Ball screw device and actuator

Abstract

To provide a ball screw device capable of preventing wrong assembly of a nut.SOLUTION: A ball screw device of the present disclosure comprises: a screw shaft to which rotational motion is transmitted; a nut into which the screw shaft is inserted; a plurality of balls arranged between the screw shaft and the nut; and a circulation part provided on the nut. An outer peripheral surface of the nut is provided with a plurality of detents to support the nut so that it can move relative to other components in an axial direction parallel to the screw shaft and cannot rotate around the screw shaft. The plurality of detents is arranged at uneven intervals in the circumference.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a ball screw device and an actuator. [Background technology]

[0002] A ball screw device is a device that converts rotational motion into linear motion and linear motion into rotational motion. In the ball screw device of the following patent document, a detent is provided on the outer peripheral surface of the nut, and the nut is supported by the housing so as not to rotate. Then, rotational motion is transmitted to the screw shaft, and the nut performs linear motion. The nut of the ball screw device may have a circulation part to circulate the balls. Examples of the circulation part provided on the nut include an S-shaped groove surface, a top, a deflector, and a tube.

[0003] Incidentally, an external load may act on the nut or the screw shaft. This causes the screw shaft to be displaced in the radial direction relative to the center of the nut, and a load is input from the screw shaft to the inner peripheral raceway surface of the nut. Hereinafter, the direction in which the screw shaft is displaced relative to the center of the nut may be referred to as the displacement direction of the screw shaft.

[0004] Here, if an S-shaped groove surface is disposed in the displacement direction of the screw shaft, the S-shaped groove surface cannot bear the load from the screw shaft. Therefore, the surface pressure of the inner raceway surface near the connection portion that connects to the S-shaped groove surface increases. As a result, there is a possibility that one or more of the following may be damaged: the vicinity of the connection portion of the inner raceway surface, the portion of the screw shaft that faces the vicinity of the connection portion of the inner raceway surface, and the balls among the multiple balls that come into contact with the vicinity of the connection portion of the inner raceway surface. Hereinafter, these are collectively referred to as damage to the vicinity of the connection portion of the inner raceway surface, etc.

[0005] In addition, although the S-shaped groove surface is mentioned above as a circulation part, the block, the deflector, and the entrance and exit of the tube cannot bear the load from the screw shaft either. Hereinafter, the S-shaped groove surface, the block, the deflector, and the entrance and exit of the tube are collectively referred to as the unsupported area.

[0006] For this reason, the nut is usually laid out so that no unsupported area is located in the displacement direction of the screw shaft when viewed from the center of the nut. In addition, as described above, the nut is made non-rotatable. Therefore, the nut does not rotate during operation of the ball screw device, and no unsupported area is located in the displacement direction of the screw shaft. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Pat. No. 4,442,928 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the nut in the above patent document has two detents that are equally spaced in the circumferential direction. In other words, the nut can be assembled to a housing or the like even when rotated 180° from a predetermined angle. Such misassembly may result in an unsupported area being disposed in the direction of displacement of the screw shaft.

[0009] The present disclosure has been made in consideration of the above, and has an object to provide a ball screw device and an actuator that prevent incorrect assembly of a nut. [Means for solving the problem]

[0010] In order to achieve the above object, the ball screw device according to the present disclosure includes a screw shaft to which a rotational motion is transmitted, a nut into which the screw shaft is inserted, a plurality of balls arranged between the screw shaft and the nut, and a circulation part provided in the nut. The outer peripheral surface of the nut is provided with a plurality of detents for supporting the nut so as to be movable relative to other components in an axial direction parallel to the screw shaft and unrotatable around the screw shaft. The plurality of detents are arranged at uneven intervals in the circumferential direction.

[0011] According to the present disclosure, if the nut is deviated from a predetermined angle, the nut cannot be assembled to another component, thus preventing misassembly of the nut.

[0012] In the ball screw device, the nut has an inner peripheral side provided with an unsupported region in which the circulating portion is disposed and which cannot receive a load from the screw shaft. The direction in which the screw shaft is displaced radially relative to the center of the nut when an external load acts on the nut or the screw shaft is defined as the displacement direction of the screw shaft. When viewed from the center of the nut, the unsupported region is not disposed in the displacement direction of the screw shaft.

[0013] According to the above-mentioned configuration, even if an external load acts on the screw shaft or the nut, no unsupported area is disposed in the direction of displacement of the screw shaft, so that damage to the vicinity of the connection portion of the inner circumferential raceway surface can be avoided.

[0014] In the ball screw device, the positions of the plurality of rotation stoppers when they are assumed to be disposed at equal intervals in the circumferential direction are defined as equally spaced positions. The range in which the angle formed by the angle of the center of the nut as a vertex and the equally spaced positions is 30° or less is defined as an equally spaced vicinity region. When one of the plurality of rotation stoppers is disposed at one of the equally spaced positions, and when there is only one other rotation stopper, the other rotation stopper is disposed in the equally spaced vicinity region of the remaining equally spaced positions where the one rotation stopper is not disposed. When there are two or more other rotation stoppers, the other rotation stoppers are disposed in each of the equally spaced vicinity regions of the remaining equally spaced positions where the one rotation stopper is not disposed.

