FR2957530A1 - Nitrogen oxide trapping device for internal combustion engine of motor vehicle, has control unit regulating quantity of nitrogen oxides in downstream of one of nitrogen oxide traps by controlling valves based on storage capacity of traps - Google Patents

Abstract

The device (1) has a particle filter (4) arranged between two nitrogen oxide traps (3, 5). An exhaust gas recirculation circuit (6) connects an exhaust manifold with an intake manifold. Another exhaust gas recirculation circuit (7) connects a zone located downstream from the filter with a zone located upstream of the intake manifold. The recirculation circuits are provided with valves (6a, 7a). A control unit regulates quantity of nitrogen oxides in downstream of one of the two nitrogen oxide traps by controlling the valves based on storage capacity of the nitrogen oxide traps. An independent claim is also included for a motor vehicle, comprising a nitrogen oxide trapping device.

Description

The present invention relates to a device for trapping nitrogen oxides in a motor vehicle engine with internal combustion. It also relates to a motor vehicle comprising such a device. In the field of pollution control, in order to meet the lower thresholds for emissions of gaseous pollutants from motor vehicles, increasingly complex gas after-treatment systems are arranged in the exhaust line of the engines. internal combustion system operating in a lean mixture. These devices make it possible in particular to reduce the emissions of particles and nitrogen oxides (NOx) in addition to carbon monoxide and unburned hydrocarbons. Unlike conventional oxidation catalysts, these systems operate discontinuously or alternately, that is to say that in normal operation they trap pollutants but only treat them during regeneration phases. Thus, to be regenerated, these traps require specific modes of combustion to ensure the necessary levels of heat and / or wealth.

Among these post-treatment systems, a particularly used system is the nitrogen oxide trap, also called NO trap, or "NO, Trap" in English language. The nitrogen oxide trap continuously captures the nitrogen oxides contained in the exhaust gas generated by the internal combustion engine.

It is necessary to periodically regenerate the nitrogen oxide trap to unload it, which is done by means of a so-called purge operation during which the nitrogen oxides are reduced. It is known to carry out this purge by temporarily controlling an increase in the engine's richness, such that the richness of the exhaust gases upstream of the nitrogen oxide trap is greater than 1 and the concentration of oxygen low. A conventionally used system includes a first nitrogen oxide trap, a second nitrogen oxide trap disposed downstream of the first nitrogen oxide trap, and a particulate filter disposed between the first and second oxide traps. nitrogen. A difficulty consists in effectively controlling the amount of nitrogen oxides present downstream of the second nitrogen oxide trap.

The invention aims to achieve this objective. The invention thus relates to a device for trapping nitrogen oxides in an internal combustion engine vehicle engine comprising an intake manifold and an exhaust manifold, the device comprising, downstream of the engine, a first trap for nitrogen oxides, a second nitrogen oxide trap disposed downstream of the first nitrogen oxide trap and a particulate filter disposed between the first and the second nitrogen oxide trap. The device according to the invention also comprises a first exhaust gas recirculation circuit connecting the exhaust manifold to the intake manifold, a second exhaust gas recirculation circuit connecting an area located downstream of the exhaust filter. particles at an area upstream of the intake manifold, each recirculation circuit being provided with a valve that can be in the closed position, so as to interrupt the flow of exhaust gas in the circuit, or in the open position, of to allow the circulation of exhaust gas in the circuit. The device according to the invention also comprises control means able to adjust the amount of nitrogen oxides present downstream of the second nitrogen oxide trap by controlling the valves of the first and second recirculation circuits, depending on the the storage capacity of the first and the second nitrogen oxide trap. The amount of nitrogen oxides can thus be adjusted using the two exhaust gas recirculation circuits. The control is made according to the storage capacity of the two traps, so as to optimize the setting.

The control means may be able to adjust the fuel consumption of the engine by controlling the valves of the first and second recirculation circuits.

The control means may be suitable, if the storage capacity of the second nitrogen oxide trap is less than a predetermined value and if the storage capacity of the first nitrogen oxide trap is at a high capacity greater than a value. predetermined, to command the closing of the valve of the second recirculation circuit and the opening of the valve of the first recirculation circuit. The control means may be suitable if the storage capacity of the second nitrogen oxide trap is less than a predetermined value and if the storage capacity of the first nitrogen oxide trap is at an intermediate capacity between two values. predetermined, to control the opening of the valves of the first and second recirculation circuit. The control means may be suitable, if the storage capacity of the second nitrogen oxide trap is less than a predetermined value and if the storage capacity of the first nitrogen oxide trap is at a low capacity less than a value. predetermined, controlling the opening of the valve of the second recirculation circuit and closing the valve of the first recirculation circuit, or controlling the opening of the valves of the first and second recirculation circuit.

