JP2014062494A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation of accuracy in controlling an air-fuel ratio by restricting an injection pulse width within the minimum pulse width to ensure linearity of a fuel injection amount versus a pulse width of an injection pulse signal, in a case of failure of means for variably adjusting a pressure of a fuel.SOLUTION: It is determined that the higher a fuel pressure, the longer a minimum pulse width MIN, and in a case when an injection pulse width TI calculated on the basis of an engine operating condition is lower than the minimum pulse width MIN, the injection pulse width TI is set to the minimum pulse width MIN, and the injection pulse width TI is changed in a region of the minimum pulse width MIN or more. Here, in a case that fuel pressure adjusting means is failed and the fuel pressure does not converge to a target value, the minimum pulse width MIN for the same fuel pressure is shortened in comparison with a case when the fuel pressure adjusting means is normal. Thus occurence of rich misfire in deceleration or the like can be suppressed by restriction within the minimum pulse width MIN, even when the fuel pressure becomes higher than the target value due to the failure of the fuel pressure adjusting means.

Description

  The present invention relates to a control device for an internal combustion engine that outputs an injection pulse signal for controlling a valve opening period of a fuel injection valve.

  Patent Document 1 discloses that the pulse width of an injection pulse signal that controls the valve opening period of the fuel injection valve is limited to a minimum pulse width that is variably set according to the fuel pressure.

Japanese Patent Laid-Open No. 11-132076

By limiting the pulse width of the injection pulse signal to the minimum pulse width or more to ensure linearity in which the fuel injection amount is proportional to the length of the valve opening period, the pressure of the fuel supplied to the fuel injection valve is high. Since the low injection amount region in which the linearity deteriorates increases, the minimum pulse width is set to a longer value as the fuel pressure increases.
However, if the fuel pressure becomes higher than normal due to a failure in the means for variably adjusting the fuel pressure, the injection pulse width is limited by the minimum pulse width (variable range of pulse width) corresponding to this high fuel pressure. For example, under engine operating conditions where it is required to reduce the fuel injection amount such as during deceleration operation, the fuel injection amount may be excessive due to the injection pulse width being raised to the minimum pulse width, which may cause a rich misfire. there were.

  The present invention has been made in view of the above problems, and when the means for variably adjusting the fuel pressure has failed, the control accuracy of the air-fuel ratio is deteriorated by changing the injection pulse width within the variable range. An object of the present invention is to provide a control device for an internal combustion engine that can suppress this.

  Therefore, in the present invention, the low pulse width side of the variable range of the pulse width of the injection pulse signal is changed according to the fuel pressure, and when the fuel pressure adjusting means fails, the variable is compared with the normal state. The range was expanded to the low pulse width side.

  According to the above-described invention, when the fuel pressure adjusting means fails, the fuel injection amount becomes excessive and the control accuracy of the air-fuel ratio deteriorates by raising the injection pulse width to a value within the variable range. Can be suppressed.

1 is a system configuration diagram of an internal combustion engine in an embodiment. It is a figure which shows the correlation with the injection pulse width of a fuel injection valve, and injection amount dispersion | variation. It is a flowchart which shows the calculation process of the injection pulse width in embodiment. It is a figure which shows the correlation with the fuel pressure and minimum pulse width in embodiment. It is a flowchart which shows the setting process of the minimum pulse width in embodiment. It is a flowchart which shows the setting process of the minimum pulse width in embodiment. It is a figure which shows the characteristic of the minimum pulse width in embodiment. It is a flowchart which shows the correction process according to the temperature and voltage of the minimum pulse width in embodiment. It is a flowchart which shows the setting process of the minimum pulse width based on the fuel pressure and intake pipe internal pressure in embodiment.

Embodiments of the present invention will be described below.
FIG. 1 is a system configuration diagram of a vehicle internal combustion engine to which a control device according to the present invention is applied.
In FIG. 1, an internal combustion engine (engine) 1 includes a fuel injection valve 3 in an intake pipe (intake port) 2 upstream of the intake valve 4. The fuel injection valve 3 injects fuel into the intake pipe 2.
The fuel injected by the fuel injection valve 3 is sucked into the combustion chamber 5 together with air through the intake valve 4 to form an air-fuel mixture. The air-fuel mixture in the combustion chamber 5 is ignited and burned by spark ignition by the spark plug 6.

The combustion gas in the combustion chamber 5 is discharged to the exhaust pipe 8 through the exhaust valve 7.
The electronic control throttle 10 is a means for adjusting the intake air amount of the internal combustion engine 1 by changing the opening degree by the throttle motor 9. The electronic control throttle 10 is provided upstream of the portion of the intake pipe 2 where the fuel injection valve 3 is disposed.

The fuel supply device 13 is a device that pumps the fuel in the fuel tank 11 to the fuel injection valve 3 by the fuel pump 12.
The fuel supply device 13 includes a fuel tank 11, a fuel pump 12, a pressure regulating valve (pressure regulator) 14, an orifice 15, a fuel gallery pipe 16, a fuel supply pipe 17, a fuel return pipe 18, a jet pump 19, and a fuel transfer pipe 20. I have.

The fuel pump 12 is an electric pump and is provided in the fuel tank 11.
The fuel supply pipe 17 is a pipe connecting the fuel pump 12 and the fuel gallery pipe 16, one end of the fuel supply pipe 17 is connected to the discharge port of the fuel pump 12, and the fuel gallery pipe is connected to the other end of the fuel supply pipe 17. 16 is connected.

Further, the fuel supply port of the fuel injection valve 3 is connected to the fuel gallery pipe 16, and fuel is distributed to each fuel injection valve 3 through the fuel gallery pipe 16.
The fuel return pipe 18 branches from the fuel supply pipe 17 in the fuel tank 11, and the end of the fuel return pipe 18 opens into the fuel tank 11.
The fuel return pipe 18 is provided with a pressure regulating valve 14, an orifice 15, and a jet pump 19 in order from the upstream side.

