Bistable Coupling Spring for Hand-Held Power Tool Gear Switching
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Solution Overview
Problem
Existing hand-held power tools with switchable planetary gears face difficulties in reliably and ergonomically switching between gear positions, especially under load, due to engagement issues and the need for precise spring force management to prevent accidental adjustments.
Innovation Solution
A bistable coupling spring is used to transmit the actuating movement and apply force to the switching element, eliminating the need for additional spring elements and ensuring stable positions in two switching states, while an unstable intermediate position facilitates smooth transitions between them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional spring elements are used to force the ring gear into the desired shift position, then the reliability of gear engagement is improved, but the device complexity and component stress increase
Solution Approach 1:
The patent combines the coupling element and spring element into a single integrated component. The coupling element is designed with elastic properties that allow it to perform both the coupling function (transmitting actuating movement) and the spring function (applying force to secure the ring gear in the desired position). This merging eliminates the need for separate spring elements, thereby reducing device complexity while maintaining gear engagement reliability.
Solution Approach 2:
The coupling element is designed to serve multiple functions simultaneously: it acts as a mechanical coupler to transmit movement from the control element to the ring gear, and also functions as a spring element to apply restoring force and secure the gear position. This multi-functionality reduces the total number of components needed in the switching mechanism.
2Reliability
If spring force is increased to prevent accidental adjustment of the gear selector, then the security against inadvertent adjustments is improved, but the ease of operation deteriorates due to higher actuation force required
Solution Approach 1:
The coupling element is designed with elastic properties that allow it to dynamically adapt to different operational states. During normal operation, the elastic coupling element maintains a secure connection that prevents accidental adjustments. During intentional gear switching, the control element can overcome this elastic force to actuate the ring gear. The elastic nature provides a dynamic balance between security and operability.
Solution Approach 2:
The coupling element is designed with optimized elastic properties that provide sufficient securing force under normal conditions but can be easily overcome during intentional actuation. The spring constant and preload are carefully selected to provide just enough force to prevent accidental shifts while requiring only moderate force for deliberate gear changes by the operator.
3Ease of operation
If the coupling element is designed as a rigid connection, then the transmission of actuating movement is improved, but the ability to apply securing force to switching positions is lost
Solution Approach 1:
The coupling element is designed with specific elastic parameters (spring constant, damping characteristics, preload force) that allow it to effectively transmit actuating movements while simultaneously providing securing forces. By carefully selecting these parameters, the coupling element can be made sufficiently compliant to transmit motion smoothly yet sufficiently stiff to maintain stable switching positions and prevent accidental shifts.
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
This design simplifies the mechanism, reduces component loading, and enhances security against inadvertent adjustments, allowing reliable and ergonomic gear switching under various operating conditions, including load, without additional spring components.
Implementation Method 1
the coupling element, which transmits the actuating movement of the control element to the switching element mounted in the mechanical housing, is designed as a bistable coupling spring
Implementation Method 2
Bistability is preferably achieved or at least supported by pre-tensioning the spring ring, whereby the spring ring assumes a stable position in the two pivoted positions, whereas in an intermediate position the spring ring is unstable
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a hand-held power tool having a switchable mechanism with at least two operating positions, said positions being set via an adjustable operating element (11), wherein the operating element is coupled to an adjustable switching member (13) via a coupling element. The coupling element is configured as a bistable coupling spring (12).