JP2014145465A - Ball screw device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw device in which a movable body and a ball nut are connected so as to integrally movable in an axial direction while a ball nut is prevented from rotating without using a fastening member such as a screw.SOLUTION: A ball screw device 50 comprises: a screw shaft 22 inserted into a second body 9; a ball nut 24 screwed to the screw shaft 22 via a plurality of balls 23; a piston 25 including a surrounding portion 32 surrounding the ball nut 24; and a key fitting structure K1 regulating both axial movement and rotation of the ball nut 24 with respect to the piston 25.

Description

  The present invention relates to a ball screw device.

  In recent years, electric brake devices have been developed as brake devices in place of conventional hydraulic brake devices. In this electric brake device, a ball screw device is included in an actuator for generating a pressing force for pressing a pad against a disk (see Patent Document 1).

JP 2007-126032 A

In such a ball screw device, it is necessary to provide the ball nut so as to be integrally movable in the axial direction on the moving body connected to the pad. Further, it is necessary to prevent the ball nut from rotating by the moving body.
In order to achieve these problems, it is conceivable that the moving body is formed in a bottomed cylindrical shape having a bottom portion facing the tip of the screw shaft and a cylindrical surrounding portion surrounding the outer periphery of the screw shaft. Then, in order to provide the movable body and the ball nut having such a shape so as to be relatively prevented from rotating and integrally movable in the axial direction, it is conceivable to connect the movable body and the ball nut by screw fastening. Specifically, it is conceivable to fasten the bottom of the moving body and the end surface of the nut with a bolt.

However, in this case, it is necessary to ensure that the thickness of the nut in the radial direction of rotation is larger than the diameter of the bolt. Therefore, when the size of the ball screw device is reduced, the bolt becomes a small size, and the number of parts may be increased by increasing the number of bolts to compensate for the lack of strength.
The present invention has been made under such a background, and connects the moving body and the ball nut so as to be integrally movable in the axial direction while preventing rotation of the ball nut without using a fastening member such as a screw. An object of the present invention is to provide an improved ball screw device.

  In order to achieve the above object, the invention according to claim 1 includes a cylindrical housing (9), a screw shaft (22) inserted through the housing, the screw shaft and a plurality of balls. A ball nut (24) to be screwed, a moving body (25) having a surrounding portion (32) surrounding the ball nut, a ball nut side keyway (35) formed on an outer peripheral surface of the ball nut, A movable body side key recessed portion (33) formed on the inner peripheral surface of the surrounding portion, and a key (36; 36C) fitted over the ball nut side key groove and the movable body side key recessed portion, A ball screw device (50; 150) including a key fitting structure (K1; K2) for restricting axial movement and rotation of the ball nut.

In this section, the alphanumeric characters in parentheses represent reference signs of corresponding components in the embodiments described later, but the scope of the claims is not limited to the embodiments by these reference numerals.
According to this configuration, the ball nut and the moving body are provided so as to be integrally movable by the keys that are respectively fitted into the ball nut side keyway and the moving body side key recess. When the movement of the moving body is permitted while its rotation is restricted, rotation of the ball nut is also achieved by the key fitting structure. Accordingly, the moving body and the ball nut can be coupled so as to be integrally movable in the axial direction while preventing the ball nut from rotating.

According to a second aspect of the present invention, the movable body side key recess is a through hole (33) penetrating the surrounding portion in the thickness direction, and a depth of a portion of the key fitted into the ball nut side key groove. The dimension (Wa) is a ball screw device (50) according to claim 1, wherein the dimension (Wa) is larger than a distance (Wb) from the bottom of the movable body side key recess to the key.
According to this configuration, since the key cannot be removed from the key nut-side keyway, disengagement between the key and the ball nut is prevented. Thereby, the ball nut and the moving body can be held in a state in which they can move integrally.

  According to a third aspect of the present invention, the movable body side key recess is a through hole that penetrates the surrounding portion in the thickness direction, and the key fitting structure (K2) is formed on an inner peripheral surface of the housing. The housing includes a housing side groove (135), and the key (36C) is fitted into the housing side groove via the movable body side key recess, thereby allowing the movable body to move in the axial direction relative to the housing. The ball screw device (150) according to claim 1, wherein the rotation of the movable body relative to is controlled.

