Speed reducer for underground driving and underground tool assembly

Abstract

The embodiment of the invention provides a speed reducer used for underground driving and an underground tool assembly. The speed reducer comprises an input shaft, an output shaft and an output shaft, an output shaft; a gear train disposed between the input shaft and the output shaft and providing a first power transmission path having a first gear ratio and a second power transmission path having a second gear ratio greater than the first gear ratio; a pressure sensing part of the pressure driving assembly is exposed in the underground environment outside the speed reducer to sense the environment pressure, and the pressure driving assembly is configured to drive the speed reducer to rotate by means of force generated by the environment pressure when the environment pressure exceeds a preset pressure threshold value. The gear train is automatically switched from operating through the first power transmission path to operating through the second power transmission path.

Description

Technical Field

[0001] This disclosure relates to the field of oil and gas extraction equipment technology, and in particular to a reducer and downhole tool assembly for downhole drive. Background Technology

[0002] Traditional oil and gas well completion techniques heavily rely on manual intervention on the surface for reservoir management, such as adjusting production zones, controlling flow rates, and monitoring data. These operations typically require lowering specialized tools thousands of meters downhole using wirelines, coiled tubing, or other methods. This process is not only cumbersome, risky, and costly, but also inefficient and time-consuming. As oil and gas exploration and development move towards deepwater, deep formations, and reservoirs with complex well structures, the multi-branch well and multi-section combined production models make traditional manual intervention increasingly difficult, both technically and economically. More importantly, this passive management approach cannot achieve real-time, precise control of reservoir production dynamics, making it difficult to achieve optimal reservoir exploitation results.

[0003] To overcome these inherent limitations, intelligent well completion technology, which deeply integrates mechatronics, sensor technology, and modern well completion engineering, has emerged and rapidly become the core development direction of modern well completion technology. Internationally, a series of advanced intelligent well completion systems such as "SmartWell," "SCRAMS," and "Incharge" have been successfully developed and commercially applied. The core function of these systems is to achieve real-time monitoring and remote, precise control of oil and gas production or fluid injection in each production zone through monitoring and control equipment permanently placed downhole. In this system, the key to the physical execution level relies on a stable and reliable downhole drive system. These drive systems typically consist of a downhole motor, controller, and reducer, which precisely manipulates the opening of downhole tools (such as the nozzle or sleeve of a flow control valve) to achieve precise management of fluids in each zone.

[0004] Downhole drive systems operate in extremely harsh environments, typically facing the dual challenges of high temperature and high pressure, which pose significant challenges to the system's performance, reliability, and lifespan. Industry data shows that downhole ambient temperatures can reach 175°C or even higher, while ambient pressure can reach 40 MPa, and in ultra-deep wells, these values ​​are far exceeded.

[0005] First, high-temperature environments have a significant negative impact on motor performance. Permanent magnet motors, commonly used in downhole drive systems, face the risk of irreversible demagnetization of the permanent magnets under sustained high temperatures. The Joule heat generated by the motor itself during operation further exacerbates the temperature rise, accelerating the demagnetization process. The decrease in the residual magnetic flux density of the permanent magnets and the increase in armature winding resistance with temperature directly lead to a significant reduction in the motor's inherent torque output capacity and operating efficiency. Second, high-pressure environments significantly increase the mechanical load on the drive mechanism. The high ambient hydrostatic pressure within the wellbore and the pressure difference between the formation and the wellbore directly affect the moving parts of the flow control valve, such as the sliding sleeve and valve core, resulting in a significant increase in their motion friction resistance and the compressive friction of the seals. This additional load requires the drive motor to provide torque far exceeding that under normal pressure to complete the intended opening or closing action. In summary, high temperatures weaken the motor's output "capacity," while high pressure increases the requirements for the motor's "capacity." The combined effect of these two factors often causes traditional downhole drive systems to fail to drive the load under extreme conditions due to insufficient output torque, resulting in flow control valve sticking and inability to open or close properly. This failure not only seriously affects the functionality of intelligent completion systems and the refined management of reservoirs, but may even lead to production interruptions and cause huge economic losses.

