Actuator and actuator manufacturing method

Abstract

This actuator comprises: a screw shaft that has one end pointing in a first direction and the other end pointing in a second direction; a nut that penetrates the screw shaft; a plurality of balls that are disposed between the screw shaft and the nut; and a rotary component that is connected to an end portion of the screw shaft in the second direction and transmits torque to the screw shaft. The rotary component has: a first end surface facing in the first direction; a first protrusion that protrudes in the first direction from the first end surface and co-rotates with the rotary component; a second end surface facing in the second direction; and a recessed part recessed in the first direction from the second end surface. The nut has a second protrusion that protrudes into the trajectory of the rotating first protrusion and contacts the first protrusion. The first protrusion has a contact surface that faces in the circumferential direction and contacts the second protrusion.

Description

Actuator and Method for Manufacturing Actuator

[0001] The present disclosure relates to an actuator and a method for manufacturing an actuator.

[0002] The actuator includes a ball screw device that converts rotational motion into linear motion. The ball screw device has a screw shaft, a nut penetrated by the screw shaft, and a plurality of balls disposed between the screw shaft and the nut. In the actuator of the following patent document, a carrier (rotating part) for transmitting torque is attached to the screw shaft, and the nut moves in the axial direction.

[0003] Further, the actuator of the following patent document has a stopper. The stopper has a first protrusion protruding from the carrier toward the nut side and a second protrusion protruding from the nut toward the carrier side. Therefore, in the actuator of the following patent document, when the advanced nut retreats and the nut tries to return to a predetermined position (hereinafter referred to as the initial position), the first protrusion and the second protrusion come into contact. As a result, the rotation of the screw shaft stops, and the nut is surely disposed at the initial position. Hereinafter, the surface of the first protrusion that contacts the second protrusion is referred to as the contact surface.

[0004] Japanese Patent Application Laid-Open No. 2023-159531

[0005] By the way, forming the protrusion (the first protrusion) by cutting is not preferable because it causes a decrease in yield.

[0006] The present disclosure has been made in view of the above, and an object thereof is to provide an actuator and a method for manufacturing an actuator that can avoid a decrease in the yield of rotating parts.

[0007] To achieve the above objective, an actuator according to one aspect of the present disclosure comprises a screw shaft having one end pointing in a first direction and the other end pointing in a second direction, a nut passing through the screw shaft, a plurality of balls disposed between the screw shaft and the nut, and a rotating part connected to the end of the screw shaft in the second direction and transmitting torque to the screw shaft. The rotating part has a first end face facing the first direction, a first projection protruding from the first end face in the first direction and rotating together with the rotating part, a second end face facing the second direction, and a recess recessing from the second end face in the first direction. The nut has a second projection that enters the trajectory of the rotating first projection and contacts the first projection. The first projection has a contact surface facing in the circumferential direction and contacting the second projection.

[0008] According to this disclosure, when manufacturing a rotating part, applying pressure to the second end face of the rotating part deforms it so that a part of the rotating part moves in a first direction, a recess is formed on the second end face. The part that moves in the first direction (the flesh portion) forms a convex portion that protrudes from the first end face. By shaping this convex portion, a first projection can be formed. In other words, the flesh portion used to form the recess can be used for the first projection, thereby improving yield.

[0009] Furthermore, in the actuator described above, the screw shaft has a screw shaft body on which an outer peripheral raceway surface is formed on its outer peripheral surface, and a connecting portion that protrudes in the second direction from the end face in the second direction of the screw shaft body and has a smaller diameter than the screw shaft body. The rotating part has a boss portion that protrudes in the first direction from the first end face and abuts against the end face in the second direction of the screw shaft body, and a connecting hole formed on the end face in the first direction of the boss portion into which the connecting portion is inserted.

[0010] According to the above configuration, the material used to form the recess can also be used for the boss portion, thereby improving yield.

[0011] Furthermore, in the actuator described above, the first projection is arranged on the outer circumference of the boss portion, and the boss portion and the first projection are continuous.

[0012] According to the above configuration, the first projection is continuous with the boss portion, improving rigidity.

[0013] Furthermore, in the actuator described above, the first projection may be arranged on the outer circumference of the boss portion, and the first projection may be spaced apart from the boss portion.

[0014] Furthermore, in the actuator described above, the rotating part has a concave surface that is recessed in the second direction from the first end face. The first projection and the boss portion protrude from the concave surface in the first direction. The concave surface has a bottom surface that extends in a direction perpendicular to the central axis of the screw shaft, and a wall surface that connects the bottom surface and the first end face. The corner where the bottom surface and the contact surface intersect is rounded (R-shaped).

[0015] Incidentally, in order to avoid stress concentration at the base (root) of the first projection, the corner where the end face of the carrier (rotating part) and the contact surface of the first projection intersect is often rounded (R-shaped). However, the part of the contact surface where the R-shaped portion is formed cannot be used as the part that the second projection contacts. For this reason, forming the R-shaped portion increases the protrusion amount of the first projection by the length of the R-shaped portion, making the rotating part larger in the axial direction. On the other hand, according to the above configuration, the first projection is formed on a concave surface. Therefore, the protrusion amount of the first projection projecting in the first direction from the first end face is smaller by the depth of the concave surface. From the above, the rotating part is made smaller in the axial direction.

