JPH07172326A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To provide a motor-driven power steering device which can afford large steering auxiliary power by using plural motors and is small-sized. CONSTITUTION:Large steering auxiliary power is obtained by means of two motors 10, 20 for steering assistance. The rotary power of respective motors 10, 20 is transmitted to a steering mechanism through individual deceleration mechanisms 7A, 7B. Respective speed reduction mechanisms 7A, 7B possess worm gears 71A, 71B and worm wheels 72A, 72B. The respective speed reduction mechanisms 7A, 7B only transmit the rotary power of the motors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device.

[0002]

2. Description of the Related Art Conventionally, in a light vehicle, an electric power steering device for transmitting a rotational force of a DC motor to a steering mechanism has been used to assist steering in accordance with a steering torque applied to a steering shaft. In this electric power steering device, a motor is attached to a steering column that holds a steering shaft, and the rotational force of the motor is applied to the steering shaft via, for example, a worm gear. Further, a torsion bar is interposed in the middle of the steering shaft, and when the steering wheel is operated,
Since the torsion bar is slightly twisted and a relative displacement occurs between the input shaft and the output shaft connected via the torsion bar, this relative displacement is detected by the torque sensor, and the direct current is detected based on this detection result. The input current to the motor is controlled to assist the steering force according to the steering torque applied to the steering shaft.

[0003]

The above electric power steering device is being applied to not only light vehicles but also ordinary vehicles because it is possible to perform fine control according to running conditions. about,
The motor is required to have a high output in order to obtain a desired steering assist force.

Therefore, it is conceivable to increase the assisting force by using two small motors. In this case, two worm gears are connected to each motor, and each worm gear is meshed with one worm wheel, or two small motors are connected to one worm gear.
If a structure that meshes with one worm wheel is adopted, one worm wheel will transmit all outputs in any case. Therefore, it is necessary to improve the strength of the worm wheel, resulting in an increase in the size of the electric power steering device.

On the other hand, conventionally, there has been a problem of gear rattling noise caused by backlash in the worm gear mechanism. Further, in order to prevent this, at the time of production, strict backlash management has been performed, in which the worm gear and the worm wheel are grouped by size and assembled in a combination that reduces rattling noise. However, such backlash management requires a great deal of time and labor for assembling the electric power steering, which is very troublesome.

Further, when a plurality of motors are adopted as described above, there is a problem that the electric power steering device becomes large depending on the direction in which the motors are arranged. Furthermore, in a DC motor used as a motor, cogging (torque fluctuation) occurs due to a change in magnetic flux when the rotor passes through the magnetic flux, and this cogging tends to increase as the motor has a higher output. Therefore, the electric power steering device for an ordinary vehicle has a problem that the steering feeling is deteriorated by the cogging.

The present invention has been made in view of the above problems, and a first object of the present invention is to provide a small electric power steering apparatus using a plurality of motors. A second object of the present invention is to provide an electric power steering device capable of reducing gear rattling noise caused by backlash without requiring strict backlash management.

A third object of the present invention is to provide a small electric power steering device using a plurality of motors. A fourth object of the present invention is to provide an electric power steering device that can obtain a large steering assist force and has a good steering feeling.

[0009]

In order to achieve the above first object, an electric power steering apparatus according to a first aspect of the present invention includes a plurality of motors driven based on a steering torque applied to a steering shaft, and a plurality of motors. A plurality of reduction gears that are connected to the motors and transmit the rotational force of each motor to the steering mechanism. Each reduction gear is connected to the rotation shaft of the corresponding motor, and a worm gear that meshes with the worm gear. And a wheel, respectively.

In order to achieve the second object, the electric power steering apparatus according to claim 2 is the electric power steering apparatus according to claim 1.
In the electric power steering apparatus described above, the phases in which the maximum eccentric portion of the outer diameter with respect to the inner diameter of each worm wheel meshes with the corresponding worm gear are shifted from each other. In order to achieve the third object, the electric power steering apparatus according to claim 3 is the electric power steering apparatus according to claim 1 or 2, wherein the motors are arranged in the same direction. It is characterized by.

