AIR-FLOATING CENTRIFUGAL COMPRESSOR

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serial no. 202310417453.3, filed on Apr. 18, 2023, China application serial no. 202310417458.6, filed on Apr. 18, 2023 and China application serial no. 202310483855.3, filed on May 4, 2023. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND
Technical Field

The present invention relates to the field of thermal management technology, and in particular to an air-floating centrifugal compressor.

Description of Related Art

Thermal management refers to the management and control of the temperature of the total system, discrete components, or their environments, with the aim of maintaining the normal operation of each component or improving their performance or lifetime. Currently, thermal management is usually required in fields such as electrochemical energy storage, and the thermal management has a significant impact on the performance, lifetime, and safety of energy storage systems. Due to the strong heat exchange capacity of the liquid-cooled thermal management system, the temperature difference of the battery core can be achieved within 3° C. Therefore, the lifetime of the energy storage system can be significantly improved compared to the air-cooled system. In view of this, liquid-cooled systems are mostly used in the field of energy storage at present.

The refrigeration capacity required for energy storage liquid-cooled systems is usually 100 kW or less, and scroll compressors are mostly used for this small cooling capacity refrigeration cycles. However, scroll compressors mostly use oil for lubrication, which tends to reduce the reliability of the compressor and the liquid-cooled system. In addition, the bearings in scroll compressors are usually contact ball bearings, which are prone to wear and tear, therefore their lifetime is usually the bottleneck in the lifetime of the liquid-cooled system. At the same time, the volume and mass of the scroll compressor are relatively large, which is not favorable for improving the energy density of the energy storage system, and especially with the increase of the power density of the energy storage system, the demand for refrigeration capacity increases significantly, and the disadvantages of the scroll compressor in this regard will be even more significant.

SUMMARY

Aiming at some or all of the problems in the prior art, the present invention provides an air-floating centrifugal compressor, comprising:

- a motor, which comprises:
- a housing, wherein a first chamber and a second chamber are respectively arranged at two ends of its interior;
- a rotor, wherein a radial bearing is arranged on the rotor, the radial bearing is an air-bearing; and
- a stator;
- an impeller, which is arranged at an end of the rotor and located in the first chamber and/or the second chamber;
- an air inlet, which is connected to the air inlet of the first chamber;
- an outlet port, which is connected to the air outlet of the second chamber; and
- a connecting pipe, the two ends of which are respectively connected to the air outlet of the first chamber and the air inlet of the second chamber.

Furthermore, the rotor comprises:

- a core shaft, which is internally hollow;
- a right half shaft and a left half shaft, which are connected to the two ends of the core shaft, respectively;
- a hollow magnet steel, which is sleeved on the core shaft; and
- a protective sleeve, the two ends of the inner wall of which are located on the left half shaft and the right half shaft, and the hollow magnetic steel is located between the core shaft and the protective sleeve, the protective sleeve is configured to fix the hollow magnetic steel.

Furthermore, the motor is a high-speed permanent magnet synchronous motor.

Furthermore, the air-floating centrifugal compressor further comprises:

- a thrust disc, which is arranged at an end of the rotor; and
- thrust bearings, which are arranged on one or two sides of the thrust disc and are air-bearings.

Furthermore, the air-floating radial bearing is a foil type dynamic pressure air-bearing.

Furthermore, the first chamber or the second chamber comprises a multi-stage impeller.

Furthermore, the impeller is fixed to the end of the rotor by means of a lock nut.

Furthermore, the impeller is a closed impeller, and obtained by manufacturing according to the following steps:

- providing an impeller and an impeller cover;
- arranging the impeller and the impeller cover in a vacuum of a diffusion welding equipment;
- heating the impeller and the impeller cover in the vacuum of the diffusion welding equipment; and
- pressing the contact surfaces between the impeller and the impeller cover using a clamp to cause plastic deformation of the contact surfaces and welding the impeller and the impeller cover together by means of eutectic reaction of atomic inter-diffusion.

Furthermore, the impeller is a hoop type closed impeller, and comprises:

- an impeller cover;
- an impeller, which is connected to the impeller cover by means of a hoop; and
- a hoop, which comprises:
- an impeller cover side crimp, which is connected to the impeller cover;
- an impeller side crimp, which is connected to the impeller; and
- a crimp connection portion, which connects the impeller cover side crimp to the impeller side crimp.

Furthermore, the impeller is a riveting type closed impeller, and comprises:

- an impeller cover;
- an impeller, which is connected to the impeller cover by means of a rivet; and
- a rivet, which comprises:
- a rivet impeller cover segment, which is connected to the impeller cover;
- a rivet impeller segment, which is connected to the impeller; and
- a rivet intermediate segment, which connects the rivet impeller cover segment to the rivet impeller segment.

Furthermore, a sealing structure is arranged on the side of the impeller cover of the impeller.

Furthermore, end caps are arranged at the air outlets of the first chamber and the second chamber.

Furthermore, the air-floating centrifugal compressor further comprises an interstage air supplement port, and the interstage air supplement port is arranged on the connecting pipe.

The present invention provides an air-floating centrifugal compressor that uses air-bearings, and therefore does not need to use lubricating oil, which can eliminate the need for oil return line, and thus improve the reliability of the compressor and the system. At the same time, because the rotation shaft is not in contact with the bearing when the air-bearing is in operation, but rather the rotor of the motor is suspended by an air film, the bearing life can also be increased by at least one time. In addition, under the same cooling capacity, the size of the centrifugal compressor based on high-speed permanent magnet synchronous motor will be about 50% smaller than that of the scroll compressor, and the mass can be reduced by about 90%, which makes it possible to arrange more batteries in the container of the same size when it is applied to the energy storage system, which in turn facilitates enhancement of the energy density of the storage system, and with the increase of the refrigeration power demand of the energy storage system, the advantages of high-speed centrifugal compressor in this regard will be more significant.

