Abstract:
A detection device for an internal combustion engine is preferably applied to the internal combustion engine which includes a temperature varying member, which is provided in an exhaust system, and whose temperature varies due to gas flow in the exhaust system. A temperature correlation value detection unit detects a correlation value which correlates with the temperature of the temperature varying member. The term correlation value herein includes impedance of the temperature varying member, a signal output value such as current and voltage output sent from the temperature varying member, and/or the temperature varying member&#39;s own temperature. A variation calculating unit calculates a variation of the correlation value, in a time period when the gas flow arises, detected by the temperature correlation value detection unit.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a detection device for an internal combustion engine which detects inhibitors such as particulate matters. 
       BACKGROUND TECHNIQUE 
       [0002]    In an exhaust system of an internal combustion engine, various sensors such as an air-fuel ratio sensor (A/F sensor) for detecting an air-fuel ratio in the exhaust gas are provided. When inhibitors such as particulate matters in the exhaust gas adhere to a detection unit of these kinds of sensors, the sensors become unable to obtain accurate detection values, and thereby the detection accuracy is deteriorated. As a technique for dealing with this, in Patent Reference-1, there is described a technique which determines, at the time when an operation state of a engine is a static state, whether an output value of an oxygen sensor is smaller than a predetermined value or larger than the predetermined value, and which burns up the particulate matters by increasing temperature of an electrical heater for heating up a detection element of the oxygen sensor at the time when the output value is larger than the predetermined value. In Patent References-2 and -3, there are also described technique which relates to the present invention. 
         [0003]    Patent Reference-1: Japanese Patent Application Laid-open under No. H11-82112 
         [0004]    Patent Reference-2: Japanese Patent No. 3744486 
         [0005]    Patent Reference-3: Japanese Patent No. 3958755 
       DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
       [0006]    However, by the technique described in Patent Reference-1, it is not clear whether the deviation of the output value supplied from the sensor is caused by adhesions of inhibitors or by deterioration of the sensor itself. In the case where the deviation of the output value is caused by the deterioration of the sensor itself, it is meaningless to burn up the particulate matters. 
         [0007]    The present invention has been achieved in order to solve the above problem. It is an object of this invention to provide a detection device for an internal combustion engine which can precisely detect adhesions of inhibitors. 
       Means for Solving the Problem 
       [0008]    According to one aspect of the present invention, there is provided a detection device for an internal combustion engine which is applied to the internal combustion engine including a temperature varying member, which is provided in an exhaust system, and whose temperature varies due to gas flow in the exhaust system, including a temperature correlation value detection unit which detects a correlation value which correlates with the temperature of the temperature varying member, and a variation calculating unit which calculates a variation of the correlation value, in a time period when the gas flow arises, detected by the temperature correlation value detection unit. 
         [0009]    The above detection device for an internal combustion engine is preferably applied to the internal combustion engine which includes a temperature varying member, which is provided in an exhaust system, and whose temperature varies due to gas flow in the exhaust system. The detection device for the internal combustion engine is for example an ECU (Electronic Control Unit) and functions as a temperature correlation value detection unit and a variation calculating unit. The temperature correlation value detection unit detects a correlation value which correlates with the temperature of the temperature varying member. The term correlation value herein includes impedance of the temperature varying member, a signal output value such as current and voltage sent from the temperature varying member, and the temperature varying member&#39;s own temperature. The variation calculating unit calculates a variation of the correlation value, in a time period when the gas flow arises, detected by the temperature correlation value detection unit. According to whether or not inhibitors adhere to the temperature varying member, levels of the difficulty in cooling the temperature varying member and the difficulty in heating up the temperature varying member vary and the variation of the correlation value also varies. Thus, by calculating the variation of the temperature varying member, it becomes possible to precisely detect whether or not inhibitors adhere to the temperature varying member. 
         [0010]    In a preferable embodiment of the detection device for an internal combustion engine, the temperature varying member is an electric heater of a gas sensor, and the temperature correlation value detection unit detects impedance of the electric heater as the correlation value. 
         [0011]    In another preferable embodiment of the detection device for an internal combustion engine, the temperature varying member is a temperature sensor, and the temperature correlation value detection unit detects a signal output value supplied from the temperature sensor as the correlation value. 
         [0012]    In another manner of the detection device for an internal combustion engine, an exhaust temperature sensor which detects temperature of the gas is provided on a streamline which is approximately same as the streamline where the temperature varying member is provided in the exhaust system, and the variation calculating unit calculates a rate of the variation of the correlation value to a variation of an exhaust temperature detected by the exhaust temperature sensor. Thereby it is also possible to precisely detect whether or not inhibitors adhere to the temperature varying member. Additionally, thereby it becomes possible to detect whether or not inhibitors adhere to the temperature varying member only by keeping the gas flow approximately constant during a predetermined time period when the exhaust temperature varies. 
         [0013]    In another manner of the detection device for an internal combustion engine, a filter member is provided in the exhaust system, and the temperature varying member is provided at the downstream side of the filter member. Thereby, it becomes possible to determine whether or not the filter is functioning normally. 
