Intermediate gear spiral combination for a reduction gear and turboprop engine

Abstract

The application discloses a middle gear spiral combination for a reducer and a turbofan engine, which comprises a gear shaft with a pinion, a left shaft neck and a right shaft neck, and a large gear cooperating with the pinion to reduce transmission. The large gear and the pinion are both spiral gears, and the pitch circle diameter of the large gear is larger than that of the pinion. The middle gear spiral combination further comprises a connecting adjustment structure, the large gear is screwed on the outer circle of the gear shaft through the connecting adjustment structure, and is positioned between the pinion and the right shaft neck. The "Y" shaped reducer of the application can adjust the angle of the middle gear spiral combination, so that all the transmission tooth surfaces can be normally engaged without interference, and the effective transmission of power is facilitated. The "Y" shaped transmission scheme of the application divides the power flow into two parts, the radial pressure of the tooth surface is reduced to one half, the directions of the pressure vectors of the tooth surface are different, the vector sum is smaller than the sum of the values, the bearing life is prolonged, and the gear strength margin of the engine is improved.

Description

Technical Field

[0001] This invention relates to the field of aero-engines, and more particularly, to an intermediate gear helical assembly for a reduction gear. Furthermore, this invention also relates to a turboprop engine comprising the aforementioned intermediate gear helical assembly for a reduction gear. Background Technology II. Background Technology

[0003] Currently, there are few models of low-power (100-400kW) turboprop engines for general aviation. Furthermore, the market price of aviation gasoline is several times higher than that of aviation kerosene, making medium-power aviation piston engines particularly uneconomical, while turbofan engines have an extremely high probability of bird strikes. With increasing emphasis on environmental protection, there is an urgent need to develop several models of low-power turboprop engines for aircraft weighing less than one ton and tiltrotor aircraft. The design speed range of the power turbine is 35,000-40,000 RPM, which needs to be reduced to the propeller's design speed range of 2,000-2,300 RPM (propeller diameter approximately 98-78 inches), achieving a reduction ratio of 15-20. Because the efficiency of each gear transmission stage is 97-98%, adding an additional stage of reduction will increase engine fuel consumption by two to three percentage points, and significantly increase the frontal area and weight. Therefore, in existing technology, low-power turboprop engines still use only two stages of external cylindrical gear reduction, limiting the gear diameter and using a combination of two intermediate gears to minimize frontal area and weight while meeting gear strength requirements.

[0004] In the design of speed reducers, stringent requirements are placed on design indicators such as size, weight, reliability, and service life to meet the most stringent quality standards. The speed reduction transmission in speed reducers relies on intermediate gear combinations to reduce tangential velocity and increase the torque of the output gears. In existing technologies, intermediate gear combinations generally consist of two coaxial gears, one large and one small, and use helical gears with high load capacity. However, because the axial distance between the large and small gears is relatively short, the large gear hinders the hobbing and grinding of the small gear. The advanced technology of high-performance turboprop engines dictates that the high-power, high-speed transmission gears in speed reducers must be helical gears, and the axial distance of the coaxial gears should be minimized. Therefore, the hobbing and grinding of the small helical gear must be completed in advance.

[0005] In existing technologies, vacuum electron beam welding is used to form intermediate gear assemblies, which are used in high-power turboshaft and turboprop engines. However, in vacuum electron beam welding of intermediate gear assemblies, the welding heat affects the tooth profile and direction, thus reducing gear precision and resulting in a certain rate of welding scrap. Summary of the Invention

[0006] This invention provides an intermediate gear helical assembly for a speed reducer and a turboprop engine, to solve the technical problems of existing intermediate gear assemblies using vacuum electron beam welding, which are only applicable to high-power turboshaft and turboprop engines, have low gear precision, and result in welding scrap rates.

[0007] The technical solution adopted in this invention is as follows:

[0008] An intermediate gear helical assembly for a speed reducer includes: a gear shaft with a pinion, a left journal, and a right journal, and a large gear that cooperates with the pinion to reduce speed; both the large gear and the pinion are helical gears, and the pitch circle diameter of the large gear is larger than that of the pinion; the intermediate gear helical assembly also includes a connecting adjustment structure, wherein the large gear is threaded onto the outer circle of the gear shaft through the connecting adjustment structure and is positioned between the pinion and the right journal.

