Electromagnetic actuator and transmission system equipped with such an actuator

Abstract

The invention relates to an electromagnetic actuator (50) for a transmission system, comprising: - a base (51) and an outer casing (52) defining a hollow housing (50a); - a solenoid (57) placed inside the housing; - a closure cover (59) attached to the base (51) in order to form an annular opening in the housing, said closure cover covering one of the lateral faces of the solenoid; - a piston (54) of cylindrical shape comprising a piston body (54a) and a pusher part (54b), which is axially movable within the housing between a retracted position and a deployed position in which the piston body (54a) bears on the closure cover and the pusher part (54b) passes through the annular opening.

Description

Description Title of the invention: Electromagnetic actuator and transmission system equipped with such an actuator Technical field

[0001] The invention relates to the field of vehicle transmission chains.

[0002] It relates more particularly to an electromagnetic actuator for a transmission system and the transmission system equipped with such an actuator.

[0003] The invention also relates to a differential type transmission system for transmitting and distributing torque from an engine to two wheel shafts of an axle of the vehicle. This comprises a first element intended to be driven by an engine, a second element intended to drive at least one wheel shaft of a vehicle, a coupling device capable of selectively coupling the first element to the second element and said electromagnetic actuator for controlling the coupling device. Technological background

[0004] Document DE102013111891 A1 discloses a differential-type transmission system. The transmission system comprises a differential housing rotatable about an axis A which is equipped with a toothed wheel driven by a vehicle engine. Inside the housing are housed a carrier ring gear guided in rotation in the housing, two planetary gears which are mounted in rotation on the carrier ring gear about an axis B perpendicular to the axis A, and two planetary gears which each mesh with the two planetary gears and which are each integral in rotation with a wheel shaft. Used on a motor vehicle, the differential-type transmission system allows the drive wheels to rotate at different speeds when passing through a bend: the wheels located on the outside of the bend rotate faster than those located on the inside.

[0005] Furthermore, the transmission system comprises a coupling device which allows either the transmission system housing to be coupled to the carrier ring gear in order to enable transmission and distribution of torque from the engine to the two wheel shafts of the axle or to uncouple them in order to interrupt the transmission of torque between the engine and the wheel shafts. The coupling device is a dog clutch device. It comprises a first coupling part having an annular part arranged outside the housing and projecting elements which extend from the annular part and pass through orifices provided in the housing, which allows the first coupling part and the housing to be rotationally secured. The second coupling part of the coupling device comprises the carrier ring. The projecting elements comprise teeth intended to cooperate with complementary grooves provided on the carrier ring. The first coupling part is axially movable relative to the housing between an uncoupled position and a coupled position in which the teeth of the first coupling part mesh with the grooves of the carrier ring.

[0006] An electromagnetic actuator is capable of exerting an axial force on the first coupling part so as to move it from the uncoupled position to the coupled position. The actuator comprises in particular a piston made of two separate parts having different materials, a piston body made of ferromagnetic material to react to the action of the magnetic flux of the actuator and a pusher part made of paramagnetic material to prevent unwanted leakage of magnetic flux to other components of the transmission system. Such an electromagnetic actuator is not fully satisfactory because it requires the use of expensive and rare material, which increases its complexity and cost.

[0007] Furthermore, the transmission system comprises an annular target which is axially fixed to the annular part of the first coupling portion. The annular target is arranged axially opposite a sensor, such as a Hall effect sensor, which delivers a signal representative of an axial distance between the sensor and the annular target.

[0008] The transmission system further comprises an elastic washer which is arranged axially between the annular target and the housing. This elastic washer has the function in particular of exerting a return force on the first coupling part so as to return it to its uncoupled position when the electromagnetic actuator no longer exerts force on the first coupling part.

[0009] Such a transmission system is not fully satisfactory because it has many different parts, in particular to ensure the target and return functions of the coupling device in its uncoupled position, which increases its complexity and bulk. Summary

[0010] One idea behind the invention is to propose an electromagnetic actuator that does not require the use of paramagnetic material to avoid unwanted leaks. of magnetic flux to other components of the transmission system; this actuator being simpler to manufacture.

