KR20090017522A - Engine comprising a catalytic converter with failsafe operation - Google Patents

Abstract

The invention proposes an engine (11) comprising a catalytic converter (12c), a first probe (120) able to deliver a first signal (Vsp) proportional to the oxygen content of an exhaust gas and installed upstream of the converter, a second oxygen probe (130) downstream of the converter and able to provide a second signal (Vsb), and means (13) for making a diagnosis regarding the operating condition of the converter, characterized in that: the second oxygen probe (130) is of the on/off type and the means (13) are designed to convert the first signal (Vsp) into a third signal (Vspb) of the on/off type and to make the diagnosis on the basis of the second and third signals (Vsb, Vspb).

Description

Engine comprising a catalytic converter with failsafe operation

The present invention relates to a method for diagnosing the efficiency of an internal combustion engine, in particular a catalytic converter installed in an exhaust line of a diesel engine.

Catalytic converters aimed at by the present invention are converters specifically designed to trap nitrogen oxides present in the gas.

Internal combustion engines are known to produce exhaust gases comprising nitrogen oxides (NOx) as described above and contaminants such as unburnt hydro carbon.

These pollutants must be treated so that the emissions of smoke substances meet the standards described in standards, for example the European standard.

To do this, one known technique used to reduce this emissions is to incorporate a catalytic converter in the exhaust line of the engine.

These converters, on the one hand, reduce these pollutants to store NOx and to release them into the atmosphere in the form of nitrogen (N2) and carbon dioxide (CO2) during a special stage of operation known as purging the catalyst.

On the other hand, such catalytic converters have the function of oxidizing reducing species such as carbon monoxide (CO) and unburned hydrocarbons (HC).

In order to achieve this result, the catalytic converter that captures NOx comprises a catalytic phase in a cell of a monolith that is in contact with the gas as originally known.

The catalyst phase typically comprises platinum, palladium, rhodium, and / or alkaline earth metals.

One or more of the problems with catalytic converters are that they lose their effectiveness as the catalyst phase ages.

In particular, this phase aging often results in a reduction in the number of NOx storage spaces, thereby lowering the effectiveness of NOx, HC, and CO being stored and processed.

In any case, once the pollutant levels specifically indicated in the standard have been established, there are other factors that lead to deterioration of converter performance as the converter ages, and the use of catalytic converters for nitrogen oxide capture generally avoids problematic changes. This entails monitoring of the same behavior as the transducer.

Surveillance systems have already been proposed.

In general, the function of the monitoring system is to detect the failure of a component of the part of the pollutant reduction installation installed in the vehicle and to inform the driver of any failures that would cause the above-mentioned emission levels to be exceeded so that repairs can be carried out quickly.

Therefore, FR 2 866 926 uses a mixer concentration lambda probe installed downstream of the catalytic converter to measure the concentration of exhaust gas downstream of the catalytic converter, and from this it relates to the operating state of the converter. Initiate a monitoring system for diagnosis.

More specifically, the diagnosis is based on measuring the effective time required to reduce the stored NOx, which is a function of the voltage applied by the lambda probe.

In addition, US Pat. No. 5,228,335 is based on two proportional mixture richness probes, one installed upstream of the converter and one downstream, wherein the voltage applied by the probe is proportional to the concentration. A system for detecting a failure of a catalytic converter is disclosed.

More specifically, such a system makes a diagnosis based on integrating over time the difference between the signals applied by each of the two probes.

This diagnosis therefore relies on calculating an area that is a function of the measurement signals from the probes, and this area is compared against a threshold to evaluate the operating state of the transducer (or this area is equal to the degree of aging). ).

While these systems have proved to be the most useful, such systems are relatively expensive and difficult to implement.

It is therefore an object of the present invention to provide a method and system for robustly and reliably monitoring the operating state of a catalytic converter at low cost.

For this purpose, the present invention,

A catalytic converter, a first probe installed upstream of the catalytic converter and capable of supplying a first signal proportional to the oxygen content in the exhaust gas, and a second oxygen probe capable of supplying a second signal downstream of the catalytic converter; An engine, comprising means for making a diagnosis regarding the operating state of the catalytic converter,

The second oxygen probe is of the on / off type,

-The means proposes an engine, characterized in that it is designed to convert the first signal into a third signal of the on-off type and to make a diagnosis based on the second signal and the third signal.

