Patent Publication Number: US-2022235772-A1

Title: Vacuum pumping system having an oil-lubricated vacuum pump

Description:
RELATED APPLICATIONS 
     This application is a divisional under 35 U.S.C. § 121 of U.S. patent application Ser. No. 16/507,972, filed Jul. 10, 2019; which claims priority to European Patent Application No. EP 18184580.1, filed Jul. 19, 2018, titled “VACUUM PUMPING SYSTEM HAVING AN OIL-LUBRICATED VACUUM PUMP,” the contents of each of which are incorporated by reference herein in their entireties. 
    
    
     TECHNICAL FIELD 
     The present invention relates to vacuum pumping systems and, more particularly, it concerns a vacuum pumping system having an oil-lubricated vacuum pump. 
     BACKGROUND 
     Vacuum pumps are used to achieve vacuum conditions, i.e. for evacuating a chamber (so-called “vacuum chamber”) and establishing sub-atmospheric pressure conditions in said chamber. Many different kinds of vacuum pumps, having different structures and operating principles, are known and each time a specific vacuum pump is to be selected according to the needs of a specific application, namely according to the degree of vacuum that is to be attained in the corresponding vacuum chamber. 
     In general, a vacuum pump comprises a pump casing, in which one or more pump inlets and one or more pump outlets are provided, and pumping elements, arranged in said pump casing and configured for pumping a gas from said pump inlet(s) to said pump outlet(s): by connecting the pump inlet(s) to the vacuum chamber, the vacuum pump allows the gas in the vacuum chamber to be evacuated, thus creating vacuum conditions in said chamber. 
     More specifically, in a kind of vacuum pumps, the pumping elements comprise a stator defining a pumping chamber and a rotor rotatable in said pumping chamber, and the stator and the rotor cooperate with each other for pumping the gas from the pump inlet(s) to the pump outlet(s). In such vacuum pumps, the rotor is generally mounted to a rotating shaft which is driven by a motor, namely by an electric motor. 
     Even more specifically, vacuum pumping systems are known in which the vacuum pump is connected to an oil tank, whereby oil can be transferred from the oil tank to the vacuum pump, and in particular to the pumping chamber, for acting as coolant and lubricating fluid and for sealing the chamber. Among such systems, those using rotary vane vacuum pumps can be mentioned, and the following description will refer to a system of that kind. 
     A conventional vacuum pumping system using a rotary vane vacuum pump is shown in  FIG. 1  and is generally denoted  10 . 
     Pumping system  10  essentially comprises a rotary vane vacuum pump  20  and an electric motor  30  for driving pump  20 . 
     Pump  20  comprises a pump casing  21  in which one or more pump inlets and one or more pump outlets (not shown in the Figure) are defined. Pump casing  21 , which is refined so as to act also as pump stator, internally defines a pumping chamber in which a pump rotor  23  eccentrically rotates. Rotor  23  is fastened to or integral with a pump shaft  24  driven in rotation by motor  30  and is provided with one or more radially slidable vanes  25  (only one being visible in the drawing) that, during rotation of the rotor  23 , move in contact with the inner walls of the pumping chamber. As known, in such kind of pump, oil is introduced into the pumping chamber for lubricating and cooling the pump and separating the regions at different pressures. 
     Motor  30  in turn comprises a casing  31 , fastened to pump casing  21  and enclosing a motor stator  32  and a motor rotor  33 . Motor stator  32  and motor rotor  33  cooperate with each other so as to drive pump rotor  23  into rotation by means of a drive shaft  34 , associated with motor rotor  33 . Drive shaft  34  can be coupled to pump shaft  24  or it can be made as an integral unit with pump shaft  24  and pump rotor  23 , as shown in the Figure. End walls  35 ,  36  close a chamber housing motor rotor  33  and rotatably support, in association with suitable rolling bearings, the end portions of shaft  34 . 
     To prevent oil and possibly toxic gases present in the pumping chamber from passing to motor  30  and escaping in the environment through the motor casing  31 , a dynamic seal  40 , typically a lip seal, is provided around shaft  34  between motor casing  31  and pump casing  21 . The dynamic seal  40  is also to prevent dust inlet into the pumping chamber. 
     U.S. Pat. No. 6,644,942 discloses a pumping system in which the motor rotor and stator are accommodated in a resin jacket preventing lubricant present in a chamber adjacent to the motor module from leaking into the motor module itself. Yet, the prior art is concerned with a dry vacuum pump, in particular a dual-rotor pump with two parallel rotors coupled via a gear assembly located in a casing containing oil, and the chamber containing oil is not the pumping chamber, but is the casing housing the gear assembly. This pumping system still needs the provision of a lip seal around the shaft, at the wall separating the two chambers to be isolated. 
