JP2020091017A - Power transmission device and electric power steering device including the same - Google Patents

Abstract

To improve performance measuring accuracy of an electric motor used in a power transmission device.SOLUTION: A power transmission device 60 includes: an electric motor 50 having a rotary shaft 51 serving as an output shaft; a worm gear 43 provided at the rotary shaft 51; a worm wheel 44 which engages with the worm gear 43; and a housing 45 which houses the worm gear 43 and the worm wheel 44. The housing 45 has a second housing hole 47 in which the worm wheel 44 is housed. An inner peripheral surface 47a of the second housing hole 47 is provided with a recessed part 47b recessed to the radial outer side.SELECTED DRAWING: Figure 3

Description

The present invention relates to a power transmission device and an electric power steering device including the power transmission device.

Patent Document 1 discloses a power transmission device that transmits the power of an electric motor via a worm mechanism. A worm gear is formed on the rotary shaft of the electric motor of the power transmission device.

JP, 2003-113909, A

In the power transmission device described in Patent Document 1, since the worm gear supported by the housing is formed on the rotating shaft of the electric motor, the performance of the electric motor is confirmed in the state of being assembled in the housing. However, since the worm wheel is also attached to the housing, the performance of the electric motor is confirmed when the worm gear and the worm wheel are in mesh with each other. When various performances such as cogging torque and torque ripple of the electric motor are measured in such a state, it is clear whether the measurement result is caused by the electric motor or whether the worm gear and the worm wheel are affected by the meshing condition. Not. Therefore, it is difficult to accurately determine whether or not the electric motor satisfies a predetermined performance.

In order to accurately measure the performance of the electric motor when assembled in the housing, it may be possible to assemble the worm wheel in the housing after confirming the performance of the electric motor. However, since the worm gear formed on the rotary shaft of the electric motor is a spiral gear, it is difficult to assemble the worm wheel into the housing after the worm gear is assembled.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the performance measurement accuracy of an electric motor used in a power transmission device.

According to the present invention, a power transmission device includes an electric motor having an output shaft, a worm gear provided on the output shaft, a worm wheel that meshes with the worm gear, and a housing that houses the worm gear and the worm wheel, and the housing is the worm wheel. Is accommodated, and a concave portion that is recessed radially outward is provided on the inner peripheral surface of the accommodation hole.

In the present invention, the recessed portion that is recessed radially outward is provided on the inner peripheral surface of the accommodation hole that accommodates the worm wheel. Therefore, by inserting the worm wheel into the housing while inserting a part of the worm wheel into the recess, it is possible to assemble the worm wheel into the housing even after the rotary shaft having the worm gear is formed in the housing. It is possible. Therefore, the performance of the electric motor can be measured without the worm wheel being attached to the housing.

The present invention is characterized in that the concave portion has a depth toward the outside in the radial direction of at least the amount of meshing between the worm gear and the worm wheel.

In the present invention, the depth of the recess from the inner peripheral surface of the accommodation hole is set to be larger than the amount of meshing between the worm gear and the worm wheel. That is, it is possible to release the meshing between the worm gear and the worm wheel by shifting the worm wheel toward the recess side. By providing such a recess on the inner peripheral surface of the accommodation hole, the worm wheel can be assembled to the housing even after the rotary shaft having the worm gear is assembled to the housing.

The present invention is characterized in that the concave portion is provided only on the side far from the worm gear when the inner peripheral surface of the accommodation hole is divided into a side close to the worm gear and a side far from the worm gear.

In the present invention, the recess is provided only on the side far from the worm gear when the inner peripheral surface of the accommodation hole is divided into the side close to the worm gear and the side far from the worm gear. That is, the concave portion is provided not on the entire circumference of the inner peripheral surface of the accommodation hole but only on a part of the inner peripheral surface. Therefore, as compared with the case where the recess is provided on the entire circumference of the inner peripheral surface, the processing cost of the recess is reduced, so that the manufacturing cost of the power transmission device can be reduced. Further, as compared with the case where the recess is provided on the entire circumference of the inner peripheral surface, the portion where the thickness of the housing is thin is reduced, so that the strength of the housing can be secured even when the recess is provided.

The present invention is characterized in that the inner peripheral surface of the accommodation hole is provided with a guide surface that is inclined from the opening end side of the accommodation hole toward the recess.

