JPH0670386B2 - 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, since the vehicle engine is used in a wide range of operation from low speed low load to high speed high load, suitability of air-fuel ratio control in transient motion conditions such as acceleration and deceleration greatly affects drivability and exhaust emission. .

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 or control method described above is being adopted in many vehicle engines. (Prior art examples of this type of control method include, for example, JP-A Nos. 58-144632, 144634, 144636 and 15).
See 0033, 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. It is based on the method of optimizing the air-fuel ratio by making a correction according to the cooling water temperature.Therefore, as described above, the intake system always fluctuates 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 amount of floating fuel, but in this case there are many judgment conditions regarding the necessity of correction, etc. However, many steps are required for the matching work to satisfy the requirements of drivability and exhaust emission.

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, it was possible to obtain an air-fuel ratio characteristic with good response regardless of acceleration and deceleration compared to the conventional one, but it is specified that the engine is stopped immediately after acceleration and restarted immediately thereafter. When restarting the vehicle, it is conceivable that the exhaust emission and the startability may be deteriorated due to excessive supply of fuel.

Explaining this, in the air-fuel ratio control, the difference value (M0−
Higher because many fuel supplied M) is large, at the time of engine startup to perform the increasing correction to increase startability, M ₁ the initial value M ₁ for the predicted value at initialization routine (predictors) M By setting = 0, (M0-M) is increased.

The start-up time when the initial value of M can be set to zero is a start-up time in which the start-up time is long and the cold start-up is performed. Floating fuel does not remain, so it is in good agreement with the actual situation. On the other hand, when the idle operation is not performed immediately after acceleration or the engine is stopped with little deceleration time and restarted immediately thereafter, adhesion of the intake system and floating fuel remain.

Even at such a restart, in the previous application, the control is started by uniformly setting the initial value of the predicted value to zero, so that the remaining intake system adhesion and the floating fuel amount are supplied in large numbers, and the predetermined amount is supplied. If the air-fuel ratio is deviated from the air-fuel mixture, the air-fuel ratio becomes rich, and the engine startability becomes poor due to an increase in harmful emissions such as CO and smoldering of the spark plug.

In order to prevent such excess fuel, it is necessary to predict the adhesion of the intake system remaining in the intake system and the amount of floating fuel. Here, the adhesion of the intake system and the amount of floating fuel are the engine temperature at that time. Therefore, if the engine temperature is used as a parameter, it is possible to predict the adhesion of the intake system remaining in the intake system and the amount of floating fuel. If this value is used as the initial value, the adhesion of the remaining intake system , The amount of floating fuel is taken into the air-fuel ratio control.

Further, in the one disclosed in JP-A-56-154133, the temperature of the cooling water and the temperature of the intake pipe at the time of restart of the engine are detected, and the adhesion of the intake system and the residual amount of floating fuel are detected from these temperatures. It is determined whether or not the fuel increase correction at the time of restart is performed. However, this method only determines the necessity of fuel correction at start-up in a binary manner, and the adhesion of the intake system, the estimated value of the residual amount of floating fuel, and the adherence of the intake system according to the operating state at restarting. However, the fuel amount at the time of starting is not corrected by the difference value with the equilibrium amount of floating fuel. For this reason, it has not been possible to sufficiently supply fuel at the time of start-up to improve restartability.

This invention was made with attention to these problems,
It is an object of the present invention to provide an air-fuel ratio control device which calculates an initial value of a predicted value of adhesion of an intake system and a floating fuel amount according to an engine temperature at a start, and supplies fuel based on the initial value. I am trying.

(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 a basic injection amount Tp of fuel based on the operating state of the engine, and an intake system adhesion based on the engine speed, engine load and engine temperature,
The balance amount calculation means 3 for calculating the equilibrium amount M0 of the floating fuel, the adhesion calculated by the balance amount calculation means 3, the equilibrium amount M0 of the floating fuel and the adhesion of the intake system at that time, and the prediction variable M of the floating fuel The difference value calculating means 4 for calculating the difference value M0-M, and the correction coefficient DK indicating how much the difference value M0-M calculated by the difference value calculating means 4 are reflected in the correction of the fuel injection amount, , Correction coefficient calculation means 5 for calculating based on engine load and engine temperature
And a transient correction amount calculation means 6 for calculating a transient correction amount DM based on the difference value M0-M and the correction coefficient DK, and a transient correction amount DM calculated by the transient correction amount calculation means 6 and the adhesion and floating. Prediction variable calculation means 7 for adding the prediction variable M of fuel in synchronism with fuel injection and updating the prediction variable M with the added value, the basic injection amount Tp calculated by the basic injection amount calculation means 2 and the transient Fuel injection amount calculation means 8 for calculating the fuel injection amount Ti based on the transient correction amount DM calculated by the correction amount calculation means 6 and outputting an injection signal, and fuel for supplying fuel to the engine based on the injection signal. A supply means 9, an engine start detection means 10 for detecting the start of the engine, and an initial value calculation means 11 for calculating the initial value of the predictive variable M based on the engine temperature when the engine is started.
Equipped with.

