Ball screw device

Abstract

This ball screw device 1 comprises: a screw shaft 2 having a first spiral groove 10 on an outer circumference thereof; a nut 4 having, on an inner circumference thereof, a second spiral groove 12 which constitutes a spiral orbit 14 between the first spiral groove 10 and the second spiral groove; a ball array L including a plurality of balls 6 disposed on the spiral orbit 14; and a retainer 8 which is disposed in an annular space K between the screw shaft 2 and the nut 4 and retains the plurality of balls 6, wherein the retainer 8 comprises an annular section 20 disposed in the annular space K so as to be able to rotate about the center line C of the screw shaft 2 and so as to be unable to relatively move in the axial direction with respect to the nut 4, a plurality of columns 22 which extend to one side in the axial direction from one end surface 20a which is one side of the annular section 20 in the axial direction, and a plurality of pockets 32 which is provided between a pair of columns 22 adjacent to each other in the circumferential direction among the plurality of columns 22 and rollably retains the plurality of balls 6.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a ball screw device applicable to a braking device of an automobile. This ball screw device includes a screw shaft having a first spiral groove on the outer periphery, a nut having a second spiral groove on the inner periphery that forms a spiral orbit with the first spiral groove, and a ball row composed of a plurality of balls arranged in the spiral orbit. 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 a non-circulating type device in which a plurality of balls remain and roll in the spiral orbit of the nut, rather than a type in which a plurality of balls circulate when the nut moves.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above-described conventional non-circulating ball screw device includes a first coil spring provided in the spiral orbit and abutting against one end of the ball row, and a second coil spring provided in the spiral orbit and abutting against the other end of the ball row. In the above ball screw device, both ends of the ball row are held by both coil springs. When a rotational force is applied to the screw shaft and it rotates relative to the nut, the ball row moves within the spiral orbit within the expansion and contraction range of both coil springs, and the nut is moved along the axial direction. Therefore, the stroke of the screw shaft accompanying the movement of the ball row is determined according to the expansion and contraction amount of the coil spring. Here, there is a limit to the amount of expansion and contraction of the coil spring that can be arranged within the spiral orbit. Even if the axial length of the nut is extended further, it has been difficult to secure a large stroke accompanied by the movement of the ball row.

Means for Solving the Problems

[0005] The ball screw device according to an embodiment includes a screw shaft having a first spiral groove on the outer periphery, a nut having a second spiral groove on the inner periphery that forms a spiral orbit with the first spiral groove, a ball row including a plurality of balls arranged in the spiral orbit, and a cage arranged in the annular space between the screw shaft and the nut and holding the plurality of balls. The cage includes an annular portion rotatable around the center line of the screw shaft and arranged in the annular space so as to be axially non-relatively movable with respect to the nut, a plurality of columns extending axially from one end surface on one axial side of the annular portion and intersecting the spiral orbit at a plurality of locations, and a plurality of pockets provided between a pair of adjacent columns in the circumferential direction among the plurality of columns and rotatably holding the plurality of balls.

[0006] Also, the ball screw device according to an embodiment viewed from another perspective includes a screw shaft having a first spiral groove on the outer periphery, a nut having a second spiral groove on the inner periphery that forms a spiral orbit with the first spiral groove, a ball row including a plurality of balls arranged in the spiral orbit, and a cage arranged in the annular space between the screw shaft and the nut and holding the plurality of balls. The cage includes a cylindrical main body portion rotatable around the center line of the screw shaft and arranged in the annular space so as to be axially non-relatively movable with respect to the nut, and a plurality of pockets provided along the circumferential direction on the main body portion and holding the plurality of balls. The plurality of pockets extend axially and intersect the spiral orbit at a plurality of locations.

Advantages of the Invention

[0007] According to the present disclosure, it is possible to secure a larger stroke accompanied by the movement of the ball row.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

[0009] First, the contents of the embodiment will be listed and described. [Outline of the Embodiment] (1) The ball screw device according to the embodiment includes a screw shaft having a first spiral groove on the outer periphery, a nut having a second spiral groove on the inner periphery that forms a spiral orbit with the first spiral groove, a ball train including a plurality of balls arranged in the spiral orbit, and a cage that is arranged in the annular space between the screw shaft and the nut and holds the plurality of balls. The cage includes an annular portion that is rotatable around the center line of the screw shaft and is arranged in the annular space so as not to be axially relatively movable with respect to the nut, a plurality of columns that extend axially from one end surface on the axial one side of the annular portion and intersect the spiral orbit at a plurality of locations, and a plurality of pockets that are provided between a pair of adjacent columns in the circumferential direction among the plurality of columns and rotatably hold the plurality of balls.

[0010] According to the above configuration, since the pockets are provided between the columns that intersect the spiral orbit at a plurality of locations, the pockets extend along the axial direction and intersect the spiral orbit at a plurality of locations. Each ball is held at the location where the pocket and the spiral orbit intersect. When the ball train moves in the spiral orbit, the cage rotates according to the movement of the ball train. At this time, each ball moves axially along the pocket of the cage. Therefore, the ball train can move in the spiral orbit within the range where each ball can move axially along the pocket. Therefore, the stroke accompanied by the movement of the ball train can be determined by the axial length of the pocket, and a larger stroke accompanied by the movement of the ball train can be ensured compared to the case of using a coil spring as in the above conventional example.

[0011] (2) In the above ball screw device, it is preferable that the cage further includes a connecting annular portion that connects the tips on the axial one side of the plurality of columns. In this case, the rigidity of the cage can be increased by the connecting annular portion.

[0012] (3) In the above ball screw device, the circumferential interval between the pair of columns may be an interval capable of holding one of the balls. In this case, one ball is held at the intersection of the pocket and the spiral track. Therefore, when assembling the ball screw device, each ball may be arranged at the intersection of the pocket and the spiral track (the first spiral groove or the second spiral groove). Compared with the case where a plurality of balls are held at the intersection of the pocket and the spiral track, the assembly becomes easier.

[0013] (4) In the ball screw device, it is preferable that one of the balls is held in each of the plurality of pockets.

[0014] (5) In the ball screw device, the circumferential interval between the pair of columns may be set to an interval capable of holding a predetermined number of two or more of the balls. In this case, a plurality of balls are held at the intersection of the pocket and the spiral track. Therefore, the number of columns can be reduced as compared with the case where one ball is held at the intersection of the pocket and the spiral track.

