EP3074303A1

EP3074303A1 - Variable gear ratio device

Info

Publication number: EP3074303A1
Application number: EP14815058.4A
Authority: EP
Inventors: Davide MAZZINI; Alessandro BURCHIANTI
Original assignee: CMS SpA
Current assignee: CMS SpA
Priority date: 2013-11-29
Filing date: 2014-11-27
Publication date: 2016-10-05
Also published as: ITMI20131995A1; WO2015079399A1

Abstract

A variable gear ratio device (1) is provided for comprising a planet gear (10) defining a rotation axis (10a), suitable to continuously vary the gear ratio and comprising at least one rocker gear (11); a spider (12) suitable to support the rocker gear (11) and defining a spider axis (12a) inclined in relation to the axis (10a); a sun gear (13) and a crown (14) defining, respectively, an inner (13a) and outer contact area (14a) for the rocker gear (11); wherein the inner contact area (13a) and the outer contact area (14a) are tapered in the same direction along the rotation axis (10a); and respectively define, at the points of contact with the rocker gear (11) and in relation to the rotation axis (10a), a first angle of inclination and a second angle of inclination different from each other; and wherein, on account of said torque variation, the rocker gear (11) is apt to passively translate in relation to said spider (12) along said spider axis (12a) varying its distance from said rotation axis (10a) and said contact points with said contact area (13a, 14a) and thus, the gear ratio of the variable gear ratio device (1); a torque regulator (16) suitable to command a reciprocal translation of said contact areas (13a, 14a) depending on such translation of the rocker gear (11).

Description

DESC RIPTION

VARIABLE GEAR RATIO DEVICE

The present invention relates to a variable gear ratio device of the type as recited in the preamble of the first claim.

In particular, the invention relates to a particular device suitable to continuously vary the gear ratio without interruption between two limit values.

As is known, variable gear devices, commercially named with the acronym CVT, are used to produce, from a constant input speed, a continuously variable output speed as a function of the torque and, to be precise, of the stall torque.

A first example of a continuously variable gear ratio device provides for a V-belt gear in which at least one of the two pulleys consists of two elements having conical contact areas for the belts mutually axially mobile so as to vary the effective gear ratio depending on their axial distance and, thus, on the point of contact of the belt with the contact areas.

Such devices have a reduced range of variation of the gear ratio limited by the geometric dimensions and, in the most common applications such as those relative to motorcycles, by high wear and low mechanical efficiency.

Consequently, in recent years devices comprising a toroidal system have been conceived and designed comprising a sun gear defining a first contact area; a crown defining a second contact area; rocker gears apt to roll on said areas so as to transmit the motion between the sun gear and crown; and a regulation apparatus suitable to permit a variation of the inclination of the rocker gears and, thus, their point of contact with the areas so as to change the gear ratio.

An example of these devices is described in the patent application US-A- 2003/0087722. Another type of variable gear ratio device is described in the PCT application WO- A-2002088573A2 in which the rocker gears are spheres having an inclined rotation axis so as to vary the points of contact with the sun gear and the crown and, consequently, the gear ratio of the device.

A further example is described in the patent US-B-6461268 having rocker gears consisting of spheres suitable to roll on the inner areas defined by two pairs of portions of spherical caps. In this case the variation in transmission is achieved by connecting each pair of said portions to a movement mechanism which, by creating a reciprocal translation between the portions, varies the contact points of the sphere on said inner areas, and thus the gear ratio.

The known technique cited above has some significant drawbacks.

A first important drawback is identifiable in that the known devices are characterised by mechanisms which do not allow the gear ratio to be achieved with zero speed of the cam follower.

Another drawback is the extreme constructional complexity of the known devices. This aspect is evident in the cited documents WO-A-2002088573A2 and US-B- 6461268 which illustrate complex mechanisms for the gear variation.

A further drawback is that some known devices are inverting, i.e. characterised by an output motion in an opposite direction to the input motion.

This problem is evident in the case of application of the device to a bicycle where the possible inversion of the motion would impose pedalling in the opposite and unnatural direction and, therefore requires the adoption of further inversion mechanisms of the motion which further complicate these devices.

In this situation the technical purpose of the present invention is to develop a variable gear ratio device able to substantially overcome the drawbacks mentioned above.

Within the sphere of said technical purpose one important aim of the invention is to have a variable gear ratio device, appropriately non-inverting and with a high range of variability of the gear ratio with high mechanical efficiency.