The control means may be suitable, if the storage capacity of the second nitrogen oxide trap is greater than a predetermined value and if the storage capacity of the first nitrogen oxide trap is greater than a predetermined value, to be controlled closing the valve of the second recirculation circuit and opening the valve of the first recirculation circuit. The control means may be suitable, if the storage capacity of the second nitrogen oxide trap is greater than a predetermined value and if the storage capacity of the first nitrogen oxide trap is less than a predetermined value, to be controlled opening the valve of the second recirculation circuit and closing the valve of the first recirculation circuit. The control means may be suitable, if the storage capacity of the second nitrogen oxide trap is greater than a predetermined value and if the storage capacity of the first nitrogen oxide trap is between two predetermined values, to be controlled the opening of the valves of the first and second recirculation circuits. The invention also relates to a motor vehicle comprising a device described above. Other features and advantages of the present invention will emerge more clearly on reading the following description given by way of illustrative and nonlimiting example and with reference to the appended drawings, in which: FIG. 1 schematically illustrates a device according to the invention, - Figure 2 is a diagram useful for understanding the invention, - Figure 3 is a block diagram diagram illustrating an embodiment of the device of the invention, and - the FIG. 4 is a diagram in the form of a block diagram illustrating a variant of the embodiment of FIG. 3. The device 1 for trapping nitrogen oxides, as illustrated in FIG. 1, comprises successively in FIG. the exhaust line 2 of an internal combustion engine a first nitrogen oxide trap 3, a particulate filter 4 and a second nitrogen oxide trap 5. The device 1 further comprises a particular system ofexhaust gas recirculation. With a view to reducing the emissions of nitrogen oxides (NO 3), it is known to equip combustion internal combustion engines with an exhaust gas recirculation system, also known as EGR for "Exhaust Gas Recirculation". in English language. The principle of an EGR system is to take a part of the exhaust gas, including inert gases, to recirculate it in the intake circuit. The presence in the intake zone of the inert gases of the exhaust gases makes it possible to slow down the rate of combustion and to absorb the calories, and thus causes a decrease in the emission of nitrogen oxides. The exhaust gases can be taken directly from the engine outlet. In this case, we speak of high pressure EGR mode. The exhaust gases can also be taken downstream of the particulate filter. In this case, we speak of low pressure EGR mode. Exhaust gas recirculation downstream of the aftertreatment elements is of particular interest since the gases collected contain less soot, which makes it possible to limit the fouling of the EGR system and to lower the level of NO emission. by lowering the temperature and increasing the amount of recirculated gas. When the exhaust gas temperatures are low, especially when starting the vehicle, is used rather high pressure EGR mode, so as to warm up the engine as quickly as possible, in order to reduce fuel consumption . Indeed, the exhaust gases in high pressure EGR mode are hot out of the exhaust manifold and are immediately sent to the intake. The device 1 comprises both a high-pressure EGR circuit 6 and a low-pressure EGR circuit 7. Each of the two EGR circuits 6, 7 comprises a control valve 6a, 7a making it possible to determine the quantity of EGR flowing in each of the two. circuits 6.7. The graph of FIG. 2 shows the storage capacity of each nitrogen oxide trap as a function of the temperature upstream of the first nitrogen oxide trap. It is noted that depending on the temperature, the nitrogen oxides are not trapped in full, hence the interest of the device according to the invention which extends the storage range of nitrogen oxides. We make sure that the storage efficiency curves of the two traps are complementary. In fact: - the second nitrogen oxide trap takes longer to reach its minimum temperature of effectiveness than the first nitrogen oxide trap, - the first nitrogen oxide trap stores the NO better, cold because it reaches its zone of optimum efficiency more quickly, - the second nitrogen oxide trap stores the NO better, hot, because it is in its zone of optimum efficiency when the first nitrogen oxide trap, then too much hot, is out of its optimal zone.

The invention consists in controlling the flows of high pressure EGR and low pressure EGR in such a way that the total quantities of nitrogen oxides present in the exhaust of the complete system are as small as possible. The invention also describes a way of designing and controlling the system to obtain an optimized balance between fuel consumption (CO2 production) and system cost (total volume of nitrogen oxide trap) for a given emission target. NO, in the exhaust line.

