Ball screw device

Abstract

This ball screw device 10 includes: a screw shaft 11 having a first spiral groove 15 on the outer periphery; a cylindrical nut 12 having, on the inner periphery thereof, a second spiral groove 16 facing the first spiral groove 15, the nut 12 surrounding a portion of the screw shaft 11; a plurality of balls 13 arranged in a rolling passage 17 formed between the first spiral groove 15 and the second spiral groove 16; and an annular flange 30 fixed to the outer peripheral side of the nut 12. The nut 12 has, in the middle of the second spiral groove 16, a circulation groove 23 for returning the balls 13 from the end side to the start side of the rolling passage 17. The inner diameter D1 of the flange 30 is larger than the outer diameter d1 of the nut 12 at an attachment part 25 for attachment to the flange 30. A resin part 40 fixed to an inner peripheral surface 31 of the flange 30 and an outer peripheral surface 26 of the attachment part 25 is included between the inner peripheral surface 31 and the outer peripheral surface 26.

Description

Ball screw device

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

[0002] A ball screw device is known as a device for converting rotational motion into linear motion (see, for example, Patent Document 1). The ball screw device has a screw shaft, a cylindrical nut, and multiple balls. The screw shaft has a first helical groove on its outer periphery. The nut has a second helical groove on its inner periphery. The multiple balls are arranged in a rolling path formed between the first and second helical grooves. The nut has a circulation groove in the middle of the second helical groove for returning the balls from the end point side of the rolling path to the start point side.

[0003] In the device disclosed in Patent Document 1, a worm wheel is fixed to the outer peripheral surface of a nut. The nut and the worm wheel are fixed together by press-fitting the nut onto the inner peripheral surface of the worm wheel.

[0004] Japanese Patent Application Publication No. 10-110800

[0005] As described above, when a nut is press-fitted onto the inner peripheral surface of a member such as a worm wheel, high machining accuracy (dimensional accuracy) is required for the inner peripheral surface of the member and the outer peripheral surface of the nut. As a result, there is a problem that the manufacturing cost of the ball screw device is high. Therefore, an object of the present invention is to provide a ball screw device that can reduce manufacturing costs.

[0006] A ball screw device according to an embodiment of the present invention comprises a screw shaft having a first spiral groove on its outer periphery, a cylindrical nut having a second spiral groove on its inner periphery that faces the first spiral groove and surrounds a portion of the screw shaft, a plurality of balls arranged in a rolling path obtained between the first spiral groove and the second spiral groove, and a ring-shaped flange fixed to the outer periphery of the nut, wherein the nut has a circulation groove in the middle of the second spiral groove for returning the balls from the end side of the rolling path to the start side, the inner diameter of the flange is larger than the outer diameter of the nut at the mounting portion of the flange, and a resin portion fixed to the inner periphery and the outer periphery is provided between the inner periphery of the flange and the outer periphery of the mounting portion.

[0007] According to the ball screw device according to the embodiment of the present invention, it is possible to reduce manufacturing costs.

[0008] Fig. 1 is a cross-sectional view of a ball screw device. Fig. 2 is a perspective view of a nut block. Fig. 3 is a cross-sectional view of the nut block. Fig. 4 is an exploded perspective view of the nut block shown in Fig. 3. Fig. 5 is a cross-sectional view showing a modified example of the nut block shown in Fig. 3. Fig. 6 is a cross-sectional view showing a second embodiment of the nut block. Fig. 7 is a cross-sectional view showing a third embodiment of the nut block. Fig. 8 is a cross-sectional view showing a fourth embodiment of the nut block.

[0009] <Outline of Embodiments of the Present Invention> The following is a description of outlines of embodiments of the present invention. (1) A ball screw device according to an embodiment of the present invention includes a screw shaft having a first helical groove on its outer periphery, a cylindrical nut having a second helical groove on its inner periphery that faces the first helical groove and surrounds a portion of the screw shaft, a plurality of balls arranged in a rolling path obtained between the first helical groove and the second helical groove, and an annular flange fixed to the outer periphery of the nut, the nut having a circulation groove in the middle of the second helical groove for returning the balls from the end point side to the start point side of the rolling path, the inner diameter of the flange being larger than the outer diameter of an attachment portion of the nut at which the flange is attached, and a resin portion fixed to the inner periphery and the outer periphery between an inner periphery of the flange and an outer periphery of the attachment portion.