BRIEF DESCRIPTION OF THE DRAWINGS

To further explain the above and other advantages and features of various embodiments of the present invention, a more specific description of various embodiments of the present invention will be provided with reference to the accompanying drawings. It can be appreciated that these accompanying drawings depict only typical embodiments of the present invention, and therefore will not be construed as limiting their scope. In the accompanying drawings, identical or corresponding parts will be indicated by the same or similar reference numerals for the sake of clarity.

FIG. 1 illustrates a schematic diagram of the configuration of an air-floating centrifugal compressor according to an embodiment of the present invention;

FIGS. 2A to 2D illustrate schematic diagrams of the configuration of the air-floating centrifugal compressor according to other embodiments of the present invention, respectively;

FIG. 4 illustrates a structural schematic diagram of a small cooling capacity air-floating centrifugal compressor for energy storage thermal management according to an embodiment of the present invention;

FIG. 5 illustrates a sectional schematic diagram of a small cooling capacity air-floating centrifugal compressor for energy storage thermal management according to an embodiment of the present invention;

FIG. 6 illustrates a structural schematic diagram of a rotor according to an embodiment of the present invention;

FIG. 7A illustrates a structural schematic diagram of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7B illustrates a front view diagram of an impeller cover of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7C illustrates a side view diagram of an impeller cover of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7D illustrates a front view diagram of an impeller of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7E illustrates a rear view diagram of an impeller of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7F illustrates a schematic diagram of a connection between an impeller cover hub and an impeller shaft hole of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7G illustrates a structural schematic diagram of a hoop of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 7H illustrates an enlarged schematic diagram of the hoop arrangement of a hoop type closed impeller according to an embodiment of the present invention;

FIG. 8A illustrates a structural schematic diagram of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8B illustrates a front view diagram of an impeller cover of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8C illustrates a side view diagram of an impeller cover of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8D illustrates a front view diagram of an impeller of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8E illustrates a structural schematic diagram of a rivet of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8F illustrates a schematic diagram of a connection between an impeller cover hub and an impeller shaft hole of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8G illustrates a schematic diagram of an arrangement of impeller rivet holes of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 8H illustrates an enlarged schematic diagram of a rivet arrangement of a riveting type closed impeller according to an embodiment of the present invention;

FIG. 9A illustrates a structural sectional schematic diagram of a closed impeller according to an embodiment of the present invention;

FIG. 9B illustrates a schematic diagram of a method for manufacturing the closed impeller according to an embodiment of the present invention; and

FIG. 9C illustrates a sectional schematic diagram of an assembly structure of a closed impeller and a diffusion welding equipment according to an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

In the following description, the present invention is described with reference to various embodiments. However, those skilled in the art will recognize that various embodiments can be implemented without one or more specific details or with other alternative and/or additional methods, materials, or components. In other situations, well-known structures, materials, or operations are not shown or described in detail so as not to obscure the inventive point of the present invention. Similarly, for the purpose of explanation, specific quantities, materials, and configurations are set forth in order to provide a comprehensive understanding of embodiments of the present invention. However, the present invention is not limited to these particular details. Furthermore, it should be appreciated that the embodiments illustrated in the accompanying drawings are illustrative representations and are not necessarily drawn to the correct scale.

In this specification, a reference to “one embodiment” or “the embodiment” means that particular feature, structure or characteristic described in connection with the embodiment are included in at least one embodiment of the present invention. The phrase “in one embodiment” appearing throughout this description may not necessarily all refer to the same embodiment.

It should be noted that the embodiments of the present invention describe the process steps in a specific order, however this is only for the purpose of illustrating the specific embodiment, rather than limiting the order of the steps. On the contrary, in different embodiments of the present invention, the order of the steps can be modified according to the adjustment of the process.

In embodiments of the present invention, the term “main gas path” refers to the gas flow path in which gas enters the compressor along the air inlet and is compressed and then discharged through the outlet port. The term “high-pressure side” refers to the side with higher internal air pressure in the compressor, i.e. the side where the final stage impeller is located, while the term “low-pressure side” refers to the internal side of the compressor relative to the high-pressure side. Under normal circumstances, gas flows from the high-pressure side to the low-pressure side through the air-bearing and then returns to the main gas path.

In order to enhance the reliability of the compressor and at the same time reduce its size and weight, the present invention provides an air-floating centrifugal compressor, which uses an air-bearing and introduces gas in the main gas path of the compressor into the bearing position by rotating the rotor to form a gas film, and further achieve the air-floating effect. The specific scheme of the present invention will be further described below in conjunction with the accompanying drawings of the embodiments.

FIG. 1 and FIGS. 2A to 2D illustrate schematic diagrams of the configuration of the air-floating centrifugal compressor according to different embodiments of the present invention, respectively. As shown in the figures, in embodiments of the present invention, the air-floating centrifugal compressor comprises a motor and an impeller 200. Wherein the rotor system of the motor comprises radial air-bearings 111, and when the rotation shaft of the motor rotates, the radial air-bearings inhale gas to form an air film to support the rotor rotating at a high speed, and at the same time the thrust bearings (if any) also form an air film, so that there is no contact between the thrust rotation shaft and the bearings, and the bearings are almost wear-free, and mechanical losses and noise can be substantially reduced or even eliminated. As shown in the figures, the impeller 200 is arranged at the end of the rotor 101 for pressing the low-temperature and low-pressure refrigerant gas from the evaporator to form high-temperature and high-pressure refrigerant gas to be discharged into the condenser. Herein, the terms “radial” and “axial” refer to the radial and axial directions of the rotor or its axis of rotation.

