JP2013193565A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which achieves space-saving and facilitates manufacturing while reducing the number of parts.SOLUTION: An electric power steering device is composed of a rack shaft 105, a first motor 10, a second motor, a first drive pulley 11 and a second drive pulley which rotate and drive in synchronization with respective output shafts (10a or the like) of the first motor 10 and second motor, a ball screw 105b formed in the rack shaft 105, a plurality of balls 111 moving the ball screw 105b, a ball nut 112 which interposes a ball 111 in a space with the ball screw 105b, a ball nut mechanism 110 which converts rotary motion around an axial center of the rack shaft 105 into linear motion in an axial direction of the rack shaft 105, a driven pulley 113 which is coupled to the ball nut 112 of the ball nut mechanism 110 to rotate together with the ball nut 112, and a belt 30 laid between the driven pulley 113 and the first drive pulley 11 and second driving pulley.

Description

  The present invention relates to an electric power steering apparatus.

In recent years, an apparatus using two electric motors has been proposed in order to reduce the steering force of a steering wheel in a large vehicle.
For example, the electric power steering device described in Patent Document 1 includes two electric motors, and transmits the auxiliary torque of the first electric motor to the rack shaft via the first belt-type transmission mechanism and the ball screw. A torque mechanism; and a second auxiliary torque mechanism that transmits auxiliary torque of the second electric motor to the rack shaft via the second belt-type transmission mechanism and a ball screw.

JP 2004-74831 A

A simple structure of the electric power steering apparatus is preferable from the viewpoint of reducing the number of parts, saving space, and facilitating manufacturing.
It is an object of the present invention to provide an electric power steering apparatus that can reduce the number of parts and can save space and facilitate manufacture.

  For this purpose, the present invention provides a rack shaft, a plurality of electric motors, a plurality of drive members that rotate in conjunction with output shafts of the plurality of electric motors, and balls formed on the rack shaft. A screw, a plurality of balls that move the ball screw, and a ball nut that interposes the ball between the ball screws, and rotational movement about the axis of the rack shaft in the axial direction of the rack shaft. A ball nut mechanism for converting into linear motion, a rotating member connected to the ball nut of the ball nut mechanism and rotating together with the ball nut, the plurality of driving members, and a belt stretched around the rotating member; And an electric power steering device.

Here, the axial direction of the plurality of electric motors is substantially the same as the axial direction of the rack shaft, and the plurality of electric motors may be disposed on the same side with respect to the belt.
Alternatively, the axial direction of the plurality of electric motors is substantially the same as the axial direction of the rack shaft, and some of the electric motors of the plurality of electric motors are opposite to the other electric motors with respect to the belt. It is good to be arranged.
Further, two electric motors may be provided as the plurality of electric motors, and lines connecting the rotation centers of the two electric motors and the rotation center of the rack shaft may form an acute angle.

  According to the present invention, the number of components can be reduced, and space saving and manufacturing can be facilitated.

It is a figure which shows schematic structure of the electric power steering apparatus which concerns on this Embodiment. It is an external view which shows the relationship between a 1st motor, a 2nd motor, and a rack shaft. It is the figure which looked at the inside in a rack housing in the axial direction of a rack shaft. It is sectional drawing of the IV-IV part of FIG. It is a figure which shows the steering device which concerns on another form.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an electric power steering apparatus 100 according to the present embodiment.
An electric power steering apparatus 100 according to the present embodiment (hereinafter sometimes simply referred to as “steering apparatus 100”) is a steering apparatus for arbitrarily changing the traveling direction of a vehicle. The structure applied to is illustrated.

  The steering device 100 includes a wheel-like steering wheel (handle) 101 operated by a driver, and a steering shaft 102 provided integrally with the steering wheel 101. The steering device 100 includes an upper connecting shaft 103 connected to the steering shaft 102 via a universal joint 103a, and a lower connecting shaft 108 connected to the upper connecting shaft 103 via a universal joint 103b. . The lower connecting shaft 108 rotates in conjunction with the rotation of the steering wheel 101.

  The steering device 100 includes a tie rod 104 connected to each of the left and right front wheels 250 as rolling wheels, and a rack shaft 105 connected to the tie rod 104. Further, the steering device 100 includes a pinion 106 a that constitutes a rack and pinion mechanism together with rack teeth 105 a formed on the rack shaft 105. The pinion 106 a is formed at the lower end portion of the pinion shaft 106.

  The steering device 100 also has a steering gear box 107 that houses the pinion shaft 106. The pinion shaft 106 is coaxially connected to the above-described lower connection shaft 108 via a torsion bar (not shown) inside the steering gear box 107. The pinion shaft 106 and the lower connecting shaft 108 are rotatably supported inside the steering gear box 107.