[0010] The flange is fixed to the nut by fixing the resin part to the inner peripheral surface of the flange and the outer peripheral surface of the attachment part of the nut. The resin part is molded by injection molding, with the flange and the nut as part of the mold. The processing precision of the inner peripheral surface of the flange and the outer peripheral surface of the attachment part of the nut can be lower than in the past, making it possible to reduce manufacturing costs.

[0011] (2) Preferably, at least one of the inner peripheral surface of the flange and the outer peripheral surface of the mounting portion has a recess or a protrusion, and the resin portion has a portion that fits into the recess or a portion that covers the protrusion. With this configuration, the flange is more firmly fixed to the nut.

[0012] (3) In the ball screw device of (2), at least one of the inner peripheral surface of the flange and the outer peripheral surface of the mounting portion has a circumferential groove as the recess, and the resin portion has a circumferential ridge portion that fits into the circumferential groove. This configuration increases the axial fixing strength between the flange and the nut.

[0013] (4) In the ball screw device of (2) or (3), at least one of the inner peripheral surface of the flange and the outer peripheral surface of the mounting portion has an axial groove as the recess, and the resin portion has an axial ridge portion that fits into the axial groove. This configuration increases the circumferential fixing strength between the flange and the nut.

[0014] (5) Preferably, in the ball screw device of any one of (2) to (4), the inner peripheral surface of the flange has a circumferential groove as the recess, the circumferential groove being located at an axial end of the flange and opening on the inner peripheral side and one axial side of the flange. With this configuration, the circumferential groove of the flange can be formed by forging or pressing. Forming the circumferential groove is easier than forming the circumferential groove in the axial center of the inner peripheral surface of the flange.

[0015] <Details of the embodiment of the present invention> An embodiment of the present invention will be described below. [Overall configuration of ball screw device] Fig. 1 is a cross-sectional view of a ball screw device. The ball screw device 10 is used, for example, in a brake device of a vehicle (automobile). The ball screw device 10 has a screw shaft 11, a nut 12, a plurality of balls 13, a flange 30, and a resin part 40. The screw shaft 11, the nut 12, the balls 13, and the flange 30 are made of metal.

[0016] The resin part 40 is made of thermoplastic resin and is formed by injection molding using the flange 30 and the nut 12 as part of a mold. In other words, the flange 30 and the nut 12 are inserted parts when the resin part 40 is injection molded. The nut 12, the flange 30, and the resin part 40 form a nut block B as a single component.

[0017] The ball screw device 10 is a circulating type, and the ball screw device 10 shown in Fig. 1 is a so-called "top type." The nut 12 has a cylindrical tube portion 21 and a "top 14" attached to the tube portion 21. In this embodiment, the ball screw device 10 has a plurality of tops 14.

[0018] The screw shaft 11 is connected to a drive device including a motor (not shown). The drive device causes the screw shaft 11 to rotate forward and backward around its own central axis C. An annular flange 30 is fixed to the outer periphery of the nut 12. This fixing is achieved by a resin part 40. The structure for this fixing will be described later.

[0019] 2 is a perspective view of a nut block B having a nut 12, a flange 30, and a resin part 40. In the embodiment shown in FIGS. 1 and 2, the flange 30 has a recess 33 on its outer peripheral surface 32. A support member (e.g., a pin member) not shown fits into the recess 33, making the flange 30 unable to rotate around the central axis C. The flange 30 is fixed to the nut 12. Therefore, the nut 12 also becomes unable to rotate around the central axis C. The flange 30 functions as a rotation stopper for the nut 12.

