JP2010038143A - Internal combustion engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel supply device for an internal combustion engine having improved combustion stability and exhaust properties by detecting the malfunction of a selector valve, the internal combustion engine having a fuel pressure change-over means for changing over fuel injection pressure with the opening/closing operation of the selector valve. <P>SOLUTION: The internal combustion engine 10 sets the selector valve 34 into an opened condition to make set fuel pressure in a delivery pipe low, and sets it into a closed condition to make the set fuel pressure high. When outputting a command signal to the selector valve 34 to make the set fuel pressure high, an electronic control device 50 diagnoses the malfunction of the selector valve 34 in accordance with the ratio of an actual air-fuel ratio to a target air-fuel ratio at this time. On determining the malfunction of the selector valve 34, it controls the drive of a throttle valve 15 to restrict an intake air amount and suppress the combustion of mixture in a lean condition when a target fuel injection amount each time is greater than the maximum fuel injection amount at each engine speed in the low fuel pressure state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that switches a fuel injection pressure by switching a fuel supply path with a switching valve.

In recent years, in order to respond to demands such as the use of a mixed fuel of alcohol and gasoline having a theoretical air / fuel ratio smaller than that of gasoline fuel and higher output of the internal combustion engine, the internal combustion engine has been controlled appropriately. It is requested. In order to meet such demands, it is necessary to increase the fuel injection amount in accordance with the operating state of the internal combustion engine. Generally, by changing the pressure of fuel supplied to the delivery pipe to which the fuel injection valve is connected. It corresponds. As an apparatus that enables such fuel supply, for example, as disclosed in Patent Document 1, a low-pressure fuel pump and a high-pressure fuel pump are provided, and the fuel in a low fuel pressure state sent from the low-pressure fuel pump is boosted by the high-pressure pump. Thus, there is known a fuel supply apparatus that supplies fuel in a high fuel pressure state corresponding to the operating state of the high-pressure pump to a fuel injection valve. The fuel supply device includes a fuel pressure sensor that detects a fuel injection pressure, adjusts the amount of fuel supplied from the high-pressure pump to the fuel injection valve based on a detection signal of the fuel pressure sensor, and brings the fuel into a high fuel pressure state at a desired pressure. To do. In addition to this, as shown in Patent Document 2, a high pressure return passage provided with a high pressure regulator and a low pressure return passage for returning surplus fuel to the fuel tank when the fuel injection pressure exceeds a predetermined pressure. There is also known a fuel supply device that includes a low-pressure return passage provided with a regulator, and changes the fuel injection pressure in a plurality of stages according to the operating state of the internal combustion engine by switching the flow in these two return passages with a switching valve. Yes. In any fuel supply device, the fuel injection amount corresponding to the operation state is secured by increasing the fuel injection amount in the unit opening period of the fuel injection valve by holding the fuel in a high fuel pressure state.
JP 2000-130232 A JP-A-5-59976

  By the way, in the fuel supply device that varies the fuel injection pressure, in order to boost the fuel in the low fuel pressure state discharged from the fuel pump by the various configurations described above to generate a high fuel pressure state, various fuel pressure boosting devices are used. If an abnormality occurs in the configuration, the fuel cannot be maintained in a high fuel pressure state. Even in such a case, if the air-fuel ratio feedback control is being executed as in the low-rotation low-load operation state, the air-fuel ratio correction coefficient is calculated so that the air-fuel ratio at that time becomes the stoichiometric air-fuel ratio. Since the fuel injection amount is adjusted based on the air-fuel ratio correction coefficient, the excess or deficiency of the fuel injection amount is corrected autonomously. On the other hand, in a situation where it is desired to ensure the engine output as in the high rotation / high load operation state, the above-described air / fuel ratio feedback control is not executed, and the fuel injection amount is set so that the target air / fuel ratio is set to be rich in advance. Because the so-called open control that is adjusted is executed, even if fuel in a low fuel pressure state is actually being supplied due to an abnormality in the fuel supply device, the valve opening time of the fuel injection valve is in a high fuel pressure state It will be time corresponding to the fuel. As a result, not only is it difficult to secure the fuel injection amount according to the intake air amount, but also the unburned air-fuel mixture is supplied to the exhaust gas purification device due to misfire due to a decrease in ignitability, and the purification catalyst is caused by excessive temperature rise of the purification catalyst. This will cause the problem of deterioration.

With respect to this problem, in Patent Document 1, when it is determined that the fuel cannot be maintained in a high fuel pressure state based on a detection signal or the like of the fuel pressure sensor, the high pressure pump is stopped and the fuel is maintained in a low fuel pressure state. Misfire is suppressed by restricting the intake air amount so that the injection amount is equal to or less than the allowable fuel injection amount for each rotation speed. However, in such fuel supply control, a fuel pressure sensor is required to determine whether or not a high fuel pressure state can be maintained. Therefore, the fuel supply control cannot be applied to a fuel supply device not equipped with a fuel pressure sensor, or A fuel pressure sensor must be provided separately. In particular, in the fuel supply device using the switching valve as in Patent Document 2, there are many examples in which the fuel pressure sensor is not mounted because the fuel can be brought into a desired fuel pressure state only by switching the fuel supply path by the switching valve. . Therefore, in a fuel supply apparatus that does not have such a fuel pressure sensor, there is no way to detect whether or not a high fuel pressure state can be maintained, in other words, that an abnormality has occurred in the switching valve. As a result, the combustion stability is lowered and the exhaust properties are lowered.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to detect an operation abnormality of a switching valve in an internal combustion engine having a fuel pressure switching means that switches fuel injection pressure by opening and closing the switching valve. An object of the present invention is to provide a fuel supply device for an internal combustion engine with improved combustion stability and exhaust properties.

