Crankshaft Gear Positioning for Engine Weight Reduction
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Solution Overview
Problem
In engines with two-plane type crankshafts, the conventional placement of the gear for engagement with the balancer shaft at the center increases the crankshaft length and weight, making it difficult to achieve weight reduction while ensuring high reliability due to increased torsional resonance forces.
Innovation Solution
The gear for engagement with the balancer shaft is positioned further outward than the first crank web in the vehicle width direction, reducing the crankshaft length and weight, and a balancer shaft with a second gear is used to reduce primary force couples, while maintaining high reliability through a two-plane type crankshaft configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the gear for engagement with the balancer shaft is disposed substantially in the center of the crankshaft in the direction of the axial line, then the disposition balance of inertia mass is improved and the rotation speed at which resonance reaches the peak is increased, but the length of the crankshaft is increased, leading to increased weight and increased torsional resonance forces
Solution Approach 1:
The gear is repositioned from a central axial location to an outer peripheral location on the crank web. This spatial relocation changes the dimensional arrangement from axial concentration to radial distribution, allowing the gear to engage the balancer shaft while maintaining a compact crankshaft length and reducing torsional resonance forces.
2Speed
If the gear for engagement with the balancer shaft is disposed substantially in the center of the crankshaft, then the rotation speed at which resonance reaches the peak is increased, but the diameter of the crankshaft must be increased to secure reliability, further increasing weight
Solution Approach 1:
The gear is positioned on the outer periphery of the crank web rather than at the center, which shortens the crankshaft length and reduces torsional resonance forces, thereby maintaining reliability without increasing diameter.
Solution Approach 2:
The gear is specifically positioned on the outer periphery of the first crank web, utilizing the local structural characteristics of that region to achieve engagement with the balancer shaft while optimizing the overall crankshaft dynamics and reducing resonance forces.
3Ease of operation
If the gear for engagement with the balancer shaft is disposed substantially in the center of the crankshaft, then the engagement with the balancer shaft is achieved, but the length of the crankshaft is increased, making weight reduction difficult
Solution Approach 1:
The gear is relocated from the central axial position to the outer periphery of the crank web, changing the spatial arrangement from axial to radial. This allows engagement with the balancer shaft to be achieved while maintaining a compact crankshaft length.
Solution Approach 2:
The gear is formed directly on the outer periphery of the crank web, integrating the engagement function into the existing crank web structure rather than adding a separate central component, thereby avoiding length increase.
Data Source
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AI summary
To implement a weight reduction while securing high reliability in an engine including a two-plane type crankshaft, an engine 20 can include a two-plane type crankshaft 30 and a balancer shaft 50 for reducing a primary force couple. The crankshaft 30 includes a crankshaft body 30a and a first gear 38. The first gear 38 is disposed closer to one end side than a first crank web pair 31a disposed closest to the one end side in an direction of the axial line of the crankshaft 30.