COMPOSITE DUAL-MASS FLYWHEEL, SYSTEM COMPRISING SAID FLYWHEEL, AND RELATED METHOD

Abstract

A composite flywheel (13), comprising a primary flywheel (15) integral with an input shaft (31) and a secondary flywheel (17) coaxial with the primary flywheel (15). The secondary flywheel (17) and the primary flywheel (15) are constrained so that they can rotate freely with respect to each other. A coupling device (61) is further provided, adapted selectively to: transmit power from the input shaft (31) to the secondary flywheel (17); and disengage the secondary flywheel (17) from the input shaft (31).

Claims

1. A system comprising: a power source; a driven machine actuated by said power source through a mechanical transmission having an input shaft and an output shaft; in said power transmission, a composite flywheel, comprising: a primary flywheel torsionally constrained to the input shaft to rotate therewith; a secondary flywheel coaxial with the primary flywheel, wherein the secondary flywheel and the primary flywheel are coupled so that they can rotate freely with respect to each other; a coupling device adapted selectively to transmit power from the input shaft to the secondary flywheel, and to disengage the secondary flywheel from the input shaft; wherein the system is adapted to: start rotation of the mechanical transmission and of the primary flywheel with the coupling device disengaged and gradually increasing the rotation speed of the primary flywheel, while keeping the secondary flywheel idle and disengaged from the primary flywheel; and when a switching operational condition has been achieved, switching the coupling device so as to transmit torque from the input shaft to the secondary flywheel.

2. The system of claim 1, wherein the coupling device is adapted selectively to couple and decouple torsionally the primary flywheel and the secondary flywheel with respect to each other.

3. The system of claim 1, wherein the secondary flywheel is supported rotatable on the output shaft and is adapted to be selectively coupled to and decoupled from the primary flywheel through the coupling device.

4. The system of claim 1, wherein the coupling device is adapted to modulate the torque transmitted to the secondary flywheel; preferably according to the rotation speed of the secondary flywheel or of the primary flywheel.

5. The system of claim 1, wherein the coupling device comprises a clutch.

6. The system of claim 1, wherein the coupling device is a hydraulically controlled device.

7. The system of claim 6, comprising a supply duct in the output shaft, adapted to supply a control fluid to the coupling device.

8. The system of claim 7, wherein the output shaft has a first end for coupling to the power source and a second end for coupling to the driven machine; wherein the supply duct has an opening on the second end of the output shaft; and wherein preferably a rotating joint is associated with the second end of the output shaft.

9. The system of claim 1, wherein the secondary flywheel is torsionally constrained to a support shaft of the secondary flywheel, and wherein bearings are arranged inside the support shaft of the secondary flywheel for rotatingly supporting the secondary flywheel on the output shaft.

10. The system of claim 9, wherein at least one feeding port is arranged inside the support shaft of the secondary flywheel for feeding a control fluid of the coupling device; and wherein preferably said at least one port is fluidly connected with a pressure chamber where a piston of the coupling device is housed.

11. The system of claim 9, wherein the primary flywheel is mounted rotatable on the support shaft of the secondary flywheel; wherein the primary flywheel is integral with a support shaft of the primary flywheel, coaxial with the support shaft of the secondary flywheel; and wherein bearings are interposed between the support shaft of the primary flywheel and the support shaft of the secondary flywheel, said bearings allowing the rotation of the support shaft of the primary flywheel and the support shaft of the secondary flywheel, one with respect to the other.

12. The system of claim 9, wherein the coupling device is arranged outside the support shaft of the secondary flywheel and coaxially thereto.

13. The system of claim 9, wherein the support shaft of the secondary flywheel is integral with an external body of the coupling device.

14. The system of claim 13, wherein in the external body of the coupling device there are arranged: first drawing discs constrained to the primary flywheel to rotate integrally therewith; second drawing discs constrained to the secondary flywheel to rotate integrally therewith; a piston mounted around the support shaft of the secondary flywheel and adapted to bias the first drawing discs and the second drawing discs against each another; and wherein preferably the support shaft, a flange of the coupling device and the piston form a pressure chamber adapted to receive a control fluid of the coupling device.

