JP6745032B2 - Ball screw device - Google Patents

Description

The present invention relates to a ball screw device.

In a ball screw device in which a main ball row is interposed between a male thread groove on the outer circumference of a screw shaft and a female thread groove on the inner circumference of a ball nut, a main ball at the end of the main ball row and a pocket provided at the end of the ball nut. It has been proposed to interpose a coil spring between the groove and the concave portion (for example, see Patent Document 1).
In this type of ball non-circulation type ball screw device, the coil spring does not contract when the screw shaft is rotationally driven under a low axial force, so the balls in the ball row and the ball nut do not move relative to each other. .. Therefore, the ball nut makes a stroke while causing a slip between the balls of the ball row and the screw shaft.

On the other hand, when the screw shaft is driven to rotate with a high axial force applied, the coil spring contracts, the main ball rolls with respect to both the ball nut and the screw shaft, and the ball nut makes a stroke. .. This achieves highly efficient screw transmission.

Japanese Patent Publication No. 2010-505072

In order to directly engage the tip of the coil spring with the main ball at the end, the inner diameter of the tip of the coil spring is guided by the main ball at the end. On the other hand, the outer circumference of the coil spring is pressed against the inner circumference of the ball nut in the state of being housed in the trackway. That is, the tip end portion of the coil spring guided by the main ball at the end portion is guided toward the inner diameter side compared to the other portions of the coil spring. Therefore, the tip of the coil spring has an inflection point at which the curvature rapidly changes. As a result of stress concentration at this inflection point, breakage or breakage of the spring at the inflection point occurs. May occur.

Therefore, an object of the present invention is to provide a ball screw device in which damage to a coil spring is suppressed or prevented.

This invention, the inner peripheral (30b), a ball nut (30) including a female thread groove screw is formed on the inner circumferential (33), an outer peripheral (28a), a screw is formed on the outer periphery A plurality of main balls (29) housed in a raceway (K) formed by the screw shaft (28) including the male screw groove (34) inserted into the ball nut, and the female screw groove and the male screw groove. And a coil spring (51) that is housed in the raceway and elastically presses the main ball (29a) at the end (La) of the main ball row toward the main ball row. Interposing between the coil spring and the ball (29a) in the raceway, engaging the ball and radiating an end portion (511) of the coil spring with respect to a center circle (C1) of the raceway. A ball screw device (22) including a spring guide member (90) for guiding outward in a direction (R).

In one embodiment of the invention, the spring guide member, guide the end portion of the coil spring such that the outer edge of said end portion (511a) is in contact with the inner periphery of the ball nut.
In one embodiment of the present invention, the spring guide member includes a main body (91) housed in the track and a main body along the track on the outer side of the central circle of the track. columnar portion projecting and (92) including. Then, the columnar section, it is fitted into the end portion of the coil spring.

In one embodiment of this invention, the spring guide member has a body portion (91) housed in the trackway. It said body portion, the outer substantially cylindrical peripheral surface (95) including. The peripheral surface includes a first peripheral surface (97) facing the female thread groove and a second peripheral surface (98) facing the male thread groove . The cross section of the first peripheral surface orthogonal to the screw axis is arcuate along the female screw groove, and the cross section of the second peripheral surface orthogonal to the screw axis is the male screw groove. to name an arc shape along.

In one embodiment of the present invention, the ball including the main ball end of the main ball train.
In another embodiment of the present invention, the ball includes a stopper ball housed on the opposite side of the coil spring in the raceway from the main ball row.
In the above description, the numbers in parentheses and the like represent reference numerals of corresponding constituent elements in the embodiments described later, but these reference numerals do not mean that the scope of the claims is limited.

According to the present invention , the end portion of the coil spring is guided outward in the radial direction with respect to the center circle of the raceway by the spring guide member engaging with the ball. Therefore, it is possible to suppress or prevent the occurrence of the inflection point at the end portion of the coil spring in the state of being housed in the spiral track path. Therefore, it is possible to avoid the concentration of spring stress on the end portion of the coil spring, thereby providing a ball screw device in which damage to the coil spring is suppressed or prevented.

According to the embodiment of the present invention, the end portion of the coil spring is guided by the spring guide member such that the outer edge portion of the coil spring contacts the inner circumference of the ball nut. Therefore, the generation of the inflection point at the end portion of the coil spring can be more effectively suppressed or prevented in the state of being accommodated in the spiral track path.
According to one embodiment of the present invention, the second end portion of the coil spring is fitted into the columnar portion projecting from the main body portion outside the central circle, so that the end portion of the coil spring is located relative to the central circle. It is possible to relatively easily realize the structure of guiding the outer side in the radial direction.

