Tandem dual-rotor unmanned aerial vehicle transmission system and rotor aircraft

Abstract

Reversing speed reduction units of a front rotor wing and a rear rotor wing are connected through multiple sections of synchronous long shafts, and the tandem type double-rotor-wing unmanned aerial vehicle transmission system comprises a three-stage speed reduction structure including a first-stage synchronous belt speed reduction structure, a second-stage bevel gear speed reduction structure and a third-stage planetary gear train speed reduction structure. The first-stage synchronous belt speed reducer is connected with an engine output shaft and a large belt wheel through a synchronous belt, the second-stage bevel gear speed reducer achieves power transmission through a bevel gear, and the third-stage planetary gear train speed reducer transmits power to a rotor shaft through meshing of a planetary gear, a sun gear and a gear ring. The system solves the problems that a traditional tandem rotorcraft transmission system is single in structure, slow in clutch response, difficult in engine starting, insufficient in power, poor in emergency risk avoiding capacity and difficult to maintain, and the performance and reliability of the unmanned aerial vehicle are improved.

Description

Technical Field

[0001] The present invention belongs to the field of aerospace technology, and relates to a tandem dual-rotor UAV transmission system and a rotorcraft, and particularly to a tandem dual-rotor UAV transmission system that uses the power input of a double-piston engine and a three-stage reduction mechanism to work together, combines a centrifugal clutch and an overrunning clutch to achieve dynamic decoupling, ensures the co-rotation speed of the front and rear rotors through multi-section synchronous long shafts, and has a redundant transmission topology and a lightweight design. Background Art

[0002] In the field of aerospace, the performance of the UAV transmission system directly affects its flight stability and mission execution ability. Most traditional UAV transmission systems use a single engine for drive, which is prone to problems such as insufficient power or single-point failures under complex working conditions, and it is difficult to meet the requirements of special scenarios such as heavy-load transportation and high-altitude patrol. The tandem dual-rotor UAV has significant advantages in hovering efficiency and vertical takeoff and landing flexibility due to its unique rotor layout. However, its transmission system needs to achieve lightweight and high reliability while ensuring efficient power transmission, which poses higher requirements for the design.

[0003] As the core of power transmission, the transmission system of the tandem dual-rotor UAV undertakes the key task of reasonably distributing the engine power to the rotors. Existing transmission systems have problems such as a single reduction structure and a slow response of the clutch mechanism, which not only result in low transmission efficiency but also may cause component damage due to inertial drag; moreover, they lack redundant design, and once the engine fails, it is extremely easy to cause a flight accident. In addition, as the UAV application scenarios expand to extreme environments, the shortcomings of traditional transmission systems in terms of weight, maintenance convenience, etc. become increasingly prominent, and they cannot meet the diverse mission requirements. Summary of the Invention

[0004] In view of this, the present invention provides a tandem dual-rotor UAV transmission system and a rotorcraft to solve the problems of the current tandem rotorcraft transmission system, such as a single structure, slow clutch response, difficult starting of the piston engine, insufficient power of single-engine drive, insufficient emergency avoidance ability, and difficult component maintainability.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A tandem dual-rotor UAV transmission system. The front rotor commutation and reduction unit and the rear rotor commutation and reduction unit connected by multiple sections of synchronous long shafts both include a first-stage belt reduction small pulley and a first-stage belt reduction large pulley connected by a synchronous belt. The first-stage belt reduction small pulley is connected to a piston engine through an engine output shaft. The first-stage belt reduction large pulley is connected to a second-stage commutation reduction output shaft through a first-stage large pulley output shaft and a second-stage commutation reduction input shaft. A second-stage commutation reduction input bevel gear is fixedly installed on the second-stage commutation reduction input shaft, and a second-stage commutation reduction output bevel gear meshing with the second-stage commutation reduction input bevel gear is fixedly installed on the second-stage commutation reduction output shaft. The second-stage commutation reduction output shaft is connected to a third-stage planetary gear train reduction sun gear. Multiple third-stage planetary gear train reduction planet gears are evenly installed on the third-stage planetary gear train reduction planet carrier. The third-stage planetary gear train reduction planet gears are simultaneously meshed with the third-stage planetary gear train reduction sun gear and the third-stage planetary gear train reduction ring gear. The third-stage planetary gear train reduction ring gear is sleeved outside the multiple third-stage planetary gear train reduction planet gears. A rotor shaft is drivingly connected to the third-stage planetary gear train reduction planet carrier to realize the transmission of power to the rotor.

