Electronic parking brake execution device

Abstract

The utility model discloses an electronic parking braking executing device. The electronic parking braking executing device comprises a gear box body, a gear box cover, a motor, a first-stage transmission gear assembly, a second-stage transmission gear assembly and a planetary gear transmission assembly. The first-stage transmission gear assembly is provided with a first limiting part and a second limiting part and is limited between the gear box cover and the gear box body through the first limiting part and the second limiting part. According to the electronic parking brake executing device, a traditional press-fitting process is removed, the axial positioning precision is improved by improving the rotating shaft design and the positioning mode of the first-stage transmission gear assembly, the quality control of the first-stage transmission gear assembly is more stable, the service life is prolonged, and the cost is reduced. The problem that noise is generated due to abnormal meshing between gears of an existing product is solved.

Description

Technical Field

[0001] This utility model relates to the field of vehicle braking technology, and in particular to an electronic parking brake actuator. Background Technology

[0002] The electronic parking brake actuator includes a motor and a transmission mechanism. The transmission mechanism reduces the motor's output speed while increasing the output torque, which is then transmitted to the brake caliper to achieve the parking function. The transmission mechanism can employ various transmission methods, such as belt drives, worm gear drives, cylindrical gear drives, and planetary gear drives. To achieve a specific reduction ratio, multi-stage transmissions can also be used. Compared to other transmission methods, planetary gear drives offer advantages such as high reduction ratios, compact structure, and stable operation.

[0003] In existing parking brake actuators, the connecting shafts of each gear transmission stage are usually designed with press-fit shafts. This design suffers from inaccurate axial positioning, which can easily lead to abnormal meshing between gears, causing abnormal noise and affecting service life. Furthermore, linear press-fitting quality control is difficult, and the process requires multiple press-fitting and positioning devices, making the process complex. Utility Model Content

[0004] The purpose of this invention is to propose an electronic parking brake actuator, which proposes a split positioning method and improves the axial positioning method through structural design to solve the problem of not being able to adapt to torque transmission requirements.

[0005] According to a first aspect of the present invention, an electronic parking brake actuator is provided, comprising:

[0006] A gearbox housing, comprising a motor housing cavity and a gear cavity, wherein the gear cavity is located at the front end of the motor housing cavity and communicates with the motor housing cavity, wherein an internal gear ring is provided inside the gear cavity and an output spline hole is provided on the gearbox housing at the center position corresponding to the internal gear ring;

[0007] A gearbox cover that covers the gearbox body and seals the gear cavity;

[0008] An electric motor is assembled inside the motor housing cavity, the output shaft of the motor extends into the gear cavity, and a first gear is fixed on the output shaft of the motor;

[0009] A primary transmission gear assembly includes a second gear and a third gear coaxially arranged. The second gear meshes with the first gear. The third gear is disposed on the lower end face of the second gear. A first limiting part that cooperates with the gearbox cover is provided at the center position of the upper end face of the second gear. A second limiting part extends downward from the center position of the third gear. The primary transmission gear assembly is limited between the gearbox cover and the gearbox body by the first limiting part and the second limiting part.

[0010] The secondary transmission gear assembly includes a fourth gear and a sun gear arranged coaxially, wherein the fourth gear meshes with the third gear;

[0011] A planetary gear transmission assembly includes a planet carrier, a plurality of planet gears, and an output spline. The plurality of planet gears are mounted on a first end face of the planet carrier, and the output spline is disposed on a second end face of the planet carrier. The first end face and the second end face are opposite sides of the planet carrier. The sun gear is located at the center of the plurality of planet gears and meshes with each of the plurality of planet gears. The output spline extends out of the gearbox body from the output spline hole.

[0012] 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 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.

[0013] A further improvement of the electronic parking brake actuator of this utility model is that the first limiting part is an annular column, and the gearbox cover is provided with a corresponding positioning slot; or, the first limiting part is a positioning slot, and the gearbox cover is provided with a corresponding annular column; wherein, by inserting the annular column into the positioning slot, one end of the primary transmission gear assembly is pre-positioned.

