JP2002266890A - Joint and steering assisting device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint capable of connecting an output shaft of an electric motor with a rotary shaft rotated and driven by the output shaft with a small space and at a low cost, of damping vibration of the rotary shaft, and of tolerating relative rotation between both shafts, when rotation resistance of the output shaft or rotation shaft abnormally increases, and a steering assisting device using the joint. SOLUTION: The output shaft 60 of the electric motor 6 and a worm shaft 70 are connected through the joint 8. The joint 8 has a cylindrical elastic body 8 made of rubber or the like interposed between a first cylindrical transmission member 81 attached to the output shaft 60 and a second cylindrical transition member 82 enveloping the first transmission member 81. Rotation of the second transmission member 82b is transmitted to a third transmission member 83 connected to the worm shaft 70 through a torque limiter 85.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joint 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. 6, 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 the first steering shaft 10
A steering torque is detected by a torque sensor 105 based on the relative rotational displacement between the second steering shaft 104 and the second steering shaft 104, and an electric motor 106 for assisting steering is driven based on the detection result of the torque sensor 105. A mechanism is provided in which the rotation of the electric motor 106 is decelerated by a speed reduction mechanism 109 and transmitted to the second steering shaft 104, thereby assisting the manual steering force of the steered wheels 101.

The speed reduction mechanism 109 includes 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 1.
06 is connected via a joint so as to be integrally rotatable. The worm shaft 107 and the second steering shaft 104 are respectively 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, when 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. Therefore, 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 if the backlash is adjusted during the manufacture of the device, it is difficult to avoid the occurrence of the backlash because the teeth of the worm shaft 107 and the worm wheel 108 are worn with the use of the steering assist device. It is. 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 biased toward the worm wheel 108.
A steering assisting device has been proposed in which a spring is urged toward the worm wheel by a spring to prevent backlash and increase in rotational torque (for example, JP-A-2000-43939). reference).

[0005]

However, in this steering assist device, since it is necessary to allow the eccentricity and inclination of the worm shaft 107 with respect to the output shaft of the electric motor 106, a long joint such as a universal joint is required. It is necessary to connect both by using. For this reason, there has been a problem that a space for connection becomes large, the device becomes large, and the cost increases. The electric motor 10
The worm shaft 107 is likely to vibrate during the rotation of the wheel 6, and the vibration may be transmitted to the steered wheels 101 to lower the steering feeling. Furthermore, when the electric motor 106 fails and the rotational resistance of the output shaft increases abnormally, there is a possibility that the steering operation becomes extremely heavy. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can connect an output shaft of an electric motor and a rotation shaft driven to rotate by the output shaft in a small space at a low cost. Can be attenuated, and
It is an object of the present invention to provide a joint capable of permitting relative rotation between the two shafts when the rotation resistance of the output shaft or the rotation shaft abnormally increases, and a steering assist device using the same.

[0006]

According to another aspect of the present invention, there is provided a joint for connecting a rotary shaft to an output shaft of an electric motor so as to be integrally rotatable. A first transmission member to be attached, a second transmission member surrounding the first transmission member with a gap, and a first transmission member interposed between the first transmission member and the second transmission member; An elastic body that transmits rotation to the second transmission member, a third transmission member that connects the rotation shaft so as to be integrally rotatable, and a second transmission member that regulates relative rotation between the second transmission member and the third transmission member; A torque limiter that permits the relative rotation when the rotation resistance of the member or the third transmission member exceeds a predetermined value (claim 1).

According to the joint having such a configuration, the rotation of the output shaft of the electric motor is transmitted to the second transmission member via the first transmission member and the elastic member, and the rotation of the second transmission member is torqued. Power can be transmitted to the rotating shaft via the limiter and the third transmission member. Further, the eccentricity and inclination between the output shaft and the rotating shaft of the electric motor can be absorbed or allowed by the elastic body, and even when the rotating shaft vibrates, the vibration can be attenuated by the elastic body. Further, when the rotation resistance of the second transmission member or the third transmission member exceeds a predetermined value, the relative rotation of both transmission members can be allowed by the torque limiter. Moreover, the structure of the joint is simple, and its axial length can be reduced.