[0016] Furthermore, in the actuator described above, the first projection has an inner diameter surface facing radially inward. The corner where the inner diameter surface and the bottom surface intersect may be a rounded (R) portion.

[0017] Furthermore, in the actuator described above, the concave surface may extend in the circumferential direction and form an annular shape with respect to the central axis.

[0018] Furthermore, in the actuator described above, the concave surface may be formed only around the first projection.

[0019] Furthermore, in the actuator described above, the rotating part has a fleshy portion which is positioned in the first direction relative to the bottom surface, and the surface facing the first direction is the first end face. The fleshy portion is positioned radially outward of the first projection, and the first projection and the fleshy portion are continuous. The first projection faces radially outward and has an outer diameter surface whose end in the second direction intersects with the first end face. The corner where the outer diameter surface and the first end face intersect is rounded (R-shaped).

[0020] According to the above configuration, the portion of the carrier positioned on the outer circumference of the first projection is continuous with the first projection. As a result, the rigidity of the first projection is improved.

[0021] Furthermore, in order to achieve the above objective, in a method for manufacturing an actuator according to one aspect of this disclosure, the actuator comprises a screw shaft having one end pointing in a first direction and the other end pointing in a second direction, a nut passing through the screw shaft, a plurality of balls disposed between the screw shaft and the nut, and a rotating part connected to the end of the screw shaft in the second direction and transmitting torque to the screw shaft. The rotating part also has a first end face facing the first direction, a first projection protruding from the first end face in the first direction and rotating together with the rotating part, a second end face facing the second direction, and a recess recessing from the second end face in the first direction. The nut has a second projection that enters the trajectory of the rotating first projection and contacts the first projection. The first projection faces in the circumferential direction and has a contact surface that contacts the second projection. The method for manufacturing the actuator also includes a manufacturing step for manufacturing the rotating part. The manufacturing process includes a preparation step of preparing a blank material and a forging step of forging the blank material after the preparation step. The blank material has a surface facing one direction in the thickness direction of the blank material and a back surface facing the opposite direction to the surface. The forging step applies pressure to a part of the back surface of the blank material to cause a part of the blank material to protrude from the surface, thereby forming the recess on the back surface of the blank material and forming the first projection on the surface.

[0022] According to this disclosure, when the second end face of a rotating part is pressed during the forging process, and a portion of the rotating part is deformed to move in a first direction, a recess is formed on the second end face. The portion that moves in the first direction (the flesh portion) forms a convex portion that protrudes from the first end face. Furthermore, in the forging process, the convex portion is shaped to form a first projection. Therefore, the flesh portion that was used to form the recess is utilized for the first projection, thereby improving the yield.

[0023] Furthermore, in the method for manufacturing the actuator described above, the screw shaft comprises a screw shaft body having an outer peripheral raceway surface formed on its outer peripheral surface, and a connecting portion that protrudes in the second direction from the end face in the second direction of the screw shaft body and has a smaller diameter than the screw shaft body. The rotating part comprises a boss portion that protrudes in the first direction from the first end face and abuts against the end face in the second direction of the screw shaft body, and a connecting hole that penetrates the end face in the first direction of the boss portion and the bottom surface of the recess, into which the connecting portion is inserted. The forging process forms the boss portion together with the first projection on the surface. The manufacturing process includes a connecting hole forming step after the forging process in which the connecting hole is formed in the blank material.

[0024] According to the above configuration, the material used to form the recess is also used for the boss portion, thereby improving the yield.

[0025] Furthermore, in the method for manufacturing the actuator described above, the manufacturing process may include a cutting process in which the blank material is cut after the forging process.

[0026] According to this disclosure, a decrease in the yield of rotating parts can be avoided.

[0027] Figure 1 is a cross-sectional view of the actuator of Embodiment 1, cut in the axial direction. Figure 2 is a view of the carrier of Embodiment 1 from a first direction. Figure 3 is a cross-sectional view taken along the line III-III in Figure 2. Figure 4 is a schematic diagram showing a cross-section of the first projection of the carrier of a comparative example, more specifically a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the first projection protrudes. Figure 5 is a schematic diagram showing a cross-section of the first projection of the carrier of Modification 1, more specifically a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the first projection protrudes. Figure 6 is a schematic diagram showing a cross-section of the first projection of the carrier of Modification 2, more specifically a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the first projection protrudes. Figure 7 is an enlarged perspective view of a part of the first end face of the carrier of Modification 3. Figure 8 is an enlarged perspective view of a part of the first end face of the carrier of Modification 4. Figure 9 is an enlarged perspective view of a part of the first end face of the carrier of Modification 5. Figure 10 is an enlarged perspective view of a part of the first end face of the carrier of Modification 6. Figure 11 is a cross-sectional view taken along the line XI-XI in Figure 10. Figure 12 is a cross-sectional view of the actuator of Embodiment 2, cut in the axial direction. Figure 13 is a view of the carrier (rotating part) of Embodiment 2 from a second direction. Figure 14 is a schematic diagram showing the manufacturing process of the carrier (rotating part) of Embodiment 2. Figure 15 is a cross-sectional view of the driven pulley (rotating part) of Modification 7, cut in the axial direction. Figure 16 is a cross-sectional view of the carrier (rotating part) of Modification 8, cut in the axial direction.

