JP3603490B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a technology for performing feedback control of an air-fuel ratio of an internal combustion engine, and more particularly to a technology for changing a target output when an output of an air-fuel ratio sensor provided in an exhaust passage has a predetermined target value. .
[0002]
[Prior art]
Conventionally, in an internal combustion engine for a vehicle, feedback control of the air-fuel ratio is performed based on the output of an air-fuel ratio sensor, but the air-fuel ratio corresponding to the air-fuel ratio target value is changed due to a change in the operating state of the engine and other reasons. In some cases, the target output of the sensor is changed.
[0003]
For example, after the engine is started, whether or not the air-fuel ratio sensor has been activated is determined by determining whether the output of the air-fuel ratio sensor is different from the first predetermined value corresponding to the target air-fuel ratio at the time of air-fuel ratio feedback after engine warm-up. In such a case, when it is confirmed that the air-fuel ratio sensor has been activated and the air-fuel ratio feedback control is started, the target output of the sensor becomes , From the second predetermined value to the first predetermined value.
[0004]
In order to follow the change in the target output, the air-fuel ratio feedback amount increases in the direction in which the target output changes as compared with the case where the target output is not changed. For example, when the target output is changed to the lean side, feedback is performed so that the actual air-fuel ratio is also corrected to the lean side, so that the amount of the feedback amount in the lean direction is increased.
[0005]
In a situation where the response of the air-fuel ratio sensor is low, such as at low temperatures, feedback overcorrection is likely to occur, and when the target output is changed as described above, the overcorrection increases as the feedback correction amount increases. Would.
Various devices have been proposed to prevent overcorrection of the response of the air-fuel ratio sensor.
[0006]
As one of such measures, for example, there is a technique disclosed in JP-A-61-232348. In this example, if the air-fuel ratio feedback cycle becomes longer due to a decrease in air-fuel ratio sensor response or other reasons, the feedback gain is reduced to reduce feedback overcorrection.
[0007]
[Problems to be solved by the invention]
However, in these conventional methods, although the response of the air-fuel ratio sensor is detected by some method, and the feedback gain is reduced in accordance with the response reduction margin, the above-described method in which the target output of the air-fuel ratio sensor changes is used. In such a case, the required amount of feedback gain reduction varies depending on the variation width of the target output.However, in order to calculate the required amount of feedback gain reduction, the conventional contrivance requires an empty space as described above. Since the response of the fuel ratio sensor has to be detected by some method, when the target output changes, the required reduction margin of the feedback gain cannot be calculated.
[0008]
Therefore, in order to prevent the air-fuel ratio feedback overcorrection, the feedback gain must be reduced with a margin, and consequently, the correction speed for the disturbance of the air-fuel ratio is reduced, and the control accuracy of the air-fuel ratio is reduced. Lower it. Alternatively, if an attempt is made to reduce the feedback gain without making it too small, the rate of change of the target output must be suppressed, and the period during which the air-fuel ratio is rich or lean from the target will be prolonged. . In such a case, the air-fuel ratio deviates from an appropriate value due to a decrease in the correction speed of the air-fuel ratio or a deviation of the target air-fuel ratio, which may be undesirable in terms of engine operability and exhaust emission. .
[0009]
The present invention has been made in view of such a conventional problem, and by changing the target output at an appropriate speed according to the response of the air-fuel ratio sensor, it is possible to suppress a large deviation in the air-fuel ratio and improve the output. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine in which air-fuel ratio feedback control is performed.
[0010]
[Means for Solving the Problems]
Therefore, the invention according to claim 1 is, as shown in FIG.
An air-fuel ratio sensor that detects an air-fuel ratio of an air-fuel mixture supplied to the engine in response to a specific component in the exhaust;
Air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio so that the output of the air-fuel ratio sensor becomes the target output,
Target output changing means for changing a target output of the air-fuel ratio sensor,
In an air-fuel ratio control device for an internal combustion engine including
Response measurement means for measuring the response of the air-fuel ratio sensor,
Target output change speed setting means for setting a change speed of a target output of the air-fuel ratio sensor according to the measured response of the air-fuel ratio sensor,
And when the target output is changed, the target output is changed at the set change speed.
