JP2003081104A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device to improve support rigidity of a rack shaft and ensure smooth slide of a ball screw part. SOLUTION: In the electric power steering device, a rack shaft 2 of a steering mechanism so formed that rotation of a handle is transmitted through a pinion is supported by one end part of a rack housing, and a rack guide part to press the rack shaft against the pinion side by the other end of the rack housing, and steering assist is effected by an electric motor, an inside diameter 12a of the ball screw nut 12 is brought into opposite contact with an outside diameter 2a of the crank shaft 2 with micro clearance C1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for assisting steering force of a steering wheel.

[0002]

2. Description of the Related Art Detecting torque applied to a steering wheel,
An electric power steering apparatus is known in which an assist force corresponding to the torque is obtained by an electric motor.

As shown in FIG. 1, this electric power steering apparatus has an input shaft for transmitting rotation from a handle 17, the input shaft and the input shaft so as to be relatively rotatable via the input shaft and a torsion bar. A torque sensor 18 that detects the rotational torque of the torsion bar as a relative rotational displacement amount of the input shaft and the output shaft, a rack shaft 2 of a steering mechanism that meshes with a pinion 3 provided on the output shaft, and the torque. An electric motor 19 controlled by a signal from a sensor 18, and a cylindrical ball screw nut 12 fixed to a motor shaft 11 of the electric motor 19 and screwed into the rack shaft 2, the rack shaft 2 being a rack housing. 1
Supported at three points: a bearing portion 5 formed at one end of the rack housing, a ball screw portion 6 of a ball screw nut 12, and a rack guide 7 that presses the rack shaft 2 toward the pinion 3 side at the other end of the rack housing 1. It is a configuration.

[0004]

As shown in FIGS. 4 and 5, the ball screw portion of the conventional electric power steering apparatus has a ball screw groove 10 and a ball screw nut 12 provided on the rack shaft 2. A ball 13 is inserted between the ball screw groove 14 and the ball screw groove 14 provided so that the inner diameter of the ball screw nut 12 faces the outer diameter of the rack shaft 2 with a required gap 16 between them. The ball clearance (backlash) of the screw groove 14 is the ball screw groove 10 and the ball screw nut 1 on the rack shaft 2 side.
It is regulated by the diameter of the ball 13 inserted between the two. The three-point support of the rack shaft 2 is ideally set so that the axis of the rack shaft 2 can be set on a straight line. The rack shaft 2 is moved in the radial direction to close the ball clearance. Also, during steering, a similar phenomenon occurs due to bending of the rack shaft 2 due to input from the tire side. For this reason, the ball screw portion may not slide smoothly, resulting in a torque fluctuation of the motor shaft 11, which may have other adverse effects.

An object of the present invention is to provide an electric power steering apparatus which improves the support rigidity of the rack shaft and ensures smooth sliding of the ball screw portion.

[0006]

In order to achieve the above object, the present invention provides a rack shaft of a steering mechanism, in which rotation of a handle is transmitted through a pinion, as described in claim 1, and a rack housing. Bearing portion formed at one end of the rack shaft, a ball screw portion of a cylindrical ball screw nut fixed to the motor shaft and screwed into the rack shaft, and the other end of the rack housing presses the rack shaft toward the pinion side. In an electric power steering device that is supported by a rack guide section and rotates the ball screw nut by an electric motor to give axial movement force to the rack shaft to perform steering assist, change the inner diameter of the ball screw nut. It is characterized in that it is in contact with the outer diameter of the rack shaft with a minute clearance.

Further, as described in claim 2, a space is formed on both sides of the ball screw groove of the ball screw nut passing through the ball center.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an electric power steering apparatus to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a rack housing, and a rack shaft 2 of a steering mechanism is supported in the rack housing 1 so as to be axially movable. Three
Is a pinion meshing with a rack 4 provided on the rack shaft 1. The pinion 3 is provided on an output shaft that is rotatably connected to the input shaft that transmits the rotation from the handle 17 via a torsion bar, and the rotational torque of the torsion bar is transmitted between the input shaft and the output shaft. Torque sensor 1 that detects relative rotational displacement
8, the handle 17 is provided by the torque sensor 18.
The torque applied to the motor is detected, and an assisting force corresponding to this torque is obtained by the electric motor 19 described later.

A ball screw groove 10 is provided on the outer diameter of the rack shaft 2, and a cylindrical ball screw nut 12 is screwed into the ball screw groove 10 via a ball 13. That is, a ball screw groove 14 is provided in the inner diameter of the ball screw nut 12, and a ball 13 is inserted between the ball screw groove 14 of the ball screw nut 12 and the ball screw groove 10 of the rack shaft 2 to form a ball screw. By rotating the nut 12, the rack shaft 2 is axially moved by the screw leads of the ball screw grooves 10 and 14.

Reference numeral 19 is an electric motor. The ball screw nut 12 is fixed to the motor shaft 11 of the electric motor 19, and the torque applied to the steering wheel 17 at the time of left / right steering is detected by the torque sensor 18, and the motor shaft 11 of the electric motor 19 is responded to the left / right steering. When the ball screw nut 12 is rotated by forward / reverse rotation control, the rack shaft 2 is axially moved in the left or right direction, and an assist force corresponding to the torque applied to the handle 17 is obtained.

