Ball screw device

Abstract

To provide a ball screw device suppressed in vibration of balls.SOLUTION: A ball screw device includes: a screw shaft rotatably supported; a nut through which the screw shaft penetrates and which is movable in an axial direction in parallel with the screw shaft; and a plurality of balls. The nut has a cylindrical nut main body, and a plurality of circulation portions for returning the ball that has moved one lead by one lead. One direction orthogonal to the axial direction is determined as a first orthogonal direction. A direction orthogonal to both of the axial direction and the first orthogonal direction is determined as a second orthogonal direction. The nut is supported tiltably on a virtual line extending in the first orthogonal direction as a center. An end face at one end of the nut main body is a pressing face. The pressing face is inclined toward the other side of the second orthogonal direction to be positioned at the other side in the axial direction when observed from the first orthogonal direction. The plurality of circulation portions have other end-side circulation portions closest to the other end of the nut main body. The other end-side circulation portions are disposed on positions excluding one side of the second orthogonal direction when observed from the screw shaft.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a ball screw device.

Background Art

[0002] A ball screw device is a device that efficiently converts rotational motion into linear motion or linear motion into rotational motion and is mounted on an actuator or the like. As shown in Patent Document 1 below, the ball screw device includes a screw shaft, a nut penetrated by the screw shaft, and a plurality of balls. A spiral outer peripheral raceway surface is provided on the outer peripheral surface of the screw shaft. A spiral inner peripheral raceway surface facing the outer peripheral raceway surface is provided on the inner peripheral surface of the nut. A spiral raceway is formed between the outer peripheral raceway surface and the inner peripheral raceway surface. A plurality of balls are arranged in the raceway. When the ball screw device operates, the balls move from one end of the raceway to the other end. The balls that have moved to the other end of the raceway circulate to one end of the raceway by a circulation part.

[0003] Examples of the circulation part for returning the balls that have moved one lead by one lead include an S-shaped groove formed on the inner peripheral surface of the nut and a collar assembled to the nut. When such a circulation part for returning one lead is used, the nut cannot support a radial load, specifically, a load in the direction in which the circulation part is arranged as viewed from the screw shaft. Therefore, a plurality of circulation parts are arranged dispersedly in the circumferential direction. As a result, the nut can support the screw shaft from all angles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, when a ball screw device is assembled into an actuator or the like, the screw shaft or nut may tilt due to various factors such as tolerances, weight, part precision, and misalignment. In other words, a moment load may be applied unintentionally. Furthermore, even outside of assembly, the screw shaft or nut may tilt (a moment load may be applied) due to external loads or vibrations. Hereinafter, the unintentional moment load generated by the assembly of a ball screw device will be referred to as the assembly moment load. Also, the circulation part located near the end of the nut will be referred to as the end-side circulation part.

[0006] In this case, the assembly moment load may increase the load acting on the balls rolling near the circulation section. In particular, excessive load may be placed on the balls rolling near the end-side circulation section among the multiple circulation sections. If the ball screw device operates under such conditions, the balls rolling near the end-side circulation section may vibrate, which is undesirable.

[0007] This disclosure has been made in view of the above, and aims to provide a ball screw device in which vibration of balls rolling near the end-side circulation section is suppressed even when an assembly moment load is applied. [Means for solving the problem]

[0008] To achieve the above objective, a ball screw device according to a first aspect of this disclosure comprises a screw shaft that is rotatably supported, a nut that passes through the screw shaft and is movable in an axial direction parallel to the screw shaft, and a plurality of balls disposed between the screw shaft and the nut. The nut has a cylindrical nut body and a plurality of circulation parts that return a ball that has moved one lead by one lead. One direction perpendicular to the axial direction is called the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is called the second orthogonal direction. The nut is supported so as to be tiltable about a virtual line extending in the first orthogonal direction. An end face provided at one end of the nut body is a pressing surface that presses against an object to be pressed. The pressing surface is inclined so as to be located in the other axial direction toward the other of the second orthogonal directions when viewed from the first orthogonal direction. The plurality of circulation parts have one-end side circulation parts located closest to one end of the nut body and other-end side circulation parts located closest to the other end of the nut body. The circulation portion at one end is positioned in a direction other than the other of the second orthogonal directions when viewed from the screw shaft. The circulation portion at the other end is positioned in a direction other than the other of the second orthogonal directions when viewed from the screw shaft.

[0009] The nut in this disclosure is supported so as to be able to tilt. Also, the pressing surface of the nut is inclined. Therefore, when the nut presses against an object, it receives a reaction force from the object and tilts. In other words, the reaction force directed toward the other axial direction is converted into a moment load. From the above, a moment load (hereinafter referred to as preload moment load) acts on the ball screw device of this disclosure. In addition, the nut in this disclosure tilts such that one end of the nut moves to the other in the second orthogonal direction, and the other end of the nut moves to one in the second orthogonal direction. As a result, among the multiple balls rolling near one end of the nut, the load on the ball rolling in the other in the second orthogonal direction as viewed from the screw axis increases. On the other hand, among the multiple balls rolling near the other end of the nut, the load on the ball rolling in one in the second orthogonal direction as viewed from the screw axis increases. Here, the one-end circulation part of this disclosure is located in a direction other than the other in the second orthogonal direction as viewed from the screw axis. Furthermore, the other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the screw axis. Therefore, even if a preload moment load is applied, the load on the balls rolling near the end-side circulation section (one end circulation section and the other end circulation section) does not increase. Moreover, according to the ball screw device of this disclosure, because a preload moment load is applied, even if an unintended assembly moment load is applied, the nut is less likely to tilt in the direction of the assembly moment load. In other words, even if an assembly moment is applied to the nut, the amount by which the nut tilts in the direction of the assembly moment is kept small. In other words, the amount by which the end-side circulation section approaches the screw axis is kept small. As a result, the load on the balls rolling near the end-side circulation section (one end circulation section and the other end circulation section) does not become excessive, and ball vibration is avoided.

[0010] Furthermore, in order to achieve the above objective, a ball screw device according to a second aspect of this disclosure comprises a nut that is cylindrical in shape around its own centerline and movable in a direction parallel to the centerline, a screw shaft that penetrates the nut and is rotatable around its own axis, and a plurality of balls disposed between the screw shaft and the nut. The nut has a cylindrical nut body and a plurality of circulation parts that return a ball that has moved one lead by one lead. One direction perpendicular to the direction of the centerline is defined as the first orthogonal direction. A direction perpendicular to both the direction of the centerline and the first orthogonal direction is defined as the second orthogonal direction. The axis is inclined so as viewed from the first orthogonal direction, from one end of the nut body toward the other end of the nut body, to be located in one of the second orthogonal directions. The plurality of circulation parts include an end-side circulation part located closest to one end of the nut body and an end-side circulation part located closest to the other end of the nut body. The end-side circulation part is located in a direction other than the other of the second orthogonal directions as viewed from the centerline. The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the center line.

