Endothermic reciprocating engines with spark ignition, among them also the turbo-compressed engines, are fed obtaining an air-fuel mixture upstream of the combustion chamber.

Said air-fuel mixture is usually obtained taking the fuel from a tank by means of a suitable electro-pump and conveying it to an injector. Said injector injects the fuel nebulizing it inside the intake duct wherein the air flows.

Through the intake duct the air-fuel mixture is then conveyed to the combustion chamber Such an injection method is called Single Point Injection (SPI), while it is also known another injection method, i. e. the Multi Point Injection (MPI), which provides for an injector in each one of the cylinders, located near the inlet of the cylinder.

The SPI and MPI injection methods employ electric injectors with electromagnetic control, consisting of a needle sliding inside a body where the fuel flows. The needle id provided at its end with a shutter, whose movement allows a greater or smaller quantity of fuel to flow out from a nozzle. The control is electromagnetic, so that the needle is provided on its middle with a magnetic keeper, while inside the injector body a suitable coil is located for magnetically controlling the needle, according to the known pattern of a solenoid valve.

Also injectors are known which, instead of the magnetic control, employ piezoelectric means for opening the electric valve.

The known injectors, being located sideways of the intake duct, do not allow an optimal mixing of the fuel with the air flowing in the duct. Moreover such injectors often produce a nebulization of the fuel in drops, which is not sufficient for an optimal combustion. In fact, if the size of the fuel drop injected in the air is greater than a determined value, it may happen that a part of the drop is not burnt, so impairing the engine efficiency. Such injectors also

show the high inertia typical of the electromechanical systems, so that the injecting frequency is limited to a few hundreds of Hz, resulting in a not so flexible injection control.

Furthermore such injectors work with an injection pressure of a few bars, so that the fuel is always under pressure, with evident risks in case of breakage of the fuel ducts, for instance due to an accident, so requiring the additional presence of inertial breakers in the fuel feeding circuit.

The present invention has the aim of avoiding the above cited disadvantages and of indicating a fuel injector device for internal combustion engines, having an improved and more efficient structure in respect of the known solutions.

In particular, the main aim of the present invention is that of indicating a fuel injector device for internal combustion engines and/or a fuel injection method for internal combustion engines, which allow for obtaining the micronization of the fuel at the moment of the creation of the feeding air-fuel mixture.

A further aim of the present invention is that of indicating a fuel injector device for internal combustion engines and/or a fuel injection method for internal combustion engines which allow for a uniform mixing of the fuel and the air.

A further aim of the present invention is that of indicating a fuel injector device for internal combustion engines and/or a fuel injection method for internal combustion engines which allow for the use of fuel substantially at low pressure.

A further aim of the present invention is that of indicating a fuel injector device for internal combustion engines and/or a fuel injection method for internal combustion engines which allow for the control and the variation of the size of the injecte fuel drops.

For reaching the above indicated aims, the subject of the present invention is a fuel injector device for internal combustion engines and/or a fuel injection method for internal combustion engines having the characteristics of the attached claims, which are an integral part of the present description.

Further aims, characteristics and advantages of the present invention will be clear from the following detailed description and the attached drawings, which are given as an explanatory and not limiting example only, wherein: -fig. 1 shows the basic schematic diagram of a fuel injection system for internal combustion engines according to the invention;

-fig. 2 shows the basic schematic diagram of a fuel injection device for internal combustion engines according to the invention; -fig. 3 shows a perspective view of a detail of the fuel injection device for internal combustion engines according to fig. 1; -fig. 4 shows the basic schematic diagram of a part of the fuel injection system for internal combustion engines according to fig. 1.

In fig. 1 there is shown the basic schematic diagram of a fuel injection system 1 according to the invention. There is shown an intake duct 2, collecting the air necessary for the combustion mixture from the not shown air inlets of the motor vehicle. In the intake duct 2 there is provided a filter 3 for the air, and downstream in respect of the filter there is located a butterfly body 4, comprising a butterfly valve 5.

Downstream in respect of the butterfly body 4 there is located an air"plenum"6, from which departs a plurality of intake ducts 7, ending in a not shown cylinders head. The above said elements are all known and will not be described in detail.

There is also provided a fuel tank 9, from which departs a hydraulic fuel conveying circuit 10, indicated by a thicker line. Said hydraulic fuel conveying circuit 10 is operated by means of a fuel pump 11, and downstream in respect of the pump there is located a fuel filter 12. This arrangement of elements is in itself known too.

Downstream in respect of the fuel filter 12, the hydraulic fuel conveying circuit 10 comprises a dosing device 13. Inside the intake duct 2 there is located an injector device 14. Said injector device 14 has a streamlined housing 15, which is hold up by proper supports 19, so that the housing 15 is axially arranged in respect of the intake duct 2. On the circumference of the housing 15 there are provided a number of slots 20. The hydraulic fuel conveying circuit 10 continues beyond the dosing device 13 and reaches inside the housing 15, thanks to one of the supports 19, which is hollow and has the shape of a pipe.