[0014] A further improvement of the electronic parking brake actuator of this utility model is that the second limiting part is a positioning shaft, and the gearbox body is correspondingly provided with a first positioning hole; wherein, by the positioning shaft cooperating with the first positioning hole, the other end of the primary transmission gear assembly is pre-positioned.

[0015] A further improvement of the electronic parking brake actuator of this utility model is that the primary transmission gear assembly further includes a central shaft passing through the second gear and the third gear, and the first limiting part and the second limiting part are the two ends of the central shaft.

[0016] A further improvement of the electronic parking brake actuator of this utility model is that the secondary transmission gear assembly further includes an annular positioning part disposed at the center of the fourth gear. The annular positioning part and the sun gear are disposed on opposite sides of the fourth gear, and the gearbox cover is provided with a second positioning hole that cooperates with the annular positioning part.

[0017] A further improvement of the electronic parking brake actuator of this utility model is that a sun gear positioning hole is provided at the center of the sun gear, and the planetary gear transmission assembly also includes a sun gear positioning shaft disposed on the planetary gear carrier. The sun gear positioning shaft is located at the center of the planetary gear carrier and is located on the same side as the plurality of planet gears.

[0018] A further improvement of the electronic parking brake actuator of this utility model is that the sun gear positioning shaft and the output spline are integrally stamped and formed, and are integrally coated with plastic with the sun gear; wherein, the output spline is made of powder metallurgy or other metal materials.

[0019] A further improvement of the electronic parking brake actuator of this utility model is that the annular positioning part is integrally injection molded with the fourth gear, and the sun gear is encased in plastic at the center of the fourth gear.

[0020] A further improvement of the electronic parking brake actuator of this utility model is that the sun gear is plastically encased in the center of the fourth gear, the center of the fourth gear and the center of the sun gear are provided with a mounting slot, and the gearbox cover is provided with a connecting shaft that matches the mounting slot.

[0021] A further improvement of the electronic parking brake actuator of this utility model is that the peripheral edge of the planetary gear carrier is provided with an inwardly recessed step portion, the step portion being located on one side of the planetary gear carrier where the output spline is located, and a support flange being provided inside the gearbox, the support flange being located on the side of the internal gear ring away from the gearbox cover.

[0022] A further improvement of the electronic parking brake actuator of this utility model is that the gearbox cover is provided with a positioning pin, and the gearbox body is provided with a corresponding positioning pin hole. The positioning pin cooperates with the positioning pin hole so that the gearbox cover covers the gearbox body and seals the gear cavity.

[0023] A further improvement of the electronic parking brake actuator of this utility model is that at least two positioning pins are provided on the gearbox cover, and a matching number of positioning pin holes are provided on the gearbox body; wherein the two positioning pins are respectively located on opposite sides of the gearbox cover.

[0024] The electronic parking brake actuator provided by this utility model eliminates the traditional press-fitting process. By improving the design and positioning method of the shaft of the primary transmission gear assembly, the axial positioning accuracy is improved, making the quality control of the primary transmission gear assembly more stable, increasing its service life, and solving the problem of noise caused by abnormal meshing between gears in existing products. Attached Figure Description

[0025] The present invention will now be described in detail with reference to the accompanying drawings and exemplary embodiments, wherein:

[0026] Figure 1 An exploded view of an electronic parking brake actuator provided in an embodiment of the present invention is shown;

[0027] Figure 2 This is a cross-sectional view of an electronic parking brake actuator provided in an embodiment of the present invention;

[0028] Figure 3 This shows a cross-sectional view of a gearbox body provided in an embodiment of the present invention;

[0029] Figure 4 This diagram shows a structural schematic of a gearbox cover provided in an embodiment of the present invention;

[0030] Figure 5 This diagram shows a structural schematic of a primary transmission gear assembly provided in one embodiment of the present invention.

