JP2002019623A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To freely rotate a steering wheel even when an electric motor and/or a steering control system is broken down by using a small-sized and lightweight clutch having a simple structure. SOLUTION: In this electric power steering device 10, the clutch 40 permitting only transmission of turning effort from the electric motor 20 to a power transmission device 21 is provided between the electric motor 20 and the power transmission device 21. The clutch 40 is provided with a driving plate 41 integrally rotating with the electric motor 20, a driven plate 43 integrally rotating with the power transmission device 21, and an intermediate plate 42 placed between the driving plate 41 and the driven plate 43 and capable of being displaced to axial direction. A ball 53 is provided between ball pressing and holding surfaces 51A and 52A of the driving plate 41 and the intermediate plate 42 facing to each other. A distance between the ball pressing and holding surfaces 51A and 52A is brought closer toward outside along radial direction. A ball abutting part 51B abutting onto the ball 53 along rotational direction of the driving plate 41 is formed on the ball pressing and holding surface 51A of the driving plate 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An electric power steering apparatus assists a steering force by connecting wheels to a rack shaft interlocking with a steering input shaft and transmitting an output of an electric motor to the rack shaft via a speed reducer.

In this electric power steering apparatus, the steering wheel is connected to the electric motor via the input shaft, the rack shaft, and the speed reducer. May be caused. 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 steering wheel is connected to a rack shaft interlocked with a steering input shaft, and an output of an electric motor is transmitted to the rack shaft via a power transmission member to thereby provide a steering force. In an electric power steering device to assist, between an electric motor and a power transmission device,
A clutch is provided that allows transmission of torque only from the electric motor to the power transmission device and disables transmission of torque from the power transmission device to the electric motor.The clutch has a drive plate that rotates integrally with the electric motor. A driven plate that rotates integrally with the power transmission device, and an intermediate plate that can be axially displaced between the drive plate and the driven plate,
A ball is interposed between the opposing drive plate and the ball pressing surface of the intermediate plate, and the distance between the ball pressing surfaces is gradually approached outward in the radial direction. Forming a ball abutting portion for abutting the ball by rotating the driving plate by the electric motor, and rotating the ball along with the ball, and displacing the ball outward by centrifugal force to remove both the ball of the driving plate and the intermediate plate. By widening the interval between the pressing surfaces, the drive plate, the ball, the intermediate plate, and the driven plate are pressed and integrated with each other to rotate the power transmission device.

[0008]

According to the first aspect of the present invention, the following effects are obtained. The clutch connects the electric motor to the power transmission 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 by centrifugal force,
The distance between the drive plate and the intermediate plate is increased, and the drive plate, the ball, the intermediate plate, and the driven plate are pressed and integrated with each other to rotate the power transmission device. This allows
The torque of the electric motor is transmitted to the rack shaft via a power transmission device to assist the steering force.

As long as the electric motor does not rotate, the clutch does not apply centrifugal force to the ball no matter how much the driven plate that rotates integrally with the power transmission device rotates.
Do not connect the power transmission to the electric motor. This allows
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, and FIG. 2 is a sectional view showing a clutch.

The electric power steering apparatus 10 is shown in FIG.
As shown in FIG. 1, a pinion shaft 13 is connected to a steering input shaft 12 to which a steering wheel 11 is connected, and a rack 14A meshed with a pinion 13A of the pinion shaft 13.
Is supported so as to be movable left and right. Left and right tie rods 15A are provided at both left and right ends of the rack shaft 14,
The left and right wheels 16A, 16B are connected via 15B.

The electric power steering device 10 has an electric motor 20. The output shaft of the electric motor 20 has a worm gear 2 of a power transmission device 21 including a worm reducer.
2 is connected, and a worm wheel 23 meshing with the worm gear 22 is fixed to the pinion shaft 13.

The electric power steering device 10 has a steering control device 30. 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 pinion shaft 13 and the rack shaft 14 via the power transmission device 21, and the driver operates the steering wheel 1.
Assist the steering force given to 1.

However, the electric power steering device 10
Allows only transmission of torque from the electric motor 20 to the power transmission device 21 between the electric motor 20 and the power transmission device 21 and disables transmission of torque from the power transmission device 21 to the electric motor 20. The clutch 40 is provided.