FIGS. 3A to 3D illustrate schematic diagrams of the configuration of different rotor systems in the air-floating centrifugal compressor according to embodiments of the present invention, respectively. As shown in the figures, in embodiments of the present invention, the rotor system 101 comprises two radial bearings, and the two radial bearings have a certain distance between them and can be symmetrically distributed on the rotor. In one embodiment of the present invention, the radial bearings use foil type dynamic pressure air-bearings, and an air film can be formed when gas is introduced into the bearing position, thus achieving the air-floating effect.

In order to withstand the axial thrust generated during the operation of the compressor, in one embodiment of the present invention, the rotor system is further provided with thrust disc 112 and thrust bearing 113. The thrust disc 112 and the thrust bearing 113 are optional. As shown in FIGS. 3A to 3D, the thrust disc 112 may be arranged at either end of the rotor, or a thrust disc 112 may be arranged at each of the two ends of the rotor respectively. When only one thrust disc is arranged, a thrust bearing 113 may be arranged on each of the two sides of the thrust disc 112 respectively. As shown in the figures, the acting surfaces of the two thrust bearings 113 are both oriented toward the thrust disc 112, and thus can respectively withstand axial thrust in different directions, specifically, the two thrust bearings 113 can withstand axial thrust in opposite directions. When two thrust discs are arranged, one thrust bearing 113 may be arranged on each of the two opposite sides of the two thrust discs 112, or on each of the two sides far away from each other, as shown in the figures, the acting surfaces of the two thrust bearings 113 are both oriented toward the thrust disc 112, and thus can respectively withstand axial thrust in different directions, specifically, the two thrust bearings 113 can withstand axial thrust in opposite directions. In one embodiment of the present invention, the thrust bearings use foil type dynamic pressure air-bearings, an air film can be formed when gas is introduced into the bearing position, thus achieving the air-floating effect.

As shown in FIG. 1 and FIGS. 2A to 2D, in different embodiments of the present invention, single-stage, double-stage or multi-stage impellers may be arranged according to actual needs. Specifically, when only a single-stage impeller is arranged, as shown in FIG. 1 and FIG. 2A, the impeller 200 may be arranged at either end of the rotor, then the side arranged with the impeller may be noted as the high-pressure side, and the side not arranged with the impeller is noted as the low-pressure side. When double-stage impellers are arranged, as shown in FIGS. 2B and 2C, the two impellers may be respectively arranged at two ends of the rotor or all of them may be arranged at either end of the rotor, and when respectively arranged at two ends of the rotor, the side arranged with the former-stage impeller may be noted as the low-pressure side, and the side arranged with the latter-stage impeller may be noted as the high-pressure side, and when all of them are arranged at one end of the rotor, the side arranged with the impellers is noted as the high-pressure side, and the side not arranged with the impeller is noted as the low-pressure side. Similarly, as shown in FIG. 2D, when multi-stage impellers are arranged, the multiple impellers can be equally or unequally arranged at two ends of the rotor respectively, or all can be arranged at either end of the rotor, and when respectively arranged at two ends of the rotor, the side arranged with the former-stage impeller may be noted as the low-pressure side, and the side arranged with the latter-stage impeller may be noted as the high-pressure side, and when all of them are arranged at one end of the rotor, the side arranged with the impellers is noted as the high-pressure side, and the side not arranged with the impeller is noted as the low-pressure side. Based on this, as shown in FIGS. 1 and 2A to 2D, when the rotor rotates, a portion of the high-pressure gas compressed by the impeller in the main gas path will enter the radial bearing on the high-pressure side under pressure, and then enter the radial bearing on the low-pressure side through the air gap between the stator and the rotor of the motor, and return to the main gas path. When a thrust disc and a thrust bearing are arranged, the high-pressure gas will also pass through the thrust bearing to form an air film to withstand axial thrust. In order to effectively reduce the axial thrust to which the thrust bearing is subjected, in one embodiment of the present invention, the impeller on the low-pressure side and the impeller on the high-pressure side are arranged in a back-to-back manner, so that the axial thrusts of the impellers on the high-pressure side and low-pressure side have opposite direction to offset each other. In one embodiment of the present invention, the impeller is a closed impeller. In one embodiment of the present invention, the impeller is fixed to the rotor by means of a lock nut.

The following is a detailed description of the specific structure and working principle of the air-floating centrifugal compressor in the embodiment of the present invention, using the configuration shown in FIG. 2B as an example. It should be understood that the structure and working principle of the air-floating centrifugal compressor using other configurations are basically the same as that of this embodiment, and the difference only lies in the number and position of the impellers and/or the number and position of the thrust discs, which will not be repeated herein. The air-floating centrifugal compressor in this embodiment is suitable for energy storage thermal management, and is a small cooling capacity air-floating centrifugal compressor that can be used in an energy storage liquid-cooled system.

FIG. 4 and FIG. 5 illustrate a structural schematic diagram and a schematic diagram of cross-segment, respectively, of a small cooling capacity air-floating centrifugal compressor for energy storage thermal management according to an embodiment of the present invention. As shown in the figures, a small cooling capacity air-floating centrifugal compressor for energy storage thermal management comprises a motor 100, an impeller, an air inlet 301, an outlet port 302, and a connecting pipe 303.

