JP2722805B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio of an internal combustion engine in which an air-fuel ratio is feedback-controlled based on outputs of air-fuel ratio sensors disposed upstream and downstream of a catalytic converter. The present invention relates to a fuel ratio control device.

Disposed upstream and the air-fuel ratio sensor, for example O ₂ sensor, respectively at the downstream side of the catalytic converter of the prior art internal combustion engine, upstream O ₂
Performs air-fuel ratio feedback control mainly on the output signal of the sensor, and learns the bias of the overall air-fuel ratio of the air-fuel ratio feedback control by the upstream O ₂ sensor based on the output signal of the downstream O ₂ sensor. Conventionally, an air-fuel ratio control device that corrects the air-fuel ratio has been known (for example, see
-205441).

That is, during execution of the air-fuel ratio feedback control,
A feedback correction coefficient α is calculated based on the output signal of the upstream O ₂ sensor mainly by, for example, pseudo proportional integral control, and the feedback correction coefficient α is calculated based on the basic fuel injection amount.
By multiplying Tp, closed-loop control of the air-fuel ratio is performed. Therefore, the actual air-fuel ratio repeats inversion of rich and lean at a cycle of about 1 to 2 Hz. On the other hand, on the downstream side of the catalytic converter, the fluctuation of the residual oxygen concentration becomes very gentle due to the O ₂ storage capacity of the catalyst, so the output signal of the downstream O ₂ sensor is
The fluctuation width is smaller and the cycle is longer than that of the O ₂ sensor. In other words, the shape changes very slowly.

Then, if the air-fuel ratio by the air-fuel ratio feedback control using the upstream O ₂ sensor is generally offset to the lean side due to aging or the like, the output signal of the downstream O ₂ sensor becomes continuous on the lean side, and If the air-fuel ratio is biased toward the rich side, the air-fuel ratio becomes continuous on the rich side. Therefore, according to the overall bias tendency of the air-fuel ratio, for example, a learning value P _HOS is assigned to each operation region, and the feedback correction coefficient α given at the time of rich → lean inversion and at the time of lean → rich inversion is calculated. By correcting the proportional components P _L and P _R (see FIG. 4) using the learning value P _HOS , it is possible to compensate for the above-described aging.

On the other hand, it has been widely known that secondary air is introduced into an exhaust system as a means for purifying exhaust gas of an internal combustion engine. Generally, secondary air is introduced, and during this secondary air introduction, so-called open-loop control is generally performed while maintaining the feedback correction coefficient α at a fixed value of α ≒ 1. In addition, as the position where the secondary air is introduced,
Naturally, it is on the upstream side of the catalytic converter.
Incidentally, while an open loop control as described above, the learning correction using the downstream O ₂ sensor is stopped course.

Problems to be Solved by the Invention As described above, upstream and downstream of the catalytic converter
Equipped with an O ₂ sensor (air-fuel ratio sensor)
In the configuration in which the secondary air is introduced, if the idle operation is continuously performed for a certain period, the output of the downstream O ₂ sensor becomes as shown in FIG. 7 (b) due to the influence of the secondary air supplied upstream of the catalytic converter. As shown, a continuous lean state is obtained.
Moreover, the excess oxygen is accumulated in the catalyst by the O ₂ storage capability possessed by the catalyst.

Therefore, the next time the vehicle starts to this idle 7 (b), even if the actual air-fuel ratio becomes rich tendency, since the oxygen accumulated in the catalyst continues to be released, the downstream O ₂ The output of the sensor remains in a lean state for a while, as shown in FIG. Therefore, when the learning correction is performed based on the output of the downstream O ₂ sensor, the learning value P _HOS continues to increase to correct the rich side as shown in (c) of FIG. 7, and the air-fuel ratio becomes excessively rich. Try to make it. Therefore, the convergence of the air-fuel ratio after the start is deteriorated, and there is a possibility that the exhaust gas purification performance and the drivability may be temporarily deteriorated.

