JP2019219028A - Speed reducer - Google Patents

Abstract

To provide a speed reducer which enables reduction of its weight while maintaining stable assemblability.SOLUTION: A speed reducer 10 includes: a shaft 50 having a worm 40 (a gear); a resin bush 60 rotatably supporting the shaft 50; and a housing 20 which houses the shaft 50 and the resin bush 60. The housing 20 includes: a bush holding part 70 having a cylindrical space 75 for fitting the resin bush 60 attached to the shaft 50; and an insertion part 80 opening at one end part and having a through hole 81 into which the shaft 50 and the resin bush 60 are inserted from the one end part to the bush holding part 70. An outer diameter Ds5 of the worm 40 is smaller than an inner diameter d1 of the through hole 81, and an inner diameter d2 of the bush holding part 70 is larger than an inner diameter d1 of the through hole 81. The resin bush 60 has a slit 61 in which at least a part as seen in a circumferential direction opens.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reduction gear used for an electric tilt / telescopic adjustment steering column.

  2. Description of the Related Art Conventionally, in a speed reducer such as a worm speed reducer, a worm shaft is rotatably held in a metal housing via a metal ball bearing (for example, see Patent Document 1).

JP 2004-225768 A

  By the way, in recent years, reduction of the weight of the reduction gear by using a bearing as a resin has been studied. However, it is difficult to press-fit the resin member into the housing, and a stable assembling property may not be obtained.

  Therefore, an object of the present invention is to provide a speed reducer that can be reduced in weight while maintaining stable assemblability.

  In order to solve the above-described problem, a speed reducer according to one embodiment of the present invention includes a shaft having gears, a resin bush that rotatably supports the shaft, and a housing that houses the shaft and the resin bush. Is a bush holding portion having a cylindrical space for fitting a resin bush attached to the shaft, and one end is open, and the shaft and the resin bush are inserted from the one end to the bush holding portion. An outer diameter of the gear is smaller than an inner diameter of the through hole, an inner diameter of the bush holding part is larger than an inner diameter of the through hole, and the resin bush has a part in a circumferential direction. Has an open slit.

  According to the present invention, it is possible to provide a speed reducer that can be reduced in weight while maintaining stable assemblability.

It is a sectional view showing the schematic structure of the reduction gear concerning an embodiment. It is sectional drawing which shows the schematic structure of the bush holding part which concerns on embodiment. It is a top view showing the schematic structure of the shaft concerning an embodiment. It is a top view showing the schematic structure of the 1st bush concerning an embodiment. It is sectional drawing which shows the state which the 1st bush and 2nd bush which concern on embodiment were attached to the shaft, and were fitted in the bush holding part. It is an explanatory view showing one process of a manufacturing method of a reduction gear concerning an embodiment. It is an explanatory view showing one process of a manufacturing method of a reduction gear concerning an embodiment. It is an explanatory view showing one process of a manufacturing method of a reduction gear concerning an embodiment. FIG. 9 is a cross-sectional view illustrating a bush holding unit according to a first modification. FIG. 9 is a cross-sectional view illustrating a speed reducer according to a second modification.

  Hereinafter, embodiments will be specifically described with reference to the drawings. Each of the embodiments described below shows a comprehensive or specific example. Numerical values, shapes, materials, constituent elements, arrangement positions of constituent elements, connection forms, and the like shown in the following embodiments are merely examples, and do not limit the present invention. Further, among the components in the following embodiments, components not described in the independent claims indicating the highest concept are described as arbitrary components.

  In addition, the drawings are schematic diagrams in which emphasis, omission, and adjustment of ratios are appropriately performed in order to show the present invention, and may be different from actual shapes, positional relationships, and ratios.

  FIG. 1 is a sectional view showing a schematic configuration of a speed reducer 10 according to the embodiment. As shown in FIG. 1, the reduction gear 10 includes a housing 20, a worm wheel 30, a worm 40, a shaft 50, and a resin bush 60.

