Ball screw device

Abstract

In the present invention, a housing (30) includes a first axial surface (AX1) oriented in a first direction. A load from a ball screw (20) along a second direction is received by the first axial surface (AX1) via an inner ring (41), a rolling body (43), and an outer ring (42). A bearing (40) includes a restricting member (50) disposed in contact with the outer ring (42). The restricting member (50) includes a third axial surface disposed facing a second axial surface (AX2). When a screw shaft (21) or a nut (22) is rotated with respect to the housing (30), relative movement in a circumferential direction is performed between the second axial surface (AX2) and the third axial surface (AX3). Relative axial movement of the inner ring (41) relative to the outer ring (42) in the first direction is restricted on the basis of an axial positional relationship between the second axial surface (AX2) and the third axial surface (AX3).

Description

Ball screw device

[0001] This application claims priority to Japanese Patent Application Nos. 2024-012036 and 2024-012062, filed on January 30, 2024, the contents of which are incorporated herein by reference.

[0002] A ball screw includes a screw shaft, a nut, and a plurality of balls disposed between the screw shaft and the nut. In one example of a ball screw device, the rotational motion of the output shaft of a motor is converted into linear motion by a ball screw. In ball screw devices, a bearing is generally installed between the ball screw and a housing to support the rotation of the ball screw (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2004-284444

[0004] In ball screw devices with high load specifications, a technology is known that uses a bearing capable of withstanding both radial and axial loads, such as a tapered roller bearing, as the bearing between the ball screw and the housing. Ball screw devices that use bearings for radial loads, such as general ball bearings, require large-sized bearings that can withstand high loads, which tends to lead to an increase in the size of the device. Ball screw devices that use bearings suitable for both radial and axial loads avoid an increase in the size of the device, even in high-load specifications.

[0005] However, in such a ball screw device, for example, relative axial movement is likely to occur between the inner ring and the outer ring of the bearing. The relative axial movement between the inner ring and the outer ring may cause the end of the outer ring to come into contact with the outer surface of the rolling element, which may damage the bearing. Furthermore, the ball screw device may generate abnormal noise.

[0006] Furthermore, ball screw devices are being used in a wide variety of fields, and there is a demand for compact and simple configurations.

[0007] An object of the present invention is to provide a ball screw device that is preferably applicable to high load specifications, is advantageous in terms of compactness and reduction in assembly steps, and / or is highly reliable and has a long life.

[0008] A ball screw device according to one aspect of the present invention includes a ball screw having a screw shaft, a nut, and multiple balls, a housing supporting the ball screw, and a bearing having an inner ring, an outer ring, and multiple rolling elements. The bearing is disposed between the ball screw and the housing and is configured to be able to bear radial loads and axial loads. The housing has a first axial surface facing a first direction. An axial load from the ball screw along a second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring. The inner ring has a second axial surface facing the first direction. The bearing further includes a restricting member disposed in contact with the outer ring, the restricting member having a third axial surface disposed facing the second axial surface. When the screw shaft or the nut rotates relative to the housing, relative circumferential movement occurs between the second axial surface and the third axial surface. Relative axial movement of the inner ring in the first direction with respect to the outer ring is restricted based on the axial positional relationship between the second axial surface and the third axial surface.

[0009] A ball screw device according to another aspect of the present invention includes a ball screw having a screw shaft, a nut, and a plurality of balls, and a support body supporting the ball screw. The ball screw has an inner ring raceway surface provided on the screw shaft or the nut, and the support body has an outer ring raceway surface. A plurality of tapered rollers are disposed as rolling elements between the inner ring raceway surface and the outer ring raceway surface.

[0010] According to one aspect of the present invention, a ball screw device can be provided that is preferably applicable to high-load specifications, is advantageous for compactness or reducing assembly labor, and / or has high reliability and a long life.

[0011] FIG. 1 is a schematic cross-sectional view showing a ball screw device according to a first embodiment, which is an example in which a roller bearing is applied. FIG. 2 is a schematic cross-sectional view showing an example in which an angular contact ball bearing is applied. FIG. 3 is a diagram for explaining the contact angle α, where (a) relates to a tapered roller bearing and (b) relates to an angular contact ball bearing. FIG. 4 is a diagram for explaining dimensional values ​​of a tapered roller bearing. FIG. 5 is a schematic, partially enlarged cross-sectional view showing a ball screw device according to the first embodiment. FIG. 6 is a schematic, partially enlarged cross-sectional view showing a ball screw device according to a second embodiment. FIG. 7 is a schematic, partially enlarged cross-sectional view showing a ball screw device according to a third embodiment. FIG. 8 is a schematic, partially enlarged cross-sectional view showing a modified example of the third embodiment. FIG. 9 is a schematic cross-sectional view showing a ball screw device according to a fourth embodiment, which is an example in which a roller bearing is applied. FIG. 10 is a schematic cross-sectional view showing an example in which an angular contact ball bearing is applied. Fig. 11 is a schematic partially enlarged cross-sectional view showing a ball screw device, with (a) part, (b) part, and (c) part showing ball screw devices according to fourth, fifth, and sixth embodiments, respectively. Fig. 12 is a schematic cross-sectional view showing a ball screw device according to seventh embodiment. Fig. 13 is a schematic cross-sectional view showing a ball screw device according to eighth embodiment. Fig. 14 is a schematic cross-sectional view showing an example of a nut. Fig. 15 is a schematic cross-sectional view showing an example in which an angular contact ball bearing is applied. Fig. 16 is a schematic cross-sectional view showing a ball screw device according to ninth embodiment. Fig. 17 is a schematic cross-sectional view showing an example in which an angular contact ball bearing is applied.

[0012] An embodiment of the present invention will be described with reference to the drawings. In one embodiment, a ball screw device is incorporated into various mechanical devices, such as an electric brake device for a vehicle, an automatic manual transmission (AMT), or a positioning device for a machine tool, and is used to convert the rotational motion of a drive source, such as an electric motor, into linear motion to operate a driven part (actuating part). Various types of electric brake devices are applicable, such as an electro-mechanical brake (EMB) that applies braking force via a ball screw driven by a motor, and an electro-hydraulic brake (EHB) that controls the hydraulic pressure of a hydraulic brake via a ball screw driven by a motor. The ball screw device can also be applied to mechanical devices other than those mentioned above.

[0013] In the following description, unless otherwise specified, the terms axial direction, radial direction, and circumferential direction refer to the direction along the central axis of the ball screw, the radial direction of the ball screw, and the direction around the central axis of the ball screw, respectively. Furthermore, the direction from the input side to the output side along the central axis of the ball screw is referred to as the first direction (first orientation), and the direction from the output side to the input side is referred to as the second direction (second orientation).

[0014] 1 is a schematic cross-sectional view of a ball screw device 11 according to a first embodiment. The ball screw device 11 includes a ball screw 20, a housing 30 that supports the ball screw 20, and a bearing 40 that is disposed between the ball screw 20 and the housing 30.

[0015] As shown in FIG. 1 , the ball screw 20 includes a screw shaft 21, a nut 22, and a plurality of balls 23 disposed between the screw shaft 21 and the nut 22. In one example, a first shaft 91, to which a driving force of a motor (not shown) is transmitted, is connected to the nut 22. The ball screw 20 converts rotational motion into linear motion. A speed reducer may be additionally disposed between the ball screw 20 and the motor. Alternatively, the driving force may be transmitted to the nut 22 via a speed reduction mechanism using gears (including planetary gears, etc.) or pulleys disposed in a preferred position. In one example in which the ball screw device 11 is applied to an electric brake device for a vehicle, the vehicle's brake pads operate against a brake disc in response to linear motion. The ball screw 20 and the mechanism using the ball screw 20 are not limited to this example, and various configurations are applicable.

