FR3085751A1 - SYSTEM AND METHOD FOR DEGRADATION OF A GAS EFFLUENT TREATMENT MEMBER OF AN EXHAUST LINE OF A CONTROLLED IGNITION INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

Method for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst formed by monolithic blocks by scanning the chamber in a rich mixture until a value is reached of the internal temperature threshold of the catalyst on a positive-ignition engine.

Description

System and method for degrading a device for treating gaseous effluents from an exhaust line of an internal combustion engine with positive ignition

The present invention relates to the field of gaseous effluent treatment organs with which the exhaust line of an internal combustion engine of a motor vehicle is provided, such as for example a "catalytic converter" or "oxidation catalyst -reduction ".

More particularly, the invention relates to the generation of faulty catalysts from the point of view of an on-board diagnostic system or On-board diagnostics, from the acronym OBD in English terms, intended to be used during motor vehicle approval tests. or engine development phases.

Internal combustion engines produce exhaust gases that contain polluting substances such as nitrogen oxides, unburnt hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _X ). It is necessary to treat these polluting substances before discharging them into the atmosphere. Motor vehicles are provided, for this purpose, with a catalytic converter installed in the engine exhaust line, in order to oxidize the reducing molecules constituted by carbon monoxide (CO) and unburnt hydrocarbons (HC), and to process the molecules of nitrogen oxides (NO _X ), under the action of carbon monoxide, to transform them into dinitrogen (N2) and carbon dioxide (CO2).

The progressive thermal aging of such catalytic converters causes a reduction in the efficiency of conversion of unburnt hydrocarbons and carbon monoxide to water and carbon dioxide as well as in the efficiency of conversion of nitrogen oxides, under the action carbon monoxide, nitrogen and carbon dioxide, said decrease being due inter alia to the decrease in the active surface for treatment of pollutants within the catalytic converter. This results in an increase in the thermal initiation temperature of the oxidation and reduction reactions, and therefore an increase in polluting emissions. In addition, when the catalytic converter is placed upstream of a particulate filter, it normally serves to provide aid for the regeneration of the filter, so that severe degradation of the converter can lead to the impossibility of regenerating the filter. to particles because it becomes impossible to increase the temperature sufficiently by using the exothermicity of the conversion reactions.

It is therefore necessary to check the correct operation of the catalytic converter. For this purpose, motor vehicles are generally provided with a device for monitoring its condition, known as on-board diagnostic system or On-board diagnostics, from the acronym OBD in English terms, capable of signaling any malfunction. from catalyst to conductor.

The OBD on-board diagnostic system checks whether the quantity of harmful exhaust gases emitted remains below a limit threshold value imposed by the pollution abatement standards in force, and also checks whether the efficiency of treatment of the polluting particles by the catalyst. in flue gases is above a minimum efficiency threshold required. In the event of failure of either the engine or the catalyst, the on-board diagnostic system alerts the driver.

Before being put on the market, a prototype of a new mass-produced motor vehicle must pass approval tests. During these tests, the proper functioning of various systems on board the vehicle, such as in particular the OBD on-board diagnostic system, are checked. In order to demonstrate the conformity of the diagnosis, the car manufacturer supplies degraded or even faulty parts, such as in particular catalysts which are faulty from an OBD on-board diagnostic system point of view. A properly functioning OBD on-board diagnostic system must issue an alert signal when diagnosing these faulty catalysts, that is to say those whose treatment efficiency of polluting particles is below a predetermined threshold.

It is therefore necessary to manufacture and supply degraded or even faulty catalysts for the approval test of new motor vehicles.

Indeed, carrying out, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst is interesting in the development phase of new projects in order to demonstrate the performance of the OBD diagnosis, in particular in terms of sufficient efficiency of the post-treatment system after normal aging, and in terms of switching on an alert device, for example a "malfunction indicator lamp", with the acronym MIL in English terms -saxons when the catalyst is too degraded.

