Ball screw device

Abstract

A housing (30) has a first axial surface (AX1) oriented in a first direction and a second axial surface (AX2) oriented in a second direction. A load from a ball screw (20) along the second direction is received by the first axial surface (AX1) via an inner race (41), a rolling body (43), and an outer race (42). A bearing (40) or the ball screw (20) has a third axial surface (AX3) disposed facing the second axial surface (AX2). When a screw shaft (21) or a nut (22) is rotated with respect to the housing (30), relative movement in the circumferential direction occurs between the second axial surface (AX2) and the third axial surface (AX3). Axial relative movement of the inner race (41) with respect to the outer race (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. 2024-012032 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 or 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 and a second axial surface facing a second direction. An axial load from the ball screw along the second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring. The bearing or the ball screw has 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 relative 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, partially enlarged cross-sectional view showing a ball screw device according to a fourth embodiment. FIG. 10 is a schematic, partially enlarged cross-sectional view showing a ball screw device, where (a), (b), and (c) show ball screw devices according to fifth, sixth, and seventh embodiments, respectively. FIG. 11 is a schematic cross-sectional view showing a ball screw device according to an eighth embodiment, which is an example in which a roller bearing is applied. FIG. 12 is a schematic cross-sectional view showing an example in which an angular contact ball bearing is applied. FIG. 13 is a schematic partially enlarged cross-sectional view showing a ball screw device, where (a) , (b) , and (c) show ball screw devices according to the eighth, ninth, and tenth embodiments, respectively. FIG. 14 is a schematic partially enlarged cross-sectional view showing a ball screw device, where (a) , (b) , and (c) show ball screw devices according to the eleventh, twelfth, and thirteenth embodiments, respectively. FIG. 15 is a schematic cross-sectional view showing a ball screw device according to a fourteenth embodiment. FIG. 16 is a schematic cross-sectional view showing an example of a nut. FIG. 17 is a schematic cross-sectional view showing an example in which an angular contact ball bearing is applied. FIG. 18 is a schematic cross-sectional view showing a ball screw device according to a fifteenth embodiment. FIG. 19 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 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 10 ). 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. The axial surface 415 is provided at the end of the inner ring 41 in the first direction in the axial 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 ball screw 20 or the bearing 40 includes a sliding member 50. The sliding member 50 is provided as a separate member from the main body (screw shaft main body / nut main body) of the ball screw 20 or the main body (inner ring / outer ring) of the bearing 40. The sliding member 50 has a ring shape and includes a first surface 501 facing a first direction and a second surface 502 facing a second direction. The sliding member 50 is disposed between the axial surface 225 of the nut 22 and the axial end surface 415 of the inner ring 41. The axial surface 225 of the nut 22 abuts against the first surface 501 of the sliding member 50. The axial end surface 415 of the inner ring 41 abuts against the second surface 502 of the sliding member 50. The sliding member 50 is fixed to the nut 22 and the inner ring 41 by being sandwiched between the nut 22 and the inner ring 41. The sliding member 50 is incorporated as part of a second assembly (inner assembly, rotating body) 70. The second assembly 70 is rotatably supported by the first assembly (outer assembly, support) 60. In this embodiment, the first assembly 60 includes the housing 30, the outer ring 42, etc. The second assembly 70 includes the nut 22, the inner ring 41, the sliding member 50, etc. In one example, a member having a similar configuration to a sliding bearing is used as the sliding member 50. In another example, a member having a relatively simple configuration like a spacer is used as the sliding member 50.

[0032] 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.

[0033] 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.

[0034] 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 axial surface 425 of the outer ring 42 and the axial surface 311 of the housing 30 face each other and abut against each other. The end face 425 of the outer ring 42 is supported by the axial surface 311 of the housing 30. In FIG. 5 , the axial surface 312 of the housing 30 is an axial surface formed integrally with the main body of the housing 30 and faces in the second direction. The axial surface 312 of the housing 30 (second axial surface AX2) and the first surface 501 (third axial surface AX3) of the sliding member 50 are arranged to face each other. The axial surface 312 and the first surface 501 face each other and abut against each other, or face each other with a gap therebetween.

[0035] 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, sliding member 50, 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 sliding member 50, 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.

[0036] In the first mode, the sliding member 50 and the inner ring 41 are subjected to a strong force in the second direction based on an axial load (reaction force). This force acts in a direction that causes the first surface 501 of the sliding member 50 to move axially away from the axial surface 312 of the housing 30. In one example, the ball screw device 11 is designed so that a substantial gap 900 is generated between the axial surface 312 of the housing 30 and the first surface 501 of the sliding member 50 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 axial surface 312 of the housing 30 and the first surface 501 of the sliding member 50 is substantially zero when a high load is applied in the second direction.

