Electric Assist Bicycle Motor Control for Pedal Force Chattering
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Solution Overview
Problem
Existing electric assist bicycles experience uncomfortable chattering and fail to stop traveling as intended due to frequent motor start and stop cycles and excessive travel distance when pedaling is stopped, especially at high speeds, leading to safety concerns and discomfort.
Innovation Solution
An electric assist bicycle equipped with a pedal force detector, travel distance detector, and motor control unit that stops the motor when a predetermined upper limit distance or time is reached after the pedal force drops below a reference value, allowing for precise control based on travel speed to prevent excessive travel and chattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the motor is stopped immediately when pedal force drops below the drive stop reference value, then the motor stops quickly, but the motor stops and starts frequently during pedaling causing chattering
Solution Approach 1:
The control unit predicts future pedal force based on past detection results before actually stopping the motor. By anticipating when pedal force will drop below the threshold, the system stops the motor at the optimal moment, preventing both chattering and excessive travel distance. This predictive approach resolves the contradiction by acting in advance based on learned patterns.
2Ease of operation
If the motor continues driving for a fixed upper limit time after pedal force drops below reference value, then chattering is prevented, but the bicycle travels excessive distance at high speed
Solution Approach 1:
The upper limit time is made variable rather than fixed. The control unit adjusts the upper limit time based on detected travel speed - shorter times at high speeds and longer times at low speeds. This dynamic adjustment prevents excessive travel distance at high speed while maintaining sufficient buffer time at low speed to prevent chattering, resolving the contradiction between these two requirements.
3Length of moving object
If the upper limit time is shortened to prevent excessive travel at high speed, then travel distance is controlled, but chattering occurs during low-speed pedaling
Solution Approach 1:
The system dynamically adjusts the upper limit time parameter based on real-time travel speed detection. When traveling at high speed, a shorter upper limit time is applied to control travel distance. When traveling at low speed, a longer upper limit time is applied to prevent chattering. This speed-dependent parameter adjustment resolves the contradiction by adapting the same parameter to different operating conditions.
4Ease of operation
If pedal force threshold values are set to avoid chattering, then riding comfort improves, but the motor fails to stop when rider intends to stop
Solution Approach 1:
The control unit continuously monitors pedal force and uses past detection results to predict future force levels. This feedback mechanism allows the system to distinguish between temporary force fluctuations during pedaling and genuine stop intentions. By comparing current force with predicted future force and adjusting the upper limit time accordingly, the system maintains high stop accuracy while preventing chattering through adaptive threshold management.
Data Source
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AI summary
An object of the present invention is to provide an electric assist bicycle by which a comfortable ride can be achieved without causing a rapid change in pedal force when stopping pedaling during traveling at low speed, and safe travel can be achieved as the rider intends by swiftly stopping a driven motor when stopping pedaling during traveling at high speed. The driven motor is stopped when travel distance L in a state in which detected pedal force F is not larger than predetermined drive stop reference value FL reaches not smaller than predetermined upper limit distance L0.