1. A fuel injection system (1) for a spark ignition internal combustion engine, the fuel injection system (1) comprising:

a plurality of cylinders (11), the cylinders (11) receiving a gas mixture comprising fresh air and defining therein a plurality of respective main combustion chambers (MC);

a plurality of first injectors (2), each first injector (2) being coupled to a respective cylinder (11), the first injectors (2) injecting fuel at a pressure into the cylinders (11) during a combustion cycle;

a plurality of spark plugs (13), each spark plug (13) being coupled to a respective cylinder (11) to periodically determine the ignition of the fuel present in the main combustion chamber (MC);

a plurality of combustion chambers (PC), each obtained in the region of a respective spark plug (13), in which combustion of a gas mixture containing fresh air and fuel is carried out to increase the turbulence inside the main combustion chamber (MC) of the respective cylinder (11);

the injection system (1) is characterized in that it comprises:

a plurality of extraction ducts (17; 28), each extraction duct (17; 28) originating from a respective cylinder (11) in the region of an extraction point (P) to extract the gas mixture present inside a respective main combustion chamber (MC) during a combustion cycle;

at least one reservoir (18), said reservoir (18) receiving a gas mixture from an extraction duct (17; 28); inside the reservoir (18), the gas mixture coming from the extraction duct (17; 28) is mixed with an amount of fuel inside the combustion front chamber (PC) necessary to obtain combustion under stoichiometric conditions;

a plurality of second injectors (27), each second injector (27) being coupled to a respective combustion pre-chamber (PC), the second injectors (27) injecting the gas and fuel mixture from the reservoir (18) into the combustion pre-chambers (PC); and

a third injector (22), said third injector (22) feeding fuel to a reservoir (18) and being connected to the low-pressure pump (8) or alternatively to the high-pressure pump (4) through a first conduit (23).

2. The system according to claim 1, characterized by comprising a plurality of fourth injectors (20), each fourth injector (20) being arranged along a respective extraction duct (17; 28) to extract the gas mixture from the main combustion chamber (MC) of the respective cylinder (11) and feed it to the reservoir (18).

3. System according to claim 2, characterized by comprising a plurality of filters (21), each filter (21) being arranged along a respective extraction duct (17; 28) and upstream of the fourth injector (20).

4. System according to claim 2, characterized by comprising a plurality of pumping devices (29) housed along the extraction duct (17) upstream of the reservoir (18) and downstream of the fourth injector (20).

5. System according to claim 1, characterized in that each cylinder (11) houses a respective piston (12) and in that the extraction point (P) is obtained above the top dead centre of the stroke of the piston (12).

6. System according to claim 1, characterized in that each cylinder (11) houses a respective piston (12) and in that said extraction point (P) is obtained below the top dead centre of the stroke of the piston (12).

7. A system according to claim 1, characterized by comprising a plurality of first control valves (19), each first control valve (19) being arranged along a respective extraction duct (17) in the vicinity of an extraction point (P) and being designed to regulate the flow rate of the gas mixture passing through the extraction duct (17).

8. The system according to claim 1, characterized by comprising a fuel pressure sensor (26) arranged along the first conduit (23).

9. System according to claim 1, characterized in that the reservoir (18) is provided with temperature and pressure sensors (24) and an oxygen sensor (25) to read the fuel-air equivalence ratio of the gas and fuel mixture.

10. The system according to claim 1, characterized by comprising a plurality of second ducts (28), the plurality of second ducts (28) feeding the gas and fuel mixture from the reservoir (18) to the respective second injectors (27).

11. System according to claim 10, characterized by comprising a plurality of pumping means (29) housed along the second duct (28).

12. The system according to claim 11, characterized by comprising a pressure sensor (30; 31) for the pressure of the gas and fuel mixture, said pressure sensor (30; 31) being housed along the second duct (28) and being interposed between the pumping device (29) and the second injector (27).

13. System according to claim 11, characterized in that said second injector (27) is suitable both for injecting the gas and fuel mixture from the reservoir (18) into the respective combustion chamber (PC) and for extracting the gas mixture from the main combustion chamber (MC) of the respective cylinder (11) and feeding it to the reservoir (18); and comprises a plurality of third ducts (33), the third ducts (33) feeding the gas mixture from the respective main combustion chambers (MC) to the reservoir (18).

14. The system according to claim 13, characterized by comprising a plurality of second control valves (32), said second control valves (32) being designed to regulate the passage of the gas and fuel mixture through the second duct (28); and a plurality of third control valves (34), the third control valves (34) being designed to regulate the passage of the gas mixture through the third duct (33).

