JP2002235829A - Ball screw and electric power steering device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw capable of preventing balls from mixing into a non-circulating part in assembling. SOLUTION: This ball screw is manufactured by mounting plural piece members 24 having connecting grooves 28 for connecting internal thread grooves 26 of a rotary nut 22, on the rotary nut 22. Plural balls are continuously arranged on rolling passages 27 respectively formed between the ball screw shaft and each internal thread groove 26. The non-circulating part 32 held by the piece members 24 and free from the circulation of the balls, among the rolling passages 27 is provided with the packing 33 for filling the non-circulating part 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piece-type ball screw and an electric power steering device having the ball screw.

[0002]

2. Description of the Related Art An electric power steering apparatus for an automobile supplements a steering force of a steering wheel with an electric motor.
There are various types. One of them is to apply an axial moving force from a steering wheel to a retractable steering shaft connected to a wheel steering mechanism through a conversion mechanism such as a rack and pinion mechanism, and to output the output of an electric motor to a ball screw. There is one that is applied as an axial moving force via a. There are various types of ball screws having different ball circulation types, and one type is a so-called bridge type.

FIG. 10 shows an example of a conventional piece type ball screw mechanism. The ball screw shaft 51 has an outer thread groove 52 on the outer surface, and the rotating nut 53 has an inner thread groove 54 corresponding to the outer thread groove 52, and is fitted between the two thread grooves 52, 54. It is screwed to the ball screw shaft 51 via many balls 55. An elliptical fitting hole 56 that penetrates the inner and outer peripheral surfaces and cuts out a part of the inner thread groove 54 is formed in the cylindrical body of the rotating nut 53, and the elliptical fitting hole 56 is formed in the fitting hole 56. The piece 57 is fitted. The piece 57 is a component in which a connecting groove 58 for connecting adjacent one peripheral portions of the inner screw groove 54 to each other is formed.
Five rolling paths are configured. Internal and external thread grooves 5 in the rolling path
A large number of balls 55 interposed between the two
Rolls 2 and 54 are guided by the connecting groove 58 of the piece 57, and can return to the adjacent inner screw groove 54 over the thread of the ball screw shaft 51 and can be circulated.

FIG. 11 is a developed view of the rotary nut 53 in the above-described piece type ball screw, as viewed from the inner peripheral side. In the case of a piece-type ball screw, between the rolling piece 57 and an adjacent piece 57 between the rolling paths (indicated by hatching with dashed lines) of each circumference, which is approximately one circumference, in the inner screw groove 54. , A non-circulating portion 59 (shown by hatching with a dashed dotted line) which is a space where no ball exists.

In the assembling process of such a piece-type ball screw mechanism, as shown in FIG. 12, a temporary shaft 60 in place of the ball screw shaft 51 is fitted in the rotating nut 53 with the end thereof positioned at the position of the piece 57. After the setting, the balls 55 (for example, 17 balls) for one round of the circulation path are inserted into the rotation nut 53, and these balls 55 are guided to the circulation path with tweezers.

[0006]

However, in such a ball screw mechanism, the ball 55 is not attached to the non-circulating portion 59 during assembly.
May be mixed. If the ball 55 is used with the ball 55 mixed in the non-circulating portion 59, there is a risk that the rolling path of the ball 55 is broken and the ball screw is locked.
Therefore, in the assembly of such a piece-type ball screw mechanism, in the above-described operation of inserting the ball 55, the operator visually pays attention so that the ball 55 does not enter the non-circulation portion 59, or moves the ball 55 to the rolling path. They manage the number of balls to put. However, such management and caution during operation alone cannot completely prevent the ball 55 from being mixed into the non-circulating portion 59, and it is difficult to sufficiently avoid the risk of locking the ball screw. .

An object of the present invention is to provide a ball screw capable of reliably preventing balls from being mixed into a non-circulating portion during assembly, and an electric power steering device including the same.

