Patent Publication Number: US-11384762-B2

Title: Cylindrical symmetric volumetric machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/IB2018/056924, filed Sep. 11, 2018, claiming priority based on Belgian Patent Application No. BE 2017/5672 filed on Sep. 21, 2017, the contents of all of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a cylindrical symmetric volumetric machine. 
     Background 
     A volumetric machine is also known under the name “positive displacement machine”. 
     In particular, the invention is intended for machines such as expanders, compressors and pumps with a cylindrical symmetry with two rotors, namely an inner rotor mounted rotatably in an outer rotor. 
     Such machines are already known and are described in U.S. Pat. No. 1,892,217 among others. It is also known that the rotors can have a cylindrical or conical shape. 
     It is known that such machines can be driven with an electric motor. 
     From Belgian patent application no. BE 2017/5459 it is already known that the electric motor can be mounted around the outer rotor, whereby the motor stator directly drives the outer rotor. 
     Such machine has many advantages in relation to the known machines whereby the motor shaft is connected by means of a transmission with the rotor shaft of the outer or inner rotor. 
     Thus, the machine will not only be a lot more compact, such that the footprint is smaller, it also means less shaft seals and bearings are required. 
     In known machines and the machine of BE 2017/5459, the rotors, bearings and other components need to be lubricated and cooled. An injection circuit is provided for this which will inject a liquid, such as oil or water, for example, in the machine, for lubrication, sealing and cooling. This injection circuit also comprises a system to pressurise the liquid and to be able to inject it in the machine. 
     There is also an injection of liquid between the inner rotor and the outer rotor, whereby this injection necessarily takes place at the inlet, which results in an increase of the inlet temperature. 
     There can also be an injection of liquid on the level of the motor, whereby the motor stator is provided with slots to let the liquid pass through. The motor may also be air-cooled. 
     As the liquid is also injected between the inner rotor and outer rotor, the gas will contain an amount of liquid at the outlet of the machine. That is why it is necessary that downstream from the machine a liquid separation takes place, whereby the injected liquid is separated from the gas. 
     Consequently, not only a separate liquid separator needs to be provided. Furthermore, in the case of a compressor, this also means a pressure loss. 
     The purpose of the present invention is to improve the lubrication and cooling for a machine as specified in BE 2017/5459. 
     SUMMARY OF THE INVENTION 
     To this end, the invention relates to a cylindrical symmetric volumetric machine, whereby the machine comprises a housing with an inlet opening and an outlet opening, with two co-operating rotors in the housing, namely an outer rotor which is mounted rotatably in the housing and an inner rotor which is mounted rotatably in the outer rotor, whereby liquid is injected in the machine, characterised in that at the outlet opening on the level of the inner rotor and outer rotor, a liquid separation takes place, whereby the separated liquid flows back into the machine, and in that the outer rotor has an axial extension on the level of the outlet opening which extends around this outlet opening almost up against the housing such that between the axial extension and the housing there is a space. 
     As both the inner rotor and the outer rotor will rotate at high speed at the outlet opening, the liquid particles will be flung outward by the centrifugal forces, i.e. toward the inside of the outer rotor. In this way they will be removed from the compressed air. 
     This provides the advantage that no separate liquid separator needs to be included, but that the separation happens in the machine itself. 
     Not only will this make the machine more compact, it will also ensure that, in the case the machine is a compressor, the pressure loss in the liquid separator can be avoided. 
     Preferably at least a part of the separated liquid ends up back into the machine via the liquid channels in the outer rotor. 
     ‘Liquid channels in the outer rotor’ means that the liquid channels effectively run through the outer rotor. In other words, the outer rotor is provided with hollow channels in which or through which liquid can flow. 
     By providing liquid channels in the outer rotor, these particles can be collected and drained via the liquid channels. 
     The outer rotor has an axial extension on the level of the outlet opening, which extends around this outlet opening almost up against the housing such that between the axial extension and the housing there is a space. 
     Due to the centrifugal forces and the movement of the gas toward the outlet opening, the liquid particles will end up in said space between the housing and the axial extension of the outer rotor. The liquid can then be drained via this space. 
