Method to Determine the Oxygen Storage Capacity of a Catalytic Converter of an Exhaust Gas System of an Internal Combustion Engine

Abstract

A method to determine the oxygen storage capacity of a catalytic converter of an exhaust gas system of an internal combustion engine is described; wherein the exhaust gas system is provided with an exhaust duct, along which catalytic converter is housed; a lambda sensor housed along exhaust duct downstream of catalytic converter to detect the concentration of oxygen in the exhaust gases; and an exhaust gas after-treatment system having a burner designed to introduce exhaust gases into exhaust duct; wherein inside burner there is defined a combustion chamber, which receives fresh air through a first supply circuit and fuel from a second supply circuit. The method comprises a step in which to recognise that internal combustion engine is in a stop phase or in a slow running mode; a step in which to control the first and the second supply circuit so as to obtain a given objective lambda value, in particular other than one; a step in which to determine a delay with which lambda sensor detects the change in objective lambda value; and a step in which to calculate the oxygen storage capacity of catalytic converter by means of said delay.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102023000024141 filed on Nov. 14, 2023, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE ART

The present invention relates to a method for determining the oxygen storage capacity of a catalytic converter of an exhaust gas system of an internal combustion engine.

PRIOR ART

As is well known, an internal combustion engine is typically equipped with a number of cylinders, each of which is connected to an intake manifold and an exhaust manifold, to which an exhaust duct is connected, which feeds the exhaust gases produced by combustion to an exhaust system, which emits the gases produced by combustion into the atmosphere.

An exhaust gas after-treatment system usually comprises a precatalyst arranged along the exhaust duct; a particle filter also arranged along the exhaust duct, downstream of the precatalyst; and a catalytic converter arranged along the exhaust duct, upstream of the particle filter. Finally, the exhaust gas after-treatment system also comprises a burner designed to introduce exhaust gases (and consequently heat) into the exhaust duct in order to speed up the heating of the catalytic converter and facilitate the regeneration of the particulate filter.

Since it is of utmost importance to be able to contain the pollutants produced by the internal combustion engine, it is crucial that the catalytic converter operates correctly. Any faults or malfunctions of the catalytic converter are diagnosed by measuring its oxygen storage capacity (OSC) in order to estimate the conversion efficiency of the exhaust gases passing through the catalytic converter itself.

Typically, the measurement of the oxygen storage capacity is performed by means of a diagnosis strategy in which the development of the objective lambda value of the internal combustion engine is set; during the implementation of the diagnosis strategy, the objective lambda value has a stepwise development in which objective lambda values greater than one and objective lambda values less than one alternate. However, the implementation of this catalytic converter diagnosis strategy results in a significant increase in emissions.

DISCLOSURE OF THE INVENTION

The purpose of the present invention is to provide a method to determine the oxygen storage capacity of a catalytic converter of an exhaust gas system of an internal combustion engine, which is free from the drawbacks described above and, in particular, which is easy and inexpensive to implement.

According to the present invention, a method to determine the oxygen storage capacity of a catalytic converter of an exhaust gas system of an internal combustion engine according to the appended claims is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which show a non-limiting embodiment thereof, wherein:

FIG. 1 schematically shows an internal combustion engine equipped with an exhaust gas after-treatment system and an electronic control unit to implement the method covered by the present invention;

FIG. 2 schematically illustrates the exhaust gas after-treatment system in FIG. 1; and

FIG. 3 schematically illustrates the development of an objective lambda value and the development of the lambda value measured by a lambda sensor from FIGS. 1 and 2.

PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, the number 1 denotes a supercharged internal combustion engine, equipped with an exhaust gas system 2 in a motor vehicle (not illustrated) and having a number of cylinders 3, each of which is connected to an intake manifold 4 and an exhaust manifold 5 via at least one respective exhaust valve (not illustrated).

The intake manifold 4 receives fresh air, i.e. air from the outside environment, via an intake duct 6, which is equipped with an air filter for fresh air flow and is regulated by a throttle valve 8. An air flow meter 9 is also arranged along the intake duct 6 downstream of air filter 7.

An exhaust duct 10 is connected to exhaust manifold 5, which feeds the exhaust gases produced by combustion to exhaust system 2, which emits the gases produced by combustion into the atmosphere.

Supercharged internal combustion engine 1 comprises a supercharged system of internal combustion engine 1, implemented through a turbocharger 11 provided with a turbine 12, which is arranged along exhaust duct 10 to rotate at high speed under the action of the exhaust gases expelled by cylinders 3, and a compressor 13, which is arranged along intake duct 6 and is mechanically connected to turbine 12 to be driven in rotation by turbine 12 itself so as to increase the air pressure present in intake duct 6.