In the following, means for achieving the above object and its effects are described.
According to a first aspect of the present invention, there is provided a switching valve that pumps fuel stored in a fuel tank of an internal combustion engine to a fuel injection mechanism to change a fuel flow path between the fuel tank and the fuel injection mechanism. The fuel pressure switching means for switching the fuel pressure in the fuel injection mechanism between the first pressure and the second pressure higher than the first pressure, and the intake air amount control means for controlling the intake air amount to the internal combustion engine The fuel pressure in the fuel injection mechanism is selected based on the operating state of the internal combustion engine so that the air-fuel ratio in the internal combustion engine becomes the target air-fuel ratio, and the injection period corresponding to the selected fuel pressure is A control device for an internal combustion engine for controlling a fuel injection amount of a fuel injection mechanism, wherein when the second pressure is selected, switching to the second pressure is impossible. The intake air volume to The gist of the Rukoto.

  In such a configuration, when the second pressure is selected by the fuel pressure switching means, the injection period for injecting fuel is defined on the assumption that the fuel pressure in the fuel injection mechanism is the second pressure. In such a state, when an abnormality occurs in the switching valve and switching to the second pressure becomes impossible, the fuel under the first pressure is injected in the injection period corresponding to the second pressure. End up. As a result, the fuel injection amount in the unit injection period decreases due to a shortage of fuel injection pressure, and the desired fuel injection amount cannot be secured, and the air-fuel ratio of the air-fuel mixture in the internal combustion engine is lean relative to the target air-fuel ratio. It becomes. According to the present invention, when the switching to the second pressure is impossible, the intake air amount is limited, so that the lean state of the air-fuel mixture can be suppressed, and thus the combustion stability and the exhaust gas can be suppressed. Properties can be improved.

  According to a second aspect of the present invention, the second pressure is selected on the condition that the degree of deviation between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine is not less than a specified value when the second pressure is selected. The gist is to determine that switching to pressure is impossible.

  According to the present invention, the determination that the switching to the second pressure is impossible, in other words, the determination that the switching valve is operating abnormally is based on the degree of deviation between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine. Therefore, the abnormal operation can be appropriately determined based on the lean state of the air-fuel mixture in the internal combustion engine. Therefore, it is possible to detect an abnormal operation of the switching valve without using a fuel pressure sensor based on such a determination based on the degree of deviation. And if it is judged that the switching valve is abnormal, the amount of intake air is limited, so that the lean state of the air-fuel mixture can be immediately suppressed, which in turn improves the combustion stability and exhaust properties. Can do.

According to a third aspect of the present invention, when it is determined that the switching to the second pressure is impossible, the fuel injection amount of the fuel injection mechanism is a maximum that can be injected at the first pressure. The gist of the invention is to limit the intake air amount to the internal combustion engine when the maximum fuel injection amount is larger than the maximum fuel injection amount.

  According to the present invention, the intake air amount is restricted so that the fuel injection amount in the fuel injection mechanism does not exceed the maximum fuel injection amount at the first pressure. Therefore, even if it is impossible to switch to the second pressure, there is no restriction on the intake air amount if the required fuel injection amount can be injected at the first pressure. That is, since the intake air amount is limited only when the fuel injection amount of the fuel injection mechanism becomes larger than the maximum fuel injection amount, compared with the case where the intake air amount is limited over the entire period during which switching is impossible, The amount of intake air corresponding to the required load on the internal combustion engine can be realized, and consequently the engine output corresponding to the required load can be realized.

The gist of the invention described in claim 4 is that the degree of deviation is a ratio of an air-fuel ratio in the internal combustion engine to the target air-fuel ratio.
When switching to the second pressure is impossible, the difference between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine is governed by the difference between the actual fuel injection amount in the fuel injection mechanism and the target value. According to such a configuration, since the degree of divergence, which is the determination criterion for non-switching described above, is the ratio between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine, the difference value between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine, etc. Compared to the case of the deviation degree, the influence of the intake air amount on the deviation degree can be reduced. Since the degree of divergence, which is the determination criterion for non-switching, functions with high accuracy as an indicator of the difference between the actual fuel injection amount and its target value, it is possible to accurately determine whether the switching valve is abnormal.

  According to a fifth aspect of the present invention, the fuel pressure switching means is formed by branching from the main passage connecting the fuel tank and the fuel injection mechanism, and the fuel from the main passage. A low pressure return passage that returns to the tank, a low pressure regulator that is provided in the low pressure return passage and opens when the fuel pressure in the low pressure return passage is equal to or higher than the first pressure, and discharges fuel to the fuel tank side; A high-pressure return passage connected to the fuel injection mechanism for returning the fuel in the fuel injection mechanism to the fuel tank; and a fuel pressure in the high-pressure return passage provided in the high-pressure return passage is equal to or higher than the second pressure. And a high-pressure regulator that discharges fuel to the fuel tank side, and the switching valve switches between opening and closing of the low-pressure return passage. That.

  In such a configuration, when a valve closing command is output to the switching valve to select the second pressure, the fuel pressure in the fuel injection mechanism is the second pressure during the injection period for injecting fuel. It is defined on the assumption of When the switching valve cannot be closed in such a state, the fuel under the first pressure is injected in the injection period corresponding to the second pressure. As a result, the fuel injection amount in the unit injection period decreases due to a shortage of fuel injection pressure, and the desired fuel injection amount cannot be secured, and the air-fuel ratio of the air-fuel mixture in the internal combustion engine is lean relative to the target air-fuel ratio. It becomes.

  According to the present invention, the determination that the switching valve cannot be closed is made based on the degree of deviation between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine. It is possible to appropriately determine that the valve cannot be closed. When it is determined that the switching valve is abnormal, the intake air amount is limited, so that the lean state of the air-fuel mixture can be suppressed, and as a result, combustion stability and exhaust properties can be improved.

DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment in which a control device for an internal combustion engine according to the present invention is embodied in a control device for an internal combustion engine mounted on a flexible fuel vehicle (FFV) will be described with reference to FIGS. . FFV refers to a vehicle that can use only alcohol fuel (alcohol concentration 100%), only gasoline fuel (alcohol concentration 0%), or a mixed fuel in which alcohol and gasoline are arbitrarily mixed.

