Transmission system for aircraft propulsion assembly with the ability to decouple two rotating elements in a fast mode and in a slow mode

Abstract

A decoupling transmission system (2) for an aircraft propulsion unit (1) comprises: a first rotating element (3) carrying a ramp (131), a second rotating element (7), and coupling means (116) for these; an actuator (40) comprising a plunger (140) movable from a rest position to an operating position to actuate the ramp (131) towards a decoupling position of the rotating elements (3, 7), and a cam (50). The plunger (140) carries a cam follower (56) held in contact with a surface (54) of the cam by means of a plunger return means (144). A displacement of the cam (50) by a first angular distance (θ1) in a first direction (D1) moves the plunger (140) from its rest position to its operating position.A displacement of the cam (50) by a second smaller angular distance (θ2), and in a second opposite angular direction (D2), moves the plunger (140) from its rest position to its operating position. See Figure 3 for abbreviations.

Description

Title of the invention: Transmission system for an aircraft propulsion system with the ability to decouple two rotating elements in a fast mode and in a slow mode. Technical field

[0001] The present invention relates to the field of aircraft propulsion systems and more particularly concerns a transmission system with the ability to decouple two rotating elements.

[0002] Such transmission systems are intended in particular to allow efficient torque transmission between a turbomachine and an electric machine, while allowing decoupling between them in the event of failure, or to prevent failure of the electric motor, or of equipment, components or systems related to the latter, without requiring the complete shutdown of the turbomachine.

[0003] Aircraft main propulsion engines generally drive non-propulsive electrical power generation machines at moderate speeds, typically on the order of a few thousand revolutions per minute. These electrical machines are sometimes subject to failures, particularly of mechanical origin, with relatively high prevalence rates compared to the reliability required for the main engines. One way to continue using the propulsion engine is to mechanically disconnect the electrical machine from the turbomachine.

[0004] With the development of hybrid thermal / electric propulsion systems, it is desirable to develop reliable, lightweight, inexpensive, and easily integrable mechanical decoupling systems, which are also adapted to the specific characteristics of such systems.

[0005] Indeed, in propulsion assemblies comprising a turbogenerator intended to generate propulsive electrical energy (i.e. of a level sufficient for driving propulsion components such as propellers or blowers), the electric machines have a power of an order of magnitude comparable to the power of the turbomachine (this nevertheless depends on the number of electric machines driven by the turbomachine), whereas the non-propulsive electric machine of a conventional propulsion assembly is relatively "small" compared to the heat engine.

[0006] Moreover, the mechanical power received by an electric machine within such a propulsion system is considerably greater than that received by a non-propulsive electric machine in a conventional propulsion system.

[0007] Furthermore, the mass of such a machine is not negligible compared to that of the complete propulsion system, which translates into a strong interest in optimizing this mass by the use of high-speed electric machines (on the order of several tens of thousands of revolutions per minute) and / or by the use of permanent magnet machines, also called "PMGs" according to the Anglo-Saxon terminology "Permanent Magnet Generators", which have a high power mass density, but for which short-circuit cases cannot be dealt with simply by de-excitation of the rotor.

[0008] Furthermore, transmission systems with decoupling capability also find application in "parallel" hybrid propulsion systems, where power can be selectively supplied by a thermal engine and / or an electric motor to a propulsion unit such as a propeller. When reversible electric machines are to be used, particularly to perform functions such as recharging power batteries, it is then advantageous, or even necessary, to also have decoupling mechanisms between the electric motor-generator and the propulsion unit.

[0009] The invention is the result of technological research aimed at significantly improving aircraft performance and, in this respect, contributes to reducing their environmental impact and combating climate change. Prior art

[0010] Document GB2592973B discloses a decoupling transmission system for an aircraft propulsion assembly, comprising: a first rotating element and a second rotating element, for example two shafts; coupling means for mechanically coupling the first and second rotating elements to each other and capable of being disengaged by moving the second rotating element relative to the first rotating element along an axis, from a coupling position to a decoupling position; a ramp formed on the second rotating element;and an actuator comprising a plunger configured such that a movement of the plunger from a rest position to a service position causes a ramp engagement element, carried by the plunger, to come into contact with the ramp, such that a rotational movement of the second rotating element causes the ramp to be stressed by the ramp engagement element towards the decoupling position, due to a shape of the ramp provided for this purpose.

[0011] In addition, this transmission system includes a spring arranged to move the plunger towards its service position, and a locking device to retain the plunger in its rest position.

[0012] When a command is given for this purpose, the locking member is placed in an inoperative state so that the plunger is pushed into its service position by the spring and thus engages the ramp. The ramp is shaped so that, under the effect of the rotation of the second rotating element which carries the ramp, the contact of the ramp engagement element carried by the plunger against the ramp causes a displacement of the second rotating element relative to the first rotating element along the axis, resulting in the disengagement of the coupling means and therefore a decoupling of the two rotating elements.

[0013] However, in known decoupling transmission systems, such as that described in the aforementioned GB2592973B, reconnecting—that is, re-engaging the coupling means—after decoupling requires that the rotating elements be stopped beforehand. Otherwise, the mechanical stresses imposed on the rotating elements and their associated components would present an unacceptably high risk of damaging these elements and components. Furthermore, such re-engaging the coupling means generally requires manual operation.

