Patent Publication Number: US-2023133871-A1

Title: Aircraft turbine engine with an off-axis propeller

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to FR 2109787, filed Sep. 17, 2021, the disclosure of which is hereby expressly incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to an aircraft turbine engine comprising a turbine shaft and a propulsion propeller which have parallel but offset axes of rotation. 
     BACKGROUND 
     The technical background includes, in particular, the documents FR-A1-3 031 562, FR-A1-3 034 158, US-A1-2018/128183, US-A1-2021/270189 and FR-A1-3 026 389. 
     An aircraft turbine engine classically comprises a gas generator which comprises from upstream to downstream, in the direction of flow of the gases in operation, at least one compressor, an annular combustion chamber, and at least one turbine. The turbine comprises a shaft which rotates about an axis of rotation and drives a propeller located generally upstream of the gas generator. 
     The propeller may be ducted and called a fan, or it may be unducted. It is connected to a propeller shaft which has an axis of rotation parallel to the axis of the turbine. 
     The newer generations of dual flow turbine engine, in particular, those with high bypass ratios, comprise a mechanical reduction gear to drive the shaft of the propeller. Typically, the purpose of the reduction gear is to transform the so-called fast rotation speed for the shaft of the power turbine into a slower rotation speed for the shaft of the fan. 
     Such a reduction gear comprises a central pinion, called the sun gear, a ring gear and pinions called planet gears, which are engaged between the sun gear and the ring gear. The planet gears are held in place by a frame called a planet carrier. 
     There are several reduction gear architectures. In the prior art of the dual flow turbine engines, the reduction gears are of the planetary or epicyclic type. In other similar applications, there are so-called differential or “compound” architectures. 
     On a planetary reduction gear, the planet carrier is fixed and the ring gear consists of the output shaft of the device, which turns in the opposite direction to the sun gear. 
     On an epicyclic reduction gear, the ring gear is fixed and the planet carrier is the output shaft of the device which rotates in the same direction as the sun gear. 
     On a compound reduction gear, no element is fixed in rotation. The ring gear rotates in the opposite direction to the sun gear and the planet carrier. 
     To increase the bypass ratio of a turbine engine, it is known to increase the diameter of its propeller. However, the larger the diameter of the propeller, the bulkier the turbine engine is in the radial direction with respect to the axis of the turbine. 
       FIG.  1    shows a turbine engine  10  suspended under the wing  12  of an aircraft. The diameter D 1  of the propeller  14  may be limited by the ground clearance that must be maintained between the propeller  14  and the ground  16 , i.e., the safety distance H 1  between the propeller  14  and the ground  16 . This safety distance prevents impacts between the turbine engine  10  and the ground  16  during extreme maneuvers. 
     A solution to increase the diameter D 1  of the propeller  14  while maintaining sufficient ground clearance would be to increase the height H 2  of the landing gear  18 . However, this solution would not be satisfactory as it would have too great an impact on the weight of the landing gear  18  and on the aircraft. 
     Another solution would be to mount the turbine engine  10  elsewhere than under the wing  12 , but this solution would be complex and costly in particular because it would have a significant impact on the weight and structure of the aircraft. 
     The ideal solution to this problem is therefore to offset the propeller  14  from the turbine  20 . The propeller  14  is driven by a shaft which then has an axis of rotation  22  parallel to and at a distance from the axis of rotation  24  of the shaft of the turbine  20 . It is then possible to position the axis  22  of the propeller  14  vertically above the axis  24  of the turbine so that the increase in the diameter D 1  of the propeller  14  is compensated for by an increase in the center distance R between the propeller and turbine shafts. 
     In the present technique shown in  FIG.  2   , a power transmission system  26  is interposed axially between the shaft  28  of the turbine  20  and the reduction gear  32  to allow this misalignment between the axes  22 ,  24 . This transmission system  26  comprises meshed pinions  34 , for example beveled. The disadvantage of this solution is that it significantly impacts the length and therefore the axial bulk of the turbine engine  10 . Another potential disadvantage is that it does not allow the mechanical moments that are applied to the various meshings of the reduction gear and transmission system  26  to be managed effectively during operation. 