Another important purpose of the invention is to develop a device with a variable gear ratio characterised by greater constructional simplicity and increased reliability.

The technical purpose and specified aims are achieved by a variable gear ratio device as claimed in the appended Claim 1 .

Preferred embodiments are evident from the dependent claims.

The characteristics and advantages of the invention are clearly evident from the following detailed description of a preferred embodiment thereof, with reference to the accompanying drawings, in which:

Fig. 1 shows a cross-section of the variable gear ratio device according to the invention;

Fig. 2 shows a cutaway view of the variable gear ratio device;

Fig. 3 shows an assembly forming part of the variable gear ratio device according to the invention;

Fig. 4 shows the assembly of Fig. 3 in a different configuration;

Fig. 5 shows the assembly of Fig. 3 in another configuration; and

Fig. 6 shows a diagram of the forces on a detail of the variable gear ratio according to the invention.

With reference to said drawings, reference numeral 1 globally denotes the variable gear ratio device according to the invention.

As shown in Fig. 1 , it is suitable to be positioned between a source 1a of motion, for example a combustion engine, an electric motor, the blades of a wind turbine system, the gears of a bicycle, and an output 1 b, for example the wheels of a vehicle, an electrical generator, with the aim of continuously varying the gear ratio through torque control, i.e. varying the gear ratio between the source 1 a and output 1 b as a function of the torque applied to the device 1 by the source and/or by the output b.

The variable gear ratio device 1 comprises a planet gear 10 defining a rotation axis 10a, suitable to continuously vary the gear ratio according to the torque applied to the variable gear ratio device 1 ; and, appropriately, an additional planet gear 20 suitable to functionally position itself between the plant gear 10 and the output 1 b or source 1a amplifying the range of variation of the gear ratio of the variable gear ratio device 1 .

Additionally, the variable gear ratio device 1 may provide for a casing 30 defining a housing chamber for the planet gears 10 and 20; and a central shaft 40 extending substantially along the axis 10a and suitable to support the planet gears 10 and 20 and to protrude from the casing 30 making it possible to connect the device 1 to an external structure.

The planet gear 10 comprises at least one or more rocker gears 11 ; a spider 12 suitable to support the rocker gear 1 and defining at least one spider axis 12a; a sun gear 13 defining an inner contact area 13a for the rocker gear 11 ; and a crown 14 defining an outer contact area 14a for the rocker gear 1 1. Said terms are commonly used for the description of planetary gear systems, in themselves known.

The spider 12, the sun gear 13 and the crown 14 are suitable to rotate around the rotation axis 10a and, consequently, the planet gear 10 is provided with bearings or other similar components, for simplicity illustrated only in Fig. 1 , suitable to position themselves between the central shaft 40 and said elements, allowing a mutual rotation thereof.

The crown 14 is directly connected to the source 1a and constitutes the input of the motion in the planet gear 10 and, in particular, in the device 1.

It comprises an input member 14b of the motion, consisting of a toothed wheel, a pulley or other element suitable to receive the motion from the source 1a, and a main body 14c rigidly coupled to the input member 14b, defining the outer area 14a and, appropriately, suitable to house within it the rocker gears 1 1 , the spider 12 and the sun gear 13.

The contact areas 14a and 13a are tapered in the same direction along the rotation axis 10a so as to have their cross-sections proximal to each other in relation to a normal plane to the axis 10a, of minimum extension, or of maximum extension. In particular, the areas 14a and 13a are monotonically tapered, more particularly, monotonically tapered with sections of maximum extension distal from the input 14b. Preferably, the areas 13a and 14a are substantially conical and, appropriately, have substantially constant first and second angles of inclination, defined below.

The contact areas 13a and 14a define, substantially at the points of simultaneous contact with the rocker gears 1 1 , angles of inclination with respect to the rotation axis 10a different from each other. In other words, in every position they may assume, the rocker gears are in contact with portions of areas 13a and 14a of different mutual inclinations. More in detail the two contact areas 13a and 14a may be conical areas with different inclination or taper angles.

In detail, the first inclination angle, i.e. the angle defined by the straight line tangent to the inner area 13a in the position in question, is less than the second inclination angle, i.e. the angle defined by the straight line tangent to the outer area 14a in said position. In detail, the difference between the second and the first angle of inclination is preferably practically less than 5° and, in more detail, substantially less than 3°. Preferably, said difference is substantially less than 1.5° and, more preferably yet, substantially comprised between 0.2° and 1 °.