[0020] The nut 12 cannot rotate around the central axis C, but can move in a direction parallel to the central axis C. When the screw shaft 11 rotates, the balls 13 between the screw shaft 11 and the nut 12 roll, causing the nut 12 to move linearly in a direction along the central axis C.

[0021] The directions of the ball screw device 10 will now be described. The direction along the central axis C of the screw shaft 11 is defined as the "axial direction." The axial direction also includes a direction parallel to the central axis C. The direction perpendicular to the central axis C is defined as the "radial direction." The direction along an imaginary circle centered on the central axis C is defined as the "circumferential direction." The rotation direction of the screw shaft 11 is the circumferential direction, and the movement direction of the nut 12 is the axial direction.

[0022] The screw shaft 11 has a long cylindrical shape (see FIG. 1 ). The screw shaft 11 has a first spiral groove 15 on its outer periphery. The first spiral groove 15 is a spiral groove formed along the axial direction. The groove shape of the first spiral groove 15 is an arc-shaped cross section. The nut 12 has a cylindrical shape. The nut 12 is located radially outward of the screw shaft 11 and surrounds a portion of the screw shaft 11. The central axis of the nut 12 coincides with the central axis C of the screw shaft 11. The nut 12 has a second spiral groove 16 on its inner periphery. The second spiral groove 16 faces the first spiral groove 15 in the radial direction. The groove shape of the second spiral groove 16 is an arc-shaped cross section.

[0023] A rolling path 17 along which the balls 13 pass is formed between the first spiral groove 15 and the second spiral groove 16. A plurality of balls 13 are arranged in the rolling path 17. When the screw shaft 11 rotates in a first direction, the balls 13 apply an axial force to the nut 12 while rolling along the rolling path 17. The axial force causes the nut 12 to move toward a first side in the axial direction. When the screw shaft 11 rotates in a second direction opposite to the first direction, the balls 13 apply an axial force to the nut 12 while rolling along the rolling path 17. The axial force causes the nut 12 to move toward a second side in the axial direction.

[0024] The nut 12 has a cylindrical portion 21 with a peripheral wall provided with through holes 18 that penetrate in the radial direction. A plurality of through holes 18 are provided at intervals in the circumferential direction. In the present embodiment, four through holes 18 are provided at 90° intervals along the circumferential direction. These through holes 18 are arranged at different positions in the axial direction.

[0025] Each top 14 is mounted in one through-hole 18. The top 14 is mounted in the through-hole 18 while being positioned in the axial and circumferential directions. The top 14 mounted in the through-hole 18 cannot be displaced in the axial and circumferential directions.

[0026] The ball screw device 10 has a cover 41. The cover 41 is cylindrical and is located on the outer periphery of the cylindrical portion 21 of the nut 12. The cover 41 is located radially outward of the top 14. The cover 41 prevents the top 14 attached to the through hole 18 from being displaced radially outward.

[0027] The top 14 has a circulation groove 23 that allows the ball 13 to pass through (see FIG. 1 ). The circulation groove 23 is a groove for returning the ball 13 from the end point side to the start point side of the rolling path 17. The nut 12 of this embodiment has the top 14 in the middle of the second spiral groove 16, and has the circulation groove 23 in the middle of the second spiral groove 16. The top 14 of this embodiment is, for example, a forged product made of metal. The top 14 may also be made of resin.

[0028] [Fixing Structure of Nut 12 and Flange 30] Figure 3 is a cross-sectional view of the nut block B. The inner diameter D1 of the flange 30 is larger than the outer diameter d1 of the nut 12 at the mounting portion 25 of the flange 30 (D1 > d1). In this embodiment, the mounting portion 25 of the flange 30 is the end portion on the first side (the left side in Figure 3) in the axial direction of the nut 12.

[0029] The resin portion 40 is located between the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25. As described above, the resin portion 40 is made of a thermoplastic resin, and is formed by injection molding using the flange 30 and the nut 12 as part of a mold. Through this molding, the resin portion 40 is fixed to the inner peripheral surface 31 of the flange 30 and also to the outer peripheral surface 26 of the mounting portion 25.

