FR2935151A1 - METHOD AND DEVICE FOR DETECTING AN DEFECTIVE CATALYST INSTALLED IN THE EXHAUST GAS VEHICLE OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

A method and a device for controlling the operability of a catalyst (28) installed in the exhaust gas vein of an internal combustion engine (10). The implementation of the conversion of the pollutants in the catalyst (28) is detected from the variation of the signal (S24) emitted by an exhaust gas probe (24) downstream of the catalyst (28). the temperature (T) of the catalyst (28), it is estimated that the catalyst (28) is defective if the temperature (T) during the implementation of the conversion is greater than a predefined threshold value. The implementation of the conversion is detected from the variation of the signal (S24) emitted by the exhaust gas probe (24). This variation occurs during the operation of the engine (10) without variations in the Lambda air coefficient between an excess of air and a lack of air, exhaust gases arriving on the catalyst (28) and containing unburned hydrocarbons .

Description

FIELD OF THE INVENTION The present invention relates to a method for controlling the operability of a catalyst installed in the vein of the exhaust gases of an internal combustion engine, according to which the implementation of the conversion of the pollutants in the catalyst from a variation of the signal emitted by an exhaust gas probe installed downstream of the catalyst, the temperature of the catalyst is determined, it is estimated that the catalyst is defective if the temperature during the the implementation of the conversion of the polluting products is greater than a predefined threshold value. The invention also relates to a control apparatus for carrying out this method and to a program product for the control apparatus comprising a program code readable by a machine.

State of the art A method and a device of the type defined above are known according to DE 42 11 092. According to the known method, the internal combustion engine is operated with a permanent alternation between a rich air / fuel mixture. and poor so that the Lambda air coefficient at the inlet of the catalyst varies continuously. As long as the cold catalyst does not provide the conversion, this variation also appears at the outlet of the catalyst. As the temperature of the catalyst increases, its ability to accumulate oxygen as a function of temperature also increases so that its pollutant conversion capacity increases. This increase is reflected in a continuous damping of the variations in the air coefficient, Lambda measurable in the exhaust gas downstream of the catalyst.

As a measure of the damping, in the known method, the ratio of the Lambda air coefficient variations seized downstream of the catalyst and the variations seized upstream of the catalyst are used. As the temperature of the catalyst increases, the quotient decreases and ultimately falls below a predefined threshold value characterizing the beginning of the conversion. The temperature of the

2 catalyst that exists at this time will be noted. This temperature of the catalyst at the start of the conversion increases as the age of the catalyst increases and thus constitutes a measure of its operability. If the temperature exceeds a certain threshold value, the catalyst will be considered no longer sufficiently capable of functioning. The known method thus assumes, in particular, that the Lambda air coefficient varies. However, this air coefficient is that of the internal combustion engine after the cold start, during the subsequent phase of hot operation, which periodically oscillates between air coefficients greater than 1 (mixture) and coefficients of operation. less than 1 (rich mixture). In addition to this known process, carried out with a first cold catalyst and which is heating up, there is another method based on the measurement of the capacity to accumulate oxygen in an already sufficiently hot catalyst volume. It is known that the emissions of a motor vehicle after the cold start depend very much on the time necessary to reach the beginning of the conversion. The shorter the time and the fewer the emissions. Taking into account the state of the catalyst, this time depends less on the overall capacity to accumulate oxygen than is measured for a hot catalyst. On the other hand, according to the experiment, this time strongly depends on the state of aging of the frontal zone of the catalyst, because this zone heats the most rapidly during the heating of the catalyst and thus begins the fastest to convert. Taking into account the ever stricter regulation concerning the exhaust gases, it is interesting to detect the catalysts whose frontal zone is damaged. When the catalyst is hot, it can not be reliably observed damage to the frontal area. This is particularly true if, for cost reasons, the volume of the catalyst has not been divided into two separate partial catalysts and the overall capacity for oxygen storage by the volume of catalyst is evaluated. Damage to the frontal zone may nevertheless cause the hydrocarbons to be