[0011]
(Action / Effect)
The air-fuel ratio feedback control is performed so that the output of the air-fuel ratio sensor becomes the target output. When the target output is changed, the response of the air-fuel ratio sensor is measured, and the target output is changed at a change speed set in accordance with the response. To change.
Thereby, when the response of the air-fuel ratio sensor is slow, the over-correction of the air-fuel ratio feedback control is prevented by slowing down the change speed of the target output in accordance with this, and when the response of the air-fuel ratio sensor is fast, By accelerating the change speed of the target output, it is possible to quickly converge on the final target output, so that appropriate air-fuel ratio feedback control can always be performed, and exhaust purification performance can be improved.
[0015]
The invention according to claim 4 is
The target output changing means sets a final target output, and ends the change of the target output when the target output changed at the set change speed reaches the final target output. I do.
(Action / Effect)
For example, when changing from the target output for activation determination to the target output for target air-fuel ratio determination, the final target output for target air-fuel ratio determination is set, and the change speed set in accordance with the response of the air-fuel ratio sensor. When the target output to be changed reaches the final target output, further changes are prohibited. This makes it possible to easily and reliably change the target output.
[0016]
The invention according to claim 5 is
The response measuring means measures the response by the time from when the output of the air-fuel ratio sensor crosses the previous target output to when it crosses the current target output after the start of the air-fuel ratio feedback control. I do.
(Action / Effect)
When the response of the air-fuel ratio sensor is relatively fast, after the output of the air-fuel ratio sensor once crosses the target output, the air-fuel ratio is controlled to be lean or rich so that the air-fuel ratio approaches the target output. If the time required to cross the output is short, and conversely, if the response of the air-fuel ratio sensor is slow, the time required to cross the target output once and cross again will be long. Can be measured.
[0017]
The invention according to claim 6 is
The response measuring means measures a response based on a time required until the output value of the air-fuel ratio sensor at the start of the air-fuel ratio feedback control changes to a set value shifted by a predetermined amount from the output value.
(Action / Effect)
The time required for the output value of the air-fuel ratio sensor to change from the output value at the start of the air-fuel ratio feedback control to a set value shifted by a predetermined amount from the output value is short when the response of the air-fuel ratio sensor is fast, and the response is slow. Since the time becomes longer, the response of the air-fuel ratio sensor can be measured by measuring this time.
[0018]
In addition, since the response can be measured within a short time, the target output can be changed at a change speed according to the response at each time.
The invention according to claim 7 is
The air-fuel ratio sensor detects stepwise whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio.
[0019]
(Action / Effect)
The present invention can be applied to air-fuel ratio feedback control using an air-fuel ratio sensor such as a so-called oxygen sensor that detects whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 2 showing a configuration of an embodiment, an intake passage 12 of an engine 11 is provided with an air flow meter 13 for detecting an intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with an accelerator pedal. An electromagnetic fuel injection valve 15 as fuel supply means is provided for each cylinder in the downstream manifold portion.
[0021]
The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 containing a microcomputer, and injects fuel supplied from a fuel pump (not shown) under pressure and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting a cooling water temperature Tw in a cooling jacket of the engine 11 is provided, and an air-fuel ratio sensor 19 for detecting an air-fuel ratio of an intake air-fuel mixture by detecting an oxygen concentration in exhaust gas in an exhaust passage 18. And a three-way catalyst 20 for oxidizing CO and HC in the exhaust gas on the downstream side and reducing NO _X to purify the exhaust gas.
[0022]
A distributor (not shown) has a built-in crank angle sensor 21 which counts a crank unit angle signal output from the crank angle sensor 21 in synchronization with the engine rotation for a certain period of time, or a crank reference angle signal. Is measured and the engine speed N is detected.
The calculation of the fuel injection amount from the fuel injection valve 15 may be controlled so as to be other than the stoichiometric air-fuel ratio depending on conditions such as the cooling water temperature. The final fuel injection amount is calculated by the following equation based on the product of the correction coefficient for calculating the fuel injection amount and the air-fuel ratio feedback correction coefficient α shown below.
