Coupling structure of wheel-side driving box vehicle body rack and transmission system supporting piece

Abstract

A coupling structure of a wheel-side driving box vehicle body rack and a transmission system supporting piece comprises a first coupling unit for fixedly connecting a second-stage planet wheel shaft with the rack, and further comprises a second coupling unit for fixedly connecting a first-stage inner gear ring with a second-stage planet carrier. According to the coupling structure of the wheel-side driving box vehicle body rack and the transmission system supporting piece, a stable whole is formed through design cooperation of the first coupling unit and the second coupling unit, the structure is compact, the overall structural strength is improved, and meanwhile a planetary unit can operate stably; all parts are simple in structure and convenient to machine and assemble. And meanwhile, through mutual matching of a limiting boss and a groove, axial rotation of the second-stage planet wheel shaft is limited, and the lubricating through hole is located below all the time.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the wheel edge drive technical field, concretely relates to a wheel edge drive box vehicle body frame and transmission system support coupling structure. BACKGROUND

[0002] The mine transport vehicle has the characteristics of heavy load, strong power and high efficiency, and becomes the main transport equipment of open pit mining. The wheel edge drive device is one of the core parts of the electric drive transport vehicle, which provides power for the vehicle, reduces speed and increases torque, and also bears the weight load of the whole vehicle. Therefore, the reliability of the wheel edge drive device in the use process is an important symbol to measure the performance of the product. The working condition of the mine transport vehicle is often complex and changeable. With the trend of large-scale load, good structure design is the key to improve the reliability of the wheel edge drive device.

[0003] At present, the structure design of the wheel edge drive device generally has the problem of complex part structure, which will lead to difficult machining and assembly, poor load distribution effect, and further affect the service life of the gear. The rack is the load-bearing main body of the wheel edge drive device, and most parts are directly or indirectly connected to the rack. The rack and its matching parts need to be designed in the direction of simple structure, stable load effect and good structural stiffness to provide stable support for the planetary gear train and the whole vehicle, to enhance the structural strength of the whole drive device system and improve the reliability. SUMMARY

[0004] In view of the above problems, the utility model aims at providing a wheel edge drive box vehicle body frame and transmission system support coupling structure, based on the design of a two-stage NGW planetary structure wheel edge drive device developed by the application team, to solve the problems of load distribution performance and support performance of each stage of planetary gear set, and the problem of complex part structure

[0005] To achieve the above purpose, the technical scheme adopted by the utility model comprises:

[0006] A wheel edge drive box vehicle body frame and transmission system support coupling structure, comprising a first coupling unit for connecting the two-stage planetary gear shaft and the rack, and a second coupling unit for connecting the first-stage inner tooth ring and the two-stage planetary carrier.

[0007] Preferably, the first coupling unit comprises a convex part arranged at the inner end of the two-stage planetary gear shaft, a concave part matched with the convex part structure at the outer end of the rack, and a first fixed shaft axially passing through the inner cavity of the two-stage planetary gear shaft, the convex part and the inner cavity of the rack in sequence.

[0008] Preferably, the first coupling unit comprises a limiting blind hole coaxial with the inner hole of the second planetary gear shaft at the outer end of the frame, further comprises a limiting pin penetrating into the inner hole of the second planetary gear shaft and the limiting blind hole in sequence, and further comprises a second fixed shaft penetrating into the limiting pin and the frame in sequence.

[0009] Preferably, the first coupling unit comprises a baffle fixed at the outer end of the second planetary gear shaft, the baffle covers the outer port of the inner cavity of the second planetary gear shaft, and the third fixed shaft penetrates through the baffle and the inner cavity of the second planetary gear shaft and the frame in sequence.

[0010] Preferably, the first coupling unit further comprises a limiting boss arranged at the outer end of the second planetary gear shaft, and the second planetary carrier is provided with a groove matched with the limiting boss in structure.

