Ball screw device

Abstract

To provide a ball screw device excellent in reliability and longevity and advantageous for compactification, which can be applied to high load specifications favorably.SOLUTION: A housing (30) includes a first axial plane (AX1) directed to a first direction. A load from a ball screw (20) along a second direction is received by the first axial plane (AX1) through an inner ring (41), a rolling element (43), and an outer ring (42). A bearing (40) includes a regulation member (50) arranged in contact with the outer ring (42). The regulation member (50) includes a third axial plane arranged facing a second axial plane (AX2). A relative movement in a circumferential direction is performed between the second axial plane (AX2) and the third axial plane (AX3) when a screw shaft (21) or a nut (22) is rotated relative to the housing (30). An axial relative movement in the first direction of the inner ring (41) with respect to the outer ring (42) is regulated on the basis of axial positional relationships between the second axial plane (AX2) and the third axial plane (AX3).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball screw device. [Background technology]

[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). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-284444 Summary of the Invention [Problem to be solved by the invention]

[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] An object of the present invention is to provide a ball screw device that is preferably applicable to high load specifications, is advantageous in terms of compactness, and has high reliability and a long life. [Means for solving the problem]

[0007] A ball screw device according to one aspect of the present invention includes a ball screw having a screw shaft, a nut, and multiple balls; a housing supporting the ball screw; and a bearing having an inner ring, an outer ring, and multiple rolling elements. The bearing is disposed between the ball screw and the housing and is configured to be able to bear radial loads and axial loads. The housing has a first axial surface facing a first direction. An axial load from the ball screw along a second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring. The inner ring has a second axial surface facing the first direction. The bearing further includes a restricting member disposed in contact with the outer ring, the restricting member having a third axial surface disposed facing the second axial surface. When the screw shaft or the nut rotates relative to the housing, relative circumferential movement occurs between the second axial surface and the third axial surface. Relative axial movement of the inner ring in the first direction with respect to the outer ring is restricted based on the axial positional relationship between the second axial surface and the third axial surface. [Effects of the Invention]

[0008] 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, and has high reliability and a long lifespan. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a ball screw device according to a first embodiment. [Figure 2] 1A is a diagram illustrating the contact angle α in a tapered roller bearing, and FIG. 1B is a diagram illustrating the contact angle α in an angular contact ball bearing. [Figure 3]FIG. 2 is a diagram for explaining dimensional values ​​of a tapered roller bearing. [Figure 4] FIG. 1 is a schematic, partially enlarged cross-sectional view showing a ball screw device according to a first embodiment. [Figure 5] FIG. 6 is a schematic partially enlarged cross-sectional view showing a ball screw device according to a second embodiment. [Figure 6] FIG. 10 is a schematic enlarged partial cross-sectional view showing a ball screw device according to a third embodiment. [Figure 7] FIG. 11 is a schematic enlarged partial cross-sectional view showing a modified example of the third embodiment. [Figure 8] FIG. 10 is a schematic cross-sectional view showing a ball screw device according to a fourth embodiment. [Figure 9] 10(a), 10(b), and 10(c) are schematic partially enlarged cross-sectional views showing ball screw devices according to fourth, fifth, and sixth embodiments, respectively. [Figure 10] FIG. 13 is a schematic cross-sectional view showing a ball screw device according to a seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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 (operating 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.

[0011] In the following description, unless otherwise specified, the 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).

[0012] (First embodiment) 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.

[0013] As shown in FIG. 1, the ball screw 20 includes a screw shaft 21, a nut 22, and a plurality of balls 23 arranged 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. In one example in which the ball screw device 11 is applied to an electric brake device for a vehicle, brake pads of the vehicle operate against a brake disc in response to the linear motion. The ball screw 20 and the mechanism using the same are not limited to this example, and various forms are applicable.

[0014] 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.

[0015] The nut 22 has a cylindrical nut body and a helical thread groove (helical inner peripheral rolling groove) provided on the inner peripheral 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 peripheral 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 threads in the thread groove is set to one, two, or more. In other examples, various shapes are applicable to the nut 22.

