JP2018008545A - Electric power steering device - Google Patents

Abstract

An object of the present invention is to suppress an increase in torque ripple of a motor when an electric power steering device is externally input. A shaft coupling 58 is interposed between a worm and a motor, and includes a first transmission member 60 provided on the motor side and a second transmission member 62 provided on the worm side. In the radial direction, the radial intermediate member 84 is disposed in a region sandwiched between the small diameter cylindrical portion 70 of the first transmission member 60 and the large diameter cylindrical portion 78 of the second transmission member 62. The radial intermediate member 84 is made of an elastic material, and convex portions are arranged at intervals in the circumferential direction. The convex portion is the high-rigidity portion 86, and the concave portion between the convex portions is the low-rigidity portion 88. The low rigidity portion 88 is disposed substantially corresponding to the position where the torque peak occurs. When a force that decenters the rotor of the motor is input from the worm, the eccentric force is hardly transmitted by the low-rigidity portion 88, the eccentricity of the rotor is suppressed, and an increase in torque ripple is suppressed. [Selection] Figure 4

Description

  The present invention relates to an electric power steering device for an automobile, and more particularly to its structure.

  2. Description of the Related Art In an automobile steering device, an electric power steering device that assists a driver's steering force with the torque of a motor is known (for example, Patent Document 1 below). In the apparatus disclosed in Patent Document 1 below, a worm wheel (25) is provided on a steering shaft (3), and a worm (26) that meshes with the worm wheel (25) is driven by a motor (21) to thereby obtain a steering force. Assistance. In order to pack backlash between the worm (26) and the worm wheel (25), the worm (26) is biased towards the worm wheel (25). At this time, the axis of the motor (21) and the axis of the worm (26) are inclined, and a shaft coupling (47) is provided between the motor shaft (21a) and the worm (26) to allow this inclination. The shaft coupling (47) has an elastic body (46), and the inclination of the motor shaft (21a) and the worm (26) is allowed by this elastic body. In addition, the code | symbol in () is used by the following patent document 1, and is not related with the code | symbol used by description of embodiment of this application.

JP 2010-1000012 A

  If there is an external input to the motor shaft of the electric power steering device, the rotor may be eccentric and torque ripple of the motor may increase. For example, when there is an input from the steering wheel, the input is transmitted to the worm via the worm wheel. When this force is transmitted to the motor shaft, the rotor is eccentric, and the torque ripple of the motor increases.

  An object of the present invention is to suppress torque ripple of a motor when there is input from a steering wheel in an electric power steering apparatus.

  An electric power steering apparatus according to the present invention includes a worm wheel fixed to a steering shaft, a worm meshing with the worm wheel, a motor for rotationally driving the worm, and a shaft coupling interposed between the worm and the motor. The motor is a fractional slot motor in which the number of slots (the number of teeth) and the number of permanent magnets are different. In addition, the motor has teeth arranged in the circumferential direction as magnetic poles, a stator that generates a rotating magnetic field, and permanent magnets are arranged along the circumferential direction, and the rotating magnetic field generated by the stator interacts with the permanent magnets. And a rotating rotor. The shaft coupling includes a first transmission member provided on the motor side and having a first cylindrical surface, a second transmission member provided on the worm side and having a second cylindrical surface opposed to the first cylindrical surface in the radial direction, It has a radial direction intermediate member which is arranged between the 1st cylindrical surface and the 2nd cylindrical surface, and the high-rigidity part and the low-rigidity part were arranged by turns in the peripheral direction. The first transmission member rotates integrally with the rotor of the motor. The high rigidity portion of the radial intermediate member is arranged at an angular interval obtained by dividing the entire circumference by the least common multiple of the number of teeth and the number of permanent magnets, and is further partially at a position corresponding to the circumferential center position of each permanent magnet. The highly rigid part of is located.

