E-Bike Drive Unit Torque Sensing via Elastic Deformation
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Solution Overview
Problem
Existing electric bicycle drive units with coaxially arranged input and output shafts are heavy, complex, and lack efficient torque measurement capabilities, compromising compactness and cost-effectiveness.
Innovation Solution
A drive unit design with rotationally fixed output element and two spatially spaced signal transmitters on the drive assembly, generating measurement signals whose time intervals vary with the magnitudes of muscle-powered and externally powered torques, allowing for electronic inference and control of motor assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If coaxially arranged input and output shafts are used, then the drive unit design is more compact, but the output shaft becomes heavier and the construction becomes more complex
Solution Approach 1:
The drive unit is segmented into functionally independent components: the drive shaft for muscle-powered torque and the output element for motor torque transmission. This segmentation eliminates the need for a complex coaxial hollow shaft design, reducing weight and construction complexity while maintaining compactness through separate functional pathways.
Solution Approach 2:
The output element serves multiple functions: it transmits motor torque from the electric motor, receives and combines it with muscle-powered torque from the drive shaft, and provides mounting for signal transmitters. This multi-functionality eliminates the need for separate components, reducing overall weight and complexity compared to traditional coaxial designs.
2Volume of moving object
If coaxially arranged input and output shafts are used, then the drive unit design is more compact, but torque measurement becomes difficult due to differing force input at left and right ends
Solution Approach 1:
Torque measurement is segmented into two independent measurement systems: one for muscle-powered torque on the drive shaft and another for motor torque on the output element. This segmentation allows each torque component to be measured independently using simple signal transmitters, avoiding the complexity of measuring combined torque in a coaxial system with differing force inputs.
Solution Approach 2:
Signal transmitters are introduced as intermediary devices that convert mechanical torque information into electrical signals. These transmitters are mounted on the output element and drive shaft, providing indirect but accurate measurement of torque magnitudes without interfering with the mechanical torque transmission path, thus enabling easy torque measurement while maintaining compact design.
3Measurement precision
If two spatially spaced signal transmitters are used to measure torque, then precise torque measurement is achieved, but device complexity increases
Solution Approach 1:
The output element is designed as a multi-functional component that simultaneously transmits motor torque, receives muscle-powered torque, and serves as the mounting structure for both signal transmitters. This integration of multiple functions into a single component reduces device complexity compared to using separate components for each function.
Solution Approach 2:
The measurement function is merged with the torque transmission function by mounting the signal transmitters directly on the output element and drive shaft. This merging eliminates the need for separate measurement devices and complex installation structures, achieving precise torque measurement while maintaining simple device architecture.
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
Enables precise, cost-effective measurement and control of total torque without additional sensors, reducing weight and complexity while allowing finely graduated motor assistance.
Implementation Method 1
the time interval between which varies depending on the magnitude of the first and second drive torques... a change in the phase shift between the two measurement signals provided by the signal transmitters can be evaluated... This allows for electronic inferences about the current level of a (total) torque
Data Source
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AI summary
The proposed solution relates in particular to a drive unit (A) for an electric bicycle (1), comprising - an output element (4) for providing a torque for driving the electric bicycle (1), - a drive shaft (T) for generating a first drive torque by a driver of the electric bicycle (1) by means of muscle force, - an electric motor (E) for the generation by external force of a second drive torque at a rotor shaft (3) coupled to the electric motor (E), and - a transmission device (30, 40) for transmitting the second drive torque to the output element (4). In a proposed drive unit (A), the output element (4) is connected in a rotationally fixed manner to the drive shaft (T). Furthermore, the drive unit (A) has at least two signal transmitters (50, 52; 50, 51), which are spaced apart from one another spatially in relation to one another, on a drive assembly which comprises the output element (4) and the drive shaft (T), via which, during operation of the drive unit (A), two temporally successive measurement signals (αBasis, αGes; αBasis, αFahrer) can be generated, the time interval of which varies as a function of the levels of the first and second drive torques.