Screw mechanism and manufacturing method for screw mechanism

Abstract

To provide a screw mechanism advantageous for cost reduction, and a manufacturing method for the screw mechanism.SOLUTION: A screw mechanism (11) comprises a screw shaft (21), a nut (22) combined with the screw shaft (21), and a component (50) fixed to the screw shaft (21). Rotary motion and linear motion are mutually converted between the screw shaft (21) the nut (22). The component (50) comprises an inner peripheral surface (51) having an uneven shape. The screw shaft (21) comprises a first portion (31) provided with a helical groove (33), and a second portion (32) fitted to the inner peripheral surface (51) of the component (50) with an interference. A space (90) adjacent to a fitting part (80) and allowing the storage of chips generated at the time of fitting is provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a screw mechanism and a method for manufacturing a screw mechanism. [Background technology]

[0002] The screw mechanism includes a screw shaft and a nut, and rotational motion and linear motion are converted between the screw shaft and the nut. As an example of the screw mechanism, a ball screw mechanism including a screw shaft, a nut, and a plurality of balls disposed between the screw shaft and the nut is known (see, for example, Patent Document 1).

[0003] In the ball screw mechanism of Patent Document 1, a stopper part is attached to the screw shaft. The stopper part abuts against a part of the nut, thereby restricting relative rotation between the screw shaft and the nut. The inner peripheral surface of the stopper part and the outer peripheral surface of the screw shaft each have a spline formed by machining. The screw shaft is inserted into a hole in the stopper part, and the splines engage with each other, thereby engaging the stopper part and the screw shaft. This spline engagement prevents relative rotation between the screw shaft and the stopper part, and transmits torque between the screw shaft and the stopper part. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-178023 Summary of the Invention [Problem to be solved by the invention]

[0005] In the screw mechanism in which a predetermined part is fixed to a screw shaft by spline engagement as described above, it is necessary to form splines on both the screw shaft and the predetermined part by machining. Furthermore, when a predetermined part such as a stopper part is attached to the end of the screw shaft, it is necessary to prevent the predetermined part from coming off the screw shaft in the axial direction by another part attached to the screw shaft.

[0006] An object of the present invention is to provide a screw mechanism and a method for manufacturing a screw mechanism that are advantageous in terms of cost reduction. Another object of the present invention is to provide a screw mechanism and a method for manufacturing a screw mechanism that are advantageous in terms of compactness. [Means for solving the problem]

[0007] In one aspect of the present invention, a screw mechanism includes a screw shaft, a nut combined with the screw shaft, where rotational motion and linear motion are converted between the screw shaft and the nut, and a part fixed to the screw shaft, where torque is transmitted between the screw shaft and the part. The part has an inner circumferential surface with a concave-convex shape. The screw shaft has a first part provided with a spiral groove and a second part fitted with an interference to the inner circumferential surface of the part. The screw mechanism includes a space adjacent to the fitting portion between the inner circumferential surface and the second part, which allows for the accommodation of chips generated during the fitting.

[0008] In another aspect of the present invention, a method for manufacturing a screw mechanism includes the steps of: preparing a screw shaft having a first portion with a spiral groove and a second portion provided at a different position in the axial direction from the first portion; and preparing a nut; assembling the nut to the screw shaft to enable conversion between rotational motion and linear motion; and fixing a part having an uneven inner peripheral surface to the screw shaft to enable torque transmission between the part and the screw shaft. The step of fixing the part includes fitting the second portion to the inner peripheral surface of the part with an interference and providing a space adjacent to the fitting portion to accommodate chips generated during fitting. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a screw mechanism and a method for manufacturing a screw mechanism that are advantageous for reducing costs. Also, according to the present invention, it is possible to provide a screw mechanism and a method for manufacturing a screw mechanism that are advantageous for reducing size. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic cross-sectional view of a screw mechanism. [Figure 2] FIG. 10 is a view of the stopper part attached to the screw shaft as viewed in the axial direction. [Figure 3] 10A-10C show the screw mechanism prior to the mating process. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a fitting portion. [Figure 5] FIG. 2 is an enlarged schematic cross-sectional view showing a sealing structure. [Figure 6] FIG. 10 is a schematic cross-sectional view showing a modified example of the sealing structure. [Figure 7] FIG. 10 is a schematic cross-sectional view showing another modified example of the sealing structure. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described with reference to the drawings. In one embodiment, the screw mechanism is a ball screw mechanism. In other embodiments, the screw mechanism can be a mechanism other than a ball screw type, such as a lead screw mechanism or a roller screw mechanism.

