JP2017057870A - Speed reducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speed reducer capable of preventing the looseness of a screw member fixing a bearing without increasing a number of components.SOLUTION: A speed reducer is equipped with a worm shaft to which drive force from a drive source is inputted; a worm wheel engaged with a worm on a worm shaft outer periphery; an output shaft integrally rotated with the worm wheel; a bearing rotatably supporting the worm shaft; a case which stores the worm shaft, the worm wheel, and the bearing; and a plug which has a male screw portion screwed with a female screw portion formed on the case, on an outer peripheral surface, and presses the bearing on the case to fix that. The male screw portion and the female screw portion are formed by screws partially different from each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reduction gear.

  Patent Document 1 describes a reduction gear used for an electric power steering apparatus. The reduction gear described in Patent Literature 1 includes a worm shaft connected to the output shaft of the electric motor, a rolling bearing that rotatably supports the worm shaft, and a worm wheel that meshes with the worm shaft.

  In the reduction gear described in Patent Document 1, a rolling bearing on the electric motor side is attached to the housing by a screw member.

JP 2002-211141 A

  In the speed reducer described in Patent Document 1, if the screw member that fixes the rolling bearing is loosened, the worm shaft vibrates together with the rolling bearing, which may cause noise and wear. For this reason, it is conceivable to use a lock nut to prevent the screw member from loosening. However, if the lock nut is used, the number of parts increases.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a reduction gear that can prevent the screw member that fixes the bearing from being loosened without increasing the number of parts.

  1st invention is a reduction gear, Comprising: The worm shaft into which the driving force from a drive source is input, The worm wheel which meshes with the worm of outer periphery of a worm shaft, The output shaft which rotates integrally with a worm wheel, A worm shaft A bearing that rotatably supports the worm shaft, a worm wheel, a case that accommodates the worm wheel, and a bearing, and a male screw portion that engages with a female screw portion formed in the case on the outer peripheral surface, and the bearing is pressed against the case and fixed The male screw portion and the female screw portion are formed by screws that are partially different from each other.

  In the first invention, since the male screw portion and the female screw portion are partially formed by different screws, the male screw portion is forcibly screwed into the female screw portion, whereby the screw thread of the male screw portion and the screw groove of the female screw portion are formed. The contact surface pressure increases. Thereby, since the frictional resistance between the external thread part and the internal thread part becomes large, it can prevent that a plug loosens.

  The second invention is characterized in that the male screw portion or the female screw portion has a plurality of screw regions having different pitches.

  In the second aspect of the present invention, the plug can be prevented from loosening only by forming a plurality of screw regions having different pitches.

  According to a third aspect of the invention, the plug has a small diameter portion and a large diameter portion, and the male screw portion is a first male screw portion formed on the outer peripheral surface of the small diameter portion, and a second screw formed on the outer peripheral surface of the large diameter portion. An internal thread portion, and the internal thread portion includes a first internal thread portion that is screwed with the first external thread portion, and a second internal thread portion that is engaged with the second external thread portion, and the first external thread portion and the first external thread portion A screw having the same pitch and effective diameter is formed in one female screw portion, and screws having different pitches or effective diameters are formed in the second male screw portion and the second female screw portion.

  According to a fourth aspect of the invention, the plug has a small diameter portion and a large diameter portion, and the male screw portion is a first male screw portion formed on the outer peripheral surface of the small diameter portion, and a second screw formed on the outer peripheral surface of the large diameter portion. An internal thread portion, and the internal thread portion includes a first internal thread portion that is screwed with the first external thread portion, and a second internal thread portion that is engaged with the second external thread portion, and the first external thread portion and the first external thread portion A screw having the same pitch and effective diameter is formed in one female screw portion, and the pitch and effective diameter are the same in the second male screw portion and the second female screw portion, and the first male screw portion and the first female screw are provided. The screw is formed such that the pitch is shifted from each other in a state where the portion is screwed.