Moreover, the first angle of inclination is preferably less than 40°, in particular, between 20° and 5° and, more in particular, substantially comprised between 8° and 15°. The second angle of inclination is preferably less than 40°, in particular, between 22° and 5° and, more in particular, between 8.5° and 15.5°.

Additionally the sun gear 13 comprises, distal from the input member 14b, an additional inner area 13b defining a first angle of inclination practically at least equal to the second angle of inclination of the outer area 14a and/or an additional inner area 13c proximal to the member 14a and defining a first angle of inclination practically less than the first angle of inclination of the inner area 14a.

In particular, the additional inner area 13b defines a first angle of inclination substantially equal to the second angle of inclination of the outer contact area 14a which thus appears as almost parallel to the spider axis 12a.

Positioned between the outer area 14a and inner area 13a, the planet gear 10 has the spiders 12 and, equally angularly spaced along the normal section, the rocker gears 11 . Preferably, the planet gear 10 has three rocker gears 11 having, between them, an angular distance substantially equal to 120°.

The spider 12 comprises one or more shafts 12b each of which is suitable to support a rocker gear 1 1 and to define a spider axis 12a; a first disc 12c proximal to the input 14a and a second disc 12d distal from the source 1a and proximal to the additional planet gear 20.

The spider axis 12a is inclined in relation to the rotation axis 10a, in particular, has, with respect to said rotation axis 10a, an inclination substantially comprised between the first and the second angle of inclination of the areas 13a and 14a. More particularly, the spider axis 12a is almost parallel to one of the contact areas 13a and 14a and, more particularly, substantially parallel to the outer contact area 14a.

The discs 12c and 12d are integral with the shafts 12b and hinged to the shaft 40 allowing the spider 12 to rotate around the rotation axis 10a and the rocker gears 1 1 to perform a revolution around the axis 10a.

The rocker gears 1 1 are detachably connected to the shafts 12b so as to rotate in relation thereto preferably around the spider axis 12a and to translate passively in relation to said shafts 12b along the spider axis12a varying its distance from the rotation axis 10a and the points of contact with the areas 13a and 14a. This variation occurs due to a torque variation at the planet gear 10. In detail, the term "passively" means that the rocker gears 1 1 are suitable to slide along the spider axis 2a exclusively in response to a variation of the torque applied to the device 1 and, therefore, without being moved by pistons, actuators or other active motor elements suitable to control said translation, but nevertheless possibly connected to elastic elements and the like.

In order to passively adjust the position of the rocker gears 11 along the spider axis 12a, the planet gear 10 comprises, associated with each rocker gear 1 1 , a passive balancing element 15 suitable to exert on the rocker gear 1 1 a thrust force parallel to the main spider axis 12a depending on the position of the rocker gear 1 1 along the spider axis 12a. The balancing element 15 comprises a spring interposed between a rocker gear 1 1 and one of the discs 12c and 2d, enveloping the shaft 12b so as to exert said thrust force. Preferably, it comprises a compression spring suitable to functionally connect a rocker gear 1 1 to the second disc 12d.

In addition, the planet gear 10 comprises a torque regulator 16 (Figs. 3-5) suitable to vary, preferably as a function of a translation of the rocker gears 1 1 along the spider axis 12a (as described in detail below), the distance between the contact areas 13a and 14a and, thus, between sun gear 13 and crown 14 ensuring the contact of the rocker gears 1 1 on the contact areas 3a and 14a.

The torque controller 16 is suitable to control, as a function of a variation of the torque applied to the planet gear 10, a mutual translation, along the axis 10a, between the sun gear 13 and the crown 14 and, in detail, a translation of the sun gear 13, while keeping the crown 14 practically axially stationary.

Preferably, it is almost completely housed in a seat made on the sun gear 13.

Appropriately the controller 16 is suitable to define at least one condition of equilibrium in which the contact areas 13a and 14a do not translate reciprocally along the axis 10a; and at least a transitory condition in which the contact areas 13a and 14a reciprocally translate along the rotation axis 10a. In detail, the controller 16 in the condition of equilibrium prevents both contact areas 13a and 14a from moving with respect to the shaft 40 and along the axis 10a and, in the transitory condition, allows at least one of the contact areas 13a and 14a to translate along the rotation axis 10a and with respect to the central shaft 40.