[0016] 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 (the direction of relative rotation) 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 .

[0017] 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.

[0018] The bearing 40 has an inner ring 41, an outer ring 42, and a plurality of rolling elements 43 arranged between the inner ring 41 and the outer ring 42. The plurality of rolling elements 43 are held between the inner ring 41 and the outer ring 42 via a cage 45. The bearing 40 may additionally have a seal structure 47 that seals in a lubricant.

[0019] In this embodiment, a bearing capable of bearing radial and axial loads is used as the bearing 40. For example, the bearing 40 is a single-row tapered roller bearing or a single-row angular contact ball bearing. In one example, the bearing 40 is a single-row tapered roller bearing, and rollers (tapered rollers) are used as the rolling elements 43. In another example, the bearing 40 is a single-row angular contact ball bearing, and balls are used as the rolling elements 43. Tapered roller bearings have a higher load capacity than angular contact ball bearings. Angular contact ball bearings are more preferably used for high-speed rotation specifications than tapered roller bearings. The use of such a single bearing (a configuration that avoids a configuration in which two bearings are opposed to each other or a configuration in which two or more bearings are combined) is advantageous for making the ball screw device 11 more compact. Alternatively, other types of bearings can be used.

[0020] 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.

[0021] 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 (e.g., polyamide) cage. In another example, the balls are held in place by a different structure.

[0022] In tapered roller bearings and angular contact ball bearings, the contact angle α is appropriately set as shown in Figure 2. 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.

[0023] In this embodiment, the contact angle α (see FIG. 2(a)) of the tapered roller bearing used as bearing 40 of 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 present invention is not limited to these.

[0024] In this embodiment, the contact angle α (see FIG. 2(b)) of the angular contact ball bearing used as bearing 40 of 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 present invention is not limited to these.

[0025] In this embodiment, in the example of a single-row tapered roller bearing shown in FIG. 3, when the axial width of the outer ring is L and the distance between the rolling elements and the end of the outer ring is a, 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 bearing 40 and abnormal noise due to relative axial movement can be reliably prevented. The above numerical values ​​are merely examples and are not limiting.

[0026] 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 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.

[0027] As shown in FIG. 4 , 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. 4 , 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 clearance (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.

[0028] 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 surface 221 and the outer surface 222 in the radial direction, and has, for example, a surface perpendicular to the axial direction. The inner ring 41 of the bearing 40 has an axial surface (axial end surface) 415 facing the first direction, which is an axial surface integrally formed with the body of the inner ring 41. The axial surface 415 is provided at the end of the inner ring 41 in the first direction, and has, for example, a surface perpendicular to the axial direction. The axial surface 415 is also provided between the inner surface 411 and the outer surface 412 in the radial direction. The axial surface 225 of the nut 22 is disposed opposite the axial end surface 415 of the inner ring 41.

[0029] In this embodiment, the bearing 40 includes a restricting member 50 attached to the outer ring 42. The restricting member 50 is provided as a separate member from the main body of the outer ring 42. The restricting member 50 has a circumferential portion 511 extending in the axial direction and a radial portion 512 extending in the radial direction. In one example, the cross-sectional shape of the restricting member 50 is substantially L-shaped. In other examples, various shapes can be applied to the restricting member 50.

[0030] In this embodiment, the regulating member 50 has a structure in which a circumferential portion 511 and a radial portion 512 are connected via a bent portion. The outer ring 42 has an outer surface 421 and an outer surface 422 having a smaller diameter than the outer surface 421. A step is provided between the outer surfaces 421 and 422. The circumferential portion 511 of the regulating member 50 has an inner diameter corresponding to the outer surface 422 of the outer ring 42 and an outer diameter corresponding to the outer surface 421 of the outer ring 42. For example, the outer diameter of the outer surface of the circumferential portion 511 is set to be smaller than the outer diameter of the outer surface 421 of the outer ring 42 and smaller than the inner diameter of the inner surface 302 of the housing 30. This is advantageous for improving the ease of assembly of the bearing 40 to the housing 30. In one example, the circumferential portion 511 of the regulating member 50 is axially press-fitted into the outer surface 422 of the outer ring 42, thereby fixing the regulating member 50 to the outer ring 42. In other examples, various configurations for attaching the restricting member 50 to the outer ring 42 are applicable.

