Method for manufacturing ball screws and ball screw nuts

Abstract

The present invention provides a ball screw that reduces manufacturing costs and improves the degree of freedom in arranging the circulation groove compared to conventional technology, and a method for manufacturing a nut for this ball screw. [Solution] The ball screw nut 1 has an inner circumferential helical groove and a plurality of circulation grooves 40. Viewed from the axial direction, the plurality of circulation grooves 40 are unequally arranged in the circumferential direction. That is, a plurality of central angles are set for the circulation grooves, each being the central angle between two adjacent circulation grooves in the circumferential direction, and in the unequal arrangement, at least one of the plurality of central angles (e.g., central angle α) is different from another central angle (e.g., central angle β). The manufacturing method for the ball screw nut includes a circulation groove forming step in which two or more circulation grooves 40 are formed on the inner circumferential surface 12 of the nut 1 by a forging process with multiple simultaneous strikes.

Description

Technical Field

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[0001] The present invention relates to a method for manufacturing a ball screw and a nut for a ball screw.

Background Art

[0002] Conventionally, in a ball screw having a nut, a screw shaft, and a plurality of rolling elements, as one of the circuit structures for circulating the plurality of rolling elements, a return path (return orbit) formed on the inner peripheral surface of the nut is provided separately from the groove for the main path (main orbit). A structure provided with a circulation groove is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0006] Therefore, the present invention aims to provide a ball screw that can reduce manufacturing costs and improve the degree of freedom in arranging the circulation groove compared to the prior art, and a method for manufacturing a nut for this ball screw. [Means for solving the problem]

[0007] To solve the above problems, this invention proposes the following means. A ball screw according to a first aspect of the present invention comprises a screw shaft, a nut, and a plurality of rolling elements disposed between the nut and the screw shaft, wherein the nut has a spiral groove formed on its inner circumferential surface, on which the plurality of rolling elements roll, and a plurality of circulation grooves formed on its inner circumferential surface, on which the rolling elements return from one end of the spiral groove to the other, and the plurality of circulation grooves are unequally arranged in the circumferential direction of the nut when viewed from the axial direction of the nut.

[0008] A method for manufacturing a ball screw nut according to a first aspect of the present invention is a method for manufacturing a ball screw nut having a helical groove on which a plurality of rolling elements roll, and a circulation groove that returns the rolling elements from one end to the other end of the helical groove, comprising a circulation groove forming step of forming two or more of the circulation grooves on the inner circumferential surface of the nut by a forging process of multiple simultaneous strikes, and a helical groove forming step of forming the helical groove on the inner circumferential surface by a removal process, wherein in the circulation groove forming step, a plurality of the circulation grooves are formed such that, when viewed from the axial direction of the nut, the plurality of circulation grooves are unequally arranged in the circumferential direction of the nut. [Effects of the Invention]

[0009] The present invention provides a method for manufacturing a ball screw and a ball screw nut that reduces manufacturing costs and improves the degree of freedom in arranging the circulation groove compared to the prior art, and a method for manufacturing the ball screw nut. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view showing a ball screw according to the first embodiment. [Figure 2] A side view of a ball screw nut according to the first embodiment, viewed from the axial direction. [Figure 3] A schematic diagram showing the inner circumferential surface of the nut body. [Figure 4] A flowchart showing the process for manufacturing a ball screw nut according to the first embodiment. [Figure 5] A side view of a nut showing the circulation groove formed by the first circulation groove formation process. [Figure 6] A side view of a nut showing the circulation groove formed by the second circulation groove formation process. [Figure 7] An explanatory diagram showing a forging process using a mold and a cam mechanism. [Figure 8] An explanatory diagram showing one step in the circulation groove formation process. [Figure 9] An explanatory diagram showing one step in the circulation groove formation process. [Figure 10] An explanatory diagram showing one step in the circulation groove formation process. [Figure 11] An explanatory diagram showing one step in the circulation groove formation process. [Figure 12] A side view of a nut showing the circulation groove formed by the first circulation groove forming step of the second embodiment. [Figure 13] A side view of a nut showing the circulation groove formed by the second circulation groove formation step of the second embodiment. [Figure 14] A flowchart showing the process for manufacturing a ball screw nut according to the third embodiment. [Figure 15] A side view of a nut showing the circulation groove formed by the first circulation groove forming step of the third embodiment. [Figure 16]Side view of the nut showing the circulation groove formed by the second circulation groove forming step of the third embodiment. [Figure 17] Side view of the nut for explaining the nut removing step of the third embodiment. [Figure 18] Side view of the ball screw nut according to the third embodiment as viewed from the axial direction. **[Embodiments for Carrying Out the Invention]**

[0011] Embodiments of the present invention will be described with reference to the drawings. In one embodiment, the ball screw 10 is incorporated into various mechanical devices such as, for example, an electric brake device of a vehicle, an automated manual transmission (AMT), and a positioning device of a machine tool, and is used for converting the rotational motion of a drive source such as an electric motor into a linear motion to operate a driven part (operating part). As the electric brake device, various types such as an EMB (Electro-Mechanical Brake) that applies braking force through a ball screw driven by a motor and an EHB (Electro-Hydraulic Brake) that controls the hydraulic pressure of a hydraulic brake through a ball screw driven by a motor are applicable. The ball screw 10 is also applicable to mechanical devices other than those described above.

[0012] In the following description, unless otherwise specified, the axial direction, the radial direction, and the circumferential direction refer to the direction along the central axis C of the ball screw 10 (nut 1), the radial direction of the ball screw 10 (nut 1), and the direction around the central axis C of the ball screw 10 (nut 1), respectively.

[0013] (First Embodiment) FIG. 1 is a schematic cross-sectional view showing the ball screw 10 according to the first embodiment. The ball screw 10 is a device that converts rotational motion into linear motion. As shown in FIG. 1, the ball screw 10 includes a screw shaft 2, a nut 1 (the ball screw nut 1 of the claim), and a plurality of rolling elements 3 disposed between the screw shaft 2 and the nut 1.

