JP4222097B2 - Fuel system diagnostic device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for diagnosing the presence or absence of an abnormality in a fuel system of an internal combustion engine that performs feedback control of fuel discharge pressure while variably controlling the fuel discharge amount of a fuel pump according to a required fuel injection amount from a fuel injection valve.
[0002]
[Prior art]
Japanese Laid-Open Patent Publication No. 10-176589 discloses a fuel system having a variable displacement high-pressure fuel pump that feedback-controls fuel discharge pressure (hereinafter simply referred to as fuel pressure) while variably controlling the fuel discharge amount of the fuel pump as described above. There is something that was done.
[0003]
When diagnosing such an abnormality in the fuel system, a conventional diagnosis method based on the correspondence between the fuel discharge amount and the fuel pressure is adopted, and it is diagnosed that there is an abnormality when the fuel pressure deviates from the normal range with respect to the fuel discharge amount. be able to.
[0004]
[Problems to be solved by the invention]
However, in the above conventional diagnostic method, the fuel pressure is determined by the flow rate balance between the fuel discharge amount from the fuel pump and the fuel injection amount from the fuel injection valve, so the fuel pressure range determined from the normal flow range is very wide, Since the fuel pressure range that can be diagnosed as abnormal is very narrow, good diagnostic accuracy could not be obtained.
[0005]
The present invention has been made paying attention to such a conventional problem, and as described above, a diagnostic apparatus capable of highly accurately diagnosing a fuel system that feedback controls the fuel pressure while variably controlling the fuel discharge amount of the fuel pump. The purpose is to provide.
[0006]
[Means for Solving the Problems]
For this reason, the present invention provides a difference between the fuel discharge amount from the fuel pump and the fuel injection amount from the fuel injection valve in the diagnosis of the presence or absence of abnormality in the fuel system of the internal combustion engine that feedback-controls the fuel discharge pressure as described above. However, when the required fuel injection amount is larger, the configuration is such that an abnormality is diagnosed when the predetermined fuel injection amount is greater than a predetermined value .
[0007]
In this way, the determination value for discriminating between the normal range and the abnormal range of the fuel discharge amount of the fuel pump can be set separately for each engine operating state (required fuel injection amount). improves.
In addition, since the predetermined value is set larger as the fuel injection amount is larger, an easy and highly accurate diagnosis can be performed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the configuration of a fuel system of a direct injection type internal combustion engine equipped with a high-pressure fuel pump according to the present invention.
[0009]
The fuel discharged from the electric low-pressure fuel pump (feed pump) 2 disposed in the fuel tank 1 passes through the fuel filter 3 and the low-pressure pressure regulator 4 to a predetermined low pressure (about 0.3 to 0.5 MPa). Then, the pressure is fed to the high-pressure fuel pump 6 through the low-pressure fuel passage 5, pressurized to a high pressure by the engine-driven high-pressure fuel pump 6, and supplied to the fuel injection valve 8 through the high-pressure fuel passage 7. A fuel pressure sensor 9 is interposed in the high pressure fuel passage 7, and a fuel pressure signal detected by the fuel pressure sensor 9 is output to the control unit 10. In addition to this, the control unit 10 includes a signal from the crank angle sensor 11 that detects the engine rotational speed Ne, a cylinder discrimination signal from the cylinder discrimination signal sensor 12, an accelerator opening sensor 13 that detects the accelerator opening, A signal from the air flow meter 14 for detecting the intake air flow rate Qa is input.
[0010]
In the high-pressure fuel pump 6, the discharge amount from the pump body 6 b is variably controlled by the electromagnetic control valve 6 a according to a signal from the control unit 10, and is adjusted to an arbitrary high pressure (about 3 to 15 MPa).
[0011]
In this fuel system, the fuel pressure is feedback-controlled by the flow rate balance between the fuel discharge amount of the high-pressure fuel pump 6 and the fuel injection amount of the fuel injection valve 8, so the control factor of the fuel pressure feedback control is that of the high-pressure fuel pump 6. Discharge amount. When the actual fuel pressure detected by the fuel pressure sensor 9 is lower than the target fuel pressure, the fuel pressure of the high-pressure fuel pump 6 is increased so that the fuel pressure is increased until the target fuel pressure is reached, and the actual fuel pressure is higher than the target fuel pressure. In this case, conversely, the fuel discharge amount of the high-pressure fuel pump 6 is reduced and the fuel pressure is controlled to decrease until the target fuel pressure is reached.
[0012]
Actually, in addition to the fuel discharge amount of the high-pressure fuel pump 6 and the fuel injection amount of the fuel injection valve 8, the fuel pressure of the high-pressure system depends on the volume elastic modulus of the fuel, the rigidity of the high-pressure fuel passage (pipe) 7, and the volume of the high-pressure portion. Is determined.
