Method for controlling fuel injection in an internal combustion engine and associated system

Abstract

This method for controlling fuel injection in a spark-ignition internal combustion engine (2) of a motor vehicle equipped with an exhaust gas aftertreatment device comprising at least one three-way catalyst (4), includes the steps of: Determining the maximum oxygen storage capacity of the catalyst (4), Calculating an estimated fuel-air ratio setpoint, Calculating an estimated amount of oxygen storage in the catalyst (4) based on the estimated fuel-air ratio setpoint, and Commanding resumption of injection when the estimated amount of oxygen storage in the catalyst (4) reaches a threshold value determined based on the maximum oxygen storage capacity of the catalyst (4). Figure for the abstract: [Fig 1]

Description

Title of the invention: Method for controlling fuel injection in an internal combustion engine and associated system. Technical field

[0001] The invention relates to a method for controlling fuel injection in an internal combustion engine.

[0002] It finds an advantageous application in a motor vehicle equipped with a spark-ignition engine. Previous techniques

[0003] A motor vehicle equipped with a combustion engine is generally equipped with a system for after-treatment of pollutants from the vehicle's exhaust gases in order to reduce emissions of these pollutants.

[0004] The aftertreatment system of a spark-ignition engine (of the type running on gasoline, in particular) generally includes a three-way catalyst that performs catalytic treatment of the exhaust gases, such as, for example, the oxidation of carbon monoxide and unburned hydrocarbons, and the reduction of nitrogen oxides. The treatment efficiency of the different pollutants depends on the amount of oxygen stored in the catalyst.

[0005] When the amount of oxygen stored in the catalyst is close to zero, the oxidation efficiency of certain polluting species decreases. This is particularly the case for unburned hydrocarbons and carbon monoxide.

[0006] When the amount of oxygen stored is close to the maximum oxygen storage capacity of the catalyst, the efficiency of reducing polluting species, for example for nitrogen oxides, decreases.

[0007] The amount of oxygen stored in the catalyst depends on the injection of an air-fuel mixture.

[0008] During certain driving situations, for example during a gear change or a so-called deceleration phase, fuel injection is automatically cut off to reduce fuel consumption, and air is sent into the aftertreatment system. The amount of oxygen stored in the catalyst then increases, for example up to the catalyst's maximum storage capacity, and pollutants are no longer treated effectively, particularly nitrogen oxides (NOx), which consist mainly of nitric oxide and nitrogen dioxide.

[0009] When fuel injection resumes, the amount of oxygen stored in the catalyst has reached its maximum oxygen storage capacity, meaning that When the catalyst becomes saturated with oxygen, a strategy to purge or reduce the oxygen load on the catalyst is generally implemented. The catalyst purging strategy involves increasing the richness of the injected air-fuel mixture to a ratio greater than 1, meaning the proportion of fuel in the injected air-fuel mixture is increased so that it exceeds the stoichiometric air-fuel mixture ratio, thus rapidly decreasing the amount of oxygen stored in the catalyst. However, the catalyst purging strategy significantly increases the vehicle's fuel consumption.

[0010] It is known that the richness of the injected air-fuel mixture influences the amount of oxygen stored in the catalyst. Thus, one solution to limit the increase in the amount of oxygen stored in the catalyst, for example during a gear change, is to maintain the richness of the injected air-fuel mixture in stoichiometric proportions by delaying the fuel injection cut-off mentioned above, so as not to saturate the catalyst with oxygen. The delay before fuel injection cut-off is generally set to a predetermined and constant duration, as described in unpublished patent application FR 2 101 953. In particular, this constant duration does not depend on the vehicle's wear and tear, and more specifically on the variation in the catalyst's oxygen storage capacity during aging, which leads to increased fuel consumption or oxygen saturation of the catalyst.The oxygen storage capacity of an aged catalyst compared to a new catalyst can, for example, vary by 35%.

[0011] An improvement proposed in unpublished patent application FR 2 202 809 sets the delay before fuel injection cutoff to a duration dependent on the maximum current oxygen storage capacity of the catalyst. However, this strategy does not take into account the possible variability in gear shift times. For example, a slow shift leads to maximizing the oxygen loading of the catalyst.

