JP2008062717A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device allowing the miniaturizing of a speed reduction mechanism, reducing costs, and ensuring silence. <P>SOLUTION: This device is provided with a driving gear 14 connected to an electric motor 6, and a driven gear 15 having an annular tooth portion 15a formed with in its peripheral surface gear teeth meshed with the driving gear 14 and a boss portion 15b integrally connected to the inner periphery of the tooth portion 15a and coupled to a steering shaft 4. Steering assisting force is applied by rotation of the electric motor 6. The tooth portion 15a and boss portion 15b of the driven gear 15 are formed from sintered metal having mutually different density, and the tooth portion 15a is finished with forging. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering device that is mounted on a vehicle such as an automobile and assists a driver's steering operation using an electric motor.

  An electric power steering apparatus for a vehicle includes an electric motor for assisting steering and a speed reduction mechanism that decelerates and transmits the rotational force of the electric motor to the steering means, and the operation of the steering means according to the rotation of the steering means. Is assisted by the rotation of the electric motor to reduce the labor burden of the driver for steering.

A reduction mechanism for a column type or pinion type electric power steering apparatus includes a worm shaft as a drive gear having a base end connected to the output shaft of the electric motor and a worm provided on the outer periphery thereof, and a worm shaft of the worm shaft. A worm gear having a worm wheel as a driven gear coupled to a steering shaft is employed. And as said worm wheel, what integrated the tooth part which forms a gear tooth on the outer peripheral surface made of resin (MC (monomer cast) nylon, polyamide 66, etc.) on the outer periphery of a metal core tube It is used, and noise countermeasures are taken by meshing a metal worm shaft and resin gear teeth (see, for example, Patent Document 1).
On the other hand, the number of vehicles equipped with electric power steering devices is increasing year by year, and column-type electric power steering devices are also being installed in high-end models with a displacement of 2000 cc or more.
JP 2006-44306 A

In order to cope with higher output in the electric power steering device of Patent Document 1, it is necessary to increase the size of the speed reduction mechanism, but considering the vehicle mounting layout, the size increase of the speed reduction mechanism is in a very severe state. . In addition, since a high-grade resin material is used as the tooth portion of the worm wheel, there is a problem that the cost is high.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electric power steering device capable of reducing the size and cost of the speed reduction mechanism and ensuring quietness.

In order to achieve the above object, the present invention takes the following technical means.
That is, the electric power steering device of the present invention includes a drive gear connected to the electric motor,
An annular tooth portion formed on the outer peripheral surface of the gear teeth meshing with the drive gear, and a driven gear having a boss portion integrally connected to the inner periphery of the tooth portion and connected to the steering shaft. ,
In the electric power steering device that applies steering assist force by rotation of the electric motor,
The tooth part and the boss part of the driven gear are formed of sintered metals having different densities, and the tooth part is finished by forging.

  According to this structure, since the tooth | gear part of a driven gear is formed with the sintered forging metal, since strength and toughness improve and allowable load goes up, it can reduce in size compared with resin-made tooth parts. . In addition, since the tooth portion is manufactured by sintering forging, materials and processing steps can be reduced, thereby reducing cost. Furthermore, using a sintered metal with high vibration damping characteristics as the driven gear, and further varying the density of the tooth part and the boss part can suppress the propagation of vibration and noise, thereby enhancing the vibration isolation effect Can do.

  In the electric power steering apparatus, it is preferable that the density of the tooth portion of the driven gear is higher than the density of the boss portion. In this case, the strength of the tooth portion can be further improved.

  According to the electric power steering apparatus of the present invention, it is possible to reduce the size and cost of the speed reduction mechanism and to ensure quietness.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a main configuration of a power steering apparatus according to an embodiment of the present invention.
The power steering device PS includes a first steering shaft 2 to which a steering wheel (steering wheel) 1 is attached at the upper end, and a cylindrical second steering shaft connected to the lower end of the first steering shaft 2 via a torsion bar 3. 4, a torque sensor 5 that detects a steering torque based on a relative rotational displacement amount between the first steering shaft 2 and the second steering shaft 4, a detection result of the torque sensor 5, a vehicle speed, and a steering angle of the steering wheel 1. The steering assisting electric motor 6 driven on the basis of the above and a reduction mechanism A for reducing the rotation of the electric motor 6 and transmitting it to the second steering shaft 4 are provided.
The first steering shaft 2 is supported by being surrounded by a first steering column 7 and a second steering column 8, and the first steering column 7 is attached to the vehicle body via a bracket (not shown). The torque sensor 5 is accommodated in a sensor housing 9. The speed reduction mechanism A is accommodated in the gear housing 10, and the electric motor 6 is attached to the gear housing 10.