[0014] The screw shaft 2 comprises a shaft body 20 and a helical screw groove (outer helical groove 21) provided on the outer circumferential surface of the shaft body 20. In one example, at least a portion of the screw shaft 2 is made of metal. The outer helical groove 21 is formed by machining or plastic deformation (e.g., rolling) on ​​the outer circumferential surface of the shaft body 20. Grinding can be additionally performed in the formation of the outer helical groove 21. The cross-sectional shape of the outer helical groove 21 is, for example, a Gothic arch or a circular arc containing two arcs.

[0015] The nut 1 comprises a cylindrical nut body 11 and a helical screw groove (inner helical groove 15 (helical groove of the claim)) provided on the inner circumferential surface 12 of the nut body 11. A screw shaft 2 is inserted and positioned inside the nut 1. In one example, at least a part of the nut 1 is made of metal. The inner helical groove 15 is formed by machining or plastic deformation on the inner circumferential surface 12 of the nut body 11. Grinding can be additionally performed in the formation of the inner helical groove 15. The cross-sectional shape of the inner helical groove 15 corresponds to the shape of the outer helical groove 21 of the screw shaft 2, and is, for example, a Gothic arch or a circular arc. The detailed configuration of the nut 1 will be described later.

[0016] Multiple rolling elements 3 are arranged between the screw shaft 2 and the nut 1. The rolling elements 3 are, for example, balls. In Figure 1, two rolling elements 3 are shown by a dashed line. In practice, the ball screw 10 comprises multiple rolling elements 3. In one example, the multiple rolling elements 3 are made of metal (such as steel) or ceramics. When the screw shaft 2 and the nut 1 are assembled, a spiral rolling path 25 is formed by the opposing arrangement of the outer helical groove 21 formed on the screw shaft 2 and the inner helical groove 15 formed on the nut 1. The rolling elements 3 move within this rolling path 25 as the relative rotation between the screw shaft 2 and the nut 1 occurs.

[0017] Figure 2 is a side view of the ball screw nut 1 according to the first embodiment, viewed from the axial direction. Figure 3 is a schematic diagram showing the inner circumferential surface 12 of the nut body 11 (unfolded view of the inner circumferential surface 12). As shown in Figures 1 to 3, the inner circumferential surface 12 of the nut 1 has multiple circulation grooves 40 in addition to the inner helical groove 15. The circulation grooves 40 connect one end 16 and the other end 17 of the helical rolling path 25 formed by the nut 1 and the screw shaft 2, forming an infinite circulation circuit. When multiple rolling elements 3 are filled into this infinite circulation circuit, the rolling elements 3 circulate infinitely within the circuit. As shown in Figure 3, in plan view the circulation grooves 40 are greatly curved, for example, S-shaped. The circulation grooves 40 are formed in a curved surface shape with a U-shaped cross-section corresponding to the spherical surface of the rolling element 3. The maximum depth of the circulation grooves 40 is set to be greater than the maximum depth of the rolling path 25. For example, the depth of the circulation grooves 40 is set to such an extent that the rolling elements 3 can overcome the threads of the screw shaft 2 when the screw shaft 2 and the nut 1 are assembled.

[0018] As the screw shaft 2 and the nut 1 rotate relative to each other, the rolling elements 3 move along the rolling path 25 (outer spiral groove 21 and inner spiral groove 15). As shown in Figure 3, in one example, the rolling elements 3 move from the first end 16 (starting point) to the second end 17 (ending point) of the rolling path 25. The balls that have moved to the second end 17 of the rolling path 25 are guided into the circulation groove 40. The rolling elements 3 placed in the circulation groove 40 are pushed by subsequent rolling elements 3 and move from the entrance / exit 40a to the entrance / exit 40b of the circulation groove 40. That is, the rolling elements 3 that entered the circulation groove 40 from the second end 17 of the rolling path 25 return to the first end 16 of the rolling path 25 via the circulation groove 40. The starting and ending points of the rolling path 25 are swapped depending on the relative rotation direction of the screw shaft 2 and the nut 1. In the relative rotation in the opposite direction, the rolling element 3 moves from the second end 17 (starting point) of the rolling path 25 to the first end 16 (ending point). Having moved to the first end 16 of the rolling path 25, the rolling element 3 is guided into the circulation groove 40 and moves from the inlet / outlet 40b to the inlet / outlet 40a of the circulation groove 40. That is, the rolling element 3 that entered the circulation groove 40 from the first end 16 of the rolling path 25 returns to the second end 17 of the rolling path 25 via the circulation groove 40. In this way, in the ball screw 10, the rolling element 3 can continuously circulate along the circulation path (circulation circuit) including the rolling path 25 and the circulation groove 40 in conjunction with the relative rotation of the screw shaft 2 and the nut 1.

[0019] In this embodiment, as will be described later, in the manufacturing process of the nut 1, the circulation groove 40 is formed by forging, and then the inner circumferential helical groove 15 is formed by cutting. When the circulation groove 40 is formed, two or more of the multiple circulation grooves 40 (for example, circulation grooves 41, 42, and 43 in Figure 2) are formed simultaneously in a single forging operation. That is, the circulation groove 40 is formed by forging multiple grooves simultaneously. In the following description, multiple circulation grooves (for example, circulation grooves 41, 42, and 43) formed simultaneously in a single forging operation may be referred to as a group of circulation grooves.

[0020] As shown in Figure 2, in this embodiment, a total of five circulation grooves 40 are provided. Specifically, the multiple circulation grooves 40 include circulation groove 41, circulation groove 42, circulation groove 43, circulation groove 44, and circulation groove 45. Note that when circulation grooves 41 to 45 are not distinguished from each other, or when referring to all of them, they may simply be called circulation groove 40. In addition, when explaining the relative positional relationship of each circulation groove in the circumferential direction, the central angle may be used for explanation. The central angle is the angle formed by the line connecting the groove bottom of a predetermined circulation groove and the central axis (central axis line C) of the nut 1, and the line connecting the groove bottom of another circulation groove and the central axis of the nut 1, when the nut 1 is viewed from the axial direction. Note that in an actual nut 1, the multiple circulation grooves 40 are each provided at different positions in the axial direction. For this reason, even if circulation grooves (for example, circulation groove 42 and circulation groove 43) are drawn to partially overlap in the side view of Figure 2, these circulation grooves do not actually connect to each other.