     The present disclosure provides an improvement which provides a simple, effective and economical solution to at least some of the above problems. 
     SUMMARY 
     The disclosure relates to an aircraft turbine engine, comprising: 
     a turbine shaft having a first axis of rotation 
     a propulsion propeller connected to a propeller shaft having a second axis of rotation parallel to and spaced from the first axis, and 
     a mechanical reduction gear coupled to the turbine shaft and configured to drive in rotation the propeller shaft, the reduction gear comprising a sun gear, a ring gear and at least two planet gears meshed with the sun gear and the ring gear, 
     characterized in that 
     the turbine shaft is connected to the sun gear, 
     the propeller shaft is connected to the ring gear, which comprises an internal toothing, 
     each of the planet gears comprises a first external toothing which is located outside the ring gear and which is meshed with an external toothing of the sun gear, and a second external toothing which is located inside the ring gear and which is meshed with the internal toothing of the ring gear. 
     The present disclosure thus proposes to integrate the property of misalignment between the turbine and the propeller into the reduction gear, thus avoiding the need to combine a reduction gear and a power transmission system for misalignment. The use of a reduction ring gear with internal toothing is particularly advantageous because the internal space of the ring gear can be occupied at least in part by the planet gears meshed with this ring gear, as well as by one or more equipment for example. 
     The turbine engine according to the disclosure may comprise one or more of the following features, taken in isolation from each other, or in combination with each other: 
     the sun gear and planet gears are located below a horizontal plane passing through the second axis, 
     the turbine engine further comprises an equipment comprising a shaft carrying a pinion, this pinion being meshed with the toothing of the ring gear and located above the horizontal plane, 
     the first toothing of each planet gear is directly meshed with the external toothing of the sun gear, 
     the first toothing of each planet gear is meshed via at least one pinion with the toothing of the sun gear, 
     the planet gears are evenly distributed around the second axis, 
     the toothing of the sun gear is meshed with the planet gears via a single pinion which is aligned with the second axis, 
     the toothing of the sun gear is meshed with the planet gears via identical K pinions, K being the number of planet gears and each of the pinions being mounted between the sun gear and one of the planet gears, 
     the pinions are non-regularly distributed around the second axis, 
     the toothing of the sun gear are engaged with the planet gears by means of K pinions, at least two of which are different, K being the number of planet gears and each of the pinions being mounted between the sun gear and one of the planet gears, 
     the pinions are evenly distributed about the second axis, 
     the toothing of the sun gear and the first toothing of each planet gear are each double-stage and each comprise two annular rows of teeth located at an axial distance from each other, 
     the number of planet gears is between 2 and 5, and is preferably 2 or 3, 
     the number of pinions is at least 1, 
     the diameter of the ring gear, and in particular of its teeth, is greater than 2 or even 2.5 times the maximum diameter of the planet gears. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of the disclosed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG.  1    is a schematic axial sectional view of a turbine engine and landing gear attached under the wing of an aircraft; 
         FIG.  2    is a very schematic axial cross-sectional view of an aircraft turbine engine with the propeller offset from the turbine; 
         FIG.  3    is a very schematic axial sectional view of a reduction gear for a turbine engine with an off-axis propeller according to the disclosure; 
         FIG.  4    is a schematic perspective view of the reduction gear of  FIG.  3   ; 
         FIG.  5    is a view similar to that of  FIG.  3    and illustrating an alternative embodiment of the reduction gear; 
         FIG.  6    is a view similar to that of  FIG.  3    and illustrating another alternative embodiment of the reduction gear; 
         FIG.  7    is a view similar to that of  FIG.  4    and illustrating another alternative embodiment of the reduction gear; 
         FIG.  8    is a view similar to that of  FIG.  4    and illustrating another alternative embodiment of the reduction gear; 
         FIG.  9    is a view similar to that of  FIG.  4    and illustrating a further alternative embodiment of the reduction gear. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth above in connection with the appended drawings, where like numerals reference like elements, are intended as a description of various embodiments of the present disclosure and are not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Similarly, any steps described herein may be interchangeable with other steps, or combinations of steps, in order to achieve the same or substantially similar result. 