         [0014]    In another manner of the detection device for an internal combustion engine, a threshold of the variation is set according to an amount of inhibitors which adhere to the temperature varying member, and the detection device further includes a determining unit which determines whether or not the variation calculated by the variation calculating unit is smaller than the threshold. The determining unit is an ECU for example. Thereby it is possible to determine whether or not the amount of the inhibitors which adhere to the temperature varying member is larger than the amount of inhibitors corresponding to the threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a configuration diagram which shows a configuration of an internal combustion engine in the first embodiment; 
           [0016]      FIG. 2  is a cross-section diagram showing a configuration of the A/F sensor; 
           [0017]      FIG. 3  shows the graphs indicating the time variation of the temperature of the heater of the A/F sensor; 
           [0018]      FIG. 4  is a flow chart indicating the clogging detection method for the A/F sensor; 
           [0019]      FIG. 5  is a configuration diagram showing a part of the exhaust passage of the internal combustion engine in the second embodiment; 
           [0020]      FIGS. 6A and 6B  show the graphs each of which indicates the time variation of each temperature at the heater of the A/F sensor and the exhaust temperature sensor and graphs each of which indicates the relationship between the temperature of the heater and the exhaust temperature. 
           [0021]      FIG. 7  shows graphs each of which indicates the time variation of the temperature of the heater of the A/F sensor; 
           [0022]      FIG. 8  shows a configuration diagram showing a part of the exhaust passage of the internal combustion engine in the fourth embodiment; and 
           [0023]      FIGS. 9A and 9B  show the graphs each of which indicates the time variation of the temperature of the heater of the A/F sensor and the graphs each of which indicates the relationship between the temperature of the heater and the exhaust temperature. 
       
    
    
     BRIEF DESCRIPTION OF THE REFERENCE NUMBER 
       [0024]      3  Intake air valve 
         [0025]      4  Exhaust valve 
         [0026]      5  Fuel injection valve 
         [0027]      12  Cylinder 
         [0028]      13  Intake air passage 
         [0029]      14  Exhaust passage 
         [0030]      17  EGR passage 
         [0031]      18  Turbocharger 
         [0032]      34  Throttle valve 
         [0033]      42  A/F sensor 
         [0034]      50  ECU 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    Preferred embodiments of the present invention will be explained hereinafter with reference to the drawings. 
       First Embodiment 
       [0036]    The first embodiment of the present invention will be described.  FIG. 1  is a configuration diagram which shows a configuration of an internal combustion engine in the first embodiment. In  FIG. 1 , the solid arrows show the flows of gas and the broken arrows show the flows of signals. 
         [0037]    The internal combustion engine (engine) is, for example, a diesel engine which is mounted as a power source for driving on a vehicle such as an automobile, and includes plural cylinders  12 , an intake air passage  13  and an exhaust passage  14  which are connected to each of the cylinders  12 , and a turbocharger  18  which is arranged in series with the intake air passage  13  and the exhaust passage  14 . It is noted that the internal combustion engine may be a gasoline engine instead of the diesel engine. 
         [0038]    On the exhaust passage  14 , there is provided an EGR (Exhaust Gas Recirculation) passage  17  for recirculating a part of exhaust gas from the exhaust passage  14  to the intake air passage  13 . Hereinafter, the part of the exhaust gas recirculated by the EGR passage  17  is referred to as the EGR gas. An EGR cooler  23  for cooling the EGR gas, and an EGR valve  33  for controlling an amount of the EGR gas are provided on the EGR passage  17 . The EGR valve  33  is controlled by the control signal S 33  supplied from the ECU  50 . 
         [0039]    On the intake air passage  13 , there are provided an air cleaner  21 , an air flow meter  41  which detects an amount of air (intake air) drawn in from the external, a throttle valve  34  for controlling the intake air amount, a compressor  18   a  of the turbocharger  18 , an intercooler  22 , and a surge tank  16  which can store the intake gas (mixed gas of the EGR gas and the intake air). The air flow meter  41  detects the intake air amount and sends the detection signal S 41  corresponding to the detected intake air amount to the ECU  50 . The throttle valve  34  is controlled by the control signal S 34  supplied from the ECU  50 . 
         [0040]    On the exhaust passage  14 , a turbine  18   b  of the turbocharger  18 , an air-fuel ratio sensor (A/F sensor)  42 , and a filter  24  are provided. The A/F sensor  42  detects an air-fuel ratio in the exhaust gas and sends the detection signal S 42  corresponding to the detected air-fuel ratio to the ECU  50 . The filter  24  collects particulate matters in the exhaust gas. Here, the filter is not limited to what only has the filtering function. Instead, what also has a function of a NOx absorber catalyst which absorbs and reduces NOx in the exhaust gas besides the filtering function may be used. 
         [0041]    In the turbocharger  18 , the compressor  18   a  and the turbine  18   b  are configured to revolve integrally. Here, the turbocharger  18 , as shown in  FIG. 1 , may be a variable geometry turbocharger which has a variable nozzle vane  19  and can control the supercharging pressure for example. In the variable geometry turbocharger, the supercharging pressure is controlled by adjusting the opening degree and controlling the amount of the exhaust gas. It is noted that, instead of the turbocharger  18 , another supercharger such as an electrical supercharger can be used as the supercharger. 
         [0042]    The intake air passage  13  and the exhaust passage  14  are connected to the combustion chamber  12   b  of the cylinder  12 , and a fuel injection valve  5  for injecting fuel in the combustion chamber  12   b  is provided on the combustion chamber  12   b.  The fuel injection valve  5  is controlled by the control signal S 5  supplied from the ECU  50 . Also, an intake air valve  3  and an exhaust valve  4  are provided on the cylinder  12 . The intake air valve  3  controls the flow and cutoff between the intake air passage  13  and the combustion chamber  12   b  by opening and closing. The exhaust valve  4  controls the flow and cutoff between the exhaust passage  14  and the combustion chamber  12   b  by opening and closing. In the cylinder  12 , a force which depresses the piston  12   c  to the bottom dead center is transmitted to the crank shaft  15  via the connecting rod  12   d,  and then the crank shaft  15  rotates. Here, a crank angle sensor  44  is provided near the crank shaft  15 . The crank angle sensor  44  detects the rotation angle (crank angle) of the crank shaft  15  and sends the detection signal S 44  corresponding to the detected crank angle to the ECU  50 . 
