Ball Nut Radial Raceway Layout for Bending Load Isolation
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Solution Overview
Problem
Conventional ball nut and screw assemblies are prone to wear and seizing due to radial loads induced by bending moments, especially in articulating actuators like door opening systems and spoiler actuators.
Innovation Solution
The design incorporates additional radial outboard raceways at either end of the conventional helical raceway, allowing bearing balls to contact the outer surface of the screw between the conventional grooves, thereby isolating the conventional ball rows from radial loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional helical raceway design is used, then axial load transmission is achieved, but radial loads from bending moments cause wear and seizing
Solution Approach 1:
The invention segments the load-bearing function by introducing separate radial outboard raceways at each end of the helical raceway. These radial raceways isolate the outermost ball rows from radial loads generated by bending moments, while the central helical raceway continues to handle axial load transmission. This segmentation prevents radial loads from affecting the main load-bearing balls, thereby reducing wear and seizing.
Solution Approach 2:
The radial outboard raceways act as intermediary structures that intercept and accommodate radial loads before they can affect the primary helical raceway balls. By providing dedicated radial load paths through these outboard raceways, the invention protects the main load-bearing balls from harmful radial forces, extending assembly life.
2Reliability
If additional radial outboard raceways are added, then protection from radial loads is achieved, but device complexity increases
Solution Approach 1:
The invention merges the radial and axial load-bearing functions into a single integrated ballscrew assembly structure. The radial outboard raceways are incorporated at the ends of the helical raceway, creating a unified system that handles both radial and axial loads without requiring separate protective mechanisms. This merging approach achieves reliability improvement while controlling overall device complexity.
Data Source
AI summary
A ball nut and screw assembly includes a screw, and a nut received on the screw. A first raceway having a helical portion is defined between a convex groove of the screw and a concave groove of the nut. The first raceway has adjacent concave grooves to provide said helical portion. A first plurality of balls are in said first raceway, and a first radial outboard raceway is provided at a first end of the first raceway and a second radial outboard raceway provided at a second end of said first raceway. The first and second outboard radial raceways are formed between a concave groove formed in a first outboard component and the outermost, external surface of the screw that is in a position between said adjacent grooves of said screw and at least a first bearing ball is provided in said first radial outboard raceway.