The present invention concerns a continuously variable mechanical transmission by means of at least one flexible member and comprising a drive pulley and a driven pulley.

US3,613,468A discloses a continuously variable mechanical transmission by means of a flexible member, comprising conical elements with parallel axes, on which longitudinally slidable pulley segments are mounted and which constitute composite pulleys engaged by means of the flexible member. The simultaneous movement of the pulley segments and of the flexible member changes the ratio between the diameters of the pulleys, when the pulley segments move longitudinally and radially along the conical elements. Hydraulic cylinder control means are provided to move the pulley segments and the flexible member simultaneously. Motor means and flywheel means can be coupled to the conical members.

The mechanical transmission disclosed by US3,613,468A is structurally complex and has significant overall dimensions. Moreover, synchronization of the movements of the pulleys is difficult to implement.

US4,878,883A discloses a mechanical transmission by means of a chain member, wherein a pulley comprises a plurality of radially sliding elements supporting respective sprocket wheels that mesh with the chain member in succession. Each of said sliding elements is controlled by means of respective hydraulic piston- cylinder means so as to extend and retract simultaneously to the other sliding elements.

The mechanical transmission disclosed in US4,878,883A is structurally complex and has significant overall dimensions.

JP2014167306A discloses a mechanical transmission by means of a flexible member, wherein a drive pulley and a driven pulley are divided into a plurality of respective pulley segments. The pulley segments are movable in radial direction and can be adjusted individually by means of a respective actuator, such as an electric motor, so as to gradually vary the diameter of the respective pulley. Said elements are adjustable in radial direction when the flexible member is not in contact with the respective pulley. Therefore, the teachings of JP2014167306A do not allow a continuously variable mechanical transmission to be obtained.

US 2017/082178 A1 discloses a continuously variable mechanical transmission by means of at least one flexible member comprising:

- a drive shaft and a driven shaft with mutually spaced and parallel axes, wherein said drive shaft is rotated by means of motor means;

- a drive pulley, connected to said drive shaft, and a driven pulley, connected to said driven shaft, said pulleys being arranged in a common plane orthogonal to the axes of said shafts and said flexible member being circulated between said pulleys, in said plane;

- a plurality of first operating cylinders controlled by means of pressurized fluid, provided in said drive pulley in radial arrangement, and a plurality of second operating cylinders controlled by means of pressurized fluid, provided in said driven pulley in radial arrangement;

- wherein each first operating cylinder comprises a respective sliding piston and a corresponding rod, which is movable between a position radially retracted with respect to said drive pulley and a position radially extended with respect to said drive pulley, and wherein the rod of each first operating cylinder supports at the free end a corresponding first shoe, cooperating with said flexible member;

- wherein each second operating cylinder comprises a respective sliding piston and a corresponding rod, which is movable between a position radially retracted with respect to said driven pulley and a position radially extended with respect to said driven pulley, and wherein the rod of each second operating cylinder supports at the free end a corresponding second shoe, cooperating with said flexible member;

- wherein said flexible member is partially wound on said drive pulley and on said driven pulley, engaging a plurality of said first shoes and a plurality of said second shoes, and kinematically connects said drive pulley and said driven pulley, continuously transmitting the motion between said drive shaft and said driven shaft. The present invention, considering the drawbacks of the prior art illustrated above, intends to remedy these.

An object of the present invention is to provide a continuously variable mechanical transmission by means of at least one flexible member and comprising a drive pulley and a driven pulley, which allows the diameter of said pulleys to be varied in a continuous and mutually correlated manner automatically, the at least one flexible member being in contact with said pulleys, and having a high efficiency.

Another object of the present invention is to provide a mechanical transmission of the type specified, which is structurally simple, has limited overall dimensions, operates safely and allows automatic correlation of variations in the diameters of the pulleys.

In view of these objects, the present invention provides a continuously variable mechanical transmission by means of a flexible member, the essential characteristic of which forms the subject matter of claim 1 .

