JP2581046B2 - Fuel injection method for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection method for an internal combustion engine, and more particularly to a fuel injection method at the time of deceleration.

[Conventional technology]

Conventionally, a fuel injection valve is provided for each cylinder so as to protrude into the intake manifold, or a single fuel injection valve is provided upstream of the throttle valve, and input from various sensors including an air flow meter by a micro computer or the like. 2. Description of the Related Art There is known a fuel injection method in which an engine operating state is determined by processing an engine signal and an amount of fuel corresponding to the operating state is injected.
In this fuel injection method, the basic fuel injection time is determined so as to be proportional to the amount of intake air per one revolution of the engine, and the fuel injection time is determined by correcting the basic fuel injection time according to the intake air temperature, the engine cooling water temperature and the like. The fuel injection amount is controlled by opening the fuel injection valve for a time corresponding to the fuel injection time independently of each cylinder or simultaneously with each cylinder in synchronization with the crank angle.

However, in an internal combustion engine in which the fuel injection amount is controlled by such a fuel injection method, the throttle valve is rapidly closed at the time of deceleration, so that the air remaining in the intake pipe or the surge tank is supplied to the engine combustion chamber at the time of deceleration. That means
At the time of deceleration, since the throttle valve is fully closed, the amount of air passing through the throttle valve almost disappears, and between the intake air amount detected by the air flow meter and the actual intake air amount supplied to the engine combustion chamber. Large differences occur. For this reason, the amount of intake air per one rotation of the engine measured by the air flow meter decreases, the fuel supply amount decreases, the air-fuel ratio in the combustion chamber becomes lean, misfire occurs, and required torque is not generated. For this reason, a minus torque is generated, and the minus torque resonates with the natural frequency of the engine, causing a hiccup phenomenon and a drive surge, and a deceleration shock, thereby giving the driver discomfort and anxiety. For this reason, conventionally, as shown in JP-A-59-231144, the fuel injection time immediately before deceleration is held for a certain period of time, and the value obtained by gradually reducing the held fuel injection time is used as a limit value. The output of the air flow meter was corrected to prevent the air-fuel ratio from becoming overlean during deceleration.

[Problems to be solved by the invention]

However, in the conventional fuel injection method, it is necessary to increase the holding time of the fuel injection time immediately before the deceleration in order to completely take measures such as deceleration shock and hiccup,
As a result, the air-fuel ratio becomes overloaded during deceleration, and HC and CO emissions increase.At the same time, the air-fuel ratio becomes a level at which catalyst exhaust odor becomes a problem, and it is necessary to solve these problems. There was a problem that it was not possible to completely countermeasures. That is, in order to optimally correct the output of the air flow meter when the vehicle is decelerated, the actual amount of intake air actually sucked into the cylinder and the amount of air adhering to the intake manifold inner wall just before deceleration are supplied to the combustion chamber at the time of deceleration. The actual amount of intake air actually drawn into the cylinder during deceleration depends on the volume of the intake system downstream of the throttle valve, the amount of intake air at the start of deceleration, With the conventional method of maintaining the fuel injection time immediately before deceleration for a fixed time as in the past, the actual amount of intake air actually sucked into the cylinder cannot be estimated correctly, and it sticks to the inner wall of the intake manifold. It is not possible to correct that the fuel that was being supplied during deceleration and the air-fuel ratio becomes rich. Positive could not be.

The present invention has been made to solve the above problems,
An object of the present invention is to provide a fuel injection method for an internal combustion engine in which an air-fuel ratio overlitch or an overlean does not occur by estimating an actual intake air amount drawn into a cylinder during deceleration.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an internal combustion engine having a throttle valve arranged in the middle of an intake pipe and a bypass passage arranged to bypass the throttle valve. In a fuel injection method for an internal combustion engine in which a fuel injection amount is determined based on a measured intake air amount per one revolution of the engine to inject fuel into the engine, it is assumed that no fresh air is supplied during deceleration. An estimated value of the intake air amount per rotation of the engine taken into the cylinder is calculated, and the measured intake air amount per rotation of the engine is only obtained during deceleration and when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Is determined so that the fuel injection amount is not less than the estimated value.

