A drive shaft assembly for screw drills

Abstract

This invention provides a drive shaft assembly for a screw drill, comprising: a mandrel; a housing sleeved on the mandrel; a thrust bearing assembly for transmitting axial force; a deep groove ball bearing assembly for suppressing radial vibration of the mandrel; and a sealing assembly disposed between the mandrel and the housing, comprising a first floating isolation ring, a second floating isolation ring, and a sealing element spaced apart from top to bottom. A first lubrication cavity and a second lubrication cavity are formed axially between the first floating isolation ring, the second floating isolation ring, and the sealing element, respectively, for filling with lubricating oil. The thrust bearing assembly and the deep groove ball bearing assembly are both installed in the second lubrication cavity, with the deep groove ball bearing assembly located at the lower end of the thrust bearing assembly. The first and second floating isolation rings can move axially when the lubricating oil expands due to high temperature, thereby isolating the lubricating oil in the second lubrication cavity.

Description

Technical Field

[0001] This invention belongs to the field of oil drilling tool technology, specifically relating to a drive shaft assembly for screw drills. Background Technology

[0002] The screw drill mainly consists of three parts: a motor, a universal joint, and a drive shaft assembly. The main function of the drive shaft assembly is to transmit axial forces such as drilling pressure through the thrust bearing and stabilize the mandrel through the TC radial bearing, while the mandrel rotates and the housing remains stationary.

[0003] To reduce the temperature and wear of thrust bearings and TC radial bearings, most drive shaft assemblies currently employ an open structure, using drilling fluid for cooling and lubrication. However, drilling fluid contains a large amount of solids such as sand particles, resulting in poor lubrication and significant bearing wear, greatly reducing bearing lifespan. The clearance between the inner and outer races of the TC radial bearing is typically 0.15mm. While this creates flow resistance that effectively limits drilling fluid flow, the clearance also results in a 0.15mm allowance for spindle movement. This leads to poor vibration suppression in the TC shaft, making it prone to fatigue failure.

[0004] Chinese patent document 201320693139.X discloses a sealed thrust bearing for a screw drill drive shaft. It specifically discloses the structure for sealing the bearing, but does not consider the changes in sealing pressure caused by high temperature and pressure changes downhole. Large pressure can easily damage the sealing structure, leading to seal failure.

[0005] Chinese patent document 201110226400.0 discloses an oil-sealed screw drill drive shaft assembly with pressure compensation function for oil and gas drilling. It includes a piston cylinder sealing device and a pressure compensation device. Although sealing pressure compensation is considered, the compensation capacity of the conical spring used in the pressure compensation device is very limited. Furthermore, it does not consider the fixation and fatigue failure of the mandrel, and therefore cannot improve the life and fatigue resistance of the screw drill mandrel. Summary of the Invention

[0006] In view of the technical problems mentioned above, the present invention aims to provide a drive shaft assembly for screw drills. This drive shaft assembly for screw drills can significantly improve the life and fatigue resistance of the screw drill drive shaft, which is very beneficial to improving the overall life of the screw drill, increasing downhole drilling footage, and reducing drilling costs.

[0007] Therefore, according to the present invention, a drive shaft assembly for a screw drill is provided, comprising: a mandrel; a housing sleeved on the mandrel; a thrust bearing assembly for transmitting axial force; a deep groove ball bearing assembly for suppressing radial vibration of the mandrel; and a sealing assembly disposed between the mandrel and the housing, comprising a first floating isolation ring, a second floating isolation ring, and a sealing element spaced apart from top to bottom, wherein a first lubrication cavity and a second lubrication cavity are formed axially between the first floating isolation ring, the second floating isolation ring, and the sealing element, respectively, for filling with lubricating oil; wherein the thrust bearing assembly and the deep groove ball bearing assembly are both installed in the second lubrication cavity, and the deep groove ball bearing assembly is located at the lower end of the thrust bearing assembly; the first floating isolation ring and the second floating isolation ring are capable of moving axially when the lubricating oil expands due to high temperature, thereby isolating the lubricating oil in the second lubrication cavity.