In the present invention, the guide surface that is inclined from the opening end side of the accommodation hole toward the recess is provided on the inner peripheral surface of the accommodation hole. When the worm wheel is assembled into the housing, it is possible to easily guide a part of the worm wheel into the recess by moving the worm wheel along the guide surface. Therefore, by providing the guide surface, the assemblability of the power transmission device can be improved.

According to the present invention, in an electric power steering apparatus including the power transmission device having the above-described configuration, a worm wheel is provided on a steering shaft that rotates by receiving a steering torque from a steering handle, and an electric motor is provided via a worm gear. A rotational torque that assists the steering torque is applied to the steering shaft by rotationally driving.

In the present invention, the power transmission device having the above configuration is used in the electric power steering device. As described above, by adopting the power transmission device including the electric motor that is confirmed to satisfy the predetermined performance, it is possible to stabilize the operation of the electric power steering device.

According to the present invention, it is possible to improve the performance measurement accuracy of the electric motor used in the power transmission device.

FIG. 1 is a configuration diagram of an electric power steering device in which a power transmission device according to an embodiment of the present invention is used. 2 is a sectional view of the power transmission device taken along the line II-II of FIG. 3 is a cross-sectional view of the power transmission device taken along the line III-III in FIG. FIG. 4 is a view for explaining the assembling procedure of the power transmission device, and is a cross-sectional view showing the same cross section as FIG. 2. FIG. 5A is a view for explaining the assembling procedure of the power transmission device, and is a cross-sectional view showing the same cross section as FIG. 3. FIG. 5B is a view for explaining the assembling procedure of the power transmission device, and is a cross-sectional view showing the same cross section as FIG. 3. FIG. 5C is a view for explaining the assembling procedure of the power transmission device, and is a cross-sectional view showing the same cross section as FIG. 3. FIG. 5D is a diagram for explaining the assembling procedure of the power transmission device, and is a cross-sectional view showing the same cross section as FIG. 3. FIG. 6 is a view for explaining the assembling procedure of the power transmission device, and is a cross-sectional view showing the same cross section as FIG. 2.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

With reference to FIG. 1, a power transmission device 60 according to an embodiment of the present invention and an electric power steering device 100 using the power transmission device 60 will be described. FIG. 1 is a configuration diagram of an electric power steering device 100 in which a power transmission device 60 is used.

The electric power steering device 100 is a device that is installed in a vehicle and assists a steering force with respect to a steering device that steers wheels 1 by converting a steering torque applied to a steering wheel 10 as a steering wheel by a driver. ..

As shown in FIG. 1, the electric power steering apparatus 100 includes a steering shaft 20 that rotates by a steering torque input from a steering wheel 10, a rack shaft 30 that steers the wheels 1 as the steering shaft 20 rotates, The power transmission device 60 applies a rotational torque to the steering shaft 20 to assist the steering torque.

The steering shaft 20 includes an input shaft 21 that rotates with a steering operation performed by a driver who operates the steering wheel 10, an output shaft 22 that displaces the rack shaft 30, and a torsion bar that connects the input shaft 21 and the output shaft 22. 23 and.

The rack shaft 30 is connected to the wheel 1 via a tie rod 31 and a knuckle arm 32, and the wheel 1 is steered by the displacement of the rack shaft 30.

The output shaft 22 and the rack shaft 30 are connected to each other via a transmission unit 41. The transmission unit 41 is a rack and pinion mechanism including a pinion gear 41a provided on the end of the output shaft 22 and a rack gear 41b provided on the rack shaft 30. The pinion gear 41a and the rack gear 41b mesh with each other, and the torque of the output shaft 22 is converted into an axial load of the rack shaft 30 and transmitted to the rack shaft 30 via the pinion gear 41a and the rack gear 41b. As a result, the rack shaft 30 is displaced in the axial direction by the transmitted torque and steers the wheel 1.

The power transmission device 60 includes an electric motor 50 that is a brushless motor, and a reduction unit 42 that reduces the rotation of the electric motor 50 and transmits the rotation to the steering shaft 20. The specific configuration of the power transmission device 60 will be described later.

The reduction unit 42 is a worm gear mechanism including a worm gear 43 as a drive gear provided on a rotating shaft 51, which will be described later, as an output shaft of the electric motor 50, and a worm wheel 44 as a driven gear provided on the output shaft 22. .. The worm gear 43 and the worm wheel 44 mesh with each other, and the torque of the electric motor 50 is transmitted to the output shaft 22 via the worm gear 43 and the worm wheel 44. The torque transmitted from the electric motor 50 to the output shaft 22 is further transmitted to the rack shaft 30 via the pinion gear 41a and the rack gear 41b.

