JP2000016314A - Electrically-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep transmission efficiency high particularly in case of low load by making the central axis of an outer rotor and the central axis of an inner rotor of a wedge roller type decelerating mechanism mutually eccentric. SOLUTION: The shaft center of an inner rotor 23 and the shaft center of an outer rotor 22 are parallel to each other, but they are eccentric by a distance (d). Accordingly, an annular space with a variable width is partitioned between the outer rotor 22 and the inner rotor 23. An idle roller 42 is arranged in the widest space. An idle roller 41, 43 are arranged in the narrowest space. Though the idle rollers 41, 43 can freely enter the further narrower space, the movement thereof going out of the space is limited by the mechanism. By this arrangement, the respective idle rollers 41, 42, 43 are firmly engaged with the inner rotor 23 and the outer rotor 22, and power is transmitted between the inner rotor 23 and the outer rotor 22 at a designated speed reduction ratio.

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 for a vehicle, and more particularly to an improvement in a speed reduction mechanism disposed between a rotor of an electric motor and a ball screw mechanism.

[0002]

2. Description of the Related Art As a power steering device of a vehicle used for assisting a steering force, an electric power steering device configured to assist a driver's steering force of a steering wheel by utilizing a rotation output of an electric motor. Is conventionally known.

As an example of this type of electric power steering apparatus, there is known an electric power steering apparatus of a coaxial ball screw type in which a nut of a ball screw provided on a rack shaft is driven by an electric motor. In this case, a reduction mechanism for reducing the rotation of the electric motor and transmitting the rotation to the rack shaft is provided between the rotor of the electric motor and the nut of the ball screw.

[0004] Examples of such a speed reduction mechanism include, for example, Japanese Utility Model Laid-Open No. 6-39666 and Japanese Utility Model Laid-Open No. 63-93.
As disclosed in Japanese Unexamined Patent Publication No. 273 and the like, a device using a spur gear is proposed. Another example is disclosed in
As described in JP-A-1549495, an apparatus using a planetary gear is known.

Japanese Patent Laid-Open Publication No. 63-43866 discloses a speed reduction mechanism including a sun roller and a plurality of planetary rollers.

[0006]

However, in the case of a reduction mechanism using a gear such as a spur gear or a planetary gear as in the conventional example, a dimensional gap is provided at the contact portion between the teeth so that the gear operates smoothly. In the case where the steering wheel operation is repeated left and right, there is a problem that the teeth hit each other in the gap portion and a hitting sound is generated. Further, during operation, there is also a problem that gear noise is generated due to relative slip between teeth at the contact portion.

[0007] In addition, there is a problem that the transmission efficiency of a normal planetary roller may be reduced especially at a low load, and a desired transmission efficiency cannot always be obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electric power steering equipped with a speed reduction mechanism which does not generate abnormal noise such as striking noise, does not generate operating noise due to gears, and which does not cause a reduction in transmission efficiency. It is to provide a device.

[0009]

In order to achieve the above object, an electric power steering apparatus according to the present invention uses a ball screw mechanism to convert the rotational motion of an electric motor into a linear motion of a rack shaft for steering wheels. In the electric power steering device for converting and assisting the operation, an inner rotor that rotates integrally with the output of the electric motor between an output shaft of the electric motor and a ball screw mechanism, and an inner rotor that faces the inner rotor. A wedge roller type speed reduction mechanism comprising an outer rotor rotating integrally with a screw nut of the ball screw mechanism, and a plurality of wedge roller type idle rollers interposed between the inner rotor and the outer rotor in contact therewith. And the center axis of the outer rotor and the center axis of the inner rotor It is characterized in that it is the mind.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the electric power steering apparatus according to the present invention, a wedge roller type reduction mechanism is provided between the electric motor and the ball screw mechanism. Since there is no occurrence and the relative slip between the rollers is extremely small, no operation noise such as gear reduction is generated. Further, since the rollers are arranged in a wedge roller, the contact pressure between the rollers is proportional to the transmission torque, so that the contact pressure of the rollers at a low load is small, and the torque transmission efficiency can be maintained high.

