JP7708181B2 - Ball screw device - Google Patents

Description

The present invention relates to a ball screw device.

Patent Document 1 discloses a ball screw device that can be applied to an automobile brake device.
This ball screw device includes a screw shaft having a first helical groove on its outer periphery, a nut having a second helical groove on its inner periphery that forms a helical track between the first helical groove, and a ball train consisting of a plurality of balls arranged on the helical track. When the screw shaft rotates, the nut moves along the axial direction of the screw shaft. The ball screw device disclosed in Patent Document 1 is not a device in which a plurality of balls circulates when the nut moves, but a non-circulating device in which a plurality of balls remain and roll within the helical track of the nut.

JP 2016-35322 A

The above-mentioned conventional non-recirculating ball screw device includes a first coil spring that is provided in the helical raceway and abuts against one end of the row of balls, and a second coil spring that is provided in the helical raceway and abuts against the other end of the row of balls.
In the above-mentioned ball screw device, both ends of the ball train are held by two coil springs, and when a rotational force is applied to the screw shaft and it rotates relative to the nut, the ball train moves in a spiral track within the expansion and contraction range of both coil springs, moving the nut along the axial direction.
Therefore, the stroke of the screw shaft accompanying the movement of the ball train is determined according to the amount of expansion and contraction of the coil spring.
However, there is a limit to the amount of expansion and contraction of the coil spring that can be placed within the spiral track, and even if the axial length of the nut was extended, it was difficult to ensure a large stroke accompanied by movement of the ball row.

The ball screw device according to the embodiment includes a screw shaft having a first spiral groove on its outer circumference, a nut having a second spiral groove on its inner circumference that forms a spiral track between the first spiral groove, a ball row including a plurality of balls arranged on the spiral track, and a retainer arranged in an annular space between the screw shaft and the nut and holding the plurality of balls. The retainer includes an annular portion arranged in the annular space so as to be rotatable around the center line of the screw shaft and immovable in the axial direction relative to the nut, a plurality of columns extending from one end face on one axial side of the annular portion to one axial direction side and intersecting the spiral track at multiple points, and a plurality of pockets provided between a pair of circumferentially adjacent columns among the plurality of columns and holding the plurality of balls so as to be rollable.

A ball screw device according to another embodiment from another viewpoint includes a screw shaft having a first spiral groove on its outer circumference, a nut having a second spiral groove on its inner circumference that forms a spiral track between the first spiral groove, a ball train including a plurality of balls arranged on the spiral track, and a retainer arranged in an annular space between the screw shaft and the nut and holding the plurality of balls. The retainer includes a cylindrical main body portion arranged in the annular space so as to be rotatable around the center line of the screw shaft and immovable in the axial direction relative to the nut, and a plurality of pockets provided in the main body portion along the circumferential direction and holding the plurality of balls, the plurality of pockets extending in the axial direction intersecting the spiral track at a plurality of points.

According to the present disclosure, a larger stroke involving movement of the ball row can be ensured.

FIG. 1 is a perspective view of a ball screw device according to a first embodiment. FIG. 2 is a cross-sectional view of the ball screw device. FIG. 3(a) is a perspective view showing the cage in a state in which it is arranged on the outer periphery side of the screw shaft, and FIG. 3(b) is a perspective view showing the cage. 4A and 4B are diagrams showing the positional relationship between the cage and the balls, in which FIG. 4A shows the case where the ball row is located at a first position, and FIG. 4B shows the case where the ball row is located at a second position. FIG. 5 is a cross-sectional view of a main portion of a ball screw device according to a modified example of the first embodiment. FIG. 6 is an exploded perspective view of the ball screw device according to the second embodiment. FIG. 7 is a cross-sectional view of a main portion of a ball screw device according to a second embodiment. FIG. 8 is a diagram showing the cage in a state in which it is disposed on the outer periphery of the screw shaft. FIG. 9 is a diagram showing a cage of a ball screw device according to a modified example of the second embodiment. FIG. 10 is a diagram showing a cage of a ball screw device according to a second modified example of the second embodiment. FIG. 11 is an enlarged view of the second inner end surface of the annular connecting portion in FIG. FIG. 12 is a plan view showing the cage.

First, the contents of the embodiment will be listed and described.
[Overview of the embodiment]
(1) A ball screw device according to an embodiment includes a screw shaft having a first helical groove on an outer periphery, a nut having a second helical groove on an inner periphery that forms a helical track between the first helical groove, a ball train including a plurality of balls arranged on the helical track, and a cage arranged in an annular space between the screw shaft and the nut and holding the plurality of balls. The cage includes an annular portion arranged in the annular space to be rotatable around a center line of the screw shaft and immovable in the axial direction relative to the nut, a plurality of pillars extending from one end face on one axial side of the annular portion to one axial side and intersecting the helical track at a plurality of points, and a plurality of pockets provided between a pair of circumferentially adjacent pillars among the plurality of pillars and holding the plurality of balls so as to be rollable.

According to the above-mentioned configuration, the pockets are provided between the posts that intersect the helical track at multiple points, so that the pockets extend along the axial direction and intersect the helical track at multiple points, and each ball is held at a point where the pocket intersects with the helical track.
When the ball train moves in the helical orbit, the cage rotates in response to the movement of the ball train. At this time, each ball moves in the axial direction along the pocket of the cage. Therefore, the ball train can move in the helical orbit within a range in which each ball can move in the axial direction along the pocket.
Therefore, the stroke accompanied by the movement of the ball row can be determined by the axial length of the pocket, and a larger stroke accompanied by the movement of the ball row can be ensured compared to the case in which a coil spring is used as in the conventional example described above.

(2) In the above ball screw device, it is preferable that the cage further includes a connecting annular portion connecting tips of the plurality of posts on one axial side.
In this case, the rigidity of the cage can be increased by the annular connecting portion.

(3) In the above ball screw device, a circumferential distance between the pair of posts may be set to a distance that is sufficient to hold one of the balls.
In this case, one ball is held at the point where the pocket intersects with the spiral trajectory.
Therefore, when assembling the ball screw device, it is sufficient to place each ball one by one at the point where the pocket and the spiral track (the first spiral groove or the second spiral groove) intersect, making assembly easier than when multiple balls are held at the point where the pocket and the spiral track intersect.

(4) In the above ball screw device, it is preferable that each of the multiple pockets holds one of the balls.

(5) In the above ball screw device, the circumferential distance between the pair of posts may be set to a distance that is sufficient to hold a predetermined number of the balls, which may be two or more.
In this case, multiple balls are held at the points where the pockets intersect with the spiral trajectory.
Therefore, the number of pillars can be reduced compared to when one ball is held at the intersection of the pocket and the spiral trajectory.

