JPS63189640A - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a fluctuation in an r.p.m. in idling, by making a reference value in air-fuel ratio feedback control larger than a normal value when an automatic transmission is in a drive range to make an air-fuel ratio rich. CONSTITUTION:An electronic control unit 5 calculates a basic amount of fuel injection based on values sensed by a suction gas absolute pressure sensor 8 and an r.p.m. sensor 10 and compares a value sensed by an O2 sensor 13 with a reference value for effecting feedback control of an air-fuel ratio by proportional integral control. The electronic control unit 5 determines whether a speed change position of an automatic transmission is in a drive range. When it is in the drive range, the electronic control unit 5 makes the reference value large to make an air-fuel ratio rich.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine equipped with an automatic transmission, and particularly to an air-fuel ratio feedback control method for an internal combustion engine equipped with an automatic transmission. The present invention relates to an air-fuel ratio feedback control method that can be used to control air-fuel ratios.

(Prior art and its problems) Conventionally, an exhaust concentration value detected by an exhaust concentration detector disposed in the exhaust system of an internal combustion engine is compared with a first reference value,
Air-fuel ratio feedback control for an internal combustion engine that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine to a predetermined target air-fuel ratio according to the comparison result, thereby improving exhaust gas characteristics and driving performance. Methods are known (for example, Japanese Patent Laid-Open No. 188743/1983).

In this air-fuel ratio feedback control method, the target air-fuel ratio is made to match the stoichiometric air-fuel ratio over the entire feedback control region, so that when the internal combustion engine equipped with an automatic transmission is in an idling operating state and There has been a problem in that feedback control cannot be performed appropriately when the automatic transmission is in the drive range.

That is, in an internal combustion engine with an automatic transmission, when the engine is in idle operation.

When the automatic transmission is in the drive range, it is necessary to supply hydraulic pressure to the clutch of the automatic transmission from the oil pump driven by the engine, and the engine is required to output as high as the hydraulic pressure. The engine speed is set higher than when the automatic transmission is in the neutral range or parking range.

Therefore, when the conventional air-fuel ratio feedback control method is applied to an internal combustion engine equipped with an automatic transmission,
When the engine is in idle operation and the automatic transmission is in the drive range, the engine speed is high even though the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the target air-fuel ratio. There was a problem in that the combustion temperature of the engine rose, resulting in an increase in nitrogen oxide (NOX) emissions, leading to a deterioration in the exhaust gas characteristics of the engine.

(Object of the Invention) The present invention has been made in order to solve the problems of the prior art described above. An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine, which improves the exhaust gas characteristics of an internal combustion engine.

(Means for Solving the Problems) In order to achieve the above object, the present invention uses an exhaust concentration value detected by an exhaust concentration detector disposed in the exhaust system of an internal combustion engine equipped with an automatic transmission and a first standard. In the air-fuel ratio feedback control method for an internal combustion engine, the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to a predetermined target air-fuel ratio according to the comparison result. It detects whether or not the shift state is in the drive range, and when it is detected that the shift state is in the drive range, the reference value to be compared with the exhaust gas concentration value is set to a second reference value that is larger than the first reference value. This is how you set it.

(Example) An embodiment of the present invention will be described below 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 FIG. The driving force of the engine 1 is transmitted to a drive shaft (not shown) of the vehicle via an automatic transmission 15. Further, the speed change state of the automatic transmission 15 is switched to a drive range, a neutral range, etc. by a range select lever (not shown).

An intake pipe 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 arranged inside. A throttle valve opening (θ〒H) sensor 4 is connected to this throttle valve 3', which converts the valve opening of the throttle valve 3' into an electrical signal and converts the valve opening of the throttle valve 3' into an electric signal to an electronic control unit (hereinafter referred to as rEcUJ).
5).

A fuel injection valve 6 is provided between the engine 1 and the throttle body 3 in the intake pipe 2 for each cylinder, slightly upstream of the 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 3.

As will be described later, the opening time of the fuel injection valve 6 is controlled by a drive signal from the ECU 3.

On the other hand, an absolute pressure (Pg^) sensor 7 is disposed downstream of the throttle valve 3' of the intake pipe 2 via a pipe 7', and the absolute pressure converted into an electrical signal by the absolute pressure sensor 7 is The signal is guided to ECU3.

The engine 1 body is provided with an engine water temperature sensor (hereinafter referred to as rTw sensor) 8. The sTw sensor 8 consists of a thermistor, etc., and is installed in the circumferential wall of the engine cylinder filled with cooling water, and the detected water temperature signal is transmitted to the ECU 3. supply to.