[0015] When the ball screw device is operated, a torque acts on the detent from the nut in the same direction as the rotation of the screw shaft. Meanwhile, a reaction force acts on the detent from other parts in the opposite direction to the rotation of the screw shaft. Here, if the detents are arranged at equal intervals in the circumferential direction, the resultant force obtained by adding up the reaction forces acting on each detent is zero. However, in the present disclosure, the detents are arranged at uneven intervals in the circumferential direction. In other words, the resultant force obtained by adding up the reaction forces is not zero, and a radial load acts on the nut. If the resultant force (radial load) acting on the nut is large, the sliding property of the nut against other parts may be greatly reduced. According to the present disclosure, all the detents are arranged in a near-equal distribution area with a deviation of 30° or less from the evenly distributed position (the position when the detents are arranged at equal intervals in the circumferential direction). Therefore, the resultant force acting on the nut is also small, and the decrease in the sliding property of the nut is suppressed to a small extent.

[0016] In the ball screw device, an external load causes the screw shaft to be relatively displaced radially from the center of the nut. The direction in which the screw shaft is relatively displaced is defined as the displacement direction of the screw shaft. One direction around the screw shaft is defined as a first rotation direction. The other direction around the screw shaft is defined as a second rotation direction. The radial load acting on the nut from the screw shaft is greater when the screw shaft rotates in the first rotation direction than when the screw shaft rotates in the second rotation direction. The direction of the resultant reaction force that each of the multiple detents receives from the other parts is opposite to the displacement direction of the screw shaft when the screw shaft rotates in the first rotation direction, and is the same as the displacement direction of the screw shaft when the screw shaft rotates in the second rotation direction.

[0017] According to the above configuration, when the screw shaft rotates in the first rotation direction, a resultant force in the opposite direction to the displacement direction of the screw shaft acts on the nut. This reduces the radial load acting on the nut, and reduces the deterioration of the slidability of the nut. On the other hand, when the screw shaft rotates in the second rotation direction, a resultant force in the same direction as the displacement direction of the screw shaft acts on the nut. This increases the radial load acting on the nut. However, the radial load when rotating in the second rotation direction is smaller than when rotating in the first rotation direction. Therefore, even if the load of the nut increases due to the resultant force, the deterioration of the slidability of the nut is reduced.

[0018] In order to achieve the above object, an actuator according to the present disclosure includes the ball screw device described above and a motor that generates torque for rotating the screw shaft.

[0019] The actuator according to the present disclosure prevents incorrect assembly of the nuts. Effect of the Invention

[0020] The ball screw device and actuator of the present disclosure prevent incorrect assembly of the nut. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a cross-sectional view of the actuator of the first embodiment taken along the axial direction. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1, viewed from the direction of the arrow. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the ball screw device of the first embodiment taken along an orthogonal direction. [Figure 4] FIG. 4 is a cross-sectional view of the nut and the housing of the first embodiment taken perpendicularly to each other. [Diagram 5] FIG. 5 is a cross-sectional view of the nut and the housing of the comparative example taken perpendicularly to each other. [Figure 6] FIG. 6 is a cross-sectional view of the ball screw device of the second embodiment taken along the axial direction. [Figure 7] FIG. 7 is a schematic cross-sectional view of a ball screw device according to the second embodiment, taken along an orthogonal direction. [Figure 8] FIG. 8 is a schematic diagram of a vehicle equipped with the actuator of the third embodiment, as viewed from above. [Figure 9] FIG. 9 is a schematic diagram of the actuator as viewed from the direction of arrow IX in FIG. [Figure 10] FIG. 10 is a schematic diagram of the actuator as viewed from the direction of arrow X in FIG. [Figure 11] FIG. 11 is a schematic cross-sectional view of the ball screw device of the first modification taken along an orthogonal direction. [Figure 12] FIG. 12 is a schematic cross-sectional view of a ball screw device according to the second modification taken along an orthogonal direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The embodiments for carrying out the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the contents described in the following description. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the components described below can be appropriately combined.

[0023] (Embodiment 1) Fig. 1 is an axial cross-sectional view of the actuator of embodiment 1. As shown in Fig. 1, the actuator 100 of embodiment 1 includes a motor (not shown), a reduction gear (not shown), a ball screw device 101 that converts rotational motion into linear motion, and a housing 120.

[0024] The reduction gear is a device that reduces the speed of the rotational motion generated by the motor and transmits it to the screw shaft 1 of the ball screw device 101. Examples of the reduction gear include a planetary gear mechanism and a pulley, but the present disclosure is not limited to these. In addition, although the actuator 100 of the embodiment includes a reduction gear, the present disclosure does not necessarily need to include a reduction gear.

[0025] The ball screw device 101 includes a screw shaft 1, a nut 2, and balls 3 (not shown in FIG. 1; see FIG. 2). The screw shaft 1 includes a power transmission unit 10 to which rotational motion is transmitted from the reduction gear device, and a screw shaft body 11. An outer peripheral raceway surface 12 extending in the spiral direction is formed on the outer peripheral surface of the screw shaft body 11. Hereinafter, a direction parallel to the center O1 of the screw shaft 1 will be referred to as the axial direction. In addition, in the axial direction, the direction in which the screw shaft body 11 is disposed as viewed from the power transmission unit 10 will be referred to as the first direction X1, and the direction opposite to the first direction X1 will be referred to as the second direction X2. Furthermore, a direction perpendicular to the axial direction will be referred to as the orthogonal direction.

[0026] The nut 2 includes a nut body 20 and a plurality of links 30 (only one is shown in FIG. 1). In this embodiment, a link is given as an example of a circulation part, but in the present disclosure, the circulation part may be an S-groove surface formed on the inner peripheral surface of the nut body by forging, a deflector (middle deflector and end deflector), or a tube, and there is no particular limitation on the type of the circulation part.

