Ball screw device and method of manufacturing the same

Abstract

The present application realizes a ball screw device capable of transmitting axial load between a threaded portion and a clamping member without causing a decrease in the service life of the ball screw device. A fitting shaft portion (10) that is disposed in abutment with the threaded portion (9) on the axial one side thereof and is externally fitted to the threaded shaft (2) without being able to rotate relative to the threaded shaft (2) and has an outer diameter smaller than that of the threaded portion (9) is externally fitted to the threaded shaft (2). A drive member (6) as the clamping member is disposed in abutment with the axial one side of the stopper (5) and clamps the stopper (5) in the axial direction between the threaded portion (9). The axial load is transmitted between the drive member (6) and the threaded portion (9) without acting on the stopper (5) as a moment.

Description

Technical Field

[0001] This invention relates to ball screw devices and their manufacturing methods. Background Technology

[0002] Ball screw mechanisms cause balls to roll between a threaded shaft and a nut, thus achieving higher efficiency compared to sliding screw mechanisms where the threaded shaft and nut are in direct contact. Therefore, ball screw mechanisms are used in various mechanical devices such as electric braking systems in automobiles, automatic manual transmissions (AMTs), and positioning devices in machine tools to convert rotary motion from drive sources such as electric motors into linear motion.

[0003] A ball screw assembly comprises: a threaded shaft with helical ball thread grooves on its outer circumferential surface; a nut with helical ball thread grooves on its inner circumferential surface; and a plurality of balls disposed between the ball thread grooves on the shaft side and the ball thread grooves on the nut side. Depending on the application, the ball screw assembly may use one of the threaded shaft and the nut as a rotary motion element, and the other as a linear motion element.

[0004] In a ball screw assembly, in order to prevent the linear motion element from moving beyond a predetermined range, an operation is performed to limit the end of the stroke of the linear motion element. Figure 22 The present invention discloses a ball screw device 100 having a conventional structure having a structure for limiting the end of the stroke of a linear motion element, as described in Japanese Patent Application Publication No. 2016-70281.

[0005] The ball screw assembly 100 includes a threaded shaft 101, a nut 102, a plurality of balls (not shown), and a stop 103.

[0006] The threaded shaft 101 has a threaded portion 104 and a mating shaft portion 105 disposed adjacent to one axial side of the threaded portion 104. The threaded portion 104 has a helical axial ball thread groove 106 on its outer peripheral surface. The mating shaft portion 105 has an outer diameter smaller than that of the threaded portion 104 and has external splines at equal intervals in the circumferential direction on its outer peripheral surface. The threaded shaft 101 is coaxially disposed with the nut 102 when the threaded portion 104 is inserted into the inside of the nut 102.

[0007] The nut 102 has a cylindrical shape and has a helical ball thread groove (not shown) and a generally S-shaped circulation groove on its inner circumferential surface. The nut 102 has a first engaging portion 107 at one end on the axial side.

[0008] The shaft-side ball thread groove 106 and the nut-side ball thread groove are arranged radially opposite to each other, forming a helical load path. The beginning and end points of the load path are connected by a circulation groove formed on the inner circumferential surface of the nut 102. Therefore, the balls reaching the end point of the load path return to the beginning point of the load path through the circulation groove. Furthermore, the beginning and end points of the load path are interchanged according to the direction of the relative axial displacement between the threaded shaft 101 and the nut 102.

[0009] The stop member 103 includes a boss portion 108 with an annular shape and a second engaging portion 109 with a protruding shape. The boss portion 108 is externally engaged with the engaging shaft portion 105 of the threaded shaft 101 without relative rotation. Specifically, the boss portion 108 is externally engaged with the external spline teeth formed on the inner peripheral surface of the boss portion 105 by engaging with the external spline teeth formed on the outer peripheral surface of the engaging shaft portion 105. The second engaging portion 109 protrudes radially from a portion of the circumferential direction of the outer peripheral surface of the boss portion 108.

[0010] In the existing ball screw assembly 100, when either the threaded shaft 101 or the nut 102 reaches the end of its stroke due to linear motion, the first engaging portion 107 provided on the nut 102 and the second engaging portion 109 provided on the stop member 103 engage in the circumferential direction. This prevents rotation of either the threaded shaft 101 or the nut 102, thus limiting the end of the stroke of the linear motion element.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2016-70281 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] In the existing ball screw device 100 disclosed in Japanese Patent Application Publication No. 2016-70281, the stop member 103 is used only to limit the end of the stroke of the linear motion element.

[0016] In recent years, the applications of ball screw devices have diversified, and the following usage methods are being explored: the stop is arranged between the threaded part and the clamping part of the drive component, etc., in an axial clamping manner, so as to transmit axial load between the threaded part and the clamping part.

[0017] However, in the existing ball screw device 100, the axial sides of the stop member 103 are respectively configured as flat surfaces. In other words, the axial side of the boss portion 108 and the axial side of the second engaging portion 109 are located on the same plane.

[0018] Therefore, for example, when an axial load is transmitted to the clamping member from one axial side of the stop 103, the entire axial side of the stop 103, including the axial side of the second engaging portion 109, contacts the clamping member. The second engaging portion 109 is only provided on a portion of the circumferential direction of the outer peripheral surface of the boss portion 108, so the contact surface of the stop 103 with respect to the clamping member has a non-rotationally symmetrical shape about the central axis of the stop 103. Therefore, there is a possibility of applying an off-center load or a moment load to the stop 103.

[0019] Specifically, such as Figure 23 As shown, when an axial load is transmitted from one side of the stop 103 to a clamping member (not shown), the load is transmitted from the central axis O of the stop 103 to one radial half of the stop 103, including the second engaging portion 109. Figure 23 The distance (torque length) L1 from the load application point A of the upper half of the stop 103 is greater than the distance from the central axis O of the stop 103 to the radial direction of the other half of the stop 103. Figure 23 The distance L2 from the load application point B on the lower half of the stop 103 is longer (L1 > L2). Therefore, when the axial load distribution is converted into a concentrated load, the line of action of the concentrated load is offset radially from the central axis O of the stop 103. As a result, the load acting on the stop 103... Figure 23 The torque in the direction indicated by the arrow X.

[0020] If a torque is applied to the stop 103, the threaded shaft 101 with the stop 103 embedded in it is prone to tilting, making it difficult to apply an equal load to the balls rolling in the load path. As a result, there is a possibility that the lifespan of the ball screw assembly 100 may be reduced.

[0021] The present invention was made to solve the above-mentioned problems, and its object is to provide a ball screw device that can transmit axial load between the threaded portion and the clamping component without reducing the life of the ball screw device.

[0022] Solution for solving the problem

[0023] One aspect of the present invention provides a ball screw device comprising a threaded shaft, a nut, a plurality of balls, a stop element, and a clamping component.

[0024] The aforementioned threaded shaft has a threaded portion having a helical axial ball thread groove on its outer peripheral surface and a fitting shaft portion adjacent to the threaded portion on one axial side, having an outer diameter smaller than the threaded portion.

[0025] The nut has a helical ball thread groove on its inner circumferential surface and a first engaging portion at one end on the axial side.

[0026] The aforementioned multiple balls are arranged between the aforementioned shaft-side ball thread groove and the aforementioned nut-side ball thread groove.

[0027] The aforementioned stop member has a boss portion that is externally fitted into the aforementioned engagement shaft portion and cannot be rotated relative to it, and a second engagement portion that protrudes radially from the outer peripheral surface of the aforementioned boss portion and can engage with the aforementioned first engagement portion in the circumferential direction.

[0028] The clamping member is disposed adjacent to the stop member on one axial side and clamps the stop member axially between the clamping member and the threaded portion.

[0029] In one embodiment of the present invention, the ball screw device transmits axial loads between the threaded portion and the clamping member via the stop member without applying torque to the stop member.

[0030] In a ball screw device according to one aspect of the present invention, the stop member can have a first contact surface on one side of the axial direction and a second contact surface on the other side of the axial direction. The first contact surface is formed by a flat surface existing on an imaginary plane orthogonal to the central axis of the stop member and has a shape that is rotationally symmetrical about the central axis of the stop member and contacts the clamping member. The second contact surface is formed by a flat surface existing on an imaginary plane orthogonal to the central axis of the stop member and has a shape that is rotationally symmetrical about the central axis of the stop member and contacts the threaded portion.

[0031] In a ball screw device according to one aspect of the present invention, the first contact surface can be formed by the side of the boss portion on one axial side, and the second contact surface can be formed by the side of the boss portion on the other axial side.

[0032] In a ball screw device according to one aspect of the present invention, the side of the second engagement portion on one axial side can be offset in an axial position relative to the side of the boss portion on one axial side, and the side of the second engagement portion on the other axial side can be offset in an axial position relative to the side of the boss portion on the other axial side.

