Abstract:
A gear case assembly includes an upper gear case and a lower gear case accommodating a drive axle, at least one rotation axle receiving power from the drive axle, and a power transmission unit for transmitting the power to the at least one rotation axis. The upper and lower gear cases are horizontally divided, and upper and a lower shrouds are integrally formed on the upper and lower gear cases proximate to ends of the rotation axis. The upper and lower shrouds form a surface for guiding a fluid that flows from an impeller connected to the rotation axle, and are horizontally divided. Scroll cases mounted on the upper and lower gear cases, together with the upper and lower shrouds, define a path for guiding the fluid that flows from the impeller. A common plane divides the upper and lower gear cases, and also divides the upper and lower shrouds.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2007-0031965, filed on Mar. 30, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a gear case assembly, and more particularly, to a gear case assembly that accommodates a rotation body used for a turbo compressor, a centrifugal compressor, or another mechanical device that increases the pressure of a gas by reducing its volume. 
         [0004]    2. Description of the Related Art 
         [0005]    A rotation body, such as an impeller on an axle, may be installed in a compressor, a blower, a turbo charger, or a marine engine. In order to drive the rotation body, a power transmission unit is accommodated in a gear case assembly to transmit power from a drive source to the impeller. Alternatively, a rotation body such as a turbine on an axle may be installed in an expander or another mechanical device that extracts energy from a fluid flow, and may provide a drive source from which power may be transmitted via a gear case assembly. 
         [0006]    A known gear case assembly includes a gear case divided into, for example, an upper gear case and a lower gear case for supporting the rotation body and the power transmission unit therein. A shroud may be integrally formed on the gear case. The shroud defines a surface for guiding a fluid that flows from an impeller, and includes a roughly circular shape around a central bore. For example, a circular shroud is formed on a front portion of the lower gear case and protrudes toward the upper gear case. 
         [0007]    According to the known gear case assembly, the rotation body includes an impeller disposed on an axle and driven by a drive source via the power transmission unit. The impeller is mounted at an end of the axle and has a diameter greater than that of the axle. The axle is accommodated in the gear case assembly, and the impeller is disposed outside the shroud of the gear case assembly. In order to accommodate the axle in the gear case assembly, a bore is formed in the gear case through the shroud. 
         [0008]    However, when the impeller is preassembled to the axle, such a rotation body assembly cannot be mounted on the lower gear case as a whole since the diameter of the bore of the shroud is frequently less than the diameter of the impeller. Thus, the impeller must be disassembled from the axle in order to insert the rotation body assembly through the bore in the shroud of the lower gear case of the gear case assembly. Thereafter, a seal must be interposed between the gear case assembly and the rotation body assembly to prevent a leak from occurring therebetween. 
         [0009]    However, before installing the rotation body assembly, a balancing operation is performed on the rotation body assembly before being disassembled. After installing the axle, the impeller is reassembled on the axle. As a result, the rotation body assembly may be out of balance due to the disassembling and reassembling of the rotation body assembly after the balancing operation is performed. 
         [0010]    Also, in order to insert the rotation body assembly in the bore of a known gear case assembly, the bore must be of sufficient size in order to prevent interference between the elongated rotation body assembly and the gear case. Therefore, a seal holder needs to be additionally interposed between the rotation body assembly and the bore of the gear case and, as a result, the number of components increases, the assembly process becomes more complicated, and production costs also increase. Additionally, it is difficult to cast the gear case having the protruding shroud at the front portion of the lower gear case and it is also hard to perform a milling process, such as a cutting process or a finishing process, on the lower gear case because of limited working space. 
         [0011]    Furthermore, because a groove that is required for a sealing O-ring is difficult to form in the lower gear case, the groove that is required for the sealing O-ring must be formed in the upper gear case. However, it is disadvantageous to turn the upper gear case upside down to form the groove required for the sealing O-ring. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a gear case assembly that simplifies the assembly process, has improved efficiency in terms of repair and maintenance, and has a reduced number of components. 
         [0013]    In accordance with an aspect of the present invention, there is provided a gear case assembly including an upper gear case and a lower gear case accommodating a driving axis rotatably driven by a driving unit, at least one rotation axis receiving power from the driving axis and rotating, a power transmit unit for transmitting the power to the rotation axis, the upper gear case is horizontally divided from the lower gear case; an upper shroud and a lower shroud are integrally formed in end regions of the rotation axis of the upper and lower gear cases, respectively, to form a surface for guiding a fluid that flows from an impeller connected to the rotation axis, the upper shroud is horizontally divided from the lower shroud; and scroll cases are mounted in the end regions of the upper and lower gear cases opposite the upper and lower shrouds, respectively, to form a path for guiding the fluid that flows from the impeller together with the upper and lower shrouds. A bottom surface of the upper gear case is on the same level with a bottom surface of the upper shroud, and a top surface of the lower gear case is on the same level with a top surface of the lower shroud. 