There are nowadays various processes for manufacturing degraded catalysts. For example, it is known to place the motor vehicle on a dynamometer and let it run for several days. During the test, a particular thermal cycle is used to cause accelerated aging of the catalyst. However, this technique requires the use of the complete vehicle, which generates an increased cost of production.

It is also possible to generate thermal aging of the catalyst by placing it in an oven heated between 1100 ° C. and 1300 ° C. The catalyst body consists of a monolithic block, preferably of a cellular structure, impregnated with precious materials such as, for example, platinum, palladium or rhodium. A gas stream comprising oxygen, water and nitrogen is then introduced at one end of the catalyst body to simulate the passage of the exhaust gas. The flow is programmed according to an aging cycle adapted to the type of motor.

However, with such a process, it is not possible to obtain precise aging of the catalyst. Indeed, the duration and the conditions of aging of the catalyst in the furnace are not proportional to the loss of performance of the catalyst.

The thermal degradation of a catalyst is also known by the gases originating from combustion, for example by degradation of the combustion setting or by injection of air into the exhaust to increase the exhaust temperature, by generation of misfires. combustion, known by the term misfire in English terms, or by a burner with hot gases.

However, although these methods are performed on an engine and can monitor the degree of degradation either by measuring the OBD diagnostic parameter of the catalyst or by measuring the efficiency of the catalyst, these methods are complex because they may require integration an exhaust air injection system external to the engine control on spark-ignition engines. This increases the cost of the system and the complexity of implementation. The technique of using misfires has the drawback of having a high maintenance cost because of the reduction in the service life of the engine when misfires are generated continuously, in particular because of the vibrations generated. .

Current pollution control standards (Euro6, Euro7) require the precise generation of faulty catalysts, which is not possible with known methods.

Document EP 1 204 489 - B1 also discloses a method of impregnating a monolithic block forming part of a catalyst. However, such a method is not applied to adjust the aging of a catalyst.

The present invention aims to improve the diagnostic methods and devices for generating a faulty catalyst from the point of view of the OBD on-board diagnostic system.

More particularly, the present invention aims to provide a process for degrading a catalyst capable of degrading, in an accelerated and controlled manner, a catalyst with a desired degraded efficiency, while continuously monitoring the degree of degradation of the catalyst during accelerated aging, in order to stop the degradation at the precise moment when the loss of efficiency reaches the desired value.

The subject of the invention is a method for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst formed by monolithic blocks by scanning of chambers, known as scavenging in Anglo-Saxon terms, and with an operation of the engine in rich mixture, until reaching a threshold value of internal temperature of the catalyst on a supercharged engine with spark ignition.

Chamber sweeping consists of opening the intake and exhaust valves simultaneously to the top dead center of piston crossing on a high load and low speed operating point, when the pressure at the intake valve is higher than pressure at the exhaust valve.

When the chamber sweep takes place during the air intake phase, fresh air is directly transferred from the intake to the exhaust during the crossover phase and oxygen is sent to the catalyst.

When the quantity of fuel injected is increased at an engine operating point with the chamber sweep in order to obtain an excess of unburned fuel in the combustion chamber (rich mixture, i.e. operation at richness strictly greater than 1), fuel and oxygen are present in the catalyst, which generates a high exothermic temperature which makes it possible to degrade the catalyst while remaining at an operating point of the engine without vibrations and with a low temperature at intake valve and without requiring an external air injection system.

Advantageously, a threshold value of the oxygen storage capacity is defined. The efficiency of the catalyst in terms of oxidation-reduction is linked to the oxygen storage capacity.

For example, the internal temperature threshold value of the catalyst is defined. For example, the temperature value is equal to

950 ° C in order to obtain a catalyst equivalent to a catalyst having traveled 160,000 km.

The catalyst can be stabilized, for example 2 hours at 650 ° C.