(6) In the above ball screw device, it is preferable that each of the multiple pockets holds the predetermined number of balls.

(7) In the above-described ball screw device, it is preferable that a friction member be provided between the nut and the annular portion to provide resistance to rotation of the cage relative to the nut.
In this case, if the rotational torque acting between the screw shaft and the nut is low enough that the cage and the nut are held rotatably together by the resistance of the friction member, the ball screw device functions as a sliding screw. On the other hand, if the rotational torque acting between the screw shaft and the nut is high enough that the cage and the nut cannot be held rotatably together by the resistance of the friction member, the cage rotates relative to the screw shaft and the nut and functions as a ball screw.
Therefore, the state where the screw functions as a sliding screw and the state where the screw functions as a ball screw can be switched according to the rotational torque acting between the screw shaft and the nut. Also, by adjusting the resistance of the friction member, the timing of switching between the state where the screw functions as a sliding screw and the state where the screw functions as a ball screw can be adjusted.

(8) In the above ball screw device, the friction member may include a rubber ring interposed between the nut and an outer circumferential surface of the annular portion.
In this case, a frictional force can be generated between the nut and the annular portion with a simple structure, and resistance can be applied to the rotation of the cage relative to the nut.

(9) In the above-mentioned ball screw device, the nut has a cylindrical inner circumferential surface that accommodates the annular portion radially inward, and a step surface that extends radially inward from the cylindrical inner circumferential surface and connects the cylindrical inner circumferential surface and the second spiral groove, and the friction member may include a wave washer that presses the annular portion to one axial side and abuts the step surface facing the one end face of the annular portion against the one end face.
In this case, frictional force can be generated between the nut and the annular part by abutting and pressing the step surface against the one end surface. Also, by selecting the dimensions and characteristics of the wave washer, the resistance applied between the nut and the cage can be easily adjusted.

(10) In the above ball screw device, each of the multiple pockets is defined by side surfaces of the pair of pillars and a first inner end surface of the annular portion, the first inner end surface has a first circumferential surface along the circumferential direction and a first inclined surface, a first end of the first circumferential surface is an end of both circumferential ends of the first circumferential surface that has a smaller axial distance from a groove top of the first spiral groove when the pocket is viewed from the front, the first inclined surface is provided to connect a first side surface of the side surfaces of the pair of pillars on the first end side and the first end, and is inclined to approach a second side surface of the side surfaces of the pair of pillars as it moves from the first side surface to the first end, the first inclined surface being capable of contacting the ball in a state in which it is in contact with the second side surface, and when the ball contacts the first inclined surface and the second side surface, the first circumferential surface is a surface that is not in contact with the ball.
With the above configuration, when the ball moving along the spiral trajectory reaches the first inner end face, the ball can be brought into contact with the first inclined surface without coming into contact with the first circumferential surface.
Here, since the first inclined surface is inclined so as to approach the second side surface from the first side surface toward the first end, the angle between the groove top located on one axial side of the ball and the first inclined surface can be made relatively large, thereby making it possible to prevent the ball from getting caught between the helical track and the first inclined surface.
Therefore, when a ball moving along the spiral trajectory reaches the first inner end face and abuts against the first inclined surface, it is possible to prevent the ball from getting caught between the spiral trajectory and the first inclined surface.

(11) When multiple first inner end faces are arranged along the circumferential direction, when a ball located at the end of the ball row moves axially to reach a first inner end face and abuts against the first end face, a force from the screw shaft and the nut acts on this one ball, and the force from the screw shaft and the nut does not act significantly on the other balls.
For this reason, it is preferable that the multiple first inner end faces are aligned along the lead angle direction of the first spiral groove.
In this case, the plurality of balls can be brought into contact with the plurality of first inner end faces at the same time, which allows the force acting from the screw shaft and the nut to be evenly distributed to the plurality of balls, thereby more effectively preventing the balls from getting stuck.

(12) In the above ball screw device, the cage further includes a connecting annular portion connecting tips of the plurality of pillars on one side in the axial direction, each of the pockets is defined by side surfaces of the pair of pillars, a first inner end surface of the annular portion, and a second inner end surface of the connecting annular portion, the second inner end surface having a second circumferential surface along the circumferential direction and a second inclined surface, and a second end portion of the second circumferential surface is a groove top of the first spiral groove when the pocket is viewed from the front, of both circumferential ends of the second circumferential surface, the axial distance from the groove top of the first spiral groove when the pocket is viewed from the front is is the smaller end, the second inclined surface is provided to connect a second side surface of the side surfaces of the pair of pillars that is closer to the second end and is inclined to approach a first side surface of the side surfaces of the pair of pillars as it extends from the second side surface toward the second end, the second inclined surface is capable of coming into contact with the ball in a state in which the ball is in contact with the first side surface, and when the ball comes into contact with the second inclined surface and the first side surface, the second circumferential surface is a surface that does not come into contact with the ball.
In the above configuration, when the ball moving along the spiral trajectory reaches the second inner end face, the ball can be brought into contact with the second inclined surface without coming into contact with the second circumferential surface.
Here, since the second inclined surface is inclined so as to approach the first side surface from the second side surface toward the second end, the angle between the groove top located on the other axial side of the ball and the second inclined surface can be made relatively large, thereby making it possible to prevent the ball from getting caught between the helical track and the second inclined surface.
Therefore, when a ball moving along the spiral trajectory reaches the second inner end face and abuts against the second inclined surface, it is possible to prevent the ball from getting caught between the spiral trajectory and the second inclined surface.

(13) In the above ball screw device, it is preferable that the second inner end faces are aligned along a lead angle direction of the first spiral groove.
In this case, the plurality of balls can be brought into contact with the plurality of second inner end faces at the same time, which allows the force acting from the screw shaft and the nut to be evenly distributed to the plurality of balls, thereby effectively preventing the balls from becoming jammed.

(14) A ball screw device according to another embodiment from another viewpoint includes a screw shaft having a first spiral groove on its outer periphery, a nut having a second spiral groove on its inner periphery that forms a spiral track between the first spiral groove, a ball row including a plurality of balls arranged on the spiral track, and a retainer arranged in an annular space between the screw shaft and the nut and holding the plurality of balls. The retainer includes a cylindrical main body portion arranged in the annular space so as to be rotatable around the center line of the screw shaft and immovable in the axial direction relative to the nut, and a plurality of pockets provided in the main body portion along the circumferential direction and holding the plurality of balls. The plurality of pockets extend along the axial direction and intersect the spiral track at multiple points.

