JP2010126115A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for improving a steering responsive feel during the neutral of a steering wheel by utilizing the input from a turning wheel side for moving a rack shaft in the axial direction without operating a ball screw mechanism. <P>SOLUTION: The electric power steering device includes the rack shaft 12 stored in a housing 11 movably in the axial direction, a ball screw shaft 15 supported rotatably around an axis parallel to the rack shaft, a ball nut 22 threaded to the ball screw shaft and movable in the axial direction of the ball screw shaft, an electric motor 13 arranged parallel to the rack shaft for driving the ball screw shaft to be rotated, driving transmission members 24, 124 for driving the axial movement of the ball nut to be transmitted to the rack shaft, and elastically energizing parts 24a, 51, 52 arranged between the rack shaft and the ball nut for elastically energizing the rack shaft against the ball nut to its axial neutral position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus capable of improving the responsiveness of steering when a steering wheel is neutral.

  In the electric power steering device, for example, as described in Patent Document 1, a ball nut is screwed onto a ball screw shaft formed on a rack shaft via a ball, and an electric motor is arranged in parallel with the ball nut. There is a motor parallel type electric power steering device. A drive gear is connected to the motor shaft of the electric motor, and a driven gear that is meshed with the drive gear directly or via an intermediate gear is attached to the ball nut so that the rotation of the electric motor is transmitted to the ball nut at a reduced speed. It has become.

In this type of electric power steering apparatus, both ends of the rack shaft are connected to the steered wheels via tie rods and knuckle arms, and the ball screw shaft (rack shaft) is moved in the axial direction by the rotation of the ball nut by the electric motor. The steered wheels (tires) are steered.
JP 2008-105649 A

  By the way, in the electric power steering apparatus described in Patent Document 1, even when an input is applied to the rack shaft from the steered wheel side according to the road surface condition at the time of the neutral position of the steering wheel, due to the influence of the inertial mass and friction on the upstream side. The ball nut cannot rotate and the rack shaft cannot move in the axial direction. As a result, there is dissatisfaction that it is not possible to feel a sense of responsiveness about the road surface on which the vehicle is traveling. That is, when the steering wheel is neutral, for example, even if a relatively small input (road reaction force) of about 200 to 300 N is applied from the steered wheel side, the rack shaft cannot move. There are indications that the road surface condition cannot be transmitted, which is undesirable in terms of steering feeling.

  The present invention has been made in view of the above circumstances, and is configured so that the rack shaft can be moved in the axial direction even when the ball screw mechanism is not operated by an input from the steered wheel side. An object of the present invention is to provide an electric power steering apparatus that can improve the steering response feeling.

  In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that a housing, a rack shaft accommodated in the housing so as to be movable in an axial direction, and accommodated in the housing in parallel with the rack shaft, A ball screw shaft rotatably supported about an axis parallel to the rack shaft, a ball nut threadably engaged with the ball screw shaft and movable in the axial direction of the ball screw shaft, and the housing parallel to the rack shaft An electric motor that rotationally drives the ball screw shaft, a drive transmission member that transmits the axial movement of the ball nut to the rack shaft, and a space between the rack shaft and the ball nut. And an elastic urging portion that elastically urges the rack shaft to a neutral position in the axial direction with respect to the ball nut, and when the rack shaft receives an input from a road surface, the elastic urging portion resists the elastic urging portion. in front The rack shaft is that constituted so as to be relatively moved in the axial direction with respect to the ball nut.

  A feature of the invention according to claim 2 is that, in claim 1, the elastic urging portion is constituted by a pair of elastic deformation portions formed on the drive transmission member.

  The invention according to claim 3 is characterized in that, in claim 2, the pair of elastically deformable portions can be elastically deformed by forming a slit in the central portion of the rack shaft in the axial direction of the drive transmission member. This is because the pair of elastically deforming portions are engaged with the two chamfered portions cut out in the rack shaft.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the drive transmission member is fitted to the ball nut so as to be relatively movable only in the axial direction, and the elastic biasing portion is connected to both end portions of the drive transmission member. And a pair of elastic urging members inserted between the ball nuts.

