JP2518219B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

The present invention relates to an air-fuel ratio control method for an internal combustion engine, and more particularly to an air-fuel ratio in a high intake air amount region using a learning value updated in a low intake air amount region. The present invention relates to a method for controlling an air-fuel ratio of an internal combustion engine that is controlled.

[Conventional technology]

Conventionally, the fuel injection time TA is calculated based on the following equation (1).
There is known an air-fuel ratio control method for an internal combustion engine, in which U is calculated to control the fuel injection amount to control the air-fuel ratio (JP-A-60-50249).

TAU = TP (FAF + FG) K (1) However, TP is Q / λ, which is the intake air amount Q and the engine speed N.
・ Basic fuel injection time expressed as N (however, λ
Air-fuel ratio), the air-fuel ratio fed back correction coefficient FAF that the O ₂ sensor output is gradually reduced when illustrating the air-fuel ratio Ritsuchi and O ₂ sensor output is gradually increased when indicating the air-fuel ratio lean, FG advanced The learning value represented by the sum (FGHAC + FGAFM / Q) of the compensation learning value FGHAC and the learning value FGAFM for the air flow meter per unit intake air amount, and K is the increase correction coefficient determined by the intake air temperature, the engine cooling water temperature, and the like.

The learning value FG is a predetermined value (for example, 1.0) of the average value FAFAV of the air-fuel ratio feedback back correction coefficient FAF in the low intake air amount area, that is, the air-fuel ratio feedback back control area.
It is updated by increasing / decreasing so that. The learning value FG is learned in the air-fuel ratio feedback control area as described above, and is applied to the above equation (1) in the entire operation area to calculate the fuel injection time TAU.

Therefore, according to the conventional air-fuel ratio control method, even when deposits and the like adhere to the air flow meter due to changes over time and the characteristics of the air flow meter change, or atmospheric pressure changes due to altitude changes and the mass of intake air changes. The air-fuel ratio feedback correction coefficient FAF and the learning value FG become a value of approximately 1.0, which makes it possible to control the air-fuel ratio to the target air-fuel ratio in the air-fuel ratio feedback control area. Also, outside the high intake air amount area, that is, outside the air-fuel ratio feedback control area, the update of the learning value is stopped, the value of the air-fuel ratio feedback correction coefficient FAF is set to 1.0, and the air-fuel ratio feedback control is stopped, and the air-fuel ratio feedback control is stopped. Since the fuel injection time TAU is calculated using the learning value updated in the region, it is possible to compensate for the change in the air-fuel ratio due to the characteristic change of the air flow meter or the altitude change.

[Problems to be solved by the invention]

However, in the conventional air-fuel ratio control method, the learning value FG learned in the air-fuel ratio feedback control area, which is a low intake air amount area, is used without changing the value outside the air-fuel ratio feedback control area, which is a high intake air amount area. Since the air-fuel ratio is controlled, the correction amount C of the fuel injection amount corrected by the learning value FG is expressed by the following equation (2) outside the air-fuel ratio feedback control region.

Therefore, the correction amount C increases as the intake air amount Q increases, and the correction amount C decreases as the engine speed N decreases.
Becomes larger and the increase correction coefficient K becomes larger, the correction amount C
Becomes large, and the correction amount C becomes large when the target air-fuel ratio λ is made small (the air-fuel ratio is adjusted to the latch side). Therefore, if the air-fuel ratio is controlled or the learning value is erroneously learned by using the air flow meter whose characteristics are deviated between the low intake air amount side and the high intake air amount side, the air-fuel ratio deviates from the target air-fuel ratio. The air-fuel ratio outside the feedback control area becomes over-lit (when the correction amount C is positive), the output is reduced or misfire occurs, and the air-fuel ratio is lean (when the correction amount C is negative). Then, there was a problem that knocking and pre-ignition occurred. That is, for example, when controlling the air-fuel ratio using an air flow meter that shows a value lower than the actual intake air amount on the low intake air amount side and an output higher than the actual intake air amount on the high intake air amount side, The learning value FG is updated so that it becomes large on the low intake air amount side, and when this learning value FG is used on the high intake air amount side, the correction amount of the fuel injection amount by the learning value FG becomes large and the air-fuel ratio becomes overlit.

