FR2915769A1 - METHOD FOR CONTROLLING THE REGENERATION OF A PARTICLE FILTER. - Google Patents

Abstract

A method of regulating the regeneration of a particulate filter (42) in an exhaust gas system of an internal combustion engine (10) by controlling the combustion of particles in the particulate filter (42) during a regeneration operation by regulating the oxygen content of the exhaust gas; and / or regulating the temperature of the exhaust gas or at least one component of an exhaust gas aftertreatment system (40). A regulating action is performed to regulate the oxygen content and / or the temperature of the aftertreatment system components (40) only for stable combustion conditions of the internal combustion engine (10).

Description

Field of the Invention The present invention relates to a method of

  regulating the regeneration of a particulate filter in an exhaust system of an internal combustion engine in which the combustion of the particles in the particulate filter is controlled during a regeneration operation by the regulating the oxygen content of the exhaust gas, and / or regulating the temperature of the exhaust gas or at least one component of an exhaust gas aftertreatment system.

  It also relates to an application of this method. STATE OF THE ART According to the document DE-103 33 441-A1 a process is known for controlling an exhaust gas post-treatment system, in particular a particle filter of a combustion engine. internally according to which a set value (LAS) of a lambda signal (L) or a variation of a lambda signal L is predefined and the real value of the lambda signal (L) is entered and based on the comparison between the real value and the setpoint, a control signal for an actuating element is preset to control the reaction in the exhaust aftertreatment system so that the actual value approaches the setpoint. The preset value (LAS) can be preset to establish a pre-defined particle combustion rate of an exhaust gas aftertreatment system particulate filter and / or to obtain a pre-set temperature in the system. aftertreatment of the exhaust gases. By such a controlled regeneration mode, limited in oxygen for the particulate filter, it is possible to effectively control the burning rate of the carbon black and thus also the increase of the temperature conditioned by this exothermic reaction in the particulate filter. It is particularly necessary to limit the maximum temperature produced during a regeneration phase, especially if compared to standard materials such as SiC, more expensive materials such as Cordierite are used as the material for the particulate filter. because these materials have a lower thermal resistance. Thus for such expensive materials, the temperature of the particulate filter being regenerated must not exceed a maximum value of the order of 850 C to 1000 C. DE-103 33 441-A1 also describes a control device for an exhaust gas after-treatment system, in particular a particulate filter of an internal combustion engine comprising means that predefine a set point value LAS for the lambda signal L or a variation of the lambda signal L, means which enter the actual value of the lambda signal L or the variation of the lambda signal L and means which, starting from the comparison between the actual value and the set value LAS of the lambda signal L or the variation of the Lambda signal L, predefines a control signal for an actuating element with which the reaction is controlled in the aftertreatment system of the exhaust gases so that the actual value approaches the setpoint value . With the aid of the actuating element the amount of oxygen in the exhaust gases can be influenced. The actuating element may be an exhaust gas recirculation valve, the throttle valve, or a means for influencing an exhaust gas turbo-compressor; it can also be a fuel metering system that performs at least one post-fuel injection in the internal combustion engine. The effectiveness of the control actions described depends strongly on the operating conditions of the internal combustion engine. For example, it is necessary to define means for regulating the lambda coefficient in the injection system, for example in the form of a post-injection which burns with a neutral torque in the internal combustion engine. Otherwise excessive emissions of unburned hydrocarbons can produce excessive exothermic reaction in the aftertreatment system of the exhaust gases, especially in the oxidation catalyst resulting in a large increase in temperature and thus in the example cited, damage to the oxidation catalyst.

  OBJECT OF THE INVENTION The object of the present invention is to develop a process which makes it possible to avoid with certainty any unacceptable rise in the temperature of the aftertreatment system of the exhaust gases of an internal combustion engine generated by internal combustion engines. control actions to control the combustion of soot particles or carbon black during the regeneration of particulate filters. DESCRIPTION AND ADVANTAGES OF THE INVENTION This problem is solved according to the invention by a process of the type defined above, characterized in that a regulating action is performed to regulate the oxygen content and / or the temperature of the components of the invention. exhaust aftertreatment system only for stable combustion conditions of the internal combustion engine.