[0011] The invention aims to remedy this problem by proposing an electromagnetic actuator for a transmission system comprising: - a base and an external casing defining a hollow housing; - a solenoid placed inside the housing; - a closing cover attached to the base to form an annular opening in the housing, said closing cover covering one of the side faces of the solenoid; - a piston, of revolution shape around a main axis X comprising a piston body and a pusher part, which is axially movable within the housing between a retracted position and a deployed position in which the piston body comes to bear on the closing cover and the pusher part passes through the annular opening, the electromagnetic actuator being remarkable in that the piston, made in a single piece from a ferromagnetic material, surrounds the solenoid and comprises a stop surface defining an air gap with the closing cover, said stop surface being frustoconical or partially spherical.

[0012] This electromagnetic actuator with its piston, made from a single piece of ferromagnetic material such as steel, has the advantage of being more responsive than a piston made partially from paramagnetic material such as brass, which has a higher density. The single-piece piston is therefore lighter.

[0013] The base can be made in several parts, for example an inner tube equipped with a closing plate. In this case, the inner tube, the closing plate and the outer casing define the hollow housing.

[0014] Advantageously, the closure cover may comprise a stop face complementary to the stop surface of the piston, respectively of truncated cone or partially spherical shape, the air gap being produced between the stop surface of the piston and the stop face of the closure cover. According to one variant, the truncated cone surface of the piston and the complementary truncated cone surface of the closure cover have similar angles. According to another variant, the truncated cone surface of the piston and the complementary truncated cone surface of the closure cover have different angles. This avoids the phenomenon of adhesion of the two surfaces. More generally, the invention aims to protect any type of geometry for which the stop surface and the stop face are not perpendicular to the main axis X.

[0015] Preferably, the air gap may be located on a diameter larger than the outer diameter of the solenoid. The particular geometry of the piston and the closing cover thus limits unwanted leakage of magnetic flux outside the actuator. For example, the air gap is defined by the outer diameter of the closing cover.

[0016] Advantageously, the pusher portion of the piston may comprise an external collar extending radially from the piston body, the external collar being located outside the housing of the electromagnetic actuator.

[0017] Preferably, the outer collar may form a stop with the outer casing of the housing when the piston is in its retracted position. The particular geometry of the pusher portion defines a stable retracted position for the piston.

[0018] Advantageously, the pusher portion of the piston may comprise a bearing surface arranged to bear on a component of the transmission system. The bearing surface is perpendicular to the main axis X.

[0019] Preferably, the bearing surface of the piston may include a surface treatment facilitating sliding. This limits wear on the end of the piston, particularly when the other component slides circumferentially on the lateral bearing surface.

[0020] Advantageously, the closing cover may comprise a shoulder against which a shoulder of the piston body abuts when the piston is in the deployed position.

[0021] Preferably, the piston body may comprise two cylindrical centering portions arranged opposite the bore of the external casing.

[0022] Another idea underlying the invention is to propose a transmission system equipped with a coupling device, a target and a sensor capable of delivering a signal representative of the state of the coupling device; this transmission system being simpler and / or less bulky.

[0023] The invention according to another of its aspects aims to remedy this problem by proposing a transmission system for a motor vehicle comprising: - a first element and a second element movable in rotation relative to each other around a main axis X, one of the first and second elements being intended to be driven by a motor and the other of the first and second elements being intended to drive at least one wheel shaft of the motor vehicle; and - a coupling device which comprises: - a first coupling part which is rotationally fixed to the first element and a second coupling part which is rotationally fixed to the second element, the first coupling part being axially movable relative to the first element between a coupled position in which the first coupling part is coupled with the second coupling part to transmit a torque between the first element and the second element and an uncoupled position in which the first coupling part and the second coupling part are uncoupled from each other, - an elastic return device partially fixed to the first element and arranged to deform elastically during the movement of the first coupling part between the uncoupled position and the coupled position and to exert a return force capable of elastically returning the first coupling part towards the uncoupled position or towards the coupled position, said elastic return device comprising an actuating portion axially movable relative to the first element and - the electromagnetic actuator incorporating all or part of the characteristics mentioned above, in which the piston bears axially on the actuating portion of the elastic return device.

[0024] Thus, the elastic return device jointly ensures the interface between the coupling device and the electromagnetic actuator while ensuring the return of the first coupling part to its uncoupled position or to its coupled position. This makes it possible to reduce the cost, complexity and size of such a transmission system.

[0025] Advantageously, the elastic return device comprises a first fixing zone fixed to the first coupling part, a second fixing zone fixed to the first element and an elastic return portion connecting the first fixing zone to the second fixing zone.

