JP2003194190A - Reduction gear and motor-driven power steering device including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem with a reduction gear: that, when a synthetic resin is used for the teeth of a worm wheel and the teeth are engaged with a metallic worm, teeth sounds caused by a backlash will occur and the need to strictly control the backlash arises; for this, the gears are grouped according to dimensional tolerance and matching groups are combined, but these operations are very troublesome and the backlash is clogged by the temperature expansion of the synthetic resin. <P>SOLUTION: The worm 19 has a columnar core 22 and a synthetic resin member 24 for molding the core 22. The core 22 has a shank 25. Irregularities such as indentations 28 are formed on the peripheral surface of the shank 25 to secure the strength of connection between the core 22 and the synthetic resin member 24, mainly in the direction of rotation of the worm 19. Flanges 26 for receiving the end face of the synthetic resin member 24 are formed at each end of the core 22. An axial force produced by engagement reaction is received by the flanges 26. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a worm speed reducer for transmitting the rotation of a worm shaft to a worm wheel to reduce the speed.
And an electric power steering apparatus using the same.

[0002]

2. Description of the Related Art Generally, in an electric power steering apparatus, the rotation of an electric motor for steering assist is decelerated through a speed reducer and transmitted to a steering mechanism such as a rack and pinion mechanism. ing. As the speed reducer, a speed reducer having a worm and a worm wheel is often used. Conventionally, in this type of speed reducer, a worm wheel made of a synthetic resin is used in combination with a worm made of a metal in order to reduce noise associated with gear meshing.

On the other hand, a proper backlash is required for the meshing of the worm and the worm wheel, but when running on a bad road, for example, a rattling noise may be generated due to the backlash. In order to prevent the rattling noise, it is necessary to strictly adjust the amount of backlash generated between the worm and the worm wheel within the range of machining accuracy. Conventionally, when assembling a worm and a worm wheel, each part is selected according to the degree of variation in dimensional accuracy, and the ones with the correct combination accuracy are combined (so-called matching assembly). It takes a lot of work.

Further, when the worm wheel made of synthetic resin, which has a larger diameter than the worm, expands in temperature, backlash is reduced and the rotational resistance of the gear is increased. The present invention has been made in view of the above problems,
An object of the present invention is to provide a speed reducer that can reduce noise and is easy to assemble, and an electric power steering apparatus including the speed reducer.

[0005]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the invention according to claim 1 is a speed reducer for reducing the rotation of a worm by means of a worm wheel. A reduction gear having a cored bar along a central axis and a synthetic resin member that molds the cored bar and forms at least a tooth portion, and has irregularities formed on a peripheral surface of the cored bar.

In the present invention, since the teeth of the worm are made of synthetic resin, noise can be reduced. In addition, due to the unevenness provided on the peripheral surface of the cored bar, the bonding strength between the cored bar and the synthetic resin member can be increased, and by extension, sufficient strength as a worm can be obtained. Further, since the worm has a small diameter, the amount of thermal expansion is small even if a synthetic resin is used for a part of the worm. Therefore, the backlash is less likely to be packed due to the temperature expansion.

According to a second aspect of the present invention, in the first aspect, the irregularities include serrations. By the serration, it is possible to reliably prevent the shift in the rotational direction between the core metal and the synthetic resin member. Also,
If it is serration, it can be easily molded on the surface of the core bar,
Manufacturing costs can be reduced. According to a third aspect of the present invention, in the first or second aspect, a flange-shaped portion that restricts axial movement of the synthetic resin member is formed at an end portion of the core metal. A large meshing reaction force is applied to the worm in its axial direction, but this can be received by the collar-shaped portion, and a high bonding strength between the core metal and the synthetic resin member can be secured.

According to a fourth aspect of the present invention, in the first, second or third aspect, the tooth portion of the worm wheel is made of synthetic resin. In this case, since the synthetic resins mesh with each other, the noise can be significantly reduced without controlling the backlash so strictly. As a result, it is possible to alleviate or eliminate so-called matching assembly for backlash management. According to a fifth aspect of the present invention, in the first, second or third aspect, the tooth portion of the worm wheel is made of metal. In this case, it is possible to achieve meshing by a combination of a synthetic resin and a metal, which has already been proven, and it is possible to improve reliability.

