JP2015155745A - Worm reduction gear and dual pinion type electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve reduction in size and weight while suppressing an increase in manufacturing cost.

SOLUTION: A pair of flat surface parts 32, 32 which are parallel with each other are provided on an outer peripheral surface of a base end part of a pinion shaft 10a, and those flat surface parts 32, 32 are connected by projection curved surface parts 33, 33 whose sectional shapes are partial arcs having their centers on the center axis of the pinion shaft 10a. Both the projection curved surface parts 33, 33 are fitted in an engagement hole 20a of a worm wheel 16b so as to align the pinion shaft 10a with the worm wheel 16b. Further, both the flat surface parts 32, 32 are gripped with a tool when a worm reduction gear is assembled or has its performance tested.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention is, for example, an electric power steering apparatus for reducing the force required for a driver to operate a steering wheel by incorporating it in an automobile steering apparatus and using the output of an electric motor as an auxiliary power source. The present invention relates to improvement of a worm reduction gear to be used and a dual pinion type electric power steering apparatus incorporating the worm reduction gear.

  As a device for reducing the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts), power steering devices are widely used. It is used. An electric power steering device that uses an electric motor as an auxiliary power source in such a power steering device is also known, for example, as described in Patent Documents 1 to 3. The electric power steering device can be made smaller and lighter than the hydraulic power steering device, has advantages such as easy control of the magnitude (torque) of auxiliary power and less power loss of the engine. FIG. 11 shows a steering device in which such an electric power steering device called a dual pinion type is incorporated.

  In this steering apparatus, the movement of the steering wheel 1 is transmitted to the input shaft 6 constituting the steering gear 5 via the steering shaft 2, the universal joint 3a, the intermediate shaft 4, and the universal joint 3b. The input shaft 6 is rotatably supported in the housing 7, and the rack 8 is displaced in the axial direction along with the rotation, and a pair of tie rods 9, 9 ( The steering angle is given to the steered wheel via FIG. For this purpose, the rack 8 is supported by the housing 7 so that the intermediate portion thereof can be displaced in the axial direction. The input shaft 6 is arranged in a twisted positional relationship with the rack 8. A pinion formed on the outer peripheral surface of the lower end portion of the input shaft 6 is engaged with the rack 8.

  Further, a part of the rack 8 and a portion that is axially disengaged from the pinion provided on the outer peripheral surface of the input shaft 6 are pinion shafts (assist shafts) corresponding to the worm wheel shafts described in the claims. 10 is arranged. A second pinion provided on the outer peripheral surface of the lower end portion of the pinion shaft 10 is engaged with the rack 8. An electric motor 12 is supported on the side of a housing 11 provided with the pinion shaft 10 inside. The electric motor 12 is used to apply an auxiliary force in the rotational direction to the pinion shaft 10 via the speed reducer 13. That is, when the driver operates the steering wheel 1 and the steering shaft 2 rotates, a torque sensor (not shown) detects the rotation direction and torque of the steering shaft 2 and outputs a signal representing the detected value. Send to controller (not shown). Then, this controller energizes the electric motor 12 to rotate the pinion shaft 10 in the same direction as the rotation direction of the steering shaft 2 based on the operation of the steering wheel 1 via the speed reducer 13. As a result, the rack 8 is displaced in the axial direction by the auxiliary force generated by the electric motor 12 based on energization in addition to the force applied from the input shaft 6 based on the force applied by the driver to the steering wheel 1. Therefore, the force required to displace the rack 8 in the axial direction and the force required to operate the steering wheel 1 can be reduced by this auxiliary power. As such a speed reducer 13, a worm speed reducer having a large lead angle and having reversibility in the power transmission direction is generally used.

  FIG. 12 shows an example of a conventional structure of a worm speed reducer described in Patent Document 4. This worm speed reducer is provided inside a speed reducer housing 11 a to which an electric motor 12 is fixed, and a worm shaft 15 having a worm 14 formed in an intermediate portion in the axial direction, and a worm meshed with the worm 14. A wheel 16. Of these, the worm shaft 15 is rotatably supported inside the housing 11a by a pair of ball bearings 17 and 17 fitted on both ends in the axial direction. At the same time, the worm shaft 15 is rotatably driven by connecting the base end portion (left end portion in FIG. 12) of the worm shaft 15 to the drive shaft 18 of the electric motor 12. The worm wheel 16 is supported at an axial intermediate portion of the worm wheel shaft 19 (corresponding to the pinion shaft 10 of the dual pinion type electric power steering apparatus shown in FIG. 11 described above). Thereby, the rotational driving force generated by the electric motor 12 can be transmitted to the worm wheel shaft 19 via the worm speed reducer including the worm shaft 15 and the worm wheel 16.

