JP2013132988A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of suppressing degrading in the steering feeling of a driver by appropriately disposing an elastic body supporting a cylindrical body, which coaxially rotates with a rack shaft.SOLUTION: The electric power steering device has a resin-made annular elastic body, which is disposed between an inner end face of a housing provided in the axial direction of a bearing and an outer ring of the bearing and supports the cylindrical body so that it is movable in the axial direction relative to the housing. The elastic body is formed so that an inner peripheral part is thinner than an outer peripheral part.

Description

  The present invention relates to an electric power steering apparatus including a cylindrical body that rotates coaxially with a rack shaft.

  Conventionally, in this type of electric power steering device, the rudder angle of the vehicle steering wheel, that is, the traveling direction of the vehicle is changed by reciprocating the rack shaft in the axial direction in conjunction with the steering wheel operation by the driver. It has come to be.

  Some electric power steering apparatuses are provided with an assist force from a motor on a rack shaft. In such an apparatus, a rack shaft is inserted inside, and a ball screw nut having a thread groove formed on the inner periphery is disposed, and is rotated by driving of a motor. A plurality of balls are arranged in a rolling path formed between a thread groove in a ball screw nut as a cylindrical body and a thread groove formed on the outer periphery of the rack shaft. And the rotational motion accompanying the drive of a motor is converted into the linear motion to the axial direction of a rack shaft through a ball screw nut and a plurality of balls.

  Incidentally, in the electric power steering apparatus, a bearing is disposed between the housing and the ball screw nut, and the ball screw nut is held in the housing. Also known is an annular rubber body that is elastically supported so as to be movable (finely movable) with respect to the axial direction of the ball screw nut (see Patent Document 1). It has been attempted to reduce the rattling noise by suppressing the vibration in the axial direction and improve the steering feeling at the start of turning the steering wheel.

JP 2002-145080 A

  However, in such an electric power steering device, for example, the annular rubber body slides inward in the radial direction along with the compression of the annular rubber body in the elastic support mechanism. There is a possibility that the driver's steering feeling may be impaired without being deformed.

  Therefore, the present invention provides an electric power steering apparatus that can suppress a decrease in the steering feeling of the driver by appropriately disposing an elastic body that supports a cylindrical body that rotates coaxially with the rack shaft. There is.

  In order to achieve the above object, the invention described in claim 1 includes a housing, a cylindrical body that is housed in the housing and has a first threaded portion having a first thread groove formed on an inner periphery thereof, and the cylinder. A rack shaft having a second threaded portion that is inserted coaxially with the body into the cylindrical body and has a second threaded groove formed on the outer periphery thereof, and a rolling path constituted by the first threaded groove and the second threaded groove A plurality of balls disposed on the housing, a bearing disposed between an inner peripheral surface of the housing and an outer peripheral surface of the cylindrical body, and supporting the cylindrical body in a radial direction with respect to the housing; An annular elastic body made of resin, which is disposed between an inner end surface of the housing provided in the axial direction of the bearing and an outer ring of the bearing and supports the cylindrical body movably in the axial direction with respect to the housing. And a motor for rotating the cylindrical body. In power steering apparatus, the elastic body, and summarized in that towards the inner periphery is formed thinner than the outer peripheral portion.

  According to the above configuration, the elastic body supports the cylindrical body rotating coaxially with the rack shaft so as to be movable in the axial direction via the bearing, and the inner peripheral portion is formed thinner than the outer peripheral portion. . For this reason, by making the rigidity of the inner peripheral part of the elastic body lower than that of the outer peripheral part, it becomes difficult for the elastic body to move radially inward, and by appropriately arranging the elastic body, the driver's steering feeling is reduced. The decrease can be suppressed.

The gist of the invention according to claim 2 is that, in the electric power steering device according to claim 1, a recess is formed in the inner peripheral surface of the elastic body.
The invention described in claim 3 is summarized in that, in the electric power steering apparatus according to claim 1, a convex portion is formed on the inner peripheral surface of the elastic body.

  According to the present invention, it is possible to suppress a decrease in the driver's steering feeling by appropriately disposing the elastic body that supports the cylindrical body that rotates coaxially with the rack shaft.

