FR2852395A1 - Nitrogen oxide (NOx) detector diagnosis procedure, uses comparative values of two signals at different times and default signal when difference drops below permitted threshold level - Google Patents

Abstract

The NOx detector (15) diagnosis procedure consists of measuring two values for the signal (NO) from the detector at different times, determining difference between the values, comparing the difference with set threshold levels (SW1 - SW5), and emitting a default signal (FS) if the difference drops below a threshold level. The compared signals can be taken during a lean burn phase of an i.c. engine and at the end of a suppression signal. At least two signal differences are formed, and a default signal is emitted only when the differences are below all the threshold values.

Description

Field of the invention

  The present invention relates to a method for diagnosing a nitrogen oxide NOx detector installed downstream of a catalyst accumulating nitrogen oxide NOx in which during the lean phase of an internal combustion engine is accumulated nitrogen oxides NOx and which are regenerated in a regeneration phase of the internal combustion engine.

  State of the art According to the document DE 198 43 879 AI, a process is known for managing or implementing an internal combustion engine equipped with a nitrogen oxide NO accumulator catalyst. in the exhaust area. During a first operating phase during which the internal combustion engine operates in lean mode in the context of a stratified charge (filling) of the cylinders, the NO components are stored. generated in the NO accumulator catalyst. In a second operating phase during which the internal combustion engine operates in a stoichiometric or rich regime with homogeneous filling of the cylinders, the nitrogen oxide NO accumulator catalyst is regenerated. A NO nitrogen oxide detector, installed downstream of the NO oxide accumulator catalyst. detects an increasing concentration of nitrogen oxide NO. in the exhaust gas during the first phase of operation. A switch is started to the second operating phase as soon as the nitrogen oxide NO concentration. exceeds a predetermined threshold.

  In other embodiments, the switching from the first to the second operating phase is done if the NO oxide mass flow rate. or if the integral of the NO oxide mass flow, in the first operating phase downstream of the NO nitrogen accumulator catalyst. exceeds a predetermined threshold. The mass flow rate 30 of nitrogen oxide NO. downstream of the NO nitrogen accumulator catalyst. can be obtained from the NO oxide detector signal. and the mass flow rate of exhaust gas which is determined from the measured mass flow rate of the intake air.

  Document DE 197 39 848 AI also describes a process for implementing or managing an internal combustion engine the exhaust zone of which is equipped with a nitrogen oxide accumulator catalyst NOS. Switching from the first operating phase to the second operating phase takes place as a function of the mass of nitrogen oxide NO, accumulated in the nitrogen oxide storage catalyst NO. The mass is determined from the integral mass flow of nitrogen oxide NO .; this flow rate is itself determined from the measured mass flow rate or from the known load of the internal combustion engine. If necessary, the speed of the internal combustion engine (speed of rotation) and / or the lambda coefficient of the exhaust gases and / or the temperature of the catalyst and / or the behavior in saturation of the catalyst can also be taken into account.

  OBJECT OF THE INVENTION The aim of the present invention is to develop a method for diagnosing a NOx sensor exhibiting very high reliability.

  Description and advantages of the invention To this end, the invention relates to a method of the type defined above, characterized in that at least two values of si15 gnal of the signal of the nitrogen oxide detector NOx are considered. at different times, at least one difference between the signal values is determined, the difference is compared to a threshold and a fault signal is emitted if the difference falls below the threshold.

  The method according to the invention makes it possible to diagnose the detector signal emitted by the nitrogen oxide detector NOx by monitoring whether the detector signal has changed from a predicted difference at different time intervals. This diagnosis corresponds to a plausibility analysis of the NOx nitrogen oxide detector signal.

  Thanks to the diagnosis, the method according to the invention guarantees compliance with predefined limit values of the exhaust gases in that in the event of a difference with respect to the foreseeable variations of the signal of nitrogen oxide detector NO. at different times, the nitrogen oxide NOx detector signal is no longer taken into account when deciding to change the operating phase.

