JP2016094066A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device that can transmit steering force to a rack shaft without restricting rotation of a rotation element when some motors of a plurality of motors fail.SOLUTION: An electric power steering device 100, which steers wheels by moving a rack shaft 1 in a shaft direction, comprises: a first motor 5 and a second motor 6 which generate steering force; a rack driving portion 7 which rotates to drive the rack shaft 1 in the shaft direction; and a planetary gear mechanism 8 which transmits driving force of at least one of the first motor 5 and the second motor 6 to the rack driving portion 7. The planetary gear mechanism 8 comprises: a sun gear 14 which is connected to the first motor; a ring gear 15 which is connected to the second motor 6 to rotationally drive the rack driving portion 7; a planetary gear 16 which engages with an external tooth 14a of the sun gear 14 and an internal tooth 15a of the ring gear 15; and a carrier 17 which supports the planetary gear 16 so as not to revolve.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electric power steering device mounted on a vehicle.

  Patent Document 1 describes an electric power steering device that transmits a turning force to a rack shaft by two electric motors. In this electric power steering apparatus, even if one of the electric motors fails, the other electric motor can generate a turning force.

  The rotational torques of the two electric motors are input to the rack shaft via the planetary gear mechanism. The first motor is connected to the sun gear, and the second motor is connected to the ring gear drive gear that meshes with the outer teeth of the ring gear. The carrier that supports the rotation shafts of the three planetary gears is integrally fixed to a steered input shaft that is connected to the rack shaft.

JP 2006-15865 A

  In the above conventional technique, when the first motor fails, the rotation of the second motor is transmitted to the sun gear via the ring gear and the planetary gear, so that a sufficient steering force is transmitted to the steering input shaft. It is necessary to regulate the rotation of the sun gear. Further, when the second motor fails, the rotation of the first motor is transmitted to the ring gear drive gear via the planetary gear and the ring gear, so that a sufficient turning force is transmitted to the turning input shaft. Needs to regulate the rotation of the ring gear drive gear. That is, it is necessary to separately provide a mechanism for restricting the rotation of the gear for fail-safe assuming a motor failure.

  In addition, since a sufficient turning force cannot be transmitted to the turning input shaft from the time one of the motors fails until the sun gear or ring gear drive gear rotation is restricted, the operability at the time of failure May be reduced.

  The present invention has been made in view of such a technical problem. When a part of a plurality of motors fails, the present invention steers to the rack shaft without restricting the rotation of the rotating element. An object is to provide an electric power steering apparatus capable of transmitting force.

  The present invention relates to an electric power steering device that moves a rack shaft in an axial direction to steer a wheel, and rotates the rack shaft in the axial direction by rotating with a first motor and a second motor that generate a steering force. And a planetary gear mechanism that transmits at least one of the driving force of the first motor and the second motor to the rack driving unit, and the planetary gear mechanism includes a sun gear coupled to the first motor; A ring gear coupled to the second motor for rotationally driving the rack drive unit, a planetary gear meshing with the outer teeth of the sun gear and the inner teeth of the ring gear, and a carrier for supporting the planetary gear so as not to revolve. It is characterized by.

  According to the present invention, the first motor is connected to the sun gear, the second motor is connected to the ring gear, and the ring gear rotationally drives the rack driving unit. As a result, when the first motor fails, the rotation of the second motor is directly transmitted to the rack drive unit. When the second motor fails, the rotation of the first motor is transmitted from the sun gear via the planetary gear and the ring gear. Is transmitted to. Therefore, even if some of the plurality of motors fail, the turning force can be transmitted to the rack shaft without restricting the rotation of the rotating element, thereby improving the operability at the time of failure. Can do.

1 is a plan view of an electric power steering device according to an embodiment of the present invention. It is sectional drawing which shows the cross section which cut | disconnected the electric power steering apparatus of FIG. 1 in parallel with the rack axis | shaft. It is sectional drawing which shows the III-III cross section of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a plan view of an electric power steering apparatus 100 according to this embodiment.

  The electric power steering apparatus 100 is a rack assist type electric power steering apparatus 100 that independently inputs a steering force by a driver and an assist driving force by an electric motor to the rack shaft 1.

