JP6638255B2 - Rotary-to-linear motion converter for electric power steering device, electric power steering device including the same, and vehicle - Google Patents

Description

The present invention relates to a rotary-linear motion conversion device for converting a rotary motion and a linear motion to each other, about the rotary-linear motion conversion device can be suitably employed in the electric power steering system.

  As this kind of rotary-to-linear motion conversion device, for example, a ball screw is used in many types of 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 a circulating structure for circulating the ball is required as a rolling element. Further, a ball screw has a problem that it is difficult to cope with a small lead because a ball is interposed between a screw shaft and a nut.
Therefore, the present invention has been made in view of such a problem, and a rotation / linear motion conversion device for an electric power steering device capable of obtaining relatively high quietness, an electric power steering device including the same, and It is an object to provide a vehicle.

In order to solve the above problems, a rotary-to-linear motion converter for an electric power steering device according to one aspect of the present invention is arranged so as to surround a shaft having an outer peripheral surface having a cylindrical shaft portion and the shaft. A flat rectangular parallelepiped housing is provided, and a drum-shaped roller rotatably supported by the housing via a support shaft is limited to two, and the two rollers satisfy the following conditions 1 to 4 .
Condition 1: The two rollers are spaced apart from each other by 180 ° in the circumferential direction with respect to the shaft and are opposed to each other in a direction along a long side of a flat rectangular parallelepiped in the housing in a cross-sectional view of the shaft .

Condition 2: The two rollers are supported at the same inclination angle in the direction of twist with respect to the axis of the shaft.
Condition 3: The two rollers are brought into sliding contact with each other with a preload applied so that traction driving force (friction driving force due to rolling contact) can be transmitted to the shaft portion of the shaft.
Condition 4: the two rollers are such that the outer peripheral surface of the drum shape of each roller is centered on a center point of a line connecting two contact points with the shaft portion of the shaft in an axial cross section. is formed in an arc concave shall be the center of the constricted position perpendicular to the support shaft.

According to the rotary-to-linear motion converter for an electric power steering device according to one aspect of the present invention, two shafts whose outer peripheral surfaces are opposed to each other by 180 ° in the circumferential direction of the shaft with respect to a shaft having a cylindrical shaft portion are provided. The rollers were rotatably supported on the housing with the same inclination angle in the direction of torsion with respect to the axis, and a preload was applied so that the two rollers could transmit traction driving force to the shaft of the shaft. When the shaft is rotated, the two rollers and the housing for fixing the rollers can be linearly moved along the shaft by an amount corresponding to the tilt angle by traction drive. Further, if the housing is rotated while the shaft is prevented from rotating outside, the shaft can be moved linearly.

According to the rotation / linear motion converter for an electric power steering device according to one aspect of the present invention, unlike a ball screw, a traction drive mechanism is configured using only two rollers of a rotation system. In addition, a high quietness can be obtained, and a small lead can be used as compared with a ball screw. Further, since it is unnecessary to form a thread groove such as a ball screw on the shaft, the shaft is relatively excellent in maintainability.

According to another embodiment of the present invention, there is provided an electric power steering device including the rotation / linear motion converter for an electric power steering device according to one embodiment of the present invention. According to the electric power steering device according to one embodiment of the present invention, since provided the electric power steering device for converting rotary motion into linear motion device according to one embodiment of the present invention, the rotational electric power steering apparatus according to an embodiment of the present invention straight Due to the operation and effect of the dynamic conversion device, relatively high quietness can be obtained.
Further, to solve the above problem, a vehicle according to one embodiment of the present invention includes an electric power steering device according to one embodiment of the present invention. According to the vehicle of one embodiment of the present invention, the electric power steering device of one embodiment of the present invention includes the electric power steering device of one embodiment of the present invention. can get.

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

BRIEF DESCRIPTION OF THE DRAWINGS It is a front view of one Embodiment of the rotary-to-linear motion converter which concerns on one aspect of this invention, Comprising: In FIG. It is XX sectional drawing of FIG. 1 is an explanatory diagram of a steering unit of a vehicle equipped with an electric power steering device according to one embodiment of the present invention. 3A and 3B are views for explaining main parts of FIG. 3, in which FIG. 3A is a vertical cross-sectional view along an axis of the main parts (excluding a rotary-to-linear motion converter), and FIG. It is a ZZ sectional view.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. The drawings are schematic. Therefore, it should be noted that the relationship between the thickness and the plane dimension, the ratio, and the like are different from actual ones, and the drawings include portions having different dimensional relationships and ratios. The embodiments described below exemplify an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention is based on the material, shape, structure, and arrangement of component parts. Are not specified in the following embodiments.