(Operation) With this configuration, the adhesion of the intake system and the floating fuel remaining in the intake system are obtained according to the engine temperature at that time.

For example, when the engine temperature is high, the amount of remaining intake system adhered and the amount of floating fuel are large, but the amount of adhered intake system and residual amount of floating fuel are set to initial values. Therefore, the difference value (M0
-M) becomes small, and the final injection amount calculated based on this difference value is decreased.

That is, when the intake system adheres to the intake system, and when the engine is restarted immediately after the suspended fuel remains with the suspended fuel remaining, the injection amount is supplied in advance in anticipation of the adherence of the intake system remaining in the intake system and the floating fuel amount. As a result, even if the engine is stopped immediately after acceleration, the intake system adheres to the intake system, and even if it restarts immediately after leaving a large amount of floating fuel remaining, an increase in harmful emissions due to excessive fuel supply and poor startability may occur. It can be prevented.

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.

Describing from the parts that are almost the same as the previous application, an air flow rate sensor 20 that detects the intake air amount Qa, a crank angle sensor 21 that detects the engine rotation speed N, and a water temperature sensor that detects the cooling water temperature Tw.
22, further various signals from the air-fuel ratio sensor 23 for detecting the actual air-fuel ratio necessary for feedback control are input to the control unit 30, and the control unit 30 controls the drive of the injection valve 17 based on these signals. To do.

In contrast to such a configuration, in the present invention, it is necessary to know the engine temperature at the time of starting, and the engine temperature is substituted by the cooling water temperature Tw, and the starter switch 24
The signal from is input to the control unit 30.

During the transition, it is basically determined from the amount of change in the throttle opening corresponding to the accelerator pedal opening from the throttle sensor 25 and the amount of change in the engine speed N.

The control unit 30 is composed of a microcomputer including a CPU 31, a ROM 32, a RAM 33, an I / O port 34, etc., and has all the functions of the remaining means except the means 1, 9, 10 shown in FIG. Processes relating to air-fuel ratio control (injection amount control) are intensively performed.

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 6 are flow charts for explaining the routine executed in the control unit. Of these, FIG.
Fig. 4 shows the main routine of pulse width control,
FIG. 6 and FIG. 6 correspond to a subroutine for obtaining a correction value and the like used in the process. The numbers in the figure indicate the process numbers. The processes of FIGS. 3, 5, and 6 are synchronized with the engine rotation at predetermined time intervals or in synchronization with the engine rotation, and only the processing of FIG. 4 is synchronized with the engine rotation ( (Exactly 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 intake air flow rate detected by the air flow rate sensor 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 determined based on the output of the air-fuel ratio sensor 23 and the total COEF of other correction coefficients, and the invalid pulse width Ts is added to 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 such an injection pulse width TI, a 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 function as in the previous application, in 41, the adhering amount of the intake system and the equilibrium amount M0 of floating fuel, which are the basis of the correction, 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 in which temperature region the actual water temperature Tw is divided by the reference temperatures Tw0 to Tw4 (Tw0 >>...> Tw4), and if Tw ≧ Tw1 is assumed, then Tw is closest to Tw. Reference temperature that is higher than
From the two-dimensional table (for example, the M01 table is shown in FIG. 7) for Tw0 and the reference temperature Tw1 which is also lower than Tw, the table values M00 and M0 corresponding to N and Tp at that time are obtained.
1 (M0 for Tw0, Tw1) is calculated, and these values M00, M01
Using the reference temperatures Tw0, Tw1 and the current temperature Tw, M0 is calculated by the following linear interpolation calculation formula (step 60).
~ 63). Note that M00 to M04 for the reference temperatures Tw0 to Tw4 are
It is obtained from actual measurement using N and Tp as parameters.

M0 = M00 + (M01−M00) × (Tw0−Tw) / (Tw0−Tw1) In step 42, the adhering intake system at the present time and the predictive variable M of the floating fuel are the units with respect to M0 obtained in this way. A coefficient DK representing the rate of approaching at each cycle (for example, every one rotation of the crankshaft) is calculated from the product of the coefficients DKTw and DKN (steps 80 to 82 in FIG. 6).

