Fuel injection system for a spark-ignition internal combustion engine and related control method

Abstract

A fuel injection system (1) for a spark ignition internal combustion engine, having: a plurality of cylinders (11) defining a plurality of respective main combustion chambers (MC) therein; a plurality of first injectors (2) and spark plugs (13) coupled to the cylinders (11); a plurality of pre-chambers (PC), each pre-chamber (PC) being obtained in the region of a respective spark plug (13); a plurality of extraction ducts (17; 28), the extraction ducts (17; 28) originating from respective cylinders (11) to extract the gas mixture present inside the respective main combustion chambers (MC); a reservoir (18) in which the gas extracted by the extraction ducts (17; 28) is mixed with a quantity of fuel necessary for combustion to occur under stoichiometric conditions inside the pre-chambers (PC); and a plurality of second injectors (27), each second injector (27) being coupled to a respective pre-chamber (PC), the second injectors (27) injecting the gas and fuel mixture from the reservoir (18) into the pre-chambers (PC).

Description

[0001] Cross - reference to related applications

[0002] This patent application claims the priority of Italian patent application No. 102020000005683 filed on March 17, 2020, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a fuel injection system for a spark - ignition internal combustion engine and a related control method. Background art

[0004] As is known, a fuel injection system for a spark - ignition internal combustion engine typically comprises: a plurality of injectors; a common rail that supplies fuel to the injectors at 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 a fuel tank to the high - pressure pump through a supply pipe.

[0005] A spark - ignition internal combustion engine also includes a plurality of cylinders, each cylinder accommodating a respective piston that is mechanically connected to a crankshaft by a connecting rod in order to transmit the force generated by the combustion inside the cylinder to the crankshaft itself.

[0006] Furthermore, the engine includes a spark plug for each cylinder in order to periodically determine the ignition of the gas mixture present inside the cylinder. In particular, each spark plug is periodically activated in order to determine the ignition of the compressed gas inside the main combustion chamber defined inside the cylinder at the end of each compression stroke of the combustion cycle of the cylinder.

[0007] For each cylinder, a respective injector is provided; alternatively, the injection can be indirect injection and thus each injector is arranged upstream of the cylinder in the intake pipe, or the injection can be direct injection and thus each injector is partially arranged inside the cylinder.

[0008] Furthermore, the use of an injection system is known in which combustion takes place inside a pre - combustion chamber (or auxiliary combustion chamber) defined near each spark plug under stoichiometric conditions; a given quantity of fuel and air is injected into the pre - combustion chamber, and the ignition of the fuel present in the gas mixture inside the pre - combustion chamber (which amounts to approximately 2 - 3% in total percentage of the total injected fuel) enables a higher combustion efficiency inside the main combustion chamber, which is arranged downstream of the respective cylinder.

[0009] Fresh air is supplied to the pre - combustion chamber by means of the main combustion chamber through holes obtained in the top region of the pre - combustion chamber (so - called passive pre - combustion chamber). Alternatively, in a system with a so - called active pre - combustion chamber, in addition to the air from the main combustion chamber, an air - fuel mixture can also be supplied. Typically, the pre - combustion chamber receives fresh air (i.e., air from the outside) through a duct along which preferably an electric compressor device is accommodated for preparing the air - fuel mixture upstream of the injector.

[0010] The document DE 10 2015 221286 A1 discloses an example of a fuel injection system of the type described so far for a spark - ignition internal combustion engine.

[0011] However, the known compressor devices for supplying air to the pre - combustion chamber do not ensure supply only within a pressure range of 6 - 7 bar. Summary of the Invention

[0012] The object of the present invention is to provide a fuel injection system for a spark - ignition internal combustion engine which is not affected by the above - mentioned drawbacks and is in particular easy and economical to manufacture.

[0013] Another object of the present invention is to provide a method for controlling a fuel injection system for a spark - ignition internal combustion engine which is not affected by the above - mentioned drawbacks and is in particular easy and economical to implement.