Further advantageous characteristics of the mechanical transmission according to the invention are described in the dependent claims.

Other characteristics and advantages of the invention will become more apparent from the following detailed description of an example of embodiment of the invention with reference to the figures in the accompanying drawing, which show important details for the invention, and from the claims. The characteristics illustrated are not necessarily to scale and are represented so that the specific features according to the invention are clearly highlighted. The different characteristics can be produced individually or in any combination with one another, as variants of the invention.

In the accompanying drawing:

- Fig. 1 is a schematic top plan view of an example of embodiment of the continuously variable mechanical transmission by means of a flexible member and comprising a drive pulley and a driven pulley, according to the present invention;

- Fig. 2 is a partial schematic view in the direction of the arrow II of Fig. 1 , showing the two pulleys and the flexible member that engages these pulleys and wherein the drive pulley has a smaller diameter than the diameter of the driven pulley; - Fig. 3 shows a similar view to that of Fig. 2, but wherein the pulleys have substantially the same diameter as each other;

- Fig. 4 is a sectional view and in a larger scale according to the line IV-IV of Fig. 3;

- Fig. 5 is a sectional view and in a larger scale according to the line V-V of Fig. 3; - Fig. 6 is a sectional view according to the line VI-VI of Fig. 5;

- Fig. 7 is a similar view to that of Fig. 6, but wherein the pulley illustrated has a larger diameter than the diameter of the pulley of Fig. 6;

- Fig. 8 is a similar view to that of Fig. 2, but wherein the drive pulley has a larger diameter than the diameter of the driven pulley.

With reference to the drawing, the reference numeral 10 (Fig. 1 ) indicates as a whole the continuously variable mechanical transmission by means of a flexible member 1 1 , according to said example of embodiment of the present invention. Said mechanical transmission 10 comprises a drive shaft 12.1 and a driven shaft 12.2 with mutually spaced and parallel axes, wherein said drive shaft 12.1 is rotated by means of motor means M, for example electric motor means. Said mechanical transmission 10 also comprises a drive pulley 13.1 , integral and coaxial with respect to said drive shaft 12.1 , and a driven pulley 13.2, integral and coaxial with respect to said driven shaft 12.2. Said pulleys 13.1 , 13.2 are arranged in a common plane orthogonal to the axes of said shafts 12.1 , 12.2 and said flexible member 1 1 is engaged and circulated with respect to said pulleys 13.1 , 13.2, in said plane.

According to the present invention, a plurality of first operating cylinders 14.1 (Fig. 4), controlled by means of pressurized fluid, is provided in said drive pulley 13.1 , in radial arrangement, and a plurality of second operating cylinders 14.2 (Fig. 5), controlled by means of pressurized fluid, is provided in said driven pulley 13.2, in radial arrangement.

Each first operating cylinder 14.1 comprises a respective sliding piston 14.3' and a corresponding rod 14.31 , which is movable between a position radially retracted with respect to said drive pulley 13.1 (Fig. 2) and a position radially extended with respect to said drive pulley 13.1 (Fig. 3). The rod 14.31 of each first operating cylinder 14.1 supports at the free end a corresponding first shoe 14.32, cooperating with said flexible member 1 1 .

Each second operating cylinder 14.2 comprises a respective sliding piston 14.4 and a corresponding rod 14.41 , which is movable between a position radially retracted with respect to said driven pulley 13.2 (Fig. 3) and a position radially extended with respect to said driven pulley 13.2 (Fig. 2). The rod 14.41 of each second operating cylinder 14.2 supports at the free end a corresponding second shoe 14.42, cooperating with said flexible member 1 1 . Between each shoe 14.42 and the respective second operating cylinder 14.2 there is interposed a respective elastic means 14.22, for example a compression coil spring, which is elastically loaded when the rod 14.41 is retracted in the same cylinder 14.2.

