JP2017082864A - Rotational linear motion conversion device, electric power steering device including the same, vehicle, and mechanical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotation/linear motion conversion device which can provide relatively-high quietness.SOLUTION: A rotation/linear motion conversion device 20 comprises: a shaft 7 having a shaft part 30 whose external peripheral face is cylindrical; a housing 40 which is externally fit to the shaft 7 with a clearance; and two rollers 50 which are oppositely arranged while separating from each other at 180° in a circumferential direction with respect to the shaft 7, and rotatably supported to the housing 40 via a support shaft. The two rollers 50 are supported at the same inclination angle α in a torsional direction with respect to an axial line of the shaft 7, and in slide contact with the shaft part 30 of the shaft 7 so as to be able to transmit a traction drive force in a state of having a preload applied thereon.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rotation / linear motion conversion device that mutually converts a rotation motion and a linear motion, and is suitable for a mechanical device such as an industrial linear motion table or a rack assist type electric power steering device. The present invention relates to a dynamic conversion device.

As this type of rotation / linear motion conversion device, for example, a ball screw is used in many of various mechanical devices such as a vehicle including an electric power steering device (for example, see Patent Document 1).

JP-A-60-25853

However, the ball screw has a problem that it is difficult to obtain quietness because it requires a circulation structure for circulating the ball as a rolling element. In addition, since the ball screw is interposed between the screw shaft and the nut, there is a problem that it is difficult to handle a small lead.
Therefore, the present invention has been made paying attention to such problems, and provides a rotation / linear motion conversion device that can obtain relatively high quietness, an electric power steering device including the same, a vehicle, and a mechanical device. The issue is to provide.

In order to solve the above-mentioned problems, a rotation / linear motion conversion device according to an aspect of the present invention is supported in a freely rotatable manner by a housing, a shaft having an outer peripheral surface having a cylindrical shaft portion, and a support shaft. The two rollers satisfy the following conditions 1 to 3.
Condition 1: The two rollers are arranged to face each other at a distance of 180 ° in the circumferential direction with respect to the shaft.

Condition 2: The two rollers are supported with the same inclination angle in the direction of twist with respect to the axis of the shaft.
Condition 3: The two rollers have a traction driving force (with respect to the shaft portion of the shaft)
The frictional driving force due to rolling contact) is slidably contacted in a state where a preload is applied.

According to the rotation / linear motion conversion device according to one aspect of the present invention, two rollers disposed opposite to each other at 180 ° in the circumferential direction of the shaft with respect to the shaft having a cylindrical shaft portion on the outer peripheral surface with respect to the axis line. The two rollers are slidably contacted with a preload applied so that the traction driving force can be transmitted to the shaft part of the shaft. Therefore, if the shaft is rotated, the two rollers and the housing for fixing the two rollers can be linearly moved along the shaft by an amount corresponding to the inclination angle by traction drive. Further, if the shaft is prevented from rotating outside and the housing is rotated, the shaft can be moved linearly.

According to the rotation / linear motion conversion device according to one aspect of the present invention, unlike the ball screw, since the traction drive mechanism is configured using only two rollers of the rotation system, relatively high quietness is achieved. It is also possible to deal with small leads compared to ball screws. Further, since it is not necessary to form a screw groove like a ball screw on the shaft, it is relatively easy to maintain.

Moreover, in order to solve the said subject, the electric power steering apparatus which concerns on 1 aspect of this invention is provided with the rotation / linear motion conversion apparatus which concerns on 1 aspect of this invention. According to the electric power steering device according to one aspect of the present invention, since the rotation / linear motion conversion device according to one aspect of the present invention is provided, the operation effect of the rotation / linear motion conversion device according to one aspect of the present invention is relatively high. High quietness can be obtained.
In order to solve the above problem, a vehicle according to an aspect of the present invention includes the electric power steering device according to an aspect of the present invention. According to the vehicle according to one aspect of the present invention, since the electric power steering device according to one aspect of the present invention is provided, a relatively high quietness is achieved by the operational effect of the electric power steering device according to one aspect of the present invention. can get.