  The housing 20 houses the worm wheel 30, the worm 40, the shaft 50, and the resin bush 60. Specifically, the housing 20 includes a first portion 21 that houses the worm wheel 30 and a second portion 22 that houses the worm 40, the shaft 50, and the resin bush 60.

  The first part 21 has a flat housing space 211 for housing the worm wheel 30. The first portion 21 is provided with a bearing 35 (see FIG. 6 and the like) for rotatably holding the rotating shaft 31 of the worm wheel 30 disposed in the housing space 211. Further, the rotating shaft 31 is connected to a drive shaft of the tilt / telescopic adjustment steering column.

  The second part 22 is a part provided continuously to the first part 21. Specifically, the second part 22 has a long storage space 221 that is continuous with the storage space 211 of the first part 21. The accommodation space 221 of the second portion 22 extends substantially parallel to the tangential direction of the worm wheel 30. The worm 40, the shaft 50, and the resin bush 60 are accommodated in the accommodation space 221. The extending direction of the housing space 221 is parallel to the axial direction of the shaft 50.

  The second part 22 includes a bush holding part 70 and an insertion part 80.

  The bush holding part 70 is a part for holding the resin bush 60 attached to the shaft 50. Specifically, the bush holding portion 70 has a cylindrical space 75 into which the resin bush 60 attached to the shaft 50 fits. This space 75 is a part of the accommodation space 221. The bush holding portion 70 has a first end surface 71 for defining a space 75, a second end surface 72, and an inner peripheral surface 73. The first end face 71 is disposed outside the housing 20 with respect to the second end face 72, and the first end face 71 and the second end face 72 face each other in the extending direction of the housing space 221. The inner peripheral surface 73 is disposed between the first end surface 71 and the second end surface 72, and has a uniform shape in the extending direction.

  FIG. 2 is a cross-sectional view illustrating a schematic configuration of the bush holding unit 70 according to the embodiment. Specifically, FIG. 2 is a cross-sectional view of the section taken along line II-II in FIG. In FIG. 2, the resin bush 60 (second bush 60b) arranged in the bush holding portion 70 is illustrated by a broken line.

  As shown in FIG. 2, a projection 74 protruding inward is provided on an inner peripheral surface 73 of the bush holding portion 70. The projection 74 fits into a slit 61 (described later) of the resin bush 60. Thereby, rotation of the resin bush 60 in the bush holding part 70 can be restricted. The protrusion 74 is provided continuously with respect to the entire bush holding portion 70 in the extending direction, but is not provided on the insertion portion 80.

  Here, the housing 20 is formed of, for example, a resin such as a reinforced resin. As shown in FIG. 2, the parting line L <b> 1 in the housing 20 is provided so as to pass over the protrusion 74.

  The insertion portion 80 is a portion that guides the shaft 50 and the resin bush 60 when inserting them into the housing 20. More specifically, one end of the insertion portion 80 is open, and has a through hole 81 into which the shaft 50 and the resin bush 60 are inserted from the one end to the bush holding portion 70. That is, the through hole 81 has one end communicating with the outside and the other end communicating with the space 75. The inner peripheral surface 82 forming the through hole 81 in the insertion portion 80 is a tapered surface that tapers toward the other end.

  Next, the shaft 50 will be described. FIG. 3 is a plan view showing a schematic configuration of the shaft 50 according to the embodiment. As shown in FIG. 3, the shaft 50 includes a shaft 51, a flange 52, a large diameter portion 53, and a small diameter portion 54.

  The shaft body 51 has the worm 40. The worm 40 is an example of a gear that meshes with the worm wheel 30, and is specifically a screw gear. The worm 40 is arranged coaxially with the shaft body 51. One end of the shaft body 51 projects outward of the housing 20 from the insertion portion 80 as shown in FIG. One end of the shaft body 51 is connected to a drive source (not shown) such as a motor. The rotation transmitted from the drive source to the shaft body 51 is reduced by being transmitted from the worm 40 to the worm wheel 30. The reduced rotation is transmitted from the worm wheel 30 to the drive shaft of the tilt / telescopic adjustment steering column.