[0012] The screw mechanism is incorporated into electric actuators in various mechanical devices, such as electric brake devices for vehicles, automatic manual transmissions (AMTs), and positioning devices for machine tools. For example, in an electric actuator, the screw mechanism converts the rotational motion of a drive source such as an electric motor into linear motion, thereby operating a driven part (actuating part). Various types of electric brake devices are applicable, such as electro-mechanical brakes (EMBs) that apply braking force via a ball screw mechanism driven by a motor, and electro-hydraulic brakes (EHBs) that control the hydraulic pressure of a hydraulic brake via a ball screw mechanism driven by a motor. The screw mechanism can also be applied to mechanical devices other than those mentioned above.

[0013] In the following description, unless otherwise specified, the axial direction, radial direction, and circumferential direction refer to the direction along the central axis of the screw mechanism, the radial direction relative to the central axis, and the direction around the central axis, respectively.

[0014] As shown in Figures 1 and 2, the ball screw mechanism (screw mechanism) 11 comprises a screw shaft 21, a nut 22 combined with the screw shaft 21, and a plurality of balls 23 arranged between the screw shaft 21 and the nut 22.

[0015] In one example, the driving force of a motor (not shown) is transmitted to the screw shaft 21 or the nut 22. In the ball screw mechanism 11, rotational motion is converted into linear motion. A reducer can be additionally disposed between the ball screw mechanism 11 and the motor. In one example in which the ball screw mechanism 11 is applied to an electric brake device for a vehicle, brake pads of the vehicle operate against a brake disc in response to the linear motion. The ball screw mechanism 11 and the device using it are not limited to this example, and various forms are applicable.

[0016] The screw shaft 21 has a main portion (first portion) 31 and a sub-portion (second portion) 32. The main portion 31 of the screw shaft 21 is provided with a helical groove (thread groove, helical outer peripheral rolling groove) 33. A stopper component 50 is fixed to the sub-portion 32 of the screw shaft 21. In the screw shaft 21, the axial position of the sub-portion 32 is different from the axial position of the main portion 31. In one example, the main portion 31 and the sub-portion 32 are arranged adjacent to each other in the axial direction. For example, the sub-portion 32 is located at one end of the screw shaft 21 in the axial direction. The outer diameter (e.g., maximum outer diameter) of the sub-portion 32 is smaller than the outer diameter (e.g., maximum outer diameter) of the main portion 31. A step is provided between the outer surface of the main portion 31 and the outer surface of the sub-portion 32. In other examples, the screw shaft 21 may have a shape different from that described above.

[0017] In one example, at least a portion of the screw shaft 21 is made of metal. The spiral groove 33 of the screw shaft 21 is formed by cutting or rolling the outer circumferential surface of the main body portion 31 of the screw shaft 21. In forming the spiral groove 33, a grinding process can be additionally performed. In the screw shaft 21, the shape (groove bottom shape) of the spiral groove 33 is, for example, a Gothic arch groove or a circular arc groove. The number of threads of the spiral groove 33 is set to one, two, or more. In other examples, various forms are applicable to the screw shaft 21.

[0018] The nut 22 has a cylindrical nut body 41 and a spiral groove (thread groove, spiral inner peripheral rolling groove) 43 provided on the inner peripheral surface of the nut body 41. In one example, at least a portion of the nut 22 is made of metal. The spiral groove 43 of the nut 22 is formed by cutting or rolling the inner peripheral surface of the nut body 41. In forming the spiral groove 43, a grinding process can be additionally performed. In the nut 22, the shape (groove bottom shape) of the spiral groove 43 corresponds to the groove shape of the screw shaft 21, and is, for example, a Gothic arch groove or a circular arc groove. The number of threads of the spiral groove 43 is set to one, two, or more. In other examples, various shapes are applicable to the nut 22.

