Patent Publication Number: US-2022235848-A1

Title: Transmission structure of coreless tubular motor

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention belongs to the technical field of motor devices, and particularly relates to a transmission structure of a coreless tubular motor. 
     BACKGROUND OF THE INVENTION 
     With the rapid development of the mechanical and electrical industry, motors have been widely used people&#39;s life at present. For example, as driving devices, tubular motors have the advantages of compact structure, large torque, low rotating speed and the like, so the tubular motors are increasingly used in products that use motors to realize lifting motion, such as roller shutters, sun shading systems and projection screens. Since the motor shafts of the tubular motors are too high in rotating speed, for ease of use, speed reducers are generally provided on the tubular motors, so that the rotating speed of the output shafts satisfies the requirements for normal use. Existing DC tubular motors are generally ordinary rare-earth or ferrite motors, that is, they have the structural characteristic that rotor cores and magnetic shoes are attached to the housing. The existing tubular rare-earth or ferrite motors have many deficiencies. For example, firstly, due to the large mass of the rotor cores, the rotors have slow response, high energy consumption and large vibration, resulting in a serious damage to components and limiting the service life of the whole machine. Then, the rotor cores will generate eddy current in the magnetic field, resulting in motor heating, high energy consumption and low efficiency. Secondly, since the magnetic shoes (permanent magnets) are fixed on the housing, the magnetic shoes (permanent magnets) must have a certain thickness. When the outer diameter of the motors is given, the outer diameter of the motor rotors will be greatly limited, and the output torque of the motors is thus greatly limited. In addition, the speed reducers of the existing tubular motors cannot satisfy the requirements in term of the speed reduction ratio and are not compact enough in structure and poor in stability during the transmission process. These problems have caused great inconvenience to the existing tubular motors when in use. 
     In order to solve the deficiencies in the prior art, long-term exploration has been conducted, and a variety of solutions have been proposed. For example, Chinese Parent Document disclosed a planetary reducer of a tubular motor [200720184522.7], including a sun gear, an inner toothed end cover, an inner toothed sleeve and an inner toothed sleeve seat, wherein the planetary reducer is internally provided with: a primary support main body, on which three support pins are provided, primary planetary gears being provided on the support pins, gears being provided at lower ends of the primary planetary gears; a secondary support main body, on which three support pins being provided on the secondary support main body, secondary planetary gears being provided on the support pins, gears being provided at lower ends of the support pins; and, a tertiary support main body, on which three support pins are provided, tertiary planetary gears being provided on the support pins, output shafts being provided at lower ends of the support pins. Although the above solution solves the problem that the speed reducers of the existing tubular motors cannot satisfy the requirements in terms of the speed reduction ratio to a certain extent, this solution still has many deficiencies of ordinary rare-earth or ferrite motor. Meanwhile, this solution still has other deficiencies such as poor transmission stability. 
     SUMMARY OF THE INVENTION 
     In view of the above problems, an objective of the present invention is to provide a transmission structure of a coreless tubular motor, which has rational structure and uses a coreless motor structure with high transmission stability. 
     In order to achieve the above objective, the present invention employs the following technical solutions. A transmission structure of a coreless tubular motor is provided, including a motor main body, the motor main body being connected to one end of a primary gear ring through a motor connecting seat, a motor shaft of the motor main body being connected to a primary planetary gear assembly provided in the primary gear ring, the other end of the primary gear ring being connected to a secondary/tertiary gear ring having a secondary planetary gear assembly and a tertiary planetary gear assembly, an input end of the tertiary planetary gear assembly being connected to an output end of the secondary planetary gear assembly while an output end thereof being connected to an output shaft, wherein the motor main body is a coreless motor; a brake driving member and a brake driven member which are coaxially provided are provided in and pass through the brake outer sleeve; the brake driving member is connected to an output end of the primary planetary gear assembly, the brake driven member is connected to an input end of the secondary planetary gear assembly, and the brake driving member is in transmission connection with the brake driven member; and, a braking assembly connected to the brake driving member and the brake driven member is provided on the inner side of the brake outer sleeve in the circumferential direction. 
