Abstract:
When A denotes a required oil lower limit amount for one bearing near an oil supply source, and B and C respectively denote a required oil lower limit amount and a safety surplus oil amount for the other bearing away from the source, an amount of oil equal to A+B+C is supplied from the source and a hole diameter and the number of first oil holes are set such that an amount of oil to be supplied to the one bearing is equal to the amount A. Thus, the oil with the amount A can be securely supplied to the one bearing. Also, oil with the sum of the amounts B and C is supplied to the other bearing so that the oil with the amount B can be securely supplied to the other bearing which tends to receive oil insufficiently because of its remoteness from the source.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2014-67817 filed Mar. 28, 2014 the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a bearing lubricating structure for a gas turbine engine, the engine including a low-pressure system shaft, and a high-pressure system shaft fitted to an outer periphery of the low-pressure system shaft in a relatively rotatable manner, in which the low-pressure system shaft is supported by a casing via a first bearing, the high-pressure system shaft is supported by the low-pressure system shaft via a second bearing, and oil is supplied to the first bearing and the second bearing from an oil supply source. 
         [0004]    2. Description of the Related Art 
         [0005]    A twin-spool gas turbine engine, in which a high-pressure system shaft is disposed on an outer periphery of a low-pressure system shaft in a relatively rotatable manner, includes: a bearing with which the low-pressure system shaft and the high-pressure system shaft are supported by a casing; and a differential bearing disposed between the low-pressure system shaft and the high-pressure system shaft. The low-pressure system shaft and the high-pressure system shaft are designed to rotate reversely to each other for the purpose of enhancing aerodynamic performances of a compressor and a turbine. Thus, relative rotation speed between an inner race and an outer race becomes large in the differential bearing disposed between the low-pressure system shaft and the high-pressure system shaft so that an amount of oil needed to lubricate the differential bearing increases. Against this background, Japanese Patent Application Laid-open No. 10-299416 has made publicly known a gas turbine engine in which oil injected from an oil jet is supplied to the differential bearing via oil passages, oil reservoirs and oil holes. 
         [0006]    However, the foregoing conventional gas turbine engine is likely to be unable to supply a sufficient amount of oil to the differential bearing which needs a larger amount of oil because the bearing with which the low-pressure system shaft is supported by the casing is disposed in a supply passage of the oil from the oil jet to the differential bearing so that the bearing consumes the oil. Supplying of the sufficient amount of oil to the differential bearing may be achieved by increasing capacity of an oil pump. However, the increase in the capacity of the oil pump raises a problem of: making an oil tank and the oil pump bulky in size; and accordingly increasing weight and cost of the gas turbine engine. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has been made with the foregoing situation taken into consideration. An object of the present invention is to enable a necessary and sufficient amount of oil to be supplied to multiple bearings for supporting a low-pressure system shaft and a high-pressure system shaft in a gas turbine engine. 
         [0008]    In order to achieve the object, according to a first aspect of the present invention, there is provided a bearing lubricating structure for a gas turbine engine, the engine including a low-pressure system shaft, and a high-pressure system shaft fitted to an outer periphery of the low-pressure system shaft in a relatively rotatable manner, in which the low-pressure system shaft is supported by a casing via a first bearing, the high-pressure system shaft is supported by the low-pressure system shaft via a second bearing, and oil is supplied to the first bearing and the second bearing from an oil supply source, the structure comprising: a first oil passage for supplying the oil to one bearing of the first and second bearings from the oil supply source; a first oil reservoir connected to a downstream portion of the first oil passage, and formed inside the one bearing in a radial direction; first oil holes extending outward in the radial direction from the first oil reservoir, and communicating with the one bearing; a second oil passage for supplying the oil to the other bearing of the first and second bearings from the first oil reservoir; a second oil reservoir connected to a downstream portion of the second oil passage, and formed inside the other bearing in the radial direction; and second oil holes extending outward in the radial direction from the second oil reservoir, and communicating with the other bearing, wherein when A denotes a required oil lower limit amount for the one bearing, as well as B and C respectively denote a required oil lower limit amount and a safety surplus oil amount for the other bearing, an amount of oil equal to A+B+C is supplied from the oil supply source, and a hole diameter and the number of the first oil holes are set such that an amount of oil to be supplied to the one bearing is equal to the required oil lower limit amount A. 