3 sufficiently converted during an exhaust test provided by the regulations, that several seconds late compared to an undamaged catalyst, this significantly deteriorates the test result. In addition, it is interesting to heat as quickly as possible a catalyst after cold start. The known heating means provide, for example, for operating the internal combustion engine with a rich Lambda coefficient in the combustion chamber and injecting secondary air. The reaction of the unburned hydrocarbons from the rich charge of the combustion chamber with secondary air blown up results in the rapid, desired heating of the exhaust gas system, including the catalyst. During the injection of secondary air, there is always a surplus of air in the exhaust gas so that the Lambda air coefficient is in general between 1.1 and 1.5. means such as for example a reheating operation with a lean mixture result in a deterioration of the yield and a composition of the exhaust gas which is slightly lean (Lambda substantially equal to 1.05). The excess air remaining permanently as a result of the secondary air injection and / or reheating in lean mode, produces no change in the Lambda air coefficient in the exhaust gases which would allow the use of the exhaust air. the method of detecting damage to the frontal area as described above. The process described above for controlling the operability of the catalyst can not, under these conditions, be used in connection with a secondary air injection for reheating and / or reheating carried out in lean mode. Object of the invention From this state of the art, the object of the present invention is to develop a method for detecting damage in the frontal zone of the catalyst even if secondary air is injected and / or if the heating is done in lean mode and / or for another operation of the internal combustion engine does not

4 producing no alternation between a lean mode and a rich mode in the exhaust gas upstream of the catalyst. DESCRIPTION AND ADVANTAGES OF THE INVENTION For this purpose, the present invention relates to a process of the type defined above, characterized in that the implementation of the conversion of the polluting products is detected from the variation of the signal emitted by the exhaust gas sensor installed downstream of the catalyst, this variation occurring during the operation of the internal combustion engine without variations in the Lambda air coefficient between an excess of air and a lack of air, the gases of exhaust reaching the catalyst and containing unburnt hydrocarbons. According to another advantageous characteristic of the process, the variation of the signal emitted by the exhaust gas probe installed downstream of the catalyst is detected by the comparison of signals emitted by this exhaust gas probe at different times. According to another advantageous characteristic of the method, the signal emitted by the exhaust gas probe installed downstream of the catalyst is captured and stored at a first instant, at which time the operation of the internal combustion engine begins without variations in the coefficient of air Lambda between an excess of air and a lack of air, corresponding to the exhaust gas entering the catalyst, at least one difference is formed between a subsequently entered signal emitted by the exhaust gas probe installed downstream of the catalyst and the memorized signal, the difference is compared with a threshold value, and a variation of the signal emitted by the exhaust gas sensor installed downstream of the catalyst is recognized if the difference exceeds the predefined threshold value. According to another advantageous characteristic of the method, the variation of the signal of the exhaust gas probe installed downstream of the catalyst is detected by comparing this signal with a signal from an upstream exhaust gas sensor. catalyst. The invention also relates to a control apparatus for checking the operability of the catalyst installed in the exhaust gas vein of an internal combustion engine, of the type defined above, characterized in that this control device for determining a measurement of the temperature of the catalyst for which the conversion of the pollutants occurs in the catalyst, this measurement being compared with a threshold value and the implementation of the conversion of the pollutants can be recognized by the variation of the signal an exhaust gas sensor installed downstream of the catalyst. The control apparatus is adapted to recognize the implementation of the pollutant conversion from a variation of the signal emitted by the exhaust gas sensor installed downstream of the catalyst, a variation which occurs for an operation of the internal combustion engine without air-Lambda coefficient switching between an excess of air and a lack of air in the exhaust gas arriving on the catalyst.

