JP2009248852A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device equipped with a worm gear of a single thread eliminating rotation unevenness. <P>SOLUTION: The electric power steering device drives an electric motor in accordance with steering input, transmits driving force of the electric motor to a steering system through the worm gear 61, and steers a vehicle. The worm gear 61 comprises the single thread. A gear cutting length L is an integer multiple N of a pitch length P, and a center of balance C of teeth of the worm gear 61 matches with an axis O. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus using an electric motor as a drive source.

FIG. 9 is a schematic diagram showing an installation state of a conventional electric power steering apparatus.
As shown in FIG. 9, conventionally, an electric power steering apparatus 100 using an electric motor 300, 300 as a power source is used as a power steering apparatus for reducing the steering force of the steering wheel 200 (for example, Patent Document 1). 1). The electric power steering apparatus 100 generally assists the driver's steering operation by boosting the rotational torque of the electric motor 300 by the speed reduction mechanism 400 and applying it to the rack shaft 500 via the rack and pinion mechanism.

FIG. 10 is a perspective view showing a speed reduction mechanism in which a conventional electric power steering apparatus is installed.
As shown in FIG. 10, the conventional reduction mechanism 400 includes a worm gear 410 and a worm wheel 420 installed on the rotor shaft of the electric motor 300 (see FIG. 9).
In recent years, the demand for mounting the electric power steering apparatus 100 on a large vehicle has increased with the spread of the spread. In a large vehicle, since the front axle load is large, it is necessary to increase the generated torque by increasing the size of the electric motor 300 and to increase the strength of the speed reduction mechanism 400 as the torque of the electric motor 300 increases in order to cope with it. There is.

However, when the speed reduction mechanism 400 is enlarged, there is a problem that the speed reduction mechanism 400 reduces the space near the driver's knees and the space at the feet, thereby reducing the driver's living space (see FIG. 9). . For this reason, it is desired to reduce the speed reduction mechanism 400 and to reduce the size of the electric power steering apparatus 100 as a whole.
As an apparatus for improving the strength of the speed reduction mechanism 400, for example, a device in which the worm gear 410 is made of a single metal screw and the tooth thickness of the worm wheel 420 is set larger than the tooth depth (for example, patents) is known. Reference 2).

  11A and 11B are diagrams showing a worm gear used in a conventional electric power steering apparatus, where FIG. 11A is a front view and FIG. 11B is a YY sectional view. FIG. 12 is a view showing a worm gear used in another conventional electric power steering apparatus, where (a) is a front view and (b) is a ZZ cross-sectional view.

As other methods for increasing the strength of the speed reduction mechanism 400 and the bending rigidity of the worm gear 410, worm gears 600 and 700 having a wide cross-sectional area in the direction perpendicular to the axis as shown in FIGS. 11 and 12 are known.
The worm gear 600 shown in FIGS. 11 (a) and 11 (b) is composed of a double thread and the tooth cross section is formed symmetrically with respect to the axis O in the cross section perpendicular to the axis. The position of the center of gravity C of the entire cross section including the tooth portion coincides with the axis O.
On the other hand, the worm gear 700 shown in FIGS. 12A and 12B is a single thread having a wide cross-sectional area in the direction perpendicular to the axis, and the tooth section is formed only at one location. The position of the center of gravity C of the entire cross section including the portion and the tooth portion is at a position shifted from the position of the axis O by the radius r.
JP 2006-77809 A JP 2004-66949 A

  In the case of the worm gear 600 having two threads as shown in FIGS. 11A and 11B, the number of teeth of the worm wheel increases as the number of threads of the worm gear 600 increases. In addition, there is a problem that the weight increases.

On the other hand, the single thread worm gear 700 shown in FIGS. 12A and 12B is located at a position where the center of gravity C deviates from the axis O by the radius r. Therefore, when the worm gear 700 rotates, the gear itself vibrates. As a result, there is a problem that the steering feeling deteriorates due to uneven rotation and touching.
Further, the allowable load of the worm gear 700 is reduced due to the centrifugal force generated when the center of gravity C is deviated from the axis O by the radius r.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering apparatus including a single-thread screw worm gear that eliminates rotation unevenness.

In order to solve the above problems, the electric power steering apparatus according to claim 1 drives an electric motor according to a steering input, and transmits the driving force of the electric motor to a steering system via a worm gear. An electric power steering apparatus for steering a vehicle, wherein the worm gear is composed of a single thread, and the gear cutting length is an integral multiple of the pitch length, and the center of gravity of the teeth of the worm gear is aligned with the axis. It is characterized by.
Here, the “tooth cutting length” is the total length of the portion where the tooth profile of the worm gear is formed.

