JP2013189112A - Electric power steering device - Google Patents

Abstract

An electric power steering apparatus capable of reducing the size and weight of a steering shaft while maintaining steering performance is provided.
A shaft coupling 43 that connects a motor shaft and a worm shaft includes a pair of yokes 51, 52 each having a plurality of claw portions 54, 55 protruding in opposite directions, and each claw portion 54, And a coupling member 53 formed with a plurality of engaging portions 64 that are engaged with 55 in the circumferential direction. A surface that covers the entire circumference of the core member 61 including the core member 61 having the engaging portion 64 disposed between the claw portions 54 and 55 and the engaging surfaces on both sides in the circumferential direction of the engaging portion 64. The member 62 is configured. Then, hemispherical protrusions 65 that are plastically deformed by abutting the claw portions 54 and 55 and applying a torque equal to or greater than a predetermined torque are formed at each portion facing the engaging surface of the surface member 62.
[Selection] Figure 3

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, power steering apparatuses for vehicles include an electric power steering apparatus (EPS) using a motor as a drive source. In such an EPS, a configuration in which the rotation of a motor is decelerated by a deceleration mechanism (for example, worm and wheel) and transmitted to a steering system is common (for example, Patent Documents 1 to 3).

  In addition, the motor shaft of the motor and the drive gear of the speed reduction mechanism are usually connected via a shaft coupling including a pair of yokes (joints) having a plurality of claw portions protruding in directions facing each other. In the EPS of Patent Document 1, an elastic body is interposed between a pair of yokes so that one end of a worm shaft as a drive gear is tiltably connected to a motor shaft, and the other end is connected to a worm by a spring or the like. The backlash is removed by urging it close to the wheel.

JP 2006-8008 A JP 2011-230553 A Japanese Patent No. 4397083

  In the conventional EPS, for example, when a reverse input is applied to the steered wheels due to a curb collision, the steering shaft rotates as the rack shaft moves in the axial direction, and the motor rotates via the speed reduction mechanism. When the end of the rack shaft (rack end) collides with the rack housing and the rack shaft suddenly stops, a large impact torque acts on the steering shaft or the like due to the influence of inertia. Moreover, the magnitude of the reverse input that is input to the steered wheels varies, and in some cases, the impact torque may become very large.

  Therefore, in order to prevent the steering shaft from being damaged by such an impact torque and reliably maintain the steering performance, it is necessary to set the strength of the steering shaft sufficiently high. Therefore, it is difficult to reduce the size and weight of the steering shaft, and there is still room for improvement in this respect.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an electric power steering device capable of reducing the size and weight of the steering shaft while maintaining the steering performance. is there.

  In order to achieve the above object, the invention described in claim 1 is directed to a steering shaft connected to a steering wheel, a rack shaft that moves in an axial direction in accordance with the rotation of the steering shaft, and a steering operation via a speed reduction mechanism. In an electric power steering apparatus including a motor that applies assisting force to assist a steering system, shaft couplings that connect the motor shaft of the motor and the drive gear of the speed reduction mechanism protrude in opposite directions. A pair of yokes each having a plurality of claw portions; and a coupling member having a plurality of engagement portions that engage with the claw portions in the circumferential direction. The engaging surfaces on both sides in the direction are provided with protrusions that abut against the respective claw portions and that are plastically deformed when a torque greater than a predetermined torque is applied. The gist.

  According to the above configuration, when a reverse input is applied and an impact torque greater than or equal to a predetermined torque is applied to the steering shaft, the speed reduction mechanism, and the motor, the impact torque is absorbed by plastic deformation of the projection of the shaft coupling. Thereby, since the impact torque acting on the steering shaft is reduced, even if the steering shaft is reduced in size and weight, the steering shaft can be prevented from being damaged and the steering performance can be maintained. In addition, after the protrusions are plastically deformed, a gap is generated between the yoke claw and the plastically deformed protrusion, so that abnormal noise is generated when the claw and the protrusion come into contact with each other by a steering operation. To come. As a result, it is possible to notify the driver that an abnormal impact has occurred due to excessive impact torque, and it is possible to quickly go to a repair shop or the like. Further, in many cases, it is only necessary to replace the shaft coupling at the time of repair. Therefore, the coupling member (shaft coupling) that has been easily deformed can be easily replaced by substantially the same operation as the replacement of the motor.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the speed reduction mechanism includes a worm shaft that is the drive gear and a worm wheel that meshes with the worm shaft, and the worm shaft includes the worm shaft. The end opposite to the shaft coupling is urged toward the worm wheel by an urging member, and the coupling member is made of an elastic material and has an engaging portion and an outer periphery of the core member. And a surface member having the protrusions.

