Electric Motor Torque Control for Variable Transmission Stability
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Solution Overview
Problem
Existing electric power-assisted bicycles experience varying riding behavior and comfort due to torque changes with different transmission gear ratios, leading to inconsistent performance even with the same pedal stepping force and electric current input.
Innovation Solution
A method and power unit for controlling an electric vehicle motor that transmits output via a variable transmission, where the target motor torque is calculated independently of the transmission gear ratio, ensuring constant torque on the wheel, and the motor is driven at this torque, maintaining stability and comfort regardless of gear selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If constant electric current is applied to the electric motor regardless of transmission gear ratio, then the control system is simple, but the torque on the wheel varies causing inconsistent riding comfort
Solution Approach 1:
The control system dynamically adjusts motor torque based on the selected transmission gear ratio. The controller receives gear ratio information and modifies the motor output accordingly to compensate for the mechanical advantage/disadvantage introduced by different gear ratios, ensuring consistent wheel torque and riding comfort across all gear selections.
Solution Approach 2:
The system changes the motor torque parameter in response to gear ratio changes. By detecting the transmission gear ratio and adjusting the motor torque parameter accordingly, the system maintains constant wheel torque despite variations in transmission mechanical advantage, resolving the contradiction between control simplicity and riding comfort consistency.
2Speed
If transmission gear with small gear ratio is selected, then acceleration is high, but the rider feels abrupt acceleration and reduced comfort
Solution Approach 1:
The control system applies preliminary anti-action by reducing motor torque when a small gear ratio (high acceleration) is selected. This compensates for the naturally high acceleration effect of small gear ratios, preventing abrupt acceleration and maintaining smooth, comfortable riding experience while still achieving the desired speed increase.
3Stability of the object's composition
If transmission gear with large gear ratio is selected, then riding comfort is improved, but the torque on the wheel becomes too weak for effective propulsion
Solution Approach 1:
The control system performs preliminary action by increasing motor torque in advance when a large gear ratio (low acceleration) is selected. This compensates for the mechanical disadvantage of large gear ratios, ensuring sufficient wheel torque is delivered even though the transmission provides smooth, gradual acceleration.
Data Source
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AI summary
An electric vehicle 1 includes an electric motor 12, a transmission 14 to which a driving force of the electric motor 12 is transmitted, a wheel 6 to which the driving force of the electric motor 12 is transmitted via the transmission 14, a rotation speed aequisition unit 41 that acquires motor rotation speed M of the electric motor 12, and further includes a target motor power determination unit 31 that determines a target motor power W of the electric motor which is desired to be output from the electric motor 12 regardless of a transmission gear ratio G of the transmission 14, a target motor torque calculation unit 32 that calculates a target motor torque t that is obtained by dividing the target motor power W by the motor rotation speed M, and a motor control unit 33 that drives the electric motor 12 at the target motor torque t.