[0011] According to this disclosure, the screw axis is inclined with respect to the center line of the nut. That is, with respect to the screw axis, the nut is inclined with respect to the screw axis, and a preload moment load is applied to the nut, similar to the ball screw device of the first embodiment. Furthermore, due to the inclination of the nut, the load on the ball rolling in the other direction in the second orthogonal direction as viewed from the screw axis increases among the multiple balls rolling near one end of the nut. On the other hand, the load on the ball rolling in one direction in the second orthogonal direction as viewed from the screw axis increases among the multiple balls rolling near the other end of the nut. Here, the one-end circulation section of this disclosure is located in a direction other than the other direction in the second orthogonal direction as viewed from the screw axis. Also, the other-end circulation section is located in a direction other than the one direction in the second orthogonal direction as viewed from the screw axis. Therefore, even if a preload moment load is applied, the load on the balls rolling near the end-side circulation section (one-end circulation section and other-end circulation section) does not increase. Furthermore, with the ball screw device of this disclosure, even if an unintended assembly moment load is applied, the amount by which the nut tilts in the direction of the assembly moment is kept small. Therefore, the load on the balls rolling near the end-side circulation section (one end circulation section and the other end circulation section) does not become excessive, and vibration of the balls is avoided.

[0012] Furthermore, in order to achieve the above objective, a ball screw device according to a third aspect of this disclosure comprises a screw shaft that is rotatably supported, a nut that passes through the screw shaft and is movable in an axial direction parallel to the screw shaft, and a plurality of balls disposed between the screw shaft and the nut. The nut has a cylindrical nut body and a plurality of circulation parts that return a ball that has moved one lead by one lead. One direction perpendicular to the axial direction is called the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is called the second orthogonal direction. The nut body has an outer circumferential surface centered on the axis of the screw shaft, an inner circumferential surface centered on a virtual line, and an inner circumferential raceway surface provided on the inner circumferential surface. The virtual line is inclined so as to be located on the other side of the second orthogonal direction, from one end of the nut body toward the other end of the nut body when viewed from the first orthogonal direction. The plurality of circulation parts have one-end side circulation parts located closest to one end of the nut body and other-end side circulation parts located closest to the other end of the nut body. The circulation portion at one end is positioned in a direction other than the other of the second orthogonal directions when viewed from the screw shaft. The circulation portion at the other end is positioned in a direction other than the other of the second orthogonal directions when viewed from the screw shaft.

[0013] According to this disclosure, the inner raceway surface is inclined with respect to the screw axis. That is, with respect to the screw axis, the nut is inclined with respect to the screw axis, and a preload moment load is applied to the nut, similar to the ball screw device of the first embodiment. Furthermore, due to the inclination of the nut, the load on the ball rolling in the other direction in the second orthogonal direction as viewed from the screw axis increases among the multiple balls rolling near one end of the nut. On the other hand, the load on the ball rolling in one direction in the second orthogonal direction as viewed from the screw axis increases among the multiple balls rolling near the other end of the nut. Here, the one-end circulation section of this disclosure is located in a direction other than the other direction in the second orthogonal direction as viewed from the screw axis. Also, the other-end circulation section is located in a direction other than the one direction in the second orthogonal direction as viewed from the screw axis. Therefore, even if a preload moment load is applied, the load on the balls rolling near the end-side circulation section (one-end circulation section and other-end circulation section) does not increase. Furthermore, with the ball screw device of this disclosure, even if an unintended assembly moment load is applied, the amount by which the nut tilts in the direction of the assembly moment is kept small. Therefore, the load on the balls rolling near the end-side circulation section (one end circulation section and the other end circulation section) does not become excessive, and vibration of the balls is avoided.

[0014] Furthermore, in the ball screw device described above, the one-end circulation section is positioned in one of the second orthogonal directions when viewed from the screw shaft (the center line).

[0015] According to the aforementioned ball screw device, due to the preload moment load, the load on the ball rolling in one of the second orthogonal directions from the screw axis is the smallest among the multiple balls rolling near one end of the nut. Therefore, with the above configuration, the load acting on the balls rolling near the circulation section on the one end is greatly reduced, and the vibration of the balls is reliably suppressed.

[0016] Furthermore, in the ball screw device described above, the other end circulation section is located in the other direction perpendicular to the second direction when viewed from the screw axis (the center line).

[0017] According to the ball screw device described above, due to the preload moment load, among the plurality of balls that roll closer to the other end of the nut, the load on the ball that rolls in the other direction of the second orthogonal direction as viewed from the screw shaft is the smallest. Therefore, according to the above configuration, the load acting on the ball that rolls near the circulation part on the other end side is greatly reduced, and the vibration of the ball is reliably suppressed.

Advantages of the Invention

[0018] According to the ball screw device of the present disclosure, even when an assembly moment load acts, the load acting on the ball that rolls near the circulation part on the end side does not become excessive, and the vibration of the ball is suppressed.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is a cross-sectional view taken axially of the brake caliper of Embodiment 1 in a state before operation. [Figure 2] FIG. 2 is a view of the nut of Embodiment 1 as viewed from the piston side. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the nut of Embodiment 1 taken axially. [Figure 4] FIG. 4 is an enlarged view of the nut of the brake caliper of Embodiment 1 during operation. [Figure 5] FIG. 5 is a cross-sectional view taken axially of the brake caliper of Embodiment 2 in a state before operation. [Figure 6] FIG. 6 is a cross-sectional view taken axially of the electric actuator according to the modified example. [Figure 7] FIG. 7 is a cross-sectional view taken axially of the nut and piston of the brake caliper of Embodiment 3.

Modes for Carrying Out the Invention

[0020] Embodiments for implementing the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by the content described in the following description. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and substantially identical ones. Furthermore, the constituent elements described below can be combined as appropriate.

[0021] (Embodiment 1) FIG. 1 is a cross-sectional view taken axially of the brake caliper of Embodiment 1 in a state before operation. As shown in FIG. 1, the brake device of Embodiment 1 is a brake caliper 100. The brake caliper 100 is a device that sandwiches a brake disk 101 that rotates with a wheel (not shown) between two brake pads 102 and 103 to apply a braking force to the wheel. In the embodiment, an example of applying the ball screw device of the present disclosure to the brake caliper 100 is given, but it may be applied to other devices such as a brake booster.

[0022] The brake caliper 100 includes a brake disk 101, two brake pads 102 and 103, a housing 120, a piston 40, and an electric actuator 104 that operates the piston 40.

