WO2019092998A1 - Electric power steering apparatus - Google Patents

Electric power steering apparatus Download PDF

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Publication number
WO2019092998A1
WO2019092998A1 PCT/JP2018/035374 JP2018035374W WO2019092998A1 WO 2019092998 A1 WO2019092998 A1 WO 2019092998A1 JP 2018035374 W JP2018035374 W JP 2018035374W WO 2019092998 A1 WO2019092998 A1 WO 2019092998A1
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WO
WIPO (PCT)
Prior art keywords
nut
electric power
power steering
steering apparatus
rack
Prior art date
Application number
PCT/JP2018/035374
Other languages
French (fr)
Japanese (ja)
Inventor
眞徳 渡部
洋祐 田部
高太郎 椎野
Original Assignee
日立オートモティブシステムズ株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日立オートモティブシステムズ株式会社 filed Critical 日立オートモティブシステムズ株式会社
Publication of WO2019092998A1 publication Critical patent/WO2019092998A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
    • F16C33/30—Parts of ball or roller bearings
    • F16C33/58—Raceways; Race rings
    • F16C33/64—Special methods of manufacture
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H19/00—Gearings comprising essentially only toothed gears or friction members and not capable of conveying indefinitely-continuing rotary motion
    • F16H19/02—Gearings comprising essentially only toothed gears or friction members and not capable of conveying indefinitely-continuing rotary motion for interconverting rotary or oscillating motion and reciprocating motion
    • F16H19/04—Gearings comprising essentially only toothed gears or friction members and not capable of conveying indefinitely-continuing rotary motion for interconverting rotary or oscillating motion and reciprocating motion comprising a rack
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
    • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
    • F16H25/20—Screw mechanisms
    • F16H25/22—Screw mechanisms with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
    • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
    • F16H25/20—Screw mechanisms
    • F16H25/24—Elements essential to such mechanisms, e.g. screws, nuts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H7/00—Gearings for conveying rotary motion by endless flexible members
    • F16H7/02—Gearings for conveying rotary motion by endless flexible members with belts; with V-belts

Definitions

  • the present invention relates to an electric power steering apparatus, and more particularly to a noise reduction technology for electric power steering.
  • the electric power steering device is a device for assisting the steering force of the driver with a motor and changing the traveling direction of the vehicle.
  • One such type is a belt drive type electric power steering device in which the axis of the motor and the rack shaft are disposed in parallel and the power of the motor is transmitted to the rack shaft by the belt and the ball screw. This type of electric power steering apparatus is applied to a wide range of vehicles because of its advantages in power transmission efficiency and steering feeling.
  • the electric power steering apparatus disclosed in Patent Document 1 includes a ball screw mechanism that converts rotational movement of a nut into axial movement of a rack shaft, a belt that transmits driving force of a motor to the nut, and a nut at one end side of the nut in the axial direction. And a bearing for rotatably supporting, and a reaction force generating mechanism for generating a reaction force that opposes the tension of the belt acting directly or indirectly on the nut.
  • the reaction force generating mechanism is constituted by an inclined surface formed on the inner peripheral surface of the housing on which the outer race of the bearing abuts. In the electric power steering apparatus of Patent Document 1, the inclination of the nut due to the belt tension is prevented by the reaction force generation mechanism, and the noise is reduced (see abstract and paragraph 0010).
  • the valleys of the screw grooves at both ends of the screw grooves of the nut are set deeper than the valleys of the screw groove at the central portion.
  • the degree of freedom in the bending deformation of the rack shaft is made larger at both ends with respect to the central part of the nut, and the contact pressure between the screw groove of the ball screw and the ball The center and both ends are almost even.
  • the electric power steering device of Patent Document 1 reduces the noise generated by the contact between the ball and the nut.
  • Patent Document 1 and Patent Document 2 since the thickness of the nut is the same in the circumferential direction and the axial direction, the natural frequency is fixed to one. If it is excited by a ball or the like at the natural frequency, a resonance phenomenon is caused by the frequency characteristic having a sharp peak of a single frequency. In order to avoid such a resonance phenomenon, it is considered necessary to disperse natural frequencies in the circumferential direction or axial direction of the nut.
  • An object of the present invention is to reduce the noise of an electric power steering apparatus.
  • the electric power steering apparatus of the present invention is: A rack having a rack side ball screw groove spirally formed along the rack rotation axis; A nut having a nut side ball screw groove spirally formed along the nut rotation axis, and arranged coaxially with the rack rotation axis; A plurality of balls disposed in a ball circulation groove constituted by the rack side ball screw groove and the nut side ball screw groove; An electric motor that outputs power to the nut via a belt; Equipped with The nut has a first range, a second range, and a third range so that the nut-side ball screw groove does not overlap each other at a central angle of 120 ° in a range of a continuous central angle of 360 ° of the nut-side ball screw groove. When dividing into three ranges of ranges, the first range, the second range, and the third range have mutually different radial thickness areas.
  • the natural frequency of the vibration generated by the ball vibration can be dispersed in the circumferential direction or the axial direction of the nut, reducing offensive peak frequency noise. it can.
  • FIG. 2 is a cross-sectional view perpendicular to an axial direction of a rack, showing a portion of a steering mechanism 2 of the electric power steering apparatus 1 of FIG. 1.
  • FIG. 2 is a cross-sectional view perpendicular to the axial direction of the rack, showing a portion of a ball screw mechanism 20 of the electric power steering apparatus 1 of FIG. 1;
  • FIG. 2 is a cross-sectional view including a rotation axis L1 of the rack 6 and showing a portion of the ball screw mechanism 20 of the electric power steering apparatus 1 of FIG.
  • FIG. 5 is a schematic view showing a cross section including a rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in the ball screw mechanism 20A according to the first embodiment of the present invention.
  • FIG. 9 is a schematic view of the BAC section of FIG.
  • FIG. 21 is a schematic view showing a cross section including a rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in a ball screw mechanism 20C according to a third embodiment of the present invention.
  • the entire configuration of the electric power steering apparatus 1 according to the present invention will be described.
  • the configuration of one embodiment of the electric power steering apparatus 1 to which the first to seventh embodiments described later are applied will be described, the electric power steering apparatus 1 to which each embodiment is applied is limited to the configuration described below. It is not the case.
  • FIG. 1 is a front view partially showing an electric power steering apparatus 1 according to an embodiment of the present invention in cross section.
  • FIG. 2 is a cross-sectional view perpendicular to the axial direction of the rack, showing a portion of the steering mechanism 2 in the electric power steering apparatus 1 of FIG.
  • FIG. 3 is a cross-sectional view perpendicular to the axial direction of the rack, showing a portion of the ball screw mechanism 20 in the electric power steering apparatus 1 of FIG.
  • FIG. 4 is a cross-sectional view including the rotation axis L1 of the rack 6 and showing a portion of the ball screw mechanism 20 of the electric power steering apparatus 1 of FIG. 1 and parallel to the rotation axis L1 of the rack 6.
  • the electric power steering apparatus 1 is mounted on a vehicle having an engine as a drive source.
  • the electric power steering apparatus 1 includes a steering mechanism 2, a gear housing 3 and an electric motor 4.
  • the steering mechanism 2 steers the steered wheels (not shown) as the steering wheel (not shown) rotates.
  • a steering mechanism 2 is accommodated in the gear housing 3.
  • the electric motor 4 applies a steering force to the steering mechanism 2.
  • the steering mechanism 2 includes a steering shaft 5 and a rack (steering shaft) 6.
  • the steering shaft 5 has a steering shaft 7 and a pinion shaft 8.
  • the steering shaft 7 rotates integrally with the steering wheel.
  • the pinion shaft 8 is connected to the steering shaft 7 via a torsion bar 9.
  • a pinion gear 8 a is formed on the outer periphery of the pinion shaft 8.
  • the pinion gear 8 a meshes with a rack gear 6 a formed in a predetermined range on the outer periphery of the rack 6.
  • the rack 6 moves along the vehicle body width direction (axial direction of the rack 6) according to the rotation of the steering shaft 5.
  • the rack 6 has teeth 6b cut in a rod-like member (shaft) 6a.
  • the rod-like member 6a is called a rack bar, and the teeth 6b cut in a rod-like member are called a rack gear.
  • the rack 6 is formed using an iron-based metal material such as steel.
  • ends of a pair of tie rods 10 are connected to both ends of the rack 6 (rack bar 6 a).
  • the gear housing 3 has a two-divided structure in which the first gear housing portion 3 a and the second gear housing portion 3 b are butted in an axial direction (vehicle width direction) of the rack 6.
  • the first gear housing portion 3a and the second gear housing portion 3b are formed by die casting using an aluminum alloy. Openings 3i, 3i through which the rack 6 penetrates are provided at a pair of ends of the gear housing 3.
  • the vehicle width direction inner end of the dust boot 11 is fixed to a pair of ends of the gear housing 3.
  • the dust boot 11 is for suppressing the entry of moisture into the gear housing 3 from the outside.
  • the dust boot 11 is formed as an annular member having a bellows shape using a synthetic resin.
  • the vehicle width direction outer end of the dust boot 11 is fixed to the vehicle width direction inner end of the tie rod 10.
  • the steering shaft 5 is provided with a torque sensor 12.
  • the torque sensor 12 detects a steering torque (torsion bar torque) generated in the steering mechanism 2.
  • the torque sensor 12 has a torsion bar 9, a detection unit 12a and a sensor housing 12b.
  • the detection unit 12 a detects the amount of torsion of the torsion bar 9.
  • the sensor housing 12b is provided on the upper side in the vertical direction of the second gear housing portion 3b in the on-vehicle state.
  • a three-phase brushless motor is used as the electric motor 4.
  • the electric motor 4 is accommodated in a motor housing 13.
  • the motor housing 13 is joined to the first gear housing portion 3a.
  • the motor housing 13 is integrally formed with the first gear housing portion 3a.
  • the electric motor 4 has a motor shaft 4a, a rotor 4b and a stator 4c.
  • the motor shaft 4a is provided integrally with the rotor 4b.
  • An input pulley (motor-side pulley) 14 is attached to the motor shaft 4a.
  • the input pulley 14 is formed in a cylindrical shape.
  • the rotor 4 b is rotatably supported by the motor housing 13 around the axial direction of the motor shaft 4 a (in the circumferential direction around the axial center).
  • the stator 4 c is fixed to the motor housing 13.
  • the electric motor 4 is drive-controlled by the control device 15 in which the microcomputer 15a is mounted.
  • the controller 15 has an ECU housing 16.
  • the ECU housing 16 has an ECU housing main body portion 17, a lid member 18 and a connector portion 19.
  • the ECU housing main body 17 is joined to the motor housing 13.
  • An ECU housing main body opening 17 a formed so as to expose the inside of the ECU housing main body 17 is provided on the side opposite to the electric motor 4 in the ECU housing main body 17.
  • a circuit board 15 b is accommodated in the ECU housing main body 17.
  • a microcomputer 15a including a CPU, a RAM, a ROM and the like and a power module (not shown) are mounted.
  • the ECU housing main body opening 17 a is closed by the lid member 18.
  • the ECU housing main body 17 and the lid member 18 are formed using an aluminum alloy.
  • the connector portion 19 is provided to be exposed to the outside of the ECU housing main body portion 17.
  • the connector portion 19 is formed using a synthetic resin.
  • a power supply system harness for supplying power from the vehicle side is electrically connected to the connector portion 19.
  • a signal system harness for inputting an output signal of the torque sensor 12 and a signal of information (such as a vehicle speed) related to the traveling state of the vehicle is electrically connected to the connector portion 19.
  • the power and signal input to the connector unit 19 are input to the control device 15 via a bus bar (not shown).
  • the control device 15 calculates a motor torque command for driving and controlling the electric motor 4 based on each input signal, and supplies the electric motor 4 with the electric power according to the motor torque command.
  • a ball screw mechanism 20 is provided between the electric motor 4 and the rack 6.
  • the ball screw mechanism 20 is accommodated in a ball screw mechanism accommodating portion 3 c of the gear housing 3.
  • the ball screw mechanism accommodating portion 3 c is provided above the joint surface A of the first gear housing portion 3 a and the second gear housing portion 3 b in the vertical direction when the gear housing 3 is mounted on the vehicle.
  • the first gear housing portion 3 a has an opening 3 e facing the joint surface A.
  • a recess 3f facing the opening 3e is provided at the lower end in the vertical direction of the first gear housing portion 3a.
  • the recess 3 f is formed to be recessed downward in the vertical direction when the gear housing 3 is mounted on the vehicle (see FIG. 3).
  • the recess 3 f is provided with a transmission side unit 30 of a moisture detection system for detecting moisture that has entered the gear housing 3.
  • the transmission side unit 30 is fixed to the gear housing 3 by being sandwiched between the first gear housing portion 3a and the second gear housing portion 3b at the joint surface A. Thereby, drop-off
  • the vertically lower portion of the gear housing 3 in the mounted state of the gear housing 3 is inclined toward the vertically lower side as it approaches the opening 3e. It has an inclined surface 3g formed.
  • a groove 3h is formed in a part of the inclined surface 3g provided in the first gear housing 3a.
  • the groove 3 h is formed so as to be recessed downward in the vertical direction and extend toward the transmission unit 30 in the vehicle-mounted state of the gear housing 3.
  • the rack accommodating portion 3 d in which the rack 6 is accommodated is formed to extend cylindrically from the ball screw mechanism accommodating portion 3 c toward the right turning wheel and the left turning wheel.
  • the ball screw mechanism 20 is a reduction gear that transmits the rotational force of the electric motor 4 to the rack 6.
  • the ball screw mechanism 20 has a steered shaft side ball screw groove (rack side ball screw groove) 21, a nut 22, a nut side ball screw groove 23, a ball 24 and a return tube 25.
  • the steered shaft side ball screw groove 21 is a spiral groove provided on the outer peripheral side of the rack 6.
  • the nut 22 is provided to surround the rack 6.
  • the nut 22 is annularly formed using a steel material.
  • the nut 22 is rotatably supported relative to the gear housing 3 and axially immovably supported relative to the gear housing 3.
  • An output pulley (nut side pulley) 26 is fixed to the outer periphery of the nut 22.
  • the output pulley 26 is formed in a cylindrical shape so as to surround the rack 6.
  • the output pulley 26 rotates as the nut 22 rotates.
  • a belt (transmission member) 27 is hung on the output pulley 26.
  • the belt 27 transmits the rotation of the input pulley 14 to the output pulley 26.
  • the second reference axis L2 serving as the rotation axis (rotation center line) of the input pulley 14 is in the radial direction with respect to the first reference axis L1. It is arranged to be offset.