In order to solve the above-described problem, a mechanical device according to one aspect of the present invention includes the rotation-linear motion conversion device according to one aspect of the present invention. According to the mechanical device according to one aspect of the present invention, the rotation / linear motion conversion device according to one aspect of the present invention is provided. Silence can be obtained.

  As described above, according to the present invention, relatively high silence can be obtained.

1 is a front view of an embodiment of a rotary / linear motion conversion device according to an aspect of the present invention, in which a portion of a roller on the front side is illustrated in a cross section along its axis. It is XX sectional drawing of FIG. It is explanatory drawing of the steering part of the vehicle equipped with the electric power steering device which concerns on 1 aspect of this invention. It is a figure explaining the principal part of FIG. 3, The figure (a) is a longitudinal cross-sectional view (except the part of a rotation linear motion conversion apparatus) along the axis line of the principal part, (b) is in (a). It is ZZ sectional drawing. It is a front view of 2nd Embodiment of the rotation / linear motion conversion apparatus which concerns on 1 aspect of this invention.

[First Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. The drawings are schematic. For this reason, it should be noted that the relationship between the thickness and the planar dimension, the ratio, and the like are different from the actual ones, and the dimensional relationship and the ratio are different between the drawings. Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, and arrangement of components. Etc. are not specified in the following embodiments.

[Rotary linear motion converter]
As shown in FIG. 1 and FIG. 2, the rotation / linear motion conversion device 20 includes a housing 40, a shaft 7 having a shaft portion 30 having a cylindrical outer peripheral surface, and a housing 40 that is rotatable via a support shaft 52. And two supported rollers 50. The two rollers 50 are held in a predetermined arrangement and a predetermined posture with respect to the shaft 7.

Specifically, as a predetermined arrangement, the plurality of rollers 50 are 180 ° in the circumferential direction of the shaft 7.
They are spaced apart from each other (Condition 1 described in “Means for Solving the Problems”). In addition,
As for the shape of the shaft 7, the structure of other portions is not limited as long as the outer peripheral surface has a cylindrical shaft portion 30 in relation to the rotation / linear motion conversion device 20. For example, as will be described later, the shaft 7 can be applied to a rack shaft of a rack assist type electric power steering apparatus.

Each roller 50 is a hollow cylindrical member, and rotates on a support shaft 52 via a pair of bearings 55 and 56 that are respectively fitted in concave step portions formed at both ends in the axial direction and separated in the axial direction. The housing 40 is freely supported. In the present embodiment, angular ball bearings are used for the pair of bearings 55 and 56, and the bearings having a contact angle of, for example, 30 ° are arranged in a rear combination so that a large moment load can be applied. . Between the pair of bearings 55, 56, a cylindrical sleeve 51 is interposed between the inner rings of the bearings 55, 56.

In this embodiment, the outer peripheral surface of each roller 50 is the roller 5 around the contact point P with the shaft portion 30.
It is formed in a concave arc having a substantially drum shape centered at a position orthogonal to the zero support shaft 52. Thereby, since the cylindrical (substantially drum-shaped) outer peripheral surface of each roller 50 is a concave arc centered on the contact P, the centering effect on the shaft 7 is improved, and the two rollers The pinching state by 50 is securely held, and the rotation / linear motion conversion device 20 is prevented from falling off. Further, since the position of the axis RL of the support shaft 52 can be arranged closer to the axis CL of the shaft 7 by the concave arc of each roller 50, the height of the clamping mechanism portion by the two rollers 50 can be kept low and the housing 40 can be made more compact. Can be configured.

