Gear Crank Toothing for Torque Sensor Bottom Bracket
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Solution Overview
Problem
Existing torque sensor bottom brackets face challenges due to a large distance between the pedal crank and chainring shaft, leading to limited space for magnetic field sensors and electronics, and a time-consuming assembly process with screw connections.
Innovation Solution
A bottom bracket shell with a hollow shaft featuring teeth on one end for axial engagement with a complementary bottom bracket shaft, minimizing radial clearance and allowing for efficient torque transmission, combined with magnetized areas and magnetic field sensors for torque detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a screw connection is used to connect the chainring shaft and the shaft, then a non-rotatable connection is achieved, but the assembly process becomes time-consuming and requires predetermined tightening torque
Solution Approach 1:
The patent replaces the screw connection (mechanical fastening system) with a press-fit connection system. The chainring shaft is pressed directly onto the hollow shaft, eliminating the need for screws, tightening torque control, and complex assembly procedures. This substitution maintains the non-rotatable connection requirement while dramatically reducing assembly time and complexity.
2Reliability
If a screw connection is used to connect the chainring shaft and the shaft, then a non-rotatable connection is achieved, but the connection becomes complex
Solution Approach 1:
The patent extracts and removes the screw connection components entirely from the system. By eliminating the screws, washers, and associated fastening mechanisms, the connection system becomes simpler while maintaining its functional integrity. The press-fit connection between the chainring shaft and hollow shaft provides the necessary non-rotatable connection without the complexity of threaded fasteners.
3Strength
If the hollow shaft has a minimum material thickness, then structural strength is maintained, but the distance between the pedal crank and chainring shaft increases
Solution Approach 1:
The patent addresses the space constraint by changing the dimensional approach to torque sensing. Instead of using a long axial distance for torque measurement, the invention employs magnetic field sensors that detect torque through magnetic field changes in the hollow shaft wall. This allows torque detection through the shaft thickness rather than requiring significant axial length, enabling compact design while maintaining structural strength.
4Area of stationary object
If the radial clearance between the bottom bracket spindle and hollow shaft is minimized, then space utilization is improved, but the torque transmission through toothing becomes critical
Solution Approach 1:
The patent applies local quality by creating toothing features at specific locations on the hollow shaft and chainring shaft. These localized toothing elements are positioned to engage precisely, ensuring reliable torque transmission through the minimal radial clearance. The toothing provides localized mechanical interlocking that guarantees dependable torque transfer despite the overall compact radial dimensions.
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 design enables compact installation of magnetic field sensors, reduces assembly time, and effectively detects total torque from both pedal cranks, improving the efficiency and space utilization of torque sensor bottom brackets.
Implementation Method 1
the hollow shaft has teeth on the end face at a second axial end region, which teeth are provided for engagement with grooves of a bottom bracket shaft
Implementation Method 2
the hollow shaft has at least one magnetized area between the first and the second axial end area
Implementation Method 3
with which a magnetic field change caused by a torque applied to the bottom bracket shell can be detected
Data Source
Figure 1~2
Figure 3~4
AI summary
The bottom bracket sleeve (100) according to the invention for a torque sensor bottom bracket comprises a hollow shaft (110) and the bottom bracket sleeve (100) can be coupled at a first axial end region (111) of the hollow shaft to an output device, in particular a chainring carrier; wherein the hollow shaft (110) has end-face teeth (120) at a second axial end region (112) which are provided for engagement with grooves of a bottom bracket shaft; and wherein the hollow shaft (110) has at least one magnetized region (131, 132) between the first (111) and the second axial end region (112).