[Rotary linear motion converter]
As shown in FIGS. 1 and 2, the rotary-to-linear motion converter 20 is rotatably connected to a housing 40, a shaft 7 having a cylindrical shaft portion 30 with an outer peripheral surface, and a housing 40 through a support shaft 52. And two rollers 50 supported. 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 arranged facing each other at a distance of 180 ° in the circumferential direction of the shaft 7 (condition 1 described in “Means for Solving the Problem”). The shape of the shaft 7 is not limited in relation to the rotary-to-linear motion converter 20 as long as the outer peripheral surface has the cylindrical shaft portion 30. For example, as described later, the shaft 7 can be applied to a rack shaft of a rack assist type electric power steering device.

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

  In the present embodiment, the outer peripheral surface of each roller 50 is formed in a substantially circular concave arcuate centered on a position orthogonal to the support shaft 52 of the roller 50 about the contact point P with the shaft 30. I have. As a result, the cylindrical (substantially drum-shaped) outer peripheral surface of each roller 50 has a concave arc centered on the contact point P, so that the centering effect on the shaft 7 is improved and the two rollers 50 The holding state of the rotary / linear motion conversion device 20 is prevented by reliably holding the holding state by the 50. 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 holding mechanism portion by the two rollers 50 is suppressed low, and the housing 40 is more compact. Configurable.

  In the present embodiment, an example is shown in which the hollow cylindrical roller 50 is rotatably supported by the support shaft 52 via a pair of bearings 55 and 56. However, the present invention is not limited to this. As long as the bearing has a cylindrical or annular outer peripheral surface, various types of bearings having a cylindrical outer ring can be used. For example, a cam follower may be used as the roller 50 in addition to a combination bearing and 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 (the position of the diagonal intersection). The shaft 30 of the shaft 7 is inserted through 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 are rotatably supported and the plurality of rollers 50 can be held in a predetermined posture with respect to the shaft 7. However, while holding the two rollers 50 so as to be opposed to each other by 180 ° in the circumferential direction with respect to the shaft 7 while reducing the space occupied by itself, the two rollers 50 are fitted to the shaft 7 with a gap therebetween. Is preferably provided.

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

On the other hand, the support shaft 52 includes, in order from the front, a large-diameter portion 52a fitted into the large-diameter hole 42a of the mounting hole 42, a shaft portion 42b fitted into the medium-diameter hole 42b of the mounting hole 42, and a shaft portion. It has a female screw 42c formed on the end face of 42b coaxially.
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 the fixing nut 54 screwed into the male screw 42 c at the end of the support shaft 52 is tightened in the counterbore hole 43. Thereby, it is mounted on the housing 40. A spacer 53 is interposed between the rear wall surface of the housing recess 45 and the inner ring of the bearing 55, and the support shaft 52 is fixed by a fixing nut 54 via the spacer 53, so that an expected result is obtained. Is applied.

Here, the inclination angle α of the two rollers 50 in the predetermined posture is defined by the angle of the support shaft 52 of the roller 50 about the contact point P, where P is the contact point between the outer peripheral surface of the shaft 7 and the outer peripheral surface of the roller 50. This is the angle formed between the axis CL and the axis RL when the axis RL is tilted in the torsional direction.
In addition, 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). As a result, the plurality of rollers 50 are supported in a predetermined posture at the same inclination angle α in the direction of twist 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, the rollers 50 are slid in contact with the shaft portion 30 of the shaft 7 in a state where a preload is applied so that traction driving force can be transmitted. Means 3).
In the present embodiment, the preload is set such 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 surfaces of the shaft portion 30 and the roller 50 are mirror-finished so that the traction driving force can be transmitted more reliably. (Condition 4).

