Screw device

Patent metadata

Field	Value
Publication number	US-9568078-B2
Application number	US-201414890657-A
Country	US
Kind code	B2
Filing date	May 20, 2014
Priority date	May 31, 2013
Publication date	Feb 14, 2017
Grant date	Feb 14, 2017

Abstract

Provided is a screw device in which a sudden change in force on or a sudden change in the positions of the rolling members can be suppressed at the boundary between a helical loaded rolling-member rolling path and a return path of the screw device.
A curvature radius change section is provided in the return path of the screw device. When viewed in the axial direction of a nut, the curvature radius change section is configured so that the curvature radius of a track centerline of the rolling members in the return path is equal to or larger than the curvature radius of a track centerline of the rolling members in the loaded rolling-member rolling path, and so that the curvature radius of the track centerline of the rolling members in the return path increases gradually or in a stepped manner with increasing distance from the loaded rolling-member rolling path.

First claim

The invention claimed is:

1. A screw device comprising:
a screw shaft having a helical rolling-member rolling groove on an outer circumferential surface thereof;
a nut having a helical loaded rolling-member rolling groove opposed to the rolling-member rolling groove on an inner circumferential surface thereof;
a return path connecting one end and the other end of a helical loaded rolling-member rolling path formed by the rolling-member rolling groove of the screw shaft and the loaded rolling-member rolling groove of the nut; and
a plurality of rolling members arranged in the loaded rolling-member rolling path and the return path, wherein
when viewed in the axial direction of the nut,
a curvature radius change section is provided in the return path
the curvature radius change section is configured so that a curvature radius of a track centerline of the rolling members in the return path is equal to or larger than a curvature radius of a track centerline of the rolling members in the loaded rolling-member rolling path, and so that the curvature radius of the track centerline of the rolling members in the return path increases continuously or in a stepped manner by combining two or more arcs with increasing distance from the loaded rolling-member rolling path, and
each of a sectional shape orthogonal to a longitudinal direction of the loaded rolling-member rolling groove of the nut and a sectional shape orthogonal to a longitudinal direction of an outer circumferential side of the curvature radius change section is formed into a gothic arch groove shape which comes into contact with balls at two points, the balls serving as the rolling members.

2. The screw device of claim 1 ,
wherein the nut comprises a nut body having the loaded rolling-member rolling groove and a circulation component which is attached to the nut body and having at least part of the return path, and
wherein the curvature radius change section includes the outer circumferential side formed on the nut body by extending the loaded rolling-member rolling groove of the nut body.

3. The screw device of claim 2 , wherein
the curvature radius change section includes an inner circumferential side at least part of which is configured by the outer circumferential surface of the screw shaft.

4. The screw device of claim 3 , wherein
the inner circumferential side of the curvature radius change section includes a remaining part which is other than the at least part, the remaining part being formed in the circulation component.

5. The screw device of claim 1 , wherein
a track centerline of the rolling members moving along the outer circumferential side of the curvature radius change section is either a transition curve or a combined curve formed by combining a plurality of arcs of mutually different curvature radiuses.

6. The screw device of claim 2 , wherein
a track centerline of the rolling members moving along the outer circumferential side of the curvature radius change section is either a transition curve or a combined curve formed by combining a plurality of arcs of mutually different curvature radiuses.

7. The screw device of claim 3 , wherein
a track centerline of the rolling members moving along the outer circumferential side of the curvature radius change section is either a transition curve or a combined curve formed by combining a plurality of arcs of mutually different curvature radiuses.

8. The screw device of claim 4 , wherein
a track centerline of the rolling members moving along the outer circumferential side of the curvature radius change section is either a transition curve or a combined curve formed by combining a plurality of arcs of mutually different curvature radiuses.

9. The screw device of claim 1 , wherein
a length of the curvature radius change section in a longitudinal direction thereof is more than twice as large as a diameter of the balls serving as the rolling members.

10. The screw device of claim 2 , wherein
a length of the curvature radius change section in a longitudinal direction thereof is more than twice as large as a diameter of the balls serving as the rolling members.

11. The screw device of claim 3 , wherein
a length of the curvature radius change section in a longitudinal direction thereof is more than twice as large as a diameter of the balls serving as the rolling members.

12. The screw device of claim 4 , wherein
a length of the curvature radius change section in a longitudinal direction thereof is more than twice as large as a diameter of the balls serving as the rolling members.

Assignees

• Thk Co Ltd

Inventors

• Suzuki Atsushi

Classifications

• F16H25/2214 Primary

  with elements for guiding the circulating balls · CPC title

• F16H25/2219 Primary

  Axially mounted end-deflectors · CPC title

• F16H25/22

  with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members · CPC title

• F16H25/24

  Elements essential to such mechanisms, e.g. screws, nuts (F16H25/22 takes precedence) · CPC title