     Generally speaking, a turbine engine  10  comprises a propeller  14  and a gas generator which comprises from upstream to downstream at least one compressor  36 , an annular combustion chamber  38 , and at least one turbine  40 . 
     In the case of  FIG.  2   , the gas generator comprises a high-pressure compressor  36  and a high-pressure turbine  40 , the rotors of which are connected to each other by a high-pressure shaft (not shown). This shaft and the rotors of the compressor  36  and the turbine  40  form a high-pressure body. The gas generator also comprises a low-pressure turbine  20  located downstream of the high-pressure casing, the rotor of which is connected to the shaft  28 . This shaft  28  passes through the high-pressure casing and its upstream end is coupled to the shaft  42  of the propeller  14  by a reduction gear in accordance with the disclosure. 
       FIGS.  3  and  4    illustrate a first embodiment of the mechanical reduction gear  44 . 
     The reduction gear  44  comprises a sun gear  46 , a ring gear  48  and at least two planet gears  50  meshing with the sun gear  46  and the ring gear  48 . The planet gears  50  are carried by a planet carrier (not shown) which is fixed and forms part of a stator of the turbine engine  10 . Each of the planet gears  50  has an axis of rotation parallel to the axes  22 ,  24 . 
     The ring gear  48  has the particularity of comprising an internal toothing  48   a,  i.e. it comprises a ring inside which the toothing  48   a  is located. The ring gear  48  and its toothing  48   a  extend substantially in a first transverse plane P 2 , perpendicular to the axis  24  of the turbine. 
     The ring gear  48  is connected to the drive shaft  42  of the propeller  14 , which has an axis of rotation  22  parallel to the axis  24  and at a distance from this axis  24 . 
     The sun gear  46  comprises an external toothing  46   a  which extends substantially in a second transverse plane P 1  parallel to the plane P 2 . 
     The planet gears  50  are two in number in the example shown. Each of the planet gears comprises a first external toothing  50   a  meshed with the toothing  46   a  of the sun gear  46  and located substantially in the plane P 1 , and a second external toothing  50   b  meshed with the toothing  48   a  of the ring gear  48  and located substantially in the plane P 2 . It is therefore understood that the first toothings  50   a  of the planet gears  50  are located outside the ring gear  48  and that the second toothings  50   b  of the planet gears  50  are housed inside the ring gear  48 . The planet gears  50  are partly engaged in the ring gear  48 . 
       FIGS.  3  and  4    show that the diameters of the toothing  46   a,    50   a,    50   b  of the sun gear  46  and of the planet gears  50  are significantly smaller than the diameter of the ring gear  48  and its toothing  48   a.    
     In some embodiments, the diameter of the ring gear  48  and in particular of its toothing  48   a  is greater than 2 or 2.5 times the maximum diameter of the planet gears  50 . 
     The toothings  46   a,    50   a,    50   b  of the sun gear  46  and the planet gears  50  may be straight or herringbone. The use of herringbone toothing allows to limit the axial length of the reduction gear  44 , which allows to optimize the size of the turbine engine  10 . 
     Ph is defined as a horizontal plane passing through the axis  22  of the propeller shaft  42 . This plane Ph intersects the ring gear  48  in two halves, upper and lower respectively. The figures show that the sun gear  46  and the planet gears  50  are arranged under this plane Ph and are therefore located in the lower part or half of the ring gear  48 . The sun gear  46  is here arranged between the planet gears  50  and slightly above them. These planet gears  50  are identical here. 
     The upper part or half of the ring gear  48  and in particular its inner space, is therefore left free. 
       FIG.  5    illustrates an alternative embodiment of the reduction gear  44 , which is further associated with an equipment  52  (torque sensor, rotating oil transfer, de-icing, etc.). 
     This equipment  52  comprises a shaft  54  equipped with a pinion  56 . The shaft  54  extends parallel to the axes  22 ,  44  and the pinion  56  is engaged in the ring gear  48  and meshed with the toothing  48   a  of the ring gear  48 . 
