Screw Fastener Torque Limiter Using Segmented Disk Stack
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Solution Overview
Problem
Conventional screw fasteners with torque limiters are large in size and difficult to assemble and service, as they require high spring biasing force to set a high torque limit value.
Innovation Solution
A screw fastener design featuring a multiple plate torque limiter with drive and driven disk members, a spring member, and a retaining mechanism that allows for a high torque limit without increasing size or spring force, facilitated by a disk supporting shaft with a polygonal cross-section for tool engagement and thin corrosion-resistant sheets to prevent surface seizure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional torque limiter structures are used, then the torque limit function is achieved, but the size of the fastener increases
Solution Approach 1:
The torque limiter is segmented into multiple thin disk members (drive disks and driven disks) that are stacked together. This segmentation allows the torque limiting function to be distributed across multiple interfaces, achieving the required torque limit without increasing the overall fastener diameter. The multiple disks create multiple friction surfaces that collectively provide the necessary torque resistance.
Solution Approach 2:
The invention transitions from a single-plane friction interface to a multi-layer stacked configuration. By arranging drive and driven disks in alternating layers along the axial direction, the torque limiting function is achieved through cumulative friction across multiple interfaces rather than requiring a large single friction surface, thus maintaining a compact radial dimension.
2Reliability
If high spring biasing force is used to set high torque limit value, then the torque limit value increases, but the spring force becomes excessively large
Solution Approach 1:
The torque limiting function is distributed across multiple disk interfaces rather than relying on a single high-force friction interface. Each interface contributes a portion of the total torque limit, allowing the use of multiple moderate-force springs instead of one high-force spring, thereby reducing the peak spring biasing force required.
Solution Approach 2:
Multiple drive disks and driven disks are combined in a stacked arrangement, creating multiple torque-limiting interfaces in series. The cumulative effect of friction across all interfaces achieves the desired torque limit value while allowing each individual spring to exert a lower, more manageable force.
3Reliability
If conventional torque limiter structures are used, then the torque limit function is achieved, but the assembly and servicing difficulty increases
Solution Approach 1:
The torque limiter is designed as a modular stack of discrete drive disks and driven disks that can be individually assembled and disassembled. This segmentation allows for easy maintenance and repair, as individual disk members can be replaced or adjusted without affecting the entire fastener assembly, significantly improving serviceability.
Solution Approach 2:
The disk members are designed with rotational freedom around a central axis, allowing them to be easily installed and removed. The dynamic capability of the disks to rotate independently facilitates simple assembly procedures and enables straightforward servicing by allowing technicians to access and replace individual components without complex disassembly.
4Device complexity
If friction surfaces are used without corrosion protection, then the structure remains simple, but surface seizure occurs due to corrosion
Solution Approach 1:
Thin corrosion-resistant films or coatings are applied to the friction surfaces of the disk members. These thin protective layers prevent corrosion and surface seizure while maintaining the simplicity of the overall structure. The films do not significantly increase device complexity but provide essential corrosion protection for reliable operation.
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
Enables easy assembly and servicing with a high torque limit value, reducing the need for separate tools and minimizing the risk of corrosion, while maintaining a compact size and lower spring force.
Implementation Method 1
the fastening torque is transmitted from the head member to the male thread member owing to the frictional engagement between the mutually opposing slopes
Implementation Method 2
a spring member (58) disposed on the outer circumferential surface of the disk supporting shaft portion (36) to urge the drive disk members (50) and the driven disk members (52) toward the annular end surface (18)
Implementation Method 3
when the head member is turned with a fastening torque greater than the prescribed limit value, the mutually opposing slopes start slipping relative to each other so that the male thread member is prevented from being threaded into the nut with a fastening torque exceeding the prescribed limit value
Data Source
AI summary
Provided is a screw fastener provided with the function of a torque limiter which allows a high limit value to be set for the fastening torque without increasing the size thereof or the spring force of the spring member, and is easy to assemble and service. A multiple plate torque limiter is formed by a plurality of drive disk members (50) and a plurality of driven disk members (52) between a first member (10) and a second member (30), and the first member (10) and the second member (30) are detachably joined to each other by a retaining screw (22).