JP3951110B2 - Anti-vibration structure of electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an anti-vibration structure for reducing rattling noise at a coupling portion between an electric assist motor and a worm shaft in an electric power steering apparatus for an automobile.
[0002]
[Prior art]
FIG. 3 is an explanatory diagram showing a schematic structure of the well-known electric power steering apparatus 100. That is, the electric power steering apparatus for an automobile basically has a torsion bar 103 for detecting a steering torque by a torque sensor 105 at the tip of a steering input shaft 102 extending from a steering wheel 101 as shown in FIG. A steering rack 104 (not shown) that changes the direction of the axle by moving to the left and right is engaged with a pinion formed on the steering output shaft 104. A worm wheel 108 is attached to the steering output shaft 104, and a worm gear 107 connected to the output shaft of the electric assist motor 106 is engaged with the worm wheel 108.
[0003]
That is, the electric power steering apparatus 100 of this type has a torsion bar 103 interposed between the steering input shaft 102 and the steering output shaft 104 by a steering torque when the driver tries to rotate the steering wheel (handle) 101. When the torsional deformation is applied, the direction and magnitude of the torsional torque is detected by the torque sensor 105, and applied to the electric assist motor 106 by a control device (not shown) based on the detection signal and vehicle speed data. Power is controlled. The driving torque of the electric assist motor 106 is applied to the steering output shaft 104 by a speed reduction mechanism comprising a worm gear 107 formed on a worm shaft 109 connected to the output shaft and a worm wheel 108 meshing with the worm gear 109. An auxiliary steering torque is applied in the direction of the steering torque by the steering wheel 101.
[0004]
FIG. 4 shows a conventional coupling structure between the worm shaft 109 and the output shaft of the electric assist motor 106 in the electric power steering apparatus 100. That is, in the prior art, the spline shaft portion 110 is formed at the shaft end of the output shaft of the electric assist motor 106. On the other hand, the worm shaft 109 is disposed coaxially with the output shaft of the electric assist motor 106, and the vicinity of both ends is supported via bearings 111. A spline shaft 112 is formed at the end of the worm shaft 109 on the electric assist motor 106 side. The spline shaft portion 110 of the worm shaft 109 and the spline shaft portion 112 of the output shaft of the electric assist motor 106 that are opposed to each other are inserted and engaged with a common cylindrical joint 113 having a spline hole formed on the inner periphery. Thus, the driving torque of the rotor 110 of the electric assist motor 106 is transmitted to the worm shaft 109 via the cylindrical joint 113.
[0005]
[Problems to be solved by the invention]
However, according to the above conventional structure, the spline shaft portion 110 of the worm shaft 109 and the spline shaft portion 112 of the output shaft of the electric assist motor 106 and the cylindrical joint 113 are engaged with each other by the spline tooth surfaces extending in the axial direction. Therefore, rattling in the axial direction occurs at the meshing portion.
[0006]
In particular, since the required backlash is set between the spline shaft portions 110 and 112 and the spline tooth surfaces of the cylindrical joint 113, for example, the driver cuts the steering wheel in one direction (the steering wheel 101 is changed). In the case where the steering wheel is immediately turned in the opposite direction after the rotation, the direction of the auxiliary steering torque by the electric assist motor 106 is reversed according to the steering direction by the steering wheel 101. The cylindrical joint 113 has a problem that the tooth surfaces opposite to the tooth surfaces that have been in contact with each other collide with each other due to the presence of backlash, and a relatively loud sound is generated. Such a hitting sound is an annoying metal sound, which makes the driver uncomfortable.
[0007]
The present invention has been made in view of the above-described problems, and a technical problem thereof is an electric power steering apparatus that can effectively reduce noise caused by rattling noise at a coupling portion between an electric assist motor and a worm shaft. It is to provide an anti-vibration structure.
[0008]
[Means for Solving the Problems]
As a means for effectively solving the above technical problem, the vibration isolating structure of the electric power steering apparatus according to the first aspect of the present invention is such that the worm gear provided on the worm shaft rotated by the electric assist motor has a steering output. In an electric power steering device having a structure meshed with a worm wheel mounted on a shaft, one of the output shafts of the worm shaft and the electric assist motor is provided on the outer periphery of one shaft end via a damper made of a rubber-like elastic material. And a mating member having a toothed surface corresponding to the tapered toothed surface provided at the other shaft end of the worm shaft and the output shaft meshes in a state without backlash. It has been done.
