JPH06146964A - Air/fuel ratio controlling device of engine - Google Patents

Abstract

PURPOSE:To prevent unnecessary fuel quantity increasing and misfire by prohibiting feedback control for a long time while the larger is a difference between objective values for air/fuel ratio before and after switching in switching the objective values for ail/fuel ratios in consideration of the long delay of response a linear O2 (air/fuel ratio) sensor in changing in air/fuel ratios. CONSTITUTION:In the case where based on the output of a linear O2 sensor 11, air fuel ratio feedback control is made to perform, when it is judged that a running range in previous controlling corresponds to fuel supply stopping range, air/fuel ratio control in transition is carried out. In this control, an objective air/fuel ratio in the feedback control range shifted from the current fuel supply stopping range is firstly set, and then, the response delay time T1 of the linear O2 sensor 11 corresponding to this objective air/fuel ratio is determined from a map. This map is set such that the smaller is an objective air/fuel ratio (in the richer side), the longer the response delay time T1 becomes so as to prohibit feedback control for a specified time based on the response delay time T1 determined from this map.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio control device using an air-fuel ratio sensor such as a linear O ₂ sensor which produces an output substantially proportional to the air-fuel ratio.

[0002]

2. Description of the Related Art In an engine for an automobile or the like, an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber is appropriately controlled in order to improve fuel efficiency. In this air-fuel ratio control, the residual oxygen concentration in the exhaust gas is detected by an O ₂ sensor installed in the exhaust passage, and the fuel supply amount is feedback-controlled according to the concentration, so that the air-fuel ratio is, for example, the theoretical air-fuel ratio. A / F (air / fuel) = 14.7 is made to converge, and in that case, the above O
_{As the 2} sensor, an output inversion type sensor whose output is turned on and off depending on whether the air-fuel ratio is richer (fuel excess state) or leaner (air excess state) than the theoretical air-fuel ratio is generally used.

On the other hand, in recent years, lean-burn type engines are being put to practical use in order to further improve fuel efficiency. In this lean burn engine, the target value of the air-fuel ratio control is set to a different value depending on the operating region, and in a specific operating region, the target value is considerably leaner than the theoretical air-fuel ratio (for example, A / F = 22.0)
Is adopted. Therefore, in controlling the air-fuel ratio of such an engine, a linear air-fuel ratio sensor that generates an output substantially proportional to the air-fuel ratio is required as the air-fuel ratio sensor, instead of the output inversion type O ₂ sensor as described above. For example, according to Japanese Patent Laid-Open No. 64-60746, a linear O
An air-fuel ratio control device using _two sensors is disclosed.

[0004]

By the way, when the feedback control of the air-fuel ratio is performed in a predetermined operating region by using the linear O ₂ sensor as described above, the fuel supply is stopped particularly in the deceleration region. In the engine, when transitioning from this fuel stop region to the feedback control region,
The following problems may occur.

That is, in the fuel stop region, air is only discharged from the combustion chamber to the exhaust passage, so the linear O ₂ sensor installed in the exhaust passage detects the over-lean state and outputs its output value. Is the maximum value. Then, when the fuel supply is restarted from this state and the feedback control of the air-fuel ratio is started, first, the fuel supplied to the combustion chamber is burned, and the exhaust gas generated at that time is exhausted. with dead time constant to reach to the installation position of the linear O ₂ sensor has passed in until the linear O ₂ sensor detects the residual oxygen concentration in the exhaust gas, it generates an output proportional to the concentration In addition, the response delay time of the sensor itself elapses. Therefore, when performing feedback control of the fuel supply amount according to the sensor output, the sensor output initially has the maximum value as described above, and therefore, the fuel is tried to be converged to the target value by trying to converge the air-fuel ratio to the target value. Will be controlled to supply a large amount. Then, the fuel supply is drastically reduced in an attempt to eliminate the overrich condition due to the large supply, and as a result, the air-fuel ratio hunts, and the transition to the feedback control is not performed well.

