JPH0726566B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an internal combustion engine such as an automobile, and more particularly to a fuel injection control device that predicts a temperature of a fuel adhesion portion and obtains a transient correction amount based on the result. Regarding the control device.

(Prior Art) When the required output to the engine of a vehicle such as an automobile changes, it is necessary to control the fuel injection amount with high responsiveness according to the required degree. This is especially the air-fuel ratio during transient operation. Influences the driving performance such as drive feeling and exhaust composition.

Generally, the deviation of the air-fuel ratio from the target air-fuel ratio during acceleration / deceleration of the engine is caused by the quantitative change of the adhered fuel and the suspended fuel adhering to the intake manifold and the intake port of the intake system. The amount of floating fuel changes greatly depending on the operating condition of the engine.

Against this background, a conventional fuel injection control device for an internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-18758. In this device, the required load per unit rotation of the engine is obtained from the output of the air flow meter provided on the upstream side of the throttle valve, and the fuel injection amount is calculated from this. Further, at the time of transition, the fuel injection amount is corrected by the transient correction amount, and so-called wall flow is taken into consideration. Note that the transient correction amount is a wall flow correction amount and is not necessarily used during acceleration / deceleration, and is also used immediately after the start, which is greatly affected by the wall flow, or immediately after recovery from the fuel cut, for example.

(Problems to be Solved by the Invention) However, in such a conventional fuel injection control device for an internal combustion engine, the wall flow component corresponding to the transient correction amount is obtained from the cooling water temperature, so that it is sufficient. However, there is a problem in that it is not possible to perform various transient corrections.

That is, the wall temperature of the adhering part is an important parameter in the evaporation of the wall flow, but the temperature of the adhering part greatly differs depending on the operating conditions as shown in FIG. 7, and has a delay as shown in FIG. In other words, the tendency for the temperature of the adhered part to rise differs depending on the operating conditions, which appears as a difference in the delay time constant. Therefore, the adhering portion temperature varies depending on the operating conditions before acceleration or the like, and the air-fuel ratio at the time of transition such as acceleration or deceleration becomes improper and the drivability deteriorates.

Particularly, in a multi-point injection type engine, as shown in FIG. 11, injector A directly injects fuel toward cylinder head 31, and injector B directly injects fuel into the wall of the intake port. As shown in FIG. 12, the change in the air-fuel ratio after the start is different from that in the case where the fuel is injected toward, and the change in the air-fuel ratio is more remarkable when the fuel is injected into the intake valve 32. That is, the intake valve 32
The error due to the temperature is large, and such a phenomenon tends to occur not only immediately after starting, but also under operating conditions where the valve temperature is different from normal, for example, immediately after the fuel cut recovery. Therefore, hesitation is likely to occur at the time of acceleration, and deviation from the three-way point in the three-way catalyst occurs due to fluctuations in the air-fuel ratio, and exhaust purification performance deteriorates.

A wall temperature sensor, for example, may be provided to detect the temperature of the adhering portion, but this is not preferable because it not only increases the cost but also reduces the productivity of mounting.

(Object of the Invention) Therefore, the present invention aims to improve the operating performance and the exhaust gas purification performance by appropriately predicting the adhering portion temperature from various operating conditions, thereby making the transient correction amount appropriate and not increasing the cost. Has an aim.

(Means for Solving the Problem) In order to achieve the above object, a fuel injection control device for an internal combustion engine according to the present invention has an operating state detecting means for detecting an operating state of the engine as shown in a basic conceptual diagram of FIG. a, an equilibrium temperature calculating means b for obtaining the equilibrium temperature of the fuel adhering portion in the intake pipe based on the operating state of the engine, and a delay time constant for the temperature of the fuel adhering portion in the intake pipe based on the operating state of the engine. The delay calculating means c, the predicting means d for predicting the temperature of the fuel adhering portion in the intake pipe based on the outputs of the equilibrium temperature calculating means b and the delay calculating means c, and at least the predicting means when the engine is in a predetermined temperature state. The correction amount calculation means e that calculates the transient correction amount that corrects the fuel injection amount using the output of d, and the fuel injection amount that is calculated based on the operating state of the engine An injection amount calculation means f for correcting the fuel injection amount according to the transient correction amount;
Fuel injection means g for injecting fuel based on the output of the injection amount calculation means f.

(Operation) In the present invention, the equilibrium state temperature of the fuel adhering portion in the intake pipe and the delay time constant of the adhering portion temperature are obtained based on the operating state of the engine, and the adhering portion temperature is predicted from this. Then, at the time of calculating the transient correction amount, at least the predicted value of the adhesion portion temperature is added to one of the calculation parameters.