The rack shaft 2 has a bearing portion 5 having one end formed at one end of the rack housing 1, a ball screw groove 14 of a ball screw nut 12, and a ball screw groove 10 of the rack shaft 2. It is supported at three points: a ball screw portion 6 including a ball 13 that is inserted, and a rack guide 7 that presses the rack shaft 2 toward the pinion 3 side at the other end of the rack shaft 2. The rack guide 7 includes a rack housing 1 and a rack shaft 2
Is slidably inserted in a direction orthogonal to the axis of the rack shaft 2 by a spring 9 interposed between a rear end of the rack guide 7 and a plug 8 screwed into the rack housing 1. The rack 4 is pressed against the pinion 3 in a meshing direction with an appropriate pressing force.

Therefore, according to the embodiment of the present invention, in the electric power steering apparatus having the above-mentioned structure, as shown in FIGS. 2 and 3, the inner diameter 12a of the ball screw nut 12 is placed outside the rack shaft 2. It is characterized in that it is in contact with the diameter 2a with a minute clearance C1.

Further, the embodiment of the present invention is characterized in that, in addition to the above structure, the space portions 15 are formed on both sides of the ball screw groove 14 of the ball screw nut 12 passing through the center of the ball 13. It is a thing.

In the embodiment of the present invention, the inner diameter 12a of the ball screw nut 12 is set to the outer diameter 2a of the rack shaft 2.
Due to the structure in which the rack shaft 2 is opposed to each other with a minute clearance C1, the rack shaft 2 is not supported only by the balls 13 alone, but the inner diameter 1 of the ball screw nut 12 is not supported.
The rack shaft 2 can also be supported by 2a, and in addition to the above-mentioned three-point support, the support portion of the rack shaft 2 is restricted by the support by the inner diameter 12a of the ball screw nut 12 for a convenience of four points, and various loads on the rack shaft 2 are achieved. The radial displacement of the rack shaft 2 due to the eccentric load due to the load and the bending of the rack shaft 2 due to the input from the tire side during steering can be suppressed, and the smooth sliding of the ball screw portion 6 is ensured. .

Further, in the embodiment of the present invention, the hitting sound and rolling noise of the ball 13 are prevented. When the rack shaft 2 is axially moved by the screw leads of the ball screw grooves 10 and 14 via the ball 13 by the rotation of the ball screw nut 12, the hitting sound and rolling sound of the ball 13 are generated by the ball screw nut 12 side. Ball 13 located in ball screw groove 14
Contacts the side of the ball screw groove 14 by the screw lead. This is the cause of the hitting sound and rolling sound of the ball 13.

Therefore, the embodiment of the present invention has a structure in which the space portions 15 are formed on both sides of the ball screw groove 14 of the ball screw nut 12 which pass through the center of the ball 13, and thus the space portion 15 and the space portion 15 are formed. The filled grease forms a gap between the ball 13 and the side portion of the ball screw groove 14, so that the ball 13 is prevented from coming into contact with the side portion of the ball screw groove 14 and the impact sound and rolling noise of the ball 13 are prevented. Can be suppressed.

[0017]

As described above, according to the present invention, in the structure of claim 1, the rack shaft supporting rigidity is improved by a simple structure in which the clearance between the ball screw nut and the rack shaft is minute, and various structures for the rack shaft are obtained. It is possible to suppress radial displacement of the rack shaft due to unbalanced load due to load and bending of the rack shaft due to input from the tire side during steering, etc., and to ensure smooth sliding of the ball screw part. In addition to the above advantages, the structure according to claim 2 has the advantage of suppressing quietness and rolling noise of the ball generated by the ball coming into contact with the side portion of the ball screw groove of the ball screw nut, and ensuring quietness. It is possible to provide an electric power steering apparatus having the following.

[Brief description of drawings]

FIG. 1 is a sectional view of an electric power steering device.

FIG. 2 is a sectional view of the ball screw portion of the present invention.

FIG. 3 is an enlarged sectional view of a ball screw portion of the present invention.

FIG. 4 is a sectional view of a conventional ball screw portion.

FIG. 5 is an enlarged sectional view of a conventional ball screw portion.

[Explanation of symbols]

1 rack housing 2 rack shaft 2a Rack shaft outer diameter 3 pinion 4 racks 5 Bearing part 6 Ball screw part 7 Rack guide 10 Ball screw groove (rack shaft side) 11 motor shaft 12 Ball screw nut 12a Ball screw nut inner diameter 13 balls 14 Ball screw groove (ball screw nut side) 15 spaces 19 Electric motor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Kawabata             1-1 Asahi-cho, Kariya city, Aichi             Machine Co., Ltd. F-term (reference) 3D033 CA02 CA03 CA04 CA16 CA22                       JB03 JB17

Claims (2)

[Claims] 1. A cylinder in which a rack shaft of a steering mechanism, in which the rotation of a handle is transmitted through a pinion, is fixed to a bearing portion formed at one end of a rack housing and screwed onto the rack shaft. Supported by the ball screw part of the ball screw nut and the rack guide part that presses the rack shaft to the pinion side at the other end of the rack housing, and the ball screw nut is rotated by the electric motor to move the shaft to the rack shaft. In the electric power steering apparatus for providing steering assistance by providing the electric power steering apparatus, the inner diameter of the ball screw nut is in contact with the outer diameter of the rack shaft with a minute clearance. 2. The electric power steering apparatus according to claim 1, wherein space portions are formed on both sides of the ball screw groove of the ball screw nut, the space passing through the ball center.