Ball screw device and method of manufacturing the same

Abstract

The present application provides a ball screw device, which can effectively prevent the axial relative displacement of the nut and the fitting cylinder without increasing the manufacturing cost, and realize the miniaturization of the whole device and the increase of the load capacity. The nut (3) has a first fitting surface (17) with a first retainer groove (20) at the end on the other axial side, the fitting cylinder (5) has a second fitting surface (27) with a second retainer groove (29) at the end on the one axial side, and the retainer (6) is clamped between the first retainer groove (20) and the second retainer groove (29) in a manner of being erected.

Description

Technical Field

[0001] This disclosure relates to a ball screw device and a method for manufacturing the same. Background Technology

[0002] Ball screw systems achieve higher efficiency than sliding screw systems, which involve direct contact between the threaded shaft and the nut, because the balls roll between them. Therefore, ball screw systems are used in various mechanical devices, such as electric braking systems in automobiles, automatic transmissions (AMTs), and positioning devices in machine tools, to convert the rotary motion of drive sources like 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 uses one of the threaded shaft and the nut as a rotary motion element and the other as a linear motion element.

[0004] In ball screw devices, it is used to fix pistons and other components that serve as linear motion elements. Figure 23 A conventional ball screw device 100 is shown, which is disclosed in Japanese Patent Application Publication No. 2016-35322, and has a structure in which a piston 104 is fitted and fixed in place by a nut 102.

[0005] The ball screw assembly 100 includes a threaded shaft 101, a nut 102, multiple balls 103, a piston 104, and a housing (caliper) 105.

[0006] The threaded shaft 101 has helical axial ball thread grooves 106 on its outer circumferential surface and rotates during use. Therefore, the threaded shaft 101 is a rotational element and is rotatably supported relative to the housing 105 by rolling bearings 107. A driven gear 108 is fixed to the threaded shaft 101. The rotation of the output shaft of an electric motor (not shown) is transmitted to the driven gear 108 via an idle gear 109. Therefore, the threaded shaft 101 is driven to rotate based on the energization of the electric motor.

[0007] The nut 102 has a helical ball thread groove 110 on its inner circumferential surface and moves linearly during use. Therefore, the nut 102 is a linear motion element, and as will be described later, relative rotation with respect to the housing 105 is prevented.

[0008] The threaded shaft 101 is inserted into the inside of the nut 102 and is coaxially configured with the nut 102. The shaft-side ball thread groove 106 and the nut-side ball thread groove 110 are arranged opposite each other in the radial direction, forming a helical load path 111.

[0009] The start and end points of load path 111 are connected by a circulation unit (not shown). The ball 103 that reaches the end point of load path 111 returns to the start point of load path 111 via the circulation unit. Furthermore, the start and end points of load path 111 are interchanged according to the direction of the relative displacement (relative rotation direction) between the threaded shaft 101 and the nut 102 in the axial direction.

[0010] The piston 104 is a bottomed cylindrical shape and is externally fixed to the nut 102 without being able to rotate relative to it. In particular, in the conventional ball screw device 100, the piston 104 is externally fitted into the nut 102 in such a way that it covers the entire nut 102. In other words, the entire nut 102 is inserted into the inside of the piston 104.

[0011] In the existing ball screw assembly 100, to prevent axial relative displacement between the nut 102 and the piston 104, the axial end face of the nut 102 abuts against the stepped surface 112 provided on the inner circumferential surface of the piston 104, and the retaining ring 113 is secured to the inner circumferential surface of the piston 104. Thus, the nut 102 is clamped axially from both sides between the stepped surface 112 and the retaining ring 113, preventing axial relative displacement between the nut 102 and the piston 104.

[0012] In addition, in order to prevent the nut 102 from rotating relative to the housing 105, a keyway 114 extending in the axial direction is provided on the outer peripheral surface of the piston 104, which is externally fitted relative to the nut 102 and cannot rotate relative to it.

[0013] The housing 105 has an insertion hole (cylinder bore) 115 through which the piston 104 can be inserted axially. A fitting groove 116 is provided on the inner circumferential surface of the insertion hole 115. A key 117 is embedded in the fitting groove 116. Furthermore, a portion of the key 117 extending radially inward from the inner circumferential surface of the insertion hole 115 is axially slidably engaged with a keyway 114 provided on the outer circumferential surface of the piston 104. This structure prevents the nut 102 from rotating relative to the housing 105, enabling linear movement of the nut 102.

[0014] Existing technical documents

[0015] Patent documents

[0016] Patent Document 1: Japanese Patent Application Publication No. 2016-35322 Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] In the existing ball screw device 100, in order to prevent the axial relative displacement between the nut 102 and the piston 104, the piston 104 is externally embedded in the nut 102 in a manner that covers the entire nut 102, and the nut 102 is clamped from both sides axially between the stepped surface 112 provided on the inner circumferential surface of the piston 104 and the retaining ring 113 locked on the inner circumferential surface of the piston 104.

[0019] Therefore, the inner diameter of the piston 104 needs to be larger than the outer diameter (maximum outer diameter) of the nut 102, making it easier to scale up the ball screw assembly 100. Furthermore, the outer diameter of the nut 102 is constrained by the inner diameter of the piston 104, which is disadvantageous in terms of increasing the load capacity of the ball screw assembly 100.

[0020] To address this, one approach is to prevent axial displacement between the nut and piston by directly pressing a portion of the piston's axial direction into a portion of the nut's axial direction. However, in this case, depending on the combination of the metals constituting the nut (e.g., iron-based alloys) and the piston (e.g., aluminum-based alloys), the difference in their coefficients of thermal expansion may reduce the interference fit, thus failing to effectively prevent axial displacement between the nut and piston. Strict management of the interference fit is required to effectively prevent axial displacement between the nut and piston, contributing to increased manufacturing costs for ball screw systems.

[0021] Alternatively, welding can be used to secure the piston and nut. However, in this case, depending on the combination of the metals constituting the nut (e.g., iron-based alloys) and the metal constituting the piston (e.g., aluminum-based alloys), intermetallic compounds may form during welding, resulting in insufficient joint strength. Therefore, it is still possible that axial displacement between the nut and piston cannot be effectively prevented.

[0022] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a ball screw device that can effectively prevent the axial relative displacement of the nut and the fitting sleeve without increasing the manufacturing cost, and to achieve the miniaturization of the overall device and the increase of the load capacity.

[0023] In addition, the purpose of this disclosure is to provide a ball screw device that, as needed, allows for easy confirmation of whether a retaining ring is installed after assembly.

[0024] Solution for solving the problem

[0025] One disclosed ball screw assembly comprises a threaded shaft, a nut, multiple balls, a fitting sleeve, and a retaining ring.

[0026] The threaded shaft has a helical axial ball thread groove on its outer circumferential surface and rotates during use.

[0027] The nut has a helical ball thread groove on its inner circumferential surface and moves linearly during use.

[0028] The plurality of balls are disposed between the shaft-side ball thread groove and the nut-side ball thread groove.

[0029] Regarding the fitting cylinder, one axial end is fitted and fixed to the other axial end of the nut, and moves linearly together with the nut.

[0030] The retaining ring prevents axial relative displacement between the nut and the fitting sleeve.

[0031] In one aspect of the ball screw device disclosed herein, the nut has a first mating surface with a first retaining ring groove at its end on the other axial side, and the mating cylinder has a second mating surface with a second retaining ring groove at its end on one axial side, the portion of which is radially opposite to the first retaining ring groove.

[0032] The retaining ring is fixed between the first retaining ring groove and the second retaining ring groove by means of a mounting.

[0033] In a ball screw device according to one aspect of this disclosure, the maximum outer diameter of the fitting sleeve can be made the same as the maximum outer diameter of the nut. Furthermore, the situation where the maximum outer diameter of the fitting sleeve is the same as the maximum outer diameter of the nut is not limited to the case where the maximum outer diameter of the fitting sleeve is exactly the same as the maximum outer diameter of the nut, but also includes the case where the maximum outer diameter of the fitting sleeve and the maximum outer diameter of the nut are substantially the same within a range of unavoidable manufacturing tolerances.

[0034] In one aspect of the ball screw device disclosed herein, the fitting sleeve can be engaged relative to the nut by press-fitting or clearance fit.

[0035] When the fitting sleeve is engaged relative to the nut by pressing it in, the first fitting surface and the second fitting surface can be in interference contact along the entire axial length, or they can be in interference contact along a portion of the axial direction.

[0036] In one embodiment of the ball screw device disclosed herein, the cross-sectional shape of the retaining ring can be set to rectangular or circular.

[0037] In a ball screw device of one embodiment of the present disclosure, the end face of the nut on the other axial side and the first mating surface can be connected via a first chamfer, and the end face of the mating cylinder on one axial side and the second mating surface can be connected via a second chamfer.

[0038] The ball screw device of this disclosure is capable of transmitting axial force between the nut and the fitting sleeve by means of the end face of the nut on the other side of the axial direction or the end face of the fitting sleeve on one side of the axial direction when the nut is moved relative to the other side of the thread axis, and transmitting axial force between the nut and the fitting sleeve via the retaining ring when the nut is moved relative to the other side of the axial direction of the thread axis.

[0039] In a ball screw device of one embodiment of the present disclosure, the outer peripheral surface of the nut can have a first mating surface, a large-diameter surface that is adjacent to the first mating surface on one axial side and is larger than the outer diameter of the first mating surface, and a stepped surface that is disposed between the first mating surface and the large-diameter surface and faces the other axial side.

[0040] Furthermore, the fitting sleeve can be externally fixed relative to the nut, and the end face on one side of the axial direction can be axially abutted against the stepped surface.

[0041] In this case, when the nut is moved relative to the other side of the thread axis, axial force can be transmitted between the nut and the fitting sleeve via the contact portion between the end face of the fitting sleeve on one side of the axis and the stepped surface of the nut.

[0042] When the above-described structure is used to fix the fitting sleeve to the outside of the nut, the first retaining ring groove can be formed with the stepped surface of the nut as a reference, and the second retaining ring groove can be formed with the end face of one axial side of the fitting sleeve as a reference.

[0043] When the above-described structure is used to fix the fitting sleeve externally relative to the nut, the first retaining ring groove can be fitted to the portion that is axially separated from the ball thread groove on the nut side.

[0044] When the above-described structure is used to fix the fitting sleeve to the outside of the nut, a small-diameter stepped portion can be provided at one end of the outer peripheral surface of the fitting sleeve on one side of the axial direction.

[0045] When the above-described structure is used to fix the fitting sleeve to the outside of the nut, it can include: a housing having an insertion hole that allows the nut and the fitting sleeve to be inserted axially; and an anti-rotation member that prevents the nut from rotating relative to the housing.

[0046] In this case, the insertion hole has a guide groove on its inner circumferential surface that engages circumferentially with the radially outer portion of the anti-rotation member and extends axially, and the nut has a retaining recess on its large-diameter surface that engages circumferentially with the radially inner portion of the anti-rotation member and includes a closed surface facing the other axial direction and an opening on the stepped surface.

[0047] In addition, the radially inner portion of the anti-rotation member can be positioned inside the retaining recess while sandwiched between the end face of the closing surface and the axial side of the fitting cylinder, and the radially outer portion can be slidably positioned inside the guide groove.

[0048] In this case, the axial dimension of the anti-rotation component can be made smaller than the axial distance between the closing surface and the end face (stepped surface of the nut) on one side of the axial direction of the fitting cylinder.

[0049] Alternatively, the axial dimension of the anti-rotation component and the axial distance between the end face of the sealing surface and the end face of the fitting cylinder on one side of the axial direction can be made the same.

