Patent Publication Number: US-11649754-B2

Title: Method to control a burner for an exhaust system of an internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority from Italian patent application no. 102021000017258 filed on Jun. 30, 2021, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a method to control a burner for an exhaust system of an internal combustion engine. 
     PRIOR ART 
     As is known, an internal combustion engine is typically provided 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 precatalytic converter arranged along the exhaust duct; a particulate filter also arranged along the exhaust duct, downstream of the precatalytic converter; and a catalytic converter arranged along the exhaust duct, upstream of the particulate filter. 
     Also provided along the exhaust duct are a first lambda sensor housed along the exhaust duct and arranged upstream of the precatalytic converter to detect the air/fuel ratio (or titer) of the exhaust gases entering the precatalytic converter; a second lambda sensor housed along the exhaust duct and interposed between the precatalytic converter and the assembly defined by the catalytic converter and by the particulate filter to detect the oxygen concentration inside the exhaust gases downstream of the precatalytic converter; and lastly, a third lambda sensor housed along the exhaust duct and arranged downstream of the assembly defined by the catalytic converter and by the particulate filter to detect the oxygen concentration inside the exhaust gases downstream of the assembly defined by the catalytic converter and by the particulate filter. 
     Lastly, the exhaust gas after-treatment system also comprises a burner suited to introduce the exhaust gases (and consequently heat) into the exhaust duct so as to speed up heating of the catalytic converter and so as to facilitate the regeneration of the particulate filter. 
     A combustion chamber is defined inside the burner, the chamber receives fresh air and receives fuel from an injector, which is designed to cyclically inject fuel inside the combustion chamber. In addition, a spark plug is coupled to the burner to determine the ignition of the mixture present inside the combustion chamber. 
     It is of utmost importance to be able to control the combustion that occurs inside the burner so as to ensure that the optimal thermal power and the desired/objective value of the air/fuel ratio of the exhaust gases exiting the burner are achieved. 
     For this reason, it has been proposed to house a further lambda sensor along a duct adapted to discharge the exhaust gases exiting the burner into the exhaust duct; said further lambda sensor is dedicated exclusively to detecting the air/fuel ratio of the exhaust gases exiting the burner. However, this solution is economically disadvantageous as it involves the use of a further lambda sensor. 
     To overcome this problem, it has been proposed to arrange the burner so as to introduce the exhaust gases into the exhaust duct between the first lambda sensor (so that the first lambda sensor is exclusively hit by the exhaust gases produced by the internal combustion engine) and the second lambda sensor (so that the second lambda sensor is hit by both the exhaust gases produced by the internal combustion engine and the exhaust gases produced by the burner); and use the signals coming from the first lambda sensor and from the second lambda sensor to control the burner and operate the air flow rate and fuel fed to the burner. 
     The document US2003221425 relates to a method to control an exhaust system of an internal combustion engine provided with a burner. 
     DESCRIPTION OF THE INVENTION 
     The aim of the present invention is to provide a method to control a burner for an exhaust system of an internal combustion engine which is free of the drawbacks described above and, in particular, is easy and inexpensive to implement. 
     According to the present invention, a method to control a burner for an exhaust system of an internal combustion engine is provided according to what is claimed in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described with reference to the appended drawings, which illustrate a non-limiting embodiment thereof, wherein: 
         FIG.  1    schematically shows an internal combustion engine provided with a first variant of an exhaust gas after-treatment system having an electronic control unit that implements the control method obtained in accordance with the present invention; 
         FIG.  2    illustrates a second variant of the exhaust gas after-treatment system of  FIG.  1   ; 
         FIG.  3    schematically illustrates a detail of the exhaust gas after-treatment system illustrated in  FIGS.  1  and  2   ; 
         FIGS.  4  and  6    are block diagrams that schematically illustrate a first variant of the method to control the air flow rate object of the present invention; 
         FIG.  5    is a block diagram that schematically illustrates the method to control the fuel flow rate object of the present invention; 
         FIGS.  7  and  8    are block diagrams that schematically illustrate a second variant of the method to control the air flow rate object of the present invention; 
         FIGS.  9  and  10    are block diagrams that schematically illustrate a third variant of the method to control the air flow rate object of the present invention; 
         FIGS.  11  and  12    are block diagrams that schematically illustrate a fourth variant of the method to control the air flow object of the present invention; and 
         FIG.  13    schematically illustrates a detail of the internal combustion engine of  FIG.  1   ; and 
         FIG.  14    schematically illustrates a further embodiment of a detail of  FIG.  3   . 
     
