Mechanical power transmission system, power transmission box and aircraft

Abstract

The transmission system (10) according to the invention comprises a driving shaft (1), a driven shaft (2), and a linkage device (3) enabling said driving shaft (1) to transmit a mechanical torque to said driven shaft (2), as well as guiding devices (5, 6, 7, 8) guiding said driving shaft (1) in rotation about a driving axis (AXMA) and said driven shaft (2) about a driven axis (AXME). When said transmission system (10) is at rest, said driving axis (AXMA) and said driven axis (AXME) are misaligned, and move closer to each other when said transmission system (10) transmits a torque from said driving shaft (1) to said driven shaft (2). (Shorthand figure: Figure 1)

Description

Title of the invention: Mechanical power transmission system, power transmission box and aircraft

[0001] The present invention is in the field of power transmission devices.

[0002] The present invention relates to a transmission system, a power transmission gearbox, and an aircraft, as well as a method for limiting parasitic forces in such a transmission system. In particular, a transmission system may have the function of mechanically transmitting power between an engine and a rotor of an aircraft.

[0003] A known transmission system includes a linkage device that transfers rotational motion and mechanical torque from a driving shaft to a driven shaft. Furthermore, the transmission system may include one or more guiding devices for rotating the driving shaft and the driven shaft relative to a support. Such guiding devices may include, for example, ball or roller bearings. Moreover, the driving shaft and the driven shaft are aligned and coaxial.

[0004] However, under certain operating conditions of the transmission system, the driving shaft and the driven shaft may be subjected to significant radial, or even axial, loads that can cause deformations and displacements, generating radial and / or angular misalignment between them. Such misalignment can tend to generate parasitic stresses in the power transmission system that can cause wear and / or damage to the linkage and / or guide devices, or even to the driving shaft and / or the driven shaft.

[0005] To at least limit the transmission of parasitic forces between the leading and led trees, various solutions have been developed.

[0006] For example, document FR 3057850 describes a transmission system comprising a first and a second shaft attached respectively to two coupling means. This transmission system also includes a linkage system, referred to as a "flexible" linkage, comprising at least one intermediate shaft connecting the two coupling means and passing longitudinally through the second shaft.

[0007] Furthermore, the length of the intermediate tree can be maximized to minimize the effect of any misalignment between the first and second trees. Indeed, the longer the intermediate tree, the less significant the parasitic forces generated by a given misalignment between the first and second trees.

[0008] Complementarily or alternatively, the intermediate shaft may have intrinsic flexibility allowing it to tolerate misalignments between the first shaft and the second shaft in order to limit the parasitic forces generated.

[0009] Furthermore, according to this document FR 3057850, the connecting device may include special coupling means to minimize the impact of axial, radial, and angular misalignments. These coupling means may, for example, take the form of diaphragms or plate systems.

[0010] According to another example, US patent 5286117 describes a bearing whose outer ring is asymmetrical such that its mounting in a cylindrical housing and around a shaft allows for radial or axial clearance between this outer ring and the housing, but only over a portion of the outer ring's circumference. Consequently, this bearing reduces the stresses caused by misalignment between the inner and outer rings of the bearing in order to limit load peaks on the rolling elements of the bearing, as well as other parts of the system.

[0011] Alternative solutions exist. For example, document FR 2988789 describes an axial positioning device for a bearing mounted on a shaft. This axial positioning device includes an angular positioning means and an operating clearance allowing limited angular movement of the bearing.

[0012] According to one technology, the housing or casing of a transmission system can be very rigid to limit the amplitude of shaft misalignment. Although effective, this solution has a cost in terms of mass.

[0013] The present invention then aims to propose an alternative power transmission system capable of minimizing the transmission of parasitic forces, in particular between a driving shaft and a driven shaft of the transmission system during its operation.

[0014] According to the invention, a transmission system comprises a driving shaft, a driven shaft, and a linkage device mechanically connecting the driving shaft and the driven shaft, the linkage device enabling the driving shaft to rotate the driven shaft. In this way, the linkage device allows the transmission of a rotational torque at least from the driving shaft to the driven shaft, and possibly also from the driven shaft to the driving shaft.

[0015] The transmission system also includes at least two first housings and at least two first guide devices for guiding the driving shaft in rotation about a driving axis AXMA, each first housing receiving one of the first guide devices. The transmission system also includes at least two second housings and at least two second guide devices. allowing the driven shaft to be guided in rotation around a driven axis AXME, each second housing receiving one of the second guiding devices.

[0016] The transmission system may further include a housing in which the first and second housings are formed. This housing may be a single piece or composed of several assembled sub-assemblies.

[0017] The transmission system according to the invention is particularly remarkable in that the driving shaft AXMA and the driven shaft AXME are misaligned when the transmission system is at rest, the driving shaft as well as the driven shaft and the linkage device being located around a median line LM of the driving shaft AXMA and the driven shaft AXME.

[0018] This median line LM is defined as being, in each plane perpendicular to this median line LM, equidistant from the leading axis AXMA and the driven axis AXME. The driving shaft, the driven shaft, and the connecting device are located around this median line LM, and are thus in line with each other, the connecting device being located between the driving shaft and the driven shaft.

