Tapered Lobular Driver Geometry for Multi-Size Fastener Torque
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Solution Overview
Problem
Existing torque transmission drivers are limited in their ability to efficiently drive multiple sizes of fasteners without cam-out, inefficiency, and increased mis-installation, particularly in small fasteners due to dedicated driver sizes and susceptibility to cam-out and strip-out.
Innovation Solution
A torque transmission driver system featuring a tapered bit with alternating lobes and troughs, where each lobe has a tapering height and width with a constant ratio, and a driver side wall with a taper angle less than the recess side wall, allowing for engagement with multiple fastener sizes and reducing cam-out through a reverse drive angle and catch portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated driver size is used for each fastener size, then torque transmission reliability is improved, but device complexity and assembly efficiency deteriorate due to requiring multiple driver sizes
Solution Approach 1:
The driver bit is designed with a tapered geometry and lobular drive surfaces that can accommodate multiple fastener sizes within a range. The taper angle of the driver bit side wall is less than the taper angle of the fastener recess side wall, allowing the driver to engage with fasteners of varying sizes while maintaining reliable torque transmission. This eliminates the need for multiple dedicated driver sizes.
2Ease of operation
If angled drive surfaces are used to enable sliding movement, then ease of operation is improved, but harmful factors increase due to cam-out causing damage and mis-installation
Solution Approach 1:
The driver bit and fastener recess feature asymmetric lobular drive surfaces with specific taper angles. The driver bit taper angle is deliberately made less than the fastener recess taper angle, creating a geometric relationship that prevents cam-out while maintaining ease of insertion. This asymmetric geometry ensures the driver seats properly without generating harmful sliding movements.
3Productivity
If higher torques are applied to reduce fastening time, then productivity is improved, but reliability deteriorates due to lobe strip-out and driver failure
Solution Approach 1:
The invention optimizes the taper angles of both the driver bit and fastener recess as key geometric parameters. By setting the driver bit taper angle to be less than the fastener recess taper angle, the design allows for higher torque application during fastening operations without causing lobe strip-out or driver failure, thereby improving productivity while maintaining reliability.
Data Source
Figure 1A~1D
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Figure 6~7
AI summary
A fastener systems includes a fastener and a driver, each of which have three alternating lobes and troughs that define the drive surfaces. The three alternating lobes and troughs are each defined by an outer radius portion, a drive side transition, an inner transition radius, and a reverse drive portion. The fastener recess and the driver each also have a side wall defined by the outer transition radius that tapers at a taper angle relative to the rotational axis. The fastener side wall may taper at about 60. The driver side wall may taper at about 60. Alternatively, the driver side wall may taper at angle at least 10 less than the taper angle of the recess side wall, such as 42. The drive side transition defines a drive angle which may be between 0 and 5.