Ball screw device and actuator

Abstract

To provide a ball screw device for preventing wrong assembly of a nut.SOLUTION: A ball screw device comprises a screw shaft to which rotational motion is transmitted, a nut into which a screw shaft is inserted, a plurality of balls arranged between the screw shaft and the nut, and a circulation part provided in 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 are arranged at equal intervals in a circumferential direction. The plurality of detents include a first detent and a second detent. The first detent and the second detent have different shapes when viewed in the axial direction.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] A ball screw device is a device that converts rotational motion into linear motion or linear motion into rotational motion. In the ball screw device of the following patent document, a rotation prevention 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. Further, the nut of the ball screw device may have a circulation portion in order to circulate the balls. Examples of the circulation portion provided in the nut include an S-shaped groove surface, a bobbin, a deflector, and a tube.

[0003] By the way, an external load may act on the nut or the screw shaft. As a result, the screw shaft is displaced radially relative to the central axis 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 relatively displaced as viewed from the central axis of the nut may be referred to as the displacement direction of the screw shaft.

[0004] Here, for example, if an S-shaped groove surface is arranged in the displacement direction of the screw shaft, the S-shaped groove surface cannot receive the load from the screw shaft, so the surface pressure in the vicinity of the connection portion connecting to the S-shaped groove surface of the inner peripheral raceway surface increases. As a result, any one or more of the vicinity of the connection portion of the inner peripheral raceway surface, the portion of the screw shaft facing the vicinity of the connection portion of the inner peripheral raceway surface, and the balls contacting the vicinity of the connection portion of the inner peripheral raceway surface among the plurality of balls may be damaged. Hereinafter, it is collectively referred to as damage such as the vicinity of the connection portion of the inner peripheral raceway surface.

[0005] In addition, although the S-shaped groove surface is mentioned as the circulation portion above, the entrances and exits of the bobbin, the deflector, and the tube cannot receive the load from the screw shaft either. Hereinafter, the S-shaped groove surface, the bobbin, the deflector, and the entrances and exits of the tube are collectively referred to as an unsupported region.

[0006] For these reasons, usually, when viewed from the central axis of the nut, the layout is such that no unsupported region is arranged in the displacement direction of the screw axis. In addition, as described above, the nut is non-rotatable. Therefore, during the operation of the ball screw device, the nut does not rotate, and there is no situation where an unsupported region is arranged in the displacement direction of the screw axis.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the nut anti-rotation means in the above patent document is two and is arranged at equal intervals in the circumferential direction. That is, even when the nut is rotated 180° from a predetermined angle, it can be assembled to the housing or the like. And due to such incorrect assembly, there is a possibility that an unsupported region is arranged in the displacement direction of the screw axis.

[0009] The present disclosure has been made in view of the above, and an object thereof is to provide a ball screw device and an actuator that prevent incorrect assembly of a nut.

Means for Solving the Problems

[0010] To achieve the above object, the ball screw device according to the present disclosure includes 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, and a circulation portion provided in the nut. A plurality of anti-rotation members are provided on the outer peripheral surface of the nut for being supported so as to be movable in the axial direction parallel to the screw shaft and non-rotatable around the screw shaft with respect to other components. The plurality of anti-rotation members are arranged at equal intervals in the circumferential direction. The plurality of anti-rotation members include a first anti-rotation member and a second anti-rotation member. The shapes of the first anti-rotation member and the second anti-rotation member as viewed from the axial direction are different from each other.

[0011] According to the present disclosure, if the nut is displaced from a predetermined angle, the nut cannot be assembled to other components. Therefore, incorrect assembly of the nut is prevented.

[0012] In the above ball screw device, the anti-rotation member may protrude radially outward from the outer peripheral surface of the nut, and the widths of the first anti-rotation member and the second anti-rotation member as viewed from the axial direction may be different from each other. Alternatively, the anti-rotation member may protrude radially outward from the outer peripheral surface of the nut, and the protruding amounts of the first anti-rotation member and the second anti-rotation member from the outer peripheral surface of the nut may be different from each other. Alternatively, the anti-rotation member may be a guide groove that is recessed radially inward from the outer peripheral side of the nut, and the widths of the guide groove constituting the first anti-rotation member and the guide groove constituting the second anti-rotation member as viewed from the axial direction may be different from each other. Alternatively, the anti-rotation member may be a guide groove that is recessed radially inward from the outer peripheral side of the nut, and the recessed amounts of the guide groove constituting the first anti-rotation member and the guide groove constituting the second anti-rotation member from the outer peripheral surface of the nut may be different from each other.

[0013] In the above ball screw device, the anti-rotation member projects radially outward from the outer peripheral surface of the nut, and the projecting amounts of the first anti-rotation member and the second anti-rotation member from the outer peripheral surface of the nut are different from each other. The anti-rotation member is composed of a recess formed in the outer peripheral surface of the nut and a key that partially fits into the recess and the remaining part projects radially outward from the outer peripheral surface. The recesses of the first anti-rotation member and the second anti-rotation member have different amounts of depression from the outer peripheral surface of the nut.

[0014] According to the above configuration, the key inserted into the recess of the first anti-rotation member and the key inserted into the recess of the second anti-rotation member can be common components. Therefore, the number of parts of the ball screw device can be reduced.

[0015] In the above ball screw device, the anti-rotation member is a guide groove that is recessed radially inward from the outer peripheral side of the nut. The other component may have a facing surface facing the outer peripheral surface of the nut, a groove recessed radially outward from the facing surface, and a protruding member that is partially accommodated in the groove and the remaining part fits into the guide groove. Alternatively, the other component may have a facing surface facing the outer peripheral surface of the nut and a protrusion that projects radially inward from the facing surface and fits into the guide groove.

[0016] Further, in the ball screw device described above, an unsupported region where the circulation portion is disposed on the inner peripheral side of the nut and cannot receive the load from the screw shaft is provided. When an external load acts on the nut or the screw shaft and the screw shaft is displaced radially relative to the central axis of the nut, the direction of displacement of the screw shaft is defined as the displacement direction of the screw shaft. When viewed from the central axis of the nut, the unsupported region is not disposed in the displacement direction of the screw shaft.