To solve this problem, the feedback control is temporarily prohibited from starting at the time of shifting from the fuel stop region to the feedback control region, and during that time, the fuel is supplied by a constant amount calculated from the target air-fuel ratio. It is conceivable that the open loop control is performed and the feedback control is started at the time when the air-fuel ratio becomes almost the target value by the open loop control. However, even in this case, how to set the inhibition time of the feedback control becomes a problem, and if this is not appropriate, the following problem further occurs.

First, when the prohibition time is relatively short with respect to the dead time at the start of the feedback control, the response delay time of the sensor, etc., the actual air-fuel ratio is substantially controlled by the open loop control during the feedback prohibition period. Despite the fuel ratio, the sensor output has not sufficiently decreased from the maximum value when the fuel supply was stopped, and the feedback control is started in the state where the value indicating the lean state is output. . Therefore, the fuel is supplied more than necessary immediately after the start of the feedback control, causing hunting of the air-fuel ratio or deteriorating the fuel efficiency as in the case described above. Immediately after the fuel supply is restarted, problems such as misfire due to excessive fuel supply occur.

Further, if the prohibition time becomes longer than necessary, the start of the fine control of the air-fuel ratio by the feedback control will be delayed by that much, and the improvement of fuel efficiency during that time will be impeded.

This problem is not limited to the above-mentioned transition from the fuel stop region to the air-fuel ratio feedback control, but also during the transition from the air-fuel ratio open loop control region to the feedback control region. In a lean burn system engine, the same occurs when the target value of the feedback control of the air-fuel ratio is significantly changed.

Therefore, the present invention focuses on that the response delay time of a linear air-fuel ratio sensor such as a linear O ₂ sensor which produces an output substantially proportional to the air-fuel ratio changes according to a constant characteristic. The feedback control is always started at the optimum time point during transition such as transition from the fuel stop region to the feedback control region by using The challenge is to keep the fuel running smoothly while avoiding unnecessary fuel supply and misfire.

[0011]

In order to solve the above problems, the present invention is characterized in that it is configured as follows.

First, the invention according to claim 1 of the present application (hereinafter,
(First invention) uses a linear air-fuel ratio sensor that generates an output that is substantially proportional to the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber, and is configured to perform feedback control of the air-fuel ratio to a target value in a predetermined operating region. In this engine, the feedback control is temporarily performed when the target air-fuel ratio is switched at the time of transition from the region other than the feedback control region to the feedback control region, or when the target air-fuel ratio is switched in the feedback control region. And a feedback prohibiting means for switching the prohibition time and increasing the difference as the difference between the front and rear target air-fuel ratios increases.

Further, in the invention according to claim 2 (hereinafter referred to as the second invention), similar to the first invention, the linear air-fuel ratio sensor is used to perform feedback control of the air-fuel ratio in a predetermined operation region, and In an engine configured to stop the fuel supply to the combustion chamber in an operating region other than this feedback control region, at the time of transition from the fuel stop region to the feedback control region, the target air-fuel ratio in this feedback control region Is characterized by providing feedback prohibiting means for prohibiting the feedback control for a longer time.

The invention according to claim 3 (hereinafter, referred to as the third
According to the invention), a linear O ₂ sensor that generates a voltage proportional to the oxygen concentration in the exhaust gas is used as the linear air-fuel ratio sensor in the first and second inventions.

[0015]

According to the above construction, in the case of the first aspect of the invention, when the target air-fuel ratio is switched at the time of transition from a region other than the air-fuel ratio feedback control region to the feedback control region, or within the feedback control region. At the time of switching of the target air-fuel ratio at, and according to the second invention, at the time of shifting from the fuel stop region to the feedback control region,
In either case, the feedback control is temporarily prohibited, but the prohibition time is set to be longer as the difference between the values before and after the switching of the target air-fuel ratio is larger in the first invention. In the second aspect of the invention, the richer the target air-fuel ratio in the feedback control region, the longer the time.