Said flexible member 1 1 is partially wound on said drive pulley 13.1 and on said driven pulley 13.2, engaging in sequence a plurality of said first shoes 14.32 and a plurality of said second shoes 14.42, and kinematically connects said drive pulley 13.1 and said driven pulley 13.2, transmitting the motion between said drive shaft 12.1 and said driven shaft 12.2.

Said mechanical transmission 10 further comprises a first control operating cylinder 20.1 , operating by means of pressurized fluid, provided stationary and comprising a piston and a corresponding piston rod 20.10, which is kinematically connected with respect to said drive shaft 12.1 and transforms the circular motion of said drive shaft 12.1 into harmonic motion of the respective piston.

A second control operating cylinder 20.2, operating by means of pressurized fluid, is provided stationary and comprises a piston and a corresponding piston rod 20.20, which is kinematically connected with respect to said drive shaft 12.1 and transforms the circular motion of said drive shaft 12.1 into harmonic motion of the respective piston.

The kinematic connection of said drive shaft 12.1 and of the respective piston rods 20.10, 20.20 of said first control operating cylinder 20.1 and of said second control operating cylinder 20.2, respectively, is configured so that the piston of said second control operating cylinder 20.2 operates in counter-phase with respect to the piston of said first control operating cylinder 20.1 . According to the example illustrated in Fig. 1 , said kinematic connection is produced by means of a drive shaft 12.1 with two cranks, 12.10. 12.1 1 respectively connected to the piston rods 20.10, 20.20 of the first control operating cylinder 20.1 and of the second control operating cylinder 20.2. Said two cranks 12.10, 12.1 1 are offset by 180° with respect to the axis of the drive shaft 12.1 . The connection between each crank 12.10, 12.1 1 and the respective piston rod 20.10, 20.20 is of the connecting rod - crank type. Alternative embodiments are possible, for example by means of a cam drive shaft kinematically connected with respect to the piston rods of the control operating cylinders by means of a configuration similar to the tappets of an internal combustion engine.

Said mechanical transmission 10 further comprises a first control fluid circuit 15.1 , operating by means of pressurized fluid, branched in a fluid-tight manner between a passage 20.1 1 of pressurized fluid of said first control operating cylinder 20.1 , a fluid passage 16.1 1 (Fig. 4) of pressurized fluid of a first fluid-tight chamber 16.1 for distribution of pressurized fluid, provided stationary in said drive pulley 13.1 , and fluid tank means 17.1 (Fig. 1 ).

In particular, said drive pulley 13.1 has said first stationary fluid distribution chamber 16.1 provided between a stationary hub part 13.3 and a rotating annular ring part 13.31 , arranged coaxial and in a fluid-tight manner with respect to said hub part 13.3. Said first controlled operating cylinders 14.1 are provided in radial arrangement in said annular ring part 13.31 of said drive pulley 13.1 and are connected sequentially in a fluid-tight manner, at the opposite end to the end from which the respective rod 14.31 extends, with said first fluid distribution chamber 16.1 . Moreover, said first fluid-tight chamber 16.1 is structured as a partial ring and partially surrounds said stationary hub part 13.3, according to a slightly larger angular width with respect to the arc of circumference described (with respect to the axis of the pulley 13.1 ) by the flexible member 1 1 engaged on the corresponding drive pulley 13.1 . Said arc of circumference described by the flexible member 1 1 and said first chamber 16.1 have a mutually corresponding arrangement. A second fluid control circuit 15.2, operating by means of pressurized fluid, is branched in a fluid-tight manner between a passage 20.21 of pressurized fluid of said second control operating cylinder 20.2, a fluid passage 16.21 (Fig. 5) of pressurized fluid of a second fluid-tight chamber for distribution of fluid 16.2 provided stationary in said driven pulley 13.2, and fluid tank means 17.2. (Fig. 1 ). In particular, said driven pulley 13.2 (Figs. 5, 6, 7) has said second stationary fluid distribution chamber 16.2 provided between a stationary hub part 14.3 and a rotating annular ring part 14.30, arranged coaxial and in a fluid-tight manner with respect to said hub part 14.3. Said second operating cylinders 14.2 are provided in radial arrangement in said annular ring part 14.30 of said driven pulley 13.2 and are connected sequentially in a fluid-tight manner, at the opposite end to the end from which the respective rod 14.41 extends, with said second fluid distribution chamber 16.2. Moreover, said second fluid distribution chamber 16.2 is structured as a partial ring and partially surrounds said stationary hub part 14.3, according to a slightly larger angular width with respect to the arc of circumference described (with respect to the axis of the pulley 13.2) by the flexible member 1 1 (not illustrated in Figs. 6, 7) engaged on the corresponding driven pulley 13.2. Said arc of circumference described by the flexible member 1 1 and said second chamber 16.2 have mutually corresponding arrangement.