The torque limiter is engaged with one of the second transmission member and the third transmission member,
It may be provided with a locking member slidably in contact with the other transmission member, and a spring for applying frictional resistance to the contact surface between the other transmission member and the locking member. Item 2). In this case, due to the frictional resistance applied to the contact surface between the other transmitting member and the locking member by the spring, the second
The rotation of the transmission member can be transmitted to the third transmission member via the locking member. Further, when the rotation resistance of the second transmission member exceeds a predetermined value, a slip occurs between the locking member and the other transmission member, and the relative position between the second transmission member and the third transmission member is increased. Rotation can be tolerated.

In the torque limiter, a spring is interposed between an end face of the second transmission member and a spring receiving portion provided on a third transmission member facing the end face, and the second transmission member and the third transmission member are provided. The relative rotation of both transmission members may be restricted by frictional resistance of a contact surface between at least one of the transmission members and the spring (claim 3). In this case, the rotation of the second transmission member can be transmitted to the third transmission member by the frictional resistance of the contact surface between at least one of the second transmission member and the third transmission member and the spring. Further, when the rotation resistance of the second transmission member exceeds a predetermined value, a slip is generated on the contact surface, and the relative rotation between the second transmission member and the third transmission member can be allowed.

It is preferable that the first transmission member, the second transmission member, the elastic body and the third transmission member are each formed of a cylindrical body arranged concentrically (claim 4). The structure can be made very simple. The joint may form a flat surface with the outer periphery of the first transmission member and the inner periphery of the second transmission member facing each other (claim 5). In this case, since the relative rotation between the first transmission member and the second transmission member is limited by each flat surface, the rotation of the electric motor is easily and reliably transmitted to the second transmission member via the elastic body. Can be transmitted. Further, the load acting on the elastic body when the torque limiter is operated can be received by the flat surface, so that an excessive load can be prevented from being applied to the elastic body.

The steering assist device according to the present invention transmits the rotation of the electric motor 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. Thus, in a steering assist device for assisting steering, an output shaft of the electric motor and a worm shaft are connected using the joint according to any one of claims 1 to 5 (claim). Item 6).

According to the steering assist device having such a configuration,
The rotation of the output shaft of the electric motor is transmitted to the second transmission member via the first transmission member and the elastic body, and the rotation of the second transmission member is transmitted to the worm shaft via the torque limiter and the third transmission member. can do. Further, the eccentricity and inclination between the output shaft of the electric motor and the worm shaft can be absorbed or tolerated by the elastic body, and even when the worm shaft vibrates, the vibration can be attenuated by the elastic body. Further, the second transmission member or the third transmission member
When the rotational resistance of the transmission member exceeds a predetermined value, the relative rotation of both transmission members can be allowed by the torque limiter. In addition, the structure of the joint is simple and its axial length can be reduced, so that the output shaft of the electric motor and the worm shaft can be connected in a small space.

The steering assist device preferably supports the worm shaft so as to be biased toward the worm wheel, and biases the worm shaft toward the worm wheel by a biasing means. In this case, since the worm shaft can be deflected toward the worm wheel, the worm shaft is worm-coupled with the point that the worm shaft is allowed to be eccentric and inclined with respect to the output shaft of the electric motor by the elastic body of the joint. It can be easily moved toward the wheel. For this reason, the worm can be reliably moved by following the wear of the worm wheel by the urging means.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 4 is a sectional view showing an embodiment of the steering assist device according to 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, an electric motor 6 for steering assistance driven based on a detection result of the torque sensor 5, A speed reduction mechanism 7 for reducing the rotation of the electric motor 6 and transmitting the rotation to the second steering shaft 4. The first steering shaft 2 is supported while being surrounded by a first steering column 9 and a second steering column 10, and the first steering column 9 is attached to a vehicle body A via a bracket 12. The torque sensor 5 is housed in a sensor housing H1, the speed reduction mechanism 7 is housed in a gear housing H2, and the electric motor 6 is mounted on the gear housing H2.

