JP5045601B2 - Engine system abnormality diagnosis device - Google Patents

Description

  The present invention relates to an abnormality diagnosis device for an engine system having a variable compression ratio mechanism.

  In an internal combustion engine equipped with a variable compression ratio mechanism that can change the compression ratio of the engine, the compression ratio is set to a set value according to the operating state of the engine in order to improve output performance, fuel consumption, exhaust emission, etc. Be controlled.

In recent years, so-called mixed fuel engines that allow gasoline and alcohol to be used together as fuel have been put into practical use (see, for example, Patent Documents 1 to 3). An automobile equipped with this type of engine is generally called a flexible fuel vehicle (FFV), and any one of alcohol alone, gasoline alone, or a mixed fuel in which alcohol and gasoline are mixed is used as fuel. Can also be driven. By the way, if the alcohol concentration of the fuel is different, the theoretical air-fuel ratio changes accordingly. Therefore, in the mixed fuel engine, the alcohol concentration of the fuel is detected by an alcohol concentration sensor, and the amount of fuel supplied to the engine is adjusted based on this. It is common. The engine is provided with an electronic control unit (ECU) for controlling the engine. The output signals of various sensors are input to the ECU, and control signals are output to a variable valve mechanism, a fuel injection system, and the like based on these signals. However, an engine system including a variable valve mechanism, a fuel injection system, various sensors, etc. may fail for some reason.
Japanese Patent Publication No.7-153508 Japanese Utility Model Publication No. 6-6216 JP 2008-2328 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an abnormality diagnosis device for an engine system that can preferably diagnose whether there is an abnormality in an engine system having a variable compression ratio mechanism. There is to do.

In order to achieve the above object, the abnormality diagnosis device for an engine system according to the present invention employs the following means. That is,
Applied to a variable compression ratio engine having a variable compression ratio mechanism capable of controlling the compression ratio of the engine to a target compression ratio according to the operating state of the engine;
In a state in which the compression ratio of the engine is controlled to the target compression ratio, the required retard angle value required for the ignition timing of the engine according to the knocking strength generated in the engine and the initial value at the start of the engine. An acquisition means for acquiring, as an acquired value, at least one of values correlated with a total injection amount of fuel injected from the fuel injection valve until an explosion occurs (hereinafter referred to as a total injection amount at start-up);
An abnormality determination value setting means for setting an abnormality determination value for the acquired value acquired by the acquisition means according to the target compression ratio;
An abnormality diagnosing means for diagnosing an abnormality in the engine system when the acquired value acquired by the acquiring means exceeds the abnormality determination value;
It is characterized by providing.

The knocking strength represents the degree of knocking strength generated in the engine.
For example, when the magnitude of engine vibration is detected by a known knocking sensor, it can be determined that the greater the detected value, the greater the knocking strength. When knocking occurs in the engine, a request for retarding the ignition timing of the engine is issued in order to reduce or suppress knocking. The retard required value in the present invention means the magnitude of the correction amount when the ignition timing is corrected (changed) to the retard side in accordance with the knocking strength. In this case, the retardation correction amount for one retardation correction with respect to the ignition timing may be adopted as the retardation request value, or an acquisition time for acquiring the retardation request value is determined in advance and the acquisition time The integrated value of the retardation angle correction amount may be adopted as the retardation requirement value. Regardless of which is adopted, the relationship that the required retardation value increases as the knocking strength increases. Hereinafter, when simply referred to as “retarding required value” in the present specification, it is used as the meaning of the required retarding value required for the ignition timing of the engine in accordance with the knocking intensity generated in the engine.

  In addition, the “value correlated with the total injection amount at the start” includes, in addition to the total injection amount at the start, fuel required for the initial explosion from the start of fuel injection related to engine start from the fuel injection valve. This corresponds to the number of injections (hereinafter referred to as the number of injections at start-up), the time required from the start of fuel injection related to engine start to the occurrence of the first explosion (hereinafter referred to as the initial explosion required time), and the like. For example, when the fuel injection amount of fuel injected in one combustion cycle is equal at the start of the engine, the larger the total injection amount at the start, the more the number of injections at the start and the longer the initial explosion time. Hereinafter, when simply describing “a value that correlates to the total injection amount at the start” in the present specification, it correlates with the total injection amount of fuel injected from the fuel injection valve until the first explosion occurs at the start of the engine. It shall be used as the meaning of the value to be.

  An abnormality may occur in the engine system for some reason. The engine system in this specification is a concept that includes a variable compression ratio mechanism, a fuel injection system, various sensors for detecting the operating state and fuel properties of the engine, and the like. As an abnormality in the engine system, the target compression ratio is not set as an appropriate value for the actual operating state of the engine due to the detection of abnormalities in various sensors. Even if the target compression ratio is set to an appropriate value, the compression ratio remains as set. It is possible to exemplify a situation in which control of fuel injection by the fuel injection valve cannot be performed appropriately.

  When the above abnormality occurs in the engine system, when the variable compression ratio mechanism is operated so as to control the engine compression ratio to the target compression ratio, a value that correlates to the required retard angle value or the total injection amount at start-up becomes It deviates from the normal range (the range assumed in the normal operation state) and becomes excessively large. This is because the knocking strength generated in the engine and the startability of the engine (the degree of ease of starting) change depending on whether there is an abnormality in the engine system.

  Therefore, in the present invention, in a state where the compression ratio of the engine is controlled to the target compression ratio, it correlates with the retardation required value that changes in magnitude depending on whether there is an abnormality in the engine system and the total injection amount at start-up. At least one of the values is acquired as an acquired value, and whether the engine system has an abnormality is diagnosed by comparing the acquired acquired value with an abnormality determination value.

  The abnormality determination value is a reference value for determining whether or not the acquired value acquired by the acquiring means (the retardation request value or the value correlated with the starting total injection amount) exhibits an abnormal value. Naturally, the abnormality determination value may be set to a different value between the case where the acquisition unit acquires the retard angle request value and the case where the acquisition unit acquires a value correlated with the starting total injection amount. If the abnormality determination value set for the retard required value is the first abnormality determination value, and the abnormality determination value set for the value correlated with the total injection amount at start is the second abnormality determination value, these are: Further, it can be considered as an upper limit value of each of the retard angle required value when the engine system can be determined to be normal and a value correlated with the total injection amount at the start.

Here, since the compression ratio of the engine affects the knocking strength and the startability of the engine, the optimum value for the abnormality determination value also changes according to the target compression ratio. In the present invention, since the abnormality determination value is set to a value corresponding to the target compression ratio, the abnormality determination value can be set to an appropriate value in consideration of the target compression ratio. Thereby, the abnormality diagnosis of the engine system can be executed with high accuracy.

  Here, when the engine in the present invention is a mixed fuel engine that can use a mixed fuel of gasoline and alcohol and includes a concentration detection device that detects the alcohol concentration of the fuel, the target compression ratio is the alcohol concentration. The higher the detected value, the higher is set as the value on the high compression ratio side, the abnormality determination value setting means sets the abnormality determination value according to the detection value of alcohol concentration and the target compression ratio, and the abnormality diagnosis means is acquired by the acquisition means When the acquired value exceeds the abnormality determination value, it may be diagnosed that there is an abnormality in the concentration detection device. Here, the fact that a mixed fuel of gasoline and alcohol can be used means that, in addition to the above-mentioned mixed fuel, fuel of only gasoline (alcohol concentration 0%) or only alcohol (alcohol concentration 100%) can be used.

  In this configuration, a method for acquiring the retardation request value as an acquired value and diagnosing whether or not the alcohol concentration is excessively detected in the concentration detection device will be described. This excessive detection means that the detected value of the alcohol concentration is erroneously detected on the higher concentration side than the actual (true) alcohol concentration (hereinafter referred to as the actual alcohol concentration).

  Here, the volatility of the fuel is lower when the alcohol concentration is higher than when the alcohol concentration is low, and the fuel supplied to the engine is less likely to vaporize. Accordingly, when the other conditions are equal, the higher the actual alcohol concentration, the lower the combustion temperature and combustion speed of the air-fuel mixture, so that the knocking strength is reduced. Conversely, when the other conditions are equal, the higher the compression ratio of the engine, the higher the knocking strength.

  According to this configuration, the target compression ratio is set as a value on the higher compression ratio side as the alcohol concentration detection value is higher. Therefore, the target compression ratio is set higher when it is determined that the fuel properties are unlikely to induce knocking, and conversely, the target compression ratio is set lower when it is determined that the fuel properties are likely to induce knocking. Is done. Therefore, if the concentration detection device is normal and the detected value of the alcohol concentration substantially matches the actual alcohol concentration, even if the actual alcohol concentration of the fuel changes, the value of the target compression ratio is appropriately changed according to the concentration. Therefore, the knocking strength does not increase excessively.

  However, if the detected value of the alcohol concentration by the concentration detector is erroneously detected higher than the actual alcohol concentration (over detection of alcohol concentration), it is erroneously determined that the volatility of the fuel is lower than the actual value. . As a result, the value of the target compression ratio is set disproportionately high in relation to the actual alcohol concentration. Therefore, when the alcohol concentration is detected normally because the set target compression ratio value is too high for the actual alcohol concentration even though it is appropriate in relation to the alcohol concentration that is erroneously detected on the high concentration side. The knocking strength generated in the engine increases compared to

  Next, a method for acquiring a value correlated with the starting total injection amount as an acquired value and diagnosing whether or not the alcohol concentration is underdetected in the concentration detection device will be described. This under-detection means that the detected value of the alcohol concentration is erroneously detected on the lower concentration side than the actual alcohol concentration.

As described above, if other conditions are equal, the higher the actual alcohol concentration, the lower the volatility of the fuel, making it difficult to start the engine (startability is reduced). That is, as the actual alcohol concentration is higher, the total injection amount at start, the number of injections at start, and the time required for the first explosion tend to increase, and the value correlated with the total injection amount at start shows a larger value. On the other hand, the higher the compression ratio at the time of engine start, the higher the in-cylinder temperature. Therefore, if other conditions are equal, the value correlated with the total injection amount at start shows a smaller value.

  In this configuration, when it is determined that the alcohol concentration detection value is low and the engine startability is high, the target compression ratio is set low, and when the alcohol concentration detection value is high and it is determined that the startability is low. The target compression ratio is set higher. Therefore, if the concentration detection device is normal and the detected value of the alcohol concentration substantially matches the actual alcohol concentration, the target compression ratio is set according to the concentration even if the actual alcohol concentration changes. The value correlated with the hourly total injection amount does not increase excessively.

  However, if the detected value of the alcohol concentration by the concentration detector is erroneously detected to a lower concentration side than the actual alcohol concentration (under detection of alcohol concentration), it is erroneously determined that the fuel volatility is higher than the actual value. . Thereby, the value of the target compression ratio is set disproportionately low in relation to the actual alcohol concentration. Therefore, when the alcohol concentration is detected normally because the set target compression ratio value is too low for the actual alcohol concentration, even though it is appropriate in relation to the alcohol concentration misdetected on the low concentration side. Compared with the engine startability is worse.

  As described above, the actual alcohol concentration and the compression ratio of the fuel affect the engine knocking strength and the engine startability. In contrast, according to this configuration, the abnormality determination value is set according to the detected value of the alcohol concentration and the target compression ratio. For this reason, the first abnormality determination value is set so that the retardation request value acquired when the alcohol concentration is excessively detected by the concentration detection device exceeds the first abnormality determination value, and the alcohol concentration is detected too low. In this case, the second abnormality determination value can be set so that the value correlated with the starting total injection amount acquired in the case exceeds the second abnormality determination value.

  For example, when the compression ratio of the engine is controlled to a target compression ratio set corresponding to the detected value of the alcohol concentration, if the detected value of the alcohol concentration substantially matches the actual alcohol concentration, the delay to be obtained. An upper limit value of the corner required value is obtained, and the first abnormality determination value can be set as a value obtained by adding a predetermined margin to the upper limit value. Further, when the engine is started by controlling the engine compression ratio to the target compression ratio set corresponding to the detected value of the alcohol concentration, the detected value of the alcohol concentration substantially matches the actual alcohol concentration. If this is the case, an upper limit value that correlates with the starting total injection amount to be obtained can be obtained, and the second abnormality determination value can be set as a value obtained by adding a predetermined margin to the upper limit value.

