JPH0252105B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to an intake air amount correction method for an electronically controlled engine, and in particular, an exhaust gas correction method suitable for use in an automobile engine in which exhaust gas purification measures are taken using a three-way catalyst. The air-fuel ratio of the air-fuel mixture is feedback-controlled according to the deviation between the actual air-fuel ratio determined from the secondary air-fuel ratio and the target air-fuel ratio. An air-fuel ratio feedback correction coefficient for correcting the air-fuel ratio of the air-fuel mixture according to the deviation from the fuel ratio, a high-altitude correction coefficient for correcting the intake air amount to atmospheric pressure, and a detection error for correcting intake air amount detection errors. This invention relates to an improvement in an intake air amount correction method for an electronically controlled engine in which error correction coefficients and the like are learned and corrected.

[Conventional technology]

One of the methods for supplying an air-fuel mixture at a predetermined air-fuel ratio to the combustion chamber of an internal combustion engine (referred to as an engine) is to use a so-called electronically controlled fuel injection device.
In this method, an injector for injecting fuel into the engine is installed in the intake manifold or throttle body of the engine, for example, in several or one engine cylinder, and the valve opening time of the injector is controlled according to the operating state of the engine. By doing so, an air-fuel mixture with a predetermined air-fuel ratio is supplied to the engine combustion chamber. There are various types of such electronically controlled fuel injection devices, but in recent years, particularly, digital electronically controlled fuel injection devices in which the electronic control circuit has been digitized have been developed. In such an electronically controlled fuel injection device, normally,
The basic fuel injection amount is calculated according to the engine rotation speed detected from the engine intake air amount detected using an air flow meter etc. and the engine rotation signal input from a distributor etc. In order to improve startability or responsiveness immediately after acceleration, synchronous injection that always injects at the same crank position in synchronization with the engine rotation by making corrections based on signals input from the installed sensor according to the engine status, etc. Apart from normal synchronous injection, asynchronous injection is performed in which a predetermined amount of injection is performed only immediately after a signal from a sensor is received in accordance with the driving condition. The synchronous injection time during which the injector is open corresponding to the synchronous injection is, for example, the basic injection time calculated using the intake air amount from the air flow meter and the rotation signal from the distributor, and the signal from each sensor. Therefore, the injection time is multiplied by a correction coefficient to correct the injection time according to the engine condition at that time, such as when cold or accelerating, and the invalid injection time is added to correct for the injector operation delay due to voltage fluctuation. It has been decided accordingly. For example, in order to improve engine startability, the basic injection time is corrected at the time of engine startup by setting it to a predetermined time regardless of the intake air amount and engine speed when starting the engine. In order to stabilize the engine rotation, the amount is increased for a certain period of time after the engine starts, and the amount is compensated for after the engine starts.Furthermore, when the intake air temperature is low, the air density increases and the amount of air increases. In order to prevent deviations in the air-fuel ratio, the intake air temperature is corrected by increasing the amount when the intake air temperature is low, and
In order to ensure drivability when cold, the amount of cooling water is increased when the temperature is low to compensate for the warm-up increase.Furthermore, to prevent sluggishness immediately after acceleration and improve acceleration performance, the amount of cooling water is increased at a constant level immediately after acceleration. The time is corrected by increasing the amount of acceleration during warm-up by increasing the amount, and in order to increase the engine output at high loads, by increasing the amount at high loads when the throttle valve opening is, for example, 60 degrees or more. In order to bring the air-fuel ratio of the air-fuel mixture to a predetermined air-fuel ratio, for example, near the stoichiometric air-fuel ratio, the air-fuel ratio feedback correction is performed by changing the increase ratio according to the oxygen concentration in the exhaust gas. has been done. Additionally, in order to prevent overheating of the catalytic converter and reduce fuel consumption, or to forcefully suppress the vehicle speed, fuel injection is stopped and fuel