Centered Piston Pin and Cylinder Bore Profile for Lower Friction
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Solution Overview
Problem
The offset center of the piston pin from the piston center in internal combustion engines increases the frictional force and shortens the expansion period, leading to a decrease in work efficiency.
Innovation Solution
The internal combustion engine design features a piston pin centered at the piston, combined with a cylinder sliding surface that has a larger inner diameter in the central portion than in the upper end portion, reducing frictional force and maintaining expansion period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the center of the piston pin is offset from the center of the piston, then the impact force that the skirt portion exerts on the sliding surface is reduced, but the frictional force increases and the expansion period shortens
Solution Approach 1:
The sliding surface is designed with an asymmetric shape where the inner diameter of the central portion is larger than that of the upper end portion. This asymmetric geometry compensates for the symmetric piston pin positioning, reducing impact force while maintaining appropriate clearance to minimize frictional losses and preserve expansion period.
Solution Approach 2:
Different portions of the sliding surface are given different inner diameters to serve different functions: the upper end portion has a smaller inner diameter to reduce impact force during piston movement, while the central portion has a larger inner diameter to reduce frictional force and maintain expansion period. This local differentiation resolves the contradiction between reducing impact and minimizing friction.
2Force
If the center of the piston pin is offset from the center of the piston, then the impact force is reduced, but the expansion period shortens resulting in decreased work efficiency
Solution Approach 1:
The asymmetric sliding surface geometry with varying inner diameters allows the piston to maintain a centered pin position while achieving reduced impact forces. The larger central portion inner diameter ensures adequate clearance throughout the expansion stroke, preventing premature contact and maintaining the full expansion period for work efficiency.
Solution Approach 2:
The sliding surface is differentiated into zones with different inner diameters: the upper end portion with smaller diameter addresses impact reduction, while the central portion with larger diameter preserves expansion period duration. This local quality variation enables simultaneous achievement of both goals without offsetting the piston pin.
Data Source
AI summary
An internal combustion engine includes a piston, a cylinder that has a sliding surface on which the piston slides, and a piston pin that connects the piston and a connecting rod. The sliding surface has a shape in which the inner diameter of a central portion in the axial direction is larger than the inner diameter of an upper end portion, and the center of the piston pin is located at the center of the piston.