JP2536117B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fuel injection control device for an internal combustion engine.

[Conventional technology]

During the fuel injection internal combustion period, the basic fuel injection amount is calculated from the normal intake pipe negative pressure and engine speed, or from the intake air amount and engine speed, and the oxygen concentration detector (hereinafter referred to as O ₂ By correcting the basic fuel injection amount based on the output signal of a sensor), feedback control is performed so that the air-fuel mixture supplied into the engine cylinder has a predetermined target air-fuel ratio, for example, the theoretical air-fuel ratio. However, even if the feedback control is performed in this way, when the fuel injection amount is rapidly increased, such as during acceleration operation, the amount of injected fuel that adheres to the intake port inner wall surface in the form of liquid fuel increases. Since the adhered liquid fuel is not supplied to the engine cylinder immediately after it is adhered, the air-fuel mixture supplied to the engine cylinder becomes primarily lean, that is, lean, whereas the absolute pressure in the intake port is low during deceleration operation. As a result, the evaporation amount of the liquid fuel adhering to the inner wall surface of the intake port and the like increases, so that the air-fuel mixture supplied into the engine cylinder temporarily becomes rich, that is, rich. Therefore, in a normal fuel injection type internal combustion engine, even in a transient operation state such as acceleration operation or deceleration operation, injection is performed during acceleration operation so that the air-fuel mixture supplied to the engine cylinder has a target air-fuel ratio, for example, a theoretical air-fuel ratio. The amount of fuel is increased, and the amount of injected fuel is reduced during deceleration operation. Therefore, in such a fuel injection type internal combustion engine, the air-fuel mixture supplied into the engine cylinder is controlled to a target air-fuel ratio regardless of the operating state of the engine.

However, in such an internal combustion engine, for example, blow-by gas or lubricating oil penetrates into the intake port through the space between the intake valve stem and the stem guide, and if the engine is used for a long period of time, the blow-by gas or lubricating oil may be contained in the internal combustion engine. The carbon fine particles contained therein are gradually deposited on the back surface of the cover of the intake valve or on the inner wall surface of the intake port. The deposits such as carbon fine particles, that is, the deposit has a property of retaining the liquid fuel. Therefore, when the deposit is accumulated on the inner wall surface of the intake port, the amount of the liquid fuel adhering to the inner wall surface of the intake port increases, and the inner wall surface of the intake port also increases. It takes a long time for the liquid fuel adhering to etc. to flow into the engine cylinder after adhering. Therefore, while the engine is relatively new, the air-fuel mixture supplied into the engine cylinder is controlled to the stoichiometric air-fuel ratio regardless of the operating condition of the engine, but the engine is used for a long period of time and the deposit is kept in the intake port. If it adheres to the wall surface, it takes time for the injected fuel adhering to the inner wall of the intake port to flow into the engine cylinder, so the mixture supplied to the engine cylinder becomes lean during acceleration operation. Further, since the amount of injected fuel adhering to the inner wall surface of the intake port and the like increases, the air-fuel mixture supplied to the engine cylinder becomes rich during deceleration operation. As described above, the degree of richness of the air-fuel mixture during the acceleration operation and the richness of the air-fuel mixture during the deceleration operation increase as the amount of deposit increases. In this case, for example, the greater the degree of leanness during acceleration operation, the longer the lean time of the air-fuel mixture.

Therefore, the time when the air-fuel mixture supplied to the engine cylinder becomes lean and rich is calculated within a certain time after the acceleration operation is started, and the lean time and the rich time are calculated from these lean time and rich time. Also, a fuel injection control device is known in which the acceleration increase value of the injected fuel is corrected so that the air-fuel mixture supplied into the engine cylinder has a target air-fuel ratio (see Japanese Patent Laid-Open No. 59-128944).

[Problems to be Solved by the Invention]

By the way, as described above, the greater the degree of leanness during acceleration operation, the longer the time the mixture becomes lean with it, so compare the time when the mixture becomes lean and the time when it becomes rich during acceleration operation. If the lean time is longer than the rich time, it can be determined that the air-fuel mixture is lean during the acceleration operation. However, in reality, when the lean time becomes longer, the rich time may also become longer accordingly. In such a case, the lean time and rich time within a fixed time after the start of acceleration are compared as in the fuel injection control device described above. Then, the lean time becomes equal to the rich time, thus causing a problem of erroneously determining that the air-fuel mixture is not lean.

Further, when the air-fuel mixture is maintained at substantially the stoichiometric air-fuel ratio even during the acceleration operation, the air-fuel mixture repeats lean and rich in a substantially constant cycle even during the acceleration operation. In such a case, when comparing the lean time and the rich time within a certain time after the start of acceleration as in the fuel injection control device described above, the lean time becomes longer than the rich time depending on how to select the certain time, or conversely, the rich time. There is a problem in that the air-fuel mixture is erroneously judged to be lean or rich even though the air-fuel mixture is not lean or rich because it becomes longer than the lean time.

