Ball Screw Nut Enlarged Diameter Portions Reduce Retainer Friction
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Solution Overview
Problem
Ball screw mechanisms in steering systems experience increased friction and contact between the retainer and the nut due to tolerances and clearance, leading to potential axial end contact and elevated friction torque.
Innovation Solution
The nut features uniform and enlarged diameter portions with specific tapered angles to minimize contact with the retainer when it becomes inclined, reducing friction and allowing for reduced friction torque by avoiding contact between the retainer and nut axial ends.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If clearance is provided between the retainer groove and balls to allow for tolerances, then the retainer can move radially and accommodate manufacturing variations, but the axial ends of the retainer may come into contact with the axial ends of the nut, increasing friction and contact
Solution Approach 1:
The nut is designed with different diameter portions at different axial locations. The first enlarged diameter portion is provided at the axial end region to prevent contact with the retainer, while the second enlarged diameter portion is provided at the intermediate axial region to maintain proper ball engagement. This local differentiation allows the nut to simultaneously accommodate retainer movement while preventing harmful contact.
Solution Approach 2:
Instead of addressing the contact problem in the radial dimension only, the invention introduces axial dimension variations through enlarged diameter portions at different axial positions. This transforms the solution from a purely radial clearance problem to a three-dimensional geometric solution that prevents contact while maintaining functional clearance.
2Reliability
If the retainer is allowed to move radially to accommodate tolerances, then manufacturing variations can be absorbed, but friction torque of the nut increases due to contact between the retainer and nut axial ends
Solution Approach 1:
The nut incorporates localized enlarged diameter portions at specific axial regions. The first enlarged diameter portion at the axial end prevents retainer contact and reduces friction torque, while the second enlarged diameter portion at the intermediate region maintains proper ball engagement. This localized geometric modification allows the system to maintain reliability through tolerance compensation while minimizing energy loss from friction.
3Ease of manufacture
If the nut has a uniform diameter throughout, then manufacturing is simpler, but the axial ends of the retainer are more likely to contact the nut when the retainer is inclined, increasing wear and reducing durability
Solution Approach 1:
Rather than making the entire nut non-uniform, the invention applies localized enlarged diameter portions only at critical axial regions. The first enlarged diameter portion prevents contact at the axial end, and the second enlarged diameter portion maintains engagement at the intermediate region. This localized approach preserves manufacturing simplicity while significantly improving durability and wear resistance.
Solution Approach 2:
The nut's axial length is segmented into different functional regions with different diameter characteristics. The axial end region has an enlarged diameter to prevent contact, the intermediate region has an enlarged diameter to maintain engagement, and other regions maintain uniform diameter. This segmentation allows the nut to perform multiple functions with minimal geometric complexity.
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
This design effectively reduces friction and wear, enhancing the durability of the retainer and ball screw mechanism while improving steering system performance and quietness by minimizing contact and noise.
Implementation Method 1
a screw shaft with a helical screw groove on the outer circumferential surface and a nut with a helical screw groove corresponding to the screw groove of the screw shaft. When the nut is threadedly engaged with the screw groove of the screw shaft through balls, an axial force is applied to the screw shaft in accordance with rotation of the nut.
Implementation Method 2
The enlarged diameter portion is provided at at least one of opposite axial ends of a region on the inner circumferential surface of the nut. The region faces the retainer groove and retainer ends adjoining to opposite axial ends of the retainer groove. When the axial ends of the retainer approach the axial ends of the nut, the axial end of the nut provided with the enlarged diameter portion is less likely to come into contact with the axial end of the retainer. This allows a reduction in contact and friction between the retainer and the nut, thus making it possible to reduce a friction torque of the nut.
Data Source
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AI summary
A ball screw mechanism that allows a reduction in contact and friction between a retainer and a nut is provided. In a ball screw mechanism, a nut (31) is threadedly engaged with a screw groove of a rack shaft through balls retained in a retainer groove of a retainer, and an axial force is applied to the rack shaft in accordance with rotation of the nut (31). The nut (31) includes a uniform diameter portion (60) having a uniform inside diameter and enlarged diameter portions (70, 80) each having an inside diameter larger than that of the uniform diameter portion (60). The enlarged diameter portions (70, 80) are provided at opposite axial ends (31a, 31b) of a region on an inner circumferential surface of the nut (31). The region faces the retainer groove and retainer ends adjoining to opposite axial ends of the retainer groove.