  • the rack 6 and the nut 22 are arranged such that their rotational axes coincide in an ideal state in which the belt 27 is not tensioned. For this reason, the second reference axis L2 is also arranged to be radially offset with respect to the rotation axis of the nut 22.
  • the nut-side ball screw groove 23 is a spiral groove provided on the inner periphery of the nut 22.
  • the nut side ball screw groove 23 constitutes a ball circulation groove together with the steered shaft side ball screw groove 21.
  • a plurality of balls 24 are provided in the ball circulation grooves 21 and 23.
  • the balls 24 are formed using steel.
  • the return tube 25 is provided on the outer peripheral side of the nut 22, and the ball 24 reaching the one end side or the other end side of the ball circulation grooves 21, 23 is the other end side of the ball circulation grooves 21, 23 via the return tube 25 Or it is returned to one end.
  • the ball screw mechanism 20 moves a plurality of balls 24 in the ball circulation grooves 21 and 23, and the rack 6 with respect to the nut 22 moves in the longitudinal direction of the rack bar 6a Move to).
  • the nut 22 is supported at one end in the direction of the first reference axis L 1 by the bearing 31 on the second gear housing 3 b of the gear housing 3.
  • This support structure supports the nut 22 in a cantilever manner.
  • the bearing 31 is composed of a bearing ball 37 and an outer race 32.
  • the inner race constituting the bearing 31 is constituted by the nut 22.
  • the present invention reduces the noise of the electric power steering apparatus 1, in particular, disperses the natural frequency (natural frequency) generated by the nut 22 of the ball screw mechanism 20 and reduces the noise.
  • the nut 22 is formed with a nut-side ball screw groove 23 in which the ball 24 is disposed.
  • the nut-side ball screw groove 23 is formed helically along the rotation axis.
  • the spiral groove 23 is configured such that each of the 120 ° sections (ranges) has a region of different wall thickness (average thickness) when the continuous 360 ° range is divided into 120 ° intervals. .
  • the thickness of the nut 22 may be changed continuously.
  • the nut may be formed such that its outer peripheral surface is tapered.
  • Example 1 In order to explain the features of the embodiment according to the present invention in an easy-to-understand manner, first, a comparative example to the embodiment according to the present invention will be described with reference to FIG. 5 to FIG.
  • FIG. 5 is a schematic view showing, in a partial cross section, a structure around a ball screw mechanism 20 ', which is a comparative example with the ball screw mechanism 20 according to the present invention.
  • the cross section shown in FIG. 5 is a cross sectional view including the rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6.
  • the ball screw mechanism 20 ′ comprises a rack 6, a nut 22 ′ and a ball 24.
  • a nut side pulley 26 is attached to a nut 22 'of the ball screw mechanism 20', and a belt 27 is stretched between the motor side pulley 14 and the nut side pulley 26.
  • the motor 4 is connected to the motor side pulley 14 on which the belt 27 is stretched, as in FIG. 4, and the power of the motor 4 is transmitted to the nut 22 ′ by the belt 27.
  • the nut 22 ′ is connected to the second gear housing portion 3 b constituting the housing via the bearing 31 constituted by the bearing balls 37 and the outer race 32.
  • FIG. 6 is a schematic view showing a state in which the belt 27 is tensioned in the ball screw mechanism 20 'of the comparative example of FIG.
  • the belt 27 is tensioned. Further, one end of the nut 22 'in the direction of the first reference axis L1 is supported by the bearing 31 on the second gear housing 3b. This support structure supports the nut 22 'in a cantilever manner. Therefore, as shown in FIG. 6, the belt tension acts on the other end side of the nut 22 'on which the belt 5 is hung. As a result, the other end side (the pulley 26 side) of the nut 22 'is drawn to the motor side pulley 14 side, and the nut 22' is inclined. That is, an inclination angle ⁇ is generated between the direction of the first reference axis L1 and the direction of the rotation axis L3 of the nut 22 '.
  • a ball circulating groove is constituted by the groove (nut side ball screw groove) 23 of the nut 22' through which the ball 24 passes and rotates and the groove (rack side ball screw groove) 21 of the rack 6.
  • the groove (nut side ball screw groove) 23 of the nut 22' through which the ball 24 passes and rotates and the groove (rack side ball screw groove) 21 of the rack 6.
  • the depth dimensions of the ball circulation grooves 21 and 23 are large on the side to be pulled on the pulley 26 side of the nut 22 ′ and become small on the opposite side.
  • balls 24a black balls 24 which receive a large load are present.
  • FIG. 7 is a view showing a model of the ball screw mechanism 20 'of the comparative example of FIG.
  • the model of FIG. 7 has a rack 6, a ball 24, a nut 22 ′, and ball circulation grooves 21 and 23.
  • the ball circulation grooves 21 and 23 are helical, but in this model, they are circular in a simple circle.
  • the ball 24 rotates while rotating the ball circulation grooves 21 and 23 between the nut 22 ′ and the rack 6.
  • the ball 24 applies an excitation force to the nut 22 ', and the nut 22' resonates at the natural frequency.
  • the vibration of each ball 24 has the same natural frequency. In this case, the same natural frequency as the number of balls 24 exists, and a sharp peak is generated at one frequency, which may cause a kind of resonance.
  • FIG. 8 is a schematic view showing a cross section including the rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in the ball screw mechanism 20A according to the first embodiment of the present invention.
  • the ball screw mechanism 20A of the present embodiment includes a rack 6, a nut 22A, and a ball 24.
  • the rack 6 has a rack-side ball screw groove 21 spirally formed along its rotation axis (rack rotation axis) L1.
  • the nut 22 has a nut-side ball screw groove spirally formed along the rotation axis (nut rotation axis) L3 and is disposed coaxially with the rack rotation axis L1.
  • the rack rotation axis L1 and the nut rotation axis L3 coincide with each other.
  • a nut side pulley 26 is attached to a nut 22A of the ball screw mechanism 20A, and a belt 27 is stretched between the motor side pulley 14 and the nut side pulley 26.
  • the nut 22A is connected to the second gear housing 3b constituting the gear housing 3 via the bearing 31 constituted by the bearing balls 37 and the outer race 32.
  • one end of the nut 22 in the direction of the first reference axis L1 is supported by the bearing 31 in a cantilevered manner by the second gear housing 3b as in the comparative example described above.
  • the ball screw mechanism 20A of this embodiment is characterized in that the outer peripheral surface of the nut 22A is formed in a tapered shape. That is, in the nut 22A, the outer diameter of one end in the direction of the first reference axis L1 is larger than that of the other end, and the diameter of the outer peripheral surface decreases from one end to the other It is formed as.
  • the nut 22A is formed such that the outer diameter of the side supported by the bearing 31 is larger than the outer diameter of the side on which the nut side pulley 26 is provided. It is also possible to form the nut 22A such that the outer diameter of the side supported by the bearing 31 is smaller than the outer diameter of the side on which the nut side pulley 26 is provided.
  • a region (a tapered region) in which the thickness T of the nut 22A changes is an effective range (force transmission range or a force transmission range or a ball screw structure where the ball 24 exists between the nut 22D and the rack 6 to transmit force). It is provided to the end where the nut side pulley 26 is provided, including the bearing ball interposed area 33).
  • the diameter (inner diameter) of the inner peripheral surface of the nut 22A in the portion where the nut-side ball screw groove 23 is formed is constant within the range of manufacturing error in the direction of the first reference axis L1. Further, the depth dimension of the nut-side ball screw groove 23 from the inner peripheral surface of the nut 22A is also constant within the range of manufacturing error in the direction of the first reference axis L1.
  • the thickness of the nut 22A is different in the direction of the first reference axis L1 (the rack axis direction) by forming the outer peripheral surface of the nut 22A in a tapered shape, it is unique to the excitation of each ball 24 The frequency can be dispersed, and resonance of the nut 22A can be avoided.
  • an undercut is not formed on the nut 22A, molding with a mold or the like becomes easy, and the nut 22A becomes easy to process.
  • the thickness in the radial direction of the opposite end side (pulley 26 side) thinner than the end side supported by the bearing 31, the opposite side to the bearing 31 side, that is, the belt 27 The side gets lighter. As a result, there is an advantage that the moment of inertia can be reduced when the nut 22A rotates with the bearing 31 side as the fixed end.
  • FIG. 9 is a schematic view of the BAC section of FIG. 8 projected on a plane perpendicular to the first reference axis L1.
  • the BAC cross section shows a cross section obtained by cutting the ball screw mechanism 20A along a spiral drawn by the ball circulation grooves 21 and 23.
  • the BAC cross section is a vertical line (first reference axis L1) which has been passed through the spiral nut side ball screw groove 23 or the ball circulation grooves 21 and 23 from the radially outer side of the nut 22A and dropped to the first reference axis L1.
  • the BAC cross section may be referred to as a cross section along a spiral.
  • the points B and C are separated by 360 ° at the central angle ⁇ a of the spiral, and are separated in the direction of the first reference axis L1.
  • the BAC section projected on a plane perpendicular to the first reference axis L1 will be referred to as a BAC projected section.
  • the BAC section projected on a plane perpendicular to the first reference axis L1 may be referred to as a projected section along a spiral.
  • the thickness (thickness dimension) T in the radial direction of the nut 22A differs on the circumference (the circumferential direction about the first reference axis L1). ing. That is, the thickness T of the nut 22A on the BAC projected cross section changes in the circumferential direction about the first reference axis L1. In a cross section perpendicular to the first reference axis L1, the thickness T of the nut 22A is constant in the circumferential direction.
  • the radial thickness T of the nut 22A continuously changes in the circumferential direction of the outer peripheral surface on the BAC projected cross section.
  • the thickness T of the ranges R1 (first range), R2 (second range), R3 (third range) is from point B toward point C, or from point C toward point B, Each changes in a predetermined numerical range.
  • the thickness T of the range R1 is not less than the maximum value of the thickness T of the range R2, and the thickness T of the range R2 is not less than the maximum value of the thickness T of the range R3.
  • the thickness T of the range R1 is equal to the thickness T of the range R2 at the boundary between the ranges R1 and R2, and the thickness T of the range R2 and the thickness T of the range R3 at the boundary between the ranges R2 and R3. equal.
  • the nut 22A (22) may be configured as described below.
  • the ball circulation grooves 21 and 23 are wide on the upper side of the paper surface and below the paper surface. It is narrow on the side. That is, in the range of the central angle 180 ° on the upper side of the drawing, the ball circulation grooves 21 and 23 are wider than the range of the central angle 180 ° on the lower side of the drawing.
  • the nut 22A receives an exciting force from each ball 24 particularly in the range of a central angle of 180 ° on the lower side of the drawing where the ball circulation grooves 21 and 23 become narrow.
  • 3 continuous ball circulation grooves 21 and 23 in the range of 360 ° from the point B (starting point) to the point C (end point) have a central angle of 120 ° that do not overlap each other.
  • the two ranges R1, R2 and R3 are divided so that the nut 22A has mutually different areas of thickness T in each range R1, R2 and R3.
  • range R1 has a region of thickness T1
  • range R2 has a region of thickness T2
  • range R3 has a region of thickness T3
  • thicknesses T1, T2 and T3 are mutually different values (Thickness dimension).
  • the thickness T changes continuously from the point B to the point C on the BAC projected cross section, but from the viewpoint, the average value of the thickness T of the nut 22A is in each range R1. , R2, R3 can also be viewed differently.
  • the thickness T of the nut 22A is different at every central angle of 120 °, so at least 2 in the range of the central angle of 180 ° above the paper surface of the ball circulating grooves 21 and 23 and in the range of 180 ° at the lower surface of the paper. It will have one natural frequency. That is, in the present embodiment, the natural frequency in the range R1 and the natural frequency in the range R3 exist in the range of the central angle 180 ° on the upper side of the sheet, and the range R1 (center There are natural frequencies according to the angle 30 °), natural frequencies according to the range R2 and natural frequencies according to the range R3 (central angle 30 °).
  • the natural frequencies can be dispersed into two in the range of the central angle 180 °. .
  • the position of the point B as the starting point is always changed in the range of the central angle 180 °
  • the natural frequencies can be split into two.
  • FIG. 10 is a schematic view of one revolution of the ball circulation grooves 21 and 23 developed in a straight line.
  • the thickness T in the radial direction of the nut 22A changes linearly in one rotation on the BAC projected section of the ball circulation grooves 21 and 23. Is shown.
  • the change in the thickness T in the radial direction of the nut 22A it is only necessary that the change in the thickness T in the radial direction of the nut 22A be continuous. It may be a curved shape that is convex or a curved shape that is convex downward.
  • the change in thickness T in the radial direction on the BAC projected cross section does not have to be continuous in one rotation from the point B to the point C, but changes intermittently (discretely) You may
  • the thickness T may be intermittently (discretely) changed every three ranges R1, R2 and R3 having a central angle of 120 °.
  • FIG. 11 is a schematic view showing a cross section perpendicular to the first reference axis L1 in the ball screw mechanism 20B according to the second embodiment of the present invention.
  • the radial thickness T of the nut 20B changes in the circumferential direction about the first reference axis L1.
  • the thickness T in the vertical direction in the drawing is long, and the thickness T in the horizontal direction is short.
  • the outer periphery of the nut 20B has an elliptical shape.
  • the outer circumference of the nut 20B on one side (that is, the thickness T) and the outer circumference of the nut 20B on the other side with respect to the second straight line L5 (that is, the thickness T) are line symmetrical with respect to the second straight line L5. is there.
  • the nut 20B of the present embodiment can disperse natural frequencies in the circumferential direction.
  • the other configuration is the same as that of the first embodiment.
  • an elliptical shape is shown as an example of a point-symmetrical shape, but portions having the same thickness T of the rack 6 may be arranged at equal intervals in the circumferential direction. That is, the nut 22B is formed such that changes in the thickness T in the radial direction are repeated at equal intervals in the circumferential direction around the first reference axis L1 (nut rotating shaft).
  • FIG. 12 is a schematic view showing a cross section including the rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in the ball screw mechanism 20C according to the third embodiment of the present invention.
  • the nut 22C has such a shape that there is no undercut so as to have an outer peripheral surface that decreases in diameter from the predetermined position in the central portion in the direction of the first reference axis L1. .
  • it has a so-called barrel shape in which the central portion in the first reference axis L1 direction (the rack axial direction) of the nut 22C bulges radially outward as compared with the both end portions.
  • the other configuration is the same as that of the first embodiment.
  • the nut 22C can disperse natural frequencies as in the first embodiment.
