Planetary Gear Transmission for Compact Multi-Speed Power Tools
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Solution Overview
Problem
Rotary power tools face challenges in achieving a balance between outputting various rotational speeds while maintaining a compact and miniaturized design, as existing solutions require a large number of reduction gears, which increases the length of the gearbox and hinders miniaturization.
Innovation Solution
The implementation of a transmission mechanism with multi-stage planetary gear sets, including a first-stage planetary gear set that can switch between drive and variable states, and a clutch mechanism to prevent over-torque, allowing for multiple output speeds with a reduced number of gears, thereby maintaining compactness and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple reduction gears are used to achieve multiple rotational speeds, then the number of output gears increases, but the length of the gearbox increases
Solution Approach 1:
The patent employs multi-stage planetary gear sets where planet gears are arranged in multiple stages along the axial direction. Each planetary gear set is nested within the same axial space, allowing multiple gear ratios to be achieved without proportionally increasing the gearbox length. The planet gears of different stages share the same central axis and are positioned concentrically, effectively nesting multiple transmission functions within a compact radial and axial envelope.
Solution Approach 2:
The patent transitions from a linear arrangement of reduction gears to a multi-dimensional planetary gear configuration. By arranging planet gears in multiple stages along the axial direction and utilizing the radial dimension for gear meshing, the system achieves multiple output speeds without extending the gearbox length proportionally. This dimensional reorganization allows compact packaging of multiple transmission functions.
2Length of stationary object
If the number of reduction gears is reduced for miniaturization, then the gearbox length decreases, but the ability to output various rotational speeds is compromised
Solution Approach 1:
Each planetary gear set is designed to serve multiple functions: it can operate in a drive state with a gear ratio of approximately 1 for direct power transmission, or in a variable state with gear ratios greater than or less than 1 for speed reduction or multiplication. The clutch mechanism enables each planetary gear set to be selectively engaged or disengaged, allowing a single planetary gear set to provide multiple output speed options depending on which clutches are activated.
Solution Approach 2:
The patent introduces a dynamic clutch mechanism that can selectively engage or disengage each planetary gear set based on operational requirements. This dynamic control allows the transmission system to adaptively switch between different gear ratios and operational modes (drive state or variable state) without requiring a fixed, complex mechanical linkage for each possible output speed, thereby achieving multiple speeds with fewer physical gears.
3Length of stationary object
If multi-stage planetary gear sets are used with fewer gears, then the gearbox length decreases, but the complexity of controlling gear ratios increases
Solution Approach 1:
The clutch mechanism is designed to automatically engage or disengage based on torque thresholds and operational conditions. When torque transmitted from the output shaft exceeds a set threshold, the clutch mechanism automatically prevents the output shaft from being driven through the transmission mechanism, providing over-torque protection without requiring external intervention. This self-regulating behavior reduces the need for complex external control systems.
Data Source
AI summary
A power tool includes a transmission mechanism provided with transmission gears for making an output shaft output different rotational speeds, where the number of transmission gears is greater than or equal to 3; the transmission mechanism includes multi-stage planetary gear sets; each stage of the multi-stage planetary gear sets includes one layer of planet gears in an axial direction; the total number of the multi-stage planetary gear sets is less than or equal to the number of transmission gears; and among the multi-stage planetary gear sets in the multiple stages, a first-stage planetary gear set closest to a motor shaft includes a first drive state and a first variable state, and any one of the remaining planetary gear sets is connected to a clutch mechanism.