         [0009]    According to the first aspect, the gas turbine engine includes the low-pressure system shaft and the high-pressure system shaft which are respectively disposed inward and outward in the radial direction, and which rotate relative to each other. The low-pressure system shaft is supported by the casing via the first bearing, and the high-pressure system shaft is supported by the low-pressure system shaft via the second bearing. The oil is supplied to the first bearing and the second bearing from the oil supply source. Part of the oil from the oil supply source is supplied to the one bearing of the first and second bearings via the first oil passage, the first oil reservoir and the first oil holes. The rest of the oil is supplied to the other bearing of the first and second bearings from the first oil reservoir via the second oil passage, the second oil reservoir and the second oil holes. 
         [0010]    When A denotes the required oil lower limit amount for the one bearing, as well as B and C respectively denote the required oil lower limit amount and the safety surplus oil amount for the other bearing, the amount of oil equal to A+B+C is supplied from the oil supply source, and the hole diameter and the number of the first oil holes are set such that the amount of oil to be supplied to the one bearing is equal to the required oil lower limit amount A. For this reason, not only can the oil with the required oil lower limit amount A be securely supplied to the one bearing. But also, the oil with the sum of the required oil lower limit amount B and the safety surplus oil amount C can be supplied to the other bearing. Thereby, the oil with the required oil lower limit amount B can be securely supplied to the other bearing, which tends to receive an insufficient amount of oil because of its remoteness from the oil supply source. 
         [0011]    According to a second aspect of the present invention, in addition to the first aspect, the low-pressure system shaft and the high-pressure system shaft rotate reversely to each other, and the other bearing is the second bearing. 
         [0012]    According to the second aspect, the low-pressure system shaft and the high-pressure system shaft rotate reversely to each other. This increases load of the second bearing so as to increase an amount of oil needed for the second bearing. However, the oil with the sum of the required oil lower limit amount B and the safety surplus oil amount C is supplied to the second bearing which tends to receive an insufficient amount of oil because of its remoteness from the oil supply source. Thereby, insufficient lubrication of the second bearing can be securely prevented. 
         [0013]    It should be noted that: an inner casing  12  of an embodiment corresponds to the casing of the present invention; a rear first bearing  14  of the embodiment corresponds to the one bearing or the first bearing of the present invention; a rear second bearing  18  of the embodiment corresponds to the other bearing or the second bearing of the present invention; and an oil jet  55  of the embodiment corresponds to the oil supply source of the present invention. 
         [0014]    The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiment which will be provided below while referring to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a view showing an overall structure of a twin-spool turbofan engine. 
           [0016]      FIG. 2  is an enlarged view of a section  2  in  FIG. 1 . 
           [0017]      FIG. 3  is a sectional view taken along a  3 - 3  line in  FIG. 2 . 
           [0018]      FIG. 4  is a sectional view taken along a  4 - 4  line in  FIG. 2 . 
           [0019]      FIG. 5  is a schematic diagram of an oil supply passage. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    Descriptions will be hereinbelow provided for an embodiment of the present invention on the basis of  FIGS. 1 to 5 . 
         [0021]    As shown in  FIG. 1 , a twin-spool turbofan engine for an aircraft to which the present invention is applied includes an outer casing  11  and an inner casing  12 . Front and rear portions of a low-pressure system shaft  15  are rotatably supported by an inside of the inner casing  12  via front and rear first bearings  13 ,  14 , respectively. A tubular high-pressure system shaft  16  is fitted to an outer periphery of an axial-direction intermediate portion of the low-pressure system shaft  15  in a relatively rotatable manner. A front portion of the high-pressure system shaft  16  is rotatably supported by the inner casing  12  via a front second bearing  17 , while a rear portion of the high-pressure system shaft  16  is supported by the low-pressure system shaft  15  in a relatively rotatable manner via a rear second bearing  18 . 
         [0022]    A front fan  19  having blade ends which face an inner surface of the outer casing  11  is fixed to a front end of the low-pressure system shaft  15 . Part of air sucked by the front fan  19  passes through stator vanes  20  disposed between the outer casing  11  and the inner casing  12 . Part of the air having passed through the stator vanes  20  thereafter passes through an annular bypass duct  21  formed between the outer casing  11  and the inner casing  12 , and is jetted rearward. Other part of the air is supplied to an axial low-pressure compressor  22  and a centrifugal high-pressure compressor  23  which are disposed inside the inner casing  12 . 
