JPH09151761A - Fuel control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain good acceleration performance while preventing generation of exhaust black smoke at acceleration time due to a response delay in an engine EGR system. SOLUTION: An engine control circuit (ECU) 30 controlling a fuel injection amount of a Diesel engine 1 is provided. In the ECU, an opening of an EGR control valve 9 is adjusted in accordance with an operating condition of the engine, its exhaust gas recirculation amount is controlled, also averaging control, increasing a fuel injection amount by each fixed amount in each turn of the engine, is performed when it is accelerated. In this way, in accordance with a substitution degree of residual EGR gas in an intake system, the fuel injection amount at acceleration time is increased, good acceleration performance can be obtained while preventing generation of black smoke.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel control device for an internal combustion engine, and more particularly to a fuel control device for an internal combustion engine having an EGR device for returning a part of exhaust gas to an intake system.

[0002]

2. Description of the Related Art An EGR (exhaust gas recirculation) device is generally used to reduce engine combustion temperature and pumping loss by recirculating a part of engine exhaust to an engine intake system and restricting inflow of fresh air into the engine. It is used, for example, in a diesel engine, since excessive air combustion is performed under normal operating conditions, a relatively large amount of exhaust gas recirculation is performed during normal operation. However, in an engine that performs exhaust gas recirculation, if the amount of fuel supplied to the engine is rapidly increased in accordance with the acceleration state during engine acceleration, etc. There is a problem that the supply amount of fresh air is insufficient with respect to the supply amount, incomplete combustion occurs during acceleration, and exhaust black smoke is generated.

In order to prevent the problem of generation of exhaust black smoke at the time of acceleration, the exhaust gas recirculation is stopped at the time of engine acceleration, and the amount of fuel increase at the time of acceleration is reduced to prevent the generation of exhaust black smoke. Fuel control technology is known. As an example of this type of fuel control technique, for example, Japanese Patent Laid-Open No. 64-64-
There is one described in Japanese Patent No. 66447. The publication is E
The present invention relates to fuel injection amount control of a diesel engine having a GR device, and accelerates by using a reduction correction value based on a state before the exhaust gas recirculation is stopped for a predetermined time after the exhaust gas recirculation is stopped during acceleration. At this time, the correction amount of the fuel increase amount is constantly maintained, and after the elapse of a predetermined time, the decrease correction value is decreased every time the predetermined time period elapses.

EGR for controlling the exhaust gas recirculation amount in general
The control valve has a delay in operation response, and it takes some time to completely close after the stop signal is input to the EGR control valve. Therefore, even after the exhaust gas recirculation is stopped, the amount of exhaust gas supplied to the engine intake system does not immediately become zero but tends to gradually decrease with time. Therefore, if the amount of fuel supplied to the engine was increased at the same time as the exhaust gas recirculation was stopped during engine acceleration, the amount of fuel supplied would increase before the amount of fresh air supplied to the engine had increased sufficiently, resulting in an increase in the initial acceleration. There is a problem that exhaust black smoke is generated.

In the fuel injection control described in the above-mentioned Japanese Patent Laid-Open No. 64-66447, the fuel increase amount during acceleration is corrected by a fixed amount reduction for a certain time after the exhaust gas recirculation is stopped at the initial stage of acceleration, and then gradually increases with the passage of time. By increasing the fuel supply amount, the fuel supply amount is increased according to the increase in the flow rate of fresh air flowing into the engine, and the generation of exhaust black smoke at the initial stage of acceleration is prevented.

[0006]

However, in the fuel injection control disclosed in Japanese Patent Laid-Open No. 64-66447, the correction for reducing the amount of fuel increase during acceleration is independent of the engine operating state after the exhaust gas recirculation is stopped. However, since it is performed only based on the elapsed time after the exhaust gas recirculation is stopped, there is a problem that it is not always possible to perform an appropriate reduction correction.

For example, when the engine is operated in a state where the intake air amount is small, the residual exhaust gas in the intake system and the exhaust gas supplied to the intake system due to the response delay of the EGR control valve are It takes a relatively long time to be replaced. For this reason, the amount of fresh air in the intake system gradually increases even after the exhaust gas recirculation is stopped, and therefore it is necessary to perform the fuel reduction correction for a relatively long time. However, when the engine intake air amount is large, residual exhaust gas in the intake system and E
The exhaust gas supplied due to the delay in the operation of the GR control valve is replaced with fresh air in a short time, the amount of fresh air in the intake system immediately increases, and black smoke is generated even if the reduction correction is completed in a short time. There is no problem.

Therefore, as in the fuel injection control of Japanese Unexamined Patent Publication (Kokai) No. 64-66447, based on only the elapsed time after the exhaust gas recirculation stop, regardless of the engine operating state after the exhaust gas recirculation stop. If uniform weight reduction correction is performed, for example, even though the residual exhaust gas in the intake system has not actually been completely replaced with fresh air, the fuel weight reduction correction ends and the exhaust black during acceleration is reduced. In some cases, smoke is generated. Also, to prevent this problem, if you set a long time to perform fuel reduction correction with a margin, unnecessarily reducing the amount of exhaust gas may occur even if residual exhaust gas in the intake system is replaced with fresh air depending on operating conditions. There may be a problem that the correction continues and the acceleration of the engine deteriorates.

In view of the above problems, the present invention can consider the degree of replacement of the residual exhaust gas in the intake system depending on the engine operating condition, and can perform the fuel reduction correction during acceleration according to the degree of replacement. An object is to provide a fuel control device for an internal combustion engine.

[0010]

According to the present invention, there is provided a fuel control device for an internal combustion engine having an EGR device for recirculating a part of engine exhaust gas to an engine intake system, the fuel control device being set according to an operating state of the engine. EGR control means for recirculating the amount of exhaust gas to the intake system, basic fuel amount setting means for setting the basic fuel amount for the amount of fuel supplied to the engine in accordance with the operating state of the engine, and the engine in the accelerating state. And the acceleration detection means for detecting that the basic fuel amount is reduced in accordance with the degree of replacement of the residual exhaust gas with fresh air in the engine intake system when the engine is detected to be in an accelerated state. There is provided a fuel control device for an internal combustion engine, comprising: a correction means for accelerating acceleration.

That is, in the fuel control device of the present invention, the fuel amount reduction correction is performed according to the degree of replacement of the residual exhaust gas in the intake system with the fresh air, so that the fuel amount reduction correction during acceleration is performed regardless of operating conditions. There is no excess or deficiency.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to a diesel engine with an exhaust supercharger. In FIG. 1, 1 is a diesel engine, 2 and 3 are an intake passage and an exhaust passage of the engine 1, and 5 is a turbocharger. Further, in the present embodiment, an EGR device that recirculates a part of the exhaust gas of the engine 1 to the surge tank 2a of the intake passage 2 is provided. The EGR device includes an EGR passage 7 that connects the exhaust passage 3 and the surge tank 2 a of the intake passage 2, and an EGR passage 7
And an EGR control valve 9 provided above. Reference numeral 9a in FIG. 1 denotes an EGR actuator of an appropriate type such as a negative pressure actuator for driving the EGR control valve 9 or a stepper motor. In the present embodiment, as will be described later, the control circuit 30 of the engine 1 drives the EGR actuator 9a according to the fuel injection amount of the engine 1 to adjust the opening degree of the EGR control valve 9. As a result, the amount of the most recirculated exhaust gas (hereinafter referred to as “EGR gas”) that flows back from the engine exhaust passage 3 to the intake passage 2 through the EGR passage 7 is controlled.

Reference numeral 30 in FIG. 1 is a control circuit (ECU) of the engine 1. In the present embodiment, the ECU 30
ROM (Read Only Memory) 32, RAM (Random Access Memory) 33, CPU (Microprocessor)
34, and an input port 35 and an output port 36 are connected to each other by a bidirectional bus 31 to constitute a known type of digital computer. The ECU 30 performs basic control such as fuel injection control of the engine 1, and in the present embodiment, the EGR control that controls the opening degree of the EGR control valve 9 and the fuel according to the degree of replacement of the EGR gas in the intake passage during acceleration. Each control such as the later-described smoothing control for reducing the injection amount is performed.

For these controls, the input port 35 of the ECU 30 receives a voltage signal corresponding to the intake pipe pressure from the intake pressure sensor 11 provided in the surge tank 2a of the intake passage, and an accelerator pedal (not shown). A voltage signal corresponding to the amount of depression of the accelerator pedal by the driver is input from the accelerator opening sensor 15 provided in the vehicle via the AD converter 21, and is also arranged on the crankshaft (not shown) of the engine 1. A pulse signal representing the rotation speed of the engine 1 is input from the rotation speed sensor 13.

The output port 36 of the ECU 30 is connected to a fuel injection valve (not shown) of each cylinder of the engine 1 through a drive circuit 23 to control the amount of fuel injected into the engine and to control the EGR control valve. 9 is connected to the actuator 9a to control the opening degree of the EGR control valve 9. Next, the EGR control of this embodiment will be described. In the present embodiment, the EGR gas amount is controlled so that the intake EGR rate E _R exhibits the change characteristic shown in FIG. 2 with respect to the excess air ratio equivalent value λ ′. Here, the EGR rate E _R is 1 of the engine 1.
The amount of EGR gas Qg (grams / revolution) supplied per revolution and the total amount of intake air per revolution of the engine (fresh air amount Qa
(Gram / revolution) and EGR gas amount Qg) is defined as the ratio. That is, E _R = Qg / (Qa +
Qg).

The excess air ratio equivalent value λ'is the air-fuel ratio of the air-fuel mixture in the combustion chamber with respect to the total intake air amount per engine revolution and the actual fuel injection amount Qf _(fin) per engine revolution. It is defined as the ratio with the air amount Qr _(fin) required to obtain the stoichiometric air-fuel ratio. That is, λ '=
(Qa + Qg) / Qr _(fin) . Note that Qr _(fin)
The _{value, Qr (fin) = (Qf} (fin) × S a × γ × n /
2) / 1000 (gram / revolution). Here, S _a is the theoretical air-fuel ratio (for example, S _a = 14.7), γ
Is the fuel specific gravity (for example, about γ = 0.87), and n is the number of cylinders of the engine.

As shown in FIG. 2, the change characteristic of the EGR rate E _R of this embodiment has a large value of E _R in a region where the air excess ratio equivalent value λ'is large, and becomes relatively large as λ'decreases. In the region where it gradually decreases and λ'is small, λ '
The E _R with decreasing rapidly decreased, lambda 'predetermined value lambda
_When reaching ₀ , E _R is set to zero (the EGR control valve 9 is fully closed).

That is, in the present embodiment, in the region where λ'is large (the region where the fuel injection amount Qf _(fin) is small), as much EGR gas as possible is supplied to the engine to suppress the generation of NO _X , and λ'is reduced. Small area (fuel injection amount Q
In the region where f _(fin) is large), EGR
By reducing the amount of gas and relatively increasing the amount of fresh air in the intake air, the generation of exhaust black smoke is prevented. It should be noted that λ ₀ is a value such that λ′≈1.25 (in this case, since the EGR rate becomes zero, the value of the excess air ratio λ and the excess air ratio equivalent value λ ′
And the values will be equal).

Further, the fuel injection amount for the black smoke generation prevention as described below, the upper limit value corresponding to the fresh air supply amount Qa of the engine Qf _(ful) is set, the actual in the lambda ₀ The value of the fuel injection amount Qf _(fin) is set to a value smaller than Qf _(ful) . That is, the actual fuel injection amount Qf
_{As (fin)} increases, the EGR rate decreases and Qf _(fin)
The EGR control valve 9 is always fully closed before reaching Qf _(ful) .

In FIG. 2, λ _(ful) is Q
It is a value corresponding to λ ′ when f _(fin) = Qf _(ful) . FIG. 3 is a diagram showing the relationship between the fuel injection amount upper limit value Qf _(ful) and Qa described above. As mentioned above, Qf
_(ful) is given as the maximum fuel amount that does not generate black smoke with respect to the fresh air supply amount Qa, and the excess air ratio λ _(ful) = Qa / Q
r _(ful) is a value near 1.25 and λ _(ful) <1.2
It is set to a constant value of 5. (Qr _(ful) fuel injection amount upper limit value Qf (amount of air required to obtain the stoichiometric air-fuel ratio with respect to _ful)) Therefore, as shown in FIG. 3, Qf _(ful)
Is set to a value substantially proportional to the fresh air supply amount Qa.

Next, referring to FIG. 4, the change of the EGR rate shown in FIG.
The opening degree control of the EGR control valve 9 for obtaining the conversion characteristic
explain. As described in FIG. 2, the change characteristic of the EGR rate
Is the fuel injection amount Qf_(fin)Is the upper limit Qf_(ful)Reach
EGR rate E before_RMust be set to zero
There is. Therefore, the target opening degree of the EGR control valve 9 is also Qf.
_(ful)And Qf_(fin)It is necessary to set it in consideration of both
is there. Therefore, in the present embodiment, the eyes of the EGR control valve 9 are
Standard opening Qf_(fin)And Qf_(ful)Ratio R (fuel amount parameter
It is designed to be set using a meter.

FIG. 4 shows the EGR control valve opening target values EV and R.
(R = Qf _(fin) / Qf _(ful) ). As shown in FIG. 4, the target opening value EV has a value of the fuel amount parameter R of 1.0 (that is, Qf _(fin) = Qf
₍ a point where it becomes _(ful) ), the value sharply decreases near R = R ₀ (where R <1.0), but becomes 0 at other points, and R << 1.
In the region of 0, the opening target value EV is set to be a substantially constant value.

As shown in FIG. 4, the EGR control valve opening target value EV
The reason why the characteristic of the EGR rate E _R shown in FIG. 2 is obtained when is set will be described below. In this embodiment,
The engine 1 is provided with a turbocharger 5. Therefore, the boost pressure of the engine 1 increases as the energy of the exhaust gas increases, that is, the amount of fuel supplied to the engine increases. Therefore, in the steady state, when the fuel injection amount Qf _(fin) increases, the fresh air intake amount Qa per engine revolution also increases accordingly. When the EGR rate E _R decreases due to the increase of Qf _(fin), the EGR gas amount should decrease if the value of Qa is constant.
_{Since the} supercharging pressure increases and the fresh air amount Qa increases as _(fin) increases, the EGR gas amount also needs to increase in accordance with the increase in Qa.

Therefore, in a region in which the change in EGR rate E _R with respect to a change in λ ′ is relatively small, such as in a region in which Qf _(fin) is small in FIG. 2 _(a region in which the excess air ratio equivalent value λ ′ is large), Qf Even if _(fin) is increased, the decrease in the EGR gas amount due to the decrease in the EGR rate target value and the increase in the EGR gas amount due to the increase in the fresh air amount Qa cancel each other, so that Qf
_{Even if (fin)} changes, the EGR gas amount hardly changes. Therefore, as shown in FIG. 4, in the region where Qf _(fin) is small (the region where R << 1.0), the fuel amount parameter R
The target valve opening value EV of the control valve hardly changes even when is changed.

On the other hand, as shown in FIG. 2, as the value of Qf _(fin) increases and the value of λ ′ approaches λ _(ful) , EGR
The rate E _R decreases sharply. Therefore, in this region, the decrease in the EGR rate E _R is larger than the increase in the fresh air amount Qa, and it becomes necessary to greatly decrease the EGR gas amount when Qf _(fin) increases. Therefore, as shown in FIG.
When the value of f _(fin) approaches Qf _(ful) (the value of R is 1.0
(Approx.), The value of the control valve opening target value EV sharply decreases with respect to the change in the value of the fuel amount parameter R.

Therefore, based on the fuel parameter R, E
The GR gas amount target value (EGR control valve opening target value EV)
By controlling as shown in FIG. 4, the characteristic of the EGR rate E _R shown in FIG. 2 can be obtained. In the present embodiment, the ECU 30 calculates the ratio R between the fuel injection amounts Qf _(fin) and Qf _(ful) set in the fuel injection control routine described later by a routine (not shown) executed at regular time intervals, 4 determines the opening degree EV of the EGR control valve 9 and outputs an opening degree instruction signal to the actuator 9a of the EGR control valve 9. As a result, the control valve opening degree EV is set according to the value of the fuel amount parameter R, and the EGR rate change characteristic of FIG. 2 can be obtained.

By the way, in actual operation, if the EGR rate is always controlled to the value shown in FIG. 2 regardless of the operating state of the engine, no problem such as generation of black smoke should occur. However, in actuality, when the operating state of the engine changes moment by moment such as during transient operation other than steady operation (for example, during acceleration of the engine), the actual EGR rate is always set to the value shown in FIG. It can be difficult to maintain.

For example, when the EGR rate E _R changes significantly in FIG. 2, the actual EGR rate changes to the target EGR rate because the residual EGR gas already supplied exists in the intake system. There will be a delay before. Also,
This delay time is not constant, and is greatly affected by the fresh air supply amount Qa per engine revolution and the engine speed NE. That is, the fresh air supply amount Qa and the engine speed NE
Is large, the replacement of the residual EGR gas with the fresh air is performed in a short time, so that the actual EGR rate reaches the target EGR rate of FIG. 2 with almost no delay even when the operating conditions change significantly, but Qa and NE Is small, it takes a relatively long time for the actual EGR rate to reach the target EGR rate.

Therefore, if it takes a long time to replace the residual EGR gas with the fresh air when the fuel injection amount Qf _(fin) is rapidly increased during engine acceleration, etc., the actual E
Q even though the GR rate has not dropped to the value in Figure 2.
Only f _(fin) increases, the amount of fuel becomes excessive, and there arises a problem that exhaust black smoke is generated. On the other hand, if the increase rate of the fuel injection amount Qf _(fin) is uniformly set low during acceleration as described above, on the contrary, in the case where replacement of the residual EGR gas with fresh air is performed in a short time, As a result, the increase of the fuel injection amount Qf _(fin) is delayed more than necessary, resulting in a problem such as deterioration of acceleration.

In order to prevent the above problem, in this embodiment, the EGR gas is corrected by reducing the fuel injection amount during acceleration according to the degree of replacement of the residual EGR gas in the engine intake system (time required for replacement). The above problem is solved by suppressing an increase in the fuel injection amount according to the degree of replacement of Hereinafter, the fuel injection amount reduction correction (moderation control) during acceleration according to the present embodiment will be described. As described above, the residual E in the intake system
The degree of replacement of the GR gas changes depending on the engine speed NE and the fresh air amount Qa. 5, the residual degree of substitution of the EGR gas (the time required for replacement) the changing trend of T _R, the fresh air intake amount Qa per engine revolution speed NE and the engine 1
It is the figure which represented and as a parameter.

The vertical axis in FIG. 5 indicates the degree of replacement of the residual EGR gas (time required for replacement) T _R when the amount of EGR gas is constant.
The horizontal axis indicates the fresh air intake amount Qa per engine revolution. Further, in the figure, the curves from NE1 to NE3 show the relationship between T _R and Qa when the rotational speed is constant, and the mutual relationship of rotational speeds is NE1>NE2> NE3.

As shown in FIG. 5, the substitution degree T _R is equal to the EGR
Under the condition that the gas amount is constant, if the engine speed NE is the same, the larger the fresh air intake amount Qa per engine revolution, the smaller the amount. Further, if the fresh air intake amount Qa is the same, it decreases in inverse proportion to the engine speed. FIG. 5 shows the substitution degree T _R under the condition that the EGR gas amount is constant, but in the present embodiment, the EGR rate E _R is controlled based on FIG. 2. Therefore, in reality, when the fresh air intake amount Qa increases, the EGR gas amount also increases accordingly. Therefore, under the condition where the rotation speed is constant, the replacement time T _R hardly changes even if Qa changes. do not do. Therefore, in the present embodiment, the substitution degree T _R changes in inverse proportion to only the engine speed NE. That is, in the present embodiment, if the engine speed is high, the residual EGR gas is replaced in a short time, so that it is possible to set the increasing speed of the fuel injection amount to be large, and conversely, if the engine speed is low, Since it takes time to replace the residual EGR gas, the fuel amount reduction correction that suppresses the increase rate of the fuel injection amount to a small amount (annealing control)
Is required.

As described above, the fuel smoothing control according to the substitution degree T _R can be achieved by controlling the fuel increase amount per unit time in proportion to the engine speed NE during engine acceleration. is there. For this purpose, the fuel may be increased at regular time intervals during acceleration, and the amount of increase per time may be increased in proportion to the engine speed. However, in this case, since it is necessary to change the amount of increase in the fuel at regular intervals, there is a problem that the control becomes slightly complicated. Therefore, in the present embodiment, the fuel increase amount per time is fixed to a constant value, and the fuel injection amount is increased by this constant value for each revolution of the engine at the time of engine acceleration, thereby performing the moderation control. When the fuel is increased for each revolution of the engine, the number of times the fuel injection amount is increased per unit time increases in proportion to the engine revolution speed. Is
The fuel injection amount increase rate per unit time proportional to the engine speed can be obtained. Therefore, the residual EG
It is possible to control the annealing of the fuel according to the degree of replacement of the R gas.

6 and 7 are flowcharts showing the fuel injection control of this embodiment. In the present embodiment, the routine of FIG. 6 is executed by the ECU 30 to determine the crankshaft 1 of the engine 1.
It is executed every rotation. When the routine starts in FIG. 6, in step 601, the intake pressure sensor 1 of FIG.
1, the rotation speed sensor 13, the accelerator opening sensor 15,
Intake pipe pressure PM, engine speed NE, accelerator opening θ
Are read respectively.

Next, at step 603, the basic fuel injection amount Qf _(gov) is calculated based on the engine speed NE and the accelerator opening θ read as described above. FIG.
Is Qf _(gov) and engine speed N in this embodiment.
FIG. 5 is a diagram showing a relationship between E and accelerator opening degree θ. As shown in FIG. 8, the basic fuel injection amount Qf _(gov) is equal to the engine speed N.
If E is the same, the larger the accelerator opening θ is, the larger the value is. If the accelerator opening θ is the same, the engine speed NE is increased.
The lower is, the larger the value is set.

The value of each Qf _{(gov) in} FIG. 8 is previously stored in the ECU 3 in the form of a numerical map using NE and θ as parameters.
0 is stored in the ROM 32, and in step 603, NE and θ read in step 601 are used.
The value of Qf _(gov) is read from this numerical map. Next, at step 605, the fresh air intake amount Qa per one revolution of the engine is calculated from the intake pipe pressure PM and the rotational speed NE read at step 601. As is known,
In a diesel engine, the fresh air intake amount per engine revolution is uniquely determined from the intake pipe pressure PM and the engine speed NE. In the present embodiment, the value of Qa measured by changing the conditions of PM and NE in advance is stored in the ROM 32 of the ECU 30 in the form of a numerical map using PM and NE. In step 605, this numerical map is stored. Based on the above, the fresh air intake amount Qa is calculated.

After calculating Qa from the above, step 60
In FIG. 7, the calculated Qa value is used to determine the upper limit value Qf _(ful) of the fuel injection amount at the current Qa from the relationship shown in FIG.
Is calculated, and in step 608, the two determination values Qf _(ref1) and Qf _{(ref2) of} the fuel injection amount are Qf _(ref1) = 0.
It is calculated as 8 × Qf _(ful) and Qf _(ref2) = 0.9 × Qf _(ref2) . The judgment values Qf _(ref1) and Qf _(ref2) will be described later.

Next, at step 611 in FIG. 7, the value of Qf _(gov) (basic fuel injection amount) calculated at step 603 is the actual fuel injection amount Qf _{(fin) i-1} at the time of execution of the previous routine.
It is determined whether it is greater than. Where Qf _(gov) > Q
If it is f _{(fin) i-1} , the basic fuel injection amount at the time of execution of this routine, which is determined from the engine speed NE and the accelerator opening θ, that is, the fuel amount Qf _(gov) required by the driver
Is the actual fuel injection amount Qf _{(fin) i-1} at the time of the previous routine execution
Since it is larger, it is determined that the engine is currently in acceleration operation. In this case, since it is necessary to adjust the increasing rate of the fuel injection amount so that exhaust black smoke is not generated, the smoothing control of the fuel injection amount from step 613 to step 621 is executed. In step 611, Qf _(gov) ≤
If it is Qf _{(fin ) i-1} , the engine is currently in steady operation or deceleration operation, and since there is no need for smoothing control of the fuel injection amount, the steps which will be described later directly without performing smoothing control. Proceed to 633.

Next, steps 613 to 621.
The moderation control of the fuel injection amount will be described. In this embodiment, the EGR control valve is controlled so as to maintain the target EGR rate shown in FIG. 2 even during acceleration. Therefore, during acceleration, the target EGR rate decreases with time according to the engine operating state. However, for example, when the engine speed is low, it takes a relatively long time until the EGR gas remaining in the intake system is replaced with fresh air or newly supplied EGR gas. Therefore, when the engine speed is low, the actual reduction rate of the EGR rate during acceleration is the target EGR rate.
The rate is smaller than the rate of decrease. That is, during acceleration, the actual EGR rate> target EGR rate occurs. In this case, if the fuel injection amount is increased based on the target EGR rate by ignoring the actual change in the EGR rate, the target EGR rate is dealt with even though the EGR rate has not actually decreased much. Since a large amount of fuel is injected, problems such as generation of black smoke will occur. In the present embodiment, the routines of FIGS. 6 and 7 are executed for each revolution of the engine to increase the fuel injection amount by a fixed amount. Therefore, when the engine speed is low, the increasing speed of the fuel injection amount becomes smaller according to the rotating speed, and the fuel is changed according to the degree of replacement of the residual EGR gas in the intake system, that is, the actual changing speed of the EGR rate. The injection amount is set.

On the other hand, when the engine speed is high, the EGR gas remaining in the intake system is immediately replaced, so that a large difference does not occur between the actual EGR rate and the target EGR rate even during acceleration. Therefore, the actual fuel injection amount is the target EG
Even if it is controlled according to the R rate, the problem of black smoke generation does not occur.
In the present embodiment, since the fuel injection amount is increased by a constant amount for each revolution of the engine in steps 613 to 621, the fuel injection amount increases rapidly when the engine speed is high. Therefore, in this case as well, the actual fuel injection amount changes the actual EGR rate change (in this case, the target EGR rate).
The speed of the engine is increased rapidly in accordance with the above-mentioned ratio), and excessive fuel injection amount smoothing is prevented and good acceleration of the engine can be obtained.

That is, in this embodiment, by increasing the fuel injection amount by a constant amount each time the routine is executed, the increasing speed of the fuel injection amount changes according to the degree of replacement of the residual EGR gas in the intake system, and is always appropriate. It is possible to obtain a high fuel injection increase speed. Further, FIG. 7 step 61
From 3 to step 621, the increment (constant value) of the fuel injection amount for each engine revolution is calculated as the actual fuel injection amount Qf.
_(fin) and the upper limit value Qf _(ful) of the fuel injection amount are changed stepwise according to the value of the ratio R (steps 613 and 61).
7, 621). That is, R = Qf _(fin) / Qf _(ful)
As the value of increases (approaches R = 1.0), the increment of the fuel injection amount per engine revolution is set to a smaller value.

The reason why the increment of the fuel injection amount is changed according to the value of R is as follows. That is, as described with reference to FIG. 4, the opening degree EV of the EGR control valve 9
Is set according to the value of R = Qf _(fin) / Qf _(ful) ,
When R is relatively small, EV is substantially constant, but as R approaches 1.0, it sharply decreases to R = 1.0.
Before, the EGR control valve is fully closed (EV = 0). Therefore, in the region where R approaches 1.0, EV changes greatly even if R slightly changes. Therefore, in this area R
When the change amount per one time (that is, the change amount of Qf _(fin) ) becomes large, the accuracy of the opening control of the EGR control valve may decrease. Therefore, in the present embodiment, as the value of R approaches 1.0, the amount of increase in the fuel injection amount for each injection is set to decrease gradually.