  In the case of the worm speed reducer as described above that is used by being incorporated in the dual pinion type electric power steering device as described above, the worm wheel is formed by, for example, press-fitting the worm wheel shaft into the engagement hole provided at the center thereof. The worm wheel shaft is supported at a portion near one axial end of the worm wheel shaft so as to rotate concentrically with the worm wheel shaft and in synchronization with the worm wheel shaft. In order to facilitate the work of press-fitting the worm wheel, the engagement between the engagement portion (holding portion) with the worm wheel and the portion adjacent to one side in the axial direction on the outer peripheral surface of the worm wheel shaft. It is effective to provide a guide portion that functions as a centering guide for centering with the hole. In the case of the worm wheel shaft of the worm speed reducer constituting the dual pinion type electric power steering device, a tool is attached to one end in the axial direction, for example, during assembly or performance test of the worm speed reducer (depending on the tool). To be gripped), a mounted part (held part) is provided. However, if a holding portion, a guide portion, and a mounted portion are provided in series in the axial direction on one half of the worm wheel shaft in the axial direction, the axial length of the worm wheel shaft increases, and the worm speed reducer Increases in size and weight. In addition, the material cost may increase, and the processing for forming the holding portion, the guide portion, and the attached portion may be troublesome, and the manufacturing cost may increase.

JP 2002-154442 A JP 2007-245804 A JP 2005-289298 A JP 2006-142400 A

  In view of the circumstances as described above, the present invention has been invented to realize a structure of a worm speed reducer and a dual pinion type electric power steering device that can be reduced in size and weight while suppressing an increase in manufacturing cost.

Of the worm reducer and the dual pinion type electric power steering device according to the present invention, the worm reducer according to claim 1 is:
A worm wheel shaft,
A worm wheel that can rotate in synchronization with the worm wheel shaft by engaging an engagement hole provided in the center with a holding portion provided on the worm wheel shaft;
In a worm reduction gear having a worm meshed with the worm wheel, and a worm shaft coupled to a drive shaft disposed at a twisted position with respect to the worm wheel shaft,
The worm wheel shaft is a guide in which a diameter of a circumscribed circle is equal to or less than an outer diameter of the holding portion at a portion where the tool is attached and a portion where the position in the axial direction coincides with at least a part of the portion to be attached Part.

Of the worm reducer and dual pinion type electric power steering apparatus of the present invention, the worm reducer includes a housing, a worm wheel shaft, a worm wheel, and a worm shaft.
Of these, the worm wheel shaft is rotatably supported inside the housing.
In the worm wheel, an engagement hole provided in the central shaft is formed in a holding portion provided in a portion near the one end of the worm wheel shaft in the axial direction, for example, fitting and fixing by press-fitting (press fitting), key engagement, By engaging in a state in which relative rotation is prevented by spline engagement or serration engagement, rotation synchronized with the worm wheel shaft is freely supported and fixed.
The worm shaft is coupled to a drive shaft that is twisted with respect to the worm wheel shaft in the housing, and a worm provided at an intermediate portion is engaged with the worm wheel. Thus, it is rotatably supported inside the housing.

  In particular, in the worm speed reducer of the present invention, the worm wheel shaft is inserted into the engagement hole from one end side in the axial direction, and the holding portion and the engagement hole are engaged. In addition, a mounting portion for mounting a tool is provided at one axial end portion of the worm wheel shaft, and an outer peripheral surface of a portion of the worm wheel shaft whose phase in the axial direction coincides with a portion where the mounting portion is provided. In addition, when the diameter of the circumscribed circle is equal to or smaller than the outer diameter of the holding portion, and when the holding portion and the engaging hole are engaged, a guide portion for aligning the holding portion and the engaging hole is provided. Provide.