15. The system of claim 1, comprising a hydraulic unit adapted to supply pressurized control fluid to the coupling device, and wherein a central control unit is associated with a control valve for controlling a pressure under which the control fluid is supplied to the coupling device, the modulation of the pressure of the control fluid causing the modulation of the torque transmitted to the secondary flywheel.

16. The system of claim 15, comprising at least one sensor adapted to detect the speed of at least one of the primary flywheel and the secondary flywheel.

17. A method for actuating a driven machine through a power source and a mechanical transmission comprising a composite flywheel, said composite flywheel comprising a primary flywheel integral with an input shaft, a secondary flywheel coaxial with the primary flywheel, and a coupling device adapted selectively to transmit power from the input shaft to the secondary flywheel, and disengage the secondary flywheel from the input shaft; the method comprising the steps of: starting rotation of the transmission and of the primary flywheel with the coupling device disengaged, gradually increasing the rotation speed of the primary flywheel keeping the secondary flywheel disengaged from the primary flywheel and idle on an output shaft of the composite flywheel; when a switching operational condition has been achieved, switching the coupling device so as to connect the secondary flywheel to the primary flywheel and to transmit torque from the primary flywheel to the secondary flywheel.

18. The method of claim 17, further comprising at least one of the following steps: gradually accelerating the secondary flywheel up to achieving the rotation speed of the primary flywheel through a gradual increase in the torque transmitted from the shaft to the secondary flywheel; further accelerating the primary flywheel and the secondary flywheel once the secondary flywheel has achieved the rotation speed of the primary flywheel.

19. A method for braking a driven machine actuated by means of a power source and a mechanical transmission including a composite flywheel, said composite flywheel including a primary flywheel integral with an input shaft, a secondary flywheel coaxial with the primary flywheel, and a coupling device adapted selectively to transmit power from the input shaft to the secondary flywheel, and disengage the secondary flywheel from the input shaft; said method comprising the step of disengaging the secondary flywheel from the primary flywheel through the coupling device, and braking the driven machine with the secondary flywheel idle with respect to the mechanical transmission.

20. A composite flywheel, comprising: a power input shaft; a primary flywheel torsionally constrained to the input shaft; a secondary flywheel torsionally constrained to a support shaft of the secondary flywheel coaxial with the primary flywheel; the secondary flywheel and the primary flywheel being coupled so that they can rotate freely with respect to each other; a coupling device adapted selectively to couple and decouple torsionally the primary flywheel and the secondary flywheel with respect to each other; a power output shaft, on which the secondary flywheel is rotatably supported; wherein bearings arranged inside the support shaft of the secondary flywheel are configured for rotatably supporting the secondary flywheel on the output shaft; wherein the primary flywheel is integral with a support shaft of the primary flywheel, coaxial with the support shaft of the secondary flywheel, and wherein bearings are interposed between the support shaft of the primary flywheel and the support shaft of the secondary flywheel and rotatably support the support shaft of the primary flywheel and the support shaft of the secondary flywheel, one with respect to the other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will be better understood by following the description and the accompanying drawing, which shows a non-limiting exemplary embodiment of the invention. More in particular, in the drawing:

[0037] FIG. 1 is a diagram of a power source and a driven machine, connected to each other by means of a mechanical transmission with a flywheel;

[0038] FIG. 2 is a cross-section of a flywheel in an embodiment;

[0039] FIG. 3 is an enlargement of FIG. 2;

[0040] FIG. 4 is a section of a flywheel in a further embodiment.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0041] The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

[0042] Reference throughout the specification to one embodiment or an embodiment or some embodiments means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase in one embodiment or in an embodiment or in some embodiments in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0043] FIG. 1 shows an arrangement 1 comprising a power source 3, a driven machine 5, hereinafter also generally referred to as a load, and a mechanical transmission 7 connecting the power source 3 to the driven machine 5. In the example embodiment of FIG. 1, the power source is an IC engine 9 of a tractor 10. Reference number 11 indicates a hydraulic unit, with which the tractor 10 is provided, which supplies pressurized oil for the purposes which will be explained below. In other embodiments, the hydraulic unit 11 can be on board the driven machine 5 instead of the tractor 3.

