JP2002323059A - Joint structure and steering assisting device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint structure in which an output shaft of an electric motor and a rotating shaft rotationally driven by the output shaft can be connected in a small space, and adjustment widths in eccentricity and tilt of the output shaft and the rotating shaft can be enlarged, whereby the connecting work of the output shaft and the rotating shaft is easily conducted, and to provide a steering assisting device using the same. SOLUTION: The joint structure 8 is provided with a first bearing 16 mounted on one end 70a of a worm shaft (a rotating shaft) 70 so as to rotatably support the worm shaft 70, a recess 8a provided at the side of the one end 70a of the worm shaft 70 and a projection 8b provided at the side of the output shaft 60 of the electric motor 6 and engaged with the recess 8a are contained, whereby the output shaft 60 of the electric motor 6 and the worm shaft 70 are connected. The central position of the connected part of the output shaft 60 and the worm shaft 70 is substantially made consistent with the central position of the first bearing 16 in the axial direction of the worm shaft 70.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joint structure for connecting an output shaft and a rotary shaft of an electric motor, and a steering assist device using the same.

[0002]

2. Description of the Related Art Conventionally, as a steering assist device for an automobile,
As shown in FIG. 5, a first steering shaft 102 to which a steering wheel (handle) 101 is attached, and a second steering shaft 104 provided in series below the first steering shaft 102 are connected via a torsion bar 103. And based on the relative rotational displacement of the first steering shaft 102 and the second steering shaft 104,
The steering torque is detected by the torque sensor 105, and the steering assist electric motor 106 is driven based on the detection result of the torque sensor 105.
A device that assists the manual steering force of the steered wheels 101 by transmitting the rotation of No. 06 to the second steering shaft 104 after being decelerated by the deceleration mechanism 109 is provided.

The speed reduction mechanism 109 comprises a worm shaft 107 provided with a worm, and a worm wheel 108 made of synthetic resin which is attached to the second steering shaft 104 so as to be integrally rotatable with the worm. The worm shaft 107 is connected to the electric motor 106.
Are connected via a joint so as to be integrally rotatable. Further, the worm shaft 107 and the second steering shaft 104
Are supported by bearings at both ends in the axial direction, and are prevented from moving in the radial direction and the axial direction.

In the conventional steering assist device described above, if backlash occurs at the meshing portion between the worm of the worm shaft 107 and the worm wheel 108, a so-called rattling sound is generated, which leaks into the vehicle and causes the driver or passenger to ride. May cause discomfort to the person. For this reason, the dimensions of the worm shaft 107 and the worm wheel 108 are selected at the time of manufacturing the device, and the two are combined so that the backlash does not occur. However, even when the backlash is adjusted during the manufacture of the device, the use of the steering assist device prevents wear of the worm of the worm shaft 107 and the teeth of the worm wheel 108, thereby avoiding the occurrence of backlash. It is difficult. Further, the worm wheel 108 made of synthetic resin may expand due to water absorption, heat, or the like, and the rotational torque (rotational resistance) may increase. Therefore, the worm shaft 107 is supported so as to be able to be biased toward the worm wheel 108, and the worm shaft 107 is biased toward the worm wheel 108 by a spring. There has been proposed a steering assist device that prevents such a situation.

More specifically, in FIG. 6, in this conventional steering assist device, the worm shaft 107 is rotatably supported by a gear housing 110 via first and second bearings 111 and 112. One end of the worm shaft 107 has a serration 113 press-fitted into a serration hole 114 a formed in a cylindrical joint member 114. This joint member 114 includes the electric motor 1
The output shaft 106a is press-fitted so as to be integrally rotatable.
4, the worm shaft 107 and the output shaft 106a are connected so as to be integrally rotatable.

The first bearing 111 is constituted by a ball bearing. One end of the worm shaft 107 is press-fitted into an inner ring thereof and inserted into a first bearing hole 110a of the gear housing 110. I have. A cylindrical screw body 115 is screwed into the first bearing hole 110a to abut against the outer ring of the first bearing 111 to prevent the worm shaft 107 from rattling in the axial direction. . The second bearing 112 is constituted by a ball bearing, and is attached to the second bearing hole 110b of the gear housing 110 so as to be able to be deflected toward the worm wheel 108. That is, the second inner portion of the second bearing hole 110b and the second
An arc-shaped gap 110c is provided between the bearing 112 and the second bearing 112 such that the second bearing 112 can move toward the worm wheel 108 by the gap 110c. When the second bearing 112 is displaced in the direction of the worm wheel 108, the displacement of the one end of the worm shaft 107 causes the backlash due to the radial clearance of the first bearing 111 or the gap between the output shaft 106 a and the joint member 114. And the worm shaft 107 is allowed to be eccentric and inclined with respect to the output shaft 106a.

