Ball screw device, method of manufacturing ball screw device, and steering system including ball screw device

Patent metadata

Field	Value
Publication number	US-10850764-B2
Application number	US-201816107029-A
Country	US
Kind code	B2
Filing date	Aug 21, 2018
Priority date	Aug 28, 2017
Publication date	Dec 1, 2020
Grant date	Dec 1, 2020

Abstract

In a ball screw device, an inner peripheral rolling groove of a nut includes, between openings of mounting holes, a constant pitch circle diameter region where a pitch circle diameter is constant and gradually-changing pitch circle diameter regions where the pitch circle diameter gradually increases, in the ranges from opposite ends of the constant pitch circle diameter region to the respective openings. At least the constant pitch circle diameter region has a surface hardness greater than or equal to a predetermined value, among the constant pitch circle diameter region and the gradually-changing pitch circle diameter regions excluding edges at the boundaries between the respective openings and the inner peripheral rolling groove, and the edges at the boundaries between the respective openings and the inner peripheral rolling groove have a surface hardness less than the predetermined value.

First claim

What is claimed is:

1. A ball screw device comprising:
a screw shaft having an outer peripheral surface provided with a helical outer peripheral rolling groove;
a nut formed in a tubular shape, the nut having an inner peripheral surface provided with a helical inner peripheral rolling groove, the nut being disposed on an outer peripheral side of the screw shaft, and the nut having a plurality of mounting holes extending between two different single-turn rolling grooves of single-turn rolling grooves aligned in an axial direction thereof and an outer peripheral surface thereof, the inner peripheral rolling groove being defined as a collection of the single-turn rolling grooves aligned in the axial direction and each having a single turn about an axis thereof;
rolling elements arranged in a rollable manner in a rolling path defined between the outer peripheral rolling groove and the inner peripheral rolling groove;
a return path that short-circuits between openings of the plurality of mounting holes that are open to the rolling path and are respectively formed in the two different single-turn rolling grooves, the return path allowing the rolling elements rolling in the rolling path to circulate endlessly; and
a deflector accommodated and fixed in a mounting hole of the plurality of mounting holes, that defines a part of or the entire return path therein, the deflector being configured to guide the rolling elements rolling in the rolling path to the return path and return the rolling elements to the rolling path;
wherein:
the inner peripheral rolling groove of the nut includes, in a range between the openings of the mounting holes;
a constant pitch circle diameter region spaced apart from the openings and formed such that a pitch circle diameter of the rolling path is constant, and
gradually-changing pitch circle diameter regions formed such that the pitch circle diameter gradually increases from the constant pitch circle diameter region in ranges from opposite ends of the constant pitch circle diameter region to the respective openings; and

at least the constant pitch circle diameter region has a surface hardness greater than or equal to a predetermined value, among the constant pitch circle diameter region and the gradually-changing pitch circle diameter regions excluding edges at boundaries between the respective openings and the inner peripheral rolling groove, and the edges at the boundaries between the respective openings and the inner peripheral rolling groove have a surface hardness less than the predetermined value.

2. The ball screw device according to claim 1 , wherein in the inner peripheral rolling groove, the entire constant pitch circle diameter region and a part of the gradually-changing pitch circle diameter regions have the surface hardness greater than or equal to the predetermined value.

3. The ball screw device according to claim 1 , wherein the surface hardness greater than or equal to the predetermined value is obtained through an induction hardening operation.

4. A method of manufacturing the ball screw device of claim 1 , wherein:
in the inner peripheral rolling groove, an induction hardening operation is performed on at least the constant pitch circle diameter region, among the constant pitch circle diameter region and the gradually-changing pitch circle diameter regions excluding the edges at the boundaries between the respective openings and the inner peripheral rolling groove; and
at least the constant pitch circle diameter region is formed to have the surface hardness greater than or equal to the predetermined value through the induction hardening operation.

5. A steering system comprising the ball screw device of claim 1 .

Assignees

• Jtekt Corp

Inventors

• Yamaguchi Masashi

Classifications

• F16H25/2233

  with cages or means to hold the balls in position · CPC title

• F16H2025/2481

  Special features for facilitating the manufacturing of spindles, nuts, or sleeves of screw devices · CPC title

• F16H25/2214

  with elements for guiding the circulating balls · CPC title

• F16H2025/2081

  Parallel arrangement of drive motor to screw axis · CPC title

• F16H25/2204

  with balls · CPC title