Planetary Roller Screw Bearing Layout for Rear Axle Steering
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Solution Overview
Problem
Existing planetary roller screws in motor vehicle steering systems experience undesirable tilting moments and deflections in the second bearing due to tensile forces from belt drives, leading to inefficiencies and potential misalignment.
Innovation Solution
A planetary roller screw design with a sleeve connecting flanges in a rotationally fixed and axially actuating manner, incorporating a multi-part nut with a tensioning element to prevent tilting and ensure precise bearing spacing, and a non-rotatable connection to avoid planet entanglement, allowing for reliable operation and reduced sizing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a floating bearing is used for the second bearing to allow axial movement, then the planet carrier can accommodate axial play, but tensile forces from the belt drive cause undesirable tilting moments and deflections
Solution Approach 1:
The planet carrier is divided into two flanges connected by a sleeve, with each flange independently supporting a bearing. This segmentation allows the first flange to be stabilized against tilting moments while the second flange maintains necessary axial play, resolving the contradiction between stability and adjustability.
2Stability of the object's composition
If the two flanges are rigidly connected without play, then rotational stability is improved, but axial adjustment capability is lost
Solution Approach 1:
The connection between flanges is designed with differentiated properties: rotationally fixed (rigid) to prevent tilting moments, but axially movable with play to allow adjustment. This local quality differentiation resolves the contradiction by providing stability where needed while maintaining adjustability where required.
3Manufacturing precision
If the bearing spacing is fixed during manufacturing, then manufacturing precision is improved, but the ability to precisely set bearing spacing during assembly is lost
Solution Approach 1:
The bearing spacing is designed to be dynamically adjustable during assembly through the axial play between flanges, while maintaining precise positioning once assembled. This allows manufacturers to use standard tolerances during production while enabling field adjustment for precise bearing spacing setup.
4Device complexity
If a single-part nut is used, then device complexity is reduced, but the ability to pretension planets and reduce mounting sizing is lost
Solution Approach 1:
The nut is divided into multiple parts with a tensioning element that can independently pretension the planets. This segmentation enables the pretensioning function to be separated from the mounting structure, allowing smaller mounting sizing while maintaining the required planet pretensioning capability.
Data Source
AI summary
Planetary roller screw having a threaded spindle, and having a nut element arranged on the threaded spindle, and having planets arranged distributed around the periphery of the threaded spindle, which mesh on one side with the threaded spindle and on the other side with the nut element, which is rotatably mounted in both axial directions in each case by means of a first bearing on a rotationally driven planet carrier which receives the planets and is rotatably mounted on a housing by means of a second bearing. The planet carrier has a sleeve encompassing the nut element, at the axial ends of which a flange respectively having a first bearing seat of the first bearing and a second bearing seat of the second bearing is arranged, the flanges being connected with play to one another by means of the sleeve in a rotationally fixed manner and axially with actuating play.