KR20170079875A - Electrical Steering Apparatus and Method to assemble the same - Google Patents

Abstract

The present invention relates to an electric steering apparatus and a method of assembling the same, and more particularly, to a worm wheel unit having a worm wheel gear on its outer periphery and a plurality of worm protrusions on its inner periphery, and a plurality of coupling protrusions engaging with a plurality of worms of the worm wheel unit, A boss inner portion formed in the worm wheel portion and having a through hole through which the steering shaft is fitted and coupled to the worm wheel and the boss inner portion so as to define a gap between the worm projection of the worm wheel portion and the boss inner portion, Or a damper part for reducing an impact, thereby preventing the noise generated during rotation and improving the reliability of the product.

Description

[0001] ELECTRIC STEERING APPARATUS AND METHOD TO ASSEMBLY THE SAME [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electric steering apparatus and a method of assembling the same, and more particularly, to an electric steering apparatus and a method of assembling the same, And more particularly, to an electric steering apparatus and its assembly method in which the structure thereof is improved.

BACKGROUND ART [0002] Generally, a steering apparatus of a vehicle is a device for changing a traveling direction of a vehicle according to a driver's will, and is a device for assisting a driver to advance a vehicle in a desired direction by arbitrarily changing a turning center of a front wheel of the vehicle .

In such a steering apparatus for an automobile, there is an MDPS (Motor-Driven Power Steering) in which the steering force is controlled by a motor. Depending on the driving conditions of the vehicle sensed by various sensors such as a vehicle speed sensor and a steering torque sensor The electronic control unit drives the motor precisely and the torque generated by the motor is transmitted to the steering column or the pinion through the speed reducer to assist the driver in steering the steering wheel connected to the steering column and the pinion.

Accordingly, the electric power steering device provides a light and comfortable steering condition at low speeds, a heavy and stable steering condition at high speeds, a rapid steering operation in response to sudden emergency situations, So as to maintain an optimum steering condition.

Such an electric power steering apparatus can be divided into various types depending on the mounting position. The steering apparatus includes a steering column portion for fixing a steering shaft connecting a steering wheel of a driver's seat and a gear box of a vehicle lower portion to a vehicle body, A gearbox provided with a motor, and the like, and the rotational force of the steering wheel operated by the driver can be transmitted to the rack bar by the motor and the speed reducer.

In a structure in which a reverse input load is introduced due to factors such as impact transmitted from the road surface during the operation of the vehicle in which the electric power steering apparatus of the column type is applied, or a rotational force is transmitted between the gears, In particular, rattle noise is inevitably generated at a portion where the worm shaft and the worm wheel are rotated by the increase in the axial clearance of the worm shaft.

In order to prevent such a phenomenon, a ratchet spring has been used to prevent the worm shaft from being pressed against the worm shaft so as to eliminate a gap between the worm shaft and the worm wheel.

Therefore, the conventional column type electric power steering apparatus generally has a means for preventing the rattling phenomenon as described above. This means is made by compensating the clearance of the worm shaft and the worm wheel gear, and for example, A structure in which a rubber structure is put on both ends or a structure in which the worm wheel is tilted is applied.

Conventional prior art for preventing rattle noise is disclosed in Korean Patent Registration No. 10-0645766, for example, as disclosed in Japanese Patent Application Laid-Open No. 10-0645766, entitled "Rattler Noise Avoiding Type Electric Vehicle Steering Device for Automotive Vehicles (Registered on November 6, 2006) A wedge preventing means for blocking the generation of a gap between a worm shaft rotated by a motor and a worm wheel transmitting steering power for operating a gear box connected to the steering shaft is provided on an end shaft portion of a worm shaft rotated by a motor assisting steering power A tapered slider that is inserted into a space between the inner surface of the housing housing the worm wheel rotated to engage with the worm shaft to transmit the rotational force to the worm shaft and the support bearing to continuously apply a pressing force to the worm shaft, Lt; / RTI >

In the prior art, the prior art is applied to a worm shaft. On the other hand, as another prior art which is applied to a worm wheel, as disclosed in Korean Patent Laid-Open Publication No. 10-2012-0137027, an electric power steering apparatus (published on December 20, 2012) A worm wheel portion having an outer circumferential surface engaged with the worm gear, a hub portion rotated by engaging with an inner circumferential surface of the worm wheel portion, a motor portion rotating the worm shaft portion, and a vibration preventing portion mounted on the hub portion to suppress noise, .

