Piston Skirt Concave Profile for Thrust Load Distribution
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Solution Overview
Problem
Pistons in engines experience non-uniform thermal expansion and rigidity, leading to stress concentrations, friction, and potential scuffing of the cylinder wall due to thermal expansion and rocking motions, which results in efficiency loss and possible seizure.
Innovation Solution
A piston design with a skirt portion featuring a lower skirt profile, an intermediate skirt profile with concave curvature, and an upper skirt profile, which provides a more uniform load distribution and reduces rocking angle, focusing thrust reaction forces to minimize scuffing and improve guidance within the cylinder bore.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the piston outer radius is increased to improve guidance and reduce rocking, then the piston stability improves, but the friction and contact force with the bore wall increases causing potential seizure
Solution Approach 1:
The piston skirt is designed with non-uniform thickness distribution, making it thinner at the lower portion and thicker at the upper portion. This local variation in geometry allows the lower skirt to have greater flexibility for guidance while the upper skirt provides structural strength, resolving the contradiction between stability and friction.
Solution Approach 2:
The invention changes the geometric parameters of the piston skirt by introducing a concave curvature in the intermediate skirt profile and varying the skirt thickness axially. These parameter changes optimize the balance between guidance stability and friction reduction, allowing the piston to maintain proper alignment without excessive contact force.
2Loss of energy
If the piston outer radius is decreased to reduce friction, then the friction loss decreases, but the piston guidance deteriorates causing excessive rocking and vibration
Solution Approach 1:
The differential skirt thickness design allows the lower portion to be more flexible for reduced friction while the upper portion maintains structural integrity for guidance. This local quality variation enables the piston to achieve both low friction and stable guidance simultaneously.
3Ease of manufacture
If the piston skirt is made uniformly thick to simplify manufacturing, then the manufacturing ease improves, but the thermal expansion uniformity deteriorates causing stress concentrations
Solution Approach 1:
The piston skirt employs non-uniform thickness distribution with a concave curvature profile, creating local variations in mass and thermal capacity. This design accepts increased manufacturing complexity in exchange for uniform thermal expansion characteristics, preventing stress concentrations that would occur with uniform thickness.
4Productivity
If the clearance between piston and cylinder wall is reduced to improve efficiency, then the engine efficiency improves, but the risk of scuffing and seizure increases
Solution Approach 1:
The invention optimizes the clearance parameters by designing the piston skirt with concave curvature and variable thickness. This parameter optimization allows smaller clearances for improved efficiency while the flexible lower skirt compensates for thermal expansion and loading variations, preventing scuffing and seizure.
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 enhances piston guidance, reduces friction, and allows for smaller clearance gaps between the piston and cylinder wall, improving engine performance and efficiency by distributing thrust loads uniformly and reducing the likelihood of scuffing.
Implementation Method 1
the piston may have non-uniform thermal expansion and non-uniform rigidity
Implementation Method 2
the piston may include a skirt that is shaped to bear against the cylinder wall (with a hydrodynamic layer therebetween to provide lubrication) as the piston is reciprocated in the cylinder bore
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The invention relates to an internal combustion engine, comprising at least one wall (210) defining a bore (205); and a piston (300) disposed in the bore (205) and coupled to a piston rod (102) to pivot about a pivot axis (305), the piston comprising a substantially circumferential outer surface having a head-portion (310) and a skirt profile line (320) below the head portion (310), at least a portion of the outer surface bearing against the wall (210) in a thrust plane when the piston (300) is substantially at operating temperature and subject to a thrust force (T), the portion of the thrust force (T) borne by the skirt profile line (320) in the thrust plane is definable by a skirt force centroid (R 1 ), the skirt force centroid (R 1 ) being positioned at an axial height at or below the pivot axis (305), wherein the head portion (310) of the outer surface has radii that are larger than at least some of the radii of the skirt profile line (320) of the outer surface when the piston is substantially at operating temperature.