More appropriately in the equilibrium condition, the controller 16 keeps the sun gear 13 stationary in the direction of rotational translation and, therefore, with respect to the central shaft 40 and, in the at least one transitory condition, translates the sun gear only 13 and, therefore, only one area 13a along the rotation axis 10a and with respect to the central shaft 40.

The controller 16, therefore, comprises a first plate 16a integral with the sun gear 13 and suitable to rotate and slide with respect to the central shaft 40 around the axis 10a; a second plate 16b integral with the centra! shaft 40 and suitable to engage the first plate 16a transforming a relative rotation between the plates 16a and 16b into a mutual translation of said plates 16a and 16b; and, in some cases, a crankcase 16c suitable to substantially enclose within it the plates 16a and 16b. Appropriately, the crankcase 16c is positioned between the plates 16a and 16b and the sun gear 13 and, in particular, is integrally connected to both the first plate 16a and the sun gear 13 and idly to the second plate 16b and to the shaft 40 so as to slide and translate in relation thereto.

The plates 16a and 16b thus have contact faces 16d reciprocally counter-shaped so as to engage with each other and, through their relative rotation, appropriately around the axis 10a, to transform a torque acting on the first plate 16a into a translation force along the rotation axis 10a acting on said first plate 16a and thus on the sun gear 13 (Figs. 3 and 4) and suitable to translate the sun gear 13 with respect to the crown 4.

It may be seen how in the equilibrium condition the plates 16a and 16b are mutually integral preventing a reciprocal translation of the contact areas 13a and 14a along the rotation axis 10a and, in the transitory condition, the plates 16a and 16b mutually rotate by imposing on the contact areas 13a and 14a a mutual translation along the rotation axis 10a.

Said contact faces 16d thus have a helical profile, appropriately continuous, suitable to define a coefficient of correlation between axial force, i.e. parallel to the axis 10a and exercised by the controller 16 on the sun gear 13, and torque acting on the sun gear 13 and, thus, on the first plate 16a substantially less than 1000 N / Nm and, appropriately, substantially between 100-400 N / Nm. In detail, the helical profile of the faces 16d defines a pitch, calculated as the ratio between the correlation coefficient and 2π, along the axis 10a practically equal to 17 mm.

In order to reduce the friction between the plates 16a and 16b, by imposing a speed of reciprocal sliding between said plates, the torque controller 16 may present the plates 16a and 16b mutually offset with respect to the rotation axis 10a so as to reduce the friction between the contact faces 16d. In particular, the misalignment between the plates 16a and 16b is substantially less than 2 mm.

Alternatively or in addition, the controller 16 comprises a friction reducer, preferably comprising a plurality of metal sheets substantially counter-shaped to the contact faces 16d, interposed between the plates 16a and 16b so as to reduce friction between the faces 6d.

Lastly, the planet gear 10 may provide for an additional torque controller 17 suitable to allow the operator to command a mutual translation between the sun gear 13 and crown 14 along the rotation axis 10a and, therefore, to vary, appropriately at the operator's command, the gear ratio, as described in detail below; and an external command 18 suitable to allow the operator to control the additional controller 17.

The additional controller 17, illustrated in Figs. 3-5, includes an additional first plate 17a and additional second plate 17b suitable to engage each other so as to transform the relative rotation between them in a movement along the axis 10a between said plates; an elastic body 17c, preferably a cup or compression spring wound around the shaft 40, interposed between the additional second plate 17b and the sun gear 13 and, in particular, the crankcase 16c so as to transform the axial translation between the additional plates 17a and 17b into a force parallel to the axis 10a on the sun gear 13.

The first additional plate 17a is integral with the shaft 40, while the second additional plate 17b is idle with respect to the shaft 40 so as to rotate and translate with respect to the first additional plate 17a.

In order to transform the relative rotation between the additional plates 17a and 17b a reciprocal translation thereof and, in particular, a rotation of the second additional plate 17b with respect to the first plate 17a into a translation of said second additional plate 17b with respect to the first plate 17a (Figs. 3 and 5). The additional plates 17a and 17b have mutual contact areas 17d having a saw tooth or, alternatively, helical extension similar to that of the contact faces 16d of the plates 16a and 16b.