The present invention has been made to solve the above problems, and the air-fuel ratio is the target even when the air-fuel ratio outside the air-fuel ratio feedback control region is controlled using the learning value learned in the air-fuel ratio feedback control region. It is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine that does not deviate from the value.

(Means for Solving the Problems) In order to achieve the above object, the present invention is designed so that the average value of the air-fuel ratio feedback correction coefficient obtained from the O ₂ sensor output in the air-fuel ratio feedback control region becomes a predetermined value. Based on the intake air amount measured by the air flow meter, which updates the learning value and shows a value lower than the actual intake air amount in the low intake air amount region and a value higher than the actual intake air amount in the high intake air amount region. Feed-back control the air-fuel ratio based on the basic fuel injection amount and the air-fuel ratio feed back correction coefficient and the learning value, and stop the update of the learning value outside the air-fuel ratio feed back control region and the basic fuel injection amount and the In an air-fuel ratio control method for an internal combustion engine, which performs open-loop control of the air-fuel ratio based on the learning value updated in the air-fuel ratio feedback control region Outside the air-fuel ratio feedback control region, the absolute value of the learning value is made smaller than that in the air-fuel ratio feedback control region, and the absolute value of the learning value is reduced as the intake air amount increases. Is characterized by.

[Action]

According to the present invention, in the air-fuel ratio feedback control region (low intake air amount region side), the learning value FG is set so that the average value FAFAV of the air-fuel ratio feedback correction coefficient FAF obtained from the O ₂ sensor output becomes a predetermined value. The fuel injection time TAU is updated based on the equation (1) using the basic fuel injection amount TP, which is updated and is determined based on the intake air amount Q measured by the air flow meter, the air-fuel ratio feedback back correction coefficient FAF, and the learning value FG. Is calculated and the fuel injection valve is opened for a time corresponding to this fuel injection time TAU, and the air-fuel ratio is feedback-controlled.

By the way, when an air flow meter that shows a value lower than the actual intake air amount in the low intake air amount region and a value higher than the actual intake air amount in the high intake air amount region is used as the air flow meter, the air-fuel ratio feedback In the control region (on the low intake air amount region side), a value lower than the actual intake air amount is measured as the intake air amount Q, and the value of the basic fuel injection amount TP also becomes small. Therefore, the learning value FG is updated so as to increase.

On the other hand, outside the air-fuel ratio feedback control region (on the high intake air amount region side), the learning value FG is stopped from being updated and the air-fuel ratio feedback control is stopped, and the basic fuel injection amount is reduced.
Using TP and the learning value FG, which is updated so as to be large in the air-fuel ratio feedback control range, the absolute value of the learning value FG is made small and becomes smaller as the intake air amount Q increases (1) The fuel injection time TAU is calculated based on the equation, and the air-fuel ratio is open-loop controlled by the same method as above.

〔The invention's effect〕

As described above, according to the present invention, the learning value outside the air-fuel ratio feedback control area is set to be smaller than that in the air-fuel ratio feedback control area, and is reduced as the intake air amount increases, so that the low intake air amount region Shows a value lower than the actual intake air amount, and shows a value higher than the actual intake air amount in the high intake air amount region Even when controlling the air-fuel ratio using the air flow meter, the air-fuel ratio feedback control region with a large intake air amount Outside, the effect that the air-fuel ratio can be prevented from becoming over-lit can be obtained.