One embodiment of the device according to the invention is illustrated in FIG. 3. Below an efficiency threshold Eff2 of the second nitrogen oxide trap, especially when its temperature is too low, for example below With a temperature of the order of 100 ° C., it is not possible to use it for storing the nitrogen oxides. In this case, consider the state of the first nitrogen oxide trap. If it is in conditions leading to an efficiency greater than an Effl threshold, we choose to use only the high pressure EGR circuit and the air instructions (fresh air and EGR) are from a first calibration set A.

The efficiency of the first nitrogen oxide trap depends on several modeled or measured parameters. Among these are essentially: the amount of nitrogen oxides stored, the temperature, the mass of sulfur and the aging of the first nitrogen oxide trap. The fact of using the high pressure EGR circuit makes it possible to limit the flow rate of gas passing through the first nitrogen oxide trap and this improves its storage efficiency. In addition, the heat losses in the exhaust line are then reduced and this allows a faster thermal setting of the second nitrogen oxide trap. If the efficiency of the first nitrogen oxide trap is not greater than Eff1, its potential efficiency is compared to a second Effl 'threshold below Effl. If the first nitrogen oxide trap is in a state where its efficiency is between Effl and Effl ', the two low pressure EGR and low pressure EGR circuits are simultaneously used by means of a second calibration set B. use of the low-pressure EGR circuit makes it possible to limit the flow of nitrogen oxides at the outlet of the engine in order to limit the quantity to be stored by the first nitrogen oxide trap. The use of the high-pressure EGR circuit makes it possible to continue the temperature rise of the second nitrogen oxide trap and to optimize the storage of nitrogen oxides of the first nitrogen oxide trap thanks to a flow rate of moderate gas at its terminals. If the first NT1 nitrogen oxide trap has too low efficiency (less than Effi '), since it is in a configuration where the second nitrogen oxide trap can not process nitrogen oxides neither, it becomes important to limit as much as possible the flow of nitrogen oxides from the engine. For this purpose, a third calibration set C is used based on the use of the low pressure EGR circuit or on the simultaneous use of the high pressure EGR circuit and the low pressure EGR circuit, which makes it possible to obtain EGR rates are as high as possible under constraints of other pollutants and other benefits. In a configuration where the second nitrogen oxide trap is able to treat the nitrogen oxides, that is to say essentially if it has a sufficient temperature, there are two configurations.

If the first nitrogen oxide trap has a high potential efficiency (greater than Effi "), we will use the high pressure EGR circuit and its associated calibration set E. This makes it possible to take advantage of the first nitrogen oxide trap. to store the nitrogen oxides, while using low EGR rates that limit the fuel consumption of the engine and therefore the CO2 emissions.On the contrary, if the first trap nitrogen oxides n ' is not able to be effective, we use the low pressure EGR circuit thanks to a final set of calibration D. This allows to limit the production of nitrogen oxides of the engine on the one hand and to treat those produced On the other hand, this leads to a good overall compromise: in the case where the efficiency of the second nitrogen oxide trap is greater than Eff2 and the efficiency of the first nitrogen oxide trap is less than Effi ", it is possible to set up an intermediate zone da the first nitrogen oxide trap has an average efficiency greater than a threshold but less than Effi ". In this case, the two low pressure EGR and high pressure EGR circuits are used simultaneously (calibration set F). This allows a smoother transition between different states. In particular, it is likely that when switching from the use of the high pressure EGR circuit to the use of the low pressure EGR circuit, the first nitrogen oxide trap desorbs nitrogen oxides, which are difficult to store in a controlled manner. massive by the second nitrogen oxide trap. On the other hand, in this intermediate zone, a judicious compromise can be found between fuel consumption and emissions of nitrogen oxides. In a variant, as illustrated in FIG. 4, it is assumed that it is impossible to operate simultaneously the high pressure EGR circuit and the low pressure EGR circuit. In the zone where the efficiency of the second nitrogen oxide trap is greater than Eff2 and the efficiency of the first nitrogen oxide trap is less than Effi ", the freedom to choose between 2 types of calibration: CO2 (calibration set G) or nitrogen oxides (calibration set D) The choice criterion between these two sets of calibration D and G depends on parameters such as, for example, the speed of the vehicle or the speed or the Engine load The conditions for the purging of nitrogen oxide traps during the changeover to a motor richness of 1 are given in the following table: Purge conditions Favorable purge conditions for the first unfavorable for the first trap trap Purge Conditions Using a Purge Using a Favorable Calibration to Allow it to Purge Treatment Suitable for the Second NOx Trap Treatment in the Two NOx NOx Traps on the Second Trap (long purge) only (high richness to rapidly introduce reducers to the second trap) Purge conditions Use of an unfavorable purge step calibration for purge suitable for the second NOx trap treatment on the first trap only (with few hydrocarbon output engine for good efficiency on the first trap and limited in duration to avoid desorption on the second trap) Table 1