The invention generally relates to a control apparatus for carrying out the method defined above or a program product for a control unit with program code recorded on a machine-readable medium. Drawings The present invention will be described below in more detail with the aid of the accompanying drawings in which: - Figure 1 shows the technical environment of the invention, - Figure 2 shows timing diagrams resulting from the implementation of the invention in the case of a new catalyst and that of a catalyst which no longer functions sufficiently, - Figure 3 is a block diagram of an embodiment of the invention. DESCRIPTION OF EMBODIMENTS OF THE INVENTION In a detailed manner, FIG. 1 shows an internal combustion engine 10 equipped with an exhaust system 12, a fuel supply system 14 and a system 16 and a control device 18 and different sensors 20, 22, 24, 26 transmitting the operating parameters BPM, S22, S24, T of the internal combustion engine 10 and / or the gas system. exhaust 12 to the control unit 18.

The invention is not limited to internal combustion engines operating according to a certain mode of combustion; it can be applied to internal combustion spark-ignition engines, non-spark ignition engines and internal combustion engines with spark ignition and / or non-controlled depending on the operating point. The exhaust system 12 comprises at least one catalyst 28. The catalyst 28 can accumulate oxygen. Examples of such catalysts are so-called three-way catalysts, nitrogen oxide storage catalysts, and oxidation catalysts. The sensors 20 correspond to a set of sensors as used in current internal combustion engines to enter the BPM operating parameters. Examples of such sensors are: intake air mass flowmeter, intake air temperature sensor where appropriate load pressure sensor, coolant temperature sensor, fuel pressure sensor, sensor rotational speed, camshaft position sensor, etc .... A first exhaust gas probe 22 is installed upstream of the catalyst 28. It supplies a signal S22 to the control unit 18. An exhaust gas probe 24 installed downstream of the catalyst 28 supplies a signal S24 to the control apparatus 18. According to a preferred embodiment, the signals S22, S24 constitute the values of the Lambda air coefficient of the Exhaust gas atmosphere at the appropriate locations upstream and downstream of the catalyst 28. A temperature sensor 26 captures the temperature of the front zone of the catalyst 28 and transmits a signal T corresponding to this temperature to the device. 18. Alternatively or additionally, it is also possible to model by calculation to obtain the temperature T of the front zone of the catalyst 28 and also the operating parameters of the internal combustion engine 10 and / or the gas system. exhaust 12 if necessary by supplementing with other parameters such as the speed of displacement.

Such temperature models are known to those skilled in the art and

7 are applied by the control apparatus 18 according to one embodiment. For the rest, the control device 18 processes the signals BPM, T, S22, S24 to form the control variables for controlling the internal combustion engine 10. FIG. 1 explicitly shows a control variable SK representing an action on the fuel system 14 and an adjustment variable SL representing an action on the air supply system 16 of the engine. The fuel supply system 14 comprises in this embodiment, one or more fuel injectors for metering the fuel into the air that arrives in the internal combustion engine 10. In one embodiment, the air system 16 comprises a throttle flap for regulating the mass of the inlet air supplying the internal combustion engine 10. Alternatively or in addition, the air system 16 comprises actuating means for adjusting the load of the chambers of combustion of the internal combustion engine 10 by actions on the alternating control of the gases of the internal combustion engine 10. A secondary air supply pump 30 and a secondary air supply valve 32 serve to inject the air in the exhaust gas expelled from the combustion chambers of the internal combustion engine 10, these fans are controlled by the control unit 18 with a control variable S30. The injection of secondary air is a possibility to supply the air necessary for exothermic reactions in exhaust gases. But the invention is not limited to the use of an air injection. For the rest, the control apparatus 18 is designed and in particular programmed to carry out at least the method as presented above for checking the operability of the catalyst 28. The execution of the method means the control of the unfolding of the process. When the control device 18 finds that the catalyst 28 is no longer sufficiently capable of operating, it emits a fault signal F which, according to one embodiment, activates a fault indicator 34.

