Nut for ball screw device and ball screw device

Abstract

To provide a nut for a ball screw device in which a dimension in an axial direction can be reduced.SOLUTION: A nut 8 for a ball screw device includes: a nut body 19; a flange part 20 projecting from an outer peripheral surface of the nut body 19 toward a radial outer side; and a circulation tops 21a-21c attached to attachment holes 24a-24c of the nut body 19. The flange part 20 is configured of a plurality of flange pieces 22 arranged to be spaced apart in a circumferential direction. The circulation top 21a is provided at a portion of the nut body 19 which is away from the flange piece 22 in a circumferential direction and at which an axial position overlaps with the flange piece 22.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a nut for a ball screw device and a ball screw device. [Background technology]

[0002] A ball screw device uses balls to roll between a screw shaft and a nut, and is therefore more efficient than a sliding screw device in which the screw shaft and the nut are in direct contact with each other. For this reason, ball screw devices are incorporated into various types of machinery, such as electric brake devices and automatic manual transmissions (AMTs) for automobiles, and positioning devices for machine tools, in order to convert the rotational motion of a drive source, such as an electric motor, into linear motion.

[0003] The ball screw device has a screw shaft having a helical shaft-side ball screw groove on its outer circumferential surface, a nut having a helical nut-side ball screw groove on its inner circumferential surface, and a number of balls arranged between the shaft-side ball screw groove and the nut-side ball screw groove. The shaft-side ball screw groove and the nut-side ball screw groove are arranged to face each other in the radial direction and form a helical load path. The start point and end point of the load path are connected by a circulation means. The circulation means returns the balls that have reached the end point of the load path to the start point of the load path, circulating the balls.

[0004] The start point and the end point of the load path are switched depending on the direction of relative displacement in the axial direction between the screw shaft and the nut (relative rotation direction). In addition, in the ball screw device, one of the screw shaft and the nut is used as a rotational motion element, and the other of the screw shaft and the nut is used as a linear motion element depending on the application.

[0005] Various structures have been considered as circulating means for circulating the balls, but a circulating top is widely used because it allows the ball screw device to be configured compactly.

[0006] For example, Japanese Patent Application Laid-Open No. 2016-114185 (Patent Document 1) discloses a top-type ball screw device using a circulating top. Fig. 14 shows a ball screw device 100 of a conventional structure described in Japanese Patent Application Laid-Open No. 2016-114185.

[0007] The ball screw device 100 includes a screw shaft 101, a nut 102, and a plurality of balls 103. In this specification and claims, the axial direction, radial direction, and circumferential direction refer to the axial direction, radial direction, and circumferential direction with respect to the screw shaft, unless otherwise specified.

[0008] The screw shaft 101 has on its outer circumferential surface a spiral shaft-side ball screw groove 104. The screw shaft 101 is inserted into the inside of a nut 102 and is disposed coaxially with the nut 102.

[0009] The nut 102 has a helical nut-side ball screw groove 105 and a plurality of circulating grooves 106 on its inner circumferential surface.

[0010] The nut 102 is composed of a nut body 107 , a flange portion 108 , and a plurality of circulating tops 109 .

[0011] The nut body 107 has a cylindrical shape and has a nut-side ball screw groove 105 on its inner circumferential surface. The nut-side ball screw groove 105 and the shaft-side ball screw groove 104 are disposed so as to face each other in the radial direction, forming a helical load path 110. The nut body 107 also has a plurality of mounting holes 111 that penetrate the nut-side ball screw groove 105 in the radial direction so as to cut out the nut-side ball screw groove 105.

[0012] The flange portion 108 protrudes radially outward from the outer circumferential surface of the nut body 107. The flange portion 108 has a circular ring shape that is continuous in the circumferential direction, and is provided at one end in the axial direction of the outer circumferential surface of the nut body 107. The flange portion 108 is used for fixing the nut 102 to another mechanical component.

[0013] The circulation top 109 is attached to a mounting hole 111 of the nut body 107. The circulation top 109 has a substantially S-shaped circulation groove 106 on its radially inner surface facing the shaft-side ball screw groove 104. The circulation groove 106 connects the start point and the end point of the load path 110.

[0014] A plurality of balls 103 are arranged to be capable of rolling in the load path 110 and the circulation groove 106 .

[0015] In a ball screw device 100 having a conventional structure, a nut 102 is reciprocated in the axial direction by rotating a screw shaft 101. During this process, a ball 103 rolls inside a load path 110. Then, the ball 103 that has reached the end point of the load path 110 is returned to the start point of the load path 110 through a circulation groove 106. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] JP 2016-114185 A [Patent Document 2] JP 2021-122843 A Summary of the Invention [Problem to be solved by the invention]

[0017] The mounting holes for mounting the circulating tops are often formed by cutting the nut body. For this reason, in a structure in which an annular flange portion 108 is provided on the outer circumferential surface of the nut body 107, such as the ball screw device 100 of the conventional structure, the mounting holes 111 are formed in a portion of the nut body 107 that is axially offset from the flange portion 108, rather than in the portion where the flange portion 108 is provided. This is because, if a mounting hole is formed in the portion where the flange portion is provided, the amount of machining increases by the amount of the flange portion, leading to increased costs.

[0018] Therefore, in a structure in which an annular flange portion 108 is provided on the outer circumferential surface of a nut body 107, such as the ball screw device 100 of the conventional structure, it is difficult to arrange the circulation groove 106 in a portion of the inner circumferential surface of the nut body 107 that overlaps with the flange portion 108 in the axial direction. As a result, it is necessary to lengthen the axial dimension of the portion of the nut body 107 that is axially displaced from the flange portion 108, which makes it easy for the axial dimension of the nut 102 to become large.

[0019] The above problems occur not only in nuts having a circular flange portion used for fixing the flange portion to other mechanical components, but also in nuts used for applications such as engaging the flange portion with an anti-rotation member in the circumferential direction to prevent the nut from rotating relative to the screw shaft, as disclosed in Patent Publication No. 2021-122843 (Patent Document 2).

[0020] The present invention has been made to solve the above-mentioned problems, and has an object to provide a nut for a ball screw device that can reduce the axial dimension, and a ball screw device equipped with the nut for a ball screw device. [Means for solving the problem]

[0021] A nut for a ball screw device according to one aspect of the present invention has a helical nut-side ball screw groove and one or more circulation grooves on its inner circumferential surface, and includes a nut body, a flange portion, and a circulation top. The nut body is generally cylindrical in shape, has the nut side ball screw groove on its inner circumferential surface, and has one or more mounting holes that penetrate radially so as to cut out the nut side ball screw groove. The flange portion protrudes radially outward from an outer circumferential surface of the nut body. The circulating top is attached to the attachment hole. In the nut for a ball screw device according to one aspect of the present invention, at least one of the circulation grooves is provided in the circulation top. The flange portion is composed of a plurality of flange pieces spaced apart in the circumferential direction, or a single flange piece having a notch portion partially formed in the circumferential direction. In addition, when the flange portion is composed of a plurality of the flange pieces, the circumferential top is provided in a portion of the nut body that is circumferentially offset from the flange piece and that overlaps with the flange piece in the axial direction, and when the flange portion is composed of a single flange piece having the cutout portion, the circumferential top is provided in a portion whose circumferential phase coincides with that of the cutout portion and that overlaps with the flange piece in the axial direction.

[0022] In addition, when the circulating top is provided in a portion that overlaps with the flange piece in the axial direction, this does not necessarily mean that the entire circulating top is provided in the portion of the nut body that overlaps with the flange piece in the axial direction, but also includes the case where only a portion of the circulating top is provided. In any case, when multiple circulating tops are provided, it is not necessary for all of the circulating tops to be provided in the part where their axial position overlaps with the flange piece; it is sufficient that at least one of the circulating tops is provided in the part where its axial position overlaps with the flange piece.