[Means for solving the problem]

In order to solve the above-mentioned problems, according to the present invention, as shown in the block diagram of the invention of FIG. 1, the engine concentration in the engine cylinder is based on the output signal of the oxygen concentration detector 19 arranged in the engine exhaust passage A. A fuel injection control unit B that controls the fuel injection amount so that the supplied air-fuel mixture has a target air-fuel ratio, and a period in which the air-fuel mixture becomes lean or rich during acceleration operation or an integral multiple of the period, which is the lean / rich determination period. After the acceleration operation is started based on the detection results of the storage means C, which stores the acceleration operation status, the acceleration operation status detection means D for detecting the acceleration operation status, the oxygen concentration detector 19 and the acceleration operation status detection means D. Deviation calculating means E for calculating the deviation between the lean time and the rich time of the air-fuel mixture only during the rich judgment period, and the deviation calculating means E
The fuel injection amount increasing means F increases the fuel injection amount when the lean time is longer than the rich time and the above deviation exceeds a predetermined set value.

〔Example〕

Referring to FIG. 2, 1 is an engine body, 2 is a piston,
3 is a cylinder head, 4 is a combustion chamber formed between the piston 2 and the cylinder head 3, 5 is a spark plug, 6 is an intake valve, 7
Is an intake port, 8 is an exhaust valve, and 9 is an exhaust port. Each intake port 7 is connected to a surge tank 11 via a corresponding branch pipe 10, and each branch pipe 10 has a corresponding intake port 7
A fuel injection valve 12 for injecting fuel inward is attached. The fuel injection from each fuel injection valve 12 is an electronic control unit.
Controlled based on 30 output signals. The surge tank 11 is connected to an air cleaner 14 via an intake duct 13, and a throttle valve 15 is arranged in the intake duct 13. Throttle valve
A bypass passage 16 that bypasses 15 is connected to the intake duct 13, and a bypass air amount control valve 17 is arranged in the bypass passage 16. Each exhaust port 9 is connected to an exhaust manifold 18, and an O ₂ sensor 19 is mounted in the exhaust manifold 18.

The electronic control unit 30 is composed of a digital computer, and has a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and an input port 35 which are mutually connected by a bidirectional bus 31.
And an output port 36. A backup RAM 32a is connected to the CPU 34 via a bus 31a. A water temperature sensor 20 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 20 is input to an input port 35 via an AD converter 37. The output voltage of the O ₂ sensor 19 is input to the input port 35 via the AD converter 38. Surge tank 11 has surge tank
An absolute pressure sensor 21 that generates an output voltage proportional to the absolute pressure in 11 is installed. The output voltage of this absolute pressure sensor 21 is AD
It is input to the input port 35 via the converter 39. A throttle switch 22 for detecting that the throttle valve 15 is at the fully closed position is attached to the throttle valve 15, and an output signal of the throttle switch 22 is input to an input port 35.
The rotation speed sensor 23 generates an output pulse each time the crankshaft rotates a predetermined crank angle, and the output pulse of the rotation speed sensor 23 is input to the input port 35. The engine speed is calculated in the CPU 34 from this output pulse. on the other hand,
The output port 36 is connected to the fuel injection valve 12 and the bypass air amount control valve 17 via the corresponding drive circuits 40 and 41. The bypass air amount control valve 17 is provided to control the engine idling speed, and the bypass air amount control valve 17 moves the inside of the bypass passage 16 so that the engine idling speed becomes the target speed during engine idling operation. The amount of bypass air flowing is controlled.

On the other hand, the fuel injection time TAU of the fuel injection valve 12 is calculated based on the following equation.

TAU = (TP + K ・ TPAEW) ・ FAF ・ F (1) where TP: Basic fuel injection time TPAEW: Corrected fuel injection time during transition, that is, during acceleration / deceleration K: Corrected fuel injection time due to deposit accumulation TP
AEW correction coefficient FAF: Feedback correction coefficient F: Correction coefficient determined by intake air temperature, engine cooling water temperature, etc. The basic fuel injection time TP is calculated from the absolute pressure PM in the surge tank 11 and the engine speed NE. The relationship between the basic fuel injection time TP, the absolute pressure PM, and the engine speed NE is the mixture that is supplied into the engine cylinder when fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP during steady operation. Air-fuel ratio,
For example, the theoretical air-fuel ratio has been previously obtained by experiments, and this relationship is stored in the ROM 32. Therefore, when steady operation is performed, basically, if fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP calculated based on the relationship stored in the ROM 32 from the absolute pressure PM and the engine speed NE, Indicates that the air-fuel mixture supplied into the engine cylinder has a target air-fuel ratio. O ₂ The use of the O ₂ sensor capable of detecting any air-fuel ratio sensor 19 to the target air-fuel ratio can be arbitrarily set, but less so as to be able to easily understand the present invention, the stoichiometric air-fuel ratio the target air-fuel ratio The case of setting to will be described. In this case, if the fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP, the air-fuel mixture basically supplied to the engine cylinder has almost the stoichiometric air-fuel ratio.

The corrected fuel injection time TPAEW becomes zero when not in the transient operation state, that is, in the steady operation. Therefore, at this time, the above equation (1) is expressed as the following equation.

TAU = TP ・ FAF ・ F (2) That is, this fuel injection time TAU is the basic fuel injection time TP,
It is determined by the feedback correction section FAF and the correction coefficient F. The correction coefficient F is determined by the intake air temperature, the period cooling water temperature, etc., for example, before completion of warm-up when the engine cooling water temperature is low.
A value greater than 1.0, and a value close to 1.0 after completion of warming up,
Or it will be 1.0. The feedback correction factor FAF is set so that the air-fuel mixture supplied into the engine cylinder has the stoichiometric air-fuel ratio.
It changes based on the output signal of the O ₂ sensor 19. Next, the feedback correction coefficient FAF will be described.

