JPH08207797A - Motor-driven power steering system - Google Patents

Abstract

PURPOSE: To provide a motor-driven power steering system that can prevent the twist or the like of a nut member while being inexpensive and of the same compact constitution as the conventional one. CONSTITUTION: Elastic bodies 49, 50 are provided to elastically support a support body 48 itself for rotatably supporting a ball screw nut 44. The support body 48 can thereby be minutely displaced in the axial and radial directions according to machining eccentricity, assembling eccentricity and operational eccentricity generated between the ball screw nut 44 and a rack shaft 7, so that the ball screw nut 44 is not twisted in relation to the rack shaft 7 or supported bearings 45, 46.

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 device.

[0002]

2. Description of the Related Art As an electric power steering device for a vehicle, there is known a type in which a rotary output of an electric motor is converted into a linear motion through a ball screw mechanism and a rack shaft is directly driven (for example, Japanese Unexamined Patent Application Publication No. 2002-242242) 60-2585
4 publication).

The ball screw mechanism used in such an electric power steering apparatus of the prior art is connected to a rack shaft and is movable only in the axial direction, and a ball screw shaft having an outer thread groove formed on the outer periphery thereof. ,
The nut member is connected to the electric motor and is rotatably provided around the rack shaft. The nut member has an inner thread groove formed on the inner circumference, and a plurality of balls that can roll between the outer thread groove and the inner thread groove. ing. When the rotation output from the electric motor rotates the nut member, the ball screw shaft does not rotate,
The ball screw shaft moves in the axial direction with respect to the nut member in proportion to the pitch of the thread groove. The plurality of balls are arranged in a row in both thread grooves at a predetermined interval and function to reduce the frictional force generated between the nut member and the ball screw shaft when the nut member rotates.

[0004]

By the way, in such a ball screw mechanism, when a nut member is rotatably supported with respect to a housing, a normal bearing is used,
The axis line between the nut member and the ball screw shaft may be displaced, resulting in twisting of the nut member. On the other hand, if the aligning bearing is used to support the nut member, such twisting can be effectively prevented, but the aligning bearing is expensive, which causes an increase in manufacturing cost.

Further, in order to prevent the nut member from twisting, there has been proposed a structure in which the nut member is swingably supported in a floating manner. However, according to this proposal, since the nut member is supported only in the swinging direction, there is a problem that twisting of the nut member is not effectively prevented.

It is an object of the present invention to provide an electric power steering apparatus which is inexpensive and has a compact structure similar to the conventional apparatus, but which can prevent the nut member from being twisted.

[0007]

In order to achieve the above object, an electric power steering apparatus of the present invention comprises a housing,
A handle shaft that is connected to the handle and rotates together with the handle, a rack shaft that is capable of linear movement to perform a turning motion of a steering wheel, and the handle shaft and the rack shaft that are drivingly connected to the handle shaft. Rack and pinion gear means, which comprises a pinion gear that rotates in accordance with the above, and a rack gear that is provided on the rack shaft and that meshes with the pinion gear; Means and a plurality of balls arranged in series in a rolling path formed between the rotating nut means and the screw means for transmitting a force between the rotating nut means and the screw means. A ball screw means, a support for rotatably supporting the rotating nut means, and an axial direction of the support with respect to the housing. An elastic member minutely displaceably resiliently supported in the fine radial direction, and the electric motor unit coupled to the rotating nut means consists of.

[0008]

According to the present invention, the elastic body for elastically supporting the supporting body itself for rotatably supporting the rotating nut means is provided, so that the rotating nut means and the self-supporting body are interposed between the rotating nut means. Misalignment due to processing, misalignment due to assembly,
Depending on the misalignment during operation, the support can be displaced axially and radially slightly so that the rotary nut means does not twist against the screw means or the support.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of an electric power steering apparatus that is an embodiment of the present invention.

In FIG. 1, a handle 1 is attached to the upper end of a handle shaft 2 and is integral therewith, and is rotatably supported by a vehicle body (not shown). The handle shaft 2 is connected to the pinion shaft 5 via the universal joint 6.
It is connected to. The pinion shaft 5 has a pinion gear at its tip, and the pinion gear meshes with a rack formed on a horizontally long rack shaft 7 provided movably in the left-right direction in the drawing in a steering device main body 3 described later. By rotating the pinion shaft 5, the rack shaft 7 moves in the left-right direction in the figure in a known manner.

The pinion shaft 5 for transmitting the rotational output from the handle 1 is provided with a torque detecting means 4 around it. The torque detecting means 4 uses a torsion bar which is twisted in proportion to the received torque. The torque received by the pinion shaft 5 is measured by converting the twist into an axial amount and measuring it with a potentiometer. , To the control circuit 11. This detecting means itself is already known as represented by, for example, Japanese Utility Model Laid-Open No. 60-179944, and therefore its configuration will not be described in detail below.