[0023]
Ti = Tp × COEF × α
Here, Ti: final fuel injection amount Tp: basic fuel injection amount COEF: correction coefficient α: air-fuel ratio feedback correction coefficient Further, the air-fuel ratio learning value obtained by learning and storing the air-fuel ratio feedback correction coefficient α is added to the above equation. May be added.
[0024]
When the stoichiometric air-fuel ratio is to be controlled, the air-fuel ratio is feedback-corrected based on the output of the air-fuel ratio sensor 19 in order to more accurately control the stoichiometric air-fuel ratio.
The air-fuel ratio sensor 19, for example, what is called an oxygen sensor is used. As shown in FIG. 3, the oxygen sensor has a rich output (about 1 V) and a lean output (about 0) near the stoichiometric air-fuel ratio. Has the characteristic of rapidly reversing.
[0025]
The air-fuel ratio is determined by comparing the output of the air-fuel ratio sensor 19 (hereinafter referred to as VO2) with a target output SL (= SLN) corresponding to the stoichiometric air-fuel ratio. If VO2> SL, it is determined that the air-fuel ratio is rich, and VO2 <SL If so, it is determined to be lean.
When the air-fuel ratio sensor detects that the air-fuel ratio is rich, the fuel is reduced to make a lean correction, and when the air-fuel ratio is detected that the air-fuel ratio is lean, the fuel is increased to make a rich correction. Thus, the air-fuel ratio is corrected based on the output value of the air-fuel ratio sensor 19 on the upstream side of the catalyst 20.
[0026]
Further, after starting, in order to determine whether the air-fuel ratio sensor 19 has been activated, first, the output VO2 of the air-fuel ratio sensor is set to an activation determination output SL (set on the rich side from a value corresponding to the stoichiometric air-fuel ratio). = SL1H). When the output of the air-fuel ratio sensor 19 reaches the activation determination output SLH , it is determined that the air-fuel ratio sensor 19 has been activated. Thereafter, the target output is changed from SLH to the target output SL for stoichiometric air-fuel ratio determination. (= SLN), and the air-fuel ratio feedback control for bringing the air-fuel ratio close to the stoichiometric air-fuel ratio is started.
[0027]
When the target output of the air-fuel ratio sensor is changed in this way, the air-fuel ratio correction is extraly performed by the amount that the air-fuel ratio output follows the change. If the detection of the air-fuel ratio by the air-fuel ratio sensor is not delayed or the delay is small, this chasing does not matter much, but if the response of the air-fuel ratio sensor is slow, the chasing time due to this response delay is Therefore, the air-fuel ratio correction is largely overcorrected. Since the above-described oxygen sensor has a characteristic in which the rich output and the lean output ( approximately 0 ) are rapidly reversed near the stoichiometric air-fuel ratio , changing the target output does not affect the control. As can be seen, when the response of the air-fuel ratio sensor is low, if the target output changes, the change in the chase time until the target output increases, and therefore, by appropriately setting the target output change speed, overcorrection can be prevented.
[0028]
It is conceivable to reduce the amount of movement of the SL so that the output VO2 of the air-fuel ratio sensor does not take much time to catch up with the movement of the target output SL. It takes a lot of time to reach the final target output, and it is difficult to control the air-fuel ratio to an appropriate value, which affects the driving performance and the exhaust purification performance during that time.
[0029]
Therefore, in the present invention, while the response of the air-fuel ratio sensor is measured, the SL is changed at a change speed set in accordance with the response result, thereby overcorrecting the air-fuel ratio feedback when the response of the air-fuel ratio sensor is slow. And when the response of the air-fuel ratio sensor is fast, the convergence to the final target value is expedited so that appropriate air-fuel ratio feedback control is performed.
[0030]
Hereinafter, the air-fuel ratio control routine including the air-fuel ratio feedback control performed while changing the target output of the air-fuel ratio sensor by the control unit 16 will be described with reference to the flowcharts of FIGS.