In the present embodiment, an example in which the hollow cylindrical roller 50 is rotatably supported by the support shaft 52 via a pair of bearings 55 and 56 is shown, but the present invention is not limited to this. ,
A bearing having various cylindrical outer rings can be used as long as it has a cylindrical or annular outer peripheral surface. For example, a cam follower may be used as the roller 50 in addition to a combination bearing or a double row ball bearing that can receive a moment load.

As shown in FIG. 2, the housing 40 is a block-shaped member having a rectangular shape when viewed from the axial direction, and has a circular through-hole 41 along the axial direction at the center (position of the intersection of diagonal lines).
The shaft portion 30 of the shaft 7 is inserted into the through hole 41 with a gap in the radial direction.
The outer shape of the housing 40 is not limited as long as the plurality of rollers 50 can be held in a predetermined posture with respect to the shaft 7 while rotatably supporting the plurality of rollers 50. However, the two rollers 50 are held so as to be opposed to each other by 180 degrees in the circumferential direction with respect to the shaft 7 while reducing the occupied space of the shaft 7, and the shaft 7 is fitted to the shaft 7 with a gap. It is preferable to be provided.

On the left and right outer surfaces of the housing 40, housing recesses 45 having a depth capable of housing each roller 50 are formed. As shown in FIG. 1, the mounting hole 42 formed in the housing 40 so that the axis RL of the support shaft 52 has an inclination angle α with respect to each roller 50 on the front and back wall surfaces of the housing recess 45. Has been processed.
The mounting holes 42 are formed in order from the front (right side of the figure) in a large diameter hole 42a formed through the front wall surface, a medium diameter hole 42b formed in the front side portion of the rear wall surface, and an intermediate portion of the rear wall surface. The small-diameter hole 42c is coaxially formed, and a counterbore hole 43 coaxial with the small-diameter hole 42c of the mounting hole 42 is processed in a rear side portion of the rear wall surface.

On the other hand, the support shaft 52 is, in order from the front, a large-diameter portion 52a that fits into the large-diameter hole 42a of the mounting hole 42, a shaft portion 42b that fits into the medium-diameter hole 42b of the mounting hole 42, and a shaft portion. A female screw 42c formed on the end face of 42b is coaxially provided.
In each roller 50, the shaft portion 42 b of the support shaft 52 is inserted into the mounting hole 42 from the large-diameter hole 42 a side, and a fixing nut 54 that is screwed into the male screw 42 c at the end of the support shaft 52 is fastened to the counterbore hole 43. This is attached to the housing 40. A spacer 53 is interposed between the wall surface behind the housing recess 45 and the inner ring of the bearing 55, and the fixing nut 5 is interposed via the spacer 53.
By fixing the support shaft 52 by 4, an intended preload is applied.

Here, the inclination angle α of the two rollers 50 in a predetermined posture is set so that the contact point between the outer peripheral surface of the shaft 7 and the outer peripheral surface of the roller 50 is P, and the support shaft 52 of the roller 50 is centered on the contact P.
The angle between the axis line CL and the axis line RL when the axis line RL is inclined in the twisting direction.
The contact point P of each roller 50 is located on the same circumference orthogonal to the axis CL, and the center of each roller 50 at the position of the contact point P is P.P. C. D. (Pitch Circle Diameter) Accordingly, the plurality of rollers 50 are supported in a predetermined posture with the same inclination angle α in the direction of twisting with respect to the axis CL of the shaft 7 (Condition 2 described in “Means for Solving the Problems”) ).

Further, each roller 50 is attached to the housing 40 when the shaft portion 30 of the shaft 7 is attached.
Slidably contacted with a preload applied so that traction drive force can be transmitted (
Condition 3) described in “Means for Solving the Problem”.
In this embodiment, the preload is set so that the contact surface pressure of each roller 50 is in the range of 0.6 to 3 GPa. In the present embodiment, the outer peripheral surface of the shaft portion 30 and the roller 50 of the shaft 7 is mirror-finished so that the traction driving force can be transmitted more reliably, and the mirror-finishing is performed with a surface roughness Ra of 0.2 or less. (Condition 4).