According to the embodiment of the present invention, the first peripheral surface of the main body portion has a cross-sectional shape orthogonal to the screw axis in an arc shape along the female screw groove. In addition, the second peripheral surface has an arc-shaped cross section orthogonal to the screw axis along the male screw groove. Therefore, when the main body is housed in the track, the main body can be suppressed or prevented from rotating around the axis passing through the main body. Thereby, the posture of the coil spring can be stably maintained.

According to one embodiment of the present invention, the spring guide member that engages with the main ball at the end of the main ball row guides the end of the coil spring to the outer side in the radial direction with respect to the center circle of the raceway. it can.

FIG. 1 is a schematic cross-sectional view of a brake device to which a ball screw device according to an embodiment of the present invention is applied, showing a non-braking state. FIG. 2 is an exploded perspective view showing the configuration of the ball screw device. FIG. 3 is an enlarged cross-sectional view of a main part of the brake device. FIG. 4 is an enlarged sectional view of the ball nut. 5A and 5B are cross-sectional views taken along the section line VV in FIG. 4. 5A shows the second end side of the first coil spring, and FIG. 5B shows the first end side of the first coil spring. FIG. 6A is a diagram showing a spring guide member. FIG. 6B is a view of FIG. 6A viewed from the arrow VIB. FIG. 7 is an enlarged cross-sectional view showing a main part of FIG. 5B.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of a brake device 1 to which a ball screw device 22 according to an embodiment of the present invention is applied, showing a non-braking state. The brake device 1 is a device that applies a braking force due to friction to a disc 2 that rotates integrally with a wheel of an automobile or the like.
The brake device 1 is provided with a floating caliper 3 movably supported by, for example, a knuckle (not shown) and a disc 2, and the first backup is supported by the caliper 3 so as to be able to approach and separate from each other. The plate 4 and the second backup plate 5, and the first pad 6 and the second pad which are fixed to the first backup plate 4 and the second backup plate 5, respectively, and can press the corresponding side surfaces of the disk 2 respectively. 7 and.

The caliper 3 includes a first body 8 and a second body 9 fixed to each other, and a cover 10 fixed to the second body 9. The first body 8 includes a main body 11 to which one end of the second body 9 is fixed, and an arm 12 connected to the main body 11 in an orthogonal manner. The second backup plate 5 is fixed to the arm 12.
The second body 9 has a box-shaped cylinder 13 (corresponding to a brake cylinder) fixed to the main body 11 of the first body 8, a lid 16 that opens and closes the opening of the cylinder 13, and extends from the cylinder 13. The extended plate 14 is provided.

The cylinder 13 has a first end portion 151 and a second end portion 152 that face each other in the axial direction AX, and the tubular portion 15 having the first end portion 151 open and the second portion of the tubular portion 15 End face plate 16 connected to the end portion 152 of the. The cylinder 13 accommodates a piston 17 (corresponding to a brake piston) that is movable in the axial direction AX.
One end 171 of the piston 17 protrudes toward the disc 2 through an open portion of one end of the cylinder 13 (corresponding to the first end 151 of the tubular portion 15) and is fixed to the first backup plate 4.

A sealing member 18 that seals between the outer periphery 17a of the piston 17 and the inner periphery of the cylinder 13 (corresponding to the inner periphery 15b of the tubular portion 15) is interposed. The sealing member 18 may be an O-ring housed in a housing groove formed on the inner circumference of the cylinder 13 (the inner circumference 15b of the tubular portion 15).
Both the outer circumference 17a of the piston 17 and the inner circumference of the cylinder 13 (the inner circumference 15b of the tubular portion 15) are connected via a key 19 arranged across a key groove provided in the both. .. The movement of the piston 17 in the axial direction AX is guided through the key connection using the key 19, and the rotation of the piston 17 with respect to the cylinder 13 is restricted.