[0009] Furthermore, the gear shaft also includes a hollow cylindrical mounting shaft body; the pinion is integrally formed with the mounting shaft body; the left journal and the right journal are respectively located on both sides of the pinion, and the mounting shaft body between the pinion and the right journal protrudes to form an annular limiting flange; the large gear is mounted on the outer circle of the mounting shaft body, and is limited between the limiting flange and the right journal by a connecting adjustment structure.

[0010] Furthermore, the connection adjustment structure includes a connection structure for threaded connection between the large gear and the gear shaft. The connection structure includes a right-hand thread on the outer circle of the mounting shaft, a shaft hole penetrating the center of the large gear, and an internal thread on the inner circumferential surface of the shaft hole that engages with the right-hand thread. The right-hand thread is adaptively configured according to the direction of the engine's operating torque so that the large gear becomes tighter as it operates normally under vibration. The large gear is threaded onto the outer circle of the mounting shaft through the engagement of the internal thread on its shaft hole with the right-hand thread.

[0011] Furthermore, the nominal diameter of the right-hand thread is 40–50 mm; the length of the right-hand thread is 25–35 mm; the tightening torque of the right-hand thread is greater than the working torque, and the tightening torque is 40–50 kg·m.

[0012] Furthermore, the connection adjustment structure also includes a connecting adhesive layer formed by applying connecting adhesive between the large gear and the mounting shaft, and between the side end face of the large gear and the side end face of the limiting flange.

[0013] Furthermore, the connection adjustment structure also includes an adjusting shim and a limiting retaining ring; the adjusting shim is installed on the outer circle of the mounting shaft and is clamped between the side end face of the limiting flange and the side end face of the large gear, so as to adjust the angular position of the large gear relative to the small gear; the limiting retaining ring is installed on the outer circle of the mounting shaft and is limited between the right journal and the large gear, so as to block the rollers of the roller bearing installed on the outer circle of the right journal when not in operation.

[0014] Furthermore, the gear disk of the large gear is also machined with a concave and annular semi-circular groove; the intermediate gear helical assembly also includes a damping ring for vibration reduction, which is fitted into the semi-circular groove.

[0015] Furthermore, the normal module of the large gear is 1.25; the helix angles of both the small and large gears are integers.

[0016] According to another aspect of the present invention, a turboprop engine is also provided, comprising a reduction gear, the reduction gear comprising: a propeller shaft for mounting a propeller, a power turbine shaft for connecting to a power turbine, and two sets of intermediate gear helical assemblies as described above; an input gear is further provided on the outer circumference of the power turbine shaft, and an output gear is further provided on the outer circumference of the propeller shaft; the two sets of intermediate gear helical assemblies are respectively disposed on both sides of the power turbine shaft, and the large gear of each set of intermediate gear helical assemblies meshes externally with the input gear, and the small gear of each set of intermediate gear helical assemblies meshes externally with the output gear.

[0017] Furthermore, the propeller shaft and the power turbine shaft are arranged in parallel intervals; the two sets of intermediate gears are arranged symmetrically in a helical combination; the pitch circle diameter of the input gear is smaller than that of the large gear, and the pitch circle diameter of the small gear is smaller than that of the output gear.

