JP2004217046A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering system without lowering motor efficiency and upsizing system size. <P>SOLUTION: The electric power steering system transmits the torque of an output shaft 15 of an electric motor 11 to a steering shaft 6 via a planetary roller mechanism 17, a reduction mechanism 21 including a bevel gear, and a conversion mechanism 23 including a ball screw mechanism. Since the torque of the output shaft 15 decreases in the planetary roller mechanism 17, it is possible to reduce the revolutions of the bevel gear without reducing the revolutions of the electric motor to reduce the rattling noise and so on of the reduction mechanism 21 and the like. Further, since a main wheel 20 of the reduction mechanism 21 is placed to surround the steering shaft 6, it is possible to downsize the reduction mechanism 21. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device.
[0002]
[Prior art]
As a so-called rack assist type electric power steering device, a driving force of an electric motor for assisting steering is applied to a steered shaft (rack shaft) via a rotation conversion mechanism such as a reduction mechanism including a bevel gear and a ball screw mechanism. An electric power steering device is provided.
Further, there is also provided a reduction gear that reduces the driving force of the electric motor via a first-stage planetary gear type reduction mechanism and a second-stage planetary gear reduction mechanism. In this reduction gear transmission, there has been proposed a reduction gear mechanism using a roller instead of a gear as the first-stage reduction gear mechanism (for example, see Patent Document 1). By using rollers instead of gears, noise generated by the speed reduction mechanism is reduced.
[0003]
[Patent Document 1]
Registered Utility Model No. 2538139.
[0004]
[Problems to be solved by the invention]
In the above-described electric power steering apparatus, when the bevel gear rotates by the driving force of the electric motor and the rotation conversion mechanism is driven, rattling noise occurs in the bevel gear, and the rolling conversion of a rolling element such as a ball in the rotation conversion mechanism. Sounds and the like are generated, and these noises cause occupants to feel uncomfortable.
By reducing the rotation speed of the electric motor and the rotation speed of the bevel gear and the like, it is possible to reduce the rattling noise and the rolling noise, but in this case, it is necessary to reduce the reduction ratio of the bevel gear, It is necessary to increase the torque generated by the electric motor, which causes problems such as a reduction in motor efficiency.
[0005]
On the other hand, in order to reduce noise, it is conceivable to apply the driving force of the electric motor to the steered shaft by using the reduction gear of Patent Document 1, but in this case, it is necessary to provide two planetary reduction gears. Therefore, the device becomes large.
The present invention has been made under such a background, and an object of the present invention is to provide an electric power steering device improved so as to reduce the generation of noise without reducing motor efficiency and increasing the size of the device. I do.
[0006]
Mechanism for solving the problem and effect of the invention
In order to achieve the above object, a first invention is directed to a reduction differential transmission mechanism having an input element connected to an output shaft of an electric motor, and a small gear connected to an output element of the reduction differential transmission mechanism. And a reduction gear including a large gear that meshes with the small gear and surrounds the steering shaft, and a rotating cylinder that rotates integrally with the large gear of the reduction mechanism, and converts the rotation of the rotation cylinder into axial movement of the steering shaft. And an electric power steering device, comprising:
[0007]
According to the present invention, the rotation of the output shaft of the electric motor is reduced by the reduction differential transmission mechanism and transmitted to the small gear. For this reason, it is possible to reduce the number of rotations of the small gear and the large gear of the reduction mechanism and the rotation cylinder of the conversion mechanism without reducing the number of rotations of the output shaft of the electric motor, thereby reducing noise generated by the reduction mechanism and the conversion mechanism. be able to.
In addition, since the large gear of the speed reduction mechanism is arranged so as to surround the steered shaft, the speed reduction mechanism can be made compact, and the size of the entire apparatus does not increase.
[0008]
In a second aspect based on the first aspect, the differential transmission mechanism for deceleration includes a planetary roller mechanism. According to the present invention, by reducing the rotation of the output shaft of the electric motor using the planetary roller mechanism, the noise generated from the differential transmission mechanism for deceleration can be made extremely low, which makes the driver uncomfortable. Is not given.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device according to one embodiment of the present invention. With reference to FIG. 1, the electric power steering apparatus 1 includes a first steering shaft 3a integrally rotatably connected to a steering member 2 such as a steering wheel, and a first steering shaft 3a and a torsion bar 3b. The vehicle includes a second steering shaft 3c coaxially connected thereto, and a steering mechanism 5 including a rack-and-pinion mechanism or the like connected to the second steering shaft 3c to achieve steering of the steered wheels 4.