     Preferably a liquid channel extends in the axial extension which ends in the space between the housing and the axial extension. 
     Because the liquid ends up in the space, a kind of axial bearing will form between the housing and the outer rotor. As a result of this the forces that work on the ball bearing which supports the outer rotor, will become smaller. Consequently, a smaller ball bearing can be applied. 
     In a practical embodiment, the liquid channels in the outer rotor lead to one or more of the following locations:
         one or more injection points to the space between the inner rotor and the outer rotor;   one or more injection points to one or more bearings of the machine.       

     The liquid channels allow the liquid to be led to the desired locations that need lubrication and/or cooling. 
     This provides the advantage that the injection between the inner rotor and the outer rotor does not have to be at the inlet side as the liquid channels can be made to end downstream from the inlet side to the space between the inner rotor and the outer rotor. This avoids an increase of the inlet temperature following injection at the inlet opening. 
     According to a preferred characteristic of the invention, the outer rotor has an open structure with passages for the sucked in gas, such that gas that is sucked in via the inlet opening must pass via the passages of the open structure before it ends up between the inner rotor and the outer rotor. 
     This has the advantage that a kind of air cooling of the machine is obtained, whereby the outer rotor can be cooled by the sucked in air. 
     This principle will also allow cooling of the liquid in the liquid channels. 
     Moreover, if the machine relates to a machine of BE2017/5459, it means the magnets embedded in the outer rotor can be actively cooled as well. 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
       With the intention of better showing the characteristics of the invention, a few preferred embodiments of a cylindrical symmetric volumetric machine according to the invention are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein: 
         FIG. 1  schematically shows a machine according to the invention; 
         FIG. 2  shows the section indicated in  FIG. 1  by F 2  on a larger scale; 
         FIG. 3  shows a variant of  FIG. 2 ; 
         FIG. 4  shows the section indicated in  FIG. 1  by F 4  on a larger scale; 
         FIG. 5  shows the section indicated in  FIG. 4  by F 5  on a larger scale; 
         FIG. 6  shows a variant of  FIG. 5 ; 
         FIG. 7  shows another embodiment of  FIG. 4 ; 
         FIG. 8  shows the section indicated in  FIG. 1  by F 8  on a larger scale; 
         FIG. 9  shows the section indicated in  FIG. 1  by F 9  on a larger scale. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The machine  1  schematically shown in  FIG. 1  is a compressor device in this case. 
     According to the invention it is also possible that the machine  1  relates to an expander device. The invention can also relate to a pump device. 
     The machine  1  is a cylindrical symmetric volumetric machine  1 . This means the machine  1  has a cylindrical symmetry, i.e. the same symmetrical properties as a cone. 
     The machine  1  comprises a housing  2  that is provided with an inlet opening  3  to suck in gas to be compressed and with an outlet opening  4  for compressed gas. The housing defines a chamber  5 . 
     Two co-operating rotors  6   a ,  6   b , namely an outer rotor  6   a  mounted rotatably in the housing  2  and an inner rotor  6   b  mounted rotatably in the outer rotor  6   a  are located in the chamber  5  in the housing  2  of the machine  1 . 
     Both rotors  6   a ,  6   b  are provided with lobes  7  and can turn into each other co-operatively, whereby between the lobes  7  a compression chamber  8  is created, the volume of which can be reduced by the rotation of the rotors  6   a ,  6   b , such that the gas that is caught in this compression chamber  8  is compressed. The principle is very similar to the known adjacent co-operating screw rotors. 
     The rotors  6   a ,  6   b  are mounted on bearings in the machine  1 , whereby the inner rotor  6   b  on one end  9   a  is mounted in the machine  1  on a bearing and the other end  9   b  of the inner rotor  6   b  is supported or borne by the outer rotor  6   a  as it were. 
     In the example shown, the outer rotor  6   a  is mounted at both ends  9   a ,  9   b  in the machine  1  on bearings. At least one axial bearing  10  is used for this. 
     The end  9   a  will also be referred to as the inlet side  9   a  of the inner and outer rotor  6   a ,  6   b  and the end  9   b  of the inner and outer rotor  6   a ,  6   b  will be referred to as the outlet side  9   b  in what follows. 