15. A method of controlling an injection system (1) according to claim 1, the method comprising in sequence:

-a pumping step during which a gas mixture is pumped from the main combustion chamber (MC) of the cylinder (11);

-a mixing step during which the gas mixture coming from the cylinder (11) is mixed with the fuel inside the reservoir (18);

-an injection step during which a gas and fuel mixture is injected into the combustion chamber (PC); and

-an ignition step, during which a spark plug (13) is ignited to ignite the gas and fuel mixture into the combustion chamber (PC).

16. Method according to claim 15, characterized in that the suction step and/or the injection step and/or the ignition step of the spark plug (13) are limited within an angular window of the whole combustion cycle.

Background

As is known, a fuel injection system for a spark ignition internal combustion engine is generally provided with: a plurality of injectors; a common rail that supplies fuel to the injector under a certain pressure; a high-pressure pump that supplies fuel to the common rail through a supply pipe; and a low-pressure pump that supplies fuel from the fuel tank to the high-pressure pump through a supply pipe.

The spark-ignition internal combustion engine also comprises a plurality of cylinders, each housing a respective piston, which is mechanically connected to the crankshaft by a connecting rod, so as to transmit the force generated by the combustion inside the cylinder to the crankshaft itself.

Furthermore, the engine comprises a spark plug for each cylinder in order to periodically determine the ignition of the gas mixture present in the cylinder. In particular, each spark plug is periodically activated to determine ignition of compressed gas within a main combustion chamber defined within the cylinder at the end of each compression stroke of a combustion cycle of the cylinder.

For each cylinder, a respective injector is provided; alternatively, the injection may be an indirect injection and thus each injector is arranged upstream of the cylinder in the intake conduit, or the injection may be a direct injection and thus each injector is arranged partly inside the cylinder.

Furthermore, the use of injection systems is known, in which combustion is carried out under stoichiometric conditions in a combustion chamber (or auxiliary combustion chamber) defined in the vicinity of each spark plug; a given amount of fuel and air is injected into the combustion front chamber and the ignition of the fuel present in the gas mixture inside the combustion front chamber (in percentages amounting to about 2-3% of the total amount of injected fuel) makes the combustion more efficient inside the main combustion chamber arranged downstream of the respective cylinder.

Fresh air is supplied to the combustion chamber by means of the main combustion chamber through holes obtained in the top region of the combustion chamber (so-called passive combustion chamber). Alternatively, in systems with so-called active combustion pre-chambers, an air-fuel mixture may be supplied in addition to the air from the main combustion chamber. Typically, the combustion chamber receives fresh air (i.e. air from the outside) through a duct along which a preferably electric compressor device is housed, for preparing said air-fuel mixture upstream of the injector.

Document DE 102015221286 a1 discloses an example of a fuel injection system for a spark-ignition internal combustion engine of the type described so far.

However, known compressor devices for supplying air to the combustion chamber cannot ensure that the supply takes place only in the pressure range of 6-7 bar.

Disclosure of Invention

It is an object of the present invention to provide a fuel injection system for a spark-ignition internal combustion engine which does not suffer from the above-mentioned disadvantages and which is particularly easy and economical to manufacture.

Another object of the present invention is to provide a method of controlling a fuel injection system for a spark-ignition internal combustion engine which does not suffer from the above-mentioned drawbacks and which is particularly easy and economical to implement.

According to the present invention, there is provided a fuel injection system for a spark ignition internal combustion engine, the fuel injection system having: a plurality of cylinders that receive a gas mixture comprising fresh air and define a plurality of respective main combustion chambers therein; a plurality of first injectors, each coupled to a respective cylinder, the first injectors injecting fuel into the cylinders at a pressure during a combustion cycle; a plurality of spark plugs, each spark plug coupled to a respective cylinder to periodically determine ignition of fuel present in the main combustion chamber; a plurality of combustion chambers, each obtained in the region of a respective spark plug, in which combustion of a gaseous mixture containing fresh air and fuel is carried out to increase the turbulence inside the main combustion chamber of the respective cylinder; a plurality of extraction ducts, each extraction duct originating from a respective cylinder in the region of an extraction point to extract the gas mixture present inside a respective main combustion chamber (MC) during a combustion cycle; at least one reservoir that receives the gas mixture from the extraction conduit; inside the reservoir, the gas mixture coming from the extraction duct is mixed with an amount of fuel inside the combustion chamber required to obtain combustion under stoichiometric conditions; a plurality of second injectors, each coupled to a respective combustion pre-chamber, the second injectors injecting the gas and fuel mixture from the reservoir into the combustion pre-chamber; and a third injector feeding fuel to the reservoir and connected to the low-pressure pump or alternatively to the high-pressure pump by a first conduit.

