FR2853009A1 - Internal combustion engine e.g. four stroke diesel engine, particle filter regenerating process, involves modifying fuel injection retarding based on difference between effective and theoretical values of exterior factor - Google Patents

Abstract

The process involves retarding fuel injection at an angle. An effective value of an exterior factor influencing exhaust gas temperature of an internal combustion engine (1) is found. The retarding of fuel injection is modified with respect to a difference between the effective value and a theoretical value of the exterior factor. The injected fuel quantity is modified to maintain a constant engine torque. The angle is found based on a high dead point and depends on a functioning point of the internal combustion engine. An independent claim is also included for an automobile having a device for regeneration of a particle filter.

Description

METHOD FOR REGENERATING A PARTICLE FILTER AND DEVICE FOR IMPLEMENTING IT

WORK OF SUCH A PROCESS

  The present invention relates to a method for the regeneration of a particulate filter inserted in an exhaust circuit of an internal combustion engine.

  The invention also relates to a device 10 allowing the implementation of this regeneration process.

  The invention finds a particularly advantageous, but not exclusive, application in the automotive field.

  The operation of an internal combustion engine always generates particle emissions because the combustion of a hydrocarbon is never completely complete there, regardless of the nature of the fuel used. These solid particles, commonly called soot, are composed mainly of carbon and unburnt hydrocarbons and are transported by the exhaust gases.

  To eliminate this type of discharge and thus reduce pollution of the engine, it is known to use a particle filter inserted in the exhaust circuit. The principle is conventional, a purely mechanical filtration which consists schematically in trapping the particles in the passage of the exhaust gases, by blocking and storing them by means of a porous structure.

  To ensure the proper functioning of a particulate filter, and in particular to prevent its clogging by soot, it is necessary to periodically perform a regeneration. This operation consists of burning the 5 particles accumulated on the filter by raising the temperature of the exhaust gases to around 600 ° C. Indeed, in this temperature range and in the presence of oxygen, the combustion of soot occurs naturally. Such an increase in temperature is generally obtained by degrading the efficiency of the internal combustion engine by suitable means.

  A current method consists in delaying the main fuel injection by an angle <which is determined relative to the top dead center and which is dependent on the engine operating point. While it is generally carried out before top dead center in normal use, the main injection is carried out after this zone of optimum yield during the regeneration phase. The combustion efficiency is thus significantly degraded, which means that with the same amount of fuel injected, less mechanical energy will be recovered from the piston but, on the other hand, more thermal energy from the exhaust. In fact, the engine efficiency is deliberately degraded in terms of mechanical energy recovered. More thermal energy is thus recovered at the exhaust, which consequently makes it possible to increase the temperature inside the exhaust line. In practice, the implementation of the various means allowing the regeneration is controlled by the engine control computer which determines, as a function of several factors, the instant of the regeneration, its duration, as well as the injection parameters during this phase: number of injections, flow rate, duration and phasing of each injection.

  However, this type of regeneration process has the disadvantage of being defined for given conditions of use, which are fixed during the configuration of the various means allowing the implementation of said process, for example using a bench. 10 motor. The temperature rise is in fact preprogrammed independently of the actual conditions of use, and as such it takes into account only values determined for external factors liable to have an impact on the exhaust temperature.

  It should be noted that throughout this text, an external factor designates any parameter or physical quantity which is external to the engine block itself, such as for example the exhaust back pressure or the air temperature of admission. The effective value of this external factor is that which corresponds to the actual conditions of use of the engine at the time of regeneration. Its theoretical value is that which corresponds to the conditions of use taken into account when configuring the regeneration.

  In any event, the actual value of each of these external factors may vary in use significantly from its theoretical value.

  This type of external factor is therefore able to modify the temperature of the exhaust gases in equally significant proportions, whether down or up. However, the regeneration temperature range is relatively narrow, in particular in the case of a catalytic particle filter. It may thus be necessary not to regenerate the filter if the temperature of the exhaust gases is too low, for example less than 5700C in the case of a catalytic filter. If on the other hand the temperature were to be too high, for example higher than 6500C in the case of a catalytic particle filter, certain elements of the exhaust circuit could be damaged. One thinks for example of the active part of a catalytic filter and / or the turbine of a supercharging device.