Advantageously, to assess the state of degradation of the catalyst, that is to say to determine the value of its residual efficiency, after the chamber scanning step, the richness setpoint is intrusively modified by imposing first a rich slot for, for example 3s, to empty the oxygen catalyst, then a lean slot to fill the oxygen catalyst and during this lean phase, the oxygen storage capacity is calculated. The value obtained from the oxygen storage capacity corresponds unequivocally to a given efficiency value of the catalyst.

The calculated value of the oxygen storage capacity can then be compared with the threshold value, when the calculated value of the oxygen storage capacity is greater than the threshold value, the catalyst is not sufficiently degraded, a rich mixture chamber sweep is again carried out until the calculated value of the oxygen storage capacity is less than the threshold value. In this case, the catalyst has failed and the diagnostic system should issue a catalyst failure signal.

According to a second aspect, the invention relates to a system for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst formed by monolithic blocks comprising a module chamber sweep, known as scavenging in Anglo-Saxon terms, in a rich mixture, until a threshold temperature value is reached for the internal temperature of the catalyst on a supercharged spark-ignition engine.

The system includes, for example, a module for defining a threshold value for the oxygen storage capacity.

The efficiency of the catalyst in terms of oxidation-reduction is linked to the oxygen storage capacity.

The system may also include a module for defining an internal temperature value of the catalyst. For example, the temperature value is equal to 950 ° C in order to obtain a catalyst equivalent to a catalyst which has traveled 160,000 km.

The system can also understand a module of stabilization of the catalyst, for example 2h at 650 ° C. Advantageously, the system understands a module of modification so intrusive of a locker of wealth in

first imposing a rich slot during, for example 3s to empty the oxygen catalyst, then a lean slot to fill the oxygen catalyst and a module for calculating, during this lean phase, the storage capacity of oxygen.

The system includes, for example, a module for comparing the calculated value of the oxygen storage capacity with the threshold value, when the calculated value of the oxygen storage capacity is greater than the threshold value, the catalyst is not sufficiently degraded, the chamber scanning module again carries out a chamber scanning in a rich mixture, and so on until the calculated value of the oxygen storage capacity is less than the threshold value.

Other objects, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

- Figure 1 illustrates, schematically, the structure of an internal combustion engine of an automobile engine equipped with an exhaust line provided with a catalyst associated with an OBD diagnostic system and a generation system d an accelerated degradation of the treatment efficiency of polluting emissions of the catalyst according to the invention;

- Figure 2 shows in detail the system for generating an accelerated degradation of the treatment efficiency of polluting emissions of the catalyst of Figure 1; and

- Figure 3 shows an embodiment of a method for generating a faulty catalyst from the point of view of the OBD on-board diagnostic system according to the invention.

In Figure 1, there is shown, schematically and by way of example, the general structure of an internal combustion engine 1 with positive ignition of a motor vehicle.

In the example illustrated, the internal combustion engine 1 comprises four cylinders 2 in line, only one of which is shown in FIG. 1, a fresh air intake manifold 3, an exhaust manifold 4 and, in the non-limiting case of a supercharged engine as shown in FIG. 1, a turbocharging system 5.

The cylinders 2 are supplied with air by means of the intake distributor 3, itself supplied by a pipe 6 provided with an air filter 7, and with the turbocharger 5 for supercharging the engine 1 with air.

The turbocharger 5 essentially comprises a turbine 8 driven by the exhaust gases and a compressor 9 mounted on the same axis as the turbine 8 and ensuring compression of the air distributed by the air filter 7, with the aim of increasing the quantity of air admitted into the cylinders 2 of the engine 1.

Regarding the exhaust manifold 4, it collects the exhaust gases from the combustion and evacuates them to the outside, via a gas exhaust duct 10 leading to the turbine 8 of the turbocharger 5 and by an exhaust line 11.

The exhaust line 11 illustrated in FIG. 1 comprises a first monolithic block 12 and a second monolithic block 13 arranged in series. Each of the monolithic blocks 12, 13 is a cylinder comprising a non-impregnated part and a part impregnated with precious materials. The monolithic block has a honeycomb structure comprising several empty channels extending along the length of said block without communicating with each other.