The schematic diagram explaining the electric power steering apparatus in 1st Embodiment. Sectional drawing which shows the ball screw mechanism in 1st Embodiment. Sectional drawing which shows the elastic support mechanism in 1st Embodiment. (A) And (b) is sectional drawing which shows the elastic support mechanism in 1st Embodiment. (A) And (b) is sectional drawing which shows the elastic support mechanism in 2nd Embodiment. (A) And (b) is a schematic diagram explaining the elastic body in another embodiment. The schematic diagram explaining the electric power steering device in another embodiment.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, in the electric power steering apparatus 10 as a vehicle steering apparatus, the rotation axis P of the motor shaft 26 rotated by driving the motor 11 is substantially the same as the rotation axis P of the rack shaft 12 as an output member. This is a rack coaxial type device in which the motor 11 is installed. Such an electric power steering apparatus 10 is provided with a steering shaft 14 to which a steering 13 is fixed. The steering shaft 14 is connected to the rack shaft 12 via a rack and pinion mechanism 15. Then, the rotation of the steering shaft 14 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 12 by the rack and pinion mechanism 15.

  The steering shaft 14 of the present embodiment is formed by connecting a column shaft 14a, an intermediate shaft 14b, and a pinion shaft 14c. The reciprocating linear motion of the rack shaft 12 accompanying the rotation of the steering shaft 14 is transmitted to the knuckle (not shown) via the tie rods 16 connected to both ends of the rack shaft 12, so that the steering angle of the steered wheels 17, The traveling direction of the vehicle is changed.

  In addition, the electric power steering apparatus 10 includes a housing 18 into which the rack shaft 12 is inserted, and the motor 11 is attached to the housing 18. The housing 18 accommodates a ball screw mechanism 21 as a conversion mechanism for transmitting a driving force from the motor 11 disposed in the housing 18 to the rack shaft 12. The motor shaft 26 is screwed into the ball screw mechanism 21 at one end thereof, and rotates as a unit by the transmitted rotation.

  The motor 11 is driven according to the movement of the rack shaft 12. That is, the motor 11 is driven according to the rotation of the steering shaft 14. For this reason, the motor 11 is not driven immediately after the operation of the steering 13 is started, and is not particularly driven when the steering angle is small, for example, during high speed traveling.

Here, the ball screw mechanism 21 in the present embodiment will be described below with reference to FIG.
As shown in FIG. 2, the ball screw mechanism 21 includes a sleeve-shaped ball screw nut 31 configured to rotate integrally with the motor shaft 26, and the ball screw nut 31 and the rack shaft in the radial direction centering on the rotation axis P. 12 and a plurality of balls 32 disposed between the two. In the present embodiment, the direction along the rotation axis P is simply indicated as “axial direction”.

  The ball screw nut 31 has a thread groove 31a threaded on the inner periphery thereof. Further, the rack shaft 12 has a screw groove 12a threaded on the outer periphery thereof. The plurality of balls 32 are arranged in a rolling path formed between the screw groove 12 a formed on the outer periphery of the rack shaft 12 and the screw groove 31 a formed on the inner periphery of the ball screw nut 31.

  Thus, the ball screw mechanism 21 is formed by the rack shaft 12 being screwed with the ball screw nut 31 via the ball 32 inserted into the ball screw nut 31. That is, the rack shaft 12 is coaxially inserted into the ball screw nut 31, and the rotation of the ball screw nut 31 is transmitted to the rack shaft 12 as an assisting force via a plurality of balls 32.

  In the present embodiment, the motor shaft 26 and the ball screw nut 31 correspond to a cylindrical body. In the present embodiment, the portion where the screw groove 31a as the first screw groove is formed corresponds to the first screw portion, and the portion where the screw groove 12a as the second screw groove is formed is the second screw portion. Equivalent to.

  The ball screw nut 31 is supported by the housing 18 through a bearing 40 in a rotatable state. The bearing 40 is a ball bearing including an inner ring 41, an outer ring 42, and a spherical rolling element 43 interposed between the inner ring 41 and the outer ring 42.