[0023] The housing 120 is provided with a housing hole 121 that opens toward the brake pad 102. The piston 40 and the electric actuator 104 are housed in this housing hole 121. The housing hole 121 is formed in a cylindrical shape around a virtual line K1. This virtual line K1 extends in a direction orthogonal to the brake pad 102. The inner peripheral surface of the housing hole 121 has a small-diameter first wall surface 122 and a large-diameter second wall surface 123. The first wall surface 122 is provided closer to the brake pad 102 in the housing hole 121. The second wall surface 123 is provided on the opposite side of the brake pad 102 across the first wall surface 122.

[0024] The piston 40 is positioned inside the first wall surface 122. The piston 40 has a pressing portion 41 that contacts the brake pad 102, and a cylindrical portion 42 that extends from the pressing portion 41 in the direction opposite to the brake pad 102. The pressing portion 41 is formed in a disc shape around the imaginary line K1. The cylindrical portion 42 is formed in a cylindrical shape around the imaginary line K1. The outer circumferential surface of the cylindrical portion 42 faces the first wall surface 122. A minute gap is provided between the outer circumferential surface of the cylindrical portion 42 and the first wall surface 122. Therefore, the piston 40 is supported in the housing 120 so as to be slidable in a direction parallel to the imaginary line K1.

[0025] The electric actuator 104 includes a motor (not shown) that generates rotational motion, a reduction gear 110 that reduces the rotational motion, and a ball screw device 1 that converts the rotational motion into linear motion.

[0026] The reduction gear 110 is a planetary gear mechanism and is located inside the second wall surface 123. The reduction gear 110 comprises an input shaft 111, a sun gear 112, a ring gear 113, a plurality of planetary gears 114, a plurality of transmission shafts 115, and a carrier 116.

[0027] The rotational motion of the motor is input to the input shaft 111. The input shaft 111 is located coaxially with the virtual line K1. The sun gear 112 passes through the input shaft 111 and is fixed to the input shaft 111 in a non-rotatable manner. The ring gear 113 is an internal gear centered on the input shaft 111. The outer circumferential surface of the ring gear 113 is fitted into the second wall surface 123 of the housing 120.

[0028] The planetary gear 114 is positioned between the sun gear 112 and the ring gear 113. The planetary gear 114 also meshes with the sun gear 112 and the ring gear 113. The planetary gear 114 passes through the transmission shaft 115. Furthermore, the planetary gear 114 is rotatably supported around the transmission shaft 115.

[0029] The carrier 116 is an annular component centered on the imaginary line K1. The outer surface of the carrier 116 fits onto the inner ring of the bearing 117, and the carrier 116 is fixed so as not to fall off the inner ring of the bearing 117. The carrier 116 also has a flange that abuts against the inner ring of the bearing 117. Thus, the carrier 116 is fixed so as not to shift towards the sun gear 112. The outer ring of the bearing 117 is clamped between the stepped surface of the housing 120 and a retaining ring. As a result, the bearing 117 is fixed so as not to move in a direction parallel to the imaginary line K1. The transmission shaft 115 passes through the carrier 116 at a position eccentrically outward in the radial direction from the center.

[0030] The ball screw device 1 comprises a screw shaft 2, a nut 3, and a ball 4. The axis O1 of the screw shaft 2 is located coaxially with the imaginary line K1. Hereinafter, the direction parallel to the axis O1 of the screw shaft 2 will be referred to as the axial direction. Furthermore, within the axial direction, the direction in which the brake disc 101 is located, as viewed from the ball screw device 1, will be referred to as the first direction X1, and the direction opposite to the first direction X1 will be referred to as the second direction X2.

[0031] The screw shaft 2 comprises a power transmission unit 10 positioned inside the second wall surface 123 and a screw shaft body 11 positioned inside the first wall surface 122. The power transmission unit 10 penetrates the central part of the carrier 116. The power transmission unit 10 and the carrier 116 are spline-fitted. Therefore, the carrier 116 and the screw shaft 2 are connected in such a way that they do not rotate relative to each other.

[0032] The outer circumferential surface of the screw shaft body 11 is provided with an outer circumferential raceway surface 12 that extends in the helical direction. Furthermore, the screw shaft body 11 has a larger diameter than the power transmission unit 10. Therefore, a stepped surface facing the second direction X2 is provided between the power transmission unit 10 and the screw shaft body 11. This stepped surface abuts against the side surface of the carrier 116. Thus, the screw shaft 2 is fixed so as not to shift position in the second direction X2.

[0033] With the above configuration, when rotational motion is input to the input shaft 111, the sun gear 112 rotates around the axis O1. The planetary gear 114 rotates (rotates) around the transmission shaft 115 while also rotating (revolving) around the axis O1. As a result, the carrier 116 and the screw shaft 2 rotate around the axis O1. Furthermore, the rotational speed of the screw shaft 2 is slower than the rotational speed of the input shaft 111.

[0034] The nut 3 is positioned inside the first wall surface 122. The nut 3 has a nut body 20 and an S-shaped groove 21 which is a circulation section. In this embodiment, the circulation section is given as an S-shaped groove 21, but the circulation section of this disclosure may be a spool or other, and is not particularly limited.

[0035] Figure 2 is a view of the nut of Embodiment 1 from the piston side. As shown in Figure 2, the first wall surface 122 of the housing 120 is provided with two guide grooves 124 that extend in the axial direction. The two guide grooves 124 are arranged point-symmetrically with respect to the axis O1. That is, the two guide grooves 124 are arranged at a 180° interval with respect to the axis O1. Hereinafter, the direction in which the two guide grooves 124 are arranged when viewed from the screw shaft 2 will be referred to as the first orthogonal direction. The direction that is orthogonal to both the axial direction and the first orthogonal direction will be referred to as the second orthogonal direction.

[0036] The nut body 20 is formed in a cylindrical shape with respect to the axis O1. Two projections 23 are provided on the outer circumferential surface 22 of the nut body 20, projecting radially outward. The two projections 23 are arranged point-symmetrically with respect to the outer circumferential surface 22 with respect to the axis O1. In other words, the two projections 23 are arranged at a 180° interval with respect to the axis O1 and project in opposite directions. Furthermore, the direction in which the two projections 23 project is a first orthogonal direction. Therefore, the projections 23 are inserted into the guide groove 124. As a result, the nut 3 is supported by the housing 120 so that it can move freely in the axial direction (slidable) but cannot rotate around the axis O1.

[0037] Figure 3 is an enlarged cross-sectional view of the nut of Embodiment 1, cut in the axial direction. As shown in Figure 3, the projection 23 is circular when viewed from the first orthogonal direction. In other words, the projection 23 is formed in a cylindrical shape. As a result, the nut 3 can tilt around the projection 23, or in other words, around a virtual line extending in the first orthogonal direction. Also, the outer diameter of the nut body 20 is smaller than the inner diameter of the first wall surface 122. Therefore, a space S is provided between the outer circumferential surface 22 of the nut body 20 and the first wall surface 122, allowing the nut body 20 to tilt.

