Patent Publication Number: US-9850837-B2

Title: Monitoring device for fuel injection amount control apparatus

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2015-087665 filed on April 22, 2015 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a monitoring device for a fuel injection amount control apparatus. 
     2. Description of Related Art 
     A fuel injection amount control apparatus for an engine that is mounted in a vehicle or the like drives injectors of the engine based on an injection amount command value calculated by a calculation unit, thereby controlling the amount of fuel injection by the injectors. At the time of normal engine operation, for example, after the completion of warm-up of the engine, the calculation unit of the fuel injection amount control apparatus obtains a basic injection amount based on an operation state of the engine such as an accelerator operation amount and an engine rotational speed, and assigns the basic injection amount to the aforementioned injection amount command value to calculate the injection amount command value. 
     Besides, in Japanese Patent Application Publication No. 2013-238203 (JP 2013-238203 A), there is described a monitoring device that determines whether or not there is an abnormality in the aforementioned calculation unit in the fuel injection amount control apparatus. This monitoring device calculates a monitoring injection amount equivalent to the aforementioned basic injection amount, based on the operation state of the engine such as the accelerator operation amount and the engine rotational speed, in parallel with calculation of the injection amount command value by the aforementioned calculation unit. Then, when the injection amount command value calculated by the aforementioned calculation unit deviates, in an increasing manner, from the aforementioned monitoring injection amount, the monitoring device determines that an abnormality has occurred in a function of calculating the injection command value in the aforementioned calculation unit. 
     Incidentally, the aforementioned accelerator operation amount is detected through the use of an accelerator position sensor, and the aforementioned engine rotational speed is detected through the use of a crank angle sensor. Incidentally, this accelerator position sensor and this crank angle sensor have a function of detecting a sensor abnormality, and can output a detection signal that is guaranteed to be natural, with the aid of the function. 
     By the way, the calculation unit of the fuel injection amount control apparatus obtains a start-up injection amount for enhancing the startability of the engine based on a cooling fluid temperature of the engine that is detected by a fluid temperature sensor from the start of start-up of the engine to the completion of start-up, and assigns the start-up injection amount to the injection amount command value to calculate the injection amount command value. Furthermore, after the completion of start-up of the engine, the aforementioned calculation unit assigns the larger one of the aforementioned start-up injection amount that decreases as the cooling fluid temperature of the engine rises, and the aforementioned basic injection amount that is obtained based on the operation state of the engine, to the injection amount command value, thereby calculating the injection amount command value. 
     On the other hand, it is preferable that the monitoring device determine whether or not there is an abnormality in the aforementioned calculation unit, immediately after the completion of start-up of the engine. It should be noted, however, that when the device calculates the aforementioned monitoring injection amount, sensors that do not have the function of detecting the presence of an abnormality upon the occurrence thereof, such as the fluid temperature sensor and the like, namely, sensors incapable of detecting a detection signal that is guaranteed to be normal cannot be employed to calculate the aforementioned monitoring injection amount. For this reason, the aforementioned monitoring injection amount cannot be calculated as a value equivalent to the start-up injection amount, based on the cooling fluid temperature detected by the fluid temperature sensor. Accordingly, at this time as well, the monitoring injection amount must be calculated through the use of sensors capable of outputting a detection signal that is guaranteed to be normal, such as the accelerator position sensor, the crank angle sensor and the like. There is no choice but to calculate the monitoring injection amount equivalent to the aforementioned basic injection amount, through the use of such sensors. 
     Therefore, in the case where the start-up injection amount becomes larger than the basic injection amount as a result of lowness of the cooling fluid temperature of the engine immediately after the completion of start-up of the engine and the start-up injection amount is assigned to the injection amount command value, even when the calculation unit is normal, the injection amount command value (equivalent to the start-up injection amount) deviates, in an increasing manner, from the monitoring injection amount (equivalent to the basic injection amount). Then, it may be erroneously determined, based on this deviation between the injection amount command value and the monitoring injection amount, that an abnormality has occurred in the calculation unit. 
       FIG. 8  is a time chart showing changes in the start-up injection amount, the basic injection amount and the injection amount command value from the start of start-up of the engine to the completion of start-up. As is apparent from the drawing, after the completion of start-up of the engine, while the larger one of the basic injection amount and the start-up injection amount is adopted as the injection amount command value (indicated by a broken line), the monitoring injection amount is calculated as a value equivalent to the basic injection amount. Therefore, when the start-up injection amount is larger than the basic injection amount, for example, immediately after the completion of start-up of the engine or the like, the injection amount command value may greatly deviate, in an increasing manner, from the monitoring injection amount in spite of normal calculation of the injection amount command value (equivalent to the start-up injection amount), and it may be erroneously determined, based on the deviation, that an abnormality has occurred in the calculation unit for calculating the injection amount command value. 
     SUMMARY OF THE INVENTION 
     In view of the aforementioned problem, the invention provides a monitoring device for a fuel injection amount control apparatus that can suppress the occurrence of an erroneous determination that an abnormality has occurred in a calculation unit after the completion of start-up of an engine. 