         [0043]    The ECU (Electronic Control Unit)  50  includes a CPU, a ROM, a RAM, an A/D converter, and input-output interfaces, which are not shown, and controls the engine based on the detection signals supplied from various sensors. Concretely, the ECU  50  receives the detection signals supplied from the air flow meter  41 , the crank angle sensor  44 , and the A/F sensor  42 . The ECU  50  detects operation state of the engine based on the detection signals supplied from these various sensors. The ECU  50  also receives the detection signals according to each of the pedal opening degrees of the accelerator pedal and the brake pedal supplied from the accelerator sensor  45  and the brake sensor  46 . The ECU  50  detects the operation request based on the detection signals supplied from these various sensors. The ECU  50  sends the control signals to the EGR valve  33 , the throttle valve  34 , and the fuel injection valve  5  on the basis of the detected operation state and the detected operation request of the engine. 
         [0044]    Here, a description will be given of a configuration of the A/F sensor  42  with reference to  FIG. 2 .  FIG. 2  is a cross-section diagram showing a configuration of the A/F sensor  42 . 
         [0045]    As shown in  FIG. 2 , the A/F sensor  92  is a glass-type A/F sensor for example, and includes a sensor element  60 , a cover  65 , and a heater  68 . 
         [0046]    The sensor element  60  includes a solid electrolyte  61 , an atmosphere side electrode  62  which is provided on the inner surface of the solid electrolyte  61 , an exhaust side electrode  63  which is provided on the outer surface of the solid electrolyte  61 , and a ceramic coating  64  which covers the exhaust side electrode  63 . The heater  68  is provided at the inside of the atmosphere side electrode  62 . 
         [0047]    The solid electrolyte  61  is made of zirconia for example and is configured to function (become activated) as an oxygen ion conductor on a hot condition of equal to or higher than 300 degree for example. The heater  68  is an electric heater, and heats up and activates the solid electrolyte  61 . The heater  68  is controlled by the ECU  50 . The exhaust side electrode  63  and the atmosphere side electrode  62  are porous-platinum electrodes. In the inside of the solid electrolyte  61 , oxygen ions can transfer freely, and if there is a difference (a difference of the oxygen partial pressure) of the oxygen densities in the both ends, the oxygen ions transfer from one side to the other side in order to reduce the density difference. This transfer phenomenon of the oxygen ions become the transfers of electrons and generate electromotive force between the pair of electrodes consisting of the exhaust side electrode  63  and the atmosphere side electrode  62 . This electromotive force becomes the output voltage of the A/F sensor  42 , and the larger the difference of the oxygen densities is, the larger the voltage becomes. 
         [0048]    The cover  65  is provided to cover the sensor element  60  and includes an inner cover  66  and an outer cover  67 . 
         [0049]    On the cover  65 , small holes are provided to let the exhaust gas pass through. Concretely, as shown in  FIG. 2 , small holes  66   a  and  67   a  are provided on the inner cover  66  and the outer cover  67 , respectively. In the example shown in  FIG. 2 , the holes  66   a  of the inner cover  66  and the holes  67   a  of the outer cover  67  are provided not to overlap with each other. It is noted that the holes  66   a  of the inner cover  66  and the holes  67   a  of the outer cover  67  may be provided to overlap with each other. 
         [0050]    Here, in the holes of the cover  65 , clogging is likely to happen due to adhesions of inhibitors such as particulate matters in the exhaust gas at the time when the exhaust gas passes. For example, in a case where a reductant addition valve is set on the exhaust passage  14  at the upstream side of the A/F sensor  42 , droplets of the reductant adhere to these holes of the cover  65  and the inhibitors adhere to the holes by letting the adherent reductant function as a binder and thereby the clogging in the holes of the cover  65  occurs. Once the clogging in the holes of the cover  65  occurs, it becomes hard for the exhaust gas to reach the sensor element  60  and the detection accuracy of the A/F sensor  42  degrades. For this reason, it is important to know whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. 
         [0051]    Hence, in the detection method for the internal combustion engine in the first embodiment, the ECU  50  determines whether or not the clogging in the holes of the cover  65  of the A/F sensor occurs based on a temperature variation of the heater  68  in a predetermined time period. A concrete description will be given below. 
         [0052]      FIG. 3  shows the graphs each of which indicates the time variation of temperature in the heater  68  of the A/F sensor  42 . The graph  101  indicates a graph in a case where the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur, and the graph  102  indicates a graph in a case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. 
         [0053]    At the time t 1 , the temperature of the heater  68  is L 1  in both of the case where the clogging in the holes of the cover  65  does not occur and the case where the clogging in the holes of the cover  65  occurs. At the time t 1 , the ECU  50  stops the fuel injection by the fuel injection valve  5  thereby to stop the combustion in the cylinders  12  and lets the gas pass through the exhaust passage  14  from the intake air passage  13 . In this case, since the cold gas blows down to the A/F sensor  42 , the temperature of the heater  68  decrease bit by bit as time goes on. 