[0026] According to one embodiment, the elastic return device may be an annular disc comprising on its internal periphery the actuating portion, the disc being capable of elastically deforming between the actuating portion and the second fixing zone during axial movement of the piston. In this embodiment, the actuating portion is contiguous with the first fixing zone.

[0027] According to a variant of this embodiment, the disc is made of spring steel, such as XC 70 steel, advantageously pre-hardened. The disc may have a thickness of between 0.4 and 1.2 mm, for example of the order of 0.8 mm.

[0028] According to another variant of this embodiment, the disc is made of stainless steel which is a non-magnetic metal, which also limits unwanted leakage of magnetic flux.

[0029] Preferably, the disc may be dimensioned to generate a stiffness opposing axial movement of the piston towards the first coupling part which is between 5 and 500 N / mm. The disc thus generates an axial preload on the piston, even when the latter is in its retracted position.

[0030] Advantageously, the disc may comprise a plurality of elastic return portions each produced in the form of an elastic blade which connects the first fixing zone to the second fixing zone.

[0031] Preferably, the actuating portion of the disc may be an internal annular portion which bears on the bearing surface of the piston. When the first coupling portion is coupled with the second coupling portion, the actuating portion slides on the bearing surface of the piston and when the first coupling portion is uncoupled with the second coupling portion, the actuating portion is in static support on the bearing surface of the piston.

[0032] Advantageously, the disc may include an outer annular target portion that moves axially in conjunction with the actuating portion as the piston moves from its retracted position to its extended position.

[0033] In this embodiment, the transmission system may include a sensor that is disposed opposite the outer annular portion of the disk and that is configured to deliver a signal representative of a distance between the sensor and the target annular portion.

[0034] Thus, the disc has a dual functionality, namely, on the one hand, forming the target whose position is capable of being detected by a sensor so as to deliver a signal indicating the position of the first part of the coupling device and, on the other hand, ensuring the return of the first coupling part to its uncoupled position. This makes it possible to reduce the cost, complexity and size of such a transmission system.

[0035] According to another embodiment, the elastic return device may comprise a set of helical springs distributed circumferentially around the main axis X which form the elastic return portion.

[0036] According to another embodiment, the elastic return device may comprise a corrugated washer extending circumferentially around the main axis X which forms the elastic return portion.

[0037] The transmission system according to the invention may have one or other of the characteristics described below combined with each other or taken independently of each other: - the sensor is arranged axially opposite the annular portion of the disc. - during the movement of the first coupling part from the uncoupled position to the coupled position, the elastic return portion is elastically constrained between a support zone of the transmission system and the fixing zone. - the support zone is axially fixed relative to the second coupling part. - each of the elastic blades has a free end. - the elastic blade rests against the support zone of the transmission system via the ends of the elastic blades. - each elastic blade is arranged in a window formed in the disc. - the elastic blades are regularly distributed around the X axis so as not to generate imbalance. - the elastic blades are located radially inside the annular portion forming the target, which makes it possible to limit the radial size of the disc. - each elastic blade extends in a direction having a circumferential component around the X axis. This makes it possible to obtain, for a given radial size, elastic blades of greater length and, consequently, of lower stiffness. - the first element comprises a housing inside which the second coupling part is housed, the first coupling part comprising an annular part which is housed inside the housing and a plurality of connecting pads which axially connect the annular part of the first coupling part with the disc, each of the connecting pads passing through a corresponding opening provided in the housing. - the disc is arranged outside the housing and is fixed to the plurality of connecting pads of the first coupling part. - the housing comprises bosses projecting axially towards the outside of the housing towards the disc, each boss having one end forming support zones associated with the second disc fixing zone. - the bosses have an axial dimension greater than or equal to the travel of the first coupling part between the coupled position and the uncoupled position. - the first element is a differential box. - the second element comprises a carrier ring which is guided in rotation around the main axis X inside the housing, two satellite gears which are mounted in rotation on the carrier ring around a secondary axis Z perpendicular to the main axis X and two planetary gears which are movable in rotation around the main axis X, are each engaged with the two satellite gears and are each intended to be integral in rotation with a wheel shaft. Thus, the transmission system forms a differential allowing the wheel shafts to rotate at different speeds. - the two satellite gears each have a bevel gear which meshes with a complementary bevel gear of the two planetary gears. - the second coupling part of the coupling device is rotationally fixed to the carrier ring relative to the main axis X. Thus, when the coupling device is in the coupled position, the transmission system distributes the torque coming from the engine to the two wheel shafts. Conversely, the transmission of torque is interrupted between the housing and the carrier ring in the uncoupled position of the coupling device. - the second coupling part of the coupling device is formed in one piece with the carrier crown. - the second coupling part is rotationally fixed to one of the planetary gears. In such an embodiment, when the latter is in the coupled position, the torque is transmitted between the first element and the second element via the gears but the differential function is blocked by the coupling device, which prevents the wheel shafts from rotating at different speeds.