[0007] Furthermore, the output end of the piston engine is connected to the engine output shaft through a coupling, and the coupling adopts an elastic coupling.

[0008] Furthermore, the synchronous belt is a toothed belt, and an automatic tensioning device is installed outside the synchronous belt. This device adopts a spring-guide wheel structure. The guide wheel is installed on an adjustable bracket through a sliding bearing. The adjustable bracket automatically adjusts the position of the guide wheel under the action of spring force according to the tightness of the synchronous belt to realize the real-time adaptive adjustment of the tension force of the synchronous belt.

[0009] Furthermore, an overrunning clutch is arranged between the first-stage belt reduction large pulley and the first-stage large pulley output shaft. The inner ring of the overrunning clutch is connected to the first-stage large pulley output shaft, and the outer ring is fixedly connected to the first-stage belt reduction large pulley to realize the one-way clutch between the first-stage belt reduction large pulley and the first-stage large pulley output shaft.

[0010] Furthermore, the first-stage large pulley output shaft and the second-stage commutation reduction input shaft are connected through a centrifugal clutch. Deep groove ball bearings are installed on the first-stage output shaft and the second-stage commutation reduction input shaft to provide support.

[0011] Furthermore, both the second-stage commutation reduction input shaft and the second-stage commutation reduction input bevel gear, and the second-stage commutation reduction output shaft and the second-stage commutation reduction output bevel gear are of an integrated structure.

[0012] Furthermore, the third-stage planetary gear train reduction sun gear is connected to the second-stage commutation reduction output shaft through a spline to ensure the coaxiality and torque transmission accuracy between the sun gear and the second-stage commutation reduction output shaft.

[0013] Furthermore, the third-stage planetary gear train reduction planet carrier is fixedly installed on the body frame through a double-row tapered roller bearing. The double-row tapered roller bearing is installed in a back-to-back manner, and an appropriate preload is applied through a preload nut to improve the rigidity and rotational accuracy of the bearing, while effectively bearing the axial force and radial force generated during the transmission of the planetary gear train.

[0014] Furthermore, the third-stage planetary gear train reduction planet carrier is connected to the rotor shaft through a spline to achieve the transmission of power to the rotor.

[0015] Furthermore, the synchronous long shaft includes a synchronous long shaft input shaft, a synchronous long shaft output shaft, and a diaphragm coupling for connecting the synchronous long shaft input shaft and the synchronous long shaft output shaft.

[0016] Furthermore, the synchronous long shaft output shaft is respectively arranged on one side close to the front rotor commutation reduction unit and the rear rotor commutation reduction unit. A synchronous long shaft output bevel gear meshing with the second-stage commutation reduction output bevel gear on the corresponding side is fixedly installed on the synchronous long shaft output shaft, and the synchronous long shaft output shaft and the synchronous long shaft output bevel gear are of an integral structure.

[0017] Furthermore, the diaphragm coupling is connected to the synchronous long shaft input shaft and the synchronous long shaft output shaft through splines to ensure that the front and rear rotors maintain the same rotational speed during operation.