[0031] 4, 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.

[0032] In this embodiment, the housing 30 has an axial surface (axial wall surface, first axial surface AX1) 311 facing a first direction and an axial surface (axial wall surface, second axial surface AX2) 312 facing a 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.

[0033] The housing 30 is provided with a recess 450 including a space surrounded by the inner surface 302, the axial surface 311, and the axial surface 312. The bearing 40 is disposed in the recess 450. The bearing 40 is inserted into the recess 450 of the housing 30 so that the outer surface 421 of the outer ring 42 faces the inner surface 302 of the housing 30, and the bearing 40 (outer ring 42) and the housing 30 are fitted together. An appropriate interference or gap (loose fit) is provided in the fit between the outer ring 42 and the housing 30. The outer surface (outer peripheral surface) 421 of the bearing 40 (outer ring 42) is supported by the inner surface 302 of the housing 30. The outer ring 42 has an axial surface (axial end surface) 425 facing in the second direction. The axial surface 425 is provided at the end of the outer ring 42 in the second direction and has, for example, a surface perpendicular to the axial direction. The shaft surface 425 of the outer ring 42 and the shaft surface 311 of the housing 30 face each other and abut against each other. The end surface 425 of the outer ring 42 is supported by the shaft surface 311 of the housing 30.

[0034] In this embodiment, a radial portion 512 of the regulating member 50 is disposed between the axial surface 312 of the housing 30 and the axial surface 415 of the inner ring 41. The radial portion 512 of the regulating member 50 has a first surface 501 facing a first direction and a second surface 502 facing a second direction. The first surface 501 is disposed at a position axially spaced apart from the axial surface 312 of the housing. At least a portion of the second surface 502 is disposed facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 502 and the axial surface 415 face and abut each other, or face each other across a gap. The regulating member 50 is incorporated as part of a first assembly (outer assembly, support body) 60. A second assembly 70 (inner assembly, rotating body) is rotatably supported by the first assembly 60. In this embodiment, the first assembly 60 includes the housing 30, the outer ring 42, the regulating member 50, etc. The second assembly 70 includes a nut 22, an inner ring 41, and the like.

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

[0036] In the first mode, the inner ring 41 receives a strong force in the second direction based on an axial load (reaction force). This force acts in a direction that causes the axial surface 415 of the inner ring 41 to move axially away from the second surface 502 of the regulating member 50. In one example, the ball screw device 11 is designed so that a substantial gap 900 is generated between the second surface 502 of the regulating member 50 and the axial surface 415 of the inner ring 41 when a high load in the second direction is received. The design value of the gap 900 in the first mode (high load mode) is defined as the "allowable axial clearance (C1)." In another example, the ball screw device 11 is designed so that the gap 900 (allowable axial clearance C1) between the second surface 502 of the regulating member 50 and the axial surface 415 of the inner ring 41 is substantially zero when a high load in the second direction is received.

[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 second surface 502 of the regulating member 50 and the axial surface 415 of the inner ring 41. In the ball screw device 11, when the allowable axial clearance C1 greater than zero is set, a rotational load (frictional load) due to contact between the inner ring 41 and the regulating member 50 in the first mode is avoided.

[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 second surface 502 of the restricting member 50 and the axial surface 415 of the inner ring 41. Furthermore, in a low-load or no-load state, for example, when the ball screw 20 is operated in an initial state or in a predetermined direction, the substantial gap 900 may occur. When the substantial gap 900 exists, there is a possibility that the inner ring 41 will tend to move in a direction away from the outer ring 42 (first direction). This is due to, for example, the fact that the bearing 40 has a structure that is easily separated in the axial direction and / or the fact 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 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 50. In other words, the relative axial movement of the inner ring 41 is restricted to within the range of the design value (allowable axial clearance C1) of the gap 900 between the axial surface 415 (second axial surface AX2) and the second surface 502 (third axial surface AX3).