[0038] According to one embodiment of the invention, the coupling device is a dog clutch device, one of the first and second coupling parts comprising teeth and the other comprising corresponding grooves in which are engaged said teeth when the first coupling part is in the coupled position.

[0039] According to another embodiment of the invention, the coupling device is a disconnecting device capable of selectively interrupting the transmission of torque between the first element and the second element.

[0040] According to another of its aspects, the invention also relates to a motor vehicle and a transmission system incorporating all or part of the characteristics mentioned above.

[0041] Advantageously, the motor vehicle comprises an electric machine and the first element of the transmission system is capable of being driven by the electric machine.

[0042] The electric machine and transmission system can be integrated into an electric axle.

[0043] Other characteristics and advantages of the invention are highlighted by the following description of non-limiting examples of embodiments of the different aspects of the invention. Brief description of the figures

[0044] The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the accompanying drawings. [fig.1] Figure 1 is an overall view, in section, of a transmission system equipped with an electromagnetic actuator according to a first embodiment. [fig.2] Figure 2 is an isometric view of the transmission system of Figure 1. [fig.3] Figure 3 is a detail view of the electromagnetic actuator in the retracted position of Figure 1. [fig.4] Figure 4 is an isometric view of the piston of the electromagnetic actuator of Figure 1. Description of the embodiments

[0045] In the description and the claims, the terms "external" and "internal" as well as the orientations "axial" and "radial" will be used to designate, according to the definitions given in the description, elements of the transmission system. By convention, the "radial" orientation is directed orthogonally to the main axis X of rotation of the transmission system determining the "axial" orientation and, from the inside to the outside moving away from said axis, the "circumferential" orientation is directed orthogonally to the main axis X and orthogonally to the radial direction.

[0046] Figures 1 to 4 illustrate a transmission system 1 according to a first embodiment. The transmission system is here a differential which is used, in a transmission chain of a vehicle, to transmit and distribute a torque coming from a thermal or electric engine, not illustrated, to two wheel shafts 2, 3 of an axle of a motor vehicle. Such a transmission system can, for example, be part of a secondary transmission chain capable of transmitting a torque from a secondary engine of the vehicle, such as an electric motor, to a rear or front axle of a vehicle while a primary transmission chain is capable of transmitting a torque from a main engine, for example a thermal engine, to the wheel shafts of another axle of the vehicle. According to other embodiments not illustrated, the transmission system can also take a form other than that of a differential.

[0047] The transmission system comprises a first element 4, movable in rotation around the main axis X, and intended to be driven by a motor, such as an electric motor not shown, a second element 5, also movable in rotation around the main axis X and intended to drive the wheel shafts 2, 3, and a coupling device 6 capable of selectively coupling or uncoupling the first element 4 and the second element 5.

[0048] The first element 4 comprises a toothed wheel 7 which is intended to be driven by the motor via a reduction gear train 40, shown here schematically. This first element 4 also comprises a housing 8 which is integral in rotation with the toothed wheel 7. The housing 8 is here illustrated in a single piece, but could be composed of several parts fixed together.

[0049] The second element 5 comprises a carrier ring 13 of annular shape which is guided in rotation, around the main axis X, inside the housing 8. To do this, the housing 8 comprises an internal cylindrical portion cooperating with a cylindrical external surface of the carrier ring 13 in order to guide it in rotation relative to the housing 8. The second element 5 further comprises two satellite gears 14, 15, visible in FIG. 1, which are mounted in rotation on the carrier ring 13 around a secondary axis Z, perpendicular to the main axis X. The two satellite gears 14, 15 each comprise a bevel gear which meshes with a complementary bevel gear of two planetary gears 16, 17. The two planetary gears 16, 17 are rotatable around the main axis X and are each integral in rotation with one of the two wheel axles 2, 3. The carrier crown 13, the satellite gears 14, 15 and the planetary gears 16, 17 form a differential allowing the two wheel shafts 2, 3 to rotate at different speeds.