  In the third and fourth inventions, the first male screw portion, the first female screw portion, the second male screw portion, and the second female screw portion need only be formed with one type of screw, so that the screws can be easily formed. Can do.

  ADVANTAGE OF THE INVENTION According to this invention, the reduction gear which enabled the locking prevention of the screw member which fixes a bearing, without increasing a number of parts can be provided.

FIG. 1 is a cross-sectional view of a speed reducer according to an embodiment of the present invention. FIG. 2 is an enlarged view of a portion A in FIG. FIG. 3 is a partially enlarged view of the reduction gear according to the second embodiment of the present invention. FIG. 4 is a diagram showing a deviation of the screw pitch of the plug in the reduction gear according to the third embodiment of the present invention. FIG. 5 is a partially enlarged view showing a screwed state of the plug in the reduction gear according to the third embodiment of the present invention.

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

<First Embodiment>
A reduction gear 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  The reduction gear 100 is used for an electric power steering device, for example. An electric power steering device is a device that is mounted on a vehicle and assists a steering force when a driver operates a steering wheel. Specifically, the electric power steering apparatus decelerates the driving force of the electric motor 60 by the speed reducer 100 and applies it to the output shaft 21 of the steering shaft as rotational torque that assists the steering of the steering wheel by the driver.

  As shown in FIG. 1, the speed reducer 100 rotates integrally with a worm shaft 10 to which a driving force from an electric motor 60 as a driving source is input, a worm wheel 20 that meshes with the worm shaft 10, and the worm wheel 20. Output shaft 21, bearings 31 and 32 that rotatably support worm shaft 10, and worm shaft 10, worm wheel 20, and case 40 that accommodates bearings 31 and 32. The case 40 is formed of a metal material such as aluminum.

  On the outer periphery of the worm shaft 10, a tooth portion (worm) 11 that meshes with the tooth portion 22 of the worm wheel 20 is formed. The worm shaft 10 is connected to a rotating shaft (not shown) of the electric motor 60 by a connecting member (not shown).

  The case 40 is formed with a receiving hole 41 having a bottom 44 and receiving the worm shaft 10. An accommodation recess 42 having an inner diameter larger than that of the accommodation hole 41 is formed in the opening located on the electric motor 60 side of the accommodation hole 41.

  The bearings 31 and 32 are ball bearings each including inner rings 31a and 32a, outer rings 31b and 32b, and balls 31c and 32c supported by a cage and accommodated between the inner rings 31a and 32a and the outer rings 31b and 31b. It is.

  The worm shaft 10 is in contact with the inner ring 31a of the bearing 31 and has a locking portion 10C having an outer diameter larger than the inner diameter of the inner ring 31a. The worm shaft 10 is in contact with the inner ring 32a of the bearing 32 and has an outer diameter larger than the inner diameter of the inner ring 32a. A locking portion 10D is provided.

  Both end portions 10A and 10B of the worm shaft 10 are rotatably supported by a bearing 31 fixed to the receiving recess 42 formed in the receiving hole 41 and a bearing 32 fixed to the bottom 44 of the receiving hole 41, respectively. The

  The bearing 31 is fixed so that the outer ring 31 b is pressed against the stepped portion 43 serving as the bottom of the housing recess 42 by screwing the annular plug 50 into the female screw portion 45 formed in the housing recess 42. The bearing 32 is fixed by being press-fitted so that the outer ring 32 b comes into contact with the bottom 44 of the accommodation hole 41.

  An annular joint 70 is press-fitted into the end portion 10 </ b> A of the worm shaft 10 so as to sandwich the inner ring 31 a of the bearing 31 with the locking portion 10 </ b> C. Since the bearing 31 is fixed to the case 40 by the plug 50 as described above, the worm shaft 10 is restricted from moving in the axial direction by the bearing 31.

  Operation | movement of the reduction gear 100 comprised in this way is demonstrated.