is cut when the engine brakes or when the vehicle speed exceeds the specified maximum speed. is being used. Such an electronically controlled fuel injection device, particularly a digital electronically controlled fuel injection device, is characterized in that it is possible to control the fuel injection amount extremely precisely. In an electronically controlled engine equipped with such an electronically controlled fuel injection device, the intake air amount detected by an air flow meter etc. includes the fuel injection amount, ignition timing output increase, increase/decrease during acceleration/deceleration, and exhaust gas recirculation amount. It is used to control such things and has become an important parameter. However, the air density changes depending on the altitude at which the vehicle travels, and the output characteristics of intake air amount detection means such as an air flow meter, for example,
Accurate fuel injection is achieved because the flow rate of intake air leaking from around the measuring plate, which oscillates in relation to the intake air flow, changes as dirt accumulates on the intake wall of the air flow meter. In order to calculate the intake air amount, ignition timing, etc., it is necessary to correct the output of the air flow meter and calculate the intake air amount. Therefore, in an electronically controlled engine that performs feedback control of the air-fuel ratio of the air-fuel mixture according to the deviation between the actual air-fuel ratio determined from the secondary air-fuel ratio of exhaust gas and the target air-fuel ratio, the actual air-fuel ratio during feedback control is In addition to learning and correcting the air-fuel ratio feedback correction coefficient for correcting the air-fuel ratio of the air-fuel mixture according to the deviation between the air-fuel ratio (matching the target air-fuel ratio) and the preset basic air-fuel ratio of the air-fuel mixture, It has been proposed to learn and correct a high altitude correction coefficient for correcting the intake air amount to atmospheric pressure, an air flow meter correction coefficient for correcting a detection error of the intake air amount in an air flow meter, and the like. For example, in Japanese Patent Publication No. 62-12380, the altitude correction value and the correction value of the output of the air flow meter are stored in a non-volatile storage element, and these correction values themselves are corrected according to the engine operating condition, and when the engine is stopped, A technique has also been proposed in which this correction value is retained and used even after the next engine start. By doing this, the problem that occurs when the determination of the correction value is corrected only by feedback correction, i.e., when the engine operation is temporarily stopped and then restarted, the air-fuel ratio sensor (O ₂ sensor ) takes a certain amount of time to properly heat up and generate effective output, and the correction amount of the air flow meter is a non-linear characteristic that changes depending on the amount of intake air, so it depends on the amount detected by the air flow meter during transient operation. It is possible to solve the problem that the error increases when a large value is corrected. By adopting such learning correction,
This improves the accuracy of correcting the intake air amount, etc., and improves the control accuracy of the air-fuel ratio, etc.

[Problem to be achieved by the invention]

However, if such an erroneous correction occurs in the learning correction of the correction coefficient, there is a risk that the engine stalls or cannot be started. For this reason, as disclosed in JP-A-55-134731, it is possible to limit the amount of correction by providing upper and lower limits for each correction coefficient. However, it is not possible to narrow the limit on this amount of correction. This also narrows the correction range in which learning correction can be performed. That is, the upper and lower limit guards for each correction coefficient cannot be made narrower than necessary. Furthermore, for example, in an electronically controlled engine that also uses an O ₂ sensor that measures the oxygen concentration in exhaust gas to determine the aforementioned actual air-fuel ratio, if the wiring for this O ₂ sensor becomes disconnected, the aforementioned The air-fuel ratio feedback correction coefficient, high altitude correction coefficient, and air flow meter correction coefficient all become maximum correction values in the negative direction. Even if a correction guard of ±20% is provided for each of these correction coefficients, the correction amount at this time will be -20% x 3 = -60%, leading to the problem of engine stall. be. The present invention was made to solve the above-mentioned conventional drawbacks, and for correction coefficients to be corrected by learning,
It is an object of the present invention to provide a method for correcting the intake air amount of an electronically controlled engine in which an appropriate guard is provided and, therefore, an engine stall or inability to start due to incorrect correction does not occur.