[0040] In this embodiment, contact between the axial surface 415 of the inner ring 41 and the second surface 502 of the regulating member 50 is permitted. Relative axial movement of the inner ring 41 in the first direction is restricted based on the axial surface 415 of the inner ring 41 contacting the second surface 502 of the regulating member 50. The range of an area (sliding area, contact area, opposing area) 910 where the axial surface 415 and the second surface 502 can come into contact with each other is set appropriately in advance. Appropriate setting of the sliding area 910 contributes to stable operation of the bearing 40 and is advantageous for reducing rotational load and extending the life of the bearing 40.

[0041] In this embodiment, slippage is permitted between the axial surface 415 of the inner ring 41 and the second surface 502 of the regulating member 50. In the ball screw device 11, when the axial surface 415 of the inner ring 41 abuts against the second surface 502 of the regulating member 50 during rotation, relative circumferential movement (circumferential slippage) occurs between the second surface 502 and the axial surface 415 accompanied by contact. That is, slippage (contact slippage) occurs in at least a portion of the sliding region 910. In the ball screw device 11, due to the configuration that permits contact slippage, relative axial movement of the inner ring 41 in the first direction is restricted even during rotation.

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

[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 415 of the inner ring 41 and the second surface 502 of the restricting member 50. For example, a rotational load (frictional load) based on preload occurs in the slip region 910. In addition, in the second mode (low load mode), contact slippage also occurs between the axial surface 415 and the second surface 502. In this example, the rotational load in the slip region 910 may change between the first mode and the second mode. Note that in this example, the change in the relative axial position of the inner ring 41 and the outer ring 42 between the first mode and the second mode is small, and the posture of the bearing 40 is kept relatively constant.

[0044] In this embodiment, contact slip occurs between the shaft surface 415 of the inner ring 41 and the second surface 502 of the regulating member 50. By appropriately designing the sliding structure, such as the material, surface precision, surface roughness, and surface shape of the regulating member 50, it is possible to reduce wear, improve assembly ease, and improve positioning accuracy, which is advantageous for extending the life of the device.

[0045] In this embodiment, the regulating member 50 is disposed to surround the side of the bearing 40 facing the first direction. In one example, the regulating member 50 has a continuous surface 550 that surrounds at least a portion of the axial surface (axial end surface) 415 of the inner ring 41, at least a portion of the axial surface (axial end surface) 424 of the outer ring 42, and the gap (gap space) 405 between the axial surface 415 and the axial surface 424. The continuous surface 550 faces the gap 405 of the bearing 40 and is disposed in the vicinity thereof. The ball screw device 11 may have a seal structure 47 that includes a portion of the regulating member 50 (e.g., the continuous surface 550). Such a configuration may have a sealing function and / or a function that assists sealing. For example, this configuration contributes to preventing leakage of lubricant from the bearing 40 and is advantageous in improving the device life.

[0046] As described above, according to this embodiment, high reliability and long life are achieved while having a compact configuration and high load specifications, based on the configuration that restricts relative axial movement of the bearing 40.

[0047] (Second embodiment) FIG. 5 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 given the same reference numerals, and their description will be omitted or simplified. In this embodiment, unlike the first embodiment, no step for attaching the regulating member 52 is provided on the outer ring 42. The bearing 40 includes a regulating member 52 attached to the outer ring 42. The regulating member 52 is provided as a separate member from the main body of the outer ring 42.

[0048] 5, the housing 30 further includes an inner surface (inner wall surface) 305 having a diameter larger than that of the inner surface 302. A step is provided between the inner surfaces 305 and 302. For example, the housing 30 has a divided structure including a first element 391 and a second element 392 that are coupled to each other, with the first element 391 being provided with the inner surface 302 and the second element 392 being provided with the inner surface 305. A circumferential portion 511 of the restricting member 52 has an outer diameter that is the same as or smaller than that of the inner surface 305 of the housing 30 and an inner diameter that corresponds to the outer surface 422 of the outer ring 42. For example, the restricting member 52 is attached to the outer ring 42 by axially press-fitting the circumferential portion 511 of the restricting member 52 into the outer surface 421 of the outer ring 42.

