JP2010084675A - Abnormality detection device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent erroneous determination in abnormality detection in a fuel system for an internal combustion engine. <P>SOLUTION: An ECU 40 detects a fuel system abnormality of the engine 10 based on a compared result of an air-fuel ratio correction value for matching an air-fuel ratio detection value with an oxygen sensor 26 installed in an exhaust pipe 24 with a target value, and a prescribed determination value. Further, the ECU 40 detects the alcohol concentration of the fuel supplied to the engine 10, and changes the prescribed determination value to a side for increasing a normal range of the air-fuel ratio correction value during a period after starting of the engine 10 until the completion of detection of the alcohol concentration in the fuel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an abnormality detection device for an internal combustion engine, and more particularly to an abnormality detection device for an internal combustion engine that detects a fuel system abnormality of the internal combustion engine using an air-fuel ratio correction amount.

  Conventionally, an air-fuel ratio of exhaust gas is detected from an output value of an air-fuel ratio sensor disposed in an exhaust pipe of an internal combustion engine, and air-fuel ratio feedback control is performed so that the detected air-fuel ratio is stabilized at a target value. Further, in order to realize good air-fuel ratio control, it has been proposed to detect a fuel system abnormality of an internal combustion engine based on an air-fuel ratio correction amount for making the detected air-fuel ratio coincide with a target value (for example, patents) Reference 1). In Patent Document 1, it is determined whether the air-fuel ratio correction amount for each cylinder is within a predetermined range, and when the air-fuel ratio correction amount for each cylinder exceeds the predetermined range, a fuel system abnormality occurs in that cylinder. It is disclosed that it is determined that the

In recent years, alcohol fuels have attracted attention as alternatives to fossil fuels such as gasoline, against the backdrop of concerns about the depletion of petroleum resources and the mitigation of global warming. It is used as fuel for internal combustion engines. Based on such a background, various methods for suitably performing combustion control of an internal combustion engine using a fuel containing alcohol have been proposed (see, for example, Patent Document 2).
Japanese Patent No. 2684011 JP 2006-322401 A

  By the way, fuel properties are different between gasoline and alcohol. For example, with respect to the theoretical air-fuel ratio, alcohol is smaller than gasoline. Therefore, in order to control the air-fuel ratio with a target value (for example, the theoretical air-fuel ratio), it is necessary to increase the fuel injection amount for alcohol than for gasoline. Therefore, for example, if the alcohol concentration in the fuel changes due to refueling or the like, and the fuel injection control is performed with the alcohol concentration in the current fuel set to the alcohol concentration before the concentration change, it is considered that the fuel amount is excessive or insufficient . In such a case, the air-fuel ratio correction amount greatly changes to the rich side or the lean side.As a result, in the abnormality detection based on the air-fuel ratio correction amount, the air-fuel ratio correction amount is actually an appropriate air-fuel ratio correction amount according to the alcohol concentration after the concentration change. There is a concern that there may be a false detection that an abnormality has occurred despite this fact. On the other hand, there is a concern that an erroneous detection may be made that no abnormality has occurred despite the fact that the air-fuel ratio correction amount is an abnormal value with respect to the alcohol concentration after the concentration change.

  The present invention has been made to solve the above-described problems, and has as its main object to provide an abnormality detection device for an internal combustion engine that can prevent erroneous determination in the detection of a fuel system abnormality in the internal combustion engine.

  The present invention employs the following means in order to solve the above problems.

  The invention according to claim 1 is a comparison between an air-fuel ratio correction value for matching an air-fuel ratio detection value by an air-fuel ratio sensor installed in an exhaust passage of an internal combustion engine with a target value, and a predetermined predetermined determination value. An abnormality detection device for an internal combustion engine that detects an abnormality in a fuel system of the internal combustion engine based on a result, a fuel property detection means for detecting a property of fuel supplied to the internal combustion engine, and the fuel property after the internal combustion engine is started And changing means for changing the predetermined determination value to the side of expanding the normal range of the air-fuel ratio correction value until the detection of the fuel property by the detecting means is completed.

  By monitoring the air-fuel ratio correction value, the presence or absence of a fuel system abnormality in the internal combustion engine is detected. Here, since the fuel amount for making the air-fuel ratio detected value coincide with the target value differs depending on the property of the fuel supplied to the internal combustion engine, it is necessary to correct the fuel injection amount in the internal combustion engine according to the property of the fuel. There is. At this time, if the fuel property is different between the previous operation and the current operation of the internal combustion engine, the fuel correction according to the fuel property cannot be properly performed until the fuel property detection process is completed. As a result, it is conceivable that the air-fuel ratio correction value greatly changes to the rich side or the lean side. In such a case, in the abnormality detection based on the air-fuel ratio correction value, there is a concern that an erroneous determination is made that an abnormality has occurred even though the air-fuel ratio correction value is actually an appropriate air-fuel ratio correction value according to the current fuel property. Is done.

  In that respect, in the present invention, until the fuel property detection process is completed after the internal combustion engine is started, the predetermined determination value used in the abnormality determination based on the air-fuel ratio correction value is increased to the side where the normal range of the air-fuel ratio correction value is expanded. Therefore, when the air-fuel ratio correction value changes to the rich side or the lean side due to the fact that the fuel property has not been detected, the change can be prevented from being erroneously determined as a fuel system abnormality. .