[0015] (6) In the ball screw device, it is preferable that the predetermined number of the balls are held in each of the plurality of pockets.

[0016] (7) In the ball screw device, it is preferable to further include a friction member provided between the nut and the annular portion and applying resistance to the rotation of the retainer with respect to the nut. In this case, when the rotational torque acting between the screw shaft and the nut is low to such an extent that the retainer and the nut are integrally rotatably held by the resistance of the friction member, the ball screw device functions as a slipping screw. On the other hand, when the rotational torque acting between the screw shaft and the nut is large to such an extent that the retainer and the nut cannot be integrally rotatably held by the resistance of the friction member, the retainer rotates with respect to the screw shaft and the nut and functions as a ball screw. Therefore, it is possible to switch between the state of functioning as a sliding screw and the state of functioning as a ball screw according to the rotational torque acting between the screw shaft and the nut. Further, by adjusting the resistance of the friction member, it is possible to adjust the timing of switching between the state of functioning as a sliding screw and the state of functioning as a ball screw.

[0017] (8) In the ball screw device, the friction member may include a rubber ring interposed between the nut and the outer peripheral surface of the annular portion. In this case, a frictional force can be generated between the nut and the annular portion with a simple configuration, and resistance can be imparted to the rotation of the cage with respect to the nut.

[0018] (9) In the ball screw device, the nut has a cylindrical inner peripheral surface that radially inwardly accommodates the annular portion, and a stepped surface that extends radially inward from the cylindrical inner peripheral surface and connects the cylindrical inner peripheral surface and the second spiral groove. The friction member may include a wave washer that presses the annular portion axially on one side and brings the stepped surface facing the one end surface of the annular portion into contact with the one end surface. In this case, a frictional force can be generated between the nut and the annular portion by bringing the stepped surface into contact with and pressing the one end surface. Further, by selecting the dimensions and characteristics of the wave washer, the resistance applied between the nut and the cage can be easily adjusted.

[0019] (10) In the above ball screw device, each of the plurality of pockets is defined by the side surfaces of the pair of columns and the 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. The first end of the first circumferential surface is the end of the two circumferential ends of the first circumferential surface where the axial distance from the groove top of the first spiral groove when the pocket is viewed from the front is smaller. The first inclined surface is provided so as to connect the first side surface on the first end side of the side surfaces of the pair of columns and the first end. The first inclined surface is inclined so as to approach the second side surface of the side surfaces of the pair of columns as it goes from the first side surface to the first end. The first inclined surface can be in contact with the ball in a state of being in contact with the second side surface. When the ball is in contact with the first inclined surface and the second side surface, it is preferable that the first circumferential surface is a surface that is not in contact with the ball. In the above configuration, when the ball moving along the spiral track reaches the first inner end surface, the ball can be brought into contact with the first inclined surface without bringing the ball into contact with the first circumferential surface. Here, since the first inclined surface is inclined so as to approach the second side surface as it goes from the first side surface to the first end, the angle formed by the groove top located on one axial side with respect to the ball and the first inclined surface can be made relatively large. Thereby, it is possible to suppress the ball from getting caught between the spiral track and the first inclined surface. Therefore, when the ball moving along the spiral track reaches the first inner end surface and abuts against the first inclined surface, it is possible to suppress the ball from getting caught between the spiral track and the first inclined surface.

[0020] (11) When a plurality of the first inner end surfaces are arranged along the circumferential direction, when the ball located at the end of the ball row moves axially and reaches the first inner end surface and abuts against the first end surface, a force from the screw shaft and the nut acts on this one ball, and a large force from the screw shaft and the nut does not act on the other balls. For this reason, it is preferable that the plurality of the first inner end surfaces are arranged along the lead angle direction of the first spiral groove. In this case, a plurality of balls can be made to contact a plurality of first inner end faces at the same timing. As a result, the force acting from the screw shaft and the nut can be evenly distributed among the plurality of balls, and the meshing of the balls can be more effectively suppressed.

[0021] (12) In the ball screw device, the cage further includes a connecting annular portion that connects the tips of the plurality of columns on one axial side, and each of the pockets is defined by the side surfaces of the pair of columns, the first inner end face of the annular portion, and the second inner end face of the connecting annular portion. The second inner end face has a second circumferential surface along the circumferential direction and a second inclined surface. The second end of the second circumferential surface is the end with a smaller axial distance from the groove top of the first spiral groove when the pocket is viewed from the front among the circumferential both ends of the second circumferential surface. The second inclined surface is provided so as to connect the second side surface on the second end side of the side surfaces of the pair of columns and the second end, and is inclined so as to approach the first side surface of the side surfaces of the pair of columns as it goes from the second side surface to the second end. The second inclined surface can be in contact with the ball in a state of being in contact with the first side surface, and when the ball is in contact with the second inclined surface and the first side surface, it is preferable that the second circumferential surface is a surface that is not in contact with the ball. In the above configuration, when the ball moving along the spiral orbit reaches the second inner end face, the ball can be brought into contact with the second inclined surface without contacting the second circumferential surface. Here, since the second inclined surface is inclined so as to approach the first side surface as it goes from the second side surface to the second end, the angle formed by the groove top located on the other axial side with respect to the ball and the second inclined surface can be made relatively large. Thereby, it is possible to suppress the ball from getting caught between the spiral orbit and the second inclined surface. Therefore, when the ball moving along the spiral orbit reaches the second inner end face and abuts against the second inclined surface, it is possible to suppress the ball from getting caught between the spiral orbit and the second inclined surface.

[0022] (13) In the above ball screw device, it is preferable that the plurality of second inner end faces are arranged 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 second inner end faces at the same timing. As a result, the forces acting from the screw shaft and the nut can be evenly distributed among the plurality of balls, and the engagement of the balls can be effectively suppressed.

[0023] (14) A ball screw device according to an embodiment viewed from another aspect 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 orbit with the first spiral groove, a ball row including a plurality of balls arranged in the spiral orbit, and a cage that is arranged in an annular space between the screw shaft and the nut and holds the plurality of balls. The cage includes a cylindrical main body portion that is rotatable around the center line of the screw shaft and is arranged in the annular space so as to be axially non-movable relative to the nut, and a plurality of pockets that are provided in the main body portion along the circumferential direction and hold the plurality of balls. The plurality of pockets extend along the axial direction and intersect the spiral orbit at a plurality of locations.