  The flange portion 52 is an annular portion provided at one end of the shaft body 51 with respect to the worm 40. The flange portion 52 is arranged coaxially with the shaft body 51. The outer diameter Ds2 of the flange portion 52 is larger than the outer diameter Ds1 of the shaft body 51 and smaller than the smallest inner diameter d1 of the through hole 81 of the insertion portion 80 (see FIG. 5). The inner diameter d1 is larger than the outer diameter Ds5 of the worm 40.

  The large diameter portion 53 is provided on the other end side of the shaft portion 51 with respect to the flange portion 52, and is an annular portion overlapping the flange portion 52. The large diameter portion 53 is disposed coaxially with the shaft body 51. The outer diameter Ds3 of the large diameter portion 53 is larger than the outer diameter Ds1 of the shaft body 51 and smaller than the outer diameter Ds2 of the flange portion 52. The outer diameter Ds3 of the large diameter portion 53 is larger than the outer diameter Ds5 of the worm 40.

  The small diameter portion 54 is provided on one end side of the flange portion 52 of the shaft body 51 and is an annular portion overlapping the flange portion 52. The small diameter portion 54 is arranged coaxially with the shaft body 51. The outer diameter Ds4 of the small diameter portion 54 is larger than the outer diameter Ds1 of the shaft body 51 and smaller than the outer diameter Ds3 of the large diameter portion 53. The outer diameter Ds4 of the small diameter portion 54 is smaller than the outer diameter Ds5 of the worm 40.

  Next, the resin bush 60 will be described. As shown in FIG. 2, the resin bush 60 includes a first bush 60a and a second bush 60b. Since the first bush 60a and the second bush 60b are the same, only the first bush 60a will be described here, and the description of the second bush 60b will be omitted.

  FIG. 4 is a plan view showing a schematic configuration of the first bush 60a according to the embodiment. As shown in FIG. 4, the first bush 60a has a slit 61 in the annular resin member that is partially open in the circumferential direction. In other words, the first bush 60a has a C-shape in plan view (in FIG. 4, it is shown as an inverted C-shape). Due to such a shape, the first bush 60a can be elastically deformed so as to narrow the slit 61. When the slit 61 is narrowed, the outer diameter of the first bush 60a itself becomes small.

  The first bush 60 a may be formed of a resin, but is preferably formed of a resin having lower rigidity than the housing 20. For example, the first bush 60a is formed of a non-reinforced resin containing no aggregate. For this reason, the first bush 60a is easily elastically deformed. However, since the first bush 60a rotatably supports the shaft 50 as described later, it is necessary to secure a certain rigidity in order to stably support the shaft 50.

  In the first bush 60a, a concave portion 62 is formed on the outer peripheral surface 603 at a position facing the slit 61. The recess 62 is a thin portion that is thinner than other portions of the first bush 60a. Since the first bush 60a has the thin portion, the first bush 60a is easily elastically deformed starting from the thin portion.

  Here, the outer edge of the first bush 60a on the other end side is chamfered and has an inclined surface 63 (see FIG. 5 and the like). The inclination of the inclined surface 63 corresponds to the inclination of the inner peripheral surface 82 of the insertion portion 80. The inclined surface 63 is not provided in the concave portion 62. Hereinafter, the end face on the other end side of the first bush 60a is referred to as a second face 602, and the end face on the one end side is referred to as a first face 601 (see FIG. 5 and the like).

  FIG. 5 is a cross-sectional view showing a state in which the first bush 60a and the second bush 60b according to the embodiment are attached to the shaft 50 and fitted to the bush holding portion 70. FIG. 5 is a sectional view of a portion surrounded by a broken line L2 in FIG.

  As shown in FIG. 5, in the bush holding portion 70, the flange portion 52, the large diameter portion 53, and the small diameter portion 54 of the shaft 50 are arranged, and the first bush 60a and the second bush 60b are arranged. I have.