  Under such stable combustion conditions, a regulating action avoids, for example, any emission of unacceptable level of unburned hydrocarbons. Therefore, the regulating action does not produce a too strongly exothermic reaction in the aftertreatment system of the exhaust gases of the internal combustion engine, particularly in the oxidation catalyst. In addition, it is safe to avoid that, because of the high hydrocarbon emission, the measurement of the lambda coefficient in the exhaust gas duct is distorted by the transverse sensitivity of the lambda probe with respect to the hydrocarbons. The regulation of the oxygen content during the regeneration phase of the particulate filter is based on the lambda signal as measured. A high concentration of unburned hydrocarbons in the exhaust gas distorts the lambda signal measured in the direction of a lean exhaust gas composition, which in turn produces a regulating action to reduce the oxygen content in the exhaust gases. exhaust gas ; this increases the con-centration of unburned hydrocarbons in the exhaust gas. The method according to the invention makes it possible to safely avoid such a sequence. Unauthorized control actions can be safely avoided while combustion conditions are not sufficiently stable in that regeneration of the particulate filter takes place only if the combustion conditions of the internal combustion engine are stable. . Particularly in the case of a cold internal combustion engine, it may happen that the state of implementation of the preheating system is used to determine the state of stable combustion conditions of the internal combustion engine . As confirmed by measurements made on internal combustion engines, for a very cold internal combustion engine, at -20 C, it is possible to have a sufficiently stable combustion for a regulation action if the preheating installation is activated. On the other hand, if the combustion of the engine is done while preheating is cut off, the unburnt hydrocarbon concentration in the exhaust gases increases with the effects already described on the regulation of the lambda coefficient. Thus the control actions in the case of a cold internal combustion engine must be limited to the phases during which the preheating is implemented. According to a preferred embodiment of the invention, the stability of the rotational speed of the internal combustion engine is used to detect the stable combustion conditions of the engine. The stability of the rotation speed makes it possible to directly detect the stability of the combustion of the engine. If the irregularity of the rotational speed exceeds a predefined threshold, it can be concluded that the stability of the combustion is insufficient to effect an action on the aftertreatment system of the exhaust gases. In general, the rotational speed of a subordinate control of the internal combustion engine is available as a rotational speed signal. The process can be particularly advantageously applied to regulate the regeneration of particulate filters having a cordierite base body. The use of cordierite as a particulate filter material significantly reduces the manufacturing costs of particulate filters. This requires precise compliance with the maximum particle filter temperature constraints and thus the use of lambda coefficient and temperature regulators.

  Drawings The present invention will be described below in more detail with the aid of embodiment examples shown in the accompanying drawings in which: - Figure 1 is a schematic view of the technical environment in which falls the invention; - Figure 2 shows a first diagram showing the relationship between the stability of combustion and preheating; FIG. 3 shows a second diagram of the lambda signal as a function of preheating; FIG. 4 shows a third diagram with the timing diagram of the lambda control variable as a function of preheating; and FIG. 5 shows a diagram with a temperature curve of an oxidation catalyst as a function of a regulating action. DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 schematically shows the technical environment in which the invention applies, showing an internal combustion engine 10 such as a diesel engine equipped with a fuel metering system. 11, an air supply line 20 in which passes a supply air flow 21 and an exhaust gas duct 30 in which runs the exhaust gas stream 32 of the internal combustion engine 10. In the direction of passage of the supply air stream 21 into the air supply channel 20 there is a compression stage 23 of a turbo compressor 22 and a throttle flap 24. An exhaust gas recirculation means 25 connects via an exhaust gas recirculation valve 26, the air supply duct 20 to the exhaust gas duct 30. In the direction of passage of the gas stream exhaust 32, after the internal combustion engine 10 there is a turbine of exhaust gas 31 from the turbo-compressor 22 as well as the components of an exhaust after-treatment system 40, namely a first lambda probe 43, a fuel supply 45, a catalytic converter, oxidation 41 in the form of a die-salt oxidation catalyst, a second lambda probe 44 and a particulate filter 42 in the form of a diesel particulate filter. In order to apply the invention, at least one second lambda probe 43, 44 is provided. The air supply duct 20 supplies the internal combustion engine 10 with fresh air. The fresh air is compressed by the compression stage 23 of the turbo-compressor 22 driven by the exhaust turbine 31 installed in the exhaust gas channel 32. The throttle flap 24 makes it possible to adjust the quantity supplied air. In order to reduce pollutant emissions, the exhaust gas stream 25, through the exhaust gas recirculation means 25, mixes with the exhaust gas stream 25 amounts of exhaust gas from the exhaust gas line. according to a mixture depending on the operating parameters of the internal combustion engine 10. The exhaust gas recirculation coefficient is adjusted by means of the exhaust gas recirculation valve 26.

