WO2025158237A1

WO2025158237A1 - A continuously variable transmission, and vehicle comprising the transmission

Info

Publication number: WO2025158237A1
Application number: PCT/IB2025/050375
Authority: WO
Inventors: Walter MARIOTTI
Original assignee: Piaggio and C SpA
Current assignee: Piaggio and C SpA
Priority date: 2024-01-22
Filing date: 2025-01-13
Publication date: 2025-07-31
Anticipated expiration: 2026-07-22
Also published as: IT202400001077A1

Abstract

The transmission comprises a driving pulley (23) and a driven pulley (25), with a transmission belt entrained between the two pulleys. Each pulley has two half-pulleys which move axially with respect to each other to change the transmission ratio via a centrifugal mass mechanism. An automatic clutch (33) is provided at the output of the driving pulley, which connects the driving pulley to a driven shaft, which can be connected to a driving wheel. The clutch comprises a mechanical device adapted to increase or reduce the radially movable centrifugal masses (41, 51) of the automatic clutch, as a function of the mutual axial position between the half-pulleys of the driven pulley. The mechanical device is configured so as to increase the radially movable centrifugal masses as the transmission ratio between the driving pulley and the driven pulley increases.

Description

A CONTINUOUSLY VARIABLE TRANSMISSION, AND VEHICLE

COMPRISING THE TRANSMISSION

DESCRIPTION

TECHNICAL FIELD

[0001] The present invention relates to transmissions for motor vehicles, in particular for vehicles with internal combustion engine or other vehicles requiring a change of transmission ratio between a motor and a driving wheel.

[0002] Embodiments described herein relate to a continuously variable transmission.

BACKGROUND ART

[0003] In many motor applications, for example in two-, three- or four-wheeled vehicles, automatic continuously variable transmissions are used to transmit motion, with a continuously variable transmission ratio, between the motor and the driving wheel(s).

[0004] Some continuously variable transmissions comprise a driving pulley, connected directly or indirectly to a drive shaft, and a driven pulley. A belt entrained around the driving pulley and the driven pulley transmits motion from the driving pulley to the driven pulley. Each of the two pulleys comprises a first half-pulley and a second half-pulley, coaxial and torsionally coupled to each other so as to rotate together around the respective shaft. The two half-pulleys of each pulley are movable axially, i.e., parallel to the rotation axis, so as to vary the width of the groove in which the belt, typically a V-belt, is inserted. To vary the transmission ratio, a mechanism is provided which brings the half-pulleys of the driving pulley closer together in an axial direction. This movement corresponds to a corresponding and opposite movement of mutual distancing of the half-pulleys of the driven pulley. These opposite axial displacements of the driving and driven half-pulleys cause a change in the position of the belt. In particular, when the driving half-pulleys approach each other, the belt entrained around the driving pulley translates radially outwards due to the reduction of the groove in which it is inserted and thus increases the radius around which the belt is guided. Conversely, this displacement of the belt causes a widening of the groove between the driven half-pulleys, with a consequent reduction in the radius around which the belt is entrained around the driven pulley. This simultaneous and opposite variation in the size of the grooves of the driving pulley and the driven pulley causes a variation in the transmission ratio and more precisely an increase in the transmission ratio between the driving pulley (and thus the motor) and the driven pulley (and thus the driving wheel connected thereto).

[0005] The reverse occurs when the driving half-pulleys move away from each other, resulting in the driven half-pulleys approaching each other.

[0006] The mutual approaching movement of the driving half-pulleys is controlled by a centrifugal mechanism. The latter comprises rollers or balls arranged around the rotation axis of the driving pulley and enclosed between two opposite conical walls, one of which is integral with one of the two driving half-pulleys. As the rotation speed of the drive shaft and thus of the rollers or balls around the drive shaft increases, the centrifugal force acting on the rollers or balls causes them to be pushed in a centrifugal radial direction and consequently push the driving half-pulley integral with the conical surface co-acting with the rollers or balls towards the other driving half-pulley. Typically, one of the two driving half-pulleys is fixed and the other is axially movable. Similarly, one of the two driven half-pulleys is axially fixed and the other axially movable. What is called a torque corrector is associated with the driven pulley and compensates the torque variations.

[0007] The driven pulley is associated with an automatic clutch, having an input shaft, which transmits the torque from the driven pulley to the clutch, and an output shaft, which connects the clutch to the driving wheel(s) of the vehicle, possibly with the interposition of a reduction gearbox.

[0008] The clutch has masses which are radially movable under the effect of centrifugal force, which tend to move radially outwards as the rotation speed of the driven pulley increases. Thereby, starting from zero speed, the clutch engages, i.e., it establishes a mechanical connection between the input shaft and the output shaft of the motion (and thus a mechanical connection between the motor and the driven wheel(s)), when the angular speed of the movable masses reaches a sufficient value.

[0009] A continuously variable transmission with automatic clutch of this type is disclosed in W02020141413A1 [0010] US4830163 discloses another continuously variable transmission with an automatic clutch. In this known mechanical transmission, the automatic clutch comprises a first set of centrifugal masses and a second set of centrifugal masses placed on opposite sides of a rotating disc. The centrifugal masses of the first set may differ from the centrifugal masses of the second set by two factors: the amount of mass and/or the elastic characteristic of the elements which bias the centrifugal masses in the rest position (i.e., toward the axis of rotation). In this way, the number of centrifugal masses contributing to torque transmission may vary as angular speed varies.