[0008]

A ball screw according to the present invention comprises: a ball screw shaft; a rotating nut having an inner thread groove on an inner periphery opposed to the ball screw shaft; And a plurality of balls for transmitting a force between the rotary nut and the ball screw shaft, which are arranged in series with the rolling path formed between the rotary nut and the internal screw grooves connected to the rotary nut. A plurality of bridge members having a connection groove, and a padding for filling this portion is disposed in a non-circulating portion of the rolling path, which is sandwiched between the bridge members and does not circulate the ball. According to this configuration, since the padding is disposed in the non-circulating portion, the padding prevents the ball from being mixed into the non-circulating portion of the internal thread groove during the operation of inserting the ball into the rolling path during assembly. You. Therefore, the balls are not mixed into the non-circulating portion due to an assembly error or the like, and locking of the ball screw caused by the balls mixed in the non-lubricating portion is reliably prevented.

In the present invention, the padding may be formed in a shape substantially equal to the shape of the non-circulating portion, and may be formed of a separate elastic member elastically mounted between the piece members. As described above, since the padding is a member separate from the rotating nut, it is not necessary to process a portion corresponding to the padding on the rotating nut, and the rotating nut is the same as a general ball screw rotating nut without padding. I'm done. Further, since the padding is formed in a shape substantially equal to the shape of the non-circulating portion and is elastically mounted between the bridge members, the operation of mounting the padding on the rotating nut can be easily performed.

In the present invention, the arm member is provided with an arm which engages with the internal thread groove of the rotary nut to position the arm member in the axial direction with respect to the rotary nut. You may fill it. The positioning arm of the bridge member is for ensuring the positioning of the bridge member in the axial direction. In this way, by using the positioning arm as a padding for filling the non-circulating portion, it is only necessary to form the positioning arm longer than usual. Can also be reduced.

[0011] The piece member may be fitted into a piece member opening formed in the rotary nut from the inside of the rotary nut. In this way, by adopting a configuration in which the piece is fitted from the inside, the piece member can be easily fixed without the need for retaining.

The piece member may have a plurality of the connection grooves. As described above, by forming a plurality of connecting grooves in one piece member, the pitch of the inner thread grooves can be reduced as compared with the case where a piece member is provided for each connecting groove. Therefore, the number of circulating balls can be increased and the load capacity can be increased without increasing the axial length of the rotating nut.

[0013] The piece member may be formed of a sintered alloy. When the bridge member is made of a sintered alloy, it can be manufactured by molding and sintering by injection molding or the like. Therefore, machining such as turning and grinding is unnecessary, and mass productivity is good.
Thereby, inexpensive production is possible.

An electric power steering apparatus according to the present invention converts a rotational force from a handle, a steering shaft connected to a steering mechanism for steering wheels, and a steering wheel into a force for moving the steering shaft in a longitudinal direction. A ball screw whose part of the steering shaft is a ball screw shaft, and an electric motor fitted to a rotating nut of the ball screw. And a ball screw having any one of the above configurations. With this configuration, the ball screw that transmits the output of the electric motor
The safety can be achieved without lock, and the safety and reliability of the electric power steering device are improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the ball screw 20 includes a ball screw shaft 21, a rotating nut 22,
The rotating nut 22 includes a plurality of balls 23, and the rotating nut 22 is configured by attaching a bridge member 24 to a nut main body 22a. The ball screw shaft 21 has an external thread groove 25. Rotating nut 2
2 is provided on the inner periphery of the cylindrical nut body 22a,
It has an inner thread groove 26 facing the outer thread groove 25. The ball 23 is arranged so as to be continuous with a rolling path 27 formed between an outer thread groove 25 of the ball screw shaft 21 and an inner thread groove 26 of the rotating nut 22. The rotating nut 22 has a rough surface portion 29 formed by knurling or the like on a part of the outer circumferential surface in a circumferential direction, and is used for coupling to a motor rotor or the like.

