JP2001171531A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate adjustment, in particular, for a backlash in a spur bevel gear transmission mechanism such as a worm gear mechanism constituting a power transmission mechanism, and to eliminate a hob cutting process to reduce a cost, in an electric power steering device. SOLUTION: A worm 30a driven by an electric motor is meshed with a tapered helical gear 23 provided in an output shaft 3. The backlash is easily adjusted by adjusting an axial-directional position of the output shaft 3 or the helical gear 23 with adjustment of shims A, B. Since the helical gear 23 is formed by injection molding without using a hob, hobbing is not required, and a manufacturing cost is reduced thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus capable of adjusting a backlash of a staggered gear transmission mechanism such as a worm gear mechanism constituting a power transmission mechanism.

[0002]

2. Description of the Related Art As an electric power steering device for a vehicle, the rotational output of an electric motor, which is an auxiliary steering torque, is reduced by a gear device and transmitted to an output shaft of a steering mechanism, thereby assisting the steering force applied to a steering wheel. There is known an apparatus which is configured to provide power and perform steering of a wheel with light torque.

In such an electric power steering device, a power transmission mechanism such as a worm gear mechanism provided in a housing is used to transmit power to an output shaft while reducing the rotation of the electric motor.

[0004]

One problem with an electric power steering system using a staggered gear transmission such as a worm gear mechanism is that two gears such as a worm and a worm wheel that constitute the staggered gear transmission. The point is how to properly set the backlash that occurs between the tooth surfaces.

[0005] That is, if the backlash is too small, the meshing teeth will compete with each other, and if the backlash is too large, the meshing teeth will abut against each other due to a sudden change in torque, thereby causing a hitting sound and a tooth surface. Premature wear and the like may be caused, and smooth torque transmission may be impaired, which may impair the function of the electric power steering device. Therefore, it is necessary to set the amount of backlash between the tooth surfaces to an appropriate value.

Here, in the conventional electric power steering apparatus, an output shaft having one gear such as a worm wheel attached thereto, and an electric motor having the other gear such as a worm engaged with the output shaft attached to a rotary shaft. Are mounted in the same housing, so that the amount of such backlash is kept within the desired range:
It is necessary to considerably improve the dimensional and shape accuracy of the housing and the two gears such as the worm and the worm wheel.

However, aside from the housing, the tooth surfaces of gears such as a worm and a worm wheel have a complicated shape. Therefore, in order to obtain a tooth shape necessary for setting a desired backlash between the tooth surfaces, Extremely precise processing is required, which inevitably increases manufacturing costs.

On the other hand, even if a tooth surface having a desired shape is formed by performing precision processing, and an appropriate amount of backlash is set, even if the worm and the worm wheel are used for a long period of time, Tooth surface wear occurs on the gear. Tooth surface wear increases the amount of backlash and prevents the initial proper state from being maintained.

However, it is difficult to adjust the backlash, which has been increased due to the tooth surface wear, back to the initial value. Therefore, by replacing the gears such as the worm and the worm wheel which can still be used with new ones, the electric type can be changed. The power steering device is used continuously.
Such replacement of the worm and worm wheel gears results in wasteful consumption of the user.

Therefore, the present invention has been made in view of such a problem,
By enabling the adjustment of the backlash occurring between the tooth surfaces of the two gears constituting the staggered gear transmission,
An object of the present invention is to provide an electric power steering device with reduced manufacturing cost and improved reliability.

Further, the present invention can be applied to a case where two gears of a worm and a worm wheel are worn over a long period of time and the amount of backlash is increased due to the occurrence of tooth flank wear. An object of the present invention is to provide an electric power steering device that can be adjusted to a backlash amount.

The pitch diameter of the hob used for machining the teeth of the worm wheel in the electric power steering apparatus is set to be larger (about five times) than the pitch diameter of the worm. Therefore, the teeth of the worm wheel at positions deviated from the center position are positively displaced, and the tooth thickness is larger than the meshing center.

