Abstract:
A combustion engine evaluation unit is provided that includes, but is not limited to a microcontroller receiving measurement signals from a gas flow control system and outputting a state signal of the gas flow control system. The microcontroller includes, but is not limited to input ports for receiving as first set of measurement signals. Furthermore, the microcontroller includes, but not limited to input ports for receiving as a second set of measurement signals. The microcontroller is configured to calculate a first set of predicted values with a gas flow model based on the first set of measurement signals and calculate a second set of predicted values with a nominal model based on the second set of measurement signals. The microcontroller is also configured to generate the state signal based on a comparison of the first set of predicted values with the second set of predicted values.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to British Patent Application No. 1016727.8, filed Oct. 5, 2010, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field is related to gas flow control and more particularly to a system for diagnosing error conditions of a gas flow control system for a diesel engine. 
       BACKGROUND 
       [0003]    Since the 1990s, the common rail system or storage injection system has been introduced for diesel engines of passenger cars. The use of a common rail injection is, however, not limited to passenger cars, but it also includes heavy duty diesel engines, for example ship engines. A common rail injection uses common high pressure storage with corresponding outlets to supply the cylinders with fuel. The common rail injection optimizes the combustion process and the engine run and reduces the emission of particles. Due to the very high pressure of up to 2000 bar, the fuel is atomized very finely. Since small fuel drops have a high surface area, the combustion process is accelerated and the particle size of emission particles is decreased. Moreover, the separation of the pressure generation and the injection process allows for an injection process that is electronically controlled by using characteristic maps in a control unit, such as an engine control unit (ECU). The ECU may also be used to monitor the functionality of air handling control mechanisms for faults or failures that may occur during operation thereof. Error detection has been made mandatory in US and EU on-board diagnosis requirements. 
         [0004]    The common rail injection system may be combined with a turbocharger to provide more driving comfort, especially for diesel engines in passenger cars. However, when combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). These emissions increase when a turbocharger is used to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen in the combustion chamber when temperatures are high during or after the combustion event. 
         [0005]    One known technique for reducing unwanted emissions like NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. Thereby, the oxygen concentration in the combustion mixture is reduced, the fuel burns slower and peak combustion temperatures are accordingly reduced and the production of NOx is reduced. One way of introducing chemically inert gases is through the use of a so-called Exhaust Gas Recirculation (EGR) system. EGR operation is typically not required under all engine operating conditions, and known EGR systems accordingly include a valve, commonly referred to as an EGR valve, for controlled introduction of exhaust gas to the intake manifold. Through the use of an on-board microcontroller, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors. To achieve exhaust gas recycling, high pressure and low pressure EGR systems are used alone or in combination. 
         [0006]    In addition to an EGR valve, air handling systems for modern turbocharged internal combustion engines are known to include one or more supplemental or alternate air handling control mechanisms for modifying the swallowing capacity and/or efficiency of the turbocharger. For example, the air handling system may include a waste gate disposed between an inlet and outlet of the turbocharger turbine to selectively route exhaust gas around the turbine and thereby control the swallowing capacity of the turbocharger. Alternatively or additionally, the system may comprise an exhaust throttle disposed in line with the exhaust conduit either upstream or downstream of the turbocharger turbine to control the effective flow area of the exhaust is throttle and thereby the efficiency of the turbocharger. 
         [0007]    The turbocharger may also comprise a variable geometry turbine, which is used to control the swallowing capacity of the turbocharger by controlling the geometry of the turbine. By using a variable nozzle ring geometry, the turbocharger operating envelope and performance can be changed during operation to optimize the engine performance for certain conditions. This type of turbochargers is useful e.g. in lean burn gas engines, where combustion is sensitive to gas quality and air temperature variations. VTG technology can also be used for heavy diesel engines, such as train and ship engines. However, the operating conditions of a turbocharger on a heavy fuel engine are rather demanding and VTG technology is, at least today, not commonly used for heavy fuel engines. 
         [0008]    It is at least one object to provide an improved fault diagnostic for a gas flow control system of a turbocharged engine for a passenger car, especially of a common rail turbo diesel engine. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0009]    A combustion engine evaluation unit is provided that comprises a microcontroller for receiving measurement signals from a gas flow control system of a combustion engine and for outputting a state signal indicating a state of the gas flow control system. The microcontroller comprising input ports for receiving a first set of measurement signals that comprises at least an intake pressure downstream of a high pressure exhaust gas recirculation valve, an intake temperature downstream of a high pressure exhaust gas recirculation valve and an intake air flow rate downstream of an air filter. Furthermore, the microcontroller also comprises input ports for receiving for second set of measurement signals which comprises at least a motor revolution speed and a flap valve position signal. The flap valve position signal may be provided by a flap valve control signal or also by a position sensor at the flap valve. Flap valves are useful for controlling the motion of intake gas into cylinders of the engine. It is advantageous to observe the air mass flow to detect leakages and/or constrictions in the air flow path. In order to accurately determine the gas flow rates, it is advantageous to use the position of flap valves according to the application as an input for a fault detection system which is based on computations of air mass flows according to the application. The microcontroller is furthermore adapted to calculate a first set of predicted values by using a gas flow model, based on the first set of measurement signals and to calculate a second set of predicted values by using a nominal model, based on the second set of measurement signals. 
         [0010]    The comparison of the first set of predicted values with the second set of predicted values may be provided by at least one differentiator which is technically easy to realize. Advantageously, one differentiator is provided for each predicted value of the nominal model. More specifically, a residual generation unit with differentiators is provided for the comparison of the first set of predicted values and the second set of predicted values and the differentiators are adapted to generate residuals by subtracting values of the second set of predicted values from corresponding values of the second set of predicted values with the differentiators. The use of differentiators instead of more complicated units is an advantage of the present application. However, the comparison of predicted values may also be provided by at least one correlator that provides a statistical correlation. 
         [0011]    The nominal model may be provided by a nominal model unit which comprises an interpolation unit. More specifically, the interpolation unit may be provided by a realization of a semi-physical model, a neuronal network, a local linear model tree model, abbreviated as LOLIMOT or as LLM, or another empirical model. Specifically, the interpolations may be based on values of a look up table which is pre-computed based on the aforementioned models during a calibration procedure. 