When implementing the worm speed reducer of the present invention as described above, preferably, a convex curved surface portion having a partially arcuate cross section is formed in at least two positions on the radially opposite side of the guide portion.
When carrying out such an invention, preferably, the radial distance between the convex curved surface portions (twice the radius of curvature of the convex curved surface portion) is made smaller than the outer diameter of the holding portion. And these convex curved surface part and holding | maintenance part are continued by the inclined surface part which inclined in the direction in which an outer diameter becomes small, so that it goes to the axial direction one end side of the said worm wheel axis | shaft.
Preferably, the convex curved surface portion is a partially conical convex surface having a radius that decreases toward one end in the axial direction of the worm wheel shaft.

Further, when the present invention as described above is carried out, preferably, the mounted portion is parallel to each other formed at least at two positions on the radially opposite end outer peripheral surface of the axial end portion of the worm wheel shaft. And a pair of flat surface portions.
Alternatively, the attached portion is provided in a state of opening to one end surface in the axial direction of the worm wheel shaft, and includes a pair of flat surface portions parallel to each other at least two positions on the radially opposite side of the inner peripheral surface. A concave hole is used.
In addition, as long as the flat surface part which comprises the said to-be-attached part is two or more, you may provide four, six, eight, etc., for example.

  When implementing the present invention as described above, for example, the worm wheel shaft is a pinion shaft provided with pinion teeth on the outer peripheral surface near the other end in the axial direction.

The dual pinion type electric power steering apparatus includes a worm reduction gear, an electric motor, a steering shaft, a pinion, a rack, a sub-pinion, a torque sensor, and a controller.
Of these, the worm reducer is the worm reducer of the present invention.
The electric motor rotationally drives a worm shaft constituting the worm speed reducer.
The steering shaft supports and fixes a steering wheel at the rear end.
The pinion is provided on the front end side of the steering shaft.
The rack meshes with the pinion or a member supported by the pinion.
The sub-pinion is formed near the other end of the worm wheel shaft constituting the worm speed reducer, and meshes with the rack at a position separated from the pinion in the axial direction of the rack shaft.
The torque sensor detects the direction and magnitude of torque applied to the steering shaft or the pinion.
The controller controls a driving state of the electric motor based on a signal input from the torque sensor.

  According to the worm speed reducer and the dual pinion type electric power steering apparatus of the present invention configured as described above, it is possible to reduce the size and weight while suppressing an increase in manufacturing cost. That is, a guide portion that functions as a centering guide when the worm wheel shaft is supported by the worm wheel shaft is attached with a tool (gripped by the tool) during the assembly or performance test of the worm speed reducer. Or a portion where the attached portion for inserting a tool is provided and the outer peripheral surface of the portion where the phase in the axial direction coincides. For this reason, since the axial direction length of the worm wheel shaft can be reduced as compared with the case where the holding portion, the guide portion and the attached portion (gripped portion) are provided in series in the axial direction, The size and weight can be reduced, and the manufacturing cost can be reduced by reducing the material cost.

Sectional drawing which shows the 1st example of embodiment of this invention. Sectional drawing (A) which takes out and shows a worm wheel and a pinion axis | shaft, End view (B) seen from the left side of (A), XX sectional drawing (C) of (A). The Y section expanded sectional view of (A) of FIG. The principal part enlarged side view which shows the 2nd example of embodiment of this invention. The figure similar to FIG. 4 which shows the 3rd example. The principal part enlarged side view (A) which shows the 4th example, the end view (B) seen from the left of (A), and the top view (C) which shows the state seen from the upper part of (A). The principal part expanded sectional view (A) which shows the 5th example, the end view (B) seen from the left of (A), and the top view (C) which shows the state seen from the upper part of (A). Modification (D) of the fifth example. Modifications (A) to (D) of the fifth example. The figure which cuts and shows the column-assist type electric power steering. The figure which cuts and shows a pinion assist type electric power steering. The figure which cuts a part and shows the dual pinion type electric power steering conventionally known. Sectional drawing which shows an example of the structure of the worm reduction gear conventionally known.

[First example of embodiment]
1 to 3 show a first example of an embodiment of the present invention corresponding to claims 1-2, 5, and 7-8. The feature of this example is that the structure of the pinion shaft 10a, which corresponds to the worm wheel shaft described in the claims, is devised, and the increase in the manufacturing cost of the worm speed reducer 24 is suppressed, and a reduction in size and weight is realized. There is in point to do. Since the configuration and operation of the other parts are the same as those of the conventional structure shown in FIGS. 11 to 12 described above, overlapping illustrations and descriptions are omitted.