[0033] In this case, the side of the second engaging portion on one axial side can be connected to the side of the boss portion on one axial side via a stepped portion having an arc-shaped cross-section, and the side of the second engaging portion on the other axial side can be connected to the side of the boss portion on the other axial side via a stepped portion having an arc-shaped cross-section.

[0034] Alternatively or additionally, the misalignment of the side surface of the second engaging portion relative to the side surface of the boss portion on one axial side towards the other axial side can be made equal to the misalignment of the side surface of the second engaging portion relative to the side surface of the boss portion on the other axial side towards one axial side. In other words, the side surfaces of the stop member on one axial side and the side surface of the boss portion on the other axial side can be configured to be mirror symmetrical.

[0035] In a ball screw device according to one aspect of the present invention, the axial thickness of the second engagement portion can be kept constant throughout the radial direction.

[0036] Alternatively, the axial thickness of the second engaging portion can be made smaller as it moves further outward toward the radial direction.

[0037] In a ball screw device according to one aspect of the present invention, the side of the second engaging portion that engages with the first engaging portion in the circumferential direction can be smoothly connected to the outer peripheral surface of the boss portion via a concave curved surface having an arc-shaped profile when viewed from the axial direction. Furthermore, the side of the second engaging portion that does not engage with the first engaging portion in the circumferential direction can be connected, when viewed from the axial direction, to the outer peripheral surface of the boss portion along the tangential direction of the outer peripheral surface of the boss portion.

[0038] In a ball screw device according to one aspect of the present invention, the aforementioned mating shaft portion can have a flat shape having a pair of flat outer surfaces that are parallel to each other on the outer peripheral surface, and the aforementioned boss portion can have a mating hole having a flat shape having a pair of flat inner surfaces that are parallel to each other on the inner peripheral surface.

[0039] Alternatively, the aforementioned mating shaft portion may have external splines on its outer peripheral surface, and the aforementioned boss portion may have a locking hole with internal splines on its inner peripheral surface.

[0040] In a ball screw device according to one aspect of the present invention, the stop member can be loosely inserted relative to the mating shaft portion in a manner that allows for axial relative displacement, and the clamping member can be inserted relative to the threaded shaft, such as the mating shaft portion, by pressing it in.

[0041] Alternatively, the stop member can be externally inserted relative to the mating shaft by pressing, and the clamping member can be externally inserted relative to the threaded shaft by pressing.

[0042] In one embodiment of the ball screw device of the present invention, the threaded shaft can be a rotary motion element that rotates during use, the nut can be a linear motion element that moves linearly during use, and the clamping member can be a drive member that rotates the threaded shaft or a rolling bearing that rotatably supports the threaded shaft. In this case, the drive member can be composed of any one of a gear, pulley, sprocket, or motor shaft.

[0043] Alternatively, in a ball screw device according to one aspect of the present invention, the threaded shaft can be a linear motion element that moves linearly during use, the nut can be a rotary motion element that moves rotaryly during use, and the clamping member can be a piston that moves linearly together with the threaded shaft.

[0044] A method for manufacturing a ball screw device according to one aspect of the present invention comprises the following steps: forging a raw material to form an intermediate raw material having the general shape of the stop member, and then machining the axial sides of the intermediate raw material to manufacture the stop member.

[0045] In the process of manufacturing the aforementioned stop, it is preferable to forge the aforementioned element to form the aforementioned intermediate material having the general shape of the aforementioned stop and having axially symmetrical sides, and then machine the aforementioned axially symmetrical sides of the aforementioned intermediate material to form the aforementioned first contact surface and the aforementioned second contact surface.

[0046] The effects of the invention

[0047] The ball screw device of the present invention does not exert torque on the stop member, and can transmit axial load between the threaded portion and the clamping member via the stop member. Therefore, it can transmit axial load between the threaded portion and the clamping member without reducing the life of the ball screw device. Attached Figure Description

[0048] Figure 1 This is a front view of the ball screw device of the first embodiment of the present invention, viewed from the axial direction.

[0049] Figure 2 yes Figure 1 A-A line sectional view.

[0050] Figure 3 yes Figure 2 A magnified view of a portion of the image.

[0051] Figure 4 This is a perspective view of the ball screw device in the first example, omitting the drive components.

[0052] Figure 5 This is a front view of the stop component constituting the first example of the ball screw device, viewed from the axial side.

[0053] Figure 6 yes Figure 5 Sectional view along line B-B.

[0054] Figure 7 This is a three-dimensional view of the stop component in the first example.

[0055] Figure 8 The stop in the second example is equivalent to Figure 5 of.

[0056] Figure 9 The stop in the second example is equivalent to Figure 6 The image.

[0057] Figure 10 The stop in the second example is equivalent to Figure 7 The image.

[0058] Figure 11 The stop in the third example is equivalent to Figure 5 The image.

[0059] Figure 12 The stop in the third example is equivalent to Figure 6 The image.

[0060] Figure 13 The stop in the third example is equivalent to Figure 7 The image.

[0061] Figure 14 (A) is equivalent to the ball screw device in the fourth example. Figure 4 The picture, Figure 14 (B) is the equivalent of the ball screw device in the fourth variation. Figure 4 The image.

[0062] Figure 15 It is equivalent to the stop of the ball screw device constituting the fourth example. Figure 7 The image.

[0063] Figure 16 (A) is equivalent to the ball screw device in the fifth example. Figure 4 The picture, Figure 16 (B) is the ball screw device of the fifth variation, equivalent to Figure 4 The image.

[0064] Figure 17 It is equivalent to the stop of the ball screw device constituting the fifth example. Figure 7 The image.

[0065] Figure 18It is equivalent to the stop of the ball screw device constituting the sixth example. Figure 2 The image.

[0066] Figure 19 The stop in the sixth example is equivalent to Figure 3 The image.

[0067] Figure 20 It is equivalent to the stop of the ball screw device constituting the seventh example. Figure 2 The image.

[0068] Figure 21 The stop in the seventh example is equivalent to Figure 3 The image.

[0069] Figure 22 This is a perspective view of an existing ball screw device.

[0070] Figure 23 This is a cross-sectional view of the stop component constituting the ball screw device, shown to illustrate the problem of the existing ball screw device structure. Detailed Implementation

[0071] [First example]

[0072] use Figures 1 to 7 The first example of an embodiment of the present invention will be described below.

[0073] [Overall structure of the ball screw assembly]

[0074] In this example, the ball screw device 1 is installed in an electric brake booster device to convert the rotary motion of the electric motor, which is the drive source, into linear motion, thereby actuating the piston of the hydraulic cylinder.

[0075] The ball screw assembly 1 includes a threaded shaft 2, a nut 3, multiple balls 4, a stop 5, and a drive component 6, which acts as a clamping component. In this example, the threaded shaft 2 constitutes a rotary motion element that rotates during use, and the nut 3 constitutes a linear motion element that moves linearly during use. That is, the ball screw assembly 1 in this example is used in a manner that drives the threaded shaft 2 to rotate, causing the nut 3 to move linearly.

[0076] The threaded shaft 2 is inserted into the inside of the nut 3 and is coaxially arranged with the nut 3. A helical load path 7 is provided between the outer circumferential surface of the threaded shaft 2 and the inner circumferential surface of the nut 3. A plurality of balls 4 are rotatably arranged in the load path 7. When the threaded shaft 2 and the nut 3 are rotated relative to each other, the balls 4 that have reached the end of the load path 7 pass through the circulation groove 8 formed on the inner circumferential surface of the nut 3 and return to the beginning of the load path 7. The structure of each component of the ball screw device 1 will be described below.

[0077] In the following description, unless otherwise specified, axial, radial, and circumferential directions refer to the axial, radial, and circumferential directions related to the threaded shaft. Additionally, axial side refers to... Figure 2 , Figure 3 as well as Figure 6 The right side Figure 4 The left side, the other side of the axis refers to Figure 2 , Figure 3 as well as Figure 6 left side Figure 4 On the right side.

[0078] <Threaded Shaft>

[0079] The threaded shaft 2 is made of metal and has a threaded portion 9 and a mating shaft portion 10 adjacent to the threaded portion 9 on one axial side. The threaded portion 9 and the mating shaft portion 10 are coaxially arranged and constitute a single unit. The mating shaft portion 10 has an outer diameter smaller than that of the threaded portion 9. Therefore, the threaded shaft 2 has a stepped surface 11 facing one axial side between the threaded portion 9 and the mating shaft portion 10. In the illustrated example, the stepped surface 11 is formed by a flat surface on the axial side of the threaded portion 9, that is, on an imaginary plane orthogonal to the central axis of the threaded shaft 2.