As shown in FIG. 2, the clutch 40 has a drive plate 41 provided on a drive shaft 20A which rotates integrally with the electric motor 20, and a driven shaft 21A provided on a driven shaft 21A which rotates integrally with the power transmission device 21. It has a plate 43 and an intermediate plate 42 that can be displaced in the axial direction between the drive plate 41 and the driven plate 43. At this time, the drive shaft 20A is supported by the bearing 44 and the driven shaft 21A is supported by the bearing 45. The drive shaft 20A and the driven shaft 21A are coaxial, and the intermediate shaft 46 is supported by the bearings 47 and 48 coaxially between them. Have been. The drive plate 41 is integrated with the drive shaft 20A. The intermediate plate 42 includes first to third three plates 42A to 42C.
A to 42C are engaged with the engaging grooves on the outer periphery of the intermediate shaft 46 in the rotational direction, and are slidably coupled in the axial direction.
The driven plate 43 is made up 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 shaft 21A. The plate 43C is slidably coupled in the axial direction, and the plate 43C is integrated with the driven shaft 21A.

The clutch 40 is provided with a drive plate 4 opposite to the 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 51B 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 pressed and integrated with each other in the axial direction, and the power transmission device 21 is rotated. The driving plate 41, the ball 53, the intermediate plate 42, and the driven plate 4
3, the ball 53 abuts against the ball abutting portion 51B of the drive plate 41 and is prevented from rotating, whereby the rotational force of the drive plate 41 is reduced.
2A can be transmitted.

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 power transmission device 21 regardless of whether the motor is driven forward or backward. 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 by centrifugal force, the distance between the drive plate 41 and the intermediate plate 42 is increased, and the drive plate 41, the ball 53, the intermediate plate 42, and the driven plate 43 are pressed and integrated with each other to rotate the power transmission device 21. Let it. Thus, the torque of the electric motor 20 is transmitted to the rack shaft 14 via the power transmission device 21 to assist the steering force.

As long as the electric motor 20 does not rotate, the clutch 40 does not apply centrifugal force to the ball 53 no matter how much the driven plate 43 rotates integrally with the power transmission device 21. The electric motor 2
Do not connect to 0. 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 scope 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 shaft 20A, and the ball may be a roller body.

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

Further, the electric power steering apparatus of the present invention is not limited to the electric power steering apparatus which is connected to the steering wheel and transmits the steering force of the steering wheel to the rack shaft by the electric motor, but is connected to the steering wheel. A pinion shaft dedicated to assisting the transmission of the rotational force of the electric motor directly to the rack shaft without using the above-mentioned pinion shaft to which the steering wheel is connected is provided separately, and the clutch of the present invention is provided on the output side of the electric motor. good.

[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 clutch.

[Explanation of symbols]

 Reference Signs List 10 electric power steering device 12 steering input shaft 14 rack shaft 16A, 16B wheel 20 electric motor 21 power transmission member 40 clutch 41 drive plate 42 intermediate plate 43 driven plate 51A, 52A ball pressing surface 51B, 52B ball contact portion 53 ball

Claims (1)

[Claims] 1. An electric power steering apparatus which assists a steering force by connecting wheels to a rack shaft interlocked with a steering input shaft and transmitting an output of an electric motor to the rack shaft via a power transmission member. A clutch is provided between the power transmission devices that allows transmission of torque only from the electric motor to the power transmission device and disables transmission of torque from the power transmission device to the electric motor. A drive plate that rotates integrally, a driven plate that rotates integrally with the power transmission device, and an intermediate plate that is interposed between the drive plate and the driven plate and that can be displaced in the axial direction. A ball is interposed between the pressing surfaces, and the distance between the pressing surfaces is asymptotic toward the outside in the radial direction. A ball abutting portion that abuts the ball in the rotation direction of the drive plate is formed, and the ball is rotated together with the drive plate by the rotation of the drive plate by the electric motor, and the ball is displaced outward by centrifugal force to form the drive plate. An electric power steering apparatus characterized in that the power transmission device is rotated by expanding the gap between the two ball pressing surfaces of the intermediate plate so that the drive plate, the ball, the intermediate plate, and the driven plate are pressed and integrated with each other.