  The pressure regulating valve 14 is generally configured by a valve body 14a that opens and closes the fuel return pipe 18 and an elastic member 14b such as a coil spring that presses the valve body 14a toward the valve seat upstream of the fuel return pipe 18. . The pressure regulating valve 14 opens when the fuel pressure supplied to the fuel injection valve 3 exceeds a set pressure (valve opening pressure) FPMIN, and closes when the fuel pressure is equal to or lower than the set pressure FPMIN. .

The pressure adjustment valve 14 is opened when the fuel pressure supplied to the fuel injection valve 3 becomes higher than the set pressure FPMIN. However, the orifice 15 provided on the downstream side of the pressure adjustment valve 14 passes through the fuel return pipe 18. The fuel flow rate returned to the fuel tank 11 is reduced. For this reason, the fuel pressure can be increased to a pressure exceeding the set pressure FPMIN by increasing the amount of fuel discharged from the fuel pump 12.
In addition, without providing the orifice 15, for example, the pressure regulating valve 14 can have a function of restricting the return flow rate.

The jet pump 19 transfers fuel through the fuel transfer pipe 20 by the flow of fuel returned into the fuel tank 11 through the pressure regulating valve 14 and the orifice 15.
The fuel tank 11 is a so-called vertical fuel tank in which a part of the bottom surface is raised and the bottom space is divided into two regions 11a and 11b. Since the suction port of the fuel pump 12 opens into the region 11a, the fuel in the region 11b remains unless the fuel in the region 11b is transferred to the region 11a side.

  Therefore, the jet pump 19 applies a negative pressure to the fuel transfer pipe 20 by the flow of fuel returned into the region 11a of the fuel tank 11 via the pressure regulating valve 14 and the orifice 15, and the fuel transfer pipe 20 is opened. The fuel in the region 11b to be conducted is guided to the jet pump 19 through the fuel transfer pipe 20, and is discharged into the region 11a together with the return fuel.

  In the present embodiment, the jet pump 19 is provided as described above. However, when the fuel tank 11 is not a so-called saddle type, that is, the bottom space of the fuel tank 11 is not separated, the fuel is supplied from the suction port of the fuel pump 12. When the fuel in the tank 11 can be sucked without remaining, the jet pump 19 and the fuel transfer pipe 20 can be omitted. Further, the fuel tank 11 is not a so-called saddle type, and the fuel supply device 13 can be provided without the fuel return pipe 18, the pressure adjustment valve 14, the orifice 15, the jet pump 19, and the fuel transfer pipe 20.

An ECM (engine control module) 31 including a microcomputer is a control device that outputs an injection pulse signal for controlling the valve opening period of the fuel injection valve 3, and also includes an ignition timing by the spark plug 6, an electronic control throttle 10. It has a function to control the opening degree.
An FPCM (fuel pump control module) 30 including a microcomputer outputs a drive signal of the fuel pump 12 to control the fuel pump 12.

The ECM 31 and the FPCM 30 can communicate with each other, and the ECM 31 transmits a signal PINS for instructing a drive duty ratio (operation amount) of the fuel pump 12 to the FPCM 30.
The drive duty ratio (%) of the fuel pump 12 is an operation amount for controlling the applied voltage of the motor that rotationally drives the fuel pump 12, and indicates the energization time ratio (on-time ratio) per cycle. Increases, the average applied voltage of the motor increases, and the discharge pressure (discharge flow rate) of the fuel pump 12 increases.

Further, the FPCM 30 transmits a signal DIAG or the like indicating the result of the self-diagnosis to the ECM 31.
The ECM 31 includes a fuel pressure sensor (pressure detecting means) 33 for detecting the fuel pressure FUPR in the fuel gallery pipe 16 corresponding to the pressure of the fuel supplied to the fuel injection valve 3, and an accelerator pedal depression amount (accelerator opening degree) not shown. ) Accelerator opening sensor 34 for detecting ACC, airflow sensor 35 for detecting intake air flow rate QA of internal combustion engine 1, rotation sensor 36 for detecting rotational speed NE of internal combustion engine 1, cooling water temperature TW (engine) A detection signal is input from a water temperature sensor 37 for detecting the temperature), an air-fuel ratio sensor 38 for detecting the air-fuel ratio A / F of the internal combustion engine 1 in accordance with the oxygen concentration of the exhaust gas, and the like.

The ECM 31 calculates the ignition timing (ignition advance value) based on engine operating conditions such as the load of the internal combustion engine 1 and the engine speed NE, and spark discharge by the spark plug 6 is performed at the ignition timing. Controls energization to an ignition coil (not shown).
The ECM 31 calculates the target opening of the electronic control throttle 10 from engine operating conditions such as the accelerator opening ACC, and controls the throttle motor 9 so that the actual opening of the electronic control throttle 10 approaches the target opening.

Further, the ECM 31 is configured so that the fuel pressure FUPR (actual fuel pressure) detected by the fuel pressure sensor 33 approaches the target fuel pressure TGFUPR determined based on the operating conditions (load, rotational speed, etc.) of the internal combustion engine 1 ( A duty ratio DUTY in the duty control of the motor is determined, and a pulse signal PINS indicating the duty ratio DUTY (%) is transmitted to the FPCM 30 as a drive instruction signal for the fuel pump 12.
For example, the ECM 31 performs feedback control in which the duty ratio DUTY is determined by calculating a proportional part, an integral part, and a derivative part based on a deviation between the fuel pressure FUPR and the target fuel pressure TGFUPR.

The FPCM 30 sets a duty ratio DUTY (%) in the duty control of the motor of the fuel pump 12 based on the pulse signal PINS received from the ECM 31 side, and performs duty control of power supply to the motor of the fuel pump 12.
As described above, the ECM 31, the FPCM 30, the fuel pressure sensor 33, the electric fuel pump 12 and the like constitute fuel pressure adjusting means (fuel pressure adjusting device) that variably adjusts the pressure of the fuel supplied to the fuel injection valve 3.
It should be noted that the ECM 31 includes a circuit and a control function that the FPCM 30 includes, whereby a fuel pressure control system in which the ECM 31 and the FPCM 30 are integrated can be obtained.