An envelope (not shown) is provided to surround the monolithic blocks in series in order to constitute a catalyst with residual effectiveness in depolluting harmful gases.

During the operation of the catalyst, the polluting particles of the combustion gases, such as carbon monoxide CO, unburnt hydrocarbons HC and nitrogen oxides NO _X arrive via an inlet to the catalyst and pass through the series monolithic block. The precious materials incorporated in said monolithic block chemically react with the exhaust gases through oxidation and reduction reactions. Thus, at the outlet of the catalyst, part of the exhaust gases is transformed into carbon dioxide CO2, water H2O, dinitrogen N2 and carbon dioxide CO2.

A first oxygen sensor 14, of proportional type, is located downstream of the turbine 8 and upstream of the first monolithic block

12. This first oxygen sensor 14 provides a linear voltage or current signal to be transformed into a stoichiometric richness signal as a function of time.

A second oxygen sensor 15, of binary type, is located downstream of the first monolithic block 12 and upstream of the second monolithic block 13. This second oxygen sensor 15 gives a non-linear voltage signal making it possible to act only in the event of excess oxygen (lean mixture) or lack of oxygen (rich mixture).

Temperature sensors 16 are arranged at different locations on the exhaust line 11, in particular at the level of the first monolithic block 12, of the second monolithic block 13 and between said monolithic blocks 12, 13.

The output signals from the oxygen sensors 12, 13 and the temperature sensors 16 are shaped in an electronic control unit, “ECU”, or on-board computer 20. This signal contains information on the residual oxygen content of the exhaust gas and also on the momentary fuel and air ratio of the mixture drawn in by the engine 1. The air / fuel ratio is also called "richness".

The on-board control unit or computer 20 essentially ensures the control of the operation of the engine 1, in particular the adjustment of its operating parameters, and comprises an on-board diagnostic system 22 OBD for controlling the operation of the catalytic converter made up of monolithic blocks 12, 13 in order to detect excessive aging which can lead to an increase in polluting emissions.

The control unit 20 comprises a system 30 for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of the oxidation-reduction catalyst formed by the monolithic blocks 12, 13.

The system 30 for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions from the oxidation-reduction catalyst is illustrated in detail in FIG. 2.

Said system 30 comprises a module 3 1 for defining a threshold value SI of the oxygen storage capacity. The efficiency of the catalyst in terms of oxidation-reduction is linked to the oxygen storage capacity, in a one-to-one manner.

Said system 30 further comprises a module 32 for defining an internal temperature value T1 of the monolithic block

12. For example, the temperature T1 is equal to 950 ° C. in order to obtain a catalyst equivalent to a catalyst having traveled 160,000 km.

Said system 30 comprises a module 33 for stabilizing the catalyst, for example 2 hours at 650 ° C.

Said system 30 further comprises a chamber scanning module 34, called scavenging in English terms, in a rich mixture, until the desired internal temperature T1 is reached. Chamber sweeping consists of opening the intake and exhaust valves simultaneously to the top dead center of piston crossing on a high load and low speed operating point, when the pressure at the intake valve is higher than pressure at the exhaust valve.

When the chamber sweep takes place during the air intake phase, fresh air is directly transferred from the intake to the exhaust during the crossover phase and oxygen is sent to the catalyst.

When the quantity of fuel injected is increased at an operating point of the engine with the chamber sweep in order to obtain an excess of unburned fuel in the combustion chamber, fuel and oxygen are present in the catalyst. which generates a high exotherm to allow the catalyst to degrade while remaining at an engine operating point without vibrations and with a low temperature at the intake valve and without requiring an external air injection system.