     According to one aspect of the invention, there is provided a monitoring device for a fuel injection amount control apparatus that is configured to drive an injector provided in an engine based on an injection amount command value. The monitoring device is equipped with a calculation unit and a determination unit. The calculation unit is configured to, in calculating the injection amount command value at intervals of a specified time, (i) calculate a start-up injection amount based on a cooling fluid temperature of the engine such that the start-up injection amount becomes smaller when the cooling fluid temperature is high than when the cooling fluid temperature is low, (ii) use the start-up injection amount as the injection amount command value from start of start-up of the engine to the completion of start-up of the engine, and (iii) use the larger one of the aforementioned start-up injection amount and a basic injection amount that is calculated based on an operation state of the engine, as the injection amount command value, after the completion of start-up of the engine. Besides, the aforementioned determination unit is configured to, in calculating a monitoring injection amount at intervals of a specified time, (i) use the larger one of a monitoring start-up injection amount that is calculated based on the start-up injection amount and a monitoring basic injection amount that is calculated based on the operation state of the engine, as the monitoring injection amount, (ii) use a start-up injection amount calculated this time by the aforementioned calculation unit, as the monitoring start-up injection amount, from start of start-up of the engine to the completion of start-up of the engine, (iii) use the smaller one of the start-up injection amount calculated this time by the aforementioned calculation unit and a last monitoring start-up injection amount that is calculated by the aforementioned determination unit, as a current monitoring start-up injection amount, after the completion of start-up of the engine, and (iv) determine that the calculation unit is abnormal when an injection amount command value calculated this time by the calculation unit deviates, in an increasing manner, from a monitoring injection amount calculated this time. 
     According to the configuration of the monitoring device for the fuel injection amount control apparatus as described above, when the start-up injection amount becomes larger than the basic injection amount, for example, immediately after the completion of start-up of the engine or the like, the start-up injection amount is adopted as the injection amount command value, and the injection amount command value is thereby calculated by the aforementioned calculation unit. Then, when this injection amount command value deviates, in an increasing manner, from the aforementioned monitoring injection amount, it is determined by the aforementioned determination unit that the aforementioned calculation unit is abnormal. 
     The aforementioned determination unit calculates the aforementioned monitoring injection amount as follows. That is, the aforementioned determination unit uses the larger one of the monitoring start-up injection amount that is calculated based on the start-up injection amount calculated by the aforementioned calculation unit, and the monitoring basic injection amount that is calculated based on the operation state of the engine by the aforementioned determination unit separately from the basic injection amount that is calculated by the aforementioned calculation unit, as the monitoring injection amount. Then, under the condition that there is no abnormality in the aforementioned calculation unit, when the start-up injection amount becomes larger than the basic injection amount and is used as the injection amount command value, for example, immediately after the completion of start-up of the engine or the like, the monitoring start-up injection amount becomes larger than the monitoring basic injection amount and is used as the monitoring injection amount. 
     It should be noted herein that since the cooling fluid temperature of the engine after the completion of start-up gradually rises, the start-up injection amount that is calculated based on the cooling fluid temperature by the aforementioned calculation unit gradually decreases. Therefore, in the case where the start-up injection amount becomes larger than the basic injection amount and is used as the injection amount command value immediately after the completion of start-up of the engine, when there is no abnormality in the aforementioned calculation unit, the start-up injection amount calculated this time by the calculation unit does not become larger than the start-up injection amount calculated last time. Furthermore, at this time, the monitoring start-up injection amount calculated this time by the aforementioned determination unit does not become larger than the monitoring start-up injection amount calculated last time, either. This is because the smaller one of the start-up injection amount calculated this time by the aforementioned calculation unit and the monitoring start-up injection amount calculated last time by the aforementioned determination unit is used as the current monitoring start-up injection amount, after the completion of start-up of the engine. 
     In the case where the start-up injection amount becomes larger than the basic injection amount and is used as the injection amount command value immediately after the completion of start-up of the engine, when the start-up injection amount calculated this time by the aforementioned calculation unit is larger than the start-up injection amount calculated last time, the possibility of the occurrence of an abnormality in the aforementioned calculation unit is high. In this case, as a result of the abnormality in the aforementioned calculation unit, the start-up injection amount calculated this time by the aforementioned calculation unit becomes larger than the last monitoring start-up injection amount calculated by the aforementioned determination unit. Thus, the aforementioned last monitoring start-up injection amount is used as the current monitoring start-up injection amount. Furthermore, at this time, the monitoring start-up injection amount becomes larger than the monitoring basic injection amount and is used as the monitoring injection amount. Thus, the injection amount command value (the start-up injection amount calculated this time) deviates, in an increasing manner, from the monitoring injection amount (the last monitoring start-up injection amount). Then, it can be determined, based on the deviation, that an abnormality has occurred in the aforementioned calculation unit for calculating the injection amount command value. 
     On the other hand, in the case where the start-up injection amount becomes larger than the basic injection amount and is used as the injection amount command value immediately after the completion of start-up of the engine, when there is no abnormality in the aforementioned calculation unit, the start-up injection amount calculated this time becomes smaller than the start-up injection amount calculated last time. At this time, the start-up injection amount calculated this time by the aforementioned calculation unit becomes smaller than the last monitoring start-up injection amount calculated by the aforementioned determination unit. Therefore, the start-up injection amount calculated this time is used as the current monitoring start-up injection amount. Furthermore, at this time, the monitoring start-up injection amount becomes larger than the monitoring basic injection amount and is used as the monitoring injection amount. Thus, the injection amount command value calculated by the aforementioned calculation unit (the start-up injection amount calculated this time) does not deviate, in an increasing manner, from the monitoring injection amount (the current monitoring start-up injection amount). Therefore, the occurrence of an erroneous determination that an abnormality has occurred in the calculation unit for calculating the injection amount command value, based on a deviation of the injection amount command value, in an increasing manner, from the monitoring injection amount in spite of normalness of the calculation unit, can be suppressed. 