[0044] Just by way of particularly advantageous but not limiting example, the driven machine 5 is a large square baler. As mentioned above, in these machines the resistant torque varies significantly. The power supplied by the power source 3 is used, in this case, to drive a piston 5.1 by means of a crankshaft 5.2 and a rod 5.3. The piston 5.1 moves reciprocatingly (double arrow f5) in a chamber 5.4.

[0045] The crank shaft 5.2 is housed in a casing or box 5.6, in which a transmission shaft enters, described below, to which a composite flywheel 13 is associated, the structure of which will be described in detail hereinafter with reference to FIGS. 2 and 3. The flywheel 13 is a composite flywheel, i.e. it comprises a primary flywheel and a secondary flywheel, which can be selectively coupled to each other to rotate together, or can be torsionally disengaged from each other, so that while one rotates integrally with the mechanical transmission 7, the other one is idle and therefore does not absorb power from the transmission. The primary flywheel and the secondary flywheel form a dual-mass system, where the masses can both be connected to the power source 3, or one is connected to the power source 3 and the other remains idle. In this way it is possible to modulate the flywheel inertia as required, as described in detail below.

[0046] With a flywheel of this type, it is possible to have a very high inertial mass, represented by the sum of the primary flywheel and the secondary flywheel, when the system comprising the driven machine 5 and the power source 3 rotate at working speed. The high inertia of the large rotating mass makes the operation uniform. Vice versa, when it is useful to have a lower inertial mass, especially in the start and stop transients, the inertial mass mechanically connected to the transmission 7 to receive power from the power source 3 is only the mass of the primary flywheel.

[0047] It should be understood that the concept can be extended to more than two masses. In general, there will be a primary flywheel and one or more secondary flywheels, each of which can be selectively torsionally coupled to, or decoupled from, the primary flywheel.

[0048] Furthermore, while in FIGS. 2 and 3 the primary flywheel and the secondary flywheel have approximately the same mass and substantially the same inertia, it must be understood that this is not necessary. In some embodiments, for example, the primary flywheel can have a mass smaller or larger than the secondary flywheel and/or such a mass distribution as to present a lower or greater inertia. For example, the primary flywheel can have a mass equal to half the mass of the secondary flywheel.

[0049] The composite flywheel described herein may be particularly useful in applications in which the flywheel rotates at speeds in the order of 1000-1200 revolutions per minute. In applications of particular interest, for example for the transmission of motion to large square balers, the flywheel can have a diameter of 1 m or more and a weight equal to, or greater than, 600 kg, for example comprised between 600 and 900 kg. Flywheels of this size are particularly suitable for use in large square balers with pistons having for example 45-50 strokes per minute.

[0050] With reference to FIGS. 2 and 3, in the illustrated embodiment the composite flywheel 13 comprises a primary flywheel 15 and a secondary flywheel 17, coaxial to each other. The axis of the composite flywheel 13, which coincides with the axis of a shaft 19 of the driven machine or load 5, is indicated with A-A. The shaft 19 also represents the power output shaft from the composite flywheel 13 towards the driven machine 5. The primary flywheel 15 is torsionally coupled to the shaft 19 while the secondary flywheel 17 is supported idle on the shaft 19 in the manner described below.

[0051] The shaft 19 has a first end 19A facing the power source 3 and a second end 19B inserted in the casing 5.6 of the driven machine 5. The second end 19B is provided with a gear, for example in this case a bevel gear 21, which transmits rotary motion from the shaft 19 to the crankshaft 5.2 through mechanical members, not shown, housed in the casing 5.6. The reference numbers 23 and 25 indicate bearings supporting the shaft 19 in the casing 5.6.

[0052] The primary flywheel 15 is permanently coupled torsionally to the shaft 19 by means of a connecting element 27. In the illustrated embodiment, the connecting element 27 comprises a disk 29 coaxial with the shaft 19 and coupled torsionally to the first end 19A of the shaft 19, for example by means of a coupling 29 with splined profile. The connecting element 27 also forms a mechanical connection with an input shaft 31 of the composite flywheel 13. The input shaft 31 comprises a flange 31.1 and a splined profile 31.2, through which the input shaft 31 is connected to the other components of the mechanical transmission 7.