An electric power steering system according to a fourth aspect is the electric power steering system according to any one of the first to third aspects, in which the phase of each motor suppresses fluctuations in the rotational force transmitted to the steering mechanism. It is characterized in that they are displaced from each other as much as possible.

[0012]

According to the structure of the invention described in claim 1, the reduction mechanism including the worm gear and the worm wheel is provided corresponding to each of the plurality of motors. Therefore, each deceleration mechanism is loaded with only one motor output. The configuration of the invention according to claim 2 has the following effects. In other words, the rattling noise due to backlash is due to the fact that the worm wheel can rotate for the amount of backlash without rotation of the worm gear and the motor, and therefore tooth contact (torque transmission by meshing) starts at a certain rotation speed. Occur. Then, at a certain moment, a rattling noise is generated from the speed reduction mechanism having the smallest backlash among the speed reduction mechanisms. In addition, the backlash mainly depends on the eccentricity of the worm wheel. The present inventor pays attention to these matters and shifts the phases in which the maximum eccentric portion of each worm wheel meshes with the corresponding worm gears from each other, so that the cycles of backlash change in each reduction mechanism can be shifted from each other.

According to the configuration of the invention according to claim 3 above,
Since the motors are arranged in the same direction, the electric power steering device can be downsized. According to the configuration of the invention according to the fourth aspect, the phases of the motors are shifted from each other, so that the cogging is canceled by the motors and the fluctuation of the rotational force transmitted to the steering mechanism can be suppressed.

[0014]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 2 is a schematic perspective view showing a state in which the electric power steering apparatus A of the present invention is connected to the steering mechanism B. In the electric power steering apparatus A, a steering shaft 2 having a steering wheel 1 attached to an upper end thereof is rotatably held by a steering column 3, and a column bracket 31 of the steering column 3 is provided.
Two steering assisting motors 10 and 20 are attached to the steering wheel 2 and the rotational force of the motors 10 and 20 is applied to the steering shaft 2 and transmitted to the steering mechanism B.

More specifically, the above two motors 1
0 and 20 are arranged in parallel on one side of the steering shaft 2 with their respective motor shafts 11 and 21 (see FIG. 3) oriented in the radial direction of the steering shaft 2.
Further, referring to FIG. 3, the motor shafts 11 and 21 of the respective motors 10 and 20 are displaced from each other in the axial direction of the steering shaft 2 by a deviation amount k (see FIG. 1, and in FIG.
21) and the extension lines of the shaft center of the worm gears 71A and 71B, which are coaxial with each other (indicating the amount of deviation between the worm gears 71A and 71B), face each other with the steering shaft 2 interposed therebetween.

Referring to FIGS. 1 and 3, one motor 10
Is applied to the output shaft 2a via the electromagnetic clutch 30 and the speed reduction mechanism 7A.
The rotational force of the other motor 20 is applied to the output shaft 2a via the electromagnetic clutch 40 and the speed reduction mechanism 7B. In this way, the rotational force of each motor 10, 20 is individually and simultaneously applied to the output shaft 2a via the individual speed reducing mechanisms 7A, 7B. The reduction mechanism 7A is a worm gear 71A that is integrally rotatably connected to the motor shaft 11 via the electromagnetic clutch 30, and a worm wheel 72A that is meshed with the worm gear 71A and is integrally rotatably attached to the output shaft 2a. It has and. The reduction mechanism 7B is a worm gear 71B that is integrally rotatably connected to the motor shaft 21 via the electromagnetic clutch 40, and a worm that is individually meshed with the worm gear 71B and is integrally rotatably attached to the output shaft 2a. And a wheel 72B.