Further, in the present embodiment, traction grease or traction oil is applied to the shaft portion 30 of the shaft 7 and the outer peripheral surface of each roller 50 so that the traction driving force can be transmitted more reliably (condition 5). .
As the traction grease or traction oil used in the present embodiment, for example, a traction drive fluid described in Japanese Patent No. 3599231 or Japanese Patent No. 4444225 disclosed in Patent Publications may be used. It is preferable to use an additive for traction drive oil described in Japanese Patent No. 4007144 as an additive.

Next, the operation and effect of the rotary / linear motion converter 20 will be described.
As described above, the rotary-to-linear motion conversion device 20 is configured such that the two rollers 50 that are disposed to be opposed to each other by 180 degrees in the circumferential direction with respect to the shaft portion 30 of the shaft 7 are disposed at the twist position, Is composed.
That is, according to the rotary-to-linear motion converter 20, the two rollers 50 are arranged at the twist positions with respect to the shaft 7 having the cylindrical shaft portion 30, and the inclination angle α of the twist is the same for both the rollers 50. When the shaft 7 is rotated, 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 40 for fixing the rollers 50 are driven by traction drive. 7, a linear motion can be made. If the shaft 7 is prevented from rotating outside, by rotating the housing 40, the shaft 7 can be moved linearly.

  Therefore, unlike the ball screw, the configuration of the rotary-to-linear motion converter 20 is based on traction drive using only the roller 50 of the rotation system, so that relatively high quietness can be obtained as compared with the ball screw. Compatible with small lead angles not possible with ball screws. Further, since a thread groove such as a ball screw is not required for the shaft 7, the workability and the maintainability of the shaft 7 are excellent.

In particular, in the rotary-to-linear conversion device 20, the two rollers 50 are arranged in a state where a preload capable of traction drive is applied to the shaft portion 30 of the shaft 7, so that the two rollers 50 are like rolled ball screws. This is suitable for preventing the occurrence of loose play.
In the rotary-to-linear motion converter 20, the outer peripheral surfaces of the shaft portion 30 of the shaft 7 and the roller 50 are mirror-finished, and traction grease or traction oil is formed on the outer peripheral surface of the shaft portion 30 of the shaft 7 and the roller 50. Is applied, slip can be more reliably prevented, and traction drive can be performed more efficiently.

  In particular, in the rotary-to-linear motion converter 20, since the outer peripheral surface of each roller 50 is a concave arc centered on the contact point P, the centering effect on the shaft 7 is improved, and the two rollers 50 pinch. The state is reliably maintained, and the rotation-to-linear motion converter 20 is prevented from falling off. In addition, 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 is suppressed low, and the housing 40 is more compact. Can be configured.

[Rack assist type electric power steering system]
Next, as an example of a mechanical device provided with the rotary-to-linear motion converter 20, an automobile equipped with a rack-assisted electric power steering device will be described.
As shown in FIG. 3, the steering unit 1 of the vehicle includes a rack and pinion type electric power steering device 10 including a pinion mechanism 2 and a rack mechanism 3. The pinion mechanism 2 has a pinion shaft 5 rotatably supported by a pinion housing 4. The pinion shaft 5 is connected to a steering wheel via a steering shaft (not shown) or 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 serving 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 rotary / linear motion converter 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. 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-assisted 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 30 of FIG.

  As shown in FIG. 4, the EPS 10 has a cylindrical EPS housing 11. The EPS housing 11 includes a cylindrical main body 12 disposed substantially at the center in the axial direction, and a right end of the main body 12 in the figure. A plurality of connecting bolts 16 are connected to a cylindrical conversion device housing 13 coaxially connected to the main body 12 and annular lids 14 and 15 for closing left and right openings of the main body 12 and the conversion device housing 13 respectively. , 17 are fixed. Packings 18 are interposed between the left and right lids 14 and 15 and the outer peripheral surface of the shaft 30, respectively.