[0006] Currently, the conventional technical solution for addressing changes in downhole torque demand is a combination of a motor and a fixed-ratio reducer. When downhole tools (such as valves) require greater torque due to pressure differentials, the surface control system issues a command to forcibly increase the output torque by increasing the input power (i.e., current) supplied to the downhole motor. While this solution is simple in principle, its fundamental system-level defects have been exposed in practical applications.

[0007] The fatal weakness of this approach lies in its absolute dependence on the well-to-surface communication link. In cabled intelligent completion systems, data communication and power transmission between the surface and downhole tools typically rely on a single-core armored cable thousands of meters long. This cable operates in a complex environment of high temperature, high pressure, strong vibration, and corrosive fluids, making its resistive-capacitive (RC) electrical parameters highly susceptible to drift. This parameter drift can lead to severe attenuation and distortion of control signals during long-distance transmission, a sharp increase in the bit error rate, and even complete signal loss in extreme cases. Therefore, when the surface system determines that it needs to increase the motor torque based on monitoring data and issues a command to increase power, this command may not be accurately and reliably transmitted to the downhole controller. This causes the downhole motor to be unable to adjust its output in a timely manner according to actual operating conditions, ultimately causing the entire drive system to "lose control" at the critical moment when high torque is most needed, rendering it unable to perform operations.

[0008] The problem has transcended simple materials science (such as motor demagnetization) or mechanical design (such as high frictional loads), evolving into a system-level control architecture failure issue. Any torque regulation scheme that relies on this fragile remote electronic control loop will inherit its inherent unreliability. Summary of the Invention

[0009] To address the aforementioned technical problems, this disclosure aims to provide a downhole drive reducer and downhole tool assembly that can solve the execution failure problem caused by the reliance on unreliable well-to-surface communication links for torque adjustment in existing downhole drive systems under high temperature and high pressure environments. Specifically, the technical problem this disclosure aims to solve is: how to enable a downhole drive system to autonomously sense the increase in downhole environmental pressure without relying on any external electrical control signals, and automatically and mechanically increase its output torque to ensure reliable drive of downhole tools to complete predetermined actions under various operating conditions, especially under high pressure conditions.

[0010] The technical solution disclosed herein is implemented as follows: In a first aspect, embodiments of this disclosure provide a downhole drive reducer, the reducer comprising: Input axis; Output shaft; A gear transmission system, wherein the gear transmission system is disposed between the input shaft and the output shaft, and provides a first power transmission path having a first transmission ratio and a second power transmission path having a second transmission ratio greater than the first transmission ratio; and A pressure-driven assembly, wherein the pressure-sensing part of the pressure-driven assembly is exposed to the downhole environment outside the reducer to sense the ambient pressure, and the pressure-driven assembly is configured to automatically switch the gear transmission system from operating through the first power transmission path to operating through the second power transmission path by utilizing the force generated by the ambient pressure when the ambient pressure exceeds a preset pressure threshold.

[0011] Secondly, embodiments of this disclosure provide a downhole tool assembly, the downhole tool assembly comprising: The reducer for downhole drive as described in the first aspect; and The driven component is mechanically coupled to the output shaft of the reducer.