[0049] In this embodiment, processing of the bearing 40, such as forming a step on the outer surface of the outer ring 42, is avoided. In addition, the restricting member 50 is housed in a space formed by the step provided in the housing 30. The ball screw device 12 simplifies the processing and assembly processes, which is advantageous for reducing costs.

[0050] (Third embodiment) 6 is a schematic partial cross-sectional view showing a ball screw device 13 according to a third embodiment. In the following description of the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted or simplified. In this embodiment, the shape of the regulating member 53 is different from that of the regulating member 50 in the first embodiment. The regulating member 53 is provided as a separate member from the main body of the housing 30 or the main body of the bearing 40.

[0051] In this embodiment, as shown in FIG. 6 , the restricting member 53 has a radial portion 512 extending in the radial direction, a first circumferential portion 531 extending from the radial portion 512 in a first direction, and a second circumferential portion 532 extending from the radial portion 512 in a second direction. An outer peripheral surface 535 of the restricting member 53 includes the outer peripheral surface of the first circumferential portion 531 and the outer peripheral surface of the second circumferential portion 532. For example, the outer peripheral surface 535 has a diameter corresponding to the inner surface 302 of the housing 30. In one example, the radial thickness of the first circumferential portion 531 of the restricting member 53 is larger than the radial thickness of the second circumferential portion 532. The radial thicknesses of the circumferential portions 531 and 532 can be set arbitrarily. In another example, the radial thickness of the first circumferential portion 531 can be the same as or smaller than the radial thickness of the second circumferential portion.

[0052] In this embodiment, the regulating member 53 and the outer ring 42 are arranged side by side in the axial direction. The regulating member 53 is arranged between the axial surface 312 of the housing 30 and the axial surface 424 of the outer ring 42. In one example, the regulating member 53 is sandwiched between the axial surface 312 and the axial surface 424 with a preload. In another example, the regulating member 53 is arranged between the axial surface 312 and the axial surface 424 with substantially no preload. An axial end surface of the first circumferential portion 531 can abut against the axial surface 312 of the housing 30. An axial end surface of the second circumferential portion 532 can abut against the axial surface 424 of the outer ring 42. At least a portion of the second surface 502 of the regulating member 53 is arranged facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 502 and the axial surface 415 face and abut against each other, or face each other with a gap therebetween.

[0053] In this embodiment, similar to the first embodiment, the relative axial movement of the inner ring 41 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 53. That is, the relative axial movement of the inner ring 41 is restricted within the range of the design value (allowable axial clearance C1) of the gap 900 between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 53. The axial surface 415 of the inner ring 41 contacts the second surface 502 of the restricting member 53, thereby restricting the relative axial movement of the inner ring 41 in the first direction. Furthermore, based on the contact sliding in the sliding region 910, the relative axial movement of the inner ring 41 in the first direction is restricted even during rotation.

[0054] In this embodiment, the regulating member 53 has a diameter portion 512 provided for the inner ring 41 of the bearing 40 and a second circumferential portion 532 provided for the outer ring 42. The ball screw device 13 has a reduced number of parts and a simplified assembly process, which is advantageous for reducing costs. The ball screw device 13 can also have a seal structure 47 that includes a portion of the regulating member 53 (for example, the continuous surface 550). In this case, the seal structure 47 contributes to preventing leakage of lubricant from the bearing 40, which is advantageous for improving the life of the device.