However, since the anti-rattle structure related to the existing worm axis is equipped with the anti-rattle means, the external impact is directly transmitted to the worm shaft because the worm shaft is continuously provided with the pressing force, and the component may be easily damaged by repetitive impact.

In addition, the anti-rattle structure provided in the conventional worm wheel has a structure for suppressing noise by providing a vibration preventing portion having a viscous fluid and a cover tube. However, in this case, when the viscous fluid flows out, There is a fear of loss and it is troublesome to inject viscous fluid from time to time.

Korean Patent Registration No. 10-0645766 (2006.11.06) Korean Patent Publication No. 10-2012-0137027 (2012.12.20)

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and its object is to provide a damper unit of a simple structure to a worm wheel, not a worm shaft, but also to provide a buffer for a load transmitted from a steering shaft and a worm shaft And a method of assembling the same.

According to an aspect of the present invention, there is provided an electric steering apparatus including a worm wheel unit having a worm wheel gear on an outer periphery thereof and a plurality of worm protrusions formed on an inner periphery of the worm wheel unit, A plurality of coupling protrusions formed on an outer circumferential surface of the worm wheel and having a through hole formed therethrough for fitting the steering shaft therebetween; and a plurality of coupling protrusions arranged between the worm protrusions and the coupling protrusions And a damper portion for reducing vibrations or shocks generated when gears are coupled.

Here, the damper portion may include a first damping surface that comes into surface contact with the front end surface of the worm protrusion, a second damping surface that comes in surface contact with the front end surface of the coupling protrusion, and a second damping surface that faces the side surface of the worm projection and the side surface of the coupling protrusion And a third damping surface in contact with the surface at the same time, and a plurality of the first damping surface to the third damping surface may be arranged in a ring shape continuously.

The second damping surface may be formed with an elastic variable groove having a predetermined depth between the third damping surfaces on both sides so that a resiliently deformed volume of the damper portion is moved when the damper is impacted in the rotational direction.

In addition, the damper portion may be made of a rubber material.

In addition, the boss inner portion may include a worm wheel separation preventing surface for preventing axial deviation of the steering shaft of the worm wheel portion when the worm wheel and the coupling protrusion are engaged with each other so that the worm wheel and the coupling protrusion are engaged with each other in the axial direction of the steering shaft. And the damper portion may be assembled such that one side edge of the damper portion is spaced apart from the worm wheel separation preventing surface by a predetermined distance.

The gib bolt inner portion may be provided with a stop step larger than the thickness of the one end of the rim of the damper portion between the worm wheel release preventing surface and one end of the rim of the damper portion.

In addition, the worm wheel portion may be formed with a boss release preventing surface for preventing the boss inner portion, which is received in the insertion portion, from being detached in the insertion direction, and the damper portion may be assembled such that the side edge of the rim is in close contact with the boss deviation preventing surface.

Further, the steering shaft is fitted in the inward direction provided with the boss inner portion from the outside of the worm wheel portion where the boss departure prevention surface is formed, the engagement end is engaged with the outer side surface of the boss departure prevention surface, A flat washer and a C-ring may be interposed between the outer side of the prevention surface and the engagement end of the steering shaft.

According to a first aspect of the present invention, there is provided a method of assembling an electric steering system comprising the steps of: joining a steering shaft into a through hole of an inner boss of a boss; And a plurality of worms formed on an inner periphery of the worm wheel portion, the boss inner portion having the damper portion coupled to the damper portion, the worm wheel having a plurality of worms, Wherein the first damping surface is in surface contact with the front end surface of the coupling protrusion and the third damping surface is brought into surface contact with the side surface of the worm protrusion and the side surface of the coupling protrusion at the same time, And a boss inner-portion bonding step.