         [0054]    Here, compared to the case where the clogging in the holes of the cover  65  does not occur, in the case where the clogging in the holes of the cover  65  occurs, it becomes hard for the gas to pass through the holes, and thereby wind force of the gas to the sensor element  60  of the A/F sensor  42  becomes weak and it is difficult for the heater  68  to be cooled by the gas. For this reason, as shown in  FIG. 3 , compared to the case (see the graph  101 ) where the clogging in the holes of the cover  65  does not occur, in the case (see the graph  102 ) where the clogging in the holes of the cover  65  occurs, the amount of the temperature decrease over time becomes smaller. For example, at the time t 2  when a predetermined time period Δt has elapsed since the time t 1 , in the case where the clogging in the holes of the cover  65  does not occur, the temperature of the heater  68  becomes L 2   a  as indicated by the white arrow in  FIG. 3 . In contrast, in the case where the clogging in the holes of the cover  65  occurs, the temperature of the heater becomes L 2   b  (&gt;L 2   a ) as indicated by the black arrow in  FIG. 3 . 
         [0055]    Hence, in the detection method for the internal combustion engine in the first embodiment, at the time t 2 , the ECU  50  determines whether or not the amount of the temperature decrease of the heater  68  becomes smaller than a clogging criterion value predetermined in advance. Here, the clogging criterion value, for example, is set to the amount |L 2   a −L 1 | (corresponding to the length of the white arrow in  FIG. 3 ) of the temperature decrease of the heater  68  in the case where the clogging in the holes of the cover  65  does not occur. The ECU  50  determines that the clogging in the holes of the cover  65  occurs in the case where the amount of the temperature decrease of the heater  68  is smaller than the clogging criterion value, and determines that the clogging in the holes of the cover  65  does not occur in the case where the amount of the temperature decrease of the heater  68  is equal or larger than the clogging criterion value. Thereby the ECU  50  can detect whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. 
         [0056]    Next, a description will be given of the above clogging detection method which detects the clogging of the cover  65  of the A/F sensor  42  with reference to  FIG. 4 .  FIG. 4  is a flow chart indicating the clogging detection method. 
         [0057]    At step S 101 , the ECU  50  recognizes a request to stop the engine on the basis of the operation state of the engine and then the process goes to step S 102 . The ECU  50  recognizes the request to stop the engine, for example, due to the change to an idle operation state or a motoring time of a hybrid vehicle which mounts the engine. 
         [0058]    At step S 102 , the ECU  50  detects the temperature of the heater  68  and determines whether or not the temperature of the heater  68  is equal to or larger than a predetermined temperature. Here, the predetermined temperature is, for example, temperature of the heater  68  at which the A/F sensor  42  is activated. The ECU  50 , for example, measures the impedance of the heater  68  and then can detect the temperature of the heater  68  on the basis of the impedance measured. When the ECU  50  determines that the temperature of the heater  68  is equal to or larger than the predetermined temperature (step S 102 : Yes), the process goes to step S 103 . On the other hand, when determining that the temperature of the heater  68  is smaller than the predetermined temperature (step S 102 : No), the ECU  50  executes a normal control process of stopping the engine and then ends the control process. 
         [0059]    At step S 103 , the ECU  50  obtains the temperature L 1  of the heater  68  at this time. After then, the ECU  50  proceeds to the process at step S 104 . 
         [0060]    At step S 104 , the ECU  50  executes the preliminary control of stopping the engine. Concretely, by sending the control signal S 5  to the fuel injection valve  5  thereby to stop the fuel injection, the ECU  50  stops the combustion in the cylinder  12 . Also, by sending the control signal S 33  to the EGR valve  33  thereby to let the EGR valve  33  be fully closed, and sending the control signal S 34  to the throttle valve  34  thereby to control the opening degrees, the ECU  50  keeps the gas flow amount in the exhaust passage  14  approximately constant. It is noted that, for a variable geometry turbocharger, the ECU  50  additionally controls the opening degrees of the variable nozzle vane  19  in order to keep the gas flow amount in the exhaust passage  14  approximately constant. Thereby it becomes possible to let the cold gas (air) pass through the exhaust passage  14  from the intake air passage  13 . After this, the ECU  50  proceeds to the process at step S 105 . 
         [0061]    At step S 105 , the ECU  50  determines whether or not the predetermined time period Δt has elapsed since the preliminary control of stopping the engine was conducted, and when determining that the predetermined time period Δt has not passed (step S 105 : No), the ECU  50  repeatedly executes the process at step S 105 . On the other hand, when determining that the predetermined time period Δt has elapsed (step S 105 : Yes), the ECU  50  proceeds to the process at step S 106 , and for example by measuring the impedance of the heater  68 , the ECU  50  obtains the temperature L 2  at this time. After this, the ECU  50  proceeds to the process at step S 107 . 
         [0062]    At step S 107 , the ECU  50  executes a control of stopping the engine. Concretely, the ECU  50  decreases the number of engine revolution to 0 and thereby stops the engine completely. After this, the ECU  50  proceeds to the process at step S 108 . 
