Sealing System for Magnetic Levitating Centrifugal Compressor and Magnetic Levitating Centrifugal Compressor

This application is a continuation-in-part of U.S. patent application Ser. No. 18/153,789 filed Jan. 12, 2023, the contents of which in its entirety are herein incorporated by reference, which claims priority to Chinese Patent Application No. 202210047178.6, filed Jan. 17, 2022, and all the benefits accruing therefrom under 35 U.S.C. § 119, the contents of which in its entirety are herein incorporated by reference.

The present invention relates to the field of refrigeration technology, in particular to a sealing system for magnetic levitating centrifugal compressor, further to a magnetic levitating centrifugal compressor provided with said sealing system, and to a refrigeration system configured with said magnetic levitating centrifugal compressor.

Currently, centrifugal compressors gradually adopt oil-free lubrication technology to replace the former oil circuit lubrication, thus eliminating the management of the lubricating oil system, such as oil circuit maintenance, oil return management and maintenance of the oil circuit system. On the other hand, oil-free lubrication also represents higher operating efficiency of compressor and higher operating efficiency of refrigeration system, lower vibration and noise, stable operation and much lower cost, cleaner and better customer experience.

Magnetic levitating bearings are an important way and means to solve the problem of oil-free lubrication of centrifugal compressors. Centrifugal compressor supported by magnetic levitating bearings consists of shell, volute, impeller, magnetic levitating bearings and high-speed motor and other parts. In the working process, the high-speed motor is supported by the magnetic levitating bearings at the left and right ends, with low rotary resistance and high rotational speed. In this type of bearing mechanism, there is often a touchdown bearing, which is designed to prevent the damage of the magnetic levitating bearing part resulted from the collision of the magnetic levitating bearings with the motor shaft when the magnetic levitating bearings fail. Therefore, the radial clearance between the touchdown bearing and a spacer on the motor shaft is typically smaller than the radial clearance between the magnetic levitating bearings and the motor shaft, for example, the radial clearance between the touchdown bearing and the spacer on the motor shaft is half of the radial clearance between the magnetic levitating bearings and the motor shaft. In addition, in order to prevent airflow from the impeller side entering into the motor cavity, a seal is provided between the impeller and the motor cavity, said seal is typically a fixed labyrinth seal structure with teeth and fixed to the shell of the motor cavity. In order to avoid tooth damage due to collision between said motor shaft and said seal, the radial clearance between said seal and said motor shaft is designed to be relatively large, generally more than twice the touchdown bearing clearance, thus the sealing effect of said seal is relatively poor, and the amount of gas leaking from the impeller side is high, resulting in lower efficiency of the magnetic levitating centrifugal compressor.

In view of this, according to a first aspect of the present invention, it provides a sealing system for magnetic levitating centrifugal compressor, thereby effectively solving the above-mentioned problems and the problems of other aspects that exist in the prior art. Said magnetic levitating centrifugal compressor comprises a motor cavity and a motor shaft disposed within said motor cavity, an end of said motor shaft extends out from said motor cavity and is mounted with an impeller. In the sealing system for magnetic levitating centrifugal compressor according to the present invention, said sealing system comprises: a seal, said seal is sleeved on the outer side of said motor shaft and is disposed between said impeller and said motor cavity, for reducing the flow of fluid from said impeller to said motor cavity; a first magnet, said first magnet is fixed at an outer surface of said motor shaft; and a second magnet, said second magnet is fixed at a side of said seal facing said motor shaft, wherein said first magnet and said second magnet form a radial repulsive force in the radial direction of said motor shaft, so that said seal can be levitated in relative to said motor shaft.

In a further embodiment of the sealing system according to the present invention, a tension spring is provided on top of said seal for resisting the gravity of said seal, one end of said tension spring rests against said seal and the other end of said tension spring rests against a housing, said housing is fixedly connected to the shell of said motor cavity.

In another embodiment of the sealing system according to the present invention, a compression spring is provided at the bottom of said seal for resisting the gravity of said seal, one end of said compression spring rests against said seal and the other end of said compression spring rests against a housing, said housing is fixedly connected to the shell of said motor cavity.