     Dynamic seals are rather expensive. Moreover, in the case of vacuum pumping systems comprising a rotary vane vacuum pump, these dynamic seals are the main cause of oil leaks during operation of the pump. 
     SUMMARY 
     To address the foregoing needs, in whole or in part, and/or other needs that may have been observed by persons skilled in the art, the present disclosure provides methods, processes, systems, apparatus, instruments, and/or devices, as described by way of example in implementations set forth below. 
     It is an object of the invention to provide a pumping system using an oil-lubricated vacuum pump, which has a more effective sealing system for preventing oil leaks from the pumping chamber. 
     It is another object of the invention to provide a pumping system using an oil-lubricated vacuum pump, which does not require dynamic seals between the vacuum pump and the motor, and thus can be made in a more cost-effective manner than the prior art systems. 
     These objects may be attained by a pumping system as disclosed herein. 
     More particularly, the invention provides a vacuum pumping system comprising an oil-lubricated vacuum pump and an electric motor driving the pump, in which the system further comprises an oil-tight unit arranged to enclose at least a portion of the motor rotor and forming at least part of a container intended to collect and keep inside the motor any oil leaking from the pump. 
     Advantageously, the oil-tight unit has at least a portion clamped between a motor casing and a pump casing. 
     In a first embodiment of the invention, said unit comprises a substantially cylindrical jacket made of sheet metal, enclosing the whole of the rotor and forming said container. 
     According to a preferred feature of the first embodiment of the invention, the jacket has a side wall located in an air gap separating the motor rotor from the motor stator, is open at a first end, where it is clamped between the motor casing and the pump casing, and is closed, at a second end opposite the first end, by a bottom wall accommodated inside the motor casing. 
     According to another preferred feature of this embodiment, the open end of said jacket has a rim that projects radially outwards and forms the jacket portion clamped between the motor casing and the pump casing. In this case, a static seal is provided between a surface of said rim facing the pump casing and the confronting surface of the pump casing. 
     In a second embodiment of the invention, said unit still comprises a substantially cylindrical jacket forming said container. Like in the first embodiment, the jacket encloses the whole of the rotor, has a side wall located in an air gap separating the motor rotor from the motor stator, and is open at a first end, where it is clamped between the motor casing and the pump casing. 
     In this second embodiment the jacket is made of a non-metallic material, preferably an oil-resistant, electrically insulating thermosetting or thermoplastic resin, and the side wall is a very thin layer of the resin. 
     According to a preferred feature of the second embodiment of the invention, the jacket is provided, at both ends, with bases having a larger diameter than the side wall and protruding radially outwards from the side wall, and the base provided at the open end engages in oil-tight manner a complementarily shaped axial recess formed in the pump casing. 
     According to another preferred feature of this embodiment, in the radially protruding portions of said bases, the surfaces turned towards each other are shaped so as to define annular circumferential axial recesses accommodating opposite axial ends of the motor stator. 
     Advantageously, the circumferential axial recesses are radially delimited towards the outside of the motor by a respective annular axial projection located between the motor stator and the motor casing and, towards the inside of the motor, by a thickened end portion of the side wall of the jacket. 
     Thanks to the use of a jacket made of resin and having a very thin side wall, there is no need of increasing the air gap between the stator and the rotor of the motor in order to accommodate a metal jacket like that used in the first embodiment and to take into account its thermal expansion. 
     In a third embodiment of the invention, said unit comprises first and second disc-shaped components accommodating opposite axial end portions of both the motor rotor and the motor stator and forming, together with the motor stator, the container intended to collect and keep inside the motor any oil leaking from the pump. The first component forms the portion of the unit clamped between the motor casing and the pump casing and engages in oil-tight manner a complementarily shaped axial recess formed in the pump casing. 
     The two components are made of a non-metallic material, preferably an oil-resistant, electrically insulating thermosetting or thermoplastic resin. 
     According to a preferred feature of this second embodiment, both the first and the second component have, on their face turned towards the other component, a circumferential axial recess accommodating a respective axial end of the motor stator. 
     Advantageously, the circumferential axial recesses are radially delimited towards the outside of the motor by a respective first annular axial projection located between the motor stator and the motor casing and, towards the inside of the motor, by a respective second annular axial projection located between the motor stator and the motor rotor. 