[Details of the embodiment]
Hereinafter, preferred embodiments will be described with reference to the drawings.
[Regarding the first embodiment]
Fig. 1 is a perspective view of a ball screw device according to a first embodiment, and Fig. 2 is a cross-sectional view of the ball screw device, the cross-sectional view being taken along a plane including the center line of the ball screw device.
The ball screw device 1 is used in a brake device of a vehicle such as an automobile, a power transmission device including a multi-plate clutch, and the like.
The ball screw device 1 includes a screw shaft 2 , a nut 4 provided on the outer periphery of the screw shaft 2 , a plurality of balls 6 , and a cage 8 that holds the plurality of balls 6 .
In this embodiment, the direction parallel to the center line C of the screw shaft 2 is defined as the axial direction, the direction perpendicular to the center line C is defined as the radial direction, and the direction along a circle centered on the center line C is defined as the circumferential direction.
1 and 2, the side in the axial direction where the retaining ring 9 is not provided at the opening of the nut 4 is defined as one axial side, and the side where the retaining ring 9 is provided is defined as the other axial side.

The screw shaft 2 is inserted into the nut 4 and has a first spiral groove 10 on its outer periphery.
The nut 4 is a cylindrical member. The center line of the nut 4 coincides with the center line C. The nut 4 has a second spiral groove 12 on its inner circumference. In addition, a cylindrical inner circumferential surface 4a is provided at the other axial end of the inner circumference of the nut 4.
The first helical groove 10 of the screw shaft 2 and the second helical groove 12 of the nut 4 form a helical track 14 in which a plurality of balls 6 are arranged.
The outer diameter of the groove apex 10a of the first spiral groove 10 is smaller than the inner diameter of the groove apex 12a of the second spiral groove 12. Thus, an annular space K is provided between the screw shaft 2 and the nut 4.

The cage 8 is disposed in the annular space K between the screw shaft 2 and the nut 4 .
The retainer 8 includes an annular portion 20 and a plurality of posts 22 .
The annular portion 20 is accommodated radially inward of the cylindrical inner peripheral surface 4 a. The annular portion 20 is disposed between the cylindrical inner peripheral surface 4 a and the screw shaft 2.
An annular groove 4b in which a retaining ring 9 is fitted is provided on the cylindrical inner peripheral surface 4a.
One end face 20a on one axial side of the annular portion 20 faces a stepped surface 24 of the nut 4. The stepped surface 24 is a surface that extends radially inward from the cylindrical inner circumferential surface 4a and connects between the cylindrical inner circumferential surface 4a and the second spiral groove 12.
The other end face 20 b on the other axial side of the annular portion 20 faces the inner surface 9 a of the retaining ring 9 .

In addition, a slight clearance is provided between the inner peripheral surface 20c of the annular portion 20 and the groove apex 10a of the first spiral groove 10 of the screw shaft 2. In addition, a slight clearance is provided between the outer peripheral surface 20d of the annular portion 20 and the cylindrical inner peripheral surface 4a.
As a result, the annular portion 20 is disposed within the annular space K so as to be rotatable around the center line C but unable to move axially relative to the nut 4 .

An outer circumferential groove 20d1 is provided in the outer circumferential surface 20d of the annular portion 20. A friction member 26 is provided in the outer circumferential groove 20d1.
In the present embodiment, the friction member 26 is a rubber ring. The friction member 26 is fitted into the outer circumferential groove 20d1.
The friction member 26 is interposed between the cylindrical inner peripheral surface 4a and the outer peripheral groove 20d1, and is in contact with the cylindrical inner peripheral surface 4a and the outer peripheral groove 20d1. In other words, the friction member 26 is provided between the nut 4 and the annular portion 20. The friction member 26 applies resistance to the rotation of the cage 8 relative to the nut 4 by a frictional force generated by contact with the cylindrical inner peripheral surface 4a and the outer peripheral groove 20d1.
Therefore, if the force acting between the nut 4 and the retainer 8 to cause relative rotation is smaller than the resistance by the friction member 26, the retainer 8 will rotate integrally with the nut 4, and if the force acting to cause relative rotation is greater than the resistance by the friction member 26, the retainer 8 will be able to rotate relative to the nut 4.

The retainer 8 has multiple pillars 22 that extend from one end face 20a of the annular portion 20 to one side in the axial direction. The retainer 8 of this embodiment has three pillars 22. The three pillars 22 are arranged at equal intervals in the circumferential direction.

FIG. 3( a ) is a perspective view showing the cage 8 in a state in which it is arranged on the outer periphery side of the screw shaft 2 , and FIG. 3( b ) is a perspective view showing the cage 8 .
As shown in Figures 2 and 3, the three pillars 22 extend axially across between the groove apex 10a of the first spiral groove 10 of the screw shaft 2 and the groove apex 12a of the second spiral groove 12 of the nut 4, and intersect the spiral track 14 at multiple points.

The retainer 8 also includes a connecting annular portion 30 that connects the tips 22a of the posts 22 on one axial side. The center line of the connecting annular portion 30 coincides with the center line C and is concentric with the annular portion 20. One end face 30a on one axial side of the connecting annular portion 30 approximately coincides with one end face 4c on one axial side of the nut 4. In this manner, the connecting annular portion 30 is provided at the end portion on one axial side of the nut 4.

The cage 8 further includes a plurality of pockets 32 that hold the plurality of balls 6 in a rollable manner.
The pocket 32 is provided between a pair of circumferentially adjacent columns 22 among the three columns 22. Thus, the cage 8 of the present embodiment includes three pockets 32.
The pocket 32 is a rectangular space surrounded by a pair of circumferentially adjacent pillars 22 , the annular portion 20 , and the connecting annular portion 30 .
Thus, the pockets 32 extend along the axial direction and intersect with the helical track 14 at multiple points.

The pocket 32 is defined by the side surfaces 22 b of a pair of circumferentially adjacent pillars 22 , a first inner end surface 32 a of the annular portion 20 , and a second inner end surface 32 b of the connecting annular portion 30 .
The first inner end surface 32a is an end surface on one axial side of the annular portion 20. The second inner end surface 32b is an end surface on the other axial side of the connecting annular portion 30.
The pair of side surfaces 22b extend along the axial direction, and the first inner end surface 32a and the second inner end surface 32b extend along the circumferential direction.
The circumferential distance between a pair of circumferentially adjacent pillars 22 is set to a distance capable of holding two balls 6, as shown in Figs. 4(a) and 4(b).

The plurality of balls 6 are arranged in the helical track 14 to form a ball train L. In this embodiment, the ball train L includes six balls 6.
As described above, the circumferential distance between a pair of circumferentially adjacent posts 22 is a distance that can hold two balls 6. Thus, three posts 22 are interposed in the ball row L. The three posts 22 are interposed so as to divide the balls 6 in the ball row L aligned in the longitudinal direction of the row into three.
In other words, each of the three pockets 32 holds two balls 6 aligned in the longitudinal direction of the row.

