Nuts and ball screw devices for ball screw devices

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 Art]

[0002] A ball screw device causes balls to roll between a screw shaft and a nut, so higher efficiency is obtained compared to a sliding screw device in which the screw shaft and the nut are in direct contact. For this reason, ball screw devices are incorporated into various mechanical devices, for example, to convert the rotational motion of a drive source such as an electric motor into linear motion, such as in electric brake devices for automobiles, automatic manual transmissions (AMT), and positioning devices for machine tools.

[0003] A ball screw device includes a screw shaft having a helical shaft-side ball screw groove on an outer peripheral surface thereof, a nut having a helical nut-side ball screw groove on an inner peripheral surface thereof, and a plurality of balls disposed 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 disposed so as to face each other in the radial direction, and form a helical load path. The start point and the 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, and circulates the balls.

[0004] Note that the start point and the end point of the load path are switched depending on the direction of relative displacement (relative rotational direction) in the axial direction between the screw shaft and the nut. Further, depending on the application, a ball screw device uses one of the screw shaft and the nut as a rotational motion element and the other of the screw shaft and the nut as a linear motion element.

[0005] Various structures have been conventionally considered as circulation means for circulating balls, but deflector devices are widely used for reasons such as enabling the ball screw device to be configured in a small size.

[0006] For example, Japanese Patent Publication No. 2016-114185 (Patent Document 1) discloses a ball screw device of the ball screw type that uses a circulating ball. Figure 14 shows a conventional ball screw device 100 as described in Japanese Patent Publication No. 2016-114185.

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

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

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

[0010] The nut 102 consists of a nut body 107, a flange portion 108, and a plurality of circulating valves 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 arranged to face each other radially, forming a helical load path 110. The nut body 107 also has a plurality of mounting holes 111 that penetrate radially, cutting 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 continuous annular shape in the circumferential direction and is provided at one axial end of the outer circumferential surface of the nut body 107. The flange portion 108 is used to fasten the nut 102 to other machine parts.

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

[0014] Multiple balls 103 are arranged to be rotatable in the load path 110 and the circulation groove 106.

[0015] In a conventional ball screw device 100, the screw shaft 101 is rotationally driven to reciprocate the nut 102 in the axial direction. During this process, the ball 103 rolls inside the load path 110. When the ball 103 reaches the end of the load path 110, it is returned to the starting point of the load path 110 via the circulation groove 106. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] Japanese Patent Publication No. 2016-114185 [Patent Document 2] Japanese Patent Publication No. 2021-122843 [Overview of the project] [Problems that the invention aims to solve]

[0017] Mounting holes for attaching the circulating valve are often formed by machining the nut body. Therefore, in a structure like the conventional ball screw device 100, which has an annular flange portion 108 on the outer circumference of the nut body 107, the mounting hole 111 is formed not in the part of the nut body 107 where the flange portion 108 is located, but in a part that is axially offset from the flange portion 108. This is because forming the mounting hole in the part where the flange portion is located would increase the amount of machining required for the flange portion, leading to increased costs.

[0018] Therefore, in a structure like the conventional ball screw device 100, which has an annular flange portion 108 on the outer circumferential surface of the nut body 107, it is difficult to place the circulation groove 106 in the portion of the inner circumferential surface of the nut body 107 that overlaps with the flange portion 108 in terms of axial position. As a result, the axial dimension of the portion of the nut body 107 that is axially separated from the flange portion 108 needs to be increased accordingly, which tends to increase the axial dimension of the nut 102.

[0019] The problems described above occur not only with nuts having an annular flange portion, but also with nuts that have the flange portion used to fix the flange portion to other machine parts, such as those disclosed in Japanese Patent Application Publication No. 2021-122843 (Patent Document 2), which have the flange portion used to prevent the nut from rotating with the screw shaft by engaging the flange portion with an anti-rotation member in the circumferential direction.

[0020] The present invention was made to solve the above problems, and aims to provide a ball screw device nut that can reduce the axial dimension, and a ball screw device equipped with the ball screw device nut. [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 comprises a nut body, a flange portion, and a circulation nut. The nut body is substantially cylindrical in shape, has a nut-side ball screw groove on its inner circumferential surface, and has one or more mounting holes that penetrate radially so as to notch the nut-side ball screw groove. The flange portion protrudes radially outward from the outer circumferential surface of the nut body. The aforementioned circulating valve is attached to the aforementioned mounting hole. In a 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 nut. Further, the flange portion is composed of a plurality of flange pieces arranged spaced apart in the circumferential direction, or a single flange piece provided with a notch portion in a part of the circumferential direction. Further, when the flange portion is composed of the plurality of flange pieces, the circulation piece is provided in a portion of the nut body that is offset from the flange piece in the circumferential direction and overlaps the flange piece in axial position; and when the flange portion is composed of the single flange piece provided with the notch portion, the circulation piece is provided in a portion where the circumferential phase matches the notch portion and overlaps the flange piece in axial position.

[0022] Note that the statement that the circulation piece is provided in a portion overlapping the flange piece in axial position is not limited to the case where the entire circulation piece is provided in the portion of the nut body overlapping the flange piece in axial position, but also includes the case where only a part of the circulation piece is provided in said portion. In any case, when a plurality of said circulation pieces are provided, it is not necessary for all of the circulation pieces to be provided in portions overlapping the flange pieces in axial position, and it is sufficient that at least one circulation piece is provided in a portion overlapping the corresponding flange piece in axial position.

[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 piece. Alternatively, in the nut for a ball screw device according to one aspect of the present invention, a part of the circulation grooves can be provided in the circulation piece, and the remaining circulation grooves can 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 pieces can be provided. Further, the plurality of circulation pieces can be arranged at equal intervals in the circumferential direction. Alternatively, in the nut for a ball screw device according to one aspect of the present invention, only one circulation piece can be provided.