[0021] Viewed from the axial direction of nut 1, the multiple (five in this embodiment) circulation grooves 41-45 are unequally arranged in the circumferential direction. In other words, among the multiple circulation grooves 41-45 arranged in the circumferential direction of nut 1, the central angles formed by at least one pair of circumferentially adjacent circulation grooves (for example, the central angle α formed by circulation grooves 41 and 42 in Figure 2) and the central angles formed by another pair of circumferentially adjacent circulation grooves (for example, the central angle β formed by circulation grooves 42 and 43 in Figure 2) are different from each other (α≠β). Multiple central angles are set for the multiple circulation grooves 41-45. Each of the multiple central angles is the central angle between two circumferentially adjacent circulation grooves (a pair of circulation grooves) when viewed in the axial direction, and corresponds to the circumferential distance (circumferential spacing) between two circumferentially adjacent circulation grooves (groove positions). The central angle of a pair of circulation grooves is the angle formed by the line connecting the reference position (groove center position, groove bottom position, etc.) of one circulation groove to the central axis C, and the line connecting the reference position of the other circulation groove to the central axis C. For multiple circulation grooves 41-45, at least one central angle (first angle) among the multiple central angles is substantially different from another central angle (second angle). For example, the difference between the first angle and the second angle is 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50° or more. The above values ​​are examples only and are not limited thereto.

[0022] More specifically, when viewed from the axial direction of nut 1, the circulation grooves 41 to 45 are arranged in the circumferential direction counterclockwise in the order of circulation groove 41, circulation groove 42, circulation groove 43, circulation groove 44, and circulation groove 45. If the line connecting the groove bottom of circulation groove 41 and the central axis C is taken as the central angle 0° (reference), then circulation groove 42 is located at a central angle of 90° relative to circulation groove 41. Circulation groove 43 is located at a central angle of 120° relative to circulation groove 41. Circulation groove 44 is located at a central angle of 240° relative to circulation groove 41. Circulation groove 45 is located at a central angle of 270° relative to circulation groove 41.

[0023] Of these multiple circulation grooves 40, two or more circulation grooves are equally spaced relative to each other in the circumferential direction when viewed from the axial direction. In this embodiment, circulation grooves 41, 43, and 44 of the multiple circulation grooves 40 constitute the first circulation groove group 31. The multiple circulation grooves 41, 43, and 44 belonging to the first circulation groove group 31 are equally spaced (at 120° intervals) in the circumferential direction when viewed from the axial direction. The multiple circulation grooves 41, 43, and 44 belonging to the first circulation groove group 31 are formed simultaneously in a single forging process during the circulation groove formation process described later.

[0024] Of the multiple circulation grooves 40, the circulation grooves 42 and 45 other than the first circulation groove group 31 are designated as the second circulation groove group 32. The multiple circulation grooves 42 and 45 belonging to the second circulation groove group 32 are equally spaced (at 180° intervals) in the circumferential direction when viewed from the axial direction. The multiple circulation grooves 42 and 45 belonging to the second circulation groove group 32 are formed simultaneously in a single forging process during the circulation groove formation process described later. As described above, in this embodiment, the number of circulation grooves belonging to the first circulation groove group 31 (3 in this embodiment) and the number of circulation grooves belonging to the second circulation groove group 32 (2 in this embodiment) are different from each other.

[0025] (Method of manufacturing ball screw nuts) Next, a method for manufacturing the nut 1 for the ball screw 10 described above will be explained. Figure 4 is a flowchart showing the process of manufacturing the ball screw nut 1 according to the first embodiment. Figure 5 is a side view of the nut 1 showing the circulation groove formed by the first circulation groove forming step ST11. Figure 6 is a side view of the nut 1 showing the circulation groove formed by the second circulation groove forming step ST12. As shown in Figure 4, the manufacturing method of the nut 1 comprises a circulation groove forming step ST01 and a helical groove forming step ST02. The circulation groove forming step ST01 comprises a first circulation groove forming step ST11 and a second circulation groove forming step ST12. First, a cylindrical nut body 11 is prepared.

[0026] Next, the first circulation groove formation process ST11 is performed. In the first circulation groove formation process ST11, as shown in Figure 5, the first circulation groove group 31 is formed on the inner circumferential surface 12 of the nut body 11 by plastic deformation such as forging. In other words, circulation grooves 41, 43, and 44 are formed on the inner circumferential surface 12 of the nut body 11. In this embodiment, in the first circulation groove formation process ST11, plastic deformation (forging) is performed using a mold 81 and a cam mechanism 80 (see also Figure 8, etc.).

[0027] Figure 7 is an explanatory diagram showing a forging process using a mold 81 and a cam mechanism 80. Figures 8 to 11 are explanatory diagrams showing one step of the circulation groove formation process ST01. Although Figures 8 to 11 only show the formation of a single circulation groove 40 for illustrative purposes, in reality, as shown in Figure 7, multiple (for example, three) circulation grooves are formed in a single forging process. As shown in Figure 8, in the cam mechanism 80, the nut body 11 is held in the holder 83. The mold 81 has an outer diameter corresponding to the inner diameter of the nut body 11. The mold 81 is inserted into the nut body 11 along the axial direction, and the mold 81 is set relative to the nut body 11. A punch 82 is attached to the mold 81 so as to be movable in a direction perpendicular to the axial direction of the mold 81. The mold 81 has a hole 87 that extends in the axial direction, and the shape of the hole 87 corresponds to the outer diameter shape of the mandrill 84. The mold 81 may be a single-piece structure or a segmented structure.