According to a sixth aspect of the present invention, there is provided an electric power steering apparatus characterized in that the rotation of an electric motor for steering assistance is reduced by the speed reducer according to any one of the first to fifth aspects. . According to the present invention, in the electric power steering apparatus, the same effect as that of any one of the first to fifth aspects can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus including a speed reducer according to an embodiment of the present invention. Referring to FIG. 1, the electric power steering apparatus 1 includes a steering shaft 3 connected to a steering wheel 2, a pinion gear 4 provided at a tip end portion of the steering shaft 3, and a rack gear 5 meshing with the pinion gear 4. And a rack bar 6 extending in the left-right direction of the vehicle.

Tie rods 7 are respectively connected to both ends of the rack bar 6, and each tie rod 7 is connected to a corresponding wheel 8 via a corresponding knuckle arm (not shown). When the steering wheel 2 is operated and the steering shaft 3 is rotated, this rotation is converted by the pinion gear 4 and the rack gear 5 into a linear movement of the rack shaft 6 along the left-right direction of the vehicle. As a result, steering of the wheels 8 is achieved.

The steering shaft 3 is divided into a first steering shaft 9 as a cylindrical input shaft connected to the steering wheel 2 and a second steering shaft 10 as an output shaft connected to the pinion gear 4. The first and second steering shafts 10 are connected to each other on the same axis via a torsion bar 11. A torque sensor 12 is provided which detects a steering torque based on a relative rotational displacement amount between the first steering shaft 9 and the second steering shaft 10 via the torsion bar 11. The torque detection result of the torque sensor 12 is a control unit. Given to 13. The control unit 13 controls the voltage applied to the steering assist electric motor 15 via the driver 14 based on the torque detection result. The rotation of the rotating shaft 16 (see FIG. 2) of the electric motor 15 is transmitted to the second steering shaft 10 via the speed reducer 17 to assist the steering.

Referring to FIG. 2, the speed reducer 17 is integrally rotatably connected to the rotary shaft 16 of the electric motor 15 via a joint mechanism using a spline 18, for example.
9 and a worm wheel 20 as a reduction gear that meshes with the worm 19. The first and second end portions 19a and 19b of the worm 19 in the axial direction correspond to the corresponding first
And the second bearings 41 and 42, respectively, so that the reduction gear housing 40 is rotatably supported.

The first and second bearings 41 and 42 are held in corresponding bearing holding holes 43 and 44 of the reduction gear housing 40, respectively. Further, 45 is a screw member for adjusting the preload. The screw member 45 is screwed into a screw hole 46 formed so as to be continuous with the bearing holding hole 44, thereby applying a preload to the first and second bearings 41 and 42, and
Position the worm 19 axially. Reference numeral 47 is a lock member for fixing the screw member 45 after adjustment.

With reference to FIGS. 3A and 3B, the worm 19 has a cylindrical or cylindrical cored bar 22 along a central axis 21 of the worm 19, and the cored bar 22 molded into at least a tooth. And a synthetic resin member 24 forming the portion 23. The cored bar 22 is inserted into the mold when the synthetic resin member 24 is molded with resin. The synthetic resin member 24 is made of, for example, polyacetal resin (POM) or polyamide resin (PA: nylon).

The core metal 22 has a shaft portion 25, and the shaft portion 25
Has brim-shaped portions 26 made of, for example, annular flanges at both ends thereof. A synthetic resin member 24 having a diameter substantially the same as that of the collar-shaped portion 26 is disposed between these collar-shaped portions 26. Each end surface 27 of the synthetic resin member 24 is along the corresponding collar-shaped portion 26, and the axial load applied to the worm 19 is applied to the collar-shaped portion 2.
It is supposed to be received by 6. For example, serrations 28 are formed on the peripheral surface of the shaft portion 25 as irregularities, and particularly the coupling strength between the synthetic resin member 24 and the cored bar 22 is increased in the rotation direction of the worm 19.

