JPH0670382B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to improving the air-fuel ratio control accuracy in a transient operation state of a spark ignition type internal combustion engine. To an improved air-fuel ratio control device.

(Prior Art) In an internal combustion engine for vehicles, etc., how to appropriately control the amount of fuel or the air-fuel ratio supplied to the engine from the viewpoint of meeting the demand for exhaust gas purification while improving the output performance and drivability originally required for the engine. Whether you do it is an important issue. In particular, vehicle engines are used in a wide operating range from low-speed low-load to high-speed high-load, so the suitability of air-fuel ratio control in transient operating conditions such as acceleration and deceleration greatly affects drivability and exhaust emissions. .

Therefore, based on an electronically controlled fuel injection device with excellent fuel metering accuracy, the fuel injection amount is increased or decreased during acceleration or deceleration so that an appropriate air-fuel ratio can be obtained in all operating conditions including transitions. The control device and control method described above are being adopted in many vehicle engines. (As a known example of this type of control method, for example, JP-A-58-144632, 144634, 144636, 1500
See Nos. 33, 150042 and 150043. ) The reason why such transient correction is necessary is that fuel that adheres to the inner wall surface of the intake pipe or the intake port before reaching the engine cylinder or fuel that is not sucked and floats in the intake pipe (these fuels are The amount of "adhesion of the intake system, floating fuel") affects the air-fuel ratio or engine performance during a transient state. Since the part adheres to the intake system and causes a delay in the supply response, the actual air-fuel ratio becomes too thin and the acceleration performance deteriorates.

(Problems to be solved by the invention) By the way, the adhesion of the intake system and the amount of floating fuel change according to the operating state of the engine, and the rotation speed and the engine temperature as well as the absolute pressure of the intake pipe and the volatilization of the fuel. However, in the conventional air-fuel ratio control, the transient fuel excess / deficiency amount is approximately calculated by a correction method that has been experimentally determined in advance using the change of the intake pipe pressure as a parameter. The method is based on the method of optimizing the air-fuel ratio by making a correction according to the cooling water temperature.Therefore, as mentioned above, it is necessary to always respond to the intake pipe adhesion and floating fuel amount that fluctuate based on various factors. It is not always possible to obtain an appropriate air-fuel ratio, and it is inevitable that an error will occur except under the specific operating conditions that are the design points.

However, in order to solve this, it is necessary to detect and correct all the factors that affect the adhesion of the intake system and the floating fuel, but in this case, there are many judgment conditions regarding the necessity of correction, etc. Many steps are required for the matching work to satisfy the drivability and exhaust emission requirements.

Therefore, paying attention to these points, the intake system adhesion and the floating fuel equilibrium amount M0 are calculated, and the difference value M0-M between the equilibrium amount M0 and the intake system adherence and floating fuel prediction variable M at that time point. And a correction coefficient DK indicating how much this difference value is reflected in the correction of the fuel injection amount, the transient correction amount DM is obtained, and the predictive variable M is updated in synchronization with the fuel injection. People have proposed it first (see Japanese Patent Application No. 60-243605),
This invention is an improvement over the prior application.

That is, in the prior application, the air-fuel ratio characteristic can be markedly flattened regardless of the acceleration / deceleration as compared with the conventional case. Immediately after a short period (for example 0.2 ~
A lack of air-fuel ratio correction was observed, which left dissatisfaction with the response in the initial stage of acceleration, resulting in insufficient reduction of harmful emissions such as CO in the early stage of deceleration.

It is conceivable that the following factors contribute to this.

1. When the transient change is abrupt, the calculation speed of the microcomputer becomes insufficient and there is a fuel supply delay with respect to the change of the air flow rate.

2. The difference between the amount of fuel adhering to the inside of the intake pipe and the amount of fuel carried away from the intake pipe is particularly large during rapid acceleration / deceleration and immediately thereafter. For example, in an engine that injects fuel upstream of a throttle valve, if a large amount of fuel that has adhered to the intake pipe upstream becomes wall-flowed during acceleration, this wall-flowed fuel will flow to the cylinder until it reaches the air velocity. Have a delay against.

In order to avoid such a response delay, it is sufficient to supply a larger amount of fuel as the amount of transient change is larger. However, there is not a certain operating state at the time of sudden acceleration / deceleration. It was not considered.

This invention was made with attention to these problems,
The purpose is to improve the prior application by increasing the correction coefficient DK when the load change amount is equal to or greater than a predetermined value.