  According to this configuration, the key that is fitted in the ball nut side keyway and the moving body side key recess is also fitted in the housing side groove, so that the moving body is allowed to move in the axial direction by the housing and is prevented from rotating. Is planned. As a result, the ball nut can be prevented from rotating while the number of parts is reduced, and the movable body and the ball nut can be coupled so as to be integrally movable in the axial direction.

1 is a schematic cross-sectional view of an electric brake device to which a ball screw device according to an embodiment of the present invention is applied, and shows a non-braking time. It is a schematic sectional drawing of the electric brake device shown to FIG. 1A, and has shown the time of braking. It is a disassembled perspective view which shows a key fitting structure. It is a principal part expanded sectional view which shows a key fitting structure. It is a principal part expanded sectional view of the electric brake device with which the ball screw apparatus which concerns on other embodiment of this invention was applied.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1A is a schematic cross-sectional view of an electric brake device 1 to which a ball screw device according to an embodiment of the present invention is applied in a non-braking state. FIG. 1B is a schematic sectional view of the electric brake device 1 in a braking state. 1A and 1B, an electric brake device 1 is a device that applies a braking force by friction to a disk 2 that rotates integrally with a wheel of an automobile or the like.

  The electric brake device 1 includes, for example, a floating type caliper 3 supported so as to be movable by a knuckle (not shown) and the like, and a first backup supported by the caliper 3 so as to be able to approach / separate from each other. The first pad 6 and the second backup plate 5 are fixed to the first backup plate 4 and the second backup plate 5, respectively, and the corresponding side surfaces of the disk 2 can be pressed as shown in FIG. 1B. And a pad 7.

The caliper 3 includes a first body 8 and a second body (housing) 9 fixed to each other, and a cover 10 fixed to the second body 9. The first body 8 includes a main body portion 8A and an arm portion 8C connected to the main body portion 8A via a bridging portion 8B.
The first back plate 4 is fixed to one end 12A of a support shaft 12 supported in an axial direction (corresponding to a thrust direction ST described later) in a support hole 11 inserted through the main body portion 8A. A piston 25 is fixedly attached to the other end 12 </ b> B of the support shaft 12. The second backup plate 5 is fixed to the arm portion 8A. The second body 9 is fixed to the main body portion 8A. The second body 9 has a substantially cylindrical shape and is formed using an aluminum material.

The caliper 3 functions to generate a braking force by pressing the pads 6 and 7 against the disk 2. Specifically, the caliper 3 includes an electric actuator 13 that generates a thrust force F (see FIG. 1B) in a thrust direction ST parallel to the wheel axis direction X1, and a thrust force F generated by the electric actuator 13 that is applied to the pads 6, 7 is provided.
The electric actuator 13 includes an electric motor 16 having a motor housing 16A fixed to a mounting stay 15 extended from the second body 9 and a rotating shaft 16B as an output shaft, while reducing the rotational output of the electric motor 16. A gear mechanism 17 for transmission and a ball screw mechanism 18 as a motion conversion mechanism for converting the rotational motion transmitted through the gear mechanism 17 into a linear motion in the thrust direction ST are provided.

  The gear mechanism 17 includes a drive gear 19 attached to one end of the rotary shaft 16B so as to be integrally rotatable, an idle gear 20 that meshes with the drive gear 19, and a driven gear 21 that meshes with the idle gear 20 and rotates around the central axis C1. It has. The idle gear 20 is rotatably supported by the second body 9. The driven gear 21 is coaxially fixed to a screw shaft 22 described below. The cover 10 is fixed to the second body 9 so as to cover the gear mechanism 17.

The ball screw mechanism 18 includes a screw shaft 22 as an input member, and a ball nut 24 as an output member screwed to the screw shaft 22 via a ball 23.
Specifically, the screw shaft 22 is supported by a rolling bearing 30 fixed to the inner periphery of the support hole 27. Thereby, the screw shaft 22 is rotatably provided while movement in the axial direction (thrust direction ST) is restricted.

  The ball nut 24 is connected to the piston 25 by a key fitting structure K1. The key fitting structure K1 regulates movement of the ball nut 24 relative to the piston 25 in the axial direction (direction along the thrust direction ST) and rotation of the ball nut 24. In this embodiment, the ball screw mechanism 50, the piston 25, and the key fitting structure K1 constitute the ball screw device 50 described in the claims.