[0016] The screw shaft 21 has a shaft body and a spiral thread groove (spiral outer peripheral rolling groove) provided on the outer peripheral surface of the shaft body. In one example, at least a portion of the screw shaft 21 is made of metal. The thread groove of the screw shaft 21 is formed by cutting or rolling the outer peripheral surface of the shaft body. In forming the thread groove, grinding can be additionally performed. The thread groove shape (groove bottom shape) of the screw shaft 21 is, for example, a Gothic arch groove or a circular arc groove. The number of threads in the thread groove is set to one, two, or more. In other examples, various forms are applicable to the screw shaft 21.

[0017] The nut 22 has a cylindrical nut body and a helical thread groove (helical inner circumferential rolling groove) provided on the inner circumferential surface of the nut body. The screw shaft 21 is inserted into and disposed inside the nut 22. In one example, at least a portion of the nut 22 is made of metal. The thread groove of the nut 22 is formed by cutting or rolling the inner circumferential surface of the nut body. In forming the thread groove, grinding can be additionally performed. The thread groove shape (groove bottom shape) of the nut 22 corresponds to the groove shape of the screw shaft 21, and is, for example, a Gothic arch groove or a circular arc groove. The number of thread grooves is set to one, two, or more. In other examples, various shapes are applicable to the nut 22.

[0018] A plurality of balls 23 are disposed between the screw shaft 21 and the nut 22. The plurality of balls 23 are disposed in a space (rolling path) formed by the opposing arrangement of the screw groove of the screw shaft 21 and the screw groove of the nut 22. In FIG. 1 , two balls 23 are indicated by two-dot chain lines. In reality, the ball screw 20 includes a large number of balls 23. In one example, the plurality of balls 23 are made of metal (such as steel) or ceramics. The plurality of balls 23 roll in the rolling path as the screw shaft 21 and the nut 22 rotate relative to each other. In one example, the balls 23 return from the end point of the rolling path to the start point via a circulation path provided in the nut 22. The balls 23 disposed in the rolling path move while receiving a compressive load. The balls 23 disposed in the circulation path are pushed and moved by the subsequent balls 23. The start point and end point of the rolling path are interchanged depending on the direction of relative displacement (relative rotation direction) between the screw shaft 21 and the nut 22. In other examples, the ball screw 20 can have a different structure for circulating the balls 23 .

[0019] The housing 30 supports the ball screw 20 via bearings 40 and the like. Various additional support structures can be applied to the housing 30. At least a portion of the ball screw 20 is enclosed by the housing 30. At least a portion of the ball screw 20 is disposed in the inner space of the housing 30. In one example, at least a portion of the housing 30 is made of metal. In another example, at least a portion of the housing 30 is made of a material other than metal. The housing 30 is fixed to a predetermined structure (not shown). In one example, the housing 30 has a substantially divided structure. The division position of the housing 30 is appropriately set in consideration of the assembly process. In another example, the housing 30 can have a different structure.

[0020] The bearing 40 has an inner ring 41, an outer ring 42, and a plurality of rolling elements 43 arranged between the inner ring 41 and the outer ring 42. The plurality of rolling elements 43 are held between the inner ring 41 and the outer ring 42 via a cage 45. The bearing 40 may additionally have a seal structure 47 that seals in a lubricant.

[0021] In this embodiment, the bearing 40 is a bearing capable of bearing radial and axial loads. For example, the bearing 40 may be a single-row tapered roller bearing or a single-row angular contact ball bearing. In one example shown in FIG. 1 , the bearing 40 is a single-row tapered roller bearing, with rollers (tapered rollers) as the rolling elements 43. In another example shown in FIG. 2 , the bearing 40 is a single-row angular contact ball bearing, with balls as the rolling elements 43. Tapered roller bearings have a higher load capacity than angular contact ball bearings. Angular contact ball bearings are more suitable for high-speed rotation than tapered roller bearings. The use of a single bearing (a configuration that avoids two bearings facing each other or a configuration that combines two or more bearings) is advantageous for making the ball screw device 11 more compact. Alternatively, other types of bearings may be used.

[0022] Generally, tapered roller bearings are designed so that the raceway surface of the inner ring, the raceway surface of the outer ring, and the apex of the roller cone substantially converge on a single point on the bearing center axis. The rollers have a generally truncated conical shape. Tapered roller bearings can withstand radial loads and unidirectional axial loads. In one example, the rollers are held by a stamped steel cage or a plastic cage. In another example, the rollers are held by a pin-type cage or another structure.

[0023] Generally, angular contact ball bearings are designed so that the line connecting the contact points between the outer ring and the balls and the inner ring and the balls is inclined relative to the radial direction of the bearing. Angular contact ball bearings can support radial loads and unidirectional axial loads. In one example, the balls are held in place by a stamped steel cage or a resin cage (e.g., polyamide). In another example, the balls are held in place by a different structure.

[0024] In tapered roller bearings and angular contact ball bearings, the contact angle α is appropriately set as shown in Figure 3. Bearings with a relatively small contact angle α generally have a relatively high load capacity against radial loads. Bearings with a relatively large contact angle α generally have a high load capacity against axial loads.

[0025] In this embodiment, the contact angle α (see FIG. 3( a)) of the tapered roller bearing used as bearing 40 in ball screw device 11 of FIG. 1 is set to, for example, approximately 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35°. In one example, a tapered roller bearing with a contact angle of 20° or more is used in a ball screw device 11 with high load specifications. In another example, a tapered roller bearing with a contact angle of 25° or more is used in a ball screw device 11 with even higher load specifications. The above numerical values ​​are by way of example only, and the invention is not limited to these.

[0026] In this embodiment, the contact angle α (see FIG. 3(b)) of the angular contact ball bearing used as the bearing 40 of the ball screw device 11 of FIG. 1 is set to, for example, approximately 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, or 45°. In one example, an angular contact ball bearing with a contact angle of 27° or 32° or more is used in a ball screw device 11 with high load specifications. The above numerical values ​​are merely examples, and the invention is not limited to these.

[0027] In this embodiment, in the example of a single-row tapered roller bearing shown in FIG. 4 , where L is the axial width of the outer ring and a is the distance between the rolling elements and the end of the outer ring, a / L is set to approximately 1 / 20, 1 / 18, 1 / 16, 1 / 14, 1 / 12, 1 / 10, 1 / 8, or 1 / 6 or more. In one example, a bearing with a / L of 1 / 10 or more is used. By appropriately setting the correspondence relationship between the value of a / L and the design value of the allowable axial clearance (gap 900 described below), problems such as damage to the bearing 40 and abnormal noise caused by relative axial movement can be reliably prevented. The above numerical values ​​are merely examples and are not limiting.

[0028] Returning to FIG. 1 , in this embodiment, the inner ring 41 of the bearing 40 is attached to the nut 22 of the ball screw 20, and the outer ring 42 of the bearing 40 is attached to the housing 30. Additionally and / or alternatively, various structures can be applied that include a separate member (not shown) (such as a thrust collar, a C-shaped retaining ring, or an annular plate) for supporting the axial position of the inner ring 41 relative to the nut 22. Similarly, various structures can be applied that include a separate member (not shown) (such as a thrust collar, a C-shaped retaining ring, or annular plate) for supporting the axial position of the outer ring 42 relative to the housing 30. In the following description, an example in which a tapered roller bearing is used as the bearing 40 is shown ( FIGS. 5 to 8 ). An angular contact ball bearing can also be used as the bearing 40.

