JPH01313641A - Air-fuel ratio control device for internal combustion engines - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention detects oxygen in the exhaust gas of an internal combustion engine using an oxygen sensor, and controls the air-fuel ratio of the internal combustion engine by feedback control using PI control. This invention relates to an air-fuel ratio control device.

[Conventional technology]

Conventionally, feedback control has been used to detect oxygen in the exhaust gas of an internal combustion engine using an oxygen sensor (hereinafter referred to as 02 sensor), adjust the flow rate of fuel or air according to the detected value, and set the air-fuel ratio to a target value. Air-fuel ratio control is being performed. This will be specifically explained using FIGS. 10 and 11.

It is a schematic block diagram of air-fuel ratio control by feedback control using a 10 m Fi Oz sensor. 10th
In the figure, an air-fuel ratio control means 45 adjusts the flow rate of fuel or air according to a control signal from a control unit (hereinafter referred to as ECU) 23. Meanwhile, the mixture of fuel and air is combusted in the cylinder of engine E.

Combustion products (NOx, CO, HC, etc.) are exhausted from the engine E through an exhaust pipe (not shown). An Ox sensor 17 disposed in the exhaust pipe detects the oxygen concentration in the exhaust gas and sends the signal to the ECU 23. ECU
23 determines whether the air-fuel ratio is leaf or rich based on the signal from the 02 sensor 17, and sends a control signal to the air-fuel ratio control means 45. That is, the gcU 23 adjusts the flow rate of fuel or air according to the feedback signal from the 02 sensor 17 to maintain the required air-fuel ratio.

By the way, the 0! used in this type of device! Since the senna is a sensor that has a switching characteristic in which its output signal suddenly changes after reaching the stoichiometric air-fuel ratio, linear feedback cannot be performed in the above-mentioned air-fuel ratio control. Therefore, as shown in Fig. 11, the limit value (
limit cycle) control is being performed. That is, in FIG. 11, the ECU adds or subtracts the integral gain Ii of the control signal according to the output of the Os sensor every sampling time Ts of reconnaissance. (Ii is added if the Os sensor output is lean, and Ii is subtracted if it is rich.) [Problem to be solved by the invention] In the conventional feedback control of the air-fuel ratio using 0 and Senna The exhaust gas purification efficiency improves when the average air-fuel ratio fluctuation is within ±5% of the stoichiometric air-fuel ratio due to its limit value (limit cycle) control.
FIGS. 12 and 13 a to C.
-+L+Tt, -+FL), and its value is l/(TI'L4L+TL→R). (T.R.
→L is lean delay time.

However, in the conventional air-fuel ratio control device, the integral gain Ii in the PI sub-control is increased or decreased according to the response delay time of the control system, and the frequency of air-fuel ratio fluctuation is reduced to 1/(T' a-+t.

+TL→R). Also.

When the exhaust gas temperature of the engine is not high enough, such as during idling, the response of the zero sensor is delayed (Fig. 14 al b), and therefore the delay time of the control system becomes large, and the amplitude of the air-fuel ratio fluctuation (Fig. There has also been a problem in that Δλ) in the figure becomes large, deteriorating the exhaust gas purification efficiency.

[Means to solve the problem]

In view of the above, the present invention provides 0! The frequency of air-fuel ratio fluctuation during sensor feedback control is 1/(Ta→I, +TL→R)
This prevents the amplitude Δλ of the motion from becoming large.

This is an air-fuel ratio control device for an internal combustion engine that improves exhaust gas purification efficiency, and as shown in the complaint response diagram in Figure 1,
A comparison means 48 detects oxygen in the exhaust gas of the internal combustion engine E using the oxygen sensor 17 and compares this detected value with a comparison reference value 47, and a comparison result obtained by the comparison means is converted into PI. In a device that performs feedback control of the air-fuel ratio of an internal combustion engine based on a control value, the enriching proportional gain and lean proportional gain of the PI conversion are set to appropriate the amplitude of periodic fluctuations in the air-fuel ratio during the feedback control. a proportional gain setting means 231 that outputs a gain, the oxygen sensor enrichment response delay time information in response to the air-fuel ratio enrichment control signal of the control system, and the oxygen sensor lean response delay time information in response to the air-fuel ratio lean control signal of the control system; response delay time setting means 232 that sets response delay time information based on the load and rotational speed of the internal combustion engine; and a response delay time setting means 232 that sets the enrichment integral gain when performing the PI conversion based on the oxygen sensor enrichment response delay time information and Integral gain setting means 233 that increases or decreases the lean integral gain when performing the PI conversion depending on the lean proportional gain and increases or decreases the lean integral gain depending on the oxygen sensor lean response delay time information and the enriching proportional gain. It is characterized by having the following.