[0028] As shown in Figure 9, when the mandrill 84 is inserted axially into the hole 87 of the mold 81, the punch 82, pressed by the tapered surface 88 of the mandrill 84, moves radially outward and is pressed into the nut body 11. As a result, a predetermined shape of circulation groove 40 is formed on the inner circumferential surface 12 of the nut body 11. As shown in Figure 10, when the mandrill 84 retracts along the axial direction, the punch 82 moves radially inward and separates from the nut body 11. Then, as shown in Figure 11, the mold 81 is moved along the axial direction and removed from the nut body 11.

[0029] As shown in Figure 7, the cam mechanism 80 used in the first circulation groove forming step ST11 has three punches 82. Each punch 82 is equally spaced at 120° intervals in the circumferential direction. As a result, the first circulation groove group 31 (circulation grooves 41, 43, 44) shown in Figure 5 is formed on the inner circumferential surface 12 of the nut body 11.

[0030] Once the first circulation groove formation process ST11 is completed, the second circulation groove formation process ST12 is then carried out. In the second circulation groove formation process ST12, as shown in Figure 6, a second group of circulation grooves 32 is formed on the inner circumferential surface 12 of the nut body 11 by forging. In other words, circulation grooves 42 and 45 are formed on the inner circumferential surface 12 of the nut body 11. In the second circulation groove formation process ST12, forging is performed using a mold and a cam mechanism, similar to the first circulation groove formation process ST11. The cam mechanism (not shown) used in the second circulation groove formation process ST12 is different from the cam mechanism 80 used in the first circulation groove formation process ST11. The difference is that the cam mechanism used in the second circulation groove formation process ST12 has two punches 82. Each punch 82 is equally spaced at 180° intervals in the circumferential direction. As a result, the second group of circulation grooves 32 (circulation grooves 42 and 45) as shown in Figure 6 is additionally formed on the inner circumferential surface 12 of the nut body 11.

[0031] In other words, in the circulation groove formation process ST01, two or more circulation grooves 40 are formed on the inner circumferential surface 12 of the nut body 11 by forging with multiple simultaneous strikes. Furthermore, in the circulation groove formation process ST01, multiple circulation grooves 40 are formed such that, when viewed from the axial direction of the nut 1, the multiple circulation grooves 40 are unequally arranged in the circumferential direction. In other words, multiple circulation grooves 40 are formed such that the central angles between at least one pair of adjacent circulation grooves in the circumferential direction of the nut 1 (for example, circulation groove 41 and circulation groove 42) and the central angles between another pair of adjacent circulation grooves in the circumferential direction (for example, circulation groove 42 and circulation groove 43) are different from each other (see also Figure 2).

[0032] In the first circulation groove formation step ST11, a first circulation groove group 31, including multiple circulation grooves 41, 43, and 44, is formed on the inner circumferential surface 12 of the nut body 11 by forging with multiple simultaneous strikes. At this time, the first circulation groove group 31 is formed such that, when viewed from the axial direction, the multiple circulation grooves 41, 43, and 44 belonging to the first circulation groove group 31 are equally spaced relative to each other in the circumferential direction. In the second circulation groove formation step ST12, a second circulation groove group 32, including multiple circulation grooves 42 and 45 other than those in the first circulation groove group 31, is formed on the inner circumferential surface 12 of the nut body 11 by forging with multiple simultaneous strikes. At this time, the second circulation groove group 32 is formed such that, when viewed from the axial direction, the multiple circulation grooves 42 and 45 belonging to the second circulation groove group 32 are equally spaced relative to each other in the circumferential direction. In both the first circulation groove forming step ST11 and the second circulation groove forming step ST12, the multiple circulation grooves 40 formed simultaneously are equally spaced, thereby reducing the resultant force of the reaction force received by the punch when the punch 82 is pressed against the inner circumferential surface 12 of the nut body 11 (see also Figure 7).

[0033] Once the circulation groove formation process ST01 is completed, the spiral groove formation process ST02 is then carried out. In the spiral groove formation process ST02, an inner spiral groove 15 is formed on the inner surface 12 of the nut body 11 by a removal process such as cutting. At this time, the inner spiral groove 15 is formed so that its inner shape is smaller than that of the circulation groove 40. The inner shape refers to the size of the cross-sectional shape of the groove (groove depth, cross-sectional area, etc.) in a cross section perpendicular to the direction of travel of the rolling elements 3 that roll in the circulation groove 40 or the inner spiral groove 15. In other words, the cross-sectional shape of the inner spiral groove 15 is smaller than that of the circulation groove 40. As a result, for example, one end of the circulation groove 40 is connected to a part of the inner spiral groove 15, and the other end of the circulation groove 40 is connected to another part of the inner spiral groove 15.

[0034] By going through the above steps, a nut 1 having an inner helical groove 15 and a circulation groove 40 on its inner circumferential surface 12 is formed. Although not explained in the above embodiment, for example, a rough forming step may be included before the circulation groove forming step ST01 to obtain a blank of the nut body 11 by roughly forming the outer shape of the nut body 11 from the base material. Alternatively, an outer circumferential finishing step may be included to form gears, flanges, etc., on the outer circumferential surface of the blank of the nut body 11 by performing plastic working or removal processing on the outer circumferential surface of the nut body 11. A chamfering step may be included separately to chamfer the boundary between the circulation groove 40 and the inner helical groove 15. After the helical groove forming step ST02 and the chamfering step, a heat treatment step such as carburizing, carbonitriding, quenching, or tempering may be included separately.

