JPH11182637A - Worm gear transmission device, and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To greatly reduce the reduction in the axial direction of a worm by providing a first tooth part of a right-hand thread manner on one side in the axial direction, and a second tooth part of a left-hand thread manner on the other side, and interlockingly turning a driven gear between a pair of worm wheels to be respectively engaged with the first and second tooth parts on each side in the radial direction of the worm. SOLUTION: A fist tooth part 1a is formed on an outer circumference on a bearing 11 support side of a worm 11 in a right-hand thread manner, and a second tooth part 1b is formed on an outer circumferential of a bearing 12 support side in a left- hand thread manner. Wheel shafts 30, 40 are arranged parallel to each other and approximately orthogonal to the worm 1, and worm wheels 3, 4 are arranged concentric therewith. The wheel 3, 4 are engaged with the first tooth part 1a or the second tooth part 1b of the worm 1 from each side in the radial direction of the worm 1. That is, the direction of each component force to be applied to the first and second tooth parts 1a, 1b is opposites to each other and canceled with each other. The force actually applied to the whole worm is reduced, and the deflection of the worm 1 caused by the force effect can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a worm gear transmission in which torque is transmitted from a driving side to a driven side by a worm and a worm wheel meshing with the worm, and an electric power steering apparatus using the worm gear transmission.

[0002]

2. Description of the Related Art A worm gear transmission configured to transmit torque between a worm on a drive shaft side and a worm wheel on a driven shaft side can provide a large reduction ratio in a compact configuration. For example, it is widely used as a transmission device that is convenient for a transmission system in which an installation space is limited, such as an electric power steering device configured to transmit the rotational torque of an electric motor to a steering shaft to assist steering.

FIG. 5 is a plan view schematically showing the structure of a general worm gear transmission. As shown in the figure, the worm gear transmission transmits torque between the drive shaft 10 and the driven shaft 20 having axes that intersect each other at an appropriate distance from each other. The drive shaft 10 driven by a motor M, Yes formed worm W ₁ of cylindrical shape having a right threaded or left threaded tooth portion is integrally with the driven shaft 20,
Worm wheel W ₂ in the form of gear teeth formed on its outer periphery, is integrally rotatably supported on the same axis.

The worm gear transmission is provided with the worm W
₁ and the worm wheel W ₂ are meshed at respective opposing positions, and the rotational torque of the motor M as a drive source is screwed in the axial direction according to the rotation of the drive shaft 10. The teeth of the worm W ₁ are transmitted to the worm wheel W ₂ and the driven shaft 20 by pressing the teeth on the outer periphery of the worm wheel W ₂ meshing with the worm W ₁ .

[0005]

[SUMMARY OF THE INVENTION However, in the above-described worm gear when the teeth of the worm W ₁ is transmission by pressing the teeth of the outer periphery of the worm wheel W ₂ is made, the reaction force of the pressing force T ₁ since T ₂ is applied in the axial direction of the worm W _1, the great thrust load bearing 11 and 12 supporting the drive shaft 10 on both sides of the teeth act, enlargement of these bearings 11 and 12 There was an inevitable inconvenience.

[0006] The reaction force T ₂ are, from acting perpendicular to the tooth surface of the worm W _1, when employing a tooth profile having a general trapezoidal section as the teeth of the worm W _1, further
When the worm wheel W ₂ is formed as a helical tooth to increase the load capacity, the worm wheel W ₂ is actuated by the component force of the reaction force T _2.
1 and the drive shaft 10 are bent, and the meshing state with the worm wheel W ₂ cannot be maintained in a good state, which causes problems such as deterioration of transmission efficiency, wear of tooth surfaces, increase of operation noise, and the like. .

The present invention has been made in view of such circumstances, and a worm gear transmission capable of greatly reducing a reaction force applied in the axial direction of a worm and solving the above-described inconvenience caused by the reaction force. And an electric power steering device using the same.

[0008]

A worm gear transmission according to a first aspect of the present invention has a right-handed first tooth portion on one side in the axial direction and a left-handed second tooth portion on the other side. A worm, which is provided in each case and rotates in conjunction with a drive shaft; a pair of worm wheels meshing with the first and second teeth on both radial sides of the worm; and a pair of worm wheels between these worm wheels. It is characterized by having a driven gear that meshes with the driven shaft and rotates in conjunction with the driven shaft.

