JP2005343308A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of reducing the deflection of a rack shaft to be supported by a gear housing. <P>SOLUTION: In the electric power steering device 10, a bush 40 is stretched over a ball nut 32 supported by a first gear housing 11A and a bush supporting part 17 facing the ball nut 32 of a second gear housing 11B. The bush 40 is fixed to one of the ball nut 32 and the bush supporting part 17, and the rack shaft 14 is supported in a straight movable manner while being rotatably supported by the other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus.

As an electric power steering device, as described in Patent Document 1, a gear housing that supports a rack shaft so as to be linearly movable is divided, and a ball nut that meshes with the rack shaft is rotatably supported on one gear housing. There is one that transmits the rotational force of the electric motor fixed to the gear housing to the ball nut so that the rack shaft can be moved linearly.
JP-A-60-25853

  In the electric power steering device of Patent Document 1, a rack shaft that meshes with a ball nut supported by one gear housing is supported by a bush supported by the other gear housing so as to be linearly movable. For this reason, it is necessary to increase the clearance of the bush with respect to the rack shaft from the assembling relationship of inserting the rack shaft engaged with the ball nut on one gear housing side into the bush on the other gear housing side. As a result, the swing of the rack shaft due to the externally applied load acting on the rack shaft is large, and an operation noise is generated.

  When the clearance of the bush with respect to the rack shaft is reduced, the assemblability of the rack shaft is deteriorated and the friction loss accompanying the operation of the rack shaft is also increased.

  An object of the present invention is to reduce the swing of a rack shaft supported by a gear housing in an electric power steering apparatus.

  According to the first aspect of the present invention, the gear housing that supports the rack shaft so as to be linearly movable is divided, and a ball nut that meshes with the rack shaft is rotatably supported by one of the gear housings, and is fixed to one of the gear housings. In the electric power steering apparatus that transmits the rotational force of the motor to the ball nut and enables the rack shaft to move linearly, a ball nut supported by one gear housing, and a bush support portion opposed to the ball nut of the other gear housing The bush is fixedly provided on one of the ball nut and the bush support portion, and the rack shaft is supported so as to be linearly movable while being rotatably supported on the other. .

  According to a second aspect of the present invention, in the first aspect of the present invention, the driving pulley is coupled to the rotating shaft of the electric motor, the driven pulley is coupled to the ball nut, and the driving pulley and the driven pulley are connected by a belt. It is a thing.

  According to a third aspect of the present invention, in the first aspect of the present invention, the drive gear is coupled to the rotating shaft of the electric motor, the driven gear is coupled to the ball nut, and the drive gear and the driven gear are meshed and connected. It is a thing.

  The invention of claim 4 is the invention according to any one of claims 1 to 3, wherein the bush is press-fitted into a ball nut.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the bush has a lubricating coating layer on a sliding portion with a ball nut or a bush support portion and a sliding portion with a rack shaft. It is intended to be prepared.

(Claims 1 to 3)
(a) A rack shaft that meshes with a ball nut supported by one gear housing is supported by a bush spanned between the ball nut and a bush support provided on the other gear housing so as to be linearly movable. Accordingly, the rack shaft engaged with the ball nut on one gear housing side can be easily inserted into the bush provided over the other gear housing side for assembly. The clearance of the bush with respect to the rack shaft can be easily reduced without impairing the assemblability, and the swing of the rack shaft due to an external load acting on the rack shaft can be reduced, and the operation noise can be reduced.

(Claim 4)
(b) By pressing the bush into the ball nut, the bush clearance with respect to the rack shaft engaged with the ball nut can be easily reduced.

(Claim 5)
(c) Since the bush is provided with a lubricating coating layer on the sliding portion with the ball nut or the bush support portion and the sliding portion with the rack shaft, the operation of the rack shaft is performed while reducing the clearance of the bush with respect to the rack shaft. It is possible to reduce the friction loss caused by.

  1 is an overall side view showing an electric power steering apparatus according to a first embodiment, FIG. 2 is a cross-sectional view showing an essential part of the electric power steering apparatus, FIG. 3 is an enlarged view of the essential part of FIG. 2, and FIG. FIG. 5 is a cross-sectional view showing a main part of the second embodiment.

Example 1 (FIGS. 1 to 4)
As shown in FIG. 1, the electric power steering apparatus 10 includes a first gear housing 11A and a second gear housing 11B in which the gear housing 11 is divided, and a steering input is input to the gear housing 11 (first gear housing 11A). The shaft 12 is supported, an output shaft (not shown) is connected to the input shaft 12 via a torsion bar 13, a pinion (not shown) is provided on the output shaft, and the rack shaft 14 meshing with the pinion is connected to the gear housing 11. It is supported so that it can move linearly in the left-right direction. A steering torque sensor (not shown) is provided between the input shaft 12 and the output shaft. The steering torque sensor detects the steering torque based on the relative rotational displacement generated between the input shaft 12 and the output shaft due to elastic torsional deformation of the torsion bar caused by the steering torque applied to the steering wheel.