  The electric power steering apparatus 100 includes a rack shaft 1 connected to a steered wheel (not shown) of a vehicle, a cylindrical rack housing 2 having the rack shaft 1 therein, and a pinion that rotates in accordance with a driver's steering operation. A pinion housing 3 that supports a shaft (not shown) and a steering assist mechanism 4 that transmits an assist driving force by an electric motor to the rack shaft 1 are provided.

  Both ends of the rack shaft 1 are coupled to the steered wheels via tie rods (not shown), and the steered wheels are steered by moving in the axial direction. The rack shaft 1 is formed with rack teeth (not shown) that mesh with a pinion gear (not shown) of the pinion shaft.

  The rack housing 2 accommodates the rack shaft 1 so as to be capable of linear movement, a pinion housing 3 is formed on one end side, and a steering assist mechanism 4 is provided on the other end side.

  The pinion housing 3 supports a pinion shaft connected to a steering wheel (not shown), and meshes the pinion gear of the pinion shaft with the rack teeth carved on the rack shaft 1.

  FIG. 2 is a cross-sectional view showing a cross section of the electric power steering apparatus 100 of FIG. 1 cut in parallel to the rack shaft 1. 3 is a cross-sectional view showing a cross section taken along the line III-III in FIG.

  The steering assist mechanism 4 includes a first motor 5 and a second motor 6 as electric motors that generate an assist driving force, a rack drive unit 7 that rotates to drive the rack shaft 1 in the axial direction, and a first motor 5. And a planetary gear mechanism 8 that transmits the driving force of at least one of the second motor 6 to the rack driving unit 7.

  The first motor 5 and the second motor 6 are motors having the same rated capacity, and are opposed to each other on both sides of the planetary gear mechanism 8. The first motor 5 is disposed on one side (left side in FIG. 2) of the planetary gear mechanism 8, and the second motor 6 is disposed on the other side (right side in FIG. 2). The 1st motor 5 and the 2nd motor 6 are arranged on the same straight line so that a rotation axis may correspond.

  The first motor 5 and the second motor 6 are housed in the first motor housing 9 and the second motor housing 10, respectively. The first motor housing 9 and the second motor housing 10 are each fixed to the rack housing 2.

  The outputs of the first motor 5 and the second motor 6 are controlled so as to generate a predetermined assist driving force according to the driver's steering force detected by a controller (not shown) by a torque sensor (not shown). .

  The rack drive unit 7 includes a ball nut 11 coupled to the rack shaft 1 by a ball screw mechanism, a pulley 12 integrally fixed to the outer periphery of the ball nut 11, and a belt 13 that transmits rotation from the planetary gear mechanism 8 to the pulley 12. And having.

  The ball nut 11 is screwed into a thread groove 1a formed on the outer periphery of the rack shaft 1 via a ball (not shown). The ball nut 11 is restricted from moving in the axial direction by the rack housing 2. When the ball nut 11 rotates, rotational torque is transmitted to the rack shaft 1 via the balls, and the rack shaft 1 moves in the axial direction.

  The pulley 12 has a belt 13 wound around an outer peripheral surface thereof, and rotates together with the ball nut 11 by a rotational torque transmitted from the planetary gear mechanism 8 via the belt 13.

  The planetary gear mechanism 8 includes a sun gear 14 disposed at the center, an annular ring gear 15 disposed coaxially with the sun gear 14 and having a larger diameter than the sun gear 14, outer teeth 14 a of the sun gear 14, and inner teeth of the ring gear 15. Three planetary gears 16 (FIG. 3) meshing with 15a, and a carrier 17 that supports the planetary gears 16 so as not to revolve by integrally connecting the rotation shafts of the three planetary gears 16 together.

  The sun gear 14 is connected to the rotating shaft 19 of the first motor 5. The ring gear 15 is formed in a bottomed cylindrical shape that opens to the first motor 5 side, and the bottom portion 15 b is connected to the rotating shaft 20 of the second motor 6. The ring gear 15 accommodates the sun gear 14 and the planetary gear 16 therein, and the open end is supported by the rack housing 2 via a bearing 18. The outer diameter of the ring gear 15 is formed to be smaller than the outer diameter of the pulley 12, and the rotation of the ring gear 15 is decelerated and transmitted to the pulley 12 (FIG. 3).