[0019] The plurality of balls 23 are disposed between the screw shaft 21 and the nut 22. The screw shaft 21 is inserted into the nut 22. The plurality of balls 23 are disposed in a space (rolling path) formed by the opposing arrangement of the spiral groove 33 of the screw shaft 21 and the spiral groove 43 of the nut 22. In FIG. 1, two balls 23 are indicated by two-dot chain lines. In reality, the ball screw mechanism 11 is equipped with a large number of balls 23.

[0020] In one example, the multiple balls 23 are made of metal (such as steel) or ceramic. The multiple balls 23 roll in the rolling path as the screw shaft 21 and the nut 22 rotate relative to each other. In one example, the balls 23 return from the end point of the rolling path to the start point via a circulation path provided in the nut 22. The balls 23 arranged in the rolling path move while being subjected to a compressive load. The balls 23 arranged in the circulation path move by being pushed by the subsequent balls 23. The start point and end point of the rolling path are interchanged depending on the direction of relative displacement (direction of relative rotation) between the screw shaft 21 and the nut 22. In another example, the ball screw mechanism 11 can have another structure for circulating the balls 23.

[0021] In one example of the ball screw mechanism 11, the screw shaft 21 is supported rotatably about a central axis 25, and its movement in a direction along the central axis 25 is restricted. The nut 22 is movable in a direction along the central axis 25, and its rotation around the central axis 25 is restricted. For example, when the screw shaft 21 is driven, it rotates about the central axis 25, and relative rotational motion occurs between the screw shaft 21 and the nut 22. The rotational motion of the screw shaft 21 is converted into linear motion of the nut 22, and the nut 22 moves in a direction along the central axis 25. In another example, the nut 22 is supported rotatably, and its rotation is restricted. As the nut 22 rotates, the screw shaft 21 moves in the axial direction.

[0022] The ball screw mechanism 11 includes a stopper component (fixed component, predetermined component) 50 fixed to the secondary portion (second component, one end) 32 of the screw shaft 21 and a locking component (protrusion) 47 provided on the end surface 45 of the nut 22. In the screw mechanism 11, as the screw shaft 21 or the nut 22 rotates, the nut 22 or the screw shaft 21 moves along the central axis 25. When the nut 22 approaches the secondary portion 32 of the screw shaft 21, the stopper component 50 and the locking component 47 of the nut 22 come to face each other in the circumferential direction. When the stopper component 50 and the locking component 47 finally abut each other in the circumferential direction, the relative motion (relative rotational motion and relative linear motion) between the screw shaft 21 and the nut 22 is stopped. FIG. 1 shows the secondary portion 32 of the screw shaft 21 (stopper component 50) and the end surface 45 of the nut 22 closest to each other in the axial direction. FIG. 2 shows a state in which the stopper part 50 and the locking part 47 are in contact with each other.

[0023] FIG. 3 is a diagram showing an example of the screw mechanism 11 in a preliminary stage of the fitting process. The stopper part 50 is press-fitted onto the secondary portion 32 of the screw shaft 21 with an interference. As shown in FIG. 3, in the preliminary stage of the fitting process, the stopper part 50 has an inner peripheral surface (inner wall surface) 51 having an uneven shape. In the stopper part 50, the inner peripheral surface 51 defines a fixing hole 52 into which the screw shaft 21 is inserted. In the example of FIG. 3, the inner peripheral surface 51 is provided along the circumference of a circle. In other examples, the inner peripheral surface 51 can be provided along the circumference of another shape, such as a polygon.