[0050] Furthermore, the transmission system 1 comprises a coupling device 6 which, in the coupled position, makes it possible to transmit a torque between the first element 4 and one of the components of the second element 5, here the carrier ring 13. Thus, the transmission system makes it possible, when the coupling device 6 is in the coupled position, to transmit a torque from the engine to the wheel shafts 2, 3 by exercising the differential function allowing different rotation speeds of the wheel shafts 2, 3.

[0051] The coupling device 6 comprises a first coupling part 18 which is rotationally fixed to the housing 8 while being axially movable along the main axis X relative to said housing 8. The first coupling part 18 is movable between an uncoupled position, shown in FIG. 1, and a coupled position. In the uncoupled position, the first coupling part 18 is uncoupled from a second coupling part 19 rotationally fixed to the carrier ring 13 so that the transmission of torque is interrupted between the housing 8 and the carrier ring 13. On the contrary, in the coupled position, the first coupling part 18 is coupled to the second coupling part 19, which allows the transmission of torque between the housing 8 and the carrier ring 13.

[0052] In the embodiment shown, the coupling device 6 is a dog clutch device. Thus, one of the first and second coupling parts 18, 19 comprises teeth while the other comprises corresponding grooves in which said teeth are engaged when the first coupling part 18 is in the coupled position. In the embodiment shown, the second coupling part 19 is formed in one piece with the carrier crown 13. In other words, teeth or grooves are provided in the lateral face of the carrier crown 13 which is turned opposite the first coupling part 18. However, although the invention is described in connection with a dog coupling device, it is not limited thereto and the coupling device may be of another type and in particular be a friction coupling device.

[0053] As shown in Figure 3, the first coupling part 18 comprises an annular part 20 which is housed inside the housing 8 and connecting pads 22 which are regularly distributed around the main axis X and which each pass through a corresponding opening 82 provided in the housing 8. The first coupling part 18 comprises an external groove formed on the periphery of the annular part 20 which slides axially in an internal groove of the housing 8. This makes it possible to secure the first coupling part 18 in rotation to the housing 8 while allowing relative axial movement between the first coupling part 18 and the housing 8.

[0054] Furthermore, the transmission system 1 comprises an electromagnetic actuator 50, illustrated in more detail in FIG. 3, making it possible to axially move the first coupling part 18. The electromagnetic actuator 50 comprises a protective casing which is intended to be mounted on the chassis of the vehicle, fixed in rotation relative to the latter, by means of fixing members not illustrated. The protective casing comprises in particular a base 51 and an external casing 52 forming a hollow housing 50a.

[0055] The electromagnetic actuator 50 comprises a solenoid 57 and a piston 54 axially movable within the housing 50a between a retracted position, illustrated in FIG. 3, and an extended position. The solenoid may be a coil consisting of a metal electrical wire wound regularly in a helix around a plastic support (for insulation). The outside diameter of the coil defines the outside diameter of the solenoid. In another variant of the invention, a soft iron core may be added to the solenoid 57 to form an electromagnet.

[0056] The electromagnetic actuator 50 also comprises a closing cover 59 attached to the base 51 to form an annular opening in the housing, said closing cover covering one of the lateral faces of the solenoid. The closing cover 59 closes the housing 50a and comprises a stop face 60 to define the deployed position of the piston 54.

[0057] The piston 54, of revolution shape around the main axis X, comprises a piston body 54a and a pusher part 54b, which is axially movable within the housing between a retracted position and a deployed position in which the piston body 54a comes to bear on the closing cover 59 and the pusher part passes through the annular opening,

[0058] According to the invention, the electromagnetic actuator is remarkable in that the piston 54, made in a single piece from a ferromagnetic material, surrounds the solenoid 57 and comprises a frustoconical stop surface 54c defining an air gap E with the closing cover 59. The closing cover 59 also comprises a frustoconical stop face 60 complementary to the stop surface 54c of the piston, the air gap E being made between the two truncated cones of the piston and the closing cover. In the embodiment illustrated in Figure 3, the truncated conical stop surface 54c of the piston 54 and the truncated conical stop face 60 of the closing cover 59 have different angles. This avoids the phenomenon of adhesion of the two surfaces.

[0059] According to an alternative embodiment of the invention not shown, the stop surface 54c and the stop face 60 may be partially spherical, that is to say that it is a portion of the surface of a sphere comprised between two parallel planes which intersect this sphere, the two planes being perpendicular to the main axis X. More generally, the stop surface 54c and the stop face 60 are not perpendicular to the main axis X.