An engine rotational speed (No.) sensor 9 and a cylinder discrimination sensor 10 are attached around a camshaft or a crankshaft (not shown) of the engine 1. The engine rotation speed sensor 9 sends a predetermined control signal (hereinafter referred to as rTDC signal) pulse at a predetermined crank angle position before top dead center (TDC) of each cylinder every 1801 revolutions of the crankshaft of the engine 1. The cylinder discrimination sensor 10 outputs cylinder discrimination signal pulses at predetermined crank angle positions of specific cylinders, and these signal pulses are supplied to the ECU 3.

On the other hand, a three-way catalyst 12 is disposed in the exhaust pipe 11 of the engine 1 to purify HC, Go, and NOx components in the exhaust gas. The 02 sensor (
An exhaust gas concentration detector) 13 is inserted into the exhaust pipe 11.

The o3 sensor 13 outputs a rich signal to the ECU 3 when the detected output voltage value vO□ representing the oxygen concentration in the exhaust gas exceeds a predetermined reference value Vr, which will be described later, and outputs a lean signal to the ECU 3 when the o3 sensor 13 falls below a predetermined reference value Vr. The signals indicate that the air-fuel mixture is richer or leaner than the target air-fuel ratio, respectively;
A vehicle speed (Sp) sensor 14 is connected to the CU3.

The vehicle speed sensor 14 detects vehicle speed, and its detection signal is supplied to the ECU 3.

The ECU 3 includes an input circuit 5a and a central processing circuit (hereinafter referred to as "central processing circuit") having functions such as shaping input signal waveforms from the various sensors described above, correcting voltage levels to predetermined levels, and converting analog signal values into digital signal values. rCPUJ)5
b, a storage means 5c for storing various calculation programs executed by the CPU 5b and their calculation results, and an output circuit 5d for sending a drive signal to the fuel injection valve 6. The ECU 3 controls the fuel injection valve 6 given by the following formula based on various parameter signals introduced from each of the sensors.
The fuel injection time Toυ〒 is calculated.

Tou = TiXKo, XK1+, ・= (1)
Here, Ti indicates the basic fuel injection time of the fuel injection valve 6, and this basic injection time is read from the storage means 5c in the ECUS based on, for example, the intake pipe absolute pressure Pa^ and the engine speed Ne.

KO□ is a 0□ feedback correction coefficient calculated from a calculation program flowchart (FIG. 2) according to the present invention, which will be described later. Further, K1 and Ks are correction coefficients and correction variables respectively calculated according to various engine parameter signals, and are necessary to optimize various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to engine operating conditions. set to the value.

The ECU 3 calculates the fuel injection time Toυ obtained as described above.
A drive signal is supplied to the fuel injection valve 6 to open the fuel injection valve 6 based on 〒.

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 explained.

FIG. 2 shows a flowchart of a subroutine for calculating the feedback correction coefficient Ko according to the control method of the present invention. This program is executed by the ECU 3 every time a TDC signal pulse is generated.

First, it is determined whether the activation of the 03 sensor 13 has been completed (step 201), that is, the internal resistance of the 08 sensor 13 is detected by the internal resistance detection method. It is detected whether the output voltage of the sensor 13 has reached the activation start point VX (for example, 0.6 V), and when it has reached Vx, it is determined that it is activated.

If this answer is negative (No), the coefficient value Ko is set to 1
．． Set it to 0 and exit this program (step 20
2).

If the answer to step 201 is affirmative (Yes), it is determined whether the engine 1 is in the oven loop control region (step 203). The high-load operation range includes a rotation range, a lean mixture range, etc., and the high-load operation range is, for example, a range in which the fuel injection time Tou〒 is set to a value larger than a predetermined value TWOT. Here, Two is a constant and is the lower limit of the amount of fuel supplied necessary to enrich the air-fuel mixture during high-load operation such as when the throttle valve is fully open. The low rotation range is an area where the engine rotation speed No is less than a predetermined value NLOP (for example, 700 rpm), and the high rotation area is an area where the engine rotation speed No is greater than the predetermined rotation speed NHOP (for example, 3000 rpm). The air-fuel mixture lean region is the intake pipe absolute pressure P
This is a region where a^ is smaller than the discrimination value PaIJ, which is set to a larger value as the engine speed No increases.

