Planetary roller screws, linear actuators, and electromechanical brakes

Abstract

To suppress the decrease in transmission efficiency when converting rotational force into linear force. [Solution] The device comprises a nut 20 formed in a cylindrical shape and having a nut-side threaded portion 21 on its inner circumferential surface, a roller 30 positioned inside the nut 20 and having a roller-side threaded portion 31 formed in a round bar shape that engages with the nut-side threaded portion 21, and a roller-side engagement portion 32 positioned at a different location from the roller-side threaded portion 31 and having repeating axial irregularities that extend along the circumferential direction of the round bar, and a shaft 50 positioned inside the nut 20 and having a shaft-side engagement portion 51 on its outer circumferential surface that engages with the roller-side engagement portion 32, wherein multiple rollers 30 are arranged in a line along the inner circumferential surface of the nut 20 and along the circumferential direction of the nut 20, and the multiple rollers 30 are held together with the rollers 30 by a retainer 40 positioned inside the nut 20, and the retainer 40 rotatably supports multiple positions on the roller 30.

Description

Technical Field

[0001] The present disclosure relates to a planetary roller screw, a linear actuator, and an electromechanical brake.

Background Art

[0002] A planetary roller screw has been proposed that includes a rotating shaft, a plurality of rollers arranged around the shaft, and a nut that moves relative to the shaft in accordance with the axial relative movement of the rollers with respect to the shaft. In the planetary roller screw configured as described above, when the force in the rotational direction of the shaft is transmitted to the nut via the rollers, it is transmitted as a force that moves the nut in the axial direction of the shaft. Therefore, the planetary roller screw can convert the force in the rotational direction into the force in the linear motion direction.

[0003] For example, in the planetary roller screw described in Patent Document 1, a shaft having a spiral thread portion, a plurality of rollers arranged around the shaft and having a thread portion that meshes with the thread portion formed on the shaft, and having non-spiral groove portions on both sides of the thread portion, and a nut that covers the plurality of rollers and has a groove portion on the inner peripheral surface that meshes with the non-spiral groove portion of the roller. In the planetary roller screw described in Patent Document 1, when the shaft and the nut rotate relative to each other, the rollers move axially relative to the shaft while rotating, so that the nut also moves axially relative to the shaft together with the rollers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, the roller needs to be positioned so that it can rotate on its own axis while revolving around the shaft. However, as in Patent Document 1, if the roller is supported at both ends by different members so that it can rotate, when the roller revolves, the members supporting it at both ends may shift slightly in the circumferential direction of the revolution, potentially causing the roller to tilt with respect to the axial direction of the shaft. If the roller tilts with respect to the shaft, it will also tilt with respect to the axial movement of the nut relative to the shaft. When the roller tilts with respect to the shaft in this way, the transmission efficiency decreases when the rotation of the shaft is transmitted from the shaft to the nut via the rotation and axial movement of the roller. This reduces the transmission efficiency when converting the rotational force of the planetary roller screw into a linear force. For this reason, there was room for improvement in conventional planetary roller screws in terms of ensuring transmission efficiency.

[0006] This disclosure has been made in view of the above, and aims to provide a planetary roller screw, a linear actuator, and an electromechanical brake that can suppress a decrease in transmission efficiency when converting rotational force into linear force. [Means for solving the problem]

[0007] The planetary roller screw of this disclosure comprises a nut formed in a cylindrical shape and having a nut-side threaded portion formed helically on its inner circumferential surface; a roller positioned inside the nut and formed in a round bar shape extending along the axial direction of the nut, having a roller-side threaded portion that engages with the nut-side threaded portion; a roller positioned at a different location in the axial direction from the roller-side threaded portion and having a roller-side engagement portion with repeating irregularities in the axial direction extending along the circumferential direction of the round bar; and a shaft positioned inside the nut and having a shaft-side engagement portion with repeating irregularities in the axial direction on its outer circumferential surface that engages with the roller-side engagement portion. The rollers are arranged in a row along the inner circumferential surface of the nut and along the circumferential direction of the nut, and the plurality of rollers are held by a retainer positioned inside the nut together with the rollers, and the retainer rotatably supports the rollers while restricting their positional relationship with the rollers at multiple axial positions on the rollers.

[0008] In this configuration, the rotation of the nut is transmitted to the roller by the threaded portion on the roller side that meshes with the threaded portion on the nut side. As a result, the rotation of the nut can be transmitted from the nut to the roller with a large reduction ratio, and the force exerted when the roller moves axially can be increased. Furthermore, the axial force transmitted between the roller and the shaft can be transmitted by the meshing portion on the roller side and the meshing portion on the shaft side. Therefore, a large axial force from the roller to the shaft can be transmitted without hindering the roller's revolution around the central axis of the nut. As a result, the shaft moves axially relative to the nut with a large thrust, together with the roller. Thus, the planetary roller screw can convert the rotational force input to the nut from the power source into a large linear force through the axial movement of the shaft.

[0009] In this process, since the roller is supported at multiple positions by the retainer, the retainer prevents the roller from tilting toward the circumferential direction of the nut relative to its central axis as it rotates and revolves along the circumferential direction of the nut. This suppresses the increase in resistance between the nut / shaft and the roller caused by the roller's tilt during its rotation and revolving, and suppresses the decrease in transmission efficiency when the rotation of the nut is transmitted from the nut to the shaft via the roller. As a result, the decrease in transmission efficiency when converting rotational force into linear force can be suppressed.

[0010] In a preferred configuration, the retainer is formed in a cylindrical shape and supports the portion of the roller between the roller-side threaded portion and the roller-side meshing portion, and the portion of the roller opposite to the side on which the roller-side meshing portion is located relative to the roller-side threaded portion.

[0011] With this configuration, the retainer supports the roller on both sides of the threaded portion on the roller side. Therefore, even when a force acts on the threaded portion on the roller side that tilts the roller in the circumferential direction of the nut, the tilting of the threaded portion on the roller side can be suppressed. As a result, the retainer can support the roller while suppressing its tilt, and can suppress the increase in resistance between the nut or shaft and the roller when the roller rotates or revolves, which is caused by the roller's tilt. Consequently, the decrease in transmission efficiency when converting rotational force into linear force can be suppressed.

[0012] In a desirable configuration, the shaft has rolling portions that contact the outer circumferential surface of the end of the roller near the end on which the roller-side meshing portion is located, from the inside in the radial direction of the shaft.

[0013] In this configuration, the shaft has rolling parts that contact the outer circumferential surface near the end of the roller shaft, thus preventing the roller from tilting radially along the shaft. This suppresses the increase in resistance between the nut / shaft and the roller when the roller rotates or revolves, which is caused by the roller's tilt. As a result, it is possible to suppress the decrease in transmission efficiency when converting rotational force into linear force.

[0014] In a desirable configuration, the roller has an outer diameter smaller than the outer diameter of the threaded portion on the roller side.

[0015] In this configuration, since the outer diameter of the roller-side meshing portion is smaller than the outer diameter of the roller-side threaded portion, contact between the roller-side meshing portion and the nut can be suppressed. As a result, the roller-side meshing portion can be arranged coaxially with the roller-side threaded portion without requiring a separate component to transmit the force of the roller's axial movement to the shaft. Consequently, the increase in the number of parts of the planetary roller screw can be suppressed, and the planetary roller screw can be made smaller.

[0016] In a desirable configuration, the threaded portion on the nut side and the threaded portion on the roller side have spiral directions opposite to each other.

[0017] In this configuration, the threads on the nut side and the threads on the roller side have opposite helical directions. Therefore, the rotation of the nut is transmitted to the roller via the threads on the nut side and the roller side, allowing the roller to rotate in the same direction as the nut's rotation. This allows the roller to move axially while rotating in the same direction as the nut's rotation, enabling a simple structure to convert rotational force into linear force. As a result, the manufacturing cost of planetary roller screws that convert rotational force into linear force can be reduced.

[0018] The linear actuator of this disclosure comprises a planetary roller screw having a nut formed in a cylindrical shape and having a nut-side threaded portion formed helically on its inner circumferential surface, a roller positioned inside the nut and formed in a round bar shape extending along the axial direction of the nut and engaging with the nut-side threaded portion, a roller-side engaging portion positioned at a different location in the axial direction from the roller-side threaded portion and having repeating irregularities in the axial direction extending along the circumferential direction of the round bar, and a shaft positioned inside the nut and having a shaft-side engaging portion with repeating irregularities in the axial direction extending along the circumferential direction of the outer surface and engaging with the roller-side engaging portion, and a motor that applies driving force to the nut, the Multiple rollers are arranged in a line along the inner circumferential surface of the nut and along the circumferential direction of the nut, and the multiple rollers are held by a retainer positioned inside the nut together with the rollers, and the retainer supports the rollers so that they can rotate while restricting their positional relationship with the rollers at multiple axial positions on the rollers, and the rollers rotate and move relative to the nut in the axial direction as the rotation of the nut, which rotates due to the driving force from the motor, is transmitted from the nut-side threaded portion to the roller-side threaded portion, and the shaft moves relative to the nut in the axial direction together with the rollers as the axial movement of the rollers is transmitted from the roller-side meshing portion to the shaft-side meshing portion.

[0019] This configuration includes a planetary roller screw and a motor that applies driving force to the nut of the planetary roller screw. As a result, the rotation of the nut, which is rotated by the motor's driving force, can be transmitted from the nut to the roller with a large reduction ratio. This increases the force exerted when the roller moves axially, and also increases the axial thrust of the shaft, which moves axially with the roller. Therefore, the rotational force input from the motor to the nut can be converted into a large linear force by the axial movement of the shaft and output.

[0020] Furthermore, in the planetary roller screw of a linear actuator, multiple positions of the rollers are supported by a single retainer. This prevents the rollers from tilting toward the circumferential direction of the nut even when the rollers revolve. This suppresses the increase in resistance caused by the tilt of the rollers, and thus suppresses the decrease in transmission efficiency when the rotation of the nut, which rotates due to the motor's driving force, is transmitted to the shaft. As a result, it is possible to suppress the decrease in transmission efficiency when converting the rotational force output from the motor into linear force.

[0021] In a preferred configuration, a nut adapter having a fitting hole is attached to the nut at the axial end of the nut, and the motor is connected to the nut via the nut adapter by fitting the drive shaft of the motor into the fitting hole of the nut adapter.

[0022] In this configuration, the motor is connected to the nut via a nut adapter, allowing for easy connection of the motor's drive shaft to the nut. By connecting the motor's drive shaft to the nut via the nut adapter, the driving force from the motor's drive shaft, which is formed in a round bar shape, can be easily transmitted to the cylindrical nut. As a result, the ease of assembly of the linear actuator can be improved.

