Bicycle Drive Unit Torque Consistency via Segmented Transmission
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Solution Overview
Problem
Conventional bicycle drive units face a reduction in assisting force due to varying rotational speeds of the crank, which affects the output torque of the motor.
Innovation Solution
A bicycle drive unit with a transmission system featuring multiple gear shift stages, a motor, and a switching mechanism with a one-way clutch and connection switching unit, allowing torque from the motor to be selectively transmitted to the output unit, merging with manual drive force to maintain assisting force consistency across different crank rotational speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the motor rotational speed is directly proportional to the crank rotational speed, then the system structure is simple, but the output torque becomes insufficient at certain crank speeds
Solution Approach 1:
The transmission system is divided into multiple independent gear shift stages (first and second stages), each with separate input and output rotating bodies. This segmentation allows independent optimization of each stage's gear ratio to maintain appropriate motor rotational speed across different crank speeds, preventing torque deficiency while keeping each stage's structure relatively simple.
Solution Approach 2:
The transmission system dynamically adjusts the gear ratio through the switching mechanism that can engage or disengage different gear shift stages based on the crank rotational speed. This dynamic adjustment ensures the motor operates in its optimal torque range across varying pedaling speeds, resolving the torque insufficiency problem without requiring a completely complex fixed-ratio system.
2Device complexity
If a single gear ratio is used, then the device complexity is reduced, but the assisting force varies with crank rotational speed
Solution Approach 1:
The transmission system dynamically switches between different gear shift stages based on the detected crank rotational speed. When the crank speed is low, the first gear shift stage is engaged; when the crank speed is high, the second gear shift stage is engaged. This dynamic adaptation maintains consistent assisting force across different pedaling speeds without requiring an overly complex multi-speed system.
Solution Approach 2:
The system changes the transmission ratio parameter by switching between different gear shift stages. The first gear shift stage provides a larger ratio for low-speed operation, while the second gear shift stage provides a smaller ratio for high-speed operation. This parameter adjustment ensures the motor operates efficiently across the full range of crank speeds, maintaining assisting force consistency.
3Power
If multiple gear shift stages are added to maintain torque across different speeds, then the output torque consistency is improved, but the device complexity increases
Solution Approach 1:
The transmission system is divided into two independent gear shift stages, each with its own input and output rotating bodies and gear mechanisms. This segmentation allows each stage to be optimized for specific speed ranges, maintaining torque consistency without requiring a single overly complex gear system. Each stage can be designed and manufactured independently, simplifying the overall production process.
Solution Approach 2:
Both the first and second gear shift stages share common components such as the input rotating body connected to the crankshaft and the output rotating body connected to the wheel. This multi-functionality allows the system to achieve multiple gear ratios without proportionally increasing the number of unique components, thereby controlling device complexity while maintaining torque consistency across different speeds.
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 effectively prevents a reduction in assisting force by adjusting the transmission ratio based on crank rotational speed, ensuring consistent torque delivery and improved pedaling assistance.
Implementation Method 1
a switching mechanism comprising a one-way clutch and a connection switching unit
Data Source
AI summary
A bicycle drive unit has a transmission and a motor that transmits torque to the transmission. The transmission includes first and second input side rotating bodies, first and second output side rotating bodies, an output unit and a switching mechanism. The first and second output side rotating bodies are coupled to the first and second input side rotating bodies, respectively. The switching mechanism switches between a first state in which rotation of the first input side rotating body is transmitted to the output unit, and a second state in which rotation of the second input side rotating body is transmitted to the output unit. Only torque of the motor is transmitted from the first and second input side rotating bodies to the output unit, while torque outputted from the output unit merges with a manual drive force in a drive force transmission path from the output unit to a wheel.