JP2016013821A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device in which a shaft-direction dimension of a steering assistance mechanism can be reduced and thereby a sufficient collapse stroke is secured.SOLUTION: The electric power steering device has an electric motor 20 and a speed reducer 30 that are controlled based on torque detection values obtained by detecting individually rotation angles of an input shaft 10a and an output shaft 10b connected by a torsion bar 10c and generate steering assistance force to the output shaft 10b. The speed reducer 30 has: an internal gear 31 that is fastened coaxially to the output shaft 10b; an external gear 32 that is meshed with the internal gear 31, eccentric to the output shaft 10b and rotatable accompanying a rotor 22 of the electric motor 20; and an output plate 33, to which rotation force from the external gear 32 is transmitted, which is fastened to the output shaft 10 so as to rotate together with the output shaft 10b.

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force by an electric motor to a steering system of a vehicle, and in particular, detects a torque by detecting a rotation angle difference between an input shaft and an output shaft connected by a torsion bar. The present invention relates to an electric power steering apparatus provided with torque detecting means.

2. Description of the Related Art Conventionally, there has been proposed an electric power steering device in which an electric motor for assisting steering is arranged coaxially with a steering shaft for the purpose of improving the mountability of an electric power steering (EPS), particularly a column type EPS, on a vehicle.
Among such electric power steering devices, there has been proposed one that transmits the output of the rotor of the electric motor to the steering shaft as it is without using a reduction gear.

  Here, if the steering assist force is to be realized only by the output of the electric motor without using the reduction gear, the structure of the electric motor becomes complicated (larger) in order to obtain the assist force necessary for EPS. Therefore, for example, a technique disclosed in Patent Document 1 has been proposed. In Patent Document 1, in order to enable high output, a bottomed cylindrical rotor fixed coaxially to a rotating shaft, an inner peripheral surface and an outer peripheral surface of the rotor are provided to face each other, and the housing is provided. A motor with two fixed stators is disclosed. However, in such a technique, the motor structure is complicated in order to obtain the motor output, so that there is a problem that the assembly of the EPS becomes complicated and the cost becomes high.

Therefore, an electric power steering apparatus has been proposed in which a reduction gear is provided between a steering shaft and an electric motor coaxial with the steering shaft to obtain a steering assist force (see Patent Document 2).
The technique described in Patent Document 2 is an electric power steering apparatus in which a print motor as an electric motor and a harmonic drive (registered trademark) reducer are arranged coaxially with respect to a steering shaft.

JP 2003-309957 A JP-A-10-129510

However, the electric power steering apparatus using the electric motor coaxially arranged on the steering shaft including the technique described in Patent Document 2 is a relatively large-diameter part such as an electric motor or a speed reducer constituting a steering assist mechanism. Are arranged in the axial direction. Therefore, the dimension of the steering assist mechanism in the axial direction is increased, and there is a problem of increasing the size of the entire column.
For the same reason, many of the electric power steering devices using the electric motor arranged coaxially with the steering shaft have a problem that the energy collision performance at the time of the vehicle collision and the collapse adjustment amount may be inferior.
Therefore, the present invention has been made paying attention to the above-mentioned problem, and an object thereof is to provide an electric power steering device that can reduce the axial dimension of the steering assist mechanism and secure a sufficient collapse stroke. Yes.

In order to achieve the above object, an aspect of an electric power steering apparatus is controlled based on a detected torque value obtained by individually detecting the rotation angles of an input shaft and an output shaft connected by a torsion bar provided in a vehicle steering system. An electric motor that generates a steering assist force with respect to the output shaft and a speed reducer,
The electric motor includes a stator and a hollow rotor that is rotatably installed with respect to the stator and the output shaft via a first bearing that is coaxially installed with the output shaft.
The reducer is
An annular internal gear fixed to the housing and provided with a plurality of teeth on the inner peripheral surface;
One end of the rotor in the axial direction is rotatably provided via a second bearing that is provided so as to overlap the first bearing in a direction orthogonal to the output shaft and that is eccentric with respect to the output shaft. An annular external gear provided on the outer peripheral surface with a plurality of teeth meshing with a plurality of teeth provided on the internal gear,
A rotating force is transmitted from the external gear, and an output plate is fixed to the output shaft so as to rotate integrally with the output shaft.