[0014] 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 containing fresh air and in which a plurality of respective main combustion chambers are defined; a plurality of first injectors, each first injector being coupled to a respective cylinder, and during a combustion cycle, the first injector injects fuel into the cylinder at a certain pressure; a plurality of spark plugs, each spark plug being coupled to a respective cylinder to periodically determine the ignition of the fuel present in the main combustion chamber; a plurality of pre-chambers, each pre-chamber being obtained in the region of a respective spark plug, and in the pre-chamber, combustion of a gas 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 within an extraction point region to extract the gas mixture present inside the respective main combustion chamber (MC) during a combustion cycle; at least one reservoir that receives the gas mixture from the extraction ducts; inside the reservoir, the gas mixture from the extraction ducts is mixed with a certain amount of fuel required for combustion under stoichiometric conditions inside the pre-chamber; a plurality of second injectors, each second injector being coupled to a respective pre-chamber, and the second injector injects the gas and fuel mixture from the reservoir into the pre-chamber; and a third injector that supplies fuel to the reservoir and is connected to a low-pressure pump or alternatively to a high-pressure pump through a first pipe.

[0015] According to the present invention, there is further provided a method for controlling the injection system, the method sequentially having the following steps: a suction step during which the gas mixture is suctioned from the main combustion chamber of the cylinder; a mixing step during which the gas mixture from the cylinder is mixed with the fuel inside the reservoir; an injection step during which the gas and fuel mixture is injected into the pre-chamber; and an ignition step during which the spark plug is ignited to ignite the gas and fuel mixture into the pre-chamber. Description of the Drawings

[0016] The present invention will now be described with reference to the drawings showing non-limiting embodiments thereof, in which:

[0017] - Figure 1 is a schematic view of a spark ignition internal combustion engine, with some details removed for greater clarity;

[0018] - Figure 2 is a schematic view of a first embodiment of a fuel injection system for an internal combustion engine according to the present invention for Figure 1 ;

[0019] - Figure 3 is a schematic view of a second embodiment of a fuel injection system for an internal combustion engine according to the present invention for Figure 1 ;

[0020] - Figure 4 is a schematic diagram of a third embodiment of a fuel injection system for an Figure 1 internal combustion engine according to the present invention;

[0021] - Figure 5 is a schematic diagram of a fourth embodiment of a fuel injection system for an Figure 1 internal combustion engine according to the present invention. DETAILED DESCRIPTION

[0022] In Figure 1 , the reference numeral 1 as a whole indicates a fuel injection system for a spark ignition internal combustion engine.

[0023] The injection system 1 includes: a plurality of injectors 2; a common rail 3 that supplies fuel to the injectors 2 at a certain pressure; a high-pressure pump 4 that supplies fuel to the common rail 3 through a supply pipe 5, and the high-pressure pump 4 is provided with a flow rate regulating device 6; an electronic control unit 7 that causes the fuel pressure inside the common rail 3 to reach an expected value, which generally varies with time according to the engine operating conditions; and a low-pressure pump 8 that supplies fuel from a fuel tank 9 to the high-pressure pump 4 through a supply pipe 10.

[0024] The electronic control unit 7 is connected to the flow rate regulating device 6 in order to control the flow rate of the high-pressure pump 4 so as to instantaneously supply the required amount of fuel with an expected pressure value inside the common rail 3 to the common rail 3.

[0025] The spark ignition internal combustion engine further includes a plurality of (in particular four) cylinders 11, preferably arranged in a straight line. Each cylinder 11 houses a corresponding piston 12, which is mechanically connected to the crankshaft through a connecting rod so as to transmit the force generated by the combustion inside the cylinder 11 to the crankshaft itself.

[0026] Furthermore, in the case of a spark ignition engine, four spark plugs 13 (one spark plug 13 for each cylinder 11) are coupled to the cylinders 11 in order to periodically determine the ignition of the gas mixture present inside the cylinders 11. Each spark plug 13 is periodically activated in order 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.

[0027] According to Figure 2 , the intake manifold 43 is through two intake valves 14 (in Figure 2Only one of them (only one of them is shown in [the figure]) is connected to each cylinder 11. The intake manifold 43 receives the mixture gas containing fresh air (i.e., air from the outside), and may also contain EGR if necessary, from the intake valve 14. In addition, the internal combustion engine includes an exhaust manifold 15 which is connected to each cylinder 11 through two exhaust valves 16 (only one of them is shown in [the figure]) and leads to an exhaust pipe (not shown) to release the gas generated by combustion into the atmosphere. Figure 2 Only one of them (only one of them is shown in [the figure]) is connected to each cylinder 11 and leads to an exhaust pipe (not shown) to release the gas generated by combustion into the atmosphere.