[0012] Publication FR-A-3 101 673 discloses a method for adjusting the fuel mixture in a motor vehicle internal combustion engine equipped with an upstream and a downstream catalyst. The fuel mixture is continuously adjusted to achieve an oxygen storage setpoint in the upstream catalyst between a minimum and a maximum threshold. In this configuration, the downstream catalyst tends to be almost constantly saturated with oxygen. After a deceleration phase, the oxygen storage setpoint is adjusted for a predetermined duration to the value of the minimum threshold, in order to decrease the amount of oxygen present in the downstream catalyst and improve the overall emissions control performance of both catalysts. catalysts. However, this curative process is only applicable to an architecture with two catalysts arranged in series and consists of temporarily lowering the value of the oxygen storage setpoint in the upstream catalyst in order to allow there to be leaks of HC and / or CO downstream of the upstream catalyst in order to consume the oxygen inside the downstream catalyst. Description of the invention

[0013] In view of the foregoing, the invention aims to strengthen the robustness of the treatment of polluting substances, in particular NOx.

[0014] The invention relates to a method for controlling fuel injection in a spark-ignition internal combustion engine of a motor vehicle equipped with a gaseous effluent aftertreatment device comprising at least one three-way type catalyst.

[0015] This process includes the steps of: - Determination of the catalyst's maximum oxygen storage capacity, - Calculation of an estimated fuel-air mixture setpoint, - Calculation of an estimated quantity of oxygen stored in the catalyst as a function of the estimated fuel-air ratio setpoint, and - Resumption of injection command when the estimated quantity of oxygen stored in the catalyst reaches a threshold value determined according to the maximum oxygen storage capacity of the catalyst.

[0016] The control method of the invention makes it possible to control fuel injection by a preventive type strategy which avoids oxygen saturation of the catalyst and which helps to strengthen the effectiveness of the treatment of polluting substances, in particular nitrogen oxides.

[0017] Advantageously, the threshold value is determined as a percentage of the maximum oxygen storage capacity of the catalyst.

[0018] For example, the percentage is greater than 80%.

[0019] According to one feature, the maximum oxygen storage capacity is determined during a transition from a lean mixture engine operating mode, capable of saturating the catalyst with oxygen, to a rich mixture engine operating mode, capable of emptying the catalyst of its oxygen stock, the beginning of said saturation being evidenced by the switching of an oxygen sensor located downstream of the catalyst to an exceptionally low voltage level, and the beginning of said emptying being evidenced by the switching of said oxygen sensor located downstream of the catalyst to an exceptionally high voltage level.

[0020] According to another characteristic, the maximum oxygen storage capacity OSC is determined from an exhaust gas flow rate Qech of the engine and an air-fuel ratio RX from a sensor located upstream of the catalyst using the following equation:

[0021] / \ / , x , (Eq.3) [fl - ax OSC = ...Q, x (1 - R,) xx dtv r ] ■ tO^ech X AJ

[0022] in which: - ro2 refers to the mass concentration of oxygen in the air (approximately 23%), - tO represents the instant when the electronic control unit switches the engine to rich mixture operation, immediately after the switch to an exceptionally low voltage from the oxygen sensor located downstream of the catalyst, - tl represents the instant when the probe located downstream of the catalyst switches to an exceptionally high voltage, - a denotes a constant approximately equal to 90%, and - [3 denotes a constant approximately equal to 40%.

[0023] Advantageously, the estimated richness setpoint is calculated based on a transit time of the gases between the engine and an exhaust line.

[0024] For example, the transit delay is mapped in advance in a memory of an electronic motor control unit, said delay depending on a motor operating point and its geometry.

[0025] According to another aspect, the invention also relates to a fuel injection control system in a spark-ignition internal combustion engine of a motor vehicle equipped with a gaseous effluent aftertreatment device comprising at least one three-way type catalyst.

[0026] The system includes means for determining the maximum oxygen storage capacity of the catalyst, means for calculating an estimated richness setpoint, means for calculating an estimated quantity of oxygen storage of the catalyst as a function of the estimated richness setpoint, and means for resuming injection when the estimated quantity of oxygen storage of the catalyst reaches a threshold value determined as a function of the maximum oxygen storage capacity of the catalyst.

[0027] According to another aspect, the invention also relates to a motor vehicle equipped with a fuel injection control system as described above. Brief description of the drawings

[0028] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0029] [Fig. 1] illustrates, schematically, the structure of an internal combustion engine internal of a motor vehicle equipped with a fuel injection control system according to the invention; and

[0030] [Fig.2] illustrates an early resumption strategy of injection according to the invention; and

[0031] [Fig.3] illustrates a flowchart of the steps of a fuel injection control method according to the invention. Detailed description of at least one embodiment

[0032] Figure 1 shows a device 1 for treating pollutants emitted by an internal combustion engine 2, in particular a motor vehicle engine. The engine 2 is a spark-ignition engine with direct or indirect injection. It may, but is not limited to, be naturally aspirated or turbocharged. It may also have other features, such as being associated with at least one partial exhaust gas recirculation circuit at the intake.