[0023] The electromechanical brake of this disclosure comprises a planetary roller screw having a nut formed in a cylindrical shape and having a nut-side threaded portion formed helically on its inner circumferential surface; a roller positioned inside the nut and formed in a round bar shape extending along the axial direction of the nut and engaging with the nut-side threaded portion; a roller positioned at a different location in the axial direction from the roller-side threaded portion and having a roller-side engaging portion with repeating irregularities in the axial direction extending along the circumferential direction of the round bar; a shaft positioned inside the nut and having a shaft-side engaging portion with repeating irregularities in the axial direction extending along the circumferential direction of the outer circumferential surface and engaging with the roller-side engaging portion; a motor that applies driving force to the nut; a disc-shaped brake rotor; a brake pad that contacts the brake rotor; and a brake caliper that holds the brake pad, wherein the roller is the nut Multiple rollers are arranged in a line along the inner circumferential surface of the nut and along the circumferential direction of the nut, and the multiple rollers are held together with the rollers by a retainer positioned inside the nut, the retainer supports the rollers so that they can rotate while restricting their positional relationship with the rollers at multiple axial positions on the rollers, the rollers rotate as the rotation of the nut, which rotates due to the driving force from the motor, is transmitted from the nut-side threaded portion to the roller-side threaded portion and moves relative to the nut in the axial direction, the shaft moves relative to the nut together with the rollers as the axial movement of the rollers is transmitted from the roller-side meshing portion to the shaft-side meshing portion, and the shaft, by moving relative to the nut in the axial direction, applies a pressing force to the brake pads in a direction that presses them against the brake rotor.

[0024] According to this configuration, since the rotation of the nut that is rotated by the driving force of the motor can be transmitted from the nut to the roller at a large reduction ratio, the force when the roller moves in the axial direction can be increased, and the axial thrust of the shaft that moves axially together with the roller can also be increased. As a result, the force in the rotational direction input from the motor to the nut can be converted into a large force in the linear motion direction by the axial movement of the shaft and output, and the pressing force applied to the brake pad from the shaft via the nut cover can be ensured.

[0025] In addition, since the rollers of the planetary roller screw of the electromechanical brake are supported at a plurality of positions of the rollers by one cage, even when the rollers revolve, the rollers are suppressed from tilting in the circumferential direction of the nut. As a result, an increase in resistance due to the tilt of the rollers can be suppressed, and a decrease in transmission efficiency when the rotation of the nut that rotates by the driving force of the motor is transmitted to the shaft can be suppressed. As a result, a decrease in transmission efficiency when converting the force in the rotational direction output from the motor into a force in the linear motion direction can be suppressed.

[0026] In a desirable form, a nut cover is attached to an end portion of the shaft on the opposite side of the side where the roller-side screw portion of the roller in the axial direction is disposed. The nut cover has an outer peripheral portion that covers the nut from the outside in the radial direction of the nut, and a bottom surface portion that closes a portion of the nut on the side where the nut cover is disposed in the axial direction. The bottom surface portion of the nut cover abuts on the brake pad.

[0027] According to this configuration, a nut cover can be attached to the end of the shaft. The nut cover has a bottom surface portion that closes the portion of the nut on the side where the nut cover is disposed. The brake pad has the bottom surface portion of the nut cover abutting thereon. Thereby, since the pressing force applied from the shaft to the brake pad can be applied from the bottom surface portion of the nut cover formed in a planar shape, a pressing force can be stably applied to the brake pad. As a result, a braking force can be stably generated.

Advantages of the Invention

[0028] The planetary roller screw, linear actuator, and electromechanical brake according to the present disclosure have an effect of suppressing a decrease in transmission efficiency when converting a force in the rotational direction into a force in the linear direction.

Brief Description of the Drawings

[0029] [Figure 1] FIG. 1 is a cross-sectional view of a planetary roller screw according to an embodiment. [Figure 2] FIG. 2 is a view showing the outer shapes of the shaft and roller shown in FIG. 1 and a cross-section of the nut. [Figure 3] FIG. 3 is an exploded perspective view of the planetary roller screw. [Figure 4] FIG. 4 is an exploded perspective view of the planetary roller screw viewed from a direction different from that of FIG. 3. [Figure 5] FIG. 5 is an explanatory view showing a state in which the shaft shown in FIG. 1 relatively moves axially with respect to the nut. [Figure 6] FIG. 6 is a cross-sectional view of a main part of an electromechanical brake according to an embodiment.

Modes for Carrying Out the Invention

[0030] The present disclosure will be described in detail below with reference to the drawings. However, the present disclosure is not limited to the embodiments described below. Furthermore, the components in the embodiments below include those easily conceivable by those skilled in the art, those substantially identical, and those within the scope of equivalents. Moreover, the components disclosed in the embodiments below can be combined as appropriate.

[0031] [Embodiment] Figure 1 is a cross-sectional view of a planetary roller screw 10 according to an embodiment. Figure 2 is a diagram showing the outer shapes of the shaft 50 and roller 30 and the cross-section of the nut 20 shown in Figure 1. Figure 3 is an exploded perspective view of the planetary roller screw 10. Figure 4 is an exploded perspective view of the planetary roller screw 10 viewed from a different direction than Figure 3. The planetary roller screw 10 includes a nut 20, a nut adapter 24, a roller 30, a shaft 50, and a retainer 40. Of these, the nut 20, roller 30, and shaft 50 are made of heat-treated iron. The retainer 40 is made of a self-lubricating metal, such as brass.

[0032] The nut 20 is formed in a substantially cylindrical shape and has a spirally formed nut-side threaded portion 21 on its inner circumferential surface. The nut-side threaded portion 21 is a threaded portion formed spirally on the inner circumferential surface of the nut 20 with respect to the central axis AX of the nut 20. In other words, the crests and valleys of the threads of the nut-side threaded portion 21 extend in the circumferential direction with respect to the central axis AX of the nut 20, and are formed inclined toward the direction in which the central axis AX of the nut 20 extends. The nut-side threaded portion 21 is formed across both ends in the axial direction on the inner circumferential surface of the nut 20.

[0033] The nut 20 has an adapter connecting portion 22 at one end in the axial direction for attaching a nut adapter 24. The adapter connecting portion 22 has a larger outer diameter than the rest of the nut 20. Therefore, the adapter connecting portion 22 is thicker in the radial direction than the rest of the nut 20.

[0034] The adapter connecting portion 22 has a pin hole 22a into which a pin 28 for attaching the nut adapter 24 to the nut 20 is inserted. The pin hole 22a is formed on the axial end face of the nut 20, that is, on the end face of the adapter connecting portion 22, with its depth direction aligned with the axial direction of the nut 20.

[0035] The nut adapter 24 has a flange portion 25 formed in a substantially disc shape and an insertion portion 26 formed in a substantially cylindrical shape. The outer diameter of the flange portion 25 is formed to be substantially the same as the outer diameter of the adapter connecting portion 22 of the nut 20.

[0036] The flange portion 25 has a pin hole 25a into which a pin 28 for attaching the nut adapter 24 to the nut 20 is inserted. The pin hole 25a formed in the flange portion 25 is a hole that penetrates the flange portion 25 in the thickness direction of the flange portion 25, and is positioned so that the distance from the central axis of the flange portion 25 is the same as the distance from the central axis AX of the pin hole 22a formed in the adapter connecting portion 22 of the nut 20 to the central axis AX of the nut 20.

[0037] In this embodiment, the nut adapter 24 is attached to the nut 20 by two pins 28. For this reason, there are two pin holes 22a formed in the adapter connecting portion 22 of the nut 20 and two pin holes 25a formed in the flange portion 25 of the nut adapter 24.

[0038] The insertion portion 26 of the nut adapter 24 is positioned on one side of the flange portion 25 in the thickness direction, and the central axis of the cylindrical shape of the insertion portion 26 is positioned to coincide with the central axis of the flange portion 25. The outer diameter of the insertion portion 26 is formed with a radius smaller than the distance from the central axis AX of the nut 20 to the position of the roller 30 in the radial direction of the nut 20, as described later, when the roller 30 is positioned inside the nut 20. For this reason, the insertion portion 26 of the nut adapter 24 is positioned inside the nut 20 in the radial direction with respect to the roller 30 which is positioned inside the nut 20.

[0039] Furthermore, a through hole 27 is formed on the inside of the insertion portion 26, along the central axis of the insertion portion 26 and in the longitudinal direction of the insertion portion 26. The through hole 27 has multiple sections with different diameters, and a portion of the through hole 27 is formed as a fitting hole 27a into which the drive shaft of a power source connected to the nut adapter 24 and used to rotate the nut adapter 24 can be fitted. The fitting hole 27a is designed so that relative rotation with respect to the drive shaft of the power source is impossible, allowing the drive shaft to be fitted, and in this embodiment, a spline is formed in the fitting hole 27a.

[0040] The nut adapter 24 is attached to the nut 20 with its insertion portion 26 facing inward, and its flange portion 25 in contact with the end of the nut 20 on the side where the adapter connecting portion 22 is located in the axial direction. The nut adapter 24 is attached to the nut 20 by a short, round pin 28. The pin 28 for attaching the nut adapter 24 to the nut 20 is press-fitted into both a pin hole 25a formed in the nut adapter 24 and a pin hole 22a formed in the adapter connecting portion 22 of the nut 20. In this way, the nut adapter 24 is attached to the nut 20 by the pin 28.

[0041] The roller 30 is formed in the shape of a round bar. The roller 30 is positioned inside the nut 20, extending in the axial direction of the nut 20. In this embodiment, the length of the roller 30 is slightly longer than the length of the nut 20.

[0042] The roller 30 has a roller-side threaded portion 31 on its outer circumferential surface, which is a threaded portion that can engage with the nut-side threaded portion 21 formed on the nut 20. That is, the roller-side threaded portion 31 formed on the outer circumferential surface of the roller 30 is a threaded portion formed in a spiral shape centered on the axis of the round bar-shaped roller 30, and engages with the nut-side threaded portion 21 formed on the inner circumferential surface of the nut 20 from the inside in the radial direction of the nut 20. The spiral direction of the roller-side threaded portion 31 formed in this way is opposite to that of the nut-side threaded portion 21.

[0043] Furthermore, the threaded portion 21 on the nut side and the threaded portion 31 on the roller side have different lead angles, with the lead angle of the threaded portion 21 on the nut side being larger than the lead angle of the threaded portion 31 on the roller side. In other words, the angle of inclination of the spiral of the threaded portion 21 on the nut side with respect to the circumferential direction of the nut 20 in the longitudinal direction is larger than the angle of inclination of the spiral of the threaded portion 31 on the roller side with respect to the circumferential direction of the roller 30 in the longitudinal direction of the roller 30.

[0044] The insertion portion 26 of the nut adapter 24, which is attached to the nut 20, has an end opposite to the side where the flange portion 25 is located in the axial direction of the nut 20, and this end is located within the range where the roller-side threaded portion 31 is positioned in the axial direction.