The first steering shaft 2 has a cylindrical first shaft 2a having the steering wheel 1 attached to the upper end thereof, and the lower end of the first shaft 2a is allowed to move in the axial direction. And a cylindrical third shaft body 2d connected to the second shaft body 2b by a pin 2c. The first shaft body 2 a is rotatably supported at its intermediate portion by the cylindrical first steering column 9 via a bearing 13. Further, between the first and second shaft bodies 2a and 2b, there is provided a buffer member 2e made of synthetic resin for absorbing impact energy acting on the steering wheel 1 from a driver at the time of a collision of an automobile or the like. ing. 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. In addition, the first steering column 9 can be moved in the axial direction with respect to the second steering column 10. The torsion bar 3 is introduced inside the second steering shaft 4,
The 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. Also,
An intermediate portion of the second steering shaft 4 in the axial direction is a pair of bearings 1.
The worm wheel 72 is rotatably supported by the gear housing H2 via the gears 4 and 15, and the inner circumference of the worm wheel 72 is rotatably fitted in the space 4b between the bearings 14 and 15.

As shown in FIG. 1, the speed reduction mechanism 7 is fitted to the worm shaft 70 connected to the output shaft 60 of the electric motor 6 via a joint 8 so as to be integrally rotatable with the second steering shaft 4. The worm wheel 72 is provided. A worm 71 is integrally formed at an axially intermediate portion of the worm shaft 70, and the worm 71 is engaged with the 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. 4).

As shown in FIGS. 1 and 2, a joint 8 connecting the output shaft 60 of the electric motor 6 and the worm shaft 70 includes a first transmission member 81 attached to the output shaft 60 and a first transmission member 81. A second transmission member 82 surrounding the first transmission member 81 with a gap, a third transmission member 83 to which the worm shaft 70 is attached, and a space between the first transmission member 81 and the second transmission member 82 A tubular elastic body 84 interposed,
A torque limiter 85 is provided in a space between the first transmission member 81 and the third transmission member 83.

The first transmission member 81 comprises a short cylinder,
The inner circumference is press-fitted to the outer circumference of the output shaft 60 so as to be integrally rotatable. Flat surfaces 81a parallel to each other are formed at two opposing locations on the outer periphery of the first transmission member 81 (see FIG. 3). The second transmission member 82 is formed of a cylindrical body having a larger diameter and a shorter dimension than the first transmission member 81, and the first transmission member 81 and the first transmission member 81 are surrounded by a gap S1 around the outer periphery of the first transmission member 81. It is arranged concentrically. At two opposing locations on the inner periphery of the second transmission member 82, flat surfaces 82a parallel to each other are formed so as to face the flat surface 81a of the first transmission member 81. Therefore, the relative rotation of the transmission members 81 and 82 by a certain angle or more is restricted by the flat surfaces 81a and 82a.

The third transmission member 83 is formed of a cylindrical body having a larger diameter and a longer length than the second transmission member 82, and the second transmission member 82 is surrounded by a gap S2 around the outer periphery of the second transmission member 82. 82 and concentrically. The worm shaft 70
In FIG. 1, the right end is fitted to the left end on the inner periphery of the third transmission member 83, and the relative rotation between the two is restricted by a rotation preventing means such as serration. A step portion is provided inside the third transmission member 83, and an end surface of the step portion facing the end surface of the second transmission member 82 is configured as a spring receiving portion 83a. The elastic body 84 is formed of a cylindrical body made of rubber or synthetic resin, with its inner periphery adhered to the outer periphery of the first transmission member 81 and its outer periphery adhered to the inner periphery of the second transmission member 82, respectively.
It is interposed in the gap S1.

The torque limiter 85 includes a spring 85a interposed between the one end face 82b of the second transmission member 82 and the spring receiving portion 83a, and a service member as an engagement member engaged with the third transmission member 83. And the clip 85b. The spring 85a is a compression coil spring, and is interposed between the one end face 82b and the spring receiving portion 83a in a state where the spring 85a is elastically contracted by a predetermined amount. The outer peripheral side of the circlip 85b is mounted in an annular groove 83c formed on the inner periphery of the end of the third transmission member 83 on the electric motor 6 side in a state where movement in the circumferential direction is restricted. The peripheral side is slidably contacted with the outer peripheral corner on the other end face 82c side of the second transmission member 82. Thus, the second transmission member 82 is prevented from being pulled out, and the contact surface between the circlip 85b and the second transmission member 82 is
A frictional resistance corresponding to the urging force of the spring 85a is provided.

