Method of control for the prevention of backfire

Abstract

A method (100) of control for preventing backfire of a fuel in internal combustion engines equipped with at least one injector per engine cylinder, the method comprising the following steps: - calculating the limits of a fuel injection as a function of the valve opening, limits within which backfire is prevented, - calculating the opening delay (OD) and the closing delay (CD) of an injector with respect to the electrical injection command signal, - correcting the electrical injection command signal in terms of advance and duration, - performing a redundant control of the end of injection in terms of electrical injection command signal.

Description

[0001] METHOD OF CONTROL FOR THE PREVENTION OF BACKFIRE

[0002] DESCRIPTION

[0003] Technical Sector of the Invention

[0004] The present invention relates to a control method for the prevention of backfire in internal combustion engines. The method is particularly suitable for internal combustion engines powered by hydrogen, but not limited to this fuel.

[0005] Background art

[0006] Motor vehicles typically operate using an internal combustion engine to convert the energy of a fuel, such as gasoline or diesel, into mechanical energy to power the vehicle and consequently supply motion to the wheels of the vehicle. Unfortunately, fossil fuels are expensive and contribute to environmental pollution. Because of these drawbacks, increasing attention is being paid to reducing fuel consumption and pollutants emitted by automobiles and other road vehicles.

[0007] To alleviate some of these drawbacks, internal combustion engines powered by hydrogen have been proposed that do not produce polluting emissions except for negligible amounts of nitrogen oxides. However, such engines require special measures to ensure proper operation.

[0008] Reference is made, in particular, to engines powered by hydrogen by means of indirect injection (or PFI, from the English Port Fuel Injection), with hydrogen injected into the intake duct of each cylinder upstream of the corresponding intake valve. Anomalous combustion phenomena limit the improvement of the performance of these internal combustion engines PFI: one of these is the backfire, deriving from the high flame propagation speed of hydrogen combustion in such engines. This flame front propagates from the combustion chamber backwards along the intake ducts causing damage to both the intake system and the fuel injection system. The problem of backfire is, therefore, typical of hydrogen, while for other fuels, such as gasoline or natural gas (CNG), this problem, although present, does not present the same criticalities.

[0009] Several factors can cause backfire, for example fuel pre-ignition, spontaneous detonation (knock) of the air-hydrogen mixture inside the combustion chamber and the resulting noise, the reflux of exhaust gases. In particular, pre-ignition has been considered the main cause of backfire and, among the various reasons that can cause pre-ignition of hydrogen, the most important is the injection of the hydrogen itself both in terms of timing and duration.

[0010] Figure 1 is a diagram of the valve lifts (exhaust and intake) as the rotation angle of the crankshaft varies.

[0011] The injection, normally, takes place within the intake phase from - 360° to -180° of the engine shaft. Under these conditions, probability of a backfire occurring is low (in Figure 1, the field delimited by the green arrows, Low Backfire). If, for any reason (engine control strategy, injector drift, etc.), the injection advance changes or changes its overall duration, there is a risk of entering the zone in which there is a higher probability of a backfire occurring (in Figure 1, the field delimited by the red arrows, High Backfire).

[0012] In fact, the fuel injection times are correlated to the air / fuel equivalence ratios of the mixture around the intake valve seats at the beginning of the intake phase. If hydrogen injection starts too early, hydrogen-rich zones form on the back of the valve seats before the intake valves open. An air / hydrogen mixture rich in hydrogen would be ignited by the exhaust gases at high temperature for the entire duration of the intake valves. In the other situation, the end of the injection is delayed, hydrogen is still dispensed after the intake valves close. The air / hydrogen mixture rich in hydrogen would accumulate around the intake valve seats and would be ignited at the beginning of the intake phase in the next cycle. Ultimately, as reported in Figure 1, the closer the start of hydrogen injection is to the opening of the intake valve, the greater the possibility of backfire; moreover, the closer the end of hydrogen injection is to the closing of the intake valve, the greater the possibility of backfire. Therefore, the phenomenon of backfire depends on the combined effect of the valve phasing and phasing of the injection.

[0013] Therefore, there is a need to define countermeasures to solve the problem of backfire in internal combustion engines powered by hydrogen.

[0014] Summary of the Invention

[0015] To substantially solve the technical problems highlighted above, one purpose of the present invention is a control method for the prevention of backfire in internal combustion engines, particularly in internal combustion engines powered by hydrogen, the method being based on the control of the timing and duration of hydrogen injection.