The worm gears 71A and 71B are arranged at positions which are 180 ° out of phase with each other in terms of the rotation angle of the steering shaft 2. On the other hand, each worm gear 71
Worm wheel 72 that meshes with A and 71B respectively
A and 72B are arranged so that the portion where the eccentricity of the outer diameter with respect to the inner diameter is the maximum is oriented in the same direction (the maximum eccentric portion is the worm wheel 72A, 72B in FIG. 3).
, For example, part C, and each maximum eccentric part rotates in the same phase. ). As a result, the phases at which the maximum eccentric portions of the worm wheels 72A, 72B mesh with the corresponding worm gears 71A, 71B are shifted by 180 ° (the rotation angle of the steering shaft 2) from each other.

In this way, the reduction mechanism 7A,
This is to reduce the rattling noise due to backlash of 7B. That is, the above rattling noise is generated by the worm wheel 7
2A, 72B is the backlash, worm gear 71
Since the A, 71B and the motors 10, 20 can rotate without rotation, they occur when tooth contact (torque transmission by meshing) is started at a certain rotation speed. On the other hand, the inventor of the present application has found that the above-mentioned backlash mainly depends on the eccentricity of the worm wheels 72A and 72B. Therefore, as described above, the maximum eccentric portion of each worm wheel 72A, 72B is set to a phase in which the maximum eccentric portion meshes with the corresponding worm gear 71A, 71B.
Since they are shifted by 0 °, the cycles of backlash changes in the respective reduction mechanisms 7A and 7B can be mutually shifted by 180 ° (see FIG. 4, M in FIG. 4 indicates the maximum amount of backlash that contributes to vibration, etc.). As a result, vibration and noise caused by backlash can be reduced. In addition,
The worm wheels 72A and 72B are assembled with the maximum eccentric portion facing the same direction as described above during assembly.

The two motors 10 and 20 are configured to have a small output, and by driving the two motors at the same time, the steering assist force necessary for the electric power steering apparatus A for ordinary vehicles is secured. be able to.
Referring to FIGS. 1 and 4, the steering shaft 2
A torsion bar 90 is interposed in the middle of the
When the steering wheel 1 is operated, the torsion bar 90 is slightly twisted, and a relative displacement is generated between the input shaft 2b and the output shaft 2a connected to each other by the torsion bar 90. Then, the output shaft 2a
Is connected to a rack and pinion type steering mechanism B through a universal joint 81, and the relative displacement generated between the input shaft 2b and the output shaft 2a is attached to the column bracket 31. Torque sensor 4
And the controller 5 controls the input current to the motors 10 and 20 based on the detection result.
This assists the steering force in accordance with the steering torque applied to the steering shaft 2.

Further, the two motors 10 and 20 are
In order to suppress the fluctuation of the rotational force transmitted to the steering mechanism B, they are provided with their phases shifted from each other. Figure 5
FIG. 4 is a schematic diagram for explaining the state in which the phases are shifted, and the stators 12, 22 and the rotors 13, 22 when the one motor 10 and the other motor 20 are assumed to be coaxially arranged. 23 shows the positional relationship of 23. As shown in the figure, each of the motors 10, 20 has a stator 12,
The positions of the rotors 22 in the circumferential direction coincide with each other, and the positions of the rotors 13 and 23 in the circumferential direction are displaced and fixed by a predetermined angle θ. That is, when the rotor 13 of the motor 10 is in the rotation position where the cogging torque of the motor 10 is maximum (see the solid line in the figure), the rotor 23 of the motor 20 is
The rotor 1 of the motor 10 is positioned so that the cogging torque of the motor 20 is at the minimum (see the broken line in the figure).
By fixing the motor 3 and the rotor 23 of the motor 20 to the respective motor shafts 11 and 21 in a state of being displaced by a predetermined angle θ, the phases of the motors 10 and 20 are displaced from each other.