A hydraulic pressure that biases the piston 17 toward the disk 2 may be supplied into the cylinder 13 from a hydraulic path (not shown). In that case, the cylinder 13 and the piston 17 constitute a hydraulic actuator.
The caliper 3 has a function of pressing both pads 6 and 7 against the disc 2 to generate a braking force. The caliper 3 converts the electric motor 20, a speed reducer 21 that reduces the rotation of the electric motor 20, and the rotational motion transmitted from the electric motor 20 via the speed reducer 21 into a linear motion of the piston 17 in the axial direction AX. And a ball screw device 22 for

The electric motor 20 includes a motor housing 23 fixed to the extension plate 14 of the second body 9 and an output shaft 24.
The reduction gear device 21 includes a drive gear 25 that is integrally rotatably attached to one end of an output shaft 24 of the electric motor 20, an idle gear 26 that meshes with the drive gear 25, and a driven gear 27 that meshes with the idle gear 26. .. The idle gear 26 is rotatably supported by the second body 9. The cover 10 is fixed to the second body 9 so as to cover the speed reducer 21.

FIG. 2 is an exploded perspective view showing the configuration of the ball screw device 22. In FIG. 2, the configuration including the piston 17 is shown as a ball screw device 22.
As shown in FIGS. 1 and 2, the ball screw device 22 includes a screw shaft 28 as an input member and a ball nut 30 as a rotatable output member screwed onto the screw shaft 28 via a plurality of main balls 29. And a retaining ring 40 and a piston 17. A ball nut 30 is inserted through the screw shaft 28. The screw shaft 28 is supported by the second body 9 so as to be immovable and rotatable in the axial direction (axial direction AX). The ball nut 30 is supported by the second body 9 so as to be axially movable and non-rotatable. Hereinafter, the radial direction of the screw shaft 28 and the ball nut 30 will be described as the radial direction R.

As shown in FIG. 1, specifically, the screw shaft 28 is arranged so as to be inserted through a support hole 31 provided in the lid 16. The screw shaft 28 is rotatably and immovably supported in the axial direction (axial direction AX) by the screw shaft support mechanism 32. The screw shaft support mechanism 32 is provided integrally with the screw shaft 28, and has a flange portion 282 (not shown in FIG. 2) provided on the outer circumference of the screw shaft 28 near one end 281 of the screw shaft 28, and a flange portion 282. It includes a thrust bearing 41 and an alignment unit 42 which are interposed between the lid 16 and the lid 16 along the axial direction of the screw shaft 28. Further, the screw shaft support mechanism 32 has a cylindrical axial force sensor 44 for detecting a load in the axial direction (axial direction AX), a first lock nut 45 arranged on the outer periphery of the axial force sensor 44, It includes a second lock nut 46 arranged on the opening side (rightward in FIG. 2) in the axial direction (axial direction AX) with respect to the axial force sensor 44 and the first lock nut 45.

The driven gear 27 is integrally rotatably connected to one end 281 of the screw shaft 28 via a joint 43.
FIG. 3 is an enlarged cross-sectional view of a main part of the brake device 1. As shown in FIG. 3, the ball nut 30 includes an outer circumference 30a and an inner circumference 30b in which a female screw groove 33 is formed. The screw shaft 28 has an outer circumference 28a in which a male screw groove 34 is formed. Rows of main balls 29 are interposed between the female screw groove 33 and the male screw groove 34.

The outer circumference 30a of the ball nut 30 includes a rotation restricting portion 36 that engages with the rotation restricting portion 35 of the inner circumference 17b of the piston 17, and a cylindrical surface portion 38 that is fitted to the cylindrical surface portion 37 of the inner circumference 17b of the piston 17. The relative rotation between the piston 17 and the ball nut 30 is regulated by the engagement between the both rotation regulation portions 35 and 36.
The ball nut 30 includes a first end portion 301 on the disc 2 side and a second end portion 302 on the opposite side of the first end portion 301 in the ball nut axial direction (axial direction AX).

The first end 301 of the ball nut 30 is in contact with the positioning step 39 on the inner circumference 17 b of the piston 17. A retaining ring 40 fitted in an annular groove provided on the inner circumference 17 b of the piston 17 is engaged with the end surface 303 of the second end 302 of the ball nut 30. As a result, the piston 17 and the ball nut 30 are connected so as to be integrally movable in the axial direction AX.

When the rotation of the output shaft 24 of the electric motor 20 is transmitted via the speed reducer 21 and the screw shaft 28 rotates, the ball nut 30 moves in the axial direction AX. At this time, the piston 17 is moved integrally with the ball nut 30 in the axial direction AX under the guidance of the key 19.
FIG. 4 is an enlarged sectional view of the ball nut 30.

