Internal-Deflection Ball Screw Drive for Compact Ball Recirculation

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Solution Overview

Problem

Ball screw drives with external deflection systems increase the outer diameter and volume of components, complicating compact integration, and external transfer channels often require thick spindle nuts, which may not be feasible in all applications.

Innovation Solution

A ball screw drive with internal deflection and a transfer channel oriented towards the central axis, utilizing a threaded spindle with a radially outward-extending hollow cylinder and a cylindrical core composed of skewed core halves, featuring a secant ball deflection path and symmetrical transfer channel design to minimize outer diameter and reduce rolling resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If external deflection systems are used, then ball recirculation is achieved, but the outer diameter and volume of components increase

Engineering Contradiction:

Improveball recirculationVSAvoidouter diameter

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent inverts the conventional external deflection approach by implementing internal deflection within the threaded spindle. Instead of deflecting balls outward from the ball channel, the transfer channel is positioned inside the threaded spindle, redirecting balls inward and then back to the ball channel. This inversion resolves the contradiction by achieving ball recirculation while reducing the outer diameter of the spindle nut assembly.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The transfer channel is nested within the threaded spindle structure, specifically utilizing the internal space of the hollow cylinder. The transfer channel runs through the cylindrical core that fills the cavity of the hollow cylinder, effectively nesting the ball deflection mechanism within the existing structural components. This nesting approach enables ball recirculation without increasing the overall volume of the drive system.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If external transfer channels are mounted on the spindle nut, then ball recirculation is achieved, but compact integration is complicated

Engineering Contradiction:

Improveball recirculationVSAvoidintegration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The transfer channel is merged with the threaded spindle structure rather than being mounted externally on the spindle nut. The transfer channel, cylindrical core, and hollow cylinder are integrated into a unified internal structure within the threaded spindle. This merging eliminates the need for separate external mounting components and simplifies the overall integration of the ball recirculation system into the drive assembly.

Inventive Principle:

Principle #5Merging (Combining)

3Volume of moving object

If transfer channels are recessed into the cylindrical wall of the spindle nut, then compact integration is improved, but the spindle nut requires corresponding thickness

Engineering Contradiction:

Improvecompact integrationVSAvoidspindle nut thickness

Core Design Contradiction:

Volume of moving objectVSLength of stationary object

Solution Approach 1:

Instead of recessing the transfer channel into the external cylindrical wall of the spindle nut, the patent inverts the approach by positioning the transfer channel inside the threaded spindle. The transfer channel utilizes the internal cavity space of the hollow cylinder, redirecting balls inward rather than outward. This inversion resolves the contradiction by achieving compact integration without requiring increased spindle nut thickness.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentEP4671568A1Ball screw drive with internal deflection, use and procedure for pre-assembly of a ball screw drive

Publication Date: 2025.12.31 SFS GROUP INTERNATIONAL AG

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AI summary

A ball screw drive comprises a threaded spindle (300), a spindle nut (200), and a plurality of balls (400) that circulate in a helical ball channel in the space between the threaded spindle and the spindle nut. Two ball deflectors (510, 520) engaging in the ball channel and a transfer channel (530) running between them, together with a section of the ball channel, form a closed orbital path for the balls. The ball recirculation used here is designed as an internal deflection. The threaded spindle has, at least in sections, a radially outer hollow cylinder with a centrally symmetrical inner cavity (360) and a cylindrical core (310) filling this cavity, the cylindrical core of the threaded spindle being composed of a first and a second core half (330, 350). The transfer channel is arranged in the common parting surface (370) of the two core halves.A characteristic feature here is that the two core halves are designed as skewed halves, whose common dividing surface forms a plane that intersects the central axis (450) of the core at only one point.