Electric Motor Drive Unit Q Factor Reduction
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Solution Overview
Problem
Conventional drive units for electric-motor-assisted bicycles increase the Q Factor, which is the distance between the pedal attachment portions of the crankarms, thereby affecting the traveling performance, especially in racing bicycles.
Innovation Solution
A drive unit design that reduces the Q Factor by optimizing the housing dimensions and components, including a motor, crank axle, reduction gear, and one-way clutch, with a bush bearing used to limit axial movement without washers, allowing for a more compact configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional drive unit is attached to the vehicle-body frame, then the driving force is transmitted to the rear wheel, but the Q Factor increases
Solution Approach 1:
The patent repositions the motor output shaft from a conventional horizontal arrangement to a vertical arrangement, perpendicular to the crank axle. This dimensional change allows the reduction gear to be positioned above the crank axle, significantly reducing the Q Factor while maintaining effective power transmission to the rear wheel through the chain drive.
Solution Approach 2:
The reduction gear is positioned within the housing in such a way that it nests around the motor output shaft, with the rotatable shaft of the reduction gear positioned above the crank axle. This nested configuration minimizes the horizontal space required, thereby reducing the Q Factor while maintaining all necessary mechanical functions.
2Length of moving object
If the housing dimensions are reduced to decrease Q Factor, then the traveling performance improves, but the motor and reduction gear may not fit properly
Solution Approach 1:
The drive unit is divided into distinct functional modules: the motor housed in a motor housing, the reduction gear housed in a reduction gear housing, and the crank axle assembly. This segmentation allows each component to be manufactured and assembled independently, facilitating easier manufacturing and assembly even within reduced overall dimensions.
Solution Approach 2:
The motor housing and reduction gear housing are combined into a single integrated housing structure that contains both the motor and reduction gear. This merging reduces the overall number of external components and simplifies the assembly process while maintaining the compact configuration necessary for reduced Q Factor.
3Stability of the object's composition
If washers are used to limit axial movement of the rotatable shaft, then the axial position is stable, but the housing dimensions increase
Solution Approach 1:
The patent eliminates the need for separate washers to limit axial movement by integrating the axial positioning function directly into the bush bearing structure. The bush bearing is designed with features that inherently limit axial movement of the rotatable shaft, thereby removing the need for additional washer components and reducing overall housing dimensions.
Solution Approach 2:
The bush bearing serves multiple functions: it supports the rotatable shaft, limits axial movement, and provides a mounting surface for the reduction gear. This multi-functionality eliminates the need for separate washers or additional positioning components, maintaining axial stability while minimizing housing 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
The solution effectively reduces the Q Factor, enhancing the traveling performance of electric-motor-assisted bicycles by minimizing the crank axle length and housing dimensions, thus improving pedaling efficiency and reducing noise.
Implementation Method 1
The inner periphery of the bush bearing is permitted to slide in a circumferential direction relative to the small-diameter portion
Implementation Method 2
The cylindrical portion includes a helical gear provided thereon. This helical gear engages the helical gear on the motor output shaft
Implementation Method 3
The one-way clutch is located between the rotatable shaft and the cylindrical portion as determined along a radial direction of the rotatable shaft
Data Source
Figure 1
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AI summary
Q Factor is reduced in an electric-motor-assisted bicycle (10). A motor (25) includes a motor output shaft (2522) including a helical gear (252A) provided thereon. A reduction gear (24) includes a rotatable shaft (241) and a cylindrical portion (242). The rotatable shaft is inserted through the cylindrical portion. A helical gear (242A) provided on the cylindrical portion engages the helical gear on the motor output shaft. The rotatable shaft includes a first large-diameter portion (2415), a small-diameter portion (2417) and a second large-diameter portion (2416). The driving gear (241A) is provided on the first large-diameter portion. The small-diameter portion is connected to the first large-diameter portion such that these portions are arranged in the axial direction of the rotatable shaft. The second large-diameter portion is connected to the small-diameter portion such that these portions are arranged in the axial direction of the rotatable shaft. The reduction gear further includes a bush bearing (244). The bush bearing is disposed between an end surface of the first large-diameter portion and an end surface of the second large-diameter portion as determined along the axial direction of the rotatable shaft. The outer periphery of the bush bearing is fixed to the cylindrical portion. The inner periphery of the bush bearing is permitted to slide in a circumferential direction relative to the small-diameter portion. The bush bearing is permitted to move in the axial direction.