  In the fractional slot motor, a torque ripple having a cycle twice the value obtained by dividing the entire circumference by the least common multiple of the number of slots and the number of permanent magnets is generated. For example, when the number of slots is 12 and the number of permanent magnets is 10, a torque ripple having a cycle of 12 ° is generated. In this case, torque nodes appear at a cycle of 6 °, and the torque has a peak between the nodes, that is, at the antinode position. In the circumferential direction, a torque node is obtained when the center of one of the permanent magnets coincides with the center of the tooth. If the rotor rotation angle when the center of a certain permanent magnet coincides with the center of the tooth is 0 °, a torque ripple node appears every time the rotor rotates 6 °.

  When the rotor is eccentric, the peak value of some torque becomes larger and the torque ripple becomes larger. If the eccentricity of the rotor is suppressed at the torque peak position, that is, the torque antinode position, the torque amplitude is reduced and the torque ripple is suppressed. The high rigidity portion of the radial intermediate member is disposed at a position corresponding to the torque ripple node, and the low rigidity portion is disposed therebetween. When a force is applied to decenter the rotor via the low-rigidity portion, the force from the worm to the rotor is difficult to be transmitted, so the torque amplitude is reduced.

  By disposing the low-rigidity portion of the radial intermediate member at a position where a torque peak appears, the force transmitted from the worm to the rotor is reduced, the amount of eccentricity of the rotor is suppressed, and an increase in torque ripple is suppressed.

It is a mimetic diagram showing a schematic structure of an electric power steering device. It is sectional drawing which shows schematic structure of an assist unit. It is a perspective view which shows schematic structure of an assist unit. It is a disassembled perspective view which shows the structure of a shaft coupling. It is a perspective view which fractures | ruptures and shows the assembled shaft coupling in an axis orthogonal surface. It is an axis orthogonal sectional view of a motor. It is an axis orthogonal sectional view of a shaft coupling. It is a figure which shows a torque ripple.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of the electric power steering apparatus 10. The steering wheel 12 is connected to a steering gear 16 via a steering shaft 14. The steering gear 16 is connected to the steering wheel 20 via a tie rod 18. When the steering wheel 12 is operated, the tie rod 18 moves back and forth, and the direction of the steering wheel 20 changes. The steering shaft 14 is provided with an assist unit 22 that assists the steering force. The assist unit 22 includes a motor 24 and a worm gear 26 that transmits the driving force of the motor 24 to the steering shaft 14. The worm gear 26 includes a worm wheel 28 fixed to the steering shaft 14 and a worm 30 that is coupled to the output shaft of the motor 24 and meshes with the worm wheel 28.

  2 and 3 are diagrams showing a schematic configuration of the assist unit 22, FIG. 2 is a cross-sectional view, and FIG. 3 is a perspective view of a main part. The worm wheel 28 and the worm 30 are accommodated in a case 32, and the motor 24 is partially fitted into an opening 34 provided in the case 32 and fixed. The worm 30 is supported by two bearings 36 and 38 arranged so as to sandwich the meshing position with the worm wheel 28. Of the two bearings 36, 38, the bearing on the motor 24 side (right side in the drawing) is referred to as a first bearing 36, and the other is referred to as a second bearing 38. The first bearing 36 is disposed in a first bearing housing portion 40 provided in the case 32. The second bearing 38 is disposed in a second bearing accommodating portion 42 provided in the case 32. A gap is formed between the outer diameter of the second bearing 38 and the inner diameter of the second bearing housing portion 42, and the urging member 44 is inserted into this gap. The urging member 44 urges the second bearing 38 downward in the drawing, whereby the worm 30 is urged toward the worm wheel 28 at the left end thereof. By this urging, the teeth of the worm 30 and the worm wheel 28 are brought into contact with each other on the tooth surfaces, and the rattles are packed. By filling the backlash, it is possible to assist the steering force immediately, that is, without a backlash section even when the direction of rotation of the worm is reversed.