[0031] Figure 6 This diagram shows a structural schematic of a primary transmission gear assembly provided in another embodiment of the present invention;

[0032] Figure 7 This utility model is shown Figure 6 A sectional view of the primary transmission gear assembly;

[0033] Figure 8 This diagram shows a structural schematic of a two-stage transmission gear assembly provided in an embodiment of the present invention;

[0034] Figure 9 This diagram shows a structural schematic of a planetary gear transmission assembly provided in one embodiment of the present invention.

[0035] Figure 10 This diagram shows a cross-sectional view of a two-stage transmission gear assembly provided in another embodiment of the present invention.

[0036] Figure 11 This diagram shows a cross-sectional view of a two-stage transmission gear assembly provided in another embodiment of the present invention.

[0037] Figure 12 Showing with Figure 9 or Figure 10 A schematic diagram of the assembled gearbox cover;

[0038] Figure 13 Showing with Figure 9 or Figure 10 A schematic diagram of the assembled planetary gear carrier.

[0039] The accompanying drawings are merely illustrative and not necessarily drawn to scale. Furthermore, they only show those parts necessary to illustrate the present invention, while other parts may be omitted or simply mentioned. That is, the present invention may include other parts besides those shown in the drawings. Detailed Implementation

[0040] The following specific embodiments illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. Although the description of this utility model will be presented in conjunction with preferred embodiments, this does not mean that the features of this utility model are limited to this embodiment. On the contrary, the purpose of describing the utility model in conjunction with the embodiments is to cover other options or modifications that may be derived based on the claims of this utility model. To provide a deep understanding of this utility model, many specific details will be included in the following description. This utility model may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of this utility model, some specific details will be omitted in the description. It should be noted that, without conflict, the embodiments and features in the embodiments of this utility model can be combined with each other.

[0041] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0042] In the description of this embodiment, it should be noted that the terms "upper" and "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the utility model product is usually placed during use. They are only for the convenience of describing the utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the utility model.

[0043] The terms “first”, “second”, etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0044] In the description of this embodiment, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment based on the specific circumstances.

[0045] To make the objectives, technical solutions, and advantages of this utility model clearer, the embodiments of this utility model will be described in further detail below with reference to the accompanying drawings.

[0046] Figure 1 An exploded view of an electronic parking brake actuator provided in an embodiment of the present invention is shown; Figure 2 This is a cross-sectional view of an electronic parking brake actuator provided in an embodiment of the present invention; Figure 3 This shows a cross-sectional view of a gearbox body provided in an embodiment of the present invention; Figure 4 This diagram shows a structural schematic of a gearbox cover provided in an embodiment of the present invention; Figure 5 This diagram shows a structural schematic of a primary transmission gear assembly provided in one embodiment of the present invention. Figure 6 This diagram shows a structural schematic of a two-stage transmission gear assembly provided in an embodiment of the present invention; Figure 7 This diagram shows a schematic representation of a planetary gear transmission assembly provided in an embodiment of the present invention.

[0047] Reference Figures 1 to 7 The electronic parking brake actuator of this utility model embodiment includes a gearbox body 10, a gearbox cover 20, a motor 30, a primary transmission gear assembly 40, a secondary transmission gear assembly 50, and a planetary gear transmission assembly 60.

[0048] The gearbox 10 includes a motor housing 11 and a gear cavity 12. The gear cavity 12 is located at the front end of the motor housing 11 and communicates with the motor 30 housing cavity. The gear cavity 12 is used to accommodate the primary transmission gear assembly 40, the secondary transmission gear assembly 50, and the planetary gear transmission assembly 60. In this invention, the front end of the motor 30 housing cavity is the end where the motor output shaft is located. The gearbox cover 20 is used to cover the gearbox 10 and seal the gear cavity 12. An internal gear ring 13 is provided inside the gear cavity 12, and an output spline hole is opened on the gearbox 10 at the center position of the internal gear ring 13. The internal teeth of the internal gear ring 13 can be made of powder metallurgy or other metal materials to enhance the output torque of the internal gear ring 13.