  When expanding the normal range of the air-fuel ratio correction value, there is a concern that if the range is excessively expanded, an abnormal detection failure occurs and the detection accuracy is lowered. In view of this point, the invention according to claim 2 includes storage means for storing the fuel property detected by the fuel property detection means, wherein the changing means is the fuel property associated with the current start of the internal combustion engine. The predetermined determination value is changed based on the fuel property stored in the storage unit when the internal combustion engine is started until the detection of the fuel property by the detection unit is completed. According to this configuration, since the predetermined determination value used in the abnormality detection is changed based on the previous detection value of the fuel property, the determination value is set according to the degree of change in the fuel property that can be taken from the previous detection value of the fuel property. can do. Thereby, it is possible to carry out abnormality determination while maintaining a balance between prevention of erroneous determination that there is an abnormality and prevention of detection of abnormal detection.

  When gasoline or alcohol is used alone as fuel, or a mixed fuel of gasoline and alcohol is used, the theoretical air-fuel ratio of alcohol is smaller than that of gasoline. Requires more fuel injection in alcohol than gasoline. Therefore, until the alcohol concentration detection is completed, if the alcohol concentration in the fuel differs between the previous operation and the current operation of the internal combustion engine, the air-fuel ratio correction value greatly changes to the rich side or the lean side. It is possible to do. At this time, if the previous detected value of the alcohol concentration of the fuel is relatively high, the amount of change in the air-fuel ratio correction value tends to be larger on the lean side than on the rich side. Further, when the previous detected value of the alcohol concentration of the fuel is relatively low, the change amount of the air-fuel ratio correction value tends to be larger on the rich side than on the lean side.

  In view of this point, in the invention according to claim 3, the predetermined determination value is determined on the increase side determination value determined on the fuel increase side of the air-fuel ratio correction value and on the fuel decrease side of the air-fuel ratio correction value. The fuel property detecting means detects the alcohol concentration of the fuel as the fuel property, and the changing means is the fuel stored in the storage means when the internal combustion engine is started. As the alcohol concentration is higher, the change amount of the increase side determination value is decreased and the change amount of the decrease side determination value is increased. According to this configuration, since the change amount of the increase-side determination value and the change amount of the decrease-side determination value are respectively set according to the previous detection value of the alcohol concentration, the determination value can be used to suppress an abnormality detection failure. It can be set relatively easily at an appropriate value.

  According to a fourth aspect of the present invention, the changing means is configured to increase the increase side by an amount corresponding to a deviation between the maximum value of the alcohol concentration of the fuel assumed every time and the alcohol concentration stored in the storage means when the internal combustion engine is started. The judgment value is changed to the rich side, and the reduction side judgment value is set to the lean side by the deviation between the minimum value of the alcohol concentration of the fuel assumed every time and the alcohol concentration stored in the storage means when the internal combustion engine is started. It has been changed to. According to this configuration, the increase side determination value and the decrease side determination value are each set assuming that the amount of change in the alcohol concentration between the previous operation and the current operation of the internal combustion engine is maximized. This is suitable for preventing erroneous determination that there is an abnormality based on the change in the air-fuel ratio correction value resulting from the undetected alcohol concentration.

  It is considered that the alcohol concentration in the fuel is different between the previous operation and the current operation of the internal combustion engine due to the refueling. At this time, the possible value of the alcohol concentration of the fuel after refueling changes according to the remaining amount of fuel at the time of refueling and the alcohol concentration of the remaining fuel. In view of this point, the invention according to claim 5 includes a fuel measuring unit that measures the remaining amount of fuel during refueling of the internal combustion engine, and the changing unit includes a remaining fuel amount measured by the fuel measuring unit, Based on the alcohol concentration of the remaining fuel stored in the storage means when refueling the internal combustion engine, the maximum value and the minimum value of the alcohol concentration of fuel that can be taken after refueling the internal combustion engine are calculated, and the maximum value and the minimum value are calculated. The increase side determination value and the decrease side determination value are changed based on the value. According to this configuration, when calculating the increase side determination value and the decrease side determination value, the fuel remaining amount at the time of refueling and the alcohol concentration of the remaining fuel are taken into consideration, so that the alcohol concentration of the fuel is the same as the previous operation. When different from the current operation, it is possible to more accurately determine the maximum value and the minimum value of the alcohol concentration assumed every time. As a result, the increase-side determination value and the decrease-side determination value can be set to appropriate values, and thus erroneous determination of abnormality detection can be suitably prevented.

  The case where the fuel property changes between the previous operation and the current operation of the internal combustion engine corresponds to the case where refueling is performed while the internal combustion engine is stopped. On the other hand, when refueling is not performed, it is generally considered that the fuel properties do not differ between the previous operation and the current operation of the internal combustion engine. In view of this point, the invention described in claim 6 is provided with fuel supply detection means for detecting that fuel is supplied to the fuel tank of the internal combustion engine, and the change means is supplied to the fuel tank by the fuel supply detection means. When the refueling is detected, the predetermined determination value is changed. According to this configuration, when refueling is not performed, the determination value is not changed even if the fuel property is not detected, so the normal range of the air-fuel ratio correction value is not expanded. As a result, it is possible to suppress a decrease in detection accuracy of the fuel system abnormality.