[0035] (Effect, Action) The manufacturing method for the ball screw nut 1 of this embodiment and the ball screw 10 manufactured by this method provide the following advantages. Specifically, in the manufacturing method for the ball screw nut 1 of this embodiment, in the circulation groove formation step ST01, two or more circulation grooves 40 are formed on the inner circumferential surface 12 of the nut 1 by forging with multiple simultaneous strikes. By performing multiple simultaneous strikes, the number of dies and forging cycles can be reduced compared to the conventional technique of forming circulation grooves 40 one at a time. For example, when forming a total of five circulation grooves 40 on the inner circumferential surface 12 of the nut 1 using forging equipment that can perform forging three times per unit, in the conventional technique, first, three circulation grooves are formed by performing forging three times using three dies in the first forging equipment. Then, in order to form the remaining two circulation grooves with another die, the nut 1 is transported to the second forging equipment and forged two more times. This forms a total of five circulation grooves. In contrast, according to the manufacturing method of the ball screw nut 1 of this embodiment, first, three circulation grooves 41, 43, and 44 are formed simultaneously in the first forging process. Next, two circulation grooves 42 and 45 are formed simultaneously in the second forging process. That is, a total of five circulation grooves 41 to 45 can be formed by going through two forging processes. Therefore, all of the multiple circulation grooves 40 can be formed with a single forging machine. In addition, the process of transporting materials between multiple forging machines can be reduced. Therefore, compared to the conventional technology, capital investment can be suppressed and lead time can be shortened. This reduces the cost of manufacturing the nut 1. In the circulation groove formation process ST01, a nut 1 can be manufactured in which multiple circulation grooves 40 are unequally arranged in the circumferential direction when viewed from the axial direction of the nut 1. Therefore, the degree of freedom in the arrangement of the circulation grooves 40 can be improved. By appropriately arranging the circulation grooves 40, the axial length of the nut 1 can be shortened. Therefore, compared to conventional technology, it is possible to provide a ball screw 10 that reduces manufacturing costs and improves the degree of freedom in arranging the circulation groove 40, and a method for manufacturing the nut 1 for this ball screw.

[0036] Two or more of the multiple circulation grooves 40 are equally spaced in the circumferential direction when viewed from the axial direction. In this embodiment, the three circulation grooves 41, 43, and 44 formed by the first forging process and the two circulation grooves 42 and 45 formed by the second forging process are each equally spaced when viewed from the axial direction. By simultaneously forming multiple equally spaced circulation grooves (e.g., circulation grooves 41, 43, and 44) ​​in a single forging process, the stress during forging is distributed at equal intervals in the circumferential direction, even when multiple forging processes are performed simultaneously. Therefore, the complexity of pressure control during forging can be suppressed. Thus, the circulation grooves 40 can be easily formed, and the cost of manufacturing the nut 1 can be reduced.

[0037] The multiple circulation grooves 40 are comprised of a first circulation groove group 31 and a second circulation groove group 32, and the multiple circulation grooves 40 belonging to each circulation groove group 31 and 32 are equally arranged in the circumferential direction when viewed from the axial direction. This allows the stress during forging to be distributed in the circumferential direction when forming the circulation grooves 41, 43, and 44 of the first circulation groove group 31 by a forging process with multiple simultaneous strikes. Similarly, when forming the circulation grooves 42 and 45 of the second circulation groove group 32 by a forging process with multiple simultaneous strikes, the stress during forging can be distributed in the circumferential direction. Therefore, the complexity of pressure control during forging can be suppressed. Thus, the circulation grooves 40 can be easily formed, and the cost of manufacturing the nut 1 can be reduced. Furthermore, compared to a nut 1 having, for example, five circulation grooves 40 where each circulation groove is equally spaced at 72° intervals when viewed from the axial direction, the nut 1 of this embodiment, which has a first circulation groove group 31 spaced at 120° intervals and a second circulation groove group 32 spaced at 180° intervals, can shorten the axial length. Also, if the axial length is shortened by arranging four of the five circulation grooves 40 equally at 72° intervals and the remaining one at an interval of 72° or less, the load distribution may worsen, and the surface pressure in some parts of the rolling path 25 may increase. In contrast, according to the configuration of this embodiment, since there is a first circulation groove group 31 spaced at 120° intervals and a second circulation groove group 32 spaced at 180° intervals, the load distribution becomes uniform, and unevenness in surface pressure can be suppressed.

[0038] The number of circulation grooves 41, 43, and 44 belonging to the first circulation groove group 31 is different from the number of circulation grooves 42 and 45 belonging to the second circulation groove group 32. This allows for the formation of circulation grooves 40 in various arrangements through various combinations. Thus, the degree of freedom in the arrangement of circulation grooves 40 can be improved.

[0039] (Second Embodiment) Next, a second embodiment of the present invention will be described. In the following description, components similar to those in the first embodiment described above will be denoted by the same reference numerals and their descriptions will be omitted as appropriate. Note that the specific configurations are not limited to these embodiments and can be modified as appropriate without departing from the spirit of the present invention. Figure 12 is a side view of a nut 201 showing the circulation groove 240 formed by the first circulation groove forming step ST11 of the second embodiment. Figure 13 is a side view of a nut 201 showing the circulation groove 240 formed by the second circulation groove forming step ST12 of the second embodiment. In the second embodiment, the arrangement of the first circulation groove group 231 formed in the first circulation groove forming step ST11 differs from that of the first embodiment described above.

[0040] As shown in Figure 12, in the second embodiment, in the first circulation groove forming step ST11, a first circulation groove group 231 is formed on the inner circumferential surface 12 of the nut body 11 by forging. The first circulation groove group 231 includes circulation groove 241, circulation groove 243, and circulation groove 244. The circulation grooves 241, 243, and 244 belonging to the first circulation groove group 231 are symmetrical with respect to a vertical line L1 passing through the center of the nut 201 when viewed from the axial direction, and are formed to be located in both the region A3 above and the region A4 below the horizontal line L2 passing through the center of the nut 201. The vertical line L1 and the horizontal line L2 are orthogonal to each other. Specifically, in this embodiment, for example, with respect to circulation groove 241, circulation groove 243 is provided at a central angle of 135° with respect to circulation groove 241. Circulation groove 244 is provided at a central angle of 225° with respect to circulation groove 241. In other words, the multiple circulation grooves 241, 243, and 244 belonging to the first circulation groove group 231 are unequally arranged in the circumferential direction when viewed from the axial direction.