Further, the ECM 31 calculates the injection pulse width TI (ms) of the injection pulse signal that controls the valve opening period of the fuel injection valve 3 as follows.
The ECM 31 calculates a basic injection pulse width TP (ms) suitable for the case where the fuel pressure is a reference value based on engine operating conditions such as the intake air flow rate QA and the engine rotational speed NE, and this basic injection pulse width TP. Is corrected based on the fuel pressure FUPR, the output (air-fuel ratio) of the air-fuel ratio sensor 38, etc., and the final injection pulse width TI is calculated.

When the fuel injection timing of each cylinder comes, an injection pulse signal having an injection pulse width TI is output to the fuel injection valve 3, and the fuel injection amount and injection timing by the fuel injection valve 3 are controlled. The fuel injection valve 3 opens for a period corresponding to the injection pulse width TI, and injects an amount of fuel proportional to the valve opening period (ms).
Here, since the fuel injection amount by the fuel injection valve 3 has linearity proportional to the length of the valve opening period (injection pulse width), the fuel measurement accuracy by the fuel injection valve 3 is maintained. However, in a region where the valve opening period is short from zero to a predetermined value, the linearity deteriorates, and an amount of fuel commensurate with the injection pulse width cannot be injected with high accuracy.

FIG. 2A shows the correlation between the injection pulse width TI and the total injection amount when the fuel pressure is fixed and the valve is opened by the injection pulse width TI.
As shown in FIG. 2A, in the region where the injection pulse width TI is long, the injection amount changes in proportion to the change in the injection pulse width TI, but in the region where the injection pulse width TI is short, the injection pulse width The change in the TI and the change in the injection amount are not proportional, and the control accuracy of the fuel injection amount based on the injection pulse width TI (linearity of the fuel injection amount with respect to the injection pulse width) deteriorates.

As the injection pulse width TI becomes shorter, the ratio of the actual injection amount to the amount corresponding to the injection pulse width TI decreases, and the air-fuel ratio becomes leaner and lean misfire occurs.
Therefore, as shown in FIG. 2B, even when the injection amount is the smallest in the variation range of the injection amount (variation lower limit), the variation in the injection amount is within the allowable range (for example, within ± 3%). The minimum pulse width MIN is determined in advance based on the injection pulse width TIMIN that falls within the range, and the injection pulse width TI is not reduced below this minimum pulse width MIN. In other words, a range equal to or larger than the minimum pulse width MIN is set as a variable range of the injection pulse width TI.
As a result, the injection pulse width TI is controlled in a region (within the variable range) where the linearity in which the fuel injection amount is proportional to the length of the injection pulse width TI (valve opening period) is ensured.

When a value smaller than the minimum pulse width MIN is calculated as the injection pulse width TI, the ECM 31 sets the final injection pulse width TI by setting the pulse width of the minimum pulse width MIN to the final injection pulse width TI. When the value within the variable range is set to a value greater than or equal to the minimum pulse width MIN as the injection pulse width TI, that is, a value within the variable range is calculated, the injection pulse width TI is used as the final injection pulse width TI.
The flowchart of FIG. 3 shows the calculation process of the injection pulse width TI, including the limiting process (change process on the low pulse width side of the variable range of the pulse width) performed by the ECM 31.

The routine shown in the flowchart of FIG. 3 is executed at regular intervals by the ECM 31. First, in step S101, engine operating conditions such as the intake air flow rate QA, the engine rotational speed NE, and the fuel pressure FUPR are read.
In step S102, the basic injection pulse width TP (ms) is calculated based on the engine operating conditions, and in the next step S103, the basic injection pulse width TP is subjected to various corrections based on the engine operating conditions, and the injection pulses are calculated. The width TI (ms) is calculated.

In step S104, a separately set minimum pulse width MIN is read.
In step S105, the minimum pulse width MIN read in step S104 is compared with the injection pulse width TI calculated in step S103. If the injection pulse width TI is equal to or greater than the minimum pulse width MIN (the injection pulse width TI is variable). If it is within, this routine is terminated as it is.
As a result, the injection pulse width TI calculated in step S103 is set as the final injection pulse width TI, and an injection pulse signal having this final injection pulse width TI is output to the fuel injection valve 3.

On the other hand, if the injection pulse width TI is less than the minimum pulse width MIN, that is, if the injection pulse width TI is shorter than the low pulse width side of the variable range, the process proceeds to step S106 and the injection pulse width TI has the minimum pulse. By setting the pulse width of the width MIN, the minimum pulse width MIN larger than the injection pulse width TI calculated in step S103 is set as the final injection pulse width TI.
As a result, an injection pulse width TI (TI = MIN) that matches the pulse width of the minimum pulse width MIN, that is, an injection pulse signal having an injection pulse width TI within the variable range is output to the fuel injection valve 3.

By the way, the minimum pulse width MIN that can ensure the linearity in the fuel injection valve 3 varies depending on the pressure of the fuel supplied to the fuel injection valve 3, and the higher the fuel pressure, the more the variation width of the fuel injection amount exceeds the allowable value. The width region is expanded, and the minimum pulse width that can ensure linearity becomes longer.
That is, since the fuel pressure acts in the closing direction of the fuel injection valve 3, when the pressure of the fuel supplied to the fuel injection valve 3 increases, the valve opening response of the fuel injection valve 3 is delayed until the fuel injection valve 3 is fully opened. Since the delay increases and the variation in the injection amount until it is fully opened increases, the higher the fuel pressure, the longer the minimum pulse width that can ensure linearity.
In other words, in order to ensure linearity, it is necessary to shift the low pulse side of the variable range of the injection pulse width TI in the direction of increasing the pulse width and narrow the variable range as the fuel pressure increases.

Therefore, as shown in FIG. 4, the ECM 31 sets a longer minimum pulse width MIN as the fuel pressure is higher, and limits the injection pulse width TI to be equal to or greater than the minimum pulse width MIN.
Furthermore, when the fuel pressure adjusting means is set to a fuel pressure (a fuel pressure different from the target fuel pressure) different from that when the fuel pressure is normally adjusted due to a failure of the fuel pressure adjusting means (abnormality of the fuel pressure adjusting function), the ECM 31 It has a function of setting a minimum pulse width MIN (variable range of pulse width) different from that in the normal state.