[0023] In the nut for a ball screw device according to one aspect of the present invention, all of the circulation grooves can be provided in the circulation top. Alternatively, in a nut for a ball screw device according to one aspect of the present invention, a portion of the circulation grooves may be provided on the circulation top, and the remaining circulation grooves may be provided directly on the inner circumferential surface of the nut body.

[0024] In the nut for a ball screw device according to one aspect of the present invention, a plurality of the circulation tops may be provided, and the plurality of circulation tops may be disposed at equal intervals in the circumferential direction. Alternatively, the nut for a ball screw device according to one aspect of the present invention may include only one circulating top.

[0025] In the nut for a ball screw device according to one aspect of the present invention, the flange portion can be configured from a plurality of the flange pieces, and the plurality of flange pieces can be disposed at equal intervals in the circumferential direction. Alternatively, in the nut for a ball screw device according to one aspect of the present invention, the flange portion may be formed from a plurality of the flange pieces, and the plurality of the flange pieces may be arranged at unequal intervals in the circumferential direction.

[0026] In the nut for a ball screw device according to one aspect of the present invention, the flange piece may have a guide portion that can be engaged with a rotation prevention member in the circumferential direction. In this case, the flange piece may be provided with a function of engaging with the rotation prevention member in the circumferential direction to prevent the nut from rotating with respect to the screw shaft. As the guide portion, in addition to a guide hole penetrating the flange piece in the axial direction, a guide groove having a groove shape or a guide protrusion having a protrusion shape can also be used.

[0027] In a nut for a ball screw device according to one embodiment of the present invention, the flange piece can be given the function of engaging with an engagement recess provided on the inner surface of a rotating member such as a pulley or gear, thereby preventing relative rotation with respect to the rotating member.

[0028] In a nut for a ball screw device according to one aspect of the present invention, the nut body can have an axial protrusion on a circumferential portion of an end face on one axial side for preventing relative rotation with the screw shaft.

[0029] In a nut for a ball screw device according to one embodiment of the present invention, the axial protrusion can be arranged with a circumferential phase shift relative to the circulating top that is positioned furthest to one side in the axial direction among the circulating tops. In the nut for a ball screw device according to one aspect of the present invention, the axial protrusion can be disposed at a portion that is in phase with the flange piece in the circumferential direction.

[0030] The nut for a ball screw device according to one aspect of the present invention may include a sleeve fitted onto the nut body.

[0031] In one embodiment of the present invention, a nut for a ball screw device has the flange portion at one axial end of the nut body, and the sleeve has a cylindrical shape, and the end at one axial end can cover from the radial outside at least a portion of the circulating top that is positioned furthest to one axial end among the circulating tops.

[0032] In a nut for a ball screw device according to one aspect of the present invention, the flange portion can be provided at one axial end of the nut body and can be composed of a plurality of the flange pieces, and the sleeve can have a plurality of cover pieces arranged at one axial end at a distance in the circumferential direction. The cover pieces can be arranged between the flange pieces adjacent in the circumferential direction, and the cover pieces can cover the circulation top arranged furthest to the axial end from the radial outside.

[0033] In the nut for a ball screw device according to one aspect of the present invention, the circulation top can be fixed to the nut body by crimping. Alternatively, in the nut for a ball screw device according to one aspect of the present invention, the circulating top can be adhesively fixed to the nut body.

[0034] A ball screw device according to one aspect of the present invention includes a screw shaft, a nut, and a plurality of balls, and the nut can be a nut for a ball screw device according to one aspect of the present invention. Effect of the Invention

[0035] According to the nut for a ball screw device according to one aspect of the present invention, the axial dimension can be reduced. [Brief description of the drawings]

[0036] [Figure 1]FIG. 1 is a cross-sectional view showing an electric actuator equipped with a ball screw device according to a first embodiment. [Diagram 2] FIG. 2 is an end view of an electric actuator including a ball screw device according to a first embodiment, from which a second housing portion, an electric motor, and rolling bearings have been removed, as viewed from one axial side. [Diagram 3] FIG. 3 is an end view of a nut constituting a ball screw device according to a first example of the embodiment, with a circulating top attached, as viewed from one axial side. [Figure 4] FIG. 4 is a schematic diagram corresponding to a cross section taken along line AA in FIG. [Diagram 5] FIG. 5 is a perspective view showing a nut constituting a ball screw device according to a first example of the embodiment. [Figure 6] FIG. 6 is a view of a ball screw device according to a first example of the embodiment, seen from the radial outside with a sleeve and a circulating top removed from the nut. [Figure 7] FIG. 7 is a perspective view showing a ball screw device according to a first example of the embodiment, with a sleeve and a circulating top removed from the nut. [Figure 8] FIG. 8 is a diagram showing a second example of the embodiment, and corresponds to FIG. [Figure 9] FIG. 9 is a perspective view showing a sleeve taken out from a nut constituting a ball screw device according to a second example of the embodiment. [Figure 10] FIG. 10 is an end view showing a state in which a pulley is fitted onto a nut constituting a ball screw device according to a third example of the embodiment. [Figure 11] FIG. 11 is a diagram showing a third example of the embodiment, and corresponds to FIG. [Figure 12] FIG. 12 is a diagram showing a fourth example of the embodiment, and corresponds to FIG. [Figure 13] FIG. 13 is a diagram showing a fifth example of the embodiment, and corresponds to FIG. [Figure 14] FIG. 14 is a cross-sectional view showing a ball screw device of a conventional structure.

[0037] [First Example of Implementation] A first example of the embodiment will be described with reference to FIGS. 1 to 7. FIG.

[0038] [Overall configuration of ball screw device] The ball screw device 1 in this example is a top-type ball screw device that is incorporated into an electric actuator 2 such as an electric brake booster and is used to convert the rotational motion of an electric motor 3, which is the drive source, into linear motion of a piston 4.

[0039] The electric actuator 2 includes a ball screw device 1, an electric motor 3, a piston 4, and a housing 5.

[0040] The electric actuator 2 converts the rotational motion of the electric motor 3 into linear motion using the ball screw device 1, and causes a piston 4 to stroke within a cylinder hole 6 in a housing 5, thereby generating a target brake hydraulic pressure.

[0041] The ball screw device 1 includes a screw shaft 7, a nut 8, and a plurality of balls 9.

[0042] The screw shaft 7 is a rotational motion element that is rotationally driven by the electric motor 3 and rotates when in use. The screw shaft 7 is inserted into the nut 8 and arranged coaxially with the nut 8. The nut 8 is prevented from co-rotating with the screw shaft 7 by a rotation-preventing member 10 fixed to the housing 5, and is a linear motion element that moves linearly when in use. For this reason, the ball screw device 1 of this example is used in a mode in which the screw shaft 7 is rotationally driven to cause the nut 8 to move linearly. A piston 4 is fitted onto the nut 8, which is a linear motion element.

[0043] A spiral load path 11 is provided between the outer peripheral surface of the screw shaft 7 and the inner peripheral surface of the nut 8. A plurality of balls 9 are arranged in a rollable manner in the load path 11. When the screw shaft 7 and the nut 8 are rotated relative to each other, the balls 9 that have reached the end point of the load path 11 are returned to the start point of the load path 11 through circulation grooves 12a to 12d provided on the inner peripheral surface of the nut 8.

[0044] The structure of each component of the ball screw device 1 will be described below. In the following description, unless otherwise specified, the axial direction, radial direction, and circumferential direction refer to the axial direction, radial direction, and circumferential direction with respect to the screw shaft 7. Moreover, one axial side refers to the right side in Figs. 1, 4, and 6, and the other axial side refers to the left side in Figs. 1, 4, and 6.

[0045] [Screw shaft] The screw shaft 7 is made of metal and has a threaded portion 13 and a fitting shaft portion 14 arranged adjacent to one axial side of the threaded portion 13. The threaded portion 13 and the fitting shaft portion 14 are arranged coaxially and are integrally formed with each other.