〔Example〕

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

FIG. 2 is an overall configuration diagram of an air-fuel ratio control device for an internal combustion engine according to the present invention. In Figure 2, the engine (internal combustion engine)
E is an intake passage 2 and an exhaust passage 3 that communicate with the combustion chamber 1.
The intake passage 2 and the combustion chamber 1 are controlled to communicate with each other by an intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are controlled to communicate with each other by an exhaust valve 5.

In addition, an air cleaner 6 is installed in the intake passage 2 in order from the upstream side.
, throttle valve 7 and electromagnetic fuel injection valve (electromagnetic valve) 8
is provided in the exhaust passage 3.

A catalytic converter (three-way catalyst) 9 for purifying exhaust gas and a muffler (silencer) (not shown) are provided in order from the upstream side. Although not shown in the drawing, the intake passage 2 is provided with a surge tank.

Furthermore, solenoid valves 8 are provided in the intake manifold portion for the same number of cylinders. Now, assuming that the engine B of this embodiment is an in-line four-cylinder engine, four solenoid valves 8 are provided. That is, so-called multi-point fuel injection (
It can be said that it is an engine based on the MPI method.

Further, the throttle valve 7 is connected to the accelerator pedal via a wire cable, so that the opening degree changes depending on the amount of depression of the accelerator pedal.
Furthermore, the opening/closing operation is also performed by the idle speed control motor (ISC motor) 10, so that there is no need to press the accelerator pedal during idle link.

It is also possible to change the opening degree of the throttle valve 7.

With this configuration, air sucked through the air cleaner 6 according to the opening degree of the throttle valve 7 is passed through the solenoid valve 8. The air-fuel mixture is mixed with the fuel from the combustion chamber 1 at an appropriate air-fuel ratio and ignited at an appropriate timing in the combustion chamber 1 to combust it and generate engine torque. C in the exhaust gas is discharged to the exhaust passage 3 as a
01 After the three harmful components of HC and NOx have been purified.

The sound is muffled by a muffler and released into the atmosphere.

Furthermore, in order to control this engine B, various sensors are provided. First, on the intake passage 2 side, an air flow sensor 11 that detects the amount of intake air from Karman vortex information, an intake air temperature sensor 12 that detects the intake air temperature, and an atmospheric pressure sensor 13 that detects the atmospheric pressure are installed on the side of the intake passage 2. is provided, and a potentiometer-type throttle sensor 14. which detects the opening degree of the throttle valve 7 is provided in the throttle valve arrangement part. An idle switch 15 for detecting an idle link state and a motor position sensor 16 for detecting the position of the SC motor 10 are provided.

Furthermore, an 02 sensor 17 is provided on the upstream side of the catalytic converter 9 on the exhaust passage 3 side to detect the oxygen concentration (0, concentration) in the exhaust gas.

Here, the zero sensor 17 applies the principle of a solid electrolyte oxygen concentration battery, and its output voltage has the characteristic of rapidly changing near the stoichiometric air-fuel ratio, and the voltage on the lean side of the stoichiometric air-fuel ratio is low, and the voltage on the rich side is higher than the stoichiometric air-fuel ratio. In other words, these 0° C/S 17 are so-called λ type 0
It is configured as two sensors.

In addition, other sensors include a water temperature sensor 19 that detects engine cooling water temperature and a vehicle speed sensor 20 that detects vehicle speed.
(See Figure 3).

