Patent Publication Number: US-2017370288-A1

Title: Oil distribution system and turbomachine with an oil distribution system

Description:
This application claims priority to German Patent Application DE102016111855.9 filed Jun. 28, 2016, the entirety of which is incorporated by reference herein. 
     This invention relates to an oil distribution system in accordance with the features of Claim  1  and to a turbomachine having an oil distribution system in accordance with the features of Claim  12 . 
     In turbomachines, in particular aircraft engines, oil is used for example to lubricate components, to cool components, to seal off rotating components and/or to prevent corrosion in or on gearboxes and bearings. Distribution devices distribute the oil to the respective consumers, for example gears, splines or rolling bearings. For planetary gearboxes, an oil distribution system is known for example from EP 1 767 814 B1 or the article by Krug et al., “Experimental investigation into the efficiency of an aero engine oil jet supply system”, in Proceedings of the ASME Turbo Expo 2014, Jun. 16-20, 2014, Düsseldorf. 
     The object is to provide efficient and dependable oil distribution systems. 
     Solution is provided by an oil distribution system in accordance with the features of Claim  1 . 
     To do so, an oil distribution system for a casing having at least one component to be supplied with oil is used in the interior of the casing, where the oil can be fed into the interior of the casing by at least one distribution device and where during operation the oil is conveyed by a centrifugal force to the at least one component to be supplied. At least one seal, in particular a contact seal or labyrinth seal, is used to seal off the casing from the environment, with the at least one seal being designed and/or arranged in the oil distribution system such that during operation it releases, due to the centrifugal force, at least one sealing gap for pressure equalization to provide a connection between the interior of the casing and the environment. 
     In one embodiment, the at least one component to be supplied with oil is a bearing, a plain bearing, a rolling bearing, a gear and/or an oil seal. 
     In a further embodiment, the at least one seal is arranged on a non-rotating component and the sealing gap is formed towards to a rotating component during operation. Alternatively, the at least one seal is arranged on a rotating component and the sealing gap is formed towards to a non-rotating component during operation. Depending on the geometrical arrangement, the seal can in this way release the sealing gap due to the centrifugal force effective during operation. 
     In one embodiment, the distribution device for oil is surrounded radially on the inside and/or the outside by a circumferentially arranged surrounding element forming the sealing gap in each case in interaction with the at least one seal. The surrounding element can, for example, be used as an oil guide element of the oil duct. 
     In a further embodiment, the at least one distribution device for the oil has a nozzle or an opening, where the distribution device sprays oil in particular in the axial, in the radial, in an inclined direction between the axial and radial directions or in the tangential direction. In the case of spraying in the tangential direction, the oil can already be sprayed at an appropriate speed onto a rotating component. 
     Furthermore, in another embodiment the oil is conveyed via a collecting device, in particular a groove and/or a distribution device, to the at least one component to be supplied with oil. This allows the oil to be supplied also to areas (e.g. areas that are offset in the axial direction) that cannot be reached at all or only with difficulty using solely the centrifugal force, which is only effective radially. 
     In a further embodiment, the casing is a gearbox casing, in particular for an epicyclic gearbox, a planetary gearbox, a power gearbox for a turbofan engine or a bearing casing. An oil supply inside these casings is particularly relevant. 
     In a further embodiment, the at least one seal is designed as a radial seal or radial shaft seal. These types of seals can be produced inexpensively. 
     In one embodiment, the oil distribution system can also have a self-adjusting oil supply for at least one component to be supplied with oil. In operation, a self-adjusting oil supply can be achieved by the opening of the sealing gap, while sealing off from the environment is assured due to the at least one seal in the stationary state. 
     Solution is provided by an aircraft engine, in particular a turbofan engine, in accordance with the features of Claim  12 . 
