Electronic parking brake execution device

Abstract

The utility model discloses an electronic parking brake executing device which comprises a gear box body, a gear box cover, a motor, a primary transmission gear assembly, a secondary transmission gear assembly, a planetary gear transmission assembly and an inner gear ring, and the inner gear ring is fixed in a gear cavity of the gear box body in an injection molding mode. A plurality of planet gears in the planet gear transmission assembly are located in the inner gear ring and meshed with the inner gear ring, and at least the inner tooth part of the inner gear ring is made of powder metallurgy or other metal materials. According to the electronic parking brake executing device, the inner gear ring is designed to be an independent part and then fixed in the gear box body in a plastic coating mode, the inner tooth part of the inner gear ring is made of powder metallurgy or other metal materials, the design scheme for manufacturing different parameters is met, and the manufacturing cost is reduced. And the strength and the manufacturing precision of the inner gear ring can be improved, the stability of meshing efficiency is improved, and therefore the range of adaptive torque can be expanded.

Description

TECHNICAL FIELD

[0001] The utility model relates to vehicle brake technical field, especially electronic parking brake execution device. BACKGROUND

[0002] Electronic parking brake execution device includes motor and transmission mechanism, transmission mechanism reduces the output speed of motor and improves the output torque transmission to brake caliper and realizes parking function. Transmission mechanism can adopt multiple transmission modes, such as belt transmission mechanism, worm transmission mechanism, cylindrical gear transmission mechanism, planetary gear transmission mechanism etc. Compared with other transmission modes, planetary gear transmission mechanism has the advantages of high reduction ratio, compact structure and stable operation.

[0003] Among them, the inner tooth ring in the parking brake execution device is used for meshing with the planetary gear in the planetary transmission mechanism, and the existing inner tooth ring and gear box are formed by integral injection molding, so that the torque upper limit value borne by the inner tooth ring is lower, and the torque transmission requirement cannot be matched. UTILITY MODEL CONTENTS

[0004] The utility model discloses electronic parking brake execution device can improve the strength and manufacturing precision of inner tooth ring, improve the stability of meshing efficiency, solve the problem that the torque transmission requirement cannot be matched.

[0005] According to the first aspect of the utility model embodiment, electronic parking brake execution device is provided, including:

[0006] Gear box, gear box includes motor accommodating cavity and gear chamber, gear chamber sets up at the front end of motor accommodating cavity and with motor accommodating cavity communication;

[0007] Gear box cover, cover in gear box and seal the gear chamber;

[0008] Motor, assemble in motor accommodating cavity, the output shaft of motor extends to gear chamber, and the first gear is fixed on the output shaft of motor;

[0009] Primary transmission gear assembly, including coaxial second gear and third gear, the second gear is engaged with the first gear;

[0010] Second transmission gear assembly, including coaxial fourth gear and sun gear, the fourth gear is engaged with the third gear;

[0011] The planetary gear transmission assembly comprises a planetary carrier, a plurality of planetary gears and an output spline, the plurality of planetary gears are assembled on a first end surface of the planetary carrier, the output spline is assembled on a second end surface of the planetary carrier, the first end surface and the second end surface are opposite surfaces of the planetary carrier, a sun gear is located at a central position of the plurality of planetary gears and is engaged with the plurality of planetary gears respectively, and the output spline extends out along a bottom of the motor accommodating cavity.

[0012] The inner ring gear is fixed in the gear cavity by injection molding, the plurality of planetary gears are located in the inner ring gear and are engaged with the inner ring gear respectively, and at least an inner tooth part of the inner ring gear is made of powder metallurgy or other similar metal materials.

[0013] The further improvement of the electronic parking brake execution device is that the inner ring gear is made of powder metallurgy or other similar metal materials.

[0014] The further improvement of the electronic parking brake execution device is that a mounting part is arranged on a circumferential side surface of the inner ring gear, and an inner wall of the gear cavity is provided with a matching part; wherein, before the inner ring gear is fixed in the gear cavity by injection molding, the inner ring gear is positioned in the gear cavity by matching and assembling the mounting part and the matching part.

[0015] The further improvement of the electronic parking brake execution device is that the mounting part is a plurality of mounting parts which are evenly arranged on the circumferential side surface of the inner ring gear, and the number of the matching parts is the same as that of the mounting parts and corresponds to the mounting parts one by one.