[0014] Furthermore, with such known decoupling-capable transmission systems, in which the coupling means transmit torque through obstacles, these coupling means being, for example, splines, dog clutches, or curved radial teeth (also called "curving couplings"), decoupling of the rotating elements results in axial sliding of the coupling means relative to one another. If such decoupling occurs while the transmission system is operating under load, it can result in mechanical stresses of a level capable of damaging the coupling means themselves and thus reducing the reliability of the transmission system.

[0015] Transmission systems such as that of the aforementioned document GB2592973B also have a disadvantage in that the engagement of the diver with the ramp generally results in a shock between the diver and the ramp, which is likely to promote wear on the latter.

[0016] These drawbacks particularly limit the possibilities of regularly testing such a transmission system to verify its proper functioning, especially in terms of decoupling and reconnection. A manual reconnection method requires a complex and costly operation, necessitating, for example, opening the covers of the propulsion unit and the availability of one or more operators, which is hardly compatible with airport constraints. Furthermore, too frequent testing of such a system results in premature wear of the various contact surfaces involved in the coupling and actuation means (such as the plunger and its associated ramp). Description of the invention

[0017] The invention aims to remedy at least partially these drawbacks.

[0018] To this end, it proposes a transmission system with decoupling capability for an aircraft propulsion system, comprising: - a first rotating element and a second rotating element; - coupling means configured to mechanically couple the first and second rotating elements together and which can be disengaged by means of a displacement of the first rotating element relative to the second rotating element along an axis, from a coupling position to a decoupling position; - a ramp formed on the first rotating element; - an actuator comprising a plunger configured such that a movement of the plunger from a rest position to a service position causes a ramp engagement element, carried by the plunger, to come into contact with the ramp, so that a rotational movement of the first rotating element causes the ramp to be stressed by the ramp engagement element in the direction of the decoupling position, due to a shape of the ramp provided for this purpose;

[0019] in which: - the actuator comprises an actuating cam mounted for rotation about a cam axis and having a cam surface extending around the cam axis at a variable distance from the latter, the cam surface comprising a distal portion defined as the portion of the cam surface furthest from the cam axis; and - the diver wears a cam follower held in contact with the cam surface by means of a diver return mechanism which pulls the diver towards its service position;

[0020] the cam surface having an asymmetrical shape with respect to any plane including the cam axis such that, the cam follower is initially in contact with the distal portion: - a displacement of the actuating cam by a first angular distance and in a first angular direction around the cam axis causes a displacement of the plunger from its rest position to its operating position; and - a displacement of the actuating cam by a second angular distance, less than the first angular distance, and in a second direction Opposite angular movement, around the cam axis, causes the plunger to move from its rest position to its service position.

[0021] Thus, provided that the angular displacement of the actuating cam occurs at a constant speed, the displacement of the actuating cam in the first angular direction generally allows for a relatively slow deployment of the plunger from its rest position to its operating position, while the displacement of the actuating cam in the second angular direction allows for a faster, even near-instantaneous, deployment of the plunger from its rest position to its operating position. The relatively rapid deployment mode of the plunger can be advantageously implemented when the propulsion assembly equipped with the transmission system is in operation and an event occurs requiring rapid decoupling between the rotating elements. The relatively slow deployment mode of the plunger can also be advantageously implemented during maintenance operations on the transmission system, in order to test the proper functioning of the coupling means.The relatively slow movement of the plunger then minimizes damage and wear on the various contact surfaces involved in the coupling means and the actuation means defined by the plunger and the associated ramp.

[0022] In preferred embodiments of the invention, the cam surface further comprises: - a proximal portion defined as the portion closest to the cam axis and in contact with which the cam follower is located when the plunger is in the service position; - a first transition portion defined as the portion connecting the distal portion to the proximal portion in the second angular direction, extending over 180 degrees around the cam axis; and - a second transition portion defined as the portion connecting the distal portion to the proximal portion in the first angular direction, extending less than 180 degrees around the cam axis; - the cam surface being shaped such that, the cam follower is initially in contact with the distal portion: - the movement of the actuating cam around the cam axis in the first angular direction and along the first angular distance results in a movement of the cam follower along the entire first transition portion up to the proximal portion; and - the displacement of the actuating cam around the cam axis in the second angular direction and along the second angular distance results in by moving the cam follower along the entire second transition portion up to the proximal portion.

[0023] Preferably, the distal portion and the first transition portion are of convex cross-section shapes transverse to the cam axis.

[0024] Preferably, the first transition portion has a spiral cross-section transverse to the cam axis.

[0025] Preferably, the second transition portion defines a discontinuity in the cam surface.

[0026] Preferably, the second transition portion is, at least in part, concave in shape.

[0027] In preferred embodiments of the invention, the actuator includes a drive device configured to selectively drive, on command, a displacement of the actuating cam around the cam axis in either the first or second angular direction.

[0028] Preferably, the drive device is an electric motor.

