Torque-Dependent Disconnect Coupling for Overtightening Protection
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Solution Overview
Problem
Existing disconnect couplings in electric hand-held power tools, such as screwdrivers, fail to reliably and efficiently prevent overtightening or motor overload during screw connections, leading to potential damage.
Innovation Solution
A torque-dependent releasable disconnect coupling with a cam ring and guide rings that axially pretension a switching element, allowing for defined switching positions and reliable opening when release torques are exceeded, ensuring robust operation and protection against overtightening or motor overload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing disconnect couplings are used to prevent overtightening, then protection function is provided, but reliability is insufficient and wear is high
Solution Approach 1:
The disconnect coupling is segmented into functionally independent components: the cam ring with cam track for torque-dependent switching, the guide ring for precise ball guidance, and the spring element for axial pretensioning. This segmentation allows each component to be optimized for its specific function, improving overall reliability while reducing wear through distributed load paths.
Solution Approach 2:
The disconnect coupling employs dynamic elements including a movable cam ring that can shift axially under torque load, a spring element that provides dynamic pretensioning, and switching elements (balls) that move between engaged and disengaged positions. This dynamic design allows the coupling to adapt to varying torque conditions reliably while reducing impact loads that cause wear.
2Reliability
If disconnect coupling components are added to prevent overtightening, then protection function is improved, but device complexity increases
Solution Approach 1:
The invention merges multiple functions into a compact integrated structure: the cam ring simultaneously provides torque transmission, torque sensing, and switching actuation; the guide ring combines axial guidance and radial containment functions; and the spring element integrates pretensioning and reset functions. This merging reduces the number of separate components while maintaining reliable protection against overtightening.
Solution Approach 2:
The cam ring serves multiple functions: it transmits torque during normal operation, senses when release torque is exceeded, and actuates the switching elements to open the coupling. The guide ring provides both axial positioning and radial confinement of the switching elements. This multi-functionality reduces component count and simplifies the overall device structure while ensuring reliable protection.
3Reliability
If switching elements are guided with high precision to define switching positions, then switching reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The invention employs curved cam tracks in the cam ring and corresponding curved guide paths in the guide ring, replacing straight-line guidance. The spherical switching elements (balls) move along these curved paths, which naturally accommodate manufacturing tolerances while maintaining well-defined switching positions. The curved geometry distributes contact stresses and reduces sensitivity to dimensional variations.
Solution Approach 2:
The design allows for adjustment of the axial pretensioning force via the spring element, which compensates for variations in manufacturing precision. By adjusting the pretensioning parameter, the switching characteristics can be optimized to ensure reliable position definition even with moderate manufacturing tolerances in the cam and guide ring dimensions.
4Reliability
If axial pretensioning is applied to switching elements, then switching reliability is improved, but force requirements increase
Solution Approach 1:
The spring element provides dynamic axial pretensioning that automatically adjusts to operational conditions. The pretensioning force is not fixed but varies with the operational state, providing sufficient force for reliable torque transmission during normal operation while allowing the coupling to open when release torque is exceeded. This dynamic approach reduces the peak force requirements compared to a rigid pretensioning system.
Solution Approach 2:
The axial pretensioning force can be adjusted by selecting different spring elements or modifying the spring pre-compression, allowing optimization of the force parameter to achieve the minimum required for reliable operation. This parameter adjustment capability enables the system to maintain reliable torque transmission with minimized pretensioning forces.
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 coupling ensures reliable protection of screw connections from overtightening and motor protection by defining switching positions, providing a simple design with low wear, low vibration, and low noise operation, while maintaining ease of implementation.
Implementation Method 1
The cam ring and the second guide ring are axially pretensioned against one another and accommodate the at least one switching element axially between them
Data Source
AI summary
A torque-dependent releasable disconnect coupling for an electric hand-held power tool, in particular a screwdriver, for selectively transmitting a torque from a drive shaft to an output shaft that is coaxial with respect to the drive shaft. An axially nondisplaceable guide ring guides a switching element, in particular a ball, and a second guide ring. A cam ring and the second guide ring are axially pretensioned against one another and accommodate the switching element axially between them. The disconnect coupling may be brought from a first, non-torque-transmitting switching position into a second, torque-transmitting switching position. The switching element is deflected in the axial direction relative to the cam ring, against the action of the pretensioning, when a first release torque in the first switching position is exceeded, thus bringing he disconnect coupling into the second switching position.