Patent Publication Number: US-10309455-B2

Title: Squeeze film damper bearing device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-33476 filed Feb. 24, 2017 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a squeeze film damper bearing device having an inner race that is fitted around an outer periphery of a rotating shaft, an outer race that is supported on an inner periphery of a bearing retaining member via an annular space, a plurality of rolling bodies that are disposed between the inner race and the outer race, and an oil supply source that supplies oil to the annular space via an oil passage so as to form a squeeze film. 
     Description of the Related Art 
     A squeeze film damper bearing device for damping vibration of a rotating shaft, which rotates at high speed, of a gas turbine engine, etc. is known from for example Japanese Patent Application Laid-open No. 2003-83325. 
     When the rotational speed of the rotating shaft of the gas turbine engine approaches a predetermined rotational speed, the rotating shaft can sometimes resonate and enter a high vibration mode in which it vibrates strongly. In order to avoid this, conventionally the distance in the axial direction of a plurality of bearings supporting the rotating shaft is changed, or the shaft diameter (rigidity) of the rotating shaft is changed, thereby the rotational speed at which the rotating shaft resonates and enters a high vibration mode is changed from a regular rotational speed region to the low rotational speed side or the high rotational speed side. 
     However, changing the position in the axial direction of the bearing supporting the rotating shaft has the problem that the degree of freedom in design of the position of the bearing is degraded or the dimensions of the gas turbine engine increase, and changing the shaft diameter of the rotating shaft has the problem that the strength of the rotating shaft is degraded or the weight is increased. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in light of the above circumstances, and it is an object thereof to provide a squeeze film damper bearing device that can reliably prevent, with a simple structure, a rotating shaft supported thereby from entering a high vibration mode. 
     In order to achieve the object, according to a first aspect of the present invention, there is provided a squeeze film damper bearing device including an inner race that is fitted around an outer periphery of a rotating shaft, an outer race that is supported on an inner periphery of a bearing retaining member via an annular space, a plurality of rolling bodies that are disposed between the inner race and the outer race, and an oil supply source that supplies oil to the annular space via an oil passage so as to form a squeeze film, wherein the device further includes an open/close valve that opens and closes the oil passage, and when a rotational speed of the rotating shaft reaches a predetermined rotational speed, the open/close valve is controlled so as to change oil pressure of the squeeze film, thus changing vibration characteristics of the rotating shaft. 
     According to a second aspect of the present invention, there is provided a squeeze film damper bearing device including an inner race that is fitted around an outer periphery of a rotating shaft, an outer race that is supported on an inner periphery of a bearing retaining member via an annular space, a plurality of rolling bodies that are disposed between the inner race and the outer race, and an oil supply source that supplies oil to the annular space via an oil passage so as to form a squeeze film, wherein the device further includes oil temperature adjustor that adjusts a temperature of the oil, and when a rotational speed of the rotating shaft reaches a predetermined rotational speed, the temperature of the oil is adjusted by the oil temperature adjustor so as to change a viscosity of oil of the squeeze film, thus changing vibration characteristics of the rotating shaft. 
     In accordance with the first or second aspect, since the squeeze film damper bearing device includes the inner race fitted around the outer periphery of the rotating shaft, the outer race supported on the inner periphery of the bearing retaining member via the annular space, the plurality of rolling bodies disposed between the inner race and the outer race, and the oil supply source for supplying oil to the annular space via the oil passage so as to form a squeeze film, when the outer race is displaced relative to the inner periphery of the bearing retaining member in response to vibration of the rotating shaft, the squeeze film formed in the annular space sandwiched between the inner periphery of the bearing retaining member and the outer periphery of the outer race resists movement of the outer race, thus enabling the vibration of the rotating shaft to be damped. 
     There is a possibility that when the rotational speed of the rotating shaft approaches a predetermined rotational speed the rotating shaft will resonate and enter a high vibration mode, but in accordance with the first aspect of the present invention, since the open/close valve for opening and closing the oil passage is provided, and when the rotational speed of the rotating shaft reaches a predetermined rotational speed, the open/close valve is controlled so as to change the oil pressure of the squeeze film, thus changing the vibration characteristics of the rotating shaft, it is possible, by shifting the resonant frequency, to prevent the rotating shaft from entering a high vibration mode, thereby avoiding any degradation in the durability of the bearing. 
     There is a possibility that when the rotational speed of the rotating shaft approaches a predetermined rotational speed the rotating shaft will resonate and enter a high vibration mode, but in accordance with the second aspect of the present invention, since the oil temperature adjuster for adjusting the temperature of the oil is provided, and when the rotational speed of the rotating shaft reaches a predetermined rotational speed, the temperature of the oil is adjusted by the oil temperature adjuster so as to change the viscosity of oil of the squeeze film, thus changing the vibration characteristics of the rotating shaft, it is possible, by shifting the resonant frequency, to prevent the rotating shaft from entering a high vibration mode, thereby avoiding any degradation in the durability of the bearing. 