[0046] The threaded portion 13 has a helical shaft-side ball screw groove 15 on its outer circumferential surface. The shaft-side ball screw groove 15 is formed on the outer circumferential surface of the threaded portion 13 by cutting (grinding) or rolling such as through-feed. In this example, the shaft-side ball screw groove 15 has one thread. The cross-sectional groove shape (groove bottom shape) of the shaft-side ball screw groove 15 is a gothic arch groove or a circular arc groove. The threaded portion 13 has a flat abutment surface 16 on one axial end face.

[0047] The fitting shaft portion 14 has an outer diameter smaller than that of the threaded portion 13. The fitting shaft portion 14 has male spline teeth 17 on its outer circumferential surface over the entire circumference.

[0048] 〔nut〕 The nut 8 has a helical nut-side ball screw groove 18 and a plurality of (four in the illustrated example) circulation grooves 12a to 12d on its inner circumferential surface.

[0049] The nut 8 includes a nut body 19 having a substantially cylindrical shape, a flange portion 20 protruding radially outward from the outer circumferential surface of the nut body 19, and a plurality of circulation tops 21a to 21d.

[0050] In this example, by devising the structure of the flange portion 20, it is possible to arrange the circulation top 21a in a portion of the nut body 19 that overlaps with the flange portion 20 in the axial direction, thereby realizing a reduction in the axial dimension of the nut 8. For this reason, first, the structure of the flange portion 20 will be described, and then the structures of the nut body 19 and the circulation tops 21a to 21d will be described.

[0051] <Flange> In this example, of the flange portion which has a circular ring shape in the conventional structure, only the portion necessary to ensure functionality and strength is retained and the other portions are removed, so that the flange portion 20 is not a circular ring shape which is continuous in the circumferential direction, but an interrupted flange which is discontinuous in the circumferential direction.

[0052] The flange portion 20 in this example is composed of a plurality of (three in the illustrated example) flange pieces 22 arranged at a distance in the circumferential direction. When the flange portion is composed of a plurality of flange pieces, the number of flange pieces is not limited to three, and can be appropriately determined based on the function, strength, etc. required for the flange pieces.

[0053] Each of the multiple flange pieces 22 is provided integrally with the nut body 19, and is provided at one axial end of the outer circumferential surface of the nut body 19. However, the flange pieces can also be formed separately from the nut body and fixed to the nut body.

[0054] The flange pieces 22 have the same shape. In this example, the flange pieces 22 are configured in a substantially rectangular plate shape. However, the shapes of the flange pieces may be different from each other.

[0055] The multiple flange pieces 22 are arranged at equal intervals in the circumferential direction. In the illustrated example, three flange pieces 22 are arranged at intervals of 120 degrees. However, the multiple flange pieces may also be arranged at unequal intervals in the circumferential direction.

[0056] Each of the flange pieces 22 has a guide hole 23 that corresponds to a guide portion recited in the claims and can be engaged with the anti-rotation member 10 in the circumferential direction. Therefore, the flange pieces 22 engage with the anti-rotation member 10 in the circumferential direction to exhibit the function of preventing the nut 8 from co-rotating with the screw shaft 7.

[0057] The guide hole 23 is provided in the radial middle part of the flange piece 22, and penetrates the flange piece 22 in the axial direction. The anti-rotation member 10 is inserted into the guide hole 23 so as to be slidable in the axial direction. The anti-rotation member 10 can also be inserted into the inside of the guide hole 23 via a sliding bush.

[0058] In the illustrated example, the cross-sectional shape of the anti-rotation member 10 is circular, and therefore the cross-sectional shape (opening shape) of the guide hole 23 is also circular. The cross-sectional shape of the guide hole is not limited to circular, and other shapes such as rectangular or semicircular arc can be adopted as long as the nut can be prevented from rotating by engaging with the anti-rotation member in the circumferential direction. In order to prevent the nut from rotating, a guide groove in the shape of a groove or a guide protrusion in the shape of a protrusion that can be engaged with the anti-rotation member in the circumferential direction can be provided on the radially outer surface of the flange piece.

[0059] A side surface on one axial direction side of the flange piece 22 is disposed flush with an end face on one axial direction side of the nut body 19. However, the side surface on one axial direction side of the flange piece 22 can also be disposed offset from the end face on one axial direction side of the nut body 19 toward the other axial direction side.

[0060] The circumferential dimension, axial dimension, and radial dimension (radial protrusion amount) of the flange piece 22 are determined based on the function, strength, etc. required for the flange piece 22. When the flange piece 22 is used for preventing the nut 8 from rotating together as in this example, the circumferential dimension of the flange piece 22 can be about 1 / 20 to 1 / 4 of the circumferential length of the outer peripheral surface of the nut body 19, and in the illustrated example, it is about 1 / 9 of the circumferential length of the outer peripheral surface of the nut body 19. In addition, in the application of this example, the axial dimension of the flange piece 22 can be about 1 / 4 to 1 / 10 of the axial dimension (total length) of the nut body 19, and in the illustrated example, it is about 1 / 6 of the axial dimension of the nut body 19. In addition, in the application of this example, the radial dimension of the flange piece 22 can be about 0.5 to 3 times the radial thickness dimension of the nut body 19, and in the illustrated example, it is about 1.5 times the radial thickness dimension of the nut body 19.

[0061] <Nut body> The nut body 19 is made of metal and has a cylindrical shape. The nut body 19 has a spiral nut-side ball screw groove 18 on its inner circumferential surface. The nut body 19 also has mounting holes 24a to 24d that penetrate the nut-side ball screw groove 18 in the radial direction so as to cut out the nut-side ball screw groove 18.

[0062] In this example, as described above, the flange portion 20 provided at one axial end of the outer circumferential surface of the nut body 19 is composed of a plurality of flange pieces 22 spaced apart in the circumferential direction. Therefore, the nut body 19 has, at one axial end, a partially annular flange-forming portion 25 having flange pieces 22 provided on the outer circumferential surface and a partially annular flange-free portion 26 having no flange pieces 22 provided on the outer circumferential surface, which are arranged alternately in the circumferential direction.

[0063] The flange-free portion 26 is present in a portion of the nut body 19 that is circumferentially offset from the flange piece 22 and coincides with the axial position of the flange piece 22. The outer peripheral surface (radial outer surface) of the flange-free portion 26 is configured by a partial cylindrical surface centered on the central axis of the nut body 19. As shown in Figures 6 and 7, the flange-free portion 26 may have the same diameter as the end portion or intermediate portion on the other axial side of the outer peripheral surface of the nut body 19, or may have a different diameter.

[0064] In the illustrated example, the nut body 19 has three flanged portions 25 and three non-flanged portions 26.

[0065] In this example, the circulation grooves 12a-12d are not provided directly on the inner peripheral surface of the nut body 19. Therefore, all of the circulation grooves 12a-12d provided on the nut 8 are provided on the circulation tops 21a-21d. However, among the circulation grooves provided on the nut, all or some of the circulation grooves except for the circulation groove whose axial position coincides with the flange portion may be provided on the circulation tops, and the remaining circulation grooves may be provided directly on the inner peripheral surface of the nut body.

[0066] The nut side ball screw groove 18 has a helical shape, and is formed by, for example, cutting (grinding) or rolling tapping (cutting tapping) on ​​the inner peripheral surface of the nut body 19. In this example, the nut side ball screw groove 18 is formed in a range from one end on the axial side to the other end on the axial side of the inner peripheral surface of the nut body 19.