Therefore, the transient correction amount becomes appropriate without increasing the cost, and the operation performance and the exhaust gas purification performance are improved.

(Example) Hereinafter, the present invention will be described with reference to the drawings.

2 to 10 are views showing an embodiment of a fuel injection control device for an internal combustion engine according to the present invention.

First, the configuration will be described. FIG. 2 is a diagram showing the overall configuration of this device. In FIG. 2, 1 is an engine,
The intake air passes from the air cleaner 2 through the intake pipe 3, and the fuel is injected from the injector (fuel injection means) 4 based on the injection signal Si. Then, the exhaust gas burned in the cylinder is introduced into the catalytic converter 6 through the exhaust pipe 5, and in the catalytic converter 6, harmful components (CO, HC, NOx) in the exhaust gas are cleaned and discharged by the three-way catalyst.

The flow rate Qa of the intake air is detected by a hot wire type air flow meter 7 and controlled by a throttle valve 8 in the intake pipe 3. The type of the air flow meter 7 may be a hot film type, and any type that measures the flow rate of intake air may be used.

The opening TVO of the throttle valve 8 is detected by the throttle opening sensor 9,
The rotation speed N of the engine 1 is detected by the crank angle sensor 10. Further, the temperature Tw of the cooling water flowing through the water jacket is detected by the water temperature sensor 11, and the oxygen concentration in the exhaust gas is detected by the oxygen sensor 12. As the oxygen sensor 12, a sensor having a characteristic of widely detecting the air-fuel ratio from rich to lean is used. Further, the operation of the starter motor is detected by the start switch 13.

The air flow meter 7, the throttle valve opening sensor 9, the crank angle sensor 10, the water temperature sensor 11, the oxygen sensor 12 and the start switch 13 constitute an operating state detecting means 14, and the output from the operating state detecting means 14 is controlled. Unit 20
Entered in.

The control unit 20 has functions as an equilibrium temperature calculating means, a delay calculating means, a predicting means, a correction amount calculating means and an injection amount calculating means, and is composed of a CPU 21, a ROM 22, a RAM 23 and an I / O port 24. The CPU21 takes in the external data required from the I / O port 24 according to the program written in the ROM22, and also exchanges the data with the RAM23 while calculating the processing values required for fuel injection control. I / O port 2
Output to 4. The I / O port 24 receives the signal from the operating state detecting means 14, and the I / O port 24 outputs the injection signal Si. The ROM 22 stores the calculation program in the CPU 21, and the RAM 23 stores the data used for the calculation in the form of a map or the like.

Next, the operation will be described.

FIG. 3 shows the temperature of fuel adhesion in the intake pipe 3 (hereinafter,
It is a flow chart showing a program for calculating Th and a delay time constant SPTF (simply referred to as adhesion temperature), and this program is executed once a second, for example, in synchronization with a timer.

First, in P ₁ , it is determined whether or not the start switch 13 is ON. When the start switch 13 is ON, it is determined that cranking is in progress, and in P ₅ , the adhesion temperature Th is the cooling water temperature at that time. Equal to Tw and proceed to P ₆ . On the other hand, when the start switch 13 is not ON, it is determined that the cranking has already been completed, and the equilibrium adhesion temperature Tho of the fuel adhesion portion is obtained at P ₂ . From the map shown in FIG. 7, the equilibrium adhering temperature Tho is determined by operating conditions with the intake air amount Qcy1 (the same map characteristic is obtained even if the intake negative pressure is replaced with the intake air amount) and the engine speed N as parameters. It is calculated based on the lookup. Note that Qcy1 is the amount of air taken into the cylinder, which corresponds to the engine load. The map shown in FIG. 7 is created in advance through experiments and the like, and accurately matches the actual equilibrium adhesion temperature Tho.

Then, it is determined whether or not the engine is under fuel cut in P _3,
Branches to P ₅ when the engine is under fuel cut, when it is not in the fuel cut goes to P _4. At P ₄ , the adhesion temperature Th is calculated according to the following equation.

Th = Tho− (80−Tw) × C1− (25−Ta) × C2 However, C1, C2: Constant Tw: Cooling water temperature Ta: Intake air temperature Eq. The adhesion temperature Th corresponding to the operating conditions of is accurately obtained.
Next, at P ₆ , the delay time constant SPTF is obtained by looking up from the map shown in FIG. 8 based on the operating conditions Qcy1 and N. The delay time constant SPTF corresponds to the changing speed of the adhesion temperature Th,
In FIG. 8, this is represented by [%].