[0028] The forms for implementing this disclosure will be described in detail with reference to the drawings. This disclosure is not limited by the contents described below. Furthermore, the components described below include those that are readily conceivable to a person skilled in the art, and those that are substantially the same. In addition, the components described below can be combined as appropriate.

[0029] (Embodiment 1) Figure 1 is a cross-sectional view of the actuator of Embodiment 1, cut in the axial direction. As shown in Figure 1, the actuator 100 of Embodiment 1 comprises a motor (not shown), a planetary gear mechanism 101, a ball screw device 1, a stopper 4, and a housing 120 (partially shown). The actuator 100 can be applied to brake boosters and brake calipers of brake systems.

[0030] In the following description, the direction parallel to the central axis O of the screw shaft 2 of the ball screw device 1 is referred to as the axial direction. In the axial direction, the direction in which the ball screw device 1 is positioned as viewed from the planetary gear mechanism 101 is referred to as the first direction X1, and the direction opposite to the first direction X1 is referred to as the second direction X2. In addition, the direction perpendicular to the central axis O is referred to as the radial direction.

[0031] The planetary gear mechanism 101 is a device that reduces the rotational motion transmitted from the motor. The planetary gear mechanism 101 comprises an input shaft 102, a sun gear 103, a ring gear 104, multiple planetary gears 105, multiple transmission shafts 106, a rotating component called a carrier 107, and a bearing device 108.

[0032] Rotational motion is transmitted to the input shaft 102. The input shaft 102 is arranged coaxially with the central axis O. The input shaft 102 in this disclosure may be configured as the output shaft of a motor.

[0033] The sun gear 103 passes through the input shaft 102 and is fixed to the input shaft 102 in a non-rotatable manner. The ring gear 104 is an internal gear that forms an annular shape around the input shaft 102. The outer surface of the ring gear 104 is fitted into the housing 120.

[0034] The planetary gear 105 is positioned between the sun gear 103 and the ring gear 104, and engages with the sun gear 103 and the ring gear 104, respectively. The carrier 107 has a through hole 110 that penetrates axially. The through hole 110 is located eccentrically radially outward from the central axis O. The transmission shaft 106 is inserted into the through hole 110. The planetary gear 105 is supported by the carrier 107 so as to be rotatable around the transmission shaft 106.

[0035] The carrier 107 is a disc-shaped component centered on a central axis O. The carrier 107 is rotatably supported by the housing 120 via a bearing device 108. Furthermore, an outer circumferential raceway surface 111 is formed on the outer circumferential surface of the carrier 107. In other words, the inner ring of the bearing device 108 is integrally formed with the carrier 107. However, in this disclosure, the carrier 107 and the inner ring may be separate components.

[0036] The carrier 107 has a female spline hole 112 which serves as a connecting hole. This female spline hole 112 penetrates the central part of the carrier 107 in the axial direction. Multiple internal teeth extending in the axial direction are formed on the inner circumferential surface of the female spline hole 112.

[0037] The carrier 107 has a first end face 113 facing a first direction X1. The first end face 113 has a concave surface 40 that recesses from the first end face 113 in a second direction X2, a first projection 41 that protrudes from the concave surface 40 in the first direction X1, and a boss portion 42 that protrudes from the concave surface 40 in the first direction X1. The concave surface 40, the first projection 41, and the boss portion 42 will be described later.

[0038] The ball screw device 1 comprises a screw shaft 2, a nut 3, and a plurality of balls (not shown). The screw shaft 2 comprises a male spline portion 10 which is a connecting portion, and a screw shaft body 11.

[0039] The male spline portion 10 is the part for connecting to the carrier 107. The male spline portion 10 is formed to have a smaller diameter than the screw shaft body 11. The male spline portion 10 extends in the second direction X2 from the end face 13 of the screw shaft body 11 in the second direction X2. Multiple external teeth extending in the axial direction are formed on the outer circumferential surface of the male spline portion 10.

[0040] The male spline portion 10 is inserted into the female spline hole 112 of the carrier 107 and is in spline fit. Specifically, the external teeth of the male spline portion 10 are inserted between the internal teeth of the female spline hole 112. And the external teeth of the male spline portion 10 and the internal teeth of the female spline hole 112 are in contact with each other in the circumferential direction. Through this spline fit, the carrier 107 and the screw shaft 2 are connected so as not to be relatively rotatable. In this embodiment, the screw shaft 2 and the carrier (rotating part) 107 are connected by spline fit, but the present disclosure may adopt other connection methods. That is, the connecting portion (or connecting hole) may have a configuration other than the male spline portion 10 (or female spline hole), and the connection method between the connecting portion and the connecting hole is not particularly limited.

[0041] On the outer peripheral surface of the screw shaft body 11, an outer peripheral raceway surface 12 extending in the helical direction is provided. The end surface 13 of the screw shaft body 11 in the second direction X2 is a plane orthogonal to the central axis O. The end surface 13 is in contact with the end surface of the boss portion 42 of the carrier 107 facing the first direction X1. Thereby, the screw shaft 2 is positioned so as not to move in the second direction X2.

