Actuator

Abstract

To provide an actuator that can be suppressed in an increase in the number of components.SOLUTION: An actuator of the present disclosure comprises: a cylindrically-shaped cylindrical component; a housing which houses the cylindrical components; and a spline mechanism which supports the cylindrical components in a non-rotatable manner around the central axis thereof. One of the axial direction parallel to the central axis of the cylindrical components is defined as a first direction, and the other is defined as a second direction. The housing has an inner surface facing the outer peripheral surface of the cylindrical components. The spline mechanism has a plurality of outer peripheral spline grooves provided in the outer peripheral surface of the cylindrical components, a plurality of inner peripheral spline grooves which are provided in the inner peripheral surface of the housing, extend in the axial direction and face the outer peripheral spline grooves; a plurality of rolling elements each of which is arranged between the outer peripheral spline groove and the inner peripheral spline groove, at least a part of which enters each of the outer peripheral spline groove and the inner peripheral spline groove; a first wall portion which closes the end of the outer peripheral spline groove in the first direction; and a second wall portion which closes the end in the second direction, of the inner peripheral spline groove.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to actuators. [Background technology]

[0002] The actuator includes a ball screw device that converts rotational motion into linear motion. The actuator of the following patent document uses a ball screw device to transmit rotational motion to a screw shaft and linearly move a nut. The actuator of the following patent document also uses a ball spline to restrict the rotation of the nut and smooth the linear motion of the nut. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 017458 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in order to detect the axial position of the nut, the actuator requires a stopper mechanism to position the nut in an initial position. However, if a conventional stopper mechanism is directly installed in the actuator, it will result in an increase in the number of parts.

[0005] The present disclosure has been made in view of the above, and aims to provide an actuator that can suppress an increase in the number of parts. [Means for solving the problem]

[0006] To achieve the above object, an actuator according to one aspect of the present disclosure includes a cylindrical part, a housing that accommodates the cylindrical part, and a spline mechanism that supports the cylindrical part so that it cannot rotate around a central axis of the cylindrical part. One axial direction parallel to the central axis of the cylindrical part is defined as a first direction, and the other axial direction is defined as a second direction. The housing has an inner circumferential surface that faces the outer circumferential surface of the cylindrical part. The spline mechanism includes: a plurality of outer circumferential spline grooves that are provided on the outer circumferential surface of the cylindrical part and extend in the axial direction; a plurality of inner circumferential spline grooves that are provided on the inner circumferential surface of the housing and extend in the axial direction and face the outer circumferential spline grooves; a plurality of rolling elements that are disposed between the outer circumferential spline groove and the inner circumferential spline groove, at least a portion of which is inserted into the outer circumferential spline groove and the inner circumferential spline groove; a first wall portion that closes an end of the outer circumferential spline groove in the first direction; and a second wall portion that closes an end of the inner circumferential spline groove in the second direction.

[0007] According to the present disclosure, even if a load (torque) around the central axis is transmitted to the tubular part, the rolling elements are caught in the outer peripheral spline groove and the inner peripheral spline groove, preventing the tubular part from rotating. Furthermore, when the tubular part moves axially, the rolling elements roll in the outer peripheral spline groove and the inner peripheral spline groove. Therefore, the tubular part moves smoothly. Furthermore, when the tubular part moves in the second direction, the rolling elements also roll in the second direction. Furthermore, when the rolling elements contact the second wall portion, the rolling (movement) of the rolling elements in the second direction is restricted. Furthermore, when the tubular part moves in the second direction, the movement of the tubular part in the second direction is restricted when the first wall portion contacts the rolling elements. Therefore, the state in which the rolling elements abut against the first wall portion and the second wall portion can be set as the initial position of the tubular part. According to the present disclosure, the tubular part can be positioned in its initial position by a spline mechanism (outer peripheral spline groove, inner peripheral spline groove, and rolling elements) that prevents the tubular part from rotating. In other words, there is no need to provide a separate stopper mechanism, and an increase in the number of parts is avoided. Also, the cylindrical part is in contact with the rolling elements from the outer periphery. Therefore, the cylindrical part is supported by the housing from the radially outer side via the balls.

[0008] In a preferred embodiment of the ball screw device, the spline mechanism includes a cage that is disposed between the outer peripheral surface of the tubular part and the inner peripheral surface of the housing and that holds the rolling elements.

[0009] According to the above configuration, the rolling elements are held by the cage, which makes it easy to assemble the actuator.

[0010] In a preferred embodiment of the ball screw device, the spline mechanism has an opening that opens an end of the outer-peripheral spline groove in the second direction and a third wall that closes an end of the inner-peripheral spline groove in the first direction. The outer-peripheral spline groove has a length in the axial direction that is greater than that of the inner-peripheral spline groove.

[0011] According to this configuration, the amount of axial movement of the rolling element is limited to the distance between the second wall portion and the third wall portion, i.e., the length of the inner peripheral spline groove, so that the rolling element is less likely to fall off from the end (opening) of the outer peripheral spline groove in the second direction.

[0012] In a preferred embodiment of the ball screw device, the spline mechanism includes a groove provided on the outer peripheral surface of the cylindrical part, extending in the circumferential direction, and a retaining ring fitted into the groove, the retaining ring closing the end of the outer peripheral spline groove in the second direction.

[0013] According to this configuration, the rolling elements do not fall off from the ends (openings) of the outer-periphery spline grooves in the second direction.

[0014] In a preferred embodiment of the ball screw device, the spline mechanism has a fourth wall portion that closes the second direction end of the outer-peripheral spline groove and an opening portion that opens the first direction end of the inner-peripheral spline groove. The inner-peripheral spline groove has a longer axial length than the outer-peripheral spline groove.

[0015] According to this configuration, the amount of axial movement of the rolling element is limited to the distance between the first wall portion and the fourth wall portion, i.e., the length of the outer peripheral spline groove, which reduces the possibility that the rolling element will fall off from the end (opening) of the inner peripheral spline groove in the first direction.

[0016] In a preferred embodiment of the ball screw device, the spline mechanism includes a groove formed on the inner peripheral surface of the housing and extending in the circumferential direction, and a retaining ring fitted into the groove, the retaining ring closing an end of the inner peripheral spline groove in the first direction.

[0017] According to this configuration, the rolling elements do not fall off from the ends (openings) of the inner peripheral spline grooves in the first direction.

[0018] In a preferred embodiment of the ball screw device, the plurality of outer peripheral spline grooves and the plurality of inner peripheral spline grooves are arranged at equal intervals in the circumferential direction.

[0019] According to the above-described configuration, the pockets for accommodating the rolling elements are formed at equal intervals, which makes it possible to use a general cage used in rolling bearings such as ball bearings and cylindrical roller bearings.

[0020] In a preferred embodiment of the ball screw device, the plurality of outer peripheral spline grooves and the plurality of inner peripheral spline grooves are arranged at uneven intervals in the circumferential direction.

[0021] According to the above configuration, if the tubular part is misaligned from a predetermined angle, the tubular part cannot be assembled to the housing. This prevents misassembly of the tubular part. Furthermore, according to the above configuration, the rolling elements are also arranged at uneven intervals in the circumferential direction. In other words, the rolling elements are densely packed in a portion of the circumferential direction, creating an area with high load capacity. By arranging the area with high load capacity in the direction in which the external load acts as viewed from the central axis of the tubular part, the tubular part is supported by the housing from the radial outside via the rolling elements.

[0022] In a preferred embodiment of the ball screw device, a plurality of rolling elements are disposed between a pair of the outer peripheral spline groove and the inner peripheral spline groove that face each other.