  • the distribution of natural frequencies can be adjusted by adjusting the degree of expansion of the barrel shape.
  • FIG. 13 is a schematic view showing a cross section including a rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in a ball screw mechanism 20D according to a fourth embodiment of the present invention.
  • the ball 24 is present between the nut 22D and the rack 6 to transmit the force to the effective range (force transmission range or bearing ball intervening range) 33 of the ball screw structure.
  • the effective range force transmission range or bearing ball intervening range
  • the other configuration is the same as that of the first embodiment.
  • natural frequencies can be dispersed as in the first embodiment.
  • the nut 22D of the present embodiment has cylindrical portions 34 and 35 formed in a cylindrical shape over the entire circumference of the outer peripheral surface at least a part in the first reference axis L1 direction (rotational axis direction).
  • the cylindrical portion 34 is formed at one end where the bearing 31 is provided in the direction of the first reference axis L1, and the cylindrical portion 34 includes the bearing outer race 32, the bearing ball 37, and the like.
  • the cylindrical portion 35 is formed at the other end opposite to the end where the bearing 31 is provided in the direction of the first reference axis L1, and the nut side pulley 26 is attached to the cylindrical portion 35.
  • the presence of the cylindrical portions 34 and 35 has the advantage of facilitating clamping.
  • the presence of the cylindrical portion 34 makes the surface constituting the inner race of the bearing 31 parallel to the outer race 32, and the bearing 31 can be easily configured. Further, the presence of the cylindrical portion 35 facilitates the attachment of the nut-side pulley 26.
  • FIG. 14 is a schematic view showing a cross section perpendicular to the first reference axis L1 in a ball screw mechanism 20E according to a fifth embodiment of the present invention.
  • the ball screw mechanism 20E of the present embodiment has the nut 22B of the second embodiment.
  • the thickness of the nut 22B changes in the circumferential direction.
  • a return tube 25 is provided at the thickened portion of the thickness T of the nut 22B.
  • the thick portion (thick portion T6 portion) of the thickness T has an advantage that the return tube 25 can be easily fixed.
  • the other configuration is the same as that of the first embodiment and the second embodiment.
  • FIG. 15 is a view showing a modification of the ball screw mechanism 20E of the fifth embodiment of the present invention, and is a schematic view showing a cross section perpendicular to the first reference axis L1.
  • the return tube 25 of the fifth embodiment is attached to the portion (the portion of the thickness T7) in which the thickness T of the nut 22B is reduced.
  • the return tube 25 can be disposed inside the maximum outer diameter (diameter of the thick portion of the wall thickness T) of the nut 22B.
  • the protruding portion can be reduced.
  • the ball screw mechanism 20E (20) can be miniaturized.
  • the other configuration is the same as that of the first embodiment and the second embodiment.
  • the present invention is not limited to the above-described embodiments, but includes various modifications.
  • the embodiments described above are described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations.
  • part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment.
  • SYMBOLS 1 Electric power steering device, 4 ... Electric motor, 6 ... Rack, 20, 20A, 20B, 20C, 20D, 20E ... Ball screw mechanism, 21 ... Rack side ball screw groove, 22, 22A, 22B, 22C, 22D ... Nut, 23 ... Nut side ball screw groove, (21, 23) ... Ball circulation groove, 24 ... Ball, 25 ... Return tube, 26 ... Pulley, 27 ... Belt, 31 ... Bearing (bearing), 33 ...
  • Ball screw effective range (Range in which a ball intervenes between the nut and the rack), 34, 35: cylindrical portion
  • L1 rack rotation shaft (first reference axis, nut rotation shaft)
  • L3 nut rotation shaft
  • L4 first straight line
  • L5 second straight line
  • R1 first range of nut side ball screw groove
  • R2 second range of nut side ball screw groove
  • R3 third range of nut side ball screw groove
  • T, T The radial thickness of the T2, T3 ... nut, T6 ... the thickness of the thick part of the wall thickness, the thickness of the thin portion of the T7 ... thickness.

Abstract

The purpose of the present invention is to provide a low-noise power steering apparatus. An electric power steering apparatus of the present invention comprises: a rack 6 having a rack-side ball screw groove 21 formed in a spiral shape; a nut 22A having a nut-side ball screw groove 23 formed in a spiral shape; and a plurality of balls 24 arranged in a ball circulation groove that is constituted by the rack-side ball screw groove 21 and the nut-side ball screw groove 23. Assuming that the nut-side ball screw groove 23 is divided into three ranges including a first range R1, a second range R2, and a third range R3 so that each range has a central angle of 120° in a continuous range with a central angle of 360° of the nut-side ball screw groove 23 and the three ranges do not overlap with each other, the first range R1, the second range R2, and the third range R3 in the nut 22A have thick regions T1, T2, and T3 extending in the radial direction and having mutually different thickness, respectively.

Description

電動パワーステアリング装置Electric power steering device
　本発明は、電動パワーステアリング装置に係り、特に電動パワーステアリングの低騒音化技術に関する。 The present invention relates to an electric power steering apparatus, and more particularly to a noise reduction technology for electric power steering.
　電動パワーステアリング装置は、運転者の操舵力をモータでアシストし、車両進行方向を変えるための装置である。その一種で、モータの軸線とラック軸とを平行に配置し、モータの動力をベルトとボールねじとでラック軸に伝達するベルト駆動式の電動パワーステアリング装置がある。この種の電動パワーステアリング装置は、動力伝達効率や操舵感に利点があることから幅広い車両に適用されている。 The electric power steering device is a device for assisting the steering force of the driver with a motor and changing the traveling direction of the vehicle. One such type is a belt drive type electric power steering device in which the axis of the motor and the rack shaft are disposed in parallel and the power of the motor is transmitted to the rack shaft by the belt and the ball screw. This type of electric power steering apparatus is applied to a wide range of vehicles because of its advantages in power transmission efficiency and steering feeling.
　近年では、快適性向上の観点から、電動パワーステアリング装置においても低騒音化のニーズが高まってきている。電動パワーステアリング装置の低騒音化に関しては、これまで様々な発明がなされている。特に、加振源の一つであるボールねじ構造に関する技術として、特開２０１７－７５８７号公報（特許文献１）及び特開平１１－１１３３４号公報（特許文献２）に開示された発明が知られている。 In recent years, the need for noise reduction has also increased in the electric power steering apparatus from the viewpoint of improving comfort. Various inventions have been made so far for reducing the noise of the electric power steering apparatus. In particular, as a technology relating to a ball screw structure which is one of the vibration sources, the inventions disclosed in JP-A-2017-7587 (Patent Document 1) and JP-A-11-11334 (Patent Document 2) are known. ing.
　特許文献１の電動パワーステアリング装置は、ナットの回転運動をラック軸の軸方向運動に変換するボールねじ機構と、モータの駆動力をナットに伝達するベルトと、ナットの軸方向の一端側においてナットを回転可能に支持するベアリングと、を備え、ナットに直接又は間接に作用するベルトの張力に対向する反力を発生させる反力発生機構を設けている。反力発生機構は、ベアリングのアウターレースが当接するハウジングの内周面に形成された傾斜面により構成される。特許文献１の電動パワーステアリング装置は、反力発生機構により、ベルトテンションによるナットの傾きを防止し、騒音低減を図っている（要約及び段落００１０参照）。 The electric power steering apparatus disclosed in Patent Document 1 includes a ball screw mechanism that converts rotational movement of a nut into axial movement of a rack shaft, a belt that transmits driving force of a motor to the nut, and a nut at one end side of the nut in the axial direction. And a bearing for rotatably supporting, and a reaction force generating mechanism for generating a reaction force that opposes the tension of the belt acting directly or indirectly on the nut. The reaction force generating mechanism is constituted by an inclined surface formed on the inner peripheral surface of the housing on which the outer race of the bearing abuts. In the electric power steering apparatus of Patent Document 1, the inclination of the nut due to the belt tension is prevented by the reaction force generation mechanism, and the noise is reduced (see abstract and paragraph 0010).
　また特許文献２の電動パワーステアリング装置は、ナットのねじ溝のうち、両端部のねじ溝の谷を、中央部のねじ溝の谷よりも深く設定している。これにより、特許文献１の電動パワーステアリング装置は、ラック軸のたわみ変形における自由度をナットの中央部に対して両端部の方が大きくなるようにし、ボールねじのねじ溝とボールとの接触圧力を中央と両端とでほぼ均等にしている。これにより、特許文献１の電動パワーステアリング装置は、ボールとナットとの接触によって発生する騒音を低減している。 Further, in the electric power steering device of Patent Document 2, the valleys of the screw grooves at both ends of the screw grooves of the nut are set deeper than the valleys of the screw groove at the central portion. Thus, in the electric power steering apparatus of Patent Document 1, the degree of freedom in the bending deformation of the rack shaft is made larger at both ends with respect to the central part of the nut, and the contact pressure between the screw groove of the ball screw and the ball The center and both ends are almost even. Thus, the electric power steering device of Patent Document 1 reduces the noise generated by the contact between the ball and the nut.
特開２０１７－７５８７号公報Unexamined-Japanese-Patent No. 2017-7587 特開平１１－１１３３４号公報JP 11-11334 A
　しかしながら、特許文献１や特許文献２においては、ナット肉厚が円周方向や軸方向において同一であるため、固有周波数が一つに固定される。もしその固有周波数においてボール等で加振されれば、単一周波数の鋭いピークをもつ周波数特性により共振現象を起こす。このような共振現象を回避するには、ナットの周方向や軸方向で固有周波数を分散することが必要であると考える。 However, in Patent Document 1 and Patent Document 2, since the thickness of the nut is the same in the circumferential direction and the axial direction, the natural frequency is fixed to one. If it is excited by a ball or the like at the natural frequency, a resonance phenomenon is caused by the frequency characteristic having a sharp peak of a single frequency. In order to avoid such a resonance phenomenon, it is considered necessary to disperse natural frequencies in the circumferential direction or axial direction of the nut.
　本発明の目的は、電動パワーステアリング装置の低騒音化を図ることにある。 An object of the present invention is to reduce the noise of an electric power steering apparatus.
　上記目的を達成するために、本発明の電動パワーステアリング装置は、
　ラック回転軸に沿って螺旋状に形成されたラック側ボールねじ溝を有するラックと、
　ナット回転軸に沿って螺旋状に形成されたナット側ボールねじ溝を有し、かつ前記ラック回転軸と同軸上に配置されるナットと、
　前記ラック側ボールねじ溝と前記ナット側ボールねじ溝とによって構成されるボール循環溝に配置される複数のボールと、
　ベルトを介して前記ナットに動力を出力する電動モータと、
を備え、
　前記ナットは、前記ナット側ボールねじ溝の連続する中心角３６０°の範囲において、前記ナット側ボールねじ溝を中心角１２０°毎に相互に重ならないように第１範囲、第２範囲及び第３範囲の３つの範囲に区分する場合、第１範囲、第２範囲及び第３範囲が相互に異なる径方向の肉厚の領域を有する。 In order to achieve the above object, the electric power steering apparatus of the present invention is:
A rack having a rack side ball screw groove spirally formed along the rack rotation axis;
A nut having a nut side ball screw groove spirally formed along the nut rotation axis, and arranged coaxially with the rack rotation axis;
A plurality of balls disposed in a ball circulation groove constituted by the rack side ball screw groove and the nut side ball screw groove;
An electric motor that outputs power to the nut via a belt;
Equipped with
The nut has a first range, a second range, and a third range so that the nut-side ball screw groove does not overlap each other at a central angle of 120 ° in a range of a continuous central angle of 360 ° of the nut-side ball screw groove. When dividing into three ranges of ranges, the first range, the second range, and the third range have mutually different radial thickness areas.
　本発明によれば、ナット厚みが周方向又は軸方向で異なるため、ボール加振によって発生する振動の固有周波数をナットの周方向又は軸方向で分散させることができ、耳障りなピーク周波数騒音を低減できる。上記した以外の課題，構成及び効果は，以下の実施形態の説明により明らかにされる。 According to the present invention, since the thickness of the nut is different in the circumferential direction or in the axial direction, the natural frequency of the vibration generated by the ball vibration can be dispersed in the circumferential direction or the axial direction of the nut, reducing offensive peak frequency noise. it can. Problems, configurations, and effects other than those described above will be clarified by the description of the embodiments below.
本発明の電動パワーステアリング装置１の一実施例について、一部を断面で示す正面図である。It is a front view which shows a part in a cross section about one Example of the electrically-driven power steering apparatus 1 of this invention. 図１の電動パワーステアリング装置１について、操舵機構２の部分を示す、ラックの軸方向に垂直な断面図である。FIG. 2 is a cross-sectional view perpendicular to an axial direction of a rack, showing a portion of a steering mechanism 2 of the electric power steering apparatus 1 of FIG. 1. 図１の電動パワーステアリング装置１について、ボールねじ機構２０の部分を示す、ラックの軸方向に垂直な断面図である。FIG. 2 is a cross-sectional view perpendicular to the axial direction of the rack, showing a portion of a ball screw mechanism 20 of the electric power steering apparatus 1 of FIG. 1; 図１の電動パワーステアリング装置１について、ボールねじ機構２０の部分を示す、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面図である。FIG. 2 is a cross-sectional view including a rotation axis L1 of the rack 6 and showing a portion of the ball screw mechanism 20 of the electric power steering apparatus 1 of FIG. 1 and parallel to the rotation axis L1 of the rack 6; 本発明に係るボールねじ機構２０との比較例となるボールねじ機構２０’周辺の構造を、一部断面で示す概略図である。It is the schematic which shows the structure of ball screw mechanism 20 'periphery which becomes a comparative example with the ball screw mechanism 20 which concerns on this invention by a partial cross section. 図５の比較例のボールねじ機構２０’において、ベルト２７にテンションがかかった状態を示す概略図である。In ball screw mechanism 20 'of a comparative example of Drawing 5, it is a schematic diagram showing the state where tension was applied to belt 27. FIG. 図５の比較例のボールねじ機構２０’のモデルを示す図である。It is a figure which shows the model of ball screw mechanism 20 'of the comparative example of FIG. 本発明の第１実施例に係るボールねじ機構２０Ａについて、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面を示す概略図である。FIG. 5 is a schematic view showing a cross section including a rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in the ball screw mechanism 20A according to the first embodiment of the present invention. 図８のＢ－Ａ－Ｃ断面を第１基準軸線Ｌ１に垂直な平面に投影した概略図である。FIG. 9 is a schematic view of the BAC section of FIG. 8 projected onto a plane perpendicular to a first reference axis L1. ボール循環溝２１，２３の１周分を直線状に展開した概略図である。It is the schematic which expanded 1 round's worth of ball | bowl circulation grooves 21 and 23 in linear form. 本発明の第２実施例に係るボールねじ機構２０Ｂについて、第１基準軸線Ｌ１に垂直な断面を示す概略図である。It is the schematic which shows the cross section perpendicular | vertical to the 1st reference axis line L1 about the ball screw mechanism 20B which concerns on 2nd Example of this invention. 本発明の第３実施例に係るボールねじ機構２０Ｃについて、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面を示す概略図である。FIG. 21 is a schematic view showing a cross section including a rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in a ball screw mechanism 20C according to a third embodiment of the present invention. 本発明の第４実施例に係るボールねじ機構２０Ｄについて、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面を示す概略図である。It is the schematic which shows the cross section parallel to the rotating shaft L1 of the rack 6 including the rotating shaft L1 of the rack 6 about ball screw mechanism 20D which concerns on 4th Example of this invention. 本発明の第５実施例に係るボールねじ機構２０Ｅについて、第１基準軸線Ｌ１に垂直な断面を示す概略図である。It is the schematic which shows the cross section perpendicular | vertical to the 1st reference axis line L1 about the ball screw mechanism 20E which concerns on 5th Example of this invention. 本発明の第５実施例のボールねじ機構２０Ｅの変更例を示す図であり、第１基準軸線Ｌ１に垂直な断面を示す概略図である。It is a figure which shows the modification of the ball screw mechanism 20E of 5th Example of this invention, and is the schematic which shows a cross section perpendicular | vertical to the 1st reference axis line L1.