In the present invention, the rotational torque of the worm that rotates in conjunction with the drive shaft is a worm wheel that meshes with the right-hand threaded first tooth portion and a second worm wheel that is left-hand threaded from a side different from the worm wheel. The worm wheel is transmitted to the meshing worm wheel and these worm wheels rotate in the same direction, and are transmitted to the driven shaft via the driven gear meshing with both. At this time, the directions of the reaction forces acting from the respective worm wheels at the first and second tooth portions are opposite to each other and are canceled out with each other, so that the reaction force acting on the entire worm is greatly reduced.

[0010] In addition, the worm wheel is characterized in that the meshing portion with the worm is a helical tooth and the meshing portion with the driven gear is a flat tooth.

In the present invention, since the worm wheel meshes with the helical teeth of the worm, the load capacity is increased by increasing the contact area between the two. Further, the meshing position of the worm wheel meshing with the driven gear and the spur teeth can be freely set around the driven gear and the driven shaft while maintaining the meshing state with the worm. The degree of freedom in design can be increased.

Further, the electric power steering apparatus according to the present invention is configured to transmit a rotational torque of a motor driven in accordance with a steering operation to a steering shaft, and to assist the steering performed in accordance with the operation of the steering shaft. In the power steering device, a worm gear transmission according to claim 1 or 2 is formed in a transmission system between a drive shaft driven by the motor and a driven shaft for transmission to the steering shaft. It is characterized by the following.

In the present invention, the transmission from the drive shaft driven by the steering assist motor to the steering shaft is performed by the worm gear transmission described above, and the inconvenience caused by the reaction force acting on the worm due to the transmission is eliminated. And to reduce the size of the transmission system while ensuring stable transmission over a long period of time. Further, using a worm wheel having a helical tooth and a spur tooth, the degree of freedom of the arrangement position of the steering assist motor with respect to the driven shaft fixed in position for transmission to the steering shaft is increased, It can be installed in a limited space around the steering shaft.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a side view schematically showing a configuration of a worm gear transmission according to the present invention.
FIG. 2 is a plan view taken along line II-II in FIG.

The illustrated worm gear transmission transmits torque between a drive shaft 10 and a driven shaft 20 having axes that cross each other, similarly to the conventional worm gear transmission shown in FIG.

The drive shaft 10 driven by the motor M is supported at both ends by a pair of bearings 11 and 12, and a cylindrical worm 1 is integrally formed between these support portions. On one side of the worm 1, that is, on the outer periphery on the support side by the bearing 11, a first tooth portion 1 a is formed in a right-handed screw shape, and on the other side, that is, on the outer periphery on the support side by the bearing 12. , The second tooth portion 1b is formed in a left-handed screw shape.

On both radial sides of the worm 1, wheel shafts 30, 40 are disposed substantially perpendicular to the worm 1 and parallel to each other. The worm wheels 3 and 4 are supported on these wheel shafts 30 and 40 so as to be coaxially and integrally rotatable. The worm wheel 3 is provided with a first tooth portion 1 a of the worm 1.
The worm wheel 4 is meshed with the second tooth portion 1b of the worm 1 from each side, that is, both sides in the radial direction of the worm 1.

As shown in FIG. 1, the worm wheels 3 and 4 extend from the meshing position with the worm 1 to the same side in the axial direction. The driven shaft 20 faces one end between the extension portions of the worm wheels 3 and 4, and the driven shaft 20
It is supported substantially parallel to each of 0 and 40. Driven shaft 2
A driven gear 2 rotatably mounted coaxially with the one end side is attached to the one end side of the driven gear 2, and the driven gear 2 is meshed with an extension of the worm wheels 3, 4. FIG. 1,
In FIG. 2, the illustration of the support structure of the wheel shafts 30, 40 and the driven shaft 20 is omitted.

In the worm gear transmission according to the present invention configured as described above, the rotational torque of the motor M is transmitted to the drive shaft 10 and the worm 1 formed integrally therewith, and the first worm 1 Tooth part 1a and second tooth part 1b
Are transmitted to the worm wheels 3 and 4 respectively meshing with each other.

The first and second teeth 1a and 1b of the worm 1 are
The worm wheels 3 and 4 are formed so as to have screw shapes in opposite directions to each other.
Since the worm 1 is meshed from both sides in the radial direction, the worm wheels 3 and 4 rotate in the same direction when the torque is transmitted as described above. In FIG. 2, the rotation direction of the motor M and the rotation directions of the worm wheels 3 and 4 corresponding to the rotation are indicated by arrows.