[0023] According to the above configuration, the radial load capacity for supporting the cylindrical part is increased.

[0024] In a preferred embodiment of the ball screw device, the rolling elements are cylindrical rollers.

[0025] According to the above configuration, the radial load capacity for supporting the cylindrical part is greater than when balls are used as the rolling elements.

[0026] In addition, a preferred embodiment of the ball screw device is provided with a sliding bearing that fits into the inner peripheral surface of the housing and abuts against the outer peripheral surface of the tubular part.

[0027] According to the above configuration, even if a radial load acts on the tubular part, the tubular part is less likely to tilt.

[0028] In a preferred embodiment of the ball screw device, the housing includes a cylindrical first part having the inner peripheral surface and a second part having a fitting surface into which the outer peripheral surface of the first part fits, and the plurality of inner peripheral spline grooves are formed on the inner peripheral surface of the first part.

[0029] Although the housing of the present disclosure may be constructed from a single component, the above-described configuration has the inner circumferential spline groove formed in a part of the housing, i.e., in a first component that is smaller than the housing, which makes it easier to process the inner circumferential spline groove and allows the inner circumferential spline groove to be formed with high precision.

[0030] In a preferred embodiment of the ball screw device, the second component has an annular wall surface that abuts against an end face of the first component in the second direction, and the wall surface closes an end of the inner peripheral spline groove in the second direction.

[0031] According to this configuration, the rolling elements do not fall off from the ends (openings) of the inner peripheral spline grooves in the first direction.

[0032] The ball screw device may include a ball screw device having a screw shaft, a nut, and a plurality of balls, and the cylindrical part may be the nut. Alternatively, the ball screw device may include a ball screw device having a screw shaft, a nut, and a plurality of balls, and a piston fitted into the nut, and the cylindrical part may be the piston. [Effects of the Invention]

[0033] According to the actuator of the present disclosure, an increase in the number of parts is suppressed. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a cross-sectional view of the actuator of the first embodiment taken along the axial direction. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is an enlarged view of the spline mechanism of FIG. [Figure 4] FIG. 4 is a diagram showing the assembly process of the actuator of the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing a state in which the nut has moved in a first direction from an initial position in the actuator of the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing a state in which the nut has moved to the maximum extent in the first direction in the actuator of the first embodiment. [Figure 7] FIG. 7 is a cross section of the actuator of the first modification cut in the axial direction, and is an enlarged view of a part of the cross section. [Figure 8] FIG. 8 is a cross section of the actuator of Modification 2 cut in the axial direction, and is an enlarged view of a part of the cross section. [Figure 9] FIG. 9 is a cross section of the actuator of Modification 3 taken along the axial direction, and is an enlarged view of a part of the cross section. [Figure 10] FIG. 10 is a cross section of the actuator of Modification 4 taken along the axial direction, and is an enlarged view of a part of the cross section. [Figure 11] FIG. 11 is a cross-sectional view of the actuator of the fifth modification taken along the axial direction. [Figure 12] FIG. 12 is a cross-sectional view of the actuator of the sixth modification taken along the axial direction. [Figure 13] FIG. 13 is a cross section of the actuator of the seventh modification taken along the axial direction, and is an enlarged view of a part of the cross section. [Figure 14] FIG. 14 is a cross-sectional view of the actuator of the eighth modification taken in a direction perpendicular to the axial direction. [Figure 15] FIG. 15 is an enlarged view of the cylindrical roller in FIG. [Figure 16] FIG. 16 is a cross-sectional view of the actuator (electric brake) of the ninth modification taken along the axial direction. [Figure 17] FIG. 17 is a cross-sectional view taken along the axial direction of the actuator (electric brake) of the ninth modification example in an actuated state. [Figure 18] FIG. 18 is a cross-sectional view taken along the line XVIII-XVIII in FIG. [Figure 19] FIG. 19 is a cross-sectional view of the actuator (electric brake) of the tenth modification taken along the axial direction. [Figure 20] FIG. 20 is a cross-sectional view of an actuator (electric brake) of the eleventh modification taken along the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0035] The actuator of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0036] (Embodiment 1) Fig. 1 is an axial cross-sectional view of the actuator of embodiment 1. As shown in Fig. 1, the actuator 100 of embodiment 1 includes a motor (not shown), a reduction gear (not shown), a ball screw device 1 that converts rotational motion into linear motion, a housing 20, and a spline mechanism 40.

[0037] The reduction gear is a device that reduces the speed of the rotational motion generated by the motor and transmits it to the screw shaft 2 of the ball screw device 1. Examples of reduction gears include a planetary gear mechanism and a pulley, but the present disclosure is not limited to these. Furthermore, although the actuator 100 of the embodiment includes a reduction gear, the present disclosure does not necessarily include a reduction gear.

[0038] The ball screw device 1 includes a screw shaft 2, a nut 3, and a plurality of balls 4. Hereinafter, the direction parallel to the central axis O3 of the nut 3 will be referred to as the axial direction. The screw shaft 2 includes a power transmission unit 5 and a screw shaft main body 6. The power transmission unit 5 is formed in a cylindrical shape. Rotational motion is transmitted to the power transmission unit 5 from a reduction gear device. An outer peripheral raceway surface 7 extending in a spiral direction is formed on the outer peripheral surface of the screw shaft main body 6. Hereinafter, within the axial direction, the side in which the screw shaft main body 6 is disposed as viewed from the power transmission unit 5 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. Furthermore, the direction perpendicular to the axial direction will be referred to as the radial direction.

[0039] The nut 3 is a cylindrical part. When viewed from the axial direction, the inner peripheral surface 10 and the outer peripheral surface 11 of the nut 3 are each circular (see FIG. 2). In other words, the nut 3 is formed in a cylindrical shape. The nut 3 also has a first end face 3a facing the first direction X1 and a second end face 3b facing the second direction X2. The central axis O3 of the nut 3 is arranged coaxially with the central axis O2 of the screw shaft 2. The inner peripheral surface 10 of the nut 3 is provided with a plurality of inner peripheral raceway surfaces 12 and a plurality of circulation portions 13 (see FIG. 2).

[0040] The inner circumferential raceway surface 12 is a groove surface that is recessed radially outward from the inner circumferential surface 10 of the nut 3 and extends approximately one turn (approximately one lead) in the spiral direction. The inner circumferential raceway surface 12 faces the outer circumferential raceway surface 7 of the screw shaft 2 in the radial direction. A raceway is formed between the inner circumferential raceway surface 12 and the outer circumferential raceway surface 7. A plurality of balls 4 are arranged in each raceway.

[0041] 2 is a cross-sectional view taken along line II-II in FIG. 1. In FIG. 2, the screw shaft 2 and balls 4 are omitted to make the cross-sectional shape easier to see. For the same reason, the screw shaft 2 and balls 4 are also omitted in FIGS. 14, 18, and 19. As shown in FIG. 2, the circulation portion 13 in this embodiment is an S-groove surface formed on the inner peripheral surface 10 of the nut 3 by forging. The S-groove surface is connected to one end and the other end of the inner peripheral raceway surface 12 in the spiral direction. As a result, the balls 4 that move from one end of the raceway to the other end are circulated to one end of the raceway by the S-groove surface.

[0042] In this embodiment, an S-shaped groove surface formed by forging is used as the circulation portion 13, but the present disclosure is not limited thereto. For example, a block, a tube, or a deflector (end deflector, middle deflector) may also be used. In addition, in this embodiment, the circulation portion 13 is provided on the nut 3, but the circulation portion 13 may also be provided on the screw shaft 2. Furthermore, examples of the circulation portion 13 used on the screw shaft 2 include an S-shaped groove surface or a block formed by forging.