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

[0026] In a nut for a ball screw device according to one aspect of the present invention, the flange piece may have a guide portion that can engage with an anti-rotation member in the circumferential direction. In this case, the flange piece may be provided with a function to prevent the nut from rotating with the screw shaft by engaging with the anti-rotation member in the circumferential direction. In addition to a guide hole that penetrates the flange piece in the axial direction, the guide portion may also be a grooved guide groove or a protruding guide projection.

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

[0028] In one embodiment of the present invention, the nut body may have an axial projection on a portion of the circumferential direction of one end face on the axial side for preventing relative rotation with respect to the screw shaft.

[0029] In a nut for a ball screw device according to one aspect of the present invention, the axial projection can be positioned with a circumferential phase shift relative to the circulating spindle that is positioned furthest to the axial side among the circulating spindles. In a nut for a ball screw device according to one aspect of the present invention, the axial projection can be positioned in a portion of the flange piece where its phase in the circumferential direction coincides with that of the flange piece.

[0030] In one embodiment of the present invention, a nut for a ball screw device may be provided with a sleeve fitted onto the nut body.

[0031] In a nut for a ball screw device according to one aspect of the present invention, the flange portion is provided at one axial end of the nut body, and the sleeve has a cylindrical shape and, by its axial end, can cover at least a portion of the circulating spindle that is positioned furthest to the axial side of the circulating spindles from the radially outer side.

[0032] In a nut for a ball screw device according to one aspect of the present invention, the flange portion is provided at one axial end of the nut body and is composed of a plurality of flange pieces, and the sleeve may have a plurality of covering pieces arranged at circumferential distances from each other at one axial end. The covering pieces are then placed in the space between adjacent flange pieces in the circumferential direction, and the covering pieces can cover the circulating ball that is positioned furthest to the axial side of the circulating ball from the radially outer side.

[0033] In a nut for a ball screw device according to one aspect of the present invention, the circulating spindle can be crimped and fixed to the nut body. Alternatively, in a ball screw device nut according to one aspect of the present invention, the circulating spool can be adhesively fixed to the nut body.

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

[0035] According to one embodiment of the present invention, a nut for a ball screw device can be made smaller in terms of axial dimension. [Brief explanation of the drawing]

[0036] [Figure 1]Figure 1 is a cross-sectional view showing an electric actuator equipped with a ball screw device according to a first example of the embodiment. [Figure 2] Figure 2 is an end view taken from one axial side of an electric actuator equipped with a ball screw device according to the first embodiment, with the second housing, electric motor, and rolling bearing removed. [Figure 3] Figure 3 is an end view of a nut constituting a ball screw device according to the first embodiment, with a circulating spool attached, viewed from one side in the axial direction. [Figure 4] Figure 4 is a schematic diagram corresponding to the cross-section along line AA in Figure 3. [Figure 5] Figure 5 is a perspective view showing a nut that constitutes a ball screw device according to the first example of the embodiment. [Figure 6] Figure 6 shows a view from the radially outer side of a ball screw device according to the first embodiment, with the sleeve and circulating spool removed from the nut. [Figure 7] Figure 7 is a perspective view showing the ball screw device according to the first embodiment, with the sleeve and circulating spool removed from the nut. [Figure 8] Figure 8 is a diagram corresponding to Figure 5, showing a second example of the embodiment. [Figure 9] Figure 9 is a perspective view showing the sleeve removed from the nut that constitutes the ball screw device according to the second embodiment. [Figure 10] Figure 10 is an end view showing a ball screw device according to a third embodiment, with a pulley fitted onto the nut. [Figure 11] Figure 11 is a diagram corresponding to Figure 5, showing a third example of the embodiment. [Figure 12] Figure 12 is a diagram corresponding to Figure 5, showing a fourth example of the embodiment. [Figure 13] Figure 13 is a diagram corresponding to Figure 5, showing a fifth example of the embodiment. [Figure 14] Figure 14 is a cross-sectional view showing a conventional ball screw device.

[0037] [First example of an embodiment] A first example of the embodiment will be described with reference to Figures 1 to 7.

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

[0039] The electric actuator 2 comprises 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 generates the target brake hydraulic pressure by causing the piston 4 to stroke within the cylinder bore 6 of the housing 5.

[0041] The ball screw device 1 comprises 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 during use. The screw shaft 7 is inserted inside the nut 8 and is arranged coaxially with the nut 8. The nut 8 is prevented from rotating with the screw shaft 7 by an anti-rotation member 10 fixed to the housing 5 and is a linear motion element that rotates linearly during use. Therefore, the ball screw device 1 in this example is used in a manner in which the screw shaft 7 is rotationally driven and the nut 8 rotates 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 surface of the screw shaft 7 and the inner surface of the nut 8. Multiple balls 9 are arranged to roll along the load path 11. When the screw shaft 7 and the nut 8 are rotated relative to each other, the balls 9 that reach the end of the load path 11 are returned to the starting point of the load path 11 through circulation grooves 12a to 12d provided on the inner 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, axial, radial, and circumferential directions refer to the axial, radial, and circumferential directions with respect to the screw shaft 7. Furthermore, one axial side refers to the right side in Figures 1, 4, and 6, and the other axial side refers to the left side in Figures 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 that is positioned adjacent to the threaded portion 13 on one axial side. 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 axial-side ball screw groove 15 on its outer circumferential surface. The axial-side ball screw groove 15 is formed on the outer circumferential surface of the threaded portion 13 by cutting (grinding) or rolling, such as a through-feed type. In this example, the number of threads in the axial-side ball screw groove 15 is one. The groove shape (groove bottom shape) of the cross-section of the axial-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 end face in the axial direction.

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

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

[0049] The nut 8 comprises 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 circulating spools 21a to 21d.

[0050] In this example, by devising the structure of the flange portion 20, it is possible to place the circulating spool 21a in the portion of the nut body 19 whose axial position overlaps with that of the flange portion 20, thereby achieving a reduction in the axial dimension of the nut 8. For this reason, the structure of the flange portion 20 will be explained first, and then the structures of the nut body 19 and the circulating spools 21a to 21d will be explained.