The O ₂ sensor 19 generates an output voltage of about 0.1 V when the air-fuel mixture supplied to the engine cylinder is larger than the theoretical air-fuel ratio, that is, when it is lean, and when it is smaller than the theoretical air-fuel ratio, that is, 0.9 when it is rich. It produces an output voltage of the order of volts. Therefore, it is possible to determine from the output signal of the O ₂ sensor 19 whether the air-fuel mixture supplied into the engine cylinder is lean or rich. FIG. 3 shows a routine for calculating the feedback correction coefficient FAF from the output signal of the O ₂ sensor 19. Referring to FIG. 3, first step 10
At 0, it is determined whether or not the air-fuel ratio feedback control test has been established. For example, not when starting the engine,
When the engine cooling water temperature is not below the predetermined value, it is determined that the feedback control condition is satisfied. When the feedback control condition is not satisfied, the routine proceeds to step 101, where the feedback correction coefficient FAF is set to 1.0. Therefore, during steady operation in which the feedback control condition is not satisfied, the fuel injection time TAU is calculated based on the following equation.

On the other hand, when it is judged that the feedback control condition is satisfied, the routine proceeds to step 102, where it is judged from the output signal of the O ₂ sensor 19 whether or not the air-fuel mixture supplied to the engine cylinder is rich. Is determined. It was lean in the previous processing cycle, and if it changed to rich in this processing cycle, proceed to step 103 to reset the flag CAFL, and then reset the flag CAFR that is reset when changing from rich to lean in step 104. It is determined whether or not it has been done. When changing from lean to rich, the flag CAFR has been reset, so the routine proceeds to step 105, where a predetermined skip value Rs is subtracted from the feedback correction coefficient FAF. Then step 106
Then the flag CAFR is set. Therefore, in the next processing cycle, the routine proceeds from step 104 to step 107, where the feedback correction coefficient FAF is set to a predetermined constant value K; (Ki << R
s) is subtracted.

On the other hand, if the change from rich to lean proceeds from step 102 to step 108, the flag CAFR is reset, then proceeds to step 109, and it is determined whether or not the flag CAFL has been reset. At this time, since the flag CAFL has been reset, the routine proceeds to step 110, where the skip value Rs is added to the feedback correction coefficient FAF, and then the flag CAFL is set at step 111. Therefore, in the next processing cycle, the routine proceeds from step 109 to step 112 where the constant value Ki is added to the feedback correction coefficient FAF.
Therefore, the feedback correction coefficient FAF changes as shown in FIG. When it becomes rich, the feedback correction coefficient FAF is reduced and the fuel injection time TAU becomes short, and when it becomes lean, the feedback correction coefficient FAF is increased and the fuel injection time TAU becomes long, and thus the fuel injection time TAU becomes longer. The supplied air-fuel mixture is controlled to the stoichiometric air-fuel ratio.

As described above, when the feedback control is performed in the steady operation state, the air-fuel mixture supplied into the engine cylinder is controlled to the stoichiometric air-fuel ratio. However, if the fuel injection time TAU is calculated based on the above equation (2), even if the feedback control is performed in the transient operation state such as the acceleration operation or the deceleration operation, the deposit further adheres to the inner wall surface of the intake port. Even if not, the air-fuel mixture supplied into the engine cylinder will deviate from the stoichiometric air-fuel ratio. That is, the air-fuel mixture becomes temporarily lean during the acceleration operation, and becomes temporarily rich during the deceleration operation. The deviation of the air-fuel ratio in such a transient operation state is due to the time delay from the start of the calculation of the fuel injection time TAU until the actual fuel injection, and the liquid injection fuel adhering to the inner wall surface of the intake port, etc. This is due to the time delay until it flows into the cylinder. Therefore, these time delays during acceleration operation will be described first with reference to FIGS. 5 and 6.

FIG. 5 shows the deviation of the air-fuel ratio based on the time delay from the start of calculation of the fuel injection time TAU to the actual fuel injection. As shown in Fig. 5, if the absolute pressure PM in the surge tank 11 rises from PM ₁ to PM ₂ due to acceleration operation, the basic pressure calculated from the absolute pressure PM and engine speed NE The fuel injection time TP also rises. If the calculation of the fuel injection time TAU is started at time ta, the absolute pressure PM at this time is PMa, so this absolute pressure P
The basic fuel injection time TP is calculated based on Ma, and the basic fuel injection time TP at this time is set to TPa. By the way, the calculation of the normal fuel injection time TAU is started at a predetermined crank angle, and then the actual fuel injection is started after a fixed crank angle. That is, in FIG. 5, when the calculation of the fuel injection time TAU is started at time ta, the actual fuel injection is started at time tb. However, at time tb, the absolute pressure PM is PM
The PMb is higher than a, and at this time, the basic fuel injection time required to bring the mixture to the stoichiometric air-fuel ratio is TPb longer than TPa. Nevertheless, at time tb, the fuel is injected only for the time calculated based on the basic fuel injection time TPa, so the fuel injection becomes less than the injected fuel required to make the air-fuel mixture the stoichiometric air-fuel ratio, Thus, the air-fuel mixture becomes lean. That is, since the basic fuel injection time TP actually changes along the broken line W, the air-fuel mixture becomes lean as shown by Y ₁ while it is shown by the broken line W.