In a further embodiment of the sealing system according to the present invention, there are a plurality of said first magnets and a plurality of said second magnets, wherein the plurality of said first magnets are arranged at an outer surface of said motor shaft at equal intervals along the radial direction of said motor shaft, and the plurality of said second magnets are arranged at equal intervals on a side of said seal facing said motor shaft.

In a further embodiment of the sealing system according to the present invention, said motor shaft is provided with a sleeve, and said first magnets are fixed to said sleeve in an inserted manner.

In another embodiment of the sealing system according to the present invention, the plurality of said first magnets are fixed at the outer surface of said motor shaft by means of a carbon fiber tape in a winding manner.

In a further embodiment of the sealing system according to the present invention, said sealing system further comprises an anti-rotation pin, said anti-rotation pin is inserted between said seal and said housing for preventing said seal from rotating relative to said housing.

In a further embodiment of the sealing system according to the present invention, there are a plurality of said anti-rotation pins, and the plurality of said anti-rotation pins are arranged at equal intervals in the circumferential direction of said seal.

In a further embodiment of the sealing system according to the present invention, a side of said seal fits against said housing, the fitting surfaces between said seal and said housing are provided with a wear resistant coating.

In yet another embodiment of the sealing system according to the present invention, said first magnet and said second magnet are radially magnetizing permanent magnets; or that said first magnet and said second magnet are axially magnetizing permanent magnets.

Furthermore, according to a second aspect of the present invention, it also provides a magnetic levitating centrifugal compressor, said magnetic levitating centrifugal compressor is provided with a sealing system as described above.

Furthermore, according to a third aspect of the present invention, it also provides a refrigeration system, said refrigeration system is configured with a magnetic levitating centrifugal compressor as described above.

Further, according to a fourth aspect of the present invention, it also provides a sealing system for magnetic levitating centrifugal compressor, said magnetic levitating centrifugal compressor comprises a motor cavity and a motor shaft disposed within said motor cavity, said motor shaft has a first end and a second end extending out from said motor cavity, said first end of said motor shaft is mounted with a first impeller, said second end of said motor shaft is mounted with a second impeller, said sealing system comprises: a first seal, said first seal is sleeved on the outer side of said motor shaft and is disposed between said first impeller and said motor cavity, for reducing the flow of fluid from said first impeller to said motor cavity; a second seal, said second seal is sleeved on the outer side of said motor shaft and is disposed between said second impeller and motor cavity, for reducing the flow of fluid from said second impeller to said motor cavity; a first magnet assembly, said first magnet assembly comprises a first magnet and a second magnet, said first magnet is fixed at an outer surface of said motor shaft and said second magnet is fixed at a side of said first seal facing said motor shaft; and a second magnet assembly, said second magnet assembly comprises a third magnet and a fourth magnet, said third magnet is fixed at an outer surface of said motor shaft and said fourth magnet is fixed at a side of said second seal facing said motor shaft, wherein said first magnet and said second magnet form a repulsive force in the radial direction of said motor shaft to keep said first seal and said motor shaft in a concentric levitation, and wherein said third magnet and said fourth magnet form a repulsive force in the radial direction of said motor shaft to keep said second seal and said motor shaft in a concentric levitation.

Furthermore, according to a fifth aspect of the present invention, it also provides a magnetic levitating centrifugal compressor, said magnetic levitating centrifugal compressor is provided with the sealing system as described above.

Furthermore, according to a sixth aspect of the present invention, it also provides a refrigeration system, said refrigeration system is configured with a magnetic levitating centrifugal compressor as described above.

It can be understood that the sealing system for magnetic levitating centrifugal compressor of the present invention is of a follow-up construction, using mutually repulsive magnetic forces to enable the seal to be levitated in relative to the motor shaft. As a result, the radial clearance between the seal of said sealing system and the motor shaft can be designed to be as small as possible without the use of additional tooling or special designs, further reducing the gas leakage from the impeller side.