[0029] As shown in FIG. 5 , the outer diameter of the bearing 40 is larger than the outer diameter of the nut 22. In another example, the outer diameter of the bearing 40 can be smaller than the outer diameter of the nut 22. In FIG. 5 , the bearing 40 is disposed substantially radially outward of the nut 22. The nut 22 has outer surfaces 221, 222 facing radially outward. The outer surface (outer circumferential surface) 222 of the nut 22 has an outer diameter corresponding to the diameter of the hole of the bearing 40 (the inner diameter of the inner ring 41). The nut 22 and the bearing 40 (inner ring 41) are fitted together by inserting a portion of the nut 22 into the hole of the bearing 40 so that the outer surface 222 of the nut 22 and the inner surface (inner circumferential surface) 411 of the inner ring 41 face each other. The inner surface 411 of the bearing 40 (inner ring 41) is supported by the outer surface 222 of the nut 22. An appropriate interference or gap (loose fit) is provided in the fit between the nut 22 and the inner ring 41. In another example, a configuration in which the nut 22 and the inner ring 41 are integrally formed can be applied.

[0030] In this embodiment, the nut 22 has an axial surface (axial wall surface) 225 facing the second direction. The axial surface 225 is provided between the outer surfaces 221 and 222 in the radial direction and has, for example, a surface perpendicular to the axial direction. The inner ring 41 of the bearing 40 has an axial surface (axial end surface) 415 facing the first direction, which is an axial surface integrally formed with the body of the inner ring 41. The axial surface 415 is provided at the end of the inner ring 41 in the first direction and has, for example, a surface perpendicular to the axial direction. The axial surface 415 is also provided between the inner surface 411 and the outer surface 412 in the radial direction. The axial surface 225 of the nut 22 is disposed opposite the axial end surface 415 of the inner ring 41.

[0031] In this embodiment, the bearing 40 includes a restricting member 50 attached to the outer ring 42. The restricting member 50 is provided as a separate member from the main body of the outer ring 42. The restricting member 50 has a circumferential portion 511 extending in the axial direction and a diameter portion 512 extending in the radial direction. In one example, the cross-sectional shape of the restricting member 50 is substantially L-shaped. In other examples, various shapes are applicable to the restricting member 50.

[0032] In this embodiment, the regulating member 50 has a structure in which a circumferential portion 511 and a radial portion 512 are connected via a bent portion. The outer ring 42 has an outer surface 421 and an outer surface 422 having a smaller diameter than the outer surface 421. A step is provided between the outer surfaces 421 and 422. The circumferential portion 511 of the regulating member 50 has an inner diameter corresponding to the outer surface 422 of the outer ring 42 and an outer diameter corresponding to the outer surface 421 of the outer ring 42. For example, the outer diameter of the outer surface of the circumferential portion 511 is set to be smaller than the outer diameter of the outer surface 421 of the outer ring 42 and smaller than the inner diameter of the inner surface 302 of the housing 30. This is advantageous for improving the ease of assembly of the bearing 40 to the housing 30. In one example, the circumferential portion 511 of the regulating member 50 is axially press-fitted into the outer surface 422 of the outer ring 42, thereby fixing the regulating member 50 to the outer ring 42. In other examples, various configurations for attaching the restricting member 50 to the outer ring 42 are applicable.

[0033] 5 , the housing 30 has inner surfaces (inner wall surfaces) 301, 302, and 303 that are provided to surround the ball screw 20. The inner surface (inner peripheral surface) 302 is disposed between the inner surfaces 301 and 303 in the axial direction. The inner surface 302 has an inner diameter that corresponds to the outer diameter of the bearing 40 (the outer diameter of the outer ring 42). The inner surfaces 301, 302, and 303 face a space in which the ball screw 20 and structures connected to the ball screw 20 are disposed.

[0034] In this embodiment, the housing 30 has an axial surface (axial wall surface, first axial surface AX1) 311 facing the first direction and an axial surface (axial wall surface, second axial surface AX2) 312 facing the second direction. The axial surface 311 is provided between the inner surfaces 302 and 303 in the radial direction and has, for example, a surface perpendicular to the axial direction. The axial surface 312 is provided between the inner surfaces 302 and 301 in the radial direction and has, for example, a surface perpendicular to the axial direction.

[0035] The housing 30 is provided with a recess 450 including a space surrounded by the inner surface 302, the axial surface 311, and the axial surface 312. The bearing 40 is disposed in the recess 450. The bearing 40 is inserted into the recess 450 of the housing 30 so that the outer surface 421 of the outer ring 42 faces the inner surface 302 of the housing 30, and the bearing 40 (outer ring 42) and the housing 30 are fitted together. An appropriate interference or gap (loose fit) is provided in the fit between the outer ring 42 and the housing 30. The outer surface (outer peripheral surface) 421 of the bearing 40 (outer ring 42) is supported by the inner surface 302 of the housing 30. The outer ring 42 has an axial surface (axial end surface) 425 facing in the second direction. The axial surface 425 is provided at the end of the outer ring 42 in the second direction and has, for example, a surface perpendicular to the axial direction. The shaft surface 425 of the outer ring 42 and the shaft surface 311 of the housing 30 face each other and abut against each other. The end surface 425 of the outer ring 42 is supported by the shaft surface 311 of the housing 30.

[0036] In this embodiment, a radial portion 512 of the regulating member 50 is disposed between the axial surface 312 of the housing 30 and the axial surface 415 of the inner ring 41. The radial portion 512 of the regulating member 50 has a first surface 501 facing a first direction and a second surface 502 facing a second direction. The first surface 501 is disposed at a position axially spaced apart from the axial surface 312 of the housing. At least a portion of the second surface 502 is disposed facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 502 and the axial surface 415 face and abut each other, or face each other across a gap. The regulating member 50 is incorporated as part of a first assembly (outer assembly, support body) 60. A second assembly 70 (inner assembly, rotating body) is rotatably supported by the first assembly 60. In this embodiment, the first assembly 60 includes the housing 30, the outer ring 42, the regulating member 50, etc. The second assembly 70 includes a nut 22, an inner ring 41, and the like.

[0037] In this embodiment, during high-load driving, a high load (reaction force, axial load) acts in the second direction (first mode, high-load mode). In the ball screw 20, a high reaction force in the second direction caused by high-load driving acts on the nut 22 via the ball screw 20. In this first mode, the force in the second direction due to the high load is transmitted in the following order: nut 22, inner ring 41, rolling elements 43, outer ring 42, and housing 30. That is, the axial load from the ball screw 20 is received by the axial surface 311 of the housing 30 via the inner ring 41, rolling elements 43, and outer ring 42. In the bearing 40, the inner ring 41 rotates relative to the outer ring 42 while bearing a radial load and an axial load. In this ball screw device 11, even when a high axial load acts, the rotational motion of the second assembly 70 (e.g., nut 22) relative to the first assembly 60 (e.g., housing 30) is stably supported. The ball screw device 11 of this embodiment is preferably applied to high load specifications and is advantageous in terms of compactness.

[0038] In the first mode, the inner ring 41 receives a strong force in the second direction based on an axial load (reaction force). This force acts in a direction that causes the axial surface 415 of the inner ring 41 to move axially away from the second surface 502 of the regulating member 50. In one example, the ball screw device 11 is designed so that a substantial gap 900 is generated between the second surface 502 of the regulating member 50 and the axial surface 415 of the inner ring 41 when a high load is applied in the second direction. The design value of the gap 900 in the first mode (high load mode) is defined as an "allowable axial clearance (C1)." In another example, the ball screw device 11 is designed so that the gap 900 (allowable axial clearance C1) between the second surface 502 of the regulating member 50 and the axial surface 415 of the inner ring 41 is substantially zero when a high load is applied in the second direction.