  Inside the main body 12, a tubular stator 8a is fixed, and a coil 8b composed of a plurality of segments that winds a part of the stator 8a 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 sleeve 9 is rotatably supported on the EPS housing 11 by a bearing 22 on the outer periphery of a middle portion on the right side. The bearing 22 is an angular contact type ball bearing. An 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. In the vicinity of the left end of the sleeve 9, a motor rotation angle detection unit 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 arranged concentrically with the stator 81 and supported so as to be relatively rotatable. The stator 81 has a plurality of pole pieces having a plurality of pole piece teeth at a tip end thereof, and is fixedly supported by a plurality of pole pieces at equal circumferential positions, and each 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 row of teeth formed in the circumferential direction to face the pole piece teeth of the stator 81 with a gap. The motor rotation angle detection unit 80 can A / D convert a plurality of resolver signals having different phases obtained according to a change in reluctance between the rotor 82 and the stator 81 to output a digital rotation angle signal. I have.

  The above-described rotary / linear motion converter 20 is housed in the cylindrical converter housing 13 at the right end of the sleeve 9. In the housing 40 of the rotary-to-linear motion converter 20, two rollers 50 satisfying the above-described conditions 1 to 3 (more preferably, the above-described conditions 1 to 5) are rotatable with respect to the shaft portion 30 of the rack shaft 7. 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 being fixed with the bolt 19 so that the housing 40 is integrated with the sleeve 9. Have been.

  Further, in the EPS housing 11, a guide roller device 90 for guiding the rack shaft 7 is provided inside the cylindrical flange portion 14a 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 portion 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 arranged in the same posture at intervals of 90 ° in the circumferential direction. The support shaft 92 of each guide roller 91 is arranged orthogonal to the axis of the shaft portion 30 of the rack shaft 7, and each guide roller 91 rotates along the direction of linear movement of the rack shaft 7, and The operation is smoothly guided.
Further, a linear encoder 100 is provided between the guide roller device 90 and the left end of the sleeve 9 so as to detect the amount of movement and the direction of movement of the rack shaft 7 in the linear motion direction. The linear encoder 100 includes a magnetic encoder unit 101 including a multi-pole magnet and a magnetic sensor unit 102. The magnetic encoder section 101 is provided on the outer peripheral surface of the shaft section 30 of the rack shaft 7 over a range in which the rack shaft 7 can be moved directly. And is alternately magnetized in the axial direction.

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

  Since the magnetic encoder unit 101 is formed directly on the outer peripheral surface of the shaft unit 30, the magnetic encoder unit 101 also moves directly with the linear movement of 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 changes periodically as the magnetic encoder unit 101 moves directly. A magnetic flux from the magnetic encoder unit 101 passes through the magnetic sensor unit 102. 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 change in the magnetic flux. Output a signal. The two-phase pulse signals are A-phase and B-phase. At the sampling timing, the linear motion information calculator of the magnetic sensor unit 102 simultaneously obtains the sampling values of the A-phase and B-phase magnetic detection signals, and based on the two-phase pulse signals having mutually shifted phases, 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 of the shaft 30, is calculated periodically.

  The driving of the electric motor 60 is 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 rotation sensor detected by the magnetic sensor unit 102 of the linear encoder 100. A steering assist torque command value is calculated from the obtained linear motion information, a motor drive current for generating a 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. It is configured to be.

  In particular, in the present embodiment, a traction drive mechanism that does not use a ball screw is employed in the rotary-to-linear motion conversion device 20. Therefore, when calculating the steering assist torque command value, the rotation angle information detected by the motor rotation angle detection unit 80 is used. The linear motion information detected by the magnetic sensor unit 102 is fed back to the motor control device 70 at any time, so that a 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. It has been calculated.

Next, the operation and effect of the EPS 10 will be described.
In this vehicle, the steering torque when the steering wheel is steered is transmitted to the pinion shaft 5 and converted into 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. The steering wheel is transmitted to the steered wheel via the tie rod 8 and the steered wheel is steered.

  When the steering torque is transmitted to the pinion shaft 5, the EPS 10 drives the electric motor 60, whereby the sleeve 9 is driven to rotate accordingly, and the rotation / linear motion converter 20 integrally connected to the sleeve 9. Is rotationally driven. Thereby, 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, and the steering force can be assisted.

  Here, in a rack assist type electric power steering device, a ball screw mechanism is often used as a rotary-to-linear motion conversion device, but the ball screw mechanism needs a circulation structure for circulating balls as rolling elements, so that vibration and A 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, and thus may cause discomfort to the driver.