Means for Solving the Problems Therefore, the present invention performs feedback control by the downstream air-fuel ratio sensor so that the output of the downstream air-fuel ratio sensor becomes equivalent to the stoichiometric air-fuel ratio at the time of idle when secondary air is introduced. I did it. That is, as shown in FIG. 1, the air-fuel ratio control device for an internal combustion engine according to the present invention is disposed upstream of a catalytic converter interposed in an exhaust passage, and has an abrupt output change at a stoichiometric air-fuel ratio. And a downstream air-fuel ratio sensor 2 having a characteristic that the output also changes suddenly at the stoichiometric air-fuel ratio, and disposed downstream of the catalytic converter. Basic fuel injection amount setting means 3 for setting a basic fuel injection amount according to conditions, idle determination means 9 for detecting an idle state of the internal combustion engine, and an output of the upstream air-fuel ratio sensor 1 when a predetermined feedback control condition is satisfied. A normal-time correction coefficient setting means 4 for setting the feedback correction coefficient based on the feedback correction coefficient based on the output of the downstream air-fuel ratio sensor 2 during the normal-time feedback control. A correction coefficient for calculating an average value of the feedback correction coefficient based on an output of the upstream air-fuel ratio sensor 1 when the shift to the idle state is detected by the learning correction means 5 to be corrected and the idle determination means 9. Average value calculation means 10
A secondary air control means 6 for introducing secondary air into the exhaust passage after calculating the average value; and after starting the introduction of the secondary air, using the average value as an initial value and setting the downstream air-fuel ratio sensor 2 And an idle time correction coefficient setting means 7 for setting a feedback correction coefficient based on the output of the sensor 2 so that the output of the sensor 2 becomes equivalent to the stoichiometric air-fuel ratio. An injection amount correcting means 8 is provided.

When the predetermined feedback control condition is satisfied, a feedback correction coefficient is set based on the output of the upstream air-fuel ratio sensor 1, and the fuel injection amount is corrected. At this time, the output of the downstream air-fuel ratio sensor 2 is used for learning correction so as to compensate for the overall deviation of the air-fuel ratio due to aging or the like.

On the other hand, at the time of engine idling, when the idling determining means 9 detects that the engine has shifted to the idling state, prior to the introduction of the secondary air, the correction coefficient average value calculating means 10 first calculates the average value of the feedback correction coefficient at that time. Desired. After obtaining the average value, the introduction of the secondary air is started, and the feedback control by the upstream air-fuel ratio sensor 1 is stopped. Then, instead of this, feedback control is performed based on the output of the downstream air-fuel ratio sensor 2 so that the output of the sensor becomes equivalent to the stoichiometric air-fuel ratio. At this time, the feedback control by the downstream air-fuel ratio sensor 2 is started using the average value as an initial value of the feedback correction coefficient.

Therefore, the excess oxygen is not accumulated in the catalytic converter during the idling operation, and when the vehicle starts next, an accurate output can be obtained from the downstream air-fuel ratio sensor 2 immediately after the vehicle starts.

In particular, as described above, after the idle determination, prior to the introduction of the secondary air, the average value of the feedback correction coefficient is obtained based on the output of the upstream air-fuel ratio sensor 1 having a good response to the exhaust gas composition, By using this as the initial value of the feedback correction coefficient after the start of the secondary air introduction, when the control is shifted to the feedback control by the downstream air-fuel ratio sensor 2 at the start of the secondary air introduction, the fuel with the appropriate feedback correction coefficient is immediately obtained. Injection amount control can be realized. In other words, since the change cycle of the air-fuel ratio is long downstream of the catalyst, the so-called O
In the N, OFF type downstream air-fuel ratio sensor 2, the output change appears very slowly with respect to the change in the exhaust gas composition. However, in the present invention, by setting the initial value as described above, an appropriate Control can be started.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a structural explanatory view showing a mechanical structure of one embodiment of the present invention, in which 11 is an internal combustion engine, 12 is an intake passage, 13
Indicates an exhaust passage. In the intake passage 12, a fuel injection valve 14 for supplying fuel to each intake port is provided for each cylinder, and a throttle valve 15 is interposed. For example, a hot-wire type air flow meter 16 for detecting the temperature is provided.