[0017] According to the above configuration, even when an external load acts on the screw shaft or the nut, the unsupported region is not disposed in the displacement direction of the screw shaft. Therefore, breakage near the connection portion of the inner peripheral raceway surface or the like is avoided.

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

[0019] According to the actuator of the present disclosure, misassembly of the nut is prevented.

Effects of the Invention

[0020] According to the ball screw device and the actuator of the present disclosure, misassembly of the nut is prevented.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Mode for Carrying Out the Invention

[0022] The mode for carrying out the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by the content described in the following description. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and substantially identical ones. Furthermore, the constituent elements described below can be combined as appropriate.

[0023] (Embodiment 1) FIG. 1 is a cross-sectional view of the actuator of Embodiment 1 cut in the axial direction. Specifically, it is a view of the cross section taken along line I-I of FIG. 3 as viewed from the arrow direction. As shown in FIG. 1, the actuator 100 of Embodiment 1 includes a motor (not shown), a speed reduction device (not shown), a ball screw device 101 that converts rotational motion into linear motion, and a housing 120. The actuator 100 is used for an electric brake such as an EMB (Electro Mechanical Brake) or an EHB (Electro-Hydraulic Brake). Note that the actuator of the present disclosure may be used for other than an electric brake.

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

[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 portion 10 to which rotational motion is transmitted from a speed reduction device, and a screw shaft main body 11. An outer peripheral raceway surface 12 extending in a spiral direction is formed on the outer peripheral surface of the screw shaft main body 11.

[0026] Hereinafter, the direction parallel to the central axis O1 of the screw shaft 1 is referred to as the axial direction. Also, among the axial directions, the direction in which the power transmission portion 10 is arranged when viewed from the screw shaft main body 11 is referred to as the first direction X1, and the direction opposite to the first direction X1 is referred to as the second direction X2. Further, the direction orthogonal to the axial direction is referred to as the orthogonal direction.

[0027] The nut 2 includes a nut main body 20 and a plurality of disks 30 (only one is shown in FIG. 1).

[0028] FIG. 2 is a view of the cross section taken along line II-II of FIG. 1 as viewed from the arrow direction. As shown in FIG. 2, the nut main body 20 is formed in a cylindrical shape about the central axis O2 of the nut main body 20. That is, the inner peripheral surface 21 and the outer peripheral surface 22 of the nut main body 20 are circular about the central axis O2. Also, when no external load is acting on the ball screw device 101, the central axis O2 of the nut main body 20 is arranged coaxially with the central axis O1 of the screw shaft 1.

[0029] The outer peripheral surface 22 of the nut main body 20 faces the inner peripheral surface 122 of the housing 120. Also, a minute gap (not shown) is provided between the outer peripheral surface 22 and the inner peripheral surface 122 of the nut main body 20. Thereby, the nut 2 is supported slidably in the axial direction with respect to the inner peripheral surface 122. Note that the space in the housing 120 in which the nut 2 is accommodated (the space surrounded by the inner peripheral surface 122) is referred to as the accommodation space 123.

[0030] As shown in FIG. 1, an inner circumferential raceway surface 23 is formed on the inner circumferential surface 21 of the 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 arranged in the space (raceway) between the inner circumferential raceway surface 23 and the outer circumferential raceway surface 12. Although not particularly shown, the raceway makes approximately one turn (about one lead) in the helical direction. Further, a portion of the inner circumferential raceway surface 23 that connects to the bobbin 30 (through hole 24) is referred to as a connecting portion.

[0031] A plurality of through holes 24 penetrating the inner circumferential surface 21 and the outer circumferential surface 22 are formed in the nut body 20. The bobbin 30 is accommodated in the through hole 24. The bobbin 30 is a circulation component that returns the ball 3 that has moved from one end to the other end of the raceway to one end of the raceway. More specifically, an S-shaped groove surface is formed on the inner circumferential surface of the bobbin 30. The S-shaped groove surface connects one end and the other end of the inner circumferential raceway surface 23. The S-shaped groove surface has an increasing amount of depression from both ends in the length direction in which the S-shaped groove surface extends toward the central portion in the length direction. As a result, the ball that has entered the S-shaped groove surface from the other end of the raceway is gradually arranged radially outward as it moves toward the central portion in the length direction of the S-shaped groove surface, and can overcome the thread of the screw shaft 1. Further, after the ball 3 has overcome the thread of the screw shaft 1, it is gradually arranged radially inward and returns to one end of the raceway.

[0032] Further, the ball 3 that has returned to one end of the raceway contacts each of the inner circumferential raceway surface 23 and the outer circumferential raceway surface 12, and transmits the load from the screw shaft 1 to the nut 2. On the other hand, since the depression amount of the S-shaped groove surface of the bobbin 30 is larger than that of the inner circumferential raceway surface 23, the ball 3 that has entered the S-shaped groove surface separates from the outer circumferential raceway surface 12. That is, the load from the screw shaft 1 is not transmitted to the S-shaped groove surface, and the bobbin 30 cannot receive the load from the screw shaft 1.

[0033] In addition, in the present embodiment, since there are three discs 30, three through holes 24 are also formed. The three through holes 24 are arranged offset in the axial direction. Further, the three through holes 24 are arranged at 120° intervals. Therefore, the discs 30 are also arranged offset in the axial direction and are arranged at 120° intervals (see FIG. 3). And according to the ball screw device 101 of Embodiment 1, when the ball 3 moves about one turn (one lead) in the spiral direction, it returns about one turn (one lead) by the disc 30.

[0034] The nut body 20 is provided with a rotation stopper 40. The rotation stopper 40 of the present embodiment is composed of a recess 40a formed on the outer peripheral surface 22 of the nut and a key 40b. A part of the key 40b is fitted into the recess 40a, and the remaining part protrudes radially outward from the outer peripheral surface 22. Further, the key 40b is inserted into a guide groove 130 on the inner peripheral surface 122 of the housing 120. The guide groove 130 extends in the axial direction. Thereby, the nut 2 is supported by the housing 120 so as not to be rotatable about the central axis O2 and to be movable in the axial direction.

