JPH11171027A - Electric power steering device - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To prevent occurrence of a tapping sound in a deceleration and power transmission unit while having a simple configuration. An electric power steering device includes a housing, a motor mounted on the housing and configured to generate an auxiliary steering force on a rotating shaft, bearings (50L, 50R) rotatably supporting a rotating shaft, and axial directions thereof. The motor has an output shaft 14 that transmits a steering force to wheels by the movement of the motor, a first gear 40 connected to the rotating shaft, and a second gear 24 connected to the output shaft and meshing with the first gear. And a gear mechanism for transmitting the auxiliary steering force to the output shaft. Further, an elastic body is interposed between the rotating shaft or the housing and the bearing, and a bush is fitted on a portion of the bearing that slides with the rotating shaft or the housing, and the tooth surfaces of the first gear and the second gear are connected to each other. When the contact is made, the elastic body is deformed and the rotating shaft is moved in the axial direction with respect to the housing via the bush.

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 apparatus, and more particularly to an electric power steering apparatus capable of reducing noise of gears constituting a reduction and power transmission mechanism.

[0002]

2. Description of the Related Art As an electric power steering device for a vehicle, the rotational output of an electric motor, which becomes an auxiliary steering torque, is reduced and transmitted to an output shaft of a steering mechanism, and a manual steering force applied to a steering wheel is assisted. In addition, a steering wheel is known. Various gear devices are suitably used as the reduction and power transmission mechanism.

[0003]

By the way, when a worm gear mechanism is used as a reduction and power transmission mechanism,
It is necessary to set an appropriate backlash between the worm and the tooth surface of the worm wheel. That is, if the backlash is too small, the meshing teeth compete with each other, the operating torque becomes heavy, and the steering wheel returns poorly.
Further, the machining accuracy of the worm and the worm wheel must be considerably improved, and the production cost increases.

[0004] On the other hand, if the backlash is increased to some extent, competition between the teeth does not occur, and if power is transmitted in one direction in the worm gear mechanism, no particular problem occurs. However, in the electric power steering device, the power transmission direction may be reversed depending on the steering condition of the steering wheel or based on vibration input from a road surface via wheels. When the transmission direction of the power is reversed in this way, the tooth surface on the back side of the tooth surface of the worm or worm wheel which has hitherto moved suddenly by the amount of backlash and abuts against the tooth surface of the other party. A loud bang is produced. The beating sound is caused by the material of the meshing gear,
The sound quality also changes depending on the rigidity, and tends to increase as the backlash increases. In particular, between iron-based gears, the beating sound becomes an unpleasant impact sound, and gives the driver discomfort.

[0005] Such a tapping noise can be reduced by reducing the backlash between the worm and the tooth surface of the worm wheel, but in that case, the above-described problem occurs. In addition, although one of the worm and the worm wheel can be reduced to some extent by using resin, it cannot be sufficiently eliminated, and in this case, a low-frequency muffled sound may be generated.

Accordingly, the present invention has been made in view of such a problem,
It is an object of the present invention to provide an electric power steering device that has a simple configuration and can reduce the generation of a tapping sound in a deceleration and power transmission unit.

[0007]

In order to achieve the above object,
An electric power steering apparatus according to the present invention includes a housing, a motor attached to the housing and generating an auxiliary steering force on a rotating shaft, a bearing rotatably supporting the rotating shaft, and a wheel driven by the axial movement. An output shaft for transmitting a steering force to the first shaft, a first gear connected to the rotation shaft, and a second gear connected to the output shaft and meshing with the first gear.
A gear mechanism that transmits auxiliary steering force of the motor to the output shaft, an elastic body is interposed between the rotating shaft or the housing and the bearing, and the bearing has A bush is fitted on the rotating shaft or a portion that slides with the housing, and when the tooth surfaces of the first gear and the second gear abut against each other, the elastic body is deformed to cause the elastic member to deform with respect to the housing. The rotary shaft is moved in the axial direction via a bush.

