JP2006076353A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent or suppress the generation of noise in a speed reduction mechanism at the time of a non-operation of steering assistance. <P>SOLUTION: This electric power steering device assists steering by driving electric motors 5 and 6 according to the operation of a steering member 1. The device is provided with first and second driving gears 71 and 72 connected to each of rotary shafts 5a and 6a of each of the first and second electric motors 5 and 6, a driven gear 73 fitted to a steering shaft 2 to be engaged with the first and second driving gears 71 and 72, and a control means 261B (a CPU of a microcomputer 26 included in an ECU 8) for controlling the driving of the first and second electric motors 5 and 6 to apply rotary force of mutually opposite directions from the first and second driving gears 71 and 72 to the driven gear 73 at the time of the non-operation of steering assistance. The driven gear 73 is locked not to rotate in any direction in a state of tooth parts of the driving gears 71 and 72 and the driven gear 73 being in pressure contact with each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that assists a driver's steering by driving an electric motor in accordance with an operation of a steering member such as a steering wheel (handle) performed by the driver, and in particular, the electric motor rotates. The present invention relates to an electric power steering apparatus provided with a speed reduction mechanism that decelerates and transmits it to a steering shaft.

  The electric power steering device includes a torque sensor that detects a steering torque of a steering wheel by a driver, an electric motor for assisting steering, a speed reduction mechanism that decelerates rotation of the electric motor and transmits the rotation to the steering shaft, a torque sensor, and the like And an electronic control unit (ECU) that controls the electric motor based on the sensor signal (see, for example, Patent Document 1).

  The speed reduction mechanism includes, for example, a worm shaft as a drive gear connected to the rotating shaft of the electric motor and a worm wheel as a driven gear fitted to the steering shaft, and by meshing between the worm shaft and the worm wheel, By decelerating the rotation of the electric motor and transmitting it to the steering shaft, the sum of the steering torque applied by the driver's steering wheel operation and the steering assist torque generated by the electric motor is given to the steering mechanism as an output torque. .

By the way, in the electric power steering apparatus described above, when the steering assist is performed, the tooth portions of the worm shaft and the worm wheel are in pressure contact with the steering assist torque generated by the electric motor. However, when the steering wheel is hardly operated, such as when driving straight ahead, the rotation of the electric motor is stopped and the rotation torque of the electric motor is not applied to the worm shaft. The teeth are not in pressure contact. Therefore, when vibration is transmitted from the wheel side, noise is generated between the teeth of the worm shaft and the worm wheel according to the vibration, and this noise is supported so that the steering shaft and the steering shaft can rotate. There is a problem that it propagates into the passenger compartment through a housing, a column and the like.
JP 2003-182601 A

  An object of the present invention is to prevent or suppress the generation of noise in a speed reduction mechanism when steering assistance by an electric motor is not performed.

  An electric power steering apparatus according to the present invention is an electric power steering apparatus that assists steering by driving an electric motor in accordance with an operation of a steering member, and includes a first drive gear coupled to a rotation shaft of the first electric motor; A second drive gear coupled to the rotating shaft of the second electric motor; a driven gear fitted to the steering shaft and meshed with the first and second drive gears; and the first and second when the steering assist is not operating. Brake control means is provided for controlling the driving of the first and second electric motors so that rotational forces in opposite directions are applied from the drive gear to the driven gear.

  In the electric power steering apparatus having the above-described configuration, when the steering assist by the electric motor is not performed, for example, when the vehicle is traveling straight and the steering member is hardly operated, the steering assist is inactive. Thus, the braking control means drives the first and second electric motors, and causes the first and second drive gears to act on the driven gear in opposite directions. The driven gear is locked so as not to rotate in any direction by being driven to rotate in opposite directions. In this case, the teeth of both the drive gear and the driven gear are kept in pressure contact. Therefore, even if vibration is transmitted from the wheel side, generation of noise due to gearing is prevented or suppressed.

  In the above configuration, since the two drive gears mesh with a single driven gear, the meshing portions can be dispersed to reduce the stress at each meshing portion, and the durability can be improved.

  According to the present invention, it is possible to prevent or suppress the generation of noise when the steering assist is not operating, such as when traveling straight ahead, and to quiet the interior of the vehicle.

  Hereinafter, an electric power steering apparatus according to the best mode of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view of a speed reduction mechanism of the electric power steering apparatus, and illustrates related configurations. 2 is a block diagram of the ECU of the apparatus of FIG. 1, and FIG. 3 is a flowchart showing the operation of the apparatus of FIG.

  The electric power steering apparatus according to the present embodiment assists steering by two electric motors, and is connected to a steering shaft 2 having one end fixed to a steering member 1 such as a steering wheel and the other end of the steering shaft 2. A steering mechanism 3 including a rack and pinion mechanism, a torque sensor 4 for detecting a steering torque applied to the steering shaft 2 by the operation of the steering member 1 by the driver, and a driver's load due to the steering operation of the steering member 1. The first and second electric motors 5 and 6 that generate steering assist torque to reduce, and the speed reduction mechanism 7 that transmits the steering assist torque generated by the first and second electric motors 5 and 6 to the steering shaft 2. An electronic control unit (ECU) 8 for controlling the driving of the first and second electric motors 5 and 6 based on sensor signals from the torque sensor 4 and the like, and an ignition switch 9 And a vehicle-mounted battery 10 for supplying power to ECU8 Te.