[0035] As shown in FIG. 2, in the present embodiment, two rotation stoppers 40 are provided. The two rotation stoppers 40 are a first rotation stopper 41 and a second rotation stopper 42. Of the two guide grooves 130, the one into which the first rotation stopper 41 is inserted is referred to as a first guide groove 131, and the one into which the second rotation stopper 42 is inserted is referred to as a second guide groove 132. Also, the direction orthogonal to the virtual line extending radially from the central axis O2 of the nut 2 as viewed from the axial direction is referred to as the width direction.

[0036] The virtual line K1 shown in FIG. 2 extends radially from the central axis O2 of the nut 2 and passes through the central portion in the width direction of the first rotation stopper 41. The virtual line K2 shown in FIG. 2 extends radially from the central axis O2 of the nut 2 and passes through the central portion in the width direction of the second rotation stopper 42. The first rotation stopper 41 and the second rotation stopper 42 are arranged at equal intervals in the circumferential direction. That is, the angle θ1 formed by the virtual line K1 and the virtual line K2 is 180°.

[0037] The width of the first rotation stopper 41 is W1. Also, the width of the first guide groove 131 is such that a minute gap is formed between the side surfaces of the first rotation stopper 41 to ensure the slidability of the first rotation stopper 41. Therefore, the width of the first guide groove 131 is substantially the same as the width W1 of the first guide groove 131.

[0038] The width of the second rotation stopper 42 is W2. The width W2 of the second rotation stopper 42 is larger than the width W1 of the first rotation stopper 41 (W2 > W1. Refer to the auxiliary line H in Fig. 2). Therefore, the second rotation stopper 42 is sized such that it cannot be inserted into the first guide groove 131. Also, the width of the second guide groove 132 is such that a minute gap is formed between the side surfaces of the second rotation stopper 42 to ensure the slidability of the second rotation stopper 42. Therefore, the width of the second guide groove 132 is substantially the same as the width W2 of the second rotation stopper 42. From the above, the first rotation stopper 41 and the second rotation stopper 42 of Embodiment 1 have different shapes when viewed from the axial direction.

[0039] Next, a method for assembling the nut 2 to the housing 120 will be described. As shown in Fig. 1, the guide groove 130 and the accommodation space 123 are each open at the end in the first direction X1. Therefore, when assembling the nut 2 to the housing 120, first, the nut 2 is placed in the first direction X1 of the accommodation space 123.

[0040] Next, the angle of the nut 2 is adjusted. Specifically, the first rotation stopper 41 is placed in the first direction X1 of the first guide groove 131, and the second rotation stopper 42 is placed in the first direction X1 of the second guide groove 132. Next, the nut 2 is moved in the second direction X2, and the nut 2 is inserted into the accommodation space 123. As a result, each rotation stopper 40 is inserted into each guide groove 130, and the nut 2 is assembled to the housing 120.

[0041] Here, when adjusting the angle of the nut 2, if the nut 2 rotates 180° from the above-described angle, the second anti-rotation member 42 is arranged in the first direction X1 of the first guide groove 131. Also, the first anti-rotation member 41 is arranged in the first direction X1 of the second guide groove 132. Therefore, even if the nut 2 is moved in the second direction X2, the second anti-rotation member 42 is not inserted into the first guide groove 131, and the nut 2 cannot be assembled to the housing 120.

[0042] FIG. 3 is a schematic cross-sectional view of the ball screw device according to Embodiment 1, cut in the orthogonal direction. Note that the three frames 30 are shifted from each other in the axial direction. Normally, in a cross-sectional view of the ball screw device 101 cut in the orthogonal direction, all three frames 30 do not appear. However, in FIG. 3, all three frames 30 are shown in one cross-section for easy understanding of the circumferential positional relationship of the frames 30. For the same reason, all the frames are also shown in FIGS. 5, 6, 7, and 8.

[0043] Next, the relationship between the external load acting on the ball screw device 101 and the arrangement of the frames 30 will be described with reference to FIG. 3. Hereinafter, when explaining the circumferential positions of the respective components, the virtual line K1 (the first anti-rotation member 41) is used as a reference, and the circumferential position is explained based on how many degrees the object to be explained is shifted from the virtual line K1. Also, the angles described below are angles when the central axis O2 of the nut 2 is the vertex. Further, when shifted in the clockwise direction Y from the virtual line K1, the symbol + (plus) is used, and when shifted in the counterclockwise direction Z from the virtual line K1, the symbol - (minus) is used.

[0044] 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 the direction of +90° from the virtual line K1. Therefore, the nut 2 moves in the direction of +90° from the virtual 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 central axis O2 of the nut 2) is the direction of -90° from the virtual line K1. Therefore, the nut 2 receives a radial load F101 from the screw shaft 1 in the direction of -90° from the virtual line K1. From the above, in the inner circumferential track surface 23 of the nut 2, the position shifted by -90° from the virtual line K1 is a region where a radial load F101 is input from the screw shaft 1 and the surface pressure is relatively large (hereinafter referred to as the high load region 23F).

[0045] Next, the position of the 30th block will be described. The portion of the inner circumferential surface 21 of the nut 2 where the 30th block is arranged cannot receive the load from the screw shaft 1. Therefore, in the following description, the region of the inner circumferential surface 21 where the 30th block is arranged is referred to as the unsupported region 50. Further, since there are three 30th blocks in this embodiment, the three unsupported regions 50 are referred to as the first unsupported region 51, the second unsupported region 52, and the third unsupported region 53.

[0046] The first unsupported region 51 is arranged shifted by +90° from the virtual line K1 (θ11 = 90°). The second unsupported region 52 is arranged shifted by -150° from the virtual line K1 (θ12 = 150°). The third unsupported region 53 is arranged shifted by -30° from the virtual line K1 (θ13 = 30°). That is, the high load region 23F (the position shifted by -90° from the virtual line K1) and the three unsupported regions 50 are arranged so as not to overlap.

[0047] As described above, according to Embodiment 1, it is avoided that the high load region 23F and the unsupported region 50 overlap, that is, the surface pressure near the connection portion connecting to the unsupported region 50 in the inner circumferential track surface 23 becomes large and the connection portion near the inner circumferential track surface 23 is damaged.