The motor 100 comprises a rotor 101, a stator 102, and a housing 103. The stator 102 is fixed inside the housing 103, and the central axis of the rotor 101 coincides with the central axis of the stator 102. The rotor 101 is provided with two radial air-bearings 111, meanwhile a thrust disc 112 is arranged on one side close to the air inlet 301, and air-floating thrust bearings 113 are respectively arranged on two sides of the thrust disc, the two thrust bearings are arranged oppositely to withstand axial thrust directed to the low-pressure side or the high-pressure side respectively.

FIG. 6 illustrates a structural schematic diagram of a rotor according to an embodiment of the present invention. As shown in FIG. 6, in one embodiment of the present invention, the rotor uses a hollow rotor structure, which comprises a core shaft 602, a right half shaft 604, a left half shaft 601, a hollow magnetic steel 603, and a protective sleeve 605. Wherein the interior of the core shaft 602 is hollow, effectively reducing the weight of the rotation shaft. The right half shaft 604 and the left half shaft 601 are respectively connected to the two ends of the core shaft 602, providing a fixing effect on the core shaft 602. The hollow magnetic steel 603 is provided on the core shaft 602 to reduce the amount of usage of magnetic steel. In one embodiment of the present invention, the magnetic steel sleeve is fitted to the core shaft with a small clearance, the clearance being between 0.01 and 0.03 mm. The two ends of the inner wall of the protective sleeve 605 are located on the left half shaft 601 and the right half shaft 604, and the hollow magnetic steel 603 is located between the core shaft 602 and the protective sleeve 605, and then fixed. The protective sleeve is simultaneously fitted to the left half shaft, the right half shaft, and the magnetic steel sleeve with an interference fit, with the interference amount being 0.1-0.15 mm, the protective sleeve needs to be heated to 500° C. for installation, and after cooling, the bearing fitting surface, the thrust disc fitting surface, and the impeller fitting surface need to be precision machined to ensure coaxiality. By reducing the overall mass of the rotation shaft, the dynamic balance intensity level is improved, such that the rotor can to adapt to a higher rotational speed. In one embodiment of the present invention, both the left half shaft 601 and the right half shaft 604 are provided with a cavity to accommodate the core shaft 602. The cavity is provided with internal threads, and both ends of the core shaft 602 are provided with external threads that match it, and then enables the core shaft 602 to be connected to the left half shaft 601 and the right half shaft 604 by means of threaded connection. In one embodiment of the present invention, the tightening torque between the core shaft and the left half shaft is ≥500 N·m to ensure an axial preload force of greater than 150 kN, and the tightening torque between the core shaft and the right half shaft 602 is ≥300 N·m to ensure an axial preload force of greater than 130 kN, and a hexagonal head is designed in the middle of the core shaft, which facilitates application of the tightening torque. In one embodiment of the present invention, the left half shaft 601 and the right half shaft 604 are further provided with a first bearing fitting surface 611 and a second bearing fitting surface 641 for installing bearings, and a first impeller fitting surface 612 and a second impeller fitting surface 642 for installing impellers. In one embodiment of the present invention, the left half shaft 601 is further provided with a thrust disc fitting surface 613 for installing the thrust disc. As shown in the figure, a first chamber and a second chamber are respectively arranged at two ends of the interior of the housing 103. Wherein, the air inlet of the first chamber is connected to the air inlet 301 of the compressor, which can also be understood that the air inlet 301 is the air inlet of the first chamber, and a first impeller 201 is arranged inside the first chamber, and the first impeller 201 is fixed to the first end of the rotor 101. A connecting pipe 303 is arranged between the first chamber and the second chamber, and the gas compressed by the first impeller 201 flows out from the air outlet of the first chamber into the connecting pipe 303, and then flows into the second chamber through the air inlet of the second chamber. A second impeller 202 is arranged in the second chamber, the second impeller 202 is fixed to the second end of the rotor 101, and most of the gas compressed by the second impeller 202 flows out from the air outlet of the second chamber, and the air outlet of the second chamber is connected to the outlet port 302 of the compressor, which can also be understood that the outlet port 302 is the air outlet of the second chamber. As shown in the figure, in the embodiment of the present invention, a first end cap 135 and a second end cap 136 are also arranged at the air outlets of the first chamber and the second chamber, respectively, and there is a gap between the first end cap 135 and the second end cap 136 on the one hand and the rotor 101 on the other hand, and at the same time, there is a certain gap between the first end cap 135 and the first impeller 201, through which the gas flowing through the air-bearing can return to the main gas path, and there is also a certain gap between the second end cap 136 and the second impeller 202, through which a part of the gas compressed by the second impeller 202 can enter the air-bearing under pressure. In one embodiment of the present invention, the first impeller 201 and the second impeller 202 are both closed impellers, compared with the open impeller, the closed impeller can effectively eliminate the secondary flow from the blade pressure surface to the suction surface caused by the blade tip clearance, which can effectively improve the aerodynamic efficiency of the compressor. In one embodiment of the present invention, as described above, the first impeller 201 and second impeller 202 are designed in a back-to-back manner, so that the axial thrust of the first and second impellers are in opposite directions and offset each other, thereby effectively reducing the axial thrust received by the thrust bearing. In one embodiment of the present invention, the first impeller 201 and the second impeller 202 are fixed to the rotor 101 by means of a first lock nut 211 and a second lock nut 221, respectively.

