Patent Publication Number: US-2023137631-A1

Title: Method For The Diagnosis Of An Air Supply Circuit Supplying Air To A Burner Of An Exhaust Gas After-Treatment System 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. 102021000027893 filed on Oct. 29, 2021, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL SECTOR 
     The invention relates to a method for the diagnosis of an air supply circuit supplying air to a burner of an exhaust gas after-treatment system for an exhaust system of an internal combustion engine. 
     BACKGROUND ART 
     An internal combustion engine is typically provided with a number of cylinders, each connected to an intake manifold and to an exhaust manifold, to which an exhaust duct is connected in order to supply the exhaust gases produced by the combustion to an exhaust system, which releases the exhaust gases produced by the combustion into the atmosphere. 
     An exhaust gas after-treatment system usually comprises a pre-catalytic converter, which is arranged along the exhaust duct; a particulate filter, which is also arranged along the exhaust duct, downstream of the pre-catalytic converter; and a catalytic converter, which is arranged along the exhaust duct, upstream of the particulate filter. 
     The exhaust gas after-treatment system finally comprises, in addition, a burner. Inside the burner there is defined a combustion chamber, which receives fresh air from an air supply circuit and receives fuel from an injector, which is suited to inject fuel into the combustion chamber. Furthermore, a spark plug is coupled to the burner in order to ignite the mixture present inside the combustion chamber. The air supply circuit is typically provided with a pumping device, which draws from a tank, preferably with the interposition of an air filtering element, and supplies air to the burner by means of a duct adjusted by a shut-off valve. 
     The burner is suited to introduce exhaust gases (and, as a consequence, heat) into the exhaust duct in order to speed up the heating of the catalytic converter and so as to facilitate the regeneration of the particulate filter. In order to be able to control the combustion taking place inside the combustion chamber (and, as a consequence, the exhaust gases produced), it is extremely important that the quantity of air introduced by the air supply circuit can be controlled and that possible faults of the components, such as for example the pumping member or the adjustment valve, can promptly be recognized. 
     Document DE102010060136 discloses a method to control an air supply circuit supplying air to a burner of an exhaust gas after-treatment system for an exhaust system of an internal combustion engine. The supply circuit comprises a de Laval nozzle designed to keep the quantity of air supplied to the burner constant, regardless of the pressure variations that can occur in an exhaust duct of the exhaust system. 
     DESCRIPTION OF THE INVENTION 
     The object of the invention is to provide a method for the diagnosis of an air supply circuit supplying air to a burner of an exhaust gas after-treatment system for an exhaust system of an internal combustion engine, which does not suffer from the drawbacks described above and, in particular, is easy and economical to be implemented. 
     According to the invention there is provided a method for the diagnosis of an air supply circuit supplying air to a burner of an exhaust gas after-treatment system for an exhaust system of an internal combustion engine according to the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings showing a non-limiting embodiment thereof, wherein: 
         FIG.  1    schematically shows an internal combustion engine provided with an exhaust gas after-treatment system provided with a control unit implementing the diagnosis method according to the invention; 
         FIG.  2    schematically shows a detail of the exhaust gas after-treatment system shown in  FIG.  1   ; and 
         FIG.  3    is a block diagram showing the diagnosis method according to the invention. 
     