As shown in FIG. 4, a spiral track K is formed between the female screw groove 33 and the male screw groove 34 of the ball nut 30. The plurality of main balls 29 held in the female screw groove 33 of the ball nut 30 form a main ball row L lined up along the spiral track K. The main ball row L includes a first end La and a second end Lb.
The ball screw device 22 includes a first coil spring (coil spring) 51 and a second coil spring 52 arranged on both sides of the main ball row L in the track K.

The first coil spring 51 elastically presses the main ball (end main ball) 29a of the first end La of the main ball row L toward the main ball row L side. 511 and a second end 512. In order to realize the smooth expansion and contraction operation of the first coil spring 51, the spring diameter of the first coil spring 51 is set to be smaller than the radial width of the track K. Therefore, as shown in FIG. 7, the inner diameter E1 of the first end 511 as the end turn portion of the first coil spring 51 is smaller than the diameter d of the main ball 29 (d>E1).

The second coil spring 52 has a first end 521 that elastically presses the main ball 29b of the second end Lb of the main ball row L toward the main ball row L, and a second end 522. Prepare In order to realize the smooth expansion/contraction operation of the second coil spring 52, the spring diameter of the second coil spring 52 is set to be smaller than the radial width of the track K.
5A and 5B are cross-sectional views taken along the section line VV in FIG. 4. 5A shows the second end portion 512 side of the first coil spring 51, and FIG. 5B shows the first end portion 511 side of the first coil spring 51.

As shown in FIGS. 4 and 5A, a recess 60 as a first stopper is formed on the inner circumference 30b of the ball nut 30. The recess 60 is formed, for example, by forging in the axial direction AX.
As shown in FIG. 5A, the ball screw device 22 includes a first stopper ball 81 held in the recess 60 and interposed between the recess 60 and the second end 512 of the first coil spring 51. .. The second end 512 of the first coil spring 51 is received in the recess 60 via the first stopper ball 81.

As shown in FIG. 5B, the ball screw device 22 includes a first end portion (end turn portion) 511 of the first coil spring 51 and a first end portion La of the main ball row L in the raceway K. It further includes a spring guide member 90 interposed between the spring guide member 90 and the main ball 29a. The spring guide member 90 guides the first end 511 of the first coil spring 51 to the outside of the center circle of the track K (concentric circle passing through the center of the track K) C1. The spring guide member 90 is attached to the first end 511 of the first coil spring 51 and guides the inner diameter of the first end 511. In other words, the spring guide member 90 supports the first end portion 511. The first end 511 of the first coil spring 51 is received by the main ball 29a of the first end La via the spring guide member 90.

FIG. 6A is a diagram showing the spring guide member 90. FIG. 6B is a view of FIG. 6A viewed from the arrow VIB.
The spring guide member 90 integrally includes a main body portion 91 and a columnar columnar portion 92 protruding from the main body portion 91 along the track K. The spring guide member 90 is made of, for example, a synthetic resin material.

The main body portion 91 is provided in a shape (substantially circular shape) and size that matches the track K so that the track K can be almost completely closed. The main body portion 91 is provided on the first surface 93 as a spring seat surface that engages with the first end portion 511 of the first coil spring 51, and on the side opposite to the first surface 93, and the main ball row is provided. The first end La of L (see FIG. 4) includes a second surface 94 as an engaging portion that engages with the main ball 29a, and a peripheral surface 95 having a substantially cylindrical outer shape. The second surface 94 has a recess 96 that can be engaged with the main ball 29a. In this embodiment, the bottom surface of the recess 96 is a concave spherical surface. The recess 96 may not be formed in the second surface 94.

The peripheral surface 95 of the main body portion 91 includes a first peripheral surface 97 that closely faces the female thread groove 33 and a second peripheral surface 98 that closely faces the male thread groove 34 when accommodated in the track K. .. The first peripheral surface 97 is formed of a convex curved surface, and a cross-section (a cross section perpendicular to the axis) orthogonal to the screw shaft 28 has an arc shape along the bottom of the female screw groove 33. The second peripheral surface 98 is formed of a concave curved surface, and has a cross-sectional shape perpendicular to the axis of an arc along the bottom of the male screw groove 34. Therefore, in the state where the main body 91 is accommodated in the track K, the main body 91 rotates about a virtual axis (axis passing through (the center of) the main body 91) V1 along the direction in which the track K extends. Can be suppressed or prevented.