[0008]

According to the electric power steering apparatus of the present invention, when the tooth surfaces of the first gear and the second gear come into contact with each other, the elastic body is deformed and the housing is connected to the housing via the bush. Since the rotating shaft is moved in the axial direction, the collision between the tooth surfaces is reduced,
Thereby, the beating sound of the tooth surface can be reduced.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a partial cross-sectional view of an electric power steering apparatus 100 according to a first embodiment of the present invention, and FIG. 2 is an enlarged view of a main part thereof. In FIG. 1, an electric power steering device 100 includes a horizontally extending tube 90, a housing 10 disposed at the left end thereof, and an electric motor 30. The tube 90 is fixed to a vehicle body (not shown) by a bracket 92. In the housing 10, an input shaft 12 connected to a steering wheel (not shown) extends from right to left, and a left end is connected to a steering mechanism (not shown) via a torsion bar (not shown) in the tube 90. The output shaft 14 is connected to the right end (not shown). The center of the output shaft 14 is rotatably supported by two bearings 16. The outer ring of the bearing 16 is supported by a bearing holder 18, and the bearing holder 18 is fixed to the housing 10 by bolts 20. Note that a lock nut 22 is screwed to the output shaft 14 to hold down the inner ring of the bearing 16.

The electric motor 30 is arranged in a direction crossing the housing 10 (a direction perpendicular to the plane of FIG. 1).
The electric motor 30 is connected to a CPU (not shown), and receives an output of a torque sensor (not shown) and information such as a vehicle speed from the CPU to generate an appropriate auxiliary torque.
A worm wheel 24 made of resin is fixed near the right end (not shown) of the output shaft 14 so as not to rotate relatively. A worm 40 is fixed to the rotating shaft 32 of the electric motor 30 so as not to rotate relatively, and meshes with the worm wheel 24.

FIG. 2A is a view of the electric power steering apparatus 100 shown in FIG.
(B) is an enlarged view of a part A. In FIG. 2A, the electric motor 3 to which the driving power is supplied by the power supply line 41
The zero rotation shaft 32 has a serration 34 at the left end, supporting portions 36L and 36R and flanges 38L and 38R near the right and left ends, and a worm 40 between the flanges. The serration portion 34 is engaged with a serration hole of a rotor (output shaft) 42, and
And the rotating shaft 32 rotate integrally. Each bearing 50L, 5
0R is attached to the support section via bushes 60L, 60R having an L-shaped cross section interposed between the inner rings 52L, 52R and the support sections 36L, 36R.

The left bearing 50L is restricted from moving leftward by bringing the retaining ring 46 attached to the inner peripheral surface of the housing 10 into contact with the left end surface of the outer ring 54L. As shown in FIG. 2B, the flange 6 of the bush 60L
An O-ring 48L made of rubber or resin is interposed as an elastic member between the 4L and the flange portion 38L of the rotating shaft 32. That is, the circumferential groove 49L is formed at the root of the flange 38L.
Are formed, and an O-ring 48L is mounted therein. O-rings 48L, 48R and bush 60L,
The 60R may be interposed between the bearings 50L and 50R and the housing 10.

As shown in FIG. 2A, the left bush 60L comprises a cylindrical mounting portion 62L and a flange portion 64L extending radially outward from one end thereof, and has an L-shaped cross section (single flange). Type). The attachment portion 62L has substantially the same width as the width of the inner ring 52L, and the flange portion 64L
Is approximately the same as the height (thickness) of the inner ring 52L. As shown in FIG. 3, a slit 66L is formed in the bush 60L in the axial direction over a predetermined length of the cylindrical portion to increase the deformability. The bush 60L was formed by coating Teflon on one surface of a steel plate (surface in contact with the support portion 36L), and was mounted at the illustrated position by press fitting. Since the situation is almost the same for the right bearing 50R, the corresponding members and elements are replaced with R instead of L.
And a detailed description is omitted. The flange portion 64L of the bush 60L and the flange 38 of the rotary shaft 32
L is set to Δ1, and the gap between the flange portion 64R and the flange 38R is set to Δ2 (Δ1 ≒ Δ2).
It has been.