         [0023]    The low-pressure compressor  22  includes: stator vanes  24  fixed to the inside of the inner casing  12 ; and a low-pressure compressor wheel  25  having compressor blades on its outer periphery, and fixed to the low-pressure system shaft  15 . The high-pressure compressor  23  includes stator vanes  26  fixed to the inside of the inner casing  12 ; and a high-pressure compressor wheel  27  having compressor blades on its outer periphery, and fixed to the high-pressure system shaft  16 . 
         [0024]    A reverse-flow combustion chamber  29  is disposed in a rear of a diffuser  28  connected to an outer periphery of the high-pressure compressor wheel  27 . Fuel injection nozzles  30  inject fuel into the reverse-flow combustion chamber  29 . The fuel and the air are mixed together and combusted inside the reverse-flow combustion chamber  29 . The generated combustion gas is supplied to a high-pressure turbine  31  and a low-pressure turbine  32 . 
         [0025]    The high-pressure turbine  31  includes: nozzle guide vanes  33  fixed to the inside of the inner casing  12 ; and a high-pressure turbine wheel  34  having turbine blades on its outer periphery, and fixed to the high-pressure system shaft  16 . The low-pressure turbine  32  includes: nozzle guide vanes  35  fixed to the inside of the inner casing  12 ; and low-pressure turbine wheels  36  each having turbine blades on its outer periphery, and fixed to the low-pressure system shaft  15 . 
         [0026]    For this reason, once the high-pressure system shaft  16  is driven by a starter motor (not illustrated), air sucked by the high-pressure compressor wheel  27  is supplied to the reverse-flow combustion chamber  29 , and mixed with the fuel to be combusted. The generated combustion gas drives the high-pressure turbine wheel  34  and the low-pressure turbine wheels  36 . As a result, the low-pressure system shaft  15  and the high-pressure system shaft  16  rotate. Accordingly, the front fan  19 , the low-pressure compressor wheel  25  and the high-pressure compressor wheel  27  compress air, and supply the compressed air to the reverse-flow combustion chamber  29 . Thereby, even after operation of the starter motor is stopped, the turbofan engine continues its operation. 
         [0027]    While the turbofan engine is in operation, part of air sucked by the front fan  19  passes through the bypass duct  21 , and is jetted rearward so as to, particularly during low-speed flight, generate main thrust. The remaining part of the air sucked by the front fan  19  is supplied to the reverse-flow combustion chamber  29 , and is mixed with the fuel to be combusted. The combusted gas drives the low-pressure system shaft  15  and the high-pressure system shaft  16 , and is thereafter jetted rearward, generating thrust. 
         [0028]    Next, descriptions will be provided for an oil supply passage to the rear first bearing  14  and the rear second bearing  18  on the basis of  FIGS. 2 to 5 . 
         [0029]    A sleeve  41  for supporting the two low-pressure turbine wheels  36  is fitted to an outer periphery of the low-pressure system shaft  15  via a spline  42 , and is fastened to the low-pressure system shaft  15  with an oil guide member  43  which is screwed onto an outer periphery of an axial end of the low-pressure system shaft  15 . The rear first bearing  14  includes: an inner race  45  fitted to an outer periphery of the sleeve  41 ; an outer race  46  fitted to an inner periphery of a bearing holding member  44  of the inner casing  12 ; and multiple rollers  47  disposed between the inner race  45  and the outer race  46 . The bearing holding member  44  and the outer race  46  are fastened to the inner casing  12  with bolts  48 . The inner race  45  is fastened to the sleeve  41  with a nut  49  which is screwed onto an outer periphery of an end portion of the sleeve  41 . 
         [0030]    The rear second bearing  18  includes: an inner race  52  fitted to an outer periphery of the high-pressure system shaft  16  which is fitted to the outer periphery of the sleeve  41  in a relatively rotatable manner, and fastened to the high-pressure system shaft  16  with a nut  50 ; an outer race  53  fixed to the sleeve  41  with bolts  51 ; and multiple rollers  54  disposed between the inner race  52  and the outer race  53 . 