Exhaust system 2 is equipped with an exhaust gas after-treatment system 14 comprising a precatalyst 15 arranged along exhaust duct 10, downstream of turbocharger 11 and a particulate filter 16 (also known as Gasoline Particulate Filter) also arranged along exhaust duct 10, downstream of precatalyst 15. According to a preferred embodiment, exhaust gas after-treatment system 14 is equipped with a catalytic converter 17 arranged along exhaust duct 10 upstream of particulate filter 16. According to a preferred embodiment, catalytic converter 17 and particulate filter 16 are arranged one after the other within a common tubular container.

According to a preferred embodiment, internal combustion engine 1 is further provided with a linear oxygen probe 18 of the UHEGO or UEGO type housed along exhaust duct 10 and interposed between turbocharger 11 and precatalyst 15; with a lambda probe 19 housed along exhaust duct 10 and interposed between precatalyst 15 and the assembly defined by catalytic converter 17 and particulate filter 16 to detect the oxygen concentration within the exhaust gas downstream of precatalyst 15; and finally, a lambda sensor 20 housed along exhaust duct 10 and arranged downstream of the assembly defined by catalytic converter 17 and particulate filter 16 to detect the oxygen concentration within the exhaust gas downstream of the assembly defined by catalytic converter 17 and particulate filter 16.

Exhaust gas after-treatment system 14 then comprises a burner 21 designed to introduce exhaust gases (and thus heat) into exhaust duct 10 in order to speed up the heating of precatalyst 15 and/or catalytic converter 17 and to facilitate the regeneration of particulate filter 16. Burner 21 is arranged so that the exhaust gases are introduced into exhaust duct 10 upstream of precatalyst 15 or upstream of catalytic converter 17.

As best illustrated in FIG. 2, a combustion chamber 22 is defined inside burner 21, which receives fresh air (i.e., air from the external environment) via an air supply circuit 23 provided with a pumping device 24 (of a type known and not described in detail), preferably with the interposition of an air filtering element, and supplies air to the burner 21 via a duct 25. According to a first embodiment, pumping device 24 is of the fixed flow type, and a shut-off valve 26 housed along duct 25 (arranged downstream of pumping device 24) is provided to regulate the air flow. Alternatively, pumping device 24 is of the variable flow type (PWM-controlled) and there is a non-return valve 26 housed along duct 25 (arranged downstream of pumping device 24).

Combustion chamber 22 also receives fuel from an injector 27, which is designed to inject fuel into combustion chamber 22. In addition, a spark plug 28 is coupled to burner 21 to determine the ignition of the mixture inside combustion chamber 22. Internal combustion engine 1 then comprises a fuel supply circuit 29 equipped with a pumping device 30 which draws fuel from a tank 39 and feeds it through a duct 31 regulated by a valve 38.

The air-fuel mixture that is fed into combustion chamber 22 is defined as rich in the case of an excess of fuel over the stoichiometric value and is defined as lean in the case of an excess of air over the stoichiometric value. As is conventionally known, lambda λ represents the excess air coefficient relative to the air-fuel mixture under stoichiometric conditions. For rich mixtures, lambda λ is less than one and for lean mixtures lambda λ is greater than one.

Probes 18, 19, 20 are provided to detect/measure the amount of oxygen in the exhaust gas and to provide either a binary on/off output or a linear output, which indicates the oxygen content in the exhaust gas to allow an electronic control unit (usually called “ECU”) to calculate the air/fuel ratio of the exhaust gases. In other words, probes 18, 19 and 20 provide an output that indicates whether the detected lambda value λ for the exhaust gas is above or below the stoichiometric value (i.e. one).

Finally, internal combustion engine 1 includes a control system, which is designed to oversee the operation of internal combustion engine 1 itself. The control system comprises at least electronic control unit ECU, which oversees the operation of the various components of internal combustion engine 1. It is evident that electronic control unit ECU introduced in the foregoing discussion may be a dedicated electronic control unit ECU overseeing the operation of burner 21 or it may be an electronic control unit ECU overseeing the operation of internal combustion engine 1. Spark plug 28 is driven by electronic control unit ECU to strike a spark between its electrodes and thus ignite the compressed gases inside combustion chamber 22.