  According to the first aspect of the invention, a drive transmission member that drives and transmits the axial movement of the ball nut screwed to the ball screw shaft rotatably supported about an axis parallel to the rack shaft to the rack shaft; It is provided between the rack shaft and the ball nut, and is provided with an elastic urging portion that elastically urges the rack shaft to the neutral position in the axial direction with respect to the ball nut, and is elastic when there is input from the road surface to the rack shaft. Since the rack shaft can be moved relative to the ball nut in the axial direction against the urging portion, the rack shaft is elastically biased when a relatively small input is transmitted from the road surface to the rack shaft when the handle is neutral. It can move in the axial direction against the elastic biasing force of the part. As a result, even if the ball screw mechanism does not operate, the rack shaft can be moved by the road surface input, and the axial movement of the rack shaft can give the driver operating the handle a sense of responsiveness according to the road surface condition. it can.

  Moreover, according to the first aspect of the present invention, the ball screw shaft and the electric motor coaxial therewith are disposed in a radial offset from the rack shaft, and the rack shaft is accommodated in the housing on the axis of the rack shaft. Thus, the diameter of the housing on the axis of the rack shaft can be reduced over the entire length. Thereby, even in a vehicle in which an oil pan or the like of an engine is arranged close to the axis of the rack shaft, for example, interference between the housing and the oil pan or the like can be easily avoided.

  According to the second aspect of the present invention, since the elastic urging portion is constituted by a pair of elastic deformation portions formed on the drive transmission member, only by forming the pair of elastic deformation portions on the drive transmission member, The rack shaft can be easily moved in the axial direction with respect to the ball nut.

  According to the third aspect of the present invention, the pair of elastically deformable portions can be elastically deformed by forming a slit in the central portion of the rack shaft in the axial direction of the drive shaft, and the pair of elastically deformable portions can be used as the rack shaft. Since the cut two chamfered portions are engaged, the rack shaft can be reliably moved in the axial direction by the slit amount with respect to the ball nut by the road surface input overcoming the elastic urging portion formed in the drive transmission member.

  According to the invention of claim 4, the drive transmission member is fitted to the ball nut so as to be relatively movable only in the axial direction, and the elastic urging portion is inserted between the both ends of the drive transmission member and the ball nut. The rack shaft is surely secured in the axial direction by the slit amount with respect to the ball nut by the road surface input overcoming the elastic urging portion interposed between the drive transmission member and the ball nut. Can be moved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an entire electric power steering apparatus 10 according to a first embodiment. The electric power steering apparatus 10 includes a housing 11 that extends in the left-right direction of the vehicle. Yes. The housing 11 includes a first housing 11a in which a rack housing portion 11a1 for housing substantially half of the rack shaft 12 in the axial direction (substantially right half in FIG. 1) and the remaining half of the rack shaft 12 in the axial direction (see FIG. And a second housing 11b in which a ball screw accommodating portion 11b2 for accommodating the ball screw shaft 15 in parallel with the rack shaft 12 is formed.

  A pinion shaft 17 rotated by a steering wheel (not shown) is supported on the first housing 11 a so as to be rotatable about an axis intersecting the rack shaft 12, and the pinion shaft 17 is engaged with the rack shaft 12. The first housing 11 a is provided with a support yoke 18 that presses the rack shaft 12 toward the pinion shaft 17, and the support yoke 18 maintains the meshing between the rack shaft 12 and the pinion shaft 17 appropriately. I have to.

  As shown in FIG. 2, the second housing 11b has a substantially dharma-shaped cross section in which a rack housing portion 11b1 and a cylindrical ball screw housing portion 11b2 are integrally formed. As shown in FIG. 1, flange portions 11a3 and 11b3 are formed on the opposing peripheral portions of the first housing 11a and the second housing 11b, respectively, and these flange portions 11a3 and 11b3 are integrally connected by bolts not shown. It has come to be. A motor mounting portion 11a4 is formed on the flange portion 11a3, and an electric motor 13 is mounted on the motor mounting portion 11a4 in parallel with the rack shaft 12 and coaxially with the ball screw shaft 15. The electric motor 13 applies an assist force in the axial direction to the rack shaft 12 via a ball screw mechanism 27 described later. A motor shaft 13 a of the electric motor 13 is connected to one end of the ball screw shaft 15.