[0024] [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 the first embodiment, and FIG. 2 is a cross-sectional view of the ball screw device. Note that FIG. 2 is a cross-sectional view along a plane including the center line of the ball screw device. This ball screw device 1 is used in a brake device of a vehicle such as an automobile or a power transmission device including a multi-plate clutch. The ball screw device 1 includes a screw shaft 2, a nut 4 provided on the outer peripheral side of the screw shaft 2, a plurality of balls 6, and a cage 8 that holds the plurality of balls 6. In the present embodiment, a direction parallel to the center line C of the screw shaft 2 is defined as the axial direction, a direction orthogonal to the center line C is defined as the radial direction, and a direction along a circle centered on the center line C is defined as the circumferential direction. In FIGS. 1 and 2, in the axial direction, the side 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.

[0025] The screw shaft 2 is inserted through the nut 4 and has a first helical 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 helical groove 12 on its inner periphery. Also, a cylindrical inner peripheral surface 4a is provided at the end on the other axial side of the inner periphery of the nut 4. The first helical groove 10 of the screw shaft 2 and the second helical groove 12 of the nut 4 constitute a helical track 14 in which a plurality of balls 6 are arranged. Also, the outer diameter dimension of the groove top 10a of the first helical groove 10 is smaller than the inner diameter dimension of the groove top 12a of the second helical groove 12. Therefore, an annular space K is provided between the screw shaft 2 and the nut 4.

[0026] The cage 8 is arranged in the annular space K between the screw shaft 2 and the nut 4. The cage 8 includes an annular portion 20 and a plurality of columns 22. The annular portion 20 is accommodated radially inward of the cylindrical inner peripheral surface 4a. The annular portion 20 is arranged between the cylindrical inner peripheral surface 4a and the screw shaft 2. An annular groove 4b into which the 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 the stepped surface 24 of the nut 4. The stepped surface 24 is a surface that extends radially inward from the cylindrical inner peripheral surface 4a and connects between the cylindrical inner peripheral surface 4a and the second helical groove 12. Also, the other end face 20b on the other axial side of the annular portion 20 faces the inner surface 9a of the retaining ring 9.

[0027] Also, a slight clearance is provided between the inner peripheral surface 20c of the annular portion 20 and the groove top 10a of the first helical groove 10 of the screw shaft 2. Also, 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 in the annular space K so as to be rotatable about the center line C and non-axially movable relative to the nut 4.

[0028] An outer peripheral groove 20d1 is provided on the outer peripheral surface 20d of the annular portion 20. A friction member 26 is provided in the outer peripheral groove 20d1. In the present embodiment, the friction member 26 is a rubber ring. The friction member 26 is fitted into the outer peripheral 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. That is, the friction member 26 is provided between the nut 4 and the annular portion 20. The friction member 26 imparts resistance to the rotation of the cage 8 relative to the nut 4 by the frictional force generated by contact with the cylindrical inner peripheral surface 4a and the outer peripheral groove 20d1. Therefore, if the force attempting to cause relative rotation acting between the nut 4 and the cage 8 is smaller than the resistance by the friction member 26, the cage 8 rotates integrally with the nut 4, and if the force attempting to cause relative rotation is larger than the resistance by the friction member 26, the cage 8 is relatively rotatable with respect to the nut 4.

[0029] The plurality of columns 22 of the cage 8 extend axially from one end surface 20a of the annular portion 20 to one side in the axial direction. The cage 8 of the present embodiment includes three columns 22. The three columns 22 are arranged at equal intervals in the circumferential direction.

[0030] FIG. 3(a) is a perspective view showing the cage 8 disposed on the outer peripheral side of the screw shaft 2, and FIG. 3(b) is a perspective view showing the cage 8. As shown in FIGS. 2 and 3, the three columns 22 extend axially so as to cross between the groove top 10a of the first spiral groove 10 of the screw shaft 2 and the groove top 12a of the second spiral groove 12 of the nut 4, and intersect the spiral track 14 at a plurality of locations.

[0031] Further, the cage 8 includes a connecting annular portion 30 that connects the tip 22a on one axial side of the column 22. 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 substantially coincides with the end face 4c on one axial side of the nut 4. Thus, the connecting annular portion 30 is provided at the end on one axial side of the nut 4.

[0032] The cage 8 further includes a plurality of pockets 32 that rotatably hold a plurality of balls 6. The pockets 32 are provided between a pair of columns 22 adjacent to each other in the circumferential direction 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 columns 22 adjacent to each other in the circumferential direction, the annular portion 20, and the connecting annular portion 30. Therefore, the pocket 32 extends along the axial direction and intersects the spiral track 14 at a plurality of locations.

[0033] The pocket 32 is defined by side faces 22b of a pair of columns 22 adjacent to each other in the circumferential direction, a first inner end face 32a of the annular portion 20, and a second inner end face 32b of the connecting annular portion 30. The first inner end face 32a is an end face on one axial side of the annular portion 20. The second inner end face 32b is an end face on the other axial side of the connecting annular portion 30. The pair of side faces 22b are along the axial direction. The first inner end face 32a and the second inner end face 32b are along the circumferential direction. The circumferential interval between a pair of columns 22 adjacent to each other in the circumferential direction is set to an interval capable of holding two balls 6 as shown in FIGS. 4(a) and 4(b).

[0034] The plurality of balls 6 are arranged in the spiral track 14 to form a ball row L. In the present embodiment, the ball row L includes six balls 6. As described above, the circumferential interval between a pair of adjacent columns 22 in the circumferential direction is an interval capable of holding two balls 6. Therefore, three columns 22 are interposed in the ball row L. The three columns 22 are interposed so as to divide the balls 6 in the ball row L arranged in the column longitudinal direction into three. That is, each of the three pockets 32 holds two balls 6 arranged in the column longitudinal direction.

[0035] When the screw shaft 2 rotates relative to the nut 4 and further the cage 8 rotates around the center line C, the ball row L moves within the spiral orbit 14. As the ball row L moves within the spiral orbit 14, the ball screw device 1 functions as a ball screw. Here, since the balls 6 are held in the pockets 32, the axial movement range of the ball row L is restricted by the cage 8.

