Method and device for controlling a spark ignition engine to improve the efficiency of a particulate filter

Abstract

The present invention relates to a method for controlling a spark-ignition engine (1) equipped with an exhaust gas treatment system comprising a particulate filter (7) and a three-way catalytic converter (6) by controlling the injection of fuel into the combustion chamber (8) of the engine (1) and by controlling the ignition of the air-fuel mixture present in the combustion chamber (8) of the engine (1). The fuel injection comprises one or more fuel injection sequences, each fuel injection sequence comprising injections triggered around top dead center to produce an ignition delay in a mixture that is rich enough to generate particulate deposits in the exhaust gas treatment system.

Description

Technical Field

[0001] The present invention relates to control of operating modes of a spark-ignition type internal combustion engine (particularly one operated with gasoline).

[0002] More specifically, the present invention relates to exhaust control for an internal combustion engine concerning the filtration efficiency of a particulate filter mounted in the exhaust section of the above-mentioned engine.

Background Art

[0003] A particulate filter for an internal combustion engine, abbreviated as "DPF", can greatly reduce the mass and quantity of particulates exhausted in a vehicle exhaust section by collecting and filtering combustion gas from the engine.

[0004] For example, a distinction can be made between so-called "heavy" particulates of relatively large size on the order of 100 nanometers in diameter, and fine particulates of small size, for example less than 2.5 microns, particularly less than 1 micron. While gasoline engines do not emit a large amount of "heavy" particulates, they emit large quantities of fine particulates that are extremely harmful to the environment and human health.

[0005] A DPF for a gasoline engine operates in a two-sequence cycle. The first sequence consists of collecting particulates, which is performed during the normal operating mode of a rich engine 1, and the second sequence consists of removing those particulates. In practice, the first step causes the DPF to capture particulates present in the combustion gas that form a layer of heavy particulates, particularly soot, on the filter walls. When an excessive amount of soot accumulates, the second step, called regeneration, allows the DPF to be cleaned by burning this accumulated layer of particulates.

[0006] For spark-ignition engines, there are several types of DPF regeneration. Passive regeneration and active regeneration are distinguished. Passive regeneration is not triggered by any action on the engine's mode of adjustment, and combustion occurs spontaneously under the action of characteristic temperature and flow rates. Active regeneration occurs when the engine's operating mode is changed by switching to a slightly leaner mixture (generally richness of 0.05 to 0.98), and its effect is to cause combustion of particles in the filter. This second type of regeneration of the DPF in a gasoline engine is in itself a well-known form, and can be performed, for example, just before the mass of fine particles reaches a critical threshold and clogs the filter, or more specifically, when the temperature and flow conditions are not met before the filter is passively regenerated.

[0007] In gasoline engine DPFs, the overall efficiency is low at the time of factory shipment; that is, the retention of particles released into the engine's combustion gases is low. More specifically, the filter does not retain the finest particles released in large quantities, because these particles easily pass through the filter walls. The level of efficiency improves over time as a result of the formation of a soot deposit layer caused by the accumulation of particles released by the engine. The accumulation of heavy particles on the filter walls easily clogs the filter, and the filter becomes relatively permeable to the lightest particles. Subsequently, even with DPF regeneration in gasoline engines, the soot deposits cannot be completely removed, and its filtration efficiency with respect to the finest particles is maintained to some extent.

[0008] As shown in Figure 1, the change in particulate matter emissions from the exhaust system as a function of the change in mileage (km) is plotted in terms of particle count (PN). Curves c1 and c2 represent driving with heavy foot pressure, i.e., driving with almost no stress on the vehicle's accelerator pedal, and driving with light foot pressure, respectively. As a result, the particle level in the exhaust system stabilizes at approximately 6000 km. Consequently, the DPF operating mode of the gasoline engine also becomes efficient at approximately 6000 km.

[0009] Patent Document 1 describes a system for aftertreatment of exhaust gas from the exhaust line of a spark-ignition internal combustion engine, comprising a ternary oxidation-reduction catalytic converter, a first particulate filter mounted directly downstream of the catalytic converter, and a second particulate filter located downstream of the first particulate filter.

