JP2002037104A - Electric power steering device - Google Patents

Abstract

(57) [Summary] [Problem] To use a clutch having a small and light weight and a simple configuration,
The steering wheel can be freely rotated even if the electric motor or the steering control system fails. The electric power steering device (10) is provided with a clutch (40) between an electric motor (20) and a nut (27) of a ball screw device (25) that only allows transmission of rotational force from the electric motor (20) to the nut (27). 40
Is a drive plate 41 which rotates integrally with the electric motor 20.
A driven plate 43 that rotates integrally with the nut 27;
It has a driving plate 41 and an intermediate plate 42 that can be displaced in the axial direction between the driven plate 43 and the opposing driving plate 41 and the ball pressing surface 51 of the intermediate plate 42.
A, a ball 53 is interposed between 52A and 52A,
The distance between 1A and 52A is asymptotic toward the outside in the radial direction,
A ball pressing portion 51B formed on a ball pressing surface 51A of a drive plate 41 to abut against a ball 53 in the rotation direction of the drive plate 41.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an electric power steering device.

[0002]

2. Description of the Related Art As an electric power steering device, wheels are connected to a rack shaft interlocked with a steering input shaft.
An electric motor is provided around a rack shaft, and the steering force is assisted by transmitting the output of the electric motor to the rack shaft via a ball screw device.

In this electric power steering device, the steering wheel is connected to the electric motor via the input shaft, the rack shaft, and the ball screw device. There is a possibility that steering becomes impossible. Further, even if the electric motor is not locked for rotation, if the electric motor is not driven due to a failure of the steering control system, inertia of the motor is added to the steering wheel, and manual steering performance is deteriorated.

On the other hand, Japanese Patent No. 2691579 discloses that a clutch composed of a planetary gear device is provided on the output side of an electric motor so that the steering wheel can be freely rotated even if the electric motor or the steering control system fails as described above. And

[0005]

[0006] However, Patent 2691
The clutch composed of the 579 planetary gear unit has an extremely complicated structure, is disadvantageous in response when driving the motor, and is large and heavy.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to freely rotate a steering wheel even if an electric motor or a steering control system fails by using a clutch having a small and light weight and a simple configuration.

[0007]

According to a first aspect of the present invention, a wheel is connected to a rack shaft interlocking with a steering input shaft, an electric motor is installed around the rack shaft, and the output of the electric motor is connected to a ball screw device. In an electric power steering device that assists a steering force by transmitting a torque to a rack shaft through a nut, only transmission of rotational force from the electric motor to the nut is allowed between the electric motor and a nut of the ball screw device, and the electric motor is transmitted from the nut to the electric motor. A clutch that disables transmission of rotational force to the motor is provided.The clutch includes a driving plate that rotates integrally with the electric motor, a driven plate that rotates integrally with the nut, and an axial direction sandwiched between the driving plate and the driven plate. Having a displaceable intermediate plate, interposing a ball between the opposing drive plate and the ball pressing surface of the intermediate plate,
The distance between the ball pressure surfaces is asymptotic toward the outside in the radial direction,
A ball abutting portion is formed on the ball pressing surface of the drive plate to abut against the ball in the direction of rotation of the drive plate, and the ball is rotated by the rotation of the drive plate by the electric motor, and the ball is removed by centrifugal force. The drive plate, the ball, the intermediate plate, and the driven plate are pressed and integrated with each other to rotate the nut by displacing the drive plate and the gap between the ball pressing surfaces of the drive plate and the intermediate plate. .

[0008]

According to the first aspect of the present invention, the following effects are obtained. The clutch connects the electric motor to the nut of the ball screw device regardless of whether the electric motor is driven forward or reverse during steering assist. That is, the ball that rotates with the rotation of the drive plate that rotates integrally with the electric motor is displaced outward due to centrifugal force, widens the distance between the drive plate and the intermediate plate, and moves the drive plate, the ball, the intermediate plate, and the driven plate. The nuts are rotated by pressing and integrating with each other. Thus, the torque of the electric motor is transmitted to the rack shaft via the ball screw device, and assists the steering force.

As long as the electric motor does not rotate, the ball screw device does not apply a centrifugal force to the electric motor no matter how much the driven plate rotates integrally with the nut of the ball screw device. Do not connect.
Thus, when the electric motor or the steering control system breaks down, the steering wheel is separated from the electric motor and can rotate freely.

