JPH04234553A - Air-fuel ratio control of internal combustion engine - Google Patents

Abstract

PURPOSE:To control air-fuel ratio accurately by calculating the weight of fuel vapour to be evaporated from a fuel tank and supplied to an intake system. CONSTITUTION:Fuel vapour weight GVQ supplied to an intake valve through a canister is found from both air volume Q4 supplied to the canister and air- vapour added volume Q1 supplied from the canister to an intake system of an engine, and by using the ratio of the fuel-vapour weight and fuel injection volume supplied to the engine, air-fuel ratio of air-fuel mixture supplied to the engine is corrected.

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 method for an internal combustion engine having a fuel vapor emission control device.

0002

2. Description of the Related Art Conventionally, fuel vapor emission control devices have been widely used to prevent fuel vapor generated from fuel within a fuel tank from being released into the atmosphere. In this device, fuel vapor is temporarily stored in a canister, and the stored vaporized fuel is supplied to the engine intake system. By supplying (purging) this evaporated fuel to the intake system, the air-fuel mixture supplied to the engine momentarily becomes richer, but if the amount of purge is small, the air-fuel ratio of the air-fuel mixture is quickly adjusted to the desired control target value by air-fuel ratio feedback control. , and there is almost no change in the air-fuel ratio.

However, when the amount of purge is large, fluctuations in the air-fuel ratio occur. For example, a large amount of fuel vapor may be generated immediately after refueling the fuel tank, and in order to prevent fluctuations in the air-fuel ratio due to purge immediately after refueling, the engine is started immediately after refueling until the vehicle speed reaches a predetermined value.
A purge flow rate control device is known in which the purge amount is reduced until the cumulative time during which the vehicle speed exceeds the predetermined value reaches a predetermined time (e.g., Japanese Patent Laid-Open No. 111277/1983). .

[0004] Furthermore, purge is performed in advance at a small amount that causes almost no air-fuel ratio fluctuation, and the amount of fluctuation in the feedback correction coefficient in air-fuel ratio feedback control due to this purge is detected, and the purge amount is determined based on this amount of fluctuation. The correction coefficient when increased is predicted, and the predicted value is used as a feedback correction coefficient to reduce the supplied fuel amount in synchronization with increasing the actual purge amount, and even if the purge amount is large, the air-fuel ratio is Air-fuel ratio control devices designed to suppress fluctuations are known (for example, Japanese Patent Application Laid-Open No. 1983-1999)
131962).

[0005]

[Problems to be Solved by the Invention] However, in the former device of the above-mentioned prior art, accurate air-fuel ratio control cannot be performed because the actual purge amount is not detected when controlling the purge flow rate. There are things I can't do. That is, the amount of fuel evaporated by refueling varies depending on the amount of fuel remaining in the fuel tank before refueling, and therefore the amount of purge after refueling is not constant. Therefore, with this device, if the expected purge amount after refueling is set to a relatively small value and purge is performed at a large flow rate, fluctuations in the air-fuel ratio are unavoidable. If purge is performed, fluctuations in the air-fuel ratio can be avoided, but the processing capacity of the fuel vapor emission control device cannot be fully utilized.

[0006]Furthermore, the latter device of the above-mentioned prior art does not directly detect the actual purge amount, but estimates the purge amount based on fluctuations in the air-fuel ratio feedback correction coefficient, and Since this method predicts the variation of the coefficient due to a large amount of purge from the variation of the coefficient when the amount of purge is small, it has been impossible to accurately control the air-fuel ratio due to purge.

[0007] Therefore, there has been a problem in that the air-fuel ratio fluctuates, which deteriorates the exhaust gas characteristics and causes the output torque to fluctuate.

The present invention was made in view of the above circumstances, and it detects the actual fuel vapor that evaporates from the fuel tank and is supplied to the intake system, and calculates its weight to accurately control the air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that makes it possible to

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a canister and a canister for adsorbing fuel vapor generated in the fuel tank between the fuel tank and the intake system of the engine. In an air-fuel ratio control method for an internal combustion engine including a control valve for supplying fuel vapor adsorbed in a canister to an intake system of an engine, the amount of air supplied to the canister and from the canister to the intake system of an engine are disclosed. The weight of the fuel vapor supplied to the intake system via the canister is determined from the total amount of air vapor supplied, and the ratio of the fuel vapor weight to the injection amount of fuel supplied to the engine is used to determine the weight of the fuel vapor supplied to the intake system. An air-fuel ratio control method for an internal combustion engine is provided, which is characterized by correcting the air-fuel ratio of a supplied air-fuel mixture.