[0060] It will also be specified that the air gap E is located on a diameter De greater than the outside diameter of the solenoid 57. The particular geometry of the piston 54 and the closing cover 59 thus limits unwanted leaks of magnetic flux outside the actuator. For example, the air gap E is defined by the outside diameter of the closing cover 59.

[0061] The electromagnetic actuator 50 is protected by the cylindrical outer casing 52 which has an axial rim 61 to define the retracted position of the piston 54. The piston 54 bears on the axial rim 61 by means of an external collar 54d arranged on the outer periphery of the piston.

[0062] Crossed by an alternating or direct current, via the electrical connection 58, with an intensity greater than a threshold intensity, the solenoid 57 produces a magnetic field in its vicinity, the force of the magnetic field making it possible to move the piston 54 axially within the chamber between a retracted position and a deployed position in which the piston comes to bear on the closing cover. The annular opening of the housing produced by the closing cover 59 tends to create an electromagnetic leak which attracts the piston 54. The piston 54 then moves axially until it stops on the closing cover 59. This defines the deployed position.

[0063] When the piston is in the deployed position, the closing cover 59 exerts an attraction on the piston body 54a, which allows it to be maintained in the deployed position. The supply intensity of the electromagnet 57 can then be reduced as long as it remains greater than said threshold intensity. When the electromagnet 57 is switched off or is supplied with an intensity lower than the threshold intensity, an elastic return device 30, described below, allows the first coupling part 18 to be returned to the uncoupled position.

[0064] The elastic return device 30 is partially fixed to the first element 4 and deforms elastically during the movement of the first coupling part 18 between the uncoupled position and the coupled position. Said elastic return device is produced in the present case in the form of a multifunctional disc 30, visible in FIG. 2, which is formed in a single piece and is fixed axially to the first coupling part 18. The disc 30 provides numerous functionalities described below and thus makes it possible to limit the cost, complexity and size of the coupling device 6.

[0065] The pusher part 54b comprises a bearing surface 54f arranged to bear on the disc 30 of the transmission system by which the actuating force is transmitted to the first coupling part 18. The bearing surface 54f is perpendicular to the main axis X.

[0066] Firstly, the disc 30 provides the function of target 34 for evaluating the position of the piston 54. To do this, the disc comprises an annular portion 37, arranged at the radially external periphery of the disc 30. This external annular portion 37 is arranged axially opposite the sensor 70 and thus forms the target 34. The target 34 is fixed axially to the first coupling part 18. Furthermore, the coupling device 6 comprises a contactless sensor 70, shown in FIG. 1, which is positioned axially opposite the target 34 and which is configured to deliver a signal representative of the axial distance between the target 34 and the sensor 70.Thus, the sensor 70 is capable of delivering a signal representative of the position of the first coupling part 18, such a signal being used to ensure the reliability of the control of the coupling device 6 and in particular to verify that the coupling device 6 is indeed in the uncoupled position or in the coupled position. The sensor 70 is for example a Hall effect sensor.

[0067] Secondly, the disc 30 makes it possible to transmit the actuating force between the piston 54 of the electromagnetic actuator 50 and the first coupling part 18. To do this, said elastic return device comprises an actuating portion 35 which can be moved axially relative to the first element 4. The piston 54 is in contact against an internal annular portion 35 of the disc 30 which defines the actuating portion.

[0068] Thirdly, the disc 30 acts as an elastic return means for returning the first coupling part 18 to the uncoupled position when the piston 54 of the electromagnetic actuator 50 returns to the retracted position.

[0069] To do this, the disc 30 comprises a first fixing zone fixed to the first coupling part 18, a second fixing zone fixed to the first element 4 and an elastic return portion 31 connecting the first fixing zone to the second fixing zone. The annular disc 30 comprises on its internal periphery the actuating portion 35 and deforms elastically between the actuating portion 35 and the second fixing zone during the axial movement of the piston 54.

[0070] The disc 30 comprises a plurality of elastic return portions 31 each made in the form of an elastic blade which connects the first fixing zone to the second fixing zone. The elastic blades 31 each have a free end 32 which bears against a bearing zone of the housing 8 and a proximal end connected to the rest of the disc 30. The elastic blades 31 are each formed in windows 33 positioned radially inside the annular portion 37. The elastic blades 31 extend circumferentially around the main axis X, which makes it possible to obtain, for a given radial size, elastic blades 31 of greater length and, consequently, of lower stiffness. As shown in FIG. 2, the free end 32 of the elastic blades 31 bears against the ends of bosses 81 projecting axially from the housing 8 towards the disc 36.The bosses 81 protrude by an axial dimension greater than the travel of the first coupling part 18 between the uncoupled position and the coupled position. The disc 30 comprises four elastic blades 31 in the embodiment shown.

