JP2008223828A - Reduction gear and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent damage or deformation of teeth of worm shaft and teeth of worm wheel in assembling the worm shaft and the worm wheel. <P>SOLUTION: A reduction gear 10 is provided with the worm shaft 16, the worm wheel 17, a first housing 36 defining a worm shaft holding hole 39, and a second housing 37 defining a worm wheel holding hole 39. Contact of the worm shaft 16 and the worm wheel 17 is not released under a condition where a part of a worm tooth shape forming part 26 of the worm shaft 16 where a bearing is not installed on a second support shaft 28 of the worm shaft 16 is displaced to an escape space 46. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a speed reducer and a method for manufacturing the same.

A worm speed reducer in which a worm shaft and a worm wheel are housed in a gear housing is known (see, for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 11-20724 JP-A-9-49552

As a method of assembling the worm shaft and the worm wheel, for example, as described in Patent Document 2, the worm wheel is accommodated in a gear housing, and the worm is moved along the tangential direction of the outer periphery of the worm wheel. Move the shaft straight (in a straight line) to engage them.
By the way, when the worm shaft and the worm wheel are meshed with each other, it is required to make the worm shaft and the worm wheel come into contact with each other smoothly so that neither the worm shaft nor the worm wheel is scratched or deformed.

  The present invention has been made under such a background, and an object of the present invention is to provide a speed reducer that can reliably prevent the worm shaft and the worm wheel from being scratched or deformed during assembly and a method for manufacturing the same. .

  In order to achieve the above object, the present invention comprises a cylindrical first housing (36) that defines a worm shaft accommodation hole (39), and a cylinder that defines a worm wheel accommodation hole (38). A second housing (37) that intersects with one housing (36), a worm shaft (16) received in the worm shaft receiving hole (39), and a worm hole receiving hole (38). A worm wheel (17) meshing with the worm shaft (16), the worm shaft (16) being relatively close to an electric motor (11) for driving the worm shaft (16). (31) and a second end (28) disposed on the opposite side of the first end (31), and the worm shaft receiving hole (39) is a worm shaft (16) worm Warp across the tooth forming part (26) The escape space (46; 46A) includes a relief space (46; 46A) opposed to the wheel (17), and a part of the worm tooth forming portion (26) of the worm shaft (16) not mounted with the bearing (33). The speed reducer (10) is characterized in that the contact between the worm shaft (16) and the worm wheel (17) is released in a state where the worm shaft (16) is displaced. .

In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
According to the present invention, when the worm shaft is inserted into the worm shaft accommodation hole, the worm shaft can be inserted while avoiding contact with the worm wheel by disposing a part of the worm tooth forming portion in the clearance space. Further, the worm shaft and the worm wheel can be engaged with each other by displacing the worm shaft, in which a part of the worm tooth forming portion is disposed in the escape space, to the worm wheel side. As a result, when the worm shaft and the worm wheel are combined, the tooth portion of the worm shaft and the tooth forming portion of the worm wheel can be prevented from coming into strong contact, and both the worm shaft and the worm wheel are scratched or deformed. Can be surely prevented.

  In the present invention, the worm shaft accommodation hole (39) is a bearing holding hole (35; 35C) for holding the bearing (33) that supports the second end (28) of the worm shaft (16). A bearing insertion hole (45) through which the bearing (33) can be inserted into the bearing holding hole (35; 35C) is formed at the end (36b) of the first housing (36). A lid member (44) that covers the bearing insertion hole (45) may be attached to the housing (36) (claim 2). In this case, the bearing can be attached to the second end portion after the worm shaft is accommodated in the worm shaft accommodation hole. Further, the bearing insertion hole can be closed with the lid member, and foreign matter can be prevented from entering the bearing holding hole.

  In the present invention, the cross section of the portion including the escape space (46; 46A) of the worm shaft accommodation hole (39) may have a gourd shape, an oval shape or an oval shape (claims). Item 3). In this case, the escape space can be made as small as possible, and the worm shaft accommodation hole can be made small. For example, when the grease as the lubricant is filled in the worm shaft accommodation hole, the amount of grease necessary for filling can be reduced.