[0051] <Flange section> In this example, the flange portion 20, which had an annular shape in the conventional structure, is made discontinuous in the circumferential direction, rather than having a continuous annular shape in the circumferential direction, by retaining the portion necessary to ensure function and strength and removing the other portion.

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

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

[0054] Multiple flange pieces 22 have the same shape as each other. In this example, the flange pieces 22 are configured in a roughly rectangular plate shape. However, the shapes of the flange pieces can also be different from each other.

[0055] Multiple flange pieces 22 are arranged at equal intervals in the circumferential direction. In the illustrated example, three flange pieces 22 are arranged at 120-degree intervals. However, multiple flange pieces can also be arranged at unequal intervals in the circumferential direction.

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

[0057] The guide hole 23 is located in the radial middle of the flange piece 22 and penetrates the flange piece 22 axially. The anti-rotation member 10 is axially slidably inserted through the guide hole 23. The anti-rotation member 10 can also be inserted inside 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, so the cross-sectional shape (opening shape) of the guide hole 23 is also circular. However, the cross-sectional shape of the guide hole is not limited to a circle; other shapes such as rectangular or semi-circular can be used as long as the nut can be prevented from rotating by engaging with the anti-rotation member in the circumferential direction. Furthermore, to prevent the nut from rotating, a groove-shaped guide recess or a projection-shaped guide projection that can engage with the anti-rotation member in the circumferential direction can also be provided on the radially outer surface of the flange piece.

[0059] The axial side of the flange piece 22 is positioned flush with the axial end face of the nut body 19. However, the axial side of the flange piece 22 may also be positioned offset to the other axial side from the axial end face of the nut body 19.

[0060] The circumferential, axial, and radial dimensions (radial projection) of the flange piece 22 are determined based on the required function and strength of the flange piece 22. In this example, when the flange piece 22 is used to prevent the nut 8 from rotating together, the circumferential dimension of the flange piece 22 can be about 1 / 20 to 1 / 4 of the circumference of the outer surface of the nut body 19, and in the illustrated example, it is about 1 / 9 of the circumference of the outer surface of the nut body 19. In this application, 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 this application, the radial dimension of the flange piece 22 can be about 0.5 to 3 times the radial thickness of the nut body 19, and in the illustrated example, it is about 1.5 times the radial thickness 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 helical nut-side ball screw groove 18 on its inner circumference. The nut body 19 also has mounting holes 24a to 24d that penetrate radially, cutting 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, alternately in the circumferential direction, a partially annular flange-forming portion 25 with flange pieces 22 provided on its outer circumferential surface and a partially annular non-flange-forming portion 26 without flange pieces 22 on its outer circumferential surface.

[0063] The flange-less portion 26 is located in the nut body 19 in a portion that is circumferentially separated from the flange piece 22, and whose axial position coincides with that of the flange piece 22. The outer circumferential surface (radial outer surface) of the flange-less portion 26 is composed of a partial cylindrical surface centered on the central axis of the nut body 19. As shown in Figures 6 and 7, the flange-less portion 26 may have the same diameter as the other axial end or middle portion of the outer circumferential surface of the nut body 19, or it may have a different diameter.

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

[0065] In this example, the inner circumferential surface of the nut body 19 does not directly have circulation grooves 12a to 12d. Therefore, all the circulation grooves 12a to 12d provided by the nut 8 are located on the circulation sprockets 21a to 21d. However, it is also possible to provide all or some of the circulation grooves of the nut, excluding those whose axial position coincides with the flange portion, on the circulation sprockets, and provide the remaining circulation grooves directly on the inner circumferential surface of the nut body.

[0066] The nut-side ball screw groove 18 has a helical shape and is formed on the inner circumferential surface of the nut body 19 by, for example, cutting (grinding) or rolling tapping (cutting tapping). In this example, the nut-side ball screw groove 18 is formed in a range extending from one end on the axial side to the other end on the inner circumferential 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, with the threaded portion 13 of the screw shaft 7 inserted inside the nut 8, the shaft-side ball screw groove 15 and the nut-side ball screw groove 18 are arranged to face each other radially, forming a helical load path 11. The nut-side ball screw groove 18 has one thread, the same as the shaft-side ball screw groove 15. The groove shape of the cross-section of the nut-side ball screw groove 18 is also the same as the shaft-side ball screw groove 15, being either a Gothic arch groove or a circular arc groove. In this example, one axial end of the nut-side ball screw groove 18 is provided in a portion that overlaps with the axial position of the flange piece 22.

[0068] Each of the mounting holes 24a to 24d is a through hole for attaching the circulating valves 21a to 21d, and is open on both the inner and outer surfaces of the nut body 19.

[0069] In this example, multiple mounting holes 24a to 24d are provided. The multiple mounting holes 24a to 24d are arranged so that their circumferential and axial positions are offset from each other.

[0070] In this example, the mounting hole 24a, which is furthest to the axial side among the multiple mounting holes 24a to 24d, is formed in one of the multiple flange-less portions 26 that constitute the axial end of the nut body 19. Specifically, one axial half of the mounting hole 24a is formed in the flange-less portion 26. The other axial half of the mounting hole 24a is formed in the portion that is offset from the flange-less portion 26 in the other axial direction. However, the entire mounting hole can also be formed in the flange-less portion.

[0071] Of the multiple mounting holes 24a to 24d, the mounting hole 24d furthest to the other axial side is formed at the other axial end of the nut body 19. The remaining mounting holes 24b and 24c are formed in the axial middle portion of the nut body 19.

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

[0073] Each of the mounting holes 24a to 24d is formed by machining using a cutting tool such as an end mill, and opens on the outer and inner surfaces of the nut body 19, respectively. Each of the mounting holes 24a to 24d is formed by cutting out a portion of the nut-side ball screw groove 18 formed on the inner surface of the nut body 19. The central axis of each of the mounting holes 24a to 24d is positioned radially toward the nut body 19.

[0074] Each of the mounting holes 24a to 24d has a rectangular (rounded rectangular) cross-sectional shape, with its longitudinal direction oriented circumferentially and its short direction oriented axially. In other words, each of the mounting holes 24a to 24d has a greater circumferential width than its axial width. However, the circumferential width of the mounting holes 24a to 24d is smaller than the circumferential dimension of the outer surface of the flange-less portion 26.