  The first bush 60a is arranged at a position corresponding to the large diameter portion 53. Specifically, the first bush 60a is fitted to the large diameter portion 53 in the bush holding portion 70. In this state, the first bush 60 a has the second surface 602 abutting on the second end surface 72 of the bush holding portion 70, and the first surface 601 abutting on the flange portion 52. In the first bush 60 a, a portion of the outer peripheral surface 603 excluding the concave portion 62 is in contact with the inner peripheral surface 73 of the bush holding portion 70. That is, the first bush 60a is sandwiched between the second end surface 72 of the bush holding portion 70 and the flange portion 52 in the axial direction, and is sandwiched between the inner peripheral surface 73 of the bush holding portion 70 and the large diameter portion 53 in the radial direction. ing. Thus, the first bush 60a is fitted to the bush holding portion 70.

  The second bush 60b is arranged in the bush holding portion 70 at a position corresponding to the small diameter portion 54. The second bush 60 b has a second surface 602 abutting on the flange portion 52, and a first surface 601 abutting on the first end surface 71 of the bush holding portion 70. In the second bush 60 b, a portion of the outer peripheral surface 603 excluding the concave portion 62 is in contact with the inner peripheral surface 73 of the bush holding portion 70. In this state, the second bush 60b is separated from the small diameter portion 54. That is, the second bush 60b is sandwiched between the flange portion 52 and the first end surface 71 of the bush holding portion 70 in the axial direction, and is in contact with only the inner peripheral surface 73 of the bush holding portion 70 in the radial direction. . Thus, the second bush 60b is fitted to the bush holding part 70.

  The dimensions of each part in this state are compared. The inner diameter d2 of the bush holding portion 70 is larger than the smallest inner diameter d1 of the through hole 81 of the insertion portion 80. The inner diameter d2 of the bush holding portion 70 is larger than the inner diameter d3 of the second portion 22 on the side opposite to the insertion portion 80 with respect to the bush holding portion 70. Note that the inner diameter d2 is a value ignoring the protrusion 74.

  The outer diameter Db1 of the first bush 60a and the second bush 60b substantially matches the inner diameter d2 of the bush holding portion 70. The inner diameter Db2 of the first bush 60a and the second bush 60b substantially matches the outer diameter Ds3 of the large diameter portion 53 of the shaft 50.

  In the bush holding portion 70, the axial movement of the shaft 50 is restricted because the flange portion 52 of the shaft 50 is sandwiched between the first bush 60a and the second bush 60b in the axial direction. Further, in the bush holding portion 70, the large diameter portion 53 of the shaft 50 is sandwiched in the radial direction by the inner peripheral surface 73 of the bush holding portion 70 and the large diameter portion 53, so that the movement of the shaft 50 in the radial direction is prevented. Regulated. Therefore, the shaft 50 can rotate stably without moving in the axial direction and the radial direction.

  During rotation, the shaft 50 slides on the inner peripheral surface 604 of the first bush 60a and the first surface 601. Specifically, the large diameter portion 53 of the shaft 50 slides on the inner peripheral surface 604 of the first bush 60a, and the flange portion 52 slides on the first surface 601. During rotation, the shaft 50 slides on the second surface 602 of the second bush 60b. Specifically, the flange portion 52 of the shaft 50 slides on the second surface 602 of the second bush 60b. Thus, the first bush 60a and the second bush 60b rotatably support the shaft 50.

  Here, it is assumed that the first bush 60a and the second bush 60b are not elastically deformed in the bush holding portion 70 and maintain their original shapes. As a result, the first bush 60a and the second bush 60b do not apply an excessive frictional force to the shaft 50. Note that the first bush 60a and the second bush 60b may be slightly (about several percent) elastically deformed in the bush holding portion 70.

  Next, a method for manufacturing the speed reducer 10 according to the embodiment will be described. In the following description, a case where the operator assembles the speed reducer 10 will be described as an example. However, the same procedure can be performed when the manufacturing apparatus assembles the speed reducer 10.

