This invention relates to a variable-speed drive with torque conversion, of synergically integrated electromechanical type.

Mechanical variable-speed drives with torque conversion are known, connected between the exit of a heat engine and an external user.

A known mechanical variable-speed drive is represented by a manual or automatic transmission, which enables only stepped speed variations to be achieved, provides only a limited number of ratios, is of considerable constructional complexity and is of low efficiency.

Mechanical variable-speed drives of pulley type are also known, based essentially on the principle of varying the transmission ratio by varying the diameter of the pulleys, which are connected together by a belt.

There are currently no variable-speed drives with torque conversion which are able to integrate the mechanical energy with the electrical energy in relation of the changing conditions of use.

The main object of the present invention is to provide a variable-speed drive with torque conversion which is able to

effect synergic integration between the mechanical energy produced by a heat engine and the mechanical energy produced by an electric motor.

A further object of the invention is to provide an electromechanical variable-speed drive applicable to a motor vehicle to enable it to be used with mechanical, electrical or mixed traction at choice.

A further object of the invention is to provide an electromechanical variable-speed drive with rotational speed infinitely variable from 0 to maximum value.

A further object of the invention is to provide an infinitely variable electromechanical variable-speed drive of high efficiency.

A further object of the invention is to provide an infinitely variable electromechanical variable-speed drive which enables a heat engine operating at constant speed to be used.

A further object of the invention is to provide an electromechanical variable-speed drive which can be coupled to an external user of mechanical energy, such as a motor vehicle, without the need for a friction clutch.

All these objects and further ones are attained, according to the invention, through a variable-speed drive

with torque conversion, of synergically integrated electromechanical type as described in claim 1.

A preferred embodiment of the present invention is described in detail hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a schematic block diagram of the variable-speed drive with torque conversion according to the invention; Figure 2 shows schematically it applied to a two-wheel drive vehicle; and

Figure 3 shows it applied to a four-wheel drive vehicle.

As can be seen from the figures, the variable-speed drive with torque conversion according to the invention comprises a heat engine 2, which can be an internal combustion engine or a turbine.

The exit shaft of said heat engine 2 is directly coupled to the drive shaft of a differential 4, for example of epicyclic type, having one driven shaft coupled to the rotor of an electric generator 6 and the other driven shaft coupled to the rotor of an electric motor 8, the stator of which is powered by the electric generator 6.

From the same rotor of the electric motor 8 there is derived a power take-off for the external user, which can be

for example the transmission shaft 10 of a motor vehicle.

The invention also comprises an electronic control unit 12 arranged to perform a plurality of functions, such as controlling the energization of the electric generator 6 ^' on the basis of the rotational speed of the heat engine 2 and/or the required power, controlling the feed of electric power produced by the generator 6 to the motor 8 and/or batteries 14, and controlling the feed of electric power from the batteries 14 to the motor 8 and from the motor 8 to the batteries 14.

The variable-speed drive with torque conversion according to the invention operates as follows: it will be assumed initially that the control unit 12 is set so as not to provide energization current to the generator 6 for rotational speeds of the heat engine 2 below a predetermined threshold value V _Q and that a load, for example the vehicle transmission shaft 10, is applied to the rotor of the electric motor 8.

Consequently while said engine 2 rotates at a speed less than V _Q , the mechanical energy generated by the engine 2 is totally transmitted to the rotor of the generator 6, which rotates idly.

If the rotational speed of the engine 2 is now increased

to a value exceeding V _Q , for example by operating the accelerator, or if the intervention threshold for energization of the electric generator 6 is reduced by operating a suitable control on the control unit 12, this latter causes an energization current to be fed from the batteries 14 to the generator 6, which begins to generate electrical energy with the result that on the one hand the electric motor 8 is powered and on the other hand a counter- electromotive force is generated in the generator 6 tending to brake the driven shaft coupled to said generator and to hence deviate towards the electric motor 8 a part of the

« mechanical energy received from the heat engine 2.