[0011] In fact, if all centrifugal masses are equal, but the first set of centrifugal masses is associated with “harder” elastic members (i.e., having a higher elastic constant) than the elastic members of the second set, the masses of the first set begin to move radially in a centrifugal direction at a lower number of revolutions, compared to the masses of the second set of centrifugal masses, because the force required to achieve centrifugal displacement is lower for the first set of masses than for the second set of masses. Conversely, if the elastic members associated with the two sets of masses are equal, but the centrifugal masses of the first set are larger (thus they each have a greater mass) than the centrifugal masses of the second set, the centrifugal radial motion of the first set of masses begins at a lower number of revolutions, since the centrifugal force generated is proportional to the square of the number of revolutions and to the mass subjected to the rotational motion. The two effects can be combined, i.e., the two sets of centrifugal masses can differ from each other in the amount of mass and in the characteristics of the elastic return members. As a matter of fact, the centrifugal masses of the first set or the second set, calibrated as described above, freely make a larger or smaller radial displacement, depending on the speed of rotation.

[0012] To ensure that the clutch engagement is smooth and does not involve excessively sudden movements of the vehicle upon engagement, the movable masses of the clutch are relatively light, so that they move radially outwards and engage the clutch at a relatively high number of revolutions of the driven pulley of the continuously variable transmission. At higher motor revolutions, more motor torque is available, thus avoiding problems with vehicle acceleration or jerking.

[0013] This does, however, mean that it is impossible to lower the motor speed when the vehicle is travelling with a high transmission ratio. In fact, lowering the motor speed, and thus the driven pulley, causes a retraction of the movable masses and a consequent opening, or at least a slipping, of the automatic clutch.

[0014] This means that vehicles equipped with this type of transmission, typically scooters or other saddle-driven vehicles, cannot be driven in high gear (high transmission ratio) and low revolutions, adversely affecting not only the driving comfort, but also the consumption.

[0015] The object of the present invention is to alleviate or eliminate these drawbacks of the continuously variable transmissions of the prior art.

SUMMARY

[0016] According to one aspect, a continuously variable transmission is disclosed herein, comprising a driving pulley, comprising a first driving half-pulley and a second driving half-pulley, movable with respect to each other parallel to a rotation axis, and associated with a centrifugal force mechanism adapted to control a mutual approaching movement of the first driving half-pulley and the second driving half-pulley as the rotation speed of the driving pulley increases.

[0017] The continuously variable transmission further comprises a driven pulley, in turn comprising a first driven half-pulley and a second driven half-pulley, movable with respect to each other parallel to a rotation axis of the driven pulley and associated with an elastic member adapted to urge the first driven half-pulley and the second driven half-pulley towards each other. A transmission belt entrained around the driving pulley and the driven pulley is provided for transmitting motion from the driving pulley to the driven pulley.

[0018] The continuously variable transmission further comprises an automatic clutch. The automatic clutch is interposed: between a motion input shaft from the driven pulley to the automatic clutch, and a motion output shaft from the automatic clutch.

[0019] The automatic clutch comprises centrifugal masses, movable radially with respect to the rotation axis of the driven pulley. A centrifugal radial movement of the centrifugal masses of the automatic clutch causes the engagement of the automatic clutch and the transmission of the motion through the automatic clutch from the motion input shaft to the motion output shaft when the driven pulley has reached a first angular speed.

[0020] The clutch is associated with a mechanical device adapted to increase or reduce the number of radially movable centrifugal masses of the automatic clutch, as a function of the mutual axial position between the first driven half-pulley and the second driven half-pulley. The mechanical device is configured so as to increase the number of centrifugal masses which are free to move radially as the transmission ratio between the driving pulley and the driven pulley increases. With this device it becomes possible to engage the clutch at a number of revolutions which is different from the number of revolutions at which the clutch disengages, since the overall mass subject to centrifugal force of the movable masses of the automatic clutch varies as a function of the transmission ratio.

[0021] While in the prior art (US4830163) the centrifugal masses are all always free to move, and what changes is the speed of rotation required to achieve equilibrium between centrifugal force and elastic force acting on the different centrifugal masses, in the transmission of the present invention there is a mechanical member that selectively locks or unlocks some of the centrifugal masses as a function of the transmission ratio. In other words, the number of masses having a degree of freedom (radial motion) changes as a function of the transmission ratio.

[0022] As will be clear from what will be described below in relation to an exemplary embodiment, the number of movable masses under the effect of the centrifugal force, and thus the total mass subject to movement due to the centrifugal force, changes as the mutual axial distance between the driven half-pulleys changes, and therefore as a function of the transmission ratio between the driving pulley and the driven pulley.

[0023] Specifically, when a low transmission ratio is set, i.e., a short gear (with the driven half-pulleys close to each other and the driving half-pulleys far from each other), the centrifugal masses of the automatic clutch, movable due to the centrifugal force, are smaller than the centrifugal masses movable when a high transmission ratio is set, i.e., a long gear (with the driven half-pulleys far from each other and the driving half-pulleys close to each other).