[0010] A first filter located downstream of the catalytic converter is generally kept empty enough to accumulate very large particles, while a second filter located downstream of the first DPF is kept full enough to accumulate relatively fine particles. Each filter consists of a regeneration system comprising a differential pressure sensor and a sensor capable of detecting particle mass. This regeneration system operates in a mode that keeps the first filter downstream of the catalytic converter empty and maintains the second filter downstream of the first DPF unaffected by the regeneration of the downstream first filter.

[0011] However, when the engine and particulate filter are new, the first DPF is not yet fully filled, and therefore its efficiency in processing fine particles remains insufficient. This document does not describe how to achieve a sufficient initial filling of the first filter. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] French Patent Application Publication No. 3096403 [Overview of the project]

[0013] Therefore, the present invention aims to accelerate the deposition of fine particles in a particulate filter of a gasoline engine, which is positioned downstream of a three-way catalytic converter, in order to improve the filtration efficiency of the particulate filter.

[0014] The present invention relates to a method for controlling a spark-ignition engine equipped with an exhaust gas treatment system comprising a particulate filter and a three-way catalytic converter, by controlling the injection of fuel into the engine's combustion chamber and by controlling the ignition of the air-fuel mixture present in the engine's combustion chamber.

[0015] The fuel injection includes one or more fuel injection sequences, each including an injection triggered around the top dead center of the engine to create an ignition delay in a mixture that is rich enough to generate particulate deposits in the exhaust gas treatment system.

[0016] According to one embodiment of the present invention, the injection centered on the top dead center of the engine is the last injection in the injection sequence.

[0017] Advantageously, fuel injection occurs at an engine cycle angle between 180° and -20° of the crankshaft, i.e., between bottom dead center and 20° after top dead center throughout the engine compression cycle.

[0018] Preferably, this gap is shortened to an angle of 80° to -12° of the crankshaft.

[0019] Ignition can be triggered after the end of the last injection around top dead center, with an interval of 3° to 8° on the crankshaft that separates the end of the last injection from the ignition, so that ignition occurs at crankshaft -4° to -28°.

[0020] According to one embodiment, the method is carried out during the catalyst heating phase. Therefore, the method can be carried out when the engine is running at a low temperature and the vehicle is starting up, making it possible to accelerate the deposition of fine particles in the DPF of a gasoline engine.

[0021] The present invention also relates to a system for controlling a spark ignition engine equipped with an exhaust gas treatment system comprising a particulate filter and a three-way catalytic converter.

[0022] The system comprises injection control means for generating one or more fuel injection sequences, wherein the fuel injection sequence includes an injection triggered to generate an ignition delay in an air-fuel mixture sufficiently rich to generate particulate deposits in an exhaust gas treatment system, centered on top dead center.

[0023] Advantageously, the control means is configured such that said injection centered on top dead center is the last injection of the sequence.

[0024] According to one embodiment, the control means is configured such that the injection is performed at an engine cycle angle of between 180° and -20° of the crankshaft, preferably between 80° and -12° of the crankshaft.

[0025] Advantageously, the system comprises ignition control means configured to perform ignition after the end of the last injection at an interval of 3° to 8° of the crankshaft, such that ignition occurs at between -4° and -28° of the crankshaft.

[0026] The present invention also relates to a motor vehicle comprising a control system as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] [Figure 1] It graphically shows the change in particulate matter emission (PN) in an exhaust section as a function of traveled distance (km), which has already been described. [Figure 2] It schematically shows the structure of an internal combustion engine for a motor vehicle engine equipped with the control system according to the present invention. [Figure 3] It graphically shows an embodiment of the present invention, according to which a sequence of three injections is performed in a combustion chamber of an engine between an intake bottom dead center and an exhaust bottom dead center. [Figure 4] It graphically shows the particle number (PN) calculated according to each phase of the method according to the present invention. [Figure 5] It graphically shows the trend of particle emissivity with various combustion parameters. [Figure 6]This diagram schematically shows the wall of a DPF in a spark-ignition internal combustion engine under new conditions and after the formation of a particle deposit layer. [Modes for carrying out the invention]

[0028] Other objects, features, and advantageous effects of the present invention should become apparent from reading the following description, which is given only as a non-limiting example and with reference to the accompanying drawings.