[0049] The motor 30 is assembled within the motor housing 11, and the motor output shaft extends into the gear cavity 12. A first gear 31 is fixed on the motor output shaft, which engages with the primary transmission gear assembly 40. A motor cover 32 is provided at the rear end of the motor housing 11, and the motor cover 32 is assembled at the rear end of the motor housing 11 to seal the motor 30 within the motor housing 11. A motor spring 33 is also provided between the motor cover 32 and the motor 30, and the axial clearance of the motor 30 is adjusted by covering the motor spring 33.

[0050] The primary transmission gear assembly 40 includes a second gear 41 and a third gear 42 coaxially arranged. The second gear 41 meshes with the first gear 31. When the motor 30 drives the first gear 31 to rotate, it synchronously drives the second gear 41 to rotate, thus causing the primary transmission gear assembly 40 to rotate. The third gear 42 is disposed on the lower end face of the second gear 41, and the diameter of the second gear 41 is larger than the diameter of the third gear 42. A first limiting part 43 that cooperates with the gearbox cover 20 is provided at the center of the upper end face of the second gear 41. A second limiting part 44 extends downward from the center of the third gear 42. The primary transmission gear assembly 40 is limited between the gearbox cover 20 and the gearbox body 10 by the first limiting part 43 and the second limiting part 44. The primary transmission gear assembly 40 of this utility model adopts an integrated structure, eliminating the traditional press-fit process and avoiding inaccurate axial positioning. The primary transmission gear assembly 40 is positioned between the gearbox cover 20 and the gearbox body 10, making the quality control of the primary transmission gear assembly 40 more stable.

[0051] In one embodiment, such as Figures 1 to 5 As shown, the first limiting part 43 is an annular column, and the gearbox cover 20 is provided with a corresponding positioning slot 21. The annular column is inserted into the positioning slot 21 to pre-position one end of the primary transmission gear assembly 40. Alternatively, in another embodiment, the first limiting part 43 is a positioning slot, and the gearbox cover 20 is provided with a corresponding annular column. The annular column is inserted into the positioning slot to pre-position one end of the primary transmission gear assembly 40.

[0052] Furthermore, the second limiting part 44 serves as a positioning shaft, and the gearbox body 10 is correspondingly provided with a first positioning hole 15. The positioning shaft engages with the first positioning hole 15 to pre-position the other end of the primary transmission gear assembly 40. Since the third gear 42 is smaller, a positioning shaft is provided on the third gear 42. In this invention, the first limiting part 43, the second gear 41, the third gear 42, and the second limiting part 44 are integrally injection molded, thus making the primary transmission gear assembly 40 a one-piece structure, resulting in more precise axial positioning and a simpler assembly method with the gearbox body 10 and gearbox cover 20.

[0053] In yet another embodiment, such as Figures 1 to 4 Combination Figure 6 and Figure 7 As shown, the primary transmission gear assembly 40 also includes a central shaft 45 passing through the second gear 41 and the third gear 42. The first limiting part 43 and the second limiting part 44 are the two ends of the central shaft 45. The central shaft 45 can be assembled with the second gear 41 and the third gear 42 by press fitting, or it can be pre-assembled and then fixed by plastic coating. No specific limitation is made here; any assembly method is applicable to this utility model.

[0054] The secondary transmission gear assembly 50 includes a fourth gear 51 and a sun gear 52 arranged coaxially. The fourth gear 51 meshes with the third gear 42, and the secondary transmission gear assembly 50 rotates through the transmission of the third gear 42.