[0018] A rotorcraft includes the above-described tandem dual-rotor UAV transmission system.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. For the tandem dual-rotor UAV transmission system disclosed in the present invention, both the front and rear reducers include three-stage reduction, namely the first-stage synchronous belt reduction, the second-stage bevel gear reduction, and the third-stage planetary gear train reduction. The front and rear engines are respectively connected to a piston engine. The engine output shaft transmits power to the first-stage output shaft through the first-stage synchronous belt reduction, then transmits the power to the second-stage commutation reduction output shaft through the second-stage commutation reduction bevel gear, and finally transmits the power to the planet carrier through the third-stage planetary gear train, and then the planet carrier transmits the power to the rotor shaft. This structure is more compact than the traditional tandem transmission system structure, has high power utilization efficiency, can greatly reduce the system weight and reduce the structural size.

[0021] 2. For the tandem dual-rotor UAV transmission system disclosed in the present invention, the first-stage belt reduction small pulley is installed on the engine output shaft, the first-stage belt reduction large pulley is installed on the first-stage large pulley output shaft, and the first-stage belt reduction large pulley and the first-stage belt reduction small pulley are connected by a toothed synchronous belt, which can reduce vibration during the operation of the piston engine, achieve smooth transmission, and provide overload protection.

[0022] 3. In the tandem dual-rotor UAV transmission system disclosed by the present invention, an overrunning clutch is installed between the first-stage belt reduction large pulley and the output shaft of the first-stage large pulley, which can realize the engagement and disconnection of the engine through the overrunning clutch when one side of the engine fails; if the speeds of the two engines are different at a certain moment, when the speed is transmitted to the first-stage large pulley through the synchronous long shaft, there is a speed difference between the first-stage large pulley on one side and the first-stage belt reduction small pulley. At this time, the overrunning clutch can be disengaged. When the speed of this side of the engine increases and there is no speed difference between the two pulleys, the overrunning clutch closes again. The speed difference of the engine can also meet the co-speed of the rotor shafts; when the engine lands and shuts off, the engine can be disconnected through the overrunning clutch to protect the components from damage caused by inertial drag.

[0023] 4. In the tandem dual-rotor UAV transmission system disclosed by the present invention, a centrifugal clutch is used to realize the separation and engagement of the output shaft of the first-stage large pulley and the input shaft of the second-stage reversing reduction. The initial torque of the piston engine is small and the speed is low at this time, and the centrifugal clutch is in the disengaged state. When a certain speed is reached, the centrifugal clutch automatically engages the two shafts to ensure the normal start of the piston engine. Compared with the traditional clutch scheme, it does not require a pneumatic or hydraulic system, reducing the system mass.

[0024] 5. In the tandem dual-rotor UAV transmission system disclosed by the present invention, an automatic tensioning device is installed on the outside of the toothed synchronous belt, which can adaptively adjust the tension force in real time, avoid slipping, tooth skipping and abnormal wear, reduce the maintenance frequency, ensure stable power transmission, improve the reliability and service life of the transmission system under different working conditions, and reduce the flight risk of the UAV caused by transmission failures.

[0025] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0027] Figure 1 is a schematic structural diagram of the tandem dual-rotor UAV transmission system of the present invention;

[0028] Figure 2 is a schematic structural diagram of the front rotor reversing reduction unit in the tandem dual-rotor UAV transmission system of the present invention;

[0029] Figure 3Schematic diagram of the structure of the synchronous long shaft in the drive system of the tandem dual-rotor UAV of the present invention;

[0030] Figure 4 Schematic diagram of the structure of the automatic tensioning device in the drive system of the tandem dual-rotor UAV of the present invention;

[0031] Figure 5 Drive principle diagram of the drive system of the tandem dual-rotor UAV of the present invention.

[0032] Reference numerals: piston engine 1, coupling 2, engine output shaft 4, first-stage belt reduction small pulley 5, toothed synchronous belt 6, first-stage belt reduction large pulley 7, overrunning clutch 8, first-stage large pulley output shaft 9, centrifugal clutch 10, second-stage reversing reduction input shaft 11, second-stage reversing reduction input bevel gear 13, rotor shaft 15, third-stage planetary gear train reduction planet carrier 17, third-stage planetary gear train reduction planet gear 18, third-stage planetary gear train reduction gear ring 19, second-stage reversing reduction output bevel gear 20, synchronous long shaft output bevel gear 22, synchronous long shaft output shaft 23, third-stage planetary gear train reduction sun gear 29, second-stage reversing reduction output shaft 32, long shaft 25, diaphragm couplings 26, 33, 40, deep groove ball bearings 12, 28, 24, 27, 35, 36, tapered roller bearings 21, 34, cylindrical roller bearings 14, 31, four-point contact ball bearings 3, 37, double-row tapered roller bearings 16, 30, guide pulley 38, spring 39. Specific embodiments