  In the present invention, the worm shaft accommodation hole (39) is a bearing holding hole (35; 35C) for holding the bearing (33) that supports the second end (28) of the worm shaft (16). The bearing holding hole (35; 35C) may hold the bearing (33) in a state of restricting radial movement of the bearing (33). In this case, the bearing can be reliably held by the first housing.

Further, in the method of manufacturing the speed reducer (10), after the worm wheel (17) is accommodated in the worm wheel accommodation hole (38) of the second housing (37), the bearing (33) is not mounted. The worm shaft (16) may be inserted into the worm shaft accommodation hole (39) of the first housing (36) from the end (28) side of the second housing (Claim 5).
In this case, when the worm shaft is inserted into the worm shaft accommodation hole, the worm shaft can be inserted while avoiding contact with the worm wheel by disposing a part of the worm tooth forming portion in the clearance space. Further, the worm shaft and the worm wheel can be engaged with each other by displacing the worm shaft, in which a part of the worm tooth forming portion is disposed in the escape space, to the worm wheel side. As a result, when the worm shaft and the worm wheel are combined, the tooth portion of the worm shaft and the tooth portion of the worm wheel can be prevented from coming into strong contact, and both the worm shaft and the worm wheel can be scratched or deformed. Can be reliably prevented.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of an electric power steering apparatus including a reduction gear according to an embodiment of the present invention. Referring to FIG. 1, in this electric power steering apparatus (hereinafter also simply referred to as a power steering apparatus), a first steering shaft 2 as an input shaft to which a steering wheel 1 is connected, a rack and pinion A second steering shaft 3 as an output shaft connected to a steering mechanism (not shown) such as a mechanism is coaxially connected via a torsion bar 4.

The housing 5 that supports the first and second steering shafts 2 and 3 is made of, for example, an aluminum alloy and is attached to a vehicle body (not shown). The housing 5 includes a sensor housing 6 and a gear housing 7 that are fitted together.
Specifically, the gear housing 7 is integrally formed using a single material to form a cylindrical shape, and an annular edge portion 7 a at the upper end thereof is an annular step portion on the outer periphery of the lower end of the sensor housing 6. 6a.

The gear housing 7 accommodates a worm gear mechanism 8, and the sensor housing 6 accommodates a torque sensor 9. The reduction gear 10 is configured by housing the worm gear mechanism 8 in the gear housing 7.
2 is a cross-sectional view taken along line II-II in FIG. Referring to FIGS. 1 and 2, an electric motor 11 for generating a steering assist force is provided. The housing 12 of the electric motor 11 is fixed to the annular flange 13 of the gear housing 7 using a bolt or the like (not shown).

The worm gear mechanism 8 decelerates the output of the electric motor 11 and transmits it to the second steering shaft 3, and is connected to the output shaft 14 of the electric motor 11 via a joint 15 such as a spline joint. And a worm wheel 17 that meshes with the worm shaft 16 and can rotate integrally with an intermediate portion in the axial direction of the second steering shaft 3 and is restricted from moving in the axial direction.
The worm wheel 17 includes an annular cored bar 17a coupled to the second steering shaft 3 so as to be integrally rotatable, and a synthetic resin member 17b that surrounds the cored bar 17a and forms a tooth forming portion 18 on the outer peripheral surface. I have. The cored bar 17a is inserted into a mold when, for example, the resin of the synthetic resin member 17b is formed. The teeth of the tooth forming portion 18 of the worm wheel 17 are, for example, helical that have a hourglass shape.

In the gear housing 7, the meshing area A of the worm shaft 16 and the worm wheel 17 is filled with a lubricant. That is, the lubricant may be filled only in the meshing region A, or may be filled in the entire meshing region A and the entire periphery of the worm shaft 16 or in the entire gear housing 7.
Referring to FIG. 1, the second steering shaft 3 is rotatably supported by first and second bearings 19 and 20 that are arranged with a worm wheel 17 sandwiched between the upper and lower sides in the axial direction.