     Note that a low pressure system shaft  15  and a sleeve  41  of embodiments correspond to the rotating shaft of the present invention, balls  47  of the embodiments correspond to the rolling bodies of the present invention, an oil pump  55  of the embodiments corresponds to the oil supply source of the present invention, and an oil heater  60  of the embodiments corresponds to the oil temperature adjustor of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiments which will be provided below while referring to the attached drawings. 
         FIG. 1  is a diagram showing the overall structure of a gas turbine engine. (first embodiment) 
         FIG. 2  is an enlarged view of part  2  in  FIG. 1 . (first embodiment) 
         FIG. 3  is a view corresponding to  FIG. 2 . (second embodiment) 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention is explained below with reference to  FIGS. 1 and 2 . 
     As shown in  FIG. 1 , a gas turbine engine for an aircraft to which the present invention is applied includes an outer casing  11  and an inner casing  12 , and a front part and a rear part of a low pressure system shaft  15  are rotatably supported in the interior of the inner casing  12  via a front first bearing  13  and a rear first bearing  14  respectively. A tubular high pressure system shaft  16  is relatively rotatably fitted around the outer periphery of an intermediate part in the axial direction of the low pressure system shaft  15 , a front part of the high pressure system shaft  16  is rotatably supported on the inner casing  12  via a front second bearing  17 , and a rear part of the high pressure system shaft  16  is relatively rotatably supported on the low pressure system shaft  15  via a rear second bearing  18 . 
     A front fan  19  is fixed to the front end of the low pressure system shaft  15 , blade ends of the front fan  19  facing an inner face of the outer casing  11 . Part of the air drawn or sucked in by the front fan  19  passes through stator vanes  20  disposed between the outer casing  11  and the inner casing  12 , part thereof then passes through an annular bypass duct  21  formed between the outer casing  11  and the inner casing  12  and is jetted rearward, and another part thereof is supplied to an axial type low pressure compressor  22  and a centrifugal type high pressure compressor  23  disposed in the interior of the inner casing  12 . 
     The low pressure compressor  22  includes stator vanes  24  fixed to the interior of the inner casing  12  and a low pressure compressor wheel  25  equipped with compressor blades on the outer periphery and fixed to the low pressure system shaft  15 . The high pressure compressor  23  includes stator vanes  26  fixed to the interior of the inner casing  12  and a high pressure compressor wheel  27  equipped with compressor blades on the outer periphery and fixed to the high pressure system shaft  16 . 
     A reverse flow combustion chamber  29  is disposed to the rear of a diffuser  28  connected to the outer periphery of the high pressure compressor wheel  27 , and fuel is injected into the interior of the reverse flow combustion chamber  29  from a fuel injection nozzle  30 . Fuel and air are mixed in the interior of the reverse flow combustion chamber  29  and undergo combustion, and the combustion gas thus generated is supplied to a high pressure turbine  31  and a low pressure turbine  32 . 
     The high pressure turbine  31  includes nozzle guide vanes  33  fixed to the interior of the inner casing  12  and a high pressure turbine wheel  34  equipped with turbine blades on the outer periphery and fixed to the high pressure system shaft  16 . The low pressure turbine  32  includes nozzle guide vanes  35  fixed to the interior of the inner casing  12  and a low pressure turbine wheel  36  equipped with turbine blades on the outer periphery and fixed to the low pressure system shaft  15 . 
     Therefore, when the high pressure system shaft  16  is driven with a starter motor (not shown), air that has been drawn or sucked in by the high pressure compressor wheel  27  is supplied to the reverse flow combustion chamber  29 , mixed with fuel and undergoes combustion, and the combustion gas thus generated drives the high pressure turbine wheel  34  and the low pressure turbine wheel  36 . As a result, the low pressure system shaft  15  and the high pressure system shaft  16  rotate, and the front fan  19 , the low pressure compressor wheel  25 , and the high pressure compressor wheel  27  compress air and supply it to the reverse flow combustion chamber  29 , thus enabling the gas turbine engine to continue to run even when the starter motor is stopped. 
     While the gas turbine engine is running, part of the air drawn or sucked in by the front fan  19  passes through the bypass duct  21  and is jetted rearward thus generating the main thrust, particularly when flying at low speed. The remaining part of the air drawn or sucked in by the front fan  19  is supplied to the reverse flow combustion chamber  29 , mixed with fuel, and undergoes combustion, and it drives the low pressure system shaft  15  and the high pressure system shaft  16  and is then jetted rearward, thus generating thrust. 
