Electric Assist Bicycle Drive System Mode Change Timing
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Solution Overview
Problem
Electric assist bicycles experience uncomfortable mode changes due to sudden decreases in pedaling force when assist ratios increase, leading to discomfort for riders as the load applied from the pedal decreases significantly.
Innovation Solution
A drive system for electric assist bicycles that includes a sensor to detect pedaling force, an electric motor, and a controller programmed to calculate assist ratios, allowing for mode changes from a first mode to a second mode when the pedal is between specific angular positions, thereby shifting the time of mode change to prevent sudden load changes and reduce component costs by eliminating the need for dedicated sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the assist ratio increases due to mode change at the same time point at which the mode change condition is fulfilled, then the control system can respond quickly to rider needs, but the rider may feel uncomfortable because the load applied from the pedal significantly decreases
Solution Approach 1:
The controller performs preliminary determination of the pedal angular position before executing mode change. By checking whether the pedal is located between the first angular position (45 degrees after lowermost) and second angular position (45 degrees before lowermost), the system prepares to execute mode change at an optimal moment that minimizes rider discomfort while maintaining responsive control.
Solution Approach 2:
The system dynamically adjusts the timing of mode change based on real-time detection of pedal angular position and pedaling force. Instead of fixed timing, the controller adapts the mode change moment to the current pedaling cycle phase, creating a dynamic control strategy that balances responsiveness with comfort.
2Measurement precision
If a dedicated sensor to detect angular position is added, then the system can precisely control mode change timing, but the device complexity and cost increase
Solution Approach 1:
The existing torque sensor, originally designed to detect pedaling force, is made multi-functional by using its output to determine both the mode change condition and the pedal angular position. The controller calculates angular position information from the torque sensor signals, eliminating the need for a separate angular position sensor while maintaining precise control capability.
Solution Approach 2:
The torque sensor serves itself by providing dual purposes: detecting pedaling force for mode change determination and providing data for calculating pedal angular position. This self-service approach eliminates additional hardware requirements while maintaining system functionality.
Data Source
AI summary
An electric assist bicycle and a drive system therefor includes a controller that includes control modes in which different assist ratios are calculated as control modes of the electric motor, and that stores a mode change condition that determines a change of the control mode. The controller performs the mode change when a pedal is located between an angular position that follows by 45 degrees a lowermost position of a locus of the pedal and an angular position that precedes by 45 degrees the lowermost position. Accordingly, the mode change is performed when the pedaling force exerted by a rider is relatively low such that the rider does not feel uncomfortable due to a rapid change of the load applied to the rider.