  6 to 8 are explanatory diagrams illustrating one process of a method for manufacturing the speed reducer 10 according to the embodiment. As shown in FIG. 6, first, the worker attaches the first bush 60 a to the second portion 22 of the housing 20. Specifically, the operator inserts the first bush 60a from the through hole 81 of the insertion section 80. At this time, since the inclined surface 63 of the first bush 60a comes into surface contact with the inner peripheral surface 82 of the insertion portion 80 and is pushed, the first bush 60a gradually narrows the interval between the slits 61 so that the radial direction is reduced. While passing through the insertion portion 80. In FIG. 6, the first bush 60a contracted in the radial direction is illustrated by a broken line. As described above, since the inclined surface 63 of the first bush 60a is in surface contact with the inner peripheral surface 82 of the insertion portion 80, the first bush 60a can be elastically deformed smoothly.

  The first bush 60a is disposed in the bush holding portion 70 when passing through the insertion portion 80. When the slit 61 of the first bush 60a and the projection 74 are aligned in the bush holding portion 70, the first bush 60a elastically returns to its original shape. As a result, the first bush 60a is fitted into the bush holding portion 70 (see FIG. 2: the first bush 60a is the same as the second bush 60b shown in FIG. 2). Further, since the protrusion 74 is fitted into the slit 61 of the first bush 60a, the rotation of the first bush 60a is restricted.

  Next, as shown in FIG. 7, the worker attaches the shaft 50 to the second portion 22 of the housing 20. Specifically, the operator inserts the shaft 50 into the insertion section 80 from the worm 40 side. When the worm 40 passes through the insertion portion 80 and the first bush 60a, the large-diameter portion 53 of the shaft 50 is fitted to the inner peripheral surface 604 of the first bush 60a, and the flange portion 52 is connected to the first bush 60a. It comes into contact with one surface 601. At this time, since the first bush 60a is pushed by the flange portion 52, the second surface 602 of the first bush 60a contacts the second end surface 72 of the bush holding portion 70, so that the first bush 60a is At a predetermined position.

  Next, as shown in FIG. 8, the worker attaches the second bush 60 b to the second portion 22 of the housing 20. Specifically, the operator inserts the second bush 60b from the through hole 81 of the insertion section 80. At this time, since the inclined surface 63 of the second bush 60b comes into surface contact with the inner peripheral surface 82 of the insertion portion 80 and is pushed, the second bush 60b gradually narrows the interval between the slits 61 in the radial direction. It passes through the insertion portion 80 while shrinking. In FIG. 8, the second bush 60b contracted in the radial direction is illustrated by a broken line. Also in the second bush 60b, since the inclined surface 63 is in surface contact with the inner peripheral surface 82 of the insertion portion 80, the second bush 60b can be smoothly elastically deformed.

  When the second bush 60b passes through the insertion portion 80, the second bush 60b is disposed in the bush holding portion 70, and the second surface 602 of the second bush 60b contacts the flange portion 52. Thereby, the second bush 60b is arranged at a position corresponding to the small diameter portion 54 of the shaft 50. Further, in this state, when the slit 61 of the second bush 60b and the projection 74 are aligned, the second bush 60b is elastically restored to its original shape. As a result, the second bush 60b fits into the bush holding portion 70 (see FIG. 2). Further, since the protrusion 74 is fitted into the slit 61 of the second bush 60b, the rotation of the second bush 60b is restricted.

  As shown in FIG. 2, when the protrusion 74 is fitted to the slit 61 of the first bush 60a and the second bush 60b, the parting line L1 of the housing 20 is positioned at the position corresponding to the slit 61 and the recess 62. Will be placed in

  Finally, the worker attaches the worm wheel 30 to the first portion 21 of the housing 20 and engages the worm wheel 30 with the worm 40. Thus, the speed reducer 10 is assembled (see FIG. 1).