On the other hand, FIG. 6 shows the deviation of the air-fuel ratio due to the time delay until the liquid injected fuel adhering to the inner wall surface of the intake port and the like flows into the engine cylinder. Note that FIG. 6 also shows a case where the absolute pressure PM in the surge tank 11 rises from PM ₁ to PM ₂ . In FIG. 6, curves TPc and TPd show changes in the basic fuel injection time TP, and hatching Xa and Xb show the amount of liquid fuel flowing into the engine cylinder. The liquid fuel amount flowing into the engine cylinder depends on the injected fuel amount, that is, the fuel amount adhering to the inner wall surface of the intake port,
Therefore, as the fuel injection amount increases, the amount of liquid fuel flowing into the engine cylinder increases. The amount of the liquid fuel is substantially constant when the engine is in the steady operation, and the amount of the liquid fuel increases as the engine load becomes higher when the engine is in the steady operation. Xa in Fig. 6 shows the case where it is assumed that the same amount of liquid fuel is supplied into the engine cylinder for each absolute pressure PM as in the steady operation. In this case, the engine cylinder is also accelerated during the acceleration operation. The air-fuel mixture supplied inside is maintained at the stoichiometric air-fuel ratio. However, in actual practice, acceleration operation is performed, and even if the amount of fuel adhering to the inner wall of the intake port increases, not all of the adhered fuel immediately flows into the engine cylinder, so the liquid that flows into the engine cylinder during acceleration operation The fuel will be less than indicated by Xa. When the amount of the adhered fuel increases, the amount of the liquid fuel flowing into the engine cylinder gradually increases, and after the completion of the acceleration operation, this liquid fuel amount becomes equal to the liquid fuel amount during the steady operation. Xb in FIG. 6 shows the amount of liquid fuel actually flowing into the engine cylinder. Therefore, the liquid fuel amount Xb flowing into the engine cylinder for a while after the acceleration operation is started and after the acceleration is completed is smaller than the liquid fuel amount Xa in the steady operation, and therefore the air-fuel mixture is indicated by Y ₂ during this period. To become lean.

Therefore, as shown by Y in Fig. 7, Y ₁
The lean indicated by and the lean indicated by Y ₂ are overlapped. Therefore, as shown in Fig. 7, Y ₁
If the fuel amount is increased by the amount C ₂ ΔPM · C ₄ corresponding to, and the fuel amount is increased by the amount C ₃ (ΔPM + C ₁ ΣΔPM) · C ₄ corresponding to Y ₂ , the air-fuel mixture becomes almost the theoretical air-fuel ratio as indicated by Z. Will be maintained. Here, ΔPM is the change rate of the absolute pressure PM, and C ₄ is a coefficient for converting the absolute pressure into time.

That is, in Fig. 5, the shortage amount of the basic fuel injection time TP (TPb-TPa) is the time (tb-t) at ΔPM · C ₄ at time ta.
a) multiplied by and is approximately equal to the time (tb−ta)
Is expressed as C ₂ , the shortage of the basic fuel injection time TP is C ₂ ΔPM
It will be represented by C ₄ . Since time (tb-ta) corresponds to the crank angle, C ₂ is a function of the engine speed NE.

On the other hand, the curve corresponding to the curve shown by Y ₂ is C ₃ (ΔPM +
It can be expressed by C ₁ ΣΔPM) and C ₄ . here
C ₁ is called an attenuation coefficient and has a value smaller than 1.0. That is, C ₃ (ΔPM + C ₁ ΣΔPM) / C ₄ is calculated when calculating the fuel injection time TAU, and the value of C ₃ (ΔPM + C ₁ ΣΔPM) / C ₄ increases rapidly when ΔPM is large, and ΔPM Decreases slowly, it decreases slowly. When the engine temperature and the intake air temperature become low, the amount of liquid fuel adhering to the inner wall surface of the intake port and the like increases, and the air-fuel mixture becomes leaner accordingly. Therefore, C ₃ is a function of engine temperature and intake air temperature.

Therefore, during acceleration operation, C ₂ ΔPM ・ C ₄ and C ₃ (ΔPM + C ₁ ΔPM)
・ The fuel-air mixture can be maintained at the stoichiometric air-fuel ratio by increasing the amount of fuel added with C ₄ . This added value becomes the corrected fuel injection time TPAEW at the time of the transition in the above equation (1). That is T
PAEW is expressed by the following equation.

TPAEW = {C ₂ ΔPM + C ₃ (ΔPM + C ₁ ΣΔPM)} C ₄ (3) Note that the rich state during deceleration operation is also Y ₁ and Y _{2 in} FIGS. 5 and 6, and therefore the above (3 ) Expression TP
Similarly, if the AEW is used, the air-fuel mixture supplied into the engine cylinder is maintained at the stoichiometric air-fuel ratio. However, TPAEW becomes negative because ΔPM becomes negative during deceleration operation.

Therefore, when the deposit does not adhere to the inner wall surface of the intake port or the like, if the fuel injection time TAU is calculated based on the following equation, the air-fuel mixture can be maintained at the stoichiometric air-fuel ratio regardless of the operating state of the engine.