  It should be noted that in the particular case where a turbine is present in the exhaust circuit, it appears essential to respect the maximum admissible temperature before said turbine. Indeed, as it is positioned in the exhaust line between the engine and the particle filter, the turbine 20 systematically undergoes higher temperatures than those of said particle filter. However, since it is also necessary to have relatively high temperatures at the level of the particle filter in order to be able to regenerate it, this means that the turbine will have to withstand even greater thermal stresses. However, today, we have reached the limits of what a current technology turbine can withstand, so that it is imperative to control the temperature well in order not to damage it.

  Also the technical problem to be solved, by the object of the present invention, is to propose a method of regenerating a particulate filter operating in an exhaust circuit of an internal combustion engine, the method consisting in delaying the main fuel injection of a preprogrammed angle <p which is determined with respect to the top dead center and which depends on the engine operating point, a regeneration process which would avoid the problems of the state of the art in in particular guaranteeing an exhaust gas temperature compatible with the regeneration temperature range of the particulate filter, regardless of the variations in external factors liable to influence said temperature of the exhaust gases.

  The solution to the technical problem posed consists, according to the present invention, in that the method also comprises the steps consisting in: - determining the effective value of at least one external factor capable of influencing the engine exhaust temperature , - modify the main injection delay <preprogrammed, depending on the difference between the actual value and the theoretical value of each external factor, - modify the quantity of fuel injected so as to keep the engine torque constant.

  We know the influence of each external factor on the temperature of the exhaust gases. It is known to vary the exhaust temperature by injection settings, in particular the injection angle. Consequently, it is known to correct the main injection delay in order to bring the temperature of the exhaust gases to an optimum range for regeneration. Furthermore, the influence of the injection angle on the engine torque is known. We also know how to modulate the engine torque depending on the amount of fuel injected. Consequently, it is known to correct the quantity of fuel injected so as to keep the engine torque constant.

  The invention as defined has the advantage of taking into account the actual conditions of use to generate an exhaust gas temperature compatible with the regeneration of the particulate filter. It makes it possible to make corrections with respect to preprogrammed standard settings, to compensate for the effects induced by external factors capable of influencing the temperature of the exhaust gases, and thus maintain said temperature at the desired value.

  The invention can be applied to both conventional and catalytic particle filters, even if its advantage turns out to be more significant in the case of the latter cited. The regeneration of a catalytic filter indeed requires a reduced temperature range and therefore better controlled, in order to preserve the oxidation catalyst with which it is impregnated and which allows it to obtain spontaneous combustion of the soot at higher temperatures. low. It should be noted that currently, particulate filters are mainly used in diesel engines, but it is perfectly possible that they will one day generalize to petrol engines, in particular direct injection.

  According to a feature of the invention, when the difference between the effective value of an external factor and its theoretical value is such that it tends to cause a decrease in the temperature of the exhaust gases, the second step consists in controlling a main injection delay ('greater than the main injection delay <preprogrammed and to increase the quantity of fuel injected.

  According to another feature of the invention, when the difference between the effective value of an external factor and its theoretical value is such that it tends to cause an increase in the temperature of the exhaust gases, the second step 15 consists in order a main injection delay q '' lower than the pre-programmed main injection delay <p and reduce the amount of fuel injected.

  According to a currently preferred embodiment of the invention, the determination of the effective value of an external factor capable of influencing the exhaust temperature is carried out by means of a measurement sensor.

  However, according to a variant of the invention, the determination of the effective value of an external factor capable of influencing the exhaust temperature can be carried out by means of a mathematical model.

  In a particularly advantageous manner, an external factor taken into account by the method according to the invention is the back pressure of the exhaust gases.

  According to another advantageous characteristic of the process according to the invention, an external factor taken into account is the temperature of the intake air.