Non-limiting but preferred aspects of such an engine are as follows.

The signal conversion means comprises a probe model that depends on the first signal, such as a map of the on-off type.

The probe model is designed such that the third signal supplied by the probe model is in the form of a square wave having a predetermined upper and lower value.

The probe model is designed such that the third signal supplied by the probe model is switched from an upper value to a lower value and vice versa when the first signal passes a first predetermined threshold, the one of the upper value and the lower value Is preferably substantially equal to the first threshold.

The means is also designed to control the temperature of the element sensing the oxygen content in the second probe.

The control means are designed to lower the temperature to a predetermined temperature value, preferably in the range between 400 and 500 ° C., before the means for making the diagnosis use the second and third signals. .

The invention also relates to a method for monitoring the operating state of a catalytic converter of an engine:

Obtaining a first signal proportional to the oxygen content in the gas from a first probe located upstream of said catalytic converter;

Obtaining a second signal from a second probe of the on-off type disposed downstream of said catalytic converter;

Converting the first signal into a third signal of an on-off type; And

Diagnosing the operating state of the catalytic converter on the basis of the second signal and the third signal.

Preferred but non-limiting aspects of the method are as follows.

In the diagnosis step, a diagnostic criterion Cdiag is determined based on the area of the difference between the second signal and the third signal.

In the diagnosis step, the diagnostic criteria are compared to three predetermined thresholds S1diag, S2diag, S3diag, each defining three ranges of values corresponding to three different transducer operating conditions.

The execution of the diagnostic step is controlled by whether the first signal and / or the second signal meet at least one predetermined criterion.

The diagnostic criteria are of the form:

이고,

ego,

Cdiag, t1, t2, and Dgaz respectively represent the diagnostic criteria used, the two predetermined moments in time, and the flow rate of the exhaust gas through the catalytic converter.

Other aspects, objects and advantages of the invention will become more apparent upon reading the following description of the invention, which is made with reference to the accompanying drawings in which: FIG.

1 shows an engine according to a preferred embodiment of the present invention.

2 shows a flowchart of a method according to one preferred embodiment of the invention.

3 shows a graphical simulation of the probes installed in the engine and the signals output by the probe model.

1 shows an engine 10 according to a preferred embodiment of the present invention.

Such an engine is provided with the engine block 11, the exhaust line 12 which the exhaust gas discharged | emitted by the engine block passes through as a conventional method, and control means for controlling engine performance.

As described by way of non-limiting example, the engine block in particular has an inlet manifold 10a and an exhaust manifold 11b.

Exhaust line 12 is in particular an exhaust gas recirculation system or EGR system 12a (EGR is a widely accepted abbreviation for English representation of exhaust gas recirculation) and a turbine capable of driving compressor 10. A turbocharger 12b equipped with 100 and a catalytic converter 12c.

The turbine 100 receives the exhaust gas from the exhaust manifold 11b in a conventional manner, and the compressor supercharging the inlet manifold 11a by receiving fresh air from the air filter 12d. .

Catalytic converter 12c is connected to the outlet of the turbine.

In particular for these turbines the catalytic converter is arranged to receive the exhaust gases from the turbine after driving the rotation of such turbines.

The purpose of the catalytic converter is to capture the nitrogen oxides present in the gas.

It is obtained by saturating the cells of the porous structure of the monolithic cells with a large surface area for contact with the gas into the catalytic phase.

As originally known, the monolith is a particulate filter such that post-treatment of gases by reducing nitrogen oxides NOx is associated with pretreatment of particulates and unburned hydrocarbons (HC) and carbon monoxide (CO). Or an oxidation catalyst.

The engine further comprises an oxygen probe 120 installed upstream of the catalytic converter, preferably at the inlet of the catalytic converter.

This oxygen probe is a proportional probe, ie the oxygen probe supplies a signal proportional to the oxygen content in contact with the sensing element from which the oxygen probe is made.

The engine also has a probe 130 in binary form, i.e., a probe that supplies an on / off type of signal depending on the oxygen content in contact with the sensing element of the probe.

On / off here means that the supplied signal takes two completely distinguishable values.

These two values may typically be close to zero and greater than zero, for example one.

It should be noted here that the signals supplied by the two probes 120, 130 in accordance with the preferred embodiment of the present invention are signals in the form of voltage.