  According to this configuration, the worm gear is composed of a single thread, and the center of gravity of the entire gear is formed by aligning the center of gravity of the teeth of the worm gear with the shaft center with the gear cutting length being an integral multiple of the pitch length. And the shaft center coincide with each other, so that uneven rotation and vibration can be eliminated. Thus, by eliminating the unbalance of the center of gravity of the worm gear, the meshing between the worm gear and the worm wheel becomes smooth, and the operation noise can be reduced and the steering feeling can be improved. Further, it is possible to suppress a reduction in the allowable load of the worm gear due to the centrifugal force generated when the center of gravity of the gear is shifted from the axis.

  A second aspect of the present invention is the electric power steering apparatus according to the first aspect, wherein the worm gear includes a gear cutting start position and an end position. Are formed at the same position in the radial direction.

  According to such a configuration, the worm gear has a gear cutting start position and an end position formed at the same radial position so that the center of gravity of the entire gear coincides with the shaft center. Since the weight balance is improved, the runout can be suppressed.

  According to a third aspect of the present invention, there is provided an electric power steering apparatus for driving a vehicle by driving an electric motor in accordance with a steering input and transmitting a driving force of the electric motor to a steering system via a worm gear. The worm gear is composed of a single thread, and the gear cutting length is an integral multiple of the pitch length, and the offset weight (offset mass) is offset from the position of the center of gravity of the tooth of the worm gear and the axis. The center of gravity offset length for correcting the centroid is added to the centroid offset length.

  According to such a configuration, the worm gear adds the gear cutting length, an integral multiple of the pitch length, and the center of gravity offset length that corrects the offset weight offset from the position of the center of gravity of the worm gear teeth and the axis. Even if the gear cutting length is set to an integral multiple of the pitch length, if the position of the center of gravity of the worm gear teeth and the center of the shaft shifts, the length obtained by adding the center of gravity offset length If so, the shift of the center of gravity can be corrected.

  The electric power steering apparatus according to the present invention can provide an electric power steering apparatus including a single-threaded worm gear that eliminates rotation unevenness. Further, by eliminating the unbalance of the center of gravity of the worm gear, the meshing between the worm gear and the worm wheel becomes good, and the operation noise can be reduced and the steering feeling can be improved. Furthermore, the heat generated by the meshing between the worm gear and the worm wheel is reduced, and the durability can be improved. As a result, good steering feeling can be maintained over a long period of time.

Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described.
FIG. 1 is a schematic configuration diagram showing an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a speed reduction mechanism of the electric power steering apparatus according to the embodiment of the present invention. FIG. 3 is an explanatory view showing a worm gear of the electric power steering apparatus according to the embodiment of the present invention.

≪Configuration of electric power steering device≫
As shown in FIG. 1, the electric power steering apparatus 1 drives an electric motor 7 in accordance with a steering input, and transmits the power of the electric motor 7 to a steering system via a speed reduction mechanism 6, thereby turning the vehicle. It is a device that performs assist. The electric power steering apparatus 1 includes a steering shaft 3 coupled to the steering wheel 2, a steering torque sensor 4 that detects a steering torque acting on the steering shaft 3, a vehicle speed sensor 5 that detects a vehicle speed, and a speed reduction mechanism 6. An electric motor 7 for applying a steering assist force to the steering shaft 3, a drive control unit (ECU) 8 for controlling the driving of the electric motor 7, and a rack shaft 10 connected through a rack and pinion mechanism 9. ing. A steered wheel (front wheel) 12 is connected to both ends of the rack shaft 10 (one side of the rack shaft 10 is not shown in FIG. 1) via a tie rod 11 or the like.

≪Electric motor configuration≫
As shown in FIG. 1, the electric motor 7 is composed of, for example, a brushless DC motor provided with a resolver (not shown) for detecting the rotation angle of the rotor, and houses, for example, the speed reduction mechanism 6 and the rack and pinion mechanism 9. Is housed in a gear housing (not shown). As shown in FIG. 2, a worm gear shaft 61a is coupled to a rotor shaft 7a that rotates integrally with the rotor of the electric motor 7 with a coupling 7b made of an elastic body such as rubber or serrations. 7 rotation and torque are transmitted to the worm gear 61.