[0029] Figure 2 schematically shows the general structure of an internal combustion engine 1 (particularly gasoline-powered) of a motor vehicle equipped with a control system according to the present invention, which is of the spark ignition type.

[0030] Engine 1 is, in this case, an inline four-cylinder engine 2. Engine 1 comprises an intake manifold 3 that ensures the intake of outside air into cylinder 2, an exhaust manifold 4 that ensures the collection of exhaust gases, and an exhaust line 5 equipped with a system for exhaust gas aftertreatment, the system comprising a ternary oxidation catalyst 6 and a DPF particulate filter 7 positioned downstream of the catalyst 6, which is considered in terms of the direction of exhaust gas flow.

[0031] The position of the piston in cylinder 2 is measured as a function of the crankshaft angle, in units of crankshaft degrees. The piston moves up and down within the combustion chamber 8 according to the cycle of engine 1.

[0032] Furthermore, each cylinder 2 is equipped with a fuel injector 9 and a spark plug 10, which can trigger the combustion of the air-fuel mixture, both of which are located not far from the top dead center (TDP_comb) of the combustion chamber 8.

[0033] The fuel injection and ignition phases of the air-fuel mixture are controlled by a control system 12 that includes injection control means 13 and ignition control means 14.

[0034] Referring to Figure 3, the injection control means 13 enables the generation of one or more fuel injection sequences 15 such that the injection 16 is centered on the top dead center TDP_comb of the combustion chamber 8, and in the case of a sequence 15 of multiple fuel injections, the last injection 16 of the sequence is centered on the top dead center TDP_comb of the combustion chamber 8. This late injection is performed immediately before AVA ignition.

[0035] One or more injections 15 are generated, one of which occurs immediately before AVA ignition, resulting in a rich and poorly homogenized air-fuel mixture, i.e., an air-fuel mixture consisting mainly of fuel, at the time of AVA ignition. This process induces some of the fuel to remain unburned, and therefore more hydrocarbons (HC), carbon monoxide (CO), and fine or microparticles are formed in the combustion chamber 8. These particles are then released through the exhaust line 5 of the engine 1 and are first filtered by a three-way catalytic converter 6, which in particular oxidizes the engine's HC and CO and reduces NOx, and then filtered by a particulate filter 7 located downstream of the three-way catalytic converter 6, which processes the particles according to the stepwise mode already described above.

[0036] In one embodiment, a slow fuel injection centered on top dead center is performed during the heating phase of the three-way catalytic converter 6, which occurs when the vehicle is started while the engine 1 is still cold. According to this embodiment, it is possible to generate a large amount of particles when the three-way catalytic converter 6 is not yet sufficiently efficient. When the three-way catalytic converter 6 is not functioning, the filtration performed by this component is not optimal, and therefore a large amount of particles are sent directly to the DPF 7 of the gasoline engine. Thus, the process of particle 21 deposition on the walls of the DPF 7 of the gasoline engine is accelerated, and consequently the efficiency of its filtration is also accelerated.

[0037] The spark-ignition engine 1 operates in four stages. The first stage is the intake stage, in which air is drawn in through the intake manifold 3. The second stage is the compression stage, in which the air-fuel mixture is compressed until the compression piston reaches top dead center (TDP_comb). The third stage is the combustion stage, in which a spark ignites, causing the air-fuel mixture to burn. Finally, the fourth stage is the exhaust stage, in which the engine expels its burnt gases toward the exhaust pipe.

[0038] The injection control means 13 is configured to trigger one or more fuel injections 15 during the compression phase of the engine 1 at crankshaft angles of 180° to -20°. Preferably, this interval can be shortened to a crankshaft interval of 80° to -12°.

[0039] One or more injections 15 performed by the injection control means 13 make it possible to generate a delayed ignition AVA. This AVA ignition is performed by the ignition control means 14 and is triggered by the end of the last injection 16 at a crankshaft delta deviation of 3° to 8°. Since the end of the last injection can be at crankshaft -1° to -20°, AVA ignition occurs at crankshaft -4° to -28°.

