Tapered Lobular Fastener Interface to Reduce Cam-Out
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Solution Overview
Problem
Existing torque transmission systems face inefficiencies and failures due to limited compatibility with multiple fastener sizes, leading to increased mis-installation and wear, particularly in small fasteners, as they often require separate drivers and are prone to cam-out and strip-out under torque.
Innovation Solution
A fastener system with a recess defined by alternating lobes and troughs, and a driver with corresponding tapered lobes and troughs, allowing a single driver to effectively engage and torque multiple fastener sizes, with a taper angle and drive transition design that reduces cam-out and enhances strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate drivers are used for each fastener size, then torque transmission reliability is improved, but device complexity and operational efficiency deteriorate due to requiring multiple drivers and frequent changes
Solution Approach 1:
The driver bit is designed with a universal geometry that can engage multiple fastener sizes through a single interface. The lobular drive system with alternating convex and concave surfaces creates a standardized engagement pattern that accommodates various fastener dimensions without requiring different driver types, thus improving operational efficiency while maintaining reliable torque transmission.
Solution Approach 2:
The driver and fastener interface uses variable drive angles and lobe geometries that can accommodate different fastener sizes. By changing the engagement parameters (lobe width, drive angle, surface curvature) rather than the fundamental driver design, the system maintains reliable torque transmission across multiple fastener sizes with a single driver.
2Ease of manufacture
If traditional spline-type torque drive systems are used, then manufacturing ease is improved, but torque transmission strength deteriorates due to inability to retain drive angles less than five degrees and resulting lobe failure
Solution Approach 1:
The lobular drive system replaces traditional spline surfaces with alternating convex and concave curved surfaces. This curvature allows the interface to maintain lower drive angles (less than five degrees) while distributing stress more evenly, preventing lobe failure and strip-out. The curved surfaces enable smoother torque transmission and reduce stress concentration points that lead to fatigue failure.
Solution Approach 2:
The driver and fastener interface combines complementary geometric features (convex lobes on one component, concave lobes on the other) to create a unified torque transmission system. This composite geometric approach allows the system to achieve both manufacturing feasibility and high torque capacity by distributing loads across multiple engagement surfaces.
3Productivity
If higher torques are applied to traditional drive systems, then productivity is improved, but reliability deteriorates due to force components causing lobe strip-out and driver cam-out
Solution Approach 1:
The curved lobular surfaces distribute applied torque more evenly across the engagement interface, reducing peak stress concentrations that cause strip-out. The alternating convex and concave geometry creates multiple load paths, allowing higher torques to be applied without compromising lobe engagement reliability, thus enabling faster fastening operations.
Solution Approach 2:
The lobular drive geometry converts the potentially harmful cam-out tendency into a beneficial self-centering effect. The alternating convex and concave surfaces create engagement forces that naturally align the driver with the fastener axis, preventing cam-out even under high torque conditions and maintaining reliable connection during high-speed operations.
4Strength
If zero drive angle with elliptically curved surfaces is used, then torque transmission strength is improved, but adaptability deteriorates due to inability to accommodate multiple fastener sizes with single driver
Solution Approach 1:
The lobular drive interface with alternating convex and concave surfaces creates a universal engagement pattern that maintains effective torque transmission across multiple fastener sizes. The standardized geometric relationship between driver and fastener lobes allows a single driver design to reliably engage various fastener dimensions while preserving the strength benefits of the curved surface geometry.
Data Source
AI summary
A fastener system includes a fastener and a driver, each of which have three alternating lobes and troughs that define the drive surfaces. Each alternating lobes and troughs is 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 a 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 an 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°.