FIG. 4 is a flow chart showing a program for calculating a predicted value Tf of the temperature of the fuel adhesion portion (hereinafter, referred to as an adhesion temperature prediction value). This program is also timer-synchronized, for example, 1s.
It is executed once every ec. In P ₁₁ and P ₁₂ , the adhesion temperature Th and the delay time constant SPTF obtained in the subroutine of FIG.
Is input, and the adhesion temperature predicted value Tf is calculated in P ₁₃ according to the following equation.

Tf = Th x SPTF + Tf _-1 x (1-SPTF) ... However, Tf _-1 : The adhesion temperature predicted value Tf is obtained as a first-order lag of the adhesion temperature Th by the calculation of the previous value formula.

FIG. 5 is a flow chart showing a program for calculating the transient correction amount Kathos, and this program is executed once every 10 msec. First, the equilibrium adhesion amount Mfh fuel wall flow amount in the intake pipe 3 at P _21. This is calculated, for example, by adding the correction based on the estimated adhesion temperature value Tf to the equation AvTp × Mfhtvo. In the formula, Avtp is a smooth injection amount, and in order to accurately obtain the air amount flowing through the injector 4, the output of the air flow meter 7 is smoothed with a first-order lag, and the smoothed air amount is used as the fuel injection amount. It is calculated. Therefore, Avtp is calculated as a pulse width [ms] corresponding to the cylinder air amount. Note that the Avtp calculation method has already been disclosed in another application by the applicant at about the same time as the present application. On the other hand, Mfhtvo is an adhesion ratio [unit is times], which is obtained from the load and the rotational speed for each cooling water temperature Tw. In such a process, unlike the conventional case, the predicted adhesion temperature value Tf is required when calculating Mfh, so that the equilibrium adhesion amount Mfh is highly accurate.

Then, in P ₂₂ , the proportion Kmf [%] is calculated. This is calculated, for example, by adding a correction based on the predicted adhesion temperature value Tf to the equation Kmfat × Kmfn ... In the formula, Kmfat is the basic quantity ratio [%] α
-Using the N flow rate Qho and the cooling water temperature Tw, it is obtained from a predetermined map with interpolation calculation. The α-N flow rate is the throttle valve opening.
The air flow rate is obtained from TVO and the rotation speed N, which is already known. Further, Kmfn [times] is a quantity ratio rotation correction factor, which is obtained from a predetermined table with interpolation calculation from the rotation speed N. In the calculation of the quantity ratio Kmf, the adhesion temperature predicted value Tf is used unlike the conventional case, so that the calculation accuracy is high. Then, the deposition rate Vmf in P ₂₃ [ms]
Is calculated according to the following equation.

Vmf = [Mfh−Mf] × Kmf …… In the formula, Mf is the adhesion amount [ms], and is calculated by the formula Mf = (Mf−1ref) + Vmf. (Mf-1ref) is the adhesion amount before one rotation (at the time of previous injection). The deposition speed Vmf is the flow rate of the fuel taken by the wall flow, and is obtained as the flow rate per rotation. Then, determined according to the following equation correction factor Ghf (%) at P _24.

Ghf = Ghfgen × KtgKL …… In the formula, Ghfgen is the weight reduction correction factor, Ghfgen = 0 for acceleration (when Vmf ≧ 0), and if not, the correction factor load term Ghfg or Ghfdn, whichever is greater. Use the value. Here, Ghfg is obtained by looking up a table without interpolation based on the balanced injection amount Avtp. KtgKL is a transient learning low frequency coefficient, and a value around 1.0 is used, for example. Next, at P ₂₅ , the transient correction amount Kathos is calculated according to the following equation.

Kathos = Vmf × Ghf ... After obtaining Kathos by the above processing, the actual injection amount Ti is calculated according to the following equation in step P ₃₁ of the program shown in FIG.

Ti = (Tp × αm + Kathos) × α + Ts (where Tp: basic injection amount α is a λ control correction coefficient of the air-fuel ratio based on the output of the oxygen sensor 12, and αm is a mixture ratio learning control correction coefficient). Ts is the invalid pulse width.

The actual operation by the execution of each program is shown in the timing chart of FIG. FIG. 9 shows an example in which the engine 1 is accelerated about 4 minutes after the engine 1 is started. The wall-flow attachment temperature Th is a value in the case of equilibrium in a steady state, and thus increases stepwise at the same time as starting as shown in the figure, and also increases stepwise during acceleration. However, such step changes do not match the actual deposition temperature.