         [0063]    At step S 108 , the ECU  50  determines whether or not the temperature difference |L 2 −L 1 | of the temperatures of the heater  68  is smaller than the clogging criterion value ΔLc. Here, the clogging criterion value ΔLc is the amount of the temperature decrease of the heater  68  after the predetermined time period Δt in the case where the clogging in the holes of the cover  65  does not occur. When determining that the temperature difference |L 2 −L 1 | is smaller than the clogging criterion value ΔLc (step S 108 :Yes), the ECU  50  determines that the A/F sensor  42  is functioning normally, i.e., the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur (step S 109 ). On the other hand, when determining that the temperature difference |L 2 −L 1 | is equal to or larger than the clogging criterion value ΔLc (step S 108 : No), the A/F sensor  42  has an abnormality, i.e., the clogging in the holes of the cover  65  of the A/F sensor  42  occurs (step S 110 ). After executing the processes at step S 109  or step S 110 , the ECU  50  ends the control process. It is noted that the ECU  50  may execute the processes at step S 108  to S 110  and the process at step S 107  in the inverse order. Namely, the ECU  50  may execute the control of stopping the engine at step S 107  after executing the processes at step S 108  to S 110 . 
         [0064]    As described above, in the detection method for the internal combustion engine in the first embodiment, the ECU  50  lets the cold gas (air) pass through the exhaust passage  14  during the predetermined time period and calculates the amount of the temperature decrease of the heater  68  in the predetermined time period. The amount of the temperature decrease of the heater  68  varies due to whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. Therefore, by calculating the amount of the temperature decrease of the heater  68 , the ECU  50  can detect whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. Also, in the detection method for the internal combustion engine in the first embodiment, since the temperature variation of the heater  68  is used, it is possible to precisely detect whether or not the clogging in the holes of the cover  65  occurs without an influence by the degree of deterioration of the sensor element  60 . 
       Second Embodiment 
       [0065]    Next, the second embodiment of the present invention will be described below. 
         [0066]      FIG. 5  is a configuration diagram showing a part of the exhaust passage of the internal combustion engine in the second embodiment. The configuration of the internal combustion engine in the second embodiment has an exhaust temperature sensor  43  on the exhaust passage  14  in addition to the configuration of the internal combustion engine in the first embodiment. Concretely, the exhaust temperature sensor  43  is provided on a streamline which is approximately same as the streamline where the A/F sensor  42  is provided and is exposed to the exhaust gas which has approximately-same temperature as the exhaust gas to which the A/F sensor  42  is exposed. For example, an exhaust temperature sensor for estimating the temperature of the filter  24 , which is originally provided on the exhaust passage  14  at the upstream side of the filter  24 , can be used as this kind of exhaust temperature sensor  43 . 
         [0067]      FIG. 6A  shows the graphs each of which indicates the time variation of each temperature at the heater  68  of the A/F sensor  42  and the exhaust temperature sensor  43 . The graph  201  indicates the temperature variation of the heater  68  in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur, and the graph  202  indicates the temperature variation of the heater  68  in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs, and the graph  203  indicates the variation of the temperature which is detected by the exhaust temperature sensor  43 . Hereinafter, temperature which is detected by the exhaust temperature sensor  43  is referred to as “exhaust temperature”. 
         [0068]    At the time t 1 , the ECU  50  stops the fuel injection by the fuel injection valve  5  thereby to stop the combustion in the cylinders  12  and lets the gas pass through the exhaust passage  14  from the intake air passage  13 . Temperature which is detected by the exhaust temperature sensor at this time t 1  is expressed as “MO”, and temperature of the heater  68  of the A/F sensor  42  at the time t 1  is expressed as “L 1 ”. 
         [0069]      FIG. 6B  shows the graphs each of which indicates the relationship between the temperature of the heater  68  and the exhaust temperature. In  FIG. 6B , the graphs in  FIG. 6A  is modified to the graphs each of which indicates the relationship between the temperature of the heater  68  and the exhaust temperature. The graph  301  is a graph which indicates the relationship between the temperature of the heater  68  and the exhaust temperature in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur. The graph  302  is a graph which indicates the relationship between the temperature of the heater  68  and the exhaust temperature in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. 
         [0070]    As shown in  FIG. 6B , whereas the graph  301  is approximately linear, the graph  302  is curved toward the direction where the temperature of the heater  68  becomes higher. As indicated by the graph  301 , in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur, the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature is approximately constant. In contrast, as indicated by the graph  302 , in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs, the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature varies significantly. 
         [0071]    For example, in response to the decrease of the exhaust temperature to a smaller value than the temperature MO, the ratio of the temperature decrease of the heater  68  in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur becomes approximately constant as indicated by the graph  301 . On the other hand, as indicated by the tangent lines IL 1 , IL 2  to the graph  302 , the gradients of the tangent lines to the graph  302  becomes larger and larger in response to the decrease of the exhaust temperature to a smaller value than the temperature MO. In other words, the ratio of the temperature decrease of the heater  68 , in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs, becomes larger and larger as the exhaust temperature decreases from the temperature MO. 
         [0072]    Hence, in the detection method for the in the internal combustion engine in the second embodiment, the ECU  50  calculates the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature and determines whether or not the ratio of the temperature variation is approximately constant. For example, the ECU  50  detects temperature of the heater  68  per a predetermined time period while the exhaust gas varies, and calculates a map, like what is shown in  FIG. 6B , which indicates a relationship between the exhaust temperature and the temperature of the heater  68 . Then, by using the map, the ECU  50  calculates the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature and determines whether or not the ratio calculated is approximately constant. When determining that the ratio calculated is approximately constant, the ECU  50  determines that the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur. In contrast, the ECU  50  determines that the clogging in the holes of the cover  65  of the A/F sensor  42  occurs in a case where the ratio calculated is not constant and is changing toward the direction where the temperature of the heater  68  becomes higher over the variation of the exhaust temperature as indicated by the graph  302 . For example, in the case where the ratio of the temperature decrease of the heater  68  becomes larger and larger as the exhaust temperature decreases from the temperature MO, the ECU  50  determines that the temperature of the heater  68  is changing toward the direction where the temperature of the heater  68  becomes higher and that the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. 