[0033] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] As Figures 1-5 shown, a drive system for a tandem dual-rotor UAV adopts a symmetric layout and connects the front rotor reversing reduction unit and the rear rotor reversing reduction unit through multiple sections of synchronous long shafts 25. The front rotor reversing reduction unit and the rear rotor reversing reduction unit have symmetric structures and both are provided with three-stage reductions: the first-stage synchronous belt reduction, the second-stage bevel gear reduction, and the third-stage planetary gear train reduction. The system is equipped with a double piston engine, which is respectively connected to the front and rear reducer units to form a dual power input mode.

[0035] Both the front rotor commutation and reduction unit and the rear rotor commutation and reduction unit include a first-stage belt reduction small pulley 5 and a first-stage belt reduction large pulley 7 connected by a toothed synchronous belt 6. The first-stage belt reduction small pulley 5 is connected to the piston engine 1 through the engine output shaft 4. The first-stage belt reduction large pulley 7 is connected to the second-stage commutation reduction output shaft 32 through the first-stage large pulley output shaft 9 and the second-stage commutation reduction input shaft 11. A second-stage commutation reduction input bevel gear 13 is fixedly installed on the second-stage commutation reduction input shaft 11, and a second-stage commutation reduction output bevel gear 20 meshing with the second-stage commutation reduction input bevel gear 13 is fixedly installed on the second-stage commutation reduction output shaft 32. The second-stage commutation reduction output shaft 32 is connected to the third-stage planetary gear train reduction sun gear 29. A plurality of third-stage planetary gear train reduction planet gears 18 are evenly installed on the third-stage planetary gear train reduction planet carrier 17. The third-stage planetary gear train reduction planet gears 18 are simultaneously meshed with the third-stage planetary gear train reduction sun gear 29 and the third-stage planetary gear train reduction ring gear 19. The third-stage planetary gear train reduction ring gear 19 is sleeved on a plurality of third-stage planetary gear train reduction planet gears 18. A rotor shaft 15 is drivingly connected to the third-stage planetary gear train reduction planet carrier 17 to realize the transmission of power to the rotor.

[0036] The output end of the piston engine 1 is connected to the engine output shaft 4 through a coupling 2. The first-stage large pulley output shaft 9 and the second-stage commutation reduction input shaft 11 are connected through a centrifugal clutch 10.

[0037] The cooperation of the first-stage belt reduction small pulley 5, the toothed synchronous belt 6, and the first-stage belt reduction large pulley 7 realizes the first-stage synchronous belt reduction of the front rotor commutation and reduction unit.

[0038] Specifically, the output end of the piston engine 1 is connected to the engine output shaft 4 through a coupling 2. The coupling 2 adopts an elastic coupling, and the vibration and impact generated by the engine operation are absorbed through elastic elements to realize the flexible connection between the engine and the transmission system and the reliable transmission of power.

[0039] The engine output shaft 4 is installed on the four-point contact ball bearings 3 and 37 with an interference fit, and can simultaneously bear radial and bidirectional axial loads to ensure stable power output.

[0040] A first-stage belt reduction small pulley 5 is coaxially installed at one end of the engine output shaft 4 and fixed by a key connection to ensure synchronous rotation of the first-stage belt reduction small pulley 5 and the engine output shaft 4. At the same time, a first-stage belt reduction large pulley 7 is installed on the first-stage large pulley output shaft 9. An overrunning clutch 8 is provided between the first-stage belt reduction large pulley 7 and the first-stage large pulley output shaft 9. The inner ring of the overrunning clutch 8 is connected to the first-stage large pulley output shaft 9, and the outer ring is fixedly connected to the first-stage belt reduction large pulley 7 to realize the one-way clutch function between the first-stage belt reduction large pulley 7 and the first-stage large pulley output shaft 9.

