Abstract:
A pump includes a pump body defining first and second cavities. First and second rotors are disposed in the first and second cavities between an inlet passage and an outlet passage and are in sealing relationship with each other during rotation of the rotors. A drive transmission mechanism is coupled to the first and second rotors for rotating the rotors in opposite directions. During a revolution of the first rotor, a vane projecting from the first rotor emerges from a recess of the second rotor, passes the inlet passage and the outlet passage, and enters a recess of the second rotor, while the inlet passage remains sealed from the outlet passage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of U.S. Provisional Application No. 61/505,991 filed Jul. 8, 2011, the entire disclosure of which is hereby incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The subject matter of this application relates to a pump. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with a first aspect of the subject matter disclosed herein there is provided a pump comprising a pump body defining an interior space having a first cavity and a second cavity, the first cavity having a cylindrical bounding surface and the second cavity having a bounding surface that includes a cylindrical portion, and the pump body also defining an inlet chamber and an outlet chamber positioned at least partially between the first and second cavities, an input passage opening into the inlet chamber, and an output passage opening from the outlet chamber, a first rotor member supported in the first cavity for rotating about a first rotational axis that coincides substantially with a central axis of the cylindrical bounding surface of the first cavity, the first rotor member having a cylindrical external surface and n vanes (n greater than one) projecting radially therefrom in equiangularly spaced relationship about the first axis, the vanes having tips lying on a cylindrical surface that is substantially equal in diameter to the cylindrical bounding surface of the first cavity, whereby during rotation of the first rotor member the tips of the vanes pass in effective sealing relationship with the bounding surface region of the first cavity, and wherein the cylindrical bounding surface of the first cavity extends at least 360/n degrees about said first axis, and a second rotor member supported in the second cavity for rotating about a second rotational axis that is parallel with the first rotational axis and coincides substantially with a central axis of the two cylindrical portions of the bounding surface of the second cavity, the second rotor member having a cylindrical external surface substantially equal in diameter to the cylindrical portion of the bounding surface of the second cavity, whereby during rotation of the second rotor member the cylindrical external surface of the second rotor member is in effective sealing relationship with the cylindrical portion of the bounding surface of the second cavity, and wherein the cylindrical external surface of the second rotor has n recesses therein in equiangularly spaced relationship about the second axis, wherein the first and second rotor members are disposed between the inlet chamber and the outlet chamber and the first and second rotor members are in effective sealing relationship with each other during rotation of the rotor members, the cylindrical portion of the bounding surface of the second cavity subtends an angle at the second axis at least as great as the angle subtended at the second axis by each recess in the cylindrical external surface of the second rotor member, and the pump further comprises a drive transmission mechanism coupled to the first and second rotor members for rotating the rotor members in opposite directions at equal angular velocities so that during a complete revolution of the first rotor member each vane successively emerges from a recess of the second rotor member, passes the inlet passage and the outlet passage, and enters a recess of the second rotor member, while the inlet chamber remains effectively sealed from the outlet chamber. 
         [0004]    In accordance with a second aspect of the subject matter disclosed herein there is provided a pump comprising a pump body defining an interior space having a first cavity and a second cavity, the first cavity having a cylindrical bounding surface and the second cavity having a bounding surface that includes a cylindrical portion, and the pump body also defining an inlet chamber and an outlet chamber positioned at least partially between the first and second cavities, an input passage opening into the inlet chamber, and an output passage opening from the outlet chamber, a first rotor member supported in the first cavity for rotating about a first rotational axis that coincides substantially with a central axis of the cylindrical bounding surface of the first cavity, the first rotor member having a cylindrical external surface and n vanes (n greater than one) projecting radially therefrom in equiangularly spaced relationship about the first axis, the vanes having tips lying on a cylindrical surface that is substantially equal in diameter to the cylindrical bounding surface of the first cavity, whereby during rotation of the first rotor member the tips of the vanes pass in effective sealing relationship with the bounding surface region of the first cavity, and wherein the cylindrical bounding surface of the first cavity extends at least 360/n degrees about said first axis, and a second rotor member supported in the second cavity for rotating about a second rotational axis that is parallel with the first rotational axis and coincides substantially with a central axis of the two cylindrical portions of the bounding surface of the second cavity, the second rotor member having a cylindrical external surface substantially equal in diameter to the cylindrical portion of the bounding surface of the second cavity, whereby during rotation of the second rotor member the cylindrical external surface of the