Advantageously, electronic control unit ECU is also provided to implement the “Stop and Start” management mode, which provides for shutting down internal combustion engine 1 when the vehicle is stopped or close to a stop typically for traffic-related reasons, such as a red light or an intersection without right-of-way, and provides for restarting internal combustion engine 1 as soon as the user operates the clutch pedal. More generally, “Stop and Start” mode shuts down internal combustion engine 1 even with the vehicle moving at low speed if the driver does not require traction, i.e., releases the accelerator pedal.

Finally, the control system comprises a plurality of sensors connected to electronic control unit ECU. The sensors comprise, in particular, a temperature and pressure sensor 33 of the air flow fed to the burner 21 preferably housed along duct 25 (in other words, sensor 33 is housed along duct 25 downstream of pumping device 24, preferably interposed between pumping device 24 and shut-off valve 26); a temperature and pressure sensor 34 of the exhaust gases exiting burner 21 housed along an outlet duct 35; a pressure sensor 36 of the fuel fed to burner 21 housed along duct 31. Electronic control unit ECU is also connected to UHEGO or UEGO linear oxygen probe 18 and lambda probes 19, 20 from which it receives signals indicative of the air/fuel ratio of the exhaust gases.

The method implemented by electronic control unit ECU to carry out diagnostics on the correct operation of precatalyst 15 is described below. More specifically, the method implemented by electronic control unit ECU to calculate the oxygen storage capacity (OSC) of precatalyst 15 is described below. In order to be able to implement the strategy of calculating the capacity of precatalyst 15 to store oxygen, internal combustion engine 1 must be in a particular operating condition. In particular, electronic control unit ECU is configured to recognise the occurrence of any of the following operating conditions:

• • internal combustion engine 1 is switched off after one operating cycle (“after run” condition); or
  • internal combustion engine 1 is switched off before starting; or
  • internal combustion engine 1 is in a stop phase driven by “Stop and Start” management mode; or
  • internal combustion engine 1 is in a standstill phase in hybrid drive vehicles while driving in electric mode; or
  • internal combustion engine 1 is running but with a minimal air flow.

In turn, burner 21 may be ignited during the stop phases of internal combustion engine 1 (to heat precatalyst 15 or to calculate the capacity of precatalyst 15 to store oxygen); more specifically, burner 21 may be ignited during the shutdown phases of internal combustion engine 1 driven by “Stop and Start” management mode, during the “after run” phases after an operating cycle, during the “pre-run” phase, or during the electric mode run phases in hybrid drive vehicles.

Electronic control unit ECU is then configured to drive air supply circuit 23 to implement an objective air flow rate and fuel supply circuit 29 to implement an objective lambda value λ_OBJ. More in detail, electronic control unit ECU is configured to drive air supply circuit 23 and fuel supply circuit 29 in such a way that objective lambda value λ_OBJ only implements a step-like development in the event that the diagnosis of precatalyst 15 is requested by calculating oxygen storage capacity OSC. As illustrated in FIG. 3, the development of the objective lambda value λ_OBJ starts with an objective lambda value λ_OBJ greater than 1 and when the strategy for calculating the oxygen storage capacity of precatalyst 15 is implemented there is an alternation between at least one time interval ΔT_R in which the objective lambda value λ_OBJ is less than 1 and at least one time interval ΔT_L in which the objective lambda value λ_OBJ is greater than 1. Preferably, the time intervals ΔT_L, ΔT_R have variable durations. In more detail, the time intervals ΔT_L, ΔT_R have a variable duration depending on the mass flow rate through precatalyst 15, the actual lambda value A and the thermal and ageing state of precatalyst 15.

Advantageously, in time interval ΔT_R (between instants t₀ and t₁) objective lambda value λ_OBJ is less than 1; according to a preferred embodiment, objective lambda value λ_OBJ is equal to 0.9.

Advantageously, in time interval ΔT_L (between instants t₁ and t₂) objective lambda value λ_OBJ is greater than 1; according to a preferred embodiment, objective lambda value λ_OBJ is equal to 1.1.

Advantageously, electronic control unit ECU is configured to implement a predetermined number of steps (i.e., a predetermined number of times the transition from the objective lambda value λ_OBJ less than one to the objective lambda value λ_OBJ greater than one is implemented).

FIG. 3 shows the development of lambda value λ_D detected by lambda probe 19 arranged downstream of precatalyst 15; TV_L indicates a threshold value for detecting a lean mixture via lambda probe 19 and TV_R indicates a threshold value for detecting a rich mixture via lambda probe 19.