Furthermore, in this embodiment, traction grease or traction oil is applied to the outer peripheral surface of the shaft portion 30 and each roller 50 of the shaft 7 so that the traction driving force can be transmitted more reliably (Condition 5). .
In addition, as the traction grease or traction oil employed in this embodiment,
For example, Japanese Patent No. 3599231 and Japanese Patent No. 40442, which are disclosed in Patent Publications.
It is preferable to use the traction drive fluid described in Japanese Patent No. 25 or the additive for traction drive oil described in Japanese Patent No. 4005714 as an additive.

Next, the operation and effect of the rotation / linear motion conversion device 20 will be described.
As described above, the rotation / linear motion conversion device 20 is 18 in the circumferential direction with respect to the shaft portion 30 of the shaft 7.
A traction drive mechanism is configured after two rollers 50 arranged opposite to each other with a separation of 0 ° are arranged at twisted positions.
That is, according to the linear motion converter 20, the shaft 7 having the cylindrical shaft portion 30.
On the other hand, since the two rollers 50 are arranged at the twist position and the twist angle α of the twist is predetermined in advance for both of the two rollers 50, by rotating the shaft 7, only the amount corresponding to the tilt angle is obtained. The housing 40 advances in the axial direction of the shaft 7, and the plurality of rollers 50 and the housing 40 that fixes the rollers 50 can be linearly moved along the shaft 7 by traction drive. Further, if the shaft 7 is prevented from rotating outside, the shaft 7 can be linearly moved by rotating the housing 40.

Therefore, unlike the ball screw, the configuration of the rotation / linear motion conversion device 20 is based on traction drive that uses only the rotating roller 50, so that relatively high quietness can be obtained compared to the ball screw. It can handle small lead angles that cannot be achieved with a ball screw. Further, since the shaft 7 does not require a thread groove such as a ball screw, the workability and maintainability of the shaft 7 are excellent.

In particular, in the rotation / linear motion conversion device 20, the two rollers 50 are arranged in a state in which a preload that can be traction driven is applied to the shaft portion 30 of the shaft 7. This is suitable for preventing the occurrence of backlash.
Further, in the rotation / linear motion conversion device 20, the shaft portion 30 of the shaft 7 and the outer peripheral surface of the roller 50 are mirror-finished, and traction grease or traction oil is applied to the outer peripheral surface of the shaft portion 30 and the roller 50 of the shaft 7. Therefore, slipping can be prevented more reliably and traction drive can be performed more efficiently.

In particular, in the rotation / linear motion conversion device 20, the outer peripheral surface of each roller 50 is a concave arc centered on the contact point P, so that the centering effect on the shaft 7 is improved and the rollers 50 are clamped by the two rollers 50. The state is reliably maintained, and the rotation / linear motion conversion device 20 is prevented from falling off. Further, since the position of the axis RL of the support shaft 52 can be arranged closer to the axis CL of the shaft 7 by the concave arc of each roller 50, the height of the clamping mechanism portion by the two rollers 50 can be kept low and the housing 40 can be made more compact. Can be configured.

[Rack-assisted electric power steering device]
Next, a vehicle equipped with a rack-assist type electric power steering device will be described as an example of a mechanical device including the rotation / linear motion conversion device 20.
As shown in FIG. 3, the steering unit 1 of the automobile includes a rack and pinion type electric power steering device 10 that includes a pinion mechanism 2 and a rack mechanism 3. Pinion mechanism 2
Has a pinion shaft 5 rotatably supported by the pinion housing 4. Pinion shaft 5
Is connected to the steering wheel via a steering shaft (not shown).