A crank angle sensor 21 that detects the crank angle (this crank angle sensor 21 also serves as a rotational speed sensor that detects the engine rotational speed) and a TDC sensor 22 that detects the top dead center of the first cylinder (reference cylinder), respectively. It is provided in the distributor 46.

The detection signals from these sensors 11 to 22 are
It is designed to be input to an electronic control unit (ECU) 23.

Note that a voltage signal from a battery sensor 25 that detects the voltage of the battery 24 and a signal from an ignition switch (key switch) 26 are also input to the gcU 23 .

The nordware configuration of the ECU 23 is shown in Figure 3, but this BCU 23 has a CPU as its main part.
U27 is provided, and this CPU 27 is connected to an intake air temperature riser 12. Atmospheric pressure sensor 13. Throttle sensor 14.
O*sensor 17. Water temperature SE: yf% 19 and the detection signal from the battery sensor 25 are inputted via the input interface 28 and the A/D converter 30, and the idle sensor 15. Detection signals from the vehicle speed sensor 20 and the ignition switch 26 are input via the input interface 29, and the air flow sensor 11. Detection signals from the crank angle sensor 21 and TDC sensor 22 are directly input to the input port.

Further, the CPU is connected via a pass line to a ROM 31 that stores program data and fixed value data, a RAM 32 that is updated and sequentially rewritten, and a battery 24, the storage contents of which are retained while the battery 24 is connected. As a result, data is exchanged with a battery backup RAM (BURAM) 33 backed up.

In addition, the data in RAM32 is stored in Ibunirashun Switch 2.
When 6 is turned off, it disappears and is reset.

Now, let's focus on fuel injection control (air-fuel ratio control).

A fuel injection control signal calculated by a method described later is output from the CPU 27 via the driver 34.

For example, four solenoid valves 8 are sequentially driven.

A functional block diagram for such fuel injection control (electromagnetic valve drive time control) is shown in FIG. 4.

That is, when looking at this BCU 23 from a software perspective, the BCU 23 first calculates the basic drive time T for the solenoid valve 8.
It has a basic driving time determining means 35 for determining B,
This basic drive time determining means 35 is an air flow sensor (A
The intake air amount Q/N e information per engine rotation is determined from the intake air amount Q information from FS)ll and the engine rotation speed Ne information from the crank angle sensor 21, and the basic drive time TB is determined based on this information. It is something to do.

In addition, an air-fuel ratio correction coefficient setting means (depending on the engine speed and load) sets a first air-fuel ratio correction coefficient KAPI from a map according to the engine speed and engine load (the above Q/Ne information has engine load information). (corresponding air-fuel ratio correction means) 36 and O, a second air-fuel ratio correction coefficient KAF for forcibly changing the air-fuel ratio during senna feedback
O to set snow.

A sensor feedback correction means 37 is provided,
The air-fuel ratio correction coefficient setting means 36 and the 0° sensor feedback correction means 37 are selectively selected by switching means 38 and 39 which are switched in conjunction with each other.

Further, cooling water temperature correction means 40 sets a correction coefficient KWT according to the engine cooling water temperature. Intake temperature correction means 41 for setting the correction coefficient KAT according to the intake air temperature; atmospheric pressure e correction means 42 for setting the correction coefficient KAP according to the atmospheric pressure. An acceleration increase correction means 43 that sets a correction coefficient KAC for acceleration increase according to the rate of change of Q/14m, and a dead time correction means that sets a dead time (invalid time) TD to correct the drive time according to the battery voltage. 4
4 is provided, and at the time of 02 feedback correction, the drive time TINJ of the solenoid valve 8 is set to TBXKWTXK.
ATXKAPXKACXKAF'Hiroshi+To, the solenoid valve 8 is driven with this time T INJ, while the driving time of the solenoid valve 8 other than during zero feedback correction is 'f INJ t-TnXKwTXKArXKApXK
AcXKAr++ Tn and %+? Knee O time T
Solenoid valve 8 is driven by TNJ.

The above fuel injection control (air-fuel ratio control) is shown in flowcharts as shown in FIGS. 5 to 7.