[0030] In the embodiment shown in Fig. 3, the cover 41 that covers the top 14 from the radial outside is also made of resin (thermoplastic resin). The cover 41 is molded at the same time as the resin portion 40 is molded. Therefore, the resin portion 40, which is located between the inner circumferential surface 31 of the flange 30 and the outer circumferential surface 26 of the mounting portion 25, and the cover 41 are seamlessly integrated. The cover 41 has a cylindrical shape that extends from the resin portion 40 to the second axial side of the nut 12 (the right side in Fig. 3).

[0031] The resin portion 40 is fixed to the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25, thereby fixing the flange 30 to the nut 12. The flange 30 and the nut 12 are integrally fixed to each other and cannot rotate around the central axis C, but can move along the central axis C.

[0032] In order to further strengthen the fixation between the flange 30 and the nut 12, the inner peripheral surface 31 of the flange 30 has a recess 33 (hereinafter referred to as the "external recess 33"), and the outer peripheral surface 26 of the mounting portion 25 has a recess 34 (hereinafter referred to as the "internal recess 34"). The resin portion 40 has a portion 43 (hereinafter referred to as the "external fixing portion 43") that fits into the external recess 33, and a portion 44 (hereinafter referred to as the "internal fixing portion 44") that fits into the internal recess 34.

[0033] Figure 4 is an exploded perspective view of the nut block B shown in Figure 3. As described above, the resin part 40 and the cover 41 are formed by injection molding using the flange 30 and the nut 12 as part of the mold. Therefore, the nut block B cannot actually be disassembled.

[0034] The inner peripheral surface 31 of the flange 30 has a circumferential groove 331 (hereinafter referred to as the "outer-circumferential groove 331") as part of the outer recess 33. The outer peripheral surface 26 of the mounting portion 25 of the nut 12 has a circumferential groove 341 (hereinafter referred to as the "inner-circumferential groove 341") as part of the inner recess 34. The outer-circumferential groove 331 and the inner-circumferential groove 341 are each grooves provided along the circumferential direction.

[0035] The resin part 40 has, as part of the outer fixed part 43, a first circumferential ridge part 431 that fits into the outer circumferential groove 331. The resin part 40 has, as part of the inner fixed part 44, a second circumferential ridge part 441 that fits into the inner circumferential groove 341.

[0036] The outer-circumferential groove 331 is a groove that is provided continuously in the circumferential direction along the inner peripheral surface 31 of the flange 30. Corresponding to the shape of the outer-circumferential groove 331, the first circumferential ridge portion 431 that the resin part 40 has is continuous in the circumferential direction. The outer-circumferential groove 331 is provided at two locations spaced apart in the axial direction on the inner circumference of the flange 30. Corresponding to the arrangement of the outer-circumferential groove 331, the first circumferential ridge portions 431 are provided at two locations spaced apart in the axial direction on the outer periphery of the resin part 40.

[0037] The arrangement of the two outer-circumferential grooves 331 will be described. The outer-circumferential groove 331 on the first axial side (left side in FIG. 3 ) is located at an end 301L on the first axial side of the flange 30, and opens on the inner circumferential side and one axial side (left side in FIG. 3 ) of the flange 30. The outer-circumferential groove 331 on the second axial side (right side in FIG. 3 ) is located at an end 301R on the second axial side of the flange 30, and opens on the inner circumferential side and one axial side (right side in FIG. 3 ) of the flange 30.

[0038] As described above, the flange 30 is made of metal and manufactured by forging or pressing. The outer-circumferential groove 331 is located at the axial end 301L (301R) and has a shape that opens on the inner circumferential side and one axial side of the flange 30, as described above. Therefore, the outer-circumferential groove 331 can be formed by forging or pressing at the same time as forming the flange 30. Although not shown, the outer-circumferential groove 331 may be formed in the axial center portion of the inner circumferential surface 31 of the flange 30. However, compared to that case, according to the embodiment shown in FIGS. 3 and 4, the outer-circumferential groove 331 is also formed at the same time as forging or pressing the flange 30, making it easier to obtain the outer-circumferential groove 331.

