JPH06280642A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To restrain torque shock upon fuel recovery while preventing misfiring, by controlling the air-fuel ratio so that the air-fuel ratio around a spark plug is lean upon recovery of fuel from the time of fuel cut, in comparison with that during normal operation, but the air fuel ratio in the outer peripheral part remote from the spark plug is rich. CONSTITUTION:An engine air-fuel ratio control device comprises first determining means P1 for determining a time of no torque requirement during engine deceleration, fuel cut means P2 for carrying out a fuel cut at the time of no torque requirement, in accordance with a result of determination by the first determining means P1, second determining means P2 for determining whether the time is on recovery from a fuel cut or not, fuel supply recovery means P4 for recovering the fuel supply during recovery from a fuel cut in accordance with a result of determination by the second determining means P3, and further, air-fuel ratio changing means P5 for controlling the air-fuel ratio so that the air-fuel ratio is lean around a spark plug during recovery from fuel cut off in comparison with normal operation, is rich in the outer peripheral part remote from the spark plug.

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 engine, which controls the air-fuel ratio when returning from deceleration fuel cut, for example.

[0002]

2. Description of the Related Art Generally, when the engine speed is equal to or higher than a predetermined speed and the throttle valve opening TVO is substantially fully closed or decelerated (when no output is required), fuel consumption is improved, misfire is prevented, and exhaust gas is exhausted. A fuel cut is executed for the purpose of preventing afterburn and exhaust gas temperature rise in the system.

When returning from this fuel cut, as disclosed in Japanese Patent Publication No. Sho 56-38781, a means for gradually increasing the amount of fuel for a predetermined time from the basic fuel injection amount is adopted. In other words, as shown in the time chart of FIG. 11, when returning from the deceleration fuel cut, without returning the air-fuel ratio to A / F = 14.7 at a time,
By gradually returning to A / F = 14.7 from the lean state,
It is configured to prevent torque shock when returning to fuel.

Such a structure is used for a lean air-fuel ratio combustion engine (lean
-burn engine, lean-burn engine), the air-fuel ratio is lean (for example, A / F = 22.0) during normal operation in the lean-burn operation region, and the air-fuel ratio is further increased when returning from deceleration fuel cut. Since it becomes lean, it is not possible to prevent torque shock at the time of fuel recovery, but of course, there is a problem that it causes a misfire due to entering the lean limit, and this misfire causes a large shock. It was

[0005]

According to the first aspect of the present invention, when returning from the fuel cut, the air-fuel ratio in the peripheral portion of the spark plug is made leaner than in the normal state.
It is an object of the present invention to provide an engine air-fuel ratio control device capable of preventing misfire while suppressing torque shock at the time of fuel return by controlling the air-fuel ratio of the outer peripheral portion separated from the spark plug to be rich.

According to a second aspect of the present invention, in addition to the object of the first aspect of the invention, the swirl generating means and the fuel injection timing varying means can be effectively used without separately providing a unique device. Then, an object of the present invention is to provide an air-fuel ratio control device for an engine that can suppress torque shock and prevent misfire.

According to the invention of claim 3 of the present invention, in addition to the object of the invention of claim 1 or 2, by executing the air-fuel ratio variable control during lean burn operation, misfire occurs at the time of fuel recovery. Under the condition that the probability of
An object of the present invention is to provide an engine air-fuel ratio control device capable of reliably preventing such misfire.

[0008]

According to a first aspect of the present invention, there is provided first determining means for determining when torque is not needed during engine deceleration, and when torque is not needed based on the determination result of the first determining means. Fuel cut means for executing the fuel cut, second judgment means for judging whether or not it is time to return from the fuel cut, and fuel supply for returning at the time of return from the fuel cut based on the judgment result of the second judgment means. An air-fuel ratio control device for an engine, comprising fuel supply returning means, wherein when returning from the fuel cut, the air-fuel ratio in the peripheral portion of the ignition plug is made leaner than in the normal state, and the outer periphery separated from the ignition plug. The air-fuel ratio control device for an engine is provided with an air-fuel ratio varying means for controlling the air-fuel ratio of a portion to be rich.