DAR indicates the delay with which lambda probe 19 detects the change in objective lambda value λ_OBJ from instant t₀. In other words, delay DAR represents the delay with which lambda probe 19 detects the transition from objective lambda value λ_OBJ greater than 1 to objective lambda value λ_OBJ less than 1. Alternatively, DL denotes the delay with which lambda probe 19 detects the change in objective lambda value λ_OBJ from instant t₁. In other words, delay DAL represents the delay with which lambda probe 19 detects the transition from objective lambda value λ_OBJ less than 1 to objective lambda value λ_OBJ greater than 1. In other words, D_λR and D_λL represent the delay with which lambda probe 19 reaches threshold value TV_R or threshold value TV_L respectively.

Once D_λR and D_λL have been determined, electronic control unit ECU is finally configured to calculate the oxygen storage capacity of catalyst 15.

In more detail, oxygen storage capacity OSC is calculated using formula:

$\begin{array}{cc}\mathrm{OSC}=M_{\mathrm{AF}}*0,23*\frac{❘1-{\lambda }_{\mathrm{AVG}}❘}{{\lambda }_{\mathrm{AVG}}}*D_{\lambda }& \left[1\right]\end{array}$

• • wherein:
  • M_AF represents the mass flow rate of exhaust gases in precatalyst 15;
  • λ_AVG average lambda value in range ΔT_L or ΔT_R;
  • 0.23 percentage (23%) of oxygen in the air; and
  • D_λ delay of lambda probe 19.

D_λ is equal to D_λR for the calculation of oxygen storage capacity OSC during the rich step (OSC_RICH); while DA is equal to D_λL for the calculation of oxygen storage capacity OSC during the lean step (OS_CLEAN). According to a first variant, only the oxygen storage capacity value OSC during the lean step (OS_CLEAN) is used; alternatively, a final oxygen storage capacity OSC value (OSC_FINAL) calculated as the average oxygen storage capacity value OSC between the oxygen storage capacity OSC during the lean step (OS_CLEAN) and the oxygen storage capacity OSC during the rich step (OSC_RICH) is used.

Advantageously, the M_AF mass flow rate of exhaust gas flowing through precatalyst 15 can easily be kept stable and uniform (constant) when the measurement of oxygen storage capacity OSC is performed using burner 21.

If the diagnosis of the correct operation of catalyst 15 is carried out several times within one operating cycle, the average oxygen storage capacity value OSC can be determined. For example, the oxygen storage capacity OSC is calculated by averaging oxygen storage capacity OSC calculated in time interval ΔT_L and in time interval ΔT_R.

The oxygen storage capacity value OSC or average oxygen storage capacity OSC can be advantageously corrected according to the temperature of precatalyst 15.

Alternatively, in the event that the temperature precatalyst 15 is below a threshold value representing the limit below which the calculation of oxygen storage capacity value OSC is unrepresentative, before proceeding with the diagnostic strategy, electronic control unit ECU is configured to heat precatalyst 15 to reach said threshold value.

Subsequently, the oxygen storage capacity value OSC or average oxygen storage capacity value OSC are compared with a minimum oxygen storage capacity value OSC, which defines the threshold below which precatalyst 15 is defined as either faulty or inoperative. If the oxygen storage capacity OSC or the average oxygen storage capacity OSC is greater than or equal to said minimum value, the diagnostic strategy concludes positively; whereas, if the oxygen storage capacity OSC or the average oxygen storage capacity OSC is less than said minimum value, the diagnostic strategy concludes negatively and the ECU unit is configured to signal a malfunction.

In the preceding discussion, explicit reference was made to the processing of the signal from lambda probe 19, but the diagnosis strategy described in the preceding discussion can also be advantageously applied when using the signal from lambda probe 20; in this case, the diagnosis strategy makes it possible to calculate the oxygen storage capacity OSC of precatalyst 15 and catalytic converter 17. The applicant has verified experimentally that the diagnosis strategy using burner 21 described in the preceding discussion has several advantages, in particular over the known strategy using internal combustion engine 1 while providing essentially the same oxygen storage capacity values.

In particular, the diagnosis strategy using burner 21 described in the preceding discussion reduces pollutant emissions compared to the known strategy using internal combustion engine 1; moreover, the calculation of oxygen storage capacity OSC is more accurate and reliable due to the fact that it is carried out under stable conditions (in particular, with precatalyst 15 sufficiently hot and internal combustion engine 1 switched off or at idle speed).