Additionally, the additional torque controller 17 comprises a thrust bearing 17e or other similar element suitable to allow a rotation of the crankcase 16c and, in particular, of the sun gear 13 with respect to the elastic body 17c; and, in some cases, an abutment 17f idle in relation to the shaft 40, axially movable in relation to the additional second plate 17b and positioned between the bearing 17e and elastic body 17c thus defining a thrust surface for the body 17c and thus preventing the elastic body 17c from interfering with the thrust bearing 17e.

The external command 18 is suitable to enable the operator to control a relative rotation between the additional plates 17a and 17b and, in particular, a rotation of the second additional plate 17b in relation to the first additional plate 17a.

As shown in Fig. 1 , it comprises an arm 18a integral with one of the additional plates 17a and 17b and, in particular, the second plate 17b; and a tie-rod 18b having one end integral with the arm 18a so that the operator is able to control the rotation of the arm 18a and, thus, of the plate 17b by means of the tie-rod 18b. In particular, the arm 18a has a support surface/channel 18c arched with respect to the axis 10a to which one end of the tie rod 18b is connected and along which the tie rod 18b, at least partially lies, so that it slides on the surface 18c thereof when actuated by the operator. Preferably, the support surface 18c is circular and, more preferably, identifiable in a sector of a cylinder axis substantially coinciding with the rotation axis 10a.

Additionally, the external command 18 may provide for a compression spring, preferably alternatively to the spring 17c, suitable to transform the translation of the tie-rod 18b into a force acting on the arm 18a and/or a torsion spring interposed between the arm 18a and the second plate 17b so as to transform the translation of the tie-rod 18b and, thus, the rotation of the arm 18a into a torque acting on the second additional plate 17b.

Functionally connected to the planet gear 10, the variable gear ratio device 1 has an additional planet gear 20, preferably with a fixed gear ratio, suitable to receive the motion from the planet gear 10 and to transmit it to the output 1 b.

The additional planet gear 20, as shown in Figs. 1 and 2, has an axis substantially coinciding with the rotation axis 10a and comprises one or more additional rocker gears 21 , an additional spider 22 suitable to support the additional rocker gears 21 and defining, for each additional rocker gear 21 , an additional rotation axis 22a, preferably substantially parallel to the rotation axis 10a; an additional sun gear 23 suitable to be rigidly connected to the output 1 b, and an additional crown 24.

In detail, the additional sun gear 23 is integral with the casing 30, which, in turn, is integral with the output 1 b thus allowing a passage of motion from the additional sun gear 23 to the output 1 b.

In order to have a motion in output and in input in the device 1 concurring with each other, the additional planet gear 20 has the additional crown 24 integral with the crown 14 at the section of maximum extension and the additional spider 22 integral with the spider 12 at the second disc 12d.

The additional spider 22, the additional sun gear 23 and the additional crown 24 are suitable to rotate around an axis approximately parallel and, preferably, substantially coinciding with the rotation axis 10a.

The additional spider 22 comprises additional shafts 22b each of which is suitable to support an additional rocker gear 21 and defining, for said rocker gear 21 , an additional axis 22a; additional bearings or other similar means interposed in the way of additional rocker gears 21 rotating exclusively in relation to the additional shafts 22b; and a ring integral with the shafts 22b and the second additional disc 12d. Alternatively, the shafts 22b are directly integrally connected to the second disc 12d.

Lastly, the additional rocker gears 21 are identifiable in gear wheels, and the additional sun gear 23 and the additional crown 24 have teeth, respectively inner and outer, engaging the additional rocker gears 21.

The functioning of a variable gear ratio device, described above in a structural sense, is as follows.

When the torques and speeds applied to the variable gear ratio device 1 and, therefore, to the planet gear 0 by the source 1a and output 1b are substantially constant, the variable gear ratio device 1 and the planet gear 0 are in a condition of equilibrium.

In this condition, the crowns 14 and 24 moved by the torque transmitted from the source 1 a to the input 14b, revolve integrally around the rotation axis 10a. This rotation, due to the pure contact between the outer contact area 14a and the rocker gears 1 1 , imposes on the rocker gears 1 1 a rotation around the main axis of the spider 12a and, accordingly, both a motion of revolution of the rocker gears 1 1 and a rotation of the spider 12 around the rotation axis 10a.

The rocker gears 11 , being in contact, suitably in pure contact, with the inner area 13a, transmit to the sun gear 13 and to the first plate 16a a torque which, thanks to the friction between the faces 16d, is countered by the torque controller 16 which leaves the sun gear 13 stationary in a rotational and translational direction.