When the screw shaft 2 rotates relative to the nut 4 and the cage 8 rotates about the center line C, the ball train L moves within the helical track 14. As the ball train L moves within the helical track 14, the ball screw device 1 functions as a ball screw.
Here, since the balls 6 are held in the pockets 32 , the range of movement of the ball row L in the axial direction is limited by the cage 8 .

For example, as shown in Figure 4 (a), when the ball 6a, among the six balls 6, located at the end on the other axial side in the ball row L abuts against the first inner end face 32a of the annular portion 20 and the side face 22b of the pillar 22, the axial position of the ball row L in the retainer 8 becomes the position closest to the other axial side (first position).
In addition, in order to facilitate understanding, the nut 4 is omitted in FIGS. 4(a) and 4(b).

When the screw shaft 2 is rotated relative to the nut 4 and the ball row L at the first position is moved toward one axial side, as shown in Fig. 4(b) , of the six balls 6, a ball 6b located at one end of the ball row L on one axial side comes into contact with the second inner end surface 32b of the connecting annular portion 30 and the side surface 22b of the pillar 22. The ball 6b is restricted from moving further toward the one axial side along the helical track 14 by the connecting annular portion 30 and the pillar 22. Therefore, as shown in Fig. 4(b) , when the ball 6b comes into contact with the connecting annular portion 30 and the pillar 22, the axial position of the ball row L in the cage 8 becomes the position closest to the one axial side within the cage 8 (the second position).
In this manner, the axial movement range of the ball row L is limited by the cage 8 .

The ball screw device 1 rotates the screw shaft 2 relative to the nut 4, and functions as a ball screw while the ball row L moves from the first position to the second position.
If the screw shaft 2 is further rotated relative to the nut 4 after the ball row L reaches the first position from the second position, the axial movement of the ball row L is restricted, so that the ball screw device 1 does not function as a ball screw but as a sliding screw.
Conversely, the ball screw device 1 also functions as a ball screw while the ball row L moves from the second position to the first position.
If the screw shaft 2 is further rotated relative to the nut 4 after the ball row L reaches the first position from the second position, the axial movement of the ball row L is also restricted, so that the ball screw device 1 does not function as a ball screw but as a sliding screw.

In this way, the ball screw device 1 functions as a ball screw while the screw shaft 2 rotates relative to the nut 4 and the ball train L moves between the first position and the second position in the cage 8. On the other hand, when the ball train L does not move, the ball screw device 1 functions as a sliding screw.

The ball screw device 1 having the above configuration is used for applying a rotational force to the screw shaft 2 and rotating the screw shaft 2 relative to the nut 4, thereby moving the nut along the axial direction and converting the rotational motion applied to the screw shaft 2 into linear motion.
When the screw shaft 2 rotates relative to the nut 4, if the ball train L moves within the helical track 14 as described above, the ball screw device 1 functions as a ball screw and moves the nut 4 in the axial direction after decelerating the rotational force transmitted to the screw shaft 2. In other words, during the stroke of the ball screw device 1, while the ball train L moves between the first position and the second position, the rotational force applied to the screw shaft 2 is decelerated.
On the other hand, when the ball train L does not move within the helical track 14, the ball screw device 1 functions as a sliding screw and moves the nut 4 in the axial direction in response to the rotation applied to the screw shaft 2.

According to the above-described configuration, the pockets 32 are provided between the posts 22 that intersect the helical track 14 at multiple points, so that the pockets 32 extend along the axial direction and intersect the helical track 14 at multiple points. Each ball 6 is held at a point where the pocket 32 and the helical track 14 intersect.
When the ball row L moves within the helical track 14, the cage 8 rotates in response to the movement of the ball row L. At this time, each ball 6 moves in the axial direction along the pocket 32 of the cage 8. Therefore, the ball row L can move within the helical track 14 within a range in which each ball 6 can move in the axial direction along the pocket 32.
Therefore, the stroke accompanied by the movement of the ball row L can be determined by the axial length of the pocket 32, and a larger stroke accompanied by the movement of the ball row can be ensured compared to the case in which a coil spring is used as in the conventional example described above.

In addition, in this embodiment, a friction member 26 is provided between the nut 4 and the annular portion 20 of the retainer 8, so that the timing of switching between a state in which the ball screw device 1 functions as a sliding screw and a state in which it functions as a ball screw can be adjusted.
For example, when the screw shaft 2 and the nut 4 are rotated relative to each other to move the nut 4 to the other axial side from the state shown in Figure 4 (a), if the rotational torque acting between the screw shaft 2 and the nut 4 is relatively small, the friction member 26 holds the retainer 8 so that it can rotate integrally with the nut 4 due to the resistance generated by contact with the nut 4 and the annular portion 20.
When the cage 8 does not rotate relative to the nut 4, the ball train L does not move within the helical track 14, and the ball screw device 1 functions as a sliding screw.

On the other hand, when the rotational torque acting between the screw shaft 2 and the nut 4 is relatively large and the force acting between the nut 4 and the retainer 8 to cause relative rotation becomes greater than the resistance provided by the friction member 26, relative rotation of the retainer 8 with respect to the nut 4 is permitted.
In this case, the ball train L is capable of moving within the helical track 14, so that the ball screw device 1 functions as a ball screw.

In this manner, in the present embodiment, a friction member 26 is provided between the nut 4 and the annular portion 20 of the retainer 8, so that switching between a state where it functions as a sliding screw and a state where it functions as a ball screw can be performed in accordance with the rotational torque acting between the screw shaft 2 and the nut 4.
Furthermore, by adjusting the resistance of the friction member 26, the timing of switching between the state where it functions as a sliding screw and the state where it functions as a ball screw can be adjusted.
In this embodiment, the friction member 26 is made of a rubber ring, so that a frictional force can be generated between the nut 4 and the annular portion 20 with a simple configuration, and resistance can be applied to the rotation of the retainer 8 relative to the nut 4.

In addition, in this embodiment, since the cage 8 is provided with the connecting annular portion 30 at the tip 22a of the post 22, the rigidity of the cage 8 can be increased.
In addition, by providing the connecting annular portion 30, the ball 6b at the end on one axial side of the ball row L when the axial position of the ball row L is in the first position can be more firmly restricted from moving further axially to one side.

In addition, in this embodiment, the circumferential spacing between a pair of circumferentially adjacent pillars 22 is set to a spacing that is capable of holding two balls 6, so that two balls 6 are held at the point where the pocket 32 and the spiral track 14 intersect.
Therefore, the number of pillars 22 can be reduced compared to the case where one ball 6 is held at the intersection of the pocket 32 and the helical track 14 .