  The worm reducer 24 rotatably supports the other axial end portion (right end portion in FIG. 1) and the axial intermediate portion of the pinion shaft 10a with respect to the housing 11b by rolling bearings 25a and 25b, respectively. . And the pinion tooth | gear 26 provided in the axial direction other end part vicinity of the said pinion shaft 10a and the rack tooth | gear 27 provided in the front surface (upper side surface of FIG. 1) of the rack 8a are meshed | engaged. In the case of this example, the backlash of the meshing portion between the pinion tooth 26 and the rack tooth 27 is eliminated, and the power is transmitted to the rack 8a with the meshing portion between the two teeth 26 and 27. Regardless of the force in the direction away from the pinion shaft 10a, the rack 8a is elastically pressed toward the pinion shaft 10a in order to properly maintain the meshing state of the meshing portion. For this purpose, a cylindrical cylinder portion 28 is provided in the housing 11b, and a pressing block 29 is fitted in the cylinder portion 28. A spring 31 is provided between the lid 30 screwed into the opening of the cylinder portion 28 and the pressing block 29 to press the pressing block 29 toward the rack 8a. In addition, a worm wheel 16b is provided on a holding portion 21a provided near the one axial end (left end in FIG. 1) of the pinion shaft 10a, and provided on the outer peripheral surface of the holding portion 21a and the central portion of the worm wheel 16b. By engaging the inner peripheral surface of the engagement hole 20a with a state where relative rotation is prevented by fitting and fixing {press-fit (or key engagement, spline engagement, serration engagement, etc.)} by interference fitting, The support is fixed. The worm wheel 16b meshes with a worm 14a provided at an intermediate portion in the axial direction of a worm shaft 15a that is rotationally driven by the electric motor 12 (see FIGS. 11 to 12).

  In the case of this example, a mounted portion 23a is provided at one end of the pinion shaft 10a in the axial direction, and the pinion shaft 10a has an outer peripheral surface of a portion whose phase in the axial direction coincides with the mounted portion 23a. A guide portion 22a is provided. For this purpose, the attached portion 23a having a pair of flat surface portions 32, 32 parallel to each other is provided at one axial end portion of the pinion shaft 10a, and a cross-sectional shape is formed between the flat surface portions 32, 32. Is continued by convex curved surface portions 33, 33 constituting the guide portion 22a, which is a partial arc shape centering on the central axis of the pinion shaft 10a. In the case of this example, the radial distance between the two convex curved surface portions 33, 33 corresponding to the diameter of the circumscribed circle of the guide portion 22a (twice the radius of curvature of the two convex curved surface portions 33, 33) D33 Is smaller than the outer diameter D21 of the holding portion 21a. Therefore, the pinion shaft 10a is inserted into the engagement hole 20a of the worm wheel 16b from the right side of FIG. 1, and the worm wheel 16b is supported (press-fitted) into the holding portion 21a of the pinion shaft 10a in the initial stage of the operation. By roughly inserting the two convex curved surface portions 33, 33 inside the engagement hole 20a, the pinion shaft 10a and the worm wheel 16b can be roughly aligned. On the other hand, when assembling the worm speed reducer 24 or performing a performance test, the two flat surface portions 32, 32 constituting the attached portion 23a are held or externally fitted by a tool. Such flat surface portions 32 and 32 are not limited to a pair, and a plurality of sets (for example, 2 to 4 sets) may be provided. Further, the attached portion 23a may be a prismatic shape such as a triangle or a pentagon in cross section. In this case, the diameter of the circumscribed circle of the attached portion 23a is made smaller than the outer diameter D21 of the holding portion 21a.

  According to the worm speed reducer 24 of this example as described above, it is possible to reduce the size and weight while suppressing an increase in manufacturing cost. In other words, in the case of this example, the guide portion 22a is provided on the outer peripheral surface of a portion of the pinion shaft 10a where the phase in the axial direction coincides with the portion where the attached portion 23a is provided. For this reason, the axial length L of one end portion of the pinion shaft 10a in the axial direction (the portion protruding in the axial direction from the holding portion 21a) is set to be longer than the case where the holding portion, the guide portion, and the attached portion are provided in series in the axial direction. The pinion shaft 10a can be reduced in length in the axial direction. As a result, the overall size and weight of the worm reducer 24 can be reduced, the material cost of the pinion shaft 10a can be reduced, and the manufacturing cost of the worm reducer 24 can be reduced. Further, in the case of this example, the guide portion 22a and the mounted portion 23a are subjected to cutting or grinding on the outer peripheral surface of one end of the pinion shaft 10a in the axial direction, and the shape of the outer peripheral surface is once cylindrical. After that, the pair of flat surface portions 32 and 32 can be provided simultaneously (continuously), and the manufacturing cost of the worm speed reducer 24 can also be suppressed from this surface.