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     In  FIG.  1   , indicated as a whole by the number  1  is a boosted internal combustion engine provided with an exhaust system  2  for the exhaust gases in a motor vehicle (not illustrated) and having a number of cylinders  3 , each of which is connected to an intake manifold  4  and to an exhaust manifold  5  by at least one respective exhaust valve (not illustrated). 
     Also, according to a preferred embodiment, the following disclosure finds advantageous yet not exclusive application in the case of an internal combustion engine  1  in which the fuel fed is gasoline. 
     The intake manifold  4  receives air coming from the external environment through an intake duct  6 , which is provided with an air filter  7  for the flow of fresh air and is regulated by a throttle valve  8 . A mass air flow sensor  9  (better known as Air Flow Meter) is also arranged along the intake duct  6  downstream of the air filter  7 . 
     The exhaust manifold  5  is connected to an exhaust duct  10  that feeds the exhaust gases produced by combustion to the exhaust system  2 , which emits the gases produced by combustion into the atmosphere. 
     The boosting system of the internal combustion engine  1  comprises a turbocompressor  11  provided with a turbine  12 , which is arranged along the exhaust duct  10  to rotate at high speed under the action of the exhaust gases expelled from the cylinders  3 , and a compressor  13 , which is arranged along the intake duct  6  and is mechanically connected to the turbine  12  to be dragged into rotation by said turbine  12  so as to increase the pressure of the air present in the intake duct  6 . 
     The gas exhaust system  2  is provided with an exhaust gas after-treatment system  14  comprising a precatalytic converter  15  arranged along the exhaust duct  10 , downstream of the turbocompressor  11  and a particulate filter  16  (also known as Gasoline Particulate Filter) also arranged along the exhaust duct  10 , downstream of the precatalytic converter. According to a preferred embodiment, the exhaust after-treatment system  14  is provided with a catalytic converter  17  arranged along the exhaust duct  10 , upstream of the particulate filter  16 . According to a preferred embodiment, the catalytic converter  17  and the particulate filter  16  are arranged one after the other inside a common tubular container. 
     According to a first variant, the internal combustion engine  1  is also provided with a linear oxygen sensor  18  of the UHEGO or UEGO type housed along the exhaust duct  10  and interposed between the turbocompressor  11  and the precatalytic converter  15  so as to detect the air/fuel ratio (or titer) of the exhaust gases (providing a linear output indicating the content of oxygen in the exhaust gases) downstream of the turbocompressor  11  and upstream of the precatalytic converter  15 . 
     The internal combustion engine is also provided with a lambda sensor  19  intended to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct  10  and interposed between the precatalytic converter  15  and the assembly defined by the catalytic converter  17  and by the particulate filter  16  to detect the oxygen concentration inside the exhaust gases downstream of the precatalytic converter  15 ; and finally, a lambda sensor  20  suited to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct  10  and arranged downstream of the assembly defined by the catalytic converter  17  and by the particulate filter  16  to detect the oxygen concentration inside the exhaust gases downstream of the assembly defined by the catalytic converter  17  and the particulate filter  16 . 
     According to a second variant illustrated in  FIG.  2   , the internal combustion engine  1  is also provided with a lambda sensor  19 * suited to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct  10  and interposed between the turbocompressor  11  and the precatalytic converter  15  to detect the air/fuel ratio (or titer) of the exhaust gases downstream of the turbocompressor  11  and upstream of the precatalytic converter  15 . 
     The internal combustion engine  1  is also provided with a UHEGO or UEGO type linear oxygen sensor  18 * housed along the exhaust duct  10  and interposed between the precatalytic converter  15  and the assembly defined by the catalytic converter  17  and by the particulate filter  16  to detect the oxygen concentration inside the exhaust gases downstream of the precatalytic converter  15  (a linear output indicating the content of oxygen in the exhaust gases); and lastly, a lambda sensor  20  suited to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct  10  and arranged downstream of the assembly defined by the catalytic converter  17  and by the particulate filter  16  to detect the oxygen concentration inside the exhaust gases downstream of the assembly defined by the catalytic converter  17  and by the particulate filter  16 . 
     The exhaust gas after-treatment system  14  then comprises a burner  21  suited to introduce exhaust gases (and consequently heat) into the exhaust duct  10  so as to speed up the heating of the precatalytic converter  15  and/or of the catalytic converter  17  and so as to facilitate the regeneration of the particulate filter  16 . 
     According to what is better illustrated in  FIG.  3   , a combustion chamber  22  is defined inside the burner  21 , the chamber receives fresh air (i.e., air coming from the outside environment) through an air feeding circuit  23  provided with a pumping device  24  that feeds the air by means of a duct  25  regulated by an on/off type shut-off valve  26 . The combustion chamber  22  also receives fuel from an injector  27  designed to cyclically inject fuel inside the combustion chamber  22 . In addition, a spark plug  28  is coupled to the burner  21  to determine the ignition of the mixture present inside said combustion chamber  22 . The internal combustion engine  1  then comprises a fuel feeding circuit  29  provided with a pumping device  30  that feeds the fuel by means of a duct  31 . 
     Lastly, the internal combustion engine  1  comprises a control system  32  which is adapted to oversee the operation of said internal combustion engine  1 . The control system  32  comprises at least one electronic control unit (normally referred to as an “ECU”—“Electronic Control Unit”), which oversees the operation of the various components of the internal combustion engine  1 . 
     The spark plug  28  is operated by the electronic control unit ECU to make a spark between its electrodes and therefore determine the ignition of the gases compressed inside the combustion chamber  22 . The control system  32  also comprises a plurality of sensors connected to the electronic control unit ECU. 
     The sensors comprise, in particular, a sensor  33  for the temperature and pressure of the air flow fed to the burner  21  preferably housed along the duct  25 ; a sensor  34  for the temperature and pressure of the exhaust gases exiting the burner  21  housed along an outlet duct  35  for discharging the exhaust gases exiting the burner  21  into the exhaust duct  10 ; a sensor  36  for the pressure of fuel fed to the burner  21  housed along the duct  31 ; and a sensor  37  for the pressure and temperature of the air flow fed to the pumping device  24 . 
     The electronic control unit ECU is also connected to the UHEGO or UEGO type linear oxygen sensor  18 ,  18 * and to the lambda sensors  19 ,  19 *,  20 . 
     According to a first embodiment illustrated in  FIG.  1   , the burner  21  is arranged so as to introduce the exhaust gases into the exhaust duct  10  upstream of the UHEGO or UEGO type linear oxygen sensor  18  and upstream of the precatalytic converter  15 . 
     According to a second embodiment illustrated in  FIG.  2   , the burner  21  is arranged so as to introduce the exhaust gases into the exhaust duct  10  upstream of the UHEGO or UEGO type linear oxygen sensor  18 * and upstream of the assembly defined by the catalytic converter  17  and by the particulate filter  16 . 
     The method implemented by the electronic control unit ECU to control the burner  21  is described in the following. 
     Firstly, the strategy described in the following disclosure may be implemented exclusively when the UHEGO or UEGO type linear oxygen sensor  18 ,  18 * is hit exclusively by the exhaust gases produced by the burner  21  (in other words, it is necessary that the UHEGO or UEGO type linear oxygen sensor  18 ,  18 * is not hit by the exhaust gases produced by the internal combustion engine  1 ). 
     Therefore, the condition of enabling the control strategy for the burner  21  is that said burner  21  is turned on and the internal combustion engine  1  is instead turned off. 
     In particular, the following two conditions may occur alternatively:
         a) burner  21  turned on with the “cold” exhaust system  2  (i.e., with a detected temperature below a limit value, ranging from 180° C. to 200° C.); or   b) burner  21  turned on with the “hot” exhaust system  2  (i.e., with a detected temperature above a limit value, ranging from 180° C. to 200° C.).       