The rack mechanism 3 has a rack housing 6, and the rack housing 6 is fixed to the vehicle body by a bracket (not shown). A rack shaft 7 as a steering shaft is slidably supported inside the rack housing 6. Both ends of the rack shaft 7 are connected to tie rods 8 respectively. The rack shaft 7 corresponds to the shaft 7 of the rotation / linear motion conversion device 20 described above.
The pinion shaft 5 and the rack shaft 7 are meshed with each other by a rack and pinion gear so that the rotational force transmitted to the pinion shaft 5 can be converted into the direct power of the rack shaft 7. here,
The rack shaft 7 has a rack portion (not shown) with which the pinion shaft 5 is engaged, and a cylindrical shaft portion 30 formed on the right end side of the rack portion in FIG. A rack-assist type electric power steering device (EPS: Electr)
ic Power Steering (hereinafter, also simply referred to as “EPS”) 10 is disposed.

This EPS 10 has a cylindrical EPS housing 11 as shown in FIG.
The housing 11 includes a tubular main body portion 12 disposed substantially at the center in the axial direction, a tubular conversion device housing portion 13 coaxially connected to the right end of the main body portion 12, the main body portion 12, and the conversion device. Ring-shaped lid portions 14 and 15 that respectively close left and right openings with the accommodating portion 13 are fixed to each other with a plurality of connecting bolts 16 and 17. Packings 18 are interposed between the left and right lid portions 14 and 15 and the outer peripheral surface of the shaft portion 30.

In the main body 12, a tubular stator 8a is fixed, and a coil 8b composed of a plurality of segments around which a part of the stator 8a is wound is provided. Inside the stator 8a, a tubular rotor 8c is attached so as to rotate integrally around a tubular sleeve 9 longer than the rotor 8c. The stator 8a, the coil 8b, the rotor 8c, and the sleeve 9 constitute a brushless type electric motor 60.

The outer periphery of the middle portion on the right side of the sleeve 9 is supported by the bearing 22 so as to be rotatable with respect to the EPS housing 11. The bearing 22 is an angular contact type ball bearing, and the inner ring of the bearing 22 is provided with a predetermined preload to the bearing 22 by fixing a substantially annular pressing member 21 with a bolt 19. Near the left end of the sleeve 9, a motor rotation angle detector 80 capable of detecting the rotation state of the electric motor 60 is provided.

The motor rotation angle detection unit 80 includes an annular stator 81 and an annular rotor 82 that is concentric with the stator 81 and supported so as to be relatively rotatable. The stator 81 is fixedly supported by a plurality of pole pieces having a plurality of pole piece teeth at the tip portion, and the pole piece has both N-phase excitation and signal output. Are wound in series for each phase. The rotor 82 constitutes a resolver by having a tooth row formed in the circumferential direction so as to face the pole piece teeth of the stator 81 with a gap. The motor rotation angle detection unit 80 can output a digital rotation angle signal by A / D converting a plurality of resolver signals having different phases obtained in accordance with changes in reluctance between the rotor 82 and the stator 81. Yes.

And the above-mentioned rotation linear motion converter 20 is accommodated in the cylindrical converter accommodation part 13 of the sleeve 9 right end. In the housing 40 of the rotation / linear motion conversion device 20, two rollers 50 satisfying the above conditions 1 to 3 (more preferably, the above conditions 1 to 5) are rotatable with respect to the shaft portion 30 of the rack shaft 7. It is supported. In the present embodiment, the housing 40 is connected to the right end of the sleeve 9 via the pressing member 21 at the same time as the bolt 19 so that the housing 40 is integrated with the sleeve 9, and the housing 40 can rotate integrally with the sleeve 9. Has been.

Further, a guide roller device 90 for guiding the rack shaft 7 is provided inside the EPS housing 11 inside the cylindrical flange portion 14 a of the lid portion 14 on the left side of the left end of the sleeve 9. The guide roller device 90 includes a plurality of support blocks 93 fixed to the inner surface of the cylindrical flange 14a, and a plurality of guide rollers 91 rotatably supported by a support shaft 92 between adjacent support blocks 93. Have.

