DESCRIPTION

Technical Field

The present invention relates to a mechanical speed variator for large inertial flywheels.

More particularly, the present invention relates to a mechanical variator for controlling the angular speed of large inertial flywheels used as kinetic energy accumulators.

Prior Art

A wide variety of mechanical speed variators of different types are known to the state of the art: in the course of time numerous devices for applications on apparatus and machines in all sorts of technical fields have been devised and realized.

With the recent developments of electronics and of inverter technologies, controlled variation of the angular speed of the shaft of electrical motors has to a large extent supplanted several devices of the mechanical type. In addition, the improvement of hydraulic components has provided variators with continuous control between drive shaft and driven shaft. The use of large inertial flywheel as kinetic energy accumulators is known and of increasingly growing interest.

In the specific application of mechanical speed variators to large inertial flywheels for a strictly controlled acceleration and deceleration in kinetic energy accumulators, specific problems arise in terms of low energy dissipation (performance demands of over 95 %) and precision of the instantaneous control of angular speed, with the power of the variators to be installed ranging in the order of hundreds of kW. In such application specific solutions are also required in order to achieve high reliability, low noise and low maintenance.

Despite the wide range of mechanical speed variators available on the market, said variators of known type do not appear to be able to meet all the specifications outlined above.

The main object of the present invention is to overcome the limitations of prior art by providing a mechanical speed variator suitable for being applied to large inertial flywheels.

More particularly, the main object of the present invention is to provide a mechanical speed variator capable of yielding high performances in terms of efficiency, precision and reliability.

This and other objects are achieved by the mechanical speed variator as claimed in the appended claims.

Summary of the Invention

The mechanical speed variator comprises a shaft and a bell-shaped element mounted externally on a middle portion of said shaft.

Said middle portion in the longitudinal direction is conical and widens from a minimum radius to a maximum radius; when seen in cross- section, it has a suitably contoured cam profile comprising a pair of lobes substantially identical and diametrically opposite to each other.

The mechanical variator according to the invention further comprises actuating means for varying the axial position of said shaft and, in particular, of its middle portion.

Thanks to the specific geometric configuration of the shaft middle portion on which said bell-shaped element is mounted and to the presence of means for varying the axial position, with the same rotational speed of the shaft it is possible to continuously vary the rotational speed of the outer bell-shaped element.

In a preferred embodiment of the invention, the means for varying the axial position of said shaft are controlled by a controller, preferably by means of a PLC device (Programmable Logic Controller) .

Brief Description of the Drawings

Further features and advantages of the present invention will be more apparent from a detailed description of a preferred embodiment, given by way of non-limiting example, with reference to the annexed drawings, in which:

Figure 1 is a schematic view of a mechanical speed variator according to the invention;

Figure 1A is a cross-sectional view taken along line A-A of the variator of Figure 1; Figure IB is an enlarged view of detail B of the variator of Figure 1, shown in cross-section;

Figure 2 is a cross-sectional view of the portion C of the mechanical variator of Figure 1 ;

Figure 2A is an enlarged sectional view along the line K-K of detail D of Figure 2;

Figures 3A and 3B are an enlarged front view and an enlarged cross- sectional view of the detail E of Figure 2, respectively;

Figures 4A and 4B are an enlarged front view and an enlarged cross- sectional view of the detail F of Figure 2, respectively;

Figure 5 is a diagram showing the transmission ratios between the components of the mechanical variator of Figure 1 , and more particularly between the central shaft and the bell-shaped element of said variator. Description of Preferred Embodiments of the Invention

Referring to Figure 1, the kinematic mechanism as a whole is schematically illustrated.

A main motor 1 rotates at the angular speed co _m and, via a coupling 2, transmits the rotation to a hub 3, on which a central shaft 9 slides axially (along the axis XO - XO in Figure 1), arranged longitudinally aligned with respect to the shaft of the motor 1 (i.e. along the axis XO - XO in Figure 1). At the opposite end, the shaft 9 is connected to a sleeve 7, which is free to rotate thereon. By controlling an actuator 8 integral with a fixed base 6, said sleeve 7 can be translated along the longitudinal axis XO - XO. A support 5 is rigidly fixed on the base 6.