[0038] An inner circumferential raceway surface 25 is provided on the inner circumferential surface 24 of the nut body 20. The inner circumferential raceway surface 25 faces the outer circumferential raceway surface 12 of the screw shaft 2 (see Figure 1) and extends in the helical direction. The inner circumferential raceway surface 25 extends for one full turn (1 lead) in the helical direction. A raceway is formed between each inner circumferential raceway surface 25 and the outer circumferential raceway surface 12. Multiple balls 4 (see Figure 1) are arranged in each raceway.

[0039] The S-shaped groove 21 in this embodiment is an S-shaped groove surface formed on the inner circumferential surface 24 of the nut body 20 by forging. The S-shaped groove 21 connects one end and the other end of the inner circumferential raceway surface 25 in the helical direction. As a result, the ball 4 that has moved from one end of the raceway to the other circulates back to the one end of the raceway via the S-shaped groove 21.

[0040] In this embodiment, four inner circumferential raceway surfaces 25 and four S-shaped grooves 21 are provided. Therefore, there are also four raceways. Hereinafter, the four inner circumferential raceway surfaces 25 will be referred to as the first inner circumferential raceway surface 25a, the second inner circumferential raceway surface 25b, the third inner circumferential raceway surface 25c, and the fourth inner circumferential raceway surface 25d, in order from the first direction X1. Similarly, the four S-shaped grooves 21 will be referred to as the first S-shaped groove 21a, the second S-shaped groove 21b, the third S-shaped groove 21c (see Figure 2), and the fourth S-shaped groove 21d, in order from the first direction X1.

[0041] Furthermore, the first S-shaped groove 21a, which is located closest to the object being pressed (piston) among the four S-shaped grooves 21, in other words, closer to one end of the nut body 20, is sometimes referred to as the one-end circulation section. Also, the fourth S-shaped groove 21d, which is located closest to the other end of the nut body 20 among the four S-shaped grooves 21, is sometimes referred to as the other-end circulation section or end-side circulation section.

[0042] As shown in Figure 2, when the four S-shaped grooves 21 are viewed from the first direction X1, they are arranged in the order of the first S-shaped groove 21a, the second S-shaped groove 21b, the third S-shaped groove 21c, and the fourth S-shaped groove 21d, at 90-degree intervals in a clockwise direction. In other words, the first S-shaped groove 21a is located in the other direction Y2 of the first orthogonal direction when viewed from the axis O1. The second S-shaped groove 21b is located in the one direction Z1 of the second orthogonal direction when viewed from the axis O1. The third S-shaped groove 21c is located in the one direction Y1 of the first orthogonal direction when viewed from the axis O1. The fourth S-shaped groove 21d is located in the other direction Z2 of the second orthogonal direction when viewed from the axis O1.

[0043] Here, the first inner raceway surface 25a of the nut 3 supports the screw shaft 2 from the radially outer direction via the ball 4. On the other hand, the first S-shaped groove 21a connecting the first inner raceway surface 25a cannot support the screw shaft 2 via the ball 4. Therefore, the first inner raceway surface 25a cannot support a load directed from the axis O1 toward the other direction Y2 in the first orthogonal direction (see arrow A1 in Figure 2). Similarly, the second inner raceway surface 25b cannot support a load directed from the axis O1 toward one direction Z1 in the second orthogonal direction (see arrow A2 in Figure 2). The third inner raceway surface 25c cannot support a load directed from the axis O1 toward one direction Y1 in the first orthogonal direction (see arrow A3 in Figure 2). The fourth inner raceway surface 25d cannot support a load directed from the axis O1 toward the other direction Z2 in the second orthogonal direction (see arrow A4 in Figure 2). In this embodiment, the four S-shaped grooves 21 are distributed circumferentially, and the areas that cannot be supported from the radially outer side do not overlap. Therefore, the nut 3 supports the screw shaft 2 from all angles. As a result, the load on the balls 4 arranged in each raceway is evenly distributed, which can extend the lifespan of the ball screw device 1.

[0044] As shown in Figure 3, the end face of the nut body 20 in the first direction X1 is a pressing surface 27 that presses against the piston 40. The pressing surface 27 is inclined so as to be located in the second direction X2 toward the other direction Z2 of the second orthogonal direction when viewed from the first orthogonal direction. Therefore, when the ball screw device 1 is not operating, only the portion 27a of the pressing surface 27 located in the second orthogonal direction Z1 when viewed from the axis O1 is in contact with the piston 40. Note that in Figure 3, the degree of inclination of the pressing surface 27 in Embodiment 1 is exaggerated in order to make it easier to understand. The pressing surface 27 is also shown in Figure 4, but similarly the degree of inclination of the pressing surface 27 is exaggerated in that figure as well.

[0045] Figure 4 is an enlarged view of the nut of the brake caliper in Embodiment 1 during operation. Next, the operation of the ball screw device 1 in Embodiment 1 will be described. When the brake caliper 100 is in operation, the nut 3 moves in the first direction X1 and presses the piston 40 in the first direction X1. Therefore, the pressing surface 27 of the nut 3 receives a reaction force from the piston 40 in the second direction X2. Of the pressing surface 27, only the portion 27a located in one of the second orthogonal directions Z1 when viewed from the axis O1 is in contact with the piston 40 (see Figure 3). Therefore, portion 27a of the pressing surface 27 is pressed in the second direction X2. As a result, as shown in Figure 4, the nut 3 tilts around the projection 23. Therefore, when the ball screw device 1 is in operation, the reaction force from the piston 40 is converted into a moment load (hereinafter referred to as "preload moment load").

[0046] Furthermore, due to the preload moment load, the nut 3 tilts such that the pressing surface 27 moves to one side Z1 in the second orthogonal direction (see arrow B1 in Figure 3). As a result, the load on the multiple balls 4 rolling near the end of the nut 3 in the first direction X1, in other words, the load on the balls 4 rolling in the other side Z2 in the second orthogonal direction as viewed from the screw shaft 2, among the multiple balls 4 rolling on the first inner circumferential raceway surface 25a, increases. Here, the first S-shaped groove 21a in this embodiment is located in the other side Y2 in the second orthogonal direction from the axis O1, and is located in a direction other than the other side Z2 in the second orthogonal direction as viewed from the screw shaft 2. Therefore, the load acting on the balls 4 rolling near the first S-shaped groove 21a does not increase.

