WO1998011364A1

WO1998011364A1 - A stepless speed change gear

Info

Publication number: WO1998011364A1
Application number: PCT/IT1997/000221
Authority: WO
Inventors: Enrico Nino
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-09-09
Filing date: 1997-09-10
Publication date: 1998-03-19
Anticipated expiration: 1999-03-13
Also published as: AU4396497A

Abstract

The invention relates to a stepless speed change gear able to provide a continuously-selectable variation ratio in output angular velocity with respect to input velocity. The main characteristic of the invention is that the drive transmission between a motor and a user is guaranteed by a system of two cogwheels (2) set at a distance from a rotation axis of a main plate (1) which enmesh in a link-roller chain (4) functioning as a rolling track for the cogwheels (2). During functioning the cogwheels (2) can be relocated continuously at varying distances from the rotation axis of the plate (1) and thus can vary a circumference of a revolution, realising different angular velocities with equal input angular velocity. The invention, which exploits normal-type chain gearings, can transmit considerable tangential forces synchronously without slippage among the various components.

Description

Pescription

A Stepless Speed Change Gear

Technical Field

The invention concerns a stepless speed change gear. In particular, it is used in drive transmission between a motor and a user with the aim of providing an angular velocity variation ratio in output on a rotating shaft with respect to an input speed, with continuous variation selection. Background Art

It is well known that motion from a primary motor to a user is transmitted by means of an interpositioning of special mechanisms, usually known as gears or reducers, constituted by a series of gearings having apt dimensions for achieving a desired reduction or multiplication of angular velocity and of the torque supplied by the primary motor. An obvious application of this is in the common automobile, where the selection limits are often set at five different ratios (mechanical transmissions) to cover the whole field of use of the motor and the vehicle. Attempts at eliminating the problematics connected with the use of mechanical transmissions having a limited number of gear ratios have included the adoption of pulley torque converters. These converters exploit the principle by which a trapezoid-section transmission belt can be set in rotation by means of two conical pulleys (a drive pulley and a driven pulley) which can vary the distance between the two conical plates constituting the pulley. By varying this distance the trapezoid belt wedges in the pulley at a variable distance (rotation radius) from the rotation axis of the pulley. In effect, this kind of transmission can simultaneously vary the distance between the conical plates of the two pulleys constituting the transmission itself, so that the maximum length of the belt wound around them remains the same. By varying the distance between the plates of the two pulleys the drive belt is forced to wedge at different radii on the two pulleys, producing the desired variation in the transmission ratio between the drive pulley and the driven pulley.

Even though the above-described variable transmission has been applied in numerous industrial and vehicular gear mechanisms, it is prone to certain drawbacks which limit its applicability. The first of these relates to the maximum transmittable torque, which is limited by the fact that drive transmission is guaranteed by the friction forces developing between the conical plates of the pulleys and the sides of the transmission belt and not, for example, by the shear stress resistance of the teeth constituting the gearings of a traditional mechanical transmission. The maximum transmittable power is further limited by the resistance to traction of the belt used, which may be synthetic in the case of more economical applications, or which may be made of metal. In the latter case a special conformation is used, using metal belts and anchors constituting the belt itself. In the case of the metal belt, although the transmittable torque increases due to the increase in resistance to traction of the belts themselves with respect to synthetic ones, disadvantages derive from the extreme rigidity of the metal anchors, which in order to wedge unslippingly in the pulley throats require a decidedly superior working precision to that required by models having a synthetic belt. In any case, for both types of belt, at least during the transmission ratio adjustment phase, it is inevitable that there will be slippage between the belt and the pulley, which slippage leads to early wear and breakage of the belts. Also, the maximum rotation speed of the pulleys (and therefore the maximum transmittable power) is limited due to the centrifugal forces developing and tends to raise the belt from the pulley throat. Another type of known-type device for continuous drive variation is constituted by hydraulic converters, essentially consisting of a variable-delivery pump and a hydraulic actuator. The principle is as follows: drive is transmitted to the variable delivery pump and a variable delivery of hydraulic oil is obtained; by sending the oil to an actuator (hydraulic motor), the latter will assume a rotation velocity which depends on the delivery sent thereto, different from the delivery supplied to the pump, thus realising the requested variation in speed. Obviously the energy efficiency of this device is particularly low, given the inevitable losses incurred when supplying and removing energy from the hydraulic oil. Disclosure of Invention