[Second Example of Embodiment]
FIG. 4 shows a second example of an embodiment of the present invention corresponding to claims 1-3, 5, and 7-8. In the case of this example, the outer peripheral surface of the holding portion 21a of the pinion shaft 10b and the convex curved surface portion 33 are inclined in a direction in which the outer diameter becomes smaller toward the one end side (left side in FIG. 4) of the pinion shaft 10b. The inclined surface portion 34 is continuous. Therefore, when the holding portion 21a is supported (press-fitted) into the engaging hole 20a (see FIG. 1) of the worm wheel 16a, the peripheral portion of the engaging hole 20a is connected to the outer peripheral surface of the holding portion 21a The press-fitting operation can be facilitated by preventing collision with the stepped portion between the convex curved surface portion 33. In the case of the illustrated example, the bus bar shape of the inclined surface portion 34 is a straight line, but the bus bar shape may be a partially convex arc shape or a partially concave arc shape.
Since the configuration and operation of the other parts are the same as those of the first example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

[Third example of embodiment]
FIG. 5 shows a third example of an embodiment of the present invention corresponding to claims 1-2, 4-5, and 7-8. In the case of the pinion shaft 10c of the present example, the pair of convex curved surface portions 33a constituting the guide portion 22b are partially conical with a radius becoming smaller toward the one end side in the axial direction of the pinion shaft 10c (left side in FIG. 5). Convex surface. In the case of this example, the operation of aligning the engagement hole 20a (see FIG. 1) of the worm wheel 16a and the pinion shaft 10c and supporting the worm wheel 16a on the pinion shaft 10c is performed as described above. Compared with the case of the first example of the embodiment, it can be performed more smoothly.
Since the configuration and operation of the other parts are the same as those in the first example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

[Fourth Example of Embodiment]
FIG. 6 shows a fourth example of an embodiment of the present invention corresponding to claims 1-2, 5, and 7-8. In the case of the pinion shaft 10d of this example, the radial distance between the pair of convex curved surface portions 33b and 33b corresponding to the diameter of the circumscribed circle of the guide portion 22c (the radius of curvature of the both convex curved surface portions 33b and 33b). 2 times) and the outer diameter of the holding portion 21a are the same.
Since the configuration and operation of the other parts are the same as those in the first example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

[Fifth Example of Embodiment]
FIG. 7 shows a fifth example of an embodiment of the present invention corresponding to claims 1 to 2 and 6 to 8. In the case of the pinion shaft 10e of this example, the guide portion 22d is a single cylindrical surface having the same outer diameter as the holding portion 21a. In addition, a recessed hole 35 as an attached portion is provided so as to open to the end face of the guide portion 22d. The inner peripheral surface of the concave hole 35 is formed by connecting a pair of parallel flat surface portions 36 and 36 parallel to each other by partially cylindrical concave curved surface portions 37 and 37 centering on the central axis of the pinion shaft 10e. In the case of this example, when assembling the worm speed reducer 24 (see FIG. 1) or performing a performance test, a part of the tool is inserted into the concave hole 35 to support the posture of the pinion shaft 10e. The flat portions 36 and 36 may be continued by a pair of parallel planes. Further, the inner peripheral surface of the concave hole 35 may be a rectangular tube having a hexagonal cross section as shown in FIG. Further, the inner peripheral surface of the concave hole 35 may have an octagonal cross section as shown in FIG. Further, the inner peripheral surface of the concave hole 35 may have a rectangular cross section as shown in FIG. Further, the inner peripheral surface of the concave hole 35 may have a cross-sectional shape, for example, as shown in FIG. 8C. Further, the inner peripheral surface of the concave hole 35 may have a cross-sectional shape, for example, a star shape as shown in FIG.
Since the configuration and operation of the other parts are the same as those in the first example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