　以下、本発明の実施例について説明する。 Hereinafter, examples of the present invention will be described.
　まず、本発明に係る電動パワーステアリング装置１の全体構成について、説明する。後述する実施例１～７が適用される電動パワーステアリング装置１の一実施例の構成を説明するが、各実施例が適用される電動パワーステアリング装置１は、以下で説明する構成のものに限定される訳ではない。 First, the entire configuration of the electric power steering apparatus 1 according to the present invention will be described. Although the configuration of one embodiment of the electric power steering apparatus 1 to which the first to seventh embodiments described later are applied will be described, the electric power steering apparatus 1 to which each embodiment is applied is limited to the configuration described below. It is not the case.
　［電動パワーステアリング装置］
　図１は、本発明の電動パワーステアリング装置１の一実施例について、一部を断面で示す正面図である。図２は、図１の電動パワーステアリング装置１について、操舵機構２の部分を示す、ラックの軸方向に垂直な断面図である。図３は、図１の電動パワーステアリング装置１について、ボールねじ機構２０の部分を示す、ラックの軸方向に垂直な断面図である。図４は、図１の電動パワーステアリング装置１について、ボールねじ機構２０の部分を示す、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面図である。 [Electric power steering device]
FIG. 1 is a front view partially showing an electric power steering apparatus 1 according to an embodiment of the present invention in cross section. FIG. 2 is a cross-sectional view perpendicular to the axial direction of the rack, showing a portion of the steering mechanism 2 in the electric power steering apparatus 1 of FIG. FIG. 3 is a cross-sectional view perpendicular to the axial direction of the rack, showing a portion of the ball screw mechanism 20 in the electric power steering apparatus 1 of FIG. FIG. 4 is a cross-sectional view including the rotation axis L1 of the rack 6 and showing a portion of the ball screw mechanism 20 of the electric power steering apparatus 1 of FIG. 1 and parallel to the rotation axis L1 of the rack 6.
　電動パワーステアリング装置1は、エンジンを駆動源とする車両に搭載されている。電動パワーステアリング装置1は、操舵機構２、ギアハウジング３および電動モータ４を備える。操舵機構２は、ステアリングホイール（図示せず）の回転に伴い転舵輪（図示せず）を転舵させる。ギアハウジング３内には、操舵機構２が収容されている。電動モータ４は、操舵機構２に操舵力を付与する。 The electric power steering apparatus 1 is mounted on a vehicle having an engine as a drive source. The electric power steering apparatus 1 includes a steering mechanism 2, a gear housing 3 and an electric motor 4. The steering mechanism 2 steers the steered wheels (not shown) as the steering wheel (not shown) rotates. A steering mechanism 2 is accommodated in the gear housing 3. The electric motor 4 applies a steering force to the steering mechanism 2.
　操舵機構２は、操舵軸５およびラック（転舵軸）６を備える。操舵軸５は、ステアリングシャフト７およびピニオンシャフト８を有する。ステアリングシャフト7は、ステアリングホイールと一体に回転する。ピニオンシャフト８は、トーションバー９を介してステアリングシャフト７と接続されている。ピニオンシャフト８の外周には、ピニオンギア８ａが形成されている。ピニオンギア８ａは、ラック６の外周の所定範囲に形成されたラックギア６ａと噛み合う。ラック６は、操舵軸５の回転に応じて車体幅方向（ラック６の軸方向）にそって運動する。ラック６は棒状部材（軸）６ａに歯６ｂを切ったものであり、棒状部材６ａをラックバーと呼び、棒状部材に切られた歯６ｂをラックギアと呼ぶ。ラック６は、鋼材等の鉄系金属材料を用いて形成されている。 The steering mechanism 2 includes a steering shaft 5 and a rack (steering shaft) 6. The steering shaft 5 has a steering shaft 7 and a pinion shaft 8. The steering shaft 7 rotates integrally with the steering wheel. The pinion shaft 8 is connected to the steering shaft 7 via a torsion bar 9. A pinion gear 8 a is formed on the outer periphery of the pinion shaft 8. The pinion gear 8 a meshes with a rack gear 6 a formed in a predetermined range on the outer periphery of the rack 6. The rack 6 moves along the vehicle body width direction (axial direction of the rack 6) according to the rotation of the steering shaft 5. The rack 6 has teeth 6b cut in a rod-like member (shaft) 6a. The rod-like member 6a is called a rack bar, and the teeth 6b cut in a rod-like member are called a rack gear. The rack 6 is formed using an iron-based metal material such as steel.
　図１に示すように、ラック６（ラックバー６ａ）の両端には、１対のタイロッド１０，１０の端部が接続されている。ギアハウジング３内には、操舵軸５の一部およびラック６の一部が収容されている。ギアハウジング３は、第１ギアハウジング部３ａおよび第２ギアハウジング部３ｂがラック６の軸方向（車幅方向）に突き当て状態で接合された二分割構造を有する。第１ギアハウジング部３ａ及び第２ギアハウジング部３ｂは、アルミニウム合金を用いて金型鋳造により形成されている。ギアハウジング３の１対の端部には、ラックク６が貫通する開口部３ｉ，３ｉが設けられている。ギアハウジング３の１対の端部には、ダストブーツ１１の車幅方向内側端が固定されている。ダストブーツ１１は、外部からギアハウジング３内への水分の侵入を抑制するためのものである。ダストブーツ１１は、合成樹脂を用いて蛇腹形状を成す環状部材として形成されている。ダストブーツ１１の車幅方向外側端は、タイロッド１０の車幅方向内側端に固定されている。 As shown in FIG. 1, ends of a pair of tie rods 10 are connected to both ends of the rack 6 (rack bar 6 a). In the gear housing 3, a part of the steering shaft 5 and a part of the rack 6 are accommodated. The gear housing 3 has a two-divided structure in which the first gear housing portion 3 a and the second gear housing portion 3 b are butted in an axial direction (vehicle width direction) of the rack 6. The first gear housing portion 3a and the second gear housing portion 3b are formed by die casting using an aluminum alloy. Openings 3i, 3i through which the rack 6 penetrates are provided at a pair of ends of the gear housing 3. The vehicle width direction inner end of the dust boot 11 is fixed to a pair of ends of the gear housing 3. The dust boot 11 is for suppressing the entry of moisture into the gear housing 3 from the outside. The dust boot 11 is formed as an annular member having a bellows shape using a synthetic resin. The vehicle width direction outer end of the dust boot 11 is fixed to the vehicle width direction inner end of the tie rod 10.
　図２に示すように、操舵軸５には、トルクセンサ１２が設けられている。トルクセンサ１２は、操舵機構２に生じる操舵トルク（トーションバートルク）を検出する。トルクセンサ１２は、トーションバー９、検出ユニット１２ａ及びセンサハウジング１２ｂを有する。検出ユニット１２ａは、トーションバー９の捩れ量を検出する。センサハウジング１２ｂは、車載状態において、第２ギアハウジング部３ｂの鉛直方向上側に設けられている。 As shown in FIG. 2, the steering shaft 5 is provided with a torque sensor 12. The torque sensor 12 detects a steering torque (torsion bar torque) generated in the steering mechanism 2. The torque sensor 12 has a torsion bar 9, a detection unit 12a and a sensor housing 12b. The detection unit 12 a detects the amount of torsion of the torsion bar 9. The sensor housing 12b is provided on the upper side in the vertical direction of the second gear housing portion 3b in the on-vehicle state.
　図３及び図４に示すように、電動モータ４は、三相ブラシレスモータが用いられている。電動モータ４は、モータハウジング１３内に収容されている。モータハウジング１３は、第１ギアハウジング部３ａに接合されている。特に本実施例では、モータハウジング１３は第１ギアハウジング部３ａと一体に成形されている。電動モータ４は、モータシャフト４ａ、ロータ４ｂ及びステータ４ｃを有する。モータシャフト４ａは、ロータ４ｂと一体に設けられている。モータシャフト４ａには、入力プーリ（モータ側プーリ）１４が取り付けられている。入力プーリ１４は、円筒状に形成されている。ロータ４ｂは、モータハウジング１３に対しモータシャフト４ａの軸方向周り（軸中心を中心とする周方向）に回転可能に支持されている。ステータ４ｃは、モータハウジング１３に固定されている。電動モータ４は、マイクロコンピュータ１５ａが搭載された制御装置１５によって駆動制御される。 As shown in FIGS. 3 and 4, a three-phase brushless motor is used as the electric motor 4. The electric motor 4 is accommodated in a motor housing 13. The motor housing 13 is joined to the first gear housing portion 3a. In particular, in the present embodiment, the motor housing 13 is integrally formed with the first gear housing portion 3a. The electric motor 4 has a motor shaft 4a, a rotor 4b and a stator 4c. The motor shaft 4a is provided integrally with the rotor 4b. An input pulley (motor-side pulley) 14 is attached to the motor shaft 4a. The input pulley 14 is formed in a cylindrical shape. The rotor 4 b is rotatably supported by the motor housing 13 around the axial direction of the motor shaft 4 a (in the circumferential direction around the axial center). The stator 4 c is fixed to the motor housing 13. The electric motor 4 is drive-controlled by the control device 15 in which the microcomputer 15a is mounted.
　制御装置１５は、ＥＣＵハウジング１６を有する。ＥＣＵハウジング１６は、ＥＣＵハウジング本体部１７、蓋部材１８およびコネクタ部１９を有する。ＥＣＵハウジング本体部１７は、モータハウジング１３と接合されている。ＥＣＵハウジング本体部１７において電動モータ４と反対側には、ＥＣＵハウジング本体部１７の内部が露出するように形成されたＥＣＵハウジング本体開口部１７ａが設けられている。ＥＣＵハウジング本体部１７の内部には、回路基板１５ｂが収容されている。回路基板１５ｂには、ＣＰＵ、ＲＡＭ、ＲＯＭ等を含むマイクロコンピュータ１５ａや図外のパワーモジュールが実装されている。ＥＣＵハウジング本体開口部１７ａは蓋部材１８により閉塞されている。ＥＣＵハウジング本体部１７及び蓋部材１８は、アルミニウム合金を用いて形成されている。 The controller 15 has an ECU housing 16. The ECU housing 16 has an ECU housing main body portion 17, a lid member 18 and a connector portion 19. The ECU housing main body 17 is joined to the motor housing 13. An ECU housing main body opening 17 a formed so as to expose the inside of the ECU housing main body 17 is provided on the side opposite to the electric motor 4 in the ECU housing main body 17. A circuit board 15 b is accommodated in the ECU housing main body 17. On the circuit board 15b, a microcomputer 15a including a CPU, a RAM, a ROM and the like and a power module (not shown) are mounted. The ECU housing main body opening 17 a is closed by the lid member 18. The ECU housing main body 17 and the lid member 18 are formed using an aluminum alloy.
　コネクタ部１９は、ＥＣＵハウジング本体部１７の外部に露出するように設けられている。コネクタ部１９は、合成樹脂を用いて形成されている。コネクタ部１９には、車両側から電力を供給するための電源系ハーネスが電気的に接続される。また、コネクタ部１９には、トルクセンサ１２の出力信号や車両の走行状態に関する情報（車速等）の信号を入力するための信号系ハーネスが電気的に接続される。コネクタ部１９に入力された電力及び信号は、図外のバスバーを介して制御装置１５に入力される。制御装置１５は、入力された各信号に基づき、電動モータ４を駆動制御するためのモータトルク指令を演算し、モータトルク指令に応じた電力を電動モータ４に供給する。 The connector portion 19 is provided to be exposed to the outside of the ECU housing main body portion 17. The connector portion 19 is formed using a synthetic resin. A power supply system harness for supplying power from the vehicle side is electrically connected to the connector portion 19. Further, a signal system harness for inputting an output signal of the torque sensor 12 and a signal of information (such as a vehicle speed) related to the traveling state of the vehicle is electrically connected to the connector portion 19. The power and signal input to the connector unit 19 are input to the control device 15 via a bus bar (not shown). The control device 15 calculates a motor torque command for driving and controlling the electric motor 4 based on each input signal, and supplies the electric motor 4 with the electric power according to the motor torque command.