  According to this, when an abnormality occurs in the concentration detection device, it is possible to reliably detect the abnormality, and when the concentration detection device is normal, an erroneous diagnosis is made that it is abnormal. Can be reliably suppressed. In addition, according to this configuration, as the alcohol concentration of the fuel is higher, the engine startability is lowered. However, the engine startability can be improved by increasing the compression ratio at the time of start-up. In addition, even after the engine is started, the higher the alcohol concentration of the fuel, the higher the compression ratio can be made without increasing the knocking strength, so that the engine output and fuel efficiency can be improved as much as possible. Can do.

  In the present invention, the ignition timing of the engine may be controlled to be advanced as the alcohol concentration detection value is higher. The knocking strength of the engine increases as the ignition timing is controlled to the advance side if other conditions are equal. Therefore, in this case, the abnormality determination value setting means sets the abnormality determination value (that is, the first abnormality determination value) set for the retardation required value as the alcohol concentration detection value, the target compression ratio, and the ignition timing. It is preferable to set according to the set value. According to this, the abnormality diagnosis of the concentration detection device can be performed with higher accuracy by setting the first abnormality determination value in consideration of the ignition timing that affects the knocking strength of the engine.

  By the way, even when other conditions are equal, knocking is likely to occur when the engine load is high compared to when the engine load is low, and the knocking strength tends to increase as the load increases. . Therefore, when the acquisition unit acquires the retardation request value, the abnormality determination value setting unit uses the abnormality determination value (that is, the first abnormality determination value) set for the retardation request value as the engine load increases. It should be set as a large value. According to this, even if the engine load at the time of abnormality diagnosis of the concentration detection device is different, the first abnormality determination value can be set more finely according to the load at that time. For example, even if the knocking strength increases due to an extremely high engine load at the time of abnormality diagnosis of the concentration detection device, it is possible to suppress erroneous diagnosis regarding the presence or absence of abnormality in the concentration detection device.

  In the present invention, the fuel injection amount of the fuel injected from the fuel injection valve into one combustion cycle at the time of engine start (hereinafter referred to as start-up injection amount) is controlled so as to increase as the alcohol concentration detection value increases. May be. Since the startability of the engine is improved as the start-up injection amount increases if other conditions are equal, the value correlated with the start-up total injection amount also decreases accordingly. Therefore, when the acquisition unit acquires a value correlated with the starting total injection amount as the acquired value, the abnormality determination value setting unit sets the abnormality determination value (that is, the first determination value) for the value correlated with the starting total injection amount. 2 abnormality determination value) may be set according to the alcohol concentration detection value, the target compression ratio, and the starting injection amount. According to this, since the second abnormality determination value can be set in consideration of the starting injection amount that affects the engine startability, abnormality diagnosis of the concentration detection device can be performed with higher accuracy.

  Here, consider the relationship between engine startability, engine temperature at the time of engine start (hereinafter referred to as engine temperature at start-up), and fuel alcohol concentration. With regard to such a relationship, the engine startability decreases as the engine temperature at the start of the engine is lower under the condition where the alcohol concentration is equal, and the engine startability decreases as the alcohol concentration increases under the condition where the engine temperature at the start is equal. Therefore, in the present invention, when the acquisition unit acquires a value that correlates with the starting total injection amount, the abnormality determination value setting unit sets the starting total injection as the starting engine temperature is lower under the condition that the alcohol concentration detection value is equal. The abnormality determination value (that is, the second abnormality determination value) set for the value correlated with the quantity may be set as a larger value. Further, under the condition that the engine temperature at start is equal, the higher the alcohol concentration detection value, the larger the second abnormality determination value may be set.

  According to this, for example, the actual alcohol concentration is relatively high and the starting engine temperature is in a low temperature range under a condition in which the deterioration of the engine startability becomes remarkable and the increase in the value correlated with the total injection amount at the start becomes remarkable. Even when the engine is started when the engine is in the normal state, if the concentration detection device is normal, the second abnormality determination value is set to a larger value in accordance with the detected values of the engine temperature and alcohol concentration at the start. The value correlated with the total injection amount does not exceed the second abnormality determination value. Therefore, it is possible to reliably suppress erroneous diagnosis that the concentration detection apparatus is abnormal although it is normal. On the other hand, when the alcohol concentration is under-detected by the concentration detection device, the second abnormality determination value is set disproportionately small in the relationship between the starting engine temperature and the actual alcohol concentration. As a result, the value correlated with the starting total injection amount surely exceeds the second abnormality determination value, so that it is possible to reliably detect that the alcohol concentration is underdetected in the concentration detection device.

In addition, even when the difference between the detected value of the alcohol concentration and the actual alcohol concentration when the alcohol concentration is under-detected by the concentration detection device is the same, it is lower when the engine temperature at the start is lower than when the engine temperature is high. As compared with the case where there is no abnormality in the concentration detection device, the degree of increase in the value correlated with the total injection amount at the time of starting becomes larger. Therefore, when performing abnormality diagnosis of the concentration detection device, the accuracy of abnormality diagnosis is determined by performing abnormality diagnosis of the concentration detection device when the engine temperature at the start is in a low temperature region that is relatively lower than that in the normal temperature region. The effect that can be improved more.

  However, when the engine temperature at the start is in a predetermined cryogenic region, the startability of the engine deteriorates excessively, and the degree of variation in the value correlated with the total injection amount at the start acquired by the acquisition means is excessive. Is likely to increase. Then, there is a possibility that the reliability of the diagnosis result with respect to the presence or absence of abnormality of the concentration detection device based on the acquired value is significantly lowered. This extremely low temperature state is a relatively lower temperature region than the low temperature state described above. For example, when a value correlated with the total injection amount at start-up is acquired, it can be regarded as a temperature region on a lower temperature side than a lower limit temperature at which it is determined that the reliability of the acquired value can be sufficiently maintained. Thus, when the engine temperature at start is in the extremely low temperature range, it is preferable that acquisition of a value correlated with the total injection amount at start by the acquisition means is prohibited. According to this configuration, since the acquisition of a value that correlates to the total injection amount at the start is prohibited under the condition that the reliability with respect to the diagnosis result regarding the presence / absence of the abnormality of the concentration detection device is reduced, the presence / absence of the abnormality Diagnosis can be reliably avoided.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  ADVANTAGE OF THE INVENTION According to this invention, the abnormality diagnosis apparatus of the engine system which can diagnose suitably whether there exists abnormality in the engine system provided with the variable compression ratio mechanism can be provided.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

<Basic configuration>
A first embodiment for carrying out the present invention will be described. FIG. 1 is a diagram illustrating a schematic configuration of an engine 1 including a variable compression ratio mechanism 18 to which an abnormality diagnosis device for an engine system in the present embodiment is applied. The engine 1 in this embodiment is a mixed fuel engine that can be used as a fuel that is a mixed fuel in which gasoline and alcohol are mixed, only alcohol or only gasoline, and is a so-called flexible fuel vehicle. Vehicle
: FFV).
In the present embodiment, in order to display the internal combustion engine 1 in a concise manner, some components are not shown.

  The engine 1 shown in FIG. 1 is a four-stroke cycle gasoline engine having four cylinders 2. An intake pipe 5 is connected to a combustion chamber in the cylinder 2 of the engine 1 via an intake port 4 provided in the cylinder head 3. Inflow of intake air from the intake port 4 to the combustion chamber in the cylinder 2 is controlled by an intake valve 6. An exhaust pipe 8 is connected to the combustion chamber in the cylinder 2 via an exhaust port 7 provided in the cylinder head 3. Exhaust gas discharge from the combustion chamber in the cylinder 2 to the exhaust port 7 outside the cylinder 2 is controlled by an exhaust valve 9.

A fuel injection valve 10 is disposed in the intake port 4. The fuel injection valve 10 is connected to a fuel tank 12 via a fuel supply pipe 11, and fuel from the fuel tank 12 is supplied to the fuel injection valve 10. The engine 1 of this embodiment is a so-called mixed fuel engine that can use a mixed fuel of gasoline and alcohol. Therefore, in the fuel tank 12, alcohol mixed fuel in which alcohol is mixed in gasoline, or gasoline (alcohol concentration 0%),
Or alcohol (alcohol concentration 100%) is stored. An alcohol concentration sensor 13 for detecting the alcohol concentration of the fuel supplied to the fuel injection valve 10 is disposed in the middle of the fuel supply pipe 11. This alcohol concentration sensor 13 has a pair of platinum electrodes immersed in fuel, and the output voltage changes due to a change in resistance value between the electrodes according to the alcohol concentration. In this embodiment, the alcohol concentration sensor 13 corresponds to the concentration detection device in the present invention.

  A spark plug 14 is disposed at the top of the cylinder 2. The spark plug 14 ignites an air-fuel mixture in which fuel and air in the combustion chamber in the cylinder 2 are mixed. When the air-fuel mixture is ignited, the piston 17 connected to the crankshaft 15 via the connecting rod 16 reciprocates in the cylinder 2. A crank position sensor 22 that detects a rotation angle (crank angle) of the crankshaft 15 is disposed in the vicinity of the crankshaft 15. A knocking sensor 23 is attached to the cylinder block 19 of the engine 1. The knocking sensor 23 has a voltage element and outputs an electrical signal corresponding to the magnitude (level) of vibration of the engine 1.

  Further, the opening of the intake pipe 5 of the engine 1 is changed in conjunction with the amount of depression of an accelerator pedal (not shown) so that the cross-sectional area of the intake air flowing through the intake pipe 5 can be changed. A throttle valve 25 is provided. An air flow meter 26 that outputs an electrical signal corresponding to the flow rate of the intake air flowing through the intake pipe 5 is disposed upstream of the throttle valve 25 in the intake pipe 5. Further, an exhaust purification device (for example, a three-way catalyst) (not shown) is disposed in the exhaust pipe 8 of the engine 1, and the air-fuel ratio of the exhaust is detected upstream of the exhaust purification device 28 in the exhaust pipe 8. An air-fuel ratio sensor 29 is attached.

  The compression ratio variable mechanism 18 changes the compression ratio of the engine 1 by moving the cylinder block 19 relative to the crankcase 20 in the axial direction of the cylinder 2. That is, the compression ratio variable mechanism 18 is configured by the cylinder block 19, the cylinder head 3 and the piston 17 by moving the cylinder head 3 together with the cylinder block 19 relative to the crankcase 20 in the axial direction of the cylinder 2. The volume of the combustion chamber is changed, and as a result, the compression ratio of the engine 1 is changed. For example, when the cylinder block 19 is relatively moved away from the crankcase 20, the combustion chamber volume increases and the compression ratio decreases. On the other hand, when the cylinder block 19 is relatively moved in the direction approaching the crankcase 20, the volume of the combustion chamber is reduced and the compression ratio is increased.

  The detailed configuration of the compression ratio variable mechanism 18 will be described. The compression ratio variable mechanism 18 includes a shaft portion 18a and a circular cam fixed to the shaft portion 18a while being eccentric with respect to the central axis of the shaft portion 18a. A cam portion 18b having a profile, a movable bearing portion 18c having the same outer shape as the cam portion 18b, rotatable with respect to the shaft portion 18a and attached in an eccentric state like the cam portion 18b, and concentric with the shaft portion 18a A worm wheel 18d provided in a shape, a worm 18e meshing with the worm wheel 18d, a motor 18f for rotating the worm 18e, and the like. The cam portion 18 b is installed in a storage hole provided in the cylinder block 19, the movable bearing portion 18 c is installed in a storage hole provided in the crankcase 20, and the motor 18 f is fixed to the cylinder block 19. And moves integrally with the cylinder block 19. Here, the driving force from the motor 18f is transmitted to the shaft portion 18a via the worm 18e and the worm wheel 18d. Then, the cam block 18b and the movable bearing portion 18c in an eccentric state are driven, whereby the cylinder block 19 is moved relative to the crankcase 20 in the axial direction of the cylinder 2.

