Planetary gearboxes for gas turbine engines

Abstract

An aircraft includes: first and second engines; one or more aircraft rotors associated with the first and second engines; a first epicyclic gearbox having: a) an output operatively connected to at least one of the one or more aircraft rotors, and b) an input defined by a sun gear of the first epicyclic gearbox; and a second epicyclic gearbox having: a) an output operatively connected to at least one of the one or more aircraft rotors, and b) an input defined by the sun gear of the second epicyclic gearbox. The output of the first epicyclic gearbox is defined by a carrier. The output of the second epicyclic gearbox is defined by its ring gear. A multi-engine aircraft and a method of operating a multi-engine aircraft are also described.

Description

Technical Field

[0001] The present disclosure relates generally to aircraft engines and, more particularly, to gearboxes for use in aircraft engines such as gas turbine engines. Background Art

[0002] A turboprop engine is a gas turbine engine coupled to a propeller via a reduction gearbox. One known type of reduction gearbox is a planetary gearbox. In contrast to a turbofan engine, where bypass airflow and core exhaust airflow are used to generate thrust, a turboprop engine drives a propeller to generate forward motion. However, the rotational speed of the turbine may be too high to be directly coupled to the propeller. Therefore, reduction gearboxes exist in the prior art for reducing the rotational speed of the propeller relative to the turbine. While prior art gearbox arrangements may be suitable for their intended purpose, improvements are always desirable in the aerospace industry. Summary of the Invention

[0003] In one aspect, an aircraft is provided, comprising: a first engine and a second engine; one or more aircraft rotors associated with the first engine and the second engine; a first epicyclic gearbox having: a) an output operably connected to at least one of the one or more aircraft rotors, and b) an input defined by a sun gear of the first epicyclic gearbox; and a second epicyclic gearbox having: a) an output operably connected to at least one of the one or more aircraft rotors, and b) an input defined by the sun gear of the second epicyclic gearbox; and wherein: the first engine is operably connected to the input of the first epicyclic gearbox; the second engine is operably connected to the input of the second epicyclic gearbox; each of the first and second epicyclic gearboxes has a gear carried by a bracket and a ring gear meshing with the gear, the output of the first epicyclic gearbox being defined by the bracket of the first epicyclic gearbox, and the output of the second epicyclic gearbox being defined by the ring gear of the second epicyclic gearbox.

[0004] The aircraft, engine and / or gearbox as defined above and herein may also comprise, in whole or in part and in any combination, one or more of the following features.

[0005] In some embodiments, the ring gear of the first epicyclic gearbox is prevented from rotating, and the bracket of the second epicyclic gearbox is prevented from rotating.

[0006] In some embodiments, each gear of the gears of the bracket of the second epicyclic gearbox includes: a large radius gear, which is meshed with the sun gear of the second epicyclic gearbox; a small radius gear, which is attached to the large radius gear and is meshed with the ring gear of the second epicyclic gearbox, the large radius gear, the small radius gear and the ring gear forming an interconnected set of three gears; one tooth of each gear in the interconnected set of three gears is aligned with one tooth of each of the other two gears in the interconnected set of three gears; each gear of the second epicyclic gearbox has a plurality of teeth; the number of teeth of all three gears in the interconnected set of three gears is one of an even number and an odd number; and the number of teeth of each of the sun gear and the ring gear of the second epicyclic gearbox can be divided by the number of teeth of the bracket of the second epicyclic gearbox.

[0007] In some embodiments, in each of the first and second epicyclic gearboxes, each gear of the support of the gearbox includes: a large radius gear meshed with the sun gear of the gearbox, a small radius gear attached to the large radius gear and meshed with the ring gear of the gearbox, and the teeth of the large radius gear, the small radius gear and the ring gear are shaped so that when rotating: a) the apex of each tooth of the large radius gear and the apex of the teeth of the small radius gear pass through the top dead center position at the same time, and b) when at the top dead center position, the apex of the teeth of the small radius gear is aligned with the valley of the space between the teeth of the ring gear, and the valley is now engaged by the teeth of the small radius gear.

[0008] In some embodiments, the output of the second epicyclic gearbox is operably connected to at least one of the one or more aircraft rotors via a rotor shaft assembly; and the ring gear of the second epicyclic gearbox has a radially inward facing surface and a radially outward facing surface, and: includes teeth on the radially inward facing surface and the radially outward facing surface, mates with a pinion of each of the gears of the carrier of the second epicyclic gearbox via the teeth on the radially inward facing surface, and is connected to the rotor shaft assembly via a spline connection including teeth on the radially outward facing surface.

[0009] In some embodiments, the rotor shaft assembly includes a ring gear coupling; and the ring gear coupling has teeth that mate with teeth on a radially outward facing surface of the ring gear of the second epicyclic gearbox and define a spline connection.

[0010] In some embodiments, the aircraft includes markings disposed on each large radius gear, each small radius gear, and each ring gear at respective positions corresponding to the top dead center position.