[0024] In order to vary the total amount of mass of the automatic clutch movable due to the centrifugal force, in some embodiments it can be envisaged that the movable centrifugal masses of the automatic clutch comprise: (a) a set of first movable centrifugal masses, configured to move radially under the effect of centrifugal force in any operating condition of the transmission; and (b) a set of second centrifugal masses, configured to be locked in a radially retracted position, when the transmission ratio is low, and to move radially in a centrifugal direction with respect to the radially retracted position due to the centrifugal force, when the transmission ratio is high. As used here, the terms “high” and “low” are relative terms, in the sense that the “high” transmission ratio is a higher transmission ratio than the “low” transmission ratio. In embodiments, a selective locking device is provided, for selectively locking the second centrifugal masses as a function of the mutual axial position between the first driven half-pulley and the second driven half-pulley. Since each mutual axial distance between the driven half-pulleys corresponds to a given transmission ratio, the locking device controlled by the mutual distance between the driven half-pulleys is in practice controlled depending on the transmission ratio set from time to time between the driving pulley and the moving pulley.

[0025] In practical embodiments, the selective locking device is mechanically connected to the driven pulley such that, depending on the mutual distance between the first driven half-pulley and the second driven half-pulley, it takes selectively: (a) a locking position, in which it holds the second centrifugal masses in the radially retracted position; and (b) an unlocked position, in which it allows the centrifugal radial movement of the second centrifugal masses from the radially retracted position.

[0026] When the second centrifugal masses are free to move with a centrifugal radial motion, they can co-act with the first centrifugal masses in the clutch engagement movement, wherein such movement can be an outward radial movement through which the centrifugal masses establish a mechanical connection between the motion input shaft and the motion output shaft. For this purpose, it can be envisaged that the centrifugal masses are constrained to the motion input shaft and are surrounded by a bell integral with the motion output shaft.

[0027] In the present context, “radial” movement generally means a movement which has a radial component, i.e., distancing/approaching with respect to a rotation axis. Radial movement can be achieved, for example, as a pivoting motion around a hinge axis parallel to the rotation axis and preferably spaced therefrom. The pivoting movement involves a radial movement with respect to the rotation axis.

[0028] In some embodiments, it can be envisaged that the second centrifugal masses are adapted to work in parallel with the first centrifugal masses when they are in a position free to move radially. In other embodiments, as described below, it is advantageously envisaged that each second centrifugal mass is constrained to a respective first centrifugal mass, such that, when the second centrifugal masses are free to move radially, the centrifugal force acting on each second centrifugal mass is added to the centrifugal force acting on the corresponding first centrifugal mass.

[0029] This can be achieved, for example, by envisaging that each first centrifugal mass is hinged to a disc, torsionally integral with the motion input shaft, via a hinge pin parallel to the rotation axis of the motion input shaft, and that it is further connected to at least one elastic element adapted to elastically urge the first centrifugal mass into a radially retracted position. Furthermore, it is envisaged that each second centrifugal mass is hinged around the same hinge pin of a corresponding first centrifugal mass, and has an abutment cooperating with the respective first centrifugal mass, when the second centrifugal mass is free to move radially, to apply a centrifugal thrust from the second centrifugal mass to the first centrifugal mass.

[0030] In some embodiments, the selective locking device comprises a rotating cam, adapted to perform rotational movements around the rotation axis of the motion input shaft. The rotating cam comprises a plurality of cam profiles, each of which co-acts with a respective second centrifugal mass.

[0031] The angular movement of the rotating cam can be controlled by a torque servo, or torque controller, associated with the driven pulley.

[0032] Further advantageous features and embodiments of the transmission are described below and set forth in the appended claims.

[0033] According to a further aspect, a motor vehicle is provided, comprising a motor, at least one driving wheel, and a continuously variable transmission as defined above.

[0034] The motor vehicle can in particular be a saddle motor vehicle, comprising one or two rear driving wheel(s) and one or two front steering wheel(s).

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will be better understood by following the description and the attached drawings, which illustrate an exemplary and non-limiting embodiment of the invention. More in particular, the drawings show in:

Fig. l a motor vehicle, in particular a scooter, with a continuously variable transmission;

Fig.2 a functional diagram of the continuously variable transmission between a motor and a driving wheel, for example of a two-wheeled vehicle;

Fig.3 a longitudinal section of the driven pulley and automatic clutch of the continuously variable transmission in low gear conditions, i.e., low transmission ratio;

Figs.4, 5 and 6 cross-sections according to IV-IV, V-V and VI- VI of Fig.3, respectively;

Fig.7 a cross-section according to VII- VII of Fig.5;

Fig.8 an axonometric view of the driven pulley with the rotating cam mounted, in the position of Figs. 3 to 7;

Fig.9 an axonometric view similar to Fig.8, with the cam removed;

Fig.10 a longitudinal section of the driven pulley and automatic clutch of the continuously variable transmission in high gear conditions, i.e., high transmission ratio;

Figs.11, 12 and 13 cross-sections according to XI-XI, XII-XII and XIII-XIII of Fig.10, respectively;

Fig.14 a cross-section according to XIV-XIV of Fig.12;

Fig.15 an axonometric view of the driven pulley with the rotating cam mounted, in the position of Figs. 11 to 14;

Fig.16 an axonometric view similar to Fig.15, with the cam removed;

Fig.17 an axonometric view of a first movable mass; and

Fig.18 an axonometric view of a second movable mass.

DETAILED DESCRIPTION

[0036] Fig.1 shows by way of example a scooter 1 on which a continuously variable transmission according to the present invention can be installed. The scooter 1 comprises a frame 3, a saddle 5, a handlebar 7, a front wheel 9, a rear wheel 11, a motor 13 and a continuously variable transmission 15.

[0037] Fig.2 schematically shows the main elements of the continuously variable transmission 15 connected to the motor 13, depicted only schematically here, and to the driving wheel 11, also shown schematically. The number 17 generally indicates a reducer placed between the continuously variable transmission 15 and the rear driving wheel 11.