  When the electric motor 60 is driven, the worm shaft 10 is rotated accordingly. With the rotation of the worm shaft 10, the worm wheel 20 is decelerated and rotated by a reduction ratio according to the number of teeth 11 of the worm shaft 10 and the number of teeth 22 of the worm wheel 20. Thereby, the driving force of the electric motor 60 is transmitted to the output shaft 21.

  Next, the loosening prevention of the plug 50 will be described with reference to FIG. FIG. 2 is an enlarged view of a portion A in FIG. 1, and is an enlarged view of a screw portion when the plug 50 is screwed.

  A male thread portion 51 is formed on the outer peripheral surface of the plug 50. The male screw portion 51 is a first male screw portion 51A that is a first screw region in which a screw having a pitch a is formed, and a second screw region in which screws having a pitch b that is larger than the pitch a are formed. A second male threaded portion 51B. The first male screw portion 51A and the second male screw portion 51B are successively formed in order from the bearing 31 side. The plug 50 is formed of a metal material such as iron. The second male screw portion 51B has about 2 to 4 threads.

  A female screw portion 45 having a screw having the same screw pitch (pitch a) and effective diameter as the first male screw portion 51A is formed on the inner peripheral surface of the housing recess 42 of the case 40.

  When the plug 50 is screwed into the female screw portion 45 formed in the receiving recess 42 in a state where the bearing 31 is received in the receiving recess 42, the first male screw portion 51A of the plug 50 and the female screw portion 45 of the receiving recess 42 are screwed. The plug 50 enters the housing recess 42 while being combined. When the tip of the plug 50 enters the position just before the tip of the plug 50 contacts the bearing 31 (position before the thread 1 or 2), the second male thread 51B and the female thread 45 of the plug 50 start to be screwed together.

  Since the screw pitches of the second male screw portion 51B and the female screw portion 45 are different from each other, the second male screw portion 51B cannot be screwed into the female screw portion 45 with normal torque. Therefore, a large torque is applied to the plug 50 from this state, and the second male screw portion 51B is forcibly screwed into the female screw portion 45. In this way, when the second male screw portion 51B is forcibly screwed into the female screw portion 45, the surface pressure of the contact surface between the screw thread of the second male screw portion 51B and the screw groove of the female screw portion 45 increases. Thereby, the frictional resistance between the external thread part 51 and the internal thread part 45 becomes large. Therefore, even when a force that rotates in the direction in which the screw is loosened due to vibration or the like acts on the plug 50, the state in which the plug 50 is fastened to the female screw portion 45 is maintained. Therefore, the plug 50 can be prevented from loosening.

  When the second male screw portion 51B is forcibly screwed into the female screw portion 45, the second male screw portion 51B or the female screw portion 45 may be deformed. Further, the screw pitch (pitch b) of the second male screw portion 51B may be smaller than the screw pitch (pitch a) of the first male screw portion 51A.

  In the reducer 100, a plurality of screw regions (first male screw portion 51A and second male screw portion 51B) having different screw pitches are formed in the male screw portion 51. Instead, a plurality of screw regions having different screw pitches may be formed in the female screw portion 45. In the reduction gear 100, the screw pitch of the first male screw portion 51A and the second male screw portion 51B is different from each other. Instead, the first male screw portion 51A, the second male screw portion 51B, and the female screw portion 45 have the same screw pitch, and the effective diameter of the screw of the second male screw portion 51B is larger than the effective diameter of the screw of the female screw portion 45. By doing so, the screw of the first male screw portion 51A and the screw of the second male screw portion 51B may be different.

  According to the above 1st Embodiment, there exist the following effects.