In one embodiment of the present invention, the first and second impellers use a hoop type closed impeller. FIG. 7A illustrates a structural schematic diagram of a hoop type closed impeller according to an embodiment of the present invention. As shown in FIG. 7A, the closed impeller comprises an impeller cover 701, a hoop 702, and an impeller 703, wherein the hoop 702 connects the impeller cover 701 to the impeller 703, and when the centrifugal compressor is running, the hoop type closed impeller rotates at a high speed, and through the flow passage between the impeller cover 701 and the impeller 703, the gas sequentially passes through the guide blades 712 in the impeller cover 701 and the impeller blades 732 in the impeller 703 and is pressurized, forms a high-pressure gas and is discharged. The pressure difference between the pressure surface and the suction surface of the guide blades 712 and the impeller blades 732 will cause gas to instinctively flow from one side of the blade to the other side of the blade while bypassing the top of the blade to form a tip leakage flow, whereas the presence of the impeller cover 701 can suppress the formation of tip leakage and improve the efficiency of the impeller. FIGS. 7B and 7C illustrate a front view diagram and a side view diagram of an impeller cover of a hoop type closed impeller according to an embodiment of the present invention, respectively. As shown in the figures, the impeller cover 701 comprises an impeller cover wall 711, a guide blade 712, an impeller cover shaft hole 713, and an impeller cover hub 714. The impeller cover 701 can be formed by mechanical processing in one-piece, wherein at the center of the impeller cover wall 711, an impeller cover shaft hole 713 is arranged, the guide blades 712 are arranged around the impeller cover shaft hole 713 on the impeller cover wall 711, and the impeller cover hub 714 is connected to the impeller cover wall 711 through the guide blades 712. The impeller cover wall 711 can form the main body of the impeller cover 701, and the guide blades 712 can perform a first pressurization of the gas that is about to enter the impeller 703, allowing the airflow to smoothly enter the impeller blades 732. FIGS. 7D and 7E illustrates a front view diagram and a rear view diagram of an impeller of a hoop type closed impeller according to an embodiment of the present invention, respectively. As shown in the figures, the impeller 703 comprises an impeller disc 731, impeller blades 732, an impeller shaft hole 733, and an impeller hoop groove 734. The impeller 703 can be formed by mechanical processing in one-piece, wherein at the center of the impeller disc 731, an impeller shaft hole 733 is arranged and the impeller hoop groove 734 is provided at the edge of the impeller disc 731. The impeller blades 732 are arranged on the impeller disc 731, and the diameter of the impeller disc 731 can be greater than or equal to 1.05 times of the diameter of the trailing edge of the impeller blades 732, and the number of impeller blades 732 is the same as the number of the guide blades 732. The impeller shaft hole 733 is fitted to the impeller cover hub 714 to connect the impeller 703 to the impeller cover 701, wherein the fitting means is, for example, a clearance fit, a transition fit, or an interference fit. The impeller disc 731 can form the main body of the impeller 703, and the impeller blades 732 can perform a second pressurization on the airflow at the outlet of the guide blades 712, so that the airflow is smoothly discharged and the target pressure is efficiently achieved. FIG. 7F illustrates a schematic diagram of a connection between an impeller cover hub and an impeller shaft hole of a hoop type closed impeller according to an embodiment of the present invention. As shown in the figure, after the impeller shaft hole 733 is fitted and connected to the impeller cover hub 714, in order to increase the connection strength, the impeller disc 731 can be further welded together with the impeller cover hub 714. FIG. 7G illustrates a structural schematic diagram of a hoop of a hoop type closed impeller according to an embodiment of the present invention. As shown in the figure, the hoop 702 comprises an impeller cover side crimp 721, an impeller side crimp 722, and a crimp connecting portion 723, the crimp connecting portion 723 connects the impeller cover side crimp 721 with the impeller side crimp 722. The hoop 702 can be formed by laser cutting, and the thickness of the impeller cover side crimp 721 and/or the impeller side crimp 722 can be greater than or equal to 0.5 mm. FIG. 7H illustrates an enlarged schematic diagram of the hoop arrangement of a hoop type closed impeller according to an embodiment of the present invention. As shown in the figure, the impeller cover side crimp 721 is connected with the impeller cover wall 711, and the impeller side crimp 722 is connected with the impeller disc 731, wherein protrusions can be provided on the impeller side crimp 722, the protrusions can be embedded in the impeller hoop groove 734 to achieve circumferential positioning of the hoop 702, preventing the relative motion between the hoop 702 and the impeller 703 during high-speed rotation of the impeller 703. The elastic modulus of the material of the hoop 702 is greater than the elastic modulus of the impeller cover 701 and the impeller 703, which causes the amount of deformation of the hoop 702 to be smaller than the amount of deformation of the impeller cover 701 and the impeller 703 when the impeller 703 rotates at high speed, thereby it can prevents the separation of the impeller cover 701 from the impeller 703.

