Flat Plane Crankshaft Rigidity Weight Trade-off
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Solution Overview
Problem
Crankshafts for in-line four cylinder engines face a trade-off between achieving sufficient rigidity to reduce vibrations and minimizing weight to enhance fuel efficiency, as traditional reinforcement methods increase the moment of inertia and weight of the engine.
Innovation Solution
A flat plane crankshaft design with specific configurations of crank journals, pins, and arms, where certain crank arms have reduced widths with counterweights strategically placed to minimize weight while maintaining rigidity, and ratios of arm widths are optimized to balance weight reduction and rigidity preservation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If partial reinforcement is provided to crank arms to suppress torsional vibrations, then rigidity of the crankshaft is improved, but weight of the crankshaft increases
Solution Approach 1:
The patent applies local quality by providing reinforcement only to specific crank arms (second, third, and sixth crank arms) rather than uniformly reinforcing all crank arms. This selective reinforcement targets areas experiencing higher torsional vibrations while leaving other areas with standard dimensions, thereby improving rigidity where needed while minimizing overall weight increase.
Solution Approach 2:
The patent segments the crankshaft into distinct crank arms with different width specifications. By dividing the crankshaft structure into individually optimized segments (crank arms 2-6 with enhanced widths and crank arms 1, 4-7 with standard widths), the design achieves localized rigidity enhancement without uniformly increasing the entire crankshaft's weight.
2Weight of moving object
If crank arms are reduced in weight to decrease rotation moment, then weight of the crankshaft is reduced, but rigidity of the crank arms deteriorates
Solution Approach 1:
The patent implements local quality by assigning different width dimensions to different crank arms based on their specific operational requirements. Crank arms subjected to higher vibration loads (second, third, and sixth) are given increased widths for enhanced rigidity, while other crank arms maintain smaller widths to minimize weight, achieving an optimal balance between weight reduction and rigidity preservation.
Solution Approach 2:
The patent applies parameter changes by varying the width parameter of different crank arms. Specifically, the second, third, and sixth crank arms have widths greater than the standard dimension, while other crank arms use the standard dimension. This parameter variation allows the design to optimize the balance between weight and rigidity for each specific crank arm location.
Data Source
AI summary
A flat plane crankshaft for an in-line four cylinder engine includes eight crank arms. A fourth crank arm and a fifth crank arm are respectively provided with counter weights. Each of a width of the fourth crank arm and a width of the fifth crank arm is configured to be smaller than a width of a second crank arm. Each of a width of the third crank arm and a width of the sixth crank arm is configured to be greater than the width of the second crank arm.