[0033] An exhaust line 3 allows the exhaust gases G from the engine 2 to be vented to the outside atmosphere. A post-treatment device for purifying the exhaust gases G is interposed in the line 3. It mainly comprises at least one three-way catalyst 4. The catalyst 4 treats several pollutants such as nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon oxides (CO) present in the combustion gases of the engine 2.

[0034] The treatment device 1 for polluting species may further include a second post-treatment device (not shown) mainly comprising a fine particle filter.

[0035] The engine 2 is associated with a fuel supply circuit comprising, for example, fuel injectors (not referenced) injecting fuel directly into each cylinder from a fuel tank (not shown).

[0036] Furthermore, the engine includes an electronic control unit 5 programmed to control the various elements of the engine 2 or, more generally, of the vehicle's propulsion system, from data collected by sensors at different locations in the engine 2.

[0037] The electronic control unit 5 comprises an information storage module 5a, in this case a memory, a calculation module 5b, a measurement module 5c and a control module 5d.

[0038] The electronic control unit 5 determines the quantity of fuel Qcarb to be injected into the engine 2 so that the mixture richness is as close as possible to a given richness, for example, a richness value of 1 corresponding to the stoichiometric proportions of the air-fuel mixture. The electronic control unit 5 controls the deactivation and activation of the fuel injectors.

[0039] The richness of the air-fuel mixture is controlled by the electronic unit of command 5 from information and parameters such as the pressure in the intake manifold of engine 2, the engine speed of engine 2 and representative information of the richness of the air-fuel mixture.

[0040] In the example illustrated in [Fig.1], the electronic control unit 5 is thus connected to a pressure sensor 6 which allows a value of the pressure prevailing in the intake manifold of the engine 2 to be determined, to a sensor 7 which allows the number of passages at top dead center of one of the pistons of the engine 2 to be determined, and to a first oxygen probe 8 mounted upstream of the catalyst 4.

[0041] The probe 8 located upstream of the catalyst 4 is of the proportional type. It provides information, generally a voltage signal, which is representative of the richness of the mixture and which allows its value to be determined.

[0042] The electronic control unit 5 is further connected to a second oxygen sensor 9 mounted downstream of the catalyst 4. This sensor 9 can be of the binary type, i.e. providing an output signal which only allows the rich or lean state of the mixture to be known.

[0043] Fig. 2 illustrates the evolution over time of the data measured during a gear change of an internal combustion engine, accompanied by data from modeling and an early injection recovery strategy implemented by means of an injection control method according to the invention.

[0044] Figure 2 shows the evolution of the measured data during a fuel injection cut-off resulting from a gear change. The invention also applies to deceleration phases, when the driver lifts their foot from the accelerator pedal, causing a fuel injection cut-off.

[0045] In the illustrated example, a change of gearbox ratio results in a cut-off of the fuel injection, represented by the parameter inj_cut with a value of 1 in the event of a cut-off of the injection and a value of 0 otherwise.

[0046] Curve 10 represents the richness determined on the basis of measurements made by the oxygen probe 8 located upstream of the catalyst 4.

[0047] Curve 11 represents the richness setpoint used for regulating the engine's richness.

[0048] When fuel injection is restored, in other words when the inj_cut parameter returns to a zero value, there is a delay before its impact on the measured air-fuel ratio 10 is observed, mainly due to the transit time of the gases from the engine cylinders 2 to the oxygen sensor 8 located upstream of the catalytic converter 4. The value of this delay is generally already available to the electronic control unit 5 because it is used in standard air-fuel ratio control methods. This delay can, for example, be determined and stored in advance as a car tography in memory 5a of the electronic control unit 5. The delay value depends on the operating point of the motor and its geometry.

[0049] This delay is taken into account to anticipate the resumption of fuel injection by calculating an estimated richness setpoint represented by curve 12 of [Fig.2] which thus precedes curve 11 representing the richness setpoint used classically.

[0050] Depending on the estimated richness setpoint, the electronic control unit 5 also calculates an estimated quantity of oxygen storage of the catalyst 4, illustrated by curve 13 and shifted with respect to curve 14 representing the quantity of oxygen storage of the catalyst 4 calculated without anticipation.

[0051] The OSC parameter represents the maximum oxygen storage capacity of the catalyst 4, illustrated by the substantially constant level 15.