The main aim of the present invention is to realize a speed change gear which can obviate the above-described limitations and drawbacks inherent in the prior art. In a first version, the present invention achieves the above-mentioned aim by providing a speed change gear able to transmit motion from a first to a second shaft, as characterized in the claims that follow numbered from 1 to 8, comprising: at least one support solidly constrained to the first shaft; at least two rotatable gearwheels, solid in rotation with the support and connected by means of a mechanical transmission to the second shaft and able on command to vary in distance from the rotation axis of the first shaft; at least one flexible mechanical organ, enmeshing with the gearwheels, on which organ the gearwheels revolve, which organ is conformed and arranged in such a way that one of the wheels in always enmeshed; means for adjusting the timing among the cogs of the cogwheels and the flexible mechanical organ according to the distance of the wheels from the rotation axis of the first shaft. The means for timing adjustment might comprise means for impressing rotation on the cogwheels about their respective axes by moving them radially with respect to the axis of the first shaft. Preferably but not necessarily, the means for impressing rotation might comprise two splined shafts wherein the splines are helicoid, along each of which splines a gearwheel of the mechanical transmission can slide; the gearwheel being part of the mechanical transmission connecting the gearwheels to the second shaft. The speed change gear can comprise, for example, at least one driving gear of the flexible mechanical organ, a position of which driving gear is variable on command.

In a preferred embodiment the gear wheels are slidable on radial guides predisposed on the first support. The speed change gear can comprise a plurality of idler gears, solid in rotation with the first support, arranged circumferentially thereto, on which the flexible mechanical organ is wound and enmeshes. The idler gears can be commanded to vary their distance from the rotation axis of the first shaft. Preferably, though not indispensably, the mechanical transmission connecting the gear wheels to the second shaft is geared and can comprise at least one gearwheel able to slide radially with respect to the rotation axis of the first shaft. The flexible mechanical organ can be, for example, a normal chain or roller track, or a Morse chain, or other known devices having linked toothings, preferably semi-circularly or semi-polygonally wound around a rotating or fixed support. The flexible mechanical organ functions as a rolling track for two gearwheels which engage alternatingly thereon. The rolling track, constituted for example by the chain or other like device, is wound in such a way as to give rise to an open ring, substantially a semi-circumference. The two gearwheels are located symmetrically with respect to the rotation axis of the support, which can be, for example, a main plate drawing the two gear wheels in rotation. For each revolution of the plate a number of gearwheel revolutions is obtained which number is greater than one and which depends on the position of the gearwheels with respect to the centre of rotation of the plate. The motion can be imparted to the gearwheels in such a way that, by rotating the main plate, a number of output revolutions will be obtained that which depends, as in the previous case, on the position of the gearwheels with respect to the centre of the plate, but which is in any case smaller than the number of input revolutions. In the first case the invention behaves as a multiplier, or overgear, of the number of input revolutions with respect to the output revolutions, while in the second case it behaves as a reducer. The coupling of two main plates gives rise to a device which can multiply the angular input speed or reduce it, realising a synchronous transmission and obviating slide problems, and considerably increasing the transmittable tangential force.

In a second embodiment, the invention achieves the above-mentioned aim by providing a speed change gear for transmitting motion from a first shaft to a second shaft, as characterized in the appended claims numbered from 9 to 16, comprising: at least one first support, solidly constrained to the first shaft at least two rotatable gearwheels, solid in rotation with the support and connected by means of a mechanical transmission to the second shaft and able on command to vary in distance from the rotation axis of the first shaft; at least one flexible mechanical organ, enmeshing with the gearwheels, on which organ the gearwheels revolve, which organ is conformed and arranged in such a way that one of the wheels in always enmeshed; means for adjusting the timing among the cogs of the cogwheels and the flexible mechanical organ according to the distance of the wheels from the rotation axis of the first shaft. The timing adjustment means can comprise means for rotating the gearwheels about their respective axes by effect of displacing them radially about the axis of the first shaft. The means for rotating preferably comprise a second flexible mechanical organ enmeshing with the gear wheels and having adjustable-position ends.