  One development plans to provide a suppression signal which preferably begins at the end of the first operating phase of the internal combustion engine and ends in the first following operating phase. This means makes it possible to block the nitrogen oxide NOx detector signal during the second operating phase of the internal combustion engine for further processing of the signal since it cannot be excluded that due to the increase the concentration of nitrogen oxides NO. in the exhaust gases during the second phase of operation, the NO nitrogen detector signal saturates and no longer provides a reliable value for the signal. The suppression signal does not have to be neutralized directly at the end of the second operating phase so that the NOQ nitrogen oxide detector signal thus has a recovery time. The cancellation signal advantageously ends under these conditions only after the start of the first operating phase.

  A development of the method provides for forming the difference between the values of the signals before and during the first phase of operation.

  Another development of this embodiment provides for entering the first value of the signal in the first operating phase at the end of the suppression signal and the second value of the signal at the end of the first operating phase.

  A development provides for entering the first signal value at the end of the first operating phase and the second signal value at the end of the second operating phase.

  According to a development, the first value of the signal is entered at the end of the second operating phase and the second value of the signal at the end of the suppression signal.

  According to another development, the first signal value is entered at the end of the first operating phase and the second signal value at the end of the suppression signal.

  One development is to form at least one other difference to the extent that by forming the first difference the predetermined threshold has been passed down. This avoids the emission of the fault signal after sporadically produced faults.

  Drawings The present invention will be described below in more detail with the aid of the appended drawings in which: - Figure 1 shows the technical field to which the invention applies, - Figures 2a-2c are timing diagrams of signals.

  Description of embodiments

  FIG. 1 shows an internal combustion engine 1 which supplies a speed (rev) signal N to a motor control 11. An air quantity detector or air mass flow detector 12 is installed in the suction zone for supplying an air quantity signal or an air mass signal LS to the motor control 1 1; this control also receives the PW signal from the accelerator pedal. In the exhaust gas zone of the internal combustion engine 10 there is provided an accumulator catalyst 13 of nitrogen oxide NO .; this catalyst will be designated below by the reference Kat. Behind the Kat 13 catalyst there is a lambda coefficient detector 14. This detector provides a lambda LAM signal to the engine control 11. Downstream of the Kat 13 catalyst there is also a nitrogen oxide NO detector. 15.

  This detector provides a NO signal corresponding to NO nitrogen oxides.

  This signal is applied to the motor control 11 to be supplied to a 10 up to three memories 16, 17, 18. In FIG. 1, it is indicated that the lambda sensor 14 and the nitrogen oxide detector NO . 15 can form a single constructive whole.

  The engine control 1 supplies a fuel metering signal KS to the internal combustion engine 10 and an operating phase signal B to a time clock 19 as well as to the second and to the third memory 17, 18. L the clock 19 supplies a cancellation signal A to the first memory 16. The memories 16, 17, 18 transmit the values of detector signals NO. , stored at a signal processing means 20 which receives the threshold values SW1, SW2, SW3, SW4. The signal generator 20 then emits a fault signal FS.

  FIG. 2a shows the timing diagram of the lambda signal LAM and of the signal NO of the nitrogen oxide detector NO. At a first instant Tl there is a first value NO 1; at a third instant there is a second value N02; at a fourth instant T4 there is a third value 25 N03; at a fifth time T5 there is a fourth value N04 and at a sixth time T6 there is a fifth value N05 of the signal NO supplied by the nitrogen oxide detector NO. At a second time T2 there is a first value LAM 1 and at a fifth instant T5 there is a second value LAM2 of the lambda signal LAM. A first difference DI 30 is recorded between the second value N02 and the third value NO3, a second difference D2 between the third value N03 and the fourth value NO4, a third difference D3 between the second value N02 and the fourth value N04, a fourth difference D4 between the third value N03 and the fifth value N05 as well as a fifth difference D5 between the fourth value N04 and the fifth value NO. of the NO signal supplied by the NOS nitrogen oxide detector.

  FIG. 2b shows the signal B of the operating phase indicating a first regeneration phase RI situated between the first and the second instant Ti, T2; it also indicates a lean first phase MI situated between the second instant T2 and the third instant T4; it indicates a second regeneration phase R2 situated between the fourth and the fifth instant T4, T5 and a second lean phase M2 starting with the fifth instant T5.

  FIG. 2c shows the suppression signal A supplied by the clock 16; this signal occurs between the first and the third instant Tl, T3 as well as between the fourth and the sixth instant T4, T6.