In another embodiment of the present invention, the first and second impellers use a riveting type closed impeller. FIG. 8A illustrates a structural schematic diagram of a riveting type closed impeller according to an embodiment of the present invention. As shown in the figure, the closed impeller comprises an impeller cover 801, a rivet 802, and an impeller 803, wherein the rivet 802 connects the impeller cover 801 with the impeller 803, and when the centrifugal compressor is running, the riveting type closed impeller rotates at a high speed, and through the flow passage between the impeller cover 801 and the impeller 803, the gas sequentially passes through the guide blades 812 in the impeller cover 801 and the impeller blades 832 in the impeller 803 and is pressurized, forms a high-pressure gas and is discharged. The pressure difference between the pressure surface and the suction surface of the guide blades 812 and the impeller blades 832 will cause gas to instinctively flow from one side of the blade to the other side of the blade while bypassing the top of the blade to form a tip leakage flow, whereas the presence of the impeller cover 801 can suppress the formation of tip leakage and improve the efficiency of the impeller. FIGS. 8B and 8C illustrate a front view diagram and a side view diagram of an impeller cover of a riveting type closed impeller according to an embodiment of the present invention, respectively. As shown in the figures, the impeller cover 801 comprises an impeller cover wall 811, a guide blade 812, an impeller cover shaft hole 813, an impeller cover hub 814, and an impeller cover rivet hole 815. The impeller cover 801 can be formed by mechanical processing in one-piece, wherein at the center of the impeller cover wall 811, an impeller cover shaft hole 813 is arranged, and the guide blades 812 are arranged around the impeller cover shaft hole 813 on the impeller cover wall 811, and the impeller cover hub 814 is connected with the impeller cover wall 811 through the guide blades 812. Multiple impeller cover rivet holes 815 are arranged on the impeller cover wall 811 for connection with rivet 802. The impeller cover wall 811 can form the main body of the impeller cover 801, and the guide blades 812 can perform a first pressurization of the gas that is about to enter the impeller 803, allowing the airflow to smoothly enter the impeller blades 832. FIG. 8D illustrates a front view diagram of an impeller of a riveting type closed impeller according to an embodiment of the present invention. As shown in the figure, the impeller 803 comprises an impeller disc 831, impeller blades 832, an impeller shaft hole 833, and an impeller rivet hole 834. The impeller 803 can be formed by mechanical processing in one-piece, wherein at the center of the impeller disc 831, an impeller shaft hole 833 is arranged and the impeller blades 832 are arranged around the impeller shaft hole 833 on the impeller disc 831. The impeller disc 831 can form the main body of the impeller 803, and the impeller blades 832 can perform a second pressurization on the airflow at the outlet of the guide blades 812, so that the airflow is smoothly discharged and the target pressure is efficiently achieved. The impeller shaft hole 833 is fitted to the impeller cover hub 814 to connect the impeller 803 to the impeller cover 801, wherein the fitting means is, for example, a clearance fit, a transition fit, or an interference fit. FIG. 8F illustrates a schematic diagram of a connection between an impeller cover hub and an impeller shaft hole of a riveting type closed impeller according to an embodiment of the present invention. As shown in the figure, after the impeller shaft hole 833 is fitted and connected to the impeller cover hub 814, in order to increase the connection strength, the impeller disc 831 can be further welded together with the impeller cover hub 814. FIG. 8G illustrates a schematic diagram of an arrangement of impeller rivet holes of a riveting type closed impeller according to an embodiment of the present invention. As shown in the figure, the impeller rivet hole 834 is arranged on the impeller disc 801 for connection with rivet 802, wherein the impeller rivet hole 834 can be arranged around the outer circumference of the impeller blade 832, and the center of the circle of the impeller rivet hole 834 is located in the tangential direction of the trailing edge of the impeller blade 832. The distance between the center of the circle of the impeller rivet hole 834 and the center of the impeller shaft hole 833 is greater than or equal to 1.05 times of the radius of the trailing edge of the impeller blade 832. The position of the impeller cover rivet hole 815 on the impeller cover wall 811 corresponds to the position of the impeller rivet hole 834 on the impeller disc 831. FIG. 8E illustrates a structural schematic diagram of a rivet of a riveting type closed impeller according to an embodiment of the present invention. As shown in the figure, the rivet 802 comprises a rivet impeller cover segment 821, a rivet intermediate segment 822, and a rivet impeller segment 823. The rivet 802 can be formed by mechanical processing in one-piece. The rivet intermediate segment 822 connects the rivet impeller cover segment 821 to the rivet impeller segment 823, wherein the rivet impeller cover segment 821 is connected with the impeller cover rivet hole 815, and the rivet impeller segment 823 is connected with the impeller rivet hole 304 to connect the impeller cover 801 with the impeller 803. The number of arranged rivets 802 can be the same as or less than the number of the impeller blades 832, with a minimum of 4. The diameter of the rivet impeller cover segment 821 and the diameter of the rivet impeller segment 823 are smaller than the diameter of the rivet intermediate segment 822, wherein a step surface is formed at the connection of the rivet impeller cover segment 821 and the rivet impeller segment 823 with the rivet intermediate segment 822, and the step surface can support the impeller cover 801 and the impeller 803 when the rivet 802 connects the impeller cover 801 with the impeller 803, to prevent damage to the impeller blade 832 caused by contact between the impeller cover 801 and the impeller blade 832 during the riveting process. During the riveting process, the rivet impeller cover segment 821 is firstly connected with the impeller cover rivet hole 815 and the rivet impeller segment 823 is connected with the impeller rivet hole 834 through clearance fit, and the rivet 802 is compressed and expanded to form an interference fit between the rivet impeller cover segment 821 and the impeller cover rivet hole 205 and between the rivet impeller segment 823 and the impeller rivet hole 834. FIG. 8H illustrates an enlarged schematic diagram of a rivet arrangement of a riveting type closed impeller according to an embodiment of the present invention. As shown in the figure, after connecting the impeller cover 801 to the impeller 803 by means of the rivet 802, in order to further increase the connection strength, the rivet 802 can be welded together with the impeller cover wall 811 and the impeller disc 831 at one or more welding positions shown in FIG. 8H.

