Hollow-Shaft Linear Actuator Layout for Reduced Axial Space

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Solution Overview

Problem

Existing electromechanical linear actuators face challenges with large axial space requirements and complex manufacturing due to the arrangement of the electric motor and threaded components, which affect weight and radial dimensions.

Innovation Solution

An electromechanical linear actuator design featuring a threaded spindle coupled to a hollow shaft via a rotationally fixed connection, with the threaded nut partially or fully retractable into the electric motor's hollow shaft, minimizing axial space and protected by a boom tube, and utilizing a screw drive with optimized length ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the threaded nut is arranged adjacent to the electric motor in the axial direction, then the linear actuator can be compact in radial dimensions, but the axial space requirement becomes large

Engineering Contradiction:

Improveradial dimensionsVSAvoidaxial space requirement

Core Design Contradiction:

Area of stationary objectVSLength of stationary object

Solution Approach 1:

The threaded nut is nested inside the hollow shaft of the electric motor, utilizing the internal space of the hollow shaft to house the threaded nut. This eliminates the need for axial space between the motor and threaded nut, as the threaded nut is contained within the motor's hollow shaft structure, thereby resolving the contradiction between radial compactness and axial space requirement

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

Instead of arranging the threaded nut in the axial direction adjacent to the motor, the design moves the threaded nut into the radial dimension by placing it inside the hollow shaft. This dimensional transition from axial arrangement to radial containment allows the threaded nut to be positioned without increasing axial space, while maintaining radial compactness

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Device complexity

If the threaded spindle is exposed, then the linear actuator has simpler structure, but the threaded spindle is vulnerable to dirt and mechanical damage

Engineering Contradiction:

Improvestructure simplicityVSAvoiddirt and mechanical damage

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The threaded spindle is nested inside the boom tube, which serves as a protective enclosure. The boom tube contains the threaded spindle while allowing it to function, protecting it from dirt and mechanical damage without significantly complicating the overall structure

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The boom tube acts as an intermediary protective element between the threaded spindle and the external environment. It shields the threaded spindle from harmful factors like dirt and mechanical damage while still allowing the screw drive mechanism to operate effectively

Inventive Principle:

Principle #24Intermediary (Mediator)

3Length of stationary object

If the threaded nut is completely retracted into the hollow shaft, then the axial space is minimized and length ratio is maximized, but the threaded nut may interfere with the electric motor windings

Engineering Contradiction:

Improveaxial spaceVSAvoidinterference with windings

Core Design Contradiction:

Length of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The threaded nut is designed to be dynamically positionable within the hollow shaft, capable of moving between a retracted position (minimizing axial space) and an extended position (avoiding interference with windings). This dynamic adjustment allows the system to optimize axial space when needed while avoiding interference with motor components when the threaded nut needs to be accessed

Inventive Principle:

Principle #15Dynamics

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

The design achieves reduced weight and optimized radial dimensions by minimizing axial space requirements while protecting the threaded spindle from dirt and mechanical damage, improving thermal balance and service life through oil lubrication and sealing.

Implementation Method 1

a screw drive comprising a threaded spindle (7) and a threaded nut (8)... During operation of the linear actuator, the threaded spindle (7) rotates and is not moved linearly. The threaded nut (8) does not rotate and is moved linearly.

Methodology Applied

Scientific EffectScrew mechanism: Screw

Implementation Method 2

an electric motor (3) with a hollow shaft (1)... the windings (3a) of the electric motor (3) are located on the outer circumference of the hollow shaft (1)

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Data Source

PatentEP4303466B1Electromechanical linear actuator with a hollow shaft motor

Publication Date: 2025.10.15 ROBERT BOSCH GMBH

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AI summary

An electromechanical linear actuator with a threaded drive comprising a threaded spindle (7) and a threaded nut (8). The threaded spindle is coupled to a hollow shaft (1) of an electric motor (3) via a rotationally fixed connection (14). The threaded nut is attached to a linearly movable extension tube (9). In the fully retracted position of the extension tube, the threaded nut is at least partially, and preferably completely, retracted into the interior of the hollow shaft. During operation of the linear actuator, the threaded spindle rotates and is not moved linearly. The threaded nut does not rotate and is moved linearly.