         [0014]    The upper gear case that is integrally formed with the upper shroud and the lower gear case that is integrally formed with the lower shroud using, for example, a bolt, and the bottom surface of the upper gear case may be on the same level with the top surface of the lower gear case. 
         [0015]    Therefore, since a rotation axis assembly can be assembled to the gear case assembly without disjointing the impeller from the rotation axis assembly, an assembling process and repair and maintenance work can be facilitated, and the rotation axis assembly can be well balanced. Also, a milling process can be easily performed on the upper and lower gear cases at low cost since the bottom surface of the upper gear case and the top surface of the lower gear case are both plane. Furthermore, the upper and lower gear cases can be easily manufactures using a casting process. 
         [0016]    A seal, for example, an O-ring, may be disposed between the top surface of the lower gear case, and the bottom surface of the upper gear case. 
         [0017]    Since the top surface of the lower shroud is on the same level with the top surface of the lower gear case, a groove used for disposing the O-ring can be formed in the lower gear case. In this case, a surface of the lower gear case to be processed (i.e., the top surface of the lower gear surface) faces upward, so that it is unnecessary to turn the lower gear case upside down. Therefore, the groove used for disposing the O-ring can be easily processed in the top surface of the lower gear case that is combined with the bottom surface of the upper gear case. 
         [0018]    A carbon seal may be interposed between the rotation axis and the upper and lower gear cases in a rear end region of the third impeller. In this case, it is unnecessary to enlarge a bore formed in the upper and lower gear cases to assemble the elongated rotation axis assembly unlike in the conventional case. Therefore, an additional component is not required to mount the carbon seal between the rotation axis and the upper and lower gear cases. 
         [0019]    In accordance with another aspect of the present invention, there is provided a gear case assembly that includes a first gear case and a second gear case that accommodate a drive axle that is adapted to be rotatably driven by a driving unit, a first rotation axle that receives power from and is rotated by the drive axle, a power transmission unit that transmits the power from the drive axle to the first rotation axle, and a plane that divides the first and second gear cases. A first shroud and a second shroud are respectively integrally formed on the first and second gear cases and proximate a first end of the first rotation axle, the first and second shrouds form a first surface for guiding a fluid that flows from a first impeller disposed on the first rotation axle, the plane divides the first and second shrouds, and a first scroll case mounted on the first and second gear cases and proximate to the first and second shrouds, the first scroll case and the first surface define a path for guiding the fluid that flows from the first impeller. Wherein mating surfaces of the first and second gear cases coincide with the plane, and mating surfaces of the first and second shrouds coincide with the plane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0021]      FIG. 1  is a front view of a gear case assembly used for a turbo compressor according to an embodiment of the present invention; 
           [0022]      FIG. 2  is a plan view of a lower gear case assembly of the gear case assembly shown in  FIG. 1 , according to an embodiment of the present invention; and 
           [0023]      FIG. 3  is a magnified view of region “A” of  FIG. 2 , according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which show exemplary embodiments according to aspects of the invention. 
         [0025]      FIG. 1  is a front view of a gear case assembly used for a turbo compressor according to an exemplary embodiment of the present invention,  FIG. 2  is a plan view of a lower gear case assembly of the gear case assembly shown in  FIG. 1 , according to an exemplary embodiment of the present invention, and  FIG. 3  is an enlarged view of region “A” of  FIG. 2 , according to an exemplary embodiment of the present invention. 
         [0026]    Referring to  FIGS. 1 through 3 , the gear case assembly used for the turbo compressor according to an exemplary embodiment of the present invention includes an upper gear case  20 , a lower gear case  10 , first through third upper shrouds (only first and third upper shrouds  21  and  23  are shown in  FIG. 1 ), first through third lower shrouds  11 ,  12 , and  13 , and first through third impellers  41 ,  42 , and  43 . The upper gear case  20  is horizontally divided from the lower gear case  10 . The upper gear case  20  is combined with the lower gear case  10  such that a bottom surface of the upper gear case  20  is in contact with a top surface of the lower gear case  10 , and the bottom surface of the upper gear case  20  forms a planar surface with the top surface of the lower gear case  10 . A drive axle  30  and first and second rotation axles  31  and  32 , are accommodated between the upper and lower gear cases  20  and  10 . 