Several embodiments of the present invention will be described in detail below in connection with the accompanying drawings. It should be noted that the orientation terms such as up, down, left, right, front, back, inside, outside, top, bottom, etc., mentioned or may mentioned in this description are defined relative to the construction shown in each of the accompanying drawings, and they are relative concepts, and therefore may change accordingly depending on the different location and different state of use in which they are located. Therefore, these or other orientation terms should not be interpreted as restrictive terms.

illustrates a magnetic levitating centrifugal compressorusing a sealing system in an example embodiment. The magnetic levitating centrifugal compressorincludes a motor having a rotorand a statorpositioned in a motor cavity. A motor shaftis connected to the rotor. A radial clearanceis located between the rotorthe stator.

The motor shaftis supported on each end by a magnetic levitating bearing assembly. Axially outward of each magnetic levitating bearing assembly, along the motor shaft, is a touchdown bearing. Axially outward of each touchdown bearing, along the motor shaft, is a sealing system, which is described in further detail with respect to. The motor shaftdrives a first impeller, located axially outward of one sealing system, along the motor shaft. The motor shaftdrives a second impeller, located axially outward of another sealing system, along the motor shaft. Refrigerant received at inletis provided to first impellerand the second impeller. The first impellercompresses the refrigerant and discharges the compressed refrigerant to a first volute. The second impellercompresses the refrigerant and discharges the compressed refrigerant to a second volute.

The magnetic levitating centrifugal compressorincludes a housingthat fixedly connected to a shellof said motor cavity.

is an enlarged view of a portion of. The magnetic levitating bearing assemblyincludes a radial magnetic bearing statorand a radial magnetic bearing rotorpress fit onto the motor shaft. A first clearanceis provided between the radial magnetic bearing statorand a radial magnetic bearing rotor.

A spaceris press fit on the motor shaftand is located radially inward of the touchdown bearing. A second clearanceis provided between the touchdown bearing and the spacer.

The second radial clearancebetween the touchdown bearingand the spaceris typically smaller than the first radial clearancebetween the between the radial magnetic bearing statorand a radial magnetic bearing rotor. For example, the second radial clearanceis half of the first radial clearance.

The magnetic levitating centrifugal compressormay be part of a refrigeration systemas shown in. The refrigeration systemincludes the magnetic levitating centrifugal compressor, a condenser, an expansion device, and an evaporator, through which refrigerant is circulated in series, as known in the art.

As shown in, it illustrates schematically in general terms the structure of one embodiment of the sealing systemfor magnetic levitating centrifugal compressorof the present invention. Said magnetic levitating centrifugal compressorincludes a motor cavityand a motor shaft, said motor shaftis located within said motor cavityand supported in rotation by a magnetic levitating bearing assembly, an end of said motor shaftextends out from said motor cavityand is mounted with) a first impellerand a second impellerand touchdown bearings. Said magnetic levitating bearing assemblymay include: a radial magnetic levitating bearing (not shown), an axially magnetic levitating bearing (not shown). There is a radial clearancebetween said touchdown bearingand a spaceron the motor shaft, the radial clearanceis smaller than the radial clearancebetween the stator portion and the rotor stack of said radial magnetic levitating bearing (the rotor stack of said radial magnetic levitating bearing is fixedly mounted on the outer side of the motor shaft), thus avoiding collision between the rotor stack and the stator portion of said radial magnetic levitating bearing in the event of a stoppage or a sudden power failure of said magnetic levitating centrifugal compressor. Said touchdown bearingmay be in the form of a ball bearing. As can be clearly seen from, said sealing system comprises: a seal, a first magnetand a second magnet. The seal, for example in the form of a labyrinth seal structure with teeth, is sleeved on the outer side of said motor shaftand is disposed between said impeller and said motor cavity so as to reduce the flow of fluid from said impeller (/) to said motor cavity. In general, there is a radial clearancebetween said sealand the motor shaft, said radial clearanceis greater than the radial clearanceexisting between said touchdown bearingand the spaceron the motor shaft, so as to prevent tooth damage of the labyrinth seal structure due to collision of said sealwith the motor shaftin case of stoppage or sudden power failure of said magnetic levitating centrifugal compressor.