Further, the means for timing adjustment can comprise means for lengthening and shortening a tract of the flexible mechanical organ comprised between the gearwheels. The lengthening and shortening means preferably, though not necessarily, comprise a wheel coupled with the above-mentioned tract, with possibility of varying the distance of said wheel from the axis of the first shaft. In a preferred embodiment of the invention, it can comprise: a second support solidly constrained to the second shaft; at least two gearwheels, solid in rotation with the second support, said at least two gearwheels on command being able to vary their distance from the rotation axis of the second shaft, said gearwheels enmeshing with the first flexible mechanical organ in such a way that at least one thereof is always enmeshed; means for adjusting, according to the distance of the gearwheels from the rotation axis of the second shaft, the timing between the cogs of the wheels and the first flexible organ. While in the first embodiment of the invention (claims from 1 to 8) the flexible mechanical organ functions as a rolling track for the gearwheels and during functioning is practically stationary (at least until the gear ratio is changed), in this second embodiment (claims from 9 to 16) the first flexible mechanical organ - which might be, for example, a normal chain with links and rollers - is mobile during functioning and is used for the transmission of motion between the two gearings (drive gearing and driven gearing) comprising the gearwheels located at the variable-radius circumference. The chain enmeshes on the specially- synchronised gearwheels, eliminating slippage problems (through creating a synchronous transmission) and considerably increasing the transmittable tangential force.

For a better understanding of how the invention works, there follows a non- limiting description of two embodiments, illustrated with reference to the accompanying figures of the drawings, in which: figure 1 shows a schematic and simplified plan view of a first embodiment of the gear speed change of the invention; figure 2 shows the device of figure 1 in a different operative configuration; figure 3 is an enlarged-scale schematic section made according to the III-III of figure 2; figure 4 is a schematic and simplified plan view of a second embodiment of the invention; figure 5 is a schematic perspective view of the gear speed change of figure 4. There now follows a first embodiment of the invention, with reference to above -mentioned figures 1-3, which show a gear speed change comprising: a first support constituted by a main plate 1 ; two gearwheels 2; a series of idler wheels 3; a link and roller chain 4 having the same step as the gearwheels 2; a central crown wheel 5; two geared crown wheels 6 keyed on the gearwheels 2; two splined shafts 7; four pinions 8 located at the two ends of the splined shafts 7; two idler intermediate wheels 9 for the chain 4; two chain-tighteners 10; a first rotation shaft 1 1 keyed on the main plate 1; a second rotation shaft 12, keyed on the central crown ring 5, coaxial with the first shaft 1 1 , a series of sliding guides constituted by radial grooves 13 made in the main plate 1 and in which the gearwheels 2 and the idler wheels 3 engage.

In this embodiment the chain 4 is wound in such a way as to form an open polygon, the number of sides thereof depending on the number of gearwheels 2 and idler wheels 3 present; in effect, the chain 4 represents a variable- configuration rolling track, symmetrical in a vertical plane; the two gearwheels 2 can be located either internally or externally of the rolling track. The invention functions as follows. When the first shaft 11 is rotated, the main plate 1 is drawn along with it. There are two gearwheels 2 on the main plate 1 , connected thereto by bearings or other known means so that the gearwheels 2 can rotate on their own axes (which are orthogonal to the plate 1 ) and, when necessary, perform radial translations along the grooves 13. One of the two gearwheels 2 is securely enmeshed in the chain 4 , as can be seen in figures 1 and 2. The chain 4 is constrained at its opposite ends by two chain-tighteners 10, so that the gear wheel 2 enmeshed in the chain 4 is forced to rotate in an opposite direction to the rotation direction of the main plate 1. The remaining gearwheel 2 is also set in rotation, since the motion is transmitted by the enmeshed gearwheel 2, by means of the crown 6 solidly constrained thereto, from the crown 6 to a pinion 8, from the pinion 8 to the splined shaft 7, then to the other pinion 8 and then to the central crown 5; then from the central crown 5 (in inverse order) through another pinion 8, the other splined shaft 7, the other pinion 8, and thence to the crown 6 keyed on the other gearwheel 2 not engaged on the chain 4. The motion between the two wheels 2 can also be transmitted using other known means without any consequent loss in the invention^" s validity.