  The first steering shaft 2 is integrally formed with a cylindrical first shaft body 2a having the steering wheel attached to an upper end portion thereof and a movement of the first shaft body 2a on the lower end portion of the first shaft body 2a with axial movement permitted. A rod-shaped second shaft body 2b fitted rotatably is provided, and a cylindrical third shaft body 2d connected to the second shaft body 2b by a pin 2c. The intermediate portion of the first shaft body 2 a is rotatably supported by a cylindrical first steering column 7 via a bearing 11. In addition, a buffer member 2e made of a synthetic resin is provided between the first and second shaft bodies 2a and 2b for absorbing impact energy acting on the steering wheel 1 from the driver at the time of a car collision or the like. . Further, the torque sensor 5 is provided between the third shaft body 2 d and the second steering shaft 4.

The second steering column 8 has an upper end portion slidably fitted to the first steering column 7 and a lower end portion fitted to the sensor housing 9, and when absorbing the impact energy, One steering column 7 can be moved in the axial direction with respect to the second steering column 8.
A torsion bar 3 is introduced into the second steering shaft 4, and a lower end portion of the second steering shaft 4 is connected to the torsion bar 3 by a pin 4a so as to be integrally rotatable. An intermediate portion of the second steering shaft 4 in the axial direction is rotatably supported by the gear housing 10 via a pair of bearings 12 and 13, and a worm described later is interposed between the bearings 12 and 13. The inner periphery of the wheel 15 is fitted so as to be integrally rotatable.

As shown in FIG. 2, the speed reduction mechanism A is a worm as a driving gear whose base end portion is connected to the output shaft 6 a of the electric motor 6 and is orthogonal to the axis of the second steering shaft 4. The worm is constituted by a shaft 14 and a worm wheel 15 as a driven gear fitted to the second steering shaft 4 so as to be integrally rotatable. The worm is integrally formed at the axial intermediate portion of the outer periphery of the worm shaft 14. 14 a is engaged with the worm wheel 15.
Therefore, a steering torque based on the relative rotational displacement between the third shaft body 2d and the second steering shaft 4 is detected by the torque sensor 5, and the electric motor 6 is driven based on the detection result of the torque sensor 5. The rotation of the electric motor 6 is decelerated by the worm 14 a and the worm wheel 15 and transmitted to the second steering shaft 4. Then, the rotation of the second steering shaft 4 is transmitted to, for example, a rack and pinion type steering means connected to the wheels via a universal joint J (see FIG. 1).

The worm shaft 14 of the speed reduction mechanism A includes a metal shaft member having a worm 14a at the center and shafts 14b and 14c at both ends. The shaft portion 14b at one end has an uneven portion 14d made of serrations on the outer peripheral portion, and is electrically supported by the gear housing 10 made of aluminum via a first bearing 16 made of a ball bearing so as to be rotatable. 6 to the output shaft 6a. The other end shaft portion 14c is supported by the gear housing 10 via a second bearing 17 formed of a ball bearing. The shaft portions 14b and 14c are press-fitted into the inner rings 16a and 17a of the bearings 16 and 17, respectively.
The worm wheel 15 includes an annular tooth portion 15a having gear teeth formed on the outer peripheral surface, and a boss portion 15b integrally coupled to the inner periphery of the tooth portion 15a. The boss portion 15b is a second steering shaft. 4 is fitted and fixed in the middle.

The output shaft 6 a of the electric motor 6 and the shaft portion 14 b of the worm shaft 14 are joined via a shaft joint 18. This shaft coupling 18 is an interlocking connecting cylinder having a concave and convex strip 14d of a shaft portion 14b, one end of which is externally fitted to the output shaft 6a so as to be integrally rotatable, and the other end of the concave and convex strip 19a meshing with the concave and convex strip 14d. 19.
The gear housing 10 houses a worm shaft 14, a first housing portion 20 that rotatably supports shaft portions 14 b and 14 c of the worm shaft 14 via bearings 16 and 17, and a worm wheel 15. It has the 2nd accommodating part 21 which supported the worm wheel 15 via the 2nd steering shaft 4 and the two bearings 12 and 13 (refer FIG. 1) fitted by this 2nd steering shaft 4. As shown in FIG.
The first housing portion 20 is elongated in the axial direction of the worm shaft 14, and a support hole 20a for fitting and supporting the first bearing 16 at one end in the longitudinal direction, and a screw hole 20b connected to the support hole 20a. And a cylindrical motor mounting portion 20c connected to the screw hole 20b. And the outer ring | wheel 16b of the 1st bearing 16 is fitted in the support hole 20a, and the movement to the axial length direction of the 1st bearing 16 is controlled by the screw ring 22 screwed by the screw hole 20b. The electric motor 6 is attached to the motor attachment portion 20c.