  The motor 24 includes a substantially cylindrical rotor 46 and a substantially cylindrical stator 48 disposed so as to surround the rotor 46. Ten permanent magnets 50 are arranged in the circumferential direction on the outer periphery of the rotor 46, and twelve teeth 54 each having a coil 52 mounted thereon are arranged in the circumferential direction on the cylindrical inner circumferential surface of the stator 48. (See FIG. 6). The rotor 46 has a rotor shaft 56 that serves as an output shaft of the motor 24. As in this example, a motor having a different number of teeth and a different number of permanent magnets is called a fractional slot motor. The slot is a space portion between the teeth, and the number of slots is the same as the number of teeth.

  The worm 30 and the motor 24 are coupled via a shaft coupling 58. The shaft coupling 58 includes a first transmission member 60 fixedly coupled to the rotor shaft 56, a second transmission member 62 fixedly coupled to the worm 30, and the first transmission member 60 and the second transmission member 62. An intermediate member 64 (see FIG. 4) interposed therebetween is provided. The intermediate member 64 is made of an elastic material, and allows an inclination of the axis of the worm 30 with respect to the axis of the rotor shaft 56. Thereby, the movement of the worm 30 by the urging force of the urging member 44 is allowed, the worm 30 is inclined and approaches the worm wheel 28, and both tooth surface contact is realized.

  4 and 5 are perspective views showing the structure of the shaft coupling 58. FIG. FIG. 4 is an exploded perspective view, and FIG. 5 shows the assembled state with a part of the first transmission member 60 omitted. The first transmission member 60 has a shaft portion 66 and a flange portion 68. The shaft portion 66 is coupled to the rotor shaft 56. A small diameter cylindrical portion 70 is provided on the second transmission member 62 side of the flange portion 68, and a claw 72 extending radially inward is provided on the inner wall surface of the small diameter cylindrical portion 70. The second transmission member 62 has a shaft portion 74 and a flange portion 76. The shaft portion 74 is coupled to the worm 30. A large-diameter cylindrical portion 78 is provided on the first transmission member 60 side of the flange portion 76. Further, a claw 80 is provided on the surface of the flange portion 76 that faces the first transmission member 60. The claw 80 is disposed at a distance from the large diameter cylindrical portion 78 inward in the radial direction. When the shaft coupling 58 is assembled, the claws 72 of the first transmission member 60 and the claws 80 of the second transmission member 62 are alternately arranged in the circumferential direction at intervals as shown in FIG. When the shaft coupling 58 is assembled, the outer peripheral surface 70a of the small diameter cylindrical portion 70 and the inner peripheral surface 78a of the large diameter cylindrical portion 78 are opposed to each other in the radial direction.

  An intermediate member 64 is interposed between the first transmission member 60 and the second transmission member 62. The intermediate member 64 is made of a deformable material, for example, an elastic material, and thereby the inclination of the axis of the first and second transmission members 60 and 62 is allowed. The intermediate member 64 is provided between the circumferential intermediate member 82 having a portion interposed between the claws 72 and 80 of the first and second transmission members 60 and 62, and between the small diameter cylindrical portion 70 and the large diameter cylindrical portion 78. An intervening radial intermediate member 84 is included. The circumferential intermediate member 82 is responsible for transmitting torque of the motor 24, and the radial intermediate member 84 serves to maintain the mutual coaxiality of the first and second transmission members 60, 62.

  FIG. 6 is a cross-sectional view perpendicular to the axis of the motor 24. Ten permanent magnets 50 are arranged on the outer peripheral surface of the rotor 46 in the circumferential direction. The stator 48 arranged so as to surround the periphery of the rotor 46 has twelve teeth 54 extending toward the rotor 46 on the radially inner side. A coil 52 (see FIG. 3) is attached to the tooth 54, and a magnetic field that rotates inside the stator 48 is formed by passing a predetermined current through the coil 52. This rotating magnetic field and the magnetic field of the permanent magnet 50 interact to rotate the rotor 46.

