Abstract:
An exemplary embodiment of the present disclosure provides a method for operating an internal combustion engine comprising: monitoring a value of a temperature parameter of a diesel particulate filter of the internal combustion engine; monitoring a value of an operating parameter of the internal combustion engine indicative of an engine load; using the monitored value of the engine load parameter to determine a threshold value of the diesel particulate filter temperature parameter; testing whether the monitored value of the diesel particulate filter temperature parameter exceeds the determined threshold value thereof; and diagnosing that the diesel particulate filter is overheated if the test returns positive.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to British Patent Application No. 1116599.0, filed Sep. 26, 2011, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field generally relates to a method for operating an internal combustion engine, typically an internal combustion engine of a motor vehicle. 
       BACKGROUND 
       [0003]    It is known that the exhaust gas produced by the fuel combustion within the cylinders of an internal combustion engine is discharged into the environment through an exhaust system, which generally comprises an exhaust manifold in communication with the engine cylinders, an exhaust pipe coming off the exhaust manifold, and one or more aftertreatment devices located in the exhaust pipe for trapping and/or changing the composition of the pollutant contained in the exhaust gas. 
         [0004]    Among these aftertreatment devices, a Diesel engine generally comprises a Diesel Oxidation Catalyst (DOC) for degrading the residual hydrocarbons and carbon monoxides contained in the exhaust gas into carbon dioxides and water, and a Diesel Particulate Filter (DPF), which is located in the exhaust pipe downstream of the DOC, for trapping and thus removing diesel particulate matter (soot) from the exhaust gas. 
         [0005]    A side effect of this aftertreatment device is that the DPF is heated by the exhaust gas flowing therein, so that it may overheat, if the temperature of the exhaust gas becomes excessive. This may damage the DPF. 
         [0006]    In view of the above, it is desirable to reliably evaluate whether the DPF is overheated, in order to prevent any DPF damage and malfunction. It is also desirable to achieve this goal with a simple, rational and rather inexpensive solution. 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 
       [0007]    In one of various exemplary embodiments, provided is a method for operating an internal combustion engine comprising:
       monitoring a value of a temperature parameter of a diesel particulate filter (DPF) of the internal combustion engine, typically a value of the exhaust gas temperature at the DPF inlet,   monitoring a value of one or more operating parameter(s) of the internal combustion engine indicative of an engine load, typically a value of an engine torque and/or a value of an engine speed,   using the monitored value of the engine load parameter(s) to determine a threshold value of the DPF temperature parameter,   testing whether the monitored value of the DPF temperature parameter exceeds the determined threshold value thereof, and   diagnosing that the diesel particulate filter is overheated if the test returns positive.       
 
         [0013]    In other words, the present solution provides to diagnose a DPF overheating by comparing a current value of the DPF temperature parameter, which can be monitored by means of a dedicated sensor, with a dynamic threshold value thereof, which depends on the current value of the engine load parameter(s). 
         [0014]    In this way, the present solution has the advantage that the diagnosis of the DPF overheating is reliable over a wide range of values of the engine load parameter(s). 
         [0015]    Another advantage of the present solution is that, due to the simplicity of the algorithm and the few parameters involved, the diagnosis of the DPF overheating requires a small computational effort, which can be provided by a conventional engine control unit (ECU). 
         [0016]    Still another advantage is that the diagnosis of the DPF overheating does not imply any additional sensor, because the engine load parameter(s) and the DPF temperature parameter are already monitored and used in many other control strategies of the internal combustion engine. 
         [0017]    According to one of various aspects of the present disclosure, the monitored value of the engine load parameter(s) is (are) filtered before being used to determine the threshold value of the DPF temperature parameter. 
         [0018]    This aspect is advantageous because the engine load parameters generally vary very fast, whereas the thermodynamic behavior of the DPF takes more time to change in response of a variation of the engine load parameters. As a consequence, the threshold value of the DPF temperature parameter, which is determined on the basis of the actual value of the engine load parameter(s), could vary too rapidly and become instable, thereby causing the diagnosis to fail, namely to return a false DPF overheating or to return a true DPF overheating but too late. The filtering stage of the monitored value of the engine operating parameter(s), which can be performed for example by means of a low pass filter, has the advantage of overcoming, or at least of positively reducing, the above mentioned drawback. 
         [0019]    According to another of various aspects of the present disclosure, the threshold value of the DPF temperature parameter is determined by means of a calibrated model or map that receives as input the monitored value of the engine load parameter(s) and returns as output the threshold value. 
         [0020]    This solution has the advantage that the model or map can be calibrated by means of an empirical activity, and then stored in a memory system associated to the ECU, so that the latter can carry out the diagnosis of the DPF overheating very rapidly and with a minimum of computational effort. 
         [0021]    According to still another one of various aspects of the present disclosure, the engine operating method can comprise:
       using the monitored value of the DPF temperature parameter to calculate a value of a gradient of the DPF temperature parameter,   performing the test only if the calculated value of the gradient of the DPF temperature parameter is positive.       
 