  In the speed reducer 100, the second male screw portion 51B and the female screw portion 45 of the plug 50 are formed with mutually different screw pitches. For this reason, by forcibly screwing the second male screw portion 51B into the female screw portion 45, the surface pressure of the contact surface between the screw thread of the second male screw portion 51B and the screw groove of the female screw portion 45 increases. Thereby, since the frictional resistance between the external thread part 51 and the internal thread part 45 becomes large, it can prevent that the plug 50 loosens. Further, since no lock nut or the like is used, the plug 50 can be prevented from loosening without increasing the number of parts. Further, in the reduction gear 100, since the loosening prevention can be performed only by screwing the plug 50, the manufacturing process can be simplified as compared with the loosening prevention using caulking, adhesive, or the like.

Second Embodiment
Next, a reduction gear 200 according to a second embodiment of the present invention will be described with reference to FIG. Below, it demonstrates centering on a different point from the said 1st Embodiment, the same code | symbol is attached | subjected to the structure same as the reduction gear 100 of the said 1st Embodiment, and description is abbreviate | omitted.

  The reducer 100 according to the first embodiment is an annular member in which the plug 50 is configured with a single diameter, whereas the reducer 200 according to the second embodiment has a plug 150 having a small diameter portion 150A and a large diameter. It is different in that it is an annular member provided with the portion 150B.

  As shown in FIG. 3, the plug 150 includes a small diameter portion 150A and a large diameter portion 150B located on the opposite side of the bearing 31 with respect to the small diameter portion 150A and having a larger diameter than the small diameter portion 150A.

  A male screw portion 151 is formed on the outer periphery of the plug 150. The male screw portion 151 includes a first male screw portion 151A having a pitch a screw formed on the outer peripheral surface of the small diameter portion 150A, and a second male screw portion 151B having a pitch b screw formed on the outer peripheral surface of the large diameter portion 150B. Have

  A female screw portion 145 is formed in the housing recess 42 of the case 40. The female screw portion 145 includes a first female screw portion 145A that is screwed with the first male screw portion 151A, and a second female screw portion 145B that is screwed with the second male screw portion 151B. A screw having the same screw pitch (pitch a) and effective diameter as the first male screw portion 151A is formed in the first female screw portion 145A. The second female screw portion 145B is formed with a screw having the same pitch (pitch a) as the first male screw portion 151A and the first female screw portion 145A. As described above, since the screw having the pitch b is formed in the second male screw portion 151B, the second female screw portion 145B and the second male screw portion 151B have different screw pitches.

  In the speed reducer 200 configured as described above, when the plug 150 is screwed into the female screw portion 145 formed in the housing recess 42 with the bearing 31 in contact with the stepped portion 43, the first male screw portion of the plug 150 is obtained. The plug 150 enters the housing recess 42 while 151A and the first female thread portion 145A of the housing recess 42 are screwed together. When the tip of the plug 150 enters a position just before the tip of the plug 150 contacts the bearing 31 (a position before the thread 1 or 2), the second male thread 151B and the second female thread 145B of the plug 150 start to be screwed together. .

  Since the screw pitches of the second male screw portion 151B and the second female screw portion 145B are different from each other, the second male screw portion 151B cannot be screwed into the second female screw portion 145B with a normal torque. Therefore, a large torque is applied to the plug 150 from this state, and the second male screw portion 151B is forcibly screwed into the second female screw portion 145B. When the second male screw portion 151B is forcibly screwed into the female screw portion 45 in this way, the surface pressure of the contact surface between the screw thread of the second male screw portion 151B and the screw groove of the second female screw portion 145B increases. Thereby, the frictional resistance between the external thread part 151 and the internal thread part 145 becomes large. Therefore, even when a force that rotates in the direction in which the screw is loosened due to vibration or the like acts on the plug 150, the state in which the plug 150 is fastened to the female screw portion 145 is maintained. Therefore, the plug 150 can be prevented from loosening.

  When the second male screw portion 51B is forcibly screwed into the female screw portion 45, the second male screw portion 51B or the female screw portion 45 may be deformed.