The steering apparatus main body 3 supported by a bracket (not shown) on a vehicle body (not shown) converts a steering rotation input into a linear motion for turning to a steering wheel (not shown) of the vehicle. It has a motor unit 8 for power assistance. The motor unit 8 and the clutch unit 9 are electrically connected to the control circuit 11. Under the control of the control circuit 11, the rotation output from the motor unit 8 is converted into a linear motion by the steering device main body 3 via the clutch unit 9 and then drives the rack shaft 7. Motor unit 8 to rack shaft 7
The output transmission system to the will be described in detail below with reference to FIG.

FIG. 2 is an enlarged sectional view of the steering apparatus main body 3 of FIG. A three-part housing 30 in which a circular left portion 30a, an intermediate portion 30b, and a right portion 30c are connected in series around the rack shaft 7 is connected to brackets 14 and 15 (see FIG. 1) on a vehicle body not shown. Is attached through. The motor unit 8 is configured in the right portion 30c. A circular tubular permanent magnet 30d is fixed to the inner periphery of the right side portion 30c, and a substantially circular tubular armature 32 is also provided inside the permanent magnet 30d.
It is attached around. The sleeve 17 is rotatably supported by the housing 30 by a pair of bearings 31.

A slider 33 is attached to the left end of the armature 32. An annular brush 35 supported by a brush holder 34 attached to the housing 30 faces the slider 33 around the slider 33. Brush 3
Electric power to 5 is supplied from the control circuit 11 of FIG. 1 as needed, and the armature 32 and the sleeve 17 are rotated with a torque corresponding thereto.

A clutch unit 9 is formed inside the intermediate portion 30b. A male spline portion 7a is formed on the left end of the sleeve 17, and a female spline portion 37a is formed on the inner circumference of a substantially annular friction plate holder 37 having a central opening. By engaging both spline portions, ,
The friction plate holder 37 is attached to the sleeve 17 so as to be movable in the axial direction but not in the rotational direction. An electromagnet 39 supported by an electromagnet holder 38 with respect to the housing 30 is provided on the right side of the friction plate holder 37 so as to directly face the friction plate holder 38. The electric power to the electromagnet 39 is supplied from the control circuit 11 of FIG. 1 as needed, and the electromagnet 39 generates a magnetic force in response thereto.

A friction plate 37b is bonded to the left end surface of the friction plate holder 37 adjacent to the electromagnet 39, and the friction plate 37b is a disc-shaped clutch plate 4 made of a magnetic material.
It is facing 0. When the electromagnet 39 generates a magnetic force, the clutch plate 40 is urged toward the electromagnet 39, and the friction plate 37b is pressed between the clutch plate 40 and the friction plate holder 37, whereby it is necessary to transmit the rotational force. A frictional force will be generated. That is, the clutch unit 9 is engaged by the engagement signal from the control circuit 11 and disengaged by the disengagement signal. The clutch plate 40 is abutted by a plurality of connecting screws 41, and the connecting screw 41 allows the position of the transmission annular member 43 to be adjusted in the axial direction. The transmission annular member 43 is rotatably supported by the clutch sleeve 17 via a bearing 42, and is fitted to the right end of a ball screw nut 44.

A substantially cylindrical ball screw nut 44
Are rotatably supported by bearings 45 and 46.
The ball screw nut 44 has an inner thread groove 44a on the inside.
The inner thread groove 44a forms a rolling path facing the outer thread groove 7b formed on the left side portion of the rack shaft 7, and a plurality of balls 47 are accommodated in the rolling path. There is. Ball 47
Is used to reduce the frictional force generated when the ball screw nut 44 and the rack shaft 7 slide and rotate. Although not shown, the ball screw nut 44 has a circulation passage therein, and the ball 47 can circulate during operation via the circulation passage. The internal thread groove 44a
And the outer screw groove 7b constitute a screw means, and the ball screw nut 44 constitutes a rotating nut means.

The bearings 45 and 46 are preloaded to the substantially cylindrical support, that is, the holder 48, by preload adjusting nuts 53 screwed to the inner circumference of the inner end of the holder (that is, the outer rings are close to each other). (Pressed in the direction), and is supported by the holder 48. Further, the holder 48 is elastically supported by the elastic members 49 and 50 with respect to the housing 30 so as to be displaceable in the axial direction and the radial direction. Incidentally, 54 is a lock nut of the preload adjusting nut 53.

FIG. 3 is a perspective view of the elastic member 49. The elastic member 49 is made of a hard resin, and has an elastic force of slightly bending when receiving a normal operating force from the rack shaft 7. The elastic member 49 further has a side portion 49a and a bottom portion 49b. Note that the elastic member 50 is the same as the elastic member 49 in this embodiment, so its details are omitted. In FIG. 2 again, the bottom of the elastic member 49 contacts the inside of the shoulder 30e of the housing left side portion 30a, and the bottom of the elastic member 50 contacts the ring 51 that restricts axial movement. The side portions of the elastic members 49 and 50 are in contact with the inner circumference of the left side portion 30a of the housing. It should be noted that the dustproof cover member 52, which is only partially shown at the left end of the housing 30,
Is attached.