[0036] For example, as shown in Fig. 4(a), when the ball 6a located at the axially other end in the ball row L among the six balls 6 abuts against the first inner end face 32a of the annular portion 20 and the side face 22b of the column 22, the axial position of the ball row L in the cage 8 becomes the position closest to the axially other side (the first position). In addition, in Figs. 4(a) and 4(b), the nut 4 is omitted for easy understanding.

[0037] When the screw shaft 2 is rotated relative to the nut 4 and the ball row L in the first position is moved axially toward one side, as shown in Fig. 4(b), among the six balls 6, the ball 6b located at the axially one end in the ball row L abuts against the second inner end face 32b of the connecting annular portion 30 and the side face 22b of the column 22. The ball 6b is restricted from further moving axially along the spiral orbit 14 by the connecting annular portion 30 and the column 22. Therefore, as shown in Fig. 4(b), when the ball 6b abuts against the connecting annular portion 30 and the column 22, the axial position of the ball row L in the cage 8 becomes the position closest to the axially one side (the second position) within the cage 8. In this way, the axial movement range of the ball row L is restricted by the cage 8.

[0038] The ball screw device 1 functions as a ball screw by relatively rotating the screw shaft 2 with respect to the nut 4 while the ball row L moves from the first position to the second position. After the ball row L reaches from the first position to the second position, if the screw shaft 2 is further relatively rotated with respect to the nut 4, the axial movement of the ball row L is restricted, so the ball screw device 1 does not function as a ball screw but functions as a plain 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. After the ball row L reaches from the second position to the first position, if the screw shaft 2 is further relatively rotated with respect to the nut 4, in this case too, the axial movement of the ball row L is restricted, so the ball screw device 1 does not function as a ball screw but functions as a plain screw.

[0039] Thus, the ball screw device 1 functions as a ball screw by relatively rotating the screw shaft 2 with respect to the nut 4 while the ball row L moves between the first position and the second position in the cage 8. On the other hand, when the ball row L does not move, the ball screw device 1 functions as a plain screw.

[0040] The ball screw device 1 configured as described above is used for the purpose of applying a rotational force to the screw shaft 2, relatively rotating the screw shaft 2 with respect to the nut 4, moving the nut axially along, and converting the rotational motion applied to the screw shaft 2 into a linear motion. When the screw shaft 2 relatively rotates with respect to the nut 4, as described above, if the ball row L moves within the spiral orbit 14, the ball screw device 1 functions as a ball screw, decelerates the rotational force transmitted to the screw shaft 2, and then moves the nut 4 axially. That is, during the stroke of the ball screw device 1, while the ball row 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 row L does not move within the spiral orbit 14, the ball screw device 1 functions as a plain screw and moves the nut 4 axially according to the rotation applied to the screw shaft 2.

[0041] According to the above configuration, since the pocket 32 is provided between the columns 22 that intersect the spiral orbit 14 at a plurality of locations, the pocket 32 extends along the axial direction and intersects the spiral orbit 14 at a plurality of locations. Each ball 6 is held at a location where the pocket 32 and the spiral orbit 14 intersect. When the ball row L moves within the spiral orbit 14, the cage 8 rotates according to the movement of the ball row L. At this time, each ball 6 moves axially along the pocket 32 of the cage 8. Therefore, the ball row L can move within the spiral orbit 14 within a range where each ball 6 can move axially 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 as compared with the case of using a coil spring as in the above conventional example.

[0042] Also, in the present embodiment, since the friction member 26 is provided between the nut 4 and the annular portion 20 of the cage 8, the timing of switching between the state in which the ball screw device 1 functions as a sliding screw and the state in which it functions as a ball screw can be adjusted. For example, when trying to move the nut 4 to the other axial side from the state shown in FIG. 4(a) and relatively rotating the screw shaft 2 and the nut 4, if the rotational torque acting between the screw shaft 2 and the nut 4 is relatively small, the friction member 26 integrally rotatably holds the cage 8 with respect to the nut 4 by the resistance generated by contacting the nut 4 and the annular portion 20. When the cage 8 does not rotate relative to the nut 4, the ball row L does not move within the spiral orbit 14, so the ball screw device 1 functions as a sliding screw.

[0043] On the other hand, when the rotational torque acting between the screw shaft 2 and the nut 4 is relatively large and the force trying to cause relative rotation between the nut 4 and the cage 8 becomes larger than the resistance by the friction member 26, relative rotation of the cage 8 with respect to the nut 4 is allowed. In this case, since the ball row L can move within the spiral orbit 14, the ball screw device 1 functions as a ball screw.

[0044] Thus, in the present embodiment, since the friction member 26 is provided between the nut 4 and the annular portion 20 of the cage 8, the switching between the state of functioning as a sliding screw and the state of functioning as a ball screw can be performed according to the rotational torque acting between the screw shaft 2 and the nut 4. Also, by adjusting the resistance of the friction member 26, the timing of switching between the state of functioning as a sliding screw and the state of functioning as a ball screw can be adjusted. In the present embodiment, since the friction member 26 is constituted by a rubber ring, a frictional force can be generated between the nut 4 and the annular portion 20 with a simple configuration, and resistance can be imparted to the rotation of the cage 8 with respect to the nut 4.

[0045] Also, in the present embodiment, since the cage 8 is provided with the connecting annular portion 30 at the tip 22a of the column 22, the rigidity of the cage 8 can be enhanced. Also, by providing the connecting annular portion 30, it is possible to more strongly restrict the further movement of the ball 6b on the one axial side of the ball row L in the axial direction when the axial position of the ball row L is at the first position.

[0046] Also, in the present embodiment, since the circumferential interval between a pair of adjacent columns 22 in the circumferential direction is set to an interval capable of holding two balls 6, two balls 6 are held at the location where the pocket 32 and the spiral orbit 14 intersect. Therefore, the number of columns 22 can be reduced as compared with the case where one ball 6 is held at the location where the pocket 32 and the spiral orbit 14 intersect.

[0047] 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-described embodiment, the case where the friction member 26 is constituted by an O-ring has been shown. However, in this modification, the case where the friction member 26 is constituted by a wave washer is shown. The friction member 26 of the present 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) in one axial direction. Thereby, the friction member 26 brings the stepped surface 24 of the nut 4 into contact with one end surface 20a of the annular portion 20, and imparts resistance to the rotation of the retainer 8 with respect to the nut 4 by the frictional force between the stepped surface 24 and the one end surface 20a.