  In the speed reducer 200, the second male screw portion 151B is formed with a screw pitch different from that of the other screw portions. Instead of this, only the second female screw portion 145B may be formed with a screw pitch different from that of the other screw portions. Moreover, in the reduction gear 200, the screw pitch of the 2nd internal thread part 145B and the 2nd external thread part 151B is formed so that it may mutually differ. Instead, the second female screw portion 145B and the second male screw portion 151B have the same screw pitch, and the effective diameter of the second male screw portion 151B is larger than the effective diameter of the second female screw portion 145B. Thus, the screw of the second male screw portion 151B and the screw of the second female screw portion 145B may be different.

  According to the second embodiment described above, the following effects are obtained in addition to the effects of the first embodiment.

  The first male screw portion 151A and the second male screw portion 151B having different screw pitches are separately formed in the small diameter portion 150A and the large diameter portion 150B, respectively. Therefore, since it is only necessary to process one type of screw at each location, the male thread portion 151 of the plug 150 can be easily formed.

<Third Embodiment>
Next, a reduction gear 300 according to a third embodiment of the present invention will be described with reference to FIGS. 4 and 5. Below, it demonstrates centering on a different point from the said 2nd Embodiment, the same code | symbol is attached | subjected to the structure same as the reduction gear 200 of the said 2nd Embodiment, and description is abbreviate | omitted.

  The speed reducer 200 according to the second embodiment is different from the first embodiment in that the first and second male screw portions 151A and 151B having different screw pitches are formed in the small diameter portion 150A and the large diameter portion 150B of the plug 150. The speed reducer 300 in the embodiment is different in that first and second male screw portions 251A and 251B having the same screw pitch are formed in the small diameter portion 250A and the large diameter portion 250B of the plug 250.

  As shown in FIGS. 4 and 5, the plug 250 includes a small diameter portion 250A and a large diameter portion 250B located on the opposite side of the bearing 32 with respect to the small diameter portion 250A and having a larger diameter than the small diameter portion.

  A male screw portion 251 is formed on the outer periphery of the plug 250. The male screw portion 251 includes a first male screw portion 251A in which a screw having a pitch a is formed on the outer peripheral surface of the small diameter portion 250A, a second male screw portion 251B in which a screw having a pitch a is formed on the outer peripheral surface of the large diameter portion 250B, Have

  The first male screw portion 251A is screwed with the first female screw portion 145A, and the second male screw portion 251B is screwed with the second female screw portion 145B.

  A screw having the same screw pitch (pitch a) and effective diameter as the first female screw portion 145A is formed in the first male screw portion 251A. A screw having the same screw pitch (pitch a) and effective diameter as the second female screw portion 145B is formed in the second male screw portion 251B. The screw of the second male screw portion 251B is such that the phase of the screw pitch is shifted by the distance c with respect to the second female screw portion 145B in a state where the first male screw portion 251A and the first female screw portion 145A are screwed together. Formed (see FIG. 4).

  Next, the loosening prevention of the plug 250 will be described.

  When the plug 250 is screwed into the female screw portion 145 formed in the housing recess 42, the first male screw portion 251A of the plug 250 and the first female screw portion 145A of the housing recess 42 are screwed together, and the plug 250 is accommodated in the housing recess 42. Enter inside. When the tip of the plug 250 enters a position just before the tip of the plug 250 comes into contact with the bearing 31 (a position before the thread 1 or 2), the second male thread 251B and the second female thread 145B of the plug 250 start to be screwed together. (See FIG. 4).