0010

[Operation] According to the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio of the air-fuel mixture is detected, and the amount of fuel injected and supplied to the engine is corrected by feedback based on the detected value, while the amount of fuel that is evaporated in the fuel tank is The fuel is supplied to the engine via the canister, intake system, etc.

[0011] From the amount of air supplied to the canister and the total amount of air vapor supplied from the canister to the intake system of the engine, the weight of the fuel vapor supplied to the intake system via the canister is determined, and the weight of the fuel vapor and the engine are calculated. The air-fuel ratio of the air-fuel mixture supplied to the engine is corrected using the ratio between the amount of fuel injected and the amount of fuel supplied to the engine.

[0012] This realizes accurate control of the air-fuel ratio.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control device including an evaporated fuel purge device for an internal combustion engine to which the air-fuel ratio control method of the present invention is applied. Reference numeral 1 indicates, for example, a four-cylinder internal combustion engine; A throttle body 3 is provided in the middle of an intake pipe 2 of the engine 1, and a throttle valve 301 is disposed inside the throttle body 3. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 301.
An electrical signal corresponding to the opening degree of the throttle valve 301 is output and supplied to the electronic control unit (hereinafter referred to as "ECU") 5.

The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 301 and slightly upstream of the intake valve (not shown) in the intake pipe 2. Connected to fuel tank 8 and EC
The ECU 5 is electrically connected to the ECU 5, and the opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 10 is provided immediately downstream of the throttle valve 301 via a pipe 9, and the absolute pressure signal converted into an electrical signal by this absolute pressure sensor 10 is It is supplied to the ECU5.

The engine rotational speed (NE) sensor 11 is installed around the camshaft or crankshaft (not shown) of the engine 1, and generates a signal pulse (hereinafter referred to as TDC signal pulse) is output, and this signal pulse is sent to the ECU.
5.

O2 sensor 1 as exhaust gas concentration detector
2 is attached to the exhaust pipe 13 of the engine 1, detects the oxygen concentration in the exhaust gas, outputs a signal according to the detected value, and supplies it to the ECU 5.

Between the upper part of the sealed fuel tank 8 and the intake pipe 2 downstream of the throttle body 3, there are a two-way valve 14 and an adsorbent 151 constituting a fuel evaporative gas emission suppressing device.
The purge control valve 1 is a linear control valve (EACV) having a solenoid that drives the valve.
6 is provided. The solenoid of the purge control valve 16 is EC.
It is connected to U5 and is controlled according to a signal from ECU 5 to linearly change the valve opening amount. According to this fuel evaporative gas emission suppression device, when the evaporative gas generated in the fuel tank 8 reaches a predetermined set pressure, it pushes open the positive pressure valve of the two-way valve 14, flows into the canister 15, and enters the canister 15. is adsorbed and stored by the adsorbent 151. On the other hand, when the solenoid is not energized by the control signal from the ECU 5, the purge control valve 16 is closed, but when the solenoid is energized by the control signal, the valve opens only by the amount corresponding to the energization amount. The purge control valve 16 is opened, and the evaporated fuel temporarily stored in the canister 15 is transferred to the outside air intake port 152 provided in the canister 15 due to negative pressure in the intake pipe 2.
It is sucked into the intake pipe 2 through the throttle body 3 along with the outside air taken in from the throttle body 3, and sent to the cylinders. Further, when the fuel tank 8 is cooled due to the influence of outside air and the negative pressure inside the fuel tank increases, the negative pressure valve of the two-way valve 14 opens, and the vaporized fuel temporarily stored in the canister 15 is transferred to the fuel tank 8. be returned to. In this way, fuel evaporative gas generated in the fuel tank 8 is prevented from being released into the atmosphere.

By the way, the outside air intake port 15 of the canister 15
2 is provided with an orifice 153, and canister 1
An orifice 171 is also provided on the purge control valve 16 side of the pipe 17 that connects the purge control valve 16 to the purge control valve 16 . Further, a pressure gauge 19 is installed in the pipe 17 between the orifice 171 and the purge control valve 16 via a pipe 18, and the canister 1
A pressure gauge 21 is installed through a pipe 20 in the space above the adsorbent 151 of No. 5. The pressure gauges 19 and 21 are constituted by atmospheric pressure differential pressure gauges, and the pressure gauge 19 is a tube 1 for atmospheric pressure.
Detects the relative pressure P1 within 7 and sends the detection signal to the ECU 5.
The pressure gauge 21 is connected to the canister 15 against atmospheric pressure.
Detects the relative pressure P2 inside and supplies the detection signal to the ECU 5.