[0011] In some embodiments, the second epicyclic gearbox includes a housing; the ring gear coupling, the ring gear, the carrier and the sun gear of the second epicyclic gearbox are disposed within the housing; and the carrier of the second epicyclic gearbox is splined to the housing.

[0012] In some embodiments, the housing includes a rear portion and a front portion, the front portion is operably connected to the rear portion so as to be removable therefrom; and the rotor shaft assembly is connected to the front portion so as to be removable together with the front portion relative to the rear portion.

[0013] In some embodiments, when the first engine is operating, the first engine drives the sun gear of the first epicyclic gearbox in a given direction, and when the second engine is operating, the second engine drives the sun gear of the second epicyclic gearbox in a given direction.

[0014] On the other hand, a multi-engine aircraft having a plurality of aircraft rotors is provided, comprising: a first engine, the first engine being operably connected to an input of a first epicyclic gearbox, the input of the first epicyclic gearbox being defined by a sun gear of the first epicyclic gearbox, the first epicyclic gearbox having an output, the output being operably connected to a first aircraft rotor of the plurality of aircraft rotors; and a second engine, the first engine being operably connected to an input of a second epicyclic gearbox, the input of the second epicyclic gearbox being defined by a sun gear of the second epicyclic gearbox, the second epicyclic gearbox having an output, the output being operably connected to a second aircraft rotor of the plurality of aircraft rotors; and wherein each of the first and second epicyclic gearboxes has a gear carried by a bracket and a ring gear meshing with the gear of the bracket, the output of the first epicyclic gearbox being defined by the bracket of the first epicyclic gearbox, and the output of the second epicyclic gearbox being defined by the ring gear of the second epicyclic gearbox.

[0015] The aircraft, engine and / or gearbox as defined above and herein may also comprise, in whole or in part and in any combination, one or more of the following features.

[0016] In some embodiments, the rotation of the ring gear of the first epicyclic gearbox is statically or variably restricted, and the rotation of the carrier of the second epicyclic gearbox is statically or variably restricted.

[0017] In some embodiments, the rotation of the ring gear of the first epicyclic gearbox is statically restricted, and the rotation of the carrier of the second epicyclic gearbox is statically restricted.

[0018] On the other hand, a method of operating a multi-engine aircraft having a first gas turbine engine and a second gas turbine engine is provided, the method comprising: rotating a sun gear in a first epicyclic gearbox of the first gas turbine engine and rotating a sun gear in a second epicyclic gearbox of the second gas turbine engine, the sun gears being meshed with corresponding gears of the brackets of the first and second epicyclic gearboxes; rotating the bracket of the first epicyclic gearbox relative to the ring gear of the first epicyclic gearbox and transmitting the rotation of the bracket of the first epicyclic gearbox to the first rotor shaft of the aircraft; and rotating the ring gear of the second epicyclic gearbox relative to the bracket of the second epicyclic gearbox and transmitting the rotation of the ring gear of the second epicyclic gearbox to the second rotor shaft of the aircraft.

[0019] The method as defined above and herein may also comprise, in whole or in part and in any combination, one or more of the following features / steps.

[0020] In some embodiments, the method includes restricting rotation of at least one of: a ring gear of the first epicyclic gearbox; and a bracket of the second epicyclic gearbox.

[0021] In some embodiments, transferring the rotation of the ring gear of the second epicyclic gearbox to the second rotor shaft is performed via a radially outward facing surface of the ring gear of the second epicyclic gearbox.

[0022] In some embodiments, rotating the sun gear of the first epicyclic gearbox is in the same direction as rotating the sun gear of the second epicyclic gearbox.

[0023] In some embodiments, the method includes transferring rotation of the first rotor shaft to a first rotor of the aircraft, and transferring rotation of the second rotor shaft to a second rotor of the aircraft.

[0024] In some embodiments, the first rotor and the second rotor are first and second propellers, respectively.

[0025] In some embodiments, rotating the sun gear of the first epicyclic gearbox is performed via a turbine section of a first gas turbine engine of the aircraft; and rotating the sun gear of the second epicyclic gearbox is performed via a turbine section of a second gas turbine engine of the aircraft.

