Patent Publication Number: US-8978598-B2

Title: Sensor abnormality detection apparatus and a block heater installation determining apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application of International Application No. PCT/JP2010/053903, filed Mar. 9, 2010, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention is related to a sensor abnormality detection apparatus which is installed in a vehicle with an electric water pump for circulating engine cooling water, a block heater installation determining apparatus, etc. 
     BACKGROUND ART 
     JP2008-298058A discloses a controller of an engine which has a function of warming engine cooling water by energizing a block heater, which is installed on the engine, during an engine off period in cold climates, wherein a relationship between the presence or absence of energization of the block heater during the engine off period and a behavior of a temperature of a cooling medium immediately after the engine starts is utilized to determine whether there has been energization of the block heater during the engine off period. If it is determined that there has been energization of the block heater, an abnormality diagnosing process related to a cooling system is prevented or an abnormality diagnosing condition is changed. 
     However, in the case of a vehicle which includes an electric water pump for circulating engine cooling water, driving the electric water pump before the warming-up of the engine is not useful, except for a special situation, in terms of energy saving. On the other hand, if the electric water pump is not driven before the warming-up of the engine, the presence or absence of energization of the block heater cannot be determined with high accuracy, which leads to a problem that an abnormality detection of a cooling water temperature sensor, etc cannot be performed with high accuracy. 
     SUMMARY OF INVENTION 
     Therefore, it is an object of the present invention to provide a sensor abnormality detection apparatus, a block heater installation determining apparatus, etc., which can detect the presence or absence of energization of the block heater with high accuracy and use it for a sensor abnormality determination, while saving energy. 
     In order to achieve the aforementioned objects, according to the first aspect of the present invention, a sensor abnormality detection apparatus is provided which is installed in a vehicle with an electric water pump for circulating engine cooling water and is configured to perform an abnormality detecting process related to a first temperature sensor or a second temperature sensor based on a relationship between a detection result of the first temperature sensor for detecting a temperature of the engine cooling water and a detection result of the second temperature sensor for detecting a temperature of another medium which is correlated with the temperature of the engine cooling water or an estimation result of the temperature of the engine cooling water. 
     The sensor abnormality detection apparatus includes a water pump forced-operating part configured to force the electric water pump to operate if the detection result of the first temperature sensor and the detection result of the second temperature sensor or the estimation result of the temperature of the engine cooling water do not meet a predetermined relationship, under a condition where the electric water pump is not operated after an engine starts. 
     The sensor abnormality detection apparatus is configured such that if a decrease in the temperature of the engine cooling water is observed based on the detection result of the first temperature sensor after the forced-operation of the electric water pump by the water pump forced-operating part, the abnormality detecting process is prevented, an abnormality detection result is invalidated, or an abnormality detecting way of the abnormality detecting process is changed. 
     According to the present invention, it is possible to obtain a sensor abnormality detection apparatus, a block heater installation determining apparatus, etc., which can detect the presence or absence of energization of the block heater with high accuracy and use it for a sensor abnormality determination, while saving energy. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for schematically illustrating an engine control system as a whole according to an embodiment of the present invention; 
         FIG. 2  is a function diagram for illustrating a main functional part of an ECU  41  related to an abnormality detection; 
         FIG. 3  is a flowchart for showing an example of a main process executed by a sensor abnormality detecting apparatus  50  according to the embodiment; 
         FIG. 4  is a graph which shows a relationship between a soak time, a cooling water temperature and an intake air temperature. 
         FIG. 5  is a diagram for schematically illustrating several examples of a variation pattern of the cooling water temperature after the engine starts according to the presence or absence of energization of the block heater; 
         FIG. 6  is a flowchart for showing another example of the main process executed by a sensor abnormality detecting apparatus  50  according to the embodiment; 
         FIG. 7  is a flowchart for showing yet another example of the main process executed by a sensor abnormality detecting apparatus  50  according to the embodiment; and 
         FIG. 8  is a flowchart for showing an example of a main process executed by a controller  70  of an electric water pump according to the embodiment. 