A biasing means 116 for biasing the second bearing 112 toward the worm wheel 108 is attached to the opening side of the second bearing hole 110b. The biasing means 116 is movably disposed in the second bearing hole 110b, and is supported by the support yoke 116a which contacts the outer ring of the second bearing 112, and is held by the support yoke 116a.
A spring 116b for urging the second bearing 112 toward the worm wheel 108, and a screw body 116c screwed to an end of the second bearing hole 110b for adjusting the amount of deflection of the spring 116b.
And the lock nut 11 screwed into the screw body 116c
6d. With the above configuration, in this conventional steering assist device, the worm 107a of the worm shaft 107
When the teeth of the worm wheel 108 are worn, the worm shaft 107 is moved by the spring 116b to the worm wheel 1.
By biasing in the 08 direction, backlash was prevented from occurring. When the worm wheel 108 expands due to water absorption, heat, or the like, the worm shaft 10
7 to the opposite side of the worm wheel 108 to prevent the rotation torque from increasing.

[0008]

However, in the conventional steering assist device as described above, the worm shaft 107 and the output shaft 106a are connected by using the serration 113 and the joint member 114. It is necessary to project one end of the shaft 107 from the first bearing 111 to the electric motor 106 side, and the worm shaft 1
There is a problem that the axial length of the 07 becomes long and the device becomes large.

Further, one end of the worm shaft 107 is projected from the first bearing 111 toward the electric motor 106 so that the output shaft 1
06a, the one end is connected to the output shaft 106a.
a, the backlash due to the radial gap of the first bearing 111 cannot be used effectively, and the adjustment amount of the bias amount by the urging means 116 at the other end of the worm shaft 107, that is, The adjustment range of the eccentricity and tilting between the output shaft 106a and the worm shaft 107 is limited to a small value. Also,
As described above, the adjustment width of the eccentricity and the tilt of the output shaft 106a and the worm shaft 107 is limited to a small value, so that the worm shaft 107 and the electric motor 1 are mounted on the gear housing 110.
06, the output shaft 106a and the worm shaft 1
07 needs to be performed with high precision, and it is difficult to connect the output shaft 106a and the worm shaft 107.

In view of the above-mentioned conventional problems, the present invention can connect an output shaft of an electric motor and a rotation shaft driven by the output shaft in a small space, and can reduce the output shaft. The object of the present invention is to provide a joint structure and a steering assist device using the same, which can increase the adjustment width of eccentricity and tilting between the shaft and the rotating shaft, thereby facilitating the connection work between the output shaft and the rotating shaft. I do.

[0011]

A joint structure according to the present invention is a joint structure in which a rotating shaft rotatably supported by a bearing is connected to an output shaft of an electric motor so as to be integrally rotatable. The rotation shaft and the output shaft are connected to each other with the center position of the connection portion between the one end of the rotation shaft and the output shaft substantially coincident with the center position of the bearing in the direction. (Claim 1).

[0012] According to the joint structure configured as described above, the center position of the connecting portion between the one end of the rotating shaft and the output shaft of the electric motor substantially coincides with the center position of the bearing. By rotatably supporting the rotary shaft by the bearing, the back end of the rotary shaft can be largely deviated with respect to the output shaft by utilizing the play of the radial gap of the bearing very effectively. Therefore, the adjustment range of the eccentricity and the tilt of the output shaft and the rotation shaft can be increased, and thus, the work of connecting the output shaft and the rotation shaft can be easily performed. Moreover, the joint structure is simple, and its axial length can be reduced.

In the joint structure (claim 1), it is preferable that the rotating shaft and the output shaft are connected to each other so as to be swingable (claim 2). In this case, the adjustment width of the eccentricity and the tilt of the output shaft and the rotation shaft can be made larger, and thus, the work of connecting the output shaft and the rotation shaft can be more easily performed.