[0080] The threaded portion 9 has a helical axial ball thread groove 12 on its outer peripheral surface. The axial ball thread groove 12 is formed by grinding, cutting, or rolling the outer peripheral surface of the threaded portion 9. In this example, the number of axial ball thread grooves 12 is set to one. The axial ball thread groove 12 has a Gothic arch or arc-shaped groove shape.

[0081] The mating shaft portion 10 has a plurality of external spline teeth 13 on its outer peripheral surface. The external spline teeth 13 are arranged at equal intervals in the circumferential direction on the outer peripheral surface of the mating shaft portion 10. That is, the mating shaft portion 10 is composed of a spline shaft portion. In the illustrated example, each external spline tooth 13 is composed of involute spline teeth, but it can also be composed of square spline teeth or serrations.

[0082] With the threaded portion 9 inserted into the inside of the nut 3, the threaded shaft 2 is coaxially arranged with the nut 3. In this example, the threaded shaft 2 is composed of the threaded portion 9 and the fitting shaft portion 10. However, in the implementation of the present invention, the threaded shaft may also include a second fitting shaft portion for fixing a rolling bearing or the like that is rotatably supported relative to the housing or the like.

[0083] <Nut>

[0084] Nut 3 is made of metal and has an overall cylindrical shape. Nut 3 has a helical ball thread groove 14 and a circulation groove 8 on its inner circumferential surface.

[0085] The nut-side ball thread groove 14 has a helical shape. The nut-side ball thread groove 14 is formed by performing processes such as grinding, cutting, tap rolling, or tap grinding on the inner circumferential surface of the nut 3. The nut-side ball thread groove 14 has the same pitch as the shaft-side ball thread groove 12. Therefore, with the threaded portion 9 of the threaded shaft 2 inserted into the inner side of the nut 3, the shaft-side ball thread groove 12 and the nut-side ball thread groove 14 are arranged radially opposite each other, forming a helical load path 7. The number of nut-side ball thread grooves 14 is the same as that of the shaft-side ball thread groove 12, which is one. The nut-side ball thread groove 14, like the shaft-side ball thread groove 12, has a Gothic arched or arc-shaped groove shape.

[0086] The circulation groove 8 has a generally S-shaped form. The circulation groove 8 is formed on the inner circumferential surface of the nut 3 by, for example, cold forging. The circulation groove 8 smoothly connects the axially adjacent portions of the ball thread grooves 14 on the nut side, connecting the start and end points of the load path 7. Therefore, the ball 4 that has reached the end point of the load path 7 returns to the start point of the load path 7 via the circulation groove 8. Furthermore, the start and end points of the load path 7 are interchanged according to the direction of the axial relative displacement between the thread shaft 2 and the nut 3; in other words, according to the relative rotational direction between the thread shaft 2 and the nut 3.

[0087] The circulation groove 8 has a generally semi-circular cross-sectional shape. The circulation groove 8 has a groove width slightly larger than the diameter of the ball 4, and a groove depth that allows the ball 4 moving in the circulation groove 8 to pass over the thread teeth of the axial ball thread groove 12.

[0088] The nut 3 has a first engaging portion 15 at one end on the axial side. The first engaging portion 15 is located on a circumferential portion of the axial end of the nut 3, protruding from the cylindrical main body towards the axial side. The first engaging portion 15 has a fan-shaped profile and an axial protrusion approximately the same size as the axial thickness of the stop 5. The first engaging portion 15 is located on the circumferential side... Figure 4 The left side of the nut 3 has a flat first stop surface 16. The first stop surface 16 is arranged substantially parallel to the central axis of the nut 3. In the illustrated example, the nut 3 includes a first engaging portion 15 integrally formed. However, in implementing the present invention, it is also possible to fix a cylindrical main body portion having a nut-side ball thread groove on its inner circumferential surface and a first engaging portion separately formed from the main body portion relative to the main body portion.

[0089] In this example, the ball screw device 1 uses the nut 3 as a linear motion element. Therefore, in this example, the nut 3 is prevented from rotating by an anti-rotation mechanism (not shown). As the anti-rotation mechanism, various known structures can be adopted. For example, a structure in which a protrusion (key) provided on the inner circumferential surface of a fixed component such as a housing engages with a groove 50 formed axially on the outer circumferential surface of the nut 3.

[0090] <ball bearing>

[0091] The ball 4 is a steel ball with a predetermined diameter, which is rolled in the load path 7 and the circulation groove 8. The ball 4 arranged in the load path 7 rolls while bearing a compressive load, while the ball 4 arranged in the circulation groove 8 does not bear a compressive load and is pushed by the subsequent ball 4 to roll.

[0092] <Stop>

[0093] The stop 5 is made of metal and has an overall shape roughly like the number 6. In this example, the stop 5 not only functions to limit the end of the stroke of the nut 3, which is a linear motion element, but also functions to transmit axial load between the threaded portion 9 and the drive component 6 located on both sides of the axial direction.

[0094] The stop member 5 has a boss portion 17 with an annular shape and a second engaging portion 18 with a protruding shape.

[0095] The boss portion 17 is externally fitted to the mating shaft portion 10 of the threaded shaft 2 without relative rotation. The boss portion 17 has a locking hole 19 at its radial center, through which the mating shaft portion 10 can be inserted axially. In this example, the locking hole 19 has a plurality of internal spline teeth 20 on its inner circumferential surface. The internal spline teeth 20 are arranged at equal intervals in the circumferential direction on the inner circumferential surface of the locking hole 19. That is, the locking hole 19 is formed by a spline hole. By spline-fitting the mating shaft portion 10 into the locking hole 19, the boss portion 17 is externally fitted to the mating shaft portion 10 without relative rotation. In this example, the boss portion 17 is loosely spline-fitted relative to the mating shaft portion 10 with axial relative displacement, but the boss portion 17 can also be spline-fitted relative to the mating shaft portion 10 in a press-in state. The axial thickness of the boss portion 17 is sufficiently smaller than the axial dimension of the mating shaft portion 10.

[0096] The boss portion 17 has a cylindrical outer peripheral surface and an outer diameter that is approximately the same size as the outer diameter of the stepped surface 11 provided on the threaded shaft 2.

[0097] The second engaging portion 18 is provided on a portion of the outer peripheral surface of the boss portion 17 in the circumferential direction and protrudes radially outward. The outer peripheral surface of the second engaging portion 18 is configured as a partially cylindrical surface and has an circumferential circle diameter that is approximately the same size as the outer diameter of the nut 3.

[0098] The second engaging part 18 is on the side of the other side in the circumferential direction ( Figure 5 The right side of the nut 3 has a flat second stop surface 21. The second stop surface 21 contacts the first stop surface 16 when the nut 3 has moved relative to the threaded shaft 2 in one axial direction and reached the end of its stroke. Therefore, in this example, the second stop surface 21 is arranged approximately parallel to the central axis of the stop 5. In this example, the side of the second engaging portion 18 in the other circumferential direction, i.e., the second stop surface 21, corresponds to the side of the first engaging portion 15 that engages in the circumferential direction, and the side of the second engaging portion 18 in one circumferential direction corresponds to the side of the first engaging portion 15 that does not engage in the circumferential direction.

[0099] The outer peripheral surfaces of the second stop surface 21 and the boss portion 17 are smoothly connected via a concave surface 53 having an arc-shaped profile when viewed from the axial direction. The radius of curvature R of the concave surface 53 is set to be as large as possible within the range of satisfying the following first and second conditions. The first condition is that the radial dimension L21 of the second stop surface 21 is larger than the radial dimension L16 of the first stop surface 16 (L21 > L16). The second condition is that the difference between the radial dimension L21 of the second stop surface 21 and the radial dimension L16 of the first stop surface 16 (L21 - L16) is more than 1 / 10 of the radial dimension L16 of the first stop surface 16 (L21 - L16 ≥ 1 / 10 × L16). In this example, the radius of curvature R of the concave surface 53 is set in such a way that the first and second conditions are satisfied. Specifically, the radius of curvature R of the concave surface 53 is preferably more than 1 / 5 and less than 1 / 2 of the diameter D of the boss portion 17. In the example shown, the radius of curvature R of the concave surface 53 is about 1 / 3 of the diameter D of the boss portion 17.

[0100] The side of the second engaging part 18 in the circumferential direction ( Figure 5 The left side of the second engaging portion 18 is configured as a flat surface, extending along the tangential direction of the outer peripheral surface of the boss portion 17. Therefore, the circumferential side of the second engaging portion 18, when viewed axially, is connected to the outer peripheral surface of the boss portion 17 in the tangential direction of the outer peripheral surface of the boss portion 17. Therefore, the second engaging portion 18 has a tapered shape whose width decreases from the radially inward side towards the radially outward side in the circumferential direction; in other words, when viewed axially, it has a generally trapezoidal end face shape.