[0048] In this modification, by bringing the stepped surface 24 into contact with and pressing the one end surface 20a, a frictional force can be generated between the nut 4 and the annular portion 20. Further, by selecting the dimensions and characteristics of the friction member 26 which is a wave washer, the frictional force between the stepped 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 of functioning as a slip screw and the state of functioning as a ball screw can be easily adjusted.

[0049] 〔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. In addition, in FIGS. 6 and 7, the balls 6 are omitted and shown.

[0050] Similar to the first embodiment, the ball screw device 1 of the present embodiment also includes a screw shaft 2 having a first spiral groove 10 on the outer periphery, a nut 4 having a second spiral groove 12 on the inner periphery that forms a spiral track 14 with the first spiral groove 10, a ball row L including a plurality of balls 6 arranged in the spiral track 14, and a retainer 8 that is arranged in the annular space K between the screw shaft 2 and the nut 4 and holds the plurality of balls 6. Further, the cage 8 includes an annular portion 20 that is rotatable about the center line C of the screw shaft 2 and is disposed in the annular space K so as to be axially non-movable relative to the nut 4, a plurality of columns 22 that extend axially from one end surface 20a on one axial side of the annular portion 20 and intersect the spiral orbit 14 at a plurality of locations, a connecting annular portion 30 that connects the tips of the plurality of columns 22, and a plurality of pockets 32 that are provided between a pair of adjacent columns in the circumferential direction among the plurality of columns 22 and rotatably hold the plurality of balls 6.

[0051] This embodiment is different from the first embodiment in that it has a sleeve 36 disposed on the other axial side of the cage 8, and the circumferential interval between a pair of adjacent columns 22 in the circumferential direction is set to an interval capable of holding one ball 6.

[0052] The sleeve 36 is disposed on the outer peripheral side of the screw shaft 2 and is fitted and fixed to the cylindrical inner peripheral surface 4a of the nut 4. One end surface 36a on one axial side of the sleeve 36 abuts against the other end surface 20b of the annular portion 20. Thereby, the annular portion 20 is made axially non-movable relative to the nut 4 by the stepped surface 24 of the nut 4 and the one end surface 36a of the sleeve 36.

[0053] FIG. 8 is a view showing the cage 8 disposed on the outer peripheral side of the screw shaft 2. The cage 8 of this embodiment has 14 columns 22. Therefore, the cage 8 has 14 pockets 32. The ball row L of this embodiment includes, for example, 14 balls 6. Therefore, each pocket 32 holds one ball 6. In this case, one ball 6 is held at the location where the pocket 32 and the spiral orbit 14 intersect. Therefore, when assembling the ball screw device 1, each ball 6 may be disposed at the location where the pocket 32 and the spiral orbit 14 (the first spiral groove 10 or the second spiral groove 12) intersect, and the assembly becomes easier compared to the case where a plurality of balls 6 are held at the location where the pocket 32 and the spiral orbit 14 intersect.

[0054] FIG. 9 is a view showing a cage 8 of a ball screw device 1 according to a first modification of the second embodiment. In this first modification, the first inner end surface 32a of the annular portion 20 includes a circumferential surface 32a1 along the circumferential direction and an inclined surface 32a2 inclined with respect to the circumferential surface 32a1, and the second inner end surface 32b of the connecting annular portion 30 includes a circumferential surface 32b1 along the circumferential direction and an inclined surface 32b2 inclined with respect to the circumferential surface 32b1. This is different from the second embodiment in that it is configured to include.

[0055] As shown in FIG. 9, of both circumferential ends of the circumferential surface 32a1, an inclined surface 32a2 is provided on one end portion 32a11 side where the axial distance from the groove top 10a is small when the pocket 32 is viewed from the front. One end portion 32a11 is an end portion on one circumferential side of both circumferential ends of the circumferential surface 32a1. The inclined surface 32a2 is provided so as to connect one end portion 32a11 of the circumferential surface 32a1 and the side surface 22b of the column 22. The inclined surface 32a2 is inclined toward one axial side from the one end portion 32a11 toward the side surface 22b of the column 22. Therefore, the angle formed by the inclined surface 32a2 and the side surface 22b is 90 degrees or more.

[0056] When the axial position of the ball row L is at the first position and the ball 6a located at the other axial end in the ball row L abuts against the first inner end surface 32a and the side surface 22b of the column 22, the ball 6a abuts against the side surface 22b of the column 22 and the inclined surface 32a2 of the first inner end surface 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 being caught between the inclined surface 32a2 and the side surface 22b.

[0057] Similarly, of both circumferential ends of the circumferential surface 32b1 of the second inner end surface 32b, an inclined surface 32b2 is provided on the other end portion 32b11 side where the axial distance from the groove top 10a is small when the pocket 32 is viewed from the front. The other end portion 32b11 is an end portion on the other circumferential side of both circumferential ends of the circumferential surface 32b1. The inclined surface 32b2 is provided so as to connect the other end portion 32b11 of the circumferential direction surface 32b1 and the side surface 22b of the column 22. The inclined surface 32b2 is inclined toward the other axial direction side from the other end portion 32b11 toward the side surface 22b side. Therefore, the angle formed by the inclined surface 32b2 and the side surface 22b is 90 degrees or more.

[0058] When the axial position of the ball row L is located at the second position and the ball 6b located at one axial end of the ball row L abuts against the second inner end surface 32b and the side surface 22b of the column 22, the ball 6b abuts against the side surface 22b of the column 22 and the inclined surface 32b2 of the second inner end surface 32b. At this time, since the angle formed by the inclined surface 32b2 and the side surface 22b is 90 degrees or more, it is possible to suppress the ball 6b from biting between the inclined surface 32b2 and the side surface 22b.

[0059] FIG. 10 is a view showing the cage 8 of the ball screw device 1 according to the second modification of the second embodiment. This second modification is different from the first modification in that the plurality of first inner end surfaces 32a and the plurality of second inner end surfaces 32b are arranged along the lead angle direction of the spiral track 14 (first spiral groove 10).

[0060] Also in this modification, similar to the first modification, the first inner end surface 32a of the annular portion 20 is configured to include a circumferential direction surface 32a1 along the circumferential direction and an inclined surface 32a2, and the second inner end surface 32b of the connecting annular portion 30 is configured to include a circumferential direction surface 32b1 along the circumferential direction and an inclined surface 32b2.

