Ball screw

Abstract

To provide a ball screw capable of suppressing increase in size while suppressing rattling of components.SOLUTION: A ball screw 1 comprises: a screw shaft 2 having an outer peripheral rolling groove 25; a nut 3 having an inner peripheral rolling groove 31; a plurality of rolling elements 4 arranged in a rolling path 40 formed by the inner peripheral rolling groove 31 and the outer peripheral rolling groove 25; a piece 5; a cylindrical member 6; and a fitting member 7. The piece 5 is attached to the nut 3, and has a circulation path 57 that returns the rolling elements 4 from one end to the other end of the rolling path 40. The cylindrical member 6 is fitted into an outer peripheral part of the nut 3, and covers the piece 5 from the radial outside. The fitting member 7 is provided without overlapping with the cylindrical member 6 in an axial direction, and is fitted into the outer peripheral part of the nut 3. The fitting member 7 covers at least a part of the piece 5 from the radial outside.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A ball screw is known that includes a nut, a screw shaft that passes through the nut, and a number of rolling elements that are arranged between the nut and the screw shaft. For example, Patent Document 1 discloses a ball screw configuration that includes, in addition to the nut, the screw shaft, and the rolling elements, a number of pieces that are provided on the nut and return the rolling elements from one end to the other end of the rolling path, and a sleeve that holds the pieces from the outside in the radial direction. A part of the piece protrudes radially outward from the outer periphery of the nut when attached to the nut. The sleeve is also fixed to the nut by crimping. According to the technology described in Patent Document 1, since a part of the piece protrudes radially outward from the outer periphery of the nut, the pressing force of the piece by the sleeve can be adjusted, which is said to suppress the occurrence of abnormal noise and malfunction during the operation of the ball screw. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4716244 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when using a ball screw for an application in which the nut rotates and the screw shaft moves linearly, various members such as bearings and drive parts (hereinafter, fitting members) may be arranged on the outer periphery of the nut. For example, in the technology described in the above-mentioned Patent Document 1, a sleeve is arranged so as to cover all the links, and further, a fitting member (bearing) is arranged in line with the sleeve in the axial direction. In such a conventional technology, it is necessary to secure extra axial length of the nut in order to arrange the fitting member, so there is a risk that the nut will become large in the axial direction. In order to prevent the nut from becoming large, a method of arranging a fitting member on the outer periphery of the sleeve is considered. However, in this case, the dimensional accuracy of the sleeve made of thin metal or the like and the fitting member such as a bearing cannot be maintained at a sufficiently high level, so there is a risk that the positioning accuracy of the fitting member relative to the nut will decrease. As a result, there is a risk that the fitting member will rattle during operation.

[0005] Therefore, in the prior art, in a ball screw having a sleeve and a part other than the sleeve (a mating member) on its outer periphery, there was room for improvement in terms of suppressing the rattle of the parts while suppressing the increase in axial size of the nut.

[0006] Therefore, an object of the present invention is to provide a ball screw that can suppress rattling of components while suppressing an increase in size. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention proposes the following means. A ball screw according to a first aspect of the present invention comprises a screw shaft having a spiral outer circumferential rolling groove on its outer circumferential surface, a nut having a spiral inner circumferential rolling groove on its inner circumferential surface, a plurality of rolling elements arranged in a rolling path formed by the inner circumferential rolling groove of the nut and the outer circumferential rolling groove of the screw shaft, a top attached to the nut and having a circulation path that returns the rolling elements from one end of the rolling path to the other end, a cylindrical member that fits into the outer circumferential part of the nut and covers the top from the radial outside, and a fitting member that is provided in the axial direction of the screw shaft without overlapping with the cylindrical member and fits into the outer circumferential part of the nut, and the fitting member covers at least a portion of the top from the radial outside. Effect of the Invention

[0008] According to the ball screw of the present invention, it is possible to provide a ball screw that can suppress rattling of components while suppressing an increase in size. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a ball screw according to a first embodiment. [Diagram 2] FIG. 1 is an external perspective view of a ball screw according to a first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view of the nut according to the first embodiment. [Figure 4] Enlarged view of part IV in Figure 1. [Diagram 5] Enlarged view of part V in Figure 1. [Figure 6] An explanatory diagram of the first cleaning method. [Figure 7] An explanatory diagram of the second cleaning method. [Figure 8] An explanatory diagram of the third cleaning method. [Figure 9] FIG. 6 is a cross-sectional view of a ball screw according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the axial direction, radial direction, and circumferential direction refer to the axial direction, radial direction, and circumferential direction of the center axis C of the ball screw 1, unless otherwise specified.

