Abstract:
A compressor and a method for compressing fluid according to which a liner is disposed on the inner wall of a housing defining a bore. At least one slot and at least one discharge port are provided in the liner. A rotor is rotated in the housing with its outer surface in a closely spaced relation to the inner wall of the liner, and an additional rotor extends through the slot in the liner and intermeshes with the first rotor to compress fluid introduced between the rotors before it is discharged through the port.

Description:
BACKGROUND  
       [0001]     This invention is directed to a compressor, such as a rotary screw compressor, for compressing a fluid, such as air.  
         [0002]     Screw compressors use two or more intermeshing rotors, each provided with helical lobes to produce compression when the rotors are rotated. A fluid, such as air, is introduced into the compressor and is trapped between the rotors and compressed to the required discharge pressure.  
         [0003]     However, these compressors are expensive to manufacture since they are provided with windows, slots, ports, passages, and the like, which are formed by fairly intricate castings and weldments. Also, when it is desired to change the operating parameters of the compressor, such as its discharge pressure, flow rate, and capacity, the housing has to be replaced with a new cast housing having a different arrangement of windows, slots, ports, passages, and the like, which adds to the expense.  
         [0004]     Therefore, what is needed is a compressor of the above type that eliminates, or at least reduces, these problems. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0005]      FIGS. 1 and 3  are sectional views of a screw compressor according to an embodiment of the invention.  
         [0006]      FIG. 2  is a sectional view of a component of the invention.  
         [0007]      FIG. 4  is an exploded isometric view of some components of the compressor of  FIGS. 1 and 2 .  
         [0008]      FIGS. 5A, 5B , and  5 C are diagrammatic views depicting three operation modes of the compressor of  FIGS. 1 and 3 . 
     
    
     DETAILED DESCRIPTION  
       [0009]     Referring to  FIG. 1  of the drawing, a screw compressor according to an embodiment of the invention is referred to, in general, by the reference numeral  10 . The compressor  10  includes a housing  12 , preferably formed of a forged billet and having a series of openings, bores, and chambers formed therein as will be described. A drive shaft  14  is supported in a longitudinal through bore  12   a  formed in the housing by a pair of axially spaced bearing assemblies  16  and  18  which are supported in the housing by two carriers  20  and  22 , respectively, that are mounted in the bore. It is understood that the shaft  14  is connected to a driver, such as an electric motor, for rotating the shaft.  
         [0010]     A rotor  24  is supported on the shaft  14  for rotation therewith, extends in the above bore  12   a , and will be described in detail later. A cylindrical liner  26  is affixed to the inner surface of the housing  12  defining the bore  12   a , and is very slightly spaced from the outer surface of the rotor  24 . The rotor  24  and the liner  26  will be described in detail later.  
         [0011]     A cover  28  is bolted over one end of the housing  12  and has a through opening in alignment with an opening formed in the carrier  22  to define an inlet  30  for a fluid, such as air, to be compressed. A passage  22   a  is formed in the carrier  22  that connects the inlet  30  to the bore  12   a . A cover  32  extends over the other end of the housing  12  and has a through opening that receives a portion of the bearing  16 . A radially extending discharge passage  34  is formed through the housing  12  for discharging the compressed fluid to external equipment.  
         [0012]     A seal  36  extends adjacent the bearing  16  and around the shaft  14  to seal against the egress of the fluid from the bore  12   a . One end of a drain passage  38  extends from the bore  12   a  near the seal  36 , through the carrier  20 , and is vented to a collection point. A radially extending drain connection  42  also extends from the bore  12   a  through the housing  12 .  
         [0013]     The liner  26  is shown in detail in  FIG. 2  and includes an elongated, variable-width, slot  26   a  extending through a wall portion of the liner, along with a discharge port  26   b  in a slightly spaced relation to the slot. Although only one slot  26   a  and discharge port  26   b  are shown, it is understood that another slot  26   a  and discharge port  26   b  are formed through the liner  26  in a diametrically opposed relation to the slot  26   a  and discharge port  26   b  shown in  FIG. 2 . It is also understood that the discharge ports  26   b  are connected by internal passages (not shown) in the housing  12  to the discharge passage  34 . The liner  26  is interchangeable, e.g., it can be replaced by a different liner, it can be used to replace a different liner, or it can be added to a compressor that was initially designed without a liner.  
         [0014]     Referring to  FIG. 3 , a gate rotor assembly  50  is located in a chamber formed in the housing  12  to one side of the shaft  14  and the main rotor  24 , with the axis of the assembly extending transverse to the axis of the rotor. The assembly  50  includes a cylindrical support  54  having an annular flange  54   a  extending therefrom. A shaft  56  extends through the support  54  and the lower end portion of the shaft  56 , as viewed in  FIG. 3 , projects from the corresponding lower end of the support  54 , through a thrust bearing  58  and a thrust washer  60 , and into a cover  62  bolted to the housing  12 . The other end portion of the shaft  56  projects from the upper end of the support  54  and extends into a cover  64  affixed to the housing  12 , to permit rotation of the assembly  50  in the housing  12 .  
         [0015]     An annular gate rotor  66  is affixed to the upper surface of the flange  54   a , and extends, with the flange, through one of the slots  26   a  formed through the liner  26 , so as to mesh with the main rotor  24 . Rotation of the main rotor  24  thus causes corresponding rotation of the gate rotor  66  for reasons to be described.  
         [0016]     Another gate rotor assembly  70  is provided on the opposite side of the main rotor  24 , is inverted when compared to the gate rotor assembly  50 , and includes a rotor  72  which extends through the other slot  26   a  of the liner  26  and also meshes with the main rotor  24 . Since the gate rotor  70  is identical to the gate rotor assembly  50 , it will not be described in detail.  
         [0017]     As shown in  FIG. 4  the main rotor  24  has a plurality of lobes  24   a  which engage corresponding lobes  66   a  and  72   a  formed on the gate rotors  66  and  72 , respectively, so that rotation of the rotor  24  causes a successive intermeshing with the lobes  24   a  and the lobes  66   a  and  72   a  and thus compresses fluid introduced between the lobes, in a manner to be described.  
         [0018]      FIGS. 5A, 5B , and  5 C depict the above compression in various stages of operation. In particular, the shaft  14 , and therefore the rotor  24 , is rotated, which causes corresponding rotation of the gate rotors  66  and  72 . Fluid, such as air, enters the compressor  10  via the inlet  30  ( FIG. 1 ) and passes though the passage  22   a , into the bore  12   a  and through the slots  26   a  ( FIGS. 1 and 2 ) in the liner  26 . The fluid then fills the screw grooves defined by the lobes  24   a  of the main rotor  24 , as shown in  FIG. 5A . As the rotors  24 ,  66 , and  72  rotate further, lobes  66   a  and  72   a  of the gate rotors  66  and  72 , respectively, enter the latter screw grooves, trapping the air, and actual air compression begins, as shown in  FIG. 5B . As the rotation continues, the trapped air is compressed as the length and the volume of each groove is reduced. When the main rotor  24  rotates far enough, each groove passes the discharge ports  26   b  ( FIG. 2 ) of the liner  26 , thus delivering the compressed air to the discharge passage  34 , via the above-mentioned internal passages in the housing  12 , for delivery to external equipment, such as a discharge manifold, or the like.  
         [0019]     Also, since the shape and/or location of the slots  26   a  and the discharge ports  26   b  of the liner  26  dictate the operating parameters of the compressor, including its discharge pressure, flow rate, and capacity, these parameters can be changed by simply replacing the liner  26  with another liner having slots and/or discharge ports of a different shape and/or location. Thus, a compressor system could consist of the compressor  10 , and two or more liners similar to the liner  26 , with the location and size of the slots and/or discharge ports of each liner being designed for a particular different application of the system. Also, an existing compressor that does not have a liner can be fitted with a liner similar to the liner  26  with the slots and discharge ports being designed for the specific desired operating parameters.  
         [0020]     As a result, there is provided a simple, easy, and cost-effective technique of varying the operating parameters of the compressor without having to resort to providing a relatively expensive new housing having formed windows, slots, ports, and passages formed therein to achieve the operating parameters. Even if only one liner is used, it also can be appreciated that the liner reduces the number and depth of the passages and ports that must be formed in the housing to achieve the desired flow characteristics.  
         [0021]     Although not shown in the drawings, it is understood that the compressor  10  can be provided with a water injection system that supplies a continuous flow of cool filtered water to the compressor. This water is injected into the air stream as the air passes through the compressor  10  and is compressed in the above-described manner. The water mixes with the air and the mixture discharges from the compressor  10 , via the discharge passage  34 , to a separator (not shown) where the water is removed and collected. The pressure of the compressed air in the separator provides the force to circulate the water through the water injection system and inject it into the compressor  10 .  
         [0022]     It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, the invention is not limited to a screw compressor, but is equally applicable to any type of rotary machine having two intermeshing rotors. Also, any number of gate, or secondary, rotors that engage the main rotor can be utilized. Also spatial references, such as “upward”, “downward”, “vertical”, etc., are for the purpose of illustration only and also do not limit the specific orientation or location of the structure described above.  
         [0023]     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many other modifications are possible in these embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.