  The exhaust after-treatment system 40 converts or filters the pollutants emitted by the internal combustion engine 10. Thus, in the oxidation catalyst 41, the hydrocarbons are oxidized while in the particulate filter 42 the particles of soot (or particles of carbon black) are retained.

  Fuel can be introduced into the exhaust gas conduit 30 through the fuel supply 45. The control and regulating units, temperature sensors as well as particle filter load diagnostic units 32 necessary for the operation of the internal combustion engine 10 and exhaust after-treatment system 40 are not shown. The operation of the internal combustion engine 10 charges the particulate filter 42 until the exhaustion of its storage capacity is reported. Then, a regeneration phase of the particulate filter 42 is started according to which the particles accumulated in the particulate filter 42 are burned by an exothermic reaction. To initiate this exothermic reaction, it is necessary that the particulate filter 42 is at exhaust gas temperatures of the order of 600 C to 650 C. As in the normal operating conditions of the internal combustion engine 10 is reached such temperatures that close to the maximum load, it is necessary to produce the temperature rise by complementary means. Particularly in the case of low motor load and rotational speed, besides the actions on the feed system, for example via the throttle flap 24, other measures in the field of safety can be envisaged. fuel injection using the fuel metering system 11. These measurements can be internal engine measurements such as the shift in the direction of the delay of the main injection or a post-injection PoI2 which burns neutrally. for the torque provided by the internal combustion engine 10 or a Poll post-injection introduced by the fuel supply means 45 into the exhaust gas conduit 30 upstream of the oxidation catalyst 41 or burning in the catalyst In addition, the exhaust gas recirculation coefficient can be modified by the exhaust gas recirculation valve 26. The above-mentioned means not only influence the temperature of the exhaust gases, but also the exhaust gas recirculation valve 26. exhaust but also the composition of the exhaust gases in particular their oxygen content. Since the oxygen content has a significant influence on the rate of combustion of the particles accumulated in the particulate filter 42 during the regeneration operation and thus on the energy released per unit of time, it is known to regulate the evolution of the combustion of the particles and thus the temperature of the particulate filter by regulating the oxygen content of the exhaust gas using the means mentioned. For this purpose, the signal or signal variation of at least one of the two lambda probes 43, 44 of a control unit (not shown) is compared with a predefined value and, depending on the control difference, it is assumed that one of the measures mentioned or a combination thereof.

  By regulating the temperature of the particulate filter 42 by means of the oxygen content of the exhaust gas, the maximum temperature of the particulate filter 42 can be limited. This allows, in comparison with standard materials such as SiC, use more economical materials such as for example cordierite but which have a lower thermal resistance.