[0042] The nut 3 includes a nut body 20 and a second protrusion 22 protruding in the second direction X2 from the end surface 21 of the nut body 20 in the second direction X2. The nut body 20 is formed in a cylindrical shape around the central axis O. On the inner peripheral surface 23 of the nut body 20, a plurality of inner peripheral raceway surfaces 24 and a plurality of circulation portions 25 are formed.

[0043] The inner peripheral raceway surface 24 faces the outer peripheral raceway surface 12 of the screw shaft 2. The space between the inner peripheral raceway surface 24 and the outer peripheral raceway surface 12 constitutes a raceway. A plurality of balls (not shown) are arranged in each raceway.

[0044] The circulation portion 25 circulates the balls that have moved from one end to the other end of the raceway to one end of the raceway. The circulation portion 25 of this embodiment is an S-shaped groove surface formed by cutting the inner peripheral surface 23. As an example of the circulation portion 25, in this embodiment, an S-shaped groove surface is given, but the present disclosure may be a comma, an end deflector, a middle deflector, a tube, etc., and the type of the circulation portion is not particularly limited.

[0045] The nut 3 is supported by the housing 120 so as not to rotate by a rotation prevention member (not shown). Further, the nut 3 is supported by the housing 120 so as to be movable in the axial direction. From the above, when the motor is driven and the carrier 107 rotates, the screw shaft 2 also rotates. Further, the nut 3 moves in the axial direction without rotating with the screw shaft 2.

[0046] Hereinafter, the rotation direction of the carrier 107 when the nut 3 moves in the first direction X1 is referred to as the first rotation direction L1 (see FIG. 2). Further, the rotation direction of the carrier 107 when the nut 3 moves in the second direction X2 is referred to as the second rotation direction L2 (see FIG. 2).

[0047] The stopper 4 has a first protrusion 41 and a second protrusion 22. When the nut 3 is disposed at the initial position, the first protrusion 41 and the second protrusion 22 are in contact with each other. To explain the operation of the stopper 4, when the carrier 107 rotates in the second rotation direction L2 and the nut 3 moves in the second direction X2, the first protrusion 41 rotates in the second rotation direction L2 together with the carrier 107. Further, the second protrusion 22 moves in the second direction X2 together with the nut 3. Then, when the nut 3 approaches the initial position, the second protrusion 22 enters the locus of the rotating first protrusion 41 and contacts the first protrusion 41. As a result, the rotation of the carrier 107 and the screw shaft 2 in the second direction X2 stops. The nut 3 stops moving in the second direction X2 and is disposed at the initial position.

[0048] Next, the details of the concave surface 40, the first protrusion 41, and the boss portion 42 will be described.

[0049] Figure 2 is a view of the carrier of Embodiment 1 from a first direction. Figure 3 is a cross-sectional view taken along the line III-III in Figure 2. As shown in Figure 2, a female spline hole 112 is located in the center of the first end face 113. The boss portion 42 is located radially outside the female spline hole 112 and is annular in shape so as to surround the outer circumference of the female spline hole 112. The first projection 41 is located radially outside the boss portion 42. The radially inner portion of the first projection 41 is continuous with the outer circumference of the boss portion 42. This improves the rigidity of the first projection 41. The concave surface 40 is located radially outside the boss portion 42 and the first projection 41 and is annular in shape so as to surround the outer circumference of the boss portion 42 and the first projection 41. The first end face 113 is located radially outside the concave surface 40 and is annular in shape so as to surround the outer circumference of the concave surface 40.

[0050] As shown in Figure 3, the depth of the concave surface 40 from the first end face 113 is formed to be H1. The concave surface 40 has a bottom surface 44 and a wall surface 45 positioned between the first end face 113 and the bottom surface 44.

[0051] The base surface 44 extends in a direction perpendicular to the central axis O. The wall surface 45 is an inclined surface that is positioned in a first direction X1 as it extends radially outward. However, this disclosure is not particularly limited, and the wall surface 45 may extend in the axial direction.

[0052] As shown in Figure 2, the bottom surface 44 is annular in shape so as to surround the outer circumference of the first projection 41 and the boss portion 42. Therefore, the first projection 41 and the boss portion 42 protrude in the first direction X1 from the bottom surface 44 (concave surface 40) rather than from the first end surface 113.

[0053] As shown in Figure 3, the axial length of the first projection 41 is H2. Similarly, the axial length of the boss portion 42 is also H2. This length H2 is greater than the depth H1 of the concave surface 40. Therefore, the first projection 41 and the boss portion 42 each protrude in the first direction X1 beyond the first end face 113.

[0054] Hereinafter, the first projection 41 and the boss portion 42 will be collectively referred to as the projection 50. As shown in Figure 2, the projection 50 has an outer peripheral surface 51 facing radially outward. The outer peripheral surface 51 of the projection 50 is composed of the outer peripheral surface 52 of the boss portion 42 and the side surface 53 of the first projection 41. The side surface 53 of the first projection 41 has a contact surface 54 facing the second rotation direction L2, an outer diameter surface 55 facing radially outward, and a back surface 56 facing the first rotation direction L1.

[0055] The corner where the outer circumferential surface 51 and the bottom surface 44 of the protruding portion 50 intersect is an R-shaped portion 60. The R-shaped portion 60 has an arc-shaped cross-section when cut along a virtual plane perpendicular to the outer circumferential surface 51 and the bottom surface 44, respectively. This R-shaped portion 60 encircles the corner where the outer circumferential surface 51 and the bottom surface 44 of the protruding portion 50 intersect, forming an annular shape.