[0027] Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, viewed from the direction of the arrow. As shown in Fig. 2, the nut body 20 is formed in a cylindrical shape with a center O2 of the nut body 20. In other words, the inner peripheral surface 21 and the outer peripheral surface 22 of the nut body 20 are circular with the center O2 as the center. In addition, when no external load is applied to the ball screw device 101, the center O2 of the nut body 20 is arranged coaxially with the center O1 of the screw shaft 1.

[0028] The outer peripheral surface 22 of the nut body 20 faces the second inner peripheral surface 122 of the housing 120. A minute gap (not shown) is provided between the outer peripheral surface 22 of the nut body 20 and the second inner peripheral surface 122. This allows the nut 2 to be supported axially slidably relative to the second inner peripheral surface 122.

[0029] 1, an inner circumferential raceway surface 23 is formed on an inner circumferential surface 21 of a nut body 20. The inner circumferential raceway surface 23 faces the outer circumferential raceway surface 12 of the screw shaft 1 and extends in the helical direction. A plurality of balls 3 are disposed in the space (raceway) between the inner circumferential raceway surface 23 and the outer circumferential raceway surface 12.

[0030] The nut body 20 has a plurality of through holes 24 penetrating the inner peripheral surface 21 and the outer peripheral surface 22. The through holes 24 accommodate the pieces 30. In this embodiment, since there are three pieces 30, three through holes 24 are also formed. The three through holes 24 are arranged with a shift in the axial direction. In addition, the three through holes 24 are arranged at intervals of 120°. Therefore, the pieces 30 accommodated in the through holes 24 are also arranged with a shift in the axial direction and at intervals of 120°. From the above, in the ball screw device 101 of this embodiment, when the ball 3 moves one revolution (one lead) in the spiral direction, the piece 30 moves back one revolution (one lead). Note that the part of the inner peripheral raceway surface 23 that connects with the piece 30 (through hole 24) is called a connection part.

[0031] The nut body 20 is provided with a rotation stopper 40. In this embodiment, the rotation stopper 40 is composed of a recess 41 formed on the outer circumferential surface 22 of the nut and a key 42 arranged in the recess 41. The key 42 fits into the recess 41 and protrudes radially outward from the outer circumferential surface 22. The key 42 is also inserted into a guide groove 123 in a second inner circumferential surface 122 of the housing 120. The guide groove 123 extends in the axial direction. As a result, the nut 2 is supported by the housing 120 so as to be unrotatable about a center O2 and movable in the axial direction.

[0032] 2, this embodiment is provided with two rotation stoppers 40. One of the two rotation stoppers 40 is referred to as a first rotation stopper 40A, and the other is referred to as a second rotation stopper 40B.

[0033] The circumferential position of each part will be described below. In this description, the virtual line K1 extending radially from the center O2 is used as a reference, and the circumferential position will be described based on how many degrees the object of description is shifted from the virtual line K1. The angles described below are angles when the center O2 of the nut 2 is the vertex. If the object is shifted in the clockwise direction Y from the virtual line K1, a + (plus) sign is used, and if the object is shifted in the counterclockwise direction Z from the virtual line K1, a - (minus) sign is used. In each drawing, the virtual line K1 extends from the center O2 upward on the paper.

[0034] In addition, imaginary lines K2 and K3 are shown in Fig. 2. The imaginary line K2 extends radially from the center O2 and passes through the center of the second anti-rotation device 40B in the width direction. The imaginary line K3 is a line obtained by rotating the imaginary line K1 by 180 degrees around the center O2. In addition, when describing the circumferential position, the imaginary line K3 may be used as a reference instead of the imaginary line K1.

[0035] The first rotation stopper 40A is disposed so that its widthwise center overlaps with the imaginary line K1. In other words, the first rotation stopper 40A is disposed at a position of 0° from the imaginary line K1. The second rotation stopper 40B is disposed at a position offset by +170° from the imaginary line K1 (θ1=170°). The positions when two rotation stoppers 40 are disposed at equal intervals in the circumferential direction are referred to as the evenly spaced positions. When one rotation stopper 40 (the first rotation stopper 40A) is disposed at an evenly spaced position, the second rotation stopper 40B is disposed at a position offset by -10° from the evenly spaced position (imaginary line K3) (θ2=10°).

[0036] From the above, the first and second detents 40A and 40B of this embodiment are arranged at unequal intervals in the circumferential direction. According to this, when the nut 2 is assembled to the housing 120, for example, if the second detent 40B is arranged at 0° from the imaginary line K1, the first detent 40A is arranged at a position shifted by −170° from the imaginary line K1. Therefore, the first detent 40A cannot be inserted into the guide groove 123, and the nut 2 cannot be assembled. In other words, if there is an error in the assembly angle of the nut 2, the nut 2 cannot be assembled to the housing 120.

[0037] FIG. 3 is a schematic cross-sectional view of the ball screw device of the first embodiment, cut in an orthogonal direction. The three tops 30 are offset from each other in the axial direction, and all three tops 30 would not appear in a cross-sectional view of the ball screw device 101 cut in an orthogonal direction. However, in order to make it easier to understand the circumferential positional relationship of the tops 30, all three tops 30 are shown in one cross section in FIG. 3. For the same reason, all the tops are also shown in FIGS. 7, 9, 10, 11, and 12. Next, the relationship between the external load acting on the ball screw device 101 and the arrangement of the tops 30 will be described with reference to FIG. 3.