The ECU 5 includes an input circuit having functions such as shaping input signal waveforms from various sensors, correcting voltage levels to predetermined levels, and converting analog signal values into digital signal values, and a correction coefficient VQKO2 and a correction coefficient VQKO2 to be described later. Central processing circuit (hereinafter referred to as “C”) that executes the EACV value calculation program, etc.
PU"), various calculation programs executed by the CPU, storage means for storing Q1 and Q4 tables described later, Ti maps, calculation results, etc., and an output for supplying drive signals to the fuel injection valve 6 and the purge control valve 16. It consists of circuits, etc.

Based on the above-mentioned various engine parameter signals, the CPU determines various engine operating states such as a feedback control operating range and an open loop control operating range depending on the oxygen concentration in the exhaust gas, and also determines various engine operating states depending on the engine operating state. , the fuel injection time Tout of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated based on the following equation (1).

[0023]

[Math. 1] Tout=Ti×KO2×VQKO2+K1+K2
...(1) Here, Ti is the injection time Tou of the fuel injection valve 6
This is a reference value of t, and is read from a Ti map set according to the engine speed NE and the intake pipe absolute pressure PBA.

KO2 is an air-fuel ratio feedback correction coefficient, which is set according to the oxygen concentration in the exhaust gas detected by the O2 sensor 12 during feedback control; This is a coefficient set according to each driving region.

VQKO2 is a vapor amount correction coefficient according to the present invention, and is a value set according to the vapor amount detected when purging is being executed. The details will be described later with reference to FIG.

[0026] K1 and K2 are other correction coefficients and correction variables respectively calculated according to various engine parameter signals, and are used to optimize various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to engine operating conditions. The predetermined value is determined as follows.

The CPU supplies the fuel injection valve 6 with a drive signal to open the fuel injection valve 6 via the output circuit based on the fuel injection time Tout determined as described above.

FIG. 2 shows the correction coefficient VQKO2 according to the present invention.
and EACV value calculation program, which is executed by the CPU.

First, in step S1, orifice 1
Based on the jet area of 71 and the relative pressures P1 and P2 detected by the pressure gauges 19 and 21, the total air vapor flow rate Q1 passing through the orifice 171 is read out based on the Q1 table stored in the storage means of the ECU 5. Relative pressure P1, P2
represents the pressure inside the pipe 17 and the pressure inside the canister 15 with respect to atmospheric pressure, so the pressure difference P1-P2 corresponds to the pressure difference between the pressure on the inlet side and the outlet side of the orifice 171. The Q1 table shows the jet area of the orifice 171 and the differential pressure P1.
-P2 is determined, the flow rate of gas passing through the orifice 171 is uniquely determined. . The total air vapor flow rate Q1 is the sum of the vapor flow rate VQ due to the fuel vapor (vapor) coming from the fuel tank 8 and adsorbed in the canister 15 and the air flow rate Q4 due to the air taken in from the outside air intake port 152 of the canister 15. This is the total flow rate. Note that the total air vapor flow rate Q1 includes direct flow from the fuel tank 8 to the canister 15.
The vapor that passes through the orifice 171 without being adsorbed is also included, but since this is highly concentrated fuel vapor, it will be included in the vapor flow rate VQ.

Next, in step S2, orifice 1
Jet area of 53 and relative pressure P detected by pressure gauge 21
2 and the air flow rate Q4 passing through the orifice 153,
Read based on the Q4 table stored in the storage means of the ECU 5. The relative pressure P2 is the canister 1 relative to atmospheric pressure.
5, the relative pressure P2 is the orifice 153.
This corresponds to the difference in pressure between the inlet side and the outlet side. Q4
The table shows the jet area of the orifice 153 and the differential pressure P
2 is determined, the flow rate of gas passing through the orifice 153 is uniquely determined, and the table stores the air flow rate Q4 corresponding to each value of the differential pressure P2.

In step S3, the vapor flow rate VQ due to the fuel vapor adsorbed in the canister 15 or the fuel vapor directly coming from the fuel tank 8, and the air flow rate Q4 due to the air taken in from the outside air intake port 152 of the canister 15 are determined. The vapor flow rate VQ is calculated by subtracting the air flow rate Q4 from the total flow rate Q1.

Based on the calculated vapor flow rate VQ, a vapor amount correction coefficient VQKO2 is calculated in step S4. That is, first, the vapor flow rate VQ is converted into a liquid gasoline weight equivalent amount GVQ (g/min) based on the following equation (2).

[0033]

[Equation 2] KVQ is a coefficient indicating the ratio of gasoline vapor amount (l/min) included in vapor flow rate VQ (l/min),
It is 1/1.69. VMOL is 1 molar volume value,
It is represented by 22.4 l/MOL value at 0°C. Gasoline vapor molecular weight is approximately 64. Using the gasoline weight equivalent amount GVQ (g/min) obtained in this way, the following formula (3
), the vapor amount correction coefficient VQKO2 is calculated.

