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 shaft 20 having a shaft-side threaded portion 21, a roller 30 having a roller-side threaded portion 31 formed in the shape of a round bar and engaging with the shaft-side threaded portion 21, and a roller-side engagement portion 32 positioned at a different location from the roller-side threaded portion 31 in the axial direction and having repeating ridges and grooves extending along the circumferential direction of the round bar, and a nut 50 formed in the shape of a cylinder with the shaft 20 and roller 30 arranged inside, and having a nut-side engagement portion 52 on its inner circumferential surface that engages with the roller-side engagement portion 32, wherein multiple rollers 30 are arranged around the shaft 20 in the circumferential direction of the shaft 20, and the multiple rollers 30 are held together with the rollers 30 by a retainer 40 positioned inside the nut 50, and the retainer 40 supports multiple positions on each 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 a 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 helical 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 non-helical 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-helical groove portions of the rollers. In the planetary roller screw described in Patent Document 1, by being configured as described above, when the shaft and the nut rotate relative to each other, the rollers move axially relative to the shaft while rotating, and thus 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, thus reducing 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 shaft having a shaft-side threaded portion formed helically on its outer circumference, a roller having a round bar shape extending along the axial direction of the shaft and engaging with the shaft-side threaded portion, a roller having a roller-side engagement portion positioned at a different location from the roller-side threaded portion in the axial direction and having repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, and a nut having a cylindrical shape with the shaft and roller positioned inside, and having a nut-side engagement portion with repeating irregularities in the axial direction that extend along the circumferential direction of the inner surface and engage with the roller-side engagement portion, wherein a plurality of rollers are arranged around the shaft in the circumferential direction of the shaft, and the plurality of rollers are held together with the rollers by a retainer positioned inside the nut, and 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.

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

[0009] In this configuration, the roller is supported by a retainer so that it can rotate freely at multiple positions. As the roller rotates on its own axis and revolves along the circumferential direction of the shaft, the retainer prevents the roller from tilting toward the circumferential direction of the shaft relative to its central axis. This suppresses the increase in resistance between the shaft / nut and the roller caused by the roller's tilt during its rotation and revolving, and reduces the decrease in transmission efficiency when the rotation of the shaft is transmitted from the shaft to the nut 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 shaft, 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 shaft / nut 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 preferred configuration, the nut is provided with a nut cover on the end of the roller where the roller-side engagement portion is located, and the nut cover has a rolling portion that contacts the outer circumferential surface of the roller near the end from the inside in the radial direction of the shaft.

[0013] In this configuration, a nut cover is positioned on the side of the nut where the roller-side engagement portion is located, having a rolling portion that contacts the outer circumferential surface near the end of the roller. This prevents the roller from tilting in the radial direction of the shaft. As a result, the increase in resistance between the shaft, nut, and roller when the roller rotates or revolves, caused by the roller's tilt, can be suppressed. Consequently, the decrease in transmission efficiency when converting rotational force into linear force can be suppressed.

[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 shaft 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 from the roller to transmit the force of the roller's axial movement to the nut. 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 shaft side and the threaded portion on the roller side have spiral directions opposite to each other.

[0017] In this configuration, the threads on the shaft and the roller are oriented in opposite directions. Therefore, the rotation of the shaft is transmitted to the roller via the threads, allowing the roller to rotate in the opposite direction to the shaft's rotation. This enables the roller to move axially while rotating in the opposite direction to the shaft's rotation, thus realizing a structure that converts rotational force into linear force with a simple structure. 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 shaft having a shaft-side threaded portion formed helically on its outer circumference, a roller having a roller-side threaded portion formed in a round bar shape extending along the axial direction of the shaft and engaging with the shaft-side threaded portion, a roller-side engaging portion having repeating ridges and grooves in the axial direction that extend along the circumferential direction of the round bar and positioned at a different location from the roller-side threaded portion in the axial direction, and a nut having a nut-side engaging portion having repeating ridges and grooves in the axial direction that extend along the circumferential direction of the inner surface and engage with the roller-side engaging portion, and a motor that applies driving force to the shaft. The rollers are arranged in a plurality around the shaft in the circumferential direction, and the plurality of 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 shaft, which rotates due to the driving force from the motor, is transmitted from the shaft-side threaded portion to the roller-side threaded portion, and the rollers move relative to the shaft in the axial direction, and the nut moves relative to the shaft 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 nut-side meshing portion.

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

[0020] Furthermore, in the planetary roller screw of a linear actuator, the rollers are supported at multiple positions by a single cage, allowing them to rotate freely. This prevents the rollers from tilting in the circumferential direction of the shaft even when they are revolving. As a result, the increase in resistance caused by the tilt of the rollers is suppressed, and the decrease in transmission efficiency when the rotation of the shaft, which is driven by the motor, is transmitted to the nut is suppressed. Consequently, the decrease in transmission efficiency when converting the rotational force output from the motor into linear force is suppressed.

[0021] The electromechanical brake of this disclosure comprises a planetary roller screw having a shaft having a shaft-side threaded portion formed helically on its outer circumference, a roller having a round bar shape extending along the axial direction of the shaft and engaging with the shaft-side threaded portion, a roller having a roller-side engagement portion positioned at a different location from the roller-side threaded portion in the axial direction and having repeating irregularities in the axial direction extending along the circumferential direction of the round bar, a nut having a cylindrical shape with the shaft and roller positioned inside and having a nut-side engagement portion having repeating irregularities in the axial direction on its inner circumference that engage with the roller-side engagement portion, a motor that applies driving force to the shaft, a disc-shaped brake rotor, brake pads that contact the brake rotor, and a brake caliper that holds the brake pads, wherein the roller is front Multiple rollers are arranged around the shaft in the circumferential direction, 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 shaft, which rotates due to the driving force from the motor, is transmitted from the shaft-side threaded portion to the roller-side threaded portion, and the rollers move relative to the shaft in the axial direction, the nut moves relative to the shaft 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 nut-side meshing portion, and the nut, by moving relative to the shaft in the axial direction, applies a pressing force to the brake pads in a direction that presses them against the brake rotor.

