Bicycle Pawl Freewheel Torque Sensing With Position-Independent Measurement
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Solution Overview
Problem
Existing bicycle freewheels, particularly in e-bikes, suffer from imprecise measurement of transmitted drive force due to deformation caused by radial forces and varying relative positions of connected shafts, leading to disturbances in torque detection.
Innovation Solution
A pawl freewheel design with a first ring having alternating toothed and toothless sections, combined with a sensor device to detect deformation, ensures precise torque measurement by minimizing the influence of radial forces and relative positions, using strain gauges or other sensors to calculate torque based on deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a freewheel is used to transmit torque in a locked position, then power transmission from crank axle to wheel is enabled, but radial forces deform the freewheel causing imprecise torque measurement
Solution Approach 1:
The freewheel is divided into two separate rings: a first ring that rotates with the crank axle and a second ring that rotates with the wheel. This segmentation allows the torque measurement to be taken on the first ring away from the engagement point, eliminating the deformation caused by radial forces while still enabling power transmission through the pawl-teeth engagement between the two rings.
2Measurement precision
If the freewheel connects two shafts in a rotationally fixed manner, then drive power transmission is enabled, but the detected deformation corresponds only imprecisely to the transmitted drive force
Solution Approach 1:
The pawl acts as an intermediary mechanism between the two rings. It engages with the teeth on the first ring to transmit torque while allowing the sensor on the first ring to measure deformation away from the engagement point. This intermediary arrangement maintains reliable power transmission through mechanical engagement while enabling precise torque measurement at a location不受 radial forces.
3Measurement precision
If a sensor device detects deformation of the first ring, then torque measurement is enabled, but positional dependence causes disturbances in the detected drive force
Solution Approach 1:
The torque measurement function is extracted from the engagement interface between the pawl and teeth. By placing the sensor on the first ring at a location away from where the pawl engages with the teeth, the measurement is taken at a point that does not experience the positional variations and radial forces associated with the engagement, thereby eliminating positional dependence while maintaining torque measurement capability.
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
The design allows for accurate and position-independent torque measurement, enabling effective power control and gear shifting in bicycles, particularly e-bikes, by reducing disturbances from radial forces and varying engagement positions.
Implementation Method 1
The sensor device can, for example, include one or more strain gauges attached to the first ring
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a drive arrangement for a bicycle with a pawl freewheel (50), which has a first ring (52) with teeth and a second ring (54) with at least one pawl (56) movably mounted thereon. The pawl (56) is in a locked position in engagement with the teeth. The drive arrangement also includes a sensor device designed to detect deformation of the first ring (52) of the pawl freewheel (50) due to an applied drive force. The first ring (52) has at least one toothed section (60, 62) and one toothless section (64, 66) in the circumferential direction. The invention further relates to a bicycle.