  The inner ring 41 of the bearing 40 abuts on the ball screw nut 31 on its inner peripheral surface 41a. The inner ring 41 of the bearing 40 contacts the stepped portion 31b formed on the ball screw nut 31 at one end surface 41b with respect to the axial direction, and contacts the nut 33 at the other end surface 41c. The nut 33 is screwed onto the outer periphery of the ball screw nut 31. Thus, the inner ring 41 of the bearing 40 rotatably supports the ball screw nut 31 on its inner peripheral surface 41a.

  Further, the outer ring 42 of the bearing 40 contacts the inner peripheral surface 18a of the housing 18 at the outer peripheral surface 42a. In this embodiment, a groove 18b is formed on the inner peripheral surface 18a of the housing 18 so as to face the outer peripheral surface 42a of the outer ring 42, and an O-ring O1 is disposed in the groove 18b. . In this manner, the O-ring O1 is sandwiched between the groove 18b of the housing 18 and the outer peripheral surface 42a of the outer ring 42.

  Moreover, the outer ring | wheel 42 of the bearing 40 contact | abuts with the elastic support mechanism 50 in each of the both end surfaces 42b and 42c with respect to an axial direction. The elastic support mechanism 50 is composed of a rubber-made annular elastic body 52 and elastically supports the outer ring 42 of the bearing 40 so as to be displaceable in the axial direction. The outer ring 42 of the bearing 40 is provided integrally with the inner ring 41 of the bearing 40 via the rolling elements 43, and the inner ring 41 of the bearing 40 is fixed integrally with the ball screw nut 31. That is, the elastic support mechanism 50 supports the ball screw nut 31 and the motor shaft 26 via the bearing 40 so that they can be displaced in the axial direction.

Further, the motor shaft 26 in the present embodiment will be described below with reference to FIG.
As shown in FIG. 3, the motor shaft 26 is rotatable to the housing 18 via a bearing 45 in the vicinity of the open end 26a opposite to the portion screwed with the ball screw nut 31 (see FIG. 2). It is supported by. The bearing 45 is a reverse ball bearing including an inner ring 46, an outer ring 47, and a spherical rolling element 48 interposed between the inner ring 46 and the outer ring 47.

  The inner ring 46 of the bearing 45 abuts on the motor shaft 26 on its inner peripheral surface 46a. The inner ring 46 of the bearing 45 contacts the nut 34 at one end surface 46b with respect to the axial direction, and contacts the stepped portion 26b formed on the motor shaft 26 at the other end surface 46c. The nut 34 is screwed onto the outer periphery of the motor shaft 26. Thus, the inner ring 46 of the bearing 45 supports the motor shaft 26 rotatably on the inner peripheral surface 46a.

  Further, the outer ring 47 of the bearing 45 is in contact with the inner peripheral surface 18c of the housing 18 at the outer peripheral surface 47a. In the present embodiment, a groove 18d is formed on the inner peripheral surface 18c of the housing 18 so as to face the outer peripheral surface 47a of the outer ring 47, and O-rings O2 and O3 are disposed in the groove 18d. ing. Thus, the O-rings O2 and O3 are sandwiched between the groove 18d of the housing 18 and the outer peripheral surface 47a of the outer ring 47.

  Further, the outer ring 47 of the bearing 45 abuts against the elastic support mechanism 50 at both end faces 47b and 47c with respect to the axial direction. The end surface 47 b of the outer ring 47 of the bearing 45 sandwiches the elastic support mechanism 50 between the inner end surface 18 e of the housing 18, and the end surface 47 c of the outer ring 47 of the bearing 45 is screwed to the inner surface of the housing 18. The elastic support mechanism 50 is sandwiched between the nut 35. Further, the elastic support mechanism 50 is the same mechanism that elastically supports the bearing 40, and thus the description thereof is omitted. The outer ring 47 of the bearing 45 is provided integrally with the inner ring 46 of the bearing 45 via the rolling element 48, and the inner ring 46 of the bearing 45 is fixed integrally with the motor shaft 26. That is, the elastic support mechanism 50 supports the motor shaft 26 via the bearing 45 so as to be displaceable with respect to the axial direction.