     The structure around the rear first bearing  14  is now explained by reference to  FIG. 2 . 
     A sleeve  41  for supporting the low pressure turbine wheel  36  is fitted around the outer periphery of the low pressure system shaft  15  by a spline fitting  42 . The sleeve  41  is fastened to the low pressure system shaft  15  by screwing a first nut member  43  around the outer periphery of a shaft end of the low pressure system shaft  15  so as to push the sleeve  41  leftward in  FIG. 2 , thereby pressing a step portion  41   a  formed on the inner periphery of the sleeve  41  against a step portion  15   a  formed on the outer periphery of the low pressure system shaft  15 . 
     The rear first bearing  14  includes an inner race  45  fitted around the outer periphery of the sleeve  41 , an outer race  46  fitted into the inner periphery of a bearing retaining member  44  provided on the inner casing  12 , a plurality of balls  47  disposed between the inner race  45  and the outer race  46 , and a retainer  48  retaining the balls  47  at predetermined intervals in the peripheral direction. The bearing retaining member  44  and the outer race  46  are fastened to the inner casing  12  by bolts  49 , and the inner race  45  is fastened by being urged leftward in  FIG. 2  by a second nut member  50  screwed around the outer periphery of an end part of the sleeve  41 , thereby being pressed against a step portion  41   b  formed on the outer periphery of the sleeve  41 . 
     The outer race  46  includes a plurality of slit-shaped cutouts  46   b  extending in the axial direction and a plurality of rod-shaped spring portions  46   c  sandwiched between the plurality of cutouts  46   b  and extending in the axial direction, and a main body part of the outer race  46  retaining the balls  47  is therefore floatingly supported so as to be capable of moving relative to the inner casing  12 . 
     The direction in which the first nut member  43  is screwed and the direction in which the second nut member  50  is screwed are set so as to be opposite to each other. That is, when the first nut member  43  is a right-hand screw, the second nut member  50  is a left-hand screw, and when the first nut member  43  is a left-hand screw, the second nut member  50  is a right-hand screw. A plurality of first groove portions  43   a  opening rightward in the axial direction in  FIG. 2  are formed in the outer periphery of an end part of the first nut member  43  at equal intervals in the peripheral direction, and a plurality of second groove portions  50   a  opening rightward in the axial direction in  FIG. 2  are formed in the outer periphery of the second nut member  50  at equal intervals in the peripheral direction. 
     An annular linking member  51  disposed between the first nut member  43  and the second nut member  50  includes two first projecting portions  51   a  that are disposed at intervals of 180° in the circumferential direction and can engage with the first groove portions  43   a  of the first nut member  43 , and three second projecting portions  51   b  that are disposed at intervals of 120° in the circumferential direction and can engage with the second groove portions  50   a  of the second nut member  50 . 
     A ring spring  52  that makes the linking member  51  latch with the second nut member  50  is one that is formed by winding a flat elastic metal plate with substantially two rotations into a ring shape, and an outer peripheral part thereof can engage with step portions  50   b  formed on the inner periphery of an end part of the second nut member  50 . 
     Since the directions in which the first nut member  43  and the second nut member  50  are screwed are opposite to each other, if the first nut member  43  attempts to rotate in a direction in which it is loosened, the rotation acts on the second nut member  50  via the linking member  51  so as to tighten it, and it is thus possible to prevent both the first nut member  43  and the second nut member  50  from becoming loosened. Conversely, if the second nut member  50  attempts to rotate in a direction in which it is loosened, since the rotation acts on the first nut member  43  via the linking member  51  so as to tighten it, it is possible to simultaneously prevent both the first nut member  43  and the second nut member  50  from becoming loosened. 
     The rear first bearing  14  supporting the rear part of the low pressure system shaft  15  forms a squeeze film damper bearing, and seal rings  53  are fitted into a pair of seal ring grooves  46   a  formed in the outer periphery of the outer race  46  thereof. The seal rings  53  expand radially outward due to self resilience and resiliently abut against the inner periphery of the bearing retaining member  44 , and an annular space  54  having a predetermined gap in the radial direction is defined between the outer periphery of the outer race  46 , the inner periphery of the bearing retaining member  44 , and the pair of seal rings  53 . Therefore, the outer race  46  can undergo relative movement within the range of the above gap in the radial direction relative to the bearing retaining member  44 , and in this process the seal rings  53  undergo elastic deformation within the seal ring grooves  46   a , thus maintaining a state of abutment against the inner periphery of the bearing retaining member  44 . 
     Oil sucked up from the oil tank  56  by the oil pump  55  is supplied to the annular space  54  via an oil passage  57  formed in the interior of the inner casing  12  and the bearing retaining member  44 . An open/close valve  58 , which preferably is a solenoid valve, is disposed in the oil passage  57  in the interior of the inner casing  12 ; when the open/close valve  58  closes, the oil passage  57  is blocked, and supply of oil from the oil pump  55  to the annular space  54  is cut off. 