[0038] As shown in FIG. 3, in this embodiment, an external load F100 acts on the nut 2. The external load F100 acting on the nut 2 is a load in a direction of +90° from the imaginary line K1. Therefore, the nut 2 moves in a direction of +90° from the imaginary line K1. In this case, the displacement direction of the screw shaft 1 (the relative movement direction of the screw shaft 1 viewed from the center O2 of the nut 2) is a direction of -90° from the imaginary line K1. Therefore, the nut 2 receives a radial load F101 from the screw shaft 1 in a direction of -90° from the imaginary line K1.

[0039] Hereinafter, the portion of the inner raceway surface 23 of the nut 2 that is arranged in the direction in which the radial load F101 is input as viewed from the screw shaft 1 will be referred to as the high load region 23F. The high load region 23F is arranged at -90° from the virtual line K1. Note that the portion of the inner surface 21 of the nut 2 where the top 30 is arranged cannot receive the load from the screw shaft 1. Therefore, in the following description, the region of the inner surface 21 where the top 30 is arranged will be referred to as the unsupported region 50. In addition, since there are three tops 30 in this embodiment, the three unsupported regions 50 will be referred to as the first unsupported region 51, the second unsupported region 52, and the third unsupported region 53.

[0040] The first unsupported region 51 is disposed at a +90° offset from the virtual line K1 (θ11=90°). The second unsupported region 52 is disposed at a -150° offset from the virtual line K1 (θ12=150°). The third unsupported region 53 is disposed at a -30° offset from the virtual line K1 (θ13=30°). For this reason, the high load region 23F (position offset at -90° from the virtual line K1) and the three unsupported regions 50 are disposed so as not to overlap.

[0041] Therefore, according to the first embodiment, it is possible to prevent the high load region 23F and the unsupported region 50 from overlapping, that is, to prevent the surface pressure of the inner raceway surface 23 near the connection portion that connects to the unsupported region 50 from increasing, thereby preventing damage to the inner raceway surface 23 near the connection portion, etc.

[0042] In addition, if the first and second detents 40A and 40B were evenly arranged in the circumferential direction, there is a possibility that the nut 2 would be misassembled to the housing 120 after being rotated 180°. If such a misassembly occurs, the first unsupported region 51 would overlap with the high load region 23F (see dashed line 51K in FIG. 3). However, in this embodiment, if there is an error in the assembly angle of the nut 2, it cannot be assembled to the housing 120. In other words, it is designed to prevent the first unsupported region 51 from overlapping with the high load region 23F due to misassembly.

[0043] Next, a description will be given of the load acting on the nut 2 from the anti-rotation stopper 40. In addition, in this description, a comparative example will be used.

[0044] FIG. 4 is a cross-sectional view of the nut and the housing of the first embodiment cut in an orthogonal direction. As shown in FIG. 4, when the screw shaft 1 rotates in the clockwise direction Y (see arrow L1), a load in the clockwise direction Y also acts on the nut 2 and the rotation stopper 40. On the other hand, the rotation stopper 40 receives reaction forces A1 and A2 in the counterclockwise direction Z from the guide groove 123 of the housing 120. Therefore, a resultant force A3, which is a combination of the reaction forces A1 and A2, acts on the nut 2 to which the two rotation stoppers 40 are fixed. Note that the arrow A1' in FIG. 4 is a starting point of the reaction force A1 moved in parallel so as to overlap with the center O2 of the nut 2. Also, the arrow A2' in FIG. 4 is a starting point of the reaction force A2 moved in parallel so as to overlap with the center O2 of the nut.

[0045] The reaction forces A1 and A2 are equal in magnitude. Reaction force A1 is a load in the direction of -90° from the imaginary line K1 (see arrow A1'). Reaction force A2 is a load in the direction of +80° from the imaginary line K1 (see arrow A2'). Therefore, reaction forces A1 and A2 do not face in opposite directions, and resultant force A3 does not become zero. Resultant force A3 acts on nut 2 as a radial load in the direction of approximately -5° from the imaginary line K1 when viewed from center O2.

[0046] Although detailed description is omitted, when the screw shaft 1 rotates in the counterclockwise direction Z, the resultant force A3 is in the opposite direction. Furthermore, imaginary lines K123 in FIG. 4 indicate the equally spaced guide grooves 123. Furthermore, reaction force A4 shown in FIG. 4 indicates the reaction force acting on the second anti-rotation stopper 40B from the equally spaced guide grooves 123. If the first anti-rotation stopper 40A and the second anti-rotation stopper 40B are evenly spaced in the circumferential direction, the reaction force A4 is in the direction of +90° from the imaginary line K1. The reaction forces A1 and A4 are in the opposite directions to each other and are offset. In other words, the resultant force becomes zero, and no radial load acts on the nut 2.

[0047] 5 is a cross-sectional view of the nut and housing of the comparative example taken in a perpendicular direction. The actuator 1100 of the comparative example differs from the embodiment in that the second anti-rotation stopper 1040B is disposed at a position offset by -60° (θ20=60°) from the imaginary line K3. The other configurations are the same as those of the first embodiment.

[0048] In the comparative example, the reaction force B1 acting on the first anti-rotation element 1040A is a load in the direction of -90° from the imaginary line K1 (see arrow B1'), similar to the reaction force A1 in the embodiment. The reaction force B2 acting on the second anti-rotation element 1040B is a load in the direction of +30° from the imaginary line K1 (see arrow B2'). Therefore, the reaction forces B1 and B2 are not directed in opposite directions, and the resultant force B3 is not zero. In other words, the resultant force B3 acts on the nut 1002.