According to a second aspect of the present invention, there is provided a method of assembling a motor-driven steering device, the damper including a damper portion having a second damping surface in surface contact with a front end surface of a plurality of coupling protrusions formed on an inner surface of the boss, A plurality of worm protrusions formed on an inner periphery of the worm wheel portion and the boss inner portion coupled with the damper portion are received and coupled to the worm wheel portion such that the plurality of coupling protrusions are engaged with each other, A boss inner engaging step of engaging the boss inner engaging portion so that the third damping surface contacts the side surface of the worm protrusion and the side surface of the engaging projection at the same time in a surface contact manner; And a steering shaft coupling step for coupling the steering shaft.

Since the damper portion is interposed between the worm protrusion of the worm wheel portion and the coupling protrusion of the inner boss portion of the worm wheel, the worm wheel structure can be applied to the worm wheel structure in a simple configuration as compared with the complicated anti-rattle structure provided at both ends of the conventional worm shaft, It has a useful effect.

Further, the present invention has a beneficial effect that the worm wheel structure can be easily assembled to improve productivity, and the shock absorbing function can be performed not only on the load transmitted from the worm shaft but also on the load transmitted from the steering shaft.

In addition, since the second damping surface of the damper portion is provided with the resilient variable groove that is corrugated in the radial direction, it is possible to prevent damage (tear) of the damper portion by absorbing radial impact, thereby improving durability .

1 is a perspective view showing a worm wheel structure of an electric power steering apparatus according to the present invention,
FIG. 2 is a perspective view showing one side and another side of the structure of FIG. 1 in which the worm wheel and the boss inner part are engaged,
FIGS. 3A and 3B are exploded perspective views showing one surface and another surface of the pre-coupling state of FIG. 2,
4 is a cross-sectional view taken along the line AA in Fig. 2,
5 is a cross-sectional view taken along line BB in Fig. 2,
FIG. 6 is a cutaway perspective view taken along line CC of FIG. 2,
7 is an assembly flow chart showing a first embodiment of an assembling method of an electric power steering apparatus according to the present invention,
8 is an assembling flowchart showing a second embodiment of a method of assembling an electric steering system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of an electric power steering apparatus and an assembling method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a worm wheel structure of an electric power steering apparatus according to the present invention. FIG. 2 is a perspective view showing a worm wheel and a boss inner part of the structure of FIG. FIG. 3B is an exploded perspective view illustrating one side and the other side of the pre-engagement state of FIG. 2, FIG. 4 is a cross-sectional view taken along line AA of FIG. 2, FIG. 6 is a cutaway perspective view taken along line CC in FIG. 2; FIG.

First, a preferred embodiment of the electric power steering system according to the present invention will be described.

1, the worm wheel structure of an electric steering system according to the present invention includes a gear tooth 22 of a worm gear 20 connected to a rotating shaft of an electric motor (not shown) in a speed reducer case 10, Respectively.

1 to 6, a worm wheel gear 31, which meshes with the gear teeth 22 of the worm gear 20 described above, is mounted on the outer periphery of the worm wheel gear 31 A worm wheel portion 30 having a plurality of worm protrusions 34 formed on its inner periphery and a plurality of coupling protrusions 44 engaging with a plurality of worm protrusions 34 of the worm wheel portion 30 are formed on the outer circumferential surface, A boss inner portion 40 having a through hole 41 into which the steering shaft 80 is fitted and a boss inner portion 40 formed between the worm projection 34 of the worm wheel portion 30 and the coupling protrusion 44 of the boss inner portion 40, And a damper unit 50 for reducing vibrations or shocks generated during gear engagement between the worm protrusions 34 and the engagement protrusions 44.

Here, the structure constituted by the worm wheel portion 30, the boss inner portion 40 and the damper portion 50 can be referred to as a worm wheel structure (not shown) for convenience.