[0039] A portion of one of the tops 14 (see FIG. 4) is covered from the radially outer side by the flange 30 via the resin portion 40. For this reason, the inner-circumferential groove 341 is a long groove along the circumferential direction, but is provided along the entire circumferential direction of the mounting portion 25 of the nut 12, excluding a portion of the circumferential direction. The inner circumferential ridge portion 441 of the resin portion 40 has a shape corresponding to the inner-circumferential groove 341 described above, and is provided along the circumferential direction, excluding a portion of the circumferential direction. Although not shown, if the flange 30 does not cover the top 14 from the radially outer side, the inner-circumferential groove 341 may be a groove that continues in the circumferential direction.

[0040] In this way, since the resin part 40 has (two) first circumferential ridge portions 431 on its outer periphery and the second circumferential ridge portion 441 on its inner periphery, the flange 30 and the nut 12 cannot be displaced relative to each other in the axial direction, and the axial fixing strength between the flange 30 and the nut 12 is increased.

[0041] 3, both the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 have recesses 33, 34, and the resin portion 40 has portions 43, 44 that fit into the recesses 33, 34. Alternatively, one of the recesses 33, 34 may be omitted, and at least one of the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 may have a recess that is long in the circumferential direction as described above.

[0042] Fig. 5 is a cross-sectional view showing a modified example of the nut block B shown in Fig. 3. As shown in Fig. 5, the inner peripheral surface 31 of the flange 30 may have a first convex portion 51, the outer peripheral surface 26 of the mounting portion 25 may have a second convex portion 52, and the resin portion 40 may have a portion 53 that covers the first convex portion 51 and a portion 54 that covers the second convex portion 52. Note that the same components in the nut block B shown in Fig. 5 and the nut block B shown in Fig. 3 are denoted by the same reference numerals, and description of those components will be omitted here.

[0043] 5, one of the first convex portion 51 and the second convex portion 52 may be omitted. That is, it is sufficient that at least one of the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 has a convex portion (51, 52), and the resin portion 40 has portions (53, 54) that cover the convex portions (51, 52).

[0044] 3 and 5, in the ball screw device 10 of the present disclosure, at least one of the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 has a recess or a protrusion, and the resin portion 40 has a portion that fits into the recess or a portion that covers the protrusion. This increases the fixing strength between the flange 30 and the nut 12.

[0045] The ball screw device 10 has a configuration for increasing the circumferential fixing strength between the flange 30 and the nut 12. The configuration will be described below. The inner peripheral surface 31 of the flange 30 (see FIG. 4) further has an axial groove 332 (hereinafter referred to as the "outer-axial groove 332") as the outer recess 33. The outer peripheral surface 26 of the mounting portion 25 further has an axial groove 342 (hereinafter referred to as the "inner-axial groove 342") as the inner recess 34. The outer-axial groove 332 and the inner-axial groove 342 are each grooves provided along the axial direction.

[0046] The resin part 40 further has, as the outer fixing part 43, a first axial ridge part 432 that fits into the outer axial groove 332. The resin part 40 further has, as the inner fixing part 44, a second axial ridge part 442 that fits into the inner axial groove 342.

[0047] The outer axial groove 332 of the flange 30 is located between the two outer circumferential grooves 331. A plurality of outer axial grooves 332 are provided along the inner circumferential surface 31 of the flange 30. Due to the plurality of outer axial grooves 332, the inner circumferential surface 31 of the flange 30 has a serrated shape, as shown in FIG. 4 . Corresponding to the shape and arrangement of the outer axial grooves 332, a plurality of axial ridge portions 432 on the outer circumferential side of the resin portion 40 are provided along the circumferential direction. Due to the plurality of axial ridge portions 432, the outer circumferential surface of the resin portion 40 has a serrated shape, as shown in FIG. 4 .