  The electric power steering apparatus 10 has both end portions of the rack shaft 14 projecting from both sides of the gear housing 11 (first gear housing 11A, second gear housing 11B), and tie rods 15A, 15B are connected to the end portions of the rack shaft 14, The left and right wheels can be steered via tie rods 15A and 15B that are linked to the 14 linear movements.

  As shown in FIG. 2, the electric power steering apparatus 10 fixes the electric motor 20 to a holder 22 with mounting bolts 21 (not shown), and the holder 22 can be attached to and detached from the first gear housing 11 </ b> A with mounting bolts 23. . At this time, the holder 22 supports the central shaft 25 of the drive pulley 24 and engages the joint 26A at the shaft end of the rotating shaft 20A of the electric motor 20 with the joint 26B at the shaft end of the central shaft 25 from the axial direction. The drive pulley 24 is supported on the holder 22 by bearings 27 and 28 at both ends of the center shaft 25. Reference numeral 29 denotes a retaining ring for fixing the outer ring of the bearing 28.

  The electric power steering apparatus 10 is provided with a ball screw 30 on the rack shaft 14, a ball nut 32 that meshes with the ball screw 30 via a ball 31, and a bearing 33 supported by the gear housing 11 (first gear housing 11 </ b> A). Thus, the ball nut 32 is rotatably supported. Reference numeral 34 denotes an outer ring fixing nut of the bearing 33. A driven pulley 36 is fixed to the outer periphery of the ball nut 32 by a lock nut 35.

  The electric power steering apparatus 10 wraps a belt 37 around a drive pulley 24 on the electric motor 20 side and a driven pulley 36 on the ball nut 32 side, and rotates the rotational force of the drive pulley 24 from the belt 37 via the driven pulley 36. This is transmitted to the nut 32, and consequently to the rack shaft 14, and the rack shaft 14 is linearly moved.

  The electric power steering apparatus 10 passes the rack shaft 14 supported by the first gear housing 11A through the second gear housing 11B, covers the holder 22 attached to the first gear housing 11A with the second gear housing 11B, The first gear housing 11 </ b> A and the second gear housing 11 </ b> B are fastened with a plurality of fastening bolts 16. At this time, as shown in FIG. 2, the first gear housing 11A and the second gear housing 11B are driven by the plurality of cylindrical knock pins 16A so that both end portions of the knock pins 16A are driven and aligned. The fastening bolt 16 inserted through 16A is screwed and fastened. Some fastening bolts 16 are screwed to the first gear housing 11A through the knock pins 16A, and other fastening bolts 16 are screwed to the second gear housing 11B through the knock pins 16A.

  However, the electric power steering apparatus 10 has the following configuration in order to reduce the swing of the rack shaft 14 supported by the gear housings 11A and 11B.

  In the second gear housing 11 </ b> B, a portion facing the ball nut 32 supported by the first gear housing 11 </ b> A is a bush support portion 17, and the bush 40 is bridged between the ball nut 32 and the bush support portion 17. As shown in FIG. 3, the bush 40 is press-fitted into the inner peripheral portion on the tip end side of the ball nut 32 and fixedly provided, and is supported by the inner peripheral portion of the bush support portion 17 so as to be rotatable and slidable. The shaft 14 is supported so as to be linearly slidable.

  As shown in FIG. 4, the bush 40 has a part of the outer periphery of a cylindrical body 41 made of metal or the like in the axial direction as a sliding part 42 with the bush support part 17, and the entire inner periphery slides with the rack shaft 14. Part 43 is assumed. The sliding portions 42 and 43 are provided by providing a lubricating coating layer such as an oil-containing polyacetal resin or a tetrafluoroethylene resin on the surface of the cylindrical body 41 by coating or the like.

The electric power steering device 10 is assembled by the following procedure, for example.
(1) A ball nut 32 meshed with the ball screw 30 of the rack shaft 14 and to which the driven pulley 36 is fixed is supported on the first gear housing 11A by the bearing 33. A bush 40 is provided on the ball nut 32.

  (2) The holder 22 that supports the drive pulley 24 and to which the electric motor 20 is attached is fixed to the first gear housing 11A with the attachment bolt 23.

  (3) The bush support portion 17 of the second gear housing 11B is inserted into the bush 40 provided on the ball nut 32 of (1) described above, and the second gear housing 11B is fastened to the first gear housing 11A by the fastening bolt 16. To do.

