Multi-Part Opposed-Piston Structure for Low-Friction Ring Belt Support
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Solution Overview
Problem
Existing piston constructions for two-stroke opposed-piston engines face challenges in achieving a balance between minimizing piston/bore friction and maintaining engine performance, as the thickness of the skirt wall affects engine efficiency and manufacturability, particularly in forming a second ring belt region without increasing the piston's mass or requiring additional machining.
Innovation Solution
A multi-part piston design is implemented, where a crown part with a first circumferential ring belt region is joined to a skirt part with a sidewall and an outer part having a second circumferential ring belt region, using multiple weld seams to achieve a thin or thick skirt wall configuration while supporting an outer ring belt region, allowing for improved friction reduction and manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the skirt wall thickness is increased to support the second ring belt region, then the structural strength and manufacturability are improved, but the piston mass increases and friction with the bore surface increases
Solution Approach 1:
The piston is divided into multiple segments including the crown, skirt, and separate ring belt regions. The second ring belt region is formed as a distinct structural feature on the skirt part, allowing the skirt wall to be thin in non-critical areas while providing localized thickness and strength where the ring belts are positioned. This segmentation enables the piston to maintain structural integrity for supporting ring belts without uniformly increasing wall thickness throughout the entire skirt, thereby minimizing overall piston mass.
2Strength
If the skirt wall thickness is increased to support the second ring belt region, then the structural strength is improved, but the friction with the bore surface increases
Solution Approach 1:
The skirt part is designed with non-uniform wall thickness distribution, featuring localized thickening specifically at the regions where the second ring belt is positioned. This local quality approach ensures that the skirt wall provides sufficient strength and support exactly where the ring belts require it, while maintaining thinner wall sections in areas that contact the bore surface. Consequently, the piston achieves the necessary structural strength for ring belt support without increasing friction in the bore contact zones.
3Manufacturing precision
If additional machining is performed to form the second ring belt region, then the manufacturing precision is improved, but the productivity decreases and manufacturing complexity increases
Solution Approach 1:
The second ring belt region is formed during the initial forging or casting process of the skirt part, rather than requiring subsequent machining operations. This preliminary action integrates the formation of the ring belt region into the primary manufacturing step, ensuring precise dimensional accuracy and proper geometric configuration are achieved upfront. By pre-forming the ring belt region with the required precision during manufacturing, the need for additional time-consuming machining operations is eliminated, thereby maintaining high productivity and manufacturing efficiency.
4Weight of moving object
If the skirt wall is made thin to reduce mass, then the piston mass is reduced, but the ability to support the second ring belt region is compromised
Solution Approach 1:
The second ring belt region is nested within the skirt part structure, with the ring belt grooves and supporting features integrated into the skirt wall geometry. This nesting allows the thin skirt wall to provide adequate support for the ring belts by utilizing the nested configuration where the ring belt features are positioned within recesses or designated zones of the skirt. The nested design ensures that even with reduced overall wall thickness, the local structural support required for the second ring belt is maintained through the integrated geometry.
Data Source
AI summary
A piston for an internal combustion opposed-piston engine includes a crown part, a skirt part, and an outer part. The crown part includes a first ring belt region for supporting compression rings and an end surface shaped to form a combustion chamber with an end surface of an opposing piston. The skirt part includes a sidewall and a wristpin bore with a first opening and a second opening formed in the sidewall. The outer part includes a second ring belt region for supporting oil control rings. The crown part is joined to an upper end of the sidewall with one or more welding seams. The outer part is joined to a lower end of the sidewall with a welding seam.