  Here, the elastic support mechanism 50 in this embodiment is demonstrated below with reference to FIG. The elastic support mechanism 50 that contacts the end surface 47b of the outer ring 47 of the bearing 45 and the elastic support mechanism 50 that contacts the end surface 47c have the same shape, and the elastic support mechanism 50 of the outer ring 42 of the bearing 40 has the same configuration. It is. Therefore, the elastic support mechanism 50 that contacts the end surface 47b of the outer ring 47 of the bearing 45 will be mainly described, and the description of the elastic support mechanism 50 that contacts the end surface 47c and the elastic support mechanism 50 of the outer ring 42 of the bearing 40 will be omitted. To do.

  As shown in FIG. 4A, an annular step 18 f is formed on the inner end surface 18 e of the housing 18. The step portion 18f is formed on the entire circumference so as to face the end surface 47b of the outer ring 47 of the bearing 45. The inner end face 18e is composed of a first inner end face 18g and a second inner end face 18h.

  In the stepped portion 18f, the second inner end surface 18h is parallel to the first inner end surface 18g, and is formed radially outside and closer to the outer ring 47 of the bearing 45 than the first inner end surface 18g. ing. The inner peripheral surface 18 i of the step portion 18 f is in contact with the outer peripheral surface 52 b of the elastic body 52.

  Further, the second inner end face 18h and the outer ring 47 of the bearing 45 are in contact with the end face 47b of the outer ring 47 of the bearing 45 at one end face 52c of the elastic body 52 and in contact with the first inner end face 18g at the other end face 52d. A gap 53 is formed between the end surface 47b.

  The elastic body 52 in the elastic support mechanism 50 is a member having elasticity, and is a member for enabling the outer ring 47 of the bearing 45 to be displaced in the axial direction. The elastic body 52 has an outer diameter that is slightly smaller than the inner diameter of the inner peripheral surface 18 i of the stepped portion 18 f of the housing 18, and is disposed so as to face the entire periphery of the end surface 47 b of the outer ring 47 of the bearing 45.

  Further, as shown in FIG. 4B, the outer ring 47 of the bearing 45 is movable in the axial direction toward the first inner end face 18g until the end face 47b contacts the second inner end face 18h. In other words, the end surface 47b of the outer ring 47 of the bearing 45 is in contact with the second inner end surface 18h, thereby restricting movement of the bearing 45 and the motor shaft 26 in the axial direction.

  Further, as shown in FIG. 4A, an annular recess 52 e is formed on the inner peripheral surface 52 a of the elastic body 52, and a gap 49 is formed. The recess 52 e is a groove having a rectangular cross section in the radial direction, and is formed on the entire circumference of the inner peripheral surface 52 a of the elastic body 52. The recess 52e makes it difficult for the elastic body 52 to be deformed inward in the radial direction when the elastic body 52 is compressed in the axial direction, and mainly releases the leg portion 52f of the elastic body 52 into the gap 49 to form the elastic body. It is formed so that 52 can be deformed.

  On the other hand, the elastic body 52 has a chamfered portion 52g formed on the outer peripheral surface 52b. The chamfered portion 52g is formed in an annular shape at both ends of the outer peripheral surface 52b, and is formed on the entire outer periphery 52b of the elastic body 52. The chamfered portion 52g is formed to facilitate deformation so that the leg portion 52f of the elastic body 52 escapes into the gap 49 when the elastic body 52 is compressed in the axial direction.

  Further, in the elastic body 52, the width in which the concave portion 52e is formed is longer than the width in which the chamfered portion 52g is formed. That is, in the elastic body 52, the inner peripheral portion 52h near the inner peripheral surface 52a (inner peripheral edge) is formed thinner than the outer peripheral portion 52i near the outer peripheral surface 52b (outer peripheral edge), and the rigidity is reduced. In the present embodiment, the elastic body 52 is not bonded to the housing 18 or the outer ring 47 of the bearing 45 by an adhesive.

(Operation of the embodiment)
Here, the operation of the electric power steering apparatus 10 configured as described above will be described.

  First, in the electric power steering apparatus 10, the motor shaft 26 of the motor 11 is screwed into the ball screw nut 31. The ball screw nut 31 is supported with respect to the housing 18 by the inner peripheral surface 41 a of the inner ring 41 of the bearing 40.