[0055] The planetary gear transmission assembly 60 includes a planet carrier 61, a plurality of planet gears 62, and an output spline 63. The plurality of planet gears 62 are mounted on a first end face 611 of the planet carrier 61, and the output spline 63 is mounted on a second end face 612 of the planet carrier 61. The first end face 611 and the second end face 612 are opposite sides of the planet carrier 61. A sun gear 52 is located at the center of the plurality of planet gears 62 and meshes with each of the planet gears 62. The output spline 63 extends along the bottom of the motor housing cavity 11. Specifically, the central axis of the output spline 63 coincides with the central axis of the planet carrier 61.

[0056] In one embodiment, the planetary gear carrier 61 has a frustum structure, and the planetary gear transmission assembly 60 includes four planetary gears 62. The first end face 611 of the planetary gear carrier 61 is evenly provided with four planetary gear shafts 64. The four planetary gears 62 are assembled one-to-one with the four planetary gear shafts 64, so that the four planetary gears 62 can be rotatably assembled on the first end face 611 of the planetary gear carrier 61.

[0057] In one embodiment, such as Figures 3 to 9 As shown, the secondary transmission gear assembly 50 also includes an annular positioning part 53 disposed at the center of the fourth gear 51. The annular positioning part 53 is a hollow annular structure. The annular positioning part 53 and the sun gear 52 are disposed on opposite sides of the fourth gear 51. The gearbox cover 20 is provided with a second positioning hole 22 that cooperates with the annular positioning part 53, so that one end of the secondary transmission gear assembly 50 is positioned on the gearbox cover 20.

[0058] In one scheme, such as Figures 3 to 9As shown, the annular positioning part 53 is integrally injection molded with the fourth gear 51, and the sun gear 52 is molded around the center of the fourth gear 51. The sun gear 52 has a sun gear positioning hole 521 at its center, which is a recessed hole for assembly with the planetary gear transmission assembly 60. The sun gear 52 can be made of powder metallurgy or other metal materials.

[0059] Correspondingly, the planetary gear transmission assembly 60 also includes a sun gear positioning shaft 65 disposed on the planetary gear carrier 61 for assembly with the sun gear 52, specifically with the sun gear positioning hole 521. The sun gear positioning shaft 65 is located at the center of the planetary gear carrier 61 and on the same side as the multiple planetary gears 62. The sun gear positioning shaft 65 is integrally stamped with the output spline 63 and integrally coated with plastic with the sun gear 52, thereby positioning the secondary transmission gear assembly 50 on the planetary gear transmission assembly 60. The upper end of the secondary transmission gear assembly 50 is positioned on the gearbox cover 20, thus achieving the positioning of the secondary transmission gear assembly 50.

[0060] Since the sun gear 52 is used to mesh with multiple planet gears 62, it requires a high output torque. The output spline 63 is made of powder metallurgy or other metal-like materials. The planet gear carrier 61 and the four planet gear shafts 64 are integrally injection molded. The sun gear positioning shaft 65 and the output spline 63 are integrally stamped and then coated with plastic together with the planet gear carrier 61.

[0061] In another option, such as Figure 10 Combination Figure 12 and Figure 13 In this design, the fourth gear 51 has an annular positioning part 53, which is integrally injection molded with the fourth gear 51. The sun gear 52 is molded around the center of the fourth gear 51. Compared to the previous design, the sun gear 52 in this design is a solid structure and can be made of powder metallurgy or other metal-like materials. The planetary gear carrier 61 no longer needs a sun gear positioning shaft, and the sun gear 52 meshes with multiple planet gears 62.

[0062] In another embodiment, such as Figures 11 to 13 The sun gear 52 is encased in plastic at the center of the fourth gear 51. A mounting slot 511 is provided at the center of the fourth gear 51 and the sun gear 52. A connecting shaft 24 matching the mounting slot 511 is provided on the gearbox cover 20. In this embodiment, the connecting shaft 24 on the gearbox cover 20 is inserted into the mounting slot 511 to position the secondary transmission gear assembly 50. The planetary gear carrier 61 does not require a sun gear positioning shaft, and the sun gear 52 meshes with multiple planet gears 62.