The exhaust passage 13 is provided with a catalytic converter 17 using a three-way catalyst, and an upstream O ₂ sensor 18 at a position upstream of the catalytic converter 17 and a downstream sensor at a downstream position.
O ₂ sensor 19 is disposed, respectively. O ₂ sensor 18, 19 as the air-fuel ratio sensor is for generating an electromotive force corresponding to the residual oxygen concentration in the exhaust gas, in particular, the electromotive force changes suddenly bordering the stoichiometric air-fuel ratio, excessive than the stoichiometric air-fuel ratio Dark side (rich side)
To a high level (about 1V) and to a low level (about 100mV) on the lean side (lean side).

Also, at the upstream side of the catalytic converter 17 in the exhaust passage 13,
The tip of the next air passage 20 is connected. The secondary air passage 20 includes an air pump 21 for introducing secondary air, and a secondary air control valve 22 for controlling the introduction and stop of secondary air is interposed in the passage. ing. If a sufficiently large exhaust pulsation can be obtained, secondary air is introduced by a pressure difference via a reed valve or the like, and the above air pump is used.
It is also possible to omit 21.

Further, reference numeral 23 denotes a water temperature sensor that detects a cooling water temperature of the internal combustion engine, 25 denotes a rotation speed sensor that detects an engine rotation speed, specifically, a crank angle sensor that emits a pulse signal at every predetermined crank angle, and 25 denotes a determination of an engine idle state. Throttle valve for
15 shows a throttle opening sensor that outputs an output in accordance with the opening of No. 15.

The control unit 26 to which the detection signals of the various sensors described above are input uses a so-called microcomputer system, and controls the injection amount of the fuel injection valve 14 based on the output signals of the O ₂ sensors 18 and 19, that is, a feedback control method. Various controls of the internal combustion engine, such as air-fuel ratio control and secondary air control via the secondary air control valve 22, are executed.

Next, the contents of the control in the above embodiment will be described.

First, the outline of the air-fuel ratio feedback control under normal operating conditions will be described. This normal air-fuel ratio feedback control is performed mainly based on the output of the upstream O ₂ sensor 18. First, the intake air amount Q detected by the air flow meter 16 and the engine speed detected by the crank angle sensor 24. N
Then, the basic pulse width Tp (basic fuel injection amount) is calculated with Tp = Q / N. Then, the actual drive pulse width Ti (fuel injection amount) of the fuel injection valve 14 is determined by adding various increase corrections and feedback corrections thereto. Specifically, the pulse width Ti is obtained by the following equation.

Ti = Tp × CO × α + Ts Here, CO is various increase correction coefficients, and includes, for example, water temperature increase correction according to the water temperature, air-fuel ratio correction at high speed and high load, and the like. Ts is a voltage correction coefficient added according to the battery voltage so as to compensate for the invalid time of the fuel injection valve 14.

Α is a feedback correction coefficient calculated mainly based on the detection signal of the upstream O ₂ sensor 18. That is, the output signal of the upstream O ₂ sensor 18 is compared with a predetermined slice level (corresponding to the stoichiometric air-fuel ratio), and a value obtained by pseudo proportional integral control based on the inversion to the lean side and the rich side. If the value is 1 or more, the air-fuel ratio is controlled to the rich side, and if it is 1 or less, the air-fuel ratio is controlled to the lean side.