    
    
     
       The invention is explained in connection with the exemplary embodiments shown in the figures. Here, 
         FIG. 1  shows a schematic representation of an aircraft engine in turbofan design, having a planetary gearbox as a power gearbox, 
         FIG. 2  shows a schematic view of an oil distribution system known from the state of the art, 
         FIG. 3  shows a first embodiment of an oil distribution system having a contact seal that permits pressure equalization under the effect of a centrifugal force, 
         FIG. 3A  shows a detail of the sealing gap of the embodiment in accordance with  FIG. 3 , 
         FIG. 3B  shows a detail of an alternative embodiment to  FIG. 3A , 
         FIG. 4  shows a second embodiment of an oil distribution system having a contact seal that permits pressure equalization under the effect of a centrifugal force, 
         FIG. 5  shows a further embodiment of an oil distribution system having a contact seal that permits pressure equalization under the effect of a centrifugal force, 
         FIGS. 6A , B show a schematic representation of the setting of the oil level. 
     
    
    
     Before a detailed explanation of embodiments of the oil distribution system is made, firstly an aircraft engine  200  known per se in turbofan design with oil-consuming components, in this case a power gearbox  201  and a ball bearing  101  (see  FIG. 2 ) of a shaft bearing  300 , is shown as an example in connection with  FIG. 1 . 
     The aircraft engine  200  has here a rotational axis  210 . Viewed in the main flow direction, the aircraft engine  200  has an air inlet  220 , a fan stage  230 , which can here be regarded as part of a low-pressure compressor  240  located behind it, a high-pressure compressor  250 , a combustion chamber  260 , a high-pressure turbine  270 , a low-pressure turbine  280  and an outlet nozzle  290 . A nacelle  291  surrounds the interior of the aircraft engine  200  and defines the air inlet  220 . 
     The aircraft engine  200  operates in a manner known per se, where the air entering the air inlet  210  is accelerated by the fan stage  230 , with two airflows being generated. A first airflow passes into the low-pressure compressor  240  inside a core engine  292 . This airflow is then further compressed by the high-pressure compressor  250  and routed into the combustion chamber  260  for combustion. The resultant hot combustion gases are relieved in the high-pressure turbine  270  and the low-pressure turbine  280 , with said gases driving the fan stage  230 , the low-pressure compressor  240  and the high-pressure compressor  250  via a corresponding shaft system and finally exiting through the outlet nozzle  290 . 
     A second airflow flows through a bypass duct  293  to generate most of the thrust. 
     With the turbofan design, the speed of the drive of the fan stage  230  is decoupled by the power gearbox  201  from the low-pressure turbine  280  providing the drive. The power gearbox  201  is a reduction gear using which the speed of the fan stage  230  is reduced relative to the speed of the low-pressure turbine  280 . This allows the low-pressure turbine  280  to be operated more efficiently at higher speeds. The fan stage  230  can thus provide a higher thrust. 
     The power gearbox  201  can be designed as an epicyclic gearbox, here for example as a planetary gearbox, that has a considerable requirement for oil O and is surrounded by a casing  100 .  FIG. 1  shows schematically a sun gear  202  and planetary gears  203  of the power gearbox  201 . 
     A further component that must be supplied with oil O is a ball bearing  101  in a shaft bearing  300  with a casing  100  (see  FIG. 2 ). 
     In other embodiments, not shown here, the aircraft engine  200  can have a different design, e.g. with a different number of shafts being used. Also, it is not essential for the aircraft engine  200  to be of the turbofan type. 
     The oil supply to a ball bearing  101  inside a shaft bearing  300  with an oil supply system known per se is shown in  FIG. 2 , where for reasons of greater clarity the bearing casing  100  is not shown. Inside the shaft bearing, a ball bearing  101  is the component to be supplied with oil O. 
     The oil O is here sprayed in the axial direction from a distribution device  1 , in this case a nozzle, into a collecting device  102 . In alternative embodiments, the oil can also be sprayed in the radial direction (see  FIG. 5 ) or at an angle (i.e. tangentially or at an angle between the radial and axial directions). 
       FIG. 2  shows only one distribution device. Further distribution devices are arranged in the circumferential direction at defined intervals. In alternative embodiments, apertures or other spraying means can also be used as the distribution device  1 . 