[0038] The motor 13 comprises a drive shaft 21, onto which a driving pulley 23 of the continuously variable transmission 15 is fitted. The driving pulley 23 comprises a first driving half-pulley 23.1 and a second driving half-pulley 23.2 which form a groove 24 of variable axial size therebetween, i.e., a groove whose width in the direction of the rotation axis A- A of the drive shaft 21 can vary depending on the driving conditions, as illustrated in detail below. The continuously variable transmission 15 further comprises a driven pulley 25, including a first driven half-pulley 25.1 and a second driven half-pulley 25.2, rotatable around a rotation axis B-B of the driven pulley 25.1. The driven half-pulleys 25.1, 25.2 are also movable with respect to each other in an axial direction, i.e., parallel to the rotation axis B-B, so as to vary the width of a groove 26 defined between the driven half-pulleys 25.1, 25.2.

[0039] A belt 27 is entrained between the two pulleys 23, 25, which transmits motion from the driving pulley to the driven pulley 25.

[0040] In the illustrated embodiment, the first driving half-pulley 24.1 is movable parallel to the rotation axis A-A of the drive shaft 21 according to the double arrow f23, in the manner and for the purposes described below, but torsionally coupled to the drive shaft 21, so as to rotate integrally therewith. The second driving half-pulley 23.2 is, instead, keyed in an axially fixed position on the drive shaft 21, so as to rotate with the drive shaft 21 and without the possibility of axial movement therealong. In the following, therefore, the first driving half-pulley 23.1 will also be referred to as the movable driving half-pulley and the second driving half-pulley 23.2 will also be referred to as the fixed driving half-pulley, where the definitions movable and fixed refer to an axial movement with respect to the rotation axis A-A of the drive shaft 21 to which the driving pulley 23 is torsionally coupled. [0041] The movement of the movable driving half-pulley 23.1 is controlled by a centrifugal force mechanism 29. The centrifugal force mechanism 29 comprises one or more rolling bodies 29.1, for example spherical or cylindrical, housed between a shaped disc 29.2 and the outer side surface of the movable driving half-pulley 23.1. The shaped disc 29.2 is keyed onto the drive shaft 21 in a fixed position, while (as indicated above) the movable driving half-pulley 23.1 is coupled to the drive shaft 21 so as to rotate therewith, but to be able to slide axially according to the double arrow £23. The belt 27, of trapezoidal section, is tensioned by an elastic device associated with the driven pulley 25, described below, due to which the belt 27 tends to be pulled towards the axis A- A of the drive shaft 21, pushing the movable driving half-pulley 23.1 to move away from the fixed driving half-pulley 23.2.

[0042] When the drive shaft 21 rotates around the axis A- A dragged by the motor 13, the rolling body/bodies 29.1 are subject to a centrifugal force which tends to move them radially away from the rotation axis A-A of the drive shaft 21. Due to the opposite conical shapes of the disc 29.2 and the movable driving half-pulley 23.1, the thrust generated by the centrifugal force causes an axial force which pushes the movable driving half-pulley 23.1 towards the fixed driving half-pulley 23.2. The thrust and the consequent mutual approach of the two driving half-pulleys 23.1, 23.2 causes a radial movement towards the outside of the portion of the belt 27 accommodated in the groove of the driving pulley 23, defined between the two driving half-pulleys 23.1, 23.2.

[0043] This outward radial movement caused by the centrifugal force modifies the transmission ratio between the driving pulley 23 and the driven pulley 25, due to the displacement of the loop of the belt 27 entrained around the two pulleys. In fact, the movement of the belt 27 away from the axis A-A of the drive shaft 21, due to the substantial inextensibility of the belt 27, causes the loop of the belt 27 entrained around the driven pulley 25 to move closer to the rotation axis B-B of the driven shaft 31. The movement of the loop of the belt 27 entrained in the groove 26 of the driven pulley 25 closer to the axis B-B occurs simultaneously with a mutual distancing movement between the driven half-pulleys 25.1, 25.2. More in particular, in the illustrated embodiment, the driven half-pulley 25.2 is torsionally and axially fixed with respect to the driven shaft 31. Conversely, the driven half-pulley 25.1 is torsionally coupled to the driven shaft 31 and rotates integrally therewith, but is movable according to the double arrow £25 with respect to the driven shaft 31. The driven half-pulley 25.1 is thus also referred to here as the movable driven half-pulley, while the half-pulley 25.2 is referred to as the fixed driven half-pulley.

[0044] The approaching/distancing movement of the half-pulleys therefore essentially modifies the circumference around which the belt 27 is entrained around the pulleys: when the circumference around the axis A-A increases, the circumference around B-B decreases, with a consequent increase in the transmission ratio (thus a passage from a short gear to a long gear), and vice versa.

[0045] An automatic clutch 33 and a torque corrector 35, which will be described in more detail below, are associated with the driven pulley 25 and the driven shaft 31.

[0046] The automatic clutch 33 is shown in particular in Figs. 3 to 7, which illustrate the position of the automatic clutch 33 in an operating condition. The automatic clutch 33 comprises a motion input shaft from the driven pulley 25 to the automatic clutch 33. The motion input shaft is indicated with 37 and is rigidly coupled to the fixed driven half-pulley 25.2, so as to rotate integrally with the driven pulley 25 and not move axially along the axis B-B. The motion input shaft 37 is hollow and a motion output shaft from the automatic clutch passes therein. The motion output shaft is in practice the driven shaft which, via the gearbox or reducer 17, transmits the motion to the driving wheel 11. Therefore, in this embodiment the motion input shaft 37 to the clutch and the motion output shaft 31 from the clutch are not only coaxial, but also concentric. A different arrangement is not excluded, in which the two shafts are for example coaxial but not concentric, rather they are arranged aligned with each other in sequence.