[0061] In FIG. 10, one end portion 32a11 (first end portion) is an end portion on one circumferential direction side of the circumferential direction surface 32a1 (first circumferential direction surface). The other end portion 32a12 is an end portion on the other circumferential direction side of the circumferential direction surface 32a1. The axial distance between the one end portion 32a11 and the groove top portion 10a when the pocket 32 is viewed from the front is smaller than the axial distance between the other end portion 32a12 and the groove top portion 10a. That is, one end portion 32a11 of the circumferential surface 32a1 is the end portion with a smaller axial distance from the groove top 10a when the pocket 32 is viewed from the front among the two end portions of the circumferential surface 32a1.

[0062] The inclined surface 32a2 (the first inclined surface) is provided so as to connect the first side surface 22b1 and one end portion 32a11. The inclined surface 32a2 connects the end portion 22b11 of the first side surface 22b1 and one end portion 32a11. Further, the inclined surface 32a2 is inclined so as to approach the second side surface 22b2 as it goes from the first side surface 22b1 toward one end portion 32a11. The first side surface 22b1 is the side surface 22b on the one end portion 32a11 side among the side surfaces 22b of the pair of columns 22 that define the pocket 32. The second side surface 22b2 is the other side surface among the side surfaces 22b of the pair of columns 22. The angle formed by the inclined surface 32a2 and the first side surface 22b1 is 90 degrees or more.

[0063] The inclined surface 32a2 can be in contact with the ball 6 in a state of being in contact with the second side surface 22b2. Also, when the ball 6 is in contact with the inclined surface 32a2 and the second side surface 22b2, the circumferential surface 32a1 is a surface that is not in contact with the ball 6.

[0064] In FIG. 10, the axial distance between the other end portion 32b11 and the groove top 10a when the pocket 32 is viewed from the front is smaller than the axial distance between one end portion 32b12 and the groove top 10a. One end portion 32b12 is the end portion on one circumferential side of the circumferential surface 32b1. The other end portion 32b11 (the second end portion) is the end portion on the other circumferential side of the circumferential surface 32b1 (the second circumferential surface). That is, the other end portion 32b11 of the circumferential surface 32b1 is the end portion with a smaller axial distance from the groove top 10a when the pocket 32 is viewed from the front among the two end portions of the circumferential surface 32b1.

[0065] The inclined surface 32b2 (the 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. Further, the inclined surface 32b2 is inclined so as to approach the first side surface 22b1 as it extends from the second side surface 22b2 toward the other end portion 32b11. The second side surface 22b2 is the side surface on the other end portion 32b11 side among the side surfaces 22b of the pair of columns 22 that define the pocket 32. The angle formed between the inclined surface 32b2 and the second side surface 22b2 is 90 degrees or more.

[0066] The inclined surface 32b2 is capable of contacting the ball 6 in a state where the ball 6 is in contact with the first side surface 22b1. Further, when the ball 6 contacts the inclined surface 32b2 and the first side surface 22b1, the circumferential direction surface 32b1 is a surface that does not contact the ball 6.

[0067] (a) in FIG. 11 is an enlarged view of the second inner end surface 32b of the connecting annular portion 30 in FIG. 10. In (a) in FIG. 11, the ball 6b is shown in a case where the ball row L is located at the second position. The ball 6b is the ball 6 located at one axial end of the ball row L as described above.

[0068] In (a) in FIG. 11, the axial distance W1 is the axial distance between the other end portion 32b11 and the edge 40 of the groove top 10a. The axial distance W2 is the axial distance between one end portion 32b12 and the edge 40 of the groove top 10a. As shown in (a) in FIG. 11, the first spiral groove 10 has a lead angle that slopes downward to the lower left in the plane of the paper. Therefore, the axial distance W1 is smaller than the axial distance W2. Note that the above axial distances W1 and W2 are values based on the edge 40 of the groove top 10a on the other axial side of the ball 6b. However, as long as it is a portion parallel to the lead angle direction of the spiral track 14, a location on the groove top 10a other than the edge 40 can be used as the reference for the axial distances W1 and W2.

[0069] In (a) in FIG. 11, it is assumed that 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. For this reason, the ball 6b is in contact with the inclined surface 32b2. Since the ball 6b is in contact with the inclined surface 32a2, the axial movement of the ball row L along the spiral track 14 is restricted. Therefore, even if the screw shaft 2 and the nut 4 attempt to move the ball 6b toward the second side surface 22b2, slipping occurs between the first spiral groove 10 (spiral track 14) and the ball 6b, and the ball 6b remains in a state where its axial movement along the spiral track 14 is restricted. In this case, the ball screw device 1 functions as a slipping screw.

[0070] 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 contacting the circumferential surface 32b1. Further, since the inclined surface 32b2 is inclined so as to approach the first side surface 22b1 as it goes from the second side surface 22b2 toward the other end portion 32b11, the angle θ1 formed by the edge portion 40 of the groove crest 10a located on the other axial side with respect to 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 surface 32b and abuts against the inclined surface 32b2, it is possible to suppress the ball 6b from biting between the first spiral groove 10 (spiral track 14) and the inclined surface 32b2.

[0071] That is, as shown in (b) of FIG. 11, when the second inner end surface 32b does not have the inclined surface 32b2, the angle θ2 formed by the edge portion 40 of the groove crest 10a and the second inner end surface 32b is almost the same as the lead angle of the first spiral groove 10 (spiral track 14), and becomes an extremely acute angle. As a result, a wedge shape is formed between the edge portion 40 and the second inner end surface 32b. Therefore, in (b) of FIG. 11, when the ball 6b moving along the spiral track 14 reaches the second inner end surface 32b, the ball 6b bites between the edge portion 40 and the second inner end surface 32b. When the ball 6b bites between the edge portion 40 and the second inner end surface 32b, the ball 6b cannot slide with respect to the spiral track 14, and the function as a slipping screw is impaired.

[0072] In this regard, in this modified example, since the second inner end face 32b has the inclined face 32b2, the angle θ1 can be made larger as compared with the angle θ2 in the case where the second inner end face 32b does not have the inclined face 32b2. As a result, the biting-in of the ball 6b can be suppressed, and it is possible to suppress the loss of the function as a sliding screw.

