JP2001271891A - Worm gear and motor-driven power steering using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge a range of transmitting driving force through two wheel tooth parts in a worm gear using a multiple double-lead worm, and a motor- driven power steering, using the worm gear. SOLUTION: The motor-driven power steering is composed of the worm gear, comprising a worm wheel 30 connected to a steering shaft 15, and a double-lead worm 20 having a plurality of worm tooth parts 21, 22 meshed with wheel tooth parts 31 of the worm wheel 30, and an electric motor 13 for rotating driving the worm 20. In the worm 20, the worm tooth parts of the same shape are arranged, shifted only in the axial direction so that the same dimensional shaped ones are continuously and alternately arranged by the number of the worm tooth parts in the cross section of the respective worm tooth parts on a plane, including the center axis of the worm, and the cross section of a tooth space between them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a worm gear device including a worm wheel and a worm that meshes with the worm wheel, and an electric power steering device using the worm gear device.

[0002]

2. Description of the Related Art FIG. 4 shows a main part of a worm gear device comprising two worms 1 and a worm wheel 30 meshing with the worms 1 used in a conventional electric power steering apparatus of this kind. The worm 1 has a constant tooth thickness t and a tooth groove width s of each worm tooth portion 2, 3 along the pitch line P1, that is, a pitch p of one tooth surface 2x, 3x and a pitch p of the other tooth surfaces 2y, 3y. p are the same (therefore, each tooth surface 2
The x, 3x, 2y, 3y leads (same for 2p) are normal, and the worm wheel 30 is a normal hob machined. In the state shown in FIG.
When the two teeth 31x and 31y of the worm wheel 30 are engaged simultaneously with the worm teeth 2 and 3 of the worm 1, and the worm 1 drives the worm wheel 30 in either the clockwise direction or the counterclockwise direction. But
The driving force is the two teeth 31x, 31 of the worm wheel 30.
Since y is applied simultaneously, the load applied to one tooth is reduced. However, due to machining errors, etc.,
If a backlash occurs between the wheel 3 and the wheel teeth 31, it cannot be adjusted.

As a means for adjusting such backlash, there is a method in which the worm is a double lead worm. FIG. 5 shows such an example. The worm 6 has leads (= 2) on one tooth surface 7x, 8x of each of the worm teeth 7, 8.
p−γ) and the lead of the other tooth surfaces 7 y and 8 y (= 2p +
γ) is changed so that the tooth thickness gradually increases toward the right, and is used in combination with an ordinary worm wheel 30 machined with a standard hob as in the case of FIG. . The two worm teeth 7 and 8 have the same shape, and have the same axial position and are arranged with a phase difference of 180 degrees around the central axis O1 of the worm 6.

The worm 6 has two worm teeth 7, 8 on a plane (the paper surface of FIG. 5) including the center axis O1.
Pitch line P1 of each section 7a, 8a, 7b, 8b, 7c
, T5... Along the right side in the axial direction increase at a constant rate, and the tooth gap widths s1,
The numbers s2,... s5,... decrease at the same rate as going rightward in the axial direction. Pitch pa between one tooth surface 7x, 8x of each worm tooth portion 7, 8
The pitch pb between the tooth surface 2y and the other tooth surface 3y has a different value. The specific relationship between them is as follows: t2-t1 = t3-t2 = t4-t3 = t5-t4 = γ
> 0 s1−s2 = s2−s3 = s3−s4 = γ> 0 pa−pb = γ (γ is a constant). According to this configuration, the backlash between the worm teeth 7, 8 and the wheel teeth 31 increases when the worm 20 is moved to the right, and decreases when the worm 20 is moved to the left. Can be adjusted.

[0005] However, in the state shown in FIG. 5, the worm gear device has one tooth 3 of the worm wheel 30.
1z only meshes with the worm teeth 7, 8 of the worm 6 at the same time. Even when the worm 6 drives the worm wheel 30 in either the clockwise direction or the counterclockwise direction, the driving force is reduced. Since it is only given to one tooth 31z of the worm wheel 30, there is a problem that the load applied to one tooth increases. In the multiple lead worm shown in FIG. 5, the lead of one of the tooth surfaces 7x and 8x is 2p.
Assuming that the lead of the other tooth surfaces 7y and 8y is 2p + 2γ, the driving force is
However, since the driving force is applied to only one tooth in the clockwise direction, the load applied to one tooth also increases.