[0056] To describe the R-section 60 in detail, a part of the R-section 60 (hereinafter referred to as the first R-section 61) is located at the corner where the contact surface 54 and the bottom surface 44 intersect. Another part of the R-section 60 (hereinafter referred to as the second R-section 62) is located at the corner where the outer diameter surface 55 and the bottom surface 44 intersect. A part of the R-section 60 (hereinafter referred to as the third R-section 63) is located at the corner where the back surface 56 and the bottom surface 44 intersect. A part of the R-section 60 (hereinafter referred to as the fourth R-section 64) is located at the corner where the outer peripheral surface 52 of the boss section 42 and the bottom surface 44 intersect.

[0057] The axial length of the contact surface 54 is H4. This axial length H4 of the contact surface 54 is long enough to contact the second projection 22 and reliably stop the movement of the second projection 22. The axial length of the R portion 60 is H3. The axial length H2 of the first projection 41 (projection 50) is the sum of the axial length H4 of the contact surface 54 and the axial length H3 of the R portion 60. From the above, the first projection 41 in this embodiment is larger by the axial length H3 than in the case where the R portion 60 is not formed.

[0058] Furthermore, the axial length H3 of the R portion 60 coincides with the depth H1 of the concave surface 40. Therefore, the R portion 60 does not protrude from the first end face 113 in the first direction X1.

[0059] Next, the effects of Embodiment 1 will be explained using a comparative example.

[0060] Figure 4 is a schematic diagram showing a cross-section of the first projection of the carrier of the comparative example, and more specifically, it is a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the first projection protrudes. As shown in Figure 4, a first projection 202 is formed on the first end face 201 of the carrier 200 of the comparative example. An R-shaped portion 204 is formed at the corner between the contact surface 203 of the first projection 202 and the first end face 201. Therefore, the difference from the embodiment is that a concave surface 40 is not formed in the comparative example.

[0061] The axial length H34 of the contact surface 203 in the comparative example is the same as the axial length H4 of the contact surface 54 in Embodiment 1 (H34 = H4). The axial length H33 of the R portion 204 in the comparative example is the same as the axial length H3 of the first R portion 61 in Embodiment 1 (H33 = H3). The axial length H32 of the first projection 202 in the comparative example is the same as the axial length H2 of the first projection 41 in Embodiment 1 (H32 = H2).

[0062] In the comparative example, the amount of protrusion H35 of the first projection 202 projecting in the first direction X1 from the first end face 201 is equal to the axial length H32 of the first projection 202 (H35 = H32). On the other hand, in Embodiment 1, the amount of protrusion of the first projection 41 (projection 50) projecting in the first direction X1 from the first end face 113 is H5, which is the axial length H2 of the first projection 41 (projection 50) minus the depth H1 of the concave surface 40. Therefore, the amount of protrusion H5 of the first projection 41 in Embodiment 1 is smaller than the amount of protrusion H35 of the first projection 202 in the comparative example (H5 < H35). For this reason, the carrier 107 in Embodiment 1 is smaller in the axial direction.

[0063] Next, a modified example in which a part of the actuator 100 of Embodiment 1 is changed will be described. Furthermore, the following description will focus on the differences from Embodiment 1.

[0064] (Modification 1, Modification 2) Figure 5 is a schematic diagram showing a cross-section of the first projection of the carrier in Modification 1, and more specifically, it is a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the first projection protrudes. As shown in Figure 5, Modification 1 differs from Embodiment 1 in that the axial length of the first R portion 61A of the carrier 107A, H13, is changed to H13. The length H13 of the first R portion 61A is smaller than the depth H1 of the concave surface 40.

[0065] Figure 6 is a schematic diagram showing a cross-section of the first projection of the carrier in Modified Example 2, and more specifically, it is a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the first projection protrudes. As shown in Figure 6, Modified Example 2 differs from Embodiment 1 in that the axial length of the first R portion 61B of the carrier 107B is changed to H23. The length H23 of the first R portion 61B is greater than the depth H1 of the concave surface 40.

[0066] According to the above-described modifications 1 and 2, the amount of protrusion of the first projections 41A and 41B projecting from the first end face 113 in the first direction X1 is reduced by the depth H1 of the concave surface 40. Therefore, similar to embodiment 1, the carriers 107A and 107B are miniaturized in the axial direction.

[0067] (Modifications 3, 4, 5, and 6) Figure 7 is an enlarged perspective view of a part of the first end face of the carrier of Modification 3. As shown in Figure 7, Modification 3 differs from Embodiment 1 in that the carrier 107C does not have a boss portion 42 formed on the inner circumference side of the first projection 41.

[0068] Figure 8 is an enlarged perspective view of a portion of the first end face of the carrier of Modified Example 4. As shown in Figure 8, the carrier 107D of Modified Example 4 differs from Embodiment 1 in that the first projection 41 and the boss portion 42 are not continuous. Therefore, the side surface 53 of the first projection 41 has an inner diameter surface 57 that faces radially inward. The corner where the inner diameter surface 57 and the bottom surface 44 intersect is an R portion 65.