[0067] The nut-side ball screw groove 18 has the same lead as the shaft-side ball screw groove 15. Therefore, when the threaded portion 13 of the screw shaft 7 is inserted into the inside of the nut 8, the shaft-side ball screw groove 15 and the nut-side ball screw groove 18 are arranged to face each other in the radial direction, forming a helical load path 11. The number of threads of the nut-side ball screw groove 18 is one, similar to the shaft-side ball screw groove 15. The groove shape of the cross section of the nut-side ball screw groove 18 is also a gothic arch groove or a circular arc groove, similar to the shaft-side ball screw groove 15. In this example, one axial end of the nut-side ball screw groove 18 is provided in a portion that overlaps with the flange piece 22 in the axial direction.

[0068] The mounting holes 24a to 24d are through holes for mounting the circulation tops 21a to 21d, respectively, and are open on both the inner and outer peripheral surfaces of the nut body 19.

[0069] In this example, a plurality of mounting holes 24a to 24d are provided. The mounting holes 24a to 24d are arranged so as to be shifted from one another in the circumferential and axial positions.

[0070] In this example, the mounting hole 24a closest to one axial direction side among the multiple mounting holes 24a to 24d is formed in one of the multiple non-flange-forming portions 26 constituting the end portion on one axial direction side of the nut body 19. Specifically, one half of the mounting hole 24a on one axial direction side is formed in the non-flange-forming portion 26. The other half of the mounting hole 24a on the other axial direction side is formed in a portion offset from the non-flange-forming portion 26 to the other axial direction side. However, the entire mounting hole may be formed in the non-flange-forming portion.

[0071] Among the multiple mounting holes 24a to 24d, mounting hole 24d which is closest to the other axial direction is formed at the other axial end of nut body 19. The remaining mounting holes 24b, 24c are formed in the middle of nut body 19 in the axial direction.

[0072] The multiple mounting holes 24a to 24d are arranged at equal intervals in the circumferential direction. In the illustrated example, the four mounting holes 24a to 24d are arranged at 90 degree intervals.

[0073] Each of the mounting holes 24a to 24d is formed by cutting using a cutting tool such as an end mill, and opens on the outer peripheral surface and the inner peripheral surface of the nut body 19. Each of the mounting holes 24a to 24d is formed so as to cut out a part of the nut-side ball screw groove 18 formed on the inner peripheral surface of the nut body 19. The central axis of each of the mounting holes 24a to 24d is arranged in the radial direction of the nut body 19.

[0074] Each of the mounting holes 24a-24d has a rectangular (rounded rectangular) cross-sectional shape, with the long side oriented in the circumferential direction and the short side oriented in the axial direction. That is, each of the mounting holes 24a-24d has a larger circumferential width than its axial width. However, the circumferential width of the mounting holes 24a-24d is smaller than the circumferential dimension of the outer circumferential surface of the flange-free portion 26.

[0075] <Circulating Top> The circulation tops 21a to 21d have circulation grooves 12a to 12d, respectively. The circulation tops 21a to 21d are provided in the same number as the mounting holes 24a to 24d provided in the nut body 19 (four in the illustrated example).

[0076] The circulation tops 21a to 21d are attached to the mounting holes 24a to 24d. Specifically, the circulation tops 21a to 21d are attached to the mounting hole 24a formed in the flange-free portion 26 constituting one axial end of the nut body 19, the mounting hole 24d formed in the other axial end of the nut body 19, and the mounting holes 24b and 24c formed in the axial middle portion of the nut body 19, one each.

[0077] The circulation top 21a furthest on one axial side is attached to the mounting hole 24a of the flange-free portion 26, and is provided in a portion of the nut body 19 that is circumferentially removed from the flange piece 22 and that overlaps in the axial direction with the flange piece 22. Specifically, the circulation top 21a has one axial half provided in a portion that overlaps in the axial direction with the flange piece 22. For this reason, the circulation groove 12a provided in the circulation top 21a is disposed in a portion of the inner circumferential surface of the nut body 19 that overlaps in the axial direction with the flange piece 22.

[0078] The multiple circulation tops 21a-21d are arranged at equal intervals in the circumferential direction. In the illustrated example, four circulation tops 21a-21d are arranged at 90 degree intervals. Moreover, the four circulation tops 21a-21d are arranged at equal intervals in the axial direction.

[0079] Each of the circulation tops 21a to 21d is made of metal or synthetic resin. When each of the circulation tops 21a to 21d is made of metal, they can be manufactured by metal powder injection molding (MIM) using metal powder (MIM alloy) such as Fe-Ni-C (1 to 8% Ni, up to 0.8% C), Fe-Cr-C (0.5 to 2% Cr, up to 0.8% C), SCM415, or SUS630 as a raw material.

[0080] Each of the circulation tops 21a to 21d has a substantially rectangular prism shape and is inserted into the inside of the mounting holes 24a to 24d with its central axis aligned with the central axis of the mounting holes 24a to 24d. The shape of the circulation top is not limited to a substantially rectangular prism shape, and may be a cylinder or an oval cylinder shape to match the shape of the mounting hole.

[0081] Each of the circulation tops 21a to 21d has a circulation groove 12a to 12d curved in a substantially S-shape on a radially inner surface (tip surface) radially facing the shaft-side ball screw groove 15. Each of the circulation grooves 12a to 12d smoothly connects adjacent screw grooves in the axial direction of the nut-side ball screw groove 18. Each of the circulation grooves 12a to 12d has a semi-elliptical cross-sectional shape. Each of the circulation grooves 12a to 12d has a groove width slightly larger than the diameter of the ball 9, and has a groove depth that allows the ball 9 moving in the circulation groove 12a to 12d to ride over the screw threads of the shaft-side ball screw groove 15.

[0082] With the circulation tops 21a to 21d attached to the nut body 19, a pair of openings of the circulation grooves 12a to 12d open to opposite sides in the circumferential direction and are connected to adjacent screw grooves in the axial direction of the nut side ball screw groove 18. As a result, each of the circulation grooves 12a to 12d is connected to the start point and end point of the load path 11. The circulation grooves 12a to 12d and the load path 11 formed between the shaft side ball screw groove 15 and the nut side ball screw groove 18 (within a range of approximately one turn) form one circuit. In other words, the start point and end point of the load path 11 are the connection points between the load path 11 and the circulation grooves 12a to 12d. The start point and end point of the load path 11 are replaced with each other as the direction of relative displacement (relative rotation direction) between the screw shaft 7 and the nut 8 in the axial direction changes and the moving direction of the balls 9 changes.

[0083] In this example, although not shown, when the circulation tops 21a to 21d are inserted into the mounting holes 24a to 24d from the radially outer side, the outward flanges provided on the radially outer side of the outer circumferential side of the circulation tops 21a to 21d abut against the bottom surfaces (seat surfaces) of the recesses provided on the opening edges of the mounting holes 24a to 24d. This prevents the circulation tops 21a to 21d from slipping out radially inward from the mounting holes 24a to 24d.

[0084] <Axial protrusion> The nut body 19 further includes an axial protrusion 27. The axial protrusion 27 is provided on a circumferential portion of a side surface on one axial side of the nut body 19, and protrudes toward one axial side. The axial protrusion 27 is used to regulate the stroke end of the nut 8. In this example, the axial protrusion 27 is provided integrally with the nut body 19, but the axial protrusion may also be separate from the nut body and fixed to the nut body.

[0085] The axial projection 27 is provided on one axial side of the flange forming portion 25 that constitutes one axial end of the nut body 19. Therefore, the axial projection 27 is out of phase with the circumferential top 21a that is disposed most toward one axial side. In the illustrated example, the axial projection 27 is out of phase with the circumferential top 21a that is disposed most toward one axial side by 180 degrees.

[0086] <sleeve> The nut 8 further includes a sleeve 28 for preventing the circulation tops 21a to 21d from slipping out radially outward from the mounting holes 24a to 24d.