It is a further object of the present invention to make use of this fact to easily adjust the backlash amount of the worm and the worm wheel in the electric power steering apparatus.

Conventionally, in an electric power steering apparatus, a staggered gear transmission (a gear transmission in which two axes are not parallel and do not intersect) constituted by a worm and a worm wheel has been employed. In recent years, worm wheels have often been constituted by a metal core and a gear portion made of resin on the outer periphery thereof. This gear portion is integrally formed with a core (or a core into which the output shaft is press-fitted) placed at the center of the mold. At this time, since the tooth profile portion of the worm wheel cannot be formed by such a mold (does not come off from the mold), since it is formed by hobbing in a later step, a separate step is provided, which leads to an increase in cost. I was

Another object of the present invention is to provide an electric power steering apparatus which solves the above-mentioned problem and eliminates the worm wheel hobbing step as described above and can reduce the cost. It is an issue.

[0016]

In order to achieve the above object, the present invention takes the following means.

According to a first aspect of the present invention, an electric power steering apparatus includes a housing, an input shaft rotatably supported in the housing, an output shaft rotatably supported in the housing, and the input shaft. A torsion bar provided between the output shaft, an electric motor, and a staggered gear transmission in which one gear is provided on the output shaft, and the other gear meshing with the gear is connected to the electric motor; and A steering force detection device that detects a steering force by detecting a relative rotation angle between a shaft and the output shaft, and a control device that controls the motor based on the steering force detected by the steering force detection device. An electric power steering device, wherein the gear provided on the output shaft of the staggered gear transmission has teeth whose dislocation amount and outer diameter substantially increase along the axial direction. To a gear, the adjusting device is provided that allows adjusting the axial position of the gear.

When the steering wheel is steered, this rotation is transmitted to the input shaft, and the torsion bar is twisted in accordance with the steering force, causing relative rotation between the input shaft and the output shaft. The steering force detection device outputs a signal according to the direction and amount of the relative rotation. Based on this signal, the control device rotates the electric motor in a direction that eliminates the torsion of the torsion bar to generate an auxiliary steering force. The rotation of the electric motor is reduced by the staggered gear transmission to reduce the output shaft 3.
To the steering mechanism.

In such an electric power steering apparatus, the adjusting means can adjust the axial position of the gear provided on the output shaft, and the staggered gear transmission meshes with the gear provided on the output shaft. Since the backlash generated between the two gears can be adjusted, the backlash amount can be adjusted to an appropriate amount without increasing the accuracy of these two gears more than necessary. Also, even if the tooth surfaces of the two gears are worn while using the electric power steering device, the backlash can be properly adjusted without replacement.

According to a second aspect of the present invention, there is provided an electric power steering apparatus according to the first aspect, wherein the staggered gear transmission comprises a worm wheel and a worm, and the output shaft is provided with a worm wheel. With such a configuration, the worm wheel and the worm that are commonly used in the conventional electric power steering apparatus can be used as they are.

A third aspect of the present invention provides the electric power steering apparatus according to the first aspect, wherein the staggered gear transmission comprises a tapered helical gear and a worm, and the output shaft has a tapered helical gear. Since the taper helical gear can be manufactured by injection molding,
There is no need to hob the teeth, making it easy to manufacture and reducing manufacturing costs.

According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to the first to third aspects, wherein the adjusting device is provided between the casing and the output shaft and between the casing and the output shaft. Since the backlash adjustment is performed by a shim provided on one or both of the output shaft and the gear transmission, fine adjustment and stable adjustment can be performed by changing the thickness or combination of the shims.

According to a fifth aspect of the present invention, there is provided an electric power steering apparatus according to the first to third aspects, wherein the adjusting device is provided between the casing and the output shaft, and Since backlash adjustment is performed by a shim provided on one or both of the output shaft and the output shaft of the staggered gear transmission, fine adjustment and stable adjustment can be performed by changing the thickness or combination of the shims. It becomes possible.