[0041] The toothed synchronous belt 6 is a toothed belt. The toothed synchronous belt 6 is selected to connect the first-stage belt reduction small pulley 5 and the first-stage belt reduction large pulley 7. An automatic tensioning device is installed on the outer side of the toothed synchronous belt 6. This device adopts a spring-guide wheel structure. The guide wheel 38 is installed on the adjustable bracket through a sliding bearing. The bracket automatically adjusts the position of the guide wheel 38 under the action of the spring 39 force according to the tightness of the toothed synchronous belt 6, realizing the real-time adaptive adjustment of the tension force of the toothed synchronous belt 6.

[0042] The centrifugal clutch 10 is installed between the output shaft 9 of the first-stage large pulley and the input shaft 11 of the second-stage reversing reduction. The driving disk of the centrifugal clutch 10 is fixedly connected to the output shaft 9 of the first-stage large pulley, and the driven disk is connected to the input shaft 11 of the second-stage reversing reduction. Deep groove ball bearings 12, 28, 35, and 36 are respectively installed on the output shaft 9 of the first-stage large pulley and the input shaft 11 of the second-stage reversing reduction. The deep groove ball bearings 12, 28, 35, and 36 adopt a double-sided fixed installation method. The axial displacement of the bearings is restricted by the shaft shoulder and the bearing end cover, providing radial support for the shaft and a certain axial load-bearing capacity.

[0043] The cooperation of the second-stage reversing reduction input bevel gear 13 and the second-stage reversing reduction output bevel gear 20 realizes the second-stage bevel gear reduction of the front rotor reversing reduction unit.

[0044] Specifically, the second-stage reversing reduction input shaft 11 and the second-stage reversing reduction input bevel gear 13 are of an integrated structure, and the second-stage reversing reduction output shaft 32 and the second-stage reversing reduction output bevel gear 20 are also of an integrated structure. Assemble the second-stage reversing reduction input shaft 11 and the second-stage reversing reduction output shaft 32 so that the second-stage reversing reduction input bevel gear 13 meshes with the second-stage reversing reduction output bevel gear 20. Adjust the axial position of the two shafts through the adjusting shim to realize the meshing of the second-stage reversing reduction input bevel gear 13 and the second-stage reversing reduction output bevel gear 20.

[0045] The cooperation of the third-stage planetary gear train reduction planet carrier 17, the third-stage planetary gear train reduction planet gear 18, the third-stage planetary gear train reduction sun gear 29, and the third-stage planetary gear train reduction ring gear 19 realizes the third-stage planetary gear train reduction of the front rotor reversing reduction unit.

[0046] Connect the third-stage planetary gear train reduction sun gear 29 to the second-stage reversing reduction output shaft 32 through a spline to ensure the coaxiality and torque transmission accuracy between the third-stage planetary gear train reduction sun gear 29 and the second-stage reversing reduction output shaft 32.

[0047] A plurality of third-stage planetary gear train reduction planet gears 18 are evenly installed on the third-stage planetary gear train reduction planet carrier 17. The third-stage planetary gear train reduction planet gears 18 are connected to the third-stage planetary gear train reduction planet carrier 17 through cylindrical pins and bearings to ensure that the third-stage planetary gear train reduction planet gears 18 can rotate flexibly. The third-stage planetary gear train reduction planet gears 18 are simultaneously meshed with the third-stage planetary gear train reduction sun gear 29 and the third-stage planetary gear train reduction ring gear 19 to form a planetary gear train transmission structure.