The piece member 24 is a member provided with a connecting groove 28 for connecting adjacent one peripheral portions of the inner screw groove 26. A plurality of connecting grooves 28 are provided in one piece member 24.
Each of the connection grooves 28 connects one circumferential portion of the inner thread groove 26 which is different from each other. In this embodiment,
One adjacent circumferential portion of the inner screw groove 26 is connected to each other by a connecting groove 28. The inner thread groove 26 of the rotating nut 22 is connected by a connection groove 28 to form one continuous circuit path (circulation portion). Accordingly, the inner thread groove 26 of the rotating nut 22 is separated into a plurality of circumferential paths (circulating portions) within the axial length where the bridge member 24 is provided. The depth of each connection groove 28 is set so that the ball 23 can exceed the thread of the external thread groove 25 of the ball screw shaft 21 in the connection groove 28.

The bridge member 24 is attached to the nut body 22a at two locations spaced apart in the axial direction.
Are circumferentially spaced from each other by 180 °. The number of the connection grooves 28 of the two piece members 24 may be different from each other. In FIG. 1, three connecting grooves 28 are provided for one piece member 24, and two connecting grooves 28 are provided for the other piece member 24. One rotating nut 2
The number of the piece members 24 provided in 2 may be three or more.

FIG. 2 is a developed view showing the inner diameter side of the rotating nut 22, and FIG. 3 is an exploded perspective view showing a half of the rotating nut 22 in cross section. Nut body 22a of rotating nut 22
The opening 30 for the bridge member is provided through the inner and outer peripheral surfaces, and the bridge member 24 is fitted into the opening 30 from the inner diameter side.

The bridge member 24 has a pair of arms 31, 31 which engage with the internal thread groove 26 of the rotary nut 22 to position the bridge member 24 in the axial direction with respect to the nut body 22a of the rotary nut 22. ing. These arms 31, 31
Are provided at both ends in the axial direction of the piece member 24 so as to protrude in opposite directions in the circumferential direction. Each arm 31 is formed in a semicircular cross-sectional shape that fits into the internal thread groove 26. In addition, the cross-sectional shape of the inner and outer thread grooves 25 and 26 is specifically a Gothic arch shape.

As shown in FIG. 1 (C), a pair of guide walls 36 rising to the outer diameter side are provided on both side edges in the circumferential direction of the rotating nut of the piece member 24 along the side face of the piece member 24 facing the circumferential direction. It is provided. The guide walls 36 elastically contact a pair of inner side surfaces of the nut body 22a facing the opening 30 for the bridge member. These guide walls 36
Are engaged with the opening edge of the opening 30 for the piece member. The piece member 24 is fitted into the piece member opening 30 of the nut main body 22a from the inner diameter side, the pair of arms 31 is fitted into the inner screw groove 26, and the tip end of the guide wall 36 is connected to the piece member opening 30. By engaging with the opening edge, it is fixed to the nut main body 22a.

The material of the bridge member 24 may be a sintered alloy. When the bridge member 24 is made of a sintered alloy, it may be manufactured by the following metal injection molding in addition to the normal manufacturing method. In the case of metal injection molding, it is performed by adjusting a metal powder to a plastic shape and molding it with an injection molding machine. At the time of this injection molding, first, a metal powder and a binder made of plastic and wax are kneaded by a kneader, and the kneaded product is granulated into pellets. The granulated pellets are supplied to a hopper of an injection molding machine, and are molded by being pressed into a mold in a heated and molten state. The metal powder is preferably a material that can be later carburized and quenched. For example, carbon (C) is 0.3% and nickel (Ni) is 1-2.
%, The balance being iron (Fe). The nut main body 22a of the rotary nut 22 may be made of a sintered alloy as in the case of the bridge member 24.