[0037] As the second assembly 70 rotates relative to the first assembly 60, a relative movement (relative rotation) occurs in the circumferential direction between the axial surface 312 of the housing 30 and the first surface 501 of the sliding member 50. In the ball screw device 11, when the allowable axial clearance C1 is set to be greater than zero, a rotational load (frictional load) due to contact between the housing 30 and the sliding member 50 in the first mode is avoided.

[0038] 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 axial surface 312 of the housing 30 and the first surface 501 of the sliding member 50. Furthermore, in a low-load or no-load state, such as 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.

[0039] 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 312 (second axial surface AX2) of the housing 30 and the first surface 501 (third axial surface AX3) of the sliding 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 312 (second axial surface AX2) and the first surface 501 (third axial surface AX3).

[0040] In this embodiment, contact between the axial surface 312 of the housing 30 and the first surface 501 of the sliding member 50 is permitted. Based on the contact of the first surface 501 with the axial surface 312, relative axial movement of the inner ring 41 in the first direction is limited. The range of a region 910 (sliding region, contact region, opposing region) where the axial surface 312 and the first surface 501 can contact each other is appropriately set in advance. In one example, the radial range of the sliding region 910 is set to include a position (region 910A) radially inward from the outer surface (outer peripheral surface) 412 of the inner ring 41. In other words, contact between the housing 30 and the sliding member 50 is permitted at a position radially inward from the outer surface 412 of the inner ring 41. In other examples, the radial range of the sliding region 910 may be set to a range different from the above. Appropriate setting of the sliding region 910 contributes to stable operation of the bearing 40 and is advantageous for reducing rotational load and extending the life of the bearing 40.

[0041] In this embodiment, slippage is permitted between the axial surface 312 of the housing 30 and the first surface 501 of the sliding member 50. In the ball screw device 11, when the first surface 501 abuts against the axial surface 312 during rotation, relative circumferential movement (circumferential slippage) occurs between the axial surface 312 and the first surface 501 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, the configuration that permits contact slippage restricts relative axial movement of the inner ring 41 in the first direction even during rotation.

[0042] 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, contact slippage does not occur between the axial surface 312 and the first surface 501 in the first mode (high load mode). This is because the high axial load from the ball screw 20 pushes the inner ring 41 in the second direction, and the presence of the clearance 900 prevents the first surface from contacting the axial surface 312 (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 first surface 501 abuts against the axial surface 312 during rotation, contact slippage occurs between the axial surface 312 and the first surface 501. In this example, the state of slippage changes between the non-contact state in the first mode and the contact state in the second mode. The rotational load occurring in the sliding region 910 is suppressed to be relatively small.

[0043] 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 312 and the first surface 501. 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 312 and the first surface 501. 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.

[0044] In this embodiment, contact sliding occurs between the first surface 501 of the sliding member 50 and the shaft surface 312 of the housing 30. Because the member that contacts the housing 30 is a separate member from the inner ring 41, there is a high degree of freedom in designing the sliding member 50 in terms of material, surface precision, surface roughness, surface shape, etc. Appropriate design of the sliding structure can reduce wear, improve assembly ease, and improve positioning accuracy, which is advantageous for extending the life of the device.

[0045] 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.

[0046] 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. Unlike the first embodiment, this embodiment does not include a sliding member between the housing 30 and the inner ring 41. Furthermore, in this embodiment, the first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, etc. The second assembly (inner assembly, rotating body) 70 includes the nut 22, the inner ring 41, etc.

[0047] In this embodiment, the axial end surface 415 of the inner ring 41 is designed to directly abut against the axial surface 225 of the nut 22. Furthermore, the axial surface 312 (second axial surface AX2) of the housing 30 and the axial end surface 415 (third axial surface AX3) of the inner ring 41 are arranged to face each other. The axial end surface 415 is an axial surface formed integrally with the main body of the inner ring 41 and faces in the first direction. The axial surface 312 of the housing 30 is an axial surface formed integrally with the main body of the housing 30 and faces in the second direction. The axial end surface 415 and the axial surface 312 face and abut against each other, or face each other with a gap therebetween.

[0048] In this embodiment, during high-load driving, a force in the second direction due to the high load is transmitted in this order: nut 22, inner ring 41, rolling elements 43, outer ring 42, and housing 30 (first mode, high-load mode). 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 the ball screw device 12, even when a high axial load is applied, 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 12 of this embodiment is preferably applied to high-load specifications and is advantageous for compactness.