Claims (9)

REVENDICATIONS1. Device (1) for trapping nitrogen oxides in an internal combustion engine vehicle engine comprising an intake manifold and an exhaust manifold, the device (1) comprising, downstream of the engine, a first trap (3) nitrogen oxides, a second nitrogen oxide trap (5) disposed downstream of the first nitrogen oxide trap (3) and a particulate filter (4) disposed between the first (3) and the second nitrogen oxide trap (5), characterized in that the device (1) further comprises a first exhaust gas recirculation circuit (6) connecting the exhaust manifold to the intake manifold, a second an exhaust gas recirculation circuit (7) connecting an area downstream of the particulate filter (4) to an area upstream of the intake manifold, each recirculation circuit (6, 7) being provided with a valve (6a, 7a) can be in the closed position, so as to interrupt the flow of gas e exhaust in the circuit (6, 7), or in the open position, so as to allow the circulation of exhaust gas in the circuit (6, 7), and in that the device (1) comprises suitable control means adjusting the amount of nitrogen oxides present downstream of the second nitrogen oxide trap (5) by controlling the valves (6a, 7a) of the first (6) and second (7) recirculation circuits, depending on the storage capacity of the first (3) and second (5) nitrogen oxide trap. 2. Device (1) according to claim 1, characterized in that the control means are also able to adjust the fuel consumption of the engine by controlling the valves (6a, 7a) of the first (6) and second (7) recirculation circuit. 3. Device (1) according to claim 1 or 2, characterized in that the control means are suitable, if the storage capacity of the second nitrogen oxide trap (5) is less than a predetermined value (Eff2) and if the storage capacity of the first nitrogen oxide trap (3) is at a high capacity greater than a predetermined value (Eff1), controlling the closure of the valve (7a) of the second recirculation circuit (7) and opening of the valve (6a) of the first recirculation circuit (6a). 4. Device (1) according to one of claims 1 to 3, characterized in that the control means are suitable, if the storage capacity of the second trap (5) to nitrogen oxides is less than a predetermined value ( Eff2) and if the storage capacity of the first nitrogen oxide trap (3) is at an intermediate capacity between two predetermined values (Effl ', Eff1), controlling the opening of the valves (6a, 7a) of the first (6) and the second (7) recirculation circuit. 5. Device (1) according to one of claims 1 to 4, characterized in that the control means are capable, if the storage capacity of the second trap (5) to nitrogen oxides is less than a predetermined value ( Eff2) and if the storage capacity of the first nitrogen oxide trap (3) is at a low capacity lower than a predetermined value (Eff1 '), controlling the opening of the valve (7a) of the second circuit (7) ) of recirculation and closing the valve (6a) of the first recirculation circuit (6), or to control the opening of the valves (6a, 7a) of the first (3) and second (5) recirculation circuit. 6. Device (1) according to one of claims 1 to 5, characterized in that the control means are suitable, if the storage capacity of the second (5) nitrogen oxide trap is greater than a predetermined value ( Eff2) and if the storage capacity of the first nitrogen oxide trap (3) is greater than a predetermined value (Eff1 "), controlling the closing of the valve of the second recirculation circuit and the opening of the valve ( 6a) of the first recirculation circuit (6a). 7. Device (1) according to one of claims 1 to 6, characterized in that the control means are capable, if the storage capacity of the second trap (5) to nitrogen oxides is greater than a predetermined value ( Eff2) and if the storage capacity of the first nitrogen oxide trap (3) is less than a predetermined value (Eff1 "), controlling the opening of the valve (7a) of the second recirculation circuit (7) and closing the valve of the first recirculation circuit. 8. Device (1) according to one of claims 1 to 7, characterized in that the control means are suitable, if the storage capacity of the second trap (5) to nitrogen oxides is greater than a predetermined value ( Eff2) and if the storage capacity of the first (3) nitrogen oxide trap is between two predetermined values (Eff1 ", Eff1"), to control the opening of the valves (6a, 7a) of the first (3) ) and the second (5) recirculation circuit. 9. Motor vehicle, characterized in that it comprises a device (1) according to one of claims 1 to 8.