In the electric power steering apparatus, it is preferable that the output plate includes holes that respectively engage with a plurality of protrusions provided in the circumferential direction on one end face of the external gear.
In the electric power steering apparatus, it is preferable that the output plate includes protrusions that respectively engage with a plurality of holes provided in the circumferential direction on one end face of the external gear.
In the electric power steering apparatus, it is preferable that the plurality of protrusions or the plurality of holes are provided at equal intervals in the circumferential direction on one end face of the external gear.

In the electric power steering apparatus, it is preferable that the number of teeth of the internal gear is equal to or greater than the number of ends of the external gear.
In the electric power steering apparatus, it is preferable that the stator is fixed to the casing.
In the electric power steering apparatus, it is preferable that an outer diameter dimension of the internal gear is smaller than an inner diameter dimension of the stator.

In the electric power steering apparatus, it is preferable that the speed reducer and the electric motor are arranged so as to overlap in the output shaft direction.
Further, in the electric power steering apparatus, an annular shape that is installed through the output shaft at the other end in the axial direction of the rotor and that individually detects the rotation angles of the input shaft and the output shaft. The outer diameter dimension of the torque sensor is preferably smaller than the inner diameter dimension of the stator.
In the electric power steering apparatus, it is preferable that the torque sensor and the electric motor are arranged so as to overlap in the output shaft direction.

  ADVANTAGE OF THE INVENTION According to this invention, the dimension of the axial direction of a steering assistance mechanism can be made small, and the electric power steering apparatus which ensured sufficient collapse stroke can be provided.

It is a disassembled perspective view which shows the structure in a certain aspect of an electric power steering apparatus. It is sectional drawing which follows the steering-axis direction which shows the structure of an electric power steering apparatus. It is a disassembled perspective view which shows the structure of the modification in a certain aspect of an electric power steering apparatus. It is sectional drawing which follows the steering-axis direction which shows the structure in the other aspect of an electric power steering apparatus.

FIG. 1 is an exploded perspective view showing a configuration in an aspect of an electric power steering apparatus. FIG. 2 is a cross-sectional view along the steering shaft direction showing the configuration of an aspect of the electric power steering apparatus.
The electric power steering apparatus 1 according to the present embodiment includes a steering shaft 10, an electric motor 20, and a speed reducer 30. A combination of the electric motor 20 and the speed reducer 30 may be referred to as a steering assist mechanism. In addition, the electric power steering apparatus 1 of this embodiment is provided with the body (not shown) which hold | maintains each component. This housing is preferably composed of a housing formed mainly of aluminum die casting. In FIG. 1, the steering shaft 10 between the electric motor 20 and the speed reducer 30 is not shown.

<Steering shaft>
The steering shaft 10 includes an input shaft 10a and an output shaft 10b connected to the input shaft 10a via a torsion bar 10c. A steering force applied from the driver is transmitted to the input shaft 10a via a steering wheel (not shown).
The steering force transmitted to the output shaft 10b is transmitted to the lower shaft and the pinion shaft via a plurality of universal joints, and turns the steered wheels via a steering gear mechanism and a tie rod.

A steering assist mechanism for transmitting a steering assist force to the output shaft 10b is connected to the output shaft 10b of the steering shaft 10. This steering assist mechanism includes an electric motor 20 and a speed reducer 30. The output shaft 10b passes through the inner diameter of the rotor 22 of the electric motor 20 and the inner diameter of the speed reducer 30, which will be described later.
The speed reducer 30 is connected to an output shaft 10b that penetrates the inner diameter thereof. On the other hand, the electric motor 20 is connected to the speed reducer 30 to generate a steering assist force.

Further, the electric power steering apparatus 1 includes a torque sensor unit 40 as a torque detection unit that detects a torsional angular displacement of a torsion bar 10c disposed between the input shaft 10a and the output shaft 10b to detect a steering torque. Is provided.
The outer diameter dimension of the torque sensor unit 40 is set smaller than the inner diameter dimension of the stator 21 of the electric motor 20, and the torque sensor unit 40 and the stator 21 are arranged so as to overlap in the axial direction. By adopting such a layout, it is possible to suppress the axial dimension of the steering assist mechanism, and it is possible to ensure a collapse stroke almost equivalent to that of a power steering device using a conventional worm wheel reducer. .