≪Deceleration mechanism configuration≫
The speed reduction mechanism 6 shown in FIG. 2 has a function of boosting the rotational torque of the electric motor 7 and transmitting it to the steering shaft 3 and is composed of a speed reduction gear mechanism. The speed reduction mechanism 6 is configured, for example, by engaging a worm gear 61 connected to the rotor shaft (output shaft) 7a of the electric motor 7 and rotating with a worm wheel 62 provided on the steering shaft 3, for example. is doing.

<Configuration of worm gear>
As shown in FIG. 2, the worm gear 61 is composed of a single thread and includes a worm gear shaft 61a connected to the rotor shaft 7a and a gear cutting portion 61b formed integrally with the worm gear shaft 61a. As shown in FIG. 3, the worm gear 61 is formed such that the gear cutting length L is substantially an integral multiple N of the pitch length P, and the center of gravity C of the entire gear cutting portion 61 b of the worm gear 61 is aligned with the axis O. .
2 and 3 show an example in which teeth of 4 pitches are formed in the gear cutting portion 61b of the worm gear 61. FIG. In this case, the worm gear 61 is formed so that the gear cutting length L is four times the pitch length P. The worm gear 61 has a gear cutting start position 61c and a gear end position 61d formed at the same radial position in the gear cutting portion 61b. For this reason, the center of gravity C of the entire teeth of the worm gear 61 coincides with the axis O.

The worm gear shaft 61a is rotatably supported by bearings 63 and 64 installed at both ends of the gear cutting portion 61b so that the rotor shaft 7a of the electric motor 7 rotates in the same direction.
The gear cutting portion 61b is a tooth profile portion in which the tooth profile of the worm gear 61 is formed, and is formed from the gear start start position 61c to the end position 61d. The worm gear 61 is disposed so as to mesh with the worm wheel 62 at the central portion of the gear cutting portion 61b.

<Configuration of worm wheel and bearing>
A worm wheel 62 shown in FIG. 2 is a gear for decelerating and transmitting the rotation of the worm gear 61 to the steering shaft 3. In the case of a so-called column type electric power steering apparatus 1 as shown in FIG. 1, the worm wheel 62 is integrally provided on the steering shaft 3. In the case of the pinion type electric power steering apparatus 100 as shown in FIG. 9, it is provided integrally with the pinion shaft.
The bearings 63 and 64 are ball bearings, and are installed so that the inner ring rotates integrally with the worm gear shaft 61a. The outer ring is mounted on the inner wall of a gear housing (not shown).

≪Action≫
Next, the operation of the electric power steering apparatus 1 according to the embodiment of the present invention will be described with reference to FIGS.
In the electric power steering apparatus 1 shown in FIG. 1, when the driver steers the steering wheel 2, the rack shaft 10 linearly reciprocates via the rack and pinion mechanism 9 by the steering torque applied to the steering shaft 3, and the tie rod 11. The steered wheels 12 are steered through the above.

  At this time, the drive control unit (ECU) 8 sets a target current value to flow to the electric motor 7 based on the steering torque signal input from the steering torque sensor 4 and the vehicle speed signal input from the vehicle speed sensor 5, The electric motor 7 is driven by current feedback control so that a deviation between the target current value and a motor current value input from a motor current sensor (not shown) becomes zero. As a result, the electric motor 7 generates an appropriate steering assist force (assist force), and this steering assist force is applied to the steering shaft 3 via the speed reduction mechanism 6 so that the steering force during the steering operation of the driver is achieved. Can be reduced.

Next, the operation of the speed reduction mechanism 6 of the electric power steering apparatus 1 according to the embodiment of the present invention will be described with reference to FIGS.
FIG. 4 is an explanatory diagram showing the locus of the center of gravity of the tooth portion in the worm gear of the electric power steering apparatus according to the embodiment of the present invention. FIG. 5 is a cross-sectional view taken along the line XX of FIG.

As shown in FIG. 2, the speed reduction mechanism 6 includes a worm gear 61 composed of a single thread and a worm wheel 62 meshing with the worm gear 61.
As shown in FIG. 3, the worm gear 61 is formed such that the gear cutting length L is an integral multiple N of the pitch length P. The locus of the position of the center of gravity C of the tooth portion in the cross section perpendicular to the axis of the worm gear 61 is as shown by a two-dot chain line in FIG. That is, as shown in FIG. 4, the position of the center of gravity C in the cross section in the direction perpendicular to the axis of each part of the worm gear 61 is spirally formed along the shape of the tooth portion with the center line OO as the center. It is deviated from O and eccentric.

