JP2000120470A - Evaporated fuel processing device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure an always excellent driving state by setting a desired value of a purge gas rate showing a rate of a purge gas quantity to a fuel injection quantity, and controlling at least one of the purge gas quantity or the fuel injection quantity so that the purge gas rate becomes the desired value. SOLUTION: Fuel vapor generated in a fuel tank 26 is sent in a canister 22 through a conduit 25 to be adsorbed in activated charcoal 21. When opening a purge control valve 28, the fuel vapor separated from the activated charcoal 21 is mixed with air by the introduction of the air to be purged in a surge tank 13 as purge gas to be supplied to a combustion chamber 5 of an engine 1 to be burnt. In this case, a target vapor gas rate showing a rate of a purge gas flow rate to a basic injection quantity per a short time is controlled so as to increase as the basic injection quantity increases, and the target vapor gas rate is set so as to gradually increase just after starting the purge action.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor treatment system for an internal combustion engine.

[0002]

2. Description of the Related Art A canister for temporarily storing fuel vapor, a purge control valve for controlling the amount of purge gas purged from the canister into an intake passage downstream of a throttle valve, and an air-fuel ratio disposed in an engine exhaust passage A purge control valve that controls a degree of opening of the purge control valve so that a purge ratio (= purge gas amount / intake air amount), which is a ratio of a purge gas amount and an intake air amount, becomes a target purge rate. The purged fuel vapor amount is obtained from the deviation amount of the air-fuel ratio from the stoichiometric air-fuel ratio based on the output signal, and the fuel injection amount is reduced and corrected by an amount corresponding to this fuel vapor amount so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Such an internal combustion engine is known (see JP-A-5-52139). In this internal combustion engine, when the purge action is started, the target purge rate is gradually increased, and after a lapse of a certain period from the start of the purge action, the target purge rate is maintained at a constant value.

The reason why the purge rate is kept constant is to prevent the air-fuel ratio from changing when the intake air amount changes. That is, if the purge rate changes when the intake air amount changes, the ratio of the purge gas amount in the intake air changes, and as a result, the air-fuel ratio changes. Therefore, the purge rate is kept constant so that the ratio of the purge gas amount in the intake air does not change even if the intake air amount changes. As described above, the purge control is not limited to the above-described internal combustion engine, but is generally performed in the internal combustion engine in which the purge control is performed so that the purge rate is constant, that is, the purge gas amount increases in proportion to the intake air amount. Is performed.

[0004]

In an internal combustion engine in which purge control is conventionally performed, the fuel injection amount is increased as the intake air amount is increased, thereby increasing the output of the engine. That is, in this internal combustion engine, the output of the engine is controlled by increasing and decreasing the amount of intake air. In such an internal combustion engine, the fuel injection amount is increased as the intake air amount increases. Therefore, if the purge gas amount is increased as the intake air amount increases, the air-fuel ratio is kept constant without fluctuation of the engine output. It is possible to do.

[0005] However, depending on the internal combustion engine, if the purge rate is maintained at a constant value, there are internal combustion engines in which the output fluctuates and the exhaust emission deteriorates. A typical example of such an internal combustion engine is a stratified combustion internal combustion engine in which an air-fuel mixture is formed in a limited region in a combustion chamber. In this internal combustion engine, the air-fuel mixture is burned under excess air. Therefore, even if the intake air amount is increased, the output of the engine does not increase, and it is necessary to increase the fuel injection amount to increase the output of the engine. . That is, in this type of internal combustion engine, the output of the engine is controlled by increasing and decreasing the fuel injection amount. In such an internal combustion engine, generally, the ratio of the intake air amount to the fuel injection amount increases or decreases according to the operating state.

However, in such an internal combustion engine, if the purge rate is kept constant as in the conventional internal combustion engine,
That is, when the purge gas amount is increased as the intake air amount increases, the ratio of the purge gas amount to the fuel injection amount increases or decreases according to the operating state of the engine. As described above, when the ratio of the purge gas amount to the fuel injection amount increases or decreases, the output of the engine increases and decreases accordingly, and when the ratio of the purge gas amount to the fuel injection amount increases, the exhaust emission deteriorates. Therefore, when the amount of purge gas is changed in proportion to the amount of intake air as in a conventional internal combustion engine, the output of the engine fluctuates, causing a problem that the exhaust emission deteriorates.

[0007]

According to a first aspect of the present invention, there is provided a purge passage for purging fuel vapor generated in a fuel tank into an intake passage, and a purge passage from the purge passage to the intake passage. A purge control valve for controlling an amount of purge gas to be purged, an injection amount calculation unit for calculating a fuel injection amount, and a setting unit for setting a target value of a purge gas rate indicating a ratio of the purge gas amount to the fuel injection amount, And control means for controlling at least one of the purge gas amount and the fuel injection amount so that the purge gas rate becomes a target value.

[0008] In the second invention, in the first invention,
An air-fuel mixture is formed in a limited area in the combustion chamber, and the air-fuel mixture is ignited by a spark plug. In a third aspect based on the first aspect, the target value of the purge gas rate is changed according to the operating state of the engine. In a fourth aspect based on the third aspect, the target value of the purge gas rate is increased as the fuel injection amount increases.

According to a fifth aspect, in the third aspect,
The operating state of the engine includes a first operating state in which an air-fuel mixture is formed in a limited area in the combustion chamber, and a second operating state in which an air-fuel mixture is formed in the entire combustion chamber. In the state, the target value of the purge gas rate is set higher than in the first operation state. In a sixth aspect based on the first aspect, the target value of the purge gas rate is a constant value.

[0010] In a seventh invention, in the first invention,
Output fluctuation detecting means for detecting fluctuations in the output of the engine, wherein the control means gradually increases the purge gas rate toward a target value when the fluctuation in the output of the engine is smaller than a predetermined fluctuation amount; When the output fluctuation is larger than a predetermined fluctuation amount, the purge gas rate is gradually reduced.

According to an eighth aspect, in the first aspect,
Fuel vapor for estimating the amount of fuel vapor in the purge gas
And the basic fuel injection amount according to the required load.
Storage means to remember the basic fuel injection amount.
Injection by subtracting the amount of fuel vapor in the storage gas
The amount of fuel to be calculated is calculated. In the ninth invention, the first
In the present invention, it is assumed that the air-fuel ratio of the inflowing exhaust gas is lean.
NO_xIs the theoretical value of the air-fuel ratio of the exhaust gas
NO absorbed when air-fuel ratio or rich_xRelease N
O_xThe absorbent is placed in the engine exhaust passage, and NO _xAbsorbent or
NO_xTo release NO_xFlows into the absorbent
The air-fuel ratio of the exhaust gas is set to the stoichiometric air-fuel ratio or rich.

[0012] In the ninth invention is a tenth invention, the target value of the purge gas rate is raised when _the NO _x releasing processing from _the NO _x absorbent. In the eleventh invention, 9
In th invention, the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is made rich to when releasing the SO _x from _the NO _x absorbent. In a twelfth aspect based on the eleventh aspect, the target value of the purge gas rate is increased during the process of releasing SO _x from the NO _x absorbent.

According to a thirteenth aspect, in the first aspect, a throttle valve is disposed in the engine intake passage, a negative pressure generated in the intake passage downstream of the throttle valve is guided, and the negative pressure increases a braking force. The opening degree of the throttle valve is reduced when the negative pressure introduced into the brake booster decreases.

According to a fourteenth aspect, in the thirteenth aspect, the target value of the purge gas rate is increased when the opening degree of the throttle valve is reduced when the negative pressure introduced into the brake booster is reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is a main body of a stratified combustion internal combustion engine, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, and 6 is an inner wall surface of the cylinder head 3. A fuel injection valve 7 arranged at the peripheral portion, an ignition plug 7 arranged at the center of the inner wall surface of the cylinder head 3, 8
Represents an intake valve, 9 represents an intake port, 10 represents an exhaust valve, and 11 represents an exhaust port. The intake port 9 is connected to the corresponding intake branch 1
2 is connected to a surge tank 13, and the surge tank 13 is connected to an air cleaner 15 via an intake duct 14. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 14. On the other hand, the exhaust port 11 is connected to an exhaust manifold 18. The exhaust manifold 18 and the surge tank 13 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 19, and an electrically controlled EGR control valve 20 is provided in the EGR passage 19.
Is arranged.

[0016] As shown in FIG.
1 is provided. The canister 23 has a fuel vapor chamber 23 and an atmosphere chamber 24 on both sides of the activated carbon 21, respectively. The fuel vapor chamber 23 is on the one hand a conduit 25
To the fuel tank 26, and on the other hand a conduit 27
Through the surge tank 13. A purge control valve 28 controlled by an output signal of the electronic control unit 40 is disposed in the conduit 27. The fuel vapor generated in the fuel tank 26 is sent into the canister 22 via the conduit 25 and is adsorbed on the activated carbon 21. Purge control valve 2
When the valve 8 is opened, air is sent from the atmosphere chamber 24 through the activated carbon 21 and into the conduit 27. When the air passes through the activated carbon 21, the fuel vapor adsorbed on the activated carbon 21 is desorbed from the activated carbon 21, so that the air containing the fuel vapor, that is, the purge gas, enters the surge tank 13 through the conduit 27. Purged.