  The rack shaft 12 is inserted through the rack accommodating portions 11a1 and 11b1 of the first and second housings 11a and 11b, and steered wheels are coupled to both ends via unillustrated tie rods and knuckle arms. It has become.

  In the ball screw housing portion 11b2 of the second housing 11a, the ball screw shaft 15 is rotatable about an axis parallel to the rack shaft 12 by a bearing 21 at a position offset by a predetermined amount in the radial direction from the axis of the rack shaft 12. It is supported. A ball nut 22 is screwed onto the ball screw shaft 15 via a ball (not shown). A drive transmission member 24 is integrally attached to the ball nut 22.

  One end of the drive transmission member 24 has a bifurcated shape as shown in FIG. In the bifurcated portion, a slit 24a1 is formed in the central portion of the rack shaft 12 in the axial direction, and a pair of elastically deformable portions 24a and 24a that are elastically deformable as elastic biasing portions are provided on both sides of the slit 24a1. ing. The pair of elastic deformation portions 24 a and 24 a are elastically engaged with the two chamfered portions 12 a cut out in the rack shaft 12. As a result, the drive transmission member 24 attached to the ball nut 22 is prevented from rotating, and the axial movement of the ball nut 22 is transmitted to the rack shaft 12 via the elastic deformation portions 24 a and 24 a provided in the drive transmission member 24. It has come to be.

  The pair of elastic deformation portions 24a and 24a provided in the drive transmission member 24 is one of the pair of elastic deformation portions 24a and 24a when the rack shaft 12 is moved rightward or leftward by an input from the road surface. Is elastically deformed by the amount of the slit 24a1, but the strength is set so that no further elastic deformation occurs, and thereafter the drive transmission member 24 functions as a rigid body.

  With the above configuration, when the ball screw shaft 15 is rotated by the electric motor 13, the ball nut 22 is moved in the axial direction along the ball screw shaft 15, and the rack shaft 12 is moved to the ball screw shaft via the drive transmission member 24. 15 is moved in the axial direction. The ball screw shaft 15, the ball, and the ball nut 22 constitute a ball screw mechanism 27 that converts the rotational motion of the ball screw shaft 15 into the axial motion of the rack shaft 12.

  As described above, the ball screw shaft 15 and the electric motor 13 are disposed so as to be offset in the radial direction with respect to the rack shaft 12, so that the shaft of the rack shaft 12 of the housing 11 (first and second housings 11a and 11b) is provided. Since only the substantially cylindrical rack accommodating portions 11a1 and 11b1 for accommodating the rack shaft 12 need be formed on the line, the diameter of the housing 11 on the axis of the rack shaft 12 can be reduced over the entire length. When mounted on a vehicle, interference with components provided in the engine room, such as an engine oil pan, can be easily avoided.

  In the figure, reference numerals 41 and 42 denote mount portions provided in the first housing 11a and the second housing 11b, respectively, and the first housing 11a and the second housing 11b are not shown via the mount portions 41 and 42. Supported by the body. Reference numeral 43 denotes a rack guide mounted on the second housing 11b. The rack guide 43 supports the end of the rack shaft 12 opposite to the support yoke 18 so as to be slidable.

  Next, the operation of the electric power steering apparatus 10 according to the first embodiment configured as described above will be described. When a steering wheel (not shown) is steered, steering torque is input to the pinion shaft 17, and the rack shaft 12 is moved in the axial direction by the rack and pinion mechanism.