[0101] Furthermore, in implementing this invention, if the circumferential side of the second engaging portion is smoothly connected to the outer peripheral surface of the boss portion—that is, when viewed axially, the tangent line of the circumferential side of the second engaging portion at the connection point with the outer peripheral surface of the boss portion and the tangent line of the outer peripheral surface of the boss portion at the connection point with the circumferential side of the second engaging portion exist on the same straight line—then it is not necessary to form a flat surface. For example, the circumferential side of the second engaging portion can also be formed by a convex surface having a radius of curvature larger than that of the outer peripheral surface of the boss portion.

[0102] The axial thickness of the second engaging portion 18 is constant throughout the radial direction and is smaller than the axial thickness of the boss portion 17. Therefore, the axial side 18x of the second engaging portion 18 is offset axially to the opposite side relative to the axial side 17x of the boss portion 17, and the axial side 18y of the second engaging portion 18 is offset axially to one side relative to the axial side 17y of the boss portion 17. In other words, the axial side 17x of the boss portion 17 protrudes axially more than the axial side 18x of the second engaging portion 18, and the axial side 17y of the boss portion 17 protrudes axially more than the axial side 18y of the second engaging portion 18.

[0103] Therefore, the two axial sides of the stop 5 are not flat surfaces, but rather stepped. The axial side 17x of the boss 17 and the axial side 18x of the second engaging portion 18 are connected via a stepped portion 54x with an arc-shaped cross-section. The axial side 17y of the boss 17 and the axial side 18y of the second engaging portion 18 are connected via a stepped portion 54y with an arc-shaped cross-section. In this example, the radii of curvature of each of the stepped portions 54x and 54y are set to approximately 1 / 25 to 1 / 2 times the axial dimension T of the stop 5, preferably approximately 1 / 10 to 1 / 3 times.

[0104] In this example, the misalignment (offset, height of the step) t1 of the side 18x on one axial side of the second engaging portion 18 relative to the side 17x on one axial side of the boss portion 17 and the misalignment t2 of the side 18y on the other axial side of the second engaging portion 18 relative to the side 17y on the other axial side of the boss portion 17 are the same (t1 = t2). In other words, the side 18x on one axial side and the side 17y on the other axial side of the stop 5 are configured to be mirror symmetrical. As a result, by contacting the second engaging portion 18 with the first engaging portion 15, even if the second engaging portion 18 is deformed, interference between the second engaging portion 18 and the nut 3 and the drive component 6 can be prevented, and the installation state of the stop 5 can be stabilized.

[0105] In this example, the misalignment amounts t1 and t2 of the axial sides 18x and 18y of the second engaging portion 18 are set to approximately 1 / 20 to 1 / 5 of the axial dimension T of the stop 5, preferably a small value of approximately 1 / 15 to 1 / 8. In the illustrated example, the axial dimension T of the stop 5 is set to 5 mm, and the misalignment amounts t1 and t2 of the axial sides 18x and 18y of the second engaging portion 18 are each set to 0.5 mm.

[0106] In this example, the side 17x of the annular boss portion 17, which protrudes axially from one side of the axial side of the stop 5 compared to the side 18x of the second engaging portion 18, serves as the first contact surface 22 that contacts the annular surface 28 of the drive member 6, described later. The side 17y of the annular boss portion 17, which protrudes axially from the other side of the axial side of the stop 5 compared to the side 18y of the second engaging portion 18, serves as the second contact surface 23 that contacts the stepped surface 11 of the threaded portion 9.

[0107] The first contact surface 22 is formed by a flat surface existing on an imaginary plane orthogonal to the central axis of the stop 5, and has a shape that is rotationally symmetrical about the central axis of the stop 5. Specifically, the first contact surface 22 is n-fold symmetrical (n is the number of internal splines formed on the inner circumferential surface of the engagement hole 19).

[0108] The second contact surface 23 is composed of a flat surface existing on an imaginary plane orthogonal to the central axis of the stop 5, and has a shape that is rotationally symmetrical about the central axis of the stop 5. Specifically, the second contact surface 23 is n-fold symmetrical (n is the number of internal splines formed on the inner circumferential surface of the engagement hole 19).

[0109] In this example, the first contact surface 22 and the second contact surface 23 each have a circular outer periphery and a concave-convex inner periphery, and they are of the same shape and size. The stop 5 in this example is symmetrical about the axial direction. Figure 6 It has a shape that is symmetrical from left to right.

[0110] The stop 5 described above can be manufactured as follows: First, a metal raw material, for example, having a cylindrical shape, is subjected to multi-stage forging, such as cold forging, to gradually plastically deform the shape of the raw material into the approximate shape of the stop 5, thereby manufacturing an intermediate raw material having the approximate shape of the stop 5. That is, by casting the raw material, an intermediate raw material is obtained having an annular boss portion with multiple internal splines on its inner circumferential surface and a protruding second engaging portion. Then, the axial sides of the boss portion, which become the first contact surface 22 and the second contact surface 23 on the axial sides of the intermediate raw material, are respectively subjected to machining such as cutting and grinding. This improves the flatness of the axial sides of the boss portion, forming the first contact surface 22 and the second contact surface 23 on the axial sides of the boss portion. Then, the stop 5 is obtained as a finished product. The axial sides of the second engaging portion can be used directly in the forging state. However, the axial sides of the second engaging portion can also be machined such as cutting and grinding.

[0111] If the misalignment amount t1 of the axial side surface 18x of the second engaging portion 18 relative to the axial side surface 17x of the boss portion 17 and the misalignment amount t2 of the axial side surface 18y of the second engaging portion 18 relative to the axial side surface 17y of the boss portion 17 are misaligned in one direction relative to the other direction of the boss portion 17, the material flow is prone to deviation during forging. If at least one of the misalignment amounts t1 and t2 is set to a large value, the amount of material elongation (collapse) during forging increases, stress concentration occurs in the axial direction, and cracks are prone to form at the boundary between the second engaging portion 18 and the boss portion 17. If, as in this example, the misalignment amounts t1 and t2 of the axial side surfaces 18x and 18y of the second engaging portion 18 relative to the axial dimension T of the stop member 5 are set to a small value, crack formation can be prevented.

[0112] However, in implementing the present invention, as long as cracks can be prevented, the misalignment of the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion relative to the side of the boss relative to the side of the second engaging portion can be made different.

[0113] <Drive Components>

[0114] The drive component 6 is a gear, pulley, or other component that drives the threaded shaft 2 to rotate by transmitting torque input from a drive source such as an electric motor. The drive component 6 is disposed adjacent to the stop 5 on one axial side and clamps the stop 5 axially between the drive component 6 and the threaded portion 9.

[0115] The drive component 6 has a circular plate portion 24 and a cylindrical portion 25.

[0116] The circular plate portion 24 has a mounting hole 26 extending axially through its radial center. The mounting hole 26 has a plurality of internal spline teeth 27 on its inner circumferential surface. The internal spline teeth 27 are arranged at equal intervals along the circumferential direction of the inner circumferential surface of the mounting hole 26. That is, the mounting hole 26 is formed by a spline hole. By engaging a portion of the spline in the fitting shaft portion 10 that separates axially from the portion with the externally fitted stop 5 into the mounting hole 26, the circular plate portion 24 is externally fitted relative to the fitting shaft portion 10 without relative rotation. In this example, the fitting shaft portion 10 is engaged in the mounting hole 26 of the circular plate portion 24 by pressing in the spline. However, it is also possible to prevent axial displacement of the drive component relative to the threaded shaft by loosely engaging the spline in the mounting hole of the drive component, and by threading a stop nut or locking stop ring onto the portion of the fitting shaft portion that protrudes axially from the circular plate portion of the drive component. The circular plate portion 24 has a radially inner portion on the side of the opposite axial direction with an annular surface 28. The annular surface 28 is composed of a flat surface existing on an imaginary plane orthogonal to the central axis of the drive member 6.

[0117] The cylindrical portion 25 extends axially from the radially outer portion of the side of the circular plate portion 24 on the opposite side. The cylindrical portion 25 has an inner diameter slightly larger than the outer diameter of the nut 3. The cylindrical portion 25 covers the periphery of the end of the stop 5 and the threaded portion 9 on one side of the axial direction.

[0118] Teeth can also be formed on the outer peripheral surface of the circular plate portion 24 or the cylindrical portion 25, or belt components can also be mounted thereon.

