FR2937084A1 - Catalytic element's i.e. post-treatment system, state diagnosing method for diesel engine of motor vehicle, involves establishing expected exothermic curves, establishing measured exothermic curves, and comparing exothermic curves in pairs - Google Patents

Abstract

The method involves carrying out post-injection and injection of fuel at an exhaust, and establishing expected exothermic curves respectively obtained from the post-injection and the injection by using a computing model that takes into account an operating characteristic e.g. engine speed, of a diesel engine (M). Measured exothermic curves, respectively obtained from the post-injection and the injection, are established using measurement of temperature in downstream of an oxidation catalyst (DOC) and from measurement of temperature at an inlet of the catalyst. The curves are compared in pairs.

Description

The present invention is in the field of depollution of diesel engines. In order to meet the lower thresholds for the emission of gaseous pollutants from motor vehicles, more and more complex gas after-treatment systems are located in the exhaust line of lean-burn engines (ie ie operating with a large amount of air for a small amount of fuel). These reduce emissions of particulate matter and nitrogen oxides, in addition to carbon monoxide and unburned hydrocarbon emissions. In contrast to a traditional oxidation catalyst, these systems operate discontinuously or alternatively, 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 temperature and / or wealth levels. When it is necessary to envisage a regeneration phase of a particulate filter, the desulphurization of a NOx nitrogen oxide trap (to eliminate the stored sulfur for a renewed efficiency), or more generally the treatment of pollutants with high temperature an operating point of the motor is chosen which is favorable to the regeneration process. This process begins with a system warm-up phase because purging only begins when the system temperature is sufficient. Unfortunately, the behavior of a driver can not be determined when a regeneration process is initiated. The probability of maintaining the favorable purge conditions is inversely proportional to the heating time of the post-treatment system. So, whatever the heating strategy used, the goal is to reach as quickly as possible the temperature from which the post-treatment system is effective and to maintain it. During the regeneration phases of these post-treatment means, an oxidation catalyst (or DOC) may be used to raise the temperature of the exhaust gas downstream thereof. To do this, reducers are injected into the exhaust line by means of post-injections or injections to the exhaust. The catalytic reaction between these reducing agents and the catalyst will cause an exothermic reaction and thus generate the heat necessary for regeneration.

However, for this exothermic reaction to occur, it is necessary for the catalyst temperature to be above a certain temperature, called the catalyst activation temperature, and for the catalyst to be in good condition. When these conditions are not met, the reducers are not oxidized (or not enough) and then do not provide enough heat to the exhaust gases, resulting in inefficient purges of the after-treatment systems. It is therefore important to be able to ensure that the oxidation catalyst is not deteriorated and that it meets the exothermic expectations for the regeneration phases of the post-treatment systems. Currently, the exothermic reaction to provide the temperature necessary for the regeneration of the after-treatment systems is achieved by a post-injection of fuel into a cylinder of the engine and / or an injection of fuel at the exhaust.

Thus, FIG. 1 appended shows a diesel engine M provided with four cylinders C. Its exhaust line 2 comprises a post-treatment system 1 with a DOC oxidation catalyst and a particulate filter FAP. The references I and J respectively designate the injection system integrated in the engine, and an additional injector placed on the exhaust line Z just upstream of the DOC. The introduction of the quantity of fuel required to comply with these conditions can be achieved by implementing two post injections, namely: - a close post-injection: the fuel is injected between 20 and 70 ° after the top dead center (after the main injection). This injection is intended to burn completely in the cylinder so as to produce a rise in the temperature before the turbine and, consequently, at the inlet of the catalyst. Nevertheless, on some operating points, the combustion is only partial and will generate a quantity of reducing agents, causing an exothermic reaction in the catalyst; a remote post-injection: the fuel is injected between 80 and 150 ° after the top dead center. This injection is intended to produce the quantity of necessary reducers which, during their treatment in the DOC, will make it possible to reach the input temperature level of the post-processing system placed downstream. Another configuration is that of the injection of fuel into the exhaust line: The exhaust injector J, often called the 5th injector, is used to replace the post-injection, the latter not producing dilution of the oil by the fuel.

However, the latter is limited in its range of use. The principle of this strategy is to inject the fuel directly into the exhaust gases to react in the DOC, thus creating the exothermic reaction for the regeneration of downstream post-treatment systems.