  The inner ring 41 of the bearing 40 abuts on the stepped portion 31b formed on the ball screw nut 31 at one end surface 41b and abuts on the nut 33 on the other end surface 41c, so that it can rotate together with the ball screw nut 31 and the motor shaft 26. It is arranged. The outer ring 42 of the bearing 40 has an outer peripheral surface 42 a abutting against the inner peripheral surface 18 a of the housing 18, and is elastically supported by the elastic support mechanism 50 at both end surfaces 42 b and 42 c.

  The motor shaft 26 is supported with respect to the housing 18 by an inner peripheral surface 46 a of the inner ring 46 of the bearing 45. Further, the inner ring 46 of the bearing 45 abuts on the nut 34 at one end face 46b and abuts on the stepped portion 26b formed on the motor shaft 26 at the other end face 41c, so that the inner ring 46 can be rotated together with the motor shaft 26. The The outer ring 47 of the bearing 45 has an outer peripheral surface 47 a abutting against the inner peripheral surface 18 c of the housing 18, and is elastically supported by the elastic support mechanism 50 at both end surfaces 47 b and 47 c.

  The elastic support mechanism 50 that elastically supports the end face 47b of the outer ring 47 of the bearing 45 will be described as a representative. The elastic body 52 of the elastic support mechanism 50 has one end face 52c on the end face 47b of the outer ring 47 of the bearing 45 and the other end face. 52d contacts the first inner end face 18g. The outer ring 47 of the bearing 45 is elastically supported from the axial direction by the elastic body 52 without contacting the second inner end face 18h at the end face 47b.

  When the steering wheel 13 is operated by the driver, the rotational motion is transmitted to the rack and pinion mechanism 15 via the steering shaft 14, and further the reciprocating linear motion of the rack shaft 12 is performed.

  Thus, the motor 11 is not driven at the so-called turning start timing at which the operation of the steering wheel 13 has just started. For this reason, the rack shaft 12 reciprocates linearly by the operation of the steering wheel 13 by the driver in the state where the assist force of the rack shaft 12 is not applied.

  When the reciprocating linear motion of the rack shaft 12 is performed, friction is generated between the plurality of balls 32 arranged in the thread grooves 12 a formed on the outer periphery of the rack shaft 12. Accordingly, friction occurs between the plurality of balls 32 and the ball screw nut 31, between the ball screw nut 31 and the bearing 40, and between the bearing 40 and the elastic support mechanism 50. Further, friction also occurs between the ball screw nut 31 and the motor shaft 26, between the motor shaft 26 and the bearing 45, and between the bearing 45 and the elastic support mechanism 50.

  The elastic support mechanism 50 that elastically supports the end face 47b of the outer ring 47 of the bearing 45 will be described as a representative. The elastic body 52 of the elastic support mechanism 50 is subjected to a force in the axial direction in which the rack shaft 12 performs a reciprocating linear motion. Is transmitted from the end face 47 b of the outer ring 47. The elastic body 52 in contact with the first inner end face 18g is deformed by being compressed in the axial direction, and the outer ring 47 of the bearing 45 moves in the axial direction.

  Thus, when the outer ring 47 of the bearing 45 moves in the axial direction, the inner ring 46 and the motor shaft 26 of the bearing 45 mainly move in the axial direction in which the rack shaft 12 performs a reciprocating linear motion. For this reason, at the timing of starting the turning of the steering wheel 13, the frictional force according to the reciprocating linear motion of the rack shaft 12 is reduced, thereby improving the driver's steering feeling and suppressing the rattling noise.

  Further, even when the elastic body 52 is compressed in the axial direction, a concave portion 52e is formed on the inner peripheral surface 52a thereof, and the inner peripheral portion 52h has lower rigidity than the outer peripheral portion 54i. Therefore, the elastic body 52 is prevented from coming off in the radial direction. Furthermore, even when the elastic body 52 is compressed in the axial direction, since the recess 52e is formed, the elastic body 52 escapes the leg portion 52f of the elastic body 52 into the gap 49 or the like in the recess 52e. Can be easily deformed. The elastic body 52 has a chamfered portion 52g formed at the end of the outer peripheral surface 52b. For this reason, the leg part 52f of the elastic body 52 is easy to escape to the clearance 49 etc. in the recessed part 52e, and the elastic body 52 becomes easy to deform | transform.

