JP4039271B2 - Reduction gear - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reduction gear for reducing the output rotation of an electric motor for assisting steering.
[0002]
[Prior art]
In general, in an electric power steering apparatus, the rotation of an electric motor for assisting steering is reduced through a reduction gear and transmitted to a steering mechanism such as a rack and pinion mechanism. As the speed reducer, a speed reducer having a worm shaft and a worm wheel is often used. The worm shaft is connected to the output shaft of the electric motor via a joint.
[0003]
2. Description of the Related Art Conventionally, a housing for a reduction gear has a large-diameter and short first cylindrical portion for accommodating a worm wheel and a small-diameter and long second cylindrical portion for accommodating a worm shaft orthogonally. It was comprised by the integrally molded housing (for example, patent document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 6-40344
[Problems to be solved by the invention]
In the speed reducer using this type of integrally molded housing, after the worm shaft is inserted from the opening of the second cylindrical portion and the worm shaft is accommodated in the second cylindrical portion, the first cylindrical portion The speed reducer is assembled by inserting the worm wheel from the open portion and housing the worm wheel in the first tubular portion while slightly engaging the worm wheel with the worm shaft.
[0006]
In such assembling, it is not possible to assemble unless a considerably large backlash is provided for the meshing between the worm shaft and the worm wheel.
However, when the backlash is set large enough to enable such assembly, for example, when driving on a rough road, a rattling sound due to backlash is generated due to reverse input from the road surface, and the noise Cause.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a speed reducer that can be easily assembled and can reduce noise.
[0007]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, according to the present invention, there is provided a reduction gear that decelerates the output rotation of an electric motor for assisting steering through a small gear and a large gear. The two split housings are combined, and the mating surfaces of the first and second split housings include a plane that substantially includes the rotation axis of the small gear and that is substantially perpendicular to the rotation axis of the large gear. Thus, the first and second divided housings include a receiving portion that receives a bearing that is fitted into at least one end of the small gear, and the receiving portion of the first divided housing is an unmounted portion of the second divided housing. A shape in which the bearing at the corresponding end of the small gear received in the mounted state can be displaced in a direction away from the large gear housing portion of the first divided housing, and combined with the first divided housing. Receiving portion of the second split housing is characterized in that to regulate the displacement in the direction away from the large gear housing of the bearing.
[0008]
In the present invention, for example, it is possible to easily assemble a reduction gear by combining a small gear and a large gear in advance and, for example, simultaneously incorporating the first gear into the first divided housing and then combining the second divided housing. Become. It is not necessary to increase the backlash due to the incorporation of the small gear and the large gear, and therefore noise can be reduced.
Further, the first and second divided housing includes a receiving portion for receiving the bearings fitted on at least one end portion of the small gear, the receiving portion of the first split housing is not yet in the second divided housing The second end in a state where the bearing at the corresponding end of the small gear received in the mounted state can be displaced in a direction away from the large gear housing portion of the first split housing and combined with the first split housing. Since the receiving part of the divided housing restricts the displacement of the bearing in the direction away from the large gear housing part, it has the following advantages.
[0009]
For example, a small gear in the state of mounting the bearing at one end, incorporated in the first housing segment, after the bearing received by the receiving portion of the first split housing, is still large gear the bearing The large gear can be easily incorporated into the large gear housing by displacing the small gear slightly away from the large gear housing by displacing away from the unmounted large gear housing. Next, by incorporating the second divided housing and restricting the position of the bearing, the small gear can be restricted to the regular assembly position.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view of an electric power steering apparatus according to an embodiment of the present invention. With reference to FIG. 1, in this electric power steering apparatus, it is connected to a first steering shaft 2 as an input shaft to which a steering wheel 1 is attached and a steering mechanism (not shown) such as a rack and pinion mechanism. A second steering shaft 3 serving as an output shaft is coaxially connected via a torsion bar 4.
[0011]
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.
The gear housing 7 accommodates a worm gear mechanism 8 as a speed reduction mechanism, and the sensor housing 6 accommodates a torque sensor 9, a control board 10, and the like. The worm gear mechanism 8 includes a worm shaft (small gear) 11 and a worm wheel (large gear) 12 that meshes with the worm shaft (small gear) 11. The reduction gear 50 is configured by housing the worm gear mechanism 8 in the gear housing 7.