[0022] According to this configuration, the rotation of the shaft rotated by the driving force of the motor can be transmitted from the shaft to the roller with a large reduction ratio, so that the force when the roller moves in the axial direction can be increased, and the axial thrust of the nut 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 shaft can be converted into a large force in the linear motion direction by the movement of the nut in the axial direction and output, and the pressing force applied to the brake pad from the nut can be ensured.

[0023] In addition, the rollers of the planetary roller screw of the electromechanical brake are rotatably supported at a plurality of positions of the rollers by one cage. Therefore, even when the rollers revolve, the rollers are suppressed from tilting in the circumferential direction of the shaft. Thereby, an increase in resistance due to the tilt of the roller can be suppressed, and a decrease in transmission efficiency when the rotation of the shaft rotated by the driving force of the motor is transmitted to the nut can be suppressed. As a result, a decrease in transmission efficiency when converting the force in the rotational direction output from the motor into the force in the linear motion direction can be suppressed.

Advantages of the Invention

[0024] 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 motion direction.

Brief Description of the Drawings

[0025] [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 the roller shown in FIG. 1 and the 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]Figure 5 is a cross-sectional view of the main part of an electromechanical brake according to an embodiment. [Figure 6] Figure 6 is a modified example of the planetary roller screw according to the embodiment, and is a cross-sectional view showing a form in which the nut cover has an insertion hole. [Modes for carrying out the invention]

[0026] 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.

[0027] [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 20 and roller 30 and a cross-section of the nut 50 shown in Figure 1. The planetary roller screw 10 includes a shaft 20, a roller 30, a nut 50, and a retainer 40. Of these, the shaft 20, roller 30, and nut 50 are made of heat-treated iron. The retainer 40 is made of a self-lubricating metal, such as brass.

[0028] The shaft 20 is an axial member, and a through hole 23 is formed on the inside of the shaft 20 along the central axis AX of the shaft 20 in the longitudinal direction of the shaft 20. The through hole 23 has multiple sections with different diameters, and a part of the through hole 23 is formed as a fitting hole 24 into which the drive shaft of a power source connected to the shaft 20 and used to rotate the shaft 20 can be fitted. The fitting hole 24 is designed so that relative rotation with respect to the drive shaft of the power source is not possible, allowing the drive shaft to be fitted, and in this embodiment, a spline is formed in the fitting hole 24.

[0029] Furthermore, the shaft 20 has a flange portion 22 formed in a flange shape on its outer circumferential surface near one end of the shaft 20 in the longitudinal direction. The flange portion 22 is formed to protrude outward from the outer circumferential surface of the shaft 20 in a disc shape in the radial direction of the shaft 20.

[0030] Furthermore, the shaft 20 has a shaft-side threaded portion 21 formed spirally on its outer circumferential surface. The shaft-side threaded portion 21 is a threaded portion formed spirally on the outer circumferential surface of the shaft 20, with the central axis AX of the shaft 20 as the center. In other words, the crests and valleys of the thread of the shaft-side threaded portion 21 extend in the circumferential direction with respect to the central axis AX of the shaft 20, and are formed inclined toward the direction in which the central axis AX of the shaft 20 extends. The shaft-side threaded portion 21 is formed on the outer circumferential surface of the shaft 20 from a position near the flange portion 22 toward the side where the end opposite to the end on which the flange portion 22 is located is located.

[0031] The roller 30 is formed in the shape of a round bar, with an outer diameter smaller than the outer diameter of the shaft 20, and is positioned near the shaft 20, extending along the axial direction of the shaft 20. In this embodiment, the length of the roller 30 is approximately the same as the length of the shaft 20.

[0032] 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 shaft-side threaded portion 21 formed on the shaft 20. That is, the roller-side threaded portion 31 formed on the outer circumferential surface of the roller 30 is a threaded portion that is formed in a spiral shape centered on the axis of the round bar-shaped roller 30. The spiral direction of the roller-side threaded portion 31 formed in this way is opposite to that of the shaft-side threaded portion 21.

[0033] Furthermore, the lead angles of the threads in the shaft-side threaded portion 21 and the roller-side threaded portion 31 are different, with the lead angle of the shaft-side threaded portion 21 being larger than the lead angle of the roller-side threaded portion 31. In other words, the angle of inclination of the helix in the shaft-side threaded portion 21 relative to the circumferential direction of the shaft 20 in the longitudinal direction of the shaft 20 is larger than the angle of inclination of the helix in the roller-side threaded portion 31 relative to the circumferential direction of the roller 30 in the longitudinal direction of the roller 30.

[0034] 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.

[0035] 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.

[0036] 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 shaft 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.

[0037] 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.

[0038] 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.

[0039] 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 in Figure 3. The planetary roller screw 10 has a plurality of rollers 30 formed in the manner shown. The plurality of rollers 30 are all substantially the same shape and are arranged around the shaft 20 with the axial direction of the rollers 30 aligned with the central axis AX of the shaft 20. In addition, the plurality of rollers 30 are positioned so that the roller-side threaded portion 31 of each roller 30 engages with the shaft-side threaded portion 21, and the plurality of rollers 30 are arranged at equal intervals in the circumferential direction of the shaft 20.

[0040] 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 shaft side, arranged around the shaft 20 at equal intervals in the circumferential direction.

[0041] The nut 50 is formed in a substantially cylindrical shape, and its length in the axial direction of the cylinder is approximately the same as the length of the roller 30. The shaft 20 and the roller 30 are arranged inside the nut 50. The cylindrical nut 50 has a large-diameter portion 51 and a nut-side engagement portion 52 on its inner circumferential surface. The large-diameter portion 51 is formed with an inner diameter larger than the inner diameter of the nut-side engagement portion 52.

[0042] The nut-side engagement portion 52 is formed by repeating irregularities along the axial direction of the cylindrical nut 50 or the shaft 20, extending along the circumferential direction of the inner surface, and is capable of engaging with the roller-side engagement portion 32 of the roller 30. In other words, the nut-side engagement portion 52 is formed by repeating irregularities in the axial direction that extend along the circumferential direction of the cylindrical shape of the nut 50. Specifically, the nut-side engagement portion 52 is formed by convex portions that extend radially inward from the inner surface of the nut 50, and these convex portions are arranged in a line along the longitudinal direction of the nut 50, spaced apart from each other in the longitudinal direction of the nut 50.