1 to 3B, a worm wheel gear 31 is formed on the outer circumferential surface of the worm wheel portion 30 so as to mesh with a gear tooth 22 formed on the outer periphery of the worm gear 20.

The worm wheel 30 has a boss inner portion 40 at its center and a through hole 32 for insertion of a steering shaft 80 to be described later. The plurality of worm protrusions 34 are formed so as to protrude toward the center of the through-hole 32 in the inner periphery corresponding to the inner circumference of the through-

The worm wheel 30 includes a boss departure prevention surface 37 for preventing the boss inner portion 40 from being separated from the through hole 32 in the fitting direction with respect to either the one end or the other end of the through hole 32 May be formed.

3B, the boss departure prevention surface 37 has an inner diameter extending a predetermined length from the inner diameter of the through hole 32 toward the center of the boss. The outer diameter of the boss inner diameter portion 40 is smaller than the outer diameter of the boss inner portion 40, May be formed in the shape of a hole having an inner diameter larger than the inner diameter of the through hole 41 formed in the inner portion 40.

The boss inner portion 40 is formed with the aforementioned through hole 41 having an inner circumferential surface in which the steering shaft 80 is forcedly inserted at the center thereof and the inner circumferential surface of the through hole 41 is provided with a plurality of A plurality of engagement protrusions 44 capable of interlocking with the worm protrusions 34 can be formed.

3A and 5, the plurality of coupling protrusions 44 includes a first protrusion 42 through which the damper portion 50 is inserted to absorb the impact, and a second protrusion 42 through which the damper portion 50 is directly inserted And a second projection 43 that is in contact with the plurality of worms 34.

The damper portion 50 is formed so as to be interposed between the first projection 42 and the second projection 43. The height of the damper portion 50 is smaller than the thickness of the edge of the damper portion 50, A portion 47 may be provided.

The engagement step 47 serves to divide the first protrusion 42 and the second protrusion 43 and divide the boundary between the first protrusion 42 and the second protrusion 43 so that one end of the rim of the damper portion 50 is closely contacted and supported. Further, the other side edge of the damper portion 50 can be closely contacted with the boss deviation preventing surface 37 described above.

That is, the engagement stepped portion 47 is formed so as to be stepped on the boss inner portion 40 between the worm wheel separation preventing surface 48, which will be described later, and the one side edge of the damper portion 50, And the boss deviation preventing surface 37 is formed in the worm wheel portion 30 and serves to support the other side edge of the damper portion 50 in close contact with each other.

A worm wheel separation preventing surface 48 may be formed on the outer surface of the boss inner portion 40 where the second protrusion 43 is formed to prevent the axial deviation of the steering shaft 80 of the worm wheel 30 .

The worm wheel deviation preventing surface 48 is formed so as to have the same outer diameter as the outer diameter of the second projections 43 among the plurality of coupling projections 44 and has a shape that fills an empty space between adjacent second projections 43 As shown in FIG.

3B and 5, the worm wheel separation portion 48 is in contact with one side surface of the plurality of worm bosses 34 so that the worm wheel portion 30 is separated from the axial deviation of the steering shaft 80 .

When the boss inner portion 40 is received in the worm wheel portion 30, the outer surface of the boss inner portion 40 facing the outer surface of the boss release preventing surface 48 37 may be formed at the fixed end 49 protruding through the through-hole. The fixed end 49 is a portion where a flat washer 60 and a seed ring 70 to be described later are fixed. This will be described later in detail.

The damper portion 50 is interposed between the worm protrusion 34 of the worm wheel portion 30 and the coupling protrusion 44 of the boss inner portion 40 so that the gear meshing of the worm wheel portion 30 and the boss inner portion 40 Thereby reducing vibrations or shocks generated between the worm protrusions 34 and the engagement protrusions 44 during the rotation operation.

