JP6111737B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, there is provided a driven member that is inserted through a rack shaft and rotated by a motor drive, and the rotation of the driven member is converted into axial movement of the rack shaft by a ball screw mechanism, thereby providing an assist force to the steering system. A rack assist type electric power steering device (EPS) is known (for example, Patent Documents 1 and 2). In such EPS, the ball screw mechanism has a ball screw nut that rotates integrally with the driven member, and a screw groove that is screwed on the inner periphery of the ball screw nut and a screw groove that is screwed on the outer periphery of the rack shaft. Are arranged by arranging a plurality of balls in a spiral ball track.

JP2013-6470A JP 2006-224784 A

  By the way, in the EPS as described above, the rack shaft is slidably supported by a bush provided on the inner periphery of the rack housing. Usually, the bush supports the rack shaft at a cylindrical portion (support portion) having almost no unevenness along the axial direction of the rack shaft, as in the EPS described in Patent Document 1.

  Here, in the configuration in which the bush supports the rack shaft support portion, the support portion needs to have an axial length (axial length) that is at least greater than the rack shaft stroke range, but an EPS (rack shaft) is mounted. Depending on the vehicle model, the axial length of the support portion may not be ensured. In this case, it is conceivable that the bush supports the rack shaft with the screw portion in which the screw groove is formed, as in the EPS described in Patent Document 2 above. However, since the screw portion has an uneven shape along the axial direction, there is a problem that abnormal noise and wear powder are easily generated when the screw portion is supported.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an electric power steering apparatus capable of suppressing the generation of abnormal noise and wear powder.

An electric power steering apparatus that solves the above problems includes a rack shaft that is reciprocally movable in a rack housing in an axial direction, a driven member that rotates by driving a motor, and the rotation of the driven member in the axial direction of the rack shaft. A ball screw mechanism that converts to movement, the ball screw mechanism screwed into the outer periphery of the rack shaft and the screw groove screwed into the inner periphery of a ball screw nut that rotates integrally with the driven member. Is formed by disposing a plurality of balls in a spiral ball track that is opposed to each other, and a cylindrical shape that is fitted to the outer periphery of the screw portion in which the screw groove in the rack shaft is formed and the sleeve is provided on the inner periphery of the rack housing, and a bush for slidably supporting the outer periphery of the sleeve, the sleeve includes an inner which extends on the inner peripheral side Parts is formed, said sleeve such that said inner protrusion is axially moved Tsureda' the axial movement of the rack shaft by engaging with the rack shaft, the inner periphery has a predetermined interference The gist is that the screw is fitted to the outer periphery of the screw portion.

  According to the above configuration, since the sleeve is positively moved in the axial direction along with the axial movement of the rack shaft by engaging the inner convex portion with the rack shaft, the bush provided on the inner periphery of the rack housing. As compared with the case where the rack shaft is directly supported, the sliding amount between the rack shaft and the sleeve with respect to the stroke amount of the rack shaft is reduced. Therefore, even if the rack shaft is supported by the outer peripheral portion of the screw portion, it is possible to suppress the generation of abnormal noise and wear powder.

  In the electric power steering apparatus, a concave portion into which the inner convex portion is inserted is formed on an outer periphery of the rack shaft, and the sleeve is relative to the rack shaft within an axial range in which the concave portion is formed. It is preferable that the screw part is fitted to the outer periphery so as to be movable.

  According to the above configuration, when the rack shaft moves in the axial direction, the sleeve moves relative to the rack shaft until the inner convex portion engages with the axial end of the concave portion, and the inner convex portion is in the concave portion. After engaging with the end portion in the axial direction, it moves axially integrally with the rack shaft. Therefore, an axial range longer than the axial length of the sleeve on the rack shaft can be supported by the sleeve. Thereby, for example, the axial length of the sleeve can be shortened while stably supporting the rack shaft.

In the electric power steering apparatus, it is preferable that the sleeve is fitted to an outer periphery of the screw portion so as not to be relatively movable with respect to the rack shaft.
According to the above configuration, the rack shaft and the sleeve are prevented from moving relative to each other, and the rack shaft and the sleeve do not slide relative to each other.