[0028] As is known, a complete combustion cycle is the result of four consecutive strokes. At the end of the combustion cycle, the crankshaft has made two full rotations, 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 during 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 air-fuel mixture in the cylinder 11, thus starting the actual combustion, which results in an increase in temperature and pressure. Finally, during the exhaust stroke, the movement of the piston 12 allows the combustion gas to be discharged through the corresponding exhaust valve 16 so as to be released into the exhaust manifold 15.

[0029] For each cylinder 11, a corresponding injector 2 is provided; alternatively, the injection can be indirect injection, and thus each injector 2 is arranged upstream of the cylinder 11 in the intake pipe connecting the intake manifold 43 to the cylinder 11, or the injection can be direct injection, and thus each injector 2 is partially arranged inside the cylinder 11.

[0030] Each cylinder 11 is also provided with a respective pipe 17 which originates from the side wall of the cylinder 11 in the region of the extraction point P to extract a gas mixture (fresh air and EGR and / or fuel) from the main combustion chamber MC of the respective cylinder 11 and to direct it until a common reservoir 18 shared by the four cylinders 11. The extraction point P can alternatively be obtained above or below the top dead center of the piston 12 stroke. A control valve 19 is housed along the extraction pipe 17, which control valve 19 is designed to regulate the passage of the gas mixture through the extraction pipe 17; the control valve 19 is arranged near 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 the leakage of oil during the compression stroke and the 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 injector 20 is connected to the electronic control unit 7 and is controlled to extract the gas mixture from the main combustion chamber MC of the respective cylinder 11 and supply it to the reservoir 18 during the compression stroke of the combustion cycle. In particular, the injector 20 is controlled by the electronic control unit 7 so as to extract the gas mixture from the main combustion chamber MC of the respective cylinder 11 when (i.e., within a given angular window of the combustion cycle) the pressure inside the said main combustion chamber MC is equal to or greater than the injection pressure in the pre-combustion chamber PC. The injection pressure in the pre-combustion chamber PC ranges from 8 to 12 bar; preferably, the injection pressure in the pre-combustion chamber PC is equal to 10 bar.

[0031] According to a preferred variant, a filter 21 is housed along the extraction pipe 16, which filter 21 is preferably interposed between the injector 20 and the control valve 19 to protect the injector 20.

[0032] Furthermore, an injector 22 is provided which is adapted to supply a given quantity of fuel required for combustion under stoichiometric conditions inside the pre-combustion chamber PC to the reservoir 18, as described in more detail below. The injector 22 is connected by a pipe 23 to the low-pressure pump 8 or alternatively to the high-pressure pump 4. According to a preferred variant, the reservoir 18 is also provided with a temperature and pressure sensor 24 which is connected to the electronic control unit 7, and an oxygen sensor (lambda sensor) 25 to read the fuel-air equivalence ratio of the gas mixture, which sensor 25 is also connected to the electronic control unit 7. According to a preferred variant, a fuel pressure sensor 26 is housed along the pipe 23, which fuel pressure sensor 26 is connected to the electronic control unit 7 and is also adapted to diagnose possible faults.

[0033] Each cylinder 11 is also provided with an injector 27 which is connected to a reservoir 18 via a respective pipe 28; the injector 27 is designed to supply a gas and fuel mixture contained in the reservoir 18 into a pre-combustion chamber PC (or auxiliary combustion chamber) defined near the spark plug 13. The fuel present in the gas mixture injected into the pre-combustion chamber PC (which amounts to approximately 2 - 3% in total percentage of the total injected fuel) allows ignition 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, the injector 27 is controlled by an electronic control unit 7 so as to supply the gas and fuel mixture contained in the reservoir 18 into the pre-combustion chamber PC when (i.e., within a given angular window of the combustion cycle) the pressure inside the said pre-combustion chamber PC is less than the pressure value when the gas mixture is aspirated from the main combustion chamber MC.

[0034] Figure 3 Differently from Figure 2 is that the injection system 1 includes a pumping device 29 accommodated along the pipe 28 upstream of the injector 27. The presence of the pumping device 29 allows for greater flexibility in the injection into the pre-combustion chamber PC, since it is always possible to control the injector 27 so as to supply 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). In addition, a pressure sensor 30 for the gas and fuel mixture is provided, which is accommodated along the pipe 28 and 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 pre-combustion chamber PC.

