JP2017040343A - Rotation-linear motion converting device, and electric power steering device, vehicle and machine device equipped therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotation-linear motion converting device for achieving relatively high quietness.SOLUTION: A rotation-linear motion converting device 20 includes a shaft 7 having a shank 30 whose outer peripheral face is cylindrically shaped, a housing 40 externally fitted to the shaft 7 across a gap, a plurality of rollers 50 fixed at its base end to the housing 40 and equally spaced from the shaft 7 in the peripheral direction, cover members 46, 48 externally fitted to the shaft 7 across gaps for covering areas on the axial front and rear sides of the housing 40, respectively, and packings 18 mounted between each of the cover members 46, 48 and the shank 30, respectively. The plurality of rollers 50 are supported on the housing 40 rotatably at the same inclination angle α to the axis of the shaft 7 in the torsional direction, and also put in slide contact with the shank 30 of the shaft 7 while applying a preload thereto to enable the transmission of traction driving force.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 (see, for example, 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-described problem, a rotation / linear motion conversion device according to an aspect of the present invention includes a shaft having a cylindrical shaft portion on an outer peripheral surface, a housing that is fitted on the shaft with a gap therebetween, and the housing A plurality of rollers rotatably supported via a support shaft, a cover member that is externally fitted to the shaft with a gap and covers the plurality of rollers and the housing in the axial direction, the cover member, A packing interposed between the shaft portion of the shaft and the plurality of rollers satisfy the following conditions 1 to 3.

Condition 1: The plurality of rollers are equally spaced apart from the shaft in the circumferential direction.
Condition 2: The plurality of rollers are supported with the same inclination angle in the direction of twist with respect to the axis of the shaft.
Condition 3: The plurality of rollers are in sliding contact with a preload applied so that traction driving force (friction driving force by rolling contact) can be transmitted to the shaft portion of the shaft.

  According to the rotation / linear motion conversion device according to one aspect of the present invention, a plurality of rollers equally spaced apart in the circumferential direction of the shaft are twisted with respect to the axis with respect to a shaft having an outer peripheral surface having a cylindrical shaft portion. A plurality of rollers are slidably contacted with a preload applied so that a traction driving force can be transmitted to the shaft portion of the shaft. Therefore, if the shaft is rotated, the plurality of rollers and the housing for fixing the 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.

In addition, according to the rotation / linear motion conversion device according to one aspect of the present invention, it is possible to cope with a small lead as compared with a ball screw. Further, since it is not necessary to form a screw groove like a ball screw on the shaft, it is relatively easy to maintain.
Furthermore, according to the rotation / linear motion conversion device according to one aspect of the present invention, unlike the ball screw, the traction drive mechanism is configured by using only the rollers of the rotating system, so that relatively high silence can be obtained. In particular, according to the rotation / linear motion conversion device according to one aspect of the present invention, the cover member that is externally fitted to the shaft with a gap and covers the front and rear in the axial direction of the housing, and the cover member and the shaft portion are interposed Since it is provided with the packing to be mounted, silence can be further improved by the cover member, grease and oil can be prevented from leaking out, and foreign matter can be prevented from entering from the outside.

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.

It is a front view of one embodiment of a rotation / linear motion conversion device according to an aspect of the present invention. It is a right view 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. 4A and 4B are diagrams illustrating a main part of FIG. 3, in which FIG. 3A is a vertical cross-sectional view along the axis of the main part, and FIG. 3B is a ZZ cross-sectional view of FIG.

  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. A plurality of supported rollers 50, cover members 46 and 48 covering the front and rear of the housing 40 in the axial direction, and a packing 18 interposed between the cover members 46 and 48 and the shaft portion 30 are provided. In the present embodiment, a cam follower in which the roller 50 and the support shaft 52 are integrally formed via a needle bearing 53 is used, and the plurality of rollers 50 are held in a predetermined arrangement and a predetermined posture with respect to the shaft 7. Is done.

  Specifically, as a predetermined arrangement, the plurality of rollers 50 are equally spaced apart from the shaft 7 in the circumferential direction (condition 1 described in “Means for Solving the Problems”). In the present embodiment, four rollers 50 are provided, and the four rollers 50 are arranged in the same posture at intervals of 90 ° in the circumferential direction. Note that the number of the plurality of rollers 50 is not limited to four, and can be various aspects as long as it is two or more. The number of the plurality of rollers 50 is preferably 3 or more.

In addition, the shape of the shaft 7 is not limited in the structure of other portions as long as it 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.
In this embodiment, an example in which a cam follower (roller follower) is used for each roller 50 has been described. However, the present invention is not limited to this, and the roller 50 includes a roller having a cylindrical or annular outer peripheral surface. If there are, bearings having various cylindrical outer rings can be used. For example, a combination bearing or a double row ball bearing that can receive a moment load may be used.