More specifically, as shown in Fig. 4, the damper portion 50 includes a first damping surface 55 in surface contact with the distal end surface 34a of the worm protrusion 34, A third damping surface 54 which comes into surface contact with the front end surface 44a and a third damping surface 54 which comes into surface contact with the side surfaces 34b and 34c of the worm projection 34 and the side surfaces 44b and 44c of the engagement protrusion 44, Damping surface 56 may be included. Here, a plurality of the first damping surface 55 to the third damping surface 56 may be arranged in a ring shape continuously.

The first damping surface 55 is disposed so as to define a front end surface 34a of the worm projection 34 of the worm wheel portion 30 and a part of the outer circumferential surface 40a of the boss inner portion 40, The shock at the time of radial direction of the boss inner portion 40 (that is, reference numeral "A" in FIG. 4) is elastically deformed and absorbed to reduce vibration or impact.

The second damping surface 54 is disposed so as to define a front end surface 44a of the engagement protrusion 44 of the boss inner portion 40 and a part of the inner peripheral surface 32a of the through hole 32 of the worm wheel 30, Like the damping surface 55, absorbs the impact when it is in the radial direction (A) while being elastically deformed, thereby reducing vibration or impact.

The third damping surface 56 is disposed so as to partition each side of both ends of the worm projection 34 of the worm wheel portion 30 and each side of both ends of the engagement projection 44 of the boss inner portion 40, ) And the boss inner portion 40 (see the reference numeral "b" in FIG. 4), the shock due to the engagement of the respective gears is absorbed while being elastically deformed to reduce vibration or impact.

The first damping surface 55 preferably has a thickness such that the front end surface 34a of the worm projection 34 of the worm wheel portion 30 and the outer circumferential surface 40a of the boss inner portion 40 are pressed on both surfaces Do. The second damping surface 54 is spaced a predetermined distance between the inner circumferential surface 32a of the through hole 32 of the worm wheel portion 30 and the tip end surface 44a of the coupling protrusion 44 of the boss inner portion 40 It is preferable to have a thickness to be arranged.

This somewhat alleviates the impact upon radial clearance of the worm wheel portion 30 and the boss inner portion 40 through the first damping surface 55 while the second damping surface 54 has a volume fraction So that the damper unit 50 is prevented from being torn and broken.

More preferably, the third damping surface 56 is also formed on the side surfaces 34b, 34c of the worm projection 34 of the worm wheel portion 30 and the side surfaces 44b, 34c of the engagement projection 44 of the boss inner portion 40, And 44c.

The damper portion 50 may be formed in a linear shape such that the second damping surface 54 interconnects the third damping surfaces 56 on both sides as shown in Figure 4, At least one concave elastic deforming groove 57a and 57b may be formed between the third damping surface 56 of the first and second damping surfaces 56a and 57b.

The elastic variable grooves 57a and 57b are formed in such a manner that a part of the elastically deformed volume of the damper portion 50 when the shock in the rotational direction is applied to the inner peripheral surface 32a of the through hole 32 of the worm wheel portion 30 and the inner peripheral surface 32a of the boss inner portion 40 So that it can be easily moved between the distal end surfaces 44a of the engagement projections 44. [

By providing such resilient variable grooves 57a and 57b, the damper portion 50 can be prevented from being damaged by absorbing the impact while a part of the volume of the damper portion 50 is moved. As a result, the durability of the product can be improved .

The damper portion 50 may be made of a rubber material capable of elastically deforming to absorb a rotational impact between the worm wheel portion 30 and the boss inner portion 40 and to facilitate the movement of a part of the volume. However, it should be noted that the present invention is not necessarily limited to the rubber material, and thus the true scope of the present invention should not be limited.

The damper portion 50 is coupled to receive the plurality of coupling protrusions 44 of the boss inner portion 40 before the boss inner portion 40 is received in the worm wheel portion 30, When the boss inner portion 40 is engaged with the worm wheel portion 30, the worm protrusion 34 of the worm wheel portion 30 and the coupling protrusion 44 of the boss inner portion 40 are partitioned to perform the damping function .