         [0024]    This solution is advantageous because, in general, the DPF temperature parameter decreases very slowly. For example, the DPF temperature parameter decreases much more slowly than the engine load parameter(s) used to determine its dynamic threshold value. As a consequence, while the DPF temperature parameter is decreasing, it may happen that the dynamic threshold value decreases too quickly compared to the actual value of DPF temperature parameter, causing the diagnostic strategy to detect a false DPF overheating. By performing the test generally only if the gradient value of the DPF temperature parameter is positive (namely only if the DPF temperature parameter value is actually increasing), the above mentioned drawback is advantageously overcame. 
         [0025]    An auxiliary aspect of this solution provides that the monitored value of the DPF temperature parameter is filtered before being used to calculate the gradient value thereof. 
         [0026]    This filtering stage of the monitored value of the DPF temperature parameter, which can be performed for example by means of a low pass filter, has the advantage of improving the robustness of the gradient calculation, in order to better recognize whether the DPF temperature parameter is actually increasing or not. 
         [0027]    According to one of various aspects of the present disclosure, the engine operating method can comprise:
       activating a recovery strategy suitable to stop the increase of the DPF temperature, if the overheating of the DPF is diagnosed.       
 
         [0029]    By way of example, the recovery strategy may provide for reducing the quantity of fuel and/or air which is supplied into the internal combustion engine. 
         [0030]    In this way, it is advantageously possible to stop and control the temperature increase of the DPF, thereby preventing damages of the DPF itself as well as of other engine components. 
         [0031]    The methods according to the various teachings of the present disclosure can be carried out with the help of a computer program comprising a program-code for carrying out the method described above, and in the form of a computer program product comprising the computer program. 
         [0032]    The computer program product can be embodied as an internal combustion engine comprising a diesel particulate filter, an engine control unit (ECU), a memory system associated to the engine control unit, and the computer program stored in the memory system, so that, when the ECU executes the computer program, the method described above is carried out. 
         [0033]    The method can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out the method. 
         [0034]    Another exemplary embodiment of the present disclosure provides an apparatus for operating an internal combustion engine equipped with a diesel particulate filter, comprising:
       means for monitoring a value of a temperature parameter of the DPF,   means for monitoring a value of one or more operating parameter(s) of the internal combustion engine indicative of an engine load,   means for using the monitored value of the engine load parameter(s) to determine a threshold value of the DPF temperature parameter,   means for testing whether the monitored value of the DPF temperature parameter exceeds the determined threshold value thereof, and   means for diagnosing that the DPF is overheated if the test returns positive.       
 
