Planetary Gear Reduction Mechanism Housing Size
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Solution Overview
Problem
Existing electric power tools, such as impact drivers, face a challenge in reducing the size of the housing due to the increased diameter of the carrier and bearing required for the speed change mechanism, which results in a larger tool size.
Innovation Solution
The electric power tool design includes a planetary gear reduction mechanism with a separate gear portion that is assembled between the final-stage carrier and planetary gears, allowing the size of the carrier and bearing to be set independently of the gear portion's diameter, thereby reducing the overall housing size without increasing the number of assembly parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the gear portion is integrally connected to the carrier, then the structure is simplified, but the carrier and bearing must increase in diameter to accommodate the gear portion, resulting in a larger housing size
Solution Approach 1:
The gear portion is separated from the carrier into an independent component. The carrier no longer needs to accommodate an integral gear portion, allowing the carrier diameter to be reduced. The bearing can also be sized independently without being constrained by the gear portion diameter, thereby reducing the overall housing size while maintaining functional integration through separate assembly.
2Ease of manufacture
If the bearing is assembled from the rear side of the carrier with an integral gear portion, then the assembly process is simplified, but the inner diameter of the bearing must be greater than the outer diameter of the gear portion, increasing the carrier and bearing diameter
Solution Approach 1:
By separating the gear portion from the carrier, the bearing can be assembled with a smaller inner diameter that does not need to accommodate the gear portion. The gear portion can be assembled separately or attached afterward, allowing the bearing diameter to be optimized for its actual functional requirements rather than being constrained by the gear portion size.
Solution Approach 2:
The gear portion is positioned in a different spatial arrangement relative to the carrier and bearing assembly. Instead of requiring the bearing to accommodate the gear portion diameter in the radial direction, the gear portion is arranged such that the bearing can be assembled with a smaller diameter, effectively changing the dimensional relationship between these components.
3Speed
If the internal gear is positioned to mesh with both planetary gears and gear portion, then speed reduction is cancelled for high-speed mode, but the gear portion diameter constrains the bearing and carrier size
Solution Approach 1:
The separation of the gear portion from the carrier allows the bearing and carrier to be sized independently of the gear portion diameter. This enables the internal gear to be positioned optimally for achieving high-speed mode by meshing with both planetary gears and the separate gear portion, without being constrained by the need to accommodate an integral gear portion in the carrier.
Data Source
AI summary
An electric power tool includes a housing (2), a motor (4) disposed in the housing (2), a planetary gear reduction mechanism (6) and an internal gear (22). The planetary gear reduction mechanism (6) includes multi-stage planetary gears (21, 24), multi-stage carriers (20, 23) each configured to carry a plurality of planetary gears (21, 24), and a bearing (25) assembled with a final-stage carrier (23) from a rear side of the final-stage carrier (23) to rotatably support the final-stage carrier (23). The internal gear (22) is configured to be rotatable and axially slidable while allowing planetary motion of final-stage planetary gears (24) supported by the final-stage carrier (23). A gear portion provided on the final-stage carrier (23) is formed as a separate gear (29) which is assembled with the final-stage carrier (23) from the rear side of the final-stage carrier (23) after assembling the bearing (25) with the final-stage carrier (23).