second rotor member is in effective sealing relationship with the cylindrical portion of the bounding surface of the second cavity, and wherein the cylindrical external surface of the second rotor has at least one recess therein, wherein the first and second rotor members are disposed between the inlet chamber and the outlet chamber and the first and second rotor members are in effective sealing relationship with each other during rotation of the rotor members, the cylindrical portion of the bounding surface of the second cavity subtends an angle at the second axis at least as great as the angle subtended at the second axis by said recess in the cylindrical external surface of the second rotor member, and the pump further comprises a drive transmission mechanism coupled to the first and second rotor members for rotating the rotor members in opposite directions at angular velocities such that during a complete revolution of the first rotor member each vane successively emerges from a recess of the second rotor member, passes the inlet passage and the outlet passage, and enters a recess of the second rotor member, while the inlet chamber remains effectively sealed from the outlet chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: 
           [0006]      FIG. 1  is a perspective view of a pump, 
           [0007]      FIG. 2  is a side elevation of a pump, 
           [0008]      FIG. 3  is a sectional view of the pump taken on the line  3 - 3  in  FIG. 2 , 
           [0009]      FIG. 4  is a sectional view of the pump taken on the line  4 - 4  in  FIG. 2 , and 
           [0010]      FIG. 5  is an exploded perspective view of the pump. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to  FIGS. 2 and 3 , the illustrated pump comprises a pump body  10  composed of a pump rotor housing  14 , a gear housing  18  and two end caps  22 ,  26 . The end cap  22  is formed with two recesses that accommodate respective ball bearings  27 ,  28  and the gear housing  18  is similarly formed with two recesses that accommodate respective ball bearings  29 ,  30 . The outer races of the ball bearings are press fitted in the respective recesses. First and second rotor drive shafts  31 ,  34  are press fitted in the inner races of the bearings and extend parallel to one another through the interior space of the pump rotor housing  14 . The interior space of the pump rotor housing is composed of two generally cylindrical cavities  36 ,  37  that intersect in a region X ( FIG. 3 ). Two seals (only one of which, designated  35 , is shown in  FIG. 5 ) surround the periphery of the interior space and are in sealing engagement with the end cap  22  and the gear housing  18  respectively. A work rotor  38  and a sealing rotor  42  are mounted on the shafts  30 ,  34  respectively and are keyed for rotation with the shafts. The rotors are located in the cavities  36 ,  37  respectively. 
         [0012]    The gear housing  18  is formed on the opposite side from the bearing recesses with a gear recess  46  ( FIG. 4 ) into which the two shafts  31 ,  34  extend. Two spur gears  50 ,  54  of equal size are fitted on the shafts  31 ,  34  respectively and are located in the gear recess  46 . The two spur gears are in meshing engagement. Each gear includes a cylindrical boss that projects into a recess  56  in the end cap  26 . 
         [0013]    An electric motor (not shown) having a drive shaft  58  is attached to the end cap  26 . A drive pinion  62  is attached to the drive shaft of the motor and is in meshing engagement with the spur gear  50 . Accordingly, when the motor drives the pinion  62 , the two spur gears  50 ,  54  are driven at equal speeds in opposite directions. 
         [0014]    The work rotor  38  is generally cylindrical and has two diametrically opposed vanes  66 ,  68  extending parallel to the central axis of the work rotor and projecting radially therefrom. When the work rotor rotates within the cavity  36  of the interior space, a small clearance exists between the tip of the vanes and the surface bounding the cavity  36 . Thus, as the work rotor rotates, the work rotor and the pump rotor housing are in an effective sealing relationship. The cylindrical surface of the lower cavity extends at least  180  degrees about the central axis of the work rotor so that there is always at least one vane between the inlet passage and the outlet passage. 
         [0015]    The pump rotor housing  14  is formed with an inlet passage  69  and an outlet passage  70  that communicate with the cavity  36 . The upper end of each passage is internally threaded to receive a suitable hose attachment fitting. 
         [0016]    The sealing rotor  42  is generally cylindrical and is formed with two peripheral notches  73 ,  74  that extend longitudinally of the rotor parallel to the axis of rotation of the rotor. 
         [0017]    It will be appreciated from examination of  FIG. 3  that the configuration of the work rotor  38  corresponds to a spur gear in which all the teeth but two have been removed and the configuration of the sealing rotor  42  corresponds to a spur gear in which all the spaces but two between the teeth have been filled. 
         [0018]    The radius of curvature of the upper cavity  37  in the regions Y is slightly greater than the radius of the cylindrical surface of the sealing rotor. The peripheral surface of the upper cavity in each of the regions Y subtends an angle at least as great as the angle subtended by the peripheral notches  73 ,  74 , so that during rotation of the sealing rotor the external surface of the sealing rotor remains in effective sealing relationship with the pump rotor housing with respect to flow of gas around the sealing rotor. 
         [0019]    The radius of curvature of the cavity  37  between the regions Y is somewhat greater than in the regions Y, which facilitates manufacture of the pump rotor housing because the tolerance on the dimensions of the peripheral surface of the upper cavity between the regions Y may then be greater than in the regions Y. 