[0071] The elastic blades 31 thus each form an elastic return portion which is configured to flex elastically during the movement of the first coupling part 18 from the uncoupled position to the coupled position. In reaction, the elastic blades 31 exert a return force capable of returning said first coupling part 18 to the uncoupled position.

[0072] Furthermore, the disc 30 is fixed to the first coupling part 18 by means of fixing screws 90.

[0073] By way of example, according to one embodiment, the disc 30 and more particularly the elastic blades 31 are dimensioned to generate a stiffness K1 opposing the axial displacement of the first coupling part 18 towards the coupled position of between 5 and 500 N / mm, for example 50 N / mm.

[0074] Fourthly, the disc 30 provides a sliding interface limiting the friction forces caused by the relative rotation of the disc 30, which is movable in rotation around the main axis X, relative to the piston 54 which is fixed in rotation. In particular, the pusher part 54b of the piston comprises a bearing surface 54f arranged to come into support on the disc 30, as illustrated in FIG. 4. The bearing surface 54f of the piston 54 has a surface treatment facilitating sliding.

[0075] According to an advantageous variant, in order to further limit the friction likely to be generated between the piston 54 and the disc 30, the actuating portion 35 of the disc 30 comprises, on its face directed opposite the piston 54, a surface treatment facilitating sliding. For example, the surface treatment may be a treatment by adding carbon atoms to the surface of the disc. Alternatively, the surface treatment may be a treatment based on polytetrafluoroethylene (PTFE).

[0076] The disc 30 is for example made of spring steel, such as XC 70 steel, advantageously pre-hardened. For example, the disc 30 has a thickness of between 0.4 and 1.2 mm, for example of the order of 0.8 mm. Alternatively, the disc 30 is made of stainless steel.

[0077] This first embodiment of the invention illustrates the case where the elastic return device 30 is arranged to deform elastically during the movement of the first coupling part from the uncoupled position to the coupled position and to exert a return force capable of elastically returning the first coupling part to the uncoupled position. In this first embodiment, the coupling device 6 is normally open, that is to say that the first and second coupling parts 18, 19 are fitted into each other only when the electromagnetic actuator 50 is active, that is to say supplied with current via the electrical connection 58. This first embodiment makes it possible to reduce the cost, complexity and size of the transmission system.

[0078] There is another embodiment in which the elastic return device 30 is arranged to deform elastically during the movement of the first coupling part from the coupled position to the uncoupled position and to exert a return force capable of elastically returning the first coupling part to the coupled position. In this other embodiment, the coupling device 6 is normally closed, that is to say that the first and second coupling parts 18, 19 are fitted into each other when the electromagnetic actuator 50 is inactive. The structure of the electromagnetic actuator 50 remains similar to the first embodiment but the piston 54 is oriented axially in the opposite direction of the housing 8.Thus, the elastic return device 30 jointly ensures the interface between the coupling device 6 and the electromagnetic actuator while ensuring the return of the first coupling part 18 to its coupled position.

[0079] Although the invention has been described in connection with several particular embodiments, it is obvious that it is in no way limited thereto and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention, as defined by the claims.

[0080] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

Claims

1. Electromagnetic actuator (50) for a transmission system comprising: - a base (51) and an external casing (52) defining a hollow housing (50a); - a solenoid (57) placed inside the housing; - a closing cover (59) attached to the base (51) to form an annular opening in the housing (50a), said closing cover covering one of the lateral faces of the solenoid; - a piston (54), of revolution shape around a main axis (X) comprising a piston body (54a) and a pusher part (54b), which is axially movable within the housing between a retracted position and a deployed position in which the piston body (54a) comes to bear on the closing cover and the pusher part (54b) passes through the annular opening; characterized in that the piston (54), made in one piece from a ferromagnetic material, surrounds the solenoid (57) and comprises a stop surface (54c) defining an air gap (E) with the closing cover, said stop surface (54c) being frustoconical or partially spherical.