The electric power steering apparatus 100 further includes a torque sensor 72 that detects a torque acting on the torsion bar 23, and a controller 70 that controls driving of the electric motor 50 according to a detection value of the torque sensor 72.

The controller 70 includes a CPU (Central Processing Unit) that performs arithmetic processing, a ROM (Read-Only Memory) that stores a control program executed by the CPU, and a RAM (random access memory) that stores the arithmetic result of the CPU. And a microcomputer including. The controller 70 may be composed of a single microcomputer or may be composed of a plurality of microcomputers.

The torque sensor 72 detects the steering torque applied to the input shaft 21 in accordance with the steering operation by the driver, and outputs a voltage signal corresponding to the detected steering torque to the controller 70. The controller 70 calculates the torque output by the electric motor 50 based on the voltage signal from the torque sensor 72, and controls the drive of the electric motor 50 so that the torque is generated.

As described above, the electric power steering apparatus 100 detects the steering torque applied to the input shaft 21 by the torque sensor 72, and controls the drive of the electric motor 50 by the controller 70 based on the detection result, thereby controlling the driver. Assist steering operation.

Next, a specific configuration of the power transmission device 60 will be described with reference to FIGS. 2 and 3. 2 is a sectional view of the power transmission device 60 taken along the line II-II of FIG. 1, and FIG. 3 is a sectional view of the power transmission device 60 taken along the line III-III of FIG.

As described above, the power transmission device 60 has the electric motor 50 and the speed reducer 42. As shown in FIG. 2, the electric motor 50 has a rotating shaft 51 as an output shaft, a rotor 52 fixed to the rotating shaft 51, and a stator 53 arranged so as to face the rotor 52, and is decelerated. The portion 42 includes a worm gear 43 provided on the rotating shaft 51 of the electric motor 50 and a worm wheel 44 provided on the output shaft 22. Further, a controller 70 having a control board 71 for controlling the drive of the electric motor 50 is arranged adjacent to the outside of the rotating shaft 51 of the electric motor 50 in the axial direction. The controller 70 may be arranged at a position away from the electric motor 50.

The shaft provided with the worm gear 43 is not connected to the rotating shaft 51 of the electric motor 50 through a coupling such as a coupling, but is formed integrally with the shaft to which the rotor 52 is fixed, that is, the rotating shaft 51. There is.

The worm wheel 44 has a metal cored bar 44a that is press-fitted into the output shaft 22, and a resin part 44b that is molded around the cored bar 44a and has teeth 44c formed on the outer periphery. The tooth portion 44c may be formed when the resin portion 44b is molded, or may be formed on the outer periphery of the resin portion 44b after the resin portion 44b is molded around the cored bar 44a. Further, instead of the molding, the resin portion 44b having the tooth portion 44c may be press-fitted into the cored bar 44a.

The power transmission device 60 further includes a housing 45 that houses the worm gear 43 and the worm wheel 44. As shown in FIGS. 2 and 3, the housing 45 has a first accommodation hole 46 for accommodating the worm gear 43 and a second accommodation hole 47 as a accommodation hole for accommodating the worm wheel 44. It is formed so as to be orthogonal to the one accommodation hole 46. Further, an insertion hole 48 through which the output shaft 22 is inserted is formed in the housing 45 coaxially with the second accommodation hole 47.

The first accommodating hole 46 is substantially a perfect circle in the part that accommodates the worm gear 43, and has an inner diameter that forms a predetermined gap with the outer periphery of the worm gear 43. The second accommodation hole 47 is substantially a perfect circle in the portion that accommodates the worm wheel 44, and has an inner diameter that forms a predetermined gap with the outer periphery of the worm wheel 44.

The first accommodation hole 46 and the second accommodation hole 47 partially overlap and communicate with each other. As described above, the worm gear 43 and the worm wheel 44 mesh with each other in the portion where the first accommodation hole 46 and the second accommodation hole 47 communicate with each other.

A first bearing 54 and a second bearing 55 that rotatably support the rotating shaft 51 are held in the first housing hole 46 that houses the worm gear 43. The first bearing 54 and the second bearing 55 are so-called rolling bearings configured by an inner ring, an outer ring, and a plurality of rolling elements arranged between the inner ring and the outer ring. The first bearing 54 is arranged between the rotor 52 and the worm gear 43, and the second bearing 55 is arranged on the opposite side of the worm gear 43 from the first bearing 54.