[0016] The further improvement of the electronic parking brake execution device is that the mounting part is a boss arranged on the circumferential side surface of the inner ring gear, the matching part is a groove arranged on the inner wall of the gear cavity, and the boss and the groove are matched.

[0017] The further improvement of the electronic parking brake execution device is that the mounting part is a recessed part arranged on the circumferential side surface of the inner ring gear, the matching part is a protruding block arranged on the inner wall of the gear cavity, and the recessed part and the protruding block are matched.

[0018] The further improvement of the electronic parking brake execution device is that the recessed part is a groove arranged on the circumferential side surface of the inner ring gear, and the groove is arranged along the central axis direction of the inner ring gear.

[0019] The further improvement of the electronic parking brake execution device is that, after the inner ring gear is fixed in the gear cavity, an injection molding material is arranged on the end surface of the inner ring gear and the inner wall of the gear cavity, so that the inner ring gear is fixed in the gear cavity by injection molding.

[0020] The further improvement of the electronic parking brake execution device is that the inner teeth of the inner gear ring do not exceed the two side end faces of the inner gear ring in the direction of the central axis of the inner gear ring.

[0021] The further improvement of the electronic parking brake execution device is that the central axis of the first gear wheel is parallel to the central axis of the planetary gear transmission assembly and the central axis of the secondary transmission gear assembly, and the central axis of the secondary transmission gear assembly coincides with the central axis of the planetary gear transmission assembly.

[0022] The electronic parking brake execution device provided by the utility model designs the inner gear ring as an independent component, then fixes the inner gear ring in the gear box body in a plastic wrapping manner, and makes the inner teeth of the inner gear ring from powder metallurgy or other metal materials, so that different parameter design schemes can be made, the strength and manufacturing precision of the inner gear ring can be improved, the stability of the meshing efficiency can be improved, and the range of the adaptive torque can be expanded. BRIEF DESCRIPTION OF DRAWINGS

[0023] The utility model will be described in detail below by referring to the drawings and exemplary embodiments, in which:

[0024] Figure 1 An exploded view of the electronic parking brake execution device provided by an embodiment of the utility model is shown;

[0025] Figure 2 A sectional view of the electronic parking brake execution device provided by an embodiment of the utility model is shown;

[0026] Figure 3 A structural schematic view of the secondary transmission gear assembly provided by an embodiment of the utility model is shown;

[0027] Figure 4 An assembly schematic view of the gear box body and the inner gear ring provided by an embodiment of the utility model is shown;

[0028] Figure 5 An assembly schematic view of the gear box body and the inner gear ring provided by another embodiment of the utility model is shown.

[0029] The drawings are merely schematic and not necessarily drawn to scale, and in addition, they only show those parts which are necessary for the elucidation of the utility model, while other parts can be omitted or merely simply mentioned. That is, the utility model can include other components in addition to the components shown in the drawings. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present application with specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure. Although the description of the present application will be introduced in combination with the preferred embodiments, it does not mean that the features of the present application are limited to the embodiments. On the contrary, the purpose of introducing the present application in combination with the embodiments is to cover other options or modifications that can be extended based on the claims of the present application. In order to provide a deep understanding of the present application, many specific details will be included in the following description. The present application can also be implemented without using these details. In addition, in order to avoid confusion or obscure the focus of the present application, some specific details will be omitted in the description. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0031] It should be noted that in the present specification, similar reference numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0032] In the description of the present embodiment, it should be noted that the terms "upper", "inner" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly used when the present application is used, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0033] The terms "first", "second", and the like are only used for differentiation and cannot be understood as indicating or implying relative importance.

[0034] In the description of the present embodiment, it should also be noted that unless otherwise explicitly specified and limited, the terms "provided", "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present embodiment can be understood according to the specific circumstances.

[0035] In order to make the purpose, technical scheme and advantages of the present application more clear, the embodiments of the present application will be further described in detail in combination with the drawings.

[0036] Figure 1 An exploded view of an electronic parking brake execution device provided by an embodiment of the present application is shown; Figure 2The utility model discloses an embodiment provides the cross section view of electronic parking brake executing device of the utility model, Figure 2 The utility model discloses an embodiment provides the structure schematic diagram of two -stage transmission gear assembly.

