Method for regenerating particulate filters in spark-ignition internal combustion engines and related devices

Abstract

The present invention proposes a method for regenerating a particulate filter installed in the exhaust system of a spark-ignition internal combustion engine of a motor vehicle. The method includes a first mode of active conventional regeneration with a lean mixture having a richness close to 0.90, which is used when the particulate mass in the filter reaches a threshold value when the vehicle's accelerator pedal is not lifted. A key feature of the method according to the present invention is that when the accelerator pedal is fully lifted, it is determined whether there is a risk of filter runaway associated with passive regeneration of the filter triggered by cutting off fuel injection to the engine. Such a cutoff is permitted only if there is no such risk. If such a risk exists, a moderate active regeneration step is performed, in which the richness of the air-fuel mixture is controlled to a value substantially close to 0.98. Residual torque generated by combustion is absorbed by a consumer device in the vehicle, such as an alternator.

Description

[Technical Field]

[0001] The present invention relates to a method for regenerating a nitrogen oxide trap in a spark ignition internal combustion engine, and finds particular advantageous application in gasoline-powered motor vehicle engines.

[0002] The invention also relates to a drive device for carrying out the reproducing method according to the invention. [Background technology]

[0003] Modern spark-ignition internal combustion engines (especially those powered by gasoline) of motor vehicles, which are subject to increasingly stringent pollution prevention standards, are equipped with various systems for the aftertreatment of polluting molecules released in the combustion gases of said engines in order to limit the emission of harmful species into the outside air.

[0004] Spark ignition engines are increasingly being equipped with gasoline particulate filters (GPFs) to decontaminate the combustion gases, in particular in terms of particulate matter (PM), the mass and number of which are subject to regulations.

[0005] The particulate filter operates in a manner known per se: during normal operation of the engine, that is most often at a richness of 1, in other words at the stoichiometric ratio of the air-fuel mixture entering the engine, the filter stores the particulates without treating them, with a certain efficiency corresponding to the proportion of the incoming particulates that are effectively stored in it, while the remainder of this incoming amount is discharged directly at the outlet of the trap.

[0006] As the filter fills, i.e., as the mass of particulates increases, the differential pressure across it increases, resulting in more and more PM being expelled from the engine. It is then necessary to reduce the mass of PM stored in the filter and restore its efficiency. Often, for example, when the mass of stored PM reaches a threshold, the engine switches to another operating mode, called a regeneration mode, which has the effect of emptying the filter and returning the mass of stored PM to zero or at least a low value, where the differential pressure is small and the filter's efficiency is at least partially restored. This method is denoted by the expression "active regeneration."

[0007] For this purpose, it is known to switch the engine settings to lean, that is, the ratio of the air-fuel mixture introduced into the engine is strictly lower than the stoichiometric ratio, usually substantially equal to 0.90. This is manifested by a significant increase in the temperature of the engine's exhaust gases, which, under the influence of excess oxygen, can burn the PM stores into more harmless molecules (carbon dioxide CO2 and water H2O), which are the normal products of combustion.

[0008] Furthermore, it is known that particulate filters in gasoline engines can also be subject to passive or natural regeneration under certain operating conditions, i.e., spontaneous regeneration which, unlike so-called active regeneration, is not triggered by any intentional action on the engine settings.

[0009] Such operating conditions are combined with high temperatures and a large amount of oxygen being delivered to the engine's exhaust gases. This scenario is displayed when the driver completely removes their foot from the accelerator pedal of the vehicle, for example, when going down a steep slope. In this case, it is known from the prior art that fuel injection to the engine is stopped and the valve for regulating the engine's airflow is closed so that the vehicle driver can benefit from "engine braking."

[0010] The increased oxygen levels in the gases passing through the particulate filter and the increased exhaust gas temperatures can cause the same combustion of particulates observed during active filter regeneration. However, this increased oxygen level can easily lead to runaway particulate combustion reactions within the filter, causing a significant increase in temperature. Furthermore, the reduction in the overall flow rate of exhaust gases through the particulate filter due to the closure of the intake valve makes it more difficult to evacuate the heat generated by the combustion of particulates.

[0011] The prior art discloses several methods aimed at avoiding such runaway, which can cause filter damage under the influence of excessive temperatures. In particular, rather than stopping fuel injection when the driver's foot is lifted, it is possible to continue operating the engine at a richness of 1, which has the effect of completely suppressing the natural regeneration of particulates. However, such a method results in the engine generating undesirable torque, which is incompatible with the "engine braking" effect desired by the driver. On the other hand, the above method increases the frequency of active filter regeneration, in which the engine setting is changed to a lean mixture, which has many disadvantages, including, in particular, the production of large amounts of nitrogen oxides (NOx), a species that is also subject to strict regulations.