[0047] The automatic clutch 33 further comprises a bell or hollow body 39, torsionally coupled to the output shaft 31, i.e., rotatable integrally with the output shaft 31. The bell 39 has an approximately cylindrical wall 39.1, with an inner surface 39.2, with which movable centrifugal masses, described below, co-act, which act as a transmission member of the rotational movement from the motion input shaft 37 to the motion output shaft 31 when the automatic clutch 33 is engaged.

[0048] A set of first centrifugal masses, which move under the effect of the centrifugal force, is housed inside the bell 39. Each first centrifugal mass is indicated with 41. In the illustrated embodiment, three first centrifugal masses are provided, distributed at constant angles around the rotation axis B-B of the driven shaft 31 and thus around the driven pulley 25. A single first centrifugal mass 41 is shown in isolation in Fig.17 for greater clarity. Each first centrifugal mass 41 comprises a friction surface 41.1, formed by a coating element 41.2 with a high friction coefficient. The friction surface 41.1 is substantially cylindrical and co-acts with the cylindrical surface 39.2 of the side wall 39.1 of the bell 39 of the automatic clutch 33.

[0049] Each first centrifugal mass 41 is hinged via a hinge pin 43 to a disc 44 integral with the motion input shaft 37. In addition to the disc 44, the hinge pins 43 are connected to a ring 46 coaxial to the rotation axis A-A of the motion input shaft 37.

[0050] Each hinge pin 43 is accommodated in a rotation seat 41.3 of the respective first centrifugal mass 41, see Fig.17.

[0051] The first centrifugal masses 41 are urged towards a non-operating centripetal position, closer to the rotation axis B-B by elastic members. In the illustrated embodiment, the first centrifugal masses 41 are elastically urged in the non-operating position by a plurality of traction springs, for example coil springs, in a number equal to the number of first centrifugal masses 41, i.e., three springs in the exemplary embodiment. The springs are indicated with 45. In the illustrated embodiment, each spring 45 has two ends connected to two of the first centrifugal masses 41, as shown in particular in Fig.5. In the illustrated embodiment, each first centrifugal mass 41 comprises two holes 41.4, 41.5 for the attachment of the two springs 45 which connect it to the other two first centrifugal masses, see in particular Fig.17. For each first centrifugal mass 41, the two attachment points of the springs 45, consisting of the holes 41.4 and 41.5, are located on opposite sides with respect to the axis of the respective hinge pin 43 and thus on opposite sides with respect to the rotation seat 41.3. Each spring 45 is therefore stretched between a point 41.5 of a first centrifugal mass 41 and a point 41.5 of the adjacent centrifugal mass. The tension of the springs 45 tends to hold the first centrifugal masses in the position in which the respective friction surfaces 41. 1 are located closer to the rotation axis B-B and thus detached from the friction surface 39.2 of the bell 39.

[0052] The shape and pivoting point of the first centrifugal masses 41 is such that the centrifugal force exerted thereon when the motion input shaft 37 rotates around the rotation axis B-B tends to counteract the elastic force of the springs 45 and thus urges the first centrifugal masses 41 to rotate around the hinge pins 43, causing the friction surfaces 41.1 to press against the inner cylindrical surface 39.2 of the bell 39 of the clutch 33. When the centrifugal force acting on the first centrifugal masses 41 overcomes the elastic force of the traction springs 45, the automatic clutch 33 engages and the rotational motion of the motion input shaft 37 is transmitted to the motion output shaft, i.e., to the driven shaft 31.

[0053] In practice, the angular position of each first centrifugal mass 41 is determined by the balance between the elastic forces applied by the springs 45 and by the centrifugal force and thus by the rotation speed of the motion input shaft 37.

[0054] In addition to the set of first movable centrifugal masses 41, the automatic clutch 33 comprises a set of second centrifugal masses 51. The second centrifugal masses 51 are subject to a centrifugal force determined by the rotation speed of the input shaft 37 and to a locking force which acts selectively as a function of the transmission ratio between the driving pulley 23 and the driven pulley 25, in a manner which will be explained in detail below. In practice, the second centrifugal masses 51 can be inactive, when they are blocked and unable to expand in a radial direction under the effect of the centrifugal force, or they can be active, and free to expand integrally with the first centrifugal masses 41.

[0055] In practice, a locking device, described in detail below, acts selectively on the second movable centrifugal masses 51 to allow or prevent the centrifugal radial movement thereof under the effect of the centrifugal force.

[0056] In the illustrated embodiment, the second centrifugal masses 51 are mounted such that, when they are free to expand radially outward due to centrifugal force, their mass is added to that of the first centrifugal masses 41. Otherwise, when the locking device is active, the second centrifugal masses do not exert any function.

[0057] More in particular, also with reference to Fig.18, each second centrifugal mass 51 is hinged around one of the hinge pins 43 and for this purpose has a rotation seat 51.1 similar to the rotation seat 41.3. Furthermore, in embodiments, each second centrifugal mass 51 comprises a stem 51.2 housed in a slot 41.6 of the respective first centrifugal mass 41. The stem 51.2 and the slot 41.6 of each pair consisting of a first centrifugal mass 41 and a second centrifugal mass 51 hinged around the same hinge pin 43 are guided with respect to each other in the mutual pivoting movement around the hinge pin. Furthermore, the stem 51.1 and slot 41.6 system can form a abutment system such that when the second centrifugal mass 51 moves radially outwards pivoting around the hinge pin 43, the centrifugal force acting thereon is transmitted to the corresponding first centrifugal mass 41.