[0048] The inner axial grooves 342 of the mounting portion 25 of the nut 12 are located on both axial sides of one inner circumferential groove 341. A plurality of inner axial grooves 342 are provided along the outer peripheral surface 26 of the mounting portion 25. Due to the plurality of inner axial grooves 342, the outer peripheral surface 26 of the mounting portion 25 has a serrated shape, as shown in FIG. 4. Corresponding to the shape and arrangement of these inner axial grooves 342, a plurality of axial ridges 442 on the inner peripheral side of the resin portion 40 are provided along the circumferential direction. Due to the plurality of axial ridges 442, the inner peripheral surface of the resin portion 40 has a serrated shape, as shown in FIG. 4.

[0049] 3 and 4, both the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 have recesses 33, 34, and the resin portion 40 has portions 43, 44 that fit into the recesses 33, 34. Alternatively, it is sufficient that at least one of the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 has a recess (axial groove) along the axial direction as described above. Then, it is sufficient that the resin portion 40 has an axial ridge portion that fits into the recess (axial groove).

[0050] In this way, the flange 30 has an outer recess 33 (outer-axial groove 332) on its inner circumferential surface 31, and the mounting portion 25 has an inner recess 34 (inner-axial groove 342) on its outer circumferential surface 26. The resin portion 40 has a first axial ridge 432 on its outer periphery that fits into the outer recess 33 (outer-axial groove 332), and a second axial ridge 442 on its inner periphery that fits into the inner recess 34 (inner-axial groove 342). With this configuration, the flange 30 and the nut 12 cannot be displaced relative to each other in the circumferential direction. In other words, the circumferential fixing strength between the flange 30 and the nut 12 is increased.

[0051] [Second embodiment of nut block B] In the embodiment (first embodiment) shown in Figures 3 and 4, the resin part 40 and the cover 41 are integrated. Figure 6 is a cross-sectional view showing a second embodiment of the nut block B. In the second embodiment, the cover 41 is a separate member from the resin part 40. The cover 41 may be made of resin or metal. Note that the configuration of the resin part 40 in the second embodiment is the same as in the first embodiment. That is, the resin part 40 is fixed to the inner circumferential surface 31 of the flange 30 and to the outer circumferential surface 26 of the mounting portion 25 of the nut 12.

[0052] The same components in the nut block B shown in FIG. 6 and the nut block B shown in FIG. 3 are denoted by the same reference numerals, and a description of these components will be omitted here.

[0053] [Third Form of Nut Block B] In the first and second forms, the top 14 of the nut 12 and the cover 41 are separate members, and the cover 41 prevents the top 14 from falling off. Figure 7 is a cross-sectional view showing a third form of the nut block B. In the third form, the top 14 is made of resin and is formed by injection molding together with the resin part 40 and the cover 41. Therefore, the resin part 40, the cover 41, and the top 14 are a single resin part.

[0054] In the third embodiment, there is a degree of freedom in the overall contour shape of the top 14. The axial dimension L of the top 14 can be increased, ensuring the strength of the top 14. Because the top 14 is one part of a resin part and the cover 41 is another part of that resin part, it is possible to reduce the number of parts and the number of assembly steps, thereby reducing manufacturing costs.

[0055] [Fourth embodiment of nut block B] Figure 8 is a cross-sectional view showing a fourth embodiment of the nut block B. When the cover 41 is molded from resin, the top 14 is molded integrally with the cover 41 by injection molding, as in the third embodiment. The top 14 is injection molded together with the cover 41, so that the cover 41 and the top 14 become a single resin part. In the fourth embodiment, the cover 41 and the connecting portion F between the flange 30 and the nut 12 are separate members. The shape of the connecting portion F may be the same as that of the resin portion 40 in the second embodiment (see Figure 6).

[0056] In the fourth embodiment, the cover 41 is a part of a resin part and the top 14 is a separate part of the resin part, which reduces the number of parts and the assembly steps, thereby reducing manufacturing costs. Note that, as a reference invention related to the fourth embodiment, the structure of the connecting portion F between the flange 30 and the nut 12 may be other than the resin part 40, which is made of resin.

