JPH0480220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine, and particularly to a feedback control method designed to improve drivability during acceleration and deceleration in the air-fuel ratio feedback control region. This is related to.

(Technical background of the invention and its problems) A method of electrically controlling the amount of fuel supplied to an internal combustion engine according to the operating state of the engine is provided, which detects the engine load and engine cooling water temperature, and From the detected engine load and cooling water temperature, the water temperature increase coefficient, which is one of the factors that determines the fuel supply amount, is determined, and when the combustion chamber is cold,
The applicant has proposed a fuel supply control method for an internal combustion engine that enables stable combustion to be obtained even when the evaporation rate of fuel decreases due to the low temperature of the inner wall of the cylinder, etc. 187534).

By the way, when acceleration/deceleration motion is performed in the air-fuel ratio feedback control region of the air-fuel mixture, the fuel injected from the fuel injection valve adheres to the inner wall of the intake pipe during acceleration, causing the air-fuel ratio of the air-fuel mixture supplied to the engine to become lean. On the other hand, when decelerating,
The fuel adhering to the inner wall surface of the intake pipe becomes atomized and the air-fuel ratio tends to become richer. As a result, during deceleration, the air-fuel ratio becomes richer, which lowers the exhaust gas cleaning efficiency, while during acceleration, the air-fuel ratio becomes leaner, which deteriorates engine drivability. This tendency is particularly noticeable at low temperatures when the amount of fuel adhering to the wall increases. Therefore, in order to obtain an air-fuel mixture that provides stable combustion especially at low temperatures, it is necessary to appropriately control the amount of fuel supplied even during acceleration and deceleration operations.

(Purpose of the Invention) This invention was made to solve the above problem, and its purpose is to improve the fuel supply during acceleration/deceleration operation, especially at low temperatures, in the air-fuel ratio feedback control region of the air-fuel mixture. An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine, which prevents deterioration of drivability at the start of acceleration and prevents a decrease in exhaust gas purification rate at the start of deceleration by appropriately controlling the amount. be.

(Structure of the Invention) In order to achieve the above object, according to the present invention,
The amount of air-fuel mixture supplied to the engine is determined by multiplying the basic fuel amount, which is determined according to the operating state of the internal combustion engine, by a coefficient that changes depending on the output of an exhaust gas concentration detector located in the exhaust system of the engine. In an air-fuel ratio feedback control method for an internal combustion engine that controls the air-fuel ratio, an engine load is detected by a load sensor, an engine temperature is detected by a temperature sensor, and it is determined from a change in the engine load that the engine is in an acceleration state or a deceleration state. In the acceleration state, the current value of the coefficient is obtained by adding a correction value according to the amount of change in the engine load and the engine temperature in the state to the previous value of the coefficient, and in the deceleration state, the change in the engine load in the state Provided is an air-fuel ratio feedback control method for an internal combustion engine, characterized in that the current value of the coefficient is determined by subtracting a correction value according to the amount of air and engine temperature from the previous value of the coefficient.

(Embodiments of the invention) Examples of the invention will be described below based on the drawings. FIG. 1 illustrates the overall configuration of an air-fuel ratio control device to which the method of the present invention is applied. Code 1 in the diagram
shows, for example, a four-cylinder internal combustion engine, and 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 (not shown) is provided inside. A throttle valve opening (θth) sensor 4 is connected to the throttle valve, which converts the valve opening of the throttle valve into an electrical signal and guides it to an electronic control unit (hereinafter referred to as "ECU") 5. .

Engine 1 and throttle body 3 of intake pipe 2
In between, a fuel injection valve 6 is provided 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 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 will be described later.

On the other hand, an absolute pressure (P _BA ) sensor 7 is provided downstream of the throttle valve in the throttle body 3 of the intake pipe 2, and an electric signal representing the absolute pressure from the absolute pressure sensor 7 is guided to the ECU 5. .

An engine water temperature sensor (hereinafter referred to as "Tw sensor") 8 is provided in the engine 1 body. Tw
The sensor 8 is composed of a thermistor or the like, and is inserted into the circumferential wall of the engine cylinder filled with cooling water, and supplies the detected water temperature signal to the ECU 5.

