FR2906839A1 - SYSTEM AND METHOD FOR ESTIMATING THE QUANTITY OF PARTICLES SPILLED BY A PARTICLE FILTER - Google Patents

Abstract

The invention relates to a system 1 for estimating the quantity of particles trapped by a particulate filter (FAP) 4 fitted to an exhaust line 11 of a vehicle diesel engine 7, the system comprising: first, second and third evaluation means arranged to respectively provide data relating to: - the engine speed, - the air flow supplied to the engine, - the fuel flow injected into the engine ,. a control unit 2 arranged to provide an estimate of the quantity of particles trapped by the particle filter as a function of said data, characterized in that the third evaluation means comprise means for determining the richness of the mixture feeding the engine.

Description

The present invention relates to particulate filters equipping the

  diesel engines for a motor vehicle. More particularly, the present invention relates to a system and method for estimating the amount of particles trapped in a particulate filter fitted to a diesel engine for a motor vehicle. In known manner, a particulate filter (FAP) operates alternately in two phases. In a first so-called trapping phase, it retains the polluting substances emitted by the engines 10 before their release into the atmosphere. Pollutants include so-called soot particles that accumulate continuously on the FAP. In a second so-called regeneration or treatment phase, the particles retained by the FAP are burned. The transition from the trapping phase to the regeneration phase is triggered when a predefined quantity of particles accumulated on the FAP, hereinafter referred to as the regeneration threshold, is reached. However, the quantity of particles retained in the FAP influences the pressure drop in the exhaust line and the engine performance. Thus, the regeneration threshold is linked to the degradation of engine performance caused by the increase in the pressure drop in the exhaust line. The regeneration threshold is also determined according to the risks of runaway that may occur during regenerations carried out on a FAP with too much loading. In addition, too frequent regenerations cause a significant dilution of gas oil in the engine lubricating oil, which can become dangerous for the integrity of the engine. In addition, too frequent regenerations tend to unnecessarily increase fuel consumption. On the other hand, regenerations that are too far apart can result in clogging of the FAP, which is likely to cause the engine to be shut down. Therefore, the amount of particles actually retained in a DPF should be assessed as precisely as possible so that each regeneration phase is triggered at the right time.

  For this purpose, it is known to estimate the quantity of particles stored by a FAP from a particle emission model which links the engine parameters, such as the speed and the load, to the production of particles. Thus, these models provide for determining the quantity of particles trapped, in particular from the fuel injection set point imposed on the injectors. These methods are not fully satisfactory because the accuracy of the estimate of the amount of particles they produce can be improved. The existing systems therefore generate regenerations too frequent or too widely spaced, with damaging consequences on the service life, the performance and the cost of operation of the vehicle as well as on the environment. The aim of the invention is to improve the known systems and methods for estimating the quantity of particles retained in a FAP. For this purpose, a system for estimating the quantity of particles trapped by a particle filter fitted to an exhaust line of a vehicle diesel engine is provided in the context of the present invention, the system comprising: first, second and third evaluation means arranged to respectively provide data relating to: - the engine speed, the air flow supplied to the engine, - the fuel flow injected into the engine, • a unit of control arranged to provide an estimate of the amount of particles trapped by the particle filter according to said data, the third evaluation means comprising means for determining the richness of the mixture feeding the engine. Thus, the invention makes it possible to provide an estimate of the quantity of particles trapped by the FAP which is a function of the richness of the fuel injected. It is specified that the mixture is the gaseous mixture air / fuel 5 feeding the engine, and the richness is the fuel content of this mixture. The evaluation of the injected fuel flow rate is therefore not based on the injection setpoint, unlike the known estimation systems. This evaluation is therefore not influenced by the drift and dispersion of the injectors. Moreover, as identified by the applicant, the richness represents, before the engine load, the parameter of order one in the estimation of the emissions of particles. The invention therefore allows a particularly accurate and reliable estimate of the amount of particles trapped by the FAP.

  The estimation system according to the invention may furthermore optionally have at least one of the following characteristics: the third evaluation means comprise means for calculating the fuel flow injected into the engine arranged so as to perform the following operation: Qinj = Qair R 14.7 in which: Qn; : is the actual fuel injection rate expressed in mg / cp, Qa: r: is the flow of fresh air admitted into the cylinders mg / cp, R: is the richness of the mixture. the means for determining the richness of the mixture comprise at least one oxygen probe; the probe is placed in the exhaust line downstream of the engine; the system comprises a flow meter arranged in the intake line in order to measure the air flow admitted into the cylinders of the engine, the system comprises estimation correction means intended to take into account the opening of a valve equipping an associated exhaust gas recirculation circuit to the engine. Furthermore, in the context of the invention there is provided an exhaust gas treatment system derived from a diesel engine comprising an estimation system according to any one of the preceding characteristics. Optionally, it can be provided that the treatment system according to the invention comprises an exhaust line comprising a nitrogen oxide trap and an oxidation catalyst located downstream of the nitrogen oxide trap, the probe being placed downstream of the nitrogen oxide trap and upstream of the oxidation catalyst. The invention also relates to a vehicle equipped with an estimation system according to any one of the preceding characteristics. In addition, the invention provides a method for estimating the quantity of particles trapped by a particulate filter fitted to an exhaust line of a diesel engine for a vehicle, in which: data relating to: the engine speed, the air flow supplied to the engine, the fuel flow injected into the engine, • an estimate of the quantity of particles trapped in the particulate filter from said data, • an determines the richness of the mixture feeding the engine in order to evaluate the data relating to the flow of fuel injected into the engine.

  Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the accompanying drawing, given by way of non-limiting example. FIG. 1 is an overall diagram of a system for estimating the quantity of particles trapped by a FAP fitted to an exhaust line of a diesel engine for a vehicle. Referring to FIG. 1, there is illustrated an exhaust gas treatment system 20 comprising an estimation system 1 according to an exemplary embodiment. The figure shows a diesel engine 7 whose exhaust is associated with the exhaust gas treatment system 20. The exhaust gas treatment system 20 comprises an exhaust line 11 comprising a nitrogen oxide trap (NOx Trap) 10 6, an oxidation catalyst (DOC) 5 and a FAP 4 sequentially disposed along the exhaust line 11 from upstream to downstream. The upstream and downstream directions are defined by the direction of propagation of the exhaust gases along the exhaust line 11. The estimation system 1 comprises a control unit 2 in which is integrated a transmission model . The soot emission model is essentially based on three types of data, respectively relating to: - the engine speed, expressed in rpm, - the air flow rate expressed in mg / cp, 20 - the injected fuel flow rate expressed in mg / cp. The unit mg / pc representing, in known manner, an explosion mass flow rate, also called a blow, produced in the engine block 7. From mappings dependent on these three types of data, the emission model makes it possible to determine the amount of soot produced during combustion. In order to determine the data relating to the engine speed, the estimation system 1 comprises first evaluation means. For this purpose, the first evaluation means comprise, for example, a motor rotation speed sensor.

The estimation system 1 also includes second evaluation means providing air flow data and third evaluation means providing fuel flow data.

The second evaluation means comprise, for example, a flowmeter arranged to measure the flow of air admitted into the cylinders. Preferably, the flow meter is disposed in the intake line.

The third evaluation means comprise means for determining the richness of the mixture supplying the engine 7. In addition, the third evaluation means comprise calculation means. These calculation means determine the fuel flow injected into the engine 7 by performing the following operation: Qin]. = Q 14.7 where: is the actual fuel injection rate expressed in mg / cp, Q: is the flow of fresh air admitted into the cylinders mg / cp, R: is the richness of the mixture. The means for determining the richness of the mixture comprise at least one oxygen probe 3 in order to measure the richness of the mixture. This probe 3 is disposed downstream of the FAP 4 and upstream of the oxidation catalyst 5. The air flow is measured by means of a flow meter disposed in the intake line. Thus, the third evaluation means provide an evaluation of the injected fuel flow rate which is a function of the richness of the fuel injected, this richness being measured by means of an oxygen probe 3. The known models of soot emission are based on the injection instruction of the amount of fuel to determine the fuel injection rate. However, the Applicant has found that these 30 models have a significant error that varies over time. Indeed, a significant difference has been detected between the injection setpoint and the quantity actually injected. It appeared that this difference comes from the dispersion and the drift of the injectors. The injectors are in fact subjected to the high temperature and pressure conditions prevailing within the combustion chamber, which alters their physical properties and induces a change in the doses injected. This results in an estimation error of the emission model which tends to increase over the lifetime of the vehicle. The estimation system 1 according to the invention is not based on measurements from the injectors, and thus makes it possible to overcome the drift and the dispersion of the latter. Moreover, as identified by the applicant, the richness 10 represents, before the engine load, the first order parameter in the estimation of the particle emissions. However, by studying the existing estimation systems, the Applicant has noticed their close dependence on drifting engine parameters such as engine speed and load. In addition, these drifts tend to increase as and when the wear of the engine. Consequently, in the known estimation systems, the drifts of the motor parameters generate estimation errors which increase continuously. The estimation system 1 according to the invention is based on the richness and is therefore not closely influenced by the drift of the engine parameters. The invention therefore allows a particularly accurate and reliable estimate of the amount of particles trapped by the FAP 4. An oxygen sensor 3 has an aging resistance substantially greater than that of a fuel injector. In addition, the aging of an oxygen probe 3 can be controlled by integrating the resetting strategies into the estimation system. In addition, being disposed in the exhaust line 11, the probe 3 is subjected to lower temperature and pressure conditions than the injectors located in the combustion chambers. Thus the probe 3 undergoes substantially less damage than the injectors. It is, therefore, more able to retain its properties over time.

