JP2013006517A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of keeping a buffering function over a long period of time.SOLUTION: The electric power steering device includes: a housing 25 in which an attaching hole 27, an insertion hole 28 and a stepped part 27a are formed; an electric motor; a speed reduction mechanism; and a ball screw mechanism 40. The ball screw mechanism 40 includes a ball nut 41 and a ball screw part 42, a universal joint 81 is connected to the ball screw part 42, a stopper part 75 on which the universal joint 81 abuts is formed at the housing 25 near the attaching hole 27. The electric power steering device includes a buffering device 70 fitted into the attaching hole 27 in a protruded shape to the universal joint 81 side from the stopper part 75 and compressed by the universal joint 81. The buffering device 70 includes a cylindrical collar part 71 having a flange part 74 abutting on the universal joint 81 at one end, and a buffering part 72 interposed between the collar part 71 and the attaching hole 27 and compressed in the axial direction between the flange part 74 and the stepped part 27a.

Description

  The present invention relates to an electric power steering device that assists steering of a wheel by converting rotation of an electric motor into axial movement of a rack shaft by a ball screw mechanism.

  As shown in FIG. 7 (Patent Document 1), a ball screw portion 110 is inserted into the insertion hole 102 of the electric housing 100 and the speed reduction housing 101, and a ball nut 112 is engaged with the ball screw portion 110 via the ball 111. 112 is rotatably supported by the electric housing 100 via a double-row angular ball bearing 120, and a reduction gear 130 is fitted and fixed to the ball nut 112. The rotation of the rotating shaft 141 of the electric motor 140 is transmitted to the reduction gear 130 via the input shaft 142, the drive gear 143, and the intermediate gear 144, thereby rotating the ball nut 112 and converting it into the axial movement of the ball screw portion 110. is doing.

  A universal joint (not shown) is connected to one end of the ball screw part 110, and the axial movement of the ball screw part 110 is restricted by the universal joint coming into contact with the stopper part 103 of the speed reduction housing 101. A tapered mounting hole 104 is formed in the speed reduction housing 101, and a buffer member 160 made of resin is fitted into the mounting hole 104. A step portion 105 is formed between the insertion hole 102 and the mounting hole 104, and one end of the buffer member 160 is in contact with the step portion 105. Before the universal joint comes into contact with the stopper portion 103, the buffer member 160 is compressed between the universal joint and the step portion 105, so that the energy of the axial movement of the ball screw portion 110 is absorbed, and the universal joint is attached to the stopper portion 103. The effect of reducing the interference sound when contacting is obtained.

JP 2010-47111 A

  Since the buffer member 160 is short in the axial direction, the buffer member 160 is easily compressed by the universal joint, so that the buffer member 160 is likely to sag, and the buffer function of the buffer member 160 is lowered early.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering device capable of maintaining a buffer function for a long period of time.

According to the first aspect of the present invention, a housing having a mounting hole, an insertion hole and a stepped portion, an electric motor attached to the housing, a speed reduction mechanism for reducing the rotation of the electric motor, and the speed reduction mechanism reduce the speed. A ball screw mechanism for converting the rotation into an axial movement, and the ball screw mechanism engages with the ball nut and is inserted into the mounting hole and the insertion hole. A ball screw portion, a universal joint is connected to one end of the ball screw portion, a stopper portion that contacts the universal joint is formed in the housing in the vicinity of the mounting hole, and protrudes from the stopper portion to the universal joint side. In the electric power steering apparatus having a shock absorber that is fitted in the mounting hole and compressed by the universal joint and the stepped portion
The shock absorber is cylindrical and has a collar portion that has a flange portion that abuts the universal joint at one end, and is interposed between the collar portion and the mounting hole, and is compressed in the axial direction between the flange portion and the step portion. And a buffer portion.

  According to the present invention, when the buffer portion is compressed between the flange portion and the step portion, the collar portion can prevent the buffer portion from buckling, so that the axial length of the buffer portion can be increased. The buffer function can be maintained for a long time.