  For example, assuming that the axial parallel pitch of the worm gear 61 is P and the angle variable (phase angle) is θ, a cross-section in the direction perpendicular to the axis of the worm gear 61 at the position of Pθ / 2π from the gear cutting start position 61c of the gear cutting portion 61b (X -X) has a shape as shown in FIG. That is, the center of gravity C in the cross section in the direction perpendicular to the axis of the worm gear 61 is at a position shifted in the radial direction from the axis O by the radius R as shown in FIG.

  The worm gear 61 composed of such a single thread is formed such that the gear cutting length L is an integral multiple N of the pitch length P so that the center of gravity C of the entire tooth profile of the worm gear 61 coincides with the axis O. Become. In the worm gear 61 formed in this way, the center of gravity C of the entire tooth profile and the axis O coincide with each other, so that the vibration and rotation unevenness of the worm gear 61 itself are reduced, and the engagement between the worm gear 61 and the worm wheel 62 is achieved. Smooth. As a result, the steering feeling when the steering wheel 2 (see FIG. 1) is operated can be improved. Further, it is possible to suppress a reduction in the allowable load of the worm gear 61 due to the centrifugal force generated by the deviation of the center of gravity C.

≪First modification≫
The present invention is not limited to the above-described embodiment, and various modifications and changes can be made within the scope of the technical idea. The present invention extends to these modifications and changes. Of course.

  A first modification of the present invention will be described with reference to FIGS. In the first modification, when the center of gravity C of the entire gear cutting portion 61Ab of the worm gear 61A formed with the gear cutting length L being an integral multiple N of the pitch length P is deviated from the axis O, the gear cutting of the worm gear 61A is performed. A center-of-gravity offset portion 61Ae is formed in the portion 61Ab to correct the position of the center of gravity C of the entire gear cutting portion 61Ab shifted from the axis O.

  FIG. 6 is a view showing a first modification of the electric power steering apparatus according to the embodiment of the present invention, and is an explanatory view of a worm gear in which gear cuts for the center of gravity offset length are formed in the gear cut portions. FIG. 7 is a graph showing the relationship between the phase of the gravity center offset length of the worm gear and the offset weight in the first modification of the electric power steering apparatus according to the embodiment of the present invention.

As shown in FIG. 6, the effective gear cutting length at the gear cutting portion 61Ab of the worm gear 61A is L, the integer is N, the pitch is P, and the gravity center offset is formed on the end position 61Ad side to correct the position of the gravity center C. When the center of gravity offset length parts 61Ae and _{L 1,}
L = NP + L ₁
It becomes.

In other words, the center of gravity of the entire gear cutting portion 61Ab at a position shifted in the radial direction from the axis O by the radius R is added to the effective gear cutting portion 61Ab in a region having a length that is an integral multiple NP of the axial parallel pitch of the worm gear 61A. In order to move the position of C to the axis O, an extra center of gravity offset portion 61Ae having a gear cut of the center of gravity offset length L ₁ is formed and corrected.
Thus, by forming a gear cutting portion 61Ab of the center of gravity of the whole offset length L ₁ minute of the center of gravity offset portion 61Ae center of gravity C it is considering offset of minute mass offset from the axis O to the Hasetsu portion 61Ab, The position of the center of gravity C of the entire gear cutting portion 61Ab is adjusted to coincide with the axis O. As a result, in the effective gear cutting portion 61Ab in the region having a length that is an integral multiple NP of the axis parallel pitch of the worm gear 61A, the position of the center of gravity C of the entire tooth portion is corrected to the position of the axis O. For this reason, the center of gravity C of the entire tooth portion coincides with the axis O of the worm gear 61A.

On the other hand, when the phase angle θ ₁ is used for the portion of the gravity center offset length L ₁ ,
L ₁ = Pθ ₁ / 2π
It becomes.
Worm gear 61A A the area of the tooth portion in the transverse direction of the cross-section of, when the density of the material of the worm gear 61A M, offset the weight from the axis O of the teeth in the length of the center-of-gravity offset length L ₁ (Offset Mass) is

It becomes.
When the phase angle θ ₁ = π, the offset weight is maximum (see FIG. 7), and the value is PAM / π [kg]. The representation of the relationship between the phase and offset the weight of the center-of-gravity offset length L ₁ is a graph of Figure 7. As shown in FIG. 7, when the phase angle θ ₁ = 0 (and 2π), the offset weight is minimum.

