JP2623469B2 - Air-fuel ratio feedback control method for an internal combustion engine - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine having an automatic transmission, and more particularly to an appropriate control when the shift state of the automatic transmission is in a drive range. The present invention relates to an air-fuel ratio feedback control method which can be performed in a timely manner.

(Prior Art and Problems Thereof) Conventionally, an exhaust gas concentration value detected by an exhaust gas concentration detector arranged in an exhaust system of an internal combustion engine is compared with a first reference value, and supplied to the engine according to the comparison result. There is known an air-fuel ratio feedback control method for an internal combustion engine in which the air-fuel ratio of an air-fuel mixture is feedback-controlled to a predetermined target air-fuel ratio, so that the exhaust gas characteristics and the driving performance can be improved (for example, Japanese Patent Application Laid-Open No. H11-163873). No. 57-188743).

In such an air-fuel ratio feedback control method, since the target air-fuel ratio is made to match the stoichiometric air-fuel ratio over the entire feedback control region, the internal combustion engine including the automatic transmission is in an idle operation state, and There has been a problem that the feedback control cannot be properly performed when the shift state of the automatic transmission is in the drive range.

That is, in an internal combustion engine equipped with an automatic transmission,
When the shift state of the automatic transmission is in the drive range when the engine is in the idling state, it is necessary to supply oil pressure from the oil pump driven by the engine to the clutch of the automatic transmission. Since a high output is required of the engine, the engine speed is set to be higher than when the shift state of the automatic transmission is in the neutral range or the parking range.

Therefore, when the conventional air-fuel ratio feedback control method is applied to an internal combustion engine provided with an automatic transmission, when the engine is in an idling operation state and the speed change state of the automatic transmission is in a drive range, the air-fuel ratio is supplied to the engine. Although the air-fuel ratio of the air-fuel mixture is controlled to the target air-fuel ratio, the combustion temperature of the engine rises due to the high engine speed, which results in an increase in the emission of nitrogen oxides (NOx) However, there is a problem that the exhaust gas characteristics are deteriorated.

(Object of the Invention) The present invention has been made to solve the above-mentioned problems of the prior art, and is intended for a case where an internal combustion engine provided with an automatic transmission is in an idling operation state and the transmission state is in a drive range. It is an object of the present invention to provide an air-fuel ratio feedback control method for an internal combustion engine in which the exhaust gas characteristics of the engine are improved.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides an exhaust gas concentration detector that detects an exhaust gas concentration value detected by an exhaust gas concentration detector disposed in an exhaust system of an internal combustion engine equipped with an automatic transmission and a first reference value. And a feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine to a predetermined target air-fuel ratio in accordance with the comparison result. Detecting whether the engine is in a drive range, detecting whether the engine is in an idle state, detecting when the engine is in an idle state, and detecting that the speed change state is in a drive range, A reference value to be compared with the exhaust gas concentration value is set to a second reference value larger than the first reference value, and the air-fuel ratio of the air-fuel mixture is corrected to a rich side.

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

FIG. 1 shows the overall configuration of an air-fuel ratio control device to which the method of the present invention is applied. In the figure, reference numeral 1 denotes, for example, a four-cylinder internal combustion engine. An automatic transmission 15 is connected to the engine 1, and the driving force of the engine 1 is transmitted to driving wheels (not shown) of the vehicle via the automatic transmission 15. Also, automatic transmission 15
Can be switched to a drive range, a neutral range, or the like by a range select lever (not shown).

An intake sound 2 is connected to the engine 1. A throttle body 3 is provided in the middle of the intake pipe 2, and a throttle valve 3 'is disposed inside. A throttle valve opening (θ _TH ) sensor 4 is connected to the throttle valve 3 ′. The throttle valve 3 ′ converts the valve opening of the throttle valve 3 ′ into an electric signal to an electronic control unit (hereinafter referred to as “ECU”) 5. Have been guided.