[0047] Furthermore, under the preload moment load, the load on the balls 4 rolling near the end of the nut 3 in the second direction X2, in other words, the load on the balls 4 rolling in one direction Z1 of the second orthogonal direction as viewed from the screw shaft 2, among the balls 4 rolling on the fourth inner circumferential raceway surface 25d, increases. Here, the fourth S-shaped groove 21d in this embodiment is located in a direction other than one direction Y1 of the second orthogonal direction from the axis O1. Therefore, the load acting on the balls 4 rolling near the fourth S-shaped groove 21d does not increase.

[0048] Furthermore, with respect to the preload moment load, the load on the ball 4 rolling in the other direction Z2, which is second orthogonal to the screw shaft 2, is the smallest among the multiple balls 4 rolling on the fourth inner circumferential raceway surface 25d. Here, the fourth S-shaped groove 21d in this embodiment is located in the other direction Z2, which is second orthogonal to the axis O1. Therefore, the load acting on the ball 4 rolling near the fourth inner circumferential raceway surface 25d is greatly reduced.

[0049] Next, the effects of the ball screw device 1 of Embodiment 1 will be described. When the ball screw device 1 of Embodiment 1 is assembled to the housing 120, an assembly moment load may act on the nut 3 due to tolerances, external forces, etc. Below, we will explain using as an example the case in which the assembly moment load acting on the nut 3 is such that the pressing surface 27 moves to the other Z2 in the second orthogonal direction (see arrow B2 in Figure 3; hereinafter referred to as "assembly moment load in the load increasing direction").

[0050] When an assembly moment load in the direction of increasing load (see arrow B2 in Figure 3) acts on the nut 3, the fourth S-shaped groove 21d approaches the outer raceway surface 12 of the screw shaft 2. As a result, the load acting on the balls 4 rolling near the fourth S-shaped groove 21d increases. Furthermore, when the brake caliper 100 is driven in this state, the load acting on each ball 4 increases even further. In other words, the load acting on the balls 4 rolling near the fourth S-shaped groove 21d becomes excessive, and the balls 4 may vibrate.

[0051] On the other hand, according to the ball screw device 1 of this embodiment, a preload moment load (see arrow B1 in Figure 3) acts on the nut 3 when the ball screw device 1 is operating. Therefore, the nut 3 is less likely to tilt in the direction of the assembly moment load. In other words, the amount by which the nut 3 tilts in the direction of the assembly moment load is kept small due to the preload moment load. In particular, the assembly moment load in the direction of load increase (see arrow B2 in Figure 3) is a load in the opposite direction to the preload moment load (see arrow B1 in Figure 3). Therefore, the amount by which the nut 3 tilts in the direction of the assembly moment load is extremely small. As a result, the amount by which the fourth S-shaped groove 21d approaches the screw shaft 2 is kept extremely small. This prevents the load on the ball 4 rolling near the fourth S-shaped groove 21d from becoming excessive, and the vibration of the ball 4 rolling near the fourth S-shaped groove 21d is suppressed.

[0052] Furthermore, if the preload moment load is greater than the assembly moment load, the assembly moment load is offset by the preload moment load. Therefore, the nut 3 does not tilt in the direction of the assembly moment load. In other words, the fourth S-shaped groove 21d does not approach the screw shaft 2, and the load on the ball 4 rolling near the fourth S-shaped groove 21d does not increase. As a result, vibration of the ball 4 rolling near the fourth S-shaped groove 21d is reliably suppressed. Therefore, in this disclosure, it is preferable that the preload moment load be greater than the assembly moment load.

[0053] Furthermore, with respect to the first S-shaped groove 21a, a preload moment load is applied to the nut 3, so movement in the direction of the assembly moment load is kept to a minimum. Note that the assembly moment load in the load-increasing direction (see arrow B2 in Figure 3) is not a load that brings the first S-shaped groove 21a closer to the screw shaft 2. Therefore, the load on the balls 4 rolling near the first S-shaped groove 21a does not increase due to the assembly moment load in the load-increasing direction.

[0054] The above explanation has been based on the example of the assembly moment load being in the direction of increasing load, but the effects of this embodiment are also effective when the assembly moment load is in a direction other than the direction of increasing load. In other words, even when an assembly moment load is applied to the nut 3 such that the first S-shaped groove 21a is close to the screw shaft 2, the amount by which the nut 3 tilts in the direction of the assembly moment load is suppressed to a small extent by the preload moment load. That is, the amount by which the first S-shaped groove 21a is close to the screw shaft 2 is suppressed to a small extent. Therefore, the load on the ball 4 rolling near the first S-shaped groove 21a does not become excessive, and the vibration of the ball 4 rolling near the first S-shaped groove 21a is suppressed.

[0055] As described above, the ball screw device 1 of Embodiment 1 comprises a screw shaft 2 that is rotatably supported, a nut 3 that passes through the screw shaft 2 and is movable in an axial direction parallel to the screw shaft 2, and a plurality of balls 4 arranged between the screw shaft 2 and the nut 3. The nut 3 has a cylindrical nut body 20 and a plurality of circulation parts (S-shaped grooves 21) that return the ball 4 that has moved one lead by one lead. One direction perpendicular to the axial direction is called the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is called the second orthogonal direction. The nut 3 is supported so as to be tiltable around a virtual line extending in the first orthogonal direction. The end face provided at one end of the nut body 20 is a pressing surface 27 that presses against the object to be pressed (piston 40). The pressing surface 27 is inclined so as to be located in the other axial direction (second direction X2) toward the other Z2 of the second orthogonal direction when viewed from the first orthogonal direction. The multiple circulation sections include a one-end circulation section (first S-shaped groove 21a) located closest to one end of the nut body 20, and a other-end circulation section (fourth S-shaped groove 21d) located closest to the other end of the nut body 20. The one-end circulation section is located in a direction other than the other Z2 in the second orthogonal direction when viewed from the screw shaft 2. The other-end circulation section is located in a direction other than the one Z1 in the second orthogonal direction when viewed from the screw shaft 2. In Embodiment 1, the other-end circulation section (fourth S-shaped groove 21d) is located in the other Z2 in the second orthogonal direction when viewed from the screw shaft 2.

[0056] According to Embodiment 1, even when an assembly moment load is applied, the load on the balls 4 rolling near the first S-shaped groove 21a and the fourth S-shaped groove 21d does not become excessive, and vibration of the balls 4 is suppressed. In particular, the preload moment load greatly reduces the load acting on the balls 4 rolling near the fourth S-shaped groove 21d, and vibration of the balls 4 is reliably suppressed.

[0057] Although Embodiment 1 has been described above, the disclosure is not limited thereto. In Embodiment 1, the ball screw device 1 has the projection 23 and guide groove 124 arranged in a first horizontal direction with respect to the axis O1, but the disclosure states that the projection 23 and guide groove 124 do not have to be arranged in a first horizontal direction with respect to the axis O1. In other words, the projection 23 and guide groove 124 may be offset in a second orthogonal direction with respect to a virtual line extending from the axis O1 in the first horizontal direction.