According to a sixth aspect of the present invention, there is provided the electric power steering apparatus according to the first to third aspects, wherein the casing has an output side casing for supporting the output shaft and an input for supporting the input shaft. The backlash adjustment is performed by an adjustment device that includes a side casing and is provided between the output side casing and the input side casing.

According to a seventh aspect of the present invention, there is provided an electric power steering apparatus according to the first to third aspects, wherein the adjusting device comprises a bearing holder for supporting an outer ring of a bearing for supporting the output shaft. It consists of a male screw, a female screw of the casing with which this bearing holder is screwed, and a lock nut which is screwed with the above-mentioned bearing holder, adjusts the backlash by turning the bearing holder with the lock nut loosened, and then locks the lock nut. It is something to tighten.

According to an eighth aspect of the present invention, there is provided a method of manufacturing a tapered helical gear shaft having a core or a shaft concentrically fitted with a core and a gear portion formed concentrically therearound. A manufacturing method, wherein an insert pin piece that supports a core or a shaft concentrically fitted with a core, and an inner surface that is rotatably supported concentrically with the insert pin piece and that forms the tooth surface of the tapered helical gear. Having gear pieces,
Injecting resin through a passage into a mold consisting of a gate piece having a passage for injecting resin, and a metal part integrally molded with a core or a shaft on which the core is fitted concentrically. It is.

According to this method, the subsequent hobbing step becomes unnecessary, and when the tapered helical gear of the ninth invention obtained by this method is used, the tapered helical gear is moved in the axial direction. The backlash between the gear and the gear meshing with the gear can be adjusted.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First Embodiment FIG. 1 is a sectional view showing an electric power steering apparatus according to an embodiment of the present invention by cutting along an axis of an input shaft. The electric power steering apparatus of this embodiment is of a type known as a pinion type.

The housing 1 comprises an output side housing 1a and an input side housing 1b. In the housing 1, an input shaft 2 and an output shaft 3 extend.

The hollow input shaft 2 has a right end connected to a steering shaft (not shown), and the steering shaft is further connected to a steering wheel (not shown). The input shaft 2 is rotatably supported by a bearing 4 with respect to the input side housing 1b. A torsion bar 5 having a right end connected to the input shaft 2 and a left end connected to the output shaft 3 extends inside the hollow of the input shaft 2.

In the vicinity of the left end of the input shaft 2, there is provided a detecting device for detecting the steering torque, that is, a torque sensor 6, based on the fact that the torsion bar 5 is twisted in proportion to the received torque. The torque sensor 6 is a rotary non-contact torque sensor,
The relative angular displacement between the input shaft 2 and the output shaft 3 based on the torsion is detected by the coil 7 as a change in impedance in a predetermined magnetic circuit, and is output as an electric signal to a control circuit (not shown).

A pinion gear 3a is formed on the left side of the output shaft 3, and meshes with a rack tooth 11a of a rack shaft 11 extending in a direction perpendicular to the paper surface. The rack shaft 11 includes a rack guide 12a, a spring 12b, and a lock member 12c.
And is supported from the back by a well-known rack support device 12, and is pressed toward the pinion gear 3a. The rack shaft 11 is attached to a well-known steering mechanism (not shown), and is steered by the rack shaft 11 moving in a direction perpendicular to the plane of FIG. 1 as the pinion gear 3a rotates.

A worm wheel 13 is fixedly mounted around the right end of the output shaft 3 by press-fitting or the like.
The worm wheel 13 meshes with a worm 30a connected to a rotating shaft of an electric motor (not shown). This electric motor is connected to the control circuit (not shown),
This control circuit inputs information such as the output of the torque sensor 6 and the vehicle speed, and supplies predetermined electric power to the electric motor to generate an appropriate auxiliary torque. The output shaft 3 is rotatably supported by the housing 1 by a right bearing 14 and a left bearing 15 as described below.

