JP2018044530A - Fuel injection controller of internal combustion engine and fuel injection control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress air-fuel ratio fluctuation due to fuel temperature rise in a fuel sump, in an internal combustion engine where a fuel injection valve formed with the fuel sump on a downstream side of a valve body is arranged in an intake passage.SOLUTION: A controller is configured to estimate a fuel temperature INJFT in a fuel sump on the basis of a cooling water temperature detection value TW; when the fuel temperature INJFT is higher than a predetermined temperature during warming-up operation where an internal combustion engine 1 is left in an idling state from cold starting, assume that fuel injection is executed in a state where liquid fuel is not left in the fuel sump; and reduce an injection pulse width (injection amount command value) more than before.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fuel injection control device and a fuel injection control method for an internal combustion engine, and more particularly to a technique for compensating for a change in fuel flow rate due to a fuel temperature in a fuel reservoir formed downstream of a valve body of a fuel injection valve. .

  In Patent Document 1, in order to correct an air-fuel ratio shift due to vapor generation in the fuel pipe, the fuel temperature is estimated from the cooling water temperature and the intake air temperature, and preset based on the estimated fuel temperature and the intake pipe pressure. A configuration for calculating an air-fuel ratio correction coefficient from a map is disclosed.

JP-A-11-200908

By the way, in an internal combustion engine in which a fuel injection valve in which a fuel reservoir (volume chamber in which fuel remains, dead volume) is formed between a valve body downstream of the valve body and an injection hole is disposed in an intake passage. In the state where the fuel remains, the relationship of the intake passage pressure P3 <the fuel pool pressure P2 <the valve body upstream pressure P1 is satisfied.
However, when the fuel in the fuel reservoir evaporates during the valve closing period as the temperature of the tip of the fuel injection valve rises and no liquid fuel remains in the fuel reservoir, the fuel reservoir internal pressure P2 decreases and P2 ≈P1.

As a result, even if the intake passage pressure P3 and the valve body upstream pressure P1 are the same, the differential pressure across the valve body increases and the fuel flow rate (injection amount per unit time) of the fuel injection valve increases, resulting in the same injection amount. The amount of fuel injected at the command value becomes larger than when liquid fuel remains in the fuel reservoir, causing air-fuel ratio fluctuations (air-fuel ratio enrichment).
In an internal combustion engine in which air-fuel ratio feedback control for correcting an injection amount command value based on a comparison between an air-fuel ratio detection value and a target air-fuel ratio is performed, if an air-fuel ratio shift occurs as the fuel temperature in the fuel pool rises, Although the actual air-fuel ratio is to be maintained at the target air-fuel ratio by changing the correction value of the quantity command value, if the air-fuel ratio fluctuation accompanying the increase in the fuel temperature in the fuel reservoir becomes large, the air-fuel ratio feedback control will fail or the air-fuel ratio If the learning correction value is mislearned, the convergence stability of the air-fuel ratio may be impaired.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel injection control device and a fuel injection control method for an internal combustion engine that can suppress air-fuel ratio fluctuations accompanying an increase in fuel temperature in a fuel reservoir. To do.

Therefore, the fuel injection control device for an internal combustion engine according to the present invention reduces the fuel injection amount command value when the fuel temperature in the fuel reservoir is higher than a predetermined temperature compared to when it is low.
The fuel injection control method for an internal combustion engine according to the present invention includes a step of estimating the fuel temperature in the fuel reservoir, a step of comparing the estimated value of the fuel temperature with a predetermined temperature, and the estimated value of the fuel temperature from the predetermined temperature. A step of reducing the fuel injection amount command value of the fuel injection valve when the time is higher than that when the time is lower.

  According to the above invention, the fuel injection amount command value can be reduced when the fuel in the fuel reservoir is vaporized as the temperature rises and the differential pressure across the valve body increases and the fuel flow rate of the fuel injection valve increases. Thus, the occurrence of an air-fuel ratio shift due to a change in the fuel flow rate can be suppressed, and the convergence stability of the air-fuel ratio can be improved.

1 is a system configuration diagram of an internal combustion engine in an embodiment of the present invention. It is a system configuration figure of a cooling device for internal-combustion engines in an embodiment of the present invention. It is a figure which shows the correlation with the fuel temperature in embodiment of this invention, and the pressure difference before and behind a valve body. It is a flowchart which shows the procedure of the injection control in embodiment of this invention. It is a figure which illustrates the correlation with the cooling water temperature detected value TW and fuel temperature INJFT in embodiment of this invention. It is a figure which illustrates the correlation of basic injection pulse width TIB, fuel temperature INJFT, and pulse width correction value TIHOS in the embodiment of the present invention. It is a flowchart which shows the procedure of the injection control in embodiment of this invention. It is a figure which illustrates the correlation with intake air temperature detection value TA and fuel temperature INJFT in embodiment of this invention.

Embodiments of the present invention will be described below.
FIG. 1 is a system diagram showing an aspect of an internal combustion engine to which a fuel injection control device according to the present invention is applied.
The internal combustion engine 1 is a four-cycle gasoline engine mounted on a vehicle as a power source, and includes a fuel injection valve 3 in each intake port 2a branched from the intake pipe 2 and connected to the combustion chamber of each cylinder. The valve 3 injects fuel into the intake port 2a of each cylinder. That is, the fuel injection valve 3 is disposed in the intake passage of the internal combustion engine 1 and injects fuel into the intake passage.