〔Example〕

Hereinafter, an internal combustion engine (engine) including an air-fuel ratio control device to which the present invention is applicable will be described in detail with reference to the drawings. As shown in FIG. 2, an air flow meter 12 is arranged downstream of the air cleaner 10. The air flow meter 12 includes a compensation plate rotatably mounted in the damping chamber, a medializing plate connected to the compensating plate, and a potentiometer for outputting a voltage according to the opening of the medializing plate. It is composed of a Yometer 12A and a potentiometer 12A.
Is connected to a control circuit 44 composed of a microcomputer. The square of the air flow meter output (U value) is inversely proportional to the intake air amount Q. An inlet pipe 14 is mounted on the downstream side of the air flow meter 12, and the inlet pipe 14 is connected to a combustion chamber 22 formed in the engine body via an intake pipe 16 and an intake manifold 20. At the upstream side of the intake pipe 16, the throttle valve 17
The throttle switch 17 is provided with an idle switch 18 which is turned on when the throttle valve 17 is in the idle position. A supercharger 24 is arranged downstream of the throttle valve 17, and an intercooler 26 is arranged downstream of the supercharger 24. Then, a pipe line 27 is arranged so as to connect the upstream side of the supercharger 24 of the intake pipe 16 and the surge tank 21 on the downstream side of the intercooler 26, and an air bypass valve 28 is attached in the middle of this pipe line 27. ing. The air bypass valve 28 is opened and closed by a vacuum switching valve VSV controlled by a signal from the control circuit 44. Further, the outer wall of the supercharger 24 is in communication with the atmosphere via a vacuum switching valve VSV controlled by the control circuit 44. A fuel injection valve 38 is attached to the intake manifold 20 so as to project corresponding to each cylinder.

The combustion chamber 22 is connected to an exhaust pipe 32 equipped with a catalyst device via an exhaust manifold 30. On the downstream side of the exhaust manifold 30, an O ₂ sensor 34 that detects the residual oxygen concentration in the exhaust gas and outputs a signal inverted at the residual oxygen concentration corresponding to the theoretical air-fuel ratio is attached. The output of this O ₂ sensor 34 is as shown in FIG. The O ₂ sensor 34 is connected to the control circuit 44. In addition, a thermistor type water temperature sensor 36 is attached so as to project into the water jacket formed on the cylinder block of the engine body.
36 is connected to the control circuit 44. A spark plug is attached so as to project into the combustion chamber 22 of the engine, and the spark plug is connected to the control circuit 44 via the distributor 40 and an igniter 42 having an ignition coil. This distributor 40 is equipped with a rotation angle sensor 40A composed of a signal rotor fixed to the distributor shaft and a pick-up fixed to the distributor housing. Connected to 44.

As shown in FIG. 3, the control circuit 44 includes a random access memory (RAM) 58, a read only memory (ROM) 60,
Micro processing unit (MPU) 62, input / output port 64, input port 66, first output port 68, second output port 70, and bus 72 such as a data bus or control bus connecting these Has been done. The input / output port 64 is an air flow meter via an analog / digital (A / D) converter 74, a multiplexer 76 and buffers 78A and 78B.
It is connected to each of the 12 potentiometers 12A and the water temperature sensor 36. The input / output port 64 is also connected to supply a control signal to the A / D converter 74 and the multiplexer 76. The rotation angle sensor 40A is connected to the input port 66 through the waveform shaping circuit 80, and the idle switch 1
8 is connected to the O ₂ sensor 34 via the comparator 84.
Is connected.

Further, the first output port 68 is connected to the igniter 42 via the drive circuit 86, and the second output port 70 is connected to the drive circuit.
Each of the fuel injection valves 38 is connected via 88. Incidentally, 90 is a clock, and 92 is a timer. The ROM 60 previously stores a program of a control routine described below, a map of upper and lower limit values of the learning value FG shown in FIG. 6, and the like.