Following a semi-rotation of the main plate 1, the gearwheel 2 enmeshed in the chain 4 is freed, while the other gearwheel 2, up to now free, is now enmeshed and motion is transmitted therefrom to the central crown 5, then to the gearwheel 2 which has just been freed from the chain 4. After a further semi-rotation of the main plate 1 , the previously-engaged gearwheel is once more enmeshed in the chain 4, while the other is freed, and so on for the whole functioning period. This alternation between the two gearwheels 2 is permitted by the fact that they are constrained to the main plate 1 symmetrically with respect to the rotation axis of the main plate 1 itself. In fact, looking at figure 1, let us suppose that a gearwheel 2 (taken, for simplicity, to have an equal number of teeth) is enmeshed with the chain 4 so as to have its rotation axis perpendicular to axis C-D, and further let us suppose that the tooth enmeshed in the chain is lying on axis C-D (at the side indicated by C) so that said axis is lying on the axis of symmetry of the enmeshed tooth. Given the symmetry of the gearwheels 2 (equal number of teeth), the tooth opposite to the one enmeshed will lie on axis C-D. In this state axes A-B and C- D constitute axes of symmetry for the gearwheels 2 and the chain 4 wound about the semi-polygon (or semi-circle) to the left of axis C-D, and there will be a whole number of chain 4 links wound about the gearwheels 2 and part of the idler wheels 3. By varying the radial position of the gearwheel 2 and the idler wheels 3 (which happens simultaneously) a change in the transmission ratio is obtained. This change guarantees the above-described condition of symmetry about axes A-B and C-D only if the change in the number of links in the chain 4 is a whole number - which would bring about a step-change in the transmission ratio. This drawback is easily obviated by re-establishing the symmetry about axis A-B. To achieve this, the gearwheels 2, while their radial position on the main plate 1 is being changed, must rotate in opposite directions to each other - i.e., if one is made to rotate in a clockwise direction with respect to its rotation axis, the other will have to rotate through the same angle but in an anticlockwise direction. Under experimental conditions this has been achieved simply by providing a wide-pitch helical progression on the splined shafts 7 so that when the pinions 8 run on the splined channel 7 they undergo a small rotation which is transmitted to the crown 6 and thence to the gearwheel 2, so as to compensate for half of the fraction of link exceeding the whole number wound about the gearwheels 2 and part of the idler wheels 3. The symmetry about axes A-B and C-D has been used several times to describe the functioning principle of the invention, but it is not really necessary at all. Indeed, the axes of symmetry, during functioning, can be arranged in different positions from those of figure 1, which appear here purely for purposes of description. The gearwheels 2, too, can have any number of teeth, even or odd, without compromising the functioning of the invention and, therefore, without detracting from its validity.

The velocity with which the two gearwheels 2 are rotated depends on the angular velocity of the plate 1 , the dimensions of the gearwheels 2 themselves and the radial position of the gearwheels 2 on the plate 1. With geometric positions and angular velocity of the main plate 1 the same, the speed of the gearwheels 2 and thus the central crown 5 the gearwheels 2 are connected to, can be varied continuously simply by continuously varying the radial position of the gearwheels 2 by causing them to slide along the radial grooves 13. By nearing or distancing the gearwheels 2 from the rotation axis of the main plate 1 , in output, for example on the second shaft 12, a different angular velocity is obtained with respect to the input velocity, for example on the first shaft 11 , because the gearwheels 2 have to run through a shorter track (tract of chain 4) for each revolution of the main plate 1. The angular velocity thus obtained is extracted from the system by means of the second shaft 12 connected to the central crown 5. The above-described functioning refers to the invention when operating as a multiplier of angular velocity. If, instead, the drive is supplied through the second shaft 12, the gearwheels 2 receives drive from the central crown 5 and by enmeshing in the chain 4 draw the main plate 1 in rotation and, therefore, also the first shaft 1 1 connected thereto, thus providing the output. In this case the invention functions as a reducer.