[0013]
The suction / discharge of the high-pressure fuel pump 6 is performed by a pump drive cam connected to the camshaft of the engine, and is driven by the number of engine cylinders or half the number of cylinders per one rotation of the cam.
[0014]
In the intake stroke of the high-pressure fuel pump 6, the low-pressure fuel pumped from the fuel tank 1 is sucked in by the pump stroke volume, and then the electromagnetic valve 6 a is closed at an arbitrary timing in the discharge stroke so that the pump chamber is opened at a low pressure upstream side. Is cut off to start pressurizing the fuel and pump it to the high-pressure fuel passage 7.
[0015]
The required discharge amount of the high-pressure fuel pump 6 is calculated based on the target fuel pressure and the fuel injection amount, and the engine rotational speed detected by the crank angle sensor 11 and the pump drive cam phase detected by the cylinder discrimination signal from the cylinder discrimination sensor 12. The closing operation timing of the electromagnetic control valve 6a is controlled.
[0016]
FIG. 2 shows a flowchart of a routine for calculating the required discharge amount Q of the high-pressure fuel pump 6.
In step 11, various signals of the engine operating state are read. Specifically, the engine rotational speed Ne detected by the crank angle sensor 11, the intake air flow rate Qa detected by the air flow meter 14, the actual fuel pressure P detected by the fuel pressure sensor 9, and the accelerator opening sensor 13 are detected. The accelerator opening Acc and other values necessary for calculating the required discharge amount Q of the high-pressure fuel pump 6 are read.
[0017]
In step 12, an engine load (target torque) T is calculated from the accelerator opening Acc or the like.
In step 13, the target fuel pressure Pt of the high-pressure fuel pump 6 is calculated from the map shown in FIG. 3 based on the engine speed Ne and the engine load T. Specifically, the higher the engine speed Ne and the engine load T, the higher the target fuel pressure Pt is set.
[0018]
In step 14, the fuel injection amount Qi of the fuel injection valve 8 is calculated from the map shown in FIG. 4 based on the engine speed Ne and the engine load T. Specifically, the fuel injection amount Qi is set to a larger value as the engine speed Ne and the engine load T are higher.
[0019]
In step 15, the difference Pcal between the target fuel pressure Pt calculated in step 13 and the actual fuel pressure P detected by the fuel pressure sensor 9 is calculated as follows:
Pcal = Pt−P
In step 16, the discharge amount correction value Qh of the high-pressure fuel pump 6 is calculated as follows based on the pressure difference Pcal.
[0020]
Qh = Pcal · K
K: Fuel pressure feedback gain (constant)
In step 17, the discharge amount correction value Qh is added to the basic discharge amount Qbas of the high-pressure fuel pump 6 calculated from the map shown in FIG. 5 based on the engine speed Ne and the fuel injection amount Qi, and the required discharge is obtained. The quantity Q is calculated as follows:
[0021]
Q = Qbas + Qh
In this way, the fuel pressure is feedback-controlled while the fuel discharge amount of the high-pressure fuel pump 6 is variably controlled so as to be the required discharge amount Q.
[0022]
Further, the control unit 10 executes diagnosis according to the present invention for accurately diagnosing abnormality (failure) of the fuel system.
Hereinafter, a diagnosis embodiment according to the present invention will be described with reference to the flowchart shown in FIG.
[0023]
In step 1, diagnosis is started when the diagnosis start condition is satisfied. Here, the diagnosis start condition will be described.
As described above, the fuel feedback control is performed by variably adjusting the fuel discharge amount of the high-pressure fuel pump 6 with respect to the required fuel supply amount calculated from the target fuel pressure and the required fuel injection amount. That is, when the fuel injection amount and the fuel discharge amount are 1: 1, the flow rate balance is balanced and the fuel pressure is kept constant. When increasing the fuel pressure, the discharge amount of the high-pressure fuel pump 6 is temporarily increased, and the discharge amount is controlled to return to the flow rate balance = 1: 1 when the target fuel pressure is reached. The opposite is true when lowering fuel pressure.
[0024]
Here, when the signal system for calculating the fuel discharge amount of the high-pressure fuel pump 6 such as the fuel pressure sensor 9, the crank angle sensor 11 and the cylinder discrimination sensor 12 is abnormal, or when the fuel pressure is unstable immediately after the engine is started, Since normal fuel pressure control cannot be performed, fuel pressure feedback control is stopped.
[0025]
Therefore, the diagnosis start condition based on the flow rate balance according to the present invention is based on the premise that the fuel pressure feedback control is being performed, and when the diagnosis start condition is satisfied, the process proceeds to step 2 to perform the first diagnosis based on the flow rate balance. Start.