That is, in the case of a linear air-fuel ratio sensor such as a linear O ₂ sensor which produces an output substantially proportional to the air-fuel ratio,
There is a characteristic that the response delay time when the air-fuel ratio to be detected changes is longer as the difference between the air-fuel ratio before the change and the air-fuel ratio after the change becomes larger. Therefore, in the first invention, the target air-fuel ratio is When switching, the larger the difference between the target air-fuel ratios before and after the switching, the longer the feedback control is prohibited, and the air-fuel ratio before switching is infinite and the sensor output reaches the maximum value. In the case of the second invention, the richer the target air-fuel ratio after switching is, the longer the feedback control is prohibited.

As a result, in either of the first and second aspects of the invention, the target air-fuel ratio after the air-fuel ratio is substantially switched by the open-loop control during the feedback control prohibition period becomes the target air-fuel ratio, and the linear air-fuel ratio sensor accordingly. The feedback control will be started from the time when the output value of is almost the value corresponding to the target air-fuel ratio, and the feedback control is performed in a state where the output of the linear air-fuel ratio sensor does not correspond to the actual air-fuel ratio. It is avoided that the feedback control is started for a longer time than necessary or the feedback control is prohibited.

[0018]

EXAMPLES Examples of the present invention will be described below.

As shown in FIG. 1, an engine 1 according to this embodiment has an intake passage 5 and an exhaust passage 6 which communicate with a combustion chamber 4 via intake and exhaust valves 2 and 3, respectively. And
In the intake passage 5, an air cleaner 7, an air flow meter 8, a throttle valve 9 and a fuel injection valve 10 are installed from the upstream side, and in the exhaust passage 6, from the upstream side,
A linear O ₂ sensor 11 and a catalytic converter 12 are installed. The linear O ₂ sensor 11 detects the residual oxygen concentration in the exhaust gas and generates an output voltage proportional to the concentration.

Further, the engine 1 has a control unit 20, and the unit 20 has a throttle opening sensor 21 for detecting an air flow rate signal from the air flow meter 8 and an opening of the throttle valve 9. A signal, an air-fuel ratio signal from the linear O ₂ sensor 11, an engine speed signal from a speed sensor 22 for detecting the engine speed, and other signals are input. And this control unit 20
Based on each of the above signals, an injection signal is output to the fuel injection valve 10 so that a predetermined fuel injection amount or an air-fuel ratio is obtained according to a preset operating region.

Here, in this embodiment, as shown in FIG. 2, the feedback control with the theoretical air-fuel ratio of 14.7 as the target value is performed in the idle region of the low throttle opening and the low engine speed, and the low control is performed. The fuel supply stop control is performed in the region where the throttle opening is equal to or higher than the predetermined engine speed, and the target value of the air-fuel ratio is set to 2 in the region where the middle throttle opening is wide.
The lean burn feedback control of 2.0 is performed, and the theoretical air-fuel ratio is 14.
Feedback control with a target value of 7 is performed, and further, open-loop control of the air-fuel ratio with a target value of 13.0 is performed in the regions of high throttle opening and high engine speed.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. 3 showing the operation of the control unit 20.

First, in steps S1 and S2, the control unit 20 determines which of the regions shown in FIG. 2 the current operating region belongs to based on the throttle opening signal and the engine speed signal.

Then, when it belongs to the open loop control region on the high throttle opening side and the high engine speed side, step S3 is executed to calculate the fuel injection amount at which the air-fuel ratio becomes 13.0, and the injection amount An injection signal is output to the fuel control valve 10 so that the fuel is injected at. Further, when the low throttle opening degree belongs to the fuel stop region equal to or higher than the predetermined engine speed, an injection signal is output to the fuel control valve 10 so as to stop the fuel supply in step S4.

Further, if the current operating region does not belong to the open loop control region or the fuel stop region, in other words, if it belongs to the feedback control region shown by hatching in FIG. 2, in step S5. It is determined whether or not the operation area at the time of the previous control was the fuel stop area.
Then, if it is not in this fuel stop region, feedback control is executed in step S6.