[0043] As shown in Fig. 1, the housing 20 has an accommodation space 21 for accommodating the ball screw device 1. The accommodation space 21 extends in the axial direction. As shown in Fig. 2, the accommodation space 21 is formed in a circular shape when viewed from the axial direction. In other words, an inner circumferential surface 22 surrounding the accommodation space 21 has a cylindrical shape centered on a central axis O3.

[0044] The diameter of the inner peripheral surface 22 is larger than the outer diameter of the nut 3. An annular gap is formed between the inner peripheral surface 22 of the housing 20 and the outer peripheral surface 11 of the nut 3. As shown in FIG. 1, an opening 23 is formed in the first direction X1 of the accommodation space 21. Therefore, the nut 3 of the ball screw device 1 can protrude (retract) from the opening 23 in the first direction X1.

[0045] As shown in FIG. 1, the spline mechanism 40 has a plurality of outer peripheral spline grooves 41, a plurality of inner peripheral spline grooves 42, a plurality of balls (rolling elements) 43, and one cage 44.

[0046] 3 is an enlarged view of the spline mechanism of FIG. 1. The outer-periphery spline groove 41 is a groove provided in the outer peripheral surface 11 of the nut 3 and extends in the axial direction. The axial length L41 of the outer-periphery spline groove 41 is shorter than the axial length L3 of the nut 3. The outer-periphery spline groove 41 extends to the end of the outer peripheral surface 11 of the nut 3 in the second direction X2. Therefore, at the end of the outer-periphery spline groove 41 in the second direction X2, the second end face 3b of the nut 3 is cut out to form an opening 45 that opens the outer-periphery spline groove 41 in the second direction X2.

[0047] A first wall portion 46 is provided at an end portion of the outer-periphery spline groove 41 in the first direction X1, closing the outer-periphery spline groove 41 from the first direction X1. A surface 46a of the first wall portion 46 facing the second direction X2 has an upward-cut shape (arcuate shape) that is gradually positioned radially outward as it moves in the first direction X1.

[0048] The inner spline groove 42 is a groove provided on the inner circumferential surface 22 of the housing 20 and extends in the axial direction. The axial length L42 of the inner spline groove 42 is shorter than the length L41 of the outer spline groove 41. A second wall portion 47 that closes the inner spline groove 42 from the second direction X2 is provided at the end of the inner spline groove 42 in the second direction X2. A surface 47a of the second wall portion 47 facing the first direction X1 has an ascending shape (arcuate shape) that is gradually positioned radially inward as it moves in the second direction X2.

[0049] A third wall portion 48 that closes the inner peripheral spline groove 42 from the first direction X1 is provided at an end of the inner peripheral spline groove 42 in the first direction X1. A surface 48a of the third wall portion 48 facing the second direction has an upward-cut shape (arcuate shape) that is gradually positioned radially inward as it moves in the first direction.

[0050] As shown in Fig. 2, four outer-circumferential spline grooves 41 and four inner-circumferential spline grooves 42 are provided, and the outer-circumferential spline grooves 41 and the inner-circumferential spline grooves 42 are arranged at 90° intervals around the central axis O3. The outer-circumferential spline grooves 41 and the inner-circumferential spline grooves 42 face each other in the radial direction. The outer-circumferential spline grooves 41 and the inner-circumferential spline grooves 42 have a circular arc shape when viewed from the axial direction. In the present disclosure, the shapes of the outer-circumferential spline grooves 41 and the inner-circumferential spline grooves 42 when viewed from the axial direction may be a Gothic arc shape and are not particularly limited.

[0051] The balls 43 are arranged between the outer peripheral spline grooves 41 and the inner peripheral spline grooves 42. In this embodiment, four balls are provided. One ball 43 is arranged for each pair of the outer peripheral spline grooves 41 and the inner peripheral spline grooves 42 that face each other.

[0052] The balls 43 are partially inserted into the outer peripheral spline groove 41 and the inner peripheral spline groove 42. The balls 43 are in contact with the outer peripheral spline groove 41 and the inner peripheral spline groove 42. As a result, even if a load (torque) acts on the nut 3 in the rotational direction about the central axis O3, the balls 43 are caught in the outer peripheral spline groove 41 and the inner peripheral spline groove 42, and rotation of the nut 3 is restricted.

[0053] The outer peripheral surface 11 of the nut 3 is in contact with four balls 43. Therefore, even if a radial load acts on the nut 3, the nut 3 is supported by the housing 20 via the balls 43. As shown in FIG. 2, the four balls 43 are arranged at 90° intervals around the central axis O3, i.e., at equal intervals. Therefore, the radial load capacity that supports the nut 3 is uniform in the circumferential direction.

[0054] As shown in FIG. 3 , the cage 44 is an annular component. Four pockets 44a are formed in the cage 44, penetrating the cage in the radial direction. The four pockets 44a are arranged at equal intervals in the circumferential direction. Balls 43 are arranged in the pockets 44a. The pockets 44a are formed to prevent the balls 43 from falling out in the radial direction. Note that in the present disclosure, there are no particular limitations on the shape or material of the cage 44; for example, it may be a crown-shaped cage made of resin. Furthermore, according to this embodiment, since the pockets 44a are arranged at equal intervals, it is possible to use a general cage used in rolling bearings such as ball bearings and cylindrical roller bearings. In other words, there is no need to produce a cage that is used only in the actuator 100, thereby reducing production costs.

[0055] Next, a method for assembling the actuator 100 of embodiment 1 will be described. Figure 4 is a diagram showing the assembly process for the actuator of embodiment 1. First, the retainer 44 is placed in the accommodation space 21 of the housing 20. Next, alignment is performed so that the pockets 44a of the retainer 44 and the inner peripheral spline grooves 42 of the housing 20 overlap in the radial direction.

[0056] Next, the balls 43 are inserted into the pockets 44a from the inner circumferential side of the cage 44 (see arrow A1 in FIG. 4). As a result, as shown in FIG. 4, a portion of the balls 43 held in the cage 44 is inserted into the inner circumferential spline grooves 42. In the present disclosure, after the balls 43 are inserted into the pockets 44a, a cylindrical jig may be inserted into the inner circumferential side of the cage 44. In this way, the balls 43 come into contact with the jig and are restricted from moving radially inward. In other words, the balls 43 are maintained in the state inserted in the pockets 44a.

[0057] Next, the ball screw device 1 is inserted into the accommodation space 21 through the opening 23 of the housing 20 (see arrow A2 in FIG. 4). Also, alignment is performed so that the direction in which the outer-periphery spline grooves 41 are arranged coincides with the direction in which the balls 43 are arranged, as viewed from the central axis O3. As a result, part of the balls 43 enters the outer-periphery spline grooves 41 through the opening 45 (see arrow A3 in FIG. 4), and the actuator 100 is completed.

[0058] Next, the operation of the actuator 100 of embodiment 1 will be described. As shown in Fig. 3, before the actuator 100 is activated, in other words, before the nut 3 moves, the ball 43 is in contact with each of the surface 46a of the first wall portion 46 and the surface 47a of the second wall portion 47. In other words, when the ball 43 is in this state, the nut 3 is disposed in the initial position.