FIG. 5 shows a main routine for fuel injection control that is always executed when no processing is performed based on an interrupt signal to the CPU. In FIG. 5, gcU23 reads engine operating status information from various sensors (STEPI),
A determination is made as to whether or not the fuel cut zone (ie, high rotation extremely low load operating region) is reached (STBP2). Then, in the case of a 7-well cut zone, the 7-well cut (see 7-well cut 24 and 5TEP34) is reset at 5TBP3, and the integral coefficient KI (see the timer interrupt routine described later) is updated as KI=O at STgP6, and the process returns to 8TBP1 again.

On the other hand, if 5TEP2 determines that it is not in the fuel cut zone, 5TFiP7 resets the fuel cut flag, and 5TEP8 sets the cooling water temperature correction coefficient KWT, intake temperature correction coefficient K A T 1 atmospheric pressure correction coefficient KAP, and acceleration correction coefficient. Set KAC. Then, 8TEP9 determines whether the 02 sensor is activated, 5TEPIO determines whether the engine has warmed up, and 5TEP11 determines whether the 02 sensor is activated.
The above 5TBP9~5TB
If even one of the P110 conditions is not met, 5TE
P12 to 8TgP16 air-fuel ratio correction (air-fuel ratio correction 36 in FIG. 4). That is, the FB (feedback) flag is reset at 5TBP12.

At 8TBP13, the flags immediately after the start of the first and second FB are reset, and at 5TBP14, the first air-fuel ratio correction coefficient KAPI corresponding to the engine speed and engine load is read from the map (stored in R, OM), and at 5TBP14
In EP15, the integral coefficient KI is updated to KI=0, and the air-fuel ratio correction coefficient KAF is set to Jpt (sTEpt6).

On the other hand, if all the conditions of 5TEP9 to 5TEPII described above are satisfied, the process moves to Ot sensor feedback correction of 8TBP20 to 8TEP40 (Ox sensor feedback correction 37 in FIG. 4).

0, sensor feedback correction is first 0 at 8TEP20! The air-fuel ratio is set to the stoichiometric air-fuel ratio V by the sensor output Vr.
It is determined whether it is richer or leaner than rc. Then, the air-fuel ratio increases y f (V t
') If there is VrCte, 5TEP21~5TEP28
The air-fuel ratio is leaner.
(see EP32 to 8TEP35), and at the same time, it is determined in 8TEP22 whether the flag immediately after the start of the first FB is set. Here, the flag immediately after starting the first FB is set at 8TBP25, which will be described later, in a state where the air-fuel ratio is rich.

If the flag immediately after the start of the first FB is not set in 8TEP22, it is determined in STgP23 whether the F'B flag is set. And STgP2
If the FB flag is not set in step 3, that is, if this is the first time you have shifted to zero sensor feedback correction, set the FB flag in step 5TEP24, and
At step 25, the flag immediately after the start of the first F'B is set, and at S T E P26, the second air-fuel ratio correction coefficient KAF snow=
Set to 1 +K I.

Here, KI is an integral coefficient, which is determined in a timer interrupt routine (8TEP41 to 8TEP47), which will be described later.

Conversely, if the FB flag is set in 5TEP23, that is, after the FB flag is set in 5TEP24 or 5TEP34, the F flag is set in 5TEP5 or STgP12.
If the B flag shifts to 8TEP23 without being reset, specifically, if the air-fuel ratio switches from lean to rich more than once after shifting to O-sensor feedback correction, proceed to 5TBP27 and KArt. =
1 +K I P L. Here, KI is an integral coefficient (see the timer interrupt routine described later), PL is a lean proportional gain, and the rich side amplitude of the air-fuel ratio fluctuation is determined by the value of IPL (see FIG. 8).

On the other hand, if the flag immediately after the start of the first FB is set at 5TBP22, that is, the first FB starts at 8TBP25 mentioned above.
5TEP4, 8TE after the flag is set immediately after the start
P13 and 5TII! : The flag immediately after the start of the first FB is not reset at P31.

