Bicycle Control Device Maintaining Assist Force Ratio
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Solution Overview
Problem
Existing bicycle control devices fail to consistently maintain the ratio of assist force generated by a motor to human drive force input, due to output characteristics of the motor, leading to undesirable riding states.
Innovation Solution
A bicycle control device with an electronic controller that adjusts the transmission ratio in correspondence with the output torque and human drive force to maintain the predetermined ratio of assist force to human drive force, by lowering or raising the transmission ratio based on torque and rotational speed conditions, ensuring the assist force remains within suitable output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the transmission ratio is changed to adjust the load on the rider and motor, then the rotational speed of the crank and human drive force change, but the ratio of assist force to human drive force becomes difficult to maintain at the predetermined ratio due to motor output characteristics
Solution Approach 1:
The electronic controller continuously monitors the actual ratio of assist force to human drive force and adjusts the transmission ratio accordingly. When the ratio deviates from the predetermined value, the controller modifies the transmission ratio to bring it back to the target value, creating a closed-loop feedback system that maintains the desired assist force ratio despite changes in motor output characteristics.
Solution Approach 2:
The transmission ratio is made dynamically adjustable rather than fixed. The electronic controller varies the transmission ratio in real-time based on the operating conditions, including the current motor output characteristics and human drive force, allowing the system to adapt to changing conditions while maintaining the predetermined assist force ratio.
2Reliability
If the transmission ratio is lowered to decrease the output torque of the motor, then the motor operates within suitable output characteristics, but the rotational speed of the crank may become too high for certain riding conditions
Solution Approach 1:
The transmission ratio is dynamically adjusted based on real-time monitoring of motor output torque and crank rotational speed. The electronic controller lowers the transmission ratio when motor torque exceeds the predetermined threshold to keep the motor within its optimal operating characteristics, while simultaneously monitoring crank speed to ensure it remains within acceptable ranges for the given riding conditions.
Solution Approach 2:
The system changes the transmission ratio parameter in response to changes in motor output torque and crank rotational speed. By adjusting this key parameter, the system optimizes the motor's operating point while maintaining appropriate crank speed, creating a balanced operating state that satisfies both motor characteristics and riding conditions.
3Force
If the transmission ratio is raised to increase the output torque of the motor, then the motor can deliver more assist force, but the motor may operate outside its suitable output characteristics range
Solution Approach 1:
The electronic controller uses feedback from torque sensors and rotational speed sensors to monitor the motor's actual operating state. When the motor output torque approaches or exceeds the predetermined threshold, the controller adjusts the transmission ratio to bring the motor back into its optimal operating range, preventing sustained operation outside the suitable characteristics while maintaining maximum possible assist force.
Data Source
AI summary
A bicycle control device that easily maintains the ratio of the assist force generated by a motor to the human drive force input to a bicycle at a predetermined ratio includes an electronic controller that controls a transmission, which is configured to change the transmission ratio of the bicycle, and the motor, which assists propulsion of the bicycle. The electronic controller is configured to control the motor so that the ratio of the assist force generated by the motor to the human drive force inputted to the bicycle becomes equal to the predetermined ratio. The electronic controller is configured to control the transmission in correspondence with at least one of the output torque of the motor and the human drive force to maintain the predetermined ratio.