[0039] As the second assembly 70 rotates relative to the first assembly 60, a relative movement (relative rotation) occurs in the circumferential direction between the second surface 502 of the regulating member 50 and the axial surface 415 of the inner ring 41. In the ball screw device 11, when the allowable axial clearance C1 greater than zero is set, a rotational load (frictional load) due to contact between the inner ring 41 and the regulating member 50 in the first mode is avoided.

[0040] In the ball screw device 11, when the load in the second direction received from the ball screw 20 is relatively small or substantially zero (no load), relative axial movement tends to occur between the inner ring 41 and the outer ring 42 (second mode, low-load mode). As described above, in the first mode, a substantial gap 900 may occur between the second surface 502 of the restricting member 50 and the axial surface 415 of the inner ring 41. Furthermore, in a low-load or no-load state, for example, when the ball screw 20 is operated in an initial state or in a predetermined orientation, the substantial gap 900 may occur. When the substantial gap 900 exists, there is a possibility that the inner ring 41 will attempt to move in a direction away from the outer ring 42 (first direction). This is due, for example, to the fact that the bearing 40 has a structure that is easily separated in the axial direction and / or that an axial component force is generated in the bearing 40 when a radial load is applied.

[0041] In this embodiment, the relative axial movement of the inner ring 41 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 50. In other words, the relative axial movement of the inner ring 41 is restricted to within the range of the design value (allowable axial clearance C1) of the gap 900 between the axial surface 415 (second axial surface AX2) and the second surface 502 (third axial surface AX3).

[0042] In this embodiment, contact between the axial surface 415 of the inner ring 41 and the second surface 502 of the restricting member 50 is permitted. Relative axial movement of the inner ring 41 in the first direction is restricted based on the axial surface 415 of the inner ring 41 contacting the second surface 502 of the restricting member 50. The range of an area (sliding area, contact area, opposing area) 910 in which the axial surface 415 and the second surface 502 can come into contact with each other is appropriately set in advance. Appropriate setting of the sliding area 910 contributes to stable operation of the bearing 40 and is advantageous for reducing rotational load and extending the life of the bearing 40.

[0043] In the present embodiment, slippage is permitted between the axial surface 415 of the inner ring 41 and the second surface 502 of the regulating member 50. In the ball screw device 11, when the axial surface 415 of the inner ring 41 abuts against the second surface 502 of the regulating member 50 during rotation, relative circumferential movement (circumferential slippage) occurs between the second surface 502 and the axial surface 415 accompanied by contact. That is, slippage (contact slippage) occurs in at least a portion of the slip region 910. In the ball screw device 11, due to the configuration that permits contact slippage, relative axial movement of the inner ring 41 in the first direction is restricted even during rotation.

[0044] In this embodiment, a configuration can be employed in which the state of slippage changes depending on the magnitude of the load in the second direction from the ball screw 20. In one example in which the allowable axial clearance C1 is designed to be greater than zero, in the first mode (high load mode), contact slippage does not occur between the axial surface 415 of the inner ring 41 and the second surface 502 of the regulating member 50. This is because the high axial load from the ball screw 20 presses the inner ring 41 in the second direction, and the presence of the gap 900 prevents the axial surface 415 of the inner ring 41 from contacting the second surface 502 of the regulating member 50 (non-contact slippage). On the other hand, in the second mode (low load mode), the axial load in the second direction from the ball screw 20 is relatively small or zero. Therefore, the position of the inner ring 41 relative to the outer ring 42 (axial relative position) tends to move in the first direction. When the axial surface 415 of the inner ring 41 abuts against the second surface 502 of the regulating member 50 during rotation, contact slippage occurs between the axial surface 415 and the second surface 502. In this example, the slip state changes between a non-contact state in the first mode and a contact state in the second mode. The rotational load generated in the slip region 910 is suppressed to a relatively small value.

[0045] In another example, the value of the allowable axial clearance C1 is designed to be substantially zero. In the first mode (high load mode), contact slippage occurs between the axial surface 415 of the inner ring 41 and the second surface 502 of the restricting member 50. For example, a rotational load (frictional load) based on preload occurs in the slip region 910. Furthermore, in the second mode (low load mode), contact slippage also occurs between the axial surface 415 and the second surface 502. In this example, the rotational load in the slip region 910 may change between the first mode and the second mode. Note that in this example, the change in the relative axial position of the inner ring 41 and the outer ring 42 between the first mode and the second mode is small, and the attitude of the bearing 40 is kept relatively constant.

[0046] In this embodiment, contact sliding occurs between the shaft surface 415 of the inner ring 41 and the second surface 502 of the regulating member 50. By appropriately designing the sliding structure, such as the material, surface precision, surface roughness, and surface shape of the regulating member 50, it is possible to reduce wear, improve assembly ease, and improve positioning accuracy, which is advantageous for extending the life of the device.

[0047] In this embodiment, the regulating member 50 is disposed to surround the side of the bearing 40 facing the first direction. In one example, the regulating member 50 has a continuous surface 550 that surrounds at least a portion of the axial surface (axial end surface) 415 of the inner ring 41, at least a portion of the axial surface (axial end surface) 424 of the outer ring 42, and the gap (gap space) 405 between the axial surface 415 and the axial surface 424. The continuous surface 550 faces the gap 405 of the bearing 40 and is disposed in the vicinity thereof. The ball screw device 11 may have a seal structure 47 that includes a portion of the regulating member 50 (e.g., the continuous surface 550). Such a configuration may have a sealing function and / or a function that assists sealing. For example, this configuration contributes to preventing leakage of lubricant from the bearing 40 and is advantageous in improving the device life.

[0048] As described above, according to this embodiment, high reliability and a long life are achieved while having a compact configuration and high load specifications, based on a configuration that restricts relative axial movement of the bearing 40. Note that in this embodiment and its modifications, as will be described later, the nut 22 of the ball screw 20 and the inner ring of the bearing 40 can be configured to be integrally formed, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0049] Second Embodiment Fig. 6 is a schematic partial cross-sectional view showing a ball screw device 12 according to a second embodiment. In the following description of the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted or simplified. In this embodiment, unlike the first embodiment, no step for attaching the regulating member 52 is provided on the outer ring 42. The bearing 40 includes a regulating member 52 attached to the outer ring 42. The regulating member 52 is provided as a separate member from the main body of the outer ring 42.

[0050] In this embodiment, as shown in FIG. 6 , the housing 30 further includes an inner surface (inner wall surface) 305 having a larger diameter than the inner surface 302. A step is provided between the inner surface 305 and the inner surface 302. For example, the housing 30 may have a divided structure including a first element 391 and a second element 392 that are coupled to each other, with the first element 391 being provided with the inner surface 302 and the second element 392 being provided with the inner surface 305. The circumferential portion 511 of the regulating member 52 has an outer diameter that is the same as or smaller than the inner surface 305 of the housing 30 and an inner diameter that corresponds to the outer surface 422 of the outer ring 42. For example, the circumferential portion 511 of the regulating member 52 is axially press-fitted into the outer surface 421 of the outer ring 42, thereby attaching the regulating member 52 to the outer ring 42.

[0051] In this embodiment, processing of the bearing 40, such as forming a step on the outer surface of the outer ring 42, is avoided. Furthermore, the regulating member 50 is accommodated in a space defined by the step provided in the housing 30. The ball screw device 12 simplifies the processing and assembly processes, which is advantageous for reducing costs. Note that in this embodiment and its modifications, as described below, the nut 22 of the ball screw 20 and the inner ring of the bearing 40 can be integrally formed, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0052] Third Embodiment Fig. 7 is a schematic partial cross-sectional view showing a ball screw device 13 according to a third embodiment. In the following description of the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted or simplified. In this embodiment, the shape of the regulating member 53 differs from the regulating member 50 of the first embodiment. The regulating member 53 is provided as a separate member from the main body of the housing 30 or the main body of the bearing 40.