[0049] In addition, the angle between the reaction forces B1 and B2 is 120°, which is smaller than the angle (170°) between the reaction forces A1 and A2 in embodiment 1. Therefore, the load offset by the reaction forces B1 and B2 is small, and the resultant force B3 acting on the nut 1002 in the comparative example is larger than the resultant force A3 in embodiment 1.

[0050] Therefore, the nut 1002 of the comparative example is largely displaced in the radial direction by the resultant force B3, and the sliding property of the nut 1002 relative to the housing 120 is reduced. On the other hand, the resultant force A3 acting on the nut 2 of the first embodiment is smaller than that of the comparative example, and the reduction in the sliding property of the nut 2 relative to the housing 120 is kept small.

[0051] As described above, the ball screw device 101 of the first embodiment includes the screw shaft 1 to which the rotational motion is transmitted, the nut 2 into which the screw shaft 1 is inserted, a plurality of balls 3 arranged between the screw shaft 1 and the nut 2, and a circulation section (a ball 30) provided on the nut 2. The outer peripheral surface 22 of the nut 2 is provided with a plurality of detents 40 for supporting the nut 2 relative to another component (the housing 120) so as to be movable in an axial direction parallel to the screw shaft 1 and unrotatable around the screw shaft 1. The plurality of detents 40 are arranged at uneven intervals in the circumferential direction. According to the first embodiment, when the nut 2 is assembled to the housing 120, assembling the nut 2 at an incorrect angle is avoided.

[0052] The first embodiment has been described above. The angle θ2 between the second anti-rotation stopper 40B and the equally spaced position (see FIG. 2) is 10° in the first embodiment, but may be other than 10° in the present disclosure. If the angle θ2 between the second anti-rotation stopper 40B and the equally spaced position is large, as shown in the comparative example, a large resultant force is generated in the nut, which is not preferable because it may reduce the sliding properties of the nut 2. Therefore, it is preferable that the angle between the anti-rotation stopper 40 and the equally spaced position, with the center O2 of the nut 2 as the apex, is 30° or less. Hereinafter, the range in which the angle between the center O2 of the nut 2 and the equally spaced position is 30° or less is referred to as the "near-equal-spaced region."

[0053] In addition, in the first embodiment, the external load F100 acts on the nut 2, but in the present disclosure, the external load F100 may act on the screw shaft 1.

[0054] Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that the magnitude of the external load input to the ball screw device 101 changes when the rotation direction of the screw shaft 1 changes. The following description focuses on the changes from the first embodiment.

[0055] (Embodiment 2) FIG. 6 is a cross-sectional view of the ball screw device of the second embodiment cut in the axial direction. FIG. 7 is a cross-sectional view of the ball screw device of the second embodiment cut in the orthogonal direction. First, an external load F10 acting on the ball screw device 101A will be described. As shown in FIG. 6, in the second embodiment, an external load F10 acts on both ends (one end 1a and the other end 1b) of the screw shaft 1A. As a result, the nut 2A receives a radial load F11 from the screw shaft 1A in the same direction as the external load F10. Also, as shown in FIG. 7, the direction of the radial load F11 acting on the nut 2A from the screw shaft 1A is −90° from the virtual line K1.

[0056] Moreover, the magnitude of the external load F10 changes depending on the rotation direction of the screw shaft 1A. Specifically, as shown in Fig. 7, the external load F10 is larger when the screw shaft 1A rotates in the clockwise direction Y (first rotation direction) than when the screw shaft 1A rotates in the counterclockwise direction Z (second rotation direction). Therefore, the radial load F11 acting on the nut 2A from the screw shaft 1A is also larger when the screw shaft 1A rotates in the clockwise direction Y.

[0057] The ball screw device 101A of the second embodiment also differs from the first embodiment in that the arrangement of the two detents 140 is changed. More specifically, the first detent 140A is disposed at an angle of -120° from the imaginary line K1 (θ31=120°). The second detent 140B is disposed at an angle of -60° from the imaginary line K3 (θ32=60°).

[0058] According to the ball screw device 101A of the second embodiment, when the screw shaft 1 rotates in the clockwise direction Y, the first detent 140A receives a reaction force C1 from the guide groove 123. Also, the second detent 140B receives a reaction force C2 from the guide groove 123. The reaction force C1 is a load in the direction of +150° from the imaginary line K1. The reaction force C2 is a load in the direction of +30° from the imaginary line K1. Therefore, the resultant force C3 obtained by adding the reaction forces C1 and C2 is a load in the direction of +90° from the imaginary line K1. Also, the direction of the resultant force C3 is opposite to the radial load F11 acting on the nut 2A from the screw shaft 1A.

[0059] Therefore, although the nut 2A of the second embodiment is displaced in the direction of the radial load F11, the displacement due to the radial load F11 is suppressed to a small value by the resultant force C3. In other words, the sliding property of the nut 2A is improved compared to the case where the resultant force C3 is not acting.

[0060] On the other hand, when the screw shaft 1 rotates in the counterclockwise direction Z, the resultant force (not shown) acting on the nut 2A is in the opposite direction to the resultant force C. In other words, the resultant force (not shown) acting on the nut 2A is in the same direction as the radial load F11 received from the screw shaft 1A. Therefore, a load equal to the sum of the radial load F11 and the resultant force (not shown) acts on the nut 2A. However, the external load F10 (radial load F11) when the screw shaft 1 rotates in the counterclockwise direction Z is small. Therefore, even if the resultant force acts, the sliding properties of the nut 2A are not impaired.