     Besides, the aforementioned monitoring device may be further equipped with a storage unit in which a change pattern of a maximum value that can be assumed by the start-up injection amount with the lapse of time after the completion of start-up of the engine is stored. In this case, conceivably, the aforementioned determination unit may be configured to specify the current monitoring start-up injection amount after the completion of start-up of the engine as follows. That is, the aforementioned determination unit may be configured to, after completion of start-up of the engine, use the smallest one of the start-up injection amount calculated this time by the aforementioned calculation unit, the last monitoring start-up injection amount calculated by the aforementioned determination unit, and the maximum value obtained based on an elapsed time from completion of start-up of the engine using the aforementioned change pattern that is stored in the aforementioned storage unit, as the current monitoring start-up injection amount. 
     As an abnormality in the aforementioned calculation unit, there is also an abnormality that the start-up injection amount that is calculated at intervals of the specified time remains fixed. In the case where this abnormality has occurred, when the start-up injection amount becomes larger than the basic injection amount and is used as the injection amount command value immediately after the completion of start-up of the engine, the aforementioned maximum value eventually becomes smaller than the start-up injection amount calculated this time by the aforementioned calculation unit and the last monitoring start-up injection amount calculated by the aforementioned determination unit. Then, when the aforementioned maximum value becomes smaller than the start-up injection amount calculated this time by the aforementioned calculation unit and the last monitoring start-up injection amount calculated by the aforementioned determination unit, the maximum value is used as the current monitoring start-up injection amount. At this time, the monitoring start-up injection amount becomes larger than the monitoring basic injection amount and is used as the monitoring injection amount. Thus, the injection amount command value calculated by the aforementioned calculation unit (the start-up injection amount calculated this time) deviates, in an increasing manner, from the monitoring injection amount (the aforementioned maximum value as the current monitoring start-up injection amount). Then, it can be determined, based on the deviation, that an abnormality has occurred in the calculation unit for calculating the injection amount command value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of an exemplary embodiment of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a diagram schematically showing the configurations of a monitoring device for a fuel injection amount control apparatus and a fuel supply system of an engine to which the device is applied, in the embodiment as an example of the monitoring device for the fuel injection amount control apparatus according to the invention; 
         FIG. 2  is a block diagram showing the flow of a process of calculating an injection amount command value and a process of monitoring the calculation, in the embodiment of the invention; 
         FIG. 3  is a graph showing changes in a maximum value of a start-up injection amount with the lapse of time after the completion of start-up of the engine; 
         FIG. 4  is a flowchart showing a procedure of determining whether or not an abnormality has occurred in a calculation function of a microcomputer after the completion of start-up of the engine; 
         FIG. 5  is a flowchart showing a procedure of executing a failsafe process for the engine; 
         FIG. 6  is constituted of time charts (a) to (d) showing changes in a fuel injection amount of the engine, changes in a deviation amount (which will be described later), a mode of executing the failsafe process, and a mode of performing forcible stop of the engine (engine stall) respectively; 
         FIG. 7  is a time chart showing changes in the start-up injection amount, a basic injection amount, the injection amount command value and the maximum value of the start-up injection amount after the start of start-up of the engine and after the completion of start-up; and 
         FIG. 8  is a time chart showing changes in the start-up injection amount, the basic injection amount and the injection amount command value after the start of start-up of the engine and after the completion of start-up. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT 
     One embodiment of a monitoring device for a fuel injection amount control apparatus will be described hereinafter with reference to  FIGS. 1 to 7 .  FIG. 1  shows a fuel supply system of a diesel engine to which the fuel injection amount control apparatus according to this embodiment of the invention is applied. The fuel supply system of the engine is provided with a fuel pump  11  that pressurizes and discharges the fuel pumped up from a fuel tank  10 . A pressure regulating valve  12  for regulating the pressure of discharged fuel is installed in the fuel pump  11 . The fuel discharged by the fuel pump  11  is force-fed to a common rail  13  and stored therein. Then, the fuel stored in the common rail  13  is distributed and supplied to injectors  14  of respective cylinders. Incidentally, a pressure reducing valve  15  that lowers the pressure of the fuel in the common rail  13  (a rail pressure) by returning the fuel in the common rail  13  to the fuel tank  10  is disposed in the common rail  13 . 
     The engine that is equipped with this fuel supply system is controlled by an electronic control unit  20 . The electronic control unit  20  is equipped with a microcomputer  21  that executes various computation processes regarding engine control. Besides, the electronic control unit  20  is equipped with an electronic drive unit (an EDU)  23  that drives the injectors  14  of the respective cylinders in accordance with a command from the microcomputer  21 . Besides, the electronic control unit  20  is also provided with a drive circuit  24  that drives the pressure regulating valve  12  and the pressure reducing valve  15  in accordance with a command from the microcomputer  21 . 
     Detection signals of an accelerator position sensor  26  that detects an accelerator operation amount Accp, a fluid temperature sensor  27  that detects an engine fluid temperature Thw as a temperature of cooling fluid of the engine, a rail pressure sensor  28  that detects a rail pressure Per, a crank angle sensor  29  that outputs a pulse-like crank angle signal in accordance with rotation of an output shaft of the engine, and the like are input to the electronic control unit  20 . Incidentally, the detection signals of the accelerator position sensor  26 , the fluid temperature sensor  27  and the rail pressure sensor  28  are input to the microcomputer  21  after being converted into digital signals by an AD converter (an ADC)  25  that is disposed in the electronic control unit  20 . Besides, the crank angle signal output by the crank angle sensor  29  is directly input to the microcomputer  21 . 