         [0012]    The microcontroller is furthermore adapted to generate the state signal based on a comparison of the first set of predicted values with the second set of predicted values. The state signal indicates whether an error condition is present and may take on “yes/no” values or even probabilities. 
         [0013]    A gas flow control system provides a reliable identification of faulty components. The indication of faulty parts according to the application helps to avoid pollution and safety hazards that result from driving with faulty components and extends the lifetime of mechanical parts through timely exchange of the faulty components. Furthermore, a gas flow control system according to the application assists the service personnel in quickly identifying the cause of a malfunction. Apart from identifying error conditions, the gas flow control system can also be used to adjust the engine control, such as the control of the fuel injection or of the valve openings, in order to maintain the function even in the case of degrading performance of mechanical parts. 
         [0014]    According to an embodiment, the residual generation unit is adapted to generate an air efficiency residual from the first set of measurement signals and the second set of measurement signals. In a more specific realization, the air efficiency residual is based on a difference of a first predicted air efficiency from the first set of predicted values and a second predicted air efficiency from the second set of predicted values and the second predicted air efficiency is based on a lookup table value that depends on the engine speed, the intake pressure and the flap valve control or, respectively, position signal. 
         [0015]    According to another embodiment, the residual generation unit is adapted to generate an air flow oscillation amplitude residual form the first set of measurement signals and the second set of measurement signals. In a more specific realization, the second set of measurement values comprises an EGR valve position and the air flow oscillation amplitude residual is based on a difference of a first predicted air flow oscillation amplitude from the first set of predicted values and a second predicted air flow oscillation amplitude from the second set of predicted values. Moreover, the second predicted air flow oscillation amplitude is based on a lookup table value that depends on the engine speed, the intake pressure, the intake temperature and the EGR valve position. The EGR valve position may correspond to high pressure or low pressure EGR valves and the position may be derived from an actuator command signal or also by a position sensor signal. 
         [0016]    According to another embodiment, the residual generation unit is adapted to generate a pressure oscillation amplitude residual from the first set of measurement signals and the second set of measurement signals. In a more specific realization, the second set of measurement values comprises an EGR valve position and the pressure oscillation amplitude residual is based on a difference of a first predicted pressure oscillation amplitude from the first set of predicted values and a second predicted pressure oscillation amplitude from the second set of predicted values. Furthermore, the second predicted pressure oscillation amplitude is based on a lookup table value that depends on the engine speed, the intake pressure, the intake temperature and the EGR valve position. 
         [0017]    According to another embodiment, the first set of measurement signals further comprises an exhaust pressure upstream of an EGR valve and an EGR valve temperature and wherein the residual generation unit is adapted to generate at least one gas flow residual from the first set of measurement signals and the second set of measurement signals. In a more specific realization, the at least one gas flow residual is based on a difference of a first predicted mass flow from the first set of predicted values and a second predicted mass flow from the second set of predicted values. Furthermore, the second predicted mass flow is based on a lookup table value that depends on the engine speed, the pressure downstream of the EGR recirculation valve and the command signal of the flap valve. 
         [0018]    According to another embodiment, the at least one gas flow residual is based on a difference of a first predicted mass flow from the first set of predicted values and a second predicted mass flow from the second set of predicted values. The second predicted mass flow is based on the engine speed, a measurement value from a lambda or an oxygen sensor and a volume of injected fuel. For an evaluation of the residuals, a dead zone unit may be provided for setting the residual to zero if the residual lies between a lower limit and an upper limit. Advantageously the lower limit and the upper limit are based on an operating point, such as the motor revolution speed, an EGR position signal, a flap valve position signal. Especially, the operating point may depend on an engine speed and a fuel flow rate. 
         [0019]    Furthermore, an engine control unit is provided that comprises the aforementioned combustion engine evaluation unit wherein input ports of the engine control unit are connected to the input ports of the combustion engine evaluation unit and output ports of the engine control unit are connected to output ports of the combustion engine evaluation unit. Moreover, the application discloses also a combustion engine that comprises a turbocharger and gas flow control system and the aforementioned engine control unit, wherein sensor outputs and actuator inputs of the gas flow control system are connected to the engine control unit. 
         [0020]    A powertrain is provided with the aforementioned combustion engine. A crank-shaft of the combustion engine is connected to an input shaft of the powertrain and a vehicle with the aforementioned powertrain. The powertrain is connected to a wheel of the vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0022]      FIG. 1  shows a diagrammatic illustration of a gas flow control system for a turbo diesel engine; 
           [0023]      FIG. 2  illustrates error conditions of the gas flow control systems; 
           [0024]      FIG. 3  illustrates a residual generating unit for a HP-EGR cycle; 
           [0025]      FIG. 4  illustrates a residual generating unit for a LP-EGR cycle; 
           [0026]      FIG. 5  illustrates a decision logic and an error display for evaluating the residuals; 
           [0027]      FIG. 6  illustrates a neural network of a decision logic; 
           [0028]      FIG. 7  illustrates diagrams of motor speeds and motor torque for various operating points; 
           [0029]      FIG. 8  illustrates a diagram of a nominal model for a turbocharger shaft speed; 
           [0030]      FIG. 9  illustrates a flow diagram of a residual evaluation; 
           [0031]      FIG. 10  shows a partitioning of a parameter space; 
           [0032]      FIG. 11  illustrates a definition procedure for lower and upper thresholds of residuals; 
           [0033]      FIG. 12  illustrates in further detail a residual evaluation according to  FIG. 9 ; and 
           [0034]      FIG. 13  shows a detailed view of a residual generation unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0036]      FIG. 1  shows a diagrammatic illustration of a gas flow control system  10  for a turbo diesel engine  11 . A crankshaft of the diesel engine  11  is connected a drivetrain which is connected to wheels  8  of a car. For simplicity, crankshaft and drivetrain are not shown in  FIG. 1 . Between an air intake  12  and an air inlet  9  of the diesel engine  11 , the gas flow control system  10  comprises an air filter  13 , a hot film (HFM) air mass flow sensor  14 , an intake throttle  1 , and a compressor  15  of a turbocharger  16 , an intake air cooler  17  and an intake air throttle  18 . Between the diesel engine  11  and an exhaust outlet  19 , the gas flow control system  10  comprises an exhaust turbine  20  of the turbocharger  16 , a diesel particulate filter (DPF)  21  with a diesel oxidation catalyst (DOC) and an exhaust throttle  22 . 
         [0037]    The gas flow control system  10  comprises a high pressure exhaust gas recirculation (HP EGR) circuit  23 . Between an exhaust outlet  24  of the diesel engine  11  and the air intake  9  of the diesel engine  11 , the HP-EGR circuit  23  comprises a bypass branch  25 , a HP-EGR cooler  26 , a HP-EGR valve  27  and a recirculation branch  28 . Furthermore, a low pressure exhaust gas recirculation (LP-EGR) circuit  38  is provided between the DPF  21  and the compressor  15 . The LP-EGR circuit  38  comprises an LP-EGR cooler  6  and an LP-EGR valve  7  downstream of the LP-EGR cooler  6 . 