  As described above, reduction gear 10 according to the present embodiment accommodates shaft 50 having worm 40 (gear), resin bush 60 rotatably supporting shaft 50, and shaft 50 and resin bush 60. The housing 20 includes a bush holding portion 70 having a cylindrical space 75 into which the resin bush 60 attached to the shaft 50 is fitted, and one end is open, and An insertion portion 80 having a through hole 81 into which the shaft 50 and the resin bush 60 are inserted, up to the bush holding portion 70, the outer diameter Ds5 of the worm 40 being smaller than the inner diameter d1 of the through hole 81, and the bush holding portion 70 has an inner diameter d2 larger than the inner diameter d1 of the through hole 81, and the resin bush 60 has a slit 61 partially open in the circumferential direction. It is.

  According to this, since the resin bush 60 fitted to the bush holding portion 70 has the slit 61, it can be contracted in the radial direction by elastic deformation. Therefore, the resin bush 60 can reach the bush holding portion 70 through the through hole 81 of the insertion portion 80 while contracting in the radial direction. Since the inner diameter d2 of the bush holding portion 70 is larger than the inner diameter d1 of the through hole 81, the resin bush 60 that has reached the bush holding portion 70 returns to its original shape by elastic recovery and fits into the bush holding portion 70. . This makes it difficult for the resin bush 60 to move in the bush holding portion 70, and to maintain a stable assembling property. Further, since the shaft 50 is rotatably supported by the resin bush 60, the weight can be reduced as compared with a metal bearing. Thus, it is possible to provide the speed reducer 10 that can be reduced in weight while maintaining stable assemblability.

  The resin bush 60 includes a first bush 60a and a second bush 60b, and the shaft 50 is provided on one end side of the worm 40, and is larger than the inner diameter Db2 of each of the first bush 60a and the second bush 60b. A flange portion 52 having a large outer diameter Ds2 and a large diameter portion 53 provided on the other end side of the flange portion 52, the large diameter portion having an outer diameter Ds3 substantially matching the inner diameter Db2 of the first bush 60a. 53, a small-diameter portion 54 provided on one end side of the flange portion 52, the small-diameter portion 54 having an outer diameter Ds4 smaller than the inner diameter Db2 of the second bush 60b. The second bush 60b is arranged at a position corresponding to the small-diameter portion 54.

  According to this, the first bush 60a and the second bush 60b are included in the resin bush 60 fitted to the bush holding portion 70, and the first bush 60a and the second bush 60b are attached to the bush holding portion 70. When fitted, the flange portion 52 of the shaft 50 is sandwiched. Therefore, the position of the shaft 50 in the axial direction is restricted in the bush holding portion 70, so that the assemblability of the shaft 50 can be improved.

  Further, since the outer diameter Ds3 of the large diameter portion 53 substantially matches the inner diameter Db2 of the first bush 60a, the large diameter portion 53 is fitted to the first bush 60a fitted to the bush holding portion 70. Can be. As a result, the first bush 60a regulates the movement of the shaft 50 in the radial direction.

  On the other hand, since the outer diameter Ds4 of the small diameter portion 54 is smaller than the inner diameter Db2 of the second bush 60b, the small diameter portion 54 does not fit to the second bush 60b fitted to the bush holding portion 70. For this reason, even the second bush 60 b that has shrunk in the radial direction can be arranged at a position facing the small diameter portion 54 in the bush holding portion 70. Thereby, the second bush 60b can be smoothly fitted to the bush holding portion 70.

  The housing 20 is formed from a resin. According to this, since the housing 20 is formed of resin similarly to the resin bush 60, the difference in the thermal expansion coefficient between the housing 20 and the resin bush 60 can be reduced. If the difference in the coefficient of thermal expansion is small, rattling at the contact surface between the housing 20 and the resin bush 60 can be suppressed, and more stable assemblability can be realized. Further, damage due to the rattling can be suppressed.

  The resin bush 60 is provided with a concave portion 62 on the outer peripheral surface 603 at a position facing the slit 61, and the parting line L <b> 1 of the housing 20 is arranged at a position corresponding to the slit 61 and the concave portion 62.

  According to this, since the parting line L1 of the housing 20 is arranged at a position corresponding to the slit 61 and the concave portion 62, burrs and the like caused by the parting line L1 do not contact the resin bush 60. Thereby, rattling of the resin bush 60 can be suppressed, and more stable assemblability can be realized.