[0016] Therefore, according to the present invention, a control method is provided for the prevention of backfire in internal combustion engines having the characteristics stated in the independent claim, attached to the present description.

[0017] Further embodiments of the invention, preferred and / or particularly advantageous, are described according to the characteristics stated in the attached dependent claims.

[0018] Brief Description of the Drawings

[0019] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting implementation examples, in which:

[0020] - Figure 1 is a diagram of the valve lifts of an internal combustion engine with hydrogen PFI injection,

[0021] - Figure 2 is a logic diagram of a method for the prevention of backfire in internal combustion engines, according to a preferred embodiment of the invention,

[0022] - Figure 3 is a first explanatory example of the method of Figure 2,

[0023] - Figure 4 is a second explanatory example of the method of Figure 2,

[0024] - Figure 5 is a detail of the method of Figure 2,

[0025] - Figure 6 is a third explanatory example of the method of Figure 2, and - Figure 7 is a logic diagram of an actuation form complementary and implementable to the method of Figure 2.

[0026] Detailed Description

[0027] By way of purely exemplary and non-limiting example, the method for the prevention of backfire in internal combustion engines will now be described with reference to the aforementioned figures. It should be noted that the method, specifically applied to hydrogen fuel, can also be used for other fuels, modifying the fuel parameters in an obvious way for a person skilled in the art.

[0028] With particular reference to Figure 2, the method 100 according to the present invention comprises:

[0029] - a first phase 10 which is a control of the commands of the fuel injectors with respect to the geometric characteristics of the valve lift and relative "timing" and the hydraulic characteristics of the injectors, and

[0030] - a second phase 20 which is a control of the output data of the injector and, for the purposes of the present invention, detects because it performs a redundant control of the end of injection EOI (from the English End of Injection).

[0031] In particular, the first phase 10 includes the following steps:

[0032] - a first step 30 is a calculation model of the geometric limits of fuel injection as a function of valve openings, within which there is a low probability of backfire occurring,

[0033] - a second step 40 is a hydraulic calculation model of the injector. This model calculates the opening delay (OD, Opening Delay) and the closing delay (CD, Closing Delay) hydraulic of the injector with respect to the electrical control signal of the injection,

[0034] - a third step 50 verifies whether it is necessary to correct the electrical command of the injection in terms of advance and duration.

[0035] At the end of these three steps, as already mentioned, within the second phase 20, a fourth step 60 performs a redundant control of the end of injection in terms of the electrical control signal of the injection.

[0036] With reference also to Figure 3, the first step 30 assumes as input data the engine speed (Eng Spd) and the geometric and temporal parameters of the intake valves (Intake Valve) and exhaust valves (Exhaust Valve). This essentially involves: valve timing (Valve Timing), valve lift (Valve Lift) and valve duration (Valve Duration). The valve parameters can come from appropriate sensors (Sensor based) installed on the internal combustion engine or from models (Model based) specifically implemented in the engine management software. Independently of how the input data originated, this step can manage any method of valve phasing, such as, for example, the well-known Variable Valve Actuation (VVA), Variable Valve Timing (VVT) and similar.

[0037] Based on these input data, the calculation model of the geometric limits, which in step 30 calculates the hydraulic limits of the injection within which there is a low or almost zero probability of backfire occurring, is defined. The lower hydraulic limit is defined as Backfire SOI limit, in which SOI (Start of Injection) is the start of the injection, while the upper hydraulic limit is defined as Backfire EOI limit, in which EOI (End of Injection) is the end of the injection. The calculation model has as its objective to center the injection as much as possible within the interval, within the intake phase, in which there is maximum volumetric efficiency, in order to allow the cylinder to aspirate all the air and hydrogen mixture. In this way, the concentration of residual hydrogen in the intake duct is reduced (or eliminated in the theoretical case). The validation of this approach and a possible adaptation of the injection positioning then takes place with specific calibration tests on the engine.

[0038] With reference to figures 2 and 4, the second step 40 is a hydraulic calculation model of the injector. This model assumes the following input data:

[0039] - the pressure difference (Ap) between the fuel pressure, for example hydrogen, and the air supercharging pressure,

[0040] - the fuel temperature (THZ), - the battery voltage (Ubat), and

[0041] - the engine speed.