In the steering assist device according to the present invention, the rotation of the electric motor is transmitted to the steering shaft via a worm shaft as a rotating shaft provided with a worm and a worm wheel meshed with the worm of the worm shaft. A steering assist device that assists the steering by providing a bearing attached to one end of the worm shaft to rotatably support the worm shaft; and a recess provided at one end of the worm shaft; A joint structure provided on the output shaft side of the electric motor and having a projection engaging with the recess is provided at a connection portion between the worm shaft and the output shaft, and the center of the bearing in the axial direction of the worm shaft is provided. The worm shaft and the output shaft are connected to each other in a state where the center position of the connecting portion substantially matches the position. 3).

According to the steering assist device configured as described above, the rotation of the output shaft of the electric motor can be transmitted to the worm shaft via the joint structure. Further, since the other end of the worm shaft can be largely deviated with respect to the output shaft by utilizing the play caused by the radial gap of the bearing extremely effectively, the eccentricity and tilt of the output shaft and the worm shaft can be reduced. The adjustment width can be increased, and the connection operation between the output shaft and the worm shaft can be easily performed. In addition, since the joint structure is simple and its axial length can be reduced, the output shaft and the worm shaft can be connected in a small space.

Further, in the steering assist device described above, the worm shaft is supported so as to be biased toward the worm wheel, and the worm shaft is urged toward the worm wheel by urging means. Is preferable (claim 4). In this case, the worm shaft can be deflected toward the worm wheel, so that the eccentricity of the output shaft and the worm shaft and the adjustment width of the tilt are increased, so that the worm shaft can be easily directed toward the worm wheel. Can be moved. Therefore, the urging means can reliably move the worm shaft by following the wear of the worm wheel.

Further, in the above steering assist device (claim 3 or 4), the convex portion is formed by a tip of the output shaft formed in a drum shape having a regular polygonal cross section and a central portion bulging in the axial direction. It is preferable that the recess is formed by cutting one end of the worm shaft into a regular polygonal cross-section in the axial direction, and the tip is swingably connected (claim). 5). In this case, the output shaft and the worm shaft can be directly connected without providing a dedicated joint member that configures the convex portion and the concave portion, and the configuration of the device can be simplified. In addition, since the tip portion is swingably connected to the recess, the eccentricity between the output shaft and the worm shaft and the adjustment width of the tilt can be further increased, and thus the connection work between the output shaft and the worm shaft can be performed. Can be performed more easily.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments showing a joint structure and a steering assist device using the same according to the present invention will be described below with reference to the drawings. FIG. 3 is a sectional view showing the overall structure of the steering assist device of the present invention. The steering assist device includes a first steering shaft 2 to which a steering wheel 1 is attached at an upper end, a cylindrical second steering shaft 4 connected to a lower end of the first steering shaft 2 via a torsion bar 3, A torque sensor 5 for detecting a steering torque based on a relative rotational displacement between the first steering shaft 2 and the second steering shaft 4;
And a speed reduction mechanism 7 that reduces the rotation of the electric motor 6 and transmits the rotation to the second steering shaft 4. The first steering shaft 2 is supported by being surrounded by a first steering column 9 and a second steering column 10.
The steering column 9 is connected to the vehicle body A via the bracket 12.
Attached to. Further, the torque sensor 5 is housed in a sensor housing H1, and the speed reduction mechanism 7
Is accommodated in a gear housing H2, and the electric motor 6 is attached to the gear housing H2.

The first steering shaft 2 has a cylindrical first shaft body 2a having the steering wheel 1 mounted on an upper end thereof, and a lower end of the first shaft body 2a is allowed to move in the axial direction. And a cylindrical third shaft 2d connected to the second shaft 2b by a pin 2c. The first shaft body 2a has a cylindrical first steering column 9 having an intermediate portion via a bearing 13.
It is supported rotatably. In addition, the first and second
Between the shafts 2a and 2b, there is provided a cushioning member 2e made of a synthetic resin for absorbing the impact energy acting on the steered wheels 1 from the driver at the time of a collision of an automobile or the like. Further, the torque sensor 5 is disposed between the third shaft 2d and the second steering shaft 4.