  Further, the torque sensor unit 40 may integrally accommodate a rotation angle detection unit of the rotor 22 of the electric motor 20. For example, a multipolar magnet is fixed to the end face of the rotor 22, the rotation angle of the rotor 22 is detected by a Hall IC provided in the torque sensor unit 40, and the electric motor 20 is controlled. With such a configuration, it is not necessary to separately provide a rotation angle detector of the electric motor 20, and the power steering device can be reduced in size.

<Electric motor>
The electric motor 20 is an inner rotor type brushless motor, and includes a stator 21 and a rotor 22. In addition to these, the electric motor 20 provided in the electric power steering apparatus 1 of this embodiment is provided with the eccentric part 22a.
[Stator]
The stator 21 has an annular shape, is fixed to a housing (not shown) so that the output shaft 10b passes through coaxially, and is disposed so as not to rotate. The stator 21 is provided with a coil so as to surround a permanent magnet provided on the rotor 22 in the circumferential direction of the output shaft 10b.

[Rotor]
The rotor 22 has an annular shape and is provided so that the output shaft 10b passes through coaxially. A cylindrical eccentric part 22a is provided at one end of the rotor 22 (the end opposite to the steering wheel). Here, the thickness of the eccentric portion 22a (the dimension in the direction orthogonal to the axial direction of the rotor 22) is not substantially uniform in the circumferential direction, and is set so that the axis of the outer peripheral surface is eccentric with respect to the axis of the inner peripheral surface. Has been. That is, since the inner peripheral surface of the eccentric portion 22a is formed coaxially with the output shaft 10b, and the outer peripheral surface of the eccentric portion 22a is formed eccentric from the output shaft 10b, the thickness of the eccentric portion 22a is as shown in FIG. A thin range and a thick range are provided in the circumferential direction.

  The rotor 22 is provided via a first bearing 24 installed coaxially with the output shaft 10a, and a third bearing 26 provided axially spaced from the first bearing 24 and installed coaxially with the output shaft 10a. The stator 21 and the output shaft 10b are rotatably installed. Specifically, the first bearing 24 is provided so as to be sandwiched between the inner peripheral surface of the eccentric portion 22a of the rotor 22 and the output shaft 10a. At this time, the outer ring of the first bearing 24 is in contact with the inner peripheral surface of the eccentric portion 22a, and the inner ring of the first bearing 24 is in contact with the outer peripheral surface of the output shaft 10b.

Further, the inner peripheral surface 22b of the rotor 22 is fitted to the outer peripheral surface of the output shaft 10a, and the inner edge 22c of the rotor 22 abuts on the inner ring of the third bearing 26 whose outer ring is fixed to the casing (not shown). Installed.
In this manner, the output shaft 10 b is rotatably supported by the third bearing 26 whose outer peripheral surface is positioned via the rotor 22 and the fourth bearing 50.
The rotor 22 is rotatably supported by the first bearing 24 and the third bearing 26.

Furthermore, the 2nd bearing 25 which fitted the inner peripheral surface of the inner ring | wheel is provided in the outer peripheral surface of the eccentric part 22a. An external gear 32 having an inner peripheral surface fitted therein is provided on the outer peripheral surface of the outer ring of the second bearing 25.
Here, as described above, the thickness of the eccentric portion 22a installed between the outer ring of the first bearing 24 and the inner ring of the second bearing 25 includes a thin range and a thick range in the circumferential direction. The external gear 32 supported by the second bearing 25 is installed eccentrically with respect to the output shaft 10b (steering shaft 10) so as to be rotatable.

<Reduction gear>
The speed reducer 30 used in the electric power steering apparatus 1 of the present embodiment is an eccentric differential speed reducer. The reduction gear 30 is installed on the output shaft 10 b side of the electric motor 20, and includes an internal gear 31, an external gear 32, and an output plate 33.
Here, the connection unit 60 for connecting the coil ends of the stator 21 is preferably provided on the outer peripheral side of the speed reducer 30. Thereby, it becomes possible to secure a collapse stroke more.