As shown in FIG. 2, the worm wheel 13 is composed of a metal core 13a and a gear portion 1 made of a resin around the metal core 13a.
3b, and a worm tooth is formed on the gear portion 13b. A right bearing 14 is fitted near the worm wheel 13 to the right of the output shaft 3. The inner ring of the right bearing 14 is press-fitted and fixed to a step 3b formed near the right end of the output shaft 3. The outer ring of the right bearing 14 allows the output shaft 3 to move left and right during backlash adjustment described later. Thus, it is fitted to the output side housing 1a.

Further, a left bearing 15 is provided at the left end of the output shaft 3.
Are fitted. The outer ring of the left bearing 15 is a screw cover 9
Is screwed into the output side housing 1a,
The housing 1 is fixed to a step wall 1d via a shim A described later. On the other hand, the inner ring of the left bearing 15 is attached to the output shaft 3 via a shim B described later by screwing the nut 17 into the output shaft 3. Note that the left bearing 15 can be an angular contact type bearing with little backlash in the axial direction. By using such a bearing 15, the output shaft 3 can be positioned in the axial direction.

As described above, the worm 30a, the worm wheel 13, the output shaft 3, the rack shaft 11 and the like are provided on the output side housing 1a.

Now, the operation of the electric power steering apparatus shown in this embodiment will be described. Assuming that the vehicle is in a straight running state and no steering force is input to the input shaft 2 via a steering wheel and a steering shaft (not shown), the torque sensor 6 does not generate an output signal, and therefore the electric motor uses the auxiliary steering force. Does not occur.

When the driver steers a steering wheel (not shown) while the vehicle is about to make a curve, the torsion bar 5 is twisted in accordance with the steering force, and the input shaft 2 and the output shaft 3 are relatively rotated. Occurs. The torque sensor 6
A signal is output according to the direction and amount of the relative rotation.
Based on this signal, the electric motor rotates in a direction to eliminate the twist of the torsion bar and generates an auxiliary steering force. The rotation of the electric motor is reduced by the worm gear mechanism and transmitted to the output shaft 3 to assist in moving the rack shaft 11.

FIG. 3 is a cross-sectional view of the meshing portion of the worm wheel 13 and the worm 30a parallel to their axes (FIG. 1).
FIG. 3 is a cross-sectional view taken along line AA in FIG.

When the worm wheel 13 is hobbed, the worm wheel 13 is usually cut by a hob having a pitch circle diameter approximately five times larger than the pitch circle diameter of the worm meshing with the worm wheel. A positively displaced tooth is formed. As shown in FIG. 3, when viewed in the tooth section of the worm wheel 13, the tooth thickness is thinner at the center along the tooth trace direction as shown in FIG. I have. In other words, the distance between the teeth is small on both sides of the tooth muscle and large at the center.

When the tooth of the worm 30a is in contact with one surface of one of the teeth of the worm wheel 13, the opposite surface of the tooth of the worm wheel 13 adjacent thereto is separated from the worm, and this separation is caused. Is the backlash B / L.

If the backlash B / L is too small, the meshing teeth will compete with each other. If the backlash is too large, the meshing teeth will abut against each other due to a sudden torque change, thereby causing a hitting sound and a tooth surface. As described above, it is necessary to adjust the backlash B / L to an appropriate value, since it causes early wear and the like and hinders smooth torque transmission and impairs the function of the electric power steering apparatus.

In the present invention, the backlash B / L is adjusted by adjusting the axial position of the worm wheel 13.
Is adjusted. That is, in this embodiment, as is apparent from FIG. 3, if the axial position of the worm wheel 13 is shifted with respect to the worm 30a as shown by a dotted line, the tooth spacing of the worm 30a is invariable. The property that the amount of L can be reduced is utilized.

The adjustment of the axial position of the worm wheel 13 is specifically performed in this embodiment by the shim A and the shim B.
By replacing one or both of them with a different thickness. Here, both the shim A and the shim B do not always have to be provided, and only one is provided according to the amount of backlash B / L for each electric power steering device to be assembled. can do.