[0011] (First embodiment) Fig. 1 is a cross-sectional view of a ball screw 1 according to the first embodiment. Fig. 2 is a perspective view of the appearance of the ball screw 1 according to the first embodiment. The ball screw 1 is a device that converts rotational motion into linear motion. As shown in Fig. 1 and Fig. 2, the ball screw 1 of this embodiment includes a screw shaft 2, a nut 3, a plurality of rolling elements 4, a plurality of blocks 5, a cylindrical member 6, and a fitting member 7.

[0012] In the ball screw 1 of this embodiment, for example, the nut 3 rotates about the central axis C. The nut 3 is rotatable about the central axis C, but does not move in a direction along the central axis C. The screw shaft 2 connected to a driven member (not shown) does not rotate about the central axis C, but is movable in a direction along the central axis C. When the nut 3 rotates, the screw shaft 2 moves in a direction along the central axis C. The ball screw 1 is used, for example, as an electric brake device for moving a brake pad (not shown), which is an example of a driven member, of a vehicle.

[0013] (Screw shaft) The screw shaft 2 has a screw shaft body 21 and a connecting shaft 22. The screw shaft body 21 is formed in a cylindrical shape centered on a central axis C. The screw shaft body 21 is disposed inside a nut 3 described later. A spiral outer circumferential rolling groove 25 is formed on the outer periphery of the screw shaft body 21. The cross-sectional shape of the outer circumferential rolling groove 25 is a Gothic arch including two circular arcs. The outer circumferential rolling groove 25 is formed over almost the entire screw shaft body 21 in the axial direction.

[0014] The connecting shaft 22 is connected to an end face of the threaded shaft body 21 on a first axial side (the right side in FIG. 1). The connecting shaft 22 is formed integrally with the threaded shaft body 21. The connecting shaft 22 is formed in a cylindrical shape that is coaxial with the threaded shaft body 21 and has an outer diameter smaller than that of the threaded shaft body 21. A spline groove 27 is formed on the outer periphery of the connecting shaft 22. The connecting shaft 22 is connected to a driven member (not shown) by this spline groove 27. The shape of the connecting shaft 22 is not limited to a cylindrical shape. The connecting shaft 22 may be connected to the driven member by a method other than a spline, such as a gear.

[0015] (nut) FIG. 3 is a cross-sectional view of the nut 3 according to the first embodiment. In FIG. 3, a part of the inner circumferential rolling groove 31 is omitted, but in reality, the inner circumferential rolling groove 31 is formed over the entire axial direction of the nut. As shown in FIGS. 1 to 3, the nut 3 is formed in a cylindrical shape centered on the central axis C. The screw shaft body 21 is inserted into the nut 3. The inner circumferential rolling groove 31, the receiving hole 33, and the crimping recess 35 are formed in the nut 3. As shown in FIG. 3, the inner circumferential rolling groove 31 is a spiral groove provided on the inner peripheral surface of the nut 3. The cross-sectional shape of the inner circumferential rolling groove 31 is a gothic arch including two arcs. The inner circumferential rolling groove 31 is formed over almost the entire axial direction of the nut 3.

[0016] The accommodating hole 33 penetrates the nut 3 in the radial direction. The accommodating hole 33 is formed as an elongated hole along the approximate circumferential direction. A plurality of the accommodating holes 33 (four in this embodiment) are provided and arranged at equal intervals in the axial and circumferential directions. Each of the accommodating holes 33 accommodates a piece 5, which will be described in detail later. Each of the accommodating holes 33 is provided with a step portion 36 (see also FIG. 5) formed so that the diameter of the radially inner portion is smaller than that of the radially outer portion.

[0017] Fig. 4 is an enlarged view of a portion IV in Fig. 1. Fig. 5 is an enlarged view of a portion V in Fig. 1. As shown in Figs. 1 and 4, the crimping recess 35 is formed on the outer periphery of the nut 3. As shown in Fig. 1, the crimping recess 35 is provided on the second axial side (the left side in Fig. 1) of all the receiving holes 33 in the axial direction. The crimping recess 35 is a groove that continues in the circumferential direction. Note that the crimping recess 35 may be a plurality of depressions or the like that are formed discontinuously in the circumferential direction. In this embodiment, the outer circumferential surface of the nut 3 is a cylindrical surface having the same outer diameter over the entire surface, except for the above-mentioned crimping recess 35 and the accommodating hole 33. Over the entire region of the nut 3 in the axial direction, the outer diameter of the nut 3 is equal to or smaller than the inner diameter of the cylindrical member 6. In other words, the outer circumferential portion of the nut 3 is formed without having any portion (for example, a flange, a convex portion, a projection, etc.) that protrudes radially outward from the outer circumferential main surface 30 of the nut 3, which is the portion other than the crimping recess 35 and the accommodating hole 33.

