JP2976583B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine having a lean burn system for setting the air-fuel ratio to lean in a low to middle load range of the internal combustion engine to perform combustion.

[0002]

2. Description of the Related Art In an internal combustion engine equipped with a lean burn system, the air-fuel ratio is set to be lean in a low-to-medium load region and the air-fuel ratio is switched to rich in a high-load region. In order to prevent a sudden change in torque at the time of switching the air-fuel ratio, Japanese Patent Application Laid-Open No. 62-21 / 1987
Japanese Patent Application Laid-Open No. 8632/8632 proposes a method in which the intake air amount is temporarily reduced, or a method in which the ignition timing is temporarily retarded as described in JP-A-58-160549. .

[0003]

In recent years, systems for lean-burning a supercharged engine having a small displacement have been developed. This is intended to reduce pumping loss, that is, intake resistance, by reducing the amount of exhaust, improve fuel efficiency by increasing lean burn, and increase output by increasing supercharging.

[0004] In the supercharged lean burn system, a swirl control valve (SCV) is required in order to achieve both output and fuel efficiency, and lean burn is performed by closing the SCV even in a high supercharged region. Therefore, when transitioning from the high supercharged lean burn region in which the SCV is closed to the output region in which the SCV is opened, the change amount of the intake air is larger than that of the naturally aspirated engine, and the change amount of the torque is larger.

Conventionally, since a method of temporarily reducing the intake air amount at the time of switching is employed, it is difficult to precisely control the supercharging pressure, and the cost is greatly increased. Further, in the method of temporarily retarding the ignition timing at the time of switching, there is a problem that a misfire may occur in the lean limit region.

[0006] The present invention has been made in view of the above points,
The air-fuel ratio is shifted in a state where the supercharging pressure is reduced at the same time as the opening of the SCV, and the ignition timing is retarded when increasing the reduced supercharging pressure, thereby suppressing a sudden change in torque at the time of the air-fuel ratio transition. It is another object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that prevents the occurrence of misfire and the occurrence of preignition.

[0007]

FIG. 1 shows the principle of the present invention.

In FIG. 1, when the operating state detecting means M1 detects that the operating state of the internal combustion engine M2 shifts from the lean air-fuel ratio operating state to the high-output air-fuel ratio operating state, the supercharging pressure reducing means M3 turns the swirl. At the same time when the control valve (SCV) is opened, the supercharging pressure is reduced for a first predetermined period.

The retarding means M4 retards the ignition timing from the required ignition timing for a second predetermined period after a first predetermined period in which the supercharging pressure is reduced by the supercharging pressure reducing means M3.

The air-fuel ratio shifting means M5 shifts the air-fuel ratio from the lean air-fuel ratio operating state to the high output air-fuel ratio operating state during the first predetermined period.

[0011]

According to the present invention, the first operation is performed simultaneously with the opening of the SCV.
The abrupt change of the intake air amount is prevented by reducing the supercharging pressure for a predetermined period of time, the air-fuel ratio is shifted during the first predetermined period, and the ignition timing is retarded during the second predetermined period after the shift of the air-fuel ratio. By doing so, the occurrence of misfire is prevented and the sudden change in torque is suppressed. Further, since the air-fuel ratio is shifted in a state where the supercharging pressure is reduced, the rise in the intake air temperature is smaller than when the SCV is closed, so that the occurrence of preignition can be prevented.

[0012]

FIG. 2 is a block diagram showing an embodiment of the apparatus according to the present invention.

In FIG. 1, an intake port 17 is connected to an air cleaner 12 via an intake passage 11.
1, an air flow meter 13, an exhaust turbocharger (supercharger) 14, a throttle valve 15, an SCV 16, and a fuel injection device 25 are arranged. In addition, exhaust port 2
A bypass passage 22 branches from an exhaust passage 21 between the exhaust turbocharger 14 and the bypass passage 22.
Is connected to an exhaust passage 21 downstream of the exhaust turbocharger 14. A wastegate valve 23 is disposed in the bypass passage 22. The SCV 16 is driven to open and close by a valve drive unit 19 driven and controlled by an open / close signal from an electronic control circuit (ECU) 40, and the wastegate valve 23 is driven to be opened and closed by a valve drive unit 24 driven and controlled by an open / close signal from the ECU. You.

An electronic control circuit (ECU) 40 is a digital computer comprising a ROM, a RAM, a CPU, an input port, and an output port interconnected by a bidirectional bus. A throttle opening signal T from a throttle sensor 18 which detects the opening of the throttle valve 15 is input to the input port.
A and a rotation angle detection signal from the crank angle sensor 39 are input. The ECU 40 supplies an opening / closing signal to the valve driving units 18 and 24 and also transmits a fuel injection signal to the fuel injection valve 25.
To supply. Also, an ignition signal is supplied to the igniter 26,
The output of the igniter 26 is supplied to a spark plug 29 through an ignition coil 27 and a distributor 28.

FIG. 3 shows a flowchart of a control routine of the apparatus of the present invention. This control routine is a crank angle interruption routine that is executed by detecting a predetermined crank angle with the crank angle sensor 39.

Referring to FIG. 3, in step 50, the throttle opening TA is compared with a predetermined value α for closing the SCV16.
It is determined whether the flag XSCVO indicating the previous open / close state of the CV 16 is 0 and the SCV 16 is closed. If the SCV 16 is closed, the wastegate valve counter CW is set to 0 in step 52, the wastegate valve 23 is opened in step 53, and 1 is set to the flag XWAST indicating the open / closed state of the wastegate valve 23. To step 54. If the SCV 16 is open, the process proceeds directly to step 54. In step 54, the SCV 16 is opened, and 1 is set to a flag XSCV representing the current open / close state of the SCV 16.

Next, at step 55, it is determined whether or not the waste gate valve counter CW is equal to or greater than a predetermined value γ corresponding to a first predetermined period.
In step 6, the value of the counter CW is incremented by one, and in step 57, flags XWAST and XS representing the current state are set.
The value of each CV is set to a flag XWAST indicating the previous state.
O and XSCVO are set respectively, and the process is terminated. If the counter CW is equal to or greater than the predetermined value γ, the waste gate valve 23 is closed in step 58, the flag XWAST is set to 0, and in step 59, an ignition timing correction amount setting routine described later is executed, and the routine proceeds to step 57.

In step 50, the throttle opening TA
Is smaller than the predetermined value α, the throttle opening TA is compared with a predetermined value β for opening and closing the SCV 16 in step 61. Predetermined value β
Is smaller than α, and a hysteresis characteristic is given to the opening and closing of the SCV 16. If the throttle opening TA is equal to or smaller than the predetermined value β, the waste gate valve 23 is closed in step 62, the flag XWAST is set to 0, and the SCV 16 is closed in step 63, and the flag XSCV is set to 0.
Is set and the routine proceeds to step 57. Throttle opening TA
If the value exceeds the predetermined value β, the process proceeds directly to step 57.

FIG. 4 shows a flowchart of an ignition timing correction amount setting routine. In the figure, at step 65, a flag X representing the last open / close state of the waste gate valve 23 is set.
It is determined whether or not WASTO is 1, and only when this flag is 1 and the wastegate valve 23 is already open, the ignition timing counter CIG is set to 0 in step 66.

Next, at step 67, the ignition timing counter CI
G is compared with a predetermined value K ₀ corresponding to a second predetermined period.
The value of the counter CIG is set by the following equation the ignition timing correction amount ATRN in step 68 is less than the predetermined value K _0.

ATRN = K ₁ −K ₂ × CIG where K ₁ and K ₂ are constants. Thereafter, in step 69, the counter 69 sets the counter CIG.
Is incremented by one, and the process ends.

The value of the ignition timing counter CIG in step 67 the process ends by setting the 0 to the ignition timing correction amount ATRN in step 70 if the predetermined value K ₀ or more.

If the throttle opening TA exceeds the predetermined value α at time t ₀ , the waste gate valve counter CW is set to 0 as shown in FIG. 5B (step 5).
2) The waste gate valve 16 is opened as shown in FIG. 6C, and the flag XWAST is set to 1 as shown in FIG.
(Step 53). SCV16 is shown in FIG.
The flag XSCV opened as shown in FIG.
Is set to 1 (step 54). This intake air quantity will not be suddenly changed at time t ₀ as shown in FIG. 6 (D).

Thereafter, the waste gate valve counter C
At time t ₁ when the value of W reaches the predetermined value γ, the waste gate valve 23 is closed and the flag XWAST is set to 0 (step 58). The air-fuel ratio between the times t _{0 and} t ₁ is shown in FIG.
The state shifts from lean to rich as shown in FIG.

At time t ₁ when the waste gate valve 23 is closed, the amount of intake air rapidly increases as shown in FIG. However, the ignition timing counter CIG at this point in time t ₁
Is set to 0 as shown in FIG. 5D (step 66), and thereafter increases with time, and the ignition timing correction amount ATRN becomes as shown in FIG. 5E. Therefore, the ignition timing AMA determined according to the engine speed, the throttle opening, the load, etc.
The actual ignition timing obtained by subtracting the correction amount ATRN from P is shown in FIG.
(E) to a temporary delay in the time t ₁ as shown, to recover gradually later.

Therefore, as shown in FIG. 6 (F), the torque is changed from the high supercharged lean burn region (lean air-fuel ratio operation state) to SC
When switching to the V-open output region (high-output air-fuel ratio operation state), the voltage increases smoothly without sudden change.

[0027] In addition it is possible to prevent the misfire for retarding the ignition timing from the time t ₁ after the air-fuel ratio has shifted from lean to rich occurs.

In the above embodiment, the SCV 16 is opened and the wastegate valve 23 is opened to lower the supercharging pressure, and the air-fuel ratio is shifted from lean to rich. This is because when the air-fuel ratio is shifted to rich while the SCV 16 is closed and the waste gate valve 23 is closed,
This is because pre-ignition is likely to occur due to an increase in intake air temperature due to a high supercharging pressure. In the above embodiment, the supercharging pressure is reduced to prevent an increase in intake air temperature, thereby preventing the occurrence of pre-ignition.

[0029]

As described above, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention, it is possible to suppress a sudden change in torque when the air-fuel ratio is shifted, to prevent the occurrence of misfire, and to prevent the occurrence of pre-ignition. It is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram of an embodiment of the device of the present invention.

FIG. 3 is a flowchart of a control routine.

FIG. 4 is a flowchart of an ignition timing correction amount setting routine.

FIG. 5 is a timing chart for explaining the device of the present invention.

FIG. 6 is a timing chart for explaining the device of the present invention.

[Explanation of symbols]

 14 Exhaust turbocharger 15 Throttle valve 16 SCV 23 Wastegate valve 40 Electronic control circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 23/00 F02D 23/00 E H 41/04 305 41/04 305C F02P 5/15 F02P 5/15 B

Claims (1)

(57) [Claims] In an air-fuel ratio control device for an internal combustion engine having a swirl control valve in an intake passage and a supercharger, an engine operation state shifts from a lean air-fuel ratio operation state to a high-output air-fuel ratio operation state. When the swirl control valve is opened, the supercharging pressure is reduced by a first predetermined period simultaneously with the opening of the swirl control valve, and after the first predetermined period in which the supercharging pressure is reduced by the supercharging pressure lowering unit. A delay means for retarding the ignition timing from the required ignition timing during the second predetermined period; and shifting the air-fuel ratio from the lean air-fuel ratio operation state to the high-output air-fuel ratio operation state during the first predetermined period. And an air-fuel ratio control device for an internal combustion engine.