As described above, since the worm wheels 3 and 4 rotate in the same direction, the driven gear 2 meshing with the worm wheels 3 and 4 rotates therebetween, and the rotating torque of the motor M
The power is transmitted to the driven shaft 20 via the worm 1, the worm wheels 3, 4 and the driven gear 2.

In the worm gear transmission according to the present invention which operates as described above, torque transmission from the worm 1 to the worm wheels 3 and 4 is performed in the same manner as in the prior art.
The rotation of the worm 1 causes the first and second tooth portions 1a and 1b to advance, and the outer teeth of the worm wheels 3 and 4 meshing with the first and second tooth portions 1a and 1b are pressed. The reaction forces T _{12 of} the pressing forces T ₁₁ and T ₂₁ ,
T ₂₂ is to join the axial direction.

At this time, since the first and second teeth 1a and 1b formed on the worm 1 are formed in the opposite screw shapes, pressing of the worm wheel 3 by the first teeth 1a and
The pressing of the worm wheel 4 by the second tooth portion 1b is performed in a direction opposite to that of the worm wheel 4, and the reaction forces T ₁₂ and T ₂₂ caused by the pressing are performed.
Are also opposite to each other. FIG. 2 shows the directions of action of the pressing forces T ₁₁ , T ₂₁ and the reaction forces T ₁₂ , T ₂₂ generated with the rotation indicated by the arrow.

Accordingly, the first and second tooth portions 1a, 1a,
The difference between the reaction forces T ₁₂ and T ₂₂ in 1b, that is, (T ₁₂ −T ₂₂ )
Only acts in the axial direction, and the above-mentioned T ₁₂ and T
_Since it is substantially equal to ₂₂ , the thrust load is hardly applied to the bearings 11 and 12 supporting the drive shaft 10.

[0025] The reaction force T _12, T _22, in fact, since the first, second tooth portion 1a, a force acting perpendicularly to the tooth surface 1b, the first, second tooth When a tooth shape having a general trapezoidal cross section is adopted as the portions 1a and 1b, the worm 1
It is pressed in the radial direction by the component force of the reaction forces T ₁₂ and T ₂₂ .

Further, as shown in FIG. 1, the worm wheels 3 and 4 are formed as helical gears in order to increase the load capacity when transmitting torque from the worm 1, whereby the worm 1 The axial and circumferential component forces of the forces T ₁₂ and T ₂₂ are applied.

However, according to the present invention, the first and second tooth portions 1a and 1b are formed in screw shapes in opposite directions.
Since the worm wheels 3 and 4 are meshed on both sides of the worm 1 in the radial direction, the first and second worm wheels 3 and 4 are engaged.
The directions of the component forces applied to the tooth portions 1a and 1b are reversed, and these components cancel each other, so that the force actually applied to the entire worm 1 is small, and the deflection of the worm 1 due to the action of this force is small.

Accordingly, the diameter of the worm 1 can be reduced, and the size of the bearings 11 and 12 for supporting the worm 1 via the drive shaft 10 can be reduced. Further, the first and second tooth portions
The meshing state between the worm wheels 1a and 1b and the worm wheels 3 and 4 is favorably maintained without being disturbed by the bending, and the occurrence of inconveniences such as deterioration of transmission efficiency, wear of tooth surfaces, and increase of operation noise is suppressed. Can be.

FIG. 3 is a side view schematically showing another embodiment of the worm gear transmission according to the present invention. The worm gear transmission shown in this figure is similar to the worm gear transmission shown in FIGS. 1 and 2 in that the first and second teeth 1a and 1b are provided.
A worm 1 that rotates in conjunction with the drive shaft 10, a pair of worm wheels 3 and 4 that mesh with the first and second teeth 1 a and 1 b on both radial sides of the worm 1, Axis 20
And a driven gear 2 supported so as to be integrally rotatable with the driven shaft 20 to transmit the rotational torque generated by the motor M to the driven shaft 20 via the worm 1, the worm wheels 3, 4 and the driven gear 2. .