The second steering column 10 has an upper end slidably fitted to the first steering column 9 and a lower end fitted to the sensor housing H1 to absorb the impact energy. The first steering column 9 can be moved in the axial direction with respect to the second steering column 10. A torsion bar 3 is introduced inside the second steering shaft 4, and a lower end of the second steering shaft 4 is connected to the torsion bar 3 by a pin 4a so as to be integrally rotatable. The intermediate portion of the second steering shaft 4 in the axial direction is provided with a pair of bearings 14 and 1.
5, and is rotatably supported by the gear housing H2. The inner periphery of the worm wheel 72 is rotatably fitted in the space 4b between the bearings 14 and 15.

As shown in FIG. 1, the reduction mechanism 7 has a joint structure 8 of the present invention attached to the output shaft 60 of the electric motor 6.
The worm shaft 70 connected to the worm wheel 70 and the worm wheel 7 fitted to the second steering shaft 4 so as to be integrally rotatable.
2 is provided. A worm 71 is formed integrally with an intermediate portion of the worm shaft 70 in the axial direction, and the worm 71 is engaged with a worm wheel 72. Therefore, the rotation of the output shaft 60 of the electric motor 6 can be transmitted to the second steering shaft 4 at a reduced speed by the worm shaft 70 and the worm wheel 72. The rotation of the second steering shaft 4 is transmitted to, for example, a rack and pinion type steering mechanism connected to the wheels via a universal joint J (see FIG. 3).

The worm shaft 70 is disposed so as to be orthogonal to the axis of the second steering shaft 4 and has one end 70.
a and the other end 70b are the first and second bearings 16,
17 and rotatably supported by the first and second bearing holes 91 and 92 of the gear housing H2 (see FIG. 1). The first bearing 16 is formed by a ball bearing. One end 70 a of the worm shaft 70 is press-fitted into the inner ring 16 a, and the outer ring 16 b is inserted into the first bearing hole 91. Further, in the first bearing hole 91, a cylindrical screw body 18 for contacting the outer ring 16b of the first bearing 16 to prevent the worm shaft 70 from rattling in the axial direction.
Is screwed. The second bearing 17 is constituted by a metal bearing, and is attached to the second bearing hole 92 so as to be deviated in the worm wheel 72 direction. That is, as shown in FIG. 4, a gap 92 a is provided between the inner part of the second bearing hole 92 and the second bearing 17, and the second bearing 17 is warmed by the gap 92 a. It can move to the wheel 72 side.

A plug 3 is provided on the opening side of the second bearing hole 92.
4 is screwed into the plug 34 and the second bearing 17.
Between the worm wheel 72 and the second bearing 17.
Coil spring 3 as urging means for constantly urging in the direction
2 is interposed in an elastically contracted state. In the case of the figure,
The compression coil spring 32 is housed inside a bottomed cylindrical projection 17 b projecting from the outer periphery of the outer ring 17 a of the second bearing 17. The biasing force of the compression coil spring 32 is adjusted to an optimal value by adjusting the amount of screwing of the plug 34 into the second bearing hole 92. The plug 34 is fixed by a lock nut 35. In addition to the above-described configuration, the second bearing 17 is configured by a ball bearing, and the support yoke movably disposed in the second bearing hole 92 is urged by a spring, as in the case illustrated in FIG. 6, for example. By doing so, the second bearing 17 may be urged toward the worm wheel 72.

As shown in FIG. 1, the joint structure 8 includes a concave portion 8a provided on one end portion 70a of the worm shaft 70 and a convex portion provided on the output shaft 60 side and engaged with the concave portion 8a. 8b, and the center position of the connecting portion formed by the concave portion 8a and the convex portion 8b is set to the first bearing 16 in the axial direction of the worm shaft 70.
The worm shaft 7 is substantially aligned with the center position of the worm shaft 7.
0 and the output shaft 60 are connected.

As shown in FIGS. 2 (a) and 2 (b), the convex portion 8b is formed, for example, by processing the tip of the output shaft 60 into a drum shape having a central hexagonal bulge with a regular hexagonal cross section. It is comprised by. The concave portion 8a is formed by cutting out one end portion 70a of the worm shaft 70 in the axial direction, and the above-mentioned convex portion (tip portion) 8b is swingably connected. As described above, by processing the one end portion 70a of the worm shaft 70 to be connected and the distal end portion of the output shaft 60 into the concave portion 8a and the convex portion 8b, respectively, the output shaft 60 and the worm shaft 70 can be directly connected. Further, since the projection 8b is swingably connected to the recess 8a, the other end 70b of the worm shaft 70 is
Can be more greatly biased. The concave portion 8a and the convex portion 8b need only be capable of transmitting the rotation of the output shaft 60 to the worm shaft 70, and are not limited to a regular hexagonal cross section, but may have a torque from the output shaft 60 to the worm shaft 70. A cross section having a regular square to octagonal shape with little transmission loss is preferable.