  The invention according to claim 7 is a comparison between an air-fuel ratio correction value for making an air-fuel ratio detection value by an air-fuel ratio sensor installed in an exhaust passage of an internal combustion engine coincide with a target value, and a predetermined predetermined determination value. An abnormality detection device for an internal combustion engine that detects an abnormality in a fuel system of the internal combustion engine based on a result, a fuel property detection means for detecting a property of fuel supplied to the internal combustion engine, and the fuel property after the internal combustion engine is started Abnormality detection means for prohibiting detection of the fuel system abnormality until the detection of the fuel property by the detection means is completed, and detecting the fuel system abnormality after the detection of the fuel property by the fuel property detection means is completed And.

  By monitoring the air-fuel ratio correction value, the presence or absence of a fuel system abnormality in the internal combustion engine is detected. Here, since the fuel amount for making the air-fuel ratio detected value coincide with the target value differs depending on the property of the fuel supplied to the internal combustion engine, it is necessary to correct the fuel injection amount in the internal combustion engine according to the property of the fuel. There is. At this time, if the fuel properties are different between the previous operation and the current operation of the internal combustion engine, fuel correction according to the fuel properties cannot be properly performed until the fuel property detection process is completed. Therefore, it is conceivable that the air-fuel ratio correction value changes greatly to the rich side or the lean side. In such a case, in the abnormality detection based on the air-fuel ratio correction value, there is a concern that an erroneous detection may be made that an abnormality has occurred even though the air-fuel ratio correction value is actually an appropriate air-fuel ratio correction value according to the current fuel property. Is done.

  In this respect, according to the present invention, the abnormality determination based on the air-fuel ratio correction value is prohibited until the fuel property detection process is completed after the internal combustion engine is started. Abnormality detection is not performed during a period in which the fuel ratio correction value may change to the rich side or the lean side. As a result, it is possible to prevent erroneous determination that there is an abnormality even though no fuel system abnormality has occurred.

  The case where the fuel property changes between the previous operation and the current operation of the internal combustion engine corresponds to the case where refueling is performed while the internal combustion engine is stopped. On the other hand, when refueling is not performed, it is generally considered that the fuel properties do not differ between the previous operation and the current operation of the internal combustion engine. In view of this point, the invention according to claim 8 is provided with fuel supply detection means for detecting that fuel is supplied to the fuel tank of the internal combustion engine, and the abnormality detection means is operated by the fuel supply detection means. When the fuel supply is detected, the detection of the fuel system abnormality is prohibited until the detection of the fuel property by the fuel property detection means is completed. According to this configuration, when the fuel is not supplied, the fuel system abnormality is detected even if the fuel property is not detected, so that the fuel system abnormality can be detected as early as possible.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed for an in-vehicle multi-cylinder spark ignition engine that is an internal combustion engine. In this engine, at least one of gasoline and alcohol (for example, ethanol or methanol) is used as fuel. That is, in the engine, gasoline alone fuel is used, or mixed fuel in which alcohol is mixed in an arbitrary ratio is used. In the control system, an electronic control unit (hereinafter referred to as an ECU) is used as a center to control the fuel injection amount and ignition timing. FIG. 1 shows an overall schematic configuration diagram of the engine control system.

  In the engine 10 shown in FIG. 1, an air cleaner 12 is provided at the most upstream portion of the intake pipe 11, and an air flow meter 13 for detecting the intake air amount is provided downstream of the air cleaner 12. A throttle valve 14 whose opening degree is adjusted by a throttle actuator 15 such as a DC motor is provided on the downstream side of the air flow meter 13. The opening degree of the throttle valve 14 (throttle opening degree) is detected by a throttle opening degree sensor built in the throttle actuator 15.

  A surge tank 17 is provided on the downstream side of the throttle valve 14. An intake manifold 18 for introducing air into each cylinder of the engine 10 is connected to the surge tank 17. In the intake manifold 18, an electromagnetically driven fuel that injects fuel in the vicinity of the intake port of each cylinder. An injection valve 19 is attached.

  The fuel injection valve 19 is connected to a fuel tank 32 via a fuel pipe 31. The fuel tank 32 is provided with an alcohol concentration sensor 37 capable of detecting the alcohol concentration as a fuel property. Based on the detection value of the alcohol concentration sensor 37, the alcohol concentration in the fuel in the fuel tank 32 (ratio of gasoline and alcohol in the fuel in the fuel tank 32) is detected. Further, the fuel tank 32 is provided with a fuel gauge 38 for measuring the amount of fuel in the fuel tank 32.

  An intake valve 21 and an exhaust valve 22 are provided at an intake port and an exhaust port of the engine 10, respectively. The air-fuel mixture is introduced into the combustion chamber 23 by the opening operation of the intake valve 21, and the exhaust gas after combustion is discharged to the exhaust pipe 24 by the opening operation of the exhaust valve 22.

  A spark plug 27 is attached to the cylinder head of the engine 10 for each cylinder. A high voltage is applied to the spark plug 27 at a desired ignition timing through an ignition device (not shown) including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 27, and the air-fuel mixture introduced into the combustion chamber 23 is ignited and used for combustion.