Here, DKTw is a value obtained by searching a table previously formed as shown in FIG. 9 on the basis of the transient correction amount DM per unit cycle and the water temperature Tw obtained in the previous process. For example, the transient correction amount DM is The larger it is, the larger it is set in order to quickly eliminate the excess / deficiency. Further, DKN is a value obtained by searching a table similarly formed as shown in FIG. 8 on the basis of N and Tp, and is set to be larger as the rotational speed decreases, for example.

In step 43, the coefficient DK is multiplied by the difference between M0 and the predicted value M to calculate the transient correction amount DM (=
Calculate DK (M0-M)). Here, the predicted value M is a predictive variable 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 It is further corrected by the coefficient DK obtained by using N, Tp, DM and Tw as parameters.

FIG. 4 shows the process of calculating the final fuel injection pulse width TI in consideration of the transient correction amount DK thus obtained. At 50, the basic pulse width Tp is corrected and the basic fuel pulse width TpF is corrected. (= Tp + DM) is required. Then, in the prior application, this TpF is replaced with the conventional Tp at 51.

Finally, in step 53, the next predicted value M is calculated by adding the current transient correction amount 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.

FIGS. 10 to 12 show changes in various amounts in the above control as signal waveforms corresponding to changes in the operating state during acceleration, deceleration, and gear change during acceleration, and are shown as signal waveforms. In the initial stage of deceleration, fuel is being increased or decreased with good responsiveness. As a result, the control accuracy of the air-fuel ratio control during the transition is improved without the deviation from the predetermined air-fuel ratio even during the transition.

By the way, such air-fuel ratio correction can also be applied when performing recovery (injection restart) from fuel cut during deceleration, and FIG. 13 shows an example of correction processing corresponding to air-fuel ratio correction during fuel cut recovery. 14 is a waveform diagram corresponding to FIG. 11 in the case of the processing. Note that, in FIG. 13, the predetermined value MFC is zero or a very small value (constant value).

Generally, when the fuel is cut, the intake system adheres and the floating fuel is sucked into the engine during the fuel cut. Although the supplied fuel amount becomes insufficient and the air-fuel ratio becomes leaner, such leaning of the air-fuel ratio can also be avoided in the prior application considering the adhesion of the intake system and floating fuel.

Next, the characteristic part of the present invention will be described. The main part of the present invention is in the air-fuel ratio control at the time of starting, and the initial value for the predicted value is calculated according to the cooling water temperature at the time of starting. is there. That is, in the subroutine of FIG. 5, M0
This function is executed in steps 57 to 59 prior to calculating.

Here, steps 57 and 58 are parts that function as means for detecting the start time, and the signal from the starter switch 24 is
Since it is turned ON and this ON signal is the first time, the start time is detected.

Step 59 is a portion that functions as a means for calculating an initial value for the predicted value according to the cooling water temperature Tw at such a start, and the initial value M ₁ is obtained by searching the table in FIG. 15 according to Tw. .

As is clear from the figure, when the cooling water temperature Tw is high, M ₁ (= f (Tw)) is predicted to be large in consideration of the fact that the intake system remaining in the intake system and the amount of floating fuel are large. Set). Specifically, the data shown in FIG. 15 is obtained by an experiment to find the optimum value.

Next, based on FIG. 16, the operation of the present embodiment (indicated by the one-dot chain line) introducing the operation of initializing the predicted value according to the cooling water temperature at the time of restart immediately after the engine is stopped, Explaining in comparison with the case where the initial value is set to zero (indicated by the broken line) regardless of whether the intake system adheres or the floating fuel remains, the figure shows the signals of the amount of various variables after starting and after starting. The waveform is shown.

At the time of a restart shortly after the engine is stopped, the period between the start and the next start is long, and unlike the start when the engine is in a cold state, the adhesion of the intake system remaining in the intake system when the engine is stopped,
Floating fuel exists without loss.

However, in spite of the adhesion and floating of the intake system, if the control is started with the initial value M _{1 set} to zero, the intake system remaining in the intake system and the amount of floating fuel corresponding to the amount of floating fuel are excessive. Becomes

That is, although M is a predicted value, it does not predict the adherence of the intake system and the amount of floating fuel remaining at the start of the start, and the supplied fuel amount becomes excessive by the residual amount.
As shown in the figure, CO emissions immediately after restart are increased.