[0053] In this embodiment, as shown in FIG. 7 , the restricting member 53 has a radial portion 512 extending radially, a first circumferential portion 531 extending from the radial portion 512 in a first direction, and a second circumferential portion 532 extending from the radial portion 512 in a second direction. The outer peripheral surface 535 of the restricting member 53 includes the outer peripheral surface of the first circumferential portion 531 and the outer peripheral surface of the second circumferential portion 532. For example, the outer peripheral surface 535 has a diameter corresponding to the inner surface 302 of the housing 30. In one example, the radial thickness of the first circumferential portion 531 of the restricting member 53 is greater than the radial thickness of the second circumferential portion 532. The radial thicknesses of the circumferential portions 531 and 532 can be set arbitrarily. In another example, the radial thickness of the first circumferential portion 531 can be the same as or smaller than the radial thickness of the second circumferential portion.

[0054] In this embodiment, the regulating member 53 and the outer ring 42 are arranged side by side in the axial direction. The regulating member 53 is arranged between the axial surface 312 of the housing 30 and the axial surface 424 of the outer ring 42. In one example, the regulating member 53 is sandwiched between the axial surface 312 and the axial surface 424 with a preload. In another example, the regulating member 53 is arranged between the axial surface 312 and the axial surface 424 with substantially no preload. An axial end surface of the first circumferential portion 531 can abut against the axial surface 312 of the housing 30. An axial end surface of the second circumferential portion 532 can abut against the axial surface 424 of the outer ring 42. At least a portion of the second surface 502 of the regulating member 53 is arranged facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 502 and the axial surface 415 face and abut against each other, or face each other with a gap therebetween.

[0055] In this embodiment, similar to the first embodiment, the relative axial movement of the inner ring 41 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 53. That is, the relative axial movement of the inner ring 41 is restricted within the range of the design value (allowable axial clearance C1) of the gap 900 between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 53. The axial surface 415 of the inner ring 41 contacts the second surface 502 of the restricting member 53, thereby restricting the relative axial movement of the inner ring 41 in the first direction. Furthermore, based on the contact sliding in the sliding region 910, the relative axial movement of the inner ring 41 in the first direction is restricted even during rotation.

[0056] In this embodiment, the regulating member 53 has a diameter portion 512 provided relative to the inner ring 41 of the bearing 40 and a second circumferential portion 532 provided relative to the outer ring 42. The ball screw device 13 has a reduced number of parts and a simplified assembly process, which is advantageous for reducing costs. The ball screw device 13 can also have a seal structure 47 that includes a portion of the regulating member 53 (e.g., the continuous surface 550). In this case, the seal structure 47 contributes to preventing leakage of lubricant from the bearing 40, which is advantageous for improving the device's lifespan.

[0057] Alternatively, various shapes can be applied to the regulating member 53. In the modified example shown in FIG. 8 , the regulating member 53 has a diameter portion 541 extending radially and a circumferential portion 542 extending from the diameter portion 541 in the second direction. The regulating member 53 is provided as a separate member from the main body of the housing 30 or the main body of the bearing 40. The outer circumferential surface 535 of the regulating member 53 has a diameter corresponding to the inner surface 302 of the housing 30. The regulating member 53 is inserted into the recess 450 of the housing 30 so that the outer circumferential surface 535 of the regulating member 53 faces the inner surface 302 of the housing 30, and the regulating member 53 and the housing 30 are fitted together. An appropriate interference or gap (loose fit) is provided when the regulating member 53 and the housing 30 are fitted together. The regulating member 53 and the outer ring 42 are arranged side by side in the axial direction. The regulating member 53 is arranged between the axial surface 312 of the housing 30 and the axial surface 424 of the outer ring 42. An axial end surface (first surface 501) of the restricting member 53 facing the first direction can abut against the axial surface 312 of the housing 30. An axial end surface (axial end surface 545 of the circumferential portion 542) of the restricting member 53 facing the second direction can abut against the axial surface 424 of the outer ring 42. In one example, the restricting member 53 is sandwiched between the axial surface 312 and the axial surface 424 with a preload. In another example, the restricting member 53 is disposed between the axial surface 312 and the axial surface 424 with substantially no preload. In the restricting member 53, a second surface 502 facing the second direction is disposed between the first surface 501 and the axial end surface 545 in the axial direction. The second surface 502 is provided radially inward from the axial end surface 545 and has, for example, a surface perpendicular to the axial direction. At least a portion of the second surface 502 is disposed facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 502 and the axial surface 415 face and abut against each other, or face each other across a gap. In the example of Fig. 8 , the axial surface 415 of the inner ring 41 contacts the second surface 502 of the regulating member 53, thereby restricting the relative axial movement of the inner ring 41 in the first direction. In this embodiment and its modified examples, as will be described later, the nut 22 of the ball screw 20 and the inner ring of the bearing 40 can be configured to be integrally formed, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0058] (Fourth, Fifth, and Sixth Embodiments) FIGS. 9, 10, and 11 are schematic cross-sectional views showing ball screw devices 81, 82, and 83 according to fourth, fifth, and sixth embodiments. FIGS. 9, 10, and 11(a) show a ball screw device 81 according to a fourth embodiment, which is a modification of the first embodiment. FIG. 11(b) shows a ball screw device 82 according to a fifth embodiment, which is a modification of the second embodiment. FIG. 11(c) shows a ball screw device 83 according to a sixth embodiment, which is a modification of the third embodiment. In the following description, the same components as those in the above embodiments are denoted by the same reference numerals, and their description will be omitted or simplified. In the example shown in FIG. 9, the bearing 40 is a single-row tapered roller bearing, and rollers (tapered rollers) are used as the rolling elements 43. In another example shown in FIG. 10, the bearing 40 is a single-row angular contact ball bearing, and balls are used as the rolling elements 43. In the following description, an example is shown in which a tapered roller bearing is used as the bearing 40 ( FIGS. 11 and 12 ). An angular contact ball bearing can also be used as the bearing 40. In each embodiment, the ball screw devices 81, 82, and 83 are configured so that the screw shaft 21 of the ball screw 20 rotates relative to the housing 30.

[0059] 9 and 10, in the fourth embodiment, a first shaft 91 to which a driving force of a motor (not shown) is transmitted is connected to a screw shaft 21. In the ball screw 20, rotational motion is converted into linear motion.

[0060] In this embodiment, the inner ring 41 of the bearing 40 is attached to the screw shaft 21 of the ball screw 20, and the outer ring 42 of the bearing 40 is attached to the housing 30. Additionally and / or alternatively, various structures including a separate member (not shown) (such as a thrust collar, a C-shaped retaining ring, or annular plate) for supporting the axial position of the inner ring 41 relative to the screw shaft 21 can be applied.

[0061] As shown in FIG. 11( a), the outer diameter of the bearing 40 is larger than the outer diameter of the screw shaft 21. In another example, the outer diameter of the bearing 40 can be smaller than the outer diameter of the screw shaft 21. In FIG. 11( a), the bearing 40 is disposed substantially radially outward of the screw shaft 21. The screw shaft 21 has outer surfaces 211, 212 facing radially outward. The outer surface (outer circumferential surface) 212 of the screw shaft 21 has an outer diameter corresponding to the diameter of the hole of the bearing 40 (the inner diameter of the inner ring 41). A portion of the screw shaft 21 is inserted into the hole of the bearing 40 so that the outer surface 212 of the screw shaft 21 and the inner surface (inner circumferential surface) 411 of the inner ring 41 face each other, thereby fitting the screw shaft 21 and the bearing 40 (inner ring 41) to each other. The inner surface 411 of the bearing 40 (inner ring 41) is supported by the outer surface 212 of the screw shaft 21. An appropriate interference or gap (loose fit) is provided in the fit between the screw shaft 21 and the inner ring 41. In another example, a configuration in which the screw shaft 21 and the inner ring 41 are integrally formed can be applied.