An engine rotation angle position sensor 9 and a cylinder discrimination sensor 10 are attached around a camshaft or crankshaft (not shown) of the engine. The engine rotation angle position sensor 9 is located at the top dead center (hereinafter referred to as "TDC").
) signal, i.e. 180° of the engine crankshaft
At each rotation, a predetermined crank angle position signal (hereinafter referred to as "TDC signal") is generated at a predetermined crank angle position before the TDC of each cylinder, and the cylinder discrimination sensor 1
0 outputs a cylinder discrimination signal at a predetermined crank angle position of a specific cylinder, and these signals are
Guided by ECU5. On the other hand, a three-way catalyst 12 is disposed in the exhaust pipe 11 of the engine 1 to purify HC, CO, and NOx components in the exhaust gas.
Upstream of the three-way catalyst 12, for example, an O ₂ sensor 13 is inserted into the exhaust pipe 11 as an exhaust concentration detector. The _O2 sensor 13 detects the oxygen concentration in the exhaust gas and outputs a deviation signal between the detected value and a predetermined reference value.
Supply to ECU5. The ECU 5 shapes the waveforms of some of the input signals from the various sensors mentioned above, while
An input circuit 5a having functions such as correcting the voltage level of other input signals to a predetermined level and converting an analog signal value into a digital signal value, a central processing circuit (hereinafter referred to as "CPU") 5b, and this CPU 5b.
Various calculation programs executed in and their calculation results, as well as |ΔP _B |−ΔKo ₂ table, which will be described later.
It is comprised of a storage means 5c for storing the Pi _A table, the Δk table, etc., an output circuit 5d for sending a drive signal to the fuel injection valve 6, and the like.

The ECU 5 calculates the fuel injection time Tout of the fuel injection valve 6 given by the following equation based on various parameter signals introduced from each sensor.

Tout= _{Ti × Ko 2} The TDC signal mentioned above causes the CPU to
It is read out from the storage means 5c in the ECU 5 based on the engine rotation speed Ne calculated in step 5b.
Ko ₂ is an O ₂ feedback correction coefficient according to the present invention which will be described in detail later, and the correction coefficient value at the current loop during feedback control is expressed as ko ₂ n,
When the correction coefficient value at the previous loop is ko ₂ n _-1 , the O ₂ feedback correction coefficient value ko ₂ n is expressed by the following equation.

ko ₂ = ko ₂ n _-1 ±∆ko ₂ + Pi + ∆k ...(2) Here, ∆ko ₂ is a correction value determined according to the amount of change in engine load and engine temperature during acceleration or deceleration. In the example, the absolute pressure in the intake pipe is used as a parameter corresponding to the engine load.
Since P _BA is taken and the engine coolant temperature Tw is taken as the engine temperature, this correction value is ΔKo ₂
=f(ΔP _B , Tw). Note that in the formula for ΔKo ₂ , ΔP _B is the amount of change in absolute pressure during transient acceleration/deceleration. Pi changes the output of the O ₂ sensor 13 from the rich side to the lean side with respect to the predetermined reference value.
Or, the proportional term correction value Δk applied when changing from the lean side to the rich side is used to increase or decrease at predetermined intervals when the output of the O ₂ sensor 13 is on the lean side or rich side with respect to a predetermined reference value. is the integral term correction value applied to .

In addition, K ₁ and K ₂ in the above equation (1) are a correction coefficient and a correction variable respectively calculated according to various engine parameter signals, and it is possible to optimize engine operating characteristics such as fuel efficiency according to engine operating conditions. The required value is determined as follows.

The ECU 5 supplies the fuel injection valve 6 with a drive signal to open the fuel injection valve 6 based on the fuel injection time Tout determined as described above.

Next, the diagrams in Figures 2 a to d, and |ΔP _B in Figure 3
An air-fuel ratio feedback control method according to an embodiment of the present invention will be described with reference to the |-ΔKo ₂ table. As shown in Fig. 2a, the absolute pressure inside the intake pipe changes in the positive direction during acceleration (ACC), and changes in the negative direction during deceleration (DEC). In this example, the correction value ΔKo ₂ =f (ΔP _B , Tw) is obtained from the same table both during acceleration and deceleration, so the horizontal axis in FIG. 3 represents the absolute value of the amount of change. It is shown as |ΔP _B |.