[0061] Although the second embodiment in which the external load F10 acts on the screw shaft 1A has been described above, the present disclosure may also be applied to a ball screw device in which the external load F10 acts on the nut 2A.

[0062] Next, a third embodiment will be described. In the third embodiment, an EMB (Electro Mechanical Brake) equipped with an actuator will be described.

[0063] (Embodiment 3) Fig. 8 is a schematic diagram of a vehicle equipped with the actuator of embodiment 3, viewed from above. As shown in Fig. 8, a vehicle 500 has two front wheels 501, two rear wheels 502, and two EMBs 503 that apply braking force to the front wheels 501. Hereinafter, the two front wheels 501 will be referred to as a right wheel 501R and a left wheel 501L. In addition, the two EMBs 503 will be referred to as a right EMB 503R and a left EMB 503L.

[0064] Fig. 9 is a schematic diagram of the actuator as viewed from the direction of arrow IX in Fig. 8. As shown in Fig. 9, the left EMB 503L includes a left actuator 401L, a left brake pad 504L, and a left brake disc 505L that rotates together with the left wheel 501L.

[0065] Three pieces 30 are arranged at equal intervals in the circumferential direction on the left nut 302L of the left actuator 401L. Of the three pieces 30, the first is arranged at a +90° offset from the virtual line K1. The second is arranged at a -150° offset from the virtual line K1. The third is arranged at a -30° offset from the virtual line K1. In this embodiment, the virtual line K1 extends upward from the center O2 of the left nut 302. Therefore, the three pieces 30 are not arranged rearward (at a position offset by -90° from the virtual line K1) when viewed from the center O2.

[0066] In addition, the first detent 340A in the third embodiment is disposed at a +5° offset from the imaginary line K1 (θ41=5°). The second detent 340B is disposed at a -5° offset from the imaginary line K3 (θ42=5°). Therefore, the first detent 340A and the second detent 340B are not disposed evenly in the circumferential direction. This prevents the left nut 302L from being assembled incorrectly.

[0067] When the vehicle 500 moves forward, the left brake disc 505L rotates in the direction of arrow E1 together with the left wheel 501L (not shown in FIG. 9). When the left EMB 503L is actuated, the left nut 302L of the left actuator 401L presses the left brake pad 504L. This causes the left brake pad 504L to be pressed against the left brake disc 505L. The left brake pad 504L then receives a forward load (see arrow E2) from the left brake disc 505L. In addition, due to the frictional force between the left brake pad 504L and the left nut 402L, the left nut 302L receives a forward load (see arrow E2) and moves forward.

[0068] As a result, the left nut 302L moving forward receives a radial load E3 in the opposite direction (rearward) from the left screw shaft 301L. On the other hand, the top 30 is not disposed rearward as viewed from the center O2 of the left nut 302L. This prevents the surface pressure of the inner raceway surface 23 near the connection portion connected to the top 30 from increasing, which can cause damage to the inner raceway surface 23 near the connection portion.

[0069] Fig. 10 is a schematic diagram of the actuator as viewed from the direction of the arrow X in Fig. 8. As shown in Fig. 10, the right EMB 503R and the left EMB 503L are symmetrical. Therefore, the right EMB 503R will be briefly described.

[0070] As shown in FIG. 10, the right EMB 503R includes a right actuator 401R, a right brake pad 504R, and a right brake disc 505R. Three blocks 30 are arranged on the right nut 402R of the right actuator 401R. None of the three blocks 30 are arranged rearward (at a position shifted by +90° from the imaginary line K1) as viewed from the center O2. The first anti-rotation stopper 440A provided on the right nut 302R is arranged shifted by -5° from the imaginary line K1 (θ51=5°). The second anti-rotation stopper 440B is arranged shifted by +5° from the imaginary line K3 (θ52=5°). Therefore, the first anti-rotation stopper 440A and the second anti-rotation stopper 440B are not arranged evenly in the circumferential direction. This prevents the right nut 302R from being misassembled.

[0071] When the vehicle 500 moves forward, the right brake disc 505R rotates in the direction of the arrow F1 together with the right wheel 501R (not shown in FIG. 9). When the right EMB 503L is activated, the right brake pad 504R is pressed against the left brake disc 505L. Therefore, the right brake pad 504R and the right nut 302R receive a forward load (see arrow F2). As a result, the right nut 302R moving forward receives a radial load F3 in the opposite direction (rearward) from the right screw shaft 301R. On the other hand, the top 30 is not disposed rearward as viewed from the center O2 of the right nut 302R. Therefore, damage to the inner circumferential raceway surface 23 and the vicinity of the connection portion is similarly avoided in the right nut 302R.

[0072] According to the above-mentioned embodiment 3, the ball screw device 400L of the left actuator 401L and the ball screw device 400R of the right actuator 401R have the same shape. That is, the ball screw device 400L and the ball screw device 400R are common parts. Therefore, when manufacturing the actuator 401 (the left actuator 401L and the right actuator 401R), it is not necessary to manufacture two types of ball screw devices, and manufacturing costs can be reduced. On the other hand, the housing (not shown) used for the right actuator 401R and the housing (not shown) used for the ball screw device 400R have a symmetrical shape. Therefore, this shape is desirable from the viewpoint of the left and right weight balance and layout of the vehicle 500.

[0073] Although each embodiment has been described above, the present disclosure is not limited to the examples described in the embodiments. For example, in the embodiments, the housing 120 is exemplified as another part on which the nut is supported, but the present disclosure may be, for example, a cylindrical part, and is not particularly limited.