     Next, fuel injection amount control that is performed as a part of engine control by the electronic control unit  20  will be described in detail. This fuel injection amount control is realized by driving the injectors  14  based on an injection amount command value Qfin calculated by the microcomputer  21 . Incidentally, in the case where an abnormality has occurred in various calculation functions of the microcomputer  21 , when the amount of fuel injection is controlled using the injection amount command value Qfin calculated through the functions, the amount of fuel injection assumes an inappropriate value and adversely influences the operation of the engine. In order to cope with this phenomenon, the microcomputer  21  also has a function as a determination unit that determines whether or not an abnormality has occurred in the aforementioned calculation functions regarding calculation of the injection amount command value Qfin and the like, and deals with the abnormality in the aforementioned calculation functions through the use of the function as the determination unit. 
       FIG. 2  shows the outline of a calculation routine R 1  that is executed through the microcomputer  21  to calculate the injection amount command value Qfin, and the outline of a monitoring routine R 2  for monitoring whether or not the injection amount command value Qfin is normally calculated. The calculation routine R 1  and the monitoring routine R 2  are periodically executed at intervals of a specified time. As is apparent from the drawing, the aforementioned calculation routine R 1  is constituted of three processes, namely, a basic injection amount computation process P 1 , a start-up injection amount computation process P 2 , and an injection amount command value computation process P 3 . Besides, the aforementioned monitoring routine R 2  is constituted of four processes, namely, a monitoring basic injection amount computation process P 4 , a motoring start-up injection amount computation process P 5 , a monitoring injection amount computation process P 6 , and an abnormality determination process P 7 . 
     In the basic injection amount computation process P 1  of the calculation routine R 1 , a basic injection amount Qbase is calculated with reference to a map stored in the microcomputer  21 , based on an operation state of the engine such as the accelerator operation amount Accp, an engine rotational speed Ne that is obtained based on the crank angle signal, and the like. Incidentally, the basic injection amount Qbase calculated herein may be subjected to various corrections. 
     In the start-up injection amount computation process P 2 , a start-up injection amount Qst is calculated with reference to the map stored in the microcomputer  21 , based on the engine rotational speed Ne and the engine fluid temperature Thw. The start-up injection amount Qst thus calculated is smaller when the engine fluid temperature Thw is high than when the engine fluid temperature Thw is low, with the intention of enhancing the startability of the engine etc. Specifically, the start-up injection amount Qst linearly decreases as the engine fluid temperature Thw rises. Incidentally, the start-up injection amount Qst at this time is not absolutely required to linearly decrease as the engine fluid temperature Thw rises. The start-up injection amount Qst may decrease stepwise as the engine fluid temperature Thw rises. 
     In the injection amount command value computation process P 3 , the start-up injection amount Qst is assigned to the injection amount command value Qfin from the start of start-up of the engine to the completion of start-up. The larger one of the start-up injection amount Qst and the basic injection amount Qbase is assigned to the injection amount command value Qfin after the completion of start-up of the engine. The injection amount command value Qfin is calculated through this assignment. Incidentally, when executing the aforementioned injection amount command value computation process P 3 , the microcomputer  21  plays the role of the calculation unit that calculates the injection amount command value Qfin. 
     In the monitoring basic injection amount computation process P 4  of the monitoring routine R 2 , a monitoring basic injection amount Qbasem is calculated with reference to the map stored in the microcomputer  21 , based on the operation state of the engine such as the accelerator operation amount Accp, the engine rotational speed Ne that is obtained based on the crank angle signal, and the like. Incidentally, in a manner corresponding to the various corrections to which the basic injection amount Qbase is subjected in the basic injection amount computation process P 1  of the calculation routine R 1 , the monitoring basic injection amount Qbasem calculated herein is subjected to various similar corrections. The calculation of the monitoring basic injection amount Qbasem in the monitoring basic injection amount computation process P 4  is carried out in parallel with and separately from the calculation of the basic injection amount Qbase in the calculation routine R 1 . 
     In the monitoring start-up injection amount computation process P 5 , the start-up injection amount Qst that is calculated at intervals of a specified time in the calculation routine R 1  is fetched every time the calculation thereof is carried out. Furthermore, a monitoring start-up injection amount Qstm is calculated at intervals of a specified time, based on the start-up injection amount Qst thus fetched and the like. 
     In the monitoring injection amount computation process P 6 , the larger one of the monitoring basic injection amount Qbasem and the monitoring start-up injection amount Qstm is assigned to the monitoring injection amount Qfinm. The monitoring injection amount Qfinm is calculated through this assignment. 
     In the abnormality determination process P 7 , the aforementioned monitoring injection amount Qfinm is compared with the aforementioned injection amount command value Qfin calculated in the calculation routine R 1  to determine whether or not an abnormality has occurred in the calculation functions of the microcomputer  21 . Specifically, an amount ΔQ of deviation of the injection amount command value Qfin, in an increasing manner, from the monitoring injection amount Qfim is obtained. When the amount ΔQ of deviation is larger than a determination threshold H specified in advance through an experiment or the like, it is determined that an abnormality has occurred in the calculation functions of the microcomputer  21 . 