The O-rings 48L and 48R are slightly bent while the bearings 50L and 50R are
L, 38R, the bearing 50L,
A predetermined preload is applied to 50R in the axial direction, whereby the rotating shaft 32 is supported so that there is no backlash in the axial direction. Further, when a normal steering assist force is transmitted from the worm 40 to the worm wheel 24, even if one of the O-rings 48L bends and the rotating shaft moves to the maximum in one direction, the deflection of the other O-ring 48R is reduced. The amount of deflection is set so as to remain.

The outer ring 5 is provided on the right side of the right bearing 50R.
A holding plate 70 that is in contact with the right end face of the 2R is attached,
The support of the right end of the rotating shaft 32 by the bearing 50R is reinforced by screwing the nut 74 into the male screw portion 72.
The gaps Δ1 and Δ2 are adjusted by rotating the male screw portion 72 and pressing the bearing 50R via the holding plate 70.

Next, the operation of this embodiment will be described below. Assuming that the vehicle is in a straight running state and no steering force is input to the input shaft 12 via a steering wheel (not shown), a torque sensor (not shown) does not generate an output signal, and therefore, the electric motor 30 generates an auxiliary steering force. Does not occur. When the driver steers a steering wheel (not shown) when the vehicle is about to make a curve, the torsion bar (not shown) twists according to the steering force, and the relative rotation between the input shaft 12 and the output shaft 14 is made. Occur. The torque sensor is
A signal is output to a CPU (not shown) according to the direction and amount of the relative rotation, and the electric motor 30
Controlled by the PU, an auxiliary steering force is generated. The rotation of the electric motor 30 is reduced by the worm gear mechanism and transmitted to the output shaft 14.

In the case where the steering wheel is turned in one direction and then immediately turned in the opposite direction when the vehicle is moved to the width, for example, the power transmission direction is suddenly reversed.
The tooth surfaces of the worm 34 and the worm wheel 24 that are separated by the backlash abut against each other. Further, the tooth surfaces may come into contact with each other due to vibration transmitted from the wheels during traveling. However, according to the present embodiment, after the rotary shaft 32 is supported by the bearings 50L and 50R via the bushes 60L and 60R and moved in the axial direction, the impact force generated between the tooth surfaces of the worm gear is reduced by O. By bending the rings 48L and 48R and moving the rotary shaft 32 in the axial direction, the rotation can be relaxed, thereby reducing the tapping sound. On the other hand, when only the elastic bodies 48L and 48R are interposed between the bearings 50L and 50R and the bushes 60L and 60R are not arranged, it is difficult to say that the rotating shaft 32 is easily moved in the axial direction.

Hereinafter, another embodiment of the present invention will be sequentially described. The difference between the second embodiment shown in FIG. 4 and the first embodiment described above lies in the configuration of the elastic body. More specifically, the bearing 60L and the flange 38 of the rotating shaft 32
L, and between the bearing 50L and the flange 38R,
The elastic members 110L and 110R are interposed. In addition,
Since the two elastic members 110L and 110R are the same thing and are merely arranged symmetrically with respect to the worm 40, only the left elastic member 110L will be described in detail with reference to FIG. The elastic member 110L includes a cylindrical member 112L fitted on the rotating shaft 32, a flange portion 114L abutting on the flange portion 62L of the bush 60L, and the disk portion 11
6L, the flange 114L and the disc member 11
6L are connected to each other by an elastic portion 118L. Elastic part 1
A part of 18L extends thinly and axially along the inner surface of the cylindrical member 112L, and forms a thin portion 119L that is thin in the axial direction at the end of the cylindrical member.