[0024] The inner peripheral surface 51 of the stopper part 50 includes a shaped, machined surface (a profiled surface, a profiled surface, or a concave-convex surface). For example, the inner peripheral surface 51 includes one or more protrusions or teeth provided on the base surface of the stopper part 50, and / or includes multiple protrusions and multiple recesses arranged in the circumferential direction. On the inner peripheral surface 51, the one or more protrusions or teeth have a shape that protrudes radially inward relative to the base surface. In one example, the multiple protrusions or teeth are provided extending in the axial direction. For example, the multiple protrusions or teeth are provided extending in the axial direction over substantially the entire axial range of the inner peripheral surface 51. Alternatively, the multiple protrusions or teeth are provided extending in the axial direction partially or intermittently within the axial range of the inner peripheral surface 51. For example, at least a portion of the multiple protrusions or teeth extends linearly along the axial direction. In other examples, the multiple protrusions or teeth may have a shape other than the above.

[0025] The cross-sectional profile of the inner circumferential surface 51 (a cross-sectional shape perpendicular to the central axis 25) has a contour of a concave-convex shape. For example, the contour of the concave-convex shape of the inner circumferential surface 51 may include the top of a protrusion, the side of a protrusion, the bottom of a depression, a transition between the top and side (a corner, an edge, etc.), a transition between the side and bottom (a corner, a base, etc.), etc. Alternatively, the contour of the concave-convex shape may include multiple peaks and multiple valleys. For example, the inner circumferential surface 51 may include a spline-shaped surface, a serrated surface, a knurled surface, or a surface obtained by modifying any of these. Various splines, such as an involute spline or a square spline, may be applied. Alternatively, the concave-convex shape formed on the inner circumferential surface 51 is not limited to a large number of protrusions / teeth, but may have a shape including one or several protrusions / teeth. Various other concave-convex shapes may be applied to the inner circumferential surface 51.

[0026] In the example of FIG. 3 , prior to the fitting process, the sub-portion 32 of the threaded shaft 21 has a smooth or non-smooth outer peripheral surface (outer surface) 36. For example, prior to the fitting process, the sub-portion 32 has a cylindrical surface. An interference is set between the outer peripheral surface of the sub-portion 32 of the threaded shaft 21 and the inner peripheral surface 51 of the stopper component 50. For example, the interference is preferably 0.01 mm or more, more preferably 0.05 mm or more, and even more preferably 0.1 mm or more. For example, the interference can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30 mm, or more. The interference is set appropriately depending on the specifications of the ball screw mechanism 11. The above numerical values ​​are merely examples and are not limiting.

[0027] In the fitting process, the secondary portion 32 of the screw shaft 21 is inserted into the fixing hole 52 of the stopper part 50. The stopper part 50 is moved axially relative to the screw shaft 21 from one axial end toward the center of the screw shaft 21. When the secondary portion 32 of the screw shaft 21 is press-fitted into the fixing hole 52 of the stopper part 50, the protrusions on the inner peripheral surface 51 of the stopper part 50 bite into the outer peripheral surface 36 of the screw shaft 21, causing plastic deformation of the outer peripheral surface 36.

[0028] In the plastic deformation, the protrusions on the inner peripheral surface 51 of the stopper part 50 scrape and / or flow the material of the outer peripheral surface 36 of the screw shaft 21, forming recesses (depressions) on the outer peripheral surface 36. In addition, one or more protrusions (projections) are formed between the multiple recesses on the outer peripheral surface 36.

[0029] 4, the press-fitting with interference between the screw shaft 21 and the stopper part 50 provides a fitting portion 80 in which the concave and convex portions of the stopper part 50, which have been shaped in advance, and the concave and convex portions of the screw shaft 21, which have been formed by plastic deformation during fitting, are tightly engaged with each other. In the fitting portion 80 in the engaged fitted state, the stopper part 50 substantially has the convex and concave contours formed before fitting, and the screw shaft 21 has the convex and concave contours formed by plastic deformation during fitting.

[0030] The fitting portion 80 has a structure in which the concave-convex shape of the screw shaft 21 and the concave-convex shape of the stopper part 50 are combined with each other. The screw shaft 21 and the stopper part 50 are engaged with each other by an interference fit (interference fit, interference fitting). In the fitting portion 80, the adjacent walls of the screw shaft 21 and the stopper part 50 are at least partially engaged with each other. The screw shaft 21 and the stopper part 50 are fitted with each other in an engaged state.

