JP3543307B2 - Electric power steering device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electric power steering device.
[0002]
[Prior art]
2. Description of the Related Art As an electric power steering device for a vehicle, a type in which the rotation output of an electric motor is converted into linear motion via a ball screw mechanism to directly drive a rack shaft is known (for example, Japanese Patent Application Laid-Open No. S60-25854). Publication).
[0003]
A ball screw mechanism used in such a conventional electric power steering device is connected to a rack shaft and is movable only in the axial direction, and has a ball screw shaft having an outer thread groove formed on the outer periphery, and an electric motor. And a nut member provided rotatably around the rack axis and having an inner thread groove formed in the inner periphery thereof, and a plurality of balls rotatable between the outer thread groove and the inner thread groove. . When the rotation output from the electric motor rotates the nut member, the ball screw shaft does not rotate, so that 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 continuously in the two screw grooves at a predetermined interval, and function to reduce a frictional force generated between the nut member and the ball screw shaft when the nut member rotates.
[0004]
【task to solve】
By the way, in such a ball screw mechanism, when the nut member is rotatably supported with respect to the housing, if a normal bearing is used, the axis of the nut member and the ball screw shaft are shifted, and the nut member is twisted. There is a risk of inviting. On the other hand, when the aligning bearing is used to support the nut member, such twisting is effectively prevented, but the aligning bearing is expensive, which causes an increase in manufacturing cost.
[0005]
Furthermore, in order to prevent the nut member from being twisted, there has been proposed a configuration in which the nut member is swingably floating supported. However, according to this proposal, since the nut member is supported only in the swinging direction, there is a problem that the nut member is not effectively prevented from being twisted.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device which is inexpensive and has the same compact structure as a conventional device, but can prevent the nut member from being twisted.
[0007]
[Means to solve the problem]
In order to achieve the above object, an electric power steering device according to the present invention includes:
A housing,
A handle shaft connected to the handle and rotating with the handle,
A rack shaft that can move linearly to perform a turning motion of the steered wheels;
A pinion gear that is drivingly connected to the handle shaft and the rack shaft and rotates according to the handle shaft, and a rack and pinion gear means that is provided on the rack shaft and that includes a rack gear that meshes with the pinion gear;
Screw means provided on the rack shaft, a rotating nut means surrounding at least a part of the screw means, and arranged continuously in a rolling path formed between the rotating nut means and the screw means, Ball screw means comprising a plurality of balls for transmitting a force between the rotating nut means and the screw means,
A support for rotatably supporting the rotating nut means,
An elastic body that elastically supports the support body so that it can be slightly displaced in the axial direction and the radial direction with respect to the housing;
And an electric motor unit connected to the rotating nut means.
[0008]
[Action]
According to the invention of the present application, since the elastic body that elastically supports the support itself that rotatably supports the rotating nut means is provided, processing that occurs between the rotating nut means and the self-governing body. In accordance with the upper misalignment, the misalignment in assembly, and the misalignment during operation, the support can be slightly displaced in the axial direction and the radial direction, so that the rotating nut means can move with respect to the screw means or the support. , So as not to cause twisting.
[0009]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view schematically showing an electric power steering apparatus according to an embodiment of the present invention.
[0010]
In FIG. 1, a handle 1 is attached to an 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 a universal joint 6. The pinion shaft 5 has a pinion gear at its tip. The pinion gear meshes with a rack formed on a horizontally long rack shaft 7 provided in the steering device main body 3 to be described later and movable in the left-right direction in the drawing. When the pinion shaft 5 rotates, the rack shaft 7 moves in the left-right direction in the figure in a known manner.
[0011]
The pinion shaft 5 for transmitting the rotation output from the handle 1 is provided with torque detecting means 4 around the pinion shaft 5. The torque detecting means 4 uses a torsion bar that is twisted in proportion to the received torque. The torsion is converted into an axial amount and measured by a potentiometer to measure the torque received by the pinion shaft 5. , To the control circuit 11. The detecting means itself is already known, as represented by, for example, Japanese Utility Model Application Laid-Open No. Sho 60-179944, and its configuration will not be described in detail below.