The torque limiter 85 controls the rotation of the second transmission member 82 to a third transmission member 83 by frictional resistance at the contact surface between the second transmission member 82 and the circlip 85b.
To communicate. The rotation torque transmitted to the third transmission member 83 is a value that is sufficiently larger than the rotation torque required for steering assistance. On the other hand, the failure of the electric motor 6 or the worm shaft 70
If the rotation resistance of the second transmission member 82 or the third transmission member 83 exceeds a predetermined value due to poor rotation of the
By causing a slip on the contact surface between the transmission member 82 and the circlip 85b, the second transmission member 82 and the third transmission member 8
3 and relative rotation. The torque limiter 85 can arbitrarily set the torque transmission value of the torque limiter 85 only by changing the urging force of the spring 85a.

The joint 8 having the above-described configuration transmits the rotation of the output shaft 60 of the electric motor 6 to the second transmission member 82 via the first transmission member 81 and the elastic body 84.
The rotation of the transmission member 82 can be further transmitted to the worm shaft 70 via the torque limiter 85 and the third transmission member 83. At this time, the eccentricity and inclination of the output shaft 60 and the worm shaft 70 can be absorbed or allowed by the elastic body 84. Therefore, there is no need to particularly increase the connection accuracy between the worm shaft 70 and the output shaft 60, and the connection is facilitated. Further, since the rotational vibration of the worm shaft 70 can be absorbed by the elastic body 84, it is possible to prevent the vibration from being transmitted to the steered wheels 1 and reducing the steering feeling. Further, when the electric motor 6 fails and the rotational resistance of the output shaft 60 is abnormally increased, the torque limiter 85 causes the third transmission member 83 and the worm shaft 70 to rotate.
, The operation of the steering wheel 1 does not become abnormally heavy. In addition, the structure is simple, and the total length of the first transmission member 81, the second transmission member 82, the elastic body 84, and the third transmission member 83 is extremely large in combination with the concentric arrangement of each of them. The length can be shortened, and the size of the reduction mechanism 7 can be reduced accordingly.

Further, the joint 8 transmits the rotation of the output shaft 60 by the flat surfaces 81a and 82a of the first transmission member 81 and the second transmission member 82.
Can be further simplified. Also, the second
When the rotation resistance of the transmission member 82 or the third transmission member 83 exceeds the predetermined value and the torque limiter 85 operates, the load is received by the flat surfaces 81a, 82a of the transmission members 81, 82, and the elastic body 84 An excessive load can be prevented from being applied. For this reason, it is possible to prevent the elastic body 84 from being damaged due to an overload, and to improve the durability and reliability of the joint 8.

The worm shaft 70 is disposed so as to be orthogonal to the axis of the second steering shaft 4, and both ends in the axial direction of the worm shaft 70 are connected to the gear housing H 2 via first and second bearings 16 and 17. It is rotatably supported by the first and second bearing holes 91 and 92 (see FIG. 1). The first bearing 16 arranged on the base end side (the electric motor 6 side) of the worm shaft 70 is constituted by a ball bearing, and the second bearing 17 arranged on the tip end side is constituted by a metal bearing. .
The second bearing 17 disposed on the tip side of the worm shaft 70
Is mounted in the second bearing hole 92 so as to be able to be deflected in the direction of the worm wheel 72. That is, FIG.
As shown in FIG. 2, a gap 92a is provided between the inner part of the second bearing hole 92 and the second bearing 17, and
The bearing 17 has the worm wheel 72 for the gap 92a.
You can move to the 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 always urging in the direction
2 is interposed in an elastically contracted state. In the case of the figure,
The compression coil spring 32 is connected to the outer race 17 a of the second bearing 17.
Is housed inside a bottomed cylindrical projection 17b protruding from the outer periphery of. The urging force of the compression coil spring 32 is
The value is adjusted to an optimum value by adjusting the amount of screwing of the plug 34 into the bearing hole 92.

With the above arrangement, the worm shaft 70 can be tilted toward the worm wheel 72 with the joint 8 as the center. Therefore, the worm 71 of the worm shaft 70 can be elastically pressed against the worm wheel 72 by the urging force of the compression coil spring 32. Therefore, even when 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 this wear to prevent backlash. Particularly, in this embodiment, the eccentricity and the tilting of the worm shaft 70 with respect to the output shaft 60 of the electric motor 6 are allowed by the elastic body 84 of the joint 8, and the worm shaft 70 is biased by the compression coil spring 32. Can be easily moved to the worm wheel 72 side, and when the synthetic resin worm wheel 72 expands due to water absorption, heat, or the like, the worm shaft 70 is released to the opposite side of the worm wheel 72 to reduce the rotational torque. It can be prevented from increasing. Further, when the worm shaft 70 moves as described above, the worm shaft 70 is eccentric and tilted with respect to the output shaft 60.
Although the vibration of the worm shaft 70 increases, this vibration can also be effectively attenuated by the elastic body 84. Further, since the worm 71 of the worm shaft 70 can be elastically pressed against the worm wheel 72 as described above, the backlash is adjusted without being affected by a dimensional error of a component including both when the two are assembled. be able to. The worm shaft 70 is constrained by the bearings 16 and 17.
The radial clearance of the worm shaft 7 and the clearance between the bearings 16 and 17 and the worm shaft 70 do not hinder the tilting of the worm shaft 70.

