Spindle Nut Ball Return Geometry for Low-NVH Ball Screws
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Solution Overview
Problem
Ball screws experience excessive wear, noise, and vibrations due to abrupt load relief, which affects NVH (noise, vibration, harshness) criteria, and existing solutions are complex and costly to produce.
Innovation Solution
A spindle nut with straight, cylindrical load-relief bores that guide balls out of and into the ball channel, featuring a three-dimensional surface structure and specific geometric relationships between the ball groove and load-relief bores to improve load relief and reduce manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ball returns are used to lift balls radially outwardly from the ball channel, then a closed recirculation path is achieved, but excessive wear, noise, and vibrations occur due to abrupt load relief
Solution Approach 1:
The invention replaces the conventional radial ball deflection with a curved transition path that guides balls tangentially from the ball channel into the return channel. This curved geometry eliminates abrupt load relief by providing a gradual transition, thereby reducing noise, vibration, and wear while maintaining closed ball recirculation
Solution Approach 2:
The ball return system is designed to gradually reduce the load on balls before they exit the ball channel, rather than allowing abrupt load relief. The curved transition path prepares the balls for recirculation in advance, smoothing the load relief process and preventing harmful NVH effects
2Object-generated harmful factors
If complex ball return designs are implemented to improve load relief, then NVH criteria are improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention integrates the ball return function directly into the spindle nut structure by forming the return channel as a continuous curved path within the nut body. This merging of functions eliminates the need for separate complex ball return components, achieving improved NVH performance through a simplified, unified structure that is more economical to manufacture
Data Source
AI summary
A spindle nut (S) for a ball screw is conventionally designed as a hollow cylinder with a central-symmetrical middle longitudinal axis (Z). The spindle nut has an internal thread, which is designed as a ball groove (K) arranged on the cylinder inner surface. Pairs of load-relief bores (B) serve as substantially cylindrical channels for guiding the balls out of and into the ball channel (K) through the wall of the spindle nut. Each load-relief bore (B) is distinguished by a generatrix (L), which has an intersection point (C) with the thread base line of the ball channel (K) and constitutes the geometric continuation of the traveling path of a ball from the ball channel (K) into the load-relief bore (B). A tangent (T) to the cylinder surface (G) runs in a parallel manner at a spacing a >0 to the generatrix (L), both T and L being perpendicular to a common normal (R) to the middle longitudinal axis (Z).