In the assembled state, the elastic member 110L makes the disc portion 116L abut against the flange 38L of the rotating shaft 32, and makes the flange portion 114L abut the inner ring 52L of the bearing 50L via the flange portion 64L of the bush 60R. By pressing the bearing 50L and the flange 38L in the approaching direction, the elastic portion 118L, that is, the bearing 50L is pressed.
Is given a certain preload. In the assembled state, a distance L3 is provided between the flange 38L and the thin portion 119L.

FIG. 5 is a characteristic diagram showing the amount of displacement of the rotating shaft 32 when the elastic members 110L and 110R are incorporated into the rotating shaft 32 and a load is applied to the bearings 50L and 50R in the axial direction. When the displacement and the load are negative, it indicates that the rotating shaft 32 is displaced to the left by receiving the force toward the left. When the displacement and the load are positive, the force that the rotating shaft 32 is toward the right. This indicates that it has been displaced to the right in response to this. For convenience of explanation, it is assumed that the rotating shaft 32 is displaced to the left. As is apparent from FIG. 5, when the displacement exceeds L3, the load increases extremely. The reason for this is that the displacement of the elastic member 1
Only the elastic portion 118L such as 10L is elastically deformed, but when the displacement amount exceeds L3, the thin portion 119L etc.
This is because the contact with L or the like abruptly increases the load per unit displacement.

In the present embodiment, the load input to the rotating shaft 32 is relatively small based on vibrations and the like input from wheels (not shown).
Is only displaced in the axial direction within the range. Accordingly, since the thin portions 119L and the like of the elastic members 110L and 110R do not abut against the flange 38L and the like, the elastic members 110L and 110L
The rigidity of 0R is small, and the effect of reducing the rattle noise is large. On the other hand, the load input from the motor 30 side is large,
When the displacement of the rotating shaft 32 exceeds L3, the thin portion 119L
And the like come into contact with the flange 38L and the like to suppress further displacement of the rotary shaft 32. Thereby, the amount of friction between the rotating shaft 32 and the bearings 50L and 50R and the abrasion of the coupling spline portion 24 of the motor can be suppressed. Further, it is possible to prevent the worm 40 from escaping in the axial direction, and to improve control responsiveness.

FIG. 6 shows a third embodiment of the present invention. The third embodiment is different from the second embodiment in the configuration of the rotating shaft and the elastic body. As shown in FIG. 6A, the rotating shaft 32 includes flange portions 38L and 38R. The large diameter portions 39L and 39R are formed adjacent to each other. FIG.
As shown in (b), the left elastic member 120L interposed between the bearing 50L and the flange 38L of the rotating shaft 32 has:
Small-diameter hole disc portion 12 disposed on rotation shaft support portion 36L
2L and a large-diameter hole disc portion 124L arranged on the outer periphery of the large-diameter portion 39L, and both are connected by an elastic portion 126L. A part of the elastic portion 126L is a small-diameter hole disc portion 122.
A thin portion 1 having a small thickness extends between the small-diameter hole disk portion 122L and the large-diameter portion 124L, and extends thinly in the radial direction along the side surface of L.
28L are formed. The elastic member 120L makes the large-diameter hole disc portion 124L abut the flange 38L of the rotating shaft 32 in the assembled state, and the small-diameter hole disc portion 12 through the flange portion 64L of the bush 60L to the inner ring 52L of the bearing 50L.
2L are in contact with each other, and a constant preload is applied to the elastic portion 126L. The flange and the thin portion are separated by a distance L4.

As in the second embodiment, the rotating shaft 3
The elastic portion 12 of the elastic member 120L until the displacement amount of L2 reaches L4.
Although only 6L is elastically deformed, the displacement L
When it exceeds 4, the thin portion 128L comes into contact with the large diameter portion 39L,
As a result, the load for the unit displacement increases rapidly.
In the present embodiment, in addition to the effect of the second embodiment, as shown in FIG.
The hole of the small-diameter hole disc portion 122 </ b> L
The diameter is smaller than the outer diameter of L, and this cannot be incorporated into the outer periphery of the large diameter portion 39L. Therefore, it is possible to prevent erroneous assembling of the elastic member 120 </ b> L, which is erroneously installed in the outer periphery of the rotating shaft 32, in the installing direction.