FIG. 5 is a cross-sectional view of a main part of the ball screw device 1 according to a modified example of the first embodiment.
In the above embodiment, the friction member 26 is formed of a rubber ring, but in this modified example, the friction member 26 is formed of a wave washer.
The friction member 26 of this embodiment is interposed between the other end surface 20b of the annular portion 20 and the inner surface 9a of the retaining ring 9, and presses the annular portion 20 (retainer 8) toward one side in the axial direction.
As a result, the friction member 26 abuts the step surface 24 of the nut 4 against one end face 20a of the annular portion 20, and the frictional force between the step surface 24 and the one end face 20a provides resistance to the rotation of the retainer 8 relative to the nut 4.

In this modified example, the step surface 24 and the one end surface 20a are brought into contact with each other and pressed against each other, thereby generating a frictional force between the nut 4 and the annular portion 20. In addition, by selecting the dimensions and characteristics of the friction member 26, which is a wave washer, the frictional force between the step surface 24 and the one end surface 20a can be easily adjusted, and the resistance applied between the nut 4 and the retainer 8 can be easily adjusted. As a result, the timing of switching between the state in which the nut functions as a sliding screw and the state in which the nut functions as a ball screw can be easily adjusted.

[Regarding the second embodiment]
Fig. 6 is an exploded perspective view of the ball screw device 1 according to the second embodiment, and Fig. 7 is a cross-sectional view of a main part of the ball screw device 1 according to the second embodiment. Note that the balls 6 are omitted in Figs. 6 and 7.

Like the first embodiment, the ball screw device 1 of this embodiment comprises a screw shaft 2 having a first spiral groove 10 on its outer periphery, a nut 4 having a second spiral groove 12 on its inner periphery that forms a spiral track 14 between the first spiral groove 10, a ball row L including a plurality of balls 6 arranged on the spiral track 14, and a retainer 8 arranged in the annular space K between the screw shaft 2 and the nut 4 and holding the plurality of balls 6.
The retainer 8 also includes an annular portion 20 that is arranged in the annular space K so as to be rotatable around the center line C of the screw shaft 2 and so as to be immovable in the axial direction relative to the nut 4, a plurality of pillars 22 that extend axially from one end face 20a on one axial side of the annular portion 20 to one side and intersect the spiral track 14 at multiple points, a connecting annular portion 30 that connects the tips of the plurality of pillars 22, and a plurality of pockets 32 that are provided between a pair of circumferentially adjacent pillars among the plurality of pillars 22 and that hold a plurality of balls 6 in a rollable manner.

This embodiment differs from the first embodiment in that it has a sleeve 36 that is arranged on the other axial side of the retainer 8, and in that the circumferential spacing between a pair of circumferentially adjacent posts 22 is sufficient to hold one ball 6.

The sleeve 36 is disposed on the outer periphery of the screw shaft 2 and is fixedly fitted onto the cylindrical inner periphery 4 a of the nut 4 .
One end face 36a on one axial side of the sleeve 36 abuts against the other end face 20b of the annular portion 20. As a result, the annular portion 20 is prevented from moving axially relative to the nut 4 by the step surface 24 of the nut 4 and the one end face 36a of the sleeve 36.

FIG. 8 is a diagram showing the cage 8 in a state in which it is disposed on the outer periphery of the screw shaft 2. As shown in FIG.
The cage 8 in this embodiment has fourteen pillars 22. Therefore, the cage 8 has fourteen pockets 32.
In this embodiment, the ball row L includes, for example, 14 balls 6. Thus, each pocket 32 holds one ball 6.
In this case, one ball 6 is held at the point where the pocket 32 and the helical track 14 intersect.
Therefore, when assembling the ball screw device 1, it is sufficient to place each ball 6 one by one at the point where the pocket 32 and the spiral track 14 (the first spiral groove 10 or the second spiral groove 12) intersect, making assembly easier than when multiple balls 6 are held at the point where the pocket 32 and the spiral track 14 intersect.

FIG. 9 is a diagram showing the cage 8 of the ball screw device 1 according to a first modified example of the second embodiment.
This first modified example differs from the second embodiment in that the first inner end surface 32a of the annular portion 20 includes a circumferential surface 32a1 extending along the circumferential direction and an inclined surface 32a2 inclined relative to the circumferential surface 32a1, and in that the second inner end surface 32b of the connecting annular portion 30 includes a circumferential surface 32b1 extending along the circumferential direction and an inclined surface 32b2 inclined relative to the circumferential surface 32b1.

9, an inclined surface 32a2 is provided on one end 32a11 side of the circumferential end portions of the circumferential surface 32a1 that is closer in axial distance to the groove apex 10a when the pocket 32 is viewed from the front. The one end 32a11 is an end portion on one side in the circumferential direction of the circumferential end portions of the circumferential surface 32a1.
The inclined surface 32a2 is provided so as to connect one end 32a11 of the circumferential surface 32a1 and the side surface 22b of the pillar 22. The inclined surface 32a2 is inclined toward one axial side from the one end 32a11 toward the side surface 22b of the pillar 22. Therefore, the angle between the inclined surface 32a2 and the side surface 22b is 90 degrees or more.

When the axial position of the ball row L is at a first position and the ball 6a located at the other axial end of the ball row L abuts against the first inner end face 32a and the side face 22b of the pillar 22, the ball 6a abuts against the side face 22b of the pillar 22 and the inclined surface 32a2 of the first inner end face 32a.
At this time, since the angle formed by the inclined surface 32a2 and the side surface 22b is 90 degrees or more, it is possible to prevent the ball 6a from becoming caught between the inclined surface 32a2 and the side surface 22b.

Similarly, an inclined surface 32b2 is provided on the other end 32b11 side of the circumferential end portions of the circumferential surface 32b1 of the second inner end face 32b, the other end portion 32b11 being closer to the groove apex 10a in the axial direction when the pocket 32 is viewed from the front. The other end portion 32b11 is the end portion on the other circumferential side of the circumferential end portions of the circumferential surface 32b1.
The inclined surface 32b2 is provided to connect the other end 32b11 of the circumferential surface 32b1 and the side surface 22b of the pillar 22. The inclined surface 32b2 is inclined from the other end 32b11 toward the side surface 22b toward the other axial direction. Therefore, the angle between the inclined surface 32b2 and the side surface 22b is 90 degrees or more.

When the axial position of the ball row L is at the second position and the ball 6b located at one end of the ball row L in the axial direction abuts against the second inner end face 32b and the side face 22b of the pillar 22, the ball 6b abuts against the side face 22b of the pillar 22 and the inclined surface 32b2 of the second inner end face 32b.
At this time, since the angle between the inclined surface 32b2 and the side surface 22b is 90 degrees or more, it is possible to prevent the ball 6b from becoming caught between the inclined surface 32b2 and the side surface 22b.