[0063] Furthermore, refer to again Figures 1 to 9The second side 612 of the planetary gear carrier 61 has an inwardly recessed step 611 on its peripheral edge. The step 611 is located on one side of the planetary gear carrier 61 where the output spline 63 is located. The gearbox 10 has a support flange 14 located on the side of the internal gear ring 13 away from the gearbox cover 20, so that the planetary gear carrier 61 is positioned inside the gearbox 10.

[0064] After the primary transmission gear assembly 40, the secondary 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 secondary transmission gear assembly 50, and the central axis of the secondary transmission gear assembly 50 coincides with the central axis of the planetary gear transmission assembly 60. The transmission combination relationship of this utility model is as follows: 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 planet gears 62, the four planet gears 62 mesh with the internal gear ring 13, and the four planet gears 62 revolve through meshing with the internal gear ring 13, thereby driving the planetary gear carrier 61 to rotate.

[0065] To ensure precise positioning between the gearbox cover 20 and the gearbox body 10, the gearbox cover 20 is provided with a positioning pin 23, and the gearbox body 10 is provided with a corresponding positioning pin hole 16. The positioning pin 23 engages with the positioning pin hole 16 to allow the gearbox cover 20 to cover the gearbox body 10 and seal the gear cavity 12. Specifically, the edges of the gearbox cover 20 and the gearbox body 10 can be nested together. To facilitate the connection with the positioning pin 23, this invention provides a positioning post within the gear cavity 12, with the positioning pin hole 16 positioned at the center of the positioning post.

[0066] In one embodiment, the gearbox cover 20 is provided with at least two locating pins 23, and the gearbox body 10 is provided with a matching number of locating pin holes 16. The two locating pins 23 are respectively located on opposite sides of the gearbox cover 20, thereby facilitating assembly stability. The illustration of this utility model shows a configuration with two locating pins 23, but in actual applications, the gearbox cover 20 is not limited to two locating pins 23; multiple locating pins 23 can also be evenly distributed along the edge of the gearbox cover 20.

[0067] The working principle of this utility model is as follows: the motor 30 drives the first gear 31 to rotate, the first gear 31 drives the second gear 41 to rotate through meshing, the second gear 41 drives the third gear 42 to rotate, the third gear 42 drives the fourth gear 51 to rotate through meshing, the fourth gear 51 drives the sun gear 52 to rotate, the sun gear 52 drives the four planet gears 62 to rotate through meshing, the four planet gears 62 revolve through meshing with the internal gear ring 13, driving the planet gear carrier 61 to rotate, the planet gear carrier 61 drives the output spline 63 to rotate, and finally outputs power.

[0068] The electronic parking brake actuator provided by this utility model proposes a separate positioning scheme for each stage of the gear transmission assembly. Through structural design, it improves the axial positioning accuracy, making the axial positioning accuracy entirely determined by the design accuracy. This ensures precise positioning and stable operation between each stage of the gear transmission assembly, thereby increasing product lifespan. At the same time, the separate positioning scheme of this utility model eliminates all shaft press-fitting processes, thereby reducing positioning deviations caused by press-fitting, simplifying the process, improving mass production quality, and solving the problem of noise caused by abnormal meshing between gears in existing products.