[0059] FIG. 5 is a cross-sectional view showing a state in which the nut has moved in the first direction from its initial position in the actuator of the first embodiment. As shown in FIG. 5, when rotational motion is transmitted to the screw shaft 2 and the nut 3 moves in the first direction X1, the balls 43 located between the nut 3 and the housing 20 rotate. This allows the nut 3 to move smoothly in the axial direction. Furthermore, when the nut 3 moves in the first direction, the balls 43 rotate in the direction indicated by the arrow B1 in FIG. 5. Therefore, on the inner spline groove 42, the balls 43 roll in the first direction X1. On the other hand, on the outer spline groove 41, the balls 43 roll in the second direction X2.

[0060] FIG. 6 is a cross-sectional view showing a state in which the nut of the actuator of the first embodiment has moved the most in the first direction. As shown in FIG. 6, when the movement distance of the nut 3 in the first direction X1 reaches a predetermined distance, the ball 43 abuts against the surface 48a of the third wall portion 48. This restricts the ball 43 from rolling in the first direction X1. Furthermore, if the nut 3 moves further in the first direction X1 from this state, slippage (sliding friction) occurs between the ball 43 and the outer peripheral spline groove 41, preventing smooth movement of the nut 3 in the first direction X1. Therefore, the drive of the motor is restricted so that the nut 3 does not move further in the first direction X1 from the state in which the ball 43 abuts against the surface 48a of the third wall portion 48. From the above, the state in which the ball 43 abuts against the surface 48a of the third wall portion 48 is the state in which the nut 3 has moved the most in the first direction X1.

[0061] Furthermore, the outer-peripheral spline groove 41 is longer than the inner-peripheral spline groove 42. Therefore, even when the nut 3 has moved the most in the first direction X1, the balls 43 do not move to the end of the outer-peripheral spline groove 41 in the second direction X2. In other words, the balls 43 do not fall out of the openings 45 in the second direction X2.

[0062] In addition, the balls 43 may slip relative to the outer-peripheral spline grooves 41 and the inner-peripheral spline grooves 42, reducing the amount of movement of the balls 43 in the first direction X1 (see dashed line K43 in FIG. 6). In such cases, there is a possibility that the balls 43 may fall off from the openings 45. In this embodiment, the cage 44 ensures that the axial positions of the balls 43 are the same. Therefore, even if one of the four balls 43 slips, the ball 43 moves in the first direction X1 in the same way as the other balls 43. This prevents the balls 43 from falling off from the openings 45.

[0063] When the direction of the rotational motion transmitted to the screw shaft 2 is reversed, the nut 3 moves in the second direction X2. When the nut 3 moves in the second direction, the balls 43 rotate in the direction indicated by arrow B2 in FIG. 5. Therefore, on the inner spline groove 42, the balls 43 roll in the second direction X2. On the other hand, on the outer spline groove 41, the balls 43 roll in the first direction X1.

[0064] 3, when the nut 3 returns to the initial position, the ball 43 abuts against the surface 46a of the first wall portion 46 and the surface 47a of the second wall portion 47. Even if the nut 3 attempts to move further in the second direction X2, the ball 43 gets caught on the surface 46a of the first wall portion 46 and the surface 47a of the second wall portion 47. Therefore, movement of the nut 3 in the second direction X2 from the initial position is restricted. From the above, the nut 3 can be reliably aligned to the initial position.

[0065] As described above, the actuator 100 of the first embodiment includes the ball screw device 1 having the screw shaft 2, the nut 3, and a plurality of balls 4, the housing 20 that accommodates the ball screw device 1, and the spline mechanism 40 that supports the nut 3 so that it cannot rotate around the central axis O3 of the nut 3. One axial direction parallel to the central axis O3 of the nut 3 is defined as a first direction X1, and the other axial direction is defined as a second direction X2. The housing 20 has an inner circumferential surface 22 that faces the outer circumferential surface 11 of the nut 3. The spline mechanism 40 has a plurality of outer spline grooves 41 provided on the outer peripheral surface 11 of the nut 3 and extending in the axial direction, a plurality of inner spline grooves 42 provided on the inner peripheral surface 22 of the housing 20, extending in the axial direction and facing the outer spline grooves 41, a plurality of rolling elements (balls 43) arranged between the outer spline groove 41 and the inner spline groove 42 and at least a portion of which enters each of the outer spline groove 41 and the inner spline groove 42, a first wall portion 46 closing the end of the outer spline groove 41 in the first direction X1, and a second wall portion 47 closing the end of the inner spline groove 42 in the second direction X2.

[0066] According to the actuator 100 of the first embodiment, the nut 3 can be easily positioned in its initial position. Furthermore, the spline mechanism 40 that prevents the nut 3 from rotating allows the nut 3 to be positioned in its initial position. Therefore, there is no need to provide a separate component (e.g., a stopper component) for positioning the nut 3 in its initial position. This avoids an increase in the number of components in the actuator 100. Furthermore, the outer peripheral surface 11 of the nut 3 is in contact with balls (rolling elements) 43. Therefore, the nut 3 is supported by the housing 20 from the radially outer side via the balls 43.

[0067] Next, a description will be given of a modified version of the actuator 100 of embodiment 1, which is partially modified. The following description will focus on the differences from embodiment 1 and other modified versions described above.

[0068] (Variation 1) FIG. 7 is an axial cross-section of the actuator of Modification 1, and an enlarged view of a portion of the cross-section. As shown in FIG. 7, the spline mechanism 40A of the actuator 100A of Modification 1 differs from that of Embodiment 1 in that it includes a groove 50 formed on the outer peripheral surface 11 of the nut 3 and a retaining ring 51 fitted into the groove 50. The groove 50 extends circumferentially along the outer peripheral surface 11 of the nut 3 and is annular. The groove 50 is disposed at the end of each outer peripheral spline groove 41 in the second direction X2. The retaining ring 51 is C-shaped when viewed from the axial direction. The retaining ring 51 extends across the four outer peripheral spline grooves 41. The retaining ring 51 closes the end of each outer peripheral spline groove 41 in the second direction X2. Therefore, when the ball 43 moves toward the opening 45, the ball 43 comes into contact with the retaining ring 51, restricting movement of the ball 43 in the second direction X2. This reliably prevents the ball 43 from falling out of the opening 45.

[0069] (Variation 2) FIG. 8 is an axial cross-section of an actuator of Modification 2, and is an enlarged view of a portion of the cross-section. As shown in FIG. 8, a spline mechanism 40B of Modification 2 differs from Embodiment 1 in that a fourth wall portion 49 is provided at the end of the outer-peripheral spline groove 41 in the second direction X2 instead of the opening portion 45 (see FIG. 3). The spline mechanism 40B of Modification 2 also differs from Embodiment 1 in that an opening portion 52 is provided at the end of the inner-peripheral spline groove 42 in the first direction X1 instead of the third wall portion 48 (see FIG. 3). That is, the inner-peripheral spline groove 42 of Modification 2 extends to the end of the inner circumferential surface 22 of the housing 20 in the first direction X1. The opening portion 52 is formed at the end of the inner-peripheral spline groove 42 in the first direction X1 by cutting out an edge of the opening portion 23 of the housing 20, thereby opening the inner-peripheral spline groove 42 in the first direction X1.

[0070] According to the second modification, when the nut 3 moves in the first direction X1, the balls 43 roll on the outer-peripheral spline grooves 41 in the second direction X2. Furthermore, when the movement distance of the nut 3 in the first direction X1 reaches a predetermined distance, the balls 43 abut against the surface 49a of the fourth wall portion 49 facing the first direction X1. This restricts the balls 43 from rolling in the second direction X2. Furthermore, if the nut 3 moves further in the first direction X1 from this state, slippage (sliding friction) occurs between the balls 43 and the inner-peripheral spline grooves 42, preventing the nut 3 from moving smoothly in the first direction X1. Therefore, the drive of the motor is restricted so that the nut 3 does not move further in the first direction X1 from the state in which the balls 43 abut against the surface 49a of the fourth wall portion 49. From the above, the state in which the balls 43 abut against the surface 49a of the fourth wall portion 49 is the state in which the nut 3 has moved the furthest in the first direction X1.