     Said compression chamber  8  between the inner and outer rotor  6   a ,  6   b  will move from the inlet side  9   a  to the outlet side  9   b  by the rotation of the rotors  6   a ,  6   b.    
     In the example shown the rotors  6   a ,  6   b  have a conical shape, whereby the diameter D, D′ of the rotors  6   a ,  6   b  decreases in the axial direction X-X′. However, this is not necessary for the invention; the diameter D, D′ of the rotors  6   a ,  6   b  can also be constant or vary in another way in the axial direction X-X′. 
     Such design of rotors  6   a ,  6   b  is suitable both for a compressor and expander device. Alternatively, the rotors  6   a ,  6   b  can also have a cylindrical form with a constant diameter D, D′. They can then either have a variable pitch, such that there is a built-in volume ratio, in the case of a compressor or expander device, or a constant pitch, in the case the machine  1  relates to a pump device. 
     The axis  11  of the outer rotor  6   a  and the axis  12  of the inner rotor  6   b  are fixed axes  11 ,  12 , this means that the axes  11 ,  12  will not move in relation to the housing  2  of the machine  1 , however they do not run parallel, but are located at an angle α in relation to each other, whereby the axes intersect in point P. 
     However, this is not necessary for the invention. For example, if the rotors  6   a ,  6   b  have a constant diameter D, D′, the axes  10 ,  11  can run parallel. 
     Further, the machine  1  is also provided with an electric motor  13  which will drive the rotors  6   a ,  6   b . This motor  13  is provided with a motor rotor  14  and a motor stator  15 . 
     In this case, but not necessarily, the electric motor  13  is mounted around the outer rotor  6   a  whereby the motor stator  15  directly drives the outer rotor  6   a.    
     In the example shown this is realised because the outer rotor  6   a  also serves as motor rotor  14 . 
     The electric motor  13  is provided with permanent magnets  16  which are embedded in the outer rotor  6   a.    
     It is also possible of course that these magnets  16  are not embedded in the outer rotor  6   a , but are mounted on the outside thereof for example. 
     Instead of an electric motor  13  with permanent magnets  16  (i.e. a synchronous permanent magnet motor), an asynchronous induction motor can also be applied, whereby the magnets  16  are replaced with a squirrel-cage rotor. Induction from the motor stator generates a current in the squirrel-cage rotor. 
     On the other hand, the motor  13  can also be a reluctance type or induction type or a combination of types. 
     The motor stator  15  is mounted around the outer rotor  6   a  in a covering way, whereby in this case it is located in the housing  2  of the machine  1 . 
     In this way the lubrication of the motor  13  and the rotors  6   a ,  6   b  can be lubricated together, as they are located in the same housing  2  and consequently are not closed off from each other. 
     In the example shown in  FIG. 1 , the outer rotor  6   a  has an axial extension  17  on the level of the outlet opening  4 . 
     This axial extension  17  extends around the outlet opening  4  in the housing  2 , and almost up against the housing  2 . 
     In  FIG. 1  the housing  2  is provided with a similar axial extension  18  around the outlet opening, toward the axial extension  17  of the outer rotor  6   a , but this is not necessarily the case. 
     There is a space  19  or opening between the housing  2  and the axial extension, as shown in detail in  FIG. 2 . 
     In this way liquid separation will take place at the outlet opening  4  on the level of the inner rotor  6   a  and the outer rotor  6   b  via said space  19 , because the liquid particles are flung to the space  19  under the influence of the centrifugal force. 
     A liquid channel  20  extends in the axial extension  17  which ends in said space  19  and which will collect and drain the separated liquid particles. 
     It is possible that in said space  19  between the axial extension  17  and the housing  2 , a porous liquid absorbing material  21  has been applied, as shown in  FIG. 3 . 
     Said porous material  21  can for example be metal foam. 
     Said liquid channels  20  extend through the outer rotor  6   a , as shown in  FIG. 4 . 
     In the example of  FIG. 4 , the liquid channels  20  lead to the bearings  10  of the outer rotor  6   a  and to an injection point  22  to the space between the inner rotor  6   a  and the outer rotor  6   b.    