In yet another embodiment of the present invention, the first and second impellers are obtained by manufacturing using a high-temperature and high-pressure diffusion welding method. FIG. 9A illustrates a structural sectional schematic diagram of a closed impeller according to an embodiment of the present invention. As shown in the figure, the closed impeller comprises a hollow impeller shaft 911 and an impeller cover 902. Wherein the impeller shaft 911 is in a volcano shape with a narrow top and a wide bottom, a base 912 is formed at the bottom, and blades 901 are provided at the middle end of the shaft side, and the number of blades 901 is multiple, which are uniformly distributed on the side wall of the impeller shaft 911, and the plurality of blades 901 are arranged to be in a helical shape as viewed from the axial direction. The impeller cover 902 is arranged concentric axis with the impeller shaft, and the diameter of the upper end of the impeller cover 902 is greater than the diameter of the upper end of the impeller shaft, and the diameter of the lower end of the impeller cover 902 is equal to the diameter of the lower end of the impeller shaft, i.e., the axial side slope of the impeller cover 902 is greater than the axial side slope of the impeller shaft; more specifically, the impeller cover 902 comprises two shaft segments, the upper shaft segment 921 is a circular cylindrical segment, and the lower shaft segment 922 is a cylindrical segment, the side wall of which is formed by a ¼ spherical surface and the wall thickness of which is constant, and the curvature of the inner side wall of the lower shaft segment 922 is greater than the curvature of the blade 901, the upper shaft segment 921 is a circular cylindrical body, wherein the curvature of the circular cylindrical body is a constant, therefore the upper end portion of the blade 901 is in force receiving contact with the top of the lower shaft end of the impeller cover 902, i.e., the connection between the upper shaft segment and the lower shaft segment, which is also the welded place of the impeller cover 902 and the impeller, i.e., the contact surface 931; the contact surface of the impeller and/or the impeller cover 902 is covered with an intermediate layer 903, the intermediate layer 903 is extremely thin copper with a soft texture that fits well on the surface of the blade 901. FIG. 9B illustrates a schematic diagram of a manufacturing method for a closed impeller according to an embodiment of the present invention. As shown in the figure, the manufacturing method of the closed impeller comprises:

First, at step S1, the impeller 901 and the impeller cover 902 are carved out using CNC equipment respectively, and the contact surface of the impeller 901 and/or the impeller cover 902, preferably on the blade 901 are covered with an intermediate layer 903, the intermediate layer 903 can be replaced with a 2-series aluminum to improve economy and strength;

Next, at step S2: after the impeller 901 and the impeller cover 902 are processed in a vacuum chamber for removal of the oxide layer, high-temperature evaporated paste-like substance is applied to the contact surface of the impeller 901 and/or impeller cover 902 to form a paste-like layer for easy transfer to the diffusion welding equipment, the intermediate layer 903 can be covered on the paste-like layer, or the paste-like layer can be applied on the intermediate layer 903, and then the impeller 901 and the impeller cover 902 are assembled to form a closed impeller structure as shown in FIG. 9A, and the impeller 901 and impeller cover 902 are positioned by means of a graphite clamp, and the clamp is placed in a vacuum furnace to be heated to the standard melting point, e.g., 0.7-0.8 times of the melting point of the welding material, during this period, the paste-like substance evaporates; wherein the standard melting point is the lowest value of the melting point of the impeller 901, the melting point of the impeller cover 902, and the melting point of the intermediate layer 903. In one embodiment of the present invention, the diffusion coefficient

$D = D_{0} \cdot e^{\frac{- Q}{k \cdot s}}$

is set to be less than a first threshold and the heating temperature of the vacuum furnace is set according to the diffusion coefficient, so that the heating temperature of the vacuum furnace 0.7-0.8 times of the standard melting point; wherein Do is the atomic diffusion coefficient of the material, Q is the diffusion activation energy of the equipment material; k is the Boltzmann coefficient, and s is the heating temperature of the vacuum furnace; wherein the atomic diffusion coefficient of the material is the lowest value of the atomic diffusion coefficients of the materials of the impeller 901, the impeller cover 902 and the intermediate layer 903;

Next, at step S3: the temperature is maintained for 2 to 10 minutes and pressure is applied by the graphite clamp, the contact surface made of Cu serves as the intermediate layer 903. This state is maintained for 10 to 30 minutes and then the pressure is gradually released for 20 to 60 minutes; specifically, within 2 to 10 minutes of a first stage, the graphite clamp slowly increases the pressure to compress the contact surface between the impeller 901 and the impeller cover 902; within 10 to 30 minutes of a second stage, the pressure of the graphite clamp remains unchanged to maintain the pressure on the contact surface between the impeller 901 and the impeller cover 902; and within 20 to 60 minutes of a third stage, the graphite clamp slowly decreases pressure. Wherein the clamp exerts an axial force F determined according to the following formula:

$F = K_{S 1} \times P_{t} \times A_{a} / K_{r} \times e^{\frac{- Q}{k \cdot s}}$

Wherein: P_tis the current temperature material yield stress; A_ais the theoretical contact area between two workpieces; K_ris the area calculation coefficient, K_r∝A_a/A_r, wherein A_ris the actual contact area, in actual situations, the actual contact area is generally 1/1000 to 1/10,000 of the theoretical contact area, if the pressure is loaded directly according to the theoretical area, then there will be a more obvious amount of deformation, and when it is desired to control the amount of deformation, K_ris positively correlated with the temperature maintaining time T when loaded; K_S1is an empirical coefficients, and because the influence of microscopic elements such as the oxide layer, gas, and atomic size of actual materials on welding cannot be ignored, there is need for an empirical coefficient for practical applications, the coefficient is macroscopically related to temperature, surface treatment, vacuum degree, and material, all of which are controllable variables; s is the heating temperature, generally taken as 0.7-0.8 times of the melting point of the welding material; Q is the diffusion activation energy; k is the Boltzmann coefficient. The pressure application and temperature maintaining time T of the clamp are determined according to the following formula:

$T = F^{\frac{K_{S 2}}{R \cdot A_{a}}}$

Wherein F is the axial force; K_S2is the empirical coefficients obtained from actual experiments; for example, it is beneficial to use the look-up table method to generate tables according to past experience, the table's horizontal coordinate is the heating temperature column, the table's vertical coordinate is the material parameter column, etc., R is the grain growth rate; A_ais the contact area; and

Finally, at step S4: a reprocess is performed on the workpiece completed by diffusion welding, followed by dynamic balance adjustment, and after its completion, overspeed test and performance test are performed, and sampling is performed for metallographic examination.