[0050] It is also possible to make the axial dimension of the anti-rotation component larger than the axial distance between the closing surface and the stepped surface of the nut. In this case, the end face of one axial side of the fitting cylinder can be axially abutted against the end face of the other axial side of the anti-rotation component.

[0051] In a ball screw device according to one aspect of the present disclosure, the outer peripheral surface of the fitting cylinder can have: a second fitting surface; a large-diameter surface that is adjacent to the second fitting surface on the other side of the axial direction and is larger than the outer diameter of the second fitting surface; and a stepped surface that is disposed between the second fitting surface and the large-diameter surface and faces one side of the axial direction.

[0052] Furthermore, the fitting sleeve can be embedded and fixed relative to the nut, and the stepped surface can be axially abutted against the end face of the nut on the other side of the axial direction.

[0053] In this case, when the nut is moved relative to the other side of the thread axis, axial force can be transmitted between the nut and the fitting sleeve via the contact portion between the stepped surface of the fitting sleeve and the end face of the nut on the other side of the axis.

[0054] When the above-described structure is used to fix the fitting sleeve inside the nut, the first retaining ring groove can be formed with the end face on the other side of the axial direction of the nut as a reference, and the second retaining ring groove can be formed with the stepped surface of the fitting sleeve as a reference.

[0055] When the above-described structure is used to fix the fitting sleeve inside the nut, a small-diameter stepped portion can be provided at the end on the axial side of the outer circumferential surface of the nut.

[0056] When the above-described structure is used to fix the fitting sleeve inside the nut, it can include: a housing having an insertion hole that allows the nut and the fitting sleeve to be inserted axially; and an anti-rotation member that prevents the nut from rotating relative to the housing.

[0057] In this case, the insertion hole has a guide groove on its inner circumferential surface that can engage with the radially outer portion of the anti-rotation member in the circumferential direction and extend axially, and the fitting cylinder has a retaining recess on its large diameter surface that can engage with the radially inner portion of the anti-rotation member in the circumferential direction, and includes a closed surface facing one axial direction and an opening on the stepped surface.

[0058] In addition, the radially inner portion of the anti-rotation member can be positioned inside the retaining recess while sandwiched between the closing surface and the end face on the other side of the axial direction of the nut, and the radially outer portion can be slidably positioned inside the guide groove.

[0059] In this case, the axial dimension of the anti-rotation component can be made smaller than the axial distance between the closing surface and the end face (stepped surface of the fitting cylinder) on the other side of the axial direction of the nut.

[0060] Alternatively, the axial dimension of the anti-rotation component and the axial distance between the closing surface and the end face on the other side of the nut's axial direction can be made the same.

[0061] It is also possible to make the axial dimension of the anti-rotation component larger than the axial distance between the closing surface and the stepped surface of the fitting cylinder. In this case, the end face of the nut on the other axial side can be axially abutted against the end face of the anti-rotation component on one axial side.

[0062] In one embodiment of the ball screw device disclosed herein, a radially penetrating confirmation window can be provided at the portion of one end of the nut on the other axial side and the other end of the fitting cylinder on one axial side, which covers the end of the retaining ring from the radial outside and overlaps with the retaining ring in the radial direction.

[0063] In one embodiment of the ball screw device disclosed herein, the confirmation window can be made to open only on both radial sides.

[0064] Alternatively, the confirmation window can be made to open not only on both radial sides, but also in the axial direction.

[0065] In a ball screw device of one embodiment of the present disclosure, the retaining ring can have a discontinuity in a certain part of the circumferential direction, and the width dimension of the confirmation window in the circumferential direction is larger than the width dimension of the discontinuity in the circumferential direction.

[0066] Alternatively, a retaining ring may be provided with a discontinuity at one location in the circumferential direction, and the confirmation window may be provided at multiple locations in the circumferential direction at one end of the retaining ring, such that the distance between a pair of adjacent confirmation windows in the circumferential direction is larger than the width dimension in the circumferential direction of the discontinuity.

[0067] The present disclosure provides a method for manufacturing a ball screw device, comprising an inspection step for checking whether the retaining ring is properly assembled. This inspection step includes inserting the front end of an inspection fixture from the radially outer side into the inner side of the confirmation window and measuring the insertion depth of the front end of the inspection fixture, or measuring the distance from the sensor to the object (the outer peripheral surface of the retaining ring or the bottom surface of the first retaining ring groove or the second retaining ring groove) using the confirmation window via a sensor.

[0068] Invention Effects

[0069] According to one aspect of the present disclosure, the ball screw device can effectively prevent the axial relative displacement between the nut and the fitting sleeve without increasing manufacturing costs, and achieves overall miniaturization of the device and increased load capacity. Attached Figure Description

[0070] Figure 1 This is a cross-sectional view of a ball screw device according to a first embodiment of the present disclosure.

[0071] Figure 2 This is a partial sectional perspective view of the first example of a ball screw device.

[0072] Figure 3 This is a front view of the ball screw device of the first example, omitting the housing and drive components, and viewed from the axial side.

[0073] Figure 4 yes Figure 3 Sectional view along the B-O-B line.

[0074] Figure 5 yes Figure 4 A magnified view of a portion of the image.

[0075] Figure 6 yes Figure 1 A-A line sectional view.

[0076] Figure 7This is a sectional perspective view of the nut that constitutes the ball screw device in the first example.

[0077] Figure 8 The ball screw device in the first example is shown as a schematic diagram to illustrate the positional relationship between the circulation groove and the retaining recess in the circumferential direction.

[0078] Figure 9 (A) and Figure 9 (B) The ball screw device in the first example is shown in a diagram to illustrate the assembly operation of the piston relative to the nut.

[0079] Figure 10 This is the second example of a ball screw device according to an embodiment of this disclosure. Figure 5 The image.

[0080] Figure 11 This refers to the ball screw device of the third embodiment of this disclosure. Figure 4 A sectional view.

[0081] Figure 12 This is a top view of a ball screw device according to a fourth embodiment of the present disclosure, omitting the housing and drive components and viewed from the radially outer side.

[0082] Figure 13 This is a perspective view of the ball screw device in the fourth example, with the housing and drive components omitted.

[0083] Figure 14 It is about the ball screw device in the fourth example, equivalent to Figure 4 The image.

[0084] Figure 15 It is equivalent to Figure 14 A schematic diagram of the C-C line cross section.

[0085] Figure 16 This is shown to illustrate the inspection process in the manufacturing process of the ball screw device in the fourth example. Figure 14 A magnified view of a portion of the image.

[0086] Figure 17 This is the fifth embodiment of the ball screw device according to the present disclosure. Figure 12 The image.

[0087] Figure 18 It is about the ball screw device in the fifth example, equivalent to Figure 13 The image.

[0088] Figure 19 This is the sixth example of a ball screw device according to an embodiment of this disclosure. Figure 12 The image.

[0089] Figure 20 It is about the ball screw device in the sixth case, equivalent to Figure 15 The image.

[0090] Figure 21 This is a partially enlarged cross-sectional view of a ball screw device according to a seventh embodiment of the present disclosure.

[0091] Figure 22 This refers to the ball screw device of the eighth embodiment of this disclosure. Figure 14 A sectional view.

[0092] Figure 23 This is a cross-sectional view showing the existing structure of the ball screw device. Detailed Implementation

[0093] [First example]

[0094] use Figures 1-9 The first example of an embodiment of this disclosure will be described.

[0095] [Overall structure of the ball screw assembly]

[0096] The ball screw device 1 in this example is assembled into an electric brake booster device and can be used in applications that convert the rotary motion of an electric motor (not shown) as a drive source into the linear motion of the piston 5.

[0097] The ball screw assembly 1 includes a threaded shaft 2, a nut 3, multiple balls 4, a piston 5 serving as a fitting cylinder, a retaining ring 6, a housing 7, and an anti-rotation component 8.

[0098] The threaded shaft 2 is a rotary motion element that is driven by a drive source (not shown) and rotates during use. The threaded shaft 2 is inserted into the inside of the nut 3 and is coaxially configured with the nut 3. The nut 3 is a linear motion element that moves linearly within the insertion hole 9 of the housing 7, together with a piston 5 externally fixed to the nut 3. Axial relative displacement of the nut 3 relative to the piston 5 is prevented by a retaining ring 6, and relative rotation relative to the housing 7 is prevented by an anti-rotation member 8. In this example, the ball screw device 1 is used to drive the threaded shaft 2 to rotate, thereby causing the nut 3 to move linearly.

[0099] A helical load path 10 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 10. When the threaded shaft 2 and the nut 3 are rotated relative to each other, the balls 4 that reach the end of the load path 10 pass through a circulation groove 11 formed on the inner circumferential surface of the nut 3 (see reference). Figure 7 Return to the starting point of load path 10. The construction of each structural component of the ball screw device 1 will be described below.

[0100] In the following description, unless otherwise specified, axial, radial, and circumferential directions refer to the axial, radial, and circumferential directions of the threaded shaft. Additionally, axial side refers to... Figure 1 , Figure 2 , Figure 4 , Figure 5 , Figure 7 as well as Figure 9 The right side, the other side of the axis refers to Figure 1 , Figure 2 , Figure 4 , Figure 5 , Figure 7 as well as Figure 9 On the left side.

[0101] <Threaded Shaft>

[0102] The threaded shaft 2 is made of metal and has a threaded portion 12 and a mating shaft portion 13 arranged adjacent to the threaded portion 12 on one axial side. The threaded portion 12 and the mating shaft portion 13 are coaxially arranged and constitute a single unit. The mating shaft portion 13 has an outer diameter smaller than that of the threaded portion 12.

[0103] The threaded portion 12 has a helical axial ball thread groove 14 on its outer peripheral surface. The axial ball thread groove 14 is formed by performing a machining process such as grinding (cutting) or rolling on the outer peripheral surface of the threaded portion 12. In this example, there is one axial ball thread groove 14. The groove shape (groove bottom shape) of the cross-section of the axial ball thread groove 14 can be a Gothic arch groove or a circular arc groove.

[0104] The mating shaft portion 13 has external spline teeth 15 covering the entire circumference of its outer peripheral surface. Therefore, the mating shaft portion 13 is a spline shaft portion. In the illustrated example, the external spline teeth 15 are involute spline teeth, but they can also be square spline teeth. Alternatively, the mating shaft portion 13 can also be a serrated shaft portion with external serrations covering the entire circumference of its outer peripheral surface.

[0105] The threaded shaft 2 is coaxially arranged with the nut 3 when the threaded portion 12 is inserted into the inside of the nut 3. In addition, in this example, the threaded shaft 2 is composed of the threaded portion 12 and the fitting shaft portion 13, but it is also possible for the threaded shaft 2 to have a support shaft portion (second fitting shaft portion) such as a rolling bearing that is fixed for rotational support relative to the housing 7.

[0106] <Nut>

[0107] The nut 3 is made of a metal such as an iron alloy and is cylindrical in shape. The nut 3 has a helical ball thread groove 16 and a circulation groove 11 on its inner circumferential surface.

[0108] The nut-side ball thread groove 16 has a helical shape and is formed by performing a machining process on the inner circumferential surface of the nut 3, such as grinding (cutting) or roll-tapping (cutting and tapping). The nut-side ball thread groove 16 has the same lead as the shaft-side ball thread groove 14. Therefore, with the threaded portion 12 of the threaded shaft 2 inserted into the inner side of the nut 3, the shaft-side ball thread groove 14 and the nut-side ball thread groove 16 are arranged radially opposite each other, forming a helical load path 10. The number of nut-side ball thread grooves 16 is the same as that of the shaft-side ball thread groove 14, which is one. The groove shape of the cross-section of the nut-side ball thread groove 16 can also be a Gothic arch groove or a circular arc groove, just like the shaft-side ball thread groove 14.

