Abstract:
A multi-staged screw compressor system includes a gearbox, a drive gear located in the gearbox, and a first, second and third screw compressor that are fastened to the gearbox and coupled to the drive gear such that the first, second, and third screw compressors are all driven in common by the drive gear. During operation the first screw compressor compresses a flow of gaseous fluid from an inlet pressure to a first intermediate pressure, the second screw compressor compresses the flow of fluid from the first intermediate pressure to a second intermediate pressure, and the third screw compressor compresses the flow of fluid from the second intermediate pressure to a final pressure. The final pressure is at least thirty times the inlet pressure.

Description:
RELATED APPLICATION DATA 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/094,390, filed May 12, 2009, now U.S. Pat. No. ______, which is a national stage filing under 35 U.S.C. 371 of International Application No. PCT/EP2006/005558, filed Jun. 9, 2006, which claims priority to German Patent Application No. 10 2005 058 698.8, filed Dec. 8, 2005, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The invention pertains to a multi-stage screw compressor system. Preferably, the screw compressor system is a “dry-running” system for high pressures, typically 40 bar and above. A preferred area of applicability is the production of compressed air for blow-molding of plastic bottles. 
         [0003]    A two-stage screw compressor system is known from U.S. Pat. No. 3,407,996 (corresponding to DE-A-1628201). It has a gearbox with a perpendicular mounting wall, attached to which are two adjacent compressor stages that cantilever parallel with one another. Each compressor stage comprises a screw compressor with two mutually engaging screw rotors. Located in the gearbox is a transmission with a drive gear that meshes with two driven gears that rotate the rotors of the two screw compressors. Also disclosed in the document is that the invention described in it can also be used in multistage compressor systems with more than two stages. However, there is no indication of how further compressor stages can be arranged, and the design that is described in detail has no place for further compressor stages. 
         [0004]    A similar two-stage screw compressor system is also known from DE 299 22 878.9 U1. 
         [0005]    The object of the invention is to design a three-stage screw compressor system that can deliver a compressed gaseous fluid, in particular compressed air, at a very high pressure, typically about 40 bar and above, and that is characterized by its space-saving design, its simplicity and robustness. In another embodiment of the invention, the three-stage screw compressor system according to the invention allows the ratio of the RPM&#39;s of the three compressor stages to be changed in a simple manner. 
         [0006]    The screw compressor system according to the invention can compress gaseous fluid, in particular air, to a very high pressure ratio, for example 40:1, using only three compressor stages; thus, compressed air can be supplied at a high pressure as is required for industrial manufacturing processes such as blow-molding of plastic bottles. 
         [0007]    In the screw compressor system according to the invention, the screw compressors that constitute the first and second stages are located above the horizontal plane that runs through the rotating axis of the drive gear, whereas the screw compressor of the third stage is located below the screw compressors of the first and second stages and below the horizontal plane running through the rotating axis of the drive gear, and whereas its driven gear meshes with the drive gear near its lowest point. This results in an especially advantageous utilization of the existing space configurations and thus a space-saving, compact design of the compressor system. By using different exchangeable bearings and flange parts, the position of the drive shaft can be changed in the horizontal direction and the position of the third compressor stage can be changed in the vertical direction in order to adjust the gearing configuration to different diameters of gears and thus to different RPM ratios of the compressor stages. 
       SUMMARY 
       [0008]    In one construction, the invention provides a multi-staged screw compressor system with a gearbox ( 90 ), a drive gear ( 95 ) located in the gearbox, and a first, second and third screw compressor ( 60 ,  70 ,  80 ) that are fastened to the gearbox and coupled to the drive gear such that they are all driven in common by the drive gear. During operation, the first screw compressor ( 60 ) compresses a flow of gaseous fluid from an inlet pressure to a first intermediate pressure, the second screw compressor ( 70 ) compresses the flow of fluid from the first intermediate pressure to a second intermediate pressure, and the third screw compressor compresses the flow of fluid from the second intermediate pressure to a final pressure, wherein the final pressure is at least thirty times, preferably at least forty times the inlet pressure. 