  In the above-mentioned electric power steering apparatus, it is preferable that the sleeve is formed with an outer convex portion that extends to the outer peripheral side and that can be engaged with an axial end surface on one axial end side of the rack housing.

  According to the above configuration, since the outer convex portion is engaged with the shaft end surface of the rack housing, the sleeve is restricted from moving toward the center in the axial direction of the rack housing, so that the sleeve interferes with the ball screw mechanism. Can be prevented.

  According to the present invention, it is possible to suppress the generation of abnormal noise and wear powder.

1 is a partial cross-sectional view illustrating a schematic configuration of an electric power steering apparatus according to an embodiment. FIG. 3 is an enlarged cross-sectional view in the vicinity of the steering force assisting device and the end housing according to the embodiment. (A)-(d) is operation | movement explanatory drawing of the electric power steering apparatus of one Embodiment. The expanded sectional view of the axial direction one end part vicinity in the end housing of another example. The expanded sectional view of the axial direction one end part vicinity in the end housing of another example.

Hereinafter, an embodiment of an electric power steering apparatus (EPS) will be described with reference to the drawings.
As shown in FIG. 1, the EPS 1 includes a pinion shaft 2 that rotates by a steering operation, and a rack shaft that reciprocates in the axial direction according to the rotation of the pinion shaft 2 to change the steering angle of a steered wheel (not shown). 3 is provided. The EPS 1 includes a cylindrical rack housing 5 into which the rack shaft 3 is inserted so as to be able to reciprocate.

  The rack housing 5 includes a main body housing 11 formed in a cylindrical shape, and an end housing 12 formed in a cylindrical shape and fixed to one axial end side (left side in FIG. 1) of the main body housing 11. . A pinion housing portion 13 in which the pinion shaft 2 is housed is formed at the end of the main body housing 11 opposite to the end housing 12 (right side in FIG. 1). The pinion housing portion 13 has a pinion shaft. 2 is supported so as to be rotatable in a state of crossing the rack shaft 3. The rack shaft 3 is engaged with the pinion shaft 2 by being biased by a rack guide 14 provided in the main body housing 11. The pinion shaft 2 is connected to a steering shaft, and a steering wheel (both not shown) is fixed to the tip thereof.

  A tie rod (not shown) is rotatably connected to both ends of the rack shaft 3 via a rack end 15, and the tip of the tie rod is connected to a knuckle (both not shown) to which steered wheels are assembled. Has been. The rack end 15 of the present embodiment is configured as a well-known ball joint, and is connected to a tie rod and has a ball stud 16 provided with a ball portion 16a at one end, and a ball stud 16a that rotatably accommodates the ball portion 16a. A bottom cylindrical socket 17 is provided. For convenience of explanation, only the rack end 15 provided on one end side in the axial direction is illustrated. Therefore, in EPS1, the pinion shaft 2 rotates in accordance with the steering operation, and the rotation is converted into the axial movement of the rack shaft 3, thereby changing the steering angle of the steered wheels, that is, the traveling direction of the vehicle.

  The EPS 1 also includes a steering force assist device (EPS actuator) 21 that applies assist force to the steering system. The steering force assisting device 21 transmits the rotation of the motor 22 serving as a drive source to the ball screw mechanism 24 via the transmission mechanism 23 and converts the rotation to the reciprocating motion of the rack shaft 3 in the ball screw mechanism 24. Give assist power. The EPS 1 of the present embodiment is configured as a so-called rack parallel type EPS in which the axis of the motor 22 is arranged so as to be parallel to the rack shaft 3.

  More specifically, as shown in FIG. 2, the end of the main body housing 11 on the end housing 12 side (left side in FIG. 2) has a diameter larger than that of the front side (counter end housing 12 side). A cylindrical main body housing side accommodating portion 31 is formed. The main body housing side accommodating portion 31 is formed with a main body housing side bulging portion 32 having a shape in which a part of the peripheral wall is bulged in the radial direction. On the other hand, at the end of the end housing 12 on the main body housing 11 side (right side in FIG. 2), a cylindrical end housing side accommodating portion 33 that fits into the main body housing side accommodating portion 31, and a main body housing side bulging portion A plate-like end housing side bulging portion 34 covering 32 is formed. The end housing 12 is formed with a cylindrical cylindrical portion 35 extending on the opposite side to the main body housing 11 so as to be coaxial with the end housing side accommodating portion 33.