[0071] In the second modification, the axial length M42 of the inner spline groove 42 is greater than the axial length M41 of the outer spline groove 41. Therefore, even when the nut 3 has moved the most in the first direction X1, the balls 43 do not move to the end of the inner spline groove 42 in the first direction X1. In other words, the balls 43 do not fall out of the openings 52 in the first direction X1.

[0072] To briefly explain the method of assembling the actuator 100B of Modification 2, first, the nut 3 of the ball screw device 1 is inserted into the inner peripheral side of the retainer 44. Next, the balls 43 are inserted into the pockets 44a from the outer peripheral side of the retainer 44. As a result, some of the balls 43 held by the retainer 44 enter the outer peripheral spline grooves 41. In addition, the ball screw device 1, the retainer 44, and the plurality of balls 43 are integrated. Next, the ball screw device 1, the retainer 44, and the plurality of balls 43 are inserted into the accommodation space 21 through the opening 23 of the housing 20. At this time, they are aligned so that the direction in which the inner peripheral spline grooves 42 are arranged coincides with the direction in which the balls 43 are arranged, as viewed from the central axis O3. As a result, some of the balls 43 enter the inner peripheral spline grooves 42 from the opening 52, and the actuator 100B is completed.

[0073] As described above, in the actuator 100B of the second modification, an increase in the number of parts is avoided, similar to the first embodiment.

[0074] In the first embodiment and the second modified example, the length (L41, M41) of the outer-peripheral spline groove 41 and the length (L42, M42) of the inner-peripheral spline groove 42 are longer on the side where the openings 45, 52 are provided, but in the present disclosure, the spline groove on the side where the openings 45, 52 are not provided may be longer. Alternatively, in the present disclosure, the length of the outer-peripheral spline groove 41 and the length of the inner-peripheral spline groove 42 may be the same.

[0075] (Variation 3) FIG. 9 is an axial cross-section of the actuator of Modification 3, and an enlarged view of a portion of the cross-section. As shown in FIG. 9, the spline mechanism 40C of the actuator 100C of Modification 3 differs from Modification 2 in that it includes a groove 53 formed on the inner circumferential surface 22 of the housing 20 and a C-shaped retaining ring 54 that fits into the groove 53. The groove 53 extends circumferentially along the inner circumferential surface 22 and is annular. The groove 53 is disposed at the end of each of the inner spline grooves 42 in the first direction X1. The retaining ring 51 closes the end of each of the inner spline grooves 42 in the first direction X1. According to Modification 3, when the ball 43 moves toward the opening 52, the ball 43 comes into contact with the retaining ring 54. This reliably prevents the ball 43 from falling out of the opening 52.

[0076] (Variation 4) Fig. 10 is an axial cross section of the actuator of Modification 4, and an enlarged view of a portion of the cross section. As shown in Fig. 10, the actuator 100D of Modification 4 differs from Embodiment 1 in that two (plural) balls (rolling elements) 43 are arranged between a pair of opposing outer peripheral spline grooves 41 and inner peripheral spline grooves 42. According to Modification 4, the number of balls (rolling elements) 43 is increased compared to Embodiment 1, and therefore the radial load capacity for supporting the nut 3 is increased. Note that, although Modification 4 exemplifies the number of rolling elements as two, the present disclosure may also include three or more rolling elements.

[0077] (Variation 5) FIG. 11 is a cross-sectional view of an actuator of Modification 5 taken in the axial direction. As shown in FIG. 11, an actuator 100E of Modification 5 differs from Embodiment 1 in that a plain bearing 57 is disposed between the outer peripheral surface 11 of the nut 3 and the inner peripheral surface 22 of the housing 20. The outer peripheral surface 57a of the plain bearing 57 is fitted into the inner peripheral surface 22 of the housing 20. The outer peripheral surface 11 of the nut 3 slidably contacts the inner peripheral surface 57b of the plain bearing 57. The plain bearing 57 is disposed closer to the opening 23 of the accommodation space 21. In other words, the plain bearing 57 and the balls 43 are spaced apart in the axial direction. According to Modification 5, when an external radial load acts on the nut 3, the nut 3 is supported at two points: the balls 43 and the plain bearing 57. This prevents the nut 3 from tilting.

[0078] (Variation 6) Fig. 12 is a cross-sectional view of the actuator of Modification 6 taken along the axial direction. As shown in Fig. 12, a housing 20F of an actuator 100F of Modification 6 differs from that of Embodiment 1 in that it is composed of two components: a first component 110 and a second component 120. The first component 110 is formed in a cylindrical shape centered on a central axis O3. The internal space of the first component 110 forms part of the accommodation space 21. An inner peripheral surface 111 of the first component 110 faces the outer peripheral surface 11 of the nut 3.

[0079] The second component 120 is a skeletal component that forms the main body of the housing 20. Therefore, the second component 120 is larger than the first component 110. The second component 120 has a cylindrical fitting surface 121 into which the outer peripheral surface 112 of the first component 110 fits. The inner peripheral surface 111 of the first component 110 is formed with a plurality of inner peripheral spline grooves 42, a plurality of second wall portions 47, and a plurality of third wall portions 48. The materials of the first component 110 and the second component are not particularly limited, and examples thereof include resin materials and metal materials.

[0080] As described above, according to the sixth modification, the object on which the inner circumferential spline groove 42 is formed is the first component 110. In other words, the object on which the inner circumferential spline groove 42 is formed is smaller than in the first embodiment. Therefore, the inner circumferential spline groove 42 is easier to form, and can be formed (machined) with high precision. Furthermore, according to the sixth modification, the first component 110 and the second component 120 can be made of different materials. Note that, as an example of making the first component 110 and the second component 120 out of different materials, the first component 110 can be made of an iron-based alloy that has excellent strength and rigidity, and the second component 120 can be made of a light alloy such as an aluminum alloy that can be made lighter, but the present disclosure is not limited to this.

[0081] In addition, in the method of assembling the actuator 100F of Modification 6, the cage 44, the balls 43, and the ball screw device 1 are assembled to the first part 110 to be integrated. Thereafter, the first part 110 to which the ball screw device 1 and the like are assembled may be fitted to the second part 120. Alternatively, the first part 110 may be fitted to the second part 120 first. Next, the cage 44, the balls 43, and the ball screw device 1 may be assembled to the first part 110 that is fitted to the second part 120.

[0082] (Variation 7) Fig. 13 is an axial cross section of the actuator of Modification 7, and an enlarged view of a portion of the cross section. As shown in Fig. 13, the housing 20G of the actuator 100G of Modification 7 is the same as that of Modification 6 in that it is made up of two parts (a first part 110G and a second part 120G). However, it differs from Modification 6 in that the second wall portion 47 is made up of the second part 120G.

[0083] The inner spline grooves 42 of the first component 110G extend to the end of the inner circumferential surface 111 in the second direction X2. Furthermore, the end surface 113 of the first component 110G in the second direction X2 is cut out by the inner spline grooves 42. Therefore, in the seventh modification, an opening 130 is formed at the end of the inner spline groove 42 in the second direction X2.