[0075] <Circulating spinning top> Each of the circulating valves 21a to 21d has a circulating groove 12a to 12d. The circulating valves 21a to 21d are provided with the same number of mounting holes 24a to 24d in the nut body 19 (four in the illustrated example).

[0076] The circulating beads 21a to 21d are attached to the mounting holes 24a to 24d. Specifically, one circulating bead 21a to 21d is attached to the mounting hole 24a formed in the flange-less portion 26 that constitutes one axial end of the nut body 19, one mounting bead 24d formed in the mounting hole 24d formed in the other axial end of the nut body 19, and one mounting bead 24b and one mounting bead 24c formed in the axial middle portion of the nut body 19.

[0077] The circulating nut 21a on the axial side is attached to the mounting hole 24a of the flange-less portion 26, and is provided on the portion of the nut body 19 that is away from the flange piece 22 in the circumferential direction, and whose axial position overlaps with that of the flange piece 22. Specifically, one axial half of the circulating nut 21a is provided on the portion that overlaps with the axial position of the flange piece 22. For this reason, the circulating groove 12a provided on the circulating nut 21a is located on the inner circumferential surface of the nut body 19 in the portion that overlaps with the axial position of the flange piece 22.

[0078] Multiple circulating spindles 21a to 21d are arranged at equal intervals in the circumferential direction. In the illustrated example, four circulating spindles 21a to 21d are arranged at 90-degree intervals. Additionally, the four circulating spindles 21a to 21d are arranged at equal intervals in the axial direction.

[0079] Each of the circulating spheres 21a to 21d is made of metal or synthetic resin. If each of the circulating spheres 21a to 21d is made of metal, they can be manufactured by metal injection molding (MIM) using metal powders (MIM alloys) such as Fe-Ni-C (1-8% Ni, ~0.8% C), Fe-Cr-C (0.5-2% Cr, ~0.8% C), SCM415, or SUS630 as raw materials.

[0080] Each of the circulating spinnerets 21a to 21d has a roughly 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 circulating spinnerets is not limited to a roughly rectangular prism shape; they can also be configured in cylindrical or oval shapes to match the shape of the mounting holes.

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

[0082] With the circulating balls 21a to 21d attached to the nut body 19, each pair of openings in the circulating grooves 12a to 12d open on opposite sides in the circumferential direction and connect to adjacent screw grooves in the axial direction of the nut-side ball screw groove 18. In this way, each of the circulating grooves 12a to 12d is connected to the start and end points of the load path 11. The circulating 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 (approximately the range of one turn) constitute a single circuit. The start and end points of the load path 11 are, in other words, the connection points between the load path 11 and the circulating grooves 12a to 12d. Note that the start and end points of the load path 11 are swapped as the direction of relative displacement (relative rotation direction) in the axial direction between the screw shaft 7 and the nut 8 changes, and the direction of movement of the ball 9 changes.

[0083] In this example, although not shown in the diagram, the circulating spheres 21a to 21d are inserted into the mounting holes 24a to 24d from the radially outer side, and the outward-facing flanges provided on the radially outer side of the outer circumference of the circulating spheres 21a to 21d are abutted against the bottom surface (seat surface) of the recess provided on the opening edge of the mounting holes 24a to 24d. This prevents the circulating spheres 21a to 21d from coming out radially inward from the mounting holes 24a to 24d.

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

[0085] The axial projection 27 is provided on the axial side of the flange forming portion 25 that constitutes the axial end of the nut body 19. Therefore, the axial projection 27 is out of phase in the circumferential direction with respect to the circulating spool 21a located furthest to the axial side. In the illustrated example, the axial projection 27 is out of phase by 180 degrees with respect to the circulating spool 21a located furthest to the axial side.

[0086] <sleeve> The nut 8 is further equipped with a sleeve 28 to prevent the circulating spools 21a to 21d from coming out radially outward from the mounting holes 24a to 24d.

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

[0088] The sleeve 28, with its axial end, covers a portion of the circulating sphere 21a (the other half on the axial side) attached to the mounting hole 24a of the flange-less portion 26 from the radial outside. The sleeve 28, with its axial end on the other side and its axial middle portion, covers the entirety of the remaining circulating spheres 21b to 21d from the radial outside. In this way, the sleeve 28 prevents all of the circulating spheres 21a to 21d from coming out radially from the mounting holes 24a to 24d.

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

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

[0091] [Stopper] The ball screw device 1 in this example further includes a stopper 31 for restricting 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 to be unable to rotate relative to it. The stopper 31 has an annular boss portion 32 and a projection portion 33.

[0092] The boss portion 32 is fitted onto the mating shaft portion 14 in a manner that prevents relative rotation. Specifically, the boss portion 32 is fitted onto the mating shaft portion 14 in a manner that prevents relative rotation by spline-engaging the female spline teeth 34 on its inner circumferential surface with the male spline teeth 17 on the outer circumferential surface of the mating shaft portion 14. In addition, the other axial side of the boss portion 32 abuts against the abutment surface 16 of the threaded portion 13, and the one axial side of the boss portion 32 abuts against the other axial end face of the motor output shaft 44, which will be described later. The projection 33 protrudes radially from a portion of the circumferential surface of the outer circumferential 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 on the nut 8 and the projection 33 on the stopper 31 engage in the circumferential direction. This prevents the rotation of the screw shaft 7, making it possible to restrict the stroke end of the nut 8.

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

[0095] 〔housing〕 The housing 5 is formed by combining a first housing portion 35 and a second housing portion 36 in the axial direction. 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 bottomed cylindrical shape.

[0096] The first housing portion 35 has a stepped through-hole 37 inside. The through-hole 37 opens only on one axial side. The central axis of the through-hole 37 is coaxial with the central axis of the screw shaft 7.