  FIG. 1 shows an internal combustion engine 10 according to the present embodiment and its peripheral configuration. The internal combustion engine 10 shown in the figure is an engine that can use a mixed fuel in which alcohol and gasoline are arbitrarily mixed, and has a plurality of cylinders 11, and a piston 12 reciprocates in the cylinders 11. Each is housed movably. A combustion chamber 13 is defined by the top surface of the piston 12 and the inner peripheral surface of the cylinder 11.

  In the intake passage 14 for supplying air to the combustion chamber 13, a throttle valve 15 as intake air amount control means for adjusting the flow rate of the intake air amount GA flowing through the intake passage 14, and the throttle valve 15 are opened and closed. And a throttle valve actuator 16 is provided. Further, in the intake passage 14, intake ports 14 a are formed corresponding to the cylinders 11, and fuel injection valves 17 for supplying fuel into the intake ports 14 a are provided. The fuel injected from the fuel injection valve 17 is mixed with the air flowing through the intake passage 14 and supplied to the combustion chamber 13. The air-fuel mixture supplied to the combustion chamber 13 is ignited by the spark plug 18 and burned, and the exhaust gas after combustion is discharged to the exhaust passage 19. The exhaust passage 19 is provided with an exhaust purification catalyst 19 a for purifying the exhaust gas flowing through the exhaust passage 19.

  The fuel tank 20 stores a mixed fuel in which alcohol and gasoline are arbitrarily mixed, and a fuel pump 21 is provided in the fuel tank 20. The fuel pump is an electric fuel pump and is operated by the voltage supplied from the battery 22 and continuously discharges the fuel during engine operation. The fuel pump 21 is connected to the main passage 30 via a filter 23 that removes fine foreign matters contained in the fuel.

  The main passage 30 is formed by branching from the main passage 30 and temporarily returns the fuel from the main passage 30 to the low pressure return passage 31 for returning the surplus fuel in the main passage 30 to the fuel tank 20. A delivery pipe 32 to be stored is connected.

  The low pressure return passage 31 is attached with a low pressure regulator 33 that opens when the fuel pressure in the low pressure return passage 31 is equal to or higher than a first pressure Pl (for example, 284 kPa) and discharges fuel to the fuel tank 20 side. Yes. The low pressure return passage 31 is provided with a switching valve 34 that switches between opening and closing of the low pressure return passage 31 according to the operating state of the internal combustion engine 10. The switching valve 34 is a normally-open solenoid valve that is opened when the valve is not operated and is closed when a voltage is applied. When the switching valve 34 is closed, the low-pressure return passage 31 is closed.

  Connected to the delivery pipe 32 are a fuel injection valve 17 that is connected to each of the intake ports 14a and injects fuel in the delivery pipe 32, and a high-pressure return passage 35 that returns excess fuel in the delivery pipe 32 to the fuel tank 20. Has been. The fuel injection valve 17 and the delivery pipe 32 constitute a fuel injection mechanism. The high pressure return passage 35 is opened when the fuel pressure in the high pressure return passage 35 is equal to or higher than a second pressure Ph (for example, 400 kPa) higher than the first pressure Pl, and fuel is supplied to the fuel tank 20 side. A high pressure regulator 36 for discharging is attached.

With such a configuration, the fuel pressure in the delivery pipe 32 is switched through switching between opening and closing of the low pressure return passage 31 by the switching valve 34. Specifically, the low pressure return passage 31 is closed by the switching valve 34 and the pressure is adjusted by the high pressure regulator 36, so that the high pressure return passage 35 in the delivery pipe 32, which is the upstream portion of the high pressure regulator 36, and the main The fuel pressure in the passage 30 is adjusted to the second pressure Ph (high pressure side), and the fuel in the delivery pipe 32 is maintained in a high fuel pressure state. On the other hand, the low pressure return passage 31 is opened by the switching valve 34 and the pressure regulation by the low pressure regulator 33 is performed, so that the inside of the main passage 30 and the delivery pipe 32 that are upstream of the low pressure regulator 33 in the low pressure return passage 31. Is adjusted to the first pressure Pl (low pressure side), and the fuel in the delivery pipe 32 is maintained in the low fuel pressure state.

  Incidentally, when the valve opening period is the same, the fuel injection amount in the high fuel pressure state (400 kPa) is increased by about 18% compared to the fuel injection amount in the low fuel pressure state (284 kPa). In other words, the second pressure Ph and the second pressure so that the fuel injection amount per unit valve opening period in the high fuel pressure state is increased by about 18% compared to the fuel injection amount per unit period in the low fuel pressure state. A pressure Pl of 1 is set.

  The internal combustion engine is provided with various sensors for detecting various information including the engine operating state. For example, a throttle opening sensor 41 for detecting the throttle opening TA is attached to the throttle valve 15, and an engine for detecting the rotation speed, that is, the engine rotation speed NE, is provided in the vicinity of the crankshaft (not shown). A rotation speed sensor 42 is provided. Further, an accelerator position sensor 43 that detects an accelerator operation amount ACCP that is a depression amount of the accelerator pedal by the driver is provided in the vicinity of an accelerator pedal (not shown), and an intake air amount GA is detected in the intake passage 14. An intake air amount sensor 44 is provided. Further, the fuel tank 20 is provided with a fuel amount sensor 45 for detecting the fuel amount FL therein.

  Further, an upstream side of the exhaust purification catalyst 19a in the exhaust passage 19 is an empty space that detects the oxygen concentration and unburned fuel concentration in the exhaust gas in order to grasp the air-fuel ratio AF of the air-fuel mixture burned in the combustion chamber 13. A fuel ratio sensor 46 is attached, and the air fuel ratio sensor 46 detects the air fuel ratio AF of the air-fuel mixture subjected to combustion as a continuous value. Incidentally, the ethanol concentration of the fuel in the delivery pipe 32 is not always constant, and the fuel property changes due to a refueling operation or the like. In this embodiment, from the detection signal of the air-fuel ratio sensor 46, the fuel concentration in the delivery pipe 32 is changed. The fuel property, that is, the ethanol concentration (alcohol concentration) is calculated. These air-fuel ratio sensors 46 cannot detect the oxygen concentration with high accuracy when the element temperature is lower than a predetermined activation temperature. For this reason, the air-fuel ratio sensor 46 has a built-in heater for heating the element to raise the element temperature to the activation temperature when the exhaust temperature or the outside air temperature is low.