(Means for Solving Problems) In order to achieve the above object, in the present invention, as shown in FIG. 1, the operating state of an engine is detected from parameters including at least engine speed, engine load and engine temperature. Operating state detection means 1, a basic injection amount calculation means 2 for calculating the basic injection amount Tp of fuel based on the operating state of the engine, and a change amount of the engine load (for example, a change amount DAC of the accelerator pedal opening DAC).
C) load change amount calculation means 3 and engine speed,
Equilibrium amount calculation means 4 for calculating the adhesion of the intake system and the equilibrium amount M0 of the floating fuel based on the engine load and the engine temperature, and the adhesion amount and the equilibrium amount M0 of the floating fuel calculated by the equilibrium amount calculation means 4 at that time. Adhesion of intake system, difference value M0 from the predictive variable M of floating fuel
The difference value calculation means 5 for calculating −M, and the basic correction coefficient DK0 indicating how much the difference value M0−M calculated by the difference value calculation means 5 is reflected in the correction of the fuel injection amount, engine speed, engine Basic correction coefficient calculation means 6 for calculating based on load and engine temperature, correction coefficient increasing means 7 for increasing the basic correction coefficient DK0 when the load change amount is a predetermined value or more, and correction increased by the correction coefficient increasing means 7. Transient correction amount calculation means 8 for calculating a transient correction amount DM based on the coefficient DK and the difference value M0-M,
Prediction variable calculating means 9 for adding the transient correction amount DM calculated by the transient correction amount calculating means 8 and the above-mentioned predictive variable M of adhered and floating fuel in synchronization with fuel injection, and updating the predictive variable M with the added value. , The basic injection amount calculated by the basic injection amount calculation means 2
Tp and the transient correction amount DM calculated by the transient correction amount calculation means 8
Fuel injection amount calculation means 10 for calculating the fuel injection amount Ti based on the above and outputting an injection signal, and fuel supply means 11 for supplying fuel to the engine based on the injection signal.

(Operation) With this configuration, the basic correction coefficient DK0 is increased at the time of sudden acceleration / deceleration when the load change amount is equal to or greater than a predetermined value, so that the fuel injection amount finally becomes large and sufficient at the time of sudden acceleration. The fuel amount is supplied in the initial stage of acceleration, and the fuel amount is sufficiently reduced in the initial stage of deceleration during rapid deceleration.

As a result, during rapid acceleration / deceleration, even if the calculation speed of the microcomputer becomes insufficient, or the difference between the amount of fuel adhering to the intake pipe and the amount of fuel carried away from the intake pipe becomes particularly large, a flat air-fuel ratio characteristic is obtained. As a result, the response at the time of sudden acceleration and the exhaust emission at the time of sudden deceleration are improved.

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment) FIG. 2 is a mechanical configuration of an embodiment in which the present invention is applied to a so-called single-point injection type electronically controlled fuel injection device in which one fuel injection valve 17 is provided in an intake passage 16 upstream of a throttle valve 15. Indicates.

Explaining from the part that is almost the same as the previous application, the intake flow rate Qa
From an air flow meter 20 that detects the engine speed, a crank angle sensor 21 that detects the engine speed N, a water temperature sensor 22 that detects the cooling water temperature Tw, and an air-fuel ratio sensor 23 that detects the actual air-fuel ratio necessary for feedback control. The signal is input to the control unit 30 and the control unit
At 30, the drive control of the injection valve 17 is performed based on these signals.

In contrast to such a configuration, in the present invention, since the amount of change in load is calculated, the throttle sensor 25 is provided as a sensor for detecting the accelerator pedal opening ACC. In addition,
26 is a neutral switch, 27 is a clutch switch, 28
Is an idle control valve.

The control unit 30 is composed of a microcomputer including a CPU, a RAM, a ROM, an I / O device, etc., has all the functions of each means 2 to 10 shown in FIG. 1, and has an air-fuel ratio control (injection amount control). Process intensively.

By keeping the fuel pressure to the injection valve 17 constant, the injection amount is proportional to the valve opening pulse width, so that the valve opening pulse width is actually calculated in the control unit. Will be described as pulse width control.

3 to 7 are flow charts for explaining a routine executed in the control unit. Of these, FIGS. 3 and 4 correspond to the main routine of pulse width control, and FIGS. It corresponds to a subroutine for obtaining a correction value or the like used in the process. Numbers in the figure indicate process numbers. The processes shown in FIGS. 3 and 5 to 7 are synchronized with the engine rotation at predetermined time intervals or in synchronization with the engine rotation, and only the processes in FIG. 4 are synchronized with the engine rotation (accurately). Is executed in synchronization with the injection).