  The motor 22 is fixed to the body housing side bulging portion 32 so that the motor shaft 22 a is parallel to the rack shaft 3. The transmission mechanism 23 is housed in the body housing side bulging portion 32 and is connected to the motor shaft 22a so as to be integrally rotatable, and is housed in the body housing side housing portion 31 and the rack shaft 3. A driven pulley 42 arranged on the outer periphery and a drive belt 41 and a transmission belt 43 wound around the driven pulley 42 are provided. The ball screw mechanism 24 has a ball screw nut 45 provided so as to rotate integrally with the driven pulley 42, and the ball screw nut 45 is screwed to the rack shaft 3 via a plurality of balls 46. It is formed by.

  More specifically, the driven pulley 42 is formed in a cylindrical shape, and includes a winding portion 51 around which the transmission belt 43 is wound, and an extending portion 52 that extends from the winding portion 51 toward the end housing 12. Have. Further, an enlarged diameter portion 53 having an inner diameter larger than that of the end housing 12 side is formed at the end of the driven pulley 42 on the main body housing 11 side.

  The ball screw nut 45 is formed in a cylindrical shape, and an annular flange portion 54 extending outward in the radial direction is formed at an end portion on the main body housing 11 side. The outer diameter of the flange portion 54 is set substantially equal to the inner diameter of the enlarged diameter portion 53. On the other hand, a male screw portion 55 is formed at the end of the ball screw nut 45 on the end housing 12 side.

  A driven pulley 42 is fitted to the outer periphery of the ball screw nut 45 so that the flange portion 54 is inserted into the enlarged diameter portion 53, and a rolling bearing 56 is fitted so as to be adjacent to the extended portion 52. ing. Then, the lock nut 57 is screwed onto the male screw portion 55, and the driven pulley 42 and the rolling bearing 56 are sandwiched between the lock nut 57 and the flange portion 54, so that the inner rings of the driven pulley 42 and the rolling bearing 56 are made. The ball screw nut 45 is fixed so as to be integrally rotatable. That is, in this embodiment, the ball screw nut 45 corresponds to a driven member. In addition, on both sides of the rolling bearing 56, a cage 58 having a U-shaped cross section that is opened on the opposite side of the rolling bearing 56 is disposed adjacent to the outer ring, and an elastic material such as rubber is provided in the cage 58. The members 59 are disposed in a compressed state between the main body housing 11 and the end housing 12.

  Further, a screw groove 61 is screwed on the inner periphery of the ball screw nut 45, and a screw groove 62 corresponding to the screw groove 61 is screwed on the outer periphery of the rack shaft 3, and the screw grooves 61, A spiral ball trajectory R1 is formed by 62. In the ball raceway R1, each ball 46 is disposed between the screw groove 61 of the ball screw nut 45 and the screw groove 62 of the rack shaft 3. That is, the ball screw nut 45 is screwed to the outer periphery of the rack shaft 3 via each ball 46. Thereby, each ball 46 rolls in the ball track R1 while receiving the load (frictional force) in accordance with the relative rotation between the rack shaft 3 and the ball screw nut 45 (driven pulley 42). The relative position in the axial direction between the rack shaft 3 and the ball screw nut 45 is displaced by the rolling of each ball 46, whereby the torque of the motor 22 is applied to the steering system as an assist force. The ball 46 rolling in the ball raceway R1 is configured to endlessly circulate by passing through a circulation path R2 that short-circuits the two points of the ball raceway R1 provided in the ball screw nut 45.

Next, a support structure in the end housing of the rack shaft will be described.
The EPS 1 includes a sleeve 72 that is fitted to the outer periphery of a screw portion 71 in which a screw groove 62 in the rack shaft 3 is formed. The EPS 1 includes a bush (sliding bearing) 73 that is provided on the inner periphery of the cylindrical portion 35 of the end housing 12 and supports the outer periphery of the sleeve 72 so as to be slidable. The rack shaft 3 is supported in the end housing 12 (rack housing 5) through a sleeve 72 and a bush 73 so as to reciprocate.