The columnar portion 92 projects outside the center circle C1 of the track K along the direction in which the track K extends from the first surface 93. The columnar portion 92 has an outer diameter similar to the inner diameter of the first coil spring 51. The columnar portion 92 is curved in an arc shape along the direction in which the track K extends.
FIG. 7 is an enlarged cross-sectional view showing a main part of FIG. 5B. In the mounted state of the spring guide member 90 to the first end portion 511 of the first coil spring 51, the columnar portion 92 is internally fitted to the first end portion 511 of the first coil spring 51, and in this state Then, the peripheral surface 92a of the columnar portion 92 abuts on the inner circumference of the first end portion 511 of the first coil spring 51, and guides the inner diameter of the first end portion 511 of the first coil spring 51. When the columnar section 92 has a central axis C2 passing through an arc-shaped central circle, the central axis C2 of the columnar section 92 is located outside the arcuate central circle C1 of the track K in the radial direction R. It is eccentric. The columnar portion 92 guides the first end portion 511 of the first coil spring 51 to the outer side in the radial direction R with respect to the center circle C1 of the track K. In this embodiment, the outer edge portion (outer edge portion of the end portion) 511 a of the first end portion 511 to which the columnar portion 92 is attached is in contact with the inner circumference 30 b of the ball nut 30.

As shown in FIG. 4, the ball screw device 22 includes a protrusion 70 as a second stopper that protrudes into the track K. The convex portion 70 is a part of a stopper pin (not shown) that penetrates the ball nut 30, and is configured by a portion that projects into the female screw groove 33.
The ball screw device 22 includes a second stopper ball 82 housed in the track K and interposed between the convex portion 70 and the second end portion 522 of the second coil spring 52. The second end 522 of the second coil spring 52 is received by the protrusion 70 via the second stopper ball 82 accommodated in the track K.

When the screw shaft 28 is driven to rotate with a low axial force applied, the coil springs 51 and 52 do not contract, so that the main ball 29 and the ball nut 30 of the main ball row L do not move relative to each other. Therefore, the ball nut 30 makes a stroke while causing a slip between the main ball 29 of the main ball row L and the male screw groove 34 of the screw shaft 28.
On the other hand, when the screw shaft 28 is driven to rotate with a high axial force applied, the coil springs 51 and 52 contract, and the main balls 29 of the main ball row L are applied to both the ball nut 30 and the screw shaft 28. The ball nut 30 strokes while rolling. This achieves highly efficient screw transmission.

When the braking device 1 is switched from the non-braking state to the braking state, the screw shaft 28 is rotationally driven in one predetermined direction while a high axial force is applied. At this time, the first coil spring 51 comes to contract. On the other hand, when the braking device 1 is switched from the braking state to the non-braking state, the screw shaft 28 is rotationally driven in the direction opposite to the one direction while a high axial force is applied. At this time, the second coil spring 52 comes to contract.

The first coil spring 51 is linear in its free state (no load), and is housed in the track K in a state of being bent in an arc shape (spiral shape). In this housed state, a restoring force F (see FIG. 7) acts on the first coil spring 51, and the outer edge portion 51a of the first coil spring 51 receives the restoring force and the inner periphery 30b of the ball nut 30 ( It is pressed against the bottom of the female thread groove 33).

If the spring guide member 90 is eliminated and the first end portion 511 of the first coil spring 51 and the main ball 29a are directly engaged, the first end portion 511 of the first coil spring 51 ( The inner diameter of the end turn portion is guided by the main ball 29a. On the other hand, as described above, the outer edge portion 51a of the first coil spring 51 is pressed against the bottom portion of the female screw groove 33 of the ball nut 30. That is, the first end 511 guided by the main ball 29 is guided toward the inner diameter side as compared with the other parts of the first coil spring 51. Therefore, the first end portion 511 of the first coil spring 51 has an inflection point at which the curvature rapidly changes. As a result of stress concentration at this inflection point, there is a possibility that breakage, breakage of the spring, etc. may occur at the inflection point.

On the other hand, according to this embodiment, the spring guide member 90 engaging with the main ball 29 causes the outer edge 511a of the first end 511 of the first coil spring 51 to move to the bottom of the female thread groove 33 (ball nut). The first end 511 of the first coil spring 51 is guided so as to come into contact with the inner circumference 30b of 30 (outward in the radial direction R with respect to the center circle C1 of the track K). Therefore, when the first coil spring 51 is accommodated in the spiral track K, it is possible to suppress or prevent the occurrence of an inflection point at the first end 511 of the first coil spring 51. Therefore, it is possible to avoid concentration of spring stress on the first end portion 511 of the first coil spring 51, and thereby to provide the ball screw device 22 in which breakage of the first coil spring 51 is suppressed or prevented. it can.