[0058] Furthermore, while the nut 3 in Embodiment 1 is tiltable due to the projection 23, this disclosure states that, for example, the nut 3 may not have the projection 23. Also, while the nut 3 in Embodiment 1 is supported so as to be axially slidable and non-rotatable by the projection 23 and the guide groove 124, this disclosure states that the nut 3 may be supported so as to be axially slidable and non-rotatable by a method other than the projection 23 and the guide groove 124. In other words, the projection 23 and the guide groove 124 are not essential components in this disclosure. Note that in a ball screw device without the projection 23 and the guide groove 124, the direction parallel to the center line on which the nut 3 tilts becomes the first orthogonal direction. Next, a ball screw device of another embodiment will be described. In the following description, the differences from Embodiment 1 will be the focus.

[0059] (Embodiment 2) Figure 5 is a cross-sectional view of the brake caliper of Embodiment 2, taken axially in its pre-operation state. The housing 120 of Embodiment 2 differs from Embodiment 1 in that the first wall surface 122 and the second wall surface 123 are not arranged coaxially. More specifically, the first wall surface 122 is cylindrical around a virtual line K11. On the other hand, the second wall surface 123 is cylindrical around a virtual line K12 that is eccentric in a second orthogonal direction with respect to the virtual line K11. The virtual line K12 is eccentric to one side Z1 in the second orthogonal direction with respect to the virtual line K11. As a result, the rotation centers of the bearing 117 and the carrier 116 are also eccentric to one side Z1 in the second orthogonal direction.

[0060] Furthermore, the brake caliper 100A of Embodiment 2 differs from Embodiment 1 in that the outer diameter of the nut 3A is the same as the inner diameter of the first wall surface 122 of the housing 120. In other words, the nut 3A of Embodiment 2 does not tilt around the projection 23 (see Figures 2 and 3). Also, the center line C1 of the nut 3A is arranged coaxially with the imaginary line K11 of the first wall surface 122. A minute gap is provided between the outer circumferential surface 22 of the nut 3A and the first wall surface 122. Therefore, the nut 3A is supported so as to be slidable in a direction parallel to the imaginary line K11.

[0061] From the above, the screw shaft 2A is supported by the nut 3A and carrier 116, which are not arranged coaxially. Therefore, the screw shaft 2A is inclined with respect to the virtual lines K11 and K12. In other words, with respect to the screw shaft 2A as the reference, the nut 3A is inclined with respect to the screw shaft 2A. For this reason, the ball screw device 1A of Embodiment 2, like the ball screw device 1 of Embodiment 1, has a preload moment load acting on the nut 3A. In Embodiment 2, the axial direction is the direction parallel to the virtual line K11. The first direction X1 is the direction in which the brake disc 101 is positioned as viewed from the ball screw device 1, among the directions parallel to the virtual line K11, and the second direction X2 is the opposite direction to the first direction X1.

[0062] Furthermore, the axis O1 of the screw shaft 2A is inclined such that, when viewed from the first orthogonal direction, it is located on one side Z1 of the second orthogonal direction, from one end of the nut body 20 (the end in the first direction X1) toward the other end of the nut body 20 (the end in the second direction X2). As a result, among the multiple balls 4 rolling on the first inner circumferential raceway surface 25a, the load on the ball 4 rolling on the other side Z2 of the second orthogonal direction when viewed from the screw shaft 2A becomes larger. Also, among the multiple balls 4 rolling on the fourth inner circumferential raceway surface 25d, the load on the ball 4 rolling on one side Z1 of the second orthogonal direction when viewed from the screw shaft 2 becomes larger. In this embodiment, the fourth S-shaped groove 21d is located on the other side Z2 of the second orthogonal direction when viewed from the screw shaft 2. Therefore, the load acting on the balls 4 rolling near the fourth S-shaped groove 21d is reduced. On the other hand, the first S-shaped groove 21a is located in the other direction Y2 perpendicular to the center line C1 (see Figure 2). In other words, the load acting on the ball 4 rolling near the first S-shaped groove 21a does not increase.

[0063] As described above, according to the ball screw device 1A of Embodiment 2, even when an assembly moment load is applied to the nut 3A, the amount of tilt in the direction of the assembly moment load is kept small due to the preload moment load. In other words, the amount by which the end-side circulation section (first S-shaped groove 21a, fourth S-shaped groove 21d) approaches the screw shaft 2A is kept small. Therefore, the load on the balls 4 rolling near the end-side circulation section (first S-shaped groove 21a, fourth S-shaped groove 21d) does not become excessive. As a result, vibration of the balls 4 rolling near the end-side circulation section (first S-shaped groove 21a, fourth S-shaped groove 21d) is suppressed.

[0064] Figure 6 is a cross-sectional view of an electric actuator according to a modified example, cut in the axial direction. Embodiment 2 has been described above, and the screw shaft 2A in Embodiment 2 is inclined. In such a screw shaft 2A, Embodiment 2 is a so-called cantilever, and one end of the screw shaft 2A (only the power transmission unit 10) is supported, but the disclosure is not limited to this. For example, as shown in Figure 6, in the modified electric actuator 104B, the screw shaft 2B comprises a power transmission unit 10, a screw shaft body 11, and a cylindrical shaft portion 15 that protrudes in the first direction X1 from the end of the screw shaft body 11 in the first direction X1. The shaft portion 15 is supported by a bearing 130 provided in the housing 120. According to this modified example, the screw shaft 2B is a so-called double-supported structure, and the inclination state of the screw shaft 2B is stabilized. Therefore, the preload moment load acting on the screw shaft 2A is also stabilized.

[0065] (Embodiment 3) Figure 7 is a cross-sectional view of the nut and piston of the brake caliper of Embodiment 3, cut in the axial direction. As shown in Figure 7, the brake caliper 100C of Embodiment 3 is similar to Embodiment 1 in that the axis O1 of the screw shaft 2C is located coaxially with the imaginary line K1. The imaginary line K1 is the center line of the first wall surface 122 and the second wall surface 123. On the other hand, the brake caliper 100C of Embodiment 3 differs from Embodiment 1 in that the outer diameter of the nut 3C is the same as the inner diameter of the first wall surface 122 of the housing 120. Therefore, the nut 3A is supported by the housing 120 so as not to tilt toward the center of the projection 23 (see Figures 2 and 3). In addition, a small gap is provided between the outer circumferential surface 22 of the nut 3C and the first wall surface 122. Therefore, the nut 3C is supported so as to be slidable in the axial direction.