According to the invention, there is further provided a method of controlling an injection system, the method having the following steps in order: a pumping step during which a gas mixture is pumped from a main combustion chamber of the cylinder; a mixing step during which the gas mixture coming from the cylinder is mixed with the fuel inside the reservoir; an injection step during which a gas and fuel mixture is injected into the pre-combustion chamber; and an ignition step during which the spark plug is ignited to ignite the gas and fuel mixture into the pre-combustion chamber.

Drawings

The invention will now be described with reference to the accompanying drawings, which show non-limiting embodiments thereof, in which:

figure 1 is a schematic view of a spark-ignition internal combustion engine, with some details removed for greater clarity;

FIG. 2 is a schematic view of a first embodiment of a fuel injection system for the internal combustion engine of FIG. 1 according to the present disclosure;

FIG. 3 is a schematic view of a second embodiment of a fuel injection system for the internal combustion engine of FIG. 1 according to the present disclosure;

FIG. 4 is a schematic view of a third embodiment of a fuel injection system for the internal combustion engine of FIG. 1 according to the present invention;

fig. 5 is a schematic view of a fourth embodiment of a fuel injection system for the internal combustion engine of fig. 1 according to the present invention.

Detailed Description

In fig. 1, reference numeral 1 denotes a fuel injection system for a spark ignition internal combustion engine as a whole.

The injection system 1 includes: a plurality of injectors 2; a common rail 3, the common rail 3 supplying fuel to the injectors 2 under a certain pressure; a high-pressure pump 4, the high-pressure pump 4 supplying fuel to the common rail 3 through a supply pipe 5, and the high-pressure pump 4 being provided with a flow rate adjustment device 6; an electronic control unit 7, the electronic control unit 7 bringing the pressure of the fuel inside the common rail 3 to a desired value, which is normally variable over time according to the engine operating conditions; and a low-pressure pump 8, the low-pressure pump 8 supplying fuel from a fuel tank 9 to the high-pressure pump 4 through a supply pipe 10.

An electronic control unit 7 is coupled to the flow rate adjustment device 6 in order to control the flow rate of the high-pressure pump 4 in order to instantaneously supply the common rail 3 with the quantity of fuel required inside the common rail 3 at a desired pressure value.

The spark-ignition internal combustion engine also comprises a plurality of (in particular four) cylinders 11, preferably arranged in line. Each cylinder 11 houses a respective piston 12, which piston 12 is mechanically connected to the crankshaft by means of a connecting rod, so as to transmit the force generated by the combustion inside the cylinder 11 to the crankshaft itself.

Further, in the case of a spark ignition engine, four ignition plugs 13 (one ignition plug 13 per cylinder 11) are coupled to the cylinder 11 so as to periodically determine ignition of the gas mixture present inside the cylinder 11. Each spark plug 13 is periodically activated to determine the ignition of the compressed gas inside the main combustion chamber MC defined inside the cylinder 11 at the end of each compression stroke of the combustion cycle of the cylinder 11.

According to fig. 2, an intake manifold 43 is connected to each cylinder 11 through two intake valves 14 (only one of them is shown in fig. 2), and the intake manifold 43 receives a mixture gas containing fresh air (i.e., air from the outside) from the intake valves 14 and, if necessary, EGR. Furthermore, the internal combustion engine comprises an exhaust manifold 15, which exhaust manifold 15 is connected to each cylinder 11 by two exhaust valves 16 (only one of them is shown in fig. 2) and leads to an exhaust duct (not shown) for releasing the gases produced by combustion into the atmosphere.

As is known, a complete combustion cycle is the result of four consecutive strokes, at the end of which the crankshaft has made two revolutions, covering an angle of 720. Typically, fuel is injected into the combustion chamber of the cylinder 11 during the intake stroke and/or the subsequent compression stroke and/or the subsequent expansion stroke, and in the expansion stroke or in the last part of the previous compression stroke, the electrodes of the spark plug 13 generate a spark which ignites the mixture of air and fuel in the cylinder 11, thus initiating the actual combustion, which results in an increase in temperature and pressure. Finally, during the exhaust stroke, the movement of the piston 12 allows combusted gases to be expelled through a corresponding exhaust valve 16 for release into an exhaust manifold 15.

For each cylinder 11, a respective injector 2 is provided; alternatively, the injection may be an indirect injection, and thus each injector 2 is arranged upstream of the cylinder 11 in an intake pipe connecting the intake manifold 43 to the cylinder 11, or the injection may be a direct injection, and thus each injector 2 is arranged partially inside the cylinder 11.

