Multi-link Piston Crank Mechanism with Differential Surface Roughness
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Solution Overview
Problem
Conventional multi-link piston crank mechanisms for internal combustion engines face issues with shifting and shearing stress in the lower link members, leading to bolt breakage, and existing solutions do not adequately analyze the correlation between shifting and friction coefficient, resulting in high manufacturing costs due to excessive machining.
Innovation Solution
The mechanism differentiates the surface roughness of the mating surfaces in the lower link, with a rougher first mating surface and a smoother second mating surface, reducing machining complexity and cost by selectively applying grinding techniques to only the first surface to suppress shifting effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If machining is performed to the whole mating surface of the lower link to increase friction coefficient, then shifting of lower link members is suppressed, but manufacturing cost increases due to use of expensive tools and extensive machining range
Solution Approach 1:
The patent applies different surface roughness treatments to different regions of the mating surface. Specifically, the first mating surface (where shifting is more likely to occur) is given a larger surface roughness value through machining, while the second mating surface maintains a smaller surface roughness value. This local differentiation allows targeted friction enhancement where needed, avoiding unnecessary machining costs across the entire surface.
Solution Approach 2:
Instead of performing machining across the entire mating surface, the patent applies machining only to the first mating surface where shifting is more likely to occur. This partial action approach provides sufficient friction enhancement for reliability while reducing the overall machining range and associated costs.
2Reliability
If uniform machining is performed to the whole mating surface, then shifting is suppressed across all areas, but the correlation between shifting and friction coefficient is not sufficiently analyzed, leading to excessive machining
Solution Approach 1:
The patent divides the mating surface into two distinct regions with different surface roughness requirements. The first mating surface receives machining treatment to achieve larger surface roughness for shifting suppression, while the second mating surface maintains smaller surface roughness. This local quality differentiation reduces overall machining complexity by avoiding uniform treatment of the entire surface.
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 effectively reduces shifting and shearing stress, lowers manufacturing costs by simplifying machining, and extends tool life by minimizing unnecessary machining, thereby enhancing the durability and cost-effectiveness of the lower link.
Implementation Method 1
the friction coefficient of the mating surface of the lower link... the shifting of a pair of the lower link members along the mating surface... by increasing a friction coefficient by performing machining to the mating surface
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A lower link (7) is formed of two components by being divided at a dividing surface (14) including the central axis of a crank pin bearing portion (11), the two components including a lower link upper (15) with an upper pin bearing portion (12) and a lower link lower (16) with a control pin bearing portion (13). The dividing surface (14) includes a first dividing surface (14a) located more on the upper link side than the crank pin bearing portion (11) and a second dividing surface (14b) located more on the control link side than the crank pin bearing portion (11). In the lower link (7), the first dividing surface (14a) has a surface roughness larger than a surface roughness of the second dividing surface (14b).