JPS61116042A - Method of controlling air-fuel ratio of internal-combustion engine - Google Patents

Abstract

PURPOSE:To stabilize operability, by a method wherein, when an engine is in a specified operation state in which feedback control of an air-fuel ratio is stopped, based on a second factor, being an average value of air-fuel ratio feedback factors, an air-fuel ratio, which is lower than that obtained by means of a second factor, is set. CONSTITUTION:During operation of an engine, based on outputs from a sensor 7 for an absolute pressure in a suction pipe and a crank angle position sensor 11, an EGU5 determines a basic injection time, and the result is corrected by a feedback correction factor K02, determined in response to an output from an O2 sensor 15, and a correction factor, determined in response to various parameter signals. In which case, in a specified operation state, such as idle running, in which feedback control of an air-fuel ratio is not effected, a second factor, being an average value of the correction factors K02, is multiplied by an enriched correction factor to obtain a correction factor, according to which open loop control of the air-fuel ratio is effected. This enables the air-fuel ratio to be enriched, and stabilization of operability of an engine.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an air-fuel ratio control method for an air-fuel mixture supplied to an internal combustion engine, and in particular to an air-fuel ratio control method when the engine shifts from a feedback control operation region to an open loop control operation region. Regarding the method.

(Prior art and its problems) As a fuel supply control method for an internal combustion engine, the valve opening time of the engine's fuel injection device is expressed as a reference value according to the engine speed and the absolute pressure in the intake pipe to express the operating state of the engine. Specifications 1 For example, by adding and/or multiplying variables and/or coefficients according to engine speed, intake pipe absolute pressure, engine water temperature, throttle valve opening, exhaust concentration (oxygen concentration), etc. by electronic means. The present applicant has proposed a fuel supply control method in which the fuel injection amount is determined and the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled (Japanese Patent Laid-Open No. 57-137633).

According to this fuel supply control method, under normal operating conditions of the engine, the air-fuel ratio correction coefficient is changed according to the output of the exhaust gas concentration detector disposed in the exhaust system of the engine to maintain the stoichiometric air-fuel ratio or an air-fuel ratio close to it. Feedback control (closed-loop control) of the air-fuel ratio is performed to control the valve opening time of the fuel injection device so as to obtain (low engine temperature range, low engine temperature range), the average value of the first coefficient calculated in the feedback control region is applied together with the air-fuel ratio correction coefficient unique to each region. Preventing the actual air-fuel ratio from deviating from the predetermined air-fuel ratio due to manufacturing variations in the drive control system of the fuel injection device, aging, etc., and obtaining the predetermined air-fuel ratio most suited to each specific operating condition. The system uses open-loop control to improve engine fuel efficiency and driving performance.

As an air-fuel ratio control device designed to improve fuel efficiency when air-fuel ratio feedback control is stopped, such as during idling, the system provides feedback to the stoichiometric air-fuel ratio.
The deviation value between the basic air-fuel ratio and the stoichiometric air-fuel ratio is stored in advance in a storage device, and the feedback control is stopped during low-load operation of the internal combustion engine, and the air-fuel ratio while the feedback is stopped is stored as the above-mentioned stored value. A system has been proposed that controls the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio.
Utsukai 58-9945).

By the way, it is generally known that during idling operation, engine operability is stabilized when the air-fuel ratio is slightly richer than the stoichiometric air-fuel ratio (=14.7). Therefore, in the idling state, if the air-fuel ratio is made slightly leaner than the stoichiometric air-fuel ratio based on the memorized deviation between the basic air-fuel ratio and the stoichiometric air-fuel ratio as described above, or if the air-fuel ratio during feedback control is If the air-fuel ratio is fixed to approximately the stoichiometric air-fuel ratio (=14.7) based on the average value of the correction coefficients, there is a problem that the engine speed tends to fluctuate and the drivability becomes unstable. Particularly in the case of an engine with a large displacement, there is a problem in that the idling mixture condition may not be very good, resulting in unstable drivability.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and an object of the present invention is to slightly enrich the air-fuel ratio when the feedback control of the air-fuel ratio is stopped when the engine is in an idling state, thereby stabilizing the drivability. do.