[0069] Although the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions. Those skilled in the art can make various changes in form and detail, including some simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. An electronic parking brake actuator, characterized in that, include: A gearbox housing, comprising a motor housing cavity and a gear cavity, wherein the gear cavity is located at the front end of the motor housing cavity and communicates with the motor housing cavity, wherein an internal gear ring is provided inside the gear cavity and an output spline hole is provided on the gearbox housing at the center position corresponding to the internal gear ring; A gearbox cover that covers the gearbox body and seals the gear cavity; An electric motor is assembled inside the motor housing cavity, the output shaft of the motor extends into the gear cavity, and a first gear is fixed on the output shaft of the motor; A primary transmission gear assembly includes a second gear and a third gear coaxially arranged. The second gear meshes with the first gear. The third gear is disposed on the lower end face of the second gear. A first limiting part that cooperates with the gearbox cover is provided at the center position of the upper end face of the second gear. A second limiting part extends downward from the center position of the third gear. The primary transmission gear assembly is limited between the gearbox cover and the gearbox body by the first limiting part and the second limiting part. The secondary transmission gear assembly includes a fourth gear and a sun gear arranged coaxially, wherein the fourth gear meshes with the third gear; A planetary gear transmission assembly includes a planet carrier, a plurality of planet gears, and an output spline. The plurality of planet gears are mounted on a first end face of the planet carrier, and the output spline is disposed on a second end face of the planet carrier. The first end face and the second end face are opposite sides of the planet carrier. The sun gear is located at the center of the plurality of planet gears and meshes with each of the plurality of planet gears. The output spline extends out of the gearbox body from the output spline hole. 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 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.

2. The electronic parking brake actuator according to claim 1, characterized in that, The first limiting part is an annular column, and the gearbox cover is provided with a corresponding positioning slot; or, the first limiting part is a positioning slot, and the gearbox cover is provided with a corresponding annular column; wherein, the annular column is inserted into the positioning slot to pre-position one end of the primary transmission gear assembly.

3. The electronic parking brake actuator according to claim 2, characterized in that, The second limiting part is a positioning shaft, and the gearbox body is correspondingly provided with a first positioning hole; wherein, by the positioning shaft cooperating with the first positioning hole, the other end of the first-stage transmission gear assembly is pre-positioned.

4. The electronic parking brake actuator according to claim 1, characterized in that, The primary transmission gear assembly also includes a central shaft passing through the second gear and the third gear, wherein the first limiting part and the second limiting part are the two ends of the central shaft.

5. The electronic parking brake actuator according to claim 1, characterized in that, The secondary transmission gear assembly also includes an annular positioning part disposed at the center of the fourth gear. The annular positioning part and the sun gear are disposed on opposite sides of the fourth gear. The gearbox cover is provided with a second positioning hole that cooperates with the annular positioning part.

6. The electronic parking brake actuator according to claim 5, characterized in that, The sun gear has a sun gear positioning hole at its center, and the planetary gear transmission assembly also includes a sun gear positioning shaft disposed on the planetary gear carrier. The sun gear positioning shaft is located at the center of the planetary gear carrier and is on the same side as the plurality of planet gears.

7. The electronic parking brake actuator according to claim 6, characterized in that, The sun gear positioning shaft is integrally stamped with the output spline and is also integrally coated with plastic with the sun gear; wherein, the output spline is made of powder metallurgy or other metal materials.

8. The electronic parking brake actuator according to claim 5, characterized in that, The annular positioning part is integrally injection molded with the fourth gear, and the sun gear is encased in plastic at the center of the fourth gear.

9. The electronic parking brake actuator according to claim 1, characterized in that, The sun gear is encased in plastic at the center of the fourth gear, and the fourth gear and the center of the sun gear are provided with a mounting slot. The gearbox cover is provided with a connecting shaft that matches the mounting slot.

10. The electronic parking brake actuator according to claim 1, characterized in that, The planetary gear carrier has an inwardly recessed step on its peripheral edge. The step is located on the side of the planetary gear carrier where the output spline is located. The gearbox body has a support flange located on the side of the internal gear ring away from the gearbox cover.

11. The electronic parking brake actuator according to claim 1, characterized in that, The gearbox cover is provided with a positioning pin, and the gearbox body is provided with a corresponding positioning pin hole. The positioning pin cooperates with the positioning pin hole so that the gearbox cover covers the gearbox body and seals the gear cavity.

12. The electronic parking brake actuator according to claim 11, characterized in that, The gearbox cover is provided with at least two positioning pins, and the gearbox body is provided with a matching number of positioning pin holes; wherein the two positioning pins are respectively located on opposite sides of the gearbox cover.

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