  The planetary gear 16 is rotatably supported by a support pin 21 extending from the first motor 5. The carrier 17 is fixed to the housing of the first motor 5, and has three support pins 21 of each planetary gear 16 along the circumferential direction. Thereby, regardless of the rotation of the ring gear 15 and the sun gear 14, the planetary gear 16 is allowed to rotate only and does not revolve.

  Next, the operation of the electric power steering apparatus 100 will be described. FIG. 3 is a cross-sectional view showing a state of the III-III cross section of FIG. 2 viewed from the second motor 6 side. In the following description, the rotation directions of the first motor 5 and the second motor 6 refer to the rotation directions when viewed from the motor shaft side. That is, the rotation direction of the first motor 5 indicates the rotation direction when viewed from the second motor 6 side, and the rotation direction of the second motor 6 indicates the rotation direction when viewed from the first motor 5 side.

  First, a case where both the first motor 5 and the second motor 6 operate normally will be described.

  As shown in FIG. 3, when the ball nut 11 is rotated clockwise to transmit the assist driving force to the rack shaft 1, the second motor 6 is rotated counterclockwise (clockwise in the direction shown in FIG. 3). At the same time, the first motor 5 is rotated counterclockwise. Thereby, the torques of the first motor 5 and the second motor 6 are transmitted from the ring gear 15 to the pulley 12 and the ball nut 11 via the belt 13. The rotation of the ball nut 11 is transmitted to the rack shaft 1 through the ball screw mechanism, and the rack shaft 1 moves in one axial direction.

  On the contrary, when the ball nut 11 is rotated counterclockwise to transmit the assist driving force to the rack shaft 1, the second motor 6 is rotated clockwise (counterclockwise in the direction shown in FIG. 3) and the first The motor 5 is rotated clockwise. Thereby, the torques of the first motor 5 and the second motor 6 are transmitted from the ring gear 15 to the pulley 12 and the ball nut 11 via the belt 13. The rotation of the ball nut 11 is transmitted to the rack shaft 1 through the ball screw mechanism, and the rack shaft 1 moves in the other axial direction.

  Next, a case where the first motor 5 fails and does not operate normally will be described.

  In this case, since the ring gear 15 is rotated by the torque of the second motor 6, the torque is transmitted from the ring gear 15 to the pulley 12 and the ball nut 11 via the belt 13. At this time, the first motor 5 is rotated around the planetary gear 16 and the sun gear 14, so that resistance is generated in the rotation of the ring gear 15.

  However, since the second motor 6 is directly connected to the ring gear 15, it is possible to transmit an assist driving force substantially equivalent to that of the electric power steering apparatus 100 having only one assist motor to the rack shaft 1.

  Next, a case where the second motor 6 fails and does not operate normally will be described.

  In this case, the sun gear 14 is rotated by the torque of the first motor 5, and the ring gear 15 is rotated via the planetary gear 16 that meshes with the sun gear 14. Thereby, torque is transmitted from the ring gear 15 to the pulley 12 and the ball nut 11 via the belt 13. At this time, the second motor 6 is rotated along with the rotation of the ring gear 15 so that resistance is generated in the rotation of the ring gear 15.

  However, since the rotation of the first motor 5 is decelerated in the planetary gear mechanism 8 and transmitted to the pulley 12 and the ball nut 11, a sufficient assist driving force can be transmitted to the rack shaft 1 by the torque amplification effect by the deceleration. .

  According to the above embodiment, there exist the effects shown below.

  The first motor 5 is connected to the sun gear 14, the second motor 6 is connected to the ring gear 15, and the ring gear 15 rotates the ball nut 11. Thereby, when the first motor 5 fails, the rotation of the second motor 6 is directly transmitted to the ball nut 11, and when the second motor 6 fails, the first motor is transmitted from the sun gear 14 via the planetary gear 16 and the ring gear 15. The rotation of 5 is transmitted to the ball nut 11. Therefore, even if one of the two motors 5 and 6 fails, the assist driving force can be transmitted to the rack shaft 1, so that the operability and safety at the time of failure can be improved.

