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

Abstract

To provide a fuel injection device for a spark-ignition injection engine, in particular, easy in manufacturing and economical, without being troubled by disadvantages of a conventional device, and a control method thereof.SOLUTION: A fuel injection device 1 for a spark-ignition internal combustion engine includes: several cylinders 11 where main combustion chambers MC are respectively defined; first injectors 2 and spark plugs 13 coupled to the cylinders; combustion pre-chambers PC respectively obtained in an area of the spark plug; extraction ducts 17, 28 originating from each of the cylinders to extract a gas mixture existing inside of each main combustion chamber; a reserve 18 where the gases extracted by the extraction ducts are mixed with the fuel of the amount needed to obtain combustion under stoichiometric conditions inside the combustion pre-chambers; and second injectors 27 respectively coupled to each of the combustion pre-chambers to inject the gas / fuel mixture coming from the reserve.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority from Italian Patent Application No. 102020000005683, filed on March 17, 2020, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a fuel injection system and relative control method for a spark ignition internal combustion engine. [Background technology]

[0003] As is known, a fuel injection system for a spark-ignition internal combustion engine generally comprises several injectors, a common rail supplying fuel under pressure to the injectors, a high-pressure pump supplying fuel to said common rail by a supply duct, and a low-pressure pump supplying fuel from a tank to said high-pressure pump by means of a supply duct.

[0004] A spark ignition internal combustion engine further includes a number of cylinders, each housing a piston, which is mechanically connected to a crankshaft by a connecting rod and configured to transfer the force generated by combustion in the cylinders to the crankshaft itself.

[0005] Furthermore, the internal combustion engine comprises a spark plug for each cylinder for periodically determining the ignition of the mixture of gases present inside each cylinder, in particular each spark plug being periodically activated to determine the ignition of compressed gases in a main combustion chamber defined inside the cylinder at the end of each compression stroke of the combustion cycle of the cylinder.

[0006] For each cylinder there is provided a corresponding injector, which may be indirect, in which case each injector is located in the intake duct upstream of the cylinder, or it may be direct, in which case each injector is located partly within the cylinder.

[0007] Furthermore, the use of injection systems is known in which the combustion is carried out under stoichiometric conditions in defined pre-combustion chambers (or auxiliary combustion chambers) near each spark plug, where a defined amount of fuel and air is injected into the pre-combustion chamber, igniting the fuel present in the gas mixture in the pre-combustion chamber (a proportion representing approximately 2-3% of the total fuel injected), resulting in a more efficient combustion in the main combustion chamber located downstream of each cylinder.

[0008] Fresh air is supplied to the pre-combustion chamber by the main combustion chamber through holes obtained in the upper region of the pre-combustion chamber (so-called passive pre-combustion chamber). Alternatively, in systems with so-called active pre-combustion chambers, it is also possible to supply the mixture in addition to the air coming from the main combustion chamber. Usually, the pre-combustion chamber receives fresh air (i.e. air coming from the outside) for preparing said mixture upstream of the injectors, preferably by means of a duct housing an electric compressor device.

[0009] US Pat. No. 5,399,633 discloses an example of a fuel injection system for a spark ignition internal combustion engine of the type described above. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] German Patent No. 10 2015 221286 Summary of the Invention [Problem to be solved by the invention]

[0011] However, known compressor devices used to supply air to the pre-combustion chamber cannot ensure that the supply takes place only at pressures in the range of 6-7 bar.

[0012] SUMMARY OF THE DISCLOSURE It is an object of the present invention to provide a fuel injection system for spark-ignition injected engines, which does not suffer from the above-mentioned drawbacks and which is particularly easy and economical to manufacture.

[0013] A further object of the invention is to provide a method for controlling a fuel injection system of a spark-ignition injected engine, which method does not suffer from the above-mentioned drawbacks and which is particularly easy and economical to implement. [Means for solving the problem]

[0014] According to the present invention there is provided a fuel injection system for a spark ignition internal combustion engine and a relative control method according to the appended claims.