A fuel injection valve 6 is provided between the engine 1 and the throttle body 3 of the intake pipe 2 for each cylinder, slightly upstream of an intake valve (not shown) of each cylinder. The fuel injection valve 6 is connected to a fuel pump (not shown) and is also electrically connected to the ECU 5, and the opening time of the fuel injection valve 6 is controlled by a drive signal from the ECU 5 as described later.

On the other hand, an absolute pressure (P _BA ) sensor 7 is disposed downstream of the throttle valve 3 ′ of the intake pipe 2 via a pipe 7 ′, and the absolute pressure sensor 7 converts the absolute pressure into an electric signal. The signal is being led to ECU5.

An engine water temperature sensor (hereinafter, referred to as “Tw sensor”) 8 is provided on the main body of the engine 1. The Tw sensor 8 is composed of a thermistor or the like, is mounted in the peripheral wall of the engine cylinder filled with cooling water, and supplies a detected water temperature signal to the ECU 5.

Engine speed (Ne) sensor 9 and cylinder discrimination sensor
The engine 10 is mounted around a camshaft (not shown) or around a crankshaft of the engine 1. The engine speed sensor 9 outputs a predetermined control signal (hereinafter referred to as a “TDC signal”) pulse at a predetermined crank angle position before the top dead center (TDC) of each cylinder every 180 ° rotation of the crankshaft of the engine 1. The cylinder discrimination sensor 10 outputs a cylinder discrimination signal pulse at a predetermined crank angle position of a specific cylinder, and these signal pulses are supplied to the ECU 5.

On the other hand, a three-way catalyst 12 is disposed in an exhaust pipe 11 of the engine 1 to purify HC, CO, and NOx components in exhaust gas.
An O ₂ sensor (exhaust gas concentration detector) 13 is inserted into the exhaust pipe 11 on the upstream side of the three-way catalyst 12. The O ₂ sensor 13 outputs an output voltage value Vo ₂ indicating the detected oxygen concentration in the exhaust gas.
Exceeds a predetermined reference value Vr described later,
When it falls below, it outputs a lean signal to ECU5. Both signals indicate that the mixture is richer or leaner than the target air-fuel ratio. Further, a vehicle speed (Sp) sensor 14 is connected to the ECU 5. The vehicle speed sensor 14 detects the vehicle speed,
The detection signal is supplied to ECU5.

The ECU 5 is an input circuit having functions of shaping input signal waveforms from the above-described various sensors, correcting a voltage level to a predetermined level, and converting an analog signal value to a digital signal value.
5a, central processing circuit (hereinafter referred to as “CPU”) 5b, this CP
It comprises a storage means 5c for storing various calculation programs executed by the U5b and their calculation results, etc., and an output circuit 5d for sending a drive signal to the fuel injection valve 6. ECU5, based on various parameter signals introduced from each of the sensors,
The fuel injection time _TOUT of the fuel injection valve 6 given by the following equation is calculated.

T _OUT = Ti × Ko ₂ × K ₁ + K ₂ (1) Here, Ti indicates a basic fuel injection time of the fuel injection valve 6, and the basic injection time is, for example, the absolute pressure P in the intake pipe.
Recording means in ECU 5 based on _BA and engine speed Ne
Read from 5c. Ko ₂ is O ₂ calculated from an operation program flowchart (FIG. 2) according to the present invention described later.
This is a feedback correction coefficient. Also, K ₁ and K ₂ is a correction coefficient and correction variable computed according to various engine parameter signals, so that the fuel consumption characteristic according to engine operating conditions, the optimization of various properties such as the engine acceleration characteristics can be achieved Is set to the required value.

The ECU 5 supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve based on the fuel injection time _TOUT obtained as described above.

Next, the air-fuel ratio feedback control method of the present invention applied to the air-fuel ratio control device configured as described above will be described.

FIG. 2 shows a flowchart of a subroutine for calculating the O ₂ feedback correction coefficient Ko _{2 according} to the control method of the present invention. This program is executed by the ECU 5 every time a TDC signal pulse is generated.