FIG. 2 shows in particular the signal S24 emitted by the exhaust gas probe 24 installed downstream of the catalyst 28. This signal is represented as a function of the temperature T of the catalyst during the heating of the catalyst 28 after a cold start of the internal combustion engine 10. FIG. 2a shows the curve of the characteristic signal of a catalyst; Figure 2b shows the characteristic signal curve of a heavily aged catalyst. The internal combustion engine 10 operates for this with an air coefficient Lambda> 1, substantially constant for the two signal curves. This makes it possible to minimize the HC hydrocarbon emission when the conversion has not yet begun. In addition, oxygen from the excess air, the exhaust gases contain still unburned hydrocarbons. The unburned hydrocarbons result from an incomplete combustion of the charge of the combustion chamber. The amount of hydrocarbons can be increased by the post-injection of fuel into the combustion chambers as is customary. It should be noted that the Lambda air coefficient is not necessarily kept constant. It is sufficient that the internal combustion engine operates without alternating Lambda air ratio between an excess of air and a lack of air for the exhaust gas containing hydrocarbons and arriving in the catalyst 28. The curves of the signals of Figure 2 relates to exhaust gas sensors having a higher signal level at higher oxygen concentrations than at low oxygen concentrations. This is for example the case for the characteristic curve of a so-called broadband Lambda probe. This wide-band Lambda probe has a characteristic curve for which the probe signal (this is the pumping current) increases with the values of the Lambda coefficient and thus with the increasing values of the oxygen concentration. Other types of probes have other characteristic curves. Thus, for example, the two-point Lambda probe has a characteristic curve whose probe signal (this is

9 the Nernst voltage) decreases with increasing values of the Lambda coefficient. It is obvious that the invention is used independently of the type of characteristic curve of the probe. In the case shown in FIG. 2, the output signal S24 is first of all also substantially constant because of the Lambda air coefficient, which is practically constant. The temperature is first of all as is characteristic for cold start, below the T_KB conversion start temperature of a new catalyst which is at about 300 ° C.

The composition of the exhaust gas upstream of the catalyst 28 corresponds to the composition of the exhaust gas downstream of the catalyst 28. The catalyst 28 does not yet convert the hydrocarbons contained in the exhaust gas. Consequently, the hydrocarbons also appear at the level of the second exhaust gas probe 24 installed downstream of the catalyst 28. Thus, the composition of the exhaust gases produces a shift in the characteristic curve of the signals S22, S24 emitted by the two exhaust gas probes 22, 24. Such an offset is also called transverse sensitivity. Due to the transverse sensitivity of the exhaust gas probe 24, the signal S24 does not first give the actual air coefficient, but the air coefficient of a lean exhaust gas atmosphere. The actual air coefficient is represented by the lower level (u) of the signal while the lean air coefficient is represented by the upper level (o) of the signal. The conversion in catalyst 28 is established as the temperature increases. In the following, there are compositions of the exhaust gas upstream of the catalyst 28 and downstream of the catalyst 28. For example, there is a conversion of hydrocarbons that are always contained in the exhaust gas upstream of the catalyst 28. As a result, the hydrocarbon concentration decreases at the second exhaust gas probe 24 installed behind the catalyst 28. The influence of transverse sensitivity to HC hydrocarbons on the probe signal

S24, decreases as a result. As a result, the probe signal S24 decreases as the conversion is made as a function of the increase in temperature, until the u level is finally reached at high temperatures; this level (u) represents the real air coefficient. In other words, the implementation of the conversion modifies the signal emitted by the downstream exhaust gas sensor 24 which passes from the upper level (o) to the lower level (u), although the composition of the the atmosphere of the exhaust gas upstream of the catalyst 28 and in particular its real air coefficient has not changed. In particular, the front zone of the catalyst volume participates in the conversion (the front zone is located on the motor side). The behavior thus described is less dominated by the oxygen storage capacity in the total volume of the catalyst and more by the ability to accumulate oxygen as a function of the temperature in the front zone of the catalyst volume. According to the present invention, this behavior is exploited to check the operability of the catalyst 28 and in particular to check the operability of its frontal zone.