[0012] This disclosure provides a downhole drive reducer and downhole tool assembly, whose core advantage lies in its fully mechanical autonomous shifting capability. It utilizes downhole environmental pressure—the most direct and reliable physical signal—to trigger torque adjustment, completely eliminating reliance on the fragile well-to-surface communication link. This fundamentally solves the problem of downhole tool loss of control due to signal transmission failure, greatly improving the reliability and success rate of intelligent completion systems in harsh environments. The multi-gear design allows the motor to operate within its optimal efficiency range over a wider load range. At lower loads, a low gear ratio (high speed gear) allows for rapid operation; as the load increases, it automatically switches to a high gear ratio (high torque gear), mechanically amplifying torque and avoiding forced operation of the motor under high current and overload conditions for extended periods. This not only reduces energy consumption but also reduces thermal stress on the motor, effectively delaying demagnetization at high temperatures, thereby extending the motor's service life. This shifting mechanism is inherently safe. In any situation, including a failure of the pressure drive mechanism, the default force of the biasing component ensures that the reducer automatically resets or remains in a preset default gear (e.g., low torque gear). This predictable failure mode provides greater safety for downhole operations. Attached Figure Description

[0013] Figure 1 This is a longitudinal sectional view of a speed reducer according to an embodiment of the present disclosure, showing a first embodiment of a pressure drive assembly.

[0014] Figure 2 This is a schematic diagram of the overall layout of a downhole tool assembly according to an embodiment of the present disclosure.

[0015] Figure 3 This is a longitudinal sectional view of a speed reducer according to an embodiment of the present disclosure, showing a second embodiment of the pressure drive assembly.

[0016] Figure 4 This is a longitudinal sectional view of a reducer according to an embodiment of the present disclosure, showing a third embodiment of the pressure drive assembly. Detailed Implementation

[0017] The technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings.

[0018] Reference Figure 1 The reducer 10 disclosed herein includes a sealed, pressure-resistant housing 18 and a multi-stage gear transmission system encapsulated within the housing 18. Its power is supplied by a downhole motor ( Figure 1 The input shaft (not shown) is driven by the output shaft 19, which, after multi-stage reduction and torque amplification, outputs power to drive components in the downhole tool that require power to perform actions, such as... Figure 2The flow control valve 20 shown.

[0019] The power transmission path sequentially passes through the downhole motor shaft gear, the primary transmission shaft 12, the secondary transmission shaft 14, and finally reaches the output shaft 19, which integrates the core shifting mechanism. Relative to the output shaft 19, both the primary transmission shaft 12 and the secondary transmission shaft 14 can be considered as input shafts. The core of this disclosure lies in the fact that the reducer 10 can utilize the ambient pressure F within the wellbore 100 as the sole control input signal, automatically switching between two preset transmission ratios via a purely mechanical pressure drive component 17, thereby achieving adaptive adjustment of the output torque without any external electrical signal intervention.

[0020] In one embodiment, see Figure 1 The high-speed pinion 121 of the first-stage drive shaft 12 meshes with the low-speed large gear 143 of the second-stage drive shaft 14 to complete the first-stage reduction and transmit power to the second-stage drive shaft 14.

[0021] Two high-speed pinions, namely a first pinion 141 and a second pinion 142, are fixedly connected to the secondary drive shaft 14. These two pinions are in constant mesh with the first output shaft gear 191 and the second output shaft gear 192, which are respectively mounted on the output shaft 19. This constitutes two parallel, selectable final-stage power transmission paths: As in Figure 1 The first path (high transmission ratio path) shown by the dashed arrow is as follows: power is transmitted from the first pinion 141 of the secondary transmission shaft 14 to the first output shaft gear 191.

[0022] As in Figure 1 The second path (low transmission ratio path) is shown by the arrow and dotted line: power is transmitted from the second pinion 142 of the secondary transmission shaft 14 to the second output shaft gear 192.

[0023] The core mechanism of the shifting function is located on the output shaft 19, and its structure is detailed in [link to documentation]. Figure 1 It mainly consists of the following components working together: Free-rotating gears: The first output shaft gear 191 and the second output shaft gear 192 are mounted on the output shaft 19 via bearings (such as needle roller bearings). In the unlocked state, they can rotate freely relative to the output shaft 19 and do not directly transmit torque to the output shaft 19.