This embodiment is characterized in the form of teeth provided on the outer periphery of the worm wheels 3 and 4. That is, the worm wheels 3 and 4 are provided with teeth 3a and 4a formed as helical teeth on one side half of the axial length direction, and teeth formed as spur teeth on the other side half respectively. Part 3
b, 4b, and the teeth 3a, 4a are meshed with the first and second teeth 1a, 1b of the worm 1, and the teeth 3a, 4b
b and 4b are meshed with the driven gear 2.

According to this configuration, the meshing positions of the teeth 3b and 4b formed as spur teeth are determined by the driven gear 2 and the driven shaft 20.
And the worm 1 and the drive shaft 10 change in the axial direction accordingly, so that the drive shaft 10 and the motor M connected thereto can be freely designed. Increase. On the other hand, the mesh between the worm 1 and the worm wheels 3 and 4 is formed by helical teeth.
Since this is realized through 3a and 4a, the effect of increasing the load capacity and reducing the operation noise is maintained.

FIG. 4 is a partially cutaway front view showing an application example of the worm gear transmission configured as described above to an electric power steering apparatus. The rack shaft 5 as a steering axis in the figure is slidably supported in the axial direction inside the rack housing H ₁ forming the lateral direction extending in-cylinder-shaped body, not shown. Rack ends of the rack shaft 5 respectively projecting on either side of the housing H _1, each tie rods to the left and right steered wheels (not shown) 50, 50 (only one side is shown)
Is connected via a sliding of the rack shaft 5 in the rack housing H ₁ is the transmitted to the right and left steered wheels via tie rods 50, 50, are no so they are steered.

[0033] The intermediate portion of the rack housing H _1, pinion housing H ₂ is continuously provided to the embodiments is crossing this the axis. Inside the pinion housing H _2, the pinion shaft 6 rotatably at about its axis are supported. The pinion shaft 6 in FIG. 4, only the protruding end of the upper part of the pinion housing H ₂ is is shown, which is connected to a steering wheel (not shown) via a protruding Extension end, according to the operation of the steering wheel for steering It is designed to rotate around an axis.

[0034] The lower part of the pinion housing H pinion shaft 6 which extends into the interior of _2, the pinion (not shown) are formed integrally. Further, the rack shaft 5 is supported to the rack housing H _1, over a suitable length, including the intersecting position between the pinion housing H _2, is formed a rack teeth (not shown), the pinion of the lower portion of the pinion shaft 6 The rotation of the pinion shaft 6 due to the operation of the steering wheel is converted into sliding in the axial direction of the rack shaft 5 by the meshing of the pinion and the rack teeth, and is connected to both ends of the rack shaft 5. It constitutes a rack and pinion type steering mechanism in which left and right steering wheels are steered.

The rack housing H ₁ is provided with a motor housing H _{3 at a} position different from the pinion housing H _2.
There are continuously provided, the motor M for steering assist is flange fixed to the outside of the motor housing H _3.

The interior of the motor housing H ₃ is a hollow portion communicating with the inside of the rack housing H _1. The drive shaft 10 is connected to the output end of the motor 5 and projects into the hollow portion. A worm 1 having such first and second teeth 1a and 1b is integrally formed, and meshes with the first and second teeth 1a and 1b on both sides of the worm 1 in the radial direction. A pair of worm wheels 3 and 4 and a driven shaft 20 including a driven gear 2 that meshes with them are pivotally supported.

[0037] the other side of the rack housing the driven shaft 20 which extends in the interior of an H ₁ is a pinion 21 is integrally formed, the pinion 21 is formed over a predetermined length in the appropriate position of the rack shaft 5 Rack teeth 51.

As described above, the worm gear transmission according to the present invention including the worm 1, the worm wheels 3, 4 and the driven gear 2 is incorporated in the transmission system from the steering assist motor M to the rack shaft 5. , The rotational torque generated by the motor M is transmitted to the driven shaft 20 via the worm 1, the worm wheels 3, 4 and the driven gear 2,
The rotation of the driven shaft 20 is converted into sliding in the axial direction of the rack shaft 5 through the meshing portion of the pinion 21 and the rack teeth 51, and the steering performed as described above according to the sliding is performed. , And is assisted by the rotational torque of the motor M.

In the electric power steering apparatus configured as described above, when the rotational torque of the steering assist motor M is transmitted to the rack shaft 5, the reaction force acting on the worm 1 is small. Can be solved, and stable transmission can be performed over a long period of time.