         [0038]    Downstream of the intake air cooler  17  and the intake air throttle  18 , the intake manifold branches off to the cylinders of the engine  11 . The cylinders comprise a first inlet channel  2  with a swirl flap valve  3  and a second inlet channel  3 . For simplicity, only one set of inlet channels  2 ,  3  is shown. In an alternative embodiment the inlet channel  2  is connected to the recirculation branch  28  and the inlet channel  4  is connected to the intake throttle  18 . In this case, mixing in of exhaust gas occurs in the combustion chamber of the cylinder. The swirl flap valves  3  are connected to an actuator which is connected to a command line of the ECU  89 . 
         [0039]    For simplicity, pipes from and to the cylinders of the diesel engine  11  are not indicated separately. Likewise, fuel lines are not shown. The exhaust turbine  20  and the compressor  15  are linked by a compressor shaft  29  and the rotation velocity n_tc of the compressor shaft  29  is indicated by a circular arrow. The exhaust turbine has a variable geometry which is controlled by a control signal sVTG. The variable geometry of the exhaust turbine  20  is realized by adjustable turbine blades  30  which are indicated by slanted lines. Mass flow rates of the HP-EGR cycle  23  and the LP-EGR cycle are indicated by corresponding symbols and the ambient input temperature and pressure upstream of the air filter  13  are indicated by symbols T_a and p_a. 
         [0040]    Various locations of sensors in the gas flow are indicated by square symbols. The square symbol is only symbolic and does not indicate the precise shape of a gas pipe at the location of a sensor. A first sensor location  31  and corresponding temperature T_ 1  and pressure p_ 1  are indicated between the HFM air mass flow sensor  14  and the compressor  15 ; a second sensor location  32  and corresponding temperature T_ 2   c  and pressure p_ 2   c  are indicated between the compressor  15  and the intake air cooler  17 ; a third sensor location  33  and corresponding temperature T_ 2   ic  is indicated between the intake air cooler  17  and the intake air throttle  18 ; a fourth sensor location  34  and corresponding temperature T  21  and pressure p_ 2   i  are indicated between the intake air throttle  18  and the inlet  9  of the diesel engine  11  or, respectively, the HP-EGR valve  27 ; a fifth sensor location  35  and corresponding temperature T_ 3  and pressure p_ 3  are indicated between the outlet  24  of the diesel engine  11  and the HP-EGR cooler  26  or, respectively, the exhaust turbine  20 ; a sixth sensor location  36  and corresponding temperature T_ 4  and pressure p_ 4  are indicated between the exhaust turbine  20  and the DPF  21 ; a seventh sensor location  37  with corresponding temperature T_ 5  and pressure p_ 5  is indicated between the DPF  21  and the exhaust gas throttle  22 . Downstream of the exhaust throttle  22  there are an H 2 S catalyst and an exhaust silencer which are not shown in  FIG. 1 . The gas flow control system  10  may be realized with our without the low pressure EGR cycle  38 . Moreover, the HP-EGR cycle  23  may be provided separately for cylinders or groups of cylinders. A NO x  storage catalyst (NSC) may be provided upstream of the exhaust throttle  22 . 
         [0041]      FIG. 2  shows in more detail  8  error conditions that occur in a turbo diesel engine with EGR according to the application. An ECU unit  89  is shown, which is provided for evaluating the residuals and which receives sensor and actuator signals and which outputs command signals. In  FIG. 18 , the error conditions are labeled by circled numbers. 
         [0042]    A blow-by error condition ( 1 ), which is determined based on measurements at measurement location  31 , is given when the blow-by tube of the engine  11  has a leakage or is missing. The blow-by tube is not shown in  FIG. 2 . It serves to let exhaust gases escape from the crankcase which have entered the crankcase by malfunction and/or by leaky cylinders. The exhaust gases may be blown out or recycled. The blow-by error condition leads to a leakage mass flow rate indicated by the time derivative d/dt(m_leak(t)). An intercooler leakage error condition ( 2 ), which is determined based on measurements at measurement location  34 , is given by a leakage after the intercooler  17  between the compressor  15  and the turbocharger  18 . The corresponding leakage mass flow rate is indicated by d/dt(m_leak). An intercooler restriction error condition ( 3 ) that occurs when there is a restriction downstream of the intercooler  17  is determined based on measurements at the measurement location  33 . 
         [0043]    A swirl flap position error condition ( 4 ) is determined based on measurements at the measurement location  34 . The swirl flaps or flap valves, which are not shown in  FIGS. 1 and 2 , are positioned at inlet channels of the cylinders and are actuated by a common actuator which receives a flap valve command signal from the ECU. The swirl flaps are used to mix the exhaust gas of the HP-EGR cycle  23  into the combustion gas of a cylinder. In the simplified  FIGS. 1 and 2 , the position of the swirl flap is at the recirculation branch  28 . 
         [0044]    An EGR position error condition ( 5 ) is indicated at the HP-EGR valve  27 . It may be determined by direct position measurement at the HP-EGR valve  27  or based on measurements at measurement locations  35  and  34 . An exhaust leakage error condition ( 6 ) is determined based on measurements at measurement location  35 . The corresponding leakage mass flow rate is indicated by d/dt(m_leak). An HFM high ( 7 ) and an HFM low ( 8 ) error condition is indicated at the hot film airflow meter  14 . They correspond to airflow measurements which are too high or too low, respectively. 
         [0045]      FIG. 3  shows a residual generation unit  100  for generating residuals for a high pressure EGR operation. The left side shows input values from a first and a second set of measurement values which are used as input values for submodel units. The submodel units each comprise a nominal or semi physical model unit and a physical model unit. The nominal model units are indicated in  FIG. 13 . The input values are explained below. T_ 3 /T_EGR means that the temperature values T_ 3  and T_EGR may be used alternatively or in combination, for example in order to spare a sensor at the EGR valve  27  and use a sensor at measurement location  35  instead or in order to use two values instead of one to have fault tolerance through redundancy. 
         [0046]      FIG. 4  shows a residual generation unit  100 ′ which is essentially identical to the residual generation unit  100  but instead of the input values p_ 3 , s_EGR, T_ 3 /TEGR of the HP-EGR cycle  23  it uses measurement values of the LP-EGR cycle  38 , wherein dp_LEGR is a pressure difference across the LP EGR valve, s_LEPGR is a LP-EGR valve control signal, T_aDPF is a temperature downstream of the DPF  21  and upstream of the LP-EGR cooler, T_LPEGR is a temperature downstream of the LP-EGR cooler  6  and upstream of the LP-EGR valve  7 . Again, T_aDPF can be used instead of or in combination with T_LPEGR. The low pressure EGR cycle  38  may be used in addition to the HP-EGR cycle  23 . 
         [0047]    Preferentially, the flow diagram of  FIG. 3  applies to a high pressure operation mode in which the HP-EGR valve is open and the LP-EGR valve is closed and the  FIG. 4  applies to a low pressure operation mode in which the HP-EGR valve is closed and the LP-EGR valve is open. The operation of the residual generation units  100 ,  100 ′ is now explained in more detail. The residual for the air flow efficiency also known as volumetric efficiency, is calculated according to 
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         [0000]    Where u_vsa is the command signal of the VSA valve, d/dt(m_air_HFM) is the measured mass flow at the hot film meter  14  V_sub is the total volume between the HFM air flow meter  14  and a p_ 2   i  pressure meter at the measurement location  34 , V_d is the displacement volume of all cylinders, V_d=n_cylinders *V_cylinder, R is the ideal gas constant and LLM is an LLM-model. The left term corresponds to λ_a and the right term corresponds to λ_a,model of  FIG. 12 . Instead of u_vsa, a position signal from a flap valve actuator may be used. 
         [0048]    The residuals for the mass flow and p_ 2  amplitudes are computed according to 
         [0000]        r   A     {dot over (m)}     =A   {dot over (m)}     air   −Grid A     {dot over (m)}   ( n   eng ,ρ 2i   ,s   EGR )
 