[0010]
The steering mechanism 5 is arranged to extend in the left-right direction of the vehicle, and is connected to a steered shaft 6 that is movable along the axial direction via tie rods 7 at both ends of the steered shaft 6. A supporting knuckle arm 8.
By the movement of the steered shaft 6 in the axial direction, the steered wheels 4 are steered. A rack 9 is formed on a part of the steered shaft 6. The rack 9 meshes with a pinion 10 provided at an end of the second steering shaft 3c and integrally rotating with the second steering shaft 3c. When the first and second steering shafts 3a, 3c are rotationally driven in response to the operation of the steering member 2, the rotation is converted into the axial movement of the steered shaft 6 by the pinion 10 and the rack 9.
[0011]
The electric power steering apparatus 1 drives a steering assist electric motor 11 to apply a steering assist force to the steered shaft 6.
A torque sensor 12 for detecting an operation torque of the steering member 2 based on a relative rotational displacement of the first and second steering shafts 3a and 3c via the torsion bar 3b is provided. The signal from the torque sensor 12 is input to a control unit C including a microprocessor and the like. Further, a detection signal from a vehicle speed sensor 13 for detecting a vehicle speed is input to the control unit C.
[0012]
The control unit C outputs a control signal to a drive circuit 14 as a drive unit for driving the electric motor 11 in accordance with signals from the torque sensor 12 and the vehicle speed sensor 13 and the like. The drive circuit 14 supplied with the control signal supplies electric power to the electric motor 11 and drives the electric motor 11.
FIG. 2 is a partial cross-sectional view of the electric power steering device 1 around the electric motor 11.
[0013]
With reference to FIG. 2, the electric power steering device 1 includes a planetary roller mechanism 17 as a differential transmission mechanism for deceleration having an input shaft 26 as an input element connected to an output shaft 15 of the electric motor 11, and the planetary roller mechanism 17. A speed reduction mechanism 21 including a small gear 19 connected to an output shaft 31 as an output element of the roller mechanism 17 and a large gear 20 meshing with the small gear 19 and surrounding the steered shaft 6, and a large gear of the speed reduction mechanism 21 And a conversion mechanism 23 that includes a rotary cylinder 22 that rotates integrally with the rotary shaft 20 and converts the rotation of the rotary cylinder 22 into axial movement of the steered shaft 6.
[0014]
The rotation of the output shaft 15 of the electric motor 11 is converted to the rotation of a rotary cylinder 22 coaxial with the steered shaft 6 via a planetary roller mechanism 17 and a speed reduction mechanism 21, and the rotation of the rotary cylinder 22 is further converted to a conversion mechanism. This is converted into the axial movement of the steered shaft 6 by 23, and as a result, steering assist is achieved.
An end of the housing 11a of the electric motor 11 is fitted into a connection port 24a of the housing 24, and the housings 11a and 24 are fixed by fixing screws (not shown). One end of a coupling 25 is attached to the output shaft 15 of the electric motor 11 by, for example, press fitting. An input shaft 26 is fixed to the other end of the coupling 25 by, for example, spline coupling. The input shaft 26 can rotate integrally with the output shaft 15 via the coupling 25.
[0015]
The planetary roller mechanism 17 includes the input shaft 26 described above, a sun roller 16 formed at one end of the input shaft 26, a carrier 27, and a plurality (for example, 2) that are rotatably held by the carrier 27 and engaged with the sun roller 16. ), A ring 28 engaged with each of the planetary rollers 18, and an output shaft 31 arranged coaxially with the sun roller 16 and capable of rotating integrally with the carrier 27.
Each planetary roller 18 is rotatably supported by a corresponding support shaft 30 of the carrier 27. Each of these planetary rollers 18 is arranged on the outer periphery of the sun roller 16, and its circumferential surface (track) is in contact with the circumferential surface of the sun roller 16.
[0016]
The inner circumferential surface of the ring 28 is in contact with the circumferential surface of each planetary roller 18. The ring 28 is fixed to the inner periphery 29 of the housing 24 so as not to rotate. Each planetary roller 18 is pre-pressed by being sandwiched between the sun roller 16 and the ring 28.
With the above configuration, when the output shaft 15 of the electric motor 11 rotates, the input shaft 26 and the sun roller 16 rotate together with the output shaft 15. Accordingly, each planetary roller 18 rotates (revolves) about the support shaft 30 and rotates (revolves) about the sun roller 16. As the respective planetary rollers 18 revolve, the carrier 27 and the output shaft 31 rotate integrally. As a result, the rotation of the output shaft 15 of the electric motor 11 is reduced and output as the rotation of the output shaft 31.