  The resin bush 60 has a thin portion (recess 62) that is thinner than other portions.

  According to this, since the resin bush 60 has the thin portion, the resin bush 60 is easily elastically deformed starting from the thin portion. Thereby, the resin bush 60 is easily shrunk in the radial direction in the insertion portion 80, and can pass through the insertion portion 80 smoothly.

  In the present embodiment, the case where the concave portion 62 provided on the outer peripheral surface 603 of the resin bush 60 has a thin portion has been exemplified. However, a thin portion may be formed by providing a concave portion on any one of the inner peripheral surface 604, the first surface 601 and the second surface 602 of the resin bush 60.

  The inner peripheral surface 82 forming the through hole 81 in the insertion portion 80 is a tapered surface tapering toward the other end.

  According to this, since the inner peripheral surface 82 of the through-hole 81 is a tapered surface that tapers toward the other end, the resin bush 60 is pushed into the through-hole 81 from one end, so that the resin bush 60 is Following the inner peripheral surface 82, it can be contracted in the radial direction. Therefore, the resin bush 60 can smoothly pass through the insertion portion 80.

[Modification]
The configuration of the speed reducer is not limited to the configuration described in the above embodiment. Therefore, a modified example of the speed reducer will be described below with a focus on differences from the above embodiment. In the following description, the same portions as those in the above-described embodiment or other modified examples are denoted by the same reference numerals, and description thereof may be omitted.

(Modification 1)
FIG. 9 is a cross-sectional view illustrating a bush holding portion 70c according to the first modification. Specifically, FIG. 9 is a diagram corresponding to FIG. As shown in FIG. 9, the bush holding portion 70c according to the first modification has a tapered surface in which the first end face 71c tapers toward the one end side. Since the first end surface 71c is a tapered surface, the first end surface 71c presses the second bush 60c in the axial direction. Therefore, the backlash in the axial direction of the second bush 60c can be suppressed.

  In addition, the second bush 60c has a chamfered outer edge on one end side, and has an inclined surface 64. The inclination of the inclined surface 64 corresponds to the first end surface 71c of the bush holding portion 70c. Therefore, the inclined surface 64 of the second bush 60c comes into surface contact with the first end surface 71c of the bush holding portion 70c. For this reason, stress due to contact is dispersed, and friction can be suppressed.

  In the present embodiment, the case where the first end surface 71c of the bush holding portion 70c is a tapered surface is illustrated, but the second end surface 72 of the bush holding portion 70c may be a tapered surface. In this case, the second end surface 72 is a tapered surface that tapers toward the other end.

(Modification 2)
FIG. 10 is a cross-sectional view illustrating a speed reducer 10D according to a second modification. Specifically, FIG. 10 is a diagram corresponding to FIG. As shown in FIG. 10, the speed reducer 10D according to the second modification does not include the second bush 60b, but includes only the first bush 60a. Further, the reduction gear 10D includes an urging portion 90 for urging the shaft 50 toward the other end. Since the shaft 50 is pressed against the first bush 60a by the urging portion 90, the axial movement of the shaft 50 is restricted. The urging unit 90 applies an urging force to the shaft 50 in a state where the rotation of the shaft 50 is not restricted. For example, the urging unit 90 includes a spring 91 and a sliding plate 92. The base end of the spring 91 is fixed to, for example, a frame of a vehicle. A sliding plate 92 is attached to the tip of the spring 91. The sliding plate 92 is in contact with the small diameter portion 54 of the shaft 50. A biasing force of a spring 91 is applied to the shaft 50 via a sliding plate 92. Thereby, the shaft 50 is pressed against the first bush 60a. When the shaft 50 rotates, the small-diameter portion 54 slides on the sliding plate 92, so that the rotation of the shaft 50 is not restricted.

[Others]
As described above, the speed reducer according to the present invention has been described based on the above-described embodiments and modified examples, but the present invention is not limited to the above-described embodiments and modified examples.