[0012]
A gear housing 7 as a housing of the reduction gear 50 has a cylindrical shape, and an annular edge portion 71 at the upper end thereof is fitted into an annular step portion 6 a on the outer periphery of the lower end of the sensor housing 6. The gear housing 7 defines a worm shaft housing portion 51 for housing the worm shaft 11 and a worm wheel housing portion 52 for housing the worm wheel 12.
The gear housing 7 is a combination of the first and second divided housings 7A and 7B, and a worm shaft accommodating portion 51 and a worm wheel accommodating portion 52 are defined between the first and second divided housings 7A and 7B. Has been.
[0013]
The mating surfaces 72 and 73 of the first and second divided housings 7A and 7B include a surface Z that substantially includes the rotation axis X of the worm shaft 11 and is substantially orthogonal to the rotation axis Y of the worm wheel 12.
As shown in FIG. 2, the worm shaft 11 of the worm gear mechanism 8 is connected to the rotating shaft 32 of the electric motor M via a joint mechanism including, for example, a spline 33, and the worm wheel 12 meshes with the worm shaft 11 and As shown in FIG. 1, the second steering shaft 3 can rotate integrally with an intermediate portion in the axial direction and is restricted from moving in the axial direction.
[0014]
The worm wheel 12 includes an annular cored bar 12a coupled to the second steering shaft 3 so as to be integrally rotatable, and a synthetic resin member 12b that surrounds the cored bar 12a and forms teeth on the outer peripheral surface portion. The cored bar 12a is inserted into a mold at the time of resin molding of the synthetic resin member 12b, for example.
In the gear housing 7, a region including at least the meshing portion A of the worm shaft 11 and the worm wheel 12 is filled with a lubricant. That is, the lubricant may be filled only in the meshing portion A, or may be filled in the entire periphery of the meshing portion A and the worm shaft 11 or in the entire gear housing 7.
[0015]
The second steering shaft 3 is rotatably supported by a pair of bearings 13 and 14 that are disposed with the worm wheel 12 sandwiched in the axial direction.
The outer ring 15 of one bearing 13 is fitted and held in a bearing holding hole 16 provided in a cylindrical projection 6 b at the lower end of the sensor housing 6. An upper end surface of the outer ring 15 of the bearing 13 is in contact with the annular step portion 17, and movement in the axial direction with respect to the sensor housing 6 is restricted. The inner ring 18 of the bearing 13 is fitted to the second steering shaft 3 by an interference fit. The lower end surface of the inner ring 18 is in contact with the upper end surface of the core metal 12 a of the worm wheel 12.
[0016]
The outer ring 19 of the other bearing 14 is fitted and held in the bearing holding hole 20 of the gear housing 7. A lower end surface of the outer ring 19 of the bearing 14 is in contact with the annular step portion 21, and movement in the axially lower direction with respect to the gear housing 7 is restricted. The inner ring 22 of the bearing 14 is attached to the second steering shaft 3 such that the inner ring 22 is integrally rotatable and the relative movement in the axial direction is restricted. The inner ring 22 is sandwiched between a step portion 23 of the second steering shaft 3 and a nut 24 fastened to a screw portion of the second steering shaft 3.
[0017]
The torsion bar 4 passes through the first and second steering shafts 2 and 3. The upper end 4a of the torsion bar 4 is connected to the first steering shaft 2 by a connecting pin 25 so as to be integrally rotatable, and the lower end 4b of the torsion bar 4 is connected to the second steering shaft 3 by a connecting pin 26 so as to be integrally rotatable. Has been. The lower end of the second steering shaft 3 is connected to a steering mechanism such as a rack and pinion mechanism via an intermediate shaft (not shown).
The connecting pin 25 connects the third steering shaft 27 disposed coaxially with the first steering shaft 2 so as to be integrally rotatable with the first steering shaft 2. The third steering shaft 27 passes through the tube 28 constituting the steering column.
[0018]
The upper part of the first steering shaft 2 is rotatably supported by the sensor housing 6 via a bearing 29 made of, for example, a needle roller bearing. The reduced diameter portion 30 at the lower part of the first steering shaft 2 and the hole 31 at the upper part of the second steering shaft 3 restrict the relative rotation of the first and second steering shafts 2 and 3 within a predetermined range. And a predetermined play in the rotational direction.