The outer ring 19 a of the first bearing 19 is fitted and held in the first bearing holding hole 21 of the sensor housing 6. On the other hand, the inner ring 19b of the first bearing 19 is fitted to the second steering shaft 3 by an interference fit.
The outer ring 20 a of the second bearing 20 is fitted and held in the second bearing holding hole 22 of the gear housing 7. The lower end surface of the outer ring 20 a of the second bearing 20 is in contact with the annular step portion 23, and movement in the axially downward direction with respect to the gear housing 7 is restricted.

The inner ring 20b of the second bearing 20 is attached to the second steering shaft 3 such that the inner ring 20b can rotate integrally and the relative movement in the axial direction is restricted.
The upper part of the first steering shaft 2 is rotatably supported by a third bearing holding hole 25 of the sensor housing 6 via a third bearing 24 made of, for example, a needle roller bearing.
Referring to FIG. 2, the worm shaft 16 includes first and second support shafts 27 extending from a tooth forming portion 26 (worm tooth forming portion) and a pair of end portions of the tooth forming portion 26, respectively. 28. The tooth forming part 26 includes, for example, one or a plurality of male threads. The second support shaft 28 is provided as a second end portion of the worm shaft 16. At each of the pair of end portions of the tooth forming portion 26, annular step portions 29 and 30 are formed.

  A spline shaft 31 as a first end portion extends from the first support shaft 27 of the worm shaft 16, and the spline shaft 31 is disposed on the opposite side to the second support shaft 28. The output shaft 14 of the electric motor 11 is drivingly connected to the spline shaft 31 through the joint 15 described above. The spline shaft 31 is relatively close to the electric motor 11, and the second support shaft 28 is relatively far from the electric motor 11.

The worm shaft 16 is rotatably supported by the fourth and fifth bearings 32 and 33 held by the gear housing 7. The fourth and fifth bearings 32 and 33 are, for example, ball bearings as rolling bearings.
Inner rings 32 b and 33 b of the fourth and fifth bearings 32 and 33 are fitted to corresponding first and second support shafts 27 and 28 of the worm shaft 16, respectively. Further, the outer rings 32 a and 33 a of the fourth and fifth bearings 32 and 33 are held in corresponding fourth and fifth bearing holding holes 34 and 35 of the gear housing 7, respectively.

  The gear housing 7 includes a cylindrical first housing 36 and a cylindrical second housing 37 that are integrally formed using a single material. The first and second housings 36 and 37 are connected to each other in a crossing manner. The second housing 37 defines a worm wheel accommodation hole 38 that accommodates the worm wheel 17, and one side in the axial direction of the worm wheel 17 is opened as shown in FIG. 1.

FIG. 3 is an enlarged view of a main part of FIG. Referring to FIG. 3, the first housing 36 defines a worm shaft housing hole 39 for housing the worm shaft 16. The worm shaft accommodation hole 39 is formed by the inner peripheral surface 40 of the first housing 36.
The worm shaft accommodation hole 39 includes the fourth bearing holding hole 34 and the fifth bearing holding hole 35.

  The fourth bearing holding hole 34 includes an insertion port 41. The insertion port 41 is formed to insert the worm shaft 16 into the first housing 36 and is disposed at one end 36 a of the first housing 36. The fourth bearing holding hole 34 and the fifth bearing holding hole 35 each have a circular cross section, and the corresponding fourth bearing 32 and fifth bearing 33 are connected to the fourth bearing 32 and the fourth bearing 33, respectively. 5 is held in a state in which the radial movement of the bearing 33 is restricted.

  A preload is applied to the fourth and fifth bearings 32 and 33 using an elastic member 42 as an urging member. Specifically, the outer ring 32 a of the fourth bearing 32 is press-fitted and fixed in the fourth bearing holding hole 34. The inner ring 32 b of the fourth bearing 32 is sandwiched between one step portion 29 of the worm shaft 16 and the annular member 43 screwed to the first support shaft 27, and the axial movement with respect to the worm shaft 16 is restricted. Has been.