[0043] Furthermore, the axial pitch of the repeating grooves and protrusions on the nut-side meshing portion 52 is the same as the axial pitch of the grooves and protrusions on the roller-side meshing portion 32. This allows the nut-side meshing portion 52 to mesh with the roller-side meshing portion 32 of the roller 30. In other words, the radially inwardly protruding portion of the nut-side meshing portion 52 fits into the space between the protrusions on the roller-side meshing portion 32, and the radially outwardly protruding portion of the roller-side meshing portion 32 fits into the space between the protrusions on the nut-side meshing portion 52, thereby enabling the nut-side meshing portion 52 to mesh with the roller-side meshing portion 32.

[0044] As described above, the roller-side meshing portion 32 and the nut-side meshing portion 52 have repeating axial irregularities formed along the circumferential direction of the roller 30 and nut 50, respectively. Therefore, when they are meshed together, axial force can be transmitted between the roller-side meshing portion 32 and the nut-side meshing portion 52. In other words, the roller 30 and the nut 50 can transmit axial force between them through the meshing of the roller-side meshing portion 32 and the nut-side meshing portion 52.

[0045] In this process, both the roller-side meshing portion 32 and the nut-side meshing portion 52 have repeating axial irregularities formed along the circumferential direction of the roller 30 and nut 50. Therefore, when axial force is transmitted between the roller 30 and the nut 50 via the meshing roller-side meshing portion 32 and the nut-side meshing portion 52, even when the roller 30 and the nut 50 rotate relative to each other around the central axis of the roller 30 and the central axis of the nut 50, the relative positional relationship in the axial direction does not change, making it possible to transmit axial force between the roller 30 and the nut 50.

[0046] The inner diameter of the large-diameter portion 51 formed on the inner circumferential surface of the nut 50 is larger than the diameter of the portion of the nut-side engagement portion 52 that is recessed radially outward. More specifically, the inner diameter of the large-diameter portion 51 formed on the nut 50 is larger than the sum of the diameter of the shaft 20 and twice the diameter of the roller 30.

[0047] Furthermore, the position where the large-diameter portion 51 is located in the axial direction of the nut 50 is different from the position where the nut-side engagement portion 52 is located in the axial direction of the nut 50. Specifically, the large-diameter portion 51 is formed from one end of the nut 50 in the axial direction to a position near the center of the nut 50 in the axial direction. In this embodiment, the length of the large-diameter portion 51 in the axial direction of the nut 50 is approximately the same as the combined length of the roller-side engagement portion 32 and the intermediate support portion 35 in the axial direction of the roller 30.

[0048] The length of the nut-side engagement portion 52 of the nut 50 in the axial direction is approximately the same as the length of the roller-side engagement portion 32 of the roller 30 in the axial direction. The nut-side engagement portion 52 is formed from the end of the large-diameter portion 51 located near the center of the nut 50 in the axial direction, toward the opposite side of the side where the large-diameter portion 51 is located in the axial direction. The nut-side engagement portion 52, which is formed toward the opposite side of the side where the large-diameter portion 51 is located in the axial direction, does not extend to the end of the nut 50, and the end of the nut-side engagement portion 52 in the axial direction is located near the end of the nut 50.

[0049] Since the nut 50 is formed in this manner, when the shaft 20 and the roller 30 are positioned inside the nut 50, the roller 30 is positioned such that the side where the roller-side threaded portion 31 is located faces the large-diameter portion 51 of the nut 50, and the side where the roller-side meshing portion 32 is located faces the nut-side meshing portion 52 of the nut 50.

[0050] Furthermore, the roller 30 is positioned such that the axial positions of the roller-side threaded portion 31 and the intermediate support portion 35 are located in the area where the large-diameter portion 51 of the nut 50 is positioned, and the axial position of the roller-side meshing portion 32 is located in the area where the nut-side meshing portion 52 of the nut 50 is positioned. Therefore, the roller 30 positioned inside the nut 50 is positioned such that the roller-side meshing portion 32 of the roller 30 meshes with the nut-side meshing portion 52 of the nut 50. Inside the nut 50, multiple rollers 30 are arranged in these configurations, side by side in the circumferential direction inside the nut 50.

[0051] Furthermore, the shaft 20 is positioned such that the side with the flange portion 22 is located on the side with the large diameter portion 51 of the nut 50, or the side with the roller-side threaded portion 31 of the roller 30. When the shaft 20 and the multiple rollers 30 are positioned inside the nut 50, the multiple rollers 30 are arranged around the shaft 20 such that the roller-side threaded portion 31 of each roller engages with the shaft-side threaded portion 21 of the shaft 20.

[0052] In this configuration, the roller-side meshing portion 32 of each roller 30 is spaced radially outward from the shaft 20. That is, the rollers 30 are arranged around the shaft 20 with a gap between the roller-side meshing portion 32 and the shaft-side threaded portion 21.

[0053] Multiple rollers 30 positioned inside the nut 50 are held by a retainer 40 positioned inside the nut 50 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.

[0054] 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 large diameter portion 51 of the nut 50, and slightly smaller than the inner diameter of the large diameter portion 51, and an inner diameter approximately the same as the outer diameter of the shaft-side threaded portion 21 of the shaft 20, and slightly larger than the outer diameter of the shaft-side threaded portion 21. 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 outer circumferential surface toward the inside 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.

[0055] 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 a position that is the inner circumference of the annularly formed side wall portion 41 toward the radially outward 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.

[0056] 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.

[0057] 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 50 at multiple positions.

[0058] 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.

[0059] The large-diameter portion 51 formed on the nut 50 has an inner diameter that is approximately the same as the outer diameter of the retainer 40, and is slightly larger than the outer diameter of the retainer 40. When multiple rollers 30 are placed inside the nut 50 with the rollers 30 supported by the retainer 40, the retainer 40 supporting the rollers 30 is positioned inside the large-diameter portion 51 of the nut 50.