[0074] In addition, the rotation stopper 40 in the embodiment is composed of the recess 41 and the key 42, but the present disclosure is not limited thereto. For example, it may be a protrusion integrated with the nut body. Or, the rotation stopper may be a sliding groove formed on the outer peripheral surface of the nut. In this case, a rod-shaped part that fits into both the guide groove 123 of the housing 120 and the sliding groove is prepared. The sliding groove extends in the axial direction and abuts against the rod-shaped part so as to be freely slidable. In addition, the sliding groove may be provided not on the outer peripheral surface of the nut but on the radially outer end of the flange of the nut. In this way, the type of the rotation stopper of the present disclosure is not limited.

[0075] In addition, in each embodiment, two detents and three pieces (circulation parts) are provided, but the present disclosure is not limited thereto. Below, Modifications 1 and 2 in which three detents and four pieces (circulation parts) are provided will be described.

[0076] (Variation 1) 11 is a schematic cross-sectional view cut in an orthogonal direction of the ball screw device of the modified example 1. As shown in FIG 11, three detents 540 are provided on a nut 2C of a ball screw device 101C of the modified example 1.

[0077] In the embodiment, since there are two rotation stoppers 40, the equally spaced positions are spaced at 180° intervals, but in the modified example, since there are three rotation stoppers 540, the equally spaced positions are spaced at 120° intervals. Also, the imaginary line K4 shown in Fig. 11 is a line obtained by rotating the imaginary line K1 by -120°, and the imaginary line K5 is a line obtained by rotating the imaginary line K1 by +120°. Therefore, in modified example 1, the imaginary lines K1, K4, and K5 are disposed at equally spaced positions.

[0078] In the first modification, the imaginary line K1 passes through the center of the first detent 541 in the width direction. If one detent 540 (first detent 541) is arranged at an evenly spaced position, the second detent 542 is arranged at a position shifted by −60° from the imaginary line K4 (evenly spaced position) (θ60=60°). If one detent 540 (first detent 541) is arranged at an evenly spaced position, the imaginary line K5 (evenly spaced position) passes through the center of the third detent 543 in the width direction. That is, one of the three detents is arranged at an offset from the evenly spaced position. Therefore, in the first modification, the three detents are arranged at uneven intervals in the circumferential direction, so that misassembly of the nut 2C can be avoided.

[0079] In addition, a radial load G is applied to the nut 2C from the screw shaft 1C, and a high load area 23G is provided on a part of the inner peripheral surface of the nut 2C. The four pieces 30 of the first modification are arranged at 90° intervals. Furthermore, none of the four pieces 30 overlaps with the high load area 23G. As described above, according to the first modification, damage to the vicinity of the connection part of the inner peripheral raceway surface 23, etc., is avoided, as in the other embodiments.

[0080] (Variation 2) FIG. 12 is a cross-sectional view of the ball screw device of the second modification cut in an orthogonal direction. As shown in FIG. 12, three rotation stoppers 640 are provided on the nut 2D of the ball screw device 101D. The three rotation stoppers 640 are arranged at uneven intervals in the circumferential direction. In detail, in the second modification, the imaginary line K1 passes through the center of the first rotation stopper 641 in the width direction. If one rotation stopper 640 (the first rotation stopper 641) is arranged at an evenly spaced position, the second rotation stopper 642 is arranged at a position shifted by −30° from the imaginary line K4 (evenly spaced position). If one rotation stopper 640 (the first rotation stopper 641) is arranged at an evenly spaced position, the third rotation stopper 643 is arranged at a position shifted by +30° from the imaginary line K5 (evenly spaced position). That is, in the second modification, other detents (second detent 642, third detent 643) are arranged in the equally spaced vicinity areas of the remaining equally spaced positions (see imaginary lines K4 and K5 in FIG. 12) where one detent 640 (first detent 641) is not arranged. Even in the second modification, it is possible to prevent misassembly of the nut 2D and to avoid a decrease in the sliding properties of the nut 2.

[0081] In addition, in Modification 2, the four blocks 30 are arranged at 90° intervals. Furthermore, none of the four blocks 30 overlaps with the high load region 23H that receives the radial load H from the screw shaft 1D. Therefore, in Modification 2, as in the other embodiments, damage to the vicinity of the connection portion of the inner circumferential raceway surface 23 is avoided.

[0082] As described above, the first and second modifications have been described. The three detents 640 of the second modification are arranged symmetrically with respect to the imaginary line K1. Therefore, when the nut 2D is assembled, one end of the nut 2D is normally oriented to be inserted into the second inner circumferential surface 122 of the housing 120, but even if the other end of the nut 2D is erroneously oriented, the nut can be assembled to the housing 120. On the other hand, in the nut 2C of the first modification, the three detents 540 are not arranged symmetrically. Therefore, when the nut 2D is assembled, if the orientation of the nut 2C is incorrect, the nut cannot be assembled to the housing 120. Therefore, according to the first modification, it is possible to prevent misassembly regarding the axial orientation of the nut 2C.