[0026]
The first diagnosis based on the flow rate balance refers to a map in which an NG region and an OK region are set as shown in FIG. 7 based on the fuel discharge amount of the high-pressure fuel pump 6 and the fuel injection amount of the fuel injection valve 8. The determination is made by determining which of the NG area and the OK area it belongs to. Here, the NG region and the OK region can ensure the required fuel injection amount by converging the actual fuel pressure to the target fuel pressure within a normal fuel discharge amount increase / decrease range so that the first diagnosis based on the flow rate balance is possible. In some cases, the OK region is determined, and in other cases, the NG region is determined in consideration of component variations, performance deterioration, and environmental condition changes (fuel properties, fuel temperature, etc.).
[0027]
In step 3, it is determined whether or not it belongs to the NG area by the first diagnosis in step 2, and if it is determined that it belongs to the NG area, the diagnosis that the first diagnosis is abnormal in step 4 is made. Go to step 6.
[0028]
Further, if it is determined in step 3 that the fuel does not belong to the NG region in the first diagnosis but belongs to the OK region, the fuel discharge amount of the high-pressure fuel pump 6 is reduced to the minimum value MIN or the maximum value MAX in step 5. If it is determined that there is no sticking, the current state is that the first diagnosis result is normal (OK), that is, the fuel system is normal. The first diagnosis is continued in preparation for a change in state.
[0029]
If it is determined in step 5 that the fuel discharge amount of the high-pressure fuel pump 6 is stuck to the minimum value MIN or the maximum value MAX, the process proceeds to step 6.
In step 6, the second diagnosis based on the fuel pressure is started. Specifically, the target fuel pressure and the actual fuel pressure are compared, and the diagnosis is made based on the deviation (absolute value) between the two.
[0030]
That is, in step 7, it is determined whether the deviation (absolute value) between the target fuel pressure Pt and the actual fuel pressure P is greater than or equal to a predetermined value ΔP. Here, the predetermined value ΔP for determination is set to a value larger than the dead band width in the variable control of the fuel discharge pressure, specifically, set to about ± 0.3 to 0.5 MPa.
[0031]
When the deviation is determined to be less than the predetermined value ΔP, the process returns to step 2 to continue the first diagnosis. When the deviation is determined to be equal to or larger than the predetermined value ΔP, the process proceeds to step 8 and the deviation is It is determined whether or not the state of more than a predetermined value ΔP has continued for a predetermined time T or longer.
[0032]
If it is determined in step 8 that the state equal to or greater than the predetermined value ΔP has not continued for the predetermined time T or longer, the process returns to step 7 to continue the second diagnosis. The process proceeds to, and it is determined that the second diagnosis result by the fuel pressure is abnormal (NG), and this flow is terminated.
[0033]
Here, when the process reaches step 9 after passing from step 3 to step 4, that is, when the first diagnosis result is abnormal (NG) and the second diagnosis result is also abnormal (NG), the high pressure In the flow control of the fuel pump 6, since the fuel pressure cannot be converged to the target value, it can be diagnosed that the abnormality has a large level. On the other hand, when the first diagnostic result is abnormal (NG) but the second diagnostic result is not determined to be abnormal (NG), the fuel pressure can be converged to the target value in the normal range flow rate control. Although it is not possible, it is diagnosed that there is an abnormality having a relatively small level that can converge the fuel pressure to the target value by the flow rate control outside the normal range.
[0034]
On the other hand, when step 9 is reached after step 5, that is, when the fuel discharge amount of the high-pressure fuel pump 6 sticks to the minimum value MIN or the maximum value MAX, the second diagnosis result is abnormal (NG). If it is determined, the first diagnosis based on the flow rate balance cannot be diagnosed, so the second diagnosis based on the fuel pressure is performed, and as a result, it is determined that there is an abnormality (NG). In this case, the fuel pressure cannot be converged to the target fuel pressure while sticking to the current minimum value MIN or maximum value MAX, but if the required fuel injection amount shifts to an intermediate operation state, It is unknown whether the fuel pressure can be converged. That is, although the degree of abnormality cannot be determined, it can be diagnosed that there is an abnormality in which the fuel pressure cannot be converged to the target value at least in the normal range flow rate control.
[0036]
The effects of the above embodiment are listed below.
For the fuel system of the internal combustion engine that feedback-controls the fuel discharge pressure while variably controlling the fuel discharge amount of the high-pressure fuel pump 6 according to the required fuel injection amount from the fuel injection valve 8, the fuel discharge amount of the fuel pump 6 and Since the first diagnosis for diagnosing the presence or absence of abnormality based on the fuel injection amount from the fuel injection valve 8 is performed, the diagnosis determination value (NG region) is set for each operating state (requested fuel injection amount). Since it can be set separately, diagnostic accuracy is improved.