[0060] The retainer 40, which holds the multiple rollers 30, has an outer diameter smaller than the inner diameter of the large-diameter portion 51. Therefore, while positioned inside the large-diameter portion 51, it can rotate in the circumferential direction of the nut 50 and shaft 20. As a result, by positioning the retainer 40 inside the large-diameter portion 51 of the nut 50 while supporting the multiple rollers 30, the multiple rollers 30 can be supported as a single unit, allowing for free movement in the circumferential direction of the shaft 20.

[0061] Furthermore, the retainer 40 has multiple opening holes 43 formed on its outer 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 portions 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 outward from the retainer 40 through the opening holes 43.

[0062] A nut cover 60 is placed on a nut 50 that has a shaft 20 and a roller 30 positioned inside it, as shown above. The nut cover 60 is positioned on the end of the roller 30 positioned inside the nut 50 that has a roller-side meshing portion 32 located at it, in the axial direction. In other words, the nut cover 60 is positioned at the end of the roller 30 positioned inside the nut 50 that has a roller-side meshing portion 32 located at it, in the axial direction. The nut cover 60 is formed in a substantially disc shape, and its outer diameter is substantially the same as the inner diameter of the end of the nut 50 on which the nut cover 60 is positioned. The nut cover 60 formed in this way is pressed into the inside of the nut 50, thereby closing the end of the nut 50 on the side where the roller-side meshing portion 32 of the roller 30 positioned inside the nut 50 is located.

[0063] Furthermore, the nut cover 60 has a rolling portion 61 that contacts the outer circumferential surface near the end of the roller 30 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 located at the end on the roller-side threaded portion 31 side in the axial direction, and the rolling portion 61 of the nut cover 60 contacts the outer circumferential surface of the shaft end 37 on the roller-side meshing portion 32 side of the roller 30.

[0064] The rolling portion 61 is formed on the side of the disc-shaped nut cover 60 that faces the inside of the nut 50, and is formed in a substantially cylindrical shape, with its axis protruding inward from the nut 50 in a direction that coincides with the axis of the disc, which is the shape of the nut cover 60. The outer diameter of the cylindrical rolling portion 61 is formed such that the radius of the rolling portion 61 is the distance of the smallest radial distance from the central axis of the nut 50 or the central axis AX of the shaft 20 to the shaft end 37 of the roller 30, which is supported by the retainer 40 and positioned inside the nut 50. As a result, the nut cover 60 positioned at the end of the nut 50 has the outer surface of the rolling portion 61 in contact with the outer surface of the shaft end 37 of the roller 30 from the inside in the radial direction of the shaft 20.

[0065] 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, rotational force is input to the shaft 20, and a linear force is output from the nut 50 based on the rotational force input to the shaft 20. 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 shaft 20.

[0066] When connecting the power source to the shaft 20 of the planetary roller screw 10, the drive shaft of the power source is fitted into the fitting hole 24 formed in the shaft 20. As a result, power from the power source is transmitted to the shaft 20 of the planetary roller screw 10, and the planetary roller screw 10 operates as the shaft 20 rotates due to the power from the power source.

[0067] The shaft 20 has a shaft-side threaded portion 21 formed on its outer circumference, and the roller-side threaded portion 31 formed on the roller 30, which is arranged around the shaft 20, engages with the shaft-side threaded portion 21. Therefore, when the shaft 20 rotates, the rotational force of the shaft 20 is transmitted from the shaft-side threaded portion 21 to the roller-side threaded portion 31, and the roller 30 rotates due to the rotational force of the shaft 20 transmitted to the roller 30 via the shaft-side threaded portion 21 and the roller-side threaded portion 31.

[0068] Since the rotation of the shaft 20 is transmitted to the roller 30 by the meshing of the shaft-side threaded portion 21 and the roller-side threaded portion 31, when the roller 30 rotates due to the rotational force transmitted from the shaft 20, the roller 30 rotates in the opposite direction to the rotation of the shaft 20. The multiple rollers 30 arranged around the shaft 20 each rotate in the opposite direction to the rotation of the shaft 20 as the rotational force from the shaft 20 is transmitted through the meshing of the roller-side threaded portion 31 and the shaft-side threaded portion 21 of each roller 30.

[0069] Furthermore, the multiple rollers 30 are arranged around the shaft 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 50 and the shaft 20. In other words, the multiple rollers 30, which are held by the retainer 40 and arranged around the shaft 20, can revolve around the shaft 20 in the circumferential direction.

[0070] Therefore, when the rotation of the shaft 20 is transmitted to the multiple rollers 30, causing each roller 30 to rotate in the opposite direction to the rotation of the shaft 20, the multiple rollers 30 rotate on their own axes while revolving around the central axis AX of the shaft 20 together with the retainer 40 in the circumferential direction of the shaft 20. Since the revolving of the multiple rollers 30 is also caused by the transmission of force in the direction of rotation of the shaft 20, the revolving of the multiple rollers 30 rotates in the same direction as the rotation of the shaft 20.

[0071] 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 in the circumferential direction of the shaft 20 relative to the axial direction of the roller 30 is suppressed. Furthermore, each roller 30 rotates while its tilt in the radial direction of the shaft 20 is suppressed, because the rolling portion 61 of the nut cover 60 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 shaft 20.

[0072] Here, both the shaft-side threaded portion 21 and the roller-side threaded portion 31, which transmit the rotational force of the shaft 20 to the multiple rollers 30, are formed in a helical shape. Furthermore, the lead angle of the shaft-side threaded portion 21 is larger than the lead angle of the roller-side threaded portion 31. Therefore, when the rotational force of the shaft 20 is transmitted to the rollers 30 while the rollers rotate via the shaft-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 shaft-side threaded portion 21 and the lead angle of the roller-side threaded portion 31.

[0073] In this case, the amount of axial movement of the roller 30 is significantly smaller than the amount of rotation of the shaft 20. In other words, the roller 30 moves axially relative to the rotation of the shaft 20 due to the transmission of rotation by the shaft-side threaded portion 21 and the roller-side threaded portion 31, and the difference between the lead angle of the shaft-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 shaft 20. In other words, the roller 30 moves axially with a large reduction ratio relative to the rotation of the shaft 20, and consequently moves with a large thrust in the axial direction.

