Patent Abstract:
An improved pump and pumping method includes a circumferential positive displacement pump having two counter rotating rotors. A clearance gap is defined between the rotor shaft, and a body hub portion of the body that forms the chamber.

Full Description:
FIELD OF THE INVENTION 
   The invention pertains generally to the field of pumps and pumping devices and methods. More particularly, the invention pertains to external circumferential rotary piston pumps which use two counter-rotating rotors inside a housing to force material from an inlet to an outlet. 
   BACKGROUND OF THE INVENTION 
   Pumps and pumping devices are in wide use in industry. For example, one type of pump used in industries such as, for example, automotive paints, paper coatings, and other industrial processes is a positive displacement pump. One type of positive displacement pump is a rotary two-rotor pump in the form of an external circumferential piston pump. 
   An exemplary pump of this type includes a body defining a chamber having an inlet and outlet. Inside the chamber are disposed two counter rotating rotors. The rotors are driven by a motor and gear box to force the material from the inlet to the outlet. 
   An example of such a pump is depicted in  FIG. 4 . The pump  1  includes a first rotor  10  and a second rotor  12  disposed in a chamber defined by a housing body  14  which serves as a housing in combination with an end plate  15 . The first rotor  10  is driven by a drive shaft  16  and a fastening nut  17  on the shaft end, and the second rotor  12  is driven by a shaft not visible in  FIG. 4  and held by a similar nut  17 .  FIG. 4  also depicts an inlet  20  and outlet  22 . 
   A body hub clearance gap  24  exists between the rotating rotor  10  and a stationary projection referred to as a body hub  26  that is part of the housing body  14 . The rotors  10  and  12  are driven by a gear box  28 . 
     FIG. 5  is an external view of the pump  1 , indicating the section line through which the sectional views in the other drawing figures are taken. 
   Turning to the section view of  FIG. 6 , the prior art pump  1  is further illustrated. In particular, in this figure it can be seen that a seal chamber  30  is defined between an inner face  34  of the body hub  32  and an outer face  36  of the rotor  10  which is a central mounting shaft portion of the rotor  10 . 
   The dimensions of the body hub clearance gap  24  in the prior art are important to volumetric efficiency and pump performance. This is due to a relatively small sealing area that exists at the body hub clearance gap  24  and also to the location of the clearance gap  24  in the pumping path between the inlet  20  and outlet  22 . 
   The body hub  32  and the rotor  10  have surfaces that form the body hub clearance gap  24  which are subject to high fluid velocity that sometimes results in rapid wear, especially when the pumped material contains abrasive particles. In certain applications such as, for example, automotive paint and paper coatings, the abrasive wear can dramatically reduce the useful service life of the pump. 
   The body hub clearance gap  24  is a location of sliding frictional contact, or near-contact, between the end tip  25  of the body hub  32  and an exposed axial face of the rotor  10 . This sliding contact, or near-contact, accomplishes an imperfect “seal” of the contact area. This “seal” is subject to wear over time. 
   Referring to further to  FIG. 6 , it can be noted that during operation, while the pump is moving fluid from the inlet  20  to the outlet  22 , the pressure of the fluid on the outlet side  22  is raised so that the pressure is higher at the outlet side  22  than the inlet side  20 . This pressure differential (between the outlet side  22  past the rotors  10  and  12 , compared to the inlet side  20  before the rotors  10  and  12 ), causes the pumped fluid to tend to leak back towards the inlet side  20  through the body hub clearance gap  24 . 
   Although the body hub clearance gap  24  is actually a toroidal ring in its overall shape, the section view of  FIG. 6  illustrates that the body hub clearance gap  24  can be thought of two body hub clearance gaps, one gap indicated at  24  and the other gap indicated at  25 . The pumped fluid thus can be thought of as having two successive leak paths which the fluid can be thought of as leaking through in a serial fashion. 
   It would be desirable to reduce one or both of these leak paths at each rotor if possible. Accordingly, it would be desirable to reduce the pressure on the seal, referred to as a seal pressure, so that less material leaks through the clearance gap  24 , and so that in the case of abrasive materials, reduction of the wear or erosion of the components in the area of the clearance gap  24  would occur. Wear in this area is undesirable because it reduces pump efficiency over the long term. 