According to this embodiment, a plurality of motors 10, 2
Since each rotational force of 0 is transmitted by the individual speed reducing mechanism 7A, 7B, only the output of one motor is loaded on each speed reducing mechanism 7A, 7B. Therefore, the worm gears 71A, 71B of the speed reduction mechanisms 7A, 7B
As a result, there is no need to improve the strength of the worm wheel 72A, 72B, and as a result, the speed reduction mechanism 7A, 7B
Does not increase in size. Therefore, a plurality of motors 1
Large steering assist force using 0 and 20 (steering assist force required for the electric power steering device A for ordinary vehicles)
It is possible to realize a small electric power steering device while obtaining the above. Further, the load acting on each worm gear 71 and the worm wheel 72 can be reduced as compared with the case of using a single high output motor. Therefore, the durability of the worm gear 71 and the worm wheel 72 can be ensured.

Further, each worm wheel 72A, 72B
Worm gear 71A, which corresponds to the maximum eccentric deflection part of
Since the phases in which the gears 71B and 71B are shifted from each other can be shifted from each other, the cycles of backlash changes in the respective reduction mechanisms 7A and 7B can be shifted from each other, and as a result, the vibration and noise (teeth) caused by backlash can be reduced. Get out. Further, since the motors 10 and 20 are arranged in the same direction, the electric power steering device can be made smaller, and the mountability of the electric power steering device A on a vehicle can be improved. That is, the motor 10,
When the steering shafts 20 are arranged to face each other in the radial direction of the steering shaft 2 (see FIG. 6), the motors 10, 20
However, the electric power steering device A becomes large in size because it largely projects to both sides of the steering shaft 2.
Although the mountability on a vehicle deteriorates, in the above-described embodiment, since the motors 10 and 20 are arranged side by side in the same direction, the electric power steering device A can be made compact, which in turn leads to a vehicle. The mountability of can be improved.

Moreover, by mutually shifting the phases of the motors 10 and 20, the cogging of the motors 10 and 20 can be canceled by each other, and fluctuations in the rotational force transmitted to the steering mechanism B can be suppressed. Therefore, a larger steering assist force can be obtained, and an electric power steering device with a good steering feeling can be realized.

Two worm wheels 72A and 72B provided corresponding to the respective motors 10 and 20.
If one worm wheel is used, the worm gear 71 connected to one motor 10 is used.
And a worm gear 71 connected to the other motor 20.
It is necessary to make the respective twist angles opposite to each other, which increases the types of parts and complicates manufacturing and assembling, and the worm wheel 72 used
It is not preferable because it is necessary to improve the strength, and if this is not done, the size becomes large, and if this is not done, problems will occur in durability.

The motors 10 and 20 and the speed reducing mechanisms 7A and 7B are arranged in the steering mechanism B as shown in FIGS.
The rack and pinion section 80 of the motors 10 and 20 may be configured so that the rotational force of each of the motors 10 and 20 is
It can be directly attached to the pinion shaft 82 via the worm gear 71 and the worm wheel 72 provided for each 20. In this embodiment, as in the embodiment shown in FIG. 1, the torsion bar and torque sensor 4 are formed in the column bracket 31. In this respect, in the conventional electric power steering device of the type in which the steering assist force is directly applied to the pinion shaft 82, the torsion bar and the torque sensor 4 are also configured in the rack and pinion portion 80 of the steering mechanism B. Therefore, the distance between the serration portion 83 at the upper end of the pinion shaft 82 and the central portion of the rack 84 becomes large, that is, the serration height H becomes high, and the refraction angle of the universal joint 81 becomes tight. The constant velocity between the pinion shaft 82 and the pinion shaft 82 was reduced, and the steering force was uneven. However, as in this embodiment, the torsion bar and torque sensor 4
Is formed in the column bracket 31 portion, the serration height H can be reduced. As a result, a better steering feeling can be obtained. In addition, in this embodiment, since the motors 10, 20 and the like are constructed in the rack and pinion portion 80, there is also an advantage that it is not necessary to increase the strength of the column bracket 31.