LIST OF REFERENCE NUMBERS

• • 1 internal combustion engine
  • 2 exhaust system
  • 3 cylinders
  • 4 intake manifold
  • 5 exhaust manifold
  • 6 intake duct
  • 7 air filter
  • 8 throttle valve
  • 9 air flow meter
  • 10 exhaust duct
  • 11 turbocharger
  • 12 turbine
  • 13 compressor
  • 14 after-treatment system
  • 15 precatalyst
  • 16 particulate filter
  • 17 catalytic converter
  • 18 linear probe
  • 19 lambda sensor
  • 20 lambda sensor
  • 21 burner
  • 22 combustion chamber
  • 23 air supply circuit
  • 24 pumping device
  • 25 duct
  • 26 shut-off valve
  • 27 injector
  • 28 spark plug
  • 29 fuel supply circuit
  • 30 pumping device
  • 31 duct
  • 33 sensor P, T
  • 34 sensor P, T
  • 35 outlet duct
  • 36 sensor P, T
  • 38 valve
  • 39 fuel tank
  • ECU electronic control unit
  • λ_OBJ objective lambda value
  • λ_D measured lambda value
  • D_λR delay
  • D_λL delay
  • ΔT_L time interval
  • ΔT_R time interval
  • TV_L threshold value
  • TV_R threshold value
  • t₁ instant
  • t₂ instant
  • t₀ instant

Claims

1. A method to determine the oxygen storage capacity (OSC) of a catalytic converter (15, 17) of an exhaust gas system (2) of an internal combustion engine (1); wherein the exhaust gas system (2) comprises: an exhaust duct (10), along which the catalytic converter (15, 17) is housed;a lambda sensor (19, 20) housed along the exhaust duct (10) downstream of the catalytic converter (15, 17) to detect the concentration of oxygen in the exhaust gases; andan exhaust gas after-treatment system (14) having a burner (21) designed to introduce exhaust gases into the exhaust duct (10); wherein inside the burner (21) there is defined a combustion chamber (22), which receives fresh air through a first supply circuit (23) and fuel from a second supply circuit (29);the method comprises:a) a step in which to recognise that the internal combustion engine (1) is in a stop phase or in a slow running mode;b) a step in which to control the first and the second supply circuit (23, 29) to the burner (21) so as to obtain a given objective lambda value (λOBJ), in particular other than one;c) a step in which to determine a delay with which the lambda sensor (19, 20) detects the change in the objective lambda value (λOBJ); andd) a step in which to calculate the oxygen storage capacity (OSC) of the catalytic converter (15, 17) by means of said delay.

2. The method according to claim 1, wherein the objective lambda value (λOBJ) is greater than 1; in particular, the objective lambda value (λOBJ) is 1.1.

3. The method according to claim 1, wherein the objective lambda value (λOBJ) is smaller than 1; in particular, the objective lambda value (λOBJ) is 0.9.

4. The method according to claim 1, wherein the objective lambda value (λOBJ) has a step-like development, in which it alternatively is greater than 1 and smaller than 1.

5. The method according to claim 2 wherein the method step d) comprises the sub steps of: determining a delay (DλL) of the lean step with which the lambda sensor (19, 20) detects the change in the objective lambda value (λOBJ) from smaller than one to greater than one; andcalculating the oxygen storage capacity (OSC) of the catalytic converter (15, 17) by means of said delay (DλL) Of the lean step.

6. The method according to claim 4 wherein the method step d) comprises the sub steps of: determining a delay (DλL) of the lean step with which the lambda sensor (19, 20) detects the change in the objective lambda value (λOBJ) from smaller than one to greater than one;determining a delay (DλR) of the rich step with which the lambda sensor (19, 20) detects the change in the objective lambda value (λOBJ) from greater than one to smaller than one;calculating the oxygen storage capacity (OSCLEAN) Of the lean step by means of said delay (DλL) of the lean step;calculating the oxygen storage capacity (OSCRICH) of the rich step by means of said delay (DλR) of the rich step; andcalculating the average value between the oxygen storage capacity (OSCLEAN) of the lean step and the oxygen storage capacity (OSCRICH) of the rich step.

7. The method according to claim 1 and comprising: a step in which to calculate a plurality of values of the oxygen storage capacity (OSC) of the catalytic converter (15, 17) within a same operating cycle; anda step in which to determine an average value of the oxygen storage capacity (OSC) of the catalytic converter (15, 17).

8. The method according to claim 1, wherein the value of the oxygen storage capacity (OSC) or the average value of the oxygen storage capacity (OSC) are corrected based on the temperature of the catalytic converter (15, 17).

9. The method according to claim 1 and comprising a further step, prior to step b), in which to heat the catalytic converter (15, 17) so as to reach an operating temperature threshold value.