  According to the above configuration, since the core member is made of an elastic material, the worm shaft can be tilted with respect to the motor shaft by deforming the core member. Therefore, by urging the end portion of the worm shaft toward the worm wheel by the urging member, it is possible to remove the backlash while making it possible to absorb the impact torque as described above.

  According to the present invention, it is possible to provide an electric power steering apparatus capable of reducing the size and weight of a steering shaft while maintaining steering performance.

The schematic block diagram of an electric power steering device (EPS). Sectional drawing which shows the EPS actuator of one Embodiment. The perspective view of the shaft coupling of one Embodiment. Sectional drawing orthogonal to the axial direction of the shaft coupling of one Embodiment (AA sectional drawing of FIG. 2). (A)-(c) is the schematic diagram seen from the radial direction outer side of the shaft coupling of one Embodiment. (A), (b) The schematic diagram which looked at the shaft coupling of another example from the radial direction outer side.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, in an electric power steering apparatus (EPS) 1, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. The rack shaft 5 is inserted into a cylinder of a substantially cylindrical rack housing 6 and supported so as to be capable of reciprocating in the axial direction via a rack guide and a rack bush (not shown). Thereby, the rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10.

  A tie rod 13 is rotatably connected to both ends of the rack shaft 5 via a rack end 12 provided at the shaft end portion 11 thereof. The tip of the tie rod 13 is connected to a knuckle (not shown) to which the steered wheel 14 is assembled. Then, the reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to the knuckle through the tie rods 13 connected to both ends of the rack shaft 5, so that the steering angle of the steered wheels 14, that is, the vehicle The direction of travel is changed.

  The EPS 1 also includes an EPS actuator 21 that applies assist force to assist the steering operation in the steering system. The EPS actuator 21 includes a motor 22 as a driving source, and a speed reduction mechanism 23 that meshes with a worm shaft 24 as a driving gear connected to the motor 22 and a worm wheel 25 connected to the column shaft 8. . That is, the EPS 1 of the present embodiment is configured as a so-called column assist type EPS. The EPS actuator 21 is configured to apply the motor torque as an assist force to the steering system by decelerating the rotation of the motor 22 by the speed reduction mechanism 23 and transmitting it to the column shaft 8.

Next, the configuration of the EPS actuator will be described.
As shown in FIG. 2, the EPS actuator 21 includes a housing 31 that houses the speed reduction mechanism 23. The housing 31 includes a worm shaft housing portion 32 that houses the worm shaft 24, and a worm wheel housing portion 33 that is formed continuously with the worm shaft housing portion 32 and that houses the worm wheel 25. . The worm shaft accommodating portion 32 is a cylindrical space extending in the axial direction (left and right direction in FIG. 2) of the worm shaft 24, and one end side (right side in FIG. 2) has a motor fixing hole 34 to which the motor 22 is fixed. Communicating with Further, the other end side (left side in FIG. 2) of the worm shaft housing portion 32 is opened to the outside, and this opening is closed by the end cover 35.

  The motor 22 is fixed to the motor fixing hole 34 so that the axial direction of the motor shaft 36 is orthogonal to the axial direction of the steering shaft 3 (column shaft 8) penetrating the housing 31. The worm shaft 24 connected to the motor shaft 36 is rotatably supported by first and second bearings 37 and 38 provided in the housing 31 at both ends, and is connected to the steering shaft 3. It is meshed with the worm wheel 25. Thereby, the rotation of the motor 22 is decelerated by the worm shaft 24 and the worm wheel 25 and transmitted to the column shaft 8.

  Here, the EPS actuator 21 of the present embodiment incorporates a backlash adjustment mechanism that adjusts the inter-axis distance between the worm shaft 24 and the worm wheel 25 constituting the speed reduction mechanism 23 to remove backlash. ing.

  Specifically, the first bearing 37 that supports one end portion (the right end portion in FIG. 2) 24 a of the worm shaft 24 is fixed in the worm shaft housing portion 32 by a fixing member 41. On the other hand, the second bearing 38 that supports the other end portion (left end portion in FIG. 2) 24b of the worm shaft 24 is provided so as to be movable in the radial direction. Specifically, the opening 42 on the other end side of the worm shaft housing portion 32 has an inner diameter larger than the outer diameter of the second bearing 38, and the second bearing 38 is in the opening 42. By being arranged, it is provided to be movable in the radial direction. That is, the worm shaft 24 is rotatably supported by the first and second bearings 37 and 38 in a state in which tilting with respect to the motor shaft 36 is allowed.