[0074] Multiple rollers 30 rotate around their respective axes and move axially due to the difference in lead angles between the shaft-side threaded portion 21 and the roller-side threaded portion 31. The rollers 30 engage with the nut 50 through a roller-side engagement portion 32 and a nut-side engagement portion 52. Therefore, when multiple rollers 30 rotate and move axially toward the side where the nut cover 60 is positioned due to a force transmitted from the shaft 20, the force causing the rollers 30 to move axially is transmitted to the nut 50 via the transmission from the roller-side engagement portion 32 to the nut-side engagement portion 52.

[0075] 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 nut 50 via the roller-side meshing portion 32 and the nut-side meshing portion 52, and the nut 50, together with the multiple rollers 30 and the retainer 40, moves relative to the shaft 20 toward the side where the nut cover 60 is located due to the force transmitted in this manner.

[0076] In this process, the rollers 30, which move axially as the shaft 20 rotates, move with a large thrust. Therefore, the nuts 50, which move axially relative to the shaft 20 along with the multiple rollers 30, also move axially relative to the shaft 20 with a large thrust.

[0077] When moving the nut 50 relative to the shaft 20 by reversing its axial direction of movement, the rotation direction of the shaft 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 shaft 20, is also reversed, and therefore the direction of the axial relative movement of the roller 30 with respect to the shaft 20 is also reversed. That is, the roller 30 moves relative to the shaft 20 in the direction opposite to the side on which the nut cover 60 is located in the axial direction. Consequently, the direction of movement of the nut 50 relative to the shaft 20, which moves together with the roller 30, is also reversed, and it moves relative to the shaft 20 in the direction opposite to the side on which the nut cover 60 is located in the axial direction.

[0078] As described above, the planetary roller screw 10 can output a large linear thrust force from the nut 50 from the rotational force input to the shaft 20, thereby converting rotational force into linear force. For example, when the force output from the nut 50 is used as a pressing force to be applied to any member, a large pressing force can be applied by using the large linear force generated when the nut 50 moves axially relative to the shaft 20 as the pressing force.

[0079] As described above, in the planetary roller screw 10 according to this embodiment, the rotation of the shaft 20 is transmitted to the roller 30 by the roller-side threaded portion 31 that meshes with the shaft-side threaded portion 21. As a result, the rotation of the shaft 20 can be transmitted from the shaft 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 nut 50 can be transmitted by the roller-side meshing portion 32 and the nut-side meshing portion 52, which have circumferentially extending grooves and protrusions, respectively. Therefore, a large axial force from the roller 30 to the nut 50 can be transmitted without hindering the revolution of the roller 30 around the central axis AX of the shaft 20.

[0080] Thus, when the shaft 20 rotates, a large axial force is transmitted from the roller 30 to the nut 50, and the nut 50 moves relative to the shaft 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 shaft 20 from the power source into a large linear force through the axial movement of the nut 50.

[0081] In this configuration, the roller 30, positioned between the shaft 20 and the nut 50 and rotating in the axial direction as the shaft 20 rotates, is rotatably 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 shaft 20, the retainer 40, which supports the roller 30 at multiple positions, prevents the roller 30 from tilting toward the circumferential direction of the shaft 20 relative to its central axis.

[0082] 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 shaft 20. If the roller 30 tilts toward the circumferential direction of the shaft 20, the roller 30 will also tilt in relation to the direction of movement when the nut 50 moves relative to the shaft 20 in the axial direction. When the roller 30 tilts toward the shaft 20 in this way, the resistance between the shaft 20 and the nut 50 and the roller 30 increases when the roller 30 rotates or revolves, thus reducing the transmission efficiency when the rotation of the shaft 20 is transmitted from the shaft 20 to the nut 50 via the roller 30.

[0083] In contrast, in the planetary roller screw 10 according to this embodiment, each roller 30 is rotatably 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 shaft 20 is suppressed. This suppresses the increase in resistance between the shaft 20 and the nut 50 and the roller 30 caused by the tilting of the roller 30 when the roller 30 rotates or revolves, and suppresses the decrease in transmission efficiency when the rotation of the shaft 20 is transmitted from the shaft 20 to the nut 50 via the roller 30. As a result, the decrease in transmission efficiency when converting rotational force into linear force can be suppressed.

[0084] 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 shaft 20 is transmitted to the roller 30 via the shaft-side threaded portion 21 and the roller-side threaded portion 31, a force that tilts the roller 30 toward the circumferential direction of the shaft 20 also acts on the roller 30.

[0085] 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. This allows the retainer 40 to suppress the tilt of the roller-side threaded portion 31 even when a force acts on the roller-side threaded portion 31 that tilts the roller 30 in the circumferential direction of the shaft 20. As a result, the retainer 40 can support the roller 30 while suppressing its tilt, thereby suppressing the increase in resistance between the shaft 20, nut 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.

[0086] Furthermore, since the nut 50 has a nut cover 60 on the side where the roller-side meshing portion 32 is located, the nut cover 60 has a rolling portion 61 that contacts the outer circumferential surface of the shaft end portion 37 of the roller 30 from the inside in the radial direction of the shaft 20, the rolling portion 61 of the nut cover 60 can suppress the tilting of the roller 30 toward the radial direction of the shaft 20. This suppresses the increase in resistance between the shaft 20 and the nut 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.

[0087] 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 shaft 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 providing a separate component from the roller 30 to transmit the force of the roller 30 moving axially to the nut 50. Consequently, the increase in the number of parts of the planetary roller screw 10 can be suppressed, and the planetary roller screw 10 can be made more compact.

[0088] Furthermore, since the screw portion 21 on the shaft side and the screw portion 31 on the roller side have opposite helical directions, the rotation of the shaft 20 is transmitted to the roller 30 via the screw portion 21 and the roller side, allowing the roller 30 to rotate in the opposite direction to the rotation of the shaft 20. This allows the roller 30 to move axially while rotating in the opposite direction to the rotation of the shaft 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.

