Nested Piston Design Eliminates Head Joints
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Solution Overview
Problem
Multi-piece pistons for internal combustion engines typically have joints or gaps in critical areas like the piston rings or skirt, leading to thermal and mechanical stress, and existing designs often result in a joint in the piston head, which is subjected to high stress.
Innovation Solution
A two-piece piston design where the piston outer part forms the entire outer surface, with the piston inner part radially arranged inside, creating a joint-free configuration that positions the parting line outside critical areas, allowing for a secure and compact geometry with enhanced sliding characteristics and material efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-piece piston is designed with separate piston top part and piston bottom part, then manufacturing flexibility and material selection freedom are improved, but a joint or gap is created in critical areas (piston rings, piston skirt, piston head) which reduces reliability and increases stress concentration
Solution Approach 1:
The piston top part is nested within the piston bottom part, with the piston top part inserted into a cavity of the piston bottom part. This nesting arrangement allows the joint to be positioned in a non-critical area rather than creating a gap in critical regions like the piston rings or piston skirt, thereby maintaining reliability while preserving manufacturing flexibility
Solution Approach 2:
The joint is repositioned from a radial or axial gap in critical areas to a position in the axial direction within the piston body cavity. By changing the dimensional arrangement of the joint location, the design achieves material selection freedom without compromising the integrity of critical combustion chamber areas
2Device complexity
If a joint is provided in the piston head area, then multi-piece construction flexibility is improved, but the area is subjected to particularly high thermal and mechanical stresses which worsens durability
Solution Approach 1:
The joint is extracted from the critical piston head area and repositioned to a non-critical location within the piston body. The piston top part containing the joint is inserted into a cavity of the piston bottom part, removing the stress concentration issue from the high-thermal-stress piston head region while maintaining the benefits of multi-piece construction
3Ease of operation
If a joint or gap is created between piston ring portion and piston skirt, then assembly flexibility is improved, but sliding characteristics and sealing performance are worsened
Solution Approach 1:
The piston top part is nested within the piston bottom part, eliminating radial gaps between piston ring portion and piston skirt. This nesting configuration maintains continuous outer surfaces for optimal sliding characteristics and sealing performance while preserving assembly flexibility through the insertable joint design
Data Source
AI summary
The present invention relates to a multi-piece, in particular at least two-piece, piston (1) for an internal combustion engine having a longitudinal axis (L), comprising a piston outer part (10) having a closed piston head (11), which in the fitted state defines a combustion chamber, and a piston body (13) extending axially away from the piston head (11), and a piston inner part (20), which in the fitted state is connected to a connecting rod. An outer surface (2) radially defining the piston (1) is formed exclusively by at least one portion of the piston body (13) of the piston outer part (10). The piston inner part (20), viewed in an axial direction, is arranged radially entirely inside the piston body (13) or its circumferential surface.