[0066] The inner circumferential surface 24 of the nut 3C is cylindrical around the imaginary line D1. When viewed from the first orthogonal direction, this imaginary line D1 is inclined so as to be located on the other side Z2 of the second orthogonal direction, from one end of the nut body 20 (the end in the first direction X1) toward the other end of the nut body 20 (the end in the second direction X2). Therefore, the inner circumferential surface 24 of the nut 3C in Embodiment 3 differs from Embodiment 1 in that, when viewed from the first orthogonal direction, it is inclined with respect to the axis O1 (imaginary line K1). Furthermore, according to Embodiment 3, with respect to the screw shaft 2C as the reference, the nut 3C is in the same state as when it is inclined with respect to the screw shaft 2C. In other words, in the ball screw device 1C of Embodiment 3, a preload moment load is applied to the nut 3A, similar to the ball screw device 1 of Embodiment 1.

[0067] Furthermore, the imaginary line D1, which is the center line of the inner circumferential surface 24, is inclined such that, when viewed from the first orthogonal direction, it is located on the other Z2 in the second orthogonal direction, moving from one end of the nut body 20 (the end in the first direction X1) toward the other end of the nut body 20 (the end in the second direction X2). As a result, among the multiple balls 4 rolling on the first inner circumferential raceway surface 25a, the load on the ball 4 rolling on the other Z2 in the second orthogonal direction when viewed from the screw shaft 2 becomes larger. Also, among the multiple balls 4 rolling on the fourth inner circumferential raceway surface 25d, the load on the ball 4 rolling on one Z1 in the second orthogonal direction when viewed from the screw shaft 2 becomes larger. In this embodiment, the first S-shaped groove 21a is located on the other Y2 in the first orthogonal direction from the center line C1. In other words, the load acting on the ball 4 rolling near the first S-shaped groove 21a does not increase. On the other hand, the fourth S-shaped groove 21d is located on the other Z2 in the second orthogonal direction when viewed from the screw shaft 2. Therefore, the load acting on the ball 4 rolling near the fourth S-shaped groove 21d is reduced.

[0068] As described above, according to the ball screw device 1C of Embodiment 3, even when an assembly moment load is applied to the nut 3C, the amount of tilt in the direction of the assembly moment load is kept small due to the preload moment load. In other words, the amount by which the end-side circulation section (first S-shaped groove 21a, fourth S-shaped groove 21d) approaches the screw shaft 2A is kept small. Therefore, the load on the balls 4 rolling near the end-side circulation section (first S-shaped groove 21a, fourth S-shaped groove 21d) does not become excessive. As a result, vibration of the balls 4 rolling near the end-side circulation section (first S-shaped groove 21a, fourth S-shaped groove 21d) is suppressed.

[0069] Regarding the end face of the nut 3C in Embodiment 3, the pressing surface 27 is a plane perpendicular to the axis O1, and the end face of the nut 3C in the second direction X2 is a plane perpendicular to the imaginary line D1, and they are not parallel to each other. However, in this disclosure, the pressing surface 27 and the end face of the nut 3C in the second direction X2 may be parallel, and are not particularly limited.

[0070] Although each embodiment has been described above, this disclosure is not limited to the examples shown in each embodiment. For example, in the embodiments, the case in which there are four inner circumferential raceway surfaces 25 and S-shaped grooves 21 is described, but this disclosure is not limited to cases where there are two or more inner circumferential raceway surfaces 25 and S-shaped grooves 21.

[0071] Furthermore, in each embodiment, the first S-shaped groove 21a is located in the other Y2 in the first orthogonal direction when viewed from the axis O1 (center line C1). However, in this disclosure, the first S-shaped groove 21a may be located anywhere other than the other Z2 in the second orthogonal direction. If the first S-shaped groove 21a is located in the other Z2 in the second orthogonal direction, the load acting on the ball 4 rolling near the first S-shaped groove 21a will increase due to the preload moment load, and the ball 4 may vibrate. Therefore, in this disclosure, the first S-shaped groove 21a may be located in one Y1 in the first orthogonal direction when viewed from the axis O1 (center line C1). Preferably, the first S-shaped groove 21a is located in one Z1 in the second orthogonal direction from the axis O1 (center line C1). In this case, the first S-shaped groove 21a will be separated from the outer circumferential raceway surface 12 of the screw shaft 2 by the moment load in the load reduction direction. Therefore, the load acting on the ball 4 rolling near the first S-shaped groove 21a is reduced, and vibration of the ball 4 can be reliably suppressed.

[0072] Furthermore, although the fourth S-shaped groove 21d is positioned on the other Z2 in the second orthogonal direction when viewed from the axis O1 (center line C1), this disclosure states that it is sufficient if the fourth S-shaped groove 21d is positioned anywhere other than Z1 in the second orthogonal direction. This is because if the fourth S-shaped groove 21d is positioned on Z1 in the second orthogonal direction, the load acting on the ball 4 rolling near the fourth S-shaped groove 21d will increase due to the preload moment load, which may cause the ball 4 to vibrate.

[0073] Although this embodiment has been described above, the terms "identical," "same," and "matching" in the above description include not only cases where the products are completely identical, the same, or matching, but also cases where they are substantially identical, the same, or matching, such as within the range of manufacturing tolerances. In other words, "identical," "same," and "matching" in this disclosure are not to be interpreted restrictively.