If you switch to 5TBP22 again following the last time,
Specifically, if the Os sensor feedback correction has started while the air-fuel ratio is rich, but the air-fuel ratio has not yet switched from rich to rich, 8TEP2 is applied.
Proceed to 6 and set KAFt=1+KI.

Set VF=1 (see timer interrupt routine described later) and set the air-fuel ratio correction coefficient KArt to 5TEP40).
Furthermore, set dead time 'rD at 5TEP17,
Return to 5TEP 1 again.

On the other hand, at 5TEP20, the air-fuel ratio is lean (Vf≦VrC
), the process moves to feedback correction for enriching the air-fuel ratio of Fi8TEP31 to Fi8TEP38.

That is, the flag immediately after the start of the first FB (see 8TEP22 to 8TEP25 described above) is reset in s'rgpat, and it is determined in 5TEP32 whether the flag immediately after the start of the second FB is set. Here, the flag immediately after the start of the second FB means that the engine operating state is in the feedback zone (8T) when the air-fuel ratio is lean.
N at BP11. This is set in 5TEP35, which will be described later, when the change is made (from Yes to Yes).

If the FB flag is not set in 5TBP33,
That is, if you have shifted to 0□ sensor feedback correction for the first time, set the FB flag at 8TBP34, set the flag immediately after starting the second FB at 8TBP35, and set the second air-fuel ratio correction coefficient KAFm at 5TEP36.
= 1 + K I. Here, KI is an integral coefficient, and the timer interrupt routine (STgP41 to 5T
EP47), that is, STgP24 straddles 8TE
If the FB flag is set in P34 and then moves to 8TEP33 without resetting the FB flag in 5TEP5 or 5TEP12, specifically, if the air-fuel ratio is rich at least once after moving to Ox sensor feedback correction. If it is switched from to lean, the process goes to 5TBP37 and KArt=1+KI+Pn is set. Here, KI is the integral coefficient (see timer interrupt routine described later) IP
R is the enrichment proportional gain, and the lean side amplitude of air-fuel ratio fluctuation is determined by the value of +Pn (see Figure 8).
.

On the other hand, if the flag immediately after the start of the second FB is set at 5TEP32, that is, when the flag immediately after the start of the second FB is set at 5TEP32,
5 TEP 4.5 TB after the flag is set immediately after the start
Immediately after the start of the 2nd FB at P13 and 5TEP21, the flag is not reset and 8TEP is started again following the previous time.
If you have moved to 32.

Specifically, if α sensor feedback correction has started in a state where the air-fuel ratio is lean, but the air-fuel ratio has not yet been switched from lean to rich, the process advances to 5TEP36 and KAF snow=1+KI is set.

8TEP36 or 5TEP37 as described above
Once the air-fuel ratio correction coefficient KAFt is set, set VF=0 at 8TEP38 (see the timer interrupt routine described later), and set the air-fuel ratio correction coefficient KAF as appropriate at 5TEP4.
0), further sets dead time TD at 5TEP 17, and returns to 5TEPI again.

By the way, the integral coefficient KI in the above-mentioned main routine
is set in the timer interrupt routine shown in FIG. The timer interrupt routine is executed by an interrupt signal every sampling time ts, and first, in 5TEP41, it is determined whether VF set in the above-mentioned main routine is 1 or not. And VF=1. That is, when the air-fuel ratio is rich, at 5TBP42, the 08 sensor lean response delay time TR-+L corresponding to the engine operating state is read from the map stored in the memory. (Here, what is 0□ sensor lean response delay time Ta→L?

This is the time required from when the BCU sends a control signal to make the air-fuel ratio lean until the 02 sensor detects that the air-fuel ratio has become lean. It is stored in rLOM in the form of a binary map with numbers. Note that this value has been determined through experiments. )0. Once the sensor lean response delay time Tu-oL is read.

8 Set lean integral gain It in THP43. That is, it is expressed as IL=(Pn/Tu→L)ts.

Here, Pyt is a preset enrichment proportional gain. When the lean integral gain IL is set, the integral coefficient KI is updated as KI=KI-IL in STgP44 and [TU FLN is performed.