[0097] The insertion hole 37 has a nut insertion hole 38 on one axial side, through which a nut 8 can be inserted in the axial direction. Therefore, the nut insertion hole 38 has an inner diameter larger than the outer diameter of the flange portion 20 (the circumscribed circle diameter of the flange piece 22). The nut insertion hole 38 has a cylindrical inner circumferential surface.

[0098] The insertion hole 37 has a cylinder hole 6 located on the axial side of the nut insertion hole 38, and has a smaller diameter than the nut insertion hole 38. The inner circumferential surface of the cylinder hole 6 is provided with a plurality of seal grooves (not shown). O-rings (not shown) are fitted into the seal grooves to seal the space between the inner circumferential surface of the cylinder hole 6 and the outer circumferential surface of the piston 4.

[0099] The insertion hole 37 has a stepped surface 39 facing one side in the axial direction between the nut insertion hole 38 and the cylinder hole 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 in this example) in the circumferential direction of the stepped surface 39.

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

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

[0102] [Electric motor] The electric motor 3 is housed in a housing hole 41 of the second housing portion 36. The electric motor 3 is equipped with 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 on the other end face in the axial direction. Female spline teeth 46 are provided on the inner circumferential surface of the engagement hole 45 along its entire circumference. In this example, the screw shaft 7 and the motor output shaft 44 are connected in a torque-transmitting manner by inserting one end or middle portion of the fitting shaft portion 14 that constitutes the screw shaft 7 into the engagement hole 45 and spline-engaging the male spline teeth 17 provided on the outer circumferential surface of the fitting shaft portion 14 with the female spline teeth 46. Note that the motor output shaft and the screw shaft can also be connected via a reduction mechanism instead of being directly connected.

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

[0104] 〔piston〕 The piston 4 is made of metal and has a bottomed cylindrical shape. The piston 4 is externally fitted and fixed to the nut body 19. Specifically, the piston 4 is externally fitted and fixed to 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 arranged coaxially with the nut 8. The piston 4 is fitted into the cylinder bore 6 so as to be movable in the axial direction.

[0105] [Anti-rotation member] The electric actuator 2 in this example is equipped with a rotation-preventing member 10 to prevent the nut 8 from rotating with the screw shaft 7. The rotation-preventing member 10 is an axially extended shaft-shaped member. In this example, the rotation-preventing member 10 is made of 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, there are three anti-rotation members 10, the same number as the guide holes 23. The three anti-rotation members 10 are arranged at equal intervals in the circumferential direction.

[0107] The central axis of the anti-rotation member 10 is positioned 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 portion 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 portion 35. Therefore, the anti-rotation member 10 spans across the first housing portion 35 and the second housing portion 36.

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

[0109] <Operation Description> In this example, when the electric motor 3 rotates the screw shaft 7 of the electric actuator 2, 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 onto the nut 8 is stroked within the cylinder hole 6. This causes the liquid or gas filled inside the cylinder hole 6 to be discharged or drawn in through a communication hole (not shown), thereby generating the target brake hydraulic pressure.

[0110] When the nut 8 moves relative to the screw shaft 7 in one axial direction and reaches the stroke end, the axial projection 27 on the nut 8 and the projection 33 on the stopper 31 engage in the circumferential direction. This prevents the rotation of the screw shaft 7. In this way, the ball screw device 1 of this example can restrict the stroke end related to the relative movement of the nut 8 in one axial direction relative to the screw shaft 7 by the stopper 31. Note that the stroke end related to the relative movement of the nut 8 in the other axial direction relative to the screw shaft 7 can be restricted using various conventionally known stroke limiting mechanisms.

[0111] In this example, the axial dimension of the nut 8 can be reduced. In other words, the nut 8 constituting the ball screw device 1 in this example is configured such that the flange portion 20 provided on the outer circumferential surface of the nut body 19 is made up of a plurality of flange pieces 22 spaced apart in the circumferential direction, and a flange-less portion 26 is provided on the outer circumferential surface of the nut body 19 in a part where the axial position of the flange pieces 22 coincides with that of the flange pieces 22, and Flange non-formed portion A mounting hole 24a is formed in 26. Therefore, in this example, the mounting hole 24a can be machined in a portion that coincides with the axial position of the flange piece 22 without increasing the amount of machining required.

[0112] Furthermore, the circulating spool 21a attached to the mounting hole 24a of the flange-less portion 26 is positioned in the portion of the nut body 19 that is separated from the flange piece 22 in the circumferential direction, and in a portion that overlaps with the flange piece 22 in axial position. Therefore, the circulating groove 12a can be positioned in the portion of the inner circumferential surface of the nut body 19 that overlaps with the flange piece 22 in axial position. Accordingly, according to this example, the axial dimension of the portion of the nut body 19 that is separated from the flange portion 20 on the other axial side can be shortened, thus enabling a reduction in the axial dimension of the nut 8.

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

[0114] Furthermore, in this example, the axial projection 27 is positioned with a circumferential phase shift relative to the circulating spindle 21a, which is located furthest to the axial side. In other words, the circumferential phase difference between the axial projection 27 and the mounting hole 24a formed in the flange-less portion 26 is offset. As a result, the axial projection 27 is provided in a part of the nut body 19 where sufficient strength can be ensured by the circumferential phase shift from the mounting hole 24a in the flange-less portion 26, rather than in a part of the nut body 19 where the strength is reduced by forming the mounting hole 24a in the flange-less portion 26. Therefore, in this example, even if the axial projection 27 engages forcefully with the projection 33 of the stopper 31, deformation of the nut body 19 can be suppressed.

[0115] In this example, multiple circulating spools 21a to 21d are arranged at equal intervals in the circumferential direction, and the circulating grooves 12a to 12d are also arranged at equal intervals in the circumferential direction. As a result, the nut 8 can support the screw shaft 7 from the radially outer side over its entire circumference via the ball 9. In addition, it is possible to suppress changes in the rigidity of the nut 8 with respect to the circumferential direction.

[0116] Furthermore, in this example, since multiple mounting holes 24a to 24d are arranged at equal intervals in the circumferential direction, it becomes easier to ensure the rigidity of the nut 8.