It may also be noted, that in the equilibrium condition the rocker gears 11 do not translate along the spider axis 12a thanks to the return elements 15 which exert on the rocker gears 1 1 a thrust force cancelling out the resultant of the normal reactions of the areas 13a and 14a on the rocker gears 1 1 (Fig. 6).

In detail, the normal reaction Ri of the inner contact, area 3a, on account of the different inclination of the inner area 13a with respect to the outer area 14a and to the spider axis 12a, comprises a first component Ri_n, substantially perpendicular to the spider axis 12a and, thus, to the outer area 14a, annulled by the normal reaction R₂ the outer contact area 14a and a second component Ri_a, substantially parallel to the spider axis 12a, annulled by the thrust force F_s of the return element 15 on the rocker gear 1 1.

The motion, the two crowns 14 and 24 and the two spiders 12 and 22 being integral, passes from the planet gear 10 to the additional planet gear 20 without reversing its direction.

In fact, on account of such integral constraints the additional crown 24 and the additional spider 22 rotate around the rotation axis 10a by imposing a motion of revolution of the additional rocker gears 21 . This revolution motion makes the additional rocker gears 21 rotate around the additional axis 22a causing the rotation around the axis 10a of the additional sun gear 23 which thus transmits the motion to the output 1 b.

When, due to a variation of the torque applied by the source 1 a and/or by the output b to the device 1 , the device 1 and, specifically, the planet gear 10 continuously vary the gear ratio, a transitory condition occurs until a new equilibrium condition is reached in which the source 1 a has substantially the same speed and the same torque as before the torque change.

For example, suppose an increased torque at the output 1 b.

In this case, the increase of the output torque b determines a proportional torque variation in the planet gears 10 and 20 and, in particular, an increase in torque in the sun gear 13, in the crown 14 thus causing a state of imbalance in the forces acting on the rocker gears 1 1 .

In fact, the torque variation in the sun gear 13 is transmitted to the first plate 16a which is thus subject to a torque no longer balanced by the axial force acting between the contact faces 16d. Consequently, the first plate 16a rotates in relation to the second plate 16b (shown in Figs. 3 and 4) and, thanks to the helical profile of the faces 16d, undergoes a shift along the axis 10a generating, along the rotation axis 10a, an axial force that tends to approximate the sun gear 13 to the crown 14.

The action of the axial force on the sun gear 13 causes an increase of the normal reaction F^ of the inner contact area 13a on the rocker gears 1 1 and, specifically, an increase of the second component Ri_a which thus becomes greater than the thrust force F_s of the return element 15 generating said state of imbalance in the forces acting on the rocker gears 1 1.

By virtue of the imbalance, the rocker gears 11 slide along the arms 12b toward the second disc 12d determining, as the rocker gears 1 1 gradually advance, a decrease of the gear ratio of the device 1 and, consequently, an increase of the torque expressed, through the variable gear ratio device 1 , from the source 1 a until said torque expressed substantially equals the new torque applied by the output 1 b and the thrust force F_s increases to match the second component Ri_a to the normal reaction Ri of the inner area 13a.

Simultaneously to the sliding of the rocker gears 1 1 along the arms 12b, the rotation of the first plate 16a with respect to the second plate 16b, thanks to said helical profiles, controls the advancement of the sun gear 13 along the rotation axis 10a and, thus, a variation of the distance between the contact areas 13a and 14a thus ensuring the contact of the rocker gears 1 1 on both areas 13a and 14a during the sliding of the rocker gears 11 on the arms 12b.

The progress of the sun gear 13 allows the first plate 16a to perform a roto- translation away from the second plate 16b.

In conclusion, at the end of the transitory phase, the device 1 reaches a new equilibrium condition in which the rocker gears 1 1 are shifted along the axis 12a determining a new torque on the sun gear 13 which, in turn, is translated along the axis 10a allowing the torque controller 16 to vary the torque transmitted to the sun gear 13 by balancing the new torque transmitted by the rocker gears 1 to the sun gear 13 which thus, remains stationary once this state is achieved.

In this condition, the variable gear ratio device 1 presents, at the source 1a, a torque and a speed substantially equal to those before the torque variation and, at the output 1 b, a new torque and, in particular, a new speed which, in the above example, is reduced.

The invention achieves some important advantages.

A first important advantage of the variable gear ratio device 1 is identifiable in the fact that, thanks to the innovative planet gear, it has a variable gear ratio over a wide range.

