDC reference for all cylinders, the system performs separate LPP detection and HLO application for each cylinder, allowing each cylinder's TDC to be determined independently while accounting for crankshaft variations and manufacturing tolerances in that specific cylinder
Solution Approach 2:
The patent implements local quality by applying cylinder-specific correction factors and parameters to each cylinder's combustion calculations. The system uses individual LPP measurements and applies appropriate HLO values tailored to each cylinder's characteristics, ensuring that local variations in crankshaft geometry and sensor alignment are compensated for in each specific location rather than using a universal correction
3Measurement precision
If crankshaft position sensor tolerances and crankshaft manufacturing variations are not compensated, then the manufacturing precision requirements are relaxed, but the measurement precision of TDC deteriorates
Solution Approach 1:
The patent applies feedback by using the measured LPP from each cylinder as input to calculate the specific TDC offset for that cylinder. The system continuously monitors combustion pressures and LPP positions, then uses this feedback information to determine and apply appropriate HLO corrections, creating a closed-loop system that compensates for sensor and manufacturing variations without requiring ultra-precise manufacturing tolerances
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 provides precise TDC determination for each cylinder, improving engine performance by reducing errors in IMEP calculations and accommodating crankshaft variations, leading to better engine efficiency and reduced emissions.
Implementation Method 1
a high range cylinder compression sensor capable of detecting combustion pressures up to about 200 bar
Implementation Method 2
an optical or magnetic encoder mounted on the end of the engine crankshaft
Implementation Method 3
an optical or magnetic encoder mounted on the end of the engine crankshaft
Implementation Method 4
heat transfer to and from the cylinder wall surfaces during compression and expansion
Data Source
AI summary
True Top Dead Center (TDC) of an engine piston is determined through determination of the Location of Peak Pressure (LPP) using either of two simplified algorithms. A Heat Loss Offset (HLO), drawn from a look-up table based on engine speed, molar mass of the air being compressed, and heat loss rate to the cylinder walls, is added to the calculated LPP to provide a corrected and true TDC position for each piston, which corrects for errors in target wheel tooth location of a camshaft position sensor and for any misalignment in the target wheel during installation on an engine. Preferably, such a calculation is carried out for each cylinder of a multi-cylinder engine during operation thereof, thus further correcting for machining errors in the crankshaft and for crankshaft bending during the life of the engine. The invention thus allows for more accurate combustion calculations for each individual cylinder.