[0019] The driving shafts AXMA and AXME are thus close to each other, but are not coaxial when the transmission system is at rest, i.e., when no mechanical torque is transmitted between the driving shaft and the driven shaft. A gap then separates the driving shaft AXMA and the driven shaft AXME.

[0020] Thus, when the transmission system transmits a mechanical torque, particularly from the driving shaft to the driven shaft, forces, also referred to as "loads," cause the driving shaft AXMA and the driven shaft AXME to move closer together by reducing the gap between them. This movement of the driving shafts AXMA and AXME can be so close together that the driving shaft AXMA and the driven shaft AXME are substantially aligned and coaxial under predetermined conditions.

[0021] The initial misalignment between the driving axis AXMA and the driven axis AXME is thus intended to anticipate and compensate for deformations and / or displacements under loads, during the operation of the transmission system.

[0022] Bringing the driving shafts AXMA and driven shafts AXME closer together during operation limits, or even prevents, the occurrence of parasitic forces in the transmission system, particularly at the level of the driving and driven shafts. Reducing or eliminating such parasitic forces also limits the stresses experienced by the linkage and guiding devices of the transmission system, as well as by any speed reduction devices that may be located upstream of the driving shaft and downstream of the driven shaft.

[0023] Reducing, or even eliminating, such parasitic efforts advantageously improves the operation of the transmission system and increases its lifespan. life, thereby reducing the frequency of maintenance operations and / or component replacement.

[0024] The transmission system according to the invention can also allow for a mass reduction compared to solutions aimed at stiffening the transmission system.

[0025] Surprisingly, the misalignment at rest of the driving shaft AXMA and the driven shaft AXME is compatible with the operation of the transmission system, particularly during start-up or when a low mechanical torque is transmitted from the driving shaft to the driven shaft. Indeed, the linkage device, as well as any speed reduction devices, can tolerate such misalignment under these conditions without any impairment of their operation.

[0026] The method according to the invention may include one or more of the following features, taken alone or in combination.

[0027] According to one example, the linkage device includes at least one drive device enabling the driving shaft to transmit a mechanical torque to the driven shaft.

[0028] The linkage device and / or such a drive device may not include any speed reduction device, so that the driving shaft and the driven shaft rotate substantially at the same speed when the driving shaft transmits a mechanical torque to the driven shaft.

[0029] Furthermore, said at least one drive device may be permanent and similarly provide mechanical torque from the driving shaft to the driven shaft, or from the driven shaft to the driving shaft. Alternatively, said at least one drive device may be non-permanent and, in particular, provide motor torque only from the driving shaft to the driven shaft.

[0030] Said at least one drive device may, for example, comprise a device selected from a list comprising splines, at least one key, a bolted assembly, a freewheel, a clutch, a diaphragm coupling means.

[0031] The linkage device may include an intermediate shaft, said device comprising at least one drive device including a first drive device and a second drive device, the first drive device transmitting at least one mechanical torque from the driving shaft to the intermediate shaft and the second drive device transmitting at least one mechanical torque from the intermediate shaft to the driven shaft. In this case, the driving shaft, the intermediate shaft, and the driven shaft may be substantially aligned and coaxial when the driving shafts AXMA and driven shafts AXME move under load during the operation of the transmission system.

[0032] According to another example consistent with the previous ones, the driving axis AXMA and the driven axis AXME can be parallel to each other when the transmission system is at a standstill.

[0033] Alternatively, the driving axis AXMA and the driven axis AXME may be inclined relative to each other, and therefore not parallel to each other, when the transmission system is at rest. The gap between the driving axis AXMA and the driven axis AXME is in this case an angular gap.

[0034] According to another example consistent with the preceding ones, each first guide device, arranged in a first housing, has a first center of rotation around which a first inner ring of the first guide device rotates relative to a first outer ring of the first guide device. Similarly, each second guide device, arranged in a second housing, has a second center of rotation around which a second inner ring of the second guide device rotates relative to a second outer ring of the second guide device. The first and second centers of rotation are, for example, located respectively on planes of symmetry of the first and second guide devices.

[0035] The leading axis AXMA then passes through the first centers of rotation, and the driven axis AXME passes through the second centers of rotation. The leading axis AXMA is thus defined by the first centers of rotation and the driven axis AXME is defined by the second centers of rotation.

[0036] The misalignment value between the leading axis AXMA and the led axis AXME is then defined by the relative positions of the first and second centers of rotation.

[0037] In particular, if the driving axis AXMA and the driven axis AXME are parallel to each other when the transmission system is at rest, the relative positions of the first centers of rotation respectively with respect to the second centers of rotation are identical.

[0038] Alternatively, if the driving axis AXMA and the driven axis AXME are not parallel to each other when the transmission system is at rest, the relative positions of the first centers of rotation respectively with respect to the second centers of rotation are different.

[0039] According to a first variant of the transmission system according to the invention, the first housings are cylindrical and centered on the driving axis AXMA, and the second housings are cylindrical and centered on the driven axis AXME when the transmission system is at rest. In this case, the first and second housings are not coaxial.