[0037] Refer to Figures 1 to 3 The electronic parking brake executing device 100 of the utility model embodiment includes gear box 10, gear box cover 20, motor 30, primary transmission gear assembly 40, two -stage transmission gear assembly 50, planetary gear drive assembly 60 and inner tooth ring 13.

[0038] Gear box 10 includes motor accommodating cavity 11 and gear cavity 12, and the gear cavity 12 is arranged at the front end of motor accommodating cavity 11 and is communicated with motor accommodating cavity 11, and the gear cavity 12 is used to accommodate primary transmission gear assembly 40, two -stage transmission gear assembly 50, planetary gear drive assembly 60 and inner tooth ring 13. Wherein, the front end of motor accommodating cavity 11 is the end where the output shaft of motor 30 is located. Gear box cover 20 is used to cover on gear box 10 and seals gear cavity 12.

[0039] Motor 30 is assembled in motor accommodating cavity 11, and the output shaft of motor 30 extends to gear cavity 12, and a first gear 31 is fixed on the output shaft of motor 30, and the first gear 31 is used to cooperate with primary transmission gear assembly 40. The rear end of motor accommodating cavity 11 is provided with a motor cover 32, and the motor cover 32 is assembled on the rear end of motor accommodating cavity 11 to seal motor 30 in motor accommodating cavity 11. Motor 30 wave spring 33 is also arranged between motor cover 32 and motor 30, and the axial gap of motor 30 is adjusted by covering motor 30 wave spring 33.

[0040] Primary transmission gear assembly 40 includes coaxially arranged second gear 41 and third gear 42, and second gear 41 is engaged with first gear 31. In the embodiment of the utility model, the diameter of second gear 42 is greater than the diameter of third gear 41, and the center axis of second gear 41 is provided with first pin shaft 43, and third gear 42 is assembled on the first pin shaft 43, so that the third gear 42 rotates synchronously with the second gear 41. The second gear 41, the first pin shaft 43 and the third gear 42 can be made by one-piece injection molding, and the second gear 41 and the third gear 42 can also be fixed on the first pin shaft 43 by press fitting, or any one of the gears is injection molded with the first pin shaft 43 as the shaft, which is not specifically limited here.

[0041] The first pin shaft 43 extends out of the third gear 42 to be press-fitted with a positioning pin hole on the gear box 10, which is located at the bottom of the gear cavity 12. When the primary transmission gear assembly 40 is assembled, the third gear 42 is away from the gear cover 20 relative to the second gear 41. Through the meshing of the second gear 41 and the first gear 31, when the motor 30 drives the first gear 31 to rotate, the second gear 41 is synchronously driven to rotate, so that the primary transmission gear assembly 40 rotates.

[0042] The secondary transmission gear assembly 50 includes a fourth gear 51 and a sun gear 52 coaxially arranged, the fourth gear 51 is meshed with the third gear 42 to drive the secondary transmission gear assembly 50 to rotate through the transmission of the third gear 42. The secondary transmission gear assembly 50 further includes a second pin shaft 53, the fourth gear 51 and the sun gear 52 are fixed on the second pin shaft 53. The second pin shaft 53 extends out of the fourth gear 51 to be matched with the shaft hole of the gear box cover 20. The diameter of the fourth gear 51 is greater than that of the sun gear 52, the fourth gear 51, the second pin shaft 53 and the sun gear 52 can be integrally injection molded, the fourth gear 51 and the sun gear 52 can also be fixed on the second pin shaft 53 by press-fitting, or any one of the gears is injection molded with the first pin shaft 43 as the shaft, which is not limited here.

[0043] In the embodiment, since the sun gear 52 is used to mesh with a plurality of planetary gears 62, a higher output torque is required, so the sun gear 52 is made of powder metallurgy or other similar metal materials. The fourth gear 51 can be injection molded with the second pin shaft 53 as the shaft, and the sun gear 52 is press-fitted on the second pin shaft 53.