FIG. 10 is a diagram showing the cage 8 of the ball screw device 1 according to a second modified example of the second embodiment.
This second modified example differs from the first modified example in that the multiple first inner end faces 32a and the multiple second inner end faces 32b are aligned along the lead angle direction of the helical track 14 (first helical groove 10).

In this modified example, as in the first modified example, the first inner end surface 32a of the annular portion 20 includes a circumferential surface 32a1 extending along the circumferential direction and an inclined surface 32a2, and the second inner end surface 32b of the connecting annular portion 30 includes a circumferential surface 32b1 extending along the circumferential direction and an inclined surface 32b2.

10, one end 32a11 (first end) is an end on one circumferential side of the circumferential surface 32a1 (first circumferential surface), and the other end 32a12 is an end on the other circumferential side of the circumferential surface 32a1.
When the pocket 32 is viewed from the front, the axial distance between one end 32a11 and the groove apex 10a is smaller than the axial distance between the other end 32a12 and the groove apex 10a.
In other words, one end 32a11 of the circumferential surface 32a1 is the end that is closer in axial direction to the groove apex 10a when the pocket 32 is viewed from the front, out of both ends of the circumferential surface 32a1.

The inclined surface 32a2 (first inclined surface) is provided so as to connect the first side surface 22b1 and the one end portion 32a11. The inclined surface 32a2 connects the end portion 22b11 of the first side surface 22b1 and the one end portion 32a11.
The inclined surface 32a2 is inclined so as to approach the second side surface 22b2 from the first side surface 22b1 toward the one end portion 32a11.
The first side surface 22b1 is the side surface 22b on the one end portion 32a11 side of the side surfaces 22b of the pair of pillars 22 that define the pocket 32. The second side surface 22b2 is the other side surface of the side surfaces 22b of the pair of pillars 22.
The angle between the inclined surface 32a2 and the first side surface 22b1 is equal to or greater than 90 degrees.

The inclined surface 32a2 can come into contact with the ball 6 in contact with the second side surface 22b2. When the ball 6 comes into contact with the inclined surface 32a2 and the second side surface 22b2, the circumferential surface 32a1 is not in contact with the ball 6.

In FIG. 10, when the pocket 32 is viewed from the front, the axial distance between the other end 32b11 and the groove apex 10a is smaller than the axial distance between one end 32b12 and the groove apex 10a.
The one end 32b12 is an end on one circumferential side of the circumferential surface 32b1. The other end 32b11 (second end) is an end on the other circumferential side of the circumferential surface 32b1 (second circumferential surface).
In other words, the other end 32b11 of the circumferential surface 32b1 is, of both ends of the circumferential surface 32b1, the end that is closer in axial direction to the groove apex 10a when the pocket 32 is viewed from the front.

The inclined surface 32b2 (second inclined surface) is provided so as to connect the second side surface 22b2 and the other end portion 32b11. The inclined surface 32b2 connects the end portion 22b21 of the second side surface 22b2 and the other end portion 32b11.
The inclined surface 32b2 is inclined so as to approach the first side surface 22b1 from the second side surface 22b2 toward the other end portion 32b11. The second side surface 22b2 is one of the side surfaces 22b of the pair of pillars 22 that define the pocket 32, the side surface 22b being on the other end portion 32b11 side.
The angle between the inclined surface 32b2 and the second side surface 22b2 is greater than or equal to 90 degrees.

The inclined surface 32b2 can come into contact with the ball 6 when the ball 6 is in contact with the first side surface 22b1. When the ball 6 comes into contact with the inclined surface 32b2 and the first side surface 22b1, the circumferential surface 32b1 is not in contact with the ball 6.

FIG. 11A is an enlarged view of the second inner end surface 32b of the annular connecting portion 30 in FIG.
11A shows the ball 6b when the ball row L is located at the second position. As described above, the ball 6b is the ball 6 located at one end of the ball row L in the axial direction.

11A, the axial distance W1 is the axial distance between the other end 32b11 and the edge 40 of the groove apex 10a. The axial distance W2 is the axial distance between the one end 32b12 and the edge 40 of the groove apex 10a.
11A, the first spiral groove 10 has a lead angle that slopes downward to the left on the page, so that the axial distance W1 is smaller than the axial distance W2.
The axial distances W1 and W2 are values based on the edge 40 of the groove apex 10a on the other axial side of the ball 6b. However, any part of the groove apex 10a other than the edge 40 can be used as the reference for the axial distances W1 and W2 as long as it is a part parallel to the lead angle direction of the helical track 14.

11A, the relative rotation of the screw shaft 2 and the nut 4 generates a force that moves the ball 6b toward the second side surface 22b2. Therefore, the ball 6b abuts against the inclined surface 32b2.
Because the ball 6b abuts against the inclined surface 32a2, further axial movement of the ball row L is restricted along the helical track 14. Therefore, even if the screw shaft 2 and the nut 4 attempt to move the ball 6b toward the second side surface 22b2, slippage occurs between the first helical groove 10 (helical track 14) and the ball 6b, and the ball 6b maintains a state in which its axial movement along the helical track 14 is restricted. In this case, the ball screw device 1 functions as a sliding screw.

Here, in this modified example, when the ball 6b moving along the spiral track 14 reaches the second inner end surface 32b, the ball 6b can be brought into contact with the inclined surface 32b2 without coming into contact with the circumferential surface 32b1.
Furthermore, since the inclined surface 32b2 is inclined so as to approach the first side surface 22b1 as it moves from the second side surface 22b2 toward the other end portion 32b11, the angle θ1 formed between the edge portion 40 of the groove top portion 10a, which is located on the other axial side of the ball 6b, and the second inner end surface 32b can be made relatively large.
As a result, when the ball 6b moving along the spiral track 14 reaches the second inner end face 32b and abuts against the inclined surface 32b2, it is possible to prevent the ball 6b from getting caught between the first spiral groove 10 (spiral track 14) and the inclined surface 32b2.

That is, as shown in (b) of Figure 11, when the second inner end surface 32b does not have an inclined surface 32b2, the angle θ2 formed between the edge 40 of the groove apex 10a and the second inner end surface 32b becomes approximately the same angle as the lead angle of the first spiral groove 10 (spiral track 14), which is an extremely acute angle.
As a result, a wedge shape is formed between the edge portion 40 and the second inner end surface 32b.
For this reason, in FIG. 11(b), when the ball 6b moving along the helical track 14 reaches the second inner end surface 32b, the ball 6b gets caught between the edge portion 40 and the second inner end surface 32b.
If the ball 6b becomes caught between the edge portion 40 and the second inner end surface 32b, the ball 6b cannot slide along the helical raceway 14, and the function as a sliding screw is impaired.