(Summary of the Invention) In order to achieve the above object, the present invention provides a first coefficient that changes according to the output of an exhaust gas concentration detector disposed in the exhaust system of the internal combustion engine during air-fuel ratio feedback control of the internal combustion engine. and calculates a second coefficient that is an average value of the first coefficient, detects a specific operating state of the engine, and stops feedback control of the air-fuel ratio when the engine is in the specific operating state. In the air-fuel ratio control method for an internal combustion engine, when in the specific operating state, an air-fuel ratio smaller than that obtained by the second coefficient is set based on the second coefficient, and the air-fuel mixture is controlled to the thus set air-fuel ratio. The present invention provides an air-fuel ratio control method for an internal combustion engine that stabilizes drivability during open-loop control in an idling operating state.

(Example of the invention) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of a fuel control device to which the method of the present invention is applied, in which a throttle valve opening sensor 4 is connected to a throttle valve 3 provided in the middle of an intake pipe 2 of an engine 1. , outputs an electric signal corresponding to the opening degree of the throttle valve 3 and supplies it to an electronic control unit (hereinafter referred to as ECU) 5.

The fuel injection valve 6 is connected to the engine 1 and the throttle valve 3 in the intake pipe 2.
and a little upstream of the intake valve (not shown) for each cylinder, and each injection valve is connected to a fuel pump (not shown) and electrically connected to the ECU 3 so that it can be injected by signals from the ECU 3. The valve opening time of fuel injection is controlled.

On the other hand, an absolute pressure sensor (PaA) 8 is provided immediately downstream of the throttle valve 3 via a pipe 7, and an electric signal representing the absolute pressure from the absolute pressure sensor 8 is supplied to the ECU 3. Further, an intake air temperature sensor 9 is installed downstream of the intake air temperature sensor 9, which detects the intake air temperature, outputs a corresponding electric signal, and supplies it to the ECUS.

A water temperature sensor 10 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine cooling water temperature, outputs a corresponding temperature signal, and supplies the signal to the ECU 3. The engine rotational angular position sensor 11 and the cylinder discrimination sensor 12 are installed around the camshaft or crankshaft (not shown) of the engine 1, and the engine rotational angular position sensor 11 detects a predetermined crankshaft every 180 degree rotation of the engine crankshaft. A pulse signal (hereinafter referred to as a TDC signal) is output at each angular position, and the cylinder discrimination sensor 12 outputs a pulse signal at a predetermined crank angle position of a specific cylinder, and each of these pulse signals is supplied to the ECU 3. .

The three-way catalyst 14 is disposed in the exhaust pipe 13 of the engine 1, and purifies components such as HC, Go, and NOx in the exhaust gas. Exhaust gas concentration detector For example, Q2 sensor is located in exhaust pipe 1
It is installed upstream of the three-way catalyst 14 of No. 3, detects the oxygen concentration in the exhaust gas, outputs a signal according to the detected value, and supplies it to the ECU 3. An atmospheric pressure sensor 16 that detects atmospheric pressure and an engine starter switch 17 are connected to the ECU 3, and a signal from the atmospheric pressure sensor 16 and a signal indicating the on/off state of the starter switch 17 are supplied.

Furthermore, a battery 18 is connected to the ECU 3 and supplied with ECU operating voltage.

The ECU 3 shapes the waveforms of some input signals from various sensors, corrects the voltage levels of other input signals to predetermined levels,
An input circuit 5a having functions such as converting analog signal values into digital signal values, a central processing circuit (hereinafter referred to as CPU) 5b, various calculation programs executed by the CPU 5b, and a storage means 5C for storing calculation results, etc. It is composed of an output circuit 5d that supplies a drive signal to the fuel injection valve 6, and the like.

E CU 5 C Determines engine operating conditions such as the air-fuel ratio feedback control region and open loop control region based on the various engine parameter signals described above.
The fuel injection time TOUT during which the injection valve 6 should be opened is calculated based on the following equation in synchronization with the TDC signal according to the determined engine operating state.