1 is an overall view of an electric power steering device in an embodiment of the present invention. It is the sectional view on the AA line of FIG. 1 in embodiment of this invention. It is an expanded sectional view of the electric assist part of Drawing 1 in an embodiment of the present invention. It is an expanded sectional view of the ball screw mechanism of FIG. 1 in the embodiment of the present invention. It is a BB line expanded sectional view of Drawing 1 in an embodiment of the present invention. It is the BB line expanded sectional view of Drawing 1 in other embodiments of the present invention. It is an expanded sectional view of the conventional electric assist part.

  An embodiment of the present invention will be described with reference to FIGS. 1 is an overall view of the electric power steering apparatus, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, FIG. 3 is an enlarged cross-sectional view of the electric assist portion in FIG. 1, and FIG. FIG. 5 is an enlarged sectional view of the assist portion, and FIG. 5 is an enlarged sectional view taken along line BB of FIG.

  As shown in FIG. 1, the electric power steering device 10 imparts an axial assist force to the rack shaft 13 and a rack and pinion mechanism 11 that converts rotation of a steering wheel (not shown) into axial movement of the rack shaft 13. The electric assist unit 20 is included. The electric assist unit 20 includes an electric motor 21, a speed reduction mechanism 30 that decelerates the rotation of the rotary shaft 22 of the electric motor 21, and a ball screw mechanism 40 that converts the decelerated rotation into the axial movement of the rack shaft 12. Yes. Furthermore, the electric power steering device 10 controls an unillustrated ECU (Electronic Control Unit) that controls the electric motor 21 based on a signal from a torque sensor 80 (to be described later) and a signal from an unillustrated vehicle speed sensor. Have.

  As shown in FIGS. 1 and 2, the rack and pinion mechanism 11 includes a pinion shaft 12 through which rotation of a steering wheel (not shown) is transmitted through a column (not shown), and a gear that rotatably supports the pinion shaft 12. The housing 14, the rack shaft 13 that meshes with the pinion shaft 12 and converts the rotation of the pinion shaft 12 into the axial movement of the rack shaft 13, and the rack shaft 13 that meshes with the pinion shaft 12 from behind the rack shaft 13. It consists of a rack guide mechanism 60 for pressing.

  The gear housing 14 is fixed to a vehicle body not shown. Both ends of the rack shaft 13 protrude outward from a gear housing 14, an electric housing 24 and a reduction housing 25, which will be described later. Universal joints 81 are screwed to both ends of the rack shaft 13. The wheels are connected via a universal joint 18 via a tie rod (not shown) and a knuckle arm (not shown).

  The pinion shaft 12 has a torsion bar (not shown) in the middle in the axial direction thereof. When rotational torque acts on the input side of the pinion shaft 12, the input side of the pinion shaft and the output side of the pinion shaft are opposed to each other. ing. A torque sensor 80 for detecting the relative rotation between the input side and the output side is provided in the gear housing 14.

  The rack guide mechanism 60 is screwed into a guide hole 61 formed in the gear housing 14, a yoke 62 slidably fitted in the guide hole 61, and a screw hole formed at one end of the guide hole 61. And a pressing spring 64 inserted between the yoke 62 and the plug 63 and a resin sheet 65 attached to the yoke 62 and slidably contacting the rack shaft 13. The rack shaft 13 is pressed in the direction of meshing with the pinion shaft 12 by the pressing force of the pressing spring 64.

  A stopper portion 15 with which the universal joint 81 abuts is formed at one end of the gear housing 14. An annular mounting groove 16 is formed coaxially with the rack shaft 13 in the stopper portion 15, and a ring-shaped buffer member 75 is fitted into the mounting groove 16. The stopper portion 15 has a function of restricting the movement of the rack shaft 13 in the axial direction, and the buffer member 75 has a function of absorbing the energy of the movement of the rack shaft 13 in the axial direction and reducing the interference sound when it hits the stopper portion 15. . The buffer member 75 is manufactured from urethane material by injection molding or the like.

  An electric housing 24 is attached to the other end of the gear housing 14, and a reduction housing 25 is connected to the electric housing 24 via a bolt 26. An electric motor 21 is attached to the electric housing 24, and the electric motor 21 has a rotating shaft 22 that is driven to rotate.