[0058] This transmission of centrifugal force can also be obtained with a different system of mutual abutments between the first centrifugal mass 41 and the corresponding second centrifugal mass 51.

[0059] What matters is that each second centrifugal mass 51 is constrained to a respective first centrifugal mass 41, such that, when the second centrifugal masses are free to move radially, the centrifugal force acting on each second centrifugal mass is added to the centrifugal force acting on the corresponding first centrifugal mass.

[0060] The centrifugal movement of the second centrifugal masses 51 can be selectively locked by a selective locking device comprising a multiple rotating cam 55, i.e., provided with a plurality of cam profiles 55.1 in a number equal to the number of second centrifugal masses 51.

[0061] Each cam profile 55.1 co-acts with a feeler 51.3 of the respective second centrifugal mass 51. In the illustrated embodiment, each feeler 51.3 comprises a roller 51.4 (Fig.18) carried by the second centrifugal mass 51 on the opposite side of the stem 51.2 with respect to the hinge axis defined by the rotation seat 51.1. Each cam profile 55.1 has ascending ramps, which co-act with the respective feeler 51.3 to lock the respective second centrifugal mass 51 in a radially retracted position, i.e., in which the second centrifugal mass 51 does not push against the corresponding first centrifugal mass 41 with which it is associated.

[0062] In the illustrated embodiment, the rotating cam 55 is integral with a component paired with the torque corrector or torque servo 35, so that the angular position of the rotating cam 55 is a function of the operating conditions of the continuously variable transmission, in the manner described below. [0063] In the illustrated embodiment, the rotating cam 55 is integral with a sleeve 57 coaxial with the axis B-B, see in particular also Fig.8. In the illustrated embodiment, the sleeve 57 comprises at least one slot 57.1 parallel to the axis B-B. Preferably, the sleeve 57 comprises a plurality of slots 57.1 parallel to the axis B-B. In each slot 57.1, a pin 59.1 is engaged which is integral with a bush 59 of the torque servo or torque corrector 35 and protruding radially from the bush 59. Each pin 59.1 is fixed in a seat 59.2 (Fig.9) of the bush 59.

[0064] The bush 59 is fixed to the movable driven half-pulley 25.1, so that the bush 59 and the movable driven half-pulley 25.1 rotate and translate (arrow f25) integrally with each other as a single body. The number 61 indicates rigid connection elements between the movable driven half-pulley 25.1 and the bush 59.

[0065] The bush 59 comprises at least one helical slot 59.3. In the illustrated embodiment, the bush 59 comprises three helical slots 59.3 extending around the rotation axis B-B of the driven shaft 31. A pin 37.1 is engaged in each helical slot 59.2, which is integral with the motion input shaft 37 of the automatic clutch 33.

[0066] An elastic member is arranged around the sleeve 57, the bush 59 and the motion input shaft 37, in the example a coil spring 65 which tends to push the movable driven half-pulley 25.1 in the axial direction towards the fixed driven half-pulley 25.2. The force of the spring 65 therefore urges the driven half-pulleys 25.1, 25.2 to take a position of maximum juxtaposition, and thus a condition of minimum width of the groove 26 of the driven pulley 25. This condition, illustrated in Figs. 3 to 9, corresponds to a short transmission ratio between driving pulley 23 and driven pulley 25, i.e., a low gear. Due to the inextensibility of the transmission belt 27, this position of maximum juxtaposition between the driven half-pulleys 25.1, 25.2 corresponds to a position of maximum distance between the driving half-pulleys 23.1, 23.2 (see Fig.2).

[0067] Comparing Figs. 3 to 9 and Figs.10 to 16 with each other, the following is observed. In Figs. 3 to 9, the two driven half-pulleys 25.1, 25.2 are in the maximum approach condition and therefore in a low transmission ratio position. The sleeve 57 is located in a first angular position with respect to the centrifugal masses of the automatic clutch 33. In Figs. 10 to 16 (each of which corresponds to Figs. 3 to 9), the driven half-pulleys 25.1, 25.2 are in the maximum distance condition and therefore in a high transmission ratio position (long gear). Furthermore, the sleeve 57 is located in a second angular position with respect to the centrifugal masses of the automatic clutch 33. The rotation of the sleeve 57 around the axis B-B with respect to the centrifugal masses of the automatic clutch 33 is caused by the rotational movement of the bush 59 of the torque corrector 35, in turn determined by the axial displacement of the bush 59 integral with the axial movement of the movable driven half-pulley 25.1.

[0068] The angular displacement of the sleeve 57 causes an angular movement of the cam profiles 55.1 of the cam 55, integral with the sleeve 57. As can be observed by comparing in particular Figs. 5 and 12, in the position of Figs. 3 to 9 the cam profiles 55.1 are in a position, with respect to the centrifugal masses, such as to push the feelers 51.3 radially outwards. In this position, the second centrifugal masses 51 do not co-act with the first centrifugal masses 41, since the cam profiles 55.1 prevent the inward pivoting movement of the feelers 55.3 and therefore the outward movement around the pins 43 of the portion of the second centrifugal masses 51 carrying the stems 51.2. In other words, the rotation, around the axis B-B, of the centrifugal masses 41 and 51 caused by the rotation of the motion input shaft 37 generates a centrifugal force on the first centrifugal masses 41. The centrifugal force pushes the first centrifugal masses 41 with their friction surfaces 41.1 against the cylindrical friction surface 39.2 of the bell 39, generating a transmission torque between the first centrifugal masses 41 (and therefore the motion input axis 37 which rotates integrally therewith around the axis B-B) and the bell 39 and consequently the motion output shaft, representing the driven shaft 31.