Hereinafter, the setting process of the minimum pulse width MIN by the ECM 31 will be described in detail.
The flowchart of FIG. 5 shows the minimum pulse width MIN setting process executed by the ECM 31 at regular intervals.
In the flowchart of FIG. 5, in step S201, the fuel pressure FUPR obtained based on the output of the fuel pressure sensor 33 is read.

In step S202, it is determined whether or not the fuel pressure adjusting means is in a failure state, in other words, whether or not the function of bringing the actual fuel pressure closer to the target fuel pressure TGFUPR is operating normally.
For example, when the fuel pressure FUPR does not converge to the target fuel pressure TGFUPR, the failure of the fuel pressure adjusting means is determined.
Specifically, a failure state can be determined when the state where the absolute value of the deviation between the target fuel pressure TGFUPR and the fuel pressure FUPR exceeds the threshold value continues for a set time. Further, when the deviation exceeds the threshold when the set time has elapsed after the target fuel pressure TGFUPR is switched, it can be determined that a failure has occurred.

As described above, the fuel pressure adjustment means has failed when the response when the actual fuel pressure approaches the target fuel pressure TGFUPR is delayed to the extent that it is recognized as a failure (including when it is slower than the reference and when not approaching). Judge.
For example, when the duty ratio DUTY set in the energization control is less than 100%, the energization of the fuel pump 12 is actually continued due to the failure of the drive circuit of the fuel pump 12. Since the fuel pressure cannot be lowered, the actual fuel pressure does not approach the target fuel pressure TGFUPR, and it is determined that the fuel pressure adjusting means has failed.
As a method of failure diagnosis of the fuel pressure adjusting means, various known methods such as a method of determining the presence or absence of failure based on the load (current) of the fuel pump 12 can be appropriately employed.

If it is determined in step S202 that the fuel pressure adjusting means is normal, the process proceeds to step S203, and the first table in which the minimum pulse width MIN (minimum injection time) corresponding to the normal state of the fuel pressure adjusting means is stored in advance is referred to. Then, the minimum pulse width MIN corresponding to the fuel pressure FUPR read in step S201 is searched.
The first table showing the correlation between the minimum pulse width MIN and the fuel pressure FUPR (fuel pressure detection value) referred to in the above step S203 sets the minimum pulse width MIN to a longer time as the fuel pressure FUPR is higher. In addition, if the injection pulse width TI is limited to be equal to or larger than the minimum pulse width MIN obtained from the first table, the variation width of the injection amount can be within an allowable value (for example, within ± 3%). is there.
That is, as the fuel pressure FUPR is higher, the lower pulse width side of the variable range of the injection pulse width is shifted in the direction of increasing the pulse width, and the variable range is compressed to the higher pulse side than when the fuel pressure FUPR is low.

On the other hand, if it is determined that the fuel pressure adjusting means is in a failure state, the process proceeds to step S204, where a second table pre-stored with the minimum pulse width MIN corresponding to the failure state of the fuel pressure adjusting means is read and read in step S201. The minimum pulse width MIN corresponding to the fuel pressure FUPR is searched.
In the second table showing the correlation between the minimum pulse width MIN and the fuel pressure FUPR (fuel pressure detection value) referred to in step S204, the minimum pulse width MIN is set to a longer time as the fuel pressure FUPR is higher. In addition, the minimum pulse width MIN for the same fuel pressure FUPR is set to be shorter than the minimum pulse width MIN searched in the first table. That is, when the fuel pressure adjusting means fails, the variable range of the pulse width is expanded to the low pulse width side as compared with the normal case.

As a failure of the fuel pressure adjusting means, for example, when a failure that maintains a state where the actual fuel pressure is higher than the target fuel pressure TGFUPR (for example, 200 KPa to 700 KPa) (for example, 700 KPa to 950 KPa) occurs, By searching for the minimum pulse width MIN corresponding to the fuel pressure at that time, a longer minimum pulse width MIN corresponding to a fuel pressure higher than the target fuel pressure TGFUPR is set.
However, since this is an engine operating condition in which the actual fuel pressure should be adjusted to the target fuel pressure TGFUPR, if a longer minimum pulse width MIN corresponding to a higher actual fuel pressure is set, the injection pulse width TI during deceleration, etc. When the value is calculated to be short, the final injection pulse width TI is greatly increased due to the restriction based on the minimum pulse width MIN, which may cause the air-fuel ratio to be rich and misfire.
For example, when the minimum pulse width MIN corresponding to the target fuel pressure TGFUPR is α in the first table, the actual fuel pressure increases due to the failure of the fuel pressure adjusting means, and the first table is searched based on this increased fuel pressure. Assuming that the minimum pulse width MIN is β, α <β. Here, if the actual fuel pressure is controlled to the target fuel pressure TGFUPR, the injection pulse width TI can be set to be shorter up to α, but the actual fuel pressure is higher than the target fuel pressure TGFUPR. If it becomes higher, the injection pulse width TI can only be lowered to β, which may enrich the air-fuel ratio.

Therefore, in the failure state of the fuel pressure adjusting means, the failure pulse for which the minimum pulse width MIN for the same fuel pressure is set to be shorter than the minimum pulse width MIN searched in the first table for normal operation. The minimum pulse width MIN is set with reference to the second table.
As a result, if a failure occurs that maintains a state where the actual fuel pressure is higher than the target fuel pressure TGFUPR, even if the minimum pulse width MIN corresponding to the fuel pressure at that time is set, it is limited by the minimum pulse width MIN. It is possible to suppress the occurrence of rich misfire by raising the final injection pulse width TI.
That is, by setting the minimum pulse width MIN shorter (expanding the variable range of the pulse width to the low pulse width side), a shorter pulse width is allowed as the injection pulse width TI, and the air-fuel ratio is increased accordingly. It can be suppressed and rich misfire can be suppressed.