     The condition a) may occur in any of the following cases:
         a 1 ) the burner  21  is turned on when the door of the driver of the motor vehicle is opened (the opening is detected by means of a sensor or when the door is unlocked by remote control or even when the smart key is detected in proximity to the vehicle); a 2 ) the burner  21  is turned on when the motor vehicle is a hybrid vehicle that is started in electric mode and the internal combustion engine  1  has not been turned on yet after the motor vehicle has been started;   a 3 ) the burner  21  is turned on when the vehicle is a hybrid vehicle running in electric mode and the electronic control unit ECU provides for switching to thermal mode (for example, in the case where the State Of Charge of a storage system is not sufficient to proceed in electric mode); in this case, the burner  21  is turned on about 3 to 5 seconds before the start of the internal combustion engine  1 .       

     It is clear that, alternatively, in the case where the burner  21  is arranged so as to introduce the exhaust gases into the exhaust duct  10  upstream of the UHEGO or UEGO type linear oxygen sensor  18 * and upstream of the assembly defined by the catalytic converter  17  and by the particulate filter  16  (in other words, in the case where the burner  21  is interposed between the precatalytic converter  15  and the assembly defined by the catalytic converter  17  and by the particulate filter  16 ), the strategy described in the following disclosure may also be implemented in the case where the internal combustion engine  1  is turned on since the exhaust gases produced by the internal combustion engine  1  have already passed through the precatalytic converter  15 . 
     The burner  21  is then turned off if any of the following conditions occur:
         a temperature of the exhaust system  2  above a limit value ranging from 180° C. to 200° C. is detected; or   when a predetermined amount of time has elapsed since the burner  21  was turned on; or   in the case where the estimated energy supplied, for example, by means of the integral of the fuel flow rate exceeds a threshold value;   in the case where no passenger is detected to be present on board the motor vehicle for a predetermined amount of time by means of at least one recognition device housed in the passenger compartment (such as, for example, a sensor in a seat of the driver of the motor vehicle, or a sensor of the seat belt of the driver of the motor vehicle).       