[0049] In the first mode, the inner ring 41 is subjected to a strong force in the second direction based on an axial load (reaction force). This force acts in a direction that causes the axial end surface 415 of the inner ring 41 to move axially away from the axial surface 312 of the housing 30. In one example, the ball screw device 12 is designed so that, when a high load in the second direction is applied, a substantial gap 900 is generated between the axial surface 312 of the housing 30 and the axial end surface 415 of the inner ring 41. In other words, the allowable axial clearance C1 is set to be greater than zero. In another example, the ball screw device 12 is designed so that, when a high load in the second direction is applied, the gap 900 (allowable axial clearance C1) between the axial surface 312 of the housing 30 and the axial end surface 415 of the inner ring 41 is substantially zero.

[0050] As the second assembly 70 rotates relative to the first assembly 60, a relative movement (relative rotation) occurs in the circumferential direction between the axial surface 312 of the housing 30 and the axial end surface 415 of the inner ring 41. In the ball screw device 12, when the allowable axial clearance C1 is set to be greater than zero, a rotational load (frictional load) due to contact between the housing 30 and the inner ring 41 in the first mode is avoided.

[0051] In the present 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 312 (second axial surface AX2) of the housing 30 and the axial end surface 415 (third axial surface AX3) of the inner ring 41. 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 312 and the axial end surface 415. The axial relative movement of the inner ring 41 in the first direction is limited based on the contact of the axial surface 312 with the axial end surface 415 in the sliding region 910. Furthermore, in the present embodiment, sliding is permitted between the axial surface 312 of the housing 30 and the axial end surface 415 of the inner ring 41. In the ball screw device 12, the configuration that allows contact sliding restricts the relative axial movement of the inner ring 41 in the first direction even during rotation.

[0052] In this embodiment, contact slip occurs between the axial end surface 415 of the inner ring 41 and the axial surface 312 of the housing 30. The ball screw device 12 has a reduced number of parts compared to the first embodiment, which is advantageous in terms of cost reduction. 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 as an integral part, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0053] 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, unlike the first embodiment, the housing 30 includes a sliding member 53. The sliding member 53 is provided as a separate member from the main body of the housing 30 (housing main body 330). In this embodiment, the first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, etc. The housing 30 has the housing main body 330 and the sliding member 53. The second assembly 70 (inner assembly, rotating body) includes the nut 22, the inner ring 41, etc.

[0054] In this embodiment, the sliding member 53 has a ring shape and includes a first surface 531 facing a first direction and a second surface 532 facing a second direction. The sliding member 53 is fixed to the housing main body 330 with the first surface 531 facing and abutting the axial surface 312 of the housing 30. In FIG. 7 , the second surface 532 (second axial surface AX2) of the sliding member 53 and the axial end surface 415 (third axial surface AX3) of the inner ring 41 are disposed facing each other. The second surface 532 and the axial end surface 415 face each other and abut each other, or face each other across a gap. 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 fixing the sliding member 53 to the housing main body 330 are applicable. In one example, a member having a form similar to that of a so-called sliding bearing is used as the sliding member 53. In another example, a member having a relatively simple form such as a spacer is used as the sliding member 53 .

[0055] In this embodiment, similar to the second embodiment, during high-load driving, a force in the second direction due to the high load is transmitted in the order of the nut 22, inner ring 41, rolling elements 43, outer ring 42, and housing 30 (first mode, high-load mode). In the ball screw device 13, even when a high axial load is applied, the rotational motion of the second assembly 70 (nut 22, etc.) relative to the first assembly 60 (housing 30, etc.) is stably supported.

[0056] In the first mode, the inner ring 41 is subjected to a strong force in the second direction based on an axial load (reaction force). This force acts in a direction that causes the axial end surface 415 of the inner ring 41 to move axially away from the axial surface 312 of the housing 30 (the second surface 532 of the sliding member 53). In one example, the ball screw device 13 is designed so that, when a high load in the second direction is applied, a substantial gap 900 is generated between the second surface 532 of the sliding member 53 and the axial end surface 415 of the inner ring 41. In other words, the allowable axial clearance C1 is set to be greater than zero. In another example, the ball screw device 13 is designed so that, when a high load in the second direction is applied, the gap 900 (allowable axial clearance C1) between the second surface 532 of the sliding member 53 and the axial end surface 415 of the inner ring 41 is substantially zero.

[0057] 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 532 of the sliding member 53 and the axial end surface 415 of the inner ring 41. In the ball screw device 13, when the allowable axial clearance C1 is set to be greater than zero, a rotational load (frictional load) due to contact between the sliding member 53 and the inner ring 41 in the first mode is avoided.