[0011] Preferably, the second coupling unit comprises a first through hole and a first blind hole respectively arranged at the first inner ring gear and the second planetary carrier in a radial direction, the first through hole and the first blind hole are coaxial and have the same diameter, the second coupling unit further comprises a limiting column penetrating into the first through hole and the first blind hole in sequence and in interference fit with the first through hole and the first blind hole, and the second coupling unit further comprises a limiting plate fixedly arranged and covering the outer port of the first through hole.

[0012] Preferably, the second coupling unit comprises a second through hole and a second blind hole respectively arranged at the second planetary carrier and the first inner ring gear in parallel to the axis, the second through hole and the second blind hole are coaxial and have the same diameter, and the second coupling unit further comprises a fourth fixed shaft penetrating into the second through hole and the second blind hole in sequence.

[0013] Compared with the prior art, the advantages of the utility model are:

[0014] (1) The wheel drive box vehicle body frame and transmission system support coupling structure of the utility model forms a stable whole through the design and cooperation of the first coupling unit and the second coupling unit, has compact structure, increases the structural strength of the whole, and can stabilize the operation of the planetary unit.

[0015] (2) The wheel drive box vehicle body frame and transmission system support coupling structure of the utility model limits the rotation of the second planetary gear shaft around the axis through the cooperation of the limiting boss and the groove, and makes the lubricating through hole always be at the lower side. BRIEF DESCRIPTION OF DRAWINGS

[0016] The drawings are used to provide further understanding of the present application, and constitute a part of the specification, and are used to explain the present application together with the following specific embodiments, but do not constitute the limitation to the present application. In the drawings:

[0017] Figure 1 It is a structure schematic view of a two-stage NGW planetary structure wheel drive device of example 1.

[0018] Figure 2 for Figure 1 Schematic diagram of the structure of the first-level planetary unit;

[0019] Figure 3 for Figure 1 Schematic diagram of the structure of the secondary planetary unit;

[0020] Figure 4 for Figure 1 Schematic diagram of the intermediate-level planetary carrier;

[0021] Figure 5 for Figure 1 Schematic diagram of the secondary planetary support structure;

[0022] Figure 6 This is a schematic diagram of the structure of the first coupling unit in Embodiment 2;

[0023] Figure 7 This is a schematic diagram of the structure of the first coupling unit in Embodiment 3;

[0024] Figure 8 This is a schematic diagram of the structure of the first coupling unit in Embodiment 4;

[0025] Figure 9 This is a schematic diagram of the structure of the second coupling unit in Embodiment 2;

[0026] Figure 10 This is a schematic diagram of the structure of the second coupling unit in Example 5.

[0027] The labels in the diagram represent:

[0028] a is the first coupling unit, b is the second coupling unit;

[0029] a1 convex part, a2 concave part, a3 first fixed shaft, a4 limiting boss, a5 groove, a6 limiting blind hole, a7 limiting pin, a8 second fixed shaft, a9 third fixed shaft, a10 baffle.

[0030] b1 First through hole, b2 First blind hole, b3 Limiting post, b4 Limiting plate, b5 Second through hole, b6 Second blind hole, b7 Fourth fixed shaft.

[0031] 0 Hub, 1 Motor, 1-1 Power Output Shaft; 2 Frame, 3 First-level Planetary Unit, 4 Second-level Planetary Unit, 5 Sealing Tube, 6 Third Bearing, 7 Fourth Bearing, 8 Pressure Ring, 8-1 Connecting Shaft, 9 Floating Sealing Mechanism, 10 End Cover, 11 Bearing Spacer, 12 Stop Ring.