The torque limiter 85 may lock the inner peripheral side of the circlip 85b to the second transmitting member 82 and slidably abut the outer peripheral side to the third transmitting member 83. In this case, the frictional resistance at the contact surface between the circlip 85b and the third transmission member 83 may be used.
This limits the relative rotation between the two.

Further, the torque limiter 85 causes the circlip 85b to have only a function of preventing the second transmission member 82 from being pulled out, and the one end surface of the spring 85a and the second transmission member 82
The rotation of the second transmission member 82 is transmitted to the third transmission member 83 by the frictional resistance between the contact surface of the second transmission member 83 and the contact surface between the other end surface of the spring 85a and the spring receiving portion 83a of the third transmission member 83. You may make it. In this case, the spring 85a and one end face 82b of the second transmission member 82
And at least one of between the spring 85a and the spring receiving portion 83a of the third transmission member 83 to allow relative rotation between the second transmission member 82 and the third transmission member 83. Can be. Further, in the torque limiter 85, one end of the coil wire of the spring 85a may be locked to the second transmission member 82 or the third transmission member 83 so that friction does not occur at the one end.
In short, the torque limiter 85 controls the relative rotation of the transmission members by the frictional resistance of the contact surface between at least one of the second transmission member 82 and the third transmission member 83 and the spring 85a. Good.

Further, the torque limiter 85 uses a screw having abrasion resistance instead of the circlip 85b, and inserts the third transmission member 83 in a state where the screw is screwed into the third transmission member 83. , The tip of which may slidably contact the second transmission member 82,
In this case, the torque transmission value of the torque limiter 85 can be arbitrarily set by adjusting the screwing amount of the screw.

The steering assist device according to the present invention is not limited to the above-described embodiment, but includes, for example, each transmission member 81,
The opposing peripheral surfaces of 82 have a hexagonal cross section, the spring 85a of the torque limiter 85 is formed of a disc spring, etc.
Various design changes can be made. The joint 8 is connected to an output shaft 60 of the electric motor 6 and a worm shaft 70.
Not only can be used as a joint, but also can be used as a joint for connecting the output shaft 60 and various types of rotating shafts driven to rotate by the output shaft 60.

[0032]

As described above, according to the joint of the first aspect, since the structure is simple and small, the output shaft and the rotary shaft of the electric motor can be connected in a small space. Therefore, it is possible to reduce the size and cost of various devices including the electric motor and the rotating shaft. In addition, since the eccentricity and inclination between the output shaft and the rotary shaft of the electric motor can be absorbed or allowed by the elastic body, it is not necessary to align the output shaft and the rotary shaft of the electric motor with high precision. Therefore, the connection between the two becomes easy. Further, even when the rotating shaft vibrates, the vibration can be attenuated by the elastic body, thereby suppressing generation of noise. In addition, when the rotation resistance of the second transmission member or the third transmission member exceeds a predetermined value, the relative rotation of both transmission members can be allowed by the torque limiter.
Even when the rotational resistance of one of the output shaft and the rotating shaft is abnormally increased, it is possible to prevent the electric motor, components connected to the rotating shaft, and the like from being damaged.

According to the joint described in claim 2, since the torque limiter 85 includes the locking member and the spring, the structure can be extremely simplified. Further, the torque transmission value of the torque limiter can be arbitrarily set by changing the biasing force of the spring. According to the joint of the third aspect, the torque limiter faces the end face of the second transmission member and faces the end face of the third transmission member.
Since the spring is interposed between the transmission member and the spring receiving portion, the structure can be further simplified. Further, the torque transmission value of the torque limiter can be arbitrarily set by changing the biasing force of the spring.

