Cylinder Bore Recess Geometry for Piston Ring Lubrication
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Solution Overview
Problem
Internal combustion engines face challenges in minimizing friction between piston rings and cylinder liners due to varying operational parameters and surface asperities, leading to inefficiencies and wear, particularly at the extremes of piston stroke where hydrodynamic lubrication is difficult to maintain.
Innovation Solution
The engine design incorporates a bore portion with axially spaced recesses that vary in width and depth along the piston stroke, increasing in volume towards the top-dead center and bottom-dead center positions, creating a full film lubrication zone at the mid-stroke and mixed film lubrication zones elsewhere, to optimize lubrication and reduce friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piston operates at low relative speed at the extremes of stroke, then hydrodynamic lubrication becomes difficult to maintain, but friction increases due to boundary contacts and surface asperities
Solution Approach 1:
The patent applies local quality by creating recesses with specific geometric characteristics (depth, width, spacing) at specific axial positions along the cylinder bore. The recesses are strategically positioned and dimensioned to provide enhanced lubrication precisely where the piston speed is lowest (at the extremes of stroke), rather than uniformly across the entire bore. This localized modification addresses the specific lubrication challenge at low-speed regions without affecting other areas of the bore.
Solution Approach 2:
The recesses are designed to pre-position lubricant at the piston-cylinder interface before the piston reaches the extreme positions where lubrication is most critical. By having lubricant already present in the recesses at the start of the low-speed region, the system prepares for the impending lubrication challenge, ensuring that boundary contacts and surface asperities are minimized even when hydrodynamic lubrication cannot be maintained.
2Object-affected harmful factors
If recesses are added to the bore portion to enhance lubrication, then friction is reduced, but the device complexity increases
Solution Approach 1:
The lubrication enhancement is achieved by segmenting the bore surface into multiple discrete recesses rather than using a single continuous modification. Each recess is an independent feature that can be precisely controlled in terms of depth, width, and axial position. This segmentation allows the complex lubrication requirements at different axial positions to be addressed by individual recesses with optimized geometries, making the overall solution manageable and manufacturable.
Solution Approach 2:
The patent employs parameter changes by systematically varying the geometric parameters of the recesses (depth, width, axial spacing, circumferential distribution) along the axial length of the bore. These parameter variations are tailored to match the local lubrication conditions at different piston positions, with deeper recesses positioned at axial locations corresponding to low-speed regions. This parametric approach provides a controlled way to increase functional complexity while maintaining manufacturing feasibility.
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
This design effectively reduces frictional losses and wear by maintaining optimal lubrication regimes throughout the piston stroke, enhancing engine efficiency and reducing emissions.
Implementation Method 1
Lubricated sliding contacts, such as between piston rings of the piston and an inner surface of the cylinder bore, may experience frictional losses due to the shear forces generated in the lubricant
Data Source
AI summary
Methods and systems are provided for a bore. In one example, a system includes a bore portion for receiving a reciprocating piston, the bore portion having first and second ends between which the piston travels in an axial direction. The bore portion comprises a plurality of recesses, axially spaced apart, and formed in a piston facing surface of the bore portion at a plurality of axial positions, with at least one recess being provided at each axial position. Widths of the plurality of recesses decrease in the axial direction away from a mid-stroke position toward the first and second ends, and depths of the plurality of recesses increase in the axial direction away from the mid-stroke position toward the first and second ends.