     In the transmission structure of a coreless tubular motor, the braking assembly includes a brake mandrel which is provided in the brake outer sleeve through a circumferential positioning structure; a cylindrical brake drum is provided at one end of the brake mandrel, and a brake torsion spring is sleeved on the brake drum; the brake driving member is provided with two driving jaws, and one end of the brake driven member close to the brake driving member passes through the brake mandrel and is provided with two driven jaws; the driving jaws and the driven jaws are staggered one by one, and any one of the driving jaws is located on one side of any one of the driven jaws; and, a brake control structure, which can make the brake torsion spring expand in the circumferential direction and make the brake driven member rotate synchronously with the brake driving member in the same direction when the brake driving member rotates in the circumferential direction or can make the brake torsion spring contract in the circumferential direction and make the brake driven member stop in the circumferential direction when the brake driven member rotates in the circumferential direction, is provided between the driving jaws and the driven jaws. 
     In the transmission structure of a coreless tubular motor, the brake control structure includes bent legs which are formed at two ends of the brake torsion spring and bent outward in the radial direction; any one of the two driven jaws of the brake driven member is located between the two bent legs, and any one of the two bent legs is located between the driven jaws and the driving jaws; steps which extend outward in the widthwise direction of the driven jaws and are resisted against one side of the driving jaws are provided on two sides of one end of each of the driven jaws close to the brake driven member; and, gaps for allowing the bent legs to extend therein are formed between the outer side of ends of the driven jaws away from the steps and the driving jaws. 
     In the transmission structure of a coreless tubular motor, the distance between the two bent legs of the brake torsion spring in the center line direction of the brake torsion spring is greater than the width of ends of the driven jaws away from the steps. 
     In the transmission structure of a coreless tubular motor, the brake mandrel includes a mandrel ring coaxially connected to the brake drum; the mandrel ring and the brake drum are of an integral structure, and the inner circumferential side of the mandrel ring is communicated with the inner circumferential side of the brake drum to form a mandrel passage; the circumferential positioning structure includes a number of positioning slots formed on the inner circumferential side of one end of the brake outer sleeve; the positioning slots are arranged in the circumferential direction at uniform intervals and extend in the axial direction of the brake outer sleeve; a number of positioning lugs in one-to-one correspondence to the positioning slots are provided on the outer circumferential side of the mandrel ring; and, the positioning lugs are clamped into the positioning slots, respectively. 
     In the transmission structure of a coreless tubular motor, the motor main body includes a motor shell; a carbon brush set connected to a control circuit is provided at one end of the motor shell; a rotor carrier with the motor shaft is rotatably provided on the carbon brush set, and a coreless coil is provided on the motor shaft; a permanent magnet located on the inner circumferential side of the coreless coil is provided in the motor shell; and, the motor shaft passes through the permanent magnet and extends to the outer side of the motor shell. 
     In the transmission structure of a coreless tubular motor, the brake driving member includes a driving mandrel which is coaxially and rotatably provided on the inner circumferential side of one end of the brake outer sleeve through a first rotating bearing; a driving member connecting hole is formed at one end of the driving mandrel, while the other end thereof is coaxially connected to a driving ring; the driving jaws are correspondingly provided on the outer circumferential side of the driving ring, respectively; and, one end of the driving ring away from the driving mandrel is coaxially connected to a rotating drum. 
     In the transmission structure of a coreless tubular motor, the brake driven member includes a driven mandrel which is coaxially and rotatably provided on the inner circumferential side of one end of the brake outer sleeve away from the driving mandrel through a second rotating bearing; a driven member connecting hole is formed at one end of the driven mandrel, while the other end thereof passes through the mandrel passage and is coaxially connected to a driven drum; the driven jaws are correspondingly provided on the outer circumferential side of one end of the driven drum, respectively; a rotating hole for allowing the rotating drum to be inserted therein is provided at one end of the driven drum, while a limiting ring is provided at the other end thereof; and, an annular limiting step resisted against the limiting ring is provided on the inner circumferential side of the brake drum. 