The signal curve of Figure 2a is representative of a new catalyst. This catalyst is characterized by a signal variation of predefined degree d24_S which already occurs at a relatively low temperature T_KB for example of 300 ° C. The solid line represents the signal emitted by the rear probe 24 as a function of the temperature T while the broken line represents the signal of the front probe 22. Since the exhaust gas probe 22 is situated upstream of the catalyst 28, its signal is not influenced by the catalyst. In one development, this variation of the signal of the exhaust gas rear probe 24 is used to relate this variation to the signal emitted by the forward probe 22. This is preferably done by forming the difference or the quotient. Alternatively, it is also possible to report the variation of the signal of the rear probe 24 to its own signal that has been entered and stored at an earlier time and thus at a lower temperature and in particular before the use of the conversion capacity. catalyst 28.

By comparison, Figure 2b shows predictable signal curves under otherwise identical conditions for a heavily aged catalyst. The characteristic element in this case is that the conversion ability is established only at a higher temperature T_KB so that the predefined degree d24_S of the variation of the signal emitted by the second exhaust gas probe 24, is reached only for the higher temperature T_KB for example equal to 450 ° Celsius. FIG. 3 shows an exemplary embodiment showing both the aspects of the method and those of the device, in the form of a block diagram, which can be achieved by circuit or program structures in the control apparatus 18. The signal S24 emitted by the exhaust gas sensor 24 installed downstream of the catalyst 28 is captured and stored at a first time t1 for which the internal combustion engine operates without variation of the air coefficient Lambda alternating between an excess of air and a lack of air in the exhaust gas entering the catalyst 28. In addition, at least the difference between the signal S24 captured at a later time t2 by the exhaust gas probe 24 installed downstream of the catalyst 28 is compared with the stored signal, this difference is compared with a threshold value d24_S. The variation of the signal S24 emitted by the exhaust gas probe 24 installed downstream of the catalyst 28, and which indicates a start of conversion, will be recognized if the difference exceeds the predefined threshold value d24_S.

In a detailed manner, block 33 forms the difference D = S24 (t1) -S24 (t2). The first term corresponds to the signal from the downstream probe 24 at a first instant t1. In FIG. 2, this instant t1 can be associated with the temperature T (t1). The second term corresponds to the signal of the downstream probe 24 at subsequent times t2> tl. Block 35 compares the difference D with a predefined threshold value d24_S provided by the block 36 and which corresponds to the predefined degree d24_S of the variation according to FIG. 2. In parallel, the block 38 compares the temperature T of the catalyst with a predefined threshold value provided by block 40 and which corresponds, according to one embodiment, to the temperature of 450 ° C.

12 according to Figure 2b. The temperature T of the catalyst is supplied by the temperature sensor 26 of FIG. 1 or by a calculation model from the operating parameters of the internal combustion engine 10 which calculates them in the control apparatus 18.

The output signals of the two comparators 35, 38 are combined in the block 42 according to the logic function "AND" so that the exceeding of the two threshold values closes the switch 44 which activates the fault lamp 34. It is clear that the activation of the fault lamp 34 according to a development, can be made dependent on additional statistical security and / or the fault message is exploited in another way and / or reported in another way. In particular, if the difference for a temperature of less than 450 ° C exceeds the threshold, the catalyst 28 will be judged as operable. According to a preferred development, the temperature interrogation is done when the difference exceeds the threshold value. The combination of the method presented above with known methods which measure the oxygen storage capacity of the entire volume of the catalyst when the catalyst is hot to operate, makes it possible to distinguish between a generally aged catalyst and catalysts whose frontal area is damaged. By subdividing the volume 28 of the catalyst into a precatalyst and a main catalyst, distinct from the previous one, and distributing the entire volume 28 of the catalyst between the exhaust gas probes 22, 25, it is possible, for example, to distinguish a catalyst upstream, defective before the main catalyst, which is, which reduces the cost of repair. In the embodiment described, the variation of the signal S24 emitted by the exhaust gas probe 24 downstream of the catalyst 28 is detected by comparing the signals S24 emitted by this exhaust gas probe 24 at different times t1, t2. According to an alternative embodiment, the variation of the signal S24 of the exhaust gas probe 24 installed downstream of the catalyst 28, is characterized by a comparison of this signal S24 and the signal S22 of an exhaust gas probe 22 installed upstream of the catalyst 28.