The piston 25 has a bottomed cylindrical shape. The piston 25 has a bottom portion 31 fixed to the other end 12 </ b> B of the support shaft 12 and a cylindrical surrounding portion 32 that surrounds the outer periphery of the screw shaft 22. A piston-side key hole (through hole) 33 that penetrates the surrounding part 32 in the thickness direction is formed in the middle part of the surrounding part 32 in the axial direction (thrust direction ST) and the circumferential direction.
In addition, a key groove 38 is formed at a position different from the piston-side key hole 33 in the middle portion of the surrounding portion 32 in the axial direction and the circumferential direction.

  The piston 25 is accommodated and disposed in the second body 9 with the outer periphery of the surrounding portion 32 spaced apart from the inner periphery of the second body 9 by a minute distance. A key groove 39 extending in the axial direction is formed on the inner periphery of the second body 9. The rotation of the piston 25 relative to the second body 9 is restricted while the axial movement of the piston 25 relative to the second body 9 is allowed by the key 40 fitted in the key grooves 38 and 39. Therefore, the rotation of the piston 25 is prevented and the movement of the piston 25 in the axial direction is allowed.

The rotation of the rotating shaft 16B of the electric motor 16 is transmitted through the gear mechanism 17, and the screw shaft 22 is rotated around the axis. As the screw shaft 22 rotates, the ball nut 24 moves in the axial direction (thrust direction ST).
During braking of the electric brake device 1, the thrust force F generated by the electric actuator 13 is transmitted to the first pad 6 side via the transmission mechanism 14, and the first pad 6 moves to the disk 2 side as shown in FIG. 1B. The first pad 6 is pressed, and the direction opposite to the rotation direction of the disk 2 with respect to the disk 2 (for example, the direction toward the front side of the paper surface orthogonal to the paper surface) (for example, the direction orthogonal to the paper surface toward the back side of the paper surface). It exerts braking force due to frictional force.

FIG. 2 is an exploded perspective view showing the key fitting structure K1. FIG. 3 is an enlarged cross-sectional view of a main part showing the key fitting structure K1. The key fitting structure K1 will be described with reference to FIGS.
The key fitting structure K1 extends over the ball nut side key groove 35 formed on the outer peripheral surface of the ball nut 24, the piston side key hole 33 of the surrounding portion 32, the ball nut side key groove 35, and the piston side key hole 33. And a key 36 that is fitted.

The key 36 has, for example, a quadrangular prism shape. The front end portion 36A and the base end portion 36B of the key 36 are each formed with a flat surface orthogonal to the direction in which the key 36 extends.
The ball nut side keyway 35 is formed in the middle of the ball nut 24 in the axial direction and circumferential direction. The ball nut side keyway 35 has a flat bottom surface 37 along the outer peripheral surface of the ball nut 24. The cross-sectional shapes of the piston-side key hole 33 and the ball nut-side key groove 35 viewed from the circumferential direction match the cross-sectional shape of the key 36. The key 36 is fitted in the piston side key hole 33 and the ball nut side key groove 35 with almost no play.

  When the key 36 and the ball nut-side key groove 35 are fitted, the depth dimension of the portion of the key 36 that fits into the ball nut-side key groove 35 matches the groove depth Wa of the ball nut-side key groove 35. ing. In this state, the distance Wb from the bottom of the piston-side keyhole 33 (that is, the outer peripheral surface of the surrounding portion 32) to the tip 36A of the key 36 is smaller than the groove depth Wa of the ball nut-side keyway 35. Thus, the length of the key 36 and the ball nut side keyway 35 are set. Therefore, the key 36 does not come out of the ball nut side keyway 35, and as a result, disengagement between the key 36 and the ball nut 24 is prevented.

  As described above, according to this embodiment, the ball nut 24 and the piston 25 are provided so as to be integrally movable by the keys 36 fitted into the ball nut side keyway 35 and the piston side key hole 33, respectively. Since the key groove 38, 39 and the key 40 are fitted to each other, the axial movement of the piston 25 is allowed and its rotation is restricted, so that the ball nut 24 is prevented from rotating by the key fitting structure K1. . Accordingly, the piston 25 and the ball nut 24 can be connected so as to be integrally movable in the axial direction while preventing the ball nut 24 from rotating without using a fastening member such as a screw.

FIG. 4 is an enlarged cross-sectional view of a main part of an electric brake device 101 to which a ball screw device 150 according to another embodiment of the present invention is applied.
In this embodiment, the same components as those shown in FIGS. 1 to 3 are given the same reference numerals as those in FIG. 1 and the description thereof is omitted.
4 mainly differs from the configuration shown in FIGS. 1 to 3 in that a key fitting structure K2 is provided instead of the key fitting structure K1.

