Piston Crank Mechanism Axial Offset Design
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Solution Overview
Problem
The compound link type piston crank mechanism in internal combustion engines faces issues with offset deformation of the upper pin bearing, which can lead to adverse effects on the crankpin journal due to off-center or tilted loads, resulting in potential lubrication film loss and increased stress concentrations.
Innovation Solution
The piston crank mechanism is designed with a lower link comprising two parts that are fastened together with bolts, featuring a recessed area to position the crankpin journal such that the projection area of the upper pin does not obscure the crankpin, and a control link with an eccentric cam to adjust the compression ratio, minimizing deformation and maintaining a stable lubricating oil film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the upper pin bearing is positioned closer to the crankpin journal to reduce link length, then the mechanism becomes more compact, but the offset deformation of the upper pin bearing increases and adversely affects the crankpin journal
Solution Approach 1:
The patent repositions the crankpin journal in the axial direction (along the crankshaft axis) rather than only in the radial direction. By arranging the crankpin journal such that its projection area does not overlap with the upper pin bearing's projection area when viewed along the crankshaft axial direction, the design eliminates the harmful offset deformation effect while maintaining a compact link structure.
2Object-affected harmful factors
If the crankpin journal is positioned to avoid overlap with upper pin projection, then deformation is reduced, but the area available for lubrication may be limited
Solution Approach 1:
The patent utilizes the axial dimension along the crankshaft to position the crankpin journal, creating a three-dimensional arrangement where the crankpin journal and upper pin bearing projections do not overlap when viewed axially. This spatial arrangement reduces deformation while the crankpin journal's circumferential surface area remains sufficient for effective lubrication.
Solution Approach 2:
The patent applies different functional zones to the lower link structure: the crankpin journal area is optimized for rotation and lubrication with sufficient circumferential surface area, while the upper pin bearing area is positioned to minimize offset deformation. Each component is locally optimized for its specific function while maintaining overall compactness.
Data Source
AI summary
A piston crank mechanism has an upper link coupled to a piston by a piston pin, a lower link having a crankpin journal, wherein the crankpin journal is coupled to a crankpin of a crankshaft and is coupled to the upper link by an upper pin, and a control link is coupled to an eccentric cam of a control shaft that is supported by an engine block and coupled to a control pin boss by a control pin. The crankpin journal of the lower link is arranged and dimensioned relative to the upper pin such that a projection area defined by projecting the width of the upper pin along a direction line passing through a center of the piston pin and a center of the upper pin does not obscure an area defined by the crankpin during operation of the crankshaft as viewed in an axial direction of the crankpin.