A portion of the rolling path 27 formed between the inner and outer thread grooves 25 and 26 in which each piece member 24 of an adjacent orbiting path (circulating portion) is arranged adjacently in the circumferential direction (FIG. 2). In the development view of the inner thread groove 26 shown in FIG. 2, a portion sandwiched between one arm 31 of one piece member 24 and one arm 31 of the other piece member 24 adjacent to this piece member 24) is a ball 23 Is a non-circulating portion 32 that does not circulate. The portion inside the inner thread groove 26 of the non-circulating portion 32 is filled by arranging a padding 33 separate from the nut main body 22a.
The padding 33 is made of an elastic member such as a synthetic resin having a semicircular cross-sectional shape substantially equal to the cross-sectional shape of the internal thread groove 26, and is elastically attached to the internal thread groove 26 in the non-circulating portion 32. The padding 33 may be made of a member having flexibility, that is, a member that is easily plastically deformed, instead of the elastic member. Further, the padding 33 may be linear in its natural state, or may be formed in an arcuate curved state corresponding to the curvature of the internal thread groove 26. Since the padding 33 is made of an elastic member or a flexible member, the padding 33 can be fitted in the internal thread groove 26 even if it is linear as described above.

According to the ball screw 20 of this configuration, two of the rolling paths 27 formed by the inner and outer thread grooves 25 and 26 are formed.
Since the padding 33 is arranged in the non-circulating portion 32 which is a portion where the ball does not circulate between the two piece members 24, the ball 23 is mixed into the non-circulating portion 32 in the operation of inserting the ball 23 into the rolling path 27 at the time of assembly. I won't. Therefore, it is possible to reliably prevent the ball screw 20 from being locked due to the mixing of the ball 23 into the non-circulating portion 32. Further, since the padding 33 is formed in a shape substantially equal to the shape of the non-circulating portion 32 and is made of a separate elastic member elastically attached to the non-circulating portion 32, the non-circulating portion 3
2 can be easily arranged.

Further, since the piece member 24 is fitted from the inside of the rotating nut 22 into the opening 30 for the piece member formed in the rotating nut 22, the piece member 24 is not required to be prevented from coming off. Nut body 22
It can be easily fixed to a. This piece member 24 is connected to a connecting groove 28.
, The pitch of the internal thread groove 26 can be reduced, and therefore the number of circulating balls can be increased without increasing the length of the rotating nut 22, and the load capacity can be increased. Further, since the bridge member 24 is made of a sintered alloy, it can be manufactured by molding and sintering such as injection molding, so that machining such as turning or grinding is unnecessary, and mass productivity is good. Thereby, inexpensive production is possible.

FIG. 4 is an exploded view of a rotary nut in a ball screw according to another embodiment of the present invention. The ball screw 20 of this embodiment is different from the ball screw 20 of the first embodiment in that the positioning arm 31 provided on the piece member 24 in the first embodiment (the embodiment of FIGS. 1 to 3) is elongated. 33, the non-circulating portion 3 in the rolling path 27
The inner thread groove 26 side of the arm 2 is filled with the arm 31. The length of the positioning arm 31 is such that the leading ends of the positioning arms 31 of the adjacent piece members 24 are in contact with each other or close to each other so as to form a gap smaller than the ball diameter.

In the case of this configuration as well, during the operation of inserting the ball 23 into the rolling path 27 at the time of assembly, the ball 23 does not enter the non-circulating section 32 in the rolling path 27, The locking of the ball screw 20 due to the mixing of the ball 23 with the ball screw 20 can be reliably prevented. Further, a positioning arm 31 provided on the piece member 24.
Is also used as the filling to fill the non-circulating portion 32, so that the number of parts is reduced and the number of assembly steps is reduced.

FIGS. 5 and 6 show a ball screw according to still another embodiment of the present invention. The ball screw 20 of this embodiment is the first embodiment (the embodiment of FIGS. 1 to 3).
, Each piece member 24 has one connecting groove 28. Piece member 2 in this embodiment
4 has no positioning arm as in the case of the first embodiment, but is entirely elliptical, and is provided with the same elliptical piece member opening 30 formed in the rotary nut 22 and the outer side of the rotary nut 22. It is fitted and fixed from the radial side.