[0048] The third-stage planetary gear train reduction planet carrier 17 is fixedly installed on the body frame through double-row tapered roller bearings 16, 30. The double-row tapered roller bearings 16, 30 are installed in a back-to-back manner, and an appropriate preload is applied through the preload nut to improve the rigidity and rotational accuracy of the bearings, and at the same time effectively bear the axial force and radial force generated during the transmission of the planetary gear train. The third-stage planetary gear train reduction planet carrier 17 is connected to the rotor shaft 15 through a spline to achieve the transmission of power to the rotor.

[0049] The synchronous long shaft output shaft 23 is respectively arranged on one side close to the front rotor commutation reduction unit and the rear rotor commutation reduction unit. A synchronous long shaft output bevel gear 22 meshing with the corresponding second-stage commutation reduction output bevel gear 20 is fixedly installed on the synchronous long shaft output shaft 23. The tapered roller bearings 21, 34 are connected to the synchronous long shaft output shaft 23 by an interference fit to achieve the axial positioning and radial support of the synchronous long shaft output shaft 23, and suppress the axial movement and radial runout at the output end of the synchronous long shaft.

[0050] The cylindrical roller bearing 14 has an interference fit with the rotor shaft 15, which is used to provide reliable circumferential positioning and facilitate disassembly, mainly bear radial loads, and reduce operation losses and vibrations. The cylindrical roller bearing 31 is fixed to the second-stage commutation reduction output shaft 32 by an interference fit to disperse the stress concentration under alternating loads and ensure the stability of power transmission.

[0051] The synchronous long shaft is composed of multiple long shafts 25 and diaphragm couplings 26, 40 for connecting adjacent long shafts 25. The long shaft 25 is connected to the front reducer unit through the diaphragm coupling 33. The diaphragm coupling 33 is connected to the synchronous long shaft output shaft 23 through a spline. The long shaft 25 is also connected to the diaphragm coupling 26 through a spline. The diaphragm coupling 26 is connected to the diaphragm coupling 40 by bolts. The diaphragm coupling 40 is also connected to the next long shaft through a spline to ensure that the front and rear rotors maintain the same rotational speed during operation. The deep groove ball bearing 24 is interference-fitted on the diaphragm coupling 33, and the deep groove ball bearing 27 is interference-fitted on the diaphragm coupling 40 to provide dynamic stiffness for the long shaft 25.

[0052] The tandem dual-rotor UAV transmission system consists of a double-piston engine, a symmetric front / rear reducer, a clutch mechanism, and a synchronous long shaft. Both the front and rear reducers include three-stage reduction: with a reduction and shock-absorbing housing, bevel gear commutation, planetary gear train speed regulation, and efficient drive of the rotor shaft; the symmetric structure improves balance stability and simplifies manufacturing and maintenance. The combination of a centrifugal clutch and an overrunning clutch achieves dynamic decoupling. The former ensures smooth engine startup, and the latter avoids inertial damage during idling and faults; the synchronous long shaft ensures that the rotational speeds of the front and rear rotors are consistent. The system adopts a redundant topology and can still maintain dual-rotor drive when a single engine fails. Compared with traditional systems, this transmission system has the advantages of light weight, high transmission efficiency, and easy maintenance, and is suitable for complex scenarios such as heavy-load transportation and high-altitude patrol, significantly enhancing the environmental adaptability and reliability of the UAV.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A tandem dual-rotor UAV transmission system, characterized in that, The front rotor commutation and reduction unit and the rear rotor commutation and reduction unit connected by multiple sections of synchronous long shafts both include a first-stage belt reduction small pulley (5) and a first-stage belt reduction large pulley (7) connected by a toothed synchronous belt (6). The first-stage belt reduction small pulley (5) is connected to the piston engine (1) through the engine output shaft (4). The first-stage belt reduction large pulley (7) is connected to the second-stage commutation reduction output shaft (32) through the first-stage large pulley output shaft (9) and the second-stage commutation reduction input shaft (11). A second-stage commutation reduction input bevel gear (13) is fixedly installed on the second-stage commutation reduction input shaft (11), and a second-stage commutation reduction output bevel gear (20) meshing with the second-stage commutation reduction input bevel gear (13) is fixedly installed on the second-stage commutation reduction output shaft (32). The second-stage commutation reduction output shaft (32) is connected to the third-stage planetary gear train reduction sun gear (29). A plurality of third-stage planetary gear train reduction planetary gears (18) are evenly installed on the third-stage planetary gear train reduction planet carrier (17). The third-stage planetary gear train reduction planetary gears (18) are simultaneously meshed with the third-stage planetary gear train reduction sun gear (29) and the third-stage planetary gear train reduction ring gear (19). The third-stage planetary gear train reduction ring gear (19) is sleeved outside the plurality of third-stage planetary gear train reduction planetary gears (18). A rotor shaft (15) is drivingly connected to the third-stage planetary gear train reduction planet carrier (17) to realize the transmission of power to the rotor.