The exhaust manifold 18 contains, for example, a three-way catalyst.
Connected to the stored catalytic converter 29a.
The converter 29a is connected to another catalytic converter 29b.
You. An oxidation catalyst and a three-way catalyst are provided in the catalytic converter 29b.
NO when the medium and air-fuel ratio are lean_xTo reduce the air-fuel ratio.
NO absorbed when_xTo release and reduce NO
_xStorage-reduction catalyst, or large amount of unburned under excess oxygen
NO in the presence of HC_xNO to reduce_xSelective reduction catalyst
Is arranged.

The electronic control unit 40 is composed of a digital computer, and a ROM (read only memory) 42, a RAN (random access memory) 43, a CPU (microprocessor) 44, and an input port 45 interconnected by a bidirectional bus 41. And an output port 46. A pressure sensor 30 that generates an output voltage proportional to the absolute pressure in the surge tank 13 is disposed in the surge tank 13, and the output voltage of the pressure sensor 30 corresponds to A
The data is input to the input port 45 via the D converter 47. A water temperature sensor 31 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 31 is input to an input port 45 via a corresponding AD converter 47. A temperature sensor 32 for detecting an atmospheric temperature is mounted in the intake duct 14, and an output signal of the temperature sensor 32 is input to an input port 45 via a corresponding AD converter 47.

An output signal of an atmospheric pressure sensor 33 for detecting the atmospheric pressure is input to an input port 45 via a corresponding AD converter 47. A load sensor 35 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 34 is connected to the accelerator pedal 34, and the output voltage of the load sensor 35 is input to an input port 45 via a corresponding AD converter 47. . The input port 45 is connected to a crank angle sensor 36 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. An air-fuel ratio sensor 37 is disposed in the exhaust manifold 18, and an output signal of the air-fuel ratio sensor 37 is output to a corresponding AD converter 47.
Through the input port 45. On the other hand, the output port 46 is connected to the fuel injection valve 6,
The ignition plug 7, the step motor 16, the EGR control valve 20, and the purge control valve 28 are connected.

FIG. 2 shows the fuel injection amounts Q1, Q2, Q (= Q _1).
+ Q ₂ ), the injection start timing θS1, θS2, the injection completion timing θE1, θE2, and the average air-fuel ratio A in the combustion chamber 5.
/ F. In FIG. 2, the horizontal axis L indicates the amount of depression of the accelerator pedal 34, that is, the required load.
When the required load L as can be seen from Figure 2 is lower than L ₁ is the fuel injection Q2 is performed between θE2 from θS2 of the end of the compression stroke. At this time, the average air-fuel ratio A / F is considerably lean. Required load L first fuel injection Q1 is performed between θE1 from the beginning of the intake stroke of θS1 when between L ₁ and L _2, then the second fuel in between θS2 of θE2 of the end of the compression stroke Injection Q2 is performed. At this time, the air-fuel ratio is lean.

The required load L fuel injection Q in between θE1 from the beginning of the intake stroke of θS1 when greater than L ₂
1 is performed. At this time, in the region where the required load L is low, the average air-fuel ratio A / F is lean, and when the required load L increases, the average air-fuel ratio A / F becomes the stoichiometric air-fuel ratio, and when the required load L further increases, the average air-fuel ratio increases. The fuel ratio A / F is made rich. It is to be noted that the fuel injection Q1 is performed only in the operation region where the fuel injection Q2 is performed only at the end of the compression stroke, the operation region where the fuel injections Q1 and Q2 are performed twice, and only in the early stage of the intake stroke.
Is not determined only by the required load L, but is actually determined by the required load L and the engine speed.

The basic injection amount Q2 of the fuel injection at the end of the compression stroke is stored in advance in the ROM 42 in the form of a map as shown in FIG. 3A as a function of the depression amount L of the accelerator pedal 34 and the engine speed N. In addition, the basic injection amount Q1 of the fuel injection at the beginning of the intake stroke is
FIG. 3 as a function of the stepping amount L and the engine speed N of FIG.
It is stored in the ROM 42 in advance in the form of a map as shown in FIG.

The injection start timing θS2 of the fuel injection at the end of the compression stroke is stored in advance in the ROM 42 in the form of a map as shown in FIG. 4A as a function of the depression amount L of the accelerator pedal 34 and the engine speed N. The injection start timing θS1 of the fuel injection at the beginning of the intake stroke is also determined in advance in the form of a ROM as shown in FIG. 4B as a function of the depression amount L of the accelerator pedal 34 and the engine speed N.
42.

FIGS. 5A and 5B show that the required load L is L
₁ (FIG. 2), that is, a case where the fuel injection Q2 is performed only at the end of the compression stroke. FIG. 5B shows a case where the required load L is higher than that of FIG. 5A, that is, a case where the injection amount is large. FIG.
As shown in (A) and (B), a cavity 5a is formed on the top surface of the piston 4, and fuel is injected from the fuel injection valve 6 toward the bottom wall surface of the cavity 5a at the end of the compression stroke. Is done. This fuel is guided by the peripheral wall surface of the cavity 5a toward the spark plug 7, whereby an air-fuel mixture G is formed around the spark plug 7. In the embodiment according to the present invention, the space in the combustion chamber 5 around the air-fuel mixture G is filled with air or a mixed gas of air and EGR gas. Therefore, when the required load L is smaller than L ₁ (FIG. 2). The mixture G is formed in a limited area in the combustion chamber 5.

The mixture G formed around the ignition plug 7 is ignited by the ignition plug 7. In this case, if the mixture G is too thin, the mixture G will not ignite, thus causing misfire. On the other hand, if the mixture G is too rich, the spark plug 7
Carbon adheres to the electrode, and the ignition current leaks through the carbon. As a result, the ignition energy is reduced, thus also causing a misfire in this case. That is, it is necessary to form an air-fuel mixture G having an optimum concentration around the ignition plug 7 in order to ensure good ignition by the ignition plug 7.

When the volume occupied by the mixture G is the same, the concentration of the mixture G increases as the fuel injection amount increases. Therefore, in order to form an air-fuel mixture G having an optimum concentration around the ignition plug 7, the volume occupied by the air-fuel mixture G must be increased as the fuel injection amount increases. In other words, the air-fuel mixture G must be diffused as the fuel injection amount increases. In this case, the more the injection timing is advanced, the more the air-fuel mixture is diffused. Accordingly, in the embodiment according to the present invention, as shown in FIG. 2, as the required load L increases, that is, as the injection amount increases, the injection start timing θS2 is advanced. As a result, when the injection amount is large as shown in FIG. 5B, the volume occupied by the air-fuel mixture G is larger than when the injection amount is small as shown in FIG. 5A.

On the other hand, since it takes time for the mixture G to diffuse, the injection timing must be advanced as the engine speed N increases. Therefore, in the embodiment according to the present invention, the engine speed N
Is higher, the injection start timing θS2 is advanced. That is, in the embodiment according to the present invention, the injection start timing θS2 is determined so that the mixture G having the optimum concentration is formed around the ignition plug 7.

On the other hand, as described above, when the required load L is between L ₁ and L ₂ , fuel injection is performed twice. In this case, a lean mixture is formed in the combustion chamber 5 by the first fuel injection Q1 performed at the beginning of the intake stroke. Next, an air-fuel mixture having an optimum concentration is formed around the ignition plug 7 by the second fuel injection Q2 performed at the end of the compression stroke. This mixture is ignited by the spark plug 7,
This ignition flame causes the lean mixture to burn.

On the other hand, when the engine load L is greater than L ₂ homogeneous mixture of lean or stoichiometric or rich air-fuel ratio is formed in the combustion chamber 5 as shown in FIG. 2, the homogeneous mixture is It is ignited by the spark plug 7. Next, a case where the purge gas is purged from the conduit 27 into the surge tank 13 will be described.

In the embodiment according to the present invention, the required load L is L ₁
When it is smaller than the basic fuel amount, the basic fuel amount is determined from the map shown in FIG. On the other hand, the purge gas purged into the surge tank 13 is composed of a mixed gas of air and fuel vapor, and the fuel vapor in the purge gas is burned in the combustion chamber 5. That is, the fuel vapor is used to generate the output of the engine similarly to the injected fuel. Therefore, in the embodiment according to the present invention, the amount obtained by subtracting the fuel vapor amount from the basic fuel amount Q2 calculated from the map shown in FIG.