If the answer to step 203 is YES, that is, in any of the above areas, the process proceeds to step 202 and KO.

Set this 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 moves to closed loop control. (step 204), this step 204
The determination in is that the engine rotational speed Na is the predetermined rotational speed NI
DL (for example, lower than 101000 rpm and θ〒H
The sensor 4 determines whether or not the throttle valve opening degree H is substantially fully open.

If the answer to step 204 is affirmative (Yes), that is, engine 1
is in the idle operation range, the process proceeds to step 205, and the vehicle equipped with the engine is either a vehicle equipped with an automatic transmission (hereinafter referred to as an "rAT vehicle") or a vehicle equipped with a manual transmission (hereinafter referred to as an rMT vehicle). ”) and, if the vehicle is an AT vehicle, whether the automatic transmission 15 is in the drive range. The above-mentioned determination as to whether the vehicle is an AT vehicle or not is performed based on the output of a transmission type switch (not shown) which is switched between ON and OFF states depending on whether the vehicle is an AT vehicle or an MT vehicle, for example.

If the answer to step 205 is negative (No), that is, the vehicle is an MT vehicle, or even if the vehicle is an AT vehicle, the automatic transmission 15 is not in the drive range.
The reference value Vr of the second sensor 13 is set as the first reference value Vros.
(Step 206) to set the first reference value 1, for example 0.49V), and then proceed to Step 211, which will be described later.If the answer to Step 205 is affirmative (Yes), that is, the vehicle is an AT vehicle and the automatic When the shift state of the transmission 15 is in the drive range, the reference value Vr is set to a second reference value Vrob (second
Step 20
7), then proceed to step 211.

As will be described later, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is controlled to be a target air-fuel ratio corresponding to the reference value Vr, and the larger the reference value Vr, the richer the air-fuel ratio as a whole. Therefore, step 204 mentioned above
The control of ~207 enriches the air-fuel ratio of the air-fuel mixture as a whole when the internal combustion engine equipped with an automatic transmission is in an idling state and the automatic transmission is in the drive range, thereby reducing nitrogen oxides. (NOx) emissions can be reduced.

If the answer to step 204 is negative (No), that is, the engine 1 is not in the idle operating region, step 208
Then, it is determined whether the vehicle is an AT vehicle or not. If the answer to step 208 is negative (No), that is, the vehicle is M
When the vehicle is a T vehicle, the reference value Vr is set to a third reference value Vr.
Set it to 1M (for example, 0.55V) (Step 209)
, then proceed to said step 211, said step 20
If the answer to question 8 is affirmative (Yes), that is, the vehicle is an AT vehicle, the reference value Vr is set to a fourth reference value Vrt^ (for example, 0.60V) that is larger than the third reference values Vr and M. step 210), then step 211)
As a result, when the engine installed in an AT vehicle, which requires higher engine output than an MT vehicle, is in a normal feedback operation range other than the idling operation range, the air-fuel ratio is enriched as a whole. By doing so, appropriate engine output can be ensured.

In step 211, the output level of the 02 sensor 13 is set to TD.
It is determined whether or not the C signal pulse was reversed between the previous input and the current input, and if the answer is yes, the proportional term (P term) control in steps 212 and below is negated. (N
o), the integral term (1 term) control from step 217 onwards is performed, and when the answer to step 211 is affirmative (Yes), the output level of the sensor 13 is 0□.
The reference value V set at ゜207.209 or 210
r (V r o?ll, V r OD, V r
Step 212) to determine whether it is a low level (lean signal) with respect to zM or Vr, ^), and if the answer is affirmative (Yes), the P shit setting subroutine described later is executed to apply the correction value Pyt. (FIG. 3), a correction value P is determined (step 213), and then, in step 214, this correction value P11 is added to the previous same value of the coefficient value Ko, and this program ends.

On the other hand, when it is determined in step 212 that the output level of the 0□ sensor 13 is at a high level (rich signal) with respect to the reference value Vr, in order to apply the correction value PL, the Pt setting subroutine (fourth The correction value PL is determined by (step 215).

Then, in step 216, this correction value PL is subtracted from the coefficient value Ko at the previous loop, and the program ends.