Next, referring to FIG. 2, the first and second end portions 11a and 11b of the worm shaft 11 are rotatably supported by first and second bearings 34 and 35 held by the gear housing 7, respectively. ing. The first and second bearings 34 and 35 are ball bearings, for example.
[0019]
Inner rings 36 and 37 of the first and second bearings 34 and 35 are fitted into corresponding constricted portions of the worm shaft 11. Further, the outer rings 38 and 39 of the first and second bearings 34 and 35 are respectively held in corresponding bearing holding holes 40 and 41 of the gear housing 7.
Further, the outer ring 38 of the first bearing 34 that supports the first end portion 11 a of the worm shaft 11 is positioned in contact with the stepped portion 42 of the gear housing 7. On the other hand, the inner ring 36 of the first bearing 34 is in contact with the positioning step 43 of the worm shaft 11, so that the movement of the worm shaft 11 toward the second end portion 11 b is restricted.
[0020]
The inner ring 37 of the second bearing 35 that supports the vicinity of the second end portion 11 b (joint side end portion) of the worm shaft 11 is brought into contact with the positioning step portion 44 of the worm shaft 11. 1 is restricted from moving toward the end 11a.
The outer ring 38 of the second bearing 35 is urged toward the fourth bearing 34 by a preload adjusting screw member 45. The screw member 45 is screwed into a screw hole 46 formed in the gear housing 7, thereby applying preload to the first and second bearings 34 and 35 and positioning the worm shaft 11 in the axial direction. The lock nut 47 is engaged with the screw member 45 in order to stop the screw member 45 after the preload adjustment.
[0021]
3A and 3B are schematic views of the first and second divided housings 7A and 7B constituting the gear housing 7 as seen from the mating surfaces 72 and 73 side. In the present embodiment, the entire mating surfaces 72 and 73 are disposed along a surface Z (see FIG. 1) that substantially includes the rotation axis X of the worm shaft 11 and substantially perpendicular to the rotation axis Y of the worm wheel 12. And coincide with each other along the plane Z. However, as long as the worm shaft 11 and the worm wheel 12 can be incorporated, only a part of the mating surfaces 72 and 73 may be disposed along the surface Z.
[0022]
The bearing holding hole 40 for the first bearing 34 shown in FIG. 2 includes a semicircular receiving portion 40a of the first divided housing 7A shown in FIG. 3A and the first holding portion 40a shown in FIG. The two divided housings 7B are combined with a semicircular receiving portion 40b. Similarly, the bearing holding hole 41 for the second bearing 35 shown in FIG. 2 includes a receiving part 41a having a semicircular cross section of the first divided housing 7A shown in FIG. 3A, and FIG. And a receiving portion 41b having a semicircular cross section of the second divided housing 7B.
[0023]
Further, a step portion 42 for positioning the outer ring 38 of the first bearing 34 shown in FIG. 2 includes a semicircular step portion 42a of the first divided housing 7A shown in FIG. The second divided housing 7B shown in b) is combined with a semicircular step 42b.
When the first and second divided housings 7A and 7B are connected, the connection holes 74a, 75a and 76a of the first divided housing 7A shown in FIG. 3A and the corresponding connection holes of the second divided housing 7B are shown. 74b, 75b, and 76b are connected to each other, and the corresponding connecting bolts (not shown) are respectively inserted to connect the first and second divided housings 7A and 7B to each other.
[0024]
According to the present embodiment, the worm shaft 11 and the worm wheel 12 are pre-engaged with each other, and are incorporated into any one of the divided housings, for example, the first divided housing 7A, and then the second divided housing 7B. Thus, the speed reducer 50 can be easily assembled.
In order to incorporate the worm shaft 11 and the worm wheel 12 into the gear housing 7, it is not necessary to increase the backlash of the worm shaft 11 and the worm wheel 12, and as a result, noise can be reduced.
[0025]
4 to 7 show another embodiment of the present invention. Referring to FIGS. 4 (a) and 5, this embodiment differs from the embodiment of FIGS. 3 (a) and 3 (b) in that a first bearing 34 for receiving outer ring 38 is received. The relief portion 77 is provided in the receiving portion 40 of one divided housing 7A.