By the way, if the purge amount of the purge gas is reduced, the adsorption capacity of the activated carbon 21 saturates. Therefore, it is preferable to increase the purge amount of the purge gas as much as possible. However, this purge gas, ie, fuel vapor, diffuses throughout the combustion chamber 5. Therefore, when the injection amount is reduced as the fuel vapor amount increases as described above, the concentration of the air-fuel mixture G formed around the ignition plug 7 decreases as the purge gas amount increases. In this case, if the concentration of the air-fuel mixture G becomes too low, a misfire will occur.

Therefore, in the embodiment according to the present invention, the purge gas amount is reduced when the injection amount is small, and the purge gas amount is increased when the injection amount is large. That is, the purge gas amount is increased as the injection amount increases. In this case, the purge gas amount can be increased in proportion to the injection amount. That is, the purge gas ratio indicating the ratio of the purge gas amount to the injection amount can be made constant. However, it is preferable to change the purge gas rate according to the injection amount, particularly when the air-fuel mixture is formed in a limited area in the combustion chamber 5. Next, this will be described with reference to FIG.

FIGS. 6A and 6B schematically show the amount of air-fuel mixture in the combustion chamber 5. Note that FIG. 6A corresponds to FIG. 5A, and FIG. 6B corresponds to FIG. 5B. That is, FIG. 6 (A) shows a case where the injection amount is small, and therefore the air-fuel mixture is formed only in the vicinity of the ignition plug 7, and FIG. 6 (B) shows a case where the injection amount is large and the air-fuel mixture is dispersed. Is shown.

In FIGS. 6A and 6B, the solid line G
Indicates the amount of air-fuel mixture when the purging action is not performed, and the broken line G 'indicates the amount of air-fuel mixture collected around the ignition plug 7 when the purge gas is purged at the same purge gas rate. A broken line V indicates the amount of fuel vapor in the purge gas dispersed throughout the combustion chamber 5. When the purge gas is purged, the mixed gas amount G ′ collected around the ignition plug 7 is the sum of the mixed gas amount formed by the injected fuel and the fuel vapor amount V in the purge gas.

In the case shown in FIG. 6A, only a small amount of the total fuel vapor amount V in the purge gas is superimposed on the air-fuel mixture formed by the injected fuel. It becomes considerably smaller than the volume G. On the other hand, in the case shown in FIG. 6B, most of the total fuel vapor amount V in the purge gas is superimposed on the air-fuel mixture formed by the injected fuel. Not much less than G.

That is, in the case shown in FIG. 6B, even if the purge gas rate is increased, the concentration of the air-fuel mixture around the ignition plug 7 does not decrease so much. Therefore, in this case, the purge gas rate is increased. No misfires occur. On the other hand, in the case shown in FIG. 6A, when the purge gas rate is increased, the concentration of the air-fuel mixture around the ignition plug 7 is considerably reduced, thus causing a misfire. Therefore, in the case shown in FIG.
Therefore, the purge gas rate must be reduced as compared with the case shown in FIG.

Therefore, in the embodiment according to the present invention, as the basic injection amount Q increases, the basic injection amount per unit time (g / g) increases.
The target purge gas rate tPGR (l / g) indicating the ratio of the purge gas flow rate PG (l / sec) to the purge gas flow rate PG (l / g) is increased. That is, in FIG. 7, a, b, and c are a <
There is a relationship of b <c, and therefore, as can be seen from FIG. 7, the target purge rate tPGR increases as the basic injection amount Q increases.

More specifically, in FIG. 7, the horizontal axis N indicates the engine speed, and the dashed line X indicates the boundary between the region where the average air-fuel ratio A / F is lean and the region where the average air-fuel ratio A / F is stoichiometric. In the region where the average air-fuel ratio A / F is lean, that is, in the region where the injection amount Q is smaller than the boundary X, the target purge gas rate tPGR is gradually increased to c as the injection amount Q increases, and the boundary X In a region where the injection amount Q is larger than the target value, the target purge gas rate tPGR is set to the constant value c. The target purge gas rate tPGR shown in FIG. 7 is preliminarily stored in a ROM 42 as a function of the basic injection amount Q and the engine speed N.
Is stored within.

The target purge gas rate t shown in FIG.
PGR indicates the target purge gas rate after a short time from the start of the purge action, and the target purge gas rate rPGR immediately after the start of the purge action is gradually increased as shown in FIG. In FIG. 8, the horizontal axis ΣP
G (1) is the surge tank 13 after the purge action is started.
3 shows the integrated value of the flow rate of the purge gas purged.
In the embodiment according to the present invention, the rPGR and tPGR shown in FIG.
Is smaller than the target purge gas rate PGR. Therefore, it can be seen that when the purge action is started, the target purge scum ratio PGR is gradually increased along the rPGR until the target purge gas ratio PGR becomes tPGR.

Next, a method of calculating the integrated value of the purge gas flow rate ΣPG (1) will be described with reference to FIGS. FIG. 9 shows a purge gas flow rate per unit time when the purge control valve 28 is fully opened, that is, a fully opened purge gas flow rate PG100 (l / sec). This fully-open purge gas flow rate PG100 (l / sec) is a function of the pressure difference (PA-PM) between the atmospheric pressure PA and the absolute pressure PM in the surge tank 13 as shown in FIG. On the other hand, the purge control valve 28 is controlled based on the ratio of the time during which the purge control valve 28 should be opened within a certain time, that is, the duty ratio DUTY. As shown in FIG. 10, the purge gas flow rate per unit time (l / sec) is the duty ratio DUTY (%).
Is proportional to Therefore, the actual purge gas flow rate (l / sec) per unit time can be calculated by multiplying the fully open purge gas flow rate (l / sec) shown in FIG. 9 by DUTY (%) / 100%, and this purge gas flow rate (l / sec). ), An integrated value ΣPG (1) of the purge gas flow rate is obtained. Note that the relationship shown in FIG. 9 is stored in the ROM 42 in advance.

Next, the purge gas rate is set to the target purge gas rate PG
The duty ratio D of the purge control valve 28 required to set R
A method for obtaining UTY will be described. As described above, the fully open purge gas flow rate PG100 per unit time (l / se
c) shows the valve opening ratio of the purge control valve 28, that is, DUTY / 1.
When multiplied by 00, the multiplication result is PG100 · DUTY /
Reference numeral 100 denotes a purge gas flow rate PG (l / sec) per unit time when the duty ratio of the purge control valve 28 is DUTY, as shown in the following equation.

PG (l / sec) = PG100 (l / sec)
) .DUTY / 100 Therefore, the duty ratio DUTY when the purge gas amount is PG (1 / sec) is expressed as follows. DUTY = 100 · PG / PG100 On the other hand, if the engine speed is N, the basic injection amount per unit time is represented by Q · N / 60 (g / sec), so the purge gas rate is represented by the following equation.

Purge gas rate = PG (1 / sec) / (Q ·
N / 60 (g / sec)) Therefore, when the duty ratio DUTY is represented by the purge gas rate, it becomes as follows. DUTY = 100 ・ Purge gas rate ・ Q ・ (N / 60) /
PG100 Therefore, the duty ratio DUTY required to set the purge gas rate to the target purge gas rate PGR is expressed by the following equation.

DUTY = 100 · PGR · Q · (N / 6
0) PG100 If the duty ratio DUTY of the purge control valve 28 is set to the duty ratio DUTY calculated from the above equation, the purge gas rate becomes the target purge gas rate PGR. On the other hand, as described above, in the embodiment according to the present invention, the amount obtained by subtracting the fuel vapor amount in the purge gas from the basic fuel amount Q is the injection amount to be actually injected. Next, this will be described.

The fuel vapor concentration in the purge gas is set to PV (g
/ L), the amount of fuel vapor in the purge gas (g / sec)
) Is represented by the following equation. Fuel vapor amount (g / sec) = PG (l / sec) PV
(G / l) Here, when the target purge gas rate PGR is determined, the purge gas flow rate PG is determined, so the fuel vapor concentration PV in the purge gas
Once (g / l) is determined, the fuel vapor amount (g / sec) is determined.

In the embodiment according to the present invention, the fuel vapor concentration PV (g / l) in the purge gas is estimated based on the ambient temperature. That is, when the purge action is started, the amount of the fuel vapor adsorbed on the activated carbon 21 gradually decreases. Therefore, as shown in FIG. 11A, the fuel vapor concentration PV in the purge gas becomes the integrated value of the purge gas flow rate ΣPG
Decreases as the number increases. Therefore, in the embodiment according to the present invention, the relationship shown in FIG. 11A is obtained in advance by an experiment, and the fuel vapor concentration PV is estimated based on the relationship shown in FIG.

When the ambient temperature rises, the fuel tank 26
The fuel evaporating action in the inside becomes active, and as a result, FIG.
As shown in FIG. 1 (B), the increase amount ΔPV (g / l) of the fuel vapor concentration per unit time increases as the atmospheric temperature Ta increases. Therefore, in this embodiment, the relationship shown in FIG. 11B is obtained in advance by an experiment, and the increase amount ΔPV of the fuel vapor concentration per unit time is estimated based on the relationship shown in FIG. The fuel vapor concentration PV is estimated in consideration of ΔPV.

On the other hand, when the fuel vapor amount (g / sec) is obtained, a fuel vapor ratio EVR indicating the ratio of the fuel vapor amount to the basic injection amount is obtained from the following equation. EVR = fuel vapor amount (g / sec) / injection amount per unit time Q · N / 60 (g / sec) = PG · PV / (Q · N
/ 60) As described above, the fuel amount tQ to be injected is a value obtained by subtracting the fuel vapor amount from the basic injection amount Q. In this case, the injection amount to be reduced is Q · EVR. Therefore, the fuel amount tQ to be injected is expressed by the following equation.

TQ = Q · (1−EVR) As described above, the target purge gas rate PGR is set to the smaller value of rPGR and tPGR shown in FIG. In this case, the target purge gas rate PGR is rPG shown in FIG.
The smaller value of R and tPGR can be used as it is. However, in particular, when the air-fuel mixture is formed in a limited area in the combustion chamber 5, the combustion becomes unstable when the purge gas is purged, and the output torque of the engine tends to fluctuate. Therefore, it can be said that it is preferable to determine the target purge gas rate PGR so that the output torque fluctuation of the engine does not increase.

Therefore, in the embodiment according to the present invention, as long as the output torque fluctuation of the engine does not exceed a predetermined fluctuation amount, rP
The target purge gas rate PGR is gradually increased toward GR or tPGR, and then the target purge gas rate PGR is maintained at rPGR or tPGR as long as the output torque fluctuation of the engine does not exceed a predetermined fluctuation amount. In this case, if the output torque fluctuation of the engine becomes larger than a predetermined fluctuation amount, the target purge gas rate PGR is decreased.

As described above, in the embodiment according to the present invention, the target purge gas rate PGR is controlled based on the torque fluctuation amount of the engine output. Therefore, an example of a method of calculating the torque fluctuation amount will be schematically described next. For example, the angular velocity of the crankshaft while the crankshaft rotates from compression top dead center (hereinafter referred to as TDC) to 30 ° after compression top dead center (hereinafter referred to as ATDC) is referred to as a first angular velocity ωa, and the crankshaft is referred to as ATDC. The angular velocity of the crankshaft during rotation from 60 ° to ATDC 90 ° is set to a second angular velocity ω
In the case of b, when the combustion is performed in each cylinder, the combustion pressure increases the angular velocity of the crankshaft from the first angular velocity ωa to the second angular velocity ωb. At this time, assuming that the rotational inertia moment of the engine is I, the kinetic energy is changed from (1/2) · Iωa ² to (1 /
2) It is raised to Iωb ² . Roughly speaking, the amount of increase in kinetic energy (1/2) · I · (ωb ² −ω
a ² ), the generated torque is (ω
b ² −ωa ² ). Therefore, the generated torque is obtained from the difference between the square of the first angular velocity ωa and the square of the second angular velocity ωb. Next, a method of calculating the torque generated by each cylinder will be described with reference to FIG. As described above, the crank angle sensor 36 generates an output pulse every time the crankshaft rotates by 30 ° crank angle.
2, # 3, # 4 are arranged to generate output pulses at the compression top dead center TDC. Accordingly, the crank angle sensor 36 generates an output pulse every 30 ° crank angle from the TDC of each of the cylinders # 1, # 2, # 3, and # 4. The ignition sequence of the internal combustion engine used in the present invention is 1-3-4-2.

In FIG. 12, the vertical axis T30 represents the elapsed time of a 30 ° crank angle from when the crank angle sensor 36 generates an output pulse to when the next output pulse is generated. Also, Ta (i) is the AT from the TDC of the i-th cylinder.
It shows the elapsed time up to DC 30 ° and Tb (i)
Indicates the elapsed time from the ATDC of 60 ° to the ATDC of 90 ° for the i-th cylinder. Therefore, for example, Ta (l) indicates the elapsed time from TDC of the first cylinder to ATDC 30 °, and Tb (1) indicates the ATDC 60 of the first cylinder.
It indicates the elapsed time from ° to ATDC 90 °. On the other hand, the 30 ° crank angle is changed to the elapsed time T30.
, The result of the division represents the angular velocity ω.
Therefore, 30 ° crank angle / Ta (i) represents the first angular velocity ωa in the i-th cylinder, and 30 ° crank angle / Tb (i) represents the second angular velocity ωb in the i-th cylinder. Become.

FIG. 13 shows a routine for calculating the amount of torque fluctuation. This routine is executed by interruption every 30 ° crank angle. Referring to FIG. 13, first, at step 100, the ATD of the current i-th cylinder is set.
It is determined whether or not C is 30 °. If the ATDC of the i-th cylinder is not 30 °, the routine jumps to step 102, where it is determined whether or not the ATDC of the i-th cylinder is 90 °. If the ATDC of the i-th cylinder is not 90 ° at present, the processing cycle is completed.

On the other hand, in step 100, the current i
When it is determined that the ATDC of the cylinder No. 30 is 30 °, the routine proceeds to step 101, where the TD of the i-th cylinder is determined from the difference between the current time TIME and the time TIME0 before the crank angle of 30 °.
The elapsed time Ta (i) from C to 30 ° ATDC is calculated. Next, when it is determined in step 102 that the ATDC of the i-th cylinder is 90 °, the routine proceeds to step 103, where the ATDC of the i-th cylinder is obtained from the difference between the current time TIME and the time TIME0 30 ° before the crank angle.
Elapsed time Tb (i) from 60 ° to 90 ° ATDC
Is calculated.

Next, at step 104, the generated torque DN (i) of the i-th cylinder is calculated based on the following equation. DN (i) = ωb ² −ωa ² = (30 ° / Tb (i))
²⁻ (30 ° / Ta (i)) ² Next, at step 105, the torque fluctuation amount DLN (i) during one cycle of the same cylinder is calculated based on the following equation.

DLN (i) = DN (i) j−DN (i) Here, DN (i) j represents the torque generated in the same cylinder one cycle (720 ° crank angle) before DN (i). ing. Next, at step 106, the count value C is incremented by one. Next, at step 107, it is determined whether or not the count value C has become 4, that is, whether or not the torque fluctuation amount DLN (i) has been calculated for all the cylinders. When C = 4, the routine proceeds to step 108, where the average value of the torque fluctuation amounts DLN (i) of all cylinders represented by the following equation is set as the final torque fluctuation amount SM.

SM = (DLN (1) + DLN (2) + D
LN (3) + DLN (4)) / 4 Next, at step 109, the count value C is set to zero. Next, a purge control routine will be described with reference to FIGS. Referring to FIGS. 14 and 15, first, at step 200, it is determined whether or not the purge condition is satisfied. For example, when the engine cooling water temperature is 80
When the temperature is equal to or higher than 30 ° C. and 30 seconds have elapsed after the start of the engine, it is determined that the purge condition has been satisfied. When the purge condition is satisfied, the routine proceeds to step 201, where it is determined whether or not the supply of fuel is stopped. If the fuel supply has not been stopped, the routine proceeds to step 202.

In step 202, the fully open purge gas flow rate PG100 is calculated from the relationship shown in FIG. 9 based on the atmospheric pressure PA detected by the atmospheric pressure sensor 33 and the absolute pressure PM detected by the pressure sensor 30. Next, at step 203, the purge gas flow rate PG per unit time is calculated from the following equation using the current duty ratio DUTY.

PG = PG100.DUTY / 100 Next, at step 204, the purge gas flow rate PG is added to the integrated value ΣPG of the purge gas flow rate. Next, at step 205, the target purge gas rate rPGR is calculated from the relationship shown in FIG. 8 based on the integrated value ΣPG of the purge gas flow rate. Next, at step 206, the target purge gas rate tPGR is calculated from the relationship shown in FIG. Then step 2
In 07, the smaller of rPGR and tPGR is set as the allowable maximum value MAX of the target purge gas rate.

Next, at step 208, the torque variation S
M is large it is determined whether than the variation amount SM ₀ determined in advance. When SM ≦ SM _0, the routine proceeds to step 209, where a constant value ΔE1 is added to the target purge gas rate PGR. Step 2 at the time of this against SM> SM ₀
Proceeding to 10, a constant value ΔE2 is calculated from the target purge gas rate PGR.
Is subtracted. Next, at step 211, it is determined whether or not the target purge gas rate PGR is larger than the allowable maximum value MAX. When PGR ≧ MAX, the routine proceeds to step 212, where the allowable maximum value MAX is set as the target purge gas rate PGR.

That is, SM> SM₀The PGR is small
Be killed. On the other hand, SM ≦ SM ₀Then PGR is
Increased, SM ≦ SM₀PGR is MA as long as
X. Next, in step 213, FIG.
The basic injection amount Q is calculated from the map shown in FIG. This
The basic injection amount Q of FIG.₁
Is equal to Q2 and L₁≦ L <L_TwoIn the area of Q
1 is the sum of Q2 and L ≧ L_TwoIs equal to Q1 in the area
No. Next, at step 214, the relationship shown in FIG.
Is used to calculate the fuel vapor concentration PV. Then step
At 215, the fuel vapor concentration is determined from the relationship shown in FIG.
Is calculated. Then in step 216
Is the integrated value of the increase amount of the fuel vapor ΣΔPV and the increase amount Δ
PV is added. Next, at step 217, the fuel base
The integrated value ΣΔPV is added to the concentration
Is the final fuel vapor concentration PV.

Next, at step 218, a duty ratio DUTY required to set the purge gas rate to the target purge gas rate PGR is calculated based on the following equation. DUTY = 100 · (PGR · Q · N / 60) / PG1
Next, at step 219, the fuel vapor rate EVR is calculated from the following equation using the fuel vapor concentration PV.

EVR = PG · PV / (Q · N / 60) Next, at step 220, the duty ratio DUTY is set to 10
It is determined whether it is 0% or more. When DUTY <100%, the routine proceeds to step 223, where EVR is the fuel vapor rate t.
EV. On the other hand, when DUTY ≧ 100%, the routine proceeds to step 221, where the duty ratio DUTY is 1
Then, the routine proceeds to step 222, where the fuel vapor rate tEV is calculated based on the following equation.

TEV = PG100 · PV / (Q · N / 60) That is, since PG100 · PV represents the amount of fuel vapor purged when DUTY = 100%, the fuel vapor rate tEV is expressed by the above equation. Is done. Step 20
When it is determined at 0 that the purge condition is not satisfied, or when it is determined at step 201 that the supply of fuel is stopped, the routine proceeds to step 224, where the duty ratio DUTY is made zero, and then at step 225
In the above, the fuel vapor rate tEV is set to zero. At this time, the purging operation is stopped.

FIG. 16 shows a routine for controlling the fuel injection, and this routine is repeatedly executed. Referring to FIG. 16, first, in step 300, it is determined whether or not only the fuel injection Q2 is performed. When only the fuel injection Q2 is performed, the routine proceeds to step 301, where the basic injection amount Q2 is calculated from the map shown in FIG. Next, at step 302, the final injection amount tQ2 is calculated based on the following equation.

TQ2 = Q2 · (1−tEV) Next, at step 303, the injection start timing θS2 is calculated from the map shown in FIG.
2 and the engine speed N, the injection completion timing θE2 is calculated. On the other hand, when it is determined in step 300 that only the fuel injection Q2 has not been performed, the routine proceeds to step 304, where it is determined whether or not the fuel injections Q1 and Q2 are performed. When the fuel injections Q1 and Q2 are performed, the routine proceeds to step 305, where the basic injection amounts Q1 and Q2 are calculated from the maps shown in FIGS. Next, at step 306, the final injection amount tQ1 is calculated based on the following equation.
Is calculated.

TQ1 = Q1 · (1−tEV) Next, at step 307, the final injection amount tQ2 is calculated based on the following equation. tQ2 = Q2 · (1−tEV) Next, at step 308, injection start timings θS1 and θS2 are calculated from the maps shown in FIGS. 4A and 4B, and these θS1, θS2, injection amounts Q1, Q2, and engine speed are calculated. The injection completion timings θE1 and θE2 are calculated from N.

In this case, the total basic injection amount Q (= Q1
+ Q2), the total amount of fuel tQ to be injected (= Q (1-tE
V)), and determine the final injection amount tQ1 as tQ1 = tQ−
Q2, and the final injection amount tQ2 may be set to tQ2 = Q2. On the other hand, when it is determined in step 304 that the fuel injections Q1 and Q2 have not been performed, the routine proceeds to step 309, where the basic injection amount Q1 is calculated from the map shown in FIG. Next, at step 310, the final injection amount tQ1 is calculated based on the following equation.

TQ1 = Q1 ・ (1−tEV) Next, at step 311, the injection start timing θS1 is calculated from the map shown in FIG.
1 and the engine speed N, the injection completion timing θE1 is calculated. 1 to 16 with reference to FIGS.
A modification of the embodiment shown in FIG. Note that FIG.
In FIG. 7, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

Referring to FIG. 17, the internal combustion engine comprises a four-cylinder internal combustion engine having first cylinder # 1, second cylinder # 2, third cylinder # 3, and fourth cylinder # 4. The order is 1-3-4-2. In this modification, two cylinders whose ignition order is every other one, for example, the first cylinders # 1 and # 4
The second cylinder # 4 is connected to the common first exhaust manifold 18a, and the ignition sequence of the remaining second cylinder # 2 is every other cylinder # 4.
The second exhaust manifold 18 common to the second and third cylinders # 3
b. Each exhaust manifold 18a, 18b
Are connected to catalytic converters 29a each containing a three-way catalyst or an oxidation catalyst, and the outlet of each catalytic converter 29a is connected to the inlet of a catalytic converter 29b via an exhaust pipe 18c. A NO _x storage-reduction catalyst (hereinafter, referred to as a NO _x absorbent) 60 is disposed in the catalytic converter 29b,
An air-fuel ratio sensor 61 is arranged at the gathering portion of the exhaust pipe 18c.

As shown in FIG. 17, in this modification, the conduit 27 of the canister 22 is connected to the intake duct 14 downstream of the throttle valve 17, and the throttle valve 17
The negative pressure generated in the downstream intake duct 14 is led to the brake booster 70. The brake booster 70 includes a power piston 71, a first chamber 72 and a second chamber 73 formed on both sides of the power piston 71, an operating rod 75 having a plunger 74, and an operating valve 76. A push rod 77 is fixed to the power piston 71, and the push rod 77 drives a master cylinder 78 that generates a brake hydraulic pressure. The operating rod 7
5 is connected to the brake pedal 79. The first chamber 72 is connected to the intake duct 14 downstream of the throttle valve 17 via a negative pressure conduit 80, and a check valve 81 which can flow only from the first chamber 72 to the intake duct 14 in the negative pressure conduit 80. Is arranged. When a negative pressure greater than the negative pressure in the first chamber 72 is generated in the intake duct 14 downstream of the throttle valve 17, the check valve 81 opens, so that the negative pressure in the first chamber 72 is generated in the intake duct 14. Is maintained at the maximum negative pressure.

As shown in FIG. 17, the brake pedal 7
When the valve 9 is released, the first chamber 72 and the second chamber 73 are in communication with each other through a pair of communication passages 82 and 83. Therefore, the same negative pressure is maintained in the first chamber 72 and the second chamber 73. Has occurred. Next, when the brake pedal 79 is depressed, the operating valve 76 moves to the left together with the operating rod 75. As a result, the communication passage 82 is shut off by the operating valve 76, and the plunger 74 is separated from the operating valve 76, so that the second chamber 73 is opened to the atmosphere through the atmosphere communication passage 84.
Inside becomes atmospheric pressure. Therefore, a pressure difference is generated between the first chamber 72 and the second chamber 73, and the power piston 71 is moved leftward by the pressure difference.

On the other hand, when the brake pedal 79 is released, the air communication passage 84 is closed by the plunger 74 and the communication passages 82 and 83 are opened, so that the negative pressure in the first chamber 72 is reduced by the communication passages 82 and 83. Through the second chamber 73. As a result, the negative pressure in the second chamber 73 becomes the same as the negative pressure in the first chamber 72 again. As shown in FIG. 17, a pressure sensor 85 for detecting the absolute pressure in the first chamber 72 is disposed in the first chamber 72.

In the modification shown in FIG.
The torque fluctuation amount is calculated by the routine shown in FIG.
The routine shown in FIG. 14 and FIG.
Control is performed, and injection is performed according to the routine shown in FIG.
Control is performed. However, in this modification, these controls
In addition to NO_xNO from absorbent 60_xAnd SO _x
Release control and inside the first chamber 72 of the brake booster 70
Is performed. So first of all, NO_xAbsorbent
NO from 60_xThe release control will be described.

[0086] Housed in catalytic converter 29b
NO_xThe absorbent 60 uses, for example, alumina as a carrier.
For example, potassium K, sodium Na, lithium L
i, alkali metal such as cesium Cs, barium B
a, alkaline earth such as calcium Ca, lanthanum L
a, at least selected from rare earths such as yttrium Y
And a noble metal such as platinum Pt.
You. Engine intake passage, combustion chamber 5 and NO_xAbsorbent 60
Air and fuel (carbon
NO) ratio is NO_xAir-fuel ratio of exhaust gas flowing into absorbent 60
This NO_xAbsorbent 60 is air-fueled exhaust gas
NO when ratio is lean_xAbsorbs the incoming exhaust gas
NO absorbed when air-fuel ratio becomes stoichiometric or rich_x
Releases NO _xPerforms the absorption and release action. Note that NO_xSucking
Fuel (hydrocarbon) or empty space in the exhaust passage upstream of the absorbent 60
When no air is supplied, the air-fuel ratio of the inflowing exhaust gas is combustion
Equals the air-fuel ratio in the chamber 5 and therefore in this case N
O_xThe absorbent 60 has a lean air-fuel ratio in the combustion chamber 5.
Sometimes NO_xAnd the air-fuel ratio in the combustion chamber 5 becomes
NO absorbed at stoichiometric air-fuel ratio or rich_xEmit
Will be.

[0076] _the NO _x absorbent 60 be disposed the _the NO _x absorbent 60 in the engine exhaust passage is performing absorption and release action of actually NO _x is also not clear portion detailed mechanism of action out this absorbing . However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the internal combustion engine shown in FIG. 17, combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean.
Thus when the air-fuel ratio is performed is combusted in a lean state oxygen concentration in the exhaust gas is high, these oxygen O ₂ as is shown in FIG. 18 (A) at this time O ₂ ^- or O It adheres to the surface of platinum Pt in the form of ^2- . On the other hand, NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ). Then part of the produced NO ₂ while bonding with the barium oxide BaO is absorbed into the absorbent while being oxidized on the platinum Pt 28 nitrate ions as shown in (A) NO ₃ ^-
Diffuses into the absorbent in the form of In this way, NO _x becomes N
It is absorbed in the O _x absorbent 60. As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- are generated. You.

On the other hand, the air-fuel ratio of the inflowing exhaust gas is made rich.
The concentration of oxygen in the incoming exhaust gas decreases,
NO on the surface of gold Pt_TwoIs reduced. NO_Twoof
When the amount of production decreases, the reaction reverses (NO_Three ^-→ NO_Two)
And thus nitrate ion NO in the absorbent_Three ^-Is NO
_TwoReleased from the absorbent in the form of NO at this time_xAbsorbent
NO released from 60_xIs shown in FIG. 18 (B).
A large amount of unburned HC and CO contained in the inflow exhaust gas
It is reduced by reaction. In this way, platinum Pt
NO on surface_TwoWhen no longer exists, the next
NO_TwoIs released. Therefore, the air-fuel ratio of the incoming exhaust gas
Is enriched in a short time, NO _xAbsorbent 60?
NO_xIs released, and the released NO_xIs returned
NO in the atmosphere to be removed_xWill not be released
No.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at stoichiometric air-fuel ratio_xNO from absorbent 60_xIs released
Is done. However, the air-fuel ratio of the inflowing exhaust gas is
NO if ratio_xNO from absorbent 60_xGradually
NO because only _xAbsorbed by the absorbent 60
All NO_xIt takes a slightly longer time to release.

[0080] Incidentally there is a limit to the absorption of NO _x capacity of the NO _x absorbent 60, absorption of NO _x capacity of the NO _x absorbent 60 needs to release the NO _x from the NO _x absorbent 60 before saturation. For this purpose it is necessary to estimate the amount of NO _x is absorbed in the NO _x absorbent 60. Therefore, as shown in FIG. 19 (A) as a function of the NO _x absorption amount NA of the required load L and engine speed N per unit time when it is carried out the combustion under a lean air-fuel ratio in this modification It is determined in advance in the form of a map, and N per unit time when combustion is performed under a stoichiometric air-fuel ratio or a rich air-fuel ratio.
O _x emissions NB fuel ratio as shown in FIG. 19 (B) A /
Determined in advance as a function of F, and integrating the absorption of NO _x amount NA per these unit time, or per unit time NO
_the NO _x absorbent by subtracting the _x emissions NB 60
So that to estimate the amount of NO _x ΣNOX absorbed in the. NO _x is made to release from _the NO _x absorbent 60 when exceeding the permissible maximum value N _max of absorption of NO _x amount ΣNOX has been determined in advance in this modification.

The exhaust gas contains SO _x , and the NO _x absorbent 60 contains not only NO _x but also SO _x
Is also absorbed. It is considered that the mechanism of absorbing SO _x into the NO _x absorbent 60 is the same as the mechanism of absorbing NO _x . That is, the case where platinum Pt and barium Ba are carried on the carrier as in the case of the NO _x absorption mechanism will be described as an example. As described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen O ₂ Is O ₂
^- or O is deposited on the surface of the platinum Pt in ^2-form, SO ₂ in the inflowing exhaust gas on the surface of the platinum Pt O ₂ ^- or O ^2-
And SO ₃ . Next, a part of the generated SO ₃ is further oxidized on the platinum Pt, is absorbed in the absorbent and combines with the barium oxide BaO to form the sulfate ion SO 3.
₄ Diffusion into the absorbent in the form of ^2- , stable sulfate BaSO
Generate ₄ .

However, this sulfate BaSO_FourIs stable
And it is difficult to disassemble.
Sulfate BaSO_FourIs not disassembled
Will remain. Therefore NO_xAs time passes in the absorbent 60
Sulfate BaSO_FourWill increase, thus
NO as time goes by_xAbsorbent 60 absorbs
NO_xThe amount will be reduced. Therefore NO_xAbsorbent
SO absorbed in 60 _xNO when the amount increases_xSucking
SO from extractant 60_xMust be released.

When the temperature of the NO _x absorbent 60 rises, for example, when the temperature of the NO _x absorbent 60 becomes 600 ° C. or higher, sulfate BaSO ₄ is decomposed. At this time, if the air-fuel ratio of the inflowing exhaust gas is made rich, the NO _x Absorbent 60 to SO
_x is released. _The NO _x absorbent 6 to release SO _x amount SB per unit time at this time is shown in FIG. 20 (A)
It increases as the temperature TC of 0 increases. Therefore, in this modification, when the SO _x absorption amount ΣSO _x exceeds a predetermined allowable maximum value S _max , the temperature of the NO _x absorbent 60 is raised to 600 ° C. or more and the air-fuel ratio of the inflowing exhaust gas is made rich. From the NO _x absorbent 60 to SO
_x is released.

On the other hand, as described above, the braking force is determined by the pressure difference between the negative pressure in the first chamber 72 of the brake booster 70 and the pressure in the first chamber 73, that is, the atmospheric pressure PA and the first chamber 72.
The pressure difference (PA-PB) is increased by the pressure difference (PA-PB) with respect to the absolute pressure PB, and therefore, in order to secure a sufficient braking force, the pressure difference (PA-PB) is maintained at a constant pressure difference ΔP _min or more. It is necessary. Therefore by increasing the negative pressure of the pressure difference (PA-PB) is a throttle valve 17 downstream of the intake duct 14 to reduce the opening degree of the throttle valve 17 when it becomes smaller than a predetermined differential pressure [Delta] P _min in this modification, Thereby, the pressure difference (PA-PB) is increased. In practice, when the opening of the throttle valve 17 is reduced, the air-fuel ratio becomes the stoichiometric air-fuel ratio. Therefore, the opening of the throttle valve 17 is reduced when the air-fuel ratio is lean.

Next, an operation control routine will be described with reference to FIG. Referring to FIG. 21, first, at step 400, it is determined whether or not the air-fuel ratio is lean. Step 40 when the air-fuel ratio is lean
1 in willing FIG 19 absorption of NO _x amount NA per unit time calculated from the map shown in (A) is absorption of NO _x amount ΣNOX
, And then proceeds to step 403. Willing FIG 19 (B) NO _x emissions NB per unit time calculated from the relationship shown in the amount of NO _x ΣNOX to step 402 when the air-fuel ratio with respect to this is the stoichiometric air-fuel ratio or rich
, And then proceeds to step 403. Step 403 In _the amount of NO _x .SIGMA.NOX is discriminated whether or not exceeded the allowable maximum value N _max is, the flow proceeds to step 405 when .SIGMA.NOX ≦ N _max.

The sulfur content is contained in the fuel at a fixed rate. Therefore, the SO _x amount absorbed by the NO _x absorbent 60 is proportional to the injection amount Q. Therefore, in step 405, the product K · Q obtained by multiplying the injection amount Q by the constant K is the SO _x absorption amount ΣSOX.
Is added to Next, at step 406 SO _x absorption amount ΣSOX whether exceeds the allowable maximum value S _max is determined. When ΣSOX ≦ _Smax, the process proceeds to step 408.

At step 408, it is determined whether the air-fuel ratio is lean. When the air-fuel ratio is lean, the routine proceeds to step 409, where the atmospheric pressure PA detected by the atmospheric pressure sensor 33 (FIG. 1) and the absolute pressure PB in the first chamber 72 detected by the pressure sensor 85 (FIG. 17) are compared. Pressure difference (P
A-PB) whether smaller is judged than a predetermined differential pressure [Delta] P _min. When it is determined in step 408 that the air-fuel ratio is not lean, or in step 409, PA
When it is determined that −PB ≧ ΔP _min , the routine proceeds to step 410, where the opening of the throttle valve 17 is set to an opening corresponding to the operating state of the engine. Then, in step 411, the opening of the EGR control valve 20 is changed to the opening of the engine. The opening is set according to the operating state. At this time, the purge gas rate is set to the target purge gas rate tPGR shown in FIG.

On the other hand, in step 403, {NOX>
When it is determined to have become the N _max NO _x releasing processing from _the NO _x absorbent 60 proceeds to step 404 is performed. This _the NO _x releasing processing is shown in Figure 22. On the other hand, SO _x release processing from _the NO _x absorbent 60 is made the routine proceeds to step 407 when it is judged to have become the ΣSOX> S _max in step 406. This SO _x
The release process is shown in FIG. On the other hand, step 40
9, when it is determined that PA-PB <ΔP _min , the routine proceeds to step 412, where the brake booster 70
Is performed. This negative pressure recovery processing is shown in FIG.
Is shown in

[0089] FIGS. 22, 23 and 24 shows a case where _the NO _x releasing processing, SO _x release processing, the negative pressure recovery process is performed when the fuel injection Q2 is performed only at the respective end of the compression stroke ing. In FIGS. 22, 23 and 24, I indicates a double injection operation state in which fuel injections Q1 and Q2 are performed in two stages, an initial stage of the intake stroke and a final stage of the compression stroke. Only the fuel injection Q1 is performed and the air-fuel ratio is lean, and this indicates a lean air-fuel ratio uniform air-fuel mixture operation state. Respectively indicate the operating conditions of a uniform mixture of stoichiometric air-fuel ratios.

First, the NO _x release control will be described with reference to FIG. As shown in FIG.
When X> _Nmax , the operation state is sequentially switched to a double injection operation state I, a lean air-fuel ratio uniform mixture operation state II, and a stoichiometric air-fuel ratio uniform mixture operation state III. The state is switched to the uniform mixture operation state II, the double injection operation state I, or the first combustion state. In order to perform combustion by two fuel injections Q1 and Q2, it is necessary to reduce the air-fuel ratio as compared with the case of performing combustion by one fuel injection Q2 at the end of the compression stroke. Therefore, it is necessary to reduce the amount of intake air. There is. Therefore, when the NO _x release control is started, the opening of the throttle valve 17 is reduced. At this time, the opening of the EGR control valve 20 is also reduced so that the EGR rate becomes the target EGR rate.

Similarly, in order to perform combustion using a mixture having a uniform air-fuel ratio of lean air-fuel ratio, the air-fuel ratio must be reduced as compared with the case of performing combustion using two fuel injections Q1 and Q2. When the operating state is switched from the state I to the operating state II of the air-fuel mixture having a lean air-fuel ratio, the opening of the throttle valve 17 is further reduced. In addition, in order to perform combustion with a stoichiometric air-fuel ratio uniform air-fuel mixture, the air-fuel ratio must be smaller than in the case of performing combustion with a lean air-fuel ratio uniform air-fuel mixture. When the operating state is switched from II to the uniform air-fuel ratio operating state III, the opening of the throttle valve 17 is further reduced.

On the other hand, when the opening of the throttle valve 17 is reduced as described above, the pumping loss increases, and the output of the engine decreases. Therefore, in order to prevent the output of the engine from decreasing, the total injection amount Q is gradually increased as the opening of the throttle valve 17 decreases. On the other hand, when the total injection amount Q is increased, the final target purge gas rate PGR is also gradually increased in order to secure good ignition by the ignition plug 7. That is, the final target purge gas rate PGR is when _the NO _x releasing processing as shown in FIG. 22 is performed at first gradually be raised, then it would gradually be moved down.

When the NO _x release process is started and the operating state is changed to the operating state III of the homogeneous air-fuel ratio homogeneous air-fuel ratio, the injection amount Q is temporarily increased, thereby temporarily increasing the air-fuel ratio A / F. Is done. In this case NO _x is released from the NO _x absorbent 60. It should be noted that the target purge gas rate PGR can be temporarily increased when the injection amount Q is temporarily increased. NO as shown in FIG.
absorption of NO _x amount ΣNOX when _x release process is started is set to zero.

When ΣNOX> _Nmax during the double injections Q1 and Q2, the operation state is switched to the operation state II of the lean air-fuel ratio uniform air-fuel mixture, and the lean air-fuel ratio uniform air-fuel mixture is operated. Is burning
When NOX> _Nmax , the operation state is switched to the uniform mixture operation state III with the stoichiometric air-fuel ratio. Next, FIG.
While referring to the described release of SO _x control.

As shown in FIG. 23, ΣSOX> S _max
In this case as well, the operation state is sequentially switched to the double injection operation state I, the lean / fuel ratio uniform air / fuel mixture operation state II, and the stoichiometric air / fuel ratio uniform air / fuel mixture operation state III. At this time, the opening of the throttle valve 17 is gradually reduced, the opening of the EGR control valve 20 is also gradually reduced, and the total injection amount Q is gradually increased, similarly to the case of the NO _x release processing. The purge gas rate PGR is gradually increased.

Next, two cylinders whose ignition order is every other are:
For example the air-fuel ratio of No. 1 cylinder # 1 and the fourth cylinder # 4 become rich, the air-fuel ratio of the remaining second cylinder firing order is every # 2 and the third cylinder # 3 becomes lean, NO _x absorbent The injection amount Q # to the first cylinder # 1 and the fourth cylinder # 4 so that the average air-fuel ratio of the exhaust gas flowing into the cylinder 60 becomes rich.
1 and Q # 4 (shown by solid lines in FIG. 23) are increased, and the injection amounts Q # 2 and Q # 3 to the second cylinder # 2 and the third cylinder # 3 (shown by broken lines in FIG. 23). Is)
Is reduced.

That is, specifically, first, the total injection amount Q is calculated to set the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 60 to the target rich air-fuel ratio. Then the calculated fuel vapor rate tEV based on purge vapor concentration PV, the average value Q _m of the total injection quantity from the following equation on the basis of the fuel vapor rate tEV is calculated. Q _m = Q · (1−tEV) Next, the injection amounts Q # 1, Q of the first cylinder # 1 and the fourth cylinder # 4
Injection amount Q # for # 4, # 2 cylinder # 2, and # 3 cylinder # 3
2, Q # 3 is calculated based on the following equation.

[0098] The output signal of Q # 1 = Q # 4 = FAF · (Q m + α) Q # 2 = Q # 3 = FAF · (Q m -α) where FAF is an air-fuel ratio sensor 61 (FIG. 17) Indicates a feedback correction coefficient to be controlled, and α indicates a predetermined set value. That is, the feedback correction coefficient FA when the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 60 on the basis of the output signal of the air-fuel ratio sensor 61 is determined to be larger than the target rich air-fuel ratio
F is made to increase, the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 60 is the feedback correction coefficient FAF is made to decrease when it is determined to be smaller than the target rich air-fuel ratio, thereby flowing into _the NO _x absorbent 60 The air-fuel ratio of the exhaust gas is controlled to the target rich air-fuel ratio. At this time, the air-fuel ratio in the first cylinder # 1 and the fourth cylinder # 4 becomes rich, and the air-fuel ratio in the second cylinder # 2 and the third cylinder # 3 becomes lean.

As described above, the first cylinder # 1 and the fourth cylinder #
When the air-fuel ratio in the fourth cylinder is rich and the air-fuel ratio in the second cylinder # 2 and the third cylinder # 3 is lean, exhaust gas containing a large amount of unburned HC and CO is contained in the first exhaust manifold 18a. The exhaust gas containing a large amount of oxygen is discharged into the second exhaust manifold 18b. Then these large amounts of unburned HC, the exhaust gas containing exhaust gas and a large amount of oxygen containing CO flows into _the NO _x absorbent in the 60, NO _x large amount of unburned HC in the absorber within 60, CO
Is oxidized by a large amount of oxygen. As a result, the temperature of the NO _x absorbent 60 by the oxidation reaction heat is caused to rise rapidly.

On the other hand, NO_xExhaust gas flowing into the absorbent 60
Air-fuel ratio is maintained at the target rich air-fuel ratio.
NO_xWhen the temperature of the absorbent 60 exceeds, for example, 600 ° C.
NO _xSO from absorbent 60_xThe release action is started
You. SO_xWhen the release action of_xAbsorption ΣS
OX to SO of unit time shown in FIG._xRelease amount S
B are sequentially subtracted, and thus SO_xThe absorption amount ΣSOX is
First decrease. Note that, as shown in FIG.
SO per hit_xRelease amount SB is NO_xTemperature T of absorbent 60
C, and this temperature TC is shown in FIG.
The amount of depression L of the accelerator pedal 34 and the
Is stored in the ROM 42 in advance in the form of a map as a function of the number of turns N.
Remembered. On the other hand, as shown in FIG._xSucking
YieldΣNOX is SO_xWhen the release process starts, it is set to zero
You.