[0026] The foregoing are examples of possible embodiments of the present technology and are therefore non-limiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Reference is now made to the accompanying drawings, in which:

[0028] Figure 1 is a schematic cross-sectional view of a gas turbine engine;

[0029] Figure 2 is a cross-sectional view of a portion of a gas turbine engine showing a planetary gearbox;

[0030] Figure 3 yes Figure 2 3D view of the planetary gearbox;

[0031] Figure 4 yes Figure 3 A cross-sectional view of the planetary gearbox along line 4-4;

[0032] Figure 5 is a cross-sectional view of a planetary gearbox according to another embodiment;

[0033] Figure 6 yes Figure 5 3D view of a portion of a planetary gearbox;

[0034] Figure 7 yes Figure 5 A schematic front view of the gears of the gearbox showing the alignment of the gears with corresponding markings;

[0035] Figure 8 is having one of its engines operatively connected to it Figure 2 a gearbox and another one operatively connected to its engine Figure 5 A schematic diagram of a multi-engine aircraft having a gearbox; and

[0036] Figure 9 It is a method of operating a multi-engine aircraft. DETAILED DESCRIPTION

[0037] In at least some of the following figures and / or descriptions, some elements appear more than once (e.g., in a given embodiment, there may be two, three, etc. of a given component). Therefore, to maintain clarity of the drawings, only the first instance of each given element is labeled.

[0038] Figure 1A gas turbine engine 10 of the type preferably configured for subsonic flight and configured to drive a load 12 such as, but not limited to, a propeller or helicopter rotor is shown. Depending on the intended use, the engine 10 may be any suitable aircraft engine. For example, the engine 10 may be a gas turbine engine, such as a turboprop engine, or a turboshaft engine, an intermittent combustion engine, such as a Wankel engine, or a combination of one or more different engine types. In the present embodiment, the engine 10 is a gas turbine engine, more particularly a turboprop engine, and generally includes a compressor section 14 in series flow communication for pressurizing air, a combustor 16 in which the compressed air is mixed with fuel and ignited to produce an annular flow of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases.

[0039] Figure 1 The exemplary embodiment shown in FIG is a "reverse flow" engine because gases flow from an inlet 17 at the rear portion of the engine 10 to an exhaust outlet 19 at the front portion of the engine 10. This is in contrast to a "through flow" gas turbine engine, in which gases flow through the core of the engine from the front portion to the rear portion. The engine 10 can be a reverse flow engine (as shown) or a through flow engine.

[0040] In the illustrated embodiment, turbine section 18 includes a high-pressure turbine 18A in driving engagement with high-pressure compressor 14A. High-pressure turbine 18A and high-pressure compressor 14A are mounted on high-pressure shaft 15. Turbine 18 includes a low-pressure turbine, also referred to as a power turbine 18B, which is configured to drive load 12. Power turbine 18B is configured to drive low-pressure compressor 14B via a low-pressure shaft 22. Planetary gearbox 20 is configured as a reduction gearbox and operably connects low-pressure shaft 22 driven by power turbine 18B to shaft 24 in driving engagement with load 12, while providing a reduction ratio therebetween. In this embodiment, load 12 is an aircraft rotor, and more specifically, propeller 12, and therefore shaft 24 driving aircraft rotor 12 is referred to as a rotor shaft.

[0041] An epicyclic or planetary gearbox 20 allows the load 12 to be driven at a given speed that is different from the rotational speed of the low-pressure turbine 18B. The planetary gearbox 20 allows both the load 12 and the low-pressure turbine 18B to rotate at their respective optimal speeds. In the embodiment shown, the planetary gearbox 20 is axially mounted at the front end of the engine 10.

[0042] Now refer to Figure 1-Figure 4The planetary gearbox 20 may also be referred to as an epicyclic gear train, epicyclic gearbox, etc., but is generally referred to herein as an epicyclic gearbox or planetary gearbox. The planetary gearbox 20 includes a sun gear 32 mounted on a sun gear connector 34, which is connected to a layshaft 22a that is connected to the low-pressure shaft 22, although other operative connections are contemplated. For example, in an alternative embodiment, the sun gear 32 may be directly connected to the low-pressure shaft 22. The layshaft 22a, also known as the torque shaft, can be twisted a certain amount along its axis of rotation. The twist of the layshaft 22a can be monitored to indicate the torque it is transmitting.

[0043] The planetary gearbox 20 also has a set of planetary gears 36 rotatably mounted on respective shafts 38. In this embodiment, there are three planetary gears 36, although the planetary gearbox 20 may have two or more than three planetary gears 36. In the embodiment shown, all shafts 38 of the planetary gears 36 are connected to the planetary gear carrier 40 via respective bearings or any other suitable rotating assembly to form a planetary gear carrier 40. Figures 2 to 4 The planetary gear assembly 30 is shown. In the embodiment shown, the planetary gear carrier 40 is rotatable relative to the housing (H) of the planetary gearbox 20 about a central rotational axis (X).

[0044] Although different operative connections may be used in other embodiments, in this embodiment, a connector 44 connects the planet gear carrier 40 to the rotor shaft 24 to transmit the rotation of the planet gear carrier 40 to the load 12. As an example, the planet gear carrier 40 may alternatively be directly connected to the rotor shaft 24. In some embodiments, the planet gear carrier 40 may be a zero-torque carrier to reduce torsional deformation under torque by driving the planet gears 36 from an axial position corresponding to the plane of symmetry of the planet gears 36. In a particular embodiment, the zero-torque carrier is as described in U.S. Patent No. 6,663,530.