　電動モータ4とラック６との間には、ボールねじ機構２０が設けられている。ボールねじ機構２０は、ギアハウジング３のボールねじ機構収容部３ｃ内に収容されている。ボールねじ機構収容部３ｃは、ギアハウジング３の車載状態において、第１ギアハウジング部３ａ及び第２ギアハウジング部３ｂの接合面Ａの鉛直方向上側に設けられている。第１ギアハウジング部３ａは、接合面Ａに臨む開口部３ｅを有する。第１ギアハウジング部３ａの鉛直方向下端には、開口部３ｅに面した凹部３ｆが設けられている。凹部３ｆは、ギアハウジング３の車載状態において、鉛直方向下側に向かって凹むように形成されている（図３参照）。凹部３ｆには、ギアハウジング３内に侵入した水分を検知する水分検知システムの送信側ユニット３０が設けられている。送信側ユニット３０は、接合面Ａにおいて第１ギアハウジング部３ａと第２ギアハウジング部３ｂとの間に挟み込まれることにより、ギアハウジング３に固定されている。これにより、送信側ユニット３０の脱落を抑制することができる。第１ギアハウジング部３ａ及び第２ギアハウジング部３ｂの内壁のうち、ギアハウジング３の車載状態における鉛直方向下側の部分は、開口部３ｅに近づくほど鉛直方向下側に向かって傾斜するように形成された傾斜面３ｇを有する。第１ギアハウジング部３ａに設けられた傾斜面３ｇの一部には、溝部３ｈが形成されている。溝部３ｈは、ギアハウジング３の車載状態において、鉛直方向下側に向かって凹み、かつ、送信側ユニット３０側に向かって延びるように形成されている。ギアハウジング３において、ラック６が収容されたラック収容部３ｄは、ボールねじ機構収容部３ｃから右側転舵輪側及び左側転舵輪側のそれぞれに向かって筒状に延びるように形成されている。 A ball screw mechanism 20 is provided between the electric motor 4 and the rack 6. The ball screw mechanism 20 is accommodated in a ball screw mechanism accommodating portion 3 c of the gear housing 3. The ball screw mechanism accommodating portion 3 c is provided above the joint surface A of the first gear housing portion 3 a and the second gear housing portion 3 b in the vertical direction when the gear housing 3 is mounted on the vehicle. The first gear housing portion 3 a has an opening 3 e facing the joint surface A. At the lower end in the vertical direction of the first gear housing portion 3a, a recess 3f facing the opening 3e is provided. The recess 3 f is formed to be recessed downward in the vertical direction when the gear housing 3 is mounted on the vehicle (see FIG. 3). The recess 3 f is provided with a transmission side unit 30 of a moisture detection system for detecting moisture that has entered the gear housing 3. The transmission side unit 30 is fixed to the gear housing 3 by being sandwiched between the first gear housing portion 3a and the second gear housing portion 3b at the joint surface A. Thereby, drop-off | omission of the transmission side unit 30 can be suppressed. Of the inner walls of the first gear housing portion 3a and the second gear housing portion 3b, the vertically lower portion of the gear housing 3 in the mounted state of the gear housing 3 is inclined toward the vertically lower side as it approaches the opening 3e. It has an inclined surface 3g formed. A groove 3h is formed in a part of the inclined surface 3g provided in the first gear housing 3a. The groove 3 h is formed so as to be recessed downward in the vertical direction and extend toward the transmission unit 30 in the vehicle-mounted state of the gear housing 3. In the gear housing 3, the rack accommodating portion 3 d in which the rack 6 is accommodated is formed to extend cylindrically from the ball screw mechanism accommodating portion 3 c toward the right turning wheel and the left turning wheel.
　ボールねじ機構２０は、電動モータ４の回転力をラック６に伝達する減速機である。ボールねじ機構２０は、転舵軸側ボールねじ溝（ラック側ボールねじ溝）２１、ナット２２、ナット側ボールねじ溝２３、ボール２４及びリターンチューブ２５を有する。転舵軸側ボールねじ溝２１は、ラック６の外周側に設けられた螺旋状の溝である。ナット２２は、ラック６を包囲するように設けられている。ナット２２は、鋼材を用いて環状に形成されている。ナット２２は、ギアハウジング３に対し回転可能に、かつ、ギアハウジング３に対し軸方向には移動不能に支持されている。ナット２２の外周には、出力プーリ（ナット側プーリ）２６が固定されている。出力プーリ２６は、ラック６を包囲するように円筒状に形成されている。出力プーリ２６は、ナット２２の回転に伴い回転する。出力プーリ２６には、ベルト（伝達部材）２７が掛けられている。ベルト２７は、入力プーリ１４の回転を出力プーリ２６に伝達する。 The ball screw mechanism 20 is a reduction gear that transmits the rotational force of the electric motor 4 to the rack 6. The ball screw mechanism 20 has a steered shaft side ball screw groove (rack side ball screw groove) 21, a nut 22, a nut side ball screw groove 23, a ball 24 and a return tube 25. The steered shaft side ball screw groove 21 is a spiral groove provided on the outer peripheral side of the rack 6. The nut 22 is provided to surround the rack 6. The nut 22 is annularly formed using a steel material. The nut 22 is rotatably supported relative to the gear housing 3 and axially immovably supported relative to the gear housing 3. An output pulley (nut side pulley) 26 is fixed to the outer periphery of the nut 22. The output pulley 26 is formed in a cylindrical shape so as to surround the rack 6. The output pulley 26 rotates as the nut 22 rotates. A belt (transmission member) 27 is hung on the output pulley 26. The belt 27 transmits the rotation of the input pulley 14 to the output pulley 26.
　ラック６の回転軸（回転中心線）を第１基準軸線Ｌ１としたとき、入力プーリ１４の回転軸（回転中心線）となる第２基準軸線Ｌ２は、第１基準軸線Ｌ１に対し径方向にオフセットするように配置されている。ラック６とナット２２とは、ベルト２７のテンションがかかっていない理想的な状態において、両者の回転軸が一致するように配置されている。このため、第２基準軸線Ｌ２は、ナット２２の回転軸に対しても径方向にオフセットするように配置されている。 Assuming that the rotation axis (rotation center line) of the rack 6 is the first reference axis L1, the second reference axis L2 serving as the rotation axis (rotation center line) of the input pulley 14 is in the radial direction with respect to the first reference axis L1. It is arranged to be offset. The rack 6 and the nut 22 are arranged such that their rotational axes coincide in an ideal state in which the belt 27 is not tensioned. For this reason, the second reference axis L2 is also arranged to be radially offset with respect to the rotation axis of the nut 22.
　ナット側ボールねじ溝２３は、ナット２２の内周に設けられた螺旋状の溝である。ナット側ボールねじ溝２３は、転舵軸側ボールねじ溝２１と共にボール循環溝を構成する。ボール２４は、ボール循環溝２１，２３内に複数設けられている。ボール２４は、鋼材を用いて形成されている。リターンチューブ２５は、ナット２２の外周側に設けられ、ボール循環溝２１，２３の一端側または他端側に達したボール２４は、リターンチューブ２５を介してボール循環溝２１，２３の他端側または一端側へと戻される。 The nut-side ball screw groove 23 is a spiral groove provided on the inner periphery of the nut 22. The nut side ball screw groove 23 constitutes a ball circulation groove together with the steered shaft side ball screw groove 21. A plurality of balls 24 are provided in the ball circulation grooves 21 and 23. The balls 24 are formed using steel. The return tube 25 is provided on the outer peripheral side of the nut 22, and the ball 24 reaching the one end side or the other end side of the ball circulation grooves 21, 23 is the other end side of the ball circulation grooves 21, 23 via the return tube 25 Or it is returned to one end.
　ボールねじ機構２０は、ラック６に対するナット２２の回転に伴い、ボール循環溝２１，２３内を複数のボール２４が移動し、ナット２２に対してラック６をラックバー６ａの長手方向（車幅方向）に移動させる。 With the rotation of the nut 22 relative to the rack 6, the ball screw mechanism 20 moves a plurality of balls 24 in the ball circulation grooves 21 and 23, and the rack 6 with respect to the nut 22 moves in the longitudinal direction of the rack bar 6a Move to).
　ナット２２は、第１基準軸線Ｌ１方向の一端部がベアリング３１により、ギアハウジング３を構成する第２ギアハウジング部３ｂに支持されている。この支持構造は、ナット２２を片持ち状に支持している。ベアリング３１は、ベアリングボール３７とアウターレース３２とで構成される。本実施例では、ベアリング３１を構成するインナーレースはナット２２により構成されている。 The nut 22 is supported at one end in the direction of the first reference axis L 1 by the bearing 31 on the second gear housing 3 b of the gear housing 3. This support structure supports the nut 22 in a cantilever manner. The bearing 31 is composed of a bearing ball 37 and an outer race 32. In the present embodiment, the inner race constituting the bearing 31 is constituted by the nut 22.
　本発明は、電動パワーステアリング装置１の低騒音化、特に、ボールねじ機構２０のナット２２で発生する固有周波数（固有振動数）を分散し、騒音を低減する。ナット２２にはボール２４が配置されるナット側ボールねじ溝２３が形成される。ナット側ボールねじ溝２３は回転軸に沿って螺旋状に形成される。この螺旋溝２３は、連続する３６０°の範囲を１２０°毎の区間に分けた場合に、各１２０°の区間（範囲）が異なる肉厚（肉厚の平均寸法）の領域を有するようにする。ナット２２の肉厚は連続的に変化するようにするとよい。例えば、ナットはその外周面がテーパー状を成すように形成されるとよい。 The present invention reduces the noise of the electric power steering apparatus 1, in particular, disperses the natural frequency (natural frequency) generated by the nut 22 of the ball screw mechanism 20 and reduces the noise. The nut 22 is formed with a nut-side ball screw groove 23 in which the ball 24 is disposed. The nut-side ball screw groove 23 is formed helically along the rotation axis. The spiral groove 23 is configured such that each of the 120 ° sections (ranges) has a region of different wall thickness (average thickness) when the continuous 360 ° range is divided into 120 ° intervals. . The thickness of the nut 22 may be changed continuously. For example, the nut may be formed such that its outer peripheral surface is tapered.
　以下、ナット２２で発生する固有周波数を分散する実施例について、説明する。なお、以下で説明する各実施例において、共通する構成には同じ符号を付し、説明を省略する。 Hereinafter, an embodiment for dispersing the natural frequency generated by the nut 22 will be described. In each embodiment described below, the same reference numerals are given to the same components, and the description will be omitted.
　［実施例１］
　本発明に係る実施例の特徴を分かり易く説明するために、最初に、本発明に係る実施例に対する比較例について、図５乃至図７を用いて説明する。 Example 1
In order to explain the features of the embodiment according to the present invention in an easy-to-understand manner, first, a comparative example to the embodiment according to the present invention will be described with reference to FIG. 5 to FIG.
　図５は、本発明に係るボールねじ機構２０との比較例となるボールねじ機構２０’周辺の構造を、一部断面で示す概略図である。なお、図５に図示ずる断面は、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面図である。 FIG. 5 is a schematic view showing, in a partial cross section, a structure around a ball screw mechanism 20 ', which is a comparative example with the ball screw mechanism 20 according to the present invention. The cross section shown in FIG. 5 is a cross sectional view including the rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6.
　ボールねじ機構２０’は、ラック６とナット２２’とボール２４とで構成されている。ボールねじ機構２０’のナット２２’には、ナット側プーリ２６が取り付けられており、モータ側プーリ１４とナット側プーリ２６との間にはベルト２７が掛け渡される。ベルト２７が掛け渡されるモータ側プーリ１４には、図４と同様にモータ４が繋がっており、ベルト２７によってモータ４の動力がナット２２’に伝達される。また、ナット２２’はベアリングボール３７とアウターレース３２とで構成されたベアリング３１を介してハウジングを構成する第２ギアハウジング部３ｂと接続されている。 The ball screw mechanism 20 ′ comprises a rack 6, a nut 22 ′ and a ball 24. A nut side pulley 26 is attached to a nut 22 'of the ball screw mechanism 20', and a belt 27 is stretched between the motor side pulley 14 and the nut side pulley 26. The motor 4 is connected to the motor side pulley 14 on which the belt 27 is stretched, as in FIG. 4, and the power of the motor 4 is transmitted to the nut 22 ′ by the belt 27. Further, the nut 22 ′ is connected to the second gear housing portion 3 b constituting the housing via the bearing 31 constituted by the bearing balls 37 and the outer race 32.
　図６は、図５の比較例のボールねじ機構２０’において、ベルト２７にテンションがかかった状態を示す概略図である。 FIG. 6 is a schematic view showing a state in which the belt 27 is tensioned in the ball screw mechanism 20 'of the comparative example of FIG.
　モータ４が駆動すると、ベルト２７にテンションがかかる。また、ナット２２’は第１基準軸線Ｌ１方向の一端部がベアリング３１で第２ギアハウジング部３ｂに支持されている。この支持構造は、ナット２２’を片持ち状に支持している。このため、図６に示すように、ベルトテンションはナット２２’のベルト５が掛けられた他端側に働く。その結果、ナット２２’の他端側（プーリ２６側）がモータ側プーリ１４の側に引き付けられ、ナット２２’に傾きが生じる。すなわち、第１基準軸線Ｌ１の方向とナット２２’の回転軸Ｌ３の方向との間に傾き角θが生じる。 When the motor 4 is driven, the belt 27 is tensioned. Further, one end of the nut 22 'in the direction of the first reference axis L1 is supported by the bearing 31 on the second gear housing 3b. This support structure supports the nut 22 'in a cantilever manner. Therefore, as shown in FIG. 6, the belt tension acts on the other end side of the nut 22 'on which the belt 5 is hung. As a result, the other end side (the pulley 26 side) of the nut 22 'is drawn to the motor side pulley 14 side, and the nut 22' is inclined. That is, an inclination angle θ is generated between the direction of the first reference axis L1 and the direction of the rotation axis L3 of the nut 22 '.
　ナット２２’に傾きが生じると、ボール２４が通過・回転するナット２２’の溝（ナット側ボールねじ溝）２３とラック６の溝（ラック側ボールねじ溝）２１とによって構成されるボール循環溝は、ナット２２’のプーリ２６側（ベルトテンションを受ける側）では、引っ張られる側（紙面の上側）では広く、その反対側（紙面の下側）では狭くなる。すなわち、ボール循環溝２１，２３の深さ寸法は、ナット２２’のプーリ２６側において、引っ張られる側では大きく、その反対側では小さくなる。ボール循環溝２１，２３の狭いところでは、大きな荷重を受けるボール２４ａ（黒く塗りつぶしたボール２４）が存在することになる。 When the nut 22 'is inclined, a ball circulating groove is constituted by the groove (nut side ball screw groove) 23 of the nut 22' through which the ball 24 passes and rotates and the groove (rack side ball screw groove) 21 of the rack 6. Is wide on the side to be pulled (the upper side of the drawing) on the pulley 26 side (the side receiving the belt tension) of the nut 22 ′ and narrow on the opposite side (the lower side of the drawing). That is, the depth dimensions of the ball circulation grooves 21 and 23 are large on the side to be pulled on the pulley 26 side of the nut 22 ′ and become small on the opposite side. Where the ball circulation grooves 21 and 23 are narrow, balls 24a (black balls 24) which receive a large load are present.
　図７は、図５の比較例のボールねじ機構２０’のモデルを示す図である。 FIG. 7 is a view showing a model of the ball screw mechanism 20 'of the comparative example of FIG.