  Each example of the embodiment described above has been described in the case where the present invention is applied to a dual pinion type electric power steering apparatus. However, the worm speed reducer of the present invention is not limited to such a structure. For example, a column assist type electric power steering device as shown in FIG. 9 or a pinion assist type electric power as shown in FIG. It can also be applied to a steering device. For example, in the case of the column assist type structure shown in FIG. 9, a gear housing 39 is coupled and fixed to the lower end of the steering column 38 that is inserted through the steering shaft 2a, and the electric motor 12 is supported by the gear housing 39. doing. The electric motor 12 applies an auxiliary force in the rotational direction to the steering shaft 2a via a worm speed reducer (not shown) according to the present invention.

  In the case of a pinion assist type structure, an input shaft 6a having a pinion shaft coupled to a lower end portion is supported on the side of a housing 7a that is inserted into the input shaft 6a. The electric motor 12 is used to apply an auxiliary force in the rotational direction to the pinion shaft via a worm speed reducer (not shown) according to the present invention. A pinion provided on the outer peripheral surface of the lower end portion of the pinion shaft is engaged with the rack 8.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3a, 3b Universal joint 4 Intermediate shaft 5 Steering gear unit 6 Input shaft 7 Housing 8, 8a Rack 9 Tie rod 10, 10a-10e Pinion shaft 11, 11a, 11b Housing 12 Electric motor 13 Reducer 14, 14a Worm 15, 15a Worm shaft 16, 16a, 16b Worm wheel 17 Ball bearing 18 Drive shaft 19 Worm wheel shaft 20a Engagement hole 21a Holding portion 22a-22d Guide portion 23a Mounted portion 24 Worm speed reducers 25a, 25b Rolling bearing 26 Pinion tooth 27 Rack tooth 28 Cylinder part 29 Press block 30 Cover body 31 Spring 32 Flat surface part 33, 33a-33b Convex surface part 34 Inclined surface part 35 Concave hole 36 Flat surface part 37 Concave surface part 38 A ring column 39 gear housing

Claims (8)

A worm wheel shaft,
A worm wheel that can rotate in synchronization with the worm wheel shaft by engaging an engagement hole provided in the center with a holding portion provided on the worm wheel shaft;
In a worm reduction gear having a worm meshed with the worm wheel, and a worm shaft coupled to a drive shaft disposed at a twisted position with respect to the worm wheel shaft,
The worm wheel shaft is a guide in which a diameter of a circumscribed circle is equal to or less than an outer diameter of the holding portion at a portion where the tool is attached and a portion where the position in the axial direction coincides with at least a part of the portion to be attached Worm speed reducer characterized by having a part.   The worm speed reducer according to claim 1, wherein a convex curved surface portion having a partial arc shape in cross section is formed at least at two positions on the radially opposite side of the guide portion.   The radial distance between the convex curved surface portions is smaller than the outer diameter of the holding portion, and the convex curved surface portion and the outer peripheral surface of the holding portion are continuous by an inclined surface portion. The worm speed reducer described in 2.   The worm speed reducer according to any one of claims 2 to 3, wherein the convex curved surface portion is a partial conical convex surface having a radius that decreases toward one end in the axial direction.   The worm speed reducer according to any one of claims 1 to 4, wherein the attached portion has a pair of parallel flat surface portions formed at least at two positions on the radially opposite side.   A concave hole provided with a pair of flat surface portions parallel to each other at least at two positions on the radially opposite side of the inner peripheral surface, wherein the attached portion is provided in an open state on one axial end surface of the worm wheel shaft. The worm speed reducer according to any one of claims 1 to 4.   The worm speed reducer according to any one of claims 1 to 6, wherein the worm wheel shaft is a pinion shaft having pinion teeth on an outer peripheral surface.   A worm reducer according to claim 7, an electric motor for rotationally driving a worm shaft constituting the worm reducer, a steering shaft provided with a steering wheel at a rear end portion, and provided at a front end side of the steering shaft. And a rack in which this pinion or a member supported by this pinion is meshed, and a worm wheel shaft constituting the worm speed reducer, and a sub meshing with this rack at a position away from the pinion A pinion, a torque sensor for detecting the direction and magnitude of torque applied to the steering shaft or the pinion, and a controller for controlling the driving state of the electric motor based on a signal input from the torque sensor; A dual pinion type electric power steering apparatus.

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