     An electronic control unit U, which is a microcomputer, controls opening and closing of the open/close valve  58  based on the rotational speed of the low pressure system shaft  15 , that is, the rotational speed of the sleeve  41 , detected by rotational speed detector  59 . 
     The operation of the first embodiment of the present invention having the above arrangement is now explained. 
     When oil is supplied from the oil pump  55  to the annular space  54  via the inner casing  12  and the oil passage  57  of the bearing retaining member  44 , a squeeze film is formed from a thin film of oil in the annular space  54 . When the low pressure system shaft  15  vibrates in the radial direction while the gas turbine engine is running, the vibration is transmitted to the outer race  46  of the rear first bearing  14  having the inner race  45  supported on the sleeve  41  integrally fixed to the low pressure system shaft  15 . 
     In this process, since vibration in the radial direction of the outer race  46  of the rear first bearing  14  is allowed due to the spring portions  46   c  undergoing elastic deformation, the size of the gap in the radial direction of the annular space  54  increases and decreases according to the vibration in the radial direction of the outer race  46 , the outer race  46  is damped by a resistance force generated by flow and compression of viscous oil of the squeeze film within the annular space  54 , and this enables the vibration of the low pressure system shaft  15  to be suppressed. 
     When the squeeze film exhibits a damping effect, oil that has absorbed vibrational energy generates heat and its temperature increases, but oil whose temperature has increased is discharged successively via abutment clearances of the seal rings  53  and fresh oil is supplied from the oil pump  55 , thus maintaining the damping function of the squeeze film. 
     Within a regular rotational speed region of the low pressure system shaft  15  of the gas turbine engine, for example, in a predetermined high rotational speed region, the low pressure system shaft  15  can sometimes resonate and enter a high vibration mode in which it vibrates strongly. In this high vibration mode, since the low pressure system shaft  15  vibrates strongly, it becomes difficult to suppress the vibration with the regular damping force of the squeeze film. 
     However, in accordance with this embodiment, when the rotational speed of the low pressure system shaft  15  detected by the rotational speed detector  59  reaches a predetermined high rotational speed region, the electronic control unit U controls the open/close valve  58  disposed in the oil passage  57  between the oil pump  55  and the annular space  54  so as to close it, thus cutting off the supply of oil pressure to the squeeze film of the annular space  54 . This enables the characteristics of the squeeze film to be changed, and the resonant frequency of the low pressure system shaft  15  to be shifted, thus preventing the low pressure system shaft  15  from resonating and thereby avoiding any degradation in the durability of the rear first bearing  14  due to resonance. 
     As described above, in accordance with this embodiment, since the occurrence of a high vibration mode can be prevented without changing the position in the axial direction of the rear first bearing  14  supporting the sleeve  41  of the low pressure system shaft  15  and without changing the shaft diameter of the low pressure system shaft  15 , it is possible to avoid any decrease in the degree of freedom in design of the gas turbine engine and any increase in the dimensions and also to avoid any decrease in the strength of the rear first bearing  14  and any increase in the weight. 
     Second Embodiment 
     A second embodiment of the present invention is now explained with reference to  FIG. 3 . 
     In the second embodiment, instead of the open/close valve  58  of the first embodiment, an oil heater  60  for heating oil and increasing its temperature is provided. The electronic control unit U carries out feedback control of operation of the oil heater  60  such that, when the rotational speed of the low pressure system shaft  15  detected by the rotational speed detector  59  reaches a predetermined high rotational speed region, the oil heater  60  is operated so as to heat the oil and the oil temperature detected by the temperature detector  61  attains a predetermined temperature. 
     When the temperature of oil of the squeeze film of the annular space  54  is changed in this way, the viscosity of the oil is changed, the characteristics of the squeeze film change, and the resonant frequency of the low pressure system shaft  15  is shifted, thereby preventing the low pressure system shaft  15  from resonating. 
     Embodiments of the present invention are explained above, but the present invention may be modified in a variety of ways as long as the modifications do not depart from the gist of the present invention. 
     For example, the subject to which the present invention is applied is not limited to the rear first bearing  14  of the gas turbine engine of the embodiments, and it may be applied to another bearing of a gas turbine engine, and it is also possible to apply it to a bearing of any application other than a gas turbine engine. 
     Furthermore, the open/close valve  58  of the first embodiment opens and closes the oil passage  57 , but the open/close valve  58  may be one that narrows down the oil passage  57 . 
     Furthermore, the rear first bearing  14  of the embodiments is a ball bearing, but it may be another type of bearing such as a roller bearing or a needle bearing.