[0045] Furthermore, the roller-side meshing portion 32 of the roller 30 is positioned at a different location in the axial direction from the position where the roller-side threaded portion 31 is located. The roller-side meshing portion 32 is formed by repeating axial irregularities that extend along the circumferential direction of the round bar. In other words, while the threads and grooves of the roller-side threaded portion 31 extend in the circumferential direction of the roller 30 and are inclined toward the longitudinal direction of the roller 30, the repeating irregularities of the roller 30 in the longitudinal direction of the roller 30 are formed extending toward the circumferential direction of the roller 30 and are not inclined toward the longitudinal direction of the roller 30 with respect to the circumferential direction of the roller 30. To put it another way, the roller-side meshing portion 32 has convex portions that extend radially outward from the outer circumferential surface of the roller 30 and are formed around the entire circumference of the roller 30, and multiple such convex portions are arranged in the longitudinal direction of the roller 30, spaced apart from each other.

[0046] The outer diameter of the roller-side meshing portion 32 is smaller than the outer diameter of the roller-side threaded portion 31. In other words, the outer diameter of the roller-side meshing portion 32 at the position where it protrudes outward in the radial direction of the roller 30 is smaller than the outer diameter of the roller-side threaded portion 31. Furthermore, the outer diameter of the roller-side meshing portion 32 is smaller than the diameter of the threaded portion 31 at the position of the thread groove, that is, the diameter of the valley of the threaded portion 31.

[0047] The roller-side threaded portion 31 and the roller-side meshing portion 32 of the roller 30 are positioned at different locations in the axial direction of the nut 20 or in the longitudinal direction of the roller 30. In this embodiment, the length of the roller-side threaded portion 31 and the length of the roller-side meshing portion 32 in the longitudinal direction of the roller 30 are approximately the same, and the roller-side threaded portion 31 and the roller-side meshing portion 32, which are formed to be of similar length, are positioned at different locations in the longitudinal direction of the roller 30.

[0048] The roller 30, positioned inside the nut 20, is oriented such that the side with the roller-side threaded portion 31 is located on the side where the adapter connecting portion 22 and nut adapter 24 of the nut 20 are located, and the side with the roller-side meshing portion 32 is located on the opposite end of the nut 20 from the side where the adapter connecting portion 22 is located.

[0049] The roller-side threaded portion 31 and the roller-side meshing portion 32 are spaced apart from each other in the longitudinal direction of the roller 30, and the portion of the roller 30 between the roller-side threaded portion 31 and the roller-side meshing portion 32 is an intermediate support portion 35 which is supported by the retainer 40. The intermediate support portion 35 is formed in the shape of a cylinder whose diameter is smaller than the outer diameter of the roller-side threaded portion 31 and the outer diameter of the roller-side meshing portion 32.

[0050] Furthermore, of the ends on both sides in the longitudinal direction of the roller 30, the end on the side where the roller-side threaded portion 31 is located is formed as a shaft end support portion 36, which is supported by the retainer 40. The shaft end support portion 36 is formed in the shape of a cylinder with a diameter smaller than the outer diameter of the roller-side threaded portion 31, and the diameter of the shaft end support portion 36 is about the same as the diameter of the intermediate support portion 35.

[0051] The planetary roller screw 10 has multiple rollers 30 formed in this manner. The multiple rollers 30 are all substantially the same shape and are arranged circumferentially along the inner surface of the nut 20, with the axial direction of the rollers 30 aligned with the central axis AX of the nut 20. Furthermore, the multiple rollers 30 are positioned so that the roller-side threaded portion 31 of each roller 30 engages with the nut-side threaded portion 21, and the multiple rollers 30 are arranged at equal intervals in the circumferential direction of the nut 20.

[0052] In this embodiment, the rollers 30 consist of 12 rollers 30, each with a threaded portion 31 on the roller side that engages with a threaded portion 21 on the nut side, arranged circumferentially along the inner surface of the nut 20 at equal intervals in the circumferential direction of the nut 20.

[0053] The shaft 50 is formed in a substantially cylindrical shape, and a through hole 53 is formed on its inside, penetrating in the axial direction of the shaft 50. The shaft 50 is positioned inside the nut 20 in a direction extending in the axial direction of the nut 20, and the central axis of the shaft 50 is positioned to coincide with the central axis AX of the nut 20. Therefore, the shaft 50 is positioned inward relative to the roller 30 which is positioned on the inner circumferential surface of the nut 20, with the radial position of the nut 20 being inward of the roller 30.

[0054] The length of the shaft 50 is shorter than the length of the nut 20 and the roller 30. In this embodiment, the length of the shaft 50 is approximately the same as the axial distance from the end of the roller-side meshing portion 32 of the roller 30 on the roller-side threaded portion 31 side to the end of the roller 30 on the side where the roller-side meshing portion 32 is located.

[0055] The shaft 50 has a shaft-side meshing portion 51 on its outer circumferential surface. The shaft-side meshing portion 51 is formed by repeating irregularities along the axial direction of the cylindrical shaft 50 or the axial direction of the nut 20, extending along the circumferential direction of the inner circumferential surface, and is capable of meshing with the roller-side meshing portion 32 of the roller 30. In other words, the shaft-side meshing portion 51 is formed by repeating irregularities in the axial direction that extend along the circumferential direction of the cylindrical shape of the shaft 50. Specifically, the shaft-side meshing portion 51 is formed by convex portions that protrude radially outward from the outer circumferential surface of the shaft 50, extending around the circumference of the shaft 50, and multiple such convex portions are arranged in a line along the longitudinal direction of the shaft 50, spaced apart from each other in the longitudinal direction of the shaft 50.

[0056] Furthermore, the axial pitch of the repeating grooves and protrusions on the shaft-side meshing portion 51 is the same as the axial pitch of the grooves and protrusions on the roller-side meshing portion 32. This allows the shaft-side meshing portion 51 to mesh with the roller-side meshing portion 32 of the roller 30. In other words, the radially outward protruding portion of the shaft-side meshing portion 51 fits into the space between the protrusions on the roller-side meshing portion 32, and the radially outward protruding portion of the roller-side meshing portion 32 fits into the space between the protrusions on the shaft-side meshing portion 51, thereby enabling the shaft-side meshing portion 51 to mesh with the roller-side meshing portion 32.

[0057] In this way, the shaft-side meshing portion 51, which can mesh with the roller-side meshing portion 32, has an axial length of the shaft 50 that is approximately the same as the length of the roller-side meshing portion 32 of the roller 30 in the axial direction. Furthermore, the shaft 50 is positioned such that the position of the shaft-side meshing portion 51 in the axial direction is the same as the position of the roller-side meshing portion 32 of the roller 30 in the axial direction. As a result, the roller-side meshing portion 32 and the shaft-side meshing portion 51 are meshed with each other over the entire range of the roller-side meshing portion 32 and the shaft-side meshing portion 51 in the axial direction.

[0058] The roller-side meshing portion 32 and the shaft-side meshing portion 51 each have repeating axial irregularities formed along the circumferential direction of the roller 30 and shaft 50, respectively. Therefore, when they are meshed together, axial force can be transmitted between the roller-side meshing portion 32 and the shaft-side meshing portion 51. In other words, the meshing of the roller-side meshing portion 32 and the shaft-side meshing portion 51 enables the transmission of axial force between the roller 30 and the shaft 50.

[0059] In this configuration, both the roller-side meshing portion 32 and the shaft-side meshing portion 51 have repeating axial irregularities formed along the circumferential direction of the roller 30 and shaft 50. Therefore, when axial force is transmitted between the roller 30 and the shaft 50 via the meshing roller-side meshing portion 32 and the shaft-side meshing portion 51, even when the roller 30 and the shaft 50 rotate relative to each other around their respective central axes, the relative positional relationship in the axial direction remains unchanged, allowing for the transmission of axial force between the roller 30 and the shaft 50.

[0060] Furthermore, the shaft 50 is positioned such that the entire length of the shaft-side meshing portion 51 in the axial direction meshes with the roller-side meshing portion 32 of the roller 30. Therefore, it is positioned at a different location from the position where the roller-side threaded portion 31 of the roller 30 is located in the axial direction. Consequently, the shaft 50 and the insertion portion 26 of the nut adapter 24, which are positioned inside the nut 20 in the radial direction, are at different positions in the axial direction of the nut 20, and are positioned axially separated from each other on the inside of the nut 20 in the radial direction.

[0061] When the multiple rollers 30 are arranged circumferentially along the inner surface of the nut 20, these multiple rollers 30 are also arranged circumferentially along the outer surface of the shaft 50. As a result, the multiple rollers 30 are arranged circumferentially around the shaft 50 along the outer surface of the shaft 50, and the roller-side meshing portion 32 of each roller 30 meshes with the shaft-side meshing portion 51 of the shaft 50.

[0062] In this configuration, the roller-side meshing portion 32 of each roller 30 is spaced radially inward from the nut 20. That is, the rollers 30 are arranged around the shaft 50 with a gap between the roller-side meshing portion 32 and the nut-side threaded portion 21.

[0063] Multiple rollers 30 positioned inside the nut 20 are held by a retainer 40 positioned inside the nut 20 together with the rollers 30. The retainer 40 is capable of supporting the rollers 30 rotatably while regulating their positional relationship with the rollers 30 at multiple axial positions on the rollers 30.

[0064] The retainer 40 is formed in a substantially cylindrical shape, and its length is approximately the same as the distance between the intermediate support portion 35 and the shaft end support portion 36 of the roller 30. More specifically, the retainer 40 is formed in a substantially cylindrical shape, with an outer diameter approximately the same as the inner diameter of the nut 20 and slightly smaller than the inner diameter of the nut 20, and an inner diameter approximately the same as the outer diameter of the insertion portion 26 of the nut adapter 24 and slightly larger than the outer diameter of the insertion portion 26. The retainer 40 has annular side wall portions 41 formed in a plate-like shape with the thickness direction being the longitudinal direction of the cylinder at both ends in the longitudinal direction of the cylinder. The side wall portions 41 are formed at both ends in the longitudinal direction of the retainer 40, from the position of the inner circumferential surface toward the outside in the radial direction of the cylinder, and are formed over the circumference of the cylinder with a predetermined width in the radial direction of the cylinder.

[0065] A support portion 42 for supporting the roller 30 is formed on the side wall portion 41 of the retainer 40. The support portion 42 is formed in a shape that is cut out from the outer circumference of the annularly formed side wall portion 41 toward the inside in the radial direction of the side wall portion 41. The width of the notch of the support portion 42 is about the same as the diameter of the intermediate support portion 35 and shaft end support portion 36 formed on the roller 30, and is slightly larger than the diameter of the intermediate support portion 35 and shaft end support portion 36 of the roller 30.

[0066] The support portions 42 formed on the side walls 41 of the retainer 40 are formed in the same number as the number of rollers 30 on each side wall 41, and the multiple support portions 42 are arranged at equal intervals in the circumferential direction of the retainer 40. In addition, the support portions 42 formed on both sides of the side walls 41 in the longitudinal direction of the retainer 40 are at the same position relative to each other in the circumferential direction of the retainer 40. The retainer 40 supports the multiple rollers 30 so that they can rotate freely by inserting the intermediate support portions 35 and shaft end support portions 36 of the rollers 30 into the support portions 42 formed on both sides of the side walls 41 in the longitudinal direction of the retainer 40 in this manner.

