Nylon Resin Pulley Assembly for Low-Cost Ball Nut Torque Transfer
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Solution Overview
Problem
The existing torque transmitting assemblies, particularly those involving steel driven pulleys and ball nuts, are costly due to machining requirements and have complex assembly processes, including the use of screw fasteners and centering rings.
Innovation Solution
A method of fabricating a ball nut assembly with a keyway slot and a polymer pulley having an inner surface with a bore, cut-out, and radially extending torque members, allowing for a simpler assembly process where the polymer pulley is pressed onto the ball nut, reducing machining costs and assembly time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If steel driven pulley with threaded bores is used, then torque transmission is achieved, but machining costs increase
Solution Approach 1:
The patent uses a polymer material (nylon resin) instead of traditional steel for the driven pulley. The polymer is injected directly into the ball nut housing, creating a composite structure where the polymer itself forms both the pulley body and the torque transmitting features, eliminating the need for separate steel components and expensive machining operations.
Solution Approach 2:
The invention changes the material parameter from metal to polymer and modifies the manufacturing process parameters by using injection molding instead of machining. This allows features like torque members and keyway slots to be formed directly during molding, eliminating post-manufacturing machining steps.
2Reliability
If screw fasteners are used to assemble driven pulley to ball nut, then secure connection is achieved, but assembly time increases
Solution Approach 1:
The patent merges the driven pulley and ball nut into a single integrated component. The polymer pulley is injected directly into the ball nut housing, eliminating the need for separate fasteners and reducing the assembly to a single injection molding operation. The torque members are formed as integral parts of the polymer structure.
Solution Approach 2:
The polymer material itself provides the connection function through direct injection into the housing. The material flows into and around the ball nut features, creating self-contained torque transmission paths and keyway slots that eliminate the need for external fastening components.
3Manufacturing precision
If centering ring is added to locate driven pulley, then concentric alignment is achieved, but device complexity increases
Solution Approach 1:
The patent eliminates the centering ring by integrating the alignment function directly into the injection molding process. The polymer pulley is molded with built-in concentricity features that ensure proper alignment with the ball nut shaft, removing the need for separate centering components.
4Strength
If multiple machining features are created in ball nut, then torque transmission is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces traditional metal-on-metal torque transmission with a polymer-based system. The nylon resin pulley provides sufficient torque transmission capability while allowing features to be formed through injection molding rather than expensive machining operations.
Solution Approach 2:
The invention changes the manufacturing method from machining to injection molding, fundamentally altering how torque transmission features are created. The polymer material allows for direct formation of complex geometries like keyway slots and torque members without the need for subtractive machining processes.
Data Source
AI summary
A method of fabricating a ball nut assembly is provided. The method includes providing a ball nut having a keyway slot. The method also includes forming a polymer pulley having an inner surface defining a bore, a cut-out formed in the inner surface, and a torque member extending radially inward from the inner surface, wherein the keyway slot is configured to receive the torque member therein.