[0015] The invention will now be described with reference to the accompanying drawings, which show non-limiting embodiments thereof. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a spark ignition internal combustion engine with some details omitted for clarity; FIG. [Diagram 2] FIG. 2 is a schematic diagram showing a first embodiment of a fuel injection device for an internal combustion engine according to the present invention shown in FIG. [Diagram 3] 2 is a schematic diagram showing a second embodiment of a fuel injection device for an internal combustion engine according to the present invention shown in FIG. 1. [Figure 4] FIG. 2 is a schematic diagram showing a third embodiment of a fuel injection device for an internal combustion engine according to the present invention shown in FIG. [Diagram 5] FIG. 2 is a schematic diagram showing a fourth embodiment of a fuel injection device for an internal combustion engine according to the present invention shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] In FIG. 1, the reference number 1 indicates as a whole a fuel injection system for a spark-ignition internal combustion engine.

[0018] The injection system 1 comprises a number of injectors 2, a common rail 3 supplying fuel under pressure to the injectors 2, a high-pressure pump 4 supplying fuel to the common rail 3 via a supply duct 5 and equipped with a flow regulator 6, an electronic control unit 7 adjusting the fuel pressure in the common rail 3 to a desired value which generally varies over time depending on the operating conditions of the engine, and a low-pressure pump 8 supplying fuel from a tank 9 to the high-pressure pump 4 via a supply duct 10.

[0019] An electronic control unit 7 is coupled to the flow regulator 6 to control the flow rate of the high pressure pump 4, which instantaneously supplies the common rail 3 with the amount of fuel required to have a desired pressure value in the common rail 3.

[0020] The spark-ignition internal combustion engine further comprises several (in particular four) cylinders 11, preferably arranged in a row, each housing a respective piston 12, each piston 12 being mechanically connected to a crankshaft by a connecting rod and transmitting the force generated by the combustion inside the cylinders 11 to the crankshaft itself.

[0021] Furthermore, in the case of a spark ignition engine, four spark plugs 13 (one for each cylinder 11) are coupled to the cylinders 11 for periodically determining the ignition of the gas mixture present in the cylinder 11. Each spark plug 13 is cyclically actuated for determining the ignition of compressed gases in a main combustion chamber MC defined within the cylinder 11 at the end of each compression stroke of the combustion cycle of the cylinder 11.

[0022] According to Fig. 2, an intake manifold 43 is connected to each cylinder 11 by two intake valves 14 (only one of them is shown in Fig. 2) from which it takes in a mixture of fresh (i.e., from the outside) air and, if necessary, EGR. Furthermore, the internal combustion engine comprises an exhaust manifold 15, which is connected to each cylinder 11 by two exhaust valves 16 (only one of them is shown in Fig. 2) and which leads to an exhaust duct (not shown) for discharging the gases produced by combustion to the atmosphere.

[0023] As is known, a complete combustion cycle is the result of a succession of four strokes, at the end of which two revolutions of the crankshaft are completed, covering an angle of 720°. Usually, during the intake stroke and / or the subsequent compression stroke and / or the subsequent expansion stroke, fuel is injected into the combustion chamber of the cylinder 11, and during the last part of the expansion stroke or the preceding compression stroke, the electrodes of the spark plug 13 generate a spark, which ignites the air-fuel mixture in the cylinder 11, starting the actual combustion and increasing the temperature and pressure. Finally, during the exhaust stroke, the burnt gases are expelled by the movement of the piston 12 through the respective exhaust valve 16 and are discharged into the exhaust manifold 15.

[0024] For each cylinder 11 there is provided a corresponding injector 2. The injection may be indirect, in which case each injector 2 is arranged upstream of the cylinder 11 in an intake duct connecting the intake manifold 43 to the cylinder 11, or it may be direct, in which case each injector 2 is arranged partly inside the cylinder 11.

[0025] Each cylinder 11 further comprises a respective duct 17, which extends from the area of ​​an extraction point P in the side wall of the cylinder 11 to a common reserve 18 shared by the four cylinders 11, in order to extract the mixture gas (fresh air and EGR and / or fuel) from the main combustion chamber MC of each cylinder 11. Said extraction point P can be taken above or below the top dead center of the stroke of the piston 12. Along the extraction duct 17, a control valve 19 is accommodated, which is arranged near the extraction point P and is configured to regulate the mixture gas passing through the extraction duct 17. The control valve 19 is preferably set to a predetermined pressure value (in the range of 4 or 5 bar) in order to prevent oil leakage during the compression stroke and the subsequent expansion stroke of the combustion cycle. Between the control valve 19 and the reserve 18, an injector 20 is interposed, which supplies the reserve 18 with the mixture gas extracted from the main combustion chamber MC of each cylinder 11. The injectors 20 are connected to the electronic control unit 7 and are controlled to extract the mixture from the main combustion chamber MC of each cylinder 11 during the compression stroke of the combustion cycle and to feed it into the reserve 18. In particular, the injectors 20 are controlled by the electronic control unit 7 to extract the mixture from the main combustion chamber MC of each cylinder 11 when the pressure inside the main combustion chamber MC is equal to or greater than the injection pressure of the pre-combustion chamber PC (within a given angular window of the combustion cycle). The injection pressure of the pre-combustion chamber PC is in the range of 8-12 bar, preferably the injection pressure of the pre-combustion chamber PC is equal to 10 bar.