Also, if the shim A is made thicker, the worm wheel 13 is shifted to the left, and if the shim B is made thicker, the worm wheel 13 is shifted to the right. Therefore, the amount of backlash B / L can be adjusted by a combination of these thicknesses. it can.

Second Embodiment FIG. 4 is another embodiment, and is a sectional view of a main part of a column type electric power steering apparatus to which the present invention is applied. This has the same structure as the pinion-type electric power steering apparatus described above, but basically has no pinion gear 3a formed on the output shaft 3 and meshes with the pinion gear 3a. It differs greatly in that it does not have the rack shaft 11. Hereinafter, the corresponding members will be described using the same reference numerals.

The housing 1 includes an output side housing 1a and an input side housing 1b, and an input shaft 2 and an output shaft 3 extend inside the housing 1.

The hollow input shaft 2 is connected to a steering shaft, and the steering shaft is connected to a steering wheel. The input shaft 2 is rotatably supported by the input housing 1b by a bearing (not shown). A torsion bar 5 having a right end connected to the input shaft 2 and a left end connected to the output shaft 3 extends inside the hollow of the input shaft 2.

In the vicinity of the left end of the input shaft 2, a detecting device for detecting the steering torque, that is, a torque sensor 6, is provided based on the fact that the torsion bar 5 is twisted in proportion to the received torque. The torque sensor 6 is a contact-type torque sensor that detects a relative angular displacement between the input shaft 2 and the output shaft 3 based on a torsion of the torsion bar 5 based on a change in a resistance value of a potentiometer, and detects an electric signal. This is output to the control circuit shown in the figure. In the present invention, any type of torque sensor 6 may be used.

The left side of the output shaft 3 is connected to a well-known steering mechanism (not shown) via a transmission mechanism (not shown) such as a universal joint.

A worm wheel 13 is fixedly mounted on the outer periphery of the right end of the output shaft 3 by press fitting or the like.
The worm wheel 13 includes a cored bar 13a and a gear portion 13b formed of a resin around the cored bar 13a. The gear portion 13a has worm teeth. The worm wheel 13 is connected to the worm 3 connected to the rotating shaft of the electric motor M.
0a. The electric motor M is connected to the control circuit (not shown). The control circuit inputs information such as the output of the torque sensor 6 and the vehicle speed, supplies predetermined electric power to the electric motor, and This is to generate auxiliary torque. The output shaft 3 includes a right bearing 14 and a left bearing 15
And is rotatably supported by the output side housing 1a. A shim A is interposed between the inner ring of the right bearing 14 and the step wall 1 e of the output shaft 3, and a sleeve 20 is interposed between the right bearing 14 and the left bearing 15 to form a nut 21. Is fixed to the output shaft 3.

As described above, the output shaft 3 and the worm wheel 13 attached thereto belong to the output side housing 1a, and other members including the worm 30a belong to the input side housing 1b.

The operation of the column-type electric power steering apparatus described above is basically the same as that of the pinion-type electric power steering apparatus described above, and a description thereof will be omitted.

In this embodiment, the output side housing 1a
A shim B is provided at the joint between the input side housing 1b and
Since the shim A is interposed between the stepped wall 1e of the output shaft 3 and the inner ring of the right bearing 14, the worm 30a can be changed by replacing these shims with those having different thicknesses or by changing the combination. , The axial position of the worm wheel 13 can be adjusted. For the same reason as described in the previous embodiment, the amount of backlash can be adjusted by adjusting the relative position (the relative position in the axial direction of the worm wheel 13).

Third Embodiment FIG. 5 shows another embodiment, which is an electric power steering apparatus of a pinion type as in the first embodiment.

The worm wheel 13 according to the first embodiment has a tapered helical gear 23 in the first embodiment.
Helical gear 2
Reference numeral 3 denotes a core 23a and a gear portion 23b made of a resin having teeth formed around the core 23a. For this reason, the structure, the operation, and the adjustment of the backlash by the shims A and B are the same as those in the first embodiment, and therefore they will not be described.