The inner ring 33 b of the fifth bearing 33 is in contact with the other step portion 30 of the worm shaft 16 and is restricted from moving toward the fourth bearing 32. The outer ring 33 a of the fifth bearing 33 is held in the fifth bearing holding hole 35 by a clearance fit, and can move relative to the fifth bearing holding hole 35 in the axial direction.
One end of the elastic member 42 made of a disc spring or the like is in contact with the outer ring 33a of the fifth bearing 33. The other end of the elastic member 42 is received on one side surface of the lid member 44.

With the above configuration, the urging force of the elastic member 42 is transmitted to the worm shaft 16 via the outer ring 33a and the inner ring 33b of the fifth bearing 33, and further transmitted to the inner ring 33b and the outer ring 33a of the fourth bearing 32.
The lid member 44 is attached to a bearing insertion hole 45 formed in the other end 36b of the first housing 36 by, for example, screw coupling. The lid member 44 covers the bearing insertion hole 45. The bearing insertion hole 45 is for inserting the fifth bearing 33 into the fifth bearing holding hole 35.

  One of the features of the present embodiment is that a clearance space 46 facing the worm wheel 17 is provided in the worm shaft accommodation hole 39 with the tooth forming portion 26 of the worm shaft 16 interposed therebetween. Thereby, the contact between the worm shaft 16 and the worm wheel 17 is released in a state where at least a part of the tooth forming portion 26 of the worm shaft 16 is displaced to the escape space 46 when the fifth bearing 33 is not mounted. It has come to be.

4 is a cross-sectional view taken along line IV-IV in FIG. With reference to FIGS. 3 and 4, the worm shaft accommodation hole 39 includes a tooth formation portion accommodation hole 47 for accommodating the tooth formation portion 26 of the worm shaft 16, and the relief space 46 connected to the tooth formation portion accommodation hole 47. Is included.
The cross section (the cross section in FIG. 3) of the portion including the tooth forming portion receiving hole 47 and the escape recess 46 of the worm shaft receiving hole 39 has a substantially gourd shape.

The tooth forming portion accommodation hole 47 communicates with both the fourth bearing holding hole 34 and the fifth bearing holding hole 35. The tooth forming portion receiving hole 47 is partitioned into a circular shape similar to the worm shaft 16 and is formed concentrically with the worm shaft 16 on which the fourth and fifth bearings 32 and 33 are mounted.
The gap between the peripheral surface of the tooth forming portion receiving hole 47 and the tooth forming portion 26 of the worm shaft 16 is made as small as possible, and the grease in the meshing region A is prevented from entering this gap. The amount of grease filled in the gear housing 7 can be reduced, and the cost can be reduced.

  With respect to the axial direction of the fourth bearing holding hole 34, the escape space 46 extends from the fourth bearing holding hole 34 to at least the engagement region A. The escape space 46 is recessed in the inner peripheral surface 40 of the first housing 36 that faces the worm wheel 17 across the tooth forming portion 26 of the worm shaft 16 (the portion that faces the meshing area A). Not formed. The radius of curvature d1 of the inner peripheral surface 40a of the escape space 46 is set to be equal to or larger than the outer diameter d2 of the worm shaft 16 (d1 ≧ d2).

  The center 46 a of the peripheral surface of the escape space 46 is eccentric by a predetermined eccentric amount B with respect to the center 47 a of the peripheral surface of the tooth forming portion receiving hole 47. With respect to the radial direction R1 of the worm wheel 17 passing through the meshing region A, the eccentric amount B is determined so that the tooth forming portion 26 of the worm shaft 16 does not overlap the worm wheel 17 in one of the radial directions R1. It is set to a value that allows movement, and is set to, for example, about several mm.

When viewed along the axial direction S <b> 1 of the fourth bearing holding hole 34, the cross section of the portion of the worm shaft receiving hole 39 including the tooth forming portion receiving hole 47 and the escape space 46 is the same as that of the fourth bearing holding hole 34. It is smaller than the cross section and smaller than the cross section of the fifth bearing holding hole 35.
A step portion 48 orthogonal to the axial direction S1 is formed at one end of the clearance space 46 with respect to the axial direction S1.

  The speed reducer 10 is assembled as follows. That is, first, as shown in FIG. 5A, a single gear housing 7 and a worm wheel assembly 49 incorporating the worm wheel 17 are prepared. In the worm wheel assembly 49, the worm wheel 17 is held on the second steering shaft 3, and the first and second bearings 19 and 20 are attached to the second steering shaft 3.