[0044] The planetary gear transmission assembly 60 includes a planetary gear carrier 61, a plurality of planetary gears 62 and an output spline 63. The plurality of planetary gears 62 are assembled on the first end face 611 of the planetary gear carrier 61, and the output spline 63 is assembled on the second end face 612 of the planetary gear carrier 61. The first end face 611 and the second end face 612 are opposite faces of the planetary gear carrier 61. The sun gear 52 is located at the center position of the plurality of planetary gears 62 and is meshed with the plurality of planetary gears 62 respectively. The output spline 63 extends out along the bottom of the motor accommodating cavity 11.

[0045] In the embodiment of the utility model, the planetary gear carrier 61 is a circular table face structure, the planetary gear transmission assembly 60 includes four planetary gears 62, the first end face 611 of the planetary gear carrier 61 is uniformly provided with four planetary gear shafts 64, and the four planetary gears 62 are correspondingly assembled with the four planetary gear shafts 64, so that the four planetary gears 62 are rotatably assembled on the first end face 611 of the planetary gear carrier 61.

[0046] The planetary carrier 61, the four planetary shafts 64 and the output spline 63 are integrally injection molded. In another embodiment, the output spline 63 can be made of powder metallurgy or other similar metal materials, and then the planetary carrier 61 and the planetary shafts 64 are injection molded based on the output spline 63. The output spline 63 is located at the center of the planetary carrier 61, and specifically, the central axis of the output spline 63 coincides with the central axis of the planetary carrier 61.

[0047] The inner ring gear 13 is arranged in the gear cavity 12, and the plurality of planetary gears 62 are arranged in the inner ring gear 13 and mesh with the inner ring gear 13. After the first transmission gear assembly 40, the second transmission gear assembly 50 and the planetary gear transmission assembly 60 are assembled, the sun gear 52 meshes with the four planetary gears 62 to drive the four planetary gears 62 to revolve, and the four planetary gears 62 revolve by meshing with the inner ring gear 13, thereby driving the planetary carrier 61 to rotate.

[0048] After the first transmission gear assembly 40, the second transmission gear assembly 50 and the planetary gear transmission assembly 60 are assembled, the central axis of the first gear 31 is parallel to the central axis of the planetary gear transmission assembly 60 and the central axis of the second transmission gear assembly 50, and the central axis of the second transmission gear assembly 50 coincides with the central axis of the planetary gear transmission assembly 60. The transmission combination relationship of the present application is that the second gear 41 meshes with the first gear 31, the fourth gear 51 meshes with the third gear 42, the sun gear 52 meshes with the four planetary gears 62, and the four planetary gears 62 mesh with the inner ring gear 13.

[0049] The inner ring gear 13 is fixed in the gear cavity 12 by injection molding, the plurality of planetary gears 62 are arranged in the inner ring gear 13 and mesh with the inner ring gear 13, and the plurality of planetary gears 62 revolve by meshing with the inner ring gear 13, thereby driving the planetary carrier 61 to rotate. The present application separately designs the inner ring gear 13, assembles the inner ring gear 13 in the gear cavity 12, and the inner ring gear 13 is located at the bottom of the corresponding gear cavity 12 of the gear box 10. Specifically, after the inner ring gear 13 is positioned in the gear cavity 12, the end surface of the inner ring gear 13 and the inner wall of the gear cavity 12 are covered by injection molding material, so that the inner ring gear 13 is injection molded and fixed in the gear cavity 12, thereby making the inner ring gear 13 partially plastic and integrated with the gear box 10. The present application separately designs the inner ring gear 13, so that the inner ring gear 13 can be replaced according to requirements, including but not limited to materials, structures and the like.

[0050] At least the inner tooth part of the inner tooth ring 13 is made of powder metallurgy or other similar metal materials. The conventional inner tooth ring 13 is integrally injection molded with the gear box body 10, so that the torque upper limit value borne by the inner tooth ring 13 is low, which cannot meet the requirements of torque transmission. In the utility model, at least the inner tooth part of the inner tooth ring 13 is made of powder metallurgy or other similar metal materials, so as to enhance the output torque of the inner tooth ring 13.

[0051] In an embodiment, the inner tooth ring 13 is made of powder metallurgy or other similar metal materials, so as to improve the strength and manufacturing precision of the inner tooth ring 13, further improve the output torque of the inner tooth ring 13, and improve the NVH (Noise, Vibration, Harshness) performance of the product by improving the meshing precision between the inner tooth ring 13 and the plurality of planetary gears 62. The inner tooth ring 13 of the utility model can accurately adapt to different torque requirements by replacing powder metallurgy or metal with different strengths, so as to improve the economy.

