Spindle Nut Relief Bore Geometry for Low-NVH Ball Screws
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Solution Overview
Problem
Existing ball screw designs face challenges in reducing noise, vibration, and harshness (NVH) due to abrupt ball relief, leading to excessive wear and operating noise, particularly in the automotive industry, and current solutions are complex and costly to produce.
Innovation Solution
A spindle nut with rectilinear relief bores that continue the ball groove path, featuring a tangent surface parallel to the cylinder surface at a defined distance, allowing a gradual ball transition into the relief bore, reducing NVH issues while simplifying production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a traditional ball deflection design is used with abrupt ball relief, then the structure is simple, but it causes excessive wear, operating noise, and vibrations (NVH issues)
Solution Approach 1:
The invention applies curvature by designing the ball relief channel with a smooth, curved transition path instead of an abrupt straight-line relief. The curved geometry allows balls to transition gradually from the ball channel into the return channel, reducing impact forces and NVH issues while maintaining structural simplicity
Solution Approach 2:
The invention changes the geometric parameters of the ball relief channel, specifically the angle and curvature radius, to optimize the ball transition. By adjusting these parameters, the design achieves smooth ball relief that reduces wear and noise without significantly increasing structural complexity
2Object-affected harmful factors
If a tangential ball deflection design is used to improve ball relief, then NVH issues are reduced, but the production becomes technically challenging and costly
Solution Approach 1:
The invention segments the ball deflection structure into distinct functional zones: a ball channel section, a transition section with curved relief, and a return channel section. This segmentation allows each zone to be optimized independently for its specific function while simplifying the overall manufacturing process through modular design
Solution Approach 2:
The curved transition geometry is designed with standardized radius values that can be efficiently produced using conventional CNC machining or electrical discharge machining (EDM), balancing the need for smooth ball relief with manufacturing ease and cost-effectiveness
3Device complexity
If abrupt ball relief is used in the ball deflection, then the structure remains simple, but it generates resultant forces that catapult balls causing wear and noise
Solution Approach 1:
The curved relief channel geometry gradually redirects balls from the ball channel into the return channel, distributing the relief force over a longer path and reducing peak catapulting forces. This curved transition eliminates abrupt directional changes that cause impact loads and noise
Data Source
Figure 1~2
Figure 3
AI summary
A spindle nut (S) for a ball screw drive is typically designed as a hollow cylinder with a centrally symmetric longitudinal axis Z. The spindle nut has an internal thread that forms a ball groove (K) on the inner surface of the cylinder. Paired relief bores B serve as essentially cylindrical entry and exit channels for the balls to and from the ball channel (K) through the spindle nut wall. Each relief bore (B) is characterized by a generatrix (L) that intersects (C) with the thread baseline of the ball channel (K) and represents the geometric continuation of the ball's path from the ball channel (K) into the relief bore (B). A tangent (T) to the cylindrical surface (G) runs parallel to the generatrix (L) at a distance a > 0, with both T and L being perpendicular to a common perpendicular R to the longitudinal axis Z.