The clutch has a simple structure in which the drive plate, the ball, the intermediate plate, and the driven plate are simply arranged in a stacked manner, and is small and lightweight.

[0011]

FIG. 1 is a schematic view showing an electric power steering apparatus, FIG. 2 is a sectional view showing a main part of the electric power steering apparatus, and FIG. 3 is a sectional view showing a clutch. As shown in FIG. 1, the electric power steering apparatus 10 has a rack shaft 14 having a rack 14A that connects a pinion shaft 13 to a steering input shaft 12 to which a steering wheel 11 is coupled and meshes with a pinion 13A of the pinion shaft 13. Is supported so that it can move left and right. Rack axis 1
Left and right wheels 16A, 16B are connected to left and right ends of the wheel 4 via left and right tie rods 15A, 15B.

The electric power steering apparatus 10 is shown in FIG.
As shown in the figure, an electric motor 20 and a ball screw device 25 are installed around the rack shaft 14 of the housing 10A that supports the rack shaft 14 so as to be movable left and right.

The electric motor 20 includes a stator 21 fixed to the inner periphery of the housing 10A, and a rotor 22 disposed around the rack shaft 14 with a gap therebetween.

The ball screw device 25 includes a housing 10A.
Has a nut 27 held on its inner periphery via a bearing 26, and a steel ball 29 is held between a screw groove 28 A of the nut 27 and a screw groove 28 B provided on the rack shaft 14. . The ball screw device 25 includes the electric motor 2
When the rotational force of the rotor 22 due to the operation of 0 is transmitted to the nut 27 via the clutch 40 described later, this rotation is converted into the axial movement of the rack shaft 14.

The electric power steering device 10 is shown in FIG.
As shown in FIG. The steering control device 30 controls the electric motor 20 based on detection signals from a torque sensor 31 provided on the steering input shaft 12 and a vehicle speed sensor 32. As a result, the output of the electric motor 20 is transmitted to the rack shaft 14 via the ball screw device 25, and the driver
Assist the steering force given to 1.

However, the electric power steering device 10
The nut 27 of the electric motor 20 and the ball screw device 25
Between them, there is provided a clutch 40 that allows only the transmission of the rotational force from the electric motor 20 to the nut 27 and disables the transmission of the rotational force from the nut 27 to the electric motor 20.

The clutch 40 is, as shown in FIGS.
It has a drive plate 41 that rotates integrally with the rotor 22 of the electric motor 20, a driven plate 43 that rotates integrally with the nut 27, and an intermediate plate 42 that can be axially displaced between the drive plate 41 and the driven plate 43. . At this time, the drive plate 41 includes the bearing 44 and the driven plate 4
3 is supported by a bearing 45, the drive plate 41 and the driven plate 43 are coaxial, and an intermediate shaft 46 is pivotally supported by bearings 47 and 48 on the same axis sandwiched therebetween. The intermediate plate 42 includes first to third three plates 42A to 42A.
42C, and the plates 42A to 42C
Are engaged with each other in an engagement groove on the outer periphery of the motor in the rotation direction and slidably in the axial direction. In addition, the driven plate 43
Is composed of first to third three plates 43A to 43C, and the plates 43A and 43B are rotationally engaged with engagement grooves on the inner periphery of the clutch housing 49 fixed to the driven plate 43, and are axially Are slidably coupled, and the plate 43C is integrated with the driven plate 43.

The clutch 40 is connected to the opposing drive plate 4
The first and second intermediate plates 42A have ball storage grooves 51 and 52, such as V-shaped grooves and square grooves, at a plurality of circumferential positions on opposing surfaces of the first intermediate plate 42A.
1A and 52A, and both side walls of the ball storage grooves 51 and 52 are formed as ball abutting portions 51B and 52B (52B is not essential) formed so as to rise from the ball pressing surfaces 51A and 52A. That is, the clutch 40 is connected to the opposing drive plate 4
1 and the respective ball storage grooves 51, 5 of the first intermediate plate 42A.
The ball 53 is interposed between the two ball pressing surfaces 51A and 52A, and at least one of the two ball pressing surfaces 51A and 52A is formed as a gradient surface inclined in the radial direction, and the distance between them is reduced toward the outside in the radial direction. Asymptotically to a width taper, each ball abutment portion 51B, 52B can abut against the ball 53 in the rotation direction of the drive plate 41 and the first intermediate plate 42A.