     As shown in  FIG. 4 , the liquid channels  20  extend further, and further on in the inner rotor  6   a , more toward the inlet side  9   a , they will lead to one or more additional injection points  22  to the space between the inner rotor  6   a  and the outer rotor  6   b.    
     This means liquid can be injected at various points  22  along the entire length of the inner and outer rotor  6   a ,  6   b  instead of only along the inlet side  9   a  such as with the known machines  1 . 
     As shown in  FIGS. 1 and 4 , the outer rotor  6   a  is provided with one or more cooling fins  23 . 
     They are applied on the axial extension  17  of the outer rotor  6   a , but they can be applied anywhere on the outer rotor  6   a.    
     In  FIG. 4  they are perpendicular to the surface of the outer rotor  6   a , but this is not necessarily the case. 
     From the detail in  FIG. 5  it is clear that the liquid channels  20  extend through these cooling fins  23 . 
     The operation of the machine  1  is very simple and as follows. 
     During the operation of the machine  1 , the motor stator  15  will drive the motor rotor  14  and therefore drive the outer rotor  6   a  in the known way. 
     The outer rotor  6   a  will help drive the inner rotor  6   b , and the rotation of the rotors  6   a ,  6   b  sucks in gas via the inlet opening  3 , which will end up in a compression chamber  8  between the rotors  6   a ,  6   b . When the gas is sucked in via the inlet opening  3 , it will flow past the cooling fins  23 , the motor rotor  14  and the motor stator  15 . In this way the gas will cool the motor  13  as well as the cooling fins  23  and thus the liquid flowing via the cooling fins  23 . 
     Due to the rotation, this compression chamber  8  moves to the outlet  4  and at the same time will reduce in terms of volume to thus realise a compression of the gas. 
     During the compression, liquid is injected via the injection points  22  which end in the space between the inner rotor  6   a  and the outer rotor  6   b  and in the bearings  10 . 
     When the gas has reached the outlet side  9   b  of the inner and outer rotor  6   a ,  6   b , it will contain liquid particles. 
     Due to the rotation of the inner and outer rotor  6   a ,  6   b , the liquid particles are flung outward radially and separated to the space  19 , where they end up in the liquid channel  20 . The built-up pressure on the outlet side  9   b  will be used to inject the liquid in the machine  1 . 
     To prevent that the liquid particles which were flung to the space  19  are dragged to the outlet  4  together with the compressed gas, the liquid absorbing material  21  can be mounted in the space as shown in  FIG. 3 , which will catch the liquid particles as it were. 
     Also, due to the liquid present, a slide bearing is created in the space  19  between the axial extension  17  and the housing  2 . 
     This slide bearing will be able to accommodate axial forces, such that the bearing  10  needs to be able to accommodate less forces and it can be made smaller and/or lighter. 
     A small part of the liquid will be able to leave the space  19  via the opening  24  at the outer perimeter side. 
     Said effect will separate the liquid from the compressed gas at the outlet side  9   b  of the rotors  6   a ,  6   b.    
     The compressed gas can then exit the machine  1  via the outlet opening  4 . 
     Said liquid can both be water and a synthetic oil, or non-synthetic oil. 
     In the example of  FIGS. 1 to 5 , the liquid is cooled because the liquid channels  20  extend through the cooling fins  23 . The cooling fins  23  are air-cooled, and in turn will draw heat away from the liquid flowing through the cooling fins. 
     It is also possible that no cooling fins  23  are provided but that alternatively the liquid channels  20  at least partially run via a liquid pipe  24  mounted on the surface of the outer rotor  6   a.    
       FIG. 6  shows such liquid pipe  24 , whereby the pipe has a curved shape, in order to mount the longest possible pipe in a compact way on the outer rotor  6   a . It is clear that the exact shape of the liquid pipe  24  is not restrictive for the invention. One could indeed conceive other shapes which provide the same result. 
     Such liquid pipe  24  is air-cooled in a similar way as the cooling fins  23 . 
       FIG. 7  shows an alternative for the embodiment of  FIGS. 2 and 3 . 
     The outer rotor  6   a  hereby has a section  25  with a conical cross-section which connects to the axial extension  17 . 