     Having a “container” that is located between the motor stator and the motor casing solves the problems of noise and vibrations that can affect, during operation, a pumping system having a metal jacket located in the air gap between the motor stator and the rotor. Moreover, there is no need to increase the radial size of the air gap in order to allow the insertion of the jacket and to take into account the thermal expansion thereof. 
     In the second and third embodiments, the base of the jacket opposite the open end and the second disc-shaped component, respectively, can be wholly accommodated inside the motor casing. In the alternative, their surfaces turned away from the motor can have a conical profile at least partially projecting outside the motor casing. Such conical surface can then be provided with cooling fins. 
     The embodiments in which the jacket base or the second component partly come out from the motor casing allow a better thermal dissipation than the embodiments in which said elements are wholly accommodated inside the motor casing, since the jacket base or the second component can directly receive the air flow created by an external cooling system of the pumping system. Moreover, the provision of the cooling fins allows increasing the cooling surface and having a more effective circulation of the external flow of cooling air. 
     Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a longitudinal sectional view of part of a pumping system of the prior art. 
         FIG. 2  is a longitudinal sectional view, similar to  FIG. 1 , of part of a pumping system according to a first embodiment of the invention. 
         FIG. 3  is a longitudinal sectional view of a pumping system according to a second embodiment of the invention. 
         FIG. 4  is a longitudinal sectional view, similar to  FIG. 2 , of part of a pumping system according to a variant of the embodiment shown in  FIG. 3 . 
         FIG. 5  is a longitudinal sectional view, similar to  FIG. 3 , of a pumping system according to a third embodiment of the invention. 
         FIG. 6  is a longitudinal sectional view, similar to  FIG. 4 , of part of a pumping system according to a variant of the embodiment shown in  FIG. 5 . 
       In  FIGS. 2 to 6 , the same reference numerals as in  FIG. 1  have been used to denote the parts of the pump and the motor. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  shows a first embodiment of a pumping system  100  according to the invention. In order to provide a more efficient sealing of motor  30  against oil leakage from the pumping chamber, a sheet-metal jacket  50  is provided which encloses motor rotor  33  and is clamped at one end between motor casing  31  and pump casing  21 . 
     Jacket  50  is a substantially glass-shaped element, i.e. a substantially cylindrical element open at one end (the end clamped between motor casing  31  and pump casing  21 ), and has a side wall  51  located in the air gap between stator  32  and rotor  33  of motor  30 . The open end surrounds the corresponding end wall  35  of the rotor chamber, and bottom wall (or base)  52  opposite the open end is arranged internally of motor casing  31 . The open end of jacket  50  has a rim  53  projecting radially outwards, and such rim  53  is the portion of jacket  50  clamped between motor casing  31  and pump casing  21 . In order to ensure oil tightness between pump  20  and motor  30 , a sealing gasket  54 , in particular an  0 -ring, is provided between rim  53  and the confronting surface of pump casing  21 . 
     The provision of jacket  50  and O-ring  54  results in any oil leaking from the pump environment being collected within jacket  50 . As it can be readily appreciated by the skilled in the art, a static seal like O-ring  54  is much less prone to failures than dynamic seal  40  of the prior art. The provision of a jacket  50  collecting any possible oil leak moreover prevents escape of oil (or any other unwanted substance, like gases etc. developed or present for some reason in the pump  20 ) and dispersion thereof in the environment. 
     The provision of sheet-metal jacket  50  and the associated O-ring  54  overcomes the problems connected with using a lip seal, but it is open to improvements as far as some aspects are concerned, in particular: 
     since metal jacket  50  is located between stator  32  and rotor  33  of motor  30 , it can originate noise and vibrations during operation of pumping system  100 ; 
     an increase of the radial size of the air gap may be required, to allow insertion of jacket  50  itself and to take into account the thermal expansion thereof, thus entailing an increase of the radial size of the whole pumping system  100 . 
     Such improvements are achieved by system  200  shown in  FIGS. 3 and 4 . 
     More specifically, in the embodiment of  FIG. 3 , a pair of disc-shaped components  60 ,  70  are provided, which are made of a non-metallic material, in particular a leak-proof, oil-resistant and electrically insulating thermoplastic or thermosetting resin, and are configured so as to accommodate opposite axial ends of motor stator  32  and motor rotor  33 . With such an arrangement, components  60 ,  70  form, together with motor stator  32 , a sort of “container” collecting any oil leaking from pump  20  and keeping such oil within motor  30 . 