The engine 1 configured as described above is provided with an ECU 21 that is an electronic control unit for controlling the engine 1. The ECU 21 includes a CPU, a ROM, a RAM, and the like for storing various programs and maps to be described later. The ECU 21 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's request. is there.

  The ECU 21 includes various sensors such as an alcohol concentration sensor 13, a crank position sensor 22, a knocking sensor 23, an air flow meter 26, an air / fuel ratio sensor 29, and a temperature sensor 27 that outputs an electrical signal corresponding to the coolant temperature of the engine 1. Connected via electrical wiring, the output signals of these various sensors are input to the ECU 21. The ECU 21 measures the amount of intake air taken into the engine 1 based on the output signal of the air flow meter 26, and detects the engine speed NE based on the output signal of the crank position sensor 22. The ECU 21 detects the alcohol concentration Ra, the knocking strength Kc, and the engine temperature of the fuel based on the output signals of the alcohol concentration sensor 13, the knocking sensor 23, and the temperature sensor 27, respectively. The knocking strength Kc is an index representing the degree of knocking generated in the engine 1 and corresponds to the vibration level of the engine. On the other hand, the fuel injection valve 10, the spark plug 14, and the motor 18f are connected to the ECU 21 via electric wiring, and these devices are controlled by the ECU 21.

<Basic engine control>
Since the engine 1 of the present embodiment is a mixed fuel engine, fuels with different alcohol concentrations Ra (for example, 0%, 20%, 40%, 60%, 80%, 100%, etc.) are fuel injection valves. 10 is supplied to the engine 1. Thus, when the alcohol concentration Ra of the fuel is different, the theoretical air-fuel ratio corresponding to the alcohol concentration Ra is also different. More specifically, the higher the alcohol concentration Ra of the fuel, the lower the stoichiometric air-fuel ratio. Therefore, when the intake air amount is the same, the higher the alcohol concentration Ra of the fuel, the larger the fuel amount required to control the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio. In other words, in order to equalize the excess air ratio λ of the air-fuel mixture (a value obtained by dividing the air-fuel ratio of the air-fuel mixture by the stoichiometric air-fuel ratio of the fuel) when the intake air amount is the same, the higher the alcohol concentration Ra, the higher the fuel injection valve 10. Need to inject more fuel.

  Therefore, the ECU 21 calculates a basic fuel injection amount Qb corresponding to the operating state of the engine 1 from the intake air amount Ga sucked into the engine 1 and the engine speed NE. Then, each fuel injection valve 10 is corrected by correcting the basic fuel injection amount Qb with a correction value CEq set in accordance with a detection value (referred to as alcohol detection concentration) Rad of alcohol concentration Ra based on an output signal from the alcohol concentration sensor 13. From Q, a target value (hereinafter referred to as target fuel injection amount QFt) of fuel injection amount (hereinafter simply referred to as fuel injection amount) QF injected every combustion cycle is calculated (QFt = Qb · CEq). Here, the correction value CEq for correcting the basic fuel injection amount Qb according to the alcohol detection concentration Rad is set to a larger value as the alcohol detection concentration Rad is higher. Therefore, in this embodiment, if the operation state is the same, the higher the alcohol detection concentration Rad, the higher the target fuel injection amount QFt is set, and as a result, the fuel injection amount QF is controlled to be larger. The

  Next, basic control related to the compression ratio ε and ignition timing θ of the engine 1 will be described. Here, the target values of the compression ratio ε and the ignition timing θ set according to the operating state of the engine 1 are set as a basic compression ratio εb and a basic ignition timing θb, respectively. These are maps stored in the ROM of the ECU 21 and associated with the relationship between the engine speed NE representing the operating state of the engine 1 and the basic fuel injection amount Qb. Then, the ECU 21 calculates the basic compression ratio εb and the basic ignition timing θb appropriate for the operating state by substituting the engine speed NE and the basic fuel injection amount Qb into this map.

[When starting the engine]
When the engine 1 is started, crankshaft 15 is cranked by a starter (not shown), and fuel injection by fuel injection valve 10 is performed. Here, as the alcohol concentration Ra is higher, the volatility of the fuel is lower (it is harder to be vaporized), so the startability of the engine 1 is deteriorated. Therefore, when the engine is started, the ECU 21 sets a correction value CEεs according to the alcohol detection concentration Rad, and corrects the basic compression ratio εb with the correction value CEεs. Specifically, the target compression ratio εts at the time of starting the engine is calculated by multiplying the basic compression ratio εb by the correction value CEεs (εts = εb · CEεs). The correction value CEεs is set to a larger value as the alcohol detection concentration Rad is higher. Therefore, the target compression ratio εts at the time of starting the engine is set as a value on the higher compression ratio side as the alcohol detection concentration Rad is higher.

  A control signal from the ECU 21 is output to the variable compression ratio mechanism 18 (motor 18f), whereby the compression ratio ε at the time of engine start is controlled to the target compression ratio εts. As a result, as the possibility that the startability of the engine 1 deteriorates increases, the in-cylinder temperature of the cylinder 2 is further increased by controlling the compression ratio ε to the high compression ratio side, and the startability is improved. Moreover, since the fuel injection amount QF is controlled to increase as the alcohol detection concentration Rad is higher at the time of engine start, the startability of the engine is improved.

[During normal operation]
Next, the compression ratio ε and ignition timing θ during normal operation of the engine 1 will be described. The normal operation can be understood as a time excluding the engine start. If the compression ratio ε and the ignition timing θ are different, the knocking strength Kc is affected. More specifically, when the compression ratio ε is controlled to the higher compression ratio side under the condition where the ignition timing θ is equal, the ignition timing θ is controlled to the more advanced side when the compression ratio ε is equal. The knocking strength Kc is likely to increase. On the other hand, the higher the alcohol concentration Ra of the fuel, the more difficult the fuel is vaporized in the combustion chamber, so that the combustion temperature and combustion speed of the air-fuel mixture are kept low, and the knocking strength Kc is easily reduced. Therefore, during normal operation of the engine 1, the higher the alcohol detection concentration Rad, the more the compression ratio ε is driven to the higher compression ratio side and the ignition timing θ is driven to the more advanced side.

  Specifically, the correction value CEεn and the correction value CEθ for correcting the basic compression ratio εb and the basic ignition timing θb described above are set according to the alcohol detection concentration Rad. The ECU 21 calculates the target compression ratio εtn during normal operation by multiplying the basic compression ratio εb by the correction value CEεn (εtn = εb · CEεn). The correction value CEεn is set to a larger value as the alcohol detection concentration Rad is higher. Therefore, the target compression ratio εtn during normal operation is also set as a value on the higher compression ratio side as the alcohol detection concentration Rad is higher, like the target compression ratio εts during engine startup.

  On the other hand, the target ignition timing θtn during normal operation is obtained as a value obtained by adding the correction value CEθ to the basic ignition timing θb. When the correction value CEθ is added to the basic ignition timing θb, the basic ignition timing θb is corrected to the advance side if the correction value CEθ is a positive value, and is corrected to the retard side if it is a negative value. In this embodiment, the higher the alcohol detection concentration Rad, the larger the positive value is set so that the basic ignition timing θb is corrected to the advance side.

  Then, the control signal from the ECU 21 is output to the variable compression ratio mechanism 18 (motor 18f) and the spark plug 14, so that the compression ratio ε and the ignition timing θ during the normal operation of the engine 1 become the target compression ratio εtn and the target. The ignition timing θtn is controlled. Thereby, the compression ratio ε can be controlled to the higher compression ratio side and the ignition timing θ can be controlled to the more advanced side while suppressing the knocking strength Kc generated in the engine 1 from becoming excessively high. Output performance and fuel efficiency can be improved.

Further, the ECU 21 reads the output signal of the knocking sensor 23 at regular intervals during normal operation of the engine 1 and determines the presence or absence of knocking. When the occurrence of knocking is detected, the ignition timing θ of the engine 1 is corrected to the retard side in order to suppress knocking. Specifically, the ECU 21 substitutes the output signal of the knocking sensor 23 into a map in which the relationship between the knocking strength Kc and the retardation correction value CEθkc is stored, so that the retardation correction value CEθkc corresponding to the knocking strength Kc. Is calculated. This retardation correction value CEθkc takes a value of 0 or more, and is 0 (zero) if knocking has not occurred. On the other hand, if knocking has occurred, the value is positive, and the value increases as the knocking strength Kc increases. Then, the ECU 21 subtracts the calculated retard correction value CEθkc from the target ignition timing θtn to correct the ignition timing θ to the retarded ignition timing (when CEθkc> 0). As a result, knocking occurring in the engine 1 is reduced or suppressed.

<Abnormality diagnosis control of alcohol concentration sensor>
The alcohol concentration sensor 13 may cause an abnormality in the sensor output value due to a change over time or due to deposition or adhesion of metal ions to a platinum electrode immersed in fuel. If this is left unattended, the control values of the above control parameters become inappropriate, which may lead to poor startability of the engine 1, poor drivability, and poor emissions. Therefore, in this embodiment, abnormality diagnosis control for diagnosing whether or not the alcohol concentration sensor 13 is abnormal is executed. The abnormality diagnosis control described below is executed according to a program stored in the ROM of the ECU 21.

  FIG. 2 is a map showing the relationship between the control value of each control parameter and the alcohol concentration Ra of the fuel in this embodiment. FIG. 2A is a map showing the relationship between the target compression ratio εts (solid line) and the target ignition timing θtn (broken line) during normal operation and the alcohol concentration Ra. FIG. 2B is a map showing the relationship between the target compression ratio εts (solid line) and the target fuel injection amount QFt (broken line) at the time of engine start and the alcohol concentration Ra. The relationship between the control values of the control parameters corresponding to the alcohol concentration Ra is as described above. Further, in this map, the relationship between the control values of the respective control parameters corresponding to the alcohol concentration Ra is represented by a linear relationship, but is not limited to this, and may be changed as appropriate.

  Here, the symbol Rar on the horizontal axis represents the actual (true) alcohol concentration (hereinafter referred to as the actual alcohol concentration) of the fuel supplied to the fuel injection valve 10. Here, if the alcohol concentration sensor 13 is normal, the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar. In such a case, even if the fuel having different actual alcohol concentration Rar is supplied to the fuel tank 12 or the actual alcohol concentration Rar of the fuel stored in the fuel tank 12 is not uniform, the detected alcohol concentration Rad is obtained. Accordingly, the control value of each control parameter is appropriately set. That is, there is no possibility that the knocking strength Kc generated in the engine 1 during normal operation will increase excessively, and there is no possibility that rapid starting will be excessively hindered when starting the engine.

  However, when an abnormality occurs in the sensor output value of the alcohol concentration sensor 13, the alcohol detection concentration Rad deviates from the actual alcohol concentration Rar as illustrated. In FIG. 2A, the detected alcohol concentration Rad is erroneously detected on the higher concentration side than the actual alcohol concentration Rar (hereinafter, such erroneous detection on the higher concentration side is referred to as overdetection abnormality). On the other hand, in FIG. 2B, the alcohol detection concentration Rad is erroneously detected on the lower concentration side than the actual alcohol concentration Rar (hereinafter, such erroneous detection on the lower concentration side is referred to as underdetection abnormality). Hereinafter, based on FIG. 2, an overdetection abnormality diagnosis control for diagnosing whether the alcohol concentration sensor 13 overdetects the alcohol concentration Ra, and an underdetection abnormality diagnosis control for diagnosing whether underdetection occurs. Each will be described.

[Overdetection abnormality diagnosis control]
First, overdetection abnormality diagnosis control will be described with reference to FIG. Symbols εtnr and θtnr shown on the vertical axis in FIG. 2A indicate the optimum values of the compression ratio ε and the ignition timing θ during normal operation according to the actual alcohol concentration Rar. These εtnr and θtnr can be rephrased as the target compression ratio εtn and the target ignition timing θtn that should have been set if the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar.