In this regard, in this modified example, since the second inner end surface 32b has the inclined surface 32b2, the angle θ1 can be made larger than the angle θ2 when the second inner end surface 32b does not have the inclined surface 32b2. As a result, it is possible to suppress the ball 6b from becoming caught, and to suppress the loss of function as a sliding screw.

The angle θ1 is determined by the angle α between the first side surface 22b1 and the inclined surface 32b2.
By setting the angle α to an appropriate angle, the inclined surface 32b2 is provided on the second inner end surface 32b, and the ball 6b can be prevented from getting caught.
The angle θ1 is determined by the lead angle of the helical raceway 14, the coefficient of friction between the ball 6 and the helical raceway 14, the coefficient of friction between the ball 6 and the cage 8, and the like.

For example, if the angle θ1 is 10 degrees or less, there is a high possibility that the ball 6b will become stuck. Therefore, it is preferable that the angle θ1 is 20 degrees or more. It is more preferable that the angle θ1 is 30 degrees or more.

In addition, it is preferable that the circumferential length of the circumferential surface 32b1 (the length between the one end 32b12 and the other end 32b11) is smaller than the diameter of the ball 6b. In this case, the inclined surface 32b2 can be reliably abutted against the ball 6b.

Although the second inner end surface 32b has been described with reference to FIG. 11, the first inner end surface 32a has a similar configuration.
In other words, since the first inner end face 32a has an inclined surface 32a2, the angle θ1 formed between the groove apex 10a, which is located on one axial side of the end ball 6a when the ball row L is in the first position, and the first inner end face 32a can be made relatively large.
As a result, when the ball 6a moving along the spiral track 14 reaches the first inner end face 32a and abuts against the inclined surface 32a2, it is possible to prevent the ball 6a from getting caught between the first spiral groove 10 (spiral track 14) and the first inner end face 32a (inclined surface 32a2).

FIG. 12 is a plan view showing the cage 8. As shown in FIG.
12, an imaginary line D2 on the outer circumferential surface 42 of the cage 8 passes through the other ends 32a12 of the first inner end faces 32a. Therefore, the first inner end faces 32a are aligned along the imaginary line D2.
The imaginary line D3 on the outer circumferential surface 42 passes through the first ends 32b12 of the second inner end surfaces 32b. Therefore, the second inner end surfaces 32b are aligned along the imaginary line D3.
The imaginary lines D2 and D3 are parallel to a line D1 that is parallel to the lead angle direction of the helical track 14 (first helical groove 10).
Therefore, the multiple first inner end faces 32a and the multiple second inner end faces 32b are aligned along the lead angle direction of the helical track 14 (first helical groove 10).
Moreover, the imaginary lines D2 and D3 are parallel to each other.
Therefore, the multiple pockets 32 are arranged so as to be offset along the lead angle direction.

FIG. 12 shows the case where the ball row L is located at the second position.
Therefore, the ball 6b at the end of the ball row L abuts against the inclined surface 32b2 of the second inner end surface 32b.
In this modified example, the multiple second inner end faces 32b are arranged along the lead angle direction of the helical track 14, so that when the ball 6b abuts against the inclined surface 32b2, the other balls 6 also abut against the inclined surface 32b2 at the same time as the ball 6b.

9, multiple second inner end faces 32b are arranged in the circumferential direction. In this case, when the ball 6b moving along the helical track 14 reaches the second inner end face 32b and abuts against the second inner end face 32b, the movement of the ball row L along the helical track 14 is restricted. In this case, the force from the screw shaft 2 and the nut 4 acts on the ball 6b in a concentrated manner, and the force from the screw shaft 2 and the nut 4 does not act largely on the other balls 6.

In contrast, in this modified example, all of the balls 6 in the ball row L can be brought into contact with the inclined surface 32b2 at the same time. As a result, the force acting from the screw shaft 2 and the nut 4 can be evenly distributed to the multiple balls 6, and the balls 6 can be more effectively prevented from getting stuck.

FIG. 12 illustrates an example in which the ball row L is located at the second position, but the same applies to the case in which the ball row L is located at the first position.
That is, since the multiple first inner end faces 32a are arranged along the lead angle direction of the helical track 14, when the ball 6a at the end of the ball row L abuts against the inclined surface 32a2, the other balls 6 also abut against the inclined surface 32a2 at the same timing as the ball 6a.
As a result, the force acting from the screw shaft 2 and the nut 4 can be evenly distributed to the plurality of balls 6, and the jamming of the balls 6 can be more effectively suppressed.

In the ball screw device 1 of this modified example, when the screw shaft 2 and the nut 4 rotate relative to each other and the cage 8 rotates, the ball train L moves within the helical track 14. In this way, the ball screw device 1 functions as a ball screw.
Here, when the ball screw device 1 is operated so as to repeatedly reciprocate the ball train L, the position of the ball train L may gradually shift.
For example, a case will be described in which a reference position and a specified position different from the reference position are set as the relative positions of the screw shaft 2 and the nut 4, and the screw shaft 2 and the nut 4 are caused to reciprocate between the reference position and the specified position.

It is assumed that when the screw shaft 2 and the nut 4 are in a reference position, the ball row L is located at a first position, and when they are in a predetermined position, the ball row L is located at an intermediate position between the first position and the second position.
In this case, when the screw shaft 2 and the nut 4 are rotated relative to each other and repeatedly moved back and forth between a reference position and a specified position, the ball row L may not return to the first position even though the screw shaft 2 and the nut 4 are in the reference position, or the ball row L may shift toward the intermediate position even though the screw shaft 2 and the nut 4 are in the specified position.

Such misalignment of the ball row L is caused by differences in the load, stroke amount, etc., between the forward and return paths of the ball row L as it moves within the helical track 14. Such differences between the forward and return paths are caused by the elastic hysteresis of the metal material that constitutes the screw shaft 2 and the nut 4, as well as the shape and lead angle of the helical track 14. In addition, the aforementioned jamming of the balls 6 is also a cause of the misalignment of the ball row L.

In contrast, in the present embodiment, as described above, when the ball row L reaches the first position or the second position, the cage 8 restricts the axial movement of the ball row L along the helical track 14 while suppressing the entrapment of the balls 6. For example, when the ball row L moves from the intermediate position toward the first position and reaches the first position, the balls 6 come into contact with the inclined surface 32a2 of the first inner end face 32a, restricting the movement of the ball row L. As a result, even if the position of the ball row L is misaligned, the movement of the ball row L is restricted by the inclined surface 32a2, and the position of the ball row L is corrected to the first position.
In this manner, in this embodiment, the retainer 8 limits the axial movement of the ball row L along the helical track 14, so that even if a positional deviation occurs in the ball row L, the positional deviation can be corrected.
Furthermore, since the ball 6 can be prevented from getting caught when the ball row L reaches the first position or the second position, the occurrence of positional deviation of the ball row L can also be prevented.