  The signals shown in FIGS. 2 to 5 relate for example to the technical environment shown in FIG. 1 and the references are the same. FIG. 2 shows a first diagram 50 giving the relation between the combustion stability of an internal combustion engine, for example of the internal combustion engine 10 represented in FIG. 1, and preheating as a possible indicator of a stable combustion at low ambient temperatures here at -20 C. The speed of rotation 57 is represented with respect to the first time axis 51; the rotation speed is represented on the first ordinate axis 52 of the diagram 50 and the evolution of the injected dose 58 provided for each fuel injection is represented on the second ordinate axis 53. The diagram 50 is divided into one first time interval 55 and in a second time interval 56 from the switching point 54. During the first time interval 55, the preheating of the internal combustion engine 10 is started while it is switched off during the first time interval 55. second time interval 56. Diagram 50 shows how the rotational speed 57 of the internal combustion engine 10 varies according to the state of the preheating system for a constant injection dose 58 as shown by the preheating cut-off when 'establishes combustion in the engine. This increases the hydrocarbon content in the exhaust gas of the internal combustion engine 10. FIG. 3 shows in a second diagram 60, the timing diagram of the signal lambda 63 as measured represented on a third ordinate axis 62 in the gases. exhaust system of the internal combustion engine 10 according to the switching state of the incandescent shown in FIG. 2, with respect to a two-pole axis of the times 61 with the same subdivision as that represented in FIG. the first time axis 51. The switching point 54 of FIG. 2 is correspondingly taken up again. The measurement of the lambda coefficient can be done with a lambda probe 43, 44 shown in FIG. 1. The measurement of the lambda signal 63 was made for a lambda coefficient actually remaining constant at the passage of the switching point 54. measured lambda signal 63 comes from the well-known transversal sensitivity of the lambda probe 43, 44 as a function of the increase in the hydrocarbon content in the exhaust gas after the switching point 54 and then relying on a measuring defect of the lambda probe 43, 44. FIG. 4 shows a third diagram 70 with the timing diagram of the adjustment variable of the lambda coefficient for a neutral post-injection 73 from the point of view of the torque supplied, as a function of the incandescence in a circuit method of control as described for the controlled combustion of particles during the regeneration of a particulate filter 42. The evolution is shown with respect to a third temperature axis s 71 with the same division as in the situation shown in Figure 3 with the first switching axis 51, with the switching point 54; the fourth axis of ordinates 72 shows the fuel dose for the anticipated post-injection 73. The anticipated post-injection 73 of the exemplary embodiment is representative of the measures envisaged to regulate the oxygen content in the feed gases. combustion of the internal combustion engine 10 to regulate the rate of combustion of the particles during the regeneration phase of the particulate filter 42. The increase of the injected dose after the switching point 54 is based on the lambda signal 63, shown in FIG. 3. FIG. 5 shows a fourth diagram 80 with the temperature curve 83 of an oxidation catalyst 41 as a function of a regulating action for controlling the combustion rate of the particles. during the regeneration phase of the particulate filter 42. The temperature is represented on a fifth ordinate axis 82 with respect to the fourth time axis 81. time axis 81 has an elongated time interval with respect to that shown on the time axes 51, 61, 71 of FIGS. 2, 3, 4. The switching point 54 is transferred between the activated preheating state and the preheating state cut off. Due to the lambda signal 63 determined with error as shown in FIG. 3 and the increase then launched according to FIG. 4 by the anticipated post-injection 73, the unburned hydrocarbon content contained in the exhaust gases is increased. of an internal combustion engine, upstream of the oxidation catalyst 41. This results in a strong exothermic reaction in the oxidation catalyst 41 so that in this embodiment its temperature increases up to 1000 ° C. This sharp increase in the temperature in the oxidation catalyst 41 caused by the lack of action of the control circuit on the regulation of the combustion rate of the particles in the filter 42 during a regeneration operation risks The defective action of the regulation circuit is based on a measurement error of the lambda probe 43, 44 itself resulting from insufficient stability of the combustor. ion of the internal combustion engine 10.

  Thus according to the invention, it is intended to limit the planned control actions or the regeneration of the particulate filter generally to the operating phases of the internal combustion engine 10 in combustion conditions stable from the point of view of the engine. As the possibility of indirect detection of a stable combustion can be cold start of the internal combustion engine 10 use the implementation state of the preheating system. Regulating action or regeneration of the particulate filter 42 may be limited to time intervals 55 during which preheating is connected. Another possibility is to directly grasp the stability of the combustion by exploiting the irregularity of the rotational speed signal. If the irregularity of the speed of rotation exceeds a certain threshold, it can be concluded that the aftertreatment action of the exhaust gases has insufficient stability.

Claims (4)

  1) A method of regulating the regeneration of a particulate filter (42) in an exhaust gas system of an internal combustion engine (10) in which: the combustion of the particles in the filter is controlled particles (42) during a regeneration operation by regulating the oxygen content of the exhaust gas; and / or the temperature of the exhaust gas or of at least one component of an exhaust gas after-treatment system (40) is regulated, characterized in that a regulation action is carried out to regulate the the oxygen content and / or the temperature of the aftertreatment system components (40) only for stable combustion conditions of the internal combustion engine (10). 2) Process according to claim 1, characterized in that a regeneration of the particulate filter (42) is carried out only if the combustion conditions of the internal combustion engine (10) are stable. 3) Process according to claim 1, characterized in that the state of implementation of the preheating system is used to set the state of stable combustion condition of the internal combustion engine (10). 4) Process according to claim 1, characterized in that the stability of the rotational speed (57) of the internal combustion engine (10) is used to detect stable combustion conditions of the internal combustion engine (10). 5) Application of the method according to one of claims 1 to 4, for regulating the regeneration of a particulate filter (42) having a Cordierite base body.