Electric Motor Torque Compensation for E-Bike Drag
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Solution Overview
Problem
In electric bicycles with a non-rotatable connection between the crankshaft and electric motor, cyclists experience increased pedaling effort and jerky rotation due to drag torque, particularly when pedaling in the negative direction of rotation or pushing backwards, as they must overcome the motor's drag torque and cogging torque.
Innovation Solution
A method that detects the negative direction of rotation and generates a motor torque smaller than the drag torque, using existing sensors like rotor position sensors and torque sensors, to reduce the driver's effort, simulating freewheeling by activating the electric motor to assist in pedaling or pushing, with the motor torque being constant and independent of speed or driver torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a non-rotatable connection is used between the crankshaft and electric motor, then the drive unit is lighter and more compact, but the driver experiences increased pedaling effort and jerky rotation due to drag torque
Solution Approach 1:
The control device generates a counteracting motor torque in the negative rotation direction before and during pedaling operations. This preliminary anti-action compensates for the drag torque and cogging torque of the electric motor, reducing the force the driver must apply to the pedals while maintaining the lightweight non-rotatable connection design
2Ease of manufacture
If a non-rotatable connection is used between the crankshaft and electric motor, then production cost is reduced, but the driver experiences sudden or jerky rotation when pushing the bicycle backwards
Solution Approach 1:
When the control device detects negative direction rotation (pushing backwards), it generates a motor torque that counteracts the cogging torque and drag torque. This preliminary anti-action prevents the sudden or jerky rotation that would otherwise occur, maintaining manufacturing simplicity while improving operational smoothness
3Ease of operation
If the electric motor is activated to generate motor torque in the negative direction, then the force required by the driver is reduced, but the motor torque must be carefully controlled to remain smaller than the drag torque
Solution Approach 1:
The control device continuously monitors rotation direction and generates motor torque in response to detected negative direction rotation. This feedback mechanism ensures the motor torque remains appropriately controlled (smaller than drag torque) to reduce pedaling effort without requiring complex manual intervention, automatically adjusting to maintain optimal force reduction
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 method reduces the stepping force required for pedaling in the negative direction and provides a smoother pedaling experience by compensating for drag torque, making it feel like freewheeling, thereby enhancing driving comfort and reducing the perceived effort when pedaling or pushing the bicycle.
Implementation Method 1
A motor torque directed in the negative direction of rotation is generated by means of an electric motor of the drive unit when a negative direction of rotation is detected
Data Source
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AI summary
Method for freewheel compensation for a vehicle (100) with a drive unit (150), in particular an electric bicycle, wherein the drive unit (150) has at least one rotatable component, wherein the rotatable component (102, 210, 151) may have a positive direction of rotation or a negative direction of rotation, wherein the positive direction of rotation is configured to drive a drive wheel of the vehicle (100) for forward travel, wherein the method comprises the following steps: detection (310) of the negative direction of rotation of a rotatable component (102, 210, 151) of the drive unit (150), and generation (330) of a motor torque (MM) directed in a negative direction of rotation by means of an electric motor (151) of the drive unit (150) when a negative direction of rotation has been detected, wherein the generated motor torque (MM) is less than a drag torque (MB) of the electric motor (151) and is configured toto reduce the force exerted by the driver of the vehicle (100) to rotate the electric motor (151).