[Action]

According to the present invention, the fuel injection amount is determined based on the intake air amount per one revolution of the engine, and the fuel is injected, but is taken into the cylinder on the assumption that no fresh air is supplied during deceleration. Only when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the intake air amount per engine revolution is estimated, and the intake air amount per engine revolution that determines the fuel injection amount is less than the estimated value estimated as described above. It is restricted so that it does not become. Here, the estimated value of the intake air amount at the time of deceleration is calculated assuming that the supply of fresh air is not performed at the time of deceleration, but actually, the deceleration is performed via a bypass passage arranged around the throttle valve at the time of deceleration. Since fresh air is supplied, the estimated value becomes smaller than the actual intake air amount actually supplied to the engine combustion chamber.
For this reason, by restricting the intake air amount per one engine revolution measured as described above to be less than the estimated value, the estimated value is obtained when the measured intake air amount per one engine revolution is less than the estimated value. The fuel injection amount is determined on the basis of the above, and the air-fuel ratio is prevented from becoming overlean. Further, since the estimated value is smaller than the actual intake air amount, the fuel injection amount determined based on the estimated value becomes smaller than the fuel injection amount determined based on the actual intake air amount, and the intake pipe pressure increases rapidly during deceleration. Thus, even if fuel adhering to the intake manifold inner wall evaporates and is supplied to the engine combustion chamber, the air-fuel ratio is prevented from becoming overrich.

〔The invention's effect〕

As described above, according to the present invention, only when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio at the time of deceleration, the intake air amount per one rotation of the engine for determining the fuel injection amount is prevented from being less than the estimated value. Because of the restriction, it is possible to prevent the misfire due to the air-fuel ratio overlean and to prevent the increase of the exhaust emission and the generation of the catalyst odor due to the air-fuel ratio overlitch.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 schematically shows a spark ignition internal combustion engine (engine) provided with a fuel injection amount control device to which the present invention can be applied. An air flow meter 12 is provided downstream of the air cleaner 10.
Is arranged. The air flow meter 12 is provided with a compensation plate rotatably disposed in the damping chamber, a measuring plate fixed to the compensation plate, and a potentiometer for detecting an intake air amount from a change in the opening degree of the measuring plate. It is composed of a yoometer 12A. An intake air temperature sensor 12B that detects the intake air temperature is attached near the potentiometer 12A. The air flow meter 12 is connected to an intake port 22 of an engine body 20 via an intake passage 14, a surge tank 16, and an intake manifold 18. Surge tank 16
A throttle valve 24 is disposed upstream of the throttle valve 24.A throttle sensor 24A that turns on the throttle valve 24 when the throttle valve is fully closed is attached to the throttle valve 24, and the intake manifold 18 projects from each cylinder. A fuel injection valve (injector) 26 is disposed at the center. A bypass passage 24B is provided so as to bypass the throttle valve 24.

The intake port 22 is connected to the engine body 2 through the intake valve 20A.
It is connected to a combustion chamber 28 formed in the inside of the cylinder. The combustion chamber 28 is communicated with an exhaust passage 34 via an exhaust valve 20B, an exhaust port 30, and an exhaust manifold 32.
The exhaust manifold 32 is provided with an O ₂ sensor 40 that outputs a signal inverted at the stoichiometric air-fuel ratio.
The exhaust passage 34 is connected to a catalyst device 46 filled with a three-way catalyst.

A cooling water temperature sensor 38 is provided on the engine body 20 so as to penetrate the cylinder block and protrude into the water jacket.
Is installed. A spark plug (not shown) is attached to each cylinder so as to protrude into the combustion chamber 28 of the engine body 20, and this spark plug is connected to a distributor 42.
And an igniter (not shown) connected to a control circuit 45 including a micro computer.
A rotation angle sensor 48, which is composed of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing, is attached to the distributor 42. Rotation angle sensor 48 is 30 ゜
A rotation angle signal is output for each CA, and the engine rotation speed N can be calculated from the cycle of the rotation angle signal.

The potentiometer 12A, the intake air temperature sensor 12B, the throttle sensor 24A, the rotation angle sensor 48, the cooling water temperature sensor 38, and the O ₂ sensor sensor 40 are connected to a control circuit 45 so as to input signals. The fuel injection valve 26 is connected so as to be controlled by a control signal output from the control circuit 45.

