Power Tool Gear Shifting Mechanism With Spring-Locked Detents
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Solution Overview
Problem
Existing gear-shifting mechanisms in electric hand tools often experience direct coupling of the rotary selector switch to gear components, leading to undefined intermediate positions during mode switching, causing wear and potential failure.
Innovation Solution
A combined spring arrangement with two different spring types is used, where a first curved spring ensures a gradual increase in torque and a second snap spring acts as a locking mechanism to prevent undefined intermediate positions, securing the rotary selector switch against axial displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct coupling of the rotary selector switch to the gear components is used, then the structure is simple, but undefined intermediate positions occur during switching causing wear and potential failure
Solution Approach 1:
The patent introduces spring elements as intermediary components between the rotary selector switch and the gear components. These springs act as mediators that decouple the direct mechanical connection, allowing the switch to operate without directly transmitting forces that would cause intermediate positions and wear. The spring elements absorb and control the forces during switching, preventing harmful direct coupling while maintaining the switching function.
Solution Approach 2:
The spring elements are pre-loaded and positioned to provide cushioning before the switching action occurs. This beforehand cushioning prevents the harmful direct impact and intermediate positions by absorbing the switching forces in advance, ensuring that the gear components are protected from damaging collisions during mode transitions.
2Reliability
If spring elements are introduced to prevent intermediate positions, then switching reliability improves, but the device complexity increases
Solution Approach 1:
The spring elements are designed to perform multiple functions simultaneously: they provide cushioning during switching, maintain pre-loaded positions, control the timing of gear engagement, and prevent intermediate positions. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving reliable switching.
Solution Approach 2:
The patent merges the switching actuation function with the positioning and locking functions into a single integrated spring mechanism. The spring elements combine the roles of actuator, positioner, and latch, eliminating the need for separate mechanisms for each function and thus minimizing the overall complexity increase.
3Ease of operation
If the rotary selector switch is directly coupled to the shift rod, then the switching action is direct, but wear and tear increases over time
Solution Approach 1:
The spring elements serve as intermediaries between the rotary selector switch and the shift rod, maintaining the responsiveness of the switching action while protecting the components from direct wear. The springs transmit the switching motion efficiently while absorbing the harmful forces that would otherwise cause wear and tear on the direct coupling components.
Solution Approach 2:
The pre-loaded spring elements provide cushioning before the shift rod is actuated, preventing direct impact and reducing wear during the switching process. This beforehand cushioning ensures that the rotary selector switch and shift rod engage smoothly without damaging collisions, thereby extending component durability while maintaining operational responsiveness.
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 combined spring arrangement prevents undefined intermediate positions during mode switching, reducing wear and ensuring reliable operation by gradually increasing torque and locking the selected position, thus enhancing the durability of the power tool.
Implementation Method 1
a first spring element (6) designed as an arc spring attached to the shift rod (2), wherein the actuating torque is transmitted from the rotary selector switch (1) to the shift rod (2) via the first spring element (6)
Implementation Method 2
at least one second spring element (7a, 7b) designed as a snap spring which interacts with the shift gate (3) to lock the shift rod (2) in the selected shift position
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The invention relates to a gear shifting mechanism for selecting between different operating modes in an electric hand tool, comprising a manually operable rotary selector switch (1) for adjusting the angle of a shift rod (2) provided with a shift cam (3), which acts on subsequent gear elements via molded-on actuating cams to set a desired operating mode, wherein cooperating spring elements are provided for locking the shift rod (2) in the selected shift position, wherein the spring elements are designed as a combined spring arrangement, comprising at least a first spring element (6) of a first spring type, which is arranged in the chain of action between the rotary selector switch (1) and the shift rod (2), and at least a second spring element (7) of a second spring type.which interacts with the shift gate (3) of the shift rod (2) in corresponding detent positions to lock a selected shift position.