Next, the operation of this embodiment will be described with reference to FIG. When the vehicle is in a straight traveling state and the torque is not input from the steering wheel 1 to the pinion shaft 5, a substantial torque signal is not output from the torque detector 4, so the control circuit 11 causes the motor unit 8 to rotate. Is not output, and a disengagement signal is output to the clutch unit 9.
As a result, the electric power steering device is in a state where it does not output the auxiliary steering force.

On the other hand, when the vehicle is about to turn a curve, the steering wheel 1 is steered and the rotational force is transmitted to the pinion shaft 5. Therefore, a signal corresponding to the steering torque is output from the torque detector 4 to the control circuit 11. Is output to the control circuit 11,
An engagement signal is output to the clutch unit 9, and a rotation drive signal proportional to the steering torque is output to the motor unit 8. As a result, this electric power steering device outputs an auxiliary steering force according to the steering force.

By the way, during operation of the electric power steering apparatus, the rotation of the sleeve 17 shown in FIG.
The ball screw nut 44 is rotated via the clutch plate 40. Since the ball screw nut 44 is rotatable with respect to the housing 30 but is immovable in the axial direction, rotation of the ball screw nut 44 causes the outer screw groove 7 b of the rack 7 to be inserted via the ball 47. The rack shaft 7 is pressed in the axial direction, whereby the rack shaft 7 moves in the axial direction, and the wheel operation is performed via a tie rod (not shown) connected to the rack shaft 7.

When the ball screw nut 44 rotates in this manner, the series of balls 47 are formed in the screw grooves 7b,
The balls 47 rolling in the rolling path constituted by 44a while being pressed by both screw grooves and reaching one end of the inner screw groove 44a are the circulation paths (not shown) formed in the ball screw nut 44. ), And is circulated to the other end.

By the way, the holder 48 supporting the ball screw nut 44 with the two bearings 45 and 46 is supported by the elastic bodies 49 and 50 so that it can be slightly displaced in the axial direction and the radial direction. Even if a deviation occurs between the axis of the rack shaft 7 and the axis of the ball screw nut 44 during assembly or during operation, this deviation can be removed by slightly displacing the holder 48 itself in the radial direction or the axial direction. Thereby, the rack shaft 7 of the ball screw nut 44 or the bearing 45,
It is possible to prevent kinking between 46 and. The holder 48 is allowed to be slightly displaced not only in the radial direction but also in the axial direction, so that the ball screw nut is swung when the axis lines of the ball screw nut and the rack shaft are not parallel to each other. This is so that adjustment can also be performed.

Although the present invention has been described with reference to the embodiments, the present invention should not be construed as being limited to the above embodiments, and it goes without saying that appropriate modifications and improvements can be made. For example, although the elastic body is made of resin in the present embodiment, it may be made of rubber or any other material as long as an appropriate elastic force can be obtained.

[0028]

As described above, according to the electric power steering apparatus of the present invention, the elastic body for elastically supporting the supporting body itself for rotatably supporting the rotating nut means is provided. A processing misalignment that occurs between the rotating nut means and the screw means, an assembly misalignment,
Depending on the misalignment during operation, the support can be displaced axially and radially slightly so that the rotary nut means does not twist against the screw means or the support.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an electric power steering apparatus that is an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a steering device main body portion 3 of FIG.

FIG. 3 is a perspective view of an elastic member 49.

[Explanation of symbols]

 1 ... Handle 5 ... Pinion shaft 7 ... Rack shaft 44 ... Ball screw nut 47 ... Ball 48 ... Support 49, 50 ... Elastic body

Claims (1)

[Claims] 1. A housing, a handle shaft which is connected to the handle and rotates together with the handle, a rack shaft which is linearly movable for performing a turning motion of a steering wheel, and a drive shaft for driving the handle shaft and the rack shaft. Rack and pinion gear means that are connected to each other and rotate according to the handle shaft, and a rack and pinion gear means that is provided on the rack shaft and that engages with the pinion gear, a screw means provided on the rack shaft, and the screw means. Of a rotating nut means surrounding at least a part of the rotating nut means and a rolling path formed between the rotating nut means and the screw means, and the force is applied between the rotating nut means and the screw means. Ball screw means composed of a plurality of balls for transmission, a support for rotatably supporting the rotating nut means, and the support An electric power steering apparatus comprising: an elastic body that elastically supports the housing so that it can be slightly displaced in the axial direction and the radial direction; and an electric motor unit connected to the rotating nut means.