[0040] The misalignment between the leading axis AXMA and the led axis AXME is thus obtained directly from the relative positions of the first and second housings housings. In this case, the first guide devices and the second guide devices conventionally include coaxial inner and outer rings.

[0041] According to a second variant of the transmission system according to the invention, the first housings and the second housings are cylindrical, and are coaxial when the transmission system is at rest, and at least one of the first guide devices and the second guide devices has an eccentric outer ring.

[0042] This eccentric outer ring has an outer peripheral surface and an inner peripheral surface that are eccentric with respect to each other and therefore not coaxial. This eccentric outer ring thus allows the center of rotation of the guide device in question to be moved relative to the center of the housing in which the guide device is located. Conversely, the inner ring of a guide device is coaxial with the inner peripheral surface of the associated eccentric outer ring. Consequently, the inner ring of this guide device and the housing in which this guide device is located are not coaxial.

[0043] The misalignment between the driving axis AXMA and the driven axis AXME is thus achieved by means of the eccentric outer ring of at least one of the first guide devices and of the second guide devices. For example, the first two guide devices each comprise a first eccentric outer ring, the second guide devices comprising coaxial inner and outer rings.

[0044] According to a third variant of the transmission system according to the invention, the first housings and the second housings are cylindrical, and are coaxial when the transmission system is at rest, and at least one eccentric ring is inserted between on the one hand one of the first and second housings, and on the other hand one of the first and second guide devices.

[0045] This eccentric ring has an outer peripheral surface and an inner peripheral surface that are eccentric with respect to each other and therefore not coaxial. In this way, this eccentric ring allows the center of rotation of the guide device around which the eccentric ring is inserted to be moved relative to the center of the housing in which the eccentric ring is inserted. Consequently, the guide device and the housing in which this guide device is arranged are not coaxial.

[0046] The misalignment between the driving axis AXMA and the driven axis AXME is thus obtained by means of the eccentric ring(s). For example, two eccentric rings are inserted respectively between the first housings and the first two guide devices.

[0047] According to a fourth variant of the transmission system according to the invention, the transmission system comprises a casing composed of several assembled sub-assemblies of which at least a first sub-assembly and a second sub-assembly, the first sub-assembly comprising said at least two first housings and the second sub-assembly comprising said at least two second housings.

[0048] The first sub-assembly and the second sub-assembly are fixed to each other so that the driving axis AXMA and the driven axis AXME are misaligned when the transmission system is stopped.

[0049] The first and second subassemblies are thus offset from each other, relative to a position in which the driving axis AXMA and the driven axis AXME would be aligned when the transmission system is at rest. In this case, the first and second subassemblies are also offset from each other, relative to a position in which the first and second housings are coaxial when the transmission system is at rest, the first and second housings being cylindrical.

[0050] The misalignment between the driving axis AXMA and the driven axis AXME is thus obtained by means of this offset between the first subassembly and the second subassembly. This offset can be obtained by the relative positions of the connection points between the first subassembly and the second subassembly, or by means of an intermediate part adapted to the desired offset.

[0051] The first sub-assembly and the second sub-assembly can be fixed directly to each other, or via the intermediate part, for example a third sub-assembly of the housing.

[0052] The present invention also relates to a power transmission box comprising a transmission system as previously described.

[0053] The power transmission box can, for example, be positioned between an engine and a propulsion device, such as a rotor if the power transmission box is fitted to an aircraft.

[0054] The present invention further relates to an aircraft comprising a transmission system as previously described, arranged or not in a power transmission box.

[0055] The present invention finally aims at a method of limiting parasitic forces in a transmission system as previously described.

[0056] This method includes, in particular, the following steps: - determination of a relative displacement between the driving axis AXMA and the driven axis AXME during operation of the transmission system, and - misalignment, when the transmission system is stopped, of the driving axis AXMA and the driven axis AXME as a function of this relative displacement.

[0057] This method thus makes it possible to determine the value of the misalignment to be applied between the driving axis AXMA and the driven axis AXME at rest. The value of this misalignment can be determined as a function of the relative displacement between the driving axis AXMA and the driven axis AXME, itself determined by simulation and possibly confirmed by tests, or determined directly by tests.

[0058] During the step of determining a relative displacement between the driving shaft AXMA and the driven shaft AXME, the relative displacement between the driving shaft AXMA and the driven shaft AXME can be determined, for example, when the transmission system transmits a mechanical torque from the driving shaft to the driven shaft greater than or equal to a predetermined torque. This predetermined torque can, for example, correspond to a particular operating phase of the transmission system, for example, the operating phase that is most demanding in terms of the stresses experienced by the transmission system, or the most frequently used phase.

[0059] The relative displacement between the driving shaft AXMA and the driven shaft AXME can alternatively be determined as being equal to an average relative displacement of the driving shafts AXMA and driven shafts AXME when the transmission system transmits a mechanical torque from the driving shaft to the driven shaft that is within a predetermined range. This predetermined range can, for example, correspond to one or more operating phases of the transmission system, in particular the operating phases that are most demanding in terms of the stresses experienced and / or the most frequently used.

[0060] The relative displacement between the driving axis AXMA and the driven axis AXME can be determined as being equal to an average relative displacement of the driving axes AXMA and driven axes AXME when the transmission system is in one or more predetermined operating phases, for example the operating phase(s) most penalizing in terms of stresses suffered or the most used.