As mentioned above, when the engine is cold, a relatively large amount of fuel adheres to the inner wall surface of the intake pipe, but at this time, the engine is decelerated in the air-fuel ratio feedback control region, and the adhering fuel is removed due to a decrease in the absolute pressure inside the intake pipe. It becomes atomized and the air-fuel ratio becomes richer. On the other hand, when acceleration is performed in the feedback control region, an increase in the injection amount sometimes causes a large amount of fuel to adhere, causing the air-fuel ratio to become lean. This phenomenon becomes more noticeable as the temperature decreases, as the amount of attached fuel increases. In this embodiment, even if such a phenomenon occurs, the air-fuel ratio of the air-fuel mixture is controlled to be the target air-fuel ratio (for example, the stoichiometric air-fuel ratio). Therefore, the control contents will be explained separately for the temperature states when the engine cooling water temperature Tw is high, medium, and low, corresponding to the diagrams in FIGS. 2b, c, and d.

(a) At high temperatures (Tw≧Tw ₁ , equivalent to Figure 2b).
Tw ₁ is a temperature of about 80 to 90°C and the engine coolant temperature Tw is higher than this. At such high temperatures, the atomization of fuel from the inner wall of the intake pipe is good, and even if accelerated operation is performed in the air-fuel ratio feedback control region, almost no fuel will adhere to the inner wall of the intake pipe. Therefore _, in this case _, the correction value ΔKo ₂ in equation (2) is set to zero from the _| ΔP _B |−ΔKo ₂ table in FIG. Depending on the level, correction is performed using only both the proportional term correction value Pi and the integral term correction value Δk. That is, when the O ₂ sensor output changes from a rich signal to a lean signal or from a lean signal to a rich signal, the proportional term correction value Pi is applied to increase or decrease the O ₂ feedback correction coefficient Ko ₂ , respectively. When the O ₂ sensor output is on the rich side without inversion, or when it is on the lean side, the integral term correction value Δk is applied to gradually increase the O ₂ feedback correction coefficient Ko ₂ (middle area in Figure 2 b). The average value ₂ of the correction coefficient is controlled to a required value such that the air-fuel ratio of the air-fuel mixture becomes the target air-fuel ratio by performing a correction or a gradual reduction correction.

(b) At medium temperature (Tw ₁ > Tw ≧ Tw ₂ corresponds to Figure 2 c).
Tw ₂ is a temperature of about 50 to 60°C, which is when the engine cooling water temperature Tw is at a medium temperature above this temperature Tw ₂ . When the temperature drops to this level, fuel adheres to the inner wall of the intake pipe, and during deceleration this atomizes and the air-fuel ratio becomes richer, but during acceleration the adhering fuel particularly increases, causing the air-fuel ratio to become lean. start. Therefore, in this temperature range, the corresponding correction value ΔKo ₂ ' is determined from the temperature Tw and the amount of change in absolute pressure during deceleration and acceleration |ΔP _B | from the |ΔP _B |−ΔKo ₂ table in Figure 3. , this correction value ΔKo 2 ' is added to the O ₂ feedback correction coefficient Ko ₂ during acceleration, and on the other hand, this correction value ΔKo _{2 '} is subtracted during deceleration.
In this way, during acceleration (ACC), extra fuel is injected in an amount corresponding to the amount of fuel that adheres to the inner wall of the intake pipe due to a sudden change in the intake pipe absolute pressure P _BA in the increasing direction. Shift the correction coefficient Ko ₂ to a larger value by the required amount to
On the other hand, during deceleration (during DEC), a correction coefficient is used to reduce _the fuel supply by an amount corresponding to the amount of fuel atomized from the inner wall surface of the intake pipe due to a sudden change in the intake pipe absolute pressure P BA in the decreasing direction. Shift ko ₂ to a smaller value by the required amount. Then, from the point shifted by the required amount in the plus or minus direction, a proportional term correction and an integral term are added to the correction coefficient ko ₂ in the same way as in item (a) above. When the absolute pressure P _BA in the intake pipe during deceleration and acceleration reaches a steady state after a sudden change, the correction coefficient Ko ₂
The average value ₂ gradually returns to the required value that makes the air-fuel ratio of the air-fuel mixture the same as the target air-fuel ratio as in item (a) above.

(c) Low temperature (Tw ₂ >Tw≧Tw ₃ , corresponding to FIG. 2 d) This is when the engine cooling water temperature Tw is equal to or higher than Tw ₃ , which is a temperature even lower than Tw ₂ .
In this case, from the table |ΔP _B |−ΔKo ₂ ,
A larger correction value ΔKo ₂ ″ is obtained, and the correction coefficient Ko ₂ during the transition between deceleration and acceleration is corrected by this correction value ΔKo ₂ ″. The point that the proportional term correction and the integral term correction are added to the correction coefficient Ko ₂ from the point shifted by the required amount by this correction is the same as in the case (d) above. Even if the engine coolant temperature Tw falls to a low temperature in this way, the average value ₂ is controlled and corrected to a required value that makes the air-fuel ratio of the air-fuel mixture the target air-fuel ratio.