[0055] Alternatively, various shapes can be applied to the regulating member 53. In the modified example shown in FIG. 7 , the regulating member 53 has a diameter portion 541 extending in the radial direction and a circumferential portion 542 extending from the diameter portion 541 in the second direction. The regulating member 53 is provided as a separate member from the main body of the housing 30 or the main body of the bearing 40. An outer peripheral surface 535 of the regulating member 53 has a diameter corresponding to the inner surface 302 of the housing 30. The regulating member 53 is inserted into a recess 450 of the housing 30 so that the outer peripheral surface 535 of the regulating member 53 faces the inner surface 302 of the housing 30, and the regulating member 53 and the housing 30 are fitted together. An appropriate interference or gap (loose fit) is provided in the fit between the regulating member 53 and the housing 30. The regulating member 53 and the outer ring 42 are arranged side by side in the axial direction. The regulating member 53 is arranged between the axial surface 312 of the housing 30 and the axial surface 424 of the outer ring 42. An axial end surface (first surface 501) of the restricting member 53 facing the first direction can abut against the axial surface 312 of the housing 30. An axial end surface (axial end surface 545 of the circumferential portion 542) of the restricting member 53 facing the second direction can abut against the axial surface 424 of the outer ring 42. In one example, the restricting member 53 is sandwiched between the axial surface 312 and the axial surface 424 with a preload. In another example, the restricting member 53 is disposed between the axial surface 312 and the axial surface 424 with substantially no preload. In the restricting member 53, a second surface 502 facing the second direction is disposed between the first surface 501 and the axial end surface 545 in the axial direction. The second surface 502 is provided radially inward from the axial end surface 545 and has, for example, a surface perpendicular to the axial direction. At least a portion of the second surface 502 is disposed facing the axial surface 415 of the inner ring 41. At least a portion of the second surface 502 and the axial surface 415 face and abut against each other, or face each other across a gap. Also in the example of Fig. 7, the axial surface 415 of the inner ring 41 comes into contact with the second surface 502 of the restricting member 53, thereby restricting the relative axial movement of the inner ring 41 in the first direction.

[0056] (Fourth, fifth, and sixth embodiments) 8 and 9 are schematic cross-sectional views showing ball screw devices 81, 82, and 83 according to fourth, fifth, and sixth embodiments. FIGS. 8 and 9(a) show a ball screw device 81 according to a fourth embodiment, which is a modified version of the first embodiment. FIG. 9(b) shows a ball screw device 82 according to a fifth embodiment, which is a modified version of the second embodiment. FIG. 9(c) shows a ball screw device 83 according to a sixth embodiment, which is a modified version 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 81, 82, and 83 are configured so that the screw shaft 21 of the ball screw 20 rotates relative to the housing 30.

[0057] 8, in the fourth embodiment, a first shaft 91 to which a driving force of a motor (not shown) is transmitted is connected to a screw shaft 21. In the ball screw 20, rotational motion is converted into linear motion.

[0058] 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.

[0059] As shown in FIG. 9( 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. 9( 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) together. 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.

[0060] 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 surface 211 and the outer surface 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 to the axial end surface 415 of the inner ring 41.

[0061] In this embodiment, the first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, and the restricting member 50. The second assembly (inner assembly, rotating body) 70 includes the screw shaft 21, the inner ring 41, and the like.

[0062] In this embodiment, a high reaction force in the second direction caused by driving under a high load acts on the screw shaft 21 via the ball screw 20. In this first mode, the force in the second direction due to the high load is transmitted in the following order: screw shaft 21, inner ring 41, rolling elements 43, outer ring 42, and housing 30. In the ball screw device 81, even when a high axial load is applied, the rotational motion of the second assembly 70 (screw shaft 21, etc.) relative to the first assembly 60 (housing 30, etc.) is stably supported.

[0063] In this embodiment, similar to the first embodiment, the relative axial movement of the inner ring 41 in the first direction is restricted based on the axial positional relationship between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 50. That is, the relative axial movement of the inner ring 41 is restricted within the range of the design value (allowable axial clearance C1) of the gap 900 between the axial surface 415 (second axial surface AX2) of the inner ring 41 and the second surface 502 (third axial surface AX3) of the restricting member 50. The axial surface 415 of the inner ring 41 contacts the second surface 502 of the restricting member 50, thereby restricting the relative axial movement of the inner ring 41 in the first direction. Furthermore, based on the contact sliding in the sliding region 910, the relative axial movement of the inner ring 41 in the first direction is restricted even during rotation.