         [0000]        r   A     p2     =A   p2 −Grid A     p2   ( n   eng ,ρ 2i   ,s   EGR )
 
         [0000]    Where s_EGR denotes the respective signal s_LPEGR or s_HPEGR. Alternatively, the nominal amplitudes may also be computed from the engine revolution speed n_eng and the intake density ρ 21  alone by a grid model an LLM model or the like, 
         [0000]        A   {dot over (m)}     air     ,no min al =Grid A{dot over (m)} ( n   eng ,ρ 2i )
 
         [0000]        A   p2,no min al =Grid Ap2 ( n   eng ,ρ 2i )
 
         [0049]    The air mass flow and the boost pressure p_ 2  oscillate with the period of the opening and closing of the intake valves. The amplitudes A refer to the magnitudes of these oscillations. It is also possible to measure the amplitudes in the exhaust path instead of in the intake path. The oscillations can be approximated by 
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         [0050]    For a four cylinder four stroke engine, an oscillation with a period of 180° CA (crankshaft angle) results. In general, the oscillation period amounts to (720° CA*n_cylinders)/k_combustion, where k_combustion=2 for a 4-stroke and 1 for a 2 stroke combustion 
         [0051]    “Grid” refers to model values which are dependent on an operating point which is defined by the engine revolution speed n_eng, the boost density ρ_ 2   i  at measurement location  34  and the position s_EGR of an EGR valve. Herein, s_EGR refers to the HP-EGR valve for the model of  FIG. 3  and to the LP-EGR valve for the model of  FIG. 4 . The model values may be derived from a grid model but also from a neuronal net or from a local linear modeling tree model. Furthermore, the model values may be predetermined and stored in a lookup table and interpolation may be used to derive model values at intermediate grid points. 
         [0052]    The left terms are derived from sensor values of the air flow rate and the pressure p_ 2  and correspond to the physical model. Herein, the left terms correspond to the physical model and the right terms to the nominal model. The boost density may ρ_ 2   i  may be computed based on the input values p_ 2   i , T_ 2   i  shown in  FIGS. 3 ,  4  using the ideal gas equation according to ρ_ 2   i =(p_ 2   i *MW)/(R*T_ 2   i ), wherein MW is a mean molecular weight of the gas mixture and R is the ideal gas constant. 
         [0053]    The air mass flow rates are computed according to 
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                 0.5 
                 · 
                 