[0024] (For a clear purpose) Figure 1(Not shown but easily understood) Limiting block: This component is circumferentially fixed to the output shaft 19 by means of a key connection or spline, and rotates together with the output shaft. Its axial position is fixed between the first output shaft gear 191 and the second output shaft gear 192, and its outer surface (e.g., external spline) provides guidance and support for the synchronizer 16.

[0025] Synchronizer 16: This component is an axially sliding sleeve whose internal spline engages with the external spline of the limiting block, ensuring that it rotates synchronously with the output shaft 19 while sliding axially. The two ends of synchronizer 16 are designed with meshing structures, such as canine teeth, pins, or protrusions. These structures can mesh with corresponding grooves on the end faces of the first output shaft gear 191 and the second output shaft gear 192 to achieve a rigid connection (i.e., power locking). Figure 1 As shown, the groove here is also defined by protrusions protruding from the end faces of the first output shaft gear 191 and the second output shaft gear 192.

[0026] Bias component 15: At the synchronizer 16 and housing fixing component (such as in...) Figure 1 A biasing component, such as a compression spring, is provided between the synchronizer 16 and the first output shaft gear 191 shown. This spring applies a continuous axial thrust to the synchronizer 16, causing it to engage with one of the gears (e.g., first output shaft gear 191 and second output shaft gear 192) in its default state (i.e., low-pressure state). Figure 1 The second output shaft gear 192 shown in the figure remains engaged.

[0027] The aforementioned pressure-driven component 17 is the "brain" and "muscle" of this disclosure, responsible for sensing ambient pressure F and converting it into mechanical force sufficient to drive synchronizer 16 to shift gears. Three specific feasible embodiments are described below.

[0028] The first embodiment is a piston-push rod type actuator, such as in Figure 1 As shown, this embodiment employs a classic piston structure that directly converts external pressure into internal thrust.

[0029] One or more cylindrical cavities 171 are machined into the housing 18 of the reducer 10. A piston 172 is installed inside the cavity 171, with its outer end face directly exposed to the well fluid. One or more drive push rods 173 are fixed to the inner end face of the piston 172 and pass through the cavity 171. The push rods 173 and the cavity 171 are sealed by a high-pressure dynamic seal. The push rods 173 can directly act on the synchronizer 16, such as in... Figure 1 As shown, the inner end of push rod 173 may also be connected to a pressure plate, which acts on synchronizer 16.

[0030] In this context, the aforementioned high-pressure dynamic seal is crucial to the design. To cope with downhole temperatures reaching up to 175°C and corrosive media (such as H2S, CO2, and amine corrosion inhibitors), the seal is preferably made of perfluororubber, with a continuous operating temperature up to 327°C, excellent chemical resistance, and extremely low compression set, ensuring long-term reliable sealing. For conditions involving rapid pressure changes, materials with excellent resistance to rapid gas decompression can also be selected. The sealing structure can employ O-rings or T-seals with spare rings to prevent the sealing ring from being extruded under high pressure.

[0031] The second embodiment is a fully sealed metal bellows actuator, such as in Figure 3 As shown, this embodiment employs a more advanced and reliable design, completely eliminating dynamic seals by using a sealed metal bellows as the pressure-sensing and force-transmitting element.

[0032] A metal bellows 174 is integrated and mounted on the housing 18 of the reducer 10. The bellows 174 is a flexible, axially expandable metal cylinder, with one end completely sealed and the other end connected to the housing 18, thus forming a sealed cavity isolated from the outside environment. The outer surface of the bellows 174 is exposed to the wellbore environment. A push rod 173 is connected to the movable inner end cap of the bellows 174, and the push rod 173 is completely located within the sealed internal environment of the reducer, with its other end acting on the synchronizer 16.

[0033] In this case, the most prominent advantage is the achievement of a fully static seal, eliminating the wear and leakage risks of dynamic seals, thereby greatly improving the long-term reliability and maintenance-free cycle of the drive mechanism. To adapt to the harsh environment of downhole wells containing corrosive gases such as H2S, the material of the bellows 174 must be a corrosion-resistant alloy, such as a high-nickel alloy, which has excellent resistance to sulfide stress cracking and chloride pitting corrosion.