  However, if the alcohol concentration Ra is excessively detected, the ECU 21 erroneously determines that the volatility of the fuel is lower than actual. Here, the ECU 21 sets the target compression ratio εtn and the target ignition timing θtn according to the alcohol detection concentration Rad regardless of whether or not the alcohol concentration Ra is erroneously detected. Therefore, in this case, the target compression ratio εtn is set to εtnf on the high compression ratio side compared to εtnr, and the target ignition timing θtn is set to θtnf on the advance side compared to θtnr.

  That is, the target compression ratio εtn is set disproportionately high in relation to the actual alcohol concentration Rar, and the target ignition timing θtn is set disproportionately in the relation to the actual alcohol concentration Rar. As a result, the knocking strength Kc generated in the engine 1 increases excessively. Then, the retardation correction value CEθkc described above naturally increases. Therefore, in this control, the presence or absence of an overdetection abnormality of the alcohol concentration sensor 13 is diagnosed on the basis of the retardation correction value CEθkc that increases beyond the normal range when the alcohol concentration sensor 13 detects an excessive alcohol concentration. It was decided to.

  FIG. 3 is a flowchart showing a routine relating to overdetection abnormality diagnosis control in the present embodiment. This routine is stored in the ROM of the ECU 21 and is periodically executed during normal operation of the engine 1. When this routine is executed, the alcohol detection concentration Rad is acquired based on the output signal of the alcohol concentration sensor 13 in step S101.

  In step S102, the target compression ratio εtn and the target ignition timing θtn are set according to the alcohol detection concentration Rad based on the map as shown in FIG. In step S103, control signals are output to the variable compression ratio mechanism 18 (motor 18f) and the spark plug 14, and the compression ratio ε and ignition timing θ of the engine 1 are controlled to the target compression ratio εtn and the target ignition timing θtn, respectively. Is done. In step S104, measurement of the elapsed time ΔTi after the control signal is output from the ECU 21 in step S103 is started.

  In step S105, based on the output signal of the knocking sensor 23, the retardation correction value CEθkc corresponding to the knocking strength Kc is acquired, and it is determined whether or not the retardation correction value CEθkc is 0 (zero). Here, since the relationship between the retardation correction value CEθkc and the knocking strength Kc has already been described, detailed description thereof will be omitted. If a negative determination is made in this step (CEθkc takes a value greater than or equal to 0, CEθkc> 0), the process proceeds to step S106. If an affirmative determination is made (CEθkc = 0), the process proceeds to step S108.

  In step S106, the target ignition timing θtn is updated by subtracting the retard correction value CEθkc from the current value, and the ignition plug 14 is controlled so that the ignition timing θ is controlled to the updated target ignition timing θtn. A signal is issued. In subsequent step S107, the retardation correction value CEθkc from the start of measurement of the elapsed time ΔTi in step S104 is integrated, and the integrated value (hereinafter referred to as retardation correction integrated value Σθkc) is acquired.

In step S108, it is determined whether or not the elapsed time ΔTi has reached a predetermined retardation integrated value acquisition time ΔTB. This retard integrated value acquisition time ΔTB is a time during which the retard correction value CEθkc is continuously accumulated, and is determined in advance. If an affirmative determination is made in this step (ΔTi ≧ ΔTB), the process proceeds to step S109. If a negative determination is made (ΔTi <ΔTB), the process returns to step S104, and the measurement of the elapsed time ΔTi is continued.

  In step S109, a first abnormality determination value VS1 is set. The first abnormality determination value VS1 is a reference value for determining whether or not the acquired retardation correction integrated value Σθkc exhibits an abnormal value, and is a delay when it can be determined that the alcohol concentration sensor 13 is normal. This is taken as the upper limit of the angle correction integrated value. As described above, the knocking strength kc is affected by the compression ratio ε, the ignition timing θ, and the actual alcohol concentration Rar of the engine 1. Therefore, the first abnormality determination value VS1 is set according to the set values of the alcohol detection concentration Rad, the target compression ratio εtn, and the target ignition timing θtn.

  More specifically, when the engine 1 is controlled according to the map shown in FIG. 2A, if the alcohol concentration sensor 13 is normal (the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar), that is, the target compression ratio. If εtn and the target ignition timing θtn can be set to εtnr and θtnr, an upper limit value of the retard correction integrated value Σθkc obtained within the retard integrated value acquisition time ΔTB is obtained in advance by experiments or the like. The first abnormality determination value VS1 is set as a value with a predetermined margin added. The size of this margin is determined by how much a deviation amount between the alcohol detection concentration Rad and the actual alcohol concentration Rar is allowed.

  In step S110, it is determined whether or not the retard correction integrated value Σθkc exceeds the first abnormality determination value VS1. If it is determined that the retardation correction integrated value Σθkc exceeds the first abnormality determination value VS1 (Σθkc> VS1), it is diagnosed that the alcohol concentration sensor 13 has an excessive detection abnormality, and the process proceeds to step S111. On the other hand, if not (Σθkc ≦ VS1), it is determined that there is no overdetection abnormality in the alcohol concentration sensor 13, and the process proceeds to step S112.

  In the present embodiment, as described above, the first abnormality determination value VS1 is set by considering the alcohol detection concentration Rad, the target compression ratio εtn and the target ignition timing θtn corresponding thereto, and the first abnormality determination value VS1. Can be set as an appropriate value. That is, if the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar, the retardation correction integrated value Σθkc does not exceed the first abnormality determination value VS1, and thus the alcohol concentration sensor 13 is normal. It is suppressed that a misdiagnosis that it is abnormal is made.

  On the other hand, when the alcohol concentration Ra is excessively detected, the target compression ratio εtn is inappropriately high in relation to the actual alcohol concentration Rar, and the target ignition timing θtn is inappropriately set on the advance side. The knocking strength Kc of 1 increases excessively. As a result, since the retard correction integrated value Σθkc surely exceeds the first abnormality determination value VS1, an excessive detection abnormality of the alcohol concentration sensor 13 can be reliably detected.

  In step S111, the failure flag of the alcohol concentration sensor 13 is turned ON. When this failure flag is turned on, a warning lamp (not shown) in the driver's cab of the vehicle is turned on to notify the driver of an abnormality in the alcohol concentration sensor 13. Then, once the processing of this step is completed, this routine is temporarily exited. In step S112, the failure flag is turned OFF. Then, the value of the retard correction integrated value Σθkc is reset, and this routine is temporarily exited.

In this routine, the ECU 21 that acquires the retard correction integrated value Σθkc based on the output signal of the knocking sensor 23 corresponds to the acquisition means in the present invention. Further, the retard correction integrated value Σθkc corresponds to the retard request value in the present invention and the acquired value acquired by the acquiring means. The ECU 21 that sets the first abnormality determination value VS1 according to the alcohol detection concentration Rad, the target compression ratio εtn, and the target ignition timing θtn corresponds to the abnormality determination value setting means in the present invention. Further, the ECU 21 that diagnoses that the alcohol concentration sensor 13 has an overdetection abnormality when the acquired retardation correction integrated value Σθkc exceeds the first abnormality determination value VS1 corresponds to the abnormality diagnosis means in the present invention.

[Under detection abnormality diagnosis control]
Next, under detection abnormality diagnosis control will be described with reference to FIG. Symbols εtsr and QFtr shown on the vertical axis of FIG. 2B indicate the optimum values of the compression ratio ε and the target fuel injection amount QFt at the time of engine start according to the actual alcohol concentration Rar. That is, εtsr and QFtr are the target compression ratio εts and the target fuel injection amount QFt that should have been set if the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar.

  However, if the alcohol concentration Ra is detected too low as shown in FIG. 2B, the ECU 21 erroneously determines that the volatility of the fuel is higher than actual. As a result, the target compression ratio εts is set to εtsf on the lower compression ratio side than εtsr, and the target fuel injection amount QFt is set to QFtf smaller than QFtr. That is, the target compression ratio εts is set inappropriately low in relation to the actual alcohol concentration Rar, and the fuel injection amount QFt is set inappropriately low in relation to the actual alcohol concentration Rar.

  Then, the startability of the engine 1 is excessively deteriorated, and the total injection amount of fuel injected from the fuel injection valve 10 before the first explosion occurs at the time of engine start (hereinafter referred to as the total injection amount at start) ΣQFs , The number of fuel injections (hereinafter referred to as the number of injections at start-up) ΣNis required from the start of fuel injection related to engine start by the fuel injection valve 10 to the occurrence of the first explosion, and the required time (hereinafter referred to as the first explosion required) Σtms (called time) increases. Here, the starting total injection amount ΣQFs is the total amount of fuel injected from each fuel injection valve 10 until the first explosion occurs. Further, the start injection number ΣNis is counted every time fuel injection from any one of the fuel injection valves 10 is performed.

  Here, when any of the above-mentioned total injection amount ΣQFs, the injection number ΣNis, and the required initial explosion time Σtms changes, the other values change in correlation. Therefore, these are collectively referred to as “startup total injection amount correlation value”. In this embodiment, the starting total injection amount ΣQFs, the starting injection number ΣNis, and the initial explosion required time Σtms are injected from the fuel injection valve according to the present invention until the first explosion occurs at the engine startup. This corresponds to a value correlating with the total fuel injection amount. In this control, when the alcohol concentration sensor 13 detects that the alcohol concentration is too low, the alcohol concentration sensor 13 detects whether the alcohol concentration sensor 13 is underdetected abnormally, focusing on the starting total injection amount correlation value that increases beyond the normal range. Make a diagnosis.

  FIG. 4 is a flowchart showing a routine relating to underdetection abnormality diagnosis control in the present embodiment. This routine is stored in the ROM of the ECU 21, and is executed every time the ignition of the engine 1 is turned on. In this routine, the starting injection number ΣNis is acquired as the above-mentioned “starting total injection amount correlation value”, and the abnormality diagnosis of the alcohol concentration sensor 13 is performed based on this.

When this routine is executed, the alcohol detection concentration Rad is acquired based on the output signal of the alcohol concentration sensor 13 in step S201. In step S202, the target compression ratio εts and the target fuel injection amount QFt at the time of engine start are set according to the alcohol detection concentration Rad based on the map as shown in FIG. In step S203, cranking of the engine 1 is started by energizing a starter (not shown), and a control signal is issued to each fuel injection valve 10 to start fuel injection. The fuel injection amount QF at that time is controlled to the target fuel injection amount QFt. In this step, a control signal is output to the variable compression ratio mechanism 18 (motor 18f), and the compression ratio ε of the engine 1 is set to the target compression ratio εt.
controlled by s.

  In step S204, the number of injections ΣNi from the start of fuel injection from each fuel injection valve 10 in step S203 is counted. This count is counted every time fuel is injected from any of the fuel injection valves 10. Since the engine 1 of this embodiment is a four-cylinder engine, the count value of the number of injections ΣNi is 4 if fuel injection is performed once from each fuel injection valve 10.

  In step S205, it is determined whether or not the first explosion has occurred based on the output signal of the crank position sensor 22. The first explosion means that fuel is ignited in any one of the cylinders 2. When the first explosion occurs, the engine speed NE increases. Therefore, the first explosion can be detected by monitoring the engine speed NE. If it is determined in this step that an initial explosion has occurred, the process proceeds to step S206. On the other hand, if it is determined that the first explosion has not yet occurred, the process returns to step S204, and the counting of the number of injections ΣNi is continued.

  In step S206, the ECU 21 acquires the count value of the number of injections ΣNi up to the present as the number of injections at start ΣNis. In step S207, the second abnormality determination value VS2 is set. The second abnormality determination value VS2 is a reference value for determining whether or not the acquired start injection number ΣNis exhibits an abnormal value, and at the time of starting when the alcohol concentration sensor 13 can be determined to be normal. This is taken as the upper limit of the number of injections. As described above, the startability of the engine 1 is affected by the compression ratio ε, the fuel injection amount QF, and the actual alcohol concentration Rar of the engine 1. Therefore, the second abnormality determination value VS2 is set according to the alcohol detection concentration Rad, the target compression ratio εts at the time of engine start, and the target fuel injection amount QFt.

