Planetary Bicycle Transmission Layout for Compact Multi-Stage Shifting
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Solution Overview
Problem
Existing transmission devices for human-powered vehicles are large in size, particularly in the axial direction of the shaft member, which poses a challenge for compact design and efficient space utilization.
Innovation Solution
A transmission device comprising a shaft member with overlapping first and second planetary gear units, where carrier pins are arranged perpendicular to the shaft, and planetary gears of varying diameters are strategically positioned to reduce the axial and radial dimensions, along with a mechanism to switch transmission stages in steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple planetary gear units are arranged in series along the shaft member, then transmission stage switching is achieved, but the axial length of the transmission device increases
Solution Approach 1:
The patent transitions from arranging planetary gear units in series along the axial direction to overlapping them in the radial direction. Specifically, the first and second planetary gear units are positioned such that their carrier pins and planetary gears overlap when viewed from the axial direction, effectively utilizing the radial dimension to reduce axial length while maintaining multiple transmission stages
Solution Approach 2:
The patent implements a nested configuration where the first planetary gear unit and second planetary gear unit are positioned to overlap each other radially. The carrier pins and planetary gears of different units are arranged to occupy overlapping radial spaces, creating a compact nested structure that reduces overall axial length
2Ease of manufacture
If planetary gears of uniform diameter are used, then manufacturing is simplified, but the radial size of the transmission device increases
Solution Approach 1:
The patent applies local quality by using planetary gears with different diameters in different positions within the same planetary gear unit. Specifically, among the multiple planetary gears in the first planetary gear unit, at least one has a different diameter from the others, allowing optimized radial packaging and reduced overall radial size while maintaining functional performance
Data Source
AI summary
A transmission device for a human-powered vehicle basically includes a shaft member, a first planetary gear unit, and a second planetary gear unit. The first planetary gear unit includes a first planetary gear, a first carrier including a first carrier pin separate from a second carrier pin and arranged at a distance from the second carrier pin, a first sun gear, and a first ring gear. The second planetary gear unit includes a second planetary gear, a second carrier including the second carrier pin, a second sun gear, and a second ring gear. The first carrier pin and the second carrier pin are arranged overlapping a first plane. A rotational state of at least one of the first sun gear, the second sun gear, the first ring gear, and the second ring gear is controlled to switch the transmission stage in steps.