Hereinafter, the operation of the electric power steering apparatus 10 will be described.
(1) When the steering torque detected by the steering torque sensor is lower than a predetermined value, the steering assist force is unnecessary and the electric motor 20 is not driven.

  (2) Since the steering assist force is required when the steering torque detected by the steering torque sensor exceeds a predetermined value, the electric motor 20 is driven. The rotational force of the drive pulley 24 based on the torque generated by the electric motor 20 is transmitted from the belt 37 to the ball nut 32 via the driven pulley 36, and becomes a steering assist force that linearly moves the rack shaft 14 via the ball screw 30.

According to the present embodiment, the following operational effects can be obtained.
(a) The rack shaft 14 that meshes with the ball nut 32 supported by the first gear housing 11A is linearly moved by the bush 40 that spans the ball nut 32 and the bush support portion 17 provided on the second gear housing 11B. Support as possible. Therefore, the rack shaft 14 meshed with the ball nut 32 on the first gear housing 11A side can be easily inserted and assembled into the bush 40 provided over the second gear housing 11B side. The clearance of the bush 40 with respect to the rack shaft 14 can be easily reduced without impairing the assemblability, and the runout of the rack shaft 14 due to an external load acting on the rack shaft 14 can be reduced and the operation noise can be reduced. Can do.

  (b) By pressing the bush 40 into the ball nut 32, the clearance of the bush 40 with respect to the rack shaft 14 meshed with the ball nut 32 can be easily reduced.

  (c) Since the bush 40 includes the lubricating coating layer on the sliding portion 42 with the bush support portion 17 and the sliding portion 43 with the rack shaft 14, the clearance of the bush 40 with respect to the rack shaft 14 is reduced. Friction loss associated with the operation of the rack shaft 14 can be reduced.

(Example 2) (FIG. 5)
The second embodiment differs from the first embodiment in that the drive pulley 24 is replaced with the drive gear 51 and the driven pulley 36 is replaced with the driven gear 52.

  That is, in the electric power steering apparatus 10 according to the second embodiment, the drive gear 51 is coupled to the rotating shaft 20A of the electric motor 20, the driven gear 52 is coupled to the ball nut 32, and the drive gear 51 and the driven gear 52 are engaged. Connected.

  Even in the second embodiment, the bush 40 similar to the first embodiment is bridged between the ball nut 32 supported by the first gear housing 11A and the bush support portion 17 of the second gear housing 11B. Has the same effect as in.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. For example, the bush 40 may be fixedly provided on the bush support portion 17 of the second gear housing 11B and rotatably supported by the ball nut 32 on the first gear housing 11A side.

FIG. 1 is an overall side view showing an electric power steering apparatus according to a first embodiment. FIG. 2 is a cross-sectional view showing a main part of the electric power steering apparatus. FIG. 3 is an enlarged view of a main part of FIG. FIG. 4 is an enlarged view showing a portion IV in FIG. FIG. 5 is a cross-sectional view showing a main part of the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Gear housing 11A 1st gear housing 11B 2nd gear housing 14 Rack shaft 17 Bush support part 20 Electric motor 20A Rotating shaft 24 Driving pulley 32 Ball nut 36 Driven pulley 37 Belt 40 Bushing 42, 43 Sliding part 51 Drive gear 52 Driven gear

Claims (5)

The gear housing that supports the rack shaft so that it can move linearly is divided, and the ball nut that meshes with the rack shaft is supported rotatably on one gear housing, and the rotational force of the electric motor fixed to one of the gear housings is the ball nut. In the electric power steering device that allows the rack shaft to move linearly,
The bush is bridged between a ball nut supported by one gear housing and a bush support portion facing the ball nut of the other gear housing,
The bush is fixedly provided on one of the ball nut and the bush support portion, and supports the rack shaft so as to be linearly movable while being rotatably supported on the other.   The electric power steering apparatus according to claim 1, wherein a driving pulley is coupled to a rotating shaft of the electric motor, a driven pulley is coupled to the ball nut, and the driving pulley and the driven pulley are connected by a belt.   2. The electric power steering apparatus according to claim 1, wherein a driving gear is coupled to a rotating shaft of the electric motor, a driven gear is coupled to the ball nut, and the driving gear and the driven gear are meshed and connected.   The electric power steering device according to any one of claims 1 to 3, wherein the bush is press-fitted into a ball nut.   The electric power steering device according to any one of claims 1 to 4, wherein the bush includes a lubricating coating layer on a sliding portion with the ball nut or the bush support portion and a sliding portion with the rack shaft.

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