On the other hand, the worm wheel 20 is integrally rotatably connected to the second steering shaft 10 and has a tooth portion 2 on its outer periphery.
It is made of a metal member such as iron which forms 9. According to the present embodiment, since the tooth portion 23 of the worm 19 is formed of the synthetic resin member 24, noise can be reduced. The mesh between the worm 19 and the worm wheel 20 is a combination of a synthetic resin and a metal such as iron, and this combination has a proven record and is highly reliable.

Further, with respect to the rotating direction of the worm 19, there are irregularities such as serrations 28 provided on the peripheral surface of the cored bar 22, and in the axial direction of the worm 19, the cored bar 2 is provided.
By the collar-shaped portions 26 provided at both ends of the core 2,
It is possible to increase the bonding strength between the synthetic resin member 24 and
As a result, sufficient strength can be obtained as the worm 19. In particular, when the serration 28 is used as the unevenness, it can be easily formed on the surface of the cored bar 22 and the manufacturing cost can be reduced.

Furthermore, since the pitch circle diameter of the worm 19 is much smaller than that of the worm wheel 20, even if a part of the worm 19 is made of synthetic resin,
The amount of temperature expansion is small. Therefore, the backlash is less likely to be packed due to the temperature expansion. The transmission 17 can be suitably used for the electric power steering apparatus 1 because of the above-described effects.

In the above embodiment, the worm wheel 20 made of synthetic resin may be used in place of the worm wheel 20 made of metal. Specifically, referring to FIG. 4, this worm wheel 20
A includes an annular cored bar 30 that is integrally rotatably coupled to the second steering shaft 10, and a synthetic resin member 32 that surrounds the cored bar 30 and forms teeth 31 on the outer periphery thereof. The cored bar 30 is, for example, inserted into the mold during resin molding of the synthetic resin member 32. The synthetic resin member 32 is made of, for example, polyacetal resin (POM) or polyamide resin (PA: nylon).

In the present embodiment, the mesh between the worm 19 and the worm wheel 20A is a combination of the synthetic resins, and the noise reduction effect can be greatly enhanced, so that the backlash is not so strictly controlled. Get better. As a result, so-called matching assembly for backlash management can be alleviated or eliminated, and the manufacturing cost can be significantly reduced. The present invention is not limited to the above-described embodiment, and for example, knurls or the like may be provided as the irregularities formed around the cored bar 22 of the worm 19.

The brim-shaped portion 26 of the cored bar 22 does not have to be annular. Further, the collar portion 26 may be molded in the synthetic resin member 24. Further, the collar portion 26 can be omitted. Besides, various modifications can be made within the scope of the claims of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus including a speed reducer according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of the electric power steering apparatus.

FIG. 3A is a schematic side view of a worm, and FIG.
FIG. 3 is a schematic side view of a cored bar.

FIG. 4 is a sectional view of a main part of an electric power steering apparatus including a speed reducer according to another embodiment of the present invention.

[Explanation of symbols]

1 Electric power steering device 3 steering shaft 15 Electric motor 16 rotation axes 17 Reduction gear 19 Warm 20,20A worm wheel 21 central axis 22 core metal 23 Tooth 24 Synthetic resin material 25 Shaft 26 Collar 27 Edge 28 Serration 29 teeth 30 core 31 teeth 32 Synthetic resin material

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Claims (6)

[Claims] 1. A speed reducer for reducing the rotation of a worm by means of a worm wheel, wherein the worm includes a core metal along a central axis of the worm, and a synthetic resin for molding the core metal and forming at least tooth portions. And a member,
A speed reducer characterized in that irregularities are formed on the peripheral surface of a cored bar. 2. The speed reducer according to claim 1, wherein the irregularities include serrations. 3. The speed reducer according to claim 1 or 2, wherein a brim-shaped portion for restricting axial movement of the synthetic resin member is formed at an end portion of the core metal. 4. A speed reducer according to claim 1, 2 or 3, wherein the teeth of the worm wheel are made of synthetic resin. 5. A speed reducer according to claim 1, 2 or 3, wherein the teeth of the worm wheel are made of metal. 6. The rotation of an electric motor for assisting steering according to claim 1.
An electric power steering apparatus, characterized by being decelerated by the speed reducer according to any one of claims 1 to 5.