In step (denoted by S in the figure) 1, it is determined whether or not the condition is such that air-fuel ratio feedback control is possible. Conditions under which the air-fuel ratio feedback control is not possible include when the air-fuel ratio sensor 19 is not activated, during so-called fuel cut control, when the operability of the engine is unstable, and the like. Is possible.
[0031]
If it is determined in step 1 that the condition is not such that the air-fuel ratio feedback control is possible, the process proceeds to step 13 to reset the value of the flag FLGFB to 0, and further proceeds to step 100 to set the air-fuel ratio feedback correction coefficient α to The air-fuel ratio feedback control is stopped by clamping to 100% (= 1), and the air-fuel ratio is feed-forward controlled.
[0032]
On the other hand, when it is determined in step 1 that the condition for the air-fuel ratio feedback control is possible, the process proceeds to step 2, and it is determined whether the air-fuel ratio sensor 19 has reached a state in which a sufficient output can be generated, that is, whether or not the air-fuel ratio sensor 19 has been activated. The determination is made by reading the value of the flag FLGFB.
If FLGFB = 0 in step 2, it is determined that the air-fuel ratio sensor 19 has not been in a state where a sufficient output can be generated, that is, it is in an inactive state, and the process proceeds to step 10. In steps 10 and 11, it is determined whether or not the output of the air-fuel ratio sensor 19 has become a sufficient value in this determination.
[0033]
That is, in step 10, the output SL1H for determining activation of the air-fuel ratio sensor 19 is set, and in step 11, it is determined whether or not the air-fuel ratio sensor has generated a sufficient output VO2 equal to or higher than SL1H.
If it is determined that the output VO2 of the air-fuel ratio sensor 19 is sufficient (VO2 ≧ SL1H), the process proceeds to step 12, the value of the flag FLGFB is set to 1, and the output VO2 is not sufficient ( If it is determined that VO2 <SL1H), the routine proceeds to step 13, where the value of the flag FLGFB is reset to 0. At this stage, since the air-fuel ratio feedback control has not been started yet, the process proceeds to step 100, where α = 100%, and the air-fuel ratio feedforward control is continued.
[0034]
As described above, immediately after the air-fuel ratio feedback control condition is satisfied and before the activation determination of the air-fuel ratio sensor 19 is performed, the process proceeds from step 2 to step 10, and the activation determination is always performed once, and the air-fuel ratio feedback control is performed. Will start.
In this way, when the air-fuel ratio sensor 19 is activated and it is determined that a sufficient output VO2 can be generated, it is determined in the next routine that the value of the flag FLGFB is 1 in the determination in step 2 and step The process proceeds to 3 and thereafter, and the air-fuel ratio feedback control is started.
[0035]
In step 3, the output VO2 of the air-fuel ratio sensor 19 is read. If rich, the process proceeds to step 4, and if lean, the process proceeds to step 5.
In step 4, the previous determination result is referred to. If the previous time is lean (that is, the current state has changed from lean to rich), the process proceeds to step 6, and if the previous time is also rich, the process proceeds to step 7.
[0036]
Immediately after it is determined that the output of the air-fuel ratio sensor 19 has been activated beyond the target value SL1H, this state continues and the air-fuel ratio rich determination state continues. The integral IR in the lean correction direction is subtracted from the correction coefficient α, and the process proceeds to step 42, where TTSL is integrated as the duration of the rich state.
[0037]
This accumulated time TTSL is the duration of the rich state when the flow of this figure is executed in time synchronization, and the continuous rotation number of the engine in the rich state when the flow is executed in synchronization with the rotation of the engine. Become.
Further, for example, this flow is executed in synchronization with the rotation of the engine, but if it is desired to measure the time for the rich continuation, the ΔT to be integrated in step 7 is the time measured by a time measuring means different from this flow. With reference to the time, the difference between the time when the previous step 42 was executed and the current time may be used.
[0038]
Similarly, when the process proceeds from step 5 to step 9, the air-fuel ratio continues to be lean, so that the lean continuation time is measured in step 9.