[0018] The present invention has the following beneficial effects:

[0019] This invention proposes an intermediate gear helical assembly with a separate design for the pinion and gear, facilitating hobbing and grinding of the helical teeth on both gears, improving machining accuracy, and consequently increasing power transmission efficiency. In this invention, the left and right journals for bearing mounting are integrated onto the gear shaft, unlike existing designs where the left journal is on the gear shaft and the right journal on the gear. This allows for simultaneous machining of the left and right journals, improving machining efficiency and, more importantly, enhancing their coaxiality, thus improving the coaxiality of the bearings and ultimately increasing bearing life, power transmission efficiency, and engine reliability. Compared to intermediate gear assemblies formed by vacuum electron beam welding, which suffer from reduced precision due to welding heat affecting tooth profile and direction, resulting in a certain welding scrap rate, and where vacuum electron beam welding... The intermediate gear assembly is suitable for high-power turboshaft and turboprop engines. In this invention, the large gear is positioned and fixed on the gear shaft through a connecting adjustment structure, thereby avoiding welding thermal deformation and the highly difficult vacuum electron beam welding of the gear. This simplifies the processing and preparation operations, and its manufacturing cost is lower than that of the intermediate gear assembly welded by vacuum electron beam welding. Its reliability is higher than that of spline connection and pin connection. The resulting intermediate gear helical assembly is suitable for low-power turboshaft and turboprop engines, meeting the needs of existing aircraft under one ton and tiltrotor aircraft. Importantly, since the large gear is helically fixed on the gear shaft through the connecting adjustment structure, the angular position of the large gear relative to the small gear can be adjusted by rotating the large gear, allowing the large gear and small gear to mesh with their respective gears without interference. In addition, the intermediate gear helical assembly also has promotional value in higher-power aero engines, and the pass rate of the intermediate gear helical assembly is higher than that of the intermediate gear assembly welded by vacuum electron beam welding.

[0020] The "Y"-shaped reducer for a low-power turboprop engine of this invention allows for adjustable angles of the intermediate gear thread combination, ensuring normal meshing of all transmission gear surfaces without interference and facilitating efficient power transmission. Furthermore, the reducer for a low-power turboprop engine needs to address the challenges of small bearing size, high load, and high speed. In this invention, the "Y"-shaped transmission scheme divides the power flow in two, reducing the radial pressure on the gear surface to half. Moreover, the pressure vectors on the gear surfaces are in different directions, and their vector sum is less than their numerical sum, thus extending bearing life. Additionally, the "Y"-shaped reducer for the low-power turboprop engine further improves the engine gear strength margin by evenly distributing torque through the helical combination of two intermediate gears, thereby enhancing engine safety and service life. The "Y"-shaped reducer significantly improves gear overlap, resulting in smoother transmission, significant amplitude constraint and damping of vibration modes, reduced noise, and reduced gear failure.

[0021] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 This is a schematic diagram of the spatial structure of the intermediate gear helical assembly for a speed reducer according to a preferred embodiment of the present invention;

[0024] Figure 2 yes Figure 1 Design drawings;

[0025] Figure 3 yes Figure 1 A schematic diagram of the sectional front view structure;

[0026] Figure 4 This is a schematic diagram of the spatial structure of the reducer of a turboprop engine according to a preferred embodiment of the present invention;

[0027] Figure 5 yes Figure 4 Transmission route diagram;

[0028] Figure 6 yes Figure 4 A schematic diagram of tooth surface meshing in a two-stage transmission.

[0029] Legend

[0030] 1. Intermediate gear helical assembly; 10. Gear shaft; 11. Pinion; 12. Left journal; 13. Right journal; 14. Mounting shaft; 15. Limiting flange; 20. Large gear; 30. Connecting and adjusting structure; 31. Connecting structure; 32. Adjusting shim; 33. Limiting retaining ring; 34. Connecting adhesive layer; 40. Damping ring; 3. Propeller; 4. Propeller shaft; 5. Power turbine; 6. Power turbine shaft; 7. Input gear; 8. Output gear. Detailed Implementation

[0031] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0032] Reference Figure 1 and Figure 2A preferred embodiment of the present invention provides an intermediate gear helical assembly for a speed reducer, comprising: a gear shaft 10 with a pinion 11, a left journal 12, and a right journal 13, and a large gear 20 that cooperates with the pinion 11 to reduce speed. Both the large gear 20 and the pinion 11 are helical gears, and the pitch circle diameter of the large gear 20 is larger than that of the pinion 11. The intermediate gear helical assembly 1 also includes a connecting adjustment structure 30, through which the large gear 20 is threaded onto the outer circle of the gear shaft 10 and positioned between the pinion 11 and the right journal 13.