In the present embodiment, four guide rollers 91 are provided, and the four guide rollers 91 are spaced apart by 90 ° in the circumferential direction and arranged in the same posture. The support shaft 92 of each guide roller 91 is disposed orthogonal to the axis of the shaft portion 30 of the rack shaft 7, and each guide roller 91 rotates along the linear movement direction of the rack shaft 7, so Smooth movement guidance is provided.
Further, a linear encoder 100 capable of detecting a movement amount and a movement direction of the rack shaft 7 in the linear motion direction is provided at a position between the guide roller device 90 and the left end of the sleeve 9. The linear encoder 100 includes a magnetic encoder unit 101 composed of a multipolar magnet and a magnetic sensor unit 102. The magnetic encoder unit 101 includes a shaft unit 30 of the rack shaft 7.
The surface of the shaft portion 30 is configured by magnetizing the S pole and the N pole alternately in the axial direction at predetermined intervals in an annular shape. ing.

The magnetic sensor unit 102 has a magnetic sensitive surface opposed to the magnetic encoder unit 101, and
Two Hall elements 102a and 102b in which the elements are spaced apart from each other by a predetermined distance in the linear motion direction
And a circuit board 102c on which these two Hall elements 102a and 102b and a linear motion information calculator (not shown) are mounted. The circuit board 102c has a substantially L-shaped mounting angle 103.
The base end of the mounting angle 103 is attached to the front surface of the EPS housing 1.
An annular support bracket 10 fixed coaxially to the main body 12 on the inner peripheral surface of one main body 12
4 is fixed.

Since the magnetic encoder unit 101 is formed directly on the outer peripheral surface of the shaft unit 30, the rack shaft 7
The magnetic encoder unit 101 also moves linearly with the linear movement. In the magnetic sensor unit 102, the positional relationship between the two Hall elements 102a and 102b facing the magnetic encoder unit 101 periodically changes as the magnetic encoder unit 101 moves linearly. Magnetic flux from the magnetic encoder unit 101 passes through the magnetic sensor unit 102, but the two Hall elements 102a and 102b correspond to the passing magnetic flux and are two-phase pulses of the number of magnetic pole pairs whose phases are shifted according to the magnetic flux change. Output a signal. The two-phase pulse signals are A phase and B phase. The linear motion information calculator of the magnetic sensor unit 102 simultaneously acquires sampling values for the A-phase and B-phase magnetic detection signals at the sampling timing, and based on the two-phase pulse signals that are out of phase with each other, the shaft unit The linear motion information indicating the linear motion state of the shaft portion 30 such as the linear motion position, the linear motion speed, and the linear motion direction is periodically calculated.

The electric motor 60 is drive-controlled by a motor control device 70 as shown in FIG.
The motor control device 70 includes a torque sensor 71 that detects a steering torque input to a steering wheel (not shown) and a vehicle speed sensor 72 that detects a vehicle speed. Motor control device 70
The steering torque detected by the torque sensor 71, the vehicle speed detected by the vehicle speed sensor 72, the rotation angle detected by the motor rotation angle detection unit 80, and the linear motion information detected by the magnetic sensor unit 102 of the linear encoder 100. The steering assist torque command value is calculated from the calculated steering assist torque command value, the motor drive current for generating the necessary steering assist torque is obtained based on the calculated steering assist torque command value, and the motor drive current is output to the electric motor 60. Has been.

In particular, in the present embodiment, since the traction drive mechanism that does not use a ball screw is employed in the rotation / linear motion conversion device 20, the motor rotation angle detector 8 is used when calculating the steering assist torque command value.
The rotation angle information detected at 0 and the linear motion information detected by the magnetic sensor unit 102 are used as the motor control device 7.
By feeding back to 0 at any time, a correction based on the rotation angle information and the linear motion information is added to calculate a steering assist torque command value with high accuracy.