There is further provided an electronic control unit 16, which also is known in itself, and is provided with electrical connections 17 to the injector device 14, located inside the intake duct 2. The electronic control unit 16 in turn receives a signal about the position of the butterfly valve 5 through an electrical connection 18.

In fig. 2 there is shown the basic schematic diagram of a fuel injection device 14 according to the invention.

Said injection device 14, as said, is constituted by the housing 15, having a typical streamlined shape, the function of which is to define, together with the walls of the intake duct 2, a conduit having the profile of a Venturi tube. We can observe that one of the supports 19 continues inside the conduit and connects to an axial duct 22, which ideally ends the hydraulic fuel conveying circuit 10.

Said axial duct 22 acts also as a support for a number of piezo-injectors 23, located in correspondence with the slots 20. In fig. 2 two of them are shown. Each piezo-injector 23 is substantially constituted by: -a piezoelectric disk 24, which in turn is composed by a vibrating disk 25, carrying on its surface a piezoelectric ring 26, made of piezoelectric material; -a dosing disk 28, provided on its circumference with a raised rim 29.

The side of the dosing disk 28 with the raised rim 29 and the side of the piezoelectric disk 24 without the piezoelectric ring 26 are placed one on the top of the other, so that between the dosing disk 28 and the piezoelectric disk 24 there is left a substantially cylindrical chamber 30.

The axial duct 22 is provided with a number of holes 31 in correspondence with every chamber 30, in order to allow for the coming out of the fuel into the hydraulic fuel conveying circuit 10.

The piezoelectric disk 24 acts according to the known concept of the"traveling wave" piezoelectric motors. Referring now to fig. 3, the vibrating disk 25 receives the vibrations transmitted by the piezoelectric ring 26. In said piezoelectric ring 26 a traveling wave 33 is generated by superimposing two steady state waves with a phase difference of 90°. In this way a wave is generated, which runs along the circumference of the piezoelectric ring 26 and, consequently, induces a vibration along the circumference of the vibrating disk 25. By means of the piezoelectric ring 26, the two steady state waves are used applying different polarizations, e. g. applying two voltage signals having a phase difference of 90°. The direction of movement of the traveling wave 33 can be reversed by changing by 180° the phase of one of the two voltage signals.

During the propagation of the traveling wave 33 the points of the surface of the vibrating disk 25 follow an elliptic route, resulting in crests and loops on the surface of the vibrating disk 25

inside the chamber 30, as shown in fig. 3, where a perspective view of the piezo-injector 23 is depicted.

As the dosing disk 28 is fix and cannot revolve, on the contrary of the case of the traveling wave motors, where it constitutes the rotor, the twisting of the vibrating disk, which runs along the circumference, tends to move the vibrating disk 25 away from the raised rim 29, so creating nozzles 34, which let the drops of fuel spill along the circumference of the dosing disk 28.

Th injector device 14 works therefore in the following way: the fuel is conveyed, by means of the pump 11, into the fuel conveying circuit 10. The dosing device 13 feeds the injector device 14 with the necessary fuel amount, plus a light overpressure, due to the hydrostatic pressure of the fuel contained in the section of the fuel conveying circuit 10 comprised between the dosing device 13 and the axial duct 22.

But in the intake duct 2, in correspondence with the slots 20, where the housing 15 defines the gorge of the Venturi tube, there takes place a pressure drop.

Also the piezo-injector 23, due to the effect of the travelling wave, generates a spill, which moves along the circumference. The combined effect of the overpressure inside the fuel conveying circuit 10 and the pressure drop due to the housing 15, has the effect of micronizing the fuel drops of the spill and move them quickly away from the raised rim 29, so improving their mixing with the air.

The electronic control unit 16 receives information about the position of the butterfly valve 5 through the connection 18, so that it can conveniently control the rotation frequency of the travelling waves of the injector device 14. In this way, at any rotation speed of the engine, an optimal feeding is guaranteed, as the fuel consumption is concerned, as well as the compliance with the anti-pollution rules.

The electronic control unit 16 has moreover the possibility of modulating the intensity of the voltages to be sent to the piezo-injector 23. In this way the amplitude of the travelling wave and, consequently, the distance between the vibrating disk 25 and the dosing disk 28, is changed, and also the size of the fuel drops.

Hence, the injector device 14 makes use an hermetic chamber, chamber 30, where the fuel arrives with a slightly higher pressure than the room pressure. And this for the cooperating effects of the fluid pressure in the section downstream of the dosing device 13, and the

pressure drop due to the housing 15 profile in correspondence with the piezo-injectors 23.

Chamber 30 is constituted by a first element, the piezoelectric disk 24, and a second one, the dosing disk 28. The action of the piezoelectric ring 26 creates a controlled detachment (a few pm) of the piezoelectric 24 from the dosing disk, so defining a nozzle wherethrough the fuel spills into the intake duct 2, under the action of the slight pressure established inside the chamber 30. The effect of the travelling wave is therefore so that such nozzle or orifice is moving around the disk circumference, defining an injection point which is moving in time, apt to make the injection more uniform and controlling it by means the frequency and the amplitude of the voltage signals.