According to the joint of the fourth aspect, the first
The transmission member, the second transmission member, the elastic body and the third transmission member are
Since each is composed of cylindrical bodies arranged concentrically, the structure of the joint can be extremely simplified. Claim 5
According to the joint described, the rotation of the first transmission member can be easily and reliably transmitted to the second transmission member via the elastic body by the flat surfaces formed on the first transmission member and the second transmission member. In addition, the structure of the joint can be further simplified. In addition, the load acting on the elastic body when the torque limiter operates is received by the flat surface, so that an excessive load can be prevented from being applied to the elastic body. For this reason, the elastic body can be prevented from being damaged by overload, and the durability and reliability of the joint can be improved.

According to the steering assist device of the sixth aspect, the output shaft of the electric motor and the worm shaft are connected using the joint having a simple structure and a short axial length.
The size and cost of the device can be reduced. In addition, since the eccentricity and inclination between the output shaft and the worm shaft of the electric motor can be absorbed or allowed by the elastic body, it is not necessary to align the output shaft and the worm shaft of the electric motor with high precision. Therefore, the connection between the two becomes easy. Further, even when the worm shaft vibrates, the vibration can be attenuated by the elastic body, so that it is possible to prevent the steering feeling from deteriorating.
Moreover, when the rotation resistance of the second transmission member or the third transmission member exceeds a predetermined value, the relative rotation of both transmission members can be allowed by the torque limiter, so that either one of the output shaft and the worm shaft of the electric motor can be used. Rotation of the other shaft can be allowed even if the rotation resistance of the other shaft abnormally increases. Therefore, even when the rotational resistance of the output shaft of the electric motor abnormally increases, the steering wheel can be operated without any trouble.

According to the seventh aspect of the present invention, since the worm shaft can be biased toward the worm wheel, the worm shaft is eccentric and tilted with respect to the output shaft of the electric motor by the elastic body of the joint. Combined with what is possible, the worm shaft can be moved smoothly towards 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 occurrence of backlash can be easily and reliably prevented.

[Brief description of the drawings]

FIG. 1 is a 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. 2 is a sectional view of a joint.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a sectional view showing the entire structure of the steering assist device according to the present invention.

FIG. 5 is a sectional view taken along line VV of FIG. 1;

FIG. 6 is a cross-sectional view showing a 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) 71 worm 72 worm wheel 8 joint 81 first transmission member 81a flat surface 82 second transmission member 82a flat Surface 82b One end surface of second transmission member 83 Third transmission member 83a Spring receiving portion 84 Elastic body 85 Torque limiter 85a Spring 85b Circling (locking member)

Claims (7)

[Claims] 1. A joint for connecting a rotating shaft to an output shaft of an electric motor so as to be integrally rotatable, comprising: a first transmission member attached to the output shaft so as to be integrally rotatable; A second transmission member that surrounds the first transmission member, an elastic body that is interposed between the first transmission member and the second transmission member, and that transmits rotation of the first transmission member to the second transmission member; A third transmission member connected so as to be integrally rotatable, and restricting relative rotation between the second transmission member and the third transmission member, and when the rotation resistance of the second transmission member or the third transmission member exceeds a predetermined value, the relative A joint comprising a torque limiter that allows rotation. 2. The transmission device according to claim 2, wherein the torque limiter is engaged with one of the second transmission member and the third transmission member.
2. The joint according to claim 1, further comprising: a locking member slidably in contact with the other transmitting member; and a spring for applying frictional resistance to a contact surface between the other transmitting member and the locking member. 3. The second transmission member and the third transmission member are provided with a spring interposed between an end surface of the second transmission member and a spring receiving portion provided on a third transmission member facing the end surface. The joint according to claim 1, wherein relative rotation of the two transmission members is regulated by frictional resistance of a contact surface between at least one of the transmission members and the spring. 4. The joint according to claim 1, wherein the first transmission member, the second transmission member, the elastic body, and the third transmission member are each formed of a concentric cylindrical body. 5. The joint according to claim 4, wherein a flat surface is formed on an outer periphery of said first transmission member and an inner periphery of said second transmission member so as to face each other. 6. 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. A steering assist device, wherein an output shaft of the electric motor and a worm shaft are connected using the joint according to any one of claims 1 to 5. 7. The steering assist device according to claim 6, 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 urging means.