Each cylinder 11 is also provided with a respective conduit 17, which originates from the side wall of the cylinder 11 in the region of the extraction point P, to extract the gas mixture (fresh air and EGR and/or fuel) from the main combustion chamber MC of the respective cylinder 11 and leads up to a common reservoir 18 shared by the four cylinders 11. The extraction point P may alternatively be obtained above or below the top dead center of the stroke of the piston 12. Along the extraction duct 17 there is housed a control valve 19, which control valve 19 is designed to regulate the passage of the gas mixture through the extraction duct 17; the control valve 19 is arranged in the vicinity of the extraction point P. The control valve 19 is preferably set to a predetermined pressure value (in the range of 4, 5 bar) to prevent leakage of oil during the compression stroke and subsequent expansion stroke of the combustion cycle. An injector 20 is interposed between the control valve 19 and the reservoir 18 to supply the gas mixture extracted from the main combustion chamber MC of the respective cylinder 11 to the reservoir 18. The injectors 20 are connected to the electronic control unit 7 and are controlled so as to draw the gas mixture from the main combustion chambers MC of the respective cylinders 11 and supply it to the reservoir 18 during the compression stroke of the combustion cycle. In particular, the injectors 20 are controlled by the electronic control unit 7 so as to draw the gas mixture from the main combustion chamber MC of the respective cylinder 11 when the pressure inside said main combustion chamber MC (i.e. within a given angular window of the combustion cycle) is equal to or greater than the injection pressure in said combustion chamber PC. The injection pressure in the combustion front chamber PC ranges from 8 to 12 bar; preferably, the injection pressure in the combustion chamber PC is equal to 10 bar.

According to a preferred variant, a filter 21 is housed along the extraction duct 16, this filter 21 being preferably interposed between the injector 20 and the control valve 19 to protect the injector 20.

Furthermore, an injector 22 is provided, which injector 22 is adapted to supply a given amount of fuel to the reservoir 18, required for combustion to take place under stoichiometric conditions inside the combustion front chamber PC, as described in more detail below. The injectors 22 are connected to the low-pressure pump 8 or alternatively to the high-pressure pump 4 by a conduit 23. According to a preferred variant, the reservoir 18 is also provided with temperature and pressure sensors 24, the sensors 24 being connected to the electronic control unit 7, and with an oxygen sensor (lambda sensor)25 to read the fuel-air equivalence ratio of the gas mixture, the sensor 25 also being connected to the electronic control unit 7. According to a preferred variant, along the duct 23 there is housed a fuel pressure sensor 26, which fuel pressure sensor 26 is connected to the electronic control unit 7 and is also adapted to diagnose possible faults.

Each cylinder 11 is also provided with an injector 27, which injector 27 is connected to the reservoir 18 by a respective duct 28; the injector 27 is designed to feed the gas and fuel mixture contained in the reservoir 18 into a combustion front chamber PC (or auxiliary combustion chamber) defined in the vicinity of the spark plug 13. The ignition of the fuel present in the gas mixture injected into the combustion front chamber PC (in percentages amounting to approximately 2-3% of the total quantity of injected fuel) allows to increase the turbulence inside the main combustion chamber MC of the respective cylinder 11, thus improving the ignition of the fuel injected into the main combustion chamber MC of the respective cylinder 11. In particular, injector 27 is controlled by electronic control unit 7 so as to feed the gas and fuel mixture contained in reservoir 18 into combustion front chamber PC when the pressure inside said combustion front chamber PC (i.e. within a given angular window of the combustion cycle) is lower than the pressure value at which the gas mixture is drawn from main combustion chamber MC.

Fig. 3 differs from fig. 2 in that the injection system 1 comprises a pumping device 29 housed along the conduit 28 upstream of the injector 27. The presence of the pumping means 29 allows greater flexibility in the injection into the combustion chamber PC, since it always makes it possible to control the injector 27 so as to feed the gas and fuel mixture contained in the reservoir 18 into the combustion chamber PC (i.e. within any angular window of the combustion cycle). Furthermore, a pressure sensor 30 of the gas and fuel mixture is provided, which pressure sensor 30 is housed along the duct 28 and is interposed between the pumping device 29 and the injector 27; the sensor 30 is connected to the control unit 7 to allow control of the injection of the gas and fuel mixture into the combustion chamber PC.

Fig. 4 differs from fig. 3 in that the pumping means 29 are housed along the extraction duct 17 upstream of the reservoir 18 and downstream of the injector 20. In this case, the presence of the pumping means also allows greater flexibility in the injection into the pre-combustion chamber PC, since it is always possible to control the injector 27 so as to feed the gas and fuel mixture contained in the reservoir 18 into the pre-combustion chamber PC (i.e. within any angular window of the combustion cycle).