This feedback control is performed based on the output voltage of the linear O ₂ sensor 11, and when the output voltage is larger than the value corresponding to the target air-fuel ratio (14.7 or 22.0), that is, the actual value. When the air-fuel ratio is leaner than the target air-fuel ratio, an injection signal is output to the fuel injection valve 10 so as to increase the fuel injection amount, and when the output voltage is smaller than the value corresponding to the target air-fuel ratio. That is, when the actual air-fuel ratio is richer than the target air-fuel ratio, an injection signal is output to the fuel injection valve 10 so as to reduce the fuel injection amount. As a result, the air-fuel ratio of the air-fuel mixture actually supplied to the combustion chamber converges to the target air-fuel ratio.

On the other hand, when it is determined in step S5 that the operating region during the previous control was the fuel stop region, that is, when the control time this time is immediately after the transition from the fuel stop region to the feedback control region. The control unit 20 executes the air-fuel ratio control during the transition from step S7 onward.

In this control, first, step S7
Then, the target air-fuel ratio (14.7 or 22.0) is set in the feedback control region that has shifted from the fuel stop region this time, and then in step S8, the response delay of the linear O ₂ sensor 11 corresponding to this target air-fuel ratio is set. The time T1 is calculated from the map shown in FIG. In this map, the smaller the target air-fuel ratio (the richer the side), the longer the response delay time T1 of the linear O ₂ sensor 11 is set.
This is because the linear O ₂ sensor 11 detects the leanest state when the operating region belongs to the fuel stop region, so the target air-fuel ratio at the time of shifting to the feedback control region is on the rich side. This is because the change width of the air-fuel ratio to be detected is larger, and therefore the response delay time until the output voltage corresponding to the air-fuel ratio is generated becomes longer.

Now, assuming that the fuel control region has moved to the feedback control region where the target air-fuel ratio is 14.7, as indicated by the arrow x in FIG. 2, the linear O ₂ sensor 11 is determined from the map of FIG. Response delay time T1 is t1
If the target air-fuel ratio shifts to the feedback control region where the target air-fuel ratio is 22.0 as indicated by the arrow y in FIG. 2, the response delay time T1 is set to t2.

Next, in step S9, the control unit 20 determines that the sensor response delay time T1 obtained as described above and the exhaust gas is linear O after the fuel supply is started.
₂ Dead time T until reaching the installation position of the sensor 11
0 (constant value) is added to obtain the inhibition time T of the feedback control, and this inhibition time T is set in the feedback inhibition timer in step S10.

Then, in step S11, it is determined whether or not the time T has elapsed. Until the time T has elapsed, feedback control is prohibited in step S12, and
In step S13, fuel is supplied by open loop control. In this case, in this open loop control, the fuel injection amount corresponding to the target air-fuel ratio in the feedback control region is calculated, and the injection signal is output to the fuel control valve 11 so that the calculated injection amount is obtained. During this time,
The output signal from the linear O ₂ sensor 11 is ignored.

On the other hand, if it is determined in step S11 that the feedback control inhibition time T has elapsed, the control unit 20 executes step S14 to start feedback control, and thereafter, step S6.
Then, the feedback control is executed based on the output signal from the linear O ₂ sensor 11.

As described above, the feedback control is prohibited for the predetermined prohibition time T during the transition from the fuel stop region to the feedback control region, and the fuel is supplied by the open loop control during that period. Of the prohibited time T, the dead time T0 is the time required for the exhaust gas to actually reach the installation position of the linear O ₂ sensor 11 after the fuel supply is restarted, and the sensor response delay time T1 is When the air-fuel ratio detected by the linear O ₂ sensor 11 changes, this is the time required from that change until the sensor 11 actually generates an output voltage corresponding to the changed air-fuel ratio. As shown in, when the fuel stop region is shifted to the feedback control region where the target air-fuel ratio is 14.7, the fuel supply by the open loop control is performed. After the start, when the prohibition time T has elapsed, the output of the linear O ₂ sensor 11 is generating an output voltage substantially corresponding to the target air-fuel ratio of 14.7. Therefore, by starting the feedback control based on the output signal of the linear O ₂ sensor 11 from this time point, it is possible to smoothly shift to the feedback control without causing control failure such as hunting.