[0017]
The output shaft 31 is rotatably supported by the housing 24 via a bearing 32. The small gear 19 of the reduction mechanism 21 is fixed to one end 33 of the output shaft 31 so as to be integrally rotatable.
The small gear 19 and the large gear 20 of the reduction mechanism 21 are, for example, bevel gears. When the output shaft 31 of the planetary roller mechanism 17 rotates, the small gear 19 and the large gear 20 meshed with the small gear 19 rotate, and the rotation of the output shaft 31 is reduced.
[0018]
In this embodiment, a ball screw mechanism is used as the conversion mechanism 23. The conversion mechanism 23 includes the above-described rotary cylinder 22 formed of a ball nut, a screw shaft 34 formed on a part of the steering shaft 6 and supported by the housing 24 so as not to rotate, and a rolling element 35 such as a plurality of balls. And
The large gear 20 is fixed to the outer periphery 36 of the rotary cylinder 22 so as to be integrally rotatable. The rotating cylinder 22 is rotatably supported by the housing 24 via a pair of bearings 37 and 38, and is restricted from moving in the corresponding axial direction by the bearings 37 and 38. A screw groove 40 is formed on the inner periphery 39 of the rotary cylinder 22. The large gear 20 is arranged outside the screw groove 40.
[0019]
Thus, the total length of the rotary cylinder 22 is shortened and the conversion mechanism 23 is made more compact as compared with the conventional configuration in which the screw groove 40 and the large gear 20 are arranged at a distance in the axial direction of the steered shaft 6. I have. Further, by shortening the axial distance between the large gear 20 and the thread groove 40, when the rotating cylinder 22 is rotated by the rotation of the large gear 20, the twisting occurs between the rotating cylinder 22 and a rolling element 35 described later. Does not occur. Therefore, it is possible to prevent the steering feeling from being deteriorated.
[0020]
The rotary cylinder 22 concentrically surrounds a part of the screw shaft 34, and a screw groove 42 is formed on the outer periphery 41 of the screw shaft 34.
The rolling element 35 is interposed between the thread groove 40 on the inner periphery 39 of the rotating cylinder 22 and the thread groove 42 on the outer periphery 41 of the screw shaft 34. 34. The rolling elements 35 are circulated in the thread grooves 40 and 42 using a known mechanism (not shown).
[0021]
When the small gear 19 and the large gear 20 of the reduction mechanism 21 rotate, the rotating cylinder 22 is rotated, and the screw shaft 34 screwed to the rotating cylinder 22 via the rolling element 35 is moved in one of the axial directions. Sent to
The end portion 61 of the steered shaft 6 is supported by the housing 24 via at least one bush 43 made of, for example, a cylindrical resin member so as to be movable in the axial direction (one end of the steered shaft 6 in FIG. 2). Only the side of the part is shown) The bush 43 is fixed to the housing 24 with its movement in the axial direction restricted. In the present embodiment, the range in which the screw shaft 34 is provided on the steered shaft 6 is set wider than usual, and the screw shaft 34 contacts the bush 43 over the entire range of the stroke of the steered shaft 6. .
[0022]
At both ends 45 of the housing 24, a part of the tie rod 7, a joint 60 for rotatably connecting the end of the tie rod 7 to the end of the steered shaft 6, and the housing 60 protruding from the housing 24 of the steered shaft 6. Stretchable bellows-like boots 46 are provided to cover the portions in a lump (only one end 45 side of the housing 24 is shown in FIG. 2).
One end 47 of each boot 46 is fixed to the outer periphery of the corresponding end 45 of the housing 24 by being tightened with a band (not shown) or the like. The other end 59 of each boot 46 is fixed to the outer periphery of the corresponding tie rod 7 by being tightened with a wire (not shown) or the like. Thus, a space 48 is defined outside the bush 43 (on the tie rod 7 side) by the housing 24, the bush 43, the steered shaft 6, the boot 46, and the tie rod 7.
[0023]
The space 48 communicates with a space inside the bush 43 of the housing 24 (on the conversion mechanism 23 side) through the screw groove 42 of the screw shaft 34 of the steered shaft 6, and air passes through the screw groove 42. 48 can be entered and exited. Therefore, when the boot 46 expands and contracts due to the movement of the tie rod 7 and the like, it is possible to prevent the boot 46 from coming off the housing 24 and the tie rod 7 or being dented inward and causing biting.
