TECHNICAL FIELD This invention relates to a mechanical speed variator with friction generated by a barrel-shaped body interposed between rotating surfaces with slightly inclined axes.

BACKGROUND ART Stepless speed variators are known to exist based on the radial movement of idle cylindrical rollers along offset rotating plates parallel to them. To overcome the intrinsic limits of these known variator, a solution has been previously proposed in a patent of the same inventor involving a ball operating on two slightly oblique rotating plates such as to achieve self- wedging of the idle ball interposed between them. This solution has proved unsatisfactory, for a multiplicity of serious technical problems connected with its industrial production. In particular, the ratio variation movement was unable to take place along the theoretical generator of the two rotating plates. This was because of structural elastic yielding deriving from the considerable axial operating stresses generated by the small angle of inclination between the rotating plates which was necessary to achieve self-wedging of the ball. In this respect, as a result of this, force components were generated which urged the ball to also roll in a centrifugal or centripetal sense, so varying the transmission ratio in an undesired manner. This meant that the ball had to be constrained radially,

with rubbing friction being created on it, hence seriously compromising the life and efficiency of the variator. The actual contact between the ball and the inclined plates was insufficiently wide, so that unacceptable wear occurred. In this variator of the known art, the self-wedging forces alone were insufficient if using very hard contact surfaces. In the said known solution there was also the drawback of irreversibility : transmission was in fact enabled in only one direction of rotation, so that in the opposite direction lifting occurred which disengaged the ball. An object of the present invention is to define a mechanical speed variator by means of oblique offset rotating plates, having an interposed idle rolling body which is not subjected to rolling in the radial direction of said plates, even in the case of regulator sliding movements taking place along non-diametrical trajectories. Another object is to define a mechanical variator, as aforestated, having an interposed idle rolling body offering a contact surface area with the plates which is greater than that of a ball, but without requiring the rotating plates to move further apart. Another object is to define a mechanical variator, as aforestated, having a pre-loadable rolling body within the channel defined by the obliqueness of the two rotating plates, to determine and/or increase the required self-wedging effect providing the friction necessary for transmitting movement from the driving plate to the driven plate. Another object is to define a mechanical variator, as aforestated, having a rolling body of minimum mass in order to reduce both the weight and the inertia connected with the variations in the transmission ratio. Another object is to define a mechanical variator, as aforestated, having a rolling body of shape suitable to create a further self-

wedging effect resulting from any stresses tending to displace it in the plate radial direction. Another object is to define a mechanical variator, as aforestated, able to at least partially operate in both directions of rotation.

Another object is to define a mechanical variator, as aforestated, using a rolling body of high resistance to crushing.

DISCLOSURE OF THE INVENTION These and further objects will be seen to have been attained on reading the ensuing detailed description of a mechanical speed variator having the characteristic of consisting of an idle barrel-shaped rolling body interposed between two flat surfaces, specifically a driving and a driven surface, rotating with their axes slightly inclined and lying in two parallel geometrical planes, the idle barrel-shaped rolling body resting on these surfaces and able to slide on command along two of their parallel directrices in order to connect together, by self-wedging friction created by said inclination, those peripheries of said rotating flat surfaces which correspond to transmission ratios determined by the ratio of the peripheral speeds of those points of the two surfaces brought into contact with the idle barrel-shaped rolling body.

BRIEF DESCRIPTION OF DRAWINGS The invention is indicated by way of non-limiting example in the accompanying drawings, in which: Figures 1 and 2 are two perpendicular views of its constituent conceptual parts; Figure 3 shows the operating principle of the idle barrel-shaped body;

Figure 4 is a conceptual view of a mechanical structure for the support, rolling and translation of the barrel-shaped body; Figure 5 shows a constructive example of a variator comprising control means for the barrel-shaped body; Figure 6 is a view perpendicular to that of Figure 5, showing a constructive example with its input and output motion axes mutually parallel ; Figure 7 is a view perpendicular to those of Figures 5 and 6, showing a constructive example of a variator with its input and output motion axes mutually perpendicular.

BEST MODE FOR CARRYING OUT THE INVENTION With reference to the aforesaid Figures 1 and 2, a first flat output or driven plate 1 rotates in the direction indicated by the arrow 2 about an axis 3; a second flat input or driving plate 4 has a slightly oblique axis 5 lying in a plane parallel to that containing the axis 3; in Figure 1 these planes coincide with the axes 3 and 5, being perpendicular to the sheet of the drawing. This obliqueness means that the flat surfaces 1A and 4A of the rotating plates 1 and 4 slightly converge; between the surfaces 1A and 4A a very small angle a therefore exists. In Figure 2 this angle is shown exaggeratedly large (60°) to enable the parts to be better seen; however in reality the angle a is of just a few degrees, for example 5°. The true value of this angle a depends on the nature of the materials used to construct the mutually engaged parts, on which the coefficient of friction developed along the flat surfaces 1A and 4A depends. The exact value of the angle a is therefore established experimentally, depending on the results to be obtained: the higher the coefficient of friction of the materials engaged in

transmitting motion, the larger the angle a. To better conceptually understand the fundamental role played by the angle a it should be noted that, for equal types of surfaces engaged in transmitting motion, it creates a degree of friction which is greater the smaller this angle. This capacity for friction derives from a"wedging effect"created by axial components (referred to axes of rotation 3,5 of the plates) ; however the larger these axial components, the more they subject the engaged parts to wear.

Between said surfaces 1A and 4A the is interposed a rolling body 6 with barrel-shaped surfaces. It is maintained in contact with the surfaces 1A and 4A by forces obtainable in various ways : for example, by its own weight and/or by suitable reloaded springs acting on its support rod. The rolling body 6, being idle, has no conceptual limits on its diameter; it could therefore also be larger than the two surfaces 1A and 4A with which it cooperates, in order to create a very large actual contact zone (although being theoretically punctiform). Depending on the application for which the variator is intended, the rolling body 6 can be constructed of any material : steel, glass, ceramic, rubber, sintered materials, or materials of high friction type used for vehicle brakes and clutches. In this respect it should be noted that the variator operates by friction and that therefore its constructional materials can be any able to provide maximum friction, compatible with the other mechanical and technological requirements for its operation. This evidently also applies to the surfaces 1A an 4A cooperating with the barrel-shaped rolling body 6. As the axes 3 and 5 lie in parallel planes, the surfaces 1A and 4A of the plates 1 and 4 form a type of channel within which a hypothetical ball could roll along parallel

contact generators Z1 and Z2 (Figure 1). From the aforestated it will be apparent that when the plate 4 rotates in a direction 8, the barrel-shaped rolling body 6, the contact surface 19 of which rests on it with a certain eccentricity (shown in Figure 1 by a very small bracket), receives a movement 7 by friction ; although being circular, this movement is indicated in Figure 1 by a straight arrow, as it is imagined positioned above the barrel-shaped body 6. In its turn, said barrel-shaped rolling body 6 transfers its motion to the driven plate 1, causing it to rotate by friction in the direction U (Figure 2). This friction is proportional to the torsional resistance, or reaction, offered by the driven plate 1. An input torque 9 provides a force 10 (shown by dashed lines as it refers to the non-visible rear side of the edge of the plate, Figure 2) which is inversely proportional to the radius of the plate circumference along which the barrel-shaped body 6 rotates. This generic force 10 is transmitted to the barrel-shaped rolling body 6, and is indicated thereon by 11 or 11'. To understand the correctness of the directions illustrated by the arrows, it should be noted that a front part 4B (Figure 1) of the plate 4 is engaged with a part 1 B of the other plate 1 which is to the rear (relative to the"cascade"passage of motion from the axis 5 to the axis 3). On this basis, the force 10 drags the barrel-shaped body 6 towards the bottom 12 (Figure 2) of the oblique- sided channel (formed by the obliqueness between the two converging surfaces 1A and 4A) to an extent which is greater the more the barrel- shaped body 6 opposes the rotation imposed on it by the force 10. The wedging or inserting thrust exerted by the drive plate 4 on the barrel- shaped body 6 hence increases the more the driven first plate 1 hinders

the rotation of this body, because this increases its contact forces and hence the transmission friction generated by them. If the peripheral speed of the point of contact on the plate 1 should exceed the peripheral speed of the barrel-shaped body 6, this body would undergo thrusts tending to lift it from its"channel", provided to enable it to slidingly vary the transmission ratio. Proportionally, this would prevent it from transmitting the movement or torque received. The method for achieving any transmission ratio between a drive shaft 4A and a driven shaft 1 D is apparent from Figure 1; in this figure it can be seen that the barrel-shaped body 6 rests or presses on the two surfaces 4A and 1A of the plates at two contact points 14 and 15. The contact point 14 has the said eccentricity 16 to the rotation axis 5 of the plate 4; this eccentricity constitutes the radius, or arm, by which a torque 9'is defined, as it is from this radius which the peripheral speed of the point of contact 14 derives. This peripheral speed is transmitted by friction (frictional contact) to the barrel-shaped body 6, which rotates about an axis 17; this axis is perpendicular to the geometrical planes containing the axes 3 and 5, about which the driven plate 1 and the drive plate 4 rotate respectively. The contact point 14 pertains both to the rotating plate 4 and to the barrel-shaped body 6, so that the body 6 acquires the peripheral speed 7 generated by the eccentricity 16. This peripheral speed about the axis 17 is also common to the contact point 15, which the barrel-shaped body 6 assumes on the driven plate 1; it follows from this that said peripheral speed 7 becomes common also to the point 15 of the plate 1 rotating about the axis 3 with an eccentricity 18. As this eccentricity 18 (indicated by brackets) is greater than the eccentricity 16,

said peripheral speed imposed by the barrel-shaped body 6 at the point 15 of the plate 1, creates an angular velocity of said plate 1 which is less than that with which the drive plate 4 rotates. If the barrel-shaped body 6 were to assume a position in a zone closer to the axis 3 and further from the axis 5, there would be a proportional increase in the angular velocity of the driven plate 1. From the aforegoing it is therefore apparent that the barrel- shaped body 6 merely has to be shifted in the direction of the axis 17 to change, even by an infinitesimal amount, the transmission ratio between an input (or drive) shaft 4D and an output (or driven or user) shaft 1 D.

The operation of the barrel-shaped body 6 will be clarified with reference to Figure 3. This body is interposed between the plate 1 and the plate 4, which are mutually offset by means of parallel planes containing the axes 3 and 5, so that it rests on these at a point on their diametrical generators Z1 and Z2; assuming that Figure 3 is a view from above, these generators are horizontal. In this manner, the contact occurs on a diameter 6D of the barrel-shaped body 6, which also represents the distance between the operative surfaces 1A and 4A of the plates 1 and 4, i. e. the distance between the said parallel diametrical generators Z1 and Z2. Based on the already stated principles and observing Figure 3 it can be seen that, if the plate 4 rotates in a direction 90 (creating a direction 20 on the other plate) the barrel-shaped body 6 varies its wedging position between the two oblique flat surfaces of the two plates by the effect of the resistance variations offered by the rotating plate 1. The barrel-shaped body 6 is hence caused to effect the contact along other generators Z3, Z4, which are no longer diametrical; in the drawing, the distance of these generators

from the theoretical diametrical generator Z1 has been exaggerated for greater clarity. The result is that the barrel-shaped body 6 no longer rotates with a peripheral speed orientated perpendicularly as expressed by the arrow 6F, but tends to rotate in a direction 6H, created by centripetal or centrifugal components, with respect to the axes 3 and 5. Hence the barrel-shaped body 6 no longer rotates about an axis K parallel to Z1 and Z2, but about an oblique axis consequent on rotatory tendencies about an axis passing through a centre R. If a profile S of the barrel-shaped body 6 were concentric about R (i. e. if it were spherical), this obliqueness of 6H would cause the ball to roll in the centripetal or centrifugal direction of the two rotating plates 1 and 4, so changing the transmission ratio. The profile S has however a much greater radius of curvature M (the typical profile of barrels) and this prevents the barrel-shaped body 6 from rolling about its centre R. This rolling is also prevented if the barrel-shaped body 6 has its points of contact on non-diametrical generators, such as the said generators Z3 and Z4. Any rotation about its centre R would cause it to engage the flat surfaces 1A and 4A of the plates 1 and 4 at points which are not those at minimum distance apart equal to its maximum diameter 6D, but such as would result from any diagonal 6E which passes through the barrel shape. The greater length of 6E, compared with the maximum diameter 6D of the barrel shape, creates a thrust tending to cause the two plates 1 and 4 to move axially apart; however as these plates are fixed, they provide an opposing axial reaction, which results in an increase in the useful friction on the interposed barrel-shaped rolling body 6. Hence, as a result of the wedging by the effect of the reaction offered by the driven

plate 1, further wedging is generated due to the tendency of the barrel- shaped body 6 to rotate transversely about an axis passing through the centre R (in Figure 3 this axis is perpendicular to the sheet of the drawing).

Comparing Figure 1 with the analogous Figure 3, it can be seen that the directions of rotation, indicated respectively by the arrows 9,2 and 90,20, are opposite, showing that they depend on the"cascade"direction involved in motion transmission, and which must always cause wedging of the barrel-shaped body 6 between the two plates 1 and 4. A constructional example of the said barrel-shaped body 6 is shown in Figure 4, in which the two plates 1 and 4 are shown in diametrical section (as in Figure 6) and therefore appear as though their flat surfaces 1A and 4A are parallel, whereas in effect they are oblique (see Figures 1 and 2).

From this figure it can be seen that it consists of a positionable bearing 19 with a double ring of balls. This rolling body 6 differs from the normal positionable bearings in that its outer surface S is barrel-shaped, i. e. with the radius M1 greater than the radius 6d, although their centres are positioned in the same central plane 6D'. This"bearing version"of the barrel-shaped body 6 offers the advantage of being able to be shifted to achieve a transmission ratio variation by using rolling means: in this respect it is sufficient to axially shift a rod T which is torsionally unstressed (i. e. which does not rotate about its axis). This version also offers the great advantage of being able to freely preload the barrel-shaped body 6 by urging it into the"channel"present between the oblique surfaces 1A and 4A of the two plates 1 and 4 with any force P (Figure 2). This preload can be easily provided by usual methods, such as those shown in Figure

5. In that figure, a containing box 37 for the constituent members of the variator is formed from walls 38A, 38B, 38C. Two remaining walls 38E, 38F are shown in Figure 6 for a better understanding of the parallelepiped structure of said box 37 and the relative position of the various internal members. These walls are shown for purely conceptual reasons, as their construction and connection can correspond to a plurality of known designs. It should however be noted that the considerable thicknesses of these indicate the need for minimum deformation, so that the barrel- shaped rolling body can slide along a generator which coincides as far as possible with Z1 (Figure 3).

From Figure 5 it can be seen that the barrel-shaped rolling body 6 is supported by an operating rod 24 and is axially fixed to it. In this manner, by axially shifting the rod 24 in the direction 39A or 39B (Figure 4) the transmission ratio of the variator is changed. These shifts must be gradual to avoid sliding caused by inertia, especially during acceleration. During deceleration the rolling body tends to disengage spontaneously, so that maintaining it in an engaged condition on the two plates 1 and 4 depends on the preload with which it is operated. The said gradual shifting can be obtained by a screw control which, because of its irreversibility, enables the rolling body 6 to be maintained in the position for the required transmission ratio. Said control is achieved by providing the operating rod with parallel flat surfaces 23, indicated by 23A and 23B, which slide along matching flat faces 40A, 40B formed in a hole in the wall 38B. The operating rod 24 carries at one end a screw 22 engaged in a nut screw 21; said nut screw rotates on a bearing 41 to which it is axially constrained.