The minimum pulse width MIN obtained by referring to the second table for failure is the minimum pulse width (minimum pulse width MIN obtained from the first table) in which the variation width of the injection amount is within the allowable value at the current fuel pressure. Even if the injection pulse width TI is limited to be higher than the minimum pulse width MIN, there is a possibility that the variation width of the injection amount exceeds the allowable value.
For this reason, when the actual fuel pressure exceeds the target fuel pressure TGFUPR, if the injection pulse width TI is limited to the minimum pulse width MIN or more obtained from the first table, the air-fuel ratio may become rich and misfire may occur. The minimum pulse width MIN obtained by referring to the second table can sufficiently suppress misfire even when the variation in the injection amount occurs on the lean side (the side on which the injection amount decreases), and the minimum pulse width during deceleration Even if the injection pulse width TI is limited to MIN or more, the rich misfire is sufficiently suppressed.

In the example shown in FIG. 2, the injection pulse width TIMIN corresponds to the minimum pulse width MIN set in the first table, and the injection pulse width TILEAN corresponds to the minimum pulse width MIN set in the second table. In the minimum pulse width MIN set in the second table, although the variation in the injection amount (air-fuel ratio) exceeds the allowable range, even if the injection amount is minimized due to the variation, the value becomes a value that can sufficiently suppress lean misfire. It is set.
Therefore, if the minimum pulse width MIN is set as shown in the flowchart of FIG. 5, the lean misfire due to the deterioration of the linearity of the fuel injection amount, and the injection pulse width TI is limited by the excessive minimum pulse width MIN. It is possible to suppress both rich misfire caused by.

Instead of the processing shown in the flowchart of FIG. 5, when the restriction of the injection pulse width TI by the minimum pulse width MIN is canceled in the failure state of the fuel pressure adjusting means, the injection pulse width TI is reduced by the excessive minimum pulse width MIN. However, since the lower limit of the injection pulse width TI is not limited, the linearity of the fuel injection is greatly deteriorated, and a lean misfire may occur.
Further, in place of the process shown in the flowchart of FIG. 5, even when the minimum pulse width MIN is set according to the target fuel pressure TGFUPR in the failure state of the fuel pressure adjusting means, the injection pulse width TI with an excessive minimum pulse width MIN. However, in this case, since the minimum pulse width MIN is not changed according to the actual fuel pressure, there is a possibility that the linearity of fuel injection is greatly deteriorated and lean misfire occurs.
On the other hand, the process shown in the flowchart of FIG. 5 continues the variable setting of the minimum pulse width MIN (change of the variable range of the pulse width on the low pulse side) according to the actual fuel pressure when the fuel pressure adjusting means fails. If the minimum pulse width MIN is set shorter than that in the normal state (if the variable range of the pulse width is expanded to the low pulse width side), both lean misfire and rich misfire can be sufficiently suppressed.

The failure of the fuel pressure adjusting means is specified as a failure that maintains a state where the actual fuel pressure is higher than the target fuel pressure TGFUPR. When such a failure occurs, the process proceeds to step S204, and the minimum pulse width MIN is set from the second table. Even if a failure occurs in which the actual fuel pressure does not converge to the target fuel pressure TGFUPR, if the actual fuel pressure is lower than the target fuel pressure TGFUPR, the process proceeds to step S203, and the minimum pulse width MIN is obtained from the normal first table. Can be searched.
When the pressure of the fuel supplied to the fuel injection valve 3 is reduced, the valve opening response of the fuel injection valve 3 is accelerated, the delay until the fuel injection valve 3 is fully opened is reduced, and the variation in the injection amount until the fuel injection valve 3 is fully opened is reduced. Therefore, the minimum pulse width that can ensure linearity becomes shorter. Therefore, when the actual fuel pressure is lower than the target fuel pressure TGFUPR, even if the minimum pulse width MIN is retrieved from the first table, the minimum pulse width MIN is set shorter than when the actual fuel pressure converges to the target fuel pressure TGFUPR. Therefore, it is possible to suppress the occurrence of rich misfire due to the restriction by the minimum pulse width MIN.
The first table and the second table are not limited to the configuration for setting the normal minimum pulse width MIN and the fault minimum pulse width MIN. For example, the first table The minimum pulse width MIN obtained from the above can be used to limit the injection pulse width TI by changing it in a decreasing direction by a predetermined value when the fuel pressure adjusting means fails.

  Further, when the cause of the failure of the fuel pressure adjusting means is due to the failure of the fuel pressure sensor 33, the actual fuel pressure is estimated based on the load of the fuel pump 12, the discharge amount of the fuel pump 12 and the internal combustion engine 1. The actual fuel pressure can be estimated based on the fuel consumption flow rate, and the minimum pulse width MIN can be variably set with reference to the second table based on the estimated fuel pressure. Further, when the fuel pressure sensor 33 fails, correction according to the fuel pressure of the injection pulse width TI can be performed using the estimated fuel pressure.

However, when the actual fuel pressure is estimated based on the discharge amount of the fuel pump 12, the fuel consumption flow rate of the internal combustion engine 1, etc., there is a possibility that an error may occur in the estimated fuel pressure value due to variations in the discharge flow rate of the fuel pump 12. There is.
When the fuel pressure is estimated to be lower than actual and the minimum pulse width MIN is set based on the estimated fuel pressure, the minimum pulse width MIN shorter than the minimum pulse width MIN corresponding to the actual fuel pressure is set. Even when the pulse width is MIN or more, the variation in the injection amount becomes large, and there is a possibility that lean misfire may occur.

Therefore, in the failure state of the fuel pressure adjusting means, different values of the minimum pulse width MIN can be set according to the failure pattern indicating whether the fuel pressure sensor 33 is normal or has failed.
The flowchart of FIG. 6 shows the flow of processing of the ECM 31 in which the minimum pulse width MIN is set to a different value depending on whether or not the fuel pressure sensor 33 is normal in the failure state of the fuel pressure adjusting means.
That is, in the flowchart of FIG. 6, the expansion width of the variable range to the low pulse width side is changed according to the failure pattern.

The routine shown in the flowchart of FIG. 6 is executed at regular intervals by the ECM 31. First, in step S301, the fuel pressure FUPR obtained from the output of the fuel pressure sensor 33 is read, and in the next step S302, the estimated value EFUPR of the actual fuel pressure is obtained. Read.
The estimated fuel pressure EFUPR can be obtained from, for example, the current (load) of the fuel pump 12 or the correlation between the operation amount (duty ratio) of the fuel pump 12 and the fuel consumption flow rate in the internal combustion engine 1.

