Piston Skirt Dimples for Friction Reduction
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Solution Overview
Problem
The existing piston skirt coatings wear out and fail to maintain a consistent frictional property due to non-uniform surface pressure and high load areas, leading to increased frictional resistance and wear.
Innovation Solution
A piston design with resin-coated skirts featuring dimples in high-load areas and an oil ejection system to maintain lubrication, where the dimples act as reservoirs for lubricating oil and the oil ejection holes ensure efficient lubrication and reduced wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a resin coating layer is deposited on the skirt surface to reduce friction, then frictional resistance is reduced, but the resin coating wears out and peels off in high surface pressure areas
Solution Approach 1:
The invention applies different surface treatments to different areas of the skirt based on local pressure conditions. The high-pressure area receives a resin coating for friction reduction, while the medium-pressure area receives protrusions for oil retention. This localized differentiation allows each area to have the appropriate surface property for its specific operating conditions, preventing coating failure in high-pressure zones while maintaining lubrication where needed.
Solution Approach 2:
The skirt surface is divided into multiple functional zones: a high-pressure area with resin coating, a medium-pressure area with protrusions containing lubricating oil, and a low-pressure area. This segmentation allows each zone to address specific lubrication challenges independently, with the protrusions acting as reservoirs that supplement lubrication in areas where the resin coating alone is insufficient.
2Reliability
If recesses are formed in the skirt to retain lubricating oil, then lubrication is improved in recess areas, but oil film cannot be maintained in parts outside the recesses
Solution Approach 1:
The invention transitions from two-dimensional recesses to three-dimensional protrusions that extend toward the resin coating layer. These protrusions create oil reservoirs that actively supply lubricating oil to the resin coating surface, ensuring continuous oil film formation not only within the reservoir areas but also across the broader high-pressure zone where the resin coating is applied.
Solution Approach 2:
The protrusions are pre-filled with lubricating oil during the manufacturing process, creating a ready supply of lubricant before the piston begins operation. This preliminary preparation ensures that when the piston enters high-pressure conditions, the lubricating oil is already in position to form protective films on the resin coating surface, preventing direct metal-to-metal contact from the outset.
3Object-affected harmful factors
If the resin coating covers the entire skirt surface, then frictional property is improved uniformly, but wear and peeling occur in high load areas
Solution Approach 1:
The resin coating is applied selectively only to the high-pressure area where friction reduction is most critical, rather than covering the entire skirt surface. This localized application concentrates the friction-reducing benefits where they are most needed while avoiding the wear and peeling problems that occur when resin coating is applied to areas with different pressure conditions.
Solution Approach 2:
The protrusions filled with lubricating oil act as intermediary elements between the skirt structure and the resin coating. They provide a supplemental lubrication mechanism that protects the resin coating in high-load areas, reducing the mechanical stress and wear that would otherwise cause the coating to fail, thereby extending the service life of the resin coating in critical zones.
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
The design reduces frictional resistance and extends the durability of the resin coating by maintaining adequate lubrication in high-pressure areas and minimizing direct contact between the resin coating and the cylinder wall, thereby enhancing the overall lubrication and wear resistance.
Implementation Method 1
a plurality of dimples are formed in a part of the resin coating that receives a relatively large load from an inner cylinder wall
Implementation Method 2
a resin coating deposited on an outer surface of each skirt; The design reduces frictional resistance and extends the durability of the resin coating by maintaining adequate lubrication in high-pressure areas
Data Source
AI summary
To provide a piston for an internal combustion engine including a skirt which causes a relatively small frictional resistance and can maintain a favorable frictional property over an extended period of time. In a piston for an internal combustion engine having a skirt 4 on whose sliding surface a resin coating layer is deposited, the skirt 4 comprises a thin walled portion 51 located in a circumferentially middle part thereof and a pair of thick walled portions 52 provided on either lateral side of the thin walled portion 51. The resin coating layer 44 at least in the part thereof deposited on the thick walled portions 52 is formed with a plurality of dimples 45. The skirt may comprise a skirt main body 41 extending axially at a fixed distance from the central axial line of the piston in an axially middle part thereof, and a first reduced diameter portion 42 depending from the lower end of the skirt main body and having a progressively smaller diameter toward a lower end thereof. The dimples 45 may be arranged along a first boundary 6 between the skirt main body and first reduced diameter portion.