[Internal gear]
The internal gear 31 has an annular shape in which a plurality of teeth are provided on the inner peripheral surface. The internal gear 31 is fixed to the housing so as not to rotate. Here, the internal gear 31 is preferably fixed (supported) to a casing to which the stator 21 of the electric motor 20 is fixed. By fixing (supporting) the internal gear 31 in the same housing as the stator 21, it is possible to appropriately manage the eccentric amount of the differential gear composed of the internal gear 31 and the external gear 32. Become.
Here, the outer diameter of the internal gear 31 is preferably set smaller than the inner diameter of the stator 21 of the electric motor 20. Thereby, the reduction gear 30 and the stator 21 can be arrange | positioned so that it may overlap with an axial direction. By adopting such a layout, it is possible to suppress the dimension along the axial direction of the steering assist mechanism, and it is possible to ensure a collapse stroke almost equivalent to that of an electric power steering device using a conventional worm wheel reducer. It becomes.

[External gear]
The external gear 32 has an annular shape with a plurality of teeth provided on the outer peripheral surface. As described above, since the external gear 32 is eccentrically rotated with respect to the output shaft 10b (steering shaft 10) by the eccentric portion 22a, the external gear 31 is installed coaxially with the output shaft 10b. Rotate eccentrically. That is, the external gear 32 is rotatably installed on the rotor 22 via the second bearing 25 having an eccentric shaft that is eccentric with respect to the output shaft 10b.

  Here, it is preferable that the second bearing 25 for causing the external gear 32 to perform an eccentric oscillating motion and the first bearing 24 for supporting the rotor 22 are disposed at positions that substantially coincide with the axial direction of the steering shaft 10. This is to prevent the rotor 22 from being tilted by receiving the meshing reaction force input from the second bearing 25 to the rotor 22 by the first bearing 24. Moreover, the dimension of the axial direction of a steering assist mechanism can be made small by arrange | positioning the 2nd bearing 25 and a 1st bearing in the position substantially corresponded to the axial direction.

  In the external gear 32, a plurality of teeth provided on the outer peripheral surface sequentially mesh with a plurality of teeth provided on the inner peripheral surface of the internal gear 31, and the external gear 32 is provided inside the internal gear 31. It is provided so as to be accommodated in the thickness direction (axial direction). That is, the external gear 32 supported by the second bearing 25 revolves (eccentrically swings) while meshing with the internal gear 31 in the rotation period of the rotor 22, and the number of teeth with the internal gear 31. It is set up so as to rotate by differential rotation.

[Gear type]
Examples of the types of gears of the external gear 32 and the internal gear 31 include an involute gear, a trochoid gear, and an arc gear, and are appropriately selected according to the number of teeth and the purpose. Among these types of gears, involute gears are preferable in terms of ensuring the meshing accuracy between the external gear 32 and the internal gear 31, achieving smooth relative rotation, and generating high torque. The number of teeth of the internal gear 31 is preferably equal to or greater than the number of teeth of the external gear 32.

[Gear material]
Moreover, the material of each gear of the external gear 32 and the internal gear 31 is not limited to steel, and may be resin. By using at least one of the external gear 32 and the internal gear 31 as a resin gear, the effect of reducing the rattling noise of each gear can be obtained.
The external gear 32 is provided with a plurality of protrusions 32b projecting in one direction on one end face 32a facing the output shaft 10b with respect to the input shaft 10a. These protrusions 32b are preferably provided on the one end surface 32a of the external gear 32 at equal intervals in the circumferential direction.

[Output board]
The output plate 33 receives the rotational force from the external gear 32 and is fixed to the output shaft 10b so as to rotate integrally with the output shaft 10b. Specifically, the output plate 33 has a plurality of protruding pieces 33a that protrude radially at equal intervals in a direction orthogonal to the output shaft 10b according to the number of protrusions 32b provided on the external gear 32. Each of the plurality of projecting pieces 33a is provided with a hole 33b in which a protrusion 32b provided on the external gear 32 is engaged with a predetermined gap in a direction perpendicular to the output shaft 10b. . That is, each protrusion 32b provided on the external gear 32 is loosely fitted in the hole 33b.