     Incidentally, when it is determined that there is an abnormality in the aforementioned calculation functions, the microcomputer  21  executes a failsafe process for controlling the amount of fuel injection and the like such that the engine can be kept in operation to the maximum possible extent even in the case of an abnormality in the calculation functions. 
     Next, a method of calculating the monitoring start-up injection amount Qsm in the monitoring start-up injection amount computation process P 5  will be described in detail. In the monitoring start-up injection amount computation process P 5 , the start-up injection amount Qst calculated this time by the calculation routine R 1  is assigned to the monitoring start-up injection amount Qstm from the start of start-up of the engine to the completion of start-up. Incidentally, a change pattern of a maximum value Qstmax that can be assumed by the start-up injection amount Qst after the completion of start-up of the engine with the lapse of time is stored in the microcomputer  21 . The microcomputer  21  in which this change pattern of the maximum value Qstmax is stored plays the role of a storage unit for storing the change pattern of the maximum value Qstmax. 
       FIG. 3  shows changes in the aforementioned maximum value Qstmax with the lapse of time after the completion of start-up of the engine. Then, in the monitoring start-up injection amount computation process P 5  ( FIG. 2 ) after the completion of start-up of the engine, the aforementioned maximum value Qstmax is obtained based on an elapsed time after the completion of start-up of the engine, using the aforementioned stored change pattern. Furthermore, in the monitoring start-up injection amount computation process P 5  after the completion of start-up of the engine, the smallest one of the start-up injection amount Qst calculated this time, the last monitoring start-up injection amount Qstm and the aforementioned maximum value Qstmax is used as the current monitoring start-up injection amount Qstm. Thus, the current monitoring start-up injection amount Qstm is calculated. 
     Next, the monitoring of the calculation functions of the microcomputer  21  after the completion of start-up of the engine according to the monitoring routine R 2  will be described in detail.  FIG. 4  is a flowchart showing an abnormality determination routine for determining whether or not an abnormality has occurred in the calculation functions of the microcomputer  21  regarding calculation of the injection amount command value Qfin and the like after the completion of start-up of the engine. This abnormality determination routine is periodically executed, for example, by interrupt at intervals of a predetermined time, through the microcomputer  21 . 
     As the processing of step  101  (S 101 ) of the abnormality determination routine, the microcomputer  21  determines whether or not start-up of the engine is completed. Incidentally, the engine is started up through the cranking of the engine by a starter. Therefore, it can be determined that start-up of the engine is completed, based on a state where the aforementioned starter is off during rotation of the engine and the transmission of motive power between the engine and a transmission is shut off. 
     If it is determined in the processing of S 101  that start-up of the engine is not completed, namely, if the engine is in a phase from the start of start-up to the completion of start-up, the microcomputer  21  makes a transition to S 102 . As the processing of S 102 , the microcomputer  21  acquires the start-up injection amount Qst calculated this time through the start-up injection amount computation process P 2  of  FIG. 2 , and assigns the start-up injection amount Qst to the monitoring start-up injection amount Qstm. The current monitoring start-up injection amount Qstm before the completion of start-up of the engine is calculated through this assignment. After that, the microcomputer  21  makes a transition to S 104  of  FIG. 4 . 
     On the other hand, if it is determined in the processing of S 101  that start-up of the engine is completed, the microcomputer  21  makes a transition to S 103 . As the processing of S 103 , the microcomputer  21  calculates the monitoring start-up injection amount Qstm after the completion of start-up of the engine. Specifically, the microcomputer  21  obtains the maximum value Qstmax of the start-up injection amount Qst that can be assumed at the moment, based on an elapsed time from the completion of start-up of the engine. Furthermore, the microcomputer  21  assigns the smallest one of the aforementioned maximum value Qstmax, the start-up injection amount Qst calculated this time through the start-up injection amount computation process P 2  ( FIG. 2 ), and the monitoring start-up injection amount Qst calculated through the last processing of S 102  or S 103  to the monitoring start-up injection amount Qstm. The current monitoring start-up injection amount Qstm after the completion of start-up of the engine is calculated through this assignment. After that, the microcomputer  21  makes a transition to S 104 . 
     Incidentally, the aforementioned processing of S 102  and the aforementioned processing of S 103  are equivalent to the monitoring start-up injection amount computation process P 5  of  FIG. 2 . As the processing of S 104  ( FIG. 4 ), the microcomputer  21  assigns the larger one of the monitoring start-up injection amount Qstm and the monitoring basic injection amount Qbasem to the monitoring injection amount Qfinm. The calculation of the monitoring injection amount Qfinm is carried out through this assignment. This processing of S 105  is equivalent to the monitoring injection amount computation process P 6  of  FIG. 2 . Incidentally, when the start-up injection amount Qst is used as the injection amount command value Qfin based on a state where the start-up injection amount Qst is larger than the basic injection amount Qbase after the completion of start-up of the engine, the relationship in magnitude between the monitoring start-up injection amount Qstm that is calculated for monitoring and the monitoring basic injection amount Qbasem is also the same as the relationship in magnitude between the aforementioned start-up injection amount Qst and the aforementioned basic injection amount Qbase. Accordingly, when the start-up injection amount Qst is used as the injection amount command value Qfin as described above, the monitoring start-up injection amount Qstm becomes larger than the monitoring basic injection amount Qbasem, and this monitoring start-up injection amount Qstm is used as the monitoring injection amount Qfinm. 