     Component  60  is clamped between pump casing  21  and motor casing  31  and fits in oil-tight manner in a complementarily shaped recess  26  provided in the confronting surface of pump casing  21 . A central opening  65  in component  60  accommodates end wall  35  of the rotor chamber. On its surface turned towards component  70 , component  60  has two substantially parallel annular axial projections  61 ,  62  defining an annular axial recess  63  intended to receive one end of stator  32 . Outer annular projection  61  is clamped between motor stator  32  and motor casing  31 , and inner annular projection  62  is clamped between motor stator  32  on the one side and motor rotor  33  and end wall  35  on the other side. 
     Component  70  has a central hollow  75  (or possibly a central opening, like component  60 ) accommodating end wall  36  of the rotor chamber. On its surface turned towards component  60 , component  70  has two substantially parallel annular axial projections  71 ,  72  defining an axial annular recess  73  intended to receive the other end of stator  31 . Similarly to projections  61 ,  62 , outer annular projection  71  is clamped between motor stator  32  and motor casing  31 , and inner annular projection  72  is clamped between motor stator  32  on the one side and motor rotor  33  and end wall  36  on the other side. Reference  74  denotes the outer surface (i.e. the surface turned away from the motor) or base of component  70 , which, in the embodiment shown in  FIG. 3 , is flat so that component  70  is wholly housed within motor casing  31 . 
     The Figure also shows gas inlet and outlet  27 ,  28 , as well as some details of the external body of pumping system  200 . 
     The shape of components  60  and  70  and the engagement of component  60  within recess  26  in pump casing  21  ensure oil tightness without the need to use a sealing gasket like O-ring  54 . Moreover, the components are clamped between stator  32  and casing  31  of motor  30 , thus no problems of vibrations and noise arise because of the rotation of rotor  33 . At the same time, there is no need to increase the air gap between stator  32  and rotor  33  of motor  30 , as required in the embodiment shown in  FIG. 2  in order to accommodate metal jacket  50  and to take into account its thermal expansion. A proper choice of the resin also allows improving the thermal dissipation characteristics not only over the prior art, but also over the solution with metal jacket shown in  FIG. 2 . 
     A further improvement is obtained by the configuration of system  200  shown in  FIG. 4 . Like in the embodiment of  FIG. 3 , a pair of disc-shaped components  80 ,  90  are provided, which are made of a non-metallic material, in particular a leak-proof, oil-resistant and electrically insulating thermoplastic or thermosetting resin, and are configured so as to accommodate opposite axial ends of motor stator  32  and motor rotor  33 . Thus, also components  80 ,  90  form, together with motor stator  32 , a sort of container collecting any oil leaking from pump  20  and keeping such oil within motor  30 . 
     The first disc-shaped component  80  is identical to component  60  shown in  FIG. 3  and its elements are denoted by reference numerals corresponding to those used in  FIG. 3 , yet beginning with digit  8  instead of with digit  6 . The second disc-shaped component  90  differs from component  70  shown in  FIG. 3  only in respect of the configuration of its base  94 , which, instead of being flat like base  74  of component  70 , has a surface with conical profile (more particularly, shaped as a frustum of a cone) on its side turned away from motor  30 , such that base  94  projects outside motor casing  31 . Cooling fins  96  are formed on the portion of base  94  located outside casing  31 . The remaining elements of component  90  are identical to those of component  70  and they are denoted by reference numerals corresponding to those used in  FIG. 3 , yet beginning with digit  9  instead of with digit  7 . 
     Component  90  having a base  94  partly coming out from motor casing  31  allows a better thermal dissipation than component  70  wholly accommodated inside motor casing  31 , since base  94  can directly receive the air flow created by the external cooling system (not shown) of pumping system  200 . The provision of cooling fins  96  in the portion of base  94  projecting outside motor casing  31  allows increasing the cooling surface and having a more effective circulation of the external cooling air flow. 
       FIGS. 5 and 6  show a pumping system  300  according to a third embodiment of the invention. In  FIGS. 5 and 6 , elements corresponding or functionally equivalent to elements depicted in  FIGS. 3 and 4 , respectively, are denoted by the same reference numerals preceded by digit  1 . 
     More specifically, in the embodiment of  FIG. 5 , the container intended to collect and keep inside motor  30  any oil leaking from pump  20  includes a glass-shaped jacket  150 , configured so as to accommodate both rotor  33  and the axial ends of stator  32  of motor  30  and made, like the components of system  200 , of a non-metallic material, in particular a leak-proof, oil-resistant and electrically insulating thermoplastic or thermosetting resin. 