  In a vehicle equipped with the electric power steering device, when the driver operates the steering member 1, the steering torque due to the operation is detected by the torque sensor 4. The ECU 8 controls the driving of the first and second electric motors 5 and 6 based on the detected information such as the steering torque. As a result, the electric motors 5 and 6 generate steering assist torque, and these steering assist torques are transmitted to the steering shaft 2 via the speed reduction mechanism 7 so that the steering applied by the driver's operation of the steering member 1 is performed. The sum of the torque and the steering assist torque generated by the electric motors 5 and 6 is given to the steering mechanism 3 as an output torque.

  In the steering mechanism 3, the rotation of the input shaft is converted into the reciprocating motion of the rack shaft that is the output shaft. Both ends of the rack shaft are connected to a steering wheel 12 via a connecting member 11 including a tie rod and a knuckle arm, and the direction of the wheel 12 changes according to the reciprocating motion of the rack shaft.

  In the electric power steering apparatus described above, the middle portion of the steering shaft 2 includes a cylindrical input shaft 13, a torsion bar 14, and a cylindrical output shaft 15. The input shaft 13 is connected to a torsion bar 14 inserted inside the cylindrical shape by a pin 16 penetrating in the radial direction, and an upper end portion of the input shaft 13 and the torsion bar 14 is a shaft (upper part of the steering shaft 2). It is connected to the lower end of (not shown). The torsion bar 14 has a long and narrow torsion region in the middle thereof, and the large diameter upper end is connected to the input shaft 13 as described above, and the large diameter lower end is also the output shaft. The pin 17 is inserted into the cylinder 15 and connected to the output shaft 15 by a pin 17 that penetrates in the radial direction. On the outer periphery of the torsion bar 14, the input shaft 13 and the output shaft 15 extend toward the intermediate portion of the torsion bar 14 and face each other in the axial direction. The torque sensor 4 is disposed on the outer periphery of the axially facing portion between the input shaft 13 and the output shaft 15.

  The speed reduction mechanism 7 is provided with first and second worm shafts 71 and 72 as drive gears with respect to a single worm wheel 73 as a driven gear. The first worm shaft 71 is connected to the rotating shaft 5 a of the first electric motor 5, and the second worm shaft 72 is connected to the rotating shaft 6 a of the second electric motor 6. The worm wheel 73 is fitted on the outer periphery of the output shaft 15. The worm wheel 73 and the first and second worm shafts 71 and 72 are accommodated in the gear housing 18 in a state where they mesh with each other. The first worm shaft 71 and the second worm shaft 72 are arranged on both diametrical sides with the worm wheel 73 in between.

  The gear housing 18 includes a first worm shaft housing portion 181 that houses the first worm shaft 71, a second worm shaft housing portion 182 that houses the second worm shaft 72, and a worm wheel housing portion 183. The first electric motor 5 and the second electric motor 6 are mounted on the open ends of the first and second worm shaft accommodating portions 181 and 182 with their rotary shafts 5a and 6a facing inward, respectively. It has become. The first and second worm shaft accommodating portions 181 and 182 are provided in parallel on both diametrical sides of the worm wheel accommodating portion 183 corresponding to the positional relationship between the worm shafts 71 and 72 and the worm wheel 73. .

  In the first worm shaft housing portion 181 of the gear housing 18, the first worm shaft 71 has a tooth portion 71a in the middle in the axial direction and shaft portions 71b and 71c at both ends thereof. The first worm shaft accommodating portion 181 is rotatably supported through bearings 19 and 20 provided on 71 c, respectively, and one shaft portion 71 b is coaxially coupled to the rotating shaft 5 a of the first electric motor 5. Of the two bearings 19, 20, a presser ring 21 for applying an axial preload to the first worm shaft 71 is provided on the axially outer side of the bearing 19 on the first electric motor 5 side.

  Similarly to the first worm shaft 71, the second worm shaft 72 has a tooth portion 72a in the middle in the axial direction, shaft portions 72b and 72c at both ends thereof, and bearings 22 and 23 provided at both ends, respectively. The rotary shaft 6a of the second electric motor 6 is coaxially coupled to one of the shaft portions 72b. A presser ring 24 for applying an axial preload to the second worm shaft 72 is provided on the axially outer side of the bearing 22 on the second electric motor 6 side.

Next, the configuration of the ECU 8 will be described with reference to FIG. 2. The ECU 8 includes an input interface 25 that processes the sensor signal of the torque sensor 4, a microcomputer 26 that controls the center of electric power steering control, A first motor drive circuit 27 that drives the first electric motor 5 in response to the drive control signals sa ₁ and sb ₁ , and the second electric motor 6 is also driven by the drive control signals sa ₂ and sb ₂ from the microcomputer 26. And a second motor drive circuit 28.