[0109] The circulation groove 11 has a generally S-shaped shape and is formed on the inner circumferential surface of the nut 3 by, for example, forging (cold forging). The circulation groove 11 smoothly connects the axially adjacent portions of the ball thread groove 16 on the nut side, connecting the start and end points of the load path 10. Therefore, the ball 4 that has reached the end point of the load path 10 returns to the start point of the load path 10 through the circulation groove 11. Furthermore, the start and end points of the load path 10 are interchanged according to the direction of the relative displacement (relative rotation direction) between the thread shaft 2 and the nut 3 in the axial direction.

[0110] The circulation groove 11 has a generally semi-circular cross-sectional shape. The circulation groove 11 has a groove width slightly larger than the diameter of the ball 4, and a groove depth sufficient to allow the ball 4 moving in the circulation groove 11 to pass over the thread teeth of the axial ball thread groove 14. In this example, four circulation grooves 11 are provided at equal intervals (90-degree angles) in the circumferential direction on the inner circumferential surface of the nut 3. Therefore, the ball screw device 1 in this example has four circuits. Furthermore, in the ball screw device 1 of this example, the circulation groove 11 is formed directly on the inner circumferential surface of the nut 3, but it is also possible to form the circulation groove as a separate circulation component (e.g., a stop) from the nut, fixing this circulation component relative to the nut.

[0111] In this example, the outer circumferential surface of the nut 3 is formed by a stepped cylindrical surface. The nut 3 has a cylindrical first mating surface 17 at its end on the axial side of its outer circumferential surface, into which a piston 5 is fitted, and a cylindrical large-diameter surface 18 with an outer diameter larger than the first mating surface 17, extending from the axial middle portion of the outer circumferential surface to one axial side. The large-diameter surface 18 is arranged adjacent to the first mating surface 17 on one axial side. Furthermore, the outer circumferential surface of the nut 3 has an annular stepped surface 19 facing the other axial side between the first mating surface 17 and the large-diameter surface 18. The stepped surface 19 is a flat surface existing on an imaginary plane orthogonal to the central axis of the nut 3. In this example, the outer diameter of the first mating surface 17 is constant axially except for the portion where the first retaining ring groove 20 is formed. Additionally, the maximum outer diameter of the nut 3 is the outer diameter of the large-diameter surface 18.

[0112] In this example, the ball screw device 1 uses a retaining ring 6 to prevent axial relative displacement between the nut 3 and the piston 5. Therefore, a first retaining ring groove 20 for locking the inner diameter side portion of the retaining ring 6 is provided throughout the axial middle portion of the first mating surface 17. The first retaining ring groove 20 is formed by machining such as cutting, based on the stepped surface 19 provided on the outer circumferential surface of the nut 3. The first retaining ring groove 20 has a rectangular cross-sectional shape and is provided on the portion separating from the ball thread groove 16 on the nut side to the axial side. The radial depth of the first retaining ring groove 20 is the same as or slightly larger than the radial width of the retaining ring 6. Furthermore, the axial width of the first retaining ring groove 20 is slightly larger than the axial thickness of the retaining ring 6.

[0113] The end face 3x on the other axial side of the nut 3 and the first mating surface 17 are connected via a tapered first chamfered portion 21. The end face 3x on the other axial side of the nut 3 is a flat surface existing on an imaginary plane orthogonal to the central axis of the nut 3.

[0114] In this example, the ball screw device 1 uses a nut 3 as the linear motion element. Therefore, in order to prevent the nut 3 from rotating, a retaining recess 22 for retaining the anti-rotation component 8 is provided on the outer peripheral surface of the nut 3. The retaining recess 22 is provided at multiple locations in the circumferential direction on the outer peripheral surface of the nut 3 (two locations in this example). The retaining recess 22 is provided on the axial side of the large-diameter surface 18 in the outer peripheral surface of the nut 3.

[0115] The retaining recess 22 is an axially elongated groove. The end of the retaining recess 22 on one axial side has a closed surface 23 facing the other axial side. The end of the retaining recess 22 on the other axial side opens at the stepped surface 19. Therefore, the retaining recess 22 opens on both the outer circumferential surface of the nut 3 and the stepped surface 19. The central axis of the retaining recess 22 is arranged parallel to the central axis of the nut 3. The axial dimension from the stepped surface 19 to the closed surface 23 is slightly larger than the axial dimension of the anti-rotation member 8. The closed surface 23 is a flat surface existing on an imaginary plane orthogonal to the central axis of the nut 3, and is partially circular (approximately semi-circular) when viewed axially.

[0116] The retaining recess 22 has a cross-sectional shape that allows it to engage circumferentially with the radially inner portion of the anti-rotation member 8. In this example, the anti-rotation member 8 is configured as a cylinder, as described later, therefore, as Figure 6As shown, the cross-sectional shape of the retaining recess 22 on the imaginary plane orthogonal to the central axis of the nut 3 is set to an arc shape. However, the shapes of the anti-rotation member 8 and the retaining recess 22 are arbitrary, as long as they can engage with the radially inner portion of the anti-rotation member 8 in the circumferential direction. For example, the cross-sectional shape of the retaining recess can also be set to a rectangle. In this case, the anti-rotation member 8 can be set to a cylindrical shape or a prism shape. Moreover, it is also possible to combine the retaining recess with an arc-shaped cross-section and the anti-rotation member 8 with a prism shape.

[0117] In this example, the retaining recess 22 has a radius of curvature that is the same as or slightly larger than half the diameter D of the anti-rotation member 8. The circumferential opening width of the retaining recess 22 on the outer circumferential surface of the nut 3 is approximately the same as the diameter D of the anti-rotation member 8. Furthermore, the diameter of the inscribed circle of the radially deepest portion of the retaining recess 22 is greater than or equal to the outer diameter of the first mating surface 17. However, regarding the size of the anti-rotation member 8 and the retaining recess 22, they can be arbitrarily set according to their respective shapes, as long as they can engage circumferentially with the radially inner portion of the anti-rotation member 8.

[0118] The retaining recesses 22 are arranged at equal intervals in the circumferential direction on the outer circumferential surface of the nut 3. In this example, since there are two retaining recesses 22, the two retaining recesses 22 are arranged at positions 180 degrees out of phase. In addition, the retaining recesses 22 are respectively arranged at positions (phases) offset in the circumferential direction from all the circulation grooves 11 provided on the inner circumferential surface of the nut 3.

[0119] Specifically, the retaining recess 22 of one of the two retaining recesses 22 ( Figure 7 The retaining recess 22 below is positioned 45 degrees offset circumferentially from the center of a circulation groove 11 formed at the same axial position as the retaining recess 22 in the circulation groove 11 provided on the inner circumferential surface of the nut 3. Additionally, the other retaining recess 22 ( Figure 7 The retaining recess 22 above is positioned 135 degrees offset from the center of the aforementioned circulation groove 11 in the circumferential direction to the other side. Therefore, as Figure 8As shown, when viewing the nut 3 axially, the two retaining recesses 22, indicated by circles, are each positioned 45 degrees off-center in the circumferential direction relative to the two circumferentially close circulation grooves 11 (indicated by ×). In other words, one retaining recess 22 is positioned at the circumferential center of two adjacent circulation grooves 11 among the four circulation grooves 11, and the other retaining recess 22 is positioned at the circumferential center of the remaining two circulation grooves 11. Furthermore, when a structure is adopted in which circulation components such as stops with circulation grooves are fixed relative to the nut, the retaining recesses can be positioned off-center from the circulation components in the circumferential direction. Moreover, when circulation components are evenly spaced at multiple locations in the circumferential direction, the retaining recesses can be positioned off-center from the two circumferentially close circulation components by the same angular position in the circumferential direction. In other words, the retaining recesses can be positioned at the circumferential center of two adjacent circulation components.

[0120] The nut 3 has a non-rotational engagement portion 24 at one end on the axial side. The non-rotational engagement portion 24 is provided on a circumferential portion of the side surface of the nut 3 on the axial side and protrudes towards that side. The non-rotational engagement portion 24 has a fan-shaped form. In the illustrated example, the nut 3, including the non-rotational engagement portion 24, is integrally formed; however, the nut 3 can also be formed by combining and fixing a cylindrical component with a nut-side ball thread groove on its inner circumferential surface and a separately formed non-rotational engagement portion.

[0121] <ball bearing>

[0122] The ball 4 is a steel ball with a predetermined diameter, which is rotatably disposed in the load path 10 and the circulation groove 11. The ball 4 disposed in the load path 10 rolls while bearing a compressive load, while the ball 4 disposed in the circulation groove 11 does not bear a compressive load and is pushed and rolled by the subsequent ball 4.

[0123] <piston>

[0124] The piston 5, serving as a fitting cylinder, is made of a metal such as an aluminum alloy and has a bottomed cylindrical shape. The piston 5 is pressed in and fixed to the outside of the nut 3, and moves linearly together with the nut 3. The piston 5 is coaxially configured with the nut 3 and is axially movable within the insertion hole 9 provided in the housing 7. The piston 5 has a cylindrical portion 25 and a base plate portion 26 that blocks the end opening on the axially opposite side of the cylindrical portion 25.

[0125] The cylindrical portion 25 has a cylindrical second mating surface 27 at one axial side of its inner circumferential surface, which is externally fitted into the nut 3. In this example, the inner diameter of the second mating surface 27 is constant axially except for the portion forming the second retaining ring groove 29, and is slightly smaller than the outer diameter of the first mating surface 17 of the nut 3. Furthermore, in this example, the portion of the inner circumferential surface of the cylindrical portion 25 that separates from the second mating surface 27 to the other axial side also has the same inner diameter as the second mating surface 27. However, as long as the portion of the inner circumferential surface of the cylindrical portion 25 having the second mating surface 27, i.e., the mating portion with the first mating surface 17, is sized for mating with the nut 3, the inner diameter of the portion of the inner circumferential surface of the cylindrical portion 25 that separates from the mating portion to the other side can be larger or smaller than the second mating portion.

[0126] The cylindrical portion 25 has a small-diameter stepped portion 28 at one end of its outer peripheral surface on one side. The small-diameter stepped portion 28 is disposed radially outside the second mating surface 27, and its outer diameter is slightly smaller than the portion separated axially from the small-diameter stepped portion 28. Therefore, the maximum outer diameter of the piston 5, which is the outer diameter of the portion of the cylindrical portion 25 separated axially from the small-diameter stepped portion 28, can be set to be the same as the maximum outer diameter of the nut 3. Furthermore, setting the maximum outer diameter of the piston 5 to be the same as the maximum outer diameter of the nut 3 is not limited to the case where the maximum outer diameter of the piston 5 is exactly the same as the maximum outer diameter of the nut 3, but also includes the case where the maximum outer diameter of the piston 5 is substantially the same as the maximum outer diameter of the nut 3 within the range of unavoidable manufacturing tolerances.

[0127] The second mating surface 27 has a second retaining ring groove 29 extending throughout its axial middle portion for locking the outer diameter side of the retaining ring 6. The second retaining ring groove 29 is formed by machining, such as cutting, with reference to the end face 5x on one axial side of the piston 5. The second retaining ring groove 29 has a rectangular cross-sectional shape and is fitted to the portion radially opposite to the first retaining ring groove 20 when the piston 5 is externally fixed to the nut 3. The radial depth T of the second retaining ring groove 29 is... 29 The radial depth of the second retaining ring groove 29 is smaller than that of the first retaining ring groove 20, and the radial width (maximum value) T6 of the retaining ring 6 is smaller. However, if the retaining ring 6 can be fixed between the first retaining ring groove 20 and the second retaining ring groove 29 in a mounting manner, the radial depth of the second retaining ring groove 29 can be larger than the radial width of the retaining ring 6. In addition, the axial width of the second retaining ring groove 29 is the same as the axial width of the first retaining ring groove 20. The end face 5x on one axial side of the piston 5 is a flat surface existing on an imaginary plane orthogonal to the central axis of the piston 5.