[0058] In the present embodiment, the relative axial movement of the inner ring 41 in the first direction is restricted based on the axial positional relationship between the second surface 532 (second axial surface AX2) of the sliding member 53 and the axial end surface 415 (third axial surface AX3) of the inner ring 41. 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 second surface 532 and the axial end surface 415. The axial relative movement of the inner ring 41 in the first direction is restricted based on the contact of the axial end surface 415 of the inner ring 41 with the sliding member 53 in the sliding region 910. Furthermore, in the present embodiment, slippage is permitted between the second surface 532 of the sliding member 53 and the axial end surface 415 of the inner ring 41. In the ball screw device 13, the configuration that allows contact slippage restricts the relative axial movement of the inner ring 41 in the first direction even during rotation.

[0059] In this embodiment, contact sliding occurs between the second surface 532 of the sliding member 53 and the axial end surface 415 of the inner ring 41. Because the member that contacts the inner ring 41 is a member separate from the housing main body 330, appropriate design of the sliding structure can reduce wear, improve assembly ease, and improve positioning accuracy, which is advantageous for extending the life of the device.

[0060] Alternatively, various shapes are applicable to the sliding member 53. In the modification shown in FIG. 8 , the sliding member 53 has a diameter portion 581 extending radially and a circumferential portion 582 extending from the diameter portion 581 in the second direction. The outer circumferential surface of the sliding member 53 has a diameter corresponding to the inner surface 302 of the housing 30. The sliding member 53 is inserted into the recess 450 of the housing 30 so that the outer circumferential surface of the sliding member 53 faces the inner surface 302 of the housing 30, and the sliding member 53 and the housing 30 are fitted together. An interference or gap (loose fit) is appropriately provided in the fit between the sliding member 53 and the housing 30. The sliding member 53 and the outer ring 42 are arranged side by side in the axial direction. The sliding 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 531) of the sliding member 53 facing in the first direction can abut against the axial surface 312 of the housing 30. An axial end surface (axial end surface 585 of the circumferential portion 582) of the sliding member 53 facing in the second direction can abut against the axial surface 424 of the outer ring 42. In one example, the sliding member 53 is sandwiched between the axial surface 312 and the axial end surface 424 with a preload. In another example, the sliding member 53 is disposed between the axial surface 312 and the axial surface 424 with substantially no preload. A second surface 532 facing in the second direction is disposed in the sliding member 53 between the first surface 531 and the axial end surface 585 in the axial direction. The second surface 532 is disposed radially inward from the axial end surface 585 and has, for example, a surface perpendicular to the axial direction. At least a portion of the second surface 532 is disposed facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 532 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 532 of the sliding member 53, thereby restricting 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.

[0061] Fourth Embodiment Fig. 9 is a schematic partial cross-sectional view showing a ball screw device 14 according to a fourth embodiment. In the following description of the fourth 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, the ball screw 20 includes a sliding member 54. The sliding member 54 is provided as a separate member from the main body of the screw shaft 21 / nut 22. In this embodiment, the first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, etc. The second assembly 70 (inner assembly, rotating body) includes the nut 22, the inner ring 41, the sliding member 54, etc.

[0062] In this embodiment, the housing 30 has an axial surface 315 facing the second direction. The nut 22 has an axial surface 226 facing the first direction. The axial surface 315 and the axial surface 226 are arranged opposite each other. The sliding member 54 is arranged between the axial surface 315 and the axial surface 226. The sliding member 54 has a ring shape and has a first surface 541 facing the first direction and a second surface 542 facing the second direction. The sliding member 54 is fixed to the nut 22 while facing and abutting against the nut 22. The axial surface 315 (second axial surface AX2) of the housing 30 and the first surface 541 (third axial surface AX3) of the sliding member 54 are arranged facing each other. The axial surface 315 and the first surface 541 face each other and abut each other, or face each other with a gap therebetween. 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 annular plate) for fixing the sliding member 54 to the nut 22. In one example, a member having a configuration similar to that of a sliding bearing is used as the sliding member 54. In another example, a member having a configuration similar to that of a relatively simple spacer is used as the sliding member 54.

[0063] In this embodiment, as in the second embodiment, during high-load driving, a force in the second direction due to the high load is transmitted in the order of the nut 22, inner ring 41, rolling elements 43, outer ring 42, and housing 30 (first mode, high-load mode). In the ball screw device 14, even when a high axial load is applied, the rotational motion of the second assembly 70 (nut 22, etc.) relative to the first assembly 60 (housing 30, etc.) is stably supported.

[0064] In the first mode, the nut 22 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 226 of the nut 22 (the first surface 541 of the sliding member 54) to move axially away from the axial surface 315 of the housing 30. In one example, the ball screw device 14 is designed so that, when a high load in the second direction is applied, a substantial gap 900 is generated between the axial surface 315 of the housing 30 and the first surface 541 of the sliding member 54. In other words, the allowable axial clearance C1 is set to be greater than zero. In another example, the ball screw device 14 is designed so that, when a high load in the second direction is applied, the gap 900 (the allowable axial clearance C1) between the axial surface 315 of the housing 30 and the first surface 541 of the sliding member 54 is substantially zero.