                   
                     LLM 
                     
                       λ 
                       a 
                     
                   
                    
                   
                     ( 
                     
                       
                         n 
                         eng 
                       
                       , 
                       
                         p 
                         
                           2 
                            
                           
                               
                           
                            
                           i 
                         
                       
                       , 
                       
                         u 
                         VSA 
                       
                     
                     ) 
                   
                 
                 · 
                 
                   n 
                   eng 
                 
                 · 
                 
                   V 
                   d 
                 
                 · 
                 
                   
                     p 
                     
                       2 
                        
                       
                           
                       
                        
                       i 
                     
                   
                   
                     RT 
                     
                       2 
                        
                       
                           
                       
                        
                       i 
                     
                   
                 
               
               - 
               
                 
                   
                     
                       m 
                       . 
                     
                     EGR 
                   
                    
                   
                     T 
                     EGR 
                   
                 
                 
                   T 
                   
                     2 
                      
                     
                         
                     
                      
                     i 
                   
                 
               
             
           
         
       
       
         
           
             
                 
             
              
             
               
                 
                   
                     m 
                     . 
                   
                   
                     air 
                     , 
                     eng 
                     , 
                     3 
                   
                 
                 = 
                 
                   
                     
                       λ 
                       · 
                       
                         
                           m 
                           . 
                         
                         f 
                       
                       · 
                       14.5 
                     
                      
                     
                         
                     
                      
                     
                       
                         m 
                         . 
                       
                       f 
                     
                   
                   = 
                   
                     2 
                     · 
                     q 
                     · 
                     
                       n 
                       eng 
                     
                     · 
                     
                       ρ 
                       Diesel 
                     
                   
                 
               
               , 
             
           
         
       
     
         [0000]    respectively, where V_E is an intake volume which is equivalent to the above-mentioned volume V_sub, λ denotes a measurement value from an oxygen or lambda sensor before or after the turbine, d/dt(m_f) is the fuel mass flow, q is the volume of injected fuel in cubic millimeters per cycle. 
         [0054]    Herein, the left term of the second equation and the right side of the equation for d/dt(m_air,eng,3) can be regarded as outputs of nominal model units. The numerical value 0.5 applies to 4-stroke combustion. In general, the value 1/k_combustion must be used. The numerical value 14.5 represents a stoichiometric air to fuel ratio for diesel fuel. 
         [0055]    T_EGR relates to a temperature which is measured by a temperature sensor which is close to the HP-EGR or the LP-EGR valve, respectively. Preferably, the temperature sensor is placed upstream of the EGR-valve between the respective EGR valve  27  or  7  and the corresponding intercooler  26  or  6 . The EGR mass flow d/dt(m_EGR) can be modeled, for example, by taking into account a pressure difference Δp_EGR between a pressure upstream of the valve and a pressure downstream of the EGR-valve and an EGR-valve opening s_EGR which may be derived from a control signal or a position sensor. In a simple model, the EGR mass flow is proportional to both Δp_EGR and s_EGR. In a more accurate model, a temperature upstream of the respective EGR valve is used to take into account the gas density, 
         [0000]    
       
         
           
             
               
                 
                   m 
                   . 
                 
                 EGR 
               
               = 
               
                 
                    
                   
                      
                     t 
                   
                 
                  
                 
                   ( 
                   
                     Δ 
                      
                     
                         
                     
                      
                     
                       p 
                       EGR 
                     
                   
                   ) 
                 
                 × 
                 
                   
                     
                       V 
                       EGR 
                     
                      
                     
                       ( 
                       
                         s 
                         EGR 
                       
                       ) 
                     
                   
                   
                     RT 
                     EGR 
                   
                 
               
             
             , 
           
         
       
     
         [0000]    Where V_EGR is a characteristic volume that depends on the valve opening signal s_EGR. In a more accurate model, the mass flow rates through the low pressure and the high pressure EGR valves are calculated according to 
         [0000]    
       
         
           
             
               
                 m 
                 . 
               
               hpegr 
             
             = 
             
               μ 
                
               
                   
               
                
               
                 A 
                 
                   eff 
                   , 
                   hpegr 
                 
               
                
               
                 
                   p 
                   3 
                 
                 
                   
                     RT 
                     hpegr 
                   
                 
               
                
               
                 
                   
                     
                       2 
                        
                       
                         κ 
                         e 
                       
                     
                     
                       
                         κ 
                         e 
                       
                       - 
                       1 
                     
                   
                    
                   
                     [ 
                     
                       
                         
                           ( 
                           
                             
                               p 
                               
                                 2 
                                  
                                 
                                     
                                 
                                  
                                 i 
                               
                             
                             
                               p 
                               3 
                             
                           
                           ) 
                         
                         
                           2 
                           
                             κ 
                             e 
                           
                         
                       
                       - 
                       
                         
                           ( 
                           
                             
                               p 
                               
                                 2 
                                  
                                 
                                     
                                 
                                  
                                 i 
                               
                             
                             
                               p 
                               3 
                             
                           
                           ) 
                         
                         
                           
                             
                               κ 
                               e 
                             
                             + 
                             1 
                           
                           
                             κ 
                             e 
                           
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
       
         
           and 
         
       
       
         
           
             
               
                 
                   m 
                   . 
                 
                 lpegr 
               
               = 
               
                 μ 
                  
                 
                     
                 
                  