[0026] According to a preferred variant, a filter 21 is accommodated along the extraction duct 16, preferably interposed between the injector 20 and the control valve 19, protecting the injector 20.

[0027] Furthermore, an injector 22 is provided which is suitable for supplying the reserve 18 with the amount of fuel required for a combustion under stoichiometric conditions to be carried out in the pre-combustion chamber PC, as will be explained in more detail below. This injector 22 is connected by a duct 23 to the low-pressure pump 8 or to the high-pressure pump 4. According to a preferred variant, the reserve 18 further comprises a temperature and pressure sensor 24 connected to the electronic control unit 7 and a lambda sensor 25 for reading the fuel-air equivalence ratio of the mixture, said sensors also being connected to the electronic control unit 7. According to a preferred variant, a fuel pressure sensor 26 is accommodated along the duct 23, which is connected to the electronic control unit 7 and which is suitable for diagnosing possible faults.

[0028] Each cylinder 11 further comprises an injector 27 connected to the reserve 18 by a respective duct 28. This injector 27 is arranged to feed the gas-fuel mixture contained in the reserve 18 into a pre-combustion chamber PC (or auxiliary combustion chamber) defined near the spark plug 13. Ignition of the fuel present in the mixture injected into the pre-combustion chamber PC (a proportion representing approximately 2-3% of the total fuel injected) increases the turbulence in the main combustion chamber MC of each cylinder 11 and thus improves the ignition of the fuel injected into the main combustion chamber MC of each cylinder 11. In particular, the injector 27 is controlled by the electronic control unit 7 to feed the gas-fuel mixture contained in the reserve 18 into the pre-combustion chamber PC when (within a given angular window of the combustion cycle) the pressure in said pre-combustion chamber PC is less than the pressure value at which the mixture was aspirated from the main combustion chamber MC.

[0029] FIG. 3 differs from FIG. 2 in that the injection device 1 includes a pumping device 29 accommodated along the duct 28 upstream of the injector 27. The presence of the pumping device 29 increases the flexibility of the injection into the pre-combustion chamber PC, since it makes it possible to control the injector 27 in such a way that the gas-fuel mixture contained in the reserve 18 is always delivered into the pre-combustion chamber PC (within any angular window of the combustion cycle). Furthermore, a pressure sensor 30 of the gas-fuel mixture is provided. This pressure sensor 30 is accommodated along the duct 28 and is interposed between the pumping device 29 and the injector 27. This sensor 30 is connected to the control unit 7, making it possible to control the injection of the gas-fuel mixture into the pre-combustion chamber PC.

[0030] Figure 4 differs from figure 3 in that a pumping device 29 is accommodated along the extraction duct 17, upstream of the reserve 18 and downstream of the injector 20. Again, the presence of this pumping device increases the flexibility of injection into the pre-combustion chamber PC, since it makes it possible to control the injector 27 so as to always feed the gas-fuel mixture contained in the reserve 18 into the pre-combustion chamber PC (within any angular window of the combustion cycle).

[0031] Preferably, a single pumping device 29 is provided which supplies the reserve 18 with the mixed gas coming from all cylinders 11. Alternatively, one pumping device 29 is provided for each cylinder 11, suitable for supplying the reserve 18 with the mixed gas coming from each cylinder 11.

[0032] Figure 5 differs from figure 3 in that a pumping device 29 is accommodated along the extraction duct 28 upstream of the injector 27. Again, the presence of this pumping device increases the flexibility of injection into the pre-combustion chamber PC, since it makes it possible to control the injector 27 so as to always supply the mixture of gas and fuel contained in the reserve 18 into the pre-combustion chamber PC (within any angular window of the combustion cycle).