[0065] As the second assembly 70 rotates relative to the first assembly 60, a relative movement (relative rotation) occurs in the circumferential direction between the shaft surface 315 of the housing 30 and the first surface 541 of the sliding member 54. In the ball screw device 14, when the allowable axial clearance C1 is set to be greater than zero, a rotational load (frictional load) due to contact between the housing 30 and the sliding member 54 in the first mode is avoided.

[0066] In the present 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 315 (second axial surface AX2) of the housing 30 and the first surface 541 (third axial surface AX3) of the sliding member 54. 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 315 and the first surface 541. The first surface 541 of the sliding member 54 contacts the axial surface 315 of the housing 30 in a sliding region 910, thereby restricting the relative axial movement of the inner ring 41 in the first direction. Furthermore, in the present embodiment, slippage is permitted between the axial surface 315 of the housing 30 and the first surface 541 of the sliding member 54. In the ball screw device 14, the configuration that allows contact slippage restricts the relative axial movement of the inner ring 41 in the first direction even during rotation.

[0067] In this embodiment, contact sliding occurs between the shaft surface 315 of the housing 30 and the first surface 541 of the sliding member 54. Because the member that comes into contact with the housing 30 is a member separate from the nut 22, appropriate design of the sliding structure can reduce wear, improve assembly ease, and improve positioning accuracy, which is advantageous for extending the life of the device.

[0068] Furthermore, in this embodiment, the radial range of the sliding region 910 is set to include a position (region 910A) radially inward from the outer surface (outer peripheral surface) 412 of the inner ring 41, and a position (region 910B) radially inward from the rolling elements 43. In other words, contact between the housing 30 and the sliding member 54 is permitted at a position radially inward from the rolling elements 43. Appropriate setting of the sliding region 910 contributes to stable operation of the bearing 40 and is advantageous for reducing the rotational load and extending the life of the bearing 40.

[0069] 9 , the radial range of the sliding region 910 is set at a position radially inward relative to the rolling elements 43. Alternatively, at least a portion of the radial range of the sliding region 910 may be set at a position radially outward relative to the rolling elements 43. Furthermore, at least a portion of the radial range of the sliding region 910 may be set at a position radially outward relative to the outer surface (outer peripheral surface) 412 of the inner ring 41.

[0070] In the example shown in FIG. 9 , the ball screw 20 is provided with a sliding member 54. In a modified example of the embodiment shown in FIG. 9 , a configuration in which a sliding member is provided on the housing 30 at a position axially spaced from the bearing 40 can be applied. That is, a sliding member fixed to the housing 30 may be disposed between the axial surface of the housing 30 and the axial surface of the ball screw 20. In this modified example, the relative axial movement of the nut 22 and the inner ring 41 in the first direction is restricted based on the axial positional relationship between the axial surface (second axial surface AX2) of the sliding member provided on the housing 30 and the axial surface (third axial surface AX3) of the nut 22. Furthermore, in another modified example, the sliding structure may be configured without a sliding member, as in the second embodiment. In this configuration, the axial surface of the nut 22 and the axial surface of the housing 30 directly face each other at a position axially spaced from the bearing 40, and contact sliding occurs between the axial surface of the nut 22 and the axial surface of the housing 30. In this embodiment and its modified examples, as described below, the nut 22 of the ball screw 20 and the inner ring of the bearing 40 can be formed integrally, and / or an angular ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0071] (Fifth, Sixth, and Seventh Embodiments) Fig. 10 is a schematic cross-sectional view showing ball screw devices 15, 16, and 17 according to fifth, sixth, and seventh embodiments. Fig. 10(a) shows a ball screw device 15 according to a fifth embodiment, which is a modification of the first embodiment. Fig. 10(b) shows a ball screw device 16 according to a sixth embodiment, which is a modification of the second embodiment. Fig. 10(c) shows a ball screw device 17 according to a seventh 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 each embodiment, the ball screw devices 15, 16, and 17 further include a preload member 80.

[0072] In the fifth embodiment shown in FIG. 10A , the ball screw device 15 is configured so that the axial surface 312 (second axial surface AX2) of the housing 30 and the first surface 501 (third axial surface AX3) of the sliding member 50 approach each other due to the preload of the preload member 80. In one example, the preload member 80 is an elastic member, such as a disc spring. For example, the preload member 80 is disposed between the axial end surface 425 of the outer ring 42 and the axial surface 311 of the housing 30 in a pre-elastically deformed state. The preload member 80 applies a biasing force (preload) to the outer ring 42 in a first direction based on the elastic deformation. Furthermore, the shape (elastically deformed state) of the preload member 80 changes in response to a load acting on the bearing 40 in a second direction. In other examples, a preload mechanism other than those described above is used.