[0012]
The steering device main body 3 supported on the vehicle body (not shown) by the brackets 14 and 15 converts the rotational input for steering into a linear motion for turning to a steered wheel (not shown) of the vehicle. It is a mechanism unit and 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 linear motion by the steering device body 3 via the clutch unit 9, and then drives the rack shaft 7. The output transmission system from the motor unit 8 to the rack shaft 7 will be described in detail below with reference to FIG.
[0013]
FIG. 2 is an enlarged sectional view of the steering device main body 3 of FIG. Around the rack shaft 7, a three-piece housing 30 in which a tubular left portion 30a, a middle portion 30b, and a right portion 30c are connected in series, respectively, is mounted on a vehicle body (not shown) with brackets 14, 15 (see FIG. 1). Attached through. The motor unit 8 is configured in the right part 30c. A tubular permanent magnet 30d is fixed to the inner periphery of the right portion 30c, and a substantially tubular armature 32 is similarly mounted around the elongated tubular sleeve 17 inside the permanent magnet 30d. The sleeve 17 is rotatably supported on the housing 30 by a pair of bearings 31.
[0014]
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 around the slider 33. Electric power to the brush 35 is supplied from the control circuit 11 of FIG. 1 as necessary, and the armature 32 and the sleeve 17 are rotated by a torque corresponding to the electric power.
[0015]
The 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 periphery of a substantially annular friction plate holder 37 having a central opening, and 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 the 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. 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 accordingly.
[0016]
A friction plate 37b is adhered to a left end surface of the friction plate holder 37 adjacent to the electromagnet 39, and the friction plate 37b faces a disk-shaped clutch plate 40 made of a magnetic material. 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, thereby transmitting the rotational force necessary for transmitting the rotational force. A frictional force will be generated. That is, the clutch unit 9 is engaged by an engagement signal from the control circuit 11, and is disengaged by a disengagement signal. The clutch plate 40 is abutted by a plurality of connection screws 41, and the position of the transmission ring member 43 in the axial direction can be freely adjusted by the connection screws 41. 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 the ball screw nut 44.
[0017]
The substantially cylindrical ball screw nut 44 is rotatably supported by bearings 45 and 46. The ball screw nut 44 has an inner thread groove 44a inside, and the inner thread groove 44a forms a rolling path facing the outer thread groove 7b formed on the left side of the rack shaft 7, and A plurality of balls 47 are accommodated in the moving path. The ball 47 is used for reducing a 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 path therein, and the ball 47 can be circulated during operation via the circulation path. The screw means is constituted by the inner screw groove 44a and the outer screw groove 7b, and the rotating nut means is constituted by the ball screw nut 44.
[0018]
The bearings 45 and 46 are preloaded adjusted by a preload adjusting nut 53 screwed onto the inner periphery of the inner end of the holder against the substantially cylindrical support, that is, the holder 48 (that is, the outer rings are pressed in a direction in which they approach each other). ) And are supported by holder 48. Further, the holder 48 is elastically supported by the elastic members 49 and 50 so as to be displaceable in the axial direction and the radial direction with respect to the housing 30. Reference numeral 54 denotes a lock nut of the preload adjusting nut 53.
[0019]
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 to bend slightly when receiving a normal operating force from the rack shaft 7. The elastic member 49 further has a side part 49a and a bottom part 49b. In this embodiment, the elastic member 50 is the same as the elastic member 49, and therefore, the details are omitted. In FIG. 2 again, the bottom of the elastic member 49 abuts the inside of the shoulder 30e of the left side portion 30a of the housing, and the bottom of the elastic member 50 abuts on the ring 51 that limits axial movement. The side portions of the elastic members 49 and 50 are in contact with the inner periphery of the left portion 30a of the housing. In addition, a dustproof cover member 52, which is only partially shown, is attached to the left end of the housing 30.
[0020]
Next, the operation of this embodiment will be described with reference to FIG.