         [0073]    As described above, in the detection method for the in the internal combustion engine in the second embodiment, similarly to the detection method for the internal combustion engine in the first embodiment, since the temperature variation of the heater  68  is used, it is possible to precisely detect whether or not the clogging in the holes of the cover  65  occurs without the influence by the degree of deterioration of the sensor element  60 . Furthermore, in the detection method for the internal combustion engine in the second embodiment, the ECU  50  executes the clogging detection process of the cover  65  of the A/F sensor  42  on the basis of the temperature variation of the exhaust temperature which is detected by the exhaust temperature sensor  43 . Therefore, in the detection method for the internal combustion engine in the second embodiment, without stopping the combustion in the cylinders  12  and significantly decreasing the temperature of the gas which flows in the exhaust passage, only by keeping the flow amount of the exhaust gas approximately constant during the predetermined time period when the exhaust temperature is changing, it is possible to precisely detect whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. Thus, in the detection method for the internal combustion engine in the second embodiment, for example, even at the time of an idle operation state, it is possible to detect whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. 
       Third Embodiment 
       [0074]    Next, the third embodiment of the present invention will be described. The configuration of the internal combustion engine in the third embodiment is the same as the configuration ( FIG. 1 ) of the internal combustion engine in the first embodiment. 
         [0075]      FIG. 7 , similarly to  FIG. 3 , shows the graphs each of which indicates the time variation of the temperature of the heater  68  of the A/F sensor  42 . The graph  401  indicates temperature variation of the heater  68  in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur and each of the graphs  402  to  404  indicates the temperature variation of the heater  68  in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. In  FIG. 7 , the state of the A/F sensor  42  indicated by the graph  404  has the greatest degree of the clogging in the holes of the cover  65 , and the state of the A/F sensor  42  indicated by the graph  402  has the smallest degree of the clogging in the holes of the cover  65 , out of the all states of the A/F sensor  42  indicated by the graphs  402  to  404 . 
         [0076]    At the time t 1 , the temperature of the heater  68  is L 1  in both the case where the clogging in the holes of the cover  65  does not occur and the case where the clogging in the holes of the cover  65  occurs. At the time t 1 , the ECU  50  stops the fuel injection by the fuel injection valve  5  thereby to stop the combustion in the cylinders  12  and lets the gas pass through the exhaust passage  14  from the intake air passage  13 . 
         [0077]    At the time t 2  when a time period Δt predetermined has elapsed since the time t 1 , as indicated by the white arrow, the temperature of the heater  68 , in the case where the clogging in the holes of the cover  65  does not occur, becomes L 2   a . In contrast, as indicated by the black arrows, the temperatures of the heater  68 , in the case where the clogging in the holes of the cover  65  occurs, become L 2   b  to L 2   d.  In other words, the greater the degree of the clogging in the holes of the cover  65  is, the smaller the amount (the length of the black arrow) of the temperature decrease becomes. This is because, the greater the degree of the clogging in the holes of the cover  65  is, the harder it becomes for the gas to pass through the holes. 
         [0078]    Hence, in the detection method for the internal combustion engine in the third embodiment, the ECU  50  sets a threshold of the amount of the temperature decrease of the heater  68  in accordance with the amounts of inhibitors which adhere to the holes of the cover  65  and then determines whether or not the amount of the temperature decrease of the heater  68  is smaller than the threshold. Thereby it is possible to determine whether or not the amount of the inhibitors which adhere to the holes of the cover  65  is larger than the amount of inhibitors corresponding to the threshold. For example, by setting in advance the threshold in accordance with the limit amount of inhibitors which can be cleared by cleansing the A/F sensor  42 , the ECU  50  can determine whether or not inhibitors the amount of which can be cleared by the cleansing adhere to the A/F sensor  42 . Concretely, the ECU  50  determines that the inhibitors the amount of which can be cleared by the cleansing adhere to the A/F sensor  42  when the amount of the temperature decrease is smaller than the threshold. At this time, the ECU  50  can inform the driver of the abnormal state where an exchange of the A/F sensor  42  is encouraged, for example, by lighting up a caution-advisory indicator provided on the driving seat. 
         [0079]    In the above example, the first embodiment is applied as an example, but the second embodiment and the third embodiment can be combined. In the second embodiment, the ECU  50  determines that the temperature of the heater  68  is changing toward the direction which the temperature of the heater  68  becomes higher and that the clogging in the holes of the cover  65  of the A/F sensor  42  occurs in the case where the rate of the temperature decrease of the heater  68  becomes larger and larger as the exhaust temperature decreases from the temperature MO. The larger the amount of the inhibitors is, the larger the degree of the temperature increase of the heater  68  becomes. Namely, the graph  302  shown in  FIG. 6B  curves toward the direction where temperature of the heater  68  becomes higher. Thus, similarly to the above example, in the case of letting the exhaust temperature decrease from the temperature MO, by setting the threshold of the rate of the temperature decrease of the heater  68  in accordance with the amount of the inhibitors which adhere to the holes of the cover  65 , the ECU  50  can determine whether or not the amount of the inhibitors which adhere to the holes of the cover  65  is larger than the amount of inhibitors corresponding to the threshold. 
       Fourth Embodiment 
       [0080]    Next, the fourth embodiment of the present invention will be described below. 