[0009]
According to a second aspect of the invention, the damper according to the first aspect has a radial portion, and the radial portion is formed on the worm shaft or the output shaft. It is interposed between the radial step surface and the back surface opposite to the tapered tooth surface of the meshing member in a state compressed in the axial direction.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view schematically showing a part of an electric power steering apparatus provided with a vibration isolating structure according to the present invention, and FIG. In FIG. 1, reference numeral 1 is a steering output shaft of a steering column, 2 is a torsion bar, 3 is a worm wheel attached to the steering output shaft 1, 4 is an electric assist motor, and 5 is an output shaft of the electric assist motor 4. (Hereinafter referred to as the motor output shaft) 6 is connected to the motor output shaft 5, and the worm shaft is arranged so that the shaft center is coaxial with the motor output shaft 5 and intersects the steering output shaft 1 at a right angle; Reference numeral 10 denotes a housing of the apparatus.
[0011]
A worm gear 7 having a tooth surface extending in a spiral shape is formed at an axially intermediate portion of the worm shaft 6, and both axial portions of the worm shaft 6 are rotatably supported on the housing 10 via bearings 8 and 9, respectively. Has been. The tooth surfaces formed on the outer periphery of the worm wheel 3 are inclined at an angle corresponding to the tooth surfaces of the worm gear 7 with respect to the circumferential direction, and both mesh with each other.
[0012]
At the shaft end of the worm shaft 6 that protrudes from the worm gear 7 through the bearing 9 on the electric assist motor 4 side and protrudes toward the electric assist motor 4 side, a meshing element 11 is extrapolated, while the output of the electric assist motor 4 is output. A concave meshing portion 12 is formed at the shaft end of the shaft 5 as a mating meshing portion, and both mesh with each other.
[0013]
Specifically, as shown in FIG. 2, the shaft end 6a of the worm shaft 6 has a smaller diameter than the fitting portion 6c with the bearing 9 via a radial step surface 6b formed continuously in the circumferential direction. The meshing piece 11 is coupled to the outer periphery of the shaft end 6 a via a damper 13. The meshing piece 11 has a bevel gear shape. That is, the surface on the electric assist motor 4 side has a tooth surface (hereinafter referred to as a tapered tooth surface) 11a arranged in a tapered shape (bevel tooth shape). The concave meshing portion 12 has a tooth surface 12a arranged in a tapered shape corresponding to the tapered tooth surface 11a of the meshing piece 11, and both the tooth surfaces 11a and 12a mesh with each other.
[0014]
The damper 13 is formed of a rubber-like elastic material, and can be integrally vulcanized and bonded between the worm shaft 6 and the engagement piece 11. The damper 13 includes a cylindrical portion 13 a and a radial portion 13 b extending from one end thereof. The cylindrical portion 13 a is interposed between the outer peripheral surface of the shaft end 6 a of the worm shaft 6 and the inner peripheral surface of the meshing piece 11. The radial portion 13b is interposed between the radial step surface 6b of the worm shaft 6 and the boss portion back surface 11b facing the tooth surface 11a of the meshing piece 11.
[0015]
An appropriate gap G is provided between the shaft end 6 a of the worm shaft 6 and the central portion of the concave engagement portion 12 that are opposed to each other in the axial direction, and the radial portion 13 b of the damper 13 is Appropriate axial pre-compression is applied between the radial step surface 6 b and the boss back surface 11 b of the meshing piece 11. In other words, the dimensions of each component are set so that appropriate axial pre-compression is applied to the radial portion 13b of the damper 13 in the assembled state. For this reason, the taper-shaped tooth surface 11a of the meshing piece 11 is pressed against the tooth surface 12a of the concave meshing portion 12 by the restoring force of the damper 13, and the meshing portion is in a state in which no backlash exists.
[0016]
In the above configuration, when the driver rotates the steering wheel (see reference numeral 101 in FIG. 3) in any direction for steering the vehicle, the torsion bar 2 is twisted and deformed by the torque (steering torque). In addition, the electric assist motor 4 is driven based on a detection signal, vehicle speed data, and the like from a torque sensor (see reference numeral 105 in FIG. 3) that detects the direction and magnitude of the torsion torque.
[0017]
The driving torque of the electric assist motor 4 serving as an auxiliary steering torque with respect to the steering output shaft 1 of the steering column is transmitted from the output shaft 5 of the electric assist motor 4 via the engagement portion between the concave engagement portion 12 and the engagement element 11 and the damper 13. The torque is transmitted to the worm shaft 6 and further decelerated via the meshing portion between the worm gear 7 and the worm wheel 3, and is given to the steering output shaft 1 in the same direction as the rotation direction of the steering wheel. It comes to assist. For this reason, the driver can easily perform steering.
[0018]
Since the meshing element 11 and the concave meshing part 12 mesh with each other with the tooth surfaces 11a, 12a aligned in a tapered shape, the output shaft 5 and the worm shaft 6 of the electric assist motor 4 are concave with the meshing element 11. The meshing portion of the meshing portion 12 is held coaxially with each other via the damper 13.