Fig. 1 shows the predetermined time (for example, 24m) stored in the ROM.
shows a control routine executed every sec), in which the intake air amount Q and the engine speed N are taken in to calculate the load Q / N, and the current load Q / N and the current engine are acquired. It is determined whether or not the feed back control condition is satisfied by determining whether or not the rotation speed N is within the air-fuel ratio feed back control region shown in FIG. When it is judged that the feed back control condition is satisfied, the O ₂ sensor signal is taken in at step 102, and it is judged at step 104 whether or not the O ₂ sensor signal indicates the air-fuel ratio latch. When the O ₂ sensor signal indicates the air-fuel ratio latch, the integration constant α is subtracted from the air-fuel ratio feedback back correction coefficient FAF at step 106, and when the O ₂ sensor signal indicates the air-fuel ratio lean, the air-fuel ratio at step 108. The integral constant β is added to the feedback back correction coefficient FAF. As a result the air-fuel ratio fed back correction coefficient FAF is gradually increased when the gradually reduced to and O ₂ sensor signal when the O ₂ sensor signal as shown in FIG. 5 indicates the Ritsuchi indicates a lean. Immediately after the O ₂ sensor signal is inverted from rich to lean or from lean to rich, the air-fuel ratio feedback correction coefficient FAF is skipped in a predetermined direction using a value larger than the integral constants α and β to perform proportional integral operation. You may allow it. At the next step 110, O ₂
The average value of the air-fuel ratio feedback correction coefficient is calculated according to the following formula by determining whether the sensor signal is inverted from rich to lean or from lean to latch and storing the air-fuel ratio feedback back correction coefficient FAF at the time of this inversion.
Calculate FAFAV.

On the other hand, when it is determined in step 100 that the feedback control condition is not satisfied, the air-fuel ratio feedback correction coefficient FAF is set to 1.0 in step 112.

At the next step 114, the learning condition is satisfied by determining whether the feedback control is being performed, whether the engine cooling water temperature is 70 ° C. or more, and whether the fuel injection time TAU is 1 msec or more. It is determined whether or not
When all of the above conditions are affirmative, it is determined that the learning condition is satisfied, and it is determined in step 116 whether or not the idle switch is turned on. If it is determined that the idle switch is on, it is determined in step 118 whether the average value FAFAV of the air-fuel ratio feedback correction coefficient is equal to or greater than a predetermined value (for example, 1.0), and the average value FAFAV
Is larger than the predetermined value, the air flow meter compensation learning value FGAFM is increased by a predetermined value a and the altitude compensation learning value FGHAC is increased by a predetermined value b in step 120. On the other hand, when it is determined in step 118 that the average value FAFAV is less than the predetermined value, in step 122 the air flow meter compensation learning value FGAFM is decreased by the predetermined value a and the altitude compensation learning value F is reduced.
Reduce GHAC by a predetermined value b.

If it is determined in step 116 that the idle switch is off, it is determined in step 124 whether the average value FAFAV is equal to or greater than a predetermined value (for example, 1.0), and if the determination in step 124 is affirmative, the advanced value is set in step 126. Compensation learning value F
GHAC is increased by a predetermined value b, and if the determination in step 124 is negative, the learning value FGHAC for altitude compensation is decreased by a predetermined value b in step 128. Thus, the reason why the air flow meter compensation learning value FGAFM is updated when the idle switch is on, that is, in the idle state, is that the influence of the air flow meter blockage is most prominent when the throttle opening is minimum.

At the next step 130, the air flow meter output (U value) is taken in, and at step 132, the upper and lower limit values of the learning value FG corresponding to the U value are calculated from the map shown in FIG. The map of FIG. 6 is defined by the U value and the upper and lower limits of the learning value FG. While the U value decreases from 0.164 to 0.099, the upper limit value of the learning value FG decreases to 0.15 to 0 and learning The lower limit of the value FG is −0.
It is specified to increase from 15 to 0. Here, since the intake air amount Q is represented by C ₀ / U ² (C ₀ is a constant), the intake air amount Q increases as the U value decreases, and therefore the absolute value of the upper and lower limit values of the learning value FG is It is set to decrease as the intake air amount Q increases. Note that U
The value = 0.164 corresponds to the maximum value of the intake air amount Q in the air-fuel ratio feedback control region, and the point of U value = 0.099 corresponds to the intake air amount Q outside the air-fuel ratio feedback control region = 10. It corresponds to.