〔others〕
The embodiments disclosed herein are illustrative in all respects and are not restrictive.
For example, in each of the above embodiments, the case where either a rubber ring or a wave washer is used as the friction member 26 has been exemplified, but both may be used as the friction member 26 .
In addition, in each of the above embodiments, an example has been given of the retainer 8 having a connecting annular portion 30, but as long as the pillar 22 alone can restrict the axial movement of the ball 6b at one axial end of the ball row L located at the second position, the connecting annular portion 30 may be omitted.

The retainer 8 of the ball screw device 1 shown in each of the above embodiments includes an annular portion 20, a plurality of pillars 22, a connecting annular portion 30, and a plurality of pockets 32, and for example, the annular portion 20, the plurality of pillars 22, and the connecting annular portion 30 can be said to constitute a cylindrical main body. This cylindrical main body is arranged in the annular space K so as to be rotatable around the center line C of the screw shaft 2 and immovable in the axial direction relative to the nut 4. The pockets 32 are provided in this main body, extend along the axial direction, and intersect the helical track 14 at multiple points.

In addition, in the first and second modified examples of the second embodiment described above, an example was given in which the inclined surfaces 32a2 and 32b2 are provided on both the first inner end surface 32a and the second inner end surface 32b, but an inclined surface may be provided on at least one of the first inner end surface 32a and the second inner end surface 32b.

The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configurations described in the claims.

REFERENCE SIGNS LIST 1 ball screw device 2 screw shaft 4 nut 4a cylindrical inner peripheral surface 4b annular groove 4c end face 6, 6a, 6b ball 8 cage 9 retaining ring 9a inner surface 10 first spiral groove 10a groove top 12 second spiral groove 12a groove top 14 spiral track 20 annular portion 20a one end face 20b other end face 20c inner peripheral surface 20d outer peripheral surface 20d1 outer peripheral groove 22 pillar 22a tip 22b side surface 24 step surface 26 friction member 30 connecting annular portion 30a one end face 32 pocket 32a first inner end face 32a1 circumferential surface (first circumferential surface)
32a11 One end (first end) 32a12 Other end 32a2 Inclined surface (first inclined surface) 32b Second inner end surface 32b1 Circumferential surface (second circumferential surface)
32b11 Other end (second end) 32a12 One end 32b2 Inclined surface (second inclined surface) 36 Sleeve 36a One end surface 40 Edge portion 42 Outer circumferential surface C Center line D1 Line D2 Virtual line D3 Virtual line K Annular space L Row of balls

Claims (12)

a screw shaft having a first spiral groove on an outer periphery;
a nut having a second spiral groove on an inner periphery thereof, the second spiral groove forming a spiral track between the first spiral groove and the nut;
a ball train including a plurality of balls arranged on the spiral track;
a retainer disposed in an annular space between the screw shaft and the nut and retaining the plurality of balls;
The retainer is
An annular portion is disposed in the annular space so as to be rotatable about a center line of the screw shaft and to be immovable in the axial direction relative to the nut;
A plurality of columns extending from an end surface on one axial side of the annular portion to one axial side and intersecting the helical track at a plurality of points;
a plurality of pockets provided between pairs of circumferentially adjacent columns among the plurality of columns, the pockets holding the plurality of balls in a rollable manner;
a friction member provided between the nut and the annular portion and configured to provide resistance to rotation of the retainer relative to the nut . The ball screw device according to claim 1 , wherein the cage further includes a connecting annular portion connecting tips of the plurality of posts on one axial side. 3. The ball screw device according to claim 1, wherein a circumferential distance between the pair of posts is set to a distance sufficient to hold one of the balls. The ball screw device according to claim 3 , wherein each of the plurality of pockets holds one of the balls. 3. The ball screw device according to claim 1, wherein a circumferential interval between the pair of posts is set to a value sufficient to hold a predetermined number of the balls, the number being equal to or greater than two. The ball screw device according to claim 5 , wherein each of the plurality of pockets holds the predetermined number of the balls. The ball screw device according to claim 1 , wherein the friction member includes a rubber ring interposed between the nut and an outer circumferential surface of the annular portion. The nut has a cylindrical inner circumferential surface that accommodates the annular portion radially inward, and a step surface that extends radially inward from the cylindrical inner circumferential surface and connects the cylindrical inner circumferential surface and the second spiral groove,
The friction member includes a wave washer that presses the annular portion toward one side in the axial direction and brings the step surface facing the one end surface of the annular portion into contact with the one end surface.
The ball screw device according to any one of claims 1 to 7 . Each of the plurality of pockets is defined by side surfaces of the pair of posts and a first inner end surface of the annular portion;
The first inner end surface has a first circumferential surface along a circumferential direction and a first inclined surface,
the first end portion of the first circumferential surface is one of both circumferential ends of the first circumferential surface that is closer in axial direction to a groove apex of the first spiral groove when the pocket is viewed from the front,
the first inclined surface is provided to connect a first side surface of the pair of columns on the side of the first end portion and the first end portion, and is inclined so as to approach a second side surface of the pair of columns as it moves from the first side surface to the first end portion;
the first inclined surface is capable of contacting the ball when the ball is in contact with the second side surface,
9. The ball screw device according to claim 1, wherein the first circumferential surface is a surface that is not in contact with the ball when the ball contacts the first inclined surface and the second side surface. The ball screw device according to claim 9 , wherein the first inner end faces are aligned along a lead angle direction of the first spiral groove. the cage further includes a connecting annular portion connecting tips of the plurality of posts on one axial side,
each of the pockets is defined by side surfaces of the pair of posts, a first inner end surface of the annular portion, and a second inner end surface of the connecting annular portion;
The second inner end surface has a second circumferential surface along the circumferential direction and a second inclined surface,
the second end portion of the second circumferential surface is one of both circumferential ends of the second circumferential surface that is closer in axial direction to a groove apex of the first spiral groove when the pocket is viewed from the front,
the second inclined surface is provided to connect a second side surface of the pair of pillars on the second end side and the second end, and is inclined so as to approach a first side surface of the pair of pillars as it moves toward the second side surface along the circumferential direction,
the second inclined surface is capable of contacting the ball when the ball is in contact with the first side surface,
The ball screw device according to claim 1 , wherein the second circumferential surface is a surface that is not in contact with the ball when the ball contacts the second inclined surface and the first side surface. The ball screw device according to claim 11 , wherein the second inner end faces are aligned along a lead angle direction of the first spiral groove.