     Specifically, herein, the primary planetary gear assembly includes a primary planetary carrier having a primary planetary output shaft provided at its one end and connected to the driving member connecting hole; three primary planetary roller needles are provided on the primary planetary carrier in the circumferential direction at uniform intervals; primary planetary gears are provided on the primary planetary roller needles; the primary planetary gears are distributed in the circumferential direction at uniform intervals and all connected to the motor shaft of the motor main body; a number of primary gear teeth meshed with the primary planetary gears are provided on the inner circumferential side of the primary gear ring; and, the primary gear teeth and the primary planetary gears are of helical tooth structures. The secondary planetary gear assembly includes a secondary planetary carrier having a secondary planetary output shaft provided at its one end; three secondary planetary roller needles are provide at the other end of the secondary planetary carrier; secondary planetary gears are provided on the secondary planetary roller needles; the secondary planetary gears are distributed in the circumferential direction at uniform intervals and all meshed with a secondary center gear connected to the driven member connecting hole; and, a number of secondary/tertiary gear teeth meshed with the secondary planetary gears are provided on the inner circumferential side of the secondary/tertiary gear ring. The tertiary planetary gear assembly includes a tertiary planetary carrier having an output shaft provided at its one end; three tertiary planetary roller needles are provided at the other end of the tertiary planetary carrier in the circumferential direction at uniform intervals; tertiary planetary gears are provided on the tertiary planetary roller needles; the tertiary planetary gears are distributed in the circumferential direction at uniform intervals and all meshed with a small gear on the secondary planetary output shaft; and, secondary/tertiary gear teeth on the inner circumferential side of the secondary/tertiary gear ring are meshed with the tertiary planetary gears, respectively. 
     In the transmission structure of a coreless tubular motor, the brake outer sleeve is provided between the primary gear ring and the secondary/tertiary gear ring through a circumferential fixation structure. 
     In the transmission structure of a coreless tubular motor, the circumferential fixation structure includes a first concave-convex positioning assembly provided on the outer circumferential side of one end of the brake outer sleeve; a first concave-convex mating assembly corresponding to the first concave-convex positioning assembly is provided on the inner circumferential side of one end of the primary gear ring; the first concave-convex positioning assembly and the first concave-convex mating assembly are mutually clamped and positioned in the circumferential direction; a second concave-convex positioning assembly is provided on the outer circumferential side of the other end of the brake outer sleeve; a second concave-convex mating assembly corresponding to the second concave-convex positioning assembly is provided on the inner circumferential side of the secondary/tertiary gear ring; and, the second concave-convex positioning assembly and the second concave-convex mating assembly are mutually clamped and positioned in the circumferential direction. 
     Compared with the prior art, the present invention has the following advantages. 
     1. Since the rotor core structure is omitted, the coreless motor has no cogging effect and will not generate eddy current, thereby reducing heat generation, reducing energy consumption and improving efficiency. Moreover, since there is no rotor core, the mass of the whole rotor is greatly reduced, so that the response speed is greatly increased and the vibration is greatly weakened when the rotor starts or stops, and the service life of the whole machine is prolonged. 
     2. The permanent magnet is arranged inside the rotor core, so the radius of the rotor is increased when the outer diameter of the motor remains unchanged, and the output torque of the motor is thus increased. 
     3. The transmission between the primary planetary gear assembly and the secondary/tertiary planetary gear assembly is realized by the driving jaws and driven jaws, and the brake driving member and the brake driven member each have two corners and are resisted against each other, so that the transmission stability is improved, the speed reduction ratio is large, the layout of components is rational, and the structure is compact. 