The present invention relates to a worm gear device using a multi-lead worm, in which a driving force is applied to two teeth of a worm wheel even when driven in any direction within a certain range. The purpose is to solve such problems.

[0007]

SUMMARY OF THE INVENTION A worm gear device according to the present invention comprises a worm wheel and a worm having a plurality of spiral worm teeth meshing with wheel teeth of the worm wheel. In the worm gear device, wherein the leads of the tooth surfaces on both sides of each of the worm teeth are different double worms, a cross section of each of the worm teeth and a cross section of a tooth space between them on a plane including a central axis of the worm. Is characterized in that the worm tooth portions having the same shape are arranged only in the axial direction so that the worm tooth portions having the same size and shape are alternately and continuously arranged by the number of the worm tooth portions.
The cross section of each worm tooth portion and the cross section of the tooth groove between them on the plane including the central axis of the worm are identical in shape and shape, and are alternately and continuously arranged by the number of worm tooth portions. The wheel teeth mesh simultaneously with the worm teeth of the worm with the same backlash over a range.

The electric power steering apparatus according to the present invention also provides a worm having a worm wheel connected to a steering shaft, a plurality of spiral worm teeth meshing with the wheel teeth of the worm wheel, and a worm. A power assist unit comprising an electric motor that rotationally drives the worm, the worm is a double-lead worm in which the leads of the tooth surfaces on both sides of each worm tooth are different, and the worm is on a plane including the central axis of the worm. The cross section of each worm tooth section and the cross section of the tooth groove between them are arranged only in the axial direction so that the worm tooth sections having the same shape are arranged alternately and continuously in the number of worm tooth sections. It is characterized by being staggered. The cross section of each worm tooth portion and the cross section of the tooth groove between them on the plane including the central axis of the worm are identical in shape and shape, and are alternately and continuously arranged by the number of worm tooth portions. The wheel teeth mesh simultaneously with the worm teeth of the worm with the same backlash over a range.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a worm gear device according to the present invention and an electric power steering device using the same will be described below with reference to FIGS. The power assist section of this electric power steering device
As shown in FIG. 1, a worm wheel 3 connected to a steering shaft 15 rotated by a steering wheel
0 and the wheel teeth 31 of the worm wheel 30
(See FIGS. 2 and 3) A cylindrical worm 20 having two spiral worm teeth 21 and 22 (see FIGS. 2 and 3) meshing with an electric motor 13 for rotating the worm 20 These are supported by a housing 10 fixed to the steering column. The control device of the electric power steering device operates the electric motor 13 based on a steering torque detected by a torque sensor provided on the steering shaft 15, and controls the steering shaft via a worm gear device including a worm 20 and a worm wheel 30. 15 to provide assist power.

Both ends of the worm 20 are supported by the housing 10 via ball bearings 11, and the tightening nuts 12a and 12b screwed to both ends are loosened to adjust the axial position. 12a and 12b are tightened for positioning.
Is spline-coupled to the output shaft of the electric motor 13 so as to be slidable. The worm tooth portions 21 and 22 of the worm 20 have the same shape, and the leads of the worm tooth surfaces 21x and 22x on one side and the leads of the worm tooth surfaces 21y and 22y on the other side are different from each other. The two worm tooth portions 21 and 22 have the same tooth thickness portion in the same phase with respect to the center axis O1 of the worm 20 and are arranged so as to be shifted only in the axial direction, so that a plane including the center axis O1 of the worm 20 ( 2 and 3
Of the worm tooth portions 21 and 22 and the cross sections of the tooth grooves 23 and 24 between the worm tooth portions 21 and 22, two of which have the same size and shape (= the number of worm tooth portions) are alternately continued. Are lined up.

Next, the arrangement and operation of the two worm teeth 21 and 22 will be described in detail with reference to FIGS. FIG. 2 shows the wheel teeth 31 of the worm wheel 30.
Of the three consecutive teeth 31a, 31b, 31c are located on both sides of the contact point between the pitch line P1 of the worm tooth portions 21, 22 and the pitch circle P2 of the wheel tooth portion 31, and Tooth groove sections 23b, 24 of the same size and shape
FIG. 3 shows a state in which the worm wheel 30 is rotated clockwise by the rotation of the worm 20, and the left two teeth 31a and 31b of the three teeth 31a, 31b and 31c are rotated. Tooth groove section 2 located on both sides of the contact point between pitch line P1 and pitch circle P2 and having different dimensions and shapes
4d and 23e are shown in mesh with each other.