[0042] The calculation model determines the opening delay (OD) and the closing delay (CD) of the injector (curve 46) with respect to the electrical command (curve 45) of the injection itself. The opening delay is calculated in temporal values in block 41 while the closing delay is always calculated in temporal values in block 42. These quantities are calculated as a function of the first three input parameters, namely the pressure difference (Ap), the fuel temperature (THZ) and the battery voltage (Ubat). In the diagram on the side in Figure 4, these two delays (OD, CD) are represented on a temporal scale. Subsequently, these two temporal quantities are transformed, respectively in blocks 43 and 44, into angular quantities (ODCA, CDCA) referred to the crankshaft. Also the input parameters of step 40 can come from appropriate sensors (Sensor based) installed on the internal combustion engine or from models (Model based) specifically implemented in the engine management software.

[0043] With reference to Figure 5, the third step 50 assumes as input data the start of the electrical signal (SOL) and the duration of the electrical signal (ET) for the generic injector. Furthermore, it acquires the results of the two previous steps 30, 40. In particular, from step 30 it acquires the lower hydraulic limit (Backfire SOI limit) of the injection and the upper hydraulic limit (Backfire EOI limit) of the injection. From step 40 it acquires instead the opening delay (OD) and the closing delay (CD) of the injector with respect to the electrical command. The third step 50 verifies if it is necessary to correct the electrical command signal of the injector in terms of advance and duration providing as output data the final commands of the start of the electrical signal (SOL) and of the duration of the electrical signal (ET) for the generic injector.

[0044] Finally, the fourth step 60 performs a redundant check of the end of the electrical signal (EOI) of the injection command with finer resolution.

[0045] Indeed, since all the angular quantities of the end of injection are estimated based on the engine speed and the duration of the command starting from the start of the electrical signal (SOI), the estimation of the engine speed is performed by a high-level software with a frequency equal to 720° of the crankshaft (or one engine revolution) divided by the number of cylinders. For example, on an 8-cylinder engine, the engine speeds are updated with a frequency of 90°. The redundant check is performed, instead, by a low-level software, for which the resolution is much higher, since the reading of the engine position and, consequently, of the engine speeds, is done having the information of the "timing system" (crankshaft and camshaft). This means that the low-level control is able to update the value of the engine speeds and the positions of the start of the electrical signal (SOL) and of the end of the electrical signal (EOI) with a frequency equal to the angular distance between the two fronts of the teeth of the phonic wheel of the crankshaft, i.e. 6°. In this way, the conversion of the duration of the injection command and, consequently, the end of the electrical signal (EOI) starting from the start of the electrical signal (SOL) is done with a more accurate resolution, equal to the ratio between the engine speed update frequency in the high-level software and the engine speed update frequency in the low-level software. This allows a much more precise and coherent final check with the engine revolutions as up-to-date as possible, guaranteeing a higher accuracy of the control on the end of the electrical signal (EOI). The effects of the application of the methodology are illustrated in figure 6. In this figure, the phases of intake and compression of the engine are reported on a qualitative time scale. The limits defined by the methodology are then reported so that the injection takes place under conditions of low risk of backfire. In particular:

[0046] - lower hydraulic limit 1 (Backfire SOI limit) of the injection determined to prevent backfire, - upper hydraulic limit 2 (Backfire EOI limit) of the injection determined to prevent backfire,

[0047] - limit of the end of the electrical signal 3 of the injection command, evidently correlated with the upper hydraulic limit 2. In each of the three boxes, the electrical signal 4 of the injection command and the effective injection 5 of a generic injector are also reported. In particular, the start of the electrical signal (SOL) and the duration of the electrical signal (ET) are indicated for the electrical signal 4, while for the injection 5, the opening delay (OD) of the injector with respect to the start of the electrical signal (SOI), the closing delay (CD) of the injector with respect to the end of the electrical signal (EOI) and the injection duration (injected quantity) are indicated.

[0048] In the first box 6a, the electrical signal 4 and the injection 5 are reported before the method intervention for the prevention of backfire. As can be seen, there is a portion 6 of the injection that exceeds the upper hydraulic limit 2.

[0049] In the second box 6b, the electrical signal 4 and the injection 5 are represented after the intervention of correction of the electrical signal of command of the injector in terms of timing. As can be observed, the effective start of the injection, downstream of the opening delay (OD), is aligned with the lower hydraulic limit 1. However, there is still a portion 7 of the injection that exceeds the upper hydraulic limit 2.

