Harmonic Pedal-Cycle Drive With Compact High-Ratio Transmission
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Solution Overview
Problem
Conventional pedal electric cycle drive systems suffer from higher weight, volume, noise, lower reduction ratio, and transmission accuracy, which negatively impact battery endurance, riding comfort, and aesthetic design.
Innovation Solution
A harmonic drive system comprising a transmission gear device with a wave generator, flexible flexspline, rigid circular spline, gear set, and one-way clutches, integrated into the pedal electric cycle frame, enhancing reduction ratio, accuracy, and reducing weight and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a planetary gear transmission apparatus is used, then the drive system can transmit power from the electric motor to the pedal electric cycle, but the system becomes heavier and larger in volume
Solution Approach 1:
The patent replaces the conventional planetary gear transmission mechanism with a harmonic drive transmission mechanism. The harmonic drive uses a wave generator, flexible spline, and rigid circular spline to achieve power transmission through elastic deformation and meshing, rather than traditional rigid gear teeth engagement. This substitution results in a more compact structure with fewer components, directly reducing the weight of the drive system while maintaining effective power transmission from the electric motor to the wheel.
2Power
If a planetary gear transmission apparatus is used, then the drive system can provide gear reduction, but the reduction ratio is lower and transmission accuracy is reduced
Solution Approach 1:
The patent changes the fundamental transmission parameters by using a harmonic drive mechanism that achieves much higher reduction ratios (typically 50:1 to 150:1 or higher) compared to planetary gears. The wave generator creates a varying meshing pattern between the flexible and rigid splines, allowing for precise control of the transmission ratio. This parameter change enables both superior gear reduction capability and high transmission accuracy, as the elastic deformation of the flexible spline ensures continuous contact and smooth power transmission without the backlash typical of rigid gear systems.
3Productivity
If a planetary gear transmission apparatus is used, then the drive system can operate the pedal electric cycle, but the noise level increases
Solution Approach 1:
The patent employs a flexible spline as a key component of the harmonic drive mechanism. This flexible element acts as a compliant interface between the wave generator and the rigid circular spline, absorbing vibrations and reducing impact loads during meshing. The flexibility of the spline allows for smoother engagement and disengagement of gear teeth, significantly reducing mechanical noise and vibration compared to rigid planetary gear systems. This flexible component maintains full operational functionality while eliminating the harmful noise factor.
4Power
If a planetary gear transmission apparatus is used, then the drive system can transmit power, but the volume is larger affecting aesthetic design
Solution Approach 1:
The harmonic drive mechanism inherently provides a nested, compact structure where the flexible spline is deformed by the wave generator to engage with the rigid circular spline in a concentric arrangement. The components are arranged in a nested configuration that maximizes space efficiency, with the wave generator positioned centrally and the splines arranged around it. This nesting principle allows the entire transmission system to be packaged in a much smaller volume compared to planetary gear systems, improving both the aesthetic design of the pedal electric cycle and the spatial arrangement of components.
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 harmonic drive system significantly reduces weight and volume, improves transmission accuracy, and enhances battery endurance and riding comfort while improving the aesthetic design of the pedal electric cycle.
Implementation Method 1
The elliptical cam is arranged in a space defined by the inner ring surface of the flexible bearing such that the flexible hearing is deformed into elliptic cylindrical
Implementation Method 2
The wave generator is arranged in a space defined by the inner ring surface of the first end of the flexible flexspline such that the first end of the flexible flexspline is deformed into elliptic cylindrical
Implementation Method 3
The rigid circular spline has rigid-circular-spline internal gear teeth provided for meshing with the flexible-flexspline external gear teeth
Data Source
AI summary
A harmonic drive system for a pedal-electric-cycle comprises a transmission gear device including a wave generator assembled by an elliptical cam and a flexible bearing, a flexible-flexspline, a rigid-circular-spline having rigid-circular-spline internal gear teeth, a gear set, and a one-way clutch having an inner surface defining a space for containing a spindle of the pedal-electric-cycle. A first end of the flexible-flexspline has flexible-flexspline external gear teeth for meshing with the rigid-circular-spline internal gear teeth and an inner surface defining a space for containing the wave generator. The gear set has a first input portion connected to a second end of the flexible-flexspline, a second input portion having an inner surface defining a space for containing the one-way clutch, and an output portion connected to a sprocket of the pedal-electric-cycle. The first input portion has a first-input rotational axis. The second input portion has a second-input rotational axis.