Bicycle Power Assist Using Motor Reverse Current for Pedaling Force Detection
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Solution Overview
Problem
Existing power-assisted bicycles require complicated features and modifications to detect pedaling force, making it difficult to convert existing bicycles into power-assisted ones without altering their original configuration.
Innovation Solution
An electric power-assist device for bicycles that includes a crankshaft, electric motor, battery, housing, and a control unit with a dynamic brake circuit, rotational angle sensor, and current sensor, which estimates pedaling force based on reverse current caused by counter electromotive force, allowing for proper power assist control without complex detection features or modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strain gauge or pedaling force sensor is used to detect pedaling force, then power assist control can be achieved, but the device complexity and bicycle modification requirements increase
Solution Approach 1:
The system uses the motor's own electrical characteristics (counter electromotive force and reverse current) to detect pedaling force, eliminating the need for separate detection sensors. The motor serves dual purposes: providing power assist and sensing pedaling force through its electrical response during dynamic brake operation.
Solution Approach 2:
The patent replaces mechanical detection systems (strain gauges, force sensors) with an electrical detection method. By measuring reverse current during dynamic brake operation, the system electronically determines pedaling force without mechanical contact or additional sensing components.
2Reliability
If strain gauge or pedaling force sensor is used to detect pedaling force, then power assist control can be achieved, but modifications to the bicycle are required
Solution Approach 1:
The motor serves dual functions as both actuator and sensor. By utilizing the motor's inherent electrical properties during dynamic brake operation, the system eliminates the need for separate detection components that would require installation on the bicycle's existing structure.
Solution Approach 2:
The dynamic brake circuit serves multiple purposes: it provides braking function and simultaneously enables pedaling force detection through reverse current measurement. This multi-functionality reduces the need for additional components and simplifies integration with existing bicycles.
3Measurement precision
If dynamic brake circuit is activated at all crank rotational angles, then pedaling force detection is continuous, but unnecessary power assist occurs during coasting or reverse pedaling
Solution Approach 1:
The system dynamically activates the dynamic brake circuit only during specific crank rotational angle ranges when forward pedaling is detected. This conditional operation based on real-time crank position and pedaling direction prevents energy waste during coasting or reverse pedaling while maintaining detection accuracy during active pedaling phases.
Solution Approach 2:
The dynamic brake circuit operates periodically during specific intervals of the crank rotation cycle rather than continuously. By timing the activation to coincide with crank rotational angles where forward pedaling occurs, the system achieves detection precision while minimizing battery consumption during non-pedaling periods.
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
Enables accurate power assist control in response to pedaling force without complex detection systems or modifications, preventing unnecessary power assist during coasting or reverse pedaling, and ensuring efficient battery usage.
Implementation Method 1
a pedaling force estimator configured to estimate a pedaling force put on each pedal of the bicycle based on a value of reverse current caused by a counter electromotive force and detected by the current sensor when the dynamic brake circuit is in the ON state
Data Source
AI summary
An electric power assist device for bicycles includes: a dynamic brake controller configured to stop supply of a current from a battery to an electric motor and bring a dynamic brake circuit to an ON state when a crank rotational angle is within one or more predetermined crank rotational angle ranges; a pedaling force estimator configured to estimate a pedaling force put on pedals of a bicycle on a value of reverse current caused by a counter electromotive force and detected by a current sensor when the dynamic brake circuit is in the ON state; and a motor drive controller configured to control the electric motor based on the pedaling force estimated by the pedaling force estimator.