Control circuit 45 including microcomputer
Is a random access memory (RA) as shown in FIG.
M) 58, read-only memory (ROM) 60, micro-processing unit (MPU) 62, output port 68, analog-to-digital (A / D) converter 74, rotation speed signal forming circuit 76, and a data bus connecting these And a bus 72 such as a control bus.

The A / D converter 74, is inputted Surotsutorusensa 24A, potentiometer 12A, the intake air temperature sensor 12B, a water temperature sensor 38 and O ₂ sensor 40 is connected, the A / D converter 74 from these The signals are sequentially converted to digital signals. Further, a rotation angle sensor 48 is connected to the rotation speed signal forming circuit 76, and the engine rotation speed is calculated from the cycle of the signal output from the rotation angle sensor 48 every 30 ° CA. The output port 68 is connected to the fuel injection valve 26 via a drive circuit 78. Reference numeral 80 denotes a clock generation circuit.

Figure 4 is a predetermined time (e.g., 64 msec) shows a learning routine executed every, the engine coolant temperature is a predetermined temperature in step 200 (e.g., 60 ° C.) whether more, O ₂ sensor is activated It is determined whether or not the air-fuel ratio feedback control condition is satisfied by determining whether or not the fuel injection amount has been increased or not. When the air-fuel ratio feedback control condition is not satisfied (when the above determination is negative), in step 202, the value of the air-fuel ratio feedback correction coefficient FAF is set to 1.0, and this routine is terminated. When the air-fuel ratio fed back control condition is determined to be satisfied in step 200, O ₂ sensor output OX determines whether shows an air-fuel ratio Ritsuchi at step 204. When it is determined that the O ₂ sensor output OX indicates the air-fuel ratio rich, in step 208, the integration constant K is obtained from the air-fuel ratio feedback correction coefficient FAF.
I subtracted _i, O ₂ sensor output OX proceeds to step 210 by adding the integral constant K _i in the air-fuel ratio fed back correction coefficient FAF in step 206 when it is determined that indicates the air-fuel ratio lean. Step 210, the O ₂ sensor output OX is determined whether the inverted Ritsuchi lean or from lean from Ritsuchi, the average value FAFAV and step of the air-fuel ratio fed back correction coefficient calculated previously at step 212 when the determination is affirmative The average value FAFAV of the air-fuel ratio feedback correction factor FAF is calculated based on the following equation using the air-fuel ratio feedback correction factor FAF integrated in step 206 and step 208.

In the next step 214, the engine speed N and the intake air amount Q
Then, in step 216, the learning area corresponding to the current engine speed N and the intake air amount Q is determined. The learning region is determined by the engine speed N and the engine load Q / N as shown in FIG. 5, and includes a learning region A, a learning region B, and a learning region from a low intake air amount region to a high intake air amount region. The area is divided into areas C. It should be noted that the intake air amount region higher than the learning region C is the air-fuel ratio open loop control region, and the region between the learning region A and the learning region B and the region between the learning region B and the learning region C are determined by the canister. This is a canister purge region for supplying the adsorbed HC to the intake system.

In the next step 218, the average value FAFAV of the air-fuel ratio feedback correction coefficient calculated in step 212 is stored as the average value FAFAV (x) of the air-fuel ratio feedback correction coefficient in the learning region determined in step 216. Note that x indicates one of the learning area A, the learning area B, and the learning area C. In the next step 220, it is determined whether the average value FAFAV (x) of all the air-fuel ratio feedback correction coefficients exceeds 1.0, and in step 224, the average value FAFAV (x) of all the air-fuel ratio feedback correction coefficients is determined. Determine if it is less than 1.0. At step 220, all of the average values FAFAV (x) are 1.
When it is determined that the value exceeds 0, the learning value FGHAC for altitude compensation is set to a predetermined amount (for example, 0.0) in step 222.
5) If the average value FAFAV (x) is determined to be less than 1.0 in step 224, the learning value FGH is determined in step 226.
Decrease AC by a predetermined value (for example, 0.05), and
In step 8, all of the average values FAFAV (x) are set to 1.0, and the routine ends. When all of the average values FAFAV (x) are 1.0, this routine ends without updating the learning value FFGAC.