  The steering torque input to the pinion shaft 17 is detected by a torque sensor (not shown), the electric motor 13 is controlled based on the steering torque, and the ball screw shaft 15 is rotated together with the motor shaft 31. The ball nut 22 is moved in the axial direction of the ball screw shaft 15 by the rotation of the ball screw shaft 15, and the axial movement of the ball nut 22 is transmitted to the rack shaft 12 by the drive transmission member 24, and the rack shaft 12 is moved to the ball screw shaft. 15 is moved in the axial direction. In this manner, the assist force by the electric motor 13 is applied to the rack shaft 12, and the steered wheels (not shown) are steered by the assist force, and the steering force of the steering wheel by the driver is reduced.

  By the way, in the above-described first embodiment, the rack shaft 12 and the ball nut 22 are connected by the drive transmission member 24 having the elastic deformation portion 24a, so that the road surface from the tire (steered wheel) side when the steering wheel is neutral. When a relatively small input corresponding to the state is transmitted to the rack shaft 12, the rack shaft 12 moves in the axial direction while elastically deforming the elastic deformation portion 24 a of the drive transmission member 24. Thereby, even if the ball screw mechanism 27 does not operate, the rack shaft 12 can be moved in the axial direction according to the road surface condition, and the road surface is moved to the handle shaft via the pinion shaft 17 by the axial movement of the rack shaft 12. The input from can be transmitted. As a result, it is possible to give a feeling of responsiveness to the driver who operates the handle and to improve the handle feeling.

  Note that the relative movement range of the rack shaft 12 with respect to the ball nut 22 when the handle is neutral is limited to the width of the slit 24a1. Therefore, during normal steering, when the ball nut 22 is moved in the axial direction of the ball screw shaft 15 by the rotation of the ball screw shaft 15 by the electric motor 13, the axial movement of the ball nut 22 is driven by the drive transmission member. 24 is transmitted to the rack shaft 12 almost without delay, and the rack shaft 12 is moved in the axial direction almost integrally with the ball screw shaft 15.

  According to the first embodiment described above, the axial movement of the ball nut 22 is transmitted to the rack shaft 12 via the drive transmission member 24 having the elastically deforming portion 24a. Based on this, the rack shaft 12 can be moved in the axial direction without operating the ball screw mechanism 27. By the axial movement of the rack shaft 12, the pinion shaft 17 is rotated, and an input corresponding to the road surface condition can be transmitted to the handle shaft. As a result, the driver who operates the steering wheel can be given a feeling of response corresponding to the road surface condition, and the steering wheel feeling can be improved.

  In the first embodiment described above, the ball screw shaft 15 and the electric motor 13 coaxial with the ball screw shaft 15 are disposed to be offset from the rack shaft 12 in the radial direction. Since only the substantially cylindrical rack accommodating portions 11a1 and 11b1 for accommodating the shaft 12 are formed, the diameter of the housing 11 on the axis of the rack shaft 12 can be reduced over the entire length thereof. Thereby, even in a vehicle in which an oil pan or the like of an engine is arranged close to the axis of the rack shaft 12, for example, interference between the housing 11 and the oil pan or the like can be easily avoided.

  FIG. 3 shows a second embodiment of the present invention, which is different from the first embodiment in that the drive transmission member 124 made of a rigid body is used and the tire (steered wheel) side is at the neutral position of the steering wheel. When the input corresponding to the road surface condition is transmitted to the rack shaft 12, the rack shaft 12 is moved in the axial direction against the urging force of the elastic urging portion. Note that components that are basically the same as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  That is, in the second embodiment, a rigid drive transmission member 124 is fitted to the outer periphery of the ball nut 22 so as to be slidable in the axial direction of the ball screw shaft 15 and to rotate integrally. One end of the drive transmission member 124 is fixed to the outer periphery of the rack shaft 12 by a bolt 47. A disc spring 51 as an elastic urging portion is inserted between the flange portion 22 a formed at one end of the ball nut 22 and one end of the drive transmission member 124, and is screwed to the other end of the ball nut 22. A disc spring 52 as an elastic biasing portion is interposed between the receiving member 50 and the other end of the drive transmission member 124.