  The second male screw portion 251B and the second female screw portion 145B are formed such that the phase of the screw pitch is shifted by a distance c in a state where the first male screw portion 251A and the first female screw portion 145A are screwed together. With normal torque, the second male screw portion 251B cannot be screwed into the second female screw portion 145B. Therefore, from this state, by applying a large torque to the plug 250, the second male screw portion 251B is forcibly screwed into the second female screw portion 145B. In this way, when the second male screw portion 251B is forcibly screwed into the second female screw portion 145B, the screw pitch is shifted by the distance c. Therefore, the surface of the first male screw portion 251A on the electric motor 60 side. Is pressed against the surface of the screw groove of the first female screw portion 145A on the electric motor 60 side, and the surface of the second male screw portion 251B on the bearing 31 side of the thread is the surface on the bearing 31 side of the screw groove of the second female screw portion 145B (See FIG. 5). That is, the surface pressure of the contact surface between the thread of the first male screw portion 251A and the screw groove of the first female screw portion 145A, and the surface pressure of the contact surface of the screw thread of the second male screw portion 251B and the screw groove of the second female screw portion 145B. Becomes higher. Thereby, the frictional resistance between the external thread part 251 and the internal thread part 145 becomes large. Therefore, even when a force that rotates in a loosening direction due to vibration or the like acts on the plug 250, the state where the plug 250 is fastened to the female screw portion 145 is maintained. Therefore, the plug 250 can be prevented from loosening.

  As described above, the second male screw portion 251B and the second female screw portion 145B are formed such that the phase of the screw pitch is shifted by the distance c when the first male screw portion 251A and the first female screw portion 145A are screwed together. Has been. Thereby, in the speed reducer 300, the first male screw portion 251A and the second male screw portion 251B function as different screws.

  According to the above 3rd Embodiment, in addition to the effect of the said 1st Embodiment, there exist the following effects.

  The first male screw portion 251A and the second male screw portion 251B are separately formed in the small diameter portion 250A and the large diameter portion 250B, respectively. Therefore, since it is only necessary to process one type of screw at each location, the male thread portion 251 of the plug 250 can be easily formed.

  The configuration, operation, and effect of the embodiment of the present invention configured as described above will be described together.

  The reduction gears 100, 200, and 300 include a worm shaft 10 to which a driving force from a driving source (electric motor 60) is input, a worm wheel 20 that meshes with a tooth portion (worm) 11 on the outer periphery of the worm shaft 10, and a worm An output shaft 21 that rotates integrally with the wheel 20, bearings 31 and 32 that rotatably support the worm shaft 10, a case 40 that houses the worm shaft 10, the worm wheel 20, and the bearings 31 and 32, Male threads 51, 151, 251 that are screwed into the formed female threads 45, 145 on the outer peripheral surface, and plugs 50, 150, 250 that press and fix the bearing 31 against the case, the male threads 51, 151 and 251 and the female screw portions 45 and 145 are characterized in that a part thereof is formed by different screws.

  In this configuration, since the male screw portions 51, 151, 251 and the female screw portions 45, 145 are partially formed with different screws, the male screw portions 51, 151, 251 are forcibly screwed into the female screw portions 45, 145. The surface pressure of the contact surface between the screw threads of the male screw parts 51, 151 and 251 and the screw grooves of the female screw parts 45 and 145 increases. Thereby, since the frictional resistance between the male screw portions 51, 151, 251 and the female screw portions 45, 145 is increased, it is possible to prevent the plugs 50, 150, 250 from being loosened.

  The reduction gears 100 and 200 are characterized in that the male screw portions 51 and 151 or the female screw portions 45 and 145 have a plurality of screw regions having different pitches.

  In this configuration, the plugs 50 and 150 can be prevented from loosening only by forming a plurality of screw regions having different pitches.

  In the speed reducer 200, the plug 150 has a small diameter portion 150A and a large diameter portion 150B, and the male screw portion 151 includes a first male screw portion 151A formed on the outer peripheral surface of the small diameter portion 150A and an outer peripheral surface of the large diameter portion 150B. A second male screw portion 151B, and a female screw portion 145 includes a first female screw portion 145A screwed with the first male screw portion 151A and a second female screw portion 145B screwed with the second male screw portion 151B. The first male screw portion 151A and the first female screw portion 145A are formed with screws having the same pitch and effective diameter, and the second male screw portion 151B and the second female screw portion 145B are pitch or effective. Screws having different diameters are formed.