During the aging of the vehicle, the characteristics of the oxidation catalyst can be degraded: this leads to a reduction of the oxidation power. This phenomenon can then result in a temperature at the output of the DOC lower than expected, if the control of the quantities of reducers to be injected by post-injection or 5th injector is not done through a closed-loop control temperature downstream of the DOC. This then has the following consequences: a decrease in the purge / regeneration efficiency (or even no regeneration) and therefore a degradation of the future effectiveness of the post-treatment element. - if there is no post-treatment device after this DOC (which implies that it is not used for a thermal increase purpose), part of the quantity of non-oxidised reducers will be issued by the vehicle. With closed-loop DOC downstream temperature regulation, the inlet temperature of the post-treatment system is at the right level, but the excess of reducing agents is oxidized by these systems, which implies a runaway risk . An alternative is that it is not oxidized, and there is a risk of pollution. Existing strategies are to inject punctually in normal mode, as in regeneration mode, after ensuring that the catalyst was primed (DOC temperature above 300 ° C for example) a predefined amount of fuel in the exhaust line, using either the remote post-injection or the exhaust injector. By using the measurement of the temperature downstream of the catalyst and a measurement (or estimate) of the catalyst inlet temperature, an exotherm is then deduced. This exotherm will then be compared to the exotherm associated with the predefined fuel quantity. Too large a gap between the exotherms suggests a problem that can have two different origins: - the catalyst lost oxidation power, - the injector is faulty. At present, it is not possible to discriminate between these two possible sources of failure. This results in the unnecessary replacement of parts, the certainty of their malfunction not being demonstrated. This strategy can be illustrated by US-A-2005/0279156, which proposes a method for diagnosing the efficiency of HC conversion. / CO by an oxidation catalyst, injecting a late post-injection flow rate. The measured exotherm is compared to a predicted exotherm.

The present invention aims to improve this technique by providing a method for diagnosing the state of a catalytic element. Thus, the invention relates, in the first place, to a method for diagnosing the state of a catalytic element comprising an oxidation catalyst and a post-treatment device such as a particle filter, placed on the line exhaust system of a motor vehicle diesel engine, with a view to regenerating this element by raising the temperature following a fuel injection, characterized in that it consists in: - proceeding, staggered in time , post-injection and exhaust injection; - using a computer model that takes into account certain operating characteristics of the engine, establish the corresponding exothermic curves, namely: P1: expected exothermic curve coming from the post-injection, and P21: expected exothermic curve coming from exhaust injection; - from a measurement of the temperature downstream of the oxidation catalyst and a measurement or estimate of the inlet temperature of this oxidation catalyst, establish the corresponding exothermic curves, namely: P12: measured exothermic curve from post-injection, and P22: measured exothermic curve from exhaust injection; compare two by two said exothermic curves. According to other advantageous but non-limiting characteristics of this process: - a post-injection and then an injection in the exhaust, or conversely; the same quantity of fuel or a different quantity is injected; said computer model takes into account all or part of the following parameters of engine operation: speed, torque demand or accelerator pedal position, mass flow rate of the exhaust gases, measured or estimated temperature upstream of the engine; catalyst, quantity of fuel required. From these curves, the two errors defined below are calculated: P11 / exothermic curves P11 and P12, expected and measured, coming from the late post-injection, expressed in%; . E2 = mean (P21 P22 X100 = relative error between the P21 / exothermic curves P21 and P22, expected and measured, from the exhaust injection, expressed in%,

and according to the results obtained, the following diagnoses are

realized:. if E1a and E2a (in%), the injection + catalyst system is functional. 25. E1 = mean P11 - P12 X100 = relative error between. if E1 a and E2) a, the exhaust injector has failed. . if E1) a and E2 a, the post-injection system fails. . if E1) a and E2) a, the catalyst fails, with a tolerance being accepted to account for measurement and model uncertainties. Other features and advantages of the invention will appear on reading the detailed description which follows. The present invention is based on an architecture combining the use of an exhaust injector and a post-injection, these terms having the definitions given above. The object of the invention is to perform a diagnosis of these two actuators as well as the oxidation catalyst. According to the invention the computer will occasionally request a predefined quantity of fuel to be injected (in normal mode as in regeneration mode), after ensuring that the catalyst is primed. And the peculiarity of the invention is that we will make two injections before starting the diagnosis: first, for example, by the remote post-injection alone and then by the injector exhaust only (on may reverse the order and the amount of fuel may differ).