         [0031]    The rear first bearing  14  is disposed between the sleeve  41  fitted to the outer periphery of the low-pressure system shaft  15  and the bearing holding member  44  of the inner casing  12 , as well as the relative number of rotation between the inner race  45  and the outer race  46  is small. For these reasons, load of the rear first bearing  14  is relatively small. On the other hand, the rear second bearing  18  is disposed between the sleeve  41  fitted to the outer periphery of the low-pressure system shaft  15  and the high-pressure system shaft  16 , as well as the relative number of rotation between the inner race  52  and the outer race  53  is large. For these reasons, load of the rear second bearing  18  is relatively large. 
         [0032]    As shown in  FIGS. 2 and 5 , an oil introduction passage  43   a  is formed in the oil guide member  43  to which an oil jet  55  provided to the inner casing  12  is directed. A first oil passage P 1  communicates with a downstream portion of the oil introduction passage  43   a.  The first oil passage P 1  is formed from: 20 oil holes disposed inside the oil guide member  43 , arranged at equal intervals in an peripheral direction, and penetrating through the oil guide member  43  in an axial direction; and an annular passage b formed between an end surface of the oil guide member  43  and an end surface of the sleeve  41 . A first oil reservoir R 1  communicating with a downstream portion of the first oil passage P 1  is formed from  16  oil holes c disposed inside the sleeve  41 , arranged at equal intervals in an peripheral direction, and penetrating through the sleeve  41  in an axial direction. Furthermore, the first oil reservoir R 1  is connected to the rollers  47  of the rear first bearing  14  via  8  first oil holes i in total which extend outward in a radial direction from the first oil reservoir R 1 . 
         [0033]    As shown in  FIG. 3 , the first oil holes i include: 4 first oil holes i extending from 4 oil holes c which are among the 16 oil holes c formed inside the sleeve  41  and are disposed at 90-degree intervals, and communicating with the rollers  47  while penetrating through the sleeve  41  and the inner race  45  of the rear first bearing  14  in the radial direction; and other 4 first oil holes i extending from other four oil holes c which are among the 16 oil holes c and are disposed at 90-degree intervals, and communicating with the rollers  47  while penetrating through the sleeve  41  and the inner race  45  of the rear first bearing  14  in the radial direction. The former 4 first oil holes i and the latter 4 first oil holes i are separated away from one another in the axial direction, and are displaced from one another by 45 degrees in the peripheral direction. 
         [0034]    Returning to  FIGS. 2 and 5 , a second oil passage P 2  communicating with a downstream portion of the first oil reservoir R 1  is formed from: an annular passage d formed between the outer periphery of the low-pressure system shaft  15  and an inner periphery of the sleeve  41 ; 6 tooth-lacking portions e of the spline  42  with which to connect the low-pressure system shaft  15  and the sleeve  41  together. A second oil reservoir R 2  communicating with a downstream portion of the second oil passage P 2  is formed from: an annular passage f formed between the outer periphery of the low-pressure system shaft  15  and the inner periphery of the sleeve  41 ; 4 oil holes g penetrating through the sleeve  41  in the radial direction; and an annular passage h formed between the outer periphery of the sleeve  41  and an inner periphery of the high-pressure system shaft  16 . Furthermore, the annular passage h of the second oil reservoir R 2  is connected to the rollers  54  of the rear second bearing  18  via 8 second oil holes j in total which extend outward in the radial direction from the annular passage h. 
         [0035]    As shown in  FIG. 4 , the second oil holes j include: 4 second oil holes j disposed at 90-degree intervals, and communicating with the rollers  54  while penetrating through the high-pressure system shaft  16  and the inner race  52  of the rear second bearing  18 ; and the other 4 second oil holes j disposed at 90-degree intervals, and communicating with the rollers  54  while penetrating through the high-pressure system shaft  16  and the inner race  52  of the rear second bearing  18 . The former 4 second oil holes j and the latter 4 second oil holes j are separated away from one another in the axial direction, and are displaced from one another by 45 degrees in the peripheral direction. 
         [0036]    Next, descriptions will be provided for an operation of the embodiment of the present invention including the foregoing configuration. 