FIG. 6 is a development view of the rotating nut 22 on the inner diameter side.
As shown in the figure, two of the rolling members 27 formed of the inner and outer thread grooves 25 and 26 are arranged adjacently in the circumferential direction.
As in the first embodiment, a padding 33 made of an elastic member such as a synthetic resin or a flexible member is elastically mounted on the inner thread groove 26 side of the non-circulating portion 32 sandwiched between the four. Other configurations in this embodiment are the same as those in the first embodiment.

Also in this configuration, the balls 23 are not mixed into the non-circulating portion 32 in the rolling path 27 during the operation of inserting the ball into the rolling path 27 at the time of assembly. Ball screw 2 due to mixing of ball 23
0 can be reliably prevented from being locked.

FIGS. 7 and 8 show a ball screw according to still another embodiment of the present invention. As shown in FIGS. 5 and 6, in the ball screw 20 of this embodiment, in the ball screw in which each piece member 24 has only one connection groove 28, each piece member 24 is provided with an arm 31 serving as a padding. It is provided. That is, the piece member 24 has a pair of arms 31 fitted into the inner thread groove 26 of the rotating nut 22 as shown in FIG. This arm 31 allows the rolling path 2
7, the inner thread groove 26 side of the non-circulating portion 32 sandwiched between two adjacent piece members 24 is filled. The tips of the arms 31 of the two adjacent piece members 24 are in contact with each other or are close to each other. Other configurations in this embodiment are the same as those in the first embodiment. Arm 31
May be used for positioning the piece member 24 in the axial direction with respect to the nut main body 22a, or may not have a positioning function.

Also in this configuration, the balls 23 are not mixed into the non-circulating portion 32 of the rolling path 27 during the operation of inserting the ball into the rolling path 27 at the time of assembly. Ball screw 2 due to mixing of ball 23
0 can be reliably prevented from being locked. Further, since the non-circulating portion 32 is filled with the arm 31 provided at one end of the piece member 24, the number of parts is reduced, and the assembling work is facilitated.

Next, an example of an electric power steering apparatus provided with the ball screw 20 will be described. FIG.
It is a fracture side view of this electric power steering device.
In FIG. 1, a housing 1 has a bracket (not shown) and is fixed to a vehicle body. A steering shaft 2 penetrates through the housing 1, and tie rods 3 and 4 are connected to both ends of the steering shaft 2. The tie rods 3 and 4 are connected to a steering mechanism (not shown) that steers wheels. A handle shaft 5 is provided so as to extend obliquely upward from the vicinity of one end of the housing 1, and the handle is connected to the upper end of the handle shaft 5. The handle shaft 5 is rotatably supported,
The rotation of the handle shaft 5 is transmitted from its lower end to the steering shaft 2 via the conversion mechanism 6 as an axial moving force. The conversion mechanism 6 includes a rack 7 formed by a part of the steering shaft 2 in the longitudinal direction, and a pinion (not shown) provided at a lower end of the handle shaft 5. Engage with 7. The steering shaft 5 is provided with a steering torque detector (not shown) for detecting the steering torque.

The housing 1 is formed in a cylindrical shape, and is formed by connecting end members 1b and 1c to both ends of a central cylindrical body 1a. A stator 9 of the electric motor 8 is provided at a central portion of the housing 1 in the axial direction. Stator 9 includes a core and a stator coil. On the inner peripheral side of the stator 9, a rotor 10 of the electric motor 8 is provided via a gap. The rotor 10 is formed in a cylindrical shape by a magnetic material, and is attached to the outer periphery of the sleeve 11 so as to rotate integrally with the sleeve 11. The steering shaft 2 is inserted into the sleeve 11 so as to be movable in the axial direction. The electric motor 8 is controlled by a motor control circuit (not shown) according to the detection value of the steering torque detector.