[0061] When the transmission system according to the invention is fitted to a rotary-wing aircraft, for example by being positioned between an engine and a rotor of the aircraft, the most penalizing flight phases of the aircraft may be the takeoff, cruise flight, or even hovering phases, the most used flight phase generally being cruise flight.

[0062] However, this relative displacement between the driving axis AXMA and the driven axis AXME under load can prove complex to measure directly. In this case, during tests and / or simulations, parasitic forces, such as a moment and / or a shear force, can be measured in certain parts of the transmission system, and then the The relative positions of the axes leading AXMA and led AXME at rest are modified by iteration to minimize these parasitic forces under load.

[0063] The invention and its advantages will become apparent in more detail in the following description, with illustrative examples given by reference to the accompanying figures, which represent: - Fig. 1, a view of a transmission system according to the invention integrated into a power transmission box, - [Fig. 2], a schematic view of a transmission system according to the invention, - [Fig. 3], a schematic view comparing a transmission system according to the invention at rest and in operation, - [Fig. 4], a partial view of a transmission system according to the invention, - [Fig. 5], a partial view of a transmission system according to the invention, And - [Fig.6], a view of an aircraft equipped with a transmission system according to the invention.

[0064] Elements present in several separate figures are assigned one and the same reference.

[0065] Figure 1 represents a transmission system 10 for transmitting torque and mechanical power between a driving shaft 1 and a driven shaft 2. This transmission system 10 can, for example, be arranged between a motor and a propulsion device. This transmission system 10 can, for example, be integrated into a power transmission box 50, partially visible in Figure 1.

[0066] Regardless of its arrangement, the transmission system 10 comprises a driving shaft 1, a driven shaft 2, and a linkage device 3 mechanically connecting the driving shaft 1 and the driven shaft 2. The linkage device 3 secures the driving shaft 1 and the driven shaft 2 in at least one direction of rotation, such that the driving shaft 1 drives the driven shaft 2 in rotation at least in that direction, transmitting a mechanical torque to it. For this purpose, the linkage device 3 comprises at least one drive device 31, 32.

[0067] A drive device 31, 32 may, for example, include a freewheel for transmitting mechanical torque from the driving shaft 1 to the driven shaft 2 in a single direction of rotation. Alternatively, a drive device 31, 32 may include splines arranged in a complementary manner on the driving shafts 1 and 2, at least one key, or a bolted assembly for transmitting mechanical torque from the driving shaft 1 to the driven shaft 2 in both directions of rotation. A drive device 31, 32 may also include a clutch.

[0068] The linkage device 3 may also include, according to the example of transmission system 10 in [Fig. 1], an intermediate shaft 35, a first drive device 31 and a second drive device 32. The first drive device 31 transmits a mechanical torque from the driving shaft 1 to the intermediate shaft 35 and the second drive device 32 transmits a mechanical torque from the intermediate shaft 35 to the driven shaft 2. According to the example of transmission system 10, the first drive device 31 has splines and the second drive device 32 has a freewheel.

[0069] The transmission system 10 also includes at least two first housings 15, 16 and at least two respective first guide devices 5, 6 for guiding the driving shaft 1 in rotation about a driving axis AXMA. Each first housing 15, 16 receives one of the first guide devices 5, 6.

[0070] Furthermore, the transmission system 10 includes at least two second housings 17,18 and at least two second guide devices 7,8 respectively for guiding the driven shaft 2 in rotation around a driven axis AXME relative to a housing 54 of the power transmission box 50. Each second housing 17,18 receives one of the second guide devices 7,8.

[0071] The first and second housings 15-18 can be cylindrical in shape and arranged / formed in the housing 54 of the power transmission box 50. This housing 54 can include several sub-assemblies 56-59, as shown in [Fig.1], these sub-assemblies 56-59 being able to be assembled together using screws for example.

[0072] Thus, according to the example of transmission system 10 shown in [Fig.1], the transmission system 10 comprises two first housings 15,16, arranged respectively in two subsets 56,57, and two second housings 17,18, arranged respectively in two subsets 58,59.

[0073] Furthermore, the guiding devices 5-8 include, for example, bearings comprising an inner ring 52,62,72,82 and an outer ring 53,63,73,83 framing rolling elements, namely balls or rollers for example.

[0074] Each first guiding device 5, 6 has a first center of rotation, around which the driving shaft 1 is guided in rotation. The driving shaft AXMA thus passes through the first centers of rotation. Similarly, each second guiding device 7, 8 has a second center of rotation, around which the driven shaft 2 is guided in rotation. The driven shaft AXME thus passes through the second centers of rotation. The driving shaft AXMA is therefore defined by the positions of the first centers of rotation, and the driven shaft AXME is defined by the positions of the second centers of rotation.

[0075] The driving shaft 1 and the driven shaft 2 may also have teeth 14,24 in order to cooperate respectively with an input shaft 51 and an output shaft 61 of the power transmission box 50.

[0076] According to one example, the driving shaft 1 can carry the teeth 14, the first guiding devices 5,6 guiding the driven shaft 2.