[0053] The primary flywheel 15 comprises a main mass 35, which may have an annular shape to concentrate the mass of the primary flywheel 15 in the peripheral region thereof, thus increasing the inertia thereof. The main mass 35 is rigidly connected to a flange 37, which is in turn rigidly connected to a support shaft 39 of the primary flywheel 15. The support shaft 39 is substantially a flanged hollow shaft and houses bearings supporting the primary flywheel 15, as described below. Externally, the support shaft 39 of the primary flywheel 15 features means for connecting to a coupling device between the primary flywheel 15 and the secondary flywheel 17. The support shaft 39 of the primary flywheel also constitutes a drawing shaft of the secondary flywheel 17, as explained below.

[0054] The support shaft 39 of the primary flywheel 15 houses a support shaft 41 of the secondary flywheel 17. The support shaft 39 of the primary flywheel 15 and the support shaft 41 of the secondary flywheel 17 are coaxial with each other, and between the two support shafts 39, 41 bearings 43, 45 are provided, through which the primary flywheel 15 is supported on the support shaft 41 of the secondary flywheel 17. The support shaft 41 of the secondary flywheel 17 is in turn supported by bearings 47, 49 on the shaft 19. The bearings 47, 49 are arranged inside the support shaft 41 of the secondary flywheel 17.

[0055] The support shaft 41 of the secondary flywheel 17 is integral, through a flange 51, with an outer annular body 53, which is in turn rigidly connected to a flange 55 of the secondary flywheel 17. The flange 55 is rigidly connected to a main mass 57 of the secondary flywheel 17. In this way, similarly to the primary flywheel 15, also for the secondary flywheel 17 the main mass 57 is concentrated in the outer peripheral part so as to increase the inertia of the secondary flywheel 17.

[0056] In the illustrated embodiment, the two masses 35 and 57 are approximately equal, but this is not necessary. As mentioned above, the primary flywheel 15 and the secondary flywheel 17 may have different masses and therefore different inertias. In some embodiments, the primary flywheel 15 may have a lower inertia than the secondary flywheel 17. The different inertia can be obtained with different masses and/or with a different mass distribution with respect to the rotation axis A-A.

[0057] With the arrangement described above, it is possible to connect the primary flywheel 15 to the power source 3 so as to rotate the primary flywheel 15 through the input shaft 31 around the axis A-A. The primary flywheel 15 integrally rotates with the input shaft 19 of the driven machine 5 thanks to the connection provided by the splined profile 29A. The primary flywheel 15 is supported by the bearings 43, 45 and can rotate independently of the secondary flywheel 17, which is in turn supported on the shaft 19 by the bearings 47, 49.

[0058] In some operational conditions, the secondary flywheel 17 can be completely disengaged from the primary flywheel 15, remaining idle on the shaft 19 while the main flywheel 15 and the shaft 19 rotate. In other operational conditions, the secondary flywheel 17 can be torsionally coupled to the primary flywheel 15 so that a torque is applied thereto, which causes the secondary flywheel to rotate. The reciprocal coupling between primary flywheel 15 and secondary flywheel 17 can be made so as to modulate the transmitted torque, so as to gradually coupling the secondary flywheel 17 to the primary flywheel 15. In this way the primary flywheel 15 and the shaft 19 can be angularly accelerated to a first operational speed, and then the secondary flywheel 17 can be gradually accelerated to the same operational speed as the primary flywheel 15. It is also possible, once the synchronization between the primary flywheel 15 and the secondary flywheel 17 has been achieved, to accelerate the two flywheels integrally up to a second operational speed.

[0059] In order to couple the secondary flywheel 17 to the primary flywheel 15, a coupling device is provided, indicated as a whole with number 61. In some embodiments, the coupling device 61 comprises a clutch. In the illustrated embodiment, the coupling device 61 comprises a hydraulic clutch controlled by means of a control valve for controlling the pressure of a control fluid, so that, by modulating the fluid pressure, the torque transmitted from the primary flywheel 15 to the secondary flywheel is modulated.