     The condition b) may, on the other hand, occur in any of the following cases:
         b1) the burner  21  is turned on when the motor vehicle is a hybrid vehicle running in electric mode with the internal combustion engine  1  turned off;   b2) the burner  21  is turned on during the release phase with the open clutch; and   b3) the burner  21  is turned on during all the stopping phases of the motor vehicle; for example, the burner  21  is turned on during the stopping phases for a motor vehicle provided with the “Start and Stop” system, during parking manoeuvres of the motor vehicle, or even during the “after run” phase that allows the ventilation to be activated after the internal combustion engine  1  is turned off.       

     The burner  21  is then turned off in the case where any of the following conditions occur:
         c) the internal combustion engine  1  is turned on;   d) a predetermined amount of time has elapsed since the burner  21  was turned on; or   e) the adaptive strategy outlined in the following disclosure has been completed.       

     The strategy implemented by the electronic control unit ECU to operate the burner  21  is described below. 
     Firstly, the electronic control unit ECU is designed to calculate the thermal power P OBJ  required to reach the nominal operating temperature T CAT_OBJ  of the precatalytic converter  15  or the catalytic converter  17  and obtained with the objective value λ OBJ  of the air/fuel ratio. 
     To calculate the thermal power P OBJ , it should be considered that the objective is to heat the precatalytic converter  15  or the catalytic converter  17  from an initial temperature T 0  up to the nominal operating temperature T CAT_OBJ ; the heat Q CAT  required to allow this temperature increase may be calculated as follows:
 
 Q   CAT   =C   CAT   *M   CAT *( T   CAT_OBJ   −T   0 )
 
where C CAT  is the specific heat of the precatalytic converter  15  or the catalytic converter  17  and MCAT represents the mass of the precatalytic converter  15  or the catalytic converter  17  (in essence, the product C CAT *M CAT  represents the thermal capacity of the precatalytic converter  15  or the catalytic converter  17 ).
 
     In order to heat the precatalytic converter  15  or the catalytic converter  17  in an amount of time Δt and taking into account heat losses Q DISS  (by convection, gases leaving the catalytic converter, etc.), the thermal capacity P OBJ  required is therefore given by:
 
 P   OBJ =( Q   CAT   +Q   DISS )/Δ t  
 
The thermal power P t  released by the combustion in the burner  21  with an air flow {dot over (m)} A  and titer z may instead be calculated as follows:
 
 P   t   ={dot over (m)}   A /λ ST *[1/(MAX(1,λ)* H   i *η c −(1/MIN(λ,1)−1* H   v ]
 
where
         λ ST  is the stoichiometric air/fuel ratio;   λ is the combustion titer;   {dot over (m)} A  is the air mass flow rate;   H i  is the lower heating power of the fuel;   H v  is the latent heat of vaporization of the fuel; and   η c  is the combustion efficiency.       

     Therefore, once the combustion air/fuel ratio (or titer) λ is defined, the air flow rate {dot over (m)} A  required to heat the precatalytic converter  15  or the catalytic converter  17  from an initial temperature T 0  to the nominal operating temperature T CAT_OBJ  may be calculated, in the case where the internal combustion engine  1  is turned off, as follows:
 
 {dot over (m)}   A =( C   CAT   *M   CAT *( T   CAT_OBJ   −T   0 )+ Q   DISS )/Δ t )*λ ST /[1/(MAX(1,λ)* H   i *η c −(1/MIN(λ,1)−1)* H   v ]
 
In the case where the internal combustion engine  1  is turned on, the contribution due to the heat Q ENGINE  (positive if supplied or negative if subtracted) generated for the exchange of exhaust gases may be added as follows:
 
 {dot over (m)}   A =( C   CAT   *M   CAT *( T   CAT_OBJ   −T   0 )++ Q   DISS   −Q   ENGINE )/Δ t )*λ ST /[1/(MAX(1,λ)* H   i *η c −(1/MIN(λ,1)−1)* H   v ]
 
Depending on the thermal power P OBJ  required to reach the nominal operating temperature T CAT_OBJ  of the precatalytic converter  15  or of the catalytic converter  17 , the electronic control unit ECU determines both the objective air flow rate {dot over (m)} A_OBJ  and the nominal fuel flow rate {dot over (m)} F_N .
 