[0041] As shown in Figure 13, in the second circulation groove formation step ST12, a second circulation groove group 232 is formed on the inner circumferential surface 12 of the nut body 11 by forging. The second circulation groove group 232 has a circulation groove 242 and a circulation groove 245. Note that the configuration of the second circulation groove group 232 is the same as the configuration of the second circulation groove group 32 in the first embodiment, so a description is omitted. Through the process described above, a total of five circulation grooves 241 to 245 are formed on the inner circumferential surface 12 of the nut body 11.

[0042] According to the manufacturing method of the ball screw 10 and ball screw nut 201 of the second embodiment, a first circulation groove group 231 is formed by the first circulation groove forming step ST11, and a second circulation groove group 232 is formed by the second circulation groove forming step ST12. Of these, at least several circulation grooves 241, 243, and 244 belonging to the first circulation groove group 231 are symmetrical with respect to the vertical line L1 and are located in both the region A3 above the horizontal line L2 and the region A4 below it. This makes it possible to achieve the same effects as in the first embodiment, and further improves the degree of freedom in the arrangement of the circulation grooves 240. For example, when the circulation groove 240 is arranged as in the embodiment described above, the circumferential spacing (or central angle) between circulation groove 242 and circulation groove 243, and the circumferential spacing (or central angle) between circulation groove 244 and circulation groove 245 are larger compared to the first embodiment described above, thus reducing the impact on the second forging process (i.e., the second circulation groove formation process ST12).

[0043] (Third embodiment) Next, a third embodiment of the present invention will be described. In the following description, components similar to those in the first embodiment described above will be denoted by the same reference numerals and their descriptions will be omitted as appropriate. Figure 14 is a flowchart showing the process of manufacturing the ball screw nut 1 according to the third embodiment. Figure 15 is a side view of the nut 301 showing the circulation groove 340 formed by the first circulation groove forming step ST311 of the third embodiment. Figure 16 is a side view of the nut 301 showing the circulation groove 340 formed by the second circulation groove forming step ST312 of the third embodiment. Figure 17 is a side view of the nut 301 for explaining the nut removal step ST303 of the third embodiment. Figure 18 is a side view of the ball screw nut 301 according to the third embodiment viewed from the axial direction. Figures 15, 16, and 18 show side views of the nut 301 viewed from the axial direction, and Figure 17 shows a side view of the nut 301 viewed from a direction perpendicular to the axial direction (outside in the radial direction). In Figure 17, the solid lines indicate that the circulation grooves 341-344 are formed on the front side of the nut body 11, and the dotted lines indicate that the circulation grooves 345 and 346 are formed on the back side of the nut body 11. The third embodiment differs from the first embodiment described above in that the configuration (number and arrangement) of the circulation grooves 340 formed in the circulation groove formation step ST01 and the manufacturing method includes a nut removal step ST303.

[0044] As shown in Figure 14, in the third embodiment, the method for manufacturing the ball screw nut 1 comprises a circulation groove forming step ST01, a helical groove forming step ST02, and a nut removal step ST303. The circulation groove forming step ST01 includes a first circulation groove forming step ST311 and a second circulation groove forming step ST312. Note that the helical groove forming step ST02 in the third embodiment is equivalent to the helical groove forming step ST02 in the first embodiment, so its description is omitted below. As shown in Figure 15, first, the first circulation groove formation process ST311 is performed. In the first circulation groove formation process ST311, a first circulation groove group 331 is formed on the inner circumferential surface 12 of the nut body 11 by forging. The first circulation groove group 331 has circulation grooves 341, 343, and 345. The circulation grooves 341, 343, and 345 belonging to the first circulation groove group 331 are equally spaced (at 120° intervals) in the circumferential direction when viewed from the axial direction.

[0045] Next, as shown in Figure 16, the second circulation groove formation process ST312 is performed. In the second circulation groove formation process ST312, a second circulation groove group 332 is formed on the inner circumferential surface 12 of the nut body 11 by forging. The second circulation groove group 332 has circulation grooves 342, 344, and 346. The circulation grooves 342, 344, and 346 belonging to the second circulation groove group 332 are equally spaced (at 120° intervals) in the circumferential direction when viewed from the axial direction. In addition, the second circulation groove group 332 is 60° out of phase with respect to the first circulation groove group 331. As a result, when the circulation groove formation process ST01 is completed, a total of six circulation grooves 40 are formed on the inner circumferential surface 12 of the nut body 11 so as not to overlap each other in the circumferential direction. When viewed from the axial direction of the nut 301, the six circulation grooves 341 to 346 are arranged in the circumferential direction counterclockwise in the order of circulation groove 341, circulation groove 342, circulation groove 343, circulation groove 344, circulation groove 345, and circulation groove 346. The circulation grooves 341 to 346 are equally spaced (at 60° intervals) in the circumferential direction when viewed from the axial direction.

[0046] As shown in Figure 14, once the circulation groove formation process ST01 and the spiral groove formation process ST02 are completed, the nut removal process ST303 is performed. As shown in Figure 17, in the nut removal process ST303, a portion of the nut 301 in the axial direction is removed. In the nut removal process ST303, at least one of the multiple circulation grooves 340 formed in the circulation groove formation process ST01 is removed. In this embodiment, circulation groove 346 is removed. In the nut removal process ST303, the nut 301 is cut at a predetermined position in the axial direction (the position indicated by arrow B in Figure 17) so that the circulation groove 346 is removed. As a result, the area A33 corresponding to the circulation groove 346 is removed, and the area A30 corresponding to the circulation grooves 341 to 345 remains as the product. Figure 18 shows the nut 301 after the completion of the nut removal process ST303. As shown in Figure 18, because a portion of the nut 301 has been cut, a total of five circulation grooves 340 are ultimately formed in the nut body 11. Furthermore, these five circulation grooves 340, when viewed from the axial direction, have different central angles between at least two pairs of circumferentially adjacent circulation grooves (for example, the central angle α3 between circulation groove 341 and circulation groove 342) and between another pair of circumferentially adjacent circulation grooves (for example, the central angle β3 between circulation groove 341 and circulation groove 345).