[0060] With particular reference to FIG. 3, the coupling device 61 comprises a series of internal drawing discs 63, torsionally coupled to the primary flywheel 15, for example by means of a splined profile coupling 64. The internal drive discs 63 rotate integrally with the primary flywheel 15. Between internal drive disks 63, external drive disks 65 are intercalated, which are torsionally constrained, by means of a splined profile 67, to the outer annular body 53 of the secondary flywheel 17 and rotate integrally thereto. Thanks to the splined couplings 64, 67 the drive disks 63, 65 can be pressed against each other so as to transmit torque from the internal drive disks 63 (and hence from the primary flywheel 15) to the external drive disks 65 (and then to the secondary flywheel 17). To this end, the drawing discs are provided, as in the usual clutches, with coatings made of a material having high coefficient of friction.

[0061] In the illustrated embodiment, to press the internal drawing discs 63 and the external drawing discs 65 against each other a toroidal piston 69 is provided, housed in an annular cylinder 71 formed between the support shaft 41 of the secondary flywheel 17 and the flange 51. The piston 69 and the cylinder 71 form a cylinder-piston actuator of the single action type, controlling the coupling device 61. Springs 73 push the piston 69 to an idle position, moving it away from the drawing discs 63, 65. Pressure control fluid, for example oil, delivered into the annular chamber formed between the cylinder 71 and the piston 69, pushes the piston 69 against the action of the springs 73 in order to press the drawing discs 63, 65 against each other, thus generating a drawing coupling between the primary flywheel 15 and the secondary flywheel 17.

[0062] To feed the pressurized control fluid to the coupling device 61 a duct 77 may be provided in the shaft 19, preferably coaxial thereto. As can be seen in particular in FIG. 2, the duct 77 exits on the end 19B of the shaft 19, i.e. on the end facing the driven machine or load 5. The duct 77 can be connected to a hydraulic circuit 79 through a rotating joint 81, so that pressurized fluid can be fed into the duct 77 while the shaft 19 rotates. The duct 77 can be connected to one or more radial holes 83, which open into an annular groove 85. The annular groove 85 is fluidly coupled to one or more openings 87, which radially extend in the support shaft 41 of the secondary flywheel 17 and connect the annular groove 85, and therefore the duct 77, to the annular chamber formed between the piston 69, the flange 51 and the support shaft 41 of the secondary flywheel 17.

[0063] With this arrangement it is possible to deliver pressurized fluid into the cylinder of the cylinder-piston actuator, of which the toroidal piston 69 is part. The fluid pushes the piston 69 against the drawing discs 63, 65, pressing them against each other to a greater or lesser extent according to the fluid pressure. By modulating the fluid pressure, it is therefore possible to modulate the torque transmitted from the primary flywheel 15 to the secondary flywheel 17.

[0064] The composite flywheel 13 can be associated with a control system 89, controlling the coupling device 61. In FIG. 2, the control system is indicated by the reference number 89. In the embodiment schematically illustrated in FIG. 2, the control system 89 comprises at least a first sensor 91 adapted to detect the rotation speed of the primary flywheel 15. The control system 89 can comprise a second sensor 93 adapted to detect the rotation speed of the secondary flywheel 17. The control system 89 can further comprise a central control unit 95, which comprises one or more processors and associated memory and receives signals from the sensors 91 and 93. The central control unit 95 can be interfaced with an electro-proportioning pressure-reducing valve 97 connected to the hydraulic circuit 79.

[0065] The hydraulic circuit 79 can be connected to the hydraulic unit 11 of the power source 3 (FIG. 1) or to a hydraulic unit (not shown) of the driven machine 5. Pressurized fluid, for example oil, is fed, controlled by means of the control system 89, to the coupling device 61, according to the required operational conditions.

[0066] FIG. 4 is a cross section, according to a plane containing the rotation axis, of a further embodiment of a flywheel. The same reference numbers indicate the same or equivalent parts to those described with reference to FIGS. 2 and 3 and they will be not described again. The main difference between the embodiment of FIGS. 2, 3 and the embodiment of FIG. 4 is that in FIG. 4 the sizes and the shapes of the primary flywheel 15 and of the secondary flywheel 17 have been optimized, in order to improve the operation and to optimize the overall dimensions of the dual-mass flywheel 13.