  One end 24a of the worm shaft 24 is connected to the motor shaft 36 by a shaft joint 43 so as to be tiltable, and the other end 24b is close to the worm wheel 25 by a curved leaf spring 44 as an urging member. It is urged in a direction (substantially downward in FIG. 2). The curved leaf spring 44 is formed in an arc shape surrounding the second bearing 38. As a result, the worm shaft 24 is tilted so as to be close to the worm wheel 25 with its one end side as the center, so that backlash is removed.

Next, the configuration of the shaft coupling will be described in detail.
As shown in FIGS. 2 and 3, the shaft coupling 43 includes a yoke 51 connected to the motor shaft 36, a yoke 52 connected to the worm shaft 24, and a coupling member interposed between the yokes 51, 52. 53.

  The yokes 51 and 52 are each made of a metal material and are formed in a substantially annular shape. The yokes 51 and 52 are formed with a plurality of (four in this embodiment) claw portions 54 and 55 that protrude in directions opposite to each other. As shown in FIGS. 3 and 4, the claw portions 54 and 55 are formed at equal intervals in the circumferential direction, and the yoke 51 and the yoke 52 are alternately arranged in the circumferential direction. It is connected so that it may be arranged.

  The coupling member 53 includes a core member 61 made of an elastic material such as a resin, and a surface member 62 made of a metal material. The core member 61 has a base portion 63 formed in a substantially disc shape, and a plurality of (eight in the present embodiment) engagement portions 64 extending radially are equiangularly arranged on the outer peripheral surface of the base portion 63. It is formed at intervals. The engaging portion 64 is formed in a flat plate shape and is disposed between the claw portions 54 and 55. The shaft coupling 43 allows the worm shaft 24 to tilt with respect to the motor shaft 36 by elastically deforming the core member 61.

  On the other hand, the surface member 62 is formed in a band shape and is bent so as to cover the entire circumference of the core member 61 including the engaging surfaces 64a on both sides in the circumferential direction of the shaft coupling 43 in the engaging portion 64. Projections 65 that are plastically deformed when a torque equal to or greater than a predetermined torque is applied to a portion of the surface member 62 that faces the engagement surface 64a. The predetermined torque is smaller than the torque that damages the steering shaft 3 (in many cases, the intermediate shaft 9) and larger than the maximum torque of the motor 22. That is, in the present embodiment, the shaft coupling 43 is the weakest part having the lowest strength among the members that rotate as the rack shaft 5 moves in the axial direction due to application of reverse input or the like.

  Specifically, each protrusion 65 is formed in a hollow, substantially hemispherical (dome-shaped) shape, and is formed in a substantially symmetric shape with respect to the radial line. And the front-end | tip part of each protrusion 65 is made into the flat shape, and is contact | abutting to each nail | claw part 54,55. Thereby, the claw part 54 of the yoke 51 connected to the motor shaft 36 is engaged with the claw part 55 of the yoke 52 via the protrusion 65 and the engaging part 64 so as to transmit torque. In addition, the protrusion 65 of this embodiment is formed by press work.

Next, the operation of the EPS of this embodiment will be described.
As shown in FIG. 5A, at the time of normal assist, the claw portions 54 and 55 of the yokes 51 and 52 are in contact with the projection 65, and the rotation of the motor 22 is directly performed through the shaft coupling 43 as a worm shaft. 24.

  Here, for example, when a reverse input is applied to the steered wheels 14 due to curb collision, the steering shaft 3 rotates along with the axial movement of the rack shaft 5, and the motor 22 rotates through the speed reduction mechanism 23. When the rack end 12 collides with the rack housing 6 and the rack shaft 5 stops suddenly, a large impact torque acts on the steering shaft 3 and the like due to the influence of inertia. At this time, as shown in FIG. 5B, when the impact torque is equal to or greater than the predetermined torque, the impact torque is absorbed by the protrusion 65 of the coupling member 53 being plastically deformed, and the steering shaft 3 ( Damage to the intermediate shaft 9) is prevented.

  As shown in FIG. 5 (c), after the projection 65 is plastically deformed, a gap is generated between the claw portions 54 and 55 of the yokes 51 and 52 and the projection 65 of the coupling member 53. When the assist, the claw portions 54 and 55 and the crushed protrusion 65 come into contact with each other, and an abnormal noise is generated.