[0048] In addition, if the first rotation stopper 41 and the second rotation stopper 42 are evenly arranged in the circumferential direction, the nut 2 may be incorrectly assembled to the housing 120 in a state where it has rotated 180°. And if there is such an incorrect assembly, the first non-support region 51 overlaps with the high-load region 23F (see the dashed line 51K in FIG. 3). However, in the present embodiment, incorrect assembly of the nut 2 is prevented. Therefore, it does not occur that the first non-support region 51 and the high-load region 23F overlap due to incorrect assembly.

[0049] As described above, the ball screw device 101 of Embodiment 1 includes a screw shaft 1 to which a rotational motion is transmitted, a nut 2 into which the screw shaft 1 is inserted, a plurality of balls 3 disposed between the screw shaft 1 and the nut 2, and a circulation portion (roller 30) provided in the nut 2. On the outer peripheral surface 22 of the nut 2, a plurality of rotation stoppers 40 are provided for being supported so as to be movable in the axial direction parallel to the screw shaft 1 and non-rotatable around the screw shaft 1 with respect to other components (housing 120). The plurality of rotation stoppers 40 are arranged at equal intervals in the circumferential direction. The plurality of rotation stoppers 40 include a first rotation stopper 41 and a second rotation stopper 42. The first rotation stopper 41 and the second rotation stopper 42 have different shapes when viewed from the axial direction. Further, since the widths of the first rotation stopper 41 and the second rotation stopper 42 when viewed from the axial direction are different from each other, the shapes when viewed from the axial direction are different from each other. According to this Embodiment 1, when assembling the nut 2 to the housing 120, it is avoided that the nut 2 is assembled at an incorrect angle.

[0050] Next, Embodiment 2 will be described. In Embodiment 2, an example in which an actuator is used for an electric brake (more specifically, EMB) will be described. In the following description, the description will be focused on the differences from Embodiment 1.

[0051] (Embodiment 2) FIG. 4 is a schematic view of a vehicle equipped with the actuator of Embodiment 2 as viewed from above. As shown in FIG. 4, the 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 are referred to as a right wheel 501R and a left wheel 501L. Also, the two EMBs 503 are referred to as a right EMB 503R and a left EMB 503L.

[0052] FIG. 5 is a schematic view of the actuator as viewed from the direction of arrow V in FIG. 4. As shown in FIG. 5, the left EMB 503L includes a left actuator 401L, a left brake pad 504L, and a left brake disk 505L that rotates together with the left wheel 501L.

[0053] Two anti-rotation members 340 (a first anti-rotation member 341 and a second anti-rotation member 342) are provided at equal intervals in the circumferential direction on the left nut 302L of the left actuator 401L. The width W3 of the first anti-rotation member 341 is smaller than the width W4 of the second anti-rotation member 342. Therefore, incorrect assembly of the left nut 302L is prevented.

[0054] Also, when viewed from the central axis O2 of the left nut 302L, the first anti-rotation member 341 is disposed above, and the second anti-rotation member 342 is disposed below. Thus, the virtual line K1 extends upward from the central axis O2 of the left nut 302L. Also, the virtual line K2 extends downward from the central axis O2 of the left nut 302L.

[0055] Three sliders 30 are arranged at equal intervals in the circumferential direction on the left nut 302L of the left actuator 401L. The first one of the three sliders 30 is disposed deviated by +90° from the virtual line K1. The second one is disposed deviated by -150° from the virtual line K1. The third one is disposed deviated by -30° from the virtual line K1. Therefore, the three sliders 30 are not disposed behind (at a position deviated by -90° from the virtual line K1) when viewed from the central axis O2.

[0056] When the vehicle 500 moves forward, the left brake disk 505L rotates in the direction of arrow E1 together with the left wheel 501L (not shown in FIG. 5). When the left EMB 503L is activated, the left nut 302L of the left actuator 401L presses the left brake pad 504L. As a result, the left brake pad 504L is pressed against the left brake disk 505L. Then, the left brake pad 504L receives a forward load (see arrow E2) from the left brake disk 505L. Further, due to the frictional force between the left brake pad 504L and the left nut 302L, the left nut 302L receives a forward load (see arrow E2) and moves forward.

[0057] Then, by moving forward, the left nut 302L receives a radial load E3 in the opposite direction (backward) from the left screw shaft 301L. From the above, when the left EMB 503L is activated, the surface pressure of the rear surface (the position shifted -90° from the virtual line K1) of the inner peripheral surface 320L of the left nut 302L, as viewed from the central axis O2, increases. In the present embodiment, the washer 30 is not arranged rearward as viewed from the central axis O2 of the left nut 302L. Therefore, it is possible to avoid the situation where the surface pressure in the vicinity of the connection portion connecting to the washer 30 of the inner peripheral raceway surface 23 increases and the connection portion vicinity of the inner peripheral raceway surface 23 is damaged.

[0058] FIG. 6 is a schematic view of the actuator seen from the direction of arrow VI in FIG. 4. As shown in FIG. 6, the right EMB 503R includes a right actuator 401R, a right brake pad 504R, and a right brake disk 505R.

[0059] On the right nut 302R of the right actuator 401R, two anti-rotation members 440 (first anti-rotation member 441, second anti-rotation member 442) are provided at equal intervals in the circumferential direction. When viewed from the central axis O2 of the right nut 302R, the first anti-rotation member 441 is disposed below, and the second anti-rotation member 442 is disposed above. That is, the virtual line K1 extends downward from the central axis O2 of the right nut 302R. Also, the virtual line K2 extends upward from the central axis O2 of the right nut 302R. Further, the width W5 of the first anti-rotation member 441 is smaller than the width W6 of the second anti-rotation member 442. For this reason, misassembly of the right nut 302R is prevented.

[0060] On the right nut 302R of the right actuator 401R, three plates 30 are arranged at equal intervals in the circumferential direction. Among the three plates 30, the first one is arranged with a 90° shift from the virtual line K1. The second one is arranged with a -150° shift from the virtual line K1. The third one is arranged with a -30° shift from the virtual line K1. Therefore, the three plates 30 are not arranged behind (at a position shifted -90° from the virtual line K1) when viewed from the central axis O2.