[0035] Figure 4 Differently from Figure 3 is that the pumping device 29 is accommodated along the extraction pipe 17 upstream of the reservoir 18 and downstream of the injector 20. In this case, the presence of the pumping device also allows for greater flexibility in the injection into the pre-combustion chamber PC, since it is always possible to control the injector 27 so as to supply 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).

[0036] Preferably, a single pumping device 29 is provided which supplies the reservoir 18 with the gas mixture from all the cylinders 11. Alternatively, there is a pumping device 29 for each cylinder 11 which is adapted to supply the reservoir 18 with the gas mixture from the respective cylinder 11.

[0037] Figure 5 Differently from Figure 3It is also different in that the pumping device 29 is accommodated upstream of the injector 27 along the extraction pipe 28. In this case, the presence of the pumping device also allows for greater flexibility in the injection into the combustion pre-chamber PC, because it is always possible to control the injector 27 so as to supply the gas and fuel mixture contained in the reservoir 18 to the combustion pre-chamber PC (i.e., within any angular window of the combustion cycle).

[0038] In addition, the injection system 1 neither requires the injector 20 nor the extraction pipe 17. According to this embodiment, the injector 27 is suitable both for sucking out the gas mixture destined for the reservoir 18 from the main combustion chamber MC and for supplying the gas and fuel mixture from the reservoir 18 to the pre-combustion chamber PC. In addition, a pressure sensor 31 for the gas and fuel mixture is provided, which is accommodated along the pipe 28 and interposed between the pumping device 29 and the injector 27; the pressure sensor 31 is connected to the electronic control unit 7 to allow the detection of the pressure of the gas and fuel mixture and the control of the injection into the pre-combustion chamber PC. Along the pipe 28, downstream of the pumping device 29, a control valve 32 is accommodated, which is designed to regulate the passage of the gas and fuel mixture through the pipe 28; the control valve 32 is preferably set to a predetermined pressure value (in the range of about 22 bar).

[0039] In addition, another connecting pipe 33 is provided, which connects the injector 27 to the reservoir 18, and along which a corresponding control valve 34 is accommodated, which is designed to regulate the passage of the gas mixture through the pipe 33; the control valve 34 is preferably set to a predetermined pressure value (in the range of about 12 bar).

[0040] The electronic control unit 7 manages the operation of the injection system 1 and in particular controls the spark plug 13 in order to determine the ignition of the compressed gas in each cylinder 2.

[0041] A method for controlling the injection system 1 is described below, which method includes an initial suction step for sucking the gas mixture from the main 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 Figure 2 , Figure 3 and Figure 4 ) or the injector 27 (according to the embodiment shown in Figure 5 ). Obviously, the opening of the injector 20 or the injector 27 is restricted within the angular window of the entire combustion cycle, and the angular window 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 angular window is identified by the signal of a tone wheel sensor (not shown) assembled at the end of the crankshaft to detect its rotational speed. In addition, according toFigure 4 and Figure 5 In the embodiment shown in Figure 5 , the electronic control unit 7 controls the pumping device 29 to increase the pressure of the gas mixture sucked out from the main combustion chamber MC until a value that is established for the injection into the pre-combustion chamber PC and depends on the signals detected by the sensors 24, 31.

[0042] Immediately following the suction step, the method for controlling the injection system 1 includes a mixing step to mix the gas and fuel mixture inside the reservoir 18. During the mixing step, the electronic control unit 7 controls the opening of the injector 22 to supply a certain amount of fuel to the reservoir 18, and the amount of fuel is determined by the feedback (or closed-loop) control executed by the signal from the oxygen sensor 25.

[0043] Immediately following the mixing step, the method for controlling the injection system 1 includes an injection step of injecting the gas and fuel mixture into the pre-combustion 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 restricted within an angular window of the entire combustion cycle, and the angular window is stored in the electronic control unit 7; each angular window is expressed in degrees of engine angle. In addition, according to Figure 4 In the embodiment shown in Figure 5 , the electronic control unit 7 controls the pumping device 29 to increase the pressure of the gas and fuel mixture until a value that is established for the injection into the pre-combustion chamber PC and depends on the signals detected by the sensors 24, 31.

[0044] Finally, immediately following the injection step, the method for controlling the injection system 1 includes an ignition step to ignite the gas and fuel mixture inside the pre-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 restricted within an angular window of the entire combustion cycle, and the angular window is stored in the electronic control unit 7; each angular window is expressed in degrees of engine angle.