                 
                   A 
                   
                     eff 
                     , 
                     lpegr 
                   
                 
                  
                 
                   
                     p 
                     5 
                   
                   
                     
                       RT 
                       lpegr 
                     
                   
                 
                  
                 
                   
                     
                       
                         2 
                          
                         
                           κ 
                           e 
                         
                       
                       
                         
                           κ 
                           e 
                         
                         - 
                         1 
                       
                     
                      
                     
                       [ 
                       
                         
                           
                             ( 
                             
                               
                                 p 
                                 1 
                               
                               
                                 p 
                                 5 
                               
                             
                             ) 
                           
                           
                             2 
                             
                               κ 
                               e 
                             
                           
                         
                         - 
                         
                           
                             ( 
                             
                               
                                 p 
                                 1 
                               
                               
                                 p 
                                 5 
                               
                             
                             ) 
                           
                           
                             
                               
                                 κ 
                                 e 
                               
                               + 
                               1 
                             
                             
                               κ 
                               e 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
             
             , 
           
         
       
     
         [0000]    Where μA eff,hpegr =f hpegr (s hpegr ) and μA eff,lpegr =f lpegr (s lpegr ). Herein, f_egr is an approximation function, for example a polynomial and κ_e is an adiabatic exponent of the exhaust gas. P_ 2   i  and  p _ 3  and, respectively, p_ 1  and p_ 5  correspond to pressures downstream and upstream of the respective EGR valve, especially to pressures at the indicated measurement locations. 
         [0056]    From the abovementioned relationships, the corresponding residuals are computed as: 
         [0000]    
       
      
       r 
       {dot over (m)} 
       
         air 
       
       ,1-2 
       ={dot over (m)} 
       air,1 
       −{dot over (m)} 
       air,2  
      
     
         [0000]    
       
      
       r 
       {dot over (m)} 
       
         air 
       
       ,1-3 
       ={dot over (m)} 
       air,1 
       −{dot over (m)} 
       air,3  
      
     
         [0000]    
       
      
       r 
       {dot over (m)} 
       
         air 
       
       ,2-3 
       ={dot over (m)} 
       air,2 
       −{dot over (m)} 
       air,3  
      
     
         [0000]    These differences can be represented as differences between terms of a physical model unit and terms of a nominal model unit, wherein the outputs of the physical model units are defined by those terms that are not outputs of the nominal model units. 
         [0057]      FIG. 5  shows an embodiment of an evaluation unit in which the evaluation unit comprises comparators  57 ,  58 ,  59 ,  60 ,  61  and a decision logic circuit  62 . Outputs of the comparators are connected to inputs of the decision logic circuit  62 . An output of the decision logic circuit  62  is connectable to a control display  63 . The control display  63  provides display symbols  64 ,  65 ,  66 ,  67 ,  68 ,  69 ,  70 ,  71 ,  72  to indicate the error conditions of a blow-by pipe failure, an intake manifold leakage, an intake manifold blockage, an exhaust manifold leakage, an EGR-valve failure, a swirl flap failure respectively. 
         [0058]    During operation, the comparators compare the absolute value of the residuals r_λa, r_A_m_air, r_A_p_ 2   i , r_m_air_ 1 - 2 , r_m_air_ 2 - 3 , r_m_air_ 1 - 3  against corresponding limit values and generate binary output signals. Alternatively, comparators are provided to compare the value of the residuals, which may be positive as well as negative, against respective negative and positive limiting values. Furthermore, the limit values may depend on an operating point. This is shown in more detail in  FIG. 11 . 
         [0059]    The binary output signals are evaluated by the decision logic circuit  62  and an error condition signal is generated. The error condition signal may indicate a single error condition or also a combination of error conditions. In a particularly simple embodiment, the logic circuit  62  comprises a lookup table for mapping the binary outputs of the comparators  57 ,  58 ,  59 ,  60 ,  61  to an error condition value that indicates an error condition or a combination of error conditions. On the control display  63 , display symbols are displayed which correspond to the error condition value. 
         [0060]      FIG. 6  shows a further embodiment of an evaluation unit in which the evaluation unit is designed as an ANN  73  of the multi-layer perceptron type. The ANN  73  is shown by way of example. Other classification methods, such as fuzzy logic systems or LLM models may be used. The ANN  73  comprises an input layer  74  of nodes, a processing layer  75  of nodes and an output layer  76  of nodes. Nodes which are not shown for simplicity in  FIG. 6  are indicated by ellipsis dots. Residual values at two different sampling times t_ 1  and t_ 2  are provided to the nodes of the input layer  74 . During operation of the ANN  37 , the nodes of the processing layer  75  and the output layer  76  compute an output from a weighted average of their input values. 
         [0061]    During a training of the ANN  73 , values of residuals which are characteristic of certain error conditions are presented to the ANN  73  and weights of the weighted sums are adjusted such that the output values of the output layer nodes match the error condition. Here, by way of example, only the blow-by pipe, IMF leakage and EGR valve error conditions are shown. The ANN  73  may be extended to process residual values from more than just two sampling times or it may also process the current value of a residual only. Furthermore, the possible residual values may be partioned into intervals and the intervals may be assigned to different input nodes of the input layer  74 . The ANN  73  may also comprise a further processing layer of nodes between the processing layer  75  and the output layer. 
         [0062]      FIG. 7  illustrates, by way of example, engine speeds and motor torques that define operating points. The operating points are used during a training run of nominal model units. “BMEP” refers to the brake mean effective pressure. The operating point may be defined by other values than shown here, for example by engine revolution speed and fuel injection rate. 
         [0063]    The operating points are indicated by a “+” sign in the following table: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 BMEP 
                 Torque 
                 Engine speed [rpm] 
               
             
          
           
               
                 [bar] 
                 [Nm] 
                 1000 
                 1500 
                 2000 
                 2500 
                 3000 
                 3500 
               