To,,T=TiXKo,XK,+Kt++ (
1) Here, the value Ti is the reference value of the injection time determined according to the engine speed and the absolute pressure in the intake pipe, and KO2 is the air-fuel ratio correction coefficient, which is determined according to the oxygen concentration in the exhaust gas during feedback control. The coefficient K obtained in accordance with FIG. 2 and obtained during feedback control according to each operating region in multiple specific operating regions where feedback control is not performed.
o, and is multiplied by enrichment correction coefficients KO and IDL during open loop control in the idling operation range, which will be described later. Values □ and 2 are correction coefficients or correction variables that are set based on parameter values representing engine cooling water temperature, throttle valve opening, and other engine operating conditions, and are used to determine starting characteristics, exhaust gas characteristics, acceleration characteristics, etc. It is set to be optimal.

ECU3 calculates the fuel injection time TOL as described above.
A drive signal for opening the fuel injection valve 6 is supplied to the fuel injection valve 6 based on the IT.

FIG. 2 is a program flowchart showing the procedure for executing the air-fuel ratio control method of the present invention, and the program includes the TD
This is executed every time a pulse of the C signal is generated.

First, it is determined whether the activation of the 0□ sensor 15 has been completed (step 30), and if the answer is negative (No), that is, the activation of the 02 sensor 15 has not been completed yet, the operating region is in an open loop. It is determined whether or not the vehicle is in an idle region (region control in FIG. 3) where control should be performed (step 31). Determination as to whether or not the engine is in an idle range (including an idle range in which feedback control to be described later is to be performed) is performed as shown in FIG. That is, it is determined whether the engine rotation speed Ns is lower than the idle rotation speed NII)L (step 310), and if the answer is affirmative (Yes), the throttle valve opening degree θTH is in the idle range. It is determined whether or not the degree θIDL (FIG. 5) is smaller (step 311). Step 311
When the answer is affirmative (Yes), it is determined that it is based on the idle operation region (region operation in FIGS. 3 and 5) (step 312).

The answer to either step 310 or 311 is negative (N
O), it is determined that the engine is outside the idle operation range (step 313).

When the answer to step 31 is affirmative (Yes), the correction coefficient KO□ is set to the correction coefficient value KO□ obtained in feedback control in the idle operation region as described later.
to the average value of,! , , enrichment correction coefficient Koz IDL
The value multiplied by (= KREF, X Ko, IDL)
(step 41), this enrichment correction coefficient K
O21DL is set to a value slightly larger than 1, for example 1.05. Therefore, this correction coefficient KO□ makes the air-fuel ratio at the time of stopping the feedback control in the idling state slightly richer than the stoichiometric air-fuel ratio (=14.7). If the answer to step 31 is negative (NO), the correction coefficient is set to 02, and as will be described later, the feedback operation area other than the idling operation area (area ■ in FIG. 3) is set.
, hereinafter referred to as the normal feedback operation range), is set to the average value KREF of the correction coefficient Ko2 obtained by feedback control (step 42).

When the answer to step 30 is affirmative (Yes).

That is, when activation of the O2 sensor is completed, it is determined whether the engine water temperature Tw is lower than a predetermined temperature Two2 (step 32), and it is determined whether the engine is being warmed up. That is, in step 32, it is determined whether the engine water temperature Tw is lower than the predetermined temperature Two□, and if the answer is affirmative (Yes), the process proceeds to step 31, and if the answer is negative (NO), the process proceeds to step 33. .

If the answer to step 32 is negative (NO), it is determined whether the fuel injection time TOuTM is longer than the predetermined fuel injection time T%IOT (step 33).

This determination is made when the engine is in the wide open throttle region (
It determines whether or not it is in the area ■) in Figure 3.
When the answer to this step 33 is affirmative (Yes), the process proceeds to step 31, and when the answer is negative (No), it is determined whether or not the engine rotation speed Ne is in the low rotation open loop control region (region ■ in FIG. 3). (Step 34). When the answer to step 34 is affirmative (Yes), that is, when the engine speed Ne is lower than the predetermined rotation speed N L Op, the process proceeds to step 31 and determines whether or not the engine is in an idling operation region where open loop control should be performed. , denial (NO)
When this happens, the process proceeds to step 36. In step 36, the engine is in a high rotation open loop region (region V in Fig. 3).
). The determination in step 36 is made depending on whether the engine speed Ne is higher than the predetermined rotation speed NHOP. When the answer to the determination is affirmative (Yes), the process proceeds to step 31, and when the answer is negative (NO), the mixture is leaner. It is determined whether the correction coefficient KLS is smaller than 1, that is, whether the engine is in the lean region (region 3, KLS 1 in FIG. 3) (step 37).