     The processing of S 105  of  FIG. 4 , the processing of S 106  of  FIG. 4  and the processing of S 107  of  FIG. 4  in the abnormality determination routine are equivalent to the abnormality determination process P 7  of  FIG. 2 . As the processing of S 105  ( FIG. 4 ), the microcomputer  21  calculates the amount ΔQ of deviation between the injection amount command value Qfin and the monitoring injection amount Qfinm. This amount ΔQ of deviation is calculated by subtracting the monitoring injection amount Qfinm from the injection amount command value Qfin. After that, the microcomputer  21  makes a transition to S 106 . As the processing of S 106 , the microcomputer  21  determines whether or not the amount ΔQ of deviation is larger than the determination threshold H, and temporarily ends the abnormality determination routine if the result of the determination herein is negative. On the other hand, if the result of the determination in S 106  is affirmative on the ground that the amount ΔQ of deviation is larger than the determination threshold H, the microcomputer  21  makes a transition to S 107 , and determines that an abnormality has occurred in the calculation functions. In this case, the microcomputer  21  makes a transition to S 108 . 
     As the processing of S 108 , the microcomputer  21  issues a command to execute the aforementioned failsafe process on the condition that start-up of the engine is completed. After that, the microcomputer  21  temporarily ends the abnormality determination routine. In the aforementioned failsafe process, the control of the amount of fuel injection and the like is performed such that the engine can be kept in operation to the maximum possible extent, even at the time of an abnormality in the aforementioned calculation functions. It should be noted, however, that when the engine cannot be kept in operation even if the amount of fuel injection and the like are thus controlled, the engine that is kept in operation is forcibly stopped (the engine is stalled) through the failsafe process. 
       FIG. 5  is a flowchart showing a failsafe process execution routine for executing the aforementioned failsafe process. The routine is started when a command to execute the failsafe process is issued through the microcomputer  21 . After being started, the routine is periodically executed by interrupt at intervals of a predetermined time. 
     As the processing of S 201  of the failsafe process execution routine, the microcomputer  21  uses the smaller one of the injection amount command value Qfin calculated in the injection amount command value computation process P 3  of  FIG. 2  and an abnormality injection amount Qfs set to execute the failsafe process, as the new injection amount command value Qfin for fuel injection amount control. Incidentally, as the aforementioned abnormality injection amount Qfs, it is conceivable to adopt a fixed value that is optimally specified in advance through an experiment or the like as a fuel injection amount that allows the vehicle mounted with the engine to run in a retreating manner and that is smaller than at the time of normal engine operation. 
     As the processing of S 202  ( FIG. 5 ), the microcomputer  21  uses the smaller one of the monitoring injection amount Qfinm and the abnormality injection amount Qfs as the new monitoring injection amount Qfinm. As the processing of S 203 , the microcomputer  21  obtains the amount ΔQ of deviation between the newly set monitoring injection amount Qfinm and the injection amount command value Qfin (the abnormality injection amount Qfs). In the failsafe process, a relatively small value is used as the abnormality injection amount Qfs. Therefore, the abnormality injection amount Qfs is usually used as the monitoring injection amount Qfinm, and the amount ΔQ of deviation between the injection amount command value Qfin (the abnormality injection amount Qfs) and the monitoring injection amount Qfinm does not increase. 
     However, when an abnormality has occurred in the calculation functions of the microcomputer  21 , the deviation between the injection amount command value Qfin and the monitoring injection amount Qfinm may increase as a result of the aforementioned abnormality even under the aforementioned circumstance. In this case, it is difficult to keep the engine in operation even when the failsafe process is executed. Therefore, as the processing of S 204 , the microcomputer  21  determines whether or not the amount ΔQ of deviation is larger than a predetermined value A (e.g., a value smaller than the determination threshold H is adopted). If the result of the determination herein is affirmative, the microcomputer  21  forcibly stops the engine (stalls the engine) as the processing of S 205 . 
     Incidentally, if the result of the determination in S 204  is negative, the microcomputer  21  temporarily ends the failsafe process execution routine, and stops periodical execution of the failsafe process execution routine after executing the processing of S 205 . 
       FIG. 6  is constituted of time charts showing a mode of executing the failsafe process and a mode of performing forcible stop of the engine (engine stall). When the injection amount command value Qfin (indicated by a solid line) greatly deviates from the monitoring injection amount Qfinm (indicated by a broken line) as shown in  FIG. 6 ( a )  due to an abnormality in the calculation functions of the microcomputer  21 , the amount ΔQ of deviation becomes larger than the determination threshold H as shown in  FIG. 6 ( b )  (at a timing T 1 ). The failsafe process is executed as shown in  FIG. 6 ( c ) , based on a state where the amount ΔQ of deviation thus becomes larger than the determination threshold H. Furthermore, when the injection amount command value Qfin (indicated by the solid line) deviates from the monitoring injection amount Qfinm (indicated by the broken line) as shown in  FIG. 6 ( a )  even under the state where the failsafe process has been executed, the engine is forcibly stopped (the engine is stalled) as shown in  FIG. 6 ( d )  based on a state where the amount ΔQ of deviation becomes larger than the predetermined value A as shown in  FIG. 6 ( b )  (at a timing T 2 ). 