[0119] The drive member 6 is externally fixed to the fitting shaft portion 10 at a position adjacent to the axial side of the stop member 5, thereby clamping the stop member 5 axially between the drive member 6 and the threaded portion 9. This causes the annular surface 28 of the circular plate portion 24 constituting the drive member 6 to make full circumferential contact with the first contact surface 22 formed by the axial side surface 17x of the boss portion 17 on the axial side of the stop member 5. Furthermore, the stepped surface 11 of the threaded portion 9 makes full circumferential contact with the second contact surface 23 formed by the axial side surface 17y of the boss portion 17 on the other axial side of the stop member 5. In this state, a gap is formed between the axial side surface of the circular plate portion 24 and the axial side surface 18x of the second engaging portion 18 of the stop member 5. Moreover, the axial side surface 18y of the second engaging portion 18 is positioned axially closer than the stepped surface 11.

[0120] <Instructions for the Operation of the Ball Screw Mechanism>

[0121] In this example, the ball screw device 1 drives the threaded shaft 2 via a drive source (not shown) through the drive component 6 to rotate, thereby causing the nut 3 to move linearly.

[0122] By driving the threaded shaft 2 to rotate in a predetermined direction, when the nut 3 moves relative to the threaded shaft 2 in one axial direction and reaches the end of its stroke, the first stop surface 16 of the first engaging portion 15 of the nut 3 and the second stop surface 21 of the second engaging portion 18 of the stop 5 engage in the circumferential direction. In this example, the first stop surface 16 and the second stop surface 21 are in surface contact. Therefore, rotation of the threaded shaft 2 in the predetermined direction is prevented. Thus, the ball screw device 1 in this example can limit the end of the stroke of the nut 3 relative to the threaded shaft 2 in one axial direction by means of the stop 5. Furthermore, the end of the stroke of the nut 3 relative to the threaded shaft 2 in the other axial direction can be limited using various known stroke limiting mechanisms.

[0123] In this example, the ball screw device 1 transmits axial load between the threaded portion 9 and the drive member 6 via the stop member 5. For example, when the nut 3 moves relative to the threaded shaft 2 to the axial side by rotating the threaded shaft 2 in the opposite direction to the predetermined direction, an axial load (reaction force) is applied to the threaded shaft 2 in the axial direction via the balls 4 arranged in the load path 7. In this example, the axial load acting on the threaded shaft 2 in the axial direction can be transmitted from the stepped surface 11 of the threaded portion 9 to the second contact surface 23 of the stop member 5, and then from the first contact surface 22 of the stop member 5 to the annular surface 28 of the circular plate portion 24 constituting the drive member 6, supporting the drive member 6. Conversely, even if an axial load acts on the drive member 6 in the axial direction, it can be transmitted from the annular surface 28 of the circular plate portion 24 to the first contact surface 22 of the stop member 5, and then from the second contact surface 23 of the stop member 5 to the stepped surface 11 of the threaded portion 9.

[0124] According to the ball screw device 1 in the example above, axial load can be transmitted between the threaded portion 9 and the drive component 6 without reducing the lifespan of the ball screw device 1.

[0125] In this example, the first contact surface 22 and the second contact surface 23 are each composed of flat surfaces existing on an imaginary plane orthogonal to the central axis of the stop 5, and have a shape that is rotationally symmetrical about the central axis of the stop 5. Therefore, the magnitude of the load acting on the second contact surface 23 and the distance L of the load application point (load input point) from the central axis of the stop 5 are equal on both sides located on opposite sides of the central axis of the stop 5, i.e., the parts with a phase difference of 180 degrees. Further, as Figure 6 As shown, the distance L from the central axis of the stop 5 to the magnitude of the load acting on the first contact surface 22 and the load application point (load input point) is also equal on both sides of the central axis O of the stop 5, i.e., the parts with a phase difference of 180 degrees. Therefore, according to the ball screw device 1 of this example, when the axial load distribution is changed to a concentrated load, the line of action of the concentrated load can be located on the central axis O of the stop 5.

[0126] Therefore, according to the ball screw assembly 1 of this example, axial load can be transmitted between the threaded portion 9 and the drive component 6 via the stop member 5 without applying torque to the stop member 5. Thus, tilting of the threaded shaft 2 with the stop member 5 externally embedded can be prevented, and uneven application of load to the balls 4 rolling in the load path 7 can be suppressed. As a result, axial load can be transmitted between the threaded portion 9 and the drive component 6 without reducing the lifespan of the ball screw assembly 1.

[0127] In the ball screw device 1 of this example, when the first engaging portion 15 provided with the nut 3 and the second engaging portion 18 provided with the stop member 5 engage in the circumferential direction, i.e., collide, stress concentration at the stop member 5 can be effectively prevented. That is, in this example, the stop member 5 smoothly connects the second stop member surface 21 of the second engaging portion 18 and the outer peripheral surface of the boss portion 17 via a concave curved surface 53 having an arc-shaped profile when viewed from the axial direction. Furthermore, the side of the second engaging portion 18 that does not engage with the first engaging portion 15 in the circumferential direction is connected in the tangential direction of the outer peripheral surface of the boss portion 17 when viewed from the axial direction. Therefore, stress concentration at the connection between the base end portions on both sides of the second engaging portion 18 and the outer peripheral surface of the boss portion 17 can be prevented. Furthermore, in this example, the stop 5 connects the side surface 17x on one axial side of the boss portion 17 and the side surface 18x on one axial side of the engaging portion 18 via a stepped portion 54x having an arcuate cross-sectional shape, and connects the side surface 17y on the other axial side of the boss portion 17 and the side surface 18y on the other axial side of the engaging portion 18 via a stepped portion 54y having an arcuate cross-sectional shape. Additionally, the stop 5 has a shape that is symmetrical about the axial direction. Therefore, stress concentration can be prevented at the connection between the base end portions on both axial sides of the second engaging portion 18 and the boss portion 17.

[0128] In this example, as described above, when the first engaging portion 15 provided on the nut 3 and the second engaging portion 18 provided on the stop 5 engage in the circumferential direction, stress concentration in the stop 5 can be effectively prevented, thus preventing local deformation of the stop 5. Therefore, even when axial loads are transmitted from the threaded portion 9 to the drive member 6 via the stop 5 based on the inertial force of the ball 4 and the inertial torque of the electric motor that drives the rotary drive member 6, the distance (torque length) from the central axis of the stop 5 to the load application point (load input point) of the axial load remains unchanged, thus no torque is applied to the stop 5. Therefore, from this perspective, the reduction in the lifespan of the ball screw assembly 1 can also be suppressed.

[0129] In this example, the stop 5 can be manufactured by forging a metal raw material to produce an intermediate material with the approximate shape of the stop 5, and then machining such as cutting and grinding is performed on the axial sides of the boss portion that forms the first contact surface 22 and the second contact surface 23. Therefore, the manufacturing cost of the stop 5 can be suppressed, and the cost of the ball screw device 1 can be reduced.

[0130] [Second Example]

[0131] use Figures 8-10 A second example of an embodiment of the present invention will now be described.

[0132] In this example, only the structure of the second engaging part 18a constituting the stop 5a is changed from the structure of the first example.

[0133] Specifically, the axial thickness of the second engaging portion 18a is made smaller as it moves further outward. To achieve this, the side 18x on one axial side of the second engaging portion 18a is inclined in a direction that moves further outward and towards the other axial side, and the side 18y on the other axial side of the second engaging portion 18a is inclined in a direction that moves further outward and towards one axial side.

[0134] like Figure 9 As shown, in this example, the inclination angle α of the side surface 18x on one axial side of the second engaging portion 18a relative to the central axis O of the stop member 5a and the inclination angle β of the side surface 18y on the other axial side of the second engaging portion 18a relative to the central axis O of the stop member 5a are the same (α = β). However, in implementing the present invention, it is also possible to make the inclination angle of the side surface on one axial side of the second engaging portion relative to the central axis of the stop member and the inclination angle of the side surface on the other axial side of the second engaging portion relative to the central axis of the stop member different from each other. In any case, by rotating the threaded shaft 2 in a predetermined direction, when the nut 3 moves to the end of its stroke relative to the threaded shaft 2 on one axial side, a gap is formed between the side surface 18x on one axial side of the second engaging portion 18a and the side surface on the other axial side of the circular plate portion 24, and the side surface 18y on the other axial side of the second engaging portion 18a is positioned on one axial side closer to the stepped surface 11.

[0135] In this example, the two axial sides of the stop 5a are bent rather than stepped. That is, the axial side 17x of the boss portion 17 constituting the first contact surface 22 and the axial side 18x of the second engaging portion 18a are directly connected without a stepped portion. Similarly, the axial side 17y of the boss portion 17 constituting the second contact surface 23 and the axial side 18y of the second engaging portion 18a are directly connected without a stepped portion. In other words, in this example, the axial side 18x of the second engaging portion 18a is directly connected to the axial side 17x of the boss portion 17 without offsetting its axial position, and the axial side 18y of the second engaging portion 18a is directly connected to the axial side 17y of the boss portion 17 without offsetting its axial position. Furthermore, in this example, the stop 5a also has symmetrical characteristics with respect to the axial direction (…). Figure 9 It has a shape that is symmetrical from left to right.