[0033] Furthermore, the injection device 1 lacks both the injector 20 and the extraction duct 17. According to this embodiment, the injector 27 is suitable both for sucking the gas mixture from the main combustion chamber MC towards the reserve 18 and for feeding the gas-fuel mixture from the reserve 18 into the pre-combustion chamber PC. Furthermore, a pressure sensor 31 of the gas-fuel mixture is provided. This pressure sensor 31 is accommodated along the duct 28, interposed between the pumping device 29 and the injector 27. This pressure sensor 31 is connected to the electronic control unit 7 so as to be able to detect the pressure of the gas-fuel mixture and to control the injection into the pre-combustion chamber PC. Downstream of the pumping device 29, along the duct 28, a control valve 32 is accommodated. This control valve 32 is arranged to regulate the passage of the gas-fuel mixture through the duct 28. This control valve 32 is preferably set to a predefined pressure value (in the range of about 22 bar).

[0034] Furthermore, a connecting duct 33 is provided which connects the injector 27 to the reserve 18, along which a respective control valve 34 is accommodated which is arranged to regulate the passage of the mixed gas through said duct 33 and which is preferably set to a predetermined pressure value (in the range of about 12 bar).

[0035] The electronic control unit 7 manages the operation of the injectors 1 and, among other things, controls the spark plugs 13 so as to determine the ignition of the compressed gases in each cylinder 2 .

[0036] A method of controlling the injector 1 is described below. Said method comprises an initial intake stroke for aspirating the mixture from the main combustion chamber MC. The intake stroke requires the electronic control unit 7 to control the opening of the injector 20 (according to the embodiment shown in Fig. 2, Fig. 3 and Fig. 4) or the injector 27 (according to the embodiment shown in Fig. 5). Obviously, the opening of the injector 20 or the injector 27 is limited within an angle window of a complete combustion cycle stored in the electronic control unit 7. Each angle window is expressed in degrees of engine angle and is associated with the compression stroke of a complete combustion cycle of the cylinder 11. Each angle window is recognized by the signal of a phononic wheel sensor (not shown) mounted on the end of the crankshaft, detecting its rotational speed. Furthermore, according to the embodiment shown in Fig. 4 and Fig. 5, the electronic control unit 7 controls the pump device 29 in response to the signals detected by the sensors 24, 31 to increase the pressure of the mixture aspirated from the main combustion chamber MC to a value determined for injection into the pre-combustion chamber PC.

[0037] Following the intake stroke, the method of controlling the injector 1 includes a mixing step of mixing the gas and fuel mixture in the reserve 18. During this mixing step, the electronic control unit 7 controls the opening of the injector 22 to deliver an amount of fuel to the reserve 18 determined by a feedback (or closed loop) control performed via a signal from the lambda sensor 25.

[0038] Following the mixing step, the method of controlling the injector 1 includes an injection step of injecting the gas-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 which is limited within an angular window of a complete combustion cycle stored in the electronic control unit 7. Each angular 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 device 29 in response to the signals detected by the sensors 24, 31 to increase the pressure of the gas mixture aspirated from the main combustion chamber MC to a value determined for injection into the pre-combustion chamber PC.

[0039] Finally, following the injection step, the method of controlling the injector 1 includes an ignition step for igniting the mixture of gas and fuel in the pre-combustion chamber PC. During the ignition step, the electronic control unit 7 controls the firing of the spark plug 13. Obviously, the firing of the spark plug 13 is restricted to within angle windows of a complete combustion cycle that are stored in the electronic control unit 7. Each angle window is expressed in degrees of engine angle. [Explanation of symbols]

[0040] 1 Fuel injection device 2 Injectors 4. High pressure pump 8. Low Pressure Pump 11 Cylinders 12 Piston 13 Spark plug 17 Extraction duct 18 Reserve 20 Injector 22 Injector 23 Duct 24 Pressure Sensor 26 Fuel pressure pump 27 Injector 28 Extraction duct 29 Pumping Equipment 33 Duct P Extraction point PC combustion front chamber MC Main Combustion Chamber