  The invention also relates to a device 10 allowing the implementation of the previously described regeneration process. It is remarkable in that it comprises: - first means capable of determining the effective value of at least one external factor capable of influencing the engine exhaust temperature, - second means capable of modifying the delay d main injection p preprogrammed, as a function of the difference between the effective value and the theoretical value of each external factor, of the third means capable of modifying the quantity of fuel injected so as to keep the engine torque constant.

  The present invention also relates to the characteristics which will emerge during the description which follows, and which should be considered in isolation or according to all their possible technical combinations.

  This description given by way of example not

  limiting, will better understand how the invention can be realized, with reference to the accompanying drawings in which: Figure 1 schematically illustrates the interdependence between an internal combustion engine equipped with a particle filter and its control system.

  FIG. 2 represents an injection pattern corresponding to normal operation of the engine.

  FIG. 3 shows an injection pattern corresponding to a conventional operation during the regeneration phase.

  FIG. 4 shows an injection pattern corresponding, in the regeneration phase, to a first type of correction in accordance with the method according to the invention.

  FIG. 5 illustrates an injection pattern 15 corresponding, in the regeneration phase, to a second type of correction in accordance with the method according to the invention.

  For reasons of clarity, the same elements have been designated by identical references. Likewise, only the essential elements for understanding the invention have been shown, and this without respecting the scale and in a schematic manner.

  FIG. 1 illustrates an internal combustion engine which is constituted, in this particular embodiment, by an internal combustion engine 1 of the four cylinder turbo diesel type. Four rod / piston 2 assemblies respectively cooperating with four injectors 3 have in fact been shown. There is also an intake manifold 4 and an exhaust manifold 5 communicating with a particle filter 6.

  We also note the presence of a turbocharger 7 which, conventionally, consists of a compressor 8 and a turbine 9. An engine control system 10 is also shown. 5 It comprises an injection computer 11, as well as various sensors and actuators respectively symbolized by re-entering arrows f1, f2, f3 and outgoing arrows f4. The information that can be measured by the sensors can be 10 * of various origins: Engine rotation speed (arrow f3), exhaust back pressure (arrow f2), intake temperature, corresponding pedal position (arrow fi) at the driver's request, etc. The commands controlled by the computer can also be multiple, and relate for example to the piloting (arrow f5) of the injectors 3.

  At the inlet, the intake circuit is conventionally composed of an air filter 20 responsible for capturing and purifying the air intended to be admitted into the engine 1, as well as a flow meter 21 intended to inform the computer 11 on the quantity of fresh air which enters said engine 1. The intake air is then compressed in the compressor 8 before being cooled in a heat exchanger 22, then reaching the intake manifold 4 via an EGR type valve 23. This valve 23, controlled by a computer 11, conventionally allows gas recirculation from the exhaust manifold 5 to the intake manifold 4. The exhaust circuit is just as conventionally composed of the exhaust manifold 5 responsible for collecting the gases from the operation of the engine 1, as well as from the turbine 9 intended to implement it the compressor 8 thanks to the passage of said exhaust gases. We then find the particle filter 6 which precedes still other elements of the exhaust line, not shown here for the sake of clarity. We mainly think of catalysts and other silencers.

  The engine control system 10, and more precisely the computer 11, firstly comprises 10 of the first means which are able to determine the effective value of the exhaust gas back pressure, that is to say the pressure in the exhaust line between the engine 1 and the particulate filter 6. This variable is variable because as and as the filter 6 fills, it becomes less and less permeable, so that the pressure at motor output increases.

  In this exemplary embodiment, the effective value of the exhaust gas back pressure is determined by means of a measurement sensor connected to the computer 11. The pressure sensor in question is here placed between the turbine 9 and the particulate filter 6, but it is obvious that it could be positioned in any other place of the exhaust line. Furthermore, according to an alternative embodiment, it would be perfectly conceivable to quantify the back pressure of the exhaust gases by means of a mathematical model 30 stored in the computer 11. Such a tool is indeed capable of reconstructing this type of relevant information using physical equations and basic information.

  The engine control system, and more precisely the computer 11, is furthermore provided with second means which are responsible for modifying the preprogrammed main injection delay cp, as a function of the difference between the actual value and the theoretical value of exhaust gas back pressure.