On the other hand, according to the EPS 10 including the rotary-to-linear motion converting device 20 of the present embodiment, unlike the ball screw, the traction drive mechanism using only the two rollers 50 of the rotating system is employed. A relatively high quietness is obtained as compared with the mechanism, vibration and noise are reduced, and a small lead can be handled as compared with a ball screw.
Also, in a rack shaft employing a conventional ball screw mechanism, a thread groove is formed on one outer periphery and a rack portion is formed on the other side. With such a configuration, a large steering angle is secured. In order to prevent interference between the screw groove of the ball screw mechanism and the rack part, the length of the rack shaft may be increased to increase the size of the steering device or reduce the length of the rack shaft. In this case, there is a problem that the range of the effective thread groove is narrowed and the steering angle is reduced.

  On the other hand, the EPS 10 including the rotary-to-linear motion converter 20 according to the present embodiment employs a traction drive mechanism using only the rollers 50 of the rotation system, so that there is no need to form a thread groove on the rack shaft 7. In addition, the operation of the rotary / linear motion converter 20 can be performed 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 thread groove such as a ball screw on the rack shaft 7, the workability and the maintainability are relatively excellent.

In addition, since the tie rod 8 is generally attached at an angle to the rack shaft 7, 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, the aforementioned radial load and moment load are applied to the ball screw mechanism. In the case of the EPS 10 including the rotary-to-linear motion converter 20 according to the embodiment, it is not necessary to form a thread groove in the rack shaft 7, and a relatively high durability can be obtained by the traction drive mechanism using only the rotation system roller 50. Can be.

  Further, according to the EPS 10 of the present embodiment, 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 when calculating the steering assist torque command value. Since the steering assist torque command value is calculated by adding a correction based on the rotation angle information and the linear motion information, even if a radial load or a moment load is applied by the steering reaction force, the A final steering assist torque command value is obtained from the correction data, and the electric motor 60 can be controlled with high accuracy based on the command value.

  As described above, according to the above-described rotary-to-linear motion converting device 20, the electric power steering device 10 including the same, and the automobile, relatively high quietness is obtained as compared with the rotary-to-linear motion converting device using the ball screw. Obtainable. The rotary-to-linear motion converting device, the electric power steering device and the vehicle including the same are not limited to the above 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 device 10 and the automobile including the same are described as examples of the application of the rotary-to-linear motion converter according to the present invention. range is not limited to this, Ru applicable der to vehicles other than motor vehicles having a steering system.

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)
Reference Signs List 8 tie rod 10 electric power steering device 20 rotation / linear motion conversion device 30 (shaft) shaft portion 40 housing 50 roller 60 electric motor 70 motor control device 71 torque sensor 72 vehicle speed sensor 80 motor rotation angle detection portion 90 guide roller device 100 linear encoder

Claims (6)

A shaft having an outer peripheral surface having a cylindrical shaft portion,
A flat rectangular parallelepiped housing arranged to surround the shaft;

A drum-shaped roller rotatably supported by the housing via a support shaft and limited to only two,
The rotary roller / linear motion converter for an electric power steering device, wherein the two rollers satisfy the following conditions 1 to 4.
Condition 1: The two rollers are spaced apart from each other by 180 ° in the circumferential direction with respect to the shaft and are opposed to each other in a direction along a long side of a flat rectangular parallelepiped in the housing in a cross-sectional view of the shaft.
Condition 2: The two rollers are supported at 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 each other with a preload applied so that traction driving force can be transmitted to the shaft portion of the shaft.
Condition 4: the two rollers are such that the outer peripheral surface of the drum shape of each roller is centered on a center point of a line connecting two contact points with the shaft portion of the shaft in an axial cross section. is formed in an arc concave shall be the center of the constricted position perpendicular to the support shaft.   The rotary / linear motion converter for an electric power steering device according to claim 1, wherein traction grease or traction oil is applied to outer peripheral surfaces of the shaft portion and the roller of the shaft.   3. The rotary-to-linear motion converter for an electric power steering device according to claim 1, wherein the preload has a contact surface pressure in a range of 0.6 to 3 GPa.   The electric power steering device 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-finished surface has a surface roughness Ra of 0.2 or less. Rotary linear motion converter.   An electric power steering device comprising the rotary / linear motion converter for an electric power steering device according to claim 1.   A vehicle comprising the electric power steering device according to claim 5.

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