[0034]

[Equation 3] The basic injection weight is calculated by subtracting the reference value Ti of the fuel injection time from the fuel weight (
g).

Vapor amount correction coefficient VQK thus obtained
O2 is 1.0 during purge cut when the purge control valve 16 is closed, and becomes a value of 1.0 or less when the purge control valve 16 is opened and purge is executed. Using this value, the fuel injection time Tout is calculated based on the above formula (1), and the fuel injection valve 6 supplies the engine 1 with an amount of fuel that suppresses fluctuations in the air-fuel ratio due to the size of the purge amount. be done.

Furthermore, in step S5, step S3
It is determined whether the vapor flow rate VQ calculated in is equal to or greater than a predetermined value. The predetermined value is set by another program as a function of the engine motion parameter, and is used to prevent the average value of the air-fuel ratio correction coefficient KO2 from deviating significantly from 1.0 and deteriorating the responsiveness of feedback control. This is a discrimination reference value that is set taking into consideration.

If the answer to step S5 is negative (No), that is, if the calculated vapor flow rate VQ is smaller than the predetermined value, the purge control valve 16 is opened in order to increase the vapor amount and increase the fuel vapor emission suppressing ability. Controlled amount E corresponding to valve amount
The ACV value is increased by the value C from the current value (step S6
) Exit this program. The value C is an update constant for the EACV value. On the other hand, if the answer to step S5 is affirmative (Yes), that is, the calculated vapor flow rate VQ is equal to or higher than the predetermined value, the vapor amount is reduced to prevent the feedback control from deteriorating in response. Controlled amount EAC
The V value is decreased by the value C from the current value (step S7) and the program is ended.

As described above, the actual vapor amount VQ is detected, and the fuel injection amount is corrected accordingly (step S4).
, prevents fluctuations in air-fuel ratio caused by purge, and
The opening amount of the purge control valve 16 is controlled in accordance with the detected purge amount (steps S6 and S7) to prevent the average value of the air-fuel ratio correction coefficient KO2 from deviating significantly from the value 1.0. This reduces the responsiveness of the feedback control that occurs when the average value used as the initial value of the air-fuel ratio correction coefficient KO2 deviates significantly from the value 1.0 when the air-fuel ratio control shifts from the open loop mode to the feedback mode. Deterioration can be prevented.

[0039]

As described in detail above, the present invention provides a canister for adsorbing fuel vapor generated in the fuel tank between a fuel tank and an intake system of an engine, and a fuel adsorbed in the canister. In an air-fuel ratio control method for an internal combustion engine equipped with a control valve for supplying vapor to an intake system of an engine, the total amount of air supplied to the canister and the amount of air vapor supplied from the canister to the intake system of the engine From this, the weight of the fuel vapor supplied to the intake system via the canister is determined, and the air-fuel ratio of the mixture supplied to the engine is determined using the ratio between the weight of the fuel vapor and the injection amount of fuel supplied to the engine. Since this is corrected, it is possible to prevent fluctuations in the air-fuel ratio due to purge supply, and it is possible to prevent deterioration of exhaust gas characteristics and fluctuations in output torque.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a fuel supply control device including an evaporated fuel purge device for an internal combustion engine.

FIG. 2 is a flowchart of a program for calculating a correction coefficient VQKO2 and an EACV value.

[Explanation of symbols]

1 Internal combustion engine 2 Intake pipe 5 Electronic control unit (ECU) 6 Fuel injection valve 8 Fuel tank 15 Canister 16 Purge control valve 19 Pressure gauge 21 Pressure gauge

Claims (3)

[Claims] 1. A canister for adsorbing fuel vapor generated in the fuel tank between a fuel tank and an engine intake system, and a canister for supplying the fuel vapor adsorbed in the canister to the engine intake system. In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio is determined from the amount of air supplied to the canister and the total amount of air vapor supplied from the canister to the intake system of the engine via the canister. An internal combustion engine characterized by determining the weight of fuel vapor supplied to the engine and correcting the air-fuel ratio of the air-fuel mixture supplied to the engine using the ratio between the weight of the fuel vapor and the injection amount of fuel supplied to the engine. air-fuel ratio control method. 2. The air-fuel ratio is corrected using the ratio by correcting the basic fuel injection amount set by a plurality of operating parameters, such that the larger the ratio, the smaller the fuel injection amount. 2. The air-fuel ratio control method for an internal combustion engine according to claim 1, wherein the air-fuel ratio is corrected as follows. 3. The air-fuel ratio is corrected using the ratio by correcting the valve opening amount of the control valve, and the correction is made such that the larger the ratio, the smaller the valve opening amount. 2. The air-fuel ratio control method for an internal combustion engine according to claim 1.