  All the detection signals of the various sensors 41 to 46 are taken into the electronic control unit 50 of the internal combustion engine. The electronic control device 50 includes a storage unit that stores and holds various control programs, calculation maps, data calculated when various controls are executed, and the like. The electronic control unit 50 drives the fuel injection valve 17, the switching valve 34, the throttle valve 15, and the like based on detection signals of various sensors including these sensors 41 to 46, so that the fuel injection amount, the fuel injection pressure, the fuel Various controls related to fuel injection, such as the circulation mode and the intake air amount, are executed.

Next, fuel injection control executed by the electronic control unit 50 will be described with reference to FIGS. In the fuel injection control by the electronic control unit 50, first, the fuel injection amount is calculated based on the operating state of the internal combustion engine. In calculating the fuel injection amount, a basic fuel injection amount TAUB is associated with a map constructed to realize the theoretical air-fuel ratio under the condition of using gasoline fuel, for example, the intake air amount GA and the engine rotational speed NE. Based on the map, the basic fuel injection amount TAUB of the fuel injection valve 17 is calculated. Next, the target fuel injection amount TAU is calculated by multiplying the basic fuel injection amount TAUB by the air-fuel ratio correction coefficient KAF and the concentration learning value KALC according to the following equation (1).

TAU ← TAUB × KAF × KALC (1)
The air-fuel ratio correction coefficient KAF in the above equation (1) is a coefficient for correcting the target fuel injection amount TAU based on the operating state of the internal combustion engine 10 in order to bring the air-fuel ratio AF closer to the theoretical air-fuel ratio. For example, at the time of air-fuel ratio feedback control executed during low load operation or the like, an air-fuel ratio feedback correction value calculated so as to cancel the deviation between the air-fuel ratio AF and the theoretical air-fuel ratio is applied as this air-fuel ratio correction coefficient KAF. On the other hand, at the time of open control executed to ensure engine output during high load operation or the like, a correction value for increasing the target fuel injection amount TAU in order to realize a target air-fuel ratio AFT richer than the theoretical air-fuel ratio (> 1.0) is applied as the air-fuel ratio correction coefficient KAF. The air-fuel ratio correction coefficient KAF at the time of open control is calculated by using a map in which the air-fuel ratio correction coefficient KAF is associated with the required load KL and the engine speed NE based on the accelerator operation amount ACCP. Incidentally, the target air-fuel ratio AFT in such open control can be expressed by target air-fuel ratio AFT = intake air amount GA / target fuel injection amount TAU = theoretical air-fuel ratio / air-fuel ratio correction coefficient KAF.

  The concentration learning value KALC in the above equation (1) is a learning value obtained by alcohol concentration learning control executed using the air-fuel ratio feedback correction value. Since the internal combustion engine 10 also uses the mixed fuel, which is a fuel having a lower stoichiometric air / fuel ratio than gasoline fuel, the combustion properties of gasoline burned at the stoichiometric air / fuel ratio and the combustion properties of the mixed fuel are close to each other. As described above, when the above mixed fuel is used, it is necessary to correct the target fuel injection amount TAU in accordance with the alcohol concentration in the fuel. This concentration learning value KALC is a learning value calculated by the alcohol concentration learning control so as to cancel out the steady divergence between the air-fuel ratio AF obtained according to the alcohol concentration in the mixed fuel and the target air-fuel ratio AFT. Yes, it is a coefficient for increasing the target fuel injection amount TAU according to the alcohol concentration.

  Here, the fuel injection amount injected from the fuel injection valve 17 in the internal combustion engine 10 is controlled by the valve opening period of the fuel injection valve 17. Therefore, when the target fuel injection amount TAU is high and the engine rotational speed NE is high as in the high load high rotation operation, it is necessary to inject a large amount of fuel in a short valve opening period.

  Therefore, when the target fuel injection amount TAU is calculated as described above, the fuel injection control by the electronic control unit 50 should increase the pressure of the fuel in the delivery pipe 32 when a large amount of fuel needs to be injected. First, fuel pressure switching control for switching the fuel pressure state of the fuel in the delivery pipe 32 in accordance with the operating state of the internal combustion engine 10 is executed. This fuel pressure switching control is executed by opening / closing control of the switching valve 34 for switching the fuel in the delivery pipe 32 to a low fuel pressure state or a high fuel pressure state. That is, the electronic control unit 50 applies the target fuel injection amount TAU and the engine speed NE to the fuel pressure state in a map that associates each fuel pressure state with the target fuel injection amount TAU and the engine speed NE, that is, a so-called fuel pressure switching map. A state is selected. When the low fuel pressure state is selected, the high fuel pressure flag, which is a flag indicating the fuel pressure selection state, is set to OFF, and the command signal for opening the switching valve 34 is switched. It is output to the valve 34. On the other hand, when the high fuel pressure state is selected, the high fuel pressure flag is set to ON (ON), and a command signal for closing the switching valve 34 is output to the switching valve 34.

When the target fuel injection amount TAU is calculated as described above, in the fuel injection control by the electronic control unit 50, a pulse output from the engine rotation speed sensor 42 is used according to the crank angle, and the engine rotation speed is calculated. The fuel injection timing corresponding to NE is calculated. In calculating the fuel injection timing, for example, the fuel injection timing is set as an advance value with respect to a reference crank angle such as top dead center, and the fuel injection timing for obtaining the optimum combustion is determined based on the intake air amount GA and the engine speed. A map associated with NE, a so-called injection timing map is used. Then, the fuel injection timing is calculated by applying the intake air amount GA and the engine rotational speed NE to this injection timing map. When the fuel injection timing is calculated, the fuel injection control executed by the electronic control unit 50 is an injection period based on the state of the high fuel pressure flag (ON or OFF), that is, based on the fuel pressure state at that time. The valve opening period of the fuel injection valve 17 is calculated according to the target fuel injection amount TAU. Then, by appropriately controlling the fuel injection valve 17 according to the calculated valve opening period, appropriate fuel injection control corresponding to the operating state of the internal combustion engine 10 is executed.