[0067] In other words, the retainer 40 supports an intermediate support portion 35 located between the roller-side threaded portion 31 and the roller-side meshing portion 32 of the roller 30, and an axial end support portion 36 located on the opposite side of the roller-side meshing portion 32 relative to the roller-side threaded portion 31. As a result, the retainer 40 rotatably supports the roller 30 on both sides in the axial direction of the roller-side threaded portion 31, and supports the multiple rollers 30 arranged inside the nut 20 at multiple positions.

[0068] Furthermore, the retainer 40 has side walls 41 positioned on both sides of the roller-side threaded portion 31 in the axial direction of the roller 30, allowing the portion where the roller-side threaded portion 31 is located to be sandwiched from both sides in the axial direction by the two side walls 41. As a result, the retainer 40 can hold the roller 30 while regulating its positional relationship with the roller 30 at multiple positions in the axial direction of the roller 30.

[0069] The retainer 40 has a diameter at its largest radial point, i.e., the outer diameter of the retainer 40 is slightly smaller than the inner diameter of the nut-side threaded portion 21 of the nut 20. The retainer 40 is positioned inside the nut 20 while holding multiple rollers 30.

[0070] The retainer 40, which holds the multiple rollers 30, has an outer diameter smaller than the inner diameter of the nut-side threaded portion 21 formed on the inner circumferential surface of the nut 20. Therefore, while positioned inside the nut 20, it can rotate in the circumferential direction of the nut 20 and the shaft 50. As a result, by positioning the retainer 40 inside the nut 20 while supporting the multiple rollers 30, the multiple rollers 30 can be supported as a single unit, allowing them to move freely in the circumferential direction of the nut 20 and the shaft 50.

[0071] Furthermore, the retainer 40 has multiple opening holes 43 formed on its inner circumferential surface at positions corresponding to the areas where the rollers 30 are positioned in the circumferential direction, and these opening holes 43 open in the radial direction of the retainer 40. Since the opening holes 43 open at positions corresponding to the areas where the rollers 30 are positioned in the circumferential direction, their circumferential positions are the same as those of the support portions 42 formed on the side wall portion 41. The rollers 30 supported by the retainer 40 are supported in such a way that a portion of the roller-side threaded portion 31 faces the inside of the retainer 40 through the opening holes 43.

[0072] The insertion portion 26 of the nut adapter 24 and the shaft 50 are positioned radially inward of the nut 20 relative to the roller 30 held by the retainer 40. Furthermore, the insertion portion 26 of the nut adapter 24 is also positioned radially inward of the nut 20 relative to the retainer 40. For this reason, the outer diameter of the insertion portion 26 of the nut adapter 24 is smaller than the inner diameter of the retainer 40, and the insertion portion 26 is spaced radially inward of the nut 20 relative to the roller-side threaded portion 31 of the roller 30 and the retainer 40.

[0073] Furthermore, the shaft 50, positioned inside the roller 30 in the radial direction of the nut 20, has a rolling portion 55 that contacts the outer circumferential surface near the end of the roller 30 on the side where the roller-side meshing portion 32 is located. In other words, the roller 30 has a shaft end 37 at the end on the roller-side meshing portion 32 side, which is formed in a similar shape to the shaft end support portion 36 positioned at the end on the roller-side threaded portion 31 side in the axial direction, and the rolling portion 55 of the shaft 50 contacts the outer circumferential surface of the shaft end 37 on the roller-side meshing portion 32 side of the roller 30.

[0074] In the roller 30, the shaft end portion 37 that contacts the rolling portion 55 of the shaft 50 has an outer diameter smaller than the outer diameter of the roller-side meshing portion 32. More specifically, the outer diameter of the shaft end portion 37 is smaller than the diameter of the groove of the roller-side meshing portion 32.

[0075] The rolling portion 55 is formed on the shaft 50 at the end opposite to the side where the nut adapter 24 is located in the axial direction, and is formed in a cylindrical shape with an outer diameter larger than the outer diameter of the shaft-side meshing portion 51. Specifically, the outer diameter of the rolling portion 55 is formed such that the radius of the rolling portion 55 is the distance of the smallest radial distance from the central axis AX of the nut 20 or the central axis of the shaft 50 to the shaft end 37 of the roller 30, which is positioned inside the nut 20 while being supported by the retainer 40. As a result, the outer surface of the rolling portion 55 contacts the outer surface of the shaft end 37 of the roller 30 from the inside of the shaft 50 in the radial direction.

[0076] Thus, a nut cover 60 is attached to the shaft 50, which is positioned inside the nut 20 and roller 30 in the radial direction of the nut 20. The nut cover 60 is positioned on the end of the shaft 50 on the side where the rolling portion 55 is located. In other words, the nut cover 60 is attached to the end of the shaft 50 on the opposite side of the axial direction of the nut 20 from the side where the roller-side threaded portion 31 of the roller 30 is located.

[0077] The nut cover 60 has a bottom portion 61, an insertion portion 62, and an outer circumference portion 63. The bottom portion 61 is formed in the shape of a roughly circular plate, i.e., a roughly circular disc, and its outer diameter is larger than the outer diameter of the nut 20. The insertion portion 62 is formed in the shape of a roughly cylindrical shape, with an outer diameter approximately the same as the inner diameter of the through hole 53 formed in the shaft 50, and is positioned on one side of the circular bottom portion 61. The insertion portion 62 is positioned such that the central axis of the cylinder, which is the shape of the insertion portion 62, coincides with the central axis of the circle of the bottom portion 61.

[0078] The outer circumference 63 is formed in a roughly cylindrical shape with an inner diameter larger than the outer diameter of the nut 20, and the outer diameter of the outer circumference 63 is the same as the outer diameter of the bottom surface 61. The outer diameter of the outer circumference 63 is larger than the outer diameter of the adapter connecting portion 22 of the nut 20. In addition, the inner diameter of the outer circumference 63 is formed to be slightly larger than the outer diameter of the part of the nut 20 other than the adapter connecting portion 22.

[0079] The outer periphery 63 is positioned on the side of the bottom surface 61 where the insertion portion 62 is located, with the central axis of the cylindrical shape of the outer periphery 63 coinciding with the central axis of the circular bottom surface 61. Therefore, the insertion portion 62 and the outer periphery 63 are positioned on the same surface in the thickness direction of the bottom surface 61 and are formed to protrude from the bottom surface 61 in the same direction in the thickness direction of the bottom surface 61.

[0080] The nut cover 60 formed in this manner is attached to the shaft 50 from the end side where the rolling portion 55 is located. The nut cover 60 is attached to the shaft 50 with the side of the bottom portion 61 where the insertion portion 62 and the outer circumference 63 are located facing the side where the shaft 50, roller 30, and nut 20 are located.

[0081] The nut cover 60 is press-fitted into the through hole 53 of the shaft 50 from the end side of the shaft 50 where the rolling portion 55 is located, with the insertion portion 62 of the nut cover 60 being press-fitted into the through hole 53 of the shaft 50. When the insertion portion 62 of the nut cover 60 is press-fitted into the through hole 53 of the shaft 50, the bottom surface portion 61 of the nut cover 60, which is formed in a disc shape, is positioned such that the direction in which the central axis of the shaft 50 extends is the direction of the normal to the disc.

[0082] The outer circumference 63 of the nut cover 60 is formed on the same surface as the surface on which the insertion portion 62 is positioned relative to the bottom surface 61. Therefore, when the nut cover 60 is attached to the shaft 50 by press-fitting the insertion portion 62 of the nut cover 60 into the through hole 53 of the shaft 50, the outer circumference 63 covers the nut 20 from the outside in the radial direction. The outer circumference 63 of the nut cover 60 is not positioned over the adapter connecting portion 22 of the nut 20, but rather covers the portion of the nut 20 other than the adapter connecting portion 22 from the outside in the radial direction.

[0083] As a result, the nut cover 60 covers the portion of the nut 20 closest to where the nut cover 60 is positioned in the axial direction, from the radially outside with its outer circumference 63. In addition, the nut cover 60 closes the portion of the nut 20 opposite to where the nut adapter 24 is positioned in the axial direction, i.e., the portion of the nut 20 where the nut cover 60 is positioned in the axial direction, with its bottom surface 61.

[0084] Next, the operation of the planetary roller screw 10 will be explained. The planetary roller screw 10 is used to obtain a large linear force by converting rotational force into linear force. In the planetary roller screw 10, the rotational force is input to the nut 20, and based on the rotational force input to the nut 20, a linear force is output from the shaft 50. For this reason, when obtaining a linear force with the planetary roller screw 10, the power source for the rotational force is connected to the nut 20.

[0085] When connecting the power source to the nut 20 of the planetary roller screw 10, the drive shaft of the power source is fitted into the fitting hole 27a formed in the nut adapter 24, which is connected to the adapter connecting portion 22 of the nut 20. As a result, power from the power source is transmitted to the nut 20 via the nut adapter 24, and the planetary roller screw 10 operates as the nut 20 rotates due to the power from the power source.

[0086] The nut 20 has a nut-side threaded portion 21 formed on its inner circumferential surface, and the roller-side threaded portion 31 formed on the roller 30, which is positioned inside the nut 20, engages with the nut-side threaded portion 21. Therefore, when the nut 20 rotates, the rotational force of the nut 20 is transmitted from the nut-side threaded portion 21 to the roller-side threaded portion 31, and the roller 30 rotates due to the rotational force of the nut 20 transmitted to the roller 30 via the nut-side threaded portion 21 and the roller-side threaded portion 31.

[0087] The roller 30 receives rotation from the nut 20 through the meshing of the nut-side threaded portion 21 and the roller-side threaded portion 31, which mesh with the roller-side threaded portion 31 from the radially outer side of the nut 20. Therefore, when the roller 30 rotates due to the rotational force transmitted from the nut 20, the roller 30 rotates in the same direction as the rotation of the nut 20. Multiple rollers 30 arranged in a circumferential direction along the inner surface of the nut 20 each receive rotational force from the nut 20 through the meshing of the roller-side threaded portion 31 and the nut-side threaded portion 21 of each roller 30, and each rotates in the same direction as the rotation of the nut 20.

[0088] Furthermore, the multiple rollers 30 are arranged along the inner surface of the nut 20 at equal intervals in the circumferential direction by the retainer 40, and the multiple rollers 30 can rotate together with the retainer 40 in the circumferential direction of the nut 20 and shaft 50. In other words, the multiple rollers 30, which are held by the retainer 40 and arranged in a line along the inner surface of the nut 20 in the circumferential direction, can revolve along the inner surface of the nut 20 in the circumferential direction around the central axis AX of the nut 20.