[0018] (Rolling elements) As shown in FIG. 1, a plurality of rolling elements 4 are disposed between the nut 3 and the screw shaft 2. The rolling elements 4 are, for example, balls. When the nut 3 and the screw shaft 2 are assembled together, a spiral rolling path 40 is formed by an inner peripheral rolling groove 31 formed in the nut 3 and an outer peripheral rolling groove 25 formed in the screw shaft body 21. The rolling elements 4 move in this spiral rolling path 40. In FIG. 1, one rolling element 4 is indicated by a two-dot chain line. In reality, the ball screw 1 includes a plurality of rolling elements 4.

[0019] (frame) The tops 5 are accommodated in the respective accommodation holes 33 provided in the nut 3. Thus, in this embodiment, four tops 5 are provided. As shown in FIG. 5, the tops 5 are accommodated in the accommodation holes 33 from the radial outside of the nut 3. Each top 5 has a head 55 that abuts against the step portion 36 of the accommodation hole 33 and a circulation path 57 provided on the inner surface side. When the tops 5 are accommodated in the accommodation hole 33, the heads 55 of the tops 5 are formed so as to be flush with the outer circumferential surface of the nut 3, for example. In addition, when the tops 5 are accommodated in the accommodation hole 33, the heads 55 of the tops 5 may be formed so as to protrude radially outward from the outer circumferential surface of the nut 3, or may be formed so as to be recessed radially inward from the outer circumferential surface of the nut 3. As shown in FIG. 3, the circulation path 57 of the tops 5 connects one end and the other end of the spiral rolling path 40 to form an infinite circulation circuit. The infinite circulation circuit is filled with a plurality of rolling elements 4, so that the rolling elements 4 circulate infinitely within the infinite circulation circuit. In other words, the ball screw 1 of this embodiment is a so-called screw circulation type ball screw 1.

[0020] More specifically, the inner surface of the top 5 is curved with a curvature corresponding to the curved surface forming the inner peripheral surface of the nut 3, and is provided at the same height as the thread of the inner peripheral rolling groove 31. A groove-shaped circulation path 57 is formed on the inner surface of this top 5. The circulation path 57 is formed in a curved shape with a U-shaped cross section corresponding to the spherical surface of the rolling body 4. The circulation path 57 is greatly curved on the inner surface of the top 5, for example, in an S-shape. An inlet / outlet 58a at one end of the circulation path 57 is connected to one end of the inner peripheral rolling groove 31. An inlet / outlet 58b at the other end of the circulation path 57 is connected to the other end of the inner peripheral rolling groove 31. From one end to the other end of the inner peripheral rolling groove 31, the inner peripheral surface of the nut 3 makes approximately one revolution, and between the inlet / outlet 58a and the inlet / outlet 58b, there is one thread each of the thread of the nut 3 and the thread of the screw shaft 2. The circulation path 57 is gently curved in the axial and circumferential directions of the nut 3 so as to ride over the threads of the screw shaft 2 between the inlet / outlet 58a and the inlet / outlet 58b. In order to make it easier for the rolling elements 4 to ride over the threads of the screw shaft 2, the circulation path 57 is formed so that the amount of recession toward the radially outward increases toward the center of the link 5.

[0021] As a result, the rolling element 4 moves to one end of the inner rolling groove 31, changes its direction of travel through the inlet 58a, and enters the circulation path 57. The rolling element 4 that entered the circulation path 57 moves along the circulation path 57, overcomes one thread, changes its direction of travel, and moves to the other end of the inner rolling groove 31 through the inlet 58b. The rolling element 4 that moved to the other end of the inner rolling groove 31 makes one revolution around the inner surface of the nut 3 along the inner rolling groove 31, and then returns to one end of the inner rolling groove 31. The ball screw 1 of this embodiment has a plurality of infinite circulation circuits (four in this embodiment) each consisting of the inner rolling groove 31 (i.e., the rolling path 40) and the circulation path 57 in the link 5.

[0022] As shown in Fig. 2, in the following description, the four pieces 5 may be referred to as a first piece 51, a second piece 52, a third piece 53, and a fourth piece 54, respectively, from the first side in the axial direction. When there is no need to distinguish between these pieces, they may be simply referred to as pieces 5. The first to fourth pieces 51, 52, 53, and 54 are provided at different positions in the axial direction. The first to fourth pieces 51, 52, 53, and 54 may be provided at positions where they partially overlap each other in the axial direction.