  By the way, in the switching valve 34 described above, when various operational abnormalities such as disconnection of the command signal in the transmission line and the biting of foreign matter into the mechanical drive part occur, the fuel path cannot be switched. It becomes impossible to realize the fuel pressure state. If such an abnormal operation of the switching valve 34 occurs at the time of execution of the air-fuel ratio feedback control, the fuel using the air-fuel ratio feedback correction value so that the air-fuel ratio AF at that time becomes the stoichiometric air-fuel ratio. Since the injection amount is adjusted, the fuel injection amount is autonomously corrected even when there is no switching to the high fuel pressure state. On the other hand, in the case where such an abnormal operation of the switching valve 34 occurs at the time of executing the above open control, the switching valve 34 is always open, so that the fuel is increased depending on the opening period of the high fuel pressure state. Even if the injection valve 17 is driven and controlled, fuel injection is actually executed under a low fuel pressure state. Therefore, not only is it difficult to secure the target fuel injection amount TAU corresponding to the intake air amount GA due to insufficient fuel injection pressure, but also when the air-fuel ratio AF becomes excessively lean, unburned mixing due to misfiring due to a decrease in ignitability The exhaust gas is supplied to the exhaust gas purification device, and the exhaust gas purification catalyst 19a deteriorates due to excessive temperature rise of the exhaust gas purification catalyst 19a. Therefore, in the present embodiment, in order to diagnose an abnormality in which the switching valve 34 is normally open, a switching valve diagnosis process using an air-fuel ratio in a state where a command signal for closing the switching valve 34 is output is executed. Is done.

  Next, the switching valve diagnosis process described above will be described with reference to FIG. FIG. 2 is a flowchart showing the processing procedure of the switching valve diagnosis processing. A series of processing shown in this flowchart is repeatedly executed by the electronic control device 50 with a predetermined period.

  As shown in FIG. 2, in this series of processing, first, a state in which a command signal for closing the switching valve 34 is output by the fuel pressure switching control by the electronic control unit 50, that is, the high fuel pressure flag is ON. Is determined (step S101). When it is determined that the high fuel pressure flag is ON (step S101: YES), the air-fuel ratio AF based on the detection signal from the air-fuel ratio sensor 46 and the operating state of the internal combustion engine 10 at the time of the open control are subsequently determined. The air-fuel ratio correction coefficient KAF calculated based on the above is acquired (step S102), and the process proceeds to the next step S103.

  In the process of step S103, the obtained air-fuel ratio AF and air-fuel ratio correction coefficient KAF are applied to the following equation (2) to calculate a discriminant value for diagnosing the presence or absence of abnormal operation of the switching valve 34, It is determined whether the discriminant value is equal to or greater than a predetermined specified value.

Discrimination value = AF × KAF / 14.6 = AF / (14.6 / KAF) (2)
In equation (2), “14.6” indicates the theoretical air-fuel ratio in the present embodiment, and the term “14.6 / KAF” indicates the target air-fuel ratio AFT during the open control as described above. The discriminant value obtained by the equation (2) is the ratio of the air-fuel ratio AF to the target air-fuel ratio AFT, but the ratio between the intake air amount GA related to the air-fuel ratio AF and the intake air amount GA related to the target air-fuel ratio AFT is Since it is substantially constant, it can be used as an index indicating the ratio between the actual fuel injection amount and the target fuel injection amount TAU. Therefore, when the switching valve 34 is normal, for example, by applying the discriminant value when the actual fuel injection amount and the target fuel injection amount TAU are substantially equal to the specified value, whether or not there is an abnormal operation in the switching valve 34. Diagnosis becomes possible.

  For example, when there is no operation abnormality in the switching valve 34, the switching valve 34 is closed in response to a command signal for closing the switching valve 34, and the high fuel pressure state is changed according to the valve opening period of the high fuel pressure state. Fuel is injected. Therefore, the air-fuel ratio AF and the target air-fuel ratio AFT become substantially equal values, and based on this, it can be determined that there is no malfunction in the switching valve 34.

  On the other hand, when an abnormality that causes the switching valve 34 to be normally open occurs, the fuel is injected during the valve opening period corresponding to the high fuel pressure state, even though the fuel is in the low fuel pressure state. Therefore, the actual fuel injection amount becomes smaller than the target fuel injection amount TAU, and the air-fuel ratio AF becomes a value indicating lean, that is, a value larger than the target air-fuel ratio AFT. Specifically, as described above, since the fuel injection amount in the high fuel pressure state in the unit valve opening period is increased by about 18% compared to the fuel injection amount in the low fuel pressure state, the switching valve 34 has an abnormal operation. If it occurs, the actual fuel injection amount decreases by about 18% with respect to the target fuel injection amount, and the above-mentioned discriminant value increases by that amount. Therefore, it can be determined that the switching valve 34 has an abnormal operation based on the determination value being equal to or greater than the specified value.

  Then, when it is determined that the discriminant value by the arithmetic expression (2) is equal to or greater than the specified value (step S103: YES), it is determined that an abnormality that causes the switching valve 34 to be normally open has occurred. Then, an abnormality flag, which is a flag indicating an abnormal operation of the switching valve 34, is set to ON (step S105), and a series of processes is terminated.

  On the other hand, when the high fuel pressure flag is set to OFF (step S101: NO), when the discriminant value is not more than the specified value (step S103: NO), an operation abnormality has occurred in the switching valve 34. Assuming that there is no error, the abnormality flag is set to OFF (step S105), and a series of processing ends.