The worm wheel assembly 49 is moved along the axial direction of the second steering shaft 3 so that the worm wheel 17 is accommodated in the worm wheel of the second housing 37 of the gear housing 7 as shown in FIG. It is accommodated in the hole 38.
Next, as shown in FIG. 6, a worm assembly 50 is prepared. In the worm assembly 50, the inner ring 32 b of the fourth bearing 32 is fitted on the first support shaft 27 of the worm shaft 16, and the inner ring 32 b of the fourth bearing 32 is connected to the step portion 29 of the worm shaft 16 and the worm shaft. It is sandwiched between an annular member 43 screwed to 16.

  By moving the worm assembly 50 in a direction parallel to the axial direction S <b> 1, the worm assembly 50 is inserted into the worm shaft accommodation hole 39 via the insertion port 41 of the first housing 36. At this time, as shown in FIGS. 7 and 8, the worm shaft 16 is inserted straight so that the second support shaft 28 to which no bearing is attached faces the tip of the insertion, and a part thereof enters the escape space 46. Be placed.

The axis L1 of the worm shaft 16 partially disposed in the clearance space 46 is deviated by a predetermined amount in the radial direction R1 with respect to the axis L2 of the fourth bearing holding hole 34. Thereby, the worm shaft 16 is inserted into the worm shaft accommodation hole 39 without contacting the worm wheel 17.
When the worm shaft 16 is inserted into the worm shaft housing hole 39 until the tooth forming portion 26 of the worm wheel 16 faces the tooth forming portion 18 of the worm wheel 17 with respect to the radial direction R1 of the worm wheel 17, the worm shaft 16 The step portion 30 reaches the step portion 48 of the gear housing 7. It can be confirmed that the insertion of the worm shaft 16 using the clearance space 46 is completed by the contact of these step portions 30 and 48.

Next, as shown in FIG. 9, the worm shaft 16 is moved toward the worm wheel 17 in the radial direction R1, and the tooth forming portion 26 of the worm shaft 16 and the tooth forming portion 18 of the worm wheel 17 are engaged with each other. Then, the axis L1 of the worm shaft 16 overlaps with the axis L2 of the fourth bearing holding hole 34.
Next, with the worm shaft 16 and the worm wheel 17 engaged with each other, as shown in FIG. 10, the worm shaft 16 is further inserted straight into the worm shaft housing hole 39 along the axial direction S1, and the fourth The outer ring 32 a of the bearing 32 is press-fitted into the fourth bearing holding hole 34. Then, the second support shaft 28 reaches the fifth bearing holding hole 35 and is disposed in the fifth bearing holding hole 35.

In a state where the second support shaft 28 is disposed in the fifth bearing holding hole 35, the fifth bearing 33 is interposed between the second support shaft 28 and the fifth bearing holding hole 35, and thereafter Then, the elastic member 42 is inserted into the bearing insertion hole 45, and then the lid member 44 is screwed to the bearing insertion hole 45.
As a result, as shown in FIG. 11, the elastic member 42 applies preload to the fourth and fifth bearings 32 and 33. After the lid member 44 is screwed into the bearing insertion hole 45, the spline of the worm shaft 16 is connected to the output shaft 14 of the electric motor 11 via the joint 15 in a state where the worm shaft 16 is accommodated in the first housing 36. Connected to the shaft 31. At the same time, the housing 12 of the electric motor 11 is fixed to the annular flange 13 of the gear housing 7 using screws or the like (not shown). Thereby, the reduction gear 10 is completed.

According to the present embodiment, the following operational effects can be achieved. That is, when the worm shaft 16 is inserted into the worm shaft accommodating hole 39, a part of the worm tooth forming portion 26 is disposed in the escape space 46, so that the worm shaft 16 can be inserted while avoiding contact with the worm wheel 17. .
The worm shaft 16 and the worm wheel 17 are engaged with each other by displacing the worm shaft 16 in which a part of the worm tooth forming portion 26 is disposed in the escape space 46 toward the worm wheel 17 along the radial direction R1. be able to. As a result, when the worm shaft 16 and the worm wheel 17 are combined, the tooth forming portion 26 of the worm shaft 16 and the tooth forming portion 18 of the worm wheel 17 can be prevented from coming into strong contact, and the worm shaft 16 and the worm wheel 17 can be prevented. In both cases, it is possible to reliably prevent scratches and deformation.

