Bicycle Drive Unit Planetary Gear Torque Control
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Solution Overview
Problem
Conventional bicycle drive units face a reduction in assisting force and driving efficiency due to variations in crank rotational speed, as motor output torque is insufficient at different rotational speeds.
Innovation Solution
A bicycle drive unit comprising a transmission system with a planetary gear mechanism, one-way clutches, and a controller that adjusts the motor's rotational direction based on crank speed, ensuring consistent torque delivery through multiple gear ratios and directional switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the motor rotational speed is directly proportional to the crank rotational speed, then the transmission structure is simple, but the output torque becomes insufficient and driving efficiency decreases at varying crank speeds
Solution Approach 1:
The patent applies a multi-stage planetary gear mechanism with variable gear ratios that can dynamically adjust the transmission ratio between motor and crank based on operating conditions. This allows the system to maintain optimal torque multiplication across different crank speeds without requiring a complex variable geometry mechanism, thus resolving the contradiction between structural simplicity and torque sufficiency.
Solution Approach 2:
The patent changes the transmission parameter (gear ratio) by using a multi-stage planetary gear system with different gear combinations. By selecting appropriate gear ratios from the planetary gear stages, the system can maintain sufficient output torque across varying crank speeds while keeping the motor size and structure relatively simple.
2Device complexity
If the motor rotational speed is directly proportional to the crank rotational speed, then the transmission structure is simple, but the driving efficiency decreases at varying crank speeds
Solution Approach 1:
The planetary gear mechanism provides dynamic gear ratio adjustment capability that allows the motor to operate in its high-efficiency range across different crank speeds. By selecting appropriate gear ratios, the system minimizes energy losses while maintaining a relatively simple transmission structure.
3Power
If a multi-stage planetary gear mechanism is introduced to maintain torque, then the output torque is sufficient, but the transmission structure becomes complex
Solution Approach 1:
The patent merges multiple planetary gear stages into a compact integrated transmission unit. By combining the gear stages and sharing common components (such as sun gears, planet carriers, and ring gears), the system achieves sufficient torque multiplication while minimizing the overall structural complexity and component count.
Solution Approach 2:
The multi-stage planetary gear mechanism is arranged in a nested configuration where smaller gear stages are positioned within or alongside larger gear stages. This nesting approach allows the transmission system to achieve high torque multiplication ratios while maintaining a compact and relatively simple overall structure.
Data Source
AI summary
A bicycle drive unit basically has a transmission, a motor and a resultant force member. The motor is configured to transmit rotation to the transmission, and a resultant force member to which rotation from the transmission and from the manual drive force is transmitted. The transmission has a first sun gear, a second sun gear, a first ring gear, a second ring gear, a first planetary gear, a second planetary gear and a third planetary gear. The first, second and third planetary gears are separate individual gears. The first planetary gear is engaged with the first sun gear and the first ring gear. The second planetary gear is engaged with the second sun gear and the third planetary gear. The third planetary gear is engaged with the second planetary gear and the second ring gear.