BALL SCREW DEVICE, POWER TRANSFER MECHANISM, ELECTRIC POWER STEERING APPARATUS, AND METHOD FOR MANUFACTURING BALL SCREW DEVICE

• US 20150284020A1
• Filed: 03/31/2015
• Published: 10/08/2015
• Est. Priority Date: 04/07/2014
• Status: Active Grant

• Current Assignee: Jtekt Corporation (Toyota Motor Corporation)
• Original Assignee: Jtekt Corporation (Toyota Motor Corporation)
• Inventors: ASAKURA, Toshihiro, KANEKO, Tetsuya, FUJITA, Satoshi
• Granted Patent: US 9,446,787 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B23C 3/30 Milling straight grooves, e.g. keyways
• CPC Class Codes: B62D 5/0424 the axes of motor and final driven element of steering gear, e.g. rack, being parallel
• CPC Class Codes: B62D 5/0448 Ball nuts
• CPC Class Codes: F16H 2025/2081 Parallel arrangement of drive motor to screw axis
• CPC Class Codes: F16H 2025/2096 using endless flexible members
• CPC Class Codes: F16H 2025/2481 Special features for facilitating the manufacturing of spindles, nuts, or sleeves of screw devices
• CPC Class Codes: F16H 25/2204 with balls
• CPC Class Codes: F16H 25/2214 with elements for guiding the circulating balls
• CPC Class Codes: F16H 25/2223 Cross over deflectors between adjacent thread turns, e.g. S-form deflectors connecting neighbouring threads
• CPC Class Codes: Y10T 409/303752 Process
• CPC Class Codes: Y10T 74/18576 including screw and nut
• CPC Class Codes: Y10T 74/19772 Rolling element deflector

Abstract

A ball screw device is provided for which quality can be easily evaluated. The ball screw device includes a threaded shaft with a groove formed on an outer peripheral surface of the shaft, and a cylindrical nut whose screw-thread mates with the groove on the threaded shaft via a plurality of balls. The nut has a pair of mounting holes in each of which a deflector is installed and a communication groove that allows the mounting holes to communicate with each other and is open on the outer peripheral surface of the nut and through which the balls can roll. The width W of an opening of the communication groove is smaller than the diameter of the ball.

Claims

1. A ball screw device comprising:

a threaded shaft with a groove formed on an outer peripheral surface of the shaft; and

a cylindrical nut whose screw-thread mates with the groove on the threaded shaft via a plurality of balls, wherein

the nut comprises a pair of mounting holes in each of which a deflector is installed, and a communication groove that allows the mounting holes to communicate with each other,

an opening of the communication groove is formed on an outer peripheral surface of the nut, and the balls are able to roll through the communication groove, and

a width of the opening of the communication groove is smaller than a diameter of the balls.

2. The ball screw device according to claim 1, wherein

the communication groove comprises a groove having a C-shaped cross section and including an opening on the outer peripheral surface of the nut.

3. A power transfer mechanism, comprising:

the ball screw device according to claim 1; and

a power transmission device that transmits a torque from an output shaft of a motor to the nut, wherein

the power transfer mechanism converts rotating motion of the output shaft of the motor into axial reciprocating linear motion of the threaded shaft via the power transmission device and the ball screw device, and

a component of the power transmission device, which is attached to a periphery of the nut, closes the opening of the communication groove.

4. A power transfer mechanism, comprising:

the ball screw device according to claim 2; and

a power transmission device that transmits a torque from an output shaft of a motor to the nut, wherein

the power transfer mechanism converts rotating motion of the output shaft of the motor into axial reciprocating linear motion of the threaded shaft via the power transmission device and the ball screw device, and

a component of the power transmission device, which is attached to a periphery of the nut, closes the opening of the communication groove.

5. The power transfer mechanism according to claim 3, wherein

the power transmission device comprises a driving pulley attached to the output shaft of the motor, a driven pulley attached to an outer periphery of the nut, and an endless belt wound around the driving pulley and the driven pulley, and

an inner peripheral surface of the driven pulley closes the opening of the communication groove.

6. The power transfer mechanism according to claim 4, wherein

the power transmission device comprises a driving pulley attached to the output shaft of the motor, a driven pulley attached to an outer periphery of the nut, and an endless belt wound around the driving pulley and the driven pulley, and

an inner peripheral surface of the driven pulley closes the opening of the communication groove.

7. An assist mechanism for an electric power steering apparatus, the assist mechanism comprising:

an electric motor; and

the power transfer mechanism according to claim 3, wherein

a part of a steered shaft of a steering mechanism of a vehicle is used as the threaded shaft of the power transfer mechanism, and an assist force is applied to the steering mechanism using a translational force applied from the ball screw device to the steered shaft in an axial direction of the steered shaft.

8. An assist mechanism for an electric power steering apparatus, the assist mechanism comprising:

an electric motor; and

the power transfer mechanism according to claim 4, wherein

a part of a steered shaft of a steering mechanism of a vehicle is used as the threaded shaft of the power transfer mechanism, and an assist force is applied to the steering mechanism using a translational force applied from the ball screw device to the steered shaft in an axial direction of the steered shaft.

9. An assist mechanism for an electric power steering apparatus, the assist mechanism comprising:

an electric motor; and

the power transfer mechanism according to claim 5, wherein

a part of a steered shaft of a steering mechanism of a vehicle is used as the threaded shaft of the power transfer mechanism, and an assist force is applied to the steering mechanism using a translational force applied from the ball screw device to the steered shaft in an axial direction of the steered shaft.

10. An assist mechanism for an electric power steering apparatus, the assist mechanism comprising:

an electric motor; and

the power transfer mechanism according to claim 6, wherein

a part of a steered shaft of a steering mechanism of a vehicle is used as the threaded shaft of the power transfer mechanism, and an assist force is applied to the steering mechanism using a translational force applied from the ball screw device to the steered shaft in an axial direction of the steered shaft.

11. A method for manufacturing a ball screw device in which

the ball screw device comprises a threaded shaft with a groove formed on an outer peripheral surface of the shaft, and a cylindrical nut whose screw-thread mates with the groove on the threaded shaft via a plurality of balls,

the nut comprises a pair of mounting holes in each of which a deflector is installed, and a communication groove that allows the mounting holes to communicate with each other, and

an opening of the communication groove is formed on the outer peripheral surface of the nut, and the balls are able to roll through the communication groove,

the method comprising:

inserting a cutting edge portion of a ball end mill into a first mounting hole of the pair of mounting holes, and

moving the cutting edge portion of the ball end mill toward a second mounting hole of the pair of mounting holes to form the communication groove in the nut.

12. The method for manufacturing the ball screw device according to claim 11, wherein

a width of the opening of the communication groove is smaller than a diameter of the balls,

the ball end mill has a shaft portion with a diameter decreasing toward a tip of the shaft portion, and the cutting edge portion provided adjacently to the tip of the shaft portion, and

a diameter of a boundary portion between the tip of the shaft portion and the cutting edge portion is smaller than the width of the opening of the communication groove.