  In addition, a bearing insertion hole 45 through which the fifth bearing 33 can be inserted into the fifth bearing holding hole 35 is formed in the other end 36 b of the first housing 36. Thereby, after the worm shaft 16 is accommodated in the worm shaft accommodation hole 39, the fifth bearing 33 can be attached to the second support shaft 28. Further, the bearing insertion hole 45 can be closed by the lid member 44, and foreign matter can be prevented from entering the fifth bearing holding hole 35.

Further, the cross section of the portion including the escape space 46 of the worm shaft accommodation hole 39 has a gourd shape. Thereby, the escape space 46 can be made as small as possible, and the worm shaft accommodation hole 39 can be made small. When the grease is filled in the worm shaft housing hole 39, the amount of grease necessary for filling can be reduced. Thereby, cost can be reduced.
Further, the fifth bearing holding hole 35 holds the fifth bearing 33 in a state in which the radial movement of the fifth bearing 33 is restricted. As a result, the fifth bearing 33 can be reliably held by the first housing 36.

  Further, for example, when the worm shaft is first accommodated in the gear housing and then the worm wheel is accommodated in the gear housing, the drum shape is formed when the worm wheel is moved in the axial direction and accommodated in the gear housing. The tooth portion of the worm wheel that is formed makes strong contact with the tooth portion of the worm shaft, and there is a possibility that the tooth surface of the tooth portion of the worm wheel may be scratched or deformed.

  On the other hand, in the present embodiment, the tooth forming portion 26 of the worm shaft 16 is moved along the radial direction R <b> 1 of the worm wheel 17 and meshed with the worm wheel 17. Thereby, it can prevent that the tooth | gear formation part 26 of the worm wheel 17 contacts the tooth | gear formation part 18 of the worm wheel 17 strongly, and it can prevent that a crack and a deformation | transformation generate | occur | produce about both of these tooth | gear formation parts 18 and 26. .

Moreover, as a result of being able to mesh the worm shaft 16 and the worm wheel 17 without difficulty, the tooth thickness of the tooth forming portion 18 of the worm wheel 17 can be increased, and the strength of the worm wheel 17 can be further increased.
Further, by assembling the worm wheel 17 to the gear housing 7 first, the distance (inter-center distance) between the axis of the worm wheel 17 and the axis of the worm shaft accommodating hole 39 of the gear housing 7 can be measured, and the dimensions are within tolerance. The optimum worm shaft for the worm wheel 17 assembled in advance can be selected from a plurality of worm shafts having different diameters.

The present invention is not limited to the contents of the above-described embodiment, and various modifications can be made within the scope of the claims.
For example, as shown in FIG. 12, the escape space 46 </ b> A may communicate with both the fourth bearing holding hole 34 and the fifth bearing holding hole 35.
In this case, when the worm shaft 16 is inserted into the first housing 36, as shown in FIG. 13A, the axis L1 of the worm shaft 16 to which no bearing is attached is set in the fourth direction in the radial direction R1. The worm shaft 16 is inserted into the worm shaft accommodation hole 39 of the first housing 36 in a state of being eccentric from the axis L 2 of the bearing holding hole 34.

Accordingly, as shown in FIG. 13B, a part of the worm shaft 16 is disposed in the escape space 46A, and the second worm shaft 16 is in a state where contact between the worm shaft 16 and the worm wheel 17 is avoided. The support shaft 28 is inserted into the fifth bearing holding hole 35.
Thereafter, as shown in FIG. 13C, the worm shaft 16 is moved to the worm wheel 17 side along the radial direction R1, and the worm shaft 16 and the worm wheel 17 are engaged with each other. In a state where the worm shaft 16 and the worm wheel 17 are engaged with each other, the fifth bearing 33 is interposed between the fifth bearing holding hole 35 and the second support shaft 28. Further, the elastic member 42 and the lid member 44 are inserted into the bearing insertion hole 45, and the lid member 44 is screwed to the first housing 36. Next, the fourth bearing 32 is interposed between the fourth bearing holding hole 34 and the first support shaft 27. Then, the axial movement of the fourth bearing 32 relative to the worm shaft 16 is restricted by screwing the annular member 43 to the first support shaft 27.