[0061] When the vehicle 500 is moving forward, the right brake disk 505R rotates in the direction of arrow F1 together with the right wheel 501R (not shown in FIG. 5). When the right EMB 503R is actuated, the right brake pad 504R is pressed against the right brake disk 505R. For this reason, the right brake pad 504R and the right nut 302R receive a forward load (see arrow F2). As a result, the right nut 302R receives a radial load F3 in the opposite direction (rearward) from the right screw shaft 301R.

[0062] From the above, when the right EMB 503R is actuated, the surface pressure of the rear surface (the position shifted -90° from the virtual line K1) of the inner circumferential surface 320R of the right nut 302R when viewed from the central axis O2 increases. In the present embodiment, no plate 30 is arranged behind when viewed from the central axis O2 of the right nut 302R. Therefore, similarly, damage such as in the vicinity of the connection portion of the inner circumferential raceway surface 23 is avoided in the right nut 302R.

[0063] Also, the width W3 of the first rotation stopper 341 of the left nut 302L is the same as the width W5 of the first rotation stopper 441 of the right nut 302R. The width W4 of the second rotation stopper 342 of the left nut 302L is the same as the width W6 of the second rotation stopper 442 of the right nut 302R. That is, the right ball screw device 400R has the same structure as the left ball screw device 400L obtained by rotating the left nut 302L by 180°. Therefore, the left ball screw device 400L and the right ball screw device 400R are common parts, and when manufacturing the actuator 401 (left actuator 401L and right actuator 401R), it is not necessary to manufacture two types of ball screw devices, and the manufacturing cost 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 right ball screw device 400R have a vertically symmetric shape. For this reason, it is a desirable shape from the viewpoints of the left-right weight balance and layout of the vehicle 500.

[0064] As described above, each embodiment has been explained, but the present disclosure is not limited to the examples described in the embodiments. For example, in the embodiment, an external load F100 acts on the nut 2, but in the present disclosure, the external load F100 may act on the screw shaft 1.

[0065] Also, in the embodiment, the housing 120 is exemplified as another part that supports the nut, but the present disclosure may be, for example, a cylindrical part and is not particularly limited.

[0066] Also, the number of rotation stoppers in each embodiment is two, but the present disclosure is not limited to this. Hereinafter, modified examples in which the number of rotation stoppers is three or four will be described.

[0067] (Modified Example 1) FIG. 7 is a cross-sectional view schematically showing the ball screw device of Modification 1 and taken in an orthogonal direction. As shown in FIG. 7, the nut 2A of the ball screw device 101A of Modification 1 is provided with three anti-rotation members 540. The three anti-rotation members 540 are arranged at equal intervals (120° intervals) in the circumferential direction. Also, four plates 30 are provided. The four plates are arranged at equal intervals (90° intervals) in the circumferential direction. The three anti-rotation members 540 are the first anti-rotation member 541, the second anti-rotation member 542, and the third anti-rotation member 543. The width W12 of the second anti-rotation member 542 and the width W13 of the third anti-rotation member 543 are the same as each other. Also, the width W11 of the first anti-rotation member 541 is larger than the width W12 of the second anti-rotation member 542 and the width W13 of the third anti-rotation member 543. Even in such Modification 1, misassembly of the nut 2A is prevented in the same manner as in each embodiment.

[0068] (Modification 2) FIG. 8 is a cross-sectional view schematically showing the ball screw device of Modification 2 and taken in an orthogonal direction. As shown in FIG. 8, the nut 2B of the ball screw device 101B of Modification 2 is provided with four anti-rotation members 640. The four anti-rotation members 640 are arranged at equal intervals (90° intervals) in the circumferential direction. The four anti-rotation members 640 are the first anti-rotation member 641, the second anti-rotation member 642, the third anti-rotation member 643, and the fourth anti-rotation member 644. Also, three plates 30 are provided. The three plates are arranged at equal intervals (120° intervals) in the circumferential direction.

[0069] The width W21 of the first anti-rotation member 641, the width W23 of the third anti-rotation member 643, and the width W24 of the fourth anti-rotation member 644 are the same as each other. The width W22 of the second anti-rotation member 642 is smaller than each of the width W21, the width W23, and the width W24. Therefore, even in Modification 2, misassembly of the nut 2B is prevented.

[0070] As described above, the examples with three anti-rotation members and the examples with four anti-rotation members have been described, but the present disclosure may have five or more. Also, although the widths of the anti-rotation members in each modification are two types, when there are three or more anti-rotation members, the widths of the respective anti-rotation members may be different.

[0071] The above-described modification has been explained. In addition, in Embodiment 1 and Embodiment 2, the number of the sheets 30 (circulation parts) is three, but as shown in FIGS. 7 and 8, four sheets (circulation parts) may be provided. That is, in the present disclosure, the number of the circulation parts is not particularly limited.

[0072] In addition, in the above-described embodiments and modifications, as an example in which the shapes of the first rotation stopper and the second rotation stopper are different from each other when viewed from the axial direction, those having different widths when viewed from the axial direction are given as examples. However, the present disclosure is not limited to this, and it may be as shown in the following Embodiment 3.

[0073] (Embodiment 3) FIG. 9 is a cross-sectional view of the actuator of Embodiment 3 cut in the orthogonal direction. The ball screw device 101C of the actuator 100C of Embodiment 3 is different from Embodiment 1 in that it includes two rotation stoppers 740 instead of the two rotation stoppers 40. The two rotation stoppers 740 are a first rotation stopper 741 and a second rotation stopper 742. The first rotation stopper 741 and the second rotation stopper 742 are arranged at equal intervals in the circumferential direction as in Embodiment 1. Note that the width of the first rotation stopper 741 and the width of the second rotation stopper 742 are the same.