     In  FIG. 7  the inner rotor  6   b  and the outer rotor  6   a  have a conical shape, such that the section of the outer rotor  6   a , which connects to the axial extension  17 , will form said conical section  25 . 
     If the outer rotor  6   a  does not have a conical shape, a section of the axial extension  17  can have a conical shape instead. 
     Further, the housing  2  is provided with a corresponding extension  18  which fits over or around the axial extension  17  of the outer rotor  6   a  and at least partially over or around the conical section  25  of the outer rotor  6   a , whereby there is a space  19  between the extension  18  of the housing  2  on the one hand and the axial extension  17  of the outer rotor  6   a  and the conical section  25  on the other hand. 
     It is important that the housing  2  does not touch the outer rotor  6   a  anywhere. 
     In the axial extension  17  and/or in the conical section  25  a liquid channel  20  is mounted that ends in said space  19 . 
     During the operation of the machine  1  liquid will end up again in the space  19 , which can be injected back in the machine  1  via the liquid channels  20 . 
     Such configuration will create a conical axial slide bearing with a radial slide bearing. 
     As a result of this, the bearing  10  is not only relieved, but it can even be left out, as schematically shown in  FIG. 8 , which shows a variant of the section indicated in  FIG. 1  by F 8 . 
     Further, in  FIG. 8  the outer rotor  6   a  is provided with cooling fins  23  which have been mounted on the surface of the outer rotor  6   a  itself and therefore not on the axial extension  17  as in  FIG. 1 . 
     Furthermore, the outer rotor  6   a  has an open structure with passages  26  for the sucked in gas, whereby it is so that gas that is sucked in via the inlet opening  3 , must pass via the passages  26  before it ends up between the inner rotor  6   b  and the outer rotor  6   a  on the inlet side  9   a  of the rotors  6   a ,  6   b.    
     This has the advantage that the magnets  16  are actively cooled by the gas flowing in. Furthermore, the motor stator  15  does not need any slots to let the air through from the inlet opening  3  to the inlet side  9   a  of the rotors  6   a ,  6   b.    
     Additionally, but not necessarily, the outer rotor  6   a  is provided with an axial ventilator  27  on the level of the inlet opening  3  in the form of blades mounted in the open structure. 
     This will help to suck in gas and build up pressure such that a better filling ratio of the compression chamber  8  is obtained. 
       FIG. 9  shows another additional element which can be applied in all said embodiments. It relates to means to obtain a pre-separation of the liquid, i.e. before the separation that occurs on the level of the outlet opening  4 . 
     To this end the inner rotor  6   b , on the level of the end of the inner rotor  6   b  on the outlet side  9   b , is provided with blades  28  along which the gas passes before it leaves the machine  1  via the outlet opening  4 . 
     It is not excluded that the blades  4  are provided on the outer rotor  6   a  or that both the outer rotor  6   a  and the inner rotor  6   b  are provided with such blades  28 . 
     Due to their rotation the blades  28  will strengthen and support the separation further up, such that the overall efficiency of the separation, or the total amount of the separated liquid, ends up much higher. 
     Alternatively or additionally to said liquid channels  20 , it is also possible that at least a part of the separated liquid is collected in a reservoir that is located under the outer rotor  6   a  in the housing  2 . 
     Part of, or all the separated liquid can then flow down via the spaces  19  toward the reservoir instead of ending up in the channels  20 . 
     The outer rotor  6   a  is hereby provided with one or more radially oriented fingers, ribs or the like along the outer surface on the inlet side  9   a.    
     It is such that during the rotation of the outer rotor  6   a  these fingers move through the liquid in the reservoir and thus move around and carry along the liquid such that this liquid can end up in the machine  1  again. 
     This is so-called ‘splash’ lubrication, whereby the moved around liquid ends up on the inlet side  9   a  between the rotors. 
     It is possible that on the outside of the housing  2 , on the level of the reservoir, cooling fins are provided, which ensure that the liquid in the reservoir can be cooled. 
     The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a cylindrical symmetric volumetric machine according to the invention can be realised in all kinds of forms and dimensions, without departing from the scope of the invention.