Instead of the fourth bearing holding hole 34 of the embodiment shown in FIG. 12, a fourth bearing holding hole 34 shown in FIGS. 14A and 14B may be formed. This embodiment is different from the embodiment shown in FIG. 12 in that the fourth bearing holding hole 34 allows the fourth bearing 32 to move in the radial direction.
The fourth bearing holding hole 34 has a long hole shape that is relatively long in the radial direction R1 of the worm wheel 17 when viewed along the axial direction S1.

When the worm shaft 16 is inserted into the first housing 36, as shown in FIG. 15A, a part of the tooth forming portion 26 of the worm shaft 16 of the worm assembly 50 is opposed to the escape space 46A. With the worm assembly 50 disposed, the worm shaft 16 is inserted into the worm shaft accommodation hole 39 of the first housing 36.
As a result, as shown in FIG. 15B, a part of the tooth forming portion 26 of the worm shaft 16 is disposed in the escape space 46A, and the worm shaft 16 and the worm wheel 17 are avoided from contacting each other. Sixteen second support shafts 28 are inserted into the fifth bearing holding hole 35. Further, the fourth bearing 32 is inserted into the fourth bearing holding hole 34.

  Thereafter, as shown in FIG. 15C, the worm shaft 16 is moved to the worm wheel 17 side along the radial direction R1, and the worm shaft 16 and the worm wheel 17 are engaged with each other. In a state where the worm shaft 16 and the worm wheel 17 are engaged with each other, the fifth bearing 33 is interposed between the fifth bearing holding hole 35 and the second support shaft 28. Further, the elastic member 42 and the lid member 44 are inserted into the bearing insertion hole 45, and the lid member 44 is screwed to the first housing 36.

In each of the above-described embodiments, the cross section of the portion including the escape space of the worm shaft accommodation hole 39 may have an oval shape as shown in FIG. 16, or an elliptical shape as shown in FIG. It may be done.
Further, as shown in FIG. 18, a biasing mechanism 51 for biasing the second support shaft 28 of the worm shaft 16 toward the worm wheel 17 may be provided. The biasing mechanism 51 is a screw member 53 that is screwed into a through hole 52 that is continuous with the fifth bearing holding hole 35C, and an urging member that is interposed between the screw member 53 and the outer ring 33a of the fifth bearing 33. And an elastic member 54.

  The elastic member 54 includes a spring member such as a coil spring, for example, and biases the second support shaft 28 toward the worm wheel 17 via the fifth bearing 33. The fifth bearing holding hole 35C is formed in a long hole shape extending to the worm wheel 17 side, and the fifth bearing 33 can move to the worm wheel 17 side. The screw member 53 is fixed to the first housing 36 by a lock nut 55.

Moreover, you may use other spring members, such as a coil spring, as the biasing member 42 for preload loads. Furthermore, you may form the tooth | gear formation part 18 of the worm wheel 17 with iron. In this case, a larger torque can be transmitted by the worm gear mechanism 8.
Moreover, you may apply the reducer of this invention to the apparatus provided with other reducers other than a power steering apparatus.