On the other hand, in this embodiment, the adhesion temperature predicted value Tf is used, and according to this, the actual adhesion temperature is extremely accurately matched. Here, in particular, the change in the air-fuel ratio when the vehicle is accelerated at the time indicated by A in FIG. 9 is as shown in FIG. In the case of the conventional example, since the adhesion temperature is obtained from the cooling water temperature Tw, the value of the transient correction amount Kathos becomes inappropriate, and the air-fuel ratio fluctuates greatly during acceleration. On the other hand, in the present embodiment, unlike the case where the time constant is extremely large like the temperature Tw of the cooling water and equilibrium is performed in the steady state, since the adhesion temperature prediction value Tf is used, the wall flow is appropriately corrected and the transient The correction amount accurately corresponds to the actual situation. Therefore,
A change in the air-fuel ratio can be suppressed to a small level. From the above, the following effects can be obtained.

(I) The drivability is improved by appropriate acceleration correction regardless of the driving conditions before acceleration. Further, since the deviation of the air-fuel ratio from the three-point point is reduced, the beard of emission is reduced and the exhaust gas purification performance is improved.

(II) In particular, the drivability immediately after starting and the emission characteristics are improved, so that power steering can be prevented at the time of starting, and emissions can be reduced and fuel consumption can be improved by making the engine lean.

(III) The effect similar to the above is obtained immediately after the fuel cut recovery, and it is possible to prevent hesitation and reduce NOx.

(IV) The flatness of the transient air-fuel ratio is further improved.

(V) An expensive thing such as a wall temperature sensor is not used, and the software in the control unit 20 can be improved or the map data can be improved so that the cost does not increase.

(Effect) According to the present invention, since the adhering portion temperature is predicted from various operating conditions, it is possible to suppress fluctuations in the air-fuel ratio without causing an increase in cost by appropriately setting the transient correction amount, and to operate the engine. The performance and exhaust purification performance can be significantly improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 10 are diagrams showing an embodiment of a fuel injection control device for an internal combustion engine according to the present invention, FIG. 2 is an overall configuration diagram thereof, and FIG. Is a flow chart showing a program for calculating the adhesion temperature and the delay time constant, FIG. 4 is a flow chart showing a program for calculating the adhesion temperature predicted value, and FIG. 5 is a flow chart showing a program for calculating the transient correction amount. FIG. 6 is a flow chart showing a program for calculating the fuel injection amount, FIG. 7 is a diagram showing the characteristic of the adhering portion temperature, FIG. 8 is a diagram showing the characteristic of the delay time constant, and FIG. 9 is its starting time. 10 is a timing chart for explaining the action of FIG. 10, FIG. 10 is a timing chart showing changes in the air-fuel ratio during acceleration,
FIG. 11 is a diagram showing a conventional fuel injection control device for an internal combustion engine, FIG. 11 is a schematic diagram showing its injection position, and FIG. 12 is a timing chart showing variations in the air-fuel ratio during acceleration. 1 ... Engine, 4 ... Injector (fuel injection means), 7 ... Air flow meter, 9 ... Throttle valve opening sensor, 10 ... Crank angle sensor, 11 ... Water temperature sensor, 12 ... Oxygen sensor, 14 ...... Operating state detecting means, 20 ...... Control unit (equilibrium temperature calculating means, delay calculating means, predicting means, correction amount calculating means, injection amount calculating means).

Claims (1)

[Claims] 1. An a) operating state detecting means for detecting an operating state of the engine, b) an equilibrium temperature calculating means for obtaining an equilibrium temperature of a fuel adhering portion in the intake pipe based on the operating state of the engine, and c) an engine. Delay calculating means for obtaining a delay time constant of the temperature of the fuel adhering portion in the intake pipe based on the operating state of d), and d) predicting the temperature of the fuel adhering portion in the intake pipe based on the outputs of the equilibrium temperature calculating means and the delay calculating means. And e) a correction amount calculation unit for calculating a transient correction amount for correcting the fuel injection amount using at least the output of the prediction unit when the engine is in a predetermined temperature state, and f) the operating state of the engine. An injection amount calculation means for calculating the injection amount of fuel based on the above, and correcting the injection amount of the fuel according to the transient correction amount of the previous period when transitioning to a transient state; The fuel injection control device for an internal combustion engine to the fuel injection means for morphism, further comprising a featuring.