Here, when the worm gear 43 supported by the housing 45 via the bearings 54 and 55 is formed on the rotating shaft 51 of the electric motor 50 as described above, the performance of the electric motor 50 can be confirmed by checking the electric motor 50. Generally, it is performed in a state where it is assembled to the housing 45, that is, in a state where the worm gear 43 and the worm wheel 44 mesh with each other.

However, when various performances such as the cogging torque and the torque ripple of the electric motor 50 are measured in such a state, the influence of the meshing condition between the worm gear 43 and the worm wheel 44 may be attributed to whether the measurement result is due to the electric motor 50. I'm not sure if I have received it. Therefore, it is difficult to accurately determine whether or not the electric motor 50 satisfies the predetermined performance.

Therefore, in the present embodiment, in order to enable the performance of the electric motor 50 to be measured in a state where the worm wheel 44 is not assembled to the housing 45, a recess is formed in the inner peripheral surface 47a of the second accommodation hole 47. 47b is provided.

The recess 47b is a notch formed in the inner peripheral surface 47a of the second accommodation hole 47 so as to be recessed radially outward, and its axial length is longer than the tooth width of the worm wheel 44. The recess 47b is provided not on the entire circumference of the inner peripheral surface 47a of the second accommodation hole 47, but on only a part of the inner peripheral surface 47a of the second accommodation hole 47. Specifically, as shown in FIG. In addition, when the inner peripheral surface 47a is divided into a side close to the worm gear 43 and a side far from the worm gear 43 with a virtual plane P1 parallel to the rotation center C2 of the worm gear 43 including the rotation center C1 of the worm wheel 44 as a boundary, It is provided in an arc shape only on the side far from 43.

The first depth D1, which is the depth of the recess 47b from the inner peripheral surface 47a of the second accommodation hole 47, is set to be larger than the second depth D2, which is the depth of meshing between the worm gear 43 and the worm wheel 44. To be done. That is, the mesh between the worm gear 43 and the worm wheel 44 can be released by shifting the worm wheel 44 toward the recess 47b side. The size of the radial gap between the second accommodation hole 47 and the worm wheel 44 is set to be smaller than the second depth D2.

In this way, the recess 47b contacts the worm wheel 44 when the worm wheel 44 moves so that the engagement between the worm gear 43 and the worm wheel 44 on the inner peripheral surface 47a of the second accommodation hole 47 is released. It is provided in the part.

A guide surface 47c is formed on the inner peripheral surface 47a of the second accommodation hole 47 so as to extend from the opening end side of the second accommodation hole 47 toward the recess 47b. The guide surface 47c is provided to smoothly guide the worm wheel 44 into the second accommodation hole 47 when the worm wheel 44 is assembled to the housing 45.

Further, since the guide surface 47c is formed, the radial thickness of the housing 45 in the portion where the recess 47b is provided gradually increases toward the opening end of the second accommodation hole 47. Therefore, it is possible to secure a sufficient sealing surface between the housing 45 and a lid member (not shown) attached to the housing 45 so as to close the opening end of the second accommodation hole 47.

Next, the procedure for assembling the power transmission device 60 having the above configuration will be described with reference to FIGS. 4 and 6 show a cross section of the power transmission device 60 in the same portion as in FIG. 2, and FIGS. 5A to 5D show cross sections of the power transmission device 60 in the same portion as in FIG.

First, as shown in FIG. 4, the electric motor 50 including the worm gear 43 and the controller 70 are assembled to the housing 45, that is, the worm wheel 44 is not assembled.

Then, in this state, the performance of the electric motor 50 is measured. By measuring the performance of the electric motor 50 in the state where the worm wheel 44 is not assembled, the performance of the electric motor 50 alone can be accurately measured. As a result, it becomes possible to easily determine whether or not the electric motor 50 satisfies the predetermined performance.

Next, the worm wheel 44 is attached to the housing 45 whose performance of the electric motor 50 has been measured.

Specifically, first, as shown in FIG. 5A, the worm wheel 44 is inserted into the second accommodation hole 47 so that the lower end of the worm wheel 44 integrated with the output shaft 22 does not contact the worm gear 43.