[0128] The end face 5x on one side of the axial direction of the piston 5 and the second mating surface 27 are connected via a tapered second chamfered portion 30.

[0129] In this example, the axial end of the piston 5 is externally fixed relative to the axial end of the nut 3 by pressing it in. This causes the first mating surface 17 of the axial end of the nut 3 and the second mating surface 27 of the axial end of the piston 5 to be in interference contact along the entire axial length. Furthermore, with the piston 5 externally fixed to the nut 3, the axial end face 5x of the piston 5 abuts axially against the stepped surface 19 of the outer circumferential surface of the nut 3.

[0130] <Blocking ring>

[0131] The retaining ring 6 is a component used to prevent relative axial displacement between the nut 3 and the piston 5. Furthermore, in this example, the piston 5 is pressed in and fixed relative to the nut 3, thereby also preventing relative axial displacement between the nut 3 and the piston 5. Therefore, the retaining ring 6 serves as reinforcement in cases where the interference fit between the nut 3 and the piston 5 is reduced.

[0132] The retaining ring 6 is made of metal and has a rectangular cross-sectional shape, and its overall structure is a missing ring (roughly C-shaped).

[0133] The retaining ring 6 is secured between the first retaining ring groove 20 of the nut 3 and the second retaining ring groove 29 of the piston 5 in a mounting manner. Specifically, the inner diameter portion of the retaining ring 6 is secured in the first retaining ring groove 20, and the outer diameter portion of the retaining ring 6 is secured in the second retaining ring groove 29.

[0134] The outer diameter of the retaining ring 6 in its free state is at least greater than the outer diameter D of the first mating surface 17 fitted on the outer circumferential surface of the nut 3. 17 The diameter D of the groove bottom of the second retaining ring groove 29 formed on the inner circumferential surface of the piston 5 is larger, preferably greater than that of the groove bottom diameter D. 29 big.

[0135] The assembly of retaining ring 6 can be, for example, as Figure 9 (A) and Figure 9 (B) Proceed in that manner.

[0136] First, such as Figure 9 As shown in (A), by pressing the axial end of the nut 3 into the inner side of the retaining ring 6, the retaining ring 6 is elastically expanded using the first chamfered portion 21, thus securing the retaining ring 6 in the first retaining ring groove 20. Then, as... Figure 9As shown in (B), while the retaining ring 6 is elastically reduced in diameter by the second chamfered portion 30 of the piston 5 and pressed into the inside of the first retaining ring groove 20, the axial end of the nut 3 on the other side is pressed into the axial end of the piston 5. Furthermore, with the axial end face 5x of the piston 5 abutting against the stepped surface 19 of the nut 3 and the axial positions of the first retaining ring groove 20 and the second retaining ring groove 29 aligned, the retaining ring 6 elastically returns to its original position. Thus, the retaining ring 6 can be secured between the first retaining ring groove 20 of the nut 3 and the second retaining ring groove 29 of the piston 5 in a mounting manner. In this example, a shaft retaining ring that is first secured in the first retaining ring groove 20 of the nut 3 is described as the retaining ring 6; however, alternatively, a hole retaining ring that is first secured in the second retaining ring groove 29 of the piston 5 can also be used as the retaining ring 6.

[0137] <shell>

[0138] The outer casing 7 is in the shape of a bottomed cylindrical tube and has an internal through-hole 9 with a circular cross-sectional shape. The central axis of the through-hole 9 is configured to be coaxial with the central axis of the threaded shaft 2. The through-hole 9 has an inner diameter that allows the nut 3 and piston 5 to pass through axially. Specifically, the through-hole 9 has an inner diameter that is slightly larger than the cylindrical portion 25 of the piston 5 and the major diameter surface 18 of the nut 3.

[0139] The through hole 9 has a guide groove 31 on its inner circumferential surface for slidably engaging the anti-rotation member 8 along the axial direction. The guide groove 31 extends axially and is provided at multiple locations (two locations in this example) along the circumferential direction of the inner circumferential surface of the through hole 9. In this example, the guide groove 31 is provided from one end of the through hole 9 along the axial direction to the middle of the axial direction.

[0140] The end of the guide groove 31 on one axial side opens onto the end face of the housing 7 on one axial side. The end of the guide groove 31 on the other axial side has an abutment surface 32 facing the axial side. Therefore, the guide groove 31 opens on the inner circumferential surface of the insertion hole 9 and the end face of the housing 7 on one axial side, respectively. The central axis of the guide groove 31 is configured to be parallel to the central axis of the insertion hole 9. The axial dimension of the guide groove 31 is sufficiently larger than the axial dimension of the anti-rotation member 8, and is determined according to the required stroke of the nut 3 and the piston 5.

[0141] The guide groove 31 has a cross-sectional shape that allows it to engage circumferentially with the radially outer portion of the anti-rotation member 8. In this example, the anti-rotation member 8 is configured as a cylinder, as will be described later, therefore, as Figure 6As shown, the cross-sectional shape of the guide groove 31 on the imaginary plane orthogonal to the central axis of the through hole 9 is set to an arc shape. Specifically, the guide groove 31 has a semi-circular arc cross-sectional shape with a central angle of approximately 180 degrees. Therefore, the circumferential width of the guide groove 31 increases towards the radially inward direction. The guide groove 31 has a radius of curvature that is approximately the same size as the retaining recess 22 provided on the outer circumferential surface of the nut 3. The circumferential opening width of the guide groove 31 on the inner circumferential surface of the through hole 9 is approximately the same as the diameter D of the anti-rotation member 8. However, the shape of the guide groove 31 is arbitrary as long as it can engage with the radially outer portion of the anti-rotation member 8 in the circumferential direction. For example, the cross-sectional shape of the guide groove 31 can also be set to a rectangle. In addition, the size of the guide groove 31 can be arbitrarily set according to the shape of the guide groove 31 and the anti-rotation member 8 and their shape relationship, as long as it can engage with the radially outer portion of the anti-rotation member 8 in the circumferential direction.

[0142] Guide grooves 31 are arranged at equal intervals in the circumferential direction on the inner circumferential surface of the through hole 9. In this example, two guide grooves 31 are provided, and thus the two guide grooves 31 are arranged at positions with a phase difference of 180 degrees. In addition, in the assembled state of the ball screw device 1, the guide grooves 31 and the retaining recesses 22 are arranged at the same position in the circumferential direction. Therefore, the guide grooves 31 and the retaining recesses 22 are arranged opposite each other in the radial direction.

[0143] The portion of the inner circumferential surface of the through hole 9 located axially opposite to the guide groove 31 has multiple (two in the illustrated example) sealing grooves 33a and 33b. The sealing grooves 33a and 33b are annular in shape. O-rings 34a and 34b are respectively fitted into the sealing grooves 33a and 33b to seal between the inner circumferential surface of the through hole 9 and the outer circumferential surface of the piston 5.

[0144] In this example, the outer casing 7 is configured as a bottomed cylindrical shape, but the shape of the outer casing is arbitrary and can be appropriately changed. In addition, in this example, the outer casing 7 has a structure that only has a through hole (cylinder bore) 9 inside, but inside the outer casing 7, in addition to the cylinder bore, it can also have a motor housing for accommodating a motor, a gear housing for accommodating gears, etc.

[0145] <Anti-rotation component>

[0146] The anti-rotation component 8 is a metal component used to prevent the nut 3 from rotating relative to the housing 7, and it has a cylindrical shape.

[0147] The anti-rotation member 8 is configured such that, with the central shaft parallel to the central shaft of the insertion hole 9, it is radially sandwiched between the retaining recess 22 provided on the outer peripheral surface of the nut 3 and the guide groove 31 provided on the inner peripheral surface of the insertion hole 9. In other words, the anti-rotation member 8 is configured to be mounted on the retaining recess 22 and the guide groove 31.

[0148] The radially inner portion of the anti-rotation component 8 ( Figure 6 The lower part) is disposed inside the retaining recess 22. Additionally, as... Figure 5 As shown, the radially inner portion of the anti-rotation member 8 is axially sandwiched between the closing surface 23 of the retaining recess 22 and the axial end face 5x of the piston 5. In other words, the axial end face of the anti-rotation member 8 faces the closing surface 23 axially, and the axial end face of the other side of the anti-rotation member 8 faces the axial end face 5x of the piston 5. Therefore, the anti-rotation member 8 achieves axial anti-disengagement through the closing surface 23 and the axial end face 5x of the piston 5. Therefore, the radially inner portion of the anti-rotation member 8 is disposed inside the retaining recess 22 without axial movement.

[0149] In this example, the axial dimension of the anti-rotation component 8 is set to be slightly smaller than the axial dimension of the nut 3 from the stepped surface 19 to the closing surface 23 of the retaining recess 22. Therefore, with the piston 5 externally fixed to the nut 3, the axial dimension of the anti-rotation component 8 is slightly smaller than the axial distance from the end face 5x of the piston 5 on one axial side abutting the stepped surface 19 to the closing surface 23. Therefore, a gap is formed between the end face of the anti-rotation component 8 on one axial side and the closing surface 23, and / or between the end face of the anti-rotation component 8 on the other axial side and the end face 5x of the piston 5 on one axial side. In other words, the end faces on both axial sides of the anti-rotation component 8 do not simultaneously abut against the closing surface 23 and the end face 5x of the piston 5 on one axial side, which are axially opposed.

[0150] The radially outer portion of the anti-rotation component 8 ( Figure 6 The upper part) is positioned inside the guide groove 31. For example... Figure 1 As shown, the axial dimension of the guide groove 31 is set to be sufficiently larger than the axial dimension of the anti-rotation member 8, so that the radially outer portion of the anti-rotation member 8 can be slidably disposed on the inner side of the guide groove 31 in the axial direction.

[0151] During the assembly of the ball screw assembly 1, the anti-rotation member 8, coated with grease, is placed inside the retaining recess 22, thus preventing it from falling off. Alternatively or additionally, the anti-rotation member 8 can also be prevented from falling off by arranging a guide cylinder around the anti-rotation member 8, which covers the area inside the retaining recess 22.

[0152] The ball screw device 1 in this example has a limiter 35 for limiting the end of the stroke of the nut 3.

[0153] Limiters

[0154] The limiter 35 has a protrusion 36 in the shape of an annulus and a rotating side engaging portion (claw portion) 37 in the shape of a protrusion.

[0155] The protrusion 36 is externally fitted to the engagement shaft portion 13 of the threaded shaft 2 without being rotatably oriented relative to it. The protrusion 36 has a locking hole 38 at its radial center portion, which allows it to pass through the engagement shaft portion 13 axially. In this example, the locking hole 38 is a spline hole with internal spline teeth 39 formed on its inner circumferential surface. By engaging the internal spline teeth 39 formed on the inner circumferential surface of the locking hole 38 with the external spline teeth 15 formed on the outer circumferential surface of the engagement shaft portion 13, the protrusion 36 is externally fitted to the engagement shaft portion 13 without being rotatably oriented relative to it.

[0156] The protrusion 36 has a cylindrical outer peripheral surface. The rotatable engaging portion 37 is provided on a portion of the outer peripheral surface of the protrusion 36 in the circumferential direction and protrudes radially outward.

[0157] The ball screw device 1 in this example has a drive component 40 for rotating and driving the threaded shaft 2.