The fuel injected by the fuel injection valve 3 is sucked into the combustion chamber 5 together with air through the intake valve 4 and 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.
An electronic control throttle 10 that is opened and closed by a throttle motor 9 is disposed in the intake pipe 2, and the electronic control throttle 10 adjusts the intake air amount of the internal combustion engine 1.

The internal combustion engine 1 also includes a fuel supply device 13 that pumps the fuel in the fuel tank 11 to the fuel injection valve 3.
The fuel supply device 13 includes a fuel tank 11, a fuel pump 12, a fuel gallery pipe 14, a fuel supply pipe 15, a fuel filter 16, and the like.
The fuel pump 12 is an electric fluid pump that rotationally drives a pump impeller with a motor, and is disposed in the fuel tank 11.

The fuel pump 12 opens when the discharge pressure of the fuel pump 12 exceeds the upper limit pressure, and the fuel pump 12 discharges the check valve (check valve) 12a for preventing the backflow of the discharged fuel. A relief valve 12b for relieving the fuel in the fuel tank 11 is incorporated.
The check valve (return valve) 12 a and the relief valve 12 b can be separated from the fuel pump 12 and provided in the middle of the fuel supply pipe 15.

One end of the fuel supply pipe 15 is connected to the discharge port of the fuel pump 12, and the other end of the fuel supply pipe 15 is connected to the fuel gallery pipe 14.
A fuel filter 16 for filtering fuel is provided in a portion located in the fuel tank 11 in the middle of the fuel supply pipe 15.
A fuel injection valve 3 for each cylinder is connected to the fuel gallery pipe 14.

The internal combustion engine 1 includes a water cooling type cooling device.
FIG. 2 shows an embodiment of a water-cooled cooling device.
The cooling device for the internal combustion engine 1 includes a mechanical water pump 51 driven by the internal combustion engine 1, a radiator 52, a thermostat 53, and a cooling water pipe 54 that connects these to form a circulation path.

The cooling water is supplied to the cooling water passage provided in the internal combustion engine 1 by the mechanical water pump 51, and the cooling water after cooling the internal combustion engine 1 is sent to the radiator 52 to dissipate heat, and the cooling water after heat dissipation. Is sucked into the mechanical water pump 51 and sent to the internal combustion engine 1 again.
Further, a bypass path 54 a that circulates the coolant while bypassing the radiator 52, and a thermostat 53 that opens and closes the outlet of the radiator 52 are provided.

  The thermostat 53 is a device that opens and closes the outlet of the radiator 52 when the temperature sensing member is displaced in response to the temperature of the cooling water. When the cooling water temperature is low, the thermostat 53 closes the outlet of the radiator 52 so that the radiator 52 is opened. By bypassing and circulating the cooling water, when the cooling water temperature exceeds the set temperature (valve opening temperature), the outlet of the radiator 52 is opened and the cooling water is circulated through the radiator 52.

An ECM (engine control module) 31 having a microcomputer is provided as a control device (control unit) for controlling fuel injection by the fuel injection valve 3, ignition by the spark plug 6, opening of the electronic control throttle 10, and the like. .
Further, as a control device (control unit) for driving the fuel pump 12, an FPCM (fuel pump control module) 30 including a microcomputer is provided.

The ECM 31 and the FPCM 30 are configured to be able to communicate with each other, and signals indicating the duty ratio and frequency in the PWM control of the fuel pump 12 are transmitted from the ECM 31 to the FPCM 30, and diagnosis is performed from the FPCM 30 to the ECM 31. Information etc. are transmitted.
Note that the FPCM 30 can be omitted by providing the ECM 31 with the functions and circuits as the FPCM 30.

The ECM 31 receives output signals from various sensors that detect the operating conditions of the internal combustion engine 1.
As various sensors, a fuel pressure FUPR in the fuel gallery pipe 14, that is, a fuel pressure sensor 33 for detecting the fuel supply pressure (kPa) to the fuel injection valve 3, and an accelerator opening degree ACC corresponding to the amount of depression of the accelerator pedal (not shown). An accelerator opening sensor 34 for detecting, an air flow sensor 35 for detecting the intake air flow rate QA of the internal combustion engine 1, a rotation sensor 36 for detecting the rotational speed NE (rpm) of the internal combustion engine 1, and a cooling water temperature TW (° C. of the internal combustion engine 1) ) To detect the air-fuel ratio A / F of the combustion mixture of the internal combustion engine 1 according to the oxygen concentration in the exhaust gas of the internal combustion engine 1, and the intake air temperature TA (° C.) of the internal combustion engine 1. ) Is detected.
The intake air temperature sensor 39 is provided integrally with the air flow sensor 35.
The water temperature sensor 37 is disposed in the vicinity of the outlet of the cooling water passage formed in the internal combustion engine 1 in the cooling water circulation path (see FIG. 2).