At the next step 134, the learning value FGAFM / Q for the air flow meter compensation per unit intake air amount updated as described above.
And the learning value FGHAC for altitude compensation (FGHAC + FGAFM / Q), the absolute value of the learning value FG expressed by the sum (FGHAC + FGAFM / Q) is compared with the absolute value of the upper and lower limits of the learning value FG calculated in step 132. If the absolute value is greater than the upper and lower limit values, step 136
The upper and lower limit values are used as the learning value FG. Then, in step 138, the fuel injection time TAU is calculated based on the equation (1).
Is calculated, and this fuel injection time TAU is calculated for each predetermined crank angle.
The fuel injection is performed by opening the fuel injection valve for a time corresponding to the above, and thereby the air-fuel ratio is controlled.

As a result of limiting the upper and lower limits of the learning value FG as described above, the learning value is erroneously learned in the air-fuel ratio feedback control area.
The absolute value of FG is prevented from becoming abnormally large, and the absolute value of the learning value FG is reduced as the intake air amount increases outside the air-fuel ratio feedback control range, so the air-fuel ratio becomes over-lit or over-lean. Is prevented.

Although the upper and lower limits of the learning value FG are determined according to the U value, that is, the intake air amount Q in the above, the present invention is not limited to this, and the engine rotation speed can be set as described in the above equation (2). It can be determined according to the engine operating state such as the speed N, the fuel injection amount increase correction coefficient, or the throttle opening (corresponding to the intake air amount Q). Also, in the above, the learning value in the high intake air amount region (outside the air-fuel ratio feedback control region)
Although the example in which FG is reduced and reflected in the fuel injection time has been described, the learned value may not be reflected in the high intake air amount region. In the method of limiting the upper and lower limits of the learning value with the increase of the intake air amount (corresponding to the U value which is the air flow meter output) as in the present embodiment, the limits such as the knocking occurrence limit are not exceeded. Since the learned value can be reflected in the air-fuel ratio open loop control region within the allowable range in which the air-fuel ratio can be changed, an appropriate air-fuel ratio can be obtained.

[Brief description of drawings]

FIG. 1 is a flow chart showing a control routine of an embodiment of the present invention,
2 is a schematic diagram showing an internal combustion engine to which the present invention is applicable, FIG. 3 is a block diagram showing details of the control circuit of FIG. 2, and FIG.
Fig. 5 is a diagram showing the air-fuel ratio feedback control region, Fig. 5 is a diagram showing the change of the air-fuel ratio feedback compensation coefficient FAF which changes according to the O ₂ sensor signal, and Fig. 6 shows the upper and lower limits of the learning value FG. It is a diagram showing a map. 12 …… Air flow meter, 18 …… Idle switch, 38 …… Fuel injection valve.

Continuation of the front page (56) Reference JP 61-126338 (JP, A) JP 61-43235 (JP, A) JP 60-50249 (JP, A) JP 60-153448 (JP , A)

Claims (1)

(57) [Claims] 1. The learning value is updated so that the average value of the air-fuel ratio feedback correction coefficient obtained from the output of the O ₂ sensor in the air-fuel ratio feedback control area becomes a predetermined value, and the actual intake air amount is reduced in the low intake air amount area. Shows a value lower than the intake air amount, and shows a value higher than the actual intake air amount in the high intake air amount region.The basic fuel injection amount, which is determined based on the intake air amount measured by the air flow meter, the air-fuel ratio feedback correction coefficient, and the learning value. Based on the feedback control of the air-fuel ratio based on and, based on the learning value updated in the basic fuel injection amount and the air-fuel ratio feedback control region while stopping the update of the learning value outside the air-fuel ratio feedback control region In an air-fuel ratio control method for an internal combustion engine that performs open-loop control of an air-fuel ratio, the air-fuel ratio is outside the air-fuel ratio feedback control region. An air-fuel ratio control method for an internal combustion engine, wherein the absolute value of the learned value is made smaller than that in the feedback control region, and the absolute value of the learned value is made smaller as the intake air amount increases.