In the case where the contact surface between the idle roller and the inner rotor is formed as a curved surface as described above, a deviation of the axis crossing angle between the shaft of the rotor of the electric motor and the shaft of the screw nut of the ball screw mechanism can be tolerated. In addition, it is possible to set the dimensional tolerance of the component to some extent large, and it is possible to reduce the manufacturing cost.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals.

FIG. 1 is an axial sectional view showing an electric power steering apparatus 40 according to a first embodiment of the present invention. The electric power steering device 40 includes a housing 11 extending horizontally and a case 25 disposed on the right end of the housing 11 in the axial direction. The housing 11 is fixed to a vehicle body (not shown) by a bracket 17.

The input shaft 2 connected to a steering wheel (not shown) in the case 25 is mounted on the housing 11 from above.
, While a rack shaft 14 extends substantially parallel in the housing 11. The input shaft 2 is engaged with the rack shaft 14 via an output shaft (not shown) in the case 25.

A rack shaft 14 penetrating dustproof boots 12 and 13 attached to both ends of the housing 11 in the axial direction.
Are attached to a wheel steering mechanism (not shown) via rods 18 and 19, respectively.
The wheel is steered by the movement of 4 in the axial direction.

At a predetermined position in the axial direction of the rack shaft 14, a ball screw mechanism A for converting the rotational movement of the electric motor 16 into a linear movement of the rack shaft 14 and assisting the same is provided. The ball screw mechanism A includes a helical thread groove 30 engraved on the outer periphery of the rack shaft 14 with a predetermined axial width.
A substantially cylindrical screw nut 24 fitted so as to cover the screw groove 30 on the radially outer side; and a plurality of balls 31 fitted between the screw groove 30 and the screw nut 24.
It consists of The screw nut 24 is an outer rotor 22 having an enlarged diameter at one end.

A substantially cylindrical inner rotor 23 is arranged on the outer periphery of the rack shaft 14 inward in the radial direction, facing the flat inner peripheral surface of the outer rotor 22. Outer rotor 2
Between the inner rotor 2 and the inner rotor 23, three idle rollers 41, 42, 43 (see FIG. 2) are interposed in the circumferential direction. Outer rotor 22, idle rollers 41 and 42,
43 and the inner rotor 23 constitute a wedge roller type reduction mechanism B for reducing the rotation of the electric motor 16. The number of idle rollers is not limited to three, and it is needless to say that the number can be arbitrarily selected as long as necessary contact pressure and transmission efficiency can be obtained.

The electric motor 16 provided adjacent to the ball screw mechanism A has a stator 26 and a substantially cylindrical rotor 20 serving as an output shaft. The rotor 20 has a reduction mechanism B at one axial end. , And integrally rotates.

As is well known, the ball screw mechanism A transmits the rotation of the screw nut 24 integral with the outer rotor 22 to the ball 31, and the ball 31 rolls in the screw groove 30, so that the screw groove 30 is provided. Rack shaft 14
Is moved in the axial direction.

FIG. 2 is a radial sectional view taken along the line II of FIG. 1 and shows details of the speed reduction mechanism B. The outer rotor 22 surrounds three idle rollers 41, 42, and 43 that respectively engage with the inner rollers 23 to transmit power between the outer rotor 22 and the inner rotor 23. The inner roller 23 is connected to the end of the input shaft or is the end of the input shaft itself. The outer roller 21 is mounted on an output shaft, that is, on a rack shaft 14.

The axial center of the inner roller 23 and the outer roller 2
The two axes are parallel to each other but eccentric by a distance d. Accordingly, an annular space whose width changes between the outer roller 22 and the inner roller 23 is defined. The idle roller 42 is disposed in the widest space, and the idle roller 4
1, 43 are arranged in the narrowest space. The idle rollers 41 and 43 can freely enter a smaller space, but the movement out of the space is restricted by a mechanism (not shown). With such a configuration, each idle roller 4
1, 42 and 43 are the inner rotor 23 and the outer rotor 2
2 and the inner rotor 23 and the outer rotor 2
2 is transmitted at a predetermined reduction ratio.