[0087] The sleeve 28 is made of a rust-resistant metal such as a zinc-plated steel plate or a stainless steel plate, and has a cylindrical shape. The sleeve 28 is fitted onto the nut body 19. Specifically, the sleeve 28 is fitted onto a portion of the nut body 19 excluding the end portion on one axial side where the flange portion 20 is provided. The end portion on one axial side of the sleeve 28 abuts against the radially inner end portion of the side surface on the other axial side of the flange piece 22.

[0088] The sleeve 28 has an end portion on one axial side that radially covers a portion (a half portion on the other axial side) of the circulation top 21a that is attached to the mounting hole 24a of the flange-free portion 26. The sleeve 28 also has an end portion on the other axial side and an intermediate portion that radially cover the remaining circulation tops 21b to 21d. This prevents all of the circulation tops 21a to 21d from slipping out radially outward from the mounting holes 24a to 24d.

[0089] The sleeve 28 has a locking flange 29, which is a crimped portion bent radially inward, at its end on the other axial side. The locking flange 29 is locked in a locking groove 30 provided at the end on the other axial side of the outer circumferential surface of the nut body 19. This prevents the sleeve 28 from slipping out of the nut body 19 to the other axial side.

[0090] <ball> The balls 9 are steel balls having a predetermined diameter, and are arranged to be rollable in the load path 11 and the circulation grooves 12a to 12d. The balls 9 arranged in the load path 11 roll while receiving a compressive load, whereas the balls 9 arranged in the circulation grooves 12a to 12d roll by being pushed by the succeeding balls 9 without receiving a compressive load.

[0091] [Stopper] The ball screw device 1 of this embodiment further includes a stopper 31 for regulating the stroke end of the linearly moving nut 8. The stopper 31 is fitted onto the other axial end of the fitting shaft portion 14 of the screw shaft 7 so as not to rotate relative to the fitting shaft portion 14. The stopper 31 includes a boss portion 32 having an annular shape and a protrusion portion 33.

[0092] The boss portion 32 is fitted onto the fitting shaft portion 14 so as not to rotate relative thereto. Specifically, the boss portion 32 is fitted onto the fitting shaft portion 14 so as not to rotate relative thereto by spline-engaging the female spline teeth 34 on the inner peripheral surface with the male spline teeth 17 on the outer peripheral surface of the fitting shaft portion 14. The side surface on the other axial direction of the boss portion 32 abuts against the abutment surface 16 of the threaded portion 13, and the side surface on one axial direction of the boss portion 32 abuts against an end surface on the other axial direction of the motor output shaft 44, which will be described later. The protrusion portion 33 protrudes radially from a circumferential portion of the outer peripheral surface of the boss portion 32.

[0093] In the ball screw device 1 of this example, when the nut 8 moves linearly and reaches the stroke end, the axial projection 27 of the nut 8 and the projection 33 of the stopper 31 engage in the circumferential direction. This prevents the screw shaft 7 from rotating, making it possible to regulate the stroke end of the nut 8.

[0094] Next, the structures of the housing 5, the electric motor 3, and the piston 4 which constitute the electric actuator 2 together with the above-mentioned ball screw device 1 will be described.

[0095] 〔housing〕 The housing 5 is formed by axially combining a first housing portion 35 and a second housing portion 36. Each of the first housing portion 35 and the second housing portion 36 is made of a metal such as an aluminum alloy, and has a cylindrical shape with a bottom.

[0096] The first housing portion 35 has a stepped insertion hole 37 formed therein. The insertion hole 37 is open only on one axial side. The central axis of the insertion hole 37 is arranged coaxially with the central axis of the screw shaft 7.

[0097] The insertion hole 37 has a nut insertion hole 38 at one axial side, into which the nut 8 can be axially inserted. Therefore, the nut insertion hole 38 has an inner diameter larger than the outer diameter (the circumscribed circle diameter of the flange piece 22) of the flange portion 20. The nut insertion hole 38 has an inner peripheral surface that is cylindrical.

[0098] The insertion hole 37 has a cylinder hole 6, which is smaller in diameter than the nut insertion hole 38, on the other axial side of the nut insertion hole 38. A plurality of seal grooves (not shown) are provided on the inner peripheral surface of the cylinder hole 6. O-rings (not shown) that seal between the inner peripheral surface of the cylinder hole 6 and the outer peripheral surface of the piston 4 are attached to the seal grooves.

[0099] The insertion hole 37 has a stepped surface 39 facing one axial side between the nut insertion hole 38 and the cylinder bore 6. The stepped surface 39 is a flat surface perpendicular to the central axis of the insertion hole 37. The first housing portion 35 has first fixing holes 40 that open into the stepped surface 39. The first fixing holes 40 are provided at multiple locations (three locations in this example) in the circumferential direction of the stepped surface 39.

[0100] The second housing part 36 has an accommodating hole 41 therein. The accommodating hole 41 is open only on the other axial side. The accommodating hole 41 has an inner diameter smaller than the nut insertion hole 38 of the first housing part 35. The second housing part 36 has a fitting part 42 at the end on the other axial side. The fitting part 42 has an outer diameter smaller than that of a part of the second housing part 36 adjacent to one axial side of the fitting part 42. The second housing part 36 has a second fixing hole 43 that opens on the end face on the other axial side of the fitting part 42. The second fixing holes 43 are provided at multiple locations (three locations in this example) in the circumferential direction of the end face on the other axial side of the fitting part 42.

[0101] The first housing part 35 and the second housing part 36 are fixed to each other with the central axis of the insertion hole 37 aligned with the central axis of the accommodating hole 41, the circumferential phase of the first fixing hole 40 aligned with the second fixing hole 43 aligned, and one axial end of the first housing part 35 fitted externally into the mating part 42 of the second housing part 36.

[0102] [Electric motor] The electric motor 3 is accommodated in the accommodation hole 41 of the second housing part 36. The electric motor 3 includes a motor output shaft 44. The motor output shaft 44 is arranged coaxially with the screw shaft 7. The motor output shaft 44 has an engagement hole 45 that opens to the other end face in the axial direction. The inner peripheral surface of the engagement hole 45 is provided with female spline teeth 46 over the entire circumference. In this example, the end or middle part on one axial side of the fitting shaft part 14 constituting the screw shaft 7 is inserted into the inside of the engagement hole 45, and the male spline teeth 17 provided on the outer peripheral surface of the fitting shaft part 14 are spline-engaged with the female spline teeth 46, thereby connecting the screw shaft 7 and the motor output shaft 44 in a torque-transmitting manner. The motor output shaft and the screw shaft can also be connected via a reduction mechanism without being directly connected.

[0103] The motor output shaft 44 is rotatably supported by two rolling bearings 47a, 47b in the second housing portion 36. One of the rolling bearings, 47a, is a deep groove ball bearing, and rotatably supports one axial end of the motor output shaft 44 in the deep part of the accommodation hole 41. The other rolling bearing 47b is a four-point contact type ball bearing, and rotatably supports the other axial end of the motor output shaft 44 in the opening of the accommodation hole 41. In this example, the diameter of the rolling bearing 47b supporting the other axial end of the motor output shaft 44 is made larger than the diameter of the rolling bearing 47a supporting the one axial end of the motor output shaft 44.

[0104] 〔piston〕 The piston 4 is made of metal and has a cylindrical shape with a bottom. The piston 4 is fitted and fixed to the outside of the nut body 19. Specifically, the piston 4 is fitted and fixed to the outside of a small diameter portion 48 provided at the other axial end of the outer circumferential surface of the nut body 19. The piston 4 is disposed coaxially with the nut 8. The piston 4 is fitted into the cylinder hole 6 so as to be movable in the axial direction.

[0105] [Rotation prevention member] The electric actuator 2 of this example includes a rotation-preventing member 10 to prevent the nut 8 from rotating relative to the screw shaft 7. The rotation-preventing member 10 is a shaft-shaped member that extends in the axial direction. In this example, the rotation-preventing member 10 is made of a metal such as an iron-based alloy and has a cylindrical shape. Therefore, the rotation-preventing member 10 has a circular cross-sectional shape. The outer diameter of the rotation-preventing member 10 is slightly smaller than the inner diameter of the guide hole 23 provided in the nut 8.

