Multispeed Power Tool Transmission With Neutral-Biased Gear Shifting
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Solution Overview
Problem
Existing multispeed power tools face challenges in efficiently shifting between different overall gear reduction ratios and often have a high part count, leading to complexity and inefficiency.
Innovation Solution
The design incorporates a housing assembly and a transmission assembly with a reduction gearset and a speed selector mechanism. The reduction gearset features multiple planetary stages, and the speed selector mechanism includes a movable member, an actuator, and a shifter assembly to facilitate smooth gear ratio changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multispeed power tool uses multiple planetary stages in the reduction gearset, then the gear ratio change capability is improved, but the device complexity increases
Solution Approach 1:
The patent combines multiple planetary stages into a single integrated reduction gearset structure where sun gears, planet gears, and ring gears of different stages share common components. This merging approach enables multiple gear ratios to be achieved through selective engagement of braking elements rather than requiring separate, complex transmission systems for each ratio.
Solution Approach 2:
The patent introduces braking elements (such as pads or shoes) as intermediary components that selectively engage with sun gears or ring gears to control the gear ratio. These braking elements act as mediators between the motor and the output, enabling smooth transitions between different overall gear ratios without requiring complex shifting mechanisms.
2Adaptability or versatility
If the speed selector mechanism includes multiple components for gear shifting, then the gear ratio selection capability is improved, but the part count increases
Solution Approach 1:
The braking elements serve multiple functions: they act as one-way clutches during normal operation, provide over-center latching for positive engagement, and enable gear ratio selection when activated by the speed selector mechanism. This multi-functionality reduces the need for separate components for each function, thereby reducing the overall part count.
Solution Approach 2:
The over-center latching mechanism provides self-locking capability that automatically maintains the selected gear ratio without requiring continuous actuation or additional locking components. The mechanism uses its own geometry to provide stable engagement, eliminating the need for separate retaining elements or continuous control forces.
3Volume of moving object
If the transmission assembly is wholly received in the gearcase, then the tool compactness is improved, but the ease of repair deteriorates
Solution Approach 1:
The transmission assembly is designed as a modular unit with distinct components (planetary stages, braking elements, speed selector mechanism) that can be accessed and serviced independently. The gearcase is configured with access points or removable sections that allow technicians to reach internal components without disassembling the entire tool, maintaining compactness while facilitating repair.
Data Source
AI summary
A tool with a transmission having a reduction gearset and a speed selector. The speed selector has a member, an actuator and a shifter assembly. The member is movable between a first position, in which the member is non-rotatable, and a second position in which the member is coupled to a planet carrier of the reduction gearset for common rotation. The actuator includes a pivoting yoke and a follower that is coupled to the yoke. The follower engages the member so as to be axially movable with the follower. The shifter assembly has a selector switch, a switch fork, and a pair of springs. The selector switch is slidable between a first switch position and a second switch position. The shift fork is slidably coupled to the selector switch and receives the yoke. The springs cooperate to bias the shift fork relative to the selector switch into a neutral position.