Next, the integral term (1 term) control from step 217 onwards is performed as follows. First, in step 211, 02
Step 2 is performed when the output level Vo of the sensor 13 is on the same level side as in the previous loop with respect to the reference value Vr.
17, it is determined whether the output of the 02 sensor 13 is on the low level side. If the answer is affirmative (Yes), 1 is added to the count number NIL of the TDC signal pulse (step 218), and the count number NIL is a predetermined value N+
(for example, 4) is determined (step 21).
9) As a result of this determination, if the count number NIL has not yet reached N1, the coefficient value Ko is maintained at the value at the previous loop (step 220), and if the count number NIL has reached N1, the coefficient value Ko is maintained at the value at the previous loop. In order to apply the predetermined value ΔK, a predetermined value ΔK is obtained by a Δ setting subroutine (FIG. 5) described later (step 221), and then in step 222, this predetermined value ΔK is added to the same value before the coefficient value Ko, At the same time, the count number N of TDC signal pulses is reset to O (step 223), and this program is ended. That is, the predetermined value Δ is added to the coefficient value Ko every time the count number Nl reaches N+.

On the other hand, if the answer to step 217 is negative (No), 1 is added to the count number NIH of TDC signal pulses.
is added (step 224), and it is determined whether the count number NIH has reached a predetermined value N+ (step 225),
If the answer is negative (No), the value of the coefficient value Ko is maintained at the value at the previous loop (step 226), and if the answer is affirmative (Yes), the value is set to Δ as in step 221. A predetermined value ΔK is determined by the subroutine (step 227).

Next, the predetermined value ΔK is subtracted from the coefficient value Ko (step 228), the count number NIH is reset to O (step 229), and the program is ended and the coefficient value Ko is subtracted every time NtH reaches N+ as described above. , to a predetermined value Δ
Let K be subtracted.

FIG. 3 shows the coefficient value K executed in step 213 of FIG.
This is a subroutine for setting the correction value P buy in the direction of enrichment of o2.

First, in step 301, it is determined whether the engine 1 is in an idle operating state. This determination is performed using a method similar to step 204 in FIG. When the answer is Yas, that is, when the engine 1 is in an idling operating state, the correction value PR is set to the first correction value P for idling. (For example, set it to 0.15 in step 302)
, negative (No), that is, when the engine 1 is not in an idling operating state, the correction value PII is set to a second correction value Pg for off-idling, which is larger than the first correction value Pea (for example, o, go). (Step 303), thereby suppressing large fluctuations in the air-fuel ratio when the engine 1 is in an idling state with an unstable combustion state.

FIG. 4 shows the coefficient value K executed in step 215 of FIG.
This is a subroutine for setting the correction value PL in the lean direction of .o.

First, in step 401, it is determined whether the engine 1 is in an idle operating state. This discrimination method is also the second
This step is similar to step 204 in the figure and step 301 in FIG. This answer is affirmative (Yes).

That is, when the engine 1 is in the idle operating state, the process proceeds to step 402, and the correction value P+ is set to the first correction value PL for idling (for example, 0.15).

If the answer to step 401 is negative (No), that is, the engine 1 is not in an idling state, the process proceeds to step 403, where the vehicle speed SP is set to a predetermined judgment value of 5PFD (for example, 72 km).
/h).

The answer to this step 403 is negative (No), that is, Sp≦5
When PFD is established, the process proceeds to step 404, where it is determined whether the vehicle is an AT vehicle. This determination is the second
This is performed using the same method as the determination in step 208 in the figure. The answer to step 404 is affirmative (Yes
%, that is, if the vehicle is an AT vehicle, the process proceeds to step 405, where it is determined whether the intake pipe absolute pressure Pe^ is larger than a predetermined discrimination value PaA^ (for example, 460-mHg) for AT vehicles.

The answer to this step 405 is negative (No), that is, Pa^≦
When Pa^^ is established, the correction value PL is changed to the second correction value PLiL^ (for example, 0.
Step 406), affirmative (Yes);
In other words, when PBA>PB^^ is established, the correction value PL is changed to the third correction value PL1H^ for AT vehicles at low/medium speeds and high loads.
(for example, 0.90) (step 407).

If the answer to step 404 is negative (No), that is, the vehicle is a manual transmission vehicle, the process proceeds to step 408, where it is determined whether the intake pipe absolute pressure PB^ is larger than a predetermined discrimination value PBAM for manual transmission vehicles (for example, 360-8g). Determine whether The answer to this step 408 is negative (No), that is, Pa^≦PBA
When M holds true, the correction value PL is changed to the fourth correction value PL, LM (for example, 0.85
), step 409) is affirmative (Yes), that is, when PBA>PBAM holds true, the correction value PL is set to a low value.
A fifth correction value PL18M (for example, 0.76) for MT vehicles at medium speed and high load is set (step 410).