[0136] In this example, the axial sides of the stop 5a are bent rather than stepped, thus minimizing the stamping load during forging and reducing the stress applied to the forging die. This reduces the manufacturing cost of the stop 5a. Other structural features and effects are the same as in the first example.

[0137] [Third Case]

[0138] use Figures 11-13 A third example of an embodiment of the present invention will now be described.

[0139] In this example, only the construction of the second engaging portion 18b constituting the stop 5b is different from that in the first and second examples.

[0140] Specifically, the axial thickness of the second engaging portion 18b is made smaller towards the radially outward direction, similar to the construction in the second example. Furthermore, the side surfaces 18x and 18y on both axial sides of the second engaging portion 18b are offset axially relative to the side surfaces 17x and 17y on both axial sides of the boss portion 17. Therefore, the side surface 17x on one axial side of the boss portion 17 constituting the first contact surface 22 and the side surface 18x on one axial side of the second engaging portion 18b are not directly connected, but are connected via a stepped portion 54x with an arc-shaped cross-section. Similarly, the side surface 17y on the other axial side of the boss portion 17 constituting the second contact surface 23 and the side surface 18y on the other axial side of the second engaging portion 18b are not directly connected, but are connected via a stepped portion 54y with an arc-shaped cross-section. In this example, the misalignment (offset, step height) t1 of the side 18x on one axial side of the second engaging portion 18b relative to the side 17x on one axial side of the boss portion 17 towards the other axial side, and the misalignment t2 of the side 18y on the other axial side of the second engaging portion 18b relative to the side 17y on the other axial side of the boss portion 17 towards one axial side, are the same (t1 = t2). Furthermore, the stop 5b is symmetrical about the axial direction ( Figure 12 The shape is symmetrical (left and right).

[0141] In this example, the outlines of the first contact surface 22 and the second contact surface 23 on the axial sides of the boss portion 17 can be clearly defined. In other words, the boundaries between the outer periphery of the first contact surface 22 and the second contact surface 23 and the axial sides 18x and 18y of the second engaging portion 18b can be clearly defined. Therefore, compared to the construction of the second embodiment, it is possible to effectively prevent the axial sides 18x and 18y of the second engaging portion 18b from contacting the annular surface 28 of the drive member 6 (see reference). Figure 3 ) and the stepped surface 11 of the threaded portion 9 (refer to Figure 3Contact. Other structures and effects are the same as in the first and second examples.

[0142] [Fourth Case]

[0143] use Figure 14 (A) Figure 14 (B) and Figure 15 A fourth example of an embodiment of the present invention will be described.

[0144] In this example, the fixing structure of the boss portion 17a of the stop member 5c relative to the fitting shaft portion 10a of the threaded shaft 2 is changed from the structure of the first example.

[0145] Specifically, the fitting shaft portion 10a is constructed of a flat shape with an oblong (elliptical) cross-section and a pair of parallel flat outer surfaces 29 on its outer circumferential surface. Furthermore, the engaging hole 19a of the boss portion 17a is constructed of a flat shape with an oblong (elliptical) hole and a pair of parallel flat inner surfaces 30 on its inner circumferential surface.

[0146] In this example, with the threaded shaft 2's fitting shaft portion 10a loosely inserted into the inner side of the stop member 5c's engagement hole 19a, each of the pair of flat inner surfaces 30 provided on the inner circumferential surface of the engagement hole 19a and each of the pair of flat outer surfaces 29 provided on the outer circumferential surface of the fitting shaft portion 10a engage, i.e., make surface contact. This results in a non-circular fit of the stop member 5c relative to the fitting shaft portion 10a, preventing relative rotation. Furthermore, the boss portion 17a constituting the stop member 5c can also be non-circularly fitted relative to the fitting shaft portion 10a in a press-in state.

[0147] The threaded shaft 2 also includes a second fitting shaft portion 31 on one axial side of the fitting shaft portion 10a, for externally fitting a clamping member (not shown), such as a drive member 6, a rolling bearing, etc., that cannot be rotated relative to it. For example, as Figure 14 As shown in (A), the second fitting shaft portion 31 can be configured as a flat portion having an oblong cross-section at one end on one axial side and a pair of parallel flat outer surfaces 51 on its outer peripheral surface. As a variation of the fourth example, it is also possible to... Figure 14 As shown in (B), the second fitting shaft portion 31 is configured such that the end on one side of the axial direction has a spline shaft portion with external spline teeth 52 on the outer peripheral surface. In any case, the aforementioned clamping member, which is externally fitted with the second fitting shaft portion 31 without relative rotation, can prevent the stop member 5c from disengaging from the fitting shaft portion 10a to one side of the axial direction.

[0148] In this example, compared to the case of forming spline teeth, the outer shape of the mating shaft portion 10a and the inner surface shape of the engagement hole 19a can be simplified. Therefore, processing costs and manufacturing costs can be reduced. Furthermore, compared to the structure in the first example, the mating length is easier to ensure, thus reducing the axial thickness of the stop member 5c. Therefore, the ball screw assembly 1 (refer to...) can be simplified. Figure 2 Miniaturization of axial dimensions.

[0149] The other structures and effects are the same as in the first example.

[0150] Furthermore, in the fourth example described above, the following structure was explained: a second fitting shaft portion 31 with a different cross-sectional shape than the fitting shaft portion 10a is provided on one axial side of the fitting shaft portion 10a, and the clamping member is externally fitted relative to the second fitting shaft portion 31 without relative rotation. However, as another variation of the fourth example, the following structure can also be adopted: the axial length of the fitting shaft portion 10a, which has a flat shape with a pair of flat outer surfaces 29 on its outer peripheral surface, is extended, and the clamping member, which has a flat-shaped mounting hole with a pair of flat inner surfaces on its inner peripheral surface, is externally fitted in the fitting shaft portion 10a, which protrudes from the stop member 5c toward one axial side, without relative rotation.

[0151] [Fifth Case]

[0152] use Figure 16 (A) Figure 16 (B) and Figure 17 The fifth example of an embodiment of the present invention will now be described.

[0153] In this example, the fixing structure of the boss portion 17b of the stop member 5d relative to the fitting shaft portion 10b of the threaded shaft 2 is different from the structures in the first and fourth examples.

[0154] Specifically, the fitting shaft portion 10b is constructed by forming multiple (three in the illustrated example) axially elongating engaging grooves 32 at various locations along the circumference of the cylindrical outer circumferential surface. The multiple engaging grooves 32 are arranged at equal intervals in the circumferential direction.

[0155] Furthermore, the engagement holes 19b of the boss portion 17b are formed by forming engagement claw portions 33 protruding radially inward at multiple locations (three locations in the illustrated example) in the circumferential direction on the cylindrical inner circumferential surface. The multiple engagement claw portions 33 are arranged at equal intervals in the circumferential direction.

[0156] In this example, with the threaded shaft 2's mating shaft portion 10b loosely inserted into the engagement hole 19b of the boss portion 17b, each of the plurality of engagement claw portions 33 engages (key engagement) with each of the plurality of engagement grooves 32. This results in a non-circular engagement of the stop member 5d relative to the mating shaft portion 10b, preventing relative rotation. Furthermore, the boss portion 17b constituting the stop member 5d can also be non-circularly engaged with the mating shaft portion 10b in a press-in state.

[0157] In this example, the threaded shaft 2 also has a second fitting shaft portion 31 on one axial side of the fitting shaft portion 10b for non-rotatably fitting a clamping member (not shown), such as the drive member 6 or a rolling bearing. Similar to the fourth example, the second fitting shaft portion 31 can be, for example, made of... Figure 16 (A) Figure 16 The structure shown in (B)

[0158] In this example, torque is transmitted between the stop 5d and the engaging shaft 10b by utilizing multiple engaging portions of the engaging claw 33 and the engaging groove 32. Therefore, compared to the structure in the fourth example, the allowable torque can be increased. Furthermore, compared to the case of forming spline teeth, the outer surface shape of the engaging shaft 10b and the inner surface shape of the engaging hole 19b can be simplified, thus reducing processing costs and manufacturing costs. Other structural features and effects are the same as in the first and fourth examples.