  It is here the computer l1 which controls the injectors 3. However, it knows the influence of the back pressure on the temperature of the exhaust gases. He also knows how to vary the exhaust temperature by delaying the injection more or less. Consequently, the computer 11 is able to bring the temperature of the exhaust gases back to the optimum regeneration range.

  The engine control system, and more precisely the computer 11, is finally provided with third means which are capable of modifying the quantity of fuel injected so as to keep the engine torque 20 constant. Again, the computer controlling the injectors 3 knows the influence of the injection angle on the engine torque and knows how to modulate said engine torque as a function of the quantity of fuel injected. Consequently, the computer is perfectly capable of correcting the quantity of fuel injected in order to keep the engine torque constant.

  FIGS. 2 to 5 constitute diagrams relating to different injection patterns applicable to a cylinder of a diesel engine. Thus, in the particular example chosen here to illustrate the invention, the injection is carried out in the form of a sequence. It consists of a pre-injection 30 which, in normal injection, only aims to reduce engine noise, as well as a main injection 31 which is intended to achieve the engine torque requested (arrow fl) by the driver . The horizontal axis X corresponds to 5 the injection angle on an engine cycle and for a cylinder. The vertical axis Y marks the transition to top dead center, and therefore constitutes a reference.

  FIG. 2 illustrates an injection sequence during a normal operating cycle. It is very well observed that the entire injection sequence, grouping together the pre-injection 30a the main injection 31a, is carried out in this example before the shift to top dead center materialized by the Y axis, that is to say say in the optimal yield area.

  FIG. 3 shows a delayed injection sequence, of the type carried out during the regeneration of the particulate filter 6. It is noted that the injection sequence is here completely offset after the top dead center. It should be noted, however, that the quantities of fuel injected, symbolized by the length of the rectangles, have increased slightly compared to their counterparts in FIG. 2.

  As regards the pre-injection 30b, this increase is justified by reasons of engine stability. For the main injection 31b, it is in fact a question of compensating for the loss of engine torque caused by the offset of the injection in an area where the engine efficiency is lower. It is indeed imperative to respond uniformly to the driver's request in terms of engine torque, whether said engine 1 is in the normal operating phase or in the regeneration phase.

  FIG. 4 represents a first delayed injection sequence 5 which is corrected in accordance with the regeneration method according to the invention. The delay of the main injection 31c is modulated as a function of the effective value of the exhaust gas back pressure which is here greater than its theoretical value. This peculiarity being of a nature to cause an increase in the temperature of the exhaust gases, the second means have controlled, on the one hand, a main injection delay λ '' lower than the preprogrammed main injection delay y, and on the other hand, a decrease in the amount of fuel injected. The goal here is to bring the exhaust temperature down to reach the optimal value retained for regeneration.

  As the main injection 31c is less delayed than in the case of the basic regeneration in FIG. 3, the engine efficiency is less degraded. Consequently, the quantity of fuel of the main injection 31c must be less to achieve the torque requested by the driver. Because despite the thermal constraints linked to the regeneration of the particulate filter 6, the primary objective is always to do what the driver requests (arrow fi). Torque production must be maintained during regeneration and this must be completely transparent to the driver. There is however no incidence at the level of the pre-injection 30c.

  FIG. 5 illustrates a second delayed injection sequence, also corrected in accordance with the regeneration method according to the invention. The delay of the main injection 31d 5 is here always modulated as a function of the effective value of the exhaust gas back pressure.

  However, in the present case, since this effective value is less than its theoretical value, the temperature of the exhaust gases will implicitly be lower than that initially used for regeneration. To bring this exhaust temperature back to an optimal value, the second means will advantageously control, on the one hand, a main injection delay Y 'greater than the preprogrammed main injection delay p, and on the other hand, an increase in the amount of fuel injected.

  Indeed, as the main injection 31d is more delayed than in the case of the basic regeneration of FIG. 3, the engine efficiency is more degraded. Consequently, the quantity of fuel of the main injection 31d must be increased here in order to achieve the torque requested by the driver. On the other hand, here again, the quantity of fuel corresponding to the pre-injection 30d is not modified.