The answer to step 403 is affirmative (Yes), that is, SP>
When 5PFD is established, the process proceeds to step 411, where it is determined whether the vehicle in question is an AT vehicle.

If the answer to step 411 is affirmative (Yes), that is, the vehicle is an automatic transmission vehicle, the correction value PL should be set to the sixth correction value PL for automatic transmission vehicles at high speeds (for example, 0.90) in step 412. ), negative (No), that is, the vehicle MT
When the vehicle is a car, the correction value PL is set to the seventh value for manual transmission vehicles at high speeds.
The correction value PL, M (for example, 0.78) is set (step 413).

As described above, the correction value P of the coefficient value Ko in the lean direction
L is set to an optimal value depending on whether or not the engine 1 is in an idling state, the vehicle speed, whether it is an AT car or a MT car, the absolute pressure in the intake pipe, etc., so that the output level of the OT sensor 13 is on the rich side. When the air-fuel ratio is reversed, the air-fuel ratio can be appropriately controlled in the lean direction.

FIG. 5 shows step 221 or step 227 in FIG.
This is a subroutine for setting the predetermined value Δ.

First, in step 501, it is determined whether the engine 1 is in an idle operating state. The answer is yes.
), that is, when the engine 1 is in the idle operating state, it is determined whether a predetermined time 'r, (for example, 10 seconds) has elapsed after entering the idle operating state (step 50
2), if the answer to this step 502 is negative (No), that is, after the engine 1 is in the idle operating state, the predetermined time TG
has not passed, the predetermined value ΔK is changed to the first predetermined value Δ
Ko, (for example, set to 0.06) (step 503)
.

If affirmative (Yes), that is, when the predetermined time TQ has elapsed after entering the idling state, the predetermined value ΔK is set to the second predetermined value ΔKo (for example, 0.03) (step 5
04).

If the answer to step 501 is negative (No), that is, the engine 1 is not in an idling state, it is determined whether the vehicle is an AT vehicle (step 505), and the answer to step 505 is negative (No). .

That is, when the vehicle is an MT vehicle, the predetermined value ΔK is set to the first and second predetermined values ΔKo1 and ΔKo for idle.
, the third predetermined value Δ for MT vehicles is set to 1M (for example, 0.15) (step 506).

If affirmative (Yes), that is, when the vehicle is an AT vehicle, the predetermined value ΔK is set to the third predetermined value Δ, which is A greater than 1M.
The fourth predetermined value Δ for T vehicles is set to ^ (for example, 0.25) (step 507).

With the above settings, the predetermined value Δ can be optimally set depending on whether the engine 1 is in an idling state or not, and whether the vehicle is an AT vehicle or a MT vehicle. - The air-fuel ratio when maintaining the level on the negative side can be appropriately controlled in the direction of correcting it to the target air-fuel ratio.

(Effects of the Invention) As detailed above, the present invention applies when the automatic transmission of an internal combustion engine is in the drive range, and when the engine is in an idling state, the air-fuel ratio of the mixture is rich as a whole. This has the effect of reducing nitrogen oxide (NO) emissions and improving exhaust gas characteristics.In addition, the engine speed is lower when the air-fuel ratio is on the lean side. Since the range of variation is large, enriching the air-fuel ratio reduces the range of variation in engine speed, which also has the advantage of improving drivability during idling operation.

[Brief explanation of the drawing]

FIG. 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 the procedure for calculating the 0□ feedback correction coefficient Ko, and FIG. 3 is a flowchart showing the procedure for calculating the 0□ feedback correction coefficient Ko. FIG. 4 is a flowchart of the subroutine for setting the correction value PL executed in step 215 of FIG. 2, and FIG. 2 is a flowchart of a setting subroutine. 1... Internal combustion engine, 5... Electronic control unit (ECU), 13... 02 sensor (exhaust concentration detector), 15... Automatic transmission.

Claims (1)

[Claims] 1. Compare the exhaust concentration value detected by the exhaust concentration detector disposed in the exhaust system of an internal combustion engine equipped with an automatic transmission with a first reference value, and adjust the mixture supplied to the engine according to the comparison result. In the air-fuel ratio feedback control method for an internal combustion engine, the air-fuel ratio of the automatic transmission is feedback-controlled to a predetermined target air-fuel ratio. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that when a certain condition is detected, a reference value to be compared with the exhaust gas concentration value is set to a second reference value that is larger than the first reference value.