[0029] The invention also relates to an aircraft propulsion assembly, comprising a propulsion unit, an electric machine, a turbomachine and a transmission system of the type defined above, in which the first rotating element of the transmission system is kinematically connected to a rotor of the electric machine while the second rotating element of the transmission system is kinematically connected to a rotor of the turbomachine, and in which at least one of the electric machine and the turbomachine is configured to transmit propulsive power to the propulsion unit.

[0030] In preferred embodiments of the invention, the electric machine is configured to receive propulsive power from the first rotating element. Brief description of the drawings

[0031] The invention will be better understood, and other details, advantages and features thereof will become apparent from the following description, given by way of non-limiting example and with reference to the accompanying drawings in which:

[0032] [Fig-1] is a schematic axial cross-sectional view of an aircraft propulsion assembly including an electric machine, a turbomachine and a transmission system with decoupling capability;

[0033] [Fig.2] is a partial schematic axial cross-sectional view of a system of transmission with decoupling capability according to an embodiment of the invention, which may be part of the propulsion assembly of [Fig.1], and shown in a coupling configuration;

[0034] [Fig.3] is a partial schematic perspective view of the transmission system of the [Fig.2], also in the coupling configuration;

[0035] [Fig.4] is a view similar to [Fig.3] but on which part of the actuator is omitted, and in which the transmission system is shown in a decoupling configuration;

[0036] [Fig.5] is a schematic cross-sectional view of an actuating cam and a cam follower belonging to an actuator forming part of the transmission system of the [Fig.2], shown isolated from the system and in a configuration corresponding to the coupling configuration visible in Figures 2 and 3;

[0037] [Fig.6] comprises three views (a), (b) and (c), each similar to [Fig.5], illustrating the actuating cam and the cam follower respectively in the configuration corresponding to the coupling configuration visible in Figures 2 and 3, in an intermediate configuration obtained by moving the actuating cam in a first angular direction, and in a configuration corresponding to the decoupling configuration visible in [Fig.4], obtained at the end of the movement of the actuating cam in the first angular direction;

[0038] [Fig.7] comprises three views (a), (b) and (c), each similar to [Fig.5], illustrating the actuating cam and the cam follower respectively in the configuration corresponding to the coupling configuration visible in Figures 2 and 3, in an intermediate configuration obtained by moving the actuating cam in a second angular direction opposite to the first angular direction, and in the configuration corresponding to the decoupling configuration visible in [Fig.4], obtained at the end of the movement of the actuating cam in the second angular direction.

[0039] Throughout these figures, identical references may designate identical or analogous elements. Detailed presentation of preferred embodiments

[0040] Figure 1 schematically illustrates a propulsion assembly 1 for an aircraft, comprising a transmission system 2 with decoupling capability. The latter generally comprises a first rotating element 3, a second rotating element 7, and an actuator 40. The transmission system 2 is designed to transmit a rotational motion between the rotating elements 3 and 7, while allowing these elements to be decoupled on command by means of the actuator 40.

[0041] The first rotating element 3 is, for example, a sleeve-shaped disconnecting element carried by a shaft 110 itself mounted for rotation relative to a stator 150, for example by means of one or more guide bearings 117, on a first side C1 of the transmission system. The second rotating element 7 is, for example, in the form of a shaft mounted for rotation relative to the stator 150, for example by means of one or more guide bearings 127a-127b, on a second side C2 of the transmission system. Each of the rotating elements 3 and 7 can be made up of several elements fixed together in rotation with each other.

[0042] The first rotating element 3 and the second rotating element 7 are for example mounted to rotate about the same axis A, relative to the stator 150. Alternatively, the rotating elements 3 and 7 can be mounted to rotate about separate axes parallel to each other or intersecting each other, provided that an appropriate configuration of the means allows the mutual coupling of these elements.

[0043] In some embodiments, the first rotating element 3 is kinematically connected to an electric machine rotor (in this case via shaft 110), and the second rotating element 7 is kinematically connected to a turbomachine rotor. For the purposes of this description, "kinematically connected elements" generally means that the elements are rotationally fixed or form a gear, or form a gear train, by being mechanically connected via one or more pinions. The transmission system 2 is thus configured to transmit rotational motion between the electric machine rotor and the turbomachine rotor.

[0044] In the illustrated example, the shaft 110 carrying the first rotating element 3 is thus integral with the rotor 22 of an electric machine 24. In light of the above, it will be understood that the shaft 110 can, in other examples, be in direct or indirect mechanical contact with the rotor 22 of the electric machine 24, that is to say, form a gear or a gear train with the latter. Similarly, the shaft constituting the second rotating element 7 is in contact with a pinion 26, itself in contact with a rotor shaft 28 of a turbine 29 of a turbomachine 30. The pinion 26 thus ensures the transmission of rotational motion between the shaft constituting the second rotating element 7 and the rotor 28 of the turbine 29.

[0045] Furthermore, the propulsion assembly 1 illustrated also includes a propulsion element 32, such as a propeller or a fan, the drive of which relies on energy supplied by at least one of the electric machine 24 and the turbomachine 30 (where applicable, by the rotor 28 of the turbine 29), to provide propulsion for an aircraft. The energy supplied by the electric machine 24 can be electrical or mechanical, depending on the type of architecture of the propulsion assembly and the role played by the electric machine within this propulsion assembly.