Figures 1A and IB illustrate in greater detail the connection of the end of the shaft 9 to the hub 3 and to the sleeve 7, respectively.

The shaft 9 is free to slide on both ends and in both directions.

Between said ends, said shaft includes a middle portion 9' which is conical in the longitudinal direction and, when seen in cross-section, has a suitably contoured cam profile. In particular, in the longitudinal direction said middle portion 9' of said shaft 9 has a conical shape that widens from a minimum radius r _m i _n (on the side facing the motor 1) to a maximum radius r _max (on the side opposite to the motor 1); when seen in cross-section, said middle portion 9' of said shaft 9 has a cam profile with two lobes that are substantially identical and diametrically opposite to each other.

On the middle portion 9' of the shaft 9 there is mounted an outer bell- shaped element 4, which is free to rotate at the angular velocity O _c variable depending on the axial arrangement of said middle portion 9' of said shaft 9: by acting on the actuator 8 so as to vary (through the sleeve 7) the axial sliding of the shaft 9 - and therefore of its central portion 9' - continuously variable values are obtained for the rotational speed O _c of the bell-shaped element 4.

The variator according to the invention is therefore able to effect a continuous variation of the angular speed of the bell-shaped element 4 depending on the instantaneous position of the shaft 9, and in particular of its central portion 9', in the longitudinal direction.

Figures 2, 2A, 3A, 3B, 4A, 4B illustrate in greater detail the components of the mechanical speed variator schematically shown in Figure 1.

The fixed base 6 is coupled to the support 5 by means of threaded studs 15.

A plurality of secondary shafts 14 are rotatably mounted within the fixed support 5.

The rotation axes of said secondary shafts 14 are arranged along a circumference about the axis of the central shaft 9 and are equidistant from one another in the circumferential direction. Said secondary shafts can be provided in a number comprised between 4 and 6. In the embodiment illustrated in the Figures, four secondary shafts 14 are provided, arranged at 90° relative to one another on a circumference about the axis of the central shaft 9.

The secondary shafts 14 are rotatably mounted in the support 5 through the interposition of bearings 13 mounted in respective seats 12 formed in the body of said support 5.

On each secondary shaft 14 there is fitted a toothed wheel 21 (see in particular Figures 4A and 4B), which meshes internally (i.e. towards the axis of the central shaft 9) with the fixed support 5 and externally with a rotatable toothed ring gear 20.

The rotatable toothed ring gear 20 is rigidly connected to an outer flange 22, and said rotatable toothed ring gear 20 and said outer flange 22 together form the outer wall of the bell-shaped element 4 of Figure 1.

With particular reference to Figures 2A , 3A and 3B, the end of each secondary shaft 14 facing towards the end with smaller radius of the middle portion 9' of the central shaft 9 is inserted in a corresponding seat suitably formed in a rocker arm 1 1 with the interposition of a one-way bearing 25, which allows to transmit motion between said rocker arm 1 1 and a roller 28.

The roller 28 can rotate through the interposition of a bearing 24 on a pin 27. In addition, the roller 28 is mounted on a spherical seat, so that it can oscillate through an angle ± β in the direction perpendicular to the axis of the pin 27 on which it is mounted.

The roller 28 rests against the surface of the middle portion 9' of the central shaft 9 and thanks to its design the track of said roller 28 can constantly adapt to the mating track of the cam profile of said middle portion 9' of said central shaft 9, throughout the whole axial translation between the two extreme positions of said middle portion 9' of said central shaft 9.

The rocker arm 1 1 is advantageously provided with an adjustable counterweight 10, thanks to which it is perfectly balanced with respect to the rotation axis XI - XI of the respective secondary shaft 14, thus forming a perfectly balanced system.

A central rotation of the shaft 9 and of its middle portion 9' corresponds to an oscillation a of the rocker arm 1 1.

Figure 2A shows that for a portion of the oscillation of the rocker arm 1 1 , corresponding to a certain amplitude a _sen d, a transmission of the rotary motion to the secondary shaft 14 is established, while in the remaining portion with an amplitude af _ree there is no transmission of rotary motion from said rocker arm to said secondary shaft.

