E-bike Drive System Assist Ratio Transition Control
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Solution Overview
Problem
Existing electric assisted bicycles experience discomfort during mode transitions due to sudden changes in assist ratio, particularly when the assist ratio is changed near the lowest point of the pedal trajectory, leading to an uncomfortable ride.
Innovation Solution
A drive system with a sensor that detects pedaling force and an electric motor with a control device that gradually changes the assist ratio from a first mode to a second mode by starting the transition at a specific angular position (90 degrees past the uppermost point) and ending it when the pedaling force is weakened, ensuring the change is completed before reaching the uppermost point, thereby minimizing ride quality impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the assist ratio is changed when one of the pedals is close to the lowermost point, then the control mode transition can be implemented, but the ride quality becomes uncomfortable due to sudden torque changes
Solution Approach 1:
The control device starts changing the assist ratio before the pedal reaches the lowermost point, specifically at an angular position between 90 degrees and 135 degrees from the uppermost point. This preliminary action allows the assist ratio change to begin when pedaling force is still relatively high, preventing the sudden torque change that would occur if the change started at the lowermost point. The assist ratio change is completed by the time the pedal reaches an angular position of at least 45 degrees from the change start position, ensuring smooth transition without compromising ride quality.
2Speed
If the assist ratio change is completed quickly, then the response speed is improved, but the ride quality may be compromised due to sudden changes
Solution Approach 1:
The control device dynamically adjusts the assist ratio change process based on the pedal's angular position. The assist ratio change starts at a specific angular position (between 90 and 135 degrees from uppermost point) and progresses continuously until the pedal reaches at least 45 degrees from the change start position. This dynamic approach ensures that the assist ratio changes smoothly in sync with the pedaling motion, maintaining both responsiveness and ride quality by avoiding sudden torque changes while still achieving mode transition.
Data Source
AI summary
When transitioning from a first control mode to a second control mode is satisfied, a control device starts to change an assist ratio from a first assist ratio to a second assist ratio at a change start position Ps between an angular position P1 obtained by adding 90 degrees to a crank angular position corresponding to an uppermost point P0 of a trajectory of a pedal and an angular position P2 obtained by adding 135 degrees to a crank angular position corresponding to the uppermost point P0. The control device changes the assist ratio such that the assist ratio reaches the second assist ratio at a change end position Pe obtained by adding at least 45 degrees to the change start position Ps. This system can reduce an impact on ride quality caused by the change in the assist ratio associated with the change in the control mode.