  The drive transmission member 124 is normally held in a neutral position in the axial direction with respect to the ball nut 22 by the elastic biasing force of the pair of disc springs 51 and 52, and the road surface input that overcomes the biasing force of the disc springs 51 and 52 is a rack. By being added to the shaft 18, one of the disc springs 51, 52 can be elastically deformed and moved in the axial direction together with the rack shaft 18. When the disc springs 51 and 52 are elastically deformed by a predetermined amount, the relative axial movement of the drive transmission member 124 and the ball nut 22 is restricted, and the drive transmission member 124 and the ball nut 22 operate integrally.

  Therefore, also in the second embodiment described above, as in the first embodiment, the rack shaft 12 is slightly moved in the axial direction without operating the ball screw mechanism 27 based on the input from the road surface. As the rack shaft 12 moves in the axial direction, the pinion shaft 17 is rotated, and the input corresponding to the road surface condition can be transmitted to the handle shaft. As a result, the driver who operates the steering wheel can be given a feeling of response corresponding to the road surface condition, and the steering wheel feeling can be improved.

  In the above-described embodiment, the example in which the electric motor 13 is installed in the housing 11 coaxially with the ball screw shaft 15 and the rotation of the electric motor 13 is directly transmitted to the ball screw shaft 15 has been described. It is also possible to arrange a reduction gear mechanism between the motor 13 and the ball screw shaft 15 so that the rotation of the electric motor 13 is reduced and transmitted to the ball screw shaft 15. Alternatively, the electric motor can be configured by a brushless motor including a stator and a rotor that are incorporated in the housing 11 coaxially with the ball screw shaft 15.

  In the above-described embodiment, the elastic biasing portion is the elastic deformation portion 24 a provided in the drive transmission member 24 or the disc springs 51, 52 interposed between the drive transmission member 124 and the ball nut 22. The elastic biasing portion is provided between the rack shaft 12 and the ball nut 22 and elastically biases the rack shaft 12 to the neutral position in the axial direction with respect to the ball nut 22. Any configuration can be used.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the configurations described in the embodiments, and does not depart from the gist of the present invention described in the claims. It can take various forms.

1 is a cross-sectional view of an electric power steering apparatus showing a first embodiment of the present invention. It is sectional drawing cut | disconnected along 2-2 line | wire of FIG. It is sectional drawing of the electric power steering device which shows the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 11 ... Housing, 12 ... Rack shaft, 13 ... Electric motor, 15 ... Ball screw shaft, 17 ... Pinion shaft, 22 ... Ball nut, 24, 124 ... Drive transmission member, 24a, 51, 52 ... elastic biasing part, 24a1 ... slit, 27 ... ball screw mechanism.

Claims (4)

  A housing, a rack shaft housed in the housing so as to be movable in the axial direction, and a ball screw shaft housed in the housing in parallel with the rack shaft and rotatably supported about an axis parallel to the rack shaft A ball nut threadably engaged with the ball screw shaft and movable in the axial direction of the ball screw shaft; an electric motor disposed in the housing in parallel with the rack shaft and for rotating the ball screw shaft; A drive transmission member that drives and transmits the axial movement of the ball nut to the rack shaft, and is disposed between the rack shaft and the ball nut, and the rack shaft is elastically attached to a neutral position in the axial direction with respect to the ball nut. An elastic biasing portion that biases the rack shaft relative to the ball nut in the axial direction against the elastic biasing portion when the rack shaft receives an input from a road surface. An electric power steering apparatus characterized by being configured to so that.   2. The electric power steering apparatus according to claim 1, wherein the elastic urging portion is constituted by a pair of elastic deformation portions formed on the drive transmission member.   3. The pair of elastically deformable portions can be elastically deformed by forming a slit in the axially central portion of the rack shaft in the drive transmission member, and the pair of elastically deformable portions are notched in the rack shaft. An electric power steering device characterized by being engaged with the two chamfered portions.   In Claim 1, the said drive transmission member is fitted to the said ball nut so that relative movement is possible only in an axial direction, and the said elastic urging | biasing part is inserted between the both ends of the said drive transmission member, and the said ball nut. An electric power steering device comprising a pair of elastic urging members.

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