Since from 4 to 6 secondary shafts 14, and consequently from 4 to 6 corresponding rocker arms 1 1, are provided on the fixed support 5, at least two of said rocker arms will always be in a transmission connection with the toothed ring gear 20 via the respective toothed wheel 21.

Figure 5 shows a diagram illustrating the transmission ratios between the components of the previously described mechanical variator, and in particular it shows the scheme of motion transmission between the central shaft and the bell-shaped element of said variator.

As mentioned above, the central shaft 9 - maintained in rotation at the angular speed co _m by the motor 1 - has, in its middle portion 9', a cross- section with a cam profile comprising two lobes substantially equal and diametrically opposite to each other.

The surface of the middle portion 9' of the central shaft 9 is constantly in contact and in motion-transmitting relation with the tracks of the four rollers 28, which in turn transmit the motion to the four rocker arms 1 1. A rotation of the central shaft 9 corresponds to an oscillation of each rocker arm 1 1. By virtue of the one-way bearing 25, said oscillation comprises a first portion over an angle a _sen d along which the motion is transmitted to the respective secondary shaft 14 and a second portion over an angle af _ree along which the motion is not transmitted to said secondary shaft 14. At any time, at least two out of the four rocker arms 1 1 transmit the motion to the respective secondary shafts 14 and from these to the toothed wheels 21 fitted thereon.

By means of the toothed wheels 21 the motion is transmitted to the toothed ring gear 20 which (together with the flange 22) forms the outer wall of the bell-shaped element 4.

Thanks to the particular geometric configuration of the middle portion 9' of the shaft 9, the transmission ratio is continuously variable according to the axial position of said middle portion 9' of said shaft 9. Consequently, for the same angular speed co _m of the motor, the angular speed Q _c of the bell-shaped element 4 will vary in a continuous manner.

A kinematic mechanism made according to the teachings of the present invention and with oil-mist lubrication is extremely silent and very compact, and is also able to transmit powers in the order of hundreds of kW between the shaft 9 and the bell-shaped element 4. In addition, a kinematic mechanism made according to the teachings of the present invention has yields of over 90% with absolute reliability even for such high power levels.

For all the above reasons, the mechanical speed variator according to the invention effectively lends itself to applications in large inertia flywheels used as kinetic energy accumulators.

The operation of the mechanical speed variator according to the invention in such application is summarized as follows.

An arrangement of sensors constantly detects the speed of the output shaft on which the flywheels are fitted.

In the phase of speed increase (charge phase), a controller, such as a PLC (Programmable Logic Controller) device, acts upon the actuator 8 for axially moving the shaft 9 and bringing it to the axial position corresponding to the proper transmission ratio between the rotational speed of the main motor (which is constant and for example equal to 1500 rpm) and the rotational speed of the flywheel.

When the inertial flywheel has reached the maximum speed allowed for it (end of the charge phase), the variator shifts to a deactivation/ stand-by position.

In the subsequent discharge phase, in which the flywheel is connected to the alternator shaft, the PLC controller controls the movements and the position of the shaft 9 in such a way that the alternator revolutions are constant (for example 1500 rpm per minute) and the transmission ratio varies continuously as the flywheel decreases its rotational speed, transmitting its kinetic energy to the alternator.

Therefore, thanks to the mechanical speed variator according to the invention it is possible to employ electric motors and alternators of current use in commerce for use in kinetic energy storage systems by means of large inertial flywheels, achieving constructive and operational simplicity with significant economic advantages.

From what has been described above it will be immediately apparent to the person skilled in the art that the invention achieves the object set forth above. In fact, the typical operating characteristics of the mechanical speed variator according to the invention are not obtainable with other mechanical speed variators currently available on the market; in particular, its high performance, low maintenance and high transmission power make it particularly effective in applications in systems for accumulating kinetic energy with large inertial flywheels.

It will also be evident to the person skilled of the art that the detailed description provided above has been given by way of non-limiting example and that numerous modifications and variations are possible without departing from the scope of protection defined in the accompanying claims.