  The exhaust pipe 24 is provided with a catalyst 25 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas. Further, on the upstream side of the catalyst 25, an oxygen sensor 26 is provided for detecting the air-fuel ratio (oxygen concentration) of the air-fuel mixture using the exhaust gas as a detection target. In this embodiment, the oxygen sensor 26 is provided with a wide-area detection type A / F sensor that outputs a wide-range air-fuel ratio signal proportional to the oxygen concentration in the exhaust gas by applying a voltage to the sensor element.

  In addition, this system is provided with a coolant temperature sensor 29 for detecting the coolant temperature, a crank angle sensor 28 for outputting a rectangular crank angle signal for each predetermined crank angle of the engine 10, and the like.

  As is well known, the ECU 40 is mainly composed of a microcomputer (hereinafter referred to as a microcomputer) 41 composed of a CPU, ROM, RAM, and the like, and executes various control programs stored in the ROM, so that the engine operation state can be changed each time. In response, various controls of the engine 10 are performed. That is, the microcomputer 41 of the ECU 40 inputs detection signals from the various sensors described above, calculates the fuel injection amount and ignition timing based on the various detection signals, and drives the fuel injection valve 19 and the ignition device. To control.

  Regarding the fuel injection amount control, the microcomputer 41 calculates the basic fuel amount TP from the intake air amount of the engine 10 and the engine speed, and performs various corrections on the basic fuel amount Tp to calculate the final fuel amount TAU. To do. Then, the final fuel amount Te is converted into the injection time, and the fuel injection valve 19 is opened for the calculated injection time.

  As one of various corrections of the fuel injection amount, the microcomputer 41 performs air-fuel ratio feedback correction. Specifically, the air-fuel ratio correction value FAF is calculated based on the deviation between the air-fuel ratio detection value and the target value so that the air-fuel ratio detection value detected by the oxygen sensor 26 matches the target value (for example, the theoretical air-fuel ratio). To do. Then, by multiplying the basic fuel amount TP by the air-fuel ratio correction value FAF, the basic fuel amount TP is corrected to increase or decrease according to the air-fuel ratio deviation.

  Further, as one of the other corrections in the fuel injection amount, the microcomputer 41 performs correction (alcohol concentration correction) according to the alcohol concentration in the fuel. That is, the theoretical air-fuel ratio differs between gasoline and alcohol. For example, the theoretical air-fuel ratio (A / F) of gasoline is 14.7, whereas the theoretical air-fuel ratio of ethanol is 8.9. Therefore, when the air-fuel ratio is set as the target value, it is necessary to increase the amount of fuel to be injected as the alcohol concentration in the fuel increases. Therefore, the basic fuel amount TP is corrected according to the alcohol concentration in the fuel. Specifically, an alcohol concentration correction value FAL is calculated according to the alcohol concentration detected by the alcohol concentration sensor 37, and the basic fuel amount TP is multiplied by the correction value FAL. Thereby, the basic fuel amount TP is corrected to the increase side or the decrease side according to the alcohol concentration in the fuel. FIG. 2 shows the relationship between the alcohol concentration and the alcohol concentration correction value FAL. According to the relationship shown in FIG. 2, the higher the alcohol concentration, the larger the alcohol concentration correction value FAL.

  Here, in the present embodiment, a process (alcohol detection process) for detecting the alcohol concentration in the fuel is repeatedly executed at a predetermined cycle (for example, several minutes or several tens of minutes) when the ECU 40 is turned on (ignition on). . Then, the alcohol concentration detection value ALC obtained by the same process is stored in a memory that can hold the stored contents even after the ignition is turned off, such as a backup RAM of the ECU 40, and is read out by the microcomputer 41 of the ECU 40 as necessary. . In the present embodiment, the time required for the detection process is, for example, several tens of seconds.

  Further, in order to realize good air-fuel ratio control, the microcomputer 41 performs fuel system abnormality detection processing such as deterioration of the fuel injection valve 19 with time, clogging of the injection port, reduction of fuel pressure, and the like. Specifically, the air-fuel ratio correction value FAF calculated based on the deviation between the air-fuel ratio detection value and the target value is compared with a predetermined determination reference value, and an abnormality is determined based on the comparison result. In this embodiment, the determination reference value includes a rich determination reference value THXB determined on the increase side of the air-fuel ratio correction value FAF and a lean determination reference value THYB determined on the decrease side of the air-fuel ratio correction value FAF. The microcomputer 41 determines that a fuel system abnormality has occurred when the air-fuel ratio correction value FAF is larger than the rich determination reference value THXB or smaller than the lean determination reference value THYB. Note that the rich determination reference value THXB and the lean determination reference value THYB are set on a gasoline basis.