In order to regularly assess the state of degradation of the catalyst, the system 30 includes a module 35 for intrusively modifying the richness setpoint by first imposing a rich slot during, for example 3 s to empty the oxygen catalyst , then a poor window in order to fill the catalyst with oxygen. During this lean phase, the oxygen storage capacity OSCmes can be defined according to the following equation:

OSCmes = 1 (^ / 3.6 x T02 x (1-R (t)) xMAF (t) x (t2 -ti) Eq.l

With:

To2, the ratio of oxygen to the atmosphere, equal to 0.23;

R (t), the richness measured by the upstream probe;

MAF (t) \ e mass flow at intake, kg / h;

ti, the instant corresponding to the end of the rich period when the catalyst is purged of oxygen, corresponding to the moment when the upstream probe 14 indicates a richness value below 1; and t2, the instant corresponding to the end of the lean period, corresponding to the moment when the downstream probe 15 changes to the lean state.

The system 30 includes a module 36 for comparing the calculated value of the oxygen storage capacity OSCmes with the threshold value SI. When the calculated value of the oxygen storage capacity OSCmes is greater than the threshold value SI, the catalyst is not sufficiently degraded, the module 34 again carries out a chamber sweep, in a rich mixture; module 35 intrusively modifies the richness setpoint so as to calculate the oxygen storage capacity OSCmes; module 36 compares said calculated value with said threshold value SI; and so on, until the calculated value of the oxygen storage capacity OSCmes is less than the threshold value SI. In this case, the catalyst has failed and the diagnostic system 30 should issue a catalyst failure signal.

The flowchart shown in Figure 3 illustrates an example of a method 40 implemented by the system 30 shown in the figure

2.

The method 40 is configured to generate, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst formed by the monolithic blocks 12, 13 by chamber scanning, called scavenging in Anglo-Saxon terms, in a rich mixture, on an internal combustion engine of the spark-ignition type with a device for shifting the camshafts at the intake and at the exhaust. The method can be used in the case of a supercharged or atmospheric type engine.

In a first step 41, a threshold value S1 of the oxygen storage capacity is defined. The efficiency of the catalyst in terms of oxidation-reduction is linked to the oxygen storage capacity in a one-to-one manner.

In a second step 42, an internal temperature value T1 is defined for the monolithic block 12. For example, the temperature T1 is equal to 950 ° C. in order to obtain a catalyst equivalent to a catalyst having traveled 160000km.

During step 43, the catalyst is stabilized, for example 2 hours at 650 ° C.

In a step 44, a chamber sweep, known as scavenging in Anglo-Saxon terms, is carried out, in a rich mixture, until the desired internal temperature T1 is reached. Chamber sweeping consists of opening the intake and exhaust valves simultaneously to the top dead center of piston crossing on a high load and low speed operating point, when the pressure at the intake valve is higher than pressure at the exhaust valve.

When the chamber sweep takes place during the air intake phase, fresh air is directly transferred from the intake to the exhaust during the crossover phase and oxygen is sent to the catalyst.

When the quantity of fuel injected is increased at an operating point of the engine with the chamber sweep in order to obtain an excess of unburned fuel in the combustion chamber, fuel and oxygen are present in the catalyst. which generates a high exotherm to allow the catalyst to degrade while remaining at an engine operating point without vibrations and with a low temperature at the intake valve and without requiring an external air injection system.

In order to regularly assess the state of degradation of the catalyst caused by step 44, for example after two or three hours of sweeping in a rich mixture, the richness setpoint is modified in step 45, in an intrusive manner. first imposing a rich slot during, for example 3s to empty the oxygen catalyst, then a lean slot to fill the oxygen catalyst. During this lean phase, the oxygen storage capacity OSCmes can be defined according to the following equation:

OSCmes = 1 (^ / 3.6 x T02 x (1-R (t)) xMAF (t) x (t2 -ti) Eq.l

With:

To2, \ q ratio of oxygen in the atmosphere, equal to 0.23;

R (t), the richness measured by the upstream probe;

MAF (t) \ e. mass flow at intake, kg / h;

ti, the instant corresponding to the end of the rich period when the catalyst is purged of oxygen, corresponding to the moment when the upstream probe 14 indicates a richness value below 1; and

Î2, the instant corresponding to the end of the lean period, corresponding to the moment when the downstream probe 15 goes to the lean state.