Next, functions and effects of the EPS 10 will be described.
In this automobile, the steering rotational force when the steering wheel is steered is transmitted to the pinion shaft 5 and converted into the linear motion of the rack shaft 7 meshing with the pinion shaft 5, and this linear motion is connected to both ends of the rack shaft 7. Is transmitted to the steered wheels via the tie rods 8, and the steered wheels are steered.

When the steering rotational force is transmitted to the pinion shaft 5, the EPS 10 drives the electric motor 60, so that the sleeve 9 is rotationally driven accordingly, and the rotation / linear motion conversion device 20 connected integrally with the sleeve 9. The housing 40 is driven to rotate. As a result, the rack shaft 7 is linearly driven by the traction driving force transmitted from the plurality of rollers 50 mounted on the housing 40 to the shaft portion 30 to assist the steering force.

Here, in the rack assist type electric power steering device, a ball screw mechanism is often adopted as the rotation / linear motion conversion device. However, since the ball screw mechanism requires a circulation structure for circulating the ball as a rolling element, vibration and Sound is generated, and vibration and sound generated by the ball screw mechanism are transmitted to the steering wheel via the rack shaft and the steering shaft, which may cause discomfort to the driver.

On the other hand, according to the EPS 10 including the rotation / linear motion conversion device 20 of the present embodiment, unlike the ball screw, a traction drive mechanism that uses only two rollers 50 of the rotating system is adopted. Relatively high quietness is obtained compared to the mechanism, vibration and sound are reduced, and it is possible to cope with small leads compared to the ball screw.
Also, in a rack shaft employing a conventional ball screw mechanism, a thread groove is formed on the outer periphery on one side and a rack portion is formed on the other side. With such a configuration, a large steering angle can be secured. To prevent interference between the ball screw mechanism's thread groove and the rack part against the required rack axis length, the rack axis becomes longer, the steering device becomes larger, and the rack axis length should be reduced. Then, there is a problem that the range of the effective screw groove becomes narrow and the steering angle is reduced.

In contrast, the EPS 10 including the rotation / linear motion conversion device 20 according to the present embodiment employs a traction drive mechanism that uses only the rotating roller 50, so that it is not necessary to form a screw groove on the rack shaft 7. In addition, the rotation / linear motion conversion device 20 can be operated by the cylindrical shaft portion 30. Therefore, a relatively large steering angle can be ensured while having a compact configuration. Further, since it is not necessary to form a screw groove such as a ball screw on the rack shaft 7, it is relatively excellent in workability and maintainability.

In general, since the tie rod 8 is attached to the rack shaft 7 with an angle, a radial load and a moment load are applied to the rack shaft 7 as a steering reaction force in addition to the axial load.
On the other hand, in the case of a rack and pinion type electric power steering device using a conventional ball screw mechanism, since the radial load and moment load described above are applied to the ball screw mechanism, a decrease in durability becomes a problem. EPS1 provided with rotation linear motion conversion apparatus 20 of embodiment
If it is 0, it is not necessary to form a screw groove on the rack shaft 7, and a relatively high durability can be obtained by a traction drive mechanism using only the roller 50 of the rotating system.

Furthermore, with the EPS 10 of this embodiment, when calculating the steering assist torque command value, the rotation angle information detected by the motor rotation angle detection unit 80 and the linear motion information detected by the magnetic sensor unit 102 are fed back as needed. Since the steering assist torque command value is calculated by adding corrections based on the rotation angle information and the linear motion information, even when a radial load or moment load is applied by the steering reaction force, the steering assist torque command value is changed as needed. The final steering assist torque command value is obtained from the correction data, and based on this, the electric motor 60 can be controlled with high accuracy.

As described above, according to the above-described rotation / linear motion conversion device 20, the electric power steering device 10 including the same, and the automobile, compared to the rotation / linear motion conversion device using the ball screw,
Relatively high silence can be obtained. The rotation / linear motion conversion device according to the present invention, the electric power steering device including the same, and the vehicle are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. .