[0158] <Drive Components>

[0159] The drive component 40 is a gear, pulley, or similar component that transmits torque input from a drive source such as an electric motor to the threaded shaft 2, thereby rotating and driving the threaded shaft 2. The drive component 40 is arranged adjacent to the limiter 35 on one side of the axial direction.

[0160] The drive unit 40 has a base plate portion 41, a cylindrical portion 42, and a torque input portion 43.

[0161] The base plate portion 41 has a circular flat plate shape and a mounting hole 44 extending axially through its radial center. Internal spline teeth 45 are formed on the inner circumferential surface of the mounting hole 44. By engaging the internal spline teeth 45 formed on the inner circumferential surface of the mounting hole 44 with the external spline teeth 15 formed on the portion of the fitting shaft portion 13 that separates axially from the portion of the external fitting retainer 35, the base plate portion 41 is externally fitted relative to the fitting shaft portion 13 without relative rotation. Furthermore, if the fitting shaft portion 13 has external serrations, internal serrations are formed on the inner circumferential surface of the mounting hole 44, causing the external and internal serrations to engage.

[0162] The cylindrical portion 42 is provided on the radially outer side of the drive member 40. The axial end of the cylindrical portion 42 is connected to the radially outer side of the base plate portion 41. The cylindrical portion 42 has an inner diameter slightly larger than the outer diameter of the nut 3. The cylindrical portion 42 covers the periphery of the axial end of the threaded portion 12.

[0163] The torque input section 43 is provided on the outer peripheral surface of the drive member 40. In this example, the torque input section 43 is provided on the outer peripheral surface of the cylindrical portion 42. Therefore, the torque input section 43 is positioned to overlap with the threaded portion 12 in the radial direction.

[0164] The torque input unit 43 is a gear unit when a gear is used as the drive member 40, a belt member receiving surface with a belt member when a pulley is used as the drive member 40, and a toothed part with a chain mounted when a sprocket is used as the drive member 40. In any case, torque from the drive source is input to the torque input unit 43. Alternatively, the output shaft of the motor can be used as the drive member 40. In this case, the torque input unit 43 is constituted by the output shaft itself, and a spline hole with internal spline teeth 39 that engage with the external spline teeth of the fitting shaft part 13 is provided at the front end of the output shaft, or a serrated hole with internal serrations that engage with the external serrations of the fitting shaft part 13 is provided at the front end of the output shaft.

[0165] <Instructions for the Operation of the Ball Screw Mechanism>

[0166] In the ball screw device 1 of this example, when the threaded shaft 2 is rotated via the drive member 40 by a drive source (not shown), the nut 3, which prevents relative axial displacement with respect to the piston 5 by the retaining ring 6 and prevents relative rotation with respect to the housing 7 by the anti-rotation member 8, moves linearly together with the piston 5 inside the through hole 9. Thus, liquid or gas filling the through hole (cylinder bore) 9 is discharged or drawn in through a communication hole (not shown) provided in the housing 7. During the linear movement of the nut 3 and piston 5, the anti-rotation member 8 is pressed axially by the closing surface 23 of the retaining recess 22 or the end face 5x on one side of the piston 5, and moves linearly together with the nut 3 and piston 5.

[0167] In this example, when the nut 3 moves relative to the threaded shaft 2 in one axial direction to advance the piston 5, axial force (axial load) is transmitted between the nut 3 and the piston 5 via the contact portion between the stepped surface 19 of the nut 3 and the end face 5x of the piston 5 on one axial direction. Conversely, when the nut 3 moves relative to the threaded shaft 2 in one axial direction to retract the piston 5, in a structure where the end of the piston 5 on one axial direction is externally fixed relative to the end of the nut 3 on the other axial direction by pressing, as in this example, axial force is transmitted between the nut 3 and the piston 5 via the pressed-in fitting portion. However, if the interference fit of the fitting portion decreases due to the thermal expansion of the piston 5, power is transmitted between the nut 3 and the piston 5 via the retaining ring 6. Furthermore, for example, when the brake fluid is sealed in the through hole 9 of the housing 7, and the piston 5 is always subjected to load from the other side of the axial direction due to the pressure generated by the brake fluid, the axial force can be transmitted through the contact portion between the end face 5x of the piston 5 on the axial side and the stepped surface 19 of the nut 3, regardless of the direction of movement of the nut 3.

[0168] When the nut 3 moves relative to the threaded shaft 2 in one axial direction and reaches the end of its stroke, the non-rotating engagement portion 24 of the nut 3 and the rotating engagement portion 37 of the limiter 35 engage in the circumferential direction. This prevents rotation of the threaded shaft 2. 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 limiter 35. Furthermore, the end of the stroke of the nut 3 relative to the threaded shaft 2 in the other axial direction can be limited by the end face of the anti-rotation member 8 abutting against the abutting surface 32, which is the closed end of the guide groove 31, or it can be limited using various known stroke limiting mechanisms.

[0169] According to the ball screw device 1 in this example, the relative axial displacement between the nut 3 and the piston 5 can be effectively prevented without increasing the manufacturing cost, and the overall device can be miniaturized and the load capacity increased.

[0170] That is, in this example, the ball screw device 100 with the existing structure described in Japanese Patent Application Publication No. 2016-35322 (see reference) Figure 23 Unlike conventional ball screw assemblies 100, the piston 5 is not externally fitted onto the nut 3 in a manner that completely covers the nut 3. Instead, one axial end of the piston 5 is externally fitted onto the other axial end of the nut 3. Therefore, the inner diameter of the piston 5 can be kept smaller than the maximum outer diameter of the nut 3. As a result, compared with conventional ball screw assemblies 100, the radial dimension of the ball screw assembly 1 can be reduced, achieving miniaturization.

[0171] Furthermore, the outer diameter of the large-diameter surface 18 of the nut 3, which is not fitted with the piston 5, can be increased without being constrained by the inner diameter of the piston 5. That is, the large-diameter surface 18 of the nut 3 can be maximized relative to the inner diameter of the insertion hole 9 into which the piston 5 can be inserted. Therefore, the load capacity of the ball screw device 1 is increased.

[0172] In this example, not only is the axial end of the piston 5 pressed into the axial end of the nut 3, but the retaining ring 6 is also secured between the first retaining ring groove 20 on the first mating surface 17 of the nut 3 and the second retaining ring groove 29 on the second mating surface 27 of the piston 5. Therefore, even when the difference in the coefficients of thermal expansion between the nut 3 (made of an iron alloy) and the piston 5 (made of an aluminum alloy) reduces the interference fit between the first mating surface 17 and the second mating surface 27, the retaining ring 6 effectively prevents axial displacement of the nut 3 and the piston 5. Therefore, according to the ball screw device 1 of this example, axial displacement of the nut 3 and the piston 5 can be effectively prevented without increasing manufacturing costs.

[0173] By pressing the piston 5 into the axial end of the nut 3 on the other side of the axial direction, it is possible to prevent the piston 5 from wobbling relative to the nut 3. In particular, when changing (reversing) the axial movement direction of the nut 3 relative to the threaded shaft 2, it is possible to prevent the piston 5 from wobbling relative to the nut 3 and suppress the generation of noise.

[0174] By connecting the axial end face 3x of the nut 3 to the first mating surface 17 via a tapered first chamfer 21, the retaining ring 6 can be elastically expanded in diameter using the first chamfer 21 when it is locked into the first retaining ring groove 20. This improves the ease of assembling the retaining ring 6. Furthermore, by connecting the axial end face 5x of the piston 5 to the second mating surface 27 via a tapered second chamfer 30, the retaining ring 6 can be pressed into the first retaining ring groove 20 while the axial end face of the nut 3 is pressed into the axial end face of the piston 5 using the second chamfer 30. This also improves the ease of assembling the retaining ring 6.

[0175] The maximum outer diameter of nut 3 (outer diameter of large diameter surface 18) is the same as the maximum outer diameter of piston 5 (outer diameter of cylindrical portion 25), therefore, nut 3 can be incorporated as part of piston 5. In other words, the total length of piston 5 can be considered to be extended by the amount of nut 3. Therefore, tilting (wobbling) of piston 5 relative to insertion hole 9 can be suppressed.

[0176] A small-diameter step portion 28 is provided at one end of the outer peripheral surface of the piston 5 on one side of the axial direction. Therefore, as the second mating surface 27 is pressed into the first mating surface 17 and / or a second retaining ring groove 29 is formed on the second mating surface 27, even if the small-diameter step portion 28 is enlarged, it is possible to effectively prevent the small-diameter step portion 28, whose roundness has decreased due to the enlargement, from contacting the inner peripheral surface of the through hole 9.

[0177] The first retaining ring groove 20 is formed in the portion that separates from the ball thread groove 16 on the nut side to the other side in the axial direction. Therefore, it is possible to suppress the reduction in the strength of the nut 3 due to the formation of the first retaining ring groove 20.

[0178] The first retaining ring groove 20 is formed with the stepped surface 19, which serves as the abutment surface, as a reference, and the second retaining ring groove 29 is formed with the end face 5x on one axial side of the piston 5, which serves as the abutment surface, as a reference. Therefore, during the assembly of the ball screw assembly 1, when the end face 5x on one axial side of the piston 5 abuts against the stepped surface 19 of the nut 3, the axial positions of the first retaining ring groove 20 and the second retaining ring groove 29 can be precisely aligned (precisely opposed in the radial direction).

[0179] In this example, the radially inner portion of the anti-rotation member 8, located inside the retaining recess 22, is axially sandwiched between the closing surface 23 of the retaining recess 22 and the axial end face 5x of the piston 5, thereby achieving axial anti-disengagement of the anti-rotation member 8. Therefore, the ball screw device 1 of this example can omit anti-disengagement components such as retaining rings or threaded components to achieve anti-disengagement of the anti-rotation member 8. Furthermore, in this example, the anti-rotation member 8 is used separately from the nut 3 and the housing 7, thus significantly reducing manufacturing costs compared to, for example, cases where a key is integrally formed on the inner circumferential surface of the housing. Additionally, the shape accuracy of the anti-rotation member 8 can be well achieved at low cost. Therefore, according to the ball screw device 1 of this example, anti-rotation of the nut 3 can be achieved with a smaller number of parts, resulting in reduced manufacturing costs.

[0180] In this example, the axial dimension of the anti-rotation member 8 is made slightly smaller than the axial distance from the end face 5x of the piston 5 on one axial side that abuts against the stepped surface 19 of the nut 3 to the closing surface 23 of the retaining recess 22. This creates gaps between the end face of the anti-rotation member 8 on one axial side and the closing surface 23, and / or between the end face of the anti-rotation member 8 on the other axial side and the end face 5x of the piston 5 on one axial side. Therefore, axial force transmitted between the nut 3 and the piston 5 can be prevented from being transmitted via the anti-rotation member 8. In this example, axial force can be transmitted through the contact portion between the end face 5x of the piston 5 on one axial side and the stepped surface 19 of the nut 3. Therefore, coaxiality between the nut 3 and the piston 5 is easily ensured, and deformation of the anti-rotation member 8 can be prevented.

[0181] Furthermore, the retaining recesses 22 are positioned offset circumferentially from all the circulation grooves 11 provided on the inner circumferential surface of the nut 3. Specifically, when viewing the nut 3 axially, the two retaining recesses 22 are positioned offset circumferentially from the two circulation grooves 11 that are closer in the circumferential direction by the same angle (45 degrees each in this example) to opposite sides. Therefore, the reduction in strength of the nut 3 caused by the formation of the retaining recesses 22 can be suppressed. Thus, it is not necessary to blindly increase the outer diameter of the nut 3, and the enlargement of the ball screw device 1 can be prevented.

[0182] In this example, the end of the piston 5 on one axial side is fixed relative to the end of the nut 3 on the other axial side by pressing it in. However, alternatively, the end of the piston 5 on one axial side can also be fixed relative to the end of the nut 3 on the other axial side by a clearance fit.