Next, the worm gear 61A will be described using a general example of the electric power steering apparatus 1.
In a generally used reduction mechanism of an electric power steering apparatus, the reduction ratio is about 20, and this reduction ratio is formed by a worm wheel having a diameter of about 100 [mm]. For this reason, the worm gear shaft of the worm gear is formed with a diameter of 10 [mm] or less. When such a worm gear has an offset weight, a centrifugal force due to the offset weight is generated by the rotation of the worm gear, and the bending of the worm gear shaft by the centrifugal force is increased.

For example, if the rotation speed of the steering wheel 2 (see FIG. 1) is 1.5 [rps], the material density of the worm gear 61A is 7 × 10 ³ [kg / m ³ ], and the radius R of the center of gravity is 5 [mm]. The centrifugal force is about 10 [kgf].
In the electric power steering apparatus 1 having an axial force of about 1 [ton], the load that causes the worm gear 61A to bend in the direction perpendicular to the axis is about 50 [kgf]. For this reason, when the centrifugal force resulting from the offset weight of the worm gear 61A is taken into consideration, the allowable load is reduced by about 20 [%].
Here, by setting the center-of-gravity offset length L ₁ ≈0, the influence of the centrifugal force can be reduced, and the reduction of the allowable load of the worm gear 61A can be prevented. As a result, the center shake and vibration can be reduced by the centrifugal force generated by the worm gear 61A itself, and a good steering feeling can be obtained.

As described above, in the worm gear 61A, it is assumed that the center of gravity C of the teeth of the worm gear 61A is deviated from the axis O when the gear cutting length L of the gear cutting portion 61Ab is an integral multiple N of the pitch length P. However, the offset weight can be corrected to a position where the center of gravity C and the axis O of the entire gear coincide with each other by adjusting the offset of the center of gravity (L ₁ ). Thereby, the rotation nonuniformity and vibration of worm gear 61A can be eliminated. Furthermore, it is possible to suppress a reduction in the allowable load of the worm gear 61A due to the centrifugal force generated by the shift of the center of gravity C of the gear. As a result, the weight balance of the worm gear 61A as a whole is improved, and the center feeling and vibration can be suppressed to improve the steering feeling.

≪Second modification≫
Next, a second modification of the present invention will be described with reference to FIG. In the second modified example, when there is an incomplete incomplete gear cut portion 61Bf such as a rise of the gear cut portion 61Bb, and the center of gravity C position of the worm gear 61B is shifted from the center O by the incomplete gear cut portion 61Bf. It is to correct.
FIG. 8 is a view showing a second modification of the electric power steering apparatus according to the embodiment of the present invention, and is a cross-sectional view showing a worm gear having an incomplete gear cutting portion.

Worm gear 61B shown in FIG. 8 has an incomplete incomplete Hasetsu unit 61Bf, such as cut-up of the gear cutting portion 61Bb, the length of the toothed portion is formed incompletely toothed length L ₂ minutes longer ing. In the case of such a worm gear 61B, the position of the center of gravity C changes by the amount of the incomplete gear cutting portion 61Bf. Therefore, to cancel cross-sectional center of gravity offset amount of incomplete Hasetsu portion 61Bf of the worm gear 61B, corrected by adding the centroid offset length L ₁ of the gear cutting portion 61Bb as a correction length min.

In this case, for example, if the effective gear cutting length 61Bb of the worm gear 61B is L, the module is m _n , the advance angle is cos β, the integer is N, and the correction length for correcting the position of the center of gravity C is α,
L = πm _n / cos β × N + α
It becomes.

  In this manner, by adding the correction length α to the gear cutting portion 61Bb, the influence of the centrifugal force applied to the worm gear 61B is reduced and the allowable load of the worm gear 61B is reduced as in the above embodiment. Can be prevented. Further, it is possible to obtain a good steering feeling by reducing the core runout and vibration due to the centrifugal force of the worm gear 61B itself.

Further, as shown in FIG. 8, when the worm gear 61B has an incomplete gear cutting portion 61Bf such as a round-up, the phase angle in the cross section perpendicular to the axis at the boundary between the gravity center offset portion 61Be and the incomplete gear cutting portion 61Bf. Is θ ₁ , the phase angle θ _{2 at} the end position 61Bd of the incomplete gear cutting portion 61Bf, the gravity center offset length is L ₁ , and the incomplete end cutting length is L ₂ ,
θ ₁ = 2πL ₁ / P
θ ₂ = 2π (L ₁ + L ₂ ) / P
It becomes.
Relationship between the center of gravity offset length L ₁ and incomplete toothed length L ₂ for correcting the offset weight fraction of incompletely Hasetsu part 61Bf is

となる。この数式を解くと、

となる。

It becomes. Solving this formula,

It becomes.