     According to a first variant, the pumping device  24  is regulated by controlling the number N of revolutions while the shut-off valve  26  is of the on/off type. 
     The electronic control unit ECU is then designed to determine the objective air flow rate {dot over (m)} A_OBJ  and the nominal fuel flow rate {dot over (m)} F_N , which are obtained by operating the pumping device  24 , the shut-off valve  26 , the pumping device  30  and the injector  27 . 
     According to what is illustrated schematically in  FIG.  4   , the objective air flow rate {dot over (m)} A_OBJ  is provided at input to a map (typically provided by the manufacturer of the pumping device  24 ) together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the nominal number N NOM  of revolutions with which to operate the pumping device  24 . 
     However, the actual number N of revolutions with which to operate the pumping device  24  is defined by the sum of the nominal number N NOM  of revolutions and two further contributions. 
     In particular, the nominal number N NOM  of revolutions with which to operate the pumping device  24  represents the open-loop contribution and is precisely generated using the experimentally derived control map; while the closed-loop contribution N CL  is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ OBJ  of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor  18 ,  18 *. 
     The third contribution N ADAT  is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     According to what is illustrated in  FIG.  6   , the third contribution N ADAT  with which to operate the pumping device  24  is then used to update the map used previously to determine the nominal number N NOM  of revolutions. In particular, the third contribution N ADAT  is provided at input to the map together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the updated value of the estimated air flow rate {dot over (m)} A . 
     In the case where the sum of the closed-loop contribution N CL  and of the third contribution N ADAT  is greater than a calibratable threshold value THR 1 , a breakdown or fault is diagnosed. 
     According to a second variant, the pumping device  24  is not regulated by controlling the number N of revolutions while the shut-off valve  26  is produced with the variable/adjustable passage section (in other words, the shut-off valve  26  is not of the on/off type). In this case, a pressure sensor  38  is also provided in the duct  25  downstream of the shut-off valve  26  to detect the pressure of the air being fed to the burner  21 . 
     The electronic control unit ECU is therefore designed to determine the objective air flow rate {dot over (m)} A_OBJ  and the nominal fuel flow rate {dot over (m)} F_N  that are obtained by operating the shut-off valve  26 , the pumping device  30  and the injector  27 . 
     According to what is illustrated schematically in  FIG.  7   , the objective air flow rate {dot over (m)} A_OBJ  is provided at input to a map (typically provided by the manufacturer of the shut-off valve  26 ) together with further quantities that comprise the pressure P A  and the temperature T A  of the air provided by the sensor  33  and the pressure P BURN  of the air being fed to the burner  21  provided by the sensor  38 . The map provides at output the nominal passage section ∝ NOM  with which to operate the shut-off valve  26 . 
     The actual passage section ∝ OBJ  with which to operate the shut-off valve  26  is, however, defined by the sum of the nominal passage section ∝ NOM  and two further contributions. 
     In particular, the nominal passage section ∝ NOM  with which to operate the shut-off valve  26  represents the open-loop contribution and is precisely generated using the experimentally derived control map. In the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air is less than or equal to a threshold value THR, the closed-loop contribution ∝ CL  is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ OBJ  of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor  18 ,  18 *. 
     The third contribution ∝ ADAT  is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)}F). 
     According to what is illustrated in  FIG.  8   , in the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air in the duct  25  is less than the threshold value THR, the third contribution ∝ ADAT  with which to operate the shut-off valve  26  is used to update the map used previously to determine the nominal passage section ∝ NOM  with which to operate the shut-off valve  26 . In particular, the third contribution ∝ ADAT  is provided at input to the map together with further quantities that comprise the pressure P BURN  of the air being fed to the burner  21 , the pressure P A  and the temperature T A  of the air in the duct  25 . The map provides at output the updated value of the air flow rate {dot over (m)} A_RPL . 
     In the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air in the duct  25  is greater than the threshold value THR, the value V BAT  is instead provided at input to the map together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the nominal value of the air flow rate {dot over (m)} A_NOM . 
     However, the air flow rate {dot over (m)} A_RPH  is defined by the sum of the nominal value of the air flow rate {dot over (m)} A_NOM  and two further contributions. 
     In particular, the nominal value of the air flow rate {dot over (m)} A_NOM  represents the open-loop contribution and is precisely generated using the experimentally derived control map. The closed-loop contribution {dot over (m)} A_CL  is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ OBJ  of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor  18 ,  18 *. 
     The third contribution {dot over (m)} A_ADAT  is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     In the case where the sum of the closed-loop contribution ∝ CL  and the third contribution ∝ ADAT  is greater than a calibratable threshold value THR 2 , a breakdown or fault is diagnosed. 
     In the case where the sum of the closed-loop contribution {dot over (m)} A_CL  and the third contribution {dot over (m)} A_ADAT  is greater than a calibratable threshold value THR 3 , a breakdown or fault is diagnosed. 