     The collecting device  102  is in this case a kind of circumferential groove and rotating groove. Due to the rotation, the centrifugal force FZ acts on the oil, ensuring that the oil O is forced radially outwards (i.e. upwards in  FIG. 2 ). The oil O is here on the one hand forced directly into the ball bearing  101 . On the other hand, the oil O is conveyed by distribution devices  103 , in this case a duct, to other components that also have to be supplied with oil O. 
     With an application of this type, a self-adjusting oil supply can be used that affords general advantages. 
     Inside the rotating collecting device  102  and the possibly following supply lines  103 , a supply pressure is built up—as described—due to the centrifugal force FZ. 
     A system not sealed off from the environment U—as shown in  FIG. 2 —permits the option of having different liquid levels inside the rotating system. The supply pressure of the component  101  to be supplied with oil in the rotating system is dependent on the liquid level ΔR in  FIGS. 6A  (high level corresponding to high pressure) and  6 B (low level corresponding to low pressure). The oil supply, i.e. the oil quantity sprayed-in, is as a rule constant or assumes a predetermined value. 
     If the counter-pressure, i.e. the prevailing pressure in the oil consumer and the pressure loss as far as the consumer, is within an acceptable range, adjustment is possible by the liquid level in the rotating supply lines. 
     With a rising oil volume flow (i.e. rising consumption), the supply pressure rises and more oil is forced into the bearing; the level falls (see  FIG. 6B ). 
     Conversely, the supply pressure falls as the volume flow falls, and the oil system is prevented from running empty by a suitably set counter-pressure, so that a reduced but continuous oil supply is achieved. 
     A system like this has however the limitation that the supply depends on centrifugal force and hence on speed. An oil supply to the consumers under pressure at standstill is thus impossible. 
       FIGS. 3 and 4  schematically show embodiments of oil distribution systems in connection with a power gearbox  201 . The sections illustrated each show an oil supply for a planetary gearbox. 
     The single-hatched components in  FIG. 3  and  FIG. 4  are rotating components. The cross-hatched components in  FIG. 3  and  FIG. 4  are components that are stationary relative to the rotating components. 
     For sealing off the interior of the casing  100  from the environment, contact seals  10  are used here in each case, whose sealing effect is however only effective below a certain speed or at standstill. Hence, an unwelcome leakage of oil O during standstill is not possible. 
     Generally speaking, other seals, in particular labyrinth seals, can be used in this and also in other embodiments. 
     The pressure of the oil O adjusts during a rotation (e.g. between 50 and 1000 rpm) due to a balance between the centrifugal force acting on the oil O and the static pressure of the liquid column of the oil O (density approx. 950 kg/m3) under the counteracting force of gravity. 
     With a sufficiently high rotation, i.e. a sufficiently high centrifugal force FZ, the oil supply systems have a self-adjusting effect, as described in connection with  FIGS. 2, 6   a ,  6   b.    
     To do so, at least one contact seal  10  is used for sealing off the casing  100  from the environment U, and is designed and/or arranged in the oil distribution system such that during operation it creates a connection between the interior of the casing  100  and the environment U for pressure equalization due to the centrifugal force FZ. 
       FIGS. 3 and 4  each show an oil supply system in which a distribution device  1  sprays in oil in the axial direction (i.e. to the left in  FIGS. 3 and 4 ). The oil O is supplied via a distribution device  103  into the interior of the casing  100  and hence into the power gearbox  201 . 
     The distribution device  1  is arranged here in each case in a circumferentially arranged rotating surrounding element  105 ,  106 , so that oil injection is screened off radially on the inside and outside. These surrounding elements  105 ,  106  are annular elements extending in the axial direction. 
     In  FIG. 3 , a contact seal  10  in the form of a radial shaft seal is arranged on the casing of the distribution device  1  opposite the radially inner surrounding element  105 . The casing of the distribution device  1  is stationary relative to the contact seal  10 . In the stationary state (e.g. at standstill), the contact seal  10  is in contact with the inner surrounding element  105 , as shown in  FIG. 3 . During rotation, the inner surrounding element  105  is moved outwards due to the centrifugal force FZ, while the contact seal  10  is stationary. Due to the radial movement of the inner surrounding element  105  relative to the contact seal  10 , a sealing gap D is released, permitting pressure equalization between the environment U and the interior of the casing  100 . 