         [0081]      FIG. 8  is a configuration diagram showing a part of the exhaust passage of the internal combustion engine in the fourth embodiment. As shown in  FIG. 8 , in the internal combustion engine in the fourth embodiment, the A/F sensor  42  is provided on the exhaust passage  14  at the downstream side of the filter  24 . Other part of the configuration is similar to the configuration ( FIG. 1 ) of the internal combustion engine in the first embodiment. 
         [0082]    The filter  24  has a partition whose pores are open and collects the inhibitors in the exhaust gas by the partition by letting the exhaust gas pass through the partition. In the partition, oxidation catalysts such as platinum (Pt) and cerium oxide (CeO2) are supported and the inhibitors collected is oxidized by the oxidation catalysts. Therefore, when the filter  24  is functioning normally, the inhibitors do not almost adhere to the holes of the cover  65  of the A/F sensor  42  provided on the exhaust passage  14  at downstream side of the filter  24 . 
         [0083]    In contrast, in the case where the function of the filter  24  which collects the inhibitors in the exhaust gas has decreased due to cracks of the partition, the inhibitors drains into the exhaust passage  14  at downstream side of the filter  24 . Hence, in this case, the inhibitors adhere to the holes of the cover  65  of the A/F sensor  42  provided on the exhaust passage  14  at the downstream side of the filter  24  and thereby the clogging occurs. 
         [0084]    Hence, in the detection method for the internal combustion engine in the fourth embodiment, the ECU  50  calculates the temperature variation of the heater  68  of the A/F sensor  42  provided on the exhaust passage  14  at the downstream side of the filter  24  and, by using the detection method for the internal combustion engine in the first or the second embodiment, determines whether or not the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. Thereby it becomes possible to determine whether or not the filter  24  is functioning normally. Concretely, when determining that the clogging in the holes of the cover  65  of the A/F sensor  42  occurs, the ECU  50  can determine that the function of the filter  24  has decreased, and when determining that the clogging in the holes of the cover  65  of the A/F sensor  42  does not occur, the ECU  50  can determine that the function of the filter  24  is functioning normally. 
       APPLICATION 
       [0085]    Next, an application will be described below. In each of the above embodiments, the ECU  50  determines whether or not the clogging in the holes of the cover  65  occurs on the basis of the temperature variation of the heater  68 . These detection methods take advantage of the fact that the gas flow amount to the heater  68  in the case where the clogging of the cover  65  occurs is smaller than the gas flow amount to the heater  68  in the case where the clogging of the cover  65  does not occur. 
         [0086]    In contrast, the gas flow amount to the heater  68  in the case where cracking in the cover  65  occurs is larger than the gas flow amount to the heater  68  in the case where the cracking in the cover  65  does not occur. 
         [0087]      FIG. 9A , similarly to  FIG. 3 , shows the graphs each of which indicates the time variation of the temperature of the heater  68  of the A/F sensor  42 . The graph  501  indicates the temperature variation of the heater  68  in the case where both the clogging and the cracking in the cover  65  of the A/F sensor  42  do not occur, and the graph  502  indicates the temperature variation of the heater  68  in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs . The graph  503  indicates the temperature variation of the heater  68  in the case where the cracking in the cover  65  of the A/F sensor  42  occurs. 
         [0088]    At the time t 1 , the ECU  50  stops the fuel injection by the fuel injection valve  5  thereby to stop the combustion in the cylinders  12  and lets the gas pass through the exhaust passage  14  from the intake air passage  13 . 
         [0089]    At the time t 2  when a time period Δt predetermined has elapsed since the time t 1 , the temperature of the heater  68 , in the case where both the clogging and the cracking in the cover  65  do not occur, becomes L 2   a . In contrast, at the time t 2 , the temperature of the heater  68 , in the case where the clogging in the holes of the cover  65  occurs, becomes L 2   b  (&gt;L 2   a ) and the temperature of the heater  68 , in the case where the cracking in the cover  65  occurs, becomes L 2   bb  (&lt;L 2   a ). 
         [0090]    As shown in  FIG. 9A , the amount of the temperature decrease of the heater  68  over time becomes large because the amount of the gas flow to the heater  68 , in the case where the cracking in the cover  65  of the A/F sensor  42  occurs, is larger than that in the case where the cracking in the cover  65  does not occur. 
         [0091]    Hence, in the detection methods for the internal combustion engine in the applications for each of the above embodiments, the ECU  50  not only determines whether or not the clogging in the holes of the cover  65  occurs but also determines whether or not the cover  65  has cracked on the basis of the temperature variation of the heater  68 . 
         [0092]    In the application of the first embodiment, the ECU  50  not only determines whether or not the amount of the temperature decrease of the heater  68  is smaller than a predetermined clogging criterion value but also determines whether or not the amount of the temperature decrease is smaller than a predetermined cracking criterion value. Here, the cracking criterion value is a compatible value calculated by experimental trials and is set to a value which is smaller than the clogging criterion value. The ECU  50  determines that the cracking in the cover  65  occurs in the case where the amount of the temperature decrease of the heater  68  is smaller than the cracking criterion value, and determines that the cracking in the cover  65  does not occur in the case where the amount of the temperature decrease of the heater  68  is equal to or larger than the cracking criterion value. In other words, the ECU  50  determines that both the clogging and the cracking in the cover  65  of the A/F sensor  42  do not occur when the amount of the temperature decrease of the heater  68  is smaller than the clogging criterion value and equal to or larger than the cracking criterion value. 