Then, the ECM 31 detects the operating state of the internal combustion engine 1 based on the signals from the various sensors described above, and according to the detected engine operating state, the fuel injection amount and injection timing by the fuel injection valve 3, and the spark plug 6 The ignition timing, the opening degree of the electronic control throttle 10 and the like are controlled.
Further, the ECM 31 sets a target value TGFUPR of the fuel pressure FUPR based on operating conditions such as engine load, engine speed, and coolant temperature, and the detected fuel pressure value FUPR detected based on the output of the fuel pressure sensor 33 is the target value TGFUPR. The fuel pressure feedback control for determining the duty ratio (operation amount) in the PWM control of the fuel pump 12 is performed so as to approach

Further, the ECM 31 as the fuel injection control device uses the pulse width TI (ms) of the injection pulse signal output to the fuel injection valve 3 in the control of fuel injection by the fuel injection valve 3, the intake air flow rate QA, and the engine speed NE. , The air-fuel ratio A / F, the cooling water temperature TW and other engine operating conditions are calculated.
The calculation process of the pulse width TI according to the cooling water temperature TW is an injection amount increase correction process to compensate for a decrease in fuel vaporization performance in the cold state, and the air-fuel ratio A / F The processing for calculating the corresponding pulse width TI is an injection amount correction process (air-fuel ratio feedback process) for bringing the actual air-fuel ratio A / F closer to the target air-fuel ratio.

Further, the ECM 31 calculates the output timing (injection timing) of the injection pulse signal according to the engine operating state such as the intake air flow rate QA, the engine rotational speed NE, and the coolant temperature TW. The ECM 31 detects the injection timing and outputs an injection pulse signal having a pulse width TI to the fuel injection valve 3 to control the fuel injection amount and the injection timing by the fuel injection valve 3.
The fuel injection valve 3 injects an amount of fuel proportional to the pulse width TI of the injection pulse signal. That is, the injection pulse width TI is a command value for the fuel injection amount.

  Further, in the control of fuel injection by the fuel injection valve 3, the ECM 31 vaporizes the fuel in the fuel reservoir on the downstream side of the valve body of the fuel injection valve 3 as the temperature rises. In order to suppress fluctuation of the air-fuel ratio when the front-rear differential pressure increases and the injection amount (fuel flow rate) per unit time increases, the function of correcting the injection pulse width TI is provided as software.

FIG. 3 is a diagram for explaining a mechanism in which a change in the fuel flow rate occurs due to the vaporization of the fuel in the fuel reservoir.
In one mode of the fuel injection valve 3 shown in FIG. 3, the valve body 3A is provided with a sphere at the tip, and the valve body 3A is seated on the funnel-shaped valve seat 3D, and the valve is closed. When the valve body 3A is lifted, the valve body 3A is opened from the valve seat 3D, and fuel is injected from the injection hole 3B provided on the downstream side of the valve seat 3D.

A fuel reservoir 3C (dead volume) is formed between the valve body 3A of the fuel injection valve 3 and the injection hole 3B. The fuel reservoir 3C is provided as a swirl application chamber for applying a turning force to the fuel as in a fuel injection valve disclosed in Japanese Patent Application Laid-Open No. 2014-031758, for example.
FIG. 3A shows a state in which the fuel temperature at the tip of the fuel injection valve 3 immediately after the start of the cold engine (the fuel temperature in the fuel reservoir 3C) is low. In this case, the fuel during the valve closing period of the fuel injection valve 3 The reservoir 3C is filled with liquid fuel, and the relationship of intake passage pressure P3 <fuel reservoir pressure P2 <valve upstream pressure P1 is established.

When the fuel temperature at the tip of the fuel injection valve 3 rises from the state of FIG. 3A, the fuel vapor is generated in the liquid fuel in the fuel reservoir 3C during the valve closing period, and the state of FIG. .
When the fuel vapor VA is generated in the liquid fuel in the fuel reservoir 3C, the fuel reservoir internal pressure P2 is increased, so that the differential pressure between the valve body upstream pressure P1 and the fuel reservoir internal pressure P2, that is, the valve body is increased. By reducing the differential pressure before and after 3A, the injection amount (fuel flow rate) per unit time is reduced compared to the state in which no fuel vapor VA is generated in the fuel reservoir 3C in FIG. .

When the temperature of the tip of the fuel injection valve 3 further rises and the vaporization of the fuel in the fuel reservoir 3C proceeds, the liquid fuel does not remain in the fuel reservoir 3C at the time of injection (when the valve is opened). become.
In the state where the liquid fuel does not remain in the fuel reservoir 3C, the fuel reservoir internal pressure P2 decreases compared to the state of FIG. 3A in which the fuel reservoir 3C is filled with the liquid fuel, and the fuel reservoir internal pressure P2 is The pressure is substantially equal to the intake passage pressure P3. As a result, in the state where the liquid fuel does not remain in the fuel reservoir 3C shown in FIG. 3 (C), the valve body 3A is compared with the case of FIG. 3 (A) in which the fuel reservoir 3C is filled with the liquid fuel. The front-rear differential pressure increases and the injection amount (fuel flow rate) per unit time increases.

That is, fuel injection is performed with the same injection pulse width TI as in FIG. 3 (A) in which liquid fuel does not remain in the fuel reservoir 3C shown in FIG. 3 (C) and the fuel reservoir 3C is filled with liquid fuel. When fuel injection is performed by the valve 3, the amount of fuel actually injected increases, and the air-fuel ratio becomes rich.
Here, if the fuel flow rate in the case of FIG. 3C is used as a reference, the fuel flow rate is relatively small in the case of FIG. 3A or FIG. There is a possibility that the control failure such as the increase correction request by the air-fuel ratio feedback in the state of A) or FIG. 3B becomes large and the air-fuel ratio feedback correction value sticks to the limit value.

