JP3558453B2 - Fuel system diagnostic device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel system diagnostic device for an internal combustion engine that uses a relatively high-pressure fuel pump to inject fuel directly into a combustion chamber.
[0002]
[Prior art]
In recent years, even in a spark ignition type engine such as a gasoline engine, a system in which an injection hole of a fuel injection valve is installed facing a combustion chamber and fuel is directly injected into the combustion chamber by the fuel injection valve has been studied. According to the spark ignition type direct injection internal combustion engine, deterioration of transient operation characteristics and deterioration of exhaust composition due to fuel transport delay can be suppressed as compared with a premixed spark ignition engine having a fuel injection valve at an intake port. There is an advantage.
[0003]
In this type of engine, a high-pressure fuel pump is provided in the middle of a fuel supply passage as a method of increasing the fuel injection pressure in order to enhance the atomization effect of the fuel (see Japanese Patent Application Laid-Open No. 5-321783).
[0004]
[Problems to be solved by the invention]
Incidentally, diagnosis of a fuel system having a high-pressure fuel pump as described above has not been conventionally performed. However, when NG is generated in the fuel system for supplying the high-pressure fuel, the fuel system for supplying the fuel at a low pressure is used. The problem is greater than when NG occurred.
The present invention has been made in view of such a conventional problem, and has as its object to accurately perform NG diagnosis of the fuel pump.
[0005]
It is another object of the present invention to perform fail-safe when there is a possibility that the fuel pump is NG.
[0006]
For this reason, the invention according to claim 1 is, as shown in FIG.
In an internal combustion engine in which fuel discharged at a low pressure from a first fuel pump is sucked and fuel discharged at a high pressure from a second fuel pump is directly injected from a fuel injection valve into a combustion chamber of the engine,
Fuel pressure detecting means for detecting a fuel pressure in a high-pressure fuel system from the second fuel pump to a fuel injection valve;
High-pressure state detection means for detecting a state in which the discharge pressure of the second fuel pump becomes a high pressure equal to or higher than a set value according to an engine operation state ;
When a state in which the discharge pressure of the second fuel pump becomes a high pressure equal to or higher than the set value is detected for a predetermined period or more, the diagnosis of the high-pressure fuel system is performed based on the fuel pressure detected by the fuel pressure detecting means. Diagnostic means to perform;
A bypass passage for returning fuel discharged from the second fuel pump to a low-pressure source by bypassing a fuel injection valve, a normally-closed on-off valve interposed in the bypass passage, and discharge of the second fuel pump; Control means for opening the on-off valve to release the pressure increase of the fuel in the high-pressure fuel system when it is diagnosed that there is a possibility that the pressure does not become higher than the set value. When,
Is characterized by comprising.
[0007]
(Action / Effect)
More said high pressure detecting means, the engine operating state, when the state in which the discharge pressure of the second fuel pump is more than the set value of the high pressure is detected above a predetermined period, detecting the diagnosis means by said fuel pressure detecting means Diagnosis of the fuel system is performed based on the detected fuel pressure.
Then, when it is diagnosed that there is a possibility that the discharge pressure of the second fuel pump does not reach a high pressure equal to or higher than a set value , the on-off valve is opened, whereby the fuel discharged from the second fuel pump is opened. Is returned to the low-pressure source via the bypass passage, so that the pressure increase in the high-pressure fuel system is released.
Further, according to the invention of claim 2, as shown in FIG.
In an internal combustion engine in which fuel discharged at a low pressure from a first fuel pump is sucked and fuel discharged at a high pressure from a second fuel pump is directly injected from a fuel injection valve into a combustion chamber of the engine,
Fuel pressure detecting means for detecting a fuel pressure in a high-pressure fuel system from the second fuel pump to a fuel injection valve;
High-pressure state detection means for detecting a state in which the discharge pressure of the second fuel pump becomes a high pressure equal to or higher than a set value according to an engine operation state ;
When a state in which the discharge pressure of the second fuel pump is higher than the set value is detected for a predetermined period or more, the fuel system is diagnosed based on the fuel pressure detected by the fuel pressure detecting means. Diagnostic means;
When it is diagnosed that there is a possibility that the normally open on-off valve interposed in the fuel intake passage of the second fuel pump and the NG in which the discharge pressure of the second fuel pump does not become higher than the set value. Control means for closing the on-off valve, a fail-safe means comprising:
Is characterized by comprising.