  More specifically, when the engine 1 is controlled to start according to the map shown in FIG. 2B, if the alcohol concentration sensor 13 is normal (the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar), that is, target compression. If the ratio εts and the target fuel injection amount QFt can be set to εtsr and QFtr, an upper limit value of the number of start injections ΣNis obtained is obtained in advance by experiments or the like, and a value obtained by adding a predetermined margin to the upper limit value A second abnormality determination value VS2 is set. The size of this margin is determined by how much a deviation amount between the alcohol detection concentration Rad and the actual alcohol concentration Rar is allowed.

  Then, in the following step S208, it is determined whether or not the number of injections at start ΣNis exceeds the second abnormality determination value VS2. If it is determined that the number of injections at start ΣNis exceeds the second abnormality determination value VS2 (ΣNis> VS2), it is diagnosed that the alcohol concentration sensor 13 has an underdetection abnormality, and the process proceeds to step S209. On the other hand, if not (ΣNis ≦ VS2), it is determined that the alcohol concentration sensor 13 has no underdetection abnormality, and the process proceeds to step S210.

  In the present control, the second abnormality determination value VS2 is set by setting the second abnormality determination value VS2 in consideration of the alcohol detection concentration Rad, the target compression ratio εts corresponding thereto, and the target fuel injection amount QFt as described above. Can be set as an appropriate value. That is, if the alcohol detection concentration Rad coincides with the actual alcohol concentration Rar, the starting injection number ΣNis does not exceed the second abnormality determination value VS2, and thus the abnormality is detected although the alcohol concentration sensor 13 is normal. It is suppressed that the misdiagnosis that it is is made.

On the other hand, when the alcohol concentration Ra is underdetected, the target compression ratio εts is set inappropriately low and the fuel injection amount QFt is set inappropriately low in relation to the actual alcohol concentration Rar. The number of injections at start Σ
Nis certainly exceeds the second abnormality determination value VS2. As a result, an underdetection abnormality of the alcohol concentration sensor 13 can be reliably detected.

  In step S209, the failure flag of the alcohol concentration sensor 13 is turned ON. When the failure flag is turned on, a warning lamp (not shown) in the vehicle cab is turned on, so that the driver is notified of an under-detection abnormality of the alcohol concentration sensor 13. Then, once the processing of this step is completed, this routine is temporarily exited. In step S210, the failure flag is turned off. Then, the value of the starting injection number ΣNis is reset, and this routine is temporarily exited.

  In this routine, the ECU 21 that acquires the starting injection number ΣNis by counting the injection number ΣNi from the fuel injection valve 10 over a period until the occurrence of the first explosion is detected corresponds to the acquiring means in the present invention. Further, the number of injections at start ΣNis is “a value that correlates with the total injection amount of fuel injected from the fuel injection valve until the first explosion occurs at the start of the engine” in the present invention, and the acquired value acquired by the acquiring unit. It corresponds to. Further, the ECU 21 that sets the second abnormality determination value VS2 according to the alcohol detection concentration Rad, the target compression ratio εts, and the target fuel injection amount QFt corresponds to the abnormality determination value setting means in the present invention. Further, the ECU 21 that diagnoses that the alcohol concentration sensor 13 has an under-detection abnormality when the obtained start injection number ΣNis exceeds the second abnormality determination value VS2 corresponds to the abnormality diagnosis means in the present invention.

  As described above, according to the abnormality diagnosis control according to the present embodiment, the abnormality diagnosis of the alcohol concentration sensor 13 can be performed accurately and suitably.

<Other embodiments>
In the present embodiment, an example of an embodiment for carrying out the present invention has been described. However, the abnormality diagnosis control described above can be variously modified without departing from the gist of the present invention. Hereinafter, other embodiments in the present embodiment will be described.

  In the first modification, when the retardation correction value CEθkc acquired during the overdetection abnormality diagnosis control exceeds the first abnormality determination value VS1a set for the retardation correction value CEθkc, the alcohol concentration sensor 13 is set. Diagnose abnormalities. Since this retard correction value CEθkc is acquired as a larger value if the knocking strength Kc is high, the presence or absence of an overdetection abnormality in the alcohol concentration sensor 13 can be determined based on the retard correction value CEθkc. In this case, the first abnormality determination value VS1a is determined if the alcohol detection concentration Rad matches the actual alcohol concentration Rar, that is, if the target compression ratio εtn and the target ignition timing θtn can be set to εtnr and θtnr. In this case, the upper limit value of the retard correction value CEθkc to be obtained is obtained by experiment or the like, and is set as a value obtained by adding a predetermined margin thereto. Of course, the set value of the first abnormality determination value VS1a can take a value different from the first abnormality determination value VS1 described above. According to this control, when the alcohol concentration sensor 13 has an excessive detection abnormality of the alcohol concentration Ra, the retardation correction value CEθkc is larger than the first abnormality determination value VS1a, and otherwise, the first abnormality determination value. VS1a or less. Therefore, it is possible to accurately diagnose whether or not the alcohol concentration sensor 13 has an excessive detection abnormality.

In the overdetection abnormality diagnosis control of the present embodiment, during the normal operation of the engine 1, in addition to setting the target compression ratio εtn to the higher compression ratio side as the alcohol detection concentration Rad is higher, the target ignition timing θtn is set. Although it is set as a more advanced timing, the application of the present invention is not hindered even if the target ignition timing θtn is not set according to the alcohol detection concentration Rad. That is, of the target compression ratio εtn and the target ignition timing θtn, only the target compression ratio εtn can be set according to the alcohol detection concentration Rad. In such a case, the first abnormality determination value VS1 is set according to the alcohol detection concentration Rad and the target compression ratio εtn corresponding to the alcohol detection concentration Rad.

  In the second modified example, instead of acquiring the starting injection number ΣNis in the control routine of FIG. 4, the starting total injection amount ΣQFs or the initial explosion required time Σtms is acquired as the “starting total injection amount correlation value”. Here, when acquiring the total injection amount ΣQFs at the start, when the total injection amount ΣQFs at the start exceeds the second abnormality determination value VS2a set for the total injection amount ΣQFs at the start, the alcohol concentration sensor 13 is diagnosed as having an under-detection abnormality. On the other hand, when acquiring the initial explosion required time Σtms, when the initial explosion required time Σtms exceeds the second abnormality determination value VS2b set for the initial explosion required time Σtms, the alcohol concentration sensor 13 is underdetected. Diagnose that there is an abnormality. The second abnormality determination values VS2a and VS2b are set according to the alcohol detection concentration Rad, the target compression ratio εts, and the target fuel injection amount QFt, similarly to VS2. Of course, the setting values of the second abnormality determination values VS2, VS2a, and VS2b can take different values.

  In the under-detection abnormality diagnosis control of this embodiment, the target fuel injection amount QFt is set so that the fuel injection amount QF is controlled more as the alcohol detection concentration Rad at the time of engine start is higher. Even if the fuel injection amount QFt is not set in this way, the application of the present invention is not hindered. For example, among the target compression ratio εts and the target fuel injection amount QFt, only the target compression ratio εts can be set according to the alcohol detection concentration Rad. In such a case, the second abnormality determination value VS2 is set according to the alcohol detection concentration Rad and the target compression ratio εts corresponding to the alcohol detection concentration Rad.

  Although the engine 1 in the present embodiment is a so-called mixed fuel engine, the abnormality diagnosis device for the engine system according to the present embodiment can also be applied to an engine that uses a single type of fuel. In the third modification, the abnormality diagnosis device of this embodiment is applied to a normal gasoline engine. In such a case, the compression ratio ε of the engine is controlled to the basic compression ratio εb according to the operating state. When an abnormality occurs in the engine system for some reason (for example, when the variable compression ratio mechanism 18 and the fuel injection valve 10 are not normally operated), the knocking strength Kc excessively increases during normal operation of the engine. In addition, when the engine is started, the startability is excessively deteriorated. Accordingly, also in the present modification, the engine system abnormality diagnosis is performed by acquiring the retardation correction integrated value Σθkc during normal operation of the engine and comparing the acquired value with the first abnormality determination value VS1. In addition, when the engine is started, the number of injections at start ΣNis (the total injection amount at start ΣQFs or the required initial explosion time Σtms may be acquired) and the obtained value is compared with the second abnormality determination value VS2. The same abnormality is diagnosed at.

First, the difference from the control routine in FIG. 3 will be described with respect to the overdetection abnormality diagnosis control in the present modification. In such a case, the process of step S101 is omitted, and in step S102, the target compression ratio εtn and the target ignition timing θtn are set to the basic compression ratio εb and the basic ignition timing θb that are set based on the operating state of the engine. In step S103, the compression ratio ε and the ignition timing θ are controlled to the target compression ratio εtn (basic compression ratio εb) and the target ignition timing θtn (basic ignition timing θb). In step S109, the first abnormality determination value VS1 is set according to the target compression ratio εtn (that is, the basic compression ratio εb) and the target ignition timing θtn (that is, the basic ignition timing θb). This is because the knocking strength Kc also changes according to the target compression ratio εtn and the target ignition timing θtn regardless of whether the engine system is abnormal, and the optimal first abnormality determination value VS1 also changes accordingly. In step S110, if it is determined that the retard correction integrated value Σθkc exceeds the first abnormality determination value VS1, it is determined that there is an abnormality in the engine system. If not, there is no abnormality in the system. It is determined. In the former case, a warning light in the cab is turned on in step S111, so that the driver is notified that there is some abnormality in the engine system.

  Next, the difference between the under-detection abnormality diagnosis control in this modification and the control routine in FIG. 4 will be described. Here, the processing of step S201 is omitted, and in step S202, the target compression ratio εts and the target fuel injection amount QFt are set to the basic compression ratio εb and the basic fuel injection amount Qb for starting the engine. In step S206, the second abnormality determination value VS2 is set according to the target compression ratio εts (that is, the basic compression ratio εb) and the target fuel injection amount QFt (that is, the basic fuel injection amount Qb). This is because the engine startability also changes according to the target compression ratio εts and the target fuel injection amount QFt regardless of whether the engine system is abnormal, and the optimum value of the second abnormality determination value VS2 also changes accordingly. by. Further, in step S208, it is determined that there is an abnormality in the engine system when it is determined that the starting injection number ΣNis exceeds the second abnormality determination value VS2, and otherwise, it is determined that there is no abnormality. In the former case, a warning light in the cab is turned on in step S209 to notify the driver that there is some abnormality in the engine system.

  Next, a second embodiment for carrying out the present invention will be described. The schematic configuration of the engine to which the abnormality diagnosis device for the engine system of this embodiment is applied is the same as that shown in FIG.

  Even when other control conditions related to the engine 1 are equal, knocking is more likely to occur when the engine load TQ when the over-detection abnormality diagnosis control is executed is relatively high compared to when it is low. The knocking strength Kc tends to increase as the engine load TQ at that time increases. Therefore, in the present embodiment, the excessive detection abnormality diagnosis control in consideration of the engine load TQ is executed.

  FIG. 5 is a map showing the relationship between the engine load TQ and the weighting coefficient Wtvs1 for the first abnormality determination value VS1 in this embodiment. The weighting coefficient Wtvs1 is a correction coefficient for correcting the first abnormality determination value VS1 according to the engine load TQ when the overdetection abnormality diagnosis control is executed. The method for setting the first abnormality determination value VS1 is the same as that in the first embodiment. Further, the engine load TQ is acquired such that the higher the basic fuel injection amount Qb set based on the operating state of the engine 1, the higher the load side.

  In the present embodiment, the corrected first abnormality determination value AJVS1 is calculated by multiplying the first abnormality determination value VS1 by the weighting coefficient Wtvs1. Then, when it is determined that the acquired retardation correction integrated value Σθkc exceeds the corrected first abnormality determination value AJVS1, the alcohol concentration sensor 13 is diagnosed as having an excessive detection abnormality. In FIG. 5, the higher the engine load TQ, the larger the weighting coefficient Wtvs1. As a result, the corrected first abnormality determination value AJVS1 is set to a larger value as the engine load TQ is higher.