In FIG. 3, the central axis O of the worm 20 is shown.
The cross-sections 22c, 21d, 22d, 21e, 22e of the worm teeth 21, 22 and the tooth grooves 23d, 24d, 23e, 24e between them on the plane including 1 have the same dimensions and shape as described above. The tooth thicknesses V0, V1, V1, V2, V2, and the tooth groove width U1, along the pitch line P1 of the worm 20, are arranged continuously two by two.
The relationship among U1, U2, and U2 is as follows: V1-V0 = V2-V1 = [alpha]> 0 U1-U2 = [alpha]> 0. The pitches qa, qb between the tooth surfaces 21x, 22x, 21y, 22y are qa = u1 + v1 = u2 + v2 qb = v0 + u1 = v1 + u2 qa-qb = α (α is a constant). Therefore, each worm tooth portion 21, 22
Lead of one tooth surface 21x, 22x is qa + qb (=
2 × qa−α), and the lead of the other tooth surfaces 21y and 22y is 2 × qa.

In the state shown in FIG. 3, the worm tooth 2
1, 22 are cross sections 21d and 22d and cross sections 21e and 2
2e have the same dimension and shape, and the tooth groove sections 23d and 24d and the tooth groove sections 23e and 24e on the left side of each tooth section of the same dimension and shape have the same dimension and shape. The teeth 31b of the worm wheel 30 mesh with the tooth groove section 23e substantially without backlash, and the meshing is released when the worm wheel 30 further rotates clockwise. Teeth 31 of the worm wheel 30
a meshes with the tooth groove section 24d of the worm 20,
Since the tooth groove width U1 of the tooth groove section 24d is larger than the tooth groove width U2 of the tooth groove section 23e, there is a backlash corresponding to α between the tooth 31a and the tooth groove section 24d.

The cross sections 21a, 22a, 21b, 22b, 21c of the two worm teeth 21, 22 in FIG. 2 and the tooth grooves 24a, 23b, 24b, 23c therebetween are also shown in FIG.
Two of the same size and shape are continuously arranged, and their tooth thickness along the pitch line P1 of the worm 20 is V1.
−β, V1-β, V2-β, V2-β, V3-β, and the tooth groove widths are U1 + β, U2 + β, U2 + β, U3 + β
It is. By the rotation of the worm 20, the worm teeth 21,
As β moves to the right, β decreases, so that the cross-sections 21a, 22a, 21b, and 22b increase in tooth thickness to become the cross-sections 21d, 22d, 21e, and 22e in FIG. , 23b, 24b are reduced in width to become the tooth groove sections 24d, 23e, 24e of FIG.

In the state shown in FIG. 2, the worm tooth 2
1, 22 are cross sections 21a and 22a and cross sections 21b and 2
2b have the same size and shape, and the tooth shape sections 23b and 24b on the left side of each tooth section of the same size and shape have the same size and shape. And the worm wheel 30
Teeth 31b and 31c have tooth groove sections 23b and 24b, respectively.
And the backlash between them is the same value β. In this vicinity, if the worm 20 is rotated clockwise when viewed from the right side, the tooth surface 2 is rotated as shown in FIG.
2y and 21y come into contact with the teeth 31b and 31c at the same time, and the worm wheel 30 is driven to rotate clockwise. When the worm 20 is rotated in the opposite direction, the tooth surfaces 21x and 22
x simultaneously contacts the teeth 31b and 31c, and the worm wheel 30 is driven to rotate counterclockwise. That is, in a certain range centered on the state shown in FIG. 2, the driving force is simultaneously applied to the two teeth 31 b and 3 cy of the worm wheel 30 and is applied to one tooth when the worm wheel 30 is driven in any direction. The load decreases.

In the vicinity of the state shown in FIG. 3, when the worm 20 is rotated clockwise as viewed from the right and the worm wheel 30 is rotated clockwise, the tooth surfaces 21y and 2
2y simultaneously contacts the teeth 31a and 31b and is driven to rotate. When the worm 20 is rotated in the opposite direction to rotate the worm wheel 30 in the counterclockwise direction, the tooth surface 22x
Does not come into contact with the teeth 31a, only the tooth surface 21x comes into contact with the teeth 31b, and the worm wheel 30 is driven to rotate. Therefore, in a certain range centered on the state shown in FIG. 3, when the worm wheel 30 is driven to rotate clockwise by the worm 20, sufficient strength is obtained, but when the worm wheel 30 is driven to rotate counterclockwise, 1 is obtained. The load on one tooth increases. Further, the teeth 31b of the worm wheel 30 mesh with the tooth groove section 23e of the worm 20 substantially without backlash, and this meshing is released when the worm wheel 30 further rotates clockwise.