[0106] In this example, three anti-rotation members 10 are provided, the same number as the guide holes 23. The three anti-rotation members 10 are disposed at equal intervals in the circumferential direction.

[0107] The central axis of the anti-rotation member 10 is arranged parallel to the central axis of the insertion hole 37. One axial end of the anti-rotation member 10 is inserted into the second fixing hole 43 and fixed to the second housing part 36, and the other axial end of the anti-rotation member 10 is inserted into the first fixing hole 40 and fixed to the first housing part 35. Therefore, the anti-rotation member 10 spans between the first housing part 35 and the second housing part 36.

[0108] The anti-rotation member 10 is inserted axially through the guide hole 23. As a result, the anti-rotation member 10 is engaged in the circumferential direction with the guide hole 23. In addition, the anti-rotation member 10 is slidable in the axial direction with respect to the guide hole 23.

[0109] <Operation Description> In the electric actuator 2 of this example, when the screw shaft 7 is rotationally driven by the electric motor 3, the nut 8, whose relative rotation with respect to the housing 5 is prevented by the anti-rotation member 10, moves axially through the nut insertion hole 38 while sliding axially through the guide hole 23 relative to the anti-rotation member 10. Then, the piston 4 fitted on the outside of the nut 8 is caused to stroke within the cylinder bore 6. As a result, the liquid or gas filled inside the cylinder bore 6 is discharged or sucked in through a communication hole (not shown), generating the target brake hydraulic pressure.

[0110] When the nut 8 moves relative to the screw shaft 7 toward one side in the axial direction and reaches a stroke end, the axial protrusion 27 of the nut 8 and the protrusion 33 of the stopper 31 engage in the circumferential direction. This prevents the screw shaft 7 from rotating. In this manner, the ball screw device 1 of this embodiment can restrict the stroke end related to the relative movement of the nut 8 toward one side in the axial direction with respect to the screw shaft 7 by the stopper 31. The stroke end related to the relative movement of the nut 8 toward the other side in the axial direction with respect to the screw shaft 7 can be restricted by utilizing various conventionally known stroke limiting mechanisms.

[0111] In this embodiment as described above, the axial dimension of the nut 8 can be reduced. That is, the nut 8 constituting the ball screw device 1 of this example has a flange portion 20 provided on the outer peripheral surface of the nut body 19 composed of a plurality of flange pieces 22 spaced apart in the circumferential direction, and a flange-free portion 26 where the flange pieces 22 are not provided on the outer peripheral surface is provided at a portion of the nut body 19 that coincides with the axial position of the flange pieces 22, and a mounting hole 24a is formed in the flange-free portion 26. Therefore, in this example, the mounting hole 24a can be machined in the portion that coincides with the axial position of the flange pieces 22 without increasing the amount of machining.

[0112] The circulation top 21a attached to the mounting hole 24a of the flange-free portion 26 is disposed in a portion of the nut body 19 that is circumferentially displaced from the flange piece 22 and that overlaps with the flange piece 22 in the axial direction, so that the circulation groove 12a can be disposed in a portion of the inner peripheral surface of the nut body 19 that overlaps with the flange piece 22 in the axial direction. Therefore, according to this example, the axial dimension of the portion of the nut body 19 that is displaced from the flange portion 20 to the other axial side can be shortened, so that the axial dimension of the nut 8 can be reduced.

[0113] Furthermore, in this example, since the flange portion 20 is composed of a plurality of flange pieces 22 spaced apart in the circumferential direction, the weight of the nut 8 can be reduced.

[0114] In this example, the axial protrusion 27 is arranged with a circumferential phase shift with respect to the circulation top 21a arranged on the most one axial side. In other words, the axial protrusion 27 and the mounting hole 24a formed in the flange-free portion 26 are circumferentially shifted in phase. As a result, the axial protrusion 27 is provided in a portion of the nut body 19 where the strength is sufficiently ensured by being circumferentially shifted from the mounting hole 24a of the flange-free portion 26, not in a portion where the strength is reduced by forming the mounting hole 24a in the flange-free portion 26. Therefore, in this example, even if the axial protrusion 27 engages with the protrusion 33 of the stopper 31 with force, the nut body 19 can be prevented from being deformed.

[0115] In this embodiment, the circulation tops 21a-21d are arranged at equal intervals in the circumferential direction, and the circulation grooves 12a-12d are arranged at equal intervals in the circumferential direction. Therefore, the nut 8 can support the screw shaft 7 from the radially outer side over the entire circumference via the balls 9. Also, the rigidity of the nut 8 can be prevented from changing in the circumferential direction.

[0116] Furthermore, in this example, since the multiple mounting holes 24a to 24d are arranged at equal intervals in the circumferential direction, the rigidity of the nut 8 can be easily ensured.

[0117] In this example, the stopper 31 is sandwiched between the abutment surface 16 of the screw shaft 7 and the other axial end surface of the motor output shaft 44. This prevents the stopper 31 from being displaced in the axial direction relative to the fitting shaft portion 14 of the screw shaft 7. This allows the stroke end of the nut 8 to be accurately regulated.

[0118] In addition, in this example, both axial ends of the motor output shaft 44 are rotatably supported by the housing 5 by the two rolling bearings 47a, 47b, so that the coaxiality between the motor output shaft 44 and the screw shaft 7 can be improved. Furthermore, the other axial end of the motor output shaft 44 connected to the screw shaft 7 is supported by a four-point contact type rolling bearing 47b, so that the coaxiality between the motor output shaft 44 and the screw shaft 7 can be further improved. Therefore, the efficiency of the ball screw device 1 can be improved.

[0119] [Second Example of the Implementation Form] The second embodiment will be described with reference to FIGS.

[0120] In this example, only the shape of the sleeve 28a that is fitted onto the nut body 19 is changed from the structure of the first example of the embodiment.

[0121] That is, the sleeve 28a has a plurality of cover pieces 49 arranged at one axial end portion at a distance from one another in the circumferential direction, so that the end portion of the sleeve 28a at one axial end portion has a comb-tooth shape.

[0122] The multiple cover pieces 49 are disposed between the circumferentially adjacent flange pieces 22 in a state in which the sleeve 28a is fitted onto the nut body 19. In other words, each of the multiple cover pieces 49 covers the outer circumferential surface of the non-flange portion 26. As a result, the entire circulation top 21a attached to the mounting hole 24a of the non-flange portion 26 is covered by the cover pieces 49 from the radially outer side.

[0123] In the present embodiment as described above, it is possible to effectively prevent the circulation top 21a attached to the mounting hole 24a of the flange-free portion 26 from slipping outward in the radial direction. In addition, since each of the multiple cover pieces 49 is disposed between the flange pieces 22 adjacent in the circumferential direction, it is also possible to effectively prevent the sleeve 28a from rotating relative to the nut body 19. The other configurations and effects are the same as those of the first embodiment.

[0124] [Third Example of the Implementation Form] The third embodiment will be described with reference to FIGS.

[0125] In this example, the function and the position where the flange portion 20a is formed are changed from the structure of the first example of the embodiment.

[0126] That is, the flange portion 20a has a function of preventing relative rotation with respect to the pulley 50 by engaging with an engaging recess 51 provided on the inner peripheral surface of the pulley 50 which is a rotating member.

[0127] The flange portion 20a is composed of two flange pieces 22a spaced apart in the circumferential direction. Each of the flange pieces 22a is provided on the outer peripheral surface of the nut body 19a over a range (full length) from one axial end to the other axial end. The cross-sectional shape of the flange pieces 22a is a tapered trapezoid whose circumferential dimension decreases radially outward.