[0074] Furthermore, this disclosure may also be a combination of the following configurations. (1) A screw shaft that is supported to rotate freely, A nut that passes through the screw shaft and is movable in an axial direction parallel to the screw shaft, A plurality of balls are arranged between the screw shaft and the nut, Equipped with, The aforementioned nut is A cylindrical nut body, Multiple circulation units that move the ball one lead and then return it one lead, It has, One direction perpendicular to the aforementioned axial direction is defined as the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is defined as the second orthogonal direction. The nut is supported so as to be tiltable around a virtual line extending in the first orthogonal direction, The end face provided at one end of the nut body is a pressing surface that presses against the object to be pressed. The pressing surface is inclined such that, when viewed from the first orthogonal direction, it is located in the other axial direction toward the other of the second orthogonal direction, The multiple circulation units are, The one-end circulation section is located closest to one end of the nut body, The other end circulation section is located closest to the other end of the nut body, It has, The aforementioned one-end circulation section is positioned in a direction other than the other in the second orthogonal direction when viewed from the screw shaft, The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the screw shaft. Ball screw device. (2) A nut that is cylindrical in shape around its own centerline and movable in a direction parallel to the centerline, A screw shaft that penetrates the aforementioned nut and is rotatable about its own axis, A plurality of balls are arranged between the screw shaft and the nut, Equipped with, The aforementioned nut is A cylindrical nut body, Multiple circulation units that move the ball one lead and then return it one lead, It has, One direction perpendicular to the direction of the aforementioned centerline is defined as the first orthogonal direction. The direction perpendicular to both the aforementioned centerline direction and the aforementioned first orthogonal direction is defined as the second orthogonal direction. The axis is inclined such that, when viewed from the first orthogonal direction, it is located in one of the second orthogonal directions, from one end of the nut body toward the other end of the nut body. The multiple circulation units are, The one-end circulation section is located closest to one end of the nut body, The other end circulation section is located closest to the other end of the nut body, It has, The aforementioned one-end circulation section is positioned in a direction other than the other in the second orthogonal direction when viewed from the center line, The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the center line. Ball screw device. (3) A screw shaft that is supported to rotate freely, A nut that passes through the screw shaft and is movable in an axial direction parallel to the screw shaft, A plurality of balls are arranged between the screw shaft and the nut, Equipped with, The aforementioned nut is A cylindrical nut body, Multiple circulation units that move the ball one lead and then return it one lead, It has, One direction perpendicular to the aforementioned axial direction is defined as the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is defined as the second orthogonal direction. The nut body is, The outer surface centered on the axis of the screw shaft, The inner surface centered on the imaginary line, The inner circumferential raceway surface provided on the inner circumferential surface, It has, The aforementioned dashed line is inclined such that, when viewed from the first orthogonal direction, it is located on the other side of the second orthogonal direction, from one end of the nut body toward the other end of the nut body. The multiple circulation units are, The one-end circulation section is located closest to one end of the nut body, The other end circulation section is located closest to the other end of the nut body, It has, The aforementioned one-end circulation section is positioned in a direction other than the other in the second orthogonal direction when viewed from the screw shaft, The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the screw shaft. Ball screw device. (4) The aforementioned one-end circulation section is positioned in one of the second orthogonal directions when viewed from the screw shaft. (1) or (3) the ball screw device described above. (5) The other end circulation section is located in the other direction perpendicular to the second direction when viewed from the screw shaft. A ball screw device as described in any one of (1), (3), and (4). (6) The aforementioned one-end circulation section is positioned in one of the second orthogonal directions when viewed from the center line. (2) The ball screw device described above. (7) The aforementioned other end circulation section is located in the other direction of the second orthogonal direction when viewed from the center line. (2) or (6) the ball screw device described above. [Explanation of Symbols]

[0075] 1. Ball screw device 2, 2B, 2C screw shafts 3, 3A, 3C nuts 4 balls 10 Power transmission section 11 Screw shaft body 12 Outer raceway surface 21 S-shaped groove (circulation section) 21a 1st S-shaped groove (one end side circulation part) 21d 4th S-shaped groove (other end side circulation part) 23 Protrusion 24 Inner peripheral surface 25 Inner raceway surface 27 Pressing surface 40 pistons 100, 100A, 100C Brake Calipers 101 Brake Disc 102, 103 Brake Pads 104, 104B Electric Actuator 110 Reducer 120 Housing 121 Enclosure holes 122 First Wall 123 Second Wall 124 Guide grooves C1 center line D1 virtual line K1, K11, K12 virtual lines O1 axis center

Claims

1. A screw shaft that is supported to rotate freely, A nut that passes through the screw shaft and is movable in an axial direction parallel to the screw shaft, A plurality of balls are arranged between the screw shaft and the nut, Equipped with, The aforementioned nut is A cylindrical nut body, Multiple circulation units that move the ball one lead and then return it one lead, It has, One direction perpendicular to the aforementioned axial direction is defined as the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is defined as the second orthogonal direction. The nut is supported so as to be tiltable around a virtual line extending in the first orthogonal direction, The end face provided at one end of the nut body is a pressing surface that presses against the object to be pressed. The pressing surface is inclined such that, when viewed from the first orthogonal direction, it is located in the other axial direction toward the other of the second orthogonal direction, The multiple circulation units are, The one-end circulation section is located closest to one end of the nut body, The other end circulation section is located closest to the other end of the nut body, It has, The aforementioned one-end circulation section is positioned in a direction other than the other in the second orthogonal direction when viewed from the screw shaft, The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the screw shaft. Ball screw device.

2. A nut that is cylindrical in shape around its own centerline and movable in a direction parallel to the centerline, A screw shaft that penetrates the aforementioned nut and is rotatable about its own axis, A plurality of balls are arranged between the screw shaft and the nut, Equipped with, The aforementioned nut is A cylindrical nut body, Multiple circulation units that move the ball one lead and then return it one lead, It has, One direction perpendicular to the direction of the aforementioned centerline is defined as the first orthogonal direction. The direction perpendicular to both the aforementioned centerline direction and the first orthogonal direction is defined as the second orthogonal direction. The axis is inclined such that, when viewed from the first orthogonal direction, it is located in one of the second orthogonal directions, from one end of the nut body toward the other end of the nut body. The multiple circulation units are, The one-end circulation section is located closest to one end of the nut body, The other end circulation section is located closest to the other end of the nut body, It has, The aforementioned one-end circulation section is positioned in a direction other than the other in the second orthogonal direction when viewed from the center line, The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the center line. Ball screw device.

3. A screw shaft that is supported to rotate freely, A nut that passes through the screw shaft and is movable in an axial direction parallel to the screw shaft, A plurality of balls are arranged between the screw shaft and the nut, Equipped with, The aforementioned nut is A cylindrical nut body, Multiple circulation units that move the ball one lead and then return it one lead, It has, One direction perpendicular to the aforementioned axial direction is defined as the first orthogonal direction. The direction perpendicular to both the axial direction and the first orthogonal direction is defined as the second orthogonal direction. The nut body is, The outer surface centered on the axis of the screw shaft, The inner surface centered on the imaginary line, The inner circumferential raceway surface provided on the inner circumferential surface, It has, The aforementioned dashed line is inclined such that, when viewed from the first orthogonal direction, it is located on the other side of the second orthogonal direction, from one end of the nut body toward the other end of the nut body. The multiple circulation units are, The one-end circulation section is located closest to one end of the nut body, The other end circulation section is located closest to the other end of the nut body, It has, The aforementioned one-end circulation section is positioned in a direction other than the other in the second orthogonal direction when viewed from the screw shaft, The other end circulation section is positioned in a direction other than one of the second orthogonal directions when viewed from the screw shaft. Ball screw device.

4. The aforementioned one-end circulation section is positioned in one of the second orthogonal directions when viewed from the screw shaft. The ball screw device according to claim 1 or claim 3.

5. The other end circulation section is located in the other direction perpendicular to the second direction when viewed from the screw shaft. The ball screw device according to claim 1 or claim 3.

6. The aforementioned one-end circulation section is positioned in one of the second orthogonal directions when viewed from the center line. The ball screw device according to claim 2.

7. The other end circulation section is located in the other direction perpendicular to the second direction when viewed from the center line. The ball screw device according to claim 2.

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