[0062] In this embodiment, the screw shaft 21 has an axial surface (axial wall surface) 215 facing the second direction. The axial surface 215 is provided between the outer surfaces 211 and 212 in the radial direction and has, for example, a surface perpendicular to the axial direction. The axial surface 215 of the screw shaft 21 is disposed opposite an axial end surface 415 of the inner ring 41.

[0063] In this embodiment, the first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, and the restricting member 50. The second assembly (inner assembly, rotating body) 70 includes the screw shaft 21, the inner ring 41, and the like.

[0064] In this embodiment, a high reaction force in the second direction caused by driving under a high load acts on the screw shaft 21 via the ball screw 20. In this first mode, the force in the second direction due to the high load is transmitted in the following order: screw shaft 21, inner ring 41, rolling elements 43, outer ring 42, and housing 30. In the ball screw device 81, even when a high axial load is applied, the rotational motion of the second assembly 70 (screw shaft 21, etc.) relative to the first assembly 60 (housing 30, etc.) is stably supported.

[0065] In this embodiment, similar to the first embodiment, the relative axial movement of the inner ring 41 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 50. That is, the relative axial movement of the inner ring 41 is restricted within the range of the design value (allowable axial clearance C1) of the gap 900 between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 50. The axial surface 415 of the inner ring 41 contacts the second surface 502 of the restricting member 50, thereby restricting the relative axial movement of the inner ring 41 in the first direction. Furthermore, based on the contact sliding in the sliding region 910, the relative axial movement of the inner ring 41 in the first direction is restricted even during rotation.

[0066] As described above, in this embodiment, even in a configuration in which the screw shaft 21 rotates with respect to the housing 30, high reliability and a long life are achieved while maintaining a compact configuration and high load specifications based on a configuration that restricts relative axial movement of the bearing 40, as in the first embodiment. The same applies to the fifth embodiment shown in Fig. 11(b) and the sixth embodiment shown in Fig. 11(c). Note that in each of the fourth, fifth, and sixth embodiments and their modifications, as described below, the screw shaft 21 of the ball screw 20 and the inner ring of the bearing 40 can be integrally formed, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0067] 12 is a schematic partial cross-sectional view showing a ball screw device 85 according to a seventh embodiment. In the following description, the same components as those in the above-described embodiments are denoted by the same reference numerals, and the description thereof will be omitted or simplified.

[0068] In this embodiment, the ball screw device 85 is configured so that the screw shaft 21 of the ball screw 20 rotates relative to the housing 30. In Fig. 12(a) , a shaft to which the driving force of a motor is transmitted is connected to the screw shaft 21, and rotational motion is converted into linear motion via the ball screw 20, causing the nut 22 to move in the first and second directions. The inner ring 41 of the bearing 40 is attached to the screw shaft 21 of the ball screw 20, and the outer ring 42 of the bearing 40 is attached to the housing 30.

[0069] In this embodiment, the bearing 40 includes a regulating member 57 attached to the outer ring 42. As shown in the enlarged schematic view of FIG. 12( c), the regulating member 57 has a circumferential portion 571 extending in the axial direction and a radial portion 572 extending in the radial direction. The radial portion 572 of the regulating member 57 has a first surface 501 facing a first direction and a second surface 502 facing a second direction. In this embodiment, at least a portion of the first surface 501 is disposed radially inward relative to the outer surface of the nut 22. In one example, the regulating member 57 may be formed by plastic processing, and then the first surface 501 and / or the second surface 502 may be subjected to additional processing such as grinding. In other examples, various methods can be applied to processing the regulating member 57. In this embodiment shown in FIG. 12, a first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, the regulating member 57, etc. The second assembly 70 (inner assembly, rotating body) includes the screw shaft 21, the inner ring 41, and the like.

[0070] In this embodiment, similarly to the above-described embodiment, the second surface 502 (third axial surface AX3) of the regulating member 57 regulates relative axial movement of the bearing 40. Also, in this embodiment, the first surface 501 (fourth axial surface AX4) of the regulating member 57 regulates movement of the nut 22 in the second direction relative to the housing 30. That is, the regulating member 57 functions as a stopper against the movement of the ball screw 20.

[0071] 12(a), when the screw shaft 21 of the ball screw 20 rotates in a predetermined direction, the nut 22 moves in the second direction. In FIG. 12(b), when the shaft surface 227 of the nut 22 abuts against the first surface 501 of the regulating member 57, the movement of the nut 22 in the second direction is stopped.

[0072] Here, if the nut 22 abuts against the axial surface of the inner ring 41, a phenomenon of the components biting into each other may occur, and excessive torque may be required when restarting, etc. This is because the axial surface of the nut 22 in a non-rotating state abuts against the axial surface of the inner ring 41 in a rotating state. In this embodiment, the nut 22 in a non-rotating state abuts against the restricting member 57 in a non-rotating state, so the phenomenon of the components biting into each other due to the abutment is avoided. This is advantageous for improving reliability and lifespan.

[0073] Furthermore, in this embodiment, similar to the above-described embodiment, high reliability and long life are achieved while having a compact configuration and high load specifications, based on a configuration that restricts relative axial movement of the bearing 40. Note that in this embodiment and its modifications, as will be described later, the screw shaft 21 of the ball screw 20 and the inner ring of the bearing 40 can be configured to be integrally formed, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0074] Next, a configuration in which the inner ring 41 of the bearing 40 is integral with the nut 22 of the ball screw 20 (FIGS. 13 and 15), and a configuration in which the inner ring 41 of the bearing 40 is integral with the screw shaft 21 of the ball screw 20 (FIGS. 16 and 17) will be described. In the following description, the same components as those in the above embodiment will be denoted by the same reference numerals, and their description will be omitted or simplified.

[0075] Eighth Embodiment Fig. 13 is a schematic cross-sectional view showing a ball screw device 691 of an eighth embodiment as a modified example of the first embodiment (Fig. 1). In this embodiment, the inner ring of the bearing 40 is formed integrally with the nut 22 of the ball screw 20. In the ball screw device 691, for example, a first shaft 101 to which a driving force of a motor (not shown) is transmitted is connected to the nut 22. In the ball screw 20, a plurality of balls 23 are arranged in a space (rolling path) formed based on the opposing arrangement of the screw groove 275 of the screw shaft 21 and the screw groove 285 of the nut 22.

[0076] In this embodiment, the ball screw 20 has an inner ring raceway surface 250 provided on the nut 22. The support body 60 has an outer ring raceway surface 350 corresponding to the inner ring raceway surface 250. A plurality of tapered rollers 43 serving as rolling elements are arranged between the inner ring raceway surface 250 and the outer ring raceway surface 350. The tapered rollers 43 have a truncated cone shape. The inner ring raceway surface 250, the outer ring raceway surface 350, and the tapered rollers 43 form a tapered roller bearing 40. The tapered rollers 43 are held between the inner ring raceway surface 250 and the outer ring raceway surface 350 via a cage. The tapered roller bearing 40 can additionally have a seal structure that seals in a lubricant. The ball screw 20 is supported by the support body 60 via the tapered roller bearing 40.