  Specifically, the screw groove 62 is formed over an axial range from the axial center portion of the rack shaft 3 to the vicinity of one axial end portion (left end portion in FIG. 2). A protruding portion 74 that protrudes from the screw portion 71 toward the one end side in the axial direction is formed at one end portion in the axial direction of the rack shaft 3. The protrusion 74 of this embodiment is formed in a cylindrical shape, and the socket 17 of the rack end 15 is screwed to the protrusion 74. The outer diameter of the protruding portion 74 is set smaller than the maximum outer diameter of the screw portion 71, and the axial length (axial length) of the protruding portion 74 is set sufficiently shorter than the axial length of the screw portion 71. Has been. The outer diameter of the socket 17 is set larger than the maximum outer diameter of the screw portion 71. Thus, an annular recess 75 extending in the circumferential direction is formed on the outer periphery of the protrusion 74 of the rack shaft 3.

  The sleeve 72 is formed in a cylindrical shape, and the outer diameter of the sleeve 72 is set slightly smaller than the inner diameter of the cylindrical portion 35 of the end housing 12. The sleeve 72 is fitted to the outer periphery of the screw portion 71 with a predetermined tightening allowance. The bush 73 is formed in an annular shape, and is fixed at a position near one end in the axial direction on the inner periphery of the cylindrical portion 35 of the end housing 12. The bush 73 has a predetermined tightening margin and supports the sleeve 72 so as to be slidable. In addition, it is preferable that the tightening allowance between the screw portion 71 and the sleeve 72 is small. In this embodiment, the tightening allowance is set smaller than the tightening allowance between the sleeve 72 and the bush 73.

  At one end in the axial direction of the sleeve 72, an annular inner convex portion 81 extending toward the inner peripheral side is formed. The length (thickness) along the axial direction of the rack shaft 3 of the inner convex portion 81 is set sufficiently shorter than the length of the concave portion 75 along the axial direction of the rack shaft 3. The inner convex portion 81 is fitted to the outer periphery of the screw portion 71 so as to be inserted into the concave portion 75. Thereby, the sleeve 72 is arranged between the step surface 82 between the screw portion 71 and the projecting portion 74 of the rack shaft 3 and the outer bottom surface 83 of the socket 17, that is, within the axial range in which the recess 75 is formed. 3, and the inner convex portion 81 engages with the stepped surface 82 or the outer bottom surface 83 in the axial direction, so that it moves integrally with the rack shaft 3 in the axial direction.

  Further, an annular outer convex portion 84 extending to the outer peripheral side is formed at one axial end portion of the sleeve 72. The outer diameter of the outer convex portion 84 is set larger than the inner diameter of the cylindrical portion 35 of the end housing 12. Accordingly, the outer convex portion 84 can be engaged in the axial direction with respect to the shaft end surface 85 on one end side in the axial direction of the end housing 12. Note that an annular housing groove 86 that can accommodate the entire outer convex portion 84 is formed in the shaft end surface 85 of the present embodiment. Further, the axial length of the sleeve 72 is such that the other end portion in the axial direction of the sleeve 72 (the right end portion in FIG. 2) projects into the end housing side accommodating portion 33 in a state where the outer convex portion 84 is engaged with the accommodating groove 86. The length is not set.

Next, the operation of this embodiment will be described.
The sleeve 72 fitted to the outer periphery of the screw portion 71 as described above moves in the axial direction along with the axial movement of the rack shaft 3. Specifically, for example, as shown in FIG. 3A, the rack shaft 3 protrudes from the end housing 12 from a state in which the inner convex portion 81 is engaged with the outer bottom surface 83 that is one axial end portion of the concave portion 75. When the sleeve 72 moves to one end side in the axial direction (left side in FIG. 3), as shown in FIG. 3B, the sleeve 72 is engaged with the stepped surface 82 in which the inner convex portion 81 is the other axial end portion of the concave portion 75. It moves relative to the rack shaft 3 until it matches. Then, after the inner convex portion 81 and the stepped surface 82 are engaged, the sleeve 72 moves integrally with the rack shaft 3 to one end side in the axial direction (see FIG. 3C).

  On the other hand, for example, as shown in FIG. 3 (c), the other end side in the axial direction (right side in FIG. ), The sleeve 72 moves relative to the rack shaft 3 until the inner convex portion 81 engages with the outer bottom surface 83, as shown in FIG. Then, after the inner projection 81 and the outer bottom surface 83 are engaged, the sleeve 72 moves integrally with the rack shaft 3 to the other end in the axial direction (see FIG. 3A).