One end of the sleeve 11, in this example, the end on the handle shaft 5 side is rotatably supported in the housing 1 by a bearing 12. The bearing 12 may be a single bearing or a combination of a plurality of bearings, and can support a radial load and a thrust load as a whole.

The rotation of the electric motor 8 is transmitted to the steering shaft 2 via the ball screw 20 as a force for moving the steering shaft 2 in the axial direction. The ball screw 20 is such that a part of the steering shaft 2 in the axial direction becomes a ball screw shaft 21. The outer diameter of the rotating nut 22 of the ball screw 20 is the bearing 16 and the housing 1
The rotor 1 of the electric motor 8 is rotatably supported in the
0 is fitted to the outer diameter surface. An end of the rotor 10 on the side of the rotating nut 22 protrudes from the sleeve 11, and this protruding portion is fitted to the rotating nut 22. Also,
The rotating nut 22 has a rough surface portion 29 on the outer diameter surface as described above.
(FIG. 1A), and the rough surface portion 29 is fitted to the inner diameter surface of the rotor 10. The bearing 16 may be a single bearing or a combination of a plurality of bearings, and can support a radial load and a thrust load as a whole. As the bearing 16, for example, a rolling bearing such as an angular ball bearing is used, and has an inner ring, an outer ring, and a rolling element interposed between the two rings.

The operation and operation of the above configuration will be described. When the vehicle is running straight and the rotation of the steering wheel is stopped, no torque signal is output from the steering torque detector (not shown) of the steering shaft 5, and the electric motor is controlled by the motor control means (not shown). Reference numeral 8 denotes a rotation stop state. Therefore, this electric power steering device is in a state of not outputting the auxiliary steering force. When the steering wheel is steered, a torque signal is output from the steering torque detector of the handle shaft 5, and the electric motor 8 rotates the rotor 10 under the control of the motor control circuit. When the rotor 10 rotates, the rotation nut 22 of the ball screw 20 rotates together with the rotor 10,
The hitting shaft 2, which is partially constituted by the ball screw shaft 21, is moved in the axial direction, and a sail steering force is generated. At this time, the ball 23 of the ball screw 20 rolls in the rolling path formed between the inner and outer screw grooves 25 and 26 with the rotation of the rotating nut 22. In this way, the steering force of the steering wheel is supplemented by the electric motor 8.

In this electric power steering apparatus, since the ball screw 20 for transmitting the motor output, which is a main component, has the above-described structure, the occurrence of lock in the ball screw can be prevented, and the electric power steering apparatus can be prevented. The safety of the device can be improved.

[0038]

According to the ball screw of the present invention, a non-circulating portion of the rolling path, which is sandwiched between the bridge members and does not circulate the ball,
Since the padding that fills the non-circulating portion is arranged, the ball is not mixed into the non-circulating portion of the rolling path during the operation of inserting the ball into the rolling path at the time of assembling. Locking of the ball screw due to the mixing of the ball screw can be reliably prevented. In the case where the padding is formed in a shape substantially equal to the shape of the non-circulating portion and is made of a separate elastic member elastically mounted between the bridge members, the padding can be easily arranged in the non-circulating portion. . When the piece member is provided with an arm that engages with the internal thread groove of the rotating nut and positions the piece member in the axial direction with respect to the rotating nut, and this arm fills the non-circulating portion, Since the non-circulating portion is filled with the positioning arm provided on the member, the number of components is reduced, and the assembling work is also facilitated. The piece member is
In a case where the piece is fitted into the opening for the piece member formed in the rotating nut from the inside of the rotating nut, the piece member can be easily fixed without the need for retaining. When the link member has a plurality of connecting grooves, the pitch of the internal thread grooves can be reduced, so that the number of circulating balls can be increased without increasing the length of the rotating nut, thereby increasing the load capacity. Can be. When the bridge member is formed of a sintered alloy, it can be manufactured by molding and sintering such as injection molding, and machining such as turning and grinding is not required, and mass productivity is good.
Inexpensive production is possible. Since the electric power steering device of the present invention uses the ball screw of the present invention as the ball screw for transmitting the output of the electric motor, it is possible to prevent the locking of the ball screw and to make the electric power steering device safer.