  By the way, it is conceivable that the alcohol concentration of the fuel in the fuel tank 32 changes before and after refueling as a result of, for example, refueling between the previous engine operation and the current engine operation. In such a case, the value before refueling is stored in the ECU 40 as the alcohol concentration detection value ALC after the ignition is turned on at the next engine start until the alcohol detection processing is completed, so the alcohol concentration correction value FAL is accurately calculated. I can't. Therefore, the final injection amount TAU cannot be set to an appropriate value according to the alcohol concentration, and as a result, it is conceivable that a deviation in the air-fuel ratio occurs. In such a case, the air-fuel ratio correction value FAF greatly changes to the rich side or the lean side, and in the above-described abnormality detection, the air-fuel ratio correction value is actually an appropriate air-fuel ratio correction according to the alcohol concentration after refueling. There is a concern that an erroneous determination that a fuel system abnormality has occurred is made. That is, there is a risk of erroneous determination that the fuel system is abnormal based on the change in the air-fuel ratio correction value FAF accompanying the alcohol concentration correction value FAL being inappropriate.

  Therefore, in the present embodiment, when the abnormality detection of the fuel system based on the air-fuel ratio correction value FAF is performed, the determination values (the rich determination value THX and the lean determination value) used for the abnormality determination until the alcohol detection process is completed. (THY) is changed to the side that expands the normal range of the air-fuel ratio correction value FAF. In particular, in the present embodiment, the rich determination value THX and the lean determination value THY are set based on the previous value of the alcohol concentration in the fuel. This prevents misjudgment or omission of detection that a fuel system abnormality has occurred in the alcohol-containing fuel. As this process, the microcomputer 41 of the ECU 40 executes the following process.

  FIG. 3 shows a processing procedure of a process (startup determination value setting process) for setting the rich side determination value THX and the lean side determination value THY used for detecting the fuel system abnormality at the time of engine start accompanying ignition-on. It is a flowchart. This process is performed by the microcomputer 41 of the ECU 40 at predetermined intervals.

  In FIG. 3, first, in step S10, it is determined whether or not it is within a predetermined engine start period indicating that the engine is starting. Here, a determination is made based on the elapsed time since the ignition is turned on, and if the elapsed time is within a predetermined time (for example, several minutes), it is determined that it is within a predetermined engine start period. If it is within the predetermined engine start period, the process proceeds to step S11, and it is determined whether or not the alcohol detection process is completed after the ignition is turned on. If the alcohol detection process is not yet completed, the process proceeds to step S12, and it is determined whether or not the previous value (previous alcohol detection value ALCB) of the alcohol concentration detection value ALC is stored in the backup RAM or the like of the ECU 40. When the previous alcohol detection value ALCB is stored in the backup RAM or the like, the process proceeds to step S13, and the rich determination value THX and the lean determination value THY are calculated based on the previous alcohol detection value ALCB.

  Regarding the rich determination value THX and the lean determination value THY, in this embodiment, the change in alcohol concentration in the fuel in the fuel tank 32 can be taken between the previous engine operation and the current engine operation. The determination values THX and THY are calculated in consideration of the possibility of the maximum value. That is, the alcohol concentration in the fuel in the fuel tank 32 has changed from the previous alcohol detection value ALCB to the maximum value (for example, 100%) or the minimum value (for example, 0%) of the alcohol concentration in the fuel on the market. And the rich determination value THX and the lean determination value THY are calculated based on the amount of change in the air-fuel ratio correction value FAF accompanying the change in concentration.

  FIG. 4 is a diagram for explaining a calculation procedure of the rich determination value THX and the lean determination value THY. In FIG. 4, the horizontal axis indicates the alcohol concentration, and the vertical axis indicates the alcohol concentration correction value FAL. In FIG. 4, if the previous alcohol detection value ALCB is “ALC1”, the alcohol concentration correction value FAL becomes richer as the alcohol concentration in the fuel changes between the previous engine operation and the current engine operation. It changes by a maximum of x1, and changes by a maximum of y1 on the lean side. Until the detection process of alcohol concentration is completed, this change is not taken into account when calculating the final fuel amount TAU as the alcohol concentration correction value FAL. As a result, the change is reflected in the air-fuel ratio correction value FAF. It becomes. Therefore, in the present embodiment, when the previous alcohol detection value ALCB is ALC1, the value obtained by adding x1 to the rich judgment reference value FXB is set as the rich judgment value THX, and the value obtained by subtracting y1 from the lean judgment reference value FYB is set as the lean value. The determination value THY is used. Similarly, if the previous alcohol detection value ALCB is “ACL2 (> ACL1)”, when the alcohol concentration in the fuel changes, the alcohol concentration correction value FAL changes to the rich side by a maximum of x2 (<x1). However, it changes by y2 (> y1) at the maximum on the lean side. Therefore, when the previous alcohol detection value ALCB is ALC2, the value obtained by adding x2 to the rich determination reference value THXB is set as the rich determination value THX, and the value obtained by subtracting y2 from the lean determination reference value THYB is set as the lean determination value THY. .

  FIG. 5 shows the relationship between the rich determination value THX and lean determination value THY calculated by the above procedure and the previous alcohol detection value ALCB. 5A shows the rich determination value THX, and FIG. 5B shows the lean determination value THY. The relationship of FIG. 5 is stored in the ROM of the ECU 40, and in step S13 of FIG. 3, the rich side determination value THX and the lean side determination value THY are calculated from the previous alcohol detection value ALCB using this relationship. In FIG. 5A, the rich determination value THX is made smaller as the previous alcohol detection value ALCB is larger (as the previous alcohol concentration is higher). In FIG. 5B, the lean side determination value THY is set to a larger value as the previous alcohol detection value ALCB is larger.