[0052] The maximum oxygen storage capacity OSC can advantageously be determined regularly each time the engine 2 is started, in order to take into account the long-term aging of the catalyst 4 and possible failures. The value of the maximum oxygen storage capacity OSC thus determined can be stored in the memory 5a of the electronic control unit 5 for later use.

[0053] The engine's electronic control unit 5 can, in particular, trigger a transition from a lean to a rich operating mode of the engine 2. Initially, the engine's operation with a zero fuel mixture, corresponding to an injection cutoff, saturates the catalyst 4 with oxygen. The approach of the maximum oxygen storage capacity (OSC), for example 90% of this maximum OSC, is signaled by the fact that the sensor 9 located downstream of the catalyst 4 begins to switch to an exceptionally low voltage level (Umin), for example, below 150 mV.

[0054] At this point, we can consider that the following equation is verified:

[0055] OS = ax OSC (Eq.l)

[0056] with a~0.9.

[0057] In other words, the probe's tilting detects the beginning of catalyst saturation when the catalyst saturation value reaches a predetermined threshold value, for example, 90% of full saturation, i.e., a high OSC percentage close to 90%. The full saturation value can, for example, be obtained by weighing through tests carried out on a test bench.

[0058] The electronic control unit 5 then immediately applies a richness level greater than 1 when restarting after injection cut-off, so as to allow the catalyst 4 to gradually empty itself of its oxygen, until the probe 9 located downstream of the catalyst 4 observes that the mass of stored oxygen is approaching zero,

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[0069] by switching to an exceptionally high Umax voltage level, for example above 870 mV. At this moment, the amount of oxygen stored still reaches 40% of the maximum oxygen storage capacity. The following equation is then verified: OS = 0X OSC (Eq.2) with [3«0.4. In other words, the tipping of the probe here allows the detection of the beginning of the catalyst emptying, corresponding to a still significant percentage [3, equal to 40% of the OSC. Calculation module 5b then calculates the OSC oxygen storage capacity using the following equation: - aj x OSC = x (1 - x Tm x dt in which: - Qech refers to the exhaust gas flow rate, - refers to the upstream richness of the catalyst, - ro2 refers to the mass concentration of oxygen in the air (approximately 23%), - tO represents the instant when the electronic control unit switches the engine to rich mixture operation, immediately after the switch to an exceptionally low voltage from the oxygen sensor located downstream of the catalyst, - tl represents the instant when the probe located downstream of the catalyst switches to an exceptionally high voltage, - a denotes a threshold value approximately equal to 90%, and - [3 denotes a threshold value approximately equal to 40%. Referring again to [Fig.2], when the estimated quantity of oxygen storage 13 reaches a threshold value 16, the electronic control unit 5 commands the resumption of fuel injection even in the absence of a higher torque request, i.e. even if the driver has not pressed the accelerator pedal again. The threshold value 16 represents a "lean" leakage zone, i.e., a zone in which the oxygen stock in the catalyst is high enough that it no longer effectively processes nitrogen oxides. Preferably, the threshold value 16 is determined by the electronic control unit 5 as a function of the oxygen storage capacity of the catalyst 4, for example, equal to a percentage of the catalyst's oxygen storage capacity, typically greater than 80%. In the example illustrated in [Fig.2], the injection is resumed in advance with a advance of 380ms. Thus, the fuel injection cut-off time decreases from 600ms to 220ms.

[0070] It should be noted that the early resumption of injection according to the invention does not present any particular risk of engine speed surge or untimely acceleration, since the clutch is still in the disengaged position. Furthermore, setting a low ignition advance means that the injected fuel burns late in the combustion cycle without producing significant engine torque.

[0071] The preventative strategy proposed by the invention ensures that the amount of oxygen in the catalyst does not exceed a threshold value, thus guaranteeing effective treatment of pollutants, particularly NOx. This strategy offers the advantage of significantly greater robustness in NOx treatment compared to conventional methods, as it takes into account several variable parameters such as the catalyst's oxygen storage capacity and the shift duration. Furthermore, restoring fuel injection at the end of a gear change reduces fuel consumption compared to the same injection at the beginning of the shift, in other words, compared to a delayed fuel cut-off. Indeed, at the end of a gear change, the airflow decreases sharply until it reaches an asymptote corresponding to the minimum manifold pressure limit.Thus, the fuel flow rate to be injected to generate a mixture with a given richness is significantly lower.