[0067] In FIG. 4 the primary flywheel 15 has a smaller diameter than the secondary flywheel 17. In this way, the mass 35 of the primary flywheel 15 can be contained within the mass 57 of the secondary flywheel 17. Thus, the composite flywheel 13 has a reduced axial dimension, since the axial bulk of the primary flywheel 15 is contained within the overall bulk of the secondary flywheel 17. Moreover, the mass of the primary flywheel 15 and the spatial distribution thereof are such that the primary flywheel 15 has a moment of inertia substantially lower than the moment of inertia of the secondary flywheel 17. For example, the primary flywheel 15 may have a moment of inertia equal to half, or less, the inertia of the secondary flywheel 17.

[0068] Below, examples will be illustrated of use of the system described above.

[0069] When the load 5 is to be started, the IC engine 9, which represents the power source, is actuated at the appropriate number of revolutions, and the power take-off thereof is mechanically coupled to the input shaft 31 of the flywheel 13. The coupling device 61 is disengaged, with the piston 69 completely retracted. In this way, no torque is applied to the secondary flywheel 17 and all the mechanical power available from the mechanical power source 3 is used to accelerate the mass of the primary flywheel 15 and, through the shaft 19, the driven machine 5. The primary flywheel 15 rotates supported by bearings 43, 45, while the support shaft 41 of the secondary flywheel 17 is idle on the shaft 19 and does not rotate.

[0070] When the driving shaft of the internal combustion engine 9, and therefore the primary flywheel 15 and the shaft 19, have achieved a first given operational speed, which can be detected by the sensor 91, the central control unit 95 of the control system 89 activates the proportioning valve 97, through which the pressure of the control fluid is increased in the duct 77 and therefore, through the opening(s) 87, in the pressure chamber of the coupling device 61. The gradually increasing pressure of the control fluid pushes the toroidal piston 69 against the force of the springs 73 towards the drawing discs 63, 65 causing a gradual increase in the torque transmitted from the support shaft 39 to the secondary flywheel 17 by means of said drawing discs 63, 65. The support shaft 39 of the primary flywheel 15 therefore represents the driving shaft of the secondary flywheel 17.

[0071] The secondary flywheel 17 is thus gradually accelerated until the angular speed of the primary flywheel 15 is achieved, when the slipping of the hydraulic clutch represented by the coupling device 61 becomes zero. The sensor 93 can provide the control unit 95 with a speed signal, which allows to verify when the rotation speed of the secondary flywheel 17 reaches the rotation speed of the primary flywheel 15. At this point, through the transmission 7, the power source 3 can further accelerate the flywheel 13 and the shaft 19 of the driven machine 5.

[0072] It is also possible to perform the acceleration steps described above with a different sequence. For example, the primary flywheel 15 can be brought to the desired final rotation speed and then the secondary flywheel 17 can be gradually accelerated until reaching the same speed as the primary flywheel 15.

[0073] In further embodiments, it is possible to bring the primary flywheel 15 to a first operational speed and then to accelerate both the primary flywheel 15 from the first operational speed to a second operational working speed, and the secondary flywheel 17 from zero speed to the second operational working speed.

[0074] In any case, there is the advantage of starting the operating machine 5 using less power than would be required if the entire mass of the flywheel 13 should be accelerated from zero to the working speed in a single acceleration ramp.

[0075] The composite flywheel described above can be also used to facilitate the stopping of the driven machine 5. In fact, when it is necessary to stop the driven machine 5, the secondary flywheel 17 can be disengaged by opening the coupling device 61 and then slowing down the primary flywheel 15, the shaft 19 and the driven machine 5 until to stop them.

[0076] The acceleration, deceleration and stopping steps described above can be controlled by means of the control system 89, automatically or by means of the sensors 91, 93 and the central control unit 95. In simplified embodiments, the coupling and decoupling of the secondary flywheel 17 can be controlled manually, if necessary with the use of a manually controlled proportioning pressure-reducing valve 97.

[0077] Having described some embodiments of the composite flywheel, specific features of the present disclosure are set forth in the following clauses:

[0078] Clause 1. A composite flywheel, comprising a primary flywheel integral with an input shaft and a secondary flywheel coaxial with the primary flywheel; wherein the secondary flywheel and the primary flywheel are coupled so that they can rotate freely with respect to each other; and further comprising a coupling device adapted selectively to: transmit power from the input shaft to the secondary flywheel; and disengage the secondary flywheel from the input shaft.