As the worm wheels 3 and 4, FIG.
As shown in a portion of the helical teeth worm 1 and meshes, by using a worm wheel and a portion of the spur gear to the driven gear 2 in mesh, the motor M for steering assist outside the rack housing H ₁ The mounting position can be changed around the driven shaft 20. Thus, for example, with respect to the arrangement of the motor M shown by a solid line in the figure, it can be placed the motor M which is opposite to the projection direction as shown by two-dot chain line and will, only around the rack housing H ₁ In such a space, the arrangement of the motor M can be appropriately set.

FIG. 4 shows an electric power steering apparatus having a configuration in which a rotational torque of a steering assist motor M is transmitted to a rack shaft 5 as a steering shaft in a vehicle having a rack and pinion type steering mechanism. Although an application example is shown, the worm gear transmission according to the present invention has a configuration in which the rotational torque of the steering assist motor M is transmitted to the pinion shaft 6 or a column shaft connecting the pinion shaft 6 to a steering wheel. The present invention is also applicable to an electric power steering device for a vehicle including a steering mechanism of a type different from the rack and pinion type steering mechanism shown in FIG. Needless to say.

[0042]

As described above in detail, the worm gear transmission according to the present invention has a right-handed first tooth portion and a left-handed second tooth portion and rotates in conjunction with a drive shaft. A pair of worm wheels respectively meshing with the first and second teeth on both sides in the radial direction of the worm; and a driven gear that meshes with the worm wheel between these worm wheels and rotates in conjunction with a driven shaft. , The rotational torque of the drive shaft is transmitted to the worm wheel meshing with the first and second teeth, and these rotate in the same direction to rotate the driven shaft via the driven gear meshing with both. The reaction forces acting on the first and second teeth from the respective worm wheels cancel each other, the reaction force acting on the entire worm is greatly reduced, and the inconvenience caused by this reaction force is eliminated. , Warm and support And downsizing of receiving, stable and transmission can be realized over a long term.

Further, the worm wheel meshing with the first and second teeth of the worm and the driven gear has helical teeth for meshing with the worm and flat teeth for meshing with the driven gear. The meshing position of the worm wheel can be freely changed around the driven gear and the driven shaft, and the degree of freedom in the arrangement of the drive shaft and the drive source can be increased while maintaining the increased load capacity due to the action of the helical teeth. Can increase.

Further, in the electric power steering apparatus according to the present invention, since the worm gear transmission having the above-described configuration is used for the transmission system for transmitting the rotational torque of the motor driven in accordance with the steering operation to the steering shaft, Stable transmission can be performed for a long time, reliability is improved by reliable steering assist, and the arrangement position of the motor can be appropriately changed in a limited space around the steering shaft, The present invention has excellent effects such as an increase in design flexibility.

[Brief description of the drawings]

FIG. 1 is a side view schematically showing a configuration of a worm gear transmission according to the present invention.

FIG. 2 is a plan view taken along line II-II of FIG.

FIG. 3 is a side view schematically showing another embodiment of the worm gear transmission according to the present invention.

FIG. 4 is a partially cutaway front view of an electric power steering device including the worm gear transmission according to the present invention.

FIG. 5 is a plan view schematically showing a configuration of a general worm gear transmission.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Worm 1a 1st tooth 1b 2nd tooth 2 Driven gear 3, 4 Worm wheel 3a, 3b Teeth 4a, 4b Teeth 5 Rack shaft 6 Pinion shaft 10 Drive shaft 11, 12 Bearing 20 Follower shaft 21 Pinion 30, 40 Wheel shaft 51 Rack teeth M Motor

Claims (3)

[Claims] 1. A worm that has a right-handed first tooth portion on one side in the axial direction and a left-handed second tooth portion on the other side, and that rotates in conjunction with a drive shaft. A pair of worm wheels respectively meshing with the first and second teeth on both sides in the radial direction, and a driven gear that meshes between the worm wheels and rotates in conjunction with a driven shaft. A worm gear transmission. 2. The worm gear transmission according to claim 1, wherein the worm wheel has helical teeth for meshing with the worm and flat teeth for meshing with the driven gear. 3. An electric power steering apparatus configured to transmit a rotational torque of a motor driven in accordance with a steering operation to a steering shaft to assist steering performed in accordance with the operation of the steering shaft. 3. An electric power steering device comprising a worm gear transmission according to claim 1 or 2 in a transmission system between a driven shaft to be driven and a driven shaft for transmission to the steering shaft. .