[0037]
Specifically, in the first diagnosis, as shown in FIG. 7, an NG region and an OK region are set, and the fuel discharge amount from the high-pressure fuel pump 6 and the fuel injection amount from the fuel injection valve 8 are set. By configuring so as to diagnose that there is an abnormality in the fuel system when the difference is equal to or greater than a predetermined value, the first diagnosis can be easily performed.
[0038]
Similarly, as shown in FIG. 7, the ratio between the NG region and the OK region (width of the OK region) is set differently for each operation state (required fuel injection amount), and a predetermined value for determination in the first diagnosis However, since it is configured to be variably set according to the operating state (required fuel injection amount) of the engine, an easy and highly accurate diagnosis can be performed.
[0039]
Further, when the control value of the high-pressure fuel pump is maintained near the upper limit or near the lower limit (when the fuel discharge amount sticks to the minimum value MIN or the maximum value MAX), the second diagnosis is different from the first diagnosis. With this configuration, the presence or absence of abnormality in the fuel system can be diagnosed, so that the diagnosis can be switched to the second diagnosis in a state that cannot be diagnosed by the first diagnosis, and the diagnosis can be expanded. .
[0040]
Further, since the second diagnosis is configured to diagnose that there is an abnormality in the fuel system when the difference between the actual fuel pressure and the target fuel pressure is equal to or greater than a predetermined value (ΔP), the control value of the high-pressure fuel pump is determined. Is maintained near the upper limit or near the lower limit, the first diagnosis based on the fuel injection amount and the fuel discharge amount is diagnosed as normal even though there is an abnormality. Sometimes, the difference between the actual fuel pressure and the target fuel pressure becomes equal to or greater than a predetermined value (ΔP), and it can be correctly diagnosed that there is an abnormality.
[0041]
Further, the predetermined value (ΔP) of the second diagnosis is set to a value larger than the dead zone width in the variable control of the fuel discharge pressure, so that an abnormality can be reliably diagnosed. Since it may be set to a size larger than the dead zone width (± 0.3 to 0.5 MPa), the determination value of the fuel discharge pressure when diagnosing with the fuel discharge amount and the fuel discharge pressure of the conventional fuel pump ( The judgment value may be sufficiently smaller than that of about ± 5 MPa, and high diagnostic accuracy can be obtained even in an enlarged diagnostic region.
[0042]
In addition, since the second diagnosis is configured to diagnose that there is an abnormality when an abnormal state is detected for a predetermined time T or longer, a misdiagnosis due to a transient fuel pressure fluctuation can be prevented, and reliability can be improved. High diagnosis can be made.
[Brief description of the drawings]
FIG. 1 is a diagram showing a fuel system according to an embodiment of the present invention.
FIG. 2 is a flowchart of a routine for calculating a required discharge amount of the high-pressure fuel pump according to the embodiment.
FIG. 3 is a map for calculating a target fuel pressure of the high-pressure fuel pump same as above.
FIG. 4 is a map for calculating a fuel injection amount of the fuel injection valve according to the embodiment;
FIG. 5 is a map for calculating a basic discharge amount of the high-pressure fuel pump same as above.
FIG. 6 is a flowchart of abnormality diagnosis according to the embodiment.
FIG. 7 is a first diagnosis map used for the abnormality diagnosis.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 6 ... High pressure fuel pump 7 ... High pressure fuel passage 8 ... Fuel injection valve 9 ... Fuel sensor 10 ... Control unit 11 ... Crank angle sensor 12 cylinder discrimination sensor 13 ... Accelerator opening sensor 14 ... Air flow meter

Claims (2)

In a fuel system of an internal combustion engine that feedback controls the fuel discharge pressure while variably controlling the fuel discharge amount of the fuel pump according to the required fuel injection amount from the fuel injection valve,
When the difference between the fuel discharge amount from the fuel pump and the fuel injection amount from the fuel injection valve is greater than a predetermined value that is set to be larger as the fuel injection amount is larger, the fuel system is abnormal. There the first row of the diagnosis of the diagnosis,
Even when the abnormality is not diagnosed by the first diagnosis, if the control value of the fuel pump is maintained near the upper limit or the lower limit, the difference between the actual fuel pressure and the target fuel pressure is a predetermined value. A fuel system diagnostic apparatus for an internal combustion engine, which performs a second diagnosis for diagnosing that the fuel system is abnormal when the above state continues for a predetermined time or more . Wherein the predetermined value of the second diagnosis, fuel system diagnostic apparatus for an internal combustion engine according to claim 1, characterized in that it is set in the dead zone width greater than the variable control of the fuel discharge pressure.

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