On the other hand, if VF=1 is not determined in 5TEP41, that is, if the air-fuel ratio is lean, then in 5TEP45, zero sensor enrichment response delay time Tt, →R corresponding to the engine operating state is read from a map stored in the memory. (Here O
The x sensor enrichment response delay time Tt, -n is gcU
After sending a control signal to enrich the air-fuel ratio, Ox
This is the time required for the sensor to detect that the air-fuel ratio has been enriched, and like TR4L, this value is also determined experimentally in the form of a binary map of load and rotation speed.
Stored in OM. ) When the 0 rich sensor enrichment response delay time TL→R is read, the enrichment integral gain In is set at 5TEP46. That is.

It is expressed as IR=(PL/TL-tt)ts. Here P
L is a preset lean proportional gain.

And once the enrichment integral gain IR is set.

At 5TBP47, the integral coefficient KI is updated as KI=KI+IR, and )[TtJRN is performed.

FIG. 7 is a flowchart showing the control procedure for driving the electromagnetic valve. The flowchart shown in FIG. 7 is 18
It is activated by the interruption of the crank pulse every 00. First, in step 51, it is determined whether or not there is a fuel cut. If it is a fuel cut, there is no need for fuel injection, so the process returns, but if not, the process goes to step 52.

The intake air amount Q/Ne per crank angle of 1800 is set based on the number of Kalman pulses generated between the previous crank pulse and the current crank pulse and the cycle data between the Kalman pulses.

Then, in the first step 53, the basic drive time To is set according to this Q/N e, and then in step 54, the solenoid valve drive time T INJ is set as T BXKA FXKW.
An arithmetic value is calculated from TXKATXKAPXKAC+TD. In step 55, this TINJ is set in the injection timer. In step 56, this injection timer is triggered. When triggered in this way, fuel is injected for only 2 hours TrN,y. In addition, in the above formula, IKAF is.

K　A　　　+ or KArt.

Figure 8 shows 02 during feedback control by 02 senna.
This is an example of sensor output and second air-fuel ratio correction coefficient KArt characteristics. In FIG. 8, it is assumed that O, senna feedback has started at point α. That is, when the engine operating state is switched to the feedback zone while the air-fuel ratio is lean (5TEPII in FIG.
Switch from No to Yes and vf at 5TEP20
(at the time of VFC).

The second air-fuel ratio correction coefficient KAp* is Khvx = 1 +
K I (5TEP31-8T in Figure 5)
EP36).

And while e O2 sensor output Vf is lean (a
point to point b), the enrichment integral gain In is added to the integral coefficient KI at every sampling time tm (KI=KI
+In, 5TEP47 in FIG. 6), as the second air-fuel ratio correction coefficient KAFt increases, the amount of fuel injected from the solenoid valve 8 also increases.

Eventually, 0. When the sensor output Vf switches from lean to rich (point b), the second air-fuel ratio correction coefficient KAF.

is KAr, = 1 +K I-PL (5TEP20 → 5TEP21 in Figure 5 5TEP23 → 5jE
P27'). While the +02 senna output Vf is rich (from point b to point C), the lean integral gain It is subtracted from the integral coefficient KI at every sampling time tI (KI=KI-IL, 5TEP in Fig. 6).
44) As the second air-fuel ratio correction coefficient KAF decreases, the amount of fuel injected from the solenoid valve 8 also decreases.

Then 0. When the sensor output Vf switches from rich to lean (0 point), the second air-fuel ratio correction coefficient KAF2 is equal to KAF = 1 + KI + PR (5TEP in Fig. 5).
→5TEP31-8TEP33 →5TEP 37).

And 0. While the sensor output Vf is lean (from point C to
At point d), the enrichment integral gain IR is added to the integral coefficient KI at every sampling time t8 (KI=KI+IR).
, 5TEP47 in Figure 6).

As the second air-fuel ratio correction coefficient KAF increases, solenoid valve 8
The amount of fuel injected from the engine also increases.