In the above embodiment of the sealing system for magnetic levitating centrifugal compressoraccording to the present invention, said first magnetis fixed at the outer surface of said motor shaft. Said second magnetis fixed at a side of said sealfacing said motor shaft. Said first magnetand said second magnetform a radial repulsive force in the radial direction of said motor shaft(as shown by the arrow in), e.g., the magnetic poles of the opposite sides of said first magnetand said second magnetare the same, enabling said sealto be “levitated” on said motor shaft, thus preventing said seal, and in particular its toothed structure, from colliding with said motor shaft. The “levitated” here refers to a state in which the sealmaintains a relatively stable interval with respect to the motor shaft. Preferably, the sealand the motor shaftmaintain a concentric interval. Since said sealis designed in a follow-up structure, i.e. said sealcan be levitated up and down with said motor shaft, the radial clearance between said seal and said motor shaft may be designed to be as small as possible, so as to further reduce the gas leakage from the back side of said impeller near said motor cavity.

When said magnetic levitating centrifugal compressor is in normal operation, said motor shaftis levitated and running at high speed, while said sealremains concentrically arranged with said motor shaftunder the action of radial repulsive force, as shown in. When said magnetic levitating centrifugal compressorstops working or when there is a sudden power failure, said motor shaftfalls due to gravity and comes into contact with said touchdown bearing, as shown in. At this time, said sealfalls with said motor shaftunder the mutual repulsive force of said first magnetand said second magnet, at which time the radial clearance between said sealand said housingat the top becomes larger and the radial clearance between said sealand housingat the bottom becomes smaller, while no contact occurs between said sealand said motor shaft.

In order to be able to partially or even fully counteract the gravity of said sealso as to keep said sealand said motor shaftas concentric as possible under the action of the repulsive force of the magnets, an extension springis provided at the top of said seal, one end of said extension springrests against said sealand the other end of said extension springrests against the housing, said housingis fixedly connected to the shellof said motor cavity. Alternatively, a compression spring is provided at the bottom of said seal, one end of said compression spring rests against said seal and the other end of said compression spring rests against said housing, said housing is fixedly connected to the shell of said motor cavity.

In conjunction with the above embodiment, in other preferred embodiments, there are a plurality of said first magnetand said second magnet, wherein the plurality of said first magnetsare arranged at an outer surface of said motor shaftat equal intervals along the radial direction of said motor shaft, and the plurality of said second magnetsare arranged at equal intervals on a side of said sealfacing said motor shaft, as shown in. Further, said motor shaftis provided with a sleeve, said sleeveis for example tightly fitted to said motor shaft, said first magnetis fixed to said sleevein an inserted manner, thereby preventing said first magnets from flying out due to centrifugal force when the motor shaftis rotating. As an alternative, said plurality of first magnets are fixed at the outer surface of said motor shaftby means of carbon fiber tape in a winding manner.

With continued reference to, said sealing system further comprises an anti-rotation pin, said anti-rotation pinis inserted between said sealand said housingto prevent said sealfrom rotating relative to said housing, i.e., said sealcan only be levitated up and down with said motor shaft. Further, there are a plurality of said anti-rotation pinsand said plurality of anti-rotation pinsare arranged at equal intervals in the circumferential direction of said seal.

It will be readily understood by those skilled in the art that typically the volute cavity in which said impellerand/oris located is a high pressure area and said motor cavityis a low pressure area, so that the pressure on the side of said sealnear said impeller/is always greater than the pressure on the side of said sealnear said motor cavity, causing friction due to the side of said seal(on the right in the figure) abutting against said housing, as shown in the circled portion of. Thus, the wear-resistant coating may be provided on the fitting surfaces between said sealand said housing. On the other hand, due to the friction, said sealwill not be levitated when said motor shaftmoves slightly, but only be moved with the motor shaftwhen the radial movement of the motor shaftexceeds a certain value, i.e. when the repulsive force on said sealexceeds the frictional force, and the certain value of radial movement must not exceed the sealing gap between said sealand said motor shaftsurface.