[0089] Furthermore, since the lead angles of the shaft-side threaded portion 21 and the roller-side threaded portion 31 are different, rotating the shaft 20 allows the roller 30 to move axially relative to the shaft 20 according to the difference in lead angles between the shaft-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 shaft 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.

[0090] Next, an example of the application of the planetary roller screw 10 according to the embodiment will be described. Figure 5 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 5. The electromechanical brake 80 shown in Figure 5 is mounted on a vehicle as a braking device that generates braking force in a moving vehicle (not shown). The electromechanical brake 80 includes 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.

[0091] 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.

[0092] 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.

[0093] The brake caliper 90 comprises 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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 shaft 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.

[0102] 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 shaft 20, which rotates due to the driving force from the motor 71, is transmitted from the shaft-side threaded portion 21 to the roller-side threaded portion 31, and also moves relative to the shaft 20 in the axial direction. The nut 50 also moves relative to the shaft 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 nut-side meshing portion 52. 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.

[0103] 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 a nut 50 from the planetary roller screw 10. That is, the linear force of the nut 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.

[0104] 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.

[0105] In the planetary roller screw 10, a plurality of rollers 30 supported by a retainer 40 are arranged around a shaft 20, with the roller-side threaded portion 31 of each roller 30 engaging with the shaft-side threaded portion 21. The shaft 20 and the plurality of rollers 30 are positioned inside a nut 50 used as a piston 96 in an electromechanical brake 80. Thus, the planetary roller screw 10, with the shaft 20 and the plurality of rollers 30 positioned inside the nut 50, is positioned in the caliper body 91 of the brake caliper 90 by placing the nut 50 in a housing hole 92 formed in the caliper body 91.

[0106] In other words, the housing hole 92 formed in the caliper body 91 has an inner diameter approximately the same as the outer diameter of the nut 50, and the nut 50 of the planetary roller screw 10 is positioned to move axially inside the housing hole 92. In this case, the nut cover 60 that is positioned on the nut 50 of the planetary roller screw 10 is located on the side where the inner brake pad 98a is located, and the nut cover 60 is positioned in the housing hole 92 in a direction facing the inner brake pad 98a.

[0107] Furthermore, a groove 55 extending in the axial direction (see Figure 4) is formed on the outer circumferential surface of the nut 50, and a projection (not shown) that fits into the groove 55 of the nut 50 is formed on the inner circumferential surface of the housing hole 92 formed in the caliper body 91. As a result, when the nut 50, 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 55 of the nut 50 and the projection of the housing hole 92 come into contact, thereby restricting relative rotation in the circumferential direction. Therefore, the nut 50, 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.

[0108] In the caliper body 91, with the planetary roller screw 10 positioned in the housing hole 92, a flange support portion 94 is formed on the flange portion 22 formed on the shaft 20, on the side opposite to the side where the nut 50 is located. The flange support portion 94 has a hole formed therein, the inner diameter of which is slightly larger than the outer diameter of the shaft 20, and the shaft 20 is positioned by passing through this hole in the flange support portion 94. At this time, the flange portion 22 formed on the shaft 20 is positioned between the flange support portion 94 of the caliper body 91 and the nut 50 in the axial direction of the shaft 20.

[0109] A shaft-side thrust bearing 75 is positioned on the flange portion 22 formed on the shaft 20, on the side opposite to the side where the nut 50 is located in the axial direction of the shaft 20, to receive axial force from the shaft 20. That is, the shaft-side thrust bearing 75 is positioned between the flange portion 22 of the shaft 20 and the flange support portion 94 of the caliper body 91.

[0110] The shaft-side thrust bearing 75 is capable of receiving the axial load acting between the flange portion 22 of the shaft 20 and the flange support portion 94 of the caliper body 91, while allowing relative rotation between the flange portion 22 and the flange support portion 94 around the central axis AX of the shaft 20. For example, a thrust needle bearing can be used for the shaft-side thrust bearing 75.

[0111] In the electromechanical brake 80, the motor 71 used as a power source is inserted into a through hole 23 formed in the shaft 20 of the planetary roller screw 10, and the drive shaft 72 is fitted into a fitting hole 24 provided in the through hole 23. As a result, the drive shaft 72 of the motor 71 is connected to the shaft 20 of the planetary roller screw 10, and it becomes possible to apply driving force to the shaft 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 generated by the motor 71.

[0112] Furthermore, since the motor 71 is connected to the shaft 20 by inserting the drive shaft 72 into the through hole 23 of the shaft 20, the shaft 20 and the motor 71 are arranged coaxially.

[0113] 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.

[0114] 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 shaft 20 of the planetary roller screw 10 rotates together with the drive shaft 72 of the motor 71.

[0115] When the shaft 20 rotates, the planetary roller screw 10 causes the roller 30 to rotate on its own axis and move relative to the shaft 20 in the axial direction, and as the roller 30 moves relative to the shaft 20 in the axial direction, the nut 50 also moves relative to the shaft 20 in the axial direction.

[0116] For example, if the roller 30, which transmits the rotation of the shaft 20, moves relative to the shaft 20 in the axial direction away from the motor 71, the nut 50, which moves axially with the roller 30, also moves relative to the shaft 20 in the axial direction away from the motor 71. In this case, the nut 50 moves relative to the caliper body 91 on the side where the nut cover 60 is located by moving axially within the housing hole 92 formed in the caliper body 91.

[0117] The nut 50, which moves relative to the caliper body 91 on the side where the nut cover 60 is located, applies 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.

[0118] At that time, the roller 30, which moves axially as the shaft 20 rotates, moves with a large thrust, so the pressing force of the nut 50 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 50 in the housing hole 92, moves in the opposite direction to the direction in which the nut 50 applies pressing force to the inner brake pad 98a due to the reaction force when the nut 50 applies pressing force to the inner brake pad 98a.

[0119] In other words, when the nut 50 is in contact with the inner brake pad 98a and a pressing force is applied to the inner brake pad 98a, the nut 50 cannot move in the direction in which the inner brake pad 98a is located. If the nut 50 moves relative to the caliper body 91 toward the side in which the inner brake pad 98a is located in this state, the force that causes the nut 50 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 caliper body 91 applies a pressing force from the nut 50 to the inner brake pad 98a.