Thereafter, the air-fuel ratio leafing control and enriching control are repeated, and as a result, the frequency of air-fuel ratio fluctuation is 1/(TR-
L +TL-R), the rich side amplitude is PL, and the lean side amplitude is PR. If PL=PR=α05, the amplitude of the air-fuel ratio fluctuation will be ±5 degrees of the stoichiometric air-fuel ratio, and the exhaust gas purification efficiency will also be improved as shown in FIG. 13, 1m''-e.

By the way, in the above embodiment, 0. The sensor lean response delay time TR4L and the Ot sensor enrichment response delay time Tt, →R were read from separate maps (see Figure 9) stored in the memory, but these are based on the Os sensor response as shown below. Delay time T (T=TR-
, L+TL-R) is set in one map (binary map of engine/engine load and rotational speed), and by multiplying this by the rich time ratio KR or the lean time ratio Kt, the O
The snow sensor enrichment response delay times TL-R and O and the sensor lean response delay time Ta-L may be calculated. That is.

Here, the lean time ratio Kyt and the lean time ratio KL vary depending on the operating conditions, and based on experience, as the engine speed Ne increases, both approach α5 (see Figure 915), and their characteristics are approximately expressed by the linear equation below. It will be done.

1) At No≦400Orpm However, A and B are constants.

A=3.6X10-5 B=156X10' if) Ne) At 4000 rpm, KR=Kt, =α5...Mountain...
(5) Also, without using a map, the sensor enrichment response delay time TL-n and 0! Sensor lean response delay time TR→L is determined by engine speed No., load condition, rotation speed N. and 0. Response delay time T (=TR-L
+TL-on) is shown in FIG. 16, ie, equation (6).

(No-Cυ(T-CI) =C, /Ev+C4・(
61 Here, C11Ct-Cm and C4 are constants and are determined from experimental data. -As an example.

CI=200. C,=α1. C,=10400°C
,=200.

Therefore, the response delay time T is obtained by modifying equation (6) to obtain equation (7) T = (Cs/Ev +C4)/(Ns Cθ+
C* --- Determined from (7), plus the above-mentioned rich duty ratio KR.

By multiplying by the lean time ratio KL (Equations (3) 2 to (5)), Of sensor enrichment response delay time Tt, -+a and 0! without using a map! It becomes possible to calculate the response delay time Tn-L for switching to the sensor/saline state.

In the air-fuel ratio control device for an internal combustion engine having the above configuration.

During feedback control of the sensor, 0, sensor rich response delay time T+t-*L and O, sensor lean response delay time Tt according to engine operating state information.
, -n, and at each sampling time ts, the lean integral gain It, is set as IL=(PR/TR
-4L)ts, and the enrichment integral gain IR is IR=
Since it is calculated as (PL/TL-R)ts, the frequency of air-fuel ratio fluctuation is 1/(TR-L+TL-IR). That is, the frequency of the air-fuel ratio fluctuation is always at the limit value (maximum value) for the engine operating state at that time, and the exhaust gas purification efficiency of the engine is improved.

Furthermore, since the amplitude of the air-fuel ratio fluctuation is maintained at the lean proportional gain PL and the rich proportional gain PR, −0,
The amplitude of the air-fuel ratio fluctuation does not increase as the senna response delay time T increases, and the exhaust gas purification efficiency does not deteriorate. Further, when the 01 sensor output Vf switches from leaf to rich or from rich to lean, the lean proportional gain PL or so.

The second air-fuel ratio correction coefficient KAF is determined by the proportional gain PR.
, is set to 1.0, and then KAF is performed by the lean integral gain IL and the enriched integral gain IR.

As a result, the transient response of the control system immediately after the engine operating state shifts to the feedback zone is also improved.