As a result, the air-fuel ratio feedback correction coefficient is integrated so as to be gradually reduced when the O ₂ sensor output indicates rich and gradually increased when the O ₂ sensor output indicates lean air-fuel ratio, to obtain a stoichiometric air-fuel ratio. The corresponding value, namely 1.
It changes around 0. Further, the learning value FGHAC is updated to increase or decrease depending on the magnitude of the average value of the air-fuel ratio fed back correction coefficient O ₂ sensor output is calculated every time the inversion. Note that the above air-fuel ratio feedback correction coefficient FAF
The upper and lower limits of the learning value FFGAC are generally set as shown below in consideration of fail safety due to erroneous learning and the like.

0.8 ≦ FAF ≦ 1.2 (2) −0.2 ≦ FGHAC ≦ 0.2 (3) FIG. 1 shows a fuel injection routine of the present embodiment.
Uptake in step 100 and the engine rotational speed N of the intake air quantity Q, calculates the intake air quantity Q / N _i per revolution current engine by dividing the intake air amount at the current engine speed N in step 102 . Determining whether the next step 104, the O ₂ sensor output OX indicates a lean air-fuel ratio, the previously calculated in step 106 when showing the air-fuel ratio lean flow proceeds to step 114 when showing the air-fuel ratio Ritsuchi and the intake air amount Q / N _i-1 per engine revolution is compared with the intake air quantity Q / N _i per revolution current engine. The current intake air volume per engine revolution Q / N _i is the previous intake air volume per engine revolution
If it is smaller than Q / N _i-1 , it is judged as decelerating and the
Proceed to 108, and if the determination in step 106 is negative,
Proceed to 114.

In step 108 compares the intake air quantity Q / N _i per revolution current engine and estimates Q / N _i-1 · K1 of the intake air amount. Here, the constant K1 of the estimated value Q / N _i−1 · K1 is obtained as follows.

That is, the number of cylinders is n, the displacement per cylinder is V _h , and the volume of the intake system from the throttle valve to the intake valve 20A is V _i.
And then, Surotsutoru valve per air intake stroke of the weight G _o fresh air through the Surotsutoru valve remaining in the intake system to the deceleration immediately before not supplied into the cylinder from the fact that fully closed state during deceleration The density of the air remaining in the intake system immediately before the start of deceleration is
Since the G _o / V _i, the weight G _1i of the intake air sucked into the cylinder at the first intake stroke after the start deceleration of the following (4
-1) It is represented by the formula.

Similarly, the second, third,... After the start of deceleration
The weights G _2i , G _3i ,... G _mi of the intake air sucked into the cylinder in the m-th intake stroke are expressed as follows.

In the case of a four-cycle engine, one cycle is performed with two revolutions of the engine, so that the intake weight G per one revolution of the engine of a four-cycle n-cylinder engine is as follows.

Therefore, the intake air amount Q / N _o [l / rev.] Per one rotation of the engine immediately before the start of deceleration is expressed by the following equation (6), where N is the engine rotation speed and ρ _o is the air density. In the case of simultaneous injection in which fuel is simultaneously injected into all cylinders once per engine revolution, the engine 1 in the first intake stroke after deceleration
The intake air amount Q / N per rotation (estimated value) is expressed by the following equation (7).

Therefore, Then, the intake air amount Q / N (estimated value) per one rotation of the engine in the first intake stroke in the case of the simultaneous injection is expressed as follows.

Q / N = K ₁ · Q / N _o (8) Accordingly, in the second and subsequent intake strokes in the same manner as in the above equation (8), the previous intake air amount per engine revolution Q /
From N _i-1 this time the intake air amount per engine revolution Q / N _i ,
That is, the estimated value can be calculated according to the following equation.

Q / N _i = K1 · Q / N _i-1 (9) On the other hand, in the case of independent injection in which injection is performed once for each cylinder for two revolutions of the engine, the above (4-1) to (4-m) As can be understood from the formula, for each intake stroke This time, the engine 1
The intake air amount per revolution Q / N _i (estimated value) is expressed as follows using the previous intake air amount Q / _Ni-1 per engine revolution.

As described above, the estimated value of the result that the intake of fresh air is assumed to be 0 at the time of deceleration becomes smaller than the true actual intake air amount.