Therefore, the ECM 31 is a base air-fuel ratio obtained without air-fuel ratio feedback correction when the fuel temperature in the fuel reservoir 3C rises to a temperature at which liquid fuel does not remain in the fuel reservoir 3C in FIG. Has a function of correcting the injection pulse width (injection amount command value).
If the temperature at the tip of the fuel injection valve 3 is further increased than in the case of FIG. 3C, liquid fuel does not remain in the fuel reservoir 3C and the fuel vapor in the fuel passage on the upstream side of the valve body 3A. 3D, in which VA is generated. In this case, the fuel VA is mixed with the fuel injected from the fuel injection valve 3, so that the fuel density is lowered and the fuel flow rate is lowered.
However, since the state of FIG. 3D occurs under limited conditions (such as a continuous high-load operation state after warm-up), the ECM 31 does not leave liquid fuel in the fuel reservoir 3C of FIG. In order to suppress the air-fuel ratio fluctuation when the temperature condition is reached, the injection amount command value is corrected according to the fuel temperature in the fuel reservoir 3C.

FIG. 4 is a flowchart showing the procedure of the calculation process of the injection amount command value (injection pulse width TI) by the ECM 31, and the ECM 31 executes the routine shown in the flowchart of FIG. 4 by interruption processing at regular intervals.
First, the ECM 31 calculates the basic injection pulse width TIB in step S101.
The calculation process of the basic injection pulse width TIB includes the calculation of the injection pulse width according to the cylinder intake air amount, the calculation for the increase correction at the time of cooling, the calculation for the air-fuel ratio feedback correction, and the like.

In the next step S102, the ECM 31 reads the detected coolant temperature value TW.
In step S103, the ECM 31 compares the cooling water temperature detection value TW read in step S102 with the warm-up determination water temperature TWDK stored in advance.
The warm-up determination water temperature TWDK is preliminarily adapted based on experiments and simulations so that the coolant temperature detection value TW becomes higher than the warm-up determination water temperature TWDK when the internal combustion engine 1 has been warmed up.

When the cooling water temperature detection value TW is the warm-up completion state of the internal combustion engine 1 higher than the warm-up determination water temperature TWDK, the ECM 31 does not correct the injection amount command value according to the fuel temperature in the fuel reservoir 3C. This routine is terminated.
That is, it is during the warming up of the internal combustion engine 1 that the pressure difference between the front and rear of the valve body of the fuel injection valve 3 (the pressure of the fuel pool 3C) suddenly changes with the change in the fuel temperature in the fuel pool 3C. Since the fuel temperature in the fuel reservoir 3C is stabilized and a sudden change in the differential pressure (fuel flow rate) does not occur due to the fuel vaporization state in the fuel reservoir 3C, the ECM 31 sets the correction execution condition to warm-up.

On the other hand, when the cooling water temperature detection value TW is the warm-up determination water temperature TWDK or lower and the internal combustion engine 1 is being warmed up, the fuel vaporization in the fuel pool 3C shown in FIG. Since a change in state occurs, which causes a sudden change in the fuel flow rate of the fuel injection valve 3, the ECM 31 proceeds to step S104.
In step S104, the ECM 31 estimates the fuel temperature (fuel temperature at the tip of the fuel injection valve 3) INJFT in the fuel reservoir 3C based on the detected coolant temperature TW.

  When the internal combustion engine 1 is left in the idling state from the cold start, the detected coolant temperature TW and the fuel temperature INJFT in the fuel reservoir 3C are highly correlated, and the fuel temperature INJFT during the warm-up is estimated based on the detected coolant temperature TW. In the ECM 31, a conversion characteristic (an arithmetic expression or a conversion table) for converting the detected coolant temperature value TW into the fuel temperature INJFT is prepared in advance (see FIG. 5).

Next, the ECM 31 proceeds to step S105, and based on the fuel temperature INJFT (fuel temperature estimated value) and the basic injection pulse width TIB (engine load) estimated in step S104, the ECM 31 enters the fuel reservoir 3C of FIG. A pulse width correction value TIHOS is set to cancel the increase in fuel flow rate due to the increase in the differential pressure across the valve body when no liquid fuel remains.
In step S105, the ECM 31 satisfies a temperature condition in which fuel injection is performed in a state where the fuel in the fuel reservoir 3C is vaporized and no liquid fuel remains in the fuel reservoir 3C based on the fuel temperature INJFT estimated in step S104. It is determined whether or not. In other words, in step S105, the ECM 31 has reached a temperature condition in which the pressure in the fuel sump 3C when fuel injection is performed becomes lower than before as the fuel temperature in the fuel sump 3C rises. Is determined based on whether or not the fuel temperature INJFT estimated in step S104 is higher than a predetermined temperature.

Further, the ECM 31 is a basic injection that is a state quantity that correlates with the engine load whether or not the load of the internal combustion engine 1 is smaller than the predetermined engine load and is operating in a low load region including idling operation. The determination is made based on the pulse width TIB (engine load).
That is, when the internal combustion engine 1 is left in the idling state from the cold start, the state of FIG. 3 (A) is changed to the state of FIG. 3 (C) during the idling operation in accordance with the increase in the fuel temperature in the fuel reservoir 3C. It will be. Then, after the state shown in FIG. 3C and until then (before and after the fuel temperature in the fuel reservoir 3C exceeds the predetermined temperature), the injection amount command value for obtaining the target air-fuel ratio is It becomes different according to the fuel flow rate of the fuel injection valve 3 which changes with the difference in the vaporization state in the reservoir 3C.

Here, if the injection pulse width is changed to cancel the increase in the fuel flow rate due to the state of FIG. 3C, the state after the state of FIG. The base air-fuel ratio obtained without air-fuel ratio feedback correction becomes equivalent.
For this reason, the failure of the air-fuel ratio feedback correction is suppressed, and when the correction request by the air-fuel ratio feedback correction is learned as the air-fuel ratio learning correction value for each operation region, it is influenced by the fuel temperature in the fuel reservoir 3C. Thus, it becomes possible to learn an air-fuel ratio learning correction value that can converge the actual air-fuel ratio in the vicinity of the target air-fuel ratio in the low load region.

FIG. 6 shows one mode of setting processing of the pulse width correction value TIHOS by the ECM 31.
The ECM 31 uses a pulse width correction value TIHOS (TIHOS> 0), which is a correction term multiplied by the basic injection pulse width TIB, to determine that the fuel temperature INJFT in the fuel reservoir 3C is higher than a predetermined temperature and the basic injection pulse width TIB. When the (engine load) is lower than a predetermined value (predetermined engine load) (the first region in FIG. 6), a different value is set for the other (the second region in FIG. 6).
Furthermore, the ECM 31 sets the pulse width correction value TIHOS1 assigned to the first region in FIG. 6 to a value smaller than the pulse width correction value TIHOS2 assigned to the second region in FIG. Then, the injection pulse width TI (fuel injection amount command value) is decreased (decreased).

That is, when the internal combustion engine 1 is left in the idling state from the cold state, the ECM 31 has a fuel temperature condition in which fuel injection is performed in a state where the fuel temperature INJFT exceeds a predetermined temperature and no liquid fuel remains in the fuel reservoir 3C. Then, the pulse width correction value TIHOS is switched from TIHOS2 to TIHOS1, thereby increasing the reduction rate of the injection pulse width TI (injection amount command value) more than before, and even if the basic injection pulse width TIB is the same, the final The effective injection pulse width is shortened.
Thus, the injection is performed from the state where the liquid fuel remains in the fuel reservoir 3C to the state where the liquid fuel does not remain in the fuel reservoir 3C, and the differential pressure across the valve body 3A is reduced. Even if the change is increased, it is possible to suppress an increase in the amount of fuel actually injected into the internal combustion engine 1 with an increase in the differential pressure before and after.

For example, the ECM 31 sets the pulse width correction value TIHOS1 assigned to the first region in FIG. 6 to 1.0, sets the pulse width correction value TIHOS2 assigned to the second region in FIG. 6 to 1.1, or assigns it to the first region in FIG. The pulse width correction value TIHOS1 can be set to 0.9, and the pulse width correction value TIHOS2 assigned to the second region in FIG. 6 can be set to 1.0.
Here, the difference between the pulse width correction value TIHOS1 and the pulse width correction value TIHOS2, in other words, the ratio of reducing the injection amount command value in the first region with respect to the second region is the liquid fuel in the fuel reservoir 3C. The value depends on the difference in the differential pressure across the valve body 3A (fuel flow rate) between the state that is satisfied and the state in which no liquid fuel remains in the fuel reservoir 3C, and is preliminarily adapted based on experiments and simulations.

In the example of FIG. 6, the fuel temperature INJFT and the basic injection pulse width TIB (engine load) change in the vicinity of the boundary where the pulse width correction value TIHOS is switched between the pulse width correction value TIHOS1 and the pulse width correction value TIHOS2. Accordingly, the pulse width correction value TIHOS is set to change stepwise.
However, the pulse width correction value TIHOS can be directly switched from the pulse width correction value TIHOS2 to the pulse width correction value TIHOS1.

When the pulse width correction value TIHOS is set in step S105, the ECM 31 then proceeds to step S106, and the final injection pulse width TI is obtained by multiplying the basic injection pulse width TIB by the pulse width correction value TIHOS (TI = TIB). X TIHOS).
Then, the ECM 31 outputs an injection pulse signal having an injection pulse width TI to the fuel injection valve 3 at the injection timing of each cylinder, and injects an amount of fuel proportional to the injection pulse width TI from the fuel injection valve 3.

According to the fuel injection control by the ECM 31 described above, as the fuel temperature in the fuel reservoir 3C rises (in other words, as the warm-up progresses), the fuel reservoir 3C during the valve closing period is filled with liquid fuel. When the fuel injection is performed in a state where liquid fuel does not remain in the fuel reservoir 3C, the injection pulse width TI (injection amount command value) is corrected to be smaller than before.
As a result, since no liquid fuel remains in the fuel reservoir 3C, the pressure in the fuel reservoir 3C becomes equal to the pressure in the intake passage, the differential pressure across the valve body increases, and the fuel flow rate of the fuel injection valve 3 increases. However, since it is possible to suppress an increase in the amount of fuel actually injected into the internal combustion engine 1, it is possible to suppress the enrichment of the air-fuel ratio.

  Therefore, for example, when the internal combustion engine 1 is left in the idle state from the cold start, it is suppressed that the request for the air-fuel ratio feedback correction is suddenly changed in the middle, and the air-fuel ratio feedback correction fails or the air-fuel ratio learning correction value Can be prevented from being erroneously learned, the convergence stability of the air-fuel ratio in the warm-up operation can be improved, and the exhaust performance during the warm-up can be improved.

By the way, in the water-cooling type cooling device of the internal combustion engine 1, when the thermostat 53 is switched from the closed state to the open state and the cooling water is circulated through the radiator 52, the fuel temperature at the tip of the fuel injection valve 3 becomes the cooling water. While the rise continues without being affected by the switching of the circulation path, the rise in the coolant temperature detection value TW becomes transiently slow as the heat dissipation performance of the coolant changes.
Therefore, at the beginning when the coolant is circulated to the radiator 52, the correlation between the fuel temperature INJFT in the fuel reservoir 3C and the detected coolant temperature TW is lost, and the estimated accuracy of the fuel temperature INJFT is reduced. The injection pulse width correction accuracy (injection amount command value setting accuracy, air-fuel ratio control accuracy) may decrease.

The injection control by the ECM 31 that can suppress the decrease in the estimation accuracy of the fuel temperature INJFT will be described according to the flowchart of FIG.
The ECM 31 executes the routine shown in the flowchart of FIG. 7 by interruption processing at regular intervals.

In step S201, the ECM 31 calculates the basic injection pulse width TIB in the same manner as in step S101.
In the next step S202, the ECM 31 reads the coolant temperature detection value TW.
In step S203, the ECM 31 compares the cooling water temperature detection value TW read in step S202 with the warm-up determination water temperature TWDK stored in advance.

When the cooling water temperature detection value TW is the warm-up completion state of the internal combustion engine 1 higher than the warm-up determination water temperature TWDK, the ECM 31 does not correct the injection amount command value according to the fuel temperature in the fuel reservoir 3C. This routine is terminated.
On the other hand, when the cooling water temperature detection value TW is in the middle of warming up of the internal combustion engine 1 in which the cooling water temperature detection value TW is equal to or lower than the warming up determination water temperature TWDK, the ECM 31 proceeds to step S204.

In step S204, the ECM 31 calculates the amount of change per unit time of the coolant temperature detection value TW (change rate of the coolant temperature detection value TW) DTW.
In the next step S205, the ECM 31 compares the amount of change DTW obtained in step S204 with the amount of change DTCTTW for determining whether the thermostat 53 is closed (for determining whether the radiator 52 exits closed).

The change amount DTSCTW is preliminarily adapted to a value such that the change amount DTW is lower at the beginning when the outlet of the radiator 52 is opened by the thermostat 53 and the cooling water circulates through the radiator 52.
That is, immediately after switching from the state in which the cooling water circulates around the radiator 52 to the state in which the cooling water circulates to the radiator 52, the rising speed of the detected coolant temperature value TW becomes transient as the cooling water heat dissipation performance increases. During the period when the cooling water temperature detection value TW rises dull, the estimation accuracy of the fuel temperature INJFT based on the cooling water temperature detection value TW decreases.

Therefore, the ECM 31 is immediately after switching from the state in which the coolant circulates the path that bypasses the radiator 52 to the state in which the coolant circulates to the radiator 52, and the period during which the estimated accuracy of the fuel temperature INJFT based on the detected coolant temperature TW decreases. Is detected based on whether or not the change amount DTW is less than the change amount DTCTTW (whether or not the rising speed of the coolant temperature detection value TW has slowed down).
Here, when the amount of change DTW is equal to or greater than the amount of change DTSCTW, it indicates that the fuel temperature INJFT can be estimated based on the detected coolant temperature TW, not the period from the closing of the thermostat 53 to the opening. The ECM 31 proceeds to step S206 and subsequent steps, and performs a process of estimating the fuel temperature INJFT based on the detected coolant temperature value TW.

In step S206, the ECM 31 reads the detected coolant temperature value TW, and in the next step S207, similarly to step S104, estimates the fuel temperature INJFT in the fuel pool 3C from the detected coolant temperature value TW.
On the other hand, when the amount of change DTW is less than the amount of change DTCTTW, this indicates that the estimated accuracy of the fuel temperature INJFT based on the detected coolant temperature TW falls within the period when the thermostat 53 is switched from closed to open. The ECM 31 does not proceed to step S206 and thereafter (in other words, prohibits the process of estimating the fuel temperature INJFT based on the detected coolant temperature value TW), and proceeds to step S208.

In step S208, the ECM 31 reads the intake air temperature detection value TA detected by the intake air temperature sensor 39, and in the next step S209, estimates the fuel temperature INJFT in the fuel reservoir 3C based on the intake air temperature detection value TA.
In the ECM 31, a conversion characteristic (an arithmetic expression or a conversion table) for converting the intake air temperature detection value TA into the fuel temperature INJFT is prepared in advance (see FIG. 8).

The intake air temperature detection value TA is a state quantity that correlates with the fuel temperature INJFT in the fuel reservoir 3C, and is not affected by the switching of the cooling water circulation path, and is within the switching period of the thermostat 53 from closing to opening. Even if it is, it is a value that continues to rise as the warm-up progresses.
Therefore, the ECM 31 takes the intake air instead of the detected coolant temperature value TW when the thermostat 53 is within the switching period from closing to opening, that is, during the transition period when the coolant is switched to the state where the coolant is circulated to the radiator 52. By estimating the fuel temperature INJFT based on the temperature detection value TA, it is possible to suppress a transient decrease in the estimation accuracy of the fuel temperature INJFT.

When the ECM 31 estimates the fuel temperature INJFT based on the detected coolant temperature value TW or the detected intake air temperature TA, the ECM 31 proceeds to step S210, and in the same manner as in step S105, the fuel temperature INJFT and the basic injection pulse width TIB (engine load) are set. Based on this, the pulse width correction value TIHOS is set (see FIG. 6).
In the next step S211, the ECM 31 sets a result obtained by multiplying the basic injection pulse width TIB by the pulse width correction value TIHOS as a final injection pulse width TI (TI = TIB × TIHOS). Then, the ECM 31 outputs an injection pulse signal having an injection pulse width TI to the fuel injection valve 3 at the injection timing of each cylinder, and injects an amount of fuel proportional to the injection pulse width TI from the fuel injection valve 3.

  The injection control according to the flowchart of FIG. 7 differs from the injection control according to the flowchart of FIG. 4 in the estimation process of the fuel temperature INJFT, but the injection pulse width TI is corrected based on the estimated fuel temperature INJFT (injection amount command). Value change) is performed in the same manner as the injection control according to the flowchart of FIG. For this reason, the ECM 31 performs the injection control according to the flowchart of FIG. 7, thereby suppressing the failure of the air-fuel ratio feedback correction and the erroneous learning of the air-fuel ratio learning correction value, thereby stabilizing the convergence of the air-fuel ratio in the warm-up operation. The exhaust performance during warm-up is improved.

Although the contents of the present invention have been specifically described above with reference to the preferred embodiments, it is obvious that those skilled in the art can take various modifications based on the basic technical idea and teachings of the present invention. is there.
In the injection control shown in the flowchart of FIG. 7, the ECM 31 detects a switching period from closing to opening of the thermostat 53 based on the change amount DTW per unit time of the cooling water temperature detection value TW, but the cooling water temperature detection value TW The fuel temperature INJFT based on the intake air temperature detection value TA can be estimated with the period when the thermostat 53 is in the valve opening temperature region as a switching period from the closing of the thermostat 53 to the opening.

  Further, since the fuel temperature at which fuel injection is performed in a state where liquid fuel does not remain in the fuel reservoir 3C differs depending on the property of the fuel used in the internal combustion engine 1 (octane number or the like), the ECM 31 acquires information on the fuel property. Then, the estimation result of the fuel temperature INJFT can be corrected according to the fuel property, or the pulse width correction value TIHOS can be corrected according to the fuel property.

Further, the ECM 31 can estimate the fuel temperature INJFT based on the coolant temperature detection value TW at the estimation timing and the coolant temperature detection value TW at the time of start-up in the fuel temperature INJFT estimation process.
Further, the ECM 31 can estimate the fuel temperature INJFT based on the intake air temperature detection value TA from the time of cold start.

Here, the technical idea that can be understood from the above-described embodiment will be described below.
A fuel injection control device for an internal combustion engine, in one aspect thereof, is a fuel injection control device applied to an internal combustion engine in which a fuel injection valve in which a fuel sump is formed on the downstream side of a valve body is disposed in an intake passage, When the fuel temperature in the fuel pool becomes higher than a predetermined temperature, the fuel injection amount command value is reduced as compared with when the fuel temperature is lower.

In a preferred aspect of the fuel injection control device for the internal combustion engine, the fuel temperature in the fuel reservoir is estimated based on at least one of a detected coolant temperature value of the internal combustion engine and an intake air temperature detected value of the internal combustion engine.
In another preferred aspect, the fuel temperature is based on the detected intake air temperature when the cooling water of the internal combustion engine is within a predetermined period from the state in which the coolant is circulated around the radiator to the state in which it is circulated to the radiator. The fuel temperature is estimated based on the detected coolant temperature when it is outside the predetermined period.

In still another preferred aspect, a state in which the change rate of the coolant temperature detection value exceeds the threshold value is defined as the predetermined period.
In still another preferred aspect, the fuel injection amount command value is reduced during the warm-up operation of the internal combustion engine.

In still another preferred aspect, the fuel injection amount command value is reduced when the internal combustion engine is warming up and the load on the internal combustion engine is smaller than a predetermined load.
In still another preferred aspect, the fuel temperature region higher than the predetermined temperature is a temperature region in which fuel injection is performed in a state where the fuel in the fuel reservoir is vaporized and no liquid fuel remains in the fuel reservoir.