[0031] The stopper part 50 is securely fixed to the screw shaft 21 by the press-fitting in the engaged state. In the screw mechanism 11 having such a fitting portion 80, no slippage occurs between the screw shaft 21 and the stopper part 50, and torque is securely transmitted. Furthermore, rattle is prevented from occurring between the stopper part 50 and the screw shaft 21 during rotation around the axis.

[0032] Furthermore, in the engaged press-fitted state, the relative axial movement of the stopper part 50 with respect to the screw shaft 21 is restricted, eliminating the need for a separate part to prevent the stopper part 50 from coming off the screw shaft 21. This eliminates the need to provide a region on the screw shaft 21 for attaching a separate part, which is advantageous for making the entire screw mechanism 11 more compact.

[0033] At the mating portion 80, the screw shaft 21 has traces of plastic deformation (e.g., traces of unevenness formed by material flow). Examples of such traces include a relatively smooth uneven line on the stopper part 50 and a relatively rough uneven line on the screw shaft 21. Alternatively and / or additionally, the corners or edges of the wall of the stopper part 50 are relatively sharp, while the corners or edges of the wall of the screw shaft 21 are relatively gentle. Alternatively and / or additionally, the peak of the convex part of the stopper part 50 is in relatively close contact with or close contact with the bottom of the concave part of the screw shaft 21, while the peak of the convex part of the screw shaft 21 and the bottom of the concave part of the stopper part 50 are in a relatively non-contact or non-close contact state. Alternatively and / or additionally, the multiple convex parts of the stopper part 50 are relatively uniform in shape, while the multiple convex parts of the screw shaft 21 are relatively non-uniform in shape.

[0034] Here, during the press-fitting process, chips (material chips) may be generated. Chips may be generated on the outer peripheral surface 36 (see FIG. 3 ) of the screw shaft 21 when the outer peripheral surface 36 is chipped and at least a portion of the material is separated from the outer peripheral surface 36. For example, the entire chip may be separated from the outer peripheral surface 36, or a portion of the chip may remain connected to the outer peripheral surface 36. As the screw shaft 21 and the stopper part 50 move relative to each other in the axial direction during mating, the chips may move in a direction from the sub-portion 32 of the screw shaft 21 toward the main portion 31. As the stopper part 50 approaches the main portion 31 of the screw shaft 21, the chips begin to gather near the main portion 31 of the screw shaft 21.

[0035] As shown in FIG. 5, the ball screw mechanism 11 is provided with a space (accommodation space, sealed space, enclosed space) 90 that allows for the accommodation of debris generated during press-fitting. By accommodating the debris in the space 90, the debris is prevented from being discharged to the outside. In addition, the process of removing the debris generated during press-fitting is no longer necessary. This is advantageous for reducing the cost of the screw mechanism 11. If the debris moves toward the end of the screw shaft during press-fitting, a process for removing the debris would be required, or an additional structure to prevent debris would be required at the end of the screw shaft. This would result in an increase in the length of the screw shaft.

[0036] The space 90 is disposed adjacent to the fitting portion 80. That is, the space 90 is connected to an end of the fitting portion 80. For example, a portion (end) of the concave / convex portion of the fitting portion 80 faces the space 90. In one example, the space 90 is surrounded by at least the stopper component 50 and the screw shaft 21. In such a sealing structure 95 that the ball screw mechanism 11 has, chips from the fitting portion 80 are smoothly guided into the space 90.

[0037] In the example of FIG. 5, the outer diameter of the sub-portion 32 is smaller than the outer diameter of the main portion 31, and a step is formed between the main portion 31 and the sub-portion 32. A groove 91, which will be described later, provides a space 90 at the corner of the step. For example, the sealing structure 95 has a space 90 including a cavity (opening) that spans both the radially extending surface and the axially extending surface of the step portion. Utilizing the step portion is advantageous for forming a highly functional space 90 suitable for accommodating chips and for suppressing axial expansion of the screw shaft. In other examples, the space 90 may be formed at a position other than the corner portion.