[0069] Figure 9 is an enlarged perspective view of a portion of the first end face of the carrier of Modified Example 5. As shown in Figure 9, the carrier 107E of Modified Example 5 differs from Embodiment 1 in that the boss portion 42 is not formed therein. Also, the concave surface 40E of Modified Example 5 differs from Embodiment 1 in that it is formed only around the first projection 41. The wall surface 45E of the concave surface 40E is annular with respect to the first projection 41. More specifically, the wall surface 45E is formed in a rectangular shape when viewed from the axial direction, and corresponds to the shape (rectangular) of the side surface 53 of the first projection 41 (contact surface 54, outer diameter surface 55, back surface 56 and inner diameter surface 57) when viewed from the axial direction.

[0070] Figure 10 is an enlarged perspective view of a portion of the first end face of the carrier in the modified example 6. Figure 11 is a cross-sectional view taken along the line XI-XI in Figure 10. As shown in Figures 10 and 11, the portion of the carrier 107F positioned in the first direction X1 from the bottom surface 44 is referred to as the flesh portion 49. The surface of the flesh portion 49 facing the first direction X1 is the first end face 113.

[0071] As shown in Figure 10, the carrier 107F of Modified Example 6 differs from Embodiment 1 in that the boss portion 42 is not formed. Also, the carrier 107F of Modified Example 6 differs from Embodiment 1 in that the flesh portion 49 is positioned radially outward of the first projection 41, and the first projection 41 and the flesh portion 49 are continuous. As shown in Figure 11, the end of the outer diameter surface 55 in the second direction X2 intersects with the first end surface 113. The corner where the outer diameter surface 55 and the first end surface 113 intersect has a circular arc-shaped R portion 66 in cross-section.

[0072] As described above in Modifications 3 to 6, the amount of projection of the first projection 41 in the first direction X1 from the first end face 113 is smaller by the depth H1 of the concave surface 40 (see Figure 3). Therefore, the carriers 107C, 107D, 107E, and 107F are miniaturized in the axial direction, similar to Embodiment 1. Furthermore, according to Modification 6, the first projection 41 and the flesh portion 49 are continuous, and the rigidity of the first projection 41 is improved.

[0073] While embodiments and their various modifications have been described above, the embodiments mention a carrier 107 as an example of a rotating part, but this disclosure is not limited to this. The rotating part may be a pulley, gear, sprocket, or motor output shaft, and is not limited to any part that can transmit torque to a screw shaft. Furthermore, while the manufacturing method of the rotating part may be forging or cutting, this disclosure is not limited to any particular method of manufacturing the rotating part.

[0074] Next, Embodiment 2 will be described. In Embodiment 2, the description will focus on the changes from Embodiment 1.

[0075] (Embodiment 2) Figure 12 is a cross-sectional view of the actuator of Embodiment 2, cut in the axial direction. As shown in Figure 12, the carrier 107G of the actuator 100G of Embodiment 2 differs from Embodiment 1 in that it does not have a concave surface 40. In other words, the first projection 41 and boss portion 42 of Embodiment 2 are formed on the first end face 113 of the carrier 107G.

[0076] Furthermore, the carrier 107G of Embodiment 2 has a second end face 213 facing the second direction X2. It differs from Embodiment 1 in that the second end face 213 has a recess 240 formed therein that is recessed in the first direction X1.

[0077] Figure 13 is a view of the carrier (rotating part) of Embodiment 2 from a second direction. The recess 240 is located in the center of the second end face 213. The inner circumferential surface 241 of the recess 240 is formed in a circular shape around the central axis O when viewed from the axial direction. The female spline hole 112 opens from the bottom surface 242 of the recess 240 in the second direction X2. The diameter of the recess 240 (diameter of the inner circumferential surface 241) is formed to be larger in diameter than the female spline hole 112, which is a connecting hole. Also, the inner diameter of the recess 240 is smaller than the outer diameter of the boss portion 42. In this disclosure, the inner diameter of the recess 240 may be the same as the outer diameter of the boss portion 42, or it may be larger than the outer diameter of the boss portion 42.

[0078] Next, the manufacturing method for actuator 100G will be described. The manufacturing method for actuator 100G includes a manufacturing process for manufacturing carrier 107G (rotating part).

[0079] Figure 14 is a schematic diagram showing the manufacturing process of the carrier (rotating part) of Embodiment 2. The manufacturing process of the carrier 107G includes a preparation step S1, a forging step S2 performed after the preparation step S1, a connecting hole forming step S3 performed after the forging step S2, a cutting step S4 performed after the connecting hole forming step S3, and a spline forming step S5 performed after the cutting step S4.

[0080] Preparation step S1 is a step in which a blank material 300 is prepared. The blank material 300 is a steel material formed in a cylindrical shape. The blank material of this disclosure may be formed from a metal material other than steel and is not particularly limited. The blank material 300 has a surface 301 facing one direction in the thickness direction and a back surface 302 facing the opposite direction from the surface 301.

[0081] In forging process S2, pressure (see arrow A) is applied to the center of the back surface 302 of the blank material 300, pushing a portion of the material towards the front surface 301 and deforming the blank material 300. As a result, a recess 240 is formed on the back surface 302 of the blank material 300, and a protrusion 310 is formed on the front surface 301.

