Angled Fracture-Split Bearing Caps for Crankcase Fatigue Reduction
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Solution Overview
Problem
Existing engine crankcase designs face challenges in reducing fatigue stresses in crankcase web areas above fracture-split crankshaft bearing caps without altering the basic crankcase dimensions, as the use of horizontal split lines limits the formation of larger stress-reducing radii.
Innovation Solution
The crankshaft bearing cap split lines are angled downward from the horizontal plane to allow for larger radii in the crankcase support webs, achieved by controlling the shape and direction of the crack path during the fracture-splitting process using a precision mandrel, which reduces stress concentration in high-stress areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If horizontal split lines are used for bearing caps, then manufacturing simplicity is maintained, but fatigue stress levels in crankcase web members increase due to limited radius formation
Solution Approach 1:
The patent applies asymmetry by changing the bearing cap split line from a horizontal configuration to an angled configuration. The split line now angles downward from the horizontal plane, creating an asymmetric geometry that allows for larger radii in the crankcase support webs. This asymmetric design reduces stress concentration at the web-sidewall junctions while maintaining manufacturing feasibility through controlled fracture splitting processes.
2Strength
If larger radii are formed in support webs to reduce stress concentration, then fatigue strength is improved, but the basic crankcase dimensions must be changed
Solution Approach 1:
The patent resolves this contradiction by introducing a dimensional change in the orientation of the bearing cap split line. By angling the split line downward from the horizontal plane, the design creates additional spatial room within the existing crankcase envelope to form larger radii in the support webs. This dimensional reconfiguration allows stress reduction without increasing the overall crankcase dimensions.
3Strength
If the bearing cap split line is angled downward, then larger radii can be formed to reduce stress, but manufacturing precision requirements increase for crack path control
Solution Approach 1:
The patent applies preliminary action by pre-configuring the fracture splitting process to achieve the desired angled crack path. Notches are created in the horizontal plane at the inside bearing bore diameter 180 degrees apart, serving as predetermined crack initiators. The expanding mandrel is designed with specific contact point geometries that guide the crack propagation at the desired angle, ensuring consistent and controlled crack paths without requiring post-processing adjustments.
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 approach effectively reduces fatigue stress levels in the crankcase web members, enabling them to carry higher loads without significant changes to the crankcase dimensions, by creating a stronger cross-section with a larger radius at the junction of web and outer wall connections.
Implementation Method 1
The bearing caps are then fracture-split from the cast assembly by an expanding mandrel inserted through the main bearing bore from one end of the block
Implementation Method 2
Two notches are created in the horizontal plane at the inside bearing bore diameter 180 degrees apart. These serve as crack initiators for the fracture splitting process
Data Source
AI summary
The present invention provides reduced fatigue stress levels in a stressed area of an engine crankcase by lowering the outer edges of the crankshaft bearing cap fracture-split lines without changing the central axis location of the crankshaft in the crankcase. This is accomplished by causing the fracture-split lines of the bearing caps to angle downward from the horizontal plane of the crankshaft axis to a slightly lower position at the outer edges of the bearing caps. This lowers the outer edges of the bearing caps sufficiently to allow larger radii to be formed on the lateral connectors of the crankcase support webs with the adjacent sidewalls of the crankcase. Accordingly, the fatigue stress levels in the crankcase web members are reduced without requiring a significant change in the crankcase dimensions.