[0032] 3-0 primary planetary carrier, 3-01 first inner hole, 3-02 second inner hole; 3-1 primary sun shaft, 3-10 primary sun gear; 3-2 primary planetary unit, 3-21 primary planetary gear shaft, 3-22 first bearing, 3-23 primary planetary gear; 3-3 primary inner ring gear;

[0033] 4-0 secondary planetary carrier, 4-01 third inner hole; 4-1 secondary sun shaft; 4-2 secondary planetary unit, 4-21 secondary planetary gear shaft, 4-210 lubrication through hole, 4-22 second bearing, 4-23 secondary planetary gear; 4-3 secondary inner ring gear. DETAILED DESCRIPTION

[0034] The application is not limited to the following specific embodiments, and any equivalent variations made on the basis of the technical solutions of the application fall within the protection scope of the application.

[0035] It should be noted that the directional terms mentioned herein, such as "inner cavity", "inner periphery", "inner wall" and "outer side", are consistent with the specific directions on the paper of the drawings or the corresponding directions of the space shown in the drawings; all components and devices in the application, unless otherwise specified, all use components and devices known in the prior art.

[0036] Example 1

[0037] The application discloses the application object of the coupling structure of the application, based on a two-stage NGW planetary structure wheel edge driving device, which comprises a rack 2 coaxially arranged in a hub 0, and further comprises a motor 1 arranged on the inner side of the rack 2, a power output shaft 1-1 of the motor 1 is coaxially connected with a primary planetary unit 3, and the primary planetary unit 3 is located on the outer side of the rack 2; a secondary planetary unit 4 is coaxially arranged between the primary planetary unit 3 and the rack 2, and the primary planetary unit 3 and the secondary planetary unit 4 and the hub 0 are all in engagement transmission; the motor 1 outputs power, and the power is sequentially transmitted to the primary planetary unit 3 and the secondary planetary unit 4 to drive the hub 0 to rotate relative to the rack 2, so that the whole device can output large torque, the deformation of the inner ring gear is eliminated or reduced, the torsion tube is cancelled, the risk points of failure are reduced, the transmission stability and load sharing are improved; at the same time, unnecessary connecting parts are reduced, the structure is compact, the system stiffness is improved, and the load sharing effect of the planetary unit is improved.

[0038] The motor 1 power output shaft 1-1 and the rack 2 are coaxially connected with a sealing pipe 5, the inner side of the sealing pipe 5 extrudes a first rubber sealing ring located in the groove on the outer side of the motor 1, the flange on the outer side of the sealing pipe 5 is fixedly connected with the rack 2 through bolts, and the second rubber sealing ring is arranged at the groove on the outer side of the sealing pipe 5 and matched with the rack 2.

[0039] The first planetary unit 3 comprises a first planetary carrier 3-0, a first sun shaft 3-1, a first planetary unit 3-2 and a first inner gear ring 3-3. The first sun shaft 3-1 is coaxially connected with the power output shaft 1-1, and the free end of the first sun shaft 3-1 extends to the outside of the frame 2. The outer periphery of the free end of the first sun shaft 3-1 is provided with a first sun gear 3-10. The first planetary carrier 3-0 is coaxially sleeved on the outer periphery of the first sun gear 3-10. The first planetary unit 3-2 is arranged in the first planetary carrier 3-0 and meshes with the first sun gear 3-10. The first inner gear ring 3-3 is coaxially sleeved on the outer periphery of the first planetary carrier 3-0 and meshes with the first planetary unit 3-2. The first planetary carrier 3-0 meshes with the second planetary unit 4, and the first inner gear ring 3-3 is always fixed.

[0040] The first planetary unit 3-2 comprises three first planetary shafts 3-21 which are uniformly fixed in the first planetary carrier 3-0. The axis of the first planetary shaft 3-21 is parallel to the axis of the power output shaft 1-1. The outer periphery of any first planetary shaft 3-21 is coaxially sleeved with a first planetary gear 3-23. Any first planetary shaft 3-21 is provided with a first bearing 3-22 between the first planetary shaft 3-21 and the first planetary gear 3-23. Each first planetary gear 3-23 meshes with the first sun gear 3-10. The first planetary carrier 3-0 is provided with a plurality of first inner holes 3-01. The inner wall of any first inner hole 3-01 to the outer wall of the first planetary carrier 3-0 is provided with a second inner hole 3-02. Each first planetary shaft 3-21 is coaxially inserted into each first inner hole 3-01 and is fixed by being screwed into the second inner hole 3-02 to limit each first planetary shaft 3-21.