The basic pulse width control of the injection valve is well known. For example, as shown in FIGS. 3 and 4, the amount of absorbed air detected by the air flow meter 20 and the crank angle sensor 21.
A basic pulse width Tp (= K · Qa / N, where K is a constant) for obtaining a predetermined air-fuel ratio (for example, theoretical air-fuel ratio) is obtained from the relationship between Qa and the rotational speed N by table lookup or the like,
This is multiplied by the feedback correction coefficient α and other correction coefficient COEF determined based on the output of the air-fuel ratio sensor 23,
Furthermore, by adding the invalid pulse width Ts, the final injection pulse width TI
(= Tp · COEF · α + Ts) is obtained, and a drive signal based on this TI is given to the injection valve 17 (40, 51, 52).

In the prior application, in the process of obtaining the injection pulse width TI in this manner, correction corresponding to a more transient operating state is made by paying attention to intake system adhesion and floating fuel.
41 to 43 in FIG. 4 (specifically, 41 is a portion that functions as an equilibrium amount calculation means, 42 is a correction coefficient calculation means, and 43 is a portion that functions as a transient correction amount calculation means), 50, 53 (50 is fuel) in FIG. The injection amount calculation means, 53 is a part which functions as a prediction variable calculation means.).

To outline the same functions as those of the previous application, in 41, the adhesion amount of the intake system, which is the basis of the correction, and the equilibrium amount M0 of the floating fuel amount under steady operating conditions are calculated using three parameters N, Tp, and Tw. . As shown in FIG. 5, this is obtained by interpolation calculation processing of linear approximation using table search values. For example, it is determined which temperature range is divided by the actual water temperature Tw reference temperature Tw0 to Tw4 (Tw0>...> Tw4), and now
Assuming that Tw ≧ Tw1, a two-dimensional table (for example, M01) for a reference temperature Tw0 that is the temperature closest to Tw and higher than Tw and a reference temperature Tw1 that is also lower than Tw.
The table is shown in FIG. ) From the table values M00, M01 (M0 for Tw0, Tw1) corresponding to N, Tp at that time, and using these values M00, M01, the reference temperature Tw0, Tw1, and the current temperature Tw, M0 is calculated by the linear interpolation calculation formula (steps 60 to 63). The equilibrium amounts M00 to M04 with respect to the reference temperatures Tw0 to Tw4 are obtained in advance from actual measurement using N and Tp as parameters.

M0 = M00 + (M01−M00) × (Tw0−Tw) / (Tw0−Tw1) 42 For M0 obtained in this way, the intake system adhesion at the present time, the predicted value of floating fuel (predictive variable) Coefficient (basic correction coefficient) DK that represents the rate at which M approaches per unit cycle (for example, every one rotation of the crankshaft)
Is calculated from the product of the coefficients DKTw and DKN (step 8 in FIG. 6)
0,81,86).

Here, the DKTw is based on the excess / deficiency amount (transient correction amount) DM per unit cycle and the water temperature Tw obtained in the previous processing, and is set in advance as the ninth value.
It is a value obtained by searching the table formed as shown in the figure. For example, the larger the excess / deficiency amount DM, the larger the value is set to eliminate the excess / deficiency amount quickly. Also, DKN
Is a value obtained by searching a table similarly formed as shown in FIG. 10 based on N and Tp, and is set to be larger as the rotational speed becomes smaller, for example.

In 43, the excess / deficiency amount per unit cycle DM {= DK (M0− is calculated by multiplying the coefficient DK by the difference between M0 and its predicted value.
M)}. Here, the predicted value M is the predicted value of the adhesion of the intake system and the floating fuel at that time, and therefore (M0
-M) indicates the excess / deficiency amount from the equilibrium amount, and this value (M0-
M) is a coefficient DK obtained with N, Tp, DM and Tw as parameters
Will be further corrected.

After determining the excess / deficiency amount DM per unit cycle in this way, DM is further corrected by the correction factor DGI, and the correction amount KDM (= DMKGI) for the basic pulse width is calculated (steps 44, 45). .

If only DM is used for fuel with high volatility, KGI corrects the mixture too lean during deceleration, so the mixture leans.Therefore, in order to prevent misfiring due to such leaning, KGI is used during deceleration. By multiplying (= 0.9), the value DM to be reduced (having a negative value during deceleration) is substantially reduced. The processing operation of this KGI is shown in FIG. 7, where LH is the deceleration determination level.