[Means for Accomplishing the Object] The present invention provides feedback control of the air-fuel ratio of an air-fuel mixture according to the deviation between an actual air-fuel ratio determined from a secondary air-fuel ratio of exhaust gas and a target air-fuel ratio. The air-fuel ratio feedback correction coefficient is used to correct the air-fuel ratio of the air-fuel mixture according to the deviation between the actual air-fuel ratio at the time and the preset basic air-fuel ratio of the air-fuel mixture. In an intake air amount correction method for an electronically controlled engine that learns and corrects a correction coefficient, a detection error correction coefficient for correcting a detection error of intake air amount, etc., the air-fuel ratio feedback correction coefficient, high altitude correction coefficient, intake air The above object is achieved by providing a guard for a value that is a combination of at least two of the correction coefficients to be learned and corrected, such as the quantity correction coefficients. Further, the guard is provided for a value that is a combination of the air-fuel ratio feedback correction coefficient and the high altitude correction coefficient.

[Effect]

In the present invention, when there is a large deviation in the basic air-fuel ratio in air-fuel ratio learning control, if learning is performed sufficiently, the correction value due to learning will be large and the feedback correction value will be small; on the other hand, if learning is not performed sufficiently , the correction value due to learning is small,
This was done by focusing on the fact that the feedback correction value becomes large. Furthermore, even when the correction value due to learning becomes large in this way, excessive erroneous correction can be prevented by providing a guard for the value that is a combination of at least two or more correction values as described above. This prevents engine stalling and inability to start. The reason why a guard is provided for a value that is a combination of a plurality of correction values in this way is that, as described above, there is a limit to narrowing the width of the guard for each correction value.
On the other hand, if we focus on the relationship between some correction values,
Generally, when one correction value becomes large, the other correction value becomes small, and when one correction value becomes small, the other correction value becomes large. That is, in general, when one correction value becomes large, the other must become small, so it is effective to prevent incorrect correction by placing a guard between a plurality of correction values having such mutually contradictory characteristics. .

Embodiments Examples of the present invention will be described in detail below with reference to the drawings. An embodiment of an electronically controlled engine in which the intake air amount correction method according to the present invention is adopted is, as shown in FIGS. An air flow meter 16 for detecting the intake air amount of the engine, and an intake temperature sensor 1 disposed within the air flow meter 16 for detecting the intake air temperature.
8, a crank angle sensor 22 that is built into the distributor 20 and has a shaft 20a that rotates in accordance with the engine rotation and generates a pulse signal in accordance with the engine rotation, and an engine cooling water temperature sensor that is disposed in the engine block 24. a cooling water temperature sensor 26 for detecting the temperature, and an intake throttle valve 2 disposed in the intake passage 12 that opens and closes in conjunction with the accelerator pedal.
A throttle position sensor 30 for detecting the opening degree and the rate of change in the opening degree of 8 and the exhaust gas formed by combustion of the air-fuel mixture flow in for detecting the secondary air-fuel ratio of the exhaust gas. Exhaust manifold 3
The oxygen concentration sensor 36 detects the residual oxygen concentration in the catalyst inflow gas flowing into the catalytic converter 34 filled with a catalyst, for example, a three-way catalyst, and controls the air-fuel ratio of the air-fuel mixture. In order to
An injector 44 that injects fuel into the intake manifold 42 of the engine 10, and a pulse generator disposed in a surge tank 46 in the middle of the intake passage 12, for controlling the flow rate of air that bypasses the intake throttle valve 28 during idle. The basic fuel injection time is calculated according to the idle rotation speed control valve 48 consisting of a motor, an electromagnetic valve, etc., the intake air amount of the engine, and the engine rotation speed, and for the calculated basic fuel injection time, Air-fuel ratio feedback correction is performed according to the deviation between the actual air-fuel ratio determined from the secondary air-fuel ratio of exhaust gas and the target air-fuel ratio, and the actual air-fuel ratio during feedback control, that is, the target air-fuel ratio, and the preset air-fuel mixture are An air-fuel ratio feedback correction coefficient for correcting the air-fuel ratio of the air-fuel mixture according to the deviation from the basic air-fuel ratio of Learning and correcting the air flow meter correction coefficient etc. to correct the
Upper and lower limit guards are provided for each of the correction coefficients to be learned and corrected, such as the air-fuel ratio feedback correction coefficient, high altitude correction coefficient, and air flow meter correction coefficient,
It also includes a digital electronic control circuit 50 that provides upper and lower limit guards for the combined value of the air-fuel ratio feedback correction coefficient and the high altitude correction coefficient, and outputs a fuel injection signal to the injector 44. In FIG. 1, 52 is a spark plug, and in FIG. 2, 54 is a battery. As shown in detail in FIG. 2, the digital electronic control circuit 50 converts analog signals output from the air flow meter 16, intake temperature sensor 18, cooling water temperature sensor 26, oxygen concentration sensor 36, and battery 54 into digital signals. an analog-to-digital converter 60 having a multiplexer function for
An input having a buffer function that inputs the digital signals of the outputs of the crank angle sensor 22 and the throttle position sensor 30, and outputs the calculation results at a timing suitable for outputting the calculation results to the injector 44 and the idle rotation speed control valve 48. An output interface circuit 62, a central processing circuit 64 including a crystal oscillator 64a, a read-only memory 66, a random access memory 68, and a random access memory 70 for power backup.