[0045] Each planetary gear 36 includes a main (large diameter) gear 46 and front and rear (small diameter) gears 48 disposed on opposite sides of the main gear 46 and attached to the main gear 46 via any suitable structure and / or method for unitary rotation therewith. The small diameter gear 48 may also be referred to herein as the small radius gear 48. Similarly, the large diameter gear 46 may also be referred to herein as the large radius gear 48. The main gear 46 meshes with the sun gear 32. In the illustrated embodiment, the main gear 46 and the sun gear 32 are spur gears, although other types of gears, such as helical gears, may also be used. In the illustrated embodiment, the diameter 50 of the sun gear 32 is smaller than the diameter 52 of the main gear 46 to produce a first rotational speed ratio between the sun gear 32 and the main gear 46 of the planetary gear assembly 36. In some embodiments, one or more of the planetary gears 36 may each have only one small diameter gear 48.

[0046] refer to Figure 2 and Figure 3 In this embodiment, and although not necessarily in all embodiments, the planetary gearbox 20 has two ring gears 54 that mesh with the small-diameter gears 48 of the planetary gear assembly 36. In this non-limiting embodiment, the ring gears 54 are symmetrically positioned on each side of the main gear 46 so that the reaction load on the bearings is equal along the longitudinal axis of the bearings. Depending on each given embodiment of the gearbox 20 and the other gears of the gearbox 20, the ring gear(s) 54 may be, for example, spur gears and / or helical gears. Helical gears may be quieter in some applications.

[0047] In certain embodiments, the teeth of the front gear 48 can be angled in an opposite manner relative to the teeth of the rear gear 48, such that the front and rear gears 48 can be mirror images of each other. In operation, the large-diameter gear 46 of this non-limiting embodiment can tend to self-center relative to the sun gear 32 under torque. This can enhance load sharing between the ring gear 54. In the illustrated embodiment, the diameter 56 of the front and rear gears 48, 48 is smaller than the diameter 52 of the main gear 46. Thus, the planetary gearbox 20 generates a second rotational speed ratio between the planet gears 36 and the ring gear 54.

[0048] The planetary gearbox 20 can provide a rotational speed ratio between the sun gear 32 and the planetary gear carrier 40 that would require at least two conventional planetary gearboxes to achieve. In certain embodiments, fewer moving parts are required, which can result in a reduction in cost and weight of the gas turbine engine 10. In addition, the moving parts of such a gearbox require lubrication. By having fewer parts, less oil can be required. This can reduce the capacity of the required oil system and, since less heat is generated, the size of the required heat exchanger for cooling the oil of the planetary gearbox 20 can be reduced. In certain embodiments, the overall length of the gas turbine engine 10 can be reduced by having a planetary gearbox 20 as described herein instead of at least two conventional gearboxes arranged in series in the engine 10 to achieve a reduction ratio equivalent to that of the planetary gearbox 20.

[0049] In the embodiment shown, the turbine shaft 22 is operatively connected to the sun gear 32. The rotor shaft 24 is connected to the connector 44 of the planetary gear carrier 40, for example, by a spline connection, and is thus operatively connected to the planetary gear carrier 40. In this embodiment, for example, by Figure 2As shown, the ring gear 54 is fixed to the housing (H) to restrict its rotation. It should be understood that in this embodiment, the rotation of the ring gear 54 is restricted by being prevented (i.e., the ring gear 54 does not rotate relative to the housing (H)). In other embodiments, the rotation of the ring gear 54 can be partially and / or variably restricted to change the gear ratio provided by the planetary gearbox. The reduction ratio is defined as the ratio of the rotational speed of the input (in this embodiment, the low-pressure shaft 22 / sun gear 32) to the rotational speed of the output (in this embodiment, the rotor shaft 24). In this arrangement, shafts 22 and 24 rotate in the same direction relative to each other.

[0050] In an alternative embodiment, a star-shaped arrangement can be used. In this star-shaped arrangement, the planet gear carrier 40 is restricted from rotation, and the rotor shaft 24 is operatively connected to the ring gear 54. It should be understood that restricting the rotation of the planet gear carrier 40 includes completely preventing the planet gear carrier from rotating. In this alternative embodiment, the ring gear 54 is mounted and connected to the rotor shaft 24. In this alternative embodiment, the rotor shaft 24 and the turbine shaft 22 rotate in opposite directions.

[0051] By arranging the two ring gears 54 on opposite sides of the main gear 46, the load is distributed symmetrically with respect to a plane P to which the axis of rotation A of the sun gear 32 is perpendicular and which is located at half the thickness T of the main gear 46. By distributing the load symmetrically, the planetary gearbox can be adapted to withstand higher torques and to use plain bearings instead of heavier and more expensive rolling element bearings.