Claims (1)

CLAIMS 1 °) A method for controlling the operability of a catalyst (28) installed in the exhaust gas vein of an internal combustion engine (10), according to which: - the implementation of the conversion of the pollutants into the catalyst (28) from a variation of the signal (S24) emitted by an exhaust gas probe (24) installed downstream of the catalyst (28), - the temperature (T of the catalyst (28), it is considered that the catalyst (28) is defective if the temperature (T) during the implementation of the conversion of the pollutants is greater than a predefined threshold value, characterized in that the implementation of the conversion of the polluting products is detected from the variation of the signal (S24) emitted by the exhaust gas probe (24) installed downstream of the catalyst (28), this variation occurring during operation internal combustion engine (10) without variation Lambda air coefficient between an excess air and a lack of air, the exhaust gas containing unburned hydrocarbons arriving on the catalyst (28). 2) Method according to claim 1, characterized in that the variation of the signal (S24) emitted by the exhaust gas probe (24) installed downstream of the catalyst (28) is detected by the comparison of signals emitted by this probe (24) at different times. Method according to Claim 2, characterized in that the signal (S24) emitted by the exhaust gas sensor (24) installed downstream of the catalyst (28) is captured and memorized at a first instant. this instant being that at which the operation of the internal combustion engine (10) begins without variations of the air coefficient Lambda between an excess of air and a lack of air, corresponding to the exhaust gases arriving on the catalyst (28) at least one difference (D) between a subsequently entered signal emitted by the exhaust gas sensor (24) installed downstream of the catalyst (28) and the stored signal is formed, the difference (D) is compared with a threshold value (d24_S), and a variation of the signal (S24) emitted by the exhaust gas sensor (24) installed downstream of the catalyst (28) is recognized if the difference (D) exceeds the threshold value (d24_S ) predefined. Method according to Claim 1, characterized in that the variation of the signal (S24) of the exhaust gas sensor (24) installed downstream of the catalyst (28) is detected by the comparison of this signal (S24 ) and the signal (S22) of an exhaust gas sensor (22) installed upstream of the catalyst (28). (5) Control apparatus (18) for checking the operability of a catalyst (28) installed in the exhaust gas vein of an internal combustion engine (10), which control apparatus makes it possible to determine a measurement of the temperature (T_KB) of the catalyst (28) for which the conversion of the pollutants occurs in the catalyst (28), this measurement being compared with a threshold value and the implementation of the conversion of pollutants is recognizes by the variation of the signal (S24) of an exhaust gas sensor (24) installed downstream of the catalyst (28), characterized in that the control apparatus (18) is adapted to recognize the implementation of the pollutant conversion from a variation of the signal (S24) emitted by the exhaust gas sensor (24) installed downstream of the catalyst (28), which variation occurs for an operation of the internal combustion engine (10) without switching the coeff Lambda air element between an excess of air and a lack of air in the exhaust gas arriving on the catalyst (28). 56 °) control device (18) according to claim 5, characterized in that it is designed to implement a method according to claims 2 to 4. 7 °) control device program product comprising a stored program code on a machine-readable medium and implementing the method according to claims 1 to 4 when the program is executed in a control apparatus (18). io 15