[0046] The transmission system 2 is in particular intended to constitute a mechanical propulsion power transmission system within a hybrid aircraft propulsion system.

[0047] The propulsion assembly 1 illustrated is, for example, a series hybrid propulsion assembly, in which the propulsion element 32 is mechanically meshed with an electric motor 33 supplied with electrical energy by a distribution unit 34, itself supplied Electrical energy is supplied in parallel by a power battery 35, on the one hand, and by the electric machine 24, on the other. The latter is thus configured to operate as a propulsion electric power generator by converting mechanical energy received from the turbomachine 30 and supplying the resulting electrical energy to the distribution unit 34. The latter typically includes DC / AC and AC / DC conversion means. The distribution unit 34 also allows the power battery 35 to be recharged with surplus electrical power during certain operating phases. In such a case, a transmission system with decoupling capability similar to transmission system 2, which will be described in detail below, can, alternatively or in addition, provide a disengageable mechanical coupling between a shaft of the propulsion unit 32 and the rotor of the electric motor 33.

[0048] In other examples, the propulsion assembly 1 may be of the parallel hybrid type, that is to say, comprising a transmission system, for example of the type comprising a gear reducer, configured to mechanically couple the electric machine, operating selectively as a motor or generator, and the turbomachine, in parallel, to the propulsion unit. In this case, the electric machine is supplied with electrical energy by a power battery when it operates as a motor and recharges said battery when it operates as a generator driven by the turbomachine, via the transmission system.

[0049] The remainder of this description is made with reference to Figures 2 to 6 and with constant reference to [Fig.1] when necessary.

[0050] To enable the transmission of a rotational movement between the rotating elements 3 and 7, the transmission system 2 includes coupling means 116, configured to mechanically couple the first and second rotating elements 3 and 7 to each other, and thus enable a transfer of torque between these two elements, and to be able to be disengaged and thus decouple the first and second rotating elements 3 and 7 from each other, by means of a displacement of the first rotating element 3 relative to the second rotating element 7 along an axis, in this case the axis A of rotation common to the two elements 3 and 7, from a coupling position (Figures 2 and 3) to a decoupling position ([Fig.4]).

[0051] To control the coupling and decoupling of the transmission system 2, that is, the engaging and disengaging of the coupling means 116, the transmission system 2 generally comprises a ramp 131 and an actuator 40. The latter includes a plunger 140 configured such that a movement of this plunger 140 from a rest position (Figures 2 and 3) to an operating position ([Fig. 4]) causes a ramp engagement element 143, carried by the plunger 140, to come into contact with the ramp 131, such that a rotational movement The rotation of the first rotating element 3 then causes the ramp 131 to be driven by the ramp engagement element 143 towards the decoupling position of the first rotating element 3, due to a shape of the ramp 131 designed for this purpose. The coupling means 116 take, for example, the form of conventional dog clutches or, alternatively, dog clutches of the type having curved flanks and constituting what is generally called curvilinear radial teeth or "curving couplings". Alternatively, these coupling means 116 may in particular take the form of straight axial splines.

[0052] The means ensuring interaction between the diver 140 and the ramp 131, via the ramp engagement element 143, are, in the illustrated example, similar to those described in the aforementioned document GB2592973B. The detailed configuration of these means will be recalled at the end of this description for the sake of completeness.

[0053] The invention relates to a particularly advantageous actuation method of the plunger 140, which will now be described in detail.

[0054] In general, the invention provides that the actuator 40 comprises an actuating cam 50 mounted to rotate about a cam axis 52 and having a cam surface 54 extending around the cam axis 52 at a variable distance from the latter, while the plunger 140 carries a cam follower 56 maintained in contact with the cam surface 54 under the effect of a plunger return means 144 ([Fig.2]), such as a spring, forcing the plunger 140 towards its service position.

[0055] The cam follower 56 is advantageously mounted on a follower shaft 57 carried by the plunger 140, via a bearing 58 provided for this purpose ([Fig.2]). The contact of the cam follower 56 on the cam surface 54 can thus be a rolling contact.

[0056] As shown more clearly in [Fig.5], the cam surface 54 has a distal portion 54D defined as the portion of the cam surface 54 furthest from the cam axis 52.

[0057] According to the general principle of the invention, the cam surface 54 has an asymmetrical shape with respect to any plane including the cam axis 52, such that, starting from a situation in which the cam follower 56 is in contact with the distal portion 54D, a displacement of the actuating cam 50 by a first angular distance 01 and in a first angular direction DI around the cam axis 52 ([Fig. 6]) causes a displacement of the plunger 140 from its rest position (Figures 2 and 3) to its operating position ([Fig. 4]), while a displacement of the actuating cam 50 by a second angular distance 02, less than the first angular distance 01, and in a second angular direction D2 opposite to the first angular direction D1, around the cam axis 52 ([Fig. 7]), also causes a movement of the diver 140 from its rest position (figures 2 and 3) to its service position ([Fig.4]).