[0073] In this embodiment, in both the high load state (first mode) and the low load state (second mode), the preload from the preload member 80 acts on the bearing 40. Furthermore, in the second mode, the preload from the preload member 80 causes the axial surface 312 (second axial surface AX2) of the housing 30 and the first surface 501 (third axial surface AX3) of the sliding member 50 to come into contact with each other. This is also the case in the sixth embodiment shown in FIG. 10(b) and the seventh embodiment shown in FIG. 10(c). Similarly, a configuration further including the preload member 80 can also be applied to the fourth embodiment.

[0074] In the fifth, sixth, and seventh embodiments, the preload applied by the preload member 80 suppresses axial movement of the bearing 40 relative to the gap 900. As a result, problems such as damage to the bearing 40 and abnormal noise are reliably prevented, for example, by reducing noise and vibration. Note that in the fifth, sixth, and seventh embodiments and their modifications, as described below, 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.

[0075] (Eighth, Ninth, and Tenth Embodiments) FIGS. 11, 12, and 13 are schematic cross-sectional views showing ball screw devices 81, 82, and 83 according to eighth, ninth, and tenth embodiments. FIGS. 11, 12, and 13(a) show a ball screw device 81 according to an eighth embodiment, which is a modification of the first embodiment. FIG. 13(b) shows a ball screw device 82 according to a ninth embodiment, which is a modification of the second embodiment. FIG. 13(c) shows a ball screw device 83 according to a tenth 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. 11, 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. 12, 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. 13 and 14 ). 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.

[0076] 11 and 12 , in the eighth embodiment, a first shaft 91 to which the driving force of a motor (not shown) is transmitted is connected to the screw shaft 21. Alternatively, the driving force is transmitted to the screw shaft 21 via a speed reduction mechanism using gears (including planetary gears, etc.) or pulleys, etc., arranged in a preferred position. In the ball screw 20, rotational motion is converted into linear motion.

[0077] 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.

[0078] As shown in FIG. 13( 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. 13( 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.

[0079] 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.

[0080] In this embodiment, a sliding member 50 is disposed between the axial surface 215 of the screw shaft 21 and the axial end surface 415 of the inner ring 41. The sliding member 50 is fixed to the screw shaft 21 and the inner ring 41 by being sandwiched between the screw shaft 21 and the inner ring 41. In this embodiment, the first assembly (outer assembly, support body) 60 includes the housing 30, the outer ring 42, etc. The second assembly (inner assembly, rotating body) 70 includes the screw shaft 21, the inner ring 41, the sliding member 50, etc.

[0081] 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, sliding member 50, inner ring 41, rolling elements 43, outer ring 42, and housing 30. In the ball screw device 11, even when a high axial load is applied, the rotational motion of the second assembly 70 (e.g., screw shaft 21) relative to the first assembly 60 (e.g., housing 30) is stably supported.

[0082] 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 312 (second axial surface AX2) of the housing 30 and the first surface 501 (third axial surface AX3) of the sliding 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 312 (second axial surface AX2) and the first surface 501 (third axial surface AX3). The first surface 501 of the sliding member 50 contacts the axial surface 312 of the housing 30, 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.

[0083] 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 ninth embodiment shown in Fig. 13(b) and the tenth embodiment shown in Fig. 13(c). Note that in each of the eighth, ninth, and tenth embodiments and their 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 integrally formed, and / or an angular contact ball bearing can be used as the bearing 40 instead of a tapered roller bearing.

[0084] (Eleventh, Twelfth, and Thirteenth Embodiments) Fig. 14 is a schematic partial cross-sectional view showing ball screw devices 84, 85, and 86 according to eleventh, twelfth, and thirteenth embodiments. Fig. 14(a) shows a ball screw device 84 of an eleventh embodiment, which is a modification of the eighth embodiment. Fig. 14(b) shows a ball screw device 85 of a twelfth embodiment, which is a modification of the ninth embodiment. Fig. 14(c) shows a ball screw device 86 of a thirteenth embodiment, which is a modification of the tenth embodiment. In the following description, the same reference numerals will be used to designate the same components as those in the above embodiments, and their description will be omitted or simplified. In each embodiment, the ball screw devices 84, 85, and 86 further include a preload member 80.