[0077] According to the example of transmission system 10 in [Fig. 1], the leading shaft 1 may include a driving gear 141 equipped with teeth 14. This driving gear 141 is rotationally fixed to the driving shaft 1 by an additional drive device 12. The driving gear 141 is guided in rotation directly or indirectly by the first guide devices 5, 6. Optionally, the first guide devices 5, 6 guide the driving shaft 1 by guiding the driving gear 141. This driving gear 141 cooperates with an input gear 514 fixed to the input shaft 51. In this way, the driving shaft 1 can be rotated, for example, by a motor, via the input shaft 51 and the input gear 514 and driving gear 141.

[0078] Similarly, the driven shaft 2 may include a driven gear 241 having teeth 24 cooperating with an output gear 614 fixed in rotation to the output shaft 61. The driven gear 241 is guided in rotation directly or indirectly by the second guiding devices 7,8. According to the example of [Fig.1], the driven shaft 2 and the driven gear 241 form a single part.

[0079] In this way, when the driving shaft 1 transmits a mechanical torque in rotation to the driven shaft 2, this mechanical torque is transmitted to the output shaft 61, possibly with a reduction depending on the number of teeth 24 and the number of teeth of the output gear 614. A system of the type of the driving shaft with gear is conceivable.

[0080] Regardless of these aspects, the driving shafts AXMA and AXME are misaligned, and therefore not coaxial, when the transition system 10 is at rest. Indeed, a gap separates the driving shaft AXMA and the driven shaft AXME when the transmission system 10 is at rest or is not transmitting any torque from the driving shaft 1 to the driven shaft 2. Furthermore, the driving shaft 1, as well as the driven shaft 2 and the linkage device 3, are located around a midline LM which is in a position midway between the driving shaft AXMA and the driven shaft AXME.

[0081] This gap can take the form of a distance e, as shown in [Fig. 1], with the driving axis AXMA and the driven axis AXME being parallel to each other. This gap can take the form of an angle α, as shown in [Fig. 2], with the driving axis AXMA and the driven axis AXME then being inclined relative to each other, and therefore not parallel to each other. This [Fig. 2] schematically represents only the driving shaft 1, the driven shaft 2 and the connecting device 3 as well as the gear. leading 141. Such a misalignment between the leading axes AXMA and led AXME can also be defined simultaneously by a distance e and an angle a.

[0082] In Figures 1 and 2, the distance between the leading axes AXMA and AXME has been deliberately exaggerated to be clearly visible. The distance e, for example, is between 0.1 and 1 millimeter (0.1 and 1 mm). The angle α, for example, is between 0.1 and 1 degree (0.1 and 1°).

[0083] The value of this misalignment between the driving axis AXMA and the driven axis AXME, whether expressed in distance and / or angle, does not prevent the operation of the transmission system 10, in particular during its start-up or when a low torque is transmitted by the driving shaft 1 to the driven shaft 2. Indeed, the linkage device 3 as well as the input gears 514 and output gears 524 allow such a misalignment of the driving axes AXMA and driven axes AXME, without generating a significant parasitic force as long as the transmitted torques remain low.

[0084] Advantageously, as soon as the torque transmitted by the transmission system 10, and in particular from the driving shaft 1 to the driven shaft 2, increases, deformations and / or displacements occur in the transmission system 10 according to the invention, in particular at the driving shaft 1 and / or the driven shaft 2. These deformations and / or displacements tend to move / deform the driving shaft 1 and / or the driven shaft so as to reduce the misalignment between the driving axes AXMA and driven axes AXME, these driving axes AXMA and driven axes AXME advantageously approaching each other, possibly until they are coaxial and aligned.

[0085] Thus, when the torque transmitted by the transmission system 10 increases, the misalignment of the driving axes AXMA and driven axis AXME is reduced. This has the effect of limiting the occurrence of parasitic forces in the transmission system 10, and of limiting the effects of these parasitic forces on the transmission system 10 and its components, such as the guide devices 5-8, the housing 54, the drive device(s) 31, 32 and the teeth 14, 24, as well as any input gears 514 and output gears 524. Consequently, these components are subjected to less stress, which reduces maintenance operations and, therefore, the operating cost of the transmission system 10 according to the invention.

[0086] Figure 3 schematically represents the transmission system 10 in its stationary and operational state. The driving shaft 1 and the driving gear 141 are shown with solid lines for the transmission system 10 in its stationary state, and with dashed lines for the transmission system 10 in operation. The driven shaft 2 and the connecting device 3 remain unchanged whether the transmission system 10 is stationary or in operation.

[0087] When the transmission system 10 is stopped, the driving shaft 1, shown in solid line, and the driven shaft 2 are not coaxial, the driving axes AXMA and driven axes AXME being parallel to each other.

[0088] When the transmission system 10 is operating, the forces exerted are such that the driving shaft 1, shown in dotted lines, and the driven shaft 2 become substantially coaxial and aligned, the driving axes AXMA and driven axes AXME also being substantially aligned.