[0008] In one embodiment, the outer ring of the deep groove ball bearing assembly is interference-fitted with the housing, and the inner ring of the deep groove ball bearing assembly is interference-fitted with the spindle.

[0009] In one embodiment, a TC radial bearing is installed between the lower end of the housing and the mandrel. The TC radial bearing includes a TC outer sleeve fixedly connected to the housing and a TC inner sleeve fixedly connected to the mandrel.

[0010] The sealing element is disposed between the outer sleeve of the TC and the inner sleeve of the TC.

[0011] In one embodiment, a radial gap is left between the outer sleeve of the TC and the inner sleeve of the TC to allow radial vibration of the mandrel to be transmitted to the housing through the deep groove ball bearing assembly.

[0012] In one embodiment, a wear-resistant layer is provided on both the inner surface of the TC outer sleeve and the outer surface of the TC inner sleeve.

[0013] In one embodiment, a positioning component is provided at the upper end of the thrust bearing assembly for axial positioning of the thrust bearing assembly and the deep groove ball bearing assembly.

[0014] In one embodiment, the positioning assembly includes an inner positioning sleeve, an outer positioning sleeve, and a positioning nut fixed to the mandrel.

[0015] The two ends of the positioning inner sleeve abut against the positioning nut and the upper end face of the inner ring of the thrust bearing assembly, respectively. The inner wall of the outer shell is provided with a limiting step with the end face facing downward. The two ends of the positioning outer sleeve abut against the limiting step and the upper end face of the outer ring of the thrust bearing assembly, respectively.

[0016] In one embodiment, the first floating isolation ring is disposed between the inner positioning sleeve and the outer shell, and the second floating isolation ring is disposed between the inner positioning sleeve and the outer positioning sleeve.

[0017] In one embodiment, both the first floating isolation ring and the second floating isolation ring are made of polytetrafluoroethylene (PTFE).

[0018] In one embodiment, the housing is provided with a first oil inlet and a second oil inlet, the first oil inlet being connected to the first lubrication cavity and the second oil inlet being connected to the second lubrication cavity.

[0019] Compared with the prior art, the advantages of this application are:

[0020] The drive shaft assembly for screw drills according to the present invention transmits the radial vibration of the mandrel through a deep groove ball bearing assembly, effectively suppressing the radial vibration of the mandrel and significantly reducing the friction of the mandrel. Simultaneously, an isolation oil ring is formed by a first and second floating isolation ring, which acts as a buffer, greatly reducing the contamination of the bearing lubricating oil and significantly improving the wear life of the thrust bearing assembly and the deep groove ball bearing assembly. This drive shaft assembly can improve the life and fatigue resistance of the screw drill drive shaft, thereby increasing the overall life of the screw drill, which is highly beneficial for increasing downhole drilling footage and reducing drilling costs. Attached Figure Description

[0021] The present invention will now be described with reference to the accompanying drawings.

[0022] Figure 1 The structure of a drive shaft assembly for a screw drill according to the present invention is shown.

[0023] In this application, all drawings are schematic and are used only to illustrate the principles of the invention, and are not drawn to scale. Detailed Implementation

[0024] The invention will now be described with reference to the accompanying drawings.

[0025] For ease of understanding, in this application, the end closest to the wellhead is defined as the upper end, upstream end, or similar terms, for example... Figure 1 The left end is defined as the end furthest from the wellhead, while the end furthest from the wellhead is defined as the lower end, downstream end, or similar terms, for example... Figure 1 The right end of the drive shaft assembly. Meanwhile, the direction along the length of the drive shaft assembly is referred to as the longitudinal direction, axial direction, or similar terminology, while the direction perpendicular to it is referred to as the transverse direction, radial direction, or similar terminology.