               
                   
               
             
          
           
               
                 1 
                 15.1 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
               
               
                 2 
                 30.2 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
               
               
                 4 
                 60.5 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
               
               
                 6 
                 90.7 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
               
               
                 8 
                 121.0 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
               
               
                 10 
                 151.2 
                 − 
                 + 
                 + 
                 + 
                 + 
                 + 
               
               
                   
               
             
          
         
       
     
         [0064]    During the training run, the motor speed and the BMEP are held constant for the time shown in the diagrams and corresponding values for the predicted quantities are determined, either by direct measurement or based on measurements by using model calculations. Parameters of the nominal models are adjusted such that the nominal models approximate the previously determined values at the operating points. The adjustment of the parameters is also referred to as a learning or calibration process of the nominal model. The operating points may be determined by other quantities than those shown in  FIG. 7 , for example by the injected fuel, by the opening of an EGR valve, or by a flap valve position. 
         [0065]      FIG. 8  shows, by way of example, a diagram for a nominal model. In  FIG. 8 , a turbocharger shaft speed n_tc is modeled as function of the operating point (n_eng, BMEP). The model is generated by a calibration procedure and may be stored in the form of a look-up table. In  FIG. 8  the model output of the adjusted value for a given combination of BMEP and engine speed n_eng are indicated by a two dimensional surface  82 . The two dimensional surface  82  may be realized as a lookup table in a computer readable memory. The determined values of n_tc at the operating point are indicated by crosses  83  which may lie above, on or below the surface  82 . Level curves on the BMEP/engine speed plane illustrate the elevation profile of the two-dimensional plane. Similarly, nominal models for predicted values corresponding to the residuals of  FIGS. 3 and 4  are determined by an approximation to values at predetermined operating points. 
         [0066]      FIG. 9  shows a schematic flow diagram that further illustrates an evaluation of residuals according to the application. According to  FIG. 9 , m residuals are evaluated to generate n different fault conditions. In a residual generation step, the m residuals are generated by comparing output values from a model of the real process and from a nominal model. In a verification step, a verification unit  84  determines if an enabling condition is fulfilled, depending on an operating point. The operating point depends on input parameters of a nominal model, for example on the engine speed and on a fuel flow rate q_set. In a possible realization of the verification step, a residual is rejected as a valid input value for generating a fault condition if the flow rate q_set and the motor speed are not stable over a predetermined time or if the flow rate and the motor speed are not within a predetermined distance from an operating point. 
         [0067]    In a compensation step, a compensation unit  85  smoothes out outliers and other irregularities by filtering and compensates for spikes resulting from the operation of electrical switches by debouncing. In an evaluation step, an evaluation unit  86  compares the output of the compensation unit against a high threshold and a low threshold, depending on the value of the input parameters of the nominal models and on the operating point, and generates a corresponding symptom signal. In a diagnosis step, a diagnosis unit  62 ′ evaluates the m symptom signals of the evaluation units to generate an error signal which indicates, which of the n faults have occurred. The diagnosis unit  62 ′ may use inference logic, fuzzy logic or other methods which may be realized by lookup tables, for example. 
         [0068]      FIG. 10  shows, by way of example, a grouping of the parameter space of the input parameters of the nominal model into region according to the application. In this example, the parameter space is partitioned into 4 regions. To each of the four regions, a fault symptom table is associated. Operating points are indicated by circles. According to one embodiment of the application, a partitioning of the parameter space is defined through an iterative partitioning of parameter space using an LLM modeling procedure. Other classification methods, for example based on statistical methods, may also be used to partition the parameter space. 
         [0069]      FIG. 11  illustrates a definition procedure for lower and upper thresholds of residuals. The upper left diagram shows a time behavior of a residual r_PC, relating to a compressor energy conversion rate. The compressor energy conversion rate is only used as an example here. A similar procedure also applies to the other residuals of this application but with different operating points. The time behavior of residuals at predefined operating points for known error conditions are used to define upper and lower thresholds, depending on the operating points. The diagrams on the right side show, respectively, lower and upper limits for r_PC depending on operating points. In this example, the operating points are defined by a grid on a two dimensional parameter space. The two dimensional parameter space is defined by a crankshaft revolution speed n_eng in revolutions per minute and a fuel throughput per cylinder, in cubic millimeters. A dead zone element, which is shown inside the square symbol, sets the residual signal to zero if it is within the lower and upper threshold. If the residual signal lies outside the thresholds, the residual signal is passed through. 
         [0070]      FIG. 12  shows a generation of symptom values from residuals for the air flow efficiency λ_a. In  FIG. 12 , the upper flow diagram shows the generation of symptoms by comparing the sensor values at the measurement locations of  FIG. 1  with the air flow model. The air flow model is shown in further detail in  FIGS. 3 and 4 . The lower flow diagram illustrates in further detail the symptom generation in case of the air flow efficiency λ_a. 
         [0071]    The leftmost part of the diagram shows a comparison between process values of a physical model unit  95  and predicted model values of a nominal model unit  96  via the differentiator  90 . The nominal model is also referred to as “semi-physical”. The process values may simply be sensor or command values or they can also be values that are derived from sensor or command values by using a physical model. The model values are generally derived from a nominal model that depends on an operating point, which may be defined through an engine speed n_eng and further input values such as the pressure p_ 2   i , a flap valve command signal u_vsa, a boost density ρ_ 2   i , the rate of injected fuel d/dt(m_f) or also the brake mean effective pressure. Thus, in general, the differentiator  90  subtracts output values of two different model computations, wherein the second model computation is at least dependent on an engine speed n_eng. 
         [0072]    In the case of the air efficiency, the enabling conditions are realized via a condition evaluator  91  that checks if the EGR command value is below 0.6, indicating that the EGR valve is closed. A multiplier  92  is provided for fading out, and thus ignoring, the difference signal λ_a-λ_a,model depending on the opening status of the EGR valve. The debouncing and filtering unit  85  of  FIG. 5  comprises a low pass filter  85  for filtering out signal oscillations. The output signal of the low pass filter  85  is passed on to the evaluation unit  86 . 
         [0073]    A dead zone element  99  of the evaluation unit  86  sets its output value to zero if its input value lies between a lower and an upper threshold. The lower and upper threshold are each determined a first lookup table  97  and a second lookup table  98 . Threshold values that are stored in the lookup table are selected according to an operating point which is defined by the engine revolution speed n_eng and the fuel intake rate q_curr by using two dimensional lookup tables for the lower and the upper threshold. This can also be seen in  FIG. 11 . The fuel intake rate q_curr is filtered via a low pass filter  94  before it is used to select a threshold. After the output of the low pass  93 , the residual signal is output for further use. The arrangement of  FIG. 12  may also be realized without the low passes  93 ,  94 . 
         [0074]    The rows of the following table show error conditions, also referred to as system states, that correspond to the eight error conditions ( 1 ) to ( 8 ) shown in  FIG. 2 , which are labeled with F_ 1  to F_ 8  in the first column. The symbol “+” indicates a value above a positive threshold, the symbol “-” a value below of a negative threshold and “0” a value within a positive and a negative threshold. “I” indicates that the value does not contribute to identification of the error condition and is ignored and “/” stands for an “or” condition. 
         [0075]    As mentioned in conjunction with  FIG. 12 , the thresholds may depend on an operating point of the diesel motor  11  and exceed a threshold may also depend on further criteria such as surpassing the limit for at least a minimum time. The header row lists eight fault symptoms, which correspond to: the air efficiency λ_a, the air mass flow amplitude, the charge pressure amplitude, the air mass flow  1 - 2 , the air mass flow  1 - 3  and the air mass flow 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Parameters 
                 Air mass flows 
               