[0033] This invention proposes an intermediate gear helical assembly 1 with a separate design for the pinion 11 and the large gear 20. This facilitates the hobbing and grinding of the helical teeth on the pinion 11 and the large gear 20, improving the machining accuracy of the helical teeth and thus increasing power transmission efficiency. In this invention's intermediate gear helical assembly 1, the left journal 12 and right journal 13, used for mounting bearings, are integrated onto the gear shaft 10, instead of the existing design where the left journal 12 is located on the gear shaft and the right journal 13 on the large gear. This structural arrangement allows for simultaneous machining of the left journal 12 and right journal 13, improving machining efficiency and, more importantly, enhancing the coaxiality of the two journals, thereby improving the coaxiality of the bearings and ultimately increasing bearing life, power transmission efficiency, and engine reliability. Compared to intermediate gear assemblies formed by vacuum electron beam welding, which suffer from reduced gear precision due to the heat effect of welding on the tooth profile and direction, resulting in a certain welding scrap rate, vacuum electron beam welding... The intermediate gear assembly is suitable for high-power turboshaft and turboprop engines. In this invention, the large gear 20 is positioned and fixed on the gear shaft 10 through the connecting adjustment structure 30, thereby avoiding welding thermal deformation of the gear and the high difficulty of vacuum electron beam welding, simplifying the processing and preparation operations. Its manufacturing cost is lower than that of intermediate gear assemblies welded by vacuum electron beam welding, and its reliability is higher than that of spline connection and pin connection. The resulting intermediate gear helical assembly 1 is suitable for low-power turboshaft and turboprop engines, meeting the needs of existing aircraft under one ton and tiltrotor aircraft. Importantly, since the large gear 20 is helically fixed on the gear shaft 10 through the connecting adjustment structure 30, the angular position of the large gear 20 relative to the small gear 11 can be adjusted by rotating the large gear 20, so that the large gear 20 and the small gear 11 can mesh with their respective gears without interference. In addition, the intermediate gear helical assembly 1 also has promotional value in higher-power aero engines, and the pass rate of the intermediate gear helical assembly 1 is higher than that of intermediate gear assemblies welded by vacuum electron beam welding.

[0034] Optionally, such as Figure 2As shown, the gear shaft 10 also includes a hollow cylindrical mounting shaft 14. The pinion 11 is integrally formed with the mounting shaft 14, reducing the difficulty of machining and assembly, while improving structural strength and operational stability. The left journal 12 and the right journal 13 are respectively located on both sides of the pinion 11, and the mounting shaft 14 between the pinion 11 and the right journal 13 protrudes outward to form an annular limiting flange 15. The large gear 20 is mounted on the outer circle of the mounting shaft 14 and is limited between the limiting flange 15 and the right journal 13 by the connecting adjustment structure 30. In this optional scheme, the intermediate gear helical assembly 1 is simply supported on two roller bearings by the left journal 12 and the right journal 13. The left journal 12 and the right journal 13 are machined to their final state on the gear shaft 10, so that the coaxiality of the two is good, which is better than that of the intermediate gear assembly welded by vacuum electron beam welding (the front journal and the rear journal are on the large gear and the small gear respectively), thereby improving the service life of the bearings.

[0035] Optionally, such as Figure 1 and Figure 2 As shown, the connection adjustment structure 30 includes a connection structure 31 for threaded connection between the large gear 20 and the gear shaft 10. The connection structure 31 includes a right-hand thread on the outer circumference of the mounting shaft 14, a shaft hole penetrating the center of the large gear 20, and an internal thread on the inner circumferential surface of the shaft hole that engages with the right-hand thread. The right-hand thread is adaptively configured according to the direction of the engine's operating torque, so that the large gear 20 becomes increasingly tighter as it operates normally under vibration. The large gear 20 is threaded onto the outer circumference of the mounting shaft 14 through the engagement of the internal thread on its shaft hole with the right-hand thread. In the prior art, the intermediate gear assembly and hydraulic torque measuring mechanism is a technical solution for the design of aero-engine reducers. In this invention, because the right-hand thread is adaptively set according to the direction of the engine's working torque, the large gear 20 becomes tighter and tighter as it rotates during normal operation under vibration. Thus, the intermediate gear helical assembly 1 can provide an axial force proportional to the torque, while the hydraulic plunger provides buffering and damping, ensuring that the total runout 0.002 of the left journal 12 and the right journal 13 always remains within acceptable limits. This not only reduces noise but also improves the torque balance and reliability of the aero-engine, making the gears less prone to failure.