Claims

1. A fuel injection device (1) for a spark ignition internal combustion engine, comprising: a number of cylinders (11) for receiving a mixture of gases including fresh air, each of which defines a main combustion chamber (MC); a first injector (2) coupled to each cylinder (11) for injecting fuel under pressure into said cylinder (11) during a combustion cycle; a spark plug (13) associated with each cylinder (11) for periodically establishing the ignition of the fuel present in said main combustion chamber (MC); a pre-combustion chamber (PC) respectively obtained in the region of each spark plug (13) in which the combustion of a gas mixture consisting of fresh air and fuel takes place in order to increase the turbulence in said main combustion chamber (MC) of each cylinder (11); Equipped with Furthermore, the fuel injection device (1) several extraction ducts (17; 28), each emanating from each cylinder (11) in the region of an extraction point (P) and extracting the mixture of gases present in each main combustion chamber (MC) during the combustion cycle; at least one reserve (18) receiving said mixed gas from said extraction duct (17; 28), in which said mixed gas from said extraction duct (17; 28) is mixed with a quantity of fuel necessary to obtain combustion under stoichiometric conditions inside said pre-combustion chamber (PC); a second injector (27) coupled to each pre-combustion chamber (PC) for injecting a mixture of gas and fuel from said reserve (18) into each pre-combustion chamber (PC); a third injector (22) delivering fuel to the reserve (18) and connected by a first duct (23) to the low pressure pump (8) or to the high pressure pump (4); A fuel injection device comprising:

2. 2. A fuel injection system according to claim 1, further comprising a fourth injector (20) arranged along each extraction duct (17; 28) for extracting the mixture gas from the main combustion chamber (MC) of each cylinder (11) and delivering it to the reserve (18).

3. 3. A fuel injection system as claimed in claim 2, comprising a filter (21) arranged along each extraction duct (17; 28) respectively upstream of said fourth injector (20).

4. 4. A fuel injection system according to claim 2 or 3, comprising a pump device (29) arranged along the extraction duct (17), upstream of the reserve (18) and downstream of the fourth injector (20).

5. 5. A fuel injection system as claimed in any one of claims 1 to 4, wherein each cylinder (11) houses a respective piston (12) and the extraction point (P) is obtained above top dead centre of the stroke of the pistons (12).

6. 5. A fuel injection system as claimed in any one of claims 1 to 4, wherein each cylinder (11) houses a respective piston (12) and the extraction point (P) is obtained below top dead centre of the stroke of the pistons (12).

7. 7. A fuel injection system as claimed in any one of claims 1 to 6, comprising a first control valve (19) arranged along each extraction duct (17) adjacent to the extraction point (P) and configured to regulate the flow of the mixed gas through the extraction duct (17).

8. A fuel injection system as claimed in any one of the preceding claims, comprising a fuel pressure sensor (26) arranged along the first duct (23).

9. 9. A fuel injection system as claimed in any one of the preceding claims, wherein the reservoir (18) is provided with temperature and pressure sensors (24) and has a lambda sensor (25) for reading the air / fuel ratio of the gas and fuel mixture.

10. 10. A fuel injection system as claimed in any one of the preceding claims, comprising several second ducts (28) conveying the gas and fuel mixture from the reserve (18) to each of the second injectors (27).

11. A fuel injection system as claimed in claim 10, comprising a pump device (29) housed along said second duct (28).

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

13. 13. A fuel injection system according to claim 11 or 12, wherein the second injector (27) is suitable both for injecting the gas and fuel mixture coming from the reserve (18) into each pre-combustion chamber (PC) and for extracting the gas mixture from the main combustion chamber (MC) of each cylinder (11) and for sending it to the reserve (18), and comprises several tertiary ducts (33) for sending the gas mixture from each main combustion chamber (MC) to the reserve (18).

14. 14. A fuel injection system according to claim 13, comprising a second control valve (32) configured to regulate the passage of the gas and fuel mixture through the second duct (28) and a third control valve (34) configured to regulate the passage of the mixed gas through the third duct (33).

15. A method for controlling a fuel injection device (1) according to any one of claims 1 to 14, comprising the steps of: an intake stroke in which the mixed gas is drawn from the main combustion chamber (MC) of the cylinder (11); a mixing step in which the mixed gas coming from the cylinder (11) is mixed with the fuel in the reserve (18); an injection step in which the gas and fuel mixture is injected into the pre-combustion chamber (PC); an ignition step in which the spark plug (13) is fired to ignite the gas and fuel mixture in a pre-combustion chamber (PC); The control method includes, in order:

16. 16. The method of claim 15, wherein the intake stroke and / or the injection stroke and / or the ignition stroke of the spark plug (13) are limited within an angle window of a complete combustion cycle.

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