         [0093]      FIG. 93 , similarly to  FIG. 63 , shows the graphs each of which shows the relationship between the temperature of the heater  68  and the exhaust temperature. The graph  601  is a graph showing the relationship between the temperature of the heater  68  and the exhaust temperature in the case where both the clogging and the cracking in the cover  65  of the A/F sensor  42  do not occur. The graph  602  is a graph showing the relationship between the temperature of the heater  68  and the exhaust temperature in the case where the clogging in the holes of the cover  65  of the A/F sensor  42  occurs. The graph  603  is a graph showing the relationship between the temperature of the heater  68  and the exhaust temperature in the case where the cracking in the cover  65  of the A/F sensor  42  occurs. 
         [0094]    As shown in  FIG. 9B , whereas the graph  601  is approximately linear, the graph  603  is curved toward the direction where the temperature of the heater  68  becomes lower. As indicated by the graph  601 , the temperature of the heater  68 , in the case where both the clogging and the cracking in the cover  65  of the A/F sensor  42  do not occur, varies at an approximately constant rate to the variation of the exhaust temperature. In contrast, as shown in the graph  603 , in the case where the cracking in the cover  65  of the A/F sensor  42  occurs, similarly to the case (see graph  602 ) where the clogging in the holes of the cover  65  occurs, the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature varies significantly. 
         [0095]    For example, as indicated by the tangent lines IL 1   a , IL 2   a  to the graph  603 , the gradient of the tangent line to the graph  603  becomes smaller and smaller as the exhaust temperature decreases from the temperature MO. In other words, as the exhaust temperature decreases from the temperature MO, the ratio of the temperature decrease of the heater  68 , in the case where the cracking in the cover  65  of the A/F sensor  42  occurs, becomes smaller and smaller. 
         [0096]    Hence, in the application of the second embodiment, the ECU  50  determines how the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature gradually changes in the case where the ratio of the temperature variation of the heater  68  to the variation of the exhaust temperature is not approximately constant. Concretely, the ECU  50  determines that the clogging in the holes of the cover  65  of the A/F sensor  42  occurs when the temperature of the heater  68  is changing toward the direction where the temperature becomes higher with the change of the exhaust temperature as indicated by the graph  602 . On the other hand, the ECU  50  determines that the cracking in the cover  65  of the A/F sensor  42  occurs when the temperature of the heater  68  is changing toward the direction where the temperature becomes lower with the change of the exhaust temperature as indicated by the graph  603 . For example, the ECU  50  determines that the clogging in the holes of the cover  65  of the A/F sensor  42  occurs in the case where the rate of the temperature decrease of the heater  68  is larger and larger as the exhaust temperature decreases from the temperature MO, and determines that the cracking in the cover  65  of the A/F sensor  42  occurs in the case where the rate of the temperature decrease of the heater  68  is smaller and smaller. 
         [0097]    As described above, in the detection method in the application, it becomes possible not only to determine whether or not the clogging in the holes of the cover  65  occurs but also to determine whether or not the cracking in the cover  65  occurs on the basis of the temperature variation of the heater  68 . It goes without saying that in the above application whether or not the clogging in the holes of the cover  65  occurs is also determined, but instead of this, only whether or not the cracking in the cover  65  occurs may be determined. 
       MODIFICATION 
       [0098]    In each of the above embodiments and the application, the ECU  50  detects the temperature of the heater  68  based on the impedance of the heater  68  and determine whether or not the clogging in the holes of the cover  65  (or the cracking of the cover  65 ) occurs on the basis of the amount of temperature variation of the heater  68 . However, instead of by using the temperature variation, by using an amount of impedance variation of the heater  68 , the ECU  50  may determine whether or not the clogging in the holes of the cover  65  (or the cracking of the cover  65 ) occurs. For example, in the first embodiment, instead of determining whether or not the temperature variation between the time t 1  and the time t 2  is smaller than the clogging criterion value, the ECU  50  may determine whether or not the impedance variation between the time t 1  and the time t 2  is smaller than the impedance corresponding to the clogging criterion value. 
         [0099]    In addition, the present invention is not limited to what is applied to the A/F sensor, but also can be applied to other various sensors. Further, in each of the above embodiments and the application, the above detection method is executed in order to determine whether or not the clogging in the holes of the cover occurs, but it is not limited to this. Namely, by executing the above detection process for a sensor which does not have a cover, it is also possible to determine whether or not the inhibitors adhere directly to the sensor precisely. 
         [0100]    For example, instead of the A/F sensor, the present invention can also be applied to a case where a temperature sensor is used. In this case, by using the detection method in the each of the embodiments and the application, the ECU  50  can determine whether or not inhibitors adhere to the temperature sensor on the basis of the temperature variation detected by the temperature sensor. Here, it goes without saying that the ECU  50  may determine whether or not the inhibitors adhere by using a variation of a signal output value (voltage value and/or current value) correlated with the temperature supplied from the temperature sensor instead of using the temperature variation. 
         [0101]    It also goes without saying that the present invention is not limited what is applied to sensors but also applied to a temperature varying member whose temperature varies in response to the gas flow in the exhaust passage. 
         [0102]    In addition, the present invention is not limited to the above embodiments and these can be accordingly changed in the range where the changes do not go against the gist or the ideas which can be seen in all of the claims and the specification and the embodiments to which the changes is applied is also included in the technical scope of the present invention. 
       INDUSTRIAL APPLICABILITY 
       [0103]    This invention can be used for an internal combustion engine which includes a temperature varying member such as a sensor which varies in response to an exhaust temperature.