On the other hand, in this embodiment, by using the cooling water temperature Tw at that time, the table shown in FIG. 15 is searched to determine the amount of adhering intake air remaining in the intake system and the amount of floating fuel, and this value is the predicted value. The control is started with an initial value M ₁ (= f (Tw)) for

That is, by accurately predicting the adhesion of the intake system and the amount of floating fuel remaining at the time of restart by using the cooling water temperature, the fuel is supplied a little less by the amount corresponding to this residual fuel amount. Immediately after acceleration, the engine stopped and many intake systems adhered to the intake system, leaving floating fuel remaining,
Even if the engine is restarted, the amount of fuel supply does not become excessive, and an appropriate value can be obtained according to the operating state at the time of start, thus suppressing the increase of harmful emissions and excess fuel. It is possible to prevent a start failure due to.

(Effects of the Invention) As described above, according to the present invention, the initial value of the predicted value of the adherence of the intake system and the floating fuel is calculated according to the engine temperature at the time of starting. At restart, when the intake system adheres to the intake system and the engine is at a high temperature where a large amount of suspended fuel remains, a small injection amount is supplied in advance in anticipation of this residual amount, which causes harmful emissions due to excessive fuel supply. It is possible to prevent increase and start failure.

[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 6 are flow charts showing the control contents of the air-fuel ratio control corresponding to the above embodiment. FIG. 7 is a characteristic diagram showing an example of the contents of a table that gives the equilibrium amount M0 under the steady condition of the intake system adhesion and floating fuel amount in the air-fuel ratio control, and FIGS. 8 and 9 are also the air-fuel ratio control. 6 is a characteristic diagram showing an example of the contents of a table that gives a predetermined coefficient DK in FIG. FIG. 10 to FIG. 12 are waveform charts at the time of acceleration, deceleration, and gear change, which show the relationship between changes in parameters or coefficients in the air-fuel ratio control and control characteristics of the fuel injection pulse width as signal waveforms. . FIG. 13 is a flow chart showing an example of processing contents in which the air-fuel ratio control is applied at the time of recovery from deceleration fuel cut, and FIG. 14 is a waveform diagram corresponding to FIG. 11 in the case of the processing. FIG. 15 is a characteristic diagram showing an example of contents of a table which gives an initial value M ₁ for the predicted value M used in the air-fuel ratio control. FIG. 16 is a waveform diagram showing the relationship between changes in parameters or coefficients in the air-fuel ratio control and the control characteristics of the injection pulse width as signal waveforms and the waveforms after and after the start. 1 ... Operating state detection means, 2 ... Basic injection amount calculation means,
3 ... Balance amount calculation means, 4 ... Difference value calculation means, 5 ... Correction coefficient calculation means, 6 ... Transient correction amount calculation means, 7 ... Prediction variable calculation means, 8 ... Fuel quantity injection amount calculation means , 9 ……
Fuel supply means, 10 ... Engine start detection means, 11 ... Initial value calculation means, 15 ... Throttle valve, 16 ... Intake passage, 17 ...
... Fuel injection valve, 20 ... Air flow rate sensor, 21 ... Crank angle sensor, 22 ... Water temperature sensor, 23 ... Air-fuel ratio sensor, 24
...... Starter switch, 25 ...... Throttle valve opening sensor, 30 ...... Control unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 45/00 Q 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. The amount calculation means and the attachment of the intake system based on the engine speed, the engine load and the engine temperature,
Equilibrium amount calculation means for calculating the equilibrium amount of floating fuel, and the adhesion calculated by the equilibrium amount calculation means, the difference value between the equilibrium amount of floating fuel and the adhesion of the intake system at that time, and the predictive variable of floating fuel A difference value calculation means and a correction coefficient calculation for calculating a correction coefficient indicating how much the difference value calculated by the difference value calculation means is reflected in the correction of the fuel injection amount based on the engine speed, the engine load and the engine temperature. Means, and a transient correction amount calculation means for calculating a transient correction amount based on the difference value and the correction coefficient,
The transient correction amount calculated by the transient correction amount calculation means and the adhesion,
Prediction variable calculation means for adding a prediction variable of floating fuel in synchronism with fuel injection and updating the prediction variable with the added value, basic injection amount calculated by the basic injection amount calculation means, and transient correction amount calculation means The fuel injection amount calculation means for calculating the fuel injection amount based on the transient correction amount calculated in step 1 and outputting an injection signal, the fuel supply means for supplying fuel to the engine based on the injection signal, and the engine start An air-fuel ratio control apparatus for an internal combustion engine, comprising: engine start detection means for detecting; and initial value calculation means for calculating an initial value of the predictive variable based on the engine temperature when the engine is started.