     4. By making the brake torsion spring be in interference fit with the brake mandrel, the braking process is realized by the deformation of the torsion spring, thereby achieving good braking effect of the brake and high braking sensitivity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structure diagram of the present invention; 
         FIG. 2  is a sectional view of the present invention; 
         FIG. 3  is an exploded view of the present invention when the motor main body is not mounted; 
         FIG. 4  is an exploded view of the present invention from another perspective when the motor main body is not mounted in the present invention; 
         FIG. 5  is an exploded view of the present invention when each planetary gear assembly is connected; 
         FIG. 6  is an exploded view of the present invention from another perspective when each planetary gear assembly is connected; 
         FIG. 7  is a partially exploded view of the present invention; 
         FIG. 8  is a partially exploded view of the present invention from another perspective; and 
         FIG. 9  is a schematic structure diagram of a braking process in the present invention; 
     
    
    
     in which:  1 : primary gear ring;  2 : primary planetary gear assembly;  21 : primary planetary carrier;  211 : primary planetary output shaft;  22 : primary planetary roller needle;  23 : primary planetary gear;  24 : primary gear tooth;  3 : secondary/tertiary gear ring;  4 : secondary planetary gear assembly;  41 : secondary planetary carrier;  411 : secondary planetary output shaft;  42 : secondary planetary roller needle;  43 : secondary planetary gear;  44 : secondary center gear;  45 : secondary/tertiary gear tooth;  5 : tertiary planetary gear assembly;  51 : tertiary planetary carrier;  52 : tertiary planetary roller needle;  53 : tertiary planetary gear;  6 : output shaft;  7 : circumferential fixation structure;  71 : first concave-convex positioning assembly;  72 : first concave-convex mating assembly;  73 : second concave-convex positioning assembly;  74 : second concave-convex mating assembly;  8 : brake outer sleeve;  81 : brake driving member;  811 : driving jaw;  812 : driving mandrel;  8121 : driving member connecting hole;  813 : driving ring;  814 : rotating drum;  815 : first rotating bearing;  82 : brake driven member;  821 : driven jaw;  821   a : step;  821   b : gap;  822 : driven mandrel;  8221 : driven member connecting hole;  823 : driven drum;  824 : rotating hole;  825 : limiting ring;  826 : annular limiting step;  827 : second rotating bearing;  83 : brake mandrel;  831 : brake drum;  832 : mandrel ring;  833 : mandrel passage;  84 : brake torsion spring;  841 : bent leg;  85 : positioning slot;  86 : positioning lug;  9 : motor main body;  91 : motor connecting seat;  92 : motor shaft;  93 : motor shell;  931 : carbon brush set;  932 : rotor carrier;  933 : coreless coil; and,  934 : permanent magnet. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be further described below in detail by specific implementations with reference to the accompanying drawings. 
     As shown in  FIGS. 1 and 3-9 , the transmission structure of a hollow tubular motor includes a motor main body  9 . The motor main body  9  is connected to one end of a primary gear ring  1  through a motor connecting seat  91 , and a motor shaft  92  of the motor main body  9  is connected to a primary planetary gear assembly  2  provided in the primary gear ring  1 . The other end of the primary gear ring  1  is connected to a secondary/tertiary gear ring  3  having a secondary planetary gear assembly  4  and a tertiary planetary gear assembly  5 . An input end of the tertiary planetary gear assembly  5  is connected to an output end of the secondary planetary gear assembly  4 , while an output end thereof is connected to an output shaft  6 . The motor main body  9  is a coreless motor. A brake driving member  81  and a brake driven member  82  which are coaxially provided are provided in and pass through the brake outer sleeve  8 . The brake driving member  81  is connected to an output end of the primary planetary gear assembly  2 , the brake driven member  82  is connected to an input end of the secondary planetary gear assembly  4 , and the brake driving member  81  is in transmission connection with the brake driven member  82 . A braking assembly connected to the brake driving member  81  and the brake driven member  82  is provided on the inner side of the brake outer sleeve  8  in the circumferential direction. 
     Since the rotor core structure is omitted in the motor main body  9 , the coreless motor has no cogging effect and will not generate eddy current, thereby reducing heat generation, reducing energy consumption and improving efficiency. Moreover, since there is no rotor core, the mass of the whole rotor is greatly reduced, so that the response speed is greatly increased and the vibration is greatly weakened when the rotor starts or stops, and the service life of the whole machine is prolonged. Meanwhile, the permanent magnet  934  is arranged inside the rotor core, so the radius of the rotor is increased when the outer diameter of the motor remains unchanged, and the output torque of the motor is increased. 
     In this embodiment, the braking assembly includes a brake mandrel  83  which is provided in the brake outer sleeve  8  through a circumferential positioning structure. A cylindrical brake drum  831  is provided at one end of the brake mandrel  83 , and a brake torsion spring  84  is sleeved on the brake drum  831 . The brake driving member  81  is provided with two driving jaws  821 , and one end of the brake driven member  82  close to the brake driving member  81  passes through the brake mandrel  83  and is provided with two driven jaws  821 . The driving jaws  811  and the driven jaws  821  are staggered one by one, and any one of the driving jaws  811  is located on one side of any one of the driven jaws  821 . A brake control structure, which can make the brake torsion spring  84  expand in the circumferential direction and make the brake driven member  82  rotate synchronously with the brake driving member  81  in the same direction when the brake driving member  81  rotates in the circumferential direction or can make the brake torsion spring  84  contract in the circumferential direction and make the brake driven member  82  stop in the circumferential direction when the brake driven member  82  rotates in the circumferential direction, is provided between the driving jaws  811  and the driven jaws  821 . 