[0036] Preferably, in this invention, before the large gear 20 and the small gear 11 are spirally combined by the connecting structure 31, they are each shot-peened, with a shot-peening coverage of 200%; after the large gear 20 and the gear shaft 10 are combined, the large gear 20 is then subjected to a gear grinding process and an overall vibration finishing process.

[0037] In this optional design, the nominal diameter of the right-hand thread is 40–50 mm. The length of the right-hand thread is 25–35 mm. The tightening torque of the right-hand thread is greater than the working torque, and the tightening torque is 40–50 kg·m. This optimized design of the right-hand thread in this optional design ensures that the strength and rigidity of the intermediate gear helical assembly 1 meet the most stringent quality standards, thereby improving engine reliability. The nominal diameter of the right-hand thread, 40–50 mm, makes this intermediate gear helical assembly 1 a successful example of large-diameter threaded connections in aerospace gears. Its manufacturing cost is lower than that of intermediate gear assemblies welded by vacuum electron beam welding, and its reliability is higher than that of spline and pin connections. Furthermore, ensuring these design parameters and manufacturing precision of the right-hand thread is crucial to the product qualification rate.

[0038] Optionally, such as Figure 2 As shown, the connection adjustment structure 30 also includes a connection adhesive layer 34 formed by applying a connecting adhesive between the large gear 20 and the mounting shaft 14, and between the side end face of the large gear 20 and the side end face of the limiting flange 15, to enhance the stability of the connection between the large gear 20 and the gear shaft 10.

[0039] Optionally, such as Figure 3 As shown, the connecting adjustment structure 30 also includes an adjusting shim 32 and a limiting retaining ring 33. The adjusting shim 32 is mounted on the outer circle of the mounting shaft 14 and is clamped between the side end face of the limiting flange 15 and the side end face of the large gear 20, for adjusting the angular position of the large gear 20 relative to the small gear 11. In this optional embodiment, the angular position of the large gear 20 relative to the small gear 11 can be adjusted by rotating the large gear 20 by changing the thickness of the adjusting shim 32, so that the large gear 20 and the small gear 11 can mesh with their respective gears without interference. Figure 2 As shown, the limiting retaining ring 33 is installed on the outer circle of the mounting shaft 14 and is positioned between the right journal 13 and the large gear 20 to block the rollers of the roller bearing installed on the outer circle of the right journal 13 when not in operation.

[0040] Optionally, such as Figure 2 As shown, the gear disk of the large gear 20 is also machined with a concave, annular semi-circular groove. The intermediate gear helical assembly 1 also includes a damping ring 40 for vibration reduction. The damping ring 40 is fitted into the semi-circular groove. The damping ring is used to reduce the vibration of the intermediate gear helical assembly 1 during operation, making its operation smoother.

[0041] Optionally, the normal module of the large gear 20 is 1.25, which is a relatively small module that can be used in current long-life, airworthy, low-power turboshaft engines. The helix angles of both the small gear 11 and the large gear 20 are integers. Choosing integer helix angles avoids using decimals, facilitates memorization and calibration, and is also beneficial to the manufacturing process.