On the other hand, said first control circuit 15.1 comprises said fluid tank means 17.1 and the following three circuit branches:

- a first circuit branch that allows circulation of pressurized fluid between said tank means 17.1 and said first controlled operating cylinders 14.1 , through said first fluid distribution chamber 16.1 of said drive pulley 13.1 . Said first circuit branch comprises (besides the operative connection means between tank means 17.1 and said first cylinder 20.1 , better described below) stretches of fluid-tight conduit 15.1 1 , 15.12 (Fig. 1 ), respectively extended from the passage 20.1 1 of pressurized fluid of the first cylinder 20.1 to a first valve means V1 , and from these to said passage 16.1 1 of said first chamber 16.1 , wherein the pressurized fluid can flow in the direction of the arrow F1 1 ; - a second circuit branch, wherein the flow of pressurized fluid is intercepted, by means of said first valve means V1 , between the stretches of conduit 15.1 1 and 15.12 and, therefore, between said first fluid distribution chamber 16.1 of said drive pulley 13.1 and said first control operating cylinder 20.1 , preventing backflow of the fluid from said same first chamber 16.1 , so that the rods 14.31 of said first controlled operating cylinders 14.1 are maintained stationary. Said second circuit branch comprises said stretch of fluid-tight conduit 15.1 1 and a further stretch of fluid-tight conduit 15.13 branched between said first valve means V1 and said tank means 17.1 ;

- a third circuit branch between said first controlled operating cylinders 14.1 and said tank means 17.1 , through which branch pressurized fluid can flow back from said first fluid distribution chamber 16.1 of said drive pulley 13.1 into said tank means 17.1 , causing retraction of the corresponding rods 14.31 of said first controlled operating cylinders 14.1 with respect to said drive pulley 13.1 . Said third circuit branch comprises said stretch of fluid-tight conduit 15.12 (Fig. 1 ) and said further stretch of fluid-tight conduit 15.13 branched to said tank means 17.1 from said first valve means V1 , wherein the pressurized fluid can flow in the direction of the arrow F12.

It can be noted that in said first and third circuit branches the passage 16.1 1 of pressurized fluid acts respectively as fluid inlet, when the pressurized fluid flows in the direction of the arrow F1 1 , and as fluid outlet, when the pressurized fluid flows in the direction of the arrow F12.

Said second control circuit 15.2 comprises said fluid tank means 17.2 and the following three circuit branches:

- a first circuit branch between said second controlled operating cylinders

14.2 and said tank means 17.2, through which branch pressurized fluid can flow back from said second fluid distribution chamber 16.2 of said driven pulley 13.2 into said tank means 17.2, causing retraction of the corresponding rods 14.41 of said second controlled operating cylinders 14.2 with respect to said driven pulley 13.2. Said first circuit branch comprises a stretch of fluid-tight conduit 15.22 (Fig. 1 ), extended between said passage 16.21 of said second chamber 16.2 and second valve means V2, and a further stretch of conduit 15.23 branched to said tank means 17.2 from said second valve means V2, wherein the pressurized fluid can flow in the direction of the arrow F21 ; moreover, said first circuit branch comprises a stretch of fluid-tight conduit 15.21 from said fluid passage 20.21 of said second control cylinder 20.2 to said second valve means V2, and said further stretch of conduit 15.23.