TAU = (TP + TPAEW) ・ FAF ・ F (4) However, when the engine is used for a long period of time and the deposit adheres to the inner wall surface of the intake port, etc., the deposit has a property of retaining liquid fuel, so the inner wall surface of the intake port is The amount of liquid fuel adhering to the fuel tank increases, and more time is required for the liquid fuel adhering to the inner wall surface of the intake port to flow into the engine cylinder. Therefore, when the deposit adheres to the inner wall surface of the intake port, etc., if the above equation (4) is used, the flow of the liquid fuel into the engine cylinder is delayed due to the deposit during the acceleration operation, so that the air-fuel mixture becomes lean. Since the amount of liquid fuel adhering to the inner wall surface of the intake port increases, the air-fuel mixture becomes rich. Therefore, when deposits are attached, the correction coefficient K is multiplied by the correction fuel injection time TPAEW, and the correction amount K is used to correct the amount of fuel increase / decrease during acceleration / deceleration operation, so that the mixture is mixed regardless of the operating state of the engine. The stoichiometric air-fuel ratio is maintained. In this case, the fuel injection time TAU is calculated by the following equation as shown in the above equation (1).

TAU = (TP + K ・ TPAEW) ・ FAF ・ F That is, when the deposit is not adhered and therefore the air-fuel mixture supplied to the engine cylinder is maintained at the stoichiometric air-fuel ratio even during the acceleration operation, Fig. 8 ( As shown in A), after the acceleration operation is started, lean and rich are alternately repeated at substantially the same cycle, so that the lean time and the rich time do not change much. However, if the deposit adheres, the air-fuel mixture temporarily becomes lean during the acceleration operation as shown in FIG. 8 (B). In this way, when the air-fuel mixture temporarily becomes lean during acceleration operation, FIG. 8 (B)
As shown in, the lean time after the acceleration operation is started is longer than the rich time. On the other hand, if the air-fuel mixture temporarily becomes rich during the acceleration operation, then the rich time after the acceleration operation is started becomes longer than the lean time. Therefore, by comparing the lean time and the rich time, it is possible to determine whether the air-fuel mixture is temporarily lean or rich. Therefore, roughly speaking, if the lean time becomes longer than the rich time by a certain amount or more during the acceleration operation, the value of the correction coefficient K is increased and the acceleration fuel increase rate is increased, and the lean time is longer than the rich time. If it becomes shorter than a certain level, the value of the correction coefficient K is reduced, and the acceleration fuel increase rate is reduced.
On the other hand, in the deceleration operation, if the rich time is longer than the lean time by a certain amount or more, the value of the correction coefficient K is increased, and the deceleration fuel decrease amount ratio is increased, and the rich time is increased by a certain amount than the lean time. If the length is shortened below, the value of the correction coefficient K is decreased, and the deceleration fuel decrease rate is decreased.

Next, the calculation routine of the correction coefficient K, that is, the calculation routine of the deposit learning value K will be described with reference to the time chart shown in FIG. 9 and the flowcharts shown in FIG. 10 and FIG. This routine is executed by interruption every 360 crank angles.

Referring to FIGS. 10 and 11, first step
In 200, the absolute pressure PM ₁ in the surge tank 11 detected in the previous processing cycle is subtracted from the current absolute pressure PM in the surge tank 11 detected by the absolute pressure sensor 21, and the subtraction result is the change in absolute pressure. The rate is ΔPM. Next, at step 201, it is judged if feedback control based on the output signal of the O ₂ sensor 19 is being performed. When the feedback control is not being performed, the routine proceeds to step 202, where the counters CAC, CLRN1, CLRN2 are cleared. Next, when the feedback control is started, the routine proceeds to step 203, where it is judged if the counter CLRN1 is cleared. At this time, since the quanta CLRN1 has been cleared, the routine proceeds to step 204, where it is determined whether or not the counter CLRN2 has been cleared. At this time, the counter CLRN2 has been cleared, so the routine proceeds to step 205. ΔPM in step 205
Is larger than a fixed value, for example, 39 mmHg, that is, whether or not it is during acceleration operation. If ΔPM <39 mmHg, it is determined that the acceleration operation is not in progress, and the routine proceeds to step 206.
In step 206, it is determined whether or not ΔPM is smaller than a fixed value, for example, −39 mmHg, that is, whether or not deceleration operation is being performed. If ΔPM <−39 mmHg, it is determined that the deceleration operation is not being performed, and the routine proceeds to step 202, where the counters CAC, CLRN1, CLRN2 are cleared.

On the other hand, when it is determined in step 205 that ΔPM is 39 mmHg, that is, during acceleration operation, the routine proceeds to step 207, where 1 is set to the count value of the counter CLRN1. Next, the routine proceeds to the fuel injection time calculation routine. In the next processing cycle, the process proceeds from step 203 to step 208. In step 208, whether ΔPM has become lower than −5 mmHg,
That is, it is determined whether or not the vehicle has been decelerated after the start of acceleration operation, and ΔPM
If it is −5 mmHg, proceed to step 202 and set each counter CA.
C, CLRN1, CLRN2 are cleared.

On the other hand, if the acceleration operation continues, Δ
Since PM> -5 mmHg, the routine proceeds from step 208 to step 209, and the counter CLRN1 is incremented by 1.
That is, as shown in FIG. 9 (A), the acceleration operation is started and the absolute pressure PM in the surge tank 11 rises from PM ₁ to PM _2. At this time, if ΔPM exceeds 39 mmHg, the counter CLRN1 counts up. Be started.