     According to a third variant, the pumping device  24  is regulated by controlling the number N of revolutions while the shut-off valve  26  is produced with the variable/adjustable passage section (in other words, the shut-off valve  26  is not of the on/off type). Also in this case, the pressure sensor  38  is provided in the duct  25  downstream of the shut-off valve  26  to detect the pressure P BURN  of the air being fed to the burner  21 . 
     The electronic control unit ECU is therefore designed to determine the objective air flow rate {dot over (m)} A_OBJ  and the nominal fuel flow rate {dot over (m)} F_N  that are obtained by operating the pumping device  24 , the shut-off valve  26 , the pumping device  30  and the injector  27 . 
     According to what is illustrated schematically in  FIG.  9   , the objective air flow rate {dot over (m)} A_OBJ  is provided at input to a map (typically provided by the manufacturer of the shut-off valve  26 ) together with further quantities that comprise the pressure P A  and the temperature T A  of the air provided by the sensor  33  and the pressure P BURN  of the air being fed to the burner  21  provided by the sensor  38 . The map provides at output the nominal passage section ∝ NOM  with which to operate the shut-off valve  26 . 
     The actual passage section ∝ OBJ  with which to operate the shut-off valve  26  is, however, defined by the sum of the nominal passage section ∝ NOM  and any two further contributions. 
     In particular, the nominal passage section ∝ NOM  with which to operate the shut-off valve  26  represents the open-loop contribution and is precisely generated using the experimentally derived control map. In the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air is less than a threshold value THR, the closed-loop contribution ∝ CL  is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ OBJ  of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor  18 ,  18 *. 
     The third contribution ∝ ADAT  is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     In addition, the objective air flow rate {dot over (m)} A_OBJ  is also provided at input to a map (typically provided by the manufacturer of the pumping device  24 ) together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the objective air pressure P A_OBJ  in the duct  25  (which is determined depending on the objective air flow rate {dot over (m)} A_OBJ  and on the pressure P BURN  of the air being fed to the burner  21 ). The map provides at output the nominal number N NOM  of revolutions with which to operate the pumping device  24 . 
     The actual number N of revolutions with which to operate the pumping device  24  is, however, defined by the sum of the nominal number N NOM  of revolutions and any three further contributions. 
     In particular, the nominal number N NOM  of revolutions with which to operate the pumping device  24  represents the open-loop contribution and is precisely generated using the experimentally derived control map. The closed-loop contribution N CL1  is provided by means of a PID 1  controller which tries to zero an error in the air pressure, namely, a difference between the objective air pressure P A_OBJ  in the duct  25  (which is determined depending on the objective air flow rate {dot over (m)} A_OBJ  and on the pressure P BURN  of the air being fed to the burner  21 ) and the actual pressure value P A  of the air measured by the sensor  33 . 
     In addition, in the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air is greater than a threshold value THR, a further closed-loop contribution N CL2  is provided by means of a PID 2  controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ OBJ  of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor  18 ,  18 *. 
     The third contribution N ADAT  is also determined depending on the sum of the integral action of the PID 1  controller and of the PID 2  controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     In other words, regulation of the air flow rate {dot over (m)} A  is controlled depending on the ratio between the pressure P BURN  of the air being fed to the burner  21  (downstream of the shut-off valve  26 ) and on the pressure P A  of the air (upstream of the shut-off valve  26 ). When the said ratio is less than the threshold value THR, to control the air flow rate {dot over (m)} A , the opening of the shut-off valve  26  is operated; since said ratio is greater than the threshold value THR, to control the air flow rate {dot over (m)} A , the pumping device  24  is operated and the shut-off valve  26  is substantially fully open. 
     According to what is illustrated in  FIG.  10   , in the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air in the duct  25  is greater than the threshold value THR, the third contribution N ADAT  with which to operate the pumping device  24  is used to update the map used previously to determine the nominal number N NOM  of revolutions. In particular, the third contribution N ADAT  is provided at input to the map together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the updated value of the air flow rate {dot over (m)} A_RPH . 
     On the other hand, in the case where the ratio between the pressure P BURN  of the air being fed to the burner  21  and the pressure P A  of the air in the duct  25  is less than the threshold value THR, the third contribution ∝ ADAT  with which to operate the shut-off valve  26  is used to update the map used previously to determine the nominal passage section ∝ NOM  with which to operate the shut-off valve  26 . In particular, the third contribution ∝ ADAT  is provided at input to the map together with further quantities that comprise the pressure P BURN  of the air being fed to the burner  21 , the pressure P A  and the temperature T A  of the air in the duct  25 . The map provides at output the updated value of the air flow rate {dot over (m)} A_RPL . 
     In the case where the sum of the closed-loop contribution N CL  and the third contribution N ADAT  is greater than a calibratable threshold value THR 1 , a breakdown or fault is diagnosed. 