  Further, the steering device 100 detects the steering torque of the steering wheel 101 in the steering gear box 107 based on the relative rotation angle between the lower connecting shaft 108 and the pinion shaft 106, in other words, based on the torsion amount of the torsion bar. A torque sensor 109 is provided.

  In addition, the steering device 100 includes a plurality of electric motors. The steering device 100 according to the present embodiment includes a first motor 10 and a second motor 20, which are two electric motors, as shown in FIG. The steering device 100 includes a first drive pulley 11 and a second drive pulley 21 that rotate in conjunction with the rotation of the output shafts of the first motor 10 and the second motor 20.

Further, the steering device 100 includes a ball screw 105b formed of a thread groove formed on the rack shaft 105, a large number of balls 111, and a ball nut 112 attached to the ball screw 105b via the balls 111. A nut mechanism 110 is provided.
Further, the steering device 100 includes a driven pulley 113 that rotates together with the ball nut 112 of the ball nut mechanism 110, and one endless belt that is stretched over the driven pulley 113, the first drive pulley 11, and the second drive pulley 21. 30. The driven pulley 113 is fixed to the outer periphery of the ball nut 112 of the ball nut mechanism 110 with a lock nut 53 (see FIG. 4).

The steering device 100 also includes an electronic control unit (ECU) 200 that controls the operation of the first motor 10 and the second motor 20. The output value of the torque sensor 109 described above is input to the ECU 200.
The ECU 200 uses a CPU that performs various arithmetic processes, a ROM that stores programs executed by the CPU, various data, and the like, and a RAM that is used as a work memory for the CPU, and the like from the torque sensor 109. A relative angle calculation unit that calculates a relative rotation angle between the lower connecting shaft 108 and the pinion shaft 106 based on the output value is provided.

  In the steering apparatus 100 configured as described above, in consideration of the steering torque applied to the steering wheel 101 appearing as a relative rotation angle between the lower connection shaft 108 and the pinion shaft 106, the lower connection shaft 108 and the pinion shaft 106. The steering torque is grasped on the basis of the relative rotation angle with respect to. That is, the relative rotation angle between the lower connecting shaft 108 and the pinion shaft 106 is detected by the torque sensor 109, the ECU 200 grasps the steering torque based on the output value from the torque sensor 109, and the first based on the grasped steering torque. The driving of the first motor 10 and the second motor 20 is controlled.

  The torque generated by the first motor 10 and the second motor 20 is transmitted to the rack shaft 105 via the first drive pulley 11, the second drive pulley 21, the belt 30, the driven pulley 113, the ball nut mechanism 110, and the like. The rack shaft 105 is moved linearly. Thereby, the torque generated by the first motor 10 and the second motor 20 assists the driver's steering force applied to the steering wheel 101. That is, the rack shaft 105 rotates with the steering torque generated by the rotation of the steering wheel 101 and the auxiliary torque applied from the first motor 10 and the second motor 20.

Hereinafter, a mechanism for transmitting the drive torque of the first motor 10 and the second motor 20 to the rack shaft 105 will be described in detail.
FIG. 2 is an external view showing the relationship between the first motor 10 and the second motor 20 and the rack shaft 105.
FIG. 3 is a view of the inside of a rack housing 40 to be described later when viewed in the axial direction of the rack shaft 10. In other words, it is a view showing the inside of the rack housing 40 before the second rack housing 42 to be described later is fastened to the first rack housing 41.
4 is a cross-sectional view taken along a line IV-IV in FIG.

  The steering apparatus 100 includes a rack housing 40 that covers the periphery of the rack shaft 105. The rack housing 40 includes a first rack housing 41 and a second rack housing 42 that are divided in the axial direction of the rack shaft 105. Both end portions of the rack shaft 105 protrude from the first rack housing 41 and the second rack housing 42, respectively.

  The first rack housing 41 is formed at a substantially cylindrical cylindrical portion 41a extending in the vehicle width direction (lateral direction in FIG. 1) and an end portion on the second rack housing 42 side, and the ball nut of the ball nut mechanism 110 is formed. The housing portion 41b for housing 112 and the flange portion 41c are provided. Further, the first rack housing 41 is formed with two motor holes 41 d for introducing the respective rotation shafts of the first motor 10 and the second motor 20 into the rack housing 40.

As shown in FIG. 4, a bolt hole 41 e for passing a fastening bolt 50 for fastening to the second rack housing 42 and a female screw 41 f into which a male screw of the fastening bolt 50 is screwed are formed in the flange portion 41 c. As shown in FIG. 3, a plurality of bolt holes 41e and female threads 41f are formed in the flange portion 41c.
A bearing 51 that rotatably supports the ball nut 112 of the ball nut mechanism 110 is attached to the storage portion 41 b of the first rack housing 41. The bearing 51 is fixed by a fixing nut 52 for fixing the bearing 51.

