E-Bike Harmonic Drive Layout for Low Q-Factor Serviceability
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Solution Overview
Problem
Current transmission systems for electric bicycles, particularly those using harmonic drives, are difficult to integrate into bicycle frames due to increased Q-Factor and complex disassembly, making them uncomfortable for riders and challenging to service.
Innovation Solution
A transmission system incorporating a flex-spline with one-way clutches, where the flex-spline defines a locus and the clutches are located within this locus, allowing the system to be compactly housed within the bottom bracket shell, reducing Q-Factor and facilitating easier maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If harmonic drives are placed around the outside of the main drive axle, then the motorised input can be provided to the transmission system, but the Q-Factor increases beyond a comfortable or stable point for the rider
Solution Approach 1:
The patent places the harmonic drive inside the flex-spline locus rather than around the outside of the main drive axle. The flex-spline acts as a containing structure that houses the harmonic drive components (circular spline, wave generator) within its interior locus, effectively nesting the motorised input mechanism within the available space without increasing the external Q-Factor.
Solution Approach 2:
The patent transitions from a radial arrangement (around the outside of the axle) to an axial arrangement (inside the flex-spline locus). By utilizing the interior space of the flex-spline along the axial dimension, the system accommodates the harmonic drive without increasing the radial distance between pedal cranks, thus maintaining rider comfort while providing motorised input.
2Power
If harmonic drives are placed around the outside of the main drive axle, then the motorised input can be provided, but the disassembly and reassembly becomes complicated and beyond the ability of local bicycle repair persons
Solution Approach 1:
The patent divides the transmission system into separable modules: the harmonic drive unit (with circular spline, wave generator, and flex-spline) can be disassembled as a module from the main transmission. The flex-spline can be removed from the locus, allowing the harmonic drive components to be accessed and serviced independently, simplifying repair procedures for local bicycle repair persons.
Solution Approach 2:
The patent enables the harmonic drive to be extracted from the transmission system by removing the flex-spline from the locus. This extraction allows the complex harmonic drive components to be taken out as a separate unit for servicing or replacement, making the system more repairable by local bicycle repair persons without requiring complete disassembly of the entire transmission.
3Volume of moving object
If the flex-spline defines a locus and one-way clutches are located within this locus, then the system can be compactly housed within the bottom bracket shell, but the structural complexity increases
Solution Approach 1:
The patent combines multiple functions within the flex-spline locus: the harmonic drive mechanism, the one-way clutches, and the support structure are all integrated within this single defined space. The locus serves as both the structural framework and the spatial container for multiple components, reducing overall system volume while consolidating structural elements to manage complexity.
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 is compactly contained within the bicycle frame, maintaining rider comfort and enabling straightforward maintenance, with the ability to fit various rotational inputs and motor sizes, including electric and manual power sources.
Implementation Method 1
The first one-way clutch is mounted around and rotationally coupled to a bracket, and a second one-way clutch is mounted within a housing defined within the bracket
Data Source
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AI summary
The present disclosure relates to transmission systems for vehicles and especially those for use in electric bicycles, where human power is augmented with electric motor derived power. The present disclosure includes various embodiments, where the electric motor is of the harmonic drive type and wherein there is provided a secondary axle or bracket which provides the output of the systems, driven by both the manual input and the motor input, and wherein these two inputs are insulated from one another by placement of one-way clutches, between the flex-spline and the secondary axle or bracket and between the bracket and the primary drive axle. A modular assembly for such transmission systems and a method of assembly and disassembly are also disclosed.