         [0040]    This exemplary embodiment of the present disclosure has the same advantage of the method disclosed above, namely that of providing a reliable strategy to diagnose a DPF overheating, which involves a low computational effort and which can be performed by a conventional engine control system. 
         [0041]    Still another exemplary embodiment of the present disclosure provides an automotive system comprising:
       an internal combustion engine equipped with a diesel particulate filter, a first sensor for evaluating a temperature parameter of the diesel particulate filter, one or more second sensor(s) for evaluating one or more operating parameter(s) of the internal combustion engine indicative of an engine load, and an electronic control unit in communication with the first and the second sensor, wherein the electronic control unit is configured to:
           monitor with the first sensor a value of the DPF temperature parameter,   monitor with the second sensor(s) a value of the engine operating parameter(s),   use the monitored value of the engine operating parameter(s) to determine a threshold value of the DPF temperature parameter,   test whether the monitored value of the DPF temperature parameter exceeds the determined threshold value thereof,   diagnose that the DPF is overheated if the test returns positive.   
               
 
         [0048]    Also this exemplary embodiment of the present disclosure has the same advantage of the method disclosed above, namely that of providing a reliable strategy to diagnose a DPF overheating, which involves a low computational effort and which can be performed by a conventional engine control system. 
         [0049]    A person skilled in the art can gather other characteristics and advantages of the disclosure from the following description of exemplary embodiments that refers to the attached drawings, wherein the described exemplary embodiments should not be interpreted in a restrictive sense. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0051]      FIG. 1  shows an exemplary automotive system; 
           [0052]      FIG. 2  is a section of an internal combustion engine belonging to the automotive system of  FIG. 1 ; and 
           [0053]      FIG. 3  is a flowchart of a method for operating the internal combustion engine belonging to the automotive system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0055]    Some exemplary embodiments may include an automotive system  100 , as shown in  FIGS. 1 and 2 , that includes an internal combustion engine (ICE)  110 , particularly an ICE  110  of a motor vehicle, having an engine block  120  defining at least one cylinder  125  having a piston  140  coupled to rotate a crankshaft  145 . A cylinder head  130  cooperates with the piston  140  to define a combustion chamber  150 . A fuel and air mixture (not shown) is disposed in the combustion chamber  150  and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston  140 . The fuel is provided by at least one fuel injector  160  and the air through at least one intake port  210 . The fuel is provided at high pressure to the fuel injector  160  from a fuel rail  170  in fluid communication with a high pressure fuel pump  180  that increases the pressure of the fuel received from a fuel source  190 . Each of the cylinders  125  has at least two valves  215 , actuated by a camshaft  135  rotating in time with the crankshaft  145 . The valves  215  selectively allow air into the combustion chamber  150  from the port  210  and alternately allow exhaust gases to exit through at least one exhaust port  220 . In some examples, a cam phaser  155  may selectively vary the timing between the camshaft  135  and the crankshaft  145 . 
         [0056]    The air may be distributed to the air intake port(s)  210  through an intake manifold  200 . An air intake pipe  205  may provide air from the ambient environment to the intake manifold  200 . In other exemplary embodiments, a throttle body  330  may be provided to regulate the flow of air into the manifold  200 . In still other exemplary embodiments, a forced air system such as a turbocharger  230 , having a compressor  240  rotationally coupled to a turbine  250 , may be provided. Rotation of the compressor  240  increases the pressure and temperature of the air in the intake pipe  205  and manifold  200 . An intercooler  260  disposed in the intake pipe  205  may reduce the temperature of the air. The turbine  250  rotates by receiving exhaust gases from an exhaust manifold  225  that directs exhaust gases from the exhaust ports  220  and through a series of vanes prior to expansion through the turbine  250 . This example shows a variable geometry turbine (VGT) with a VGT actuator  290  arranged to move the vanes to alter the flow of the exhaust gases through the turbine  250 . In other exemplary embodiments, the turbocharger  230  may be fixed geometry and/or include a waste gate. 
         [0057]    The exhaust gases exit the turbine  250  and are directed into an exhaust system  270 . The exhaust system  270  may include an exhaust pipe  275  having one or more exhaust aftertreatment devices. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. In the present example, the aftertreatment devices can comprise a Diesel Oxidation Catalyst (DOC)  280  for degrading the residual hydrocarbons and carbon monoxides contained in the exhaust gas into carbon dioxides and water, and a Diesel Particulate Filter (DPF)  285 , located downstream of the DOC  280 , for trapping diesel particulate matter (soot) from the exhaust gas. The DOC  280  and the DPF  285  of the present example are closed coupled and accommodated inside a common external housing, however they can be also mutually separated and provided with dedicated housing. 
         [0058]    Other exemplary embodiments may include an exhaust gas recirculation (EGR) system  300  coupled between the exhaust manifold  225  and the intake manifold  200 . The EGR system  300  may include an EGR cooler  310  to reduce the temperature of the exhaust gases in the EGR system  300 . An EGR valve  320  regulates a flow of exhaust gases in the EGR system  300 . 