In step S303, as in step S202, it is determined whether or not the fuel pressure adjusting means is in a failure state.
Here, if the fuel pressure sensor 33 is normal and the fuel pressure adjusting means capable of converging the actual fuel pressure to the target fuel pressure TGFUPR is in a normal state, the process proceeds to step S304, and fuel pressure adjustment is performed as in step S203. With reference to the first table in which the minimum pulse width MIN corresponding to the normal state of the means is stored in advance, the minimum pulse width MIN corresponding to the fuel pressure FUPR read in step S301 is searched.

On the other hand, if the fuel pressure sensor 33 is faulty or if the fuel pressure adjustment means cannot fail to converge the fuel pressure FUPR to the target fuel pressure TGFUPR even if the fuel pressure sensor 33 is normal, the process proceeds to step S305.
In step S305, it is determined whether the fuel pressure sensor 33 has failed or whether a device other than the fuel pressure sensor 33 (for example, the fuel pump 12 or the fuel pump drive circuit) has failed.

If the fuel pressure sensor 33 is normal (no abnormality is recognized in the fuel pressure sensor 33) and a failure has occurred in which the actual fuel pressure cannot be converged to the target fuel pressure TGFUPR, Judge that the device is faulty.
As a failure diagnosis of the fuel pressure sensor 33, when the sensor output is stuck to the minimum value or the maximum value, it is possible to diagnose a short-circuit or disconnection failure of the sensor output line. Further, whether or not the fuel pressure sensor 33 has failed can be diagnosed based on whether or not the output change of the fuel pressure sensor 33 immediately after starting or stopping the driving of the fuel pump 12 corresponds to the starting or stopping of driving of the fuel pump 12. . In addition, a known method can be appropriately employed as a failure diagnosis method for the fuel pressure sensor 33.

When the fuel pressure sensor 33 is normal, that is, when the actual fuel pressure cannot be converged to the target fuel pressure TGFUPR due to a failure of a device other than the fuel pressure sensor 33, the process proceeds to step S306 and the second reference referred to in step S204. The minimum pulse width MIN corresponding to the fuel pressure FUPR detected by the fuel pressure sensor 33 is retrieved from the table.
On the other hand, if the fuel pressure sensor 33 has failed and the fuel pressure cannot be converged to the target fuel pressure TGFUPR, the process proceeds to step S307, and the third table in which the minimum pulse width MIN corresponding to the failure state of the fuel pressure sensor 33 is stored in advance. The minimum pulse width MIN corresponding to the estimated fuel pressure EFUPR read in step S302 is searched.

As shown in FIG. 7, when the first to third tables are referred to and the minimum pulse width MIN corresponding to the same fuel pressure is obtained from each table, the minimum pulse width MIN obtained from the normal first table is The longest minimum pulse width MIN obtained from the second table for failure other than the fuel pressure sensor 33 is set to be the shortest.
The minimum pulse width MIN obtained from the third table for failure of the fuel pressure sensor 33 is shorter than the minimum pulse width MIN obtained from the first table for normal operation, and other than that for failure other than the fuel pressure sensor 33. It is set to be longer than the minimum pulse width MIN obtained from the second table.
That is, when the first table is used as a reference, the second and third tables expand the variable range of the pulse width to the low pulse width side, and the expansion width to the low pulse side is larger than that of the third table. Two tables are made larger.

That is, “minimum pulse width MIN obtained from the first table> minimum pulse width MIN obtained from the third table> minimum pulse width MIN obtained from the second table” is satisfied in the entire fuel pressure region and the fuel pressure increases. The first to third tables are set so that the minimum pulse width MIN becomes longer.
As described above, when the fuel pressure sensor 33 has failed and the fuel pressure cannot be converged to the target fuel pressure TGFUPR, the fuel pressure is converged to the target fuel pressure TGFUPR due to a failure other than the fuel pressure sensor 33. By setting the minimum pulse width MIN to be longer than that in the case of a failure state that cannot be performed, it is possible to suppress the occurrence of lean misfire due to deterioration in linearity even if an estimation error in fuel pressure occurs.
When estimating the fuel pressure lower than the actual fuel pressure by the estimation error, if the minimum pulse width MIN is set with reference to the second table based on the estimated fuel pressure, the minimum shorter than the minimum pulse width MIN corresponding to the actual fuel pressure Since the pulse width MIN is set and the setting of the injection pulse width TI shorter than the minimum pulse width MIN corresponding to the actual fuel pressure is allowed, the linearity may be deteriorated.
On the other hand, since the minimum pulse width MIN searched with reference to the third table is longer than the minimum pulse width MIN searched with reference to the second table, it is the minimum when estimated lower than the actual fuel pressure. The pulse width MIN can be set longer and the deterioration of linearity can be suppressed.

By the way, the linearity region in the fuel injection valve 3 is changed not only by the fuel pressure but also by the fuel temperature (fuel viscosity) and the power supply voltage of the fuel injection valve 3.
Further, the pressure in the space (dead volume) downstream of the seal portion by the valve body of the fuel injection valve 3 and upstream of the injection hole causes the fuel staying in the space to vaporize during the injection stop period. By changing, the requirement of the minimum pulse width MIN changes, and fuel vaporization in the space occurs according to the pressure (boost pressure) in the intake pipe 2 that is the injection field pressure.

Therefore, the minimum pulse width MIN (the low pulse width side of the variable range of the pulse width) set according to the fuel pressure is corrected according to the temperature of the fuel, the power supply voltage, and the pressure in the intake pipe 2 to thereby minimize the minimum pulse width. By setting the width MIN more accurately, it is possible to suppress variations in the injection amount (air-fuel ratio).
Below, the flow of the correction process of the minimum pulse width MIN according to the fuel temperature and the power supply voltage will be described with reference to the flowchart of FIG.