  In the speed reducer 300, the plug 250 has a small diameter portion 250A and a large diameter portion 250B, and the male screw portion 251 includes a first male screw portion 251A formed on the outer peripheral surface of the small diameter portion 250A and an outer peripheral surface of the large diameter portion 250B. The second male screw portion 251B, and the female screw portion 145 includes a first female screw portion 145A screwed with the first male screw portion 251A and a second female screw portion 145B screwed with the second male screw portion 251B. The first male screw portion 251A and the first female screw portion 145A are formed with screws having the same pitch and effective diameter, and the second male screw portion 251B and the second female screw portion 145B are pitch and effective. The screws are formed such that the diameters are the same and the pitches are shifted from each other in a state where the first male screw portion 251A and the first female screw portion 145A are screwed together.

  In these configurations, the first male threaded portions 151A and 251A, the first female threaded portion 145A, the second male threaded portions 151B and 251B, and the second female threaded portion 145B only need to be formed with one type of screw. It can be easily formed.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  In each of the above-described embodiments, a so-called 1-pinion type electric power steering device that applies the driving force of the electric motor 60 to the steering shaft has been described as an example. The present invention can also be applied to a two-pinion type electric power steering device provided with a shaft having an assist pinion that transmits the rotation of the electric motor 60 and a reduction gear used in a steer-by-wire type electric power steering device.

100, 200, 300 ... reducer, 10 ... worm shaft, 20 ... worm wheel, 21 ... output shaft, 31, 32 ... bearing, 40 ... case, 41 ... Accommodating hole, 42 ... accommodating recess, 43 ... stepped portion, 45,145 ... female screw portion, 50, 150,250 ... plug, 51, 151,251 ... male screw portion, 51A, 151A , 251A ... first male screw part, 51B, 151B, 251B ... second male screw part, 60 ... electric motor (drive source), 150A, 250A ... small diameter part, 150B, 250B ... large Diameter

Claims (4)

A worm shaft to which a driving force from a driving source is input;
A worm wheel meshing with a worm on the outer periphery of the worm shaft;
An output shaft that rotates integrally with the worm wheel;
A bearing that rotatably supports the worm shaft;
A case housing the worm shaft, the worm wheel, and the bearing;
A male screw part that is screwed into a female screw part formed in the case on the outer peripheral surface, and a plug that presses and fixes the bearing to the case, and
The male screw portion and the female screw portion are partly formed by different screws.   The reduction gear according to claim 1, wherein the male screw portion or the female screw portion has a plurality of screw regions having different pitches. The plug has a small diameter portion and a large diameter portion,
The male screw portion has a first male screw portion formed on the outer peripheral surface of the small diameter portion, and a second male screw portion formed on the outer peripheral surface of the large diameter portion,
The female screw part has a first female screw part that is screwed with the first male screw part, and a second female screw part that is screwed with the second male screw part,
The first male screw portion and the first female screw portion are formed with screws having the same pitch and effective diameter,
The reduction gear according to claim 1, wherein the second male screw portion and the second female screw portion are formed with screws having different pitches or effective diameters. The plug has a small diameter portion and a large diameter portion,
The male screw portion has a first male screw portion formed on the outer peripheral surface of the small diameter portion, and a second male screw portion formed on the outer peripheral surface of the large diameter portion,
The female screw part has a first female screw part that is screwed with the first male screw part, and a second female screw part that is screwed with the second male screw part,
The first male screw portion and the first female screw portion are formed with screws having the same pitch and effective diameter,
The second male screw portion and the second female screw portion have a pitch and an effective diameter that are the same as each other, and the pitch is shifted from each other in a state where the first male screw portion and the first female screw portion are screwed together. The speed reducer according to claim 1, wherein:

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