         [0009]    In another construction, a multistage screw compressor system consists of a gearbox ( 9 ) 0 , to which a first, second and third screw compressor ( 60 ,  70 ,  80 ) are attached in parallel and cantilevered, and which are driven in common by a drive gear in the gearbox. A gaseous fluid is compressed by the first screw compressor ( 60 ) to a first intermediate pressure of about 3.5 bar, by a second screw compressor ( 70 ) to a second intermediate pressure of about 12 bar and by the third screw compressor ( 80 ) to an internal pressure of about 40 bar. Driven gears ( 65 ,  75 ) of the first and second screw compressors mesh with the drive gear ( 95 ) above its axis, whereas the driven gear ( 85 ) of the third screw compressor ( 80 ) meshes with the drive gear ( 95 ) near its lowest point T. The position of the axis of the drive gear ( 95 ) is able to be changed in the horizontal direction and the position of the driven gear ( 85 ) of the third screw compressor ( 80 ) is able to be changed in the vertical direction for the capability of installing gear sets with different diameter ratios. 
         [0010]    In another construction, the invention provides a multi-staged screw compressor system that includes a gearbox including a housing having a mounting wall. A drive gear is supported by the housing for rotation about a drive axis. The drive axis divides the drive gear into a first upper quadrant, a second upper quadrant, a first lower quadrant, and a second lower quadrant, each quadrant extending between a vertical plane and a horizontal plane that intersect on the drive axis. A first mating flange, a second mating flange, and a third mating flange are each formed as part of the mounting wall to define three substantially planar surfaces arranged normal to the drive axis. A low pressure screw compressor is coupled to the first mating flange and includes a first driven gear, the first driven gear disposed completely within the first upper quadrant. A middle pressure screw compressor is coupled to the second mating flange and includes a second driven gear, the second driven gear disposed completely within the second upper quadrant. A high pressure screw compressor is coupled to the third mating flange and includes a third driven gear, the third driven gear disposed within at least one of the first lower quadrant and the second lower quadrant. The low pressure screw compressor, the middle pressure screw compressor, and the high pressure screw compressor cooperate to compress a gas from a first pressure to a second pressure that is at least 30 times the first pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    One embodiment of the invention is explained in more detail with the help of the drawings. Shown are: 
           [0012]      FIG. 1  a perspective view of three-stage compressor system according to an embodiment of the invention; 
           [0013]      FIG. 2  a perspective, partial sectional view of the screw compressor that constitutes the third stage of the compressor system according to  FIG. 1 ; 
           [0014]      FIG. 3  a perspective, partial sectional view of the gearbox and transmission of the compressor system according to  FIG. 1 , with the compressor stages left out; 
           [0015]      FIG. 4  a simplified representation of the gears that make up the transmission of the compressor system; 
           [0016]      FIG. 5  a view of the mounting wall of the gearbox, partially removed in order to make the transmission visible. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  shows a perspective view of a three-stage screw compressor system with three screw compressors  60 ,  70 ,  80  that are attached to a gearbox  90  via flanges, said gearbox having essentially the shape of a perpendicular plate, and said screw compressors cantilevered parallel to one another. To accomplish this, the housing of each screw compressor  60 ,  70 ,  80  has a flange  64 ,  74  and  84  at its end facing the gearbox  90 , said flange being connected to an associated mating flange on the gearbox  90 . The three screw compressors  60 ,  70 ,  80  are driven by a common motor-driven drive gear held in the gearbox  90 ; this arrangement will be explained in more detail below. In the compressor system shown, screw compressor  60  is the initial stage (low pressure stage), with inlet opening  61  and outlet opening  63 , screw compressor  70  is the second or intermediate stage with inlet opening  71  and outlet opening  73 , and screw compressor  80  is the final stage (or high pressure stage) with inlet opening  81  and an outlet opening on the side opposite the inlet opening  81  that is not shown in  FIG. 1 .  FIG. 1  also shows an oil sump housing  76  that is flanged to the base of the gearbox  90  and that is connected to the synchronizing gears of screw compressors  60 ,  70 ,  80  and to the drive gear located in the gearbox  90 . 
         [0018]    Not shown in  FIG. 1  are the connection lines for the medium to be compressed, in particular air, which connect the inlets and outlets of the three screw compressors  60 ,  70 ,  80 . These lines are designed in a manner known to those trained in the art and can be equipped with filters, intercoolers, and/or mufflers, for example. 
         [0019]    The screw compressors  60 ,  70  of the first and second stage are located next to one another horizontally, whereas screw compressor  80 , the third stage, is located beneath the screw compressors of the first and second stage. The oil sump housing  76  has a recess  79  on its upper surface that creates additional space with which to hold the screw compressor of the third stage. 
         [0020]    Each of the three screw compressors  60 ,  70 ,  80  of  FIG. 1  has two rotors, in the usual fashion, that are rotatably held in a rotor housing with parallel axes and that mesh with one another with screw-shaped ribs and grooves. For example,  FIG. 2  shows screw compressor  80 , which constitutes the third stage of the three-stage compressor system of  FIG. 1 , said compressor being especially designed for high pressures of preferably about 40 bar and above. 