[0064] Thus, in this embodiment, even in a configuration in which the screw shaft 21 rotates relative to the housing 30, similar to the first embodiment, high reliability and long life are achieved while having a compact configuration and high load specifications based on a configuration that restricts relative axial movement of the bearing 40. The same is true for the fifth embodiment shown in Fig. 9(b) and the sixth embodiment shown in Fig. 9(c).

[0065] Seventh embodiment 10 is a schematic partial cross-sectional view showing a ball screw device 85 according to a seventh embodiment. In the following description, the same components as those in the above-described embodiments are denoted by the same reference numerals, and the description thereof will be omitted or simplified.

[0066] In this embodiment, the ball screw device 85 is configured so that the screw shaft 21 of the ball screw 20 rotates relative to the housing 30. In Fig. 10(a), a shaft to which the driving force of a motor is transmitted is connected to the screw shaft 21, and rotational motion is converted into linear motion via the ball screw 20, causing the nut 22 to move in a first direction and a second direction. An inner ring 41 of a bearing 40 is attached to the screw shaft 21 of the ball screw 20, and an outer ring 42 of the bearing 40 is attached to the housing 30.

[0067] In this embodiment, the bearing 40 includes a stop member 57 attached to the outer ring 42. As shown in the enlarged schematic view of FIG. 10( c), the stop member 57 has a circumferential portion 571 extending in the axial direction and a radial portion 572 extending in the radial direction. The radial portion 572 of the stop member 57 has a first surface 501 facing a first direction and a second surface 502 facing a second direction. In this embodiment, at least a portion of the first surface 501 is disposed radially inward relative to the outer surface of the nut 22. In one example, the stop member 57 may be formed by plastic processing, and then the first surface 501 and / or the second surface 502 may be subjected to additional processing such as grinding. In other examples, various methods can be applied to processing the stop member 57. In this embodiment shown in FIG. 10, a first assembly (outer assembly, support) 60 includes the housing 30, the outer ring 42, and the stop member 57. The second assembly 70 (inner assembly, rotating body) includes the screw shaft 21, the inner ring 41, and the like.

[0068] In this embodiment, similarly to the above-described embodiment, the relative axial movement of the bearing 40 is restricted by the second surface 502 (third axial surface AX3) of the restricting member 57. Furthermore, in this embodiment, the movement of the nut 22 in the second direction relative to the housing 30 is restricted by the first surface 501 (fourth axial surface AX4) of the restricting member 57. That is, the restricting member 57 has a stopper function against the movement of the ball screw 20.

[0069] 10(a), when the screw shaft 21 of the ball screw 20 rotates in a predetermined direction, the nut 22 moves in the second direction. In Fig. 10(b), when the shaft surface 227 of the nut 22 abuts against the first surface 501 of the regulating member 57, the movement of the nut 22 in the second direction is stopped.

[0070] Here, if the nut 22 abuts against the axial surface of the inner ring 41, the components may bite together, which may require excessive torque when restarting, etc. This is because the axial surface of the nut 22 in a non-rotating state abuts against the axial surface of the inner ring 41 in a rotating state. In this embodiment, the nut 22 in a non-rotating state abuts against the restricting member 57 in a non-rotating state, so the phenomenon of the components biting together due to the abutment is avoided. This is advantageous for improving reliability and lifespan.

[0071] Furthermore, in this embodiment, similar to the above embodiment, high reliability and long life are achieved while having a compact configuration and high load specifications based on a configuration that restricts relative axial movement of the bearing 40.

[0072] 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.