  FIG. 7 is an axial cross-sectional view of the shaft coupling 58. The claws 72 and 80 of the first and second transmission members 60 and 62 are alternately arranged in the circumferential direction, and a circumferential intermediate member 82 is buried therebetween. A radial intermediate member 84 is disposed in an annular space between the small diameter cylindrical portion 70 of the first transmission member 60 and the large diameter cylindrical portion 78 of the second transmission member 62. The radial intermediate member 84 has convex portions and concave portions alternately arranged in the circumferential direction. The convex part has higher rigidity in the radial direction than the concave part. The convex portion is the high rigidity portion 86 and the concave portion is the low rigidity portion 88. The high rigidity portion 86 and the low rigidity portion 88 may be formed by alternately arranging a hard elastic material (high elastic modulus material) and a soft elastic material (low elastic modulus material).

  The high-rigidity portion 86 and the low-rigidity portion 88 are arranged at angular intervals obtained by dividing the entire circumference by the least common multiple of the number of teeth 54 and the number of permanent magnets 50, respectively. In this embodiment, there are 12 teeth 54 and 10 permanent magnets 50, and their least common multiple is 60. When the entire circumference is divided by 360 °, 60 ° is 6 °, and the high-rigidity portion 86 and the low-rigidity portion 88 are arranged at this interval.

  As shown in FIG. 6, ten straight lines R extending radially from the center O of the rotor 46 pass through the center in the circumferential direction of each permanent magnet 50. This straight line R is referred to as a permanent magnet center line R. The permanent magnet center line R is fixed on the rotor 46 and rotates integrally with the rotor 46. This permanent magnet center line R is also shown in FIG. Since the first transmission member 60 rotates integrally with the rotor 46, the permanent magnet center line R rotates together with the first transmission member 60. Moreover, since the 1st transmission member 60 and the 2nd transmission member 62 are via the circumferential direction intermediate member 82 and the radial direction intermediate member 84 which are elastic bodies, although these members deform | transform, they move relatively relatively. Basically, it rotates together. Therefore, the permanent magnet center line R rotates integrally with the shaft coupling 58. A highly rigid portion 86 is disposed at the position of the permanent magnet center line R. And the high-rigidity part 86 is arrange | positioned every 6 degrees from this permanent magnet centerline R, and the space | interval between the high-rigidity parts 86 becomes the low-rigidity part 88.

  When there is an input from the road surface to the steering device, for example, an input that changes the direction of the steering wheel due to unevenness of the road surface, the input is transmitted through the steering shaft 14 and tries to rotate the steering wheel 12. This input is also transmitted to the assist unit 22 and rotates the worm wheel 28. The rotation of the worm wheel 28 acts so as to separate the worm 30 from the worm wheel 28, which is transmitted to the rotor 46 via the shaft coupling 58 and becomes a force F that causes the rotor 46 to be eccentric (see FIG. 6). When the rotor 46 is eccentric due to the eccentric force F, fluctuations in the output torque of the motor 24, so-called torque ripple, increases, which may cause an uncomfortable feeling in steering.

  FIG. 8 is a diagram showing fluctuations in the output torque of the motor 24. The ratio of the torque at that time to the average torque during one rotation of the motor is shown on the vertical axis as the relative torque. The solid line is the torque fluctuation when the rotor 46 is not eccentric, and the broken line is the torque fluctuation when the rotor 46 is eccentric. The position of the rotor rotation angle of 0 ° is a position where a certain permanent magnet center line R coincides with the center line of any of the teeth 54. Referring to FIG. 6, the permanent magnet center line R1 extending right above passes through the center of the tooth 54-1 positioned right above. The rotation angle of the rotor 46 at this time is set to 0 °. When the rotor 46 rotates by 6 °, the next permanent magnet center line R2 passes through the center of the tooth 54-2. When the rotor 46 rotates by 12 °, the next permanent magnet center line R3 passes through the center of the tooth 54-3. Torque fluctuation nodes appear every 6 ° from the position where the rotor rotation angle is 0 °, and peaks or valleys appear between the nodes. Comparing the solid line graph and the broken line graph of FIG. 8, it can be seen that when the rotor 46 is eccentric, higher peak peaks and lower valley peaks appear and the peak-peak amplitude increases. In other words, the torque ripple of the motor 24 increases due to the eccentricity of the rotor 46, and there is a possibility that an uncomfortable feeling may occur in the operation of the steering device.