[0057] [Each Form of Ball Screw Device 10] As described above, the ball screw device 10 of each form described above includes the screw shaft 11 having the first helical groove 15 on its outer periphery, the cylindrical nut 12 having the second helical groove 16 on its inner periphery, a plurality of balls 13 arranged in the rolling path 17 obtained between the first helical groove 15 and the second helical groove 16, and the annular flange 30 fixed to the outer periphery of the nut 12. The inner diameter D1 of the flange 30 is larger than the outer diameter d1 of the mounting portion 25 of the flange 30 of the nut 12. The ball screw device 10 includes the resin portion 40 between the inner circumferential surface 31 of the flange 30 and the outer circumferential surface 26 of the mounting portion 25.

[0058] The resin portion 40 is fixed to the inner peripheral surface 31 and the outer peripheral surface 26. With this configuration, the flange 30 is fixed to the nut 12. The resin portion 40 is formed by injection molding, with the flange 30 and the nut 12 serving as part of a mold. The processing precision (dimensional precision) of the inner peripheral surface 31 of the flange 30 and the outer peripheral surface 26 of the mounting portion 25 of the nut 12 can be lower than in the past, enabling a reduction in manufacturing costs.

[0059] [Others] As shown in Figure 3, the nut 12 may have a second circumferential groove 343 (hereinafter referred to as "second inner-circumferential groove 343") on its outer circumferential surface. The resin part 40 has a third circumferential ridge portion 443 that fits into the second inner-circumferential groove 343. This configuration further increases the axial fixing strength between the flange 30 and the nut 12.

[0060] The above-described embodiments are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims, not the above-described embodiments, and includes all modifications within the scope equivalent to the configurations described in the claims.

[0061] REFERENCE SIGNS LIST 10 ball screw device 11 screw shaft 12 nut 13 ball 15 first spiral groove 16 second spiral groove 17 rolling path 23 circulation groove 25 mounting portion 26 outer peripheral surface 30 flange 31 inner peripheral surface 33 outer recess (recess) 34 inner recess (recess) 40 resin portion 43 fixing portion (portion that fits into recess) 44 fixing portion (portion that fits into recess) 51 convex portion 52 convex portion 53 portion covering convex portion 54 portion covering convex portion 331 circumferential groove 332 axial groove 341 circumferential groove 342 axial groove 431 circumferential ridge portion 432 axial ridge portion 441 circumferential ridge portion 442 axial ridge portion 443 circumferential ridge portion D1 inner diameter of flange d1 outer diameter of mounting portion

Claims

1. A ball screw device comprising: a screw shaft having a first spiral groove on its outer periphery; a cylindrical nut having a second spiral groove on its inner periphery that faces the first spiral groove and surrounds a portion of the screw shaft; a plurality of balls arranged in a rolling path obtained between the first spiral groove and the second spiral groove; and an annular flange fixed to the outer periphery of the nut, wherein the nut has a circulation groove midway along the second spiral groove for returning the balls from the end point side to the start point side of the rolling path, the inner diameter of the flange being larger than the outer diameter of a mounting portion of the flange of the nut, and a resin portion fixed to the inner periphery and the outer periphery between the inner periphery of the flange and the outer periphery of the mounting portion.

2. A ball screw device as described in claim 1, wherein at least one of the inner peripheral surface of the flange and the outer peripheral surface of the mounting portion has a recess or a protrusion, and the resin portion has a portion that fits into the recess or a portion that covers the protrusion.

3. A ball screw device as set forth in claim 2, wherein at least one of the inner peripheral surface of the flange and the outer peripheral surface of the mounting portion has a circumferential groove as the recess, and the resin portion has a circumferential ridge portion that fits into the circumferential groove.

4. A ball screw device as set forth in claim 2 or claim 3, wherein at least one of the inner peripheral surface of the flange and the outer peripheral surface of the mounting portion has an axial groove as the recess, and the resin portion has an axial ridge portion that fits into the axial groove.

5. A ball screw device according to claim 2, wherein the inner peripheral surface of the flange has a circumferential groove as the recess, the circumferential groove being located at an axial end of the flange and opening on the inner peripheral side and one axial side of the flange.

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