"A continuously variable transmission device with a device for varying the gear shift curve"

[0001] The present invention relates to a transmission system, in particular a continuously variable transmission system for motorcycles, provided with a device for varying the gear shift curve.

[0002] In this document the term "motorcycle" means a vehicle with two, three or four wheels, pivoting or non pivoting, such as the Vespa®, Ape® or MP3® vehicles marketed by the Applicant .

[0003] The Continuously Variable Transmission (CVT) is a type of automatic transmission for vehicles in which the transmission ratio can vary continuously between two limit values. The continuous transmission is widely used in two- wheeled vehicles with a small and medium engine size, in particular motor scooters.

[0004] In a conventional CVT, the variation of the transmission ratio takes place by varying the winding diameter of the belt on two pulleys, one of which is the drive pulley and the other driven, and at least one of these has the ability to draw together and distance the two parts or half-pulleys which it is composed of.

[0005] Typically, the drive pulley comprises a speed regulator made with centrifugal masses, generically referred to as "rollers", which have the task of realizing the axial drawing together of the respective half-pulleys , passing from the low gear condition (half-pulleys distant) to the condition, of high gear, (half-pulleys juxtaposed) .

[0006] Consequently, in a conventional CVT, once the physical and geometrical characteristics of the system are set, the transmission ratio depends on the number of engine revolutions .

[0007] There is instead a need to provide a CVT transmission system in which the gear shift curve can be modified according to the acceleration or deceleration requirements of the driver.

[0008] In other words, there is a need to provide a CVT transmission system which, for example, in the case in which, starting from a certain condition, the driver accelerates or decelerates suddenly, adapts to and accommodates such request, facilitating the acceleration or the deceleration of the vehicle.

[0009] The object of the present invention is to provide a transmission device which satisfies the needs mentioned above .

[0010] Such purpose is achieved by a transmission device made according to claim 1. The dependent claims describe embodiment variants.

[0011] The characteristics and advantages of the transmission device according ·. to the invention will be evident from the description given below, by way of a non- limiting example, according to the appended drawings, wherein :

[0012] - figure 1 shows a longitudinal cross-section of a transmission device for vehicles according to one embodiment of the present invention;

[0013] - figure 2 represents a cross-section of the transmission device in figure 1, in which a cam profile of a mobile bushing is highlighted;

[0014] - figure 3 shows a longitudinal cross-section of a transmission device according to the present invention, according to a further embodiment;

[0015] - figure 4 schematically shows a pin with a hood in contact with a cam profile of the mobile bushing of the device in figure 3;

[0016] -figure 5 shows a plan view of the ^" hood in figure 4;

[0017] - figures 6a to 6d illustrate embodiment variants of cam profiles;

[0018] - figure 7 shows a longitudinal cross-section of a transmission device according to the present invention, according to yet a further embodiment;

[0019] - figure 8 schematically shows reciprocally penetrating portions of the mobile bushing and the fixed bushing of the transmission device in figure 7; and [0020] - figure 9 shows a graph representing the revolutions of the drive pulley and the driven pulley in a conventional CVT transmission system and the CVT transmission system according to the present invention.

[0021] With reference to the appended drawings, reference numeral 1 globally denotes a continuously variable transmission device, configured to be applied preferably to a two / three-wheel motorcycle, engaged with a drive shaft 2 which defines an axis of rotation X.. .

[0022] The transmission device 1 comprises a first drive pulley 4, driven in rotation by the drive shaft 2, and a second driven pulley (not shown) , connected to each other by a V-belt 6.

[0023] The drive pulley 4 is composed of a first half-pulley 8 and a second half-pulley 10, respectively provided with facing, truncated-cone active surfaces 8a, 10a, sliding along said axis of rotation X so as to juxtapose and distance the active surfaces 8a, 10a, and integral with each other in rotation.

[0024] The first half-pulley 8 comprises in particular a mobile bushing 9, which carries the active surface 8a and provides a bushing 8b coaxial to the motor shaft 2, and a speed controller 12 comprising a container 14, supported by the mobile bushing 9 and provided with a shaped seat 16, and a plurality of rollers 18, housed in the seat 16. [0025] The rollers realize centrifugal masses which, as the number of engine revolutions increases, push the first half-pulley 8, and in particular the mobile bushing 9, towards the second half-pulley 10.

[0026] This way, the winding diameter of the belt 6 on the drive pulley 4 increases and the belt, not being able to stretch, operates to decrease the winding diameter on the driven pulley, increasing the transmission ratio (high gear) .

[0027] The. drive pulley 4 further comprises a fixed bushing 11, having a main extension along the axis of rotation X, coaxial to the motor shaft 2 and coupled in rotation therewith, for example via a grooved profile.