Next, still another embodiment of the present invention will be described. These are modifications of the shape of the above-described L-shaped bush. That is, as described above (see FIG. 6), the bushes 60L and 60R having an L-shaped cross section are mounted on the bearings 50L and 50R by press-fitting the cylindrical portions 62L and 62R into the inner peripheral surfaces of the inner rings 52L and 52R. . However, in order to secure the press-fit load, the bush 60
When the thickness of L, 60R is increased, the bearing 50
The radial and axial dimensions of L and 50R increase. As a result, the manufacturing cost of the bearing increases, and an extra space is required for arranging the bearing. If the thickness of the bushes 60L and 60R having an L-shaped cross section is reduced, force is applied to the flange portions 64L and 64R of the bush when the rotary shaft 32 moves in the axial direction, and the bush may be deformed or damaged. Further, since the circumferential rigidity of the bushes 60L and 60R is different between the side having the flange portion and the side not having the flange portion, the inner diameter dimension is not stable only by mounting the bush on the bearings 50L and 50R. Had to be selected and assembled. Further, when the slit 66L (see FIG. 3) is formed in parallel with the axial direction, if the width of the slit 66L is large, even if the clearance between the bush 60L and the rotary shaft 32 is set to be small, the clearance is formed in the slit portion. As a result, a tapping sound may be generated between the worm 40 and the worm wheel 24.

In consideration of the above, in the following embodiment,
The bush was U-shaped in cross section (both brim type), and the slit was formed at a certain angle with respect to the axial direction of the bush. That is, as shown in FIGS. 7 and 8, the bushes 130L and 130R are made of a steel substrate 1.
The entire surface of the inner ring 52L, 52R on the 31L, 131R is coated with a Teflon layer 133L, 133R, and the support portions 36L, 36R of the rotating shaft 32 and the bearing 50L,
Cylindrical part 1 located between 50R inner rings 52L, 52R
32L, 132R and flange portions 134L, 134R extending radially outward from both ends thereof; 136L, 136
R. Both the outer flange portions 136L and 136R and the inner flange portions 134L and 134R have the inner ring 52.
L, 52R, and the inner flange portions 134L, 134R are elastic members 120L, 120R.
Small diameter hole disc portions 122L, 122R and inner rings 52L, 52
It is interposed between R.

The bushes 130L and 130R are shown in FIG.
As shown in the figure, a plate member 135 having an L-shaped cross section, comprising a first portion 131L having a flange shape and a second portion 133L having a cylindrical shape.
L is prepared, the inner ring 52L of the bearing 50L is set on the outer peripheral surface thereof, and then the second portion 13 as shown in FIG.
It is formed by bending a 3L distal end 137L in the same direction as the first portion 131L and in parallel with the first portion 131L. The slit 142L is formed so as to be inclined (form a certain angle) with respect to the axial direction of the bush 130L.

According to this embodiment, the following advantages can be obtained in addition to the embodiment shown in FIG. That is,
The bushes 130L and 130R have flange portions 13 at both ends.
4L, 134R; 136L, 134R are formed, and the rigidity of the left and right ends is balanced, so that the cylindrical portion 132 is formed.
The occurrence of taper (variation in thickness) in L and 134R is prevented. In addition, both flange portions 134L, 1
34R; 136L, 136R are in contact with the end faces of the inner races 52L, 52R, so that the bushing 130L, 130R may be displaced from the mounting position or the flange may be deformed even when the rotating shaft 32 moves in either direction. Damage is prevented. Further, since the slits 142L and 142R are formed obliquely, the bushes 130L and 130R are formed.
There is no backlash between the R and the rotating shaft 32, and proper clearance management becomes easy.