As an example, said first magnetand said second magnetare radially magnetizing permanent magnets, as shown in. In this embodiment, the direction of the repulsive force between the first magnetand the second magnetis along the radial direction of the motor shaft. As an alternative, said first magnetand said second magnetare axially magnetizing permanent magnets, as shown in. In this embodiment, the direction of the repulsive force between the first magnetand the second magnetis along the axial direction of the motor shaft. In order to enable the sealto levitate relative to the motor shaft, the repulsive force in the axial direction needs to be converted into a repulsive force in the radial direction by the magnetic conductive ringmade of magnetic conductive metal. Compared with the radially magnetizing permanent magnet, the axially magnetizing permanent magnet has a simpler manufacturing process and lower cost.

The present invention also proposes a sealing systemfor magnetic levitating centrifugal compressor. Said magnetic levitating centrifugal compressormay be of a back-to-back two-stage compression design. Specifically, said magnetic levitating centrifugal compressormay comprise a motor cavityand a motor shaftlocated in said motor cavity, a first impellerand a second impeller, wherein said first impellerconstitutes a low pressure stage of compression and said second impellerconstitutes a high pressure stage of compression, said second impeller, i.e., the impeller of the second stage being typically smaller than said first impeller, i.e., the impeller of the first stage, wherein the inlet of the impellerof the second stage is the outlet of the impellerof the first stage. Said motor shaftis located in said motor cavityand is supported by a magnetic levitating bearing assemblyduring rotation. Said motor shafthas a first end and a second end extending out from said motor cavity. Said first end of said motor shaft is mounted with a first impellerand a first touchdown bearing, and said second end of said motor shaft is mounted with a second impellerand a second touchdown bearing.

In the above embodiment of back-to-back two-stage compression, both of the first end and the second end of the motor shaftare provided with the sealing construction as shown in. Specifically, said sealing system comprises: a first seal, a second seal, a first magnet assembly, and a second magnet assembly. Said first seal is sleeved on the outer side of said motor shaftand is located between said first impellerand said motor cavity, thereby reducing the flow of fluid from said first impellerto said motor cavity. Said second seal is sleeved on the outside of said motor shaftand is located between said second impellerand said motor cavity, thereby reducing the flow of fluid from said second impellerto said motor cavity. Said first magnet assembly includes a first magnetand a second magnet, said first magnetis fixed at the outer surface of said motor shaftand said second magnetis fixed at a side of said first seal facing said motor shaft. Said second magnet assembly includes a third magnet and a fourth magnet, said third magnet is fixed at the outer surface of said motor shaft and said fourth magnet is fixed at a side of said second seal facing said motor shaft. Said first magnet and said second magnet form a repulsive force in the radial direction of said motor shaft and keep said first seal and said motor shaft in a concentric levitation, and said third magnet and said fourth magnet form a repulsive force in the radial direction of said motor shaft and keep said second seal and said motor shaft in a concentric levitation.

In summary, the sealing system for magnetic levitating centrifugal compressor of the present invention is of a follow-up type construction, using the radial repulsive force between the magnets to keep the seal and the motor shaft in a concentric arrangement and to enable said seal to be levitated on said motor shaft. In this way, the radial clearance between the seal and the motor shaft becomes as small as possible without the use of additional tooling or special designs, and the gas leakage from the back side of said impeller near said motor cavity is further reduced.

In addition, the present invention provides a magnetic levitating centrifugal compressor, which is provided with a sealing system as described according to various embodiments. In addition, the present invention provides a refrigeration system configured with said magnetic levitating centrifugal compressor, said refrigeration system may comprise a cooling tower, a cooling water unit and a pumping unit, etc. connected by piping, wherein said cooling water unit comprises a magnetic levitating centrifugal compressor, a condenser, a throttling device and an evaporator, etc. As pointed out in the above, by providing the above-mentioned magnetic levitating centrifugal compressor, the air tightness can be effectively improved without additional manufacturing cost, thus the efficiency of the magnetic levitating centrifugal compressor is further improved, and therefore it is recommended herein to use the above-mentioned magnetic levitating centrifugal compressor in all kinds of refrigeration systems.

The specific embodiments described above are intended only to describe more clearly the principle of the present invention, which is made easier to understand by clearly illustrating or describing the individual components. Without departing from the scope of the present invention, the person skilled in the art may easily make various modifications or variations to the present invention. Therefore, it should be understood that these modifications or variations should be included within the scope of patent protection of the present invention.