     Next, the operation of the monitoring device for the fuel injection amount control apparatus will be described. When the engine fluid temperature Thw is low, for example, immediately after the completion of start-up of the engine or the like, the start-up injection amount Qst that is obtained based on the engine fluid temperature Thw becomes larger than the basic injection amount Qbase that is obtained based on the operation state of the engine. At this time, the start-up injection amount Qst is adopted as the injection amount command value Qfin, and the injection amount command value Qfin is thereby calculated. Then, when this injection amount command value Qfin deviates, in an increasing manner, from the aforementioned monitoring injection amount Qfinm, it is determined that an abnormality has occurred in the calculation functions of the microcomputer  21 . 
     The aforementioned monitoring injection amount Qfinm for determining whether or not there is an abnormality in the calculation functions of the microcomputer  21  is calculated as follows. That is, the larger one of the monitoring start-up injection amount Qstm that is calculated based on the aforementioned start-up injection amount Qst and the like and the monitoring basic injection amount Qbasem that is calculated based on the operation state of the engine in the monitoring routine R 2  separately from the aforementioned basic injection amount Qbase is used as the monitoring injection amount Qfinm. Then, under the condition that there is no abnormality in the calculation functions of the microcomputer  21 , when the start-up injection amount Qst becomes larger than the basic injection amount Qbase and is used as the injection amount command value Qfin, for example, immediately after the completion of start-up of the engine or the like, the monitoring start-up injection amount Qstm becomes larger than the monitoring basic injection amount Qbasem and is used as the monitoring injection amount Qfinm. 
     It should be noted herein that since the fluid temperature Thw of the engine after the completion of start-up gradually rises, the aforementioned start-up injection amount Qst that is calculated based on the engine fluid temperature Thw gradually decreases. Therefore, in the case where the start-up injection amount Qst becomes larger than the basic injection amount Qbase and is used as the injection amount command value Qfin immediately after the completion of start-up of the engine, when there is no abnormality in the calculation functions of the microcomputer  21 , the start-up injection amount Qst calculated this time does not become larger than the start-up injection amount Qst calculated last time. Furthermore, at this time, the monitoring start-up injection amount Qstm calculated this time in the monitoring routine R 2  does not become larger than the monitoring start-up injection amount Qstm calculated last time, either. This is because the smallest one of the start-up injection amount Qst calculated this time, the monitoring start-up injection amount Qstm calculated last time, and the maximum value Qstmax is used as the current monitoring start-up injection amount Qstm after the completion of start-up of the engine. 
     Accordingly, in the case where the start-up injection amount Qst becomes larger than the basic injection amount Qbase and is used as the injection amount command value Qfin immediately after the completion of start-up of the engine, when the start-up injection amount Qst calculated this time is larger than the start-up injection amount Qst calculated last time, the possibility of the occurrence of an abnormality in the calculation functions of the microcomputer  21  is high. In this case, as a result of an abnormality in the aforementioned calculation functions, the start-up injection amount Qst calculated this time becomes larger than the last monitoring start-up injection amount Qstm, and the aforementioned last monitoring start-up injection amount Qstm is used as the current monitoring start-up injection amount Qstm. Furthermore, at this time, the monitoring start-up injection amount Qstm becomes larger than the monitoring basic injection amount Qbasem and is used as the monitoring injection amount Qfinm. Thus, the injection amount command value Qfin (the start-up injection amount Qst calculated this time) deviates, in an increasing manner, from the monitoring injection amount Qfinm (the last monitoring start-up injection amount Qstm). Then, it can be determined, based on the deviation, that an abnormality has occurred in the calculation functions of the microcomputer  21  for calculating the injection amount command value Qfin. 
     Incidentally, the aforementioned abnormality in the calculation functions of the microcomputer  21  (hereinafter referred to as an abnormality E1), namely, an abnormality that the start-up injection amount Qst calculated this time becomes larger than the start-up injection amount Qst calculated last time results from, for example, abnormalization of stored data. 
     On the other hand, in the case where the start-up injection amount Qst becomes larger than the basic injection amount Qbase and is used as the injection amount command value Qfin immediately after the completion of start-up of the engine, when there is no abnormality in the calculation functions of the microcomputer  21 , the start-up injection amount Qst calculated this time becomes smaller than the start-up injection amount Qst calculated last time. At this time, the start-up injection amount Qst calculated this time becomes smaller than the last monitoring start-up injection amount Qstm, and the start-up injection amount Qst calculated this time is used as the current monitoring start-up injection amount Qstm. Furthermore, at this time, the monitoring start-up injection amount Qstm becomes larger than the monitoring basic injection amount Qbasem and is used as the monitoring injection amount Qfinm. Thus, the injection amount command value Qfin (the start-up injection amount Qst calculated this time) does not deviate, in an increasing manner, from the monitoring injection amount Qfinm (the current monitoring start-up injection amount Qstm). Therefore, the occurrence of an erroneous determination that an abnormality has occurred in the calculation functions of the microcomputer  21 , based on a deviation of the injection amount command value Qfin, in an increasing manner, from the monitoring injection amount Qfinm in spite of normalness of the aforementioned calculation functions, can be suppressed. 
     Incidentally, as an abnormality in the calculation functions of the microcomputer  21 , an abnormality that the start-up injection amount Qst that is calculated at intervals of a specified time remains fixed (hereinafter referred to as an abnormality E2) also arises in addition to the aforementioned abnormality E1. 