Here, the worm wheel 15 is obtained by integrating a tooth portion 15a formed of a high-density sintered forged metal and a boss portion 15b formed of a low-density sintered forged metal by sintering bonding. .
Since the tooth portion 15a of the driven gear (worm wheel) 15 is formed of sintered forged metal, the strength and toughness are improved and the allowable load is increased, so that the size can be reduced as compared with the resin tooth portion. . Moreover, since the tooth part 15a is manufactured by sintering forging, the material and the processing steps can be reduced, thereby reducing the cost and suppressing the roughness of the tooth surface of the gear tooth. Furthermore, by using a sintered metal having a high vibration damping characteristic as the worm wheel 15 and further varying the density of the tooth portion 15a and the boss portion 15b, it is possible to suppress the propagation of vibration and noise. Can be increased. Here, the strength of the tooth portion 15a, particularly the gear teeth, can be further improved by making the tooth portion 15a have a higher density than the boss portion 15b.

The tooth part 15a and the boss | hub part 15b can be manufactured by the sintering forging method of powder metallurgy. In the sintering forging method, the raw material powder is first compressed by a powder forming press to form a green compact (powder forming step), and then the obtained green compact is heated and sintered in a sintering furnace (sintered). The sintering step) is further compressed by a forging press and hot or cold forging (forging step).
In the powder molding process, as the raw material powder for the tooth portion 15a and the boss portion 15b, one or more kinds of metal powders usually used for the worm wheel 15 can be used, and the metal used is the tooth portion 15a and the boss portion 15b. May be the same or different. When compression molding, the raw material powder of the tooth part 15a is filled more than the boss part 15b, or the green compact of the tooth part 15a is compressed by the pressure of the boss part 15b. It can be made denser than the powder.
In the sintering step, sintering is performed with the green compact of the boss portion 15b set inside the green compact of the tooth portion 15a. Thereby, both 15a and 15b are integrated by sintering coupling.
And the sintered compact of the tooth part 15a is forged at a forge process. Thereby, the intensity | strength and toughness of the tooth | gear part 15a can be improved.

In the above embodiment, the worm wheel 15 is used as the driven gear. However, the worm wheel 15 is not limited to the worm wheel 15, and for example, a helical gear or a spur gear may be used.
Moreover, although the tooth part 15a is made into the high density and the boss | hub part 15b is made into the low density, as long as the density mutually differs, the tooth part 15a may have a low density and the boss part 15b may have a high density. Although the tooth portion 15a and the boss portion 15b are integrated by sintering bonding, the bonding of the both 15a and 15b is not limited to sintering bonding, and may be bonded by a spline or the like. It is also possible to impregnate the tooth portion 15a with lubricating oil.

It is sectional drawing which shows the principal part structure of the power steering apparatus which concerns on embodiment of this invention. It is sectional drawing which shows the deceleration mechanism of the power steering apparatus which concerns on embodiment of this invention.

Explanation of symbols

6 Electric motor 14 Worm shaft (drive gear)
14a Worm 15 Worm wheel (driven gear)
15a Tooth part 15b Boss part PS Power steering device

Claims (2)

A drive gear coupled to the electric motor;
An annular tooth portion formed on the outer peripheral surface of the gear teeth meshing with the drive gear, and a driven gear having a boss portion integrally connected to the inner periphery of the tooth portion and connected to the steering shaft. ,
In the electric power steering device that applies steering assist force by rotation of the electric motor,
The electric power steering device, wherein the tooth portion and the boss portion of the driven gear are formed of sintered metals having different densities, and the tooth portion is finished by forging.   The electric power steering apparatus according to claim 1, wherein a density of a tooth portion of the driven gear is higher than a density of the boss portion.

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