Piston Assembly Offset Tight Land Profile
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Solution Overview
Problem
Internal combustion engines face efficiency reduction and increased hydrocarbon emissions due to unburned fuel trapped in the crevice volume between the piston lands and cylinder liner, leading to carbon deposits that cause wear and maintenance issues.
Innovation Solution
A piston assembly with an offset tight land profile about the top and/or second land, reducing clearance and minimizing wear and carbon deposits by controlling temperature and residence time, and using a Fourier series to model the geometry for precise clearance management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the top land height is reduced to decrease crevice volume, then hydrocarbon emissions are reduced, but top ring groove temperatures increase causing ring groove deposits
Solution Approach 1:
The patent applies asymmetry by implementing different land heights on opposite sides of the piston. The first land has a height between 0.020-0.040 inches while the second land has a height between 0.040-0.060 inches. This asymmetric configuration allows the piston to maintain tight clearances on the thrust side to reduce crevice volume and hydrocarbon emissions, while providing sufficient land height on the antithrust side to manage temperatures and prevent ring groove deposits.
Solution Approach 2:
The patent applies local quality by creating zone-specific land heights tailored to local conditions. The thrust side (first land) receives a tighter clearance design to minimize crevice volume where hydrocarbon trapping is most problematic, while the antithrust side (second land) receives a larger clearance to accommodate thermal expansion and prevent excessive temperatures. This localized optimization resolves the contradiction between emission reduction and temperature management.
2Object-generated harmful factors
If a tight land profile is implemented to reduce crevice volume, then hydrocarbon emissions decrease, but carbon deposits increase causing wear and polishing of cylinder liners
Solution Approach 1:
The asymmetric land height configuration resolves this contradiction by applying tight clearances selectively on the thrust side where crevice volume reduction is most critical for emission control, while maintaining larger clearances on the antithrust side where thermal conditions would otherwise promote carbon deposit formation and liner wear.
Solution Approach 2:
The patent implements local quality optimization by tailoring land heights to specific zones: the first land on the thrust side uses tighter clearances to minimize hydrocarbon trapping, while the second land on the antithrust side uses larger clearances to manage thermal conditions and prevent carbon deposits. This localized approach simultaneously addresses emission reduction and wear prevention.
3Manufacturing precision
If uniform tight clearances are applied to all lands, then manufacturing precision is improved, but the piston cannot accommodate thermal expansion and secondary motion variations
Solution Approach 1:
The patent deliberately introduces asymmetry in land heights to resolve the contradiction between manufacturing precision and thermal adaptability. By specifying different height ranges for the first land (0.020-0.040 inches) and second land (0.040-0.060 inches), the design maintains precise control over clearances while accommodating thermal expansion and secondary motion variations through the intentional non-uniform configuration.
Solution Approach 2:
The asymmetric land height design applies local quality by optimizing clearance characteristics for specific zones based on their operational requirements. The thrust side land is designed with tighter tolerances for precision, while the antithrust side land is designed with larger dimensions for thermal accommodation, resolving the contradiction between uniform manufacturing precision and adaptive performance.
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 offset tight land profile effectively reduces hydrocarbon emissions, minimizes wear, and extends engine longevity by maintaining tight clearances and reducing carbon deposits, enabling engines to meet emissions targets and reduce maintenance costs.
Implementation Method 1
Piston temperatures may be reduced with a tight land profile because heat conduction out of the piston to the cylinder bore has been enabled and because the heat flux into the land has been reduced.
Implementation Method 2
Another reason for the cleanliness of the tight land profile is because the oil which is on the land and in the ring groove is being constantly replenished with a fresh supply of oil between the land and the liner due to the tight clearances.
Data Source
AI summary
The present application provides a piston assembly. The piston assembly may include a cylinder bore extending from a thrust side to an antithrust side and a piston positioned within the cylinder bore. The piston may include a top land, a second land, and a skirt with an axis extending therethrough. The piston may include a tight land profile with an offset about the axis of the skirt.