[0128] In this example, the flange portion 20a provided over the entire length of the outer peripheral surface of the nut body 19a is composed of a plurality of flange pieces 22a spaced apart in the circumferential direction, so that the nut body 19a has, in the range from one axial end to the other axial end, partially annular flange-forming portions 25a having flange pieces 22a provided on the outer peripheral surface and partially annular flange-non-forming portions 26a having no flange pieces 22a provided on the outer peripheral surface, arranged alternately in the circumferential direction.

[0129] In this example as well, the non-flange-forming portion 26a is present in a portion of the nut body 19a that is offset from the flange piece 22a in the circumferential direction and coincides with the flange piece 22a in the axial direction.

[0130] In this example, all of the mounting holes 24a to 24d provided in the nut body 19a are formed in the flange-free portion 26a, and the circulation tops 21a to 21d are attached to the mounting holes 24a to 24d, respectively.

[0131] In this example, each of the circulation tops 21a to 21d is fixed to the nut body 19a by crimping. Specifically, the circulation tops 21a to 21d are fixed to the nut body 19a by crimping parts (not shown) formed by plastically deforming the radially outer opening edge of each of the mounting holes 24a to 24d. However, the circulation tops can also be crimped to the nut body by crimping parts formed by plastically deforming a part of the circulation top. Alternatively, the inner peripheral surface of the pulley 50 fitted to the nut 8 can be used to prevent the circulation tops 21a to 21d from slipping out radially outward from each of the mounting holes 24a to 24d.

[0132] In the present embodiment as described above, the sleeves for preventing the circulation tops 21a-21d from slipping out radially outward from the mounting holes 24a-24d can be omitted, so that the number of parts can be reduced and the weight can be reduced. Also, the axial dimension of the flange piece 22a is longer than that of the structure of the first embodiment, so that the strength of the flange piece 22a can be improved. The other configurations and effects are the same as those of the first embodiment.

[0133] [Fourth Example of the Implementation Form] A fourth example of the embodiment will be described with reference to FIG.

[0134] In this example, the structure of the flange portion 20b is changed from the structure in the first example of the embodiment.

[0135] That is, the flange portion 20b is composed of one flange piece 22b having a notch portion 52 in a portion in the circumferential direction.

[0136] The cutout portion 52 in this example is formed by cutting out a part of the flange portion 20b in the circumferential direction in a partially annular shape from the radially inner end to the radially outer end of the flange portion 20b. Therefore, in this example, the outer peripheral surface of the nut body 19 (flange non-forming portion 26) is exposed in the portion provided with the cutout portion 52.

[0137] The flange piece 22b has circumferential end faces 53a, 53b on both circumferential sides, each of which faces in the opposite direction in the circumferential direction. Each of the circumferential end faces 53a, 53b is a flat surface.

[0138] The circumferential dimension of the flange piece 22b is longer than the circumferential dimension of the flange piece 22 in the first example of the embodiment. The central angle of the flange piece 22b is determined based on the function and strength required of the flange piece 22b, and may be, for example, about 150 degrees to 330 degrees. In the illustrated example, the central angle of the flange piece 22b is 270 degrees.

[0139] The flange piece 22b has guide holes 23 at multiple locations (three locations in the illustrated example) in the circumferential direction. The multiple guide holes 23 are disposed at equal intervals in the circumferential direction.

[0140] In this example, the mounting hole 24a closest to one side in the axial direction is formed in a portion of the nut 8 whose circumferential phase coincides with the cutout portion 52 and whose axial position overlaps with the flange piece 22b. Therefore, the circulation top 21a attached to the mounting hole 24a is provided in a portion of the nut 8 whose circumferential phase coincides with the cutout portion 52 and whose axial position overlaps with the flange piece 22b. Therefore, the circulation groove 12a (see FIG. 4, etc.) provided in the circulation top 21a is disposed in a portion of the inner circumferential surface of the nut body 19 whose axial position overlaps with the flange piece 22b.

[0141] In this example as described above, the rigidity of the flange piece 22b can be made higher than that of the structure of the first example embodiment, so that deformation of the flange piece 22b can be effectively suppressed. This can improve the sliding property between the guide hole 23 provided in the flange piece 22b and the anti-rotation member 10. Furthermore, when the flange portion 20b (flange piece 22b) is formed by cutting, the amount of processing can be reduced compared to the structure of the first example embodiment, so that the number of processing steps can be reduced. The other configurations and effects are the same as those of the first embodiment.

[0142] [Fifth Example of the Implementation Form] A fifth example of the embodiment will be described with reference to FIG.

[0143] In this example, the structure of the flange portion 20c is changed from the structure in the first example of the embodiment.

[0144] That is, the flange portion 20c is configured from one flange piece 22c having a notch portion 52a in a portion in the circumferential direction, similar to the structure of the third example of the embodiment.

[0145] The cutout portion 52a in this example is formed by cutting out a linear portion of the circumferential direction of the flange portion 20c. Therefore, the flange piece 22c has a D-cut shape, and a flat cutout surface 54 is provided on a circumferential portion of the outer circumferential surface. The radial dimension of the flange piece 22c is smaller in the portion where the circumferential phase coincides with the cutout portion 52a than in the portion where the circumferential phase deviates from the cutout portion 52a.

[0146] In this example, the mounting hole 24a closest to one side in the axial direction is formed in a portion of the nut 8 where the circumferential phase coincides with the notch portion 52a (notch surface 54) and where the axial position overlaps with the flange piece 22b. Therefore, the circulation top 21a attached to the mounting hole 24a is provided in a portion where the circumferential phase coincides with the notch portion 52a and where the axial position overlaps with the flange piece 22c. Therefore, the circulation groove 12a (see FIG. 4, etc.) provided in the circulation top 21a is disposed in a portion of the inner peripheral surface of the nut body 19 where the axial position overlaps with the flange piece 22c.

[0147] In the case of this example as described above, the rigidity of the flange piece 22c can be made higher than that of the structure of the first example of the embodiment, so that deformation of the flange piece 22c can be effectively suppressed. Moreover, the flange piece 22c of this example can be formed by linearly moving a cutting tool such as an end mill against the annular flange portion, so that the number of processing steps can be reduced. The other configurations and effects are the same as those of the first and fourth embodiments.

[0148] Although the embodiment of the present invention has been described above, the present invention is not limited to this, and can be modified as appropriate without departing from the technical concept of the invention. Furthermore, the structures of the examples of the embodiment can be combined as appropriate as long as no contradiction occurs.

[0149] In carrying out the present invention, the flange portion constituting the nut is not limited to the axial end portion of the outer peripheral surface of the nut body, but may be provided in the axial middle portion of the nut body. Also, a plurality of flange portions may be provided axially spaced apart on the outer peripheral surface of the nut body.

[0150] In the first embodiment, the through holes in the flange pieces are used as guide holes for circumferentially engaging with the rotating member, but they can also be used as support holes for inserting and supporting pinion pins that rotatably support the planetary gears. In this case, the flange portion functions as a carrier that constitutes the planetary reduction mechanism.

[0151] A ball screw device nut according to a first aspect of the present disclosure is a ball screw device nut having a spiral nut-side ball screw groove and one or more circulation grooves on an inner circumferential surface, A substantially cylindrical nut body having the nut side ball screw groove on its inner circumferential surface and one or more mounting holes penetrating the nut side ball screw groove in a radial direction so as to cut out the nut side ball screw groove; A flange portion protruding radially outward from an outer circumferential surface of the nut body; A circulation top is attached to the mounting hole, At least one of the circulation grooves is provided in the circulation top, The flange portion is composed of a plurality of flange pieces arranged at intervals in the circumferential direction or a single flange piece having a notch portion in a portion in the circumferential direction, When the flange portion is composed of a plurality of the flange pieces, the circumferential top is provided in a portion of the nut body that is circumferentially offset from the flange piece and that overlaps with the flange piece in the axial direction; when the flange portion is composed of a single flange piece having the cutout portion, the circumferential top is provided in a portion whose circumferential phase coincides with that of the cutout portion and that overlaps with the flange piece in the axial direction.