[0073] 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 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 capable of bearing radial loads and axial loads. The housing has a first axial surface facing a first direction. An axial load from the ball screw along a second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring. The inner ring has a second axial surface facing the first direction. The bearing further includes a restricting member disposed in contact with the outer ring, the restricting member having a third axial surface disposed facing the second axial surface. The second axial surface and the third axial surface face each other and abut against each other, or face each other via a gap. When the screw shaft or the nut rotates relative to the housing, relative movement in the circumferential direction occurs between the second axial surface and the third axial surface. Axial relative movement of the inner ring in the first direction with respect to the outer ring is restricted based on an axial positional relationship between the second axial surface and the third axial surface. (2) In the ball screw device described in (1) above, the restricting member is attached to the outer ring. (3) In the ball screw device described in (1) or (2) above, contact between the second shaft surface and the third shaft surface is permitted. (4) In the ball screw device according to any one of (1) to (3) above, sliding is permitted between the second shaft surface and the third shaft surface. (5) In the ball screw device described in (4) above, the state of the slippage changes depending on the magnitude of the axial load from the ball screw. (6) In the ball screw device described in any one of (1) to (5) above, a front inner ring is attached to the screw shaft, and movement of the nut in the second direction relative to the housing is regulated by the regulating member. (7) The ball screw device according to any one of (1) to (6) above further comprises a seal structure including at least a part of the regulating member. (8) In the ball screw device according to any one of (1) to (7) above, the bearing is a single-row tapered roller bearing or a single-row angular contact ball bearing. [Explanation of symbols]

[0074] 11-13, 81-83, 85 Ball screw device, 20 ball screws, 21 screw shaft, 22 nuts, 30 housing, 40 bearings, 41 Inner circle, 42 outer ring, 43 rolling elements, 50, 52, 53, 57 Regulatory members; 60 First Assembly, 70 Second Assembly, 900 gap, AX1 1st axis plane, AX2 Second axis surface, AX3 Third axis surface.

Claims

1. a ball screw having a screw shaft, a nut, and a plurality of balls; a housing that supports the ball screw; a bearing having an inner ring, an outer ring, and a plurality of rolling elements; Equipped with the bearing is disposed between the ball screw and the housing and has a structure capable of bearing a radial load and an axial load, The housing has a first axial surface oriented in a first direction; an axial load from the ball screw along a second direction is received by the first axial surface via the inner ring, the rolling elements, and the outer ring; the inner ring has a second axial surface oriented in the first direction, the bearing further includes a regulating member arranged in contact with the outer ring, the regulating member having a third axial surface arranged facing the second axial surface, When the screw shaft or the nut rotates relative to the housing, a relative movement in a circumferential direction occurs between the second axial surface and the third axial surface, Axial relative movement of the inner ring with respect to the outer ring in the first direction is restricted based on an axial positional relationship between the second axial surface and the third axial surface. Ball screw device.

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

3. The outer ring has a fourth axial surface oriented in the first direction and a fifth axial surface oriented in the second direction, the rolling element is located between the fourth axial surface and the fifth axial surface in the axial direction, the second axial surface is located between the third axial surface and the fourth axial surface in the axial direction, A space is provided between the third axial surface and the fourth axial surface. The ball screw device according to claim 1 .

4. A ball screw device as described in claim 1, wherein the regulating member is fixed to the outer surface of the outer ring.

5. The outer ring has a fourth axial surface oriented in the first direction, the restricting member is disposed between the outer ring and the housing in the axial direction, The ball screw device according to claim 1 , wherein an end surface of the regulating member facing the second direction faces or abuts against the fourth axial surface.

6. The ball screw device according to claim 1 , wherein contact between the second shaft surface and the third shaft surface is permitted.

7. 6. The ball screw device according to claim 1, wherein sliding is permitted between the second shaft surface and the third shaft surface.

8. 8. The ball screw device according to claim 7, wherein the state of the slippage changes depending on the magnitude of the axial load from the ball screw.

9. a front inner ring attached to the screw shaft; The ball screw device according to claim 1 , wherein movement of the nut in the second direction relative to the housing is restricted by the restricting member.

10. The ball screw device according to claim 1 , further comprising a seal structure including at least a part of the restricting member.

11. 6. The ball screw device according to claim 1, wherein the bearing is a single-row tapered roller bearing or a single-row angular contact ball bearing.

Images