[0023] (Cylindrical member) As shown in FIG. 1 and FIG. 2, the cylindrical member 6 is attached to the outer periphery of the nut 3 so as to surround the outer periphery of the nut 3. The cylindrical member 6 is, for example, a sleeve formed of a thin metal plate. The inner diameter dimension of the cylindrical member 6 is equal to or larger than the outer dimension of the nut 3. The cylindrical member 6 is attached to the nut 3 by, for example, a clearance fit. As shown in FIG. 1 and FIG. 4, a crimping portion 61 is provided at the end of the cylindrical member 6 on the second side in the axial direction. The crimping portion 61 is fitted into the crimping recess 35 of the nut 3 by crimping. This allows the cylindrical member 6 to be positioned in the axial direction relative to the nut 3. As shown in FIG. 1 and FIG. 5, a flange portion 63 is provided at the end of the cylindrical member 6 on the first side in the axial direction. The flange portion 63 is formed by extending the end of the cylindrical member 6 toward the outside in the radial direction. The flange portion 63 is integrally formed with the main body of the cylindrical member 6.

[0024] In a state where the cylindrical member 6 is attached to the nut 3, the cylindrical member 6 covers at least a part of the multiple links 5 from the radial outside. In this embodiment, the cylindrical member 6 covers the whole of the third link 53 and the fourth link 54 (the second link group in the claims) from the radial outside, and covers a part of the first link 51 and the second link 52 (the first link group in the claims) from the radial outside. That is, the axial length dimension of the cylindrical member 6 is smaller than the distance dimension from the first side end of the link located on the first side among the multiple links 5 (the first link 51 in this embodiment) to the second side end of the link located on the second side among the multiple links 5 (the fourth link 54 in this embodiment).

[0025] (Fitting parts) A fitting member 7 is provided on the outer peripheral surface of the nut 3 at a position that does not overlap with the cylindrical member 6 in the axial direction. In this embodiment, the fitting member 7 is provided on the first axial side of the cylindrical member 6. The fitting member 7 is fitted to the outer peripheral portion of the nut 3. In this embodiment, the fitting member 7 is a bearing. The fitting member 7 may be, for example, a shielded bearing capable of sealing grease in the internal space. The fitting member 7 (i.e., the bearing) is attached to the nut 3 after the cylindrical member 6 is attached. The fitting member 7 is press-fitted and fixed into the nut 3. The end face of the fitting member 7 on the first axial side is arranged so as to be flush with the end face of the nut 3 on the first axial side. In a state in which the fitting member 7 is attached to the nut 3, the fitting member 7 covers at least a part of the multiple links 5 from the outside in the radial direction. In this embodiment, the fitting member 7 covers the parts of the first link 51 and the second link 52 (the first link group in the claims) that are not covered by the cylindrical member 6 from the outside in the radial direction.

[0026] Therefore, all four pieces 5 are covered from the outside in the radial direction by the cylindrical member 6 or the fitting member 7. In this embodiment, the entire area of ​​the head 55 of all four pieces 5 is covered by the cylindrical member 6 or the fitting member 7. In other words, when the cylindrical member 6 and the fitting member 7 are attached to the nut 3, the head 55 of the piece 5 is not exposed. A gap may be provided between the cylindrical member 6 and the fitting member 7 in the axial direction. In this case, the piece 5 may be attached so that a part of the piece 5 is exposed. In this embodiment, all four pieces 5 are at least partially covered by the cylindrical member 6. Therefore, by attaching the cylindrical member 6, it is possible to suppress the piece 5 from falling off the nut 3.

[0027] As shown in FIG. 5, the fitting member 7 abuts against the flange portion 63 of the cylindrical member 6 in the axial direction. As described above, in this embodiment, the outer diameter dimension of the nut 3 is equal to or smaller than the inner diameter dimension of the cylindrical member 6 over the entire region in the axial direction of the nut 3. In other words, the nut 3 is formed without having a convex portion or the like having an outer diameter larger than the outer periphery (outer periphery main surface 30) of the nut 3 with which the cylindrical member 6 is fitted, between the cylindrical member 6 and the fitting member 7 in the axial direction. Therefore, compared to the conventional technology in which a flange or the like is provided between the fitting member 7 and the cylindrical member 6, the axial distance between the cylindrical member 6 and the fitting member 7 can be shortened.