[Brief description of the drawings]

FIGS. 1A to 1C are a front view, a cross-sectional view, and a perspective view of a bridge member of a ball screw according to an embodiment of the present invention, respectively.

FIG. 2 is a development view showing an inner diameter side of a rotating nut in the ball screw.

FIG. 3 is an exploded perspective view showing a half portion of the rotary nut.

FIG. 4 is a development view showing an inner diameter side of a rotating nut in a ball screw according to another embodiment of the present invention.

FIGS. 5A and 5B are a front view and a sectional view of a ball screw according to still another embodiment of the present invention, respectively.

FIG. 6 is a development view showing an inner diameter side of a rotating nut in the ball screw.

FIG. 7 is a developed view showing an inner diameter side of a rotating nut in a ball screw according to still another embodiment of the present invention.

FIGS. 8A to 8D are a rear view, a side view, a front view, and an arm end view of a bridge member in the ball screw, respectively.

FIG. 9 is a cutaway front view of the electric power steering device according to the embodiment of the present invention.

FIG. 10 is a sectional view of a conventional ball screw.

FIG. 11 is a development view showing an inner diameter side of a rotating nut in the ball screw.

FIG. 12 is an explanatory diagram of a ball inserting operation at the time of assembling the ball screw.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Housing 2 ... Steering axis 5 ... Handle axis 6 ... Conversion mechanism 7 ... Rack 8 ... Electric motor 9 ... Stator 10 ... Rotor 11 ... Sleeve 20 ... Ball screw 21 ... Ball screw shaft 22 ... Rotating nut 23 ... Ball 24 ... Piece Member 25 ... Outer thread groove 26 ... Inner thread groove 27 ... Rolling path 28 ... Connecting groove 30 ... Opening for piece member 31 ... Arm 32 ... Non-circulating part 33 ... Filling

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kiyotake Shibata 1578 Higashikaizuka, Iwata-shi, Shizuoka F-term in NTN Corporation (reference) 3D033 CA04 3J062 AA07 AB22 AC07 BA01 CD04 CD07 CD54

Claims (7)

[Claims] 1. A ball screw shaft, a rotating nut opposed to the ball screw shaft and having an inner thread groove on an inner periphery, and a rolling path formed between the ball screw shaft and the inner screw groove. A plurality of balls for transmitting a force between the rotating nut and the ball screw shaft, and a plurality of bridge members attached to the rotating nut and having a connecting groove for connecting the inner screw grooves to each other. The ball screw according to claim 1, wherein a padding for filling the non-circulating portion is arranged in a non-circulating portion of the rolling path, which is interposed between the bridge members and does not circulate the ball. 2. The ball screw according to claim 1, wherein the padding is formed in a shape substantially equal to the shape of the non-circulating portion, and is made of a separate elastic member elastically mounted between the piece members. 3. An arm for engaging the inner thread groove of the rotary nut and axially positioning the member relative to the rotary nut is provided on the bridge member, and the arm fills the non-circulating portion. The ball screw according to claim 1, wherein: 4. The ball screw according to claim 1, wherein the piece member is fitted into a piece member opening formed in the rotary nut from inside the rotary nut. 5. The ball screw according to claim 1, wherein the piece member has a plurality of the connection grooves. 6. The ball screw according to claim 1, wherein the piece member is formed of a sintered alloy. 7. A steering mechanism connected to a housing, a steering mechanism for steering wheels, a conversion mechanism for converting a rotational force from a steering wheel into a force for moving the steering axis in a longitudinal direction, and the steering mechanism. 7. An electric power steering apparatus comprising: a ball screw having a part of a shaft serving as a ball screw shaft; and an electric motor fitted to a rotation nut of the ball screw. An electric power steering device comprising the ball screw according to any one of the above.