For example, in the above-described embodiment, the electric power steering apparatus 10 and the automobile including the same are illustrated and described as application examples of the rotation / linear motion conversion device according to the present invention. However, the application of the rotation / linear motion conversion device according to the present invention is described. The scope is not limited to this, and the present invention can be applied to vehicles other than automobiles having a steering system, and the rotation / linear motion conversion device according to the present invention includes various machines including an industrial linear motion table that can use a ball screw. Of course, it can be applied to the apparatus in place of the ball screw. The industrial linear motion table is, for example, a lathe, drilling machine, boring machine, milling machine,
It is a linear motion device mainly used for positioning, used in industrial machinery such as gear cutting machines and grinding machines.

[Second Embodiment]
FIG. 5 shows a second embodiment of the rotation / linear motion conversion device according to one aspect of the present invention. FIG. 5 is a front view similar to FIG. In the description of the present embodiment, the description of the same parts as in the first embodiment will be omitted, and different parts will be mainly described with reference numerals attached to the drawings.

  The difference between the rotation / linear motion conversion device 520 of the present embodiment and the rotation / linear motion conversion device 20 of the first embodiment is the outer peripheral shape R of the two rollers 550. In the first embodiment, the outer peripheral shape of the two rollers 50 is formed with a constant outer diameter in the axial direction, whereas in this embodiment, the outer peripheral shape R of the two rollers 550 is smooth in the axial direction. The outer diameter is different. It has a maximum diameter at the shaft end and a minimum diameter near the center in the axial direction. Thus, the positional relationship with the shaft can be further maintained by using the curved outer peripheral shape R having a large diameter on the shaft end side and a small diameter near the center in the axial direction.

DESCRIPTION OF SYMBOLS 1 Steering part 2 Pinion mechanism 3 Rack mechanism 4 Pinion housing 5 Pinion shaft 6 Rack housing 7 Rack shaft (shaft)
8 Tie rod 10 Electric power steering device 20 Rotation linear motion conversion device (first embodiment)
30 (Shaft) Shaft 40 Housing 50 Roller 60 Electric Motor 70 Motor Control Device 71 Torque Sensor 72 Vehicle Speed Sensor 80 Motor Rotation Angle Detection Unit 90 Guide Roller Device 100 Linear Encoder 520 Rotation Linear Motion Conversion Device (Second Embodiment)
550 Roller R outer peripheral shape

Claims (8)

A housing;
A shaft having an outer peripheral surface having a cylindrical shaft portion;
Two rollers rotatably supported by the housing via a support shaft,
The two rollers are rotation / linear motion conversion devices that satisfy the following conditions 1 to 3.
Condition 1: The two rollers are arranged to face each other at a distance of 180 ° in the circumferential direction with respect to the shaft.
Condition 2: The two rollers are supported with the same inclination angle in the direction of twist with respect to the axis of the shaft.
Condition 3: The two rollers are in sliding contact with a preload applied to the shaft portion of the shaft so that a traction driving force can be transmitted. The rotation / linear motion conversion device according to claim 1, wherein traction grease or traction oil is applied to the shaft portion of the shaft and the outer peripheral surface of the roller. The rotation / linear motion conversion device according to claim 1, wherein the preload is a contact surface pressure in a range of 0.6 to 3 GPa. The rotation linear motion conversion according to any one of claims 1 to 3, wherein the shaft portion of the shaft and the outer peripheral surface of the roller are mirror-finished, and the mirror-finishing has a surface roughness Ra of 0.2 or less. apparatus.   The outer peripheral shape of the two rollers is axially different from each other smoothly, and has a large diameter at the shaft end side and a small diameter near the center in the axial direction. The rotation / linear motion conversion device according to the item.   An electric power steering device comprising the rotation / linear motion conversion device according to any one of claims 1 to 5.   A vehicle comprising the electric power steering device according to claim 6.   A machine apparatus provided with the rotation / linear motion conversion apparatus as described in any one of Claims 1-5.

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