         [0021]    The screw compressor shown in  FIG. 2  has a rotor housing  1  (shown in a longitudinal section) in which two rotors  3  and  5  are rotatably held with parallel axes. The rotating axes of the rotors  3 ,  5  lie in a common vertical plane. Each rotor  3 ,  5  has a profile section  7  and  9  with a profile that contains screw-shaped ribs and grooves, wherein the ribs and grooves of the two profile sections  7 ,  9  mesh with one another to form a seal. On both sides of the profile sections  7 ,  9  are shaft pins  7   a ,  7   b ,  9   a ,  9   b , the surfaces of which cooperate with seal arrangements  11 ,  12  to seal the rotor in the rotor housing  1 . The shaft pins  7   a ,  7   b ,  9   a ,  9   b  are also rotatably held in the rotor housing  1  with bearings  13 ,  15 . 
         [0022]    The upper rotor  3  in  FIG. 2  is the main rotor, at the left end of which in  FIG. 2  is an extended shaft pin  7   c  that extends into the gearbox  90  ( FIG. 1 ) and supports a gear  85  that meshes with a drive gear in the gearbox in order to turn the rotor  3 . At the right end in  FIG. 2 , the two rotors  3 ,  5  have two gears  17 ,  19  that mesh with one another, thus forming a synchronization unit (synchronizing transmission) that conveys the rotation of the upper rotor  3  to the lower rotor  5 , which is the secondary rotor, at the desired RPM ratio; this ensures that the profile sections  7 ,  9  of the rotors  3 ,  5  mesh with one another without touching. 
         [0023]    Rotor housing  1  is surrounding by a cooling jacket or cooling housing  21 , which is for the most part designed as one-piece together with rotor housing  1 , surrounding the same at a distance. Above and below, the cooling housing  21  has large openings that are closed off using a cover plate  23  and a base plate  25  fastened with bolts. Between the rotor housing  1  and the cooling housing  21 ,  23 ,  25  is an annular cooling space  27  surrounding the rotor housing  1  in which a liquid coolant circulates, such as water. 
         [0024]    The screw compressor of the third stage shown in  FIG. 2  is a “dry-rotor” similar to the screw compressors  60 ,  70  of the first and second stage; in other words its compression chamber is kept free of oil. Oil from the oil sump  76 , which is circulated using an oil pump (not shown), is only used to lubricate the drive gear (gears  65 ,  75 ,  85 ,  95 ) and bearings  13 ,  15  as well as the synchronizing transmission ( 17 ,  19 ) of each screw compressor  60 ,  70 ,  80  (see  17 ,  19  in  FIG. 2 ); however, the oil does not enter the compression chamber of the screw compressors. 
         [0025]    At the left end of rotor housing  1  in  FIG. 2  is a flange plate  84  that is removably attached using bolts, said plate serving to fasten the screw compressor to the mounting wall  91  of the gearbox. For this purpose, the flange plate  84  contains holes for attachment bolts. By replacing the flange plate  84  with a plate with another hole pattern, the position at which the screw compressor is fastened to the gearbox  90  can be changed. 
         [0026]    In operating the compressor system shown in  FIG. 1 , air drawn in at inlet  61  of the first compressor stage  60  is compressed by it to a pressure in the range of 3 to 6 bar, preferably about 3.5 bar, and is then compressed to an intermediate pressure in the range of 10 to 15 bar, preferably about 12 bar, by the second compressor stage  70 . This pre-compressed air goes from outlet  73  of the second stage  70  through a connecting line (not shown) to inlet  81  of the third compressor stage  80 , where it is compressed to a final pressure in the range of 30 to 50 bar, preferably about 40 bar. 
         [0027]    At the preferred operating pressures cited above, the pressure ratios in each of the three screw compressors  60 ,  70 ,  80  are nearly the same and decrease only minimally from the first to the third stage. At the pressures cited, the pressure ratio between the inlet ant outlet pressures in the first screw compressor  60  is approximately 3.5, in the second screw compressor  70  it is approximately 3.4 and in the third screw compressor  80  it is approximately 3.3. 
         [0028]      FIG. 3  shows a perspective view, in part sectional, of the gearbox  90  with the transmission contained therein to drive the three screw compressors  60 ,  70 ,  80 . The gearbox  90  has a perpendicular mounting wall  91  on one side, to which the housings of the three screw compressors  60 ,  70 ,  80  (not shown in  FIG. 3 ) are attached. On the other side, the gearbox  90  is closed off by a bearing cover  92  inside of which is a drive shaft  94  held by means of a bearing ring  93  and supporting a drive gear  95 . The end of the drive shaft  94  that extends beyond the drive gear  95  is held in a bearing seat (see  FIG. 5 ) that is set into the mounting wall  91 . The drive gear  95  meshes with the three driven gears  65 ,  75 ,  85  associated with the three screw compressors  60 ,  70 ,  80 , said driven gears being distributed about the perimeter of the drive gear  95 . Each of the driven gears  65 ,  75 ,  85  sits on a rotor shaft pin of one of the three screw compressors  60 ,  70 ,  80 , said pin protruding into the gearbox  90  through a corresponding hole in the mounting wall  91 . 
         [0029]    In  FIG. 4 , the arrangement of the three drive gears  65 ,  75 ,  85  is shown in relation to the drive gear  95 . The driven gears  65 ,  75  of screw compressors  60  or  70  of the first and second stage are located above the horizontal plane B-B that runs through the rotating axis A of the drive gear  95 . On the other hand, the driven gear  85  of screw compressor  80  of the third stage is clearly below the horizontal plane B-B running through axis A, preferably near the lowest point T of the drive gear  95 . It is preferable to locate the drive gear  65  for the first compressor stage such that a line C connecting its axis  65 ′ to axis A of the drive gear  95  assumes an angle α of not more than 30° with respect to the horizontal line B-B running through axis A of the drive gear  95 . For driven gear  75  of the second compressor stage  70 , the corresponding angle β is preferred not to be more than 20°. On the other hand, driven gear  85  of the third compressor stage  80  is located close enough to the lowest point T of the drive shaft  95  such that a line D connecting the axis of the driven gear  85  with the rotating axis A of the drive gear  95  assumes an angle γ of not more than 20° with respect to the vertical plane running through the axis A of the drive gear  95 . 
         [0030]      FIG. 5  shows a view of the mounting wall  91  of the gearbox  90 . This view is shown with a cutout in the upper area in order to show the drive gear  95  located behind the wall, said gear engaging with the driven gears  65 ,  75 ,  85  of the three screw compressors  60 ,  70 ,  80  (left out in  FIG. 5 ). The mounting wall  91  has openings  68 ,  78 ,  88  through which the shaft pins (see  7   b  in  FIG. 2 ) of the screw compressors  60 ,  70 ,  80  that support the gears  65 ,  75 ,  85  can pass into the gearbox  90 . The mounting wall  91  has rib-like raised mating flanges  69 ,  79 ,  89  that surround openings  68 ,  78 ,  88 . Flanges  64 ,  74 ,  84  of the compressors  60 ,  70 ,  80  (see  FIG. 1 ) are fastened to these mating flanges with bolts and suitable gaskets. 
         [0031]    A bearing seat  97  is set into the mounting wall  91  of the gearbox  90 . The end of the drive shaft  94  (see  FIG. 3 ) supporting the drive gear  95  is held in this bearing seat. Both the bearing seat  97  and the bearing ring  93  shown in  FIG. 3  to hold the drive shaft  94  are eccentrically designed. By exchanging the bearing ring  93  and the bearing seat  97  with others having varying eccentricities, the position of the drive gear  95  can be changed in the horizontal direction, as indicated with the horizontal double arrow  98  in  FIG. 5 . 
         [0032]    Furthermore, the flange plate  84  of screw compressor  80  that constitutes the third stage is removably bolted to the mating flange  89  of the gearbox, along with the rotor housing associated with it. This flange plate can be exchanged with a flange plate having a different hole pattern, which allows the position of the screw compressor  80  and thus its driven gear  85  to change in the vertical direction as indicated by the vertical double arrow  86  in  FIG. 5 . 
         [0033]    This ability to shift the drive gear  95  in the horizontal direction  98  and to shift the driven gear of the third stage in the vertical direction  86  enables the use of different gear sets for gears  95 ,  65 ,  75   85  that make up the transmission, whereupon the gear ratios and thus the relative RPM&#39;s of the three compressor stages  60 ,  70 ,  80  can be changed by using different diameters matched with one another. In the process, all four gears  65 ,  75 ,  85 ,  95  that make up the transmission can be exchanged with such other diameters, wherein a shift of only two of these elements in two directions perpendicular to one another is sufficient, namely the drive gear  95  in the horizontal direction  98  and the gear  85  of the third stage in the vertical direction  86 , to ensure proper meshing of the gears even when the diameter ratios are changed.