　図７のモデルは、ラック６と、ボール２４と、ナット２２’と、ボール循環溝２１，２３と、を有する。本来ボール循環溝２１，２３は、螺旋状になっているが、本モデルでは単純な１周の円状とした。ボール２４がナット２２’とラック６との間のボール循環溝２１，２３を自転しながら回転する。その際に、ボール２４は、ナット２２’に加振力を与え、ナット２２’は固有周波数で共振することとなる。ここで、ナット２２’の径方向の厚みＴが円周上で均一であれば、各ボール２４の加振に対して、同一の固有周波数を持つことになる。この場合、ボール２４の数だけ同一の固有周波数が存在し、一つの周波数で鋭いピークをもつことになり、一種の共振状態を引き起こす可能性がある。 The model of FIG. 7 has a rack 6, a ball 24, a nut 22 ′, and ball circulation grooves 21 and 23. Originally, the ball circulation grooves 21 and 23 are helical, but in this model, they are circular in a simple circle. The ball 24 rotates while rotating the ball circulation grooves 21 and 23 between the nut 22 ′ and the rack 6. At that time, the ball 24 applies an excitation force to the nut 22 ', and the nut 22' resonates at the natural frequency. Here, if the thickness T in the radial direction of the nut 22 'is uniform on the circumference, the vibration of each ball 24 has the same natural frequency. In this case, the same natural frequency as the number of balls 24 exists, and a sharp peak is generated at one frequency, which may cause a kind of resonance.
　以下、このような共振現象を抑制する実施例について説明する。 Hereinafter, an embodiment for suppressing such a resonance phenomenon will be described.
　図８は、本発明の第１実施例に係るボールねじ機構２０Ａについて、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面を示す概略図である。 FIG. 8 is a schematic view showing a cross section including the rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in the ball screw mechanism 20A according to the first embodiment of the present invention.
　本実施例のボールねじ機構２０Ａは、ラック６と、ナット２２Ａと、ボール２４と、を有している。ラック６は、その回転軸（ラック回転軸）Ｌ１に沿って螺旋状に形成されたラック側ボールねじ溝２１を有する。ナット２２は、その回転軸（ナット回転軸）Ｌ３に沿って螺旋状に形成されたナット側ボールねじ溝を有し、かつラック回転軸Ｌ１と同軸上に配置される。ナット２２にベルト２７の張力が作用していない状態では、ラック回転軸Ｌ１とナット回転軸Ｌ３とは一致する。 The ball screw mechanism 20A of the present embodiment includes a rack 6, a nut 22A, and a ball 24. The rack 6 has a rack-side ball screw groove 21 spirally formed along its rotation axis (rack rotation axis) L1. The nut 22 has a nut-side ball screw groove spirally formed along the rotation axis (nut rotation axis) L3 and is disposed coaxially with the rack rotation axis L1. When the tension of the belt 27 is not applied to the nut 22, the rack rotation axis L1 and the nut rotation axis L3 coincide with each other.
　ボールねじ機構２０Ａのナット２２Ａには、ナット側プーリ２６が取り付けられており、モータ側プーリ１４とナット側プーリ２６との間にはベルト２７が掛け渡される。さらに、ナット２２Ａはベアリングボール３７とアウターレース３２とで構成されたベアリング３１を介してギアハウジング３を構成する第２ギアハウジング部３ｂと接続されている。本実施例でも、上述した比較例と同様に、ナット２２は第１基準軸線Ｌ１方向の一端部がベアリング３１で第２ギアハウジング部３ｂに片持ち状に支持されている。 A nut side pulley 26 is attached to a nut 22A of the ball screw mechanism 20A, and a belt 27 is stretched between the motor side pulley 14 and the nut side pulley 26. Further, the nut 22A is connected to the second gear housing 3b constituting the gear housing 3 via the bearing 31 constituted by the bearing balls 37 and the outer race 32. Also in the present embodiment, one end of the nut 22 in the direction of the first reference axis L1 is supported by the bearing 31 in a cantilevered manner by the second gear housing 3b as in the comparative example described above.
　本実施例のボールねじ機構２０Ａは、ナット２２Ａの外周面がテーパー状に形成されていることを特徴としている。すなわち、ナット２２Ａは、第１基準軸線Ｌ１方向の一方の端部の外径が他方の端部に対して大きく、一方の端部側から他方の端部側に向かって外周面が縮径するように形成されている。本実施例では、ベアリング３１に支持される側の外径が、ナット側プーリ２６が設けられる側の外径よりも大きくなるように、ナット２２Ａを形成している。ベアリング３１に支持される側の外径が、ナット側プーリ２６が設けられる側の外径よりも小さくなるように、ナット２２Ａを形成することも可能である。 The ball screw mechanism 20A of this embodiment is characterized in that the outer peripheral surface of the nut 22A is formed in a tapered shape. That is, in the nut 22A, the outer diameter of one end in the direction of the first reference axis L1 is larger than that of the other end, and the diameter of the outer peripheral surface decreases from one end to the other It is formed as. In the present embodiment, the nut 22A is formed such that the outer diameter of the side supported by the bearing 31 is larger than the outer diameter of the side on which the nut side pulley 26 is provided. It is also possible to form the nut 22A such that the outer diameter of the side supported by the bearing 31 is smaller than the outer diameter of the side on which the nut side pulley 26 is provided.
　ナット２２Ａの肉厚Ｔが変化する領域（テーパー状の領域）は、ボール２４がナット２２Ｄとラック６との間に存在して、力の伝達を行うボールねじ構造の有効範囲（力伝達範囲又はベアリングボール介在範囲）３３を含んで、ナット側プーリ２６が設けられる端部まで設けられている。 A region (a tapered region) in which the thickness T of the nut 22A changes is an effective range (force transmission range or a force transmission range or a ball screw structure where the ball 24 exists between the nut 22D and the rack 6 to transmit force). It is provided to the end where the nut side pulley 26 is provided, including the bearing ball interposed area 33).
　なお、ナット側ボールねじ溝２３が形成された部分の、ナット２２Ａの内周面の径（内径）は、第１基準軸線Ｌ１方向において、製造誤差の範囲内で一定である。また、ナット２２Ａの内周面からのナット側ボールねじ溝２３の深さ寸法も、第１基準軸線Ｌ１方向において、製造誤差の範囲内で一定である。 The diameter (inner diameter) of the inner peripheral surface of the nut 22A in the portion where the nut-side ball screw groove 23 is formed is constant within the range of manufacturing error in the direction of the first reference axis L1. Further, the depth dimension of the nut-side ball screw groove 23 from the inner peripheral surface of the nut 22A is also constant within the range of manufacturing error in the direction of the first reference axis L1.
　ナット２２Ａの外周面がテーパー状に形成されていることによって、ナット２２Ａの肉厚が第１基準軸線Ｌ１方向（ラック軸方向）上で異なっているため、各ボール２４の加振に対して固有周波数を分散することが出来、ナット２２Ａの共振を回避することができる。また、ナット２２Ａにアンダーカットが構成されないため、金型等での成型が容易となり、ナット２２Ａを加工し易くなる。さらに、ベアリング３１に支持される端部側に比べてその反対の端部側（プーリ２６側）の径方向の肉厚が薄い形状とすることにより、ベアリング３１側の反対側、つまり、ベルト２７側が軽くなる。その結果、ベアリング３１側を固定端としてナット２２Ａが回転するときに、慣性モーメントを小さくできるというメリットがある。 Since the thickness of the nut 22A is different in the direction of the first reference axis L1 (the rack axis direction) by forming the outer peripheral surface of the nut 22A in a tapered shape, it is unique to the excitation of each ball 24 The frequency can be dispersed, and resonance of the nut 22A can be avoided. In addition, since an undercut is not formed on the nut 22A, molding with a mold or the like becomes easy, and the nut 22A becomes easy to process. Furthermore, by making the thickness in the radial direction of the opposite end side (pulley 26 side) thinner than the end side supported by the bearing 31, the opposite side to the bearing 31 side, that is, the belt 27 The side gets lighter. As a result, there is an advantage that the moment of inertia can be reduced when the nut 22A rotates with the bearing 31 side as the fixed end.
　図９は、図８のＢ－Ａ－Ｃ断面を第１基準軸線Ｌ１に垂直な平面に投影した概略図である。Ｂ－Ａ－Ｃ断面は、ボールねじ機構２０Ａを、ボール循環溝２１，２３が描く螺旋に沿って切断した断面を示している。Ｂ－Ａ－Ｃ断面は、ナット２２Ａの径方向外側から螺旋状のナット側ボールねじ溝２３又はボール循環溝２１，２３を通過させて第１基準軸線Ｌ１に下ろした垂線（第１基準軸線Ｌ１に垂直な直線状の線分）を、ナット側ボールねじ溝２３又はボール循環溝２１，２３に沿ってＣ点まで移動させる際に、垂線が第１基準軸線Ｌ１を中心として回転しながら、且つ第１基準軸線Ｌ１に沿って移動しながら切断するナット２２Ａの断面である。Ｂ－Ａ－Ｃ断面は、螺旋に沿う断面と呼ぶ場合がある。 FIG. 9 is a schematic view of the BAC section of FIG. 8 projected on a plane perpendicular to the first reference axis L1. The BAC cross section shows a cross section obtained by cutting the ball screw mechanism 20A along a spiral drawn by the ball circulation grooves 21 and 23. The BAC cross section is a vertical line (first reference axis L1) which has been passed through the spiral nut side ball screw groove 23 or the ball circulation grooves 21 and 23 from the radially outer side of the nut 22A and dropped to the first reference axis L1. When moving the straight line segment perpendicular to the) to the point C along the nut-side ball screw groove 23 or the ball circulation groove 21, 23, while the vertical line rotates around the first reference axis L1, and It is a cross section of the nut 22A which cuts while moving along the first reference axis L1. The BAC cross section may be referred to as a cross section along a spiral.
　Ｂ点とＣ点とは、螺旋の中心角θａにおいて３６０°離間しており、第１基準軸線Ｌ１方向において離れた位置にある。以下、第１基準軸線Ｌ１に垂直な平面に投影したＢ－Ａ－Ｃ断面を、Ｂ－Ａ－Ｃ投影断面と呼んで説明する。また、第１基準軸線Ｌ１に垂直な平面に投影したＢ－Ａ－Ｃ断面は、螺旋に沿う投影断面と呼ぶ場合がある。 The points B and C are separated by 360 ° at the central angle θa of the spiral, and are separated in the direction of the first reference axis L1. Hereinafter, the BAC section projected on a plane perpendicular to the first reference axis L1 will be referred to as a BAC projected section. In addition, the BAC section projected on a plane perpendicular to the first reference axis L1 may be referred to as a projected section along a spiral.
　図９に示すように、Ｂ－Ａ－Ｃ投影断面上において、ナット２２Ａの径方向の肉厚（肉厚寸法）Ｔは円周上（第１基準軸線Ｌ１を中心とする周方向）で異なっている。すなわち、Ｂ－Ａ－Ｃ投影断面上におけるナット２２Ａの肉厚Ｔは、第１基準軸線Ｌ１を中心とする周方向において変化している。なお、第１基準軸線Ｌ１に垂直な断面上においては、ナット２２Ａの肉厚Ｔは、周方向において一定である。 As shown in FIG. 9, in the B-A-C projected cross section, the thickness (thickness dimension) T in the radial direction of the nut 22A differs on the circumference (the circumferential direction about the first reference axis L1). ing. That is, the thickness T of the nut 22A on the BAC projected cross section changes in the circumferential direction about the first reference axis L1. In a cross section perpendicular to the first reference axis L1, the thickness T of the nut 22A is constant in the circumferential direction.
　本実施例では、Ｂ－Ａ－Ｃ投影断面上において、ナット２２Ａの径方向の肉厚Ｔは、外周面の周方向に連続的に変化している。範囲Ｒ１（第１範囲），Ｒ２（第２範囲），Ｒ３（第３範囲）の肉厚Ｔは、Ｂ点側からＣ点側に向かって、或いはＣ点側からＢ点側に向かって、それぞれ所定の数値範囲で変化する。範囲Ｒ１の肉厚Ｔは範囲Ｒ２の肉厚Ｔの最大値以上であり、範囲Ｒ２の肉厚Ｔは範囲Ｒ３の肉厚Ｔの最大値以上である。なお、範囲Ｒ１とＲ２との境界で範囲Ｒ１の肉厚Ｔと範囲Ｒ２の肉厚Ｔとは等しく、範囲Ｒ２とＲ３との境界で範囲Ｒ２の肉厚Ｔと範囲Ｒ３の肉厚Ｔとは等しい。これにより、固有周波数は肉厚の変化に合わせて連続的に分散され、各ボール２４による加振によって引き起こされる共振現象の抑制効果を向上することができる。 In the present embodiment, the radial thickness T of the nut 22A continuously changes in the circumferential direction of the outer peripheral surface on the BAC projected cross section. The thickness T of the ranges R1 (first range), R2 (second range), R3 (third range) is from point B toward point C, or from point C toward point B, Each changes in a predetermined numerical range. The thickness T of the range R1 is not less than the maximum value of the thickness T of the range R2, and the thickness T of the range R2 is not less than the maximum value of the thickness T of the range R3. The thickness T of the range R1 is equal to the thickness T of the range R2 at the boundary between the ranges R1 and R2, and the thickness T of the range R2 and the thickness T of the range R3 at the boundary between the ranges R2 and R3. equal. Thereby, the natural frequency is continuously dispersed in accordance with the thickness change, and the suppression effect of the resonance phenomenon caused by the excitation by each ball 24 can be improved.
　本実施例では、固有周波数を連続的に広範囲に分散する例を示しているが、固有周波数を少なくとも２つに分散するために、ナット２２Ａ（２２）を以下で説明するように構成するとよい。 In this embodiment, an example is shown in which the natural frequency is continuously dispersed widely, but in order to disperse the natural frequency into at least two, the nut 22A (22) may be configured as described below.
　図６で説明したように、ナット２２Ａを片持ち状に支持する支持構造においては、ベルト２７のテンションによってナット２２Ａが傾くため、ボール循環溝２１，２３は、紙面の上側では広く、紙面の下側では狭くなっている。つまり、紙面上側の中心角１８０°の範囲は紙面下側の中心角１８０°の範囲よりボール循環溝２１，２３は広くなっている。ナット２２Ａは、特にボール循環溝２１，２３が狭くなる紙面下側の中心角１８０°の範囲において、各ボール２４から加振力を受けることになる。 As described in FIG. 6, in the supporting structure for supporting the nut 22A in a cantilevered manner, since the nut 22A is inclined by the tension of the belt 27, the ball circulation grooves 21 and 23 are wide on the upper side of the paper surface and below the paper surface. It is narrow on the side. That is, in the range of the central angle 180 ° on the upper side of the drawing, the ball circulation grooves 21 and 23 are wider than the range of the central angle 180 ° on the lower side of the drawing. The nut 22A receives an exciting force from each ball 24 particularly in the range of a central angle of 180 ° on the lower side of the drawing where the ball circulation grooves 21 and 23 become narrow.
