Bicycle Derailleur Motor Gear Unit Self-Locking Planetary Design
Solution Overview
Problem
Conventional electrically-driven gear changing devices for bicycles face issues with gear malfunctions due to large loads on worm gears and worm wheels, leading to wear and requiring larger, stronger components.
Innovation Solution
A bicycle derailleur motor gear unit is designed with a self-lock function using a simple configuration, incorporating an output shaft, fixed and output sun gears, planet gears, and a carrier, where the gear tooth counts and transmission coefficients are set to ensure the planet gears do not rotate or revolve under external force, locking the gears in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a worm gear and worm wheel are used to transmit motor torque to the derailleur, then the derailleur can be operated against large chain tension forces, but the large load causes gear wear and malfunctions, requiring larger and stronger components
Solution Approach 1:
The patent changes the gear configuration parameters by using a planetary gear mechanism with specific tooth count relationships. The fixed sun gear, output sun gear, and planet gears are designed with tooth counts that satisfy specific mathematical relationships, creating a self-locking condition that prevents gear backdrive under load, thereby eliminating wear and malfunction issues while maintaining the ability to operate against large chain tension forces
Solution Approach 2:
The planetary gear mechanism dynamically distributes the large chain tension forces across multiple planet gears simultaneously engaging with the sun gears. This dynamic load distribution reduces the stress on individual gear teeth compared to a single worm gear engagement, improving reliability and preventing gear wear while maintaining the required force transmission capability
2Reliability
If the size and strength of gear components are increased to withstand large loads, then gear reliability improves, but the overall device size and weight increase
Solution Approach 1:
The patent segments the load transmission function across multiple planet gears that simultaneously engage with the fixed sun gear and output sun gear. This segmentation allows the total load to be distributed among several smaller gear components rather than requiring one large, heavy gear, thereby maintaining reliability while reducing overall weight
Solution Approach 2:
The planetary gear mechanism serves multiple functions simultaneously: it transmits motor torque to the derailleur, provides mechanical advantage against chain tension, and creates a self-locking condition to prevent gear backdrive. This multi-functionality eliminates the need for additional separate components, reducing overall device weight while maintaining reliability
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
The solution effectively provides a self-lock function for the bicycle derailleur motor gear unit, preventing gear malfunctions and wear, while maintaining a compact and lightweight design.
Implementation Method 1
a fixed sun gear, an output sun gear, a plurality of planet gears (13), and a carrier (11). The output sun gear (15) is rotatable relative to the fixed sun gear (12)
Implementation Method 2
The fixed sun gear (12), the output sun gear (15), the first gear (13b), and the second gear (13d) have tooth counts, respectively, such that the fixed sun gear (12), the output sun gear (15), the first gear (13b), and the second gear (13d) lock while an external force is exerted to the output sun gear (15)
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
A bicycle derailleur motor gear unit configured to reduce motor speed of a motor and transmit motor torque of the motor to a derailleur is proposed. The bicycle derailleur motor gear unit comprises an output shaft, a fixed sun gear, an output sun gear rotatable relative to the fixed sun gear, the output sun gear being fixedly coupled to the output shaft, a plurality of planet gears, and a carrier rotatably and revolvably supporting the planet gears. Each of the planet gears has a first gear that engages with the fixed sun gear and a second gear that engages with the output sun gear, the first gear and the second gear being coaxially coupled to each other. The fixed sun gear, the output sun gear, the first gear, and the second gear have tooth counts, respectively, such that the fixed sun gear, the output sun gear, the first gear, and the second gear lock while an external force is exerted to the output sun gear.