Of FIG. 4 (a) shows an example of an output signal of the upstream O ₂ sensor 18, shows (b) the change of the feedback correction coefficient α corresponding thereto. The feedback correction coefficient α is obtained by pseudo proportional integration control as described above, and when the output of the upstream O ₂ sensor 18 crosses a predetermined slice level S / L and reverses from the rich side to the lean side, , correction coefficient α is subject to constant proportional portion P _L, and the integral component with a slope by a predetermined integral constant I _L is gradually being added gradually. Since the feedback correction coefficient α is multiplied by the basic fuel injection amount Tp as described above, the actual air-fuel ratio gradually increases. Then, when the output of the upstream O ₂ sensor 18 reverses from the lean side to the rich side, the correction coefficient α
Constant proportional amount P _R is subtracted from, and a predetermined integral constant I _R
The integral is gradually subtracted by the inclination according to. By repeating such an operation, the actual air-fuel ratio becomes 1-2 Hz.
The air-fuel ratio is maintained in the vicinity of the stoichiometric air-fuel ratio while changing with a cycle of about.

Note that the feedback correction coefficient α is cranked to 1 during non-feedback control conditions such as low water temperature, high-speed high load, or fuel cut during deceleration, in which it is necessary to perform some kind of fuel increase. Becomes

Meanwhile, in such conventional air-fuel ratio feedback control, the output signal of the downstream O ₂ sensor 19, the upstream O ₂ sensor
Used for learning correction of the overall bias of feedback control by 18.

That is, as a result of the feedback control by the upstream O ₂ sensor 18, if the actual air-fuel ratio changes periodically around the stoichiometric air-fuel ratio, the output signal of the downstream O ₂ sensor 19 gradually reverses rich and lean. Repeated form, but upstream
If the air-fuel ratio as a whole tends to be rich due to aging of the O ₂ sensor 18 or the like, the output signal of the downstream O ₂ sensor 19 becomes continuous on the rich side. Further, if the lean tendency as a whole air-fuel ratio, the output signal of the downstream O ₂ sensor 19 become continuous with the lean side. Therefore, in accordance with the overall bias tendency of the air-fuel ratio, the learning value P _HOS
The advance allocation, rich → a proportional amount P _R lean when reversing proportional portion P _L and lean → rich inversion time, it is to correct as _{P L = P L + P HOS} P R = P R -P HOS respectively. More specifically, the operating region is divided into a plurality of (n) sections by using the engine speed N and the load (for example, the basic fuel injection amount Tp) as parameters, and learning P _{HOS1 to} P _HOSn corresponding to each section are _provided by the on-board battery. And stored in a readable and writable memory that is backed up.
Then, a value corresponding to the operating condition at that time among the learning values is read out, thereby obtaining the proportional component as described above.
The correction of P _L and P _R is performed.

Incidentally, the proportional component P _L, P instead of _R, or integral constant I _L In addition to this, it is also possible to correct the I _R.

Then, the learning value P _HOS is corrected and updated when the engine operating condition has been within each section of the operating region for a certain period. That is, if the output signal is still rich side of the downstream O ₂ sensor 19, subtracts the predetermined amount [Delta] P _HOS from the learned value P _HOS, updates the stored contents as a new learning value P _HOS. Similarly, if the output signal of the downstream O ₂ sensor 19 is still on the lean side, a predetermined amount ΔP _HOS is added to the learning value P _HOS ,
The stored content is updated as a new learning value P _HOS .

Therefore, the deviation of the overall air-fuel ratio due to the aging of the upstream O ₂ sensor 18 and the individual difference of each part is corrected with higher accuracy and responsiveness, and the feedback correction coefficient α becomes α = 1.
At the center.

Further, during the execution of the air-fuel ratio feedback control as described above, the secondary air is not introduced in order to effectively exert the oxidizing and reducing actions in the catalytic converter 17. On the other hand, when the engine is idling, the secondary air control valve 22 is turned on to promote oxidation of exhaust components,
Next air is introduced. Then, in this case, the air-fuel ratio feedback control by the upstream O ₂ sensor 18 described above is stopped, the air-fuel ratio feedback control by the downstream O ₂ sensor 19 is executed in place of this.