Next, at step 210, it is judged if the count value of the counter CLRN1 is larger than a predetermined constant value A1. If CLRN1 <A1, proceed to the fuel injection time calculation routine. On the other hand, when CLRN1A1 is reached, the routine proceeds to step 211, where it is judged from the output signal of the O ₂ sensor 19 whether or not the air-fuel mixture supplied into the engine cylinder is lean. When the air-fuel mixture is lean, the routine proceeds to step 212, where the counter CAC is incremented by 1, and then the routine proceeds to step 213. On the other hand, when the air-fuel mixture is not lean, that is, when the air-fuel mixture is rich, the routine proceeds to step 214, where the counter CAC is decremented by 1, and then the routine proceeds to step 213. At step 213, the counter CLRN1 is set to a predetermined constant value B1.
It is determined whether or not it has become larger than. If CLRN1 <B1, proceed to the fuel injection time calculation routine. That is, the ninth
As shown in Fig. (A), it is determined whether the air-fuel mixture is lean or rich until the count value of the counter CLRN1 changes from A1 to B1. When the air-fuel mixture is lean, the counter CAC counts up. When the air-fuel mixture is rich, the counter CAC is counted down. Therefore, if the time during which the count value of the counter CLRN1 changes from A1 to B1 is longer than the time during which it is rich, the count value of the counter CAC increases and the time during which it is lit is lean. If it is longer than, the count value of the counter CAC decreases. Therefore, whether the air-fuel mixture is lean or rich during the acceleration operation can be determined from the count value of the counter CAC when CLRN1 becomes B1.

As described above, in the embodiment shown in FIG. 9, it is determined whether the air-fuel mixture is lean or rich until the count value of the counter CLRN1 reaches A1 to B1. Therefore, the count value of the counter CLRN1 is The period from A1 to B1 is the lean / rich judgment period. Next, the lean / rich determination period will be described with reference to FIGS. 8 (C) to 8 (H). In FIGS. 8C to 8H, the lean / rich determination period is indicated by L, L ′ or L ″.

FIGS. 8 (C), (D), and (E) show changes in the output voltage of the O ₂ sensor 19 and the behavior of the count value of the counter CAC when acceleration operation is performed in the case where Devogit is not attached. There is. In this case, FIG. 8 (C), (D),
As shown in (E), lean and rich are repeated in almost the same cycle even during acceleration operation, and the lean / rich determination period L is lean in such a state as shown in FIG. 8 (C). Alternatively, the cycle is set to be rich. In other words, in other words, the set value A for the counter CLRN1
1, B1 is set so that the period until the count value reaches from A1 to B1 is almost equal to the lean or rich cycle. When the lean / rich determination period L is determined in this manner, as shown in FIGS. 8 (C) and (D), when the deposit is not attached, the lean / rich determination period L is set.
The lean time and rich time within are almost equal,
Therefore, the count value of the counter CAC when the lean / rich determination period L has elapsed becomes substantially zero. On the other hand, as shown in FIG. 8 (E), when the lean / rich determination period L ′ becomes a half cycle of lean or rich fluctuation, the lean time in the lean / rich determination period L ′ is longer than the rich time. Therefore, the count value of the counter CAC becomes large when the lean / rich determination period L ′ elapses. Therefore, in the case shown in FIG. 8 (E), when the count value of the counter CAC when the lean / rich determination period L ′ has passed exceeds C1, it is determined that the air-fuel mixture is lean during the acceleration operation. If you do so, you will definitely make a wrong decision. Therefore, in order to avoid such an erroneous judgment, FIG.
As shown in (D), it is necessary to set the lean / rich determination period L to one cycle of lean or rich.

As described above, the lean / rich determination period L is a counter
It corresponds to the period from when the count value of CLRN1 reaches A1 to B1. By the way, fuel injection is normally started at a predetermined crank angle, while the routine shown in FIGS. 10 and 11 is executed by interruption every 360 crank angles, so that the count value of the counter CLRN1 reaches from A1 to B1. During this period, fuel injection is performed a certain number of times regardless of the engine speed. In other words, within the lean / rich determination period L, fuel injection is performed a certain number of times regardless of the engine speed. By the way, the air-fuel ratio fluctuates for each fuel injection, and the feedback control is performed with respect to this fluctuation of the air-fuel ratio, so that the lean and rich cycles depend on the number of fuel injections. Therefore, the lean / rich determination period L substantially matches the lean or rich cycle regardless of the engine speed, that is, regardless of the degree of acceleration.

On the other hand, when the deposit adheres, the air-fuel mixture becomes lean when the acceleration is started, and therefore, FIGS. 8 (F) and 8 (G).
As shown in FIG. 8, the lean time becomes longer than that in FIGS. 8 (C) and 8 (D). Therefore, the lean time in the lean / rich determination period L becomes longer than the rich time, and the count value of the counter CAC when the lean / rich determination period L has elapsed becomes large. Therefore, the fact that the count value of the counter CAC exceeds C1 makes it possible to determine that the air-fuel mixture has become lean during acceleration operation. As shown in FIGS. 8 (F) and 8 (G), it is rich when the lean / rich determination period L has elapsed, and the rich time is shown in FIG. 8 (F) by the control system of the fuel injection system. It may be shorter as shown, and the eighth
It may become longer as shown in FIG. However, if the lean / rich judgment period L in FIG. 8 (F), (G) is made to coincide with the lean / rich cycle when the deposit is not attached, the lean / rich judgment period L Regardless of the length of the rich time, it is possible to reliably judge the leanness due to the deposit adhesion.