[0012] Publication FR-A1-3029964-A1 also aims to avoid runaway of the particulate filter during regeneration. The publication discloses a method for regenerating a particulate filter in the exhaust line of an internal combustion engine belonging to a hybrid powertrain of a motor vehicle, the hybrid powertrain also comprising an electric motor associated with an electric battery, the method comprising a step of triggering regeneration of the filter while the particulates trapped in the particulate filter are combusted, the hybrid powertrain being controlled such that during filter regeneration the internal combustion engine charges the battery of the electric motor. Such a method can only be used in hybrid vehicles. Summary of the Invention

[0013] The present invention aims to overcome the deficiencies of known methods for regenerating particulate traps for spark ignition engines for motor vehicles, not necessarily associated with electric machines.

[0014] The method according to the invention proposes a method for regenerating a particulate filter installed in the exhaust circuit of a spark-ignition internal combustion engine of a motor vehicle, said method comprising at least a first mode of active regeneration of a lean mixture of the filter, which is activated when the value of the mass of particulates stored in the filter is equal to or greater than a threshold value, when the accelerator pedal of the vehicle is not fully lifted.

[0015] The main features of the method according to the invention are: - identifying a fully lifted state of said accelerator pedal; - if a lifted condition is observed, identifying the risk of the particulate filter running away in the absence of fuel injection into the engine; - if there is no risk of such a runaway, a regeneration step in a second mode of passive regeneration of the filter, in which fuel injection to the engine is interrupted; - if such a risk of runaway exists, a regeneration step in a third mode of moderate active regeneration of the filter, in which the richness of the air-fuel mixture entering the engine is set to a value substantially equal to 0.98; The further inclusion of

[0016] Other features and advantages of the present invention will become apparent from the following description of non-limiting embodiments of the invention, which is given with reference to the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of a drive device capable of implementing the method according to the invention; [Figure 2] 1 is a schematic diagram of a runaway risk area of ​​a particulate filter. [Figure 3] 1 is a flow chart of the steps of one embodiment of a method according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0018] In the following description, the same reference numbers refer to parts having the same or similar functions.

[0019] 1 shows a drive system in which the method according to the invention can be implemented, the system comprising an internal combustion engine 1 of the spark-ignition type (in particular running on gasoline), here of the supercharged type, without prejudice to the generality of the invention.

[0020] The engine 1 is associated with an intake circuit 2 and an exhaust circuit 3. The engine here is of the direct injection type, and the engine is supplied with fuel in each of its cylinders by fuel injectors 4, for example from a high-pressure common rail 5.

[0021] Fresh air drawn from the outside air enters the intake circuit 2 in the direction of arrow E. It may pass through components such as an air filter 6. In the example of FIG. 1, the engine 1 is supercharged and includes a compressor 7 of a supercharged turbocharger 8. The air passes through the compressor 7, then through a supercharged air cooler 9, a valve 10 for regulating the air flow entering the engine, or a throttle body 10, and then enters the engine's intake manifold 11 or distributor 11. In the example of FIG. 1, the distributor 11 includes a pressure sensor 12 and a temperature sensor 13, which are provided to measure the pressure Pman and temperature Tman prevailing in the distributor 11, respectively. The pressure Pman and the temperature Tman allow, in a manner known per se, to determine the value of the (mass) flow rate Qadm of gases entering the engine 1 in relation to the engine charge model. In a variant not shown, the engine may also be equipped with a flow meter at the intake, which can provide a direct measurement of the flow rate Qadm of gases entering the engine.

[0022] The combustion gases of the engine are discharged into the exhaust manifold 11 of the engine and then pass through the turbine 15 of the turbocharger 8. The turbine 15 may be of a fixed geometry type and is associated with a circuit 16 for discharge to the exhaust and is provided with a valve 17 for discharge to the exhaust (also called a "pop-off" valve). In a variant not shown, the valve 17 may be of a variable geometry type for adjusting the expansion energy taken by the turbine from the exhaust gases.

[0023] In the example of Fig. 1, the exhaust gases then pass in circulation from upstream to downstream through a first device 18 for aftertreatment of the engine's exhaust gases, for example a three-way catalytic converter 18 or a nitrogen oxide trap 18 or a combination of the two, and then through a second device 19 for aftertreatment of the gases, which according to the invention is a particulate filter 19. This filter 19 is associated with two pressure sensors, more precisely an upstream pressure sensor 20 provided to measure a pressure value Pupstream at the filter inlet and a downstream pressure sensor 21 provided to measure a pressure value Pdownstream at the filter outlet. In a variant not shown, the filter can also be equipped with a differential pressure sensor provided to provide a value for the differential pressure ΔP across the filter, said differential pressure being equal to the difference between the pressure value Pupstream at the filter inlet and the pressure value Pdownstream at the filter outlet.