  The method according to the invention will be described below in 1o in more detail using the timing diagrams shown in Figures 2a-2c.

  The internal combustion engine 10 can operate in two different operating phases. The first operating phase is the lean phase Ml, M2; the second operating phase is the regeneration phase Ri, R2. The operating phases 15 are signaled by the operating phase signal B. At the first instant T1, when the signal NO of the nitrogen oxide detector NO reaches the first value NO1, the preceding lean phase is ended and we begin the first RI regeneration phase. At the same time, the clock 19 is started at the first instant TI. At the second instant T2, on reaching the first LAMI value for the lambda signal LAM, the first regeneration phase RI is ended and the first lean phase MI is started.

  As a variant at the end of the preceding lean phase, when the first NOI value of the NO signal of the nitrogen oxide detector NOS is reached, the lean phase can be terminated by a model of the mass 25 NO. stored in the Kat 13 catalyst.

  Above we have examples of implementation to change both in one or in the other operating phase.

  The method according to the invention can be used to diagnose NOx nitrogen oxide detectors installed in the range of exhaust gases from petrol or diesel engines for motor vehicles. In the lean phase of the internal combustion engine, a lambda air coefficient> 1, for example equal to 1.5, is adjusted. In the regeneration phase, the reducing agent necessary for regeneration can be supplied internally to the engine by reducing the coefficient of lambda air. It is also possible to lower the lambda air coefficient in the case of diesel engines by using a throttle valve. Alternatively, the reducing agent can be introduced into the exhaust gas after the internal combustion engine.

  In some exemplary embodiments, the NO signal from the NO nitrogen oxide detector is used. to determine the change in operating phase. The NO nitrogen oxide detector. 15, however, is not always ready for operation, which can happen, for example, 5 when the internal combustion engine 10 starts cold, and the nitrogen oxide NOx detector 15 is not yet at its temperature. Operating. There may also be a fault with the NO nitrogen oxide detector. 15. In these cases it is necessary to switch operating phases without using the NO signal from the NO detector. otherwise there would be a risk that parts of harmful exhaust gas components would increase unacceptably. The important thing is to have a reliable diagnosis of the NO. 15 detector.

  The transition from the first regeneration phase RI to the lean first phase Ml can be done using the lambda signal LAM. i5 The arrival of the first LAM I value of the LAM lambda signal shows the start of a passage of the rich regime behind the Kat 13 catalyst for which there is a fully regenerated catalyst 13. With the start of the lean first phase MI at the second instant T2, the lambda signal LAM decreases again.

  The NO signal from the NO nitrogen oxide detector. increases during the first RI regeneration phase and then decreases relatively slowly. The decrease is determined by the actual behavior of the NO oxide detector. 15 which becomes saturated during the first regeneration phase Ri and requires a certain recovery time. During this time, the NO signal from the NOx nitrogen oxide detector reproduces a concentration of NO oxide. which doesn't actually exist. For this reason, a suppression time is provided which ends at the third instant T3. The suppression time given by the suppression signal A must be fixed at a level such that after the end of this time, the evolution of the signal NO of the nitrogen oxide detector NO. is again reliable. For this third instant T3, the second value N02 of the signal NO of the nitrogen oxide detector NO is available. which is taken up with the negative edge of the suppression signal A in the first memory 16.

  The signal NO of the nitrogen oxide detector NOx increases in the first lean phase M1 until reaching the third value N03 signaling the end of the first lean phase MI. The end marks the fourth instant T4 at which the second regeneration signal R2 begins. At the same time the suppression signal A arrives. The positive edge of the second regeneration signal R2 stores the third value N03 of the signal NO of the nitrogen oxide detector NO. in the second memory 17.

  In the presence of the two recorded values N02 and N03 it is possible to determine the first difference DI which begins in the signal processing circuit 30. By comparison of the first difference DI with the first threshold SW1 it is assumed that there is a fault signal FS if it drops below the first threshold SW1.

  During the second regeneration phase R2, the NO signal 10 of the nitrogen oxide detector NO increases to the fourth value NO4 which is recorded at the end of the second regeneration phase R2 in the third memory 18.