[0089] To obtain such operation under load of the transmission system 10, the misalignment between the leading axes AXMA and driven axes AXME was defined as a function of the relative displacements under load of the leading axes AXMA and driven axes AXME during the operation of this transmission system 10. These displacements of the leading axes AXMA and driven axes AXME were able to be determined by simulations and / or tests.

[0090] A method for limiting parasitic forces in the transmission system can make it possible to determine the value of this initial misalignment.

[0091] This method first comprises a step of determining a relative displacement between the driving axis AXMA and the driven axis AXME during operation of the transmission system. The value of this relative displacement can be determined by simulation and / or testing.

[0092] This relative displacement between the driving axis AXMA and the driven axis AXME can be determined, for example, when the transmission system 10 is in one or more particular operating phases of the transmission system 10. This or these particular operating phases may, for example, include the most penalizing operating phase(s) in terms of stresses suffered, and / or the most used.

[0093] According to a first example, this relative displacement can be determined, for example, when the transmission system 10 transmits a mechanical torque from the driving shaft 1 to the driven shaft 2 greater than or equal to a predetermined torque.

[0094] According to a second example, this relative displacement can be determined as being equal to an average relative displacement of the driving shafts AXMA and driven shafts AXME when the transmission system transmits a mechanical torque from the driving shaft to the driven shaft within a predetermined interval.

[0095] According to a third example, this relative displacement can be determined as being equal to an average relative displacement of the leading axes AXMA and led AXME when the transmission system operates according to the most penalizing operating phase(s) in terms of stresses suffered or the most used.

[0096] Next, this method includes a step of misaligning the driving axis AXMA and the driven axis AXME according to this relative displacement when the transmission system is stopped.

[0097] This method thus makes it possible to determine the value of the misalignment to be applied between the leading axis AXMA and the driven axis AXME at rest. For example, this misalignment is equal to the value of the relative displacement previously determined.

[0098] To achieve this misalignment of the leading axes AXMA and driven axes AXME, the first center of rotation of at least one of the first guiding devices 5, 6 and / or the second center of rotation of at least one of the second guiding devices 7, 8 is offset from a theoretical position in which the leading axes AXMA and driven axes AXME are coaxial and aligned. This offset of a first or second center of rotation can be achieved only radially with respect to the leading axis AXMA or the driven axis AXME, namely in a plane passing through this theoretical position and perpendicular to the leading axis AXMA or the driven axis AXME. This offset of the first or second center of rotation can also combine such a radial offset and an axial offset, parallel to the leading axis AXMA or the driven axis AXME.

[0099] The center of rotation of only one of the first and second guide devices 5-8 can be offset to obtain the desired misalignment between the driving axes AXMA and driven axes AXME, in particular when the driving axes AXMA and driven axes AXME are not parallel to each other when the transmission system 10 is stopped.

[0100] The first centers of rotation of all the first guide devices 5, 6 or the second centers of rotation of all the second guide devices 7, 8 can be offset to obtain the desired gap between the driving axes AXMA and the driven axes AXME. The offsets will be the same for each of the first guide devices 5, 6 or the second guide devices 7, 8 if the driving axes AXMA and the driven axes AXME are parallel to each other when the transmission system 10 is at rest. The offsets will be different for each of the first guide devices 5, 6 or the second guide devices 7, 8 if the driving axes AXMA and the driven axes AXME are not parallel to each other when the transmission system 10 is at rest.

[0101] Whether the leading axes AXMA and led axes AXME are parallel or not, the first centers of rotation of all the first guiding devices 5,6 and the second centers of rotation of all the second guiding devices 7,8 can also be offset.

[0102] Several technical solutions are conceivable to obtain the desired offset of a center of rotation of one of the guiding devices 5-8.

[0103] According to a first embodiment, the offset of the first or second center of rotation of one or more of the first guide devices 5, 6 and / or second guide devices 7, 8 can be obtained by means of the position of the corresponding first housings 15, 16 and / or second housings 17, 18. In this case, the first housings 15, 16 and the second housings 17, 18 are not coaxial when the transmission system 10 is at rest, as shown in [Fig. 1]. The first housings In this case, 15 and 16 are centered on the driving axis AXMA, and the second housings 17 and 18 are centered on the driven axis AXME. This offset of the first or second center of rotation of one or more of the guide devices 5-8 is obtained, for example, by machining the corresponding housing(s) 15-18 in the housing 54.

[0104] According to a second embodiment, the offset of the first or second center of rotation of one or more of the first guide devices 5, 6 and / or second guide devices 7, 8 can be achieved by means of the relevant guide device(s) 5-8. In this case, all the first housings 15, 16 and the second housings 17, 18 are coaxial when the transmission system 10 is at rest. Conversely, the relevant first or second guide device(s) 5-8 are eccentric, namely that their first or second center of rotation is eccentric with respect to the center of the housing 15-18 in which this guide device 5-8 is positioned.