Next, the feedback control during idling will be described with reference to the flowchart in FIG.

The routine shown in FIG. 3 is repeatedly executed at a predetermined time or every predetermined crank angle. First, at step 1, it is determined whether or not the engine is in an idle state. This is determined, for example, from the opening of the throttle valve 15 and the vehicle speed. If it is determined that the vehicle is in the non-idle state, the secondary air control valve 22
Is turned off (step 11), secondary air introduction is stopped, and the flag FIFBE is set to 0 (step 12). Then, the normal air-fuel ratio feedback control described above is executed (step 13).

On the other hand, if it is determined in step 1 that the vehicle is in the idle state, the process proceeds to step 2 where the flag FIFBE is determined. Immediately after shifting to the idle state, FIFBE = 0, so that the process proceeds from step 2 to step 7, where the feedback correction coefficient α
It is determined whether the calculation of the proportional integral control has been performed for four cycles. Until the four cycles are completed, the feedback control up to that time is continued (steps 11 to 13).

After the above-described calculation of the proportional integration control is performed for four cycles, the process proceeds from step 7 to step 8 to obtain an initial value of the feedback correction coefficient α during idling. More specifically, as shown in FIG. 5, eight peak values α _{1 to} α ₈ in four periods of the feedback correction coefficient α are stored, an average value α _M of the peak values is obtained, and the engine cooling value is calculated. The correction amount α _IDL based on the water temperature is added to be the initial value of the correction coefficient α. Therefore, the correction coefficient α immediately after the shift to the idle state reflects the influence of the learning up to that point and the effect of the engine cooling water temperature,
There is no sudden change in the air-fuel ratio or instability of the engine. At this point, the normal feedback control using the upstream O ₂ sensor 18 is stopped, and the downstream O ₂ sensor
The learning correction by 19 is also stopped.

Then, the secondary air control valve 22 is turned ON to start the introduction of the secondary air (step 9). At the same time, the flag FIFBE is set to 1
(Step 10).

Thus, thereafter proceeds from step 2 to step 3 and subsequent, the feedback control using the downstream O ₂ sensor 19 is started. This is because the output VRO ₂ of the downstream O ₂ sensor 19 is within a predetermined range (ISLL to
Feedback correction coefficient α so as to focus within ISLH).
In step 3, a downstream O ₂ sensor 19 is added.
The output VRO ₂ compared with the lower limit value ISLL, if VRO ₂ <ISLL, by adding a predetermined amount I ₀ and alpha new feedback correction coefficient alpha (Step 6). That is, the correction is performed so that the air-fuel ratio goes to the rich side. Also compared with the upper limit ISLH in step, if ISLH ≦ VRO _2, by subtracting a predetermined amount I ₀ from alpha as a new feedback correction coefficient alpha (Step 5). That is, the correction is performed so that the air-fuel ratio moves toward the lean side. If VRO ₂ is in the range of ISLL to ISLH, the feedback correction coefficient α is kept at the same value.

As a result, the feedback correction coefficient α gradually changes as shown in FIG.
The output of the downstream O ₂ sensor 19 in the 17 downstream air-fuel ratio is maintained to be the stoichiometric air-fuel ratio corresponding. In particular, since the average value of the feedback correction coefficient α calculated before the start of the secondary air introduction is given as the initial value of the feedback correction coefficient α as described above, when the control is shifted to the feedback control by the downstream O ₂ sensor 19, Then, appropriate control can be started immediately.