  Returning to the description of FIG. 3, in step S12, if the previous alcohol detection value ALCB is not stored in the backup RAM or the like, for example, immediately after shipment from the factory or immediately after battery replacement, the process proceeds to step S14, where the rich determination value is set. THX and lean determination value THY are calculated. Here, as to the rich determination value THX and the lean determination value THY, as shown in FIG. 5, the ranges that the determination values THX and THY can take are determined. In step S14, the maximum value of the possible range is set to the rich determination value THX and the lean determination value THY, respectively.

  Specifically, for example, in the relationship of FIG. 5, for the rich determination value THX, a value (THXB + x0) when the minimum value (for example, 0%) of the alcohol concentration in the fuel can be set as the previous alcohol detection value ALCB. And The lean determination value THY is a value (THYB + y0) when the maximum value (for example, 100%) of the alcohol concentration in the fuel is taken as the previous alcohol detection value ALCB. Here, x0 and y0 are changes in the air-fuel ratio correction value FAF corresponding to the maximum change in alcohol concentration.

  Further, when a predetermined engine start period has elapsed, or when alcohol detection processing is completed and the alcohol concentration detected after the current engine start (current alcohol detection value ALCA) is stored in the backup RAM or the like, A negative determination is made in step S10, or an affirmative determination is made in step S11, and the process proceeds to step S15, where the rich determination value THX and the lean determination value THY are set to the determination reference values THXB and THYB, respectively. In this case, since the current alcohol detection value ALCA has been detected, the alcohol concentration correction value FAL is calculated to an appropriate value based on the current alcohol detection value ALCA. Therefore, when an abnormality is determined based on the air-fuel ratio correction amount FAF, abnormality detection is performed without being affected by the alcohol concentration by comparing the air-fuel ratio correction amount FAF with the determination reference values THXB and THYB.

  FIG. 6 is a time chart showing the transition of the rich determination value THX and the lean determination value THY when the engine is started. In FIG. 6, (a) shows the case where the previous value of the alcohol concentration is relatively low, and (b) shows the case where the previous value of the alcohol concentration is relatively high.

  In FIG. 6A, since the previous value of the alcohol concentration is relatively low, when the alcohol concentration in the fuel in the fuel tank 32 changes between the previous engine operation and the current engine operation, the alcohol concentration It is conceivable that the concentration changes more greatly toward the high concentration side. Considering this, the normal range of the air-fuel ratio correction value FAF is expanded on the rich side rather than the lean side. In FIG. 6B, since the previous value of the alcohol concentration is relatively high, when the alcohol concentration in the fuel in the fuel tank 32 changes between the previous engine operation and the current engine operation, It is conceivable that the alcohol concentration changes more greatly toward the low concentration side. Considering this, the normal range of the air-fuel ratio correction value FAF is expanded on the lean side rather than the rich side. Further, when the detection of the alcohol concentration is completed, the determination values THX and THY are returned to the determination reference values THXB and THYB, respectively.

  According to the present embodiment described above, the following excellent effects are obtained.

  Until the alcohol detection process is completed when the engine is started, the rich determination value THX and the lean determination value THY used in the abnormality determination based on the air-fuel ratio correction value FAF are changed to the side that expands the normal range of the air-fuel ratio correction value FAF. Therefore, when the air-fuel ratio correction value FAF changes greatly to the rich side or the lean side because the alcohol concentration is not detected after the engine start this time, the change is erroneously determined as a fuel system abnormality. Can be prevented.

  Further, since the rich determination value THX and the lean determination value THY are changed based on the previous alcohol detection value ALCB that is the alcohol concentration stored in the backup RAM or the like at the time of the current engine start, the rich determination value THX and the lean determination value THY are changed from the previous alcohol detection value ALCB. The rich determination value THX and the lean determination value THY can be set according to the assumed density change. That is, when the previous alcohol detection value ALCB is relatively high, the air-fuel ratio correction value FAF is likely to change greatly from the rich side to the lean side. When the previous alcohol detection value ALCB is relatively low, the air-fuel ratio correction value In consideration of the fact that FAF is likely to change greatly from the lean side to the rich side, in this embodiment, the rich judgment value THX and the lean judgment value THY are set according to the previous alcohol detection value ALCB. The values THX and THY can be set relatively easily and accurately to appropriate values for suppressing detection of abnormalities. Thereby, in the alcohol-containing fuel, the abnormality determination can be performed while maintaining a balance between prevention of erroneous determination that the fuel system abnormality has occurred and prevention of detection omission.

  The rich judgment value THX is changed to the rich side by the deviation between the maximum value (for example, 100%) of the alcohol concentration in the fuel on the market and the previous alcohol detection value ALCB, and the alcohol concentration in the fuel on the market Since the lean determination value THY is changed to the lean side by the difference between the minimum value (for example, 0%) of the previous value and the previous alcohol detection value ALCB, the alcohol in the fuel during the previous engine operation and the current engine operation The rich determination value THX and the lean determination value THY can be calculated on the assumption that the amount of change in density is maximized. Accordingly, it is possible to suitably prevent erroneous determination that there is an abnormality based on the change in the air-fuel ratio correction value FAF caused by the undetected alcohol concentration.