  In this particular embodiment, it is the exhaust gas back pressure which has been taken into account to correct the injection in the regeneration phase. It would however be equally advantageous to use, as an alternative or in addition, the intake air temperature. Of course, the invention can be implemented by taking into account any other external factor capable of influencing the temperature of the exhaust gases, insofar as the impact of the variations of said external factor on the temperature of the gases d the exhaust is known to the engine control system 10, and more precisely to the computer 11.

  Of course, the invention also relates to any motor vehicle comprising a regeneration device as previously described.

Claims (15)

  1. A method of regenerating a particulate filter (6) operating in an exhaust circuit of an internal combustion engine (1), the method consisting in delaying the main injection (31b) of fuel by angle q which is determined relative to the top dead center and which depends on the engine operating point (1), characterized in that said method 10 furthermore comprises the steps consisting in - determining the effective value of at least one external factor capable of influence the engine exhaust temperature, - modify the pre-programmed main injection delay q 15, depending on the difference between the actual value and the theoretical value of each external factor, - modify the quantity of fuel injected by so as to keep the engine torque constant. 20 2. A regeneration method according to claim 1, characterized in that when the difference between the effective value of an external factor and its theoretical value is such that it tends to cause a decrease in the temperature of the exhaust gases, the second step consists in ordering a main injection delay q ′ greater than the preprogrammed main injection delay q and in increasing the quantity of fuel injected. 30 3. A regeneration method according to claim 1, characterized in that when the difference between the effective value of an external factor and its theoretical value is such that it tends to cause an increase in the temperature of the exhaust gases, the second step is to order a main injection delay À '' less than the preprogrammed main injection delay cp and to reduce the quantity of fuel injected.   4. Regeneration method according to any one of claims 1 to 3, characterized in that the determination of the effective value of an external factor capable of influencing the exhaust temperature is carried out by means of a sensor of measurement.   5. Regeneration method according to any one of claims 1 to 4, characterized in that the determination of the effective value of an external factor capable of influencing the exhaust temperature is carried out by means of a model mathematical.   6. A regeneration method according to any one of claims 1 to 5, characterized in that an external factor taken into account is the back pressure of the exhaust gases.   7. Regeneration method according to any one of claims 1 to 6, characterized in that an external factor taken into account is the temperature of the intake air.   8. Device for implementing the regeneration method according to any one of claims 1 to 7, characterized in that it comprises: first means capable of determining the effective value of at least one external factor capable of influencing on the engine exhaust temperature, - second means capable of modifying the pre-programmed main injection delay 5 9, as a function of the difference between the effective value and the theoretical value of each external factor, - third means capable of modify the quantity of fuel injected so as to keep the engine torque constant.   9. Regeneration device according to claim 8, characterized in that when the difference between the effective value of an external factor and its theoretical value is such that it tends to cause a decrease in the temperature of the exhaust gases, the second means are able to control a main injection delay 9 'greater than the main injection delay 9 and to increase the quantity of fuel injected.   10. Regeneration device according to claim 8, characterized in that when the difference between the effective value of an external factor and its theoretical value is such that it tends to cause an increase in the temperature of the exhaust gases, the second means are capable of controlling a main injection delay 9 '' less than the main injection delay 9 and of reducing the quantity of fuel injected.   11. Regeneration device according to any one of claims 8 to 10, characterized in that the first means comprise at least one measurement sensor capable of determining the effective value of an external factor capable of influencing the temperature of engine exhaust.   12. Regeneration device according to any one of claims 8 to 11, characterized in that the first means comprise at least one mathematical model capable of determining the effective value of an external factor capable of influencing the temperature of engine exhaust.   13. Regeneration device according to any one of claims 8 to 12, characterized in that it is capable of taking into account the back pressure of the exhaust gases as an external factor capable of influencing the temperature of said gases. exhaust.   14. Regeneration device according to any one of claims 1 to 13, characterized in that it is able to take into account the temperature of the intake air as an external factor capable of influencing the temperature of said exhaust gas.   15. Motor vehicle, characterized in that it comprises a regeneration device according to one   any of claims 8 to 14.