[0028] (How to clean the ball screw) Next, a method for cleaning the above-mentioned ball screw 1 will be described. In the ball screw 1, cleaning may be performed in a state in which the screw shaft 2, nut 3, rolling elements 4, and top 5 are assembled, in order to remove metal powder generated during assembly or the like. Here, in the ball screw 1 of this embodiment, the top 5 is fixed by attaching the cylindrical member 6 and the fitting member 7, but since grease is applied to the bearing which is the fitting member 7, cleaning the entire bearing may cause the grease to flow out of the bearing, resulting in malfunction. Therefore, three examples of cleaning methods suitable for the ball screw 1 of this embodiment will be described below.

[0029] (Cleaning method 1) First, the first cleaning method will be described. FIG. 6 is an explanatory diagram of the first cleaning method. In this cleaning method, first, a ball screw is prepared in a state in which the screw shaft 2, the nut 3, the rolling elements 4, the pieces 5, and the cylindrical member 6 are assembled. Since the four pieces 5 are at least partially covered by the cylindrical member 6, the pieces 5 are prevented from coming off only by the cylindrical member 6 without attaching the fitting member 7. Next, the prepared ball screw is placed in a cleaning jig (not shown) so that the axial direction of the ball screw is aligned vertically. Next, while spraying the cleaning liquid into the cleaning container 91, the screw shaft 2 and the nut 3 are rotated relative to each other and moved relative to each other in the axial direction. At this time, for example, the screw shaft 2 is fixed and the nut 3 is allowed to fall freely by its own weight, thereby rotating and moving the screw shaft 2 and the nut 3 relative to each other. Next, air is blown to remove the cleaning liquid attached to the ball screw. Finally, the ball screw is removed from the cleaning jig, and the fitting member 7 (bearing) is press-fitted into the nut 3. Through the above steps, the cleaned ball screw 1 is completed.

[0030] According to this cleaning method, the cylindrical member 6 alone can prevent the top 5 from coming off without the fitting member 7 attached, so cleaning can be performed with the bearing, which is the fitting member 7, removed. This prevents grease from leaking out. Therefore, the ball screw 1 can be cleaned simply with a minimum number of steps.

[0031] (Cleaning method 2) Next, the second cleaning method will be described. FIG. 7 is an explanatory diagram of the second cleaning method. In this cleaning method, first, a ball screw is prepared in a state in which the screw shaft 2, the nut 3, the rolling elements 4, the pieces 5, and the temporary assembly jig 92 are integrally assembled. The temporary assembly jig 92 is formed, for example, in a cylindrical shape that covers the entire outer periphery of the nut 3, and by attaching the temporary assembly jig 92, the pieces 5 are prevented from coming off the nut 3. Next, the ball screw to which the temporary assembly jig 92 is attached is placed in a cleaning container 91. The process from placing in the cleaning container 91 to air blowing is the same as the first cleaning method, so the description will be omitted. After air blowing is completed, the temporary assembly jig 92 is removed from the ball screw, and the cylindrical member 6 and the fitting member 7 are assembled. Through the above steps, the cleaned ball screw 1 is completed.

[0032] According to this cleaning method, cleaning can be performed regardless of whether the top 5 is covered by the cylindrical member 6 or the fitting member 7. For example, even if there is a top 5 that is covered only by the fitting member 7, the temporary assembly jig 92 can prevent the top 5 from falling out during cleaning. Therefore, the versatility of cleaning the ball screw 1 can be improved.

[0033] (Cleaning method 3) Next, the third cleaning method will be described. FIG. 8 is an explanatory diagram of the third cleaning method. In this cleaning method, first, a ball screw is prepared in a state in which the screw shaft 2, nut 3, rolling elements 4, sets 5, cylindrical member 6, and fitting member 7 (shielded bearing) are assembled. At this time, the bearing before the shield 71 is attached (or the bearing in which the shield 71 has been removed) is attached to the nut 3. Next, this ball screw is placed in a cleaning container 91. The process from placing in the cleaning container 91 to air blowing is the same as the first cleaning method, so the description will be omitted. After air blowing is completed, the ball screw is removed from the cleaning jig, grease is injected into the bearing, and then the shield 71 is attached to the bearing. Through the above steps, a cleaned ball screw 1 is completed.

[0034] According to this cleaning method, since grease is injected after cleaning, the ball screw 1 can be cleaned with both the cylindrical member 6 and the fitting member 7 (bearing) attached. Therefore, cleaning can be performed regardless of whether the top 5 is covered by the cylindrical member 6 or the fitting member 7. For example, even if there is a top 5 that is covered only by the fitting member 7, it can be cleaned with the fitting member 7 attached, so that it is possible to prevent the top 5 from falling off during cleaning. This improves the versatility of cleaning the ball screw 1. Furthermore, since the process of attaching the temporary assembly jig 92 (see FIG. 7) is not necessary, the cleaning process can be simplified compared to the second cleaning method described above.