[0084] The second part 120G has an end face 122 that faces the first direction X1 and abuts against the end face 113 of the first part 110G. The end face 122 also closes the opening 130. Therefore, the second part 120 forms a second wall portion 47 that closes the inner peripheral spline groove 42 from the second direction X2. As a result, as shown in FIG. 13 , when the ball 43 abuts against the first wall portion 46 and the second wall portion 47 (second part 120G) of the nut 3, the nut 3 is positioned in its initial position. Therefore, in the seventh modification, as in the first embodiment, an increase in the number of parts can be avoided and the nut 3 can be easily positioned in its initial position.

[0085] Furthermore, the second wall portion 47 of Modification 7 is chamfered (C-chamfered). That is, the surface 47a of the second wall portion 47 facing the first direction X1 is inclined in the second direction X2 as it extends radially inward. This prevents the ball 43 from being damaged even when the ball 43 comes into contact with the surface 47a. Although the second wall portion 47 of Modification 7 is C-chamfered, the present disclosure may use a second wall portion 47 that is R-chamfered or a second wall portion 47 that is not chamfered (the surface 47a extends radially). Alternatively, the surface 47a of the second wall portion 47 of Modification 7 may have an upward-cut (arcuate) cross-sectional shape when cut in the axial direction, like the surface 46a of the first wall portion 46 described in Embodiment 1.

[0086] Modification 7 also differs from Modification 6 in that a fourth wall portion 49 is provided at the end of the outer-peripheral spline groove 41 in the second direction X2. This prevents the balls 43 from falling out of the end of the outer-peripheral spline groove 41 in the second direction X2, as described in Modification 2. In other words, Modification 7 prevents the balls 43 from falling out of both the outer-peripheral spline groove 41 and the inner-peripheral spline groove 42. Note that, although Modification 7 uses a nut 3 provided with the fourth wall portion 49, the present disclosure may use a nut 3 provided with an opening 45 (the nut 3 of embodiment 1) instead of this nut 3.

[0087] In assembling the actuator 100G of the seventh modification, first, the nut 3 of the ball screw device 1 is inserted into the inner peripheral side of the retainer 44. Next, the balls 43 are inserted into the pockets 44a from the outer peripheral side of the retainer 44. As a result, some of the balls 43 held by the retainer 44 enter the outer peripheral spline grooves 41, and the ball screw device 1, the retainer 44, and the plurality of balls 43 are integrated.

[0088] Next, the integrated retainer 44, ball screw device 1, and plurality of balls 43 are inserted from the second direction X2 of the first part 110G. Here, alignment is performed so that the direction in which the inner peripheral spline grooves 42 are arranged overlaps with the direction in which the balls 43 are arranged, as viewed from the central axis O3. As a result, a portion of the balls 43 (a portion that protrudes radially outward beyond the retainer 44) passes through the opening 130 and enters the inner peripheral spline grooves 42. Next, the first part 110G, in which the retainer 44, ball screw device 1, and plurality of balls 43 are integrated, is fitted into the second part 120, and the actuator 100G is completed.

[0089] Although the example in which the second wall portion 47 is chamfered has been given in Modification 7, in the present disclosure, the other wall portions (the first wall portion 46, the third wall portion 48, and the fourth wall portion 49) may also be chamfered. Furthermore, in the present disclosure, the surface of each wall portion may have a cross-sectional shape cut in the axial direction that extends in the radial direction. In other words, in the present disclosure, the shape of the surface of each wall portion that comes into contact with the rolling elements (balls 43) is not particularly important.

[0090] (Variation 8) Fig. 14 is a cross-sectional view of the actuator of Modification 8 taken in a direction perpendicular to the axial direction. As shown in Fig. 14, a spline mechanism 40H of an actuator 100H of Modification 8 differs from that of Embodiment 1 in that it includes cylindrical rollers 43H instead of balls 43. The cylindrical rollers 43H have a greater radial load capacity for supporting the nut 3 than the balls 43. As such, the rolling elements used in the spline mechanism of the present disclosure may be rolling elements other than the balls 43.

[0091] Figure 15 is an enlarged view of the cylindrical roller in Figure 14. As shown in Figure 15, the outer-periphery spline groove 41H and the inner-periphery spline groove 42H each have a different cross-sectional shape taken in the radial direction. To explain in detail, the cross-sectional shape of the outer-periphery spline groove 41H has an outer-periphery rolling surface 141 that is perpendicular to an imaginary line K that extends radially from the center axis O3, and a pair of flange surfaces 141a that extend radially outward from both ends of the outer-periphery rolling surface 141 in the width direction.

[0092] The cross-sectional shape of the inner spline groove 42H has an inner rolling surface 142 that is perpendicular to the imaginary line K, and a pair of flange surfaces 142a that extend radially inward from both ends in the width direction of the inner rolling surface 142. Therefore, when a load (torque) around the central axis O3 is transmitted to the nut 3, the cylindrical rollers 43H are caught on the flange surfaces 141a of the outer spline groove 41H and the flange surfaces 142a of the inner spline groove 42H. Therefore, even in the spline mechanism 40H of the eighth modification, the nut 3 is prevented from rotating.

[0093] Next, actuators according to Modifications 9 to 11 will be described. Modifications 9 and onward will provide examples in which the actuator is incorporated into an electric brake. Furthermore, the electric brakes according to Modifications 9 and onward will be exemplified as EMBs (Electro Mechanical Brakes). However, the actuators according to the present disclosure may also be used in EHBs (Electro-Hydraulic Brakes) in addition to EMBs. Furthermore, the actuators according to the present disclosure may also be used in devices other than electric brakes, such as EMBs and EHBs.

[0094] (Variation 9) 16 is a cross-sectional view of an actuator (electric brake) of Modification 9 taken along the axial direction. An electric brake 200 of Modification 9 includes an actuator 100I, a brake disc 201, and a brake pad 202. The brake disc 201 and the brake pad 202 are arranged in the first direction X1 with respect to an opening 23 of the actuator 100I. The brake disc 201 rotates together with a wheel (not shown). The brake pad 202 is arranged between the brake disc 201 and the actuator 100I.

[0095] 17 is a cross-sectional view taken along the axial direction showing the actuator (electric brake) of Modification 9 in operation. As shown in Fig. 17, when the electric brake 200 is activated, the nut 3 moves in the first direction X1 and presses the brake pad 202 against the brake disc 201. This applies a braking force to the brake disc 201.

[0096] On the other hand, the brake pad 202 receives a load (see arrow D in FIG. 16) in the rotational direction of the brake disc 201 due to frictional force with the brake disc 201. As a result, a radial load (see arrow D1 in FIG. 16) in the same direction as the load (see arrow D in FIG. 16) received by the brake pad 202 acts on the nut 3. Hereinafter, the direction of the radial load acting from the brake pad 202 to the nut 3 will be simply referred to as the load direction D1.

[0097] Figure 18 is a cross-sectional view taken along the line XVIII-XVIII in Figure 17. As shown in Figure 18, in the spline mechanism 40I of the actuator 100I, the four outer-periphery spline grooves 41 and the four inner-periphery spline grooves 42 are arranged at uneven intervals in the circumferential direction. Therefore, the four balls 43 are also arranged at uneven intervals in the circumferential direction.

[0098] To explain the arrangement of the four balls 43 in detail, two balls 43 (hereinafter referred to as balls 43A and 43B) are arranged in the load direction D1 from the central axis O3, and two balls 43 (hereinafter referred to as balls 43C and 43D) are arranged in the direction D2 opposite to the load direction D1 from the central axis O3.