[0041] The second planetary unit 4 comprises a second planetary carrier 4-0, a second sun shaft 4-1, a second planetary unit 4-2 and a second inner gear ring 4-3. The second sun shaft 4-1 is coaxially sleeved on the outer periphery of the first sun shaft 3-1 located on the inner side of the first sun gear 3-10. The second sun shaft 4-1 does not contact the first sun shaft 3-1, and the second sun shaft 4-1 meshes with the first planetary carrier 3-0. The second planetary carrier 4-0 is coaxially sleeved on the outer periphery of the second sun shaft 4-1. The second planetary unit 4-2 is arranged in the second planetary carrier 4-0 and meshes with the second sun shaft 4-1. The second inner gear ring 4-3 is coaxially sleeved on the outer periphery of the second planetary carrier 4-0 and meshes with the second planetary unit 4-2. The second inner gear ring 4-3 is connected with the hub 0. The two sides of the second planetary carrier 4-0 are respectively fixedly connected with the frame 2 and the first inner gear ring 3-3. The second planetary unit 4 as a whole adopts the floating mode of the second inner gear ring 4-3 and the fixed mode of the second planetary carrier 4-0. The support rigidity of the second planetary carrier 4-0 to the second planetary unit 4-2 is increased, and the meshing precision is improved.

[0042] The two-stage planetary unit 4-2 of the embodiment comprises five two-stage planetary shafts 4-21 evenly arranged in the two-stage planetary carrier 4-0 in the circumferential direction, the axis of the two-stage planetary shaft 4-21 is parallel to the axis of the power output shaft 1-1; a two-stage planetary gear 4-23 is coaxially arranged on the outer periphery of any two-stage planetary shaft 4-21, a second bearing 4-22 is arranged between any two-stage planetary shaft 4-21 and the two-stage planetary gear 4-23, and each two-stage planetary gear 4-23 is engaged with the two-stage sun shaft 4-1. The two-stage planetary carrier 4-0 is provided with a plurality of third inner holes 4-01, and each two-stage planetary shaft 4-21 is installed and fixed to the two-stage planetary carrier 4-0 by penetrating the third inner hole 4-01.

[0043] The transmission process of the first-stage planetary unit 3 and the two-stage planetary unit 4 in the embodiment is as follows:

[0044] The motor 1 outputs power to drive the first-stage sun shaft 3-1 to rotate along its axis, which synchronously drives the first-stage sun gear 3-10 to rotate. Since the first-stage inner ring gear 3-3 is always fixed, the first-stage sun gear 3-10 gears with each first-stage planetary gear 3-23 to rotate and revolve, and the revolution of each first-stage planetary gear 3-23 drives the first-stage planetary carrier 3-0 to rotate along its axis, thereby driving the two-stage sun shaft 4-1. Since the two-stage planetary carrier 4-0 is always fixed, the two-stage sun shaft 4-1 rotates along its axis to drive each two-stage planetary gear 4-23 to rotate, thereby driving the two-stage inner ring gear 4-3 to rotate along its axis, and finally driving the wheel hub 0 to rotate relative to the frame 2, outputting a large overall torque, eliminating or reducing the deformation of the inner ring gear, canceling the torsion tube, reducing the risk of failure, improving the transmission stability and load sharing, and prolonging the service life of the gears.