[0072] We will now describe, with reference to [Fig. 3], a method 20 for regulating fuel injection in an internal combustion engine 2 as described previously. Such a method is implemented in particular by the electronic control unit 5 based on measurements delivered by the various sensors of the engine and by controlling the various elements of the engine or, more generally, of the vehicle's propulsion system.

[0073] The process 20 includes a preliminary step 21 of determining the maximum oxygen storage capacity OSC of the catalyst 4. As explained previously, the value of the maximum oxygen storage capacity OSC is determined either by a calculation carried out by the calculation module 5b from equation 3, or directly from a previously calculated OSC value available in the memory 5a of the electronic control unit 5.

[0074] In the next step 22, the process continues by calculating an estimated richness setpoint calculated by the electronic control unit 5 as a function of a transit time of the gases between the engine 2 and the exhaust line 3. The transit time is mapped in advance in a memory 5a of the electronic control unit 5 and depends on the geometry of the engine and its operating point, typically represented by the engine speed and load.

[0075] From the estimated richness setpoint, the electronic control unit 5 calculates the estimated quantity of oxygen storage of the catalyst 4 (step 23).

[0076] When the estimated quantity of oxygen storage calculated in step 23 reaches a predetermined threshold value, the process continues with a resumption command for fuel injection carried out by the control module 5d of the electronic control unit 5 (step 24).

Claims

Demands

1. A method (20) for controlling fuel injection in a spark-ignition internal combustion engine (2) of a motor vehicle equipped with a gaseous effluent aftertreatment device comprising at least one three-way type catalyst (4), said control method being characterized in that it comprises the steps of: - Determining the maximum oxygen storage capacity (OSC) of the catalyst (4), - Calculating an estimated richness setpoint, calculated as a function of a gas transit time between the engine (2) and an exhaust line (3), - Calculating an estimated amount of oxygen storage of the catalyst (4) as a function of the estimated richness setpoint, and - Commanding resumption of injection when the estimated amount of oxygen storage of the catalyst (4) reaches a threshold value determined as a function of the maximum oxygen storage capacity (OSC) of the catalyst (4).

2. Method (20) according to claim 1, wherein the threshold value is determined as a percentage of the maximum oxygen storage capacity of the catalyst (OSC).

3. Method (20) according to claim 2, wherein the percentage is greater than 80%.

4. A method (20) according to any one of claims 1 to 3, wherein the maximum oxygen storage capacity (OSC) is determined during a transition from a lean-mixture engine operating mode, capable of saturating the catalyst with oxygen, to a rich-mixture engine operating mode, capable of emptying the catalyst of its oxygen stock, the beginning of said saturation being evidenced by the switching of an oxygen sensor located downstream of the catalyst to an exceptionally low voltage level, and the beginning of said emptying being evidenced by the switching of said oxygen sensor located downstream of the catalyst to an exceptionally high voltage level.

5. A method (20) according to claim 4, wherein the maximum oxygen storage capacity (OSC) is determined from a gas flow rate exhaust (Qech) of the engine and a richness (RX) from a sensor located upstream of the catalyst using the following equation: - aj x OSC = CQeeb x (1 - x rm x dt (Eq'3) in which: - ro2 denotes the mass percentage of oxygen in the air (approximately 23%), - tO represents the instant when the electronic control unit switches the engine operation to a rich mixture, immediately after the switch to an exceptionally low voltage from the oxygen sensor located downstream of the catalyst, - tl represents the instant when the sensor located downstream of the catalyst switches to an exceptionally high voltage, - a denotes a constant approximately equal to 90%, and - [3 denotes a constant approximately equal to 40%.

6. A method (20) according to any one of claims 1 to 5, wherein the transit time is mapped in advance in a memory (5a) of an electronic control unit (5) of the motor (2), said time depending on an operating point of the motor (2) and its geometry.

7. Fuel injection control system in a spark-ignition internal combustion engine (2) of a motor vehicle equipped with an exhaust gas aftertreatment device comprising at least one three-way catalyst (4), said control system being characterized in that it comprises: - Means for determining the maximum oxygen storage capacity (OSC) of the catalyst (4), - Means for calculating an estimated fuel-air mixture setpoint, calculated as a function of a gas transit time between the engine (2) and an exhaust line (3), - Means for calculating an estimated quantity of oxygen storage of the catalyst (4) as a function of the estimated fuel-air mixture setpoint, and - Means for controlling the resumption of injection when the estimated quantity of oxygen storage of the catalyst (4) reaches a threshold value determined according to the maximum oxygen storage capacity (OSC) of the catalyst (4).

8. Motor vehicle equipped with a fuel injection control system according to claim 7.

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