In still another preferred aspect, the fuel temperature region higher than the predetermined temperature is a temperature region in which the pressure in the fuel reservoir when fuel injection is performed decreases as the fuel temperature in the fuel reservoir increases. is there.
In one aspect, the fuel injection control device for an internal combustion engine is a fuel injection control device applied to an internal combustion engine in which a fuel injection valve in which a fuel reservoir is formed on the downstream side of the valve body is disposed in an intake passage. Thus, when fuel injection is performed with no liquid fuel remaining in the fuel reservoir, the fuel injection amount command value is reduced compared to when fuel injection is performed with liquid fuel remaining in the fuel reservoir. .

  In one aspect, the fuel injection control device for an internal combustion engine is a fuel injection control device applied to an internal combustion engine in which a fuel injection valve in which a fuel reservoir is formed on the downstream side of the valve body is disposed in an intake passage. When fuel injection is performed in a state where no liquid fuel remains in the fuel reservoir and fuel vapor is not generated upstream of the valve body, the fuel injection amount command value is reduced compared to other cases. To do.

  In one aspect, the fuel injection control device for an internal combustion engine is a fuel injection control device applied to an internal combustion engine in which a fuel injection valve in which a fuel reservoir is formed on the downstream side of the valve body is disposed in an intake passage. Thus, when the pressure in the fuel reservoir when fuel injection is performed decreases as the fuel temperature in the fuel reservoir increases, the fuel injection amount command value is lower than that before the pressure in the fuel reservoir decreases. To lose weight.

  In one aspect, the fuel injection control method for the internal combustion engine is a fuel injection control method for injecting fuel into the intake passage of the internal combustion engine by a fuel injection valve in which a fuel reservoir is formed on the downstream side of the valve body. The step of estimating the fuel temperature in the fuel reservoir, the step of comparing the estimated value of the fuel temperature with a predetermined temperature, and the estimated value of the fuel temperature when higher than the predetermined temperature are lower than when the estimated value is lower. Reducing the fuel injection amount command value of the fuel injection valve.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Intake pipe, 3 ... Fuel injection valve, 3A ... Valve body, 3B ... Injection hole, 3C ... Fuel reservoir, 4 ... Intake valve, 31 ... ECM (engine control module), 33 ... Fuel pressure Sensor, 34 ... Accelerator opening sensor, 35 ... Air flow sensor, 36 ... Rotation sensor, 37 ... Water temperature sensor, 38 ... Air-fuel ratio sensor, 39 ... Intake air temperature sensor, 51 ... Mechanical water pump, 52 ... Radiator, 53 ... Thermostat

Claims (10)

A fuel injection control device applied to an internal combustion engine in which a fuel injection valve in which a fuel reservoir is formed downstream of a valve body is disposed in an intake passage,
A fuel injection control device for an internal combustion engine that reduces a fuel injection amount command value when a fuel temperature in the fuel reservoir becomes higher than a predetermined temperature as compared with a low temperature.   The fuel injection control device for an internal combustion engine according to claim 1, wherein the fuel temperature in the fuel reservoir is estimated based on at least one of a detected coolant temperature value of the internal combustion engine and an intake air temperature detected value of the internal combustion engine.   When the cooling water of the internal combustion engine bypasses the radiator and circulates from the state in which the cooling water is circulated to the radiator, the fuel temperature is estimated based on the intake air temperature detection value within a predetermined period, and the predetermined temperature 3. The fuel injection control device for an internal combustion engine according to claim 2, wherein when it is out of the period, the fuel temperature is estimated based on the detected coolant temperature value.   4. The fuel injection control device for an internal combustion engine according to claim 3, wherein a state in which the change rate of the coolant temperature detection value exceeds a threshold value is within the predetermined period.   The fuel injection control device for an internal combustion engine according to any one of claims 1 to 4, wherein the fuel injection amount command value is reduced during a warm-up operation of the internal combustion engine.   The reduction in the fuel injection amount command value is performed when the internal combustion engine is warming up and when the load on the internal combustion engine is smaller than a predetermined load. A fuel injection control device for an internal combustion engine.   The fuel temperature region higher than the predetermined temperature is a temperature region in which fuel injection is performed in a state where the fuel in the fuel reservoir is vaporized and no liquid fuel remains in the fuel reservoir. A fuel injection control device for an internal combustion engine according to any one of the above.   The fuel temperature region higher than the predetermined temperature is a temperature region in which the pressure in the fuel reservoir when fuel injection is performed decreases as the fuel temperature in the fuel reservoir increases. Item 7. The fuel injection control device for an internal combustion engine according to any one of Items 6 to 6. A fuel injection control device applied to an internal combustion engine in which a fuel injection valve in which a fuel reservoir is formed downstream of a valve body is disposed in an intake passage,
An internal combustion engine that reduces the fuel injection amount command value when fuel injection is performed with no liquid fuel remaining in the fuel reservoir, compared with when fuel injection is performed with liquid fuel remaining in the fuel reservoir. Engine fuel injection control device. A fuel injection control method for injecting fuel into an intake passage of an internal combustion engine by a fuel injection valve in which a fuel reservoir is formed downstream of a valve body,
Estimating a fuel temperature in the fuel reservoir;
Comparing the estimated value of the fuel temperature with a predetermined temperature;
Reducing the fuel injection amount command value of the fuel injection valve when the estimated value of the fuel temperature is higher than a predetermined temperature compared to when it is low;
A fuel injection control method for an internal combustion engine.