Power Unit Shift Lever Layout for Lower Center of Gravity
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Solution Overview
Problem
Conventional power units with shift drum type transmissions lack layout flexibility for the gear change mechanism, which restricts the ability to position components below the crankcase, limiting the reduction of the center of gravity and increasing the length of the link mechanism.
Innovation Solution
The power unit incorporates a shift drum with a rotation plate having recessed portions, a shift lever, a stopper lever, and an elastic member, allowing the shift lever and stopper lever to be positioned below the crankcase frame when the shift shaft is in the second rotational position, thereby increasing layout flexibility and reducing the center of gravity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gear change mechanism is located above the lower wall of the crankcase to prevent contact during shift lever rotation, then the reliability is improved, but the layout flexibility deteriorates
Solution Approach 1:
The patent allows the shift lever and stopper lever to extend into the oil pan space below the crankcase frame portion, utilizing the vertical dimension to resolve the spatial conflict. This enables the gear change mechanism to be positioned lower while maintaining operational clearance, thereby improving layout flexibility without compromising reliability
2Stability of the object's composition
If the gear change mechanism is positioned lower to reduce center of gravity, then the stability is improved, but the risk of contact between shift lever and crankcase increases
Solution Approach 1:
The patent divides the crankcase into two functional zones: the frame portion above the oil pan that maintains structural integrity, and the oil pan space below that accommodates the shift lever and stopper lever during operation. This segmentation allows the gear change mechanism to be positioned lower for improved stability while preventing contact through spatial separation
Solution Approach 2:
The shift lever and stopper lever are designed to rotate within the vertical space below the frame portion, utilizing the depth dimension of the oil pan. This dimensional approach allows lower positioning for stability while maintaining operational clearance from the crankcase frame
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 configuration allows for a lower center of gravity and increased flexibility in the gear change mechanism layout, while maintaining the structural rigidity of the crankcase and optimizing the use of space within the oil pan.
Implementation Method 1
an elastic member configured to engage with the stopper lever, so as to apply a force to the stopper lever to thereby press the stopper roller against the one recessed portion
Data Source
AI summary
A power unit includes: a crankcase 24 that houses a shift drum 50, a shift lever 66, at least a portion of a shift shaft 74, and a stopper lever 78; and an oil pan 28 disposed under a lower crankcase 26. The lower crankcase 26 includes a frame portion 26F which is located above the oil pan 28 and to which a cover 29 is attached when viewed in an axial direction of the shift shaft 74. The shift lever 66 is disposed so that when the shift shaft 74 is located at a second rotational position, a portion of a second arm 70 of the shift lever 66 is located lower than the frame portion 26F of the lower crankcase 26 and inside the oil pan 28 as viewed in the axial direction of the shift shaft 74.