(Action / Effect)
In the same manner as in the first aspect of the present invention, when it is diagnosed that there is a possibility that the discharge pressure of the second fuel pump does not become higher than the set value due to NG, the on-off valve of the fuel suction passage is closed. When the intake of fuel to the second fuel pump is shut off, the pressure increase of the fuel in the high-pressure fuel system is released.
[0008]
Also, in the invention according to claim 3, the second fuel pump is driven by an engine, and the high-pressure state detecting means determines that the state in which the high pressure occurs when the engine speed is equal to or higher than a predetermined idle speed is equal to or longer than a predetermined period. Is detected.
(Action / Effect)
When the engine rotation speed becomes equal to or higher than the predetermined idle rotation speed, it is possible to detect that the discharge pressure of the second fuel pump driven by the engine is sufficiently increased and the pressure is higher than the set value.
[0009]
Further, according to a fourth aspect of the present invention, the diagnosing means may include a step in which the fuel system detects NG when the fuel pressure experiences a state in which the fuel pressure falls below a set value of the discharge pressure of the second fuel pump for a set time or more during a predetermined time. Diagnose the possibility of
(Action / Effect)
It is possible to accurately diagnose that the state where the fuel pressure is continuously reduced due to the occurrence of NG in the fuel system by examining whether the user has experienced a state where the fuel pressure has fallen below the set pressure for a set time or more during a predetermined time. it can.
[0010]
Further, the invention according to claim 5 is characterized in that the diagnosis means performs the diagnosis in a period except during fuel injection of the fuel injection valve.
(Action / Effect)
During the fuel injection from the fuel injection valve, the fuel pressure in the fuel system temporarily decreases, so that the diagnosis is performed in a period other than the fuel injection period, thereby improving the diagnosis accuracy.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 2 shows an overall system configuration according to an embodiment of the present invention.
In FIG. 2, the engine 1 has an electromagnetic fuel injection valve 2 arranged with its injection hole facing the combustion chamber 3, and suctioned into the combustion chamber 3 through an intake port 4 and an intake valve 5. This is a spark-ignition direct-injection engine in which fuel is injected from the fuel injection valve 2 to form air-fuel mixture, and the air-fuel mixture is ignited by spark ignition by a spark plug 6.
[0016]
The exhaust gas of the engine 1 is discharged from the fuel chamber 3 through an exhaust valve 7 and an exhaust port 8, and is discharged into the atmosphere through an exhaust purification catalyst and a muffler (not shown).
After the fuel in the fuel tank 9 is discharged at a relatively low pressure by the first fuel pump 10 and filtered by the filter 12 provided in the low-pressure fuel passage 11A, the low-pressure side downstream of the filter 12 is filtered. The fuel adjusted to a constant low pressure by the low-pressure regulator 13 provided by-passing the fuel passage 11B is sent to the high-pressure second fuel pump 14.
[0017]
The high-pressure second fuel pump 14 is driven directly by a crankshaft or a camshaft of the engine 1 or indirectly via a gear or a belt, and pressurizes and discharges the low-pressure fuel to a high pressure. The fuel discharged from the second pump 14 is adjusted to a high-pressure constant fuel pressure by a high-pressure regulator 16 provided in the high-pressure side fuel passage 15 in a bypass manner.
The fuel injection valve 2 is controlled to open in response to a pulse signal of a predetermined width corresponding to the engine operating state sent from the control unit 17 containing a microcomputer at a predetermined injection timing, and the fuel adjusted to the predetermined fuel pressure is provided. Is injected into the combustion chamber 3.
[0018]
The control unit 17 includes a crank angle sensor 18 for detecting the engine rotation speed and also for detecting the rotation speed of the second fuel pump 14 for the fuel injection control, and an air flow meter for detecting the intake air flow rate. 19. Detection signals from various sensors such as a fuel pressure sensor 20 as a fuel pressure detecting means for detecting the fuel pressure in the high-pressure side fuel passage 15 are input.
[0019]
Here, the control unit 17 controls the pulse width of the injection pulse signal and controls the output start timing of the injection pulse signal, that is, the fuel injection period by the fuel injection valve 2.