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     In  FIG.  1   , number  1  indicates as a whole a supercharged internal combustion engine provided with an exhaust system  2  (not shown) and having a number of cylinders  3 , each connected to an intake manifold  4  and to an exhaust manifold  5  by means of at least one respective exhaust valve (not shown). 
     The intake manifold  4  receives a gas mixture comprising both exhaust gases and fresh air, i.e. air coming from the outside through an intake duct  6 , which is provided with an air filter for the fresh air flow and is adjusted by a throttle valve  8 . Along the intake duct  6 , downstream of the air filter  7 , there also is an air flow meter  9 . 
     The exhaust manifold  5  is connected to an exhaust duct  10 , which supplies the exhaust gases produced by the combustion to the exhaust system  2 , which releases the gases produced by the combustion into the atmosphere. 
     The supercharged internal combustion engine  1  comprises supercharging system for the internal combustion engine  1  obtained by means of a turbocharger  11  provided with a turbine  12 , which is arranged along the exhaust duct  10  so as to rotate at a high speed due to 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  so as to be caused to rotate by the turbine  12  itself in order to increase the pressure of the air present in the supply duct  6 . 
     The exhaust system  2  is provided with an exhaust gas after-treatment system  14  comprising a pre-catalytic converter  15  arranged along the exhaust duct  10 , downstream of the turbocharger  11 , and a particulate filter  16  (also known as Gasoline Particulate Filter) also arranged along the exhaust duct  10 , downstream of the pre-catalytic converter  15 . According to a preferred variant, the exhaust gas 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 on the inside of a common tubular container. 
     According to a first variant, the internal combustion engine  1  is further provided with a UHEGO or UEGO linear oxygen sensor  18  housed along the exhaust duct  10  and interposed between the turbocharger  11  and the pre-catalytic converter  15  to detect the air/fuel ratio of the exhaust gases (providing a liner output that indicates the content of oxygen in the exhaust gases) downstream of the turbocharger  11  and upstream of the pre-catalytic converter  15 . 
     The internal combustion engine is further provided with a lambda sensor  19 , which is suited to provide an on/off binary output, which indicates whether the air/fuel ratio of the exhaust gases is higher or lower than the stoichiometric value, is housed along the exhaust duct  10  and is interposed between the pre-catalytic converter  15  and the assembly defined by the catalytic converter  17  and the particular filter  16  in order to detect the concentration of oxygen in the exhaust gases downstream of the pre-catalytic converter  15 ; and, finally, a lambda sensor  20 , which is suited to provide an on/off binary output, which indicates whether the air/fuel ratio of the exhaust gases is higher or lower than the stoichiometric value, is housed along the exhaust duct  10  and is arranged downstream of the assembly defined by the catalytic converter  17  and the particular filter  16  in order to detect the concentration of oxygen in the exhaust gases downstream of the assembly defined by the catalytic converter  17  and the particular filter  16 . 
     The exhaust gas after-treatment system  14  further comprises a burner  21 , which is suited to introduce exhaust gases (and, as a consequence, heat) into the exhaust duct  10  in order to speed up the heating of the pre-catalytic converter  15  and/or of the catalytic converter  17  and so as to facilitate the regeneration of the particulate filter  16 . The burner  21  is arranged so as to introduce exhaust gases into the exhaust duct  10  upstream of the pre-catalytic converter  15  or downstream of the catalytic converter  17 . 
     According to  FIG.  2   , inside the burner  21  there is defined a combustion chamber  22 , which receives fresh air (i.e. air coming from the outside) through an air supply circuit  23 , which is provided with a pumping device  24  (of the known kind and not described in detail) pumping from a tank  39 , preferably with the interposition of an air filtering element, and supplies air to the burner  21  by means of a duct  25  adjusted by a shut-off valve  26  (arranged downstream of the pumping device  24 ). 
     The combustion chamber  22  further receives fuel from an injector  27 , which is suited to inject fuel into the combustion chamber  22 . Furthermore, a spark plug  28  is coupled to the burner  21  in order to ignite the mixture present inside the combustion chamber  22 . The internal combustion engine  1  also comprises a fuel supply circuit  29  provided with a pumping device  30 , which supplies fuel by means of a duct  31 , which is adjusted by a valve  38 . 
     The internal combustion engine  1  finally comprises a control system  32 , which is designed to control the operation of the internal combustion engine  1 . The control system  32  comprises at least one electronic control unit (also known as “ECU”), which controls the operation of the different components of the internal combustion engine  1 . It is evident that the electronic control unit ECU disclosed in the description above can be a dedicated control unit ECU, which controls the operation of the burner  21 , or can be the electronic control unit ECU controlling the operation of the internal combustion engine  1 . The spark plug  28  is controlled by the electronic control unit ECU so as to generate a spark between its electrodes, thus determining the ignition of the gases compressed inside the combustion chamber  22 . The control system  32  further comprises a plurality of sensors connected to the electronic control unit ECU. 
