Asymmetric Crank Arm Design for Flexural Rigidity
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Solution Overview
Problem
Existing crankshaft designs do not adequately address the maximum combustion pressure applied to crank arms at angles between 8 to 20 degrees, leading to insufficient flexural rigidity and weight reduction.
Innovation Solution
The design of asymmetric crank arms with varying thickness and width configurations relative to the crank arm centerline, optimizing flexural rigidity and weight reduction by maximizing area moments of inertia and thickness in the direction of maximum load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crank arms are designed with conventional symmetric shape, then manufacturing is simplified, but flexural rigidity under maximum combustion pressure is insufficient
Solution Approach 1:
The patent applies asymmetry by designing the crank arm with different thicknesses on either side of the centerline. The first thickness (t1) on the compression side is greater than the second thickness (t2) on the expansion side, creating an asymmetric cross-section that optimizes flexural rigidity under combustion pressure while maintaining manufacturing feasibility through controlled asymmetric geometry
Solution Approach 2:
The patent applies local quality by varying the thickness distribution along the crank arm length and across the cross-section. The thickness is optimized locally at different positions - greater thickness where bending moments are highest - rather than using uniform thickness throughout, thereby achieving superior flexural rigidity with minimal material
2Strength
If crank arm thickness is increased to improve flexural rigidity, then strength under combustion pressure improves, but weight increases
Solution Approach 1:
The patent applies local quality by varying the thickness distribution along the crank arm length and across the cross-section. The thickness is optimized locally at different positions - greater thickness where bending moments are highest - rather than using uniform thickness throughout, thereby achieving superior flexural rigidity with minimal material
Solution Approach 2:
The patent applies preliminary action by performing finite element analysis and optimization calculations before manufacturing to determine the optimal asymmetric thickness distribution. This preliminary design phase identifies the precise thickness values (t1 and t2) that achieve target flexural rigidity while minimizing weight, avoiding trial-and-error manufacturing
3Strength
If crank arms are designed to optimize flexural rigidity at maximum combustion pressure, then performance under load improves, but design complexity increases
Solution Approach 1:
The patent applies preliminary action by performing finite element analysis and optimization calculations before manufacturing to determine the optimal asymmetric thickness distribution. This preliminary design phase identifies the precise thickness values (t1 and t2) that achieve target flexural rigidity while minimizing weight, avoiding trial-and-error manufacturing
Solution Approach 2:
The patent applies parameter changes by systematically varying the thickness parameters (t1 and t2) through optimization analysis to find the optimal values that maximize flexural rigidity. The design transitions from conventional equal thickness to optimized asymmetric thickness by changing the geometric parameters based on load analysis
Data Source
Figure 1~2
Figure 3~4(b)
Figure 5(a)~5(b)
AI summary
Each of Crank arms (A) of a crankshaft has an asymmetric shape with respect to a crank arm centerline (Ac) connecting an axis of the crank pin (P) to an axis of the journal (J), and each of the crank arms has a maximum flexural rigidity at a point of time when the load onto the crank pin due to the combustion pressure reaches a maximum. When each of the crank arms (A) is divided by the crank arm centerline (Ac) into a right arm portion (Ar) and a left arm portion (Af), in each section of each of the crank arms (A) on a plane perpendicular to the crank arm centerline (Ac) at a position outward of the axis of the crank pin (P), an area moment of inertia of one of the right and the left arm portions that is in a side that is subjected to the maximum load is greater than an area moment of inertia of the other arm portion that is in a side opposite to the side that is subjected to the maximum load, and in each section of each of the crank arms (A) on a plane perpendicular to the crank arm centerline at a position inward of the axis of the crank pin (P), the area moment of inertia of the arm portion that is in the side opposite to the side that is subjected to the maximum load is greater than the area moment of inertia of the arm portion that is in the side that is subjected to the maximum load. The crankshaft has an increased flexural rigidity and a reduced weight.