Fixed-Ratio Bicycle Hub Drivetrain for Smooth Low-Tension Shifting
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Solution Overview
Problem
Bicycles equipped with electric motors experience higher chain tension during shifting due to the motor's continued torque input, leading to potential drive train damage and rough shifting.
Innovation Solution
A bicycle wheel hub and drive train system featuring a non-adjustable gear train with a fixed gear ratio greater than 1:1, which reduces chain tension by increasing the angular velocity of the chain ring relative to the user input component, and a gear reduction mechanism in the rear wheel hub to maintain appropriate wheel speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric motor continues to apply torque during shifting, then the motor provides continuous power assistance, but the chain tension increases causing rough shifting and potential drive train damage
Solution Approach 1:
The control system is configured to anticipate shifting operations and proactively reduce or eliminate motor torque before the shift occurs. This preliminary action prevents high chain tension from developing in the first place, allowing the shift to complete smoothly without damaging the drive train while maintaining continuous power assistance through coordinated motor re-engagement after the shift.
2Ease of operation
If the motor torque is reduced during shifting, then the chain tension decreases improving shift quality, but the continuous power assistance is interrupted
Solution Approach 1:
The control system implements periodic modulation of motor torque during shifting operations, rhythmically reducing torque during the critical shift window and then restoring full power assistance immediately after. This periodic action pattern ensures smooth shifting occurs at the right moment while maintaining continuous overall power support through rapid re-engagement of the motor.
3Force
If a gear reduction mechanism is added to the rear hub, then the chain tension is reduced during shifting, but the device complexity increases
Solution Approach 1:
A gear reduction mechanism is introduced as an intermediary element between the chain and the rear wheel hub. This mediator reduces the force transmission from the chain by providing mechanical advantage through gear ratios, thereby lowering chain tension during shifting operations. The gear train acts as a buffer that protects the drive train from excessive loads while the control system coordinates motor torque to further reduce peak tensions during shifts.
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 system reduces drive train wear, improves shifting speed and smoothness, and prevents damage during shifting by maintaining lower chain tension and appropriate wheel speed, even with motor assistance.
Implementation Method 1
A non-adjustable gear train is coupled between the driver and the shell, wherein the gear train defines a single fixed gear ratio between the driver and the shell. The gear ratio is greater than 1:1 such that the second rotational speed is less than the first rotational speed.
Implementation Method 2
The gear ratio is greater than 1:1 such that the second rotational speed is less than the first rotational speed
Implementation Method 3
A closed loop component connects the chain ring and the gear
Data Source
AI summary
A bicycle wheel hub includes a driver rotatable about an axis at a first rotational speed, wherein the driver includes a mating feature configured to engage a cassette. A shell is rotatable about the axis at a second rotational speed. A non-adjustable gear train is coupled between the driver and the shell, wherein the gear train defines a single fixed gear ratio greater than 1:1 between the driver and the shell. A bicycle drive train includes a drive unit having a user input component rotatable about a first axis at a first rotational speed, a chain ring rotatable about a second axis at a second rotational speed, and a gear train coupled between the user input component and the chain ring. The gear train defines a gear ratio less than 1:1 between the user input component and the chain ring. A method of propelling a bicycle is also provided.