     It is thus possible during operation (i.e. in rotation) to have a self-adjusting oil supply again. 
     In a similar way, a contact seal  10  is arranged on the outer side of the casing of the distribution device  1  and in the stationary state (i.e. without rotation) presses in a sealing manner against the inside of the radially outer surrounding element  106 . 
     In rotation, the radially outer surrounding element  106  is pulled outwards by the centrifugal force FZ and thus selectively releases a gap for pressure equalization between the environment U and the interior of the casing  100 . The sealing gap D of the contact seal  10  opens under rotation. 
       FIG. 3A  shows in detail the contact seal  10  for the radially inner surrounding element  105 , i.e. for the event that the centrifugal force FZ pulls the rotating surrounding element  105  outwards. This opens the sealing gap D. A similar situation results at the contact seal  10  for the radially outer surrounding element  106 . 
       FIG. 3B  shows a variation of the embodiment according to  FIG. 3A . Here too, the surrounding element  105  is pulled outwards due to the centrifugal force FZ. However, the contact seal  10  is arranged not on the distribution device  1 , but on the rotating surrounding element  105 . 
       FIG. 4  shows an embodiment in which the arrangement of the stationary and rotating parts is of somewhat different design. Both surrounding elements  105 ,  106  are designed rotating. One of the contact seals  10  is arranged on the radially outer surrounding element  106 , such that under the effect of the centrifugal force FZ it lifts off from the casing of the distribution device  1  and releases the sealing gap D. The other contact seal  10  is arranged on the non-rotating casing of the distribution device  1 , such that at this point there is no opening of the sealing gap D during rotation. 
     The embodiments according to  FIGS. 3 and 4  therefore each feature a combination of a dynamic oil seal and a contact seal. 
     In an alternative embodiment, it is also possible to use only one contact seal  10 , which is arranged such that the sealing gap D is opened during rotation. In the exemplary embodiments according to  FIGS. 3, 3A and 4 , the contact seal  10  does not rotate. It is in principle also possible for the contact seal  10  to co-rotate (see  FIG. 3B ), e.g. it is arranged on the respective outer part such that the seal is lifted off its sealing surface due to the centrifugal force FZ. 
       FIG. 5  shows an alternative embodiment in which—unlike in the embodiments of  FIGS. 3 and 4 —the oil O is sprayed out of the distribution device  1  in the radial direction. Rotating surrounding elements  107 ,  108  are used here to retain the oil O such that it can be guided in the direction of the distribution device  103 . The surrounding elements  107 ,  108  are arranged here at an angle of 90° and are also used for deflecting the oil O, which is sprayed here in the radial direction. To do so, one surrounding element  107  is arranged in the radial direction, the other surrounding element  108  in the axial direction. 
     The previous embodiments related to the oil supply of a gearbox. Alternatively, embodiments of the oil distribution system can also be used for the supply of bearings. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Distribution device, nozzle 
           10  Seal, contact seal 
           100  Casing 
           101  Component to be supplied with oil 
           102  Collecting device for oil 
           103  Distribution device for oil 
           104  Guiding surface, impingement surface 
           105  Radially inner surrounding element of distribution device 
           106  Radially outer surrounding element of distribution device 
           107  Axially aligned surrounding element of distribution device 
           108  Radially aligned surrounding element of distribution device 
           200  Aircraft engine 
           201  Power gearbox 
           202  Sun gear 
           203  Planetary gear 
           210  Rotational axis 
           220  Air inlet 
           230  Fan stage 
           240  Low-pressure compressor 
           250  High-pressure compressor 
           260  Combustion chamber 
           270  High-pressure turbine 
           280  Low-pressure turbine 
           290  Outlet nozzle 
           291  Nacelle 
           292  Core engine 
           293  Bypass duct 
           300  Shaft bearing 
         D Sealing gap 
         F z  Centrifugal force 
         Oil 
         U Environment