When the process proceeds to step 6, since the air-fuel ratio has changed from lean to rich, the proportional component P (PL when lean) is added, and in step 21, the integrated result of the TTSL so far, that is, the final lean continuation is performed. Referring to the time, this time is compared with the first reference time TTS.
[0039]
When it is determined that the lean continuation time TTSL is longer than the reference time TTS, if the change width of the SL per unit time, that is, the change speed is increased, the overshoot is concerned as described above. To reduce the SL change width DSL by DDSL.
Conversely, if it is determined that the lean continuation time TTSL is shorter than the reference time TTS, it is determined that the response of the air-fuel ratio sensor 19 has become faster, and the routine proceeds to step 23, where the change width DSL is increased by DDSL.
[0040]
If none of the above applies and it is determined that the lean duration time TTSL is substantially equal to the reference time TTS, the value of the change width DSL is maintained as it is.
Using the change width DSL appropriately corrected as described above, in step 25, a change is made to decrease SL by the amount of DSL, and the result is compared with the lower limit SLN in step 26. If so, in step 27, SL is fixed to the lower limit SLN.
[0041]
In step 41, DDSL = 0 is set to prepare for the subsequent measurement of the rich time. Similarly, when it is determined in step 5 that the air-fuel ratio has reversed from rich to lean, the process proceeds to step 8 and thereafter, while changing the change width DSL according to the rich continuation time TTSL, changing SL with DSL. After that, TTSL is set to 0 to prepare for the subsequent measurement of the lean time.
[0042]
As described above, in the present embodiment, the SL is changed at the change speed (change width) according to the response of the air-fuel ratio sensor 19, and when the response is slow, the change speed is reduced to prevent overcorrection. At the same time, when the response is fast, the change speed is increased and the SL is quickly changed to the stoichiometric air-fuel ratio, and good air-fuel ratio control accuracy can be obtained. In the present embodiment, an example in which the target output is changed to the final target output has been described.In addition, a configuration in which the change width of the target output is integrated and the change is performed until the integrated value reaches a predetermined value is adopted. Is also good.
[0043]
Further, in the present embodiment, the response of the air-fuel ratio sensor 19 is measured based on the time required from when the output of the air-fuel ratio sensor 19 crosses the previous target output to when it crosses the current target output. Alternatively, the measurement may be performed based on the time required for the output of the air-fuel ratio sensor 19 to change from the first set value to the second set value. The operation of another embodiment for measuring the response of the air-fuel ratio sensor 19 in this manner is shown in the flowcharts of FIGS.
[0044]
4 and 5 will be described. First, in order to measure the time required for the output VO2 of the air-fuel ratio sensor 19 to change from the first set value VO2H to the second set value VO2L, When the output VO2 is rich, that is, when the process proceeds from step 4 to step 7 and the integral IR is subtracted from the air-fuel ratio feedback correction coefficient α, a change in the output VO2 of the air-fuel ratio sensor 19 is observed, and the output VO2 is observed. Is measured to be equal to or less than the first set value VO2H and equal to or more than the second set value VO2L.
[0045]
That is, when it is determined in step 51 that VO2> VO2H, the process proceeds to step 41, in which TTSL is reset to 0, and the air-fuel ratio becomes lean by decreasing α, and the output VO2 decreases to become VO2H or less. When this happens, the process proceeds from step 51 to step 52 to step 42, and the TTSL is counted up by ΔT.
Further, when the output VO2 decreases and becomes less than VO2L, the process proceeds from step 52 to step 53, and it is determined whether or not TTSL is 0. Here, if VO2H> VO2L is set, TTSL (≧ ΔT) is not 0 at the point when VO2 becomes less than VO2L and first passes through step 53 since VO2 is less than VO2L once. Proceeding to step 31 and subsequent steps, the response of the air-fuel ratio sensor 19 is determined while comparing the TTSL with the reference time TTS as in the above-described embodiment, and the SL is changed in accordance with the response. Reset. However, the reference time TTS is set to a value different from that of the above embodiment.