[0120] Since the caliper body 91 is mounted so as to be able to move 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 that causes the nut 50 to move relative to it, moves relative to the caliper base 95 in the opposite direction to the direction in which the nut 50 applies pressure to the inner brake pad 98a.

[0121] 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.

[0122] 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.

[0123] 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 shaft 20 on the side where the nut cover 60 is located, a force acts on the shaft 20 in the opposite direction to the direction in which the nut cover 60 is located in the axial direction. In this embodiment, since the shaft-side thrust bearing 75 is positioned between the flange portion 22 formed on the shaft 20 and the flange support portion 94 of the caliper body 91, the shaft 20 can be rotated while the shaft-side thrust bearing 75 receives the force acting on the shaft 20 in the axial direction.

[0124] 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 shaft 20, which rotates due to the driving force from the motor 71, is transmitted to the rollers 30, causing the rollers 30 to rotate and move axially relative to the shaft 20. Along with the axial movement of the rollers 30, the nut 50 also moves axially relative to the shaft 20.

[0125] The nut 50, which moves in the axial direction, applies a pressing force to the brake pad 98 in a direction that presses it against the brake rotor 100 due to its relative axial movement with respect to the shaft 20. As a result, the electromechanical brake 80 can increase the frictional force between the brake pad 98 and the brake rotor 100, thereby generating a braking force.

[0126] 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 shaft 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 shaft 20 is transmitted, also rotates in the opposite direction to the direction of rotation when the braking force is generated.

[0127] 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 shaft 20 to the side opposite to the side where the nut cover 60 is located, that is, to the side where the flange portion 22 of the shaft 20 is located. When the roller 30 moves relative to the shaft 20 toward the side where the flange portion 22 of the shaft 20 is located, the nut 50 also moves relative to the shaft 20 in the same direction along with the roller 30. In other words, the nut 50 moves relative to the caliper body 91 toward the side where the flange portion 22 of the shaft 20 is located by moving axially within the housing hole 92 formed in the caliper body 91.

[0128] The nut 50, which moves relative to the caliper body 91 on the side where the flange portion 22 of the shaft 20 is located, moves in a direction away from the inner brake pad 98a in the thickness direction of the brake rotor 100. As a result, the pressing force applied from the nut 50 to the inner brake pad 98a is reduced, and the pressing force applied from the inner brake pad 98a to the brake rotor 100 is reduced.

[0129] When the pressing force applied from the nut 50 to the inner brake pad 98a is reduced, the caliper body 91, which holds the nut 50 in the housing hole 92, 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 claw 93 to the outer brake pad 98b.

[0130] 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.

[0131] 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 shaft 20 of the planetary roller screw 10. Therefore, the rotation of the shaft 20, which is rotated by the driving force of the motor 71, can be transmitted from the shaft 20 to the roller 30 with a large reduction ratio. This makes it possible to increase the force exerted when the roller 30 moves in the axial direction, and also increases the axial thrust of the nut 50, which moves in the axial direction together with the roller 30. Consequently, the rotational force input from the motor 71 to the shaft 20 can be converted into a large linear force by the axial movement of the nut 50 and output.

[0132] 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 shaft 20 is suppressed. This suppresses the increase in resistance between the shaft 20 and the nut 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 shaft 20, which rotates due to the driving force of the motor 71, is transmitted from the shaft 20 to the nut 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.

[0133] Furthermore, the electromechanical brake 80 according to this embodiment includes a planetary roller screw 10, a motor 71 that applies driving force to the shaft 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 shaft 20, which is rotated by the driving force of the motor 71, from the shaft 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 nut 50, which moves in the axial direction together with the roller 30. This allows the rotational force input from the motor 71 to the shaft 20 to be converted into a large linear force by the axial movement of the nut 50 and output, thereby ensuring sufficient pressing force applied from the nut 50 to the brake pad 98.

[0134] Furthermore, in the electromechanical brake 80, the rollers 30 of the planetary roller screw 10 are rotatably supported at multiple positions by a single retainer 40. This prevents the rollers 30 from tilting toward the circumferential direction of the shaft 20 even when the rollers 30 are revolving. As a result, the increase in resistance between the shaft 20 and the nut 50 and the rollers 30, caused by the tilt of the rollers 30 when the rollers 30 rotate or revolve, can be suppressed. Consequently, the decrease in transmission efficiency when the rotation of the shaft 20, which is driven by the motor 71, is transmitted from the shaft 20 to the nut 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.

[0135] Furthermore, the electromechanical brake 80 according to this embodiment can transmit the driving force of the motor 71 from the shaft 20 to the roller 30 with a large reduction ratio, and the force exerted when the roller 30 moves axially can be increased, thereby increasing the thrust of the nut 50 which moves axially together with the roller 30. As a result, a large pressing force can be applied when the nut 50 applies the pressing force to press 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 omitting the reduction gear. As a result, the electromechanical brake 80 can be miniaturized, that is, the braking device can be made smaller.

[0136] Furthermore, multiple rollers 30 are arranged around the shaft 20 in the circumferential direction, and the multiple rollers 30 are supported collectively by the retainer 40 so as to be movable in the circumferential direction of the shaft 20. Therefore, when the rotational force of the shaft 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 nut 50 moves relative to the shaft 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.

[0137] Furthermore, since the shaft 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 along the shaft 20, thereby reducing the size of the electromechanical brake 80 in the radial direction of the shaft 20. As a result, the braking device can be miniaturized.

[0138] [Differentiation] In the embodiment described above, the portion of the planetary roller screw 10 on the side where the nut cover 60 is placed is closed off by the nut cover 60, but the portion on the side where the nut cover 60 is placed does not need to be closed off.

[0139] Figure 6 is a cross-sectional view showing a modified example of the planetary roller screw 10 according to the embodiment, in which the nut cover 60 has an insertion hole 65. The nut cover 60, which is positioned on one end of the nut 50 in the axial direction, may have an insertion hole 65 formed near the center of the nut cover 60 in the radial direction, penetrating the nut 50 in the axial direction, i.e., in the thickness direction of the nut cover 60, as shown in Figure 6. In this case, the inner diameter of the insertion hole 65 is formed to be slightly larger than the outer diameter of the shaft-side threaded portion 21 on the shaft 20.

