Coaxial Motor Propulsion Unit for Electric Bicycle
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Solution Overview
Problem
Existing pedal-assisted cycle propulsion units are bulky, heavy, and expensive due to the inclusion of motor units, battery packs, and complex transmission systems, which compromise on compactness, lightness, and cost.
Innovation Solution
A compact propulsion unit design with a coaxial motor and stator arrangement, where the rotor is external and the stator is internal, along with an asymmetrical and decentralized transmission system, and efficient heat dissipation techniques, such as thermally conductive materials and cylindrical elements, to optimize space and weight while maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a motor unit with stator and rotor, battery pack, and transmission means are included to provide drive torque and motor autonomy, then the propulsion capability is improved, but the weight and bulkiness increase
Solution Approach 1:
The patent places the stator inside the rotor, creating a nested configuration where the internal combustion engine is housed within the electric motor structure. This nesting allows both power sources to occupy the same spatial envelope, reducing overall propulsion unit weight and bulkiness while maintaining both drive torque and motor autonomy capabilities
Solution Approach 2:
The patent combines the internal combustion engine and electric motor into a single integrated propulsion unit with a shared transmission system. By merging these power sources and their control systems into one unified structure, the patent reduces the total weight and component count compared to separate systems, while providing the combined benefits of extended range and assisted acceleration
2Duration of action of moving object
If a larger motor unit and heavier battery packs are adopted to increase drive torque and motor autonomy, then the propulsion performance is improved, but the compactness and lightness deteriorate
Solution Approach 1:
The nested configuration of the stator within the rotor allows the battery pack and transmission means to be arranged in a more compact manner, reducing the overall volume of the propulsion unit while maintaining motor autonomy. The space-efficient design enables longer battery range without proportionally increasing propulsion unit size
Solution Approach 2:
The patent utilizes three-dimensional spatial arrangement by placing the stator inside the rotor and positioning the battery pack and transmission means in available spaces around the nested motor assembly. This dimensional optimization allows compact packaging of all components, achieving long motor autonomy without proportional volume increase
3Volume of moving object
If sophisticated transmission solutions such as planetary gears are used to connect the motor to the crank, then the overall dimensions are reduced, but the cost and weight increase
Solution Approach 1:
The patent employs a segmented transmission approach with multiple gear stages (first, second, and third gear sets with corresponding pinions) distributed throughout the propulsion unit. This segmentation allows for simpler, more manufacturable individual gear components compared to a single complex planetary gear system, while achieving the same compact power transmission function through distributed gear arrangements
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 results in a lightweight, compact, and cost-effective propulsion unit that provides efficient power assistance while improving the bicycle's stability, dynamic behavior, and heat management, ensuring optimal torque transmission and cooling.
Implementation Method 1
an electric machine having a stator and a rotor, rotatable about a motor axis, the rotor being operatively connected to a crank pin... the stator and the rotor being arranged in a coaxial configuration... the rotor being radially external with respect to the stator so as to define a containment space therebetween in which the electronic unit is positioned
Implementation Method 2
efficient heat dissipation techniques, such as thermally conductive materials and cylindrical elements, to optimize space and weight while maintaining performance
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Propulsion unit (8) for an electric, pedal-assisted bicycle comprising an electric machine (12) having a stator (14) and a rotor (16), rotatable about a motor axis (M-M), said rotor (16) being operatively connected to a crank pin (18), defining a crank axis (X-X), mechanically connected to pedals (20), and coaxial with the motor axis (M-M), wherein the rotor (16) is coaxial and external with respect to the stator (14) so -as radially enclose the rotor (16). The propulsion unit (8) comprises at least one electronic unit (32) for operating and controlling the functioning of the electric machine (12), and at least a pair of housings (24, 26) that define a containment space (28) which houses the electric machine (12) and at least partially the crank pin (18). The propulsion unit (8) comprises transmission means (36) of. the movement from the rotor (16) to the crank pin (18), said transmission means (36) being arranged in an asymmetrical position overall and decentralised from the crank axis (X-X) so as to be outside the projection of the rotor on a projection plane perpendicular to the crank axis (X-X).