[0069] Conversely, in this angular position of the rotating cam 55, the centrifugal force acting on the second centrifugal masses 51 does not cause the centrifugal radial movement thereof, due to the locking force exerted by the cam profiles 55.1 on the feelers 51.3.

[0070] Conversely, in the angular position of the rotating cam 55 illustrated in Figs. 10 to 16, the cam profiles 55.1 are offset with respect to the feelers 51.3. This frees the pivoting movement of the second centrifugal masses 51 around the axes of the pins 43. Consequently, the centrifugal force applied to the second centrifugal masses 51 caused by the rotation around the axis B-B causes the angular movement of the second centrifugal masses 51 until the latter rest against the first centrifugal masses 41. Consequently, the centrifugal force exerted on each second centrifugal mass 51 is discharged indirectly onto the cylindrical friction surface 39.2 of the bell 39.

[0071] The consequence of this is an increase in the torque transmitted by the automatic clutch 33 at the same number of drive shaft revolutions.

[0072] In essence, the system consisting of the second centrifugal masses 51 and the selective locking device using the rotating cam 55 acting on the second centrifugal cams 51 allows the total value of the centrifugal mass in play (and thus the centrifugal force which guarantees transmission through the automatic clutch 33) to be modified as a function of the transmission ratio between the driving pulley 23 and the driven pulley 25. The consequence is as follows. When the motor vehicle must start, the centrifugal masses in play are only the first centrifugal masses 41 and therefore the clutch engages at a relatively high number of revolutions, making the start of the motor vehicle gradual.

[0073] Conversely, when the motorcycle is travelling at high speed and with a high transmission ratio (high gear, Figs. 10 to 16), the centrifugal force which guarantees the transmission of torque through the automatic clutch 33 is given by the sum of the first centrifugal masses 41 and the second centrifugal masses 51. Consequently, the automatic clutch 33 disengages (i.e., opens, ceasing to transmit driving torque to the driving wheel 11) at a lower rotation speed compared to that which causes the clutch to engage in the condition of Figs. 3 to 9 (low transmission ratio, short gear).

[0074] In summary, the locking device of the second centrifugal masses, operated by the movement of the torque servo or torque corrector, allows to engage the automatic clutch 33 at a higher number of revolutions compared to the number of revolutions at which the automatic clutch 33 disengages.

[0075] It is thereby possible to have relatively small initial centrifugal masses 41, to optimise the starting conditions of the motor vehicle, and at the same time guarantee a driving condition with low motor rotation speed and high transmission ratio, benefiting driving comfort and reduced consumption, thanks to the intervention of the second centrifugal masses 51 which are added to the initial centrifugal masses 41.

[0076] While the invention has been described in terms of various specific embodiments, it will be clear to those skilled in the art that many modifications, variations and omissions are possible without departing from the spirit and scope of the invention as defined in the following claims.

Claims

1. A continuously variable transmission (15), comprising: a driving pulley (23), a driven pulley (25) and a transmission belt (27) entrained around the driving pulley and the driven pulley; wherein the driven pulley comprises a first driven half-pulley (25.1) and a second driven half-pulley (25.2), movable with respect to each other parallel to a rotation axis (B-B) of the driven pulley (25); an automatic clutch (33), positioned between a motion input shaft (37) from the driven pulley (25) to the automatic clutch (33) and a motion output shaft (31) from the automatic clutch (33); wherein the automatic clutch (33) comprises centrifugal masses (41, 51) movable radially with respect to the rotation axis (B-B) of the driven pulley (25); a mechanical device adapted to increase or reduce the number of radially movable centrifugal masses of the automatic clutch (33), depending on the mutual axial position between the first driven half-pulley (25.1) and the second driven half-pulley (25.2).

2. The transmission of clam 1, wherein the first driving pulley comprises a first driving half-pulley (23.1) and a second driving half-pulley (23.2), movable with respect to each other parallel to a rotation axis (A-A) of the driving pulley (23), and associated with a centrifugal force mechanism (29) adapted to control a mutual approaching movement of the first driving half-pulley (23.1) and the second driving half-pulley (23.2) as the rotation speed of the driving pulley (23) increases.

3. The transmission of claim 1 or 2, wherein the first driven half-pulley (25.1) and the second driven half-pulley (25.2) are associated with an elastic member (65) adapted to urge the first driven half-pulley (25.1) and the second driven half-pul- ley (25.2) towards each other.

4. The transmission (15) of one or more of the preceding claims, wherein the centrifugal masses of the automatic clutch are configured so that a centrifugal radial movement of the centrifugal masses (41, 51) causes the engagement of the automatic clutch (33) and the transmission of the motion through the automatic clutch (33) from the motion input shaft (37) to the motion output shaft (31) when the driven pulley (25) has reached a first angular speed.

5. The transmission (15) of one or more of claims 1 to 4, wherein the mechanical device is configured so as to increase the radially movable centrifugal masses as the transmission ratio between the driving pulley (23) and the driven pulley (25) increases.