  If the absolute value of the torque peak is not increased when the eccentric force F is applied, an increase in torque ripple can be suppressed. For this reason, in this embodiment, the low-rigidity portion 88 of the radial intermediate member 84 is disposed in accordance with the peak positions of the torque peaks and valleys. When the direction of the eccentric force F passes through the low-rigidity portion 88, the force transmitted from the second transmission member 62 to the first transmission member 60 is reduced, the displacement of the rotor 46 is suppressed, and the increase in the torque peak value is suppressed. Is done. Therefore, an increase in torque ripple can be suppressed. On the other hand, when the direction of the eccentric force F passes through the high-rigidity portion 86, the relative torque is small (close to 1). Therefore, even if the eccentric force F acts on the rotor 46, the effect on the torque peak value is not affected. small.

  By providing the high-rigidity portion 86, the first transmission member 60 and the second transmission member 62 are not greatly decentered. When the first transmission member 60 and the second transmission member 62 are decentered, the distance between the claws 72 and 80 varies, and the axial symmetry of the force acting between the claws 72 and 80 is deteriorated. As a result, the torque transmitted from the motor 24 to the worm 30 varies, and the operation of the steering device may be uncomfortable. In this embodiment, the eccentricity of the first transmission member 60 and the second transmission member 62 is suppressed by providing the high rigidity portion 86.

  The number of motor teeth and permanent magnets is not limited to the above.

  DESCRIPTION OF SYMBOLS 10 Electric power steering device, 12 Steering wheel, 14 Steering shaft, 16 Steering gear, 18 Tie rod, 20 Steering wheel, 22 Assist unit, 24 Motor, 26 Worm gear, 28 Worm wheel, 30 Worm, 32 Case, 34 Opening, 36 1 bearing, 38 2nd bearing, 40 1st bearing housing part, 42 2nd bearing housing part, 44 urging member, 46 rotor, 48 stator, 50 permanent magnet, 52 coil, 54 teeth, 56 rotor shaft, 58 shaft joint , 60 1st transmission member, 62 2nd transmission member, 64 Intermediate member, 66 Shaft part, 68 Flange part, 70 Small diameter cylindrical part, 70a Outer peripheral surface (first cylindrical surface) of small diameter cylindrical part, 72 Claw, 74 Shaft part 76 Flange part 78 Large diameter cylindrical part 78a Large diameter cylinder The inner peripheral surface of the (second cylindrical surface), 80 claw, 82 circumferential intermediate member, 84 radially intermediate member 86 high rigidity portion, 88 low-rigidity area, F eccentric force, R permanent magnet centerline.

Claims (1)

An electric power steering device,
A worm wheel fixed to the steering shaft;
A worm meshing with the worm wheel;
A motor for rotationally driving the worm, which has teeth arranged in a circumferential direction as magnetic poles, a stator for generating a rotating magnetic field, and permanent magnets arranged along the circumferential direction, and rotation generated by the stator A fractional slot motor having a magnetic field and a rotor with which the permanent magnets interact to rotate;
A shaft coupling interposed between the worm and the motor, provided on the motor side, rotating integrally with the rotor and having a first cylindrical surface; and provided on the worm side A second transmission member having a second cylindrical surface opposed to the first cylindrical surface in the radial direction, and disposed between the first cylindrical surface and the second cylindrical surface, and having a high rigidity portion and a low rigidity in the circumferential direction. A shaft coupling having radial intermediate members in which rigid portions are alternately arranged;
Including
The highly rigid portions of the radial intermediate members are arranged at angular intervals obtained by dividing the entire circumference by the least common multiple of the number of teeth and the number of permanent magnets, and further correspond to the circumferential center position of each permanent magnet. A part of the high-rigidity part is located at the position
Electric power steering device.

Images