- a second circuit branch, wherein the flow of pressurized fluid is intercepted, by means of said second valve means V2, between said stretch of conduit 15.22 and said stretch of conduit 15.21 , preventing backflow of the fluid from said same second chamber 16.2, so that the rods 14.41 of said second controlled operating cylinders 14.2 are maintained stationary. Said second circuit branch comprises said stretch of fluid-tight conduit 15.21 and said further stretch of fluid-tight conduit 15.23, branched between said second valve means V2 and said tank means 17.2;

- a third circuit branch that allows the circulation of pressurized fluid between said tank means 17.2 and said second controlled operating cylinders 14.2 through said second fluid distribution chamber 16.2 of said driven pulley 13.2. Said third circuit branch comprises (besides the operative connection means between said tank means 17.2 and said second cylinder 20.2, described in more detail below) said stretch of fluid-tight conduit 15.21 and said stretch of fluid-tight conduit 15.22 (Fig. 1 ), and wherein the pressurized fluid can flow, through said second valve means V2, in the direction of the arrow F22 (Fig. 1 ).

It can be noted that in said first and third circuit branches the passage 16.21 of pressurized fluid acts respectively as fluid outlet, when the pressurized fluid flows in the direction of the arrow F21 , and as fluid inlet, when the pressurized fluid flows in the direction of the arrow F22.

Said first valve means V1 are configured to selectively allow the pressurized fluid to flow in at least one of said three branches of the first control circuit 15.1 , that is, said first valve means V1 :

- in a first operating arrangement allow the flow of fluid in the direction F1 1 along the first circuit branch 15.1 1 , 15.12 (that is, they operate as check valve according to the direction F1 1 ); - in a second operating arrangement they intercept the flow of fluid between the stretches of circuit 15.1 1 , 15.12 and, moreover, they divert the flow of fluid between the fluid passage 20.1 1 of the first control cylinder 20.1 and said tank means 17.1 along the stretches of circuit 15.1 1 and 15.13; in this second operating arrangement, the first valve means V1 perform the dual function of shut-off valve and of flow diverter valve;

- in a third operating arrangement they divert the flow of fluid from the fluid passage 16.1 1 , in the direction F12, along the stretch of circuit 15.12 and the stretch of circuit 15.13 to said tank means 17.1 , through said first valve means V1 ; moreover, said first valve means V1 divert the flow of fluid from the fluid passage 20.1 1 of the first operating cylinder 20.1 from the stretch of conduit 15.1 1 along the stretch of conduit 15.13 to the tank means 17.1 . In this a third operating arrangement, said first valve means V1 perform the dual function of check valve from the fluid passage 16.1 1 to the tank means 17.1 and of flow diverter valve from the fluid passage 20.1 1 to said tank means 17.1 .

Said second valve means V2 are configured to selectively allow the pressurized fluid to flow in at least one of said three branches of the second control circuit 15.2, that is:

- in a first operating arrangement they divert the flow of fluid from the fluid passage 16.21 in the direction F21 , along the stretch of circuit 15.22 and the stretch of circuit

15.23 to the tank means 17.2, through said same second valve means V2; moreover, said second valve means V2 divert the flow of fluid from the fluid passage 20.21 of the second control operating cylinder 20.2 and from stretch of conduit 15.21 along the stretch of conduit 15.23 to the tank means 17.2. In this first operating arrangement, said second valve means V2 perform the dual function of check valve from the fluid passage 16.2 to the tank means 17.2 and of flow diverter valve from the fluid passage 20.21 of the second cylinder 20.2 to the tank means 17.2;