  Furthermore, since the rich determination value THX and the lean determination value THY are returned to the determination reference values THXB and THYB when the detection of the alcohol concentration in the fuel is completed in the alcohol detection processing after the engine start this time, the alcohol concentration After the completion of the detection, the normal range of the air-fuel ratio correction value FAF is not expanded, which is suitable for suppressing the detection failure of the fuel system abnormality.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment. In the present embodiment, abnormality detection based on the air-fuel ratio correction value FAF is prohibited during a period until the alcohol concentration detection processing is completed at the time of engine start, and abnormality detection based on the air-fuel ratio correction value FAF is performed after the detection processing is completed. carry out.

  FIG. 7 is a flowchart showing a processing procedure of a process (abnormality detection permission / inhibition determination process) for determining whether to execute the fuel system abnormality detection based on the air-fuel ratio correction value FAF at the time of engine start accompanying ignition-on. This process is performed by the microcomputer 41 of the ECU 40 at predetermined intervals.

  In FIG. 7, in step S20, it is first determined whether or not it is within a predetermined engine start period. If it is within the predetermined engine start period, the process proceeds to step S21 to determine whether or not the alcohol concentration detection process is completed. If the alcohol concentration detection process has been completed, the process proceeds to step S22, where the abnormality detection based on the air-fuel ratio correction value FAF is permitted. On the other hand, if the alcohol concentration detection processing is incomplete and the alcohol detection value detected after the current engine start is not stored in the backup RAM or the like, the process proceeds to step S23, and the abnormality detection based on the air-fuel ratio correction value FAF is executed. Is prohibited. Thus, abnormality detection based on the air-fuel ratio correction value FAF is not performed in a period in which the air-fuel ratio correction value FAF is likely to fluctuate because the alcohol concentration correction value FAL is not an appropriate value.

  According to the present embodiment described above, the following excellent effects are obtained.

  Since the abnormality determination based on the air-fuel ratio correction value FAF is prohibited until the alcohol detection process is completed when the engine 10 is started, and the abnormality determination based on the air-fuel ratio correction value FAF is performed after the alcohol detection process is completed, this time After the engine is started, abnormality detection is not performed in a period in which the air-fuel ratio correction value FAF may change greatly to the rich side or the lean side due to the undetected alcohol concentration. As a result, it can be prevented that a change in the air-fuel ratio correction value FAF due to the undetected alcohol concentration is erroneously determined as an abnormality in the fuel system.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  In the first embodiment, the rich determination value THX and the lean determination value are based on the previous alcohol detection value ALCB when the predetermined engine start period is satisfied and the alcohol detection process is not completed. Although THY is calculated, it may be added that the fuel is further supplied as a condition for calculating the determination values THX and THY based on the previous alcohol detection value ALCB. Specifically, it is conceivable that the alcohol concentration in the fuel in the fuel tank 32 has changed when it is determined that there is refueling as a result of determining the presence or absence of refueling before the current engine start. Therefore, in this case, the rich determination value THX and the lean determination value THY are changed based on the previous alcohol detection value ALCB. On the other hand, if it is determined that there is no refueling, it is considered that the alcohol concentration in the fuel in the fuel tank 32 has not changed. Therefore, the rich determination value THX and the lean determination value THY are set to the determination reference value THXB, THYB. In this way, when the fuel concentration is not changed and the alcohol concentration in the fuel in the fuel tank 32 has not changed, the normal range of the air-fuel ratio correction value FAF is not expanded even before the alcohol concentration is detected. Therefore, it can suppress that the detection precision of fuel system abnormality falls. Here, regarding the presence or absence of refueling, for example, it is determined that there is refueling when the detected value of the fuel gauge 38 provided in the fuel tank 32 becomes large.

  Similarly, in the second embodiment, the abnormality determination based on the air-fuel ratio correction value FAF is prohibited when it is determined that there is fueling, and the abnormality based on the air-fuel ratio correction value FAF is determined when it is determined that there is no fueling. A determination may be made. By doing so, if the fuel concentration is not changed and the alcohol concentration in the fuel in the fuel tank 32 has not changed, the abnormality determination is performed even before the alcohol concentration is detected. Can be discovered as early as possible.

  In the first embodiment, the remaining amount of fuel at the time of refueling is detected, the maximum and minimum values of alcohol concentration that can be taken after refueling are calculated based on the remaining fuel amount and the alcohol concentration of the remaining fuel, The rich determination value THX and the lean determination value THY may be calculated based on the maximum value and the minimum value. In this way, when the alcohol concentration in the fuel is different between the previous operation and the current operation, the maximum value and the minimum value of the alcohol concentration assumed each time can be obtained more accurately. As a result, the rich determination value and the lean determination value can be set to appropriate values, and thus erroneous determination of abnormality detection can be suitably prevented.

  In the first embodiment, the rich determination value THX and the lean determination value THY are made variable according to the previous alcohol detection value ALCB until the alcohol detection process is completed. Regardless of the above, the rich determination value THX may be set to the rich side by the predetermined value α from the rich determination reference value THXB, and the lean determination value THY may be set to the lean side by the predetermined value β from the lean determination reference value THYB. Also in this case, until the alcohol detection process is completed, the normal range of the air-fuel ratio correction value FAF is expanded, so that the same effect as described above can be obtained. However, it is desirable to change the rich determination value THX and the lean determination value THY in accordance with the previous alcohol detection value ALCB in order to suitably prevent an erroneous determination that there is an abnormality or an abnormal detection omission.