  The second rack housing 42 is configured to pass the end of the rack shaft 105 and cover the opening of the end of the first rack housing 41. That is, the second rack housing 42 includes a peripheral portion 42a that covers the periphery of the rack shaft 105, a storage portion 42b that stores the first drive pulley 11, the second drive pulley 21, the driven pulley 113, the belt 30, and the like. The first rack housing 41 has a flange portion 41c and a flange portion 42c facing the flange portion 41c.

  As shown in FIG. 4, a bolt hole 42 e for passing a fastening bolt 50 fastened to the first rack housing 41 and a female screw 42 f into which the male screw of the fastening bolt 50 is screwed are formed in the flange portion 42 c. A part of the fastening bolts 50 that fasten the first rack housing 41 and the second rack housing 42 has bolt holes 41 e formed in the flange portion 41 c of the first rack housing 41. Then, it is screwed into a female screw 42 f formed on the flange portion 42 c of the second rack housing 42. The other fastening bolt 50 is screwed into a female screw 41 f formed in the flange portion 41 c of the first rack housing 41 through a bolt hole 42 e formed in the flange portion 42 c of the second rack housing 42.

  Note that a fitting hole for fitting a cylindrical knock pin is formed in each of the flange portion 41c of the first rack housing 41 and the flange portion 42c of the second rack housing 42, and before the fastening pin 50 is fastened, the knock pin The first rack housing 41 and the second rack housing 42 may be positioned by fitting both end portions of the first rack housing 41 into the respective fitting holes.

The steering device 100 includes a plurality of (two in the present embodiment) central shafts 12 to which the first drive pulley 11 and the second drive pulley 21 are fixed, and a plurality of (supported by the center shafts 12 so as to be rotatable). In this embodiment, two holders 13 are provided.
The center shaft 12 is rotatably supported at both ends by bearings 14 and 15 attached to the holder 13. The bearing 15 is held by an outer ring fixing retaining ring 16 so as not to fall off the holder 13.
The holder 13 is fixed to the first rack housing 41 with bolts while being inserted into the storage portion 41b of the first rack housing 41 from the motor hole 41d of the first rack housing 41.

  The first motor 10 and the second motor 20 are each fixed to the holder 13 with bolts. At that time, an intermediate joint 19 made of rubber or the like is provided between teeth provided at a plurality of positions in the circumferential direction of the joint 17 at the shaft end of the rotating shaft 10a of the first motor 10 and the joint 18 at the shaft end of the central shaft 12. Attach so that it is in a state of pinching. Although not shown, the same applies to the second motor 20.

  The outer shape of the holder 13 and the hole shape of the motor hole 41d are formed so that a predetermined gap is formed between the holder 13 and the motor hole 41d of the first rack housing 41. Further, the bolt hole formed in the holder 13 through which the bolt for mounting to the first rack housing 41 passes is formed as a long hole. Accordingly, when the holder 13 is fixed to the first rack housing 41, the position of the holder 13 with respect to the first rack housing 41 is allowed to be within a predetermined range. As a result, it is possible to adjust the tension of the belt 30 that is stretched around the first drive pulley 11 and the second drive pulley 21 that rotate in conjunction with the rotation of the output shafts of the first motor 10 and the second motor 20.

  In the steering apparatus 100 according to the present embodiment, as shown in FIG. 3, lines connecting the rotation centers of the first motor 10 and the second motor 20 and the rotation center of the rack shaft 105 are acute angles α. The first motor 10 and the second motor 20 are arranged with respect to the rack shaft 105. As a result, the overall length of the belt 30 can be shortened.

  In the steering apparatus 100 configured as described above, when the first motor 10 and the second motor 20 operate normally, the torque generated by the first motor 10 and the second motor 20 is the first drive pulley 11. The rack shaft 105 is linearly moved by being transmitted to the rack shaft 105 through the second drive pulley 21, the belt 30, the driven pulley 113, the ball nut mechanism 110, and the like. Thus, in the steering device 100 according to the present embodiment, the drive torque generated by the plurality of electric motors assists the driver's steering force applied to the steering wheel 101.

  Therefore, the assist torque can be increased as compared with the steering device 100 including only one electric motor of the same size as the first motor 10 or the second motor 20. Although it is possible to generate assist torque for a plurality of motors with only one electric motor, in such a case, the size of one electric motor is increased, or a drive pulley mounted on the rotating shaft of the electric motor It is necessary to increase the radius and increase the reduction ratio. Therefore, according to the steering device 100 according to the present embodiment, it is possible to improve the efficiency of the mounting space as compared with the configuration including one electric motor.

