Harmonic Pedal-Cycle Drive for Compact High-Ratio Reduction
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Solution Overview
Problem
Conventional pedal electric cycle drive systems suffer from high weight, volume, noise, and lower reduction ratio, leading to reduced battery endurance, comfort, and aesthetic design issues.
Innovation Solution
A harmonic drive system incorporating a transmission gear device with a wave generator, flexible flexspline, rigid circular spline, and one-way clutches, which reduces weight and volume while enhancing reduction ratio and transmission accuracy.
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 system. 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 reduces the number of components, eliminates the need for multiple planet wheels and carriers, and results in a significantly lighter and more compact drive system while maintaining high power transmission efficiency.
2Speed
If a planetary gear transmission apparatus is used, then the drive system can provide gear reduction, but the reduction ratio is relatively lower
Solution Approach 1:
The patent achieves high reduction ratios by changing the geometric parameters of the harmonic drive components. By adjusting the number of teeth on the rigid circular spline, the dimensions of the flexible spline, and the elliptical geometry of the wave generator, the system can achieve reduction ratios of 30:1 to 100:1 or higher. This parameter-based approach allows for continuous optimization of the reduction ratio without increasing device complexity, as the harmonic drive structure inherently supports high reduction through its elastic deformation mechanism.
3Force
If a planetary gear transmission apparatus is used, then the drive system can transmit torque, but the transmission accuracy is lower
Solution Approach 1:
The patent employs a flexible spline with elastic properties to achieve precise torque transmission. The flexible spline deforms elastically under the action of the wave generator, creating a precise meshing pattern with the rigid circular spline. This elastic deformation mechanism provides inherent error compensation and high transmission accuracy, as the flexible material can adapt to minor manufacturing variations and maintain consistent engagement. The result is high torque transmission capability with transmission accuracy exceeding 0.01 degrees.
4Reliability
If a planetary gear transmission apparatus is used, then the drive system can operate reliably, but the noise level is larger
Solution Approach 1:
The patent replaces the rigid gear tooth engagement of planetary gears with an elastic-deformation-based harmonic drive mechanism. The flexible spline and rigid circular spline engage through controlled elastic deformation rather than direct rigid contact, which dramatically reduces impact noise and vibration. The wave generator's elliptical geometry creates a smooth, progressive meshing action that eliminates the characteristic noise of planetary gear tooth engagement, resulting in a quiet yet reliable drive system.
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 battery endurance, enhances riding comfort, and aesthetically integrates within the pedal electric cycle frame, offering high reduction ratio, low noise, and high transmission accuracy.
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 bearing 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
Implementation Method 4
The first gear teeth of the first gear mesh with the second gear teeth of the second gear
Implementation Method 5
The first one-way clutch is arranged in a space defined by the inner surface of the second input portion of the gear set
Data Source
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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.