[0089] Therefore, when the rotation of the nut 20 is transmitted to the multiple rollers 30 and each roller 30 rotates in the same direction as the rotation of the nut 20, the multiple rollers 30 rotate on their own axes while revolving together with the retainer 40 along the inner surface of the nut 20, in the circumferential direction of the nut 20, with the central axis AX of the nut 20 as the center axis AX. In other words, the multiple rollers 30 revolve together with the retainer 40 around the shaft 50 in the circumferential direction with the central axis AX of the nut 20. The revolving of the multiple rollers 30 is also caused by the transmission of the rotational force of the nut 20, so the revolving of the multiple rollers 30 rotates in the same direction as the rotation of the nut 20.

[0090] In this process, each roller 30 is supported at two points by a single retainer 40, namely the intermediate support portion 35 and the shaft end support portion 36. Therefore, each roller 30 rotates while its tilt toward the circumferential direction of the nut 20 relative to the axial direction of the roller 30 is suppressed. Furthermore, each roller 30 rotates while its tilt toward the radial direction of the nut 20 is suppressed, because the rolling portion 55 of the shaft 50 abuts against the shaft end portion 37 on the side where the roller-side meshing portion 32 is located, from the inside in the radial direction of the nut 20.

[0091] Here, both the nut-side threaded portion 21 and the roller-side threaded portion 31, which transmit the rotational force of the nut 20 to the multiple rollers 30, are formed in a helical shape. Furthermore, the lead angle of the nut-side threaded portion 21 is larger than the lead angle of the roller-side threaded portion 31. Therefore, when the rotational force of the nut 20 is transmitted to the rollers 30 while the rollers rotate via the nut-side threaded portion 21 and the roller-side threaded portion 31, the rollers 30 also move in the axial direction according to the difference between the lead angle of the nut-side threaded portion 21 and the lead angle of the roller-side threaded portion 31.

[0092] In this case, the amount of axial movement of the roller 30 is significantly smaller than the amount of rotation of the nut 20. In other words, the roller 30 moves axially relative to the rotation of the nut 20 due to the transmission of rotation by the nut-side threaded portion 21 and the roller-side threaded portion 31, and the difference between the lead angle of the nut-side threaded portion 21 and the lead angle of the roller-side threaded portion 31. Therefore, the amount of axial movement is significantly smaller than the amount of rotation of the nut 20. To put it another way, the roller 30 moves axially with a large reduction ratio relative to the rotation of the nut 20, and consequently moves with a large thrust in the axial direction.

[0093] Figure 5 is an explanatory diagram showing the state in which the shaft 50 shown in Figure 1 moves relative to the nut 20 in the axial direction. The multiple rollers 30 rotate around the axis of each roller 30 and move in the axial direction of the rollers 30 because the lead angles of the nut-side threaded portion 21 and the roller-side threaded portion 31 are different. The rollers 30 mesh with the shaft 50 through the roller-side meshing portion 32 of the roller 30 and the shaft-side meshing portion 51 of the shaft 50. Therefore, when the force transmitted from the nut 20 causes the multiple rollers 30 to rotate and move axially toward the side where the nut cover 60 is positioned relative to the nut 20 as shown in Figure 5, the force that causes the rollers 30 to move in the axial direction is transmitted to the shaft 50 via the transmission from the roller-side meshing portion 32 to the shaft-side meshing portion 51.

[0094] As a result, the force that causes the multiple rollers 30 to move axially toward the side where the nut cover 60 is located is transmitted to the shaft 50 via the roller-side meshing portion 32 and the shaft-side meshing portion 51. The shaft 50, together with the multiple rollers 30 and the retainer 40, moves relative to the nut 20 toward the side where the nut cover 60 is located due to the force transmitted in this manner. Furthermore, since the nut cover 60 is attached to the shaft 50, when the shaft 50 moves relative to the nut 20, the nut cover 60 also moves axially relative to the nut 20 together with the shaft 50.

[0095] At that time, the roller 30, which moves axially as the nut 20 rotates, moves with a large thrust, so the shaft 50 and nut cover 60, which move axially relative to the nut 20 together with the multiple rollers 30, also move axially relative to the nut 20 with a large thrust.

[0096] When the shaft 50 is moved in the opposite direction relative to the nut 20 in the axial direction, the rotation direction of the nut 20, which is rotated by the force from the power source, is also reversed. As a result, the rotation direction of the roller 30, which is rotated by the rotation of the nut 20, is also reversed, and therefore the direction of the axial relative movement of the roller 30 with respect to the nut 20 is also reversed. That is, the roller 30 moves relative to the nut 20 in the direction opposite to the side where the nut cover 60 is located in the axial direction, i.e., the direction where the nut adapter 24 is located in the axial direction. Consequently, the direction of movement of the shaft 50 and the nut cover 60 with respect to the nut 20, which move together with the roller 30, is also reversed, and they move relative to the nut 20 in the direction where the nut adapter 24 is located in the axial direction.

[0097] As described above, the planetary roller screw 10 can output the rotational force input to the nut 20 as a large linear thrust force from the shaft 50, thus converting rotational force into linear force. For example, when the force output from the shaft 50 via the nut cover 60 is used as a pressing force applied to any member, a large pressing force can be applied by using the large linear force generated when the shaft 50 moves axially relative to the nut 20 as the pressing force.

[0098] As described above, in the planetary roller screw 10 according to this embodiment, the rotation of the nut 20 is transmitted to the roller 30 by the roller-side threaded portion 31 that meshes with the nut-side threaded portion 21. As a result, the rotation of the nut 20 can be transmitted from the nut 20 to the roller 30 with a large reduction ratio, and the force exerted when the roller 30 moves in the axial direction can be increased. Furthermore, the axial force transmitted between the roller 30 and the shaft 50 can be transmitted by the roller-side meshing portion 32 and the shaft-side meshing portion 51, which each have circumferentially extending grooves and protrusions, so that a large axial force from the roller 30 to the shaft 50 can be transmitted without hindering the revolution of the roller 30 around the central axis AX of the nut 20.

[0099] Thus, when the nut 20 rotates, a large axial force is transmitted from the roller 30 to the shaft 50, and the shaft 50 moves relative to the nut 20 in the axial direction together with the roller 30 with a large thrust. As a result, the planetary roller screw 10 can convert the rotational force input to the nut 20 from the power source via the nut adapter 24 into a large linear force through the axial movement of the shaft 50.

[0100] In this configuration, the roller 30, positioned between the nut 20 and the shaft 50 and rotating axially in conjunction with the rotation of the nut 20, is supported at multiple positions by the retainer 40. Therefore, as the roller 30 rotates on its own axis and revolves along the circumferential direction around the central axis AX of the nut 20, the retainer 40, which supports the roller 30 at multiple positions, prevents the roller 30 from tilting toward the circumferential direction of the nut 20 relative to its own axis.

[0101] In other words, if, for example, the ends of the roller 30 are supported by different members, when the roller 30 revolves, the members supporting it at both ends may shift slightly in the circumferential direction of the revolution, potentially causing the roller 30 to tilt toward the circumferential direction of the nut 20. If the roller 30 tilts toward the circumferential direction of the nut 20, the roller 30 will also tilt in relation to the direction of movement when the shaft 50 moves relative to the nut 20 in the axial direction. When the roller 30 tilts toward the nut 20 in this way, the resistance between the nut 20 and the shaft 50 and the roller 30 increases when the roller 30 rotates or revolves, thus reducing the transmission efficiency when the rotation of the nut 20 is transmitted from the nut 20 to the shaft 50 via the roller 30.

[0102] In contrast, in the planetary roller screw 10 according to this embodiment, each roller 30 is supported at multiple positions by a single retainer 40. Therefore, even when the roller 30 revolves, tilting of the roller 30 toward the circumferential direction of the nut 20 is suppressed. This suppresses the increase in resistance between the nut 20 and shaft 50 and the roller 30 when the roller 30 rotates or revolves, which is caused by the tilting of the roller 30. This suppresses a decrease in transmission efficiency when the rotation of the nut 20 is transmitted from the nut 20 to the shaft 50 via the roller 30. As a result, a decrease in transmission efficiency when converting rotational force into linear force can be suppressed.

[0103] Furthermore, the retainer 40 supports the intermediate support portion 35 located between the roller-side threaded portion 31 and the roller-side meshing portion 32 of the roller 30, and the shaft end support portion 36 located on the opposite side of the roller-side meshing portion 32 relative to the roller-side threaded portion 31. Therefore, it can support the roller 30 while suppressing its tilt. In other words, since the threads of the roller-side threaded portion 31 are formed at an angle with respect to the circumferential and axial directions of the roller 30, when the rotation of the nut 20 is transmitted to the roller 30 via the nut-side threaded portion 21 and the roller-side threaded portion 31, a force that tilts the roller 30 toward the circumferential direction of the nut 20 also acts on the roller 30.

[0104] In contrast, the retainer 40 supports the roller 30 by supporting the intermediate support portion 35 and the shaft end support portion 36, thereby supporting the roller 30 on both sides of the roller-side threaded portion 31. Therefore, even when a force acts on the roller-side threaded portion 31 that tilts the roller 30 toward the circumferential direction of the nut 20, the tilt of the roller-side threaded portion 31 can be suppressed. As a result, the retainer 40 can support the roller 30 while suppressing its tilt, thereby suppressing the increase in resistance between the nut 20, shaft 50 and the roller 30 when the roller 30 rotates or revolves, which is caused by the tilt of the roller 30. Consequently, a decrease in transmission efficiency when converting rotational force into linear force can be suppressed.

[0105] Furthermore, since the shaft 50 has rolling portions 55 that contact the outer circumferential surface of the shaft end portion 37 of the roller 30 from the inside in the radial direction of the shaft 50, the rolling portions 55 can suppress the tilting of the roller 30 toward the radial direction of the shaft 50. This suppresses the increase in resistance between the nut 20 and the shaft 50 and the roller 30 when the roller 30 rotates or revolves, which is caused by the tilting of the roller 30. As a result, it is possible to suppress the decrease in transmission efficiency when converting rotational force into linear force.

[0106] Furthermore, since the outer diameter of the roller-side meshing portion 32 of the roller 30 is smaller than the outer diameter of the roller-side threaded portion 31, contact between the roller-side meshing portion 32 and the nut 20 can be suppressed. As a result, the roller-side meshing portion 32 can be arranged coaxially with the roller-side threaded portion 31 without requiring a separate component from the roller 30 to transmit the force with which the roller 30 moves axially to the shaft 50. Consequently, the number of parts in the planetary roller screw 10 can be kept to a minimum, and the planetary roller screw 10 can be made more compact.

[0107] Furthermore, since the threads of the nut-side threaded portion 21 and the roller-side threaded portion 31 are in opposite directions, the rotation of the nut 20 is transmitted to the roller 30 via the nut-side threaded portion 21 and the roller-side threaded portion 31, allowing the roller 30 to rotate in the same direction as the rotation of the nut 20. This allows the roller 30 to move axially while rotating in the same direction as the rotation of the nut 20, and a structure that converts rotational force into linear force can be realized with a simple structure. As a result, the manufacturing cost of the planetary roller screw 10 that converts rotational force into linear force can be reduced.