[0052] The planetary gearbox 20 can be used in a variety of applications other than gas turbine engines, where a rotational speed ratio between two rotating components is required. In this embodiment, an input is provided to one of the sun gear 32, the planet gear carrier 40, and the ring gear 54, and an output is connected to the other of the sun gear 32, the planet gear carrier 40, and the ring gear 54. The rotation of the remaining one of the sun gear 32, the planet gear carrier 40, and the ring gear 54 that is not connected to the input or output is restricted.

[0053] The planetary gearbox 20 is adapted to vary the rotational speed of a rotating component relative to another rotating component. In the illustrated embodiment, the rotating component is a low-pressure shaft 22, and the other rotating component is a shaft 24. In the illustrated embodiment, the shaft 24 is connected to the load 12, but it may be connected to any other suitable component, such as, but not limited to, a helicopter rotor or an accessory of the gas turbine engine 10.

[0054] To change the rotational speed of shaft 24 relative to shaft 22, the planetary gearbox 20 first receives the torque of the low-pressure shaft 22 via the sun gear 32. This torque is then transferred to a main gear 46 of a set of planetary gears 36 that mesh with the sun gear 32. Each planetary gear 36 includes a rear gear and a front gear 48 disposed on opposite sides of the main gear 46. In the illustrated embodiment, a first rotational speed ratio is created by having a diameter 50 of the sun gear 32 that is smaller than a diameter 52 of the main gear 46.

[0055] Torque is then transmitted from the front and rear gears 48 to one of the planetary carrier 40 and the ring gear 54 meshing with the front and rear gears 48, while the other of the planetary carrier 40 and the ring gear 54 is fixed so as not to rotate. A second rotational speed ratio is generated by making the diameter 56 of the front and rear gears 48, 48 smaller than the diameter 52 of the main gear 46. The diameters 50, 52, and 56 can be adjusted to achieve a desired reduction ratio.

[0056] Now refer to Figure 5 , another epicyclic gearbox 58 is shown. The gearbox 58 includes an input defined by a sun gear 60 and an output defined by a ring gear 62. A plurality of spider gears 64 of the gearbox 58, carried by a carrier 66, operatively connect the input 60 to the output 62. More particularly, each spider gear 64 includes a large diameter gear 64A (also known as a first stage gear 64A) meshed to the sun gear 60, and a small radius gear 64B (also known as a second stage gear 64B) attached to the large radius gear 64A (in this embodiment, but not necessarily in all embodiments, by being integral with the large radius gear 64A) and meshed with the ring gear 62. The ring gear coupling 68 is splined to a radially outwardly facing surface 62A of the ring gear 62 (in this embodiment, but not necessarily in all embodiments, via free splines at each end thereof that engage the ring gear 62 and, therefore, the output shaft 24) to receive torque from the ring gear 62 and, therefore, to be rotated by the ring gear 62 about a corresponding axis of rotation (X). More particularly, and as shown Figure 5 As shown in FIG, radially outward facing surface 62A of ring gear 62 has radially outward facing teeth that mate with radially inward facing teeth defined by radially inward facing surface 68B of ring gear coupling 68.

[0057] In this embodiment, the sun gear 60, the ring gear 62, the planet gear carrier 66 and the ring gear coupling 68 are coaxial. Figure 7 As shown, in this embodiment, the gears 64, and more particularly the first stage gear 64A and the second stage gear 64B in this embodiment, are attached to each other, for example, by electron beam (EB) welding, or by any other suitable manufacturing / method / structure, such that one tooth of each first stage gear 64A is aligned with one tooth of the corresponding second stage gear 64B and with one tooth of the ring gear 62 (i.e., as shown in FIG. Figure 7 , with respective planes at 12 o'clock, 4 o'clock, and 8 o'clock, each of which contains the axis of rotation of the sun gear 60 and one tooth of each respective set of the first stage gear 64A, the second stage gear 64B, and the ring gear 62). Thus, as Figure 7 As shown in FIG, in this embodiment, the gearbox 58 includes three interconnected groups of three gears (i.e., each group has three interconnected gears, and the three groups share a common ring gear 62). Each group includes one of the first stage gears 64A, one of the second stage gears 64B, and the ring gear 62, wherein one tooth of each of the three gears 62, 64A, 64B is aligned with one tooth of each of the other two of the three gears 62, 64A, 64B.

[0058] In this embodiment, and as Figure 7 As shown in FIG, this alignment is indicated by corresponding markings 64C, 64D on each of the gears 62, 64A, 64B in corresponding positions within the respective planes contained within the plane. The number of teeth on each of these gears 62, 64A, 64B is one of: odd and even, while the number of sun gears 60 and ring gears 62 is evenly divisible by the number of spider gears 64. In one aspect, this arrangement reduces potential pitch errors. In another aspect, although not present in some embodiments, the markings can help ease assembly. While this is the case in this embodiment, markings 64C, 64D need not be located at top dead center (TDC) in all embodiments. In some embodiments, assembly can be further facilitated by meshing the driven sun gear (not shown) with the spider first stage gear 64A prior to assembling the gearbox 58. In some embodiments, the teeth of the ring gear 62, the large radius gear 64A, and the small radius gear 64B can be shaped so that when assembled and assembled relative to the rotation axis X, the apex of each tooth of each small radius gear 64B reaches the top dead center position (TDC) (i.e., the position farthest from the rotation axis X) at the same time as the apex of the tooth of the corresponding one of the large radius gears 64A, and these apexes can be aligned with the apexes of the valleys of the spaces between the teeth of the ring gear that are then engaged by the top dead center (TDC) teeth of the corresponding small radius gear 64B.