As described above, according to the present embodiment, the following effects can be obtained.
(1) Since the projecting portion 65 provided on the engaging surface 64a of the engaging portion 64 is plastically deformed, the impact torque based on the reverse input is absorbed and the steering shaft 3 is prevented from being damaged. Steering performance can be reliably maintained even if the vehicle is reduced in size and weight. In addition, after the protrusion 65 is plastically deformed, abnormal noise is generated at the time of assisting, so that the driver can be notified that an excessive shock torque has acted and an abnormality has occurred, and he can immediately go to a repair shop or the like. Is possible. Further, in many cases, only the shaft coupling 43 needs to be replaced at the time of repair. Therefore, the coupling member 53 (shaft coupling 43) that has been easily deformed by substantially the same operation as the replacement of the motor 22 is replaced. Can do.

  (2) Since the coupling member 53 includes the core member 61 made of an elastic material and the surface member 62 provided on the outer periphery of the core member 61, the worm shaft 24 is moved relative to the motor shaft 36 by deforming the core member 61. Can be tilted. Therefore, by urging the other end 24b of the worm shaft 24 toward the worm wheel 25 by the curved plate spring 44, it is possible to remove the backlash while making it possible to absorb the impact torque as described above.

In addition, the said embodiment can also be implemented in the following aspects which changed this suitably.
-In above-mentioned embodiment, although the protrusion 65 was formed in the hollow hemisphere, the shape can be changed suitably if not only this but carrying out plastic deformation by the torque more than predetermined torque. Specifically, as shown in FIG. 6A, the protrusion 65 may have a shape opened in the axial direction of the shaft coupling 43. Moreover, as shown in FIG.6 (b), you may form the protrusion 65 not in hollow, for example, in rod shape.

  In the above embodiment, the core member 61 is made of an elastic material so that the worm shaft 24 is tiltably connected to the motor shaft 36. However, in a configuration that does not employ the backlash adjustment mechanism, the core member 61 is You may comprise with a metal material etc.

In the above embodiment, the surface member 62 having the protrusion 65 is made of a metal material. However, if the protrusion 65 is plastically deformed, it may be made of another material such as a hard resin material.
In the above embodiment, the coupling member 53 includes the core member 61 and the surface member 62. However, the protrusion 65 is integrally formed on the engaging surface 64a of the core member 61, and the surface member 62 is not provided. Good.

In the above-described embodiment, the worm shaft 24 is urged by the curved leaf spring 44. However, the worm shaft 24 is not limited thereto, and may be urged by an elastic body such as a coil spring or rubber.
In the above embodiment, the present invention is applied to the column assist type EPS. However, the present invention is not limited to this, and may be applied to other EPS as long as the rotation of the motor is transmitted to the steering system via the speed reduction mechanism. Is possible. Specifically, a pinion assist type PES that rotationally drives the pinion shaft, a so-called rack parallel type EPS in which the motor is arranged in parallel with the rack shaft (for example, Patent Document 2), or rotation by a steering operation. You may apply to what is called double pinion type EPS (for example, patent document 3) etc. provided with the pinion shaft driven with a motor separately from a pinion shaft.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device (EPS), 3 ... Steering shaft, 5 ... Rack shaft, 21 ... EPS actuator, 22 ... Motor, 23 ... Reduction mechanism, 24 ... Worm shaft, 25 ... Worm wheel, 36 ... Motor shaft, 43 ... Shaft coupling, 44 ... Curved leaf spring, 51,52 ... Yoke, 53 ... Coupling member, 54,55 ... Claw part, 61 ... Core member, 62 ... Surface member, 64 ... engagement part, 64a ... engagement surface 65 ... Projection.

Claims (2)

A steering shaft to which a steering wheel is coupled, a rack shaft that moves in the axial direction in accordance with the rotation of the steering shaft, and a motor that applies an assist force to assist the steering operation via the speed reduction mechanism to the steering system. In the electric power steering device
The shaft coupling that connects the motor shaft of the motor and the drive gear of the speed reduction mechanism includes a pair of yokes each having a plurality of claw portions protruding in opposite directions, and a circumferential direction with respect to the claw portions. A coupling member formed with a plurality of engaging portions to be engaged with,
Electric power characterized in that the engaging surfaces on both sides in the circumferential direction of each engaging portion are provided with protrusions that abut against each of the claw portions and plastically deform when a torque greater than a predetermined torque acts. Steering device. The electric power steering apparatus according to claim 1, wherein
The speed reduction mechanism includes a worm shaft that is the drive gear and a worm wheel that meshes with the worm shaft,
The end of the worm shaft opposite to the shaft coupling is urged toward the worm wheel by the urging member,
The coupling member is
An electric power steering apparatus comprising: a core member made of an elastic material and having the engaging portion; and a surface member provided on an outer periphery of the core member and having the protrusion.