  The end surface 47b of the outer ring 47 of the bearing 45 does not contact the second inner end surface 18h when the elastic body 52 is not compressed in the axial direction with a predetermined load, but the elastic body 52 has a predetermined load in the axial direction. In the case of being compressed by the contact, it abuts on the second inner end face 18h. For this reason, the outer ring 47 of the bearing 45 restricts the movement of the bearing 45 itself and the motor shaft 26 in the axial direction. This prevents a large load from being applied to the elastic body 52.

  Thus, when the reciprocating linear motion of the rack shaft 12 is started, the motor shaft 26 is rotated in a direction to assist the reciprocating linear motion of the rack shaft 12 by driving the motor 11. When the motor shaft 26 rotates, the ball screw nut 31 rotates, and assist force is applied to the reciprocating linear motion of the rack shaft 12 via the plurality of balls 32.

(Effect of embodiment)
As described above in detail, the present embodiment has the following effects.
(1) The elastic body 52 includes a ball screw nut 31 and a motor shaft 26 (cylindrical body) that rotate coaxially with the rack shaft 12 in the axial direction (direction along the rotation axis P) via the bearings 40 and 45. It is elastically supported so that it can move. Further, the elastic body 52 is formed such that the inner peripheral portion 52h is thinner than the outer peripheral portion 52i. For this reason, by making the rigidity of the inner peripheral portion 52h of the elastic body 52 lower than that of the outer peripheral portion 52i and making a difference in the rigidity of the elastic body 52, the elastic body 52 becomes difficult to move inward in the radial direction. By appropriately arranging the body 52, it is possible to suppress a decrease in the driver's steering feeling.

  (2) A recess 52e is formed on the inner peripheral surface 52a of the elastic body 52. For this reason, the leg part 52f of the elastic body 52 can be smoothly escaped to the gap 49 in the recessed part 52e, and the elastic body 52 can be smoothly deformed.

  (3) Chamfered portions 52g are formed at both ends of the outer peripheral surface 52b of the elastic body 52. For this reason, the leg part 52f of the elastic body 52 can escape to the clearance gap 49 in the recessed part 52e, and can make the elastic body 52 easy to deform | transform.

  (4) The elastic body 52 is formed such that the inner peripheral portion 52h is thinner than the outer peripheral portion 52i, so that the elastic body 52 is not bonded to the outer ring 47 or the first inner end face 18g of the bearing 45 with an adhesive. The elastic body 52 is configured so as not to come off inward in the radial direction. For this reason. Curing of the elastic body by the adhesive can be prevented. Further, the bonding step can be omitted, and the number of steps during assembly can be relatively reduced.

(Second Embodiment)
Next, a second embodiment embodying the present invention will be described below. In the following description, the same components as those in the first embodiment described above are denoted by the same reference numerals, and redundant description thereof is omitted or simplified.

  In the first embodiment, the recess 52e is formed on the inner peripheral surface 52a of the elastic body 52, so that the inner peripheral portion 52h of the elastic body 52 is formed thinner than the outer peripheral portion 52i. On the other hand, in 2nd Embodiment, as shown in FIG. 5, the convex part 54e is formed in the inner periphery 54a of the elastic body 54 in the elastic support mechanism 60, and thereby the inner peripheral part 54h of the elastic body 54 is changed. It was formed thinner than the outer peripheral portion 54i.

  Specifically, as shown in FIG. 5A, the elastic body 54 has a convex portion 54e formed on the inner periphery 54a thereof. The convex portion 54e has a circular cross section in the radial direction. In addition, irregularities are not formed on the outer peripheral surface 54 b of the elastic body 54. For this reason, the elastic body 54 has a lower rigidity in the inner peripheral portion 54h than in the outer peripheral portion 54i, and is deformed and elastic as shown in FIG. 5B by being compressed in the axial direction. The body 52 is prevented from coming off inward in the radial direction.

In addition, the said embodiment can be embodied in another embodiment (another example) as follows.
-In 1st Embodiment, in order to make the inner peripheral part 52h of the elastic body 52 thin, the recessed part 52e was formed so that the inner peripheral surface 52a might be faced. However, the present invention is not limited to this. For example, as shown in FIG. 6A, the hollow portion 55b that does not face the inner peripheral surface 55a is formed in the inner peripheral portion 55h, and the inner peripheral portion 55h is formed. You may use the elastic body 55 formed thinner than the outer peripheral part 55i.