[0038] In one example of the sealing structure 95, the screw shaft 21 has a first surface 81 oriented in the axial direction. The stopper component 50 has a second surface 82 oriented in the opposite axial direction. At least a portion of the second surface 82 faces closely adjacent to or abuts the first surface 81. The space 90 is provided radially inward from a facing region 96 between the first surface 81 and the second surface 82. Chips from the mating portion 80 are smoothly guided into the space 90. For example, the facing region 96 is located radially outward from both the space 90 and the mating portion 80. The facing region 96 extends in the radial direction. This extending direction is a direction that intersects the direction of movement of chips from the mating portion 80 during press-fitting.

[0039] In one example of the sealing structure 95, the screw shaft 21 has a groove 91 having a depth in the radial and / or axial direction. The groove 91 is disposed radially inward relative to the facing region 96. The groove 91 forms at least a part of the space 90. The space 90 having a depth in the radial direction allows chips to be accommodated at a position away from the facing region 96. The space 90 having a depth in the axial direction provides a smooth route for chips to be accommodated from the fitting portion 80 to the interior of the space 90.

[0040] In one example, the groove 91 is provided at or near the corner of the step between the main portion 31 and the sub-portion 32. The groove 91 provided at the corner of the step can preferably provide the space 90 having both a radial depth and an axial depth. For example, the groove 91 is provided extending circumferentially around the entire circumference. Alternatively, the groove 91 is provided extending partially circumferentially. In other examples, the groove 91 can have a shape other than those described above.

[0041] In one example of the sealing structure 95, the screw shaft 21 has a cover surface (first cover surface) 85 that extends at least in the axial direction and faces the space 90. The cover surface 85 is disposed radially inward with respect to the facing region 96. The cover surface 85 guides chips from the fitting portion 80 into the space 90 and prevents the chips from moving toward the facing region 96.

[0042] In one example, the axial end (the end or edge portion closer to the fitting portion 80) of the cover surface 85 is located radially outward from the bottom position 83 (the radial position of the bottom of the recess) of the inner circumferential asperity of the stopper part 50. The cross-sectional shape of the cover surface 85 (the cross-sectional shape parallel to the central axis 25) can have a linear shape along the axial direction, an inclined shape with respect to the axial direction, and / or a curved shape. For example, the cover surface 85 is provided extending in the circumferential direction over the entire circumference. Alternatively, the cover surface 85 is provided extending partially or intermittently in the circumferential direction. For example, the cover surface 85 partially surrounds the space 90.

[0043] 5 , the sealing structure 95 can have an overhang region 86. In the overhang region 86, a portion of the inner circumferential surface of the stopper part 50, which has an uneven profile, protrudes from the fitting portion 80 (the fitting region of the screw shaft 21) and faces the space 90. The overhang region 86 corresponds to a portion of the axial range including the axial end of the inner circumferential surface of the stopper part 50. Chips from the fitting portion 80 are smoothly guided into the space 90 via the overhang region 86.

[0044] For example, multiple walls are arranged in the circumferential direction on the inner peripheral surface of the stopper part 50. The tops (top surfaces) of the multiple walls are directed radially inward. During the press-fitting process, as the screw shaft 21 and the stopper part 50 move relative to each other in the axial direction, some regions of the tops of the multiple walls protrude from the fitting part 80 in the axial direction and face the space 90. In the overhanging region 86, chips generated during the press-fitting are guided radially inward into the space 90.

[0045] Returning to FIG. 1 , the manufacturing method of the screw mechanism 11 includes the steps of preparing the screw shaft 21 and the nut 22, assembling the nut 22 onto the screw shaft 21, and fixing the stopper component 50 to the screw shaft 21. The order of these steps can be changed as appropriate. The step of fixing the stopper component 50 is a step of fitting the secondary portion (second portion) 32 of the screw shaft 21 to the inner circumferential surface of the stopper component 50 with an interference, and includes a step of providing a space 90 adjacent to the fitting portion 80 between the inner circumferential surface of the stopper component 50 and the secondary portion 32 of the screw shaft 21, which allows for the accommodation of chips generated during fitting. The above-described screw mechanism 11 and its manufacturing method are advantageous for reducing costs and making the device compact.