As shown in FIG. 23, the SO _x absorption amount 吸収 S
When OX becomes zero, the operating state of the air-fuel mixture with uniform stoichiometric air-fuel ratio
And then sequentially switched to a lean air-fuel ratio uniform mixture operation state II, a double injection operation state I, and a first combustion state. At this time, the opening of the throttle valve 17 is gradually increased as in the case of the NO _x release processing, and the EGR
The opening of the control valve 20 is also gradually increased, and the total injection amount Q
Is gradually decreased, and the target purge gas rate PGR is gradually decreased.

When ΣSOX> _Smax is satisfied during the double injections Q1 and Q2, the operating state is switched to the operating state II of the air-fuel mixture having a lean air-fuel ratio, and the air-fuel mixture having a uniform air-fuel ratio of a lean air-fuel ratio is obtained. Is burning
When SOX> _Smax , the operation state is switched to the stoichiometric air-fuel ratio uniform mixture operation state III, and when the stoichiometric air-fuel ratio or rich air-fuel ratio uniform mixture is combusted, ΣSOX> _Smax. 23, the injection amount Q # of the first cylinder # 1 and the fourth cylinder # 4 as shown in FIG.
1, Q # 4 is increased, and the injection amounts Q # 2, Q # 3 of the second cylinder # 2 and the third cylinder # 3 are decreased.

Next, the negative pressure recovery process of the brake booster 70 will be described with reference to FIG. As shown in FIG. 24, when PA-PB <ΔP _min , the operation state sequentially changes to a double injection operation state I, a lean air-fuel ratio uniform mixture operation state II, and a stoichiometric air-fuel ratio uniform mixture operation state III. Is switched. Opening of this case NO _x when the discharge process as well as the throttle valve 17 is gradually reduced, EGR
The opening of the control valve 20 is also gradually reduced, and the total injection amount Q
Is gradually increased, and the target purge gas rate PGR is gradually increased.

As described above, when the opening of the throttle valve 17 and the opening of the EGR control valve 20 are reduced, the absolute pressure in the intake duct 14 downstream of the throttle valve 17 decreases, and as shown in FIG. Pressure difference PA-PB
Is rapidly increased. That is, the brake booster 7
The absolute pressure within 0 is rapidly reduced. As shown in FIG. 24, the operating state is a homogeneous air-fuel mixture operating state with a stoichiometric air-fuel ratio.
Immediately after reaching III, the operating state is switched to the operating state II of the air-fuel mixture having a lean air-fuel ratio, and then to the operating state I of the double injection operation and then to the first combustion state. At this time, similarly to the case of the NO _x release processing, the opening of the throttle valve 17 is gradually increased, the opening of the EGR control valve 20 is also gradually increased, and the total injection amount Q is gradually decreased, The target purge gas rate PGR is gradually reduced.

Although the case where the present invention is applied to a stratified charge combustion type internal combustion engine has been described above, combustion with a uniform mixture of lean air-fuel ratio or combustion with a stoichiometric air-fuel ratio is performed without performing stratified charge combustion. It goes without saying that the present invention can be applied to such an internal combustion engine.

[0106]

As described above, even when the purge gas is supplied, good operation of the engine can be ensured.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing an injection amount, an injection timing, and an air-fuel ratio.

FIG. 3 is a diagram showing a map of an injection amount.

FIG. 4 is a view showing a map of an injection start timing.

FIG. 5 is a side sectional view of the internal combustion engine.

FIG. 6 is a diagram for explaining a change in an air-fuel mixture.

FIG. 7 is a diagram showing a target purge gas rate tPGR.

FIG. 8 is a diagram showing target purge gas rates rPGR and tPGR.

FIG. 9 is a diagram showing a flow rate of a fully open purge gas.

FIG. 10 is a diagram showing a purge gas flow rate.

FIG. 11 is a diagram showing fuel vapor concentration and the like.

FIG. 12 is a diagram showing changes in elapsed times Ta (i) and Tb (i).

FIG. 13 is a diagram showing a routine for calculating a torque fluctuation amount.

FIG. 14 is a flowchart for executing purge control.

FIG. 15 is a flowchart for executing purge control.

FIG. 16 is a flowchart for controlling injection.

FIG. 17 is an overall view showing a modification of the internal combustion engine.

18 is a diagram for explaining the absorbing and releasing action of NO _x.

FIG. 19 shows the NO _x absorption amounts NA and NO per unit time.
It is a figure which shows _x discharge amount NB.

20 is a diagram showing the release of SO _x amount SB and the like per unit time.

FIG. 21 is a flowchart for controlling operation of the engine.

FIG. 22 is a time chart showing NO _x release control.

FIG. 23 is a time chart showing SO _x release control.

FIG. 24 is a time chart showing a negative pressure recovery process of the brake booster.

[Explanation of symbols]

 5: Combustion chamber 6: Fuel injection valve 13: Surge tank 22: Canister 28: Purge control valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F02M 25/08 301 F02M 25/08 301J (72) Inventor Yoshihiko Budo 1st Toyota Town, Toyota City, Aichi Prefecture Toyota F-term (Reference) in Automobile Co., Ltd. MA11 MA19 MA26 NA01 NA04 NA08 NB02 NC02 ND02 ND41 NE01 NE03 NE06 NE08 NE13 NE14

Claims (14)

[Claims] 1. A purge passage for purging fuel vapor generated in a fuel tank into an intake passage, a purge control valve for controlling an amount of purge gas purged from the purge passage into the intake passage, and a fuel injection amount. Injection amount calculation means for calculating, setting means for setting a target value of the purge gas rate indicating the ratio of the purge gas amount to the fuel injection amount, and at least one of the purge gas amount or the fuel injection amount so that the purge gas rate becomes the target value. And a control means for controlling the fuel pressure. 2. An apparatus according to claim 1, wherein an air-fuel mixture is formed in a limited area in the combustion chamber, and the air-fuel mixture is ignited by an ignition plug. 3. The apparatus according to claim 1, wherein the target value of the purge gas rate is changed in accordance with an operation state of the engine. 4. The evaporative fuel processing apparatus for an internal combustion engine according to claim 3, wherein the target value of the purge gas rate is increased as the fuel injection amount increases. 5. The operating state of the engine includes a first operating state in which an air-fuel mixture is formed in a limited area in the combustion chamber, and a second operating state in which an air-fuel mixture is formed in the entire combustion chamber. 4. The evaporative fuel treatment system for an internal combustion engine according to claim 3, wherein the target value of the purge gas rate is set higher in the second operation state than in the first operation state. 6. The apparatus according to claim 1, wherein the target value of the purge gas rate is a constant value. 7. An output fluctuation detecting means for detecting an output fluctuation of the engine, wherein the control means directs the purge gas rate to the target value when the output fluctuation of the engine is smaller than a predetermined fluctuation amount. 2. The evaporative fuel treatment system for an internal combustion engine according to claim 1, wherein the purge gas rate is gradually decreased when the output fluctuation of the engine is larger than a predetermined fluctuation amount. 8. A fuel vapor amount estimating means for estimating a fuel vapor amount in the purge gas, and a storage means for storing a basic fuel injection amount according to a required load, wherein the purge gas amount is calculated from the basic fuel injection amount. 2. The apparatus according to claim 1, wherein the amount of fuel to be injected is calculated by subtracting the amount of fuel vapor therein. 9. the air-fuel ratio of the inflowing exhaust gas to release NO _x that when the lean absorbing the air-fuel ratio of the exhaust gas flowing to absorb NO _x is the stoichiometric air-fuel ratio or rich N
The O _x absorbent arranged in the engine exhaust passage, to claim 1 for when releasing the NO _x from the NO _x absorbent when the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is made the stoichiometric air-fuel ratio or rich The fuel vapor treatment device for an internal combustion engine according to claim 1. 10. _the NO _x absorbent evaporative fuel processing system for an internal combustion engine according to claim 9 in which the target value of the purge gas rate is raised when _the NO _x releasing processing from. 11. evaporative fuel processing system for an internal combustion engine according to claim 9 in when releasing the SO _x from _the NO _x absorbent when the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is made rich. 12. NO _x according target value of the purge gas rate during release of SO _x treatment from the absorbent is raised section 11
The fuel vapor treatment device for an internal combustion engine according to claim 1. 13. A brake booster having a throttle valve disposed in an engine intake passage, a negative pressure generated in an intake passage downstream of the throttle valve being guided, and a braking force increased by the negative pressure. 2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein the opening degree of the throttle valve is reduced when the negative pressure introduced into the booster decreases. 14. The evaporation of the internal combustion engine according to claim 13, wherein the target value of the purge gas rate is increased when the opening degree of the throttle valve is reduced when the negative pressure introduced into the brake booster is reduced. Fuel processor.