In fig. 4 there is shown the dosing device 13, which receives in input the hydraulic fuel conveying circuit 10 and delivers in output, through an outlet duct 38, the fuel to the injector device 14. Inside the dosing device 13 there is located a float 39, provided on the top with a pin shutter 40. The fuel, pushed by the fuel pump 11, goes into the dosing device 13 and flows through the outlet duct 38 towards the injector device 14. When the fuel level inside the dosing device 13 is such that the pin shutter 40 on the float 39 closes the fuel conveying circuit 10, the fuel feeding is interrupted. The fuel feeds the injector device 14, due to the gravity, until the fuel level decreases and the pin shutter opens again the fuel conveying circuit 10.

The dosing device 13 may however be avoided, sizing the fuel conveying circuit 10 in the way that it is a closed circuit, namely by means of a return line to the tank, so assuring a constant fuel pressure in the chamber 30. The same effect can be achieved by pressing the vibrating disk 25 onto the dosing disk 28 with a tightening force being compatible with the described operation of the system.

The injector device 14, shown in fig. 4, is provided with two piezo-injectors 23, fastened and kept in place by suitable tightening nuts 32. Of course the number of piezo-injectors 23 located in the axial duct 22 may also be greater. Furthermore the control unit 16 can control said piezo-injectors in a different way, in order to optimize the fuel injection. For instance, assuming that there are provided three piezo-injectors 23, they can be driven by means of signals which are shifted in phase of 120° each other, so that the corresponding travelling waves in the relevant three chambers 30 are consequently delayed in phase and generate a uniform distribution of the fuel, avoiding any interference.

From the given description the characteristics of the present invention as well as the relevant advantages thereof are clear.

The fuel injector device for internal combustion engines according to the invention allows for nebulizing the fuel directly inside the air intake duct, favoring the micronization and the mixing, so improving the performance of the engine. Advantageously also the fuel is distributed around all the circumference of the piezo-injector, so improving the uniformity of the injection and the quality of the mixture.

Moreover, the fuel injector device for internal combustion engines advantageously allows for an easy and efficient fuel dosing, also controlling both the rotation frequency of the travelling wave, through the frequency of the voltage signals, and the drop size through the amplitude of such signals.

Moreover the fuel injector device for internal combustion engines according to the invention allows for a low operation pressure in the fueling intake circuit from the tank to the injector device. The pressure needed at the fuel pump is of about 1 bar, so that also a simple and cheap membrane pump can be used, directly driven from the engine, or even, in the case of a favorable lay out of the hydraulic circuit, a pump may be dispensed with, taking advantage of the hydrostatic pressure.

The use of a low pressure additionally involves clear advantages in the design of the hydraulic fueling circuit. For instance it may allow for avoiding the necessity of an inertial breaker in order to stop the fuel flow in the case of an accident, because a pressure of 4-6 bar is no more present, to push the fuel out of a broken duct, independent from the engine operation.

It is clear that several variations are possible, for the man skilled in the art, to the fuel injector device and/or the injection method for internal combustion engines described by way of example, without leaving the novelty principles of the inventive idea, as well as it is also clear that, in a practical implementation, the shapes of the shown details may be different and the same may be replaced by technically equivalent elements.

The piezoelectric actuator shall not necessarily be ring shaped.

It is also clear that a suitable composition of vibration movement induced in the vibrating disk can lead to the simultaneous appearance of a number of travelling waves, yielding a number of contemporary orifices.

In a possible variant, the piezoelectric actuators that generate a travelling wave can be replaced by a matrix of piezoelectric actuators, arranged on a circumference, which, activated one after the other, generate a sequence of local spacing between the vibrating disk and the dosing disk, according to the movement of the travelling wave. Said variant has the advantage that it involves a not so substantial rubbing of the two disks and therefore less wear.

It shall be possible, taking advantage of the presence of a greater number of piezoelectric actuators, namely of available chambers, to associate to each piezoelectric actuator a different fuel, in the case of engines using more than one type of fuel. For instance one of the piezoelectric injectors can inject oil. It shall also be possible to assign to one or more of the piezoelectric injectors the injection of real gas, or of fuel additives. Moreover the piezoelectric injectors shall also inject other materials, like finely ground powders, for instance powdered coal.

Therefore the invention is also applicable to the injection of all fluids compatible with the dimensions of the hydraulic circuit. It is also clear that the ability to inject a great variety of fluids makes the injector according to the invention apt also to uses different from that described in the case of an internal combustion engine, wherever a precise dosing of micro quantities of fluid is required. Possible uses are for instance as dosing devices in chemical or pharmaceutical plants.

The injector device can also be used in association not only with the intake duct, but also as an alternative to, or in combination with the ducts which convey air to the cylinders, by analogy with the MPI technique.