6. The transmission (15) of one or more of claims 1 to 5, wherein the movable centrifugal masses comprise: i. a set of first movable centrifugal masses (41), configured to move radially under the effect of the centrifugal force in any operating condition of the transmission (15); ii. a set of second centrifugal masses (51), configured to be selectively locked in a radially retracted position, and radially movable in a centrifugal direction with respect to the radially retracted position under the effect of the centrifugal force, as a function of the transmission ratio between the driving pulley and the driven pulley.

7. The transmission (15) of claim 6, comprising a selective locking device of the second centrifugal masses (51), depending on the mutual axial position between the first driven half-pulley (25.1) and the second driven half-pulley (25.2).

8. The transmission (15) of claim 6 or 7, wherein the selective locking device is mechanically connected to the driven pulley (25), in such a way as to take, depending on the mutual distance between the first driven half-pulley (25.1) and the second driven half-pulley (25.2), selectively: a locking position, in which it holds the second centrifugal masses (51) in the radially retracted position; and an unlocked position, in which it allows the centrifugal radial movement of the second centrifugal masses (51) from the radially retracted position.

9. The transmission (15) of claim 6 or 7 or 8, wherein each second centrifugal mass (51) is constrained to a respective first centrifugal mass (41), such that, when the second centrifugal masses (51) are free to move radially, the centrifugal force acting on each second centrifugal mass (51) is added to the centrifugal force acting on the corresponding first centrifugal mass (41).

10. The transmission (15) of claim 9, wherein: each first centrifugal mass (41) is hinged to a disc (44), torsionally integral with the motion input shaft (37), via a hinge pin (43) parallel to the rotation axis (B-B) of the motion input shaft (37), and is connected to at least one elastic element (45) adapted to elastically urge the first centrifugal mass (41) into a radially retracted position; and each second centrifugal mass (51) is hinged around the same hinge pin (43) of a corresponding first centrifugal mass (41), and has an abutment (51.2) cooperating with the respective first centrifugal mass (41), when the second centrifugal mass (51) is free to move radially, to apply a centrifugal thrust from the second centrifugal mass (51) to the first centrifugal mass (41).

11. The transmission (15) of claim 10, wherein each second centrifugal mass (51) comprises a stem (51.2) parallel to the hinge pins (43) of the first centrifugal masses (41) and the second centrifugal masses (51); and wherein the stem (51.2) of each second centrifugal mass (51) is guided into a slot (41.6) of the respective first centrifugal mass (41).

12. The transmission (15) of one or more of claims 6 to 11, wherein the selective locking device comprises a rotating cam (55), adapted to perform rotational movements about the rotation axis (B-B) of the motion input shaft (37); wherein the rotating cam (55) comprises a plurality of cam profiles (55.1), each cam profile cooperating with a respective second centrifugal mass (51); and wherein the angular movement of the rotating cam (55) is controlled by a torque servo (35) associated with the driven pulley (25).

13. The transmission (15) of claim 12, wherein each second centrifugal mass (51) comprises a feeler (51.3) cooperating with the respective cam profile (55.1) of the rotating cam (55) of the selective locking device.

14. The transmission (15) of claim 12 or 13, wherein the torque servo comprises: a bush (59) integral with one of said first driven half-pulley (25.1) and second driven half-pulley (25.2) and coaxial therewith; a helical cam coupling (37.1, 59.3) between the bush (59) and the other of said first driven half-pulley (25.1) and second driven half-pulley (25.2), the coupling being such that an axial movement of mutual approach and separation between the first driven half-pulley (25.1) and the second driven half-pulley (25.2) corresponds to a relative angular movement between the first driven half-pulley (25.1) and the second driven half-pulley (25.2).

15. The transmission (15) of claim 14, wherein the bush (59) is connected to the rotating cam (55) so as to transmit to the rotating cam the rotational movements of the bush (59) but not the axial displacement movements of the bush (59).

16. The transmission (15) of claim 14 or 15, wherein the helical cam coupling comprises a helical profile (59.3) integral with the bush (59) and a radial pin (37.1) fixed to the motion input shaft (37) of the automatic clutch (33); wherein the radial pin (37.1) is inserted into the helical profile (59.3) and the bush (59) is rotatably mounted on the motion input shaft (37).

17. The transmission (15) of any one of claims 14 to 16, wherein the rotating cam (55) is integral with a sleeve (57) coaxial to the bush (59) of the servo and surrounding said bush (59).

18. The transmission (15) of claim 17, wherein the elastic member (65) associated with the driven pulley (25) comprises a helical spring surrounding the bush (57).

19. The transmission (15) of one or more of the preceding claims, wherein the motion input shaft (37) from the driven pulley (25) to the automatic clutch (33) is concentric with the motion output shaft (31) from the automatic clutch (33); wherein the automatic clutch (33) is located on one side of the driven pulley (25) and the motion output shaft (31) protrudes from the side of the driven pulley (25) opposite the automatic clutch (33).

20. The transmission (15) of one or more of the preceding claims, wherein the motion output shaft (31) from the automatic clutch (33) is integral with a bell (39) which surrounds the centrifugal masses (41, 51); wherein the bell (39) comprises an internal approximately cylindrical friction surface (39.2), cooperating with friction surfaces (41.1) of the centrifugal masses (41).

21. A motor vehicle (1) comprising: a motor (13); at least one driving wheel (11); a continuously variable transmission (15) according to any one of the preceding claims, between the motor and the driving wheel.