[0042] Reference Figures 4-6 , a preferred embodiment of the present invention further provides a turboprop engine, including a reducer, the reducer includes: a propeller shaft 4 for installing a propeller 3, a power turbine shaft 6 for connecting with a power turbine 5, and two sets of intermediate gear spiral combinations 1 as described in any one of the above. An input gear 7 is further provided on the outer circle of the power turbine shaft 6, and an output gear 8 is further installed on the outer circle of the propeller shaft 4. The two sets of intermediate gear spiral combinations 1 are respectively arranged on both sides of the power turbine shaft 6, and the large gears 20 of each set of intermediate gear spiral combinations 1 are respectively externally meshed with the input gear 7, and the small gears 11 of each set of intermediate gear spiral combinations 1 are respectively externally meshed with the output gear 8.

[0043] In the reducer of the present invention, the propeller shaft 4 and the power turbine shaft 6 are relatively arranged, and the two sets of intermediate gear spiral combinations 1 are respectively arranged on both sides of the power turbine shaft 6. Its transmission route is shaped like the Chinese character "Ya", so it is named the "Ya" - shaped reducer; the "Ya" - shaped reducer adopts two - stage external cylindrical gear over - constraint transmission, that is, the input gear 7 and the output gear 8 are respectively externally meshed with the two sets of intermediate gear spiral combinations 1 at the same time, thus forming over - constraint transmission. In over - constraint transmission, it is necessary to adjust the angular position of the threaded connection of one of the intermediate gear thread combinations to avoid tooth surface interference, otherwise it is almost impossible to assemble to make all tooth surfaces mesh with each other. In the present invention, the large gear 20 of the intermediate gear spiral combination 1 is helically connected to the gear shaft 10, so that by changing the thickness of the adjusting pad 32 to rotate the thread of the large gear 20, the angular position of the threaded connection of the intermediate gear spiral combination 1 can be adjusted, avoiding tooth surface interference and ensuring assembly in place, while making the loads of the two sets of intermediate gear spiral combinations 1 uniform, and avoiding large axial alignment errors and uneven forces of the two intermediate gear spiral combinations 1.

[0044] For the "Ya" - shaped reducer of the small - power turboprop engine of the present invention, the angle of the intermediate gear spiral combination 1 is adjustable, so that all transmission tooth surfaces can mesh normally without interference, facilitating the effective transmission of power; on the other hand, the reducer of the small - power turboprop engine needs to solve the problems of small bearing size, large load, and high speed. In the present invention, the "Ya" - shaped transmission scheme divides the power flow into two, reducing the radial pressure on the tooth surface to one - half, and the tooth surface pressure vector directions are different, and the vector sum is less than the sum of its values, thus prolonging the bearing life. Moreover, the "Ya" - shaped reducer of the small - power turboprop engine also evenly distributes the torque through the two intermediate gear spiral combinations 1, improving the gear strength margin of the engine, and further improving the safety and service life of the engine; the gear重合度 of the "Ya" - shaped reducer is significantly improved, the transmission is more stable, the amplitude constraint and damping of the vibration mode are significant, the noise is reduced, and the gears are not easily damaged.