  As shown in FIG. 2, the housing 40 is a block-like member having a substantially square shape when viewed from the axial direction, and is circular along the axial direction at the center of the substantially square shape (position of the intersection of diagonal lines). The through hole 41 is formed, and the shaft portion 30 of the shaft 7 is inserted into the through hole 41 with a gap in the radial direction. In the present embodiment, one external surface of the housing 40 is provided with two female screws 44 for connecting other members such as a table.

The 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, in order to hold the plurality of rollers 50 so as to be equally spaced apart from each other in the circumferential direction with respect to the shaft 7, it is preferable that the rollers 50 are provided so as to be externally fitted with a gap therebetween.
In the housing 40, a mounting hole 42 of the support shaft 52 having an inclination angle α and a counterbore hole 43 coaxial with the mounting hole 42 are processed for each roller 50. The roller 50 is mounted on the housing 40 by inserting the support shaft 52 into the mounting hole 42 and tightening the fixing nut 54 screwed into the male screw at the end of the support shaft 52 into the counterbore hole 43. Here, the inclination angle α in a predetermined posture is an axis of the support shaft 52 of the roller 50 with the contact P as the center when the contact between the outer peripheral surface of the shaft portion 30 of the shaft 7 and the outer peripheral surface of the roller 50 is P. This is the angle formed between the axis line CL and the axis line RL when the RL is tilted 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, when the rollers 50 are mounted on the housing 40, they are slidably contacted with a preload applied to the shaft portion 30 of the shaft 7 so that a traction driving force can be transmitted (see “Solving Problems”). Condition 3) described in “Means for”.
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).

In the present 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).
As the traction grease or traction oil employed in the present embodiment, for example, the traction drive fluid disclosed in Japanese Patent No. 3599231 and Japanese Patent No. 4044225 disclosed in the patent publication gazette is used. It is preferable to use an additive for traction drive oil described in Japanese Patent No. 4005714 as an additive.

Furthermore, in this embodiment, it has the front cover 46 provided in the some roller 50 side as a cover member which covers the axial direction front and rear of the said housing 40, and the rear cover 48 provided in the other side.
The front cover 46 includes a cylindrical portion 46a that covers the plurality of rollers 50 in the radial direction, and an annular portion 46b that is provided on the end surface of the cylindrical portion 46a and covers the plurality of rollers 50 from the axial direction. The front cover 46 is a surface on the roller 50 side of the housing 40 so that the cylindrical portion 46 a and the annular portion 46 b are fitted on the shaft portion 30 of the shaft 7 with a gap and cover the entire plurality of rollers 50. It is attached to. A packing 18 is interposed between the annular portion 46b of the front cover 46 and the shaft portion 30 to prevent leakage of grease and oil from the inside of the front cover 46 and entry of foreign matter from the outside. Has been.

  The rear cover 48 is formed of an annular member, and is externally fitted to the shaft 40 with a gap therebetween. On the opposite side of the housing 40 from the front cover 46, the mounting side of the front cover 46 is defined. It is attached to the housing so as to cover the opposite side surface portion of the housing 40. The packing 18 is also interposed between the annular rear cover 48 and the shaft portion 30. A gap in the facing direction is formed on the surface of the rear cover 48 facing the housing 40 by a concave stepped portion 48d so that interference with the side surface portion of the housing 40 is prevented.

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 configures a traction drive mechanism after arranging the plurality of rollers 50 at the twisted position with respect to the shaft portion 30 of the shaft 7.
That is, according to the rotation / linear motion conversion device 20, a plurality (preferably 3 or more) of rollers 50 are arranged at a twist position with respect to the shaft 7 having the cylindrical shaft portion 30, and the torsional inclination angle α is Since the plurality of rollers 50 are all the same and predetermined, by rotating the shaft 7, the housing 40 advances in the axial direction of the shaft 7 by an amount corresponding to the inclination angle, and the plurality of rollers 50 and the housing for fixing the rollers 50 are fixed. 40 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, the configuration of the rotation / linear motion conversion device 20 can cope with a small lead angle 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.
Further, according to the rotation / linear motion conversion device 20, unlike the ball screw, it is based on the traction drive that uses only the rotating system roller 50, so that relatively high quietness can be obtained as compared with the ball screw. In particular, according to the rotation / linear motion conversion device 20, two covers 46 and 48 which are cover members that are fitted on the shaft 7 with a gap therebetween and cover the front and rear in the axial direction of the housing 40, and the covers 46 and 48, Since the packing 18 interposed between the shaft portions 30 is provided, the space in which the plurality of rollers 50 are arranged is sealed by the two covers 46 and 48, so that silence can be further improved. In addition, leakage of grease and oil can be prevented, and entry of foreign matter from the outside can be prevented. Therefore, the lifetime of the mechanism can be extended.

Further, in the rotation / linear motion conversion device 20, the plurality of rollers 50 are arranged in a state in which a preload load capable of traction driving is applied to the shaft portion 30 of the shaft 7, so that the roller 50 is like a rolled ball screw. 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.

[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. The pinion mechanism 2 has a pinion shaft 5 that is rotatably supported by a pinion housing 4. The pinion shaft 5 is connected to a steering wheel via a steering shaft (not shown) and the like.