Then, in step 46, the calculated value of the oxygen storage capacity OSCmes is compared with the threshold value SI. When the calculated value of the oxygen storage capacity OSCmes is greater than the threshold value SI, the catalyst is not sufficiently degraded, the process resumes at step 44 during which a scanning is again carried out rich mixture chamber, for example for a new period of two to three hours, and iterates the succession of the steps 44 of scanning, 45 of determining the oxygen storage capacity OSCmes and 46 of comparing said capacity OSCmes with said threshold value SI, until the calculated value of the oxygen storage capacity OSCmes is less than the threshold value SI. In this case, the catalyst has failed and the diagnostic system 30 must emit a signal S of catalyst failure. The degradation process is complete, and the catalyst is ready for use in fine tuning the OBD system calibration or for use in vehicle approval tests.

Such a process of simultaneous supply of fuel and air makes it possible to degrade the catalyst more quickly than the standard adjustment processes of the engine in which the quantity of fuel not participating in combustion is not injected.

We can thus precisely measure the evolution of the degradation of the catalyst, in terms of loss of efficiency, by regularly determining its oxygen storage capacity, called oxygen storage capacity, acronym OSC in Anglo-Saxon terms.

This measurement can be performed without an instrument further than the standard configuration of the engine.

Claims (10)

1. Method for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst formed by monolithic blocks (12, 13) by sweeping a mixed chamber rich until reaching an internal temperature threshold value (Tl) of the catalyst on a supercharged spark-ignition engine (1). 2. Method according to claim 1, in which a threshold value (SI) of the oxygen storage capacity is defined. 3. Method according to claim 1 or 2, wherein one defines an internal temperature value (T1) of the catalyst. 4. Method according to any one of the preceding claims, in which the catalyst is stabilized. 5. Method according to any one of the preceding claims, in which after the step of sweeping the chamber in a rich mixture, the richness setpoint is intrusively modified by first imposing a rich slot to empty the catalyst d oxygen, then a lean window in order to fill the oxygen catalyst, and the oxygen storage capacity (OSCmes) is calculated during this lean phase. 6. Method according to claims 2 and 5, in which the calculated value of the oxygen storage capacity (OSCmes) is compared with the threshold value (SI), when the calculated value of the oxygen storage capacity ( OSCmes) is greater than the threshold value (SI), the catalyst is not sufficiently degraded, a chamber scan is carried out again, until the calculated value of the oxygen storage capacity (OSCmes ) is lower than the threshold value (SI). 7. System for generating, in a controlled manner, an accelerated degradation of the efficiency of treatment of polluting emissions of an oxidation-reduction catalyst formed by monolithic blocks (12, 13) comprising a module (35) sweeping the chamber in a rich mixture until reaching an internal temperature threshold value (Tl) of the catalyst on a supercharged engine (1) with spark ignition. 8. The system as claimed in claim 7, comprising a module (31) for defining a threshold value (SI) of the oxygen storage capacity, a module (32) for defining a temperature value (Tl) internal of the catalyst, and a module (33) for stabilizing the catalyst. 9. The system as claimed in claim 7 or 8, comprising a module (35) for intrusively modifying a richness setpoint by first imposing a rich slot to empty the oxygen catalyst, then a lean slot in order to fill the oxygen catalyst and a module for calculating, during this lean phase, the oxygen storage capacity (OSCmes). 10. System according to claims 8 and 9, comprising a module (36) for comparing the calculated value of the oxygen storage capacity (OSCmes) with the threshold value (SI), when the calculated value of the capacity oxygen storage (OSCmes) is greater than the threshold value (SI), the catalyst is not sufficiently degraded, the module (34) again carries out a chamber sweep in a rich mixture, until the calculated value of the oxygen storage capacity (OSCmes) is less than the threshold value (SI).