  As shown in FIGS. 1, 3, and 4, the speed reduction mechanism 30 includes an input shaft 34 disposed coaxially with the rotary shaft 22, a drive gear 31 integrally formed with the input shaft 34, and a ball nut described later. A reduction gear 33 fitted and fixed to the outer periphery of the other end of 41, an intermediate shaft 35 disposed in parallel with the rack shaft 13 and the input shaft 34, and an intermediate shaft 35 are formed integrally with the drive shaft 31. And an intermediate gear 32 that meshes with the reduction gear 33. The reduction gear 33 has a larger number of teeth than the drive gear 31, and the rotation of the drive gear 31 is reduced and transmitted to a ball nut 41 described later. A resin coupling 23 is inserted between the rotary shaft 22 and the input shaft 34, and the rotation of the rotary shaft 22 is transmitted to the input shaft 34 via the coupling 23. The coupling 23 has a role of absorbing an axial shift and inclination between the rotary shaft 22 and the input shaft 34.

  The ball screw mechanism 40 includes a ball screw portion 42 formed integrally with a part of the rack shaft 13, a ball nut 41 disposed coaxially so as to surround the periphery of the ball screw portion 42, and between the ball screw portion 42 and the ball nut 41. It consists of a plurality of intervening balls 43. A circulator (not shown) for circulating the ball 84 moved to one end side of the ball nut 41 back to the other end side of the ball nut is attached to the ball nut 41 on the inner diameter side of a double-row angular ball bearing 54 described later. ing.

  The speed reduction mechanism 30 and the ball screw mechanism 40 are accommodated in the electric housing 24 and the speed reduction housing 25. The input shaft 34 is rotatably supported by a pair of ball bearings 50 and 51 held by the electric housing 24 and the speed reduction housing 25. The intermediate shaft 35 is rotatably supported by a pair of ball bearings 52 and 53 held by the electric housing 24. The ball nut 41 is rotatably supported by a double-row angular ball bearing 54 held by the electric housing 24.

  The outer ring of the double row angular ball bearing 54 is sandwiched between the step portion of the electric housing 24 and the lock nut 44, and the lock nut 44 is screwed into the screw hole of the electric housing 24. The inner ring of the double row angular ball bearing 54 is sandwiched between the stepped portion of the ball nut 41 and the lock nut 43, and the lock nut 43 is screwed into a threaded portion on the outer periphery of one end of the ball nut 41.

  The reduction gear 33 and the ball nut 41 are cantilevered only by the double-row angular ball bearing 54. When the reduction gear 33 is cantilevered, the alignment error of the reduction gear 33 may increase. Therefore, it is preferable to provide crowning in the tooth line direction on the tooth surface of the reduction gear 33. Thereby, it is possible to suppress an increase in gear noise regardless of an increase in the alignment error.

  As shown in FIGS. 3 and 4, the deceleration housing 24 is integrally formed with a stopper portion 75 with which the universal joint 81 abuts. The stopper portion 75 is formed with an annular mounting hole 27 and an insertion hole 28 coaxially with the ball screw portion 42, and a cylindrical shock absorber 70 is fitted into the mounting hole 27. A step portion 27 a is formed between the attachment hole 27 and the insertion hole 28.

  The shock absorber 70 includes a cylindrical collar portion 71 and a shock absorber 72 fixed to the outer periphery of the collar portion 71 at equal intervals on the circumference. The collar portion 71 has a flange portion 74 protruding in the outer diameter direction at the other end, and the universal joint 81 abuts on the flange portion 74. On the outer periphery of the collar portion 71, axial grooves 73 are formed at equal intervals on the circumference, and the buffer portions 72 are fitted into the axial grooves 73 and fixed with an adhesive so as not to fall off. The axial groove 73 is formed in the axial direction of the rack shaft 13 and is recessed in the inner diameter direction. The axial groove 73 is formed up to the back surface of the flange portion 74 and is recessed on the back surface of the flange portion 74. The other end of the buffer portion 72 has a protruding portion 72 a protruding in the outer diameter direction, and this protruding portion 72 a is fitted in the axial groove 73 on the back surface of the flange portion 74. One end of the buffer portion 72 is in contact with the stepped portion 27a. In this way, the buffer portion 72 is sandwiched in the axial direction of the rack shaft 13 by the flange portion 74 and the step portion 27a.