   Accordingly, it is desirable to provide a method and apparatus that can yield improved performance and/or wear characteristics in a circumferential piston pump. 
   SUMMARY OF THE INVENTION 
   The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect a positive displacement dual rotor pumping apparatus and method is provided that in some embodiments yields improved performance and/or wear characteristics in a circumferential positive displacement pump. 
   In accordance with one embodiment of the present invention, a pump, features a body forming a chamber; at least one rotor rotating in the chamber, the rotor having a shaft with a cylindrical outward face that has a first outer diameter portion and a second outer diameter portion, with a shoulder between the first outer diameter portion and the second outer diameter portion; and a body hub portion extending from the body and oriented axially and having a cylindrical inner diameter face in rotational sliding contact with one of the first or second outer diameter portions of the shaft. 
   In accordance with another embodiment of the present invention, a pump, features a means for defining a chamber; pumping means comprising at least one rotor rotating in the chamber, the rotor having a shaft with a cylindrical outward face that has a first outer diameter portion and a second outer diameter portion, with a shoulder between the first outer diameter portion and the second outer diameter portion; and a body hub extending in the chamber and oriented axially and having a cylindrical inner diameter face in rotational sliding contact with one of the first or second outer diameter portion of the shaft. 
   In accordance with yet another embodiment of the present invention, a pump, features a body forming a chamber; at least one rotor rotating in the chamber, the rotor having a shaft portion having a cylindrical outward face; and a body hub extending from the body and oriented axially and having a cylindrical inner diameter face having a third inner diameter portion and a fourth inner diameter portion, with a shoulder between the third inner diameter portion and the fourth inner diameter portion, and the third inner diameter portion in rotational sliding contact with the outward face of the shaft. 
   In accordance with yet another embodiment of the present invention, a pump, features a means for defining a chamber; pumping means comprising at least one rotor rotating in the chamber, the rotor having a shaft with a cylindrical outward face; and a body hub extending from the body and oriented axially and having a cylindrical inner diameter face having a third inner diameter portion and a fourth inner diameter portion, with a shoulder between the third inner diameter portion and the fourth inner diameter portion, and the third inner diameter portion in rotational sliding contact with the outward face of the shaft. 
   In accordance with yet another embodiment of the present invention, a method of pumping material using at least one rotor in a body forming a chamber, features rotating at least one rotor in the chamber, the rotor having a shaft with a cylindrical outward face that has a first outer diameter portion and a second outer diameter portion, with a shoulder between the first outer diameter portion and the second outer diameter portion, wherein the body has a body hub extending from the body and oriented axially and having a cylindrical inner diameter face in rotational sliding contact with one of the first or second outer diameter portions of the shaft. 
   In accordance with yet another embodiment of the present invention, a method of pumping material using at least one rotor in a body forming a chamber, features rotating at least one rotor in the chamber, the rotor having a shaft portion with a cylindrical outward face, wherein the body has a body hub extending from the body and oriented axially and having a cylindrical inner diameter face having a third diameter portion and a fourth diameter portion, with a shoulder defined between the third diameter portion and the fourth diameter portion, and the third diameter portion in rotational sliding contact with the outward face of the shaft. 
   There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
   In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
   As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view, taken through line  1 - 1  in  FIG. 5 , of a first preferred embodiment of the present invention. 
       FIG. 2  is a sectional view, taken through line  1 - 1  in  FIG. 5 , of a second preferred embodiment of the present invention. 
       FIG. 3  is a sectional view, taken through line  1 - 1  in  FIG. 5 , of a third preferred embodiment of the present invention. 
       FIG. 4  is a cut away perspective view of a prior art pump of a type suitable for embodiments on the present invention. 
       FIG. 5  is a side view of the pump of  FIG. 4 . 
       FIG. 6  is a sectional view, taken through line  1 - 1  in  FIG. 5 , of the pump of  FIG. 4 . 
   

   DETAILED DESCRIPTION 
   The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect a positive displacement dual rotor pumping apparatus and method is provided that in some embodiments yields improved performance and/or wear characteristics in a circumferential displacement pump. 