2. The tandem dual-rotor UAV transmission system according to claim 1, wherein The toothed synchronous belt (6) is a toothed belt, and an automatic tensioning device is installed on the outside of the toothed synchronous belt. This device adopts a spring-guide wheel structure. The guide wheel (38) is installed on an adjustable bracket through a sliding bearing. The adjustable bracket automatically adjusts the position of the guide wheel (38) under the action of the spring (39) force according to the tightness of the toothed synchronous belt (6) to realize the real-time adaptive adjustment of the tension force of the toothed synchronous belt (6).

3. The tandem two-rotor UAV transmission system according to claim 1, characterized in that, An overrunning clutch (8) is provided between the first-stage belt reduction large pulley (7) and the first-stage large pulley output shaft (9). The inner ring of the overrunning clutch (8) is connected to the first-stage large pulley output shaft (9), and the outer ring is fixedly connected to the first-stage belt reduction large pulley (7) to realize the one-way clutch between the first-stage belt reduction large pulley (7) and the first-stage large pulley output shaft (9).

4. The tandem two-rotor UAV transmission system according to claim 1, wherein, The first-stage large pulley output shaft (9) and the second-stage commutation reduction input shaft (11) are connected by a centrifugal clutch (10). Deep groove ball bearings are installed on the first-stage output shaft (8) and the second-stage commutation reduction input shaft (11) to provide support.

5. The tandem dual-rotor UAV transmission system according to claim 1, wherein The second-stage commutation reduction input shaft (11) and the second-stage commutation reduction input bevel gear (13), and the second-stage commutation reduction output shaft (32) and the second-stage commutation reduction output bevel gear (20) are all of an integrated structure.

6. The tandem dual-rotor UAV transmission system according to claim 1, wherein The third-stage planetary gear train reduction sun gear (29) is connected to the second-stage commutation reduction output shaft (32) through a spline, and the third-stage planetary gear train reduction planet carrier (17) is connected to the rotor shaft (15) through a spline.

7. The tandem dual-rotor UAV transmission system according to claim 1, characterized in that, The third-stage planetary gear train reduction planetary carrier (17) is fixedly installed on the body frame through a double-row tapered roller bearing, and the double-row tapered roller bearing is installed in a back-to-back manner.

8. The tandem two-rotor UAV drive system according to claim 1, wherein The synchronous long shaft includes a synchronous long shaft output shaft (23), multiple long shafts (25), and a diaphragm coupling for connecting the multiple long shafts.

9. The tandem dual-rotor UAV transmission system according to claim 8, characterized in that, The synchronous long shaft output shaft (23) is respectively arranged on one side close to the front rotor commutation reduction unit and the rear rotor commutation reduction unit. A synchronous long shaft output bevel gear (22) meshing with the second-stage commutation reduction output bevel gear (20) on the corresponding side is fixedly installed on the synchronous long shaft output shaft (23), and the synchronous long shaft output shaft (23) and the synchronous long shaft output bevel gear (22) are of an integral structure.

10. A rotorcraft, characterized in that, It includes the tandem dual-rotor UAV transmission system according to any one of claims 1 to 9.

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