[0024]
The thread groove 42 of the screw shaft 34 of the steered shaft 6 needs to be polished in a region that can come into contact with the rolling element 35 of the conversion mechanism 23, but in the other region, only the turning process is required. Thus, the formation of the air passage for entering and exiting the space 48 is realized at low cost. Further, since there is no need to separately provide a hole for allowing the air in the space 48 to enter and leave the steering shaft 6 and the housing 24, the strength of the steering shaft 6 and the housing 24 does not decrease.
[0025]
According to the present embodiment, the rotation of the output shaft 15 of the electric motor 11 is reduced by the planetary roller mechanism 17 and transmitted to the small gear 19. Therefore, the rotation speeds of the small gear 19 and the large gear 20 of the speed reduction mechanism 21 and the rotation cylinder 22 of the conversion mechanism 23 can be reduced without lowering the rotation speed of the output shaft 15 of the electric motor 11. Noise generated by the conversion mechanism 23 can be reduced.
Further, since the large gear 20 of the speed reduction mechanism 21 is arranged so as to surround the steered shaft 6, the speed reduction mechanism 21 can be made compact, and the entire electric power steering device 1 does not become large. .
[0026]
Furthermore, by reducing the rotation of the output shaft 15 of the electric motor 11 by using the planetary roller mechanism 17, the noise generated by the differential transmission mechanism for reduction can be made extremely low, and the driver feels discomfort. Will not give.
FIG. 3 shows another embodiment of the present invention. Referring to FIG. 3, this embodiment is different from the embodiment of FIG. 2 in that the ball screw mechanism is used as conversion mechanism 23 in the embodiment of FIG. Instead, a known bearing screw mechanism is used as the conversion mechanism 50. In the conversion mechanism 50, a plurality of rolling bearings 52 are arranged at a predetermined inclination on a rotating cylinder 51 formed of a bearing nut, and the outer ring 53 of each rolling bearing 52 is held on the rotating cylinder 51, while the inner ring 54 of each rolling bearing 52 is formed. The screw thread 55 on the inner periphery is fitted into the screw groove 42 of the screw shaft 34 of the steered shaft 6.
[0027]
The rotating cylinder 51 has first and second portions 57 and 58 concentric with each other so as to be integrally rotatable via a connecting member 56 such as a pin. The first portion 57 has the same configuration as the rotary cylinder 22 of the embodiment in FIG. 2, and is provided with the large gear 20 and the like of the speed reduction mechanism 21 although not shown. Further, the second portion 58 holds the outer ring 53 of the rolling bearing 52 in an inclined circumferential groove provided on the inner periphery thereof.
In this embodiment, the same operation and effect as in the embodiment of FIG. 2 can be obtained. Further, by using a bearing screw mechanism as the conversion mechanism 50, noise generated in the conversion mechanism 50 can be further reduced as compared with the case where a ball screw mechanism is used.
[0028]
The present invention is not limited to the contents of the above embodiments, and various changes can be made within the scope of the claims. For example, the output shaft 15 of the electric motor 11 may double as the input shaft 26 of the planetary roller mechanism 17.
In addition, one of the sun roller 16, the carrier 27, and the ring 28 of the planetary roller mechanism 17 may be fixed to the housing 24, and the remaining two elements may be connected to the input shaft 26 and the output shaft 31, respectively.
[0029]
Although the planetary roller mechanism 17 is used as the differential transmission mechanism for reduction, another differential transmission mechanism for reduction such as a planetary gear reducer or a ball reducer may be used instead.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a partial cross-sectional view of the electric power steering device around the electric motor.
FIG. 3 is a sectional view of a main part of an electric power steering apparatus according to another embodiment of the present invention.
[Explanation of symbols]
6 Steering shaft 11 Electric motor 15 Output shaft 17 Planetary roller mechanism (differential transmission mechanism for deceleration)
19 Small gear 20 Large gear 21 Reduction mechanism 22 Rotating cylinder 23 Conversion mechanism 26 Input shaft (input element)
31 Output shaft (output element)
50 conversion mechanism 51 rotating cylinder

Claims (2)

A differential transmission mechanism for reduction having an input element coupled to the output shaft of the electric motor,
A speed reduction mechanism including a small gear connected to an output element of the differential transmission mechanism for reduction and a large gear meshing with the small gear and surrounding the steered shaft;
An electric power steering apparatus, comprising: a rotating cylinder that rotates integrally with a large gear of the speed reduction mechanism; and a conversion mechanism that converts rotation of the rotating cylinder into axial movement of a steered shaft. 2. The electric power steering apparatus according to claim 1, wherein the differential transmission mechanism for deceleration includes a planetary roller mechanism.

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