[0045] In actual working conditions, the two-stage planetary unit 4 is immersed in oil below the line, and since the two-stage planetary carrier 4-0 is always fixed, the lubrication performance of the two-stage planetary shaft 4-21, the two-stage planetary gear 4-23 and the second bearing 4-22 above the oil surface is poor. The actual two-stage planetary carrier 4-0 disclosed in the embodiment is provided with an oil collecting groove on the outside, the two-stage planetary shaft 4-21 is hollow, at least the inner cavity of the two-stage planetary shaft 4-21 above the oil surface is communicated with the oil collecting groove, and the side wall of the two-stage planetary shaft 4-21 is provided with a lubricating through hole 4-210 communicated with the inner cavity. During the transmission process, the rotation of the planetary unit throws lubricating oil into the oil collecting groove, so that more lubricating oil is sent into the two-stage planetary unit 4-2, i.e. the lubricating oil is sent from the oil collecting groove into the inner cavity of the two-stage planetary shaft 4-21 above the oil surface, and then into the interface between the two-stage planetary shaft 4-21 and the second bearing 4-22 through the lubricating through hole 4-210, thereby effectively improving the lubrication performance of the two-stage planetary unit 4-2 and prolonging the service life of the two-stage planetary gear 4-23 and the second bearing 4-22.

[0046] The secondary planetary wheel shaft 4-21 disclosed in the embodiment can be fixedly connected with the frame 2 through bolts. The whole can transmit greater torque, reduce the probability of shear failure of the bolts, increase the system rigidity, be conducive to improving the meshing accuracy, improve the stability of the device, and improve the transmission accuracy.

[0047] The third bearing 6 is coaxially arranged between the primary planetary carrier 3-0 and the secondary planetary carrier 4-0, which improves the stability of the device and improves the transmission accuracy. The hub 0 is rotatable relative to the frame 2 through the pair of double fourth bearings 7, and the fourth bearing 7 inner ring is positioned by the bearing spacer 11, the secondary planetary carrier 4-0 and the frame 2. The outer end of the hub 0 is coaxially connected with the compression ring 8 through the connecting shaft 8-1, the inner wall of the compression ring 8 is in meshing transmission with the outer wall of the secondary inner gear ring 4-3, and the meshing spline is axially limited by the stop ring 12. The secondary inner gear ring 4-3 is directly connected with the hub through the spline to transmit torque, which cancels the torque tube, reduces large torque transmission components, improves transmission stability, and reduces the failure probability.

[0048] The hub 0 and the frame 2 are connected with the floating sealing mechanism 9, the floating sealing mechanism 9 and the first floating sealing end cover and the second floating sealing end cover form an output end seal, and the combination surface of the first floating sealing end cover and the second floating sealing end cover forms a labyrinth seal channel. The floating sealing technology belongs to the conventional design in the field, which will not be described here. The whole makes the hub 0 rotate relative to the frame 2 and seal.

[0049] Embodiment 2

[0050] The embodiment discloses a wheel edge drive box vehicle body frame and transmission system support coupling structure of a two-stage NGW planetary structure wheel edge drive device based on the embodiment 1, which comprises a first coupling unit a for connecting and fixing the secondary planetary wheel shaft 4-21 and the frame 2, and a second coupling unit b for connecting and fixing the primary inner gear ring 3-3 and the secondary planetary carrier 4-0; the first coupling unit a and the second coupling unit b are matched to form a stable whole, so that the structure is compact, the structural strength of the whole is increased, and the planetary unit can stably operate; each part has a simple structure and is convenient to process and assemble.

[0051] The first coupling unit a disclosed in the embodiment comprises a convex part a1 arranged at the inner end of the secondary planetary wheel shaft 4-21, a concave part a2 matched with the convex part a1 in structure and arranged at the outer end of the frame 2, and a first fixing shaft a3 arranged in the secondary planetary wheel shaft 4-21 inner cavity, the convex part a1 and the frame 2 in sequence in the axial direction. The first fixing shaft a3 in the embodiment can be selected as a bolt.

[0052] The first coupling unit a disclosed in the embodiment further comprises a limiting boss a4 arranged at the outer end of the second planetary shaft 4-21, and the second planetary carrier 4-0 is provided with a groove a5 matched with the structure of the limiting boss a4; the two are matched with each other to limit the rotation of the second planetary shaft 4-21 around the axis, so that the lubricating through hole 4-210 is always below.