[0058] Thus, provided that the angular displacement of the actuating cam 50 occurs at the same speed in both cases, the displacement of the actuating cam 50 in the first angular direction DI generally allows for a relatively slow deployment of the plunger 140 from its rest position to its operating position ([Fig. 6]), while the displacement of the actuating cam 50 in the second angular direction D2 allows for a faster, even near-instantaneous, deployment of the plunger 140 from its rest position to its operating position ([Fig. 7]). The relatively rapid deployment of the plunger 140 can be advantageously implemented when the propulsion assembly equipped with the transmission system 2 is in operation and an event occurs requiring relatively rapid decoupling between the rotating elements 3 and 7.The relatively slow deployment mode of the plunger 140 can be advantageously implemented during maintenance operations on the propulsion assembly equipped with the transmission system 2, in order to test the proper functioning of the coupling means. The relatively slow movement of the plunger 140 minimizes damage and wear to the various contact surfaces involved in the coupling means 116 and the actuation means defined by the plunger 140 and the associated ramp 131. Furthermore, once the plunger 140 is in its service position, particularly after implementation of the relatively slow deployment mode, the plunger can be returned to its rest position relatively slowly by means of a reverse movement of the cam 50, that is to say, a movement of the cam in the second angular direction D2, as will become clearer below.

[0059] In the illustrated embodiment, the cam surface 54 further comprises a proximal portion 54P defined as the portion closest to the cam axis 52 and with which the cam follower 56 is in contact when the plunger 140 is in the operating position ([Fig. 6]). In other words, regardless of the direction of angular displacement of the actuating cam 50, the plunger 140 reaches its operating position when the cam follower 56 is in contact with one and the same portion of the cam surface, namely the aforementioned proximal portion 54P. Such an arrangement makes it possible to maximize the angular gap between the displacement of the actuating cam 50 in the first angular direction D1, necessary to bring the plunger 140 from its rest position to its service position, and the displacement of the actuating cam 50 in the second angular direction D2, necessary to bring the plunger 140 from its rest position to its service position.

[0060] In this context, the cam surface 54 comprises a first transition portion 54T1 defined as the portion connecting the distal portion 54D to the portion The proximal 54P is in the second angular direction D2. This first transition portion 54T1 extends over more than 180 degrees around the cam axis 52, preferably over more than 270 degrees. The cam surface 54 also includes a second transition portion 54T2 defined as the portion connecting the distal portion 54D to the proximal portion 54P in the first angular direction D1. This second transition portion 54T2 extends over less than 180 degrees around the cam axis 52, preferably over less than 90 degrees.

[0061] The cam surface 54 is shaped so that, starting from a situation in which the cam follower 56 is in contact with the distal portion 54D ([Fig.6](a)), on the one hand, the displacement of the actuating cam 50 around the cam axis 52 in the first angular direction Dl and along the first angular distance 01 results exactly in a displacement of the cam follower 56 along the entire first transition portion 54T1 ([Fig.6](b)) up to the proximal portion 54P ([Fig.6](c)). On the other hand, still starting from the situation in which the cam follower 56 is in contact with the distal portion 54D ([Fig.7](a)), the displacement of the actuating cam 50 around the cam axis 52 in the second angular direction D2 and along the second angular distance 02 results in a displacement of the cam follower 56 along the entire second transition portion 54T2 ([Fig.7](b)) up to the proximal portion 54P ([Fig.7](c)).These two movements of the actuating cam 50 each allow the plunger 140 to be moved from its rest position to its operating position.

[0062] Furthermore, starting from the situation in which the cam follower 56 is in contact with the proximal portion 54P ([Fig. 6](c)), a displacement of the actuating cam 50 around the cam axis 52 in the second angular direction D2 and along the first angular distance 01 results in the cam follower 56 returning along the entire first transition portion 54T1 to the distal portion 54D ([Fig. 6](a)). Such a displacement of the actuating cam 50 returns the plunger 140 from its operating position to its rest position.

[0063] The distal portion 54D and the first transition portion 54T1 are advantageously of convex cross-section shapes transverse to the cam axis 52, as shown in figures 5 to 7. Such a configuration makes it possible to make the movement of the plunger 140 as fluid as possible.

[0064] The first transition portion 54T1 preferably has a spiral cross-section transverse to the cam axis 52. Such a shape, which implies that the radial distance from the cam surface 54 to the cam axis 52 varies continuously from one end to the other of the first transition portion 54T1, allows for a particularly smooth movement of the plunger 140 from its rest position to its position service when the actuating cam 50 is moved in the first angular direction Dl.

[0065] In preferred embodiments of the invention such as that illustrated in Figures 5-7, the second transition portion 54T2 defines a discontinuity in the cam surface 54, that is to say a step or a relatively abrupt change in distance of the surface 54 with respect to the cam axis 52.

[0066] In the illustrated example, the second transition portion 54T2 is, at least in part, concave in shape. This feature allows for a faster movement of the plunger 140 at the beginning of its movement from its rest position to its operating position, and a certain slowing of the plunger's movement as it approaches its operating position, so as to mitigate as much as possible the shock upon engagement of the ramp engagement element 143 of the plunger 140 with the ramp 131. This geometry is also relatively well-suited for manufacturing by grinding.

[0067] Alternatively, the cam surface 54 can be shaped so that the position of the cam follower 56 on it is different when the plunger 140 is in its service position at the end of the cam 50's movement in the first angular direction D1, and when the plunger 140 is in its service position at the end of the cam 50's movement in the second angular direction D2. The difference between the first angular distance 01 and the second angular distance 02 is, in such a case, less than in the illustrated example.