As described above, in the steering assist device of the present embodiment, the worm shaft 70 and the output shaft 60 are connected by the joint structure 8 and the center position of the connection portion is set to the worm shaft 70 of the first bearing 16. Since the center position substantially coincides with the center position in the axial direction of
The other end 70b of the worm shaft 70 can be deflected about the bearing 16 with respect to the output shaft 60, and the backlash due to the radial clearance of the first bearing 16 and the backlash due to the clearance at the connecting portion can be reduced. Can be used very effectively, and the other end 70b of the worm shaft 70 can be largely deviated from the output shaft 60. Therefore, the width of adjustment of the eccentricity and tilting between the output shaft 60 and the worm shaft 70 can be increased, so that there is no need to particularly increase the connection accuracy between the worm shaft 70 and the output shaft 60, and the connection work is facilitated. I can do it. In addition, the joint structure 8 is simple, and unlike the above-described conventional example using the serrations and the joint members, the axial length can be extremely reduced.
The size of the reduction mechanism 7 can be reduced.

In this embodiment, the worm shaft 70 is supported so as to be able to be biased toward the worm wheel 72, and the worm shaft 70 is urged toward the worm wheel 72 by the compression coil spring 32. The worm 71 can be elastically pressed against the worm wheel 72. Further, in combination with the fact that the adjustment width of the eccentricity and tilting between the output shaft 60 and the worm shaft 70 is increased, the worm shaft 70 is
It can be easily moved toward 2. Therefore, even if the tooth surfaces of the worm 71 and the worm wheel 72 are worn out due to long-term use, the worm 71 can follow the wear to prevent backlash. Further, when the worm wheel 72 made of synthetic resin expands due to water absorption, heat, or the like, the worm shaft 70 can be prevented from escaping to the opposite side of the worm wheel 72 to prevent the rotation torque from increasing. Further, since the worm 71 of the worm shaft 70 can be elastically pressed against the worm wheel 72 as described above, the backlash can be adjusted without being affected by the dimensional error of the parts including both when assembling them. be able to.

The concave portion 8a and the convex portion 8b of the joint structure 8 are connected to one end 70 of the worm shaft 70 to be connected.
a and the front end of the output shaft 60 are each processed, so that the output shaft 60 and the worm shaft 70 can be connected to each other without providing a dedicated joint member for forming the concave portion 8a and the convex portion 8b. They can be directly connected, and the configuration of the device can be simplified. Furthermore, since the convex portion 8b is swingably connected to the concave portion 8a, the eccentricity and tilting adjustment width between the output shaft 60 and the worm shaft 70 can be further increased, and therefore, the output shaft 60 and the worm The connection work with the shaft 70 can be performed more easily.

In the above description, the structure in which the output shaft 60 of the electric motor 6 is connected to the worm shaft 70 has been described. However, the joint structure of the present invention is not limited to this, and the structure of the rotating shaft is not limited to this. If the center position of the connecting portion between the one end of the rotating shaft and the output shaft substantially coincides with the center position of the bearing in the direction, and the rotating shaft and the output shaft are connected, It can also be suitably used as a joint structure for connecting the rotary shaft 60 and various rotary shafts driven to rotate by the output shaft 60. For example, a spline hole and a spline shaft are provided at one end portion 70a of the worm shaft 70 and a tip end portion of the output shaft 60, respectively, and the center position of the spline connection substantially coincides with the center position of the first bearing 16. May be.

[0030]

As described above, according to the joint structure of the first aspect, the back end caused by the radial gap of the bearing is extremely effectively used to move the other end of the rotary shaft to the output shaft of the electric motor. Therefore, the width of adjustment of the eccentricity and tilt of the output shaft and the rotation shaft can be increased. As a result, there is no need to align the output shaft and the rotary shaft with high precision, and the connection between them can be performed easily. Moreover, since the joint structure is simple and small, the output shaft and the rotating shaft can be connected in a small space. Therefore, it is possible to reduce the size of various devices including the electric motor and the rotating shaft.