[0059] This alignment is illustrated by planes P1, P2, P3, which contain the axis of rotation X and divide 360 ​​degrees about the axis of rotation X into equal 120 degree sections, with one of the planes P1 being aligned with the top dead center position (TDC). Corresponding markings 64C, 64D may be provided on the gears 62, 64A, 64B to assist during assembly. As an example, in this embodiment, the markings 64C, 64D may be provided at positions corresponding to and indicating the top dead center position (TDC) and include markings on each large radius gear 64A, each small radius gear 64B, and the ring gear 62. In some embodiments, the gearbox 20 has similar alignments and similar markings 64C, 64D. Because the alignments and markings 64C, 64D may be similar, Figure 7 Alignment and markings 64C, 64D are shown for both the gearbox 20 and the gearbox 58 .

[0060] Still refer to Figure 5 Sun gear 60, ring gear 62, planet gear carrier 66, and ring gear coupling 68 can be disposed within a housing 70 of gearbox 58. Housing 70 includes a rear portion 70A and a front portion 70B removably connected to rear portion 70A. A rotor shaft assembly 72, which may include a rotor shaft 72A and bearings 72B supporting its rotation, can be connected to rear portion 70A so as to be removable relative to rear portion 70A along with front portion 70B. In some embodiments, such as the present embodiment, but not necessarily all embodiments, rotor shaft assembly 72 includes ring gear 62 connected to front portion 70B of a two-part gearbox housing 70 and is a self-contained assembly unit, meaning it is removed from rear portion 70A as a single assembly. While providing advantages in some applications, in other embodiments, housing 70 may have a different number of components and / or a different configuration than at least some prior art designs of similar size and application to facilitate assembly. For example, additional housing components may be disposed between front portion 70A and rear portion 70B such that rear portion 70A is operably connected thereto so as to be removable therefrom along with rotor shaft assembly 72 , with or without one or more intervening components.

[0061] In this embodiment, the bracket 66 is prevented from rotating relative to the axis of rotation (X) by spline-connecting the bracket 66 to the housing 70B, and in this particular embodiment, to the rear portion 70A thereof. While a spline connection may provide some benefits, such as relatively improved ease of assembly and maintenance, it is contemplated that different structures for preventing rotation of the bracket 66 may be used. In some embodiments, the rotation of the bracket 66 relative to the axis of rotation (X) may be limited, for example, variably limited, in order to change the overall gear ratio provided by the gearbox 58.

[0062] Now refer to Figure 8 , schematically illustrates an aircraft 1. The aircraft has a first engine 10A, which may be the engine 10 described above, and a second engine 10B, which may be similar to the engine 10 described above, except equipped with a gearbox 58 instead of the gearbox 20. The connections between the input and output of engine 10B and gearbox 58 may be similar to the connections between the input and output of engine 10A and gearbox 20, so these details are not repeated here. As shown, engines 10A and 10B drive corresponding rotors, which in this embodiment are propellers 12P. In other embodiments, the rotors may be different (for example, if the aircraft is a helicopter, the rotors may be helicopter rotors). In other embodiments, engines 10A and 10B may drive a single output, such as a helicopter rotor, via a suitable transmission, for example. In such embodiments, a suitable transmission may be operably provided between the outputs of engines 10A and 10B and gearboxes 20 and 58.

[0063] In this embodiment, when the engines 10A and 10B are operating, the gearboxes 20 and 58 drive the propellers 12P in opposite directions. For example, the propeller 12P of the engine 10A may be driven clockwise about the engine axis Xa of the engine 10A, in which case the propeller 12P of the engine 10B may be driven counterclockwise about the engine axis Xb of the engine 10B. In other embodiments, the directions of rotation may be reversed.

[0064] Now refer to Figure 9 The present technology also provides a method 90 for operating a multi-engine aircraft 1, including: rotating the sun gear 32 of the first epicyclic gearbox 20 and the sun gear 60 of the second epicyclic gearbox 58, the sun gears 32, 60 being meshed with the corresponding planetary gears 36, 64 of the first epicyclic gearbox 20 and the second epicyclic gearbox 58, rotating the planetary gear carrier 40 of the first epicyclic gearbox 20 relative to the ring gear 54 of the first epicyclic gearbox 20, and transmitting the rotation of the planetary gear carrier 40 of the first epicyclic gearbox 20 to the first rotor shaft 24A of the aircraft 1; and rotating the ring gear 62 of the second epicyclic gearbox 58 relative to the bracket 66 of the second epicyclic gearbox 58, and transmitting the rotation of the ring gear 62 of the second epicyclic gearbox 58 to the second rotor shaft 24B of the aircraft 1.