Claims

1. A fuel injection system (1) for a spark-ignition internal combustion engine, said fuel injection system (1) comprising: a plurality of cylinders (11) which receive a gas mixture containing fresh air and in which a plurality of respective main combustion chambers (MC) are defined; a plurality of first injectors (2), each first injector (2) being connected to a respective cylinder (11) and, during a combustion cycle, injecting fuel into the cylinder (11) at a certain pressure; a plurality of spark plugs (13), each spark plug (13) being connected to a respective cylinder (11) to periodically determine the ignition of the fuel present in the main combustion chamber (MC); a plurality of pre-chambers (PC), each pre-chamber (PC) being obtained in the region of a respective spark plug (13), in which a gas mixture containing fresh air and fuel is combusted 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) within the region of an extraction point (P) to extract the gas mixture present inside the respective main combustion chamber (MC) during a combustion cycle; at least one reservoir (18) which receives the gas mixture from the extraction ducts (17; 28); inside the reservoir (18), the gas mixture from the extraction ducts (17; 28) is mixed with a certain amount of fuel required to obtain combustion under stoichiometric conditions inside the pre-chamber (PC); a plurality of second injectors (27), each second injector (27) being connected to a respective pre-chamber (PC), the second injector (27) injecting the gas and fuel mixture from the reservoir (18) into the pre-chamber (PC); and a third injector (22) which supplies fuel to the reservoir (18) and is connected by a first duct (23) to a low-pressure pump (8) or alternatively to a high-pressure pump (4).

2. The system according to claim 1, wherein 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 supply it to the reservoir (18).

3. The system according to claim 2, wherein Comprising a plurality of filters (21), each filter (21) being arranged along a respective extraction duct (17; 28) and arranged upstream of the fourth injector (20).

4. The system according to claim 2, wherein Comprising a plurality of pumping means (29) accommodated upstream of the reservoir (18) and downstream of the fourth injector (20) along the extraction duct (17).

5. The system according to claim 1, wherein Each cylinder (11) houses a respective piston (12), and the extraction point (P) is obtained above the top dead center of the stroke of the piston (12).

6. The system according to claim 1, wherein Each cylinder (11) houses a respective piston (12), and the said extraction point (P) is obtained below the top dead center of the stroke of the piston (12).

7. The system according to claim 1, wherein 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 designed to regulate the flow rate of the gas mixture through the extraction duct (17).

8. The system according to claim 1, wherein Comprising a fuel pressure sensor (26) arranged along a first duct (23).

9. The system according to claim 1, wherein The reservoir (18) is provided with a temperature and pressure sensor (24) and an oxygen sensor (25) for reading the fuel-air equivalence ratio of the gas and fuel mixture.

10. The system according to claim 1, characterized in that Comprising a plurality of second ducts (28) which supply the gas and fuel mixture from the reservoir (18) to respective second injectors (27).

11. The system according to claim 10, wherein Comprising a plurality of pumping devices (29) accommodated along the second ducts (28).

12. The system according to claim 11, wherein Comprising pressure sensors (30; 31) for the pressure of the gas and fuel mixture, the pressure sensors (30; 31) being accommodated along the second ducts (28) and interposed between the pumping devices (29) and the second injectors (27).

13. The system according to claim 11, wherein The second injector (27) is suitable both for injecting the gas and fuel mixture from the reservoir (18) into a respective pre-combustion chamber (PC) and for extracting a gas mixture from the main combustion chamber (MC) of a respective cylinder (11) and supplying it to the reservoir (18); and comprising a plurality of third ducts (33) which supply the gas mixture from the respective main combustion chamber (MC) to the reservoir (18).

14. The system according to claim 13, wherein Comprising a plurality of second control valves (32) designed to regulate the passage of the gas and fuel mixture through the second ducts (28); and a plurality of third control valves (34) designed to regulate the passage of the gas mixture through the third ducts (33).

15. A method of controlling an injection system (1) according to claim 1, the method successively comprising: - a suction step during which a gas mixture is suctioned from the main combustion chamber (MC) of the cylinder (11); - a mixing step during which the gas mixture from the cylinder (11) is mixed with the fuel inside the reservoir (18); - an injection step during which the gas and fuel mixture is injected into the pre-combustion chamber (PC); and - an ignition step during which the spark plug (13) is ignited to ignite the gas and fuel mixture in the pre-combustion chamber (PC).

16. The 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 entire combustion cycle.

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