As is apparent from FIG. 2, the idle rollers 41, 42, 43 of the speed reduction mechanism B are in contact with the inner peripheral surface of the outer rotor 22 and the outer peripheral surface of the inner rotor 23, respectively. Idle rollers 41, 42, 4
Reference numeral 3 denotes a housing 11 which is rotatable about its rotation axis, and which does not move.
It is fixed to.

Here, the electric power steering device 4
The operation of 0 will be briefly described. When the vehicle is running straight and no steering force is input to the input shaft 2 via a steering wheel and a steering shaft (not shown), the torque sensor (not shown) does not generate an output signal, and the electric motor 16 No auxiliary steering force is generated.

When the driver steers a steering wheel (not shown), for example, when the vehicle tries to turn a curve,
A torsion bar (not shown) in the housing 11 is twisted according to the steering force, and relative rotation occurs between the input shaft 2 and the output shaft. The torque sensor outputs a signal according to the direction and amount of the relative rotation. Based on this signal, the electric motor 16 rotates to generate an auxiliary steering force. The auxiliary steering force moves the rack shaft 14 to the left and right in the axial direction via the speed reduction mechanism B and the ball screw mechanism A, thereby turning the wheels.

Since the rotor 20 of the electric motor 16 rotates integrally with the inner rotor 23 of the speed reduction mechanism B, the output of the electric motor 16 is transmitted to the inner rotor 23 and further transmitted to the outer rotor 22 via idle rollers 41, 42 and 43. Is transmitted to At this time, since the diameters of the inner rotor 23 and the outer rotor 22 are different, the output of the electric motor 16 is reduced according to the ratio of the outer diameter of the inner rotor 23 to the inner diameter of the outer rotor 22. At the time of deceleration, there is no meshing between the gears as in the prior art, so that no hitting sound or the like is generated. Each inner rotor 23, idle rollers 41, 4
2, 43 and the outer rotor 22 need to contact with a predetermined contact pressure for torque transmission, but in the first embodiment,
By the following operation, the three idle rollers 41, 42, and 43 of the speed reduction mechanism B that obtains the contact pressure are configured such that the inner and outer edges at both ends in the axial direction have a predetermined curvature over the entire circumference. It is a wedge roller type formed. Also, as described above, the inner roller 23 and the outer roller 22
Are eccentric by the offset amount d, and the idle rollers 41, 42, and 43 can move their own positions slightly. In the configuration of the first embodiment, when the torque of the inner rotor 23 is transmitted to the outer rotor 22 by the idle roller 41, the idle roller 41 tends to move toward a narrow portion of the space between the inner rotor 23 and the outer rotor 22. As a result, the contact pressure between each rotor and the idle rollers 41, 42, 43 increases, and a necessary contact pressure is obtained. The contact pressure is proportional to the driving torque due to a mechanical relationship.

Conventionally, in a speed reducer using a planetary roller, the contact pressure between the rotor and the roller is obtained by dimensional interference (negative clearance), but in the case of a wedge roller type speed reducer, the contact pressure is transmitted in advance to a maximum. The contact pressure that can withstand the torque is set, and becomes constant after it is set at the time of assembly or the like. Therefore, in a situation where a low torque less than the maximum transmission torque is transmitted, the contact pressure becomes more than necessary, and there is a fear that the rolling resistance of the rolling element increases, that is, the transmission efficiency decreases. However, even when such a situation is unacceptable, since each idle roller is formed as a wedge roller as in the first embodiment and the second embodiment described below, the contact pressure between the rollers is transmitted. It is proportional to the torque. Therefore, the contact pressure of the roller at the time of low load becomes small, and the torque transmission efficiency can be maintained high.

FIG. 3 is an axial sectional view showing an electric power steering apparatus 50 according to a second embodiment of the present invention. The electric power steering device 50 of the third embodiment has almost the same configuration as that of the first embodiment except for the configuration of the speed reduction mechanism B.

