Bicycle Controller Managing Motor Assist Force
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Solution Overview
Problem
Conventional bicycle transmission systems experience a decrease in assist force and motor driving efficiency due to the proportional relationship between motor rotational speed and crank rotational speed, leading to insufficient output torque and reduced assistance when the crank rotational speed changes.
Innovation Solution
A bicycle controller and transmission system with an electronic control unit that manages a second transmission to maintain assist force by adjusting its transmission ratio based on the condition of the bicycle, including torque and rotational speed, to prevent decreases in assist force when the crank rotational speed changes, without altering the ratio of wheel to crank rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the motor rotational speed is proportional to the crank rotational speed, then the transmission system is simple, but the output torque becomes insufficient and assist force decreases when crank rotational speed changes
Solution Approach 1:
The transmission system is divided into two independent transmission paths: a first transmission that maintains the proportional relationship between crank and motor rotational speeds, and a second transmission that independently adjusts motor rotational speed based on load conditions. This segmentation allows each transmission to perform its specific function without interfering with the other, resolving the contradiction between simplicity and sufficient assist force.
Solution Approach 2:
The second transmission is designed to dynamically adjust the motor rotational speed independently from the crank rotational speed based on detected load conditions. This dynamic adjustment capability allows the system to maintain optimal motor operating range and sufficient output torque across varying riding conditions, while the first transmission maintains the simple proportional relationship.
2Device complexity
If the motor rotational speed is proportional to the crank rotational speed, then the control system is simple, but the motor driving efficiency decreases when crank rotational speed changes
Solution Approach 1:
The control system is segmented into two independent control loops: one that maintains the proportional relationship between crank and motor speeds (first transmission), and another that independently controls motor speed based on efficiency optimization criteria (second transmission). This allows the system to maintain simple proportional control while adding targeted efficiency optimization without requiring complete system redesign.
Solution Approach 2:
The control unit detects actual motor rotational speed and load conditions, then uses feedback signals to adjust the second transmission's gear ratio accordingly. This feedback mechanism allows the system to maintain optimal motor operating range and driving efficiency across varying riding conditions while preserving the simplicity of the overall control architecture.
3Force
If a second transmission is added to adjust motor rotational speed independently, then the assist force and motor efficiency are maintained, but the device complexity increases
Solution Approach 1:
The first and second transmissions are merged into a single integrated transmission system with a unified control unit that coordinates both transmission paths. This merging approach allows the system to maintain sufficient assist force and motor efficiency while minimizing overall complexity through shared components and coordinated control, rather than treating them as completely separate systems.
Data Source
AI summary
A bicycle controller limits decreases in the assist force when the rotational speed of a crank changes. The bicycle controller can be mounted on a bicycle including a first transmission having at least two shift stages and configured to change a ratio of rotation of a wheel to rotation of a crank, a motor that provides assistance to human power input to the crank, and a second transmission configured to transmit a rotation force from the motor to a power transmission path extending from the crank to the wheel without changing the ratio of the rotation of the wheel to the rotation of the crank. The bicycle controller includes an electronic control unit that controls the second transmission in accordance with a condition of the bicycle and either one of a condition of the first transmission and a shift instruction to the first transmission.