  -In 2nd Embodiment, in order to make the inner peripheral part 54h of the elastic body 54 thin, the convex part 54e where the cross section of a radial direction is circular arc shape was formed in the inner periphery 54a. However, the present invention is not limited thereto, and as shown in FIG. 6B, a convex portion 56e having a trapezoidal cross section in the radial direction is formed on the inner peripheral surface 56a, and the inner peripheral portion 56h is formed thinner than the outer peripheral portion 56i. The formed elastic body 56 may be used.

  In the above embodiment, the concave portions 52e and the convex portions 54e in the elastic bodies 52 and 54 are formed on the entire circumference of the inner circumferential surface 52a and the inner circumference 54a of the elastic body 52. It may be formed in a part thereof. Moreover, it may be continuously provided only in a part of the entire circumference, or may be formed at predetermined intervals.

  In the above embodiment, the movement in the axial direction is restricted by the second inner end face 18h arranged on the outer side in the radial direction of the elastic bodies 52, 54. You may restrict | limit by the inner side end surface of the housing arrange | positioned radially inside, and of course you may restrict | limit by both. Although not limited to this case, a member (for example, a housing) that restricts the movement of the elastic bodies 52 and 54 in the radial direction is in contact with the inside of the elastic bodies 52 and 54 in the radial direction. Also good.

  In the above embodiment, the elastic body 52 is disposed between the inner end surface 18e (first inner end surface 18g) of the housing 18 and the end surface 47b of the outer ring 47 of the bearing 45. Even if it is other than the housing 18, the elastic body 52 may be disposed between the inner end surface of the center nut 35 and the end surface 47 b of the outer ring 47 of the bearing 45. The center nut 35 is screwed to the inner peripheral surface and the inner end surface of the housing 18 and is disposed integrally with the housing 18. That is, a member such as a center nut is also included in the housing in the claims.

  In the above embodiment, the elastic body 52 is not bonded to the elastic body 52 with an adhesive or the like. However, the present invention is not limited to this. For example, the elastic body 52 may be bonded to the housing 18 or the bearing 45 with an adhesive or the like. . As described above, even when an adhesive is used, there is a possibility that the elastic body may be peeled off with the passage of time. However, by constituting as in the above embodiment, the adhesive is peeled off. Even if it exists, drop-off | omission of an elastic body can be suppressed.

  In the above embodiment, the thread groove 31a is formed in the entire inner periphery of the ball screw nut 31. However, the present invention is not limited to this, and for example, a thread groove is formed in a part of the inner periphery of the ball screw nut 31. May be. Moreover, in the said embodiment, although the thread groove 12a was formed in the one part area | region of the outer periphery of the rack shaft 12, it is not restricted to this, For example, a thread groove may be formed in the whole region of the outer periphery of the rack shaft 12. .

  In the above embodiment, the present invention is applied to the bearing 40 in the vicinity of the ball screw nut 31 to which the motor shaft 26 is screwed and the bearing 45 in the vicinity of the open end 26a of the motor shaft 26. However, the present invention is not limited thereto. For example, if other bearings such as a bearing in the vicinity of the central portion of the motor shaft 26 are provided, it is preferable to apply the present invention.

  In the embodiment described above, the ball screw nut 31 itself is slidably supported by the bearing 40. However, the present invention is not limited to this. For example, the motor shaft 26 is slidably supported by the bearing, and the ball screw nut 31 is You may support it indirectly.

  In the above embodiment, the present invention may be adopted in a rack parallel type electric power steering device. Specifically, in the rack parallel type electric power steering apparatus, as shown in FIG. 7, a motor shaft MZ that rotates by driving of a motor 70 is disposed, and the rotation axis P1 of the motor shaft MZ is a rack shaft. The motor shaft MZ is disposed so as to be parallel to the twelve rotation axis P2. A drive pulley 72 as a speed reduction mechanism 71 is fixed to the motor shaft MZ. A belt 73 is hung on the drive pulley 72 together with a driven pulley 74 fixed to a ball screw nut 75. Thus, the motor shaft MZ is rotated by driving the motor 70, and the rotational motion is transmitted to the drive pulley 72, the belt 73, the driven pulley 74, and the ball screw nut 75. In this case, the ball screw nut 31 and the driven pulley 74 correspond to a cylindrical body. An intermediate pulley may be provided in place of the belt 73.