[0047] According to the manufacturing method of the ball screw 10 and ball screw nut 301 of the third embodiment, by removing one of the circulating grooves 340 that are equally arranged in the circumferential direction in the nut removal step ST303, unequally arranged circulating grooves 340 are formed overall. Therefore, the same effects as the first embodiment can be achieved. In addition, since the same shaped mold can be used for the first forging and the second forging, manufacturing costs can be further reduced and versatility can be increased.

[0048] It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, in the first embodiment described above, forging was performed using a mold and a cam mechanism in the circulation groove formation step ST01, but the invention is not limited to this. Plastic deformation may be performed by other methods.

[0049] In each embodiment, the number and arrangement (central angle) of the circulation grooves 40, 240, and 340 formed in the nuts 1, 201, and 301 are not limited to the number and central angle described above. The arrangement of the circulation grooves 40, 240, and 340 shown in Figures 2, 6, and 14 is just an example, and the number and arrangement of the circulation grooves 40, 240, and 340 can be appropriately changed in each embodiment. Furthermore, the number of circulation grooves belonging to the first circulation groove group 31, 231, and 331 and the number of circulation grooves belonging to the second circulation groove group 32, 232, and 332 may be different from or the same as those belonging to each other.

[0050] In addition to the circulation groove formation process ST01 and the helical groove formation process ST02, another process may be added to perform removal, plastic deformation, or both on the inner circumferential surface 12 of the nuts 1,201,301. In addition to the first and second circulation groove formation steps described above, the circulation groove formation step may also include a third circulation groove formation step, a fourth circulation groove, and so on. In other words, the forging process may be performed three or more times.

[0051] Furthermore, this disclosure may also be a combination of the following configurations. (1) Screw shaft and Nut and, A plurality of rolling elements are arranged between the nut and the screw shaft, Equipped with, The aforementioned nut is A spiral groove is formed on the inner circumferential surface of the nut, on which a plurality of the rolling elements roll, A plurality of circulation grooves are formed on the inner circumferential surface, which return the rolling element from one end to the other of the helical groove, It has, When viewed from the axial direction of the nut, the multiple circulation grooves are unequally arranged in the circumferential direction of the nut. Ball screw. (2) A plurality of central angles, each being the central angle between two adjacent circulation grooves in the circumferential direction, are set for a plurality of circulation grooves. In the aforementioned unequal arrangement, at least one of the multiple central angles differs from another central angle. (1) The ball screw described above. (3) Two or more of the multiple circulation grooves are equally spaced in the circumferential direction when viewed from the axial direction. (1) or (2) the ball screw described above. (4) The multiple circulation grooves are, A first group of circulation grooves including two or more circulation grooves, A second circulation groove group which includes two or more circulation grooves other than the first circulation groove group among the multiple circulation grooves, It has, The plurality of circulation grooves belonging to the first circulation groove group are equally spaced in the circumferential direction when viewed from the axial direction, The plurality of circulation grooves belonging to the second circulation groove group are equally arranged in the circumferential direction when viewed from the axial direction, A ball screw as described in any one of (1) through (3). (5) The number of circulation grooves belonging to the first circulation groove group is different from the number of circulation grooves belonging to the second circulation groove group. (4) The ball screw described above. (6) It includes two or more circulation grooves and has multiple groups of circulation grooves that are different from each other, The plurality of circulation grooves belonging to at least one of the plurality of circulation groove groups are symmetrical with respect to a vertical line passing through the center of the nut when viewed from the axial direction, and are provided to be located in both the region above and below the horizontal line passing through the center of the nut. A ball screw as described in any one of (1) through (5). (7) A method for manufacturing a ball screw nut having a helical groove on which multiple rolling elements roll, and a circulation groove that returns the rolling elements from one end to the other end of the helical groove, A process of forming circulation grooves on the inner surface of the nut by forging multiple simultaneous strikes, A helical groove forming step, in which the helical groove is formed on the inner circumferential surface by removal processing, Equipped with, In the circulation groove forming step, a plurality of circulation grooves are formed such that, when viewed from the axial direction of the nut, the plurality of circulation grooves are unequally arranged in the circumferential direction of the nut. A method for manufacturing ball screw nuts. (8) A plurality of central angles, each being the central angle between two adjacent circulation grooves in the circumferential direction, are set for a plurality of circulation grooves. In the aforementioned unequal arrangement, at least one of the multiple central angles differs from another central angle. (7) A method for manufacturing a ball screw nut as described in (7). (9) The aforementioned circulation groove formation step is, A first circulation groove forming step involves forming a first circulation groove group containing multiple circulation grooves on the inner circumferential surface of the nut by forging multiple simultaneous strikes, A second circulation groove forming step, in which a second circulation groove group is formed on the inner circumferential surface of the nut by a forging process involving multiple simultaneous strikes, including multiple circulation grooves other than the first circulation groove group, Includes, In the first circulation groove formation step, the first circulation groove group is formed such that, when viewed from the axial direction, the plurality of circulation grooves belonging to the first circulation groove group are equally arranged in the circumferential direction. In the second circulation groove formation step, the second circulation groove group is formed such that, when viewed from the axial direction, the plurality of circulation grooves belonging to the second circulation groove group are equally arranged in the circumferential direction. A method for manufacturing a ball screw nut as described in (7) or (8). (10) The number of circulation grooves belonging to the first circulation groove group is different from the number of circulation grooves belonging to the second circulation groove group. (9) A method for manufacturing a ball screw nut as described in (9). (11) The aforementioned circulation groove formation step is, A first circulation groove forming step involves forming a first circulation groove group containing multiple circulation grooves on the inner circumferential surface of the nut by forging multiple simultaneous strikes, A second circulation groove forming step, in which a second circulation groove group is formed on the inner circumferential surface of the nut by a forging process involving multiple simultaneous strikes, including multiple circulation grooves other than the first circulation groove group, Includes, In at least one of the first circulation groove forming step and the second circulation groove forming step, a plurality of circulation grooves belonging to the first circulation groove group are formed such that, when viewed from the axial direction, they are symmetrical with respect to a vertical line passing through the center of the nut and are located in both the region above and below the horizontal line passing through the center of the nut. A method for manufacturing a ball screw nut as described in (7) or (8). (12) The process further includes a nut removal step, in which a portion of the nut in the axial direction is removed, after the circulation groove forming step and the helical groove forming step. In the nut removal step, at least one of the multiple circulation grooves formed in the circulation groove formation step is removed. A method for manufacturing a ball screw nut as described in any one of (7) to (11). [Explanation of Symbols]