[0082] Furthermore, in the forging process S2, a mold 400 is prepared to form the protrusion 310 when pressure is applied. The mold 400 has a forming surface 401 that faces the surface 301. A recess 402 for forming the protrusion 310 is formed on this forming surface 401. As a result, the protrusion 310 that protrudes from the surface 301 is formed into a first projection 41 and a boss portion 42.

[0083] The connecting hole forming step S3 is a step in which the central part of the blank material 300 is cut to form a connecting hole 320 that penetrates the blank material 300. The connecting portion (male spline portion 10) of the screw shaft 2 is inserted into the connecting hole 320 (see Figure 1). In the connecting hole forming step S3, the connecting hole 320 may be formed using a drill or the like (not shown), or a pilot hole may be formed using a drill or the like, and then the connecting hole 320 may be formed by a boring step in which the inner circumferential surface of the pilot hole is cut. This disclosure does not particularly limit the method of forming the connecting hole 320. In addition, a through hole 110 may also be formed in the connecting hole forming step S3.

[0084] Cutting process S4 is a process of cutting the blank material 300. In cutting process S4, the inner circumferential surface 241 of the recess 240 is cut with a cutting tool 440 to a predetermined diameter, and the first projection 41 and boss portion 42 are cut to form a predetermined shape. In addition, cutting process S4 is a process of cutting the outer circumferential surface of the blank material 300 to form the outer circumferential raceway surface 111. Furthermore, the surface 301 and back surface 302 may also be cut in this process.

[0085] The spline forming step S5 is a process of broaching the inner circumferential surface of the connecting hole 320 to form the female spline hole 112. When the spline forming step S5 is completed, the rotating part, the carrier 107G, is completed. The surface 301 of the blank material 300 constitutes the first end face 113, and the back surface 302 constitutes the second end face 213.

[0086] As described above, according to Embodiment 2, the fleshy portion (protrusion 310) for forming the recess 240 is used for the first projection 41 and the boss portion 42, thereby improving the yield of the carrier 107G (rotating part).

[0087] Embodiment 2 has been described above. In this disclosure, it is sufficient that the material portion for forming the recess 240 can be used for the protrusion 310 (first projection 41), and there are no particular restrictions on the diameter or depth of the recess 240. Also, although the carrier 107G (rotating part) in Embodiment 2 has a boss portion 42, this disclosure does not require the presence of a boss portion 42.

[0088] Furthermore, regarding the formation of the outer circumferential raceway surface 111, in forging step S2 (or a forging step other than forging step S2), a concave surface that roughly forms the shape of the outer circumferential raceway surface 111 may be formed on the outer circumferential surface of the blank material 300, and then in cutting step S4, the concave surface may be cut to form the outer circumferential raceway surface 111. Alternatively, the outer circumferential raceway surface 111 may be formed by polishing the concave surface instead of cutting step S4. Thus, the method of forming the outer circumferential raceway surface 111 is not particularly limited in this disclosure.

[0089] Furthermore, in the manufacturing process of Embodiment 2, the cutting process S4 is performed after the connecting hole forming process S3, but in this disclosure, it may be performed after the forging process S2 and before the connecting hole forming process S3. Also, although the cutting process S4 is performed in Embodiment 2, in this disclosure, if the material has been formed into a predetermined shape in the forging process S2, the cutting process S4 may not be performed. Moreover, in Embodiment 2, the connecting hole 320 is a female spline hole 112, so the spline forming process S5 is performed, but in this disclosure, if the connecting hole 320 is not a female spline hole 112, the spline forming process S5 may not be performed.

[0090] Furthermore, in Embodiment 2, the present disclosure is applied to the carrier 107G of the planetary gear mechanism 101, but the rotating part of the present disclosure is not limited to a carrier. For example, the rotating part may be a pulley, gear, sprocket, or motor output shaft, and is not particularly limited as long as it is a part that can transmit torque to a screw shaft. Below, a modified example 7 in which the present disclosure is applied to a driven pulley will be described.

[0091] (Modification 7) Figure 15 is a cross-sectional view of the driven pulley (rotating part) of Modification 7, cut in the axial direction. Modification 7 differs from Embodiment 2 in that the rotating part is a driven pulley 507 of a pulley. A belt (not shown) is placed on the outer circumferential surface 508 of the driven pulley 507. A first projection 41 and a boss portion 42 are formed on the first end face 513 of the driven pulley 507. A recess 540 is formed on the second end face 523 of the driven pulley 507. Therefore, similar to the carrier 107G of Embodiment 2, the material used to form the recess 540 can be utilized for the first projection 41 and the boss portion 42, thereby improving yield.

[0092] Furthermore, this disclosure may also refer to the rotating part of the following modified example 8.

[0093] (Modification 8) Figure 16 is a cross-sectional view of the carrier (rotating part) of Modification 8, cut in the axial direction. Modification 8 differs from Embodiment 2 in that the carrier (rotating part) 107H has a concave surface 40 formed on the first end face 113. That is, the first projection 41 and the boss portion 42 protrude from the concave surface 40. For this reason, similar to Embodiment 1, the carrier 107H (rotating part) is miniaturized in the axial direction.