[0074] The first rotation stopper 741 and the second rotation stopper 742 each protrude from the outer peripheral surface 22 of the nut 2C. The recess 741a of the first rotation stopper 741 has a recess amount (depth) of D1 from the outer peripheral surface 22 of the nut 2C. The recess 742a of the second rotation stopper 742 has a recess amount (depth) of D2 from the outer peripheral surface 22 of the nut 2C. The recess amount D1 of the recess 741a and the recess amount D2 of the recess 742a are the same.

[0075] The key 741b of the first anti-rotation member 741 has a radial size of D3. The key 742b of the second anti-rotation member 742 has a radial size of D4. The size D4 of the key 742b is larger than the size D3 of the key 741b. Therefore, the protruding amount D6 from the outer peripheral surface 22 of the nut 2 in the second anti-rotation member 742 is larger than the protruding amount D5 from the outer peripheral surface 22 of the nut 2 in the first anti-rotation member 741.

[0076] Also, in FIG. 9, for the sake of easy viewing of the space between the first anti-rotation member 741 and the bottom surface of the first guide groove 131, it is shown enlarged, but actually, it is a minute gap for ensuring the slidability of the first anti-rotation member 741. That is, the recess amount of the first guide groove 131 is also approximately the same size (depth) as the protruding amount D5 of the first anti-rotation member 741. Similarly, the recess amount of the second guide groove 132 is also approximately the same size (depth) as the protruding amount D6 of the second anti-rotation member 742.

[0077] According to the above-described Embodiment 3, when the nut 2C is arranged in the first direction X1 of the accommodation space 123 in order to assemble the nut 2C, if the nut 2C is deviated by 180° from a predetermined angle, the second anti-rotation member 742 is arranged in the first direction X1 of the first guide groove 131. The protruding amount D6 of the second anti-rotation member 742 is larger than the recess amount of the first guide groove 131 (the protruding amount D5 of the first anti-rotation member 741). That is, even if the nut 2C is moved in the second direction X2, the second anti-rotation member 742 is not inserted into the first guide groove 131. Therefore, misassembly of the nut 2C is prevented.

[0078] As described above, in Embodiment 3, an example in which misassembly of the nut is prevented by the different protruding amounts of the anti-rotation members from each other has been described. Here, in Embodiment 3, by preparing keys 741b and 742b having different radial lengths, the protruding amounts of the anti-rotation members are changed, but a modification example 3 described below may also be used, and the present disclosure is not limited thereto.

[0079] (Modification Example 3) FIG. 10 is a cross-sectional view of the actuator of Modification 3 cut in the orthogonal direction. As shown in FIG. 10, in Modification 3, the radial size D13 of the key 841b of the first rotation stopper 841 and the radial size D14 of the key 842b of the second rotation stopper 842 are the same. That is, in Modification 3, the key 841b and the key 842b are common parts. Therefore, the number of parts of the ball screw device 101C can be reduced. Further, the recess amount D11 of the recess 841a of the first rotation stopper 841 is larger (deeper) than the recess amount D12 of the recess 841a of the first rotation stopper 841. For this reason, the protrusion amount D16 of the second rotation stopper 842 becomes larger than the protrusion amount D15 of the first rotation stopper 841. Even in such Modification 3, misassembly of the nut 2D is prevented.

[0080] As described above, Embodiment 3 and Modification 3 in which the protrusion amounts of the rotation stoppers are different from each other have been described. Here, although the rotation stoppers in the above-described embodiments and modifications are configured by a recess and a key, the present disclosure is not limited thereto. The rotation stopper may be, for example, a protrusion integrated with the nut body. Alternatively, the rotation stopper may be a guide groove that is recessed radially inward from the outer peripheral surface of the nut. Hereinafter, Embodiment 4 in which the rotation stopper is configured by a guide groove will be described.

[0081] (Embodiment 4) FIG. 11 is a cross-sectional view of the actuator of Embodiment 4 cut in the axial direction. FIG. 12 is a view of the cross-section taken along line XII-XII in FIG. 11 as viewed from the arrow direction. The ball screw device 101E of Embodiment 4 is different from Embodiment 1 in that the rotation stopper 40E is configured by the guide groove 940. The guide groove 940 is recessed radially inward from the outer peripheral surface 22 of the nut 2E and extends in the axial direction. Further, the housing (other part) 120 is provided with a protrusion 140 that protrudes radially inward from the inner peripheral surface 122 (opposing surface) that faces the outer peripheral surface 22 of the nut 2E. The protrusion 140 is inserted into the guide groove 940. Further, the protrusion 140 and the guide groove 940 are fitted so that the nut 2E can slide in the axial direction.

[0082] As shown in FIG. 12, the nut 2E is provided with two guide grooves 940 (a first guide groove 941 and a second guide groove 942). The first guide groove 941 and the second guide groove 942 are arranged at an interval of 180°. The first guide groove 941 and the second guide groove 942 have the same amount of depression with respect to each other. The housing 120D is provided with two protrusions 140 (a first protrusion 141 and a second protrusion 142). The first protrusion 141 and the second protrusion 142 are arranged at an interval of 180°. The first protrusion 141 and the second protrusion 142 have the same amount of protrusion with respect to each other.

[0083] Also, the width of the first protrusion 141 is such that a minute gap is formed between the first protrusion 141 and the side surface of the first guide groove 941 in order to ensure the slidability of the first guide groove 941. Therefore, the width of the first protrusion 141 is substantially the same as the width W31 of the first guide groove 941. For the same reason, the width of the second protrusion 142 is substantially the same as the width W32 of the second guide groove 942. The width W32 of the second guide groove 942 is larger than the width W31 of the first guide groove 941 (W32>W31. Refer to the auxiliary line H in FIG. 12). Therefore, the second protrusion 142 cannot be inserted into the first guide groove 941. From the above, even in the ball screw device 101E of the fourth embodiment, misassembly of the nut 2E is prevented in the same manner as in the other embodiments.

[0084] As described above, the fourth embodiment has been described. However, the guide groove is not limited to the above example. The guide groove of the fourth embodiment is formed on the outer peripheral surface of the nut. However, the present disclosure may be a guide groove formed on the outer peripheral surface of a flange protruding from the outer peripheral surface of the nut. That is, any groove that depresses radially inward from the outer peripheral side of the nut may be used. In addition, since the guide groove formed on the outer peripheral surface of the flange has a short axial length, it is necessary to lengthen the protrusion of the housing (other parts) in the axial direction. Therefore, the protrusion of the present disclosure may be a long protrusion in the axial direction.