  Thanks to this other recorded value N04, it is possible to determine both the second and the third difference D2, D3 in the signal processing circuit 20. By means of a comparison of the second difference D2 and the second threshold SW2 and / or a comparison of the third difference D3 and of the third threshold SW3 a fault signal FS is emitted if the second and / or the third threshold value SW2, SW3 are exceeded downwards.

  During the suppression signal A, the signal NO of the nitrogen oxide detector NOx falls to the fifth value N5 which is recorded with the falling edge of the suppression signal A in the first memory 16.

  The existence of the fifth recorded value N05 makes it possible to determine the fourth and the fifth difference D4, D5, which is also done in the signal processing circuit 20. By comparing the fourth difference D4 to the fourth threshold SW4 and / or at the fifth difference D5 at the fifth threshold SW5, the fault signal FS is emitted if the fourth or fifth threshold SW4, SW5 is exceeded downwards.

  In principle, it suffices to form a difference among the differences D 1. D5 described above and the comparisons with the thresholds SW1SW5. The multiple formation of differences firstly increases the security of detection of a fault in the nitrogen oxide NOx detector 13. Furthermore, it can be foreseen that in the event of a deviation observed, at least a following difference and a comparison with the corresponding threshold value are made before emitting the fault signal FS. Thanks to this measure, deviations produced sporadically are avoided. On the other hand, we can have a long-term deviation, too large, only by a difference D1 ... D5 compared to its threshold SWI-SW5. Such a case may occur if the properties of the Kat 13 catalyst vary over the long term. Alternatively, the thresholds SW1-SW5 can be adapted.

  The functions described are preferably carried out in the form of programs executed in a computer preferably fitted to the motor control 10.

Claims (7)

  1) Method for diagnosing a nitrogen oxide NOx detector (15) installed downstream of a catalyst accumulating nitrogen oxide NOx (13) in which during the lean phase (M1, M2) of an internal combustion engine (10) 5 the nitrogen oxides NOx are accumulated and that is regenerated in a regeneration phase (Ri, R2) of the internal combustion engine (10), characterized in that the at least two signal values (NO1-NO5) of the signal (NO) from the nitrogen oxide detector NOx at different times (T1-T6), at least one difference (D1-D5) between the signal values is determined (NO 1-NO5), compare the difference (D 1-D5) to a threshold (SW1-SW5) and issue a fault signal (FS) if the difference (D1- D5) falls below the threshold (SW1 -SW5).   2) Method according to claim 1, characterized by a suppression signal (A) which begins with the regeneration phase (Ri, R2) and ends in the lean phase (M1, M2). 3) Method according to claim 1, characterized by the formation of a difference (Dl, D4) of signal values (NO1, NO2, NO3, NO5) produced during the lean phase (Ml1, M2). 4) Method according to claim 2 or 3, characterized in that a signal value (NO2, NO5) is entered in the lean phase (M1, M2) at the end (T3, T6) of the suppression signal (A ) and a signal value (NO 1, 30 NO3) at the end (T1, T4) of the lean phase (M1, M2).   5) Method according to claims 2 or 3,   characterized in that a signal value (NO 1, NO3) is entered at the end (Tl, T4) of the mai35 gre phase (Ml1, M2) and a signal value (NO2, NO5) at the end (T3 , T6) of the suppression signal (A).   6) Method according to claim 5, characterized in that a signal value (NO 1, N03) is entered at the end (T1, T4) of the lean phase (M1, M2) and a signal value (N04) at the end (T2, T5) of the regeneration phase (R1, R2).   7) Method according to claims 1 and 2,   characterized in that a signal value (N04) is entered at the end (T2, T5) of the regeneration phase (R1, R2) and a signal value (N02, N05) at the end (T3, T6) of the general suppression silo (A).   8) Method according to claims 1 and 2,   characterized in that a signal value (NO 1, N03) is entered at the end (T1, T4) of the May 15 gre phase (M1, M2) and a signal value (N02, N05) at the end (T3 , T6) of the suppression signal (A).   9) Method according to claim 1, characterized in that at least two differences are formed (D l-D5) and they are compared to their threshold (SW1-SW5) and a fault signal (FS) is emitted only if all the threshold values (SW1-SW5) are exceeded downwards.