FIG. 9C illustrates a sectional schematic diagram of an assembly structure of a closed impeller and a diffusion welding equipment according to an embodiment of the present invention. As shown in the figure, the diffusion welding equipment comprises a positioning clamp 904, a workpiece clamping piece 905, a filling layer 906, and a pressure applying piece 907. Wherein the positioning clamp 904 is used to position the first end of the combination of the impeller and the impeller cover 902, the positioning clamp 904 is a disc-shaped body with a circular groove in the middle, the circular groove is used to accommodate the base of the impeller, the diameter of the groove is equal to the diameter of the base to radially limit the impeller base. After the closed impeller is placed into the positioning clamp 904, the workpiece clamping piece 905 above the closed impeller can be installed, so that the positioning clamp 904 exerts an upward bearing force on the closed impeller and the workpiece clamping piece 905 exerts a downward compression force on the closed impeller. Said workpiece clamping piece 905 comprises two portions, the first portion is a housing of circular cylinder of outer ring, which limits the outer contour of the closed impeller, and the second portion is also a circular cylinder, which is located above the impeller shaft of the impeller, and a downward axial force is exerted from the impeller shaft and the top of the impeller cover 902 in order to compress the closed impeller against the positioning clamp 904. The filler layer 906 is used to fill the clearance between the pressure applying piece 907, the workpiece clamping piece 905 and the impeller cover 902; since the outer side of the impeller cover 902 is an irregular surface such as a curved surface, the pressure applying piece 907 which has a planar surface at the bottom cannot directly act on the surface, and fine sand is used as the filler layer 906 to convert the outer surface of the impeller cover 902 into a planar surface, so as to enable the pressure applying piece 907 to exert force well. The pressure applying piece 907 is a circular cylinder, which exerts an axial force on the impeller cover 902 through the filling layer 906. Since the diameter of the second portion of the workpiece clamping piece 905 is equal to the diameter of the lower shaft segment, and the inner diameter of the pressure applying piece 907 is equal to the outer diameter of the upper shaft segment, i.e., the outer diameter of the second portion of the workpiece clamping piece 905, and the outer diameter of the pressure applying piece 907 is equal to the maximum outer diameter of the lower shaft segment, i.e., the inner diameter of the first portion of the workpiece clamping piece 905, therefore the pressure applying piece 907 can fully exert axial force to the curved surface portion of the lower shaft segment of the impeller cover 902 through the filler layer 906, and based on the above structure, there will be not generate axial force on the impeller, and therefore the compression force between the impeller cover 902 and the impeller can be increased, wherein the materials of the positioning clamp 904, the workpiece clamping piece 905 and the pressure applying piece 907 are all graphite.

As shown in the figure, a first pressure housing 131 and a second pressure housing 132 are respectively arranged at the outer sides of the two ends of the motor, and a first sealing ring 133 is arranged between the first pressure housing 131 and the first impeller 201, and a second sealing ring 134 is arranged between the second pressure housing 132 and the second impeller 202, and the first and second sealing rings can significantly reduce the backflow effect from the outlet to the inlet of the first and second impellers, which can further improve the compressor efficiency.

In order to reduce the compression power consumption of the second impeller 202, in one embodiment of the present invention, an interstage air supplement hole 331 is also arranged on the connecting pipe 303 to introduce the output gas from the economizer to cool down the gas compressed by the first impeller, and thereby achieve the purpose of reducing the compression power consumption of the high-pressure impeller and improving the efficiency of the system.

In one embodiment of the present invention, the motor 100 is a high-speed permanent magnet synchronous motor, and its bearings work as non-contact bearings, and thus can withstand higher rotational speeds than the usual ball bearings, and according to the Euler formula for compressors, Δh=U₂Cu₂−U₁Cu₁, it can be seen that, for the compressors with the same work capacity, the higher the rotational speed is, the smaller are the radial dimensions, and thus by using of permanent magnet synchronous motor, the power density of the compressor can be enhanced.

The working principle of the air-floating centrifugal compressor as described above is that the gas compressed by the second impeller enters the second radial bearing on the high-pressure side through the gap between the second impeller and the second end cap, as well as the gap between the second end cap and the rotor, and then enters the first radial bearing on the low-pressure side through the air gap between the stator and the rotor, and then passes through the two thrust bearings sequentially through the gap between the thrust disc and the motor housing as well as the gap between the thrust disc and the first end cap, and finally enters the first chamber, i.e., the outlet port of the first impeller, through the gap between the first end cap and the rotor, and the gap between the first impeller and the first end cap sequentially, and returns to the main air path to realize the internal circulation. Compared with static pressure air-bearing, the air-floating centrifugal compressor can omit the external air supplement channel, simplify the system structure and improve the reliability.

Although the various embodiments of the present invention have been described above, however, it should be understood that they are presented only as examples and not as limitations. It will be apparent to those skilled in the relevant art that various combinations, variations and changes can be made thereto without departing from the spirit and scope of the present invention. Therefore, the width and scope of the present invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should only be defined based on the accompanying claims and their equivalents.

Number	Date	Country	Kind
202310417453.3	Apr 2023	CN	national
202310417458.6	Apr 2023	CN	national
202310483855.3	May 2023	CN	national

AIR-FLOATING CENTRIFUGAL COMPRESSOR

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