[0077] FIG. 14 is a cross-sectional view showing an example of a nut 22. The nut body 280 has a first portion 281 having a thread groove 285 and a second portion 282 having an inner ring raceway surface 250. Both the thread groove 285 and the inner ring raceway surface 250 are formed on the nut body 280. The nut 22 has the nut body 280 in which the thread groove 285 and the inner ring raceway surface 250 are integrally formed. The thread groove 285 and the inner ring raceway surface 250 are formed on the material of the nut body 280. In one example, the first portion 281 and the second portion 282 are arranged side by side in the axial direction. In another example, at least a portion of the second portion 282 is arranged to overlap the first portion 281 in the axial direction. For example, the entire inner ring raceway surface 250 or at least a portion of the inner ring raceway surface 250 may be located at the same position in the axial direction as the thread groove 285. Furthermore, the entire inner ring raceway surface 250 or at least a portion of the inner ring raceway surface 250 may be disposed radially outward of the thread groove 285. In one example, the diameter (maximum diameter, minimum diameter, center diameter, or average diameter) of the inner ring raceway surface 250 is set to be approximately the same as the outer diameter (maximum diameter, minimum diameter, center diameter, or average diameter) of the first portion 281. In another example, the diameter of the inner ring raceway surface 250 is set to be larger or smaller than the outer diameter of the first portion 281.

[0078] For example, when the maximum diameter (diameter of the large diameter portion) of the inner ring raceway surface 250 is D1 and the outer diameter of the first portion 281 is D2, D1 / D2 is greater than 0.5 and is 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.5, 3.0, 3.5, or 4.0 or less. In one example, D1 / D2 is set to be equal to or greater than approximately 0.6 and equal to or less than 2.0. In another example, D1 / D2 is set to be equal to or greater than approximately 0.8 and equal to or less than 1.2. In other examples, ratios other than those described above can be set. The above numerical values ​​are merely examples and are not limiting.

[0079] Furthermore, for example, when the radial average thickness in the area where the inner ring raceway surface 250 is formed is T1 and the radial average thickness of the first portion 281 is T2, T1 / T2 is greater than 0.1 and is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.5, or 3.0 or less. In one example, T1 / T2 is set to be equal to or greater than approximately 0.4 and equal to or less than 2.0. In another example, T1 / T2 is set to be equal to or greater than approximately 0.5 and equal to or less than 1.5. In other examples, ratios other than those described above can be set. The above numerical values ​​are merely examples and are not limiting.

[0080] As shown in FIG. 14 , the second portion 282 has a first flange (large flange) 251 and a second flange (small flange) 252. The first flange 251 has a relatively large outer diameter, and the second flange 252 has a relatively small outer diameter. A groove (recess) 253 is provided between the first flange 251 and the second flange 252 in the axial direction, and an inner ring raceway surface 250 is provided at the bottom of the groove 253. The first flange 251 has an axial end face (outer axial end face) 415 facing the first direction. The second flange 252 has an axial end face (outer axial end face) 417 facing the second direction. In one example, the axial end face 417 is the axial end face (axial end face in the second direction) of the nut 22. In another example, the nut 22 may have an axial end face other than the axial end face 417 of the second flange 252.

[0081] The inner ring raceway surface 250 is a so-called tapered surface and is inclined with respect to the central axis 800. A straight line passing through and along the inner ring raceway surface 250 intersects with the central axis 800 at a reference point 850. The reference point 850 coincides with the apex of a cone having the inner ring raceway surface 250 as its side surface. In one example, the reference point 850 is located at a position spaced apart in the second direction from the axial end face (axial end face in the second direction) 417 of the nut 22. In another example, the reference point 850 is located at the same position as the axial end face (axial end face in the second direction) 417 of the nut 22 or at a position spaced apart in the first direction from the axial end face 417. The inner ring raceway surface 250 is located between the thread groove 285 of the nut 22 and the reference point 850. In the tapered roller bearing 40 shown in FIG. 13, the apex of the cone for the inner ring raceway surface 250, the apex of the cone for the tapered roller 43, and the apex of the cone for the outer ring raceway surface 350 are designed to converge at a reference point 850 (FIG. 14).

[0082] In this embodiment, the outer ring member 242 is attached to the housing 30. Additionally and / or alternatively, various structures including a separate member (not shown) (such as a thrust collar, a C-shaped retaining ring, or annular plate) for supporting the axial position of the outer ring member 242 relative to the housing 30 are applicable.

[0083] In this embodiment, the axial load from the ball screw 20 is received by the housing 30 via the tapered rollers 43 and the outer ring member 242. In the ball screw device 691, as in the first embodiment, even when a high axial load is applied, the rotational motion of the rotating body 70 (such as the nut 22) relative to the support body 60 (such as the housing 30) is stably supported. The ball screw device 691 of this embodiment is preferably applied to high-load specifications and is advantageous for compactness.

[0084] In the present embodiment, the bearing 40 includes a restricting member 50 attached to the outer ring member 242, similar to the first embodiment. In the present embodiment, the relative axial movement of the nut 22 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (first axial surface AX1, third axial surface AX3) of the nut 22 and the second surface 1502 (second axial surface AX2, fourth axial surface AX4) of the restricting member 50. In the present embodiment, the relative axial movement of the bearing 40 is restricted by the restricting member 50, and high reliability and long life are achieved despite a compact configuration and high load specifications.

[0085] In this embodiment, the nut 22 of the ball screw 20 is provided with an inner ring raceway surface 250. In other words, the ball screw device 691 has a configuration in which the nut 22 and the inner ring of the bearing 40 are integrally formed. The ball screw device 691 is advantageous in terms of compactness compared to a configuration in which the inner ring of the bearing is attached to the nut 22 as a separate component. As described above, as a modification of each of the embodiments shown in FIGS. 1 to 2 and 5 to 8, the nut 22 of the ball screw 20 and the inner ring of the bearing 40 can be integrally formed. Furthermore, in such an integral configuration, as shown in FIG. 15, an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0086] 16 is a schematic cross-sectional view showing a ball screw device 695 of a ninth embodiment as a modification of the fourth embodiment (FIG. 9). In this embodiment, the inner ring of the bearing 40 is formed integrally with the screw shaft 21 of the ball screw 20. In this embodiment, the ball screw device 695 is configured so that the screw shaft 21 of the ball screw 20 rotates relative to the housing 30.

[0087] In this embodiment, an inner ring raceway surface 250 is provided on the screw shaft 21 (shaft body 270) of the ball screw 20. An outer ring member 242 of the bearing 40 is attached to the housing 30. Tapered rollers 43 are arranged between the inner ring raceway surface 250 of the screw shaft 21 and an outer ring raceway surface 350 of the outer ring member 242.

[0088] The shaft body 270 has a first portion 271 provided with a screw groove 275 and a second portion 272 provided with an inner ring raceway surface 250. Both the screw groove 275 and the inner ring raceway surface 250 are formed on the shaft body 270. The threaded shaft 21 has a shaft body 270 in which the screw groove 275 and the inner ring raceway surface 250 are integrally formed. The screw groove 275 and the inner ring raceway surface 250 are formed on the material of the shaft body 270. In one example, the first portion 271 and the second portion 272 are arranged side by side in the axial direction. In another example, at least a portion of the second portion 272 is arranged to overlap the first portion 271 in the axial direction. For example, the entire inner ring raceway surface 250 or at least a portion of the inner ring raceway surface 250 may be located at the same position in the axial direction as the screw groove 275. Furthermore, the entire inner ring raceway surface 250 or at least a portion of the inner ring raceway surface 250 may be disposed radially outward of the thread groove 275. In one example, the diameter (maximum diameter, minimum diameter, center diameter, or average diameter) of the inner ring raceway surface 250 is set to be larger than the outer diameter (maximum diameter, minimum diameter, center diameter, or average diameter) of the first portion 271. In another example, the diameter of the inner ring raceway surface 250 is set to be approximately the same as or smaller than the outer diameter of the first portion 271.