Instead of the bush of the fourth embodiment, a device for facilitating the movement of the rotating shaft 32 in the axial direction may be provided between the worm 40 and the worm wheel 24. For example, in FIG.
30R may be removed, and instead, the tooth surface of the worm 40 may be coated with metal or synthetic resin having a low friction coefficient. By doing so, the bush 130L, 1
In addition to eliminating the need for 30R, the coating makes it easy to control the thickness of the layer, so the outer diameter of the worm 40 is stable, and an appropriate axial clearance can be set between the worm 40 and the worm wheel 24.
The generation of rust due to the contact between the worm 40 and the worm wheel 24 is prevented. In addition to the above, the present invention can be appropriately changed and improved within a range that does not impair the gist. For example, the first and second gears may be other types of gears such as spur gears.

[0029]

As described above, according to the present invention, the first gear attached to the rotating shaft of the motor (supported by the bearing with respect to the housing) and the output shaft connected to the steering device. An elastic body is interposed between the bearing and the rotating shaft or the housing for transmitting the driving force while reducing the speed between the bearing and the second gear attached to the second gear, and the bush is interposed between the bearing and the rotating shaft or the housing. Was interposed. As a result, when the tooth surfaces of the first gear and the second gear abut against each other, the rotation shaft can be smoothly moved in the axial direction due to the elastic deformation of the elastic body and the sliding property of the bush. This has the effect of alleviating the collision between the tooth surfaces and preventing the generation of tapping noise on the tooth surfaces.

[Brief description of the drawings]

FIG. 1 is a schematic view (partially cut away) showing an entire electric power steering apparatus to which the present invention is applied.

FIG. 2 (a) shows a first embodiment of the present invention, and FIG.
2 is a sectional view taken along the line II-II in FIG.

FIG. 2 (b) is an enlarged view of a portion A in FIG. 2 (a).

FIG. 2 (c) is an enlarged view of a portion B in FIG. 2 (a).

FIG. 3 is an enlarged view of a main part of FIG. 2 (a).

FIG. 4 (a) is a front view (partially cut away) showing a second embodiment of the present invention.

FIG. 4 (b) is an enlarged view of a portion C in FIG. 4 (a).

FIG. 5 is a graph for explaining the operation and effect of the second embodiment.

FIG. 6A is a front view (partially cut away) showing a third embodiment of the present invention.

FIG. 6 (b) is an enlarged view of a portion D in FIG. 6 (a).

FIG. 7 is a front view (partially broken) showing a fourth embodiment of the present invention.

FIG. 8 is an enlarged view of a main part of FIG. 7;

FIG. 9 (a) is an explanatory diagram for explaining a manufacturing process of a bush used in the fourth embodiment of the present invention.

FIG. 9 (b) is an explanatory diagram for describing a manufacturing process of a bush used in the fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Housing part 12 Input shaft 14 Output shaft 24 Worm 30 Motor 32 Rotating shaft 40 Worm wheel 50L, 50R Bearing 48L, 48R; 110L, 110R; 120L, 12
0R elastic member 60L, 60R; 130L, 130R bush

Claims (1)

[Claims] 1. A housing, a motor mounted on the housing and generating an auxiliary steering force on a rotating shaft, a bearing rotatably supporting the rotating shaft, and a steering force transmitted to wheels by axial movement thereof. An output shaft, a first gear connected to the rotating shaft, and a second gear connected to the output shaft and meshing with the first gear, and the auxiliary steering force of the motor is applied to the output shaft. A gear mechanism for transmitting, and an elastic body is interposed between the rotary shaft or the housing and the bearing, and a bush is fitted to the bearing at a portion that slides with the rotary shaft or the housing, When the tooth surfaces of the first gear and the second gear contact each other,
An electric power steering apparatus, wherein the elastic body is deformed to move the rotating shaft in the axial direction with respect to the housing via the bush.