[0117] Furthermore, in this example, the stopper 31 is clamped between the abutment surface 16 of the screw shaft 7 and the other end face on the axial side of the motor output shaft 44. This prevents the stopper 31 from being displaced axially relative to the fitting shaft portion 14 of the screw shaft 7. As a result, the stroke end of the nut 8 can be precisely controlled.

[0118] Furthermore, in this example, since both axial ends of the motor output shaft 44 are rotatably supported by two rolling bearings 47a and 47b relative to the housing 5, the coaxiality between the motor output shaft 44 and the screw shaft 7 can be increased. Moreover, since 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, the coaxiality between the motor output shaft 44 and the screw shaft 7 can be further increased. Therefore, the efficiency of the ball screw device 1 can be improved.

[0119] [Second example of an embodiment] A second example of the embodiment will be described with reference to Figures 8 and 9.

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

[0121] In other words, the sleeve 28a has a plurality of covering pieces 49 arranged at circumferential spacing at one end on the axial side. This gives the shape of the end on the axial side of the sleeve 28a a comb-like shape.

[0122] The multiple covering pieces 49 are positioned between adjacent flange pieces 22 in the circumferential direction when the sleeve 28a is fitted onto the nut body 19. In other words, each of the multiple covering pieces 49 covers the outer circumferential surface of the flange-less portion 26. As a result, the entire circulating valve 21a attached to the mounting hole 24a of the flange-less portion 26 is covered from the radially outer side by the covering pieces 49.

[0123] In this example, the circulating valve 21a attached to the mounting hole 24a of the flange-less portion 26 can be effectively prevented from coming out radially outward. Furthermore, since each of the multiple covering pieces 49 is positioned between adjacent flange pieces 22 in the circumferential direction, the sleeve 28a can also be effectively prevented from rotating relative to the nut body 19. The other configurations and effects are the same as in the first example of the embodiment.

[0124] [Third example of an embodiment] A third example of the embodiment will be described with reference to Figures 10 and 11.

[0125] In this example, the function and formation position of the flange portion 20a have been changed from the structure of the first example of the embodiment.

[0126] In other words, the flange portion 20a engages with an engaging recess 51 provided on the inner circumferential surface of the pulley 50, which is a rotating member, and has the function of preventing relative rotation with respect to the pulley 50.

[0127] The flange portion 20a is composed of two flange pieces 22a spaced apart in the circumferential direction. Each flange piece 22a is provided along the entire length of the outer surface of the nut body 19a, from one end on the axial side to the other end on the axial side. The cross-sectional shape of the flange piece 22a is a tapered, approximately trapezoidal shape, with the circumferential dimension decreasing towards the radially outward direction.

[0128] In this example, the flange portion 20a provided along the entire length of the outer circumferential surface of the nut body 19a is composed of a plurality of flange pieces 22a spaced apart in the circumferential direction. Therefore, the nut body 19a alternately comprises, in the circumferential direction, a partially annular flange-forming portion 25a with flange pieces 22a provided on its outer circumferential surface and a partially annular non-flange-forming portion 26a without flange pieces 22a provided on its outer circumferential surface, extending from one end on the axial side to the other end on the axial side.

[0129] In this example as well, the non-flange portion 26a is located in the nut body 19a in a portion that is circumferentially separated from the flange piece 22a, and whose axial position coincides with that of the flange piece 22a.

[0130] In this example, all mounting holes 24a to 24d provided in the nut body 19a are formed in the flange-less portion 26a. Then, each of the circulating valves 21a to 21d is attached to the mounting holes 24a to 24d.

[0131] In this example, each of the circulating beads 21a to 21d is crimped and fixed to the nut body 19a. Specifically, the circulating beads 21a to 21d are fixed to the nut body 19a by crimped portions (not shown) formed by plastically deforming the radially outer opening edges of each of the mounting holes 24a to 24d. However, the circulating beads can also be crimped and fixed to the nut body by crimped portions formed by plastically deforming a part of the circulating beads. Alternatively, the inner circumferential surface of the pulley 50 fitted onto the nut 8 can be used to prevent the circulating beads 21a to 21d from coming out radially outward from each of the mounting holes 24a to 24d.

[0132] In this example, the sleeves that prevent the circulating spheres 21a to 21d from coming out radially outward from the mounting holes 24a to 24d can be omitted, thus reducing the number of parts and making the structure lighter. In addition, the axial dimension of the flange piece 22a is made longer compared to the structure of the first example of the embodiment, thereby improving the strength of the flange piece 22a. The other configurations and effects are the same as in the first example of the embodiment.

[0133] [Fourth example of an embodiment] A fourth example of the embodiment will be described with reference to Figure 12.

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

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

[0136] In this example, the notch 52 cuts out a portion of the circumferential flange portion 20b in a partially annular shape, extending from the radially inner end to the radially outer end of the flange portion 20b. Therefore, in this example, the outer circumferential surface of the nut body 19 (non-flange portion 26) is exposed in the portion where the notch 52 is provided.

[0137] The flange piece 22b has circumferential end faces 53a and 53b on both sides in the circumferential direction, facing opposite directions with respect to the circumferential direction. The circumferential end faces 53a and 53b are both flat surfaces.

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

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

[0140] In this example, the mounting hole 24a on the axial side is formed in the nut 8 at a point where its circumferential phase coincides with the notch 52 and where its axial position overlaps with the flange piece 22b. Therefore, the circulating valve 21a attached to the mounting hole 24a is provided in the nut 8 at a point where its circumferential phase coincides with the notch 52 and where its axial position overlaps with the flange piece 22b. Consequently, the circulating groove 12a (see Figure 4, etc.) provided in the circulating valve 21a is located on the inner circumferential surface of the nut body 19 at a point where its axial position overlaps with the flange piece 22b.

[0141] In this example, the rigidity of the flange piece 22b can be increased compared to the structure of the first embodiment, thereby effectively suppressing deformation of the flange piece 22b. Consequently, the sliding properties between the guide hole 23 provided in the flange piece 22b and the anti-rotation member 10 can be improved. Furthermore, when the flange portion 20b (flange piece 22b) is formed by machining, the amount of machining can be reduced compared to the structure of the first embodiment, thus reducing the number of machining steps. The other configurations and effects are the same as in the first example of the embodiment.