That is, in this embodiment, the steps are performed in advance.
At 609, the fuel upper limit value Qf_(ful)R = based on the value of
Qf corresponding to 0.8 and 0.9 (see FIG. 4)_(fin)of
Each value is Qf_(ref1), Qf_(ref2)Calculated as
The actual fuel injection amount Qf_{(fin )}But Qf_(fin)<Qf
_(ref1)In the region (that is, R <0.8), a relatively large
Increase the fuel injection amount each time the routine is executed by a fixed amount (add1)
Increase (steps 611 and 613). Then Qf
_(fin)Increase, Qf_(ref1)≤Qf_(fin)<Qf
_(ref2)(That is, 0.8 ≦ R <0.9)
And the fuel increase amount is a constant value (add
1-add2) to reduce the amount of change in R
(Steps 615, 617). Furthermore, Qf_(fin)> Qf
_(ref2)Qf up to the region of (R> 0.9)_(fin)increased
In this case, increase the fuel quantity by a smaller constant value (add1-ad
d2-add3). As a result,
The sensitivity of the change of the EGR control valve opening degree EV with respect to it becomes large.
In the region, the rapid change in R is reduced according to the sensitivity of EV.
It is possible to accurately control the EGR control valve.
You.

The increase value add1 and the decrease values add2, add3 of the fuel injection amount are determined by experiments or the like according to the type of each engine, but in the present embodiment, for example, add1≈2 × add2≈3.5. It is set to be about × add3. As described above, the increase amount of the fuel injection amount changes stepwise according to the value of R. In this case as well, if the value of R is in a constant region, the amount of fuel injection increases according to the engine speed. Needless to say, since the increasing speed changes, the optimum increasing speed of the fuel injection amount according to the degree of replacement of the EGR gas in the intake system can be obtained during acceleration.

As mentioned above, steps 613 to 621.
In after setting the current fuel injection quantity Qf _(fin) in a predetermined amount is increased from the fuel injection quantity Qf _{(fin) i-1} of the previous routine execution, set in step 623,625 Qf _(fin)
Limits the value of Qf _(fin) so that does not exceed Qf _(gov) calculated in step 603. Further step 627,
At 629, the value of Qf _(fin) is restricted so as not to exceed the upper limit value Qf _(ful) , and then Qf set at step 631.
The value of _(fin) is output to the drive circuit of the fuel injection valve. As a result, Qf _(fin) of fuel is injected into each cylinder.

In step 611, Qf _(gov) > Qf
If it is _{(fin) i-1} , then in step 633 Qf
The value of _(fin) is set to the value of Qf _(gov) calculated in step 603, and step 627 and thereafter are executed.

[0047]

As described above, in the present embodiment, at the time of engine acceleration, the fuel injection amount reduction correction during acceleration is performed according to the degree of replacement of the residual EGR gas in the engine intake system (moderation control).
Therefore, regardless of the engine operating condition, it is possible to effectively prevent generation of black smoke during acceleration and maintain good acceleration performance.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an automobile diesel engine.

FIG. 2 is a diagram illustrating setting of an EGR rate according to the present embodiment.

FIG. 3 is a diagram illustrating setting of an upper limit value of a fuel injection amount according to the present embodiment.

FIG. 4 is a diagram illustrating setting of an EGR control valve opening degree according to the present embodiment.

FIG. 5 shows the degree of replacement of residual EGR gas in the intake system,
It is a figure explaining a change by engine number of rotations and the amount of intake air.

FIG. 6 Reduction correction of fuel injection amount during acceleration (moderation control)
It is a part of the flowchart which shows an example.

FIG. 7: Reduction correction of fuel injection amount during acceleration (moderation control)
It is a part of the flowchart which shows an example.

FIG. 8 is a diagram illustrating setting of a basic fuel injection amount in the flowcharts of FIGS. 6 and 7.

[Explanation of symbols]

 1 ... Diesel engine 2 ... Intake passage 3 ... Exhaust passage 5 ... Turbocharger 9 ... EGR control valve 30 ... ECU

Claims (1)

[Claims] 1. A fuel control device for an internal combustion engine having an EGR device for recirculating a part of engine exhaust gas to an engine intake system, wherein an amount of exhaust gas set according to an operating state of the engine is supplied to the intake system. EGR control means for causing recirculation, basic fuel amount setting means for setting the basic fuel amount according to the operating state of the engine, and acceleration detection means for detecting that the engine is in an accelerating state When the engine is detected to be in an accelerating state, acceleration smoothing means for reducing and correcting the basic fuel amount according to the degree of replacement of residual exhaust gas with fresh air in the engine intake system, A fuel control device for an internal combustion engine provided.