  Further, when one of the two motors 5 and 6 fails, the assist driving force can be transmitted to the rack shaft 1 without restricting the rotation of any of the rotating elements. The operation responsiveness at the time of failure can be improved, and safety can be further improved.

  Further, since the first motor 5 and the second motor 6 are coaxially arranged on both sides with the planetary gear mechanism 8 interposed therebetween, the steering assist mechanism 4 of the electric power steering device 100, in particular, can be made compact to be mounted on a vehicle. Can be improved.

  Furthermore, since the rack driving unit 7 directly drives the rack shaft 1, the assist driving force can be increased and the steering feeling can be improved as compared with the case of driving the pinion shaft.

  Furthermore, since the rotation of the ring gear 15 is decelerated and transmitted to the pulley 12, a sufficient assist driving force can be obtained while reducing the size of the first motor 5 and the second motor 6. Further, the mountability of the electric power steering apparatus 100 on a vehicle can be further improved by downsizing the first motor 5 and the second motor 6.

  The embodiment of the present invention has been described above. However, the above embodiment is merely one example of application of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  For example, in the above embodiment, the case where the first motor 5 and the second motor 6 are coaxially arranged on both sides with the planetary gear mechanism 8 interposed therebetween is exemplified, but the first motor 5 and the second motor 6 are coaxial. The first motor 5 and the second motor 6 may be disposed on one side of the planetary gear mechanism 8.

  Furthermore, in the said embodiment, since the motor with the same rated capacity is used as the 1st motor 5 and the 2nd motor 6, cost can be reduced compared with the case where two different types of motors are provided. Motors with different rated capacities may be used. In particular, since the rotation of the first motor 5 is decelerated and transmitted to the ring gear 15, the steering assist mechanism 4 is operated while securing the assist driving force by setting the capacity of the first motor 5 smaller than that of the second motor 6. Further downsizing can be achieved.

  Furthermore, although the case where the number of the planetary gears 16 is three was illustrated in the said embodiment, the number other than three may be sufficient.

  Furthermore, in the above embodiment, the rotation of the ring gear 15 is decelerated and transmitted to the rack drive unit 7, but may be transmitted to the rack drive unit 7 at a constant speed or increased.

  Furthermore, in the above embodiment, the rack assist type electric power steering apparatus 100 that inputs the steering force by the driver and the assist driving force by the electric motor to the rack shaft 1 independently is illustrated, but the rack driving unit 7 is a pinion. A pinion assist type electric power steering device that drives the shaft may be used, or a steer-by-wire type electric power steering device that does not have a pinion shaft may be used.

  Furthermore, in the above embodiment, the rotation of the ring gear 15 is transmitted to the ball nut 11 via the belt 13, but torque may be transmitted using a transmission mechanism other than the belt 13 such as a gear.

DESCRIPTION OF SYMBOLS 1 Rack shaft 5 1st motor 6 2nd motor 7 Rack drive part 8 Planetary gear mechanism 14 Sun gear 14a External gear of sun gear 15 Ring gear 15a Internal gear of ring gear 16 Planetary gear 17 Carrier 100 Electric power steering device

Claims (4)

An electric power steering device for moving a rack shaft in an axial direction to steer a wheel,
A first motor and a second motor that generate a steering force;
A rack driving unit for rotating the rack shaft in the axial direction by rotating;
A planetary gear mechanism that transmits a driving force of at least one of the first motor and the second motor to the rack driving unit;
With
The planetary gear mechanism includes a sun gear coupled to the first motor, a ring gear coupled to the second motor for rotationally driving the rack driving unit, outer teeth of the sun gear, and inner teeth of the ring gear. An intermeshing planetary gear, and a carrier that supports the planetary gear in a non-revolving manner,
An electric power steering device. The first motor and the second motor are coaxially arranged on both sides with the planetary gear mechanism in between.
The electric power steering apparatus according to claim 1. The rack driving unit directly drives the rack shaft;
The electric power steering apparatus according to claim 1 or 2, wherein The rotation of the ring gear is decelerated and transmitted to the rack driving unit.
The electric power steering apparatus according to any one of claims 1 to 3, wherein

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