If the answer to step 37 is positive (Yes), proceed to step 31; if negative (no), it is determined whether the engine is in the operating range (region ■ in Figure 3) where fuel cut is required. (step 38). The determination in step 38 is, for example, if the engine speed Ne is less than a predetermined rotation speed Npc, whether or not the throttle valve opening θTH is substantially at the fully open position; This is done depending on whether the absolute pressure PBA is smaller than a predetermined value PnApcj that is set to a higher value as the engine speed increases.

If the answer to the determination in step 38 is affirmative (affirmative), that is, if the engine is in the operating range where the fuel should be reduced, the process proceeds to step 31, and if the answer is negative (no), 0
It is determined that the sensor is in the two-sensor feedback region (region ■ in Figure 3), and the correction coefficient K in the feedback loop is determined.
o, and its average value K REF o + K REF
1 is calculated (step 43).

That is, after the activation of the 02 sensor 15 is completed, steps 32 to 3
If none of the predetermined conditions in 8 are satisfied, it is determined that the engine is in the 02 sensor feedback operation region and feedback control is performed.

Calculation of the correction coefficient Ko2 in step 43 is performed according to the flowchart shown in FIG.

First, it is determined whether the previous control was open loop control (step 430), and the answer is negative (NO).
When this happens, it is determined whether or not the previous time was in the idling range (step 431).

If the answer to step 431 is negative (NO), it is determined whether the output level of the 02 sensor has been inverted (step 432).

If the answer to step 430 is Yes, that is, open loop control was used last time, it is determined whether or not the current operating range is in the idle range (step 433);
If the answer is affirmative (Yes), the correction coefficient KO□ is set to the above value, ... (step 434), and integral control (one-term control) is started with the coefficient value KO□ as the initial value ( Step 441 et seq.).

When the answer to the determination in step 433 is negative (NO), the correction coefficient Ko is set to a value to be described later in tFl (step 435), and integral control is started with the coefficient value KO□ as the initial value (step 411). below). Here the value KI11
EFO is the average value of the coefficient Ko obtained in the feedback region of the idle region, and 1 is the average value of the coefficient Ko□ obtained in the feedback region other than the idle region.

If the answer to step 431 is affirmative (Yes), that is, if the previous operation was in the idle range, it is determined whether the current operating range is in the idle range or not (step 436);
If the answer is yes, step 43
2, if the answer is negative (NO), the process proceeds to step 435. That is, when the operating state shifts from the idle region (region ■ in FIG. 3) to the feedback region (region ■ in FIG. 3), the value Ko of the correction coefficient for starting the 02 feedback control,
is set to the average value,E,.

When the answer to the determination in step 432 is negative (No), integral control from step 441 to be described later is performed, and when affirmative (Yes), proportional control (from step 437) is performed.
P term control). That is, it is determined whether the output level of the 0□ sensor is lower than the reference value (step 437).

When the answer is affirmative (Yes), the correction value P is added to the correction coefficient Ko2 (step 438), and when the answer is negative, the correction value P is subtracted from the correction coefficient Ko2 (step 439).
), proceed to step 440. That is.

When the output level of 02 Sesan is reversed, a correction value P corresponding to the engine rotation speed is added or subtracted from the correction coefficient value KO□ in a direction to correct this reversal.

Using the correction coefficient value KO2 obtained in this manner, a correction coefficient value KREF is calculated based on the following equation (step 440), and is stored in the memory within the ECUS.