     In the case where this abnormality E2 has occurred, when the start-up injection amount Qst becomes larger than the basic injection amount Qbase and is used as the injection amount command value Qfin immediately after the completion of start-up of the engine, the aforementioned maximum value Qstmax eventually becomes smaller than the start-up injection amount Qst calculated this time and the monitoring start-up injection amount Qstm calculated last time. Then, when the aforementioned maximum value Qstmax becomes smaller than the start-up injection amount Qst calculated this time and the monitoring start-up injection amount Qstm calculated last time, the maximum value Qstmax is used as the current monitoring start-up injection amount Qstm. At this time, the monitoring start-up injection amount Qstm becomes larger than the monitoring basic injection amount Qbasem and is used as the monitoring injection amount Qfinm. Thus, the injection amount command value Qfin (the start-up injection amount Qst calculated this time) deviates, in an increasing manner, from the monitoring injection amount Qfinm (the aforementioned maximum value Qstmax as the current monitoring start-up injection amount Qstm). Then, it can be determined, based on the deviation, that the aforementioned abnormality E2 has occurred in the calculation functions of the microcomputer  21 . 
       FIG. 7  is a time chart showing changes in the start-up injection amount Qst, the basic injection amount Qbase, the injection amount command value Qfin and the maximum value Qstmax after the start of start-up of the engine and after the completion of start-up. After the completion of start-up of the engine, the larger one of the basic injection amount Qbase indicated by a solid line L 1  and the start-up injection amount Qst indicated by a solid line L 2  is adopted as the injection amount command value Qfin (indicated by a broken line L 4 ). Therefore, in the case where the start-up injection amount Qst becomes larger than the basic injection amount Qbase as a result of lowness of the engine fluid temperature Thw, for example, immediately after the completion of start-up of the engine or the like, and the start-up injection amount Qst is adopted as the injection amount command value Qfin, if the monitoring injection amount Qfinm is calculated as a value equivalent to the basic injection amount Qbase, the following problem arises. That is, even when the calculation functions of the microcomputer  21  are normal, the injection amount command value Qfin (equivalent to the start-up injection amount Qst) deviates, in an increasing manner, from the monitoring injection amount Qfinm (equivalent to the basic injection amount Qbase). It is erroneously determined, based on the deviation, that an abnormality has occurred in the aforementioned calculation functions. 
     However, the start-up injection amount Qst is used as the injection amount command value Qfin after the completion of start-up of the engine, the smallest one of the start-up injection amount Qst calculated this time, the monitoring start-up injection amount Qstm calculated last time, and the maximum value Qstmax (indicated by an alternate long and two short dashes line L 3  in the drawing) is used as the current monitoring start-up injection amount Qstm. Furthermore, the monitoring start-up injection amount Qstm is used as the monitoring injection amount Qfinm. Incidentally, in the example of  FIG. 7 , in the case where the start-up injection amount Qst calculated this time is used as the current monitoring start-up injection amount Qstm as described above when the calculation functions of the microcomputer  21  are normal and the start-up injection amount Qst is used as the injection amount command value Qfin, the monitoring injection amount Qfinm changes on the solid line L 2 . Accordingly, there is no possibility of the injection amount command value Qfin deviating from the monitoring injection amount Qfinm despite normalness of the calculation functions of the microcomputer  21 . Therefore, the occurrence of an erroneous determination, based on the deviation, that an abnormality has occurred in the calculation functions of the microcomputer  21  regarding calculation of the injection amount command value Qfin and the like is suppressed. 
     According to the present embodiment of the invention described hereinbefore in detail, the following effects are obtained. (1) The occurrence of an erroneous determination that an abnormality has occurred in the calculation functions of the microcomputer  21  regarding calculation of the injection amount command value Qfin and the like can be suppressed. 
     (2) Even when one of the aforementioned abnormalities E1 and E2 has occurred as an abnormality in the calculation functions of the microcomputer  21  regarding calculation of the injection amount command value Qfin and the like, it can be determined that an abnormality has occurred in the aforementioned calculation functions. 
     (3) When an abnormality in the calculation functions of the microcomputer  21  occurs, a measure can be taken to keep the engine in operation to the maximum possible extent by executing the failsafe process. 
     (4) Besides, when it is difficult to keep the engine in operation even through the failsafe process, the continuation of unstable operation of the engine can be avoided by forcibly stopping the engine (stalling the engine). 
     Incidentally, the aforementioned embodiment of the invention can also be modified, for example, as follows. The smaller one of the start-up injection amount Qst calculated this time and the monitoring start-up injection amount Qstm calculated last time may be used as the current monitoring start-up injection amount Qstm. In this case, when the start-up injection amount Qst is used as the injection amount command value Qfin after the completion of start-up of the engine, the smaller one of the start-up injection amount Qst calculated this time and the monitoring start-up injection amount Qstm calculated last time is used as the current monitoring start-up injection amount Qstm, and furthermore, the monitoring start-up injection amount Qstm is used as the monitoring injection amount Qfinm. Even when this configuration is adopted, it is possible to determine whether or not the aforementioned abnormality E1 has occurred as an abnormality in the calculation functions of the microcomputer  21  regarding calculation of the injection amount command value Qfin and the like. 
     The aforementioned forcible stop of the engine is not absolutely required to be performed. The aforementioned failsafe process is not absolutely required to be executed either. Although a value larger than “0” is preferably adopted as the determination threshold H, “0” can also be adopted as the determination threshold H. 
     The predetermined value A may be a value that is larger than the determination threshold H, or a value that is equal to the determination threshold H.