As shown in FIG. 1, the engine preferably further comprises an electronic control unit 13 (ECU) connected to a computer, not shown.

The ECU 13 controls the engine in a originally known manner by operating an appropriate control method.

The control method specifically comprises the step of controlling the emission of pollutants of the engine.

In this case the catalytic converter is controlled by the ECU in this way.

The control method further comprises monitoring the operating state of the catalytic converter.

These steps specifically include the diagnostic steps described below.

In any case, this monitoring step is based on the use of two probes 130, 140, so these probes exchange information with the ECU.

In particular, as shown by the link 140 in the figure, the proportional probe 120 supplies its signal in the form of a voltage to the ECU.

To make the present description easier to understand, this signal will be denoted Vsp below.

Similarly, link 141 shows on-off type probe 140 that supplies its signal to the ECU in the form of a voltage.

To make the present description easier to understand, this signal will be referred to as Vsp below.

The manner in which the engine operates and the monitoring method described above will now be described in more detail.

According to one feature of the invention, the monitoring method uses signals Vsp and Vsb supplied by the proportional probe 120 and the binary probe 130.

In particular, referring to FIG. 2, the method involves measuring 200 the oxygen content upstream and downstream of the catalytic converter and acquiring the corresponding signals Vsp, Vsb into the ECU.

In step 201, the signal Vsp from the probe 120 is converted into a signal Vspb of the on-off type.

In step 202 a diagnosis is made concerning the operation of the catalytic converter using signals Vsb and Vspb.

The diagnosis is therefore made on the basis of two signals of on-off type in which one of the signals Vspb is modeled on the proportional signal Vsp and therefore modeled on the signal originating from the proportional probe.

One advantage is that the conversion of the signal Vsp into the signal Vspb improves the quality of the diagnosis compared to the diagnosis obtained based on the combination of the proportional and binary signals.

Furthermore, the use of a binary probe downstream of the catalytic converter saves cost and at the same time improves the performance of the monitoring method as described above.

In step 203, action is taken if possible based on the results of the diagnosis.

In particular, when diagnostics indicate that the catalytic converter has reached a very severe degree of aging and is therefore incompletely operated, it is a measure to operate the indicator on the instrument panel to warn the operator to stop at the repair shop so that repairs can be made. It can be seen that.

Of course there are other measures you can think of, which will be discussed below.

One preferred embodiment of the monitoring method according to the invention will now be described in more detail.

In step 200, signals Vsb and Vsp are supplied to the ECU.

In step 201, this ECU converts the signal Vsp into an on-off type signal Vspb when it is determined that the catalytic converter is in the purge phase.

When not in this step, the method is deactivated.

As an alternative, it may be noted that the conditions in the removal step may be applied before step 200 is performed.

According to a preferred embodiment, other checks must be confirmed before the conversion is performed.

In particular, it is possible to confirm that the signal Vsp from the proportional probe 120 is not undershooted, for example below 20% of the final steady state value.

It is also possible to confirm that the signal Vsp has a transition time between two adjustable voltage values (for example 0.98 to 0.955 V) or below a predetermined value (for example 0.52 seconds).

If various conditions are met, the monitoring method according to the preferred embodiment of the present invention performs the conversion using an on-off type probe model in step 201, with one input of the probe model supplied by the probe 120. Responds to the signal Vsp.

As a non-limiting example, the probe model may be designed such that the converted signal Vspb is a square wave having a predetermined upper and lower value.

The conversion from the lower value to the upper value occurs, for example, when the voltage Vsp falls below the adjustable threshold.

Preferably the lower value is 0 volts, and the upper value may be prepared to be close to the threshold.

More preferably, the threshold value and the upper value may be substantially 1V.

In this regard, reference may be made to the limiting example of FIG. 3, which shows that the signal Vspb is close to about 0.93 V from 0 volts when the signal Vsp crosses a threshold of about 0.95 V in the downward direction. Show what can be converted.

In the form of an optional example of step 201 of the monitoring method, the probe model makes it possible to convert the signal Vsp into a binary signal Vspb using a map.

This map provides information to assist in determining the shape of the signal Vspb as a function of the signal Vsp.

And preferably the map provides the signal Vspb directly as a function of Vsp.

In any case, when the ECU has two signals, Vsb and Vspb, of the on-off type, these two signals are used to diagnose in step 202.