[0083] The present disclosure may also be implemented in the following combinations: (1) A screw shaft to which rotational motion is transmitted; A nut into which the screw shaft is inserted; A plurality of balls disposed between the screw shaft and the nut; A circulation portion provided in the nut; Equipped with A plurality of detents are provided on the outer peripheral surface of the nut to support the nut in an axial direction parallel to the screw shaft and to be non-rotatable around the screw shaft with respect to other components. The plurality of detents are arranged at uneven intervals in the circumferential direction. Ball screw device. (2) The nut has an inner peripheral side provided with an unsupported region in which the circulating portion is disposed and which cannot bear a load from the screw shaft, The direction in which the screw shaft is displaced radially relative to the center of the nut when an external load acts on the nut or the screw shaft is defined as the displacement direction of the screw shaft, When viewed from the center of the nut, the unsupported region is not disposed in the displacement direction of the screw shaft. A ball screw device as described in (1). (3) The positions of the plurality of rotation stoppers assumed to be arranged at equal intervals in the circumferential direction are defined as equal-spaced positions, The range of the angle between the center of the nut and the equally spaced position is 30° or less, and the equally spaced vicinity region is defined as the angle range of the center of the nut and the equally spaced position. When one of the plurality of rotation stoppers is disposed at one of the equally spaced positions, When there is one other rotation stopper, the other rotation stopper is disposed in the equally-spaced vicinity area of ​​the remaining equally-spaced position where one of the rotation stoppers is not disposed, When there are two or more other rotation stoppers, the other rotation stoppers are arranged in each of the equally spaced adjacent regions of the remaining equally spaced positions where one of the rotation stoppers is not arranged. A ball screw device as described in (1) or (2). (4) Due to an external load, the screw shaft is relatively displaced in the radial direction from the center of the nut, The direction in which the screw shaft is relatively displaced is defined as the displacement direction of the screw shaft, One of the directions around the screw shaft is defined as a first rotation direction, The other direction around the screw shaft is defined as a second rotation direction, A radial load acting on the nut from the screw shaft is larger when the screw shaft rotates in the first rotation direction than when the screw shaft rotates in the second rotation direction, The direction of the resultant force of the reaction forces that each of the plurality of rotation stoppers receives from the other component is When the screw shaft rotates in the first rotation direction, the direction is opposite to the displacement direction of the screw shaft, and when the screw shaft rotates in the second rotation direction, the direction is the same as the displacement direction of the screw shaft. A ball screw device according to any one of (1) to (3). (5) A ball screw device according to any one of (1) to (4), A motor that generates a torque for rotating the screw shaft; An actuator comprising: [Explanation of symbols]

[0084] 1, 1A, 1C, 1D screw shaft 2, 2A, 2C, 2D, 1002 Nut 3. Ball 20 Nut body 30 frames 23 Inner raceway surface 40, 540, 640 Anti-rotation 40A, 140A, 541, 641, 1040A 1st stopper 40B, 140B, 542, 642, 1040B 2nd anti-rotation 23F, 23G, 23H high load area 50 Unsupported area 51 1st unsupported area 52 2nd unsupported area 53 Third unsupported area 100 Actuator 101, 101A, 101C, 101D, 400L, 400R Ball screw device 120 Housing 401L Left Actuator 401R Right Actuator 301L Left-handed screw shaft 301R Right-hand screw shaft 302L Left nut 302R Right Nut 543, 643 3rd stopper

Claims

1. A screw shaft to which rotational motion is transmitted; A nut into which the screw shaft is inserted; A plurality of balls disposed between the screw shaft and the nut; A circulation portion provided in the nut; Equipped with A plurality of detents are provided on the outer peripheral surface of the nut to support the nut in an axial direction parallel to the screw shaft and to be non-rotatable around the screw shaft with respect to other components. The plurality of detents are arranged at uneven intervals in the circumferential direction. Ball screw device.

2. The nut has an inner peripheral side provided with an unsupported region in which the circulating portion is disposed and which cannot bear a load from the screw shaft, The direction in which the screw shaft is displaced radially relative to the center of the nut when an external load acts on the nut or the screw shaft is defined as the displacement direction of the screw shaft, When viewed from the center of the nut, the unsupported region is not disposed in the displacement direction of the screw shaft. The ball screw device according to claim 1 .

3. The positions of the plurality of rotation stoppers assumed to be arranged at equal intervals in the circumferential direction are defined as equal-spaced positions, The range of the angle between the center of the nut and the equally spaced position is 30° or less, and the equally spaced vicinity region is defined as the angle range of the center of the nut and the equally spaced position. When one of the plurality of rotation stoppers is disposed at one of the equally spaced positions, When there is one other rotation stopper, the other rotation stopper is disposed in the equally spaced adjacent area of ​​the remaining equally spaced position where one of the rotation stoppers is not disposed, When there are two or more other rotation stoppers, the other rotation stoppers are arranged in each of the equally spaced adjacent regions of the remaining equally spaced positions where one of the rotation stoppers is not arranged. The ball screw device according to claim 1 .

4. Due to an external load, the screw shaft is relatively displaced in the radial direction from the center of the nut, The direction in which the screw shaft is relatively displaced is defined as the displacement direction of the screw shaft, One of the directions about the screw shaft is defined as a first rotation direction, The other direction around the screw shaft is defined as a second rotation direction, a radial load acting on the nut from the screw shaft is larger when the screw shaft rotates in the first rotational direction than when the screw shaft rotates in the second rotational direction, The direction of the resultant force of the reaction forces that each of the plurality of rotation stoppers receives from the other component is When the screw shaft rotates in the first rotation direction, the direction is opposite to the displacement direction of the screw shaft, and when the screw shaft rotates in the second rotation direction, the direction is the same as the displacement direction of the screw shaft. The ball screw device according to claim 1 .

5. The ball screw device according to any one of claims 1 to 4, A motor that generates a torque for rotating the screw shaft; An actuator comprising:

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