The bearing 41 is housed in a parallelepiped plate 42 slidable within its seat 43. On the top of this plate there acts the thrust of a spring 44 reloaded by a screw 45 engaged in an auxiliary wall 46 of the containing box 37. At its other end 47, the operating rod 24 is provided with further flat surfaces 48 analogous to the surfaces 23; however these flat surfaces do not slide through a fixed wall, but through a second parallelepiped plate 49 slidable between two parallel walls 50. On the top of this second plate 49 there acts a spring 51 reloaded by a screw 52 engaged in an auxiliary wall 53. This second plate 49 slides between two parallel walls 54 and 55 provided with holes 56 and 57 arranged to allow small vertical excursions (viewing Figure 5). The position of the two plates 42 and 49 is established by the resting of the barrel-shaped rolling body 6 on the generators Z1 present on the two plates 1 and 4. In Figure 5 it can be seen that the lower region of the plate 1 is drawn with a double line to represent an edge visible by virtue of the inclination of the plate ; the other plate 4 is shown as a thin line because it lies upstream of the sectional view and is therefore not visible. In Figures 5 and 7 the rolling body 6 is positioned in an "inactive"condition ; in this respect, it can be seen that its centre line 6D coincides with the axis 5 and therefore receives zero peripheral speed from the plate 4. To prevent unnecessary contact being maintained in this inactive position between the rotating plate 4 and the non-rolling body 6, the operating rod 24 is provided with an inclined piece 58 which, by engaging against an abutment 59 present on the wall 38D, is caused to rise within the hole by overcoming the opposing action of the spring 51 (mainly) and of the spring 44 (marginally). In this manner, the rolling body

6 is non longer in contact with the two plates 1 and 4; contact is automatically restored as soon as the rod 24 is shifted in the direction 39A to disengage the inclined piece 58; by continuing in this direction the idle barrel-shaped rolling body 6 impresses a progressively greater speed on the driven plate 1. In Figure 4, the barrel-shaped body 6 is associated with a positionable ball bearing; this solution achieves in an ideal manner the effect of further secondary wedging deriving from the inward traversing of the barrel shape of said rolling body 6. However to achieve this secondary wedging, minimum inward traversing angles are sufficient, even just fractions of a degree. These minimum angles could therefore derive from the usual stack of the bearings 25 and/or from flexural elastic deformations undergone by the operating rod 24 on which they are mounted. Said bearings 25, indicated as 25A and 25B, are of rigid radial ball type and are present at the sides of the barrel-shaped rolling body 6 to enable this to comprise a solid inner ring 27, provided to offer maximum resistance to crushing of the barrel-shaped rolling body precisely in its central plane 6D, where the axial forces generating the motion transmission friction act.

These forces are particularly large, however the deformation that they cause must be of minimum extent. For this purpose, as shown in Figures 6 and 7, these forces are supported by large axial ball bearings 28 positioned under the edges of the two rotating plates 1,4, assisted by rigid radial bearings 26. To isolate the zone in which the barrel-shaped rolling body 6 operates from the zone in which these bearings, requiring lubrication, operate, usual seal rings 29,29A of various types are provided to slide on the cylindrical edges of the plates 1 and 4. As already

illustrated, these plates 1 and 4 rotate about their axes 3 and 5 and are inclined by a small angle a. If certain particular applications of the variator require its input and output axes to be parallel, this invention enables the problem to be solved by the method shown in Figure 6. This method consists of associating the movement of the two plates 1 and 4 with two bevel gear pairs 31-32 and 33-34; in this manner, input and output shafts 35,36 are obtained which are perfectly parallel, notwithstanding the obliqueness of the axes 3 and 5. In Figure 6 the ring gear 34 of said bevel gear pair is drawn with thin lines to indicate that it is located upstream of the section plane DEFG, and is therefore not visible. The ring gear 32 has its toothing only partially shown. The reference numeral 30 indicates a joining plane between two parts of the variator, to demonstrate the symmetry and hence the constructional economy of its structure.