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 meshes, 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: Electric Power Steering, hereinafter, also simply referred to as “EPS”) 10 is disposed at the position of the cylindrical shaft portion 7.

  As shown in FIG. 4, the EPS 10 includes a cylindrical EPS housing 11, and the EPS housing 11 includes a circular tubular main body portion 12 disposed substantially at the center in the axial direction, and the right end of the main body portion 12 in the figure. And a plurality of connecting bolts 16 are connected to each other by a circular tubular conversion device receiving portion 13 coaxially connected to each other, and annular lid portions 14, 15 for closing the left and right openings of the main body portion 12 and the conversion device receiving portion 13, respectively. , 17 and fixed. Packings 18 are interposed between the left and right lid portions 14 and 15 and the outer peripheral surface of the shaft portion 30. Here, in the rotation / linear motion conversion device 20 mounted on the EPS 10, the EPS housing 11 corresponds to a cover member that is fitted on the shaft (rack shaft) 7 with a gap and covers the front and rear in the axial direction of the housing 40. doing.

  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.

  The rotary / linear motion conversion device 20 is accommodated in the cylindrical conversion device accommodating portion 13 at the right end of the sleeve 9. A plurality of rollers 50 that satisfy the above-described conditions 1 to 3 (more preferably, the above-described conditions 1 to 5) are rotatable in the housing 40 of the rotation / linear motion conversion device 20 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 portion 101 is provided on the outer peripheral surface of the shaft portion 30 of the rack shaft 7 over the linear movement range of the rack shaft 7, and the surface of the shaft portion 30 has an annular shape with a predetermined interval between the S pole and the N pole. The magnet is alternately magnetized in the axial direction.

  The magnetic sensor unit 102 includes two Hall elements 102a and 102b in which a magnetically sensitive surface is disposed opposite to the magnetic encoder unit 101 and the elements are spaced apart from each other by a predetermined distance in the linear motion direction, and these two Hall elements 102a. , 102b and a circuit board 102c on which a linear motion information calculator (not shown) is mounted. The circuit board 102 c is mounted on the surface on the distal end side of the substantially L-shaped mounting angle 103, and the base end portion of the mounting angle 103 is coaxial with the main body portion 12 on the inner peripheral surface of the main body portion 12 of the EPS housing 11. It is fixed via an annular support bracket 104 fixed to the head.

  Since the magnetic encoder unit 101 is directly formed on the outer peripheral surface of the shaft unit 30, the magnetic encoder unit 101 also moves linearly together with the rack shaft 7. 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. The motor control device 70 detects 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 magnetic sensor unit 102 of the linear encoder 100. The steering assist torque command value is calculated from the linear motion information thus obtained, a motor drive current for generating the necessary steering assist torque is obtained based on the calculated steering assist torque command value, and this motor drive current is output to the electric motor 60. Is configured to do.

  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 rotation angle information detected by the motor rotation angle detector 80 when calculating the steering assist torque command value. And the linear motion information detected by the magnetic sensor unit 102 are fed back to the motor control device 70 as needed, so that correction based on the rotation angle information and the linear motion information is added, and a highly accurate steering assist torque command value is obtained. Calculated.

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 a plurality of 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. In the EPS 10 including the rotation / linear motion conversion device 20 according to the embodiment, 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 rotating system roller 50. Can do.

  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 rotation linear motion conversion device 20 and the automobile, relatively high quietness is obtained as compared with the rotation / linear motion conversion device using the ball screw. 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 a linear motion device mainly used for positioning used in industrial machinery such as a lathe, a drilling machine, a boring machine, a milling machine, a gear cutting machine, and a grinding machine.

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 18 Packing 20 Rotational linear motion conversion device 30 Shaft portion 40 Housing 46 Front cover (cover member)
48 Rear cover (cover member)
DESCRIPTION OF SYMBOLS 50 Roller 60 Electric motor 70 Motor control apparatus 71 Torque sensor 72 Vehicle speed sensor 80 Motor rotation angle detection part 90 Guide roller apparatus 100 Linear encoder

Claims (7)

A shaft having an outer peripheral surface having a cylindrical shaft portion;
A housing externally fitted to the shaft with a gap therebetween;
A plurality of rollers rotatably supported by the housing via a support shaft;
A cover member that fits around the shaft with a gap and covers the front and rear of the plurality of rollers and the housing;
A packing interposed between the cover member and the shaft portion of the shaft,
The plurality of rollers are rotation / linear motion conversion devices that satisfy the following conditions 1 to 3.
Condition 1: The plurality of rollers are equally spaced apart from the shaft in the circumferential direction.
Condition 2: The plurality of rollers are supported with the same inclination angle in the direction of twist with respect to the axis of the shaft.
Condition 3: The plurality of 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.   An electric power steering device comprising the rotation / linear motion conversion device according to any one of claims 1 to 4.   A vehicle comprising the electric power steering device according to claim 5.   A machine apparatus provided with the rotation / linear motion conversion apparatus as described in any one of Claims 1-4.

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