  In the above embodiment, the engine 10 using gasoline and alcohol as fuels has been described. However, as long as a plurality of components having different fuel properties are included, a fuel including a plurality of components other than gasoline and alcohol may be used. Specifically, for example, a mixed fuel of heavy fuel and light fuel, a mixed fuel of high octane number and low octane number, and the like can be mentioned.

1 is an overall schematic configuration diagram of an engine control system. The figure which shows the relationship between alcohol concentration and alcohol concentration correction value. The flowchart which shows the process sequence of the determination value setting process at the time of starting. The figure for demonstrating the calculation procedure of a rich determination value and a lean determination value. The figure which shows the relationship between a rich determination value, a lean determination value, and the last alcohol detection value. The time chart which shows transition of the rich judgment value and the lean judgment value at the time of engine starting. The flowchart which shows the process sequence of abnormality detection permission determination processing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 19 ... Fuel injection valve, 24 ... Exhaust pipe, 26 ... Oxygen sensor, 32 ... Fuel tank, 37 ... Alcohol concentration sensor, 38 ... Fuel meter, 40 ... ECU, 41 ... Microcomputer.

Claims (8)

The fuel of the internal combustion engine is based on a comparison result between an air-fuel ratio correction value for matching an air-fuel ratio detection value by an air-fuel ratio sensor installed in the exhaust passage of the internal combustion engine with a target value and a predetermined predetermined determination value. In an abnormality detection device for an internal combustion engine that detects a system abnormality,
Fuel property detecting means for detecting the property of the fuel supplied to the internal combustion engine;
Change means for changing the predetermined determination value to a side for expanding the normal range of the air-fuel ratio correction value during a period until the fuel property detection by the fuel property detection means is completed after starting the internal combustion engine;
An abnormality detection device for an internal combustion engine, comprising: Storage means for storing the fuel property detected by the fuel property detection means;
The changing means stores the predetermined determination value in the storage means when starting the internal combustion engine during a period until the detection of the fuel property by the fuel property detecting means accompanying the current start of the internal combustion engine. The abnormality detection device for an internal combustion engine according to claim 1, wherein the abnormality detection device is changed based on a fuel property. The predetermined determination value includes an increase side determination value determined on the fuel increase side of the air-fuel ratio correction value and a decrease side determination value determined on the fuel decrease side of the air-fuel ratio correction value,
The fuel property detecting means detects the alcohol concentration of the fuel as the fuel property,
The change means reduces the change amount of the increase side determination value and increases the change amount of the decrease side determination value as the alcohol concentration of the fuel stored in the storage means at the start of the internal combustion engine increases. Item 3. An abnormality detection apparatus for an internal combustion engine according to Item 2.   The change means changes the increase side determination value to the rich side by a deviation between the maximum value of the alcohol concentration of the fuel assumed every time and the alcohol concentration stored in the storage means when the internal combustion engine is started, 4. The reduction-side determination value is changed to a lean side by an amount corresponding to a deviation between a minimum value of the alcohol concentration of fuel assumed every time and the alcohol concentration stored in the storage unit when the internal combustion engine is started. 5. Abnormality detection device for an internal combustion engine. Comprising fuel measuring means for measuring the remaining amount of fuel during refueling of the internal combustion engine,
In the fuel that can be obtained after refueling the internal combustion engine based on the remaining fuel amount measured by the fuel measurement unit and the alcohol concentration of the remaining fuel stored in the storage unit when refueling the internal combustion engine. The abnormality detection device for an internal combustion engine according to claim 3 or 4, wherein a maximum value and a minimum value of the alcohol concentration of the engine are calculated, and the increase side determination value and the decrease side determination value are changed based on the maximum value and minimum value. . Refueling detection means for detecting that fuel has been supplied to the fuel tank of the internal combustion engine;
The abnormality detection device for an internal combustion engine according to any one of claims 1 to 5, wherein the change unit changes the predetermined determination value when the fuel supply detection unit detects fuel supply to the fuel tank. The fuel of the internal combustion engine is based on a comparison result between an air-fuel ratio correction value for matching an air-fuel ratio detection value by an air-fuel ratio sensor installed in the exhaust passage of the internal combustion engine with a target value and a predetermined predetermined determination value. In an abnormality detection device for an internal combustion engine that detects a system abnormality,
Fuel property detecting means for detecting the property of the fuel supplied to the internal combustion engine;
The detection of the fuel system abnormality is prohibited during a period after the start of the internal combustion engine until the detection of the fuel property by the fuel property detection unit is completed, and after the detection of the fuel property by the fuel property detection unit is completed, the fuel system An anomaly detection means for detecting an anomaly;
An abnormality detection device for an internal combustion engine, comprising: Refueling detection means for detecting that fuel has been supplied to the fuel tank of the internal combustion engine;
The abnormality detection unit prohibits detection of the fuel system abnormality during a period until the fuel property detection unit completes detection of fuel when the fuel supply detection unit detects fuel supply to the fuel tank. The abnormality detection device for an internal combustion engine according to claim 7.

Images