The series use of a pair of devices as above described, in a configuration in which the outputting drive from the first is sent in input to the second, constitutes a single device which is able to provide both increases and reductions in the angular speed in output with respect to that in input. The variation of the radial position of the two gearwheels 2 has to be accompanied by a variation in the radial position of the idler wheels 3 keyed by bearings and supports in the grooves 13 of the main plate 1. The function of the idler wheels 3 is to cause the chain 4 to wind in such a way as to form a semi- circumference functioning as a rolling track for the gearwheels 2. This function can be substituted, without detracting from the invention, by other known devices such as, for example, a system of rests acting externally to the main plate 1 and curving the chain so as to form the rolling track for the gearwheels 2 in the radial position required. Furthermore, the gearwheels 2 can be located externally of the semi-circumference without the invention losing its validity. The variation in the radial position of the gearwheels 2 and the idler wheels 3 on the main plate 1 can be obtained using known means such as, for example, con rods connected on one side to the gearwheels 2 and the idler wheels 3 and on the other side to a slidable sleeve on the first shaft 1 1 or the second shaft 12 and whose axial position imposes a radial position on the gearwheels 2 and the idler wheels 3. Another method could be constituted by a multiple cam device whose relative rotation with respect to the main plate 1 locates the gearwheels 2 and the idler wheels 3 in the desired radial position. In the prototype, the radial displacement of the gearwheels 2 and the idler wheels 3 was obtained by using steel cables activated by a slidable sleeve on the first shaft 1 1. The radial displacement of the gearwheels 2 and the idler wheels 3 must be accompanied by a variation in the length of the chain 4 wound in a semi-circle (or open polygon) about the gearwheels 2 and the idler wheels 3. This change in length is obtained by means of a rotation or translation of the chain-stretchers 10, whose movement is connected to the movement of the radial position command of the gearwheels 2 and the idler wheels 3, which movement is obtained using known means not described herein for reasons of brevity. The variation in the radial position of the gearwheels 2 and the idler wheels 3 must be accompanied by a change in the position of the two intermediate wheels 9, whose task is to guarantee that the chain 4 embraces the main plate 1 over a 180° span in order to prevent the gearwheels 2 from becoming both enmeshed on the chain 4; this is to prevent the gearwheels 2 and idler wheels 3 from occasioning jolts during the radial position change manoeuvre - i.e. the transmission ratio change operation. Indeed, during this operation a part of the chain 4 must be taken up (reduction of the radial distance from the rotation axis) or supplied (increase in radial distance) and should the two gearwheels 2 engage contemporaneously on the chain 4, the above-described operation would be impeded, since to achieve said shortening or lengthening it is necessary that one of the gearwheels 2 rotates in one direction and the other in the opposite direction. This difference in the rotation direction is prevented by the kinematic connection realised between the two gearwheels 2. Figures 1 and 2 show the invention in two different transmission ratio positions. In particular, in figure 1 the invention is shown in an "open" position, that is with the gearwheels 2 and the idler wheels 3 located at a greater radial distance, about halfway along the main plate 1 radius, while in figure 2 the invention has undergone an adjustment operation which has brought the gearwheels 2 and the idler wheels 3 to a smaller radial distance, in a position close to the rotation axis of the main plate 1. This adjustment, obviously, has also changed the position of the intermediate wheels 9 and the chain-stretchers 10.

What follows is a description of a second embodiment of the invention, with reference to figures 4 and 5 of the drawings, which show a gear speed change comprising: a first shaft 101 to which a drive gearing is solidly and coaxially connected; a second shaft, to which a driven gearing is solidly and coaxially connected; a main roller-and-link first chain 103, destined to interconnect the two gearings solidly connected to the first shaft 101 and the second shaft 102; an idler wheel 104 for taking up play. Each shaft 101 and relative gearing comprises a series of idler wheels 105, at least two pairs of gearwheels 106 and 107 having steps which are compatible with the first chain 103, a second chain 108 for synchronising twin gearwheels 106 and 107, two terminals 109 and 1 10 for controlling the second chain 108, an idler wheel 1 1 1 for compensating the timing displacement. Each pair of twin gearwheels 106 and 107 is constituted by two coaxial wheels constrained one to the other, one above and one below, which rotate freely on their shared axis. In figure 5 the lower of the twin gearwheels enmeshes with the first or primary chain 103, and for this reason is termed the primary wheel, while the upper wheel enmeshes with the secondary chain, in effect a timing chain 108, and so is termed the secondary wheel. The above-described synchronous gear speed change functions as follows. Starting with a description of the first shaft 101 and its relative gearings, from the figure it can be seen how the primary chain 103 winds about two of the lower wheels of the twin gearwheels 106 and 107 as well as part of the idler wheels 105. The timing or secondary chain 108 enmeshes on the upper wheels of the gearwheels 106 and 107 and also about part of the idler wheels 105. Since the primary chain 103 and the secondary chain 108 have the same step, it follows that the same number of links will be comprised between the two pairs of gearwheels wheels 106 and 107. The primary chain 103 and the secondary chain 108 lie on parallel planes. Thus, when the first shaft 101 rotates in an anticlockwise direction - with reference to figure 4 - so as to cause gearwheels 106 to leave the primary chain 103, from the area indicated by Al in the figure, the connection and therefore the torque transmission is guaranteed by gearwheels 107, still enmeshed with the primary chain 103. For this reason the take-up idler wheel 104 must guarantee an extent of primary chain 103 winding about both gearings constrained to the first and second shafts 101 and 102 which extent of winding ensures that the length of first chain 103 left on the two gearings of the shafts 101 and 102 is shorter than the length of chain comprised between the two pairs of timing gearwheels 106 and 107. As the rotation of the first shaft 101 continues, the primary wheel of gearwheels 106 re-contacts with the primary chain 103 in the zone indicated by Bl . Let us suppose that the diameter of the gearing of the first shaft 101 is such that a whole number of links of the primary chain 103 wind about it, i.e. that the circumference of the perimeter of the first shaft gearing 101 can be divided by the step of the primary chain 103 and result in a whole number. Thus, it is as if the teeth of gearwheels 106 and 107 enmeshing with the primary chain 103 were part of a crown cogwheel having the diameter of the gearing of the first shaft 101 and enmeshing with the primary chain 103. Thus the primary wheel of gearwheels 106, by effect of the rotation of the gearing of the first shaft 101 , would enmesh perfectly with the primary chain 103 at every revolution of the first shaft 101 , guaranteeing regular transmission of motion between the gearing of the first shaft 101 and the primary chain 103. It is therefore obvious that, if the primary wheel of gearwheels 106 enmeshes correctly with the primary chain 103, the primary wheel of gearwheels 107 will enmesh perfectly in every functioning condition. The above functioning description is also valid for the gearings of the second shaft 102. It must be remembered that, on the contrary to what is shown in figures 4 and 5, the gearings of shafts 101 and 102 can be constituted by devices which guarantee a perfectly circular form (for example, using a conformation with two variable- distance conical plates for housing the chain). In figures 4 and 5, for greater clarity, it was decided to adopt a situation having gearwheels situated at points of an octagon.