First determines whether or not the activation of the O ₂ sensor 13 is completed (step 201). That, O ₂ output voltage activated starting point Vx of the internal resistance detection method by the O ₂ sensor 13 of the sensor 13
(For example, 0.6 V) is detected, and when it reaches Vx, it is determined that it is activated. If the answer is negative (No), the coefficient value Ko ₂ is set to 1.0 and the program ends (step 202).

If the answer to step 201 is affirmative (Yes), it is determined whether or not the engine 1 is in the open loop control area (step 203). The open control region includes a high load operation region, a low rotation region, a high rotation region, a mixture lean region, and the like, and the high load operation region includes, for example, the fuel injection time T _OUT
Is a region set to a value larger than the predetermined value T _WOT .
Here, T _WOT is a constant and is a lower limit value of the fuel supply amount necessary for enriching the air-fuel mixture during a high load operation such as when the throttle valve is fully opened. In the low rotation range, the engine speed Ne is a predetermined value N _LOP
(For example, 700 rpm) or less, and the high rotation region is a region where the engine rotation speed Ne is larger than a predetermined rotation speed N _HOP (for example, 3000 rpm). The air-fuel mixture lean region is a region where the intake pipe absolute pressure _PBA is smaller than the discrimination value _PBLS set to a larger value as the engine speed Ne increases.
If the answer in step 203 is affirmative (Yes), that is, if the answer is in any of the above areas, the process proceeds to step 202, where Ko ₂ is
Set to 1.0 and exit this program.

On the other hand, if the answer to step 203 is negative (No), it is determined that the engine 1 is in the feedback region, and the process proceeds to the closed loop control. First, whether the engine is in the idle operation region, which is a specific region in the feedback region, is determined. Is determined (step 204). The determination in step 204 is that the engine speed Ne is equal to the predetermined speed N _IDL (for example, 10
00 rpm), and the _θTH sensor 4 determines whether or not the throttle valve opening _θTH is substantially fully closed.

When the answer to step 204 is affirmative (Yes), that is, when the engine 1 is in the idling operation region, the routine proceeds to step 205,
Whether the vehicle equipped with the engine is a vehicle equipped with an automatic transmission (hereinafter referred to as "AT vehicle"), a vehicle equipped with a manual transmission (hereinafter referred to as "MT vehicle"), If so, it is determined whether or not the shift state of the automatic transmission 15 is in the drive range. The determination as to whether or not the vehicle is an AT vehicle is made based on the output of a transmission type switch (not shown) whose ON-OFF state is switched according to whether the vehicle is an AT vehicle or an MT vehicle, for example.

If the answer to this step 205 is negative (No),
When the automatic transmission 15 is not in the drive range even if the vehicle is an T vehicle or an AT vehicle, the reference value Vr of the O ₂ sensor 13 is set to a first reference value Vr _ON (first reference value , For example, 0.49 V) (step 206), and then proceeds to step 211 described later. If the answer of step 205 is affirmative (Yes),
That the vehicle is an AT vehicle, and the automatic transmission 15 and the second reference value Vr _OD shifting state is made larger than the first reference value Vr _ON the reference value Vr when in a drive range (second
, For example, 0.58 V) (step 207), and then proceed to step 211.

As described later, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is controlled so as to be a target air-fuel ratio corresponding to the reference value Vr. Therefore, steps 204-207 described above
Control, the air-fuel ratio of the air-fuel mixture when the internal combustion engine provided with the automatic transmission is in the idling operation state and the transmission state of the automatic transmission is in the drive range is enriched as a whole, and the nitrogen oxides (NOx ) Can be reduced.

If the answer to step 204 is negative (No), that is, the engine 1
When the vehicle is not in the idling operation region, the routine proceeds to step 208, where it is determined whether or not the vehicle is an AT vehicle. If the answer to step 208 is negative (No), that is, if the vehicle is an MT vehicle, the reference value Vr is changed to the third reference value Vr _1M (for example, 0.55
V) (step 209), and then step 211
Proceed to. When the answer to step 208 is affirmative (Yes), that is, when the vehicle is an AT vehicle, the reference value Vr is changed to the fourth reference value Vr _1A (for example, 0.60 V) which is larger than the third reference value Vr _1M.
(Step 210), and then proceed to step 211. With this, when the engine mounted on the AT vehicle that requires a higher engine output compared to the MT vehicle is in a normal feedback operation region other than the idle operation region, the air-fuel ratio is also enriched as a whole by Appropriate engine output can be secured.