This aspect is further increased by the presence of the additional planet gear 20 which makes it possible to obtain a variable gear ratio between 0.14 and 0.52. In particular, the particular configuration of the device 1 makes it possible to have a maximum gear ratio equal to 4 times the minimum.

Another advantage is that, thanks to the particular connection between the planet gears 10 and 20, the variable gear ratio device 1 , for example in the configuration described above, is non-inverting, and therefore, does not require additional mechanisms to make the motion of the source 1 a and output 1 b concur.

One advantage is given by the presence of the additional inner area 13b which prevents the sun gear 13 and, thus the first plate 16a from having a shift with respect to the second plate 16b greater than the pitch of the helical profile of the contact faces 16d and, thus, not manageable by the torque controller 16.

In fact, an excessive increase of the reaction of the inner area 13a causes a translation of the rocker gears 1 1 causing them to slide on the additional area 13b. In this position, the additional area 13b, being almost parallel to the outer area 14a and to the axis 12a, determines on the rocker gears 1 1 a normal reaction devoid of the second component, not capable of commanding a further translation of the rocker gears 1 1 and thus defining a point of maximum distance between the plates 16a and 16b smaller than the pitch of the faces 16d.

Another important advantage derives from the fact that, through an appropriate sizing / geometry of the components of the planet gears 10 and 20, it is possible to have positive transmission ratios and, thus, a non-inverting device 1 , as described above, and/or negative gear ratios and, therefore, an inverting variable gear ratio device 1 .

In fact, denoting by R the rays and ω the rotation speeds of the various components of the two planet gears, and placing, as a subscript, the identification number of the component, the following equation may be set for the planet gear

10:

Eq_x: #₁₃ω₁₃ + Λι₄ω₁₄ = (fl₁₃ + #₁₄)ω₁₂

and for the additional planet gear 20:

Eq₂: #₂₃ω₂₃ + #₂4^ω2₄— (#23 + #₂₄)^ω22

From how the device 1 is constituted one has ω₀ since the crowns 14 and 24 are integral with each other; ω_ρ since the spiders 12 and 22 are integral with each other; and ω ₃ = 0 since, in a condition of equilibrium the torque controller 16 keeps the sun gear 13 at least rotationally stationary.

Solving the system Eq and Eq 2, the gear ratio, i.e. the ratio between the output speed defined by the additional sun gear 23 and the input speed defined by the crowns 14 and 24 (ω₀), is:

According to Eq3 the gear ratio is greater than 0 and, thus, the device 1 non- inverting if the radii of the sun gear 13 and the crown 14, defined by the contact points defined between rocker gears 1 1 and sun gear 13 and between rocker gears 1 1 and crown 14 during the sliding of the rocker gears 1 1 along the axis 2a, always meet the condition: «23 + « 24

Eq₄ :

«13 + « 14

and inverting if they always meet the condition:

«23 + « 24 R 24

Eq₅ - <

«13 + « 14 R 14

It should be noted that the range of variation of the gear ratio of the device 1 is defined as the gear ratios calculated when the rocker gears 1 1 are located at the ends of the contact areas 13a and 14a and, to be precise, of the inner area 13a. Another advantage that emerges from the analysis of Eq₃ is to be identified in the fact that through an appropriate sizing of the planet gears 10 and 20 and of the inclination of the surfaces 13a and 14a it is possible to vary the range of variation of the gear ratio of the device 1 and, in some cases, to have both a non-inverting and inverting device 1.

It is to be emphasised how a possible zero gear ratio condition is not an issue when changing the direction of rotation of the sun gear 23.

In fact, such a condition occurring in only one point, the rocker gear 1 would pass this condition by virtue of the speed of translation along the axis 12a acquired at the beginning of the transitory condition.

An important advantage is the fact that, by varying the geometry of the contact areas 13a and 14a, keeping them always tapered monotonically and in the same direction, it is possible to vary the variation curve of the gear ratio as a function of the torque and, therefore, to adapt it to the particular conditions of application of the variable gear ratio device 1.

One advantage is given by the values of the angles of inclination of the contact areas 13a and 14a which make it possible to optimally regulate the forces acting on the torque regulator 16 and on the rocker gears 11.

In particular, such reduction of the axial loads, i.e. parallel to the axis 10a, on the components of the variable gear ratio device 1 is ensured by a difference between the second and first angle of inclination of less than 3° and, in an even greater measure, basically equal to 1.5°.