[0026] Figure 1 The structure of a drive shaft assembly 100 for a screw drill tool according to the present invention is shown. Figure 1As shown, the drive shaft assembly 100 includes a spindle 1, a housing 2, a thrust bearing assembly 3, a deep groove ball bearing assembly 4, and a sealing assembly. The spindle 1 has a central flow channel 11 for drilling fluid circulation. The housing 2 is fitted over the spindle 1. The thrust bearing assembly 3, the deep groove ball bearing assembly 4, and the sealing assembly are disposed between the spindle 1 and the housing 2, thereby forming a rotatable connection between the spindle 1 and the housing 2. The thrust bearing assembly 3 is used to transmit axial force, and the deep groove ball bearing assembly 4 is used to suppress radial vibration of the spindle 1. The sealing assembly is disposed between the spindle 1 and the housing 2, and includes a first floating isolation ring 51, a second floating isolation ring 52, and a sealing element 53, which are spaced apart from top to bottom. For example, the first floating isolation ring 51 and the second floating isolation ring 52 form an annular first lubrication cavity 6 between their axial directions, and an annular second lubrication cavity 7 is formed between the second floating isolation ring 52 and the sealing element 53. Both the first lubrication cavity 6 and the second lubrication cavity 7 are filled with lubricating oil. Both the thrust bearing assembly 3 and the deep groove ball bearing assembly 4 are located in the second lubrication chamber 7, and the deep groove ball bearing assembly 4 is located at the lower end of the thrust bearing assembly 3. During operation, the lubricating oil in the second lubrication chamber 7 can lubricate the thrust bearing assembly 3 and the deep groove ball bearing assembly 4.

[0027] When the downhole temperature is high, or the lubricating oil expands due to the high operating temperature of the bearing, the first floating isolation ring 51 and the second floating isolation ring 52 can adapt to the expansion of the lubricating oil and move axially, thereby isolating the lubricating oil in the second lubrication chamber 7. The lubricating oil in the first lubrication chamber 6 forms an isolation oil ring and acts as a buffer, which can greatly reduce the contamination of the lubricating oil in the second lubrication chamber 7, thereby significantly improving the wear life of the thrust bearing assembly 3 and the deep groove ball bearing assembly 4.

[0028] The axial distance between the first floating isolation ring 51 and the second floating isolation ring 52 can be, for example, 10 cm.

[0029] like Figure 1 As shown, the outer casing 2 is provided with a first oil inlet 21 and a second oil inlet 22. The first oil inlet 21 is located on the side wall of the outer casing 2 corresponding to the first lubrication cavity 6, thereby communicating with the first lubrication cavity 6, and is used to inject lubricating oil into the first lubrication cavity 6. The second oil inlet 22 is located on the side wall of the outer casing 2 corresponding to the second lubrication cavity 7, thereby communicating with the second lubrication cavity 7, and is used to inject lubricating oil into the second lubrication cavity 7.

[0030] According to the present invention, the thrust bearing assembly 3 includes 5 to 7 thrust bearings, and the deep groove ball bearing assembly 4 includes 2 to 3 deep groove ball bearings 6. The thrust bearing assembly 3 and the deep groove ball bearing assembly 4 are continuously arranged and installed between the spindle 1 and the housing 2. The thrust bearing assembly 3 has a radial allowance, which can be, for example, 2 mm, but no axial allowance. The outer ring of the deep groove ball bearing assembly 4 is interference-fitted with the housing 2, and the inner ring of the deep groove ball bearing assembly is interference-fitted with the spindle 1. Thus, the deep groove ball bearing assembly 4 has no radial allowance, but has an axial allowance, which can be, for example, 1 mm.

[0031] like Figure 1 As shown, the lower end of the mandrel 1 is equipped with a stepped connecting buckle for connecting to the drill bit (not shown). The upper end of the housing 2 is constructed with a tapered connecting buckle for connecting to the drill pipe (not shown). During operation, the drill string pressure is transmitted to the mandrel 1 through the drill pipe, housing 2, and thrust bearing assembly 3, and finally to the drill bit. Since the thrust bearing assembly 3 has no axial movement, all axial forces, including the drill pressure, are borne by the thrust bearing assembly 3.