The tapered helical gear 23 has a difference in the amount of dislocation at both ends in the face width direction and connects the middle portion with a constant change amount, and can be engaged with the worm.

6A is a view of one of the teeth of the tapered helical gear 23 as viewed from the axial direction of the gear, FIG. 6B is a sectional view of the teeth taken along the line BB, and FIG. FIG. 3 is a sectional view of the tapered helical gear 23 when the teeth are viewed from the side.

The tapered helical gear 23 is conical in appearance, but the diameter of the base circle is constant in any cross section perpendicular to the axis. The tooth thickness of this tooth is determined by a cylindrical section (for example, B-
When measured on the (B cross section), the tooth thickness d1 at one end of the tooth width gradually becomes larger (thicker) toward the other end of the tooth width and becomes d2.

FIG. 6B shows the tapered helical gear 2
The cross section of the worm 30a is also shown along with the cross section of the third tooth. When the worm 30a is shifted to the right, it can be seen that the amount of backlash B / L gradually decreases as indicated by the dotted line. That is, the relative positions of the tapered helical gear 23 and the worm 30a can be shifted by changing the thicknesses of the shims A and B and the combination thereof, thereby adjusting the backlash B / L.

Fourth Embodiment FIG. 7 is a sectional view of a pinion type electric power steering apparatus according to a fourth embodiment. This embodiment differs from the third embodiment only in the structure for adjusting the backlash, and therefore, only this structure will be described.

In the fourth embodiment, no shim is used. The inner ring of the left bearing 15 is fixed to the output shaft 3 by a stepped wall of the output shaft 3 and a nut 17, and the outer ring is fixed to a stepped wall provided in an empty space of the bearing holder 24 by a tapered retaining ring 25. Have been.

A male screw is cut on the outer periphery of the bearing holder 24, and this male screw can be screwed into a female screw provided at the left end of the output side housing 1a. A lock nut 26 is screwed to the male screw. Since this electric power steering device has such a structure,
In order to change the axial position of the tapered helical gear 23 for backlash adjustment, loosen the lock nut 26, rotate the bearing holder 24 by an appropriate amount, and
Should be moved. When the adjustment is completed, lock nut 26
Again so that it does not loosen naturally.

As described above, the tapered helical gear 23 used in the electric power steering devices of the third and fourth embodiments is different from the electric power steering device of the first and second embodiments. In comparison with the worm wheel 13 used in the above, there is a very advantageous point that injection molding can be performed as described below.

FIG. 8 is a sectional view of a main part of a mold of an injection molding machine for molding the tapered helical gear 23. The entire mold 50 includes an insert pin piece 51, an outer diameter centering piece 52, a gear piece 53, and a gate piece 54.
The insert pin piece 51 inserts the output shaft 3, that is, the insert 56, which is press-fitted into the core metal 13 a, into the hole to fix and position the output shaft 3, and to constitute a part of the surface of the injection mold. The outer diameter centering piece 52 is fitted with the insert pin piece 51, and a bearing 57 described later is fitted on the upper part thereof.

The gear piece 53 has a space for forming the tooth surface of the gear portion 23b of the tapered helical gear 23, and is rotatable via the bearing 57.
The gate piece 54 has a resin passage that opens into a space formed by the gear piece 53 and the like, and has a wall surface for the gear portion 23b to be molded.

Injection molding of the gear portion 23b using the mold 50 is performed as follows. Insert pin piece 5
1. Assembling the outer diameter centering piece 52 and the gear piece 53,
8, the output shaft 3 of the insert 56 is inserted into the hole of the insert pin piece 51 from above while the gate piece 54 is pulled upward in FIG. 8, and is positioned and fixed. Next, the gate piece 54 is lowered and the lower surface is pressed against the gear piece 53 with an appropriate pressure.

