Electrically Assisted Bicycle Motor Drive Unit Segmentation
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Solution Overview
Problem
The single-shaft motor drive unit in electrically assisted bicycles experiences issues with chain durability due to smaller chain dimensions, interference with battery components, and reduced torque transmission efficiency, leading to frequent replacements and discomfort during gear changes.
Innovation Solution
The implementation of a speed reduction mechanism with low-speed and high-speed reduction gears, one-way clutches, and a selection clutch that allows for seamless gear switching without neutral states, minimizing rider discomfort and extending component lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-shaft motor drive unit is used to reduce device complexity, then the number of components is reduced, but chain durability deteriorates due to smaller chain dimensions
Solution Approach 1:
The motor drive unit is segmented into two separate shafts: a first shaft for receiving human driving force and a second shaft for outputting the resultant force. This segmentation allows the chain to be positioned on the second shaft away from the motor, enabling the use of a larger, more durable chain that can handle the combined loads without excessive wear.
Solution Approach 2:
A unidirectional transmission mechanism (one-way clutch) is introduced as an intermediary between the first shaft and the second shaft. This mediator allows torque transmission in one direction while preventing reverse torque from damaging the motor, thereby protecting the system and enabling more robust chain design.
2Adaptability or versatility
If gear switching is implemented in the single-shaft motor drive unit, then speed variability is improved, but rider comfort deteriorates due to neutral states during gear changes
Solution Approach 1:
The human driving force transmission path is designed to be continuous and independent of the gear switching mechanism. The first shaft continuously receives human pedaling force, and this force is always transmitted to the second shaft through the unidirectional mechanism, ensuring that the bicycle never enters a neutral state during gear changes and maintaining continuous propulsive force.
Solution Approach 2:
The transmission system is segmented into independent human force input path and motor force input path, both converging at the second shaft. This segmentation allows gear switching to occur in the motor path without interrupting the human force transmission, enabling smooth gear changes without loss of propulsive force.
3Device complexity
If the crank shaft receives both human driving force and auxiliary driving force at the same location, then device complexity is reduced, but torque transmission efficiency deteriorates due to force interference
Solution Approach 1:
The force reception points are segmented into two separate locations: the first shaft receives human driving force from the pedal, and the second shaft receives both the human driving force (transmitted from the first shaft) and the auxiliary driving force from the motor. This spatial segmentation prevents force interference and allows both forces to be transmitted efficiently without cancellation or interference effects.
Solution Approach 2:
The force combination is achieved in a different dimensional arrangement rather than at the same point. The human force is transmitted axially through the first shaft to the second shaft, while the motor force is applied radially or axially at the second shaft location, combining forces in multiple dimensions to achieve efficient torque transmission without interference.
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 configuration enhances torque transmission efficiency, reduces chain wear, and provides a smoother gear-changing experience by preventing neutral states, thus improving the overall performance and reliability of the electrically assisted bicycle.
Implementation Method 1
a first unidirectional transmission mechanism disposed between the first shaft and the second shaft
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An electrically assisted bicycle which can be provided with a transmission mechanism in a so-called motor drive unit and can also minimize discomfort and shock to a rider during a gear change is provided. A speed reduction mechanism 25 provided in a motor drive unit 20 includes a low-speed reduction gear 36, a high-speed reduction gear 41, a low-speed one-way clutch 51 disposed between the low-speed reduction gear 36 and a resultant-force transmission member 29, a high-speed one-way clutch 52 disposed between the high-speed reduction gear 41 and the resultant-force transmission member 29, and a selection clutch 45 removably engaged with the high-speed one-way clutch 52. The selection clutch 45 is engaged with the high-speed one-way clutch 52 so as to place the high-speed one-way clutch 52 into a free state, whereas the selection clutch 45 is disengaged from the high-speed one-way clutch 52 so as to activate the high-speed one-way clutch 52.