Next, a model taking into account the characteristics of the operating point (engine speed, torque demand or accelerator pedal position, mass flow rate of the exhaust gases, the measured catalyst upstream temperature or itself estimated, fuel quantity asked) will predict the averaged, expected exotherms on these driving cycles. Two exotherms are thus predicted: P11 the expected exotherm from late post-injection, P21 the expected exotherm from the exhaust injector. Using a temperature measurement downstream of the DOC and a measurement (or estimate) of the DOC input temperature, the actual exotherms for the two previous injections are deduced via a known model: 35 - P12 the measured exotherm from late post-injection, - P22 the exotherm measured from the exhaust injector. Once these four values are obtained, the calculator will compare the two exotherms for each source. Two errors are thus calculated: El = mean P11 - P12 X 100 = relative error between (P11 exotherms expected and measured, from late post-injection, expressed in%, P21 - P22 X100 = relative error between P21 / 10 exotherms, expected and measured, from the exhaust injection, expressed in%, According to the results obtained, the diagnoses are made as follows: if E1a and E2a (in%), with a equal to the tolerance allowed to take account of the uncertainties of measurement and model, the injection + catalyst system is functional if E1a and E2) a, the exhaust injector has failed. . if E1) a and E2 a, the post-injection system fails. 20. if E1) a and E2) a, the catalyst fails. For the fourth case, one could think that it could come from the post-injection and the injector to the exhaust. However, by performing this diagnosis frequently, this case is discarded because it is very unlikely that these two actuators become defective at the same time.

Ultimately, this invention therefore provides a diagnosis to identify the part of the vehicle actually in default. . E2 = average

Claims (6)

REVENDICATIONS1. Method for diagnosing the state of a catalytic element (1) comprising an oxidation catalyst (DOC) and a post-treatment device such as a particulate filter (DPF), placed on the exhaust line (2) ) of a diesel engine (M) of a motor vehicle, with a view to regenerating this element by raising the temperature following a fuel injection, characterized in that it consists in: - proceeding, staggered in the time, post-injection and exhaust injection; using a computer model which takes into account certain operating characteristics of the engine (M), establish the corresponding exothermic curves, namely: P11: expected exothermic curve coming from the post-injection, and P21: curve exothermic expected from the exhaust injection; - from a measurement of the temperature downstream of the oxidation catalyst (DOC) and a measurement or estimation of the inlet temperature of this oxidation catalyst (DOC), establish the corresponding exothermic curves that is: P12: measured exothermic curve from post-injection, and P22: measured exothermic curve from exhaust injection; compare two by two said exothermic curves. 2. Method according to claim 1, characterized in that one carries out a post-injection then an injection in the exhaust, or vice versa. 3. Method according to claim 2, characterized in that one injects the same amount of fuel or a different quantity. 4. Method according to one of the preceding claims, characterized in that said computer model takes into account all or part of the following parameters of engine operation: speed, torque demand or accelerator pedal position, flow rate mass of exhaust gas, measured or estimated temperature upstream of the catalyst, amount of fuel required. 5. Method according to one of the preceding claims, characterized in that one compares two by two said exothermic curves 5 using a computer. 6. Method according to one of the preceding claims, characterized in that, from said curves is calculated the two errors defined below. . E1 = mean / P11 P12 X100 = relative error between the 11/10 exothermic curves P11 and P12, expected and measured, coming from the late post-injection, expressed in%; . E2 = average (P21 P22 X100 = relative error between the P21 / exothermic curves P21 and P22, expected and measured, from the exhaust injection, expressed in%, and according to the results obtained, the following diagnoses are made: if E1a and E2a (in%), the injection + catalyst system is functional, if E1a and E2) a, the exhaust injector has failed. 20. if E1) a and E2 a, the post-injection system fails. . if E1) a and E2) a, the catalyst fails, with a consisting of the tolerance allowed to account for measurement and model uncertainties. 15