In addition, if there is only one electric motor, the assist function is lost when the electric motor fails, and the load on the steering wheel 101 (self-help steering operation) by the driver increases. . On the other hand, even if one of the plurality of electric motors fails, the assist torque of the other electric motor can be used. Further, when one or all of the plurality of electric motors fail, an electromagnetic brake force (load resistance) corresponding to the motor electromotive force is generated. However, in a configuration including a plurality of electric motors, The braking force may be dispersed. Therefore, compared with a configuration including one high-output electric motor, it is possible to increase the setting conditions that allow the self-help operation of the steering wheel 101 according to the failure mode.
In addition, by using a plurality of electric motors, the rotation angle (steering angle) of the steering wheel 101 can be calculated using signals from resolvers provided in each of the plurality of electric motors.

  In the steering apparatus 100 according to the present embodiment, the drive torque generated by the plurality of electric motors is transmitted to the rack shaft 105 by one belt 30. Compared with a configuration in which the drive torque generated by the transmission is transmitted to the rack shaft 105 by a plurality of belts, the configuration can be simplified and the number of components can be reduced. Further, when the number of belts that transmit the drive torque of the plurality of electric motors is one, the belt tension can be set by adjusting the axis of one electric motor among the plurality of electric motors, so that assembly is facilitated.

FIG. 5 is a view showing a steering apparatus 100 according to another embodiment. It is sectional drawing of the VV part of FIG.
The steering device 100 according to another embodiment is different in the mounting direction of the electric motor from the steering device 100 according to the above-described embodiment.
That is, in the steering apparatus 100 according to the above-described embodiment, all of the plurality of electric motors are attached to the first rack housing 41, but are not particularly limited to such an aspect. As shown in FIG. 5, if the power of a plurality of electric motors is transmitted by one belt 30, some of the plurality of electric motors are attached to the first rack housing 41. An electric motor may be attached to the second rack housing 42. That is, on the basis of one belt 30, the mounting direction of some of the plurality of electric motors may be opposite to the mounting direction of the other electric motors.

  Also in the steering device 100 according to another embodiment configured as described above, torque generated by a plurality of electric motors is transmitted to the rack shaft 105 via the belt 30, the driven pulley 113, the ball nut mechanism 110, and the like, and the rack shaft 105 moves linearly to assist the driver's steering force applied to the steering wheel 101. Therefore, the same effect as that of the steering device 100 according to the above-described embodiment can be obtained. Further, since the directions of the plurality of electric motors with respect to the belt 30 are not constrained, the degree of freedom in layout increases.

  Further, as long as the power of a plurality of electric motors is transmitted by one belt 30, all of the plurality of electric motors may be attached to the second rack housing 42. Also in the steering device 100 having such a configuration, the torque generated by the plurality of electric motors is transmitted to the rack shaft 105 via the belt 30, the driven pulley 113, the ball nut mechanism 110, and the like, and the steering force of the driver applied to the steering wheel 101 is achieved. Therefore, the same effect as the steering device 100 according to the above-described embodiment can be obtained. Further, since the directions of the plurality of electric motors with respect to the belt 30 are not constrained, the degree of freedom in layout increases.

DESCRIPTION OF SYMBOLS 10 ... 1st motor, 11 ... 1st drive pulley, 20 ... 2nd motor, 21 ... 2nd drive pulley, 30 ... Belt, 40 ... Rack housing, 41 ... 1st rack housing, 42 ... 2nd rack housing, 100 ... Electric power steering device, 105 ... rack shaft, 105b ... ball screw, 106 ... pinion shaft, 108 ... lower connecting shaft, 109 ... torsion bar, 110 ... ball nut mechanism, 111 ... ball, 112 ... ball nut, 113 ... driven Pulley

Claims (4)

A rack shaft,
A plurality of electric motors;
A plurality of drive members that rotate in conjunction with output shafts of the plurality of electric motors;
The ball screw formed on the rack shaft, a plurality of balls that move the ball screw, and a ball nut that interposes the ball between the ball screws, and rotational movement about the axis of the rack shaft A ball nut mechanism that converts the linear motion of the rack shaft into the linear direction,
A rotating member connected to the ball nut of the ball nut mechanism and rotating together with the ball nut;
A belt stretched over the plurality of driving members and the rotating member;
An electric power steering apparatus comprising:   2. The axial direction of the plurality of electric motors is substantially the same as the axial direction of the rack shaft, and the plurality of electric motors are disposed on the same side with respect to the belt. The electric power steering apparatus as described.   The axial directions of the plurality of electric motors are substantially the same as the axial direction of the rack shaft, and some of the plurality of electric motors are disposed on the opposite side of the belt from other electric motors. The electric power steering apparatus according to claim 1, wherein   The electric motor includes two electric motors as the plurality of electric motors, and lines connecting the rotation centers of the two electric motors and the rotation center of the rack shaft form an acute angle. The electric power steering device according to any one of the above.

Images