The routine shown in the flowchart of FIG. 8 is executed at regular intervals by the ECM 31. First, in step S401, a minimum pulse width MIN that is separately set based on the fuel pressure is read.
In the next step S402, the detected values of the fuel temperature and the power supply voltage are read.
The fuel temperature is provided with a temperature sensor for detecting the fuel temperature in the fuel pipe and can be detected from the output of the temperature sensor, or can be estimated from the coolant temperature (engine temperature) of the internal combustion engine 1 or the like. Further, when a vehicle-mounted battery is used as the power supply for the fuel injection valve 3, the voltage of this battery is detected as the power supply voltage for the fuel injection valve 3.

In step S403, a first correction value HSTEM for correcting the minimum pulse width MIN is set based on the fuel temperature read in step S402.
The first correction value HSTEM is a correction term that is multiplied by the minimum pulse width MIN, and is set to a larger value as the fuel temperature is lower, and the minimum pulse width MIN is corrected to a longer time as the fuel temperature is lower.

When the temperature of the fuel supplied to the fuel injection valve 3 is lowered, the viscosity of the fuel is increased, and the opening and closing of the fuel injection valve 3 is delayed, so that the linearity is deteriorated. In other words, when the fuel temperature is lowered, the linearity deterioration region is expanded, and the minimum injection pulse width TI that can ensure the linearity becomes longer. Therefore, the lower the fuel temperature, the longer the minimum pulse width MIN is set. Ensure linearity.
In the next step S404, a second correction value HSVB for correcting the minimum pulse width MIN is set based on the power supply voltage read in step S402.

The second correction value HSVB is a correction term that is multiplied with respect to the minimum pulse width MIN, and is set to a larger value as the power supply voltage of the fuel injection valve 3 is lower, and the minimum pulse width MIN is longer as the power supply voltage is lower. Correct for time.
When the power supply voltage of the fuel injection valve 3 becomes low, the torque for opening the valve body of the fuel injection valve 3 becomes weak, and the linearity deteriorates. In other words, when the power supply voltage is lowered, the linearity deterioration region is expanded, and the minimum injection pulse width TI that can ensure the linearity becomes longer. Therefore, the lower the power supply voltage, the longer the minimum pulse width MIN is set. Can be secured.

In step S405, the minimum pulse width MIN read in step S401 is multiplied by the first correction value HSTEM and the second correction value HSVB, and the multiplication result is set as the final minimum pulse width MIN (MIN = MIN × HSTEM × HSVB). ), And the minimum restriction process of the injection pulse width TI shown in the flowchart of FIG.
Thereby, even if the fuel temperature and the power supply voltage of the fuel injection valve 3 fluctuate, it is possible to suppress variations in the injection amount (air-fuel ratio) while suppressing the injection pulse width TI from being limited to an excessively long pulse width. The minimum pulse width can be set with high accuracy.

The minimum pulse width MIN can be corrected based on at least one of the fuel temperature and the power supply voltage.
Further, the correction term corresponding to the temperature and voltage is not limited to the multiplication term, and correction can be performed as an addition term. Further, each of the first to third tables can be set for each of a plurality of temperature conditions and for each of a plurality of power supply voltages, and the minimum pulse width MIN corresponding to the actual temperature and voltage can be obtained by interpolation calculation.

Further, when the linearity region of the fuel injection valve 3 changes due to the fuel properties (for example, heavy and light), the fuel properties are detected, and when the fuel whose linearity deteriorates is used, the linearity is relatively good. Compared to the case of using fuel, the minimum pulse width MIN can be corrected longer.
The flowchart of FIG. 9 shows the minimum pulse width MIN during normal operation and failure in the setting process of the minimum pulse width MIN shown in the flowchart of FIG. 5 in consideration of the effect of fuel vaporization on the dead volume of the fuel injection valve 3. An example of changing to set is shown.

The routine shown in the flowchart of FIG. 9 is executed at regular intervals by the ECM 31. In step S501, the fuel pressure FUPR obtained based on the output of the fuel pressure sensor 33 and the negative pressure (boost pressure) PB in the intake pipe are read.
The intake pipe internal pressure PB can be detected by a pressure sensor, and can be estimated from a throttle opening, an engine speed, and the like.

In step S502, as in step S202, it is determined whether or not the fuel pressure adjusting means is in a failure state. That is, it determines whether or not the function of bringing the actual fuel pressure closer to the target fuel pressure TGFUPR is operating normally. For example, when the fuel pressure FUPR does not converge to the target fuel pressure TGFUPR, the fuel pressure adjusting means Determine the failure.
If the fuel pressure adjusting means is normal, the process proceeds to step S503, the first map in which the minimum pulse width MIN corresponding to the normal state of the fuel pressure adjusting means is stored is referred to, and the fuel pressure FUPR and intake air read in step S501 are read. The minimum pulse width MIN corresponding to the in-tube negative pressure PB is searched.

The first map uses the fuel pressure FUPR and the intake pipe negative pressure PB as variables, and stores the minimum pulse width MIN corresponding to the combination of these variables. The minimum pulse width MIN searched from the first map is set to a longer value as the fuel pressure FUPR is higher, and is higher as the intake pipe negative pressure PB is higher (as the intake pipe 2 is lower than the atmospheric pressure). Set to a long value.
This is because the higher the fuel pressure, the worse the linearity of the fuel injection valve 3 and the longer the minimum pulse width that can ensure the linearity.

  Further, when the intake pipe negative pressure PB increases, the pressure in the dead volume of the fuel injection valve 3 decreases. As a result, more vapor is generated in the remaining fuel in the dead volume, and the linearity of the fuel injection valve 3 is caused by the vapor. Getting worse. Therefore, the minimum pulse width is set longer as the intake pipe negative pressure PB is higher (inside the intake pipe 2 is lower than the atmospheric pressure), in other words, as the amount of vapor in the dead volume of the fuel injection valve 3 is increased. To do.