[0034] The third embodiment is a high-voltage diaphragm actuator, such as in Figure 4 As shown, this embodiment utilizes a robust yet flexible diaphragm 175 to isolate the wellbore fluid from the internal mechanisms, generating tremendous driving force within a relatively short stroke through a large effective pressure-bearing area.

[0035] A diaphragm 175 is mounted on the housing 18 of the reducer 10. The diaphragm 175 is a high-strength diaphragm (e.g., made of reinforced elastomer or using a corrugated metal diaphragm) with its edges firmly clamped and sealed. The outer side of the diaphragm 175 is exposed to ambient pressure F, while the inner side is supported by a push rod 173. The push rod 173 transmits the thrust received from the diaphragm 175 to the synchronizer 16.

[0036] This design draws upon proven technologies from high-pressure diaphragm valves and actuators used in harsh industrial sectors such as petrochemicals. Its main advantages are robust construction, high driving force generation, and effective isolation of the internal mechanisms from the external medium. It is particularly suitable for applications requiring overcoming strong bias spring forces.

[0037] Despite Figure 1 , Figure 3 and Figure 4 The diagram shows that power reaches the output shaft 19 after being transmitted via a primary driveshaft 12 and a secondary driveshaft 14. However, this disclosure is not limited to this. That is, power can reach the output shaft 19 via more driveshafts and corresponding large and small gears to complete more stages of deceleration before the output shaft 19. This is well known to those skilled in the art and will not be elaborated further here.

[0038] To ensure the reliable operation of the reducer 10 throughout its long design life in the well, the selection of materials, heat treatment processes, and manufacturing precision of its key internal load-bearing components are crucial. This is not only a guarantee for achieving basic functions, but also a reflection of the technical completeness of this disclosure as an engineering product that can be deployed in extreme environments.

[0039] All gears can be made of low-alloy carburized steel. The reason for choosing carburized steel is that it can form an extremely hard, wear-resistant layer on the gear surface through heat treatment, while maintaining good toughness and ductility in the core. This combination of a hard surface and a tough core is ideal for gears subjected to tooth surface contact stress and bending fatigue stress, effectively resisting wear and impact loads.

[0040] Each stage of the drive shaft and the final output shaft 19 can be made of integral quenched and tempered high-strength alloy steel. After quenching and tempering (quenching followed by high-temperature tempering), this type of material can obtain uniform high strength, high toughness and excellent fatigue resistance across the entire cross section, making it very suitable as shaft parts that withstand high torque and bending stress.

[0041] For gears, carburizing, quenching, and low-temperature tempering processes can be used. The depth of the carburized layer is precisely controlled according to the gear module and the expected load, and the final surface hardness should reach 58-62 HRC to provide excellent wear resistance. For shafts, quenching and tempering is used to obtain tensile strength, for example, exceeding 1000 MPa, and matching toughness.

[0042] By systematically combining the above design choices, we go beyond simple material stacking to form a complete engineering solution for extreme downhole operating conditions. It organically integrates kinematic design (gear parameters) with materials science, heat treatment technology, and precision manufacturing standards, thereby elevating a conceptual design into an industrial product with high reliability and long lifespan. This systematic engineering design consideration is the key difference between this disclosure and a simple concept.

[0043] The gear transmission system of the reducer 10 operates within a sealed housing filled with lubricating oil. Considering that downhole motors typically operate in the low to medium speed range, the reducer 10 preferably employs splash lubrication. That is, by immersing part of the gears in the oil sump, the lubricating oil is agitated and splashed onto the surfaces of all gears, bearings, and moving parts during rotation, forming a lubricating oil film.