[0032] According to the present invention, such as Figure 1 As shown, a TC radial bearing is installed between the lower end of the outer casing 2 and the spindle 1. The TC radial bearing includes a TC outer sleeve 81 fixedly connected to the outer casing and a TC inner sleeve 82 fixedly connected to the spindle 1. The outer surface of the TC outer sleeve 81 has an upward-facing step, and the TC outer sleeve 81 is fixedly connected to the lower end of the outer casing 2 by threads. The lower end face of the outer casing 2 contacts the end face of the step on the TC outer sleeve 81. To ensure the sealing between the TC outer sleeve 81 and the outer casing 2, a seal (not shown) can be provided between the connecting surfaces of the outer casing 2 and the TC outer sleeve 81. The TC inner sleeve 82 is fixedly connected to the spindle 1 by threads, and the lower end face of the TC inner sleeve 82 contacts the upper end face of the stepped connecting buckle at the lower end of the spindle 1. The TC inner sleeve 82 rotates with the spindle 1, and the TC outer sleeve 81 rotates with the outer casing 2.

[0033] like Figure 1 As shown, the sealing element 53 is disposed between the TC outer sleeve 81 and the TC inner sleeve 82. For example, a sealing groove is provided on the outer surface of the TC inner sleeve 82, the sealing element 53 is installed in the sealing groove, and the outer surface of the sealing element 53 is in close contact with the inner wall surface of the TC outer sleeve 81, thereby forming a seal between the TC outer sleeve 81 and the TC inner sleeve 82. The sealing element 53 can be, for example, a Gladwell ring.

[0034] According to the present invention, a radial gap is left between the outer sleeve 81 and the inner sleeve 82 of the TC, so that the radial vibration of the spindle 1 is transmitted to the outer casing 1 through the deep groove ball bearing assembly 4. Preferably, the gap between the outer sleeve 81 and the inner sleeve 82 of the TC is 0.15 mm.

[0035] In one embodiment, a wear-resistant layer may be provided on both the inner surface of the TC outer sleeve 81 and the outer surface of the TC inner sleeve 82. The wear-resistant layer may, for example, be a sintered tungsten carbide hard alloy. This is beneficial for improving the service life of the TC radial bearing.

[0036] According to one embodiment of the present invention, both the first floating isolation ring 51 and the second floating isolation ring 52 are made of polytetrafluoroethylene (PTFE). Furthermore, the thickness of the first floating isolation ring 51 and the second floating isolation ring 52 is set to be 0.1 mm larger than the radial clearance between the mandrel 1 and the outer shell 2. This allows the first floating isolation ring 51 and the second floating isolation ring 52 to press-fit and seal between the mandrel 1 and the outer shell 2, providing good sealing and isolation, and ensuring the independence and sealing of the first lubrication cavity 6 and the second lubrication cavity 7. The first floating isolation ring 51 can move axially when a pressure difference is formed on both sides, and the second floating isolation ring 52 can also move axially when a pressure difference is formed on both sides. Therefore, during operation, the lubricating oil in the second lubrication chamber 7 lubricates the thrust bearing assembly 3 and the deep groove ball bearing assembly 4. The first lubrication chamber 6 forms an isolation oil ring on the axial outer side of the second lubrication chamber 7. This isolation oil ring can act as a buffer to protect and isolate the lubricating oil in the second lubrication chamber 7, greatly reducing the contamination of the lubricating oil (i.e., bearing lubricating oil) in the second lubrication chamber 7, and significantly improving the wear life of the thrust bearing assembly 3 and the deep groove ball bearing assembly 4.

[0037] It should be understood that the first floating isolation ring 51 and the second floating isolation ring 52 also have certain wear resistance properties. Since the first floating isolation ring 51 and the second floating isolation ring 52 are press-sealed between the spindle 1 and the outer shell 2, on the one hand, both the first floating isolation ring 51 and the second floating isolation ring 52 form a seal with the spindle 1 and the outer shell 2, thereby ensuring the sealing of the first lubrication cavity 6 and the second lubrication cavity 7. On the other hand, when the first floating isolation ring 51 and the second floating isolation ring 52 move axially under the expansion of the lubricating oil, they can clean the surfaces of the spindle 1 and the outer shell 2 that come into contact with the first floating isolation ring 51 and the second floating isolation ring 52, thereby further reducing the contamination of the lubricating oil in the first lubrication cavity 6 and the second lubrication cavity 7.