             
          
           
               
                 F 
                 S_λa 
                 S_Am 
                 S_Ap2 
                 S_m12 
                 S_m23 
                 S_m13 
               
               
                   
               
               
                 F_1 
                 + 
                 0 
                 0 
                 − 
                 0 
                 − 
               
               
                 F_2 
                 − 
                 0 
                 0 
                 + 
                 0 
                 + 
               
               
                 F_3 
                 0 
                 − 
                 − 
                 I 
                 I 
                 I 
               
               
                 F_4 
                 +/− 
                 +/− 
                 +/− 
                 I 
                 I 
                 I 
               
               
                 F_5 
                 − 
                 0 
                 0 
                 − 
                 + 
                 0 
               
               
                 F_6 
                 I 
                 I 
                 I 
                 0 
                 0 
                 0 
               
               
                 F_7 
                 − 
                 0 
                 0 
                 + 
                 0 
                 + 
               
               
                 F_8 
                 + 
                 0 
                 0 
                 − 
                 0 
                 − 
               
               
                   
               
             
          
         
       
     
         [0076]      FIG. 13  shows in more detail the residual generation unit of  FIG. 3 ,  FIG. 4 . In particular,  FIG. 14  shows the sub models of the physical modeling unit  40  and the structure of the mass flow computation, which is shown in  FIG. 13  in a simplified manner Physical airflow modeling units  40  are provided for generating a first set of predicted values λ_a, A_p 2 , A_m_air from a first set of measurement values. Furthermore, nominal modeling units  42 ,  43 ,  44 , are provided for computing second predicted values from a second set of measurement values. 
         [0077]    The modeling units  41 ,  45  for the air mass flow can be regarded as nominal modeling units. Differentiators are provided to subtract second predicted values from first predicted values. First and second predicted values for the mass flows d/dt(m_air, 1 ); d/dt(m_air, 2 ), d/dt(m_air, 3 ) are subtracted in all possible combinations. The resulting residuals r_m_ 12 , r_m_ 13 , r_m_ 23  can be represented as differences of a physical model term and a nominal model term. 
         [0078]    The output of the physical model is generally more sensitive to error conditions than the output of the nominal model. The difference in the mode units  40 ,  41  is also reflected in the input values, wherein the second set of measurement values corresponding to the nominal model unit  41  generally have a larger proportion of externally controllable quantities, such as fuel flow or ECU control signals, than the first set of measurement values. Secondly the difference of the model units is also reflected in that the nominal model unit relies more on the use of semi empirical models such as pre-calibrated lookup tables than on algebraically relationships. Due to the different behavior of the modeling units, errors can be detected by comparing the output values of the modeling units. 
         [0079]    Although the above description contains many specific details, these should not be construed as limiting the scope of the embodiments but merely providing illustration of the foreseeable embodiments. Especially, the above stated advantages of the embodiments should not be construed as limiting the scope of the embodiments but merely to explain possible achievements if the described embodiments are put into practice. These considerations also apply to the technical realization of the modeling units which may for example be realized as instructions of a computer readable program which in turn may be hardwired or stored in a computer readable memory, for example as instructions burned into an EPROM. Further realizations include lookup tables and interpolation of such lookup tables and hardwired embodiments of empirical models such as local linear model trees (also known as LOLIMOT or LLM), neuronal networks and the like. The modeling units may correspond to hardware units but also to program modules or functions. Furthermore, in other embodiments one program module or hardware module may also correspond to several modeling units and vice versa. 
         [0080]    The application applies especially to a four cylinder common rail diesel engine that is equipped with a VGT turbocharger and a high pressure exhaust gas recirculation which may also comprise a low pressure exhaust gas recirculation. But the range of application is more general. For example other numbers of cylinders, and various designs of EGR cycles are possible. Various aspects of the application also apply to other types of internal combustion engines with exhaust gas recirculation and do not necessarily require a turbocharger or a common rail system. 
         [0081]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.