It is composed of. The operation will be explained below. First, the digital electronic control circuit 50 calculates the basic fuel injection time using the following equation based on the intake air amount Q of the air flow meter 16 output and the engine rotation speed N calculated from the crank angle sensor 22 output. Calculate T _P. T _P =K・Q/N...(1) Here, K is a coefficient. Furthermore, by correcting the basic injection time T _P using the following formula according to the signals from each sensor,
Calculate the effective synchronous injection time τ ₁ . τ ₁ =T _P・f(A/F)・f(WL)・f(THA)×{1
+f(ASE)+f(AEW) +f(OTP)}×(1-f(RS)}...(2) Here, f(A/F) is the air-fuel ratio feedback correction coefficient, and f(WL) is the warm-up Increase correction coefficient, f
(THA) is the intake air temperature correction coefficient, f (ASE) is the increase correction coefficient after starting, f (AEW) is the acceleration increase correction coefficient during warm-up, f (OTP) is the overheat (output) increase coefficient, and f (RS) is the It is the weight loss coefficient. Effective synchronous injection time τ ₁ obtained in this way
As shown in the following equation, the synchronous injection time τ _s is calculated by adding the invalid injection time τ _v corresponding to the response delay time of the injector 44 when the battery voltage decreases. τ _s = τ ₁ + τ _v ...(3) A fuel injection signal corresponding to this synchronous injection time τ _s is output to the injector 44, and the injector 44 is opened for the synchronous injection time τ _s in synchronization with the engine rotation. , fuel is injected into the intake manifold 42 of the engine. In this embodiment, learning correction data for learning and correcting each correction coefficient is calculated as shown in FIG. That is, first, in step 101, the average value Q of the intake air amount per two cycles of air-fuel ratio feedback control is calculated from the detection signal of the air flow meter 16. Next, in step 102, the deviation D of the average feedback air-fuel ratio from the target air-fuel ratio in the same two cycles as the two cycles in step 101 is calculated. The unit of this deviation D is, for example, %, and the deviation D on the lean side with respect to the target air-fuel ratio is positive, and the deviation D on the rich side with respect to the target air-fuel ratio is negative. Further, in step 103, it is determined whether or not the throttle valve 28 is fully closed according to the output of the throttle position sensor 30. If the throttle valve 28 is fully closed, the process advances to step 104. On the other hand, if the throttle valve 28 is open, the process proceeds to step 105.
In step 104, the average value of the intake air amount is set in the first region Q1 to Q2 (Q1<Q2) corresponding to the idle state.
If it is within the first area, the process proceeds to step 106, while if it is not within the first area, the program is terminated. In step 106, as shown in the following equation, 1/2 of the sum of the learning correction data MA in the first storage section M1 provided for the first area and the deviation D is set as new data MA. . MA+D/2→MA (4) This data MA is cleared when the engine operation is stopped or when step 214 (FIG. 4), which will be described later, is executed. The reason why the deviation D is not used as the new data MA, but MA+D/2 is used as the new data MA is to prevent the data MA from becoming a completely unrelated value due to unforeseen causes.
