Two-Speed Gear Assembly With Linear Sleeve Shifting for Power Tools
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Solution Overview
Problem
Power tools face design challenges in varying speed and torque requirements, leading to inefficient operation, particularly during the rundown phase of tightening large screws, where low rotational speed results from high torque demands, and existing two-speed transmissions lack precise control over gear shifting, causing potential damage.
Innovation Solution
A two-speed power transmission system with a planetary gear and a gear shift assembly using an axially movable coupling sleeve displaced by a linear actuator, allowing for precise control of torque direction between high torque/low speed and low torque/high speed modes, and incorporating a linear motor with internal position sensing for accurate mode switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If one or more planetary gear steps are used to achieve high torque levels, then the desired torque levels are provided, but the rotational speed provided decreases correspondingly resulting in low rotational speed during run down
Solution Approach 1:
The patent implements a two-speed transmission system that dynamically switches between two operational modes: a first speed ratio for high-speed/low-torque operations (rundown phase) and a second speed ratio for low-speed/high-torque operations (tightening phase). This dynamic switching allows the system to adapt its characteristics based on operational requirements, resolving the contradiction between maintaining high rotational speed and providing high torque levels.
2Measurement precision
If complex mechanisms comprising synchronizing rings or bulky sensors are used to control gear shifting, then precise control of gear elements position is achieved, but the design becomes complex and requires a lot of space
Solution Approach 1:
The patent extracts and eliminates complex control mechanisms such as synchronizing rings and bulky sensors from the transmission system. Instead, it employs a simplified control approach using a control unit that receives signals from a sensor and actuates a shifting mechanism to change between speed ratios. This extraction of unnecessary components reduces design complexity while maintaining precise control through electronic control.
Solution Approach 2:
The patent replaces complex mechanical control mechanisms (synchronizing rings, mechanical sensors) with an electronic control system. A control unit receives electrical signals from a sensor detecting rotational speed or torque, processes this information, and actuates a shifting mechanism accordingly. This substitution of mechanical systems with electronic control reduces complexity and space requirements while maintaining measurement precision.
3Speed
If two-speed power transmissions are used to provide higher rotational speed during run down, then the rundown phase speed is improved, but lack of precise control over the actual current position of the gear elements may result in destroyed gears and couplings
Solution Approach 1:
The patent implements a feedback control system where a sensor continuously detects the rotational speed or torque of the drive mechanism and sends signals to a control unit. The control unit processes this feedback information and actuates the shifting mechanism to change between speed ratios at appropriate moments. This closed-loop feedback ensures precise control of gear element positioning during transitions, preventing damage while maintaining high-speed operation during rundown.
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 system provides precise and accurate control of gear shifting, ensuring efficient operation across varying torque and speed demands, preventing gear damage and optimizing the rundown and tightening phases with improved control and compact design.
Implementation Method 1
The linear actuator comprises a linearly movable push bar arranged to displace the coupling sleeve between the first and second position
Implementation Method 2
a two-speed power transmission comprising a planetary gear and a two speed gear shift assembly for directing torque through the planetary gear in a high torque/low speed drive mode or past the planetary gear in a low torque/high speed drive mode
Data Source
Figure 1~2
AI summary
The present specification relates to a power tool comprising a an input shaft and an output shaft and a two-speed power transmission (T) comprising a planetary gear (4) and a gear shift assembly for directing torque through or past the planetary gear (4) comprising a driving member, a driven member (1) and an axially movable coupling sleeve (6) arranged to intercouple in a first position the driving member (2) and the driven member (1) and to intercouple in a second position the planetary gear (4) and the driven member (1). A linear actuator (13, 14) is arranged to displace the coupling sleeve between the first and second position, wherein the linear actuator comprises a linearly movable push bar (13) arranged for displacing the coupling sleeve. The present specification also relates to a method in and a two-speed power transmission for such a power tool.