[0105] For example, [Fig. 4] represents a first housing 15 and a first guide device 5 according to this second variant. The first housing 15 is coaxial with the other first and second housings 16-18 and centered, for example, on the driven axis AXME. The first guide device 5 comprises an eccentric outer ring 53 and a "conventional," i.e., annular, inner ring 52. The outer peripheral surface 531 of this eccentric outer ring 53 is centered on the driven axis AXME, while the inner peripheral surface 532 of this eccentric outer ring 53 is centered on the driving axis AXMA. These outer peripheral surfaces 531 and inner peripheral surfaces 532 are therefore eccentric and thus not coaxial. Conversely, the "conventional" inner ring 52 has inner peripheral surfaces 522 and outer peripheral surfaces 521 that are coaxial.The eccentricity of the outer ring 53 is equal to the desired offset of the first center of rotation of this first guiding device 5.

[0106] According to a third embodiment, the offset of the first or second center of rotation of one or more of the first guide devices 5, 6 and / or second guide devices 7, 8 can be achieved by means of an eccentric ring 9 inserted between the housing 15-18 and the relevant guide device 5-8. In this case, all the first housings 15, 16 and the second housings 17, 18 are coaxial when the transmission system 10 is at rest. The first housings 15, 16 and the second housings 17, 18, and on the other hand one of the first guide devices 5, 6 and the second guide devices 7, 8 are, according to this third embodiment, "conventional," namely that their inner rings 52, 62, 72, 82 and outer rings 53, 63, 73, 83 are respectively coaxial in pairs.

[0107] The eccentric ring 9 has two external circular peripheral surfaces 91 and internal 92 which are eccentric with respect to each other, namely that their respective centers are not coaxial.

[0108] An example of a third variant is shown in [Fig. 5], in which such an eccentric ring 9 is positioned in a first housing 15 and around a first guide device 5. The first housing 15 is coaxial with the other first and second housings 16-18 and centered, for example, on the driven axis AXME. The outer peripheral surface 91 of the eccentric ring 9 is centered on the driven axis AXME, while the inner peripheral surface 92 of this eccentric ring 9 is centered on the driven axis AXMA. The outer peripheral surfaces 91 and 92 are thus eccentric and therefore not coaxial. The eccentricity of the eccentric ring 9 is equal to the desired offset of the first center of rotation of this first guide device 5.

[0109] According to a fourth variant, the transmission system 10 may include a housing 54 having at least a first sub-assembly 57 and a second sub-assembly 58. The first sub-assembly 57 has said at least two first housings 15,16 and the second sub-assembly 58 has said at least two second housings 17,18.

[0110] The first subassembly and the second subassembly are fixed to each other so that the driving shaft AXMA and the driven shaft AXME are misaligned when the transmission system 10 is stopped. An example of a fourth variant is shown in [Fig. 1].

[0111] The first subassembly 57 and the second subassembly 58 are thus offset from each other, relative to a position in which the driving axis AXMA and the driven axis AXME would be aligned when the transmission system 10 is stopped. For example, the first subassembly 57 and the second subassembly 58 are offset from each other, relative to a position in which the first housings 15, 16 and the second housings 17, 18 are coaxial when the transmission system 10 is stopped. Consequently, as a result of this offset, the first housings 15, 16 and the second housings 17, 18 are not coaxial when the transmission system 10 is stopped.

[0112] The transmission system 10 can be fitted to an aircraft 100, and in particular a power transmission 50 of this aircraft 100, as shown in [Fig. 6]. The power transmission 50 allows an engine 55 to drive a lift rotor 102 in rotation. The aircraft 100 may also include an auxiliary rotor 103 that can be driven in rotation by the engine 55, via the power transmission 50, for example. The power transmission 50 has an input shaft 51 mechanically connected to the engine 55 and an output shaft 61 mechanically connected to the lift rotor 102.

[0113] When the transmission system 10 is fitted to such an aircraft 100, the particular operating phases of the transmission system 10, used in particular to determine the relative displacement between the leading axes AXMA and led AXME, can be associated with flight phases of aircraft 100, in particular the most penalizing flight phases, which can be the takeoff, cruise flight, or even hover phases, and the most used flight phase which is generally cruise flight.

[0114] Naturally, the present invention is subject to numerous variations in its implementation. Although several embodiments have been described, it is understood that it is not conceivable to exhaustively identify all possible embodiments. It is, of course, conceivable to replace a described means with an equivalent means without departing from the scope of the present invention and the claims.

Claims

Demands

1. Transmission system (10) comprising a driving shaft (1) and a driven shaft (2) and a linkage device (3) mechanically linking said driving shaft (1) and said driven shaft (2), said driving shaft (1) rotating said driven shaft (2) via said linkage device (3), said transmission system (10) comprising at least two first housings (15, 16) and at least two first guide devices (5, 6) rotating said driving shaft (1) about a driving axis (AXMA), each first housing (15, 16) receiving one of said first guide devices (5, 6), said transmission system (10) comprising at least two second housings (17, 18) and at least two second guide devices (7, 8) rotating said driven shaft (2) about a driven axis (AXME), each second housing (17, 18) receiving one of said second guide devices (7, 8),characterized in that said driving shaft (AXMA) and said driven shaft (AXME) are misaligned when said transmission system (10) is stopped, said driving shaft (1) as well as said driven shaft (2) and said linkage device (3) being located around a median line (LM) of said driving shaft (AXMA) and said driven shaft (AXME).

2. Transmission system (10) according to claim 1, wherein said linkage device (3) comprises at least one drive device (31,32) enabling said driving shaft (1) to transmit a mechanical torque to said driven shaft (2).