FIG. 4 shows a flowchart of a subroutine for calculating the O ₂ feedback correction coefficient Ko ₂ according to the embodiment of FIG.

First, it is determined whether activation of the O ₂ sensor 13 has been completed (step 15). That is, the O ₂ sensor 13 internal resistance detection method detects whether the output voltage of the O ₂ sensor 13 has reached the activation starting point Vx (for example, 0.6 V), and when it reaches Vx, it is activated. It is determined that there is. If the answer is negative (No), the coefficient value _ko2 is set to 1 (step 16). On the other hand, if the answer is affirmative (Yes), it is determined whether the engine is in the open loop control region (step 17). If the judgment result is affirmative (Yes), the coefficient value Ko ₂ is set to 1 (step 16) in the same way as above, and the correction coefficient K ₁ is set to a value according to the engine operating condition, and this is applied. performs open loop control.

On the other hand, if the answer to step 17 is negative (No), it is determined that the engine is in the feedback region, and the system moves to closed-loop control, and the engine cooling water temperature Tw detected by the Tw sensor 8 is a temperature Tw ₁ of about 80 to 90°C. It is determined whether the temperature is higher than (step 18). This judgment result is negative (No)
If so, as mentioned above, the phenomenon of fuel adhesion and atomization on the inner wall surface of the intake pipe will appear, and the control of the air-fuel _ratio will be affected by this during acceleration and deceleration. It is determined whether acceleration is detected (step 19). If the answer is affirmative (Yes), the acceleration correction value ΔKo ₂ corresponding to the amount of change in the engine coolant temperature Tw and absolute pressure at that time |ΔP _B | is calculated from the |ΔP _B |−ΔKo ₂ table (step 20 ), this is added to the feedback correction coefficient Ko ₂ from the previous loop to obtain the corresponding correction coefficient Ko _2.
is shifted in the positive direction by the value of this correction value ΔKo ₂ (step 20). If the answer to step 19 is negative (No), the process moves to step 22 and it is determined from the change in the intake pipe absolute pressure P _BA whether deceleration has been detected. If the answer is yes _, use the same procedure as above to find the correction value ΔKo during deceleration corresponding to the amount of change in engine coolant temperature Tw and absolute pressure at that time |ΔP _B | -ΔKo ₂ table ₂ (step 23), and subtract this from the feedback correction coefficient Ko ₂ from the previous loop to obtain the corresponding correction coefficient.
Ko ₂ is shifted in the negative direction by this correction value ΔKo ₂ (step 24).

When the addition (step 21) or subtraction (step 24) of the correction value ΔKo ₂ corresponding to the above-mentioned acceleration or deceleration is completed, when the answer to step 22 is negative (No), or when the answer to step 18 is If the judgment result is affirmative (Yes),
Correct by proportional term correction or integral term correction according to the output level of the _O2 sensor. i.e. _O2 sensor 1
Determine whether the output level of 3 has been inverted between the previous input of the TDC signal and the current input (step
25), if the judgment result is affirmative (Yes), perform proportional term correction. Then, a correction value Pi is determined from a table for determining the value of Pi corresponding to the number of rotations Ne, etc. stored in the storage means 5c (step 26). Next, it is determined whether the output level of the O ₂ sensor 13 is a low level (lean signal) with respect to the reference value (step 27), and if the answer is affirmative (Yes), this correction value Pi is set in step 28. is added to the value of the coefficient value Ko ₂ from the previous loop. On the other hand, when it is determined in step 27 that the output level of the O ₂ sensor 13 is at a higher level (rich signal) than the reference value, in step 29 the coefficient value of the previous loop is determined.
Subtract the correction value Pi from Ko ₂ .