According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the air-fuel ratio varying means is a swirl producing means for producing a swirl flow in the combustion chamber, and a fuel injection timing. Is an air-fuel ratio control device for an engine, comprising: a fuel injection timing changing means for gradually changing from before the intake top to after the intake top.

According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the present invention, there is provided an engine air-fuel ratio control device for executing the air-fuel ratio variable control during lean burn operation. Is characterized by.

[0011]

According to the invention described in claim 1 of the present invention, as shown in the claim correspondence diagram of FIG. 10, when the first determining means P1 determines that the torque is not required during engine deceleration,
When the fuel cut means P2 executes the fuel cut and the second determination means P3 determines that it is time to return from the fuel cut, the fuel supply restoration means P4 restores the fuel supply,
When returning from this fuel cut, the fuel ratio varying means P5 makes the air-fuel ratio of the peripheral portion of the spark plug leaner and controls the air-fuel ratio of the outer peripheral portion separated from the spark plug to be richer than in the normal state.

Therefore, by making the air-fuel ratio around the spark plug lean, it is possible to suppress the torque shock at the time of fuel return, and to control the air-fuel ratio in the outer week part separated from the spark plug to be rich. However, misfire can be prevented by making the total air-fuel ratio in the cylinder substantially the same as in the normal state.

According to the invention of claim 2 of the present invention,
In addition to the effect of the invention described in claim 1, the air-fuel ratio varying means is constituted by a combination of the existing swirl generating means and the fuel injection timing varying means, so that a unique device is not separately provided. By effectively utilizing both of these means, it is possible to suppress torque shock and prevent misfire.

According to the invention of claim 3 of the present invention,
In addition to the effect of the invention described in claim 1 or 2, by performing the air-fuel ratio variable control during lean burn operation, such misfire is assured under operating conditions where there is a high probability of misfire occurrence during fuel recovery. There is an effect that can be prevented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. The drawing shows an air-fuel ratio control system for an engine, and FIG.
In the above, the air flow sensor 3 is connected to the rear of the element 2 of the air cleaner 1 for purifying the intake air, and the air flow sensor 3 is configured to detect the intake air amount Q.

A throttle body 4 is connected to the rear of the air flow sensor 3 described above, and a throttle chamber 5 in the throttle body 4 is provided with a throttle valve 6 for controlling the amount of intake air. And this throttle valve 6
A surge tank 7 as an expansion chamber having a predetermined capacity is connected to the downstream intake passage, and an intake manifold 9 communicating with the primary intake port 8P and the secondary intake port 8S shown in FIG. The injector 10 is connected and connected to the above-mentioned primary side intake port 8P.

On the other hand, the intake ports 8P and 8S and the exhaust port 1 which communicate with the combustion chamber 12 of the engine 11 as needed.
As shown in FIG. 2, the intake valves 14 and 14 and the exhaust valve 1 are opened and closed by a valve mechanism (not shown).
5 and 15 are attached respectively, and a spark plug 16 (see FIG. 2) having a spark gap facing the combustion chamber 12 is attached to the cylinder head.

An O 2 sensor 18 as an air-fuel ratio sensor is provided in the exhaust passage 17 communicating with the above-mentioned exhaust ports 13 and a catalytic converter 19 for detoxifying harmful gas is provided behind the exhaust passage 17 so-called. The catalyst is connected.

Further, a bypass passage 20 for bypassing the above-mentioned throttle valve 6 is provided, and an ISC valve 21 as an ISC (idle speed control) mechanism is provided in the bypass passage 20, while the air cleaner 1 is provided on the downstream side of the element 2. An intake air temperature sensor 22 is provided at the throttle body 4, a throttle sensor 23 is provided at the throttle body 4, and a water temperature sensor 24 is provided at the water jacket.

Further, a boost sensor 25 for detecting the intake negative pressure is attached to the surge tank 7, while an opening / closing valve 26 which is closed when the swirl flow S is generated in the secondary intake port 8S as shown in FIG. And the opening / closing valve 26 is configured to be opened / closed via a link rod (not shown) and an actuator 27 (see FIG. 3).

FIG. 3 shows a control circuit of the engine air-fuel ratio control device. The CPU 30 controls the intake air amount Q from the air flow sensor 3, the engine speed Ne from the distributor 28, and the air-fuel ratio A / F from the O2 sensor 18. The injector 10 and the actuator 27 (specifically, a solenoid valve for driving an actuator (not shown)) are driven and controlled in accordance with a program stored in the ROM 29 on the basis of various necessary signal inputs such as a corresponding voltage, and a RAM.
Reference numeral 31 is the map shown in FIG. 4, normal injection timing (60 degrees after intake top) TA, return injection timing (before intake top) TBO, fuel injection timing before intake top TBO
Then, necessary maps and data such as data corresponding to the increment amount ΔT (same as the tailing amount) for gradually changing to 60 degrees TA after intake top are stored.

Here, in the above-mentioned map (see FIG. 4), the horizontal axis represents the engine speed Ne, and the vertical axis represents the load (CE = Q /
Ne), and λ corresponding to the air-fuel ratio A / F = 14.7.
= 1 region, a lean burn region that controls the air-fuel ratio to A / F = 22, for example, and an F / C region that executes fuel cut.

Further, the above-mentioned CPU 30 has a first judging means (refer to the seventh step S7 in the flow chart shown in FIG. 5) for judging the time when the torque is not required at the time of deceleration of the engine, and the above-mentioned first CPU.
Means for executing fuel cut to the injector 10 when torque is not required based on the judgment result of the judgment means (see the eighth step S8 of the flowchart shown in FIG. 5), and second judgment for judging whether or not it is time to return from fuel cut Means (Fig. 5
9) and the fuel supply returning means for returning the fuel supply to the injector 10 when returning from the fuel cut based on the judgment result of the above-mentioned second judging means (see the flowchart shown in FIG. 5). First of
0 step S10), and when returning from the above-described fuel cut, the peripheral portion α of the spark plug 16 is
(See the hatched area α in FIG. 9) The air-fuel ratio is made lean, and the air-fuel ratio of the outer peripheral portion β (see the hatched area β in FIG. 9) separated from the spark plug 16 is made rich. The air-fuel ratio varying means for controlling the total air-fuel ratio in the cylinder to be substantially the same as in the normal state (for example, A / F = 22) (steps S11 and S in the flowchart shown in FIG. 5).
12, refer to the routine R1 consisting of S13).

Further, in this embodiment, the air-fuel ratio varying means (see routine R1) described above is a swirl producing means (see on-off valve 26) for producing the swirl flow S in the combustion chamber 12.
And fuel injection timing changing means for gradually changing the fuel injection timing from TBO before intake top to 60 degrees TA after intake top (see twelfth step S12 of the flowchart shown in FIG. 5). The control is configured to be executed during lean burn operation.

With reference to the flow chart shown in FIG. 5, the operation of the engine air-fuel ratio control device thus constructed will be described.
The details will be described below. In the first step S1, the CPU 30 reads the intake air amount Q from the air flow sensor 3 and the engine speed Ne from the distributor 28, and in the next second step S2, the CPU 30 calculates the arithmetic expression CE = Q /
The load CE is calculated by Ne.

Next, in a third step S3, the CPU 30 determines whether the engine operating state is within the lean burn region of the map shown in FIG. 4 based on both the current load CE and the current engine speed Ne. If NO is determined, the process returns to the first step S1, while if YES is determined, the process proceeds to the next fourth step S4. In the fourth step S4,
The CPU 30 executes lean burn operation. For example, the air-fuel ratio is leaner than the theoretical air-fuel ratio A / F = 14.7.
Driving at = 22.

Next, in a fifth step S5, the CPU 30 makes a running state other than the deceleration fuel cut, and in a next sixth step S6, the CPU 30 injects fuel at the normal injection timing TA, that is, 60 degrees after the intake top, corresponding to the normal time. To execute.

Next, in a seventh step S7, the CPU 30 determines whether or not it is in the deceleration fuel cut region under the lean burn operating condition and returns to the above-mentioned fifth step S5 in the case of NO determination, while it proceeds to the next in the case of YES determination. Then, the process proceeds to the eighth step S8.

In the eighth step S8, the CPU 30 executes the fuel cut for the injector 10, and the next ninth step is performed.
In step S9, the CPU 30 determines whether or not to return from the deceleration fuel cut, and when the NO determination is made, the process returns to the above-mentioned eighth step S8, and when the YES determination is made, the next tenth step is performed.
Control goes to step S10.

In the tenth step S10, the CPU 30
Performs a return of fuel supply to the injector 10,
In the next eleventh step S11, the CPU 30 sets the fuel injection timing to the return injection timing TBO, that is, in front of the intake top to drive the injector 10, and switches the on-off valve 26 to the closed state via the actuator 27.
A swirl flow S is generated as shown in FIG.

When the above-mentioned on-off valve 26 is closed, the flow velocity of the intake air from the primary side intake port 8P becomes large, and the combustion chamber 1 is caused by the intake air from the primary side intake port 8P.
2, a swirl flow S is generated as shown in FIG. 2, whereby the fuel injected from the injector 10 flows on the swirl flow S described above, and the region β shown in FIG. 9 (the outer periphery separated from the spark plug 16 is shown. Part), a mixture layer having a rich air-fuel ratio is formed, and in the region α (around the spark plug 16), a mixture layer having a leaner air-fuel ratio than in the normal state is formed. The total air-fuel ratio becomes substantially the same as that during normal operation during lean burn operation (A / F = 22).

Next, in a twelfth step S12, the CPU 30
Is an increment amount ΔT at the return injection timing TBO
(See FIG. 6) is added to calculate the current injection timing TB, and the injector 10 is driven at this injection timing TB = TBO + ΔT.

Next, in a thirteenth step S13, the CPU 30
Determines whether TB = TA, and when TB = TA, the first
While returning to step S1, when TB ≠ TA, the process returns to the above-mentioned twelfth step S12.

That is, the above-mentioned steps S11, S12,
By the routine R1 of S13, the CPU 30 gradually changes the fuel injection timing from TBO before intake top to 60 degrees TA after intake top.

Since the relationship of the air-fuel ratio with respect to the injection timing is as shown in FIG. 7, the fuel injection timing is variably controlled from TBO before the intake top to 60 degrees TA after the intake top, so that the periphery of the spark plug 16 (see FIG. The air-fuel ratio in the area α of 9) changes as shown by a virtual line in FIG. 8, and the total air-fuel ratio changes as shown by a solid line in FIG.

In summary, when the first determination means (see seventh step S7) determines that torque is not needed during engine deceleration, the fuel cut means (see eighth step S8) executes the fuel cut and the second determination is made. When the means (see ninth step S9) determines that it is time to return from the fuel cut, the fuel supply return means (see tenth step S10) returns the fuel supply, but at the time of return from this fuel cut. The air-fuel ratio varying means (see routine R1) leans the air-fuel ratio in the peripheral portion of the spark plug 16 (see area α in FIG. 9) in comparison with the normal air-fuel ratio (A / F = 22) during lean burn operation. , The air-fuel ratio of the outer peripheral portion (see region β in FIG. 9) separated from the ignition plug 16 is controlled to be rich.

Therefore, by making the air-fuel ratio of the above-mentioned spark plug peripheral portion α lean, it is possible to control the torque shock at the time of fuel return, and make the air-fuel ratio of the outer peripheral portion β separated from the spark plug rich. By setting the total air-fuel ratio in the cylinder to be substantially the same as the normal air-fuel ratio under lean burn operation conditions (A / F = 22), misfire can be prevented.

In addition, the above-mentioned air-fuel ratio varying means (see routine R1) is a combination of the existing swirl generating means (see on-off valve 26 etc.) and fuel injection timing varying means (see twelfth step S12). Since it is configured, it is possible to effectively utilize both of these means without separately providing a unique device to achieve suppression of torque shock and prevention of misfire when returning from deceleration fuel cut.

Further, since the above-mentioned air-fuel ratio variable control is executed during lean burn operation, there is an effect that such misfire can be surely prevented under operating conditions where there is a high probability of misfire occurrence at the time of fuel recovery.

In the correspondence between the configuration of the present invention and the above-described embodiment, the first determining means of the present invention is the CPU of the embodiment.
Corresponding to the seventh step S7 (refer to FIG. 5) by the 30 control, the fuel cut means similarly performs the eighth step S8.
The second determination means corresponds to the ninth step S9, the fuel supply return means corresponds to the tenth step S10, the air-fuel ratio varying means corresponds to the routine R1, and the swirl generating means opens and closes. Corresponding to the valve 26 and the intake port structure, the fuel injection timing varying means has a twelfth step S
The means for executing lean burn operation (lean burn means) corresponding to No. 12 corresponds to the fourth step S4, but the present invention is not limited to the configuration of the above-described embodiment.

[Brief description of drawings]

FIG. 1 is a system diagram showing an air-fuel ratio control device for an engine of the present invention.

FIG. 2 is an explanatory diagram showing generation of a swirl flow.

FIG. 3 is a control circuit block diagram of an air-fuel ratio control device for an engine.

FIG. 4 is an explanatory diagram of maps stored in a RAM.

FIG. 5 is a flowchart showing air-fuel ratio control.

FIG. 6 is a time chart showing variable fuel injection timing control.

FIG. 7 is a characteristic diagram showing the relationship between the injection timing and the air-fuel ratio.

FIG. 8 is a time chart showing the air-fuel ratio control of the engine of the present invention.

FIG. 9 is an explanatory diagram showing a peripheral area and a peripheral area of a lighting plug.

FIG. 10 is a claim correspondence diagram.

FIG. 11 is a time chart showing air-fuel ratio control of a conventional engine.

[Explanation of symbols]

 12 ... Combustion chamber 16 ... Spark plug 26 ... Open / close valve S4 ... Lean burn means S7 ... First determination means S8 ... Fuel cut means S9 ... Second determination means S10 ... Fuel supply recovery means S12 ... Fuel injection timing varying means R1 ... Empty Fuel ratio varying means S ... Swirl flow α ... Spark plug peripheral part β ... Spark plug outer peripheral part

Claims (3)

[Claims] 1. A first determining means for determining when torque is not needed during engine deceleration, a fuel cut means for executing a fuel cut when torque is not needed based on the determination result of the first determining means, and a return from fuel cut. An air-fuel ratio control device for an engine, comprising: a second determination means for determining whether it is time or not; and a fuel supply return means for returning the fuel supply when returning from the fuel cut based on the determination result of the second determination means. Therefore, when returning from the fuel cut, the air-fuel ratio of the peripheral portion of the spark plug is made leaner than in the normal state, and the air-fuel ratio variable means for controlling the air-fuel ratio of the outer peripheral portion separated from the spark plug to rich is provided. Engine air-fuel ratio control system. 2. The air-fuel ratio varying means comprises swirl producing means for producing a swirl flow in the combustion chamber, and fuel injection timing varying means for gradually varying the fuel injection timing from before the intake top to after the intake top. 1. The air-fuel ratio control device for the engine according to 1. 3. The engine air-fuel ratio control device according to claim 1, wherein the variable air-fuel ratio control is executed during lean burn operation.