Harmonic Drive Coupling for Compact E-Bike Assist
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Solution Overview
Problem
Existing drive assemblies for manually driven vehicles, such as bicycles and pedelecs, require a large amount of space and are mechanically complex, often necessitating torque sensors for controlling electric auxiliary drives, which increases complexity and cost.
Innovation Solution
A drive assembly utilizing a strain wave gear to couple the manual drive shaft and electric auxiliary drive to a common output element, eliminating the need for torque sensors by adding speeds rather than forces, allowing for a compact and economical design with adjustable torque and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional drive assemblies are used to couple manual drive and electric auxiliary drive, then the drives can be connected to a common output element, but the installation space required is large and the mechanical design is complex
Solution Approach 1:
The wave gear combines the manual drive shaft and electric auxiliary drive rotor into a single integrated coupling mechanism with a common output element. The deformable inner bushing with external teeth and outer bushing with internal teeth merge both drive inputs into one compact unit, eliminating the need for separate coupling mechanisms and reducing overall installation space.
Solution Approach 2:
The wave gear structure nests the deformable inner bushing within the outer bushing, with the wave generator positioned centrally. The inner bushing with external teeth fits inside the outer bushing with internal teeth, creating a compact nested arrangement that significantly reduces the radial and axial space required for the drive assembly.
2Ease of operation
If torque sensors are used to control the electric auxiliary drive, then the drive can be precisely controlled, but the device complexity and cost increase
Solution Approach 1:
The wave gear inherently provides speed addition functionality without requiring external torque sensors or complex control systems. The deformable inner bushing automatically transmits and combines the rotational speeds of both the manual drive shaft and electric auxiliary drive rotor through its elastic deformation, enabling self-regulating speed addition that eliminates the need for additional sensing and control components.
Solution Approach 2:
The invention replaces electronic torque sensing and control systems with a purely mechanical wave gear mechanism. The speed addition function previously requiring electronic sensors and controllers is achieved through the mechanical elastic deformation of the inner bushing, substituting complex electronic control with simple mechanical action.
3Ease of manufacture
If conventional coupling mechanisms are used, then the manual and electric drives can be connected, but the production costs are higher due to additional components like torque sensors
Solution Approach 1:
The wave gear merges multiple functions (coupling, speed addition, torque transmission) into a single integrated mechanism with fewer discrete components. By combining the coupling function and speed addition function into one device, the patent eliminates the need for separate torque sensors, controllers, and coupling mechanisms, thereby reducing component count and production costs.
Solution Approach 2:
The wave gear serves multiple functions simultaneously: it couples the manual drive shaft and electric auxiliary drive rotor, adds their rotational speeds, and transmits the combined torque to the common output element. This multi-functionality eliminates the need for separate dedicated components for each function, reducing overall system complexity and manufacturing cost.
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 enables a compact, lightweight, and cost-effective drive assembly that can support sporty driving profiles without the need for torque sensors, providing efficient power assistance by adding speeds of the manual and electric drives, thus simplifying the mechanical structure and reducing production costs.
Implementation Method 1
the wave generator is at least indirectly connected to the rotor of the electric auxiliary drive in a rotationally fixed manner
Implementation Method 2
a deformable inner bushing with external teeth
Implementation Method 3
the first drive shaft and the rotor of the electric auxiliary drive are coupled to a common output element by means of a wave gear
Data Source
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AI summary
The present invention relates to a drive assembly (10) for a manually driven vehicle (80), in particular a bicycle or a pedelec, with an electric auxiliary drive (24), wherein the drive assembly (10) has a first drive shaft (12) for a manual drive and a rotor (20) of the electric auxiliary drive (24), and wherein the first drive shaft (12) and the rotor (20) of the electric auxiliary drive (24) are coupled to a common drive element (29), wherein the first drive shaft (12) and the rotor (20) of the electric auxiliary drive (24) are coupled to the drive element (29) by means of a harmonic drive (25), wherein the harmonic drive (25) has an outer sleeve (28) with an internal toothing system (62) and a deformable inner sleeve (26) with an external toothing system (64) and a shaft generator (27), wherein the shaft generator (27) is at least indirectly connected fixedly to the rotor (20) of the electric auxiliary drive (24) so as to rotate with it, wherein the deformable inner sleeve (26) is at least indirectly connected fixedly to the first drive shaft (12) so as to rotate with it, and wherein the outer sleeve (28) forms the drive element (29). Furthermore, a method and a use are proposed.