[0038] In one embodiment, a positioning component may be provided at the upper end of the thrust bearing assembly 3 for axial positioning of the thrust bearing assembly 3 and the deep groove ball bearing assembly 4. For example... Figure 1As shown, the positioning assembly includes a positioning outer sleeve 91, a positioning inner sleeve 92, and a positioning nut 93 fixed on the spindle 1. The two ends of the positioning inner sleeve 91 abut against the positioning nut 93 and the upper end face of the inner ring of the thrust bearing assembly 3, respectively. The inner wall of the outer casing 2 is provided with a downward-facing limiting step, and the two ends of the positioning outer sleeve 92 abut against the limiting step and the upper end face of the outer ring of the thrust bearing assembly 3, respectively. Thus, through the combined action of the positioning assembly and the TC radial bearing, the thrust bearing assembly 3 and the deep groove ball bearing assembly 4 are fixedly installed between the outer casing 2 and the spindle 1. When the positioning assembly is provided, the first floating isolation ring 51 is disposed between the positioning inner sleeve 91 and the outer casing 2, and the second floating isolation ring 52 is disposed between the positioning inner sleeve 91 and the positioning outer sleeve 92. At this time, the surfaces in contact with the first floating isolation ring 51 and the second floating isolation ring 52 are the inner surface of the outer casing 2, the outer surface of the positioning inner sleeve 91, and the inner surface of the positioning outer sleeve 92.

[0039] The working process of the drive shaft assembly 100 for screw drills according to the present invention is briefly described below.

[0040] First, the lower end of the mandrel 1 is connected to the drill bit, and the upper end of the housing 2 is connected to the drill pipe, thus connecting the drive shaft assembly 100 into the drill string, which is then lowered into the wellbore for drilling operations. When the drill bit breaks the rock under drilling pressure, it generates severe radial vibration, which is transmitted to the mandrel 1. Since the deep groove ball bearing assembly 4 has no radial movement, and there is a radial gap between the TC outer sleeve 81 and the TC inner sleeve 82 of the TC radial bearing, the deep groove ball bearing assembly 4 transmits the radial vibration to the housing 2. Because the housing 1 is connected to the drill string through the drill pipe, the large weight of the drill string effectively suppresses the radial vibration, thereby improving the fatigue strength of the mandrel 1. Larger measuring forces or vibrations act on the deep groove ball bearing assembly 4, making its frictional resistance much lower than that of conventional sliding bearings. When the radial vibration is large, or when the deep groove ball bearing assembly wears, the TC radial bearing can play a certain role in suppressing radial vibration.

[0041] The combined bearing system, consisting of thrust bearing assembly 3, deep groove ball bearing assembly 4, and TC radial bearing, generates heat and wear while transmitting drilling pressure and suppressing vibration. After the drive shaft assembly 100 is lowered into the well, when the downhole temperature is high or the lubricating oil expands due to high bearing operating temperature, the first floating isolation ring 51 and the second floating isolation ring 52 will move axially upwards. After the first floating isolation ring 51 moves, the lubricating oil in the first lubrication chamber 6 comes into contact with the mandrel 2 and the outer shell 1 that were originally in contact with the mud, resulting in a small amount of contamination in the lubricating oil in the first lubrication chamber 6. After the second floating isolation ring 52 moves, the lubricating oil in the second lubrication chamber 7 comes into contact with the lubricating oil that was originally in the first lubrication chamber 6, so the contamination is at a trace level. The lubricating oil between the two floating isolation rings plays a protective and isolating role. The isolation oil ring formed by the lubricating oil in the first lubrication chamber 6 can act as a buffer to protect and isolate the lubricating oil in the second lubrication chamber 7, effectively avoiding the large amount of contamination of the lubricating oil in the second lubrication chamber 7 caused by the movement of the first floating isolation ring 51 and the second floating isolation ring 52. This greatly reduces the contamination of the bearing lubricating oil and significantly improves the wear life of the thrust bearing assembly 3 and the deep groove ball bearing assembly 4.

[0042] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] Furthermore, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A drive shaft assembly for a screw drill bit, comprising: mandrel (1); A housing (2) fitted onto the mandrel; Thrust bearing assembly (3) used to transmit axial force; A deep groove ball bearing assembly (4) for suppressing radial vibration of the mandrel (1); and The sealing assembly disposed between the spindle (1) and the housing (2) includes a first floating isolation ring (51), a second floating isolation ring (52) and a sealing element (53) distributed sequentially from top to bottom. A first lubrication cavity (6) and a second lubrication cavity (7) are formed between the first floating isolation ring (51), the second floating isolation ring (52) and the sealing element (53) in the axial direction, respectively, for filling with lubricating oil. The thrust bearing assembly (3) and the deep groove ball bearing assembly (4) are both installed in the second lubrication cavity (7), and the deep groove ball bearing assembly (4) is located at the lower end of the thrust bearing assembly (3). The first floating isolation ring (51) and the second floating isolation ring (52) can move axially when the lubricating oil expands due to high temperature, thereby isolating the lubricating oil in the second lubrication cavity (7).

2. The drive shaft assembly for a screw drill according to claim 1, characterized in that, The outer ring of the deep groove ball bearing assembly (4) is interference-fitted with the housing (2), and the inner ring of the deep groove ball bearing assembly (4) is interference-fitted with the spindle (1).

3. The drive shaft assembly for a screw drill according to claim 1 or 2, characterized in that, A TC radial bearing is installed between the lower end of the outer casing (2) and the mandrel (1). The TC radial bearing includes a TC outer sleeve (81) fixedly connected to the outer casing (2) and a TC inner sleeve (82) fixedly connected to the mandrel (1). The sealing element is disposed between the outer sleeve (81) and the inner sleeve (82) of the TC.

4. The drive shaft assembly for a screw drill according to claim 3, characterized in that, A radial gap is left between the outer sleeve (81) and the inner sleeve (82) of the TC to allow the radial vibration of the spindle (1) to be transmitted to the outer casing (2) through the deep groove ball bearing assembly (4).

5. The drive shaft assembly for a screw drill according to claim 3, characterized in that, A wear-resistant layer is provided on the inner surface of the TC outer sleeve (81) and the outer surface of the TC inner sleeve (82).

6. The drive shaft assembly for a screw drill according to claim 1 or 2, characterized in that, A positioning component is provided at the upper end of the thrust bearing assembly (3) for axial positioning of the thrust bearing assembly (3) and the deep groove ball bearing assembly (4).

7. The drive shaft assembly for a screw drill according to claim 6, characterized in that, The positioning assembly includes a positioning outer sleeve (91), a positioning inner sleeve (92), and a positioning nut (93) fixed on the mandrel (1). The two ends of the positioning inner sleeve (92) abut against the upper end face of the positioning nut (93) and the inner ring of the thrust bearing assembly (3), respectively. The inner wall of the outer shell (2) is provided with a limiting step with the end face facing downward. The two ends of the positioning outer sleeve (91) abut against the limiting step and the upper end face of the outer ring of the thrust bearing assembly (3), respectively.

8. The drive shaft assembly for a screw drill according to claim 7, characterized in that, The first floating isolation ring (51) is disposed between the inner positioning sleeve (92) and the outer shell, and the second floating isolation ring (52) is disposed between the inner positioning sleeve (92) and the outer positioning sleeve (91).

9. The drive shaft assembly for a screw drill according to claim 1 or 8, characterized in that, Both the first floating isolation ring (51) and the second floating isolation ring (52) are made of polytetrafluoroethylene.

10. The drive shaft assembly for a screw drill according to claim 1, characterized in that, The outer casing (2) is provided with a first oil inlet (21) and a second oil inlet (22). The first oil inlet (21) is connected to the first lubrication cavity (6), and the second oil inlet (22) is connected to the second lubrication cavity (7).

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