In the above embodiment, the bearing 40 may be a roller bearing that employs a roller as a rolling element.
Next, a technical idea that can be grasped from the above embodiment and another example will be added below.

  (A) The electric power steering apparatus according to any one of claims 1 to 3, wherein an outer peripheral surface of the elastic body is in contact with an inner peripheral surface of the housing.

(B) The electric power steering device according to claim 2, wherein chamfered portions are formed at both ends of the outer peripheral surface of the elastic body.
(C) The electric power steering device according to claim 3, wherein the convex portion has an arc shape.

  (D) In the electric power steering device according to any one of claims 1 to 3, (a), and (b), the inner ring of the housing may move the outer ring of the bearing within a predetermined range. An electric power steering device characterized in that a restriction surface for restriction is formed.

  MZ, 26 ... motor shaft, O1-O3 ... O-ring, P, P1, P2 ... rotation axis, 10 ... electric power steering device, 11, 70 ... motor, 12 ... Rack shaft, 12a, 31a ... thread groove, 13 ... steering, 14 ... steering shaft, 14a ... column shaft, 14b ... intermediate shaft, 14c ... pinion shaft, 15 ... -Rack and pinion mechanism, 16 ... tie rod, 17 ... steered wheel, 18 ... housing, 18a, 18c, 18i, 41a, 46a, 52a, 55a, 56a ... inner peripheral surface, 18b, 18d ... groove, 18e ... inner end face, 18f, 26b, 31b ... stepped part, 18g ... first inner end face, 18h ... second inner end face, 21 ... Ball screw mechanism, 26a ... open end, 31, 75 ... ball screw nut, 32 ... ball, 33, 34 ... nut, 35 ... center nut, 40, 45 ... bearing, 41, 46 ... inner ring, 41b, 46b, 52c ... one end face, 41c, 46c, 52d ... other end face, 42, 47 ... outer ring, 42a, 47a, 52b, 54b ... outer peripheral face 42b, 42c, 47b, 47c ... end face, 42d, 42e, 47d, 47e ... collar, 43, 48 ... rolling elements, 49, 53 ... clearance, 50, 60 ... elasticity Support mechanism, 51 ... regulating member, 51a ... one end, 51c ... other end, 52, 54, 55, 56 ... elastic body, 52e ... concave, 52f ... leg 52g, chamfered portion, 52h, 54h, 55h, 56h Inner circumference, 52i, 54i, 55i, 56i ... outer circumference, 54a ... inner circumference, 54e, 56e ... convex part, 55b ... hollow part, 71 ... reduction mechanism, 72 ..Drive pulley, 73... Belt, 74.

Claims (3)

A housing;
A cylindrical body housed in the housing and having a first threaded portion with a first thread groove formed on the inner periphery;
A rack shaft having a second threaded portion inserted coaxially with the cylindrical body into the cylindrical body and having a second thread groove formed on the outer periphery;
A plurality of balls disposed in a rolling path constituted by the first screw groove and the second screw groove;
A bearing disposed between an inner peripheral surface of the housing and an outer peripheral surface of the cylindrical body, and supporting the cylindrical body in a radial direction with respect to the housing;
An annular elastic resin made between the inner end surface of the housing provided in the axial direction of the bearing and the outer ring of the bearing and supporting the cylindrical body movably in the axial direction with respect to the housing. Body,
In an electric power steering device comprising a motor for rotating the cylindrical body,
The electric power steering device according to claim 1, wherein the elastic body is formed thinner at an inner peripheral portion than at an outer peripheral portion. The electric power steering apparatus according to claim 1, wherein
An electric power steering apparatus, wherein a recess is formed on an inner peripheral surface of the elastic body. The electric power steering apparatus according to claim 1, wherein
An electric power steering apparatus, wherein a convex portion is formed on an inner peripheral surface of the elastic body.