[0068] With reference to Figures 2 and 3, the actuator 10 comprises a drive device 60, for example an electric motor, configured to selectively drive, on command, a displacement of the actuating cam 50 around the cam axis 52 in one or the other of the first and second angular directions D1 and D2. For this purpose, the actuating cam 50 is fixed to an output shaft 62 of the drive device 60.

[0069] The decoupling, as well as the recoupling, of the rotating elements 3 and 7 can thus be implemented remotely by simply controlling the drive device 60. A test of the transmission system 2 can therefore be carried out in a considerably less costly manner than with known systems such as that of the aforementioned document GB2592973B. Moreover, such tests of the transmission system 2 can be carried out while considerably reducing the risks of wear and damage to the system, provided that the rotational speed of the ramp 131 (and therefore the rotational speed of the rotating element 3) remains limited during these tests.

[0070] The detailed configuration of the means ensuring the interaction between the diver 140 and the ramp 131 via the ramp engagement element 143 will now be recalled, with reference to Figures 2-4.

[0071] In the context of the illustrated example, the shaft 110 includes a collar 111 defining splines 114 arranged to mesh with splines 104 of the first rotating element 3. Consequently, the first rotating element 3 is made rotationally fixed to the shaft 110 by means of the meshed splines 104, 114 and can move along the axis A relative to the shaft 110. The coupling means 116 include first coupling elements 105 carried by the first rotating element 3 and second coupling elements 125 carried by the second rotating element 7, which are axially separable from each other, and which take, for example, the form of dog clutches. When engaged, the coupling elements 105, 125 transfer the rotary torque between the rotating elements 3 and 7 and thus define the coupling configuration of the coupling means 116.When the coupling elements 105, 125 are axially separated due to the relative axial separation of the first and second rotating elements 3 and 7, the coupling means are in their decoupling configuration.

[0072] The transmission system 2 further includes a coupling return means 119. The coupling return means 119 is arranged to drive the first rotating element 3 towards the second rotating element 7, and more generally to drive the coupling means 116 towards their coupling configuration.

[0073] In [Fig. 2], the coupling return means 119 is shown as a helical spring arranged around axis A, but it is understood that other suitable return means may be used instead of or in addition to a spring. A first end 119a of the coupling return means 119 bears against an internal shoulder 108 of the first rotating element 3. A second end 119b of the coupling return means 119 abuts against the shaft 110. The coupling return means 119 is arranged to be in compression so that it exerts a force to urge the first rotating element 3 in the opposite direction to the shaft 110 and therefore in the direction of the second rotating element 7, thus pushing the first coupling elements 105 into engagement with the second coupling elements 125.

[0074] A ramp sleeve 130 defining the ramp 131 is fixedly mounted on the first rotating element 3. In the illustrated example, the ramp sleeve 130 is arranged around an external circumferential surface of a first end 106 of the first rotating element 3. The ramp 131 extends around at least a portion of the angular extent of the ramp sleeve 130. Furthermore, the splines 104 of the first rotating element 3 are arranged around an external circumferential surface of a second end 107 of the first rotating element 3. Alternatively, the ramp 131 can be entirely formed by the first rotating element 3.

[0075] The plunger 140 is mounted on the stator 150 so as to be movable towards the axis A, i.e. towards the ramp sleeve 130, from the rest position to the service position of the plunger 140.

[0076] In the illustrated example, the plunger 140 comprises a cylindrical body mounted to slide in an extension 142 of the housing formed by the stator 150, along a sliding axis S orthogonal to the axis A. It is understood that the plunger 140 can alternatively be mounted to slide along an axis oblique to the axis A. The plunger 140 is thus movable along its sliding axis S, between its rest position and its service position.

[0077] The spring constituting the plunger return means 144 is disposed between the plunger 140 and a wall of the housing formed by the stator 150 so as to force the plunger 140 towards its service position, i.e. towards the axis A, but it is understood that other suitable return means can be used for this purpose.

[0078] In figures 2 and 3, the plunger 140 is in its rest position. As can be seen from the above, the plunger 140 is held in its rest position, against the force of the plunger return means 144, by the support of the cam follower 56 against the distal portion 54D of the cam surface 54 defined by the cam 50, which thus opposes the movement of the cam follower 56, and therefore of the plunger 140, along the sliding axis S.

[0079] The plunger 140 advantageously includes a bearing 141, for example a roller or ball bearing, arranged at the end of the plunger 140 directly opposite the ramp 131, and defining the ramp engagement element 143, as will become clearer in what follows.

[0080] In the service position of the plunger 140, the ramp engagement element 143 engages the ramp 131 via the bearing 141 to axially move the first rotating element 3 in the opposite direction to the second rotating element 7 in order to put the coupling means 116 into their decoupling configuration.