[0142] [Fifth example of the embodiment] A fifth example of the embodiment will be described with reference to Figure 13.

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

[0144] In other words, the flange portion 20c is composed of a single flange piece 22c having a notch 52a in a part of the circumferential direction, similar to the structure of the third example of the embodiment.

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

[0146] In this example, the mounting hole 24a on the axial side is formed in the nut 8 at a point where its circumferential phase coincides with the notch 52a (notch surface 54) and where its axial position overlaps with the flange piece 22b. Therefore, the circulating valve 21a attached to the mounting hole 24a is provided at a point where its circumferential phase coincides with the notch 52a and where its axial position overlaps with the flange piece 22c. Consequently, the circulating groove 12a (see Figure 4, etc.) provided in the circulating valve 21a is located on the inner circumferential surface of the nut body 19 at a point where its axial position overlaps with the flange piece 22c.

[0147] In this example as described above, the rigidity of the flange piece 22c can be increased compared to the structure of the first example of the embodiment, thus effectively suppressing deformation of the flange piece 22c. Furthermore, since the flange piece 22c in this example can be formed by moving a cutting tool such as an end mill linearly over the annular flange portion, the number of processing steps can be reduced. The other configurations and effects are the same as those in the first and fourth embodiments.

[0148] Although embodiments of the present invention have been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. Furthermore, the structures of each example of the embodiments can be combined as appropriate, as long as no contradictions arise.

[0149] When implementing the present invention, the flange portion constituting the nut is not limited to the axial end of the outer surface of the nut body, but can also be provided in the axial middle portion of the nut body. Furthermore, multiple flange portions can be provided on the outer surface of the nut body, spaced apart in the axial direction.

[0150] Furthermore, in the first embodiment, the case in which the through hole provided in the flange piece is used as a guide hole for engaging with the rotating member in the circumferential direction was described. However, it can also be used, for example, as a support hole for inserting and supporting a pinion pin that rotatably supports the planetary gear. In this case, the flange portion functions as a carrier constituting the planetary reduction mechanism.

[0151] A ball screw device nut according to Embodiment 1 of the present disclosure is a ball screw device nut having a helical nut-side ball screw groove and one or more circulation grooves on its inner circumferential surface, A substantially cylindrical nut body having a nut-side ball screw groove on its inner circumferential surface, and one or more mounting holes that penetrate radially so as to cut out the nut-side ball screw groove, A flange portion protruding radially outward from the outer surface of the nut body, A circulating spinneret is attached to the aforementioned mounting hole, At least one of the circulation grooves is provided in the circulation valve, The flange portion is composed of a plurality of flange pieces arranged spaced apart in the circumferential direction, or a single flange piece having a notch in a part of the circumferential direction. The circulating valve is provided in the portion of the nut body that is separated from the flange piece in the circumferential direction and whose axial position overlaps with that of the flange piece, when the flange portion is composed of a plurality of flange pieces. When the flange portion is composed of a single flange piece having the notch, the circulating valve is provided in the portion whose circumferential phase coincides with that of the notch and whose axial position overlaps with that of the flange piece.

[0152] In the ball screw device nut according to embodiment 2 of the present disclosure, all of the circulation grooves can be provided in the circulation spool in embodiment 1.

[0153] The ball screw device nut according to embodiment 3 of the present disclosure comprises a plurality of circulating spools in either embodiment 1 or embodiment 2, and the plurality of circulating spools can be arranged at equal intervals in the circumferential direction.

[0154] In any of embodiments 1 to 3, the nut for a ball screw device according to embodiment 4 of the present disclosure is configured such that the flange portion is made up of a plurality of flange pieces, and the plurality of flange pieces are arranged at equal intervals in the circumferential direction.

[0155] In any of embodiments 1 to 4, the nut for a ball screw device according to embodiment 5 of the present disclosure may have a flange piece that has a guide portion that can engage with an anti-rotation member in the circumferential direction.

[0156] In any of embodiments 1 to 4, the nut for a ball screw device according to embodiment 6 of the present disclosure may be configured such that the flange piece engages with an engaging recess provided on the inner circumferential surface of the rotating member to prevent relative rotation with respect to the rotating member.

[0157] In any of embodiments 1 to 6, the nut for a ball screw device according to embodiment 7 of the present disclosure may have an axial projection on a portion of the circumferential direction of one end face on the axial side for preventing relative rotation with respect to the screw shaft.

[0158] In the nut for a ball screw device according to embodiment 8 of the present disclosure, in embodiment 7, the axial projection can be positioned with a circumferential phase shift relative to the circulating spindle that is positioned furthest to the axial side among the circulating spindles.

[0159] The ball screw device nut according to aspect 9 of the present disclosure may include a sleeve fitted onto the nut body in any of aspects 1 to 8.

[0160] The ball screw device nut according to embodiment 10 of the present disclosure, in embodiment 9, wherein the flange portion is provided at one axial end of the outer circumferential surface of the nut body, and the sleeve has a cylindrical shape and, by its axial end, can cover at least a portion of the circulating sphere that is positioned furthest to the axial side among the circulating spheres from the radially outward direction.

[0161] The ball screw device nut according to embodiment 11 of the present disclosure, in embodiment 9, wherein the flange portion is provided at one axial end of the nut body and is composed of a plurality of flange pieces, and the sleeve has a plurality of covering pieces arranged at circumferential distances from one axial end, and the covering pieces are arranged in the space between adjacent flange pieces in the circumferential direction to cover the circulating sphere that is positioned furthest to the axial side of the circulating sphere from the radially outside.

[0162] In any of embodiments 1 to 11, the nut for a ball screw device according to embodiment 12 of this disclosure can crimp and fix the circulating spindle to the nut body.