In the second embodiment, the outer peripheral surface of the idle roller 51 of the speed reduction mechanism B is a curved surface having a predetermined curvature and expanding outward in the radial direction. The outer peripheral surface of the inner rotor 55 also has a predetermined curvature and has a curved surface 5 bulging radially outward.
It is 4. Therefore, the idle roller 51 has its curved surface inscribed in the flat inner peripheral surface of the outer rotor 22 and its curved surface of the inner rotor 53. Each idle roller 5
Reference numerals 1, 52 and 53 (not shown) are of a wedge roller type as in the first embodiment.

FIG. 4 is an axial sectional view showing details of the reduction mechanism of the electric power steering apparatus according to the second embodiment. As shown in FIG. 4, by forming the outer peripheral surface of each idle roller 51 as a curved surface as shown in FIG.
Contact the inner peripheral surface of the outer rotor 22 with the inner rotor 5
4, the output shaft of the electric motor 16, that is, the intersection angle deviation between the shaft of the rotor 20 and the shaft of the screw nut 24 can be tolerated.

When the curved surfaces (contact surfaces) 54 of the idle roller 51 and the inner rotor 55 are formed as curved surfaces as in this embodiment, the angle of the axis crossing the axis of the rotor 20 of the electric motor 16 and the axis of the screw nut 24 is shifted. Therefore, the dimensional tolerance of the part can be set to a certain large value, and the manufacturing cost can be reduced.

Also, in the second embodiment, similarly to the first embodiment, the shaft center of the inner roller 55 and the outer roller 22 are connected.
Are parallel to each other, but eccentric by a distance d. Therefore, an annular space whose width changes between the outer roller 22 and the inner roller 55 is defined. The idle roller 52 is disposed in the widest space, and the idle roller 5
Reference numerals 1 and 53 (not shown) are arranged in the narrowest space.

[0032]

According to the electric power steering apparatus of the present invention, the following effects can be obtained.

(1) Since a wedge roller type reduction mechanism having a wedge roller type idle roller is provided between the electric motor and the ball screw nut mechanism, there is no backlash, and the wedge roller type reduction mechanism is generated from the conventional gear reduction unit. The noise is gone. The commercial value can be made higher as compared with a conventional nut-rotating coaxial electric power steering device equipped with a speed reduction mechanism. Further, in the wedge roller type speed reduction mechanism, since the idle roller is a wedge roller type, the transmission loss of the motor output at low load can be further reduced, and the energy consumption of the system can be further reduced.

(2) Further, according to the embodiment of claim 2,
Since the contact surface between the idle roller and the inner rotor is formed as a curved surface, the manufacturing tolerance of the parts can be set to a certain large value, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an axial sectional view showing an electric power steering apparatus according to a first embodiment of the present invention.

FIG. 2 is a radial cross-sectional view taken along the line II of FIG. 1 and shows details of a speed reduction mechanism B;

FIG. 3 is an axial sectional view showing an electric power steering apparatus according to a second embodiment of the present invention.

FIG. 4 is an axial sectional view showing details of a speed reduction mechanism of the electric power steering apparatus according to the second embodiment.

[Explanation of symbols]

40, 50: electric power steering device 14: rack shaft 16: electric motor 20: rotor 41, 42, 43, 51, 52, 53 ... idle roller 22: outer rotor 23 , 55 ... Inner rotor A ... Ball screw mechanism B ... Wedge roller type reduction mechanism

Claims (2)

[Claims] 1. An electric power steering apparatus for converting the rotational motion of an electric motor into a linear motion of a rack shaft for steering wheels by using a ball screw mechanism, and assisting the operation thereof. Between a shaft and a ball screw mechanism, an inner rotor that rotates integrally with the output shaft of the electric motor, an outer rotor that faces the inner rotor and rotates integrally with a screw nut of the ball screw mechanism, and the inner rotor and the A wedge roller type speed reduction mechanism composed of a plurality of wedge roller type idle rollers interposed between the outer rotor and the outer rotor is arranged, and the center axis of the outer rotor and the center axis of the inner rotor are eccentric to each other. An electric power steering device characterized by the above-mentioned. 2. The electric power steering apparatus according to claim 1, wherein the outer peripheral surface of the idle roller is a curved surface bulging radially outward, and the outer peripheral surface of the inner rotor is a curved surface bulging radially outward. An electric power steering device characterized by the above-mentioned.