[0035] (Action, effect) According to the ball screw 1 of this embodiment, the ball screw 1 includes a cylindrical member 6 that covers the top 5 attached to the nut 3 from the outside in the radial direction, and a fitting member 7 that is provided at a position different from the cylindrical member 6 in the axial direction and fits to the outer periphery of the nut 3. The fitting member 7 covers at least a part of the top 5 from the outside in the radial direction. As a result, the fitting member 7 has a function equivalent to that of the cylindrical member 6, that is, a function of preventing the top 5 from coming off, so that the cylindrical member 6 and the fitting member 7 can hold the top 5 to the nut 3. Here, in the conventional technology in which all the tops are held by the cylindrical member and the fitting member (bearing) is further arranged in series with the cylindrical member in the axial direction, it was necessary to secure an extra axial length of the nut in order to further arrange the fitting member next to the cylindrical member after arranging the cylindrical member. In contrast, according to the ball screw 1 of this embodiment, the fitting member 7 takes on the function of the cylindrical member 6, so the fitting member 7 can be arranged at the location where the cylindrical member 6 was previously arranged. Therefore, there is no need to ensure an extra axial length for the nut 3, and therefore the axial increase in size of the nut 3 can be suppressed. Furthermore, for example, the dimensional accuracy of the cylindrical member 6 and the fitting member 7 can be maintained high compared to the case where the fitting member 7 is disposed on the outer periphery of the cylindrical member 6. This makes it possible to prevent a decrease in the positioning accuracy of the fitting member 7 and to prevent the fitting member 7 from wobbling during operation. Therefore, in the ball screw 1 having the cylindrical member 6 and a part other than the cylindrical member 6 (fitting member 7) on the outer periphery, it is possible to provide a ball screw 1 that can suppress rattling of the parts while suppressing an increase in size.

[0036] The fitting member 7 is a bearing. This makes it possible to suitably hold the nut 3, particularly in the ball screw 1 used in applications where the nut 3 rotates and the screw shaft 2 moves in the axial direction. This makes it possible to enhance the versatility of the ball screw 1.

[0037] The fitting member 7 may be a member other than a bearing. For example, the fitting member 7 may be a gear or a pulley. This allows the versatility of the ball screw 1 to be increased.

[0038] In the region between the cylindrical member 6 and the fitting member 7 in the axial direction, the outer diameter dimension of the nut 3 is equal to or smaller than the inner diameter dimension of the cylindrical member 6. In other words, the nut 3 is formed without having any convex parts or protrusions, etc., between the cylindrical member 6 and the fitting member 7 in the axial direction, that are larger in outer diameter than the outer periphery (outer periphery main surface 30) of the nut 3 with which the cylindrical member 6 is fitted. This allows the cylindrical member 6 and the fitting member 7 to be disposed closer to each other in the axial direction than when convex parts or protrusions are provided between the cylindrical member 6 and the fitting member 7. This allows the axial length of the nut 3 to be shortened, and the size of the nut 3 to be suppressed.

[0039] The cylindrical member 6 abuts against the fitting member 7 in the axial direction. This makes it possible to shorten the axial distance between the cylindrical member 6 and the fitting member 7, compared to when the cylindrical member 6 and the fitting member 7 are disposed with a gap between them. This makes it possible to shorten the axial length of the nut 3 and prevent the nut 3 from becoming large. In addition, the cylindrical member 6 abuts against the fitting member 7, making it possible to position the cylindrical member 6 in the axial direction.

[0040] The cylindrical member 6 has a crimping portion 61, and the nut 3 has a crimping recess 35 into which the crimping portion 61 fits. This allows the cylindrical member 6 to be easily crimped to the nut 3. Thus, the cylindrical member 6 can be fixed to the nut 3 with a simple configuration. Furthermore, by fixing the cylindrical member 6 by crimping, it is possible to position the cylindrical member 6 in the axial direction without providing a flange or the like separately to the nut 3. This allows the axial length of the nut 3 to be further shortened compared to the case where a flange or the like is separately provided to the nut 3.

[0041] A plurality of pieces 5 are provided, and the plurality of pieces 5 include a first group of pieces covered by both the fitting member 7 and the cylindrical member 6, and a second group of pieces covered only by the cylindrical member 6. In other words, all pieces 5 are at least partially covered by the cylindrical member 6 from the outside in the radial direction. Therefore, by assembling the cylindrical member 6, the pieces 5 can be temporarily held so that they do not come off the nut 3. This improves the ease of assembly of the ball screw 1. In addition, the axial length dimension of the cylindrical member 6 can be minimized, so that the cylindrical member 6 and the nut 3 can be prevented from becoming large in the axial direction. Furthermore, since the cylindrical member 6 prevents the pieces 5 from coming off, for example, cleaning of the ball screw 1 can be performed in a state where only the cylindrical member 6 is attached without attaching the fitting member 7. This prevents the manufacturing process, including cleaning of the ball screw 1, from becoming complicated.