  The microcomputer 26 includes a CPU 261, a program memory 262, a map memory 263, and a buffer memory 264.

  In this embodiment, the CPU 261 controls the driving of the first and second electric motors 5 and 6 for steering assistance based on sensor signals from the torque sensor 3 and the like, as will be described in detail later with reference to a flowchart. In addition to functioning as a steering assist control means 261A, the first and second worm shafts 71 and 72 are applied with rotational forces in opposite directions from the first and second worm shafts 71 and 72 when the steering assist is not performed. And also functions as a braking control means 261B for controlling the driving of the second electric motors 5 and 6. The braking control means 261B drives the first and second electric motors 5 and 6 when the steering assist is not in operation, so that the first and second worm shafts 71 and 72 move in the opposite directions to the worm wheel 73. The rotational force of the same torque is applied, thereby locking the worm wheel 73 so as not to rotate in any direction.

  Of the memories 262, 263, and 264, the program memory 262 is necessary for executing a basic program for executing the operation of the CPU 261 and driving control of the first and second electric motors 5 and 6 of the present embodiment. The program is stored. The map memory 263 stores a control map indicating the relationship between the steering torque and the driving amounts of the electric motors 5 and 6 for assisting steering, and the first map for the steering torque is obtained for each vehicle speed based on the control map. The driving amount of each of the second electric motors 5 and 6 can be determined. The buffer memory 264 is used for temporary storage of data when the CPU 261 performs work.

Next, the operation of the CPU 261 will be described with reference to the flowchart of FIG. In step S1, it is determined whether or not the steering torque detected by the torque sensor 4 is equal to or higher than a predetermined level. If the determination is Yes, that is, if the steering torque is greater than or equal to a predetermined level, the process proceeds to step S2, and a steering assist operation is performed in step S2 and in subsequent step S3. In step S2, the driving amount of each of the electric motors 5 and 6 is determined by referring to the map memory 263 based on the information of the steering torque obtained from the torque sensor 4, and in step S3, the driving amount corresponds to the driving amount. Drive control signals sa ₁ and sa ₂ are output to the motor drive circuits 27 and 28. As a result, each of the electric motors 5 and 6 generates a steering assist torque, which is transmitted to the steering shaft 2 via the speed reduction mechanism 7 and added to the steering torque by the driver.

  In this case, both the electric motors 5 and 6 are rotationally driven in the same phase so that the worm wheel 73 is rotated in the same direction by the worm shafts 71 and 72 directly connected, but the fluctuation of the rotation of the worm wheel 73 is reduced. Therefore, it may be rotated by shifting the phase.

In step S1, if the determination is No, that is, if the detected steering torque is less than the predetermined level, the process proceeds to step S4. In step S4, as a process corresponding to the case where the steering assist is not performed, the first and second worm shafts 71, 72 are applied to the worm wheel 73 in such a manner that torques of the same torque are applied in opposite directions to each other. Driving control signals sb ₁ and sb ₂ for braking are output to the _two motor driving circuits 27 and 28 to control driving of the first and second electric motors 5 and 6. Referring to FIG. 1, if the first worm shaft 71 applies a rotational force in the clockwise direction (in the direction of arrow A) to the worm wheel 73, the second worm shaft 72 counterclockwise ( The drive of each of the first and second electric motors 5 and 6 is controlled so as to apply a rotational force in the direction of arrow B).

  In the speed reduction mechanism 7, as described above, the worm wheel 73 does not rotate in any direction due to the mutually opposite rotational forces acting on the worm wheel 73 from the first and second worm shafts 71, 72. To be locked. In this case, since the tooth portions of the worm shafts 71 and 72 and the worm wheel 73 are kept in pressure contact with each other, no noise is generated due to gearing even if vibration is transmitted from the wheel side.

  In the above embodiment, the speed reduction mechanism 7 is not limited to the one constituted by the worm shafts 71 and 72 and the worm wheel 73, and may be constituted by another type of gear such as a helical gear.

It is sectional drawing of the deceleration mechanism of the electric power steering apparatus which concerns on the best form of this invention, and has shown the related structure collectively. FIG. 1 is a block diagram of the ECU of the apparatus shown in FIG. Flowchart showing the operation of the apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering member 2 Steering shaft 3 Steering mechanism 5 1st electric motor 5a Rotating shaft of 1st electric motor 6 2nd electric motor 6a Rotating shaft of 2nd electric motor 7 Deceleration mechanism 71 1st worm shaft (1st drive gear)
72 Second worm shaft (second drive gear)
73 Worm wheel (driven gear)
8 Electronic control unit (ECU)
15 Output shaft

Claims (1)

An electric power steering device that assists steering by driving an electric motor according to an operation of a steering member,
A first drive gear coupled to the rotating shaft of the first electric motor;
A second drive gear coupled to the rotating shaft of the second electric motor;
A driven gear fitted to the steering shaft and meshing with the first and second drive gears;
Braking control means for controlling the driving of the first and second electric motors so that rotational forces in opposite directions are applied from the first and second drive gears to the driven gear when the steering assist is not operating;
An electric power steering apparatus comprising:

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