[0052] In the utility model, in the central axis direction of the inner tooth ring 13, the inner tooth of the inner tooth ring 13 does not exceed the two side end faces of the inner tooth ring 13. In the embodiment of the utility model, in the central axis direction of the inner tooth ring 13, the size of the inner tooth of the inner tooth ring 13 is equal to the size between the two side end faces of the inner tooth ring 13, that is, the tooth width of the inner tooth ring 13 is consistent with the thickness of the inner tooth ring 13. Further, the inner tooth ring 13 can also be designed and adjusted according to the number of teeth as required, so as to facilitate the production of different parameter design schemes without the need to open a new mold.

[0053] As shown in Figure 1 , Figure 2 Combined with Figure 4 and Figure 5 , in order to facilitate the installation of the inner tooth ring 13, the utility model is provided with a mounting part 131 on the peripheral side face of the inner tooth ring 13, and the inner wall of the gear cavity 12 is provided with a matching part 121. The inner tooth ring 13 is prepositioned in the gear cavity 12 by adapting and assembling the mounting part 131 and the matching part 121. The gear box body 10 is provided with an annular step 14 in the area of the gear cavity 12 corresponding to the two-stage transmission gear assembly 50, that is, the two-stage transmission gear assembly 50 is arranged above the annular step 14, and the inner tooth ring 13 is mounted on the annular step 14, so as to fix the inner tooth ring 13 in the gear box body 10. In the utility model, the matching part 121 is arranged on the side wall of the annular step 14, and the inner tooth ring 13 is pre-fixed in the gear cavity 12 by adapting and assembling the mounting part 131 and the matching part 121, and then the inner tooth ring 13 is fused in the gear box body 10 by injection molding, so as to ensure the stability of the inner tooth ring 13.

[0054] The installation part 131 is a plurality of, and the plurality of installation parts 131 are uniformly arranged on the circumferential side surface of the inner ring gear 13, the number of the matching parts 121 is the same as that of the installation parts 131 and corresponds to the installation parts 131 one by one.

[0055] In an embodiment, as shown in the drawings, the installation part 131 is a boss arranged on the circumferential side surface of the inner ring gear 13, and the matching part 121 is a groove arranged on the inner wall of the gear cavity 12, specifically, the groove is arranged on the side wall of the annular step 14, the boss is matched with the groove, so that the inner ring gear 13 can be pre-assembled at the position of the annular step 14 in the gear cavity 12, and the rotation of the inner ring gear 13 is prevented. Figure 4 In another embodiment, as shown in the drawings, the installation part 131 is a recess arranged on the circumferential side surface of the inner ring gear 13, and the matching part 121 is a protrusion arranged on the inner wall of the gear cavity 12, specifically, the protrusion is arranged on the side wall of the annular step 14, the recess is matched with the protrusion, so that the inner ring gear 13 can be pre-assembled at the position of the annular step 14 in the gear cavity 12, and the rotation of the inner ring gear 13 is prevented.

[0056] Figure 5 In another embodiment, as shown in the drawings, the installation part 131 is a recess arranged on the circumferential side surface of the inner ring gear 13, and the matching part 121 is a protrusion arranged on the inner wall of the gear cavity 12, specifically, the protrusion is arranged on the side wall of the annular step 14, the recess is matched with the protrusion, so that the inner ring gear 13 can be pre-assembled at the position of the annular step 14 in the gear cavity 12, and the rotation of the inner ring gear 13 is prevented.

[0057] The working principle of the utility model is as follows: motor 30 drives first gear 31 to rotate, first gear 31 drives second gear 41 to rotate through meshing, second gear 41 drives third gear 42 to rotate, third gear 42 drives fourth gear 51 to rotate through meshing, fourth gear 51 drives sun gear 52 to rotate, sun gear 52 drives four planetary gears 62 to rotate through meshing, four planetary gears 62 rotate around the sun gear 52 through meshing with inner ring gear 13, drive planetary gear carrier 61 to rotate, planetary gear carrier 61 drives output spline 63 to rotate, and finally output power.