It is a schematic sectional drawing of an electric power steering device provided with the reduction gear of one embodiment of this invention. It is sectional drawing which follows the II-II line | wire of FIG. It is an enlarged view of the principal part of FIG. It is sectional drawing which follows the IV-IV line of FIG. It is sectional drawing of the principal part for demonstrating manufacture of a reduction gear, (A) has shown the state before a worm wheel is accommodated in a worm wheel accommodation hole, (B) is a worm wheel being a worm. The state accommodated in the wheel accommodation hole is shown. It is sectional drawing which shows the state before inserting a worm shaft in a worm shaft accommodation hole. It is sectional drawing which shows the state in which a part of tooth | gear formation part of the worm shaft was inserted in escape space. It is sectional drawing which follows the VIII-VIII line of FIG. It is sectional drawing which shows the state which a part of worm shaft displaced to the tooth | gear formation part accommodation hole from escape space. It is sectional drawing which shows the state in which the 2nd spindle of the worm shaft was inserted in the 5th bearing holding hole. It is sectional drawing which shows the state before attaching an electric motor to a gear housing. It is sectional drawing of the principal part of another embodiment of this invention. It is sectional drawing for demonstrating manufacture of the reduction gear of FIG. 12, (A) has shown the state which started inserting the worm shaft in a worm shaft accommodation hole, (B) is the tooth | gear formation of a worm shaft. A part of the portion is shown inserted into the escape space, and (C) shows a state where the worm shaft is engaged with the worm wheel. (A) is sectional drawing of the principal part of another embodiment of this invention, (B) is sectional drawing which follows the XIVB-XIVB line | wire of FIG. 14 (A). It is sectional drawing for demonstrating manufacture of the reduction gear of FIG. 14 (A), (A) has shown the state which started inserting the worm shaft in a worm shaft accommodation hole, (B) is a worm shaft. FIG. 2C shows a state where a part of the tooth forming portion is inserted into the escape space, and FIG. 3C shows a state where the worm shaft is engaged with the worm wheel. It is sectional drawing of the principal part of another embodiment of this invention. It is sectional drawing of the principal part of another embodiment of this invention. It is sectional drawing of the principal part of another embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Reducer, 11 ... Electric motor, 16 ... Worm shaft, 17 ... Worm wheel, 26 ... (Worm shaft) tooth formation part, 28 ... 2nd spindle (2nd end part), 33 ... 5th Bearing (bearing), 31 ... spline shaft (first end), 35; 35C ... fifth bearing holding hole (bearing holding hole), 36 ... first housing, 36b ... (of the first housing) The other end (end), 37 ... second housing, 38 ... worm wheel accommodation hole, 39 ... worm shaft accommodation hole, 44 ... lid member, 45 ... bearing insertion hole, 46, 46A ... clearance space.

Claims (5)

A first housing having a cylindrical shape defining a worm shaft accommodation hole;
A second housing that forms a cylinder that defines the worm wheel housing hole and that is continuous with the first housing;
A worm shaft housed in the worm shaft housing hole;
A worm wheel housed in the worm wheel housing hole and meshing with the worm shaft,
The worm shaft includes a first end portion that is relatively close to the electric motor that drives the worm shaft, and a second end portion that is disposed on the opposite side of the first end portion,
The worm shaft housing hole includes a clearance space facing the worm wheel across the worm tooth forming portion of the worm shaft,
A speed reducer characterized in that the contact between the worm shaft and the worm wheel is released in a state in which a part of the worm tooth forming portion of the worm shaft not mounted with the bearing is displaced into the escape space. In Claim 1, the said worm shaft accommodation hole contains the bearing holding hole for holding the bearing which supports the 2nd end part of a worm shaft,
A bearing insertion hole through which the bearing can be inserted into the bearing holding hole is formed at the end of the first housing,
A speed reducer in which a lid member that covers the bearing insertion hole is attached to the first housing.   The speed reducer according to claim 1 or 2, wherein a cross section of a portion of the worm shaft accommodation hole including the escape space has a gourd shape, an oval shape, or an elliptical shape.   4. The worm shaft housing hole according to claim 1, wherein the worm shaft housing hole includes a bearing holding hole for holding a bearing that supports the second end portion of the worm shaft, and the bearing holding hole includes the bearing. Is a speed reducer that holds the bearing in a state of restricting radial movement of the bearing. In the manufacturing method of the reduction gear of any one of Claims 1-4,
After the worm wheel is accommodated in the worm wheel accommodation hole of the second housing, the worm shaft is inserted into the worm shaft accommodation hole of the first housing from the second end side where the bearing is not mounted. A method of manufacturing a reduction gear.

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