[0079] Clause 2. The composite flywheel of clause 1, wherein the coupling device is adapted selectively to couple and decouple torsionally the primary flywheel and the secondary flywheel with respect to each other.

[0080] Clause 3. The composite flywheel of clause 1 or 2, wherein the primary flywheel is torsionally constrained to the input shaft and to an output shaft and the secondary flywheel is supported rotatable on the output shaft and is adapted to be selectively coupled to and decoupled from the primary flywheel through the coupling device.

[0081] Clause 4. The composite flywheel of clause 1 or 2 or 3, wherein the coupling device is adapted to modulate the torque transmitted to the secondary flywheel; and wherein the coupling device is preferably adapted to modulate the torque transmitted to the secondary flywheel according to the rotation speed of the secondary flywheel or of the primary flywheel.

[0082] Clause 5. The composite flywheel of one or more of the previous clauses, wherein the coupling device comprises a clutch.

[0083] Clause 6. The composite flywheel of one or more of the previous clauses, wherein the coupling device is a hydraulically controlled device.

[0084] Clause 7. The composite flywheel of clause 6, comprising an output shaft coaxial with the primary flywheel and with the secondary flywheel, provided with a supply duct for supplying a control fluid to the coupling device

[0085] Clause 8. The composite flywheel of clause 7, wherein the output shaft has a first end for coupling to a power source and a second end for coupling to a driven machine; wherein the supply duct has an opening on the second end of the output shaft; and wherein preferably a rotating joint is associated with the second end of the output shaft.

[0086] Clause 9. The composite flywheel of one or more of the previous clauses, wherein the secondary flywheel is torsionally constrained to a support shaft of the secondary flywheel, and wherein preferably bearings are arranged inside the support shaft of the secondary flywheel for supporting and rotating the secondary flywheel on an output shaft.

[0087] Clause 10. The composite flywheel of clause 9, wherein at least one feeding port is arranged inside the support shaft of the secondary flywheel for feeding a control fluid of the coupling device; and wherein preferably said at least one port is fluidly connected with a pressure chamber where a piston of the coupling device is housed.

[0088] Clause 11. The composite flywheel of clause 9 or 10, wherein the primary flywheel is mounted rotatable on the support shaft of the secondary flywheel.

[0089] Clause 12. The composite flywheel of one or more of clauses 9 to 11, wherein the primary flywheel is integral with a support shaft of the primary flywheel, coaxial with the support shaft of the secondary flywheel, and wherein preferably bearings are interposed between the support shaft of the primary flywheel and the support shaft of the secondary flywheel, the bearings allowing the rotation of the support shaft of the primary flywheel and the support shaft of the secondary flywheel, one with respect to the other.

[0090] Clause 13. The composite flywheel of one or more of clauses 9 to 12, wherein the coupling device is arranged outside the support shaft of the secondary flywheel and coaxially thereto.

[0091] Clause 14. The composite flywheel of one or more of clauses 9 to 13, wherein the support shaft of the secondary flywheel is integral with an external body of the coupling device.

[0092] Clause 15. The composite flywheel of clause 14, wherein in the external body of the coupling device there are arranged: first drawing discs constrained to the primary flywheel to rotate integrally therewith; second drawing discs constrained to the secondary flywheel to rotate integrally therewith; a piston mounted around the support shaft of the secondary flywheel and adapted to bias the first drawing discs and the second drawing discs against each another; and wherein preferably the support shaft, a flange of the coupling device and the piston form a pressure chamber adapted to receive a control fluid of the coupling device.

[0093] Clause 16. The composite flywheel of one or more of the previous clauses, wherein the primary flywheel has a different mass and/or a different diameter than that of the secondary flywheel.

[0094] Clause 17. A system including a power source, a driven machine and a mechanical transmission drivingly coupling the power source to the driven machine, said mechanical transmission including a composite flywheel according to one or more of the preceding clauses, and preferably a control unit adapted to connect the secondary flywheel to the primary flywheel upon achieving a value of an operating parameter of the driven machine, such as for instance a rotary speed.