     
    
    
     EXPLANATION FOR REFERENCE NUMBERS 
     
         
         
           
               11  engine 
               12  intake pipe 
               13  air cleaner 
               14  airflow meter 
               14   a  intake air temperature sensor 
               15  motor 
               16  throttle valve 
               17  throttle position sensor 
               18  surge tank 
               19  intake pipe pressure sensor 
               20  inlet manifold 
               21  fuel injection valve 
               22  spark plug 
               23  exhaust pipe 
               24  catalyst 
               25  exhaust gas sensor 
               26  crank angle sensor 
               28  cooling water circulating circuit 
               29  radiator 
               30  thermostat valve 
               31  electric water pump 
               32  cooling water temperature sensor 
               33  cooling fan 
               34  block heater 
               35  power cord 
               36  plug 
               41  ECU 
               42  main relay 
               42   a  relay contact 
               42   b  relay driving coil 
               43  IG switch 
               44  soak timer 
               46  warning lamp 
               50  sensor abnormality detection apparatus 
               52  sensor abnormality determining part 
               54  block heater determining part 
               60  block heater installation determining apparatus 
               70  controller of an electric water pump 
               72  W/P forced-operating part 
               74  W/P ordinary control part 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the following, the best mode for carrying out the present invention will be described in detail by referring to the accompanying drawings. 
       FIG. 1  is a diagram for schematically illustrating an engine control system as a whole according to an embodiment of the present invention. An air cleaner  13  is provided at the most upstream point in an intake pipe  12  of an engine  11  (an internal combustion engine). An airflow meter  14  for detecting an intake air flow is provided downstream of the air cleaner  13 . An intake air temperature sensor  14   a  for detecting an intake air temperature (an outside air temperature) is provided in the airflow meter  14 . It is noted that the airflow meter  14  may be a hot wire type or hot film type of an airflow meter which incorporates the intake air temperature sensor  14   a  therein. A throttle valve  16  whose position is adjusted by a motor  15  and a throttle position sensor  17  for detecting the position of the throttle valve  16  (i.e., a throttle position) are provided downstream of the airflow meter  14 . 
     A surge tank  18  is provided downstream of the throttle valve  16 . An intake pipe pressure sensor  19  for detecting an intake pipe pressure is provided in the surge tank  18 . Further, inlet manifolds  20  for introducing air into the respective cylinders of the engine  11  are connected to the surge tank  18 . Fuel injection valves  21  for injecting fuel are attached near intake ports of the inlet manifold  20 . Further, spark plugs  22  are attached to cylinder heads of the engine  11  on a cylinder basis, and air fuel mixture in the cylinders is ignited by electric arcs from the respective spark plugs  22 . 
     A catalyst  24  for catalytically clearing CO, HC, NOx, etc., in exhaust gas, such as a three way catalyst, is provided in an exhaust pipe  23  (an exhaust passage). An exhaust gas sensor  25  for detecting an air/fuel ratio of the exhaust gas or rich/lean, etc., is provided upstream of the catalyst  24 . Further, a crank angle sensor  26  for outputting pulse signals when a crank shaft is rotated a predetermined crank angle is attached to the engine  11 . A crank angle and an engine rotational speed are detected based on the output signal of the crank angle sensor  26 . 
     A cooling water circulating circuit  28  is provided in which cooling water of the engine  11  is circulated. A radiator  29  for radiating heat of the cooling water, a thermostat valve  30  for controlling flow rate of the cooling water circulating to the radiator  29 , and an electric water pump  31  for circulating the cooling water are provided in the cooling water circulating circuit  28 . The electric water pump  31  is supplied with power from an on-vehicle battery (not shown). Further, a cooling water temperature sensor  32  is provided near an outlet of the cooling water of the engine  11  in the cooling water circulating circuit  28 . The cooling water temperature sensor  32  detects a temperature of the cooling water (i.e., a circulating water temperature) which flows from the engine  11  to the cooling water circulating circuit  28 . It is noted that the cooling water temperature sensor  32  may be provided at any location as long as it can detect the temperature of the cooling water of the engine  11 . Further, a cooling fan  33  for performing forced cooling of the cooling water is provided behind the radiator  29 . 
     A block heater  34  for freeze proofing is provided on a cylinder block of the engine  11 . The block heater  34  has a power cord  35  connected thereto. During the engine off period in cold climates, a user may prevent the cooling water of the engine  11  from freezing by inserting a plug  36  of the power cord  35  of the block heater  34  into a convenience receptacle (not shown), which is an external power supply, to energize the block heater  34 . Before starting the engine  11 , the user removes the plug  36  of the power cord  35  from the convenience receptacle and stores it at any appropriate location in an engine room. 
     It is noted that since, except for cold climates, it is not necessary to warm the cooling water with the block heater  34 , the power cord  35  of the block heater  34  is kept in the engine room even during the engine off period and thus the block heater  34  is not energized. 