[0108] Furthermore, since the lead angles of the nut-side threaded portion 21 and the roller-side threaded portion 31 are different, rotating the nut 20 allows the roller 30 to move axially relative to the nut 20 according to the difference in lead angles between the nut-side threaded portion 21 and the roller-side threaded portion 31. This makes it possible to realize a structure that converts the rotational force of the nut 20 into an axial force and outputs it as a linear force with a simple structure. As a result, the manufacturing cost of the planetary roller screw 10 that converts rotational force into linear force can be reduced.

[0109] Next, an example of the application of the planetary roller screw 10 according to the embodiment will be described. Figure 6 is a cross-sectional view of the main part of the electromechanical brake 80 according to the embodiment. The planetary roller screw 10 is used, for example, in an electromechanical brake 80 as shown in Figure 6. The electromechanical brake 80 shown in Figure 6 is mounted on a vehicle as a braking device that generates braking force in a moving vehicle (not shown). The electromechanical brake 80 has a brake rotor 100 that rotates together with the wheels (not shown) of the vehicle on which the electromechanical brake 80 is mounted, a brake pad 98 that contacts the brake rotor 100 and generates frictional force between itself and the brake rotor 100, and a brake caliper 90 that holds the brake pad 98 and presses the brake pad 98 against the brake rotor 100.

[0110] The brake rotor 100 is formed in a roughly disc shape from a metal material, and is mounted on the vehicle with the axis of the disc aligned with the axis of the wheel. As a result, the brake rotor 100 rotates together with the wheel as the wheel rotates.

[0111] The brake caliper 90 and brake pads 98 are mounted on the vehicle body side, which does not rotate with the wheels. The brake pads 98 are positioned on both sides of the brake rotor 100 in the thickness direction, and contact both sides of the brake rotor 100 in the thickness direction due to the pressing force applied from the brake caliper 90. This allows the brake pads 98 to generate frictional force between themselves and the rotating brake rotor 100.

[0112] The brake caliper 90 has a caliper body 91 and a caliper base 95. The caliper base 95 holds the brake pads 98 at positions on both sides of the brake rotor 100 in the thickness direction, so that the brake pads 98 face the brake rotor 100.

[0113] The caliper body 91 holds a piston 96 that contacts one of the brake pads 98 located on both sides of the brake rotor 100 in the thickness direction, which is the inner brake pad 98a, and applies a pressing force to the brake pad 98. It is also provided with claws 93 that contact the other brake pad 98, which is the outer brake pad 98b. Specifically, the caliper body 91 has a housing hole 92 which is a hole for housing the piston 96, and by housing the piston 96 in the housing hole 92, the caliper body 91 holds the piston 96 so that it can move freely in the thickness direction of the brake rotor 100 relative to the caliper body 91.

[0114] Furthermore, the caliper body 91 is mounted to the caliper base 95 so as to be movable relative to the brake rotor 100 in the thickness direction. The brake caliper 90 according to this embodiment is configured in this way so as a so-called single-piston type brake caliper 90 or a floating type brake caliper 90.

[0115] More specifically, the housing hole 92 formed in the caliper body 91 is a hole that opens in the direction in which the piston 96 applies pressing force to the brake pad 98 within the caliper body 91. In other words, the housing hole 92 is formed in the caliper body 91 as a substantially cylindrical hole with an inner diameter approximately the same size as the outer diameter of the piston 96, and is formed in the caliper body 91 with the axial direction of the cylinder aligned with the thickness direction of the brake rotor 100.

[0116] The piston 96, which is held by the caliper body 91 by being housed in a housing hole 92 formed in the caliper body 91, contacts the inner brake pad 98a from the opposite side of the brake rotor 100 in the thickness direction of the brake rotor 100. In addition, the claws 93 of the caliper body 91 contact the outer brake pad 98b from the opposite side of the brake rotor 100 in the thickness direction of the brake rotor 100.

[0117] When generating braking force with the electromechanical brake 80, the piston 96 applies a pressing force to the inner brake pad 98a in the direction in which the brake rotor 100 is located, thereby pressing the inner brake pad 98a against the brake rotor 100.

[0118] The caliper body 91 moves in the opposite direction to the direction in which the piston 96 applies pressure to the inner brake pad 98a, due to the reaction force when the piston 96 applies pressure to the inner brake pad 98a. In other words, the caliper body 91 moves relative to the caliper base 95 in the opposite direction to the direction in which the piston 96 applies pressure to the inner brake pad 98a.

[0119] As a result, the claws 93 that contact the outer brake pad 98b apply a pressing force to the outer brake pad 98b in the direction in which the brake rotor 100 is located, and the outer brake pad 98b is pressed against the brake rotor 100. The electromechanical brake 80 then presses the brake pads 98 against the brake rotor 100 from both sides in the thickness direction, and the frictional force between the brake pads 98 that contact both sides of the brake rotor 100 and the brake rotor 100 generates a braking force that reduces the rotational speed of the rotating brake rotor 100.

[0120] The planetary roller screw 10 is applied to the electromechanical brake 80 configured in this way. When the planetary roller screw 10 is applied to the electromechanical brake 80, a motor 71 is used as a power source to provide driving force to the nut 20, and the planetary roller screw 10 is used together with the motor 71 as a linear actuator 70 that outputs a force in the linear direction by the driving force generated by the motor 71.

[0121] In other words, in a linear actuator 70 composed of a planetary roller screw 10 and a motor 71, the roller 30 of the planetary roller screw 10 rotates when the rotation of the nut 20, which rotates due to the driving force from the motor 71, is transmitted from the nut-side threaded portion 21 to the roller-side threaded portion 31, and also moves relative to the nut 20 in the axial direction. Furthermore, the shaft 50 moves relative to the nut 20 in the axial direction together with the roller 30 when the axial movement of the roller 30 is transmitted from the roller-side meshing portion 32 to the shaft-side meshing portion 51. As a result, the linear actuator 70 is able to convert the rotational force output from the motor 71 into a linear force and output it.

[0122] The motor 71 constituting the linear actuator 70 is used as a power source in the electromechanical brake 80 and is attached to the caliper body 91. The piston 96 in the electromechanical brake 80 uses the shaft 50 and nut cover 60 of the planetary roller screw 10. That is, the linear force of the shaft 50 in the linear actuator 70 is used as the pressing force applied from the piston 96 to the brake pad 98 in the electromechanical brake 80.

[0123] A control unit (hereinafter referred to as an ECU (Electronic Control Unit)) 150, which performs various vehicle controls, is electrically connected to the motor 71, and a brake sensor 161, which detects the amount of operation of the brake pedal 160, is electrically connected to the ECU 150. The electromechanical brake 80 generates a braking force corresponding to the amount of operation of the brake pedal 160 by controlling the drive of the motor 71 based on the amount of operation of the brake pedal 160 detected by the brake sensor 161, via the ECU 150.

[0124] The planetary roller screw 10 is arranged around a shaft 50 with multiple rollers 30 supported by a retainer 40, and the roller-side meshing portion 32 of each roller 30 meshing portion 51 with the shaft-side meshing portion 51, with the shaft 50 and the multiple rollers 30 positioned inside the nut 20. The planetary roller screw 10, with the shaft 50 and the multiple rollers 30 positioned inside the nut 20, is positioned inside a housing hole 92 formed in the caliper body 91 of the brake caliper 90, thereby being positioned in the caliper body 91.

[0125] In other words, the inner diameter of the housing hole 92 formed in the caliper body 91 is approximately the same as the outer diameter of the nut cover 60, which is attached to the shaft 50 and covers the nut 20. The nut cover 60 of the planetary roller screw 10 is positioned to be axially movable inside the housing hole 92. At this time, the planetary roller screw 10 is positioned such that the nut cover 60 is on the side where the inner brake pad 98a is located, and the nut cover 60 is positioned in the housing hole 92 facing the inner brake pad 98a. The bottom surface 61 of the nut cover 60 is in contact with the inner brake pad 98a, and the pressing force applied to the brake pad 98 from the shaft 50, which is used as the piston 96, and the nut cover 60 is applied from the bottom surface 61 of the nut cover 60.

[0126] Furthermore, a groove 65 extending in the axial direction (see Figures 3 and 4) is formed on the outer circumferential surface of the nut cover 60, and a projection (not shown) that fits into the groove 65 of the nut cover 60 is formed on the inner circumferential surface of the housing hole 92 formed in the caliper body 91. As a result, when the nut cover 60, which is positioned inside the housing hole 92, attempts to rotate relative to the housing hole 92 in the circumferential direction, the groove wall of the groove 65 of the nut cover 60 and the projection of the housing hole 92 come into contact, thereby restricting relative rotation in the circumferential direction. Therefore, the nut cover 60, which is positioned inside the housing hole 92, is unable to rotate relative to the housing hole 92 in the circumferential direction, but is able to move relative to the housing hole 92 in the axial direction.

[0127] The caliper body 91 has an axial support portion 94 formed on the side opposite to the side where the nut 20 is located relative to the nut adapter 24, when the planetary roller screw 10 is positioned in the housing hole 92. Therefore, when the planetary roller screw 10 is positioned inside the housing hole 92, the nut adapter 24 is positioned between the axial support portion 94 of the caliper body 91 and the nut 20 in the axial direction of the nut 20.

[0128] In the nut adapter 24, which is attached to the nut 20, a thrust bearing 75 is positioned on the side opposite to the side where the nut 20 is located in the axial direction of the nut 20, to receive the axial force from the nut 20. That is, the thrust bearing 75 is positioned between the axial support portion 94 of the caliper body 91 and the nut adapter 24.

[0129] The thrust bearing 75 is capable of receiving the axial load acting between the nut adapter 24 and the axial support portion 94 of the caliper body 91, while allowing relative rotation between the nut adapter 24 and the axial support portion 94 around the central axis AX of the nut 20. For example, a thrust needle bearing can be used as the thrust bearing 75.

[0130] In the electromechanical brake 80, the motor 71 used as a power source is inserted into a through hole 27 formed in the nut adapter 24 of the planetary roller screw 10, and the drive shaft 72 is fitted into a fitting hole 27a provided in the through hole 27. Specifically, the axial support portion 94 of the caliper body 91 has a hole formed therein whose inner diameter is larger than the outer diameter of the drive shaft 72 of the motor 71. When fitting the drive shaft 72 of the motor 71 into the fitting hole 27a of the nut adapter 24, the drive shaft 72 is fitted through the hole in the axial support portion 94 from the opposite side of the axial support portion 94 where the nut adapter 24 is located.

[0131] Since the nut adapter 24 is attached to the nut 20, by fitting the drive shaft 72 of the motor 71 into the fitting hole 27a of the nut adapter 24, the motor 71 is connected to the nut 20 of the planetary roller screw 10 via the nut adapter 24. This allows the motor 71 to apply driving force to the nut 20. In other words, the motor 71 can apply the driving force it generates to the planetary roller screw 10, and the planetary roller screw 10 can be operated by the driving force it generates.