3. Transmission system (10) according to claim 2, wherein said linkage device (3) comprises an intermediate shaft (35), said at least one drive device (31,32) comprising a first drive device (31) and a second drive device (32), said first drive device (31) transmitting a mechanical torque from said driving shaft (1) to said intermediate shaft (35) and said second drive device (31,32) transmitting a mechanical torque from said intermediate shaft (35) to said driven shaft (2).

4. Transmission system (10) according to any one of claims 2 to 3, in which said at least one drive device (31,32) comprises a device selected from a list comprising splines, at least one key, a bolted assembly, a freewheel, a clutch.

5. Transmission system (10) according to any one of claims 1 to 4, wherein said driving shaft (AXMA) and said driven shaft (AXME) are parallel to each other when said transmission system (10) is at rest.

6. Transmission system (10) according to any one of claims 1 to 4, wherein said driving shaft (AXMA) and said driven shaft (AXME) are inclined relative to each other when said transmission system (10) is at rest.

7. Transmission system (10) according to any one of claims 1 to 6, wherein each first guide device (5,6) has a first center of rotation around which a first inner ring (52,62) of said first guide device (5,6) rotates relative to a first outer ring (53,63) of said first guide device (5,6), each second guide device (7,8) has a second center of rotation around which a second inner ring (72,82) of said second guide device (7,8) rotates relative to a second outer ring (73,83) of said second guide device (7,8), said driving shaft (AXMA) passing through said first centers of rotation, said driven shaft (AXME) passing through said second centers of rotation.

8. Transmission system (10) according to any one of claims 1 to 6, wherein said first housings (15,16) and said second housings (17,18) are cylindrical and coaxial when said transmission system (10) is at rest, and at least one of said first guide devices (5,6) and said second guide devices (7,8) comprises an eccentric outer ring (53,63,73,83), said eccentric outer ring (53,63,73,83) comprising an outer peripheral surface and an inner peripheral surface which are eccentric with respect to each other.

9. Transmission system (10) according to any one of claims 1 to 7, wherein said first housings (15,16) and said second housings (17,18) are cylindrical and coaxial when said transmission system (10) is at rest, and said transmission system (10) comprises at least one eccentric ring (9) inserted between on the one hand one of said first housings (15,16) and said second housings (17,18), and on the other hand one of said first guide devices (5,6) and said second guide devices (7,8), said eccentric ring (9) comprising an external peripheral surface (91) and an internal peripheral surface (92) which are eccentric with respect to each other.

10. Transmission system (10) according to any one of claims 1 to 7, wherein said first housings (15,16) and said second housings (17,18) are cylindrical, said first housings (15,16) are centered on said driving axis (AXMA) and said second housings (17,18) are centered on said driven axis (AXME) when said transmission system (10) is at rest.

11. A transmission system (10) according to any one of claims 1 to 7, wherein said transmission system (10) comprises a housing (54) composed of several assembled subassemblies (56-59), of which at least one first subassembly (57) and a second subassembly (58) are included, said first subassembly (57) comprising said at least two first housings (15, 16) and said second subassembly (58) comprising said at least two second housings (17, 18), and said first subassembly (57) and said second subassembly (58) are fixed to each other such that said driving shaft (AXMA) and said driven shaft (AXME) are misaligned when said transmission system (10) is at rest, said first subassembly and said second subassembly being offset from each other, from a position in which said driving shaft (AXMA) and said the driven axis (AXME) would be aligned when said transmission system (10) is stopped.

12. Power transmission box (50) comprising a transmission system (10) according to any one of claims 1 to 11.

13. Aircraft (100) comprising a mechanical power transmission system (10) according to any one of claims 1 to 11

14. d 1 i. Method for limiting parasitic forces in a transmission system (10) according to any one of claims 1 to 11, said method comprising the following steps: - determination of a relative displacement between said driving axis (AXMA) and said driven axis (AXME) during operation of said mechanical system (10), - misalignment, when said transmission system is at rest, of said driving axis (AXMA) and said driven axis (AXME) as a function of said relative displacement.

15. Method according to claim 14, wherein, during said determination of a relative displacement between said driving shaft (AXMA) and said driven shaft (AXME), said relative displacement between said driving shaft (AXMA) and said driven shaft (AXME) is determined when said transmission system (10) transmits a mechanical torque from said driving shaft (1) to said driven shaft (2) greater than or equal to a predetermined torque.

16. Method according to claim 14, wherein, during said determination of a relative displacement between said driving axis (AXMA) and said driven axis (AXME), said relative displacement between said driving axis (AXMA) and said driven axis (AXME) is equal to an average relative displacement of said driving (AXMA) and driven (AXME) axes when said transmission system (10) transmits a mechanical torque from said driving shaft (1) to said driven shaft (2) within a predetermined interval.

17. A method according to claim 14, wherein, during said determination, said relative displacement between said driving axis (AXMA) and said driven axis (AXME) is equal to an average relative displacement of said driving (AXMA) and driven (AXME) axes when said transmission system (10) is in one or more predetermined operating phases. Mechanical power transmission system, power transmission box, and aircraft

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