     The output signals of the various sensors such as the cooling water temperature sensor  32  are input to an electronic control unit (referred to as an ECU, hereinafter)  41 . To a power supply terminal of the ECU  41  is applied power supply voltage Vb from the on-vehicle battery (not shown) via a main relay  42 . A relay driving coil  42   b  for driving a relay contact  42   a  of the main relay  42  is connected to a main relay control terminal of the ECU  41 . The ECU  41 , etc., are supplied with the power supply voltage when the relay contact  42   a  is turned on by energizing the relay driving coil  42   b . The power supply to the ECU  41 , etc., is stopped when the relay contact  42   a  is turned off by stopping energizing the relay driving coil  42   b.    
     An on/off signal of an ignition switch (referred to as an IG switch, hereinafter)  43  is input to an IG switch terminal of the ECU  41 . When the IG switch  43  is turned on, the main relay  42  is turned on and thus the power supply to the ECU  41 , etc., is initiated. When the IG switch  43  is turned off, the main relay  42  is turned off and thus the power supply to the ECU  41 , etc., is stopped. 
     A soak timer  44 , which is powered from a backup power supply (not shown) to perform a timer operation, is incorporated in the ECU  41 . The soak timer  44  starts the timer operation after the engine stop (for example, after the IG switch  43  is turned off) to measure an elapsed time after the engine stop. 
     The ECU  41  is configured to mainly include a microprocessor that includes a CPU, a ROM in which control programs are stored, a RAM in which calculation results are stored, a timer, a counter, an input interface, an output interface, etc., for example. The ECU  41  implements control of an injection quantity with the injection valves  21  and an ignition timing with the spark plugs  22  by the CPU executing various engine control programs stored in the ROM. 
     Further, as described in detail hereinafter, the ECU  41  implements respective embodiments of a sensor abnormality detection apparatus  50 , block heater installation determining apparatus  60  and a controller  70  of the electric water pump  31  by the CPU executing various programs stored in the ROM. 
       FIG. 2  is a function diagram for illustrating a main functional part of the ECU  41  related to a sensor abnormality detecting process. 
     The ECU  41  includes a sensor abnormality determining part  52 , a block heater determining part  54 , a W/P forced-operating part  72  for forcing the electric water pump  31  to operate and a W/P ordinary control part  74  for performing ordinary control of the electric water pump  31 , as shown in  FIG. 2 . 
     The sensor abnormality determining part  52 , the block heater determining part  54  and the W/P forced-operating part  72  implement an embodiment of the sensor abnormality detection apparatus  50  in cooperation. Further, the block heater determining part  54  and the W/P forced-operating part  72  implement an embodiment of the block heater installation determining apparatus  60  in cooperation. Further, the W/P forced-operating part  72  and the W/P ordinary control part  74  implement an embodiment of the controller  70  of the electric water pump in cooperation. Hereinafter, the functions of the respective parts are described in detail. 
       FIG. 3  is a flowchart for showing an example of a main process executed by the sensor abnormality detecting apparatus  50  according to the embodiment. The process routine shown in  FIG. 3  is started at the time of starting the engine (at the time of warming-up). 
     In step  300 , the sensor abnormality determining part  52  determines whether the vehicle has been soaked more than or equal to 7 hours based on the information from the soak timer  44 . In other words, it is determined whether the engine off state has been maintained more than or equal to 7 hours after the engine was turned off. If it is determined that the vehicle has been soaked with engine off more than or equal to 7 hours, the process routine goes to step  302 . On the other hand, if it is determined that the vehicle has not been soaked more than or equal to 7 hours (i.e., the vehicle has been soaked less than 7 hours), the process routine ends without performing any further process, determining that it is not possible to perform the sensor abnormality determination with high accuracy at this time of the engine start. 
     In step  302 , the sensor abnormality determining part  52  determines whether an absolute value of a difference between the cooling water temperature and the intake air temperature (=the cooling water temperature−the intake air temperature) is smaller than 20 degrees Celsius based on the latest detection results of the intake air temperature sensor  14   a  and the cooling water temperature sensor  32 . This is because the difference between the cooling water temperature and the intake air temperature converges to be smaller than or equal to a predetermined temperature (20 degrees Celsius, in this example) when the soak time exceeds a certain time (7 hours, in this example), as shown in  FIG. 4 . It is noted that the 7 hours and the 20 degrees Celsius are merely examples and appropriate values may be changed depending on vehicle types. Thus, the values may be determined by deriving the correlation as shown in  FIG. 4  by experiment, etc. 