And a number of diagnostic criteria are used.

According to one aspect, the criteria may be based on determining the difference between the two signals described above.

More specifically, however, as a preferred embodiment, the area of this difference is determined by calculating the integral.

As a non-limiting example, it is possible to determine the following integrals.

Where Cdiag, t1, t2, and Dgaz each represent the diagnostic criteria used, two predetermined moments in time, and the flow rate of the exhaust gas through the catalytic converter.

Preferably, t1 and t2 correspond to the start and end of the purge, respectively.

By way of example, reference may be made to FIG. 3 with hatching used to represent the area A corresponding to the results of Cdiag.

Whichever Cdiag criterion is chosen, this criterion is then compared with at least one predetermined threshold to assess the catalytic converter condition.

In a preferred embodiment of the invention, the Cdiag criterion is compared with three thresholds.

One advantage of such a comparison is that the diagnosis is more precise.

In particular, if Cdiag exceeds the first threshold S1diag, the catalytic converter efficiency is considered to be good.

If Cdiag is between S1diag and the second threshold S2diag, then the catalytic converter efficiency is considered to have decreased since the initial use, that is, to indicate the degree of first aging.

However, this loss in efficiency is considered acceptable for the engine's pollutant reduction specification.

Finally, if Cdiag is between S2diag and the third threshold S3diag, then the efficiency of the catalytic converter is considered to be significantly lowered from the time of first use.

This represents a second degree of aging that is considered unacceptable.

It will be noted that the three thresholds described above can be adjusted during the engine inspection phase.

As a non-limiting example, FIG. 3 shows two curves Vsb1 and Vsb2 respectively corresponding to the signal Vsb from the binary probe 130 when the catalytic converter shows the first and second degrees of aging, respectively. ).

In fact, it can be seen that the area between the curves Vsb1 and Vsb2 is smaller than the area between Vsb2 and Vspb.

Therefore, those skilled in the art will readily understand that the smaller the instantaneous transition between the curve Vsb from the binary probe 130 and the curve Vspb from the model, the greater the degree of aging of the catalytic converter.

In either case, once the results of the comparison have been obtained, proceed directly to step 203 for appropriate action or to step 203 for the purpose of making a complex diagnosis based on a series of diagnostics performed during use of the vehicle. It is possible to repeat the steps 200-202 described above before.

The complex diagnosis consists of specifically checking that each of the series of diagnosis produces the same result.

Of course, other complex diagnostics may be defined.

For example, the result of multiple diagnoses may be selected to be one obtained by a certain percentage of a series of diagnoses, for example 90%.

As discussed above, the actions taken in step 203 are based on the results determined in the previous step 202.

In particular, when a loss in catalytic converter efficiency and a resulting catalytic converter malfunction is detected, the action may be to indicate to the operator that the repair shop should be stopped so that the repair can be performed.

This indication is typically given by using an indicator lamp located on the instrument cluster.

Such an indication may be activated when the vehicle has been driven several times in succession while a malfunction is detected.

The action may also consist of storing together a state of malfunction in the memory and various data lists associated with this state.

For example, other variables representing the total distance traveled by the vehicle or engine parameters when a failure is detected may be recorded in this memory.

The repair shop can then easily consult the memory to determine what caused the catalytic converter to age.

Furthermore, in the case of complex diagnostics, ultimately the result of the complex diagnostics is to declare that the catalytic converter is in a state that does not require replacement, but data relating to each of the series of diagnostics may be recorded.

One advantage is that a repair shop performing some proper repairs with reference to the memory results in the lifetime of the catalytic converter.

For example, if a compound diagnosis determines that the compound diagnosis has, for example, diagnostics that indicate 80% failure compared to the 90% threshold shown above, the compound diagnosis may fail even though the operator has not yet seen a problem that is a catalytic converter problem. This may happen soon and therefore it can be warned that it is reasonable to have the repair performed as a preventive measure.

In order to further improve the monitoring method of the present invention, the steps 200 to 203 are verified in accordance with other features of the present invention to obtain the optimal sensitivity and lifespan performance. It is possible to link.

Therefore, when the monitoring method or system of the present invention is inoperative, the probe 130 is controlled to operate the system under normal conditions.

For example, a heating current is sent through the probe 130 before step 200 is performed, such that the temperature (Tip) of the oxygen content sensing element of this probe is about 700 ° C.