     In the case where the sum of the closed-loop contribution ∝ CL  and the third contribution ∝ ADAT  is greater than a calibratable threshold value THR 2 , a breakdown or fault is diagnosed. 
     According to a fourth variant schematically illustrated in  FIG.  13   , the pumping device  24  is regulated by controlling the number N of revolutions while the shut-off valve  26  is of the on/off type. 
     The electronic control unit ECU is designed to determine the objective air flow rate {dot over (m)} A_OBJ  and the nominal fuel flow rate {dot over (m)} F_N  that are obtained by operating the pumping device  24 , the pumping device  30  and the injector  27 . 
     According to what is illustrated schematically in  FIG.  11   , the objective air flow rate {dot over (m)} A_OBJ  is also provided at input to a map (typically provided by the manufacturer of the pumping device  24 ) together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the nominal number N NOM  of revolutions with which to operate the pumping device  24 . 
     The actual number N of revolutions with which to operate the pumping device  24  is, however, defined by the sum of the nominal number N NOM  of revolutions and two further contributions. 
     In particular, the nominal number N NOM  of revolutions with which to operate the pumping device  24  represents the open-loop contribution and is precisely generated using the experimentally derived control map; while the closed-loop contribution N CL  is provided by means of a PID controller which tries to zero an error in the air flow rate, namely, a difference between the objective air flow rate {dot over (m)} A_OBJ  and the air flow rate {dot over (m)} A . 
     In addition, according to what is illustrated in  FIG.  13   , the air flow rate {dot over (m)} A  is calculated by subtracting the total air flow rate {dot over (m)} TOT  detected by the mass air flow sensor  9  from the air flow rate {dot over (m)} ICE  fed to the internal combustion engine  1 . The air flow rate {dot over (m)} ICE  fed to the internal combustion engine  1  is determined, for example, by the method to determine the mass of air trapped in each cylinder of an internal combustion engine described in the patent applications EP3650678 and EP3739192A, which are incorporated herein for reference. 
     The third contribution N ADAT  is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     According to what is illustrated in  FIG.  12   , the third contribution N ADAT  with which to operate the pumping device  24  is then used to update the map used previously to determine the nominal number N NOM  of revolutions. In particular, the difference between the actual number N of revolutions with which to operate the pumping device  24  and the third contribution N ADAT  is provided at input to the map together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the updated value of the air flow rate {dot over (m)} A . 
     In the case where the sum of the closed-loop contribution N CL  and the third contribution N ADAT  is greater than a calibratable threshold value THR 1 , a breakdown or fault is diagnosed. 
     According to a fifth and final variant illustrated schematically in  FIG.  14   , the pumping device  24  is regulated by controlling the number N of revolutions while the shut-off valve  26  is of the on/off type. A mass air flow sensor  39  (better known as Air Flow Meter) is also arranged along the duct  25 , interposed between the pumping device  24  and the shut-off valve  26 . 
     According to a further embodiment (not illustrated), the mass air flow sensor is arranged along the duct  25  upstream of the pumping device  24 . 
     The electronic control unit ECU is therefore designed to determine the objective air flow rate {dot over (m)} A_OBJ  and the nominal fuel flow rate {dot over (m)} F_N  that are obtained by operating the pumping device  24 , the pumping device  30  and the injector  27 . 
     According to what is illustrated schematically in  FIG.  11   , the objective air flow rate {dot over (m)} A_OBJ  is also provided at input to a map (typically provided by the manufacturer of the pumping device  24 ) together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the nominal number N NOM  of revolutions with which to operate the pumping device  24 . 
     The actual number N of revolutions with which to operate the pumping device  24  is, however, defined by the sum of the nominal number N NOM  of revolutions and two further contributions. 
     In particular, the nominal number N NOM  of revolutions with which to operate the pumping device  24  represents the open-loop contribution and is precisely generated using the experimentally derived control map; while the closed-loop contribution N CL  is provided by means of a PID controller which tries to zero an error in the air flow rate, namely, a difference between the objective air flow rate {dot over (m)} A_OBJ  and the air flow rate {dot over (m)} A  detected by the mass air flow sensor  39 . 
     The third contribution N ADAT  is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     According to what is illustrated in  FIG.  12   , the third contribution N ADAT  with which to operate the pumping device  24  is then used to update the map used previously to determine the nominal number N NOM  of revolutions. In particular, the third contribution N ADAT  is provided at input to the map together with further quantities that comprise the ambient pressure P ATM  and the ambient temperature T ATM  provided by the sensor  37  and the pressure P A  of the air in the duct  25  provided by the sensor  33 . The map provides at output the updated value of the air flow rate {dot over (m)} A . 
     In the case where the sum of the closed-loop contribution N CL  and the third contribution N ADAT  is greater than a calibratable threshold value THR 1 , a breakdown or fault is diagnosed. 
     According to what is schematically illustrated in  FIG.  5   , once the electronic control unit ECU has determined the actual number N of revolutions with which to operate the pumping device  24  to obtain the objective air flow rate {dot over (m)} A_OBJ , the nominal fuel flow rate {dot over (m)} F_N  is calculated. 
     The nominal fuel flow rate {dot over (m)} F_N  is determined by the following formula: 
     