[0053] The second coupling unit b comprises a first through hole b1 and a first blind hole b2 respectively arranged radially in the first inner ring gear 3-3 and the second planetary carrier 4-0, the first through hole b1 and the first blind hole b2 are coaxial and equal in diameter, further comprising a limiting column b3 penetrating into the first through hole b1 and the first blind hole b2 in sequence and in interference fit with the first through hole b1 and the first blind hole b2, and further comprising a limiting plate b4 fixedly arranged and covering the outer end of the first through hole b1. The limiting column b3 in the embodiment can be an internally threaded cylindrical pin, and the design of the limiting plate b4 effectively prevents the internally threaded cylindrical pin from falling off due to long-term work.

[0054] Embodiment 3

[0055] The difference between the embodiment and the embodiment 2 is that the first coupling unit a comprises a limiting blind hole a6 coaxial and equal in diameter with the inner hole of the second planetary shaft 4-21 arranged at the outer end of the rack 2, further comprising a limiting pin a7 penetrating into the inner hole of the second planetary shaft 4-21 and the limiting blind hole a6 in sequence, and further comprising a second fixed shaft a8 penetrating into the limiting pin a7 and the rack 2 in sequence, and the second fixed shaft a8 in the embodiment can be a bolt.

[0056] Embodiment 4

[0057] The difference between the embodiment and the embodiment 2 is that the first coupling unit a comprises a baffle a10 fixedly arranged at the outer end of the second planetary shaft 4-21, the baffle a10 covers the outer end of the inner cavity of the second planetary shaft 4-21, and further comprising a third fixed shaft a9 penetrating through the baffle a10 and penetrating into the inner cavity of the second planetary shaft 4-21 and the rack 2 in sequence, and the third fixed shaft a9 in the embodiment can be a bolt.

[0058] Embodiment 5

[0059] The difference between the embodiment and the embodiment 2 is that the second coupling unit b comprises a second through hole b5 and a second blind hole b6 respectively arranged parallel to the axis in the second planetary carrier 4-0 and the first inner ring gear 3-3, the second through hole b5 and the second blind hole b6 are coaxial and equal in diameter, and further comprising a fourth fixed shaft b7 penetrating into the second through hole b5 and the second blind hole b6 in sequence, and the fourth fixed shaft b7 in the embodiment can be a bolt.

[0060] The preferred embodiments of the present disclosure are described in detail above with reference to the drawings, but the present disclosure is not limited to the specific details in the above-described embodiments. Various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0061] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not describe various possible combinations again.

[0062] In addition, various different embodiments disclosed in the present solution can also be combined in any manner as long as they do not deviate from the idea of the present solution, and they should also be considered as the contents invented by the present solution.

Claims

1. A wheel drive case vehicle body frame and drive train support coupling structure, characterized by, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

2. The wheel drive case vehicle body frame and power train support coupling structure according to claim 1, characterized by, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

3. The wheel drive case body frame and power train support coupling structure according to claim 1, characterized by, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

4. The wheel drive case body frame and power train support coupling structure of claim 1, wherein, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

5. The wheel drive case vehicle body frame and drive train support coupling structure according to any one of claims 1 to 4, characterized by, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

6. The wheel drive case body frame and power train support coupling structure according to claim 5, characterized by, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

7. The wheel drive case body frame and power train support coupling structure of claim 5, wherein, The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence. The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence. The first coupling unit (a) includes a protrusion (a1) arranged at the inner end of the secondary planetary shaft (4-21), a recess (a2) arranged at the outer end of the frame (2) and matching the structure of the protrusion (a1), and a first fixed shaft (a3) axially passing through the inner cavity of the secondary planetary shaft (4-21), the protrusion (a1) and the frame (2) in sequence.

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