[0065] In some embodiments, the method 90 may include limiting rotation of at least one of: the ring gear 54 of the first epicyclic gearbox 20; and the bracket 66 of the second epicyclic gearbox 58. As noted above, in some embodiments, limiting rotation of at least one of the ring gear 54 of the first epicyclic gearbox 20 and the bracket 66 of the second epicyclic gearbox 58 includes preventing rotation of at least one of the ring gear 54 of the first epicyclic gearbox 20 and the bracket 66 of the second epicyclic gearbox 58.

[0066] Furthermore, in some embodiments, the method 90 can include preventing rotation of the bracket 66 of the second epicyclic gearbox 58 by maintaining a splined connection between the bracket 66 of the second epicyclic gearbox 58 and the housing 70 of the second epicyclic gearbox 58 (e.g., as described above). In some embodiments, the method 90 can include variably limiting rotation of the bracket 66, for example, to change the gear ratio provided by the second epicyclic gearbox 58. In some embodiments, the method 90 can include variably limiting rotation of the ring gear 54 of the first epicyclic gearbox 20, for example, to change the gear ratio provided by the first epicyclic gearbox 20. In some such embodiments, rotation of the sun gear 32 of the first epicyclic gearbox 20 can be in the same direction as rotation of the sun gear 60 of the second epicyclic gearbox 58, respectively, to transmit rotation of the first rotor shaft to the first rotor of the aircraft and rotation of the second rotor shaft to the second rotor of the aircraft.

[0067] In some such embodiments, rotating the sun gear 32 of the first epicyclic gearbox 20 can be performed via the turbine section 18 of the first gas turbine engine 10A of the aircraft 1, and rotating the sun gear 60 of the second epicyclic gearbox 58 is performed via the turbine section 18 of the second gas turbine engine 10B of the aircraft 1.

[0068] The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. After reading this disclosure, those skilled in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. In light of this disclosure, those skilled in the art may implement further modifications that are within the scope of the present technology.

Claims

1. An aircraft (1), comprising: a first engine and a second engine (10, 10A, 10B); one or more aircraft rotors (12, 12P) associated with the first and second engines (10, 10A, 10B); a first epicyclic gearbox (20) having: a) an output operatively connected to at least one of the one or more aircraft rotors (12, 12P), and b) an input defined by a sun gear (32) of the first epicyclic gearbox (20); as well as a second epicyclic gearbox (58) having: a) an output operatively connected to at least one of the one or more aircraft rotors (12, 12P), and b) an input defined by a sun gear (60) of the second epicyclic gearbox (58); and in: The first engine (10, 10A) is operatively connected to an input of the first epicyclic gearbox (20); The second engine (10, 10B) is operatively connected to an input of the second epicyclic gearbox (58); Each of the first and second epicyclic gearboxes (20, 58) has a gear (36, 64) carried by a carrier (40, 66) and a ring gear (54, 62) meshing with the gear (36, 64), The output of the first epicyclic gearbox (20) is defined by a bracket (40) of the first epicyclic gearbox (20), The output of the second epicyclic gearbox (58) is defined by a ring gear (62) of the second epicyclic gearbox (58), and each of the gears (64) carried by the carrier (66) of the second epicyclic gearbox (58) comprises: a large radius gear (64A) meshing with the sun gear (60) of the second epicyclic gearbox (58); a small radius gear (64B) attached to the large radius gear (64A) and meshing with the ring gear (62) of the second epicyclic gearbox (58), the large radius gear (64A), the small radius gear (64B) and the ring gear (62) forming an interconnected set of three gears (62, 64A, 64B); One tooth of the small radius gear (64B) is circumferentially aligned with one tooth of the large radius gear (64A), and the apex of the tooth of the small radius gear (64B) is aligned with the valley of the space between the teeth of the ring gear (62); Each gear of the second epicyclic gearbox (58) has a plurality of teeth; The number of teeth of all three gears of the interconnected set of three gears (62, 64A, 64B) is one of an even number and an odd number; and The number of teeth of each of the sun gear (60) and the ring gear (62) of the second epicyclic gearbox (58) is divisible by the number of gears (64) of the carrier (66) of the second epicyclic gearbox (58).

2. The aircraft according to claim 1, wherein: The ring gear (54) of the first epicyclic gearbox (20) is prevented from rotating, and the bracket (66) of the second epicyclic gearbox (58) is prevented from rotating.