As shown in FIG. 6, the escape portion 77 moves away from the worm wheel housing portion 52 the first bearing 34 of the first end portion 11 a of the worm shaft 11 received when the second divided housing 7 </ b> B is not attached. A shape that can be displaced in the direction K is formed. Specifically, as shown in FIG. 5, the shape is slightly expanded in the direction K away from the outline of the semicircular cross section (indicated by a dashed line in FIG. 5).
[0026]
Referring to FIG. 4B, the corresponding receiving portion 40b of the second divided housing 7B is the same as the embodiment of FIG. 3B, and has a semicircular cross section. Therefore, as shown in FIG. 7B, the receiving portion 40b of the second divided housing 7B combined with the first divided housing 7A can regulate the movement of the first bearing 34. .
Thus, according to the present embodiment, the worm shaft 11 is incorporated into the first divided housing 7A, and the first bearing 34 is received by the first divided housing 7A as shown in FIG. 7A. After being received by 40a, as shown in FIG. 6, the first bearing 34 is displaced in a direction away from the worm wheel housing portion 52 so that the worm shaft 11 is slightly released from the worm wheel housing portion 52, and the worm wheel The worm wheel 12 can be easily incorporated into the accommodating portion 52.
[0027]
Next, as shown in FIG. 7B, the worm shaft 11 can be regulated to the regular assembly position by assembling the second divided housing 7B and regulating the position of the first bearing 34.
In the present embodiment, in the first divided housing 7A, the receiving portion 77 may be provided only in the receiving portion 41a for the second bearing 35, or for the first and second bearings 34 and 35. You may provide the escape part 77 in both the receiving parts 40a and 41a.
[0028]
Moreover, you may make it provide the escape part 77 in at least one receiving part 40b or 41b of only the 2nd division | segmentation housing 7B.
Further, although the worm shaft is exemplified as the small gear and the worm wheel is illustrated as the large gear, it may be a helical gear, a bevel gear, or a hypoid gear. Furthermore, a worm wheel may be provided with a helical portion at the center portion in the tooth line direction. In addition, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of an electric power steering apparatus to which a reduction gear according to an embodiment of the present invention is applied.
2 is a cross-sectional view taken along line II-II in FIG.
FIGS. 3A and 3B are schematic views of the first and second divided housings constituting the gear housing as viewed from the mating surface side.
4 (a) and 4 (b) are schematic views of first and second divided housings constituting the gear housing as seen from the mating surface side in another embodiment of the present invention.
FIG. 5 is a cross-sectional view of a receiving portion of a first divided housing.
6A and 6B are schematic cross-sectional views of a receiving portion and a first bearing showing an assembly process.
FIGS. 7A and 7B are schematic views showing a process of assembling the worm shaft to the first divided housing. FIGS.
[Explanation of symbols]
7 gear housing 7A first divided housing 7B second divided housing 8 worm gear mechanism 11 worm shaft (worm, small gear)
11a First end portion 11b Second end portion 12 Worm wheel (large gear)
34 First bearing 35 Second bearing 36, 37 Inner ring 38, 39 Outer ring 40, 41 Bearing holding hole 40a, 40b, 41a, 41b Receiving part 50 Reduction gear 51 Worm shaft accommodating part 52 Worm wheel accommodating part 72, 73 Alignment Surfaces 74a, 74b, 75a, 75b, 76a, 76b Connecting hole 77 Escape portion K Direction away from worm wheel accommodating portion M Electric motor X Rotational axis Y of worm shaft Rotational axis Z of worm wheel The rotation axis of the worm wheel and substantially perpendicular to the rotation axis of the worm wheel)

Claims (1)

In a reduction gear that decelerates the output rotation of an electric motor for steering assistance via a small gear and a large gear,
The housing for accommodating the small gear and the large gear is a combination of the first and second divided housings,
These mating surfaces of each other of the first and second divided housing viewed contains substantially perpendicular to the plane substantially containing and the axis of rotation of the gear wheel the axis of rotation of the pinion,
The first and second divided housings include a receiving portion that receives a bearing that is fitted into at least one end portion of the small gear,
The receiving portion of the first divided housing has a shape capable of displacing the bearing at the corresponding end of the small gear received when the second divided housing is not attached in a direction away from the large gear housing portion of the first divided housing. ,
The speed reducer , wherein the receiving portion of the second divided housing combined with the first divided housing regulates displacement of the bearing in a direction away from the large gear housing portion .

Images