5 and 6, the damper portion 50 is primarily engaged so that one end of the rim is closely contacted with the engagement stepped portion 47 formed on the boss inner portion 40, When the worm wheel 30 is received and engaged with the worm wheel 30, the other end of the worm wheel 40 is tightly coupled to the inside of the boss deviation preventing surface 37 formed in the worm wheel 30.

When the boss inner portion 40 coupled to the damper portion 50 is received in the worm wheel portion 30 as described above, the fixed end 49 of the boss inner portion 40 is fixed to the other side of the through- The length protrudes.

The flat washer 60 is fixed to the fixed end 49 on the outer side of the worm wheel portion 30 and particularly on the outer side of the boss deviation preventing surface 37 and the shearing 70 is provided on the outer side of the fixed end 49, The inner end of the flat washer 60 is overlapped with the inner end of the flat washer 60 so that the boss inner portion 40 is firmly fixed to the worm wheel 30.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method of assembling an electric power steering apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 7 is an assembling flowchart showing a first embodiment of a method for assembling an electric power steering apparatus according to the present invention, and FIG. 8 is an assembling flowchart showing a second embodiment of a method for assembling an electric power steering apparatus according to the present invention.

The first embodiment of the assembling method of the electric power steering apparatus according to the present invention is characterized in that as shown in Fig. 7, in the steering shaft coupling step (step) of inserting the steering shaft 80 into the through hole 41 of the boss inner portion 40 And a damper part engaging step of engaging the damper part 50 so that the second damping surface 54 is in surface contact with the front end surface 44a of the plurality of engaging projections 44 formed on the boss inner part 40, The boss inner portion 40 to which the damper portion 50 is coupled is received and coupled to the worm wheel portion 30 such that a plurality of worms 34 formed on the inner periphery of the worm wheel portion 30 and a plurality of engagement protrusions 44 are engaged with each other. The first damping surface 55 is in surface contact with the tip end surface 44a of the coupling projection 44 and the side surfaces 34b and 34c of the worm projection 34 and the side surfaces 44b and 44c of the coupling projection 44 And the boss inner portion 40 is brought into contact with the third damping surface 56 so that the third damping surface 56 is in surface contact with the inner surface of the boss inner portion 40 at the same time.

The second embodiment of the method for assembling an electric steering system according to the present invention is characterized in that a second damping is applied to the front end surface 44a of a plurality of coupling projections 44 formed on the boss inner portion 40, A damping portion engaging step of engaging the damper portion 50 so that the surface 54 of the worm wheel portion 30 is in surface contact with the boss inner portion 40 of the damper portion 50; The first damping surface 55 is in surface contact with the distal end surface 44a of the coupling protrusion 44 so that the protrusion 34 and the plurality of coupling protrusions 44 are engaged with the worm wheel 30, The boss inner portion 40 is engaged with the side surfaces 34b and 34c of the protrusion 34 and the side surfaces 44b and 44c of the coupling protrusion 44 so that the third damping surface 56 is in surface- And a steering shaft coupling step of inserting the steering shaft (80) into the through hole (41) of the boss inner portion (40).

The difference between the assembling method according to the first embodiment and the assembling method according to the second embodiment is that the steering shaft 80 is engaged with the through hole 41 of the boss inner portion 40, same.

The assembling method of the second embodiment is characterized in that the steering shaft 80 is press-fitted into the through hole 41 of the boss inner portion 40 at the last stage and various tests of the worm wheel itself are performed before the joining of the steering shaft 80 There is an advantage that the defective rate of the product can be lowered.

Various embodiments of the electric power steering apparatus and the assembling method thereof according to the present invention have been described in detail with reference to the accompanying drawings. It should be understood, however, that the embodiments of the present invention are not necessarily limited to the above-described embodiments, and that various modifications and equivalents may be made by those skilled in the art to which the present invention pertains will be. Therefore, it is to be understood that the true scope of the present invention is defined by the appended claims.