  Here, when the abnormality flag of the switching valve 34 is set to OFF by the switching valve diagnostic control described above, the normal control related to the throttle opening of the throttle valve 15 is executed by the electronic control unit 50. In the normal control of the throttle valve 15 executed by the electronic control unit 50, the operating state of the internal combustion engine 10 is grasped based on the required load KL based on the accelerator operation amount ACCP, the engine speed NE, and the like, and the target based on the operating state is determined. The throttle opening TAT is obtained. Based on the detection signal of the throttle opening sensor 41, the actual throttle opening TA is obtained, and the throttle valve actuator 16 is controlled so that the throttle opening TA coincides with the target throttle opening TAT.

  On the other hand, when the abnormality flag of the switching valve 34 is set to ON by the switching valve diagnostic control described above, the internal combustion engine 10 can only hold the fuel in the delivery pipe 32 in a low fuel pressure state. Therefore, the target fuel injection amount TAU calculated based on the intake air amount GA and the engine rotational speed NE exceeds the maximum fuel injection amount T720 that can be injected in the low fuel pressure state at the engine rotational speed NE at that time. There is. In such a case, combustion is performed in a state where the air-fuel ratio is lean, so that the exhaust purification catalyst 19a may be excessively heated by the exhaust gas, and the deterioration of the exhaust purification catalyst 19a may be promoted.

  Therefore, in this embodiment, when the abnormality flag of the switching valve 34 is ON, and it is determined that the calculated target fuel injection amount TAU exceeds the maximum fuel injection amount T720, the combustion stability is increased. The intake air amount restriction control is executed to ensure that the air-fuel ratio does not become lean. In the present embodiment, the intake air amount restriction control is performed by controlling the throttle opening degree TA of the throttle valve 15.

  Next, the execution procedure of the intake air amount restriction control will be described with reference to FIG. FIG. 3 is a flowchart showing an execution procedure of the intake air amount restriction control in the present embodiment. A series of processing shown in this flowchart is continuously executed after the switching valve diagnostic processing described above, and is repeatedly executed by the electronic control unit 50 at a predetermined cycle, similarly to the switching valve diagnostic processing.

  In this series of processing, first, it is determined whether the state of the abnormality flag related to the switching valve 34 is ON or OFF (step S201). If it is determined that the abnormality flag is ON, then the required load KL and the engine speed NE are acquired (step S202), and the maximum fuel injection amount that can be injected using the fuel in the low fuel pressure state is the maximum. A fuel injection amount T720 is calculated, a target throttle opening degree TAT corresponding to the required load KL is set, and a target fuel injection amount TAU is calculated based on the intake air amount GA and the engine speed NE at that time. (Step S203). Then, the calculated target fuel injection amount TAU and the maximum fuel injection amount T720 are compared to determine whether or not the target fuel injection amount TAU exceeds the maximum fuel injection amount T720 (step S204).

  Note that the maximum fuel injection amount T720 is the fuel injection amount obtained when the fuel of the first pressure Pl is continuously injected during the maximum valve opening period of the fuel injection valve 17 defined for each engine speed NE. For example, it is calculated by applying the engine speed NE to a map associating the engine speed NE with the maximum fuel injection amount T720 as shown in FIG. Incidentally, since the maximum valve opening time of the fuel injection valve 17 becomes shorter as the engine rotational speed NE becomes higher, the maximum fuel injection amount T720 decreases as the engine rotational speed NE becomes higher as shown in FIG. Set to

  When it is determined that the target fuel injection amount TAU is larger than the maximum fuel injection amount T720 (step S204: YES), the target fuel injection amount TAU is larger than the maximum fuel injection amount T720 in the fuel injection control described above. In order to avoid this, the target throttle opening degree TAT of the throttle valve 15 is limited to limit the intake air amount GA. For example, as shown in FIG. 5, the electronic control unit 50 sets the engine speed NE in a map in which the upper limit throttle opening TAL, which is the upper limit of the target throttle opening TAT that satisfies the above requirements, and the engine speed NE are associated with each other. By applying this, the upper limit throttle opening TAL is calculated, and the upper limit throttle opening TAL is set as the target throttle opening TAT of the throttle valve 15. Incidentally, since the maximum fuel injection amount T720 decreases as the engine speed NE increases, the upper limit throttle opening TAL is set such that the throttle opening closes as the engine speed NE increases, as shown in FIG. Is done.

  Then, the throttle valve actuator 16 is controlled so that the throttle opening TA coincides with the target throttle opening TAT, whereby the throttle opening TA is limited to the upper limit throttle opening TAL (step S205). Since the intake air amount GA is limited by such restriction of the opening of the throttle valve 15, it is possible to avoid the target fuel injection amount TAU from becoming larger than the maximum fuel injection amount T720 in the fuel injection control described above. Therefore, even when an abnormality occurs in which the switching valve 34 is normally open and a high fuel pressure state cannot be realized, combustion in a state where the air-fuel ratio is lean can be avoided.

As described above, according to the control apparatus for an internal combustion engine in the present embodiment, the following effects can be obtained.
(1) When a command signal for closing the switching valve 34 is output to the switching valve 34 and the high fuel pressure flag is ON, a discrimination value indicating the ratio between the target air-fuel ratio AFT and the air-fuel ratio AF is calculated. . According to this, when there is an abnormality in the switching valve 34 that is normally open, fuel is injected during the valve opening period in the high fuel pressure state under the low fuel pressure state, so that the air-fuel ratio AF becomes lean. And the discriminant value becomes large. Further, since the fuel injection amount in the high fuel pressure state during the unit valve opening period is increased by about 18% compared to the fuel injection amount in the low fuel pressure state, the switching valve 34 is in the normally open state. The ratio between the target fuel injection amount and the actual fuel injection amount is a value based on the ratio of the fuel injection amount per unit valve opening period between the low fuel pressure state and the high fuel pressure state, that is, a value equal to or greater than a specified value. Therefore, when the discriminant value is equal to or greater than the specified value, it is possible to reliably detect an abnormality in which the switching valve 34 is normally open without using a fuel pressure sensor.