The electric power steering apparatus of the present invention is
The present invention is not limited to the above-mentioned embodiment, and it is possible to add more motors and reduction gears. For example, when N motors are provided and the N worm gears are deviated by 360 ° / N by the rotation angle of the steering shaft, the position of the maximum eccentric portion of the N worm wheels is 360 ° / N.
You can shift them one by one.

Further, the stators 12 of the motors 10 and 20,
By shifting the relative position of 22, the motor 1
The phases of 0 and 20 can be shifted. Further, by using two motors having different rated outputs, a large steering assist force is obtained by using both motors when the vehicle is stopped and at low speed, and at the time of high speed, the motor having the larger rated output and the clutch connected thereto May be turned off to reduce the influence of the inertial force of the motor on the steering feeling.

Further, according to the present invention, the deceleration mechanisms are individually connected to the plurality of motors, the maximum eccentric parts of the worm wheels are shifted from each other in phase with which the worm gears mesh, and the plurality of motors are the same. The arrangements in the directions, and the respective phases of the plurality of motors being shifted from each other, can be implemented in the following combinations with respect to the configurations of or independently. That is, at least one of and may be implemented in combination, or may be implemented alone.

[0029]

According to the first aspect of the invention, the reduction mechanism including the worm gear and the worm wheel is provided for each of the plurality of motors. Therefore, each deceleration mechanism is loaded with only one motor output. Therefore, it is not necessary to improve the strength of the worm gear or the worm wheel of the reduction mechanism, and as a result, the reduction mechanism does not increase in size for the purpose of improving the strength, and the durability is excellent. Therefore, a large steering assist force can be obtained by using a plurality of motors, and a compact and durable electric power steering device can be realized.

In particular, according to the second aspect of the present invention, the eccentric maximum swing portions of the worm wheels mesh with the corresponding worm gears in different phases, so that the cycles of backlash changes in the respective reduction mechanisms are mutually changed. It can be displaced, and as a result, vibration and noise caused by backlash can be reduced. Particularly, according to the invention of claim 3, since the motors are arranged in the same direction,
The electric power steering device can be made smaller.

In particular, according to the invention of claim 4, the phases of the motors are shifted from each other, so that the cogging is canceled by the motors and the fluctuation of the rotational force transmitted to the steering mechanism can be suppressed. . Therefore, a larger steering assist force can be obtained, and an electric power steering device with a good steering feeling can be realized.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a state in which the electric power steering device is connected to a steering mechanism.

FIG. 3 is a lateral cross-sectional view of a main part of the electric power steering device.

FIG. 4 is a diagram showing a relationship between backlash and a rotation angle of a steering shaft.

FIG. 5 is a schematic diagram for explaining a phase difference.

FIG. 6 is a schematic view showing another arrangement example of motors.

FIG. 7 is a schematic perspective view showing another embodiment of the present invention.

8 is a cross-sectional view of the main parts of the embodiment shown in FIG.

[Explanation of symbols]

 2 Steering shaft 7A, 7B Reduction gear mechanism 71A, 71B Worm gear 72A, 72B Worm wheel 10, 20 Motor A Electric power steering device B Steering mechanism

Claims (4)

[Claims] 1. A plurality of motors driven on the basis of a steering torque applied to a steering shaft, and a plurality of speed reducing mechanisms connected to the respective motors for transmitting the rotational force of the respective motors to the steering mechanism. An electric power steering apparatus in which each reduction mechanism includes a worm gear connected to a rotation shaft of a corresponding motor, and a worm wheel meshing with the worm gear. 2. The electric power steering apparatus according to claim 1, wherein the maximum eccentric portion of the outer diameter with respect to the inner diameter of each worm wheel meshes with a corresponding worm gear in a mutually shifted phase. Steering device. 3. The electric power steering system according to claim 1, wherein the motors are arranged in the same direction. 4. The electric power steering apparatus according to any one of claims 1 to 3, wherein the phases of the respective motors are shifted from each other so as to suppress the fluctuation of the rotational force transmitted to the steering mechanism. An electric power steering device.