[0028] The mobile bushing 9 is engageable in rotation by the fixed bushing 11 and is axially translatable with respect to it by the engagement of respective cam profiles.

[0029] The transmission device 1 comprises a cam system operating between the fixed bushing 11 and the mobile bushing 9 suitable to transmit the rotation between the fixed bushing 11 and the mobile bushing 9, and configured to prevent the approach between the active surfaces 8a, 10a or to facilitate the approach between them.

[0030] For example, according to a first embodiment (figures 1 to 4), the drive pulley 4 comprises at least one pin 20, for example of steel (figures 1 and 2), fastened to the fixed bushing 11 and projecting radially outwards therefrom.

[0031] Correspondingly, the mobile bushing 9 has a first cam profile 22, for example composed of the closed peripheral edge of a cam opening 24 passing radially through the mobile bushing 9.

[0032] According to an embodiment variant (figures 3 and 4) the pin 20 comprises a hood 26, for example in plastic material, for example self-lubricating (for example TBD) , which covers the head, so as to come into contact with the cam profile 22 of the mobile bushing 9.

[0033] For example, the hood 26 is provided with an annular side surface 28 which produces a rounded profile, for example inscribed in an imaginary circular cylindrical surface 30. Preferably, said side surface 28 provides for flat portions 32 connected by arched portions 34.

[0034] Advantageously, this conformation of the hood makes it possible to minimise the loads transmitted by the fixed bushing 11 to the mobile bushing 9 and vice versa.

[0035] The cam profile 22 is closed and has an active portion 30a, against which the pin 20 abuts when the motor shaft 2 exerts an active torque (acceleration phase) , and a braked portion 30b, against which the pin 20 abuts when the motor shaft 2 exerts a braked torque (deceleration phase) . [0036] For example, in figure 6a, if the direction of rotation of the motor shaft 2 is indicated by the arrow F, during an acceleration phase, the pin 20 abuts with the active portion 30a of the profile 22; instead, during a deceleration phase, the pin 20 abuts with the braked portion 30b of the profile 22.

[0037] According to a first embodiment variant, the cam profile provides for a linear active portion 30a and a linear braked portion 30b, the same as the active portion 30a (figure 6a) ; according to a further embodiment variant, the cam profile 22 provides for a curved active portion 30a and a curved braked portion 30b, the same as the active portion 30a (figure 6b).

[0038] According to a further embodiment variant, the cam profile provides for a linear active portion 30a and a linear braked portion 30b, different, for example in inclination, from the active portion 30a (figure 6c) ; according to yet a further embodiment variant, the cam profile 22 provides for a curved active portion 30a and a curved braked portion 30b, different, for example in pattern, from the active portion 30a (figure 6d) .

[0039] According to a further embodiment (figures 7 and 8) the fixed bushing 11 and the mobile bushing (9) axially penetrate each other and the penetrating portions define a drive profile 32a on the fixed bushing 11 and a driven profile 32b on the mobile bushing 32b.

[0040] In this embodiment, the container 14, which carries the active surface 8a, is axially movable on the mobile bushing 9.

[0041] During normal operation of the transmission device 1, in case of active torque transmitted by the motor shaft, in the case of acceleration by the driver starting from a low gear, the cam system opposes an advancement of the active surface 8a of the first half-pulley 8 towards the active surface 10a of the second half-pulley 10, so that the gear shift is delayed and the behaviour of the transmission device is more sporting than a standard CVT.

[0042] In the · case instead of braked torque transmitted by the motor shaft, for example in the case of deceleration by the driver by releasing the throttle or braking, or with the vehicle moving downhill starting from a high gear, the cam system facilitates the distancing of the active surface 8a of the first half-pulley 8 from the active surface 10a of the second half-pulley 10, so that shift down and therefore a more accentuated deceleration compared to a standard CVT is facilitated.

[0043] Innovatively, the transmission device described above makes it possible to satisfy the aforementioned need, since it makes it possible to accommodate the driver's wish to accelerate or decelerate. [0044] Advantageously, moreover, by suitably shaping the profiles of the cam system, it is possible to design a transmission device that responds more or less abruptly to an acceleration or a deceleration.

[0045] For example, figure 9 shows the engine revolutions of the drive pulley and the driven pulley, for a conventional CVT transmission system and for a CVT transmission system according to the present invention. The latter clearly shows a greater hysteresis.

[0046] According to a further advantageous aspect, using a hood applied to the suitably shaped pin, it is possible to limit the stresses concentrated between the pin and mobile bushing .

[0047] Advantageously, moreover, if said hood is made of plastic material, it is possible to eliminate the need for lubrication between the pin and the mobile bushing.

[0048] It is clear that a person skilled in the art may make modifications to the transmission device described above so as to satisfy contingent requirements, all contained within the scope of protection as defined by the appended claims .