  The buffer portion 72 has a gap in the radial direction between the collar portion 71 and the insertion hole 28, and has a gap in the axial direction of the rack shaft 13 between the flange portion 74 and the stopper portion 75 of the collar portion 71. The stopper part 75 has a function of restricting the axial movement of the rack shaft 13, and the shock absorber 70 has a function of absorbing the energy of the axial movement of the rack shaft 13 and reducing the interference sound when it hits the stopper part 75. . By using the collar portion 71, it is possible to prevent the buffer portion 72 from buckling when the buffer portion 72 is crushed in the axial direction of the rack shaft 13. In this way, by increasing the axial length of the rack shaft 13 of the buffer portion 72, the buffer portion 72 can be prevented from sagging early. The collar portion 71 is molded from an iron-based material by a press or the like. The buffer portion 71 is molded from a rubber material by injection molding or the like.

  The reduction gear 33 and the ball nut 41 are supported only by a double-row angular ball bearing 54 having a large load capacity and strong moment load. That is, the reduction gear 33 and the ball nut 41 are cantilevered by the double-row angular ball bearing 54, and the other bearing is eliminated. Thereby, the layout which arrange | positions the stopper part 75 provided in the reduction | decrease housing 25 in the internal diameter side of the reduction gear 33 is attained substantially. By arranging the stopper portion 75 on the inner diameter side of the reduction gear 33, the axial length of the rack shaft 13 of the electric power steering apparatus 10 is shortened.

  The present invention is not limited to these embodiments, and can of course be implemented in various modes without departing from the gist of the present invention.

  In the embodiment described above, each of the drive gear 31, the reduction gear 33, and the intermediate gear 32 is constituted by a spur gear. As another embodiment, each of the drive gear 31, the reduction gear 33, and the intermediate gear 32 may be constituted by a helical gear.

  In the embodiment described above, the speed reduction mechanism 30 is configured by a parallel shaft gear mechanism. As another embodiment, the speed reduction mechanism 30 may be constituted by a belt / pulley mechanism.

  In the above-described embodiment, the substantially rectangular parallelepiped buffer portion 72 is fixed to the collar portion 71 with an adhesive. As another embodiment, as shown in FIG. 6, an annular fitting groove 93 may be formed in the collar portion 91, and a cylindrical buffer portion 92 may be fitted into the fitting groove 93. The collar portion 91 has a cylindrical shape like the collar portion 71, and has a flange portion 94 protruding in the outer diameter direction at the other end. The fitting groove 93 is formed in the axial direction of the rack shaft 13 and is recessed in the inner diameter direction. The fitting groove 93 is formed up to the back surface of the flange portion 94 and is recessed on the back surface of the flange portion 94. A ring-shaped flange portion 92 a protruding in the outer diameter direction is provided at the other end of the buffer portion 92, and the flange portion 92 a is fitted in a fitting groove 93 on the back surface of the flange portion 94. Compared with the substantially rectangular parallelepiped-shaped buffer portion 72, the buffer portion 92 is less likely to be loosened by the amount that the buffer portion 92 is continuous in the circumferential direction. The buffer unit 92 is a buffer unit 72 that is continuous in the circumferential direction.

25: Reduction housing (housing), 27: Mounting hole, 27a: Step part, 28: Insertion hole, 40: Ball screw mechanism, 41: Ball nut, 42: Ball screw part, 70: Shock absorber, 71: Collar part, 72: Buffer part, 74: Flange part, 75: Stopper part, 81: Universal joint

Claims (1)

A housing having a mounting hole, an insertion hole and a stepped portion, an electric motor attached to the housing, a speed reduction mechanism for reducing the rotation of the electric motor, and converting the rotation reduced by the speed reduction mechanism into an axial movement A ball screw mechanism, and the ball screw mechanism includes a ball nut rotatably supported by the housing, and a ball screw portion that engages with the ball nut and passes through the mounting hole and the insertion hole. A universal joint is connected to one end, and a stopper portion with which the universal joint abuts is formed in the housing in the vicinity of the attachment hole, and is fitted into the attachment hole in a form protruding from the stopper portion toward the universal joint, In the electric power steering device having a shock absorber compressed by the universal joint and the stepped portion,
The shock absorber is cylindrical and has a collar portion that has a flange portion that abuts the universal joint at one end, and is interposed between the collar portion and the mounting hole, and is compressed in the axial direction between the flange portion and the step portion. An electric power steering device characterized by comprising a buffer portion.

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