  As a result, even if the knocking strength Kc increases due to the very high engine load TQ, the corrected first abnormality determination value AJVS1 is corrected in an increasing direction as compared with the first abnormality determination value VS1, so that the alcohol Although the density sensor 13 is normal, erroneous diagnosis that it is abnormal is suppressed. As described above, according to this control, even if the engine load TQ when the over-detection abnormality diagnosis control is executed varies greatly depending on the operating state, the alcohol concentration sensor 13 is over-detected without being affected by it. It is possible to accurately diagnose whether there is an abnormality.

<Other embodiments>
Next, another embodiment in the present embodiment will be described. In the first modification, the retard correction integrated value Σθkc is corrected according to the engine load TQ instead of the first abnormality determination value VS1. Assuming that the correction coefficient for correcting the retard correction integrated value Σθkc acquired by the ECU 21 is the weighting coefficient Wtvs2, the corrected retard correction integrated value AJΣθkc is calculated by multiplying the delay correction integrated value Σθkc by the weighting coefficient Wtvs2. When it is determined that the corrected retardation correction integrated value AJΣθkc calculated in this way exceeds the first abnormality determination value VS1, it is diagnosed that the alcohol concentration sensor 13 has an abnormality related to excessive detection of the alcohol concentration Ra. The In this case, the weighting coefficient Wtvs2 is set as a smaller value as the engine load TQ is higher. For this reason, the higher the engine load TQ, the lower the corrected retardation correction integrated value AJΣθkc. Therefore, it is possible to accurately diagnose whether or not the alcohol concentration sensor 13 has an abnormality related to excessive detection of the alcohol concentration Ra without being affected by the engine load TQ when the excessive detection abnormality diagnosis control is executed.

  Next, a second modification of the overdetection abnormality diagnosis control in this embodiment will be described. Here, the difference between the control routine described in FIG. 3 and the present control will be described. In step S106 of FIG. 3, the target ignition timing θtn is subtracted from the current control value by the retardation correction value CEθkc acquired in step S105, whereas in this control, the retardation correction value CEθkc is weighted. A corrected retardation correction value ADCE θkc obtained by multiplying the coefficient Wtvs3 is subtracted from the target ignition timing θtn. The weighting coefficient Wtvs3 is a correction coefficient for correcting the retardation correction value CEθkc, and is set to a larger value as the engine load TQ is higher.

  That is, in this case, as the engine load TQ is higher, the corrected retardation correction value ADCEθkc is also increased, so that the target ignition timing θtn is changed to a more retarded side than the original required value. As a result, as the engine load TQ is higher, the retard correction integrated value Σθkc acquired in step S107 is reduced as compared with the case where this control is not performed. Therefore, even if the engine load TQ when the excessive detection abnormality diagnosis control is executed varies greatly depending on the operating state, the alcohol concentration sensor 13 has an abnormality related to excessive detection of the alcohol concentration Ra without being affected by the influence. Whether or not can be diagnosed with high accuracy.

  Next, a third embodiment for carrying out the present invention will be described. The schematic configuration of the engine to which the abnormality diagnosis device for the engine system of this embodiment is applied is the same as that shown in FIG.

Here, FIG. 6 shows an equivalence ratio Φ required for equalizing the number of injections ΣNis at the time of starting the engine and the engine temperature at the time of starting the engine (hereinafter referred to as “equivalence ratio”).
FIG. 5 is a graph showing the relationship of TH (referred to as engine temperature at start-up) for each alcohol concentration Ra (0%, 80%, 100% in this figure). Here, the relationship when the alcohol concentration Ra of the fuel is 0% is represented by E0, the relationship when the fuel concentration Ra is 80% is represented by E80, and the relationship when the alcohol concentration Ra is 100% is represented by E100. This equivalent ratio Φ is the reciprocal of the excess air ratio λ (Φ = 1 / λ), and means the ratio of the fuel actually supplied into the combustion chamber to the amount of fuel equivalent to the oxygen in the intake air used for combustion. . Therefore, as the equivalence ratio Φ increases, the oxygen excess ratio λ decreases, and the fuel injection amount QF injected from the fuel injection valve 10 increases under the same intake air amount.

Here, if the alcohol concentration Ra is equal, the lower the engine temperature TH at start-up, the more difficult the fuel is vaporized in the combustion chamber, so the startability of the engine 1 deteriorates. Therefore, in order to equalize the number of injections ΣNis at the time of starting the engine, the required equivalence ratio Φ increases as the starting engine temperature TH decreases in any of E0 to E100. Further, when E0, E80, and E100 are compared at the same engine temperature TH at the same starting time, the required equivalent ratio Φ increases as the alcohol concentration Ra increases. This is because the higher the alcohol concentration Ra, the more serious the deterioration of the volatility of the fuel accompanying the decrease in the engine temperature TH at the start, and the more the influence on the startability of the engine 1 becomes.

  Here, the rate of increase of the equivalent ratio Φ accompanying the decrease in the starting engine temperature TH (the slope at which the equivalent ratio Φ increases) increases as the alcohol concentration Ra increases. There is a temperature range in which the increase rate of the equivalence ratio Φ rapidly increases as the starting engine temperature TH decreases. The temperature range shifts to higher temperatures as the alcohol concentration Ra increases. This means that the higher the alcohol concentration Ra, the more serious the startability deteriorates from the higher start-up engine temperature TH.

  Therefore, in this embodiment, the under-detection abnormality diagnosis control is executed in consideration of the influence of the starting engine temperature TH on the startability of the engine 1. The fuel injection amount QF at the start of the engine here is the same as that in the first embodiment. That is, the target fuel injection amount QFt is set so that the excess air ratio λ becomes equal according to the alcohol concentration Ra (in this case, the equivalent ratio Φ that is the reciprocal of the excess air ratio λ is also equal). In such a case, regardless of whether or not the alcohol concentration sensor 13 is abnormal, the starting injection frequency ΣNis increases as the starting engine temperature TH is lower. Further, as the alcohol concentration Ra is higher, the increase in the number of injections ΣNis at the start associated with the decrease in the engine temperature TH at the start becomes more remarkable.

  On the other hand, in the present embodiment, the second abnormality determination value VS2 is corrected according to the engine temperature TH at the start and the alcohol detection concentration Rad when the under-detection abnormality diagnosis control is executed. FIG. 7 is a map showing the relationship between the engine temperature TH at start-up, the alcohol detection concentration Rad, and the weighting coefficient Wtvs4 in this embodiment. The weighting coefficient Wtvs4 is a correction coefficient for correcting the second abnormality determination value VS2 in accordance with the engine temperature TH at start-up and the alcohol detection concentration Rad when the under-detection abnormality diagnosis control is executed. The method for setting the second abnormality determination value VS2 is the same as that in the first embodiment. Further, the starting engine temperature TH is detected based on the output signal of the coolant temperature sensor 27.

  In the present embodiment, the corrected second abnormality determination value AJVS2 is calculated by multiplying the second abnormality determination value VS2 by the weighting coefficient Wtvs4. When it is determined that the number of injections at start ΣNis obtained in the under-detection abnormality diagnosis control exceeds the corrected second abnormality determination value AJVS2, the alcohol concentration sensor 13 has an abnormality related to the under-detection of the alcohol concentration Ra. Diagnose. In FIG. 7, the weighting coefficient Wtvs4 is set to a larger value as the starting engine temperature TH is lower under the condition that the alcohol detection concentration Rad is equal, and as a result, the corrected second abnormality determination value AJVS2 is set to a larger value. Further, under the condition that the engine temperature TH at the start is equal, the higher the alcohol detection concentration Rad is, the higher the weighting coefficient Wtvs4 is set. As a result, the corrected second abnormality determination value AJVS2 is set as a larger value.

  By calculating the corrected second abnormality determination value AJVS2 in this way, for example, the actual alcohol concentration Rar is relatively high under the condition that the startability deterioration of the engine 1 becomes remarkable and the number of start injections ΣNis is excessively large. Even when the engine 1 is started when the starting engine temperature TH is in the low temperature range, if the alcohol concentration sensor 13 is normal, the starting injection number ΣNis does not exceed the corrected second abnormality determination value AJVS2. This is because the corrected second abnormality determination value AJVS2 is set in consideration of the starting engine temperature TH and the alcohol detection concentration Rad. Therefore, it is possible to reliably suppress erroneous diagnosis that the alcohol concentration sensor 13 is abnormal even though the alcohol concentration sensor 13 is normal.

On the other hand, when the alcohol concentration Ra is detected too low, the weighting coefficient Wtvs4 is set smaller than the value corresponding to the actual alcohol concentration Rar. For example, referring to FIG. 7, the weighting coefficient Wtvs4 corresponding to the actual alcohol concentration Rar is represented by a symbol Wtr, and the weighting coefficient Wtvs4 corresponding to the alcohol detection concentration Rad erroneously detected on the low concentration side is represented by a symbol Wtrf. > Wtf is set. As a result, the corrected second abnormality determination value AJVS2 obtained by multiplying the second abnormality determination value VS2 by the value Wtr becomes disproportionately small in relation to the actual alcohol concentration Rar, and the starting injection number ΣNis is corrected to the corrected second abnormality. The determination value AJVS2 is surely exceeded. Thereby, the under-detection of the alcohol concentration Ra by the alcohol concentration sensor 13 can be reliably detected.

  In this control, instead of acquiring the number of injections ΣNis, when acquiring the starting total injection amount ΣQFs as the “starting total injection amount correlation value”, the second modification example in the first embodiment has been described. The corrected second abnormality determination value AJVS2a is set by multiplying the second abnormality determination value VS2a by the weighting coefficient Wtvs4. When the total injection amount ΣQFs at the start exceeds the correction second abnormality determination value AJVS2a, the alcohol concentration sensor 13 is underestimated. Diagnose that there is a detection error. On the other hand, when the initial explosion required time Σtms is acquired as the “starting total injection amount correlation value”, the weighting coefficient Wtvs4 is multiplied by the second abnormality determination value VS2b described in the second modification of the first embodiment. Is set to the corrected second abnormality determination value AJVS2b, and when the initial explosion required time Σtms exceeds the corrected second abnormality determination value AJVS2b, it is diagnosed that the alcohol concentration sensor 13 has an underdetection abnormality.

  Note that the weighting coefficient Wtvs4 in FIG. 7 is set so as to be proportional to the value of the equivalence ratio Φ of the air-fuel mixture required corresponding to the combination of the starting engine temperature TH and the alcohol concentration Ra shown in FIG. . According to this, the presence or absence of an underdetection abnormality by the alcohol concentration sensor 13 can be diagnosed with higher accuracy.

  Referring to FIG. 6, when the alcohol concentration Ra is under-detected (for example, the actual alcohol concentration Rar is 80% (E80), the alcohol detection concentration Rad is acquired as 100% (E100). In the case where the engine temperature TH at the start is in the low temperature region (for example, about 0 ° C.) than in the case where the engine temperature TH is in the normal temperature region (for example, about 20 ° C.). (In FIG. 6, symbols A and B). Therefore, the accuracy of the abnormality diagnosis of the alcohol concentration sensor 13 can be further improved by executing the control of the present embodiment when the engine temperature TH at the start is in the low temperature region as compared with the normal temperature region. If the difference between the alcohol detection concentration Rad and the actual alcohol concentration Rar is the same, the difference in the number of injections ΣNis at the start according to the presence or absence of abnormality in the alcohol concentration sensor 13 becomes larger when the engine temperature TH at the start is lower, This is because a determination error regarding the presence / absence of abnormality is less likely to occur.

<Other embodiments>
Another embodiment in the present embodiment will be described. In the first modified example, instead of the second abnormality determination value VS2, the number of injections at start ΣNis acquired at the time of underdetection abnormality diagnosis control is corrected. When the correction coefficient for correcting the starting injection number ΣNis acquired by the ECU 21 is a weighting coefficient Wtvs5, the corrected starting injection number AJΣNis is calculated by multiplying the starting injection number ΣNis by the weighting coefficient Wtvs5. The weighting coefficient Wtvs5 is set according to the engine temperature TH at the start and the alcohol detection concentration Rad when the under detection abnormality diagnosis control is executed.