[0045] In this alternative solution, as Figure 5 It should be noted that there may be some inaccuracies in the translation due to the possible ambiguity of the original text in some places. For example, the term "重合度" in the original text is not clearly defined. Here, it is tentatively translated as "重合度", which may need to be further determined according to the specific technical content.As shown, the propeller shaft 4 and the power turbine shaft 6 are arranged in parallel intervals. Two sets of intermediate gear helical assemblies 1 are symmetrically arranged. The pitch circle diameter of the input gear 7 is smaller than that of the large gear 20, and the pitch circle diameter of the small gear 11 is smaller than that of the output gear 8. This further optimized design makes the reducer structure more similar to an "A"-shaped reducer, thus resulting in a more significant load distribution effect and facilitating uniform load transmission.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A helical assembly for an intermediate gear in a speed reducer, characterized in that, include: A gear shaft (10) with a pinion (11), a left journal (12) and a right journal (13), and a large gear (20) that works with the pinion (11) to reduce speed and drive. Both the large gear (20) and the small gear (11) are helical gears, and the pitch circle diameter of the large gear (20) is larger than that of the small gear (11). The intermediate gear helical assembly (1) also includes a connecting adjustment structure (30). The large gear (20) is threaded onto the outer circle of the gear shaft (10) through the connecting adjustment structure (30) and is positioned between the small gear (11) and the right journal (13). The gear shaft (10) also includes a hollow cylindrical mounting shaft (14); the mounting shaft (14) between the pinion (11) and the right journal (13) protrudes outward to form an annular limiting flange (15); the large gear (20) is mounted on the outer circle of the mounting shaft (14) and is limited between the limiting flange (15) and the right journal (13) by the connecting adjustment structure (30); The connection adjustment structure (30) includes a connection structure (31) for threaded connection between the large gear (20) and the gear shaft (10). The connection structure (31) includes a right-hand thread on the outer circle of the mounting shaft (14), a shaft hole through the center of the large gear (20), and an internal thread on the inner circumferential surface of the shaft hole that cooperates with the right-hand thread. The right-hand thread is adapted to the direction of the engine working torque so that the large gear (20) becomes tighter as it rotates during normal operation under vibration. The large gear (20) is threaded onto the outer circle of the mounting shaft (14) through the cooperation of the internal thread on its shaft hole and the right-hand thread. The connecting adjustment structure (30) also includes an adjustment shim (32) and a limiting retaining ring (33); the adjustment shim (32) is installed on the outer circle of the mounting shaft (14) and is clamped between the side end face of the limiting flange (15) and the side end face of the large gear (20) to adjust the angular position of the large gear (20) relative to the small gear (11); the limiting retaining ring (33) is installed on the outer circle of the mounting shaft (14) and is limited between the right journal (13) and the large gear (20) to block the rollers of the roller bearing installed on the outer circle of the right journal (13) when not in operation.

2. The intermediate gear helical assembly for a speed reducer according to claim 1, characterized in that, The pinion (11) and the mounting shaft (14) are integrally formed; The left journal (12) and the right journal (13) are located on both sides of the pinion (11).

3. The intermediate gear helical assembly for a speed reducer according to claim 2, characterized in that, The nominal diameter of the right-hand thread is 40–50 mm; The length of a right-hand thread is 25–35 mm; The tightening torque of the right-hand thread is greater than the working torque, and the tightening torque is 40-50 kg·m.

4. The intermediate gear helical assembly for a speed reducer according to claim 1, characterized in that, The connection adjustment structure (30) also includes a connecting adhesive layer formed between the large gear (20) and the mounting shaft (14) and between the side end face of the large gear (20) and the side end face of the limiting flange (15) by applying connecting adhesive.

5. The intermediate gear helical assembly for a speed reducer according to claim 1, characterized in that, The gear disk of the large gear (20) is also machined with a concave and annular semi-circular groove; The intermediate gear helical assembly (1) also includes a damping ring (40) for vibration reduction, which is fitted into a semi-circular groove.

6. The intermediate gear helical assembly for a speed reducer according to claim 1, characterized in that, The normal module of the large gear (20) is 1.25; The helix angles of both the pinion (11) and the gear (20) are integers.

7. A turboprop engine, characterized in that, Includes a speed reducer, which includes: The propeller shaft (4) for mounting the propeller (3), the power turbine shaft (6) for connecting to the power turbine (5), and two sets of intermediate gear helical combinations (1) as described in any one of claims 1-6 above. An input gear (7) is also provided on the outer circle of the power turbine shaft (6), and an output gear (8) is also provided on the outer circle of the propeller shaft (4). Two sets of intermediate gear helical assemblies (1) are respectively located on both sides of the power turbine shaft (6), and the large gear (20) of each set of intermediate gear helical assemblies (1) meshes with the input gear (7) externally, and the small gear (11) of each set of intermediate gear helical assemblies (1) meshes with the output gear (8) externally.

8. The turboprop engine according to claim 7, characterized in that, The propeller shaft (4) and the power turbine shaft (6) are arranged in parallel at intervals; The two sets of intermediate gear helical combinations (1) are symmetrically arranged; The pitch circle diameter of the input gear (7) is smaller than that of the large gear (20), and the pitch circle diameter of the small gear (11) is smaller than that of the output gear (8).

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