[0099] The balls 43A and 43B are arranged in positions that are line-symmetric with respect to an imaginary line K3 that passes through the central axis O3 and extends in a direction parallel to the load direction D1. Similarly, the balls 43C and 43D are arranged in positions that are line-symmetric with respect to the imaginary line K3. On the other hand, the balls 43A and 43B are not arranged in positions that are line-symmetric with respect to the balls 43C and 43D with respect to an imaginary line K4 that passes through the central axis O3 and is perpendicular to the imaginary line K3.

[0100] The angle θ1 formed by the imaginary line K11 connecting the central axis O3 to the center of the ball 43A and the imaginary line K12 connecting the central axis O3 to the center of the ball 43B is less than 90°. The angle θ2 formed by the imaginary line K13 connecting the central axis O3 to the center of the ball 43C and the imaginary line K14 connecting the central axis O3 to the center of the ball 43D is 90°. The angle θ3 formed by the imaginary line K11 and the imaginary line K14 is greater than 90°. The angle θ4 formed by the imaginary line K12 and the imaginary line K13 is greater than 90°.

[0101] As described above, the balls 43C, 43D arranged in the opposite direction D2 from the imaginary line K4 are evenly arranged (arranged at 90° intervals), as in the first embodiment. On the other hand, the balls 43A, 43B arranged in the load direction D1 from the imaginary line K4 are spaced closer to each other, and the density of the balls 43 is high. In other words, the load-bearing capacity of the balls 43 in the load direction D1 as viewed from the central axis O3 is improved compared to when the balls 43 are evenly arranged. Therefore, even if a large radial load (external load) is applied to the nut 3, the nut 3 is supported by the housing 20 via the balls 43.

[0102] When the nut 3 is displaced in the load direction D1 due to a radial load, the surface pressure of the inner circumferential raceway surface 12 and the outer circumferential raceway surface 7, which are arranged in the opposite direction D2, increases. Therefore, it is preferable to arrange each circulation portion 13 while taking this surface pressure into consideration.

[0103] In addition, as shown in FIG. 2, in the first embodiment, four outer-periphery spline grooves 41 and four inner-periphery spline grooves 42 are arranged at equal intervals. Therefore, even if the nut 3 is deviated from the predetermined angle by, for example, 90°, the nut 3 can be assembled to the housing 20. On the other hand, according to the actuator 100I of the ninth modification, if the nut 3 is deviated from the predetermined angle, it cannot be assembled to the housing 20. In other words, according to the ninth modification, incorrect assembly of the nut 3 (assembling at an angle different from the predetermined angle) is prevented. This also prevents the circulation portion 13 from being disposed in the opposite direction D2 due to incorrect assembly of the nut 3, which would damage the connection portion of the inner peripheral raceway surface 12.

[0104] (Variation 10) 19 is a cross-sectional view of an actuator (electric brake) of Modification 10 taken in the axial direction. As shown in FIG. 19, the actuator 100J of Modification 10 is similar to Modification 9 in that the four outer-periphery spline grooves 41 and the four inner-periphery spline grooves 42 are arranged at uneven intervals in the circumferential direction. However, the actuator 100J of Modification 10 differs from Modification 9 in that the balls 43A and 43B are arranged in positions that are line-symmetrical with respect to the balls 43C and 43D with respect to the imaginary line K4. That is, the angle θ2 formed by the imaginary line K13 connecting the central axis O3 and the center of the ball 43C and the imaginary line K14 connecting the central axis O3 and the center of the ball 43D is the same angle as θ1 and is less than 90°.

[0105] As described above, according to the actuator 100J of the tenth modification, the balls are arranged in the direction D2 opposite to the load direction D4 with a high density when viewed from the nut 3. Therefore, the load resistance in the direction D2 opposite to the load direction D1 can be improved compared to when the balls 43 are evenly arranged.

[0106] (Variation 11) Fig. 20 is a cross-sectional view of an actuator (electric brake) of Modification 11 taken in the axial direction. As shown in Fig. 20, actuator 100K of Modification 11 differs from Modification 9 in that it has a piston 60. The piston 60 is a cylindrical part that includes a pressing portion 61 that closes the opening of the nut 3 in the first direction X1, and a cylindrical portion 62 that fits onto the outer peripheral surface 11 of the nut 3. Accordingly, when electric brake 200K is activated, piston 60 presses brake pad 202 against brake disc 201.

[0107] Also, the eleventh modification differs from the ninth modification in that the outer peripheral spline grooves 41 of the eleventh modification are formed on the outer peripheral surface 63 of the cylindrical portion 62 of the piston 60, rather than on the outer peripheral surface 11 of the nut 3. The piston 60 and the nut 3 are also prevented from rotating relative to each other. According to the eleventh modification, the piston 60 is supported by the housing 20 so as not to rotate. Therefore, the nut 3 is also supported by the housing 20 so as not to rotate via the piston 60. Furthermore, smooth movement of the piston 60 can be achieved. Furthermore, it is easy to position the piston 60 (nut 3) in the initial position.

[0108] Although the first embodiment and each modified example have been described above, the present disclosure is not limited to the above examples. For example, while the spline mechanism 40 in the first embodiment and each modified example includes a retainer 44, the present disclosure does not necessarily include a retainer 44. Furthermore, the number of outer peripheral spline grooves 41 and inner peripheral spline grooves 42 in the spline mechanism 40 is not limited to four. The spline mechanism of the present disclosure is only required to prevent rotation of the tubular part, allow smooth movement of the tubular part, and position the tubular part in its initial position, and is only required to have at least two outer peripheral spline grooves and two inner peripheral spline grooves.

[0109] Furthermore, when the cylindrical part is a nut 3, it is preferable that the circulation portion 13 and the outer peripheral spline groove 41 be arranged in different directions as viewed from the central axis O3. If the S-shaped groove surface formed by forging were arranged in the same direction as the outer peripheral spline groove 41 as viewed from the central axis O3, the thickness between the S-shaped groove surface and the outer peripheral spline groove 41 would be thin, and the nut 3 would not maintain a predetermined strength. On the other hand, if the thickness between the S-shaped groove surface and the outer peripheral spline groove 41 were set to a predetermined thickness, the entire nut would be thick, resulting in an increase in size. Furthermore, because the pieces, tubes, etc. would interfere with the balls 43 rolling in the outer peripheral spline groove 41, it would be difficult to arrange the pieces, tubes, etc. in the same direction as the outer peripheral spline groove 41 as viewed from the central axis O3. For these reasons, it is preferable that the circulation portion 13 and the outer peripheral spline groove 41 be arranged in different directions as viewed from the central axis O3.

[0110] Furthermore, in embodiment 1 and each modified example, the nut 3 and piston 60 are given as examples of tubular parts, but the present disclosure also allows for a sleeve that fits onto the outer periphery of the nut 3, and there are no particular limitations on the type of tubular part.