[0132] Furthermore, the motor 71 is connected to the nut 20 via the nut adapter 24 by inserting the drive shaft 72 into the through hole 27 of the nut adapter 24, which is attached to the nut 20. Therefore, the nut 20 and the motor 71 are arranged coaxially.

[0133] Next, the operation of the electromechanical brake 80 having a linear actuator 70 will be described. The electromechanical brake 80 generates braking force based on the amount of operation of the brake pedal 160 by the driver of the vehicle equipped with the electromechanical brake 80. Specifically, the amount of operation of the brake pedal 160 is detected by a brake sensor 161, and the detection result of the amount of operation of the brake pedal 160 by the brake sensor 161 is transmitted to the ECU 150. Based on the amount of operation of the brake pedal 160 transmitted from the brake sensor 161, the ECU 150 controls the drive of the motor 71 of the linear actuator 70.

[0134] When the motor 71 is driven by control from the ECU 150, the drive shaft 72 of the motor 71 rotates. When the drive shaft 72 of the motor 71 rotates, the nut 20 of the planetary roller screw 10 rotates together with the drive shaft 72 of the motor 71. In other words, the nut adapter 24 attached to the nut 20 rotates together with the drive shaft 72 of the motor 71, causing the nut 20 to rotate together with the nut adapter 24. As a result, the nut 20 rotates together with the drive shaft 72 of the motor 71.

[0135] When the nut 20 rotates, the planetary roller screw 10 causes the roller 30 to rotate on its own axis and move axially relative to the nut 20. As the roller 30 moves axially relative to the nut 20, the shaft 50 also moves axially relative to the nut 20.

[0136] For example, if the roller 30, which transmits the rotation of the nut 20, moves relative to the nut 20 in the axial direction away from the motor 71, then the shaft 50, which moves axially with the roller 30, also moves relative to the nut 20 in the axial direction away from the motor 71. In this case, the shaft 50, together with the nut cover 60 attached to the shaft 50, moves axially within the housing hole 92 formed in the caliper body 91, thereby moving relative to the caliper body 91 towards the side where the inner brake pad 98a is located.

[0137] The shaft 50 and nut cover 60, which move relative to the caliper body 91 on the side where the inner brake pad 98a is located, apply a pressing force to the inner brake pad 98a from the opposite side of the brake rotor 100 in the thickness direction of the brake rotor 100, in the direction in which the brake rotor 100 is located. As a result, the inner brake pad 98a is pressed against the brake rotor 100.

[0138] At that time, the roller 30, which moves axially as the nut 20 rotates, moves with a large thrust, so the pressing force of the shaft 50 and nut cover 60 against the inner brake pad 98a is large, and the inner brake pad 98a is pressed against the brake rotor 100 with a large force. The caliper body 91, which holds the nut cover 60 in the housing hole 92, moves in the opposite direction to the direction in which the shaft 50 and nut cover 60 apply pressing force to the inner brake pad 98a due to the reaction force when the shaft 50 and nut cover 60 apply pressing force to the inner brake pad 98a.

[0139] In other words, when the nut cover 60 is in contact with the inner brake pad 98a and a pressing force is applied to the inner brake pad 98a, the shaft 50 and the nut cover 60 become unable to move in the direction in which the inner brake pad 98a is located. In this state, if the shaft 50 and the nut cover 60 move relative to the caliper body 91 toward the side in which the inner brake pad 98a is located, the force that causes the shaft 50 and the nut cover 60 to move relative to the caliper body 91 acts on the caliper body 91 as a force in the opposite direction to the direction in which the shaft 50 and the nut cover 60 apply a pressing force to the inner brake pad 98a.

[0140] In other words, when the shaft 50 and nut cover 60 move in a direction that applies a pressing force to the inner brake pad 98a, the shaft 50 and nut cover 60 move relative to the nut 20 in the opposite direction to the side where the motor 71 is located in the axial direction. However, the motor 71, which is connected to the nut 20 via the nut adapter 24, is attached to the caliper body 91. Therefore, the force with which the shaft 50 and nut cover 60 move in a direction that applies a pressing force to the inner brake pad 98a acts on the caliper body 91 as a force that moves it toward the side where the motor 71 is located together with the nut 20.

[0141] Since the caliper body 91 is mounted so as to be movable relative to the caliper base 95 in the thickness direction of the brake rotor 100, the caliper body 91, which is subjected to a force acting in the direction that moves it toward the motor 71, moves relative to the caliper base 95 in the thickness direction of the brake rotor 100 in the direction toward the motor 71 due to this force.

[0142] As the caliper body 91 moves relative to the caliper base 95 in this manner, the claws 93 of the caliper body 91 that contact the outer brake pad 98b from the opposite side of the outer brake pad 98b from where the brake rotor 100 is located apply a pressing force to the outer brake pad 98b in the direction of the brake rotor 100. As a result, the outer brake pad 98b is pressed against the brake rotor 100.

[0143] Therefore, the inner brake pad 98a and the outer brake pad 98b are pressed against the brake rotor 100 from both sides in the thickness direction of the brake rotor 100, and a large frictional force is generated between the brake pads 98 that are in contact with both sides of the brake rotor 100 and the rotating brake rotor 100. The electromechanical brake 80 generates a braking force that reduces the rotational speed of the brake rotor 100 by generating a large frictional force between the rotating brake rotor 100 and the brake pads 98.

[0144] Furthermore, in order to generate braking force with the electromechanical brake 80 in this manner, when the roller 30 is moved axially relative to the nut 20 on the side where the nut cover 60 is located, a force acts on the nut 20 in the direction in which the nut adapter 24 is located in the axial direction. In this embodiment, since a thrust bearing 75 is arranged between the nut adapter 24 attached to the nut 20 and the axial support portion 94 of the caliper body 91, the nut 20 can be rotated while the thrust bearing 75 receives the force acting on the nut 20 in the axial direction.

[0145] As described above, in the electromechanical brake 80 according to this embodiment, the motor 71, which is the power source, is driven to generate braking force. As a result, the rotation of the nut 20, which rotates due to the driving force from the motor 71, is transmitted to the roller 30, causing the roller 30 to rotate and move axially relative to the nut 20. Along with the axial movement of the roller 30, the shaft 50 also moves axially relative to the nut 20.

[0146] The shaft 50, which moves axially, applies a pressing force to the brake pad 98 via the nut cover 60, through its relative axial movement with respect to the nut 20, in a direction that presses the brake pad 98 against the brake rotor 100. This allows the electromechanical brake 80 to increase the frictional force between the brake pad 98 and the brake rotor 100, thereby generating a braking force.

[0147] As described above, when releasing the braking force generated by the electromechanical brake 80, the motor 71 is driven based on the amount of operation of the brake pedal 160 transmitted from the brake sensor 161, thereby rotating the motor 71 in the opposite direction to the direction in which the electromechanical brake 80 generates the braking force. As a result, the nut 20, which rotates together with the drive shaft 72 of the motor 71, also rotates in the opposite direction, and the roller 30, to which the rotation of the nut 20 is transmitted, also rotates in the opposite direction to the direction of rotation when the braking force is generated.

[0148] When the roller 30 rotates in the opposite direction to the direction in which it generates braking force, the roller 30 moves relative to the nut 20 to the opposite side of where the nut cover 60 is located, that is, to the side where the nut adapter 24 attached to the nut 20 is located. When the roller 30 moves relative to the nut 20 toward the side where the nut adapter 24 is located, the shaft 50 also moves relative to the nut 20 in the same direction along with the roller 30. In other words, the shaft 50 moves relative to the caliper body 91 toward the side where the nut adapter 24 is located by moving axially within the housing hole 92 formed in the caliper body 91.

[0149] The shaft 50, which moves relative to the caliper body 91 on the side where the nut adapter 24 is located, moves together with the nut cover 60 in the thickness direction of the brake rotor 100 toward the inner brake pad 98a. As a result, the pressing force applied to the inner brake pad 98a from the shaft 50 and nut cover 60 is reduced, and the pressing force applied to the brake rotor 100 from the inner brake pad 98a is reduced.

[0150] When the pressing force applied to the inner brake pad 98a is reduced, the caliper body 91, which holds the nut cover 60 in the housing hole 92 and to which the motor 71 is attached, moves in the direction away from the brake rotor 100 in the thickness direction of the brake rotor 100 due to the reaction force of the pressing force applied from the claws 93 to the outer brake pad 98b.

[0151] As a result, the pressing force applied to the brake rotor 100 by the inner brake pad 98a and the outer brake pad 98b is reduced, and the frictional force between the brake pad 98 and the brake rotor 100 is reduced. By reducing the frictional force between the brake rotor 100 and the brake pad 98 in this way, the electromechanical brake 80 reduces the braking force it generates.

[0152] As described above, the linear actuator 70 according to this embodiment includes a planetary roller screw 10 and a motor 71 that applies driving force to the nut 20 of the planetary roller screw 10. Therefore, the rotation of the nut 20, which is rotated by the driving force of the motor 71, can be transmitted from the nut 20 to the roller 30 with a large reduction ratio. This increases the force exerted when the roller 30 moves in the axial direction, and also increases the axial thrust of the shaft 50, which moves axially together with the roller 30. Consequently, the rotational force input to the nut 20 from the motor 71 via the nut adapter 24 can be converted into a large linear force by the axial movement of the shaft 50 and output.

[0153] Furthermore, since the rollers 30 of the planetary roller screw 10 of the linear actuator 70 are supported at multiple positions by a single retainer 40, even when the rollers 30 revolve, tilting of the rollers 30 toward the circumferential direction of the nut 20 is suppressed. This suppresses the increase in resistance between the nut 20 or shaft 50 and the rollers 30 caused by the tilting of the rollers 30 when the rollers 30 rotate or revolve. Consequently, the decrease in transmission efficiency when the rotation of the nut 20, which rotates due to the driving force of the motor 71, is transmitted from the nut 20 to the shaft 50 via the rollers 30 can be suppressed. As a result, the decrease in transmission efficiency when converting the rotational force output from the motor 71 into linear force can be suppressed.

[0154] Furthermore, a nut adapter 24 is attached to the nut 20, and the motor 71 is connected to the nut 20 via the nut adapter 24 by fitting the drive shaft 72 of the motor 71 into the fitting hole 27a of the nut adapter 24. Thus, the drive shaft 72 of the motor 71 can be easily connected to the nut 20. In this way, by connecting the drive shaft 72 of the motor 71 to the nut 20 via the nut adapter 24, the driving force from the drive shaft 72 of the motor 71, which is formed in a round bar shape, can be easily transmitted to the nut 20, which is formed in a cylindrical shape. As a result, the ease of assembly of the linear actuator 70 can be improved.

[0155] Furthermore, the electromechanical brake 80 according to this embodiment includes a planetary roller screw 10, a motor 71 that applies driving force to the nut 20 of the planetary roller screw 10, a disc-shaped brake rotor 100, a brake pad 98 that contacts the brake rotor 100, and a brake caliper 90 that holds the brake pad 98. As a result, the electromechanical brake 80 can transmit the rotation of the nut 20, which is rotated by the driving force of the motor 71, from the nut 20 to the roller 30 with a large reduction ratio. This increases the force exerted when the roller 30 moves axially, and also increases the axial thrust of the shaft 50, which moves axially together with the roller 30. This allows the rotational force input to the nut 20 from the motor 71 via the nut adapter 24 to be converted into a large linear force by the axial movement of the shaft 50 and output, thereby ensuring the pressing force applied from the shaft 50 to the brake pad 98 via the nut cover 60.