     Specifically, herein, the brake control structure includes bent legs  841  which are formed at two ends of the brake torsion spring  84  and bent outward in the radial direction. Any one of the two driven jaws  821  of the brake driven member  82  is located between the two bent legs  841 , and any one of the two bent legs  841  is located between the driven jaws  821  and the driving jaws  811 . Steps  821   a  which extend outward in the widthwise direction of the driven jaws  821  and are resisted against one side of the driving jaws  811  are provided on two sides of one end of each of the driven jaws  821  close to the brake driven member  82 . Gaps  821   b  for allowing the bent legs  841  to extend therein are formed between the outer side of ends of the driven jaws  821   a  away from the steps and the driving jaws  821 . Herein, the distance between the two bent legs  841  of the brake torsion spring  84  in the center line direction of the brake torsion spring  84  is greater than the width of ends of the driven jaws  821  away from the steps  821   a.    
     Preferably, herein, the brake mandrel  83  includes a mandrel ring  832  coaxially connected to the brake drum  831 . The mandrel ring  832  and the brake drum  831  are of an integral structure, and the inner circumferential side of the mandrel ring  832  is communicated with the inner circumferential side of the brake drum  831  to form a mandrel passage  833 . The circumferential positioning structure includes a number of positioning slots  85  formed on the inner circumferential side of one end of the brake outer sleeve  8 . The positioning slots  85  are arranged in the circumferential direction at uniform intervals and extend in the axial direction of the brake outer sleeve  8 . A number of positioning lugs  86  in one-to-one correspondence to the positioning slots  85  are provided on the outer circumferential side of the mandrel ring  832 . The positioning lugs  86  are clamped into the positioning slots  85 , respectively. 
     The primary planetary gear assembly  2  is transmitted to the secondary planetary gear assembly  4  through the driving jaws  811  and the driven jaws  821  and then connected to the output shaft  6  through the tertiary planetary gear assembly  5 , so that the transmission stability is improved. Meanwhile, a brake mandrel  83  can be provided in the brake outer sleeve  8 , a brake torsion spring  84  is sleeved on the brake mandrel  83 , and the brake torsion spring  84  acts on the driving jaws  811  and the driven jaws  821 , respectively, so that the purpose of providing a brake between the primary planetary gear assembly and the secondary and tertiary planetary gear assemblies is achieved. 
     Specifically, as shown in  FIG. 9 , no manner when the brake driving member  81  rotates forward or backward in the circumferential direction, the driving jaws  811  are driven to rotate together. The driving jaws  811  first come into contact with one bend leg  841  of the brake torsion spring  84 . When the driving jaws  811  push the bent legs  841 , the brake torsion spring  84  expands in the circumferential direction, so that the inner diameter of the brake torsion spring  84  becomes larger, and the brake torsion spring  84  is separated from the brake mandrel  83 . When the driving jaws  811  continuously rotates to drive the bent legs  841  to move in the gaps  821   b , the inner diameter of the brake torsion spring  84  further becomes larger until one side of the driving jaws  811  is resisted against the steps  821   a  of the driven jaws  821 , so that the driving jaws  811  drive the driven jaws  821  to rotate synchronously when the brake torsion spring  841  is in an expanded state, and the power is transferred to a next stage. No matter when the brake driven member  82  rotates forward or backward in the circumferential direction, the driven jaws  821  are driven to rotate together. Before the steps  821   a  of the driven jaws  821  do not come into with the driving jaws  811 , the driven jaws  821  first make the inner diameter of the brake torsion spring  84  become smaller, so that the brake torsion spring  84  is tightly clung to the brake mandrel  83 , and a large friction is generated between the brake torsion spring  84  and the brake mandrel  83 . Thus, the whole braking process is realized, and the power will not be transferred to the brake driving member  81 . 