[0111] The present disclosure may also be implemented as a combination of the following configurations. (1) a cylindrical tubular part; a housing that accommodates the tubular part; a spline mechanism that supports the tubular part so as not to rotate around a central axis of the tubular part; Equipped with one of the axial directions parallel to the central axis of the cylindrical part is defined as a first direction, and the other is defined as a second direction; the housing has an inner circumferential surface facing an outer circumferential surface of the tubular part, The spline mechanism includes: a plurality of outer circumferential spline grooves provided on an outer circumferential surface of the tubular part and extending in the axial direction; a plurality of inner peripheral spline grooves provided on an inner peripheral surface of the housing, extending in the axial direction and facing the outer peripheral spline grooves; a plurality of rolling elements disposed between the outer peripheral spline groove and the inner peripheral spline groove, at least a portion of which is fitted into each of the outer peripheral spline groove and the inner peripheral spline groove; a first wall portion that closes an end portion of the outer-periphery spline groove in the first direction; a second wall portion that closes an end portion of the inner peripheral spline groove in the second direction; An actuator having: (2) The spline mechanism is disposed between the outer peripheral surface of the tubular part and the inner peripheral surface of the housing and includes a cage that holds the rolling elements. The actuator according to (1). (3) The spline mechanism includes: an opening that opens an end of the outer circumferential spline groove in the second direction; a third wall portion that closes an end portion of the inner peripheral spline groove in the first direction; and The outer peripheral spline groove has a length in the axial direction greater than that of the inner peripheral spline groove. The actuator according to (1) or (2). (4) The spline mechanism includes: a groove provided on an outer peripheral surface of the tubular part and extending in a circumferential direction; a retaining ring fitted into the groove; and The retaining ring closes the end of the outer circumferential spline groove in the second direction. The actuator according to (3). (5) The spline mechanism includes: a fourth wall portion that closes an end portion of the outer-periphery spline groove in the second direction; an opening that opens an end of the inner peripheral spline groove in the first direction; and The inner peripheral spline groove has a length in the axial direction greater than that of the outer peripheral spline groove. The actuator according to (1) or (2). (6) The spline mechanism includes: a groove provided on an inner peripheral surface of the housing and extending in a circumferential direction; a retaining ring fitted into the groove; and The retaining ring closes the end of the inner peripheral spline groove in the first direction. (5) The actuator according to (5). (7) The plurality of outer peripheral spline grooves and the plurality of inner peripheral spline grooves are arranged at equal intervals in the circumferential direction. An actuator according to any one of (1) to (6). (8) The plurality of outer peripheral spline grooves and the plurality of inner peripheral spline grooves are arranged at uneven intervals in the circumferential direction. An actuator according to any one of (1) to (6). (9) The rolling elements are arranged between a pair of the outer peripheral spline groove and the inner peripheral spline groove that face each other. An actuator according to any one of (1) to (8). The actuator according to claim 1. (10) The rolling elements are cylindrical rollers An actuator according to any one of (1) to (9). (11) a sliding bearing fitted to the inner peripheral surface of the housing and abutting against the outer peripheral surface of the cylindrical part; An actuator according to any one of (1) to (10). (12) The housing includes: a cylindrical first part having the inner circumferential surface; a second part having a fitting surface into which the outer peripheral surface of the first part fits; Equipped with The plurality of inner peripheral spline grooves are formed on the inner peripheral surface of the first component. An actuator according to any one of (1) to (11). (13) the second component has an annular wall surface that abuts against an end surface of the first component in the second direction, The wall surface closes the end of the inner peripheral spline groove in the second direction. The actuator according to (12). (14) a ball screw device having a screw shaft, a nut, and a plurality of balls; The cylindrical part is the nut. An actuator according to any one of (1) to (13). (15) a ball screw device having a screw shaft, a nut, and a plurality of balls; a piston fitted to the nut; Equipped with The cylindrical part is the piston. An actuator according to any one of (1) to (13). [Explanation of symbols]

[0112] 1. Ball screw device 2 screw shaft 3 nuts 4 balls 7 Outer raceway surface 11 Outer surface 12 Inner raceway surface 13 Circulation section 20, 20F, 20G housing 40, 40A, 40B, 40C, 40H spline mechanism 41, 41H outer spline groove 42, 42H inner spline groove 43, 43A, 43B, 43C, 43D Balls (rolling elements) 43H cylindrical roller 44 Cage 45 Opening 46 1st wall 47 Second wall section 48 Third wall 49 4th wall 50, 53 groove 51, 54 Retaining ring 52 Opening 57 Plain bearings 60 pistons 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G, 100H, 100I, 100J, 100K Actuators 110, 110G 1st part 120, 120G second part 130 Opening 200 Electric Brake 201 Brake disc 202 Brake pads

Claims

1. a cylindrical tubular part; a housing that accommodates the tubular part; a spline mechanism that supports the tubular part so as not to rotate around a central axis of the tubular part; Equipped with one of the axial directions parallel to the central axis of the cylindrical part is defined as a first direction, and the other is defined as a second direction; the housing has an inner circumferential surface facing an outer circumferential surface of the tubular part, The spline mechanism includes: a plurality of outer circumferential spline grooves provided on an outer circumferential surface of the tubular part and extending in the axial direction; a plurality of inner peripheral spline grooves provided on an inner peripheral surface of the housing, extending in the axial direction and facing the outer peripheral spline grooves; a plurality of rolling elements disposed between the outer peripheral spline groove and the inner peripheral spline groove, at least a portion of which is fitted into each of the outer peripheral spline groove and the inner peripheral spline groove; a first wall portion that closes an end portion of the outer-periphery spline groove in the first direction; a second wall portion that closes an end portion of the inner peripheral spline groove in the second direction; An actuator having:

2. The spline mechanism is disposed between the outer peripheral surface of the tubular part and the inner peripheral surface of the housing and includes a cage that holds the rolling elements. The actuator of claim 1 .

3. The spline mechanism includes: an opening that opens an end of the outer circumferential spline groove in the second direction; a third wall portion that closes an end portion of the inner peripheral spline groove in the first direction; and The outer peripheral spline groove has a length in the axial direction greater than that of the inner peripheral spline groove. The actuator of claim 1 .

4. The spline mechanism includes: a groove provided on an outer peripheral surface of the tubular part and extending in a circumferential direction; a retaining ring fitted into the groove; and The retaining ring closes the end of the outer circumferential spline groove in the second direction. The actuator according to claim 3 .

5. The spline mechanism includes: a fourth wall portion that closes an end portion of the outer-periphery spline groove in the second direction; an opening that opens an end of the inner peripheral spline groove in the first direction; and The inner peripheral spline groove has a length in the axial direction greater than that of the outer peripheral spline groove. The actuator of claim 1 .

6. The spline mechanism includes: a groove provided on an inner peripheral surface of the housing and extending in a circumferential direction; a retaining ring fitted into the groove; and The retaining ring closes the end of the inner peripheral spline groove in the first direction. The actuator according to claim 5 .

7. The plurality of outer peripheral spline grooves and the plurality of inner peripheral spline grooves are arranged at equal intervals in the circumferential direction. The actuator of claim 1 .

8. The plurality of outer peripheral spline grooves and the plurality of inner peripheral spline grooves are arranged at uneven intervals in the circumferential direction. The actuator of claim 1 .

9. The rolling elements are arranged between a pair of the outer peripheral spline groove and the inner peripheral spline groove that face each other. The actuator of claim 1 .

10. The rolling elements are cylindrical rollers The actuator of claim 1 .

11. a sliding bearing fitted to the inner peripheral surface of the housing and abutting against the outer peripheral surface of the cylindrical part; The actuator of claim 1 .

12. The housing includes: a cylindrical first part having the inner circumferential surface; a second part having a fitting surface into which the outer peripheral surface of the first part fits; Equipped with The plurality of inner peripheral spline grooves are formed on the inner peripheral surface of the first component. The actuator of claim 1 .

13. the second component has an annular wall surface that abuts against an end surface of the first component in the second direction, The wall surface closes the end of the inner peripheral spline groove in the second direction. The actuator of claim 12.

14. a ball screw device having a screw shaft, a nut, and a plurality of balls; The cylindrical part is the nut. The actuator of claim 1 .

15. a ball screw device having a screw shaft, a nut, and a plurality of balls; a piston fitted to the nut; Equipped with The cylindrical part is the piston. The actuator of claim 1 .

Images