This is to increase the reliability of data MA. In step 107, the value C1 of the first counter provided for the first area is incremented by one. The value C1 of this first counter is changed when the engine operation is stopped or at step 214 (see Fig. 4), which will be described later.
Cleared when executed. Next, step
In step 108, it is determined whether the first counter value C1 is 3 or more, and if C1 is 3 or more, the step
Proceed to step 109, and if C1 is less than 3, terminate the program. In step 109, the usage permission flag FA for the data in the first area is changed from 0 to 1. here,
When the flag FA is 1, learning is progressing,
This means that the data MA has become sufficiently reliable. On the other hand, in step 105, the average value Q of the intake air amount falls into a second region corresponding to low engine load.
It is determined whether it is within Q3 to Q4 (Q2<Q3<Q4), and if it is within the second region, the process proceeds to step 110, whereas if it is not within the second region, the process proceeds to step 111. move on. Steps 110, 112, 113, 114 are
This corresponds to steps 106, 107, 108, and 109 described above. That is, in step 110, as shown in the following equation,
A second storage section provided for the second area
1/2 of the sum of the learning correction data MB of M2 and the deviation D is set as new data MB. MB+D/2→MB (5) This data MB is cleared when the engine operation is stopped or when step 214 (FIG. 4), which will be described later, is executed. Next, in step 112, the value C2 of the second counter provided for the second area is incremented by one. The value C2 of this second counter is when the engine operation is stopped.
Alternatively, it is cleared when step 214 (FIG. 4), which will be described later, is executed. Further, in step 113, it is determined whether or not the value C2 of the second counter is 3 or more, and if C2 is 3 or more, the process proceeds to step 114,
If C2 is less than 3, terminate this program.
In step 114, the use permission flag FB for the data in the second area is changed from 0 to 1. Further, in step 111, the average value of the intake air amount falls into a third region corresponding to high engine load.
It is determined whether it is within Q5-Q6 (Q4<Q5<Q6), and if it is within the third region, it proceeds to step 115, while if it is not within the third region, this program is executed. finish. Steps 115, 116, 117,
118 corresponds to the aforementioned steps 106, 107, 108, and 109, respectively. That is, in step 115,
As shown in the following equation, learning correction data MC of the third storage section M3 provided for the third area,
Let 1/2 of the sum with the deviation D be the new data MC. MC+D/2→MC (6) This data MC is cleared when the engine operation is stopped or when step 214 (FIG. 4), which will be described later, is executed. Next, in step 116, the value C3 of the third counter provided for the third area is incremented by one. The value C3 of this third counter is when the engine operation is stopped.
Alternatively, it is cleared when step 214 (FIG. 4), which will be described later, is executed. Further, in step 117, it is determined whether the value C3 of the third counter is 3 or more, and if C3 is 3 or more, the process proceeds to step 118.
If C3 is less than 3, terminate this program.
In step 118, the use permission flag FC for the data in the third area is changed from 0 to 1. Next, based on the data MA, MB, and MC of the first to third storage units M1, M2, and M3 calculated according to the flowchart shown in Fig. 3, the altitude correction value is calculated.
A method of calculating FHAC and air flow meter correction value FAFM will be explained with reference to FIG. First, in step 201, flags FA and FB are both set to 1.
The flags FA and FB are both 1.
If so, proceed to step 202, and if at least one of flags FA and FB is 0, proceed to step 202.
Proceed to 203. In step 202, data MA, MB
are both 2% or more, that is, the basic air-fuel ratio is 2% toward the lean side with respect to the target stoichiometric air-fuel ratio.
