Two-Stroke Engine Offset Crankshaft Design
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Solution Overview
Problem
Conventional two-cycle engines with offset structures face challenges in optimizing output and exhaust gas emissions, as the offset amount affects both downsizing and performance, and there is a need to determine the most suitable offset for improved results.
Innovation Solution
A two-cycle engine with a shaft center offset of greater than 1 mm and less than 6 mm onto the exhaust port side, combined with an offset center of gravity for the counterweight in the rotational direction, optimizing the crankshaft and conrod positions to enhance combustion efficiency and reduce vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the offset amount is increased to improve combustion efficiency and output, then the combustion efficiency and power transmission improve, but the engine size increases and manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by optimizing the offset amount to a specific range (greater than 1 mm and less than 6 mm) rather than using extreme values. This controlled parameter adjustment achieves improved combustion efficiency and power transmission while preventing excessive engine size increase, resolving the contradiction between performance improvement and size control.
2Power
If the offset amount is increased to improve power transmission, then the explosive force transmission improves, but the side pressure on the exhaust side increases causing seizures or abnormal wear
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the offset parameter within the range of greater than 1 mm and less than 6 mm. This optimized parameter range ensures sufficient power transmission improvement while maintaining the side pressure at levels that prevent seizures and abnormal wear on the exhaust side sliding surfaces.
3Volume of moving object
If the offset amount is optimized for downsizing, then the engine size is reduced, but the combustion efficiency and emissions performance deteriorate
Solution Approach 1:
The patent overcomes this contradiction by identifying and implementing an optimal offset parameter range (greater than 1 mm and less than 6 mm) that simultaneously achieves downsizing and improved emissions performance. The specific parameter optimization ensures that the piston position at maximum cylinder pressure is delayed appropriately, improving combustion efficiency and reducing uncombusted fuel in exhaust gases.
4Productivity
If the offset amount is increased to delay piston position for better combustion, then the combustion efficiency improves, but the vibrations increase
Solution Approach 1:
The patent resolves this contradiction by optimizing the offset parameter within the controlled range of greater than 1 mm and less than 6 mm. This parameter optimization achieves the desired piston position delay for improved combustion efficiency while maintaining vibration levels at acceptable thresholds, balancing performance improvement with operational stability.
Data Source
AI summary
A two-cycle engine having a structure in which the shaft center Ccy of the cylinder 3 is offset onto the exhaust port 32 side with respect to the rotational center Ccr of the crankshaft 4, and the offset amount S of the shaft center Ccy with respect to the rotational center Ccr is set greater than 1 mm and less than 6 mm. Furthermore, in this case, the center of gravity of the counterweight 42 of the crankshaft 4 is shifted onto the rear side in the rotational direction with respect to the line passing the rotational center Ccr of the crankshaft 4 and the center Ccp of the crank pin 41.