Rocking Journal Wristpin Offset for Uniflow Opposed-Piston Engines
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Solution Overview
Problem
In two-stroke cycle, opposed-piston engines with phased crankshafts, the existing rocking journal bearings face issues with uneven oil film thickness due to synchronized load transfer points, leading to increased friction, wear, and potential bearing failure, especially during the power stroke when exhaust piston segments experience higher loading and lower oil film thickness.
Innovation Solution
Introducing a load transfer point offset for rocking journal bearings, where the exhaust piston's load transfer point is angularly offset relative to the intake piston's, ensuring adequate oil film thickness during peak combustion pressure by shifting the loading regime to later in the crankshaft cycle, thus balancing the minimum oil film thickness across all segments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If synchronized load transfer points are used in rocking journal bearings, then the bearing structure is simple and easy to manufacture, but uneven oil film thickness occurs leading to increased friction, wear, and potential bearing failure
Solution Approach 1:
The patent applies asymmetry by offsetting the load transfer point of the exhaust piston rocking journal bearing relative to the intake piston bearing. This asymmetric configuration ensures that the exhaust piston segments experience load transfer at a different crankshaft angle, allowing adequate oil film thickness to be maintained during peak combustion pressure while keeping the bearing structure relatively simple
2Reliability
If load transfer point offset is introduced to balance oil film thickness, then bearing reliability improves, but bearing structure complexity increases
Solution Approach 1:
The patent applies local quality by implementing the load transfer point offset specifically in the exhaust piston rocking journal bearing, while the intake piston bearing maintains its conventional synchronized configuration. This localized modification addresses the critical oil film thickness issue in the exhaust bearing without unnecessarily complicating the intake bearing structure
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 offset ensures balanced minimum oil film thickness across all segments, reducing friction and wear, and preventing premature bearing failure by aligning the load transfer with the cyclic peak load, enhancing the operational efficiency and longevity of the rocking journal bearings.
Implementation Method 1
ensuring adequate oil film thickness during peak combustion pressure by shifting the loading regime to later in the crankshaft cycle
Implementation Method 2
reducing friction and wear, and preventing premature bearing failure
Data Source
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AI summary
Load transfer point offset of rocking journal bearings in uniflow-scavenged, opposed-piston engines with phased crankshafts includes differing offsets for the load transfer points of opposed pistons. More specifically, under the condition that a first crankshaft leads the second crankshaft, an angular offset of a rocking journal wristpin of a piston coupled to the first crankshaft proportional to an offset of the first crankshaft relative to the second crankshaft is made to ensure adequate oil film thickness to the wristpin when it experiences a peak combustion pressure during a power stroke