JPH02181044A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent over-rich and over-lean air fuel ratio immediately after starting an engine by calculating fuel injection quantity utilizing a no-correction value in place of the mean value of coefficients changing with the output of an exhaust gas concentration detector when the fuel injection quantity is above a prescribed level. CONSTITUTION:During operating an engine 1, ECU5 detects if an engine operating condition is in an air fuel feedback control operation range or out of the air fuel feedback control operation range, and during the operation in the feedback control operation range, the coefficients changing with the output of an O2 sensor 14 as an exhaust gas concentration detector and the mean value of the coefficients are calculated. When it is judged that the operating condition of an engine is out of the feedback control operation range, fuel injection from a fuel injection valve 6 is calculated utilizing the mean value. In this case, when fuel injection quantity is above a prescribed level, the fuel injection quantity is calculated utilizing no-correction value in place of the above mean value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air-fuel ratio control method for an internal combustion engine, and particularly to an air-fuel ratio control method immediately after starting the engine.

(Prior Art) When an internal combustion engine is operated in an air-fuel ratio feedback control operating region, an air-fuel ratio correction coefficient is calculated according to the output of an exhaust gas concentration detector provided in the exhaust system of the engine, and the air-fuel ratio correction coefficient is The average value of the coefficients is calculated as a learned value, and when the engine operating state is in a region other than the air-fuel ratio feedback control operating region (hereinafter referred to as "during oven loop control"), the learned value is used to supply the power to the engine. An air-fuel ratio control method that determines the amount of fuel to be used and controls the air-fuel ratio of the air-fuel mixture is conventionally known (for example, Japanese Patent Laid-Open No. 601343 according to the present application).

According to this conventional control force method, the basic fuel injection k[i; (basic fuel injection time) determined based on the engine speed and intake pressure is combined with other correction coefficients (e.g. Intake temperature correction coefficient set according to intake temperature,
The multiplication result is multiplied by a correction variable (such as an engine water temperature correction coefficient that is set according to the engine cooling water temperature, and a post-start fuel increase coefficient that is set for the purpose of preventing engine stalling immediately after the engine starts, etc.). The fuel injection amount (fuel injection time) is calculated by adding the correction variables (correction variables etc. set accordingly).

(Problems to be Solved by the Invention) In the conventional control method described above, the learned value is calculated in the feedback operation region where the fuel oil:1 injection amount is relatively moderate; During control, the engine water temperature correction coefficient and post-start fuel increase coefficient are set to large values in order to make the fuel injection amount much larger than during feedback control for warm-up, so the learned value is applied. If the air-fuel ratio correction coefficient deviates even slightly from the appropriate value, the amount of fuel injection #J will vary greatly. That/l'l! As a result, for example, a coefficient whose learning value changes according to the output of the device and an average value of the coefficient are calculated, and when the engine operating state is outside the feedback control operation range, the average value is used to perform fuel injection. In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio of an air-fuel mixture supplied to the engine is controlled using the fuel injection amount, when the fuel injection amount is equal to or greater than a predetermined value, Instead, the fuel injection amount is calculated using an uncorrected value.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control system to which the method of the present invention is applied. Reference numeral 1 indicates, for example, a four-cylinder, four-stroke internal combustion engine, and an intake pipe 2 is connected to the engine 1. A throttle body 3 is provided in the middle of the intake pipe 2, and a throttle valve 3' is provided inside. The throttle valve 3' is equipped with a throttle valve opening sensor (r O
(referred to as "Tll sensor") 4 are connected to the throttle valve 3.
If the valve opening deviates significantly from the appropriate valve opening value of If the deviation is smaller than this value, a problem occurs in that the air-fuel ratio becomes over-lean during cold start and the combustion state becomes unstable.

The present invention was made to solve these problems, and it appropriately controls the air-fuel ratio immediately after engine startup to prevent the air-fuel ratio from becoming over-rich or over-lean, thereby ensuring a stable combustion state. An object of the present invention is to provide a method for controlling the air-fuel ratio of an internal combustion engine.

(Means for Solving the Problems) In order to achieve the above object, the present invention detects whether the internal combustion engine is being operated in the air-fuel ratio feedback control operation region or the air-fuel ratio feedback control operation region, and During operation in the feedback control operating region, the degree of tillage gas detected in the exhaust system of the engine is converted into an electrical signal and sent to an electronic control unit (hereinafter referred to as "rECU") 5. .

On the downstream side of the throttle body 3 of the intake pipe 2 and at the intake pipe 2
A fuel injection valve 6 is provided for each cylinder slightly upstream of an intake valve (not shown), and each injection valve is connected to a fuel pump (not shown) and electrically connected to the ECU 3 to receive signals from the ECU 3. The valve opening time of fuel injection is controlled by.

Further, an intake pipe absolute pressure sensor (hereinafter referred to as 11) n is provided downstream of the throttle body 3 in the intake pipe 2 via a pipe 7.
A sensor 8 (referred to as PB sensor J) is provided, and the absolute pressure signal converted into an electrical signal by this PB sensor 8 is
It is supplied to CU3. In addition, several intake air temperature sensors (hereinafter referred to as rTA sensors) 9 are installed immediately downstream of the throttle body 3, which detect the intake air temperature TA, output a corresponding electric signal, and supply it to the ECU 3. .

The engine cooling water temperature sensor (rT) is installed on the engine 1 body.
10 (referred to as "w sensor") is provided. The Tw sensor 10 consists of a thermistor, etc., and is inserted into the circumferential wall of an engine cylinder filled with cooling water, and converts the detected water temperature signal into an EC.
Supply to U3. In addition, the engine speed sensor (hereinafter referred to as 1)
A 'Ne sensor' 11 is attached around the camshaft or crankshaft (not shown) of the engine 1.

The Ne sensor 11 is set at a predetermined crank angle position every 180'' rotation of the crankshaft of the engine, that is, at a crank angle position a predetermined crank angle before the top dead center (TDC) at the start of the intake stroke of each cylinder. signal (hereinafter referred to as rT
It outputs a "DC signal"), and this TDC
The signal is sent to ECU3.

A three-way catalyst 13 is disposed in the exhaust pipe 12 of the engine 1, and purifies components such as l-IC, Co, and NOx in the exhaust gas. Q2 sensor 1 as exhaust gas concentration detector
4 is installed on the upstream side of the three-way catalyst I3 of the exhaust gas f12, detects the oxygen concentration in the antagonistic gas, outputs a signal according to the detected value, and supplies the signal to the ECU 3.

Engine water temperature correction coefficient determined according to Tw, KAS
T is the post-start fuel stabilization coefficient, KL, which is applied immediately after the engine starts for the purpose of preventing engine stall, etc.
S is a lean coefficient of the air-fuel mixture.

Further, K1 and K2 are other correction coefficients and correction variables respectively calculated according to various engine parameter signals, and optimization of engine characteristics such as fuel consumption characteristics and engine acceleration characteristics according to engine operating conditions is achieved. is set to the required value.

The ECU 3 uses the fuel injection time Tou obtained as described above.
Based on r, a drive signal to open the fuel injection valve 6 is
The fuel is supplied to the fuel injection valve 6.

FIG. 2 is a block diagram showing the circuit configuration inside the ECU 3 shown in FIG. 1. The output signal from the Ne sensor 11 shown in FIG. W (hereinafter referred to as "CPU") 50
3 and is also supplied to the Me counter 502. The Me counter 502 is the previous T from the Ne sensor 11.
A vehicle speed sensor (hereinafter referred to as "V sensor") 15 is connected to the ECU 3 and detects the traveling speed V of the vehicle during the time period from when the DC signal pulse is input to when the current TDC signal pulse is input. The signal from is ECU3
is supplied to

The ECU 3 determines various engine operating states such as an air-fuel ratio feedback control operating region and an oven loop control operating region based on the various engine parameter signals described above, and also adjusts the TDC according to the determined engine operating state.
The fuel injection time T OUT during which the fuel injection valve 6 should be opened in synchronization with the signal is calculated based on the following equation (1).

Tour=TiXKo2XKr^XKTwXKASrX
K1. sXK+102-(1) Here, TI indicates the basic fuel injection time of the fuel injection valve 6, and this basic injection time is:
For example, they are determined depending on the intake pipe absolute pressure PR8 and the engine rotation speed Ne. KO2 is an 02 feedback correction coefficient (air-fuel ratio correction coefficient) calculated from a calculation program flowchart (FIG. 3) according to the present invention, which will be described later. KT^ is an intake air temperature correction coefficient determined according to the intake air temperature TA, KTILI measures the engine coolant temperature interval, and its count value Me is proportional to the reciprocal of the engine speed Ne. The Me counter 502 uses this N1 value Me.
is supplied to the CPU 503 via the data bus 51O.

The output J signals from each sensor such as OTo sensor 4, PB^ sensor 8, T^ sensor 9, Tw sensor 10, 02 sensor 14, V sensor 15, etc. in Fig. 1 are sent to the level correction circuit 5.
After being corrected to a predetermined voltage level at step 04, the voltage is sequentially supplied to an A/1) converter 506 by a multiplexer 505.

The A/D converter 506 sequentially converts the analog output voltage from each sensor mentioned above into a digital signal and sends it to the data bus 5.
10 to the CPU 303.

The CPU 303 is further connected to a read-only memory (hereinafter referred to as rROMJ) 507, a random access memory (hereinafter referred to as rRAMJ) 508, and a drive circuit 509 via a data bus 510.
The calculation result in U303 is temporarily stored and ROU
507 is a control program executed by the CPU 303;
It stores a basic injection time Tj map, a correction coefficient map, etc. of the fuel injection valve 6 to be read based on the intake pipe absolute pressure PBA and the engine speed Ne.

The CPU 303 calculates the fuel injection time TOUT of the fuel injection valve 6 according to the various engine parameter signals mentioned above according to the control program stored in the ROM2O3.
The calculated value is supplied to the drive circuit 509 via the data bus 510. The drive circuit 509 supplies the fuel injection valve 6 with a control signal to open the fuel injection valve 6 according to the calculated value.

FIG. 3 is a program flowchart showing the procedure for executing the control method of the present invention, and the program is executed every time the TDC signal pulse occurs.

First, it is determined whether the activation of the 02 sensor 14 is completed or not (step 301), and the answer is affirmative (Yes).
If so, it is determined whether a predetermined time tx seconds (for example, 60 seconds) has elapsed during which the activation of the Q2 sensor 14 has been completed (
Step 302). If either of the answers to steps 301 and 302 is negative (No), that is, the activation of the 02 sensor 14 is not yet completed and the activation is in the idle region, the correction coefficient KO2 is set to the average value Kg of the correction coefficient KO2, which will be described later.
spo to perform oven loop control (step 307).

On the other hand, when the answer to step 306 is negative (No), the correction coefficient KO2 is set to the average value Kl! of the correction coefficient KO2, which will be described later. Set to EFI and perform oven loop control (
Step 308).

As mentioned above, if the answer to step 303 is affirmative (Yes),
That is, when the previous value of TOUT is a relatively thick value, such as larger than the predetermined injection time Tourhc, the 02 feedback correction coefficient KO2 is set to 1.0 to reduce the fluctuation of the fuel injection time TOUT and, therefore, the air-fuel ratio. This prevents fluctuations from becoming large. This is TouT>To
When urhc is established, the various correction coefficients mentioned above, especially the coefficient KTIL1. KAST is on the fuel increase side (value 1.0
(above)), the above formula (1) % formula %) becomes large, and the learned value KREF ( KREFO or KR
EFI) or the predetermined activation time tx seconds has not elapsed, the 02 feedback control cannot be performed, so the steps 303 to 308 below are performed.
Oven loop control is performed at

First, in step 303, the fuel injection time TOUT (hereinafter r
The previous value of TOUT) is the predetermined injection time
It is determined whether or not it is larger than rMc (for example, Om5ec), and if the answer is affirmative (Yes), the oven loop control is performed by setting the 02 feedback correction coefficient KO2 to the value 1.0 (uncorrected value) (step 305).

If the answer to step 303 is negative (NO), it is determined whether or not the engine is in the fully open throttle range (WOT range). If this answer is affirmative (Yes), that is, the engine is WO
When it is in the T area, step 305 of OjJ is executed.

If the answer to step 304 is negative (NO), the engine is in oven loop control 3! I! It is determined whether or not it is in the idle area of the transfer areas (step 306).
. If the answer is 1 (yes), that is, the engine uses it to calculate the fuel injection time TOUT (steps 307, 3
08) and the learned value KREp will greatly fluctuate the fuel injection time TOUT, making the combustion state unstable especially at low temperature startup.

Note that the predetermined injection time TouTr+c is the predetermined injection time
It is determined by taking into consideration the flow rate variations, etc.

When the answers to step 301 and step 302 are both affirmative (Yes), that is, when the predetermined time Lx seconds has elapsed for the activation function of sensor 02, the traveling speed of the vehicle detected by sensor 15 and the TA sensor A predetermined value TWO2 is read out from the map according to the intake air temperature T^ detected in step 9 (step 309). The map has a predetermined value TWO?
! However, as the intake air temperature T^ and the running speed V increase,
The predetermined value TWO2 is set to be small. Next, in step 310, it is determined whether the engine cooling water temperature Tw is lower than the predetermined value lower wo2 read out in step 309. If this answer is affirmative (Yes), that is, the engine coolant temperature Tw is still lower than the predetermined value Two2, the 02 feedback control is not performed and the oven loop control to increase the fuel consumption by 1 for warming up is performed from step 303 onward.

If the answer to step 310 is negative (No), it is determined in steps 311 to 315 which operating range the engine is in. That is, whether or not the engine rotation speed Ne is lower than the predetermined rotation speed NLOP (for example, 600 rpm), that is, whether the engine is in the low rotation oven loop control operation region (step 311), the step 3
Similarly to 04, whether or not the engine is in the WOT region (step 312), the engine speed Ne is the predetermined speed Nl.
whether the engine speed is higher than 10P (for example, 3500 rpm), that is, whether the engine is in the high-speed oven loop control operating region (step 313); whether the lean coefficient KLS of the air-fuel mixture is smaller than the value 1.0; That is, whether the engine is in a lean region determined by the engine load being below a predetermined value (step 314), and whether the engine is in an operating region where fuel cut is required (step 314). 3I5).

The answers to steps 311 to 315 are all negative KO.
2 (this calculation is based on the applicant's Japanese Patent Application Laid-Open No. 1989-1996:
2-157252, so detailed explanation will be omitted), the calculated correction coefficient KO2
02 feedback control is performed by calculating the fuel injection time TOUT according to the above equation (1) based on the equation (1), and injecting fuel from the respective fuel injection valves 6. Furthermore, step 3
17, when the engine is in the idle region of the 02 feedback control region, the average value KREFO of the correction coefficient KO2 is calculated, and when the engine is in the region other than the idle region of the 02 feedback control region, the average value of the correction coefficient KO2 is calculated. Calculate KREFI.

Details of this calculation will be described later based on FIG. 4.

If any of the answers to Steps 311 to 3]5 is affirmative (
Yes), that is, when the engine is in the oven loop control region, the process advances to step 318, and each time this program is executed, the engine operating state that passes through step 318 continues for a predetermined period of To seconds (for example, 0.5 seconds). Determine whether or not. When this answer is affirmative (Yes), that is, the engine is under oven loop control (No), that is, the engine is not in either the WOT region or the operating region where fuel cut is required, and NLOP≦Ne≦Nll0P and KLS≧1 hold. , the engine is assumed to be in an operating range where 02 feedback control should be performed, and the process proceeds to step 316. In step 316, the starting double fuel increase coefficient KAS
T is set to a value of 1.0, the engine water temperature correction coefficient KTW is calculated according to the following formula (2), and KTIII is set to the calculated value.

Krw=Crwo2(KTILIO-1) +1- (
2) Here, CTWO2 is a constant determined according to the engine cooling water temperature W, and KTWO is a map value of the engine water temperature correction coefficient read from the map according to the engine cooling water temperature Tw.

Next, in step 317, the average value KREFO is set as the initial value when the engine is in the feedback control operating region and the idle region, and the average value KREFI is set as the initial value when the engine is in the feedback control operating region other than the idle region. When the state continues for a predetermined time To seconds after shifting to the correction coefficient region by the P-term and 1-term addition processing according to the output value, oven loop control is performed from step 303 onwards. However, if the answer to step 318 is negative (No), that is, after the engine is shifted to the oven loop control region, the process proceeds to step 319 for a predetermined period of time LD seconds.

In step 319, it is determined whether or not 02 feedback control was performed when this program was executed when the TDC signal pulse was generated last time. This answer is affirmative (Yes
), that is, when the engine shifts from the feedback control region to the oven loop control region for the first time, step 320, which is the same as step 316, is executed and the process proceeds to the next step 321, and the answer to step 319 is negative (No). When , the step 320 has been executed, so the process skips the step 320 and proceeds to the step 321. In step 321, the correction coefficient KO2
Oven loop control is performed while maintaining the value of the correction coefficient KO2 at the time of the previous execution of this program.

Average value K of the correction coefficient KO2 in step 317
Calculation of REFO and KREFI is performed according to flowchart 1. shown in FIG.

First, the operating state of the engine is determined at snaps 401 to 405. That is, whether or not the engine cooling water temperature Tw is smaller than a predetermined value greater than the predetermined value Two2 read out in step 309,'wgap (for example, 60 degrees Celsius) (step 401), the air conditioner mounted on the vehicle is activated. (step 402), intake air temperature TA
is greater than the predetermined temperature T8g[:T (for example, 70°C) (step 405), and the engine coolant temperature Tw
It is determined whether or not TILIAICI is higher than a predetermined high temperature TILIAICI (for example, 90° C.) (step 404).

Steps 401 and 404 are for performing more accurate air-fuel ratio control by narrowing the learning range of the engine coolant temperature Tw for calculating the average values KREFO and KREFI. In step 402, the average value KREFO and Kl! of the correction coefficient KO2 is determined because the engine load fluctuates rapidly when the air conditioner is in operation, making it unsuitable for learning the correction coefficient KO2. Forbidden engine to calculate EFI, 0
When the engine is in the idle region of the 02 feedback control region, when the engine is in the idle region of the 02 feedback control region, CI! E
F is a variable experimentally set for each area, and is 1 to 655.
KO2P is the value of the correction coefficient KO2 immediately before or after proportional term (P term) operation. , KREFO' and KRεF+'
is the average value of the correction coefficient KO2 obtained up to the previous time in each corresponding operating region.

As can be seen from (3) and (4) above, the average value KRE
FO and Kl! Calculation of EFI is based on learning degree (learning speed)
This corresponds to learning the correction coefficient Ko2r according to CREF/65536.

However, the answer to step 405 is affirmative (Yes), that is, the engine load remains at the predetermined absolute pressure pHKREF. In step 403, when the intake air temperature TA is high, the intake air density decreases and the mixture becomes rich, making it unsuitable for learning the correction coefficient KO2.
This is to prohibit the calculation of FI.

If any of the answers in steps 401 to 404 is 19 constant (Yes), the o2 feedback correction coefficient K
Average value of O2 KREFO or Kl! Calculate EFI (
Since the operating state of the engine is not suitable for learning the correction coefficient KO2, the program is terminated without performing the calculation.

On the other hand, if all of the answers to steps 401 to 404 are negative (NO), the process proceeds to step 405, and it is determined whether the intake pipe absolute pressure PB^ representing the engine load is smaller than a predetermined absolute pressure P++KRpp (for example, 177 mm 1 g). Determine. If the answer is negative (NO), the average value Kl of the correction coefficient KO2 is calculated according to the following equations (3) and (4), respectively. Calculate EFO and KREFI (Step 4
06).

=20= When it is small (PB^<PBKREF), the step 406 is skipped and the average value K l of the correction coefficient KO2 is
! EFO and KREFI are not calculated, and learning of the correction coefficient KO2 when engine combustion is unstable is prohibited.

(Effects of the Invention) As described in detail above, the present invention detects whether the internal combustion engine is being operated in the air-fuel ratio feedback control operation region or the air-fuel ratio feedback control operation region, and During operation, a coefficient that changes according to the output of an exhaust gas concentration detector disposed in the exhaust system of the engine and an average value of the coefficient are calculated, and the engine operating state is outside the feedback control operating range. In the air-fuel ratio control method for an internal combustion engine, the fuel injection amount is calculated using the average value, and the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled using the fuel injection amount, when the fuel injection amount is a predetermined value. "Value of value"
In case 2, since the fuel injection amount is calculated using the uncorrected value instead of the average value, it is possible to prevent the air-fuel ratio from becoming over-rich or over-lean at 4 degrees immediately after starting the engine, and to stabilize the fuel injection amount. This has the effect of ensuring a good combustion state.

[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, FIG. 2 is a block diagram of the electronic control unit of FIG. 1, and FIG. Flowchart 1 shows the procedure for implementing the control method of the present invention, and FIG. 4 shows step 3 in FIG.
17 is a flowchart showing a subroutine for calculating the average value KREF of KO2 in Step 17. 1. Internal combustion engine, 5. Electronic control unit (E
CU), 6...Fuel injection valve, 8...Intake pipe absolute pressure (
PB^) Sensor, 1]...Engine speed (Ne) sensor, 12...Exhaust pipe, 14...02 sensor (exhaust gas concentration detector), KO2/02 feedback correction coefficient (
coefficient), Kl! Average value of EFO and KgEpt-Ko2, TOUT/fuel injection time (fuel injection time), T
own+c...Predetermined injection time (predetermined value).

Claims (1)

[Claims] 1. Detects whether the internal combustion engine is operating in an air-fuel ratio feedback control operating region or a region other than the air-fuel ratio feedback control operating region, and is disposed in the exhaust system of the engine when operating in the feedback control operating region. A coefficient that changes according to the output of the exhaust gas concentration detector and an average value of the coefficient are calculated, and when the engine operating state is in a region outside the feedback control operation region, the fuel injection amount is calculated using the average value. In an air-fuel ratio control method for an internal combustion engine, the air-fuel ratio of an air-fuel mixture supplied to the engine is controlled using the fuel injection amount,
An air-fuel ratio control method for an internal combustion engine, characterized in that when the fuel injection amount is equal to or greater than a predetermined value, the fuel injection amount is calculated using an uncorrected value instead of the average value.