It is determined whether the deviation is more than 2%, and if the deviation is 2% or more, the process proceeds to step 204, and if the deviation is less than 2%, the process proceeds to step 205. In step 204, as shown in the following formula, data MA is added to the current altitude correction value FHAC to obtain a new altitude correction value FHAC,
Proceed to step 206. FHAC+MA→FHAC...(7) In step 203, it is determined whether flags FB and FC are both 1. If flags FB and FC are both 1, the process advances to step 207, and at least one of flags FB and FC is determined. If either one is 0, this program ends. In step 207, the deviation data
Whether MB and MC are both 2% or more, that is,
It is determined whether the basic air-fuel ratio deviates from the stoichiometric air-fuel ratio by 2% or more towards the lean side. If the deviation is 2% or more, the process proceeds to step 208; if the deviation is less than 2%, the process proceeds to step 208. Proceed to 205. step 208
Then, as shown in the following formula, the current altitude correction value
Add data MC to FHAC to create new altitude correction value
As FHAC, proceed to step 206. FHAC+MC→FHAC (8) When the vehicle moves from a highland to a plain area, the actual air-fuel ratio deviates toward the lean side by more than a predetermined value in any of the first, second, and third regions. However, in some cases the engine is not operated in the third region, but only in the first and second regions, i.e. when the vehicle moves from a highland to a plain without driving under high load, or if the engine is not operated in the first region. is not operated in the area of
It is expected that the vehicle will be driven only in the third region and the third region, that is, the vehicle will descend from the highlands to the plains without stopping on the way. Therefore, step 202,
As in step 207, either the deviation data MA and MB are both 2% or more, or the deviation data MB,
If both MCs are 2% or more, it is determined that the altitude has fallen and the altitude correction value FHAC is updated. The reason why the data MB is not used to update the altitude correction value FHAC in steps 204 and 208 and the data MA or MC is used is because the data MA or MC is less affected by the release of fuel evaporative gas than the data MB. This is because the impact of Furthermore, in step 205, flags FA, FB, FC are set.
Determine whether or not both are 1, and set the flag FA,
If FB and FC are both 1, step
Proceeding to 209, if at least one of the flags FA, FB, and FC is 0, this program is terminated. In step 209, data MA, MB,
Whether all MCs are -3% or less, that is,
Determine whether or not there is a deviation of 3% or more to the excessive side with respect to the stoichiometric air-fuel ratio. If the deviation is 3% or more, proceed to step 210; if the deviation is less than 3%, proceed to step 211. . In step 210, as shown in the following equation, among the data MA, MB, and MC, the one closest to zero is added to the current altitude correction value FHAC to obtain a new altitude correction value FHAC. FHAC + min (MA, MB, MC) → FHAC ... (9) The reason why the data closest to zero is adopted here is that it may be affected by other influences other than altitude change, such as the release of fuel evaporative gas. This is because it is the least. In step 206, it is determined whether the altitude correction value FHAC is less than 5%. If it is less than 5%, the process proceeds to step 212, and if it is 5% or more, the process proceeds to step 213. In step 212, the altitude correction value FHAC is -
It is determined whether or not it exceeds 20%. If it exceeds -20%, the process proceeds to step 214; if it is less than -20%, the process proceeds to step 215. In step 213, an upper limit guard is applied to the altitude correction value FHAC, and the altitude correction value
The upper limit of FHAC is set at 5%. Also, step 215
Now, apply the lower limit guard to the altitude correction value FHAC,
Set the lower limit of altitude correction value FHAC to -20%. The range of the altitude correction value FHAC is limited here to prevent abnormal changes in the altitude correction value FHAC due to sudden causes such as failure of the oxygen concentration sensor 36. The reason why the absolute value of the upper limit guard is smaller than the absolute value of the lower limit guard is that the altitude correction value FHAC in the plain area is adopted as the reference value. Furthermore, in step 211, based on the data MC,
The value obtained by adding 1.5% to the data MA (MA +
1.5%) is smaller than the value obtained by adding 0.5% to the data MB (MB + 0.5%), and
Determine whether the value obtained by adding 0.5% (MB + 0.5%) is smaller than the data MC, and (MB + 0.5
%) is between (MA+1.5%) and MC,
The process proceeds to step 216, and if the value of (MB+0.5%) is not within the range, the process proceeds to step 217. In step 216, -1.5% is added to the current air flow meter correction value FAFM to obtain a new air flow meter correction value FAFM, as shown in the following equation. FAFM - 1.5% → FAFM ... (10) In step 217, the value obtained by adding -1.5% to the data MA (MA -