     In this step  302 , if the absolute value of the difference between the cooling water temperature and the intake air temperature is smaller than 20 degrees Celsius, the process routine goes to step  314 . On the other hand, if the absolute value of the difference between the cooling water temperature and the intake air temperature is greater than or equal to 20 degrees Celsius, the process routine goes to step  304 . 
     In step  304 , the W/P forced-operating part  72  forces the electric water pump  31  to operate. Then, the electric water pump  31  operates and thus the cooling water of the engine  11  begins to circulate in the cooling water circulating circuit  28 . 
     In step  306 , the block heater determining part  54  monitors the detection result of the cooling water temperature sensor  32  after the electric water pump  31  is forced to operate in step  304 , and determines whether a decrease in the temperature of the cooling water is observed after the electric water pump  31  is forced to operate in step  304 . 
     Here, during the engine off period, the circulation of the cooling water in the cooling water circulating circuit  28  is stopped. Thus, if the block heater  34  is energized during the engine off period, the cooling water in the cylinder block of the engine  11  which is close to the block heater  34 , compared to the rest of the cooling water in cooling water circulating circuit  28 , is sufficiently heated by the heat transferred from the block heater  34  and thus has a relatively high temperature. On the other hand, the cooling water on a side of the radiator  29  which is farther side with respect to the block heater  34  is difficult to be heated by the heat from the block heater  34 . For this reason, the temperature of the cooling water on the side of the radiator  29  tends to be substantially lower than that of the cooling water on the side of the engine  11 . Consequently, when the cooling water begins to circulate in the cooling water circulating circuit  28 , the warmed cooling water in the engine  11  flows out to the side of the radiator  29  and the cooled cooling water on the side of the radiator  29  flows into the engine  11  such that they change places. Thus, if the block heater  34  is energized during the engine off period, such a phenomenon occurs in which the cooling water temperature in the engine  11  (detected values of the cooling water temperature sensor  32 ) considerably decreases immediately after the engine starts, as indicated by lines X 1  and X 2  in  FIG. 5 . It is noted that in  FIG. 5 , the lines X 1  and X 2  indicate examples of variation patterns of the cooling water temperature (i.e., the detected values of the cooling water temperature sensor  32 ) if there has been energization of the block heater  34 , while a line X 3  indicates the cooling water temperature (i.e., the detected values of the cooling water temperature sensor  32 ) if there has been no energization of the block heater  34  or there is no block heater attached. It is noted that as indicated by the lines X 1  and X 2 , depending on a vehicle type (i.e., locations of the cooling water temperature sensor  32  and the block heater  34 , etc), in some cases the detected values of the cooling water temperature sensor  32  tend to decrease after it increases temporarily, while in other cases, the detected values of the cooling water temperature sensor  32  tend to decrease directly. In any case, by observing such a decrease in the cooling water temperature, it is possible to determine the presence or absence of energization of the block heater  34  with high accuracy. 
     In this step  306 , if the decrease in the cooling water temperature is observed, the process routine ends without performing any further process, determining that it is not possible to perform the sensor abnormality determination with high accuracy at this time of the engine start because the block heater has been energized during the engine off period. On the other hand, if the decrease in the cooling water temperature is not observed, the process routine goes to step  308 . 
     In step  308 , the sensor abnormality determining part  52  determines again whether the absolute value of a difference between the cooling water temperature and the intake air temperature is smaller than 20 degrees Celsius based on the latest detection results of the intake air temperature sensor  14   a  and the cooling water sensor  32 . In this step  308 , if the absolute value of the difference between the cooling water temperature and the intake air temperature is smaller than 20 degrees Celsius, the process routine goes to step  312 . On the other hand, if the absolute value of the difference between the cooling water temperature and the intake air temperature is greater than or equal to 20 degrees Celsius, the process routine goes to step  310 . 
     In step  310 , the sensor abnormality determining part  52  generates and outputs a determination result which indicates that at least one of the intake air temperature sensor  14   a  and the cooling water temperature sensor  32  is abnormal. In this case, the sensor abnormality determining part  52  warns the driver by turning on a warning lamp  46  provided in the instrument panel on the side of the driver seat or displaying a warning in a warning display portion, stores the abnormality information (abnormality codes) in a predetermined memory of the ECU  41 , and ends the process routine. 
     In step  312  and  314 , the sensor abnormality determining part  52  generates and outputs a determination result which indicates that the intake air temperature sensor  14   a  and the cooling water temperature sensor  32  are normal. 