FIG. 4 shows the process for calculating the final fuel injection pulse width TI in consideration of the correction amount KDM thus obtained,
At 50, the basic pulse width Tp is corrected and the fuel basic pulse width TpF (= Tp + KDM) is obtained. And in the earlier application,
This TpF at 51 replaces the conventional Tp.

Finally at 53, the next predicted value M is calculated by adding the current excess / deficiency DM to the previous predicted value M (old M) for the next processing. In the process of FIG. 4, for example, TI is calculated and injected for each revolution of the engine crankshaft, and the predicted value M is updated each time.

Next, the characteristic part of the present invention will be described with reference to FIG. 6. This figure shows a subroutine that functions as a means for calculating the correction coefficient DK, of which 80, 81, 86 are also executed in the prior application. This is where I am and I mentioned above. In this invention
At 82 to 86, the basic correction coefficient DK0 (= DKTw × DKN) is increased at the time of sudden acceleration / deceleration in which the load change amount becomes equal to or larger than a predetermined value.

That is, at 83, the absolute value of DACC, which is the amount of change in accelerator pedal opening ACC (corresponding to the amount of load change) | DACC |, is compared with a predetermined value LAC, and when | DACC | ≧ LAC, it is determined that rapid acceleration / deceleration is in progress. Then 8
4 where the absolute value of the accelerator pedal opening change amount | DA
The correction rate DKAC (≧ 1) is obtained by searching the DKAC table shown in FIG. 11 using CC |, and this is increased by multiplying the basic correction coefficient DK0 by 86. Here, the correction rate DKAC is set as a value that increases as the change in the accelerator pedal opening increases, as shown in FIG. 11, during rapid acceleration / deceleration when the amount of change in the accelerator pedal opening exceeds a predetermined value. Yes, therefore the correction coefficient DK (= DK0 × DKA
C) is increased as the degree of rapid acceleration / deceleration increases.

Next, the operation of this embodiment when the DK correction factor DKAC is introduced will be described with reference to FIG. 12, which shows changes in various amounts as signal waveforms when rapid acceleration / deceleration is performed. The solid line shows the case of this embodiment.

As is clear from the figure, according to this embodiment, by increasing the basic correction coefficient DK0 during the rapid acceleration / deceleration when the load change amount (| DACC |) becomes equal to or greater than the predetermined value LAC, In the predetermined section, DM shows a larger value than the previous application (shown by the broken line), which shows that the air-fuel ratio A / F is close to a flat characteristic even during rapid acceleration / deceleration. During rapid acceleration / deceleration, a flat air-fuel ratio characteristic can be obtained even if the calculation speed of the microcomputer becomes insufficient or the difference between the amount of fuel adhering to the intake pipe and the amount of fuel carried away from the intake pipe becomes particularly large. Is.

It should be noted that, in comparison with the correction determination level LAC in FIG. 6, when it is not during rapid acceleration / deceleration (| DACC | <LAC), sufficient flat characteristics can be obtained even in the previous application, and the correction according to the load change amount is performed. You do n’t have to
DKAC = 1.0 (83,85).

Next, in this embodiment, in order to further calculate the amount of change DACC of the accelerator pedal opening, the 1/4 interchange moving average method is used to obtain from the following equation (step 82).

DACC = (1/4) (ACC-ACC0) + (3/4) (former DACC) where ACC0 is the accelerator pedal opening before 25 msec, the former DA
CC is the DACC calculated last time, and the waveform of the DACC (solid line) obtained by this moving average method is a rectangular wave pulse (shown as a dashed line in the same figure) as shown in the DACC characteristic of FIG.
Is a signal that is slightly smoothed.

The broken line shows the air-fuel ratio characteristic when DK and then DM are obtained by a signal without such smoothing and air-fuel ratio control is performed. As is clear from the figure, in such cases, DK
Although the air-fuel ratio characteristic can be made flat as compared with the case where no correction is made (one-dot chain line), dissatisfaction still remains.

The moving average method is performed in order to bring the DACC waveform closer to the waveform (broken line) deviating from the flat air-fuel ratio, and the smoother the control becomes, the closer to this waveform change. Therefore, it is not limited to 1/4 replacement, and an optimum value may be adopted for matching.
For example, 1/2 replacement or 1/8 replacement may be used, and a high-pass filter-like calculation formula such as DACC = old DACC × 0.8 + (ACC−ACC0) may be used.
It is best to select it so that it is the same as or similar to the waveform diagram (broken line) of the air-fuel ratio characteristics when DACC is not used.