Now let us suppose that we vary the gearing of the first shaft 101, using known means not illustrated for reasons of simplicity, and consequently vary the radius of the gearing of the second shaft 102, in an opposite direction to the variation of the gearing of the first shaft 101 so as to leave the length of the primary chain 103 unchanged; let us also suppose that this variation is of such an entity as to obtain a circumference of the gearing of the first shaft 101 which, divided by the step of the primary chain 103, produces a non-whole number. In this condition the fraction of step in excess is compensated by increasing or reducing the radial displacement of the compensating idler wheel 1 1 1 , comprised between wheels 106 and 107, by a quantity sufficient to restore a whole number of links wound about the gearings of the first shaft 101. The difference between the displacement of idler wheel 1 1 1 and the displacement of the other idler wheels 105, in rapport with the variation of the diameter of the gearing of the first shaft 101 , is given by a fixed ratio: by denoting with P the step of the chain and with R the gearing of the first shaft 101 , it results that the number of links comprised in the circumference L of the gearing of the first shaft 101 is given by: M=2πR/P [1]

The equation [1] shows how the number of links is a linear function of R. In effect, by varying the diameter of the gearings of the first shaft 101 and the second shaft 102, M becomes a whole number having periodic frequency. In the passage between two whole numbers, the added radial displacement of idler wheel 111 compensates by the fraction of step P necessary to bring M back into a whole number value. Obviously the displacement of the idler wheel 1 1 1 is limited by the fact that the maximum M variation value is ± P/2. The extra displacement of idler wheel 111 (extra, that is, relatively to the other wheels 105, 106 and 107) is achieved using known means not illustrated here for reasons of brevity, and is synchronised with the radial displacement of those other wheels 105, 106 and 107 which make up the gearing. The link-number compensation can be achieved using other methods apart from the one described above; for example, by simply effecting a rotation (using known means omitted from the present description for reasons of simplification) of the pair of gearwheels 106 about a rotation axis passing through the centre of the toothing of said pair of gearwheels 106. Thus an oscillation of the gearwheels 106 is obtained which compensates the phase displacement of the primary chain 103. The oscillation can be either clockwise or anticlockwise, depending on the phase displacement of the primary chain 103, and thus dependently on the radius of the gearing of the first shaft 101. With this technique, where there is no variation in diameter of the gearing of the first shaft 101 , compensation of the phase displacement of the second chain 103 has to be carried out (by known means, omitted for reasons of brevity) at each revolution of the first shaft 101.

The above is also true when the gearing of the first shaft 101 is no longer a circumference but a polygon with N sides. The variation of diameter 2R of the gearing of the first shaft 101 means that the quantity of chain 103 wound about the various wheels must also change, in particular must increase by R and vice versa. The part of chain comprised between gearwheels 106 and 107 is guaranteed by a rotation of gearwheel 106 activated by the control terminal 109 and a rotation of gearwheel 107 activated by the control terminal 110. The entity of these rotations is clearly dependent on the variation of R. The movements of terminals 109 and 1 10 are connected with the mechanisms varying the diameter of the gearing of the first shaft 101 by means of known means, not illustrated for reasons of simplicity. The variation in the diameter of the gearing of the first shaft 101 can be carried out in all angular positions of the first shaft 101 except for those positions where there is a simultaneous enmeshing of gearwheel 106 with a tract of primary chain 103 situated in zone Bl and of wheel 107 with a tract of primary chain 103 situated in zone Al. In this situation, a variation in the quantity of primary chain 103 wound about the gearing of the first shaft 101 and second chain 108 comprised between gearwheels 106 and 107 cannot correspond to a variation in R. It should be remembered that this situation regards only a few rotation degrees and that the variation in radius R can easily be prevented (using known means not illustrated for reasons of simplicity) when the gearing of the first shaft 101 is in the previously-described angular position. The above description is equally valid for the gearing of the second shaft 102.

Claims

Claims.

1). A speed change gear for transmitting motion from a first shaft (1 1 ) to a second shaft ( 12), comprising: at least one support (1) solidly connected to the first shaft (1 1); at least two cogwheels (2), solid in rotation with said support ( 1 ), said cogwheels (2) being rotatable each about an axis thereof, and being connected by a mechanical transmission to the second shaft ( 12); a distance of said at least two cogwheels (2) from a rotation axis of the first shaft (1 1 ) being variable on command; at least a flexible mechanical organ (4) enmeshing with said cogwheels (2); said cogwheels rolling on said flexible mechanical organ (4), which mechanical organ

(4) is conformed and arranged such that one of said at least two cogwheels (2) is enmeshed therein; means for adjusting a timing of said at least two cogwheels (2) and the flexible mechanical organ (4) according to a distance of the cogwheels (2) from the rotation axis of the first shaft (11).