Here, the number of the protrusions 32b and the hole portions 33b is not particularly limited as long as the protrusions 32b can be maintained loosely in a state where all of the protrusions 32b are in contact with (sliding) each of the hole portions 33b. It is appropriately selected according to conditions such as backlash and the purpose. As the number of the protrusions 32b and the holes 33b, for example, there are three as shown in FIG.
The output plate 33 is fixed to the output shaft 10b so as to rotate integrally with the output shaft 10b. The output plate 33 may be installed so as to be rotatable integrally with the output shaft 10b, and a separate output plate may be fixed to the output shaft 10b by a method such as press fitting.

Thus, a large torque can be transmitted to the output shaft 10b through the output plate 33 by always engaging the projection 32b provided on the external gear 32 that performs the eccentric oscillating motion with the hole 33b.
Further, the hole 33b provided in the output plate 33 may be provided so as to always slide with respect to the protrusion 32b. However, as shown in FIG. 3, a rolling bearing may be interposed in the hole 33b. Good. A needle bearing is preferable as an aspect of the rolling bearing interposed in the hole 33b. By interposing the needle bearing in the hole 33b, it is possible to minimize the increase in the size of the hole 33b.

The movement of the protrusion 32b is a revolving motion with reference to the hole 33b of the output plate. Therefore, when a bearing is interposed in the hole 33b, the outer ring is fitted to the protrusion 32b, the inner ring is fitted to the hole 33b, or the rolling bearing with the inner ring and the outer ring is fitted to any one. Is preferred.
Moreover, it is preferable that the inner peripheral surface of the hole 33b or the outer peripheral surface of the protrusion 32b is heat-treated as necessary. Thereby, even if the hole 33b and the protrusion 32b roll or slide, the durability performance can be satisfied.

As described above, by using an eccentric differential reduction gear as the reduction gear, it is possible to obtain an electric power steering device that obtains a reduction ratio comparable to that of a conventional worm reduction gear. For example, when the number of teeth of the internal gear 31 is 35 and the number of teeth of the external gear 32 is 33, the rotation number of the external gear 31 per revolution of the external gear 32 is 1 / 16.5. be able to.
Further, since the reduction ratio can be set to be equivalent to that of the conventional EPS, the reverse operability of the electric power steering apparatus can be obtained with characteristics that are not significantly different from those of the conventional system.

(Other embodiments)
Next, another embodiment of the electric power steering apparatus will be described with reference to the drawings. FIG. 04 is a cross-sectional view along the steering axis direction showing the configuration of another aspect of the electric power steering apparatus. The electric power steering apparatus 1 of the present embodiment has the same configuration as that of the above-described embodiment except for the installation mode of the torque sensor unit and the motor rotation angle detection unit. Hereinafter, the same components as those in the above-described embodiment will be denoted by the same reference numerals, description thereof will be omitted or simplified, and different configurations will be mainly described. In the present embodiment as well, a housing for holding each component (steering shaft, electric motor, reduction gear) is not shown.

The electric power steering apparatus 1 according to the present embodiment is configured such that an engine control unit (ECU) 80 is integrally accommodated on the steering wheel side of the electric motor 20 with respect to the configuration of the above-described embodiment.
With such a configuration, it is possible to incorporate a torque sensor unit and a motor rotation angle detection unit into the ECU 80, and the harness connection between each sensor and the ECU 80 becomes unnecessary.

Further, the ECU 80 has an annular shape and is installed so that the steering shaft 10 penetrates coaxially.
The ECU 80 is preferably formed integrally with the housing of the electric motor 20 in order to ensure the positional accuracy of each sensor.
Furthermore, as shown in FIG. 04, it is preferable to provide a connection unit 60 for connecting the coil ends of the stator 21 on the steering wheel side of the electric motor 20. With such an arrangement, terminals can be directly connected from the connection unit 60 to the board of the ECU 80, so that it is possible to minimize wiring loss inside the EPS.