KHp=Ko2P゛ (CRHF/A)+KRI:F'
・(A -CLEF)/A...(2) Here,
The value KO□r is the value of Ko immediately after the proportional term (P term) operates, A
is a constant, CkEF is a variable set experimentally and is set to an appropriate value from 1 to A, and the value KRf:F' is the average value of KO□ obtained up to the previous time.

Variable C*I! Since the ratio of KO□r to □, ′ during each P-term operation changes depending on the value of , the above 1. By setting an appropriate value within the range of ~A, an optimal KRoF value can be obtained.

Next, the integral control from step 441 onwards is performed as follows.

First, in step 441, it is determined whether the output level of the 02 sensor 15 is on the low level side with respect to the reference value, and if the answer is affirmative (Yes), the correction variable KO is set.
2 to add a predetermined value Δ (step 442), negative (NO
), the predetermined value Δ is subtracted from the correction coefficient KO□ (step 443), and this loop is ended. In this manner, when the output level of the 02 sensor remains at a low or high level relative to the reference value, a predetermined value Δ is added or subtracted from the correction coefficient Koz in a direction to correct this.

(Effects of the Invention) As explained above, according to the present invention, during air-fuel ratio feedback control of an internal combustion engine, the first coefficient that changes depending on the output of the exhaust gas concentration detector disposed in the exhaust system of the engine is used. an internal combustion engine that controls the air-fuel ratio using the engine, calculates a second coefficient that is an average value of the first coefficient, detects a specific operating state of the engine, and stops feedback control of the air-fuel ratio when the engine is in the specific operating state; In the air-fuel ratio control method for an engine, when the engine is in the specific operating state, an air-fuel ratio smaller than that obtained by the second coefficient is set based on the second coefficient, and the air-fuel mixture is controlled to the set air-fuel ratio. Since the air-fuel ratio is enriched when the feedback control is stopped in the specific operating state, that is, the idling operating state, it is possible to stabilize the engine drivability when the feedback control is stopped. Furthermore, it is possible to prevent the actual air-fuel ratio from deviating from a predetermined air-fuel ratio due to manufacturing variations in the various detectors that detect the engine operating state, the drive control system of the fuel injection device, etc. or aging, etc. An excellent effect is that oven loop control can be performed to obtain a predetermined air-fuel ratio that is most suitable for the air-fuel ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a fuel supply control device for implementing the air-fuel ratio control method for an internal combustion engine according to the present invention, and FIG. 2 is a flow chart showing a procedure for implementing the control method of the present invention. 3 and 5 are characteristic diagrams showing the operating range of the engine, FIG. 4 is a flowchart showing the idle determination subroutine of FIG. 2, and FIG. 6 is a flowchart showing details of step 43 in FIG. 2. DESCRIPTION OF SYMBOLS 1... Engine, 2... Intake pipe, 3... Throttle valve, 5... ECU, 6... Fuel injection valve, 4, 8~
12.16...sensor, 13...exhaust pipe, 14...
-Three-way catalyst, IS...02 sensor, 18...battery, 5b...CPU.

Claims (1)

[Claims] 1. During air-fuel ratio feedback control of an internal combustion engine, the air-fuel ratio is controlled using a first coefficient that changes according to the output of an exhaust gas concentration detector disposed in the exhaust system of the engine; An air-fuel ratio control method for an internal combustion engine, which calculates a second coefficient that is an average value of the first coefficient, detects a specific operating state of the engine, and stops feedback control of the air-fuel ratio when the specific operating state is present. is characterized in that when in the specific operating state, an air-fuel ratio smaller than that obtained by the second coefficient is set based on the second coefficient, and the air-fuel mixture is controlled to the thus set air-fuel ratio. Air-fuel ratio control method for internal combustion engines. 2. The air-fuel ratio control method for an internal combustion engine according to claim 1, wherein the specific operating state is an idling operating state of the engine. 3. The air-fuel ratio of an internal combustion engine according to claim 1, wherein an air-fuel ratio smaller than the air-fuel ratio obtained by the second coefficient is set by multiplying the second coefficient by a third coefficient. Fuel ratio control method. 4. The air-fuel ratio control method for an internal combustion engine according to claim 1, wherein the time of feedback control is the time of feedback control when the engine is in an idling operating state.