[0183] In this example, the cross-sectional shape of the retaining ring 6 is set to rectangular, but alternatively, the cross-sectional shape of the retaining ring 6 can also be set to circular. In this case, the cross-sectional shapes of the first retaining ring groove 20 and the second retaining ring groove 29 can each be set to semi-circular or rectangular.

[0184] In this example, the axial dimension of the anti-rotation component 8 is made slightly smaller than the axial distance from the stepped surface 19 of the nut 3 to the closing surface 23 of the retaining recess 22. However, alternatively, the axial dimension of the anti-rotation component 8 can also be made slightly larger than the axial distance from the stepped surface 19 of the nut 3 to the closing surface 23 of the retaining recess 22. In this case, axial force can be transmitted through the contact portion between the end face 5x on one axial side of the piston 5 and the end face on the other axial side of the anti-rotation component 8.

[0185] [Second Example]

[0186] use Figure 10 A second example of an embodiment of this disclosure will be described.

[0187] In this example, the first mating surface 17a provided at the end of the outer peripheral surface of the nut 3 on the opposite side of the axial direction is provided with a stepped shape. The first mating surface 17a has a small diameter portion 46 on the axial side of the portion of the first retaining ring groove 20 that is smaller than the outer diameter of the portion on the opposite side of the first retaining ring groove 20.

[0188] Therefore, in the state where the end of the piston 5 on one axial side is externally fixed relative to the end of the nut 3 on the other axial side by pressing, the first mating surface 17a and the second mating surface 27 are in interference contact in a portion of the axial direction. Specifically, only the portion of the first mating surface 17a located on the axial side relative to the first retaining ring groove 20 is in interference contact with the second mating surface 27.

[0189] In this example, a smaller diameter portion 46 is provided on the axially opposite side of the first retaining ring groove 20 in the first mating surface 17a. Therefore, compared to the first example, the amount of diameter expansion of the retaining ring 6 when it is locked into the first retaining ring groove 20 can be reduced. Thus, the assembly operation of the ball screw device 1 is simplified.

[0190] The other structures and effects of the second example are the same as those of the first example.

[0191] [Third Case]

[0192] use Figure 11 A third example of an embodiment of this disclosure will be described.

[0193] The ball screw device 1a in this example differs from the ball screw device 1 in the first and second examples in that the piston 5a is fixedly embedded relative to the nut 3a.

[0194] In this example, the inner circumferential surface of the nut 3a is formed by a stepped cylindrical surface. The nut 3a has a cylindrical first mating surface 17b at the end on the other side of the axial direction of the inner circumferential surface, which is embedded with a piston 5a. The inner circumferential surface has a small diameter surface 47, which is smaller than the inner diameter of the first mating surface 17b and has a nut-side ball thread groove 16 formed on the inner circumferential surface, from the axial middle part to the axial side part.

[0195] The inner diameter of the first mating surface 17b, except for the portion where the first retaining ring groove 20a is formed, is axially constant throughout.

[0196] The first mating surface 17b has a first retaining ring groove 20a covering the entire circumference of the axial middle portion for locking the outer diameter side portion of the retaining ring 6. The first retaining ring groove 20a has a rectangular cross-sectional shape and is formed by machining such as cutting, with the end face 3x on the other side of the axial direction of the nut 3a as a reference. The radial depth of the first retaining ring groove 20a is smaller than the radial width of the retaining ring 6. In addition, the axial width of the first retaining ring groove 20a is slightly larger than the axial thickness of the retaining ring 6.

[0197] The nut 3a has a small-diameter stepped portion 48 at its end on the axial side of its outer peripheral surface. The small-diameter stepped portion 48 is located radially outward of the first mating surface 17b, and its outer diameter is slightly smaller than that of the portion axially separated from the small-diameter stepped portion 48. The portion of the nut 3a axially separated from the small-diameter stepped portion 48 has the same outer diameter as the large-diameter surface 49 of the piston 5a. Furthermore, the case where the portion of the nut 3a axially separated from the small-diameter stepped portion 48 has the same outer diameter as the large-diameter surface 49 of the piston 5a is not limited to having an outer diameter completely identical to the outer diameter of the large-diameter surface 49, but also includes cases where the outer diameter is substantially the same as the outer diameter of the large-diameter surface 49 within a manufacturing tolerance range.

[0198] The end face 3x on the other side of the axial direction of the nut 3a and the first mating surface 17b are connected via a tapered first chamfered portion 21a.

[0199] In this example, the outer peripheral surface of piston 5a is formed by a stepped cylindrical surface. Piston 5a has a cylindrical second mating surface 27a at one end of its outer peripheral surface along one axial direction, and a cylindrical large-diameter surface 49 extending from the axial middle portion to the other axial side of its outer peripheral surface. Furthermore, the outer peripheral surface of piston 5a has an annular stepped surface 50 facing one axial direction between the second mating surface 27a and the large-diameter surface 49. The stepped surface 50 is a flat surface existing on an imaginary plane orthogonal to the central axis of piston 5a. The outer diameter of the large-diameter surface 49 is the same as the outer diameter (maximum outer diameter) of nut 3a.

[0200] The outer diameter of the second mating surface 27a, except for the portion where the second retaining ring groove 29a is formed, is axially constant and is slightly larger than the inner diameter of the first mating surface 17a of the nut 3a.

[0201] The second mating surface 27a has a second retaining ring groove 29a extending throughout its axial middle portion for securing the inner diameter side of the retaining ring 6. The second retaining ring groove 29a is formed by machining, such as cutting, based on the stepped surface 50 of the piston 5a. The second retaining ring groove 29a has a rectangular cross-sectional shape and is positioned radially opposite to the first retaining ring groove 20a when the piston 5a is internally fixed to the nut 3a. The radial depth of the second retaining ring groove 29a is the same as or greater than the radial width of the retaining ring 6. Furthermore, the axial width of the second retaining ring groove 29a is slightly larger than the axial thickness of the retaining ring 6.

[0202] The end face 5x on one side of the axial direction of the piston 5a and the second mating surface 27a are connected via a tapered second chamfered portion 30a.

[0203] In this example, the piston 5a is pressed in and fixed to one axial side relative to the nut 3a to the other axial side. This causes the first mating surface 17b and the second mating surface 27a to have an interference fit along their entire axial length. Furthermore, with the piston 5a fixed in place by the nut 3a, the end face 3x of the nut 3a to the other axial side abuts against the stepped surface 50 on the outer circumferential surface of the piston 5a in the axial direction.

[0204] With the piston 5a embedded and fixed in the nut 3a, the retaining ring 6 is secured between the first retaining ring groove 20a of the nut 3a and the second retaining ring groove 29a of the piston 5a in a mounting manner. Specifically, the outer diameter portion of the retaining ring 6 is secured in the first retaining ring groove 20a, and the inner diameter portion of the retaining ring 6 is secured in the second retaining ring groove 29a.

[0205] In this example, the assembly of the retaining ring 6 can be performed as follows.

[0206] First, by pressing the axial end of the piston 5a into the inside of the retaining ring 6, the retaining ring 6 is elastically expanded using the second chamfer 30a, thus securing the retaining ring 6 in the second retaining ring groove 29a. Next, while reducing the diameter of the retaining ring 6 using the first chamfer 21a of the nut 3a and pressing it into the inside of the second retaining ring groove 29a, the axial end of the piston 5a is pressed into the axial end of the nut 3a. Then, with the axial end face 3x of the nut 3a abutting against the stepped surface 50 of the piston 5a and the axial positions of the first retaining ring groove 20a and the second retaining ring groove 29a aligned, the retaining ring 6 is elastically restored. Thus, the retaining ring 6 can be secured between the first retaining ring groove 20a of the nut 3a and the second retaining ring groove 29a of the piston 5a in a mounting manner.

[0207] In this example, to prevent the nut 3a from rotating, a retaining recess 22a is provided on the outer peripheral surface of the piston 5a to retain the anti-rotation component 8. The retaining recess 22a is provided at multiple locations (e.g., two locations) in the circumferential direction on the outer peripheral surface of the piston 5a. The retaining recess 22a is provided on one axial side of the large-diameter surface 49 in the outer peripheral surface of the piston 5a.

[0208] The retaining recess 22a is an axially elongated groove. The end of the retaining recess 22a on the other axial side has a closed surface 23a facing the axial side. The end of the retaining recess 22a on the axial side opens at the stepped surface 50. Therefore, the retaining recess 22a opens on both the outer peripheral surface of the piston 5a and the stepped surface 50. The central axis of the retaining recess 22a is parallel to the central axis of the piston 5a. The axial dimension from the stepped surface 50 to the closed surface 23a is slightly larger than the axial dimension of the anti-rotation member 8. The closed surface 23a is a flat surface existing on an imaginary plane orthogonal to the central axis of the piston 5a, and is partially circular (approximately semi-circular) when viewed from the axial direction.

[0209] The retaining recess 22a has a cross-sectional shape that allows it to engage circumferentially with the radially inner portion of the anti-rotation member 8. In this example, the anti-rotation member 8 is configured as a cylinder, therefore the cross-sectional shape of the retaining recess 22a on an imaginary plane orthogonal to the central axis of the piston 5a is set to an arc shape. Furthermore, the diameter of the inscribed circle of the radially deepest portion of the retaining recess 22a is greater than or equal to the outer diameter of the second mating surface 27a.

[0210] In this example, the retaining recess 22a provided on the outer peripheral surface of the piston 5a and the guide groove 31 provided on the inner peripheral surface of the insertion hole 9 of the housing 7 (not shown) (see reference) Figure 1 Between them, anti-rotation components 8 are arranged radially.

[0211] The radially inner portion of the anti-rotation member 8 is disposed inside the retaining recess 22a. Furthermore, the radially inner portion of the anti-rotation member 8 is axially sandwiched between the closing surface 23a of the retaining recess 22a and the axially opposite end face 3x of the nut 3a. In other words, the axially opposite end face of the anti-rotation member 8 faces the closing surface 23a axially, and the axially one end face of the anti-rotation member 8 faces the axially opposite end face 3x of the nut 3a. Therefore, the anti-rotation member 8 achieves axial anti-disengagement through the closing surface 23a and the axially opposite end face 3x of the nut 3a. Thus, the radially inner portion of the anti-rotation member 8 is disposed inside the retaining recess 22a without axial movement.

[0212] In this example, the axial dimension of the anti-rotation component 8 is set to be slightly smaller than the axial dimension from the stepped surface 50 of the piston 5a to the closing surface 23a of the retaining recess 22a. Therefore, when the piston 5a is embedded and fixed in the nut 3a, the axial dimension of the anti-rotation component 8 is slightly smaller than the axial distance from the end face 3x of the nut 3a on the other axial side that abuts against the stepped surface 50 to the closing surface 23a. Therefore, a gap is formed between the end face of the anti-rotation component 8 on the other axial side and the closing surface 23a, and / or between the end face of the anti-rotation component 8 on one axial side and the end face 3x of the nut 3a on the other axial side. In other words, the end faces on both axial sides of the anti-rotation component 8 do not simultaneously abut against the axially opposed closing surface 23a and the end face 3x of the nut 3a on the other axial side.

[0213] The radially outer portion of the anti-rotation component 8 is slidably disposed on the inner side of the guide groove 31.

[0214] In this case, it is also possible to effectively prevent the axial relative displacement of the nut 3a and the piston 5a without increasing manufacturing costs, and to achieve overall miniaturization of the device and increase in load capacity.