[0163] A ball screw device according to embodiment 13 of the present disclosure comprises a screw shaft, a nut, and a plurality of balls, wherein the nut may be a ball screw device nut from any of embodiments 1 to 12. [Explanation of Symbols]

[0164] 1. Ball screw device 2 Electric Actuators 3 Electric motor 4 pistons 5 Housing 6 Cylinder bore 7 Screw shaft 8 nuts 9 Balls 10 Anti-rotation member 11 Load path 12a~12d Circulation groove 13 Threaded part 14. Fitting shaft 15. Ball screw groove on the shaft side 16 Buttock surface 17 Male spline teeth 18. Ball screw groove on the nut side 19, 19a Nut body 20, 20a~20c Flange section 21a~21d Circulating spinning top 22, 22a~22c Flange pieces 23 Guide hole 24a~24d Mounting holes 25, 25a Flange forming portion 26, 26a Non-flange formed 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. Housing Department 1 36. Second Housing Department 37 Through hole 38 Nut insertion holes 39 Step surface 40 1st fixing hole 41 Inlet 42 Fitting part 43 2nd fixing hole 44 Motor output shaft 45 Engagement holes 46 Female spline teeth 47a, 47b Rolling bearings 48 Small diameter section 49 Covering pieces 50 Pulley 51 Engaging recess 52, 52a Notch 53a, 53b Circumferential end faces 54 Notched surface 100 Ball screw device 101 Screw shaft 102 Nut 103 Ball 104 Ball screw groove on the shaft side 105 Nut-side ball screw groove 106 Circulation groove 107 Nut body 108 Flange section 109 Circulating spinning top 110 Load path 111 Mounting holes

Claims

1. A ball screw device nut having a helical nut-side ball screw groove and one or more circulation grooves on its inner circumferential surface, A substantially cylindrical nut body having a nut-side ball screw groove on its inner circumferential surface, and one or more mounting holes that penetrate radially so as to cut out the nut-side ball screw groove, A flange portion protruding radially outward from the outer surface of the nut body, A circulating spinneret is attached to the aforementioned mounting hole, At least one of the circulation grooves is provided in the circulation valve, The flange portion is composed of a plurality of flange pieces arranged at equal intervals in the circumferential direction. The circulating spool is provided in the portion of the nut body that is separated from the flange piece in the circumferential direction, and in the portion that overlaps with the flange piece in the axial position. Nut for ball screw devices.

2. A ball screw device nut having a helical nut-side ball screw groove and one or more circulation grooves on its inner circumferential surface, A substantially cylindrical nut body having a nut-side ball screw groove on its inner circumferential surface, and one or more mounting holes that penetrate radially so as to cut out the nut-side ball screw groove, A flange portion protruding radially outward from the outer surface of the nut body, A circulating spinneret is attached to the aforementioned mounting hole, The nut body comprises a sleeve fitted onto the nut body, At least one of the circulation grooves is provided in the circulation valve, The flange portion is provided at one end of the nut body on the axial side and is composed of a plurality of flange pieces that are spaced apart in the circumferential direction. The circulating spool is provided in the portion of the nut body that is separated from the flange piece in the circumferential direction, and in the portion that overlaps with the flange piece in the axial position. The sleeve has a plurality of covering pieces arranged at circumferential distances from one end on the axial side, The covering piece is positioned between adjacent flange pieces in the circumferential direction and covers the circulating sphere that is positioned furthest to the axial side of the circulating sphere from the radially outer side. Nut for ball screw devices.

3. A ball screw device nut having a helical nut-side ball screw groove and one or more circulation grooves on its inner circumferential surface, A substantially cylindrical nut body having a nut-side ball screw groove on its inner circumferential surface, and one or more mounting holes that penetrate radially so as to cut out the nut-side ball screw groove, A flange portion protruding radially outward from the outer surface of the nut body, A circulating spinneret is attached to the aforementioned mounting hole, At least one of the circulation grooves is provided in the circulation valve, The flange portion is composed of a plurality of flange pieces arranged spaced apart in the circumferential direction, or a single flange piece having a notch in a part of the circumferential direction. The flange piece is provided to prevent the ball screw device nut from rotating with the screw shaft and has a guide portion that can engage in the circumferential direction with an anti-rotation member fixed to the housing. The circulating valve is provided in the portion of the nut body that is separated from the flange piece in the circumferential direction and whose axial position overlaps with that of the flange piece, when the flange portion is composed of a plurality of flange pieces, and in the portion that is separated from the flange piece in the circumferential direction and whose axial position overlaps with that of the flange piece, when the flange portion is composed of a single flange piece having the notch, the circulating valve is provided in the portion whose circumferential phase coincides with that of the notch and whose axial position overlaps with that of the flange piece. Nut for ball screw devices.

4. All of the aforementioned circulation grooves are provided on the circulation nut for a ball screw device according to any one of claims 1 to 3.

5. The aforementioned circulating spinners are provided in multiple quantities. Multiple of the aforementioned circulating tops are arranged at equal intervals in the circumferential direction. A nut for a ball screw device as described in any one of claims 1 to 3.

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

7. The nut body has an axial projection on a part of the circumferential direction of one end face on the axial side for preventing relative rotation with respect to the screw shaft, as described in any one of claims 1 to 3.

8. The nut for a ball screw device according to claim 7, wherein the axial projection is positioned with a circumferential phase shift relative to the circulating spindle that is positioned furthest to the axial side among the circulating spindles.

9. A ball screw device nut according to claim 1 or claim 3, comprising a sleeve fitted onto the nut body.

10. The flange portion is provided at one end on the axial side of the outer circumferential surface of the nut body. The sleeve has a cylindrical shape and, by its axial end, covers at least a portion of the circulating sphere that is positioned furthest to the axial side of the circulating sphere from the radially outward direction. A nut for a ball screw device as described in claim 9.

11. The circulating spool is crimped and fixed to the nut body, the nut for a ball screw device according to any one of claims 1 to 3.

12. It comprises a screw shaft, a nut, and multiple balls, A ball screw device in which the nut is a ball screw device nut as described in any one of claims 1 to 3.

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