When the lean / rich determination period L elapses as shown in FIG. 8 (F) by the fuel injection system, if the rich time is short, deposits are deposited as shown in FIG. 8 (H). The lean / rich determination period L ″ can be set to an integral multiple of the lean or rich period during acceleration operation when the lean / rich determination period is not performed.

Further, the lean / rich judgment is not performed until the counter CLRN1 reaches A1 because it takes a certain time for the air-fuel mixture supplied into the engine cylinder to become exhaust gas and reach the O ₂ sensor 19.

Returning to FIG. 11 again, if it is determined to be CLRN1B1 in step 213, the process proceeds to step 215, and it is determined whether or not the count value of the counter CAC is larger than a predetermined positive constant value C1. If it is CACC1, the routine proceeds to step 216, where it is judged if the count value of the counter CAC is smaller than a predetermined negative constant value D1. If CAC> D1, the routine proceeds to step 202, where the counters CAC, CLRN1, CLRN2 are cleared. On the other hand, in step 215 CAC
If it is determined that the value is C1, that is, if it is lean during acceleration operation, the routine proceeds to step 217, where the acceleration correction coefficient K
A predetermined constant value, for example, 0.1 is added to AC, and thus the acceleration correction coefficient KAC is increased. On the other hand, when it is determined in step 216 that it is CACD1, that is, when it is rich during acceleration operation, step 21
Proceed to step 8 and set a predetermined value from the acceleration correction coefficient KAC,
For example, 0.1 is subtracted, thus reducing the acceleration correction coefficient KAC.

On the other hand, ΔPM-39 mmHg in step 206,
That is, when it is determined that the deceleration operation is being performed, step 219
Then, the count value of the counter CLRN2 is set to 1. Next, the routine proceeds to the fuel injection time calculation routine. In the next processing cycle, the process proceeds from step 204 to step 220. In step 220, it is determined whether or not ΔPM is higher than 5 mmHg, that is, whether or not the vehicle has been accelerated after the start of deceleration operation, and ΔPM
If it is 5 mmHg, proceed to step 202 and set each counter CAC, CL
RN1 and CLRN2 are cleared. On the other hand, when the deceleration operation continues, ΔPM <5 mmHg, so the routine proceeds from step 220 to step 221, and the counter CLRN2 is incremented by one. That is, as shown in FIG. 9 (B), the deceleration operation is started and the absolute pressure PM in the surge tank 11 is
It decreased from PM ₂ to PM _1, this time ΔPM counts up the counter CLRN2 is started becomes lower than -39MmHg.

Next, at step 222, it is judged if the count value of the counter CLRN2 has become larger than a predetermined constant value A2. When CLRN2 <A2, the routine proceeds to the fuel injection time calculation routine. On the other hand, when CLRN2A2 is reached, the routine proceeds to step 223, where it is judged from the output signal of the O ₂ sensor 19 whether or not the air-fuel mixture supplied into the engine cylinder is rich. When the air-fuel mixture is rich, the routine proceeds to step 224, where the counter CAC is incremented by 1, and then the routine proceeds to step 225. On the other hand, when the air-fuel mixture is not rich, that is, when the air-fuel mixture is lean, the routine proceeds to step 226, where the counter CAC is decremented by 1, and then the routine proceeds to step 225. At step 225, the counter CLRN2 is set to a predetermined constant value B2.
It is determined whether or not it has become larger than. If CLRN2 <B2, the routine proceeds to the fuel injection time calculation routine. That is, as shown in FIG. 9 (B), mixing is performed until the count value of the counter CLRN2 changes from A2 to B2, that is, within the same lean / rich determination period as in FIG. 8 (C) during deceleration operation. It is determined whether the air-fuel mixture is rich or lean. When the air-fuel mixture is rich, the counter CAC is counted up, and when the air-fuel mixture is lean, the counter CAC is counted down. Therefore, if the count value of the counter CLRN2 changes from A2 to B2, that is, if the rich time is longer than the lean time in the lean / rich determination period, the count value of the counter CAC increases, If the lean time is longer than the rich time, the count value of the counter CAC decreases. Therefore, whether the air-fuel mixture is rich or lean during deceleration operation can be determined from the count value of the counter CAC when CLRN2 becomes B2.

If it is determined to be CLRN2B2 in step 225, the routine proceeds to step 227, where it is determined whether or not the count value of the counter CAC is larger than a predetermined positive constant value C2. If it is CACC2, proceed to step 228 and counter CAC
It is determined whether or not the count value of is smaller than a predetermined negative constant value D2. If CAC> D2, the routine proceeds to step 202, where the counters CAC, CLRN1, CLRN2 are cleared. On the other hand, when it is determined to be CACC2 in step 227, that is, when it is rich during deceleration operation, the routine proceeds to step 229, where a predetermined constant value, for example, 0.1 is added to the deceleration correction coefficient KDC, Therefore, the deceleration correction coefficient KDC is increased. Meanwhile, in step 228
When it is determined to be CACD2, that is, when lean during deceleration operation, the routine proceeds to step 230, where a predetermined constant value, for example, 0.1 is subtracted from the deceleration correction coefficient KDC, and thus the deceleration correction coefficient KDC is Can be reduced.

The acceleration correction coefficient KAC and the deceleration correction coefficient KDC represent the correction coefficient K for the corrected fuel injection time TPAEW due to the accumulation of deposits. Therefore, if the accumulation of deposits makes the engine lean during acceleration operation, the correction coefficient K is increased and the deposit If the accumulation becomes rich during deceleration operation, the correction coefficient K is similarly increased.