[0085] In the eleventh embodiment shown in FIG. 14( a), a ball screw device 84 is configured such that the axial surface 312 (second axial surface AX2) of the housing 30 and the first surface 501 (third axial surface AX3) of the sliding member 50 approach each other due to the preload of the preload member 80. In this embodiment, the preload of the preload member 80 acts on the bearing 40 in both the high load state (first mode) and the low load state (second mode). In the second mode, the preload of the preload member 80 causes the axial surface 312 (second axial surface AX2) of the housing 30 and the first surface 501 (third axial surface AX3) of the sliding member 50 to come into contact with each other. This is also true in the twelfth embodiment shown in FIG. 14( b) and the thirteenth embodiment shown in FIG. 14( c).

[0086] In each of the eleventh, twelfth, and thirteenth embodiments, the preload applied by the preload member 80 suppresses axial movement of the bearing 40 relative to the gap 900. As a result, problems such as damage to the bearing 40 and abnormal noise are reliably prevented, for example, by reducing noise vibration. Note that in each of the eleventh, twelfth, and thirteenth 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 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.

[0087] 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. 15 and 17), 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. 18 and 19) 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.

[0088] 15 is a schematic cross-sectional view showing a ball screw device 610 of a 14th 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 610, 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.

[0089] 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.

[0090] FIG. 16 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.

[0091] 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.

[0092] 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.

[0093] As shown in FIG. 16 , 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.

[0094] 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. 15, 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. 16).

[0095] 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.

[0096] 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 610, as in the first embodiment, even when a high axial load is applied, the rotational motion of the rotating body (second assembly, inner assembly) 70 such as the nut 22 relative to the support body (first assembly, outer assembly) 60 is stably supported. The ball screw device 610 of this embodiment is preferably applied to high-load specifications and is advantageous for compactness.

[0097] In this embodiment, the ball screw 20 or the bearing 40 includes a sliding member (restricting member) 50, as in the first embodiment. In this embodiment, the sliding member (restricting member) 50 restricts the relative axial movement of the bearing 40, and high reliability and long life are achieved while having a compact configuration and high load specifications.

[0098] In this embodiment, the inner ring raceway surface 250 is provided on the nut 22 of the ball screw 20. In other words, the ball screw device 610 has a configuration in which the nut 22 and the inner ring of the bearing 40 are integrally formed. The ball screw device 610 is advantageous in terms of compactness compared to a configuration in which the inner ring of the bearing, which is a separate member, is attached to the nut 22.

[0099] In this embodiment, the tapered roller bearing 40 has a structure that allows it to be relatively easily separated in the axial direction. The ball screw device 610 is advantageous in reducing the number of assembly steps. For example, the support body 60 and the ball screw 20 can be relatively easily assembled by axially moving the ball screw 20 relative to the support body 60 in the second direction. Furthermore, the ball screw 20 can be relatively easily removed from the support body 60 by axially moving the ball screw 20 relative to the support body 60 in the first direction. As described above, as a modification of each of the embodiments shown in FIGS. 1 to 2 and 5 to 10, the nut 22 of the ball screw 20 and the inner ring of the bearing 40 can be integrally formed. Furthermore, in such an integrated embodiment, an angular contact ball bearing can be used as the bearing 40 instead of the tapered roller bearing, as shown in FIG. 17.

[0100] 18 is a schematic cross-sectional view showing a ball screw device 680 of a 15th embodiment as a modification of the eighth embodiment (FIG. 11). 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 680 is configured so that the screw shaft 21 of the ball screw 20 rotates relative to the housing 30.

[0101] 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.

[0102] 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.

[0103] In this embodiment, the ball screw 20 or the bearing 40 includes a sliding member (restricting member) 53, similar to the tenth embodiment. In this embodiment, the sliding member (restricting member) 53 restricts the relative axial movement of the bearing 40, and high reliability and long life are achieved while having a compact configuration and high load specifications.

[0104] 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 680 has a configuration in which the screw shaft 21 and the inner ring of the bearing 40 are integrally formed. The ball screw device 680 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.

[0105] In this embodiment, the tapered roller bearing 40 has a structure that allows it to be relatively easily separated in the axial direction. The ball screw device 680 is advantageous in reducing the number of assembly steps. For example, the support body 60 and the ball screw 20 can be relatively easily assembled by axially moving the ball screw 20 relative to the support body 60 in the second direction. Furthermore, the ball screw 20 can be relatively easily removed from the support body 60 by axially moving the ball screw 20 relative to the support body 60 in the first direction. As described above, as a modification of each of the embodiments shown in FIGS. 11 to 14 , 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 embodiment, an angular contact ball bearing can be used as the bearing 40 instead of the tapered roller bearing, as shown in FIG. 19 .

[0106] 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.