Next, the integral term correction in steps 30 and below is performed as follows. First, in step 25, if the output level of the O ₂ sensor 13 is on the same level side as the previous loop with respect to the reference level, the process proceeds to step 30, and it is determined whether the output of the O ₂ sensor 13 is on the low level side. do. If the answer is affirmative (Yes), add 1 to the value of the count number N _IL of TDC signal pulses (step 31), and check whether the count number N _IL has reached a predetermined value N _I (for example, 4). (Step 32). As a result of this determination, if the count number N _IL has not yet reached N _I , the coefficient value Ko ₂ is maintained at the value at the previous loop (step 33), and if the count number N _IL has reached N _I A predetermined value Δk (for example, about 0.3% of Ko ₂ ) is added to Ko ₂ (step 34).
At the same time, the number of pulses N _IL counted so far is set to 0 (step 35), and a predetermined value Δk is added to Ko ₂ every time N _IL reaches N _I. On the other hand,
If the answer is negative (No) in step 30, 1 is added to the pulse count N _IH of the TDC signal (step 36), and the count N _IH is set to a predetermined value.
It is determined whether N _I has been reached (step 37), and if the answer is negative (No), the value of the coefficient value Ko ₂ is maintained at the value from the previous loop (step 38), and the answer is affirmative. If (Yes), the coefficient value Ko ₂ of the previous loop
Subtract a predetermined value Δk from Ko 2 (step 39), reset the counted pulse number N _IH to 0 (step 40), and subtract a predetermined value Δk from Ko ₂ each time N _IH reaches N _I in the same way as above. I'll do what I do.

In the above embodiment, the correction value ΔKo ₂ was obtained from the same |ΔP _B |−ΔKo ₂ table shown in FIG. 3 both during acceleration and deceleration.
The correction value ΔKo ₂ during acceleration and the correction value Δko ₂ during deceleration can also be obtained from separate tables. This makes it possible to obtain a more accurate correction value ΔKo ₂ corresponding to the difference between the amount of fuel that adheres to the inner wall surface of the intake pipe during acceleration and the amount of fuel atomized from the inner wall during deceleration.

(Effects of the Invention) As detailed above, according to the present invention, the basic fuel amount determined according to the operating state of the internal combustion engine is determined according to the output of the exhaust gas concentration detector disposed in the exhaust system of the engine. In the air-fuel ratio feedback control method for an internal combustion engine, which controls the air-fuel ratio of the air-fuel mixture supplied to the engine by multiplying the air-fuel ratio by a coefficient that changes depending on the engine, the engine load is detected by a load sensor, the engine temperature is detected by a temperature sensor, It is detected from the change in the engine load that the engine is in an acceleration state or a deceleration state, and when the engine is in an acceleration state, a correction value corresponding to the amount of change in the engine load and the engine temperature in the state is added to the previous value of the coefficient. The current value of the coefficient is determined, and during deceleration, the current value of the coefficient is determined by subtracting the correction value according to the amount of change in engine load and engine temperature in that state from the previous value of the coefficient. It is possible to prevent deterioration in drivability during deceleration, and it is also possible to prevent a decrease in exhaust gas purification rate during deceleration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of an air-fuel ratio control device applied to the present invention, Fig. 2 is a timing chart showing changes over time in the O ₂ feedback correction coefficient value Ko ₂ , and Fig. 3 is a change in absolute pressure in the intake pipe. Quantity｜
A graph showing a table of the relationship between P _B | and correction value ΔKo ₂ , and FIG. 4 is a flowchart showing the procedure for calculating the O ₂ feedback correction coefficient Ko ₂ . DESCRIPTION OF SYMBOLS 1...Internal combustion engine, 2...Intake pipe, 5...Electronic control unit, 6...Fuel injection valve, 7
...Intake pipe absolute pressure sensor, 13... _O2 sensor.

Claims (1)

[Claims] 1 The air-fuel mixture supplied to the engine is calculated by multiplying the basic fuel amount determined according to the operating state of the internal combustion engine by a coefficient that changes according to the output of an exhaust gas concentration detector located in the exhaust system of the engine. In the air-fuel ratio feedback control method for an internal combustion engine, the engine load is detected by a load sensor, the engine temperature is detected by a temperature sensor, and the engine is in an acceleration state or a deceleration state based on a change in the engine load. In the acceleration state, the current value of the coefficient is determined by adding a correction value according to the amount of change in the engine load and the engine temperature in the state to the previous value of the coefficient, and in the deceleration state, the current value of the coefficient is determined. An air-fuel ratio feedback control method for an internal combustion engine, characterized in that the current value of the coefficient is determined by subtracting a correction value according to the amount of change and engine temperature from the previous value of the coefficient.