When the vehicle is traveling straight and no torque is input from the steering wheel 1 to the pinion shaft 5, a substantial torque signal is not output from the torque detector 4, so that the control circuit 11 sends a rotation drive signal to the motor unit 8. Is not output, and a disengagement signal is output to the clutch unit 9. As a result, the electric power steering device does not output the auxiliary steering force.
[0021]
On the other hand, when the vehicle is going to turn a curve, the steering wheel 1 is steered and the torque is transmitted to the pinion shaft 5, so that a signal corresponding to the steering torque is output from the torque detector 4 to the control circuit 11. Then, the control circuit 11 outputs an engagement signal to the clutch unit 9 and outputs a rotation drive signal proportional to the steering torque to the motor unit 8. As a result, the electric power steering device outputs an auxiliary steering force according to the steering force.
[0022]
By the way, during the operation of the electric power steering apparatus, the rotation of the sleeve 17 shown in FIG. 2 rotates the ball screw nut 44 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, the rotation of the ball screw nut 44 causes the outer thread groove 7 b of the rack 7 to pass through the ball 47. The rack shaft 7 is pressed in the axial direction, whereby the rack shaft 7 moves in the axial direction, and performs a wheel steering operation via a tie rod (not shown) connected to the rack shaft 7.
[0023]
When the ball screw nut 44 rotates in this manner, the series of balls 47 rolls in the rolling path formed by the two screw grooves 7b and 44a while being pressed by the two screw grooves, and The ball 47 arriving at one end of 44a is circulated to the other end through a circulation path (not shown) formed in the ball screw nut 44.
[0024]
By the way, the holder 48 supporting the ball screw nut 44 by 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. Or, even if the axis of the rack shaft 7 and the axis of the ball screw nut 44 are misaligned during the operation, the misalignment can be removed by slightly displacing the holder 48 in the radial or axial direction. Thereby, the twisting between the ball screw nut 44 and the rack shaft 7 or the bearings 45 and 46 can be prevented. The reason why the holder 48 can be minutely displaced not only in the radial direction but also in the axial direction is to swing the ball screw nut when the axes of the ball screw nut and the rack shaft are displaced non-parallel. This is to make adjustments possible.
[0026]
As described above, the present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and it is needless to say that modifications and improvements can be made as appropriate. For example, in this embodiment, the elastic body is made of resin, but may be made of rubber or other materials as long as an appropriate elastic force is obtained.
[0028]
【The invention's effect】
As described above, according to the electric power steering device of the present invention,
Since the elastic body that elastically supports the support itself that rotatably supports the rotating nut means is provided, the processing center deviation generated between the rotating nut means and the screw means, and assembly error In accordance with the misalignment and the misalignment during operation, the support can be slightly displaced in the axial direction and the radial direction, so that the rotating nut means does not twist with respect to the screw means or the support. ing.
[Brief description of the drawings]
FIG. 1 is a view schematically showing an electric power steering apparatus according to an embodiment of the present invention.
FIG. 2 is an enlarged sectional view of the steering device main body 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 members 49, 50 Elastic body

Claims (1)

A housing,
A handle shaft connected to the handle and rotating with the handle,
A rack shaft capable of linear movement to perform a turning movement of the steering wheel,
A pinion gear that is drivingly connected to the handle shaft and the rack shaft and rotates according to the handle shaft, and a rack and pinion gear means that is provided on the rack shaft and that includes a rack gear that meshes with the pinion gear;
Screw means provided on the rack shaft, a rotating nut means surrounding at least a part of the screw means, and arranged continuously in a rolling path formed between the rotating nut means and the screw means, Ball screw means comprising a plurality of balls for transmitting a force between the rotating nut means and the screw means,
An integral support in which a bearing for rotatably supporting the rotating nut means is fixed and is included in the housing;
An elastic body that elastically supports the support body so that it can be minutely displaced in the axial direction and the radial direction with respect to the housing;
An electric motor unit connected to the rotating nut means,
Preload adjusting means disposed inside the integral support,
The electric power steering apparatus according to claim 1, wherein the preload adjusting means adjusts a preload of the bearing that rotatably supports the ball screw means on the integral support.

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