In step 211, it is determined whether or not the output level of the O ₂ sensor 13 has been inverted between the previous input of the TDC signal pulse and the present input of the TDC signal pulse, and if the answer is affirmative (Yes), step 212
The following proportional term (P term) control is performed, and in the case of negative (No), the integral term (I term) control from step 217 is performed. Step 2
When the answer to step 11 is affirmative (Yes), the output level of the O ₂ sensor 13 is lower than the reference value Vr (Vr _ON , Vr _OD , Vr _1M or Vr _1A ) set in the step 206, 207, 209 or 210 (lean signal). ) Is determined (step 21).
2) If the answer is affirmative (Yes), we obtain the correction value P _R by P _R setting subroutine to be described later so as to apply a correction value P _R (FIG. 3) (step 213). Then adds the correction value P _R to the immediately preceding value of the coefficient value Ko ₂ in step 214 by terminating the program.

On the other hand, when at step 212 the output level of the O ₂ sensor 13 is determined relative to the reference value Vr is high (rich signal), P _L setting subroutine to be described later so as to apply a correction value P _L (the The correction value P _L is obtained according to FIG. 4) (step 215). In step 216, by subtracting the correction value P _L from the coefficient value Ko ₂ of the previous loop by terminating the program.

Next, the integral term (I term) control in step 217 and subsequent steps is performed as follows. First, in step 211, when the output level Vo ₂ of the O ₂ sensor 13 is on the same level side as the previous loop with respect to the reference value Vr, proceed to step 217,
The output of the O ₂ sensor 13, it is determined whether or not a low level side. For the answer to this question is affirmative (Yes), the 1 in addition to the count number N _IL of TDC signal pulses (step 218), determines whether the count number N _IL reaches the predetermined value N _I (e.g. 4) (Step 219). As a result of this determination, the count number N
_{If IL} has not yet reached N _I , the coefficient value Ko ₂ is maintained at the value of the previous loop (step 220), and the count number N _IL is
When reaching the N _I is, [Delta] K setting subroutine (FIG. 5) to be described later so as to apply a predetermined value [Delta] K by obtaining the predetermined value [Delta] K (step 221). Then the predetermined value ΔK is added to the previous value of the coefficient value Ko ₂ in step 222, TDC simultaneously
The count number N _IL signal pulse resets to zero (step 223), followed by terminating the program. That is, the predetermined value Δ
K is added to the coefficient value Ko ₂ every time the count number N _IL reaches N _I.

On the other hand, if the answer to the question of the step 217 is negative (No), 1 is added to the count number N _{the IH} of the TDC signal pulse (step 224), whether the count number N _IN reaches a predetermined value N _I It is determined whether or not the answer is negative (step 225). If the answer is negative (No), the value of the coefficient value Ko ₂ is maintained at the value of the previous loop (step 226), and if the answer is affirmative (Yes), Determines a predetermined value ΔK by the ΔK setting subroutine in the same manner as in the step 221 (step 227).

Then, by subtracting a predetermined value ΔK from the coefficient value Ko ₂ (step 228), resets the count number N _{the IH} to 0 (step 229), similarly to the above by terminating the program N _{the IH} is N _I
The predetermined value ΔK is subtracted from the coefficient value Ko ₂ every time the value reaches.

FIG. 3 shows the coefficient value Ko ₂ executed in step 213 of FIG.
Which is a subroutine for setting the enrichment direction correction value P _R.