[0040] According to the embodiment of the present invention shown in Figure 3, the sequence of three injections 15 takes place between the intake bottom dead center BDP_a and the exhaust bottom dead center BDP_e. The first injection 18 is generated from the crankshaft at 80° and ends before the second injection 19, which begins at the crankshaft at 40°. The injection sequence then includes a third and final injection 16, which is triggered at approximately 10° of the crankshaft and stopped at approximately -10° of the crankshaft, centered around the top dead center TDP_comb of the combustion chamber of the engine 1. In this embodiment of the present invention, AVA ignition occurs at approximately -15° of the crankshaft, with a delta deviation of 5° from the end of the final injection 16.

[0041] Tests were conducted to verify this embodiment. Figure 4, which shows the number of particles (PN) calculated according to each phase of the method according to the present invention, shows that the highest number of particles (PN) is formed at the end of the last injection I3, which corresponds to the third injection in this embodiment.

[0042] On a scale of 0 to 1, the third and final injection I3 according to this embodiment forms a particle number (PN) equal to 1, while the preceding injections I1 and I2 vary between 0.095 and 0.334 PN.

[0043] The particle count (PN) is 0.292 at ignition advance angle A before decreasing at the time of the first injection I1.

[0044] Figure 5 also shows the trend of particle emissivity related to specific parameters at various phases of the experiment, and it can be seen that there is a peak in particle generation at the end of the third injection I3.

[0045] The results shown in Figure 6 indicate the formation of particle 21, more precisely, relatively heavy particle deposits, on the wall of the gasoline engine's particulate filter 7 (right side R of Figure 6). These deposits were not present on the wall of the gasoline engine's particulate filter 7 when it left the factory, i.e., in its new condition (left side L of Figure 6).

[0046] Therefore, it can be seen that the formation of this particle 21 deposit layer makes the gasoline engine's particle filter 7 more efficient, and improves the filtration of fine particles in particular, more precisely, the lightest and most numerous particles, and the smallest particles found in the exhaust line 5 of the engine 1.

Claims

1. A method for controlling a spark ignition engine (1) equipped with an exhaust gas treatment system comprising a particulate filter (7) and a three-way catalytic converter (6) by controlling the injection of fuel into the combustion chamber (8) of the engine (1) and by controlling the ignition of the air-fuel mixture present in the combustion chamber (8) of the engine (1), The fuel injection method comprises one or more fuel injection sequences (15), the fuel injection sequence (15) comprising an injection (16) triggered to generate an ignition delay (AVA) in a mixture that is rich enough to generate a deposit of fine particles (21) in the exhaust gas treatment system, centered around top dead center (TDP_comb).

2. The method according to claim 1, wherein the injection is performed in the sequence (15), and the injection (16) centered on the top dead center (TDP_comb) is the last injection in the sequence (15).

3. The method according to claim 1 or 2, wherein the injection (15) is performed at a crankshaft cycle angle of 180° to -20°, preferably 80° to -12° of the engine (1).

4. The method according to any one of claims 1 to 3, wherein the ignition (AVA) is triggered after the end of the last injection (16) in a delta (deviation) of 3° to 8° of the crankshaft, such that the ignition (AVA) occurs at a crankshaft angle of -4° to -28°.

5. The method according to any one of claims 1 to 4, which is performed after starting the vehicle during the heating phase of the catalyst (6).

6. A system for controlling a spark-ignition engine (1) equipped with an exhaust gas treatment system comprising a particulate filter (7) and a three-way catalytic converter (6), the system comprising injection control means (13) for generating one or more fuel injection sequences (15), the fuel injection sequence (15) including an injection (16) that is triggered to generate an ignition delay (AVA) in a mixture that is rich enough to generate a deposit of particulate matter (21) in the exhaust gas treatment system, centered around top dead center (TDP_comb).

7. The system according to claim 6, wherein the control means (13) is configured such that the injection (16) centered on the top dead center (TDP_comb) is the last injection of the sequence (15).

8. The system according to claim 6 or 7, wherein the control means (13) is configured to perform the injection (15) at a crankshaft angle of 180° to -20°, preferably 80° to -12°, of the engine (1) cycle.

9. The system according to any one of claims 6 to 8, comprising an ignition control means (14) configured to cause ignition (AVA) to occur after the end of the last injection (16) in a delta (deviation) of 3° to 8° of the crankshaft, such that ignition (AVA) occurs at a crankshaft angle of -4° to -28°.

10. A motor vehicle comprising the control system according to any one of claims 6 to 9.

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