[0089] In this embodiment, the bearing 40 includes a restricting member 50 attached to the outer ring member 242, similar to the fourth embodiment. In this embodiment, the relative axial movement of the nut 22 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (first axial surface AX1, third axial surface AX3) of the nut 22 and the second surface 1502 (second axial surface AX2, fourth axial surface AX4) of the restricting member 50. In this embodiment, the relative axial movement of the bearing 40 is restricted by the restricting member 50, and high reliability and long life are achieved despite a compact configuration and high load specifications.

[0090] In this embodiment, an inner ring raceway surface 250 is provided on the screw shaft 21 of the ball screw 20. The ball screw device 695 has a configuration in which the screw shaft 21 and the inner ring of the bearing 40 are integrally formed. The ball screw device 695 is advantageous in terms of compactness compared to a configuration in which the inner ring of the bearing is attached to the screw shaft 21 as a separate member. As described above, as a modification of each of the embodiments shown in FIGS. 9 to 12, the screw shaft 21 of the ball screw 20 and the inner ring of the bearing 40 can be integrally formed. Furthermore, in such an integrated configuration, as shown in FIG. 17, an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0091] The technical scope of the present invention is not limited to the scope of the embodiments. Various modifications or improvements can be made to the embodiments. Forms incorporating such modifications or improvements can also be included in the technical scope of the present invention. Furthermore, the present invention is not limited to the described embodiments, and any combination of these configurations may be used.

[0092] The present disclosure may be combined as follows. (1) In one embodiment, a ball screw device includes: a ball screw having a screw shaft, a nut, and a plurality of balls; a housing supporting the ball screw; and a bearing having an inner ring, an outer ring, and a plurality of rolling elements. The bearing is disposed between the ball screw and the housing and has a structure capable of bearing radial loads and axial loads. The housing has a first axial surface facing a first direction. An axial load from the ball screw along a second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring. The inner ring has a second axial surface facing the first direction. The bearing further includes a restricting member disposed in contact with the outer ring, the restricting member having a third axial surface disposed facing the second axial surface. The second axial surface and the third axial surface face each other and abut against each other, or face each other via a gap. When the screw shaft or the nut rotates relative to the housing, relative movement in the circumferential direction occurs between the second axial surface and the third axial surface. (2) In the ball screw device described in (1) above, the regulating member is attached to the outer ring. (3) In the ball screw device described in (1) or (2) above, contact between the second axial surface and the third axial surface is permitted. (4) In the ball screw device described in any of (1) to (3) above, slippage between the second axial surface and the third axial surface is permitted. (5) In the ball screw device described in (4) above, the state of slippage changes depending on the magnitude of the axial load from the ball screw. (6) In the ball screw device described in any of (1) to (5) above, a front inner ring is attached to the screw shaft, and movement of the nut in the second direction relative to the housing is restricted by the regulating member. (7) In the ball screw device described in any of (1) to (6) above, further comprising a seal structure including at least a part of the regulating member.(8) In the ball screw device described in any one of (1) to (7) above, the bearing is a single-row tapered roller bearing or a single-row angular contact ball bearing. (9) In the ball screw device described in any one of (1) to (8) above, the screw shaft and the inner ring are integrally formed, or the nut and the inner ring are integrally formed. (10) In one embodiment, the ball screw device includes a ball screw having a screw shaft, a nut, and a plurality of balls, and a support body supporting the ball screw. The ball screw has an inner ring raceway surface provided on the screw shaft or the nut. The support body has an outer ring raceway surface. The screw shaft or the nut is integrally formed with the inner ring raceway surface. A plurality of tapered rollers are arranged as rolling elements between the inner ring raceway surface and the outer ring raceway surface. The ball screw is assembled to the support body so as to be removably mounted in a first direction. An axial load from the ball screw along a second direction is borne by the support body. The support body has an outer ring member provided with an outer ring raceway surface. The ball screw has a third axial surface facing the first direction. The support body further includes a regulating member arranged in contact with the outer ring member, the regulating member having a fourth axial surface arranged facing the third axial surface. The third axial surface and the fourth axial surface face and abut each other, or face each other across a gap. When the screw shaft or the nut rotates relative to the support body, relative movement in the circumferential direction occurs between the third axial surface and the fourth axial surface. Relative axial movement of the ball screw relative to the support body in the first direction is regulated based on the axial positional relationship between the third axial surface and the fourth axial surface. (11) In the ball screw device described in (10) above, the regulating member is attached to the outer ring member. (12) In the ball screw device described in (10) or (11) above, contact between the third axial surface and the fourth axial surface is permitted. (13) In the ball screw device described in any of (10) to (12) above, sliding between the third axial surface and the fourth axial surface is permitted. (14) In the ball screw device described in (13) above, the state of the slippage changes depending on the magnitude of the axial load from the ball screw.(15) In the ball screw device described in any one of (10) to (14) above, movement of the nut in the second direction relative to the support body is restricted by the restricting member. (16) In the ball screw device described in any one of (10) to (15) above, a seal structure including at least a part of the restricting member is further provided.

[0093] 11 to 13, 81 to 83, 85, 691, 695 Ball screw device, 20 Ball screw, 21 Screw shaft, 22 Nut, 30 Housing, 40 Bearing, 41 Inner ring, 42 Outer ring, 43 Rolling element, 50, 52, 53, 57 Regulating member, 60 First assembly, 70 Second assembly, 242 Outer ring member 250 Inner ring raceway surface, 350 Outer ring raceway surface, 900 Gap, AX1 First axial surface, AX2 Second axial surface, AX3 Third axial surface, AX4 Fourth axial surface.

Claims

1. A ball screw device comprising: a ball screw having a screw shaft, a nut, and multiple balls; a housing supporting the ball screw; and a bearing having an inner ring, an outer ring, and multiple rolling elements, wherein the bearing is disposed between the ball screw and the housing and has a structure capable of receiving radial loads and axial loads; the housing has a first axial surface facing a first direction, and an axial load from the ball screw along a second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring; the inner ring has a second axial surface facing the first direction; the bearing further has a restricting member disposed in contact with the outer ring, the restricting member having a third axial surface disposed facing the second axial surface; when the screw shaft or the nut rotates relative to the housing, relative circumferential movement occurs between the second axial surface and the third axial surface; and the relative axial movement of the inner ring in the first direction with respect to the outer ring is restricted based on the axial positional relationship between the second axial surface and the third axial surface.

2. A ball screw device according to claim 1, wherein the regulating member is attached to the outer ring.

3. A ball screw device according to claim 1 or 2, wherein contact between the second shaft surface and the third shaft surface is permitted.

4. A ball screw device according to any one of claims 1 to 3, wherein sliding is permitted between the second shaft surface and the third shaft surface.

5. A ball screw device according to claim 4, wherein the state of the sliding changes depending on the magnitude of the axial load from the ball screw.

6. A ball screw device according to any one of claims 1 to 5, wherein a front inner ring is attached to the screw shaft, and movement of the nut in the second direction relative to the housing is restricted by the restricting member.

7. A ball screw device according to any one of claims 1 to 6, further comprising a seal structure including at least a part of the regulating member.

8. A ball screw device according to any one of claims 1 to 7, wherein the bearing is a single-row tapered roller bearing or a single-row angular contact ball bearing.

9. A ball screw device according to any one of claims 1 to 8, wherein the screw shaft and the inner ring are integrally formed, or the nut and the inner ring are integrally formed.

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