An important advantage is given by having the axis of the spider 12a parallel to the outer contact area 14a which makes it possible to change the gear ratio via a translation of the sun gear only and thus achieve the above pairing between the planet gears 0 and 20.

Another advantage given by this aspect is thus identified in the fact that the controller, having to act solely on the sun gear 13 can be housed therein thus limiting the dimensions of the device 1.

An additional benefit is given by the additional torque controller 17 which allows the operator to adjust the operation of the variable gear ratio device 1.

In fact, the operator, commanding the command rotation element 18a and, thus, the second additional plate 17b, determines an axial shift of said additional second plate 17b which compressing the elastic body 17c, imposes on the sun gear 13 a force substantially parallel to the axis 10a which increases or decreases the normal reaction of the inner area 13a thus influencing the gear ratio of the device 1.

Another advantage of no less importance of the device 1 is its simple construction compared to known devices.

The invention is susceptible to variation within the inventive concept. All the elements as described and claimed herein may be replaced with equivalent elements and the scope of the invention includes all other details, materials, shapes and dimensions.

Claims

1. Variable gear ratio device (1) comprising a planet gear (10) defining a rotation axis (10a), suitable to continuously vary the gear ratio and comprising at least one rocker gear (1 1 ); a spider (12) defining at least one spider axis (12a) and suitable for supporting said at least one rocker gear (1 1 ); a sun gear (13) defining an inner contact area (13a) for said at least one rocker gear (11 ); a crown (14) defining an outer contact area (14a) for said at least one rocker gear (11 ); said variable gear ratio device (1 ) being characterised in that said contact areas (13a, 14a) are tapered in the same direction along said rotation axis (10a); and in that said inner contact area (13a) and outer contact area (14a) respectively define, substantially in correspondence with simultaneous contact points with said at least one rocker gear (1 1 ) and in relation to said rotation axis (10a), a first angle of inclination and a second angle of inclination different from said first angle of inclination; and in that said spider axis (12a) is inclined in relation to said rotation axis (10a) and in that on account of said torque variation, said at least one rocker gear (1 1) is apt to passively translate in relation to said spider (12) along said spider axis (12a) varying its distance from said rotation axis ( 0a) and said contact points with said contact area (13a, 14a) and thus, the gear ratio of said variable gear ratio device (1 ); and characterised in that it comprises a torque regulator (16) suitable to command a reciprocal translation of said contact areas (13a, 14a) depending on a torque variation of said at least one rocker gear (11 ) along said spider axis (12a).

2. Variable gear ratio device (1 ) according to claim 1 , wherein said contact areas (13a, 14a) are monotonically tapered.

3. Variable gear ratio device (1) according to one or more of the previous claims, wherein said second angle of inclination is substantially greater than said first angle of inclination.

4. Variable gear ratio device (1 ) according to the previous claim, wherein the difference between said second angle of inclination and said first angle of inclination, is substantially less than 3°.

5. Variable gear ratio device (1) according to one or more of the previous claims, wherein said spider axis (12a) presents, in relation to said rotation axis (10a), an inclination substantially comprised between a first and second angle of inclination.

6. Variable gear ratio device (1) according to one or more of the previous claims, wherein said planet gear (10) comprises, associated to said at least one rocker gear (1 1 ), an equilibrating element (15) suitable to exercise on said at least one rocker gear (11 ) a thrust force substantially parallel to said spider axis (12a) depending on the position of said rocker gear (1 1 ) along said spider axis (12a).

7. Variable gear ratio device (1) according to the previous claim, wherein said equilibrating element (15) comprises a spring.

8. Variable gear ratio device (1 ) according to one or more of the previous claims, comprising a supplementary planet gear functionally connected to said planet gear (10); in which said supplementary planet gear (20) comprises at least one supplementary rocker gear (21), a supplementary spider (22) suitable to support said at least one supplementary rocker gear (21) and defining, for said at least one supplementary rocker gear (21 ), a supplementary rotation axis (22a), a supplementary sun gear (23), and a supplementary crown (24).

9. Variable gear ratio device (1) according to the previous claim, in which said supplementary crown (24) is integral with said crown (14); and in which said supplementary spider (22) is integral with said spider (12).

10. Variable gear ratio device (1) according to one or more of the claims 8-9, wherein said supplementary rotation axis (22a) is substantially parallel to said rotation axis ( 0a).