     The equipment  52  is located above the plane Ph and is substantially diametrically opposed with respect to the sun gear  46  and the planet gears  50 , so that the equipment  52  loads the ring gear  48  in an area which is diametrically opposed to the area of loading of the ring gear  48  by the planet gears  50 . This limits the deformation of the ring gear  48  during operation. 
       FIG.  6    illustrates another variant of the reduction gear  44  in which the toothing  46   a  of the sun gear  46  and the first toothing  50   a  of the planet gears  50  are each double-stage. This optimizes the mechanical moments applied within the reduction gear  44  during operation. 
     In the previous embodiments, these toothings  46   a,    50   a  were single stage, i.e., they comprise a single annular row of teeth which is located in the transverse plane P 1 . 
     On the contrary, a double stage toothing comprises two annular rows of teeth which are respectively located in two distinct transverse planes, i.e., these rows of teeth are at an axial distance from each other. 
     The sun gear  46  thus comprises two annular rows of teeth  46   a   1 ,  46   a   2 , which are disposed respectively in two planes P 1  and P 1 ′ disposed respectively upstream and downstream of the plane P 2  of the ring gear  48 . 
     Each planet gear  50  also comprises two annular rows of teeth  50   a   1 ,  50   a   2 , which are arranged respectively in the planes P 1  and P 1 ′ and between which the second toothing  50   b  is located. The row of teeth  46   a   1  is meshed with the row of teeth  50   a   1 , and the row of teeth  46   a   2  is meshed with the row of teeth  50   a   2 . Each of the planet gears  50  is therefore symmetrical with respect to the plane P 2 , which enables to multiply the contacts between the toothings, to reduce the mechanical moments in operation, and thus to make a much more compact reduction gear  44 . 
     The rows of teeth  46   a   2  and  46   a   1  are advantageously herringbone or helical with opposite angles. This type of toothing allows to improve the contacts compared to a conventional “straight” toothing. The fact of distributing these herringbone and/or helical toothings symmetrically between the stages allows, as indicated, to symmetrize the forces and therefore to cancel/limit the mechanical moments. 
     The alternative embodiments of the reduction gear  44  shown in  FIGS.  7  to  9    differ from the previous embodiments in that the number and arrangement of the planet gears  50  are different. The number of planet gears  50  is equal to three and they are regularly distributed around the propeller axis  22 . 
     Another difference is that the sun gear  46  is meshed with the planet gears  50  via at least one pinion  58 . 
     In the case of  FIG.  7   , the number of pinions  58  is three. They are identical and are each arranged between the sun gear  46  and one of the planet gears  50 . The number of pinions  58  is therefore equal to the number of planet gears  50 . Each pinion  58  meshes with the toothing  46   a  of the sun gear  46  and with the first toothing  50   a  of the planet gear  50 . Each pinion  58  is therefore located in the plane P 1 . The pinions  58  are not arranged in a regular manner around the axis  22  of the propeller  14 . It is the fact that the intermediate pinions are not evenly spaced around the sun gear  46  that allows to have the above-mentioned center distance. 
     In the case of  FIG.  8   , the number of pinions  58  is equal to three. They are different in that one of the pinions  58  has a larger diameter than the other two pinions  58  (which are identical). The pinions  58  are each arranged between the sun gear  46  and one of the planet gears  50 . Each pinion  58  meshes with the toothing  46   a  of the sun gear  46  and with the first toothing  50   a  of the planet gear  50 . Each pinion  58  is therefore located in the plane P 1 . The pinions  58  may be arranged in a regular manner around the axis  22  of the propeller  14 . It is the fact that the pinions  58  do not have the same diameters that allows to have the aforementioned center distance. 
     In the case of  FIG.  9   , the number of pinions  58  is equal to one. The pinion  58  is centered on the axis  22  of the propeller  14  and meshes with the first teeth  50   a  of all the planet gears  50 . The pinion  58  is therefore located in the plane P 1 . 
     The advantages of the disclosure are multiple and in particular: 
     a potential gain in mass compared to the configuration of  FIG.  2   , 
     a misalignment of the axes of the propeller and the turbine and a possibility of increasing the external diameter of the turbine engine, 
     the possibility of accommodating equipment in the free space inside the ring gear, etc.