〔Effect of the invention〕

In the air-fuel ratio control device for an internal combustion engine according to the present invention, during sensor feedback control, the air-fuel ratio control device for an internal combustion engine has a temperature of 0° depending on the operating state of the engine. Even if the response delay time of the sensor changes, the air-fuel ratio can always be varied in an ideal manner, and high exhaust gas purification efficiency can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a diagram corresponding to claims of an air-fuel ratio control device for an internal combustion engine according to the present invention, FIG. 2 is an overall configuration diagram of an embodiment of the air-fuel ratio control device, and FIG. 3 is a configuration diagram of an ECU in the same embodiment. , FIG. 4 is a flowchart showing the air-fuel ratio control in the same embodiment, and FIG. 5 is a flowchart showing the air-fuel ratio control in the same embodiment. FIG. 6 is a flowchart showing a timer interrupt executed at every sampling time ts in the same embodiment. FIG. 7 is a flowchart showing the driving of the electromagnetic valve in the same embodiment, and FIG. 8 is a flowchart showing the Ot output Vf and the second air-fuel ratio correction coefficient KAF during sensor feedback control executed by the same embodiment. FIG. 9 is a diagram showing the relationship between 0 and sensor lean response delay time Tn- in the same embodiment.
Figure 1 shows an example of a map in which the value of L is stored.
The θ diagram is the conventional 0. A schematic block diagram of feedback control using Senna. Figure 11 shows conventional O! and O! in sensor feedback control. Figure 12 is a diagram showing the relationship between the sensor output and ECU control signal, Figure 12 is a diagram showing the relationship between the frequency of air-fuel ratio fluctuation and exhaust gas purification efficiency, and Figure 13 a-(j is the amplitude of air-fuel ratio fluctuation and exhaust gas purification efficiency. Figures 14a and 14b are diagrams showing the influence of exhaust gas temperature on the response delay time and output voltage Vf of the 0. sensor, and Figure 15 is a diagram showing the relationship between engine rotational speed Ne, chi, and lean time. A diagram showing the relationship between the ratios KR and KL. Figure 16 is a diagram showing the relationship between the engine speed No. and O, and the sensor response delay time T. E: Engine (internal combustion engine) 1: Combustion chamber 2 : Intake passage 3: Exhaust passage 7: Throttle valve 8: Solenoid valve (in-jet lid) 9: Catalytic converter 10: ISC motor 11: Air flow sensor 12: Intake temperature sensor
13: Atmospheric pressure sensor 14: Throttle sensor
15: Idle switch 16: Motor body sensor 17: O. (Oxygen) sensor 19: Water temperature sensor 20: Vehicle speed sensor 21: Crank angle sensor 22:
TDC sensor 23: ECU 45: Air-fuel ratio control means 46: Distributor 47: Comparison reference value
48: Comparison means 230: Feedback control amount calculation means 231: Proportional gain setting means 232: Response delay time setting means 233: Integral gain setting means Applicant: Mitsubishi Motors Corporation Fig. 9 Fig. 02 Sensor Lean conversion / Rei Sho - aEI Imma Muff - 1-cho g-L (su) Fig. 10 Fig. 42 Fig. 1 Sho No. =wsu>jm 731 = 80011c9, '4 Interim procedural amendment (method) Display of the September 30, 1983 case Person who amended Patent Application No. 146108 of 1988 Relationship with the case Patent applicant ( Representative applicant) Appropriate drawings

Claims (1)

[Claims] Comparing means for detecting acidity in the exhaust gas of the internal combustion engine using an oxygen sensor and comparing the detected value with a comparison reference value;
In a device that performs feedback control of an air-fuel ratio of an internal combustion engine based on a control value obtained by PI conversion of a comparison result by the comparison means, settings are made to appropriate the amplitude of periodic fluctuations in the air-fuel ratio during the feedback control. proportional gain setting means for outputting enrichment proportional gains and lean proportional gains of said PI conversion, said oxygen sensor enrichment response delay time information to said control system's air-fuel ratio enrichment control signal, and said control system; response delay time setting means for setting the oxygen sensor lean response delay time information for the air-fuel ratio lean control signal based on the load and rotational speed of the internal combustion engine, and the enrichment integral when performing the PI conversion. The gain is increased or decreased depending on the oxygen sensor enrichment response delay time information and the lean proportional gain, and the lean integral gain when performing the PI conversion is determined based on the oxygen sensor lean response delay time information and the enrichment proportional gain. An air-fuel ratio control device for an internal combustion engine, comprising an integral gain setting device that increases or decreases the gain depending on the gain.