[0159] Furthermore, in the fifth example, the following structure is described: a second fitting shaft portion 31 with a different cross-sectional shape from the fitting shaft portion 10b is provided on one axial side of the fitting shaft portion 10b, and the clamping member is externally fitted relative to the second fitting shaft portion 31 without relative rotation. However, as another variation of the fifth example, the following structure can also be adopted: the axial length of the fitting shaft portion 10b having multiple engaging grooves 32 on its outer peripheral surface is extended, and the portion of the fitting shaft portion 10b protruding from the stop member 5d towards one axial side is externally fitted into the clamping member having multiple engaging claw portions on its inner peripheral surface without relative rotation.

[0160] [Sixth Case]

[0161] use Figure 18 and Figure 19 The sixth embodiment of the present invention will now be described.

[0162] In this example, the ball screw device 1a uses a rolling bearing 34 as a clamping component. This clamping component is disposed on one axial side of the stop 5 and clamps the stop 5 axially between it and the threaded portion 9.

[0163] The rolling bearing 34 has: an annular outer ring 35 having an outer ring track 35a on its inner circumferential surface; an annular inner ring 36 having an inner ring track 36a on its outer circumferential surface; and a plurality of rolling elements 37 that are freely arranged between the outer ring track 35a and the inner ring track 36a. The inner ring 36 has an annular surface 28a on its side on the opposite axial side, the annular surface 28a being formed by a flat surface existing on an imaginary plane orthogonal to the central axis of the inner ring 36.

[0164] In this example, the inner ring 36 constituting the rolling bearing 34 is pressed into the second fitting shaft portion 31, which is provided on one axial side of the fitting shaft portion 10 and has a cylindrical outer peripheral surface. Thus, the inner ring 36 is fixedly fitted with respect to the second fitting shaft portion 31 without being able to rotate relative to it. Furthermore, the radially inner portion of the annular surface 28a of the inner ring 36 abuts against the second stepped surface 38 of the threaded shaft 2, which is disposed between the fitting shaft portion 10 and the second fitting shaft portion 31 and faces one axial side.

[0165] In this example, the inner ring 36 constituting the rolling bearing 34 is externally fixed to the second engaging shaft portion 31, thereby clamping the stop member 5 axially between the inner ring 36 and the threaded portion 9. This causes the radially outer portion of the annular surface 28a of the inner ring 36 to make full circumferential contact with the first contact surface 22 formed by the axially side surface 17x of the boss portion 17 on one side of the axial direction of the stop member 5. Furthermore, the stepped surface 11 of the threaded portion 9 makes full circumferential contact with the second contact surface 23 formed by the axially side surface 17y of the boss portion 17 on the other side of the axial direction of the stop member 5. In this state, a gap is formed between the axially side surface of the outer ring 35 and the axially side surface 18x of the second engaging portion 18 of the stop member 5. Additionally, the axially side surface 18y of the second engaging portion 18 is axially recessed from the stepped surface 11.

[0166] In this example, axial load can be transmitted between the threaded portion 9 and the rolling bearing 34 without reducing the lifespan of the ball screw assembly 1a. Other structural features and effects are the same as in the first example.

[0167] [Seventh Case]

[0168] use Figure 20 and Figure 21 The seventh example of an embodiment of the present invention will now be described.

[0169] In this example, the nut 3a of the ball screw device 1b constitutes a rotary motion element that rotates during use, and the threaded shaft 2a constitutes a linear motion element that moves linearly during use. That is, the ball screw device 1b in this example is used in a manner that drives the nut 3a to rotate and causes the threaded shaft 2a to move linearly.

[0170] Therefore, in this example, the nut 3a is rotatably supported relative to the bottomed cylindrical cylinder 39, which serves as a fixed component, using a rolling bearing 40. The rolling bearing 40 is embedded and fixed to the axial side of the cylinder 39, and has an annular outer ring 41 with an outer ring track 41a on its inner circumferential surface, an annular inner ring 42 with an inner ring track 42a on its outer circumferential surface, and a plurality of rolling elements 43 rotatably disposed between the outer ring track 41a and the inner ring track 42a. In this example, the inner ring 42 is integrally formed with the nut 3a. That is, the inner ring track 42a is directly formed on the outer circumferential surface of the nut 3a.

[0171] The nut 3a has a gear portion 44 on the axial side of its outer peripheral surface for rotating and driving the nut 3a. Additionally, the nut 3a has a first engaging portion 15 (not shown) at one end on the axial side. Figure 4 ).

[0172] The threaded shaft 2a has a threaded portion 9 and a mating shaft portion 10 disposed adjacent to one side of the threaded portion 9 in the axial direction. In this example, external spline teeth 13 are also formed on the outer peripheral surface of the mating shaft portion 10.

[0173] The stop 5 has a boss portion 17 and a second engaging portion 18, and the boss portion 17 has an engaging hole 19 serving as a through hole at its radial center. In this example, the engaging hole 19 is also formed by a spline hole having a plurality of internal spline teeth 20 on its inner circumferential surface. Furthermore, the engaging shaft portion 10 is loosely engaged in the engaging hole 19 of the boss portion 17 by allowing axial relative displacement. Alternatively, the engaging shaft portion 10 can be engaged in the engaging hole 19 of the boss portion 17 constituting the stop 5 in a press-fit state.

[0174] In this example, the ball screw device 1b uses a piston 45 as a clamping member, which is arranged on one axial side of the stop 5 and clamps the stop 5 axially between it and the threaded portion 9.

[0175] The piston 45 has a generally cylindrical shape and is axially movable and fitted into the inner side of the cylinder 39. The piston 45 has a mounting hole 46 with an opening only on one axial side. The mounting hole 46 is a stepped hole, having a small-diameter bore 47 on one axial side and a large-diameter bore 48 on the other axial side. Internal splines 49 are formed on the inner circumferential surface of the small-diameter bore 47. The large-diameter bore 48 has an inner diameter on its inner side that allows the stop member 5 to be inserted. The small-diameter bore 47 and the large-diameter bore 48 are connected by an annular surface 28b, which is a flat surface facing the other axial side. The annular surface 28b exists on an imaginary plane orthogonal to the central axis of the piston 45.

[0176] By engaging the internal spline teeth 49 formed on the inner circumferential surface of the small-diameter bore 47 of the mounting hole 46 with the external spline teeth 13 formed on the portion separating axially from the portion with the stop 5, the piston 45 is externally engaged with the fitting shaft portion 10 of the threaded shaft 2, preventing relative rotation. In this example, the piston 45 is splinedly engaged with the fitting shaft portion 10 by pressing.

[0177] By externally fixing the piston 45 to the position in the fitting shaft portion 10 adjacent to the axial side of the stop member 5, the stop member 5 is axially clamped between the piston 45 and the threaded portion 9. This causes the first contact surface 22, formed by the side surface 17x of the boss portion 17 on the side of the piston 45's annular surface relative to the axial side of the stop member 5, to make full circumferential contact. Furthermore, the second contact surface 23, formed by the side surface 17y of the boss portion 17 on the other axial side of the threaded portion 9, to make full circumferential contact. In this state, a gap is formed between the annular surface 28b of the piston 45 and the side surface 18x of the second engaging portion 18 of the stop member 5 on the axial side. Additionally, the side surface 18y of the second engaging portion 18 is axially recessed from the stepped surface 11.

[0178] In this example, the ball screw assembly 1b transmits axial load between the threaded portion 9 and the piston 45 via the stop member 5. For example, when the nut 3a is rotated in a predetermined direction, causing the threaded shaft 2a to move relative to the nut 3a in one axial direction, an axial load is applied to the piston 45 from the liquid or gas disposed inside the cylinder 39, in the opposite axial direction. In this example, the axial load acting on the piston 45 in the opposite axial direction can be transmitted from the annular surface 28b of the piston 45 to the first contact surface 22 of the stop member 5, and then from the second contact surface 23 of the stop member 5 to the stepped surface 11 of the threaded portion 9. Then, it can be supported by the cylinder 39 via the nut 3a. Conversely, regarding the axial load acting on the threaded portion 9 in one axial direction, it can also be transmitted from the stepped surface 11 of the threaded portion 9 to the second contact surface 23 of the stop member 5, and then from the first contact surface 22 of the stop member 5 to the annular surface 28b of the piston 45.

[0179] Therefore, in this example, axial load can be transmitted between the threaded portion 9 and the piston 45 without reducing the lifespan of the ball screw assembly 1b. Other structural features and effects are the same as in the first example.

[0180] The embodiments of the present invention have been described above, but the present invention is not limited thereto and can be appropriately modified without departing from the technical concept of the invention. Furthermore, the structures of the first to seventh embodiments of the present invention can be appropriately combined and implemented as long as no contradictions arise.