  3A, when the outer bottom surface 83 of the socket 17 is in contact with the shaft end surface 85 of the end housing 12, the outer convex portion 84 of the sleeve 72 is connected to the receiving groove 86 of the shaft end surface 85. By engaging, the sleeve 72 is restricted from moving toward the axially central side (the main body housing 11 side) of the end housing 12. For this reason, for example, a so-called end contact occurs where the socket 17 collides with the shaft end surface 85 of the end housing 12, and the axial movement of the rack shaft 3 suddenly stops, so that the inertia force on the main body housing 11 side acts on the sleeve 72. Even so, the sleeve 72 is more reliably restricted from moving toward the main body housing 11, and interference between the sleeve 72 and the ball screw mechanism 24 is prevented.

Next, the effect of this embodiment will be described.
(1) Since the inner convex portion 81 of the sleeve 72 is engaged with the rack shaft 3 in the axial direction, the sleeve 72 is positively moved in the axial direction along with the axial movement of the rack shaft 3. For example, the sliding amount between the rack shaft 3 and the sleeve 72 with respect to the stroke amount of the rack shaft 3 can be reduced as compared with the case where the rack shaft 3 is directly supported by the bush provided on the inner periphery of the end housing 12. Thereby, even if the rack shaft 3 is supported by the outer peripheral portion of the screw portion 71, it is possible to suppress the generation of abnormal noise and wear powder.

  (2) Since the sleeve 72 is fitted to the outer periphery of the screw portion 71 so as to be movable relative to the rack shaft 3 within the axial range of the concave portion 75 provided on the outer periphery of the protruding portion 74, the rack shaft 3 (the screw portion It is possible to support the axial range longer than the axial length of the sleeve 72 in 71) by the sleeve 72. Thereby, for example, the shaft length of the sleeve 72 can be shortened while the rack shaft 3 is stably supported by the sleeve 72.

  (3) Since the bush 73 that slidably supports the outer periphery of the sleeve 72 is provided on the inner periphery of the cylindrical portion 35 of the end housing 12, the sleeve 72 can be smoothly moved relative to the end housing 12. .

  (4) Since the outer convex portion 84 extending to the outer peripheral side is formed on the sleeve 72, the outer convex portion 84 is engaged with the shaft end surface 85 of the end housing 12 in the axial direction, so that the sleeve 72 is the main body. Movement to the housing 11 side is restricted. Thereby, it is possible to prevent the sleeve 72 from interfering with the ball screw mechanism 24 even at the time of end contact, for example.

In addition, the said embodiment can also be implemented in the following aspects which changed this suitably.
In the above embodiment, the sleeve 72 is fitted to the outer periphery of the screw portion 71 so as to be relatively movable with respect to the rack shaft 3 within the axial range in which the recess 75 is formed. 72 may be fitted to the outer periphery of the screw portion 71 so as not to move relative to the rack shaft 3. In the example shown in FIG. 4, the axial length of the protruding portion 74 is set to be substantially the same as the thickness of the inner convex portion 81, and the inner convex portion 81 always engages with the step surface 82 and the outer bottom surface 83 of the socket 17. As a result, the relative movement of the sleeve 72 with respect to the rack shaft 3 is restricted. In this configuration, in addition to the effects of the above-described embodiments (1), (3), and (4), relative movement between the rack shaft 3 and the sleeve 72 is prevented, and the rack shaft 3 and the sleeve 72 do not slide relative to each other. There is an effect that the generation of abnormal noise and wear powder can be further suppressed.

  In the above embodiment, the annular recess 75 is formed on the outer periphery of the projection 74 by forming the projection 74 in a cylindrical shape having an outer diameter smaller than the outer diameter of the screw portion 71. However, the present invention is not limited to this. For example, the concave portion 75 having a shape corresponding to the notch may be formed by forming a cylindrical shape having an outer diameter substantially equal to the outer diameter of the screw portion 71 and cutting a part thereof. Further, the protrusion 74 may have a shape other than a cylindrical shape such as a square cylindrical shape. In short, the shape of the projecting portion 74 can be appropriately changed as long as the concave portion 75 into which the inner convex portion 81 of the sleeve 72 is inserted can be formed on the outer periphery of the rack shaft 3.