In particular, the sensor response delay time T1
Is set such that when the air-fuel ratio to be detected changes based on the characteristics of the linear O ₂ sensor, the larger the change width, the longer the target air-fuel ratio becomes. When moving to the 0 area, the above 1
It is set to t2 which is shorter than the time t1 at the time of shifting to the region of 4.7. Therefore, as shown by the chain line in FIG. 5, in this case as well, from the time when the sensor output becomes a value substantially corresponding to the target air-fuel ratio. Feedback control will be started.

The above-described structure is used not only in the transition from the fuel stop region to the feedback control region as described above but also in the feedback control region where the target air-fuel ratio is, for example, 22.0 to 14.7. The same applies when the target air-fuel ratio changes, such as when the target air-fuel ratio changes, such as when the target air-fuel ratio changes from the open loop control region to the feedback control region. .

[0036]

As described above, according to the present invention, the linear O
_{(2) When} controlling the engine air-fuel ratio using a linear air-fuel ratio sensor that produces an output that is almost proportional to the air-fuel ratio of the sensor, etc., the response delay time of the sensor when the air-fuel ratio changes Focusing on the characteristic that the longer the difference between the fuel ratio and the changed air-fuel ratio, the longer it becomes, and when the target value of the air-fuel ratio switches, the longer the feedback control, the longer the difference between the target value before and after the switching. Since it is prohibited, the target air-fuel ratio after the output of the sensor is switched at the time of transition from the fuel stop region or open loop control region to the feedback control region, or when the target value of feedback control is switched. The feedback control is started at the time when the value almost corresponds to.

Thus, the feedback control is prohibited for a long time without sacrificing the improvement of the fuel consumption.
When there is no unnecessary increase or misfire of fuel due to starting feedback control in a state where the output value of the linear air-fuel ratio sensor does not correspond to the actual air-fuel ratio, or hunting of the air-fuel ratio, etc. The air-fuel ratio control will always be smoothly performed.

[Brief description of drawings]

FIG. 1 is an air-fuel ratio control system diagram of an engine to which an embodiment of the present invention is applied.

FIG. 2 is a map of an air-fuel ratio control area.

FIG. 3 is a flowchart showing an operation of air-fuel ratio control when shifting from a fuel stop region to a feedback control region.

FIG. 4 is a graph showing a relationship between a target air-fuel ratio and a response delay time.

FIG. 5 is a time chart showing a relationship between a change in sensor output and a control switching timing during a transition.

[Explanation of symbols]

11 Linear air-fuel ratio sensor (linear O ₂ sensor) 20 Feedback prohibiting means (control unit)

Claims (3)

[Claims] 1. A linear air-fuel ratio sensor that produces an output that is substantially proportional to the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is used.
An air-fuel ratio control device for an engine adapted to feedback control the air-fuel ratio to a target value in a predetermined operating region, wherein the target air-fuel ratio is switched during transition from a region other than the feedback control region to the feedback control region. At the time of switching, or when switching the target air-fuel ratio in the feedback control area, feedback control is temporarily prohibited, and a feedback prohibition means that switches the prohibition time and makes it longer as the difference between the target air-fuel ratio before and after is switched is increased. An air-fuel ratio control device for an engine, which is provided. 2. A linear air-fuel ratio sensor that produces an output substantially proportional to the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is used.
An air-fuel ratio control device for an engine configured to perform feedback control of the air-fuel ratio to a target value in a predetermined operation region and stop fuel supply to a combustion chamber in an operation region other than this feedback control region. An air-fuel ratio control of an engine, which is provided with a feedback prohibiting means for prohibiting the feedback control for a longer time when the target air-fuel ratio in the feedback control region is richer when the fuel stop region is shifted to the feedback control region. apparatus. 3. The engine air-fuel ratio control device according to claim 1, wherein the linear air-fuel ratio sensor is a linear O ₂ sensor that generates an output voltage proportional to the oxygen concentration in the exhaust gas.