FIG. 12 shows a routine for calculating the fuel injection time, which is executed subsequent to the routines shown in FIGS. 10 and 11.

Referring to FIG. 12, first, at step 300, the basic fuel injection time TP is calculated from the output signals of the absolute pressure sensor 21 and the rotation speed sensor 23. Next, at step 301, ΣΔPM is calculated based on the following equation.

ΣΔPM = ΔPM + C ₁ ΣΔPM (5) Next, at step 302, the corrected fuel injection time TPAEW is calculated based on the following equation.

TPAEW = (C ₂ ΔPM + C ₃ ΣΔPM) · C ₄ (6) The above equations (5) and (6) are combined to obtain the following equation.

TPAEW = {C ₂ ΔPM + C ₃ (ΔPM + C ₁ ΣΔPM)} C ₄ This formula represents the above-mentioned formula (3). Therefore, the corrected fuel injection time TPAEW shows the mixture during transient operation when deposits are not accumulated. It represents the amount of increase or decrease of the injected fuel to maintain the stoichiometric air-fuel ratio.

Next, at step 303, it is judged if ΔPM is positive or zero. When it is determined at step 303 that ΔPM = 0, or when ΔPM> 0, that is, when it is determined that the vehicle is in the acceleration operation state, the routine proceeds to step 304, where the acceleration correction coefficient K
AC is made the correction coefficient K, and then the routine proceeds to step 306. On the other hand, when it is determined at step 304 that ΔPM <0, that is, when the vehicle is in the deceleration state, the routine proceeds to step 305, where the deceleration correction coefficient KDC is made the correction coefficient K, and then the routine proceeds to step 306.

In step 306, the fuel injection time TAU is calculated based on the following equation.

TAU = (TP + K · TPAEW) · FAF · F The correction coefficient K is increased when the engine becomes lean during acceleration operation due to the accumulation of deposits, so K · TPAEW, that is, the acceleration fuel increase rate, is increased during the next acceleration operation, which The air-fuel mixture is maintained at the stoichiometric air-fuel ratio. On the other hand, if the deposit becomes rich during deceleration operation due to the accumulation of deposits, the correction coefficient K is increased, so that K · TPAEW, that is, the deceleration fuel reduction rate, is increased during the next deceleration operation.
Thereby, the air-fuel mixture is maintained at the stoichiometric air-fuel ratio. Thus, even if the deposit adheres to the inner wall surface of the intake port or the like, the air-fuel mixture can be maintained at the stoichiometric air-fuel ratio regardless of the operating state of the engine. The acceleration correction coefficient KAC and the deceleration correction coefficient KDC are stored in the backup RAM 32a.

〔The invention's effect〕

A cycle in which the air-fuel mixture becomes lean or rich during acceleration operation or an integer multiple of the cycle is stored in advance as a lean-rich determination period, and the deviation between the lean time and rich time of the air-fuel mixture is calculated only during this lean-rich determination period. By doing so, it is possible to reliably determine that the air-fuel mixture has become lean during acceleration operation.

[Brief description of drawings]

1 is a block diagram of the invention, FIG. 2 is a diagram showing the entire internal combustion engine, FIG. 3 is a flowchart for calculating a feedback correction coefficient, FIG. 4 is a diagram showing changes in the feedback correction coefficient, and FIG. The figure is a figure for explaining the deviation of the air-fuel ratio based on the time delay from the start of the calculation of the fuel injection time until the actual fuel injection, and FIG. 6 is the figure until the liquid fuel flows into the engine cylinder. For explaining the deviation of the air-fuel ratio based on the time delay of FIG. 7, FIG. 7 is a view for explaining the fuel injection amount that should be increased or decreased during the acceleration operation, and FIG. 8 is for the lean rich condition during the acceleration operation. Diagram showing changes, FIG. 9 is a time chart showing a method for calculating the deposit learning value, FIGS. 10 and 11 are flowcharts for calculating the deposit learning value, and FIG. 12 is calculating the combustion injection time. F to do It is over chart. 6 ... intake valve, 8 ... exhaust valve, 12 ... fuel injection valve, 15 ... throttle valve, 19 ... O ₂ sensor, 21 ... absolute pressure sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Matsuoka 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor, Michihiro Ohashi 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Yukihiro Sonoda, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor, Hiroshi Sawada, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (56) References 63-201344 (JP, A) JP-A-58-8239 (JP, A) JP-A-64-60741 (JP, A) JP-A-63-159648 (JP, A)

Claims (1)

(57) [Claims] 1. A fuel injection control means for controlling a fuel injection amount so that an air-fuel mixture supplied into an engine cylinder has a target air-fuel ratio based on an output signal of an oxygen concentration detector arranged in an engine exhaust passage. A storage unit that stores in advance a cycle in which the air-fuel mixture becomes lean or rich during acceleration operation or an integral multiple of the cycle as a lean / rich determination period; an acceleration operation state detection unit that detects an acceleration operation state; Deviation calculation means for calculating the deviation between the lean time and rich time of the air-fuel mixture only during the lean / rich judgment period after the start of the acceleration operation based on the detection results of the concentration detector and the acceleration operation state detection means, and the calculation result of the deviation calculation means Internal combustion engine provided with an injection amount increasing means for increasing the fuel injection amount when the lean time is longer than the rich time and the deviation exceeds a predetermined set value based on Fuel injection control device.