         [0037]    Oil supplied from the oil jet  55  flows from the oil introduction passage  43   a  of the oil guide member  43  through the first oil passage P 1  formed from the oil holes a and the annular passage b so as to be supplied to the first oil reservoir R 1  formed from the oil holes c, and is supplied to the rear first bearing  14  through the 8 first oil holes i branching outward in the radial direction from the first oil reservoir R 1 , thereby lubricating surfaces of the rollers  47  which are in rolling contact with the inner race  45  and the outer race  46 . 
         [0038]    The rest of the oil in the other 8 oil holes c in the first oil reservoir R 1  flows further through the second oil passage P 2  formed from the annular passage d and the tooth lacking portions e of the spline  42  so as to be supplied to the second oil reservoir R 2  formed from the annular passage f, the oil holes g and the annular passage h, and is supplied to the rear second bearing  18  through the 8 second oil holes j branching outward in the radial direction from the second oil reservoir R 2 , thereby lubricating surfaces of the rollers  54  which are in rolling contact with the inner race  52  and the outer race  53 . 
         [0039]    After lubricating the rear first bearing  14  and the rear second bearing  18 , the oil is returned to an oil tank while flowing through passages indicated with arrows with broken lines in  FIG. 2 . 
         [0040]    Meanwhile, the rear first bearing  14  not only requires a smaller amount of oil, since the rear first bearing  14  is disposed between the low-pressure system shaft  15  and the inner casing  12  and the relative number of rotation between the low-pressure system shaft  15  and the inner casing  12  is small. But also, the rear first bearing  14  is easily supplied with the oil since the rear first bearing  14  is located near the oil jet  55 . On the other hand, the rear second bearing  18  not only requires a larger amount of oil, since the rear second bearing  18  is disposed between the low-pressure system shaft  15  and the high-pressure system shaft  16  and the relative number of rotation between the low-pressure system shaft  15  and the high-pressure system shaft  16  is large. But also, the rear second bearing  18  is not easily supplied with the oil since the rear second bearing  18  is located away from the oil jet  55 . 
         [0041]    In the embodiment, a total amount of oil to be supplied from the oil jet  55  is set at A+B+C, where: A denotes a required oil lower limit amount representing a minimum amount of oil needed to sufficiently lubricate the rear first bearing  14 ; B denotes a required oil lower limit amount representing a minimum amount of oil needed to sufficiently lubricate the rear second bearing  18 ; and C denotes a safety surplus oil amount representing a surplus amount of oil to be supplied to the rear second bearing  18  for the safety purpose. 
         [0042]    In addition, a hole diameter and the number of the first oil holes i communicating with the rear first bearing  14  are set such that an amount of oil to be supplied to the rear first bearing  14  is equal to the required oil lower limit amount A in the amount A+B+C of oil to be supplied from the oil jet  55 . For example, although the number of the first oil holes i is 8 in the embodiment, the hole diameter and the number of the first oil holes i are increased when the oil with the required oil lower limit amount A cannot be supplied to the rear first bearing  14 , or are decreased when the amount of oil to be supplied to the rear first bearing  14  exceeds the required oil lower limit amount A. 
         [0043]    When the oil with the required oil lower limit amount A is thus supplied to the rear first bearing  14 , oil with the sum of the required oil lower limit amount B and the safety surplus oil amount C is automatically supplied to the rear second bearing  18 . Since an oil supply passage from the oil jet  55  to the rear second bearing  18  is long, there may be a case where part of the oil leaks somewhere in the oil supply passage, and there may be a case where the amount of oil supplied to the rear first bearing  14  more or less differs from the required oil lower limit amount A. Since, however, the safety surplus oil amount C is added as an extra in anticipation of such cases, only adjustments to the hole diameter and the number of the first oil holes i, without needlessly increasing the amount of oil to be supplied from the oil jet  55 , makes it possible to supply a necessary and sufficient amount of oil to the rear second bearing  18  which is under severe lubricating conditions, and accordingly to preclude occurrence of insufficient lubrication. 
         [0044]    The foregoing descriptions have been provided for the embodiment of the present invention. Various design changes, however, can be made to the present invention within the scope not departing from the gist of the present invention. 
         [0045]    In the embodiment, for example, the oil from the oil jet  55  is supplied firstly to the rear first bearing  14 , and more oil than needed for the rear first bearing  14  is supplied to the rear second bearing  18 . However, the oil supply sequence may be reversed.