     The sensors comprise, in particular, a temperature and pressure sensor  33  for the air flow supplied to the burner  21 , which is preferably housed along the duct  25  (in other words, the sensor  33  is housed along the duct  25  downstream of the pumping device  24 , preferably interposed between the pumping device  24  and the shut-off valve  26 ); a temperature and pressure sensor  34  for the exhaust gases flowing out of the burner  21 , which is housed along an outlet duct  35 ; a pressure sensor  36  for the fuel supplied to the burner  21 , which is housed along the duct  31 . The electronic control unit ECU is further connected to the UHEGO or UEGO linear oxygen sensor  18  and to the lambda sensors  19 ,  20 , from which it receives signals indicative of the air/fuel ratio of the exhaust gases. 
     The method implemented by the electronic control unit ECU in order to carry out a diagnosis of the correct operation of the air supply circuit  23  will be described below. Said method is at least partially and schematically shown in  FIG.  3   . 
     First of all, the electronic control unit ECU is designed to determine the target value P TARGET  of the pressure downstream of the pumping device ( 24 ). 
     According to a preferred variant, the target value P TARGET  of the pressure downstream of the pumping device  24  is determined through a calculation model, which processes a plurality of quantities, such as atmospheric pressure P ATM , the pressure signal P 34  detected by the pressure sensor  34  out of the burner  21  along the outlet duct  35  and the target flow rate {dot over (m)} T  through the supply circuit  23 , in order to determine the target value P TARGET  of the pressure downstream of the pumping device  24 . 
     Then, the electronic control unit ECU is configured to acquire, by means of the sensor  33 , the value P 33  of the pressure of the air flow supplied to the burner  21  along the duct  25  and to calculate the deviation ΔP 1  between the target value P TARGET  of the pressure downstream of the pumping device  24  and the value P 33  of the pressure of the air flow supplied to the burner  21  along the duct  25 . 
     In a preliminary adjustment and set up phase, a safety limit value TV 1  is determined. 
     Finally, the electronic control unit ECU is configured to compare the deviation ΔP 1  between the target value P TARGET  of the pressure downstream of the pumping device  24  and the value P 33  of the pressure of the air flow supplied to the burner  21  along the duct  25  with the safety limit value TV 1  and to recognize a fault F, based on which an alarm signal F is sent in case said deviation ΔP 1  is greater than the safety limit value TV 1 . 
     In this case, possible faults and/or malfunctions of the pumping device  24  can be recognized, possible spills or leaks in the segment of the duct  25  from the pumping device  24  to the shut-off valve  26  can also be recognized and, finally, one can recognize when the shut-off valve  26  is locked in the open position. 
     In other words, a greater deviation ΔP 1  than the safety limit value TV 1  can indicate a fault of the pumping device  24  or a leak in the segment of the duct  25  from the pumping device  24  to the shut-off valve  26  or that the shut-off valve  26  is locked in the open position (or a combination of the aforesaid faults). 
     The control strategy described above can be actuated only in case a few enabling conditions occur. More in detail the electronic control unit ECU s configured to check whether the pumping device  24  is working and whether the shut-off valve  26  is closed or open depending on the target (opening or closing) requested to the shut-off valve  26 , which, in turn, is determined based on the target value P TARGET  of the pressure downstream of the pumping device  24 . 
     Then, the electronic control unit ECU is designed to determine the target value P TARGET_BURNER  of the pressure downstream of the burner  21 . 
     According to a preferred embodiment, the target value P TARGET_BURNER  of the pressure downstream of the burner  21  is determined through a calculation model or a map stored in the electronic control unit ECU. In particular, the target value P TARGET_BURNER  of the pressure downstream of the burner  21  is determined starting from the value P 33  of the pressure upstream of the burner  21  detected by the sensor  33  and taking into account a variable flow resistance PD depending on the target air flow rate through the air supply circuit  23 . 
     Then, the electronic control unit ECU is configured to acquire, by means of the sensor  34 , the pressure value P 34  detected out of the burner  21  along the outlet duct  35  and to calculate the deviation ΔP 2  between the target value P TARGET_BURNER  of the pressure downstream of the burner  21  and the pressure value P 34  detected by sensor  34  out of the burner  21  along the outlet duct  35 . 
     In a preliminary adjustment and set up phase, a safety limit value TV 2  is determined. 