[0044] The downhole environment is extremely hot, therefore, high-performance synthetic lubricants with excellent thermal stability and wide operating temperature range must be selected. Gear oils are preferred, as they have extremely high viscosity index, excellent oxidation resistance, and low volatility, maintaining stable lubrication performance at temperatures up to 175°C or even higher. Simultaneously, the lubricant must possess good dielectric properties to avoid electrical interference with nearby motor systems.

[0045] The housing 18 of the reducer 10 is designed as a pressure compensator. The pressure of the lubricating oil inside it is always dynamically balanced with the external wellbore environment pressure. This function is cleverly achieved simultaneously by the aforementioned pressure drive assembly 17 (piston, bellows, or diaphragm). When the external environment pressure increases, this pressure not only acts on the pressure drive assembly 17 to generate shifting force, but also transmits the pressure to the lubricating oil inside the housing 18 through the displacement of the components (piston, bellows, or diaphragm) of the pressure drive assembly 17, so that the internal oil pressure increases synchronously with the external water pressure, thereby ensuring that the pressure difference between the inside and outside of the housing 18 is always close to zero.

[0046] The dual function of the pressure drive assembly 17 (shift drive + pressure compensation) is a highly integrated and efficient design. It not only solves the power source problem for shifting but also fundamentally addresses the sealing challenge of the housing 18 under high external pressure. Without pressure compensation, external pressures up to 40 MPa would easily crush the housing 18 or cause all seals to fail. Furthermore, the pressure compensation function automatically compensates for thermal expansion and contraction of the lubricating oil due to temperature changes, preventing excessively high or low internal pressures and further ensuring the sealing integrity and operational stability of the reducer 10.

[0047] The complete working process of reducer 10 is as follows.

[0048] For low-pressure conditions (high-speed / low-torque mode), the operating condition is that the downhole ambient pressure is lower than a preset threshold pressure (e.g., less than 40 MPa). In this case, the thrust generated by the pressure drive assembly 17 (piston, bellows, or diaphragm) is less than the preload of the bias spring. The bias spring holds the synchronizer 16 in its default position, engaged with the protrusion of the second output shaft gear 192. Power is transmitted from the second pinion 142, fixed to the secondary drive shaft 14, to the second output shaft gear 192, and then through the synchronizer 16 and the limit block to the output shaft 19. If the second output shaft gear 192 has 30 teeth and the second pinion 142 has 10 teeth, the output stage gear ratio is 30 / 10 = 3. The reducer 10 operates at a relatively high speed and low torque output, suitable for operations such as quickly opening and closing valves under normal conditions.

[0049] For high-pressure conditions (low-speed / high-torque mode), the operating condition is that the downhole ambient pressure is higher than a preset threshold pressure (e.g., greater than 40 MPa). The thrust generated by the pressure drive assembly 17 overcomes the preload of the bias spring. The pressure drive assembly 17 pushes the synchronizer 16 to slide axially, disengaging it from the second output shaft gear 192 and engaging with the convex part of the high-ratio first output shaft gear 191. Power is then transmitted from the first pinion 141 fixed to the secondary drive shaft 14 to the first output shaft gear 191, and then through the synchronizer 16 and the limit block to the output shaft 19. At this time, if the first output shaft gear 191 has 40 teeth and the first pinion 141 has 8 teeth, the transmission ratio of the output stage automatically switches to 40 / 8 = 5. The output torque is increased by approximately 66% compared to the low-pressure mode, while the motor input torque remains unchanged. The reducer 10 operates at a relatively low speed and a high torque output state to overcome the huge mechanical load under high-pressure conditions.