Although the embodiment of the present invention has been described above, the present invention can be implemented in other forms.
For example, the spring guide member 90 may be attached to the second end portion 512 of the first coil spring 51 instead of the first end portion 511 of the first coil spring 51. In this case, the spring guide member 90 is interposed between the spring guide member 90 and the first stopper ball 81 in the track path K and engages with the first stopper ball 81.

Further, the spring guide member 90 may be attached to the second coil spring 52 instead of the first coil spring 51. In this case, the spring guide member 90 is interposed between the spring guide member 90 and the ball (the main ball 29b at the second end Lb of the main ball row L or the second stopper ball 82) in the track K. And engage the ball.

Further, in the above-described embodiment, an intermediate spring made of a coil spring may be interposed at one or more positions in the middle of the main ball row L, and the spring guide member 90 may be attached to this intermediate spring. Good.
Further, when the first end portion 511 of the first coil spring 51 is guided by the spring guide member 90, the outer edge portion 511a of the first end portion 511 does not come into contact with the inner circumference 30b of the ball nut 30. However, it suffices if the central axis C2 of the columnar portion 92 is located on the outer side in the radial direction R with respect to the central circle C1 of the track K.

Besides, the present invention can be variously modified within the scope of the claims.

22... Ball screw device, 28... Screw shaft, 28a... Outer periphery, 29... Main ball, 29a... Main ball of the first end (end main ball), 30... Ball nut, 30b... Inner circumference, 33... Female thread groove, 34... Male thread groove, 51... First coil spring (coil spring), 511... First end portion (end portion), 511a... Outer edge portion of first end portion (outer edge portion of end portion) ), 90... Spring guide member, 91... Main body portion, 92... Columnar portion, 94... Second surface (engaging portion), 95... Peripheral surface, 96... Recessed, 97... First peripheral surface, 98... Circumferential surface of 2, C1... Central circle, K... Orbit, L... Main ball row, La... First end (end)

Claims (5)

A ball nut including an inner circumference and an internal thread groove in which a screw is formed on the inner circumference,
An outer circumference, and a male screw groove having a screw formed on the outer circumference, a screw shaft inserted into the ball nut,
A main ball row including a plurality of main balls housed in a raceway formed by the female screw groove and the male screw groove,
A coil spring housed in the raceway and elastically pressing the main ball at the end of the main ball row toward the main ball row;
Wherein interposed between said main ball of said end portion and said coil spring in trackway, the main ball and engage and radially outward of the end portion relative to the center circle of the track path of the coil spring A ball screw device including a spring guide member for guiding to a side. The ball screw device according to claim 1, wherein the spring guide member guides the end portion of the coil spring such that an outer edge portion of the end portion contacts an inner circumference of the ball nut. The spring guide member includes a main body portion housed in the trackway, and a columnar portion projecting from the main body section along the trackway outside the central circle of the trackway,
The ball screw device according to claim 1, wherein the columnar portion is internally fitted to the end portion of the coil spring. The spring guide member has a main body portion housed in the track path,
The main body portion includes a substantially cylindrical outer peripheral surface,
The peripheral surface includes a first peripheral surface facing the female screw groove and a second peripheral surface facing the male screw groove,
The first peripheral surface has a cross-section orthogonal to the screw axis in an arc shape along the female screw groove,
The ball screw device according to any one of claims 1 to 3, wherein a cross-sectional shape of the second peripheral surface orthogonal to the screw axis is an arc shape along the male screw groove. A ball nut including an inner circumference and an internal thread groove in which a screw is formed on the inner circumference,
An outer circumference, and a male screw groove having a screw formed on the outer circumference, a screw shaft inserted into the ball nut,
A main ball row including a plurality of main balls housed in a raceway formed by the female screw groove and the male screw groove,
A coil spring housed in the raceway and elastically pressing the main ball at the end of the main ball row toward the main ball row;
In the track path, a stopper ball accommodated on the side opposite to the main ball row with respect to the coil spring,
It is interposed between the coil spring and the stopper ball in the raceway, engages with the stopper ball, and guides the end of the coil spring to the outer side in the radial direction with respect to the center circle of the raceway. A ball screw device including a spring guide member.

Images