[0052] 1,201,301 nuts 2 Screw shaft 3 Rolling element 10 Ball screws 12 Inner surface 15. Inner circumferential spiral groove (spiral groove) 31,231,331 First circulation groove group (circulation groove group) 32,232,332 Second circulation groove group (circulation groove group) 40,41,42,43,44,45,240,241,242,243,244,245,340,341,342,343,344,345,346 Circulation groove L1 vertical line L2 horizontal line A3 Upper area A4 Lower area α,β central angles ST01 Circulation Ditch Formation Project ST02 Spiral Groove Formation Project ST11, ST311 First Circulation Ditch Formation Project ST12, ST312 Second Circulation Ditch Formation Project ST303 ナット removal process

Claims

1. Screw shaft and Nut and, A plurality of rolling elements are arranged between the nut and the screw shaft, Equipped with, The aforementioned nut is A spiral groove is formed on the inner circumferential surface of the nut, on which a plurality of the rolling elements roll, A plurality of circulation grooves are formed on the inner circumferential surface, which return the rolling element from one end to the other of the helical groove, It has, When viewed from the axial direction of the nut, the multiple circulation grooves are unequally arranged in the circumferential direction of the nut. Ball screw.

2. A plurality of central angles, each being the central angle between two adjacent circulation grooves in the circumferential direction, are set for a plurality of circulation grooves. In the aforementioned unequal arrangement, at least one of the multiple central angles differs from another central angle. The ball screw according to claim 1.

3. Two or more of the multiple circulation grooves are equally spaced in the circumferential direction when viewed from the axial direction. The ball screw according to claim 1.

4. The multiple circulation grooves are, A first group of circulation grooves including two or more circulation grooves, A second circulation groove group which includes two or more circulation grooves other than the first circulation groove group among the multiple circulation grooves, It has, The plurality of circulation grooves belonging to the first circulation groove group are equally spaced in the circumferential direction when viewed from the axial direction, The plurality of circulation grooves belonging to the second circulation groove group are equally arranged in the circumferential direction when viewed from the axial direction, The ball screw according to claim 1.

5. The number of circulation grooves belonging to the first circulation groove group is different from the number of circulation grooves belonging to the second circulation groove group. The ball screw according to claim 4.

6. It includes two or more circulation grooves and has multiple groups of circulation grooves that are different from each other, The plurality of circulation grooves belonging to at least one of the plurality of circulation groove groups are symmetrical with respect to a vertical line passing through the center of the nut when viewed from the axial direction, and are provided to be located in both the region above and below the horizontal line passing through the center of the nut. The ball screw according to claim 1.

7. A method for manufacturing a ball screw nut having a spiral groove on which multiple rolling elements roll, and a circulation groove that returns the rolling elements from one end to the other of the spiral groove, A process of forming circulation grooves on the inner surface of the nut by forging multiple simultaneous strikes, A helical groove forming step, in which the helical groove is formed on the inner circumferential surface by removal processing, Equipped with, In the circulation groove forming step, a plurality of circulation grooves are formed such that, when viewed from the axial direction of the nut, the plurality of circulation grooves are unequally arranged in the circumferential direction of the nut. A method for manufacturing ball screw nuts.

8. A plurality of central angles, each being the central angle between two adjacent circulation grooves in the circumferential direction, are set for a plurality of circulation grooves. In the aforementioned unequal arrangement, at least one of the multiple central angles differs from another central angle. A method for manufacturing a ball screw nut according to claim 7.

9. The aforementioned circulation groove formation step is, A first circulation groove forming step involves forming a first circulation groove group containing multiple circulation grooves on the inner circumferential surface of the nut by forging multiple simultaneous strikes, A second circulation groove forming step, in which a second circulation groove group is formed on the inner circumferential surface of the nut by a forging process involving multiple simultaneous strikes, including multiple circulation grooves other than the first circulation groove group, Includes, In the first circulation groove formation step, the first circulation groove group is formed such that, when viewed from the axial direction, the plurality of circulation grooves belonging to the first circulation groove group are equally arranged in the circumferential direction. In the second circulation groove formation step, the second circulation groove group is formed such that, when viewed from the axial direction, the plurality of circulation grooves belonging to the second circulation groove group are equally arranged in the circumferential direction. A method for manufacturing a ball screw nut according to claim 7.

10. The number of circulation grooves belonging to the first circulation groove group is different from the number of circulation grooves belonging to the second circulation groove group. A method for manufacturing a ball screw nut according to claim 9.

11. The aforementioned circulation groove formation step is, A first circulation groove forming step involves forming a first circulation groove group containing multiple circulation grooves on the inner circumferential surface of the nut by forging multiple simultaneous strikes, A second circulation groove forming step, in which a second circulation groove group is formed on the inner circumferential surface of the nut by a forging process involving multiple simultaneous strikes, including multiple circulation grooves other than the first circulation groove group, Includes, In at least one of the first circulation groove forming step and the second circulation groove forming step, a plurality of circulation grooves belonging to the first circulation groove group are formed such that, when viewed from the axial direction, they are symmetrical with respect to a vertical line passing through the center of the nut and are located in both the region above and below the horizontal line passing through the center of the nut. A method for manufacturing a ball screw nut according to claim 7.

12. The process further includes a nut removal step, in which a portion of the nut in the axial direction is removed, after the circulation groove forming step and the helical groove forming step. In the nut removal step, at least one of the multiple circulation grooves formed in the circulation groove formation step is removed. A method for manufacturing a ball screw nut according to any one of claims 7 to 11.

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