[0140] Thus, in the example shown in Figure 6, where an insertion hole 65 is formed in the nut cover 60, the length of the shaft 20 is longer than the length of the shaft 20 in the embodiment described above, and the shaft 20 is positioned through the insertion hole 65 of the nut cover 60. That is, by being inserted through the insertion hole 65, the shaft 20 is positioned from the inside to the outside of the nut 50, which is partitioned by the nut cover 60.

[0141] In the shaft 20 formed to be longer than the shaft 20 in the embodiment, the shaft-side threaded portion 21 is formed even in the portion that is longer compared to the embodiment. In other words, the shaft-side threaded portion 21 is formed on the outer circumferential surface of the shaft 20 from near the portion where the flange portion 22 is located on the shaft 20 to the end of the shaft 20 in the axial direction, and as the length of the shaft 20 increases, the range in which the shaft-side threaded portion 21 is located in the axial direction also increases.

[0142] As a result, in the example of Figure 6, the length over which the roller 30, which has a roller-side threaded portion 31 that engages with the shaft-side threaded portion 21, can move relative to the shaft 20 in the axial direction when the shaft 20 rotates is longer compared to the embodiment described above. That is, in the example of Figure 6, the amount of linear stroke when the shaft 20 and the nut 50 move relative to each other in the axial direction is larger compared to the embodiment described above.

[0143] If it is not essential to close the end of the nut 50 with the nut cover 60, the length of the shaft 20 can be increased by forming an insertion hole 65 in the nut cover 60 in this way, thereby increasing the stroke amount in the linear direction. Therefore, it is possible to apply this to equipment and devices that require a large stroke amount, while suppressing the decrease in transmission efficiency when converting rotational force into linear force.

[0144] Furthermore, in the electromechanical brake 80 described above, the motor 71's drive shaft 72 is connected to the shaft 20 of the planetary roller screw 10, but a reduction gear may be interposed between the motor 71 and the shaft 20 of the planetary roller screw 10. The planetary roller screw 10 can convert rotational force into linear force with a large reduction ratio, but 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. As a result, the rotational force output from the motor 71 can be converted into a larger linear force, applying a larger pressing force to the brake pad 98, and thus a greater braking force can be obtained.

[0145] 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.

[0146] 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 size of the shaft 20 and the rollers 30, and the magnitude of the thrust when the rollers 30 are moved axially by the force in the rotational direction of the shaft 20.

[0147] 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]

[0148] 10 Planetary roller screws 20 shafts 21 Shaft-side threaded section 22 Flange section 23 Through hole 24 Fitting holes 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 nuts 51 Large diameter section 52 Nut-side engagement part 60 Nut Cover 61 Rolling part 70 Linear Actuator 71 Motor 72 Drive shaft 75 Shaft-side thrust bearing 80 Electromechanical brake 90 Brake caliper 91 Caliper body 92 Intake holes 94 Flange support section 95 Caliper Base 96 Pistons 98 Brake Pads 100 Brake rotors 150 ECU 160 Brake pedal 161 Brake Sensor

Claims

1. A shaft having a shaft-side threaded portion formed in a spiral shape on its outer surface, A roller having a round bar shape extending along the axial direction of the shaft and a roller-side threaded portion that engages with the shaft-side threaded portion, and a roller-side engagement portion that is positioned at a different location from the roller-side threaded portion in the axial direction and has repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, A nut having a cylindrical shape, with the shaft and roller arranged inside, and having a nut-side meshing portion that meshes with the roller-side meshing portion, with the inner circumferential surface having repeating axial irregularities that extend along the circumferential direction of the inner circumferential surface. Equipped with, Multiple rollers are arranged around the shaft in the circumferential direction of the shaft. 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. A nut cover is provided on the end of the roller where the roller-side engagement portion is located. The planetary roller screw according to claim 2, wherein the nut cover has rolling portions that contact the outer circumferential surface of the roller near the end 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 screw portion on the shaft side and the screw portion on the roller side have spiral directions opposite to each other.

6. A shaft having a shaft-side threaded portion formed in a spiral shape on its outer surface, A roller having a round bar shape extending along the axial direction of the shaft and a roller-side threaded portion that engages with the shaft-side threaded portion, and a roller-side engagement portion that is positioned at a different location from the roller-side threaded portion in the axial direction and has repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, A nut having a cylindrical shape, with the shaft and roller arranged inside, and having a nut-side meshing portion that meshes with the roller-side meshing portion, with the inner circumferential surface having repeating axial irregularities that extend along the circumferential direction of the inner circumferential surface. A planetary roller screw having, A motor that applies driving force to the aforementioned shaft, Equipped with, Multiple rollers are arranged around the shaft in the circumferential direction of the shaft. 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 shaft, which rotates due to the driving force from the motor, is transmitted from the shaft-side threaded portion to the roller-side threaded portion, and moves relative to the shaft in the axial direction. The nut is a linear actuator that moves relative to the shaft in the axial direction together with the roller when the axial movement of the roller is transmitted from the roller-side meshing portion to the nut-side meshing portion.

7. A shaft having a shaft-side threaded portion formed in a spiral shape on its outer surface, A roller having a round bar shape extending along the axial direction of the shaft and a roller-side threaded portion that engages with the shaft-side threaded portion, and a roller-side engagement portion that is positioned at a different location from the roller-side threaded portion in the axial direction and has repeating irregularities in the axial direction that extend along the circumferential direction of the round bar, A nut having a cylindrical shape, with the shaft and roller arranged inside, and having a nut-side meshing portion that meshes with the roller-side meshing portion, with the inner circumferential surface having repeating axial irregularities that extend along the circumferential direction of the inner circumferential surface. A planetary roller screw having, A motor that applies driving force to the aforementioned shaft, 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 around the shaft in the circumferential direction of the shaft. 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 shaft, which rotates due to the driving force from the motor, is transmitted from the shaft-side threaded portion to the roller-side threaded portion, and moves relative to the shaft in the axial direction. The nut moves relative to the shaft 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 nut-side meshing portion. The nut 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 shaft.

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