In the clutch 40, the electric motor 20
The rotation of the drive plate 41 by the
The ball 53 is rotated by the first ball abutment portion 51B, and the ball 53 is displaced outward by the centrifugal force of the rotation so that the ball pressing surfaces 51A and 52A of the drive plate 41 and the first intermediate plate 42A are formed. Increase the spacing. Thereby, the driving plate 41 and the ball 5
3, the intermediate plate 42 (42A to 42C) and the driven plate 43 (43A to 43C) are integrally pressed and integrated in the axial direction, and the nut 27 is rotated. When the drive plate 41, the ball 53, the intermediate plate 42, and the driven plate 43 are pressed as described above, the ball 53 abuts against the ball abutment portion 51B of the drive plate 41 to stop the rotation. The torque can be transmitted to the first intermediate plate 42A.

Therefore, according to the present embodiment, the following operations are provided. The clutch 40 is connected to the electric motor 20 during steering assist.
Is connected to the nut 27 of the ball screw device 25 irrespective of which direction is driven. That is, the ball 53 that rotates with the rotation of the drive plate 41 that rotates integrally with the electric motor 20 is displaced outward due to centrifugal force, the distance between the drive plate 41 and the intermediate plate 42 is increased, and the drive plate 41 and the ball 53 And the intermediate plate 42 and the driven plate 43 are pressed and integrated with each other to rotate the nut 27. Thus, the torque of the electric motor 20 is transmitted to the rack shaft 14 via the ball screw device 25, and assists the steering force.

As long as the electric motor 20 does not rotate, the clutch 53 does not apply a centrifugal force to the ball 53 no matter how much the driven plate 43 rotates integrally with the nut 27 of the ball screw device 25. Screw device 2
5 is not connected to the electric motor 20. Thus, when the electric motor 20 is locked or when the steering control system breaks down, the steering wheel 11 is separated from the electric motor 20 and can rotate freely.

The clutch 40 has a simple structure in which the driving plate 41, the ball 53, the intermediate plate 42, and the driven plate 43 are simply stacked and arranged, and is small and lightweight.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and the design may be changed without departing from the gist of the present invention. The present invention is also included in the present invention. For example, the intermediate shaft 46 to which the intermediate plates 42A to 42C are connected may be one integrally connected to the drive plate 41, and the ball may be a roller body. Further, when the ball storage groove is formed as a V-shaped groove, the ball pressing surface (two opposing surfaces) and the ball abutting portion can be used.

Further, the electric power steering apparatus of the present invention may be provided with an electromagnetic clutch controlled by the steering control device 30 attached to the electric motor 20.

[0025]

As described above, according to the present invention, it is possible to manually and freely rotate the steering wheel even if the electric motor or the steering control system breaks down, by using a clutch having a small and light weight and a simple configuration. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an electric power steering device.

FIG. 2 is a sectional view showing a main part of the electric power steering device.

FIG. 3 is a sectional view showing a clutch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electric power steering device 12 Steering input shaft 14 Rack shaft 16A, 16B Wheel 20 Electric motor 25 Ball screw device 27 Nut 40 Clutch 41 Drive plate 42 Intermediate plate 43 Follower plate 51A, 52A Ball clamping surface 51B, 52B Ball contact part 53 ball

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02K 7/10 H02K 7/10 A

Claims (1)

[Claims] 1. A wheel is connected to a rack shaft interlocked with a steering input shaft, an electric motor is installed around the rack shaft, and the steering force is transmitted by transmitting the output of the electric motor to the rack shaft via a ball screw device. In an assisted electric power steering device, a clutch that allows only transmission of torque from the electric motor to the nut between the electric motor and the nut of the ball screw device, and disables transmission of torque from the nut to the electric motor. The clutch has a driving plate that rotates integrally with the electric motor, a driven plate that rotates integrally with the nut, and an intermediate plate that can be axially displaced between the driving plate and the driven plate. Balls are interposed between the ball pressing surfaces of the drive plate and the intermediate plate, and the distance between the ball pressing surfaces is gradually approached outward in the radial direction. A ball abutting portion that abuts the ball in the direction of rotation of the drive plate is formed on the ball pressing surface of the drive plate, and the ball is rotated together with the ball by the rotation of the drive plate by the electric motor, and the ball is removed by centrifugal force. The drive plate, the ball, the intermediate plate, and the driven plate are pressed and integrated with each other by rotating the nut by displacing the drive plate and the gap between the ball pressing surfaces of the drive plate and the intermediate plate. Power steering device.