Compact Drive Device Radial Width Reduction via Nested Bearing
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Solution Overview
Problem
Conventional drive devices using electric motors with planetary gear mechanisms face challenges in reducing radial width due to the placement of bearings, which limits the ability to minimize the size of the device while maintaining output torque.
Innovation Solution
The drive device incorporates a motor unit with a sun gear unit, planetary gear units, and a carrier that supports the output unit via a bearing positioned radially inward of the planetary gear units, allowing for a more compact design without compromising torque output by optimizing the placement of components such as the first cylindrical portion and internal gear part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bearing is disposed radially outward of the planetary gear, then the output unit can be supported, but the radial width of the drive device increases
Solution Approach 1:
The bearing is positioned radially inward of the planetary gear units, with the first cylindrical portion of the carrier extending radially outward to provide support. This nested arrangement allows the bearing to be supported by the carrier structure rather than requiring radial space outward from the planetary gears, thereby reducing the overall radial width while maintaining support functionality
Solution Approach 2:
The support function is relocated from the radial direction to the axial direction by using the first cylindrical portion of the carrier that extends in the central axis direction. This dimensional shift allows the bearing to be supported without increasing radial width, as the support structure utilizes the axial dimension instead
2Length of moving object
If the radial width is reduced, then the device size is minimized, but the torque output may be compromised
Solution Approach 1:
The carrier is segmented into multiple functional portions: the first cylindrical portion that extends radially outward to provide support surface, the second cylindrical portion that surrounds the planetary gear units, and the connecting portion that links them. This segmentation allows each portion to be optimized for its specific function while maintaining overall compactness and torque transmission capability
Solution Approach 2:
The carrier portions are strategically positioned to provide support and torque transmission only where needed. The first cylindrical portion provides localized support for the bearing, while the second cylindrical portion provides localized support for the planetary gear units, allowing radial width reduction in non-critical areas without compromising torque output
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 enables a reduction in the radial width of the drive device while maintaining or increasing torque output, allowing for a more compact and efficient design suitable for applications like electric wheelchairs, which can accommodate larger power supplies without increasing size, thereby extending continuous driving time.
Implementation Method 1
a bearing that rotatably supports the output unit connected to the planetary gear is disposed radially outward of the planetary gear
Data Source
AI summary
A motor unit having a motor shaft, and a speed reduction mechanism connected to the motor shaft are included. The speed reduction mechanism includes a sun gear unit disposed on the motor shaft, planetary gear units meshing with the sun gear unit and arranged in the circumferential direction, a carrier at least a part of which surrounds the planetary gear units, and an output unit connected to the planetary gear units. The carrier includes a first cylindrical portion disposed outward of and above the sun gear unit and extending in the axial direction. The first cylindrical portion rotatably supports the output unit via a bearing, and the bearing is at least partly disposed radially inward of the radially outer end of the planetary gear unit.