Further, a bypass passage 21 branching from the discharge port of the second fuel pump 14 and the high-pressure side fuel passage 15 to reach the fuel tank 9 as a low-pressure source is provided, and in the middle of the bypass passage 21. An on-off valve 22 is interposed. The on-off valve 22 is normally closed, and is opened when the control unit 17 diagnoses that there is a possibility of NG in the fuel system as will be described later, and opens the fuel discharged from the second fuel pump 14. By returning the fuel injection valve 2 to the fuel tank 9 through the bypass passage, the increase in the fuel pressure in the high-pressure side fuel passage 15 is released.
[0020]
In such a system configuration, the fuel system diagnosis routine will be described with reference to the flowchart of FIG.
In step 1, the fuel pressure Pss detected by the fuel pressure sensor 20 and the engine speed Ne calculated by the signal from the crank angle sensor 18 are read.
[0021]
In step 2, it is determined whether or not the engine speed Ne has reached a predetermined idle speed Ni or higher. Here, when the engine speed is equal to or higher than the idle rotation speed Ni, the discharge pressure of the second fuel pump 14 driven by the engine is sufficiently increased, and if the fuel system is normal, the fuel pressure becomes the set fuel pressure Ph regulated by the high-pressure regulator 16. Has reached. The function of step 2 constitutes a high pressure state detecting means.
[0022]
When it is determined that the engine rotation speed Ne is equal to or higher than the idle rotation speed Ni and the discharge pressure of the second fuel pump 14 is sufficiently high, the routine proceeds to step 3. In step 3, it is determined whether or not the fuel injection period from the fuel injection valve 2 is in progress.
If it is determined that the fuel pressure is not during the fuel injection period, the routine proceeds to step 4, where the fuel pressure Pss is set at a predetermined fuel pressure Ph (or a fuel pressure obtained by subtracting ΔP therefrom) regulated by the high-pressure regulator 16 during a predetermined time. It is determined whether or not the engine has experienced the state of falling below a predetermined time, and if it has, the procedure proceeds to step 5 and the NG flag is set to 1 because there is a possibility that NG has occurred in the fuel system. The fact that there is a possibility is indicated by lighting a MIL (lamp) or the like.
[0023]
The initial value of the NG flag is reset to 0. After the NG flag is set to 1 once, it is reset when it is confirmed that the possibility of NG is eliminated by repairing the fuel system or the like. Until the set state is maintained. Alternatively, a configuration may be adopted in which diagnosis is performed periodically and reset when the possibility of NG is denied.
[0024]
After the diagnosis result is obtained, the process proceeds to step 6.
On the other hand, when it is determined in step 2 that the engine speed Ne is lower than the idle speed Ni, in step 3 when it is determined that the fuel injection period is in progress, and in step 4, the experience time of the low fuel pressure state during the predetermined time period Is shorter than the set time, the process proceeds directly to step 6.
[0025]
In step 6, the value of the NG flag is determined.
When it is determined that the NG flag is set to 1, that is, when it is diagnosed that there is a possibility of NG in the fuel system, the routine proceeds to step 7, where the on-off valve 22 provided in the bypass passage 21 is opened. Is opened to return the fuel discharged from the fuel pump 14 into the fuel tank 9 bypassing the fuel injection valve 2. As a result, even when NG occurs in the fuel system, it is possible to cancel the increase in the fuel pressure in the high-pressure side fuel passage 15.
[0026]
When it is determined in step 7 that the NG flag has been reset to 0, the fuel system has been diagnosed to be normal, so that the on-off valve 22 is kept closed to maintain high-pressure fuel injection.
With this configuration, if the engine speed Ne is equal to or higher than the predetermined idle speed Ni and the fuel system is normal, the fuel pressure in the fuel system (in the high-pressure side fuel passage 15) becomes high and the fuel When the state in which the fuel pressure falls below the set fuel pressure Ph for more than the set time within the predetermined time excluding the injection period continues, a diagnosis that the fuel system may be NG is made and displayed. A highly accurate diagnosis is performed, and a fail-safe function of canceling an increase in fuel pressure in the fuel system when it is determined that there is a possibility of NG can be obtained.
[0027]
FIG. 4 shows the state of the engine speed Ne after startup and the fuel pressure in the high-pressure side fuel passage 15. When the engine speed Ne after startup becomes equal to or higher than a predetermined idle speed Ni, the fuel pressure is normal when the fuel system is normal. Reaches the set fuel pressure Ph (for example, 5 MPa) regulated by the high-pressure regulator 16, it becomes possible to start diagnosis of the fuel system. However, when the fuel pressure state is shown in an enlarged manner, during the fuel injection period (during generation of the pulse Ti), Since the fuel pressure temporarily drops, the diagnosis accuracy can be improved by stopping the diagnosis during this period.