[0046] In the ball screw mechanism 11 shown in FIG. 1, the stopper component 50 is generally disposed near the end of the main body portion 31 of the screw shaft 21 (the axial end of the spiral groove) from the viewpoint of compactness. According to the above-described screw mechanism 11 and its manufacturing method, even with an axially compact configuration, the problem of dealing with chips generated during press-fitting can be avoided. In addition, the process of attaching the stopper component 50 can be simplified.

[0047] 6 and 7 are schematic cross-sectional views showing modified examples of the sealing structure 95. In the following description, the same components as those described above or between the two figures are denoted by the same reference numerals, and the description thereof will be omitted or simplified.

[0048] 6, the stopper part 50 has a cover surface (second cover surface) 87 that extends at least in the axial direction. The cover surface 87 faces the space 90 and is disposed radially inward relative to the facing region 96. The cover surface 87 guides chips from the fitting portion 80 into the space 90 and prevents the chips from moving toward the facing region 96.

[0049] In one example, at least a portion of the cover surface 87 is located radially outward relative to a bottom position 83 of the inner circumferential concave / convex portion of the stopper component 50 (the radial position of the bottom of the concave portion). The cross-sectional shape of the cover surface 87 (cross-sectional shape parallel to the central axis 25) can have a linear shape along the axial direction, an inclined shape with respect to the axial direction, and / or a curved shape. For example, the cover surface 87 is provided extending in the circumferential direction over the entire circumference. Alternatively, the cover surface 87 is provided extending partially or intermittently in the circumferential direction. For example, the cover surface 87 partially surrounds the space 90.

[0050] In the example of FIG. 7 , the sealing structure 95 includes both a cover surface (first cover surface) 85 provided on the screw shaft 21 and a cover surface (second cover surface) 87 provided on the stopper component 50. A groove 91 is provided on the screw shaft 21 at or near the corner of the step between the main body portion 31 and the sub-portion 32. The groove 91 provides a space 90 having both a radial depth and an axial depth. For example, the axial end of the cover surface 85 (the end or edge portion closer to the mating portion 80) and the axial end of the cover surface 87 (the end or edge portion farther from the mating portion 80) are arranged close to each other in the axial direction. In the radial direction, the axial end of the cover surface 85 can be positioned at the same position as or further outward from the axial end of the cover surface 87. Chips from near the cover surface 87 are smoothly guided into the space 90 facing the cover surface 85. Furthermore, the shavings are prevented from moving toward the facing region 96.

[0051] The sealing structure 95 having the space 90 for accommodating the cutting edge may have various other configurations. For example, the sealing structure 95 may have a labyrinth structure in which one or more steps or protrusions provided on the stopper part 50 are combined with one or more steps or protrusions provided on the screw shaft 21.

[0052] The technical scope of the present invention is not limited to the scope of the embodiments. Various modifications or improvements can be made to the embodiments. Forms incorporating such modifications or improvements can also be included in the technical scope of the present invention. Furthermore, the present invention is not limited to the described embodiments, and any combination of these configurations may be used.

[0053] The sealing structure described above is not limited to ball screw mechanisms but can also be applied to other screw mechanisms. Furthermore, the part attached to the screw shaft is not limited to a stopper part but can also be applied to other parts such as gears (planetary gear carriers), anti-rotation devices, and gears with parallel axes.