  (2) When an abnormality that is normally open occurs in the switching valve 34, the difference between the air-fuel ratio AF and the target air-fuel ratio AFT is dominated by the difference between the actual fuel injection amount and the target fuel injection amount TAU. Is done. Since the discriminant value is defined by the ratio between the target air-fuel ratio AFT and the air-fuel ratio AF with the above-described configuration, compared with the case where the difference value between the air-fuel ratio AF and the target air-fuel ratio AFT is set as the discriminant value, The influence of the intake air amount GA on the discrimination value can be reduced. Since such a discriminant value functions with high accuracy as an index of the difference between the actual fuel injection amount and the target fuel injection amount TAU, it is possible to accurately determine an abnormal operation of the switching valve 34.

  (3) Further, when an abnormal operation of the switching valve 34 is detected, the maximum fuel injection amount in the low fuel pressure state in which the target fuel injection amount TAU calculated based on the required load KL is set for each engine speed NE. If it is greater than T720, the throttle valve 15 is driven and controlled to limit the intake air amount GA. As a result, the intake air amount GA can be easily limited by using the throttle valve 15, and combustion in a lean state of the air-fuel mixture caused by a decrease in the fuel injection amount is avoided, so that the exhaust purification catalyst is exhausted. An excessive temperature rise of 19a can be suppressed, and as a result, deterioration of the exhaust purification catalyst 19a can be suppressed.

In addition, you may change the said embodiment as follows.
In the above embodiment, a port injection type internal combustion engine that injects fuel into the intake port of the internal combustion engine has been described as an example. However, the fuel pressure state of the fuel in the delivery pipe to which the fuel injection valve is connected is used as a switching valve. If the internal combustion engine is configured to be switched, the same effect as the above effect or an effect equivalent thereto can be obtained even with a direct injection type internal combustion engine that injects fuel directly into the cylinder.

  In the above embodiment, the intake air amount GA is limited by adjusting the throttle opening degree TA of the throttle valve 15 serving as the intake air amount control means. For example, the intake air amount GA may be limited by a variable intake system having a variable intake pipe length, a variable valve timing system having a variable valve opening phase or operating angle, and a throttle valve A combination with a valve or the like can be used as the intake air amount control means to limit the intake air amount GA. According to such a configuration, the intake air amount GA can be further accurately limited.

  In the above embodiment, when the switching valve 34 is normally open and the high fuel pressure flag is ON, fuel in the low fuel pressure state is injected in a short valve opening period based on the high fuel pressure state. AF always has a value indicating lean. Therefore, in diagnosing the abnormality of the switching valve 34, the air-fuel ratio AF (value indicating lean) when the switching valve 34 is abnormal is provided as a threshold, and the high fuel pressure flag is ON. It may be determined whether or not the fuel ratio AF is equal to or greater than the threshold value. Alternatively, the difference between the air-fuel ratio AF (a value indicating lean) when the switching valve 34 is abnormal and the target air-fuel ratio AFT is provided as a threshold value, and the air-fuel ratio AF is set on the condition that the high fuel pressure flag is ON. It may be determined whether the difference from the target air-fuel ratio AFT is equal to or greater than the threshold value. That is, in the above embodiment, the ratio between the air-fuel ratio AF and the target air-fuel ratio AFT is used as a discriminating value. However, in diagnosing the presence or absence of an abnormality in the switching valve 34, the difference between the air-fuel ratio AF and the target air-fuel ratio AFT. Can also be used as a discrimination value.

In each of the above embodiments, the example in which the set fuel pressure FP is switched to the two stages of the second pressure Ph and the first pressure Pl is shown, but the stage of the set fuel pressure FP is not limited to two stages, Fuel pressure switching means for switching to many stages may be provided. Moreover, about the installation location etc. of the switching valve 34 etc. in a fuel pressure switching means, you may employ | adopt not only the example mentioned above but the structure shown by FIGS.

  In FIG. 6, a high pressure return passage 141 having a high pressure regulator 142 that opens at the second pressure Ph or higher is branched from the main passage 120 and connected to the fuel tank 20 and opened at the first pressure Pl or higher. A low pressure return passage 143 having a low pressure regulator 144 to be connected is connected from the delivery pipe 32 to the fuel tank 20. A switching valve 140 that switches between opening and closing of the low pressure return passage 143 according to the engine operating state is provided in the low pressure return passage 143.

  In FIG. 7, a high-pressure return passage 241 having a high-pressure regulator 242 that opens at a pressure equal to or higher than the second pressure Ph branches from the main passage 120 and is connected to the fuel tank 20, and opens at a pressure higher than the first pressure Pl. A low pressure return passage 243 having a low pressure regulator 244 to be branched branches from the main passage 120 and is connected to the fuel tank 20. A switching valve 240 that switches between opening and closing of the low pressure return passage 243 according to the engine operating state is provided in the low pressure return passage 243.

  Even in these configurations, when the low pressure return passages 143 and 243 are closed by the switching valves 140 and 240, the fuel pressure in the delivery pipe 32 is regulated by the high pressure regulators 142 and 242, so that the relatively high set fuel pressure is obtained. The second pressure Ph that is FP is maintained. Further, when the low pressure return passages 143 and 243 are opened by the switching valves 140 and 240, the fuel pressure in the delivery pipe 32 is regulated by the low pressure regulators 144 and 244 so that the first set fuel pressure FP is relatively low. Maintained at pressure Pl. Therefore, an effect similar to the above effect or an effect equivalent thereto can be obtained.

  In FIG. 8, a high-pressure return passage 341 having a high-pressure regulator 342 that opens at the second pressure Ph or higher is connected from the delivery pipe 32 to the fuel tank 20, and a low pressure that opens at the first pressure Pl or higher. A low-pressure return passage 343 having a regulator 344 branches from the main passage 120 and is connected to the fuel tank 20. Further, an intermediate pressure return passage 345 having an intermediate pressure regulator 346 that opens at a third pressure Pm between the second pressure Ph and the first pressure Pl is branched from the main passage 120 to the fuel tank 20. Connected. A first switching valve 340 a that switches between opening and closing of the low pressure return passage 343 and a second switching valve 340 b that switches between opening and closing of the intermediate pressure return passage 345 are provided in the low pressure return passage 343 and the intermediate pressure return passage 345. It is done.