[0107] 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 receiving radial loads and axial loads. The housing has a first axial surface facing a first direction and a second axial surface facing a second direction. An axial load from the ball screw along the second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring. The bearing or the ball screw has 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, contact between the second axial surface and the third axial surface is permitted. (3) In the ball screw device described in (1) or (2) above, sliding between the second axial surface and the third axial surface is permitted. (4) In the ball screw device described in (3) above, the state of sliding changes depending on the magnitude of the axial load from the ball screw. (5) In the ball screw device described in any of (1) to (4) above, the bearing or the ball screw has an axial surface as the third axial surface formed on the bearing, the screw shaft, or the main body of the nut, or includes a sliding member having the third axial surface as a member separate from the bearing, the screw shaft, or the main body of the nut. (6) In the ball screw device described in any one of (1) to (4) above, the housing has an axial surface as the second axial surface formed on the main body of the housing, or is provided with a sliding member having the second axial surface as a separate member from the main body of the housing.(7) The ball screw device according to any one of (1) to (6) above, further comprising a preload member that applies a preload so that the second axial surface and the third axial surface approach each other. (8) The ball screw device according to any one of (1) to (7) above, wherein the bearing is a single-row tapered roller bearing or a single-row angular contact ball bearing. (9) The ball screw device according to any one of (1) to (8) above, wherein the screw shaft and the inner ring are integrally formed, or the nut and the inner ring are integrally formed. (10) The ball screw device according to (9) above, wherein the ball screw is removably assembled to the housing in the first direction, and an axial load from the ball screw along the second direction is borne by the housing. (11) In one embodiment, the ball screw device comprises a ball screw having a screw shaft, a nut, and a plurality of balls, and a support body that supports 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 formed integrally 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. (12) In the ball screw device described in (11) above, the ball screw is assembled to the support body so as to be removable in a first direction. An axial load from the ball screw along a second direction is borne by the support body. (13) In the ball screw device described in (11) or (12) above, the ball screw has a first axial surface facing the first direction, and the support body has a second axial surface facing the second direction. When the screw shaft or the nut rotates relative to the support body, relative movement in the circumferential direction occurs between the first axial surface and the second axial surface. Relative axial movement of the ball screw in the first direction relative to the support body is restricted based on the axial positional relationship between the first axial surface and the second axial surface. (14) In the ball screw device described in any of (11) to (13) above, contact between the first axial surface and the second axial surface is permitted. (15) In the ball screw device according to any one of (11) to (14) above, sliding is permitted between the first shaft surface and the second shaft surface.(16) In the ball screw device described in (15) above, the state of sliding changes depending on the magnitude of the axial load from the ball screw. (17) In the ball screw device described in any of (11) to (16) above, the ball screw has an axial surface as the first axial surface formed on the screw shaft or the main body of the nut, or includes a regulating member having the first axial surface as a separate member from the screw shaft or the main body of the nut. (18) In the ball screw device described in any of (11) to (17) above, the support body has an axial surface as the second axial surface formed on the main body of the support, or includes a regulating member having the second axial surface as a separate member from the main body of the support. (19) In the ball screw device described in any of (11) to (18) above, the ball screw device further includes a preload member that applies a preload so that the first axial surface and the second axial surface approach each other.

[0108] 11 to 17, 81 to 86, 610, 680 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, 53, 54 sliding member (sliding bearing, regulating member), 60 first assembly, 70 second assembly, 80 preload member, 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.

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 a second axial surface facing a second direction, an axial load from the ball screw along the second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring; the bearing or the ball screw has a third axial surface disposed facing the second axial surface, wherein relative circumferential movement occurs between the second axial surface and the third axial surface when the screw shaft or the nut rotates relative to the housing, and axial movement of the inner ring relative to the outer ring in the first direction 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 contact between said second shaft surface and said third shaft surface is permitted.

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

4. A ball screw device according to claim 3, wherein the state of the sliding changes depending on the magnitude of the axial load from the ball screw.

5. A ball screw device as described in any one of claims 1 to 4, wherein the bearing or the ball screw has an axial surface as the third axial surface formed on the body of the bearing, the screw shaft or the nut, or is provided with a sliding member having the third axial surface as a separate member from the body of the bearing, the screw shaft or the nut.

6. A ball screw device as described in any one of claims 1 to 4, wherein the housing has an axial surface as the second axial surface formed on the main body of the housing, or is provided with a sliding member having the second axial surface as a separate member from the main body of the housing.

7. A ball screw device according to any one of claims 1 to 6, further comprising a preload member that applies a preload so that the second axial surface and the third axial surface approach each other.

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.

10. The ball screw device according to claim 9, wherein the ball screw is removably assembled to the housing in the first direction, and an axial load from the ball screw along the second direction is borne by the housing.

Images