     In this way, according to the sensor abnormality detecting process shown in  FIG. 3 , only if the relationship between the cooling water temperature and the intake air temperature indicates an abnormality or indicates a possibility of an abnormality at the time of the engine start (at the time of warming-up), the electric water pump  31  is forced to be driven. Thus, it is possible to detect the presence or absence of energization of the block heater  34  with high accuracy and use the detection results for a sensor abnormality determination, while saving energy in comparison with a configuration where the electric water pump  31  is always driven at the time of the engine start. 
     It is noted that according to the sensor abnormality detecting process shown in  FIG. 3 , a criterion of the determination in step  302  is the same as a criterion of the determination in step  308 ; however, these criteria may be different. For example, the criterion of the determination in step  302  may be stricter than the criterion of the determination in step  308 . As an example, the criterion of the determination in step  302  may be whether the absolute value of the difference between the cooling water temperature and the intake air temperature is smaller than 15 degrees Celsius. 
       FIG. 6  is a flowchart for showing another example of the main process executed by the sensor abnormality detecting apparatus  50  according to the embodiment. The process routine shown in  FIG. 6  is started at the time of starting the engine (at the time of warming-up). With respect to the process routine shown in  FIG. 6 , the processes which may be the same as those shown in  FIG. 3  are given the same step numbers and are not explained. The sensor abnormality detecting process shown in  FIG. 6  differs from the sensor abnormality detecting process shown in  FIG. 3  in that it doesn&#39;t have the processes of step  308  and step  312 . Specifically, according to the sensor abnormality detecting process shown in  FIG. 3 , the presence or absence of energization of the block heater  34  is reflected on the sensor abnormality determination by performing a final sensor abnormality determining process of step  308  if there has been no energization of the block heater  34  while preventing the final sensor abnormality determining process of step  308  if there has been energization of the block heater  34 . To the contrary, according to the sensor abnormality detecting process shown in  FIG. 6 , the presence or absence of energization of the block heater  34  is reflected on the sensor abnormality determination by validating the abnormality determination result of step  302  if there has been no energization of the block heater  34  while invalidating the abnormality determination result of step  302  if there has been energization of the block heater  34 . 
     Similarly, according to the sensor abnormality detecting process shown in  FIG. 6 , only if the relationship between the cooling water temperature and the intake air temperature indicates an abnormality or indicates a possibility of an abnormality at the time of the engine start, the electric water pump  31  is forced to be driven. Thus, it is possible to detect the presence or absence of energization of the block heater  34  with high accuracy and use the detection results for a sensor abnormality determination, while saving energy in comparison with a configuration where the electric water pump  31  is always driven at the time of the engine start. 
       FIG. 7  is a flowchart for showing yet another example of the main process executed by a sensor abnormality detecting apparatus  50  according to the embodiment. The process routine shown in  FIG. 7  is started at the time of starting the engine (at the time of warming-up). With respect to the process routine shown in  FIG. 7 , the processes which may be the same as those shown in  FIG. 3  are given the same step numbers and are not explained. The sensor abnormality detecting process shown in  FIG. 7  differs from the sensor abnormality detecting process shown in  FIG. 3  in that a process of step  316  is added. Specifically, according to the sensor abnormality detecting process shown in  FIG. 3 , the final sensor abnormality determining process of step  308  is prevented if there has been energization of the block heater  34 . To the contrary, according to the sensor abnormality detecting process shown in  FIG. 6 , a sensor abnormality determining process is performed by using another special abnormality determining way if there has been energization of the block heater  34 . 
     More specifically, in step  306 , if the decrease in the cooling water temperature is not observed, the process routine goes to step  316  in which a sensor abnormality determining process, which is prepared for the case where there has been energization of the block heater  34 , is performed. The way of this sensor abnormality determining process may be arbitrary as long as the fact that there has been energization of the block heater  34  is taken into account. For example, a temperature near the lowest value of the cooling water temperature (see a portion P in  FIG. 5 ) after the electric water pump  31  is forced to be driven may be detected by the cooling water temperature sensor  32 , and it may be determined whether an absolute value of a difference between the detected temperature and the intake air temperature is smaller than 20 degrees Celsius. Alternatively, the determination threshold (20 degrees Celsius in this example) may be corrected (changed) by considering the effect due to the energization of the block heater  34 . 
     Similarly, according to the sensor abnormality detecting process shown in  FIG. 7 , only if the relationship between the cooling water temperature and the intake air temperature indicates an abnormality or indicates a possibility of an abnormality at the time of the engine start, the electric water pump  31  is forced to be driven. Thus, it is possible to detect the presence or absence of energization of the block heater  34  with high accuracy and use the detection results for a sensor abnormality determination, while saving energy in comparison with a configuration where the electric water pump  31  is always driven at the time of the engine start. 