  According to such a configuration, the first switching valve 340a and the second switching valve 340b are switched in accordance with the engine operating state, whereby three stages of the second pressure Ph, the first pressure Pl, and the third pressure Pm. The set fuel pressure FP can be switched to. During engine operation in which the third pressure Pm is the set fuel pressure FP, the fuel pressure state corresponding to the second pressure Ph is defined as a low fuel pressure state, and the fuel pressure state corresponding to the third pressure Pm is defined as a high fuel pressure state. Thus, the abnormality of the first switching valve 340a can be diagnosed. Further, during engine operation in which the third pressure Pm is the set fuel pressure FP, the fuel pressure state corresponding to the third pressure Pm is defined as a low fuel pressure state, and the fuel pressure state corresponding to the first pressure Pl is defined as a high fuel pressure state. By doing so, the abnormality of the second switching valve 340b can be diagnosed. The combustion stability and exhaust properties can be improved by restricting the intake air amount GA according to the switching valve determined to be abnormal.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the control apparatus of the internal combustion engine which actualized this invention with the periphery structure. The flowchart for demonstrating the control routine of the switching valve diagnostic process in this embodiment. The flowchart for demonstrating the control routine of the intake air amount restriction | limiting control in this embodiment. The graph showing the relationship between the engine speed in this embodiment and the maximum fuel injection amount. The graph which shows the relationship between the engine speed in this embodiment, and an upper limit throttle opening. The schematic block diagram shown about the modification of the fuel pressure switching means concerning this invention. The schematic block diagram shown about the other modification of the fuel pressure switching means concerning this invention. The schematic block diagram shown about the other modification of the fuel pressure switching means concerning this invention.

Explanation of symbols

  ACCP ... Accelerator operation amount, AF ... Air fuel ratio, AFT ... Target air fuel ratio, FL ... Fuel amount, FP ... Set fuel pressure, GA ... Intake air amount, KL ... Required load, KALC ... Concentration learning value, NE ... Engine speed, Pl ... first pressure, Ph ... second pressure, TA ... throttle opening, TAL ... upper throttle opening, TAT ... target throttle opening, TAU ... fuel injection amount, TAUB ... basic fuel injection amount, T720 ... maximum Fuel injection amount, 10 ... Internal combustion engine, 11 ... Cylinder, 12 ... Piston, 13 ... Combustion chamber, 14 ... Intake passage, 14a ... Intake port, 15 ... Throttle valve, 16 ... Throttle valve actuator, 17 ... Fuel injection valve, 18 DESCRIPTION OF SYMBOLS ... Spark plug, 19 ... Exhaust passage, 19a ... Exhaust purification catalyst, 20 ... Fuel tank, 21 ... Fuel pump, 22 ... Battery, 23 ... Filter, 30 ... Main passage 31 ... Low pressure return passage, 32 ... Delivery pipe, 33 ... Low pressure regulator, 34 ... Switching valve, 35 ... High pressure return passage, 36 ... High pressure regulator, 41 ... Throttle opening sensor, 42 ... Rotational speed sensor, 43 ... Accelerator position sensor , 44 ... intake air amount sensor, 45 ... fuel amount sensor, 46 ... air-fuel ratio sensor, 50 ... electronic control unit, 120, 220, 320 ... main passage, 140, 240 ... switching valve, 141, 241, 341 ... high pressure return Passage, 142, 242, 342 ... high pressure regulator, 143, 243, 343 ... low pressure return passage, 144, 244, 344 ... low pressure regulator, 340a ... first switching valve, 340b ... second switching valve, 345 ... medium pressure return passage 346: Medium pressure regulator.

Claims (5)

The fuel stored in the fuel tank of the internal combustion engine is pumped to the fuel injection mechanism, and the fuel pressure in the fuel injection mechanism is changed by a switching valve that can change the fuel flow path between the fuel tank and the fuel injection mechanism. Fuel pressure switching means for switching between a first pressure and a second pressure higher than the first pressure;
An intake air amount control means for controlling an intake air amount to the internal combustion engine,
The fuel pressure in the fuel injection mechanism is selected based on the operating state of the internal combustion engine so that the air-fuel ratio in the internal combustion engine becomes the target air-fuel ratio, and the fuel injection mechanism of the fuel injection mechanism is selected according to the injection period corresponding to the selected fuel pressure. A control device for an internal combustion engine for controlling a fuel injection amount,
A control device for an internal combustion engine, wherein when the second pressure is selected, the intake air amount to the internal combustion engine is limited if switching to the second pressure is impossible. When the second pressure is selected, it is impossible to switch to the second pressure on the condition that the degree of deviation between the air-fuel ratio and the target air-fuel ratio in the internal combustion engine is equal to or greater than a specified value. The control device for an internal combustion engine according to claim 1. In the case where switching to the second pressure is impossible, the fuel injection amount of the fuel injection mechanism is larger than the maximum fuel injection amount that is the maximum fuel injection amount that can be injected at the first pressure. The control device for an internal combustion engine according to claim 1 or 2, wherein an intake air amount to the internal combustion engine is limited. The control device for an internal combustion engine according to claim 2 or 3, wherein the degree of deviation is a ratio of an air-fuel ratio in the internal combustion engine and the target air-fuel ratio. The fuel pressure switching means is
A main passage connecting the fuel tank and the fuel injection mechanism;
A low pressure return passage formed by branching from the main passage and returning the fuel in the main passage to the fuel tank;
A low pressure regulator that is provided in the low pressure return passage and opens when the fuel pressure in the low pressure return passage is equal to or higher than the first pressure, and discharges fuel to the fuel tank side;
A high-pressure return passage connected to the fuel injection mechanism and returning the fuel in the fuel injection mechanism to the fuel tank;
A high-pressure regulator that is provided in the high-pressure return passage and opens when the fuel pressure in the high-pressure return passage is equal to or higher than the second pressure, and discharges fuel to the fuel tank side,
The control device for an internal combustion engine according to any one of claims 1 to 4, wherein the switching valve switches between opening and closing of the low-pressure return passage.

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