  As described above, according to the above embodiment, the first bearing (rotor support bearing) coaxial with the steering shaft and the second bearing (eccentric bearing) eccentric from the steering shaft substantially coincide with each other in the axial direction. Therefore, it is possible to provide an electric power steering device in which the axial dimension of the steering assist mechanism is reduced. In addition, since the axial dimension of the steering assist mechanism is reduced as described above and an eccentric differential reducer is adopted as a reducer, the same collapsing stroke as that of an electric power steering device using a conventional worm reducer is adopted. It is possible to provide an electric power steering apparatus that ensures the above.

  As mentioned above, although each embodiment of the electric power steering apparatus has been described, the present invention is not limited to this, and various changes and improvements can be made. For example, the output plate may be fixed to the output shaft so that the rotational force from the external gear is transmitted and rotates integrally with the output shaft, and is circumferentially connected to one end surface of the external gear. A plurality of holes may be provided, and protrusions that engage with the plurality of holes may be provided on the output plate. The number and arrangement of the plurality of protrusions or the plurality of holes provided on one end surface of the external gear and the plurality of holes or the plurality of protrusions provided on the output plate are the same as those of the external gear. If the rotational force with the said output board is transmitted appropriately, there will be no restriction | limiting in particular, According to the objective, it selects suitably. Moreover, in order to absorb the shift | offset | difference of the gravity center at the time of rotation of the rotor by an eccentric part, you may provide shapes, such as a hole, a notch, and a protrusion part, in a part of rotor.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 10 Steering shaft 10a Input shaft 10b Output shaft 10c Torsion bar 20 Electric motor 21 Stator 22 Rotor 22a Eccentric part 24 1st bearing (support bearing for rotors)
25 Second bearing (eccentric bearing)
26 Third bearing (support bearing for rotor)
DESCRIPTION OF SYMBOLS 30 Reduction gear 31 Internal gear 32 External gear 32b Protrusion 33 Output plate 33b Hole 40 Torque sensor unit 50 4th bearing 60 Connection unit 70 Rotor rotation angle detection unit 80 ECU

Claims (10)

An electric motor that is controlled based on a torque detection value that individually detects rotation angles of an input shaft and an output shaft that are connected by a torsion bar provided in a steering system of the vehicle, and that generates a steering assist force for the output shaft; A reduction gear,
The electric motor includes a stator and a hollow rotor that is rotatably installed with respect to the stator and the output shaft via a first bearing that is coaxially installed with the output shaft.
The speed reducer is
An annular internal gear fixed to the housing and provided with a plurality of teeth on the inner peripheral surface;
One end of the rotor in the axial direction is rotatably provided via a second bearing that is provided so as to overlap the first bearing in a direction orthogonal to the output shaft and that is eccentric with respect to the output shaft. A ring-shaped external gear provided on the outer peripheral surface with a plurality of teeth that are installed in the portion and meshed with a plurality of teeth provided on the internal gear;
An electric power steering apparatus comprising: an output plate fixed to the output shaft so as to transmit a rotational force from the external gear and rotate integrally with the output shaft.   The electric power steering apparatus according to claim 1, wherein the output plate includes holes that respectively engage with a plurality of protrusions provided in a circumferential direction on one end face of the external gear.   2. The electric power steering apparatus according to claim 1, wherein the output plate includes protrusions that respectively engage with a plurality of holes provided in a circumferential direction on one end face of the external gear.   4. The electric power steering apparatus according to claim 2, wherein the plurality of protrusions or the plurality of hole portions are provided at equal intervals in the circumferential direction on one end face of the external gear.   The electric power steering device according to claim 1, wherein the number of teeth of the internal gear is equal to or greater than the number of ends of the external gear.   The electric power steering apparatus according to claim 1, wherein the stator is fixed to the housing.   The electric power steering apparatus according to claim 1, wherein an outer diameter of the internal gear is smaller than an inner diameter of the stator.   The electric power steering apparatus according to claim 1, wherein the speed reducer and the electric motor are arranged so as to overlap in the output shaft direction.   The outer diameter of an annular torque sensor that is installed through the output shaft at the other end in the axial direction of the rotor and individually detects the rotation angles of the input shaft and the output shaft is the stator. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is smaller than an inner diameter dimension of the electric power steering apparatus.   The electric power steering apparatus according to claim 8, wherein the torque sensor and the electric motor are arranged so as to overlap in the output shaft direction.

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