[0054] The present disclosure may include the following combinations of features: (1) A screw shaft, A nut combined with the screw shaft, wherein rotational motion and linear motion are converted between the screw shaft and the nut; A part fixed to the screw shaft, and torque is transmitted between the screw shaft and the part; Equipped with The component has an inner circumferential surface having an uneven shape, The screw shaft has a first portion provided with a spiral groove and a second portion fitted to the inner circumferential surface of the part with an interference, A space is provided adjacent to the fitting portion between the inner circumferential surface and the second portion, and allows for the accommodation of chips generated during the fitting. Screw mechanism. (2) The screw mechanism according to (1), wherein, in the fitting portion, the screw shaft has a convex contour and a concave contour formed by plastic deformation. (3) The screw mechanism according to (1) or (2), wherein the space is surrounded by at least the part and the screw shaft. (4) The screw shaft has a first surface oriented in the axial direction, the component has a second surface at least partially facing the first surface; The space is provided radially inward with respect to a facing region between the first surface and the second surface. A screw mechanism according to any one of (1) to (3). (5) The screw shaft has a groove having a depth in the radial direction and / or the axial direction, The groove is disposed radially inward with respect to a facing region between the first surface and the second surface. A screw mechanism according to any one of (1) to (4). (6) The screw shaft has a first cover surface extending at least in the axial direction and facing the space, The first cover surface is disposed radially inward with respect to a facing area between the first surface and the second surface. A screw mechanism according to any one of (1) to (5). (7) the component has a second cover surface extending in at least the axial direction and facing the space; The second cover surface is disposed radially inward with respect to a facing area between the first surface and the second surface. A screw mechanism according to any one of (1) to (6). (8) A step of preparing a screw shaft having a first portion having a spiral groove and a second portion provided at a position different from the first portion in the axial direction, and a nut; A step of combining the nut with the screw shaft to enable conversion between rotational motion and linear motion; a step of fixing a part having an uneven inner circumferential surface to the screw shaft, thereby enabling torque transmission between the part and the screw shaft; Including, The step of fixing the component includes a step of fitting the second part to the inner peripheral surface of the component with an interference, and providing a space adjacent to the fitting portion capable of accommodating chips generated during fitting. Manufacturing method of screw mechanism. [Explanation of symbols]

[0055] 11 Ball screw mechanism (screw mechanism) 21 Screw shaft (shaft) 22 Nut 25 Center axis 31 Main body part (1st part) 32 Subpart (Second Part) 33 Spiral groove (screw groove) 36 Outer surface (outer surface) 41 Nut body 45 End section 47 Locking part (protrusion) 50 Stopper parts (parts) 51 Inner surface (inner wall surface) 52 fixing hole 80 Fitting part 81 Page 1 82 2nd page 85 Cover surface (first cover surface) 86 Overhang Area 87 Cover surface (second cover surface) 90 space 91 Groove 95 Sealing structure 96 Face-to-face area

Claims

1. A screw shaft, A nut combined with the screw shaft, wherein rotational motion and linear motion are converted between the screw shaft and the nut; A part fixed to the screw shaft, and torque is transmitted between the screw shaft and the part; Equipped with The component has an inner circumferential surface having an uneven shape, The screw shaft has a first portion provided with a spiral groove and a second portion fitted to the inner circumferential surface of the part with an interference, a space adjacent to the fitting portion between the inner circumferential surface and the second portion, the space allowing for the accommodation of chips generated during the fitting; Screw mechanism.

2. 2. The screw mechanism according to claim 1, wherein the threaded shaft has a convex contour and a concave contour at the fitting portion formed by plastic deformation.

3. The screw mechanism according to claim 2 , wherein the space is surrounded by at least the part and the screw shaft.

4. The screw shaft has a first surface oriented in the axial direction, the component has a second surface at least partially facing the first surface; The space is provided radially inward with respect to a facing region between the first surface and the second surface. The screw mechanism according to any one of claims 1 to 3.

5. The screw shaft has a groove having a depth in the radial direction and / or the axial direction, The groove is disposed radially inward relative to the facing region. The screw mechanism according to claim 4.

6. The screw shaft has a first cover surface extending at least in the axial direction and facing the space, The first cover surface is disposed radially inward with respect to the facing region. The screw mechanism according to claim 4.

7. the component has a second cover surface extending at least in the axial direction and facing the space; The second cover surface is disposed radially inward from the facing region. The screw mechanism according to claim 4.

8. A step of preparing a screw shaft having a first portion having a spiral groove and a second portion provided at a position different from the first portion in the axial direction, and a nut; A step of combining the nut with the screw shaft to enable conversion between rotational motion and linear motion; a step of fixing a part having an uneven inner circumferential surface to the screw shaft, thereby enabling torque transmission between the part and the screw shaft; Including, the step of fixing the component includes a step of fitting the second portion to the inner peripheral surface of the component with an interference, and providing a space adjacent to the fitting portion capable of accommodating chips generated during fitting. Manufacturing method of screw mechanism.

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