       
         
           
             
               
                 m 
                 . 
               
               
                 FUEL 
                 - 
                 N 
               
             
             = 
             
               
                 
                   m 
                   . 
                 
                 A 
               
               
                 ( 
                 
                   
                     A 
                     
                       F 
                       STEC 
                     
                   
                   * 
                   
                     λ 
                     OBJ 
                   
                 
                 ) 
               
             
           
         
       
         
         
           
             {dot over (m)} FUEL-N  nominal fuel flow rate 
             {dot over (m)} A  estimated air flow rate 
             A/F STEC  stoichiometric air and fuel ratio 
             λ OBJ  desired/objective value of the air/fuel ratio. 
           
         
       
    
     The estimated air flow rate {dot over (m)} A  is determined according to the method illustrated in  FIG.  6    and described in the preceding disclosure. 
     The objective fuel flow rate {dot over (m)} F_OBJ  is, however, defined by the sum of the nominal fuel flow rate {dot over (m)} F_N  and two further contributions. 
     In particular, the nominal fuel flow rate {dot over (m)} F_N  represents the open-loop contribution and is precisely generated using the formula described previously; while the closed-loop contribution {dot over (m)} F_CL  of the fuel flow rate is provided by a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ OBJ  of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor  18 ,  18 *. 
     The third contribution {dot over (m)} F_ADAT  of the fuel flow rate is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)} A  and fuel flow rate {dot over (m)} F ). 
     In the case where the sum of the closed-loop contribution {dot over (m)} F_CL  and the third contribution {dot over (m)} F_ADAT  is greater than a calibratable threshold value THR 4 , a breakdown or fault is diagnosed. 
     In the case of a fault of the mass air flow sensor  9  or  39 , the air flow rate {dot over (m)} A  is calculated by means of a map depending on the ambient pressure P ATM , on the ambient temperature T ATM  and on the pressure P A  of the air entering the burner  21 , the actual number N of revolutions with which to operate the pumping device  24 , and the further adaptive contribution N ADAT  of the number of revolutions with which to operate the pumping device  24 . 
     It is clear that the strategies described in the previous disclosure to control and adapt the objective fuel flow rate {dot over (m)} F_OBJ  and the air flow rate {dot over (m)} A  may be used with any layout of the exhaust system  2  (regardless of the position of the linear oxygen sensor  18 ,  18 *). 
     It is also clear that the previous disclosure may also find advantageous application in the case where the linear oxygen sensor  18 ,  18 *,  18 ** is replaced by a lambda sensor suited to provide a binary on/off type output (indicating whether the exhaust gases titer is above or below the stoichiometric value). 
     In particular, the strategies described in the previous disclosure may also find advantageous application in the case of a linear oxygen sensor  18 ** housed along the outlet duct  35 . 
     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  mass air flow sensor 
           10  exhaust duct 
           11  turbocompressor 
           12  turbine 
           13  compressor 
           14  after-treatment system 
           15  precatalytic converter 
           16  particulate filter 
           17  catalytic converter 
           18  UEHO linear sensor or HEGO switching 
           19  lambda sensor 
           20  lambda sensor 
           21  burner 
           22  combustion chamber 
           23  air feeding circuit 
           24  pumping device 
           25  duct 
           26  shut-off valve 
           27  injector 
           28  spark plug 
           29  fuel feeding circuit 
           30  pumping device 
           31  duct 
           32  control system 
           33  sensor P, T 
           34  sensor P, T 
           35  outlet duct* 
           36  sensor P, T 
           37  sensor P, T 
           38  pressure sensor* 
           39  mass air flow sensor