[0081] More specifically, the bearing 141 of the plunger 140 comprises an inner ring 141a, fixed to an end portion of the plunger 140, and an outer ring 141b separated from the inner ring 141a by rolling elements, and thus free to rotate about the sliding axis S. The bearing 141 further comprises a bearing cover constituting the ramp engagement element 143, disposed around and fixed to at least a portion of the outer circumferential surface of the outer ring 141b so as to rotate with it. The bearing cover 143 may be an integral part of the outer ring 141b by using, for example, a custom-made bearing. The bearing cover 143 may further be disposed so as to cover an axial face of the bearing 141. Thus in the illustrated example, the bearing cover 143 is arranged directly opposite the ramp sleeve 130. In the rest position, the plunger 140 is positioned so that a first half of the bearing 141 (represented on [Fig.2] to the right of the plunger 140) is arranged near, and radially outwards, the ramp sleeve 130, but without contact with it. The movement of the plunger 140 towards the service position, i.e. towards the axis A, causes the bearing 141 to engage with the ramp sleeve 130. When the bearing 141 engages the ramp 131 defined on the ramp sleeve 130, the interaction between the bearing 141 and the ramp 131 forces the ramp sleeve 130 along the axis A in such a way as to cause an axial displacement of the first rotating element 3 in the opposite direction to the second rotating element, thus disengaging the coupling means 116.

[0082] As explained in the aforementioned GB2592973B document, the use of a roller bearing prevents excessive friction between the plunger 140 and the ramped sleeve 130 during and after decoupling. By reducing friction, the risk of excessive heat generation and metal debris is reduced. Thus, the transmission system 2 can be more durable and efficient, and can withstand a greater number of decoupling and recoupling cycles. The invention described above therefore offers a synergistic advantage in combination with the roller bearing 141.

[0083] In more detail, the ramped sleeve 130 comprises an inner flat section 133, which includes an annular surface arranged around the axis A, and which extends around the entire angular range of the first rotating element 3. The ramped sleeve 130 further comprises an outer flat section 132, arranged around at least a portion of the axis A, and thus extending around at least a portion of the angular range of the first rotating element 3. The ramp 131 and the outer flat section 132 are arranged radially outside the inner flat section 133. The outer flat section 132 is axially offset, along the axis A, relative to the inner flat section 133.The outer flat section 132 is offset from the inner flat section 133 towards the flange 111, but it will be understood by a qualified person that a different arrangement can be used in different embodiments, such as in an embodiment in which the ramped sleeve would be arranged around the second rotating element 7. The ramp 131 of the ramped sleeve 130 starts at an axial position of the outer flat section 132 and inclines helically towards the axial position of the inner flat section 133, i.e. towards the second rotating element 7. Therefore, the ramp 131, by its helical shape, progressively connects the outer flat section 132 to the inner flat section 133.

[0084] Further details concerning detailed configuration examples of the ramp sleeve 130 can be found in the aforementioned GB2592973B document, in particular from page 13, line 23 to page 14, line 32.

[0085] The implementation of the transmission system 2 will now be described. As shown in Figures 2 and 3, the plunger 140 is initially in its rest position, with the cam follower 56 bearing against the distal portion 54D of the cam surface 54. The first rotating element 3 is held in its coupling position by the coupling return means 119. Consequently, the coupling means 116 are engaged, so that a rotational torque can be transferred between the first rotating element 3 and the second rotating element 7 via the coupling means 116. In this situation, the second rotating element 7, the first rotating element 3, the ramp sleeve 130, and the shaft 110 rotate together relative to the plunger 140.

[0086] When decoupling is desired or necessary, the cam 50 is rotated around the cam axis 52, optionally by the drive device 60, until the cam follower 56 reaches the proximal portion 54P. The cam 50 is moved either in the first angular direction DI if a gradual movement of the plunger 140 is desired, for example during testing, or in the second angular direction D2 if a rapid movement of the plunger 140 is necessary, for example in the event of an operating incident.

[0087] In both cases, the plunger 140 is pushed by the spring 144 towards the axis A, into its service position, illustrated by [Fig.4].

[0088] Depending on the angular position of the ramp sleeve 130 when the plunger 140 is moved to its service position, the bearing 141 will either come into contact with an outer circumferential surface of the ramp 131 or engage with the outer flat section 132. In the first case, the ramp sleeve 130 will rotate relative to the plunger 140 until the outer flat section 132 is brought into angular alignment with the bearing 141. While the plunger 140 is in contact with the outer circumferential surface of the ramp 131, the bearing cover forming the ramp engagement element 143 rotates as the bearing 141 moves along the surface of the ramp sleeve 130. In this way, the bearing cover 143 reduces friction between the moving parts, even before the bearing 141 engages the ramp 131.Once the outer flat section 132 is angularly aligned with the bearing 141, the spring 144 continues to push the plunger 140 into engagement with the outer flat section 132.