Therefore, accumulation of excess oxygen in the catalytic converter 17 is prevented while sufficiently maintaining the exhaust gas purification performance by the secondary air. Therefore, as shown in FIG. 7, when the vehicle starts from the idle state and shifts to the normal feedback control, the oxygen released from the catalytic converter 17 is not affected by the downstream O ₂ sensor 19, and , The appropriate learning value P _HOS is calculated. That is, there is no risk of erroneous learning due to the release of oxygen accumulated in the catalytic converter 17, and deterioration of the convergence of the air-fuel ratio and deterioration of the exhaust performance immediately after starting are prevented (FIGS. 7 (d) and (d)). E)).

Effects of the Invention As is apparent from the above description, according to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, the output of the downstream air-fuel ratio sensor is changed to the stoichiometric air-fuel ratio when the engine is idling where the introduction of the secondary air is performed. Since the feedback control of the air-fuel ratio is performed so as to be considerable, excess oxygen is not accumulated in the catalytic converter, and it is possible to prevent the downstream air-fuel ratio sensor from being adversely affected immediately after shifting to the non-idle state. Therefore, erroneous learning based on the output of the downstream air-fuel ratio sensor is prevented, and problems such as deterioration of convergence and temporary deterioration of exhaust performance do not occur. In particular, by setting the average value of the feedback correction coefficient calculated based on the output of the upstream air-fuel ratio sensor having a good response to the exhaust composition as the initial value of the feedback correction coefficient after the start of the secondary air introduction, When the process shifts to the feedback control by the downstream air-fuel ratio sensor having low response to the change of the composition, the fuel injection amount control by the appropriate feedback correction coefficient can be started immediately.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of an air-fuel ratio control device according to the present invention, FIG. 2 is a configuration explanatory diagram showing one embodiment of an air-fuel ratio control device according to the present invention, and FIG. FIG. 4 is a flowchart showing a main part of the control, and FIG. 4 is a waveform diagram showing an output signal of an upstream O ₂ sensor and a feedback correction coefficient in normal feedback control,
FIG. 5 is an explanatory diagram showing a feedback correction coefficient immediately after shifting to idle, FIG. 6 is a waveform diagram showing the output signal of the downstream O ₂ sensor and the feedback correction coefficient in feedback control during idling, and FIG. is an explanatory view showing a comparison of the change in the output signal and the learned value of the downstream O ₂ sensor as the conventional. 1 ... upstream air-fuel ratio sensor, 2 ... downstream air-fuel ratio sensor, 3 ... basic fuel injection amount setting means, 4 ... normal time correction coefficient setting means, 5 ... learning correction means, 6 ... secondary Air control means, 7: Idle-time correction coefficient setting means, 8: Fuel injection amount correction means, 9: Idle determination means, 10: Correction coefficient average value calculation means.

Claims (1)

(57) [Claims] An upstream air-fuel ratio sensor disposed upstream of a catalytic converter interposed in an exhaust passage and having a characteristic in which the output changes abruptly at a stoichiometric air-fuel ratio; A downstream air-fuel ratio sensor disposed downstream of the catalytic converter, a basic fuel injection amount setting means for setting a basic fuel injection amount according to operating conditions of the internal combustion engine, Idle determination means for detecting an idle state of the engine; normal correction coefficient setting means for setting a feedback correction coefficient based on an output of an upstream air-fuel ratio sensor when a predetermined feedback control condition is satisfied; Learning correction means for learning and correcting the feedback correction coefficient based on the output of the downstream air-fuel ratio sensor; and And a correction coefficient average value calculating means for calculating an average value of the feedback correction coefficient based on the output of the upstream air-fuel ratio sensor, and introducing secondary air into the exhaust passage after calculating the average value. Means for performing secondary air control, and after starting the introduction of the secondary air, based on the output of the downstream air-fuel ratio sensor using the above average value as an initial value, feedback so that the output of the downstream air-fuel ratio sensor becomes equivalent to the stoichiometric air-fuel ratio. An air-fuel ratio control apparatus for an internal combustion engine, comprising: an idle time correction coefficient setting means for setting a correction coefficient; and a fuel injection amount correction means for correcting the basic fuel injection amount using the feedback correction coefficient.