2) The speed change gear of claim 1 , wherein said flexible mechanical organ (4) is a link-and-roller chain.

3) The speed change gear of claim 1 or 2, wherein the means for adjusting the timing comprise means for impressing on said at least two cogwheels (2) rotations about the respective axes thereof by effect of a radial displacement thereof with respect to the axis of the first shaft (1 1 ).

4) The speed change gear of claim 3, wherein said means for impressing rotations comprise two splined shafts (7) each having a helical groove, along which helical groove a pinion (8) of said mechanical transmission is slidable. 5) The speed change gear of any one of the preceding claims, comprising at least one intermediate wheel (9) of the flexible mechanical organ (4), a position of which is variable on command.

6) The speed change gear of any one of the preceding claims, wherein the at least two cogwheels (2) are slidable on radial guides (13) predisposed on the first support (1 1).

7) The speed change gear of any one of the preceding claims, comprising a plurality of idler wheels (3) solid in rotation with the first support (1 ) and arranged circumferentially thereon, on which idler wheels (3) the flexible mechanical organ (4) is wound and enmeshes; said idler wheels (3) being variably positionable on command with respect to the rotation axis of the first shaft (1 1 ).

8) The speed change gear of any one of the preceding claims, wherein said mechanical transmission is of a gear-drive type and comprises at least one pinion (8) able to slide radially with respect to the rotation axis of the first shaft (1 1).

9) A speed change gear for transmitting motion from a first shaft (101 ) and a second shaft (102), comprising: at least a first support solidly constrained to a first shaft (101); at least two cogwheels (106, 107), a distance of which from a rotation axis of the first shaft (101) is variable on command; at least a first flexible mechanical organ (103), enmeshing with said cogwheels

(106, 107), conformed and arranged in such a way that one of said cogwheels

(106, 107) is always enmeshed, for transmitting motion to a second shaft (102); means for adjusting a timing between the teeth of the cogwheels (106, 107) and the first flexible organ (103) according to a distance of the cogwheels (106, 107) from the rotation axis of the first shaft (101).

10) The gear speed change of claim 9, wherein said first flexible mechanical organ (103) is a link-and-roller chain.

1 1) The speed change gear of claim 9 or 10, wherein said means for adjusting the timing comprise means for impressing on said cogwheels (106, 107) rotations about axes thereof contemporaneously with a radial displacement thereof with respect to the rotation axis of the first shaft (101).

12) The speed change gear of claim 1 1 , wherein said means for impressing rotations comprise a second flexible mechanical organ ( 108) enmeshing with said cogwheels (106, 107) and provided with ends ( 109, 1 10) which are position- adjustable.

13) The speed change gear of claim 9 or 10, wherein said means for adjusting the timing comprise means for lengthening and shortening a tract of the first flexible mechanical organ (103) comprised between said cogwheels (106, 107).

14) The speed change gear of claim 13, wherein said means for lengthening and shortening comprise an idler wheel (1 11) coupled to said tract of the first flexible mechanical organ (103), a position of which idler wheel (1 1 1 ) can be radially varied with respect to the rotation axis of the first shaft (101).

15) The speed change gear of any one of claims from 9 to 14, comprising a plurality of idler wheels (105) solid in rotation with the first support and arranged circumferentially thereto, on which the first flexible mechanical organ (103) is wound; a distance of said idler wheels (105) from the rotation axis of the first shaft (101) being variable on command.

16) The speed change gear of any one of claims from 9 to 15, comprising: a second support, solidly constrained to the second shaft (102); at least two cogwheels, solid in rotation with the second support, a distance of which at least two cogwheels from the rotation axis of the second shaft (102) is variable on command, said at least two cogwheels enmeshing with the first flexible mechanical organ (103) in such a way that one of said cogwheels enmeshes therein; means for adjusting the timing between cogs of the at least two cogwheels and the first flexible mechanical organ (103) according to a distance of said cogwheels from the rotation axis of the second shaft ( 102).