[0028]
Further, in the present embodiment, the fail-safe means is constituted by the bypass passage 21, the on-off valve 22, and the control mechanism of the on-off valve 22, but as shown by a dashed line in FIG. When a normally open on-off valve 31 is interposed in the middle of the low-pressure side fuel passage 11A (or 11B), which is an intake passage, and the control unit 17 diagnoses that there is a possibility that the fuel system is NG, The on-off valve 31 may be configured to be closed, and the intake of fuel to the second fuel pump 14 is shut off, so that the increase in the fuel pressure in the high-pressure side fuel passage 15 can be released.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration and functions of the present invention.
FIG. 2 is a diagram showing an overall system configuration according to an embodiment of the present invention.
FIG. 3 is a flowchart showing a fuel system diagnosis routine of the embodiment.
FIG. 4 is a time chart showing a fuel pressure state after the engine is started.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel injection valve 3 Combustion chamber 11A, 11B Low pressure side fuel passage 14 Second fuel pump 15 High pressure side fuel passage 17 Control unit 18 Crank angle sensor 20 Fuel pressure sensor 21 Bypass passage 22 Open / close valve 31 Open / close valve

Claims (5)

In an internal combustion engine in which fuel discharged at a low pressure from a first fuel pump is sucked and fuel discharged at a high pressure from a second fuel pump is directly injected from a fuel injection valve into a combustion chamber of the engine,
Fuel pressure detecting means for detecting a fuel pressure in a high-pressure fuel system from the second fuel pump to a fuel injection valve;
High-pressure state detection means for detecting a state in which the discharge pressure of the second fuel pump becomes a high pressure equal to or higher than a set value according to an engine operation state ;
When a state in which the discharge pressure of the second fuel pump becomes a high pressure equal to or higher than the set value is detected for a predetermined period or more, the diagnosis of the high-pressure fuel system is performed based on the fuel pressure detected by the fuel pressure detecting means. Diagnostic means to perform;
A bypass passage for returning fuel discharged from the second fuel pump to a low-pressure source by bypassing a fuel injection valve, a normally-closed on-off valve interposed in the bypass passage, and discharge of the second fuel pump; Control means for opening the on-off valve to release the pressure increase of the fuel in the high-pressure fuel system when it is diagnosed that there is a possibility that the pressure does not become higher than the set value. When,
A fuel system diagnostic device for an internal combustion engine, comprising: In an internal combustion engine in which fuel discharged at a low pressure from a first fuel pump is sucked and fuel discharged at a high pressure from a second fuel pump is directly injected from a fuel injection valve into a combustion chamber of the engine,
Fuel pressure detecting means for detecting a fuel pressure in a high-pressure fuel system from the second fuel pump to a fuel injection valve;
High-pressure state detection means for detecting a state in which the discharge pressure of the second fuel pump becomes a high pressure equal to or higher than a set value according to an engine operation state ;
When a state in which the discharge pressure of the second fuel pump is higher than the set value is detected for a predetermined period or more, the fuel system is diagnosed based on the fuel pressure detected by the fuel pressure detecting means. Diagnostic means;
When it is diagnosed that there is a possibility that the normally open on-off valve interposed in the fuel intake passage of the second fuel pump and the NG in which the discharge pressure of the second fuel pump does not become higher than the set value. Control means for closing the on-off valve, a fail-safe means comprising:
A fuel system diagnostic device for an internal combustion engine, comprising: The second fuel pump is driven by an engine,
3. The high-pressure state detecting means according to claim 1, wherein the high-pressure state detecting means detects a state where the engine is at a high pressure when the engine speed is equal to or higher than a predetermined idle speed, but is equal to or longer than a predetermined period. A fuel system diagnostic device for an internal combustion engine according to the above. The diagnosis means diagnoses that there is a possibility of NG in the fuel system when the fuel pressure experiences a state in which the fuel pressure falls below a set value of the discharge pressure of the second fuel pump for a set time or more during a predetermined time. The fuel system diagnostic device for an internal combustion engine according to any one of claims 1 to 3, wherein: 5. The fuel system diagnostic device for an internal combustion engine according to claim 1, wherein the diagnostic unit performs the diagnostic during a period excluding during fuel injection of a fuel injection valve. 6.

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