     For the brake part in this embodiment, the brake mandrel  83  and the brake outer sleeve  8  are fixed. The brake torsion spring  84  is in interference fit with the brake mandrel  83 , and the brake driving member  81  and the brake driven member  82  each have two corners. During rotation, the torque of the motor shaft  92  is transferred to the brake driving member through the primary planetary gear assembly  2 . Regardless of clockwise rotation or counterclockwise rotation, the brake driving member  81  will make the inner diameter of the brake torsion spring  84  larger, so that the brake torsion spring  84  is separated from the brake mandrel  83 , and the torque is transferred to the driven member  82 , then transferred to the secondary planetary gear assembly  4  and the tertiary planetary gear assembly  5  and finally transferred out by the output shaft  6 . When the torque is transferred from the output shaft  6  to the secondary planetary gear assembly  4  and the tertiary planetary gear assembly  5  and then to the brake driven member  82 , regardless of clockwise rotation or counterclockwise rotation, the brake driven member  82  will make the inner diameter of the brake torsion spring  84  smaller, so that the brake torsion spring  84  is tightly clung to the brake mandrel  83 , and a large friction is generated between the brake torsion spring  84  and the brake mandrel  83 . Moreover, since the brake mandrel  83  is fixed, the torque cannot be transferred to the primary planetary gear assembly  2 , thereby realizing the braking effect. 
     As shown in  FIG. 2 , the motor main body  9  includes a motor shell  93 . A carbon brush set  931  connected to a control circuit is provided at one end of the motor shell  93 . A rotor carrier  932  with the motor shaft  92  is rotatably provided on the carbon brush set  931 , and a coreless coil  933  is provided on the motor shaft  92 . A permanent magnet  934  located on the inner circumferential side of the coreless coil  933  is provided in the motor shell  93 . The motor shaft  92  passes through the permanent magnet  934  and extends to the outer side of the motor shell  93 . 
     As shown in  FIGS. 1 and 3-8 , specifically, in this embodiment, the brake driving member  81  includes a driving mandrel  812  which is coaxially and rotatably provided on the inner circumferential side of one end of the brake outer sleeve  8  through a first rotating bearing  815 . A driving member connecting hole  8121  is formed at one end of the driving mandrel  812 , while the other end thereof is coaxially connected to a driving ring  813 . The driving jaws  811  are correspondingly provided on the outer circumferential side of the driving ring  813 , respectively. One end of the driving ring  813  away from the driving mandrel  812  is coaxially connected to a rotating drum  814 . 
     Herein, the brake driven member  82  includes a driven mandrel  822  which is coaxially and rotatably provided on the inner circumferential side of one end of the brake outer sleeve  8  away from the driving mandrel  812  through a second rotating bearing  827 . A driven member connecting hole  8221  is formed at one end of the driven mandrel  822 , while the other end thereof passes through the mandrel passage  833  and is coaxially connected to a driven drum  823 . The driven jaws  821  are correspondingly provided on the outer circumferential side of one end of the driven drum  823 , respectively. A rotating hole  824  for allowing the rotating drum  814  to be inserted therein is provided at one end of the driven drum  823 , while a limiting ring  825  is provided at the other end thereof. An annular limiting step  826  resisted against the limiting ring  825  is provided on the inner circumferential side of the brake drum  831 . 
     Further, herein, the primary planetary gear assembly  2  includes a primary planetary carrier  21  having a primary planetary output shaft  211  provided at its one end and connected to the driving member connecting hole  8121 . Three primary planetary roller needles  22  are provided on the primary planetary carrier  21  in the circumferential direction at uniform intervals. Primary planetary gears  23  are provided on the primary planetary roller needles  22 , and the primary planetary gears  23  are distributed in the circumferential direction at uniform intervals and all connected to the motor shaft of the motor main body. A number of primary gear teeth  24  meshed with the primary planetary gears  23  are provided on the inner circumferential side of the primary gear ring  1 . The primary gear teeth  24  and the primary planetary gears  23  are of helical tooth structures. 
     Similarly, the secondary planetary gear assembly  4  includes a secondary planetary carrier  41  having a secondary planetary output shaft  411  provided at its one end. Three secondary planetary roller needles  42  are provide at the other end of the secondary planetary carrier  41 . Secondary planetary gears  43  are provided on the secondary planetary roller needles  42 . The secondary planetary gears  43  are distributed in the circumferential direction at uniform intervals and all meshed with a secondary center gear  44  connected to the driven member connecting hole  8221 . A number of secondary/tertiary gear teeth  45  meshed with the secondary planetary gears  43  are provided on the inner circumferential side of the secondary/tertiary gear ring  3 . Herein, the tertiary planetary gear assembly  5  includes a tertiary planetary carrier  51  having an output shaft  6  provided at its one end. Three tertiary planetary roller needles  52  are provided at the other end of the tertiary planetary carrier  51  in the circumferential direction at uniform intervals. Tertiary planetary gears  53  are provided on the tertiary planetary roller needles  52 . The tertiary planetary gears  53  are distributed in the circumferential direction at uniform intervals and all meshed with a small gear on the secondary planetary output shaft  411 . Secondary/tertiary gear teeth  45  on the inner circumferential side of the secondary/tertiary gear ring  3  are meshed with the tertiary planetary gears  53 , respectively. 