[0181] In the first to seventh embodiments of the present invention, a drive member, a rolling bearing, and a piston are shown as clamping members for holding the stop member between the stop member and the threaded portion. However, in implementing the present invention, the clamping member is not limited to these components. Furthermore, in various embodiments of the present invention, gears and pulleys are shown as drive members, but the drive member is not limited to these components; sprockets, motor shafts directly connected to the threaded shaft, couplings, etc., can also be used.

[0182] In the first to seventh examples of embodiments of the present invention, a structure in which the circulation groove is formed directly on the inner circumferential surface of the nut was described. However, in implementing the present invention, the circulation groove can also be formed on a circulation component that is separate from the nut, such as a stop block, and the circulation component can be fixed relative to the nut. In addition, the first engaging portion can be configured to be separate from the nut, and the second engaging portion can be configured to be separate from the boss portion.

[0183] In the first to seventh examples of the embodiments of the present invention, a structure was described in which the nut has only one first engaging portion and the stop member has only one second engaging portion. However, in the case of implementing the present invention, it is also possible to have the same number of first engaging portions and second engaging portions (for example, two of each).

[0184] In the first to seventh embodiments of the present invention, a configuration was described in which the first contact surface and the second contact surface were respectively provided only on the axial sides of the boss portion on both sides of the axial sides of the stop member. However, in the implementation of the present invention, it is also possible to provide a portion of each of the first contact surface and the second contact surface on the axial sides of the second engaging portion. In particular, this configuration is preferred when multiple second engaging portions are provided.

[0185] Symbol Explanation

[0186] 1, 1a, 1b—Ball screw assembly; 2, 2a—Threaded shaft; 3, 3a—Nut; 4—Ball; 5, 5a~5d—Stop; 6—Drive component; 7—Load path; 8—Circulation groove; 9—Threaded section; 10, 10a, 10b—Matching shaft section; 11—Stepped surface; 12—Shaft-side ball thread groove; 13—External spline; 14—Nut-side ball thread groove; 15—First engaging section; 16—First stop surface; 17, 17a, 17b—Boss section. 17x—Side of one side of the axial direction, 17y—Side of the other side of the axial direction, 18, 18a, 18b—Second engaging part, 18x—Side of one side of the axial direction, 18y—Side of the other side of the axial direction, 19, 19a, 19b—Engaging hole, 20—Internal spline tooth, 21—Second stop surface, 22—First contact surface, 23—Second contact surface, 24—Circular plate part, 25—Cylinder part, 26—Mounting hole, 27—Internal spline tooth, 28, 28a, 28b—Circular plate part, 25—Cylindrical part, 26—Mounting hole, 27—Internal spline tooth, 28, 28a, 28b—Circular plate part ... 29—Flat outer surface, 30—Flat inner surface, 31—Second mating shaft portion, 32—Matching groove, 33—Matching claw portion, 34—Rolling bearing, 35—Outer ring, 35a—Outer ring track, 36—Inner ring, 36a—Inner ring track, 37—Rolling element, 38—Second stepped surface, 39—Cylinder, 40—Rolling bearing, 41—Outer ring, 41a—Outer ring track, 42—Inner ring, 42a—Inner ring track, 43—Rolling element, 44—Gear portion, 45—Piston. 46—Mounting hole, 47—Small diameter hole, 48—Large diameter hole, 49—Internal spline, 50—Groove, 51—Flat outer surface, 52—External spline, 53—Concave surface, 54x, 54y—Stepped section, 100—Ball screw assembly, 101—Threaded shaft, 102—Nut, 103—Stop, 104—Threaded section, 105—Matching shaft section, 106—Shaft-side ball thread groove, 107—First engaging section, 108—Boss section, 109—Second engaging section.

Claims

1. A ball screw device, characterized in that, have: A threaded shaft having a threaded portion having a helical axial ball thread groove on its outer peripheral surface and a fitting shaft portion having an outer diameter smaller than the threaded portion and being adjacent to the threaded portion on one axial side. A nut having a helical ball thread groove on its inner circumferential surface and a first engaging portion at one end on one axial side. Multiple balls are disposed between the aforementioned shaft-side ball thread groove and the aforementioned nut-side ball thread groove; The stop member has a boss portion that is non-rotatably fitted onto the aforementioned engaging shaft portion and a second engaging portion that protrudes radially from the outer peripheral surface of the aforementioned boss portion and can engage with the aforementioned first engaging portion in the circumferential direction; and A clamping member is disposed adjacent to one axial side of the aforementioned stop member, and clamps the stop member axially between the stop member and the aforementioned threaded portion. The axial load is transmitted between the threaded portion and the clamping component via the stop without applying torque to the stop. The aforementioned stop has a first contact surface on one side of the axial direction and a second contact surface on the other side of the axial direction. The first contact surface is formed by a flat surface existing on an imaginary plane orthogonal to the central axis of the stop, and has a shape that is rotationally symmetrical about the central axis of the stop, and contacts the clamping member. The second contact surface is formed by a flat surface existing on an imaginary plane orthogonal to the central axis of the stop, and has a shape that is rotationally symmetrical about the central axis of the stop, and contacts the threaded portion. The aforementioned first contact surface is formed by the side surface of the aforementioned boss portion on one side of its axial direction. The second contact surface is formed by the side surface on the other side of the axial direction of the aforementioned boss portion. The side of the second engaging portion on one axial side is offset in the axial direction relative to the side of the boss portion on one axial side, and the side of the second engaging portion on the other axial side is offset in the axial direction relative to the side of the boss portion on the other axial side.

2. The ball screw device according to claim 1, characterized in that, The side of the second engaging portion on one axial side is connected to the side of the boss portion on one axial side via a stepped portion having an arc-shaped cross-section, and the side of the second engaging portion on the other axial side is connected to the side of the boss portion on the other axial side via a stepped portion having an arc-shaped cross-section.

3. The ball screw device according to claim 1, characterized in that, The misalignment of the side of the second engaging portion relative to the side of the boss portion on the axial side towards the other axial side and the misalignment of the side of the second engaging portion relative to the side of the boss portion on the axial side towards the other axial side are the same.

4. The ball screw device according to claim 1, characterized in that, The axial thickness of the second engaging portion is constant throughout the radial direction.

5. The ball screw device according to claim 1, characterized in that, The axial thickness of the second engaging portion decreases as it moves radially outward.

6. The ball screw device according to claim 1, characterized in that, Of the two circumferential sides of the second engaging portion, the side that engages with the first engaging portion in the circumferential direction is smoothly connected to the outer circumferential surface of the boss portion via a concave curved surface with an arc-shaped cross-section. Furthermore, of the two circumferential sides of the second engaging portion, the side that does not engage with the first engaging portion in the circumferential direction is connected to the outer circumferential surface of the boss portion along the tangential direction of the boss portion.

7. The ball screw device according to claim 1, characterized in that, The aforementioned fitting shaft portion has a flat shape with a pair of parallel flat outer surfaces on its outer peripheral surface. The aforementioned boss portion has a flat-shaped engaging hole with a pair of parallel flat inner surfaces on its inner circumferential surface.

8. The ball screw device according to claim 1, characterized in that, The aforementioned mating shaft portion has external spline teeth on its outer peripheral surface. The aforementioned boss portion also has a locking hole with internal spline teeth formed on its inner circumferential surface.

9. The ball screw device according to claim 1, characterized in that, The aforementioned stop is loosely engaged relative to the aforementioned mating shaft in a manner that allows for relative displacement in the relevant axial direction. The aforementioned clamping component is externally inserted relative to the aforementioned threaded shaft by pressing it in.

10. The ball screw device according to claim 1, characterized in that, The aforementioned stop is externally fitted relative to the aforementioned mating shaft portion by pressing it in. The aforementioned clamping component is externally inserted relative to the aforementioned threaded shaft by pressing it in.

11. The ball screw device according to claim 1, characterized in that, The aforementioned threaded shaft is a rotary motion element that rotates during use. The nut described above is a linear motion element that moves linearly during use. The aforementioned clamping component is either a drive component that rotates the aforementioned threaded shaft or a rolling bearing that rotatably supports the aforementioned threaded shaft.

12. The ball screw device according to claim 11, characterized in that, The aforementioned driving components are any one of gears, pulleys, sprockets, and motor shafts.

13. The ball screw device according to claim 1, characterized in that, The aforementioned threaded shaft is a linear motion element that moves linearly during use. The nut described above is a rotating component that rotates during use. The aforementioned clamping component is a piston that moves linearly together with the aforementioned threaded shaft.

14. A method for manufacturing a ball screw device, wherein the ball screw device is the ball screw device according to any one of claims 1 to 13, the method for manufacturing the ball screw device is characterized by comprising the following steps: After forging the raw material to form an intermediate material with the general shape of the aforementioned stop, the axial sides of the intermediate material are machined to manufacture the aforementioned stop.

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