Further, in the present embodiment, the change in the load is obtained by using the accelerator pedal opening signal, but it may be obtained by the change in the intake pipe pressure or the basic pulse width.

Incidentally, in this embodiment, the correction is made so that the DM is increased at the time of the sudden change of the load and immediately after that, therefore, even in the transient change before the warm-up in which the deviation from the predetermined air-fuel ratio becomes much larger, that much. Since (M0-M) becomes large, the followability to a predetermined air-fuel ratio is good. Therefore, it is not necessary to separately perform the correction based on the water temperature for warming up, and therefore the air-fuel ratio correction can be performed by simple signal processing.

(Effects of the Invention) As described above, according to the present invention, the basic correction coefficient DK0 is increased when the load change amount is equal to or greater than a predetermined value, and the transient correction amount DM is calculated using the increased correction coefficient DK. Therefore, it is possible to supply a sufficient amount of fuel in the initial stage of acceleration during rapid acceleration / deceleration and to sufficiently reduce the amount of fuel in the initial stage of deceleration during rapid deceleration. As a result, the calculation speed of the microcomputer becomes insufficient at the time of sudden acceleration / deceleration,
Even if the difference between the amount of fuel adhering to the intake pipe and the amount of fuel carried away from the intake pipe becomes particularly large, a flat air-fuel ratio characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conceptual configuration of the present invention. FIG. 2 is a mechanical block diagram of an embodiment of the present invention. 3 to 7 are flow charts showing the control contents of the air-fuel ratio control corresponding to the above embodiment. FIG. 8 is a characteristic diagram showing an example of the contents of a table that gives the equilibrium amount M0 under the steady condition of adhesion of the intake system and floating fuel amount in the air-fuel ratio control, and FIGS. 9 to 11 are also the air-fuel ratio control. FIG. 6 is a characteristic diagram showing an example of contents of each table used to calculate a predetermined coefficient DK in FIG. FIG. 12 is a waveform diagram showing, as a signal waveform, the relationship between changes in parameters or coefficients in the air-fuel ratio control and the air-fuel ratio control characteristics. 1 ... Operating state detection means, 2 ... Basic injection amount calculation means,
3 ... Load change amount calculating means, 4 ... Balance amount calculating means, 5
...... Difference value calculation means, 6 …… Basic correction coefficient calculation means, 7 ・ ・ ・
... correction coefficient increasing means, 8 ... transient correction amount calculating means, 9 ...
Prediction variable calculation means, 10 Fuel quantity injection amount calculation means, 11
...... Fuel supply means, 15 ...... Throttle valve, 16 ...... Intake passage, 17 ...... Fuel injection valve, 20 ...... Air flow meter, 21 ...
… Crank angle sensor, 22 …… Water temperature sensor, 23 …… Air-fuel ratio sensor, 25 …… Throttle valve opening sensor, 30 …… Control unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display area F02D 45/00 F 7536-3G

Claims (1)

[Claims] 1. An operating state detecting means for detecting an operating state of an engine from parameters including at least an engine speed, an engine load and an engine temperature, and a basic injection for calculating a basic injection amount of fuel based on the operating state of the engine. An amount calculation means, a load change amount calculation means for calculating a change amount of the engine load, and an equilibrium amount calculation means for calculating the adhering amount of the intake system and the equilibrium amount of the floating fuel based on the engine speed, the engine load and the engine temperature. Adhesion calculated by the equilibrium amount calculation means, difference value calculation means for calculating a difference value between the equilibrium amount of floating fuel and adhesion of the intake system at that time, and a predictive variable of floating fuel, and difference value calculation means Basic correction coefficient calculating means for calculating a basic correction coefficient indicating how much the difference value is reflected in the correction of the fuel injection amount based on the engine speed, the engine load and the engine temperature, and the load change amount is a predetermined value or more. With the basic supplement A correction coefficient increasing means for increasing the coefficient, a transient correction amount calculating means for calculating a transient correction amount based on the correction coefficient increased by the correction coefficient increasing means and the difference value, and a transient correction calculated by the transient correction amount calculating means. Amount and the adhering and floating fuel predictive variables are added in synchronism with the fuel injection, and the predictive variable calculating means for updating the predictive variable with the added value, the basic injection amount calculated by the basic injection amount calculating means, and the aforesaid Fuel injection amount calculation means for calculating a fuel injection amount based on the transient correction amount calculated by the transient correction amount calculation means and outputting an injection signal; and fuel supply means for supplying fuel to the engine based on the injection signal. An air-fuel ratio control device for an internal combustion engine, comprising: