Pressure relief setting structure for motor mounting chamber of vacuum pump

Abstract

The invention belongs to the technical field of vacuum pumps, and particularly relates to a decompression setting structure for a motor mounting chamber of a vacuum pump, which comprises a motor mounting cylinder, a hollow shaft motor, a hollow rotating shaft, an upper bearing, an upper bearing connecting sleeve, a lower bearing, a lower bearing mounting cover and an oil pool sealing cover. Through the mode that the hollow shaft motor, the upper bearing and the lower bearing are integrally arranged in the motor mounting cylinder, the leakage risk of a motor and bearing split type arrangement structure of a traditional vacuum pump can be effectively reduced through compact layout, the system complexity is simplified, the sealing reliability is enhanced, meanwhile, pollution of oil volatilization to internal elements is reduced, and the service life of the vacuum pump is prolonged. And the pressure in the motor mounting chamber can be prevented from being too large, oil steam leakage is prevented from directly polluting the vacuum environment, the reliability of a sealing barrier is ensured, the molecular-level pollution control requirement can be met, meanwhile, frequent maintenance and replacement of a sealing element are not needed, and the operation and maintenance cost and the equipment shutdown risk are greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum pumps, and in particular to a pressure relief arrangement structure for a motor mounting chamber of a vacuum pump. Background Art

[0002] Currently, vacuum pumps used in high-purity applications such as semiconductor wafer processing, optical coating, and high-purity material preparation require lubrication lines to ensure reliable operation of the shaft bearings driven by the vacuum pump motor. The high-speed rotation of the shaft driven by the vacuum pump motor generates high temperatures, heating some of the lubricating oil within the vacuum pump motor and shaft chambers, turning them into oil vapor. Because high-purity applications require that oil vapor from the chamber housing the vacuum pump motor and shaft be prevented from entering the high-purity vacuum environment, corresponding sealing structures are implemented. However, this seal between the vacuum environment and the oil vapor within the chamber housing the vacuum pump motor and shaft is blocked, allowing the oil vapor to accumulate within the chamber. This creates excessive pressure within the chamber, potentially breaking through the seal barrier and causing the leaked oil vapor to directly contaminate the vacuum environment, making it difficult to meet molecular-level contamination control requirements. Furthermore, frequent seal maintenance and replacement are required, increasing operational costs and the risk of equipment downtime.

[0003] Therefore, a pressure relief structure for the motor mounting chamber of a vacuum pump is needed, which can smoothly achieve oil lubrication of the rotating shaft bearing driven by the vacuum pump motor and enable the motor mounting chamber to maintain chamber pressure balance. Summary of the Invention

[0004] In view of the above problems, an object of the present invention is to provide a pressure relief structure for a motor mounting chamber of a vacuum pump.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A pressure relief structure for a motor mounting chamber of a vacuum pump, comprising a motor mounting cylinder, a hollow shaft motor, a hollow rotating shaft, an upper bearing, an upper bearing connecting sleeve, a lower bearing, a lower bearing mounting cover, and an oil pool sealing cover;

[0007] A motor mounting chamber is formed inside the motor mounting cylinder, a housing of the hollow shaft motor is mounted in the motor mounting cylinder, and the hollow rotating shaft is mounted on the hollow driving end of the hollow shaft motor;

[0008] The upper part of the motor mounting cylinder is provided with a connecting sleeve mounting hole connected to the motor mounting chamber, the upper bearing connecting sleeve is installed in the connecting sleeve mounting hole, the upper bearing is located on the outside of the motor mounting cylinder, the outer ring of the upper bearing is fixedly connected to the upper bearing connecting sleeve, the upper part of the hollow rotating shaft passes through the upper bearing connecting sleeve and is connected to the inner ring of the upper bearing, the part of the upper part of the hollow rotating shaft extending from the inner ring of the upper bearing is used to be connected to the rotor part of the vacuum pump, the upper part of the motor mounting cylinder is also provided with a pressure relief channel, the pressure relief channel has an opening connected to the outside atmosphere and an opening connected to the motor mounting chamber, and an oil-gas separator is provided at the opening of the pressure relief channel connected to the motor mounting chamber;

[0009] The lower portion of the motor mounting cylinder forms an opening communicated with the motor mounting chamber, the lower bearing mounting cover is installed at the opening of the lower portion of the motor mounting cylinder, the top of the lower bearing mounting cover extends upward into the motor mounting chamber and forms a lower bearing mounting portion, the lower bearing mounting portion of the lower bearing mounting cover is provided with a lower bearing mounting hole, the lower bearing is arranged in the lower bearing mounting hole, the inner ring of the lower bearing is connected to the lower portion of the hollow rotating shaft, the bottom of the lower bearing mounting cover is recessed inwardly to form an oil pool, the oil pool sealing cover is installed on the bottom surface of the lower bearing mounting cover and is used to close the lower side opening of the oil pool, and the lower bearing mounting cover is provided with oil drain holes respectively communicated with the motor mounting chamber and the oil pool;

[0010] An axial oil passage is provided inside the hollow rotating shaft, and an oil nozzle is connected to the lower end of the hollow rotating shaft. The oil nozzle is connected to the axial oil passage, and the oil nozzle extends into the oil pool and is connected to the oil pool. A radial oil passage A is provided on the hollow rotating shaft corresponding to the upper bearing, and the radial oil passage A is respectively connected to the axial oil passage near the upper bearing and the hollow rotating shaft.

[0011] The upper bearing and the lower bearing are both ceramic ball bearings.

[0012] A radial oil passage B is provided on the hollow rotating shaft at a position corresponding to the lower bearing, and the radial oil passage B is respectively connected with the axial oil passages close to the lower bearing and the hollow rotating shaft.

[0013] A clearance fit is formed between the outer surface of the upper portion of the hollow shaft located in the upper bearing connecting sleeve and the inner circumferential surface of the upper bearing connecting sleeve, and a spiral oil guide channel is axially provided on the outer surface of the upper portion of the hollow shaft located in the upper bearing connecting sleeve.

[0014] An oil filter is embedded in the oil drain hole.

[0015] An oil-slinging pan is provided at the lower portion of the hollow rotating shaft and above the lower bearing.

[0016] The lower side of the lower bearing is provided with a support spring, an oil baffle plate, and an axial limit piece in sequence from top to bottom. The lower bearing, support spring, oil baffle plate, and axial limit piece are all located in the lower bearing mounting hole. The support spring and oil baffle plate are respectively sleeved on the hollow rotating shaft. The upper end of the support spring rests against the outer ring of the lower bearing, and the lower end of the support spring rests against the top surface of the oil baffle plate. The axial limit piece is installed on the hollow rotating shaft for limiting the oil baffle plate from below.

[0017] The bottom of the oil baffle plate is recessed inwards to form an oil baffle groove.

[0018] The outer circumferential surface of the oil deflector plate forms a clearance fit with the inner surface of the lower bearing mounting hole, and a plurality of annular grooves are sequentially provided on the outer circumferential surface of the oil deflector plate from top to bottom.

[0019] A plurality of oil return channels are formed on the lower bearing mounting cover, each of the oil return channels has two openings, one of the openings of each oil return channel is directly connected to the oil pool, and the other opening of each oil return channel is directly connected to the lower bearing mounting hole.

[0020] The advantages and positive effects of the present invention are:

[0021] 1. The present invention integrates the hollow shaft motor, upper bearing and lower bearing into the motor mounting tube, which can effectively reduce the leakage risk of the traditional vacuum pump's motor and bearing separate arrangement structure through a compact layout, simplifying the system complexity and enhancing the sealing reliability, while reducing the contamination of internal components by oil volatilization.

[0022] 2. The present invention can avoid excessive pressure in the motor installation chamber, prevent oil vapor leakage and direct contamination of the vacuum environment, ensure the reliability of the sealing barrier, guarantee the vacuum purity and avoid carbon deposition and loss of key components, and meet the requirements of molecular-level pollution control. At the same time, there is no need for frequent maintenance and replacement of seals, which greatly reduces operation and maintenance costs and the risk of equipment downtime.

[0023] 3. This invention can break through the limitation that traditional pump bodies must be installed vertically, allowing the equipment to maintain continuous oil film coverage and stable lubrication under inclined working conditions, greatly broadening the application scenarios of the equipment in complex space environments such as aerospace and mobile platforms; the overall technical solution has the advantages of enhanced sealing efficiency and improved installation adaptability. While extending the life of the equipment and reducing operation and maintenance costs, it provides an innovative solution for the compact design and diversified application of high-vacuum dry pumps. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a schematic diagram of the structure of the present invention;

[0025] Figure 2 for Figure 1 A magnified view of point A;

[0026] Figure 3 for Figure 1 Enlarged view of point B.

[0027] In the figure: 1 is a motor mounting cylinder, 101 is a pressure relief channel, 2 is a hollow shaft motor, 3 is a hollow rotating shaft, 301 is an axial oil channel, 302 is a radial oil channel A, 303 is a spiral oil guide channel, 4 is an upper bearing, 5 is an upper bearing connecting sleeve, 6 is a lower bearing, 7 is a lower bearing mounting cover, 701 is an oil drain hole, 702 is an oil return channel, 8 is an oil sump sealing cover, 9 is an oil-gas separator, 10 is an oil nozzle, 11 is an oil filter, 12 is an oil slinger plate, 13 is a support spring, 14 is an oil baffle plate, 1401 is an annular groove, and 15 is an axial limiter;

[0028] 001 is the motor installation chamber and 002 is the oil pool. DETAILED DESCRIPTION

[0029] The following is combined with Figure 1-3 The present invention is described in further detail.

[0030] A pressure relief arrangement structure for a motor mounting chamber of a vacuum pump, such as Figure 1-3 As shown, this embodiment includes a motor mounting cylinder 1, a hollow shaft motor 2, a hollow rotating shaft 3, an upper bearing 4, an upper bearing connecting sleeve 5, a lower bearing 6, a lower bearing mounting cover 7, and an oil pool sealing cover 8.

[0031] A motor mounting chamber 001 is formed inside the motor mounting tube 1. The housing of the hollow shaft motor 2 is mounted in the motor mounting tube 1, and the hollow rotating shaft 3 is mounted on the hollow driving end of the hollow shaft motor 2. In this embodiment, the motor mounting tube 1 can adopt a bimetallic composite housing, such as an outer layer of aluminum alloy to reduce mass and an inner layer of stainless steel to provide strength and corrosion resistance; or an integrally formed composite material housing can be adopted, such as a carbon fiber reinforced resin material to meet high strength and insulation requirements. In this embodiment, the pressure relief structure of the motor mounting chamber for the vacuum pump is connected to the other structures of the vacuum pump in an overall manner using existing technology, wherein the top surface portion of the motor mounting tube 1 can also be used as the stator portion of the vacuum pump. A sealing structure is provided above the motor mounting tube 1 to prevent the oil used to flow through the upper bearing 4 from continuing to flow upward to the vacuum environment. The hollow shaft motor 2 adopts a commercially available waterproof hollow shaft motor product, and the connection method between the hollow shaft motor 2 and the external equipment adopts existing technology.

[0032] The upper portion of the motor mounting barrel 1 is provided with a connecting sleeve mounting hole connected to the motor mounting chamber 001. The upper bearing connecting sleeve 5 is installed in the connecting sleeve mounting hole. The upper bearing 4 is located outside the motor mounting barrel 1. The outer ring of the upper bearing 4 is fixedly connected to the upper bearing connecting sleeve 5. The upper portion of the hollow rotating shaft 3 passes through the upper bearing connecting sleeve 5 and is connected to the inner ring of the upper bearing 4. The portion of the upper portion of the hollow rotating shaft 3 extending from the inner ring of the upper bearing 4 is used to connect to the rotor portion of the vacuum pump. The upper portion of the motor mounting barrel 1 is also provided with a pressure relief channel 101. The pressure relief channel 101 has an opening connected to the outside atmosphere and an opening connected to the motor mounting chamber 001. An oil-gas separator 9 is provided at the opening of the pressure relief channel 101 connected to the motor mounting chamber 001. The oil-gas separator 9 is a commercially available product.

[0033] The lower part of the motor mounting tube 1 forms an opening connected to the motor mounting chamber 001, and the lower bearing mounting cover 7 is installed at the opening of the lower part of the motor mounting tube 1. The top of the lower bearing mounting cover 7 extends upward into the motor mounting chamber 001 and forms a lower bearing mounting portion. The lower bearing mounting portion of the lower bearing mounting cover 7 is provided with a lower bearing mounting hole, and the lower bearing 6 is arranged in the lower bearing mounting hole. The inner ring of the lower bearing 6 is connected to the lower part of the hollow rotating shaft 3, and the bottom of the lower bearing mounting cover 7 is recessed inward to form an oil pool 002. The oil pool sealing cover 8 is installed on the bottom surface of the lower bearing mounting cover 7 and is used to close the lower side opening of the oil pool 002. The lower bearing mounting cover 7 is provided with oil drain holes 701 respectively connected to the motor mounting chamber 001 and the oil pool 002. Most of the oil that enters the motor installation chamber 001 can flow back to the oil pool 002 from the oil drain hole 701. Although a small part of the oil will form oil vapor under the action of high temperature, under the action of air pressure, the gas can be discharged to the atmosphere through the oil-gas separator 9 and the pressure relief channel 101, thereby avoiding excessive pressure in the motor installation chamber 001, avoiding oil vapor leakage and direct contamination of the vacuum environment, ensuring the reliability of the sealing barrier, and meeting the molecular-level contamination control requirements. At the same time, there is no need to frequently maintain and replace seals, which greatly reduces operation and maintenance costs and equipment downtime risks.

[0034] An axial oil passage 301 is defined within the hollow shaft 3. An oil nozzle 10 is connected to the lower end of the hollow shaft 3. The nozzle 10 is connected to the axial oil passage 301 and extends into and communicates with the oil reservoir 002. The structure of the oil nozzle 10 itself is conventional. Radial oil passages A 302 are defined within the hollow shaft 3 corresponding to the upper bearing 4. These passages A 302 communicate with the axial oil passage 301 near the upper bearing 4 and within the hollow shaft 3, respectively. In this embodiment, the walls of the oil reservoir 002 are curved, ensuring an effective oil level coverage of 95% even when the vacuum pump is tilted at a 45° angle.

[0035] Specifically, in this embodiment, the upper bearing 4 and the lower bearing 6 are both commercially available ceramic ball bearings. A radial oil passage B is provided on the hollow shaft 3 at a position corresponding to the lower bearing 6. The radial oil passage B is connected to the axial oil passage 301 near the lower bearing 6 and the hollow shaft 3, respectively. The hollow shaft motor 2 drives the hollow shaft 3 to rotate. During the rotation of the hollow shaft 3, the oil nozzle 10 draws oil from the oil pool 002 into the axial oil passage 301. The oil then flows to the upper bearing 4 and the lower bearing 6 respectively through the radial oil passage A 302 and the radial oil passage B, and fully lubricates the upper bearing 4 and the lower bearing 6. In this embodiment, by integrating the hollow shaft motor 2, the upper bearing 4, and the lower bearing 6 into the motor mounting barrel 1, the leakage risk of the traditional vacuum pump's motor and bearing separate arrangement structure can be effectively reduced through a compact layout, simplifying the system complexity and enhancing the sealing reliability, while reducing the contamination of internal components by oil volatilization.

[0036] Specifically, if Figure 2 As shown, in this embodiment, the outer surface of the portion of the upper portion of the hollow shaft 3 located within the upper bearing connecting sleeve 5 forms a clearance fit with the inner circumference of the upper bearing connecting sleeve 5. A spiral oil guide channel 303 is axially defined on the outer surface of the portion of the upper portion of the hollow shaft 3 located within the upper bearing connecting sleeve 5. In this embodiment, the lead angle of spiral oil guide channel 303 is controlled to be between 15° and 30°, with an error of ±1°. The provision of spiral oil guide channel 303 serves to return oil flowing through the upper bearing 4 to the motor mounting chamber 001 and prevent the upward flow of large amounts of oil vapor from the motor mounting chamber 001.

[0037] Specifically, in this embodiment, an oil filter 11 is embedded in the oil drain hole 701. The oil filter 11 is a commercially available product and is used to ensure that no impurities from the motor mounting chamber 001 return to the oil pool 002 through the oil drain hole 701.

[0038] Specifically, if Figure 3 As shown, in this embodiment, an oil-slinging pan 12 is provided at the lower portion of the hollow shaft 3 and above the lower bearing 6. The oil-slinging pan 12 can fully throw off the oil flowing down the hollow shaft 3 and adhering to the oil-slinging pan 12 under the rotation of the hollow shaft 3.

[0039] The lower side of the lower bearing 6 is provided with a support spring 13, an oil baffle plate 14, and an axial limiter 15 from top to bottom. The lower bearing 6, support spring 13, oil baffle plate 14, and axial limiter 15 are all located in the lower bearing mounting hole. The support spring 13 and oil baffle plate 14 are respectively sleeved on the hollow shaft 3. The upper end of the support spring 13 abuts the outer ring of the lower bearing 6, and the lower end of the support spring 13 abuts the top surface of the oil baffle plate 14. The axial limiter 15 is installed on the hollow shaft 3 and is used to limit the oil baffle plate 14 from below. The provision of the support spring 13 is used to reduce the axial vibration to which the hollow shaft 3 as a whole is subjected during operation. The oil baffle plate 14 mainly prevents excess oil in the oil pool 002 from entering the lower bearing mounting hole and further returning to the motor mounting chamber 001.

[0040] The bottom of the oil baffle plate 14 is recessed inward to form an oil-deflecting groove. The outer circumference of the oil baffle plate 14 forms a clearance fit with the inner surface of the lower bearing mounting hole. Several annular grooves 1401 are defined on the outer circumference of the oil baffle plate 14, arranged from top to bottom. The annular grooves 1401 further effectively prevent oil vapor formed in the oil pool 002 from entering the lower bearing mounting hole through the gap between the oil baffle plate 14 and the lower bearing mounting hole. The outer circumference of the oil baffle plate 14 can be coated with a nickel-based tungsten carbide coating to improve wear resistance and seal life.

[0041] The lower bearing mounting cover 7 is formed with several oil return channels 702. Each channel 702 has two openings, one of which is directly connected to the oil sump 002, and the other is directly connected to the lower bearing mounting hole. The provision of the oil return channels 702 allows oil entering the lower bearing mounting hole to quickly flow back into the oil sump 002 through the channels 702, preventing excessive accumulation and upward flow into the motor mounting chamber 001. The liquid seal mechanism of a conventional oil sump structure is constrained by gravity and cannot meet the stable lubrication requirements of a high-vacuum dry pump in non-vertical installation conditions. However, the coordinated arrangement of the oil baffle 14 and the oil return channels 702 allows the vacuum pump to maintain lubrication stability even when the pump body is installed at an angle. This coordinated arrangement allows the vacuum pump to operate stably at angles of up to 15–30° relative to the vertical axis, breaking the limitation of conventional high-vacuum dry pumps that require horizontal installation.

Claims

1. A pressure relief structure for a motor mounting chamber of a vacuum pump, characterized in that: It comprises a motor mounting cylinder (1), a hollow shaft motor (2), a hollow rotating shaft (3), an upper bearing (4), an upper bearing connecting sleeve (5), a lower bearing (6), a lower bearing mounting cover (7), and an oil pool sealing cover (8); A motor mounting chamber (001) is formed inside the motor mounting cylinder (1), a housing of the hollow shaft motor (2) is mounted in the motor mounting cylinder (1), and the hollow rotating shaft (3) is mounted on the hollow driving end of the hollow shaft motor (2); The upper portion of the motor mounting cylinder (1) is provided with a connecting sleeve mounting hole connected to the motor mounting chamber (001); the upper bearing connecting sleeve (5) is mounted in the connecting sleeve mounting hole; the upper bearing (4) is located outside the motor mounting cylinder (1); the outer ring of the upper bearing (4) is fixedly connected to the upper bearing connecting sleeve (5); the upper portion of the hollow rotating shaft (3) passes through the upper bearing connecting sleeve (5) and is connected to the inner ring of the upper bearing (4); The portion of the upper portion of the hollow rotating shaft (3) extending out of the inner ring of the upper bearing (4) is used to connect to the rotor portion of the vacuum pump. The upper portion of the motor mounting cylinder (1) is also provided with a pressure relief channel (101). The pressure relief channel (101) has an opening connected to the outside atmosphere and an opening connected to the motor mounting chamber (001). An oil-gas separator (9) is provided at the opening of the pressure relief channel (101) connected to the motor mounting chamber (001). The lower portion of the motor mounting cylinder (1) forms an opening connected to the motor mounting chamber (001); the lower bearing mounting cover (7) is mounted at the opening of the lower portion of the motor mounting cylinder (1); the top of the lower bearing mounting cover (7) extends upward into the motor mounting chamber (001) and forms a lower bearing mounting portion; the lower bearing mounting portion of the lower bearing mounting cover (7) is provided with a lower bearing mounting hole; the lower bearing (6) is arranged in the lower bearing mounting hole; the inner ring of the lower bearing (6) is connected to the lower portion of the hollow rotating shaft (3); the bottom of the lower bearing mounting cover (7) is recessed inward to form an oil pool (002); the oil pool sealing cover (8) is mounted on the bottom surface of the lower bearing mounting cover (7) and is used to close the lower side opening of the oil pool (002); the lower bearing mounting cover (7) is provided with an oil drain hole (701) respectively connected to the motor mounting chamber (001) and the oil pool (002); An axial oil passage (301) is provided inside the hollow rotating shaft (3), an oil nozzle (10) is connected to the lower end of the hollow rotating shaft (3), the oil nozzle (10) is communicated with the axial oil passage (301), the oil nozzle (10) extends into the oil pool (002) and is communicated with the oil pool (002), a radial oil passage A (302) is provided on the hollow rotating shaft (3) at a position corresponding to the upper bearing (4), and the radial oil passage A (302) is respectively communicated with the axial oil passage (301) near the upper bearing (4) and the hollow rotating shaft (3).

2. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 1, characterized in that: The upper bearing (4) and the lower bearing (6) are both ceramic ball bearings.

3. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 1, characterized in that: A radial oil passage B is provided on the hollow rotating shaft (3) at a position corresponding to the lower bearing (6), and the radial oil passage B is respectively connected to an axial oil passage (301) near the lower bearing (6) and the hollow rotating shaft (3).

4. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 1, characterized in that: A clearance fit is formed between the outer surface of the portion of the upper part of the hollow rotating shaft (3) located in the upper bearing connecting sleeve (5) and the inner circumferential surface of the upper bearing connecting sleeve (5), and a spiral oil guide channel (303) is axially provided on the outer surface of the portion of the upper part of the hollow rotating shaft (3) located in the upper bearing connecting sleeve (5).

5. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 1, characterized in that: An oil filter (11) is embedded in the oil drain hole (701).

6. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 1, characterized in that: An oil-slinging pan (12) is provided at the lower part of the hollow rotating shaft (3) and at the upper side of the lower bearing (6).

7. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 1, characterized in that: The lower side of the lower bearing (6) is provided with a support spring (13), an oil baffle plate (14), and an axial limiter (15) in sequence from top to bottom. The lower bearing (6), the support spring (13), the oil baffle plate (14), and the axial limiter (15) are all located in the lower bearing mounting hole. The support spring (13) and the oil baffle plate (14) are respectively sleeved on the hollow rotating shaft (3). The upper end of the support spring (13) abuts against the outer ring of the lower bearing (6), and the lower end of the support spring (13) abuts against the top surface of the oil baffle plate (14). The axial limiter (15) is installed on the hollow rotating shaft (3) and is used to limit the oil baffle plate (14) from below.

8. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 7, characterized in that: The bottom of the oil baffle plate (14) is recessed inwards to form an oil baffle groove.

9. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 7, characterized in that: The outer peripheral surface of the oil baffle plate (14) forms a clearance fit with the inner hole surface of the lower bearing mounting hole, and a plurality of annular grooves (1401) are sequentially provided on the outer peripheral surface of the oil baffle plate (14) from top to bottom.

10. The pressure relief structure for a motor mounting chamber of a vacuum pump according to claim 7, characterized in that: A plurality of oil return channels (702) are formed on the lower bearing mounting cover (7), each of the oil return channels (702) having two openings, one of the openings of each oil return channel (702) being directly connected to the oil pool (002), and the other opening of each oil return channel (702) being directly connected to the lower bearing mounting hole.

Images