　そこで、Ｂ－Ａ－Ｃ投影断面上において、Ｂ点（起点）からＣ点（終点）までの３６０°の範囲の連続するボール循環溝２１，２３を、相互に重ならない中心角１２０°の３つの範囲Ｒ１，Ｒ２，Ｒ３に区分し、ナット２２Ａが各範囲Ｒ１，Ｒ２，Ｒ３に相互に肉厚Ｔの異なる領域を有するようにする。例えば、範囲Ｒ１には肉厚Ｔ１の領域があり、範囲Ｒ２には肉厚Ｔ２の領域があり、範囲Ｒ３には肉厚Ｔ３の領域があり、肉厚Ｔ１，Ｔ２，Ｔ３は相互に異なる値（肉厚寸法）である。 Therefore, in the BAC projected section, 3 continuous ball circulation grooves 21 and 23 in the range of 360 ° from the point B (starting point) to the point C (end point) have a central angle of 120 ° that do not overlap each other. The two ranges R1, R2 and R3 are divided so that the nut 22A has mutually different areas of thickness T in each range R1, R2 and R3. For example, range R1 has a region of thickness T1, range R2 has a region of thickness T2, range R3 has a region of thickness T3, and thicknesses T1, T2 and T3 are mutually different values (Thickness dimension).
　本実施例では、Ｂ－Ａ－Ｃ投影断面上において、肉厚ＴはＢ点からＣ点まで連続的に変化するが、見方を変えると、ナット２２Ａは肉厚Ｔの平均値が各範囲Ｒ１，Ｒ２，Ｒ３毎に異なっているという見方もできる。 In the present embodiment, the thickness T changes continuously from the point B to the point C on the BAC projected cross section, but from the viewpoint, the average value of the thickness T of the nut 22A is in each range R1. , R2, R3 can also be viewed differently.
　ナット２２Ａの肉厚Ｔは、中心角１２０°毎に異なるため、ボール循環溝２１，２３の紙面上側の中心角１８０°の範囲と紙面下側の中心角１８０°の範囲とに、それぞれ少なくとも２つの固有周波数をもつことになる。すなわち、本実施例では、紙面上側の中心角１８０°の範囲には範囲Ｒ１による固有周波数と範囲Ｒ３による固有周波数とが存在し、紙面下側の中心角１８０°の範囲には範囲Ｒ１（中心角３０°の範囲）による固有周波数と範囲Ｒ２による固有周波数と範囲Ｒ３（中心角３０°の範囲）による固有周波数とが存在する。したがって、肉厚Ｔが中心角３６０°の範囲で同一の場合には固有周波数は一つであるが、本実施例の場合には中心角１８０°の範囲において、固有周波数を２つに分散できる。ナット２２Ａを相互に重ならない中心角１２０°の３つの範囲Ｒ１，Ｒ２，Ｒ３に区分することで、起点となるＢ点の位置を周方向に変化させても、常に中心角１８０°の範囲において固有周波数を２つに分散できる。 The thickness T of the nut 22A is different at every central angle of 120 °, so at least 2 in the range of the central angle of 180 ° above the paper surface of the ball circulating grooves 21 and 23 and in the range of 180 ° at the lower surface of the paper. It will have one natural frequency. That is, in the present embodiment, the natural frequency in the range R1 and the natural frequency in the range R3 exist in the range of the central angle 180 ° on the upper side of the sheet, and the range R1 (center There are natural frequencies according to the angle 30 °), natural frequencies according to the range R2 and natural frequencies according to the range R3 (central angle 30 °). Therefore, when the thickness T is the same in the range of the central angle 360 °, there is one natural frequency, but in the case of this embodiment, the natural frequencies can be dispersed into two in the range of the central angle 180 °. . By dividing the nut 22A into three ranges R1, R2 and R3 with a central angle of 120 ° not overlapping with each other, the position of the point B as the starting point is always changed in the range of the central angle 180 ° The natural frequencies can be split into two.
　特に、ボール循環溝２１，２３が狭くなる紙面下側の中心角１８０°の範囲において、固有周波数を２つに分散できるようにすることにより、各ボール２４による加振によって引き起こされる共振現象の抑制効果を向上することができる。 In particular, by making it possible to disperse the natural frequency into two in the range of the central angle 180 ° on the lower side of the drawing where the ball circulation grooves 21 and 23 become narrow, the resonance phenomenon caused by the vibration by each ball 24 is suppressed. The effect can be improved.
　図１０は、ボール循環溝２１，２３の１周分を直線状に展開した概略図である。 FIG. 10 is a schematic view of one revolution of the ball circulation grooves 21 and 23 developed in a straight line.
　本実施例では、図１０に示すように、ナット２２Ａの径方向の肉厚Ｔは、ボール循環溝２１，２３のＢ－Ａ－Ｃ投影断面上における１周分において、直線的に変化する例を示している。しかし、固有周波数を肉厚Ｔの変化に合わせて連続的に分散させるためには、ナット２２Ａの径方向の肉厚Ｔの変化が連続的であればよく、例えば、図１０の紙面上方向に凸となる曲線形状や下方向に凸となる曲線形状であってもよい。 In this embodiment, as shown in FIG. 10, the thickness T in the radial direction of the nut 22A changes linearly in one rotation on the BAC projected section of the ball circulation grooves 21 and 23. Is shown. However, in order to continuously disperse the natural frequency in accordance with the change in the thickness T, it is only necessary that the change in the thickness T in the radial direction of the nut 22A be continuous. It may be a curved shape that is convex or a curved shape that is convex downward.
　また、Ｂ－Ａ－Ｃ投影断面上における径方向の肉厚Ｔの変化は、Ｂ点からＣ点までの１周分において連続的である必要はなく、断続的（離散的）に変化するようにしてもよい。例えば、肉厚Ｔは、中心角１２０°の３つの範囲Ｒ１，Ｒ２，Ｒ３毎に断続的に（離散的）に変化させてもよい。 In addition, the change in thickness T in the radial direction on the BAC projected cross section does not have to be continuous in one rotation from the point B to the point C, but changes intermittently (discretely) You may For example, the thickness T may be intermittently (discretely) changed every three ranges R1, R2 and R3 having a central angle of 120 °.
　［実施例２］
　図１１は、本発明の第２実施例に係るボールねじ機構２０Ｂについて、第１基準軸線Ｌ１に垂直な断面を示す概略図である。 Example 2
FIG. 11 is a schematic view showing a cross section perpendicular to the first reference axis L1 in the ball screw mechanism 20B according to the second embodiment of the present invention.
　本実施例においては、ナット２０Ｂの径方向の肉厚Ｔは、第１基準軸線Ｌ１を中心とする周方向において、変化している。本実施例では、紙面上下方向の肉厚Ｔが長く、左右方向の肉厚Ｔが短い。これによりナット２０Ｂの外周は楕円形状をしている。つまり、第１基準軸線Ｌ１に垂直な断面上において、第１基準軸線Ｌ１と交差する第１の直線Ｌ４を引いた場合に、第１の直線Ｌ４に対して一方の側のナット２０Ｂ外周（すなわち肉厚Ｔ）と第１の直線Ｌ４に対して他方の側のナット２０Ｂ外周（すなわち肉厚Ｔ）とは、第１の直線Ｌ４に対して線対称な形状である。さらに、第１基準軸線Ｌ１に垂直な断面上において、第１基準軸線Ｌ１と交差し第１の直線Ｌ３に垂直な第２の直線Ｌ５を引いた場合に、第２の直線Ｌ５に対して一方の側のナット２０Ｂ外周（すなわち肉厚Ｔ）と第２の直線Ｌ５に対して他方の側のナット２０Ｂ外周（すなわち肉厚Ｔ）とは、第２の直線Ｌ５に対して線対称な形状である。これにより、本実施例のナット２０Ｂは、周方向において固有周波数の分散が可能となる。その他の構成は、実施例１と同様である。 In the present embodiment, the radial thickness T of the nut 20B changes in the circumferential direction about the first reference axis L1. In the present embodiment, the thickness T in the vertical direction in the drawing is long, and the thickness T in the horizontal direction is short. Thus, the outer periphery of the nut 20B has an elliptical shape. That is, when a first straight line L4 intersecting with the first reference axis L1 is drawn on a cross section perpendicular to the first reference axis L1, the outer periphery of the nut 20B on one side with respect to the first straight line L4 (ie, The thickness T) and the outer periphery of the nut 20B on the other side with respect to the first straight line L4 (that is, the thickness T) have a shape that is line symmetrical with respect to the first straight line L4. Furthermore, when a second straight line L5 crossing the first reference axis L1 and perpendicular to the first straight line L3 is drawn on a cross section perpendicular to the first reference axis L1, one side of the second straight line L5 is obtained. The outer circumference of the nut 20B on one side (that is, the thickness T) and the outer circumference of the nut 20B on the other side with respect to the second straight line L5 (that is, the thickness T) are line symmetrical with respect to the second straight line L5. is there. Thus, the nut 20B of the present embodiment can disperse natural frequencies in the circumferential direction. The other configuration is the same as that of the first embodiment.
　本実施例は、点対称の形状の一例として楕円形状の場合を示したが、ラック６の肉厚Ｔが同じになる部分が周方向に等間隔に並んでいればよい。すなわち、ナット２２Ｂは、径方向の肉厚Ｔの変化が第１基準軸線Ｌ１（ナット回転軸）を中心とする周方向において等間隔に繰り返されるように形成されている。 In the present embodiment, an elliptical shape is shown as an example of a point-symmetrical shape, but portions having the same thickness T of the rack 6 may be arranged at equal intervals in the circumferential direction. That is, the nut 22B is formed such that changes in the thickness T in the radial direction are repeated at equal intervals in the circumferential direction around the first reference axis L1 (nut rotating shaft).
　［実施例３］
　図１２は、本発明の第３実施例に係るボールねじ機構２０Ｃについて、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面を示す概略図である。 [Example 3]
FIG. 12 is a schematic view showing a cross section including the rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in the ball screw mechanism 20C according to the third embodiment of the present invention.
　本実施例のボールねじ機構２０Ｃにおいて、ナット２２Ｃは第１基準軸線Ｌ１方向の中央部における所定の位置から両端に向かって縮径する外周面を有するようなアンダーカットがない形状を有している。例えば、ナット２２Ｃの第１基準軸線Ｌ１方向（ラック軸方向）の中央部が両端部に比べて径方向外側に膨らんだ、いわゆる、たる型形状である。その他の構成は、実施例１と同様である。 In the ball screw mechanism 20C of the present embodiment, the nut 22C has such a shape that there is no undercut so as to have an outer peripheral surface that decreases in diameter from the predetermined position in the central portion in the direction of the first reference axis L1. . For example, it has a so-called barrel shape in which the central portion in the first reference axis L1 direction (the rack axial direction) of the nut 22C bulges radially outward as compared with the both end portions. The other configuration is the same as that of the first embodiment.
　これにより、ナット２２Ｃは実施例１と同様に固有周波数を分散することができる。特に本実施例では、たる型形状の膨らみ具合を調整することにより、固有周波数の分布を調整することができる。 Thus, the nut 22C can disperse natural frequencies as in the first embodiment. In the present embodiment, in particular, the distribution of natural frequencies can be adjusted by adjusting the degree of expansion of the barrel shape.
　［実施例４］
　図１３は、本発明の第４実施例に係るボールねじ機構２０Ｄについて、ラック６の回転軸Ｌ１を含み且つラック６の回転軸Ｌ１に平行な断面を示す概略図である。 Example 4
FIG. 13 is a schematic view showing a cross section including a rotation axis L1 of the rack 6 and parallel to the rotation axis L1 of the rack 6 in a ball screw mechanism 20D according to a fourth embodiment of the present invention.
　本実施例のボールねじ機構２０Ｄにおいては、ボール２４がナット２２Ｄとラック６との間に存在して、力の伝達を行うボールねじ構造の有効範囲（力伝達範囲又はベアリングボール介在範囲）３３に限って、ナット２２Ｄの肉厚Ｔが変化する領域を有している。すなわち、ナット２２Ｄの径方向の肉厚が変化する領域は、ナット回転軸方向において、ナット２２Ｄとラック６との間にボール２４が介在する範囲３３に構成されている。その他の構成は、実施例１と同様である。 In the ball screw mechanism 20D of this embodiment, the ball 24 is present between the nut 22D and the rack 6 to transmit the force to the effective range (force transmission range or bearing ball intervening range) 33 of the ball screw structure. Limitedly, there is a region where the thickness T of the nut 22D changes. That is, the region in which the radial thickness of the nut 22D changes is configured in a range 33 in which the ball 24 is interposed between the nut 22D and the rack 6 in the nut rotational axis direction. The other configuration is the same as that of the first embodiment.
　本実施例においても第１実施例と同様に、固有周波数を分散することができる。 Also in this embodiment, natural frequencies can be dispersed as in the first embodiment.
　本実施例のナット２２Ｄは、第１基準軸線Ｌ１方向（回転軸方向）の少なくとも一部に、外周面の全周に亘って円筒形状に形成された円筒部３４，３５を有している。円筒部３４は、第１基準軸線Ｌ１方向においてベアリング３１が設けられる一端部に形成され、円筒部３４にはベアリングアウターレース３２やべリングボール３７などが構成される。また円筒部３５は、第１基準軸線Ｌ１方向において、ベアリング３１が設けられる一端部とは反対側の他端部に形成され、円筒部３５にはナット側プーリ２６が取り付けられる。 The nut 22D of the present embodiment has cylindrical portions 34 and 35 formed in a cylindrical shape over the entire circumference of the outer peripheral surface at least a part in the first reference axis L1 direction (rotational axis direction). The cylindrical portion 34 is formed at one end where the bearing 31 is provided in the direction of the first reference axis L1, and the cylindrical portion 34 includes the bearing outer race 32, the bearing ball 37, and the like. The cylindrical portion 35 is formed at the other end opposite to the end where the bearing 31 is provided in the direction of the first reference axis L1, and the nut side pulley 26 is attached to the cylindrical portion 35.