[0042] Second embodiment Next, a second embodiment of the present invention will be described. In the description of the second embodiment, the same components as those in the first embodiment will be denoted by the same reference numerals and will not be described. Note that the specific components are not limited to these embodiments and can be modified as appropriate without departing from the scope of the present invention. 9 is a cross-sectional view of a ball screw 201 according to the second embodiment. The second embodiment differs from the first embodiment in that a flange 237 is provided on the nut 203.

[0043] In the second embodiment, the nut 203 has a flange 237 instead of the crimping recess 35 in the above-described first embodiment. The flange 237 is provided at an end portion on the second axial side of the nut 203. The flange 237 protrudes radially outward from the outer peripheral main surface 30 of the nut 203 on which the multiple links 5 are arranged. In other words, the outer diameter of the flange 237 is larger than the outer diameter of the outer peripheral main surface 30 of the nut 203. The cylindrical member 206 is attached to the outer periphery of the nut 203 from a first axial side. Then, the fitting member 7 is attached from the first axial side. The cylindrical member 206 is positioned in the axial direction by being sandwiched between the flange 237 and the fitting member 7 in the axial direction.

[0044] The ball screw 201 of the second embodiment can achieve the same effects as the first embodiment. That is, compared to the conventional technology in which all the tops 5 are held by cylindrical members and fitting members (bearings) are arranged in series with the cylindrical members in the axial direction, the nut 203 can be prevented from becoming large in size in the axial direction. Also, compared to the case in which fitting members are arranged on the outer periphery of the cylindrical members, the decrease in the positioning accuracy of the fitting members 7 can be prevented, and the occurrence of rattling of the fitting members 7 during operation can be prevented. Therefore, it is possible to provide a ball screw 201 that can suppress rattling of components while suppressing an increase in size. Furthermore, the cylindrical member 206 can be attached to the nut 203 by a method other than crimping. Therefore, the versatility of the cylindrical member 206 and the nut 203 can be improved. In the second embodiment, a retaining ring (not shown) may be provided instead of the flange 237 to position the cylindrical member 206 in the axial direction. In this case, a retaining ring groove may be formed on the outer periphery of the nut 203. In the case where a retaining ring is provided, machining of the nut 203 can be made easier compared to the case where the flange 237 is provided.

[0045] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the fitting member 7 is fixed to the nut 3 by press-fitting, but this is not limited thereto. The fitting member 7 may be attached to the nut 3 by clearance fit. In this case, the fitting member 7 may be positioned in the axial direction by the cylindrical member 6 and, for example, a retaining ring or a fixing nut. The retaining ring referred to here may be a different part from the retaining ring provided in place of the flange 237 in the above second embodiment. Also, the fixing nut may be, for example, a sliding screw nut. In this case, a male thread may be formed on the outer peripheral surface of the end of the nut 3, and the fitting member 7 may be positioned in the axial direction by the fixing nut.

[0046] In the first embodiment, the flange portion 63 may not be formed on the first axial side of the cylindrical member 6. In this case, the end of the cylindrical member 6 on the first axial side and the fitting member 7 may simply come into contact with each other by butting. Also, the cylindrical member 6 and the fitting member 7 do not have to come into contact with each other. However, the configuration of this embodiment in which the cylindrical member 6 and the fitting member 7 are disposed close enough to come into contact with each other is advantageous in that the axial length of the nut 3 can be further shortened.

[0047] In the above-mentioned embodiments, the configuration in which the multiple pieces 5 have the first piece group covered by both the fitting member 7 and the cylindrical member 6 and the second piece group covered only by the cylindrical member 6 has been described, but the present invention is not limited thereto. In addition to the first piece group and the second piece group, the multiple pieces 5 may further have a third piece group covered from the radially outer side only by the fitting member 7. The multiple pieces 5 may also have only the first piece group and the third piece group. Alternatively, the multiple pieces 5 may have only the second piece group and the third piece group. However, the configuration of this embodiment in which at least a part of all pieces 5 is covered by the cylindrical member 6 is advantageous in that the dislodging of all pieces 5 is suppressed in a state in which only the cylindrical member 6 is attached without attaching the fitting member 7, and thus cleaning of the ball screw 1 can be performed in a state in which only the cylindrical member 6 is attached.