Since the core 23a, the insert pin piece 51, the gear piece 53 and the gate piece 54 form a space in the gear portion 23b to be injection-molded, the resin passage of the gate piece 54 from the resin injection hole is formed. The resin is injected into this space via the.

After the injected resin is cooled and solidified, that is, when the injection molding is completed, the gate piece 54 is pulled up, and the insert 56 is pushed up from below. Since the formed tapered helical gear has a draft, the tapered helical gear is pushed upward while the gear piece 53 is rotated by the bearing 57, and is extracted from the gear piece 53. After that, the resin in the portion corresponding to the resin passage is removed to obtain a usable tapered helical gear 23 in which the output shaft 3, the core metal 23a, and the gear portion 23b are integrated.

The tapered helical gear 23 formed in this manner does not require costly processing such as hobbing of the gear portion 23b, and can be used as it is.

In the third and fourth embodiments, the worm wheel 13 is replaced by the tapered helical gear 23 as described above. However, when the worm wheel is replaced by the tapered helical gear 23, the contact surface pressure generally increases. Is said to be large, this promotes wear,
It seems that backlash grows faster.

However, the worm wheel used in the electric power steering apparatus is usually processed with a hob having a diameter of about 5 times the pitch circle diameter. Absent.

Further, in the case of the worm wheel 13 as described above, even the teeth thereof cannot be formed by a metal mold, so that hob cutting is required. However, the worm wheel 13 is often mixed with reinforcing fibers such as glass fiber in order to increase the strength, and the resin layer is shaved by hobbing, so that the reinforcing fibers are exposed and the tooth surface of the worm meshing with the worm is scraped off. Occurs, the worm tooth surface wear is accelerated, and the proper backlash state is lost. In addition, at the time of hobbing, the abrasion of the cutting edge of the hob is promoted by the reinforcing fibers, so that the hob needs to be sharpened frequently.

On the other hand, since the above-described tapered helical gear can form the tooth surface only by injection molding, the reinforcing fibers are not exposed as in the case of hobbing. Therefore, the proper backlash state is not lost early. Further, since hobbing is not required, and re-sharpening of the hob is not required, the manufacturing cost can be reduced from this point as well.

[0076]

According to the present invention, there is provided an electric power system which can reduce the manufacturing cost and improve the reliability by enabling the adjustment of the backlash generated between the tooth surfaces of the two gears constituting the staggered gear transmission. There is an effect that a steering device can be obtained.

Further, according to the present invention, it is relatively easy to reduce the amount of backlash due to the occurrence of tooth flank wear on two gears of a staggered gear transmission such as a worm and a worm wheel during a long period of use. This has the effect of obtaining an electric power steering device that can be adjusted to the amount of backlash as originally.

The present invention utilizes the fact that the dislocation amount of the teeth of the worm wheel or the tapered helical gear is different in the axial direction to adjust the backlash amount of the worm and the worm wheel or the tapered helical gear in the electric power steering device. There is an effect that it can be easily performed.

According to the present invention, an electric power steering apparatus is provided which uses a tapered helical gear instead of a worm wheel, eliminates the need for a hob cutting step of a worm wheel, can be easily formed by injection molding, and can reduce costs. Is obtained.

Further, according to the present invention, since the tooth surface of the tapered helical gear is formed by injection molding, wear of the tooth surface can be reduced as compared with the tooth surface of the worm in the case of a worm wheel subjected to hobbing. This has the effect of extending the life of the dynamic power steering device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an electric power steering apparatus according to an embodiment of the present invention, cut along an axis of an input shaft.

FIG. 2 is a sectional view of the worm wheel 13 according to the embodiment.

FIG. 3 is a cross-sectional view when a meshing portion of the worm wheel 13 and the worm 30a is cut along a cutting plane (AA cross section in FIG. 1) parallel to these axes.

FIG. 4 is a sectional view of a main part of another embodiment of a column type electric power steering apparatus to which the present invention is applied.