1.5%) is greater than the value obtained by adding -0.5% to the data MB (MB - 0.5%), and the data
Value obtained by adding -0.5% to MB (MB - 0.5%)
is larger than the data MC, and (MB
-0.5%) is between MC and (MA-1.5%), proceed to step 218; if the value (MB-0.5%) is not within the range, the program is terminated. In step 218, 1.5% is added to the current air flow meter correction value FAFM as shown in the following formula,
Set the new air flow meter correction value FAFM. FAFM + 1.5% → FAFM ...(11) Here, we will check whether the data MA, MB, and MC exhibit characteristics such that the actual air-fuel ratio deviates more from the stoichiometric air-fuel ratio as the intake air flow rate decreases. If it is determined, 1.5% or -1.5% is added to the air flow meter correction value FAFM, and the air flow meter correction value FAFM is corrected so that the actual air-fuel ratio approaches the stoichiometric air-fuel ratio. At this time, the air-fuel ratio deviation due to the output error of the air flow meter 16 is largest during idling, and the air-fuel ratio deviation due to changes in the air flow meter correction value FAFM is the largest when the intake air amount is large. Since the air flow meter correction value FAFM is small,
In order to reduce the deviation during idling, in steps 216 and 218, a large correction of ±1.5% is made in accordance with the deviation during idling. Furthermore, in step 219, it is determined whether the air flow meter correction value FAFM is less than 5%.
If it is less than 5%, proceed to step 220, and if it is 5% or more, proceed to step 221. In step 220, it is determined whether or not the air flow meter correction value FAFM exceeds -20%. If it exceeds -20%, the process proceeds to step 214; if it is less than -20%, the process proceeds to step 222.
Proceed to. Furthermore, in step 221, an upper limit guard is applied to the air flow meter correction value FAFM, and the upper limit value of the air flow meter correction value FAFM is set to 5%.
On the other hand, in step 222, a lower limit guard is applied to the air flow meter correction value FAFM, and the lower limit value of the air flow meter correction value FAFM is set to -20%. Here, the reason why the absolute value of the lower limit guard is greater than the absolute value of the upper limit guard is that a clean and new air flow meter is used as a reference. In step 214, the first to third storage units M1 to
Clear the contents of M3, the first to third counters, and the first to third flags FA, FB, and FC,
Exit this program. According to the above program, the altitude correction value
FHAC is guarded with a lower limit of -20% and an upper limit of 5%, and although not shown, generally the lower limit guard of the air-fuel ratio feedback correction coefficient FAF is -20% and the upper limit guard is +20%. Therefore, the lower limit guard for the sum of the altitude correction value FHAC and the air-fuel ratio feedback correction coefficient FAF is -40% as it is, and the upper limit guard is +25%.
However, with such a large guard, the guard has no effective meaning, and incorrect correction may cause engine stalling, inability to start, etc. Therefore, in the present invention, as shown in FIG. 5, the air-fuel ratio feedback correction coefficient FAF and the altitude correction value are
Put the sum of FHAC in register A, and for the value put in register A, upper limit guard + 10%,
After applying a guard of -25% to the lower limit guard, the combustion injection time τ is calculated using the following formula. τ=τ ₀ × (1+A+FAFM/100) ……= In other words, in this Figure 5, first step 301
The sum of the air-fuel ratio feedback correction coefficient FAF and the altitude correction value FHAC is calculated in step 305a and step 305b. , that is, if the sum of these two correction values is +10% or more, the value of this register A is +10.
%, and furthermore, in steps 308a and 308b, lower limit guard processing is performed, that is, the sum of these two correction values is −25
% or less, the value of this register A is set to -25%. Therefore, no matter what the air-fuel ratio feedback correction coefficient FAF and altitude correction value FHAC are, the final value (after steps 308a and 308b) is The value of register A is in the range of -25% to +10%. After this, in step 313, the fuel injection time τ is determined by the above-mentioned equation (12). This makes it possible to reliably prevent erroneous corrections that may lead to engine stall. In addition, in this equation (12), as mentioned above, the air-fuel ratio feedback correction coefficient FAF and the altitude correction value
Let the sum of FHAC be A, and as shown in Figure 5,
Although a guard is set for the sum of these two correction values, the combination of how to guard the correction coefficients to be learned and corrected according to the present invention is not limited to this. For example, the air-fuel ratio feedback correction coefficient
The sum of FAF and air flow meter correction value FAFM may be guarded, or the sum of the three correction values of air-fuel ratio feedback correction coefficient FAF, altitude correction value FHAC, and air flow meter correction value FAFM may be set to A.