[0089] Once the bearing 141 is engaged with the outer flat section 132, the bearing cover 143 and the outer ring 141b rotate in response to the rotation of the outer flat section 132, thus reducing friction between the moving parts. As the ramped sleeve 130 continues to rotate relative to the plunger 140, The outer flat section 132 also does this, until the bearing 141 finally engages the ramp 131. At this point, the continued rotation of the ramp sleeve 130 relative to the plunger 140 axially stresses the ramp sleeve 130 (to the right of [Fig. 3]), thus moving the first rotating element 3 from its coupling position to its decoupling position, thereby disengaging the coupling means 116. Once the ramp sleeve 130 has been moved a sufficient distance along axis A, the continued thrust of the plunger 140 towards axis A brings the bearing 141, in this case the bearing cover forming the ramp engagement element 143, into engagement with the inner flat section 133. The engagement of the bearing 141 with the inner flat section 133 maintains the ramp sleeve 130 in an axial position that holds the first rotating element 3 in its position of decoupling, against the action of the coupling return means 119.Once the coupling means 116 are disengaged, the rotating elements 3 and 7 are free to rotate relative to each other. If the ramped sleeve 130 continues to rotate relative to the plunger 140, rolling contact is ensured between them by the bearing 141. Thus, the bearing 141 reduces wear between the plunger 140 and the ramped sleeve 130.

Claims

Demands

1. Transmission system (2) with decoupling capability for an aircraft propulsion assembly (1), comprising: • a first rotating element (3) and a second rotating element (7); • coupling means (116) configured to mechanically couple the first and second rotating elements (3, 7) to each other and capable of being disengaged by means of a displacement of the first rotating element (3) relative to the second rotating element (7) along an axis (A), from a coupling position to a decoupling position; • a ramp (131) formed on the first rotating element (3); • an actuator (40) comprising a plunger (140) configured so that a movement of the plunger from a rest position to a service position causes a ramp engagement element (143), carried by the plunger (140), to come into contact with the ramp (131), so that a rotational movement of the first rotating element (3) causes the ramp (131) to be stressed by the ramp engagement element (143) in the direction of the decoupling position, due to a shape of the ramp (131) provided for this purpose; characterized in that: • the actuator (40) includes an actuating cam (50) mounted for rotation about a cam axis (52) and having a cam surface (54) extending around the cam axis (52) at a variable distance from the latter, the cam surface (54) comprising a distal portion (54D) defined as the portion of the cam surface (54) furthest from the cam axis (52); and • the plunger (140) carries a cam follower (56) held in contact with the cam surface (54) by means of a plunger return means (144) which forces the plunger (140) towards its service position; the cam surface (54) having an asymmetrical shape with respect to any plane including the cam axis (52) such that, the cam follower (56) is initially in contact with the distal portion (54D): • a displacement of the actuating cam (50) by a first angular distance (01) and in a first angular direction (Dl) around the cam axis (52) causes a displacement of the plunger (140) from its rest position to its operating position; and • a displacement of the actuating cam (50) by a second angular distance (02), less than the first angular distance (01), and in a second angular direction (D2) opposite, around the cam axis (52), causes a displacement of the plunger (140) from its rest position to its service position.

2. A transmission system according to claim 1, wherein the cam surface (54) further comprises: • a proximal portion (54P) defined as the portion closest to the cam axis (52) and in contact with which the cam follower (56) is located when the plunger (140) is in the service position; • a first transition portion (54T1) defined as the portion connecting the distal portion (54D) to the proximal portion (54P) in the second angular direction (D2), extending over 180 degrees around the cam axis (52); and • a second transition portion (54T2) defined as the portion connecting the distal portion (54D) to the proximal portion (54P) in the first angular direction (Dl), extending less than 180 degrees around the cam axis (52); the cam surface (54) being shaped such that, the cam follower (56) is initially in contact with the distal portion (54D): • the displacement of the actuating cam (50) around the cam axis (52) in the first angular direction (Dl) and along the first angular distance (01) results

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9. by a displacement of the cam follower (56) along the entire first transition portion (54T1) to the proximal portion (54P); and • the movement of the actuating cam (50) around the cam axis (52) in the second angular direction (D2) and along the second angular distance (02) results in a movement of the cam follower (56) along the entire second transition portion (54T2) up to the proximal portion (54P). A transmission system according to claim 2, wherein the distal portion (54D) and the first transition portion (54T1) have a convex cross-section transverse to the cam axis (52). A transmission system according to claim 3, wherein the first transition portion (54T1) has a spiral cross-section transverse to the cam axis (52). Transmission system according to any one of claims 2 to 4, wherein the second transition portion (54T2) defines a discontinuity in the cam surface (54). Transmission system according to any one of claims 2 to 5, wherein the second transition portion (54T2) is, at least in part, concave in shape. Transmission system according to any one of claims 1 to 6, wherein the actuator (40) comprises a drive device (60) configured to selectively drive on command a displacement of the actuating cam (50) around the cam axis (52) in either of the first and second angular directions (D1, D2). Transmission system according to claim 7, wherein the drive device (60) is an electric motor. Propulsion assembly (1) for aircraft, comprising a propulsion unit (32), an electric machine (24), a turbomachine (30) and a transmission system (2) according to any one of claims 1 to 8, wherein the first rotating element (3) of the transmission system is kinematically connected to a rotor (22) of the electric machine (24) while the second rotating element (7) of the transmission system is kinematically connected to a rotor (28) of the turbomachine (30), and wherein at least one of the

10. The electric machine (24) and the turbomachine (30) are configured to transmit propulsive power to the propulsion unit (32). Propulsion assembly according to claim 9, wherein the electric machine (24) is configured to receive propulsive power from the first rotating element (3).

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