First, in step 301, it is determined whether or not the engine 1 is in an idle operation state. This determination is made by the same method as in step 204 in FIG. If the answer to this question is affirmative (Yes), that is, the first correction value P for idle correction value P _R when the engine 1 is idling
_R0 (for example, 0.15) is set (step 302), and negation (N
o), that is, when the engine 1 is not in the idling state to set the correction value P _R to the second correction value P _R1 (e.g. 0.80) for large becomes off idle than the first correction value P _R0 (step 303 ). This suppresses a significant change in the air-fuel ratio when the engine 1 is in an unstable idling operation state in which the combustion state is unstable.

FIG. 4 shows the coefficient value Ko ₂ executed in step 215 of FIG.
Is a subroutine for setting a correction value P _L for the leaning direction of.

First, in step 401, it is determined whether or not the engine 1 is in an idle operation state. This determination method is also the second
This is the same as step 204 in the figure and step 301 in FIG. If the answer is affirmative (Yes), that is, if the engine 1 is in the idling operation state, the routine proceeds to step 402, where the correction value P _L
Set the first correction value P _L0 for idling (for example, 0.15).

If the answer to step 401 is negative (No), that is, the engine 1
When the vehicle is not in the idling operation state, the routine proceeds to step 403, where it is determined whether or not the vehicle speed Sp is higher than a predetermined determination value Sp _FD (for example, 72 kmh). If the answer to this step 403 is negative (N
o), that is, when Sp ≦ Sp _FD is satisfied, the process proceeds to step 404, and it is determined whether or not the vehicle is an AT vehicle. This determination is performed by the same method as the determination in step 208 of FIG. When the answer to step 404 is affirmative (Yes), that is, when the vehicle is an AT vehicle, the process proceeds to step 405,
The absolute pressure P _{BA in the} intake pipe is equal to a predetermined determination value P _BAA for an AT vehicle (for example, 4
60 mmHg) is determined. This step 40
When the answer to 5 is negative (No), that is, when P _BA ≤P _BAA holds, the correction value P _{L is changed} to the second correction value P for the AT vehicle at low / medium speed / low load.
_{Set to L1LA} (for example, 0.8) (step 406) and affirmative (Ye
s), that is, a low-correction value P _L when the P _BA> P _BAA is satisfied
Third correction value P _L1HA for AT vehicles at medium speed and high load (for example, 0.9
0) (step 407).

If the answer in step 404 is negative (No), that is, the vehicle MT
If the vehicle is a car, the process proceeds to step 408, where the absolute pressure P in the intake pipe is
_It is determined whether _BA is larger than a predetermined determination value P _BAM (for example, 360 mmHg) for an MT vehicle. If the answer to this step 408 is negative (N
o), namely P _BA ≦ P low, the correction value P _L when _{the BAM} is established
Fourth correction value P _L1LM for MT vehicles at medium speed and high load (for example, 0.8
5) (step 409), and affirmative (Yes), that is, P _BA >
Correction value P _L through the low-speed high-load when the P _BAM is established
The fifth correction value P _L1HM (for example, 0.76) for the MT vehicle is set (step 410).

When the answer to the step 403 is affirmative (Yes), that is, when Sp> Sp _FD is satisfied, the process proceeds to a step 411 to determine whether or not the vehicle is an AT vehicle. If the answer to this step 411 is affirmative (Yes), that is, if the vehicle is an AT vehicle, the correction value P _L
Is set to a sixth correction value P _L2A (for example, 0.90) for the AT vehicle at the time of high speed (step 412), and negative (No), that is, the vehicle MT
When a car sets the correction value P _L to the seventh correction value P _L2M for MT vehicle during high-speed (e.g., 0.78) (step 413).

As described above, the correction value P _{L in} the leaning direction of the coefficient value Ko ₂
Indicates whether the engine 1 is in an idling state, the vehicle speed,
Another AT vehicle and MT vehicle, because it is set to an optimum value according to the intake pipe absolute pressure and the like, the output level of the O ₂ sensor 13 is controlled in the lean direction of the air-fuel ratio when the inverted to the rich side Can be done properly.

FIG. 5 is a subroutine for setting a predetermined value ΔK executed in step 221 or step 227 of FIG.