[0019]
Even if vibration is input from the axle side to the worm shaft 6 via the steering output shaft 1, the worm wheel 3 and the worm gear 7 due to, for example, unevenness on the road surface during traveling, the shaft end 6a of the worm shaft 6 is concavely engaged. An appropriate gap G exists between the central portion of the portion 12 and the worm shaft 6 and the output shaft 5 of the electric assist motor 4 are elastically connected via the damper 13. The input vibration is absorbed by the damper 13 and the vibration to the output shaft 5 can be effectively reduced.
[0020]
Further, since the tapered tooth surface 11a of the meshing piece 11 is pressed against the tooth surface 12a of the concave meshing portion 12 corresponding to the restoring force of the radial direction portion 13b of the damper 13 to which pre-compression is applied, Both tooth surfaces 11a and 12a mesh with each other in the absence of backlash. Therefore, for example, after the driver turns the steering wheel in one direction (rotates the steering wheel) and immediately turns the steering wheel in the reverse direction, the direction of the auxiliary steering torque by the electric assist motor 4 is suddenly reversed. However, rattling due to backlash of the tooth surfaces 11a and 12a does not occur, and it is possible to reduce or prevent annoying noise caused by the hitting sound.
[0021]
Note that the present invention is not limited to the illustrated embodiment. For example, the meshing element 11 is mounted on the output shaft 5 side of the electric assist motor 4 via the damper 13, and the concave meshing part 12 having the tooth surface 12 a meshing with the tapered tooth surface 11 a of the meshing element 11 is used as the axis of the worm shaft 6. The same effect as described above can be realized even if the structure is provided at the end and meshed with each other, that is, the structure in which the relationship between the output shaft 5 and the worm shaft 6 with respect to the engagement element 11 and the damper 13 is reversed from the illustrated form. be able to.
[0022]
Further, for example, the tooth surface of the meshing element 11 is formed in a tapered concave surface like the concave meshing part 12, and the tooth surface of the mating meshing part meshing with this is formed in an umbrella shape, that is, the taper direction of the meshing part Even if is reversed from the illustrated embodiment, the same effect as described above can be realized.
[0023]
【The invention's effect】
According to the vibration isolating structure of the electric power steering apparatus according to the first aspect of the present invention, even if vibration is input from the steering column side to the worm shaft via the worm wheel due to unevenness of the road surface during traveling, Since the vibration is absorbed by the damper, the vibration to the output shaft of the electric assist motor can be effectively suppressed. Moreover, the worm shaft and the output shaft of the electric assist motor are connected via a tapered mesh structure by a meshing member elastically provided via a damper and a mating meshing portion meshed without backlash. Therefore, it is possible to prevent the occurrence of rattling noise when the steering direction is changed.
[0024]
Further, according to the vibration isolating structure of the electric power steering apparatus according to claim 2 of the present invention, by applying axial compression to the damper, the tooth surface of the meshing member is pressed against the tooth surface of the mating meshing portion, and the back Since the rush is surely eliminated, the reliability of the effect of preventing the rattling noise when the steering direction is changed can be further enhanced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a part of an electric power steering apparatus to which an anti-vibration structure for an electric power steering apparatus according to the present invention is applied.
FIG. 2 is a cross-sectional view showing a preferred embodiment of a vibration isolating structure for an electric power steering apparatus according to the present invention.
FIG. 3 is an explanatory diagram showing a schematic structure of an electric power steering device for a vehicle.
FIG. 4 is a cross-sectional view showing a coupling structure between a worm shaft and an electric assist motor according to a conventional technique in an electric power steering apparatus.
[Explanation of symbols]
1 Steering output shaft 2 Torsion bar 3 Worm wheel 4 Electric assist motor 5 Motor output shaft (output shaft)
6 Worm shaft 6a Shaft end 6b Radial stepped surface 7 Worm gear 8, 9 Bearing 10 Housing 11 Engagement 11a, 12a Tooth surface 11b Boss part back (back)
12 concave meshing part (mating part)
13 damper 13a cylindrical part 13b radial direction part

Claims (2)

Electric power steering apparatus having a structure in which a worm gear (7) provided on a worm shaft (6) rotated by an electric assist motor (4) meshes with a worm wheel (3) mounted on a steering output shaft (1). 1 and the output shaft (5) of the electric assist motor (4) is provided on the outer periphery of one shaft end via a damper (13) made of a rubber-like elastic material and has a tapered tooth surface. And a tapered tooth surface (12a) corresponding to the tapered tooth surface (11a) provided at the other shaft end of the worm shaft (6) and the output shaft (5). The anti-vibration structure of the electric power steering apparatus, wherein the mating meshing portions (12) having the above are meshed with each other without backlash. The damper (13) has a radial portion (13b), and the radial portion (13b) is engaged with a radial step surface (6b) formed on the worm shaft (6) or the output shaft (5). 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is interposed between the tapered tooth surface (11 a) and the opposite back surface (11 b) in an axially compressed state. Anti-vibration structure.

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