　円筒部３４，３５があることで、クランプが容易になるというメリットがある。円筒部３４があることで、ベアリング３１のインナーレースを構成する面がアウターレース３２と平行になり、ベアリング３１を容易に構成することができる。また円筒部３５があることで、ナット側プーリ２６の取り付けが容易になる。 The presence of the cylindrical portions 34 and 35 has the advantage of facilitating clamping. The presence of the cylindrical portion 34 makes the surface constituting the inner race of the bearing 31 parallel to the outer race 32, and the bearing 31 can be easily configured. Further, the presence of the cylindrical portion 35 facilitates the attachment of the nut-side pulley 26.
　なお、円筒部３４，３５はいずれか一方を設けるようにしてもよい。 Note that either of the cylindrical portions 34 and 35 may be provided.
　［実施例５］
　図１４は、本発明の第５実施例に係るボールねじ機構２０Ｅについて、第１基準軸線Ｌ１に垂直な断面を示す概略図である。 [Example 5]
FIG. 14 is a schematic view showing a cross section perpendicular to the first reference axis L1 in a ball screw mechanism 20E according to a fifth embodiment of the present invention.
　本実施例のボールねじ機構２０Ｅでは、実施例２のナット２２Ｂを有する。ナット２２Ｂは周方向に肉厚が変化する。ナット２２Ｂの肉厚Ｔの厚くなる部分にリターンチューブ２５が設けられている。肉厚Ｔの厚い部分（肉厚Ｔ６の部分）では、リターンチューブ２５を固定しやすいというメリットがある。その他の構成は、実施例１及び実施例２と同様である。 The ball screw mechanism 20E of the present embodiment has the nut 22B of the second embodiment. The thickness of the nut 22B changes in the circumferential direction. A return tube 25 is provided at the thickened portion of the thickness T of the nut 22B. The thick portion (thick portion T6 portion) of the thickness T has an advantage that the return tube 25 can be easily fixed. The other configuration is the same as that of the first embodiment and the second embodiment.
　図１５は、本発明の第５実施例のボールねじ機構２０Ｅの変更例を示す図であり、第１基準軸線Ｌ１に垂直な断面を示す概略図である。 FIG. 15 is a view showing a modification of the ball screw mechanism 20E of the fifth embodiment of the present invention, and is a schematic view showing a cross section perpendicular to the first reference axis L1.
　本変更例では、実施例５のリターンチューブ２５を、図１５に示すように、ナット２２Ｂの肉厚Ｔが薄くなる部分（肉厚Ｔ７の部分）に取り付けている。リターンチューブ２５を肉厚Ｔの薄い部分に取り付けることによって、リターンチューブ２５をナット２２Ｂの最大外径（肉厚Ｔの厚い部分の径）の内側に配置できる。或いは、リターンチューブ２５がナット２２Ｂの最大外径の外側にはみ出す場合もそのはみだし部分を小さくすることができる。その結果、ボールねじ機構２０Ｅ（２０）の小型化が図れる。その他の構成は、実施例１及び実施例２と同様である。 In this modification, as shown in FIG. 15, the return tube 25 of the fifth embodiment is attached to the portion (the portion of the thickness T7) in which the thickness T of the nut 22B is reduced. By attaching the return tube 25 to the thin portion of the wall thickness T, the return tube 25 can be disposed inside the maximum outer diameter (diameter of the thick portion of the wall thickness T) of the nut 22B. Alternatively, even when the return tube 25 protrudes outside the maximum outer diameter of the nut 22B, the protruding portion can be reduced. As a result, the ball screw mechanism 20E (20) can be miniaturized. The other configuration is the same as that of the first embodiment and the second embodiment.
　なお、本発明は上記した各実施例に限定されるものではなく、様々な変形例が含まれる。例えば、上記した実施例は本発明を分かりやすく説明するために詳細に説明したものであり、必ずしも全ての構成を備えるものに限定されるものではない。また、ある実施例の構成の一部を他の実施例の構成に置き換えることが可能であり、また、ある実施例の構成に他の実施例の構成を加えることも可能である。また、各実施例の構成の一部について、他の構成の追加・削除・置換をすることが可能である。 The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the embodiments described above are described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, with respect to a part of the configuration of each embodiment, it is possible to add, delete, and replace other configurations.
　１…電動パワーステアリング装置、４…電動モータ、６…ラック、２０，２０Ａ，２０Ｂ，２０Ｃ，２０Ｄ，２０Ｅ…ボールねじ機構、２１…ラック側ボールねじ溝、２２，２２Ａ、２２Ｂ，２２Ｃ，２２Ｄ…ナット、２３…ナット側ボールねじ溝、（２１，２３）…ボール循環溝、２４…ボール、２５…リターンチューブ、２６…プーリ、２７…ベルト、３１…軸受（ベアリング）、３３…ボールねじ有効範囲（ナットとラックとの間にボールが介在する範囲）、３４，３５…円筒部、Ｌ１…ラック回転軸（第１基準軸線、ナット回転軸）、Ｌ３…ナット回転軸、Ｌ４…第１の直線、Ｌ５…第２の直線、Ｒ１…ナット側ボールねじ溝の第１範囲、Ｒ２…ナット側ボールねじ溝の第２範囲、Ｒ３…ナット側ボールねじ溝の第３範囲、Ｔ，Ｔ１，Ｔ２，Ｔ３…ナットの径方向肉厚、Ｔ６…肉厚の厚い部分の肉厚、Ｔ７…肉厚の薄い部分の肉厚。 DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 4 ... Electric motor, 6 ... Rack, 20, 20A, 20B, 20C, 20D, 20E ... Ball screw mechanism, 21 ... Rack side ball screw groove, 22, 22A, 22B, 22C, 22D ... Nut, 23 ... Nut side ball screw groove, (21, 23) ... Ball circulation groove, 24 ... Ball, 25 ... Return tube, 26 ... Pulley, 27 ... Belt, 31 ... Bearing (bearing), 33 ... Ball screw effective range (Range in which a ball intervenes between the nut and the rack), 34, 35: cylindrical portion, L1: rack rotation shaft (first reference axis, nut rotation shaft), L3: nut rotation shaft, L4: first straight line , L5: second straight line, R1: first range of nut side ball screw groove, R2: second range of nut side ball screw groove, R3: third range of nut side ball screw groove, T, T , The radial thickness of the T2, T3 ... nut, T6 ... the thickness of the thick part of the wall thickness, the thickness of the thin portion of the T7 ... thickness.

Claims (14)

  1. 　ラック回転軸に沿って螺旋状に形成されたラック側ボールねじ溝を有するラックと、
    　ナット回転軸に沿って螺旋状に形成されたナット側ボールねじ溝を有し、かつ前記ラック回転軸と同軸上に配置されるナットと、
    　前記ラック側ボールねじ溝と前記ナット側ボールねじ溝とによって構成されるボール循環溝に配置される複数のボールと、
    　ベルトを介して前記ナットに動力を出力する電動モータと、
    を備え、
    　前記ナットは、前記ナット側ボールねじ溝の連続する中心角３６０°の範囲において、前記ナット側ボールねじ溝を中心角１２０°毎に相互に重ならないように第１範囲、第２範囲及び第３範囲の３つの範囲に区分する場合、第１範囲、第２範囲及び第３範囲が相互に異なる径方向の肉厚の領域を有することを特徴とするとする電動パワーステアリング装置。     A rack having a rack side ball screw groove spirally formed along the rack rotation axis;
    A nut having a nut side ball screw groove spirally formed along the nut rotation axis, and arranged coaxially with the rack rotation axis;
    A plurality of balls disposed in a ball circulation groove constituted by the rack side ball screw groove and the nut side ball screw groove;
    An electric motor that outputs power to the nut via a belt;
    Equipped with
    The nut has a first range, a second range, and a third range so that the nut-side ball screw groove does not overlap each other at a central angle of 120 ° in a range of a continuous central angle of 360 ° of the nut-side ball screw groove. An electric power steering apparatus characterized in that, when divided into three ranges, the first range, the second range and the third range have mutually different radial thickness areas.
  2. 　請求項1に記載の電動パワーステアリング装置において、
    　前記ナットの前記肉厚は、前記ナット側ボールねじ溝の螺旋状に沿って連続的に変化することを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus, wherein the thickness of the nut changes continuously along a spiral of the nut-side ball screw groove.
  3. 　請求項２に記載の電動パワーステアリング装置において、
    　前記ナットは、外周面の径がナット回転軸に沿って変化するテーパー状に形成されていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 2,
    The electric power steering apparatus, wherein the nut is formed in a tapered shape in which a diameter of an outer peripheral surface changes along a nut rotation axis.
  4. 　請求項３に記載の電動パワーステアリング装置において、
    　前記ナットは、前記ベルトが掛け渡される側の径方向の肉厚が薄く、前記ベルトが掛け渡される側とは反対側の径方向の肉厚が厚くなるようなテーパー状に形成されていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 3,
    The nut is formed in a tapered shape such that the radial thickness on the side where the belt is stretched is small and the thickness on the opposite side to the side where the belt is stretched is large. An electric power steering device characterized by
  5. 　請求項1に記載の電動パワーステアリング装置において、
    　前記ナットは、径方向の肉厚変化が前記ナット回転軸を中心とする周方向において等間隔に繰り返されるように形成されていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus according to claim 1, wherein the nut is formed so that a thickness change in a radial direction is repeated at equal intervals in a circumferential direction around the nut rotation axis.
  6. 　請求項５に記載の電動パワーステアリング装置において、
    　ラック回転軸に垂直な断面上において、ラック回転軸と交差する第１の直線を引いた場合に、第１の直線に対して一方の側の前記ナットの外周と第１の直線に対して他方の側の前記ナットの外周とは、第１の直線に対して線対称な形状であり、
    　ラック回転軸に垂直な断面上において、ラック回転軸と交差し第１の直線に垂直な第２の直線を引いた場合に、第２の直線に対して一方の側の前記ナットの外周と第２の直線に対して他方の側の前記ナットの外周とは、第２の直線に対して線対称な形状であることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 5,
    When a first straight line intersecting the rack rotation axis is drawn on a cross section perpendicular to the rack rotation axis, the outer circumference of the nut on one side with respect to the first straight line and the other with respect to the first straight line And the outer circumference of the nut on the side of the line is symmetrical about a first straight line,
    When a second straight line crossing the rack rotation axis and perpendicular to the first straight line is drawn on a cross section perpendicular to the rack rotation axis, the outer circumference of the nut on one side with respect to the second straight line and the An electric power steering apparatus characterized in that the outer periphery of the nut on the other side with respect to the straight line 2 has a shape symmetrical with respect to the second straight line.
  7. 　請求項１に記載の電動パワーステアリング装置において、
    　前記ナットは、ナット回転軸方向の所定位置から両端に向かって、アンダーカットがないことを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus according to the present invention, wherein the nut has no undercut from a predetermined position in a nut rotational axis direction toward both ends.
  8. 　請求項７に記載の電動パワーステアリング装置において、
    　前記ナットは、たる型形状に形成されていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 7,
    The electric power steering apparatus, wherein the nut is formed in a barrel shape.
  9. 　請求項1に記載の電動パワーステアリング装置において、
    　前記ナットの径方向の肉厚が変化する領域は、ナット回転軸方向において、前記ナットと前記ラックとの間に前記ボールが介在する範囲に構成されていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus according to claim 1, wherein a region in which a thickness in a radial direction of the nut changes is configured in a range in which the ball intervenes between the nut and the rack in a nut rotational axis direction.
  10. 　請求項1に記載の電動パワーステアリング装置において、
    　前記ナットは、ナット回転軸方向の少なくとも一部に、円筒部を有することを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus, wherein the nut has a cylindrical portion in at least a part in a nut rotational axis direction.
  11. 　請求項１０に記載の電動パワーステアリング装置において、
    　前記円筒部に前記ナットを片持ち状に支持する軸受が設けられていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 10,
    An electric power steering apparatus characterized in that a bearing for supporting the nut in a cantilever shape is provided on the cylindrical portion.
  12. 　請求項１０に記載の電動パワーステアリング装置において、
    　前記円筒部に前記ベルトが掛け渡されるプーリが設けられていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 10,
    An electric power steering apparatus characterized in that a pulley on which the belt is stretched is provided around the cylindrical portion.
  13. 　請求項1に記載の電動パワーステアリング装置において、
    　前記ナットは、周方向に肉厚が変化し、肉厚の薄くなる部分に前記ボールのリターンチューブが設けられていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus according to claim 1, wherein a thickness of the nut changes in a circumferential direction, and a return tube of the ball is provided at a portion where the thickness is reduced.
  14. 　請求項1に記載の電動パワーステアリング装置において、
    　前記ナットは、周方向に肉厚が変化し、肉厚の厚くなる部分に前記ボールのリターンチューブが設けられていることを特徴とする電動パワーステアリング装置。     In the electric power steering apparatus according to claim 1,
    The electric power steering apparatus according to claim 1, wherein a thickness of the nut changes in a circumferential direction, and a return tube of the ball is provided in a portion where the thickness is thick.
PCT/JP2018/035374 2017-11-10 2018-09-25 Electric power steering apparatus WO2019092998A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2017-217393 2017-11-10
JP2017217393A JP2019085084A (en) 2017-11-10 2017-11-10 Electric power steering device

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003097661A (en) * 2001-09-27 2003-04-03 Ntn Corp Ball screw and wheel steering system using it
KR20120139966A (en) * 2011-06-20 2012-12-28 주식회사 만도 Rack assist type electric power steering apparatus
DE102013010012A1 (en) * 2013-06-14 2014-12-18 Volkswagen Aktiengesellschaft Electromechanical vehicle steering
JP2017007587A (en) * 2015-06-25 2017-01-12 日立オートモティブシステムズ株式会社 Electric power steering device
CN106870667A (en) * 2017-02-28 2017-06-20 安徽江淮汽车集团股份有限公司 A kind of gap adjusting method and electric direction varying device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003097661A (en) * 2001-09-27 2003-04-03 Ntn Corp Ball screw and wheel steering system using it
KR20120139966A (en) * 2011-06-20 2012-12-28 주식회사 만도 Rack assist type electric power steering apparatus
DE102013010012A1 (en) * 2013-06-14 2014-12-18 Volkswagen Aktiengesellschaft Electromechanical vehicle steering
JP2017007587A (en) * 2015-06-25 2017-01-12 日立オートモティブシステムズ株式会社 Electric power steering device
CN106870667A (en) * 2017-02-28 2017-06-20 安徽江淮汽车集团股份有限公司 A kind of gap adjusting method and electric direction varying device

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