[0024] In a manner known per se, the quantity (mass) Mpart of particulates PM stored in the filter can be determined using a pre-established map whose inputs are the flow rate Qex of exhaust gases passing through the filter and the differential pressure ΔP prevailing across the filter. For example, the flow rate Qex of exhaust gases can be determined to be equal to the sum of the flow rate Qadm of gases entering the engine and the flow rate Qfuel of injected fuel, and the differential pressure ΔP can be determined to be equal to the difference between the pressure value Pupstream at the inlet of the filter and the pressure value Pdownstream at the outlet of the filter. This amount of particulates can trigger an active regeneration of the filter by setting the engine to a richness value close to 0.90, especially when a threshold value is reached.

[0025] It should also be noted that other specific features of the drive system not shown are possible without loss of generality of the invention. For example, the exhaust circuit may include at least one circuit for partially recirculating exhaust gases to the engine intake (also called an exhaust gas recirculation "EGR" circuit), e.g., a high-pressure recirculation circuit or a low-pressure recirculation circuit.

[0026] The operation of the engine is under the supervision of an electronic computer (not shown) which determines a certain number of operating parameters of the engine from a number of sensors and controls a number of actuators of the engine.

[0027] FIG. 2 shows the runaway risk region of a spark-ignition engine particulate filter where natural filter regeneration is caused by the interruption of fuel injection during foot lifting, i.e., when the vehicle driver fully releases his / her foot from the vehicle's accelerator pedal, resulting in the closing of the engine's throttle body 10. The horizontal axis represents the particulate filter temperature Tfilter, and the vertical axis represents the particulate mass Mpart stored in the filter. Preliminary tests on a test bench can establish a curve representing the particulate mass Mpart threshold as a function of temperature, above which a runaway risk exists. Through such tests, it can be observed that the mass threshold S is a decreasing function of the filter temperature Tfilter. In other words, a runaway risk exists at low temperatures when the stored particulate mass is large, and at high temperatures when the particulate mass is relatively small. The present invention proposes to eliminate the runaway risk in the region located above the mass threshold curve, which has been well identified experimentally.

[0028] 3 shows a flowchart of the various steps of a method according to one non-limiting embodiment. The invention is based on the fact that fuel injection can be interrupted outside the runaway risk region of the particulate filter during foot lift, which advantageously allows natural regeneration of the filter without consuming fuel. Furthermore, in said runaway risk region, it is preferable to allow a limited regeneration, referred to here as moderate active regeneration, by adjusting the richness of the air-fuel mixture to a slightly lean value substantially equal to 0.98, rather than suppressing it by maintaining a richness equal to 1, as is the case in known methods. Thus, regeneration of the filter is allowed, restoring storage efficiency while limiting nitrogen oxide emissions, while the richness value is still substantially within the catalytic window of the three-way catalytic converter 18.

[0029] Advantageously, the throttle body 10 is closed to strictly limit the flow rate Q of gases entering the engine and the residual torque generated by the combustion of the injected fuel with the incoming air. This residual torque, which does not correspond to the vehicle's demand for acceleration due to the accelerator pedal, can then be advantageously absorbed by a consumer of the vehicle, for example, but not limited to, an alternator for charging the vehicle's battery or one of the air conditioning compressors. If the battery is fully charged, the additional charge can be dissipated, for example, on a heated windshield or a heated rear window of the vehicle.

[0030] More precisely, the method starts in step 100 with the vehicle in normal operation, with the engine set to a richness of 1 over most of the engine's speed-load operating points. To this end, the richness of the air-fuel mixture is set in a closed-loop mode around a richness setpoint by adjusting the time of fuel injection into the engine's cylinders, in a manner known per se, by at least one signal of the richness of the combustion gases upstream of the three-way catalytic converter 18 measured by an oxygen probe (not shown in Figure 1).

[0031] Note that this step does not exclude cases where the mixture richness is set to a value strictly greater than 1 in open-loop mode, especially at full load and / or high speed values ​​where the exhaust gas temperature is so high that a richness of 1 cannot be maintained.

[0032] During this first step 100, the particulate filter 19 is in particulate storage mode. The method includes a calculation step 200 for determining the current mass Mpart of particulates stored in the filter. For example, as mentioned above, the value of the flow rate Qex of exhaust gases passing through the filter and the value of the differential pressure ΔP prevailing across it can be determined, and then said mass value Mpart can be deduced therefrom using a pre-established correspondence map.