         [0059]    The automotive system  100  may further include an electronic control unit (ECU)  450  in communication with one or more sensors and/or devices associated with the ICE  110 . The ECU  450  may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE  110 . The sensors include, but are not limited to, a mass airflow and temperature sensor  340 , a manifold pressure and temperature sensor  350 , a combustion pressure sensor  360 , coolant and oil temperature and level sensors  380 , a fuel rail pressure sensor  400 , a camshaft position sensor  410 , a crankshaft position sensor  420 , lambda sensors  430 , an EGR temperature sensor  440 , and an accelerator pedal position sensor  445 . In the present example, the sensors further include a pressure and temperature sensors  435  for sensing the pressure and the temperature of the exhaust gas at the inlet of the DPF  285 , namely between upstream the DPF  285  and downstream the DOC  280 . Furthermore, the ECU  450  may generate output signals to various control devices that are arranged to control the operation of the ICE  110 , including, but not limited to, the fuel injectors  160 , the throttle body  330 , the EGR Valve  320 , the VGT actuator  290 , and the cam phaser  155 . Note, dashed lines are used to indicate communication between the ECU  450  and the various sensors and devices, but some are omitted for clarity. 
         [0060]    Turning now to the ECU  450 , this apparatus may include a digital central processing unit (CPU) in communication with a memory system  460  and an interface bus. The memory system  460  may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The CPU is configured to execute instructions stored as a program in the memory system  460 , and send and receive signals to/from the interface bus. The program may embody the methods disclosed herein, allowing the CPU to carryout out the methods and control the ICE  110 . 
         [0061]    For example, the ECU  450  is configured to control the fuel injection inside the combustion chamber  150 , by operating each fuel injector  160  to perform several fuel injections per engine cycle according to a controllable fuel injection pattern. 
         [0062]    The ECU  450  is also configured to diagnose whether the DPF  285  overheats, namely whether the temperature of the DPF  285  is so high to cause damages or malfunctions of the DPF  285  itself and/or of other engine components. 
         [0063]    This diagnosis may be operated by the ECU  450  by means of the routine shown in the flowchart of  FIG. 3 . 
         [0064]    The routine firstly provides for the ECU  450  to monitor (block  10 ) the current value T of the exhausts gas temperature at the inlet of the DPF  285 , namely in the exhaust pipe  275  upstream of the DPF  285  and downstream of the DOC  280 . 
         [0065]    The current value T of the exhaust gas temperature can be measured by means of the temperature sensor  435 . 
         [0066]    Contemporaneously, the routine provides for the ECU  450  to monitor (block  11 ) the current value of one or more operating parameter(s) of the ICE  110 , which are related with the engine load and which affect the thermodynamic behavior of the DPF  285 , for example the engine torque and/or the engine speed. 
         [0067]    In this particular example, the routine provides for monitoring both the current value ES of the engine speed and the current value ET of the engine torque. 
         [0068]    The current value ES of the engine speed can be measured by the ECU  450  with the aid of the crankshaft position sensor  420 , whereas the current value ET of the engine torque can be determined by the ECU  450  on the basis of the accelerator pedal position measured by the sensor  445  and other engine operating parameters. In this example, where the ICE  110  is already equipped with in-cylinder pressure sensors  360 , the current value ET of the engine torque could also be measured by the ECU  450  with the aid of these in-cylinder pressure sensors  360 . 
         [0069]    The current value of the engine load parameter(s) are then applied as inputs to a calculation module  12 , which provides as output a correlated threshold value T_th of the exhaust gas temperature at the DPF inlet. 
         [0070]    The calculation module  12  uses a simplified model of the thermodynamic behavior of the inlet DPF temperature, for example an equation or a map, which correlates the current value of the engine load parameter(s), in this case each couple of current values ES, ET of engine speed and engine torque, to a corresponding threshold value T_th of the exhaust gas temperature at the DPF inlet. 
         [0071]    As a consequence, the threshold value T_th varies dynamically in response of each possible variation of the current value of the engine load parameter(s). 
         [0072]    Each threshold value T_th represents the exhaust gas temperature value above which the temperature increase of the DPF  285 , working under the corresponding value of the engine load parameter(s), could become excessive and damage the DPF  285  itself and/or other engine components. 
         [0073]    Since it may happen that the engine load parameters vary faster than the thermodynamic behavior of the DPF  285 , the routine provides that the current value(s) of the engine load parameter(s) monitored in the block  11 , in this case both the current value ES of the engine speed and the current value ET of the engine torque, are adequately filtered (block  13 ) before being applied to the calculation module  12 , for example by means of a respective low-pass filter. In this way, it is advantageously possible to prevent wrong diagnosis due to a too fast variation of the threshold value T_th. 
         [0074]    The equation or map involved in the calculation module  12  can be empirically calibrated by means of an experimental activity, and stored in the memory system  460 . 
         [0075]    However, since the exhaust gas temperature at the DPF inlet generally decreases much more slowly than the engine load parameters, it could be difficult to calibrate the above mentioned equation or map in such a way that it can provide reliable threshold values T_th in that case. 
         [0076]    For this reason, the present example provides for completing the diagnosis only if the exhaust gas temperature at the DPF inlet is actually increasing. 
         [0077]    Accordingly, the routine provides for the ECU  450  to use the current value T of the exhaust gas temperature for calculating (block  14 ) the current value G of the variation over the time t (gradient) of the exhaust gas temperature at the DPF inlet, for example according to the following equation: 
         [0000]    
       