[0046]
Thereafter, when the process proceeds from step 52 to step 53, TTSL = 0, so that the process does not proceed to step 31 and the SL is not changed. That is, the SL is changed once each time the air becomes rich once. Of course, it is also possible to change the SL in the same manner at the time of the lean operation. However, in the present embodiment, the example in which the SL is changed only at the time of the rich operation is shown. In step 44, TTSL is reset to 0 without changing SL.
[0047]
As described above, in the present embodiment, the response of the output of the air-fuel ratio sensor 19 is measured with the time from the first set value to the second set value. As shown in FIG. Since the lag until the response measurement result is reflected in the SL change is shortened as compared with the configuration, if the response characteristic of the air-fuel ratio sensor 19 changes suddenly, a form more suitable for the characteristic at that time is used. Can change the SL. In the first embodiment, the reason why the rich continuation period indicated by the dotted arrow in FIG. 8 is not measured is that when the rich continuation period is measured, the SL is changed based on the measurement result. If this happens, the output of the air-fuel ratio sensor will cross the SL again, and a plurality of SL changes will be performed, and the SL change width must be corrected according to the number of changes, which complicates the algorithm. That's why.
[0048]
The case where the response characteristic of the air-fuel ratio sensor changes abruptly is, for example, when the temperature is low and the load is low, such as immediately after the start of the engine, the sensor is being activated, and the gas exchange rate near the sensor surface decreases. As a result, the engine response may be changed from a state in which the sensor response is lowered to an accelerated state, and the exhaust gas temperature may be increased and the gas exchange rate may be restored, so that the sensor response may suddenly change.
[0049]
As described above, according to the present invention, when the response of the air-fuel ratio sensor is decreasing, the change speed of the target output is reduced to reduce overcorrection, and when the response is good, the change speed is increased. As a result, the target output can be quickly brought close to the final target output, and the air-fuel ratio can be appropriately corrected. As a result, the exhaust purification performance can be improved, and good driving performance can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration and functions of the present invention.
FIG. 2 is a diagram showing a system configuration according to an embodiment of the present invention.
FIG. 3 is a diagram showing output characteristics of an air-fuel ratio sensor used in the embodiment.
FIG. 4 is a flowchart showing a first stage of an air-fuel ratio control routine according to the first embodiment.
FIG. 5 is a flowchart showing a latter part of the flowchart of the above.
FIG. 6 is a flowchart showing a first stage of an air-fuel ratio control routine according to the second embodiment.
FIG. 7 is a flowchart showing a latter part of the flowchart of the above.
FIG. 8 is a time chart showing the state of each state under the control of the first embodiment and the second embodiment.
[Explanation of symbols]
11 engine 15 fuel injection valve 16 control unit 19 air-fuel ratio sensor

Claims (5)

An air-fuel ratio sensor that detects an air-fuel ratio of an air-fuel mixture supplied to the engine in response to a specific component in the exhaust;
Air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio so that the output of the air-fuel ratio sensor becomes the target output,
Target output changing means for changing a target output of the air-fuel ratio sensor,
In an air-fuel ratio control device for an internal combustion engine including
Response measurement means for measuring the response of the air-fuel ratio sensor,
Target output change speed setting means for setting a change speed of a target output of the air-fuel ratio sensor according to the measured response of the air-fuel ratio sensor,
And an air-fuel ratio control device for an internal combustion engine, wherein the target output is changed at the set change speed when the target output is changed. The target output changing means sets a final target output, and ends the change of the target output when the target output changed at the set change speed reaches the final target output. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein The response measuring means measures the response by the time from when the output of the air-fuel ratio sensor crosses the previous target output to when it crosses the current target output after the start of the air-fuel ratio feedback control. The air-fuel ratio control device for an internal combustion engine according to claim 1 or 2, wherein The response measuring means measures a response based on a time required to change from an output value of the air-fuel ratio sensor at the start of the air-fuel ratio feedback control to a set value shifted by a predetermined amount from the output value. An air-fuel ratio control device for an internal combustion engine according to claim 1 or 2 . The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 4 , wherein the air-fuel ratio sensor detects whether the air-fuel ratio is richer or leaner than a stoichiometric air-fuel ratio. .

Images