First, in step 501, it is determined whether or not the engine 1 is in an idle operation state. This answer is affirmative (Ye
s), that is, when the engine 1 is in an idling operation state, a predetermined time T _G (for example,
It is determined whether or not 10 seconds have elapsed (step 502).
If the answer to step 502 is negative (No), that is, if the predetermined time _TG has not elapsed after the engine 1 enters the idle operation state, the predetermined value ΔK is changed to the first predetermined value ΔKo ₁ (for example,
0.06) (step 503), and when the result is affirmative (Yes), that is, when the predetermined time _TG has elapsed after the idle operation state, the predetermined value ΔK is set to a second predetermined value ΔKo ₂ (for example, 0.03) (for example, 0.03) ( Step 504).

If the answer to step 501 is negative (No), that is, the engine 1
When the vehicle is not in the idling operation state, it is determined whether or not the vehicle is an AT vehicle (step 505). This step 505
Is negative (No), that is, when the vehicle is an MT vehicle, the predetermined value ΔK is changed to the first and second predetermined values Δ1 for idling.
Third predetermined value ΔK for MT vehicles greater than Ko ₁ and ΔKo _2
1M (for example, 0.15) (step 506), and affirmative (Ye
s), that is, when the vehicle is an AT vehicle, the predetermined value ΔK
Is set to a fourth predetermined value ΔK _1A (for example, 0.25) for AT vehicles that is larger than the third predetermined value ΔK _1M (step 507).

With the above setting, the predetermined value ΔK can be set optimally depending on whether the engine 1 is in the idling state or not, depending on whether the vehicle is an AT vehicle or an MT vehicle, so that the output level of the O ₂ sensor 13 is rich or lean. The air-fuel ratio when the side level is maintained can be appropriately controlled in a direction to correct the target air-fuel ratio.

(Effects of the Invention) As described above in detail, the present invention relates to the case where the shift state of the automatic transmission of the internal combustion engine is in the drive range, and when the engine is in the idling state, the air-fuel ratio of the air-fuel mixture is rich as a whole. Nitrided oxide (NO
The effect of (x) is that the amount of emissions can be reduced, thereby improving the exhaust gas characteristics. Further, when the air-heat ratio is on the lean side, the fluctuation range of the engine rotation speed is large.Therefore, the fluctuation range of the engine rotation speed is reduced by enriching the air-fuel ratio, and thereby the idling operation state is reduced. It also has an advantage that drivability can be improved.

[Brief description of the drawings]

1 is an overall configuration diagram of an air-fuel ratio control device to which the present invention is applied, FIG. 2 is a flowchart showing a calculation procedure of an O ₂ feedback correction coefficient Ko ₂ , and FIG. 3 is a step 213 in FIG.
Flow chart of subroutine for setting the correction value P _R which is executed in, Figure 4 is a flow chart of the subroutine for setting the correction value P _L that is performed in step 215 of FIG. 2, FIG. 5 is executed in step 221 or step 227 9 is a flowchart of a subroutine for setting a predetermined value ΔK. 1 ...... internal combustion engine, 5 ...... electronic control unit (ECU), 13 ...... O ₂ sensor (exhaust concentration detector), 15 ......
Automatic transmission.

Claims (1)

(57) [Claims] An exhaust gas concentration detector detects an exhaust gas concentration value detected by an exhaust gas concentration detector disposed in an exhaust system of an internal combustion engine having an automatic transmission, and compares the exhaust gas concentration value with a first reference value. In the air-fuel ratio feedback control method for an internal combustion engine that performs feedback control of an air-fuel ratio of an air-fuel mixture to be performed to a predetermined target air-fuel ratio, it is detected whether a shift state of the automatic transmission is in a drive range and the engine is idle. A reference value to be compared with the exhaust gas concentration value when the engine is in an idle state and the shift state is a drive range. An air-fuel ratio feedback control method for an internal combustion engine, wherein the air-fuel ratio of the air-fuel mixture is corrected to a rich side.