Step amount of intake air per revolution time of the engine at 108 Q / N _i is the intake air amount of the engine per revolution estimated K1
When it is determined that Q / N _i-1 or more, it is determined that the potentiometer output is correct, and the routine proceeds to step 114. On the other hand, in step 108, the intake air amount Q / N _i
Estimated intake air amount K1 · Q / N per engine revolution
_If it is determined that it is smaller than _i-1 , the estimated value is estimated to be smaller than the true actual intake air amount, as described above, so that it is determined in step 110 that the potentiometer output is not correct, and the estimated value is estimated in step 110. after the intake air quantity Q / N _i of the intake air quantity K1 · Q / N _i-1 the current engine per revolution per rotation engine 1, by 1.0 the air-fuel ratio fed back coefficient FAF in step 112 The process proceeds to step 114 so as to stop the air-fuel ratio feedback. In step 114, to estimate the amount of intake air per revolution of the next engine, the amount of intake air Q /
N _i and stored in the register such that the previous intake air quantity Q / N _i-1, the fuel injection time according to the following equation at step 116 T
Calculate AU.

However λ is the target air-fuel ratio, the correction coefficient K ₂ is based on the intake air temperature and engine coolant temperature, Tinyu is ineffective injection time for correcting the operation delay time of the fuel injection valve.

Then, in the next step 118, the fuel injection valve is opened at a predetermined crank angle to execute the synchronous fuel injection so that the simultaneous injection or the independent injection described above is performed.

When Q / N _i ≧ K1 · Q / N _{i−1 at} the time of deceleration, the air-fuel ratio feedback control is performed, so that the air-fuel ratio overlit and overlean do not occur.

FIG. 6 shows an engine speed of 1600 between the present embodiment and the conventional example.
FIG. 7 is a diagram showing air-fuel ratio fluctuations and air flow changes when the vehicle is decelerated from traveling at 3rd speed at rpm. FIG. 6 (B) is a diagram showing a change in the air flow rate with respect to the elapsed time, and the actual intake air amount Q _H passing through the air flow meter and the air flow meter indicated air flow rate.
FIG. 7 is a graph showing changes in Q _A , an actual intake air amount Q _{E of} the engine, and an estimated value of the intake air amount described in the embodiment. As can be seen, the estimated value of the intake air amount of the engine intake is less than the actual air flow rate Q _E, it varies along the substantially engine intake actual air flow rate Q _E. This is the air flow meter instruction air flow rate Q _A in the under sheet Ute occurs immediately after deceleration from the Surotsutoru valve is abruptly closed when decelerating from running at the third speed by the engine rotational speed 1600rpm respect, the results Figure 6 As shown in (A), the air-fuel ratio is over-lean immediately after deceleration. On the other hand, since the estimated value of the intake air amount changes substantially along the actual intake air flow rate of the engine, the air-fuel ratio of this embodiment hardly changes as shown in FIG. 6 (A). As the synchronous fuel injection, in the case of the simultaneous injection, the fuel injection amount corresponding to the fuel injection time obtained above may be divided into two and halved for two injections. Group injection.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a fuel injection control routine according to one embodiment of the present invention, FIG. 2 is a schematic diagram showing an internal combustion engine to which the present invention can be applied, and FIG. 3 shows details of the control circuit of FIG. FIG. 4 is a flowchart showing a routine for calculating an air-fuel ratio feedback correction coefficient and a learning value of the above embodiment, FIG. 5 is a diagram showing a learning region, and FIG. 6 is a diagram showing the above embodiment and a conventional example. FIG. 4 is a graph showing a change in air-fuel ratio and a change in air flow rate. 12 ... Air flow meter, 26 ... Fuel injection valve.

Claims (1)

(57) [Claims] An internal combustion engine having a throttle valve disposed in the middle of an intake pipe and a bypass passage bypassing the throttle valve has a measured intake air amount per one revolution of the engine. In a fuel injection method for an internal combustion engine in which a fuel injection amount is determined based on a fuel injection amount, an amount of intake air per one revolution of the engine is estimated assuming that no fresh air is supplied during deceleration. Only when the vehicle is decelerating and when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the fuel injection amount is limited by limiting the measured intake air amount per rotation of the engine to be less than the estimated value. A fuel injection method for an internal combustion engine.