[0073] The angle θ1 is determined by the angle α formed by the first side face 22b1 and the inclined face 32b2. By setting the angle α to an appropriate angle, the inclined face 32b2 is provided on the second inner end face 32b, and the biting-in of the ball 6b can be suppressed. The angle θ1 is determined by the lead angle of the spiral orbit 14, the coefficient of friction between the ball 6 and the spiral orbit 14, the coefficient of friction between the ball 6 and the cage 8, and the like.

[0074] For example, when the angle θ1 is 10 degrees or less, there is a high possibility that the ball 6b will bite in. Therefore, the angle θ1 is preferably 20 degrees or more. More preferably, the angle θ1 is 30 degrees or more.

[0075] Also, the circumferential length of the circumferential face 32b1 (the length between one end portion 32b12 and the other end portion 32b11) is preferably smaller than the diameter of the ball 6b. In this case, the inclined face 32b2 can be surely brought into contact with the ball 6b.

[0076] In FIG. 11, the second inner end face 32b has been described, but the first inner end face 32a has the same configuration. That is, since the first inner end face 32a has the inclined face 32a2, the angle θ1 formed by the groove top 10a located on one axial side with respect to 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 orbit 14 reaches the first inner end face 32a and abuts against the inclined face 32a2, it is possible to suppress the ball 6a from biting in between the first spiral groove 10 (spiral orbit 14) and the first inner end face 32a (inclined face 32a2).

[0077] FIG. 12 is a view showing the cage 8 developed in a plane. In FIG. 12, the virtual line D2 on the outer peripheral surface 42 of the cage 8 passes through the plurality of other end portions 32a12 of the plurality of first inner end surfaces 32a. Therefore, the plurality of first inner end surfaces 32a are arranged along the virtual line D2. The virtual line D3 on the outer peripheral surface 42 passes through the plurality of one end portions 32b12 of the plurality of second inner end surfaces 32b. Therefore, the plurality of second inner end surfaces 32b are arranged along the virtual line D3. The virtual line D2 and the virtual line D3 are parallel to the line D1 parallel to the lead angle direction of the spiral track 14 (first spiral groove 10). Therefore, the plurality of first inner end surfaces 32a and the plurality of second inner end surfaces 32b are arranged along the lead angle direction of the spiral track 14 (first spiral groove 10). Also, the virtual lines D2 and D3 are parallel to each other. Therefore, the plurality of pockets 32 are arranged so as to be offset along the lead angle direction.

[0078] FIG. 12 shows a case where the ball row L is in the second position. Therefore, the ball 6b at the end of the ball row L is in contact with the inclined surface 32b2 of the second inner end surface 32b. In this modified example, since the plurality of second inner end surfaces 32b are arranged along the lead angle direction of the spiral track 14, when the ball 6b comes into contact with the inclined surface 32b2, the other balls 6 also come into contact with the inclined surface 32b2 at the same timing as the ball 6b.

[0079] Here, in the first modified example shown in FIG. 9, the plurality of second inner end surfaces 32b are arranged along the circumferential direction. In this case, when the ball 6b moving along the spiral track 14 reaches the second inner end surface 32b and comes into contact with the second inner end surface 32b, the movement of the ball row L along the spiral track 14 is restricted. In this case, the force from the screw shaft 2 and the nut 4 acts concentratedly on the ball 6b, and the force from the screw shaft 2 and the nut 4 does not act greatly on the other balls 6.

[0080] In contrast, in this modified example, all the balls 6 included in the ball row L can be brought into contact with the inclined surface 32b2 at the same timing. As a result, the forces acting from the screw shaft 2 and the nut 4 can be evenly distributed among the plurality of balls 6, and the meshing of the balls 6 can be more effectively suppressed.

[0081] In FIG. 12, the case where the ball row L is located at the second position is illustrated, but the same applies when the ball row L is located at the first position. That is, since the plurality of first inner end faces 32a are arranged along the lead angle direction of the spiral orbit 14, when the ball 6a at the end of the ball row L comes into contact with the inclined surface 32a2, the other balls 6 also come into contact with the inclined surface 32a2 at the same timing as the ball 6a. As a result, the forces acting from the screw shaft 2 and the nut 4 can be evenly distributed among the plurality of balls 6, and the meshing of the balls 6 can be more effectively suppressed.

[0082] 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 further the retainer 8 rotates, the ball row L moves within the spiral orbit 14. Thereby, the ball screw device 1 functions as a ball screw. Here, when the ball screw device 1 is operated so that the ball row L reciprocates repeatedly, the position of the ball row L may gradually shift. For example, regarding the relative positions of the screw shaft 2 and the nut 4, a reference position and a predetermined position different from the reference position are set, and the case where the screw shaft 2 and the nut 4 are reciprocated between the reference position and the predetermined position will be described.

[0083] Assume that the ball row L is arranged at the first position when the screw shaft 2 and the nut 4 are at the reference position, and the ball row L is arranged at an intermediate position between the first position and the second position when at the predetermined position. In this case, when the screw shaft 2 and the nut 4 are relatively rotated and repeatedly reciprocated between the reference position and the predetermined position, the ball row L may not return to the first position even though the screw shaft 2 and the nut 4 are at the reference position, or the ball row L may be displaced with respect to the intermediate position even though the screw shaft 2 and the nut 4 are at the predetermined position.

[0084] Such displacement of the ball row L is caused by differences in load, stroke amount, etc. between the forward and return paths when the ball row L moves within the spiral orbit 14. Such differences between the forward and return paths are caused by the elastic hysteresis of the metal material constituting the screw shaft 2 and the nut 4, the shape of the spiral orbit 14, the lead angle, etc. Also, the above-mentioned engagement of the balls 6 also contributes to the displacement of the ball row L.

[0085] On the other hand, in the present embodiment, as described above, while suppressing the engagement of the balls 6 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 spiral orbit 14. For example, when the ball row L moves from the intermediate position toward the first position and reaches the first position, the ball 6 abuts against the inclined surface 32a2 of the first inner end surface 32a and the movement of the ball row L is restricted. Thereby, even if the position of the ball row L is displaced, 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 be the first position. Thus, in the present embodiment, since the cage 8 restricts the axial movement of the ball row L along the spiral orbit 14, even if the ball row L is displaced, the displacement can be corrected. Also, since the engagement of the balls 6 can be suppressed when the ball row L reaches the first position or the second position, the occurrence of displacement of the ball row L can also be suppressed.