  For example, in the above embodiment, the case where the first bush 60a and the second bush 60b have the same shape is illustrated, but the first bush 60a and the second bush 60b may have different shapes.

  In the above-described embodiment, the resin bush 60 based on the annular shape has been exemplified. However, the outer shape of the resin bush may be based on another shape. Other shapes include, for example, polygonal shapes. Regardless of the shape, in the resin bush (for example, the first bush 60a) that rotatably supports the shaft 50, it is necessary to form the inner peripheral surface along a circle.

  In the above-described embodiment, the case where the housing 20 is made of resin is illustrated. However, the housing may be made of metal.

  In the above-described embodiment, the case where the resin bush 60 is chamfered and has the inclined surface 63 has been exemplified. However, the resin bush need not be chamfered.

  In addition, the present invention is realized by arbitrarily combining the components and functions of the embodiments and the modifications without departing from the spirit of the present invention, and the embodiments obtained by performing various modifications conceivable by those skilled in the art to the embodiments. Embodiments are also included in the present invention.

  INDUSTRIAL APPLICABILITY The present invention is applicable to a reduction gear used for an electric tilt / telescopic adjustment steering column.

10, 10D: Steering device, 20: Housing, 21: First part, 22: Second part, 30: Worm wheel, 31: Rotating shaft, 35: Bearing, 40: Worm (gear), 50: Shaft, 51 ... Shaft, 52 ... Flange part, 53 ... Large diameter part, 54 ... Small diameter part, 60 ... Resin bush, 60a ... First bush, 60b, 60c ... Second bush, 61 ... Slit, 62 ... Recess, 63, 64 ... Inclined surface, 70, 70c bush holding portion, 71, 71c first end surface, 72 second end surface, 73 inner peripheral surface, 74 projection, 75 space, 80 insertion portion, 81 through hole, 82 ... inner peripheral surface, 90 ... urging part, 91 ... spring, 92 ... sliding plate, 211, 221 ... accommodation space, 601 ... first surface, 602 ... second surface, 603 ... outer peripheral surface, 604 ... inner peripheral surface , L1 ... Parting line

Claims (7)

A shaft having gears;
A resin bush that rotatably supports the shaft,
A housing in which the shaft and the resin bush are housed,
The housing is
A bush holding portion having a cylindrical space for fitting the resin bush attached to the shaft,
One end is open, and from the one end to the bush holding portion, an insertion portion having a through hole into which the shaft and the resin bush are inserted,
The outer diameter of the gear is smaller than the inner diameter of the through hole, and the inner diameter of the bush holding portion is larger than the inner diameter of the through hole,
The resin bush has a slit that is partially open in the circumferential direction. The resin bush includes a first bush and a second bush,
The shaft is
A flange portion provided on the one end side of the gear and having an outer diameter larger than an inner diameter of each of the first bush and the second bush,
A large-diameter portion provided on the other end side than the flange portion, a large-diameter portion having an outer diameter substantially matching the inner diameter of the first bush,
A small-diameter portion provided on the one end side relative to the flange portion, and a small-diameter portion having an outer diameter smaller than an inner diameter of the second bush,
The reduction gear according to claim 1, wherein the first bush is arranged at a position corresponding to the large diameter portion, and the second bush is arranged at a position corresponding to the small diameter portion. The bush holding portion,
A first end face abutting against the first bush from the other end side,
A second end surface that comes into contact with the second bush from the one end side,
The speed reducer according to claim 2, wherein at least one of the first end surface and the second end surface is a tapered surface. The reduction gear according to any one of claims 1 to 3, wherein the housing is formed of a resin. The resin bush is provided with a concave portion on an outer peripheral surface at a position facing the slit,
The reduction gear according to claim 4, wherein a parting line of the housing is arranged at a position corresponding to the slit and the recess. The speed reducer according to any one of claims 1 to 5, wherein the resin bush has a thin portion that is thinner than other portions. The reduction gear according to any one of claims 1 to 6, wherein an inner peripheral surface forming the through hole in the insertion portion is a tapered surface tapering toward the other end.

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