You can also put a guard on this. Like this 3
If the sum of the two correction values is guarded, the above equation (12) becomes as follows. τ=τ ₀ ×(1+A/100) ...(12a) In the embodiment shown in FIG. 5, the sum of the air-fuel ratio feedback correction coefficient FAF and the altitude correction value FHAC is guarded, These two correction values have characteristics that are contradictory to each other. That is, for example, when operating at an altitude that requires a 9% correction for the sum of the air-fuel ratio feedback correction coefficient FAF and the altitude correction value FHAC, and under the usage conditions where learning has been completed, FHAC = -9%... ( 13a) FAF = 0% ... (13b) After that, immediately after these two correction values are reset by removing the battery terminal for vehicle maintenance at the same altitude, FHAC = 0% ... (14a) FAF=-9% (14b) Furthermore, as the vehicle driving time increases under the same altitude, the two correction values are considered to complete learning through the following process. FHAC=-3%...(15a) FAF=-6%...(15b) ↓ FHAC=-9%...(16a) FAF=0%...(16b) In this way, the air-fuel ratio feedback correction coefficient
FAF and altitude correction value FHAC are such that when one becomes large, the other becomes small, and when one becomes small, the other becomes large. That is, when one correction value becomes large, the other must become small, and it is effective to prevent erroneous correction by placing a guard between a plurality of correction values having such mutually contradictory characteristics. Furthermore, in the embodiments described above, the correction of the intake air amount according to the present invention was applied only to the control of the fuel injection time, that is, the control of the air-fuel ratio. It is clear that the scope is not limited to this and can be similarly applied to control of other items such as ignition timing.

【Effect of the invention】

As explained above, according to the present invention, an appropriate card is set for the correction coefficient to be learned and corrected, and therefore, it has the excellent effect of reliably preventing engine stalling, inability to start, etc. due to incorrect correction. .

[Brief explanation of drawings]

FIG. 1 is a sectional view, partially including a block diagram, showing the configuration of an electronically controlled engine in which the intake air amount correction method according to the present invention is adopted, and FIG. 2 is a sectional view of the digital electronic control circuit in the above embodiment. A block diagram including the circuit configuration, FIG. 3 is a flowchart showing a program for calculating and storing data used for learning correction of each correction coefficient in the embodiment, and FIG. FIG. 5 is a flowchart showing a part of the program for calculating the fuel injection time in the same embodiment as described above. DESCRIPTION OF SYMBOLS 10... Engine, 16... Air flow meter, 22... Crank angle sensor, 36... Oxygen concentration sensor, 44... Injector, 50... Digital electronic control circuit.

Claims (1)

[Claims] 1. The air-fuel ratio of the air-fuel mixture is feedback-controlled in accordance with the deviation between the actual air-fuel ratio determined from the secondary air-fuel ratio of exhaust gas and the target air-fuel ratio, and the actual air-fuel ratio during feedback control is controlled. an air-fuel ratio feedback correction coefficient for correcting the air-fuel ratio of the air-fuel mixture according to a deviation from a preset basic air-fuel ratio of the air-fuel mixture;
In an intake air amount correction method for an electronically controlled engine that learns and corrects a high altitude correction coefficient for correcting the intake air amount to atmospheric pressure, a detection error correction coefficient for correcting a detection error of the intake air amount, etc. Fuel ratio feedback correction coefficient, high altitude correction coefficient,
A method for correcting an intake air amount for an electronically controlled engine, characterized in that a guard is provided for a value that is a combination of at least two of correction coefficients to be learned and corrected, such as detection error correction coefficients. 2. The intake air amount correction method for an electronically controlled engine according to claim 1, wherein the guard is provided for a value that is a combination of the air-fuel ratio feedback correction coefficient and the high altitude correction coefficient.