[0086] 〔Others〕 The embodiments disclosed this time are illustrative in all respects and 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 is exemplified, but both may be used as the friction member 26. Also, in each of the above embodiments, the case where the cage 8 has the connecting annular portion 30 is exemplified. However, if only the column 22 can restrict the axial movement of the balls 6b at one axial end of the ball row L located at the second position, the configuration may be such that the connecting annular portion 30 is omitted.

[0087] Also, the cage 8 included in the ball screw device 1 shown in each of the above embodiments includes an annular portion 20, a plurality of columns 22, a connecting annular portion 30, and a plurality of pockets 32. For example, it can be said that the annular portion 20, the plurality of columns 22, and the connecting annular portion 30 constitute a cylindrical main body portion. This cylindrical main body portion is disposed in the annular space K so as to be rotatable around the center line C of the screw shaft 2 and axially non-relatively movable with respect to the nut 4. The pockets 32 are provided in this main body portion and can be said to intersect the spiral orbit 14 at a plurality of locations along the axial direction.

[0088] Also, in the first modification and the second modification of the second embodiment, the case where the inclined surfaces 32a2 and 32b2 are provided on both the first inner end surface 32a and the second inner end surface 32b is exemplified. However, an inclined surface may be provided on at least one of the first inner end surface 32a and the second inner end surface 32b.

[0089] The scope of the rights of the present invention is not limited to the above-described embodiments, and includes all modifications within the scope equivalent to the configuration described in the claims.

Explanation of Reference Numerals

[0090] 1 Ball screw device 2 Screw shaft 4 Nut 4a Inner peripheral surface of cylinder 4b Annular groove 4c End surface 6, 6a, 6b Balls 8 Cage 9 Retaining ring 9a Inner surface 10 First spiral groove 10a Groove top 12 Second spiral groove 12a Groove top 14 Spiral orbit 20 Annular part 20a One end face 20b The other end face 20c Inner peripheral surface 20d Outer peripheral surface 20d1 Outer peripheral groove 22 Column 22a Tip 22b Side surface 24 Step surface 26 Friction member 30 Connecting annular part 30a One end face 32 Pocket 32a First inner end face 32a1 Circumferential surface (first circumferential surface) 32a11 One end part (first end part) 32a12 The other end part 32a2 Inclined surface (first inclined surface) 32b Second inner end face 32b1 Circumferential surface (second circumferential surface) 32b11 The other end part (second end part) 32a12 One end part 32b2 Inclined surface (second inclined surface) 36 Sleeve 36a One end face 40 Edge part 42 Outer peripheral surface C Center line D1 Line D2 Virtual line D3 Virtual line K Annular space L Ball row

Claims

1. 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 with the first spiral groove, a ball row including a plurality of balls arranged in the spiral track, a cage disposed in an annular space between the screw shaft and the nut for holding the plurality of balls, and the cage includes an annular portion rotatable about the center line of the screw shaft and disposed in the annular space so as to be axially non-movable relative to the nut, a plurality of columns extending axially on one side from one end face on one axial side of the annular portion and intersecting the spiral track at a plurality of locations, a plurality of pockets provided between a pair of adjacent columns in the circumferential direction among the plurality of columns for rotatably holding the plurality of balls, and a friction member provided between the nut and the annular portion for imparting resistance to the rotation of the cage relative to the nut. A ball screw device.

2. The cage further includes a connecting annular portion connecting the tips on one axial side of the plurality of columns. The ball screw device according to Claim 1.

3. The circumferential interval between the pair of columns is set to an interval capable of holding one of the balls. The ball screw device according to Claim 1 or Claim 2.

4. One of the balls is held in each of the plurality of pockets. The ball screw device according to Claim 3.

5. The circumferential interval between the pair of columns is set to an interval capable of holding a predetermined number of two or more of the balls. The ball screw device according to Claim 1 or Claim 2.

6. The predetermined number of the balls are held in each of the plurality of pockets. The ball screw device according to Claim 5.

7. The friction member includes a rubber ring interposed between the nut and the outer peripheral surface of the annular portion. The ball screw device according to Claim 1.

8. The nut has a cylindrical inner peripheral surface for accommodating the annular portion radially inward, and a stepped surface extending radially inward from the cylindrical inner peripheral surface for connecting the cylindrical inner peripheral surface and the second spiral groove. The friction member includes a wave washer that presses the annular portion axially on one side and brings the stepped 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.

9. Each of the plurality of pockets is defined by the side surfaces of the pair of columns and the 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. The first end of the first circumferential surface is the end with a smaller axial distance from the groove crest of the first spiral groove when the pocket is viewed from the front among the two circumferential ends of the first circumferential surface. The first inclined surface is provided so as to connect the first side surface on the first end side of the side surfaces of the pair of columns and the first end, and is inclined so as to approach the second side surface of the side surfaces of the pair of columns as it goes from the first side surface to the first end. The first inclined surface can be in contact with the ball in a state of being in contact with the second side surface. When the ball is in contact with the first inclined surface and the second side surface, the first circumferential surface is a surface that is not in contact with the ball. The ball screw device according to any one of claims 1 to 8.

10. The plurality of first inner end surfaces are arranged along the lead angle direction of the first spiral groove. The ball screw device according to claim 9.

11. The cage further includes a connecting annular portion that connects the tips of the plurality of columns on one axial side. Each of the pockets is defined by the side surfaces of the pair of columns, the first inner end surface of the annular portion, and the 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 of the second circumferential surface is the end with a smaller axial distance from the groove crest of the first spiral groove when the pocket is viewed from the front among the two circumferential ends of the second circumferential surface. The second inclined surface is provided so as to connect the second side surface on the second end side of the side surfaces of the pair of columns and the second end, and is inclined so as to approach the first side surface of the side surfaces of the pair of columns as it goes along the circumferential direction toward the second side surface side. The second inclined surface can be in contact with the ball in a state of being in contact with the first side surface. When the ball is in contact with the second inclined surface and the first side surface, the second circumferential surface is a surface that is not in contact with the ball. The ball screw device according to any one of claims 1 to 10.

12. The plurality of second inner end surfaces are arranged along the lead angle direction of the first spiral groove. The ball screw device according to claim 11.

Images