         
           
             G 
             = 
             
               
                 
                    
                   T 
                 
                 
                    
                   t 
                 
               
               . 
             
           
         
       
     
         [0078]    Before being applied to the block  14 , the routine provides that the current value T of the exhaust gas temperature is adequately filtered (block  15 ), for example by means of a low-pass filter, in order to improve the robustness of the calculation of the gradient value G. 
         [0079]    The routine then provides for the ECU  450  to test (block  16 ) whether the current gradient value G is more than zero (exhaust gas temperature increasing) or not (exhaust gas temperature constant or decreasing). 
         [0080]    If this test returns negative, the routine is not completed and simply restarted from the beginning. 
         [0081]    If conversely the test returns positive, the routine provides for the ECU  450  to compare (block  17 ) the current value T of the exhaust gas temperature with the threshold value T_th that has been provided by the calculation module  12 . 
         [0082]    If the current value T is equal or below the threshold value T_th, it means that the thermal behavior of the internal combustion engine system  100  is normal, and the routine is repeated from the beginning. 
         [0083]    If conversely the current value T is above the threshold value T_th, the routine provides the ECU  450  to diagnose that the DPF  285  is overheated (block  18 ). 
         [0084]    Once a DPF overheating has been diagnosed, the ECU  450  may activate a recovery strategy (block  19 ). The recovery strategy can generally comprise any action suitable to stop the increase of the DPF temperature, in order to prevent damages of the DPF  285  itself as well as of other engine components. By way of example, the recovery strategy may provide for operating the ICE  110  according to a fuel injection pattern that reduces the amount of fuel injected in the cylinders  125 . The recovery strategy may also provide for reducing the amount of air induced into the engine cylinders  125 , for example by properly regulating the position of the throttle body  330 . 
         [0085]    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 forgoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one 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 in their legal equivalents.