[0085] Also, although the protrusion of Embodiment 4 is integrally formed with the housing (other components), the present disclosure is not limited to this. For example, a groove that recesses radially outward is formed on the inner peripheral surface of the housing (other components). Then, a part of the protrusion member is fitted into the groove. According to this, the remaining part of the protrusion member constitutes a protrusion that fits into the guide groove. Even in such a modification, incorrect assembly of the nut can be prevented. Examples of the protrusion member include a key with a short axial length and a pin with a long axial length.

[0086] Next, a modification 4 in which the anti-rotation structure is a guide groove and the recess amounts of each other are different will be described.

[0087] (Modification 4) FIG. 13 is a cross-sectional view of the actuator of Modification 4 cut in the orthogonal direction. The ball screw device 101F of Modification 4 is different from Embodiment 4 in that the first guide groove 941F and the second guide groove 942F have the same width as each other. Note that the width of the first protrusion 141F is substantially the same as the width of the first guide groove 941F, and the width of the second protrusion 142F is substantially the same as that of the second guide groove 942F.

[0088] Also, in FIG. 13, for easy viewing, the space between the bottom surface of the first guide groove 941F and the first protrusion 141F is shown enlarged, but in actuality, it is a minute gap for ensuring the slidability of the first guide groove 941F. That is, the recess amount D21 of the first guide groove 941F and the protrusion amount of the first protrusion 141F are substantially the same. For the same reason, the recess amount D22 of the second guide groove 942F and the protrusion amount of the second protrusion 142F are substantially the same.

[0089] The recess amount D22 of the second guide groove 942F is larger than the recess amount D21 of the first guide groove 941F. Therefore, the second protrusion 142F cannot be inserted into the first guide groove 941F. From the above, incorrect assembly of the nut 2F is prevented even in the ball screw device 101F of Modification 4.

[0090] The above described Embodiment 4 and Modification 4 in which the anti-rotation structure is a guide groove. Also, in each of the above-described embodiments and modifications, a koma is given as an example of the circulation part, but the present disclosure is not limited to the koma. Hereinafter, Modification 5 using another circulation part will be described.

[0091] (Modification 5) FIG. 14 is a cross-sectional view of the nut of Modification 5 cut in the axial direction. As shown in FIG. 14, the circulation part of the nut 2G of Modification 5 is different from Embodiment 1 in that it is an S-shaped groove surface 31 instead of the koma 30. The S-shaped groove surface 31 is a groove surface directly formed on the inner peripheral surface of the nut body by forging. This S-shaped groove surface 31, similar to the S-shaped groove surface of the koma 30, has an increasing amount of depression from both ends in the length direction in which the S-shaped groove surface 31 extends toward the central part in the length direction. That is, the S-shaped groove surface 31 has a larger amount of depression than the inner peripheral raceway surface 23, and the ball 3 that has entered the S-shaped groove surface 31 moves away from the outer peripheral raceway surface 12. Therefore, the S-shaped groove surface 31 corresponds to the unsupported region 50 that cannot receive the load from the screw shaft 1.

[0092] Also, in the nut 2G of Modification 5, the relationship between the S-shaped groove surface 31 (unsupported region 50) and the anti-rotation structure is the same as that of Modification 1 shown in FIG. 7. That is, in the nut 2G of Modification 5, four S-shaped groove surfaces 31 are provided at 90° intervals (one is not shown in FIG. 20). Also, in the nut 2G of Modification 5, three anti-rotation structures (only one is shown) 40G are provided at 120° intervals. And, among the three anti-rotation structures 40G, the width of one anti-rotation structure 40G is larger than the widths of the remaining two anti-rotation structures 40G.

[0093] The nut 2G using the S-shaped groove surface 31 has been described above, but the present disclosure may be a deflector (middle deflector and end deflector), a tube, or the like as the circulation part, and there is no particular limitation on the type of the circulation part.

[0094] Further, the present disclosure may be applied to the ball screw provided with a plurality of anti-rotation members having different protrusion amounts described in Embodiment 3, or the ball screw provided with a plurality of anti-rotation members having different recess amounts described in Embodiment 4, to the EMB described in Embodiment 2, or the number of anti-rotation members may be three or more as described in Modification 1 or Modification 2.

[0095] Also, although the widths of the anti-rotation members described in the embodiments and the like are two types, in the present disclosure, when there are three or more anti-rotation members, the widths of the respective anti-rotation members may be different from each other. Similarly, in the present disclosure, when there are three or more anti-rotation members, the protrusion amounts (or recess amounts) of the respective anti-rotation members may be different from each other. That is, there may be three or more types of widths or protrusion amounts (or recess amounts) of the anti-rotation members.

[0096] Alternatively, in each of the above-described embodiments and the like, an example in which the widths of the anti-rotation members are different from each other and an example in which the protrusion amounts (or recess amounts) of the anti-rotation members are different from each other are separately described, but the anti-rotation members of the present disclosure may have different widths and different protrusion amounts (or recess amounts) from each other.