- in a second operating arrangement they intercept the flow of fluid between the stretches of circuit 15.21 , 15.22 and, moreover, they divert the flow of fluid between the fluid passage 20.21 of the second control cylinder 20.2 and said tank means 17.2 along the stretches of circuit 15.21 and 15.23; in this second circuit arrangement the second valve means V2 perform the dual function of shut-off valve and of flow diverter valve;

- in a third operating arrangement they allow the flow of fluid from the fluid passage 20.21 of the second cylinder 20.2, in the direction F22 along the first circuit branch 15.21 , 15.22 (that is, said second valve means V2 operate, in this case, as check valve according to the direction F22).

On the other hand, said first control operating cylinder 20.1 is provided with a system of distribution valves (known per se, for example from the cylinders of 4- stroke endothermic engines, and not illustrated), wherein intake valve means connect the intake of said first operating cylinder 20.1 with said tank means 17.1 , while discharge valve means connect the discharge of said first operating cylinder

20.1 with said fluid passage 20.1 1 . The timing of the distribution of said first operating cylinder 20.1 is adjusted according to methods known, for example, in 4- stroke endothermic engines, and allow, during the harmonic motion of the respective piston, a step of intake of fluid from said tank means 17.1 to be alternated with a step of discharge of fluid through said fluid passage 20.1 1 .

Likewise, said second control operating cylinder 20.2 is provided with a system of distribution valves (known per se, for example from the cylinders of 4-stroke endothermic engines, and not illustrated), wherein intake valve means connect the intake of said second operating cylinder 20.2 with said tank means 17.2, while discharge valve means connect the discharge of said second operating cylinder

20.2 with said fluid passage 20.21 . The timing of the distribution of said second operating cylinder 20.2 is adjusted according to methods known, for example, in 4- stroke endothermic engines, and allows, during the harmonic motion of the respective piston, a step of intake of fluid from said tank means 17.2 to be alternated with a step of discharge of fluid through said fluid passage 20.21 .

Operation:

A possible condition for start of the operating cycle of the mechanical transmission 10 is illustrated in Fig. 2, wherein the drive pulley 13.1 has a smaller diameter than the diameter of the driven pulley 13.2. The motor M is rotated constantly and with it the drive shaft with two cranks 12.1 . The drive pulley 13.1 starts to rotate at a constant speed, which it will maintain during the whole of the operating cycle, and transmits the rotation motion, by means of the flexible member 1 1 , to the driven pulley 13.2, which will be maintained in rotation for the whole of the operating cycle.

The first control operating cylinder 20.1 , following the reciprocating motion of the respective rod, starts to perform steps of intake of fluid from the tank means 17.1 alternated with steps of discharge of pressurized fluid through the fluid passage 20.1 1 along the stretch of conduit 15.1 1 .

The first control circuit 15.1 is configured, by means of the said first valve means V1 , in its first circuit branch specified above.

The first valve means V1 of the first fluid control circuit 15.1 place said first stretch of conduit 15.1 1 in communication with the further stretch of conduit 15.12 (and prevent diversion toward the stretch of conduit 15.13). The pressurized fluid reaches the fluid passage 16.1 1 of the drive pulley 13.1 and flows into corresponding first distribution chamber 16.1 and, from this, sequentially into the first controlled operating cylinders 14.1 , the rods 14.31 of which gradually extend. The outer diameter of said drive pulley 13.1 increases progressively and the flexible member 1 1 modifies its geometry accordingly.

The second control operating cylinder 20.2 operates simultaneously in counter- phase with respect to the first control operating cylinder 20.1 . Following the reciprocating motion of the respective rod, said second control operating cylinder 20.2 performs steps of intake of pressurized fluid from said second tank means 17.2 alternated with steps of discharge of pressurized fluid through said fluid passage 20.21 .