  In the above embodiment, for example, as shown in FIG. 5, the axial position where the inner convex portion 81 is formed and the axial position where the outer convex portion 84 is formed may be shifted. Further, the outer protrusion 84 may not be formed on the sleeve 72. Further, the housing groove 86 may not be formed on the shaft end surface 85.

  In the above embodiment, the sleeve 72 is slidably supported by the bush 73 provided on the inner periphery of the end housing 12, but the sleeve 72 is slid relative to the inner periphery of the end housing 12 without providing the bush 73. It is good also as a structure. In this case, it is preferable that the sleeve 72 is made of a self-lubricating resin material or the like.

  -In above-mentioned embodiment, although the inner side convex part 81 was formed in the annular | circular shape, you may form in multiple numbers as not only this but the protrusion shape which protrudes to an inner peripheral side, for example. In short, the inner convex portion 81 can be appropriately changed as long as the inner convex portion 81 can be engaged with the rack shaft 3 in the axial direction. Similarly, the outer convex portion 84 can be appropriately changed as long as the outer convex portion 84 can be engaged with the shaft end surface 85 of the end housing 12 in the axial direction.

  -In above-mentioned embodiment, although the transmission mechanism 23 was comprised with a pair of pulley 41,42 and the transmission belt 43, it may comprise not only this but a several gearwheel, for example. The EPS 1 may be another type of EPS such as a rack coaxial type in which a motor is arranged coaxially with the rack shaft 3.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device (EPS), 3 ... Rack shaft, 5 ... Rack housing, 11 ... Main body housing, 12 ... End housing, 15 ... Rack end, 16 ... Ball stud, 17 ... Socket, 21 ... Steering force auxiliary device , 22 ... motor, 23 ... transmission mechanism, 24 ... ball screw mechanism, 35 ... cylindrical portion, 45 ... ball screw nut, 46 ... ball, 61, 62 ... screw groove, 71 ... screw portion, 72 ... sleeve, 73 ... Bush, 74 ... projecting portion, 75 ... concave portion, 81 ... inner convex portion, 82 ... stepped surface, 83 ... outer bottom surface, 84 ... outer convex portion, 85 ... shaft end surface, R1 ... ball raceway, R2 ... circulation path.

Claims (4)

A rack shaft provided in the rack housing so as to be capable of reciprocating in the axial direction, a driven member that rotates by driving a motor, and a ball screw mechanism that converts rotation of the driven member into axial movement of the rack shaft,
The ball screw mechanism is a spiral ball track formed by opposing a screw groove threaded on the outer periphery of the rack shaft and a screw groove threaded on the inner periphery of a ball screw nut that rotates integrally with the driven member. In the electric power steering device formed by disposing a plurality of balls inside,
A cylindrical sleeve fitted to the outer periphery of the screw portion in which the screw groove in the rack shaft is formed ;
A bush provided on the inner periphery of the rack housing and slidably supporting the outer periphery of the sleeve ;
The sleeve is formed with an inner convex portion extending to the inner peripheral side,
The sleeve has an inner circumference with a predetermined tightening margin so that the inner convex portion moves in the axial direction along with the axial movement of the rack shaft by engaging the inner convex portion with the rack shaft. An electric power steering device fitted on an outer periphery. The electric power steering apparatus according to claim 1, wherein
On the outer periphery of the rack shaft, a concave portion into which the inner convex portion is inserted is formed,
The electric power steering apparatus according to claim 1, wherein the sleeve is fitted to an outer periphery of the screw portion so as to be movable relative to the rack shaft within an axial range in which the concave portion is formed. The electric power steering apparatus according to claim 1, wherein
The electric power steering apparatus according to claim 1, wherein the sleeve is fitted on an outer periphery of the screw portion so as not to be relatively movable with respect to the rack shaft. In the electric power steering device according to any one of claims 1 to 3 ,
The electric power steering apparatus according to claim 1, wherein the sleeve is formed with an outer convex portion that extends to the outer peripheral side and that can be engaged with a shaft end surface on one end side in the axial direction of the rack housing.