According to the above-described embodiment, the worm wheel 3 extends over a certain range centered on the state shown in FIG.
The two wheel teeth 31 of 0 are engaged simultaneously with the worm teeth 21 and 22 of the worm 20 with the same backlash. Therefore, in this range, even when the worm wheel 30 is driven in the clockwise direction by the worm 20, or when the worm wheel 30 is driven in the counterclockwise direction, the driving force is applied from the two worm teeth 21 to the two wheel teeth 31. As a result, the load applied to one tooth of the worm wheel 30 is reduced. In addition, the worm 20 includes the worm teeth 21 and 22.
Is a double-lead worm having different tooth surfaces on both sides. The backlash between the worm tooth portions 21 and 22 and the wheel tooth portion 31 increases when the worm 20 moves to the right and decreases when the worm 20 moves to the left. So that backlash can be adjusted. This adjustment is performed by tightening nuts 12a, 1
2b is loosened, and after adjustment, tightening nuts 12a, 12b
To position the worm 20 at that position.

In the above-described embodiment, two worms have been described. However, the present invention can be applied to three or more worms.

[0019]

As described above, according to the worm gear device of the present invention and the electric power steering device using the same, two wheel teeth of the worm wheel have the same backlash and worm over a certain range. Since the worm meshes with the worm teeth at the same time, the driving force is controlled by the two worm teeth from the two worm teeth even when the worm is driven clockwise or counterclockwise by the worm. , Which reduces the load on one tooth. In addition, the worm is a multiple lead worm in which the leads of the tooth surfaces on both sides of each worm tooth part are different, and the tooth thickness of each worm tooth part increases and the tooth groove width decreases as the worm advances in one direction, so that the worm Backlash can be adjusted by moving in the axial direction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a main part of a power assist unit of an embodiment of a worm gear device and an electric power steering device using the same according to the present invention.

FIG. 2 is a drawing of the worm gear device shown in FIG. 1 in a certain meshing state.

3 is a drawing of the worm gear device shown in FIG. 2 in different engagement states.

4 is a drawing corresponding to FIG. 2 of a worm gear device according to the prior art.

5 is a drawing corresponding to FIG. 2 of a worm gear device according to the related art, which is different from FIG. 4;

[Explanation of symbols]

13: Electric motor, 15: Steering shaft, 20
... Worm, 21, 22 ... Worm teeth, 21x, 21
y, 22x, 22y ... tooth surface, 23, 24 ... tooth space, 30 ...
Worm wheel, 31 ... Wheel teeth

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshiharu Inakuma 1-1-1, Asahi-cho, Kariya-shi, Aichi Toyota Machine Works Co., Ltd. (72) Inventor Susumu Honaga 1-1-1, Asahi-cho, Kariya-shi, Aichi Toyota (72) Inventor Osamu Ogawa 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Seiji Sano 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Invention Person Jun Tano 3-5-8 Minamisenba, Chuo-ku, Osaka City, Osaka Prefecture F-term inside Koyo Seiko Co., Ltd. 3D033 JC08 3J009 DA02 DA16 EA06 EA19 EA32 EB01 FA08

Claims (2)

[Claims] 1. A worm having a worm wheel and worms having a plurality of spiral worm teeth meshing with wheel teeth of the worm wheel, wherein the worm is a lead of tooth surfaces on both sides of each worm tooth. Wherein the cross section of each worm tooth portion and the cross section of the tooth groove between them on the plane including the central axis of the worm are the same size and shape as those of the worm tooth portion. A worm gear device, wherein the worm teeth of the same shape are arranged only in the axial direction so as to be alternately and continuously arranged by the number of strips. 2. Power comprising a worm wheel connected to a steering shaft, a worm having a plurality of spiral worm teeth meshing with wheel teeth of the worm wheel, and an electric motor for rotating and driving the worm. An electric power steering apparatus comprising an assist portion, wherein the worm is a double-lead worm in which leads on both sides of the worm tooth portions are different from each other. In the electric power steering device, the worm has a plurality of worm teeth on a plane including a central axis of the worm. The cross-sections and the cross-sections of the tooth grooves between them are arranged such that the worm teeth of the same shape are shifted only in the axial direction so that the same dimensional shape is alternately and continuously arranged by the number of the worm teeth. An electric power steering device, characterized in that: