JPH0777111A - Air fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To steadily feed a purge flow without using a low duty ratio range of a flow control valve, where the operation of an internal combustion engine becomes unstable. CONSTITUTION:The amount of fuel to be fed to an internal combustion engine 1 is adjusted by an injector 6 based on the output signal from an electronic control unit(ECU), 16. The opening of a purge duty vacuum switching valve(VSV) 14 is adjusted by means of duty ratio control based on the pulse width modulation of the ECU 16, and the purge flow of air to be fed to the internal combustion engine 1 containing evaporated fuel from a canister 11, by which the evaporated fuel in a fuel tank 10 is absorbed, is adjusted. Since the purge duty VSV 14 is driven only when the duty ratio is no less than a predetermined value, variation in the purge flow is limited to a low level, resulting in no large fluctuation in air fuel ratio, and degradation of exhaust emission is thus prevented.

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 discharging evaporated fuel generated in a fuel tank to the intake side of an internal combustion engine (engine) for combustion and purging.

[0002]

2. Description of the Related Art Conventionally, as a prior art document related to an air-fuel ratio control system for an internal combustion engine, Japanese Patent Laid-Open No. 63-255559.
The one disclosed in the publication is known. In this case, the preset purge rate is gradually changed according to the operating state of the internal combustion engine (engine speed, intake air amount, etc.) until it reaches a predetermined value. This reduces the deviation between the air-fuel ratio of the air-fuel mixture actually supplied to the internal combustion engine and the target air-fuel ratio due to the detection response delay.

[0003]

By the way, in the air-fuel ratio control of an internal combustion engine, if the purge rate is extremely low, or even if the purge rate is high to some extent, if the absolute flow rate of intake air is small at idling, etc. For example, the duty ratio for pulse driving of a VSV (Vacuum Switching Valve), which is a flow control valve for, becomes low. As shown in FIG. 6, particularly when the duty ratio is 15% or less, the purge flow rate fluctuates in combination with the pressure pulsation in the intake manifold, resulting in a large disturbance of the air-fuel ratio, resulting in exhaust gas. Emissions were getting worse.

Therefore, the present invention has been made in order to solve such a problem, and in the purge control using the flow rate control valve, the purge flow rate is used without using the low duty ratio region where the operation of the internal combustion engine becomes unstable. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can stably supply the air.

[0005]

An air-fuel ratio control system for an internal combustion engine according to the present invention stores vaporized fuel generated in a fuel tank in a canister, and the vaporized fuel stored in the canister together with air from the canister to the internal combustion engine. Is an air-fuel ratio control device for an internal combustion engine, the air-fuel ratio detecting device detecting the air-fuel ratio of the internal combustion engine, and the air-fuel ratio detecting device detecting the air-fuel ratio of the internal combustion engine. Air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the determined air-fuel ratio, and the purge rate of the air containing the evaporated fuel provided in the path of the discharge passage. A flow rate control valve to be changed, and a purge rate increasing / decreasing part based on the deviation of the air-fuel ratio feedback value by the air-fuel ratio feedback means from the theoretical air-fuel ratio. It is determined whether the duty ratio of the flow rate control valve for obtaining the purge flow rate calculated based on the rate setting means and the purge rate by the purge rate setting means and the intake air amount of the air-fuel mixture is equal to or greater than a predetermined value. It is provided with a judging means and a driving means for driving the flow rate control valve based on the duty ratio when the duty ratio becomes equal to or higher than a predetermined value by the judging means.

[0006]

In the present invention, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback-controlled based on the detected air-fuel ratio. Further, the purge rate of the air containing the evaporated fuel stored in the canister is changed by the flow control valve. At this time, the purge flow rate is calculated by multiplying the purge rate, which is increased or decreased based on the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio by feedback control, by the intake air amount of the air-fuel mixture. When the duty ratio determined by the calculated purge flow rate becomes equal to or higher than a predetermined value, the flow rate control valve is controlled by the duty ratio, so that the evaporated fuel is stably discharged to the intake side of the internal combustion engine and purged. To be done.

[0007]

EXAMPLES The present invention will be described below based on specific examples.

FIG. 1 is an overall configuration diagram showing an air-fuel ratio control system for an internal combustion engine according to an embodiment of the present invention.

In FIG. 1, 1 is an internal combustion engine (engine) composed of a plurality of cylinders, 2 is an intake pipe connected to the internal combustion engine 1, and 3 is an intake pressure (PM) which is the pressure in the intake pipe 2. An intake pressure sensor, 4 is a throttle valve arranged in the intake pipe 2, 5 is a throttle sensor for detecting the throttle opening of the throttle valve 4, and 6 is arranged in the intake pipe 2 upstream of the throttle valve 4. Injector, 7 is intake pipe 2
It is an air filter disposed in the upstream side of the injector 6. Further, 8 is an exhaust pipe connected to the internal combustion engine 1, and 9
Is an oxygen (O ₂ ) sensor that is provided in the exhaust pipe 8 and serves as an air-fuel ratio detecting means. The oxygen sensor 9 outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas. Further, 10 is a fuel tank, 11 is a canister containing activated carbon that is an adsorbent that adsorbs evaporated fuel generated in the fuel tank 10, and 1
2 is a tank port passage connecting the fuel tank 10 and the canister 11, 13 is an atmosphere port passage arranged in the canister 11 for introducing outside air, and 14 is a flow rate control valve for performing purge control with a duty ratio. A purge duty VSV (Vacuum Switching Valve) 15 is a discharge passage connecting the canister 11 and the downstream side of the throttle valve 4 in the intake pipe 2, and the purge duty VSV 14 is arranged in the discharge passage 15. . Further, 16 is an ECU (Electronic Control Unit) of the electronic control device, and the ECU 16 is composed of an input signal processing circuit, an arithmetic circuit, an output signal circuit (driving circuit), a power supply circuit, and the like. Reference numeral 17 denotes an engine speed sensor for detecting the engine speed (NE) of the internal combustion engine 1, and 18 denotes the temperature of the cooling water (TH
It is a water temperature sensor that detects W). In addition to the above, as the vehicle state detection sensor group 19, an intake air temperature sensor or the like for detecting the temperature of the air taken in from the air filter 7 is arranged as necessary. Intake pressure (PM), which is the intake pipe internal pressure (negative pressure) of the intake pressure sensor 3, throttle opening (TA) of the throttle sensor 5, voltage of the oxygen sensor 9, engine speed of the engine speed sensor 17. Various signals such as (NE) and the water temperature (THW) of the water temperature sensor 18 are input to the ECU 16. Throttle valve 4
Is opened and closed by depressing a driver's throttle pedal (not shown), and the intake air amount Q of the air-fuel mixture supplied to the internal combustion engine 1 is
Adjust a. Further, the injector 6 adjusts the amount of fuel supplied to the internal combustion engine 1 based on the output signal from the ECU 16. Further, the purge duty VSV14 is the ECU 1
The opening degree is adjusted by the duty ratio control based on the pulse width modulation 6 to adjust the purge flow rate Qp of the air containing the evaporated fuel from the canister 11 that adsorbs the evaporated fuel in the fuel tank 10 supplied to the internal combustion engine 1. It should be noted that the purge duty VSV14 is configured to switch the discharge passage 15, which is a negative pressure circuit, from the closed state to the open state by sucking the valve element made of the movable iron piece that is urged by the spring when the coil is excited. ing.

Therefore, the purge duty VSV
A control signal is supplied from the ECU 16 to the
When 1 is made to communicate with the intake pipe 2 of the internal combustion engine 1 via the discharge passage 15, fresh air Qf is introduced from the atmosphere via the atmosphere port passage 13. This new air Qf ventilates the inside of the canister 11 and is sent into the intake pipe 2 of the internal combustion engine 1, whereby the canister 11 is purged and the adsorption function is restored. At this time, the purge flow rate Qp (l
/ Min) is the purge duty VSV14 from the ECU 16.
It is adjusted by changing the duty ratio of the pulse signal supplied to.

The ECU 16 inputs a signal (voltage signal) from the oxygen sensor 9 and determines rich / lean of the air-fuel mixture. Then, the ECU 16 changes (skips) the feedback correction coefficient stepwise in order to increase / decrease the fuel injection amount when reversing from rich to lean and when reversing from lean to rich, and when it is lean or rich, feedback correction is performed. The coefficient is gradually increased or decreased. It should be noted that this feedback control is not performed when the cooling water temperature of the internal combustion engine is low, or when the vehicle is running under high load and high rotation speed. Further, the ECU 16 determines the engine speed (NE)
Then, the basic injection time is obtained from the intake pressure (PM), the basic injection time is corrected by a feedback correction coefficient or the like to obtain the final injection time, and the injector 6 performs fuel injection at a predetermined injection timing.

The air-fuel ratio control system for an internal combustion engine according to this embodiment is operated by operating the following programs for air-fuel ratio feedback control, fuel injection amount control, and duty VSV control.

The operation of the embodiment will be described below for each control.

<Air-fuel ratio feedback control> The air-fuel ratio feedback control routine will be described with reference to FIG. Note that this air-fuel ratio feedback control routine takes about 4 ms.
It is executed by the ECU 16 every time.

In step S101, feedback (F
/ B) It is determined whether control is possible. The F / B condition is mainly when all the following conditions are satisfied. (1) Not at the start. (2) Fuel is not being cut.
(3) The cooling water temperature (THW) is equal to or higher than a predetermined temperature.
(4) The fuel injection amount exceeds the predetermined lower limit value. (5)
The oxygen sensor is active.

If these conditions are met, step S1
02, the oxygen sensor output is compared with the predetermined determination level, and the air-fuel ratio flag XOXR is operated at delay times H and I (ms), respectively. For example, when XOXR = 1, rich, and when XOXR = 0, lean. Next, the process proceeds to step S103, and based on the air-fuel ratio flag XOXR,
Manipulate the FAF value. That is, XOXR changes (0 →
1), (1 → 0), the FAF value is skipped by a predetermined amount, and while the XOXR continues to be 1 or 0, the integration control of the FAF value is executed. Then, in step S104, FAF
After checking the upper and lower limits of the value, the process proceeds to step S105, and the smoothing process is performed at each skip or every predetermined time based on the determined FAF value, and the FAFAV value that is the average value of the FAF value is calculated. calculate. Note that step S
If the F / B control is not established at 101, step S1
Then, the FAF value is set to 1.0. Here, the air-fuel ratio feedback coefficient FAF value is an index showing how far it deviates from the theoretical air-fuel ratio.

<Fuel Injection Amount Control> The fuel injection amount control routine will be described with reference to FIG. Note that this fuel injection amount control routine is also executed by the ECU 16 about every 4 ms.

First, in step S201, the basic fuel injection amount (TP) of the injector 6 is calculated from the engine speed (NE) and the load (for example, intake pressure (PM)), and the process proceeds to step S202 to perform various basic corrections. (Cooling water temperature, intake air temperature after starting, etc.) are executed. Next, the process proceeds to step S203, and the purge rate PG is added to the evaporation concentration average value FGPGAV.
The purge correction coefficient FPG is calculated by multiplying R. Here, since the evaporation concentration does not change significantly in a short time, the evaporation concentration average value FGPGAV is set to KPG (constant), and the purge rate PGR is set to a value set in FIG. 4 described later (the initial value is α
%) As the purge correction coefficient FPG.
Next, in step S204, FAF and FPG are substituted into the formula [1+ (FAF-1) + FPG], calculated as a correction coefficient, and reflected in the fuel injection amount TAU.

<Duty VSV Control> Duty VS
The V control routine will be described with reference to FIG. The duty VSV control routine is executed by the ECU 16 by a time interruption every 100 ms.

First, in step S301, in order to detect the operating state of the internal combustion engine 1 by reading the operating state, specifically, the engine rotational speed (NE) signal from the engine rotational speed sensor 17 and the intake pressure sensor 3 are read. Intake pressure from (P
M) Read signal and. The intake air amount Qa of the air-fuel mixture supplied to the internal combustion engine 1 based on the intake pressure (PM) signal
Is calculated. Next, the process proceeds to step S302, and it is determined whether the operating condition read in step S301 is equal to or higher than a predetermined engine speed (NE) and a predetermined intake air amount and the purge condition is satisfied. Step S302
If the purge condition is not satisfied at step S301, the process returns to step S301 and the same process is repeated. In step S302, if the purge condition is satisfied, the process proceeds to step S303, where the purge rate initial value is α% that does not affect the operating state.
(For example, a small value of about 0 or 0.1%) is set. Next, the process proceeds to step S304, and FAF that is the average value of the FAF values calculated in step S105 of FIG.
It is determined whether the AV value is stable within (1.0 ± predetermined value). The predetermined value is set to about 5%. Here, the point where the signal from the oxygen sensor 9 is inverted (from rich to lean or lean to rich) is the stoichiometric air-fuel ratio, and at the stoichiometric air-fuel ratio the FAF value is 1.0 and the FAF value is (1.0 If it exceeds (± predetermined value), the air-fuel ratio will be too stable and the air-fuel ratio will not be stable.
If the FAF value is not stable in step S304, the process proceeds to step S305, and the purge rate is set to β% (for example, 0.0% since it is likely that the exhaust emission is deteriorated).
2%). Step S304
If the FAF value is stable and is close to the stoichiometric air-fuel ratio, it is determined that the exhaust emission is good, the process proceeds to step S306, and the purge rate is β% (for example, 0.0%).
Small value (about 2%). Then step S3
07, and then step S305 or step S3
After the purge rate is changed in 06, the purge rate and the intake air amount Qa are multiplied to calculate the purge flow rate Qp. Next, the process proceeds to step S308, and the purge flow rate (l / mi
The duty ratio for the purge flow rate Qp is calculated based on the map showing the relationship between n) and the duty ratio (%). The map of FIG. 6 shows the purge duty VSV1.
4 is experimentally obtained using the differential pressure (mmHg) across the discharge passage 15 in which No. 4 is arranged and the drive frequency (Hz) of the purge duty VSV 14 as parameters. Further, as is clear from FIG. 6, when the duty ratio exceeds approximately 20%, the purge flow rate and the duty ratio linearly and stably increase and decrease. Next, the process proceeds to step S309, and it is determined whether the duty ratio is γ or more. This γ value is a limit duty ratio with which the purge flow rate can be stably supplied, and if it is more than this value, output to the purge duty VSV 14 is permitted. This limit duty ratio γ
Is the purge duty VSV1 according to the map shown in FIG.
4 is calculated based on the differential pressure across the discharge passage 15 (mmHg) and the drive frequency (Hz) of the purge duty VSV 14. The limit duty ratio γ in the middle of the map in FIG. 5 is calculated by interpolation. Step S
If the duty ratio is less than γ in 309, it is determined that the behavior of the internal combustion engine is adversely affected, and the process returns to step S304 and the same processing is repeated. When the duty ratio becomes γ or more in step S309, the process proceeds to step S310, the pulse signal corresponding to the duty ratio is output to the purge duty VSV14, and the purge control is performed. Then, the process proceeds to step S311 and step S30.
Similar to step 1, after the driving state is read, step S3
Then, the process shifts to 12, and it is determined whether the purge condition is satisfied, as in step S302. In step S312,
If the purge condition is not satisfied, the process returns to step S301 and the same processing is repeated. Then, step S312
If the purge condition is satisfied, step S3
Returning to 04, the same processing is repeated.

As described above, the air-fuel ratio control system for the internal combustion engine according to the embodiment of the present invention stores the evaporated fuel generated in the fuel tank 10 in the canister 11, and the evaporated fuel stored in the canister 11 together with the air in the canister 11. From internal combustion engine 1
Is an air-fuel ratio control device for an internal combustion engine, the air-fuel ratio detecting device comprising an oxygen sensor 9 for detecting an air-fuel ratio of the internal combustion engine 1, The air-fuel ratio feedback means including an ECU 16 for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 1 based on the air-fuel ratio detected by the air-fuel ratio detection means, and the air-fuel ratio feedback means disposed in the path of the discharge passage 15, A flow rate control valve including a purge duty VSV14 that changes the purge rate of air containing evaporated fuel, and an ECU that increases or decreases the purge rate based on the deviation of the air-fuel ratio feedback value by the air-fuel ratio feedback means from the theoretical air-fuel ratio.
The duty ratio of the flow rate control valve for obtaining the purge flow rate calculated based on the purge rate set by 16 and the purge rate set by the purge rate setting means and the intake air amount of the air-fuel mixture is a predetermined value or more. ECU 16 for determining whether
And a drive means including an ECU 16 that drives the flow rate control valve based on the duty ratio when the duty ratio exceeds a predetermined value.

Therefore, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback-controlled based on the detected air-fuel ratio. Further, the purge rate of the air containing the evaporated fuel stored in the canister is changed by the flow control valve. At this time, the purge flow rate is calculated by multiplying the purge rate, which is increased or decreased based on the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio by feedback control, by the intake air amount of the air-fuel mixture. When the duty ratio determined by the calculated purge flow rate becomes equal to or higher than a predetermined value, the flow rate control valve is controlled by the duty ratio, so that the evaporated fuel is stably discharged to the intake side of the internal combustion engine and purged. To be done.

Therefore, in the purge control using the flow control valve,
The purge flow rate can be stably supplied without using the low duty ratio region where the operation of the internal combustion engine becomes unstable.