Next, as shown in FIG. 5B from the state shown in FIG. 5A, the upper end of the worm wheel 44 farthest from the worm gear 43 is moved along the guide surface 47c to gradually move a part of the worm wheel 44 into the recess 47b. 5C, the worm wheel 44 is moved toward the bottom surface of the second accommodation hole 47, and a part of the worm wheel 44 is completely inserted into the recess 47b as shown in FIG. 5C.

Then, from the state shown in FIG. 5C, as shown in FIG. 5D, the worm wheel 44 is further moved toward the bottom surface of the second accommodation hole 47 along the axial direction of the output shaft 22. In this state, the worm gear 43 and the worm wheel 44 do not mesh with each other, as shown in FIG. 6 which shows a cross section taken along line VI-VI of FIG. 5D.

By moving the worm wheel 44 to the worm gear 43 side from the state shown in FIGS. 5D and 6, the worm gear 43 and the worm wheel 44 are brought into a meshed state as shown in FIGS. 2 and 3.

As described above, in this embodiment, by providing the recess 47b in the inner peripheral surface 47a of the second accommodation hole 47, it is possible to assemble the worm wheel 44 to the housing 45 after the performance of the electric motor 50 is measured. I am trying.

According to the above embodiment, the following effects can be obtained.

In the power transmission device 60, a recess 47b recessed outward in the radial direction is provided on the inner peripheral surface 47a of the second accommodation hole 47 in which the worm wheel 44 is accommodated. Therefore, by inserting the worm wheel 44 into the housing 45 while inserting a part of the worm wheel 44 into the recess 47b, even after the rotary shaft 51 having the worm gear 43 is assembled into the housing 45, The wheel 44 can be assembled to the housing 45.

Therefore, it is possible to measure the performance of the electric motor 50 in a state where the worm wheel 44 is not attached to the housing 45. As a result, the performance measurement accuracy of the electric motor 50 used in the power transmission device 60 can be improved.

Next, a modified example of the above embodiment will be described. The following modifications are also within the scope of the present invention, and the configurations shown in the variations and the configurations described in the above embodiments may be combined, or the configurations described in the following different variations may be combined. Is also possible.

In the above-described embodiment, the rotary shaft 51 provided with the worm gear 43 and the output shaft 22 are orthogonal to each other, but the rotary shaft 51 and the output shaft 22 may intersect diagonally.

In the above embodiment, the rack-and-pinion mechanism having the pinion gear 41a and the rack gear 41b is used as the transmission unit 41 that transmits the rotation of the output shaft 22 to the wheels 1. A link mechanism with a pitman arm to be joined may be used.

Further, in the above embodiment, the steering wheel is the steering wheel 10. Instead of this, the steering handle may be of other forms such as a bar handle or a control stick.

Hereinafter, the configuration, operation, and effect of the embodiment of the present invention will be collectively described.

The power transmission device 60 includes an electric motor 50 having a rotary shaft 51 as an output shaft, a worm gear 43 provided on the rotary shaft 51, a worm wheel 44 that meshes with the worm gear 43, and a housing 45 that houses the worm gear 43 and the worm wheel 44. The housing 45 has a second accommodation hole 47 in which the worm wheel 44 is accommodated, and the inner peripheral surface 47a of the second accommodation hole 47 is provided with a concave portion 47b recessed radially outward. Be done.

In this configuration, the inner peripheral surface 47a of the second accommodation hole 47 in which the worm wheel 44 is accommodated is provided with the concave portion 47b recessed outward in the radial direction. Therefore, by inserting the worm wheel 44 into the housing 45 while inserting a part of the worm wheel 44 into the recess 47b, even after the rotary shaft 51 having the worm gear 43 is assembled into the housing 45, The wheel 44 can be assembled to the housing 45. Therefore, it is possible to measure the performance of the electric motor 50 without the worm wheel 44 being attached to the housing 45, so that the performance measurement accuracy of the electric motor 50 used in the power transmission device 60 can be improved. it can.

Further, the recess 47b has a depth that is at least the amount of meshing between the worm gear 43 and the worm wheel 44 toward the outside in the radial direction.

In this configuration, the first depth D1 that is the depth of the recess 47b from the inner peripheral surface 47a of the second accommodation hole 47 is the second depth D2 that is the depth of meshing between the worm gear 43 and the worm wheel 44. Is set larger than. That is, the mesh between the worm gear 43 and the worm wheel 44 can be released by shifting the worm wheel 44 toward the recess 47b side. By providing such a recess 47b on the inner peripheral surface 47a of the second accommodation hole 47 in which the worm wheel 44 is accommodated, the worm wheel 44 is inserted into the recess 47b while the worm wheel 44 is housed in the housing 45. It is possible to assemble the worm wheel 44 to the housing 45 even after the rotary shaft 51 having the worm gear 43 formed thereon is assembled to the housing 45.