The use of an oxygen sensor 3 in the evaluation of the quantity of fuel injected thus contributes to enhancing the accuracy and stability of the system according to the invention. The control unit 2 participates in the control of certain members 5 of the vehicle and the engine 7. Thus, on the basis of the estimate provided by the transmission model and on the basis of other parameters 9 (command from the driver in particular), the control unit 2 determines the quantity of fuel that the injectors 10 introduce into the cylinders of the engine 7.

Furthermore, the estimation system 1 makes it possible to take into account both the storage of residues in the filter and the oxidation of soot produced by nitrogen oxide. This is a function of the concentration of nitrogen dioxide and oxygen, the internal temperature of the filter, and the mass of soot present in the filter.

In known manner, the engine 7 may be equipped with an exhaust gas recirculation circuit 8 (EGR) as shown in FIG. 1. This type of circuit 8 usually comprises a valve controlling the gas inlet of exhaust at the engine intake 7. In one embodiment of the invention, it is provided that the estimating system 1 takes into account the opening of the EGR valve in order to correct the emission model. of particles. Several variants can be provided to the estimation system 1 described above. Thus, it is possible to modify the location of the probe 3 along the exhaust downstream of the engine 7. The closer the probe 3 is to the engine 7, the more it is subjected to high thermal stresses. The further the probe 3 is away from the engine 7, the more the reactivity of the estimation system 1 decreases. It should be noted that the emission model integrated in the control unit 2 can be arranged to take into account the distance from the probe 3 to the engine 7. In an exhaust line 11 comprising an oxide trap Nitrogen 6 and an oxidation catalyst 5, to arrange the probe 3 between these two last constitutes a good compromise between the thermal stresses to which the probe 3 is subjected and the distance between the engine 7 and the probe 3. Moreover it is possible to associate the estimation system 1 with an exhaust line 11 not provided with a nitrogen oxide trap 6 and / or with an oxidation catalyst 5. In each of the embodiments, the probe 3 Oxygen allows to measure the richness of the mixture to evaluate the flow of fuel actually injected. This evaluation is independent of the dispersion and the drift of the injectors.

Therefore, the system according to the invention offers an improved estimate of the amount of particles trapped in a FAP 4, as well as better control and optimization of the regeneration phases of the different post-processing elements. Moreover, it does not involve substantial modifications and additional costs compared to existing systems. Finally, it keeps a small footprint. Of course, the present invention is not limited to the embodiments described above, but extends to any embodiment within its spirit. 20

Claims (10)

  1. System for estimating (1) the quantity of particles trapped by a particle filter (FAP) (4) fitted to an exhaust line (11) 5 of a diesel engine (7) of a vehicle, the system comprising : First, second and third evaluation means arranged to respectively provide data relating to: the engine speed, the air flow supplied to the engine, the fuel flow rate injected into the engine, a unit of control (2) arranged to provide an estimate of the amount of particles trapped by the particle filter as a function of said data, characterized in that the third evaluation means comprise means for determining the richness of the mixture feeding the engine.   2. Estimation system (1) according to the preceding claim, characterized in that the third evaluation means comprise means for calculating the fuel flow injected into the engine (7) arranged so as to perform the following operation Qinj = Qair R 14.7 in which: is the actual fuel injection rate expressed in mg / cp, Qa; r: is the fresh air flow rate admitted in the cylinders mg / cp, R: is the richness of the mixture. 30   3. Estimation system (1) according to any one of the preceding claims, characterized in that the means for determining the richness of the mixture comprise at least one oxygen probe (3). 2906839 11   4. Estimation system (1) according to the preceding claim, characterized in that the probe (3) is placed in the exhaust line (11) downstream of the engine (7).   5. Estimation system (1) according to any one of the preceding claims, characterized in that it comprises a flowmeter disposed in the intake line to measure the air flow admitted into the engine cylinders (7). ). 10   6. Estimation system (1) according to any one of the preceding claims, characterized in that it comprises correction means of the estimate, intended to take into account the opening of a valve equipping a circuit ( 8) of exhaust gas recirculation associated with the engine (7).   7. Treatment system (20) of the exhaust gas from a diesel engine (7) comprising an estimation system 1 according to any one of claims 1 to 6. 20   8. Treatment system (20) according to the preceding claim, characterized in that it comprises an exhaust line (11) comprising a nitrogen oxide trap (6) and an oxidation catalyst (5) located in downstream of the nitrogen oxide trap, the probe (3) being placed downstream of the nitrogen oxide trap and upstream of the oxidation catalyst.   9. Vehicle equipped with an estimation system (1) according to any one of claims 1 to 6. 30   10. A method for estimating the amount of particles trapped by a particulate filter (4) fitted to an exhaust line (11) of a diesel engine (7) for a vehicle, wherein: • relative data is evaluated: - at engine speed, at the air flow supplied to the engine, at the fuel flow injected into the engine, an estimate of the quantity of particles trapped in the particulate filter is made from said data, characterized in that the richness of the mixture feeding the engine is determined in order to evaluate the data relating to the flow of fuel injected into the engine.