The second control circuit 15.2 is configured, by means of said second valve means V2, in its first circuit branch described above. The pressurized fluid flows back from the fluid passage 16.21 along the stretch of conduit 15.22 in the direction F21 and, through the second valve means V2, into the tank means 17.2 through the stretch of conduit 15.23. The pressurized fluid exits from the fluid passage 20.21 and flows back through the stretches of conduit 15.21 and 15.23 and through said second valve means V2 into the tank means 17.2.

The modification of the geometry of the flexible member 1 1 due to the increase of the diameter of the drive pulley 13.1 determines a corresponding and reverse reduction of the outer diameter of the driven pulley 13.2, wherein the pistons of the second controlled operating cylinders 14.2 are no longer urged by pressurized fluid. Therefore, the pressurized fluid is evacuated from the second distribution chamber 16.2, through the fluid passage 16.21 , of the driven pulley 13.2 and the same fluid also flows out of the second controlled operating cylinders 14.2, the rods 14.42 of which gradually retract with respect to said driven pulley 13.2, while pressurized fluid flows into the tank means 17.2.

It can be noted that, as the rods 14.41 of the second controlled operating cylinders 14.2 gradually retract into the respective cylinders, the elastic means 14.22 are correspondingly elastically loaded.

When the opposing elastic force applied by said elastic means 14.22 to the flexible member 1 1 by means of the shoes 14.42 increases, there is a proportional increase in the resistance to extension of the rods 14.31 of the first controlled operating cylinders 14.1 of the drive pulley 13.1 and, therefore, also of the pressure of the fluid circulating in said first circuit branch of the first control circuit 15.1 . First gauge means M1 , branched on the stretch of conduit 15.12 of said first circuit 15.1 , detect the pressure value of the circulating fluid.

Therefore, the condition illustrated in Fig. 3 is, for example, reached, wherein drive pulley 13.1 and driven pulley 13.2 have substantially the same diameter and both pulleys 13.1 and 13.2 are rotated continuously at a same constant speed by means of the motor M and the drive shaft 12.1 .

On the other hand, it is possible to adjust the tensioning and the elastic elongation coefficients of the flexible member 1 1 to allow the outer diameter of the driven pulley 13.2 to become smaller than the outer diameter of the drive pulley 13.1 , so as to automatically produce transmission ratios that differ from the ratio 1 :1 illustrated in said Fig. 3. In particular, as shown in Fig. 8, it is possible to omit the means for automatic elastic return to the extended position of the rods 14.41 of the pistons of the second controlled operating cylinders 14.2 of the driven pulley 13.2, so as to control extension and retraction of the same rods by means of pressurized fluid alone.

When rotation of the motor M stops, said first valve means V1 are controlled (by means known per se and not illustrated) to take an operating position corresponding to said third circuit arrangement of said first control circuit 15.1 .

In this condition, the first valve means V1 are switched to the operating arrangement, in which they divert the flow of fluid according to the direction F12 between the stretches of conduit 15.12 and 15.13 and from this latter toward the tank means 17.1 . The rods of the pistons 14.31 of the first operating cylinders 14.1 retract automatically inside the same cylinders, gradually as the elastic means 14.22 urge extension of the rods of the pistons 14.41 of the second operating cylinders 14.2, until the mechanical transmission 10 returns to the starting position illustrated in Fig. 2.

It is evident to those skilled in the art that numerous other operating configurations of the continuously variable mechanical transmission by means of at least one flexible member according to the present invention are possible and are not described herein for simplicity of illustration.

As can be seen from the above, with the present invention it is possible to achieve the objects indicated in the introductory part in a simple and effective manner.

In particular, the present invention provides a continuously variable mechanical transmission by means of at least one flexible member and comprising a drive pulley and a driven pulley, which allows the diameter of said pulleys to be varied in a continuous and mutually correlated manner automatically, as the at least one flexible member is always in contact with said pulleys.

Moreover, the present invention provides a mechanical transmission of the type specified, which is structurally simple, has limited overall dimensions, operates safely and allows automatic correlation of variations of the diameters of the pulleys.