E-bike Controller Walk Mode Speed Calculation
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Solution Overview
Problem
Existing electric assisted bicycles face challenges in calculating vehicle speed and torque for walk modes, particularly when the number of magnets on the wheel is reduced, leading to delayed torque calculation and increased costs due to the need for additional sensors to sense the change gear ratio.
Innovation Solution
The system includes a controller that calculates the change gear ratio using signals from a rotation sensor and a vehicle speed sensor, allowing for vehicle speed calculation at a higher frequency without a dedicated sensor for the gear ratio, enabling smooth walking assistance from the start by calculating the target value for the electric motor based on temporary vehicle speed and load sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of magnets on the wheel is reduced, then the cost of the bicycle is reduced, but the vehicle speed calculation is delayed
Solution Approach 1:
The system calculates a temporary vehicle speed using a predetermined temporary change gear ratio before the actual change gear ratio is known. This preliminary calculation allows the target value for the electric motor to be determined immediately when the walk command is received, without waiting for the vehicle speed sensor to provide data. The temporary vehicle speed is then replaced by the calculated vehicle speed once the change gear ratio is determined, ensuring smooth transition without delay.
2Measurement precision
If a dedicated sensor to sense the change gear ratio is added, then the vehicle speed calculation accuracy is improved, but the cost of the bicycle is increased
Solution Approach 1:
The system uses existing sensors (vehicle speed sensor and rotation sensor) to calculate the change gear ratio by comparing the rotation speeds at different positions in the power transmission path. This self-service approach eliminates the need for a dedicated change gear ratio sensor, as the system derives the gear ratio information from the relationship between wheel rotation speed and motor rotation speed, maintaining measurement precision without additional hardware cost.
3Ease of operation
If the target value is calculated immediately from start of walking, then the walking assistance is smooth, but the vehicle speed sensor data may be unavailable
Solution Approach 1:
The system performs preliminary calculation of the target value using temporary vehicle speed derived from a predetermined change gear ratio when the walk command is first received. This allows immediate motor control without waiting for vehicle speed sensor data. Once the sensor data becomes available and the actual change gear ratio is calculated, the system updates the vehicle speed and target value accordingly, ensuring both immediate response and accurate ongoing control.
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
This configuration simplifies the vehicle speed sensor structure, reduces costs, and ensures smooth walking assistance by calculating the target motor value from the start of walking, regardless of the change gear ratio, while preventing excessive small assistance.
Implementation Method 1
a magnet attached to a wheel and a Hall element attached to a frame. When the magnet comes to the position of the Hall element by rotation of the wheel, the Hall element outputs a pulse caused by a change in magnetic field.
Data Source
AI summary
In a drive system of an electric assisted bicycle, a controller includes a vehicle speed calculator to calculate a change gear ratio of a change gear mechanism based on an output signal of a vehicle speed sensor and an output signal of a rotation sensor in response to acquisition of the output signal of the vehicle speed sensor, and calculate a vehicle speed based on the calculated change gear ratio and the output signal of the rotation sensor at a higher frequency than a frequency of the acquisition of the output signal of the vehicle speed sensor. The controller includes an initial target calculator to calculate target power without using the output signal of the vehicle speed sensor in a prescribed period from start of walking, when a walk command is received, and a target calculator to calculate a target power based on the vehicle speed calculated by the vehicle speed calculator after a lapse of the prescribed period.