  In this case, the weighting coefficient Wtvs5 is set to a smaller value as the starting engine temperature TH is lower under the condition where the alcohol detection concentration Rad is equal, and is set to a smaller value as the alcohol detection concentration Rad is higher under the condition where the starting engine temperature TH is equal. Is done. That is, the relationship between the weighting coefficient Wtvs5, the starting engine temperature TH, and the alcohol detection concentration Rad is a form in which the weighting coefficient Wtvs4 shown in FIG.

The correction start injection number AJΣNis thus calculated is compared with the second abnormality determination value VS2, and the alcohol concentration sensor 13 is underestimated when the correction start injection number AJΣNis exceeds the second abnormality determination value VS2. Diagnose that there is a detection error. According to this, even if the degree of influence of the starting engine temperature TH on the startability of the engine 1 changes in accordance with the alcohol concentration Ra of the fuel, it is preferable to perform misdiagnosis related to the underdetection abnormality of the alcohol concentration sensor 13. Can be suppressed.

  Further, in the second modification, the target fuel injection amount QFt at the time of starting the engine is different from the control described above. In this control, the alcohol detection concentration Rad and the engine temperature TH at the start are acquired when the engine is started, and the corresponding equivalent ratio Φ is calculated by substituting these into a map as shown in FIG. Then, the target fuel injection amount QFt is set based on the obtained equivalence ratio Φ and the intake air amount Ga. Specifically, the correction coefficient CEΦ that is set to a larger value as the equivalent ratio Φ is higher can be set, and the target fuel injection amount QFt can be calculated (QFt = Qb · CEq · CEΦ).

  According to this, even when the degree of influence of the starting engine temperature TH on the starting performance of the engine 1 changes according to the alcohol concentration Ra of the fuel, if the under-detection abnormality does not occur in the alcohol concentration sensor 13, the injection at the starting time The number of times ΣNis can be made substantially constant. Therefore, the presence or absence of underdetection abnormality in the alcohol concentration sensor 13 can be easily diagnosed simply by comparing the magnitude relationship between the number of injections at start ΣNis acquired in the underdetection abnormality diagnosis control and the second abnormality determination value VS2. Accuracy can be increased. In this control, instead of the start injection number ΣNis, the above-mentioned total start injection amount ΣQFs is compared with the second abnormality determination value VS2a, or the initial explosion required time Σtms is set to the second abnormality determination value VS2b. Of course, the present invention can also be applied in the case of comparison.

  Next, a fourth embodiment for carrying out the present invention will be described. The schematic configuration of the engine to which the abnormality diagnosis device for the engine system of this embodiment is applied is the same as that shown in FIG. Here, referring to FIG. 6, when the engine temperature TH at the start is in a very low temperature region (for example, −20 ° C. or less), it is considered that the startability of the engine 1 is significantly reduced. In such a case, the variation in the starting injection number ΣNis acquired in the under-detection abnormality diagnosis control becomes excessive, and the reliability of the diagnosis result based on the acquired value decreases. Therefore, when the starting engine temperature TH is in the extremely low temperature range, the ECU 21 is prohibited from acquiring the starting injection number ΣNis. According to this, when the possibility of misdiagnosis becomes high, execution of underdetection abnormality diagnosis control is prohibited, so that misdiagnosis can be reliably avoided. In other words, it is possible to increase the reliability of the diagnosis result as to whether or not the alcohol concentration sensor 13 is abnormal. It should be noted that the temperature range to be set as the extremely low temperature range can be obtained in advance by experiments or the like based on the degree of variation related to the acquired value of the starting injection number ΣNis.

  Next, a fifth embodiment for carrying out the present invention will be described. The fuel injection amount QF in the present embodiment is controlled in accordance with the target fuel injection amount QFt calculated according to the alcohol detection concentration Rad, as in the first embodiment. The higher the alcohol concentration Ra of the fuel, the lower the stoichiometric air-fuel ratio. Therefore, the higher the alcohol detection concentration Rad, the higher the target value (AFt) of the air-fuel ratio AF of the air-fuel mixture shifts to a higher value. In this embodiment, the air-fuel ratio AF is detected based on the output signal of the air-fuel ratio sensor 29, and the fuel injection amount QF is feedback (FB) controlled so that the air-fuel ratio AF coincides with the target value AFt. Specifically, the ECU 21 calculates an FB correction value CEfb for correcting the target fuel injection amount QFt based on the output signal of the air-fuel ratio sensor 29, and this FB correction amount CEfb is added to the target fuel injection amount QFt. . Specifically, when the air-fuel ratio AF of the air-fuel mixture is higher than the target value AFt, the FB correction amount CEfb is calculated as a positive value, so that the fuel injection amount QF is increased and corrected. On the other hand, when the air-fuel ratio AF of the air-fuel mixture is lower than the target value AFt, the FB correction amount CEfb is calculated as a negative value, thereby reducing the fuel injection amount QF.

  Here, when the absolute value (| CEfb |) of the FB correction amount CEfb becomes excessively large, it can be determined that there is a suspicion of abnormal operation of the fuel injection valve 10. However, since the engine 1 is a so-called mixed fuel engine, even if the fuel injection valve 10 is normal, if the alcohol concentration sensor 13 is abnormal, the absolute value of the FB correction amount CEfb increases. Therefore, when the absolute value of the FB correction amount CEfb becomes excessively large, it is determined that the abnormality of the fuel injection valve 10 is detected after confirming that the alcohol concentration sensor 13 is not abnormal.

  FIG. 8 is a flowchart showing a control routine in the present embodiment. This routine is stored in the ROM of the ECU 21, and is executed every time the ignition of the engine 1 is turned on. When this routine is executed, first, in step S301, it is determined whether the setting of the under-detection abnormality diagnosis flag Fs is 1 or 0. The under-detection abnormality diagnosis flag Fs is a flag for determining whether or not the under-detection abnormality diagnosis control is executed when the engine is started. If it is set to 1, the under-detection abnormality diagnosis control is executed and set to 0. In this case, the under detection abnormality diagnosis control is not executed. If it is determined in this step that the setting of the underdetection abnormality diagnosis flag Fs is 1, the process proceeds to step S302, and if it is determined to be 0, the process proceeds to step S303.

  In step S302, the under detection abnormality diagnosis control described in the first embodiment is executed, and it is determined whether or not the alcohol concentration sensor 13 has an under detection abnormality. Specifically, steps S201 to S208 of the control routine of FIG. 4 are executed here. If it is determined that the alcohol concentration sensor 13 has no under-detection abnormality, the process proceeds to step S304. If not, the process proceeds to step S305. In step S304, the under-detection abnormality diagnosis flag Fs is set to 0 (Fs ← 0), and the process proceeds to step S312 described later. In step S305, a warning lamp (not shown) for notifying the driver of abnormality of the alcohol concentration sensor 13 is turned on. When the processing of this step is completed, this routine is temporarily exited.

  In step S303, the FB correction amount CEfb is calculated based on the output signal of the air-fuel ratio sensor 29. In the subsequent step S306, it is determined whether or not the absolute value (| CEfb |) of the FB correction amount CEfb is larger than the specified value fbmax. The specified value fbmax is an absolute value of the FB correction amount CEfb that is determined to be suspected that the fuel injection valve 10 is malfunctioning, and is obtained in advance through experiments or the like. Here, even if the absolute value of the FB correction amount CEfb exceeds the specified value fbmax, it cannot be concluded immediately that the fuel injection valve 10 is malfunctioning. This is because an increase in the absolute value of the FB correction amount CEfb is predicted to increase excessively even when the fuel injection valve 10 is normal and the alcohol concentration sensor 13 is abnormal.

  If an affirmative determination is made in this step (| CEfb |> fbmax), the process proceeds to step S307, and if not, this routine is temporarily exited. In step S307, abnormality detection in the variable compression ratio mechanism 18 is executed, and it is determined whether or not there is an operation abnormality. If it is determined that there is no malfunction in the variable compression ratio mechanism 18, the process proceeds to step S308. On the other hand, if it is determined that the variable compression ratio mechanism 18 has an operation abnormality, the process proceeds to step S309, and a warning lamp (not shown) for notifying the driver of the abnormality of the variable compression ratio mechanism 18 is turned on. Then, once the processing of this step is completed, this routine is temporarily exited.

In step S308, it is determined whether the FB correction amount CEfb calculated in step S303 is a negative value (CEfb <0) or a positive value (CEfb> 0). When the FB correction amount CEfb is calculated as a negative value, it means that the air-fuel ratio AF of the air-fuel mixture is lower than the target value AFt (that is, on the rich side), and is calculated as a positive value Means that the air-fuel ratio AF is higher than the target value AFt (ie, on the lean side). Here, if the detected alcohol concentration Rad is detected to be higher than the actual alcohol concentration Rar, the target fuel injection amount QFt increases disproportionately in relation to the actual alcohol concentration Rar, and the air-fuel ratio AF of the air-fuel mixture becomes the target. It becomes lower than the value AFt. Therefore, when the FB correction amount CEfb is a negative value and the absolute value thereof is larger than the specified value fbmax, if there is an abnormality in the alcohol concentration sensor 13, there is a suspicion that an overdetection abnormality has occurred. Judgment can be made.

  On the other hand, when the alcohol detection concentration Rad is detected to be lower than the actual alcohol concentration Rar, the target fuel injection amount QFt is disproportionately reduced in relation to the actual alcohol concentration Rar, and the air-fuel ratio AF of the air-fuel mixture becomes the target value. It becomes higher than AFt. Therefore, if the FB correction amount CEfb is a positive value and the absolute value thereof is larger than the specified value fbmax, if there is an abnormality in the alcohol concentration sensor 13, there is a suspicion that an underdetection abnormality has occurred. Judgment can be made. Therefore, if it is determined in step S308 that the FB correction amount CEfb is a negative value (CEfb <0), the process proceeds to step S310, and if it is determined that the value is a positive value (CEfb> 0), the step is performed. The process proceeds to S311.

  In step S310, the excessive detection abnormality diagnosis control described in the first embodiment is executed, and it is determined whether or not the alcohol concentration sensor 13 has an excessive detection abnormality. Specifically, the processes of steps S101 to S110 in the control routine of FIG. 3 are executed here. If it is determined that the alcohol concentration sensor 13 does not have an overdetection abnormality, the process proceeds to step S312; otherwise, the process proceeds to step S305. In step S311, the underdetection abnormality diagnosis flag Fs is set to 1 (Fs ← 1), and then this routine is temporarily exited. Thus, at the next engine start, it is determined in step S301 that the setting of the under-detection abnormality diagnosis flag Fs is 1. As a result, underdetection abnormality diagnosis control is performed in step S302. If it is determined that the alcohol concentration sensor 13 has no under-detection abnormality, the process proceeds to step S312.

  In step S312, it is determined that the fuel injection valve 10 is abnormal, a warning lamp (not shown) for notifying the abnormality of the fuel injection valve 10 is turned on, and the routine is temporarily exited. In this control, it is determined in step S310 that there is no overdetection abnormality in the alcohol concentration sensor 13, or in step S302, it is determined that there is no underdetection abnormality in the alcohol concentration sensor 13, whereby the absolute value of the FB correction amount CEfb is determined. A factor that increases as the specified value fbmax is exceeded is specified as an abnormal operation of the fuel injection valve 10. Thereby, erroneous detection of abnormality in the fuel injection valve 10 due to abnormality of the alcohol concentration sensor 13 can be avoided. The abnormality diagnosis of the alcohol concentration sensor 13 is performed on the assumption that the variable compression ratio mechanism 18 operates according to the control signal of the ECU 21. Therefore, in this embodiment, the abnormality detection of the variable compression ratio mechanism 18 is executed before the abnormality diagnosis of the alcohol concentration sensor 13 is executed, and the abnormality diagnosis of the alcohol concentration sensor 13 is executed after confirming that there is no abnormality. I am going to do that.