[0033] The method continues with a test step 300, in which it is verified whether the current mass is less than a threshold value. In this case, the method returns to step 100, where particulate storage continues without filter regeneration. Otherwise, the method continues with step 400, in which a driver's foot lift is identified. For example, a signal from the accelerator pedal potentiometer can be measured. If no foot lift is detected, i.e., if a depression of the accelerator pedal corresponding to a driver's torque C and a request for vehicle acceleration is observed, the method proceeds to step 500 of active filter regeneration, during which the air / fuel mixture is set to a lean value of approximately 0.90, which is sufficient to both generate the required torque T and regenerate the filter. Any excess nitrogen oxides produced during this lean operation step can be advantageously absorbed by the engine's nitrogen oxide trap 18.

[0034] In contrast, if foot lifting is detected, it is necessary to check whether there is a risk of the filter running out of control. The method proceeds to step 600, in which the value of the filter temperature Tfilter is determined. In a simplified mode, for example, this temperature can be made equal to the temperature of the exhaust gases entering the filter, the latter being measured by a temperature sensor (not shown in FIG. 1). Therefore, by using the history of the gas temperatures upstream and downstream of the particulate filter and the engine operating point, it is possible to use various models known from the prior art.

[0035] After this step 600 of determining the temperature of the filter Tfilter, in a test step 700 it is verified whether the point on the horizontal axis of the filter temperature Tfilter and on the vertical axis of the mass of particulates Mpart lies in the runaway risk region, i.e. on the curve shown in Figure 2. In other words, for an observed value of the temperature of the filter it is verified whether the mass of particulates Mpart present in the filter is greater than a threshold value, which is temperature dependent and is a decreasing function of the temperature.

[0036] If not, the method proceeds to step 800 of natural or passive regeneration of the filter, in which fuel injection is interrupted and the throttle body 10 is advantageously closed so that the driver benefits from engine braking. On the other hand, if a runaway risk exists, the method continues with step 900 of moderate active regeneration, in which the richness of the mixture is set to a slightly lean value substantially equal to 0.98. "Substantially" should be understood to mean that the richness is set in the range of 0.98 + / - 0.05.

[0037] Advantageously, this moderate active regeneration step 900 also closes the throttle body again to limit exhaust gas flow, oxygen flow, exhaust temperature rise, and torque generated by the combustion of injected fuel. Also, advantageously, because the accelerator pedal is fully lifted, vehicle consumers, such as the engine alternator or air conditioning compressor, are engaged to absorb this torque not needed by the driver. This prevents the vehicle from accelerating too quickly. Advantageously, the alternator allows the vehicle's battery to be charged. Of course, assuming the battery is already fully charged while the alternator is running, additional charge can be dissipated to other vehicle consumers, such as a heated windshield or heated rear window.

Claims

1. A method for regenerating a particulate filter (19) installed in an exhaust circuit (3) of a spark-ignition internal combustion engine (1) of a motor vehicle, said method comprising at least a first mode (500) of active lean regeneration of said filter (19) that is activated when the value of the mass of particulates (Mpart) stored in said filter (19) is equal to or greater than a threshold value when the accelerator pedal of said vehicle is not fully lifted, and that sets an equivalence ratio of the air-fuel mixture entering said engine to a value equal to 0.90; Identifying (400) a fully lifted state of the accelerator pedal; If the lifted condition is observed, identifying (700) a risk of runaway of the particulate filter in the absence of fuel injection into the engine; a regeneration step (800) in a second mode of passive regeneration of the filter, in which, if there is no risk of such runaway, fuel injection into the engine is interrupted; a regeneration step (900) in a third mode of limited active regeneration of the filter, in which the equivalence ratio of the air-fuel mixture entering the engine is set to a value equal to 0.98 if the risk of runaway exists; The method further comprising:

2. The method described in claim 1, characterized in that in the third mode of limited active regeneration, a valve (10) for adjusting the air inflow flow rate is closed and the vehicle's consumption parts are made to absorb the residual torque generated by the combustion of the introduced fuel.

3. 3. The method of claim 2, wherein said consumer is an alternator of said engine.

4. 4. The method according to claim 2 or 3, characterized in that the consumer is an alternator or an air conditioning compressor of the vehicle.

5. 5. The method according to claim 1, wherein the risk of runaway of the particulate filter is observed when the mass of particulates present in the filter (Mpart) is equal to or greater than a threshold value that depends on the temperature of the filter (Tfilter).

6. 6. The method of claim 5, wherein the particulate mass threshold is a decreasing function of the temperature of the filter (Tfilter).

7. 7. The method according to claim 1, wherein the mass (Mpart) of the particulates in the filter (19) is determined using a map established as a function of the flow rate (Qex) of exhaust gas passing through the filter and the value of the differential pressure (ΔP) across the filter.

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