The key fitting structure K2 not only restricts the axial movement of the ball nut 24 relative to the piston 25 and the rotation of the ball nut 24, but also allows the movement of the piston 25 relative to the second body 9 in the axial direction. The rotation of the piston 25 relative to the body 9 is restricted.
The key fitting structure K2 includes a ball nut side key groove 35, a piston side key hole 33, a body side key groove 135 formed on the outer peripheral surface of the ball nut 24, a ball nut side key groove 35, and a piston side key hole. 33 and a key 36C fitted over the body side keyway 135.

The body-side keyway 135 is formed in the middle of the ball nut 24 in the axial direction and circumferential direction. The body side keyway 135 extends along the axial direction. The circumferential width of the ball nut-side keyway 35 is substantially aligned with the circumferential width of the key 36C.
The key 36C is fitted into the body-side key groove 135 through the piston-side key hole 33, whereby the axial movement of the piston 25 with respect to the second body 9 is allowed and the rotation of the piston 25 with respect to the second body 9 is allowed. Is regulated. In the embodiment of FIG. 4, since the rotation of the piston 25 relative to the second body 9 is restricted by the key 36c, the configurations of the key grooves 38 and 39 and the key 40 described in the above embodiment are omitted. . Similarly to the above-described embodiment, the ball nut 24 and the piston 25 are provided so as to be integrally movable by the keys 36C that are respectively fitted into the ball nut side keyway 35 and the piston side key hole 33.

  As described above, according to this embodiment, when the key 36C fitted in the ball nut-side key groove 35 and the piston-side key hole 33 is fitted in the body-side key groove 135, the piston 25 is connected to the second body 9. Therefore, the movement in the axial direction is allowed and the rotation is prevented. The rotation of the ball nut 24 is also restricted by the key 36C. As a result, the ball nut 24 can be prevented from rotating while the number of parts is reduced, and the piston 25 and the ball nut 24 can be connected so as to be integrally movable in the axial direction.

As mentioned above, although two embodiment of this invention was described, this invention can also be implemented with another form.
For example, the ball nut 24 and the keys 36 and 36C can be formed of materials having the same coefficient of thermal expansion. In this case, the key 36, 36C can be reliably fitted into the ball nut-side key groove 35 regardless of the usage environment of the electric brake 1, 101, whereby the key 36, 36C and the ball nut can be secured. The disengagement with 24 can be further prevented.

Moreover, in each embodiment, although the mobile body side key recessed part was demonstrated as a through-hole (piston side key hole 33), the mobile body side key recessed part can also be provided with a groove | channel.
Moreover, not only one key fitting structure K1 and K2 but two or more can also be provided.
In addition, various design changes can be made within the scope of matters described in the claims.

DESCRIPTION OF SYMBOLS 9 ... 2nd body (housing), 22 ... Screw shaft, 24 ... Ball nut, 25 ... Piston (moving body), 32 ... Enclosure, 33 ... Piston side keyhole, 35 ... Ball nut side keyway, 36, 36C ... Key, 50,150 ... Ball screw device, K1, K2 ... Key fitting structure

Claims (3)

A tubular housing;
A screw shaft inserted into the housing;
A ball nut screwed to the screw shaft via a plurality of balls;
A moving body having a surrounding portion surrounding the ball nut;
A ball nut-side key groove formed on the outer peripheral surface of the ball nut, a moving body-side key recess formed on the inner peripheral surface of the surrounding portion, and a key that fits over the ball nut-side key groove and the moving body-side key recess And a key fitting structure that restricts axial movement and rotation of the ball nut with respect to the moving body. The movable body side key recess is a through-hole penetrating the surrounding portion in the thickness direction,
2. The ball screw device according to claim 1, wherein a depth dimension of a portion of the key fitted into the ball nut-side key groove is larger than a distance from a bottom portion of the movable body-side key recess to the key. The movable body side key recess is a through-hole penetrating the surrounding portion in the thickness direction,
The key fitting structure includes a housing side groove formed on the inner peripheral surface of the housing,
The key is fitted into the housing-side groove via the movable body side key recess, so that the movement of the movable body relative to the housing is allowed while the rotation of the movable body relative to the housing is restricted. The ball screw device according to claim 1.

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