     Jacket  150  has a side wall  151  consisting of a thin resin layer located in the air gap between stator  31  and rotor  32  of motor  30 , and two bases  160 ,  170 , having a larger diameter than side wall  151 , so that said bases  160 ,  170  protrude radially outwards from side wall  151 . Base  160  at the open end of jacket  150  has a central opening  165  accommodating the corresponding closing wall  35  of the rotor chamber, is clamped between pump casing  21  and motor casing  31  and its surface turned towards pump casing  21  is configured so as to fit in oil-tight manner in a complementarily shaped recess  26  provided in the confronting surface of pump casing  21 . The other base  170  has a central hollow  175  (or possibly a central opening, like base  160 ) accommodating end wall  36  of the rotor chamber. 
     In the radially protruding portions of bases  160 ,  170 , the surfaces turned towards each other are shaped so as to define annular axial recesses  163 ,  173 , respectively, intended to accommodate the opposite axial ends of motor stator  32 . More particularly, recess  163  is defined between an edge  161  of base  160 , axially projecting towards base  170  and clamped between motor stator  32  and motor casing  31 , and a thickened end portion  162  of side wall  161 . Similarly, recess  173  is defined between an edge  171  of base  170 , axially projecting towards base  160  and clamped between motor stator  32  and motor casing  31 , and a thickened end portion  172  of side wall  151 . Reference  174  denotes the outer surface (i.e. the surface turned away from the motor) of base  170 . 
     In the embodiment shown in  FIG. 5 , said surface  174  is flat and base  170  is wholly housed within motor casing  31 . 
     The shape of jacket  150 , with base  160  engaging recess  26  in pump casing  21 , ensures oil tightness without the need to use a sealing gasket like  0 -ring  54 . Moreover, since jacket  150  is made of resin and its side wall  151  is very thin, there is no need of increasing the air gap between stator  31  and rotor  32  of motor  30  to accommodate a metal jacket like jacket  50  ( FIG. 2 ) and to take into account its thermal expansion. Moreover, no problems of vibrations and noise exist. At the same time, like in the embodiment of  FIGS. 3 and 4 , a proper choice of the resin also allows improving the thermal dissipation characteristics not only over the prior art but also over the solution with metal jacket shown in  FIG. 2 . 
     Referring now to  FIG. 6 , the container intended to collect and keep inside motor  30  any oil leaking from pump  20  includes a glass-shaped jacket  250 , similar to jacket  150  and intended to provide, over jacket  150  shown in  FIG. 5 , the same improvement as provided by the use of component  90  in pumping system  200  shown in  FIG. 4 . 
     Like jacket  150 , jacket  250  has a side wall  251  consisting of a thin resin layer located in the air gap between stator  31  and rotor  32  of motor  30 , and two bases  180 ,  190 , having a larger diameter than side wall  251 , so that said bases protrude radially outwards from side wall  251 . Jacket  250  differs from jacket  150  shown in  FIG. 5  only in respect of the configuration of base  190 , which, instead of having a flat external surface, like base  170  of jacket  150 , has an external surface  194  with conical profile (more particularly, shaped as a frustum of a cone), such that surface  194  projects outside motor casing  31 . Moreover, cooling fins  196  are formed on the portion of surface  194  located outside casing  31 . 
     Base  190  having a surface  194  partly coming out from motor casing  31  allows a better thermal dissipation than base  170  wholly accommodated inside motor casing  31 , since base  190  can directly receive the air flow created by the external cooling system (not shown) of pumping system  300 . The provision of cooling fins  196  in the portion of surface  194  outside motor casing  31  allows increasing the cooling surface and having a more effective circulation of the external cooling air flow. 
     It is to be appreciated that, when pouring the resin for forming the first and second components  60 ,  70  and  80 ,  90  of  FIGS. 3 and 4  or jackets  150  and  250  of  FIGS. 5 and 6 , some resin could become incorporated between the magnets of motor stator  32 . In view of this fact, the embodiment shown in  FIGS. 3 and 4  could even be interpreted as a limit case of the embodiment shown in  FIGS. 5 and 6 , where the resin layer forming side walls  151 ,  251  of jackets  150 ,  250  has a substantially zero thickness. 
     Of course, while leaving the principle of the invention unchanged, the embodiments and the construction details can be widely changed with respect to what has been described and shown by way of non-limiting example only, without thereby departing from the scope of the invention as defined in the following claims. 
     It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.