According to the joint structure of the second aspect,
Since the rotating shaft and the output shaft are swingably connected to each other, the adjustment range of the eccentricity and the tilt of the output shaft and the rotating shaft can be increased, and thus the connecting work between the output shaft and the rotating shaft can be reduced. More easily.

According to the third aspect of the present invention, the output shaft of the electric motor and the worm shaft are connected to each other by using a joint structure having a simple structure and a short axial length. The size can be reduced. Further, since the other end of the worm shaft can be largely deviated with respect to the output shaft by utilizing the play caused by the radial gap of the bearing extremely effectively, the eccentricity and tilt of the output shaft and the worm shaft can be reduced. The adjustment width can be increased. As a result, it is not necessary to align the output shaft and the worm shaft with high precision, and the connection between them can be performed easily.

According to the steering assist device of the fourth aspect, since the worm shaft can be biased toward the worm wheel, the eccentricity between the output shaft and the worm shaft and the adjustment width of the tilt are increased. In combination, the worm shaft can be easily moved toward the worm wheel. For this reason, the worm can be easily moved by following the wear of the worm wheel by the urging means, and the backlash can be easily and reliably prevented from occurring.

According to the steering assist device of the fifth aspect, the output shaft and the worm shaft can be directly connected without providing a dedicated joint member for forming the convex portion and the concave portion, respectively. The configuration of the device can be simplified. In addition, since the convex portion is swingably connected to the concave portion, the eccentricity of the output shaft and the worm shaft and the adjustment width of the tilt can be further increased, and therefore, the connection work between the output shaft and the worm shaft can be performed. Can be performed more easily.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an electric motor and a speed reduction mechanism of a steering assist device according to an embodiment of the present invention.

FIG. 2A is a perspective view showing a protrusion provided at a distal end of an output shaft of the electric motor shown in FIG. 1, and FIG.
It is IIb-IIb line sectional drawing.

FIG. 3 is a cross-sectional view showing the entire structure of the steering assist device according to the present invention.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 1;

FIG. 5 is a sectional view showing the entire structure of a conventional steering assist device.

FIG. 6 is a cross-sectional view showing an electric motor and a speed reduction mechanism in another conventional steering assist device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering wheel 32 compression coil spring (biasing means) 6 electric motor 60 output shaft 7 reduction mechanism 70 worm shaft (rotation shaft) 70 a one end 71 worm 72 worm wheel 8 joint structure 8 a concave portion 8 b convex portion 16 first bearing (bearing) 17) 2nd bearing

Claims (5)

[Claims] 1. A joint structure for connecting a rotating shaft rotatably supported by a bearing to an output shaft of an electric motor so as to be integrally rotatable, wherein the rotating shaft is provided at a center position of the bearing in an axial direction of the rotating shaft. A joint structure, wherein the rotating shaft and the output shaft are connected in a state where the center position of the connecting portion between the one end of the shaft and the output shaft is substantially matched. 2. The joint structure according to claim 1, wherein said rotating shaft and said output shaft are connected to each other so as to be swingable. 3. A steering assist for transmitting steering rotation of an electric motor to a steering shaft via a worm shaft as a rotating shaft provided with a worm and a worm wheel meshed with the worm of the worm shaft. An apparatus, comprising: a bearing attached to one end of the worm shaft to rotatably support the worm shaft; a recess provided at one end of the worm shaft; and a recess provided at an output shaft of the electric motor. A joint structure having a convex portion engaging with the concave portion is provided at a connecting portion between the worm shaft and the output shaft, and the center of the connecting portion is provided at a center position of the bearing in the axial direction of the worm shaft. A steering assist device wherein the worm shaft and the output shaft are connected in a state where the positions are substantially matched. 4. The steering assist device according to claim 3, wherein the worm shaft is supported so as to be biased toward the worm wheel, and the worm shaft is urged toward the worm wheel by an urging means. . 5. The output device according to claim 5, wherein the convex portion is formed by a tip of the output shaft formed in a drum shape having a regular polygonal cross section and a central portion protruding in the axial direction. The steering assist device according to claim 3 or 4, wherein one end is formed by cutting out a regular polygonal cross section in the axial direction, and the tip is swingably connected.