10: Reducer case 20: Worm gear
22: gear teeth 30: worm wheel part
31: Worm wheel gear 32: Through hole
34: Worm projection 37: Boss deviation prevention surface
40: boss inner part 41: through hole
44: engagement projection 47: engagement step
48: worm wheel deviation prevention surface 50: damper portion
60: Flat washer 70: Sealing
80: Steering axis

Claims (10)

A worm wheel portion having a worm wheel gear formed on an outer periphery thereof and having a plurality of worm protrusions formed on its inner periphery;
A boss inner portion having a plurality of coupling projections formed on an outer circumferential surface thereof to engage with a plurality of worms of the worm wheel portion and having a through hole into which the steering shaft is fitted;
And a damper portion arranged to partition between the worm protrusions of the worm wheel portion and the coupling protrusions of the boss inner portion to reduce vibration or impact generated when gears are engaged between the worm protrusions and the coupling protrusions. The method according to claim 1,
In the damper portion,
A first damping surface in surface contact with a distal end surface of the worm projection;
A second damping surface in surface contact with a distal end surface of the coupling protrusion;
And a third damping surface simultaneously in surface contact with the side surface of the worm projection and the side surface of the engagement projection,
Wherein the first damping surface to the third damping surface are arranged in a ring shape continuously. The method according to claim 1,
And an elastic variable groove having a predetermined depth is recessed in the second damping surface between the third damping surfaces on both sides so that a resiliently deformed volume of the damper portion is moved when the damper is impacted in the rotating direction. The method according to claim 1,
Wherein the damper portion is made of a rubber material. The method according to claim 1,
The boss inner portion is inserted and received so that the worm protrusion of the worm wheel portion and the coupling protrusion are engaged with each other in the axial direction of the steering shaft and a worm wheel separation preventing surface for preventing the axial deviation of the steering shaft Formed,
Wherein the damper portion is assembled so that one end of the rim is spaced apart from the worm wheel separation preventing surface by a predetermined distance. The method of claim 5,
Wherein the boss inner portion is provided between the worm wheel deviation preventing surface and one end of the rim of the damper portion and has a stop step larger than the thickness of one end of the rim of the damper portion. The method of claim 5,
Wherein the worm wheel portion has a boss separation preventing surface for preventing the boss inner portion,
Wherein the damper portion is assembled so that a side edge of the rim is in close contact with the boss deviation preventing surface. The method of claim 5,
Wherein the steering shaft is fitted in an inward direction provided with the boss inner surface from an outer side where the boss deviation preventing surface of the worm wheel portion is formed, and a locking step is engaged with an outer surface of the boss deviation preventing surface,
Wherein a flat washer and a C-ring are interposed between the outer side of the boss deviation preventing surface and the engagement end of the steering shaft. A steering shaft coupling step of inserting and coupling the steering shaft into the through hole of the boss inner part;
A damper portion engaging step of engaging a damper portion so that a second damping surface is in surface contact with a distal end face of a plurality of engaging projections formed on the boss inner portion;
Wherein the boss inner portion coupled with the damper portion is received and coupled to the worm wheel portion such that a plurality of worm protrusions formed on the inner periphery of the worm wheel portion and the plurality of coupling protrusions are engaged with each other, the first damping surface is in surface contact with the distal end surface of the coupling protrusion, And a boss inner engaging step of engaging the boss inner part so that the third damping surface contacts the side surface of the worm protrusion and the side surface of the engaging projection simultaneously. A damper part engaging step of engaging the damper part such that the second damping surface is in surface contact with the distal end surface of a plurality of engaging projections formed on the boss inner part;
Wherein the boss inner portion coupled with the damper portion is received and coupled to the worm wheel portion such that a plurality of worm protrusions formed on the inner periphery of the worm wheel portion and the plurality of coupling protrusions are engaged with each other, the first damping surface is in surface contact with the distal end surface of the coupling protrusion, A boss inner engaging step of engaging the boss inner engaging portion so that the third damping surface contacts the side surface of the worm protrusion and the side surface of the engaging projection at the same time;
And a steering shaft coupling step of inserting and coupling a steering shaft into the through hole of the boss inner portion.

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