     In order to position the primary gear ring  1  and the secondary/tertiary gear ring  3  at two ends of the brake outer sleeve  8 , herein, the brake outer sleeve  8  is provided between the primary gear ring  1  and the secondary/tertiary gear ring  3  through a circumferential fixation structure  7 . Preferably, the circumferential fixation structure  7  includes a first concave-convex positioning assembly  71  provided on the outer circumferential side of one end of the brake outer sleeve  8 . A first concave-convex mating assembly  72  corresponding to the first concave-convex positioning assembly  71  is provided on the inner circumferential side of one end of the primary gear ring  1 . The first concave-convex positioning assembly  71  and the first concave-convex mating assembly  72  are mutually clamped and positioned in the circumferential direction. A second concave-convex positioning assembly  73  is provided on the outer circumferential side of the other end of the brake outer sleeve  8 . A second concave-convex mating assembly  74  corresponding to the second concave-convex positioning assembly  73  is provided on the inner circumferential side of the secondary/tertiary gear ring  3 . The second concave-convex positioning assembly  73  and the second concave-convex mating assembly  74  are mutually clamped and positioned in the circumferential direction. Preferably, herein, all the first concave-convex positioning assembly  71 , the first concave-convex mating assembly  72 , the second concave-convex positioning assembly  73  and the second concave-convex mating assembly  74  can be of positioning teeth structures, so that circumferential positioning is realized by inserting teeth into each other. 
     The specific embodiments described herein are merely for illustrating the spirit of the present invention. Those skilled in the art can make various modifications or supplements to the specific embodiments described herein or replace the specific embodiments described herein in a similar way, without departing from the spirit of the present invention or the scope defined by the appended claims. 
     Although the terms such as the primary gear ring  1 , the primary planetary gear assembly  2 , the primary planetary carrier  21 , the primary planetary output shaft  211 , the primary planetary roller needle  22 , the primary planetary gear  23 , the primary gear tooth  24 , the secondary/tertiary gear ring  3 , the secondary planetary gear assembly  4 , the secondary planetary carrier  41 , the secondary planetary output shaft  411 , the secondary planetary roller needle  42 , the secondary planetary gear  43 , the secondary center gear  44 , the secondary/tertiary gear tooth  45 , the tertiary planetary gear assembly  5 , the tertiary planetary carrier  51 , the tertiary planetary roller needle  52 , the tertiary planetary gear  53 , the output shaft  6 , the circumferential fixation structure  7 , the first concave-convex positioning assembly  71 , the first concave-convex mating assembly  72 , the second concave-convex positioning assembly  73 , the second concave-convex mating assembly  74 , the brake outer sleeve  8 , the brake driving member  81 , the driving jaw  811 , the driving mandrel  812 , the driving member connecting hole  8121 , the driving ring  813 , the rotating drum  814 , the first rotating bearing  815 , the brake driven member  82 , the driven jaw  821 , the step  812   a , the gap  812   b , the driven mandrel  822 , the driven member connecting hole  8221 , the driven drum  823 , the rotating hole  824 , the limiting ring  825 , the annular limiting step  826 , the second rotating bearing  827 , the brake mandrel  83 , the brake drum  831 , the mandrel ring  832 , the mandrel passage  833 , the brake torsion spring  84 , the bent leg  841 , the positioning slot  85 , the positioning lug  86 , the motor main body  9 , the motor connecting seat  91 , the motor shaft  92 , the motor shell  93 , the carbon brush set  931 , the rotor carrier  932 , the coreless coil  933  and the permanent magnet  934  are frequently used herein, the possibility of using other terms is not excluded. These terms are merely used to describe and explain the essence of the present invention more conveniently, and the interpretation of the terms into any additional limitations shall be deviated from the spirit of the present invention.