Both these results cause the motor 8 to rotate, and as the control unit 12 provides the generator 6 with an energization current which is greater the greater the difference between the effective speed V _e of the engine and the threshold speed V _Q , it is apparent that on increasing the speed V _e the counter-electromotive force developed in the generator increases progressively, to cause progressive slowing down of that driven shaft of the differential 4 coupled to said generator 6, and a corresponding progressive speed and torque increase of the rotor of the electric motor 8 and hence of the vehicle transmission shaft 10 connected to

it.

Control of the energization can take place for a marked difference between V _Q and V _e or for a difference which tends to zero or which is zero. If when the rotor of the generator 6 attains a predetermined minimum speed it is caused to undergo total stoppage, for example by a brake 16 controlled by the control unit 12, there is direct mechanical coupling between the exit shaft of the heat engine 2 and the transmission shaft 10 coupled to the rotor of the electric motor 8.

As stated, the brake 16 is controlled by the control unit 12 and is preferably activated when the speed of the engine 2 exceeds the value corresponding to maximum energization, and deactivated when said speed falls below the threshold value V _Q .

It should be noted that a part of the electrical energy generated by the generator 6 can be used under the control of the control unit 12 to charge the batteries 14, the electrical energy generated by the electric motor 8 when operating as a brake during deceleration also being usable to charge the batteries 14, which can in any event be completely recharged from the electricity mains when idle.

The batteries can also be used, on request, to provide

supplementary electrical energy to the motor 8 to hence obtain greater mechanical energy in those moments when it is particularly required.

With the vehicle at rest the electrical generator 6 can also be powered by the batteries 14 via the control unit 12 so that it runs as a motor, to be advantageously used as the starter motor for the heat engine 2. The heat engine 2 can also be started by the electric motor 8 while the vehicle is running, on blocking the generator 6. As stated, the output shaft of the electric motor 8, ie its rotor shaft, can be coupled to the transmission shaft 10 of a motor vehicle, to drive in this manner the two live axles 20 of the drive wheels 22 via a differential 18.

If the particular application of the motor vehicle requires the use of a self-locking differential, instead of using this latter a normal differential 18 can be used directly coupled to the differential 4 plus two electric motors 24 applied to the two driven shafts of said differential 18, these forming the two live axles 20 of the vehicle (see Figure 2) . In this case both the motors are powered by the generator 6 via the control unit 12, which feeds electrical energy mainly to the motor 24 applied to that live axle 20 which rotates more slowly and/or possibly

brakes the motor 24 applied to the faster-rotating live shaft 20.

In the case of a vehicle with four-wheel drive, that driven shaft of the differential 4 not connected to the electric generator 6 is connected to the drive shaft of a differential 26, the driven shafts of which form the two drive shafts of two differentials 18 for the two pairs of drive wheels 22. An electric motor 24, powered by the generator 6 via the control unit 12 is applied to each of the two live axles 20 of both differentials 18 (see Figure 3) .

Regardless of the particular application of the variable-speed drive according to the invention it is especially advantageous, and in particular:

- it effects total integration between the heat engine 2 and the electric motor 8, to allow the formation of hybrid vehicles, ie of electrical, mechanical or mixed traction at choice,

- it enables the speed of the exit shaft to be varied infinitely from 0 to maximum value corresponding to direct connection,

- it can be used as an electric motor, by merely requiring possible recharging of the batteries 14, which in any event are always maintained in a charged condition during

operation. If the electric motor is powered so that it reverses its direction of rotation, reversing in the case of application to a vehicle becomes very simple, without the need for any mechanical intervention, - it provides mechanical energy at variable rotational speed while using a heat engine 2 provided for constant speed operation, and hence with high efficiensy and low harmful emission. If a turbine is used instead of an internal combustion engine, the efficiency iε even higher; in this case the control unit 12 can start and stop the turbine periodically on the basis of the battery charge conditions,

- it enables soft coupling between the heat engine 2 and the user to be achieved without requiring the use of a friction clutch, - it excludes the possibility of "runway" of the heat engine 2,

- it enables partial or total automatic control of the variable-speed drive to be achieved by suitably programming the control unit 12.