[0156] Furthermore, in the electromechanical brake 80, the rollers 30 of the planetary roller screw 10 are supported at multiple positions by a single retainer 40. This prevents the rollers 30 from tilting toward the circumferential direction of the nut 20 even when the rollers 30 revolve. This suppresses the increase in resistance between the nut 20 or shaft 50 and the rollers 30 caused by the tilt of the rollers 30 when the rollers 30 rotate or revolve. Consequently, it is possible to suppress a decrease in transmission efficiency when the rotation of the nut 20, which is rotated by the driving force of the motor 71, is transmitted from the nut 20 to the shaft 50 via the rollers 30. As a result, it is possible to suppress a decrease in transmission efficiency when converting the rotational force output from the motor 71 into linear force.

[0157] Furthermore, the electromechanical brake 80 according to this embodiment can transmit the driving force of the motor 71 to the roller 30 from the nut 20 with a large reduction ratio, and the force exerted when the roller 30 moves axially can be increased, thereby increasing the thrust of the shaft 50 which moves axially together with the roller 30. As a result, a large pressing force can be applied when the shaft 50, via the nut cover 60, presses the brake pad 98 against the brake rotor 100. Therefore, a large braking force can be obtained without providing a reduction gear to increase the reduction ratio between the mechanism that converts the driving force generated by the motor 71 into braking force and the motor 71, and the device can be made more compact by eliminating the need for a reduction gear. As a result, the electromechanical brake 80 can be miniaturized, that is, the braking device can be miniaturized.

[0158] Furthermore, in the electromechanical brake 80 according to this embodiment, a nut cover 60 is attached to the shaft 50 at the end opposite to the side where the roller-side threaded portion 31 of the roller 30 is located in the axial direction. The nut cover 60 has a bottom surface portion 61 that closes the portion of the nut 20 on the side where the nut cover 60 is located, and the bottom surface portion 61 of the nut cover 60 contacts the brake pad 98. As a result, the pressing force applied from the shaft 50 to the brake pad 98 can be applied from the bottom surface portion 61 of the flat nut cover 60, thus enabling a stable pressing force to be applied to the brake pad 98. As a result, a stable braking force can be generated.

[0159] Furthermore, since multiple rollers 30 are arranged circumferentially along the inner surface of the nut 20, and the multiple rollers 30 are supported collectively by the retainer 40 so as to be movable in the circumferential direction of the nut 20, when the rotational force of the nut 20, which rotates due to the driving force from the motor 71, is converted into an axial force by the rollers 30, the multiple rollers 30 can be used to create a large axial force. As a result, the thrust force when the shaft 50 moves relative to the nut 20 in the axial direction can be increased, and the pressing force of the brake pad 98 against the brake rotor 100 can be increased. As a result, a large braking force can be obtained while miniaturizing the brake device.

[0160] Furthermore, since the nut 20 of the planetary roller screw 10 and the motor 71 are arranged coaxially, it is possible to suppress the motor 71 from extending radially toward the nut 20, thereby reducing the size of the electromechanical brake 80 in the radial direction of the shaft 50. As a result, the brake device can be miniaturized.

[0161] [Differentiation] In the electromechanical brake 80 described above, the motor 71's drive shaft 72 is connected to the nut 20 of the planetary roller screw 10 via a nut adapter 24. However, a reduction gear may be interposed between the motor 71 and the nut 20 of the planetary roller screw 10. The planetary roller screw 10 can convert rotational force into linear force with a large reduction ratio. By interposing a reduction gear between the motor 71 and the planetary roller screw 10, the reduction ratio when converting rotational force into linear force can be made even larger. This allows the rotational force output from the motor 71 to be converted into a larger linear force, thereby applying a greater pressing force to the brake pad 98 and obtaining greater braking force.

[0162] Furthermore, although the linear actuator 70 described above is used in the electromechanical brake 80, the linear actuator 70 may be used in devices other than the electromechanical brake 80. The linear actuator 70 can be used in any device that utilizes the linear force output from the linear actuator 70, regardless of the type of device.

[0163] Furthermore, although 12 rollers 30 are used in the embodiment described above, the number of rollers 30 may be other than this. It is preferable to appropriately set the number of rollers 30 according to the relationship between the size of the nut 20 and the shaft 50 and the size of the rollers 30, and the magnitude of the thrust when the rollers 30 are moved axially by the rotational force of the nut 20.

[0164] While preferred embodiments of this disclosure have been described above, this disclosure is not limited to those described in the embodiments described above. The configurations described as embodiments and modifications may be combined as appropriate. [Explanation of Symbols]

[0165] 10 Planetary roller screws 20 nuts 21 Threaded portion on the nut side 22 Adapter connection section 22a Pin hole 24 Nut Adapter 25 Flange section 25a Pin hole 26 Insertion part 27 Through hole 27a Fitting hole 28 pins 30 Laura 31 Roller-side threaded section 32. Roller-side meshing section 35 Intermediate support part 36 Shaft end support part 37 Shaft end 40 Retainer 41 Side wall section 42 Support part 43 Opening hole 50 shaft 51 Shaft-side engagement part 53 Through hole 55 Rolling part 60 Nut Cover 61 Bottom part 62 Insertion section 63 Outer periphery 65 groove 70 Linear Actuator 71 Motor 72 Drive shaft 75 Thrust bearing 80 Electromechanical brake 90 Brake caliper 91 Caliper body 92 Intake holes 93 claws 94 Axial support 95 Caliper Base 96 Pistons 98 Brake Pads 98a Inner Brake Pads 98b Outer Brake Pads 100 Brake rotors 150 ECU 160 Brake pedal 161 Brake Sensor

Claims

1. A nut formed in a cylindrical shape, having a spirally threaded portion on its inner circumference, A roller having a round bar shape positioned inside the nut and extending along the axial direction of the nut, and a roller-side threaded portion that engages with the nut-side threaded portion, and a roller-side engagement portion positioned at a different location in the axial direction from the roller-side threaded portion and having repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, A shaft having a shaft-side meshing portion that is positioned inside the nut and has repeating axial irregularities on its outer surface that extend along the circumferential direction of the outer surface and mesh with the roller-side meshing portion, Equipped with, Multiple rollers are arranged in a line along the inner circumferential surface of the nut and along the circumferential direction of the nut. The multiple rollers are held together with the rollers by a retainer positioned inside the nut, The retainer is a planetary roller screw that supports the roller so that it can rotate while restricting the positional relationship with the roller at multiple axial positions on the roller.

2. The planetary roller screw according to claim 1, wherein the retainer is formed in a cylindrical shape and supports the portion of the roller between the roller-side threaded portion and the roller-side meshing portion, and the portion of the roller opposite to the side on which the roller-side meshing portion is located relative to the roller-side threaded portion.

3. The planetary roller screw according to claim 1, wherein the shaft has rolling portions that contact the outer circumferential surface of the end of the roller near the end on which the roller-side meshing portion is located, from the inside in the radial direction of the shaft.

4. The planetary roller screw according to claim 1, wherein the outer diameter of the roller-side meshing portion is smaller than the outer diameter of the roller-side threaded portion.

5. The planetary roller screw according to claim 1, wherein the threaded portion on the nut side and the threaded portion on the roller side have spiral directions opposite to each other.

6. A nut formed in a cylindrical shape, having a spirally threaded portion on its inner circumference, A roller having a round bar shape positioned inside the nut and extending along the axial direction of the nut, and a roller-side threaded portion that engages with the nut-side threaded portion, and a roller-side engagement portion positioned at a different location in the axial direction from the roller-side threaded portion and having repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, A shaft having a shaft-side meshing portion that is positioned inside the nut and has repeating axial irregularities on its outer surface that extend along the circumferential direction of the outer surface and mesh with the roller-side meshing portion, A planetary roller screw having, A motor that applies driving force to the nut, Equipped with, Multiple rollers are arranged in a line along the inner circumferential surface of the nut and along the circumferential direction of the nut. The multiple rollers are held together with the rollers by a retainer positioned inside the nut, The retainer supports the roller so that it can rotate while restricting the positional relationship with the roller at multiple axial positions on the roller. The roller rotates as the rotation of the nut, which rotates due to the driving force from the motor, is transmitted from the threaded portion on the nut side to the threaded portion on the roller side, and moves relative to the nut in the axial direction. The shaft is a linear actuator that moves relative to the nut in the axial direction together with the roller, as the axial movement of the roller is transmitted from the roller-side meshing portion to the shaft-side meshing portion.

7. A nut adapter having a fitting hole is attached to the nut at the axial end of the nut. The linear actuator according to claim 6, wherein the motor is connected to the nut via the nut adapter by fitting the drive shaft of the motor into the fitting hole of the nut adapter.

8. A nut formed in a cylindrical shape, having a spirally threaded portion on its inner circumference, A roller having a round bar shape positioned inside the nut and extending along the axial direction of the nut, and a roller-side threaded portion that engages with the nut-side threaded portion, and a roller-side engagement portion positioned at a different location in the axial direction from the roller-side threaded portion and having repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, A shaft having a shaft-side meshing portion that is positioned inside the nut and has repeating axial irregularities on its outer surface that extend along the circumferential direction of the outer surface and mesh with the roller-side meshing portion, A planetary roller screw having, A motor that applies driving force to the nut, A disc-shaped brake rotor, A brake pad that contacts the aforementioned brake rotor, A brake caliper that holds the aforementioned brake pad, Equipped with, Multiple rollers are arranged in a line along the inner circumferential surface of the nut and along the circumferential direction of the nut. The multiple rollers are held together with the rollers by a retainer positioned inside the nut, The retainer supports the roller so that it can rotate while restricting the positional relationship with the roller at multiple axial positions on the roller. The roller rotates as the rotation of the nut, which rotates due to the driving force from the motor, is transmitted from the threaded portion on the nut side to the threaded portion on the roller side, and moves relative to the nut in the axial direction. The shaft moves relative to the nut in the axial direction together with the roller, as the axial movement of the roller is transmitted from the roller-side meshing portion to the shaft-side meshing portion. The shaft is an electromechanical brake that applies a pressing force to the brake pad in a direction that presses the brake pad against the brake rotor by its relative axial movement with respect to the nut.

9. A nut cover is attached to the shaft at the end opposite to the side where the threaded portion of the roller on the roller side is located in the axial direction. The nut cover has an outer circumference that covers the nut from the outside in the radial direction of the nut, and a bottom surface that closes the portion of the nut on the side where the nut cover is positioned in the axial direction. The electromechanical brake according to claim 8, wherein the bottom surface of the nut cover abuts against the brake pad.

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