[0050] See Figure 2 This disclosure also provides a downhole tool assembly 1. Specifically, the reducer 10 described in this disclosure can serve as a power module and be integrated with various downhole tools or components to be driven. Figure 2 As shown, a typical application is driving the flow control valve 20. Figure 2The diagram also details the process of power transmission from the downhole motor 30 to the valve core 21 of the flow control valve 20. Power from the downhole motor 30 is reduced in speed by the reducer 10 and then input to the lead screw 50 via the output shaft 19. The output shaft 19 of the reducer 10 and the lead screw 50 are connected via a coupling 40. A nut 60 engages with the lead screw 50, and the valve core 21 of the flow control valve 20 is fixed to the nut 60 to move with it. This converts rotational motion into linear motion of the valve core 21, allowing it to move within the valve seat 22 of the flow control valve 20, thereby precisely controlling the opening of the flow control valve 20. When the ambient pressure F is low, the reducer 10 operates in a low-torque range, allowing for rapid adjustment of the flow control valve 20. When the ambient pressure F increases, causing increased resistance to the opening and closing of the flow control valve 20, the reducer 10 automatically switches to a high-torque range, ensuring reliable operation of the flow control valve 20 even under significant pressure differentials.

[0051] More broadly, the application scenarios of this disclosure can be extended to all downhole tools that require highly reliable rotary drives, such as sliding sleeves for section isolation, downhole choke valves for flow regulation, and surface-controlled downhole safety valves for wellhead safety control.

[0052] It should be noted that the technical solutions described in the embodiments of this disclosure can be combined arbitrarily without conflict.

[0053] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A reducer for downhole drive, characterized in that, include: Input axis; Output shaft; A gear transmission system is disposed between the input shaft and the output shaft, and provides a first power transmission path having a first transmission ratio and a second power transmission path having a second transmission ratio greater than the first transmission ratio. as well as A pressure-driven assembly, wherein the pressure-sensing part of the pressure-driven assembly is exposed to the downhole environment outside the reducer to sense the ambient pressure, and the pressure-driven assembly is configured to automatically switch the gear transmission system from operating through the first power transmission path to operating through the second power transmission path by utilizing the force generated by the ambient pressure when the ambient pressure exceeds a preset pressure threshold.

2. The reducer for downhole drive according to claim 1, characterized in that, The reducer also includes: A synchronizer, mechanically coupled to the gear transmission system, and movable between a first position for selecting the first power transmission path and a second position for selecting the second power transmission path; and A biasing component applies a preset biasing force to the synchronizer to hold the synchronizer in the first position when the ambient pressure is below the preset pressure threshold.

3. The reducer for downhole drive according to claim 2, characterized in that, The synchronizer is circumferentially fixed to the output shaft and configured to slide axially on the output shaft.

4. The reducer for downhole drive according to claim 3, characterized in that, The gear transmission system includes a first output shaft gear and a second output shaft gear on the output shaft. Both the first output shaft gear and the second output shaft gear can rotate freely around the output shaft. When the synchronizer slides axially to the first position, it is dynamically locked with the first output shaft gear. When the synchronizer slides axially to the second position, it is dynamically locked with the second output shaft gear.

5. The reducer for downhole drive according to claim 4, characterized in that, The synchronizer is locked to the power of the first output shaft gear or the second output shaft gear by the engagement of a dog tooth, a pin, or a protrusion with a corresponding groove.

6. The reducer for downhole drive according to claim 1, characterized in that, The pressure drive assembly includes a piston housed in a cavity within the housing of the reducer, one end of the piston being exposed to the downhole environment as the pressure-sensing part.

7. The reducer for downhole drive according to claim 1, characterized in that, The pressure drive assembly includes a sealed metal bellows integrated into the housing of the reducer, with the outer surface of the bellows serving as the pressure-sensing part.

8. The reducer for downhole drive according to claim 1, characterized in that, The pressure drive assembly includes a high-pressure diaphragm, one side of which is exposed to the downhole environment to serve as the pressure sensing element.

9. A downhole tool assembly, characterized in that, include: A reducer for downhole drive according to any one of claims 1 to 8; as well as The driven component is mechanically coupled to the output shaft of the reducer.

10. The downhole tool assembly according to claim 9, characterized in that, The component to be driven is a flow control valve.

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