In contrast, when the monitoring system is operating, the probe is controlled such that the temperature Tip is preferably at a low temperature of 400 to 500 ° C.

In this temperature range, the probe is expected to provide better performance in terms of sensitivity.

Nevertheless, the probe 130 suffers more severe damage in this temperature range than would be experienced at 700 ° C. as a result of particularly severe contamination, so that reducing the temperature of the sensing element in this way is only for an independent length of time. Is done.

At most, this decrease lasts for one or more cycles of the monitoring method.

In this way, the lifetime of the binary probe 130 is maintained.

According to one aspect, the change in temperature Tip is to change the setpoint for the heating current to heat the probe 130 from a value of 700 ° C. to a value that lies within the range.

According to another aspect, the change can be affected by several steps.

In a preferred embodiment of the present invention, two steps are used.

In a first step, the temperature Tip is reduced at a predetermined rate to reach the 400-500 ° C range.

This speed can be adjusted during the vehicle inspection.

In a second step, the temperature can be adjusted so that the temperature never leaves this range.

Whatever control method is used herein, the temperature Tip within the range may be determined in consideration of the range of production of the probe 130 and / or aging.

Of course, the invention is in no way limited to the embodiments described above and shown in the drawings.

In particular, the engine of the present invention may utilize a monitoring method when tests other than those discussed are met.

For example, the monitoring method can be implemented during removal of the catalytic converter and under additional conditions where the vehicle speed is less than a predetermined threshold, for example less than 30 km / h.

The present invention relates to a method for diagnosing the efficiency of an internal combustion engine, in particular a catalytic converter installed in an exhaust line of a diesel engine.

Claims (11)

A catalytic converter 12c, a first probe 120 installed upstream of the catalytic converter and capable of supplying a first signal Vsp proportional to the oxygen content in the exhaust gas, and downstream of the catalytic converter As an engine 11, having a second oxygen probe 130 capable of supplying a second signal Vsp, and means 13 capable of making a diagnosis concerning the operating state of the catalytic converter: The second oxygen probe 130 is of the on / off type, Said means (13) is designed to convert said first signal (Vsp) into a third signal (Vspb) of the on-off type, and to make a diagnosis based on said second signal and said third signal (Vsb, Vspb). An engine, characterized in that. The method of claim 1, And said signal converting means comprises a probe model that depends on said first signal, such as a map of an on-off type. The method of claim 2, The probe model is designed such that the third signal supplied by the probe model is in the form of a square wave having a predetermined upper and lower value. The method of claim 3, The probe model is designed such that the third signal supplied by the probe model is switched from an upper value to a lower value and vice versa when the first signal passes a first predetermined threshold, and one of the upper value and the lower value is Engine, characterized in that it is preferably substantially equal to the first threshold. The method of claim 1, wherein The means is further characterized in that it is designed to control the temperature (Ttip) of the element for sensing the oxygen content in the second probe. The method of claim 5, The control means is designed to lower the temperature to a predetermined temperature value preferably in the range between 400 and 500 ° C. before the means for making the diagnosis uses the second and third signals. Made engine. As a method of monitoring the operating state of the catalytic converter 12c of the engine 11: Obtaining (200) a first signal (Vsp) proportional to the oxygen content in the gas from a first probe (120) located upstream of said catalytic converter; Obtaining (200) a second signal (Vsb) from a second probe (130) of the on-off type arranged downstream of said catalytic converter; Converting the first signal into a third signal Vspb of the on-off type (201); And -Making a diagnosis (202) of said catalytic converter operating state based on said second signal and a third signal. The method of claim 7, wherein In the making the diagnosis, a diagnostic criterion Cdiag is determined based on an area A of the difference between the second signal and the third signal. The method of claim 8, In the diagnosing step, the diagnostic criteria are compared to three predetermined threshold values S1diag, S2diag, S3diag, each defining three ranges of values corresponding to three different transducer operating conditions. How to watch. The method according to claim 7, wherein And wherein the execution of said diagnosing step is controlled by whether said first signal and / or second signal meet at least one predetermined criterion. The method according to claim 8, wherein The diagnostic criteria are of the form:

ego, Cdiag, t1, t2, and Dgaz respectively represent the diagnostic criteria used, two predetermined moments in time, and the flow rate of the exhaust gas through the catalytic converter.

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