[0058] The electronic parking brake execution device provided by the utility model designs the inner ring gear as an independent component, then fixes the inner ring gear in the gear box through a plastic packaging mode, and the inner tooth part of the inner ring gear is made of powder metallurgy or other metal materials, so that different parameter design schemes can be made, the strength and manufacturing precision of the inner ring gear are improved, the stability of meshing efficiency is improved, and the range of adaptive torque can be expanded.

[0059] ​Although the utility model has been illustrated and described by referring to certain preferred embodiments of the utility model, it should be understood by those skilled in the art that the above content is the further detailed description of the utility model combined with the specific embodiments, and the specific implementation of the utility model cannot be limited to these descriptions. Those skilled in the art can make various changes in form and details, including making several simple inferences or replacements, without departing from the spirit and scope of the utility model.

Claims

1. An electronic parking brake execution device characterized by comprising: The application relates to a gear box. The gear box comprises a gear box body, a gear box cover, a motor and a first gear, a second gear, a third gear, a fourth gear, a sun gear, a planetary gear transmission assembly, a planetary carrier, a plurality of planetary gears and an output spline. The gear box body comprises a motor accommodating cavity and a gear cavity. The gear cavity is arranged at the front end of the motor accommodating cavity and communicates with the motor accommodating cavity. The gear box cover covers the gear box body and seals the gear cavity. The motor is assembled in the motor accommodating cavity. The output shaft of the motor extends into the gear cavity. The first gear is fixed on the output shaft of the motor.

2. The electronic parking brake execution device according to claim 1, characterized by The second gear and the third gear are coaxially arranged.

3. The electronic parking brake execution device according to claim 1, characterized by The second gear is engaged with the first gear.

4. The electronic parking brake execution device according to claim 3, characterized by The fourth gear and the sun gear are coaxially arranged.

5. The electronic parking brake execution device according to claim 4, characterized by The fourth gear is engaged with the third gear.

6. The electronic parking brake execution device according to claim 4, characterized by The planetary gears are assembled on the first end surface of the planetary carrier.

7. The electronic parking brake execution device according to claim 6, characterized by The output spline is assembled on the second end surface of the planetary carrier.

8. The electronic parking brake execution device according to any one of claims 1 to 7, characterized by, The first end surface and the second end surface are opposite surfaces of the planetary carrier.

9. The electronic parking brake execution device according to claim 1, characterized by The sun gear is located at the center of the planetary gears and is engaged with the planetary gears.

10. The electronic parking brake execution device according to claim 1, characterized by The output spline extends out along the bottom of the motor accommodating cavity. The inner tooth ring is fixed in the gear cavity by injection molding. The planetary gears are located in the inner tooth ring and are engaged with the inner tooth ring. At least the inner tooth part of the inner tooth ring is made of powder metallurgy or other similar metal materials. The inner tooth ring is made of powder metallurgy or other similar metal materials. The circumferential surface of the inner tooth ring is provided with mounting parts. The inner wall of the gear cavity is provided with matching parts. Before the inner tooth ring is fixed in the gear cavity by injection molding, the mounting parts and the matching parts are matched and assembled to make the inner tooth ring be positioned in the gear cavity. The mounting parts are uniformly arranged on the circumferential surface of the inner tooth ring. The number of the matching parts is the same as that of the mounting parts and corresponds to the mounting parts one by one. The mounting parts are bosses arranged on the circumferential surface of the inner tooth ring. The matching parts are grooves arranged on the inner wall of the gear cavity. The bosses are matched with the grooves. The mounting parts are recesses arranged on the circumferential surface of the inner tooth ring. The matching parts are protrusions arranged on the inner wall of the gear cavity. The recesses are grooves arranged on the circumferential surface of the inner tooth ring along the central axis direction of the inner tooth ring. After the inner tooth ring is fixed in the gear cavity, the injection molding material covers the end surface of the inner tooth ring and the inner wall of the gear cavity to make the inner tooth ring be fixed in the gear cavity by injection molding. In the central axis direction of the inner tooth ring, the inner tooth of the inner tooth ring does not exceed the two end surfaces of the inner tooth ring. The central axis of the first gear is parallel to the central axis of the planetary gear transmission assembly and the central axis of the second gear transmission assembly. The central axis of the second gear transmission assembly coincides with the central axis of the planetary gear transmission assembly.

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