   Some preferred embodiments will now be described with reference to the drawing figures in which like reference numbers refer to like parts through out. 
     FIG. 1  is a cross-sectional view of a first preferred embodiment of the present invention. Components in  FIGS. 1 through 6  with like numbers refer to like parts as those with like numbers in  FIGS. 4 through 6 , except where differences are shown in the drawings or described in the specification herein. 
   In the embodiment of  FIG. 1 , the outer surface of the rotor shaft  40  has a shoulder  44  leading to an increased diameter region  46 . Thus, the seal chamber  48  is in some cases smaller (compared to the device of  FIG. 6 ), and the body hub clearance gap  50  leads to an additional bushing clearance gap  52 . In addition, a suction vent port  54  penetrates through the body hub  56 . There is a close clearance fit, or close tolerance fit, between the large diameter portion of the rotor shaft  40  and the inside diameter of the body hub  56 . The close tolerance fit provides rotational sliding contact, or near-contact, between the shaft  40  and body hub  56 , and also forms at least to some degree a seal at that fit area. 
   The combination of this close clearance fit, as well as the provision of the suction vent port  54 , reduces the pressure in the seal chamber  48  in some cases compared to the prior art and thus reduces the hydraulic forces acting on the body hub clearance gap  50  and bushing clearance gap  52 . This extends the service life of the seal formed by the body hub clearance gap  50  and the bushing clearance gap  52 , and also reduces the amount of heat generated by that seal region. 
   Turning to  FIG. 2 , a second preferred embodiment is illustrated. In this second preferred embodiment, the body hub  60  is provided with a shoulder  64  that leads to a reduced inside diameter area  62  of the body hub  60 . A close clearance fit, or close tolerance fit, exits between the reduced diameter area  62  of the body hub  60  and the outer diameter face  66  of the rotor  10 . The close tolerance fit provides rotational sliding contact, or near-contact, between the shaft  40  and body hub  60 , and also forms at least to some degree a seal at that fit area. This arrangement also provides a seal chamber  68  which is in some cases smaller than the seal chamber  30  in the prior art of  FIG. 6 . Further, the body hub clearance gap  70  and the bushing clearance gap  72  are provided as shown. 
   Somewhat similar to the embodiment of  FIG. 1 , this embodiment in some cases reduces seal chamber pressure and thus can extend seal life compared to the prior art. This embodiment also has a suction vent port  74  penetrating through the body hub  60 . 
   A third preferred embodiment is illustrated in  FIG. 3 . In this third preferred embodiment, the body hub  80  is provided with a first shoulder  82  that leads into a reduced internal diameter region  84 . The reduced internal diameter region  84  has a close clearance fit, or close tolerance fit, with a first reduced outside diameter face  86  of the rotor shaft  40 . The close tolerance fit provides rotational sliding contact, or near-contact, between the shaft  40  and body hub  80 , and also forms at least to some degree a seal at that fit area. The rotor shaft  40  also has a shoulder  90  that leads to an increased outer diameter face region  92 . The body hub  80  has a corresponding shoulder  94  that leads to an increased internal diameter region  96 . A close clearance fit, or close tolerance fit, is provided between the respective rotor and body hub faces  84 ,  86 ,  92 ,  96 , thus producing a body hub clearance gap  98  and a bushing clearance gap  100 , as well as a seal chamber  102  which is in some cases reduced in size compared to the prior art. This embodiment also has a suction vent port  104  penetrating through the body hub  80 . 
   In each of the embodiments described above, the suction vent port feature  54 ,  74 ,  104  is optional. However, the utilization of the suction vent port  54 ,  74 ,  104  together with the hub and/or rotor features disclosed above can improve performance compared to an otherwise identical device without the suction vent port feature. When the suction vent port is added, in some instances, the pump efficiency will be reduced because increased slip results in less pump output. However, the modified rotor embodiment, described as the first embodiment above, and illustrated in  FIG. 1 , serves both to further reduce seal pressure and also increase pump efficiency. The body modification embodiment, described as the second embodiment above, and illustrated in  FIG. 2 , reduces seal pressure and in some instances can maintain pump performance at the level of an unmodified pump. 
   The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Technology Classification (CPC): 5