As described above, the air-fuel ratio detecting means of the above embodiment is composed of the oxygen sensor 9, but the present invention is not limited to this, and the internal combustion engine 1 is not limited to this.
Anything that detects the air-fuel ratio of In particular, when the air-fuel ratio detecting means is composed of the oxygen sensor 9, there is an effect that it is easy to detect a voltage signal according to the oxygen concentration in the exhaust gas.

The air-fuel ratio feedback means of the above embodiment is achieved by the ECU 16. However, the present invention is not limited to this, and the air-fuel ratio detection means detects the air-fuel ratio feedback means. It is sufficient that the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 1 is feedback-controlled based on the fuel ratio.

Further, although the flow control valve of the above-mentioned embodiment has the purge duty VSV, the present invention is not limited to this, and it is disposed in the path of the discharge passage 15, Anything that changes the purge rate of air containing evaporated fuel may be used.

The purge rate setting means of the above embodiment is achieved by the ECU 16. However, the present invention is not limited to this, and the air / fuel ratio feedback means provides the air / fuel ratio. The purge rate may be increased or decreased based on the deviation of the feedback value from the theoretical air-fuel ratio.

Further, the determination means of the above embodiment is the ECU 1
However, the present invention is not limited to this, and the purge calculated by the purge ratio setting means and the intake air amount of the air-fuel mixture is not limited to this. It is sufficient to determine whether the duty ratio of the flow rate control valve for obtaining the flow rate is equal to or higher than a predetermined value.

Furthermore, the drive means of the above embodiment is an EC
However, when the present invention is carried out, the present invention is not limited to this, and when the duty ratio becomes a predetermined value or more by the judging means, the flow control valve is driven based on the duty ratio. Anything can be done.

[0030]

As described above, the air-fuel ratio control system for an internal combustion engine according to the present invention uses the internal combustion engine when the evaporated fuel stored in the canister is discharged together with air through the discharge passage connected to the intake side. The air-fuel ratio of the air-fuel mixture supplied to the engine is detected and feedback-controlled, and the purge rate is increased or decreased based on the deviation of the air-fuel ratio feedback value from the theoretical air-fuel ratio,
When the duty ratio for obtaining the purge flow rate calculated based on the purge rate and the intake air amount of the air-fuel mixture is equal to or higher than the predetermined value, the flow control valve is driven based on the duty ratio, so that the internal combustion engine does not operate properly. It is possible to prevent deterioration of exhaust emission due to the use of the stable low duty ratio region and to stably supply the purge flow rate.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an air-fuel ratio control device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a flowchart showing air-fuel ratio feedback control in an air-fuel ratio control device for an internal combustion engine according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection amount control in an air-fuel ratio control system for an internal combustion engine according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a duty VSV control in an air-fuel ratio control system for an internal combustion engine according to an embodiment of the present invention.

FIG. 5 is a map showing a limit duty ratio in an air-fuel ratio control system for an internal combustion engine according to an embodiment of the present invention.

FIG. 6 is a map showing the relationship between the purge flow rate and the duty ratio according to the present invention and the related art.

[Explanation of symbols]

1 Internal Combustion Engine 3 Intake Pressure Sensor 9 Oxygen (O ₂ ) Sensor (Air-Fuel Ratio Detection Means) 10 Fuel Tank 11 Canister 14 Purge Duty VSV (Flow Control Valve) 15 Release Passage 16 ECU (Electronic Control Unit)

Claims (1)

[Claims] 1. An evaporative fuel generated in a fuel tank is stored in a canister, and the evaporative fuel stored in the canister is discharged together with air from the canister through a discharge passage connected to an intake side of an internal combustion engine. In an air-fuel ratio control device for an internal combustion engine, an air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine based on the air-fuel ratio detected by the air-fuel ratio detecting means. An air-fuel ratio feedback means for performing feedback control, a flow control valve arranged in the path of the discharge passage for changing the purge rate of the air containing the evaporated fuel, and a theory of the air-fuel ratio feedback value by the air-fuel ratio feedback means. Purge rate setting means for increasing or decreasing the purge rate based on the deviation from the air-fuel ratio; Determination means for determining whether the duty ratio of the flow rate control valve for obtaining the purge flow rate calculated based on the intake air amount of the air-fuel mixture is greater than or equal to a predetermined value; At this time, an air-fuel ratio control device for an internal combustion engine, comprising: a drive unit that drives the flow rate control valve based on the duty ratio.