[0215] In this example, a small-diameter step portion 48 is provided at the end of the outer peripheral surface of the nut 3a on the axial side. Therefore, as the second mating surface 27a is pressed into the first mating surface 17b and / or the first retaining ring groove 20a is formed on the first mating surface 17b, even if the small-diameter step portion 48 is enlarged, it is possible to effectively prevent the small-diameter step portion 48, whose roundness has decreased due to the enlargement, from sliding contact with the inner peripheral surface of the through hole 9.

[0216] The first retaining ring groove 20a is formed with reference to the end face 3x on the other side of the axial direction of the nut 3a, and the second retaining ring groove 29a is formed with reference to the stepped surface 50 provided on the piston 5a. Therefore, during the assembly operation of the ball screw device 1a, when the end face 3x on the other side of the axial direction of the nut 3a is brought into contact with the stepped surface 50 of the piston 5a, the axial positions of the first retaining ring groove 20a and the second retaining ring groove 29a can be made to be precisely aligned.

[0217] In this example, a retaining recess 22a is formed on the outer peripheral surface of the piston 5a, and it is not necessary to form a retaining recess on the outer peripheral surface of the nut 3a. Therefore, it is not necessary to increase the outer diameter (wall thickness) of the nut 3a to ensure its strength. Thus, miniaturization of the ball screw device 1a is achieved. Furthermore, it is not necessary to rely on the circulation groove 11 provided on the inner peripheral surface of the nut 3a (see...). Figure 7 The formation position of the recess 22a is maintained by considering the relationship between the two. This increases the design freedom of the ball screw device 1a, thereby reducing the manufacturing cost of the ball screw device 1a.

[0218] The other structures and effects of the third example are the same as those of the first example.

[0219] [Fourth Case]

[0220] use Figures 12-16 A fourth example of an embodiment of this disclosure will be described.

[0221] This example is a variation of the first example. In the first example, the retaining ring 6 cannot be visually confirmed from the outside after assembly of the ball screw assembly 1, therefore it is impossible to confirm from the outside whether the retaining ring 6 is assembled. Therefore, the ball screw assembly 1b in this example has a confirmation window 51 for externally confirming whether the retaining ring 6 is assembled.

[0222] In this example, the piston 5 is fixed externally relative to the nut 3. Therefore, the axial end of the cylindrical portion 25 constituting the piston 5 is configured to cover the retaining ring 6 from the radially outer side. Therefore, a confirmation window 51 that passes through radially is formed at the axial end of the cylindrical portion 25. The confirmation window 51 is formed at the portion that radially overlaps with the second retaining ring groove 29 formed on the second mating surface 27. Therefore, the confirmation window 51 is formed at the portion that radially overlaps with the retaining ring 6 that is engaged with the second retaining ring groove 29.

[0223] In this example, the confirmation window 51 is a circular through hole (circular hole) that opens only on both radially sides of the cylindrical portion 25. That is, the confirmation window 51 opens only on the small-diameter stepped portion 28 on the outer circumferential surface of the cylindrical portion 25 and the second mating surface 27 on the inner circumferential surface of the cylindrical portion 25. The confirmation window 51 has an inner diameter slightly smaller than the axial width of the second retaining ring groove 29. Therefore, the confirmation window 51 opens at the bottom of the second retaining ring groove 29. Alternatively, the inner diameter of the confirmation window can be the same as or larger than the axial width of the second retaining ring groove. In this case, the confirmation window is provided such that the second retaining ring groove is divided in the circumferential direction. Furthermore, the shape of the confirmation window can be appropriately modified.

[0224] In this example, confirmation windows 51 are provided at multiple locations along the circumference of the cylindrical portion 25 (two locations are shown in the illustrated example). The multiple confirmation windows 51 are arranged at equal intervals along the circumference. In this example, as... Figure 15 As shown, the spacing between a pair of adjacent confirmation windows 51 in the circumferential direction is set to be greater than the width W in the circumferential direction of the discontinuity 52 of the circumferential part provided on the retaining ring 6. 52 Large. Furthermore, it is confirmed that after the inspection process of the retaining ring 6 is completed, the window 51 can be covered with a pin or the like as needed.

[0225] <Manufacturing Method of Ball Screw Device>

[0226] When manufacturing the ball screw device 1b in this example, an inspection process for the retaining ring 6 can be included in the manufacturing process (after the assembly process).

[0227] The inspection process can be performed visually or using an inspection fixture 53 or a sensor such as a laser sensor. Either method can be used alone, or a combination of both methods can be employed. In the case of combining the two methods, the visual method is performed first, followed by the method using the inspection fixture 53 or a sensor.

[0228] The visual inspection method is as follows.

[0229] After the ball screw assembly 1b is assembled, the presence of the retaining ring 6 is visually confirmed through the confirmation window 51. Furthermore, since the confirmation window 51, located at a point phased with the discontinuity 52 of the retaining ring 6, cannot accurately determine whether the retaining ring 6 is assembled, if the presence of the retaining ring 6 cannot be confirmed by visually checking one confirmation window 51, the presence of the retaining ring 6 is confirmed by visually checking another confirmation window 51. Thus, in this visual inspection method, the presence of the retaining ring 6 can be easily confirmed without the use of tools.

[0230] The inspection method using inspection fixture 53 is as follows: Figure 16 Proceed as shown.

[0231] After the ball screw assembly 1b is assembled, the front end 54 of the inspection clamp 53 is inserted into the inside of the confirmation window 51. Here, the front end 54 has a shape that allows it to be inserted into the inside of the confirmation window 51 without wobbling; in the illustrated example, it has a cylindrical shape. The total length L of the front end 54 is set to be the same as the radial dimension H from the outer peripheral surface of the piston 5 to the bottom surface of the first retaining ring groove 20.

[0232] The insertion of the front end portion 54 is performed until the front end face of the front end portion 54 abuts against the object component or the front end portion 54 cannot be further inserted into the inner side of the inspection window 51. Then, in this state, the insertion depth of the front end portion 54 of the inspection fixture 53 is measured. The method for measuring the insertion depth is not particularly limited; for example, it can be performed by reading the scale marked on the outer peripheral surface of the front end portion 54 at the position of the outer peripheral surface of the cylindrical portion 25. Then, based on the insertion depth of the front end portion 54 of the inspection fixture 53, the presence or absence of the retaining ring 6 and whether the retaining ring 6 is properly assembled are determined.

[0233] Specifically, if the measured value of the insertion depth is consistent with the value obtained by subtracting the radial width T6 of the retaining ring 6 from the aforementioned radial dimension H, then the retaining ring 6 is deemed to have been properly assembled.

[0234] Conversely, if the front end 54 of the inspection fixture 53 is inserted into the inner side of the confirmation window 51 at both locations, and the measured insertion depth is consistent with the aforementioned radial dimension H, then the retaining ring 6 is determined to be unassembled. Furthermore, the reason for inserting the front end 54 into the inner side of the confirmation window 51 at both locations is that, similar to the case of visual inspection, there is a possibility that the phase of the confirmation window 51 at one location coincides with the phase of the discontinuity 52 of the retaining ring 6.

[0235] If the measured value of the insertion depth is greater than the value obtained by subtracting the radial width T6 from the radial dimension H but smaller than the radial dimension H, or smaller than the value obtained by subtracting the radial width T6 from the radial dimension H, it is determined that although the retaining ring 6 has been assembled, it has not been assembled properly.

[0236] As described above, the inspection method using the inspection fixture 53 can easily confirm not only the presence or absence of the retaining ring 6, but also whether the retaining ring 6 is properly assembled. Furthermore, the inspection process using the inspection fixture 53 can be performed automatically by the inspection device or by an operator. In addition, in the case of the inspection method using a sensor, except that the distance from the sensor to the object (the outer circumferential surface of the retaining ring 6, or the bottom surface of the first retaining ring groove 20 or the second retaining ring groove 29) is measured by the sensor through the confirmation window 51, its function and effect are basically the same as the inspection method using the inspection fixture 53.

[0237] Furthermore, if the visual inspection method is combined with the method using the inspection fixture 53 (or the laser method), the presence or absence of the retaining ring 6 can be determined early and easily through visual inspection. Therefore, only the device with the retaining ring 6 can be inspected using the inspection fixture 53 (or the laser method). Thus, inspection efficiency can be improved.

[0238] According to the ball screw device 1b in this example, the axial relative displacement between the nut 3 and the piston 5 can be effectively prevented without increasing the manufacturing cost, and the overall device can be miniaturized and the load capacity increased. Furthermore, after the ball screw device 1b is assembled, it can be easily confirmed whether the retaining ring 6 is assembled.

[0239] In particular, in this example, the confirmation window 51 provided at the end of the cylindrical portion 25 constituting the piston 5 on one axial side can easily confirm whether the retaining ring 6 is assembled. Therefore, it is possible to prevent the situation where the retaining ring 6 is forgotten to be assembled.

[0240] Furthermore, as an inspection procedure for the retaining ring 6, if the inspection fixture 53 is used, it is easy to confirm not only the presence or absence of the retaining ring 6, but also whether the retaining ring 6 is properly assembled. Therefore, it is possible to prevent damage or breakage of the ball screw assembly 1b due to improper assembly of the retaining ring 6, and to ensure the quality of the ball screw assembly 1b.

[0241] The other structures and effects of the fourth example are the same as those of the first example.

[0242] [Fifth Case]

[0243] use Figure 17 and Figure 18 A fifth example of an embodiment of this disclosure will be described.

[0244] In this example, based on the construction of the fourth example, only the shape of the confirmation window 51a is changed.

[0245] In this example, the confirmation window 51a is configured as a slit that opens not only on both radial sides of the cylindrical portion 25, but also at one end of the cylindrical portion 25 on one axial side. The confirmation window 51a is approximately oblong in shape, with its axial dimension longer than its circumferential dimension. The axial dimension of the confirmation window 51a is larger than the axial width of the second retaining ring groove 29 (retaining ring 6).

[0246] In this example, as an inspection fixture, a plate-shaped fixture with a front end that can be inserted into the inside of the confirmation window 51a without wobbling can be used.

[0247] In this example, the confirmation window 51a can be formed by cutting with a cutting machine or the like, thus reducing processing costs.

[0248] The other structures and effects of the fifth case are the same as those of the first and fourth cases.

[0249] [Sixth Case]

[0250] use Figure 19 and Figure 20 A sixth example of an embodiment of this disclosure will be described.

[0251] In this example, based on the construction of the fourth and fifth examples, the shape of the confirmation window 51b and the number of confirmation windows 51b are changed.

[0252] In this example, the confirmation window 51b is designed as an oblong through-hole (elongated oval hole) that opens only on both radial sides of the cylindrical portion 25. Furthermore, the circumferential dimension of the confirmation window 51b is larger than its axial dimension. The circumferential dimension W of the confirmation window 51b is... 51 The circumferential width W of the discontinuity 52 of the retaining ring 6 52 Big (W) 51 >W 52 ).

[0253] In this example, it will be confirmed that the window 51b is only provided in one part of the circumferential direction of the cylindrical part 25.

[0254] In this example, as an inspection fixture, a plate-shaped fixture with a front end that can be inserted into the inside of the confirmation window 51b without wobbling can be used.

[0255] In this example, the circumferential dimension W of the window opening 51b will be confirmed. 51 The width W in the circumferential direction of the discontinuity 52 of the retaining ring 6 is set as follows. 52Therefore, even when the confirmation window 51b and the discontinuity 52 are arranged to overlap radially, a portion of the retaining ring 6 will always be exposed inside the confirmation window 51b. Thus, the presence or absence of the retaining ring 6 can be easily confirmed. Furthermore, by using an inspection fixture, it can be easily confirmed whether the retaining ring is properly assembled. In this example, by forming only one confirmation window 51b, the inspection process for the retaining ring 6 can be performed, thereby reducing manufacturing costs.