Further, the recess 47b is provided only on the side far from the worm gear 43 when the inner peripheral surface 47a of the second accommodation hole 47 is divided into a side close to the worm gear 43 and a side far from the worm gear 43.

In this configuration, the recess 47b is provided only on the side far from the worm gear 43 when the inner peripheral surface 47a of the second accommodation hole 47 is divided into a side close to the worm gear 43 and a side far from the worm gear 43. That is, the recess 47b is provided not on the entire circumference of the inner peripheral surface 47a of the second accommodation hole 47, but on only a part of the inner peripheral surface 47a. Therefore, compared with the case where the recess 47b is provided on the entire circumference of the inner peripheral surface 47a, the processing cost of the recess 47b is reduced, so that the manufacturing cost of the power transmission device 60 can be reduced. Further, compared with the case where the recess 47b is provided on the entire circumference of the inner peripheral surface 47a, the portion where the wall thickness of the housing 45 is thin is reduced. can do.

Further, on the inner peripheral surface 47a of the second accommodation hole 47, a guide surface 47c that is inclined from the opening end side of the second accommodation hole 47 toward the recess 47b is provided.

In this configuration, the guide surface 47c that is inclined from the opening end side of the second accommodation hole 47 toward the recess 47b is provided on the inner peripheral surface 47a of the second accommodation hole 47. When the worm wheel 44 is assembled to the housing 45, a part of the worm wheel 44 can be easily guided into the recess 47b by moving the upper end of the worm wheel 44 along the guide surface 47c. Therefore, by providing the guide surface 47c, the assemblability of the power transmission device 60 can be improved.

Further, in the electric power steering device 100 including the power transmission device 60 having the above-described configuration, the worm wheel 44 is provided on the steering shaft 20 that rotates by receiving the steering torque from the steering wheel 10, and the electric motor 50 is connected to the worm gear 43. The steering shaft 20 is provided with a rotational torque that assists the steering torque by rotationally driving the worm wheel 44.

In this configuration, the power transmission device 60 having the above configuration is used in the electric power steering device 100. As described above, by adopting the power transmission device 60 including the electric motor 50 that is confirmed to satisfy the predetermined performance, the rotational torque that assists the steering torque is stably applied to the steering shaft 20 by the power transmission device 60. Will be granted. Therefore, the operation of the electric power steering device 100 can be stabilized.

Although the embodiment of the present invention has been described above, the above embodiment merely shows a part of the application example of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

100... Electric power steering device, 60... Power transmission device, 10... Steering wheel (steering handle), 20... Steering shaft, 42... Reduction part, 43... Worm gear, 44... ..Warm wheel, 45... Housing, 46... First housing hole, 47... Second housing hole (housing hole), 47a... Inner peripheral surface, 47b... Recessed portion, 47c...・Guide surface, 50... Electric motor, 51... Rotating shaft (output shaft)

Claims (5)

A power transmission device,
An electric motor having an output shaft,
A worm gear provided on the output shaft,
A worm wheel that meshes with the worm gear,
A housing for housing the worm gear and the worm wheel,
The housing has a housing hole for housing the worm wheel,
The power transmission device is characterized in that a recessed portion that is recessed radially outward is provided on the inner peripheral surface of the accommodation hole. The power transmission device according to claim 1, wherein the recess has a depth that is at least the amount of meshing between the worm gear and the worm wheel toward the outside in the radial direction. The recess is provided only on the side far from the worm gear when the inner peripheral surface of the accommodation hole is divided into a side close to the worm gear and a side far from the worm gear. The power transmission device described. The power guide according to any one of claims 1 to 3, wherein the inner peripheral surface of the accommodation hole is provided with a guide surface inclined from the opening end side of the accommodation hole toward the recess. Transmission device. An electric power steering device comprising the power transmission device according to claim 1.
The worm wheel is provided on a steering shaft that rotates by receiving steering torque from a steering wheel,
The electric power steering device, wherein the electric motor imparts a rotational torque for assisting the steering torque to the steering shaft by rotationally driving the worm wheel via the worm gear.

Images