         [0027]    The drive axle  30  is connected to a driving source, for example, a turbine (not shown), and rotatably driven thereby. For example, if the turbo compressor is driven by a gas turbine engine, the turbine rotates due to air heated by a combustor of the gas turbine engine and, in turn, the turbine drives the drive axle  30  of the turbo compressor. 
         [0028]    The first rotation axle  31  and the second rotation axle  32  are disposed on the left and right sides of the drive axle  30 , respectively. A power transmission unit, which transmits power from the drive axle  30  to the first and second rotation axles  31  and  32  includes a bull gear  33 , a first pinion gear  34 , and a second pinion gear  35 . The bull gear  33  is mounted on the drive axle  30 , the first pinion gear  34  is mounted on the first rotation axle  31 , and the second pinion gear  35  is mounted on the second rotation axle  32 . The bull gear  33  meshes with each of the first and second pinion gears  34  and  35 . 
         [0029]    The first impeller  41  is disposed at a front end of the first rotation axle  31 , the second impeller  42  is disposed at a rear end of the first rotation axle  31 , and the third impeller  43  is disposed at a front end of the second rotation axle  32 . The first and second rotation axles  31  and  32  receive power from the drive axle  30  and rotate the first, second, and third impellers  41 ,  42 , and  43 . 
         [0030]    Since the number of teeth and diameter of the first pinion gear  34  are smaller than those of the bull gear  33 , the first rotation axle  31  rotates at a higher rate than the drive axle  30 . Also, since the number of teeth and diameter of the second pinion gear  35  are smaller than those of the first pinion gear  34 , the second rotation axle  32  rotates at a higher rate than the drive axle  30 . Thus, air is compressed by the first impeller  41  in a first compression stage, the compressed air is further compressed by the second impeller  42  in a second compression stage, and the compressed air is further compressed by the third impeller  43  in a third compression stage. Hence, the turbo compressor according to the illustrated exemplary embodiment is a three-stage compressor. Although the gear case assembly used for the three-stage turbo compressor is exemplarily illustrated and described in the present embodiment, the present invention is not limited thereto. The present invention may be applied to any gear case assembly including a rotation body, such as the third impeller  43  disposed on the second rotation axle  32 , the lower and upper gear cases  10  and  20  accommodating the rotation body, and the third lower and third upper shrouds  13  and  23 , which are respectively formed on the gear cases  10  and  20 . 
         [0031]    The first lower shroud  11  is formed in the lower gear case  10  proximate the front end of the first rotation axle  31 . The first lower shroud  11  is horizontally divided from the first upper shroud  21  such that a top surface of the first lower shroud  11  forms a planar surface with the top surface of the lower gear case  10 , and a bottom surface of the first upper shroud  21  forms a planar surface with the bottom surface of the upper gear case  20 . 
         [0032]    Similarly, the second lower shroud  12  is formed in the lower gear case  10  proximate the rear end of the first rotation axle  31 . The second lower shroud  12  is horizontally divided from the second upper shroud (not shown). Also, the third lower shroud  13  is formed in the lower gear case  10  proximate the front end of the second rotation axle  32 . The third lower shroud  13  is horizontally divided from the third upper shroud  23 . 
         [0033]    When the first upper shroud  21  is combined with the first lower shroud  11 , a circular shroud surface having a central bore is formed. Fluid flow provided by the first impeller  41  due to rotation of the first rotation axle  31  is guided by the circular shroud surface  11  and  21 . 
         [0034]    The first through third upper shrouds  21 , (not shown), and  23  and the upper gear case  20  are integrally formed by, for example, a casting process. Also, the first through third lower shrouds  11 ,  12 , and  13  and the lower gear case  10  are integrally manufactured by, for example, a casting process. The upper gear case  20  including the first through third upper shrouds  21 , (not shown), and  23  and the lower gear case  10  including the first through third lower shrouds  11 ,  12 , and  13  may be secured together with a threaded faster such as a bolt, a bolt and nut, or another type of releasable fastener. For example, one or more bolts may pass through the upper gear case  20  and be fastened to a threaded portion of the lower gear case  10  in order to secure together the upper and lower gear cases  20  and  10 . 