[0097] Note that the present disclosure may be a combination of the following configurations. (1) A screw shaft to which rotational motion is transmitted, A nut having the screw shaft inserted therein, A plurality of balls disposed between the screw shaft and the nut, A circulation portion provided in the nut, Comprising On the outer peripheral surface of the nut, a plurality of anti-rotation members are provided for being supported so as to be movable in an axial direction parallel to the screw shaft and non-rotatable around the screw shaft with respect to other components, The plurality of anti-rotation members are arranged at equal intervals in the circumferential direction, The plurality of anti-rotation members include a first anti-rotation member and a second anti-rotation member, The first anti-rotation member and the second anti-rotation member have different shapes when viewed from the axial direction Ball screw device. (2) The anti-rotation member projects radially outward from the outer peripheral surface of the nut, The width sizes of the first anti-rotation member and the second anti-rotation member as viewed from the axial direction are different from each other. The ball screw device according to (1). (3) The anti-rotation member projects radially outward from the outer peripheral surface of the nut, The protruding amounts of the first anti-rotation member and the second anti-rotation member from the outer peripheral surface of the nut are different from each other. The ball screw device according to (1) or (2). (4) The anti-rotation member is a recess formed in the outer peripheral surface of the nut, a key that partially fits into the recess and the remaining part projects radially outward from the outer peripheral surface, and is composed of The recesses of the first anti-rotation member and the recesses of the second anti-rotation member have different amounts of depression from the outer peripheral surface of the nut. The ball screw device according to (3). (5) The anti-rotation member is a guide groove that is recessed radially inward from the outer peripheral side of the nut, The guide grooves constituting the first anti-rotation member and the guide grooves constituting the second anti-rotation member have different width sizes as viewed from the axial direction. The ball screw device according to (1). (6) The anti-rotation member is a guide groove that is recessed radially inward from the outer peripheral side of the nut, The guide grooves constituting the first anti-rotation member and the guide grooves constituting the second anti-rotation member have different amounts of depression from the outer peripheral surface of the nut. The ball screw device according to (1) or (5). (7) The other component is a facing surface facing the outer peripheral surface of the nut, a groove that is recessed radially outward from the facing surface, a protruding member that is partially accommodated in the groove and the remaining part fits into the guide groove, and has The ball screw device according to (5) or (6). (8) The other component has a facing surface facing the outer peripheral surface of the nut, and a protrusion protruding radially inward from the facing surface and fitting into the guide groove. and has The ball screw device according to (5) or (6). (9) An unsupported region where the circulation portion is arranged on the inner peripheral side of the nut and cannot receive the load from the screw shaft is provided, When an external load acts on the nut or the screw shaft and the screw shaft is displaced radially relative to the central axis of the nut, the displacement direction of the screw shaft is defined as the displacement direction of the screw shaft, when viewed from the central axis of the nut, the unsupported region is not arranged in the displacement direction of the screw shaft The ball screw device according to any one of (1) to (8). (10) The ball screw device according to any one of (1) to (9), and a motor that generates torque for rotating the screw shaft, and an actuator comprising

Explanation of reference numerals

[0098] 1 Screw shaft 2, 2A, 2B, 2E, 2G Nuts 3 Ball 12 Outer peripheral raceway surface 20 Nut body 30 Disk 31 S-shaped groove surface 40, 40E, 40G, 340, 440, 540, 640, 740 Anti-rotation 41, 341, 441, 541, 641, 741, 841 First anti-rotation 42, 342, 442, 542, 642, 742, 842 Second anti-rotation 50 Unsupported region 51 First unsupported region 52 Second unsupported region 53 Third Unsupported Area 100, 100C Actuators 101, 101A, 101B, 101C, 101E, 101F Ball Screw Devices 120 Housing 123 Accommodation Space 130, 940 Guide Grooves 131, 941, 941F First Guide Groove 132, 942, 942F Second Guide Groove 140 Protrusion 141 First Protrusion 142 Second Protrusion 500 Vehicle 503 EMB 543, 643 Third Anti-Rotation 644 Fourth Anti-Rotation

Claims

1. A screw shaft to which a rotational motion is transmitted, a nut having the screw shaft inserted therein, a plurality of balls disposed between the screw shaft and the nut, a circulation portion provided in the nut, and comprising: On the outer peripheral surface of the nut, a plurality of anti-rotation members are provided for being movably supported in an axial direction parallel to the screw shaft and non-rotatably around the screw shaft with respect to other components. The plurality of anti-rotation members are arranged at equal intervals in the circumferential direction. The plurality of anti-rotation members include a first anti-rotation member and a second anti-rotation member. The first anti-rotation member and the second anti-rotation member have different shapes when viewed from the axial direction. Ball screw device.

2. The anti-rotation member protrudes radially outward from the outer peripheral surface of the nut. The first anti-rotation member and the second anti-rotation member have different widths when viewed from the axial direction. The ball screw device according to claim 1.

3. The anti-rotation member protrudes radially outward from the outer peripheral surface of the nut. The first anti-rotation member and the second anti-rotation member have different amounts of protrusion from the outer peripheral surface of the nut. The ball screw device according to claim 1.

4. The anti-rotation member is a recess formed in the outer peripheral surface of the nut, a key that is partially fitted into the recess and the remaining portion protrudes radially outward from the outer peripheral surface, and is constituted by: The recesses of the first anti-rotation member and the recesses of the second anti-rotation member have different amounts of depression from the outer peripheral surface of the nut. The ball screw device according to claim 3.

5. The anti-rotation member is a guide groove that is recessed radially inward from the outer peripheral side of the nut. The guide groove constituting the first anti-rotation member and the guide groove constituting the second anti-rotation member have different widths when viewed from the axial direction. The ball screw device according to claim 1.

6. The anti-rotation member is a guide groove that is recessed radially inward from the outer peripheral side of the nut. The guide groove constituting the first anti-rotation member and the guide groove constituting the second anti-rotation member have different amounts of depression from the outer peripheral surface of the nut. The ball screw device according to claim 1.

7. The other component is a facing surface facing the outer peripheral surface of the nut, a groove that is recessed radially outward from the facing surface, a protruding member that is partially accommodated in the groove and the remaining portion is fitted into the guide groove, and has The ball screw device according to claim 5 or claim 6.

8. The other component is a facing surface facing the outer peripheral surface of the nut, a protrusion that protrudes radially inward from the facing surface and fits into the guide groove; having The ball screw device according to claim 5 or claim 6.

9. An unsupported region where the circulation part is arranged on the inner peripheral side of the nut and cannot receive the load from the screw shaft is provided. When an external load acts on the nut or the screw shaft, the direction in which the screw shaft is displaced radially relative to the central axis of the nut is defined as the displacement direction of the screw shaft. When viewed from the central axis of the nut, the unsupported region is not arranged in the displacement direction of the screw shaft. The ball screw device according to claim 1.

10. A ball screw device according to any one of claims 1 to 6 and claim 9, a motor that generates torque for rotating the screw shaft, An actuator comprising.

Images