[0256] The other structures and effects of the sixth case are the same as those of the first and fourth cases.

[0257] [Seventh Case]

[0258] use Figure 21 A seventh example of an embodiment of this disclosure will be described.

[0259] This example is a variation of the second example. In this example, the first mating surface 17a provided at the end of the outer peripheral surface of the nut 3 on the opposite side of the axial direction is provided with a stepped shape. The first mating surface 17a has a small diameter portion 46 in the portion on the opposite side of the axial direction that is larger than the outer diameter of the portion located on the opposite side of the first retaining ring groove 20.

[0260] In this example, a confirmation window 51 is also provided at one axial end of the cylindrical portion 25 that forms the piston 5 configured to cover the retaining ring 6 from the radially outer side. Specifically, the confirmation window 51 is formed in the portion of the cylindrical portion 25 that overlaps radially with the second retaining ring groove 29 formed on the second mating surface 27.

[0261] In this example, similar to the construction in the second example, the diameter expansion of the retaining ring 6 when it is locked in the first retaining ring groove 20 can also be reduced compared to the first example. Therefore, the assembly operation of the ball screw device 1 is simplified.

[0262] The other structures and effects of the seventh case are the same as those of the first, second and fourth cases.

[0263] [Case 8]

[0264] use Figure 22 An eighth example of an embodiment of this disclosure will be described.

[0265] This example is a variation of the third example. That is, in the ball screw assembly 1b of this example, the piston 5a is fixedly embedded relative to the nut 3a. Therefore, the axial end of the nut 3a on the other side is configured to cover the retaining ring 6 from the radially outer side.

[0266] In this example, a confirmation window 51 is formed at the end of the nut 3a on the opposite side of the axial direction, extending radially through. Specifically, the confirmation window 51 is formed in the portion that radially overlaps with the first retaining ring groove 20a formed in the first mating surface 17b. Therefore, the confirmation window 51 is formed in the portion that radially overlaps with the retaining ring 6 that is locked in the first retaining ring groove 20a.

[0267] In this example, the confirmation window 51 is a circular through hole (round hole) that opens only on both radial sides of the nut 3a. That is, the confirmation window 51 opens only on the small-diameter stepped portion 48 provided on the outer peripheral surface of the nut 3a and on the first mating surface 17b provided on the inner peripheral surface of the nut 3a. The confirmation window 51 has an inner diameter slightly smaller than the axial width of the first retaining ring groove 20a. Therefore, the confirmation window 51 opens at the bottom of the first retaining ring groove 20a.

[0268] In this example, confirmation windows 51 are provided at multiple locations along the circumference of the nut 3a. These confirmation windows 51 are arranged at equal intervals along the circumference. Furthermore, the spacing between adjacent pairs of confirmation windows 51 along the circumference is set to be greater than the discontinuity 52 of the retaining ring 6 (see reference). Figure 15 The width dimension W in the circumferential direction of ) 52 big.

[0269] In this case, the presence or absence of the retaining ring 6 and whether the retaining ring 6 is properly assembled can be confirmed by visual inspection and / or by using the inspection window 51 provided on the nut 3a.

[0270] The other structures and effects of the eighth case are the same as those of the first, third and fourth cases.

[0271] The embodiments of this disclosure have been described above, but the content of this disclosure is not limited thereto, and appropriate changes can be made without departing from the technical concept of this disclosure. In addition, the various embodiments of this disclosure can be appropriately combined and implemented as long as they do not create contradictions.

[0272] When implementing the contents of this disclosure, the shape of the confirmation window is not limited to the shapes shown in the examples, and can be appropriately modified as long as the presence or absence of the retaining ring can be confirmed. Furthermore, the number and location of the confirmation windows are not limited to the structures shown in the examples, and can be appropriately modified.

[0273] In various embodiments of this disclosure, a configuration is described in which, in order to prevent relative rotation of the nut relative to the housing, an anti-rotation member is held radially between a retaining recess on the outer peripheral surface of the nut or piston (fitting sleeve) and a guide groove on the inner peripheral surface of the insertion hole on the housing. However, in implementing this disclosure, the configuration for preventing relative rotation of the nut relative to the housing is not limited to the configuration using such an anti-rotation member; key configurations and other currently known configurations can be appropriately employed.

[0274] In the various embodiments of this disclosure, a piston was used as a fitting cylinder, but when implementing the contents of this disclosure, it is not limited to a piston, and other components with other functions can also be used.

[0275] Symbol explanation:

[0276] 1, 1a, 1b—Ball screw assembly; 2—Threaded shaft; 3, 3a—Nut; 3x—End face; 4—Ball; 5, 5a—Piston; 5x—End face; 6—Retaining ring; 7—Housing; 8—Anti-rotation component; 9—Through hole; 10—Load path; 11—Circulation groove; 12—Threaded part; 13—Matching shaft part; 14—Shaft-side ball thread groove; 15—External spline; 16—Nut-side ball thread groove; 17, 17a, 17b—First mating surface; 18—Large diameter surface 19—Stepped surface; 20, 20a—First retaining ring groove; 21, 21a—First chamfered portion; 22, 22a—Retaining recess; 23, 23a—Closed surface; 24—Non-rotating side engaging portion; 25—Cylindrical portion; 26—Base plate portion; 27, 27a—Second mating surface; 28—Small diameter stepped portion; 29, 29a—Second retaining ring groove; 30, 30a—Second chamfered portion; 31—Guiding groove; 32—Abutting surface; 33a, 33b—Sealing groove; 34a 34b—O-ring, 35—Limiter, 36—Protrusion, 37—Rotating side engagement part, 38—Engaging hole, 39—Internal spline, 40—Drive component, 41—Base plate part, 42—Cylinder part, 43—Torque input part, 44—Mounting hole, 45—Internal spline, 46—Small diameter part, 47—Small diameter surface, 48—Small diameter step part, 49—Large diameter surface, 50—Stepped surface, 51, 51a, 51b—Confirmation window, 52—Discontinuity, 53—Inspection window Fixture, 54—front end, 100—ball screw assembly, 101—threaded shaft, 102—nut, 103—ball, 104—piston, 105—housing, 106—shaft-side ball thread groove, 107—rolling bearing, 108—driven gear, 109—idle gear, 110—nut-side ball thread groove, 111—load path, 112—stepped surface, 113—retaining ring, 114—keyway, 115—through hole, 116—fitting groove, 117—key.

Claims

1. A ball screw device, characterized in that, have: A threaded shaft has a helical axial ball thread groove on its outer circumferential surface and rotates during use; A nut with a helical ball thread groove on its inner circumferential surface and a linear motion during use; Multiple balls are disposed between the shaft-side ball thread groove and the nut-side ball thread groove; A fitting sleeve, the end of which is fitted and fixed on one axial side to the end of the nut on the other axial side, and moves linearly together with the nut; and A retaining ring is used to prevent axial relative displacement between the nut and the fitting sleeve. The nut has a first mating surface with a first retaining ring groove at its end on the opposite axial side. The fitting cylinder has a second fitting surface at one end on the axial side, and the portion of the second fitting surface that is radially opposite to the first retaining ring groove has a second retaining ring groove. The retaining ring is fixed between the first retaining ring groove and the second retaining ring groove by means of a mounting.

2. The ball screw device according to claim 1, characterized in that, The maximum outer diameter of the fitting sleeve is the same as the maximum outer diameter of the nut.

3. The ball screw device according to claim 1, characterized in that, The fitting sleeve is fitted relative to the nut by press-in or clearance fit.

4. The ball screw device according to claim 1, characterized in that, The outer peripheral surface of the nut has: a first mating surface; a large-diameter surface adjacent to the first mating surface on one axial side and larger than the outer diameter of the first mating surface; and a stepped surface disposed between the first mating surface and the large-diameter surface and facing the other axial side. The fitting sleeve is fixed externally relative to the nut, and its axial end face abuts against the stepped surface in the axial direction.

5. The ball screw device according to claim 4, characterized in that, The first retaining ring groove is formed in the portion that is axially separated from the ball thread groove on the nut side.

6. The ball screw device according to claim 4 or 5, characterized in that, The fitting cylinder has a small-diameter stepped portion at one end of its outer circumferential surface on one side.

7. The ball screw device according to claim 4, characterized in that, have: The outer casing has an insertion hole through which the nut and the fitting sleeve can be inserted axially; and An anti-rotation component that prevents the nut from rotating relative to the housing. The insertion hole has a guide groove on its inner circumferential surface, which can engage with the radially outer portion of the anti-rotation component in the circumferential direction and extend axially. The nut has a retaining recess on the large-diameter surface, which engages circumferentially with the radially inner portion of the anti-rotation member, and includes a closed surface facing the opposite axial direction, and opens on the stepped surface. Regarding the anti-rotation component, the radially inner portion is disposed inside the retaining recess in a state between the end face of the closing surface and the axial side of the fitting cylinder, and the radially outer portion is slidably disposed inside the guide groove.

8. The ball screw device according to claim 1, characterized in that, The outer peripheral surface of the fitting cylinder has: a second fitting surface; a large-diameter surface that is adjacent to the second fitting surface on the other side of the axial direction and is larger than the outer diameter of the second fitting surface; and a stepped surface that is disposed between the second fitting surface and the large-diameter surface and faces one side of the axial direction. The fitting sleeve is fixedly embedded relative to the nut, and the stepped surface abuts against the end face of the nut on the opposite side of the axial direction.

9. The ball screw device according to claim 8, characterized in that, The nut has a small-diameter stepped portion at the axial end on the opposite side of its outer circumferential surface.

10. The ball screw device according to claim 8, characterized in that, have: The outer casing has an insertion hole through which the nut and the fitting sleeve can be inserted axially; and An anti-rotation component that prevents the nut from rotating relative to the housing. The insertion hole has a guide groove on its inner circumferential surface, which can engage with the radially outer portion of the anti-rotation component in the circumferential direction and extend axially. The fitting cylinder has a retaining recess on the large-diameter surface, which can engage circumferentially with the radially inner portion of the anti-rotation member, and includes a closed surface facing one axial direction, and an opening on the stepped surface. Regarding the anti-rotation component, the radially inner portion is disposed inside the retaining recess in a state between the closing surface and the end face on the other side of the axial direction of the nut, and the radially outer portion is slidably disposed inside the guide groove.

11. The ball screw device according to claim 1, characterized in that, The end of the nut on the other axial side and the end of the fitting sleeve on one axial side, which covers the retaining ring from the radial outside, has a radially penetrating confirmation window in the portion that overlaps with the retaining ring.

12. The ball screw device according to claim 11, characterized in that, The confirmation window is open only on both radial sides.

13. The ball screw device according to claim 11, characterized in that, The confirmation window is open not only on both radial sides, but also on the axial side.

14. The ball screw device according to claim 11, characterized in that, The retaining ring has a discontinuity at one location in the circumferential direction. The circumferential width of the confirmation window is larger than the circumferential width of the discontinuity.

15. The ball screw device according to claim 11, characterized in that, The retaining ring has a discontinuity at one location in the circumferential direction. The confirmation window is provided at multiple locations in the circumferential direction at one end of the device. The spacing between adjacent pairs of the confirmation windows in the circumferential direction is larger than the width dimension in the circumferential direction of the discontinuity.

16. A method for manufacturing a ball screw device, wherein the ball screw is the ball screw device according to any one of claims 11 to 15. The manufacturing method of this ball screw device is characterized by the following: It includes an inspection procedure to check whether the retaining ring has been properly assembled. The inspection process includes inserting the front end of the inspection fixture into the inner side of the confirmation window from the radial outside, and measuring the insertion depth of the front end of the inspection fixture.

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