If the center-of-gravity offset length L ₁ satisfying this is satisfied, the offset weight of the incomplete gear cutting portion 61Bf is canceled out by the center-of-gravity offset length L ₁ .
Thus, if the offset weight of the incomplete gear cutting portion 61Bf is adjusted, the same effect as that of the above embodiment can be obtained. The offset weight to be corrected may be set in advance before machining the worm gear 61B, or the deviation between the position of the center of gravity C of the entire gear cutting portion 61Bb of the worm gear 61B and the axis O position is measured after machining. Then, the deviation may be corrected.

In this case, the worm wheel meshes with the central portion of the gear cutting portion 61Bb of the worm gear 61B. Therefore, the center-of-gravity offset portion 61Be and the incomplete gear cutting portion 61Bf are easily formed by cutting the end portion of the gear cutting portion 61Bb or the like if the gear cutting portion 61B is formed with an integral multiple of the pitch. be able to.
In addition, when correcting the offset weight deviation, a part of the tooth portion of the worm gear 61B may be scraped off, or a hole may be made in the shaft center of the worm gear 61B.

≪Other variations≫
The present invention can also be applied to a structure (steer-by-wire) in which the steering wheel and the steered wheel of the steering system are mechanically separated and the electric motor generates all the steered force for the steered wheel. It is.

1 is a schematic configuration diagram illustrating an electric power steering apparatus according to an embodiment of the present invention. It is explanatory drawing which shows the deceleration mechanism of the electric power steering apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the worm gear of the electric power steering apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the locus | trajectory of the gravity center of the tooth | gear part in the worm gear of the electric power steering apparatus which concerns on embodiment of this invention. It is XX sectional drawing of FIG. It is a figure which shows the 1st modification of the electric power steering apparatus which concerns on embodiment of this invention, and is explanatory drawing of the worm gear which formed the gear cut for the gravity center offset length in the gear cut part. It is a graph which shows the relationship between the phase of the gravity center offset length of a worm gear, and offset weight in the 1st modification of the electric power steering device which concerns on embodiment of this invention. It is a figure which shows the 2nd modification of the electric power steering apparatus which concerns on embodiment of this invention, and is sectional drawing which shows the worm gear which has an incomplete gear cutting part. It is a model diagram which shows the installation state of the conventional electric power steering apparatus. It is a perspective view which shows the deceleration mechanism in which the conventional electric power steering apparatus is installed. It is a figure which shows the worm gear currently used for the conventional electric power steering apparatus, (a) Front view, (b) is a YY sectional drawing. It is a figure which shows the worm gear used for the other conventional electric power steering apparatus, (a) is a front view, (b) is ZZ sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering wheel 3 Steering shaft 6, 6A Deceleration mechanism 7 Electric motor 61, 61A, 61B Worm gear 61a, 61Aa, 61Ba Worm gear shaft 61b, 61Ab, 61Bb Tooth cutting part 61c Start position 61d, 61Ad, 61Bd End position 61e, 61Ae, 61Be Center-of-gravity offset portion 61Af, 61Bf Incomplete gear cutting portion 62 Worm wheel C Center of gravity of worm gear teeth L Gear cutting length L ₁ Center of gravity offset length L ₂ Incomplete end cutting length N Integer O Axis center P Pitch length

Claims (3)

An electric power steering device that drives an electric motor in response to a steering input and steers the vehicle by transmitting a driving force of the electric motor to a steering system via a worm gear,
The worm gear is
It consists of a single thread,
An electric power steering apparatus characterized in that a gear cutting length is an integral multiple of a pitch length, and the center of gravity of the teeth of the worm gear is aligned with the axis.   2. The electric power steering apparatus according to claim 1, wherein the worm gear has a gear cutting start position and an end position formed at the same radial position. An electric power steering device that drives an electric motor in response to a steering input and steers the vehicle by transmitting a driving force of the electric motor to a steering system via a worm gear,
The worm gear consists of a single thread,
The gear cutting length is an integral multiple of the pitch length,
A center-of-gravity offset length that corrects an offset weight component in which the position of the center of gravity and the center of the tooth of the worm gear shifts,
An electric power steering device characterized by having a length obtained by adding

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