         [0020]    As shown in  FIG. 3 , the vane  66  of the work rotor is positioned in the notch  73  of the sealing rotor. This position is referred to as the  12  o′clock position, having regard to the angular position of the vane  66 . As the work rotor rotates in the clockwise direction (and the sealing rotor rotates in the counter clockwise direction), the trailing flank of the vane  66  rolls over the flank of the notch  73  and ultimately disengages from the notch. As the rotors continue to rotate, a very narrow clearance is defined between the cylindrical surface of the work rotor and the cylindrical surface of the sealing rotor. When the work rotor has rotated through almost 180°, the vane  68  rolls into the notch  74  and the cooperation between the surface of the vane and the surface of the notch maintains a narrow clearance between the work rotor and the sealing rotor. At all angular positions of the work rotor  38 , there is a very narrow clearance between the work rotor and the sealing rotor  42 . The narrow clearance provides an effective sealing relationship between the work rotor and the sealing rotor. The seal between the work rotor and the sealing rotor is referred to herein as the rotor seal. The notches in the sealing rotor accommodate the vanes when the work rotor rotates without destroying the rotor seal. 
         [0021]    Depending on the angular position of the work rotor  38 , the sealing rotor  42  and the two vanes  66 ,  68  define two or three chambers within the cavity  36 . At the position shown in  FIG. 3 , there is an inlet chamber  71  and an outlet chamber  72 . The inlet passage  69  opens into the inlet chamber  71  and the outlet passage  70  opens from the outlet chamber  72 . 
         [0022]    Referring again to  FIG. 3 , as the work rotor rotates from the  12  o′clock position to about 2 o&#39;clock, the vane  66  reaches and passes the upper edge of the inlet passage. The inlet chamber  71  is defined between the vane  68  and the rotor seal. Thus, as the rotor rotates the volume of the inlet chamber  71  increases and tends to cause a reduction in pressure in the inlet chamber thereby inducing a flow of gas into the inlet chamber from the inlet passage  69 . 
         [0023]    When the vane  66  reaches the lower edge of the inlet passage, the inlet chamber  71  that was bounded by the trailing flank of the vane  68  becomes a transfer chamber and a new inlet chamber  73  is created between the rotor seal and the trailing flank of the vane  66 . The transfer chamber  71  between the leading flank of the vane  66  and the trailing flank of the vane  68  is isolated from the inlet passage. A quantity of gas is trapped in the transfer chamber, except for minor leakage between the tips of the vanes and the peripheral surface of the lower cavity  36 . Advancing movement of the vane  66  pushes the trapped gas in the clockwise direction about the central axis of the working rotor. 
         [0024]    As the work rotor continues to rotate, the tip of the vane  68  reaches the lower edge of the outlet passage  70 . The outlet chamber and the transfer chamber are then in communication and a new outlet chamber is thereby created between the leading flank of the vane  66  and the rotor seal. The work rotor continues to rotate and the advancing of the vane  66  decreases the volume of the outlet chamber, tending to increase the pressure in the outlet chamber and expel gas from the outlet chamber through the outlet passage  40 . The rotor seal and the narrow clearance between the peripheral surface of the upper cavity in the region Y and the cylindrical surface of the sealing rotor in the region Y provides a large resistance to leakage of gas from the outlet chamber. Accordingly, most gas is forced to leave the outlet chamber through the outlet passage. 
         [0025]    The term effective sealing relationship used herein does not require a perfect seal, with the external surfaces of the work rotor and the sealing rotor, for example, continuously in sealing contact. An effective sealing relationship between two members requires that the rate at which fluid can leak between the members should be small relative to the rate at which fluid is delivered from the inlet passage to the outlet passage. 
         [0026]    In a conventional external gear pump, the gear teeth divide the incoming flow of air into two streams, each of which is chopped by gear teeth into small volumes which are subsequently combined. This manner of operation consumes energy, resulting in heating of the gas. In the case of the pump illustrated in  FIG. 1-5 , all the gas proceeds from the inlet passage to the outlet passage along the same path and for each revolution of the work rotor, the flow of gas is chopped into only two volumes. 
         [0027]    In a modification of the pump shown in  FIGS. 1-5 , the external surfaces of the rotors and internal surfaces of the cavities are in contact, thereby improving the rotor seal and the seals between the rotors and the pump rotor housing. In order to minimize friction between surfaces, which would result in heating of the pump components and possible bear of the pump components, the surfaces may be provided with anti-friction coatings. 
         [0028]    It will be appreciated that the invention is not restricted to the particular embodiment that has been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims, as interpreted in accordance with principles of prevailing law, including the doctrine of equivalents or any other principle that enlarges the enforceable scope of a claim beyond its literal scope. For example, the invention is not restricted to the sealing rotor having the same number of notches as the number of vanes of the work rotor. With suitable adjustments in timing of rotation of the rotors, the sealing rotor may have only one notch. Moreover, the work rotor may have more than two vanes, although it will be appreciated that as the number of vanes increases, the volume of the pump available for pumping fluid will decrease. Unless the context indicates otherwise, a reference in a claim to the number of instances of an element, be it a reference to one instance or more than one instance, requires at least the stated number of instances of the element but is not intended to exclude from the scope of the claim a structure or method having more instances of that element than stated. The word “comprise” or a derivative thereof, when used in a claim, is used in a nonexclusive sense that is not intended to exclude the presence of other elements or steps in a claimed structure or method.