FIG. 5 is a sectional view of another embodiment of a column type electric power steering device to which the present invention is applied.

FIG. 6 is an explanatory diagram for explaining the engagement between the tapered helical gear and the worm.

FIG. 7 is a sectional view of another embodiment of a column type electric power steering apparatus to which the present invention is applied.

FIG. 8 is a sectional view of a main part of a mold of an injection molding machine for molding the tapered helical gear 23.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 1a Output side housing 1b Input side housing 1d, 1e Step wall 2 Input shaft 3 Output shaft 3a Pinion gear 4 Bearing 5 Torsion bar 6 Torque sensor 7 Coil 11 Rack shaft 11a Rack teeth 12 Rack support device 12a Rack guide 12b Spring 12c Locking member 13 Worm wheel 13a Core 13b Gear 14 Right bearing 15 Left bearing 17 Nut 20 Sleeve 21 Nut 23 Taper helical gear 23a Core 23b Gear part 24 Bearing holder 25 Taper retaining ring 30a Worm 50 Mold 51 Insert Pin piece 52 Outer diameter centering piece 53 Gear piece 54 Gate piece 56 Insert 57 Bearing 58 Passage 100 Electric power steering device A, B Shim M Electric motor

Claims (9)

[Claims] A housing; an input shaft rotatably supported in the housing; an output shaft rotatably supported in the housing; and a torsion bar provided between the input shaft and the output shaft. An electric motor, and one of the gears provided on the output shaft, and the other gear meshing with the output shaft is connected to the electric motor, and a staggered gear transmission, and a relative rotation angle between the input shaft and the output shaft is detected. An electric power steering device comprising: a steering force detection device that detects a steering force by controlling the motor based on the steering force detected by the steering force detection device; The gear provided on the output shaft of the device is a gear having teeth whose dislocation amount and outer diameter are substantially increased along the axial direction, and the position of the gear in the axial direction. Electric power steering apparatus characterized by adjustable with adjusting devices are provided. 2. The electric power steering apparatus according to claim 1, wherein the staggered gear transmission comprises a worm wheel and a worm, and the output shaft is provided with a worm wheel. Power steering device. 3. The electric power steering device according to claim 1, wherein the staggered gear transmission comprises a tapered helical gear and a worm, and the output shaft is provided with a tapered helical gear. Electric power steering device. 4. The electric power steering device according to claim 1, wherein the adjusting device is provided between the casing and the output shaft.
And an electric power steering device provided with a shim provided on one or both of the output shaft and the output shaft of the staggered gear transmission. 5. The electric power steering device according to claim 1, wherein the adjusting device is provided between the casing and the output shaft.
And an electric power steering device provided with a shim provided on one or both of the output shaft and the output shaft of the staggered gear transmission. 6. The electric power steering apparatus according to claim 1, wherein the casing comprises an output casing supporting an output shaft and an input casing supporting the input shaft. An electric power steering device, wherein the adjusting device is provided between the output casing and the input casing. 7. The electric power steering device according to claim 1, wherein the adjusting device includes: a male screw of a bearing holder that supports an outer ring of a bearing that supports the output shaft; An electric power steering apparatus comprising: a female screw of the casing into which a bearing holder is screwed; and a lock nut which is screwed into the bearing holder. 8. A method of manufacturing a tapered helical gear shaft having a core or a shaft concentrically fitted with the shaft and a gear portion formed concentrically around the core or the shaft, the method comprising: An insert pin piece that supports a shaft concentrically fitted; a gear piece that is rotatably supported concentrically with the insert pin piece and has an inner surface that forms the tooth surface of the tapered helical gear; and injects resin. And a gate piece having a passage for forming a metal part, by injecting a resin through the passage to form a gear part integrally with the core or the shaft on which the core is fitted concentrically. Characteristic method of manufacturing a tapered helical gear. 9. A tapered helical gear shaft manufactured by the manufacturing method according to claim 8.