     Finally, the electronic control unit ECU is configured to compare the deviation ΔP 2  between the target value P TARGET_BURNER  of the pressure downstream of the burner  21  and the pressure value P 34  detected by sensor  34  out of the burner  21  along the outlet duct  35  with the safety limit value TV 2  and to recognize a fault and/or malfunction F, based on which an alarm signal F is sent in case said deviation ΔP 2  is greater than the safety limit value TV 2 . 
     In this case, possible spills or leaks in the segment of the duct  25  from the shut-off valve  26  to the exhaust duct  10  can be recognized and one can recognize when the shut-off valve  26  is locked in the closed position. 
     In other words, a greater deviation ΔP 2  than the safety limit value TV 2  can indicate a leak in the segment of the duct  25  from the shut-off valve  26  to the exhaust duct  10  or that the shut-off valve  26  is locked in the closed position (or a combination of the two faults mentioned above). 
     In this case, again, the control strategy described above can be actuated only in case a few enabling conditions occur. More in detail, the electronic control unit ECU is configured to check whether the pumping device  24  is working and whether the shut-off valve  26  is open. 
     As it is known, the pumping device  24  is provided with an actuator device. During the normal operation, the electronic control unit ECU controls the actuator device with a command characterized by a frequency and a control amplitude that are variable in time. Therefore, considering that the pumping device  24  is supplied with an oscillating command characterized by a frequency and a control amplitude that are variable in time, the Applicant found out that the pressure values downstream and upstream of the burner  21  (detected by means of the sensors  33  and  34 ) have a development that is similar to the development of the control command of the pumping device  24 . In other words, the Applicant found out that the frequency content of the pressure signals acquired by the pressure sensors  33  and  34  have a development that is similar to the development of the control command of the pumping device  24  (namely, an oscillating development which is characterized by a frequency and a control amplitude that are variable in time and is similar to the development of the control command of the pumping device  24 ). 
     Hence, according to a further embodiment, the electronic control unit ECU is designed to analyse the frequency content of the signals acquired by the pressure sensors  33  and  34 . 
     More in detail, the frequency content of the signal acquired by the pressure sensor  33  is compared with an expected development, which is determined based on the development of the control command of the pumping device  24 . In case the deviation of the frequency content of the signal acquired by the pressure sensor  33  from the expected development is greater than a safety value, a possible fault and/or malfunction F of the pumping device  24  is recognized or a leak in the segment of the duct  25  from the pumping device  24  to the shut-off valve  26  is recognized. 
     In other words, a deviation of the frequency content of the signal acquired by the pressure sensor  33  from the expected development that is greater than a safety value indicates a fault and/or malfunction F of the pumping device  24  or a leak in the segment of the duct  25  from the pumping device  24  to the shut-off valve  26  (or a combination of the two faults mentioned above). 
     Furthermore, the frequency content of the signal acquired by the pressure sensor  34  is also compared with an expected development, which is determined based on the development of the control command of the pumping device  24 . In case the deviation of the frequency content of the signal acquired by the pressure sensor  34  from the expected development is greater than a safety value, a leak in the segment of the duct  25  from the shut-off valve  26  to the exhaust duct  10  is recognized. 
     If, on the other hand, the signal acquired by the pressure sensor  34  has a substantially constant development and, at the same time, the deviation of the frequency content of the signal acquired by the pressure sensor  33  from the expected development is smaller than or equal to the safety value, a fault of the shut-off valve  26 , which is stuck in the closed position, is diagnosed. 
     It is evident that the further embodiment that was just described can be operated alternatively to the first embodiment or in combination with it. In this last case, the embodiment that was just described is used by the electronic control unit ECU to check and validate the diagnosis made with the first embodiment concerning the operation of the shut-off valve  26  and of the pumping member  24  or possible leaks in the duct  25  and vice versa. 
     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  pre-catalytic converter
 
 16  particulate filter
 
 17  catalytic converter
 
 18  linear sensor
 
 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
 
 32  control system
 
 33  P, T sensor
 
 34  P, T sensor
 
 35  outlet duct
 
 36  P, T sensor
 
 38  valve
 
 39  air tank
 
ECU electronic control unit
 
P TARGET  target pressure value
 
P 33 , P 34  pressure value detected by the sensor  33 ,  34 
 
{dot over (m)} T  target air flow rate
 
ΔP 1 , ΔP 2  deviation
 
TV 1 , TV 2  safety limit value
 
P TARGET_BURNER  target pressure value
 
PD flow resistance