[0048] The fitting member 7 may include a plurality of parts. For example, the fitting member 7 may include two or more bearings. For example, the fitting member 7 may include a plurality of types of parts different from the cylindrical member 6, such as bearings and gears. The outer circumferential rolling groove 25 may be provided on a part of the outer circumferential part of the screw shaft body 21. Similarly, the inner circumferential rolling groove 31 may be provided on a part of the inner circumferential part of the nut 3. The number of frames 5 is not limited to the above number. In the above embodiment, for example, in Fig. 1 and the like, the fitting member 7 is illustrated as a ball bearing as an example of the bearing, but is not limited thereto. The fitting member 7 may be a roller bearing, a conical bearing, or the like.

[0049] The present disclosure may also be implemented in the following combinations: (1) A screw shaft having a spiral outer circumferential rolling groove on an outer circumferential surface thereof; A nut having a spiral inner peripheral rolling groove on an inner peripheral surface thereof; A plurality of rolling elements are disposed in a rolling path formed by the inner peripheral rolling groove of the nut and the outer peripheral rolling groove of the screw shaft; a nut having a circulation path for returning the rolling elements from one end of the rolling path to the other end; A cylindrical member that fits onto an outer periphery of the nut to cover the top from the outside in the radial direction; A fitting member that is provided without overlapping with the cylindrical member in the axial direction of the screw shaft and is fitted to an outer periphery of the nut; Equipped with The fitting member covers at least a portion of the piece from the outside in the radial direction. Ball screw. (2) The fitting member is a bearing. A ball screw as described in (1). (3) The fitting member is a gear. A ball screw as described in (1). (4) The fitting member is a pulley. 1) The ball screw described in. (5) In a region between the cylindrical member and the fitting member in the axial direction, an outer diameter dimension of the nut is equal to or smaller than an inner diameter dimension of the cylindrical member. A ball screw according to any one of (1) to (4). (6) The cylindrical member abuts against the fitting member in the axial direction. A ball screw according to any one of (1) to (5). (7) the cylindrical member has a crimping portion that is fixed to the nut by crimping, The nut has a crimping recess into which the crimping portion fits. A ball screw according to any one of (1) to (6). (8) The frame is provided in plurality, The plurality of frames include a first group of pieces covered from the outside in the radial direction by both the fitting member and the cylindrical member; a second group of pieces covered from the outside in the radial direction by only the cylindrical member; having A ball screw according to any one of (1) to (7). [Explanation of symbols]

[0050] 1,201 Ball screw 2 Screw shaft 3,203 Nuts 4 Rolling elements 5 frames 6,206 Cylindrical members 7 Fittings 25 Outer periphery rolling groove 31 Inner circumference rolling groove 35 Crimping recess 40 Rolling Path 51 First frame (first group of frames) 52 Second frame (first group of frames) 53 Third frame (Second frame group) 54 Fourth frame (second group of frames) 57 Circulation path 61 Crimping part

Claims

1. A screw shaft having a spiral outer circumferential rolling groove on an outer circumferential surface thereof; A nut having a spiral inner peripheral rolling groove on an inner peripheral surface thereof; A plurality of rolling elements are disposed in a rolling path formed by the inner peripheral rolling groove of the nut and the outer peripheral rolling groove of the screw shaft; a nut having a circulation path for returning the rolling elements from one end of the rolling path to the other end; A cylindrical member that fits onto an outer periphery of the nut to cover the top from the outside in the radial direction; A fitting member that is provided without overlapping with the cylindrical member in the axial direction of the screw shaft and is fitted to an outer periphery of the nut; Equipped with The fitting member covers at least a portion of the piece from the outside in the radial direction. Ball screw.

2. The fitting member is a bearing.

2. The ball screw according to claim 1.

3. The fitting member is a gear.

2. The ball screw according to claim 1.

4. The fitting member is a pulley.

2. The ball screw according to claim 1.

5. In a region between the cylindrical member and the fitting member in the axial direction, an outer diameter dimension of the nut is equal to or smaller than an inner diameter dimension of the cylindrical member.

2. The ball screw according to claim 1.

6. The cylindrical member abuts against the fitting member in the axial direction.

2. The ball screw according to claim 1.

7. the cylindrical member has a crimping portion that is fixed to the nut by crimping, The nut has a crimping recess into which the crimping portion fits.

2. The ball screw according to claim 1.

8. The frame is provided in plurality, The plurality of frames include a first group of pieces covered from the outside in the radial direction by both the fitting member and the cylindrical member; a second group of pieces covered from the outside in the radial direction by only the cylindrical member; having The ball screw according to any one of claims 1 to 7.

Images