[0050] Finally, in the third box 6c, the electrical signal 4 and the injection 5 are represented after the intervention of correction of the electrical signal of command in terms of duration (ET). Thanks to this further corrective intervention, in addition to the alignment of the effective start of the injection with the lower hydraulic limit 1, it is observed that the end of the injection 8, including the closing delay (CD), is aligned with the upper hydraulic limit 2 and simultaneously the end of the electrical signal (EOI) is aligned with the limit of the end of the electrical signal 3.

[0051] The method according to the present invention can be used in the case of internal combustion engines having a single injector per cylinder but also in the case of engines having two injectors per cylinder. This occurs when the engine has performance requirements in terms of power and very high torque. With reference to figure 7, in the case of double injector per cylinder, step 400 is to be understood as step 40 with the selection of one or two injectors per cylinder based on the capacity of the injector, the operating points of the engine and the limit conditions, through an intelligent software logic that allows the improvement of the performance at full load and the control of the minimum, contemporaneously. When the single injector mode is used, a further step 450 can also be provided in which an injector is selected according to an alternating selection logic between the two injectors in order to allow uniform aging of the injectors, alternating them, engine cycle per engine cycle. The results at the output of step 450 are used from step 50 as previously described.

[0052] In conclusion, the method according to the present invention guarantees safety and protection of the engine from possible flame returns of the fuel, hydrogen in particular, applying effective corrective actions.

[0053] In addition to the form of realization of the invention, as described above, it must be understood that there are numerous other variants. It must also be understood that such forms of realization are only exemplary and do not limit either the scope of the invention, nor its applications, nor its possible configurations. On the contrary, although the description above allows the skilled technician to implement the present invention at least according to one of its exemplary embodiments, it must be understood that many variants of the described components are possible, without thereby departing from the scope of the invention, as defined in the attached claims, which are interpreted literally and / or according to their legal equivalents.

Claims

C LA I M S1. Control method (100) for fuel backfire prevention in internal combustion engines equipped with at least one injector per engine cylinder, the method comprising the following steps:- calculating the limits of a fuel injection based on the intake and exhaust valve openings, limits within which backfire is prevented,- calculating the opening delay (OD) and the closing delay (CD) of an injector with respect to an electrical injection control signal,- correcting the electrical injection control signal in terms of timing and duration, providing as output data the final commands of the injector electrical signal start (SOL) and electrical signal duration (ET),- carrying out a redundant control of the end of the injection in terms of the electrical injection control signal, wherein the reading of the engine position and engine rpm has a frequency equal to the angular distance between two fronts of the teeth of a phonic wheel of the internal combustion engine.

2. Method (100) according to claim 1, wherein the step of calculating the limits of a fuel injection as a function of the valve openings takes the following quantities as input:- engine speed,- valve timing,- valve lift,- duration of valve opening.

3. Method (100) according to any of the previous claims, wherein the step of calculating the opening delay (OD) and the closing delay (CD) takes the following quantities as input:- pressure difference (Ap) between fuel pressure and air boost pressure,- fuel temperature (TH2),- battery voltage (Ubat), and- engine speed.

4. Method (100) according to claim 3, wherein the opening delay (OD) and the closing delay (CD) are determined as temporal quantities and as a function of the pressure difference (Ap), the fuel temperature (THZ) and battery voltage (Ubat).

5. Method (100) according to claim 4, wherein the opening delay (OD) and the closing delay (CD) are transformed from time quantities into angular quantities (ODCA, CDCA) referred to the crankshaft.

6. Method (100) according to any of the previous claims, wherein the step of correcting the electrical injection control signal in terms of timing and duration acquires as input:- the start of the electrical signal (SOL) and the duration of the electrical signal (ETi) of the injector,- the lower hydraulic limit of the injection and the upper hydraulic limit of the injection to prevent backfire,- the opening delay (OD) and closing delay (CD) of the injector with respect to the electrical control.

7. Method (100) according to claim 5, wherein the engine is provided with two injectors per engine cylinder and the step of calculating the opening delay (OD) and the closing delay (CD) selects one or two injectors per cylinder based on injector capacities, engine working points and limit conditions.

8. Method (100) according to claim 7, wherein when selecting a single injector, an alternating selection logic is followed between the two injectors so as to allow uniform aging of the injectors.

9. Method (100) according to claim 2, wherein the input quantities come from sensors installed on the internal combustion engine or from models implemented in the engine management software.

10. Method (100) according to any of the previous claims, wherein the fuel is hydrogen.

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