[0094] 1 Ball screw device 2 Screw shaft 3 Nut 4 Stopper 11 Screw shaft body 20 Nut body 22 Second projection 40, 40E Concave surface 41, 41A, 41B First projection 42 Boss part 44 Bottom surface 45, 45E Wall surface 50 Projection part 51, 52 Outer peripheral surface 53 Side surface 54 Contact surface 55 Outer diameter surface 56 Back surface 57 Inner diameter surface 60, 65, 66 R part 61 First R part 62 Second R part 63 Third R part 64 Fourth R part 100 Actuator 107, 107A, 107B, 107C, 107D, 107E, 107F, 107G, 107H Carrier 113 First end surface 120 Housing 213 Second end surface 240, 540 recess 300 blank material 400 mold 507 driven pulley

Claims

1. An actuator comprising: a screw shaft having one end pointing in a first direction and the other end pointing in a second direction; a nut passing through the screw shaft; a plurality of balls positioned between the screw shaft and the nut; and a rotating part connected to the end of the screw shaft in the second direction and transmitting torque to the screw shaft, wherein the rotating part has a first end face facing the first direction; a first projection protruding from the first end face in the first direction and rotating together with the rotating part; a second end face facing the second direction; and a recess extending from the second end face in the first direction, wherein the nut has a second projection that enters the trajectory of the rotating first projection and contacts the first projection, and the first projection has a contact surface facing in the circumferential direction and contacting the second projection.

2. The actuator according to claim 1, wherein the screw shaft comprises a screw shaft body having an outer peripheral raceway surface formed on its outer peripheral surface, and a connecting portion that protrudes in the second direction from the end face of the screw shaft body in the second direction and has a smaller diameter than the screw shaft body, and the rotating part comprises a boss portion that protrudes in the first direction from the first end face and abuts against the end face of the screw shaft body in the second direction, and a connecting hole formed on the end face of the boss portion in the first direction into which the connecting portion is inserted.

3. The actuator according to claim 2, wherein the first projection is arranged on the outer circumference of the boss portion, and the boss portion and the first projection are continuous.

4. The actuator according to claim 2, wherein the first projection is arranged on the outer circumference of the boss portion, and the first projection is spaced apart from the boss portion.

5. The actuator according to any one of claims 2 to 4, wherein the rotating part has a concave surface that recesses from the first end face in a second direction, the first projection and the boss portion protrude from the concave surface in a first direction, the concave surface has a bottom surface that extends in a direction perpendicular to the central axis of the screw shaft, and a wall surface that connects the bottom surface and the first end face, and the corner where the bottom surface and the contact surface intersect is a rounded portion.

6. The actuator according to claim 5, wherein the first projection has an inner diameter surface facing radially inward, and the corner where the inner diameter surface and the bottom surface intersect is an R-shaped portion.

7. The actuator according to claim 5, wherein the concave surface extends in the circumferential direction and is annular with respect to the central axis.

8. The actuator according to claim 5, wherein the concave surface is formed only around the first projection.

9. The actuator according to claim 5, wherein the rotating part has a fleshy portion that is positioned in the first direction from the bottom surface, and the surface facing the first direction is the first end surface, the fleshy portion is positioned radially outward of the first projection, the first projection and the fleshy portion are continuous, the first projection has an outer diameter surface that faces radially outward and whose end in the second direction intersects with the first end surface, and the corner where the outer diameter surface and the first end surface intersect is an R portion.

10. A method for manufacturing an actuator comprising: a screw shaft having one end pointing in a first direction and the other end pointing in a second direction; a nut passing through the screw shaft; a plurality of balls positioned between the screw shaft and the nut; and a rotating part connected to the end of the screw shaft in the second direction and transmitting torque to the screw shaft, wherein the rotating part has a first end face facing the first direction; a first projection protruding from the first end face in the first direction and rotating together with the rotating part; a second end face facing the second direction; and a recess extending from the second end face in the first direction, wherein the nut has a second projection that enters the trajectory of the rotating first projection and contacts the first projection, and the first projection has a contact surface facing in the circumferential direction and contacting the second projection, the method for manufacturing an actuator comprising a manufacturing step for manufacturing the rotating part, wherein the manufacturing step comprises: a preparation step for preparing a blank material; and a forging step for forging the blank material after the preparation step, wherein the blank material is A method for manufacturing an actuator having a surface facing one direction in the thickness direction of the blank material and a back surface facing the opposite direction to the surface, wherein the forging process involves applying pressure to a part of the back surface of the blank material to cause a part of the blank material to protrude from the surface, thereby forming the recess on the back surface of the blank material and forming the first projection on the surface.

11. The method for manufacturing an actuator according to claim 10, wherein the screw shaft comprises a screw shaft body having an outer peripheral raceway surface formed on its outer peripheral surface, and a connecting portion having a smaller diameter than the screw shaft body and protruding in the second direction from the end face of the screw shaft body in the second direction, the rotating part comprises a boss portion protruding in the first direction from the first end face and contacting the end face of the screw shaft body in the second direction, and a connecting hole penetrating the end face of the boss portion in the first direction and the bottom surface of the recess into which the connecting portion is inserted, the forging step comprises forming the boss portion together with the first projection on the surface, and the manufacturing step comprises a connecting hole forming step of forming the connecting hole in the blank material after the forging step.

12. The method for manufacturing an actuator according to claim 10 or claim 11, wherein the manufacturing process includes a cutting step of cutting the blank material after the forging step.

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