<Other embodiments>
If it is determined in step S308 of the control routine that the FB correction amount CEfb is a positive value (CEfb> 0), an underdetection abnormality diagnosis flag Fs is set so as to execute an underdetection abnormality diagnosis at the next engine start. However, in this case, the under-detection abnormality diagnosis and the abnormality detection of the fuel injection valve 10 cannot be performed until the next start. Therefore, an embodiment in which underdetection abnormality diagnosis control can be executed even after the engine is started will be described.

FIG. 9 is a diagram showing a schematic configuration of the engine 1 in a modification of the present embodiment. The engine 1 has an idle speed control function that maintains an engine speed (hereinafter referred to as “idle speed”) NEi during idle operation at a target idle speed NEit that is a target value. The target idle speed NEit is determined based on the load of an air conditioner or alternator (not shown) during idle operation, and is set to a higher speed side as the load is higher.

  The intake pipe 5 is provided with a bypass pipe 31 that bypasses the throttle valve 25. The bypass pipe 31 is provided with an idle speed control valve (hereinafter referred to as “ISC valve”) 32 that can adjust the cross-sectional area of the intake air flowing through the bypass pipe 31 by changing the opening degree thereof. . The ISC valve 32 is connected to the ECU 21 via an electrical wiring, and the opening degree (hereinafter referred to as “ISC opening degree”) ISCA of the ISC valve 32 is controlled by the ECU 21.

  FIG. 10 is a flowchart showing a second control routine in the present embodiment. This routine is stored in the ROM of the ECU 21, and is executed every time the ignition of the engine 1 is turned on. In this routine, the same processes as those in FIG. In this routine, if it is determined in step S308 that the FB correction amount CEfb is a positive value (CEfb> 0), the process proceeds to step S401. In step S401, it is determined whether the engine 1 is idling. If it is determined that the engine 1 is idling, the process proceeds to step S402. If not, the routine is temporarily exited.

  In step S402, a command is issued from the ECU 21 to the variable compression ratio mechanism 18, and the variable compression ratio 18 is controlled so that the compression ratio ε actively changes in accordance with the transition of the preset abnormality diagnosis target compression ratio εact. (This is called active control of the compression ratio ε). FIG. 11 is a time chart showing the transition of the abnormality diagnosis target compression ratio εact and the transition of the ISC opening ISCA according to the active control of the compression ratio ε. The upper part represents the transition of the target compression ratio εact for abnormality diagnosis, and the lower part represents the transition of the ISC opening ISCA. The symbol εid on the vertical axis is a compression ratio at the time when a command is issued from the ECU 21 in step S402 (hereinafter referred to as “reference compression ratio”), and is set in advance for idle operation.

  In FIG. 11, the transition of the abnormality diagnosis target compression ratio εact falls from the reference compression ratio εid toward the minimum value εact1, and reverses from the lowered state to the raised state at the minimum value εact1. Thereafter, the target compression ratio εact for abnormality diagnosis changes so as to increase again to the reference compression ratio εid. The lower solid line in the figure represents the transition of the ISC opening ISCA when the alcohol concentration sensor 13 is normal. When the compression ratio ε is actively controlled in accordance with the transition of the target compression ratio εact for abnormality diagnosis shown in the upper stage, the thermal efficiency of the engine 1 changes accordingly. As a result, the engine torque changes and the idling speed NEi fluctuates, so that the ISC opening ISCA is feedback-controlled to maintain the idling speed NEi at the target idling speed NEit.

  When the abnormality diagnosis target compression ratio εact increases, the ISC opening ISCA is controlled in the closing direction to reduce the intake air amount, thereby suppressing the increase in the idle speed NEi. Thereby, the idle speed NEi is maintained in the vicinity of the target idle speed NEit. On the other hand, when the abnormality diagnosis target compression ratio εact decreases, the ISC opening ISCA is controlled in the opening direction to increase the intake air amount, thereby suppressing the decrease in the idle rotation speed NEi, and the idle rotation speed NEi becomes the target idle rotation speed. It is maintained near NEit.

In FIG. 11, the broken line shown in the lower part represents the transition of the ISC opening degree ISCA when an under-detection abnormality has occurred in the alcohol concentration sensor 13. As described above, when the alcohol concentration sensor 13 has an under-detection abnormality, the air-fuel ratio AF is higher (to the lean side) than the target value AFt. Then, when the abnormality diagnosis target compression ratio εact in the active control is lowered, the deterioration of the combustion state of the air-fuel mixture becomes conspicuous, and the idling speed NEi is more likely to be significantly reduced. As a result, the ISC opening ISCA is controlled to the opening on the opening side, so that the ISC opening IS
The amount of change in CA increases compared to when the alcohol concentration sensor 13 is normal. In this control, when active control of the compression ratio ε is executed, the presence or absence of the under detection abnormality is diagnosed by paying attention to the difference in the amount of change in the ISC opening ISCA according to the presence or absence of the under detection abnormality of the alcohol concentration sensor 13. It was decided. More specifically, the difference (hereinafter referred to as “ISC opening change width”) ΔISCAw between the maximum value ISCAmax and the minimum value ISCAmin in the ISC opening ISCA when active control of the compression ratio ε is executed is obtained. When the ISC opening change width ΔISCAw exceeds the reference change width ΔBw, it is determined that the alcohol concentration sensor 13 has an underdetection abnormality. The reference change width ΔBw is an upper limit value of the ISC opening change width ΔISCAw that is determined that the alcohol concentration sensor 13 has no under-detection abnormality, and is obtained experimentally in advance.

  In step S402, the maximum value (ISCAmax) and the minimum value (ISCAmin) of the ISC opening ISCA are acquired. More specifically, the ECU 21 stores a control signal for controlling the ISC opening ISCA so as to maintain the idle rotation speed NE at the target idle rotation speed NEit, whereby the maximum value ISCAmax of the ISC opening ISCA is stored. And the minimum value ISCAmin is acquired. In step S403, the ISC opening change width ΔISCAw is calculated by subtracting the minimum value ISCAmin from the maximum value ISCAmax acquired in step S402.

  In step S404, it is determined whether or not the ISC opening change width ΔISCAw is larger than the reference change width ΔBw. If an affirmative determination is made in this step (ΔISCAw> ΔBw) (broken line in FIG. 11), it is determined that an under-detection abnormality has occurred in the alcohol concentration sensor 13, and the process proceeds to step S305. On the other hand, if a negative determination (ΔISCAw ≦ ΔBw) is made (solid line in FIG. 11), it is determined that an underdetection abnormality has not occurred in the alcohol concentration sensor 13, and the process proceeds to step S312. In this control, the under-detection abnormality diagnosis control of the alcohol concentration sensor 13 can be executed even after the engine is started. Therefore, the same control and abnormality detection of the fuel injection valve 10 can be performed more smoothly.

It is the figure which showed schematic structure of the engine provided with the variable compression ratio mechanism to which the abnormality diagnosis apparatus of the engine system in Example 1 is applied. 3 is a map showing a relationship between control values of respective control parameters and fuel alcohol concentration Ra in Example 1. (A) is a map showing the relationship between the target compression ratio εts and the target ignition timing θtn during normal operation and the alcohol concentration Ra. (B) is a map showing the relationship between the target compression ratio εts, the fuel injection amount QF, and the alcohol concentration Ra when the engine is started. 3 is a flowchart illustrating a routine related to overdetection abnormality diagnosis control in Embodiment 1. 3 is a flowchart illustrating a routine related to underdetection abnormality diagnosis control in the first embodiment. It is the map which showed the relationship between the engine load TQ in Example 2, and the weighting coefficient Wtvs1 with respect to 1st abnormality determination value VS1. FIG. 6 is a diagram showing a relationship between an equivalence ratio Φ required for equalizing the number of injections ΣNis at the time of engine start and the engine temperature TH at the time of start for each alcohol concentration Ra of the fuel. FIG. 10 is a map showing a relationship among a starting engine temperature TH, an alcohol detection concentration Rad, and a weighting coefficient Wtvs4 in Embodiment 3. FIG. 10 is a flowchart illustrating a control routine in Embodiment 5. FIG. 10 is a diagram showing a schematic configuration of an engine in a modified example of the fifth embodiment. 14 is a flowchart illustrating a second control routine in the fifth embodiment. 5 is a time chart showing a transition of an abnormality diagnosis target compression ratio εact and an ISC opening ISCA for active control of the compression ratio ε.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Cylinder 3 ... Cylinder head 4 ... Intake port 5 ... Intake pipe 6 ... Intake valve 7 ... Exhaust port 8 ... Exhaust pipe 9 ... Exhaust valve 10, Fuel injection valve 12, Fuel tank 13, Alcohol concentration sensor 14, Spark plug 15, Crankshaft 18, Variable compression ratio mechanism 21 ECU
23 ·· Knocking sensor 25 · · Throttle valve 26 · · Air flow meter 27 · · Temperature sensor

Claims (6)

Applied to a variable compression ratio engine having a variable compression ratio mechanism capable of controlling the compression ratio of the engine to a target compression ratio according to the operating state of the engine;
In a state in which the compression ratio of the engine is controlled to the target compression ratio, the required retard angle value required for the ignition timing of the engine according to the knocking strength generated in the engine and the initial value at the start of the engine. Acquisition means for acquiring at least one of values correlated with the total injection amount of fuel injected from the fuel injection valve until an explosion occurs as an acquired value;
An abnormality determination value setting means for setting an abnormality determination value for the acquired value acquired by the acquisition means according to the target compression ratio;
An abnormality diagnosing means for diagnosing an abnormality in the engine system when the acquired value acquired by the acquiring means exceeds the abnormality determination value;
Bei to give a,
The engine is a mixed fuel engine that can use a mixed fuel of gasoline and alcohol and includes a concentration detection device that detects an alcohol concentration of the fuel;
The target compression ratio is set as a value on the high compression ratio side as the detected value of the alcohol concentration is higher,
The abnormality determination value setting means sets the abnormality determination value according to the detected value of the alcohol concentration and the target compression ratio,
The abnormality diagnosis means, the abnormality diagnosis apparatus for an engine system, characterized that you diagnosed with the acquired value acquired by the acquisition unit is abnormal is present in the concentration detecting device when exceeding the abnormality determination value. The ignition timing of the engine is controlled to be advanced as the detected value of the alcohol concentration is higher,
When the acquisition unit acquires the retardation required value, the abnormality determination value setting unit determines an abnormality determination value set for the retardation required value as a detected value of the alcohol concentration, the target compression ratio, The abnormality diagnosis device for an engine system according to claim 1, wherein the abnormality diagnosis device is set according to a set value of the ignition timing. When the acquisition means acquires the retardation request value,
The abnormality determination value setting means, the serial to claim 1 or 2, characterized in that setting the abnormality determination value set for the load the higher the retard required value of the engine as a value greater than <br /> Abnormality diagnosis device for engine system. When the engine is started, the fuel injection amount injected from the fuel injection valve for each combustion cycle is controlled to increase as the detected value of the alcohol concentration increases.
When the acquisition unit acquires a value that correlates with the total injection amount, the abnormality determination value setting unit sets an abnormality determination value that is set for a value that correlates with the total injection amount as a detected value of the alcohol concentration. The engine system abnormality diagnosis device according to any one of claims 1 to 3, wherein the abnormality diagnosis device is set according to the target compression ratio and the fuel injection amount. When the acquisition unit acquires a value correlated with the total injection amount,
The abnormality determination value setting means includes
Under the condition where the detected value of the alcohol concentration is equal, the lower the engine temperature at the start of the engine, the higher the abnormality determination value set for the value correlated with the total injection amount,
4 claims 1 at the engine temperature is equal conditions and sets the abnormality determination value is set for a value that correlates to the detected value is higher the total injection amount of the alcohol concentration as a value greater than The abnormality diagnosis apparatus for an engine system according to any one of the above. When the engine temperature at starting of the engine is a predetermined extremely low temperature region, any one of claims 1 to 5 in which obtaining a value that correlates to the total injection amount by the acquisition means, characterized in that it is prohibited The engine system abnormality diagnosis device according to claim 1.

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