3. The aircraft according to claim 1 or 2, wherein: Each of the gears (36, 64) carried by the bracket (40, 66) of the first epicyclic gearbox (20) comprises: a large radius gear (46) meshing with the sun gear (32) of the first epicyclic gearbox (20), a small radius gear (48) attached to the large radius gear (46) and meshing with the ring gear (54) of the first epicyclic gearbox (20), and The teeth of the large radius gear (46, 64A), the small radius gear (48, 64B) and the ring gear (54, 62) are shaped so that when rotating: The apex of each tooth of the large radius gear (46, 64A) and the apex of each tooth of the small radius gear (48, 64B) pass through the top dead center position simultaneously.

4. The aircraft according to claim 3, wherein: The output of the second epicyclic gearbox (58) is operatively connected to at least one of the one or more aircraft rotors (12, 12P) via a rotor shaft assembly (72); and the ring gear (62) of the second epicyclic gearbox (58): having a radially inward facing surface (68B) and a radially outward facing surface (62A), including teeth on both said radially inward facing surface (68B) and said radially outward facing surface (62A), mates with the small radius gear (64B) of each gear (64) of the bracket (66) of the second epicyclic gearbox (58) via the teeth on said radially inwardly facing surface (68B), and The connection to the rotor shaft assembly (72) is via a spline connection including the teeth on the radially outward facing surface (62A).

5. The aircraft according to claim 4, wherein: The rotor shaft assembly (72) includes a ring gear coupling (68) having teeth that mate with teeth on a radially outward facing surface (62A) of the ring gear (62) of the second epicyclic gearbox (58) and define the spline connection, and wherein the large radius gear, the small radius gear, and the ring gear each include markings thereon at respective locations corresponding to the top dead center position.

6. The aircraft according to claim 5, wherein: The second epicyclic gearbox (58) includes a housing (70); The ring gear coupling (68), the ring gear (62), the bracket (66), and the sun gear (60) of the second epicyclic gearbox (58) are disposed within the housing (70); and The bracket (66) of the second epicyclic gearbox (58) is splined to the housing (70).

7. The aircraft according to claim 6, wherein: The housing (70) includes a rear portion (70A) and a front portion (70B), the front portion being operatively connected to the rear portion so as to be removable therefrom; as well as The rotor shaft assembly (72) is connected to the front portion (70B) so as to be removable with the front portion relative to the rear portion (70A).

8. The aircraft according to any one of claims 1-2 and 4-7, wherein: The first engine (10A) drives the sun gear (32) of the first epicyclic gearbox (20) in a given direction when the first engine is operating, and the second engine (10B) drives the sun gear (60) of the second epicyclic gearbox (58) in the given direction when the second engine is operating.

9. A method of operating a multi-engine aircraft (1) having a first gas turbine engine and a second gas turbine engine (10, 10A, 10B), the method comprising: rotating a sun gear (32) in a first epicyclic gearbox (20) of the first gas turbine engine (10A) and rotating a sun gear (60) in a second epicyclic gearbox (58) of the second gas turbine engine (10B), the sun gears (32, 60) being meshed with corresponding gears (36, 64) of brackets (40, 66) of the first and second epicyclic gearboxes (20, 58); causing a bracket (40) of the first epicyclic gearbox (20) to rotate relative to a ring gear (54) of the first epicyclic gearbox (20), and transmitting the rotation of the bracket (40) of the first epicyclic gearbox (20) to a first rotor shaft (24A) of the aircraft (1), so as to rotate the first rotor shaft (24A) and a first propeller (12P) coupled thereto in a first rotational direction; as well as Rotating the ring gear (62) of the second epicyclic gearbox (58) relative to the bracket (66) of the second epicyclic gearbox (58) and transmitting the rotation of the ring gear (62) of the second epicyclic gearbox (58) to the second rotor shaft (24B) of the aircraft (1) to rotate the second rotor shaft (24B) and the second propeller (12P) engaged therewith in a second rotational direction, the second rotational direction being opposite to the first rotational direction.

10. The method of claim 9, comprising limiting the rotation of at least one of: the ring gear (54) of the first epicyclic gearbox (20); and The bracket (66) of the second epicyclic gearbox (58).

11. The method according to claim 9 or 10, wherein: Transferring the rotation of the ring gear (62) of the second epicyclic gearbox (58) to the second rotor shaft (24B) is performed via a radially outward facing surface (62A) of the ring gear (62) of the second epicyclic gearbox (58).

12. The method according to claim 9 or 10, wherein: The sun gear (32) of the first epicyclic gearbox (20) is rotated in the same direction as the sun gear (60) of the second epicyclic gearbox (58) is rotated.

13. The method according to claim 9 or 10, wherein: Rotating the sun gear (32) of the first epicyclic gearbox (20) is performed via a turbine section (18) of a first gas turbine engine (10A) of the aircraft (1); and Rotating the sun gear (60) of the second epicyclic gearbox (58) is performed via the turbine section (18) of the second gas turbine engine (10B) of the aircraft (1).

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