On the other hand, if the fuel pressure adjusting means has failed, the process proceeds to step S504, where the fuel pressure FUPR read in step S501 and the second map in which the minimum pulse width MIN corresponding to the time of failure of the fuel pressure adjusting means is stored in advance are referred to. The minimum pulse width MIN corresponding to the intake pipe negative pressure PB is searched.
Similar to the first map, the second map stores the minimum pulse width MIN corresponding to the combination of these variables with the fuel pressure FUPR and the intake pipe negative pressure PB as variables. Further, as in the first map, the minimum pulse width MIN searched from the second map is set to a longer value as the fuel pressure FUPR is higher, and the intake pipe negative pressure PB is higher (inside the intake pipe 2). It is set to a longer value (lower the atmospheric pressure).

Further, the minimum pulse width MIN searched from the second map is set so that the fuel pressure FUPR and the intake pipe negative pressure PB are shorter than the minimum pulse width MIN searched from the first map under the same conditions.
As described above, if the minimum pulse width MIN is changed according to the intake pipe negative pressure PB, the fuel injection valve 3 can be used even if the intake pipe negative pressure PB is high and fuel vapor is generated in the dead volume of the fuel injection valve 3. Therefore, fuel injection can be performed while ensuring the linearity.

Even when the minimum pulse width MIN is set to a different value depending on whether or not the fuel pressure sensor 33 has failed, the minimum pulse width MIN can be set according to the fuel pressure and the negative pressure PB in the intake pipe.
Further, the minimum pulse width MIN set according to the fuel pressure can be corrected longer as the intake pipe negative pressure PB is higher.

Although the preferred embodiments have been specifically described above, it is obvious that those skilled in the art can take various modifications.
For example, instead of setting the minimum pulse width MIN using a table or a map, the minimum pulse width MIN can be obtained by calculating a function using the fuel pressure as a variable.
Further, when the fuel pressure adjusting means fails, the operation amount (drive duty ratio) of the fuel pump 12 can be fixed, or the fuel can be cut in a high load region of the internal combustion engine 1 that injects fuel when normal.

Here, technical ideas other than the claims that can be grasped from the above embodiment will be described together with effects.
(A) When a failure occurs in which the fuel pressure becomes higher than that of the fuel pressure adjusting means during normal operation, the expansion range of the variable range to the low pulse width side is further increased. A control apparatus for an internal combustion engine as set forth in claim 1.
According to the above invention, when the fuel pressure is higher than normal, if the linearity cannot be secured unless it is limited with a larger minimum pulse width, rich misfire occurs due to being limited to an excessively high minimum pulse width. This can be suppressed.

(B) When the fuel pressure detecting means for detecting the fuel pressure fails, the low pulse width side of the variable range is set based on the estimated value of the fuel pressure, and the variable is compared with the time other than the failure other than the fuel pressure detecting means. The control apparatus for an internal combustion engine according to claim 2, wherein the low pulse width side of the range is shifted in a direction in which the pulse width becomes longer.
According to the above invention, even if an error in the estimated value of the fuel pressure occurs, the injection pulse width is limited with a larger minimum pulse width than when the fuel pressure detecting means is normal, so that the occurrence of lean misfire can be suppressed.

(C) The fuel pressure adjusting means adjusts the fuel pressure so as to approach the target;
The control device for an internal combustion engine according to any one of claims 1 to 3, wherein a failure of the fuel pressure adjusting means is determined when a response of the fuel pressure approaching a target decreases to a predetermined value or more.
According to the above invention, when the fuel pressure does not converge to the target and becomes a pressure different from the normal time, the fuel pressure adjusting means is regarded as a failure, and the minimum pulse width is limited by reducing the minimum pulse width. Suppresses rich misfire caused by.

(D) The control apparatus for an internal combustion engine according to claim 3, wherein the lower the pulse width side of the variable range is shifted in the direction in which the pulse width becomes longer as the fuel temperature is lower.
According to the above invention, when the fuel temperature is low and the fuel viscosity is increased and the linearity of the fuel injection valve is deteriorated, the minimum pulse width is set larger and the fuel is injected with a pulse width that can sufficiently secure the linearity.

(E) The control device for an internal combustion engine according to claim 3, wherein the lower the pulse width side of the variable range is shifted in the direction in which the pulse width becomes longer as the power supply voltage of the fuel injection valve is lower.
According to the above invention, when the power supply voltage is low and the linearity of the fuel injection valve is deteriorated due to the weakness of opening the fuel injection valve, the minimum pulse width is set larger and the linearity is sufficiently increased. Inject with a pulse width that can be secured.

(F) The fuel injection valve injects fuel into the intake pipe downstream of the throttle valve;
The control apparatus for an internal combustion engine according to claim 3, wherein the lower the pulse width side of the variable range is shifted in a direction in which the pulse width becomes longer as the injection field pressure of the fuel injection valve is lower.
According to the above invention, if the injection field pressure (intake pipe internal pressure) is low, fuel vapor is generated in the dead volume of the fuel injection valve and the linearity of the fuel injection valve is deteriorated. Therefore, the minimum pulse width is set larger. Thus, it is ejected with a pulse width that can ensure sufficient linearity.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine (engine), 3 ... Fuel injection valve, 11 ... Fuel tank, 12 ... Fuel pump, 14 ... Pressure regulating valve (pressure regulator), 15 ... Fuel gallery piping, 16 ... Fuel supply piping, 17 ... Fuel return Piping, 30 ... FPCM (Fuel pump control module), 31 ... ECM (Engine control module), 33 ... Fuel pressure sensor (pressure detection means)

Claims (3)

A control device that is applied to an internal combustion engine having a fuel pressure adjusting means that variably adjusts the pressure of fuel supplied to a fuel injection valve, and that outputs an injection pulse signal for controlling a valve opening period of the fuel injection valve,
The low pulse width side of the variable range of the pulse width of the injection pulse signal is changed in accordance with the fuel pressure, and when the fuel pressure adjusting means fails, the variable range is set to a low pulse compared to the normal case. A control device for an internal combustion engine that expands to the width side.   2. The control device for an internal combustion engine according to claim 1, wherein when the fuel pressure adjusting means fails, an expansion width of the variable range to the low pulse width side is changed according to a failure pattern.   2. The control of the internal combustion engine according to claim 1, wherein the low pulse width side of the variable range is changed according to at least one of a fuel temperature, a power supply voltage of the fuel injection valve, and an injection field pressure of the fuel injection valve. apparatus.