[0152] The nut for a ball screw device according to a second aspect of the present disclosure is the nut for the first aspect, wherein all of the circulation grooves are provided in the circulation top.

[0153] The nut for a ball screw device according to aspect 3 of the present disclosure is in either aspect 1 or aspect 2, and includes a plurality of the circulation tops, which can be arranged at equal intervals in the circumferential direction.

[0154] The nut for a ball screw device according to aspect 4 of the present disclosure, in any one of aspects 1 to 3, can be configured so that the flange portion is composed of a plurality of the flange pieces, and the plurality of the flange pieces can be arranged at equal intervals in the circumferential direction.

[0155] The nut for a ball screw device according to a fifth aspect of the present disclosure is in any one of the first to fourth aspects, wherein the flange piece has a guide portion that is circumferentially engageable with a rotation-preventing member.

[0156] The nut for a ball screw device according to aspect 6 of the present disclosure, in any one of aspects 1 to 4, can be configured so that the flange piece engages with an engagement recess provided on the inner surface of the rotating member to prevent relative rotation with respect to the rotating member.

[0157] The nut for a ball screw device according to aspect 7 of the present disclosure is any one of aspects 1 to 6, in which the nut body has an axial protrusion on a circumferential portion of the end face on one axial side for preventing relative rotation with the screw shaft.

[0158] In the nut for a ball screw device according to aspect 8 of the present disclosure, in aspect 7, the axial protrusion can be arranged with a circumferential phase shift relative to the circulating top that is positioned furthest to one side in the axial direction among the circulating tops.

[0159] The nut for a ball screw device according to a ninth aspect of the present disclosure is in any one of the first to eighth aspects, and may further include a sleeve fitted onto the nut body.

[0160] The nut for a ball screw device according to aspect 10 of the present disclosure is, in the above-mentioned aspect 9, such that the flange portion is provided at one axial end of the outer peripheral surface of the nut body, and the sleeve has a cylindrical shape and is capable of covering, from the radial outside, at least a portion of the circulating top that is positioned furthest to one axial end among the circulating tops.

[0161] A nut for a ball screw device according to aspect 11 of the present disclosure is configured in such a manner that, in aspect 9, the flange portion is provided at one axial end of the nut body and is composed of a plurality of the flange pieces, and the sleeve has a plurality of cover pieces arranged circumferentially spaced apart at one axial end, the cover pieces being arranged between adjacent flange pieces in the circumferential direction, and the cover pieces cover the circulating top arranged furthest to one axial end among the circulating tops from the radial outside.

[0162] The nut for a ball screw device according to a twelfth aspect of the present disclosure is any one of the first to eleventh aspects, in which the circulating top can be fixed to the nut body by crimping.

[0163] A ball screw device according to a thirteenth aspect of the present disclosure includes a screw shaft, a nut, and a plurality of balls, and the nut can be any one of the ball screw device nuts according to the first to twelfth aspects. [Explanation of symbols]

[0164] 1. Ball screw device 2 Electric Actuator 3. Electric motor 4 Piston 5. Housing 6 Cylinder hole 7 Screw shaft 8 Nuts 9 Ball 10 Anti-rotation member 11 Load path 12a~12d Circulation groove 13 Threaded part 14 Mating shaft portion 15 Ball screw groove on shaft side 16 Abutment surface 17 male spline teeth 18 Nut side ball screw groove 19, 19a Nut body 20, 20a to 20c Flange part 21a~21d Circulation Top 22, 22a~22c Flange piece 23 Guide hole 24a~24d Mounting holes 25, 25a Flange forming part 26, 26a Flange non-forming portion 27 Axial projection 28, 28a sleeve 29 Locking flange 30 Locking groove 31 Stopper 32 Boss section 33 Protrusion 34 female spline teeth 35 1st housing section 36 Second housing section 37 Insertion hole 38 Nut insertion hole 39 Step surface 40 1st fixing hole 41 Receiving hole 42 Fitting part 43 2nd fixing hole 44 Motor output shaft 45 Engagement hole 46 female spline teeth 47a, 47b Rolling bearings 48 Small diameter section 49 Cover Piece 50 Pulley 51 Engagement recess 52, 52a Notch 53a, 53b Circumferential end faces 54 Cutout surface 100 Ball screw device 101 Screw shaft 102 Nut 103 Ball 104 Ball screw groove on shaft side 105 Nut side ball screw groove 106 Circulation groove 107 Nut body 108 Flange 109 Circulating Top 110 Load path 111 Mounting hole

Claims

1. A nut for a ball screw device having a spiral nut-side ball screw groove and one or more circulation grooves on an inner peripheral surface, A substantially cylindrical nut body having the nut side ball screw groove on an inner peripheral surface and one or more mounting holes penetrating the nut side ball screw groove in a radial direction so as to cut out the nut side ball screw groove; A flange portion protruding radially outward from an outer circumferential surface of the nut body; A circulation top is attached to the mounting hole, At least one of the circulation grooves is provided in the circulation top, The flange portion is composed of a plurality of flange pieces arranged at intervals in the circumferential direction or a single flange piece having a cutout portion in a portion in the circumferential direction, When the flange portion is composed of a plurality of flange pieces, the circulating top is provided at a portion of the nut body that is offset from the flange piece in the circumferential direction and that overlaps with the flange piece in the axial direction, and when the flange portion is composed of one flange piece having the cutout portion, the circulating top is provided at a portion that coincides with the cutout portion in the circumferential direction and that overlaps with the flange piece in the axial direction. Nut for ball screw device.

2. 2. The nut for a ball screw device according to claim 1, wherein all of said circulation grooves are provided in said circulation top.

3. The circulating top is provided in plurality, The plurality of circulating tops are arranged at equal intervals in the circumferential direction.

2. A nut for a ball screw device according to claim 1.

4. The flange portion is composed of a plurality of the flange pieces, The flange pieces are arranged at equal intervals in the circumferential direction.

2. A nut for a ball screw device according to claim 1.

5. 2. The nut for a ball screw device according to claim 1, wherein said flange piece has a guide portion that is circumferentially engageable with a rotation prevention member.

6. 2. The nut for a ball screw device according to claim 1, wherein the flange piece engages with an engaging recess provided on an inner peripheral surface of the rotating member to prevent relative rotation with respect to the rotating member.

7. 2. The nut for a ball screw device according to claim 1, wherein the nut body has an axial protrusion on a circumferential portion of an end face on one axial side for preventing relative rotation with the screw shaft.

8. 8. The nut for a ball screw device according to claim 7, wherein the axial protrusion is arranged with a circumferential phase shift relative to the circulating top that is arranged furthest to one side in the axial direction among the circulating tops.

9. 2. The nut for a ball screw device according to claim 1, further comprising a sleeve fitted onto the nut body.

10. The flange portion is provided at one axial end of the outer circumferential surface of the nut body, The sleeve has a cylindrical shape, and an end portion on one axial side covers at least a portion of the circulating top that is disposed furthest on the one axial side among the circulating tops from the radially outer side. The nut for a ball screw device according to claim 9.

11. The flange portion is provided at one axial end of the nut body and is composed of a plurality of the flange pieces, The sleeve has a plurality of cover pieces arranged at one end in an axial direction and spaced apart from each other in a circumferential direction, The cover piece is disposed between the flange pieces adjacent in the circumferential direction and covers the circulation top disposed furthest on one axial side among the circulation tops from the radially outer side. The nut for a ball screw device according to claim 9.

12. 2. The nut for a ball screw device according to claim 1, wherein said circulating top is fixed to said nut body by crimping.

13. The screw shaft, the nut, and the plurality of balls are provided. A ball screw device, wherein the nut is the nut for a ball screw device according to any one of claims 1 to 12.

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