         [0035]    Since the upper gear case  20  that is integrally formed with the first through third upper shrouds  21 , (not shown), and  23  is horizontally divided from the lower gear case  10  that is integrally formed with the first through third lower shrouds  11 ,  12 , and  13 , it is not necessary to disassemble the impellers  41 ,  42 , and  43  from the first and second rotation axles  31  and  32  in order to install the first and second rotation axles  31  and  32  in the gear case assembly. Thus, the gear case assembly can be easily assembled and, in terms of repair and maintenance, achieve improved efficiency. Additionally, preassembly and balancing of the first and second rotation axles  31  and  32  is provided such that disassembly is not required. 
         [0036]    Also, a milling process can be easily performed on the lower and upper gear cases  10  and  20  at low cost since both the bottom surface of the upper gear case  20  and the lower gear case  10  are planar. Furthermore, the upper and lower gear cases  20  and  10  can be easily manufactured by a casting process. 
         [0037]    In addition, since the upper gear case  20 , which is integrally formed with the first through third upper shrouds  21 , (not shown), and  23 , is horizontally divided from the lower gear case  10 , which is integrally formed with the first through third lower shrouds  11 ,  12 , and  13 , it is unnecessary to increase the size of bore portions  10   a  and  20   a , which are respectively formed in the upper and lower gear cases  10  and  20 , to install the rotation axles  31  and  32 , as is the case in a known gear case assembly. Thus, referring to  FIG. 3 , it is only necessary to insert a carbon seal  51  between the first and second rotation axles  31  and  32  and the lower and upper gear cases  10  and  20  in a rear region of the third impeller  43 . Unlike the known gear case assembly, a separate carbon seal holder is not required to mount the carbon seal  51 . Therefore, the number of components can be reduced, the assembly costs can be reduced, and failures caused by additional steps of the assembling process can be eliminated. Hence, the carbon seal  51  functions to prevent the leakage of air compressed by the third impeller  43 . 
         [0038]    A seal (not shown) is disposed between the top surface of the lower gear case  10  and the bottom surface of the upper gear case  20 . The seal may be an O-ring. To install the O-ring, a groove  10   b  is formed in the top surface of the lower gear case  10 , which mates with the bottom surface of the upper gear case  20 . 
         [0039]    In the known gear case assembly, since the entire shroud is integrally formed with the lower gear case  1  and protrudes upward from the lower gear case  1 , a groove, such as the groove  10   b  required for an O-ring, cannot be formed in the lower gear case  1 . Thus, with the known gear case assembly, it becomes necessary to disadvantageously turn the upper gear case  20  upside down and handle the upper gear case  20  to form the groove required for the O-ring in the upper gear case  20 . However, according to aspects of exemplary embodiments of the present embodiment, since top surfaces of the first through third lower shrouds  11 ,  12 , and  13  are on the same plane with the top surface of the lower gear case  10 , it is possible to form the groove  10   b  in the lower gear case  10 . In this case, since a surface of the lower gear case  10  that is to be processed (i.e., the top surface of the lower gear surface  10 ) faces upward, it is unnecessary to additionally handle, e.g., turn over, the lower gear case  10 . In conclusion, the groove  10   b  required for the O-ring can be easily processed. 
         [0040]    Referring particularly to  FIG. 2 , a first scroll case  36  is mounted to the lower and upper gear cases  10  and  20  proximate to the front end of the first rotation axle  31 , a second scroll case  37  is mounted to the lower and upper gear cases  10  and  20  proximate to the rear end of the first rotation axle  31 , and a third scroll case  38  is mounted to the lower and upper gear cases  10  and  20  proximate to the front end region of the second rotation axle  32 . As illustrated in  FIG. 3 , along with the third lower and upper shrouds  13  and  23 , the third scroll case  38  defines a path that guides air compressed by the third impeller  43 . Although not shown in the drawings, the third scroll case  38  may be mounted on the lower and upper gear cases  10  and  20  using, for example, bolts or other releasable fasteners. 
         [0041]    Although a gear case assembly used for a turbo compressor according to the exemplary embodiments of the present invention has been explained, the present invention is not limited thereto. For example, a gear case assembly according to exemplary embodiments of the present invention can be applied to a blower, a turbo charger, an engine, and an expander. That is, any gear case assembly including a rotation body, such as the third impeller  43  disposed on the second rotation axle  32 , the lower and upper gear cases  10  and  20  accommodating the rotation body, and any of the first through third lower shrouds  11 ,  12 , and  13 , and first through third upper shrouds  21 , (not shown), and  23  formed in the lower and upper gear cases  10  and  20 , may be within the scope of the present invention. In this case, a driving gear for driving the rotation body, such as the third impeller  43  disposed on the second rotation axle  32 , may be a turbine, a motor, or an engine. 
         [0042]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.