2. Electromagnetic actuator (50) according to claim 1, wherein the closing cover (59) comprises a stop face (60) complementary to the stop surface (54c) of the piston, respectively of truncated cone or partially spherical shape, the air gap (E) being produced between the stop surface of the piston (54) and the stop face of the closing cover.

3. Electromagnetic actuator (50) according to claim 2, in which the air gap (E) is located on a diameter (De) greater than the outer diameter of the solenoid (57).

4. An electromagnetic actuator (50) according to one of claims 1 to 3, wherein the pusher portion (54b) of the piston comprises an outer collar (54d) extending radially from the piston body (54a), the outer collar being located outside the housing (50a) of the electromagnetic actuator.

5. Electromagnetic actuator (50) according to the preceding claim, wherein the outer collar (54d) forms a stop with the outer casing (52) of the housing (50a) when the piston is in its retracted position.

6. Electromagnetic actuator (50) according to one of the preceding claims, in which the piston body (54a) comprises two cylindrical centering portions (54e) arranged opposite the bore of the external casing (52).

7. Electromagnetic actuator (50) according to one of the preceding claims, in which the pusher part (54b) of the piston comprises a bearing surface (54f) arranged to come into contact with a component of the transmission system (1).

8. Electromagnetic actuator (50) according to the preceding claim, in which the bearing surface (54f) of the piston (54) comprises a surface treatment facilitating sliding.

9. Transmission system (1) for a motor vehicle comprising: - a first element (4) and a second element (5) movable in rotation relative to each other around a main axis (X), one of the first and second elements (4, 5) being intended to be driven by a motor and the other of the first and second elements (4, 5) being intended to drive at least one wheel shaft (2, 3) of the motor vehicle; and - a coupling device (6) which comprises: - a first coupling part (18) which is rotationally fixed to the first element (4) and a second coupling part (19) which is rotationally fixed to the second element (5), the first coupling part (18) being axially movable relative to the first element (4) between a coupled position in which the first coupling part (18) is coupled with the second coupling part (19) to transmit a torque between the first element (4) and the second element (5) and an uncoupled position in which the first coupling part (18) and the second coupling part (19) are uncoupled from each other, - an elastic return device (30) partially fixed to the first element (4) and arranged to deform elastically during the movement of the first coupling part (18) between the uncoupled position and the coupled position and to exert a return force capable of elastically returning the first coupling part (18) towards the uncoupled position or towards the coupled position, said elastic return device comprising an actuating portion (35) axially movable relative to the first element (4), and - the electromagnetic actuator (50) according to one of the preceding claims, in which the piston (54) bears axially on the actuating portion (35) of the elastic return device (30).

10. Transmission system (1) according to the preceding claim, in which the elastic return device (30) comprises a first fixing zone fixed to the first coupling part (18), a second fixing zone fixed on the first element (4) and an elastic return portion (31) connecting the first fixing zone to the second fixing zone.

11. Transmission system (1) according to the preceding claim, in which the elastic return device is an annular disc (30) comprising on its internal periphery the actuating portion (35), the disc (30) being capable of deforming elastically between the actuating portion and the second fixing zone during axial movement of the piston (54).

12. Transmission system (1) according to the preceding claim, in which the actuating portion (35) of the disc (30) is an internal annular portion which bears on the bearing surface (54f) of the piston (54).

13. A transmission system (1) according to any one of claims 9 to 12, wherein the first element (4) comprises a housing (8) inside which the second coupling part (19) is housed, the first coupling part (18) comprising an annular part (20) which is housed inside the housing (8) and a plurality of connecting studs (22) which axially connect the annular part (20) of the first coupling part (18) with the disc (30), each of the connecting studs (22) passing through a corresponding opening (82) provided in the housing (8).

14. Transmission system (1) according to the preceding claim, wherein the disc (30) is arranged outside the housing (8) and is fixed on the plurality of connecting pads (22) of the first coupling part (18).

15. Transmission system (1) according to any one of claims 9 to 14, wherein the second element (5) comprises a carrier ring (13) which is guided in rotation about the main axis (X) inside the housing (8), two planetary gears (14, 15) which are rotatably mounted on the carrier ring (13) about a secondary axis (Z) perpendicular to the main axis (X) and two planetary gears (16, 17) which are rotatably movable about the main axis (X), are each engaged with the two planetary gears (14, 15) and are each intended to be rotationally secured to a wheel shaft (2, 3) and wherein the second coupling part (19) of the coupling device (6) is rotationally secured to the carrier ring (13) relative to the main axis (X).

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