Preferably, one single pumping means 29 is provided, which supplies the reservoir 18 with the gas mixture coming from all the cylinders 11. Alternatively, for each cylinder 11 there is a pumping device 29 adapted to supply the reservoir 18 with the gas mixture coming from the respective cylinder 11.

Fig. 5 also differs from fig. 3 in that a pumping device 29 is housed upstream of the injector 27 along the extraction duct 28. In this case, the presence of the pumping means also allows greater flexibility in the injection into the combustion pre-chamber PC, since it is always possible to control the injector 27 so as to feed the gas and fuel mixture contained in the reservoir 18 into the combustion pre-chamber PC (i.e. within any angular window of the combustion cycle).

Furthermore, the injection system 1 requires neither (lack) injectors 20 nor the extraction line 17. According to this embodiment, the injector 27 is both suitable for sucking the gas mixture destined to the reservoir 18 from the main combustion chamber MC, and for supplying the gas and fuel mixture from the reservoir 18 to the combustion chamber PC. Furthermore, a pressure sensor 31 of the gas and fuel mixture is provided, which pressure sensor 31 is housed along the duct 28 and is interposed between the pumping means 29 and the injector 27; a pressure sensor 31 is connected to the electronic control unit 7 to allow to detect the pressure of the gas and fuel mixture and to control the injection into the combustion front chamber PC. Along the duct 28, downstream of the pumping device 29, a control valve 32 is housed, which control valve 32 is designed to regulate the passage of the gas and fuel mixture through the duct 28; the control valve 32 is preferably set to a predetermined pressure value (in the range of about 22 bar).

Furthermore, a further connecting duct 33 is provided, which connects the injector 27 to the reservoir 18 and along which there is housed a respective control valve 34, which control valve 34 is designed for regulating the passage of the gas mixture through the duct 33; the control valve 34 is preferably set to a predetermined pressure value (in the range of about 12 bar).

The electronic control unit 7 manages the operation of the injection system 1 and in particular controls the spark plugs 13 in order to determine the ignition of the compressed gas in each cylinder 2.

The method of controlling the injection system 1 is described below, comprising an initial pumping step to pump the gas mixture from the primary combustion chamber MC. The suction step requires the electronic control unit 7 to control the opening of the injector 20 (according to the embodiment shown in figures 2, 3 and 4) or the injector 27 (according to the embodiment shown in figure 5). Obviously, the opening of the injector 20 or of the injector 27 is limited within an angular window of the whole combustion cycle, which is stored in the electronic control unit 7; each angular window is expressed in degrees of engine angle and is associated with the compression stroke of the entire combustion cycle of the cylinder 11. Each angle window is identified by a signal of a tone wheel sensor (not shown) fitted at the end of the crankshaft to detect the rotational speed thereof. Furthermore, according to the embodiment shown in fig. 4 and 5, the electronic control unit 7 controls the pumping device 29 to increase the pressure of the gas mixture sucked out of the main combustion chamber MC up to a value established for the injection into the combustion front chamber PC and depending on the signal detected by the sensors 24, 31.

Immediately after the suction step, the method of controlling the injection system 1 comprises a mixing step to mix a mixture of gas and fuel inside the reservoir 18. During the mixing step, the electronic control unit 7 controls the opening of the injector 22 so as to supply the reservoir 18 with a quantity of fuel determined by means of a feedback (or closed-loop) control executed by means of a signal sent from the oxygen sensor 25.

Immediately after the mixing step, the method of controlling the injection system 1 comprises an injection step of injecting a gas and fuel mixture into the combustion front chamber PC. During the injection step, the electronic control unit 7 controls the opening of the injector 27. The opening of the injector 27 is limited within an angular window of the whole combustion cycle, which is stored in the electronic control unit 7; each angle window is expressed in degrees of engine angle. Furthermore, according to the embodiment shown in fig. 4, the electronic control unit 7 controls the pumping means 29 so as to increase the pressure of the gas and fuel mixture up to a value established for the injection into the combustion chamber PC and depending on the signals detected by the sensors 24, 31.

Finally, immediately after the injection step, the method of controlling the injection system 1 comprises an ignition step to ignite the gas and fuel mixture inside the combustion chamber PC. During the ignition step, the electronic control unit 7 controls the ignition of the spark plug 13. Obviously, the ignition of the spark plug 13 is limited within the angular window of the whole combustion cycle, which is stored in the electronic control unit 7; each angle window is expressed in degrees of engine angle.