     It is noted that also in the sensor abnormality detecting process shown in  FIG. 7 , the processes of step  308  and step  312  may be omitted as is the case with the sensor abnormality detecting process shown in  FIG. 6 . 
       FIG. 8  is a flowchart for showing an example of a main process executed by the controller  70  of the electric water pump according to the embodiment. The process routine shown in  FIG. 8  is started at the time of starting the engine (at the time of ignition on). The process routine shown in  FIG. 8  is performed concurrently with the sensor abnormality detecting process shown in  FIG. 3 , etc., immediately after the engine starts. 
     In step  800 , the W/P forced-operating part determines whether a criterion (a W/P forced-operating criterion), which is necessary to be met in order to force the electric water pump  31  to operate, is met. As described above, the criterion, which is necessary to be met in order to force the electric water pump  31  to operate, is met if the absolute value of the difference between the cooling water temperature and the intake air temperature is greater than or equal to 20 degrees Celsius, for example, and it is reported by the sensor abnormality determining part  52 . If the criterion, which is necessary to be met in order to force the electric water pump  31  to operate, is met, the process routine goes to step  802 . On the other hand, the criterion, which is necessary to be met in order to force the electric water pump  31  to operate, is not met, the process routine goes to step  804 . 
     In step  802 , the W/P forced-operating part  72  forces the electric water pump  31  to operate (see the process described in connection with step  304 ). Then, the electric water pump  31  operates and thus the cooling water of the engine  11  begins to circulate in the cooling water circulating circuit  28 . 
     In step  804 , the W/P ordinary control part  74  determines whether a criterion at the time of an ordinary state, which is necessary to be met in order to operate the electric water pump  31 , is met. The criterion at the time of an ordinary state may be arbitrary as long as it is not such a criterion which is always met after the engine starts. For example, the criterion at the time of an ordinary state may be met at the time when the warming-up of the engine is completed. The criterion at the time of an ordinary state may be defined by plural parameters such as a vehicle speed, the number of revolutions of the engine, an intake air flow, an intake air temperature, a cooling water temperature, etc. Further, the criterion at the time of an ordinary state may also be met when the cooling water temperature sensor  32  fails. In step  804 , if the criterion at the time of an ordinary state is met, the process routine goes to step  806 . 
     In step  806 , the W/P ordinary control part  74  operates the electric water pump  31  according to a demand of a flow rate which is determined appropriately (i.e., performs an ordinary control). The ordinary control is performed continuously until the ignition switch is turned off (a affirmative determination of step  808 ). 
     The present invention is disclosed with reference to the preferred embodiments. However, it should be understood that the present invention is not limited to the above-described embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
     For example, in the embodiment described above, the sensor abnormality determination is performed by evaluating the absolute value of a difference between the cooling water temperature and the intake air temperature at the time of the engine start, utilizing the fact that there is a correlation between the cooling water temperature of the engine and the intake air temperature; however, a temperature of another medium which is correlated with the cooling water temperature may be used instead of the intake air temperature. For example, instead of the detection results of the intake air temperature sensor  14   a , detection results of an engine oil temperature sensor which detects the engine oil temperature may be used in a similar manner. Further, instead of the detection results of the intake air temperature sensor  14   a , detection results of a transmission oil temperature sensor which detects the transmission oil temperature may be used in a similar manner. Further, instead of the detection results of the intake air temperature sensor  14   a , detection results of an outdoor air temperature sensor which detects the outdoor air temperature may be used in a similar manner. Further, the relationship between these various temperatures and the cooling water temperature of the engine may be evaluated in a comprehensive manner. 
     Further, in the embodiment described above, the presence or absence of an abnormality of the cooling water temperature sensor  32  may be determined by evaluating the relationship between the cooling water temperature of the engine and its estimated value (expectation value). In this case, the estimated value may be derived by using the temperature of another medium which is correlated with the cooling water temperature, such as detection results of the intake air temperature sensor  14   a . Alternatively, the estimated value may be derived by using the detection results of the cooling water temperature sensor  32  during the soak period, which are obtained at the time of self-initiating, etc. 
     Further, in the embodiment described above, the determination result, which indicates that at least one of the intake air temperature sensor  14   a  and the cooling water temperature sensor  32  is abnormal, is generated; however, other information, etc., may be used to further identify the abnormal subject.